FR2764906A1 - New eighteen and fourteen carat grey gold@ alloys - Google Patents

Abstract

A grey gold alloy, which is free from conventional whitening elements such as Ni, Pd, Ag and Co, has the composition (by wt.) (i) (in 18 carat form) 75-78% Au, 7-13% Mn and balance Cu; or (ii) (in 14 carat form) 58.5-59.5% Au, 7-20% Mn and balance Cu. Also claimed is production of the above alloy by mixing pure gold grains with a (preferably 50/50) copper/manganese master alloy and then adding the requisite quantity of copper to achieve the desired final composition.

Description

The present invention relates essentially to 18-white gold alloys

  and 14 carats for jewelry. More specifically, the present invention essentially relates to new 18 and 14-carat white gold alloys for jewelry without the currently known whitening elements which are mainly nickel, palladium, silver, as well as cobalt, especially when the latter is combined.

with manganese.

  Thus, according to a preferred characteristic of the invention, this new alloy of gray gold is nickel-free, palladium-free, silver-free and cobalt-free. The alloy according to the invention has the advantage of eliminating the risk of the appearance of an allergy caused by the nickel contained in most common quality gray gold alloys and

  to be less expensive than gray gold alloys containing palladium.

TECHNOLOGICAL BACKGROUND

  The fashion for gray gold alloys appeared in the years 1910-1920, at the same time as platinum alloys. Platinum was very expensive and its availability was greatly weakened by its use as a strategic metal for the industry. In addition, the legal title of platinum alloys is

  95% while that of gold is 75% by weight.

  We therefore sought to obtain a precious alloy based on gold, but of which

  the color would be as close as possible to that of platinum.

  The difficulty with 18 carat gold alloys containing about 75% by weight of gold is that the only remaining 25% of elements to be added must eliminate the yellow tint of the gold. Of all the elements tested, only two have been found to be extremely effective, nickel and palladium. Their whitening effect allows them to whiten the alloy without adding any other white element. We may cite for example the document CH-A-684 616 describing an alloy of this type. In this document, gray gold alloys containing 5.5 to 18% palladium and 2 to 12% manganese are described. Gray gold alloys containing palladium are more expensive because of the high price of this element and have a low hardness which makes them sensitive to wear. In addition, these alloys are not satisfactory in the context of the lost wax casting process which is widely used in jewelry, as results from the article by Ralph H. ATKINSON in the Revue Francçaise

  des Bijoutiers-Horlogers, n 220, February 1959, p. 40-44.

  In addition, gold alloys containing nickel are very difficult to work because they are sensitive to cracking. Then, the very widespread use of nickcl in alloys constituting ornaments worn next to the skin has led to allergic sensitization to this element. Today about 10% of women and 2% of men have a reaction to nickel. This state of affairs will lead to a progressive ban on nickel in objects intended to be in prolonged contact with the skin. This allergy phenomenon is described by

  example in document CH-A-684 616 on page 3, lines 21 to 25 in particular.

  Gold and nickel alloys are known to be hard and their development

difficult.

  Examples of white or gray gold alloy containing silver are, for example

  example, described in document DE-C-43 20 928.

  They often contain zinc additions to improve their

  flowability as in DE-C-43 20 928.

  On the other hand, palladium gray gold alloys generally also contain silver as in CH-A-684 616, see examples C, D and 1 in the table on page 5. These elements being miscible, the hardness dc the alloy is weak. Often it is necessary to add other alloying elements to achieve the desired characteristics. Also, as mentioned above, the

  palladium is an expensive item.

  The document CH-A-684 616 is another good example of a gold alloy containing palladium in place of nickel, with manganese, manganese alone not having a sufficient whitening effect. There is another whitening element, usually silver. If another whitening element such as cobalt is added, the alloy becomes slightly magnetic. Before refining, the workshop waste goes through a first sorting with the magnet which must eliminate all the ferrous particles coming from the wear of the tools. If the alloy is magnetic,

  gold alloy filings will leave the circuit with ferrous waste.

OBJECT OF THE INVENTION

  Thus, the present invention aims to provide new gold alloys of gray color, either 14 or 18 carats, essentially without

  classic whitening element such as nickel, palladium, silver, cobalt.

  The main object of the present invention is also to provide a new alloy of white gold, in particular dc 14 or 18 carats, without conventional whitening element such as nickel, palladium, silver, cobalt, having a very good

  flowability as well as high hardness resulting in good abrasion resistance.

  The invention also aims to solve the new technical problems stated above by providing a gray gold alloy solution which eliminates any cause of skin reaction during prolonged contact with the skin,

  thus allowing its use in jewelry.

  The present invention also aims to solve the new technical problems stated above by providing a gray gold alloy solution which is capable of being used in the context of the lost wax casting process, an ancestral process which is advantageously used for the manufacture of jewelry, an alloy being usable in this technique only when its flowability is satisfactory.

