US3868275A

US3868275A - Manufacture of silver-cadmium oxide wire

Info

Publication number: US3868275A
Application number: US369317A
Authority: US
Inventors: Loren Godfrey; Krishnamurthy Vaithinathan
Original assignee: Engelhard Minerals and Chemicals Corp
Current assignee: BASF Catalysts LLC; Engelhard Minerals and Chemicals Corp
Priority date: 1973-06-12
Filing date: 1973-06-12
Publication date: 1975-02-25
Anticipated expiration: 1992-02-25
Also published as: AU6993574A; FR2233405B1; CA1008014A; BR7404800D0; AU477025B2; FR2233405A1; IT1013420B; DE2428029A1; GB1469313A; JPS5033115A

Abstract

Pre-oxidized silver-cadmium oxide wire, such as pre-oxidized 90Ag 10CdO wire obtained by 91Ag 9Cd alloy wire, is prepared by plural stage oxidation. The silver-cadmium alloy wire is initially prepared having a diameter greater than the diameter of the finished wire Df, e.g., in the range 1.7-2.0 Df. Following each oxidation operation comprising the plural stage oxidation the resulting oxidized wire is drawn or otherwise reduced in diameter, the desired finished diameter Df being reached after the last oxidation operation. The oxidation operations making up the plural stage oxidation are carried out such that the matrix area of the finished wire is substantially 100% oxidized, i.e., the cadmium content of the wire is substantially completely oxidized to cadmium oxide.

Description

United States Patent [191 Godfrey et a1.

[451 Feb..25, 1975 I MANUFACTURE OF SILVER-CADMIUM OXIDE WIRE [75] Inventors: Loren Godfrey, Morristown',

Krishnamurthy Vaithinathan, Edison, both of Na],

[73] Assignee: Engelhard Minerals & Chemicals Corporation, Murray Hill, NJ.

221 Filed: June 12, 1973 21 App1.No.:369,3l7

[52] US. Cl ..148/6.3,148/11.5 R, 75/173 A, 117/231 [51] Int. Cl. C23c 11/00, C21d C22c 5/00 [58] Field of Search 148/63, 11.5 R; 75/173 A; 117/231 [56] References Cited UNITED STATES PATENTS 2,932,595 4/1960 Pflumm l48/11.5 R 3,666,428 5/1972 Haarbye 75/173 A X FOREIGN PATENTS OR APPLICATIONS 960,592 6/1964 Great Britain 75/173 A Primary Examiner-John D. Welsh [57] ABSTRACT Pre-oxidized silver-cadmium oxide wire, such as preoxidized 90Ag 10CdO wire obtained by 91Ag 9Cd alloy wire, is prepared by plural stage oxidation. The silver-cadmium alloy wire is initially prepared having a diameter greaterthan the diameter of the finished wire D;, e.g., in the range 1.72.0 D Following each oxidation operation comprising the plural stage oxidation the resulting oxidized wire is drawn or otherwise reduced in diameter, the desired finished diameter D; being reached after the last oxidation operation. The oxidation operations making up the plural stage oxidation are carried out such that the matrix area of the finished wire is substantially 100% oxidized, i.e., the cadmium content of the wire is substantially completely oxidized to cadmium oxide.

22 Claims, 1 Drawing Figure MANUFACTURE OF SILVER-CADMIUM OXIDE WIRE This invention relates to the manufacture of preoxidized silver-cadmium oxide wire. More particularly, this invention is directed to the manufacture of preoxidized silver-cadmium oxide wire derived from internally oxidizable silver-cadmium alloys containing up to about 20% by weight cadmium.

Silver-cadmium oxide compositions have long been known to be useful for the manufacture of electrical contact elements and the like, see US. Pat. Nos. 2,307,668, 2,539,298, 2,796,346, 2,830,898, 2,932,595, 3,472,654, 3,477,845 and 3,666,428. The disclosures of each of the above-identified patents are herein incorporated and made part of this disclosure.

