Abstract: A sintered high-toughness alumina-based composite body consisting essentially of a plate- or rod-shaped corundum or alumina-based compound structure, a fine granular corundum structure, and inevitable impurities.

Abstract: A sintered high-toughness alumina-based composite body comprises a plate- or rod-like, corundum or alumina-based compound structure and another structure having a fine granular corundum structure and containing inevitable impurities. A sintered high-toughness alumina-based composite can be produced by mixing a crystal-growth-promoting additive with a first portion of alumina powder to prepare a mix A, mixing a crystal-growth-inhibiting additive with a second portion of alumina powder to prepare a mix B, granulating at least one of the mix A and the mix B into granules, mixing the mix A and the mix B into a mix C, forming tile mix C into a green body, and then firing the green body, whereby crystals of the corundum or alumina-based compound in the mix A are allowed to grow.

Abstract: The present invention provides a composite material suitable for use as the supporting member for a fuel cell, the composite material comprising (100-A) % by mole of MgO and A % by mole of MgAl.sub.2 O.sub.4 (wherein A is 14 to 64) and having a coefficient of thermal expansion close to that of a electrolyte YSZ, which is used as a solid electrolyte in the fuel cell, and a high thermal conductivity. By using the above supporting member, no cracking occurs in the electrolyte at high temperature during the use thereof and further during the preparation thereof, so that no lowering in the electromotive force occurs.