FR2791363A1 - SILVER ALLOY AND DECORATIVE OBJECT CONTAINING IT - Google Patents

Abstract

Disclosed is a silver alloy having a pink color and excellent corrosion resistance, the main component of which is silver and which can be a ternary Ag-Cu-Pd alloy, a quaternary Ag-Cu-Pd alloy -In or a ternary Ag-Cu-Au alloy, and which has a composition domain delimited by segments connecting the points a, b, c, d and e in the corresponding composition diagram, as well as a decorative object comprising this alloy.

Description

The present invention relates to a silver alloy and a decorative object

  the container and, in particular, a silver alloy used for decorative objects such as watch cases, watch straps, necklaces, earrings, rings, brooches, spectacle frames, lighters and buttons, in particular. Silver and silver alloys have been widely used since Antiquity in the manufacture of decorative objects. Among the silver alloys, an alloy containing 92.5% by mass of silver is known, the rest being constituted by copper, that is to say Stirling silver, and alloys containing at least 80% by mass of silver such as the alloy containing 90% by mass of silver, the remainder being made up of copper (that is to say silver for coins) and an alloy containing 95.8% of silver, the rest being copper (i.e.

Britannia money).

  Silver does not react with oxygen in the normal state. However, it reacts easily with hydrogen sulfide and sulfur dioxide, a reaction which leads to the appearance of a black coating of silver sulfide on the silver surface, which reduces the decorative effect. To avoid this sulfurization reaction, an organic compound which strongly combines with the silver is applied to the surface of the silver, or a metal or silver plating is applied.

  rhodium, or a silver alloy is formed.

  When adding up to about 14% by mass of copper to the silver to form an alloy, it is possible to improve the mechanical characteristics while retaining the color of the silver, and to improve the casting properties. because the melting point is lowered. However, it is not possible to improve the resistance to sulphurization, and the resistance to corrosion is degraded because exceeding the solubility limit of copper in silver in solid solution can lead to an eutectoid. two-phase which constitutes a local stack so

  that the silver alloy is discolored.

  Furthermore, it is known that the silver-palladium, silver-platinum and silver-gold alloys make it possible to improve the resistance to sulfurization. To completely prevent sulfurization of silver in these alloys, it is necessary to add more than 40% by mass of palladium, more than 60% by mass of platinum or more than% by mass of gold. This results in increased costs and an increase in

  melting point which deteriorates the casting properties.

  For several years now, we have wanted decorative objects based on noble metals to present a variety of colors. Yellow or rose gold is commercially accepted while there is a demand for alloys

  silver with different colors for decoration.

  The object of the present invention is to provide a silver alloy which has

  beautiful color and excellent corrosion resistance.

  The present invention also aims to provide an alloy

  silver with excellent casting properties.

  Finally, the present invention also aims to provide objects

  decorative with excellent decorative properties.

  To achieve these goals, it has been found that it is possible to prevent a silver alloy from forming a local battery under normal living conditions (work, sleep, bath, sports, in particular) by adding a noble metal (palladium , platinum or gold) to a two-phase eutectic crystal composition which is obtained by adding copper to silver, and that the addition of indium makes it possible to significantly improve the resistance to sulphurization, which leads to a beautiful

  pink silver alloy with further improved casting properties.

  More specifically, according to the present invention, there is provided a silver alloy comprising 40 to 85% by mass of silver (Ag) as the main component, 12 to 48% by mass of copper (Cu) and 3 to 20 % by mass of palladium (Pd). This silver alloy can also contain at most 10% by mass of

  platinum (Pt) and / or at most 20% by mass of gold (Au).

  Among these components, silver is the main component and copper is a component which gives a pink color. Palladium, platinum and gold are

  components that prevent training in ordinary living conditions.

  Platinum also improves resistance to sulfurization and gold strengthens the pink color. According to the present invention, there is also provided a silver alloy

  which is obtained by adding indium to a silver-copper-palladium alloy.

