Resumo em Inglês:

Abstract Mullite is a refractory material with singular properties, although high temperatures and long sintering times are required to obtain this material with good densification. In this study, aluminum hydroxide and colloidal silica were used to produce mullite through reactive sintering and MgO was employed as a sintering additive. The compositions were prepared with different amounts of MgO and sintered at 1350, 1450, and 1550 °C, and then analyzed using X-ray diffraction, scanning electron microscopy, and measurements of apparent porosity (AP) and flexural strength. The results showed that the raw materials used allowed the mullite formation at relatively low temperatures (1350 °C), regardless of the amount of MgO added but with the increase in MgO content, a spinel phase appeared, resulting in a fraction of residual α-alumina. The MgO addition lowered the densification temperature at around 50 °C. Furthermore, the higher the sintering temperature and the MgO content, the larger and more anisotropic the mullite grains were. At sintering temperatures above 1450 °C, AP was reduced to approximately 10%. The MgO addition and increase in sintering temperature improved the flexural strength of mullite materials.

Resumo em Inglês:

Abstract Recycled aggregates present a varied mineralogical composition and the grading of these particulates over their particle size distribution influence the aggregate properties as well as those of the composites that they form. This study proposed a comparative investigation of the influence of the particle size distribution of fine aggregates from two different origins, namely, natural crushed stone and construction and demolition waste (CDW). Three particle size distributions were defined, so that each aggregate had its fineness modulus (FM) ranked in the granulometric ranges, following the NBR 7211 Brazilian standard. The following tests were carried out: consistency, bulk density in the fresh state, compression strength, absorption (by immersion and capillarity), dimensional and mass variation. The results showed that the aggregate mineralogical composition impacted the mortar properties and that, when analyzed along with the particle size distribution, CDW showed different and varied behavior as a function of its particle size and distribution. Another finding was that mortars produced with CDW aggregate with granulometry below the lower optimal zone (FM<2.20) presented reduced mechanical and physical performance. Therefore, it was concluded that CDW aggregates should not be included in the same standards as conventional aggregates regarding the fine aggregate granulometric composition.

Resumo em Inglês:

Abstract The main goal of this research was to study the adsorptive capacity of an organophilic clay for the removal of textile dye Nylosan blue B113 and its further application in real textile effluent (RTE) treatment. The used clay known as Bofe was originated in the township of Boa Vista, State of Paraíba, Northeast of Brazil. Initially, the material was dried and powdered. Subsequently, the organophilic clay was synthesized by insertion of hexadecyltrimethylammonium bromide. Furthermore, the clay was characterized using the following analyses: cation exchange capacity (CEC), X-ray diffractometry (XRD), surface area analysis, and pH of point of zero charge (pHpzc). Then, batch adsorption systems were performed along with equilibrium/kinetic/thermodynamic studies. At last, keeping the same weight/volume ratio, a solution of real textile effluent was treated. Results showed CEC of 54.40 mmol/100g, lamellar expansion from 1.69 to 2.01 nm, maximum adsorptive capacity of 50 mg.g-1, and chemical oxygen demand (COD) removal of 74% (RTE).

Resumo em Inglês:

Abstract Zeolites A was synthesized from alternate sources such as filtrate from synthesized zeolite LSX and aluminate solution extracted from bauxite which produced a very good yield. The synthesized zeolite type was characterized by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). The synthesized product showed a high degree of crystallinity from the XRD results. When applied to a spent lubricating oil, the efficiency in removing the heavy metals was: 23.4% Fe, 96.8% Zn, 19.0% Cu, and 12.0% Cr. The saturates in the regenerated oil were 80% carbon, 4% residue, and 16% aromatics as compared to that of a commercial virgin oil that contained 84% saturates, 3% carbon residue, and 13% aromatics. This indicated that the spent oil can be reused.

