Master alloy and metal alloy containing the master alloy

Abstract

Master alloy, in particular for use in the production of a silver-based metal alloy, more preferably in the production of a sterling silver alloy, characterised by comprising: -zinc in a percentage between 57 and 98.6% by weight, - iron in concentrations between 70 and 1340 ppm.

Description

[0001] MASTER ALLOY AND METAL ALLOY CONTAINING THE MASTER ALLOY

[0002] The present invention relates to a metal master alloy, particularly a master alloy for making a silver-based metal alloy, and more specifically, a master alloy for making a sterling silver metal alloy. The present invention also relates to a metal alloy made from the master alloy, particularly a silver-based alloy, and more specifically, a sterling silver metal alloy.

[0003] There are known silver-based metal alloys that have a silver content equal to or greater than 925%o.

[0004] Due to the thermodynamic stability of silver (Ag) and copper (Cu) sulfides, silver and sterling silver (an alloy with 92.5% silver) tend to darken, a phenomenon known as tarnish. This phenomenon is primarily related to atmospheric corrosion, but also occurs in solution corrosion, due to the influence of sweat or saliva.

[0005] The culprits of oxidation are elements containing sulfur, chlorine, and nitrogen. Oxidation primarily refers to the formation of sulfides on the surface of silver and its alloys, caused by the effect of sulfur-containing gases in the atmosphere. In addition to the concentration of these gases, physical factors such as temperature, atmospheric humidity, and light also have a significant impact.

[0006] Early research on silver oxidation and the development of tarnish-resistant silver alloys dates back to the 19th century. Extensive studies on the oxidation resistance and mechanical properties of silver alloys were published in the 1920s. Since the final decades of the 20th century, several silver alloy systems with oxidation- resistant properties, good mechanical properties, and processability have been patented. These patented alloys are generally multicomponent systems, often containing three or four base metals, with the addition of some alloying trace elements.

[0007] The paths that are undertaken to reduce tarnish can be summarised as follows:

[0008] - reduce or eliminate phases that corrode more easily than the matrix phase: The tarnish and oxidation of copper solid solution in silver are not dramatically different than in silver. The greatest loss of corrosion resistance in silver alloys occurs due to the presence of the copper-rich phase. To reduce or replace the copper-rich phase, the new element added to the alloy must have appreciable solubility in silver. - addition of noble elements: The simplest mechanism depends on the intrinsic nobility of the element added to the alloy. For example, if an element highly resistant to the corrosiveness of a given environment is added to one with less resistance, the overall resistance can be approximated using a rule of mixtures. Au, Pd, and Pt are essentially the only three elements that fall into this category. Since all three of these elements are denser than silver, small additions in weight percent will result in a limited number of atoms in the alloy and may result in only a slight increase in oxidation resistance. The main disadvantage of these additions is their cost.

[0009] - insertion of passivating elements: In this case, it is not the intrinsic corrosion resistance of the element added to the alloy, but rather its ability to form a stable barrier film on the alloy.

[0010] - impurity reduction: Impurities, in general, reduce a metal's corrosion resistance. They tend to segregate at grain boundaries and promote galvanic action, acting as highly reactive anodic or cathodic sites.

[0011] However, modifications to alloys that improve oxidation resistance very often compromise some other important characteristic of the alloy.

[0012] The prior art also includes documents JPH10183268, WO 2006 / 106282, US 2008 / 166260 and US 2019 / 0003015.

[0013] A known alloy in the state of the art is LUX180, represented in the figures below, which comprises: Ag 93%, Cu 5.13%, Zn 0.14%, In 0.07%, Si 0.105% and B 0.003%.

[0014] The aim of the invention is to propose a mother alloy and a metal alloy that allow the drawbacks of the known solutions to be overcome.

[0015] Another aim of the invention is to propose a master alloy that can be used to produce a silver-based alloy, such as sterling silver.

[0016] Another aim of the invention is to propose a master alloy and an alloy that have a high resistance to browning. hardenable alloy and the master alloy from which this alloy can be obtained.

[0017] Another aim of the invention is to propose an alloy with refined crystalline grain, and the master alloy from which this alloy can be obtained.

[0018] Another object of the invention is to propose an alloy that does not show cracks following cooling, and the master alloy from which this alloy can be obtained.

[0019] Another object of the invention is to propose a non-brittle alloy, and the master alloy from which this alloy can be obtained.

[0020] Another aim of the invention is to propose a master alloy and an alloy that can be easily produced by casting.

[0021] Another aim of the invention is to propose an object made from said alloy and / or said mother alloy.

[0022] All these purposes, and others which will clearly result from the description, are obtained by means of a master alloy having the characteristics described in claim 1 , with an alloy having the characteristics described in claim 5 and with an object having the characteristics described in claim 9.

