MXPA00008297A - Fine silver alloys which are hardenable and resistant to superficial decoloration. - Google Patents

Abstract

The present invention refers to a composition of fine silver alloy having at least approximately 99.5 per cent in weight of silver, with the rest containing an element, or an element oxide, selected from the group which consists of: aluminum, antimony, cadmium, gallium, germanium, indium, lithium, manganese, magnesium, silicon, tin, titanium and zinc, the alloy composition has been formed combining silver having a purity of at least approximately 99.90 per cent in weight with an element, or an element oxide, selected from the group in an atmosphere substantially non-oxidant. The silver alloy composition can be hardened by internal oxidation. The composition may be hardened by aging at least to 136 per cent of its recognized harness, and its hardening may be irreversible. The composition may be resistant to the superficial decoloration and can have a hardness of the aging material of at least approximately 48 VHN. The internal oxidation may be increased by heating the alloy at a temper ature of between approximately 426.66°C (800°F) and 704.44°C in an oxygen containing atmosphere. The oxygen containing atmosphere may contain at least approximately 20% of oxygen. The non-oxidant atmosphere may be of approximately 75 per cent in hydrogen weight and approximately 25 per cent in oxygen weight. The non-oxidant atmosphere may be a reducing atmosphere. The reducing atmosphere can be a product of carbon cover and/or a reducing flame. The alloy composition can be formed starting from the silver which is substantially oxygen free. The oxygen may be removed from the silver melting the silver in a reducing atmosphere. This reducing atmosphere can be a carbon cover product, the insertion of at least one carbon rod in the silver, and the silver heating at least around 1204.44°C (2,200°F) during at least around 45 minutes.

Description

FINE SILVER / DURABLE SILVER ALLOYS RESISTANT TO SUPERFICIAL DECOLORATION Technical Field The present invention relates generally to fine silver alloys (ie, having at least 99.5 weight percent silver), and, more particularly, to improved fine silver alloys which are resistant to surface discoloration and which they can be hardened to levels beyond those possessed by pure silver.

Background of the Technique Pure silver is a lustrous, white, ductile and malleable metal that is presented in both the non-combined form and in minerals. This item is highly valuable for jewelry, tableware, and other ornamental use. Pure silver is relatively soft and non-hardening. For example, pure silver can have a hardness when annealed in the order of a Vickers Hardness Number of 35 ("VHN"). It has been the experience of the applicants that this material can not be hardened by aging. Therefore, pure silver is comparatively soft Rf.122748 and not hardenable. Because of this, it is necessary to allow the silver to be joined with other elements in an alloy in an attempt to increase the hardening capacity of the resulting alloy. For example, sterling silver typically contains 92.5 percent by weight of silver, and 7.5 percent by weight of copper. Although pure silver has a hardness when annealed at about 35 VHN, applicants experience is that the sterling silver has a hardness when annealed at about 80 VHN, and can be selectively hardened to about 110 VHN, a substantial increase about that available for pure silver. However, sterling silver easily tarnishes on its surface and is not pure. Because silver is a precious metal, it is often evaluated for its purity. Until now, it has not been possible to commercially manufacture a fine silver alloy having properties adapted for use as fine jewelry, tableware and accessories. For this purpose, applicants have developed certain fine silver alloys (ie, alloys having at least 99.5 weight percent silver). In these alloys, the high amount of the silver is bound by means of an alloy with selective elements in comparatively low amounts. However, as demonstrated here, applicants have developed various alloy compositions that are hardenable only at levels beyond those possessed by sterling silver and pure silver, and are more resistant to surface discoloration than sterling silver. .

