Thermal Expansion Characteristics of Alumina –Magnesiaand Alumina –SpinelCastables in the Temperature Range 800°– 1650°C Yung-Chao Ko* China Steel Corporation, Kaohsiung, Taiwan, Republic of China Jinn Tsang Lay Kuan-Ho Refractories Industry Corporation, Toufen, Meaoli, Taiwan, Republic of China The thermal expansion of Al 2 O3–MgOcastables containing 5.5 wt% MgO and 1.36 wt% CaO and Al 2O 3– spin