[0023] Other structural and functional characteristics of the present innovation and the related advantages with respect to the known art will become even clearer and more evident from an examination of the following description, referring to an exemplary and preferred, but not limiting, embodiment of the metal alloy which is the object of the present invention and to the figures, in which:

[0024] Figure 1 shows an object made from a freshly produced LUX180 alloy (a) and one made from an alloy according to the invention freshly produced (b), and the same product made from the LLIX180 alloy after 7 minutes (c) and the same product made from an alloy according to the invention after 7 minutes (d), and the same product made from the LUX180 alloy after 16 days (e) and the same product made from an alloy according to the invention after 16 days (f);

[0025] Figure 2 shows the variation in gloss for a product made with an alloy according to the state of the art (a) and one made with an alloy according to the invention (b); Figure 3 shows the variation of the red colorimetric parameter in a product made with an alloy according to the state of the art (a) and one made with an alloy according to the invention (b);

[0026] Figure 4 shows the variation of the yellow colorimetric parameter in a product made with an alloy according to the state of the art (a) and one made with an alloy according to the invention (b).

[0027] The present invention relates to a master alloy. A master alloy is, as is known, a metal alloy designed to be added to a pure metal in order to obtain a metal alloy with the desired properties.

[0028] Below all percentages will be expressed with respect to the weight of each element within the alloy and / or master alloy.

[0029] Advantageously, the master alloy can include zinc and iron. Suitable alloys can also include copper, silicon, and iron.

[0030] In particular, the mother alloy may include:

[0031] - The zinc concentration is preferably greater than 57%, more preferably greater than 65%, more preferably greater than 70%, more preferably greater than 80%, more preferably greater than 83%, and preferably less than 98.6%, and preferably less than 95%, and preferably less than 90%, and preferably less than 88%, and preferably less than 87%, and most preferably equal to 85.7%.

[0032] - The iron concentration is preferably greater than 70 ppm, more preferably greater than 150 ppm, more preferably greater than 300 ppm, more preferably greater than 400 ppm, more preferably greater than 415 ppm, and preferably less than 1 .4%, and preferably less than 1 .0%, and preferably less than 0.7%, and preferably less than 0.5%, and preferably less than 0.45%, and most preferably equal to 427 ppm.

[0033] - The copper concentration is preferably greater than 1 .4%, more preferably greater than 5%, more preferably greater than 10%, more preferably greater than 12%, more preferably greater than 13%, and preferably less than 27%, and preferably less than 20%, and preferably less than 18%, and preferably less than 15%, and preferably less than 14%, and most preferably equal to 13.2%.

[0034] - The silicon concentration is preferably greater than 0.001 %, more preferably greater than 0.01 %, more preferably greater than 0.1 %, more preferably greater than 0.5%, more preferably greater than 0.9%, and preferably less than 6.6%, and preferably less than 5%, and preferably less than 3%, and preferably less than 2%, and preferably less than 1 .5%, and more preferably equal to 1 %.

[0035] Suitably, the master alloy according to the invention is configured to be used in the production of a silver-based alloy, preferably a silver alloy containing at least 80% silver, and more preferably a sterling silver alloy, i.e. in which the silver is present at least 925%o.

[0036] The other components of the alloy are therefore:

[0037] - Zinc, preferably in a concentration greater than 4%, more preferably greater than 4.5%, more preferably greater than 5%, more preferably greater than 5.5%, more preferably greater than 5.8%, and preferably less than 20%, and preferably less than 15%, and preferably less than 10%, and preferably less than 8%, and preferably less than 7%, and more preferably equal to 6%,

[0038] - copper preferably in a concentration greater than 0.1 %, more preferably greater than 0.2%, more preferably greater than 0.5%, more preferably greater than 0.8%, more preferably greater than 0.9%, and preferably less than 5.3%, and preferably less than 4%, and preferably less than 2%, and preferably less than 1.5%, and preferably less than 1.0%, and more preferably equal to 0.93%.

[0039] - silicon in a concentration greater than 0.001 %, more preferably greater than 0.005%, more preferably greater than 0.01 %, more preferably greater than 0.05%, more preferably greater than 0.06%, and preferably less than 1.3%, and preferably less than 1 .0%, and preferably less than 0.5%, and preferably less than 0.2%, and preferably less than 0.1 %, and more preferably equal to 0.07%.

[0040] - iron preferably in a concentration greater than 5 ppm, more preferably greater than 10 ppm, more preferably greater than 20 ppm, more preferably greater than 30 ppm, more preferably greater than 31 ppm, and preferably less than 1000 ppm, and preferably less than 500 ppm, and preferably less than 100 ppm, and preferably less than 60 ppm, and preferably less than 40 ppm, and more preferably equal to 32 ppm.

