GB2302694A

GB2302694A - A gold alloy

Info

Publication number: GB2302694A
Application number: GB9612394A
Authority: GB
Inventors: Silverio Cerato
Original assignee: Silmar SpA
Current assignee: Silmar SpA
Priority date: 1995-06-27
Filing date: 1996-06-13
Publication date: 1997-01-29
Anticipated expiration: 2016-06-13
Also published as: GB9612394D0; DE19625807A1; CA2179374A1; TR199600540A2; TR199600540A3; IL118622A; IL118622A0; ITVI950105A1; JPH0913132A; ITVI950105A0; GB2302694B; IT1280528B1

Description

A GOLD ALLOY 2302694

FIELD OF THE INVENTION

The present invention relates to alloys made of gold useful in the jewelry field for the production of jewelry articles, coins and rods made of gold with a titer which varies between 8 karats and 22 karats with different percentages of other components among which are silver, copper and zinc and characterized by the presence of titanium which is the object of the present invention.

BACKGROUND OF THE INVENTION

It is well known that pure gold is extremely soft and that in the production of jewelry articles it is necessary to use a material which has particular properties of hardness, resistance to wear and at the same time should retain a warm and brilliant color. The hardness of the alloy is due to phenomena of precipitation in the solid phase as well as phenomena of the disorder-order transition which.occur below certain temperatures and particular atomic ratios between the elements of the alloy. It is at this point that titanium is inserted into the composition and titanium, due to the fact that it participates to the above mentioned phenomena of precipitation, imparts to the alloy novel properties.

Alloys of gold in general are made from the ternary system Au-Ag-Cu and in commerce they are available with.different titers between 8 and 24 karats. Intermediate titers in commerce are 9, 10, 12, 14, 18, 20, 21 and 22 karats. Up to very recent times the study of gold, a metal used for centuries for ornamental 1 purposes, above all because of the particular color and resistance to spotting, has been limited to alloys which are easily workable and with a pleasant color. In view of the increase in the price of gold which at certain times has even been above 800 per ounce, it is evident that it has become necessary to use lighter jewelry but equally resistant.

In addition, for articles more showy, particularly bracelets (hollow), earrings made with a circle and finally the production of very thin chains similar for instance to the products listed in the Italian patent application V195AO00085 of the same applicant, there are required lighter and more resistant products not only for economical but also aesthetic reasons. This requirement is responsible for the fact that other metals in pure state have been added to the three elements listed above for the purpose of preparing jewelry alloys.

The metal which mostly is being used to form the common quaternly alloy is zinc which is added in small quantities, less than 0.5% as a deoxidizing material or in greater amounts for instance up to 10% or even more in order to modify the color, the workability and the mechanical properties of the alloy. The combination, gold, silver, copper and zinc, constitute essentially all the gold alloys commonly used for jewelry articles. These alloys may be different one from the other due to the addition to the four basic elements small amounts of other metals such as nickel, cobalt, iron, silicon, boron, ruthenium, iridium, indium or others. By way of example, patents which describe what has been 2 summarized hereinabove and which show the variety of components being used to form a gold alloy are:

USP No. 2,141,157 in the name of Peterson, which contains 33%-84% of gold, 10%-67% of copper, 2%-10% of zinc, 2%-10% of silver and 0.1%-5% of cobalt. In this alloy the cobalt is being used to obtain reversible hardening.

USP No. 2,229,463 in the name of Leach, which contains 35%-75% of gold, 5%-25% of silver, 12%-35% copper, 0.1%-12% zinc, and 1%-5% of iron. In this alloy the iron is used to obtain both the reversible as well as irreversible hardening.

USP No. 2,248,100 in the Dame of Loebich, which contains 33%-66% of gold, U-30% of silver, 10%-55% of copper, 0.5%-15% of zinr- and 0.1%-5% of iron.

USP No. 3,981,723 describes an alloy of white gold which contains palladium, silver, indium and 0.005% of iridium or ruthenium.

More recent patents describe alloys such as USP No. 5,180,551 in the name of Leach and Garner and USP No. 5,173,132 in the name of Solomon. In these patents different combinations of cobalt and nickel are used for the purpose of improving the structure of the grain, optimizing the color and increasing the mechanical resistence.

