Resumo em Inglês:

ABSTRACT In the current study, the influences of laser remelting treatment on NiCoCrAlY/ZrO2-7 wt.% Y2O3 thermal barrier coatings fabricated via plasma spraying on GH4169 alloy were examined. The microstructure, microhardness, hot corrosion resistance at 950 ℃ of the two types of TBCs were investigated comparatively. The results indicated that the as-sprayed TBCs had a lamellar structure with high cracks and porosity. After laser remelting treatment, a laser remelted layer with a compact sub-micro sized grains arranged in a stacked structure was formed which was denser than that of the as-sprayed TBCs. The surface microhardness of the as-sprayed TBC was only 977 HV0.3, which exhibited a significant increase (over 1500 HV0.3) after laser remelting due to the fine grains of the remelted region with lower porosity. The hot corrosion resistance of the laser remelted TBCs were considerably better than the as-sprayed one. The as-sprayed TBC with a lot of defects, the molten salts could easy penetrate the coating and react with Y2O3. The consumption of Y element promoted the phase transition of t'-ZrO2 to m-ZrO2, which harmed the protective coating because of the volume expansion of the phase transition. The laser remelted TBCs was dense, which could significantly reduce the penetrate of molten salts due to the fewer cracks and holes compared to the as-sprayed TBCs. The laser remelted TBCs exhibited superior hot corrosion performance as compared to the as-sprayed TBCs.

Resumo em Português:

RESUMO Esta pesquisa experimental tem como objetivo analisar a influência dos parâmetros elétricos da usinagem por eletroerosão (EDM – Electrical Discharge Machining) na rugosidade média (Ra) do aço AISI P20, o qual é vastamente utilizado na indústria de moldes para injeção de termoplásticos. Também é proposto neste estudo a otimização destes parâmetros para a obtenção da rugosidade superficial pretendida ao material. O planejamento e os resultados estatísticos foram obtidos através da metodologia de design de experimento (DOE – Design Of Experiments). Utilizou-se do software Statistica para criar gráficos e tabelas de análise baseados na metodologia de superfície de resposta (RSM – Response Surface Methodology). A análise dos resultados mostrou que a duração do pulso de descarga (Ton) e a intensidade da corrente elétrica são os parâmetros de maior efeito para a rugosidade superficial. Baseados em outros trabalhos sobre EDM, a análise estatística apresentou resultados em conformidade quanto a influência dos fatores. O gráfico de otimização indicou coerentemente os níveis adequados de ajuste dos parâmetros para a obtenção da variável resposta desejável. Pode-se constatar nesta pesquisa em específico, quais são os parâmetros elétricos significativos para a rugosidade superficial média, sendo o seu conhecimento e controle, fundamentais para a otimização do processo. As técnicas estatísticas apresentaram-se como ferramentas muito úteis para o domínio da tecnologia industrial, principalmente em casos onde há necessidade do ajuste de muitos fatores, gerando previsibilidade, economia, agilidade e confiabilidade ao processo.

Resumo em Inglês:

ABSTRACT This experimental research aims to analyze the influence of electrical parameters of electrical discharge machining (EDM) on the average roughness (Ra) of AISI P20 steel, which is widely used in the mold industry for thermoplastic injection. It is also proposed in this study the optimization of these parameters to obtain the desired surface roughness of the material. The planning and statistical results were obtained through the experiment design methodology (DOE). Statistica software was used to create graphs and tables based on the response surface methodology (RSM). The analysis of the results showed that the duration of the discharge pulse (Ton) and the intensity of the electric current are the parameters with the greatest effect on surface roughness. Based on other studies on EDM, the statistical analysis presented results in conformity with regard to the influence of factors. The optimization graph consistently indicated the adequate levels of adjustment of the parameters to obtain the desired response. It can be verified in this research in specific, what are the significant electrical parameters for the average surface roughness, being its knowledge and control, fundamental for the optimization of the process. Statistical techniques were presented as very useful tools for mastering industrial technology, especially in cases where there is a need to adjust many factors, generating predictability, economy, agility and reliability to the process.

Resumo em Português:

RESUMO Neste estudo, biomassa da casca de Castanha-do-Brasil suportada com nanopartículas de ferro (BCB-NPsFe) foi utilizada para a descoloração do corante rodamina B (RdB) via reação catalítica de Fenton. A maior taxa de descoloração foi de 94,5% obtida nas condições: solução contendo 20 mg/L de RdB, 1,0 g/L de BCB-NPsFe, 200 mM de H2O2, pH 4,0, temperatura de 45 °C e tempo de reação de 240 minutos. A taxa de mineralização da RdB nessas mesmas condições foi de 61,3%. Por meio da equação de Arrhenius a energia de ativação da descoloração da RdB foi estimada em 36,25 kJ/mol, um valor baixo se comparado a outros estudos. A reutilização da BCB-NPsFe em cinco ciclos de descoloração mostrou que a descoloração da RdB não foi afetada. A BCB-NPsFe também foi eficiente na descoloração dos corantes verde Malaquita (97,1%), violeta cristal (87,0%), preto reativo B (91,2%) e vermelho reativo 239 (89,1%). Estes resultados indicaram que a BCB-NPsFe pode ser uma alternativa econômica e ambientalmente sustentável para o tratamento de águas residuárias contendo corantes.

Resumo em Inglês:

ABSTRACT In this study, Brazil nutshell biomass supported with iron nanoparticles (BCB-NPsFe) was used to decolorize the dye Rhodamine B (RdB) using Fenton catalytic reaction. Higher discoloration rate was 94.3% obtained at the condition: solution containing 20 mg/L RdB, 1.0 g/L BCB-NPsFe, 200 mM H2O2, pH 4.0, temperature of 45 °C, and reaction time of 240 minutes. The mineralization rate of RdB under these same conditions was 61.3%. Using the Arrhenius equation, the activation energy of RdB decolorization was estimated at 36.25 kJ/mol, a low value compared to other studies. The reusability of BCB-NPsFe in five decolorization cycles showed that the RdB decolorization was not affected. BCB-NPsFe also efficiently decolorized Malachite green (97.1%), crystal violet (87.0%), reactive black B (91.2%), and reactive red 239 (89.1%). These results indicated that BCB-NPsFe could be an economical and eco-friendly treatment strategy for wastewater containing dyes.

Resumo em Português:

RESUMO A deformação permanente nos revestimentos asfálticos constitui-se em um dos principais defeitos encontrados em pavimentos rodoviários e urbanos. Nesse contexto, estudos têm sido realizados sobre a contribuição da granulometria para minimizar esse tipo de problema. O trabalho em pauta avaliou a influência da estrutura mineral no desempenho mecânico, quanto: Índice de Densificação na Compactação, Índice de Densificação pelo Tráfego, Resistência à Tração por Compressão Diametral, Ensaio Uniaxial de Carga Repetida – Flow Number e Dano por Umidade Induzida. Pesquisaram-se duas misturas asfálticas. A primeira, composição referência, M0, habitualmente aplicada nos pavimentos manauaras e projetada segundo a metodologia Marshall. A segunda, a formulação proposta no presente estudo, M1, utilizou critérios mais atuais de dosagem, tais como: metodologia Superpave, Métodos Bailey e Faixa de Agregados Dominantes, fundamentada num forte esqueleto pétreo de graduação graúda, excluindo a areia natural presente na M0. Os resultados mostraram que a mistura asfáltica M1, relativa à composição asfáltica M0, alcançou melhor desempenho para vias com alto volume de tráfego e em condições severas, pois apresentaram deformações permanentes menores em relação a Mistura M0 comumente usadas nos pavimentos Urbanos.

Resumo em Inglês:

ABSTRACT Asphalt mixtures rutting is one of the main distresses that can happen at road and urban pavements. In this context, researches have been carried out on the aggregate gradation contribution to reduce this type of problem. This paper evaluated the influence of the mineral structure on the mechanical performance, regarding: Compaction Densification Index, Traffic Densification Index, Diametral Compression Tensile Strength, Uniaxial Repeated Load Test, Flow Number; and Moisture Induced Damage. Two asphalt mixtures were investigated. The first, reference composition M0, usually applied to Manaus pavements and designed according to the Marshall methodology. The second (M1), which is the formulation proposed in the present study, used the most current dosage criteria, such as: Superpave methodology, Bailey Method and Dominant Aggregate Size Range model, based on a strong stone skeleton of coarse grade, excluding natural sand, present at M0. The results revealed that the asphalt mixture M1, relative to the asphalt composition M0, achieved better performance for roads with high traffic volume and under severe conditions, as they presented smaller permanent deformations in relation to M0 mixture commonly used in urban pavements.

Resumo em Inglês:

ABSTRACT The use of degradable magnesium alloy as a bone implant material has gained much research attention. However, its mechanical properties cannot meet the clinical requirements of bone implantation. In the present work, the microhardness, strength and plasticity of biological Mg-Zn-Ca alloy are evaluated before and after high pressure torsion (HPT) processing. The results demonstrate an obvious increase in the microhardness of the HPT-processed Mg-Zn-Ca alloy, with higher values distributed along the edge of the sample and low values in the center. After annealing, however, the microhardness value of the HPT Mg-Zn-Ca alloy decreases, but the distribution of microhardness values becomes significantly more uniform. The tensile test results show that the HPT processing increases the tensile strength of the Mg-Zn-Ca alloy, but decreases the toughness. When the HPT Mg-Zn-Ca alloy is annealed, however, the tensile strength decreases, while the plasticity noticeably increases, with increased annealing tempera-ture. The improvements in the strength and microhardness of the HPT Mg-Zn-Ca alloy are attributed to a combination of dislocation strengthening, fine grain strengthening, and precipitation strengthening. In conclusion, the Mg-Zn-Ca alloy has excellent comprehensive mechanical properties after 5 turns of HPT processing, followed by annealing at 210 ℃ for 30 min.

