Magnesia (Basic Lining)
Magnesia (Mg0) is a basic lining. It is made from either naturally occurring carbonate ore, or is synthetically produced from sea water, It is graded in size from 0 to 5 mm, but somewhat coarser to silica ramming mass. Two types of bonds are used- either spinal bond (Mg0.Al203) or silicate bond (2Mg0.Si02).
Applications: Magnesia linings are widely used in steel melting as well as in melting of high alloyed irons, for temperature up to 16500 C. Magnesia is resistant to basic slag and high-manganese melts.
Limitations: Magnesia has very poor resistance to thermal shock, hence it serves best only with continuous furnace operation.
Different Zones in Lining:
During sintering (and also during normal working) the temperature of the lining varies considerably from its hot inner face to the cold outer face next to the asbestos sheet. Three different zones are created in the lining.
In case of any crack in the sintered zone or fritted zone, this outermost zone prevents metal penetration reaching to power coil by spreading the leaked metal in all directions.
With increase in the use of the lining, the lining slowly becomes thin, and the interfaces between these zones move towards the outer coil. Finally the unbounded zone is completely eliminated. If crack develops in the lining at this stage, metal can penetrate to power coil.