DESC:FIELD OF THE INVENTION:

This invention relates to the field of chemical engineering,

Particularly, this invention relates to an anti-tarnish silver metallic alloy

BACKGROUND:

Silver has been a used in object making since long. Silver jewelry and decorative objects can be made from pure Silver or Silver alloys. Articles made from pure Silver are subject to tarnishment when exposed to atmosphere. Tarnishment of Silver metal surface, i.e. blackening or undesirable discoloration occurs due to reaction of Silver articles with atmospheric contents that induce chemical reaction with Silver. Surface corrosion happens due to tarnishment. Corrosion of Silver surface generally occurs due to oxide-reductive reactions of chemical components with the Silver metal. Corrosive layer changes the reflective and optical properties of the Silver objects. Aesthetic appearance of Silver objects is affected due to presence of a blackened or dark colored corrosive layer.

Silver articles get corroded when exposed to chemicals in air in routine use. Jewelry made of Silver, when worn on body, chemically reacts with sweat and chemicals in air. In particular, Silver reacts with Sulfur (or its compounds), Oxygen and Chlorine, which can be present in atmosphere, air and water pollutants or body fluids like sweat. Silver’s reaction with Sulfur or its compounds and other last mentioned chemicals, results into tarnishment of Silver surface. Tarnishment of Silver results in reducing aesthetic look and affects properties of Silver objects, e.g., jewelry.

Silver reacts with Sulfur compounds, for example, hydrogen sulfide. Hydrogen sulfide is a weak acid and is found in some forms in the atmosphere. Silver reacting with Sulfur or its compounds generally produces Silver Sulphide that appears as tarnished or discolored surface exterior. Common residential and industrial environments have various forms of Sulphur in their environments. Reactions of Silver with Sulphur or its compounds results in a yellowish-brownish tinge or other discolorations on the tarnished surface. Several environmental factors like temperature and moisture work to alter the reactions leading to tarnished Silver surface. Similar chemical reactions in case of other reactants with Silver lead to tarnished exterior surface.

Alloys created by mixing Silver with other metals are a method of attacking tarnishment of Silver surfaces. Metal alloys can be formed by combining Silver with many different metals. Each combination of metals lends certain properties to the alloy. Multiple factors can vary across alloys of Silver, for example, malleability, ductility, hardness, melting point and color. A common alloy of Silver called “Sterling Silver” contains about 92.5 per cent Silver by weight and about 7.5 per cent of other metals like Copper. Alloying Silver with other metals can lead to tarnishment as other metals readily react with oxygen to form oxides which can also visually appear as tarnishment of various colorations. Alloy of Silver with other metals may reduce its utility for jewelry or similar applications where preciousness of the principal metal elements in the alloy is a relevant consideration.

BRIEF DESCRIPTION OF DRAWINGS

FIGURE 1: Figure 1 is a photograph of a Silver-Copper alloy showing dark coloration on surface after exposure to environment for an exemplary period of 20 (twenty) days;

FIGURE 2: Figure 2 is an alloy in an embodiment of the invention side-by-side with a reference Ag-Cu alloy block with 999 purity Silver in it; and

FIGURE 3: Figure 3 is a photographic representation comparing the test results of two samples.

DETAILED DESCRIPTION

The alloy’s metallic combination in an embodiment of the invention includes primarily Silver combined with other metals (hereafter “Alloy”). Silver alloy objects can be made from this Alloy. Alloy itself can be made in a furnace to fuse combination metal elements in a homogenous mixture. In particular, this Alloy is suitable for making objects, e.g., jewelry articles. Silver is combined in this Alloy with other metals to achieve properties desirable for making objects, e.g., jewelry, where properties of said Alloy include but are not limited to hardness, optical brilliance, shine, brightness and tarnish resistance. Tarnish resistance property of the alloy in an embodiment of this invention makes it a useful alloy in jewelry making application.

Further, the Alloy should be easy to form in to various shapes, good luster/shine/brightness and have longevity over a period of use with no fading or have an ugly looking tarnished outer surface that is blackish in color (See FIG.1) . While outer surface changes in Alloy in an embodiment exhibits a warm yellow-Golden color (See FIG.2) over a test period with exposure to environmental pollutants and chemicals in the air.

