Expanded pumice stone - obtd. by roasting pumice contg. ferric oxide in hot reducing gases

摘要

The pumice stone employed contains more than (wt.%) 1% Fe2O3; and is expanded by the use of hot gases which exert a reducing influence. Varieties of pumice stone contg. less than 70% SiO2 are to be pref., although pumice with a higher silica content can be expanded by the hot reducing gases. The grain size of the pumice stone is pref. max. 5 mm. The object of the invention is the successful expansion of varieties of pumice stone which cannot be expanded, or are difficult to expand, by conventional methods. In the invention the oxygen obtd. by the redn. of the Fe2O3, and/or the gaseous prods. formed by reaction of the oxygen with the hot reducing gases, serve as the expansion agent.