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.

Resumo em Inglês:

Abstract Li7-xLa3Zr2-xO12-Tax (x =0, 0.1, 0.2, 0.3) nanostructured powders were successfully synthesized using an innovative wet chemical route via spray pyrolysis technique at 800 °C for 10 seconds, followed by post heat treatment at 800 °C for 30 minutes in a muffle furnace. X-ray diffraction (XRD) analysis confirmed that Ta-doping increased the cubic phase up to 99%. Scanning Electron Microscopy (SEM) showed spherical particles with sizes ranging from slightly below 200 nm to 3 µm. The powders were then pressed at 50 MPa and sintered at 850 °C for 7 minutes using Spark Plasma Sintering, followed by post heat-treatment at 900 °C for 2 hours in a muffle furnace. XRD indicated the majority predominance of the garnet cubic phase, and SEM images showed coalescence and longitudinal growth of the particles, forming layers inside the samples. This study reports a fast synthesis and sintering method to obtain cubic garnet crystalline structure in contrast to conventional methods that are widely used and published in the literature, which require longer parameters in the synthesis stages (~24 hours) and sintering stages (over 12 hours).

Resumo em Português:

Resumo Os autores investigaram as respostas elétricas de três diferentes espessuras de cerâmica de 0,5ZrO2-0,5TiO2 com adição de LiClO4. Os sensores foram obtidos seguindo a rota de processamento tradicional e a escolha por um estudo preliminar na variação na espessura deve-se ao fato de que a distância entre as placas paralelas influi na capacitância que é inversamente proporcional a distância entre as placas, sendo que, para criar o efeito capacitivo, as superfícies planas superior e inferior das pastilhas foram revestidas com fita adesiva de carbono, sendo esta escolha da fita uma forma inédita de montagem. A análise de difração de raios-X mostrou a presença de zircônia monoclínica, titânia rutilo e de uma terceira fase cristalina oriunda de uma reação entre o Li+ do perclorato de lítio e a titânia, formando uma nova fase, o titanato de lítio. O sensor com 2 mm de espessura apresenta potencial para uso como sensor de umidade relativa do ar.

Resumo em Inglês:

Abstract The authors investigated the electrical responses of three different thicknesses of ceramic 0.5ZrO2-0,5TiO2 with addition of LiClO4. The sensors were obtained following the traditional processing route and the choice for a preliminary study in variation in thickness is due to the fact that a distance between parallel plates influences the capacitance that is inversely proportional to the distance between as plates, being that, to create the capacitive effect, as flat surfaces above and below the plates were coated with carbon adhesive tape, being this choice of tape an unprecedented form of assembly. A X-ray diffraction analysis showed a presence of zirconia (monoclinic), titanium (rutile), and a third crystalline phase derived from a reaction between the Li+ of lithium perchlorate and a titanium, forming a new phase, the Lithium titanate. The 2 mm thick sensor has potential for use as a relative humidity sensor.

Resumo em Inglês:

Abstract The thermal conductivity of engobed building ceramics was studied as a function of their microstructure. The following thermal conductivity coefficients of the samples were determined: clinker bricks with 5% water absorption - 1.04 W/(m·K) and facing bricks (ordinary) with 12% water absorption - 0.48 W/(m·K) (ignoring the voids in the samples). A comparison of the thermal conductivity of brick samples of uniform thickness without engobe and with engobe showed that the latter had a slight increase in thermal conductivity of 0.3% due to forming a denser outer layer on its surface with 2.0-0.3% water absorption. However, as the engobe coating is applied as an additional layer on the top of the ceramic bricks and the product has a greater thickness, the heat flow through the engobed bricks is 0.1-0.2 % lower. The results can be applied to technologies for achieving energy-efficient decorative and protective coatings for building ceramics.

