Patent Application
20200340078
The present application claims priority to Thai Application No. 1901002436, filed Apr. 23, 2019, the entire contents of which are incorporated herein by reference and relied upon.
The present invention relates to chemistry in relation to a gold alloy including hardness improving elements.
Gold (Au) is a natural metallic mineral. It is solid with a unique bright yellow color. Gold is inert to most chemical reactions, for example, it does not react when exposed to oxygen or acid. Therefore, it is resistant to rusting, tarnishing or corrosion by acid. Gold is soft, malleable and ductile making it capable of being formed into wires or thin sheets. With its great properties, gold became a high value metal used as collateral for foreign exchange trading, jewelry, fine arts, and is also used in other industries such as dental work, electronic circuits (CPU), coins, etc. Jewelry and fine arts are the majority of the market for gold.
Pure gold, however, is soft and therefore not suitable for making gold jewelry as it may be easily deformed and is not durable for use. Accordingly, the hardness of gold must be improved for making suitable gold jewelry by adding elements or components which increase the hardness and/or affect the color of gold, the result of which is a gold alloy. The amount (percentage) of gold in a gold alloy is indicated in units of Karat (K), for example, 18K gold or 9K gold (as shown in Table 1).
Gold alloys with lower Karat values, such as 8K-18K gold, have a higher hardness than high karat gold alloy, such as 21K-24K gold, making them suitable for making jewelry that requires durability or various complicated or slim designs. Presently, the culture or social values regarding the use of gold jewelry vary around the world. However, the use of gold may be divided into two groups. The first group of countries prefers using jewelry gold with high durability for a variety of designs, especially slim or complicated, and will use solid gold such as 8K-18K gold alloy (as shown in Table 1). These are mostly western countries. In some countries, mostly eastern countries, gold is not only used as jewelry but also used as a liquid asset or investment. This second group prefers using 21K-24K gold alloy (as shown in Table 1).
When the proportion of gold in a gold alloy increases, the hardness of the gold alloy will decrease which will limit the design capabilities of the gold alloy when compared to those of 8K-18K gold alloys of the Western countries.
75%
For Thailand, the standard purity of gold alloy is 96.5% or 23.16K according to the Office of the Consumer Protection Board (OCPB) standards. In this proportion, gold alloy has a bright yellow color suitable for making gold jewelry and accessories that are acceptable in the market.
Thailand has set the purity standard of gold alloy higher than many countries, i.e., the gold component must not be less than 96.5% (23.16K). Accordingly, additional components or elements and a particular process is required to improve the hardness of the gold alloy while maintaining the bright yellow color of 23.16K gold that is still acceptable to the standard.
Prior attempts at creating a gold alloy have been disclosed in documents such as U.S. Pat. Nos. 2,141,156; 2,141,157; 2,200,050; 2,216,495; 2,248,100; 2,576,738; 2,654,146; 4,266,973 and 4,276,086, all of which are directed to the development of 8K to 20K gold alloy.
The conventional components of a gold alloy in the market with 96.5% gold are 96.5% gold with the other 3.5% consisting of silver (Ag) and a small portion of copper (Cu).
The hardness of conventional 96.5% gold is insufficient for a design that requires durability. Accordingly, the present disclosure provides for a 23.16K gold alloy (i.e., 96.5% gold) which consists of 96.5% gold and 3.5% of others elements that results in a higher hardness than the conventional 96.5% gold alloy.
The presently disclosed gold alloy may have a proportion of gold lower than 96.5% or up to 97%. Hence, the proportion of gold in this invention can range from 96.4%-97% which is combined with 3-3.6% of other selected elements different from the conventional components (i.e., silver (Ag) and copper (Cu)).
The other selected elements of the present disclosure help improve the hardness of the gold alloy and the flowing of melted gold during the production process. Such improvements reduce “porosity” in the gold alloy and cracks in a production workpiece caused from unblended metal. As a result, the surface of a workpiece is smooth.
Furthermore, the hardening process includes solution treatment application and quenching in water, followed by aging with appropriate time and heat temperature. The process then includes letting the gold alloy cool down by air, water or Tumbling Machine, resulting in a 23.16K (Karat) gold alloy with higher hardness than conventional 96.5% gold alloys. The presently disclosed gold alloy can be formed to slim or complicated designs with no damage while still remaining smooth, glossy, and a bright golden yellow color according to the standard of 96.5% gold.
The present disclosure provides for a gold alloy including 96.4% to 97% gold by weight and the remaining percentage including other elements, such as hardness improving elements. The other elements may improve various properties of the gold alloy or the production of the gold alloy. In some examples of the present disclosure, the gold is mixed or diluted with the hardness improving elements.
In some examples, hardness improving elements are provided in the proportion of 0.1-3.6% by weight. The hardness improving elements are selected from one or more elements among: copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), gallium (Ga), tin (Sn), antimony (Sb), and iron (Fe). In some examples, if only copper (Cu) or zinc (Zn) or both are selected, then the proportion by weight of copper (Cu) and zinc (Zn) is 0.5 to 3.6%.
