Regulating the Properties of Dielectric Materials in the MgO – Al₂O₃ – TiO₂ System

Products made from granular masses of periclase can be used for lining high-temperature furnaces and apparatus operating at temperatures up to 2273 K in air or even in alkali metal vapors. Periclase has also found its use as an electrical insulating material. To expand the range of resistance of periclase products, the TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> additive began to be used. The presence of this oxide lowers the firing temperature and increases the heat resistance of products. The next innovative solution was the decision to use alumina-magnesia spinel MgAl<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> as an additive, which is positive for heat resistance, mechanical strength and does not actually reduce electrical resistance. This work establishes the mechanism of solid-phase exchange reactions that determine the subsolidus structure of the MgO – Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> – TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> system. In the region of the elementary triangle Mg<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> – MgAl<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> – MgO, only compounds with a cubic crystal lattice are present, which gives them isotropy and, along with the difference in thermal coefficients of linear expansion, allows us to expect the production of materials with high heat resistance, resistance to corrosion and high electrical resistivity. This is also confirmed by the high temperatures of eutectics in this region. Thus, theoretical studies of the subsolidus structure of the MgO – Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> – TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> system made it possible to predict the compositions of dielectric materials in the concentration range quandilite – periclase – spinel. The main physical and mechanical properties of materials whose compositions belong to this concentration range were experimentally studied.