Abstract The composition-processing-structure-properties relationship of Na2O-Al2O3-SiO2-based geopolymers containing calcium sources is critical for the design of enhanced ceramic binders. This work evaluated the addition of 1-6 wt% of calcium hydroxide (CH) to a metakaolin-based geopolymer (prepared with NaOH 12 M and colloidal silica suspension) and how it affected the performance of the prepared samples after thermal treatments up to 1000 °C. The setting time, mechanical strength, porosity, density, permanent linear change, and phase and bond type evolution of the specimens with temperature were analyzed. The incorporation of 3 or 6 wt% of CH into the designed composition led to a fast hardening of the mixtures (1.7 h), resulting in geopolymers with high green mechanical strength (18.9 to 23.9 MPa). Nepheline and albite generation in the samples containing 6 wt% of CH resulted in a ceramic with improved cold crushing strength (45.2 MPa) and lower linear shrinkage (-10.5%) when compared to the calcium-free composition.

Abstract The residue from the Bayer process has physicochemical characteristics that allow its use in the production of synthetic aggregate, although some characteristics such as low plasticity and water absorption still need better control. In this work, the influence of clay and silica addition on the sintering of synthetic aggregate produced from bauxite residue was analyzed. Compositions containing bauxite residue-sand-clay were elaborated, whose processing occurred using extrusion and crushing, followed by sintering at 1200 °C for 3 h. The X-ray diffraction analyses indicated the presence of new phases such as nepheline, originating from sodalite, and mullite resulting from the decomposition of kaolinite. Increasing the amount of free silica in the mixture resulted in an aggregate with a higher bulk density and lower water absorption, indicating that the amount of this raw material influenced the aggregate properties.

Abstract This work aimed to produce CH3NH3PbI3 and CH3NH3PbBr3 films on glass substrates via the automated spray-pyrolysis technique for application as an absorber layer of photovoltaic cells. Their properties were investigated and compared by varying deposition parameters, such as the temperature (250, 300, 350, and 400 °C) and the precursor solution flow (0.25, 0.50, and 0.75 mL/min). Structural characterization by X-ray diffraction revealed the formation of orthorhombic perovskite films. The most adequate temperature and solution flow were 300 °C and 0.50 mL/min for both bromine and iodide films. Morphologically, the films were uniform and free from cracks. CH3NH3PbI3 and CH3NH3PbBr3 films respectively had an optical gap of 1.5 and 2.3 eV, a thickness of 4.56 and 2.35 µm, an absorption coefficient of 0.58x104 and 0.50x104 cm-1, a resistivity of 21.80 and 24.20 kΩ.m, and a figure of merit of 2.66 and 2.07. It was concluded that, between the two compounds, the CH3NH3PbI3 layer has better performance for photovoltaic applications.

Abstract The environmental impacts caused by the disposal of ornamental rock waste require studies for its reuse. Gypsum, a binder widely used in civil construction, can help this recycling process. Thus, some research was carried out in gypsum composites with ornamental rock residue at levels of 0, 5%, 10%, 15%, and 20% and with the water/gypsum (w/g) ratio of 0.6 and 0.8. The properties of setting time, porosity, hardness, compressive strength, thermal conductivity, and tensile bond strength were evaluated. The setting time did not show significant changes for the different contents and w/g ratios. Porosity tended to decrease with the insertion of waste and water decrease. Hardness and compressive strength increased with the inclusion of the residue on the w/g ratio of 0.6. Thermal conductivity and tensile bond strength did not vary greatly.

Abstract The incorporation of alternative materials in partial replacement of clinker is studied to reduce the CO2 emissions that occur in the production of Portland cement. The influence of using mesquite ash as an alternative filler in LC3 cement pastes was analyzed. The alkali content of the system was adjusted by washing the ash, thus reducing the potassium content. The filler was replaced at 0, 25%, 50%, 75%, and 100% washed ash, and the same for unwashed ash. Subsulfation was corrected by adding an extra gypsum percentage. Paste performance was assessed by rheology and compressive strength, supported by hydration kinetics and microstructural development. Mesquite ash is a potential alternative filler for application in LC3. Washed ash makes the system purer, contributing to hydration and mechanical performance, however, natural ash also brings promising results.

Resumo A incorporação de materiais alternativos em substituição parcial ao clínquer é estudada afim de diminuir a emissão de CO2 que ocorre na produção do cimento Portland. Analisou-se a influência do uso da cinza de algaroba como fíler alternativo em pastas de cimento LC3. O teor de álcali do sistema foi ajustado lavando a cinza e, assim, reduzindo o teor de potássio. O fíler foi substituído em 0, 25%, 50%, 75% e 100% de cinza lavada e o mesmo para cinza não lavada. A subsulfatação foi corrigida adicionando-se uma porcentagem de gesso extra. O desempenho da pasta foi avaliado pela reologia e resistência à compressão, sustentada pela cinética de hidratação e desenvolvimento microestrutural. A cinza de algaroba é um potencial fíler alternativo para aplicação em LC3. A cinza lavada torna o sistema mais puro, contribuindo na hidratação e desempenho mecânico, entretanto, a cinza natural também traz resultados promissores.