  DETAILED DESCRIPTION OF THE INVENTION

  In the context of the invention, it has been discovered, completely unexpectedly for a person skilled in the art, that all of these stated technical problems were resolved by the supply of a gray gold alloy essentially without a conventional whitening element. such as nickel, palladium, silver and cobalt, characterized in that it essentially consists, in addition to gold, of copper and of manganese, according to the following proportions in percentage by weight: a) for an alloy of gold 18 carats: - gold .............................................. .......

  ............ 75-78 - manganese ................................. ........... DTD: .......... 7-13 - copper balance at ................... .................... DTD: ........ 100; or b) 14 carat gold having the following composition: - gold ... DTD: ................................ ................................ 58.5- 59.5 - manganese ......... ............................................ 7 to 20..DTD : - copper balance to ............................................. ........ 100.

  According to a preferred embodiment, the amount of manganese for an 18-carat gold alloy is between 7 and 13, better still between 10 and 13% by weight, while for a 14-carat alloy, the amount of manganese is preferably

  between 10 and less than 20% by weight.

  According to a more preferred embodiment, a gray gold alloy according to the present invention is chosen from the group consisting, in percentage by weight, of: a) Au75-Cul5-MnlO; b) Au75-Cul2-Mnl3; c) Au75Cul4-Mnll; d) Au75-Cul8-Mn7; e) Au75-Cul7-Mn8; f) Au75-Cul6-Mn9; g) Au75-Cul5-Mn9.9-IrO, 1 and as regards the 14-carat white gold alloys: h) Au58.5-Cu30-Mnll, 5; i) Au58.5-Cu21, 5-Mn2O;

j) Au58.5-Cu30-Mnll, 4-IrO, 1.

  The presently more preferred gray gold alloy of the present invention is an 18 carat white gold alloy consisting of Au75-Cul5-MnlO. This preferred alloy has a melting interval considered to be the best,

  namely between about 920 and 940 C.

  According to an advantageous embodiment, the alloy according to the invention can contain from 0 to 2% by weight of iridium (Ir) and / or Ruthenium (Ru), the

  presence helps to refine the metallurgical structure.

  According to a second aspect, the present invention also relates to the use of these new alloys for the manufacture of jewelry, thanks to their compatibility considered perfect with the skin even during prolonged contact with the skin because these alloys do not seem to reveal or create no detectable skin allergies. According to a third aspect, the present invention also relates to a process for the manufacture of these alloys according to which pure gold shot is mixed with a mother alloy of copper and manganese and by adding the quantity of copper necessary to reach the final composition. wanted. Advantageously, the mother alloy of copper and manganese comprises substantially equivalent amounts of copper and manganese, that is to say that it is about 50% of copper and

  about 50% of manganese, by weight.

  In the context of this process, the melting is advantageously done in a crucible, preferably of zirconia, and the ingot is poured into an ingot mold which is

  preferably copper doped with chromium.

  According to an advantageous embodiment of the process according to the invention, the melting will preferably take place under a protective atmosphere due to the reactivity

  manganese with oxygen from the air.

  The invention will also be better understood with reference to the embodiments given below simply by way of illustration and which therefore cannot in any way limit the scope of the invention. In the examples, all the percentages are given by weight, unless otherwise indicated. In addition, the temperature is the ambient temperature or is expressed in degrees Celsius and the

  pressure is atmospheric pressure, unless otherwise indicated.

  On the other hand, all the examples form an integral part of the invention,

  as well as any characteristic of the present description including the examples, which

  appears to be new vis-à-vis any prior art, and this in the form of a general characteristic and not of a particular characteristic of

The example.

Examples according to the invention

  The various alloys which are the subject of examples 1 to 8 are prepared below.

  after implementing the manufacturing method according to the invention described above, namely: - the alloys are melted by mixing pure gold shot with a mother alloy here in about 50% copper and about 50% of manganese and adding the amount of copper necessary to achieve the desired final composition. The melting takes place on a zirconia crucible and the ingot is poured into a copper ingot mold doped with chromium. The fusion takes place under a protective atmosphere

  due to the reactivity of manganese with oxygen in the air.

  According to this process, the production of alloys 1 to 8 is carried out.

in Examples 1 to 8 below.

  Example 1 An 18-carat alloy is made having the following composition: Au75-CulS-Mn10. Example 2 We manufacture an 18-carat alloy, with the following composition: Au75-Cu12-Mn13. Example 3 The manufacture of an 18-carat alloy is made, with the following composition: Au75-Cul4-Mnll.

Example 4

  We manufacture an 18-carat alloy, with the following composition: Au75-Cul8-Mn7.

Example 5

  We manufacture an 18-carat alloy, with the following composition: Au75-Cu17-Mn8.

Example 6

  We manufacture an 18-carat alloy, with the following composition: Au75-Cul6-Mn9. Example 7 We manufacture a 14-carat alloy, with the following composition:

Au58.5-Cu30-Mnl 1.5.

