Materials Science Forum Vols. 727-728

Abstract: This work had as its objective to evaluate the firing behavior and microstructure of a typical clayey ceramic body from Campos dos Goytacazes, Brazil, used to fabricate extruded rustic floor tiles. The firing behavior of samples fired at 650, 850 and 1050°C was studied by thermal analysis (DTA/TG) and their microstructural characteristics were evaluated by mercury porosimetry and X-ray diffraction. Technological properties such as water absorption, linear shrinkage and flexural strength were also evaluated. The results showed that the clayey body presents a relatively high weight loss during firing due to a significant amount of clay mineral associated with aluminum hydroxide decomposition. After firing the clayey body developed an elevated amount of porosity and low mechanical strength. Quartz was detected as the only crystalline phase originated from the unfired body. By contrast, mullite, plagioclase feldspar and hematite appeared during the firing.

Abstract: A ceramic body traditionally used to produce bricks and roofing tiles was reformulated by the addition of sand and illitic clay. The objective was to obtain a ceramic product with better technological properties. Specimens were made by uniaxial press-molding at 20 MPa and then fired at temperatures varying from 850 to 1100°C. The determined technological properties were: linear shrinkage, water absorption and flexural rupture strength. The results showed that both sand and illitic clay contribute to reduce the water absorption of the industrial clayey body. With respect to the flexural behavior, it was observed that the incorporation of sand decreased the mechanical strength. On the other hand, the illitic, incorporated in an amounts of 30 wt.% contributed to increase the mechanical strength of the clayey ceramic.

Abstract: This paper assesses the sintering in a conventional oven and microwave oven of Ni-Zn ferrite. The samples were previously synthesized by combustion reaction in the microwave, and then sintered in a conventional oven and microwave oven 1200°C/2h with a heating rate of 5°C/min. The samples were characterized by: XRD, SEM and magnetic measurements by AGM. The results indicate the formation of inverse spinel crystalline phase of Ni-Zn ferrite, with inter-and intergranular porosity and average grain size of 0.15 µm and 0.30 µm, respectively for the samples sintered in a conventional oven and microwave oven. The sample sintered in conventional furnace showed a pattern characteristic of superparamagnetic materials with saturation magnetization of 7.6 emu.g^-1, while in the microwave sintered sample showed a typical behavior of soft magnetic materials with saturation magnetization of 70 emu.g^-1.

Abstract: This paper proposes to assess the sintering of Ni-Zn ferrites synthesized by combustion reaction in advance to procure materials for applications as soft magnetic devices. The samples used for sintering have different morphological characteristics and were previously synthesized by microwave energy. The samples were uniaxially pressed and sintered in a microwave oven at 1200°C/2h with a heating rate of 5°C/min, and characterized by XRD, SEM and magnetic measurements. The results show that for all samples have the formation of Ni-Zn phase and traces hematite as secondary phase. The resulting microstructure after sintering was different and was influenced by previous morphological characteristics of the synthesized samples. As for the magnetic parameters, all samples were characteristic of soft magnetic material with saturation magnetization between 57 and 62 emu.g^-1, indicating are promising materials for the fabrication of soft magnetic devices.

Abstract: Polycrystalline CaCu₃Ti₄O₁₂ ceramics were prepared by solid state reactions by spark plasma sintering (SPS) technique. In this study, the effects of the dwell temperature on structural, microstructural and dielectric properties of CaCu₃Ti₄O₁₂ ceramics have been investigated. Powder mixtures were calcined at 900°C for 18 h before SPS consolidation. The dwell temperatures were 850, 900, 915 and 930°C. Sintered pellets were characterized by X-ray diffraction, scanning electron microscopy and impedance spectroscopy. X-ray diffraction patterns show evidences of a single-phase perovskite-type structure. The calculated lattice parameter is 7.40 Å. The hydrostatic density increases slightly with increasing dwell temperature. Scanning electron microscopy observations revealed a heterogeneous microstructure for all samples. The dielectric loss remains constant over a wide temperature range. The obtained permittivity is approximately 10³ at 1 kHz. The increase of the dwell temperature is found to produce a brittle ceramic.

