US2320962A - Treatment of copper-oxide rectifiers with nitrogen - Google Patents

Description

Patented June 1,

TREATMENT OF COPPER-OXIDE RECTI- FIERS WITH NITROGEN Earl D. Wilson, Wilkinsburg, Pa, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application September 26, 1941, Serial No. 412,423

6 Claims. (Cl. 175-366) My invention relates to copper oxide rectifiers and, in particular, relates to manufacturing methods for producing stable and invariable electrical characteristics in such rectifiers.

It has been found that copper oxide rectifiers produced by prior art methods, such, for example, as those described in the United States patent to L. 0. Grondahl No. 1,640,335, assigned-to the Union Switch 8: Signal Company of Swissvale, Pennsylvania, have a certain characteristic which is undesirable for many purposes, this characteristic being that. what may be termed reverse leakage current" increases rapidly during the first few hundred hours of their use. It is, of course, a characteristic of rectifiers generally that they conduct current quite readily in one direction and oppose a much higher resistance to current flow in the reverse direction; this resistance to reverse current flow is in no case M- tually infinite. There is always a slight so-called reverse leakage current" and it is to this that the foregoing sentence refers. Since this "reverse leakage current represents an energy loss and produces temperature rise in the rectifier, it is desirable that it should at all times be as low as possible; the above-mentioned tendency for it to increase in the course of use is, accordingly, an undesirable thing.

I have discovered thatthis tendency of "reverse leakage current to increase during use of the rectifier can be prevented by subjecting the rectifier discs during their course of manufacture to aheat treatment in an atmosphere of nitrogen. The full detailsof this process will now be explained. I

Copper elements are .first cleaned by dipping in nitric acid, rinsing with water and drying in air in the manner described in the above-men-v tioned Grondahl patent. Thereafter they are placed in a furnace containing atmospheric air and heated to a temperature of 1025 C. for a period of about fourteen minutes. Thereupon the air is quickly displaced from the furnace and an atmosphere of substantially pure nitrogen substituted for it. The elements remain in the nitrogen atmosphere at substantially 1025 C. for an additional period. While I have found that even a very brief treatment improved the rectifier discs and that the improvement increases with the length of time, at least up to thirty minutes that the treatment is continued, a treatment of three minutes is effective enough for most practical purposes and is, of course, more economical as a manufacturing method than longer treatments.

After treatment in the nitrogen atmosphere as above described, the elements are immediately.

removed to a second furnace containing atmospheric air and maintained therein at 450 C. for a period of fifteen minutes.

process of preparing the rectifier elements may follow that described in the above-mentioned Grondahl patent.

I have found that this nitrogen treatment does not appreciably affect the resistance of the rectifier elements to current flow in their highly conductive direction, while the resistance to flow of the "reverse leakage currents is increased by a large factor. This treatment is also effective in improving rectifiers which, previous to their oxidation, have been given the high vacuum treat-' similar purposes is within the purview of my invention,

I claim as my invention:

1. The method of manufacturing rectifier ele-.

ments which comprises oxidizing copper at a temperaturesomewhat below its melting point for a substantial period, immersing the. oxidized element in an atmosphere of nitrogen at'a temperature somewhat below its melting point, and thereafter cooling the element.

2. The method of'manufacturing rectifier elements which comprises oxidizing copper at a temperature somewhat below its melting point for a substantial period, immersing the oxidized element in an atmosphere of nitrogen at a temperature somewhat below its melting point, thereafter maintaining the element at a substantially lower temperature for a period of the order of minutes in duration, and thereafter chilling the element to substantially. room temperature.

' 3. The method of manufacturing rectifier elements which comprises oxidizing copper at a temperature somewhat below its melting point fora substantial period, immersing the oxidized element in an atmosphere of nitrogen at a temperature somewhat below its melting point. thereelement.

4- The method of manufacturing rectifier elev I Thereafter they are immediately quenched in water. The further taining the element at a temperature or the order of 450 C. for a period of the order of fifteen minutes, and thereafter quenching the element.

5. The method of manufacturing rectifier e1emeats which comprises oxidizing copper at a temperature of the order or 1025" C. for a substan-, tial period in an atmosphere of air, immersing the element in. an atmosphere of nitrogen at a temperature or the same order for a period of the order of three to thirty minutes, thereafter immersing the element in an air atmosphere at atemperature of the order of 450 C. for a period of the order of fifteen 'minutes -and thereafter quenching the element.

6. The method of manufacturing rectifier elemerits which comprises oxidizing copper at a temperature of the order of 1025 C. for a period of V the order of fourteen minutes, immersing the elemerit in an atmosphere of nitrogen at a. temperature of the same order for a period of the order of three to thirty minutes, thereafter immensing the element in an air atmosphere at a temperature of the order of 450 C. for a period v f the order of fifteen minutes, and'thereaiter uenching the element.

EARL D. WILSON.