Patent Application
20080318076
Recently, numerous companies in the goldware processing sector, in response to the crisis currently affecting the traditional market of jewelry made with precious metals (gold, silver, platinum and palladium) and in an attempt to cater also for the lower price sectors of the market, have offered the public ornamental articles which are made with non-precious metal alloys, such as, for example, steel or brass, achieving overall a good commercial response.
This policy of offering the public low end prices therefore results in an increasingly widespread need in the sector to provide alloys which allow the production of ornamental articles which are low-cost, but nevertheless have aesthetic properties (shininess, colour, etc.) which are comparable to those of the articles obtained with precious metal alloys.
These inexpensive alloys are generally copper based, since this metal has a good corrosion resistance and, combined with opportune alloying elements, allows to produce easily workable alloys presenting a color similar to gold or, depending on the composition, to other precious metals color.
A non-precious metals alloy of this type, which presents color, tarnish resistance and mechanical properties that simulate gold, is disclosed in U.S. Pat. No. 5,599,406. The disclosed alloy consists in copper, aluminum and indium, as main ingredients, and contains not more than 3% by total weight of a precious metal.
Another example of an alloy for ornamental articles, with a golden color and a high corrosion resistance, is the precious bronze described in BE 1 011 190: the main constituents in this case are, apart from copper, tin, aluminum and yttrium.
Also patent JP 60 177141 discloses a golden copper alloy for producing ornamental articles, where workability, mechanical properties and corrosion resistance are improved by adding aluminum, iron and a noble metal.
All the cited patents refer to different kinds of copper alloys, that involve the formation of phases that can present different structures, depending on the composition, and that just simulate gold, or the precious metal in question, in color and behavior.
In a similar manner to that envisaged for jewelry made of precious metal alloys, the production of the ornamental articles made of non-precious metal alloys envisages various surface finishing operations, such as polishing, diamond-machining, barrel finishing and brushing and in some cases also plating with precious metals, typically gold and platinum. These processing operations which essentially have the purpose of improving the final aesthetic appearance and the commercial attractiveness of these articles may not, however, be too advanced or sophisticated in order to avoid increasing unduly the production costs.
Generally, therefore, these ornamental articles made of non-precious metal alloys have, as do nearly all low-cost jewelry products, a surface finish which is substantially inferior, when compared to that which can be obtained in jewelry made of precious metal alloys. These non-precious ornamental articles also tend to be subject to more pronounced corrosion compared with precious metal alloys and alloying element release phenomena which deteriorate further the surface appearance over time and may produce allergic reactions in users.
Differently, jewelry made with precious metal alloys is almost never subject to corrosion phenomena and, for the same surface finish, has a decidedly superior colour brilliance and shininess. These excellent qualities are due to the low (nanometric) surface roughness values and the low percentages of (nanometric) specific surface area which are typically encountered in alloys with high percentages of precious metals (gold, silver, platinum and palladium).
As is known, the nanometric surface roughness is a measurement of the surface state of a material and can be measured with the aid of atomic force microscopes. The low surface roughness values which can be measured in precious metal alloys (of the order of a few nm) are responsible for the superior shininess and colour brilliance of the jewelry obtained therefrom, compared to jewelry made of non-precious metal alloys, for the same surface finishing treatment.
The nanometric specific surface area is a measurement, on a nanometric level, of the surface porosity of a material and in the case of the precious metals is related to the well-known properties of catalysis, oxidation resistance and shininess of these metals. The low specific surface area percentages which can be found in precious metal alloys therefore account, at least partly, for the oxidation resistance and, above all, the corrosion resistance. This property is also particularly important from a production point of view since it allows the possibility of performing the surface finishing treatment of rough-processed jewelry using abrasive chemicals without the fear of damaging the end product.
As is well known, the abovementioned behaviour of the precious metal alloys is closely linked to the percentages of precious metals used. The greater the percentages of these metals present in the alloy, the more pronounced are the chemical and physical properties of these metals which are transferred to the said alloy.
Conventionally, however, it is known that there exist threshold percentages which are variable depending on the precious metal considered (typically 333/1000 for gold, 800/1000 for silver, 850/1000 for platinum and 500/1000 for palladium), below which the properties of the corresponding precious metal are not transferred extensively to the alloys and instead the chemical/physical properties of the other non-precious metal alloying elements (copper, zinc, etc.) present in the alloy) start to prevail in a decisive manner.