The Thioacetamide corrosion test (TAA test), which is a standard test to determine the tarnishing effect on silver alloys, was conducted. Two samples comprising of 925 sterling silver plates were taken. The first uncoated sterling silver sample was considered as a reference, and designated as “Ag”. The second silver plate was coated with a formulation according to an embodiment of the invention (“T-PRO”) and was designated as “Ag + T-PRO”. Both the samples were exposed to a sulphuric environment for a period of eight hours. As seen in FIG.3, the tarnishing effect on samples of silver alloys after carrying out the TAA test for 8 (Eight) hours makes it quite clear that Ag + T-PRO exhibited superior anti-tarnishing performance.

Alloy in an embodiment of the invention is made with preferably Silver of about 99.9 per cent purity. Other metals that can be included in the Alloy combination are: Gold, Platinum, Palladium, Copper, Zinc, Tin and Silicon, either one or more of them or all of them may be included in the Alloy’s metallic combination. Each of the metals like Gold, Platinum, Palladium, Copper, Zinc, Tin and Silicon added to the Alloy is in varied proportions enlisted in the examples below. Other metals can also be added to the Alloy. In an embodiment, Silver is present in the Alloy where pure Silver is at least 90 per cent of weight in the Alloy. Preferably, Silver used in the Alloy is of highest possible purity, i.e., 99.9 per cent. In an embodiment, the quantity of Silver in the Alloy combination is about 92.5 per cent up to 99 per cent in the Alloy’s metallic combination.

Apart from the base metal in the alloy of Silver, the Alloy contains other combination elements that achieve a tarnish resistant-characteristic to the Alloy. One or more of the alloy metal combined with Silver give an anti-corrosive character to the Alloy.

Metallic combination of Silver of Alloy with metals can have varied proportions. E.g., one or more, including all, of these metals can be combined as in an Alloy in the next described ranges by weight. In an embodiment, Silver as noted can have a range of 92.5% to 99.5% per cent by weight in the Alloy’s metal combination. Platinum content in the Alloy can range from 0.14% to 4% by weight. Palladium can be present in the Alloy in the range from 0.05% to 1% by weight. Gold can be present in the Alloy in the range from 0.05% to 5% by weight. Other metals can be combined in the Alloy with Copper being present in the range of 1% to 5% by weight. Metal Zinc range can be from 0.5% to 3% by weight in the Alloy. Tin metal can be present in Alloy in the range of 0.05% to 0.5% by weight, and Silicon can be present in the Alloy in the range of 0.01% to 0.5% by weight.

While one or more of different metals out of Gold, Platinum and Palladium along with Copper, Zinc, Tin and Silicon or all of them can be included in the Alloy in embodiments. Some other metals can also be combined in the Alloy to achieve specific properties of the Alloy. In an embodiment, the following proportions of the metals Silver, Zinc, Copper and Palladium in the enlisted proportions in the table below can be combined to achieve tarnish-resistance properties in the Alloy. The Alloy combinations in examples and tables below exhibit tarnish-resistance properties. In the Alloy
combination in examples below, Silver and other metals form a homogenous mixture when heated. All metal melting temperatures are considered and then a temperature is set where all the metals can melt and become a homogeneous alloy.

The oxides of Zinc and Silicon help to increase tarnish resistance with less amount of Palladium required in the Alloy. Gold and Platinum are added to improve solid solution strengthening. Thus, the addition of metal combination of alloys described in other paragraphs help to improve strength without much loss in ductility and strengthening of tarnish resistance because the oxides of these alloying elements retard Copper and Sulphur that react to tarnish surface appearance. Generally, the alloys are cast at around 1200 Degree Celcius so that the molten material reaches intricate parts of mold. Casting process is monitored to prevent excess oxidation of the alloy.

Many objects and article of decorative, functional, storage, jewelry, etc., can be made from the Alloy. Exemplary articles made from said Alloy can be jewelry, utensil, object, rod, chain, wire, sheet and sculpture, while other kinds of articles can also be readily made from the Alloy. Jewelry of various kinds can be from said Alloy, for example, a bracelet, a ring, bangle, chain, ear-rings, nose-ring, arm band and a pendent.

Methods of making the Alloy can be multiple. Exemplary method includes the steps of pre-forming said Alloy into a pre-formed piece, melting said piece to form a melted said Alloy, casting said melt into a mold to form a cast article, cooling said cast article and then removing said article from said mold.