Resumo em Inglês:

Abstract The objective of this work was to produce brushite cement for orthopedic applications, based on the system wollastonite/phosphoric acid with the incorporation of polyethylene glycol (PEG) as a setting and processing additive. Brushite/PEG cement was obtained by the dissolution-precipitation method and its physicochemical properties were characterized by X-ray diffraction, compressive strength, porosimetry, and biological behavior (cell adhesion and bioactivity tests). The results indicated the formation of brushite cement with 21.4 MPa of compressive strength and 30% porosity, similar to human trabecular bone. The surface was shown to be adequate for cell adhesion and growth and bioactive with the formation of apatite layers. The incorporation of PEG improved working conditions without causing undesirable changes in the physicochemical properties and biological behavior of developed cement, thus promising for the repair of bone tissue injuries.

Resumo em Inglês:

Abstract Fe3O4 nanoparticles were synthesized and functionalized with (3-aminopropyl) trimethoxysilane (APTMS) and chitosan, forming Fe3O4-NH2 and Fe3O4-NH2-chitosan nanoparticles. The Fe3O4 nanoparticles were synthesized by a co-precipitation method and functionalization was performed in further stages. The nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential, and transmission electron microscopy (TEM). The results of XRD showed that magnetite did not experience an oxidation reaction. The functionalization of the surface of Fe3O4 nanoparticles was confirmed by FTIR and zeta potential measurements. The TEM results showed a thin layer around Fe3O4 nanoparticles due to the functionalization with the APTMS. The later functionalization by chitosan contributed to the agglomeration of nanoparticles. Functionalization provided the nanoparticles better colloidal stability mainly for a pH below 7 and this improvement was related to the protection and new functional groups from the APTMS and chitosan.

Resumo em Inglês:

Abstract Ni and La substituted M-type Ca hexaferrite of composition CaNi1Fe11O19 and CaLa1Fe11O19 were synthesized by sol-gel auto combustion method using metal nitrates as oxidants and citric acid as reducing agent. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDAX), and vibrating sample magnetometry (VSM). XRD study revealed that both samples had lattice parameters a and c within the range of M-type hexaferrite. The SEM micrographs displayed grains having irregular shapes and sizes in the nanometer range. FTIR peaks confirmed the structure of M-type hexaferrite. EDAX spectra showed the homogeneous distribution of ions in both samples. In CaNi1Fe11O19, we found saturation magnetization (Ms) of 12.18 emu/g and coercivity (Hc) of 193.2 Oe. On the other hand, in CaLa1Fe11O19, we found Ms of 0.55 emu/g and Hc of 404.4 Oe. Saturation magnetization and coercivity values obtained for La substituted M-type Ca hexaferrite are suitable for low-density magnetic recording devices.

Resumo em Inglês:

Abstract This work reports the evaluation of the microstructure, morphology, and catalytic behavior of α-Al2O3 synthesized via combustion method for esterification reaction of oleic acid in soybean oil with ethanol to produce biodiesel. The reaction was evaluated with 2 wt% of catalyst at 160 °C for 3 h when the molar ratio of fatty acid:ethanol was 1:12. To enhance the catalytic performance of α-Al2O3, its sulfation was done by a different method using mechanical milling. The microcatalysts were characterized by X-ray diffraction, Fourie transform infrared spectroscopy, granulometric analysis, and scanning electron microscopy. Results showed α-Al2O3 as the major phase, presence of SO4 2- groups, the contribution of the sulfation process to morphology with reduction of agglomerates, and particle size from 18.98 to 15.30 mm. The yield of ester was enhanced from 80% (α-Al2O3 as a catalyst) to 93% (SO4 2-/α-Al2O3 as a catalyst), which showed the milling as a fast method for synthesis of a highly efficient acid catalyst to produce biodiesel.