Resumo em Português:

RESUMO A determinação da condutividade hidráulica em solos não saturados é essencial ao realizar análises de fluxo transiente nesses meios porosos. No entanto, a execução de ensaios de laboratório e de campo para a determinação dessa propriedade hidráulica não é prática corrente no âmbito da geotecnia, por se tratar de procedimentos demorados e dispendiosos. As redes neurais artificiais (RNA) têm sido bastante empregadas em Mecânica dos Solos, permitindo a estimativa de uma forma fácil e simples de fenômenos complexos e multivariados. Desse modo, este artigo tem como objetivo apresentar um modelo de estimativa da condutividade hidráulica em solos não saturados desenvolvido a partir de um tipo de RNA conhecido como perceptron multicamadas (MLP). As variáveis de entrada do modelo são: índice de vazios inicial, teor de umidade gravimétrico inicial, percentuais de areia, silte e argila, índice de plasticidade, coeficiente de permeabilidade saturado e sucção matricial. Durante a modelagem, um total de 275 exemplos foram utilizados, dos quais 85% foram empregados na fase de treinamento, e 15% na fase de teste. O modelo proposto possui uma arquitetura A: 8-4-2-1 e apresentou coeficiente de correlação de 0,97 após 500 mil iterações em ambas as fases de treinamento e de teste. Os resultados do modelo se ajustaram satisfatoriamente aos dados experimentais utilizados nas fases de treinamento e de teste, e a rede neural proposta foi capaz de representar a influência das variáveis de entrada no comportamento hidráulico de diferentes tipos de solo.

Resumo em Inglês:

ABSTRACT The determination of hydraulic conductivity in unsaturated soils is essential when performing transient flow analysis in these porous media. However, the execution of laboratory and field tests to determine this hydraulic property is not a current practice in the scope of geotechnics, as these are time-consuming and expensive procedures. Artificial neural networks (ANN) have been widely used in Soil Mechanics, allowing the estimation of complex and multivariate phenomena in an easy and simple way. Thus, this article aims to present a model for estimating hydraulic conductivity in unsaturated soils developed from a type of ANN known as multilayer perceptron (MLP). The model’s input variables are the initial void ratio, initial gravimetric water content, sand content, silt content, clay content, plasticity index, saturated permeability coefficient and matric suction. During modeling, a total of 275 examples were used, of which 85% were used in the training phase, and 15% in the testing phase. The proposed model has an A: 8-4-2-1 architecture and presented a correlation coefficient of 0.97 after 500 thousand iterations in both training and testing phases. The results of the model adjusted satisfactorily to the experimental data used in the training and test phases, and the proposed neural network was able to represent the influence of the input variables on the hydraulic behavior of different types of soil.

Resumo em Inglês:

ABSTRACT The fatigue strength assessment of metallic components containing manufacturing defects is currently analysed by applying fracture mechanics-based methodologies. This work begins by dealing with the recently published paper entitled “Short crack propagation analysis and fatigue strength assessment of additively manufactured materials: an application to AISI 316L”, Int J Fatigue 151 (2021) 106396, by Bergant, Werner, Madia, Yawny and Zerbst, where IBESS approach and Chapetti´s short crack growth threshold models were implemented for assessing the fatigue strength of laser powder bed fusion processed AISI 316L stainless steels. The application of the Chapetti´s model is carried out here in the way its author thinks it should be made, and results show clear differences when comparing with the results of the referenced paper. Analyses of the sources of discrepancy are also carried out. Some discussions associated with other recent applications of the available fracture mechanics models and hypotheses, or their combinations, are added in order to optimize future analysis when using them for short crack growth threshold estimations. Later, several analyses are made by making general observations associated with the prediction models, their hypotheses, their combinations and their relationship to the Kitagawa-Takahashi diagram. Finally, it is shown that when applying the fracture mechanics models special attention is necessary when comparing intrinsic strengths of the analysed material and that of material-defect combinations, particularly when the defects used in the analysis are artificial and/or are relatively large comparing with the microstructural dimension.

Resumo em Inglês:

Abstract High-temperature cyclic oxidation is governed by various cycle parameters (maximum temperature, cooling and heating rates, exposure time at high temperature) and atmosphere (composition, temperature, and pressure), complicating the evaluation of the effect of each parameter by itself. This study used a factorial design to evaluate three influential parameters in cyclic oxidation: alloy composition, upper dwell time (UDT), and surface finish. The method requires fewer experiments than ones previously used and can identify interactions between parameter effects. Two alloys, a ferritic Fe-5.9Si-3.9Cr-4.5Ni-0.8C (FeSiCr) alloy and conventional austenitic stainless steel AISI 310 were exposed to air at 950 °C for 100 h. Two different surface finishes (#220 and #600 SiC sandpaper) and two UDTs (30 and 60 minutes) were used. Mass variation data from eight different exposure times and metal/oxide interface roughness were analyzed. The FeSiCr alloy oxide layer was also characterized to complement the statistical analysis results. It was observed that different test stages were governed by different parameters. The surface finish was relevant at the beginning of the test, whereas UDT was relevant at the end. Interactions were irrelevant thorough the test. FeSiCr presented a promising behavior, with similar mass variation and higher oxide spallation resistance than AISI 310.

Resumo em Inglês:

Abstract The dispersion performance of drilling fluids at high temperatures has always been a bottleneck in the research. To improve the dispersion of drilling fluid at high temperature and pressure, the natural Ca-based bentonite was modified with Na2CO3 and SDBS (sodium dodecyl benzene sulfonate: C12H25SO4Na) by microwave semi-dry method. The effects of the ratio of Na2CO3 to SDBS, radiation time, initial temperature and microwave power on the modification were investigated. In addition, the microstructure of the samples was obtained using infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and the results showed that Na2CO3/SDBS was successfully inserted into the bentonite. In addition, the dispersion performance of the modified bentonite was evaluated in this paper, and the gelling value of the modified bentonite was 525 ml/15 g with an apparent viscosity of 22.5 mPa·s. The modified bentonite was compared with drilling-grade Na-based bentonite. The fluid loss (FLHTHP) of modified bentonite at high temperature and pressure is only 8 mL, the mud productivity is up to 25.71 m3/t, and the kinetic plastic ratio of modified bentonite is 1.5. The modified bentonite has better dispersion performance at high temperature and pressure.

Resumo em Português:

RESUMO A resina furfurílica (RF) é uma bioresina obtida a partir do álcool furfurílico (AF), extraído de fontes renováveis. Essa resina quando curada apresenta excelentes características, como elevada dureza, estabilidade química e boa resistência mecânica, que viabilizam sua utilização em diferentes áreas, destacando-se os setores aeroespacial e de bioengenharia. No entanto, a sua utilização em larga escala ainda é limitada, devido ao difícil controle do seu processo de síntese, pois a reação de policondensação do AF é extremamente exotérmica. O presente trabalho visa contribuir com a área de síntese da RF, por meio do estudo de sua obtenção em meio ácido e em baixa temperatura (∼50 ºC), variando os tempos de reação (1, 2 e 3 h), visando um maior controle da exotermia do meio reacional. O sucesso das sínteses realizadas foi comprovado por análises de espectroscopia na região do infravermelho com transformada de Fourier, que evidenciaram a presença de cetonas e estruturas de acordo com Diels-Alder e de Dunlop e Peters. Medidas de viscosidade apresentaram baixos valores (230 a 470 mPa.s), os quais são concordantes com as baixas massas molares obtidas por cromatografia de permeação em gel (M¯w: ∼800 g/mol). Esses resultados mostram que as condições de síntese utilizadas desfavoreceram cineticamente o avanço da reação; porém, não promoveram picos exotérmicos. As análises termogravimétricas (TGA) das RFs curadas com ácido p-toluenosulfônico (2 e 3%, m/m) mostraram perdas de massa desde o início da análise, devido à presença de água e de frações de baixa massa molar na amostra. Esses resultados são concordantes com as imagens obtidas por microscopia eletrônica de varredura, que mostraram um elevado volume de poros. Resultados relevantes foram observados nas análises de TGA sob atmosfera inerte, com valores elevados de carbono fixo (50–60%), indicando o potencial uso das RFs sintetizadas na área de materiais carbonosos.

Resumo em Inglês:

ABSTRACT Poly(furfuryl alcohol) (PFA) is a bioresin obtained from furfuryl alcohol (FA) extracted from renewable sources. This resin, when cured, has excellent characteristics, such as high hardness, chemical stability, and good mechanical resistance, which make its use in different areas viable, especially in the aerospace and bioengineering sectors. However, its use on a large scale is still limited due to the difficult control of its synthesis process since the polycondensation reaction of FA is extremely exothermic. The present work aims to contribute to the area of PFA synthesis, through the study of its obtainment in acidic medium and at low temperature (∼50 ºC), varying the reaction times (1, 2, and 3 h), aiming at greater control of the exothermy of the reaction medium. Fourier transform infrared spectroscopy analyses confirmed the syntheses success, which showed the presence of ketones and structures according to Diels-Alder and the Dunlop and Peters. Viscosity measurements showed low values (230 to 470 mPa.s), which are in agreement with the low molar masses obtained by gel permeation chromatography (M¯w: ∼800 g/mol). These results show that the synthesis conditions used kinetically unfavored the progress of the reaction but avoided exothermic peaks. Thermogravimetric analysis (TGA) of the PFAs cured with p-toluenesulfonic acid (2 and 3%, w/w) showed mass losses since the beginning of the analysis due to the presence of water and low molar mass fractions in the sample. These data agree with the images obtained by scanning electron microscopy, which showed a high volume of pores. Relevant results were observed in the TGA analysis under an inert atmosphere, with high values of carbon yield (50–60%), indicating the potential use of synthesized PFAs in the area of carbon materials.

Resumo em Português:

RESUMO O tempo de presa dos cimentos dentários são um parâmetro clínico importante, pois estima o tempo disponível para a realização do tratamento pós preparação do cimento, que não pode ser longo ou curto. Atualmente, esse parâmetro pode ser determinado usando as normas ISO 6876/2001 e ADA 57/2000. Essas técnicas utilizam a agulha de Gilmore e realizam apenas uma análise superficial para determinar o tempo de pega, não sendo possível indicar se o cimento secou completamente. O objetivo deste trabalho foi determinar o tempo de pega utilizando o método da cavidade ressonante de cimentos à base de Hidroxiapatita (Hap) e galactomanana (Gal) extraídos de sementes de Adenanthera pavonina L. Foram preparados dois compostos: HAG (75% HAp e 25% Gal em peso como fase sólida e 0,30 mL de água destilada como fase líquida) e HAGJET (75% Hap, 2% em peso de pó de Gal com 0,10 mL de catalisador comercial JET (metacrilato de metil e dimetil-p-toluidina) e 0,20 mL de água destilada). A fase sólida em cada material foi dissolvido no líquido correspondente para cada composto formado. A inserção dos cimentos HAG e HAGJET gerou uma perturbação no campo elétrico devido à presença de água livre na amostra, onde esta perturbação diminui à medida que o cimento endurece devido à a evaporação dessa água livre. De acordo com os resultados, o cimento HAG teve o maior tempo de pega devido à ausência do ativador químico na sua preparação, enquanto o cimento HAGJET, que teve ativador em seu processamento, apresentou tempo de pega menor em ambas as técnicas.