Different alloy combinations in various embodiments that were derived from multiple experiments are described in the examples below:

Example 1
Metal Proportion Range
Per cent by Weight
Silver (Ag) 92.5 to 99
Gold (Au) 0.01 to 5.0
Platinum (Pt) 2.0 Max
Palladium(Pd) 0.01 to 2.0
Copper (Cu) 0.1 to 7.15
Zinc (Zn) 0.001 to 2.0
Tin (Sn) 0.01 to 7.0
Silicon (Si) 0.2 Max
Table 1

Proportions in terms of percentage by weight of metals can be as shown in the Table 1 above in Example 1 in an embodiment. The ranges of various metals given in the Alloy are in percentage of weights: Silver 92.5 to 99, Gold 0.01 to 5.0 in an embodiment, Platinum 2.0 Max, (i.e., maximum) in an embodiment, Palladium 0.01 to 2.0 in an embodiment, Zinc 0.001 to 2.0 in an embodiment, Copper 0.1 to 7.15 in an embodiment, Tin 0.01 to 7.0 and Silicon 0.2 Maximum in an embodiment. The ranges of metal percentage by weight in the Alloy combination are given as indicative and other metal combinations and ranges are possible in other embodiments of the invention.

In the Example 1 / Table 1, in an embodiment, the presence of Zinc in combination imparts the Alloy combination in an embodiment, property of uniform mixing, while Copper provides properties of hardness and Palldium enables properties of hardness & resistance to tarnish. Metal Platinum in pits pure form (purity level 99.99 per cent by weight) provides the Alloy combination properties of brightness. Metal Tin in the Alloy provides flexibility properties. The presence of Gold metal in the Alloy combination leads to bonding properties in the Alloy. Properties of other metals in the Alloy are as described in other paragraphs of this Application.

Example 2
Metal Proportion Range - Per cent by Weight
Silver (Ag) 93.4
Gold (Au) 0.06
Platinum (Pt) 0.03
Palladium(Pd) 0.02
Copper (Cu) 6.42
Tin (Sn) 0.03
Silicon (Si) 0.04
Table 2

Methods used for making the Example 2 / Table 2,in an embodiment, Alloy combination is similar to that for Example 2 / Table 2 in terms of the steps of the method. Properties of metals in the Alloy are as described in other paragraphs of this application. Silver is in the proportion of 93.4% by weight in the Alloy in an embodiment. Gold is used at 0.06% by weight in an embodiment. Platinum is 0.03% by weight, Palladium at 0.02% by weight, Copper 6.42% by weight in an embodiment. Tin is 0.03% by weight while Silicon is 0.04% by weight in an embodiment

Example 3
Metal Proportion Range –
Per cent by Weight
Silver (Ag) 93.15
Gold (Au) 0.06
Platinum (Pt) 0.03
Palladium(Pd) 0.02
Copper (Cu) 6.65
Tin (Sn) 0.05
Silicon (Si) 0.04
Table 3

Method used for making the Example 3 / Table 3,in an embodiment, the Alloy combination is similar to that described for Example 2 / Table 2 in terms of the steps of the method. Properties of metals in the alloy are as described in other paragraphs of this application. Silver is in proportion of 93.15% by weight in the Alloy in an embodiment. Gold is used at 0.06% by weight in an embodiment. Platinum is 0.03% by weight in an embodiment, Palladium at 0.02% by weight in an embodiment, Copper 6.65% by weight in an embodiment. Tin is 0.05% by weight while Silicon is 0.04% by weight in an embodiment.

Example 4

Metal Proportion Range
Per cent by Weight
Silver (Ag) 92.5
Zinc (Zn) 2
Copper (Cu) 2
Tin (Sn) 1.5
Palladium Pd-999 1.5
Platinum Pt-999 0.5
Table 4

The Alloy combination described in the Example 4 / Table 4 in an embodiment includes Silver (92.5% by by weight) in an embodiment, Zinc (2% by weight) in an embodiment, Copper (2% by weight) in an embodiment, Palladium (1.5% by by weight) in an embodiment, Tin (1.5% by weight) in an embodiment and Platinum (0.5% by weight) in an embodiment. The presence of Zinc in combination imparts the Alloy combination in an embodiment, property of uniform mixing, while Copper provides properties of hardness and Palladium in its pure form (purity level 99.99 per cent by weight) enables properties of resistance to tarnish & hardness. Metal Platinum in pits pure form (purity level 99.99 per cent by weight) provides the Alloy combination of Example 4 / Table 4 table properties of brightness. Metal Tin provides flexibility properties. Properties of other metals in the Alloy are as described in other paragraphs of this Application.