  More specifically, this silver alloy comprises 40 to 75% by mass of silver (Ag) as main component, 12 to 48% by mass of copper (Cu), 3 to 15% in

  mass of palladium (Pd) and 0.5 to 15% by mass of indium (In).

  This alloy can also contain at most 10% by mass of platinum and / or

not more than 20% by mass of gold.

  Indium significantly improves resistance to sulfurization and

  also greatly improves the casting properties.

  According to the present invention, there is also provided a silver alloy, the main component of which is silver and which contains copper and gold, and which has a composition range (units% by mass) delimited by segments. on the right connecting the following points in a composition diagram: (a): (X = 79, Y = 13, Z = 8); (b): (X = 47, Y = 13, Z = 40); (c): (X = 40, Y = 20, Z = 40); (d): (X = 33.3, Y = 33.3, Z = 33.3); and (e) (X = 46, Y = 46, Z = 8),

  o X is silver, Y is copper and Z is gold (X + Y + Z = 100).

  l It is possible to use these silver alloys to produce decorative objects such as watch cases, watch straps, necklaces, earrings, rings, brooches, spectacle frames, lighters , buttons, tableware, candle holders and trophies,

especially.

  Other objects and advantages of the present invention will become apparent

  better on reading the detailed description which follows and refers to the attached drawing

  in which: the single figure is a diagram representing a composition domain of a silver alloy comprising silver, copper and gold, according to

the present invention.

  A silver alloy according to the invention has a composition range which comprises 40 to 85% by mass of silver as the main component, 12 to 48%

  by mass of copper and 3 to 20% by mass of palladium.

  To obtain such a range of composition, silver is added in an amount of 40 to 85% by mass and copper in an amount of 12 to 48% by mass. Below 12% by mass, the color of silver is accentuated and the color pink does not appear. On the other hand, above 48% by mass, copper becomes the component

  main because the minimum amount of palladium is 3% by mass.

  Palladium is added in an amount of 3 to 20% by mass. Below 3% by mass, it is impossible to prevent the formation of a local battery under ordinary living conditions, and it is not possible to obtain corrosion resistance. On the other hand, above 20% by mass, it is not possible to obtain

a pink color.

  Platinum silver (Pt) may not be added to this silver alloy in an amount not exceeding 10% by mass and / or gold (Au) in an amount not exceeding

% by mass.

  The addition of Pt makes it possible not only to prevent the silver alloy from forming a local cell but also to improve the resistance to sulfurization. At-

  above 10% by mass, the pink color disappears.

  Gold is added not only to prevent the silver alloy from forming a local pile but also to give it a pink color. Beyond

  % by mass, an accentuated yellow color appears and the pink color disappears.

  In these alloys, silver is always the main component.

  A silver alloy according to the present invention which is obtained by adding indium to the above compositions has a composition range which comprises 40 to 75% by mass of silver as main component, 12 to 48 % by mass of copper, 3 to 15% by mass of palladium and 0.5 to 15% by mass

indium (In).

  To obtain this range of composition, silver is added at a rate of 75% by mass as the main component. When the quantities of copper and palladium are outside the above range, the

  same disadvantages as in the silver-copper-palladium alloy.

  Indium is added in an amount of 0.5 to 15% by mass. This addition of indium significantly improves the resistance to sulfurization. Below 0.5% by mass, the resistance to sulfurization is not improved at all and above .0% by mass the hardness is improved (150 in Vickers hardness), but it is not possible to carry out further processing. The addition of indium improves the casting properties, probably because the fluidity during melting is increased. A silver alloy according to the present invention which is constituted by a ternary silver-copper-gold alloy will now be described with reference to the single figure. As shown in the figure, the silver-copper-gold ternary alloy according to the present invention has a composition domain delimited by the segments connecting the points (a) to (e) and satisfying the condition X + Y + Z = 100 where X is

  silver, Y is copper and Z is gold.