It is clear from the above list of patents with respect to the state of the art in the field of jewelry products, the titanium ele ment does not appear because the work of alloys which contain this element requires particular precautions due to great activity

3 at high temperature with air, oxygen, nitrogen, carbon which are commonly present in forming the protective atmosphere during the treatments of solubilization, aging, cold working, fusion or others.

The only alloy of gold known at present which contains titanium is the alloy known as "gold 990". This alloy has a high karat and is the result of study carried out in the 1970 period and the purpose was to solve two types of problems, hardening an alloy with a very low percentage of alloying elements and at the same time produce an alloy which is aesthetically satisfactory, for instance with respect to color. The result has been that an alloy with karats of 23.76 in gold and 1% by weight of titanium has been made. This alloy has offered a resistance to wear equal to an alloy of 18 karats and has been claimed particularly in USP 1,023,334 and Dutch Patent No. P35 02 914.5.

The titanium is present in this alloy in the form of titanium nitride in the galvanic treatments of superficial hardening for the purpose of increasing the resistance to wear and to abrasion of jewelry articles having high karats (see A.R. Zielonka Gold'Technology No. 14, November 1994).

SUMMARY OF THE INVENTION

The object of the present invention is to provide a gold alloy having between 8 and 22 karats with the ternary system Au-Ag-Cu, which may include other elements such as Zn, 'Ru, Ir, B, Si, In or others and which contain the titanium element.

4 In particular, titanium substitutes in practice two elements which up to the present time have been employed in the production of jewelry, that is nickel and cobalt. These two elements have the drawback that they are ferromagnetic and their presence in the alloy limits the sale of jewelry in the markets in which there are some restricting laws in this respect. Further the nickel, as it is well known, may cause serious types of allergy in the skin to such an extent that in several countries such as Japan, England and Germany laws have been made which prevent the commercialization of jewelry articles which contain nickel.

With an alloy containing about 58.5% of gold, 5-10%. of silver, 15-25% of copper, 10 - 20% al! zinc and 0.1%-I% of titanium, one obtains a gold product suitable for the above described uses, of sufficient mechanical resistance and hardness (160 HV with the renewed baking and 280 HV with the aging treatment and with a grain dimension of 8 ASTM).' At the same time the alloy has a pleasant color similar to the alloy having 18 karats which is the alloy most used - see Table hereinbelow.

T-ebaked allo hardness 160 5V grain dimension 8 ASTM 1 alioy alfter the aging treat-men't 280 HV 8 ASTM The above mentioned properties are also clear from the accompanying figures:

Fig. 1 which illustrates the ratio which exists between the time and the hardness in the thermal treatment of aging.

The specific quantities of the individual pure metals, expressed in percentage weight clearly vary as a function of the specific uses of the gold alloy.

The invention, therefore, consists of providing an alloy having the ternary gold, silver, copper composition and with titanium variable as well as alloys of a quaternary type and others.

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Claims

An alloy of gold comprising at least a ternary composition of gold, silver and copper, having 8-22 carats in several percentage compositions by weight which comprises also titanium.

The alloy of claim 1, wherein the alloy is a quaternary composition containing gold, silver, copper and zinc.

The alloy of claim 1, wherein the alloy further comprises small quantities of other elements, said elements being silicon, boron, indium, iridium, ruthenium or others.

The alloy of claim 2, wherein the alloy further comprises small quantities of the elements silicon, boron, indium, ruthenium, iridium or others.

The alloy of any preceding claim wherein the titanium is present in an amount between 0. 1% and 1% by weight.

The alloy of any preceding claim wherein nickel is substantially absent.

7. The alloy of any preceding claim wherein cobalt is 7 substantially absent.

8. The alloy of any one of claims 2 to 7 consisting essentially of the following composition by weight; Gold Silver Copper Zinc Titanium about 58.5% 5 to 10% 15 to 25% 10 to 20% 0.1 to 1-05 An article being one of an item of jewellery, a coin, or a rod, formed of an alloy according to any preceding claim.

10. An alloy substantially as herein described and/or with reference to the accompanying figure.

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