Gold (Au): Pure gold - yellow metal, soft, very malleable. It is possible to deform the sheets with a thickness of 0.08 ?m or stretch in the wire, 2 km which weigh 1 g Pure gold is a good conductor of heat and electricity, it is highly resistant to chemical action. Pure gold is about 2.5 times heavier than iron (density of pure gold at 20°C is 19.32 g/cm3, and pure iron of 7.82 g/cm3). With nonmetals (except halogen: fluorine, chlorine, bromine, iodine, astatine) gold does not react.
Air pure gold does not change, even when overheated, but easily soluble in chlorinated water (not recommended for contact with bleach) and in solutions of cyanides of alkali metals (for example, toxic potassium cyanide).
Concentrated acids are sulfuric, hydrochloric, nitric do not react with gold. But if the gold react with hydrochloric acid with the addition of chloride of iron (dark brown solution used in the etching of electronic circuit boards) - this metal is easily dissolved. Pure gold is easily dissolved in a mixture of 3 volumes of hydrochloric acid and 1 volume of nitric acid (Aqua Regia).
If You have oxidized gold, it can be restored. The reducing agent can be hydrogen peroxide, two tin chloride, iron sulfate, titanium trichloride, lead oxide, manganese dioxide. For recovery of gold using various organic substances: formic and oxalic acid, hydroquinone, hydrazine, metol, acetylene, etc..
Platinum (Pt) — greyish-white metal, plastic, quite soft and malleable. There are six platinum metals. All platinum metals - refractory silver-grey metals, differing in hardness and melting point: platinum (T melt = 1769 0C) and palladium (T melt = 1554 0C) - soft and plastic osmium (T melt = 3027 0C) and ruthenium (T melt = 2334 0C) - fragile rhodium (T melt = 1963 0C) and iridium (T melt = 2447 0C), solid and durable
Use platinum metals based mainly on their chemical inertness, and high catalytic activity. Cookware made of metallic platinum is required when working with highly corrosive substances, such as fluoride melts. The grid of platinum-rhodium alloy serves as a catalyst in the production of nitric acid at the stage of oxidation ammonia.
An interesting property of one of the platinum metals, palladium is the ability to reversibly absorb hydrogen at 80 °C and atmospheric pressure of 1 volume of metal absorbs up to 900 volumes of hydrogen. Hydrogen is in the metal in atomic form and has a high chemical activity.
Chemistry of platinum metals is very complicated. Not the last role in this is played by the "electoral noble" metals. For example, even Aqua Regia at room temperature not react with osmium!
Metal silver (Ag) — brilliant, white (T melt = 962 0 C), malleable and ductile, easily machinable. Silver occupies a leading place among the metals are conductors of heat and electricity.
Although silver with oxygen does not react directly, it can dissolve a lot of this gas. The solubility of oxygen in solid crystal silver maximum at a temperature of 450 0C, when 1 volume of metal capable of absorbing 5 volumes of oxygen. Much more oxygen (up to 20 volume 1 volume of silver) is dissolved in liquid silver. This process is accompanied by a beautiful (and dangerous) phenomenon that has been known since ancient times, a sprinkling of silver. It happens that's why. When liquid silver is solidified (at a temperature of 962 0C), first, as a rule, hardens the top layer of metal. On the surface crust is formed, which is still liquid silver. If melted metal silver dissolved much oxygen, the solidification accompanied by abundant release of gas. Under the pressure of the released oxygen crust is broken, and is an explosive spray of metal, like silver spits.
Silver niello. Patina
СSilver can be covered by niello. The process of darkening is applied film sulfide silver on the surface of silver, on which the sharp needle scratched (engraved) figure. Sulfur stuck in the grooves. When heating, the product sulfur is alloyed with silver, painting the grooves in black color. Silver is not oxidized by oxygen, however, is covered with a black layer of silver sulfide: 4Ag+2H2S+О2=2Ag2S+2Н2О. Then the surface is carefully polished to achieve a metallic luster.
The surface of the silver can not only black, but also painted in other colors. Greenish-gray acquire silver objects, aged for a few minutes in a boiling solution, prepared by dissolving 10 g of potassium iodide in 10 ml of water followed by the addition of 30 ml of concentrated hydrochloric acid. Metal silver is covered with a thin film of silver iodide, which gives the product a greenish-gray tint. The film breaks the light with the formation of tiny particles of silver, also coloring the surface.