Example 5
Metal Proportion Range
Per cent by Weight
Ag 92.7
Au 0.15
Pt-999 0.15
Pd-999 2.5

alloy (S925PT) 4.5
(7% Zinc & 93% Copper)
Table 5

The Alloy combination described in the Example 5 / Table 5, in an embodiment, includes Silver (92.7% by weight) in an embodiment, Gold (0.15% by weight) in an embodiment, Platinum (0.15% by weight) in an embodiment, Palladium (2.5% by weight) in an embodiment and an alloy S925PT (4.5% by weight made of 7% Zinc and 93% Copper) in an embodiment. The presence of Gold metal in the Alloy combination leads to the bonding properties in the Alloy. The presence of Palladium in its pure form (purity level 99.99 per cent by weight) enables properties of tarnish resistance. The presence of Platinum in its pure form (purity level 99.99 per cent by weight) in an embodiment enables properties of brightness. In (S925PT), The 7% Zinc & 93% Copper alloy, combination exhibits tarnish-resistance properties in an embodiment. Properties of other metals in the Alloy are as described in other paragraphs of this Application.

Example 6
Metal Proportion Range
Per cent by Weight
Ag 95
Au 2
Pt-999 1
Pd-999 1
Zn 1
Table 6

The Alloy combination described in the Example 6 / Table 6, in an embodiment, includes Silver (95% by weight) in an embodiment, Gold (2% by weight) in an embodiment, Platinum (1% by weight) in an embodiment, Palladium (1% by weight) in an embodiment and Zinc (1% by weight) in an embodiment. The presence of Gold metal in the Alloy combination leads to bonding properties in the Alloy. The presence of Palladium in its pure form (purity level 99.99 per cent by weight) enables properties of tarnish resistance. The presence of Platinum in its pure form (purity level 99.99 per cent by weight) enables properties of brightness in an embodiment. The Zinc in combination is 1 % by weight which leads the alloy to exhibit tarnish-resistance properties in an embodiment. Properties of other metals in the Alloy are as described in other paragraphs of this Application.

Example 7
Metal Proportion Range
Percent by Weight
Ag 92.7
Au 5
Pt-999 2
Pd-999 0.3
Table 7

The Alloy combination described in the Example 7 / Table 7, in an embodiment, includes Silver (92.7% by weight) in an embodiment, Gold (5% by weight) in an embodiment, Platinum (2% by weight) in an embodiment and Palladium (0.3% by weight) in an embodiment. The presence of Gold metal in the Alloy combination leads to bonding properties in the Alloy. The presence of Palladium in its pure form (purity level 99.99 per cent by weight) enables properties of tarnish resistance. The presence of Platinum in its pure form (purity level 99.99 per cent by weight) enables properties of brightness. Properties of other metals in the Alloy are as described in other paragraphs of this application.

While this detailed description has disclosed certain specific embodiments for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.
,CLAIMS:WE CLAIM,

1. A tarnish resistant silvery alloy, comprising:
(a) Silver is present in an amount of at least about 92.7% by weight;
(b) Gold is present in an amount of at least about 0.15% by weight;
(c) Platinum is present in an amount of at least about 0.15% by weight; and
(d) Palladium is present in an amount of at least about 2.5% by weight.

2. The tarnish resistant Silvery alloy of Claim 1, comprising:
(a) a combined alloy made of Zinc and Copper;
(b) said Platinum is of 999 purity; and
(c) said Palladium is of 999 purity.

3. The tarnish resistant Silver alloy of Claim 2, comprising:
(a) said combined alloy contains Zinc in an amount of at least about 7% by weight of said alloy; and
(b) said combined alloy contains Copper in an amount of at least about 93% by weight said alloy;

4. The tarnish resistant Silvery alloy of Claim 3,comprising:
said combined alloy is present in an amount of at least about 4.5% by weight.

5. An article made from the alloy of claim 1.

6. The article of claim 5, wherein said article is one of a jewelry, utensil, object, rod, chain, wire, sheet and sculpture.

7. The article of claim 6, wherein the said jewelry is one of a bracelet, a ring, bangle, chain, ear-rings, nose-ring, arm band and a pendent.

8. A tarnish resistant silvery alloy, comprising:
Silver and a balance of said alloy including Palladium, Platinum, Copper and Tin.

