Resumo em Inglês:

Abstract Six printing mixtures with variations in cement:sand ratios (in mass) were analyzed, keeping the water/dry material ratio constant, evaluating their printability, considering visual aspects, pumpability and filament integrity. The mixtures were subjected to mini-slump tests, spread on a consistency table, squeeze-flow, and deformation under load of the printed filaments at printing intervals of 0 min, 15 min and 30 min, and then the proportions of the compatible mixtures were determined. with the print. The properties in the hardened state, resistance to bending and compression, adhesion between layers, specific mass and voids index were determined for specimens extracted from printed parts. It was possible to observe that for the printing system used there is an ideal range for these constitutive relationships, and that the mixtures, even with different viscosities, measured according to the squeeze flow, can be printable, provided they meet the ideal ranges for the determined relationships. Regarding the interface of the printed layers, these are critical points of fragility, due to factors such as the formation of regions with voids and loss of surface moisture, which favors the reduction of the mechanical performance of the parts, with the increase in the deposition time.

Resumo em Inglês:

Abstract The present research proposed the use of construction and demolition waste (CDW) in adsorption of methylene blue dye in aqueous medium. CDW was studied in its natural form and calcined aiming to improve its properties, both being characterized by different techniques and subjected to adsorption studies. From the kinetic study, it was verified that both systems presented a better fit to the experimental data for the pseudo-second-order model (R2 >0.980). The concentration and temperature variation showed a maximum adsorption capacity of 112.23 mg.g-1 (natural) and 418.6 mg.g-1 (calcined) both for the temperature of 45 ºC. The experimental data fit better with the Langmuir isotherm model, with a correlation coefficient R2 ≥0.960 for both samples. It was observed that both residues presented favorable adsorption mechanisms and effective adsorption parameters, but the calcined sample presented better results, and thinking in a low-cost material, natural sample can be more economically advantageous. In this view, CDW represents a potential and promising alternative for water purification.

Resumo em Inglês:

Abstract The slag corrosion of Al2O3-MgO-C refractories for steelmaking ladles is addressed by a dynamic test by considering their characteristics, the experimental approach, and previous cup test data and thermodynamic simulation. To obtain reliable results, an alternative to the current practice of using the samples’ dimensions to estimate the corrosion wear was proposed. The brick with the higher periclase content and high open porosity was less resistant in the dynamic test. However, in the other two bricks, the smaller particles and the lower corrosion resistance of bauxite were considered the determining factors for the greater increase in wear during the dynamic test concerning the cup test.

Resumo em Inglês:

Abstract Phosphate materials based on Turquoise composition CuAl6(PO4)4(OH)8•4H2O were prepared using aqueous solutions. The light blue or green powders were obtained by heating at 500 or 700 ºC. To obtain artificial Turquoise pellets, these were sintered by the hydrothermal hot press method at 150 ºC. The amount of water, pressure, and milling as pretreatment were studied. Molded pellets were also prepared using oil as the solvent. The resulting pellets were evaluated in terms of density and hue. In addition, the effects of post-treatment, such as heating and beeswax coating, were also examined. There were several methods to improve the density of the molded product, including increasing the amount of solvent, increasing the pressure, using castor oil, and powder refining as a pretreatment. Castor oil and beeswax coating were also methods to improve product brightness. The pellets obtained in this study showed water resistance.

Resumo em Português:

Resumo Este trabalho estuda o incremento da resistência mecânica à flexão e força de ruptura de porcelanatos através da têmpera química. A troca catiônica resulta em tensões residuais de compressão na superfície do material. Foram selecionados porcelanatos técnicos (60×60 cm) com 100%, 90% e 77% da espessura padrão. Os porcelanatos foram prensados, secos e sinterizados em forno industrial. O processo de têmpera química foi realizado com uma mistura de sais de composição correspondente a 27% de nitrato de potássio (KNO3 > 99%) e 73% de fertilizante (K2O ~ 43%). O tratamento químico foi realizado a 480 ºC durante 25 min. Os resultados mostraram que as propriedades mecânicas do material atenderam à norma vigente (ABNT 10545-4 2018). Mesmo o material com 77% da espessura padrão, obteve-se um aumento de 15% na tensão de ruptura e 16% na força de ruptura. A análise de Weibull comprovou que as propriedades mecânicas foram incrementadas após a têmpera química.

Resumo em Inglês:

Abstract This work studies the increase in flexural strength and breaking strength of porcelain tiles through chemical tempering. Ion exchange results in residual compressive stresses on the material surface. Technical porcelain tiles (60×60 cm) with 100%, 90%, and 77% of the standard thickness were selected. The tiles were pressed, dried, and sintered in an industrial kiln. The chemical tempering process was performed using a salt mixture consisting of 27% potassium nitrate (KNO3 > 99%) and 73% fertilizer (K2O ~ 43%). The chemical treatment was conducted at 480 °C for 25 min. The results demonstrated that the material’s mechanical properties met the current standard (ABNT 10545-4 2018). Even with the material reduced to 77% of the standard thickness, there was a 15% increase in rupture stress and a 16% increase in rupture strength. Weibull analysis confirmed the increment in mechanical properties after chemical tempering.

Resumo em Inglês:

Abstract In this study, we produced, through hot pressing (HP) and spark plasma sintering (SPS) techniques, Al2O3-NbC composites for applications in machining processes. We report an experimental investigation of sintered composites’ structural, thermal, morphological, physical, and mechanical properties. The results confirm that the Al2O3-NbC composite sintered by both techniques presents a heterogeneous microstructure with distinct grain sizes and irregular geometries. Another stimulating factor is the increase of 25.86% in Vickers hardness, 14.89% in Young’s modulus, and 16.52% in mechanical strength of the composite sintered by SPS about the composite sintered by HP. Thus, our results can be used to address material properties targeting the needs of specific technological applications.

Resumo em Inglês:

Abstract The objective was to evaluate the effect of oral administration of strontium (Sr) on the regeneration of a critical bone defect. Twenty Wistar rats were divided into two groups, assessed at 15 and 60 days postoperatively: GSr - oral administration of Sr; and CG - without oral administration of Sr. At 15 and 60 days, blood was collected to measure Sr and calcium (Ca), and the calvaria was removed for histomorphological and histomorphometric analyses. Sr+2 plasmatic concentrations were higher in GSr than in CG. The dosage of Ca+2 showed a small increase in the CG about the GSr. In all evaluated groups, new bone formation was restricted to the edges of the defect, and the residual area was filled with fibrous connective tissue. The oral administration of Sr associated with HA microspheres substituted by the metal, in a concentration of 23 mol%, did not affect the formation of the osteoid matrix.

Resumo em Inglês:

Abstract In the present work, an exhaustive analysis of an Argentinian commercial LECA with a multi-technique approach was successfully carried out. Five sub-types of samples were considered to study the degree of macroscopic homogeneity of the LECAs, which presented observable differences in color and morphology. The microstructural, textural, and mineralogical features of the aggregates within each category were assessed and the differences among them were described and discussed. The density values of the samples studied were between 1.01 and 1.20 g/cm3 and porosity percentages were in the range of 24 to 33 %. The samples present a similar mineralogical composition with quartz and anorthite as the main crystalline phases and almost 50 wt. % of non-crystalline phase. In addition, some variations in the Rietveld quantification were analyzed. The main challenge of LECAs industrial production is to control the raw materials and the process to obtain homogeneous LECAs with similar performance. In this regard, this type of analysis is useful for establishing and comparing some characterization strategies to control, select, design, and evaluate new LECAs.