On a Corrosion of Glass Melting Crucible, (II)

Abstract

The corrosive state and mechanism of agalmatolite crucible attacked by melting glass batch has been investigated microscopically and X-ray photo-graphicaly.
The batch of Na₂O-ZnO-SiO₂ glasses were melted in the crucible which composed of 30% clay (Sanage-Kibushi), 40% agalmatolite (Mitsuishi-Roseki) and 30% chamotte.
After burning the crucible at 900°-1000°C, its mineral compositions were observed by microscope. It has been determined that the composition of the crucible has residual dehydrated pyrophyllite, quartz, tightly coagulated diaspore pseudomorph and isotropic matrix which is the mixture of decomposed substances of clay and pyrophyllite. The texture of the crucible burning at 1400°-1500°C has been seen to be chiefly composed of fine crystal of mullite, cristoballite and Al₂O₃-rich glassy portion which often contains diaspore pseudomorph and tightly coagulated products of those mixture.
For melting of Na₂O-ZnO-SiO₂ glasses in the crucible the corrosion has been done on the inner surface of the crucible and corrosive layer has been observed to reach about 0.5-0.7mm in depth.
In case of the melting of glass composition containing a small quantity of ZnO-component, the crystal growth of mullite and a crystal of hexagonal form (the nature is still undetermined) have been found in the glass which is in contact with corrosive layer. On the contrally, in case of a large amount of ZnO-component, zinc-spinel has been found in the glass layer; and also the Al₂O₃-rich portion of corrosive layer has been considerably attacked.
Indices of the glass layer (2-3mm thickness) in contact wfth the corrosive layer are changed linearly from the layer face.
Assuming the glass composition in corrosive layer is partly the same with the crucible's, it can be shown that the calculated value of the index of glass in corrosive layer is nearly equal to the observed low limit value of the glass indices which distributed widely in value of index.