In some examples, elements improving the flowing of a melted gold alloy in the production process, reducing the shrinkage, and/or improving the surface quality of a workpiece are provided in a proportion of 0.0-0.1% by weight. These elements are selected from one or more of: iridium (Ir), palladium (Pd), aluminum (Al), indium (In), silicon (Si), germanium (Ge) and lead (Pb).
In some examples, silver (Ag) is used as a composition to refine the proportion of all components in the gold alloy to 100% by weight. In such examples, silver (Ag) is provided in proportion of 0-3.5% by weight. For example, if the above described elements compose 98% of the gold alloy composition by weight, then silver (Ag) is 2% by weight of the composition.
In at least one aspect of the present disclosure, an example gold alloy includes 96.5% gold by weight. The example gold alloy also includes 0.5-2.1% by weight of one or more elements among: copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), gallium (Ga), tin (Sn), antimony (Sb), and iron (Fe). The selected combination of copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), gallium (Ga), tin (Sn), antimony (Sb), and iron (Fe) is at least 0.5% by weight in order to achieve the desired hardness of the gold alloy but does not exceed 2.1% by weight to maintain the desired color of the gold alloy. The example gold alloy also includes 0.0-0.1% by weight of one or more elements among: iridium (Ir), palladium (Pd), aluminum (Al), indium (In), silicon (Si), germanium (Ge) and lead (Pb). The example gold alloy also includes 1.4-3% by weight of silver (Ag). If silver (Ag) is less than 1.75% by weight, the color of the gold alloy changes and is not as shiny yellow. If silver (Ag) is more than 3% by weight, the combination of hardness improving elements i.e., copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), gallium (Ga), tin (Sn), antimony (Sb) and iron (Fe) decreases resulting in reduced hardness of the gold alloy.
The presently disclosed gold alloy including hardness improving elements has a higher hardness than conventional 96.5% gold alloys which contain the same gold proportion (as shown in Table 2). In some aspects of the present disclosure, the gold alloy is produced using a procedure to increase the hardness of the gold alloy. The procedure includes forming the gold alloy by solution treatment at a temperature of 750-800° C. for 1 hour, then quenching the gold alloy in water and aging it again at a temperature of 250-350° C. for 1-2 hours. The procedure then includes cooling the gold alloy down in water or air. The preceding steps help increase the hardness of the whole work piece. The procedure then includes processing the gold alloy through a general tumbling machine which helps increase the hardness of the workpiece surface.
In the jewelry industry, the hardness of metal is generally indicated by the Vickers Hardness Test, which is measured in units of HV. Table 2 below shows samples of gold alloy compositions and the corresponding results for each of a Vickers hardness test in units of HV. Process A included a solution treatment at 760° C. for 1 hour then quenching the gold alloy in water and aging it again at 300° C. for 90 minutes. Process B included a solution treatment at 760° C. for 1 hour then quenching the gold alloy in water, aging it again at 300° C. for 90 minutes, and then grinding the gold alloy by a tumbling machine for 2 hours.
Sample 1 in the above Table 2 is a conventional 18K gold alloy with a hardness of 161.8 HV after a casting process. Sample 2 is a conventional 23.16K (i.e., 96.5% gold) gold alloy with a hardness of 37.9 HV after a casting process.
Even after being processed through processes A and B, the conventional 23.16K gold alloy only had a hardness of 38.9 HV and 61 HV, respectively.
The example samples 3-5 in the above Table 2 are example gold alloy compositions according to the present disclosure. In each example, the hardness of the presently disclosed gold alloy was greater than the conventional gold alloy of the same composition. In other examples, the compositions of the gold alloy may be different than the compositions in Table 2 according to the present disclosure.
Sample 3 is a 23.16K gold alloy with a hardness of 79.3 HV after a casting process. When sample 3 was processed through processes A or B, it had an even higher hardness of 133.6 HV and 182.8 HV, respectively. The level of hardness for sample 3 is very high, especially the B-processed gold alloy, as the hardness was almost at the same level with 18K gold alloy after casting.
Sample 4 is a 23.16K gold alloy with a hardness of 69.4 HV after a casting process. When it had been processed through processes A or B, the hardness increased to 79.5 HV and 100.7 HV, respectively.
Sample 5 is 23.16K gold alloy with a hardness of 49.6 HV after a casting process. When it had been processed through processes A or B, the hardness increased to 56.1 HV and 106.1 HV, respectively.
The presently disclosed gold alloy composition as described has a higher level of hardness compared to a conventional 23.16K gold alloy, which allows it to be formed into slim and complicated designs without breaking. The presently disclosed gold alloy composition additionally maintains physical characteristics (e.g., beautiful color, smooth surface) that are generally accepted in the gold market and the Thailand Office of the Consumer Protection Board (OCPB).
| Number | Date | Country | Kind |
|---|---|---|---|
| 1901002436 | Apr 2019 | TH | national |
