Патент USA US2406189код для вставки
Patented Aug. 20,1946 . 2,406,189 um'rso s'm'rss PATENT I OFFICE 2,408,180 _ 'Mn'rnon Foa m mmo Nowell r. Blackburn, Niagara Falls, N. Y., assign or to E. I. du Pont de Nemours & Company, I Wilmington, Del., a corporation of Delaware No Drawing. Application May 20, 1943, Serial No. 487,813 7 Claims. (0]. 204-54) 2 This invention relates to the electroplating of metals and particularly to the electrodeposition of tin from alkali metal stannate electroplating baths. with high electrode e?iciencies. . In present commercial practice for the elec troplating of tin, alkaline plating baths con- _ taining sodium stannataor potassium stannate are commonly used. Although sodium stannate electroplating baths may be operated- satisfac torily at comparatively low current densities, . anodes may be operated at high current densities , The novel alloy anodes of'my invention may be prepared by mixing molten tin with a molten alkali metal and molding the mixture in the desired form. For example, pure tin is heated in an iron or silica crucible to approximately 270° C. The required weightof alkali metal is then added to the molten tin. It may be desirable to utilize about 0.1 to 0.2% excess alkali metal to compensate for possible loss through oxidation such baths have the disadvantage that when it 1.0 is desired to operate at high current densities in during the mixing and molding operation. .The order to obtain high plating speed the anode alkali metal is introduced under the surface of e?lciency becomes so low as to make such baths the molten tin, for example, by introducing the unsatisfactory for commercial operation. Al 15 alkali metal under an inverted crucible held in though sodium stannate electroplating baths position under the surface of the molten tin. have been successfully used at current densities The mixture is agitated until all lumps have up to about 50 A/SF, no method has been avail disappeared, the surface skimmed to remove oxi able hitherto by which these electroplating baths dation products, and the melt poured into a mold could be satisfactorily operated at current den 20 and allowed to cool. sities substantially above 50 A/SF. In the case In general, the methods vcommonly used for of potassium stannate electroplating baths the ' the preparation of alkali metal alloys may be di?lculty encountered in obtaining satisfactory utilized in the preparation of my novel anodes. anode efficiencies exists at even lower current Preferably the molten mixture is protected by densities and lack of a method for operating 25 an atmosphere of inert gas such as nitrogen in _ such baths at high current densities has serious ly hampered the commercial development of the potassium stannate bath. Heretofore no method has been available which would permit operation of stannate electroplating baths at high current densities with satisfactory anode efficiency, and it has therefore been impossible to fully utilize their potential capacity. . It is one of the objects of this invention to provide a new and improved method for alkaline tin plating. Another object is to provide an electroplating bath for the electrodepositlon of tin which will operate e?lciently at high current order to avoid oxidation. The molten tin should be heated to a temperature somewhat above the melting point of the alloy to be formed. ‘ The concentration of alkali metal present in so the novel anodes of my invention may be varied over a considerable range with satisfactory re sults. Usually only relatively small amounts of alkali metal are required, 1. e. 0.1 to 10% by weight. I have found that amounts of sodium up to 10% or of potassium up to 5% of the weight of the alloy are sufficient for practical operation. When concentrations of alkali metal greater than 10% by weight are utilized the solubility of the anode in the plating solution tends to become densities. A further object is to provide a novel anode for alkali metal stannate electroplating 40 too high for satisfactory operation. Further baths. These and other objects will be apparent ' more‘, substantially higher concentrations of from the ensuing description of my invention. alkali metal may decrease ' the mechanical The above objects are attained in accordance strength of the anode below practical limits. with my invention by electroplating tin from an The particular concentration of alkali metal to alkali metal stannate plating bath having an 45 be used in any given plating bath will depend anode or anodes comprising an alloy of tin and upon the current density at which it is desired one or more alkali metals. I have discovered to operate. At low current densities concentra that when a tin anode containing a relatively tions of alkali metal as low as 0.1% may be suf small amount of alkali metal is utilized in the flcient to effect the required anode efficiency. stannate plating bath, a surprising and unex 50 When it is desired to operate at high current pected increase in anode efficiency is obtained densities, for example, current densities of 100 to and 'stannate plating baths utilizing these novel 150 A/SF, concentrations of alkali metal as high 3 4 . . as 5% sodium or 4% potassium may be required to obtain‘; the high anode eillciency necessary for satisfactory operation. new a 1.2% potassium-tin alloy anode vs. tin anode m For example, I have a sodium stannate plating bath found that when a stannate plating bath con taining 120 g./l. of sodium stannate and 15 g./l. of sodium hydroxide is operated at 90° C. and Percent emcienoy Current dentisy in AIBF at a current density of 100 A/SF, an anode e?l 1 . 27 potas eiu?i alloy anode ciency of 99% is obtained when the concentra tion of sodium in the anode is 4.6%. Similarly, in the operation of a stannate plating bath con-' P3235“ 95 M 89 .......... -. 67 . . . . . . . . .. M . . . . . . . _ . - taining 135 g./l. of potassium stannate and 21 g./1. or potassium hydroxide at 90° C. and 125 A/SF, an anode e?iciency of 90% is obtained when the concentration of potassium in the tin ‘TABLE 4 anode is 3.8%; and when the same bath is oper 15 ated at 150 A/SF using the same anode an anode 0.75% sodium-tin alloy anode vs; tin anode, in a potassium stannate plating bath e?lciency of 80% is obtained. The following tables illustrate the high anode Percent e?loiency e?iciencies obtained by the use or my novel anode. In obtaining these data sodium stannate baths 20 Current density in A/SF contained ‘120 g./l. of sodium stannate and 15 . g./l. of sodium hydroxide were used and the po tassium stannate baths contained 135 g./l. of sggi?gii pm ‘In alloy anode ‘mods potassium stannate and 21 g./1. of potassium hy droxide. These materials were dissolved in dis tilled water and the plating baths were main tained at 90° C. i ' ' 97 80 _ i B8 82 64 4o .. 