In the alkali vapor at 1500℃, silica brick has the biggest corrosion rate. Fused cast AZS block and alpha-beta fused cast alumina block have relatively lower corrosion rate. Beta Fused cast alumina block and magnesia alumina spinel brick have the lowest corrosion rate. 

 

Fused cast AZS block is available in a number of grades by zircon content (33#, 36# and 41#). All AZS blocks contain corundum crystal, baddeleyite crystal and a small amount of glass phase. The corundum crystal contains coprecipitates baddeleyite crystal, which undergo a volume expansion on cooling from casting temperatures, which often fractures the alumina plates. The glassy matrix provides relatively high strength at room temperature, but softening of the matrix decreases strength and creep resistance at service temperature. 

 

Alpha-beta fused cast alumina block is comprised essentially of alpha alumina and beta alumina crystals in a most ideal proportion which is approximately 50% and 50% respectively with a minor of glass phase. It exhibits higher strength and higher creep resistance due to its essentially biphasic crystalline nature and is successfully utilized in glass contact at temperature below 1300℃. Beta fused cast alumina block behaves in a similar manner to the alpha-beta alumina material except that penetration depths are greater due to the intrinsically larger grain and flaw size of beta alumina product. In comparison beta fused cast alumina block is restricted to relatively dry superstructure application due to its higher solubility in most silicate melts. 

 

Considering the similar cost of AZS, alpha-beta fused cast alumina block is currently considered the optimum superstructure refractory for most glass melting applications where fused cast is considered. This material has therefore been widely and successfully applied in crown and superstructure construction for oxy-fuel melting of a variety of glass compositions including soda-lime, TV panel, TV funnel and borosilicate. 

 

Magnesia alumina spinel brick is comprised essentially of spinel grains with periclase and a minor amount of glass phase. The periclase is distributed bimodally as a fine coprecipitated structure locked within the spinel grains, or as large primary magnesia dendrites. The crystal phase of spinel is featured by low thermal expansion coefficient, good high temperature performance, and nature of alkali resistance. It exhibits high strength with excellent high temperature retention, excellent corrosion resistance and extremely high creep resistance. All of the above characteristics owned by spinel have imparted it with high softening point under load, and better alkali resistance. In addition, magnesia alumina spinel brick also shows good thermal engineering properties, low thermal conductivity, low linear expansion, and especially high creep resistance. 

 

The silica brick has bad corrosion resistance to alkali vapor and batch dusts. The corrosion resistance of fused cast AZS block is better. Magnesia alumina spinel brick and fused cast alpha/beta alumina block have the best corrosion resistance. Compared to AZS, silica brick, magnesia alumina spinel brick and fused cast alumina block have low possibility of causing glass defects. They are ideal refractory materials for the crown in the Oxy-fuel glass furnaces.