Of particular interest is the process of patina for the surface of copper and bronze. Patina is called a thin film, which not only protects the metal from corrosion, but also paints it in a specific color.
For getting patina to thoroughly clean the surface from grease, dust and corrosion products. The oxide film is removed, treating the product with acid solutions. Then it should be washed under running water. Easier just to spend patina, immersing the object in a specially prepared solution.
To get golden brown color in a liter of water was dissolved 20 g of copper sulphate (CuSO4•5H2O) and 5 g potassium permanganate KMPO4, can withstand the subject of 4-5 minutes and then take out and polish the surface with a dry cloth. When using the same solution, but heated to the boiling point, it is possible to gets patina dark brown.
Patina gray-black or dark brown, you can create, using a solution of sulfuric liver. Dull green patina is formed by immersing the copper or bronze wares in a solution of 20 g of ammonium carbonate (NH4)2CO3 and 2 g of ammonium chloride NH4Cl in 100 ml of water. The chemical composition of this patina close malachite - basic carbonate of copper (CuOH)2CO3.
Bactericidal effect is negligibly small concentrations of ions silver (Ag+) is explained by the fact that it interferes with the activity of the microbes, interfering with the work of biological catalysts - enzymes. Connecting with cysteine - an amino acid that is incorporated into the enzyme, silver ions disrupt its normal operation. It is observed that bacteria in the water already dying when the concentration of silver 10-9 g/l, this concentration of ions Ag+ is created when the introduction into the water of the silver items. So, our ancestors prefer to eat from silver ware! Water infused with silver, is stored very long time.
The one who forced for many years to deal with silver and its salts, runs the risk of getting argyria: entering the body silver slowly deposited in the connective tissue on the walls of the capillaries of the kidneys, bone marrow, spleen, etc. Accumulate in the skin and mucous membranes, it gives them a grayish-green or bluish color, most pronounced in the open areas of the body exposed to light.
Develops argyria slowly: strong darkening of the skin is observed only after dozens of years. Reversed color is not possible. When argyria people may not experience any pain or disorder (unless, of course, not affected by the cornea and lens of the eye), and therefore only conditionally it is called disease. There is even one plus - argyria excludes infectious diseases: the man is so "saturated" silver that it kills all bacteria that enter in the body
Getting ultrapure metals
It is known that all the metals, without exception, contain impurities of different chemical elements. The impurities may include sulfur (S), phosphorus (P), silicon (Si), carbon (C), as well as many metals, such as molybdenum (Mo), vanadium (V), chromium (Cr), iron (Fe), aluminum (Al), etc. Impurity metals largely able to change their physico-mechanical properties, in some cases worsening, and in some cases improving performance properties. There are no metals, which are completely absent impurities, that is, even the most ultrapure metal contains impurities, but in ultrapure metal of such impurities in 100 or more times less. The percentage of impurities can be only 0,0001%. Ultrapure metals can be obtained by various methods. For example, a thin metal purification was achieved by distillation and the melting of these metals in vacuum, the dissociation of volatile compounds and zone melting. This method is based on different volatility metals. At a certain temperature to separate impurities from the less volatile metal or, on the contrary, they drive off the more volatile metal from the less volatile impurities.
Getting ultrapure metals by thermal dissociation of volatile compounds based on the ability of certain metal compounds decompose at high temperature. For example, titanium (Ti) , zirconium (Zr), form of iodine at a relatively low temperature volatile compounds - iodides, which are easily separated from impurities. At higher temperatures a pair of iodide is decomposed into the pure metal and iodine (this method is also called transport reaction).
Zone melting Method based on the different solubility of the impurities in the solid and molten metal. The process is based on the fact that the rod from the cleaned metal moves slowly in a high temperature zone. He melts. As it moves the narrow liquid zone, which is formed there, is moved in the opposite direction. In this zone, the molten metal impurities are collected, which gradually moved to the end of the rod (the end of the rod enters the zone last).This operation is repeated many times. The end of the rod containing impurities mechanically separated from a pure metal.
Ultrapure metals differ in their properties from the ordinary. If it ultrapure chrome, it has a higher ductility. Increases the electrical conductivity and thermal conductivity.