GB467024A - Improvements in or relating to electrolytic condensers and other electrolytic devices - Google Patents

Abstract

467,024. Electrolytic etching. DUBILIER CONDENSER CO. (1925), Ltd., and MOORE, N. C. Dec. 9, 1935, Nos. 34045/35, 7248/36, and 13622/36. [Class 41] Film-forming metals such as aluminium are treated by immersion in an electrolyte solution through which alternating current is passed under such conditions that minute pores or craters are produced in the surface of the metal whereby its effective surface area is increased. The metal may be disposed between the electrodes or may itself constitute an electrode. The electrolyte should be maintained at about 70‹ C. It may consist of a 1 per cent solution by volume of an acid or a mixture of acids, preferably a mixture of hydrochloric, nitric and sulphuric acids. The electrode or electrodes are preferably of graphite. The electrolyte may also consist of an aqueous solution of sodium chloride ; in this case electrodes of the metal sold under the Registered Trade Mark " Monel " may be used. In the apparatus shown in Fig. 1, aluminium foil A connected as one electrode is fed from a roll A<1> beneath rollers B<3>, B<4>, and through an electrode D consisting of a rectangular frame of carbon plates to a roller F, thence passing through spraying and washing baths to a winding drum. The electrolyte is maintained at the required temperature by a cooling coil B<1>. The concentration of the electrolyte is maintained constant by a drip feed E of dilute acid which may be regulated by hand or automatically to maintain the current between the electrodes constant. Evaporation loss may be made up by a separate feed of water. Large rollers only partially immersed may be used instead of the rollers B<3>, B4. In a modification two strips are fed through the bath so as to constitute opposite electrodes. In the apparatus shown in Fig. 2, the strip A is passed in succession through two etching baths K, L containing electrodes D2, D3 connected to a transformer C<5>, the strip constituting an intermediate electrode. The electrodes D<2>, D<3> are arranged so as to etch both sides of the strip. After leaving the bath L the strip is passed through a bath containing 2 per cent caustic soda solution at 60-70‹ C. to remove any oxide film formed during etching, then through a bath containing a 5 per cent sulphuric acid solution at 60-70‹ C. to neutralize the alkali, a gelatine bath at 100‹ C. for the removal of traces of acid and aluminium salts as described in Specification 448,163, and a final hot distilled water bath. The strip may then be dried and wound or it may be subjected directly to a forming treatment, e.g. in the manner described in Specification 398,825. The etched and formed strip may be employed in the production of condensers of the kind described in Specifications 439,530 and 453,058.