Description of the invention The present invention provides various fine silver alloy compositions having at least about 99.5 weight percent silver. In one form, the silver is attached by alloy with an element, or an oxide of an element, selected from the group consisting of: aluminum (Al), antimony (Sb), cadmium (Cd), gallium (Ga), germanium ( Ge), Indian (in), lithium '(Li), manganese (Mn), magnesium (Mg), silicon (Si), tin (Sn), titanium (Ti) and zinc (Zn) by combining silver that has a purity of at least about 99.90 weight percent with an element, or oxide of an element, selected from the group, in a substantially non-oxidizing atmosphere. The improved silver alloy composition can be formed by annealing the composition of the alloy in a substantially non-oxidizing atmosphere. The composition of the improved silver alloy can also be formed by hardening the alloy by internal oxidation. The composition of the alloy can be hardened to at least 136 percent of its annealed hardness, it can have a hardness when it is aged of at least about 48 VHN, and the hardenability of the alloy composition can be irreversible. In addition, the composition of the alloy may be resistant to surface discoloration and at least as resistant to surface discoloration like pure silver. The internal oxidation can be increased by annealing the composition of the alloy to a temperature between about 426.67 ° C (800 ° F) and 704.44 ° C (1300 ° F) in an oxygen-containing atmosphere. The oxygen-containing atmosphere can contain at least 20 percent oxygen. The non-oxidizing atmosphere can be about 75 weight percent hydrogen and about 25 weight percent nitrogen. The non-oxidizing atmosphere can also be a reducing atmosphere. The reducing atmosphere can be a product of a carbon cover and / or a reducing flame. The composition of the alloy can be formed with silver which is substantially free of oxygen. Oxygen can be removed from the silver by melting the silver in a reducing atmosphere. In this way, the reducing atmosphere can be a product of a carbon cover, the insertion of at least one carbon rod in the silver, and the heating of the silver to a temperature of at least about 1204.44 ° C (2,200 ° F) during the less approximately 45 minutes. The present invention also provides a process for manufacturing fine silver alloy compositions comprising the steps of combining silver having a purity of at least about 99.90 weight percent and being substantially free of oxygen, with at least one element of alloy, or an oxide of the element, in a substantially non-oxidizing atmosphere, annealing the composition of the alloy in a substantially non-oxidizing atmosphere, and hardening the composition of the alloy by internal oxidation. The consequence, the general object of this invention is to provide various types of improved hardenable fine silver alloys. Another object is to provide improved silver alloy compositions having at least 99.5 weight percent silver with the remainder containing a number of selected elements or oxides of these elements, with the resulting composition being capable of being hardened by aging to at least 136 percent of its hardness when annealed. In this form, the increase in hardness of the composition of the resulting alloy may be irreversible. Another object is to provide an improved fine silver alloy composition having at least 99.5 weight percent silver, with the remainder being a number of selected elements or oxides of the elements, such that the hardness when aged of the alloy thus formed is at least about 48 VHN. Another object is to provide various silver alloy compositions which exhibit a resistance to surface discoloration of the order of that for pure silver, and which are substantially more resistant to surface discoloration than sterling silver. These and other objects and advantages will become apparent from the foregoing and ongoing specification, from the drawings, and from the appended claims.

Brief Description of the Drawings Figure 1 is a bar graph showing the hardness of the annealed and aged material of a number of specific alloys, this graph shows that several alloys are being distributed in decreasing order of hardness when aged.

Figure 2 is a bar graph showing the percent increase in hardness for the different alloys shown in Figure 1, this view showing the alloys when arranged or distributed in decreasing order of the increase in hardness percentage. Figure 3 is a bar graph showing the change in color of several alloys after exposure to a surface discoloration vapor.

Description of Preferred Modality (s) At the outset, it should be clearly understood that like reference numerals are proposed to identify the same structural elements, portions, or surfaces, consistently from beginning to end of the various Figures of the drawings, such that the elements, portions or the surfaces can be described or further explained by the complete written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (eg, shading, arrangement of parts, proportion, grade, etc.) together with the specification, and are to be considered as a portion of the complete written description of this invention. When used in the following description, the terms "horizontal", "vertical", "left", "right", "up", and "down", as well as adjectival derivatives and adverbs thereof (for example, "horizontally", "vertically", "upwards", etc.), simply refer to the orientation of the illustrated structure when the Figure of the particular drawing is in front of the reader. Similarly, the terms "inward" and "outward" generally refer to the orientation of a surface relative to its longitudinal axis, or axis of rotation, when appropriate. Applicants have discovered the composition of and a process for forming a number of silver alloys having the capacity of a substantially increased hardness when undergoing a transition from an annealed condition to an aged condition. This increase in hardness is a function of the composition of the alloy and the process by which the alloy is formed, annealed, and hardened.