Abstract Ceramic compounds with complex cubic perovskite structures have shown to be promising materials for encapsulations for temperature sensors in the petroleum industry due to their high mechanical resistance and chemical inertness to the corrosive environment of crude oil. In this work, ceramic compounds were produced by solid-state calcination and the X-ray diffraction analysis verified the formation of the compound Sr2NiZrO6 with the ordered complex cubic perovskite structure of the A2BB’O6 type. The sintered Sr2NiZrO6 compound was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and Vickers microhardness. The chemical stability of the compound was verified through the structural, microstructural, and mechanical characterization of the specimens after 60 days of immersion in crude oil. The results showed that the compound did not present changes in the structure and did not suffer a chemical attack on its surface, thus presenting suitable properties for use as encapsulation for temperature sensors in oil wells.

Abstract Paraffin was employed as a pore-forming agent to achieve porous alumina. Trichloroethylene, toluene, and chloroform were utilized for dissolving paraffin to explore the impact of the solvent on the properties of porous alumina. The influence of the paraffin ratio (1, 3, 5, and 7 wt%) was also examined on the properties of porous alumina. The samples were compacted under different pressures ranging from 30 to 50 MPa. The samples were then sintered at 1400 °C. The density of the samples was examined by the Archimedes method. The porosity percentage depended on the content of the pore-forming agent and the initial pressure of the compaction process. Based on the X-ray diffraction results, the size of the crystallites was about 230 nm. The sample with 3 wt% paraffin showed the highest strength (155 MPa) which can be assigned to its proper pore size distribution. The distribution and size of the pores were investigated by a field emission scanning electron microscope. Finally, the sample prepared with 5 wt% paraffin in toluene and compacted at 40 MPa was utilized as a laser pump reflector in an Nd-YAG laser cavity. Based on the results, the reflection of the porous alumina was above 99% at the wavelength of 430 nm.

Abstract Reducing Portland cement consumption in concrete compositions, managing industrial waste, and conserving natural resources are contemporary challenges to achieving sustainable development. One solution has been the utilization of these industrial wastes as partial replacements for Portland cement or aggregates in concrete production. Due to the significant variability of these wastes, further research on this topic is necessary. Therefore, this study aimed to evaluate the properties of concrete mixtures containing porcelain polishing residue (PPR), scheelite residue (SR), and different types of Portland cement. The physical, chemical, and mineralogical characteristics of the wastes were determined. The fresh and hardened properties of the concretes, as well as the analysis of environmental impact, in terms of carbon dioxide emissions related to binder consumption, were investigated. The results showed that the utilization of these wastes resulted in reductions in consistency, water absorption, porosity, and compressive strength at 28 days by up to 33%, 16%, 13%, and 7%, respectively. Furthermore, improvements in microstructure, binder index, and CO2 index were observed. The wastes reduced the cement content and CO2 emissions per cubic meter of concrete to achieve 1 MPa by up to 12%. These findings suggested that the utilization of these wastes may be a viable and sustainable alternative to reduce Portland cement consumption and mitigate the environmental impact of the concrete industry. However, further research and studies are needed to assess other aspects, such as long-term durability and economic feasibility before their widespread adoption in the construction industry.

Abstract Porcelain is a ceramic tile used worldwide, especially for its technical and aesthetic properties. In this increasingly competitive sector, innovative products are continually developed to meet the market’s demands, such as glazed ceramic tiles with a matte surface, low surface gloss, and silky texture. In this research, a matte glaze for porcelain tiles with low surface brightness (9 to 14 UB) and silky texture was obtained. In particular, 16 formulations of ceramic glaze were studied, which were ground and applied to binil on a laboratory scale and then fired in an industrial kiln at 1192 °C for 45 min. The fired specimens were physically, chemically, thermally, and structurally characterized. The formulation that yielded the best results was tested on an industrial scale and technologically characterized. This formulation met the aesthetic (texture and gloss) and technological (resistance to staining, chemical attack, surface abrasion, and cracking) requirements of the Brazilian technical standard.

Abstract The possibility of recycling solid wastes in the production of geopolymers and advanced ceramic products has received special attention recently. This work investigated the feasibility of replacing a high amount (70-90 wt%) of metakaolin with roof tile waste (CW) in the production of Na-geopolymer composites. Additionally, the influence of this alternative material, in the phase transformations and properties evolution (elastic modulus, compressive strength, porosity, density, and linear shrinkage) of the prepared compositions after distinct thermal treatments (40-1000 °C) was evaluated. The results showed that the incorporation of CW powder into the geopolymeric compositions enhanced their thermal and mechanical properties up to 1000 °C. The best performance was reached when using 80 wt% of the selected waste, which led to ceramic specimens with high crystallinity (presenting quartz, hematite, and albite phases), compressive strength (39.6 MPa), suitable linear shrinkage (-7.4%), and improved thermal stability (without visual cracks) after firing at 1000 °C.