Resumo em Inglês:

ABSTRACT The rice husk was chemically treated with acetic acid and calcined at 600 °C, in an uncontrolled atmosphere to obtain the ash (RHA), and in an oxygen-limited atmosphere to produce the biochar (BC). The influence of the thermal treatment on the adsorbent properties for removing cationic (methylene blue) and anionic (methyl orange) dyes was investigated. Both materials showed amorphous structures rich in silica, with acicular morphology and a high roughness. High surface areas (157.2 and 215.5 m²g-1) and pH at the point of zero charge close to neutrality (6.73 and 6.58) for RHA and BC were found, respectively. The anionic dye was adsorbed only by BC due to its contribution to the π- π stacking interaction between the C=C bonds of the adsorbent and the benzene rings of the dye. In contrast, the cationic dye was adsorbed by electrostatic interaction between the Si-O-Si and Si-OH groups of the adsorbents, with the positive charge of the dye. All adsorption isotherms adjusted better to the SIPS model, suggesting adsorption in homogeneous and heterogeneous sites. The observed results suggest good adsorption capacities and the interactions between surface groups on the adsorbents and functional groups of the contaminants are the most important mechanism in the adsorption of dyes of different ionic natures on surfaces derived from rice husk.

Resumo em Português:

Resumo No presente trabalho foram investigadas as propriedades elétricas da hexaferrita do tipo M BaFe12O19 (BaM) no regime de baixas temperaturas, algo novo na literatura deste material. A técnica utilizada foi a espectroscopia de impedância, sendo as medidas realizadas no intervalo de temperatura de 300 a 50 K, com a frequência do campo elétrico externo oscilante variando de 1 Hz a 1 MHz. Nossos resultados mostram que a BaM apresenta caráter semicondutor como outras hexaferritas já reportadas na literatura.

Resumo em Inglês:

Abstract In the present work, the electrical properties of BaFe12O19 (BaM) M-type hexaferrite were investigated in the low-temperature regime, something new in the literature on this material. The technique used was impedance spectroscopy, with measurements performed in the temperature range of 300 to 50 K, with the frequency of the oscillating external electric field varying from 1 Hz to 1 MHz. Our results show that BaM has a semiconductor character like other hexaferrites already reported in the literature.

Resumo em Inglês:

Abstract This study examines the influence of fabrication parameters on the morphological, optical, and structural characteristics of zinc oxide (ZnO) films prepared using the jet nebulizer spray pyrolysis technique. Specifically, we analyze the impact of the application distance (ranging from 2 to 8 cm), substrate temperature (ranging from 325 to 425 °C), carrier air pressure (ranging from 5 to 15 psi), and the molar percentage of deionized water/ethanol in the precursor solution (ranging from 0 to 25%). Scanning electron microscopy, X-ray diffraction, and optical transmittance spectroscopy are employed for characterization. Under the employed conditions, film thicknesses ranging between 100 and 680 nm, predominantly strong orientation along the 002 crystalline plane, and visible transparency between 70 and 90% are obtained. Additionally, various morphologies are identified and inspected. Particularly, films produced at longer distances, higher temperatures, and using low or moderate water/ethanol ratios exhibit higher visible transparency (90%), a homogeneous morphology devoid of grain overgrowth, and thicknesses up to 200 nm. These features are desirable for photonic and optoelectronic applications, thus motivating further investigations using the employed technique to obtain wider thicknesses while maintaining these target properties. In summary, this work evaluates the feasibility and tunability of producing transparent and homogeneous ZnO films using the low-cost jet nebulizer spray pyrolysis and contributes to the understanding of this growth process.

Resumo em Inglês:

Abstract Glass-ceramic sponges are promising structures for many technical applications. This work deals with the preparation and characterization of porous glass-ceramic using borosilicate glass waste. The particle size distribution of Pyrex waste glass used in this study was d10:42, d50:10, and d90:2 µm. Cubic samples of 1 cm3 were shaped using the replica method. A polyurethane sponge of 25 ppi was employed as a print back for the glass-ceramic sponge. A suspension of 70% solid loading was prepared for the replication. The samples were firstly annealed at 450°C for 1 h to burn out the polyurethane sponge. Then, the temperature was raised to 650, 700, and 750°C, respectively, to enhance the strength of samples. The results revealed that the density of sintered bodies at 750 °C was 0.47 g/cm3, which represents the highest value of density reached. Moreover, the fabricated glass-ceramic sponges revealed sintering temperature-dependent properties. For instance, samples sintered at 750 ºC showed compressive strength of 0.145 ± 0.15 MPa corresponding to 65% porosity.