9. The tarnish resistant Silver alloy of Claim 8, further comprising:
Zinc.

10. The tarnish resistant Silver alloy of Claim 8 wherein said Silver, said Palladium, said Platinum, said Copper and said Tin are present in an elemental form.

11. The tarnish resistant Silver alloy of Claim 8 wherein Silver is present in an amount of at least about 92.5% by weight.

12. The tarnish resistant Silver alloy of Claim 8 wherein:
(a) said Silver is present in an amount of at least about 92.5 to 99% by weight;
(b) Gold is present in an amount of at least about 0.01-5% by weight;
(c) said Platinum is present in an amount of at least about 2 % by weight;
(d) said Palladium is present in an amount of at least about 0.01 to 2.0% by weight;
(e) said Copper is present in an amount of at least about 0.1-7.15% by weight;
(f) said Tin is present in an amount of at least about , 0.01 to 7.0 by weight;
(g) Silicon is present in an amount of at least about 0.2 % by weight; and
(h) Zinc is present in an amount of at least about 0.001 to 2.0% by weight.

13. The tarnish resistant Silver alloy of Claim 8 wherein:
(a) said Silver is present in an amount of at least about 93.4% by weight;
(b) Gold is present in an amount of at least about 0.06% by weight;
(c) said Platinum is present in an amount of at least about 0.03% by weight;
(d) said Palladium is present in an amount of at least about 0.02% by weight;
(e) said Copper is present in an amount of at least about 6.42% by weight;
(f) said Tin is present in an amount of at least about 0.03 by weight; and
(g) Silicon is present in an amount of at least about0.04 % by weight.

14. The tarnish resistant Silver alloy of Claim 8 wherein:
(a) said Silver is present in an amount of at least about 93.15% by weight;
(b) Gold is present in an amount of at least about 0.06% by weight;
(c) said Platinum is present in an amount of at least about 0.03% by weight;
(d) said Palladium is present in an amount of at least about 0.02% by weight;
(e) said Copper is present in an amount of at least about 6.65% by weight;
(f) said Tin is present in an amount of at least about 0.05 by weight; and
(g) Silicon is present in an amount of at least about 0.04 % by weight.

15. The tarnish resistant silvery alloy of Claim 8, comprising:
(a) said Silver is present in an amount of at least about 92.5% by weight;
(b) said Platinum is present in an amount of at least about 0.5% by weight and of 999 purity;
(c) said Palladium is present in an amount of at least about 1.5% by weight and of 999 purity;
(d) said Copper is present in an amount of at least about 2% by weight;
(e) Zinc is present in an amount of at least about 0.06% by weight; and
(f) said Tin is present in an amount of at least about 1.5% by weight.

16. An article made from the alloy of claim 8.

17. The article of claim 16, wherein said article is one of a jewelry, utensil, object, rod, chain, wire, sheet and sculpture.

18. The article of claim 17, wherein the said jewelry is one of a bracelet, a ring, bangle, chain, ear-rings, nose-ring, arm band and a pendent.

19. The tarnish resistant Silver alloy comprising:
Silver, Gold, Platinum and Palladium.

20. The tarnish resistant silvery alloy of Claim 19, comprising:
(a) said Silver is present in an amount of at least about 92.7 by weight;
(b) said Gold is present in an amount of at least about 5% by weight;
(c) said Platinum is present in an amount of at least about 2 % by weight; and
(d) said Palladium is present in an amount of at least about 0.3% by weight.

21. The tarnish resistant silvery alloy of Claim 19, comprising:
(a) said Silver is present in an amount of at least about 95 by weight;
(b) said Gold is present in an amount of at least about 2% by weight;
(c) said Platinum is present in an amount of at least about 1 % by weight and of 999 purity;
(d) said Palladium is present in an amount of at least about 1% by weight and of 999 purity; and
(e) Zinc is present in an amount of at least about 1% by weigh.

22. A method of making an article comprising the steps of:
(a) pre-forming an alloy according to Claim 1 into a pre-formed piece;
(b) melting said piece to form a melted alloy;
(c) casting said melt into a mold to form a cast article;
(d) cooling said cast article; and
(e) removing said article from said mold.

23. The method of claim 22, further comprising the step of:
(a) reworking alloy residue in said mold into a virgin alloy for further use in making subsequent articles of jewelry.

Dated this 23rd day of June, 2017.

CHIRAG TANNA
APPLICANT’s PATENT AGENT