US2205263A - Copper oxide rectifier - Google Patents

Description

June 18, 1940. c. c. HEIN 2,205,263

COPPER OXIDE RECTIFIER Filed llay 6, 1938 Oxidizz'ng at 10002 more than eight minutes, less than 30 minutes preferabgy 16' minutes. I

Annealing [Ominutes at 500C.

Quenchiny in cold water Rembotny Black (bupric) oxio le refmbly by dilute sulfuric acid at 80C and Zeavz'ny red (cuproasj oxide 003 inch thick.-

45C 400 I/ as Q 300 xi Standard Mtg- 3 days? mvedgzfierw g days) 32 I 0 Initial Standard value. bzz'i'ial Improved value. 7 WITNESSES: O 5 INVENTOR l u .4 V0 is (Reverse oz-zzegatwe) Carl C1190? Patented June 18, 1940 COPPER OXIDE RECTIFIER Carl C. Hein, Forest Hills, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of. Pennsylvania Application May 6, 1938, Serial No. 206,403

particularly to copper oxide rectifiers.

An object of the invention is to provide a copper oxide rectifier having a higher voltage rating. Another object of the invention is to provide a copper oxide'rectifier capable of withstanding higher reverse voltages.

Other objects and advantages of the invention will be apparent from the following description and drawing, in which Figure 1 is a;graph listing of the method steps of my invention, and

Fig. 2 is a graph illustrating the improvements of a copper oxide rectifier constructed according to my invention in comparison with a standard copper oxide. rectifier.

The rating of a copper oxide rectifier is governed by its ability to dissipate its internal losses. It has been found convenient to use cooling fins and forced ventilation for additional dissipation to obtain increased power output. My experiments disclose that the performance curves of the copper oxide rectifier show that thewattage dissipation in the reverse direction rises much more rapidly with voltage than the wattage dissipation, in the forward directionwith current output. To make matters worse, the temperature coeflicient of conductance is about 6% per degree for the reverse direction as compared with about 2% per degree for the forward direction providing more dissipation ability but the pro vision of fins and ventilation previously mentioned increases the forward current rating, but the back losses rise so steeply with voltage increase that the rating of the device has to be limited very strictly on this account. This back voltage limitation requires that a second rectifier be used in series if the voltage rating is increased even one volt beyond the rating-of the single disk. The result is that frequently the size of the rectifier must be doubled, if only one volt additional is required. This voltagelimitatidn is very serious in the application of rectiflers for electroplating and other applications requiring high currents. An additional volt or two means the doubling of the rectifier size which in these applications means the addition of several hundred plates. A small increase in voltage rating of a volt or two would eliminate the doubling of the rectifier and have enormous savings in cost and design.

I have provided a copper oxide rectifier with decidedly less leakage current by the following processing schedule. I take the copper material such as that of the commonly used copper disk pending upon the length of oxidation.

'ness of the red or cuprous oxide.

and oxide the disk in the usual well knownoxidizing furnace, but instead of oxidizing the disk merely to the desired thickness of red or cuprous oxide, I continue the oxidation until the cuprous oxide is considerably thicker than that desired in'the final form of the oxidized plate. If, for example, the final form of the plate has a euprous oxide thickness of 3 mils, I continue the oxidation until the thickness of the cuprous oxide is approximately 4 mils, or more, and preferably 10 about 6 inils thick. I obtain such a layer by oxidizing the copper at a temperature between 950 C. and the melting point of copper 1083 C. After selecting the temperature of oxidation, usually approximately 1000 C., I control the 35 thickness of the oxide layer by the length of time the copper remains in the oxidizing furnace usually more than eight minutes and preferably less than thirty minutes; I then remove the disks from the oxidizing furnace and place them 20 in an annealing furnace. After a time interval of three to fifteen minutes, the disks have reached a'temperature of approximately 500 C. when they are removed from the annealing furnace and quenched in cold water. The prac- 25 tice in making copper oxide disks heretofore has been to remove the superficial layer of cupric or black oxide. If merely the cupric oxide were removed from these thicker disks, such disks would have an' internal resistance in the forward direc- 30 tion which would be one to three times more than have the standard disks heretofore manufactured, and as a result such elements'or disks would be rejected for commercial applications. In my invention, however, I remove the excess 35 thickness of oxide obtained by the particular; oxidation schedule stated above so that the cuprous oxide layer is the same thickness as that for a standard element, namely, of the order of 3 mils. This excess thickness of cuprous oxide 40 may be anywherefrom approximately 25% or more of the thickness of the cuprous oxide, de-