In the jewelry sector it is therefore considered that, below these percentages, it is no longer convenient to introduce precious metals into the alloy, since the final effect on the aesthetic appearance of the products would be of little significance, or even negligible.
In this situation the main object of the present invention is to provide an alloy for ornamental articles having aesthetic properties comparable to those of conventional precious metal alloys and at the same time production costs comparable to those of the non-precious metal alloys used to produce ornamental articles.
Another object of the present invention is to provide an alloy for ornamental articles which may be produced in an easy and low-cost manner.
These and other objects are all achieved by the alloy for ornamental articles according to the accompanying claims.
The technical features of the invention, in accordance with the abovementioned object, may be clearly understood from the contents of the claims reproduced below and the advantages thereof will emerge more clearly from the detailed description which follows, provided with reference to the accompanying tables, which refer to a purely exemplary and non-limiting embodiment, in which:
The alloy according to the present invention may be advantageously used in the jewelry industry in order to produce ornamental articles which are low cost and have at the same time properties of shininess and colour brilliance entirely comparable to those of jewelry made with precious metal alloys.
According to the invention, the alloy comprises a base of non-precious metals, that is a base of non-ferrous metals, mainly copper and zinc, and one or more precious metal alloying elements, the latter being present in an alloy, in combination or individually, with a content by weight chosen from the range of between 0.1/1000 and 100/1000.
The zinc is present in the alloy with a content by weight of between 10% and 35%, advantageously between 30% and 33%, while the precious metal alloying elements may be chosen from the group comprising gold, silver, platinum and palladium.
According to the invention, the content by weight of the precious metal alloying elements chosen from the range of between 0.1/1000 and 100/1000 produces main concentrations of the precious metal alloying elements in phase separation structures distributed around the particles of the crystal structure. Surprisingly the presence of zinc into the alloy promotes a segregation of the precious metal alloying elements by the grain boundary and it has been observed that this particular nanometric distribution of the precious metal alloying elements imparts to the alloy a shininess and a brilliance entirely comparable to those of precious metal alloys.
The zinc atoms, in fact, present an atomic radius similar to the copper atomic radius while the gold and the silver atoms have bigger atomic radius: due to this difference, the copper atoms are preferentially substituted for zinc atoms in the crystal structure, forming only one phase with face-centered cubic crystal structure and promoting the gold, or the precious metals, arrangement by the grain boundary.
Since the outer part of the grains that constitute the alloy is formed by the precious metal segregation, the whole alloy simulates the color and the behavior of the precious metals better than the known non-precious alloys.
The term “precious metal alloy” must be understood as meaning here an alloy having a content by weight of precious metal equal to or greater than threshold values, which, as already mentioned previously, are fixed for gold at 333/1000, for silver at 800/1000, for platinum at 850/1000 and for palladium at 500/1000.
As already mentioned above, these values are regarded conventionally as limit values for being able to define an alloy as precious, since below these values the properties of the corresponding precious metal are not transferred extensively to the alloys, while the chemical/physical properties of the other non-precious metal alloying elements (copper, zinc, etc.) present in the alloys prevail in a decisive manner.
Advantageously, the alloy according to the invention has a shininess and a brilliance which are closer to those of precious metal alloying elements than those of the non-precious metals which form the base thereof.
On the other hand it has been found that alloys based on non-precious metals, which have a precious metal content less than 0.1/1000 or in the range of between 100/1000 and the abovementioned threshold values (333/1000 for gold, 800/1000 for silver, 850/1000 for platinum and 500/1000 for palladium), do not have a prevalent concentration of the precious metal alloying elements in phase separation structures distributed around the particles of the base crystal structure and have a shininess and brilliance typical of the non-precious metals which form the base thereof.
Unexpectedly and in particular differently from that which was thought on the basis of the current state of the art in the sector, it was also noted that there exists for each precious metal (gold, silver, platinum and palladium) a limited range in which the efficiency with which the precious metal reaches aesthetic surface properties similar or comparable to those of precious metal alloys is higher.
Advantageously, in these limited ranges, a shininess is obtained for the alloy according to the invention which is greater than that which can instead be obtained with alloys produced according to the invention having a higher precious metal content.
In the case of gold, the abovementioned limited range lies substantially between 0.5/1000 and 10/1000, with the maximum efficiency situated around 1/1000.
In the case of silver, the limited range lies, instead, between 10/1000 and 100/1000, with the maximum efficiency situated between 10/1000 and 20/1000.
In the case of platinum, the limited range lies, instead, between 0.1/1000 and 5/1000, with the maximum efficiency situated around 0.5/1000.