  The region situated under the segment a-e in FIG. 1 is a region in which the quantity of gold contained in the alloy is less than 8% by mass and the corresponding alloy has a low resistance to corrosion. Thus, to obtain a higher corrosion resistance, it is necessary to have a composition located in a region above the segment a-e. In Figure 1, the segment d-e indicates a mass ratio of silver to copper from 1 to 1, and the side to the left of this segment is a region in which the main component is copper. Therefore, to obtain an alloy whose main component is silver, it is necessary to use a composition located to the right of the segment d-e. In Figure 1, the color of the resulting alloy is the color of silver in a region above the segment ab, which turns yellow green above the segment bc and which turns yellow above the cd segment. Thus, an alloy of pink color is obtained when a composition located in a region is used

  below the broken line a-b-c-d.

  To obtain the composition range mentioned above, the copper is added in an amount of 13 to 46% by mass. Below 13% by mass, the color of the silver is enhanced and a pink color does not appear. Beyond 46% by mass, copper becomes the main component because the minimum quantity

of gold is 8% by mass.

  Gold is added in an amount of 8 to 40% by mass. Below 8% by mass, it is not possible to prevent the silver alloy from forming a local battery under ordinary conditions of life, and no resistance to it is obtained.

  corrosion. Above 40% by mass, the gold gives the alloy a yellow color.

  Thus, the region in which copper is present in lesser quantity corresponds

  to a yellow green color without appearing a pink color.

  The silver alloy according to the present invention is subjected to a casting process, for example a conventional lost wax casting process, to obtain various decorative objects such as rings, pendants, necklaces

  and earrings, in particular.

  The present invention will now be illustrated in more detail.

  specifies by means of the following nonlimiting examples.

Example 1

  Silver, copper, palladium, platinum and gold were mixed in different amounts shown in the following table 1 to prepare an alloy

  which was melted at a temperature of around 1000 C, poured and polished.

  We then examined its color, hardness and corrosion resistance to

  obtain the results presented in Table 1 below.

  Its color was evaluated with the naked eye to examine whether it appeared a pink coloration in comparison with Stirling silver. The samples for which a pink coloration was more noticeable than for Stirling silver have been designated by the symbol "O" and by the symbol "X" those samples for which no pink coloration has been identified. The hardness of the alloy was measured using a Vickers hardness micro-meter. In addition, its resistance to corrosion was evaluated by melting it at a temperature of 1000 C and pouring it into a semicircular ring which was then polished. After having had this ring worn for several months by several volunteers under ordinary living conditions (work, sleep, bath, sports, in particular), we checked with the naked eye, the presence or absence of discoloration of the following way: the symbol "" indicates the samples not undergoing discoloration or blackening, the symbol "O" the samples exhibiting slight discoloration and slight blackening and by "X" the samples exhibiting discoloration and blackening. In Table 1 below, the symbol "X" associated with the total evaluation indicates a

comparative example.

Table I

  Sample Composition (% by mass) Evaluation no Ag Cu Pd Pt In Color Hardness Total corrosion resistance 1 39.5 39.5 21.0 - - X (silver) 110 O X

2 40.0 40.0 20.0 - - O 115 O O

3 50.0 45.0 5.0 - - O 102 O O

4 49.0 48.0 3.0 - - O 106 O O

50.0 48.0 2.0 - - O 110 X X

6 60.0 36.0 4.0 - - O 103 O O

7 70.0 26.0 4.0 - - O 106 O O

8 75.0 22.0 3.0 - - O 100 O O

9 80.0 17.0 3.0 - - O 96 O O

85.0 12.0 3.0 - - O 95 O O

  1 1 86.0 11.0 3.0 - - X (silver) 92 O X 12 41.0 39.0 19.5 0.5 - O 100 O

13 50.0 44.0 3.0 3.0 - O 102 0

14 50.0 38.0 4.0 8.0 - O 106 O 0

45.0 40.0 5.0 11.0 - O 11 0 O

  Table 1 (continued) Sample Composition (% by mass) Evaluation no Ag Cu Pd Pt Au Color Hardness Total corrosion resistance 16 43.0 40.0 6.0 11.0 X (silver) 98 O X