Resumo em Inglês:

Abstract New limited pyrochlore solid solutions of formula Bi1.5-xMxSb1.5-xM'xZnO7 (M= Fe; M'=Fe, Cr) (x=0; 0.10; 0.15) are prepared from simple oxides at 1080°C by using the ceramic method. All the crystal phases are indexed in the cubic system (space group; No.227). Rietveld refinement method of the Bi1.5Sb1.5ZnO7 (x=0) compounds using powder XRD analysis confirms an overall A2B2O7 cubic pyrochlore structure according to Bi1.53+Zn0.52+Sb1.55+Zn0.52+O7 formula with 10.44425(3) Å and Fd3¯m space group. The substitution of Bi(III) and Sb(V) by Fe(III) and Cr(III) in the Bi1.5Sb1.5ZnO7 phase shows the appearance of solid solutions limited to x=0.15. The variation of the cell’s parameter is recorded to the element’s ionic radii. The paramagnetic character is observed in all substituted compounds. The measurements of the electrical conductivity as a function of the temperature, make evidence of the semi-conductive property. Whilst, the magnetic susceptibility satisfies the modified Curie Weiss (CW) and shows the magnetic behavior due to the magnetic moments of the iron and chromium ions being involved in the synthesis of the compounds. Besides, the UV-Visible reflectance displays light absorption in the visible domain.

Resumo em Inglês:

Abstract Heavy metals are among the most harmful pollutants to the environment and human health. They are present in various industrial processes, requiring increasingly efficient treatments for removing their excessive concentration at acceptable levels before disposal. Adsorption is a widely used technique due to its efficiency, selectivity, and low cost. In this work, alumina ceramic microspheres, both pure and Si-doped, were produced by internal gelation to serve as adsorbents in the treatment of aqueous effluents containing Zn²+, Ni²+, and Mn²+, originating from the tri-cationic phosphatization process in the automotive industry. These microspheres, calcined at 600 °C and 700 °C, were characterized according to size distribution, specific surface area, gas adsorption, XRD, SEM, and optical microscopy. The effluent was treated in a fixed-bed column filled with these microspheres. The concentration of the three heavy metals was reduced by more than 90%, indicating the high efficiency of alumina ceramic microspheres as adsorbents of these heavy metals.

Resumo em Inglês:

Abstract Cement mortar is typically formulated by blending fine aggregate and water, yielding a matrix characterized by heterogeneity and porosity. However, these inherent characteristics can exacerbate structural leakage, allowing water infiltration in buildings. Bentonite is a promising waterproofing additive for various mortar types, owing to its remarkable water swelling properties and recognized attributes of being non-toxic and cost-effective. Hence, this study examined calcium or sodium-activated bentonites as cost-effective waterproofing additives in polymer-modified cement mortars. A commercial mortar with varying amounts (0-2wt.%) of these bentonites was prepared. The research focused on characterizing the additives and assessing mortar performance regarding fluidity, water absorption, mechanical strength, resistance to water penetration under negative and positive pressure, and microstructural features. Results showed sodium bentonite had a smaller particle size, higher reactivity, and swelled three times more than calcium bentonite. These additives altered the fresh mortars rheological properties due to flocculation. Incorporating 2 wt.% of sodium bentonite into the mortar did not significantly change the water absorption or crushing strength of samples cured at room temperature for 28 days. However, it led to an 18.6% reduction in water penetration under positive pressure and prevented liquid percolation to the upper surface of the samples during tests under negative pressure.

