Materials Science Forum Vols. 530-531

Abstract: Crushed fired brick waste, known as grog, screened at two different particle size, 840 (20 mesh) and 420 μm (80 mesh), was used in mixtures with clayey body to make typical red ceramics for bricks. The effect of the grog addition up to 20 wt.% on the properties and microstructure of bricks fired at 700oC was evaluated. The results indicated that both the particle size and the amount of grog addition changed the fired properties of the clayey body. Additions above 5 wt.% of grog, with a coarser particle size, decreased the mechanical strength of both the dry body and the fired ceramic pieces. By contrast, grog with a finer particle size may be used up to 10% wt. without deteriorate the properties and corresponding microstructure of the clayey body.

Abstract: Dopants such as Ta2O5 play a major role in the formation of barriers at the grain boundary in TiO2 varistors, increasing their nonlinear coefficient and decreasing their breakdown electric field. This paper discusses the microstructural and physical properties of Ta- and Cr-doped TiO2 systems in which imported tantalum oxide was replaced with an equivalent Brazilian raw material. Preliminary results confirm that this national oxide can be utilized to obtain electroceramics such as varistors.

Abstract: The use of glass residues for the reduction of firing temperature of ceramic materials products has become an attractive alternative. For pressed or extruded products, such as tiles and bricks, the use of glass is sufficiently simple, since only milling and mixing to the industrial mass batch in partial substitution of conventional fluxes are necessary. However, in slip casting products, such as china and porcelains, the glass presence destabilizes the casting slip. This is the motivation of this work. Different types of dispersants and their influence on the properties of slips containing glass waste were evaluated. The experimental results showed that the use of conventional dispersant (sodium silicate) is not adequate. The stabilization of slips was possible only with organic dispersants. Therefore, the factors that determine the success or failure of dispersants were also analyzed.

Abstract: The polymeric precursor route based on the Pechini process was used to prepare a mixture of nano and microcrystalline powders. The zirconia powder was stabilized with 3 mol% of yttria. Powder characteristics were evaluated by the BET technique determined the specific area and the BJH method supplied the pore size distribution. The X-ray diffraction results and SEM observations were carried out to characterize both the powder mixture and the microstructures of the ceramic bodies. The sintering behavior shown in this work was studied by dilatometric experiment, being considered the shrinkage rate and densification of the microstructure.

Abstract: Ceramic powder compaction by pressing requires weak-agglomerated powders to obtain high dense compacts and consequently dense sintered ceramic body. In this work powders with different agglomerated and/or aggregated size distributions was compacted by uniaxial and isostatic pressing. The powder and compacts were characterized by mercury and nitrogen porosimetry, BET and SEM. Analysis of X-rays diffraction peaks was used to determine the particle size (diameter). The Scherrer method was used to obtain the estimated average nanoparticle size. The results showed that all aggregated and weak agglomerated powders were composed by nanoparticles. This study indicated that the nanoparticle aggregates and weak agglomerates were destroyed during the pressing stage conducting to a increase of the packing degree of the powder particles.

Abstract: The incorporation of a granite waste into a vitrified ceramic tile body was investigated. The granite waste came from an industry of stone sawing operations located in the municipal area of Santo Antônio de Pádua, State of Rio de Janeiro, Brazil. The investigated compositions were elaborated substituting partially and totally the feldspar by the granite waste. Cylindrical specimen were prepared by uniaxial pressure at 30 MPa and then fired at temperatures varying from 1050 to 1200oC. Fired properties such as bulk density, linear shrinkage, water absorption and diametrical compression were determined. The microstructure of fired samples was evaluated by scanning electron microscopy. The results showed that the replacement of feldspar by granite waste promoted a better vitrification, decreasing the open porosity and increasing the mechanical strength.

Abstract: Melt spun Ni-Cr-P alloy ribbons were used as filler metal to join Al2O3 substrates together using a vacuum brazing process. The influence of the brazing load, brazing temperature and holding time on the shear resistance of brazed joints was evaluated. The experimental results showed that the holding time was the most important parameter. At a brazing temperature of 1060°C, the shear resistance value increased from 6.17 to 93.7 MPa with increasing brazing time from 20 to 100 min, respectively.

Abstract: The leather industry creates a large quantity of organic and inorganic waste containing chromium. This research examines stabilization of particulate tannery waste in type II Portland cement. Several clays, Brazilian polycationic smectite modified in laboratory and commercial clays were used as additives with the aim of optimizing chromium adsorption. Tannery waste was added in quantities of 10, 15 and 20% relative to cement mass. The solidification components were analyzed separately and in combination in the solidified mixes using X ray diffraction. The analysis showed that reactions between the waste and the cement occurred, and that the tannery waste modified the final compounds of the system. Calcium sulfate present in the waste increased ettringite formation. Chromium also reacted with cement, since compounds with chromium and calcium were identified. Substitution of aluminum and silicon by chromium was also observed.

Abstract: The simultaneous effect of raw materials (A, B and C) on physical and technological properties of brick compositions was studied. This investigation was carried out using the statistical design of mixture experiments. Ten mixtures of three raw materials were selected and used in the experiments design. Those mixtures were processed under conditions similar to those found in the ceramics industry. Fired body characterisation results were then used to iteratively calculate statistically significant and valid regression equations (trace plots), relating linear firing shrinkage, open porosity, fired bending strength and water absorption with the proportions of raw materials. The microstructures of some selected samples were studied using scanning electron microscopy. Mixtures with high clay B contents were most adequate to produce, under constant processing conditions, a brick with specified properties. The microstructures are characterized by a low closed porosity and absence of vitreous phase.

Abstract: The mechanical properties of porcelain are strongly influenced by the generated thermal stress during processing. When quartz particle size is reduced its influence on the technical properties of ceramic products such as tiles and porcelains are changed. In this work, the properties of triaxial ceramics materials were evaluated using quartz of different particle size distribution. It was reported strong variations in mechanical strength and thermal shock strength. Although the cost of milling is increased to reduce quartz particle size, it can be compensated by its implicit advantages. The experimental results were very interesting showing the way that quartz particle size influences the analyzed properties. A significant improving in porcelain strength and thermal strength was obtained.