Reactions with glass melts

The results of practical tests with glasses and slags indicate that with porous refractories melt infiltration takes place which may change the mineralogical (phase) composition in zones even quite distant from the interface. If the melt penetrates to points of lower temperature, reactions with the melt may create new minerals, in the form of quite distinct zones parallel to the surface. The infiltration can be effected not only through pores but also by faster dissolution of the finer bond between the Coarser grog grains. Such a transformed surface layer may cause faster destruction. 

Heat treatment of related glasses melted under reducing conditions can yield a unique microfoamed material, or "gas-ceramic" (29). These materials consist of a matrix of BPO glass-ceramic filled with uniformly dispersed 1—10 p.m hydrogen-filled bubbles. The hydrogen evolves on ceranarning, most likely due to a redox reaction involving phosphite and hydroxyl ions. These materials can have densities as low as 0.5 g/cm and dielectric constants as low as 2. 

The freshly prepared material melts at 56-57 but after storage soon starts to melt at 54°, particularly if the bottle in which it is stored is opened occasionally. In contact with the moisture of the air, j >, -dinitrodiphenylurea is formed (m.p. 360°). This reaction with water is avoided if the material is sealed in a glass container. 

The polymers are crystalline, with a melting temperature of 187°C and a glass transition temperature of 87°C. In contrast, H-T PIB is a rubbery polymer, with a glass transition temperature of -61°C. Further, the polymer contains bromine end groups. As a side reaction, cyclization is observed. 

TOO gm. carbon tetrabromide are placed in a small flask fitted with a reflux condenser and warmed until it is completely melted. Then 90 ml. concentrated sulphuric acid (S.G. 1-83) are allowed to enter very slowly in drops, and the whole heated to 150° to 170° C, At the end of the reaction the mass is distilled, and the distillate, which is brown in colour because of the presence of bromine, is purified by addition of mercury in small portions, shaking and freezing. A further purification is effected by adding powdered antimony in small portions. It is distilled under reduced pressure in an all-glass apparatus with glass-to-glass connections. The product obtained is kept over antimony or silver powder in a sealed vessel. Yield 44%. 

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