US1970318A - Silver alloy - Google Patents

Description

Patented Aug. 14, 1934 UNITED STATES PATENT? OFFICE SILVER ALLOY Edward F. Kern, New York, N. Y., assignor to- The American Metal Company, Limited, New York, N. Y., a corporation of New York No Drawing. Application May 8, 1931, Serial No. 536,087

5 Claims.

This invention relates to the production of tarnish-resisting silver alloys of a fineness equivalent to sterling 925 and standard quality 900 fine, as well as the composition of other'silver alloys possessing tarnish-resisting properties.

It is well-known that silver alloys and articles made of silver when exposed to the atmosphere or when in contact with substances containing sulfur assume a. darkened color known as tarnish. The object of this invention is to provide silver alloys of fineness of sterling quality and otherwise which possess tarnish-resisting properties and also which may be readily made into articles which possess sufficient hardness to withstand the usual wear and tear.

The invention comprises the novel compositions and component mixtures comprised insuch compositions, specific embodiments of which are described hereinafter by way of example only and in accordance with what I now consider the preferred manner of practicing the invention.

' The invention comprises a tarnish-resisting silver alloy containing silver and tin and at least one other metal selected from a group consisting of cadmium, zinc, antimony, nickel-chromiiun alloy, copper, manganese, lithium, calcium and silicon. It includes alloys containing the tollowing proportions:-about 85-93% silver and small amounts of lithium, calcium or silicon or mixtures thereof and the balance tin. It also includes a melt mixture containing about 85-93% silver, plus about 1 to 4% of cadmium, copper, zinc, antimony, manganese and nickel-chromium alloy and the balance tin. It also includes a melt mixture containing about 85-93% about 1 to 4% of cadmium, copper,'zinc, antlmony, and small amounts of lithium, calcium or silicon or mixtures thereof, and the balance tin. The amount'of lithium, calciurnor silicon used s preferably such that up to about 0.7% of one or more of these metals is found in the resulting finished alloy. The proportions of lithium, silicon and calcium or mixtures thereof mentioned may exceed 0.7% if desirechbut in that case the resulting alloy is apt to be brittle although it still possesses the desired tarnish-resisting properties. A certain amount of these metalslithium, calcium, siliconls apt to be lost in melting depending on the technique employed in their addition and it is therefore well to add a somewhat larger amount thereof to the mixed melt than expected in the resulting alloy as stated, this additional'amount will depend on the technique employed and can be readily determined for a given case by making one or more melts and silver plus.

observing the resulting amount of such metal obtained in the finished melt. The percentage of copper employed in making any of the above alloys should preferably not exceed about 3.6%. In preparing the above alloys it is important that on they be substantially homogeneous throughout. The proportions just given produce homogeneous solid alloys. Heterogeneous combinations do not possess the desired properties and I there= fore have selected the homogeneous composit o5, tions given. As regards the specific efiect of the metals present in the silver alloys, the properties were determined by testing a series of the alloys. Tin forms solid solution alloys with silver up to 15% tin and silver. Tin increases the hard- 70 nesd'and lowers the melting point of the resulting alloy. Other elements as specified above impart tarnish-resisting properties to the silvertin alloy, and also increase the hardness of the resulting alloy. Q 35 The results of the tests demonstrated that the silver-tin alloys are more tarnish-resisting than the silver-zinc and the silver-antimony alloys. The inclusion of small amounts of lithium, calcium, silicon, cadmium, zinc, antimony, manganese, copper, or nickel-chromium alloy in silvertin alloys increases their tarnish-resisting properties. .Lithium, silicon and calcium added to alloys of silver-tin with small amounts. of cad= mium, zinc, antimony and copper further increase the tarnlsh-resisting properties.

Cadmium, zinc, antimony, copper, manganese and nickel-chromium alloy added to silver-tin alloys control the workability oi the resulting alloys.