Composition When used herein, the term "fine silver" refers to a silver alloy composition having at least 99.5 weight percent silver. The remainder of these alloy compositions can be an element, or an oxide of an element, selected from the group consisting of: aluminum, antimony, cadmium, gallium, germanium, indium, lithium, manganese, magnesium, silicon, tin, titanium and zinc. The alloys of the improved composition are capable of being hardened in aging to at least 136 percent of their annealed hardness, and this hardening process may be irreversible. The hardenability data of the applicant as to the number of alloys tested is described in Table 1 here. In this table, the alloys are simply identified by alloy numbers. The composition of the alloy is then specified in terms of its percentage by weight of silver and the percentage by weight of the other elements of the alloy. The hardness of the annealed (ie soft) material, the hardness of the laminated material and the hardness of the aged material are then described after this. The next column is then an expression as to the change in hardness percentage (ie, aged / soft x 100%). The column on the right hand expresses the increase in hardness between the annealed and aged values (ie, (aged-soft) / soft x 100%).

Table 2 contains the same hardenability data as described in claim 1, although the data described in Table 2 are arranged in ascending order of the hardness of the aged material. These data are plotted in Figure 1. This Figure shows a series of bar graphs in which the hardness is plotted as a function of the particular alloy number. The bar for each alloy is shown having two portions, the hardness of the annealed material and the hardness of the aged material. In this regard, the horizontal line at an indicated hardness of approximately 48 VHN which indicates the cut-off point of the alloys which are considered to be within the scope of certain of the appended claims.

Table 3 contains the same data shown in Tables 1 and 2, although classified in ascending order of hardness percentage change. These data are plotted in Figure 2, in which the change in the percentage of the hardness increase is plotted as a function of the number of the alloy. In this view, the minimum increase for inclusion within the claimed alloy is if the change in hardness percentage is greater than about 136 percent. These tested alloys that have a change in hardness percentage greater than 136 percent are considered within the scope of certain appended claims.

Applicants have also discovered that the improved alloys exhibit a resistance to surface discoloration that is of the order of, or greater than, that of pure silver, and substantially better than the resistance to surface discoloration of the sterling silver. The resistance to surface discoloration can be measured quantitatively by a change in color following exposure to a surface discoloration vapor (eg, including chlorides, sulfides and acetic acid) for about half an hour. The vapor resistance of surface discoloration and the time of exposure is believed to be interrelated amounts, and may be varied as desired. The color is measured in terms of the CIÉ units in three mutually perpendicular axes, with L * representing a brightness of the color on a black-white axis (ie L * 0 representing black and L * 100 representing white, a * which represents a variable color on a red-green axis (that is, an a * 100 that is red and an a * -100 that is green), and b * that represents another variable color on a yellow-blue axis (it is say, b * 100 is yellow and b * -100 is blue The difference (DE) between the two colors (L *? a *? b *?) and (L * 2, a * 2, b * 2) they can then be calculated as a distance between the corresponding points according to the equation: DE = [(L * 2- *? R + (a * 2 - + (b * 2 -. R 2] n 1/2 To obtain a uniform surface condition, all the samples were drilled in an abrasive medium and then in steel shot. The samples were then ultrasonically cleaned in a soapy solution and rinsed. The color of the samples is measured before and after exposure to a surface discoloration vapor for about half an hour. The color was measured by CIELAB's mathematical color measurement system, using a "C" light source, including the ultraviolet and silver mirror components, and with the observer placed at an angle of 2 degrees. The applicant's surface discoloration resistance data is shown in Figure 4: The color of the applicant's improved alloys before exposure is substantially the same as pure silver, and not substantially different from the color of sterling silver. Any differences in color between the improved alloys and the sterling silver were so light that they will be virtually indistinguishable for the human eye. Therefore, the present invention provides an improved fine silver alloy composition containing at least about 99.5 weight percent silver. The composition is capable of being hardened by aging to at least 136 percent of its annealed hardness, and this hardening can be irreversible. The hardness of the aged material is at least 48 VHN. The alloy includes at least 99.5 weight percent silver, with the remainder including an element, or an oxide of one element (or both) selected from the group consisting of aluminum, antimony, cadmium, gallium, germanium, indium, lithium , manganese, magnesium, silicon, tin, titanium and zinc.

