Alloy of silver with copper properties. Characteristics of different alloys of silver and copper. The use of silver in medicine
Silver based. One of ancient materials... Pure - soft plastic metal (HB = 30 kgf / mm2, σv = 15 kgf / mm2, δ = 48%, ψ = 90%), which forms with a plurality of fusible eutectics with metals. To increase the hardness, they are alloyed (Fig.). S. s. They are distinguished by high% electrical conductivity, resistance to oxidation, however, they are sensitive to the effects of sulfur and its compounds.
Resistance to sulfur is increased by adding magnesium, indium, cadmium, zinc, and others. most wide application received silver-copper grades SrM. The copper content in them is 4 ÷ 50%. An increase in the copper content reduces the melting point from 927 to 850 ° C, the density from 10.5 to 9.3 g / cm3. Alloys of silver with copper are used for the manufacture of low-current contacts, jewelry, for minting coins and medals. S. c, containing a platinum group, are distinguished by significant corrosion resistance. A special place is occupied by low-alloyed (up to 1%) intraoxidized
S. s. with chemically active metals - magnesium, aluminum, cadmium, lithium, beryllium, etc. These alloys are distinguished by electrical conductivity close to silver, increased erosion resistance and greater (1.5-2 times) fur. durability compared to silver. Of these, the most widespread are alloys of silver with cadmium oxide. These alloys are made as cast, followed by oxidation in air (or in oxygen) and sintering. silver powder with alloy metal oxide. They are used as discontinuous and sliding electr. contacts in low-current and medium-loaded electr. circuits (switching devices, radio equipment, telephones, etc.).
Some S. s. (PSr brands) wet well metal surfaces, forming low-melting eutectics and tight brazed joints after solidification. They are used as high-strength and vacuum-tight solders. The silver content in these alloys is 15 ÷ 72%, their melting point is 235 h-h - 780 ° C. Alloys are produced in the form of strips and wires. As alloying elements used (16-30%), (1-37%), (1-5%), (8-96%), (5.5-30%), (63-97%), ( 3-8.2%) and (0.3-2%).
Lit .: Golovin V.A., Ulyanova E.Kh. Properties of noble metals and alloys. (Reference). P. Polyakov.
You are reading an article on the topic of silver alloys
Pure silver- the metal is incredibly beautiful, but not very practical. Silver of the highest standard is soft, easily scratched, quickly loses its gloss. Openwork details of jewelry made of pure silver, with intensive wear and careless cleaning, even with soft abrasives, lose their relief and are smoothed. As a result, the silver jewelry loses its expressiveness. Its attractiveness and artistic value are reduced.
Perhaps for making jewelry does it make sense to use alloyed silver alloys? There is, and considerable - the masters of the whole world are sure. But the percentage of ligature inclusions in silver alloys is different for everyone. Someone considers 5% of additives to be sufficient, while someone boldly adds up to 50% to the precious metal, God knows what ligatures - and loudly praises their goods.
Therefore, the authorities had to introduce standards for assaying noble metal alloys. This is the only way to stop the arbitrariness of amateur craftsmen, eager to receive super-profits.
Some domestic and foreign samples of silver
Generally Russian system silver assaying complies with international standards. Three-digit number- sample number - reflects the exact number of grams precious metal in a kilogram of jewelry alloy. Copper is most often the ligature in silver alloys: the metals are "friendly" with each other, mixing well, fusing perfectly, and most importantly, communicating many useful properties to each other.
The addition of cadmium to the ligature sharply increases the price of the product, while significantly increasing the expressive properties of the metal. Instead of copper (or together with copper), aluminum, zinc, nickel can be mixed with silver. However, the generally accepted jewelry standard is silver-copper alloy.
The minimum acceptable is considered to be the 750th or 800th sample. At the same time, in the countries of the poor south, jewelry is successfully made from silver of the 600th test.