Example 8

  We manufacture a 14-carat alloy, with the following composition: Au58.5-Cu21.5-Mn20. It should be noted that for the 18-carat alloys that are the subject of Examples 1 to 6, there is little difference with the alloys whose manganese content is centered on%. Above 13% manganese, the malleability of the alloy decreases. In

  furthermore, below 8%, the quality of the gray or white color deteriorates.

  Regarding the 14 carat alloy, the one containing 20%

  manganese is more fragile and therefore not appreciated for application in jewelry.

  As mentioned above, the preferred alloy is alloy 1 of Example i having the composition Au75-Cul5-MnlO. The color of this preferred alloy is measured according to the CIELAB system using a Minolta spectrocolorimeter and the results obtained are the following: L * = 82.05, a * = 3.16, b * = 8.19. By comparison, the white gold alloy containing palladium

  commonly marketed, having the following composition: Au75-Pdl2.5-

  Cu9,5-Ag3, presents the following values of colors according to the same spectrocolorimeter:

L * 81.83, a * = 2.48, b * = 7.44.

  The colors of these two alloys can hardly be distinguished with the naked eye. Furthermore, the melting interval of the alloy 1 of Example 1 according to the invention is 920-940 C which is a melting interval the

  more suitable for melting using the lost wax process.

  The mechanical characteristics of the alloy 1 according to the invention of Example 1 are as follows: Rm = breaking strength, Re = elastic limit, A = elongation, in the raw casting state: alloy hardness HV5 Rm ( MPa) Rc (MPa) A% Example 1 148 333 257 34 Example 6 151 308 208 39 Example 7 134 311 193 48 in the annealed condition 30 minutes at 700 C and water-treated: alloy hardness HV5 | Rm (MPa) Re (MPa) A% Example 1 191 754 483 32 Example 6 168 595 320 53 Example 7 182 704 378 44 hardened by 100% by rolling: alloy hardness HV5 Rm (MPa) Re (MPa) A% Example 1 317 1036 967 0.5 Example 6 296 866 800 0.5 Example 7 286 956 950 3 work hardened by 400% by rolling: alloy hardness HV5 Rm (MPa) Re (MPa) A% Example 1 345 1097 1000 0 Example 6 332 879 871 0.4 Example 7 345 broken broken 0.2 Naturally, the invention includes all the means constituting

  technical equivalents of the means described and their various combinations.

Claims (10)

  1. Gray gold alloy cssentially without conventional whitening element such as nickel, palladium, silver and cobalt, characterized in that it essentially consists, in addition to gold, copper and manganese, according to the following proportions in percentage by weight: a) for an 18 carat gold alloy: - gold .................................. ...........   .................... 75-78 - manganese ......................... .......... CLMF: ................... 7-13 - copper balance at ........... ..... CLMF: ............................... 100; or b) 14 carat gold having the following composition: - gold ..................................... ........... .CLMF: .................. 58.5-59.5 manganese .......... ........................ CLMF: ................... 7 to 20 .. CLMF: - copper balance at ............................................ ......... 100.   2. A white gold alloy according to claim 1, characterized in that the amount of manganese for an 18 carat gold alloy is between 7 and 13, better still between 10 and 13%, by weight, while for an alloy 14 carats, the quantity   manganese is preferably between 10 ct less than 20% by weight.   3. Alloy according to claim 1 or 2, characterized in that it is chosen from the group consisting, in percentage by weight, of: a) Au75Cul5-Mnl0; b) Au75-Cul2-Mnl3; c) Au75-Cul4-Mnll; d) Au75-Cul8-Mn7; e) Au75-Cul7-Mn8; f) Au75-Cu16-Mn9; g) Au75-CulS-Mn9.9-IrO, 1; and with regard to 14-carat white gold alloys: h) Au58.5-Cu30-Mnll, 5; i) Au58.5-Cu21.5-Mn20; j) Au58.5-Cu30-Mnll, 4-IrO, 1.   4. Alloy according to one of the preceding claims, characterized in that   that it is an 18-carat white gold alloy consisting of Au75-Cul5MnlO, advantageously having a melting interval of between approximately 920 and 940 C.   5. Alloy according to one of the preceding claims, characterized in that   that it comprises from 0 to 2% by weight of iridium and / or Ruthenium.   6. Use of the alloy according to any one of claims 1 to   , for the manufacture of jewelry. 7. A method of manufacturing an alloy according to any one of   Claims 1 to 5, according to which pure gold shot is mixed with an alloy   mother of copper and manganese, and by adding the quantity of copper necessary to reach the desired final composition, the copper thus constituting the balance of the alloy 8. Method according to claim 7, characterized in that the mother alloy of copper and manganese comprises substantially equivalent amounts of copper and manganese, ie approximately 50% of copper and approximately 50% of manganese, by weight.   9. Method according to claim 7 or 8, characterized in that the melting takes place in a crucible, preferably of zirconia, and the ingot is poured into an ingot mold   which is preferably copper doped with chromium.   10. Method according to one of claims 7 to 9, characterized in that   fusion takes place under a protective atmosphere due to the reactivity of manganese with the oxygen in the air.