17 60.0 35.5 3.0 - 0.5 O 102 O O

18 50.0 42.0 3.0 - 5.0 100 O O

19 50.0 37.0 3.0 - 10.0 106 O O

50.0 32.0 3.0 - 15.0 101 O O

21 50.0 27.0 3.0 - 20.0 O 110 O O

  22 50.0 22.0 3.0 - 25.0 X (yellow) 115 O X 23 50.0 26.0 3.0 - 21.0 X (yellow) 115 O X

24 50.0 41.0 3.0 3.0 3.0 O 110 O O

50.0 36.0 4.0 5.0 5.0 O 120 O O

26 60.0 25.0 4.0 1.0 10.0 O 112 O O

27 70.0 25.0 4.0 0.5 0.5 O 108 O O

  28 50.0 20.0 10.0 0.5 19.5 O 106 O O

29 40.0 30.0 5.0 2.0 13.0 O 108 O O

60.0 32.0 4.0 2.0 2.0 O 100 O O

  In Table 1, it can be seen from samples 1 to 11 that an appropriate silver concentration range is 40 to 85% by mass, i.e. samples 1 and 2 show poor coloration

  39.5% by mass and that no color appears below 40% by mass.

  Samples 10 and 11 show that the coloration is 85% satisfactory in

  mass but poor at 86% by mass.

  It can also be seen from samples 1 to 11 that a suitable concentration range for copper is 12 to 48% by mass, that is, samples 10 and 11 show that the coloring is satisfactory. at 12% by mass but poor at 11% by mass. Sample 4 shows that the coloration is satisfactory up to 48% by mass. In reality, this value constitutes a limit because, beyond 48% by mass, copper becomes the main component. It can also be seen from samples 1 to 11 that an appropriate concentration range for palladium is 3 to 20% by mass. Other

  said, samples 4 and 5 show that at least 3% by mass is necessary.

  Sample 2 shows that the maximum quantity is 20% by mass because,

  beyond 20% by mass, a pink color does not appear.

  We can see from samples n 12 to 16 that a domain of

  concentration suitable for platinum is less than or equal to 10% by mass.

  In other words, although it is possible to obtain a satisfactory silver alloy in the absence of Pt, as in samples 1 to 11, the resistance to sulphurization is improved by the addition of Pt. note that above 10% in

mass, the pink color decreases.

  It can be seen from samples 17 to 30 that a concentration range suitable for gold is less than or equal to 20% by mass. In other words, although a satisfactory silver alloy is obtained in the absence of Au, as in samples 1 to 11, the pink color is accentuated by the addition of gold. It should be noted that above 20% by mass, a yellowish color is accentuated and that

the pink color disappears.

Example 2

  Silver alloys were prepared in the same manner as in Example I except that the amounts of silver, copper, palladium, indium, platinum and gold were changed. as shown in Table 2 below. Then their color, hardness, casting properties and corrosion resistance were examined. Table 2 below shows the results obtained. The color, hardness and corrosion resistance evaluations were carried out in the same manner as in Example 1. The casting properties were evaluated by melting the alloys at a temperature of about

  1000 C and pouring them into a semi-circular ring which is then polished.

  The presence of casting cavities was visually examined, and the symbol "" was assigned to the samples forming very few cavities, the symbol "O" to the samples forming little cavities and the symbol "X" to the samples forming

many cavities.

Table 2

  Sample Composition (% by mass) Evaluation n Ag Cu Pd In Pt At Color Hardness Resistance to Total Properties corrosion corrosion 31 39.5 39.5 16.0 5.0 - - X (silver) 115 X

