Valmir José da Silva

Resíduo de quartzito - matéria-prima alternativa para uso em massas de cerâmica estrutural

The waste generation is increasing and the appropriate destination of these became crucial for the preservation of the environment. Therefore, the use of some residues in masses that are used in industries of traditional ceramics, in addition to be an environmentally friendly solution, can reduce processing costs. This work aims to study the feasibility of incorporating quartzite residue in a mass that is used in the manufacture of structural ceramic products. The raw materials were subjected to physical, chemical and mineralogical characterization. The masses were formulated with 5, 10 and 15 wt% of quartzite residue and subsequently molded by uniaxial pressing, and sintered at 800, 900 and 1000 oC. After sintering, the samples were subjected to the physico-mechanical properties: water absorption, apparent porosity, linear shrinkage and bending strength. The color and mineralogical phases formed were also evaluated. The toxicity characteristics of residue and masses were analyzed. The results showed that, for the studied mass, it is possible to add up to 15% of the residue of quartzite.

Síntese, por reação de combustão em forno de microondas, de nanoferritas de níquel dopadas com cromo

Chromium-doped nickel nanoferrite powder was prepared by combustion reaction, using microwave energy as the external heating source, and the influence of the Cr3+concentration on the NiCrxFe2-xO4 system was investigated. The powder, which was prepared according to the concept of propellant chemistry, was heated in a microwave oven under a power of 980 W. The resulting material was characterized by XRD, BET, SEM, helium picnometry and magnetic measurements. The results indicate that it was possible to obtain chromium-doped nickel ferrite nanopowders and that raising the chromium concentration caused an increase in particle size (from 15 nm to 55 nm), and a reduction in the magnetic parameters.

Evaluation of the Potential of Using Quartzite Residue in Mass for the Production of Sanitary Ware

Currently there is a great concern on the part of the industries with the disposal of waste generated in the production process. The quartzite processing industry generates significant amount of residue, consisting primarily of quartz. The aim of this work is to evaluate the incorporation of quartzite residue, replacing partially the quartz and feldspar, in ceramic mass used in the production of sanitary ware. The raw materials were characterized by chemical and particle size analysis. Compositions were formulated by varying the amount of residue and comparing with an industrial mass, consisted of clay, kaolin, feldspar and quartz. The slip casting process was used in the preparation of the specimens. The results showed that the residue can be considered as an alternative raw material for use in sanitary ware industry, since the ceramic slip presented appropriate rheological properties and after firing process the specimens presented physical and mechanical properties according to the specifications.

Influence of Power and Synthesis Time in the Formation of Mullite Obtained by Microwave Heating

Front of the large number of applications of the mullite mineral, many researchers seek to synthesize it from the mixture of Al2O3 and SiO2 powders, or from aluminossilicates, such as smectite. The synthesis of mullite from clays via rapid heating by microwaves emerges as an alternative process. This process accelerates the kinetics of nucleation and the development of mullite phase. Thus, the aim of this work is to study the effect of power and timeon synthesis of mullite from clay, via rapid heating in microwave. The synthesis times were 15 and 20 minutes, with powers of 1.26 and 1.44kW. The obtained powderswere characterized by X-ray diffraction and scanning electron microscopy. The best results were obtained with a power of 1.44kW for 20 minutes.

Avaliação de novos depósitos de argilas do Estado da Paraíba visando sua aplicação como matérias-primas cerâmicas

In recent years, new clay deposits have been discovered in the state of Paraiba, Brazil, the characterization of these deposits having fundamental importance to establish the best industrial application. The aim of this study was to characterize clays from Cubati, PB, Brazil, to establish their appropriate uses as ceramic raw materials. Therefore, the raw materials were subjected to physical, chemical, mineralogical and thermal characterizations. The specimens were prepared by uniaxial pressing at 19 MPa, dryng at 110 oC, and fired at 750, 850, 950 and 1150 oC. The following physical and mechanical properties were studied: firing linear shrinkage, water absorption, apparent density and flexural modulus of rupture. The results showed that SiO2, Al2O3 and Fe2O3 were the main oxides present in the clays, whicht are constituted by smectite, kaolinite and quartz. The clay containing higher Al2O3/SiO2ratio, wider size distribution and the lower average particle diameter was the one that presented best mechanical performance. Three clays are suitable for use in white ceramic and one to red ceramic.