Resumo em Inglês:

ABSTRACT The setting time of dental cements is an important clinical parameter, as it estimates the time available to carry out the post-cement treatment, which cannot be long or short. Currently, this parameter can be determined using the ISO 6876/2001 and ADA 57/2000 standards. These techniques use the Gilmore needle and perform only a superficial analysis to determine the setting time, and it is not possible to indicate whether the cement has completely dried. The objective of this work was to determine the setting time using the resonant cavity method of cements based on Hydroxyapatite (Hap) and galactomannan (Gal) extracted from Adenanthera pavonina L. seeds. Two compounds were prepared: HAG (75% HAp and 25% Gal by weight as solid phase and 0.30 mL of distilled water as liquid phase) and HAGJET (75% Hap, 2% by weight of Gal powder with 0.10 mL of commercial catalyst JET (methyl dimethyl methacrylate) p-toluidine) and 0.20 ml of distilled water). The solid phase in each material was dissolved in the liquid corresponding to each compound formed. The insertion of HAG and HAGJET cements generated a disturbance in the electric field due to the presence of free water in the sample, where this disturbance decreases as the cement hardens due to the evaporation of this free water. According to the results, the HAG cement had the longest setting time due to the absence of the chemical activator in its preparation, while the HAGJET cement, which had the activator in its processing, presented the lowest setting time in both techniques.

Resumo em Português:

RESUMO A incorporação de nanomateriais em compósitos cimentícios vem se tornando cada vez mais frequente e tem, como um dos principais objetivos, promover melhorias às propriedades mecânicas e microestruturais. Dentre os diversos nanomateriais existente, os nanotubos de carbono (NTC) se destacam devido à sua elevada resistência, principalmente à tração, e à alta capacidade de deformação elástica. Entretanto, um dos impasses em sua utilização é a dificuldade de realizar uma dispersão eficaz e estável, mas pesquisas apontam que a utilização de aditivos contribui para a desaglomeração do nanomaterial. Sendo assim, este trabalho avaliou a influência de dois tipos de superplastificantes (SPA e SPB), adicionados na proporção de 1:0 a 1:3 (NTCPM:SP), em uma solução sonicada por 5 minutos. Os resultados mostraram que o aditivo SPB foi o que melhor proporcionou uma melhor dispersão com um menor consumo. Pastas de cimento Portland também foram produzidas e comprovou-se que o NTCPM reduziu a consistência das pastas e que a inserção de aditivo ajudou a diminuir esse efeito. Por fim, infere-se que o aditivo, além de melhorar a dispersão do NTCPM, também interage com o cimento Portland, promovendo pastas com maior espalhamento.

Resumo em Inglês:

ABSTRACT The incorporation of nanomaterials in cementitious composites has become more and more frequent and has, as one of the main objectives, to promote improvements to the mechanical and microstructural properties. Among the various existing nanomaterials, carbon nanotubes (CNT) stand out due to their high resistance, mainly to traction, and the high capacity of elastic deformation. However, one of the impasses in its use is the difficulty of achieving an effective and stable dispersion, but research shows that the use of additives contributes to the de-agglomeration of the nanomaterial. Thus, this work evaluated the influence of two types of superplasticizers (SPA and SPB), added in the proportion of 1: 0 to 1: 3 (MWCNT: SP), in a sonicated solution for 5 minutes. The results showed that the SPB additive was the one that best provided a better dispersion with less consumption. Portland cement pastes were also produced and it was found that the MWCNT reduced the consistency of the pastes and that the insertion of additives helped to reduce this effect. Finally, it appears that the additive, in addition to improving the dispersion of the MWCNT, also interacts with Portland cement, promoting pastes with greater spread.

Resumo em Português:

RESUMO A sílica de casca de arroz (SCA) é uma pozolana de grande potencial reativo que, ao ser adicionada em sistemas cimentícios, promove a redução da reserva alcalina. Dentro desse contexto, a incorporação de hidróxido de cálcio (CH) visa atenuar o impacto na reserva alcalina causado pela pozolana. O presente estudo visa analisar a influência da incorporação conjunta de SCA e CH (em diferentes teores) em sistemas cimentícios, sob os aspectos físico-químico e mecânico. Os resultados indicaram que a SCA em substituição parcial ao cimento provoca um retardo no ganho de resistência à compressão, porém não é prejudicial em idades mais avançadas. Também foi verificado que a SCA tende a aumentar a porosidade aparente do sistema. Em geral, a presença de SCA resultou na redução do teor de hidratos formados. A reserva alcalina foi reestabelecida quando os teores de SCA e CH foram iguais. O aumento da disponibilidade alcalina aumentou o teor de CH fixado por atividade pozolânica da SCA. A proporção de 10% de SCA e 15% de CH foi a combinação que melhor explorou o potencial reativo da pozolana, além de ter sido capaz de manter a porosidade e a reserva alcalina semelhantes à amostra de referência.

Resumo em Inglês:

ABSTRACT Rice husk ash (RHA) is a pozzolan with high reactive potential that, when added to cementitious systems, promotes the reduction of the alkaline reserve. Within this context, the incorporation of calcium hydroxide (CH) aims to attenuate the impact on the alkaline reserve caused by the pozzolan. The present study aims to analyze the influence of the joint incorporation of SCA and CH (in different contents) in cementitious systems, under the physical-chemical and mechanical aspects. The results indicated that SCA in partial replacement of cement causes a delay in the gain in compressive strength, but is not harmful at older ages. It was also verified that SCA tends to increase the apparent porosity of the system. In general, the presence of SCA resulted in a reduction in the content of hydrates formed. The alkaline reserve was reestablished when the levels of SCA and CH were equal. The increase in alkaline availability increased the CH content fixed by the pozzolanic activity of SCA. The proportion of 10% SCA and 15% CH was the combination that best explored the reactive potential of the pozzolan, in addition to being able to maintain the porosity and alkaline reserve similar to the reference sample.

Resumo em Inglês:

ABSTRACT Curing is a critical process in the compression molding of carbon fiber reinforced polymer (CFRP). It directly bears on the quality of the molded products. Based on the curing theory of resin-based polymers, a thermo-mechanical-chemical multi-field coupling model for CFRP curing in the form of thermal-chemical subprocess, matrix flow-compaction sub-process and residual stress-deformation subprocess, and sets up its data exchange and mutual call relationship. Considering the thermal physics and chemical properties of composites change with temperatures, the authors introduced the thermal viscosity stiffness coefficient and took AS4/3501CFRP molded laminate as an example, and carried out a multi-field coupling simulation of the CFRP curing through compression molding, using the finite-element software COMSOL. The proposed model was proved correct through calculation of an example in the literature. Further, the CFRP curing mechanism was revealed through a detailed analysis on the evolution of temperature, curing degree, stress and strain of the CFRP curing through compression molding. The results show that the large internal temperature gradient during the compression molding of laminates is the main reason for the residual stress of materials and the deformation of laminate. Finally, an AS4/3501CFRP molded laminate was prepared, and its temperature field was monitored by fiber Bragg grating (FBG) transducers. The temperature evolution law of the material was consistent with the finite element simulation results, which demonstrate the correctness of the simulation.

Resumo em Inglês:

ABSTRACT The ornamental rock industry generates millions of tons of waste in different stages of rock processing. These wastes are stored or disposed of inadequately, which causes environmental degradation. The objective of this study was to evaluate the concomitant use of ornamental rock processing sludge as partial replacement of Portland cement in contents of 0%, 5%, 10% and 20% and of recycled stone aggregate as total replacement of coarse natural aggregates in the production and performance of granilite concrete plates. Four concrete formulations were produced with different replacement contents and their characteristics were determined through tests of axial compression strength, flexural tensile strength, water absorption, impact strength and strength to stains. Mechanical results were inversely proportional: the higher the sludge replacement content, the higher the axial compression strength and the lower the flexural tensile strength. Water absorption tests showed a gradual decrease with an increase in sludge replacement, impact tests showed that the plates performed better at resisting shocks best up to a height of 50 cm and, in terms of stain resistance, multi-use products and butoxyethanol-based stain remover were more efficient on waterproofed granilite concretes and natural rock pieces, respectively. It was possible to conclude that it was viable to use up to 20% replacement of the aforementioned wastes in conventional concrete, with additional minimization of environmental impact associated with the extraction and processing of ornamental stones.

Resumo em Inglês:

Abstract Inspecting historic buildings with non-destructive techniques can contribute to obtaining information about the in-service status of a given building without damaging its parts. Damages map prepared by digital photogrammetry and the application of façade Thermography assessment are non-destructive techniques and possible due to technological advances. The present work aimed to apply non-destructive inspection techniques of the façade on the Zoroastro Artiaga Museum, of Art Deco Architecture, using two techniques: generation of damages map by orthoimage created from Aerophotogrammetry and the method of Damage Factor, and application of the thermographic image analysis technique. For the generation of damages map, the relevance of using UAV was observed, since for this technique it is essential to use this equipment to capture images perpendicular to the plane of the façade, when thinking about using the method by Dense Stereo Matching. The damages map generation and the analysis of the Damages Factor allowed the quantification of the incidence of pathological manifestations. The analysis of thermographic images made it possible to understand which factors contributed to the emergence of pathological manifestations, such as the possible presence of excess moisture, favoring, for example, the formation of efflorescence. It is concluded that the application of these techniques can be safely used for inspection and prior diagnosis and that the Thermography was important to identify non-visible damages to the façade, such as moisture extensions, since it was not possible to visually delimit the entire existing area of moisture through damages map generated by Aerophotogrammetry.

