Silver and its alloys characteristics. Silver and its alloys

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Replacing silver with dielectric coatings makes it possible to obtain light filters with a maximum transmittance of up to 80 - 90% with a small bandwidth.

To replace silver, it is necessary to take refractory metals, and non-oxidizing ones, since widely used ceramic masses require firing in an oxidizing environment. Such metals are platinum and palladium; both of them are scarce and expensive, which increases the cost of monolithic capacitors and limits the development of their production.

To replace silver, oxide catalysts for the oxidative dehydrogenation of methanol have been developed. The most effective of them are oxides of molybdenum and titanium. To increase the activity, up to 37% iron oxide is added to molybdenum oxides. Mixed catalysts are more active and selective; the process on them proceeds at a higher low temperatures(350 - 400 C) and with a large excess of air in the reaction mixture. These catalysts are gradually replacing silver catalysts that were previously accepted in industry.

Copper is considered one of the most promising materials to replace silver in the fuse elements of high-speed fuses. Copper is cheaper than silver by at least 300 times and is close to it in its electrophysical properties. The specific electrical resistance of copper is 5–6% higher than that of silver, which is easily compensated by an increase in the cross section of fusible elements. The modulus of elasticity of copper is 1-3 times higher than that of silver, which is unfavorable for the cyclic operation of the fuse. The thermal conductivity of copper is about 6% less than that of silver, and the melting point is more than 120 C higher.

The current trends of the increasing introduction of ceramic materials instead of oil-containing plastics for the manufacture of insulating parts of electrical installation devices and the replacement of silver and silver-containing metal-ceramic compositions with full-fledged contact materials (alloys) that do not contain precious metals in their composition for the manufacture of breaking contacts of switches and switches will receive the greatest development in the future.

Now nickel silver and related cupronickel (melchior does not contain zinc, but about 1% manganese is present) are used not only and not so much to replace silverware how much for engineering purposes: cupronickel is the most resistant (of all known alloys. It is an excellent material for taps, valves and especially condenser tubes.

Nickel silver and related cupronickel (melchior does not contain zinc, but about 1% manganese is present) are used not only and not so much to replace table silver, but for engineering purposes: cupronickel is the most resistant (of all known alloys.

The S-electrons of the alloying metal fill the vacancies in the cf bands of palladium, reducing % A, and the effect of the additive increases as one goes from Ag to Sb, and especially sharply when silver is replaced by cadmium.

Toning positive images in different colors, for example brown, blue, green and others, is based on the transformation of metallic silver in the emulsion layer into some colored compound, as well as by replacing silver with another metal or dye. When toning, only the image itself is colored, and the image may be slightly strengthened or weakened during the toning process. The composition of tinting solutions and their quantity are determined by the method used.

AT huge quantities silver is spent for the production of photo and film materials. Despite persistent attempts to replace silver in these materials with other metals or substances, the problem still remains unresolved.

Gain is used to increase the visual or copy density of an image, as well as to correct its contrast. Strengthening of the skin can be done by building up on the metallic silver present in the layer of some substance, forming a colored silver salt and replacing the silver with another substance. The amplification process is performed in one or more solutions.

In the case of phosphorus KS1 - Ag, the curve consists of two maxima at 575 and 450 Tu. The latter coincides with the K-band in the spectrum of phosphorus KS1 - Ag and is undoubtedly due to silver, and not to the base, since this peak is not observed when silver is replaced by thallium. Curve a fig. 70 depicts the absorption spectrum of x-rayed phosphorus NaCl - - Ag with a low concentration of activator.

Copper-olo-po plating, or bronzing, is used for both corrosion protection and decorative finishes product surfaces. Coating with a low tin alloy (10 - 20% tin) of golden yellow color is also used as an undercoat instead of copper and nickel coatings before chromium plating, High tin alloy (40 - 45% tin), the so-called white bronze, in some cases can serve as a substitute silver. Despite the fact that the value of the electrical resistivity of the Cu-Sn alloy is much higher than that of silver, in an industrial atmosphere, where there are impurities of sulfur compounds, it remains stable, while, like that of silver, it increases by tens of rals. For this reason, white bronze coatings are recommended for electrical contacts.

The developer treatment can be replaced by a treatment with ammonia or sodium sulfide, which precipitates mercury alone as black oxide or sulfide. Under the action of ammonia there is a simultaneous dissolution of silver chloride. The replacement of silver with the mentioned mercury compounds enhances the intensity of the blackening. Strengthening with a mixture of uranium nitrate and potassium iron cyanide is often used. Reacting with silver, this mixture deposits a dark precipitate on its grains from a mixture of iron cyanide salts of uranium and silver.

Tantalum can also replace platinum in the manufacture of various chemical glassware. In the rayon industry, tantalum is used to make mouthpieces, chemical industry for lining equipment and parts of pumps that are subject to the greatest corrosion. Tantalum is recommended as a replacement for silver in spark contact tips and as a cathode in the analysis of metal salts. High strength, thermal conductivity and acid resistance make possible application tantalum as a material for electric heaters for hydrochloric and sulfuric acids.

General information.

Pure silver is the whitest of all metals, it has the most high gloss, and in malleability and ductility it is second only to gold. Silver is considered pure if its content is 999 parts per 1000. Silver of the highest purity 999.5 is highly valued by collectors. Most jewelry is made from silver. self made. Pure silver tends to be too soft for most jewelry. For this reason, it is alloyed with other metals, increasing strength and hardness. Most often, copper is used for this purpose. In small amounts, copper brings stiffness to the alloy without reducing its luster and malleability.