By the way, quite often the market traders of the South-East persistently offer our tourists silver trinkets of a noticeably red hue, claiming that the metal of the product is quality silver full-fledged 600th test.
In fact, the reddening of the silver alloy indicates that the amount of copper in the product is simply off scale. The alloy becomes reddish even when the ratio of silver and copper is parity (50% each). How more copper- the redder the tide.
There is every reason to believe that the appearance of such products suffers greatly during the minimum time of use, because even the 720th silver test means: the decoration is yellowish, the formation of an oxide film occurs quickly ...
Nevertheless, silver 720 is used in domestic jewelry practice: as a solder between high-quality parts, as a material for fasteners and locks, springs, needles, etc.
Silver of the 800th (and even 750th) standard is considered suitable for the manufacture of cutlery, salt shakers, oil cans and other utensils. True, such silver requires constant care- that is, periodic cleaning from the oxide film.
Life is a little easier for the owners of table silver of 875-th test. This is still a low-grade alloy, but it is already possible to make from it not only dishes and cutlery - napkin rings, wine glasses, glasses and pouring containers, ashtrays - but also interior decorations.
Alloy 916 is deservedly considered good silverware. It is this alloy that is used to make sets decorated with enamel or gilding.
The famous sterling silver is a 925 sterling silver alloy. Sterling is an ancient (ΧΙV century) English coin. It is generally accepted that the sterling silver was of the highest quality. Sterling silver and today it is considered the best material for the manufacture of jewelry, art and household items.
Silver 960 used in jewelry practice does not have external differences with pure silver. Products from this alloy are distinguished by the highest artistic merits, but they require special respectful attitude... The ductility of soft metal does not in the least contribute to the durability of such jewelry.
999 silver is in high esteem among the inhabitants of the Far East. The Japanese, who have long and firmly believed in the close relationship of pure silver and the moon inhabited by deities merciful to people, eagerly buy jewelry made of silver of the 1000th test.
| Metal sampling system: | |||
|---|---|---|---|
| Metal | Metric | Zolotnikovaya | Karat |
| Gold | 375 | 36 | 9 |
| Gold | 500 | 48 | 12 |
| Gold | 583 / 585 | 56 | 14 |
| Gold | 750 | 72 | 18 |
| Gold | 958 | 92 | 23 |
| Gold | 999 | 96 | 24 |
| Silver | 750 | 72 | 18 |
| Silver | 800 | - | - |
| Silver | 875 | 84 | 21 |
| Silver | 916 | 88 | 22 |
| Silver | 925 | - | - |
| Silver | 960 | - | - |
| Silver | 999 | 96 | 24 |
| Platinum | 950 | - | - |
| Palladium | 500 | - | 12 |
| Palladium | 850 | - | - |
The pragmatic French are most fond of silver 800 - while the rest of Europeans prefer to buy items from silver alloy 935.
Types of silver
You won't surprise anyone with multi-colored gold. Silver is produced in a single color variation - white! But anyway noble metal can be different.Sterling silver is white, durable, not prone to blackening. Its color is characterized as dazzling, and its quality as a reference. Blackened silver- product of application of special jewelry technology associated with the creation of black melts.
Blackened silver jewelry They give the impression of being ancient, are considered magically powerful, and are praised as amulets and charms. Modern technologies allow full blackening to be replaced by fast and shallow oxidation. The new oxidized silver is indistinguishable from blackened silver, but it does not retain high aesthetic conditions for so long.
Filigree silver is the name for openwork products made with highlighting the smallest details. In fact, filigree silver is lace woven from thin silver wires and either soldered onto the background or placed in a frame.
In recent decades, matte silver has become popular. Micro-roughness on the surface of items is created by processing silver with a special liquid suspension of chemically active ingredients.
