查看更多>>摘要：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 a-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.
查看更多>>摘要：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.
J. V. F. L. CavalcantiC. C. da FonsecaG. M. da Silva
7页
查看更多>>摘要：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 Parafba, 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 (pH ). Then, batch adsorption systems were performed along with equilibriurn/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).
查看更多>>摘要：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.
查看更多>>摘要：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.
查看更多>>摘要：Fe_3O_4 nanoparticles were synthesized and functionalized with (3-aminopropyl) trimethoxysilane (APTMS) and chitosan, forming Fe_3O_4-NH_2 and Fe_3O_4-NH_2-chitosan nanoparticles. The Fe_3O_4 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 Fe_3O_4 nanoparticles was confirmed by FTIR and zeta potential measurements. The TEM results showed a thin layer around Fe_3O_4 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.
查看更多>>摘要：Ni and La substituted M-type Ca hexaferrite of composition CaNi_1Fe_(11)O_(19), and CaLa_1Fe_(11)O_(19) 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 CaNi_1Fe_(11)O_(19), we found saturation magnetization (M_s) of 12.18 emu/g and coercivity (H_c) of 193.2 Oe. On the other hand, in CaLa_1Fe_(11)O_(19), we found M_s of 0.55 emu/g and H_c 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.
查看更多>>摘要：This work reports the evaluation of the microstructure, morphology, and catalytic behavior of α-Al_2O_3, 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-Al_2O_3, 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-Al_2O_3 as the major phase, presence of SO_4~(2-) groups, the contribution of the sulfation process to morphology with reduction of agglomerates, and particle size from 18.98 to 15.30 μm. The yield of ester was enhanced from 80% (α-Al_2O_3 as a catalyst) to 93% (SO_4~(2-)/α-Al_2O_3, as a catalyst), which showed the milling as a fast method for synthesis of a highly efficient acid catalyst to produce biodiesel.
查看更多>>摘要：Titanium dioxide (TiO_2) 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 TiO_2. The studies showed that the TiO_2 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.
查看更多>>摘要：In this work, we report the synthesis of Yb_xZn_(1-x) O 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-0 and Yb-0 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 Yb~(3+) 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 Yb~(3+) doping by the polymer precursor method. K\Yb-doped ZnO;;nanoparticles;;Rietveld method;;polymer precursor method.
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