Sterling silver or 925 sterling silver is the most commonly used alloy. The number 925 means the number of parts of silver in a thousand, while copper makes up the remaining share of 75/1000. Sterling silver was adopted as the standard in England in the 20th century, it has also become an internationally recognized standard in the Western world.

Another standard alloy is mint silver or 900 proof. Ninety percent silver was used as the standard for minting US coins until 1966, now silver is no longer used for this purpose. Other international standards for silver coins vary up to 80/20 alloy. general trend consists in replacing silver in the monetary circulation of most countries with nickel and aluminum. The same 8oo silver was used in many countries in many old jewelry.

Among other silver alloys, it is worth mentioning "electro" - an ancient alloy of Greece and Rome, as well as dental amalgam - a material for making "silver" fillings. Beryllium silver is harder than pure silver and does not tarnish. "British silver" is a jewelry standard used in England from 1697 to 1719 to prevent sterling silver coins from being melted down for jewelry purposes; it is still the standard alloy in the British Commonwealth.

Silver/copper alloys are more prone to oxidation the higher their copper content. This circumstance also makes it possible to use various chemical reagents for coloring the surface of silver objects. Sulfides present in packaging materials, especially rubber rings, as well as atmospheric pollution are common factors that cause oxidation.

Legal standards.

The National Gold and Silver Marketing Act sets standards for assaying silver products. The standard for sterling silver calls for a minimum content of 921 parts per 100, or 915 parts for brazed products.

Since 1961, this act requires the obligatory presence (in addition to the quality certificate) of the registered brand of the manufacturer - an individual or organization, responsible for quality. However, no US law requires a primary sample. If the sample stands, the maker's mark must also stand. In the absence of such a hallmark on the sampled product, the wholesaler and / or retailer is held liable for fraud.

The sterling standard is generally accepted in the United States and in the countries of the former British Empire. Silver items from other Western countries are usually branded with a number indicating the content of parts of silver per thousand parts of the alloy. Hallmarks like "Silver" (silver), "Mexican silver" (Mexican silver), "German silver" (German silver), "Indian silver" (Indian silver) or any other similar ones do not at all guarantee the presence of silver in the product. In fact, "German silver" is another name for "nickel silver", an alloy that contains no silver at all.

Heat hardening.

Sterling silver items may be too soft to handle once soldered. When soldering, annealing of the metal often occurs. Sterling silver can be hardened by heating sterling silver items to 6oo°F (315

C) and kept at this temperature for 15 minutes. Then the product should be allowed to cool in air to room temperature.

Silver alloys.

Composition and melting point.

Percentage given

Materials for jewelry Kumanin Vladimir Igorevich

10. Silver and its alloys

10. Silver and its alloys

Silver - chemical element, metal. Atomic number 47, atomic weight 107.8. Density 10.5 g/cm3. The crystal lattice is face-centered cubic (fcc). Melting point 963 °C, boiling point 2865 °C. Brinell hardness 16.7.

Silver - metal white color. It is considered the second noble metal after gold. Polished pure silver practically does not change its color in the air. However, under the influence of hydrogen sulfide in the air, a dark coating forms on the surface over time - silver sulfide Ag2S. Silver is less stable in acids and alkalis than gold and platinum.

Silver is perfectly deformed both in a cold and in a hot state. Well polished, has a high reflectivity.

The widespread use of silver in photography and electrical engineering is due to its unique physical properties- the highest electrical and thermal conductivity among metals.

Despite the fact that silver is a relatively rare element (its content in the earth's crust is only 7 x 10-6%, in sea ​​water even less - 3 x 10-8%), it has been widely used in jewelry production for many centuries. This is primarily due to the high decorative properties of silver, as well as its unique plasticity. Silver jewelry is often made using the filigree technique - a pattern made of thin wire. Threads for silver sewing are made from silver.

For the manufacture of jewelry, as well as in the electronics industry, both pure silver and its alloys with copper and platinum are used.

Grades of silver and silver alloys are regulated by GOST 6836-80.

The standard applies to alloys intended for electrical conductors and contacts, jewelry, strings musical instruments.

According to the specified standard, silver alloys are denoted by the letters Cp, followed by ligatures (Pt - platinum, Pd - palladium, M - copper). The numbers after the letter designation of the alloy indicate the mass fraction of silver, expressed in ppm (tenths of a percent) for pure silver and silver-copper alloys (for example, Sr999, SrM91b, SrM950, etc.), or the mass fraction of the main alloying components, expressed in percent (in this case, the number is separated from the letter designation not by a space, but by a hyphen, for example: SrPl-12 (12% Pt, 88% Ag), SrPd-40 (40% Pd, 60% Ag).

All silver alloys (GOST 6836-80) can be used in the electrical industry for the production of contact groups for various purposes. For the manufacture of musical instrument strings, an alloy CPM 950 is used.

GOST 6836-80 establishes the grades of silver and silver alloys with copper, platinum and palladium, intended for the manufacture of semi-finished products by casting, hot and cold deformation. Other silver alloys are regulated by industry standards or specifications.

The chemical composition of silver and its alloys must comply with the standards specified in tables 10.1, 10.2, 10.3 (GOST 6836-80). Silver-platinum alloys, as more expensive, in jewelry industry are used less frequently.

Table 10.1

Table 10.2

Silver- copper alloys

Table 10.3

Silver-platinum alloys.