32 40.0 40.0 15.0 5.0 - - O 114 0

  33 50.0 45.0 4.5 5.0 - - O 106 OE) 0

  34 48.0 48.0 3.0 1.0 - - O 106 O O O

48.5 48.0 2.5 1.0 - 0O 110 X O X

  36 60.0 35.0 4.0 1.0 - - O 104 O O O

  37 70.0 25.5 4.0 0.5 - - O 108 O O O0

38 70.0 25.5 4.5 0 - - O 98 O X X

  39 75.0 21.5 3.0 0.5 - - O 100 O O O

  76.0 20.5 3.0 0.5 - - X (silver) 96 O O X

  41 75.0 17.0 5.0 3.0 - - O 108 O O O

42 75.0 12.0 8.0 5.0 - - O 113 (O

  43 75.0 11.0 9.0 5.0 - - X (silver) 117 X

  44 60.0 20.0 10.0 10.0 - - O 132 OE) O

60.0 20.0 5.0 15.0 - - O 144 O0

  46 60.0 20.0 4.0 16.0 - - O 151 S I X

  47 60.0 31.5 5.0 3.0 0.5 - O 110 0 0

  Table 2 (continued) Sample Composition (% by mass) Evaluation n Ag Cu Pd In Pt In Color Hardness Resistance to Properties of Total corrosion corrosion

  48 60.0 31.0 4.0 2.0 3.0 - O 104 O O

  49 50.0 36.0 4.0 2.0 8.0 - O 105 O O

50.0 35.0 3.0 2.0 10.0 - O 98 O O

  51 50.0 35.0 3.0 1.0 11.0 - X (silver) 100 O X

  52 60.0 31.5 5.0 3.0 - 0.5 E) 112 O O O

  53 50.0 37.0 5.0 3.0 - 5.0 111 O O O

  54 50.0 34.0 4.0 2.0 - 10.0 108 O O O 50.0 29.0 4.0 2.0 - 15.0 104 O O O

  56 45.0 30.0 3.0 2.0 - 20.0 O 106 O O O

  57 45.0 29.0 3.0 2.0 - 21.0 X (yellow) 101 O O X

  58 50.0 35.0 5.0 3.0 3.0 3.0 O 109 O O

  59 50.0 33.0 4.0 3.0 5.0 5.0 O 120 O O

60.0 31.0 5.0 3.0 0.5 0.5 O 104 O O

  61 40.0 32.0 5.0 3.0 0.5 19.5 O 108 O O

  62 50.0 30.0 3.0 2.0 2.0 13.0 O 109 E) O O

  63 50.0 31.5 5.0 3.0 10.0 0.5 O 118 O O

  64 50.0 28.0 3.0 3.0 8.0 8.0 O 122 O O

  It can be seen in Table 2, from samples Nos. 31 to 46, that a suitable concentration range for silver is 40.0 to 75.0% by mass. In other words, samples no. 31 and 32 show that the coloration is poor at 39.5% by mass and that no coloration appears below 40% by mass. Samples 39 and 40 show that the coloration is

  satisfactory at 75% by mass but poor at 76% by mass.

  It can be seen from samples 31 to 46 that an appropriate concentration range for copper is 12.0 to 48.0% by mass. In other words, samples no 42 and 43 show that the coloration is satisfactory at 12% by mass but poor at 11% by mass. Sample 34 shows that the coloration is satisfactory up to 48% by mass. In reality, this value constitutes a limit because, beyond 48% by mass, copper becomes the main component. We can see from samples n 31 to 46 that a domain of

  suitable concentration for palladium is 3.0 to 15.0% by mass.

  In other words, samples 34 and 35 show that a minimum quantity of 3.0% by mass is necessary. Samples 31 and 32 show that the maximum amount is 15.0% by mass and that no color appears

pink above 15.0% by mass.

  It can be seen from samples 31 to 46 that an appropriate concentration range for indium is 0.5 to 15.0% by mass. In other words, samples 37 and 38 show that the casting properties are clearly poor in the absence of indium. Samples 45 and 46 show that beyond 15.0% by mass, the hardness is too high, which leads to

  adverse effects regarding further treatment.

  In the case where platinum is added, it can be seen from samples Nos. 47 to 51 that an appropriate concentration range is at most 10.0% by mass. In other words, although a satisfactory silver alloy can be obtained in the absence of platinum as can be seen from samples 31 to 46, it has been found that the addition of platinum improves the resistance to sulfurization. He is at

  note that beyond 10% by mass, the pink color is reduced.

  If we add gold, we see from the samples

  n 52 to 57 that a concentration range of 0 to 20% by mass is appropriate.

