عنوان مقاله [English]
A basic alumina-spinel low cement castable (castable A) and with 5% addition of sodium hexa meta phosphate (castable B) are prepared and heat treated at 110ºC, 900ºC and 1400ºC. It was shown that after heat treating at 110ºC, Cold Crushing Strength (CCS) of castable B is more than 3 times and Apparent Porosity (AP) less than half of the castable A. Presence of Mg2P2O7 and AlPO4.2H2O is the main difference. At the temperature range of 800-1000ºC that hydraulic bond reverses to dehydrate condition and castable A becomes weak with high porosity, castable B shows a CCS of more than 4 times. Needles of magnesium phosphate are responsible for reinforcing microstructure of castable B at 900ºC. After firing at 1400ºC, castable B showed extra ordinary values of CCS more than 100 MPa (about 1000 kg/cm2). Reasons are discussed by X-ray diffraction and scanning electron microscopy studies.