Resumo em Inglês:

Abstract In Brazil, a significant amount of tilapia carcass waste is produced every year. The aim of this study is to evaluate the recycling of tilapia carcass waste as an alternative calcium precursor to produce biphasic calcium phosphate (BCP) powder via a wet chemical precipitation method in different HNO3 concentrations. The synthesized powders were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, average crystallite size, and refinement by the Rietveld method for the quantification of crystalline phases. The experimental results indicated the formation of a BCP bioceramic with different amounts of β-calcium pyrophosphate (β-CPP) and β-tricalcium phosphate (β-TCP), depending on the HNO3 concentration. The new BCP powders showed an average crystallite size between 57.7 and 59.2 nm. Such a result suggests a possibility of friendly recycling of tilapia carcass waste for biomedical applications.

Resumo em Inglês:

Abstract The utilization of waste or by-products in geopolymers is an effective strategy that contributes to the development of more sustainable ceramics. The present study aimed to evaluate the physico-mechanical properties of compositions prepared by partially replacing aluminosilicate precursors (metakaolin or calcined diatomite) with solid wastes (granite, roof tile chamotte, or glass powder) at contents of 10, 20, and 40 wt%. Geopolymers were synthesized by blending the solid raw materials (precursor+wastes) with an alkaline activating solution comprising NaOH and colloidal silica suspension. The samples were cured at 40 °C for 24 h, and the following analyses were conducted: elastic modulus, compressive strength, porosity, density, X-ray diffraction, and Fourier-transform infrared spectroscopy measurements. The results demonstrated that the formulation containing 10 wt% of chamotte exhibited the best performance, showing a remarkable mechanical strength of 31.7 MPa after one day of curing. Therefore, by incorporating waste materials into geopolymers, not only can the environmental impact be minimized, but it also presents an opportunity to utilize resources that would otherwise go to waste.

Resumo em Inglês:

Abstract EUROFER is a reduced-activity ferritic-martensitic steel used in the construction of nuclear fusion reactors. Despite its good properties of mechanical strength, corrosion, creep, and radioactive damage, its maximum working temperature is 500 °C due to microstructural changes that occur above this condition. This study aims to investigate the use of niobium pentoxide (Nb2O5) in EUROFER-based alloys through a high-energy milling technique. EUROFER chips were processed in a planetary ball mill with different concentrations of Nb2O5 for 10 h. The results showed a reduction of approximately 32% in the particle size distribution of the milled powders compared to pure EUROFER. The X-ray diffraction patterns revealed a decrease solely in the lattice parameters of pure EUROFER and samples containing 3% Nb2O5. The addition of Nb2O5 also resulted in a reduction in saturation magnetization, and an increase in coercivity and magnetic remanence.

Resumo em Inglês:

Abstract The present work aims to identify variations in the mechanical and optical properties of samples produced from ZrO2 powders containing different Y2O3 contents (3Y-TZP, 4Y-PSZ, and 5Y-PSZ) intended for applications such as dental prostheses. Disc-shaped samples (n=60) were uniaxially pressed, sintered at 1550 °C-2 h, and characterized. Dense ceramics were obtained for all compositions. The increase of Y2O3 content led to the increase of the cubic-ZrO2 phase with a reducing tetragonal phase. As a result, mechanical properties were reduced (flexural strength of 1375~590 MPa and fracture toughness 7.2~4.1 MPa.m1/2) while translucency was improved. Based on the requirements of ISO-6872 standard, 3Y-TZP presents versatility for non-aesthetic applications, while 5Y-PSZ is recommended for aesthetic applications such as anterior teeth due to better translucency.

Resumo em Inglês:

Abstract The Brazilian wood furniture industry generates a significant amount of fine wood dust waste. In this work, a new lightweight dense/porous bi-layered ceramic tile was developed using fine wood dust waste as a substitute for ceramic tile paste by up to 10 wt% in the porous bottom layer. The bi-layered ceramic tile pieces were prepared by double uniaxial pressing and fired at 1235 ºC. The technical properties and sintered microstructure were investigated. The results showed that the fine wood dust waste acted as an effective pore-forming agent. The new bi-layered ceramic tiles showed good technical properties (water absorption=6.16-9.66% and flexural strength=18.10-28.74 MPa). The results also suggested that up to 10 wt% of fine wood dust waste can be valorized in the production of lightweight bi-layered ceramic tiles, which brings together the precepts for sustainable environmental management applications.