Resumo em Português:

RESUMO A aplicação de materiais álcali-ativados em obras de engenharia ainda é limitada, principalmente, porque alguns precursores necessitam de cura térmica para que ocorra a ativação alcalina. Nessa perspectiva, o objetivo desta pesquisa é avaliar o comportamento no estado fresco e no estado endurecido de argamassas álcali-ativadas à base de cinza volante, curadas em temperatura ambiente. Para a produção das argamassas, utilizou-se um ativador alcalino composto de silicato e hidróxido de sódio, variou-se a relação entre solução ativadora e precursor (s/p) em 0,45, 0,55 e 0,65. Os produtos da reação de álcali-ativação foram identificados por espectroscopia de infravermelho (FTIR) e análises térmicas. No estado fresco foram executados os ensaios Flow Table e Squeeze Flow e no estado endurecido foram realizados ensaios de resistência à compressão e resistência à tração na flexão. Os resultados indicam a formação do gel N-A-S-H (aluminossilicato de sódio hidratado) como principal produto de reação. A trabalhabilidade e a resistência mecânica das argamassas álcali-ativadas foram influenciadas pela quantidade de solução alcalina e água adicional. Os resultados foram satisfatórios, registrou-se resistências à tração entre 5,4 MPa e 11,1 MPa e resistências à compressão entre 11,1 MPa e 33,3 MPa, aos 28 dias.

Resumo em Inglês:

ABSTRACT Knowledge and technology in alkali-activated materials has grown in recent years. However, the application in engineering works is still limited, mainly because some precursors require thermal curing for alkaline activation to occur. In this perspective, the objective of this research is to evaluate the behavior in the fresh state and in the hardened state of alkali-activated mortars based on fly ash, cured at ambient temperature. For the production of mortars, an alkaline activator composed of silicate and sodium hydroxide was used, the ratio between activator solution and precursor (s/p) was varied in 0.45, 0.55 and 0.65. Additionally, a conventional mortar was produced for comparison. The products of the alkali-activation reaction were identified by infrared spectroscopy (FTIR) and thermal analysis. In the fresh state, the Flow Table and Squeeze Flow tests were carried out and in the hardened state, tests of compressive strength and tensile strength in bending were carried out. The results indicate the formation of N-A-S-H gel (hydrated sodium aluminum silicate) as the main reaction product. The workability and mechanical strength of alkali-activated mortars were influenced by the amount of alkaline solution and additional water. The results were satisfactory, with tensile strengths between 5.4 MPa and 11.1 MPa and compressive strengths between 11.1 MPa and 33.3 MPa, at 28 days. These values increased as the s/p ratio increased and the additional water decreased. The conventional mortar presented flexural tensile strength of 3.3 MPa and compressive strength of 18.5 MPa. Therefore, alkali-activated mortars based on fly ash have characteristics and properties that enable their application in loco in civil construction.

Resumo em Português:

RESUMO O comportamento da alvenaria estrutural resulta do desempenho de cada componente: unidades, juntas de argamassa, grautes e armaduras. Comercialmente, os blocos para alvenaria são produzidos com concreto seco ou zero-slump. Sua dosagem e propriedades físicas se diferem consideravelmente dos concretos convencionais e dependem da eficiência de compactação das máquinas vibroprensas. Ensaiar elementos de alvenaria em tamanho natural é dispendioso e requer uma infraestrutura específica. Nessa perspectiva, modelagens computacionais baseadas em formulações numéricas como o Método dos Elementos Finitos (FEM) podem se tornar alternativas viáveis e de grande potencial. Este trabalho objetiva analisar numérica e experimentalmente a influência do tipo de agregado nas propriedades físicas e, sobretudo, mecânicas (módulo secante e resistência à compressão) de blocos vazados de concreto para alvenaria estrutural. Foram testadas três resistências de bloco (6, 12 e 24 MPa), contendo três tipos de agregado (basalto, gnaisse e calcário). Dos resultados, observou-se que em blocos menos resistentes a porosidade das misturas influenciou mais as propriedades mecânicas que a rigidez do agregado. À medida que os concretos se tornam mais densos e resistentes, esse comportamento muda. Os modelos implementados e calibrados pelos resultados experimentais reproduziram satisfatoriamente o modo de ruptura dos blocos, os resultados de módulo e de resistência.

Resumo em Inglês:

ABSTRACT The structural masonry behavior results from the performance of each component: units, mortar joints, grouts, and reinforcement. Commercially, masonry blocks are made with called dry or zero-slump concrete. Its dosage and physical properties differ considerably from conventional concretes and depend on vibropress machines compaction efficiency. Testing full-size masonry elements is expensive and demand a specific infrastructure. Thus, computer modeling based on numerical formulations such as the Finite Element Method (FEM) can become viable and high potential alternatives. This work aims to analyze numerically and experimentally the influence of aggregate type on physical and, mainly, mechanical properties (ultimate strength and secant deformation module in compression) of hollow concrete blocks for structural masonry. Units of three different strengths (6, 12 and 24 MPa) and containing three different aggregate types (basalt, gneiss, and limestone) were tested. From results, it was observed that in less resistant blocks, the mixtures porosity influenced mechanical properties more than aggregate stiffness. As concretes become denser and stronger, this behavior changes. The models implemented and calibrated by the experimental results were satisfactory in reproducing the failure mode of the blocks, secant modulus and compressive strength results.

Resumo em Inglês:

ABSTRACT This study investigated the change of impact resistance in concrete with respect to their sample size and compressive strength as experimental and theoretical. In the experimental design phase, a three-parameter, four-level L16 (43) Taguchi orthogonal array was used. For the Charpy impact tests, 16 serial samples were prepared with the following characteristics: sample width/sample length (B/L) ratio of 0.20, 0.25, 0.40 and 0.50; a sample width (B) of 100, 150, 200 and 250 mm, and a relative notch length (a/B) of 0.1, 0.2, 0.3 and 0.4. Experimental data were analyzed by two different methods. In the first stage, the optimum values were determined by performing analyses with the Taguchi method, while in the second stage, a mathematical model created by the Response Surface Method (RSM) was used as the objective function in a genetic algorithm to obtain the optimum values. Validation tests were performed based on optimum values and the results were compared. As a result of the study, it was observed that the change in sample size and compressive strength significantly affected the impact resistance of the concrete. A mathematical model was created to determine the impact resistance of the concrete.

Resumo em Inglês:

ABSTRACT Water contamination by heavy metals represents a high risk of environmental pollution and a precursor of several human diseases. The presence of these metals at high levels in wastewater treatment plants and industrial effluents motivated the search for remediating these pollutants. Among remediation methods, adsorption is extensively used to decontaminate waters containing these metals. Thus, this study prepared, characterized, optimized, and applied two types of adsorbents to a prepared metal ion solution (PMS): a bioadsorbent based on banana peel flour (BPF) and a synthetic adsorbent based on magnetite encapsulated by chitosan (MEC). A systematic study was performed with PMS containing Al (III), Ba (II), Pb (II), Cu (II), Cr (III), Fe (II), Mn (II), and Zn (II) to determine the best conditions for simultaneous metal ion adsorption Adsorption studies evaluated the experimental adsorption isotherms according to the variation in pH values, the mass of adsorbents, and contact time, and the kinetic study applied pseudo-first- and pseudo-second-order models. The best parameters were the pH of 6, a mass of adsorbents of 25 mg, and fast saturation time of around 10 minutes. The kinetic model that best fitted the process was the pseudo-second-order for all metals in both adsorbents. The PMS adsorption capacity achieved by MEC was higher than BPF. The removal by MEC was Al=Fe=Pb=Cu=Cr> Zn>Mn>Ba, in the percentages of 100, 100, 100, 100, 100, 98, 88, and 76%, respectively. The BPF showed Pb>Fe>Cr>Cu>Al>Zn>Ba>Mn, in the percentages of 97, 67, 63, 50, 46, 45, 44, and 5%, respectively. The results suggest that the affinity between adsorbents with certain metal ions is due to the characteristics of the adsorbent surface and the number of chemical species available in the solution, which may interfere with the adsorptive process. Above all, the percentage of simultaneous removal of metal ions by both adsorbents was relevant, making them promising for remediating heavy metal ions in sanitary sewage after conventional treatment and industrial effluents containing mixed metal ions.

Resumo em Português:

RESUMO O Sistema de Revestimento Cerâmico de Fachadas é tradicionalmente composto por um conjunto de camadas aderidas entre si, sendo que, a falha de alguma destas camadas pode implicar no surgimento de manifestações patológicas. A argamassa colante é a principal responsável pela adesão da placa cerâmica e, a fim de atribuir melhores características às argamassas colantes, tradicionalmente, incorporam-se aditivos poliméricos na sua formulação. Os aditivos poliméricos mais comuns empregados na produção das argamassas colantes industrializadas são: o copolímero acetato de vinila etileno (EVA) e o hidroxietilmetilcelulose (HEMC). Apesar de auxiliarem no desempenho de algumas características das argamassas colantes, esses aditivos costumam ser sensíveis a altas temperaturas. O objetivo desta pesquisa consiste em analisar a resistência de aderência à tração de placas cerâmicas assentadas utilizando argamassas colantes produzidas com três diferentes percentuais de EVA, após o sistema ser exposto a um programa de envelhecimento acelerado. Para tal, realizou-se o ensaio de resistência de aderência a tração. Os resultados demonstraram que os sistemas assentados com maiores percentuais de EVA apresentaram maior resistência quando expostos à temperatura ambiente, porém também apresentaram maior perda de resistência após a exposição aos ciclos higrotérmicos quando comparados as argamassas colantes produzidas com menor percentagem de EVA.

Resumo em Inglês:

ABSTRACT The Ceramic Facade Coating System is traditionally composed of a set of layers adhered to each other, and the failure of any of these layers can lead to the appearance of pathological manifestations. The adhesive mortar is the main responsible for the adhesion of the ceramic tile and, thus, in order to attribute better characteristics to the adhesive mortars, traditionally, polymeric additives have been incorporated in their formulation. The most common polymeric additives used in the production of industrialized adhesive mortars are: ethylene vinyl acetate copolymer (EVA) and hydroxyethyl methyl cellulose (HEMC). Although these additives help in the performance of some characteristics of adhesive mortars, they are usually sensitive to high temperatures. In this context, the aim of this research is to analyze the tensile bond strength in which ceramic slabs were laid using adhesive mortars produced with three different percentages of EVA, after the system was exposed to an accelerated aging program. To this end, tensile adherence strength testing was performed. The results showed that the systems laid with higher percentages of EVA showed greater strength when exposed to room temperature, but also showed greater loss of strength after exposure to hygrothermal cycles when compared to adhesive mortars produced with a lower percentage of EVA.

