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

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.% ZrO2. Alumina and alumina-zirconia fibres were prepared from the alumina sol and mixed sol respectively. MgO was introduced in the fibres by adding MgNO3 into the sol. Sintered alumina fibre has α-Al2O3 phase and alumina-zirconia fibre has α-Al2O3 and t-ZrO2 phases. The phase transition to α-Al2O3 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. © 2005 Elsevier Ltd. All rights reserved.