US2221614A - Method of manufacturing selenium rectifiers - Google Patents

Description

Patented Nov. 12, 1940 v r f UNITED STATES.

PATENT OFFICE METHOD OF MANUFACTURING SELENIUM Ernst Sieberh'Beriin-Siemensstadt, Germany, assignor to Westinghouse Electric a Manufacturing Company, East Pittsbnrgh h, a corporation of Pennsylvania No Drawing. Application August 12, 1939, Serial No. 289,790. In Germany Augnstflo, 1938 4 Claims. (Cl 175-866) and the selenium isas satisfactory as possible. both from a mechanical and electrical point of I view. To this end, the jet sandblast may be employed to advantage. 1

According to the invention the support of aluminum, magnesium, alloys thereof or of an equivalent light metal is pickled before applying thereto the selenium in order to roughen the surface. The advantage obtained thereby is probably based upon the .fact that the Jet sand blast causes sharp tiny points to. lie-produced on the surface. \The selenium adheres insuifi ciently or not at all to these sharp'points. Consequently, the counter-electrode which is normally sprayed ontothe selenium coating easily comes into direct contact with these points of the light metal support,.thus causing short-circults. If it should not bepossible to eliminate these short-circuits during theforming process or similar processes of treatment. the element" is of no value. The pickling has furthermore the advantage that it is not so criticalras the treat- 80 ment by means of a sand Jet; however, the joint is above all more intimate and more durable than when roughening the surface by means ofga sand jet and consequently the seasoning effect of the rectifiers is decreased.

so When pickling an aluminum surface, hydro-f chloric acid with a slight additlonof' iron is. employed according to the invention to 5 Par icularadvantage. One gram of .iron in onelitr-of f not hydrochlorioacid dilutedin the ratio 1:1 0 gives particularly satisfactory results. 'By' pickling with such an agent, the to which the selenium may adhere is increased. on

the one hand and on the other hand it is freed in an effective manner of .the foreign layers which do not co'nsistofxpure aluminum. The

adhesion is obviously based onthje formation of selenide of aluminum-inlthe=form of an intermediate layer. A foreignclayenparticularly an oxide layer preventsundercircumstances the so formation of such anintermediate-layen so that the necessary adhesion is not broughtaboutj f A rectifier according to to*thc. invcntion1i8 manufactured. for instance," in the. following manner. A support which may consist of c'ommercial aluminum is pickled in diluted hot'hy drochloric acid to which is added one gram of iron .per liter.

T0 the surface which when pickled must be protected against furtherchemical attacks, molten selenium is applied and subjected in a press to a suillcient pressure which ensures a proper and uniformdistributionof the selenium-on the surface of the aluminum plate.

The plate is then heat treated in a furnace at a temperature somewhat about 200 degree centi-q 10 grade for one or more.hours, care being taken to ensure a sufficient amount of air to be admitted.

During this period the selenium is converted into an electrically conductive state. The selenium coating is then subjected for a short time 16 to the action of sulphur vapors. -In this manner a discontinuous film of sulphur is produced on the selenium coating, on which film is sprayed a layer of a metal of low fusibility, for instance, an alloy of lead and bismuth or of cadmium and 90 bismuth. The rectifier element thus produced is then formed by the action of an electric current by applying in the inverse direction a direct voltage which increases with increasing resistance in the 25 inverse direction, for instance, from 5 to about '18 volts, the current flowing atthe beginning in the inverse direction thus decreasing under the 1 action of the voltage to a few milliamperes.

whatis claimed is: V 1. The method of manufacturing a selenium rectifier which consists of melting a. selenium coating on a support of light metal, for instance, aluminum, magnesium or the 19.110575 thereof,

which has been pickled inhydrochloric acid with 35 aaslight addition of iron before applying the selenium thereto, heat treating said rectifier at above substantially 200 degrees Centigrade, and

selenium. I 0

i spraying a of metal of low fusibility on said 1 t 2. The method asset forth in claim 1, characterized inthat the surface'is pickled in hydrochloric acid with an addition of iron amounting to substantially -1 gram of iron per liter 'of hydrochloric acid. d5 "3. The method as set forth in claim 1, characterized in that the pickling is eflected in diluted hot hydrochloric acid.

4. The method as set forth in claim 1, characterized in that the pickling is continued until 0 the surface of the discs assumes a mar-bled grey appearance. 7

' ERNST SIEBERT.