US2498240A - Selenium rectifier - Google Patents

Description

Feb. 2l, 1950 w. E. BLACKBURN 2,498,240

SELENIUM RECTIFIER original Filed' Maron 2o, 1947 Ffgl.

Cadmium M/a//Me/a/ 4l/a y Cad/Tlam .dloh/de Se/en/'um WITNESSES: INVENTOR //-Wj/ Way/7e EB/acA/burn,

ZW BY ATTORNE Patented F eb. 21, 1950 UNITED STATES PATENT OFFICE SELENIUM RECTIFIER Original application March 20, 1947, Serial No. 735,883. Divided and this application June 19, 1948, Serial No. 34,043

My invention relates to selenium rectiers and, in particular, to a counter-electrode which produces an improved barrier layer, or rectifying interface in such rectiers. It is based on the discovery that an improved rectifying ratio at a surface of selenium, or particularly a seleniumcadmium sulphide surface, is obtained by employing a counter-electrode of cadmium, or cadmium-tin, to which have been made small additions of gallium, boron, cerium selenide, columbium oxide or a metal from the alkali or alkaline-earth groups.

This application is a division of my application Serial No. 735,883 for Selenium rectifiers filed March 20, 1947.

One object of my invention is, accordingly, to produce an improved selenium rectifier.

Another object of my invention is to produce a dry-contact type rectifier having a better rectiiication layer than rectifers of the prior art.

Stili another object of my invention is to provide a dry-contact type rectifier of the type employing selenium surfaced with cadmium sulphide with a counter-electrode which improves the barrier layer of the rectifier.

A yet further object of my invention is to provide an improved type of counter-electrode for rectiners of the selenium type.

Other objects of my invention will become apparent upon reading the following description, taken in connection with the drawing, in which:

Figure 1 is a mid-section and Fig. 2 a top view of a rectifier embodying the principles of my invention.

Referring in detail to Figs. 1 and 2, a rectier in accordance with my invention may be produced by employing a backing plate l of steel, which may have a central hole 2 and which has preferably been sand-blasted and nickel-plated. This plate is coated with a layer 3 of amorphous selenium by dipping it in a molten bath of selenium and throwing off the excess thereof by centrifugal force. The free surface of the selenium is then coated by evaporation and condensation with a thin layer I of cadmium sul- 1 Claim.y (Cl. 175-366) 2 phide. This procedure may be carried out as described in more detail in my copending application, Serial No. 514,371, filed December 15, 1943,

now Patent No. 2,488,369, issued November 15,`

The unit thus produced may then be annealed at a temperature of 185 C., andthe counterelectrode 5 then applied by Schoop-spraying or other suitable process known in the art. While I have described the selenium as coated with cadmium sulphide before the application of this counter-electrode, for certain purposes it may be suitable to omit the coating with cadmium sulphide. Furthermore, it is within the scope of my invention to apply the counter-electrode before carrying out the annealing process mentioned above.

The counter-electrode is formed from an alloy or aggregate comprising substantially '10 parts cadmium, 30 parts tin, with the addition of a small amount, about 1 part of one or more substances from the following group: an alkali or alkaline-earth metal, gallium, boron, cerium selenide and columbium oxide.

Of the addition agents just listed, I have found cadmium and an alkali metal.

WAYNE BLACKBURN.

REFERENCES CITED The following references are of record in the 4o ille of this patent:

UNITED STATES PATENTS Name Date Thompson et al. Mar. 9. 1948 Number

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