Resumo em Inglês:

ABSTRACT As the urban population increases and the level of social life advances, the amount of wastewater originating from houses, institutions and industries increases as well. It is necessary for the infrastructure systems in settlements to be sustained under healthy conditions. Since the subsequent repair of infrastructure systems is difficult, appropriate selection of the materials used in these systems is of importance. Concrete pipes are widely used in sewerage systems. In the present study, it was aimed to improve the biological corrosion resistance of concrete pipes via coating with various materials. For this purpose, firstly mortar samples were coated with epoxy, crystalline insulation mortar, and polyester. Finally this specimens subjected to 0.1, 0.5, 1, and 1.5 mol sulfuric acid solutions for 7, 14, 21, 28, 35, and 42 days. It was observed that the coating materials significantly improved the biological corrosion performances of the mortar samples.

Resumo em Inglês:

ABSTRACT Thermal treatment can modify undesirable characteristics of some woods, dimensional instability, and excessive water adsorption. The present research work aimed to assess the effect of thermal treatment on the physical properties of clone GG100 Eucalyptus wood. Wood samples were obtained from 9 year-old trees. Samples were subjected to three types of thermal treatment (T1, T2, and T3). In T1, the wood was kept in a laboratory kiln at 100 °C for 180 min. In T2, hydrothermal treatment was performed in an autoclave at 120 °C for 120 min. In T3, the combined autoclave and laboratory kiln treatments were employed. The properties evaluated were apparent density (ρa); mass loss (ML); longitudinal (βl), radial (βr), tangential (βt), and volumetric shrinkage (βv); anisotropic factor; and equilibrium moisture content. The treatments caused a decrease of ρa and increase of ML. The Equilibrium Moisture Content (EMC) was lowest for T3, and had a negative correlation with ML, βt, and ∆v. The Pearson correlation analysis indicated the results of the thermal treatments were similar, but T1 presented the lowest variation of the physical properties compared to the other treatments, giving it the best predictability for practical uses.

Resumo em Inglês:

ABSTRACT The objective of this work was to investigate the adsorptive potential of a previously benefited and characterized brazilian montmorillonite sample, regarding amoxicillin trihydrate removal, a zwitterionic species, present in aqueous solutions. 500 mg capsule of antibiotic was properly characterized by XRD, FTIR, SEM/EDS and surface charge measurement through Zeta potential. Amoxicillin aqueous solution and supernatants from adsorption essays were characterized by Molecular Absorption Spectrophotometry in Ultraviolet-Visible Region (UV/VIS), from 200 to 400 nm. Three investigative essays were performed, varying montmorillonite mass (0.050, 0.525 and 1.000 g) and contact time between substances (10, 95 and 180 min). Amoxicillin sample is crystalline, morphologically prismatic, essentially composed of carbon, nitrogen, sulfur, hydrogen and oxygen. Its zwitterionic character was confirmed by Zeta potential, presenting positive (pH 2 to 4), relatively neutral (pH 4 to 6), and negative (above pH 6) surface charges. Test results indicated that the highest removals (21.4 and 41.8 %) were for the largest clay mineral masses (0.525 and 1.000 g, respectively), with pHs close to amoxicillin pka1 (2.68). Larger clay mineral masses have more adsorbent sites, which, associated with components opposite charges in desired pH range, promote a greater interaction. Thus, brazilian montmorillonite can promote amoxicillin removal from aqueous solutions.

Resumo em Inglês:

ABSTRACT Oil is a non-renewable resource, and it is essential to improve oil recovery. Surfactant flooding is a key technology in enhancing oil recovery. The present work aims to develop a new surfactant to the combination flooding system in oil displacement. The Aminosulfonic Acid Gemini Surfactant was prepared by using Hexadecylamine, 1-Butanaminium,N,N,N-tributyl-,bromide (1:1) and Sodium 2-chloroethyl sulfonate. The AminoSulfonic Acid Gemini Surfactant Sodium N,N’-Dihexadecyl-2-propanol- 1,3-ethylsulfonate SNNDPE) has better reaction temperature at 80℃. The best reaction time of SNNDPE is 12 h. Next, We made a characterization of SNNDPE. A new gemini surfactant was developed, which is beneficial to the research of material science. Then the performance of the new Gemini surfactant was tested. The surface tension tests suggested that the newly synthesized Aminosulfonic Acid Gemini Surfactant has higher surface activity. The resistance temperature of the Aminosulfonic Acid Gemini Surfactant solution is 80℃. Moreover, the oil-water interfacial tension experiment suggested that the minimum aqueous solution of the combination flooding system reaches an ultra-low level of 9.4 × 10−4 mN/m. The combination flooding system experiment results can be considered as a guidance in the design and studies of the combination flooding system for a selective.

Resumo em Inglês:

ABSTRACT The dissimilar butt welding of nickel 201 and AISI 316 was studied by utilising a 4 kW CO2 laser with the help of Response Surface Methodology (RSM). The effects of laser power are 2580–3420 W; welding speed 450–1150 mm/s; focal position –1 to 0 mm; beam angle 84–96 degrees; and beam offset 0–0.2 mm on weld geometry, i.e., depth of penetration, bead width, and the Fusion Zone Area (FZ). The required weld profile responses for dissimilar butt welding were modeled mathematically. The constructed models were tested using the sequential F-test, lack of fit test, and analysis of variance (ANOVA). Mathematical models are reflected in the output answers within the parameters of the input process. This laser welding process with an optimal condition zone was discovered using a numeric optimization technique. It aids in the optimization of this process’s regulated responses by allowing for more effective parameter combinations. It is clear from the tensile test results that the expected weld strength has been achieved. There is some delta ferrite found in the interdendritic zone in the microstructure and the solidification process reveals columnar grains.

Resumo em Inglês:

ABSTRACT Warm mixtures are an essential alternative for paving as they minimize costs and environmental impacts, and their performance is similar to hot mixtures. This research evaluated the effect of adding linseed oil obtained from Linum usitatissimum in the contents of 1, 2, 3, 4, 5, and 6% by weight on the physical and rheological properties of the asphalt binder. The asphalt binder was evaluated through tests of penetration, softening point, rotational viscosity, performance grade (PG); these tests were performed before and after the short-term aging procedure; multiple stress creep and recovery (MSCR), and linear amplitude sweep (LAS). It has been verified that the mixing temperature could be reduced by up to 15 °C for the 6% linseed oil content, but it was lost in terms of performance, level of supported traffic, and fatigue life. In the so-called ideal content found, 4% linseed oil, there is a reduction in the mixing temperature of around 10 °C, as well as a maximum temperature of PG, 58 °C, it reduces by only one step compared to the pure binder, 64 °C, in addition to presenting the second-longest fatigue life of the grades studied, being classified as ideal for standard traffic by the MSCR test. Linseed oil proved to be an excellent green alternative for the production of warm mixtures.

Resumo em Português:

RESUMO O Brasil possui um vasto território florestal que privilegia a disseminação de inúmeras espécies arbóreas. Para que uma espécie de madeira seja utilizada em um sistema estrutural, são necessárias uma série de caracterizações de suas propriedades físico-mecânicas. Neste contexto, uma das variáveis a ser estudada é o teor de umidade, cuja variabilidade pode interferir de forma significativa em suas propriedades. A norma brasileira vigente estabelece modelos de correção das resistências e rigidezes para a umidade de equilíbrio, admitindo um aumento linear inversamente proporcional ao teor de umidade. Todavia, em algumas espécies, este fenômeno pode não ocorrer, conduzindo a valores constantes ou mesmo menores. Portanto, esta pesquisa objetivou, com o auxílio da análise de variância, investigar a influência da variação do teor de umidade (de 12% ao ponto de saturação das fibras) em doze propriedades mecânicas da espécie Dipteryx odorata. Dentre tais, quatro não apresentaram variações significativas entre a umidade de 12% e o ponto de saturação, concluindo que a formulação normativa não abrange todas as propriedades, para todas as espécies. Ademais, verificou-se que os modelos de correção da norma conduzem a valores de resistência superiores àqueles obtidos experimentalmente, subestimando as estruturas e desfavorecendo a segurança.

Resumo em Inglês:

ABSTRACT Brazil has a large forest territory that favors the incidence of numerous tree species. For a wood species to be used in a structural system, a series of characterizations of its physical-mechanical properties are necessary. In this context, one of the variables to be studied is the moisture content, whose variability can significantly interfere with its properties. The current Brazilian standard establishes models for correcting strength and stiffness for equilibrium moisture, admitting a linear increase inversely proportional to the moisture content. However, in some species, this phenomenon may not occur, leading to constant or even smaller values. Therefore, this research aimed, with the aid of analysis of variance, to investigate the influence of variation in moisture content (from 12% to fiber saturation point) on twelve mechanical properties of the species Dipteryx odorata. Among these, four did not show significant variations between 12% moisture and saturation point, concluding that the standard formulation does not cover all properties for all species. Furthermore, it was found that the standard correction models lead to strength values higher than those obtained experimentally, underestimating the structures and disfavoring safety.

Resumo em Português:

RESUMO À obtenção de materiais compósitos é de grande interesse para a indústrias automotiva e aeroespacial. Este estudo tem como objetivo a obtenção via metalurgia do pó o compósito Al-4,5Cu reforçado com adições de 5%, 10% e 15% de partículas de carbeto de silício. Os pós elementares foram analisados por Microscopia Eletrônica de Varredura (MEV) e Difração de Raios-X (DRX). Para a determinação da tensão de compactação utilizou-se ensaios de compressibilidade, sendo adotada a carga de 200 MPa. A atmosfera sinterização foi de nitrogênio com elevado grau de pureza em isoterma de 590ºC durante 90 minutos. Para a caracterização microestrutural foram utilizadas técnicas de microscopia óptica (MO) e microscopia eletrônica de varredura (MEV). O comportamento polimórfico foi avaliado pela técnica de difração de Raios-X (DRX) e as microdurezas avaliadas pelo método Vickers (HV0,1). Os resultados demostraram a difusão de cobre na matriz de alumínio formando o intermetálico Al2Cu. Já à adição de carbeto de silício não afetou de forma significativa a formação do compósito. Detectou-se aumento de microdureza para adições acima de 10% de SiC. Conclui-se que existe viabilidade da obtenção de componentes com ligas compósitas de alumínio, cobre e carbeto de silício via metalurgia do pó.