Imitation silver
Imitations of silver are not necessarily fakes of a precious metal. Cupronickel and nickel silver were created as an inexpensive replacement for an expensive material. Silver leaf - a thin foil made from an aluminum-zinc alloy - is used for cladding non-metallic sculptural forms in order to give them a silvery sheen.Cupronickel- known since prehistoric times, an alloy of copper and nickel with small inclusions of iron and manganese (or without them). Cupronickel cutlery has long been considered worthy replacement silver spoons and forks, however, it is now recognized that nickel is harmful to the body.
Nickel silver- a kind of cupronickel with an admixture of zinc. The alloy is inexpensive, but it is suitable for making cutlery only conditionally: if a spoon made of nickel silver is not covered with a layer of natural silver, the food will acquire a metallic taste.
Silver imitations exist officially, on legal grounds... Counterfeit silver is alloys created to maliciously imitate natural silver. The mixture often contains a little silver and even gold (although the basis is still the same nickel silver), as well as iron.
Jewelry is made of counterfeit silver, counterfeit investment coins are minted, small bars are cast for the purpose of active sale via the Internet.
The Chinese are famous for their special skill in forging silver. For some reason, many buyers are sure that assaying silver items is not necessary, and therefore the presence of the so-called name or brand stamps, in their opinion, is equivalent to the presence of an imprint with a test. The Chinese "experts" are so adept at falsifying silver alloys and brands that they do not hesitate to release into circulation not too exact copies of the products of the most famous brands.
Jewelry sellers often use the expression "Tibetan silver" when referring to the high percentage of natural silver in the alloy. In fact, we are talking about the well-known nickel silver, really (more often - imaginary) enriched with real silver.
The best examples of the so-called Tibetan silver contain up to 30% of the precious metal. In the worst cases, silver is not found at all.
Fraudsters have introduced the concept of "Leningrad silver" into circulation. The enterprises of a St. Petersburg firm producing silver-plated brass jewelry were found to be guilty without guilt. Criminals buy up very high-quality products, equip jewelry with an embossed stamp resembling an assay stamp, hang false labels and sell the items as silver. In fact, no special "Leningrad silver" exists in nature!
How to identify a fake?
At home, it is very difficult to determine the authenticity of a silver product and the conformity of the sample to the actual quality of the metal. Common advice recommends listening to the purity of the ringing of the purchased silver, testing it for hardness and thermal conductivity, and exposing the alloy to chemicals available in everyday life.Implementation of any of the recommendations does not give reliable result... There is only one way out - you need to buy silver only from reputable suppliers of jewelry branded by the State Assay Office. All other methods of purchasing silver do not give confidence in the fairness of the transaction.
For thousands of years, people have been using the precious white metal for the production of jewelry, tableware, decorative interior items, minting coins. It is beautiful, easy to get and work with, but the list of advantages does not end there.
Silver has a shiny white color, which gives it amazing reflective properties - the reflectance is 95% - which is why it is used in the production of high-quality mirrors instead of aluminum.
Silver properties
Silver has high density, which makes it heavy and allows the production of thin foil and wire.
Another indisputable advantage is its exceptional thermal and electrical conductivity - the best among all metals - which made it practically irreplaceable in the chemical industry and in the manufacture of high-tech devices.
- Applications and properties.
- Melting temperature.
- Remelting at home.
Since ancient times, people have known disinfecting properties this metal, which also contributed to its widespread use. Also in Ancient egypt silver plates were applied to wounds, and in Persia BC, water for the fighting army was stored in silver vessels.
Nowadays, this property is also successfully used by mankind - all kinds of filters for water and air, parts in refrigerators, washing machines, medical equipment are manufactured using silver ions.
Surprisingly, silver has found its place in Food Industry- it is registered as food supplement E174 and is part of many biologically active substances although the usefulness of their use is controversial.
Colloidal silver is often credited with having beneficial effects in preventing colds and flu, as well as the ability to heal from diabetes, cancer, syndrome chronic fatigue, HIV / AIDS, tuberculosis, and other really serious diseases.