In the case of palladium, the limited range lies, instead, between 0.2/1000 and 10/1000, with the maximum efficiency situated around 0.5/1000.
All this has been confirmed experimentally by measurements of the nanometric surface roughness and the nanometric specific surface area, performed with an atomic force microscope on samples produced with alloys according to the invention having different precious metal contents in the alloy. In fact, as already mentioned above, the shininess of an alloy may be determined indirectly from the values of its nanometric surface roughness and its nanometric specific surface area, considering that it increases with a reduction in these two parameters.
In greater detail, the behaviour of the alloys according to the invention having gold as a precious metal alloying element is illustrated by way of example in
In greater detail,
Comparing the sample values, it can be seen that the lower roughness values (and therefore higher shininess values) are found among the samples produced according to the invention, with a gold content of between 0.5/1000 and 10/1000. In particular, it can be seen that the sample with a gold content of 1/1000 has a minimum roughness value (6 nm) of the same order of magnitude as that measured for the reference sample with 300/1000 of gold (5 nm). The brass sample instead has a roughness value which is decidedly higher.
Therefore, as demonstrated by the data shown in
In any case, adding to the alloy a gold content less than 0.5/1000 down to 0.1/1000 or greater than 10/1000 up to 100/1000, the shininess of the alloy remains substantially high and comparable to that of the corresponding precious metal alloys, making it possible to achieve a high efficiency with which the gold in the alloy reaches aesthetic surface properties similar or comparable to those of these precious metal alloys. As already mentioned, this is due to the particular and prevalent nanometric distribution of the gold in phase separation structures around the particles of the base crystal structure.
On the other hand, in alloys with a gold content greater than 100/1000 there is found to be no improvement in the shininess such as to justify the increase in content of this metal. In other words, exceeding the content of 100/1000 reduces the efficiency with which the gold reaches aesthetic surface properties similar or comparable to those of the corresponding precious metal alloys. In this case, the alloy is no longer mainly distributed in the abovementioned phase separation structures.
The behaviour of the alloys according to the invention having silver as the precious metal alloying element is instead illustrated, for example, in
In greater detail,
Comparing the sample values, it can be seen that the lower roughness values (and therefore higher shininess values) are found among the samples produced according to the invention, with a silver content of between 10/1000 and 100/1000. In particular, it can be seen that the sample with a silver content of 20/1000 has a minimum roughness value (about 10 nm) equivalent to that measured for the reference sample with 800/1000 of silver. The sample made of brass has a roughness value which is decidedly higher (about 60 nm).
Therefore, as demonstrated by the data shown in
In any case, also adding to the alloy a silver content less than 10/1000 down to 0.1/1000, the shininess of the alloy remains substantially high and comparable to that of precious metal alloys with silver, making it possible to achieve a high efficiency with which the silver in the alloy reaches aesthetic surface properties similar or comparable to those of the corresponding precious metal alloys. As already mentioned, this is due to the particular and prevalent nanometric distribution of the silver in phase separation structures around the particles of the base crystal structure.
On the other hand, in alloys with a silver content greater than 100/1000 there is found to be no improvement in the shininess such as to justify the increase in content of this precious metal. In other words, exceeding the content of 100/1000 reduces the efficiency with which the silver reaches aesthetic surface properties similar or comparable to those of these precious metal alloys. In this case, the silver is no longer mainly distributed in the abovementioned phase separation structures.
The behaviour of the alloys according to the invention having platinum as the precious metal alloying element is illustrated by way of example in
In greater detail,
Comparing the various samples, it can be seen that the lower roughness values (and therefore higher shininess values) can be found among the samples produced according to the invention, with a platinum content of between 0.1/1000 and 5/1000. In particular, it can be seen that the sample with a platinum content of 0.5/1000 has a minimum roughness value (3 nm) equivalent to that measured for the reference sample with 850/1000 of platinum. The brass sample instead has a roughness value which is decidedly higher (60 nm).
In any case, as already mentioned, also adding to the alloy a platinum content greater than 5/1000 up to 100/1000, the shininess of the alloy remains substantially high and comparable to that of the corresponding precious metal alloys, making it possible to achieve a high efficiency with which the platinum in the alloy reaches aesthetic surface properties similar or comparable to those of these precious metal alloys. As already mentioned, this is due to the particular and prevalent nanometric distribution of the platinum in phase separation structures around the particles of the base crystal structure.