  In other words, although a satisfactory silver alloy can be obtained in the absence of gold, as shown in samples no. 31 to 46, it has been found that the addition of gold accentuates the pink color. It should be noted that above 20% in

  mass, a yellowish color is accentuated and the pink color disappears.

  The addition of indium considerably improves the resistance to sulfurization, as shown in Table 2, and therefore has an effect greater than or equal to the addition of platinum. Regarding the casting properties, there appear fewer casting cavities due to the improved flowability. So,

  the addition of indium makes it easier to obtain a satisfactory molded object.

Example 3

  Silver alloys were prepared in the same manner as in Example 1, except that the quantities of silver, copper and gold were modified

  as shown in Table 3 below.

Table 3

  Composition (% by mass) Evaluation Sample Ag Cu Au Color Resistance to corrosion

50.0 43.0 7.0 O X

66 50.0 42.0 8.0 O O

67 46.0 46.0 8.0 O O

68 40.0 40.0 20.0 O O

69 33.3 33.3 33.3 O O

50.0 25.0 25.0 O O

71 74.0 13.0 13.0 O O

72 80.0 10.0 10.0 X (silver) O

73 60.0 20.0 20.0 O O

74 72.0 13.0 15.0 O O

  75.0 10.0 15.0 X (silver) O 76 70.0 10.0 20.0 X (silver) O 77 65.0 10.0 25.0 X (silver) O 78 60.0 10, 0 30.0 X (yellowish green) O

79 57.0 13.0 30.0 O O

62.0 30.0 8.0 O O

81 79.0 13.0 8.0 O O

82 80.0 13.0 7.0 X (silver) X

83 63.0 30.0 7.0 O X

84 55.0 25.0 20.0 O O

50.0 13.0 37.0 O O

  86 50.0 10.0 40.0 X (yellowish green) O

87 46.7 20.0 33.3 O O

  88 43.5 23.0 43.5 X (yellow) O As shown in Table 3, when the quantity of gold is less than 8% by mass (as in the case of samples no 65, 82 and 83 ), the corrosion resistance is poor. When the compositions are located in a region above the broken line abcd in the diagram of FIG. 1 (as is the case of samples 72, 75, 76, 77, 78, 86 and 88), he does not appear

no pink color.

  On the contrary, the range of composition delimited by the segments connecting the points a, b, c, d and e in the diagram of FIG. 1 makes it possible to obtain a pink color and a higher resistance to corrosion.

Claims (8)

  1. A silver alloy characterized in that it comprises 40 to 85% by mass of silver (Ag) as main component, 12 to 48% by mass of   copper (Cu) and 3 to 20% by mass of palladium (Pd).   2. Silver alloy according to claim 1, characterized in that it   contains platinum (Pt) in an amount at most equal to 10% by mass.   3. Silver alloy according to any one of claims I and 2, characterized in that it contains gold (Au) in an amount at most equal to 20% by mass. 4. Silver alloy characterized in that it comprises 40 to 75% by mass of silver (Ag) as main component, 12 to 48% by mass of copper (Cu), 3 to 15% by mass of palladium (Pd) and 0.5 to 15% by mass of indium (In).   5. Silver alloy according to claim 4, characterized in that it   contains platinum (Pt) in an amount at most equal to 10% by mass.   6. A silver alloy according to any one of claims 4 and 5,   characterized in that it contains gold (Au) in an amount at most equal to 20% in mass.   7. Silver alloy characterized in that it comprises silver as the main component, copper and gold, and in that it has a defined composition range (units:% by mass) by line segments connecting the following points: (a): (X = 79, Y = 13, Z = 8); (b): (X = 47, Y = 13, Z = 40); (c): (X = 40, Y = 20, Z = 40); (d): (X = 33.3, Y = 33.3, Z = 33.3); and (e) (X = 46, Y = 46, Z = 8),   o X is silver, Y is copper and Z is gold (X + Y + Z = 100).   8. Decorative object characterized in that it comprises a silver alloy   according to any one of the preceding claims.