Resumo em Inglês:

Abstract Titanium dioxide (TiO2) has attracted interest for sensory applications due to its high surface area and the high density of active adsorption sites. This review shows the effect of the nanostructure, synthesis technique, operating temperature, target gas, and the impact of incorporating metallic elements on the detection properties of TiO2. The studies showed that the TiO2 gas detection process is closely related to surface reactions. Therefore, sensing properties, such as sensitivity, response time, and recovery, vary with factors that influence the surface reactions, such as chemical elements, morphology, microstructure of the depletion layer, and operating temperature.

Resumo em Inglês:

Abstract In this work, we report the synthesis of YbxZn1-xO nanoparticles (0.000 ≤x≤ 0.100) by polymer precursor method and the study of their vibrational and structural properties. Thermal analysis of the polymeric precursor showed that the thermal decomposition occurs in few stages, with the crystallization of the wurtzite structure taking place at a temperature below 500 C. Fourier transform infrared spectroscopy indicated the presence of Zn-O and Yb-O bonds. X-ray diffraction data showed the formation of the ZnO wurtzite phase for all samples. The application of the Rietveld method revealed a decrease in the average particle size and an increasing trend in unit cell volume as the Yb3+ content increased. Additionally, the nearest-neighbor bond lengths along and off the c-direction, as well as the bond angles, were calculated. The results obtained provided additional evidence on the efficiency of Yb3+ doping by the polymer precursor method.

Resumo em Inglês:

Abstract Among the agro-industrial residues, the rice husk has stood out for presenting contents higher than 90% of silica, the main oxide of bioglass. Thus, the objective of this research was to compare the use of two different sources of silica, tetraethylorthosilicate (TEOS) and rice husk ash (RHA), in the sol-gel synthesis of the bioglass of the SiO2-CaO-Na2O system. For the silica extraction, the rice husk was treated with oxalic acid and calcined at 600 °C. This temperature was determined using thermogravimetry and the calcined powder was analyzed by X-ray diffraction and X-ray fluorescence spectroscopy, proving the achievement of high-purity amorphous silica. In the production of the bioglass, the solution made with the rice husk showed great synthesis efficiency, and the powder calcined was evaluated by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and scanning electron microscopy. FTIR spectra presented characteristic bands of siloxane (Si-O-Si) bonds, which indicated a vitreous network and provided the formation of silanol groups, fundamentals for the growth of the hydroxyapatite layer. The microstructures of the samples were similar, but the sample made from RHA (BRHA) presented porous agglomerates, while the BTEOS had smaller and well-defined particles. The silica obtained from rice husk showed potential to be used in the sol-gel synthesis of bioglass.

Resumo em Inglês:

Abstract The first generation of polycrystalline zirconia-based ceramic used to produce dental prosthesis showed excellent mechanical behavior; however, its low translucency limited the indication for aesthetic monolithic restorations. Thus, various strategies have been tested in order to develop a material that has high strength and good optical properties. The aim of this study was to characterize, through a literature review, the translucency of different types of zirconia-based ceramics indicated for monolithic restorations. The literature search was performed in PubMed/Medline database, from 2010 to 2019, using as keywords: zirconia, translucency, and optical properties. The 3rd (monochromatic) and 4th (multichromatic) generations of zirconia, which have high cubic phase content, showed the highest translucency among the zirconia-based ceramics investigated. Additionally, other strategies, such as the addition of lanthanum oxide and the infiltration of feldspathic glass in the zirconia surface (graded-zirconia), resulted in a good balance of optical and mechanical properties.

Resumo em Inglês:

Abstract Relevant mechanical parameters of asphalt composites, such as the dynamic modulus and phase angle, are obtained by means of four-point bending tests. It is a dynamic test based on the application of sinusoidal load pulses and sinusoidal displacement response. A sinusoidal response can be difficult to record due to different issues, such as noise during an experiment. In strain-controlled tests with the application of a low-load amplitude with asphalt mixtures at high temperatures composed with calcined clay, which is the case of the test carried out in this study, a relationship was observed between the apparent noise recorded and the frequencies of the beam’s natural vibration. This outcome led to the conclusion that these imperfections are not a result of failures in the procedure, but of the natural behavior of the beam. This conclusion can assist in the filtering of information to obtain better results.

