Rhodium is a rare precious metal and well known to lovers of jewelry. Rhodium spraying prevents the appearance of scratches and sweetes on precious products, contributing to the preservation of the initial appearance for a long time.
What it is?
Rhodium is the chemical element N45 from the periodic table of Mendeleev, relating to the noble metals of the platinum group. The element was opened by the British William Hydov Vollaston in 1803 when working with a platinum solution. In it, the chemist discovered a bright pink powder substance, called the name of Rodi, which translated from Greek means "Rose".
Rhodium is one of the rarest and expensive metals, What is due to the complexity of its extraction from platinum on an industrial scale. In nature, it is present in minerals, including several platinoids at once. Experts note that to obtain 1 kg of this metal requires several tons of native platinum. Vollarston highlighted the rhodium as follows: After the synthesis of sodium hydrogen salt, it is a long time for a pink-red powder over a hydrogen flame, as a result of which a few drops of pure metal received only a few drops.
Later by the efforts of Professor Lebedinsky was opened a new way of allocation of rhodium - Impact on the solution of platinoid salts with cold. As a result, the cooling in the solution fell out the precipitate, submitted by the compounds of Rhodium and Iridia. This method was widespread in the chemical industry and is still used. To date, by the help of the Lebedinsky technique, the order of 30 tons of pure metal is released annually.
The procedure aimed at separating platinum and getting the most pure rhodium was called affinent.
As for the appearance of the rhodium, the red-pink shades are characteristic only for its compounds, while the metal itself looks like silver, although he is inferior to it in brightness brightness. So, The amount of light reflected by this metal is 80%, while silver is 95% in silver . Despite this, in the manufacture of technical mirrors, instead of silver, it is often used by rhodium. This is due to the reflection of platinoid and its ability to operate with an elevated density of electromagnetic radiation, including the infrared range. In other words, the rhodium coating can serve for many years, while the silver spraying under similar conditions does not last day.
The characteristic of the metal would be incomplete without mentioning its value. The price of pure rhodium is constantly varied and depends on the annual production volume. So, by August 2016, Troyan Once Rhodium (31,1034768 g) cost about 700 dollars, but in subsequent years the price has increased dramatically. At the beginning of 2020, the value of the rhodium ingot weighing one ounce was $ 9,000. The high cost is due to the fact that the metal does not have its mineral and contains in native platinum, nickel and copper ore, as well as in golden sands as a companion.
However, the greatest content of rhodium is noted in the species of osmiste Iridia - Rhodium Nevyanskit, which includes about 11.3% of pure precious metals.
Composition and properties
Rhodium is a solid noble silver metal, superior to his "progenitor" platinum for chemical stability in many corrosion environments. The electronic formula of its atom looks like this: RH - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 10 4P 6 4D 8 5S 1. The metal is well dissolved in the process of boiling in the royal vodka (HCl and HnO3 mixture), in the H2SO4 concentrate (when heated) and in hydrogen peroxide. The melting point is 1964 ° C, boiling - 3697 ° C, the metal density at 20 ° C is 12.41 g / cm3. Rhodium belongs to the group of rare earth metals, in a solid state it has a silver color with a cold tint.
Rhodium is chemically stable, with the result that with nonmetals reacts very badly - exclusively to achieve the temperature of red cagine. Slowing metal oxidation is possible only in a crushed state and only at 1000 ° C.
Due to the high plasticity, which appears when heated to 850-900 degrees, the metal transformation into a thin wire is occurring, from which after several annealing and rolling gets the thinnest foil.
An important quality of metal is considered to be its ability to change its shade, which is especially valuable in jewelry. Thus, when calcining at a temperature of 800 ° C, the rhodium is coated with an oxide film disappearing by increasing the temperature to 1000 ° C. Black rhodium is especially valued, which is indispensable in the manufacture of jewelry of the most exquisite configurations. Another property of the metal is its ability to act as a catalyst for most chemical reactions. Thus, with the help of chopped rhodium powder, ordinary wine alcohol can be turned into acetic acid.
Deposit and mining
The annual global production volume of rhodium is 30 tons. Such small amounts of production are due to the low content of the element in the earth's depths and the absence of their own minerals. The main metal deposits are located in the Republic of South Africa, which supplies 75-80% of Rhodium to the overall market. Less rich deposits are located in Canada, Colombia and Russia - in countries with the average concentration of native platinum in earthly depths.
