Improvements in zinc oxide

摘要

530,858. Preparing zinc oxide. NON FERROUS METAL PRODUCTS, Ltd. June 29, 1939, No. 19022. Convention date, June 29, 1938. [Class 1 (iii)] Acicular zinc oxide is made by introducing a stream of substantially undiluted zinc vapour into a combustion zone of controlled temperature, burning the zinc vapour in the zone in a current of pre-heated air, and regulating the temperature of the combustion zone in the neighbourhood of 1225-1250‹C. in order to control twinning of the particles of zinc oxide produced. When the temperature of the combustion zone is maintained in excess of 1250‹C., the resulting zinc oxide particles are in the form of single acicular crystals, but when the temperature is mainained below 1225‹C., the particles obtained are in the form of complex twinned acicular crystals, such as threelings or fourlings. When the air is only moderately pre-heated, e.g. to 500‹C., the current should be slow and only in slight excess of that required to oxidize the zinc vapour, while if the air is intensely pre-heated, e.g. to 1000‹C., the current may be rapid and in great excess. In either case the air may be pre-heated by bringing it into countercurrent heat exchange relationship with the hot gases escaping from the combustion zone. An apparatus, suitable for carrying out the process, comprises a retort 10 for vaporizing metallic zinc, a duct 13 for zinc vapour, an air-preheating chamber 20, an annular heating jacket 15, a combustion chamber 19, a fan 23, and a zinc oxide collecting bag 25. Air enters the chamber 20 at 29. Pyrometers 27, 28, and a valve 26 for false air, are provided. Specification 406,560, [Group II], is referred to.