RU2479656C1 - Jewellery cast alloy of white colour based on palladium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to palladium-based alloys used mainly for manufacture of jewellery of assay 900 and 950 using casting methods. White-colour alloy contains the following components, wt %: palladium - 90.0-95.5; silicon - 0.1-0.3; silver is the rest.

EFFECT: high-standard white alloy based on palladium has improved casting properties, optimum hardness, high industrial safety, which allows manufacturing jewellery using casting methods with required consumer properties oriented to a world market.

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Description

The present invention relates to the metallurgy of noble metals, in particular to palladium-based alloys, used mainly for the manufacture of jewelry 900 and 950 samples by casting.

Palladium-based alloys are widely used in jewelry production due to their high consumer qualities, which bring them closer to platinum products. At a relatively low cost, they have a beautiful appearance, corrosion resistance to external factors, good polishability, are well processed by casting and metal forming methods. Recently, high-quality palladium jewelry products, in particular 900 and 950 samples, have been in greatest demand on the world market. At the same time, in Russia until recently, only jewelry palladium alloys no higher than 850 samples were standardized and produced.

In particular, an alloy based on palladium is known, containing, wt.%:

palladium 85.0-85.5; silver 12.5-13.5; nickel rest.

(State standard of the Russian Federation GOST R51152-98 "Alloys based on precious metals jewelry. Stamps" / Gosstandart of Russia. - Moscow: IPK Publishing house of standards. - 1998. - P.4).

The disadvantages of this alloy include: the impossibility of its use in the manufacture of high-grade (900 and 950 samples) jewelry. In addition, this alloy has a high melting point and also contains nickel. The high melting point makes it difficult to use this alloy in the manufacture of jewelry by casting, and nickel according to the EEC directives is not recommended for use in products that come into long-term contact with human skin. All this complicates its use in the manufacture of jewelry by casting methods oriented to the world market.

Closest to the invention in composition is a white colored jewelry alloy based on palladium, containing, wt.%:

palladium 95.0-99.5; cobalt 0.2-3.0; iridium 0.05-0.6; silver 0.1-1.5; iron 0.05-0.6; copper rest.

(Pat. 2405051 Russian Federation, IPC C22C 5/04. Jewelry white alloy based on palladium / V.N. Efimov, S.N. Yeltsin, S.N. Mamonov and others (RF) - No. 2009122355/02; Declared June 10, 2009; publ. November 27, 2010).

This alloy is adopted as a prototype.

The prototype alloy based on a complex multicomponent composition has a beautiful white color with a luster, resembles platinum and allows using it in the claimed range of component concentrations in the manufacture of high-quality products up to 990 samples by metal forming methods in the manufacture of chains, including by machine.

The main disadvantages of this alloy include:

- the content of cobalt in it is 0.2-3.0 wt.%, which is characterized by toxicity and, like nickel, it is not recommended to use it in products that come into long-term contact with human skin according to EEC directives;

- the multicomponent composition inevitably leads to the appearance of dendritic segregation, to the heterogeneity of the chemical composition and the unevenness of the physico-mechanical properties in the volume of the products obtained by casting methods, which reduces the yield of products;

- the use of alloying components in the alloy as refractory metals - cobalt, iron and iridium, and relatively low-melting metals - silver and copper, leads to an increase in the temperature range of crystallization and, as a result, causes a decrease in casting properties, complicates the technology for manufacturing jewelry casting methods and reduces the yield of products.

The main task to which the proposed technical solution is directed is to develop the composition of a white palladium-based foundry jewelry alloy, which can be used in the manufacture of high-quality jewelry up to 950 samples oriented to the world market by casting methods, as well as increasing industrial safety.

The technical result is achieved in that a white palladium-based foundry jewelry alloy containing silver is characterized in that it additionally contains silicon in the following ratio of components, wt.%:

palladium 90.0-95.5; silicon 0.1-0.3; silver rest.

Common to the known and claimed jewelry alloys based on palladium is the presence of silver in the alloy.

The choice of boundary values of the parameters of the components indicated in the claims is due to the following.

The palladium content in the alloy is determined by the required fineness for high-grade jewelry (900 or 950 samples).

The difference from the prototype alloy is the additional introduction of silicon into the inventive alloy and the absence of other components, such as cobalt, iridium, iron and copper. The optimum silicon content in the alloy was established empirically. The addition of silicon in an amount of 0.1-0.3 wt.% Reduces the temperature of the melt, improves its fluidity. A further increase in the silicon content in the composition causes an increase in the hardness of the alloy and a decrease in fluidity, a tendency to tarnish under certain environmental conditions appears, and the alloy may become completely unsuitable for subsequent processing by casting methods. When the silicon content is less than 0.1 wt.%, The required level of strength of the obtained jewelry is not ensured and their consumer value is reduced.

The decrease in the number of alloying components in the composition of the proposed alloy will significantly reduce the appearance of dendritic segregation, increase the uniformity of physical and mechanical properties in the volume of the obtained products by casting methods and increase the yield of products. In addition, the absence of cobalt alloy in the composition of the proposed alloy satisfies the EEC directives, increases industrial safety and will make it possible to produce high-quality jewelry oriented to the world market.