Resumo em Inglês:

ABSTRACT The obtainment of composite materials is of great interest for the automotive and aerospace industries. This study aims to obtain through powder metallurgy the Al-4,5Cu composite reinforced with additions of 5%, 10% and 15% of silicon carbide particles. The elemental powders were analyzed by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). To determine the compressive stress, compressibility tests were used, and a load of 200 MPa was adopted. The sintering atmosphere was high purity nitrogen at an isotherm of 590ºC for 90 minutes. For microstructural characterization Optical Microscopy (OM) and scanning electron microscopy (SEM) techniques were used. The polymorphic behavior was evaluated by X-Ray Diffraction (XRD) technique and the microhardness evaluated by Vickers method (HV0,1). The results demonstrated the diffusion of copper in the aluminum matrix forming the intermetallic Al2Cu. The addition of silicon carbide did not affect significantly the formation of the composite. An increase in microhardness was detected for additions above 10% of SiC. It is concluded that there is feasibility of obtaining components with composite alloys of aluminum, copper and silicon carbide via powder metallurgy.

Resumo em Português:

RESUMO Entende-se que as lajes pré-fabricadas mistas são sistemas compostos, nos quais se constituem por vigotas de concreto (armado ou protendido), elementos de preenchimento e uma camada de solidarização em concreto armado. É um sistema construtivo muito utilizado no mundo, principalmente, em países ibero-americanos, como o Brasil e Espanha, por exemplo. No entanto, ainda há desconhecimento sobre a compatibilidade entre os resultados teóricos para os experimentais, uma vez que são sistemas compostos e as variáveis podem ser determinantes nos modelos de previsão. Portanto, este estudo teve como objetivo comparar os resultados teóricos e experimentais de lajes mistas pré-fabricadas. Para isso, desenvolveu um programa experimental de ensaios de flexão para uma laje com vigota central protendida reforçada de cada lado com elementos de laje e uma cobertura de concreto armado com malha de 5 cm. As variáveis experimentais foram o diâmetro da armadura de aço e do material de enchimento (telhas de cerâmica ou blocos de poliestireno expandido). Este estudo tem 4 etapas: caracterização dos materiais, ensaios mecânicos da vigota, efeito do material de enchimento no comportamento estrutural e comportamento teórico e experimental do sistema na fissuração e ruptura. Vigotas protendidas romperam na região de compressão durante os testes de flexão, independentemente do diâmetro da armadura de aço. O material de enchimento não alterou a carga de ruptura das lajes, mas os blocos de EPS permitiram deflexões consideráveis. Em relação ao momento fletor máximo, os modelos teóricos selecionados apresentaram concordância de até 99% nos valores experimentais para vigotas reforçadas com aço de 4 mm de diâmetro. Entretanto, para as nervuras com fios de 5 e 6 mm, a análise não se mostrou tão válida, chegando a uma relação de aproximadamente, 70 e 60%, respectivamente.

Resumo em Inglês:

ABSTRACT The composite precast slabs are composite systems, in which they are constituted by concrete joists (reinforced or prestressed), filling components and a solidarization layer in reinforced concrete. It is a construction system widely used in the world, mainly in Ibero-American countries, such as Brazil and Spain, for example. However, there is still a lack of knowledge about the compatibility between the theoretical results and the experimental ones, since they are composite systems, and the variables can be decisive in the theoretical models. Therefore, this study aimed to compare the theoretical and experimental results of precast composite slabs. This study developed an experimental program of flexing tests for a slab with pre-stressed center joist reinforced on each side with half-longitudinal slab components and a 5 cm mesh-reinforced concrete cover. Experimental variables were the diameter of steel reinforcement and filler material (ceramic blocks or Expanded Polystyrene – EPS blocks). This study has 4 steps: materials characterization, mechanical tests of the joist, effect of filler material in the structural behavior and theoretical and experimental system behavior at fissuring and rupturing. Prestressed joists ruptured in compression regions during bending tests regardless of the diameter of steel reinforcement due to concrete low strength. Filler material did not alter the slabs rupturing load, but EPS blocks allowed considerable deflections. Regarding maximum bending moment, the selected theoretical models had an agreement of up to 99% on experimental values for 4 mm diameter steel-reinforced joists. However, for the joints with 5 and 6 mm wires, the analysis did not prove to be so valid, reaching a ratio of approximately 70 and 60%, respectively.

Resumo em Português:

RESUMO O corante azul de metileno, amplamente utilizado na indústria têxtil, é capaz de causar sérios danos, caso despejado nos corpos hídricos sem o devido tratamento. O objetivo deste trabalho foi estudar a eficiência do uso de bambu, in natura e carvão vegetal, como bioadsorvente na remoção do corante azul de metileno. Para isso, o bambu in natura e o bambu ativado termicamente foram produzidos e caracterizados por meio de análises de área superficial específica, termogravimétricas, microscopia eletrônica de varredura e espectroscopia no infravermelho. Ensaios de adsorção, em batelada, foram realizados com os bioadsorventes produzidos, utilizando planejamento experimental, do tipo fatorial 2³ e repetição do ponto central. Foram obtidas as condições do processo de adsorção para o bambu in natura, com 16 g/L de concentração de adsorvente, 50 mg/L de concentração de corante e pH =10, alcançando uma eficiência de remoção de 98,1%. As mesmas condições foram usadas com o bambu carvão, obtendo-se uma eficiência de remoção do corante de 92,2%. A diferença observada na porcentagem de remoção do corante deve-se às características de cada bioadsorvente. Os resultados demonstraram que o uso do bambu como bioadsorvente pode ser uma alternativa eficiente e sustentável para o tratamento de efluente com corantes pelo processo de adsorção.

Resumo em Inglês:

ABSTRACT The methylene blue dye, widely used in the textile industry, is capable of causing serious damage if dumped into water bodies without proper treatment. The objective of this work was to study the efficiency of using bamboo, in natura and charcoal, as bioadsorbents in the removal of methylene blue dye. For this, fresh bamboo and thermally activated bamboo were produced and characterized by specific surface area, thermogravimetric, scanning electron microscopy and infrared spectroscopy. Batch adsorption tests were carried out with the bioadsorbents produced, using an experimental design, of the 23 factorial type and repetition of the central point. The conditions of the adsorption process for bamboo in natura were obtained, with 16 g/L of adsorbent concentration, 50 mg/L of dye concentration and pH =10, achieving a removal efficiency of 98.1%. The same conditions were used with charcoal bamboo, obtaining a dye removal efficiency of 92.2%. The difference in dye removal percentage is due to the characteristics of each bioadsorbent. The results demonstrate that the use of bamboo as a bioadsorbent can be an efficient and sustainable alternative for the treatment of effluent with dyes through the adsorption process.

Resumo em Português:

RESUMO A busca por bioadsorventes eficazes e de baixo custo para a remoção de corantes de efluentes industriais tem despertado a demanda por novas pesquisas a fim de amenizar os impactos negativos causados ao meio ambiente. Nesse sentido, o objetivo do trabalho foi avaliar o potencial da pele prata de café (PPC) como bioadsorvente de baixo custo na remoção do corante azul de metileno (MB) de soluções aquosas por meio dos estudos de cinética e equilíbrio de adsorção. O resíduo foi submetido a caracterizações físico-químicas, área de superfície específica (BET), presença de grupos funcionais (FTIR), análise elementar (CHNS-O), ponto de carga zero (pHPCZ) e cristalinidade (DRX). Os resultados mostraram que a PPC apresentou estrutura preponderantemente amorfa composta por holocelulose (38,36%), lignina (34,97%) e minerais (potássio, cálcio e magnésio). A baixa área de superfície específica (0,383 m2/g) foi compensada pela diversidade de grupos funcionais de superfície contendo oxigênio, confirmados pela predominância de carbono (55,93%), oxigênio (32,91%) e hidrogênio (6,37%). A análise pHPCZ mostrou que o ponto de carga zero da PPC foi de 6,49. O processo de equilíbrio foi atingido em 24 h, propiciando uma cinética retratada pelo modelo Elovich (R2(aj.)= 0,999; χ2= 0,233), o qual apresentou valores de taxas de adsorção inicial (α) e dessorção (β), de 2,405 mg/g.min e 0,587 mg/g, respectivamente. A isoterma que melhor se ajustou aos dados de equilíbrio para o sistema foi a de Langmuir (R2(aj.)= 0,991; χ2= 99,176), indicando adsorção em monocamada. A adsorção de MB pela PPC foi favorável, apresentando fatores de separação (RL) entre 0,58 e 0,03. A capacidade máxima de adsorção da PPC (Qmax= 313,69 mg/g) foi superior a outros tipos de adsorventes de baixo custo relatados na literatura, demonstrando assim o seu potencial uso como bioadsorvente para a remoção de corantes catiônicos de solução aquosa.

Resumo em Inglês:

ABSTRACT The search for effective and low-cost adsorbents to remove dyes from industrial effluents has promoted the demand for new research aimed to mitigate negative impacts caused to the environment. In this sense, this work aimed to evaluate the potential of coffee silver skin (PPC) as a low-cost adsorbent in the removal of methylene blue (MB) dye from aqueous solutions through studies of kinetics and adsorption equilibrium. Subsequently, the material was subjected to physicochemical characterization, specific surface area (BET), presence of functional groups (FTIR), elemental analysis (CHNS-O), point of zero charge (pHPZC), and crystallinity (XRD). The results showed that PPC presented a predominantly amorphous structure composed of holocellulose (38.36%), lignin (34.97%), and minerals (potassium, calcium, and magnesium). The low specific surface area (0.383 m2/g) was compensated by the diversity of surface functional groups containing oxygen, confirmed by the predominance of carbon (55.93%), oxygen (32.91%), and hydrogen (6.37%). The pHPZC analysis showed that the point of zero charge of the PPC was 6.49. The equilibrium time of the adsorption process was 24 h, following kinetics described by the Elovich model (R2(aj.)= 0.999; χ2= 0.233), which represented an initial adsorption rate (α) and desorption rate (β) corresponding to 2.405 mg/g.min and 0.587 mg/g, respectively. The adsorption equilibrium data were better fitted by the Langmuir model (R2(aj.)= 0.991; χ2= 99.176), indicating that the adsorption of MB by PPC occurred on the monolayer. The adsorption of MB by PPC was favorable, presenting separation factors (RL) between 0.58 and 0.03. The maximum adsorption capacity of PPC (Qmax= 313.69 mg/g) was superior to other types of low-cost adsorbents reported in the literature, thus demonstrating its potential use as an adsorbent for the removal of cationic dyes from aqueous solution.

