âInfluence of addition of inorganic fillers on the performance of refractory products made ​​from aluminum sludgeâ

A borra branca à um resÃduo gerado durante a produÃÃo do alumÃnio, que contÃm Ãxidos que podem ser utilizados na indÃstria dos refratÃrios e cimentos. A borra de alumÃnio, se nÃo for inertizada, à perigosa para a saÃde humana e contaminante do meio ambiente. Neste trabalho, a borra de alumÃnio foi submetida a tratamento tÃrmico seguido de moagem e classificaÃÃo por peneiramento. Para melhorar as propriedades mecÃnicas das peÃas obtidas a partir da borra de alumÃnio, foram formuladas duas misturas com adiÃÃo de partÃculas de reforÃo inorgÃnicas eletrofundidas. Neste caso, a mulita do tipo TP-325, com porcentagens variando entre 5 e 35% e a outra com alumina do tipo AL-L 280 variando entre 20 e 30% em peso, sendo comparadas com a borra pura (matriz cerÃmica). O resÃduo e as cargas inorgÃnicas foram caracterizados por fluorescÃncia de raios x difraÃÃo de raios x e anÃlise termogravimÃtrica. As misturas dos pÃs foram submetidas a prensagem uniaxial, utilizando uma pressÃo de compactaÃÃo de 30 MPa num molde em forma de barra e estas foram sinterizadas a 1400ÂC com uma taxa de aquecimento de 5ÂC/min, permanecendo nesta temperatura durante 2 horas. Em seguida determinaram- se as propriedades fÃsico-mecÃnicas tais como: retraÃÃo linear de queima, absorÃÃo de Ãgua, porosidade aparente, massa especÃfica aparente, tensÃo de ruptura à flexÃo em trÃs pontos e microscopia eletrÃnica de varredura. Os resultados obtidos indicam que a mistura com mulita eletrofundida a 15%, promoveu um maior fechamento dos poros no material, causando assim um aumento na resistÃncia mecÃnica em relaÃÃo a mistura com alumina. A adiÃÃo desse reforÃo inorgÃnico à matriz cerÃmica (borra pura) demonstra um alto potencial de aplicaÃÃo como matÃria-prima para a indÃstria de materiais refratÃrios conformados.ABSTRACT White dross is a reject generated during aluminium production. It contains several oxides that can be useful to the refractories and cement industries. However, white dross can be hazardous both to human health and the environment. In this work, white dross was evaluated as a prospective raw material for the production of refractories. For this purpose, the dross was subjected to calcination followed by comminution and classification. In order to improve the mechanical properties of the refractory, two different kinds of electrofused particles were used separately as reinforcement: mullite and alumina. Particles of the TP-325 mullite were added to the white dross powder in proportions varying from 5 to 35% weight. The AL-L 280 alumina particles were added to another batch of refractories, in two different amounts (20 and 30% wt.). All materials were characterized by X-ray fluorescence, X-ray diffraction, and thermogravimetric analysis. Mixtures of residual powder and particles were compression molded as prismatic bars under a pressure of 30 MPa. Pressed bars were sintered in air at 1400ÂC for 2h, and the heating rate was 5ÂC/min. Mechanical and physical properties of the sintered parts were determined by means of linear shrinkage, water absorption, apparent porosity, density, MOR (three-point bending) and SEM analysis. The results obtained in this work indicate that the mixtures of white dross and 15% mullite allowed for a better compaction and density, producing parts with higher mechanical strength than the mixtures with alumina. Pyrometric cone tests at 1400ÂC show the refractoriness of the parts up to that temperature. Therefore, under the conditions of this research work, white dross with additions of mullite particles has proven to be a prospective candidate for the production of refractory parts