US 1934730 A
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Patented Nov. 14, 1%33 hurrah snares earner or ies mrnna'rn tnxrons on error York No Drawing. application July 22, 1930, Serial No. 460,913. Renewed January 31, 11933 3 Claims.
This invention relates to non-tarnishing metallic mixtures and alloys. I
It is an object of the invention to produce an intimate metallic mixture or alloy which is tar- Irish-resisting and has a pleasant color.
An appreciable amount of indium added to silver produces an intimate mixture or alloy which has tarnish-resisting properties due to the indium. The indium, however, imparts a bluish tint or color to the silver and such color is considered objectionable particularly where the alloy is employed as a finish plating.
We have discovered that the addition of a third metal to the alloy produces an improvement in color and an intimate mixture of the elements. When the alloy or-intimate mixture is used as a plating, it can be produced advantageously by plating the elements in superposed layers in elternate fashion and difl'using. While the elements may be plated individually or singly, in the present most advantageous practise, two of the elements are plated simultaneously from a plating bath, then the third metal is plated and finally by diffusing the plated layers there is produced an alloy or intimate mixture of the metals.
While various metals may be associated in the intimate mixture or alloy of the present invention, one advantageous combination is silver, gold and indium. In this alloy, the gold color counteracts the indium color and the alloy color simulates that of silver. This alloy may be produced by plating and, in the present preferred practise, the silver and gold are simultaneously plated from the same bath, the indium then plated thereon and the metals caused to mix intimately or alloy by diffusing.
In the simultaneous gold-silver plating, the anode of the bath is an alloy of gold and'silver and the cathode is the base metal, such as nickel silver or even solid silver, to be plated simultaneously by the gold and silver. While the proportions of the metals in the anode may vary, as an example, the anode may contain i2 gold and El /2% silver. The bath is advantageously a cyanide hath containing 8 ounces or. more of free potassium cyanide salt per gallon, 0.6 to 1.0 ounces of gold in the form. of a cyanide salt per gallon, and approximately 3.0 ounces of silver in the form of cyanide salt. Foe current density during the plating process is about 1/14 ampere per square inch. Under normal room temperatures, the process produces a good commercial plate containing about 12 /2% gold and 87 silver.
The plating of indium on the gold-silver plate and when all the layers have been plated, to
fuse for a suitable length of time, and at a s'ifit able temperature whereby the metals of the layers intimately mix or alloy into a homogeneous single layer.
In carrying out the process in its entirety, the
-base metal, such as nickel silver, is first thorough- 1y cleaned. A thorough cleaning of the base involves successive application of a number of cleaning steps which are Well known. An advantageous cleaning is obtained by subjecting the base metal to the following:
( 1) Hot boiling soap solution.
(2) Hot water rinse.
(3) Hot mineral cleaner.
(4) Cold running water rinse.
(5) Alkali electric, cleaner.
(6) Cold running water rinse.
(7) Dilute hydrochloric acid clip.
(3) Cold running water rinse.
After this treatment, a very thin plate of nickel may be applied in any suitable manner and the base again subjected to a cold running water rinse.
The base is now advantageously subjected to a. silver strike for about 8 seconds in a solution containingabout ounces of silver per gallon in the form of potassium salts and 9 or 10 ounces of free potassium cyanide. This treatment produces a very thin silver layer on the base surface, giving a silver interior surface, and conditions said surface for the application of the heavier gold-silver and indium plates.
The gold-silver plating is now applied to about 25 millionths of an inch (0.000025) and the article then rinsed in cold water. It is then subjected to treatment in the indium bath to obtain an indium. layer of about 20 millionths of an inch (0.000020). At this point, a. very thin layer of silver and indiurn may advantageously be applied and, in one practical method, the result is accomplished by a strike in a bath containing ounces of silver per gallon in the form of cyanide salts, about 1 110 C. for about 8 hours.