Resumo em Inglês:

ABSTRACT The state of Para is one of the greatest producers of mineral substances in Brazil. Kaolin for paper coating industry and bauxite for alumina and aluminium production are amongst the most important commodities. The latter is responsible for the generation of red mud, a well-known residue from Bayer process. The kaolin processing plants are also responsible for the generation of large amounts of wastes, in this case, very fine-grained kaolinite (white mud). The research aimed to find a final destination for such residues by developing new building materials. The proposed material is a pozzolanic pigment produced through calcination and grinding of mixtures of red mud and kaolin waste. The pozzolanic pigments provided increased mechanical strength and color stability of the colored mortars relative to the inert pigment. The pozzolanic characteristics of the pigments reduced the leaching of the mortars. The new material has proven to be promising in its application as an innovative construction material, with the possibility of using these residues in a market that is little explored in Brazilian civil construction: colored mortars and concrete.

Resumo em Português:

RESUMO Os nanomateriais (nanosílica, nanotubos de carbono e derivados do grafeno) vêm sendo investigados como potenciais adições capazes de reforçar a matriz cimentícia, principalmente em relação à resistência à tração, por meio dos mecanismos de restrição à iniciação e à propagação das fissuras na escala nanométrica. Como uma nova classe de nanomaterial em escala bidimensional, o óxido de grafeno (OG) tem recebido grande atenção no meio científico devido à sua elevada superfície específica, boa dispersão em água, condutibilidade térmica e elétrica, elevado módulo de elasticidade, além de elevada resistência à tração. Contudo, tem-se conhecimento de que a adição de nanomateriais em matrizes cimentícias pode provocar alterações na cinética da reação de hidratação do cimento. Isso ocorre devido à elevada superfície específica dos nanomateriais, que requer uma grande quantidade de água no preparo das pastas, influenciando diretamente na velocidade da reação de hidratação e no calor total acumulado. Com base nisto, buscou-se, neste trabalho, investigar os efeitos da adição do óxido de grafeno sobre o perfil térmico e calor de hidratação de pastas de cimento Portland. Foram realizados ensaios com adição de óxido de grafeno produzido e patenteado no CTNano/UFMG1 em pastas de cimento de classe CP-III-RS-40, nos teores de 0,03%OG e 0,05%OG. No ensaio de calorimetria, foram observados aumentos no pico de temperatura para as pastas de cimento com adição de OG, bem como redução do tempo de pico, o que indica que este nanomaterial de fato altera a cinética da reação de hidratação do cimento, tanto pelo efeito acelerador de pega decorrente do pH ácido da solução de OG, como pelo efeito de adsorção de moléculas de água e componentes do cimento pelos grupos funcionais de oxigênio, o que aumenta a taxa de reação.

Resumo em Inglês:

ABSTRACT Nanomaterials (nanosilica, carbon nanotubes and graphene derivatives) have been investigated as potential additions capable of reinforcing the cement matrix, mainly in relation to tensile strength, through the mechanism of restriction to the inicitation and propagation of cracks at the nanometer scale. As a new class of nano-material on a two-dimensional scale, graphene oxide (GO) has received great attention in the scientific field due to its high specific surface, good dispersion in water, thermal and electrical conductivity, high modulus of elasticity, in addition to high tensile strength. However, it is known that the addition of nanomaterials in cementitious matrices can cause changes in the kinetics of the cement hydration reaction. This is due to the high specific surface of nanomaterials, which requires a large amount of water in the preparation of the pastes, influencing the hydration reaction rate and the total accumulated heat. Based on this, the aim of this work was to investigate the effects of the addition of graphene oxide on the thermal profile and hydration heat of Portland cement pastes. Tests were carried out with the addition of graphene oxide produced and patented at CTNano/UFMG in cement pastes class CP-III-RS-40, at levels of 0.03%GO and 0.05%GO. In the calorimetry test, increases in the peak temperature were observed for the cement pastes with the addition of GO, as well as a reduction in peak time, which indicates that this nanomaterial actually changes the kinetics of the cement hydration reaction, both by the accelerating effect of setting due to the acidic pH of the GO solution, and by the adsorption effect of water molecules and cement components by the oxygen functional groups, which increases the reaction rate.

Resumo em Português:

RESUMO Os materiais compósitos de base cimentícia, incluindo pasta de cimento, argamassa e concreto, são os materiais mais comumente utilizados na construção civil. No entanto, a sua natureza frágil, elevada dureza, baixa resistência à tração e propensão às fissuras são fatores-chave que comprometem a durabilidade e resultam em altos custos de manutenção das estruturas. Materiais de reforço como barras de aço, fibras de aço, fibras de carbono, fibras de vidro e polímeros foram extensivamente aplicados em concretos nos últimos anos. Embora estes materiais possam melhorar bastante a tenacidade do concreto, solucionando bem os defeitos que ocorrem na micro escala inerentes aos materiais cimentícios, as fraturas nestes materiais persistem. Os nanomateriais (como nanosílica, nanotubos de carbono e derivados do grafeno) podem atuar complementarmente às fibras tradicionais, reforçando ainda mais os materiais cimentícios fibrosos, por meio dos mecanismos de restrição à iniciação e à propagação das fissuras na escala nanométrica, bem como disponibilização de uma área de superfície específica extremamente elevada para interação com os produtos de hidratação do cimento. Dentre os nanomateriais, o óxido de grafeno (OG) apresenta um enorme potencial para aplicação nos compósitos cimentícios. Neste trabalho foram realizados ensaios com adição de OG produzido e patenteado no CTNano/UFMG em pastas de cimento classe CP-III-RS-40. Objetivou-se avaliar as propriedades mecânicas de pastas de cimento com adição de OG, nos teores de 0,03% e 0,05%. Dentre os teores de adição analisados, o teor de 0,05%OG permitiu a obtenção dos melhores resultados aos 28 dias de cura. Foram obtidos aumentos de 19,40%, 16,86%, 27,37% e 21,55% no módulo de elasticidade, resistência à tração na flexão, tenacidade à fratura e energia de fratura, respectivamente. Diante destes resultados, pode-se inferir que o OG tem potencial para ser aplicado na construção civil, visando a melhoria das propriedades mecânicas e parâmetros de fratura de pastas de cimento.

Resumo em Inglês:

ABSTRACT Cement-based composite materials, including cement paste, mortar and concrete, are the most commonly used materials in civil construction. However, its brittle nature, high hardness, low tensile strength and propensity to cracking are key factors that compromise durability and result in high maintenance costs for structures. Reinforcement materials such as steel bars, steel fibers, carbon fibers, glass fibers and polymers have been extensively applied to concrete in recent years. Although these materials can greatly improve the toughness of concrete, solving well the defects that occur in the micro scale inherent to cementitious materials, the fractures in these materials persist. Nanomaterials (such as nanosilica, carbon nanotubes and graphene derivatives) can act as a complement to traditional fibers, further reinforcing fibrous cementitious materials, through mechanisms that restrict the initiation and propagation of cracks at the nanometer scale, as well as providing an extremely high specific surface area for interaction with cement hydration products. Among the nanomaterials, graphene oxide (GO) has an enormous potential for application in cementitious composites. In this work, tests were carried out with the addition of GO produced and patented at CTNano/UFMG in cement pastes class CP-III-RS-40. The objective was to evaluate the mechanical properties of cement pastes with the addition of GO, at the levels of 0.03% and 0.05%. Among the addition levels analyzed, the content of 0.05%GO allowed to obtain the best results at 28 days of curing. Increases of 19.40%, 16.86%, 27.37% and 21.55% were obtained in the modulus of elasticity, flexural tensile strength, fracture toughness and fracture energy, respectively. In view of these results, it can be inferred that GO has the potential to be applied in civil construction, aiming the improvement of the mechanical properties and fracture parameters of cement pastes.

Resumo em Inglês:

ABSTRACT Uranium dioxide pellets (UO2) used as fuel in nuclear power reactors are subjected to high thermal gradients and may undergo swelling during reactor operation. The swelling of UO2 pellets, resulting from the fission products, causes cracking of the material and it is thus critical to study their behaviour. This study evaluated the application of the ultrasonic method in obtaining the elastic constants of UO2 pellets. Due to the difficulties in handling nuclear material, we used tablets of alumina (Al2O3) for a comparative study. For this, two sets of 10 Al2O3pellets with densities of 92% and 96% were fabricated. Ultrasonic transmission technique was used for obtaining measurements of the travel time of longitudinal and transverse ultrasonic waves. Equations relating material density and velocity of the ultrasonic wave to the elasticity, shear and Poisson’s modules allowed the determination of these elastic constants, whose values showed excellent agreement with those available in the literature for Al2O3.

Resumo em Inglês:

ABSTRACT In this work, titanium nitride (TiN) and titanium aluminum nitride (TiAIN) films have been obtained via triode magnetron sputtering. The films were deposited using a direct current source on plasma nitrided AISI D2 tool steel (duplex treatment), non-nitrided steel, and silicon. The nitrided layer was characterized by scanning electron microscopy (SEM), Vickers microhardness, and X-ray diffraction (XRD). The films were characterized by SEM and XRD. The mechanical properties of the coatings were determined using the instrumented indentation technique (IIT) and the adhesion of the film to the substrate was qualitatively evaluated using the Rockwell C test. Both films presented no significant variation in hardness (H) and elastic modulus (E). However, compared to the films obtained in non-nitrided steel, the duplex treatment improvided the film-substrate adhesion. The improvement in adhesion can be attributed to the preliminary plasma nitriding treatment and the compressive loads acting on the nitrided surface.

