Effect of magnesium oxide on sol–gel spun alumina and alumina–zirconia fibres

Abstract

Alumina fibres and alumina–zirconia fibres were prepared by sol–gel process. The starting materials used for the preparation of alumina and zirconia sol were aluminium-tri-isopropoxide and zirconium oxychloride respectively. Alumina sol and zirconia sol were mixed in definite proportions, so that the final composition contains 10 wt.% ZrO 2. Alumina and alumina–zirconia fibres were prepared from the alumina sol and mixed sol respectively. MgO was introduced in the fibres by adding MgNO 3 into the sol. Sintered alumina fibre has α-Al 2O 3 phase and alumina–zirconia fibre has α-Al 2O 3 and t-ZrO 2 phases. The phase transition to α-Al 2O 3 takes place at higher temperature in the alumina fibre with MgO, whereas the effect is less in alumina–zirconia fibre. The addition of MgO reduces the grain size and increases the tensile strength.