Abstract The translucency of dental ceramics [feldspathic ceramic (FC), lithium disilicate glass-ceramic (LD), zirconia-reinforced lithium silicate glass-ceramic (LS), and translucent zirconia (TZ)], in two thicknesses (1 and 2 mm), using different parameters was assessed. Translucency parameters ( TP ab *, TP00), contrast ratio (CR), light transmittance at 468 nm (T%), and light attenuation were determined. Data were analyzed by ANOVA, Tukey’s test, and Pearson correlations (α=0.05). CR ranged from 0.64 (LS-1 mm) to 0.96 (TZ-2 mm). TP ab * ranged from 3.7 (TZ-2 mm) to 32.2 (LS-1 mm). TP00 ranged from 3.0 (TZ-2 mm) to 26.4 (LS-1 mm). T% ranged from 14.9 (TZ-2 mm) to 75.2 (FC-1 mm). Light attenuation varied from 54% (LS-1 mm) to 84% (TZ-2 mm). There were significant strong negative correlations between CR and TP ab * (R=-0.997), CR and TP00 (R=-0.991), TP ab * and light attenuation (R=-0.888), and TP00 and light attenuation (R=-0.867). LS showed the highest translucency, whereas TZ showed the lowest translucency. When thickness increased, CR and light attenuation also increased, while TP and transmittance decreased.

Abstract Micronized zircon (ZrSiO4) is used as an opacifier in the production of engobes, opaque glazes, and floor tile bodies. Elevated price levels incentivize researchers to develop alternative engobe formulations with reduced zircon ratios. In this study, new engobes with low zircon content were developed with varying SiO2-Al2O3 mixtures. The effect of the SiO2/Al2O3 ratio on the performance and opacity of the wall and floor tile engobes was investigated. It has been observed that the amount of zircon in the sample compositions could be reduced up to 40% by optimizing the refractoriness-water absorption balance of the engobe with the SiO2/Al2O3 ratio while keeping the opacity in the preferred levels. The color difference (∆E) value relative to the standard surface was below 1, which is acceptable for visual perception for all the samples. Other measurements such as water absorption and firing shrinkage of the floor tile samples were found to be compatible with the standard composition.

Abstract A study of ZnO-based ceramic films prepared by the spray-pyrolysis technique is presented. Pure and Ni-doped thin film samples were deposited as a coating on a glass substrate and experimentally characterized using scanning electron and atomic force microscopies, X-ray diffraction, and UV-vis-NIR spectroscopy. The morphologic, crystallographic, and optical properties were analyzed. Structural and electronic properties were compared to predictions obtained from computational calculations based on the density functional theory plus U approach (DFT+U). All these simulations provided additional data that could be used as a reference for material modeling and a better understanding of the experimental results. It was found that spray pyrolysis can be used to produce thin film ceramic samples (~300 nm) with low amounts (<5%) of Ni impurities substitutionally located at the cationic sites of the ZnO wurtzite host structure. The results of this investigation showed that an experimental and theoretical study aided in a better characterization of the thin films, and helped to outline a more robust model of the samples.

Abstract Adhesion and homogeneity of the coating-substrate were analyzed on the basis of the establishment of coating mineralogy. Substrate raw materials used were kaolin clay and a calcined alumina 4 µm; a series of higher density ceramic coatings were deposited using calcined aluminas 0.5 µm and 4 µm, silica fume, and talc. The dip coating technique was applied to all substrates and later sintered at 1300 ºC. Shrinkage and density of coatings mixtures and substrate were separately evaluated. X-ray diffraction was utilized to identify the crystalline phases present in the coatings, while optical and electron microscopy were employed for the structural characterization of the coatings. Coatings exhibited lower shrinkage compared to the substrate. Among the specimens that exhibited good adhesion, cracks were observed to extend parallel to the substrate surface. The presence of cristobalite on the coating indicated that the failure mechanism involved buckling. The crack dimension presented on the coating decreased after adding talc to the mixture.

Abstract Some experimental results concerning the performance of fiber-reinforced soil composites made of soil and shredded fibers from waste tires are presented. The composite mixtures were prepared with fiber addition of 0, 15, 30, and 45 wt%. After molding, the specimens were oven-dried and tested for unconfined compressive strength and water immersion durability. The results showed an improvement in durability with the addition of fiber. The results also indicated good compressive strength performance for the composites with a fiber content of 15 and 30 wt%. The 30 wt% fiber addiction was the best choice because of the environmental sustainability appeal to solid waste reduction.