.not necessarily desired.
ounce of indium per gallon in the form of cyanide salts, about ounce of dextrose and about 10 ounces of free potassium cyanide per gallon. The current density is about ampere per square inch for a short time.
The article is now subjected. to another goldsilver plating to about 0.000025 inches and, following this; may be subjected to successive platlngs of indium and gold-silver with the intermediate silver indium strikes and rinses until the desired thickness of plate has been built up. The application of successive steps for about ten (10) times has been found to give satisfactory results.
After the successive platings as above outlined, the produce is subjected to a diffusing process to cause the metals to alloy or mix intimately. The diffusion of the indium occurs at or about its melting point. The diffusing process is most advantageously carried out in two steps, the first step being a seasoning or readjustment to start the diiiusion between the layers and the second step the complete diffusion of the layers together. In one practical species of the process, the first step is carried on with a preliminary heating at The second is performed in an oven at 165 C. for about 18 hours. In this way, a very satisfactory homogeneous plate is produced.
With the compositions and thicknesses discussed, the final coating contains about 36% indium, 8/z% gold and silver. These ratios may be varied as desired by changes in the original compositions and thicknesses.
This surface alloy is non-tarnishing and has a color simulating pure silver. It may be applied to base metals of various kinds and may be applied to silver itself, for example, to impart preservative surface coatings to precious silver articles.
In lieu of plating the silver and gold simultaneously and the indium separately, the silver and indium may be plated simultaneously, for example, by a bath such as described or otherwise, and the gold plated separately, the layers being built up alternately and the metals then intimately mixed or alloyed by diffusion.
Metals other than gold might be employed to modify the objectionable indium color and to give a more pleasing color where real silver color is By way of example, an alloy may be of silver, palladium and indium and produced by plating the silver and palladium simultaneously and the indium separately in alternate superposed layers and then diffusing.
A suitable palladium-silver plating bath is as follows:---
Ounces per gallon Palladium (in cyanide) 0. 8 Potassium cyanide (free) 5. 0 Potassium carbonate 5. 0 Potassium nitrate 1. 0 Silver 1. 0
The plating occurs with very little agitation at a current density of about 0.1 ampere per square inch. It is likely that, by having a much larger.
taneously and the indium separately in alternate layers and then diiiusing.
A suitable cadmium-silver plating bath is as follows:-
Ounces per gallon Cadmium 0.8 Silver 2.4 Potassium cyanide 2. 4
silver, copper and indium and may be produced by plating the silver and copper simultaneously and the indium separately in alternate layers and then difiusing.
To obtain a suitable copper-silver bath, 250 grams of copper cyanide are mixed with 300 grams of potassium cyanide and 500 cubic centimeters of water added and the mixture stirred until the maximum amount of copper cyanide is dissolved. The solution is filtered and made up to two liters. The solution is a clear, light amber colored liquid, from which, when cold, a small quantity of white crystalline material is precipitated. This precipitate is the double cyanide oi copper and potassium and dissolves when the solut'on is warmed. To this solution, silver is added in the form of silver potasium cyanide with a slight excess of potassium cyanide. The added solution is prepared by mixing 50 grams of silver cyanide and 50 grams of potassium cyanide and adding enough water to give 375 cubic centimeters solution. The above ingredients can probably be varied within wide limits, but the example given has been found to give good deposits.
It 'will be noted that silver, gold and copper are in the same group and sub-group of the periodic system, viz: group 1 sub-group, or family, B, so that gold and copper may be designated generically as metals other than silver of the same group and sub-group as silver.
What is claimed is:
l. A non-tarnishing intimate mixture or alloy having a color simulating silver comprising indium, gold and silver substantially in the ratio of about 36% indium, ii gold and 55 silver.
2. A non-tarnishing mixture or alloy consisting of silver, indium and a color-modifying metal selected from the group consisting of gold, palladium, cadmium, and copper, the silver constituting more than 50% by weight of the total alloy, the indium and the color-modifying metal constituting substantially the entire remainder,