However, such a miracle is more a marketers dream, since there are no medical research confirming that colloidal silver effective in the treatment of any of these diseases.
Nevertheless, the fields of application of this metal are constantly expanding, alloys and chemical compounds can be found both in almost any apartment and in space as part of parts for satellites and spaceships.
Of the "minuses" is the property of silver items fade and darken over time on exposure to humid air. A slightly soluble plaque forms on the surface, but this is also fixable - cleaning allows you to restore its former shine.
As for the beneficial effects on human health, then in everything you need to know when to stop and remember that it is a heavy metal, the supercontent of which is drinking water dangerous for health.
It is mainly used not in pure form, because silver without impurities is a rather soft, ductile material. Most often in the silver alloy are found cadmium, nickel, zinc and copper. These components make it easier to work with metal and make the finished product stronger.
Exists many reasons, for which there is a need to melt silver. It may be a desire to make the metal cleaner, which means more expensive, freeing it from impurities.
Or maybe it was decided to melt the ring or cutlery inherited from the unloved aunt and create a new modern decoration own design. In any case, the first step is to find out at what temperature the silver melts.
Melting temperature
Silver without additives melts at a temperature of 961.9 ° C
, but boils when the mark reaches 2210˚C. It is easier to melt a silver alloy than a pure metal ingot, as impurities lower the melting point.
This stuff is so easy to handle that its not a large number of it is possible to melt even at home in the kitchen using a gas burner.
However, the process dangerous enough, violation of safety precautions can lead to burns and fires, therefore, it is not recommended to melt this metal in an apartment. If this procedure cannot be avoided, you must strictly follow the safety rules.
(Frolov V.V., Ermolaeva V.I.)
30.1. Physicochemical characteristics silver
Silver is a chemical element I B of the group of the Periodic Table of D. I. Mendeleev with serial number 47 n atomic mass 107.88. Silver crystallizes in a face-centered cubic lattice, does not undergo polymorphic transformations. Silver has the highest electrical conductivity, thermal conductivity and reflectivity among metals.
Basic physicochemical and mechanical properties silver are shown below:
TOC o "1-5" hz Density, kg / m3 ..................................... ........................................... 1049
Temperature coefficient of linear expansion,
■ 10th, city "1 ............................................ ................................. nineteen
Thermal conductivity coefficient, W cm-1 deg-1 .... 4.18
Specific heat, kJ / kg-deg ..................................... 0.235
Specific electrical resistance, μOhm-cm ... 1.59
Melting point, ° С ............................................. ................. 960.5
Ultimate tensile strength, MPa ........................................... 180
Yield strength, MPa .............................................. ......................... thirty
Elongation,% 50
Silver does not dissolve in dilute hydrochloric and sulfuric acids, it dissolves well in nitric acid, a mixture of nitric and hydrochloric acid, in hot concentrated sulfuric acid, does not interact with alkalis, silver oxides are unstable. The darkening of silver is associated with the formation of an Ag2S sulfide film on its surface in humid air containing sulfur compounds. Therefore, it is impossible to use silver and its alloys in an environment containing hydrogen sulfide, humid sulfur dioxide, as well as in contact with rubber and ebonite. Silver is used in instrument making mainly for the manufacture of contacts, in the chemical industry for the manufacture of welded structures operating in especially aggressive conditions, in cryogenic technology, and in the jewelry industry.
Various impurities even in small quantities significantly reduce the conductivity of silver. Silver is susceptible to erosion and has low arc parameters compared to other metals, lends itself well to all types of plastic processing, is welded and brazed.
Silver is produced in two grades: Ср999.9 and Ср999 (GOST 6836-80), the silver content of which is 99.99% and 99.9%, respectively. Main impurities: Pb, Fe, Sb, Bi.