The compositions made up embodying the metals indicated above were tested to determine their tarnish-resisting properties as follows:A small'cast block of the composition to be tested was highly polished and covered by a water solution of ammonium sulfide containing an excess of free sulfur. This solution of ammonium sulfide and sulfur was selected from a number of tarnish-producing materials, as the most active of the various agents tested. The most satmo isfactory solution of ammonium sulfide and free sulfur consisted of an N/lO- ammonium sulfide plus N/lOO excess free sulfur. The expressions N/ 10 and vN/lml are intended to designate respectively 10th normal and th normal solutions. In accordance with the standard practive a normal solution is one containing an equivalent weight in grams of the substance dissolved in one liter of water or other solvent. The specimen was kept in contact with this solution for nish was then observed on the specimen. When identical specimens were exposed to the atmosphere for several months, the tarnish-resisting effects observed correspondedt to those obtained in the much shorter interval required by the which are less or greater than sterling silver.

I give below a series of alloys prepared in accordance with my invention, together with the results of the above tarnish test and the Brinnell hardness test made on the alloy as cast.

, I aplo Composition of mixtures melted-parts by weight 1 cadmium 0.5 lithium cadmium, l lithium- .8 cadmium, 0.7 lithium 1.5 cadmium, 0.75 calcium- .75 cadmium, 0.75 calcium .5 cadmium, l s1licon .7 cadmium, 1 silicon. cadmium, 1.5 silicon .5 antimony. .6 antimony antimony, 0.5 lithium.-- .5 antimony, 0.5 calcium--- .25 antimony, 0.75 calcium 3 antimony, 0.5 calcium .6 antimony, 1 silicon copper pper .5 copper, 0.5 lith|um 2.8 copper, 0.7 lithium.-- .5 copper, 0.5 calcium Pro analsilver, 6.

90 silver, 6.

seesssssssssssssssssssssssssssscswsaawss As is well understood in melting volatile metals such as-cadmium and zinc there may be some oxidation and loss thereof. In making alloys therefrom such loss should be compensated in the melt mixture if recovery of the proportions of those metals therein stated is to be made.

The alloys prepared as indicated in the above examples all showed by appropriate tests that they were substantially homogeneous alloys, be-

ing substantially free from heterogeneous struc- Each of the alloys of the above examples,

ture.

when subjected to the ammonium sulfide and sulfur tests indicated above, had a tarnish-resisting property capable of resisting such treatment substantially without appearance of tarnish. Sterling silver and standard silver and various other silver alloys when subjected to this test. showed appreciable tarnish.

. rapidly oxidize.

-The silver em- 1,970,318 five minutes, then washed and dried. The tarployed in the above melts was a fine commercial electrolytic silver as crystals of a high grade of purity and the other metals were also commercial products of high purity.

The following process is carried out in forming the alloys of the metal or metals with silver and tin:-

The alloys are prepared by melting the weighed amounts of electrolytic silver and the other constituents under a flux of for example borax, or glass, and charcoal. The molten mixtures are thoroughly mixed, then cast in the usual manner. When either lithium, calcium, or silicon is made a constituent of the alloy, these metals may be added either as previously prepared alloys, or the silver alloy of lithium, calcium, or silicon may first be prepared, and then thevother constituents added. It is found that lithium, calcium, and silicon can be easily incorporated with silver by placing a layer of the electrolytic silver crystals in the crucible, placing the lithium, calcium or the silicon on the layer of silver and covering with the remaining electrolytic silver. The temperature of the crucible is raised in the case of the lithium and calcium to the melting point of the silver, bringing about the alloying of the lithium and the calcium with the silver. If these metals were added to the molten silver or to the molten silver alloys, large losses thereof would occur as oxidation occurs so readily. Due also to their low specific gravities as compared to silver, they float on the surface of the molten silver and Complete alloying of the required amounts of either lithium or calcium with the silver results according to the above process before the silver is completely melted. In the case of silicon, the combination, results when the silver is entirely melted.

The preparation of the 'alloys of tin with lith-'- ium or calcium can be performed electrolytically,

thus producing a cheaper product than is possible by using the metal lithium or calcium. The preparation oi the alloy of tin with lithium or calcium is accomplished by electrolyzing a molten batch of the halogen salts of these latter metals using a carbon anode and molten tin as the cathode, which readily dissolves the lithium and calcium as rapidly asthey are electrolytically liberated.

It will be observed herein described contain silver and tin, with silthat the various alloys To this combination of silver and 'tin is added one or more metals which alter the tarnish resistance of the silver-tin combination and change as well the workability of the resulting alloy.