70 E 53 I0 100 .................................... .. . In the tables and throughout the speci?ca tion the term "anode e?lciency" refers to the Anode e?iciencies were determined in a con 80 ventional manner. The plating solution was anode e?lciency based on tetravalent tin. Table 1 represents a comparison of the anode placed in series with a silver coulometer for. yeillciencies obtained with a pure tin anode and measuring the current used. An accurate am with sodium-tin alloy anodes over a current meter was connected in series and a volt meter density range of 35 to 150 A/SF in a sodium was connected across the bus bars of the plating ' 35 stannate plating bath. Table 2 represents a sim bath. The temperature 01’ the plating bath was ilar comparison of potassium-tin anodes with pure maintained constant throughout the operation. tin anodes in a potassium stannate plating bath. The anodes used were cylindrical and had a diam Table 3 illustrates a comparison of the results eter 01' 1/2", a length of 31A" and an area of ap obtained in using a potassium-tin anode and a proximately 5% square inches. The anodes were 40 pure tin anode in a sodium stannate plating bath. placed in the bath between two cathodes having Table 4 shows a comparison of a sodium-tin anode a total area equal tothat of the anode. The with a pure tin anode in a potassium stannate anodes were polarized before drying and weigh plating bath. ing and the coulometer cathode was air dried TABLE 1 and weighed. The baths were operated suili clently long to deposit from 2 to 3 grams oi Axons EmcIENcY Comrmusorz silver on the coulometer in each e?lciency run. Several runs were made and average values taken. Sodium-tin alloy anode vs. tin anode in sodium Anodes were kept in a polarized condition at all stannate plating bath times by increasing the current density until gasing was observed. Current density in A/BF Anode efficiencies were calculated by means of the following formula: Percent sodium 50 75 100 Ef? ciency = 6% Percent e?lcicncy where A=anode loss and C=coulometer gain. ‘0.275=-1S§g electroequivalent ratio As illustrated in the foregoing tables, the 80 novel alloy anodes of my ‘invention are espe TABLE 2 Potassium-tin alloy anode vs. tin anode in potassium stannate plating bath ' Current density in A/SF Percent potassium manode 2s 60 75 100 ' ‘125 15ercent e?lciency 150 200 , cially effective in electroplating baths operated at high current densities. However, these anodes are also effective in increasing efficiency when baths are operated at lower current densities in 65 which case concentrations of alkali metal as low as 0.1% may be su?lcient to obtain balanced elec trode efficiencies. Sodium-tin anodes may be utilized in either sodium stannate or potassium stannate baths and likewise the potassium-tin 70 anodes may be used in either electroplating bath. Generally, I prefer toutilize sodium-tin anodes since sodium is relatively inexpensive and is read- ~ ily obtainable. Although I have described my invention with particular reference to electroplating baths con 5 6 taining sodium stannate or potassium stannate ' sium stannate and potassium hydroxide with an alloy anode comprising essentially tin and at least one alkali metal, the total alkali metal content utilizing alloy anodes comprising tin alloyed with sodium or potassium or both, it is to be under stood that other alkali metals may be utilized in the novel anode of my invention, for example, of said‘ anode being 0.1 to 10% by weight. 3. A process for electroplating tin which com~ prises electrolyzingan aqueous solution of sodium stannate and sodium hydroxide with an alloy out other alkali metals. Likewise, alkali metal anode comprising essentially tin and at least one - stannate baths other than sodium and potassium alkali metal, the total-alkali metal content of said may be utilized in practicing my invention. 10 anode being 0.1 to 10% by weight. A major advantage in the anodes of my inven 4. A process for electroplating tin which com tion is the increased ef?ciency obtained, particu prises electrolyzing an aqueous solution of an larly high anode e?iciencies at high current alkali metal stannate and an alkali metal hydrox densities. A further advantage is that my in ide with an alloy anode comprising essentially tin vention makes possible balanced electrode em 15 and 0.1 to 5% by weight of potassium. ciencies over a wide current density range. Thus, 5., A process for electroplating tin which com for example, whenever the anode e?iciency is prises electrolyzing an aqueous solution of an al somewhat. low, the use of alkali metal alloy' kali metal stannate and an alkali metal hydrox anodes makes it possible to obtain increased ide with an alloy anode comprising essentially tin. anode ei?ciency without adversely effecting cath and 0.1 to 10% by weight of sodium. ode e?iciency. These and other advantages will 20 6. A process for electroplating tin which com be readily apparent to those skilled in the art. prises electrolyzing an aqueous solution of potas I claim: ' sium stannate and potassium hydroxide with an 1. A process for electroplating tin which com- I alloy anode comprising essentially tin and 0.1 to prises electrolyzing an aqueous solution of an al 5% by weight of potassium. '> 25 kali metal stannate and an alkali metal hydrox 7. A process for electroplating tin which com ide with an alloy anode comprising essentially tin prises electrolyzing an aqueous solution of po lithium or caesium, and these metals may be al loyed with an anode containing tin with or with tassium stannate and potassium hydroxide with and at least one alkali metal, the total alkali r an alloy anode comprising essentially tin and 0.1 metal content of said anode being 0.1 to 10% by ' weight. 30 to 10% by weight of sodium. 2. A process for electroplating tin which com prises electrolyzing an aqueous solution of potas " ’ NEWELL F. BLACKBURN.