[0041] It has been noted that each element in the composition plays a crucial role in achieving the desired properties. In particular, the low copper concentration prevents the precipitation of the copper-rich phase, which is typical of sterling silver alloys. Zinc is added in quantities that are soluble in silver at room temperature, increasing the solubility of copper in silver, further preventing the precipitation of the copper-rich phase. The sulfurization and / or oxidation products of zinc are colorless and therefore do not affect the aesthetic appearance of an object made with the alloy according to the invention. Silicon protects the alloy in its molten state from reactions with crucible components or other materials, particularly in the presence of gypsum, and also allows the formation of a passivating layer on the surface of an object made with the alloy according to the invention. The presence of copper, and the resulting precipitation of the copper-rich phase, allows the alloy to harden. The iron allows the alloy to be refined and avoids the risk of breakages during cooling.

[0042] As can be clearly seen, the master alloy according to the invention is advantageous, indeed optimal, as it allows the creation of an alloy which is, at the same time:

[0043] • tarnish resistant

[0044] • hardenable

[0045] • not fragile • refined

[0046] • deoxidized as cast.

Claims

CLAIMS1. Master alloy, in particular for use in the production of a silver-based metal alloy, more preferably in the production of a sterling silver alloy, characterised by comprising: copper in a percentage greater than 1 .4%, %, and less than 27%; silicon in a percentage greater than 0.001 ; zinc in a percentage between 57 and 98.6% by weight, iron in concentrations between 70 and 1340 ppm.

2. Master alloy according to the preceding claim characterised in that it comprises copper in a percentage lower than 13.8%, and preferably lower than 13.6%, and preferably lower than 13.4%, and preferably lower than 13.3% and more preferably equal to 13.2%.

3. Mother alloy according to one or more of the preceding claims characterized in that it comprises silicon in a percentage greater than 0.85%, more preferably greater than 0.9%, more preferably greater than 0.95%, more preferably greater than 0.98%, less than 1 .2%, and preferably less than 6.6% and preferably less than 1.1 %, and preferably less than 1.05%, and preferably less than 1.02% and more preferably equal to 1 %.

4. Master alloy according to one or more of the preceding claims, characterized in that it comprises zinc in a percentage greater than 57%, more preferably greater than 81 %, more preferably greater than 82%, more preferably greater than 83%, more preferably greater than 84%, more preferably greater than 85%, and preferably less than 98.6%, and preferably less than 89%, and preferably less than 88%, and preferably less than 87%, and preferably less than 86%, and more preferably equal to 85.7%.

5. Mother alloy according to one or more of the preceding claims characterised by the fact that it does not comprise Au, Pd, Pt.

6. Alloy characterized in that it comprises Ag in a percentage greater than 80%, and preferably greater than 92.5%, and a master alloy according to one or more of the preceding claims.

7. Alloy according to claim 5 characterized in that it is composed of 93% silver and a master alloy according to one or more of claims 1 - 48. Alloy according to one or more of claims 5, 6 characterised in that it comprises:zinc in an amount preferably greater than 4%, more preferably greater than 4.5%, more preferably greater than 4.8%, more preferably greater than 5.0%, more preferably greater than 5.5%, and preferably less than 20%, and preferably less than 7.2%, and preferably less than 7.0%, and preferably less than 6.8%, and preferably less than 6.5%, and more preferably equal to 6%. iron in an amount greater than 5 ppm, more preferably greater than 10 ppm, more preferably greater than 15 ppm, more preferably greater than 25 ppm, more preferably greater than 30 ppm, and preferably less than 1000 ppm, and preferably less than 80 ppm, and preferably less than 60 ppm, and preferably less than 50 ppm, and preferably less than 40 ppm, and more preferably equal to 32 ppm.

9. Alloy according to one or more of claims 5-7 characterised in that it comprises: copper preferably greater than 0.1 %, more preferably greater than 0.4%, more preferably greater than 0.6%, more preferably greater than 0.8%, more preferably greater than 0.9%, and preferably less than 5.3%, and preferably less than 1.8%, and preferably less than 1.5%, and preferably less than 1.2%, and preferably less than 1 .0%, and more preferably equal to 0.93% silicon greater than 0.001 %, more preferably greater than 0.02%, more preferably greater than 0.04%, more preferably greater than 0.06%, more preferably greater than 0.065%, and preferably less than 1 .3%, and preferably less than 0.4%, and preferably less than 0.3%, and preferably less than 0.2%, and preferably less than 0.1 %, and more preferably equal to 0.07%.

10. Object, preferably an object of jewellery or costume jewellery, such as for example a necklace, an earring, a ring or a watch, characterised by the fact that it is made from a master alloy according to one or more of claims 1 - 4 or from an alloy according to one or more of claims 5 - 8.

11. Use of a master alloy according to one or more of claims 1 - 4 in the production of a silver alloy, preferably sterling silver.

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