Resumo em Inglês:

Abstract Studies have proven that the use of waste in the production of clay ceramics is common for achieving the technical performance that is necessary for the application of these by-products. However, it is essential to analyze the feasibility of using these materials in terms of productivity and economic gains, in line with sustainability. The objective of this study is to determine the cost-benefit ratio of using rice husk ash in the production of clay ceramics. The methodological process consisted of a comparative analysis on an industrial scale between the formulation with up to 15% by volume of rice husk ash and the standard formulation previously used by the company. The economic aspects included the costs/consumption of raw materials, transport, and energy. The productivity throughout the process and technical characteristics of the final product were also evaluated. The costs of raw materials showed a financial gain of 7.0%, whereas the productivity analysis revealed that the greatest economic gain was in energy consumption during drying (13%).

Resumo em Inglês:

Abstract Strontium- and magnesium-doped lanthanum gallate ceramics exhibiting relatively high values of ionic conductivity, and chemical stability over a wide range of oxygen partial pressure are considered potential solid electrolytes for application in electrochemical devices for clean energy production. Recently, the addition of a second phase has been a strategy to improve the performance of solid electrolytes. In this work, doped-lanthanum gallate ceramics with up to 20 wt% yttria-stabilized zirconia addition were investigated to determine the effects of the minor phase on the microstructure evolution, hardness, and elastic modulus of the matrix. Composite solid electrolytes were prepared by mechanical mixing followed by solid-state sintering in the 1350-1500 ºC range. The mean grain size of composites was lower than that of the matrix for sintering temperatures up to 1400 ºC, but a fast grain growth was observed for higher temperatures. Improved mechanical properties were obtained for composites compared to those of the matrix.

Resumo em Inglês:

Abstract Ceramic composites based on Ce-TZP/Al2O3/H6A were sintered in order to promote grain growth and to study the effects of ZrO2 grain size on the properties of this material. A mixture of ZrO2-CeO2-Al2O3 powders was sintered at 1450 °C-2 h, following the manufacturer’s recommendations. Then, the samples were further treated at 1500 or 1600 °C, for 0, 2, 8, or 24 h. The sintered specimens were characterized by X-ray diffraction, relative density, and grain size distribution. Vickers nanohardness, Young’s modulus (E), and fracture toughness were measured. The materials showed complete densification for all sintering conditions studied. t-ZrO2, α-Al2O3, and cerium hexaluminate (H6A) were observed. The alumina and hexaluminate grains had average grain sizes of 0.7 and 4.5 μm (AR>3), respectively, without significant variations during the additional heat treatments. However, significant growth took place for the ZrO2 grains with increasing temperature and holding time, increasing the average grain size from 0.6~1.4 μm, when sintered at 1500 °C-2 h to 1600 °C-24 h, respectively. The materials exhibited Vickers nanohardness of 1800 HV and E=241±15 GPa. On the other hand, the considerable grain growth of the ZrO2 grains as a function of holding time reflected in a reduction of the fracture toughness, which decreased from 8.5 to 5.7 MPa.m1/2 for samples sintered at 1500 °C-2 h to 1600 °C-24 h, respectively.

Resumo em Inglês:

Abstract In the pursuit of unconventional binders that can reduce energy consumption in production, magnesium oxysulfate (MOS) cement emerges as a viable alternative. Moreover, carbon dioxide (CO2) has been employed in the curing process of certain MOS cement products, such as magnesia fiber cement, due to its capacity to enhance their performance. This study aims to assess the impact of pre-curing prior to accelerated carbonation on the physical-mechanical properties of magnesium oxide fiber cement boards. These boards were manufactured using the Hatschek process simulation and subjected to pre-curing periods of 24, 48, and 72 h post-production. The relationship between microstructural alterations and the physical-mechanical properties was examined through analyses including water absorption, apparent porosity, apparent density, four-point bending tests, X-ray diffraction, and scanning electron microscopy analyses. The results indicated that pre-curing had an influence on the physical-mechanical attributes of the manufactured boards. After 72 h, the carbonated materials exhibited a decline in mechanical performance, a phenomenon attributed to the carbonation reactions between CO2 and the hydration products responsible for enhancing the mechanical strength of the cementitious materials.

Resumo em Inglês:

Abstract The process known as powder bed fusion exhibits a lack of stabilization in the initial layers. One approach to address this challenge involves introducing a gas flow across the particulate medium. This solution enables more targeted applications of the technique, especially in zero-gravity environments. The objective of this study is to validate a methodology that utilizes computational fluid dynamics (CFD) and the discrete element method (DEM) to apply a gas flow within a porous medium under gravity-free conditions. The validity of the proposed solution was assessed using Ergun’s equation, resulting in an error of 6.65%, and the Kozeny-Carman equation, resulting in an error of 10.53%. The drag force exerted on the particles in the simulations surpassed the gravitational force (1g). Consequently, the application investigated in this study represents an effective alternative for employing 3D printing in the absence of gravitational forces.