Process The hardness described in Tables 1-3 and the resistance to surface discoloration reflected in Table 4 are not only a function of the specific elements used to form the alloy, but also the process by which the alloy is formed. Of course, the primary element of the claimed alloy is silver. To ensure that the alloy contains at least about 99.5 weight percent silver and meets the purity standards described by the National Gold and Silver Stamping Act, the ingredients used to form the alloy must be of especially high purity. In particular, the silver in which the elements of the alloy are melted should have a minimum purity of at least about 99.90 percent by weight. In addition, in the preferred embodiment, the special alloy ingredients also have a minimum purity of 9.90 percent. For the best results, silver should especially avoid metals from the copper, zinc, gold, nickel, iron or platinum group (for example, less than 25 parts per million). Not only should silver be used to form the alloy having a minimum purity of about 99.90 weight percent, it must also have a low oxygen content. Almost all commercially available silvers have a high oxygen content, which makes them brittle and prone to blisters, fractures and other defects. In addition, the exact composition of the applicants' silver alloy is difficult to control without first removing the oxygen from the silver. Consequently, the oxygen content of the silver is reduced prior to the addition of the other ingredients of the alloy. The oxygen is removed from the silver by melting the silver in a reducing atmosphere. The preferred reducing atmosphere is a carbon shell and a reducing flame. The preferred coal cover is mineral coal. The silver is placed in a crucible and covered with mineral coal. The crucible is heated and the mineral coal extracts the oxygen from the silver, while also acting as a barrier to oxygen in the surrounding air. The preferred reducing flame is carbon monoxide, which reacts with oxygen and removes it. The carbon rods are then inserted into the molten silver while they are maintained at a temperature of at least 1204.44 ° C (2,200 ° F) for at least 45 minutes. The silver is then poured into castings. The preferred shape of the cast is the grains. The spillage is effected under a non-oxidizing atmosphere to keep the absorption of oxygen to a minimum. When used herein, a non-oxidizing atmosphere means and includes a neutral / displacement atmosphere (one that contains little or no oxygen) and / or a reducing atmosphere (an atmosphere in which oxygen is actively removed). Once the silver is in the form of grains and substantially free of oxygen, it can be combined with the ingredients of the special alloy to form the claimed silver alloy. Because the ingredients of the special alloy are easily oxidized, the preferred method of mixing the ingredients is to first place half of the pure silver in a crucible, then place the ingredients of the alloy on top of the silver , and then cover the ingredients of the alloy with the remaining half of the silver. Again, it is important that the fusion of the special alloy and silver ingredients occurs in a non-oxidizing atmosphere. To achieve this, a carbon cover and a reducing flame must cover the mixture during the fusion process. The carbon must be the fourth layer in the crucible, covering the second half of the silver. This carbon coating acts as a barrier to oxygen, as well as a reducing agent. Because of the order in which the silver and the ingredients of the special alloy are mixed, the silver on the bottom of the crucible will melt first, allowing the special alloy ingredients to then fall into the molten silver. This helps to mix the alloy and prevent the oxidation of the special alloy ingredients. When the mixture is completely molten, the carbon rods are inserted to prevent further oxidation and help reduce mixing. Once the appropriate temperatures are reached, the mixture can be poured. Again, the oxidation is kept to a minimum and the molten alloy is protected from the absorption of oxygen by using a reducing flame in the mold and over the pouring stream. To maintain the ductility of the alloy when processing the alloy into a finished product, it is sometimes necessary to soften it periodically by reheating. This annealing process is also carried out in a non-oxidizing atmosphere. In the preferred process, an atmosphere of 75 percent hydrogen (H2) and 25 percent nitrogen (N2) is used. Annealing temperatures are maintained at 315.55 - 426.66 (600 - 800 ° F), depending on the thickness of the raw material and the amount of the product in the kiln. Annealing temperatures and time should be kept as low as possible to prevent grain growth. The alloy is hardened after manufacture to greatly improve its strength. Where the previous steps are formed in a non-oxidizing atmosphere, this final step is carried out in an oxidizing environment. The hardening is carried out in an oxygen-containing atmosphere, such as air (which contains about 20 percent oxygen). During this stage the oxygen is diffused into the composition of the alloy for further internal oxidation. The speed at which the alloy is hardened depends on the temperature used and the amount of oxygen available. In the preferred process, the temperature is maintained at between 426.66-704.44 ° C (800 - 1300 ° F). The hardening time varies as the square of the thickness of the alloy. Where "t" is the thickness, "T" the time, and "K" a diffusion constant (which is a function of the available oxygen, the temperature, and the elements of the alloy), the hardening time T = K t2. As a result of using the aforementioned process in combination with the alloy compositions described above, a finished silver alloy is formed, which has a high purity of the silver and a hardness which, until now, has not been able to achieve. Not only is the alloy made with a high silver content and a high hardness, but the hardening is irreversible. The benefit of the irreversibility is that the reheating of the alloy (for example the welding with torch) can be carried out without losing hardness. This provides wonderful advantages for the craftsman of the tools, the jewelers, and other craftsmen. In addition, such reheating does not lead to discoloration or tarnish found with other alloys. With the improved alloy, reheating does not lead to a "fire ladder"; Therefore, the present invention provides an improved fine silver alloy composition containing at least about 99.5 weight percent of the silver. The composition is capable of being hardened by aging to at least 136 percent of its annealed hardness, and this hardening can be irreversible. This hardening is effected through a process in which very pure silver is mixed with a selected combination of alloying ingredients in a non-oxidizing atmosphere. The annealing of the alloy is also carried out in a non-oxidizing atmosphere. The alloy is then hardened in an oxygen-containing atmosphere which promotes internal oxidation. The result is a fine-grained alloy resistant to surface discoloration and irreversibly hardened. Accordingly, although several preferred forms of the improved silver alloy compositions and a process have been shown and described, and various modifications thereof will be readily apparent to those skilled in the art so that various additional changes and modifications can be made to the prior art. do without departing from the spirit of the invention, as defined and differentiated in the following claims.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, property is claimed as contained in the following