Abstract: Densification of a precursor mixture of powders followed by drying to remove the excess of water is a necessary stage before the high temperature sintering to produce a ceramic piece. In the case of conventional red ceramics the influence of the density established during this stage has received limited attention in terms of the final product proprieties. Therefore, this work has for objective to evaluate the influence of the dry bulk density on the fired properties of red ceramics elaborated with the mixture of clays, argillite and grog. Cylindrical specimens were prepared with two different ranges of dry bulk density, 1.95-2.09 g/cm³ and 2.15-2.28 g/cm³. Specimens were fired at 1050°C in a laboratory furnace. The evaluated properties were: water absorption, diametral shrinkage and compressive strength. Microstructure of the fired ceramics was evaluated by electron scanning microscopy. Results showed that dry bulk density exercises a strong influence on the fired properties.

Abstract: Ashes generated in industrial processes are usually discarded and contribute to environmental pollution. Large scale incorporation into clayey ceramic products for civil construction, such as bricks and tiles, could be a permanent solution. Based on this rationale, this works has as its objective to characterize an ash waste from the incineration of elephant grass and to evaluate its incorporation into a clay to produce red ceramic. The waste was submitted to mineralogical and chemical characterization. Compositions were prepared with incorporation of the waste in amounts of up to 20 wt.% into the clay. Specimens were prepared by extrusion and fired in a laboratory furnace at 850°C. The physical and mechanical properties evaluated were: linear shrinkage, water absorption and flexural strength. The results showed that the waste is mainly composed of quartz and calcium compounds that sensibly reduce the linear shrinkage and does not change the other properties of the ceramic.

Abstract: The amount of discarded glass wastes is increasing in Brazil and becoming of environmental concern. A possible solution is to incorporate into construction products such as clayey ceramics. Thus, the main objective of this work was to evaluate the firing behavior of a kaolinitic clayey body from Campos dos Goytacazes-RJ incorporated with flat glass waste (FGW) from civil construction. The characterization of the FGW was done by X-ray Fluorescence and optical dilatometry. Compositions were prepared with 0, 2.5, 5 and 10 wt.% of FGW incorporated into the clayey body. Specimens were prepared by uniaxial press-molding and then fired at 850 and 1050°C. The microstructural changes due to the firing process were evaluated by X-ray diffraction (DRX) and scanning electron microscopy (SEM). The results showed that the glass waste has a potential to be successfully employed in a clayey ceramic formulation for civil construction products.

Abstract: The generation of waste is a consequence of human action as a result of user and processor of raw materials. In effluents textiles sewage treatment, waste generation, especially the sludge, is a constant making it necessary to use alternatives for its management. This work aims to study the influence of the burning temperature on the thermal decomposition of textile sludge by Thermogravimetry and Differential Thermal Analysis in order to use it as an additive in concrete and / or pre-molded. The TG curves of textile sludge burned at temperatures of 110°C, 400°C, 450°C, 500°C, 550°C and 600°C showed at two to three steps of thermal decomposition. The infrared spectrum showed characteristic bands of SiO2, OH and CH and the spectrum of the sinterized sludge showed the elimination of OH and CH bands.

Abstract: Porous ceramics can be produced by adding starch (corn, potato) and protein (animal or vegetable) to raw material as pore forming element. In this study, titanium dioxide ceramics were formed by vegetable protein consolidation. Soybean was chosen as the binding agent and pore forming. The samples, which were produced in cylindrical shape, had the following processing: material mixture, gelling, drying, pre-sintering and sintering. Heated platinum microscopy were performed by using suspensions with different compositions in order to verify protein gelling capacity and better know the temperature in which this process occurs. The samples were characterized by apparent porosity and roughness measurement. Besides, imaging by light microscopy was also performed in order to determine the sample morphology and porosity.