GB225833A - Improved manufacture of zinc-oxide - Google Patents

Abstract

In the production of zinc oxide by burning zinc vapour which is produced in a muffle or in an electric furnace and issues as a jet or stream by an outlet, the production of solid deposits around the outlet is prevented by causing a current of non-oxidizing gas such as producer-gas, hydrocarbons, or nitrogen to impinge against the circumference of the outlet. When a combustible gas is employed it may be admixed with a calculated amount of air so as to produce a reducing or neutral flame, and the protective gas may in either case be preheated. The zinc vapour outlet may have a circular shape and may be lined with a ring of refractory heat-conducting material such as carborundum or a cast iron having a high percentage of silicon or chromium; for instance a plate of such material with a circular hole may be placed in front of the vapour outlet, or the outlet may be lined with a ring of such material. The protective gas may be led to the outlet from all sides, for instance by an annular spreading device, and the zinc vapour may issue horizontally or inclined upwardly; or, as the deposit tends to appear at the lower side of the outlet, the gas may be directed in a flattened stream towards the lower side of the outlet. The mouth of the upwardly inclined gas pipe may be covered with a distributing plate or the like to avoid choking by falling oxide. In order to obtain pure zinc oxide, the first and last portions of the distillate may be collected as metallic zinc or zinc dust, the zinc oxide being produced only during the middle stage of the distillation. The protective gas would then be shut off during the first and last periods. The Specification as open to inspection under Sect. 91 (3) (a) states that the protective gas may be led against the wall of the muffle or furnace below the outlet so that the furnace wall acts as a guiding surface. This subject-matter does not appear in the Specification as accepted.