30.2. Main grades, structure and mechanical properties
Silver forms a continuous series of solid solutions with gold and palladium, alloys of which are widely used
In the silver - gold system with medium concentrations of components, the specific resistance, thermal conductivity, plasticity are maximal, the mechanical strength is low, and the good durability is high. Gold-silver alloys are hardened with copper, they are marked ZlSrM990-5, ZlSrM980-15, etc. (GOST 6835-80), where the first number indicates the gold content, the second - silver. The alloy ZlSrM990-5 contains 99.0% gold, 0.5% silver, the rest is copper. Alloys of this system contain Ag from 0.5 to 33% (by weight).
Alloys of the Ag - Pd system are produced in two grades: SrPd20 n SrPd40 with a silver content of 80 and 60%, respectively. They have properties similar to those of gold-silver alloys.
Ag - Pd - Cu alloy SrPdM30-20 (GOST 6836-80) contains 50% Ag, 20% Cu, 30% Pd.
Ag-Pt alloys form a phase diagram of the peritectic type with limited solubility of the components. Alloys with a Pt content of 10-45% (by weight) can undergo aging. Heat treatment of these alloys can achieve high hardness and strength: up to 3600 MPa after quenching at 1000 ° C and aging at 550 “C.
Ag - Cu alloys form a eutectic-type phase diagram with regions of limited solubility. Aging can significantly improve the mechanical properties of alloys. Copper increases the hardness and reduces the erosion of silver, especially in the field of eutectic alloys, but worsens the corrosion properties
30.3. Weldability of silver and its alloys
Welding of silver and its alloys is difficult due to high thermal conductivity, which requires the use of concentrated heat sources, the use of preheating up to 500-600 ° C. A high coefficient of thermal expansion can lead to significant stresses and deformation of products. Liquid silver dissolves oxygen well; during the crystallization of the metal, the formation of an Ag20-Ag eutectic with a melting point of 507 ° C is possible, the release of which embrittle the metal, and the formation of pores is also possible. During melting and welding, silver vaporizes intensely. The impurities of Al, Cu, Si, Cd contained in silver alloys can oxidize during welding, which will lead to a loss of alloy ductility. Due to the high fluidity, welding of silver and its alloys is recommended to be performed in a lower or slightly inclined position.
30.4. Welding technology for silver and its alloys
For welding of silver and its alloys, gas welding, argon-arc welding with a non-consumable electrode, and forge welding are used.
In gas welding, methane-oxygen and acetylene-oxygen normal flame is used, as well as filler wire deoxidized with aluminum, and a flux prepared on ethyl alcohol of equal amounts of borax and boric acid... The flux is applied to the joined edges or filler wire. Flame power, l / h: № = (100-150) s, where s is the thickness of the welded metal, mm. A "left" welding method is used, while the distance from the flame core to the surface of the weld pool should be 3-4 mm. The torch is positioned perpendicular or slightly inclined to the surface to be welded. Heating is carried out at the highest possible speed, without interruptions or repetitions. The assembly is carried out, as a rule, without tacks in special devices... The edges to be welded and the filler wire are melted at the same time, and the wire is heated to over high temperature... The seams are very prone to pore formation.
Mechanical properties of joints made by oxygen acetylene welding: av 98-127 MPa, bend angle 30-180 °.
Arc welding with a tungsten electrode in an argon atmosphere is carried out with direct current of direct polarity. The filler wire is selected in composition close to the metal being welded. Manual and automatic welding are possible. Manual welding is carried out "forward angle" without transverse vibrations, the angle of inclination of the torch to the surface to be welded is 60-70 °, the filler wire is fed at an angle of 90 ° to the tungsten electrode. Welding of silver butt joints is carried out in a downward or slightly tilted position. High-quality seam formation is ensured by the use of shaping linings. The mechanical properties of silver joints made by argon-arc welding with a tungsten electrode are higher than those of gas welding. Table 30.1 shows the mechanical properties of joints made by argon-arc welding on sheet silver grade Sr999.9 with a thickness of 2 mm. The original metal had a tensile strength hr = 161.9 MPa, a relative elongation 6 = 28.5%, a bend angle a = 180 °.