In addition to affinity, a perspective method of metal production is considered to be the release of its stable isotope from plutonium, uranium and thorium, widely used in nuclear power. Obtaining rhodium in this way can solve the problem of high demand and insufficient metal volumes produced in the fields. Taking into account the developed nuclear industry and the high content of rhodium in nuclear fuel (up to 400 g / t), the problem of the rhodium deficiency can be solved, and the nuclear power industry will become the main supplier of this metal to world markets.
Where is used?
The scope of the rhodium is quite wide. Metal is in demand in many areas of the chemical industry and processing, which is used as a catalyst, structural raw materials and jewelry.Catalyst
In this capacity, the metal is used in chemical reactions, the most common of which is obtaining acetic acid from methyl alcohol. It is also used when creating filters-neutralizers designed to work with spent automotive gases. And Rhodium-platinum alloys are considered the most effective catalysts in the production of HNO3 by the method of ammonia oxidation by air and in this production alternatives are not yet found.
To date, up to 81% of existing catalysts have a rhodium foundation.
Construction material
Rhodium is indispensable in the manufacture of glass of liquid crystal devices, for the production of which it takes its platinum alloy. In this regard, the metal consumption is steadily growing in proportion to the growth of the production of modern gadgets. Rhodes are actively used in the manufacture of technical mirrors, spotlights and other reflective surfaces that will be operated in extreme conditions and laser installations.
It is impossible not to mention the platinum-rhodium crucibles used to grow precious stones and crystals with electro-optical properties in laboratory conditions. . In combination with iridium or platinum metal, it is often used for the manufacture of the thermocouples necessary for measurements of the proceedable temperatures (over 2200 ° C). It is impossible not to note the role of metal in the process of manufacturing laboratory tubes and the flasks used for chemical experiments. Due to the fact that the rhodium does not interact with practically any substances, in such a dishes you can pour any kind of compositions.
Jewelry
Rhodium is widely used in the manufacture of jewelry, performing two functions at once - protective and decorative. For example, Silver covered with a subtle rhodium layer acquires a deep shine, does not darken and does not oxidize in air, And the parental gold due to the high solidness of the metal (6 units. Up. Moos) becomes more durable and wear-resistant. In addition, the metal is needed to obtain white gold, which is very popular among fans of jewelry, and its oxides are involved in the creation of black gold - the avant-garde direction in the dragmetalls fashion.
Cold, but at the same time the deep and fascinating rude shine is perfectly combined with phyanites, zirconia, diamonds and inserts from precious metals. In addition, the metal is often used as a ligature in the manufacture of platinum and palladium ornaments. Products covered with rhodium spraying do not need regular cleaning and retain the original shine for a long time.
In addition to the decorative function, the relating significantly reduces the allergenicity of white gold, which, with a constant contact with the skin, it causes redness and itching. The layer of this metal prevents unpleasant consequences of wearing decorations, which is especially valuable for people suffering from skin diseases. However, along with a large number of advantages, there are still cons of the conversion. There is still a rhodium spraying requires periodic update, and its presence itself significantly increases the price of the jewelry.
In addition to the areas of application, rhodium is used in the manufacture of coins. So, in 2009, the first purely rhodium coins were issued on the US Mint, which were not used as payment funds, and served as an object of investments. However, a little later (in 2014), the National Bank of Rwanda was released the first birth of a coin with a face value of 10 Rwandan francs, which began to be used as a payment agent.
Another sphere of application of this noble metal is the nuclear industry. Rodium detectors are successfully used as neutron flow meters in nuclear reactors.
What radio components contain?
In Soviet times, it was the opinion that many radio components were made of pure rhodium. However, it was far from the wrong, and the metal was used only to cover the contacts of the connectors. For the manufacture of the parts themselves, it was not suitable, as it was quite fragile and overly broken. But as a cover, it was indispensable, which is due to its good corrosion resistance and a high reflection coefficient of electromagnetic rays. Rhodium coating had contacts (rejoic relay) type RES-55 (a) in series of PC 4569601, RS 4569602, RS 4569603, RS 4569604 and PC 4569605.
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