The other metals just referred to and which have ver rangingupwards from approximately 85%.

been previously set forth herein are:lithium,

calcium, silicon, cadmium, copper, zinc, antimony and nickel-chromium.

While I have described'my improvements in great detail and with respect to certain preferred embodiments thereof, I do not desire to be limited to such details or embodiments since many changes and modifications may be made and the invention embodied in widely different forms without departing from the spirit and scope thereof in its broader aspects. Hence I desire to cover all equivalents and all modifications and forms coming within the language or scope of any oneor more of the appended claims.

What I claim as new and desire to secure, by

Letters Patent, is:

.1. A homogeneous tarnish-resisting silver-tin holding in solid solution as the remainder of thesalloycne or more workability-control metals, cadmium, zinc, antimony, nickel-chromium alloy, copper, manganese, lithium, calcium, selected in such amounts as will insure to the resulting alloy a Brinnell hardness of not less than 36, the aggregate amount of lithium and calcium not exceeding 1.0 per cent.

2. A tarnish-resisting silver alloy consisting of the following parts by weight silver about 85-93 per cent, tin about 3-14 per cent, less than about 1 per cent of a metal selected from the group lithium and calcium, and the remainder consisting of antimony and copper in appreciable amounts.

3. A tarnish-resisting silver alloy containing silver about 85-93 per cent by weight, an ,appreeiable amount but less than 1 percent of lithium and 1-4 percent of a metal selected from the groupcadmium, zinc, antimony, nickelchromium alloy, manganese and tin constituting the remainder. r

4. A tarnish-resisting silver alloy consisting of the following parts by weight, silver about 90-91 per cent, tin about 6-8.5 perv cent, an appreciable amount but less than 1 per cent of calcium and the remainder consisting of antimony.

5. A tarnish-resisting silver alloy containing about 85-93 per cent of silver by weight, a metal selected from the group lithium, calcium in the proportion by weightof an appreciable amount but less than 1 per cent, and tin constituting substantially the remainder of the alloy.

:ED'WARD F. KERN. I

CERTIFICATE 0t contention.

Patent No. i, 970, 31 8;

' August 14, 1934.

EDWARD r. KERN.

it is hereby certified that error apnears in the printed specification of the above numbered patent requiring correction as follows:

Page 1, lines 106-107,-

tor the misspelled word ".practive" read practice; page 2, line '121, for "batch" read bath; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 18th day .0: September, A. D. 1934.

(Seal) Leslie Frazer Acting Commissioner of "Patents,

holding in solid solution as the remainder of thesalloycne or more workability-control metals, cadmium, zinc, antimony, nickel-chromium alloy, copper, manganese, lithium, calcium, selected in such amounts as will insure to the resulting alloy a Brinnell hardness of not less than 36, the aggregate amount of lithium and calcium not exceeding 1.0 per cent.

2. A tarnish-resisting silver alloy consisting of the following parts by weight silver about 85-93 per cent, tin about 3-14 per cent, less than about 1 per cent of a metal selected from the group lithium and calcium, and the remainder consisting of antimony and copper in appreciable amounts.

3. A tarnish-resisting silver alloy containing silver about 85-93 per cent by weight, an ,appreeiable amount but less than 1 percent of lithium and 1-4 percent of a metal selected from the groupcadmium, zinc, antimony, nickelchromium alloy, manganese and tin constituting the remainder. r

4. A tarnish-resisting silver alloy consisting of the following parts by weight, silver about 90-91 per cent, tin about 6-8.5 perv cent, an appreciable amount but less than 1 per cent of calcium and the remainder consisting of antimony.

5. A tarnish-resisting silver alloy containing about 85-93 per cent of silver by weight, a metal selected from the group lithium, calcium in the proportion by weightof an appreciable amount but less than 1 per cent, and tin constituting substantially the remainder of the alloy.

:ED'WARD F. KERN. I

CERTIFICATE 0t contention.

Patent No. i, 970, 31 8;

' August 14, 1934.

EDWARD r. KERN.

it is hereby certified that error apnears in the printed specification of the above numbered patent requiring correction as follows:

Page 1, lines 106-107,-

tor the misspelled word ".practive" read practice; page 2, line '121, for "batch" read bath; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 18th day .0: September, A. D. 1934.

(Seal) Leslie Frazer Acting Commissioner of "Patents,