The most stable properties, close to those of the parent metal, are possessed by welded joints made in a chamber with a controlled atmosphere, which is associated with reliable protection of the weld pool.
With bimetallic sheets, low-carbon steel - silver, a large number of pores are observed, therefore, in some cases, it is recommended to use an intermediate cladding layer of nickel, copper or silver. At
Nowadays, you need to know and be able to distinguish silver from other metals. Silver is a noble natural white metal that is widely used both in industry and in everyday life. Most often, cutlery, dishes, heirlooms, jewelry, candlesticks, frames are made from it. It is very difficult to distinguish silver from other cheap, but similar metals, which is often used by scammers and pawnshops with a dubious reputation.
Defining real metal
To understand how to distinguish silver from other metals, you need to clearly understand the basic characteristics of imitations that are so often charged for silver. It becomes clear that modern jewelry factories and industrial factories are careful control and do not allow silver of dubious quality to enter the market. All of them work in accordance with certain norms and GOSTs, so you should not worry about the quality when purchasing silver items in reliable places and trusted jewelry stores.
Forging silver began in ancient times, when the price of silver was significantly higher than in our time. Sometimes it exceeded even pure gold in value. To replace or counterfeit this white metal, various analogs were used or alloys were made from them. Ornamental metals were lead, zinc and aluminum. Often pseudo - jewelry was made from them, and covered on top thin layer silver to divert the eyes of inexperienced buyers. But after a while, such products begin to lose their aesthetic appearance, turn black, become covered with bloom, the places of the test and hallmarks are erased. If, after thorough cleaning, these signs only worsened, then the products really turned out to be a fake.
Methods for determining silver
There are many ways to distinguish silver from other metals. This can be done at a simple home, by finding it at hand necessary substances and simple devices.
Such simple methods will help you easily recognize a real noble metal at home in a few minutes. In order not to fall for the tricks of scammers, it is imperative to purchase the product at trusted points of sale. The client always has the right to request a quality certificate for the purchased products.
Differences between silver and similar metals
Silver is very similar in its own way outward appearance with other metals that can hardly be called cheap and of poor quality. To be able to distinguish between them is not so easy, but still real. Most often, silver is confused with white gold and cupronickel, and sometimes even with aluminum.
To understand how to distinguish silver from white gold, you need to be a highly professional and well know the specifics of these metals. Doing this at home is impossible and dangerous. The wrong approach can spoil jewel... These two metals are very confused due to the fact that the basic composition of the white gold alloy has a high percentage of silver. Outwardly, these products can only differ in a more pronounced luster of white gold. But due to decorative special coatings, this distinction has lost its relevance in our days. To distinguish between these silver and white gold can only experienced specialist- a jeweler who can calculate the original by its density. In jewelry stores, you can only calculate the difference between them by looking at the price. White gold will be an order of magnitude 5-10 times more expensive than silver.
Silver is often confused with cupronickel, which is an alloy of lead, nickel and copper. Cupronickel is often a production component of silver of various technical samples. To understand how to distinguish silver from cupronickel, you first need to carefully consider the product. On cupronickel, you will not find a test mark, there will only be the MSC stamp, which deciphers its basic composition (copper, lead, nickel). To distinguish silver product and cupronickel can be used with water. When diving to the bottom cupronickel products a light will appear on the surface of the water greenish tint, and when interacting with lapis pencil dark spots form on it.
It is possible to determine the authenticity of silver from an alloy using density and weight. This can be done with the help of real jewelry specialists who will determine real authenticity metal by its own technical methods. Cupronickel also gives out a very subtle specific smell of copper, which is not so easy to identify to an unknowing person.
If you still want to use home methods, then you can use an iodine solution, which will leave a slight dark spot... There will be no such trace on cupronickel. However, then you will have to additionally clean the silver from the resulting dark spots.