Resumo em Inglês:

Abstract Lightweight mortars are indicated for services that require low specific mass composites. There are several lightweight aggregates available on the market. Waste rubber from tires is a low-density waste option that can be used as lightweight aggregate. The rubber waste when used in mortar reduces its density, in addition to bringing benefits from an environmental point of view. In this research, the mechanical behavior, and physical properties of mortars in which the natural fine aggregate contents were replaced by mixtures in different proportions of rubber, expanded vermiculite, and expanded clay were investigated. For the analysis of the properties of the composites, they were submitted to tests of dynamic modulus of elasticity, damping, compressive strength, flexural strength, coefficient of capillarity, density, and determination of ultrasonic wave transmission velocity. All tested mortars met the requirements of the Brazilian standard, being indicated for laying and covering walls and ceilings, in addition to having excellent acoustic and damping performance.

Resumo em Inglês:

Abstract The effect of adding different Y2O3 contents on the physical and mechanical properties of Ce-TZP/Al2O3 composites was investigated. Ce-TZP/Al2O3 powder blends containing 1~10 wt% Y2O3 were compacted at 100 MPa-30 s and sintered at 1500 °C-2 h or 1600 °C-2 h. The materials were characterized by X-ray diffraction and scanning electron microscopy, Raman spectroscopy, relative density, and the mechanical properties of Vickers hardness and fracture toughness. After sintering, the relative density of the sintered samples varied between 92.7% and 96.3%. Furthermore, the addition of Y2O3 resulted in an increase in the amount of cubic zirconia (c-ZrO2) and an increase in grain size in relation to the sample without the addition of Y2O3. With the increase of Y2O3 in the composition and consequent increase in the cubic ZrO2 phase content, although the hardness values did not present statistically significant variations, indicating average value of 12 GPa, a decrease in fracture toughness values was observed (10.0~5.5 MPa.m1/2) as a direct function of the reduction in the population of tetragonal zirconia grains, responsible for the toughening mechanism by phase transformation in these composites.

Resumo em Inglês:

Abstract Alternative cementitious materials able to partially replace or supplement the use of Portland cement, such as geopolymers, are becoming increasingly attractive due to lower emissions of air pollutants during their production. In addition, coupling geopolymers with additive manufacturing technologies such as 3D printing can contribute to achieving some of the Sustainable Development Goals (SDG) of settling housing issues. Additive manufacturing allows producing pre-fabricated building elements or even entire houses. However, enabling 3D printing using geopolymers requires understanding concepts of rheology, technology, and material sciences, such as different possibilities of formulations, rheological behavior, printing parameters, curing methods, reinforcement content, and fiber type. Cylindrical specimens were printed both with and without polypropylene fibers by controlling the geopolymer matrix formulation, printer displacement speed, mass percentage of fibers, and material flow through the printer’s extruder nozzle.

Resumo em Inglês:

Abstract The chemical conversion of gypsum into synthetic hydroxyapatite is an attractive approach to enhance the value of gypsum, a low-cost material, which can be discreetly implanted. The addition of biopolymers improves the resistance of the materials both before and after conversion. In this study, hydroxyapatite was produced from gypsum using a fixed water-to-gypsum ratio (w/g) of 0.7, along with gypsum/polymer composites. The polymers employed were polyhydroxybutyrate (PHB) and polyvinyl acetate (PVAc) at various mass ratios. Two methods were used to create the bodies: molding the paste and subtractive manufacturing. Mechanical compression tests were conducted both pre- and post-conversion to evaluate the impact of the conversion on material resistance and to compare it with the strength of subtractive manufacturing composites. For the gypsum/PHB composite, the best result was achieved at a 1% polymer concentration, yielding a resistance of 9.1±0.4 MPa, while for gypsum/PVAc, a compressive strength of 9.3±0.3 MPa was obtained at a 2% polymer concentration.