As indicated by the disclosures of the aboveidentified patents, there has been considerable interest in developing a satisfactory process for the preparation of pre-oxidized silver-cadmium oxide wire from silvercadmium alloys. For the most part, however, the methods and techniques known heretofore for the production of a pre-oxidized silver-cadmium oxide wire have not been completely satisfactory. For example, techniques have been developed to produce a pre-oxidized silver-cadmium oxide wire but when such wire was headed to rivets for the production of electrical contact elements the resulting rivets were unsatisfactory due to cracking. In the methods known heretofore to produce pre-oxidized silver-cadmium oxide wire and the like, the oxidation process for the production of the preoxidized wire has usually been carried out in a single stage oxidation operation. As indicated hereinabove, however, completely satisfactory results were not obtained.

lt is an object of this invention to provide an improved process for the manufacture of pre-oxidized silver-cadmium oxide wire useful for the manufacture of electrical contact elements therefrom, such as rivets and the like.

It is another object of this invention to provide an improved process for the oxidation of silver-cadmium alloys, such as silver-cadmium alloys containing up to about 20% by weight cadmium, for the manufacture of pre-oxidized silver-cadmium oxide materials, structurcs, strips or wire therefrom.

It is yet another object of this invention to provide an improved process for the preparation of pre-oxidized silver-cadmium oxide wire especially satisfactory for the production of rivets therefrom.

How these and other objects of this invention are achieved will become apparent in the light of the accompanying disclosure and particularly with reference to the accompanying drawing wherein there is illustrated a flow sheetfor the manufacture of 90Ag l CdO pre-oxidized wire in accordance with one preferred embodiment of the practices of this invention. In at least one embodimentof the practices of this invention at least one of the foregoing objects will be achieved.

ln accordance with the practices of this invention there is provided a process for the manufacture of preoxidized silver-cadmium oxide compositions and structures, such as wire, derivable from internally oxidizable silver-cadmium alloys containing up to about by weight cadmium. The practices of this invention are particularly applicable to the most common and typical internally oxidizable silver-cadmium alloy containing about 91% by weight silver and about 9% by weight cadmium which is oxidizable to the composition by weight silver and 10% by weight cadmium oxide.

Although emphasis is placed in the disclosure of this invention on silver-cadmium alloys containing up to 20% by weight cadmium, such as silver-cadmium alloys containing 515% by weight cadmium, the silvercadmium alloy which is treated in accordance with this invention to provide silver-cadmium oxide compositions particularly useful for the manufacture of electrical contact elements might also include other metal additives up to about 10% by weight of the silvercadmium alloy. Suitable such additives include cobalt, nickel, thallium, copper, potassium and calcium.

The internally oxidizable silver-cadmium alloy compositions in accordance with this invention are subjected to a plural stage oxidation operation in contact with air or oxygen-enriched air or oxygen at an elevated temperature and, if desired, at an elevated pressure, such as in the range 1-10 atm. abs. The oxidation operation is carried out in a plurality of separate oxidation operations sufficient to effect substantially oxidation of the matrix, e.g., the wire matrix or crosssection of the silver-cadmium alloy, so as to convert substantially all of the cadmium content to cadmium oxide. The plural stage oxidation operation in accordance with this invention may comprise two separate oxidation operations or as many as six or more separate oxidation operations, depending upon the shape and/or thickness of the silver-cadmium alloy material or structure undergoing oxidation. Usually, a plural stage oxidation operation made up of three separate oxidation operations is sufficient to substantially completely convert the cadmium content of the silver-cadmium alloy material or structure undergoing oxidation to cadmium oxide.

The oxidation operations making up the plural stage oxidation treatment in accordance with this invention are usually carried out at an elevated temperature, preferably at a temperature of about 1,500F., such as a temperature in the range 1,4501,550F., more or less, about 1,200F. or higher but below the melting point of the alloy undergoing oxidation, preferably at least about 25F. below the melting point. The separate oxidation operations making up the plural stage oxidation treatment need not be carried out at the same temperature or with the same temperature range, although effective and satisfactory results have been achieved by carrying out the oxidation operations at a temperature in the range from about 1,450 to about 1,550F. The individual oxidation operations making up the plural stage oxidation treatment are carried out for a period of time in the range from about 1 hour to about 100 hours, depending upon the cadmium content in the alloy undergoing oxidation. Also, depending upon the size and/or shape and/or thickness of the oxidation temperature and oxygen concentration and pressure employed, each separate oxidation operation might be satisfactorily completed within a rather short period of time, as low as 15-30 minutes, or might require a substantial period of time, such as high as 100 hours.