Resumo em Inglês:

Abstract Energy storage is essential for advancing green energy solutions, with the lead-acid battery market expected to grow by 4.4 percent a year until 2029, reaching USD 58.65 billion. Lithium-ion batteries, although predominant, face challenges such as cost, stability, safety, and environmental impacts, including a lack of efficient recycling. On the other hand, lead-acid batteries, with a 99 percent recycling rate in the US, offer a more sustainable option. Hybrid Electric Vehicles (HEVs) play a crucial role in fuel economy and pollutant reduction, requiring batteries with good dynamic charge acceptance. Problems such as sulphation in lead batteries are mitigated with additives such as carbon and sodium lignosulphonate, which improve performance. This study focuses on optimizing the composition of battery pastes, maximizing charge acceptance by analyzing the interaction between carbon and sodium lignosulphonate, to improve the efficiency and competitiveness of lead-acid batteries by evaluating their electrochemical and electrical properties.

Resumo em Inglês:

Abstract Depending on the geological origin, Palygorskite (Pal) is associated with the presence of several accessory minerals and organic matter that need to be removed so as not to interfere with its final application. In this way, the purification of raw Pal was carried out through heat treatment. The raw Pal samples were subjected to heat treatment at 100 °C, 300 °C, 500 °C, 700 °C, 800 °C, and 900 °C for 4 hours using a muffle furnace. The samples were characterized by X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), thermogravimetric analysis (TGA), physisorption employing the B.E.T method, and field emission gun scanning electron microscopy (FEG-SEM). After the purification process by heat treatment, the reduction of quartz, calcite, dolomite, and kaolinite was observed. The results of the purification process of raw Pal using heat treatment are promising, fast, low-cost, environmentally friendly, and high-yield, and can replace the chemical treatments usually used.

Resumo em Inglês:

Abstract The present study aimed to replace plaster concentrations with cellulose micro/nanofibrils (CMF/CNF), evaluating the physical and mechanical properties of the nanocomposites. To make the nanocomposites, the plaster mass was replaced by levels of 0.5; 1; 1.5, and 2% (m/m) CMF/CNF. The nanocomposites were produced in dimensions of 40 x 40 x 160 mm. They were evaluated at 28 days through apparent density, water absorption, bending strength, compression strength, and microstructural analysis of the surface of the nanocomposites. The research results indicated an increase in apparent density and a decrease in water absorption for the nanocomposite with 0.5% CMF/CNF. The mechanical properties showed equivalent values for bending strength and increased compressive strength of the nanocomposites with 0.5% CMF/CNF compared to the control. The results found present an alternative trait to produce plaster, aiming to value CMF/CNF and to promote the sustainability of the civil construction sector.

Resumo em Inglês:

Abstract ZnO and Cu-doped ZnO nanoparticles (NPs) are synthesized using a biosynthesis process utilizing Aloe barbadensis (Aloe vera) leaf extract. The investigation thoroughly explores the structural, morphological, antibacterial, optical, and photocatalytic properties exhibited by ZnO and Cu-ZnO NPs. Both NPs formed a hexagonal wurtzite phase, and the crystallite sizes of ZnO and Cu-ZnO NPs are 21.28 nm and 17.55 nm, respectively. From the morphology, it has been observed that the particle size of Cu-ZnO is 15-20 nm whereas it is 20-50 nm for undoped ZnO. The antibacterial assessment was conducted through the agar well diffusion method, employing Klebsiella pneumonia, Escherichia coli, and Bacillus zhangzhownsis bacterial mediums. The highest bacterial growth inhibition observed for Cu-ZnO against Klebsiella pneumonia is 21 mm, 35% higher than undoped ZnO. It is found that the band gap for Cu-ZnO (3.22 eV) has reduced compared to the band gap of undoped ZnO (3.37 eV). The photocatalytic capabilities of both nanoparticles were evaluated through the degradation assessment of Methylene Blue (MB) dye and natural blackberry dye. Nevertheless, improved photocatalytic activities were observed in Cu-ZnO nanoparticles (the highest value is 83.4%) compared to the un-doped ZnO.