| 摘要 |
Acicular gamma ferric oxide suitable for magnetogram carriers is produced by precipitating ferric hydroxide from a solution of a ferric salt with a more than 100% stoichiometric excess of a first alkaline solution while stirring at 10 DEG to 50 DEG C., separating the precipitate, contacting it at 20 DEG to 90 DEG C. for 10-40 hours with a second alkaline solution having a concentration of the basic substance between 3 and 20%, heating it to a temperature higher than 90 DEG C. up to the boiling point of the second alkaline solution, if desired under pressure, filtering off the precipitate, washing and drying it, converting it with reducing gases to ferriferrous oxide, and then oxidizing it with oxygen-containing gases to gamma ferric oxide. The ferric hydroxide may be precipitated from a solution of ferric chloride, nitrate or sulphate by an excess of more than 100% over the stoichiometric amount of hydroxide or carbonate of an alkali metal or of ammonia. The precipitate may be reduced to Fe3O4 with carbon monoxide, hydrogen or coal gas at up to 400 DEG C., preferably 270 DEG to 300 DEG C., and then oxidized with air at up to 400 DEG C., preferably 180 DEG to 200 DEG C. Ions of other metals, e.g. cobalt, nickel, copper, manganese, cadmium and chromium, may be present in the ferric salt solution and precipitated with the ferric hydroxide, so that up to 10% of the other metal is present in the gamma ferric oxide. Examples are given. |