Resumo em Inglês:

This paper presents a numerical procedure for estimation of the precision and accuracy of the acoustic birefringence technique for evaluation of residual and applied stresses in civil structures and components. This procedure accounts in an automatic and systematic way for the uncertainties in the input data and their propagation throughout the calculations. The acoustic birefringence is defined from the speeds of two mutually orthogonal volumetric waves of normal incidence, but when the use of a pulse-echo measurement system is feasible, the birefringence can be defined directly from the time-of-flight of the waves, since they travel the same physical space. The times-of-flight of the waves are estimated by coupling the mathematical techniques of cross correlation and data interpolation, whereas the material’s acoustoelastic constant is determined via a weighted linear regression. As an example, the estimation of the precision and accuracy in the evaluation of the stresses in a beam under bending is discussed.

Resumo em Português:

RESUMO Este estudo avalia o efeito da associação dos tratamentos térmicos de recozimento e desestabilização na precipitação e morfologia de carbonetos secundários e na dureza de uma liga de ferro fundido branco alto cromo (FFBAC) com adição de nióbio. O ferro fundido branco alto cromo é utilizado na fabricação de componentes envolvendo solicitações de desgaste, principalmente nas indústrias mineradoras, em equipamentos como chutes de transporte de minério, devido à sua elevada dureza e alta resistência ao desgaste abrasivo. Os tratamentos térmicos visam melhorar as propriedades mecânicas, por meio da precipitação de carbonetos secundários e da obtenção de matrizes martensíticas. A adição de cromo nos ferros fundidos tem como finalidade formar carbonetos e elevar a dureza da liga. A metodologia utilizada foi a fundição do material com adição de 0,5% de nióbio como elemento de liga e a caracterização metalográfica por meio de microscopias ópticas e eletrônicas, bem como a quantificação de carbonetos e a realização de ensaios de dureza. Foram analisadas amostras desestabilizadas sem e com recozimento prévio e foi verificado que o recozimento favoreceu uma maior precipitação de carbonetos secundários M7C3, possibilitando uma redução no tempo de tratamento térmico de desestabilização e a transformação da matriz austenítica em martensítica durante o resfriamento, promovendo um aumento da dureza.

Resumo em Inglês:

ABSTRACT This study evaluates the effect of association annealing and destabilizing heat treatments in precipitation and morphology of secondary carbides and hardness in a high-chromium white cast iron alloy with the addition of niobium. White cast iron is used in the manufacture of components involving wear requests, mainly in the mining industries, in equipment such as ore transport chutes, due to its high hardness and high strength to abrasive wear. The heat treatments aim to improve the mechanical properties, through the precipitation of secondary carbides and the obtaining of martensitic matrices. The addition of chromium in cast irons aims to form carbides and increase the hardness of the alloy. The methodology used was the casting of the material with the addition of 0.5% niobium as an alloying element and metallographic characterization by means of optical and electronic microscopy techniques, as well as the quantification of carbides and performance of hardness tests. Destabilized samples were analyzed without and with previous annealing and it was verified that the annealing favored a greater precipitation of secondary carbides M7C3, allowing a reduction in the thermal treatment time of destabilization and the transformation of the austenitic matrix into martensitic during the cooling, promoting an increase in hardness.

Resumo em Português:

RESUMO A escória de forno panela é um resíduo composto essencialmente por cal virgem ou cal hidratada, cujos teores dependem da matéria-prima e do processo de resfriamento que deu origem ao lote de escória. Com essa composição química, ela é utilizada pela construção civil como aglomerante hidráulico em matrizes cimentícias. Os compostos químicos citados também estão presentes no cimento Portland, que fazem parte das reações químicas de hidratação e endurecimento. No entanto, a qualidade dos lotes EFP requer atenção à expansão de volume, causada por compostos químicos cuja presença e teor pode ser controlada pelo método de resfriamento adotado na produção. Considerando o uso deste material em substituição parcial ao cimento Portland, o objetivo deste estudo foi a caracterização físico-química de amostras de EFP para avaliar a influência do método de resfriamento em seu potencial como aglomerante complementar em matrizes cimentícias. Neste sentido foram analisadas 3 amostras de diferentes lotes e os efeitos de cada processo de resfriamento. Os resultados incluem análise de massa específica, difração de laser para análise de tamanho de partícula, fluorescência de raios X e testes de difração de raios X. Verificou-se que a amostra obtida por resfriamento lento é a mais indicada como aglomerante, pois apresenta menor possibilidade de reações químicas expansivas e apresenta maior finura.

Resumo em Inglês:

ABSTRACT Ladle furnace slag is a waste composed essentially of quicklime or hydrated lime, whose contents depend on the raw material and the cooling process that led to the slag batch. With this chemical composition, it is used by civil construction as a hydraulic binder in cement matrices. The chemical compounds mentioned are also present in Portland cement, which are part of the chemical reactions of hydration and hardening. However, the quality of LFS batches calls for attention to volume expansion caused by chemical compounds whose presence and content can be controlled by the cooling method adopted in the production. Considering the use of this material as a partial replacement for Portland cement, the objective of this study was the physicochemical characterization of LFS samples to evaluate the influence of the cooling method on its potential as a complementary binder in cementitious matrices. In this sense, 3 samples from different batches were analyzed and the effects of each cooling process. The results include analysis of specific mass, laser diffraction for particle size analysis, X-ray fluorescence and X-Ray Diffraction tests. It was verified that the sample obtained by slow cooling is the most suitable as binder, as it features less possibility of expansive chemical reactions and presents greater fineness.

Resumo em Inglês:

ABSTRACT Pyrite (FeS2) is one of the main tailings derived from coal mining. When processed, pyrite has several applications with high value-added, in contrast, if improperly discarded, it causes major environmental impacts, like the acid mine drainage. For those reasons, the seeking for beneficiation techniques of Pyrite has been the target of numerous studies. One of the most employed techniques is the separation by density using heavy liquids, like bromoform, as a separation medium. In the present work, we propose the use of lithium heteropolytungstate (LST), a non-halogenated and non-toxic solution, as an alternative in the separation by density method. For the experiments, raw pyrite samples were collected from the tailings of coal extraction from a mining company in Santa Catarina, Brazil. After the separation process, the samples before and after the beneficiation were characterized by XRD, FTIR, and XRF techniques. The results revealed that the separation technique used in this work led to a significant increase in the concentration of pyrite, going from less than 10% in the raw sample and reaching almost 80% after processing. This impressive result reveals that LST represents a promising alternative for separating pyrite by density techniques, showing much greater effectiveness than other heavy liquids used in the literature, in addition to being environmentally friendly.

Resumo em Português:

RESUMO As restaurações dentárias que são realizadas com resinas compostas apresentam aspecto estético muito satisfatório, com coloração próxima à do dente e propriedades mecânicas aceitáveis. O grande desafio destas resinas é que tenham o mesmo, ou semelhante, desempenho mecânico que o dente original. O presente trabalho foi desenvolvido com o objetivo de avaliar as partículas inorgânicas do composto Al2O3-0,5B2O3-SiO2, produzidas pela técnica de spray pirólise (USP) para aplicação em resinas compostas dentárias. A síntese das partículas foi realizada empregando o método sol-gel, com os precursores nitrato de alumínio, ácido bórico e tetraetilortosilicato TEOS com pH da solução de 1,5. A fim de verificar as propriedades das partículas realizou-se caraterização físico-química pelo método de adsorção e dessorção de nitrogênio via BET, análise por MEV, FTIR, DRX, DTA-TGA, RMN e ensaio mecânico de tração. As imagens obtidas por MEV indicaram que as partículas eram esféricas de granulometria média de 1,26 ± 0,04 µm, sendo classificadas como microhíbridas. Pelos difratogramas observou-se característica amorfa, confirmando que o método de síntese aplicado é eficiente para a produção de materiais vítreos. Os testes com resina composta experimental apresentaram taxa de polimerização aceitável (16 e 9%), mas baixa resistência à compressão mecânica: entre 9,55 e 13,27 MPa.

Resumo em Inglês:

ABSTRACT Dental restorations that are performed with composite resins present a very satisfactory aesthetic appearance, with a color close to that of the tooth and acceptable mechanical properties. The great challenge of these resins is that they have the same, or similar, mechanical performance as the original tooth. The present work was developed with the objective of evaluating the inorganic particles of the compound Al2O3-0,5B2O3-SiO2, produced by spray pyrolysis (USP) for application in dental composite resins. The synthesis of the particles was carried out using the sol-gel method, with the precursors aluminum nitrate, boric acid and TEOS tetraethylorthosilicate with a pH of 1.5. In order to verify the properties of the particles, physicochemical characterization was carried out using the nitrogen adsorption and desorption method via BET, analysis by SEM, FTIR, XRD, DTA-TGA, NMR and mechanical tensile testing. The images obtained by SEM indicated that the particles were spherical with a mean granulometry of 1.26 ± 0.04 µm, being classified as microhybrid. From the diffractograms, an amorphous characteristic was observed, confirming that the applied synthesis method is efficient for the production of glassy materials. Tests with experimental composite resin showed an acceptable polymerization rate (16 and 9%), but low mechanical compressive strength: between 9.55 and 13.27 MPa.

Resumo em Inglês:

ABSTRACT Manganese oxides were synthesized during 40 min at 140 ºC via Microwave-Assisted Hydrothermal (MAH) method and treated at different temperatures in order to evaluate the phase evolution using structure refinement (Rietveld method). The samples obtained were heat treated at temperatures defined by means of thermal analysis (160 ºC, 480 ºC, 715 ºC, 870 ºC, 920 ºC and 1150 ºC) and analyzed by X-Ray Diffractometry (XRD), X-Ray Fluorescence (XRF), Fourier Transform Infrared (FTIR) spectroscopy, Raman scattering, UV-Vis absorption and Scanning Electron Microscopy (SEM). Structural characterizations allowed to identify five distinct phases: α-MnO2, Mn3O4, Mn5O8, Na2Mn5O10 and Na4Mn9O18 with weight percentages dependent on the heat treatment. The hausmannite structure (average crystallite size ranging from 28.9 nm to 99.1 nm) is present in all samples and go through various oxidation and reduction processes from 160 ºC to 1150 ºC without any major variation in the lattice parameters. Chemical characterizations identifies the presence of Na+ ions in all samples, either as substitution defects or as components of specific crystalline structures (Na2Mn5O10 and Na4Mn9O18), showing that the synthesized manganese oxides works as Na+ intercalation compounds, important materials for energy storage devices optimization. The results presented enables a better interpretation of the thermal and structural characteristics of manganese oxides synthesized via MAH.