Thus, there is a causal relationship between the hallmarks and the task at hand. The additional introduction of silicon into the composition of the white jewelry casting alloy based on palladium containing silver provides an increase in casting properties, optimal hardness, improves industrial safety and allows jewelry to be made using casting methods with the required consumer qualities that are oriented to the world market.

Example 1. Preparation of alloy 900 samples.

The preparation of a white palladium-based foundry jewelry alloy was carried out by direct fusion of pure components, namely: bullion-refined palladium (purity 99.95%); silver granules (99.95% pure); refined silicon powder (99.95% purity).

In the melting crucible made of zirconium dioxide of the induction vacuum unit UIPV-63-10-0.01 of the RELTEC company, a charge composed of the calculated amount of components was loaded, namely: palladium - 362.0 g; silver - 37.2 g; silicon - 0.8 g. The installation was evacuated to a residual pressure of 60 Pa and then filled with argon. The mixture was melted in argon medium. After complete melting of the components, the obtained melt was held for 5 minutes and drained into a massive copper mold. The temperature range of the obtained palladium alloy was determined by differential thermal analysis. After casting, the alloy was subjected to homogenization annealing in an inert gas (argon) atmosphere. Then, after cooling, the obtained alloy ingot in the form of a squared bar was extracted from the mold. After mechanical cleaning of the surface, the obtained ingot was tested. The composition of the alloy was controlled by quantitative chemical analysis.

Chemical analysis of the sample showed that the obtained jewelry alloy based on palladium corresponds to 900 samples, has a white color with a tint resembling platinum.

Example 2. Preparation of alloy 950 samples.

The preparation of this foundry jewelry alloy was carried out according to a technology that does not differ from that presented in Example 1, by direct fusion of pure components. A mixture composed of the calculated amount of components was loaded into the melting crucible, namely: palladium - 382.0 g; silver - 17.2 g; silicon - 0.8 g. After mechanical cleaning of the surface, the cast ingot was tested. Chemical analysis of the sample showed that the obtained jewelry alloy based on palladium corresponds to 950 samples, has a white color with a tint resembling platinum.

To study the technological properties of castings from the proposed alloy, the melting temperature, microhardness, and reflection coefficient in the visible wavelength range were determined (SPECORD-M40 device).

For comparison, tables 1-4 show the compositions of the inventive alloy, physico-chemical properties, and also the reflection coefficient in comparison with the known alloy.

Table 1 The compositions of the claimed and known alloys 900 samples No. p / p Alloy The chemical composition of the alloy, the mass fraction of the component, wt.% Pd Ag Si Co Ir Fe Cu one with Si content less than 0.1% 90.5 9.45 0.05 - - - - 2 claimed 90.5 9,4 0.1 - - - - 3 90.5 9.3 0.2 - - - - four 90.5 9.2 0.3 - - - - 5 with a Si content of more than 0.3% 90.5 9.15 0.35 - - - -

table 2 Properties of the claimed and known alloys 900 samples No. Alloy Maximum melting point, ° C Hardness HV, MPa Kotr.% one with Si content less than 0.1% 1445 1370 80 2 claimed 1450 1410 79 3 1452 1425 79 four 1454 1440 79 5 with a Si content of more than 0.3% 1462 1480 78

Table 3 The compositions of the claimed and known alloys 950 samples No. p / p Alloy The chemical composition of the alloy, the mass fraction of the component, wt.% Pd Ag Si Co Ir Fe Cu one with Si content less than 0.1% 95.5 4.45 0.05 - - - - 2 claimed 95.5 4.4 0.1 - - - - 3 95.5 4.3 0.2 - - - - four 95.5 4.2 0.3 - - - - 5 with a Si content of more than 0.3% 95.5 4.15 0.35 - - - - 6 famous 95.5 1,0 - 1.9 0.4 0.5 0.7

Table 4 Properties of the claimed and known alloys 950 samples No. Alloy Maximum melting point, ° C Hardness HV, MPa Kotr.% one with Si content less than 0.1% 1460 1380 81 2 claimed 1466 1420 80 3 1470 1440 80 four 1475 1460 80 5 with a Si content of more than 0.3% 1482 1500 78 6 famous 1530 1740 77

As can be seen from the tables, the inventive alloy with different chemical composition in the claimed range of component ratios (alloys No. 2-4) compared with the known due to the optimal combination of components in the alloy in the specified quantitative ratio has a lower melting point - 1450 ÷ 1475 ° C, optimal hardness - 1410 ÷ 1460 MPa, coincides in fineness and color with the main palladium alloys having samples 900 and 950.

Thus, the use of the inventive alloy in comparison with the prototype provides an increase in casting properties, achieving optimal hardness, increases industrial safety and allows the manufacture of high-quality jewelry by casting with the required consumer properties, oriented to the world market.

Claims (1)

Palladium-based white foundry jewelry alloy containing silver, characterized in that it additionally contains silicon in the following ratio of components, wt.%:
palladium 90.0-95.5 silicon 0.1-0.3 silver rest