1The Applications Of Fused Cast High Zirconia Block In Glass IndustryNews

Among fused cast refractories, the refractories comprising ZrO2 as the main component have particularly excellent corrosion resistance against molten glass. Therefore, the fused cast high zircon block having a large ZrO2 content is widely employed for glass melting furnace.

Fused cast high zirconia blocks are designed to operate in extreme condition and also require control of the making process. Elaborated by a fused cast process followed by a controlled cooling step, these materials exhibit specific thermo mechanical properties related to a microstructure containing monoclinic zirconia dendrites embedded into a silica–alumina glassy phase.

A fused cast high zirconia block comprising 80 to 95 wt% of ZrO2 as a chemical component has been used as a refractory for a glass melting furnace. The microstructure of a fused cast high zirconia block is composed of a slight quantity of pores, a large amount of baddeleyite crystals (ZrO2) and a small amount of matrix glass with which the space between the grains is filled. This matrix glass contains SiO2 as the main component and contains other oxides, such as Al2O3, Na2O and K2O.

The higher the proportion of the ZrO2 in the refractory, the better the corrosion resistance against molten glass. However, if it exceeds 95% by weight, the proportion of the matrix glass tends to be so small that cracking is likely to result, and it becomes difficult to obtain a fused cast refractory having no cracks by casting.

Al2O3 is an important component like ZrO2 to adjust the relation between the temperature and the viscosity of the matrix glass, and reduces the concentration of the ZrO2 component in the matrix glass. Al2O3 constitutes corundum crystals. The corundum crystals exhibit strong corrosion resistance and have a characteristic that they show no abnormal expansion or shrinkage due to a temperature change.

SiO2 is for forming the network of the matrix glass. Na2O constitutes a structure for modifying the network of the matrix glass and exhibits an action to control the viscosity of the matrix glass and an action to inhibit formation of mullite.

The fused cast high zirconia block has a less probability of leading to such glass defects, since it has a small amount of a matrix glass phase surrounding the baddeleyite crystal phase.

Fused cast high zirconia block, due to its high corrosion resistance against molten glass and low contamination properties, has been frequently used for a portion of contact with molten glass of a glass melting furnace which is required to have high quality, such as substrate glass for a flat panel display. However, it is expensive as its ZrO2 content is very high. So it is important consider the cost when considering employing fused cast high zirconia block for a specification.

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The Applications Of Fused Cast High Zirconia Block In Glass Industry

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