As indicated hereinabove, the internally oxidizable silver-cadmium alloy materials are subjected to a plural stage oxidation treatment which might be made up of two or more, such as six, separate oxidation operations. Each separate oxidation operation is carried out to ef feet a conversion of the cadmium of the silvercadmium alloy material undergoing oxidation to cadmium oxide so that upon completion of the plural stage oxidation treatment substantially the entire cadmium content of the silver-cadmium alloy material undergoing treatment has been converted to cadmium oxide.

By way of example, and with reference to the preferred embodiment of the practices of this invention involving a three stage oxidation operation of silvercadmium alloy wire, the first stage oxidation operation is carried out such that the matrix area of the silvercadmium alloy wire is oxidized to about -30%, i.e., 15-30% of the cross-sectional area is oxidized such that the cadmium content therein is converted to cadmium oxide. 1n the second stage oxidation operation the matrix area would be oxidized to an even greater extent, to about 30-50% of the matrix area. In the third stage operation the matrix area would be 100% oxidized, i.e., the cadmium content of the silver-cadmium alloy wire would be substantially completely converted to cadmium oxide.

Depending upon the shape and/or composition of the silver-cadmium alloy material undergoing treatment, as indicated hereinabove, the plural stage oxidation operation may be carried out in as many as two separate oxidation operations or might require as many as six separate oxidation operations. Accordingly, in a two stage oxidation treatment the first stage oxidation operation might result in the oxidation of 40-80% of the matrix area, more or less, or aslow as 5-15% of the matrix area in a six stage oxidation treatment. Upon completion of the plural stage oxidation operation, however, substantially 100% of the matrix area of the silvercadmium alloy material undergoing treatment would be completely oxidized and converted to the corresponding silver-cadmium oxide composition.

Another feature in the practices of this invention, and particularly in the preferred embodiment thereof wherein silver-cadmium alloy wire is oxidized, after each separate oxidation treatment in the plural stage oxidation the silver-cadmium alloy material or structure or wire is reduced in cross-section so that the following oxidation treatment in the plural stage oxidation is operative upon the previously oxidized silvercadmium alloy material now having a reduced crosssection. In the practices of this invention therefore the silver-cadmium alloy material undergoing treatment is supplied to the first stage oxidation operation with a cross-section substantially greater than the crosssection of the desired finished completely oxidized silver-cadmium oxide product. For example, the crosssectional area of the silver-cadmium alloy material or structure initially subjected to the plural stage oxidation operation would have a cross-sectional area or average cross-sectional area substantially larger than the cross-sectional area in the finished product. Specifically, the cross-sectional area of the silver-cadmium alloy material supplied to the first stage oxidation operation of the plural stage oxidation might be as large as or greater than twice the cross-sectional area in the finished product, such as having a cross-sectional area in the range from 2 to 9 times larger in the cross-sectional area of the finished oxidized product.

Upon completion of the first stage oxidation operation the resulting oxidized silver-cadmium alloy material or structure or wire would be reduced in crosssection say from a value of 2 times the desired finished diameter in the case of wire to about 1.2-1.8 times the diameter of the finished wire. When this material has been subjected to a second oxidation operation the resulting oxidized silver-cadmium material would be again reduced in cross-section, e.g., diameter in the case of wire, to about 1.1-1 .5 times the diameter of the finished completely oxidized product wire. Upon the completion of a third stage oxidation treatment this twice reduced silver-cadmium alloy material ,would be again reduced in cross-sectional area to substantially that of the cross-section or diameter desired in the finished product. The thus-treated material after suitable annealing, if necessary, and pickling, if necessary, could then be finished or reduced in cross-section to the cross-section desired in the finished product.

As indicated hereinabove, each oxidation treatment is followed by a size reducing or drawing operation wherein the cross-sectional area of the previously oxidized silver cadmium alloy structure is reduced. Upon the completion of the plural stage oxidation operation and the size reducing or drawing operation following the last oxidation operation the resulting oxidized silver-cadmium oxide structure would have a crosssectional area corresponding substantially to that desired in the finished product.