Claims (11)

1. A silver alloy composition, characterized in that it has at least 99.54 weight percent silver, with the balance consisting essentially of an oxide of an element selected from the group consisting of aluminum, antimony, cadmium, gallium, germanium, indium, manganese, magnesium, silicon, titanium and zinc, the effective oxide to cause the silver alloy to have a fade resistance greater than 99.98% by weight of silver when exposed to a higher fading vapor that includes chlorides, sulfides and acetic acid.

2. The silver alloy according to claim 1, characterized in that it has a hardness when it is aged of at least 48 VHN.

3. The silver alloy according to claim 2, characterized in that the hardness of the silver hardened by aging is at least 136% of a hardness of the annealed material of the silver alloy.

4. The silver alloy according to claim 3, characterized in that it is formed into an ornamental object.

5. The silver alloy according to claim 4, characterized in that a difference (DE) between a color of the silver alloy before exposure to a surface discoloration vapor and subsequently exposure to the surface discoloration vapor is less than 11. .

6. The silver alloy according to claim 5, characterized in that it has approximately 0.280%, by weight, of magnesium.

7. The silver alloy according to claim 5, characterized in that it has, by weight, approximately 0.004% titanium.

8. The silver alloy according to claim 5, characterized in that it has, by weight, approximately 0.415% germanium.

9. The silver alloy according to claim 5, characterized in that the oxide is manganese oxide.

10. The silver alloy according to claim 9, characterized in that it has, by weight, approximately 0.460% manganese.

11. The silver alloy according to claim 5, characterized in that it has, by weight, approximately 0.350% cadmium. SUMMARY OF THE INVENTION The present invention relates to a fine silver alloy composition having at least about 99.5 weight percent silver, with the remainder containing an element, or an oxide of an element, selected from the group consisting of: aluminum, antimony, cadmium, gallium, germanium, indium, lithium, manganese, magnesium, silicon, tin, titanium and zinc, the composition of the alloy has been formed by combining the silver having a purity of at least about 99.90 weight percent with a element, or an oxide of an element, selected from the group, in a substantially non-oxidizing atmosphere. The composition of the silver alloy can be hardened by internal oxidation. The composition is capable of being hardened by aging to at least 136 percent of its annealed hardness, and its hardening can be irreversible. The composition may be resistant to surface discoloration, and may have a hardness of the aged material of at least about 48 VHN. Internal oxidation can be increased by heating the alloy to a temperature between about 426.66 ° C (800 ° F) and 704.44 ° C (1300 ° F) in an oxygen-containing atmosphere. The oxygen-containing atmosphere can contain at least about 20% oxygen. The non-oxidizing atmosphere can be about 75 weight percent hydrogen and about 25 weight percent oxygen. The non-oxidizing atmosphere can be a reducing atmosphere. The reducing atmosphere can be a product of a carbon cover and / or a reducing flame. The composition of the alloy can be formed from the silver which is substantially free of oxygen. Oxygen can be removed from the silver by melting the silver in a reducing atmosphere. This reducing atmosphere can be a product of a carbon cover, the insertion of at least one carbon rod in the silver, and the heating of the silver to at least approximately 1204.44 ° C (2,200 ° F) for at least about 45 minutes .