If the cuprous oxide is 4 mils thick and 3 mils is desired in the finished product, only 25% will be 45 removed. On the other hand, if the cuprous oxide is 6 mils thick, then 50% will be removed to reduce the cuprous oxide to the desired 3 mils thickness,;- e

. I-have found it desirable to employ a dilute 50 solution of sulfuric acid at C. toremovethe black oxide or'cupric oxide and the excess thick- The bath process I employ uses 2% sulfuric acid with .1%

of hydrochloric acid at 80 0. After removal 5 from the bath, the elements are rinsed in tap water and given a few seconds dip in concen trated nitric acid with a second thorough rinse to remove all traces of acid. In annealing there is an appreciable range of temperature over which usable rectifiers can be made, namely 425 to 600 0., although 500 to 550 C. is generally employed.

The rectifier constructed according to my process will exhibit characteristics that permit the operation at higher impressed voltages than those heretofore obtainable. It is possible that the removal of the excess thickness of oxide also removes certain surface containing impurities of the copper, or it may remove some undesirable boundary condition existing between the black cupric oxide and the red cuprous oxide. I do not desire, however, to be limited to the possible explanation just stated. Experimental eiiorts have proved rectifiers made by this process are far superior to anything thus far available in copper oxide rectifiers.

A standard element and one made according to the above-described method were put on test simultaneously at nearly three times the normal output direct current voltage. it The standard unit failed in three days, butthe other unit formed according to my invention operated many weeks with only an 11 temperature rise. The curves in Fig. 2 disclose the unusually low temperature coeflicient reverse voltage curve obtained in this new rectifier as compared with the standard element. Initially, the values at'22 volts were 15 milliamperes back current for the'improved copper oxide rectifier to 48 milliamperes for the standard unit. The low temperature coefiicient of my improved copper oxide rectifier minimizes the temperature rising of the assembly and allows stable operation at high voltages which was'not obtained heretofore.

The invention applies to all shapes of rectiflers whether they be round disks, plates or other shapes and also to the rectiflers in which the l. The method of forming copper oxide rectifiers which comprises oxidizing cooper material at approximately 1000 C. to form an outer layer of black oxide and an underlying layer of red oxide and continuing saidoxidation until the red oxide is substantially more than three mils thick on the area intended to be used for rectifying, annealing the material until it reaches approximately 500 0., quenching the material, removing the black oxide and also reducing the thickness of the red oxide on' said area to substantially three mils.

2. The method of forming copper oxide rectifiers which comprises oxidizing copper material at approximately 1000 C. to form an outer layer of black oxide and an underlying layer of red oxide and continuing said oxidation until the red oxide is substantially more than three mils thick on the area intended to be used for rectifying, annealing the material until it reaches approximately 500 C., quenching the material, removing the black oxide and also reducing by treating with dilute sulfuric acid the thickness of the red oxide on said area to substantially three mils.

3. The method of forming copper-oxide rectifiers which comprises oxidizing copper material to such an extent that the thicknessof the cuprous oxide layer which is intended to cause rectification is of the order of 25% greater than that required for rectification and removing the cuprous oxide and also removing the excess thickness of cuprous oxide from said layer.

4. The method of forming copper-oxide rectifiers which comprises oxidizing copper material to such an extent that the thickness of the euprous oxide layer which is intended to cause rectification is of the order of 25% greater than that required for rectification and removing the euprous oxide and also removing by acid the excess thickness of cuprous oxide from said layer.

CARL C. HEIN.

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