Each reducing or drawing operation need not effect a reduction in cross-sectional area of the silvercadmium alloy material undergoing treatment to the same extent. Greater or lesser reduction in crosssectional area may be effected after the first or the last oxidation operation. In the overall practice of the invention, however, upon the completion of the plural stage oxidation treatment with the intermediate size reducing or drawing operations the resulting silvercadmium product will substantially correspond in size to the size desired in the finished product and the cadmium content of the silver-cadmium alloy material initially supplied to the operation will be substantially converted or oxidized to cadmium oxide.

Reference is now made to the drawing which schematically illustrates by way of a flow sheet the preferred practice of this invention directed to the treat ment of a silver-cadmium alloy wire having the composition 91% by weightsilver and 9% by weight cadmium, the wire having a diameter in the range 1.7-2.0 times that of the diameter of the finished wire D The 91Ag 9Cd alloy is eitherextruded or continuously cast and then drawn to about 1.7-2.0 times the required finished diameter. The first stage oxidation is carried out at 1,500-1,540F. in air or in oxygen-enriched air for a period of time such that about 15-30% of the matrix area is oxidized. The resulting partially oxidized wire is then reduced in diameter or drawn to 1.5-1.8 times the required finish size. The second stage oxidation operation is then carried out at a temperature of about l,500F. in air or in oxygen-enriched air for a period of time sufficient to effect oxidation of about 30-50% of the matrix area. The partially oxidized .wire from the second stage oxidation is reduced in size or drawn to about 1.1-1.5 times the required finish diameter. Thereupon, the third stage oxidation operation is carried out at a temperature of about 1,500F. in air or oxygen-enriched air to effect substantially complete or 100% oxidation of the matrix. Upon the completion of the third stage oxidation operation the original alloy of the composition 91Ag 9Cd is converted to the corresponding composition Ag 10Cd0 The resulting completely oxidized material is then cold worked, if necessary, annealed, such as by heating to a temperature of about 1,000F. and then drawn to the required finish temper. The resulting wire is then pickled in dilute sulfuric acid, if necessary.

Wire prepared in accordance with the practices of As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations, modifications and substitutions are possible in the practice of this invention without departing from the spirit this invention and having the composition 90Ag 10Cd0 5 or scope thereofwas tested for headability, i.e., rivet formation there- We Claim! from. The wire produced in accordance with this inven- A method for the manufacture of Silver-cadmium tion had good headability and had a very small crack O id Wire ing the diameter which comprises rate, if any, in the head to shank diameter ratios n rforming from silver-cadmium alloy wire having the dimally prepared. The degree of grain boundary Cd0 pre- 10 ameter from about 1.5 to about 3 D;, subjecting the re cipitation was also found to be minimum, if any It sulting formed wire to a first stage oxidation at a temwould appear that the better mechanical properties, perature in the range from about l,450 to about good ductility and headability in rivet manufacture of 1,550F. in contact with air or oxygen-enriched air or this wire might be due to the sound matrix of the aloxygen for a period of time to effect oxidation of the loy. It also appears that the intermediate cold working wire to about 15-30% of the matrix area thereof, drawand oxidation refines the grain size. The presence of ing the resulting first stage oxidized wire to a diameter cadmium oxide in the matrix seemed to slow down the in the range from about 1.2 to about 2 D,, subjecting grain growth of the matrix and helps in strengthening the thus-drawn first stage oxidized wire to a second the matrix. Short cycle of oxidation time seems to elimstage oxidation at a temperature in the range inate cracking of the oxidized wire and the width of in- 1,450-1,550F. in contact with air or oxygen-enriched terruption bands of oxidation seen in the thusair or oxygen for a period of time sufficient to effect oxproduced wire where cadmium oxide composition may idation of about 30-50% of the matrix area thereof, be deviated from average composition is very small. drawing the wire resulting from the second stage oxida- In a typical case there was found to be about 00004 tion to a diameter in the range 1.1-1.5 D subjecting inch. This could be minimized by altering oxygen pothe thus-drawn second stage oxidized wire to a third tential, temperature or cooling rate in a subsequent oxistage oxidation at a temperature in the range dation. 1,450-l ,550F. in contact with air or oxygen-enriched Wire produced in accordance with the practices of air or oxygen until 100% of the matrix area of the wire this invention as illustrated in the preferred embodihas been oxidized, subjecting the resulting third stage ment shown in the drawing provides a superior wire, oxidized wire to drawing to about D,. especially for rivet manufacture. 2.'A method in accordance with claim 1 wherein the Further illustrative of the practices of this invention silver-cadmium alloy wire contains about 5-15% cadthere are set forth in accompanying Table No. 1 procemium by weight. dures for the preparation of preoxidized silver- 3. A method in accordance with claim 1 wherein the cadmium oxide wire in accordance with the practices silver-cadmium alloy has the composition of about 91% of this invention: by weight silver and about 9% by weight cadmium and Table No. l

