| 摘要 |
Aluminium oxide films having a thickness of from 1/4 to 25 microns are produced by reducing the thickness of a central portion of an aluminium foil initially at least 50 microns thick by subjecting one or both sides of said central portion one or more times to a surface treatment consisting of anodic oxidative followed by chemical removal of the aluminium oxide formed, until the said central portion remaining consists of aluminium foil not thicker than 20 microns, supported by the untreated portion of the foil, subjecting both sides of the remaining thinned foil to anodic oxidation, chemically removing the resulting oxide layer from one side only, and then dissolving the remaining aluminium metal to leave a film of aluminium oxide supported within the untreated portion of the original foil. The initial anodic oxidation can be carried out in a bath containing an aqueous solution of 10-15% by weight of sulphuric acid or 4-8% by weight of oxalic acid, the final oxidation is preferably carried out in an electrolyte consisting of an aqueous solution of 6% by weight of boric acid and 1.5% by weight of sodium borate. The reagent which dissolves aluminium oxide, without attaching aluminium may be a mixture of hydrofluoric acid and nitric acid or a mixture of chromic acid and phosphonic acid. A preferred reagent is an aqueous solution of 10% by weight of phosphoric acid and 5% by weight of sodium bichromate. The aluminium is dissolved by a solution of concentrated hydrochloric acid containing 3% by weight of sodium bichromate and a trace of copper chloride. |