Avaliação da influência de diferentes tratamentos térmicos sobre as transformações de fases esmectitas

Smectite clays have been used in various technical applications, particularly in traditional ceramic material, for ensuring the plasticity required for the forming green and simultaneously promote the development of mullite crystals during the firing phase, which confers mechanical strength to the final product. an important innovation over the past decades in the ceramic sector is the use of fast firing, which can induce changes during thermal processing of raw materials and mixtures. to implement changes in firing parameters it is crucial the knowledge of phase transformations of clays, being necessary in some situations the formulation of new compositions. the aim of this work is to analyze the influence of different heat treatments on the mineralogical and microstructural changes of smectites, emphasizing the presence of mullite. two samples of natural bentonite and one imported commercial were used. the natural samples were initially subjected to a milling process. subsequently, they were submitted to chemical analysis by x-ray fluorescence, thermogravimetric and differential thermal analyses. the clays were treated in the 800-1250 °c range with a heating rate 30 °c/min and kept at the maximum temperature for 10 min. the results showed that the clay composition and the temperature have influence on the amount of mullite formed.

Structural and Morphology Characterization ZSM-5 Zeolite by Hydrothermal Synthesis

Zeolite ZSM-5 have been synthesized by hydrothermal method, using tetrapropylammonium bromide as template. This work aims to evaluate the preparation and characterization structural and morphology of zeolite ZSM-5 resulting in a pure and crystalline material. The ZSM-5 zeolite was prepared by hydrothermal synthesis at 170 °C, using silica, deionized water and structure-directing salt (tetrapropylammonium bromide-TPABr). Several techniques like X ray diffraction (XRD), scanning electron microscopy (SEM) and X ray energy dispersion spectrophotometer (EDX) have been utilized to characterize the framework structure and morphology of the sample. Obtaining ZSM-5 zeolite could be confirmed by X ray diffratograms. The result X ray diffraction showed that the synthesized sample presented typical peaks of the ZSM-5 zeolite. According to the XRD, it is possible to observe intense and well defined peaks. The acquired X ray patterns identified the product as highly-crystalline materials, without the presence of impurities. From the images obtained by SEM, it was possible are composed of showed that the crystal accumulations of ZSM-5 zeolite, without the presence secondary phases on the crystals.

Synthesis of Zeolite Membrane (Y/α-Alumina)

The general aim of this study was to develop materials of the type: Y zeolite (hydrothermal synthesis), ceramic support (forming of powder) and zeolite membrane (rubbing). The preparation of the Y zeolite was conducted in accordance with the hydrothermal synthesis method, the time of crystallization was one day. The ceramic support was prepared by means of the forming of powder technique and subsequently subjected to sintering at a temperature of 1400°C/1h. The zeolite membrane (Y/α-alumina) was prepared by secondary growth method (rubbing). These materials were characterized by XRD and SEM. Obtaining Y zeolite could be confirmed by X ray diffractograms. From the images obtained by SEM, it was possible to derive from analysis that the Y zeolite is composed of a homogeneous morphology, where the particles are crowded, with uniform size. The results obtained for the ceramic support (α-alumina) showed that it displays characteristics peaks of aluminum oxide. By using micrographs it was possible to observe a heterogeneous microstructure with a compact form, without cracks upon the layers. According to the XRD, for the methodof secondary growth (rubbing), it was observed that the Y zeolite wich had been synthesized on the ceramic support displayed a crystalline structure. The micrography of the zeolite membrane (Y/α-alumina) showed the formation of a layer of zeolite on the ceramic support.

Influence of the Heating Rate on the Phase and Microstructural Transformations of Smectite Clays

Clays are very important raw materials in the manufacturing of traditional ceramic products. The present study was intended to study the phase transformations of smectites submitted to thermal treatment in conventional stove, applying slow and fast cycles. We used three clays, two national and one imported, which were beneficiated and characterized by mineralogical analysis. Later, they were submitted to a thermal treatment at 1100, 1200 and 1250°C, with heating rate of 5 and 30°C/min, remaining under the maximum temperature for 60 minutes. We observed the presence of mullite peaks starting at 1100°C for all samples. It was verified that the sample with the highest alumina/silica ratio presented more intense mullite peaks, and the sample with the high MgO content, besides the mullite phase, also formed cordierite.

Production of Mullite from Bentonite Clays and Alumina Residue

Among the ceramic raw materials, mullite is highlighted for presenting features which are of great interest for industry. However, the process through which this material is obtained requires pure reagents, raising the production costs. Therefore, this work is intended to obtain mullite from bentonite clays (source of silicon and aluminum oxides) and alumina residue, resulting from the Bayer process, thus becoming an interesting process from the economic and environmental standpoint. For this purpose, we made use of the thermal treatment in conventional furnace, temperature of 1500°C, heating rate of 5°C/min and dwell time of 60 min at maximum temperature. The synthesized samples were characterized by X-ray fluorescence (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled to an EDS, besides the quantification of the phases present in the samples. The results revealed that mullite was the major phase produced, but corundum appeared as secondary phase.