OXIDATION PROCEDURES FOR Ag9%-Cd WIRE A B c o 7 Starting Diameter 095" .135" .155" 195" Oxidize 1540F 1540F., 1540F., 1540F.,

1% hour 2% hours 5 hours 8 hours Draw to .080" .115" .135" 165" Oxidize 1500F., 1500F., 1500F., 1500F., 4 hours 6 hours 11 hours 16 hours Draw to .070 .100" .115" 130" Oxidize 1500F., 1500F., l500F., 1500F.. 24 hours 40 hours 48 hours 64 hours Use for Sizes .062" 090-063" .lO5.090" .120.l05"

and below Typical properties of the resulting preoxidized silverwherein the oxidized wire resulting from the third stage cadmium oxide wire are set forth in accompanying oxidation has a composition of about 90% by weight Table O- 21 silver and about 10% by weight cadmium oxide.

Table 2 4. A method in accordance with claim 1 wherein the first stage oxidation is carried out for a period of time TYPICAL PROPERTIES OF PREOXIDIZED pi -10% CdO WIRE in h range from a t 1 o about 8 hours.

H 5. A method in accordance with claim 1 wherein said Common (Km Elong' (2 gauge) first stage, said second stage and said third stage oxida- AS oxidized a 5. 5 40.60% tion operations are carried out for a period of time in s- 7 2 1 2; 000 F. 3 33 $323 the range from about 1-8 hours, 4-16 hours and 24-64 v hours, respectively. 6. A method in accordance with claim 1 wherein the 1 L0 wire resulting from the third stage oxidation operation purities: .15 Max. and after drawing to about D is subjected to annealing Ag: Balance at a temperature of about 1,000F.

7. A method in accordance with claim 1 wherein said first stage, said second stage and said third stage oxidation operations are carried out in contact with air.

8. A method for the manufacture of silver-cadmium oxide wire having the diameter D, which comprises forming silver-cadmium alloy wire having a diameter greater than D subjecting the resulting formed wire to plural stage oxidation in contact with air or oxygenenriched air or oxygen with intermediate drawing of the resulting oxidized wire wherein after each oxidation stage the wire is reduced in diameter until the desired diameter D, is reached, each stage of said plural stage oxidation being carried out at a temperature in the range from about 1,200F. to a temperature at least about 25F. below the melting point of said silvercadmium alloy and for a period of time in the range from about minutes to about 100 hours, the plural stage oxidation being carried out so as to effect substantially complete oxidation of the cadmium present in the cadmium alloy wire to cadmium oxide.

9. A method in accordance with claim 8 wherein the silver-cadmium alloy wire has a diameter in the range 1.5-3 D,.

10. A method in accordance with claim 8 wherein said silver-cadmium alloy contains up to by weight cadmium.

11. A method in accordance with claim 8 wherein said plural stage oxidation comprises two separate oxidation operations.

12. A method in accordance with claim 8 wherein said plural stage oxidation comprises three separate oxidation operations.

13. A method in accordance with claim 8 wherein said plural stage oxidation comprises four separate oxidation operations.

14. A method in accordance with claim 8 wherein said plural stage oxidation comprises five separate oxidation operations.