Resumo em Inglês:

Abstract ZrO2-ZrSiO4 composites obtained from mixtures of 3Y-TZP and SiO2 powders were investigated. Commercial 3Y-TZP powder and mixtures containing 5 or 10 wt% of SiO2 were prepared. Specimens (n=10/group) were uniaxially compacted and sintered at 1500 °C-2 h (5 °C/min). Sintered samples were characterized by their relative density, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and Vickers nanoindentation. The monolithic-ZrO2 sample presented full densification while increasing of SiO2 content progressively reduced the relative density. The crystalline phases presented in composites were tetragonal-ZrO2, cubic-ZrO2, ZrSiO4, monoclinic-ZrO2, and residual cristobalite (SiO2). Microstructural analysis indicated a distribution of zirconia grains, with heterogeneous regions rich in SiO2 surrounded by ZrSiO4 grains. Vickers hardness of 1590±19 HV for monolithic ZrO2, 1475±27 HV for ZrO2-5 wt% SiO2, and 1336±32 HV for ZrO2-10 wt% SiO2 were obtained indicating reduction in hardness with increasing SiO2 fraction. Furthermore, a reduction in fracture toughness was observed (7.2±0.8, 6.7±0.5, and 5.4±1.0 MPa.m1/2, respectively) and Young’s moduli measured were 174.1, 169.7, and 225.9 GPa, respectively. These experiments demonstrated, preliminarily, that the ZrO2-ZrSiO4 composite, based on 3Y-TZP-SiO2 powder mixtures, can achieve good levels of densification and present reasonab le mechanical properties, requiring improvements in microstructural homogenization. However, the presence of SiO2 and ZrSiO4 can improve the adhesion of zirconia to resin cement, requiring future studies focused on adhesion to confirm its viability.

Resumo em Inglês:

Abstract The possibility of application for lignin, a byproduct of paper and pulp production, as a partial replacement for cement in producing mortars and concretes is presented. Initially, mortars were prepared with substitution rates ranging from 0.0% to 50.0% to determine the best rates for subsequent application in concretes. Statistical analysis showed that the rates with the highest potential for application in concretes were 2.5%, 5.0%, and 10.0%. After preparing the concretes, test specimens were molded and subjected to axial compression, splitting tensile strength, water absorption by immersion, void ratio, and capillary water absorption tests after the curing period. The results showed that lignin, in rates higher than 5.0%, led to decreased mechanical strength; however, all concretes with lignin significantly reduced capillary water absorption, which can lead to greater material durability.

Resumo em Inglês:

Abstract Geopolymers are chemically bonded ceramics formed at room temperature and obtained using aluminosilicates and alkali activators. Geopolymers have found applications beyond construction, such as in wastewater treatment and ceramics. This research aims to develop geopolymers using coal mining waste (CMW) for various purposes. The waste used in this study was obtained from the Barro Branco layer in companies located in southern Santa Catarina/Brazil. The waste was thermally treated at 900 °C for 160 min, followed by grinding and characterization using X-ray fluorescence spectroscopy, X-ray diffraction, and particle size analysis. Geopolymeric samples were produced using 60 wt% waste, 25 wt% sodium silicate, and 15 wt% 10 M NaOH. The specimens were divided into three groups and cured using different methods. The results showed that thermal curing enhanced waste reactivity, reduced curing time, and improved compressive strength. However, long-term submersion curing decreased compressive strength due to sodium leaching, reducing reactivity.

Resumo em Inglês:

Abstract Alumina ceramics were reinforced with different amounts of stabilized-tetragonal zirconia nanoparticles, 3Y-TZP, and their properties were evaluated aiming for future applications in orthopedic medicine. Different amounts of 3Y-TZP (3 to 15 wt%) were mixed with Al2O3 powder, using high-energy milling (400 rpm-24 h). Samples were uniaxially compacted and sintered at 1600 °C-2 h. The samples were characterized by their relative density, microstructure, and crystalline phases. Furthermore, Vickers hardness, fracture toughness, and bending strength were determined. After the high-energy milling process, a considerable amount of monoclinic (m) ZrO2 was detected in the powder mixtures, besides the α-Al2O3 and tetragonal (t) ZrO2 phases. After sintering the samples presented relative densities greater than 98.5%, regardless of the amount of the Y-TZP additions used. Furthermore, the monoclinic phase was reconverted into the tetragonal phase during sintering. The Vickers hardness varied between 1750 and 1690 HV, depending on the amount of Y-TZP added. Bending strength and fracture toughness were also sensitive to the addition of Y-TZP, with values increasing from 351.5 to 701.7 MPa and KIC from 3.5 to 5.6 MPa.m1/2, indicating that the t-ZrO2 grains enable the activation of the transformation toughening mechanisms such as t→m phase transformation and residual stress. The biological responses of the composites, evaluated by their cytotoxicity and chemical solubility, accredit the materials developed for future in vitro and in vivo studies aimed at application as biomaterials.