| http://www.w3.org/ns/prov#value | - In addition to the above-mentioned alkaline and acid reactant gases, when self-gelling sols are used, inert gases, such as air or nitrogen, may also be used as reactant gases, in which case optionally the presolidification of the sol particles can be promoted by heating the reaction zone to temperatures of up to 1,000??? C. or more, preferably 500??? to 800??? C. When a collecting sheet is used as
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