15. A method in accordance with claim 8 wherein the initial stage oxidation of said plural stage oxidation includes an oxidation operation wherein the silvercadmium alloy wire is subjected to contact with air or oxygen-enriched air or oxygen at a temperature in the range from about l,450 to about 1,550F. for a period of time in the range from about 1 to 8 hours.

16. A method in accordance with claim 8 wherein immediately following the last oxidation stage making up the plural stage oxidation the wire is drawn to the desired diameter D 17. A method in accordance with claim 8 wherein immediately following the last oxidation stage making up the plural stage oxidation the resulting oxidized wire is drawn to a diameter slightly larger than the desired diameter D followed by annealing and pickling the resulting drawn oxidized wire and then drawing the wire to the desired diameter D,

18. A method for the manufacture of a silvercadmium oxide structure having an average crosssectional area A from a silver-cadmium alloy containing up to about 20% by weight cadmium which comprises forming a silver-cadmium alloy structure having an average cross-sectional area B from said silvercadmium alloy, B being greater than A, subjecting the resulting formed silver-cadmium alloy structure to plural stage oxidation in contact with air or oxygenenriched air or oxygen to effect upon completion of the last oxidation stage substantially oxidation of the cadmium content of said cadmium alloy structure to cadmium oxide, each stage of said plural stage oxidation being carried out at a temperature in the range from about l,200 to about 25F. below the melting point of said silver-cadmium alloy and for a period of time in the range from about 15 minutes to about 100 hours, during said plural stage oxidation there being at least one intermediate size reduction of the oxidized silver-cadmium alloy structure wherein the structure is substantially reduced in cross-sectional area to a value intermediate B and A and upon completion of the plural stage oxidation reducing the cross-sectional area of the silver-cadmium oxide structure to the desired crosssectional area A.

19. 'A method in accordance with claim 18 wherein the plural stage oxidation operation comprises a plurality of separate oxidation operations from two to six in number.

20. A method in accordance with claim 18 wherein said silver-cadmium alloy contains up to about 10% by weight of an additive metal or oxide thereof based on said silver-cadmium alloy.

21. A method in accordance with claim 18 wherein said silver-cadmium alloy structure is a strip or bar.

22. A method in accordance with claim 18 wherein said silver-cadmium alloy structure is wire.

Claims

1. A METHOD FOR THE MANUFACTURE OF SILVER-CADMIUM OXIDE WIRE HAVING THE DIAMETER DF WHICH COMPRISES FORMING FROM SILVER-CADMIUM ALLOY WIRE HAVING THE RESULTING FORMED WIRE TO A FIRST TO ABOUT 3 DF, SUBJECTING THE RESULTING FORMED WIRE TO A FIRST STAGE OXIDATION AT A TEMPERATURE IN THE RANGE FROM ABOUT 1,450* TO ABOUT 1,550*F. IN CONTACT WITH AIR OR OXYGENENRICHED AIR OR OXYGEN FOR A PERIOD OF TIME TO EFFECT OXIDATION OF THE WIRE TO ABOUT 15-30% OF THE MATRIX AREA THEREOF, DRAWING THE RESULTING FIRST STAGE OXIDIZED WIRE TO A DIAMETER IN THE RANGE FROM ABOUT 1.2 TO ABOUT WDF, SUBJECTING THE THUS-DRAWN FIRST STAGE OXIDIZED WIRE TO A SECOND STAGE OXIDATION AT A TEMPERATURE IN THE RANGE 1,450*-1,550*F. IN CONTACT WITH AIR OR OXYGEN-ENRICHED AIR OR OXYGEN FOR A PERIOD OF TIME SUFFICIENT TO EFFECT OXIDATION OF ABOUT 30-50% OF THE MATRIX AREA THEREOF, DRAWING THE WIRE RESULTING FROM THE SECOND STAGE OXIDATION TO A DIAMETER IN THE RANGE 1.1-1.5 DF, SUBJECTING THE THUS-DRAWN SECOND STAGE OXIDIZED WIRE TO A THIRD STAGE OXIDATION AT A TEMPERATURE IN THE RANGE 1,450*-1,550*F. IN CONTACT WITH AIR OR OXYGEN-ENRICHED AIR OR OXYGEN UNTIL 100% OF THE MATRIX AREA OF THE WIRE HAS BEEN OXIDIZED, SUBJECTING THE RESULTING THIRD STAGE OXIDIZED WIRE TO DRAWING TO ABOUT DF.