On the other hand, in alloys with a platinum content greater than 100/1000 there is found to be no improvement in the shininess such as to justify the increase in content of this metal. In other words, exceeding the content of 100/1000 reduces the efficiency with which the platinum reaches aesthetic surface properties similar or comparable to those of the corresponding precious metal alloys. In this case, the platinum is no longer mainly distributed in the abovementioned phase separation structures.
The behaviour of the alloys according to the invention having palladium as the precious metal alloying element is illustrated by way of example in
In greater detail,
Comparing the various samples, it can be seen that the lower roughness values (and therefore higher shininess values) are found among the samples produced according to the invention, with a palladium content of between 0.2/1000 and 10/1000. In particular, it can be seen that the sample with a palladium content of 0.5/1000 has a minimum roughness value (7 nm) equivalent to that measured for the reference sample with 500/1000 of palladium. The brass sample instead has a roughness value which is decidedly higher (60 nm).
In any case, as already mentioned, also adding to the alloy a palladium content less than 0.2/1000 down to 0.1/1000 and greater than 10/1000 up to 100/1000, the shininess of the alloy remains substantially high and comparable to that of the corresponding precious metal alloys, making it possible to achieve a high efficiency with which the palladium in the alloy reaches aesthetic surface properties similar or comparable to those of these precious metal alloys. As already mentioned, this is due to the particular and prevalent nanometric distribution of the palladium in phase separation structures around the particles of the base crystal structure.
On the other hand, in alloys with a palladium content greater than 100/1000 there is found to be no improvement in the shininess such as to justify the increase in content of this metal. In other words, exceeding the content of 100/1000 reduces the efficiency with which the palladium reaches aesthetic surface properties similar or comparable to those of the corresponding precious metal alloys. In this case, the palladium is no longer mainly distributed in the abovementioned phase separation structures.
Therefore, as demonstrated by the data shown in
As already mentioned, it was possible to observe that the precious metal alloying elements present in the alloy (gold, silver, platinum and palladium) with a content by weight chosen from the range of between 0.1/1000 and 100/1000 are concentrated mainly in phase separation structures distributed around the particles of the base crystal structure. This particular distribution of the alloying elements was not observed in alloys with a lower or higher content of precious metal alloying elements than the range of 0.1/1000 to 100/1000 and seems to account for the surprising progression measured for the roughness and surface area values upon variation in the content of precious metals in the alloy.
This particular and prevalent distribution of the precious metal alloying elements was determined as a result of observation, under an atomic force microscope (AFM), of samples of the alloy according to the invention.
By way of example,
In greater detail, in
In accordance with a particular constructional solution, the alloy may be made by introducing gold and silver as the precious metal alloying elements, with a gold/silver weight ratio ranging between 1/10 and 2/10. It was possible to observe that, for the same overall content of precious metals, the alloy thus obtained has substantially the same surface roughness values as alloys according to the invention having only gold or only silver as the precious metal alloying element.
In accordance with other constructional solutions not shown here, the alloy according to the invention envisages not only the combination of gold and silver, but also other different combinations of the precious metals mentioned, namely, gold, silver, platinum and palladium.
The alloy according to the invention allows the production of ornamental articles, such as, for example, necklaces, bracelets, rings, earrings, etc. which, for the same surface finish, have a final aesthetic appearance (shininess, brilliance of colours) entirely comparable to that of similar articles made with precious metal alloys. The cost of these articles, considering the very low content of precious metals, is instead comparable to that of articles made with conventional non-precious metal alloys.
Advantageously the use of the alloy according to the present invention is not limited solely to the jewelry sector, but is also applicable to other sectors, for example the sector of watches and clocks, giftware, clothing, shoes or leatherwear, which envisage the production of articles made entirely with precious or semi-precious metal alloys or provided with accessories, parts or inserts made with these alloys.
| Number | Date | Country | Kind |
|---|---|---|---|
| PD2005A000291 | Oct 2005 | IT | national |
The present application is a continuation-in-part of International Application PCT/IB06/02850, filed Oct. 4, 2006, which designated the United States, and which claimed the benefit of Italian application no. PD2005A000291, filed Oct. 10, 2005. The entire contents of both of the above-identified applications are hereby incorporated herein by reference. The present invention relates to alloys for ornamental articles. The alloy according to the present invention may be advantageously used in the jewelry industry for the production of ornamental articles to be proposed as a commercial alternative to conventional jewelry made with precious metal alloys.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/IB06/02850 | Oct 2006 | US |
| Child | 12100752 | US |