Resumo em Inglês:

Abstract Titanium dioxide is a widely studied material with well-known applications for anatase and rutile phases. Moreover, brookite, another polymorph, which is more difficult to obtain, has caught scientific community interest, especially for photocatalysis applications. Among many methodologies for TiO2 synthesis, the hydrothermal method stands out, with the possibility of controlling different parameters that lead to a specific phase composition, allowing selective polymorphic obtainment. This method was used to synthesize TiO2 with different anatase/brookite ratios, by the use of different synthesis conditions as pH of the suspension, sodium salt concentration, and temperature, resulting in anatase-brookite photocatalyst with brookite composition ranging from 0 to 35%. The materials were characterized by X-ray diffraction, infrared spectroscopy, Raman spectroscopy, particle size measurement, and scanning electron microscopy. Photocatalysts with the highest brookite amount showed the best photocatalytic results for Remazol golden yellow (RNL) dye decolorization. Moreover, the short-range disorder also played an important role in photocatalytic behavior.

Resumo em Inglês:

Abstract Iron foundry slag and hydrated lime were used in glass preparation by the melt-quenching method. The glass obtained was heat-treated using the thermal analysis technique. A crystallization kinetics study was carried out with glass powder samples using a non-isothermal method at five different heating rates by differential scanning calorimetry (DSC). Considering that few studies compare kinetic results obtained by different methods, in this work, the activation energy (Ea) of the crystallization process was obtained using the Kissinger and Augis-Bennett models for comparison purposes. The Ea results showed negligible variation in comparing the methods used, nevertheless, linear fitting of crystallization peaks was slightly better by the Augis-Bennett than the Kissinger model. The Avrami index values showed an increasing nucleation rate for two stable phases and decreasing for the metastable phase present in the glass-ceramic. Avrami indexes obtained also indicated an interface-controlled particle growth, whose scanning electron microscopy images showed different morphologies of crystalline particles in the bulk of the glass matrix.

Resumo em Inglês:

Abstract Ceramics are widely employed as thermal insulating materials for thermal barrier coatings (TBC) due to their low thermal conductivity, chemical stability, and high wear and corrosion resistance at high temperatures. The aim of this work was to study the influence of the CO2 laser beam parameters on the single-step irradiation of pre-placed yttria-stabilized zirconia (YSZ) powders on NiCrAlY/AISI 316L substrates. In order to increase the coating’s lifetime and performance, it is proposed a laser sintering of powder-beds (LSP) technique to obtain homogenous YSZ coatings, with controlled surface microstructures. The obtained coatings were characterized by optical microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction (XRD). The laser intensity and interaction time were the main laser parameters used to control the surface temperature and the combination of these parameters were used to establish a process chart. The LSP resulted in controlled smooth coating surfaces and columnar growth with submicrometric grain size. XRD analyses showed the prevalence of non-transformable tetragonal zirconia, which is known to exhibit higher stability and thermal wear resistance.

Resumo em Inglês:

Abstract Self-healing concrete (SHC) is obtained with self-healing agents, which can seal small cracks without additional repair works, improving concrete durability. The present paper studied the influence of cement content (450, 475, and 500 kg/m3) on mechanical properties (compressive and tensile strength) and porosity (capillary water absorption, water absorption, and void index) of SHC with crystalline admixture. A crack induction was carried out in SHC, and the results were compared with two reference concretes (with and without crack induction). SHC had similar compressive strength with reference concrete made without crack induction, independently of cement content. Water absorption and void index of SHC decreased with higher cement content, and a significant reduction of capillary water absorption was found after 90 days. The crystalline admixture was very efficient in decreasing concrete porosity mainly at longer ages. SHC made with high cement content developed a higher porosity reduction.