2. A method in accordance with claim 1 wherein the silver-cadmium alloy wire contains about 5-15% cadmium by weight.

3. A method in accordance with claim 1 wherein the silver-cadmium alloy has the composition of about 91% by weight silver and about 9% by weight cadmium and wherein the oxidized wire resulting from the third stage oxidation has a composition of about 90% by weight silver and about 10% by weight cadmium oxide.

4. A method in accordance with claim 1 wherein the first stage oxidation is carried out for a period of time in the range from about 1 to about 8 hours.

5. A method in accordance with claim 1 wherein said first stage, said second stage and said third stage oxidation operations are carried out for a period of time in the range from about 1-8 hours, 4-16 hours and 24-64 hours, respectively.

6. A method in accordance with claim 1 wherein the wire resulting from the third stage oxidation operation and after drawing to about Df is subjected to annealing at a temperature of about 1,000*F.

8. A method for the manufacture of silver-cadmium oxide wire having the diameter Df which comprises forming silver-cadmium alloy wire having a diameter greater than Df, subjecting the resulting formed wire to plural stage oxidation in contact with air or oxygen-enriched air or oxygen with intermediate drawing of the resulting oxidized wire wherein after each oxidation stage the wire is reduced in diameter until the desired diameter Df is reached, each stage of said plural stage oxidation being carried out at a temperature in the range from about 1,200*F. to a temperature at least about 25*F. below the melting point of said silver-cadmium alloy and for a period of time in the range from about 15 minutes to about 100 hours, the plural stage oxidation being carried out so as to effect substantially complete oxidation of the cadmium present in the cadmium alloy wire to cadmium oxide.

9. A method in accordance with claim 8 wherein the silver-cadmium alloy wire has a diameter in the range 1.5-3 Df.

10. A method in accordance with claim 8 wherein said silver-cadmium alloy contains up to 20% by weight cadmium.

15. A method in accordance with claim 8 wherein the initial stage oxidation of said plural stage oxidation includes an oxidation operation wherein the silver-cadmium alloy wire is subjected to contact with air or oxygen-enriched air or oxygen at a temperature in the range from about 1,450* to about 1,550*F. for a period of time in the range from about 1 to 8 hours.

16. A method in accordance with claim 8 wherein immediately following the last oxidation stage making up the plural stage oxidation the wire is drawn to the desired diameter Df.

17. A method in accordance with claim 8 wherein immediately following the last oxidation stage making up the plural stage oxidation the resulting oxidized wire is drawn to a diameter slightly larger than the desired diameter Df, followed by annealing and pickling the resulting drawn oxidized wire and then drawing the wire to the desired diameter Df.

18. A method for the manufacture of a silver-cadmium oxide structure having an average cross-sectional area A from a silver-cadmium alloy containing up to about 20% by weight cadmium which comprises forming a silver-cadmium alloy structure having an average cross-sectional area B from said silver-cadmium alloy, B being greater than A, subjecting the resulting formed silver-cadmium alloy structure to plural stage oxidation in contact with air or oxygen-enriched air or oxygen to effect upon completion of the last oxidation stage substantially 100% oxidation of the cadmium content of said cadmium alloy structure to cadmium oxide, each stage of said plural stage oxidation being carried out at a temperature in the range from about 1,200* to about 25*F. below the melting point of said silver-cadmium alloy and for a period of time in the range from about 15 minutes to about 100 hours, during said plural stage oxidation there being at least one intermediate size reduction of the oxidized silver-cadmium alloy structure wherein the structure is substantially reduced in cross-sectional area to a value intermediate B and A and upon completion of the plural stage oxidation reducing the cross-sectional area of the silver-cadmium oxide structure to the desired cross-sectional area A.

19. A method in accordance with claim 18 wherein the plural stage oxidation operation comprises a plurality of separate oxidation operations from two to six in number.