The main properties of gold

Due to its chemical and physical properties, gold belongs to a small group of the most valuable and rare metals that exist in nature. Mankind appreciates this precious metal for its beauty and ability to maintain its bright and brilliant appearance in jewelry made from it, coins. And also it is used in some industries. For many centuries, gold products have been a luxury item and have never lost their value, emphasizing the high level of solvency of its owner or country owning gold and foreign exchange reserves. One can often hear that it is gold that is the international payment system that has weight and significance in the territory of any world state.

In appearance, this mineral looks like small pieces of metal of irregular round shape of straw-yellow color. The main physical properties of gold:

• metal melting occurs at a temperature equal to 1063ºС;
• the density of the substance is 19.33 g / cu. cm;
• hardness indicators, determined by the Mohs scale, can be from 2.5 to 3;
• to bring the metal to the highest boiling point is possible at t = 2948ºС;
• the level of thermal conductivity at t = 0ºС is 311.5 W / mK;
• the strength of the metal after annealing is from 100 to 140 MPa.

The structure of its crystal lattice makes gold a rather soft substance, and various impurities called ligatures are added to the metal to give hardness.

A valuable natural mineral has other unique physical properties.

• High level of ductility. From 1 gram of gold, if desired, you can stretch a wire up to 2-2.6 meters long or roll out the metal in the form of a flat sheet of foil 1 micron thick. Due to the natural softness of gold, it was noticed that within 1 year the coins that were in circulation could lose up to 0.1% of their original weight when casting.

• High reflectivity. Precious alloy in finished form has the ability to be easily polished to a bright specular sheen. Thin sheets of rolled material are used for applying gilding. This is even used in astronautics - the thinnest layers of gold are applied to the helmets of astronauts and the surface of outer space equipment to protect them from the harmful effects of infrared radiation, which manifests itself in open space.

• Possibility of spraying. A precious mineral has the property of decaying into minute fractions of a size equal to the length of light waves. This ability allows this material to be sprayed. For example, it is known that in water bodies and rivers there is a dispersion of gold that cannot be seen visually, but can be determined using special instruments. The surface, covered with the thinnest golden layer, is able to transmit the rays of the sun without heating up.

• Good ductility. Gold is soft and has the ability to take the desired shape, which is one of its most valuable qualities. For example, from 1 gram of gold it is possible to make a sheet of thin foil, the area of ​​which will be no less than 1 square meter. m. This property is used to make gilding in the form of the finest gold leaf, which goes to cover church domes and icons, is used to decorate interiors, and is used to create objects of art.

• High level of electrical conductivity. With resistance to oxidative processes, the precious mineral has good electrical conductivity. This property of the metal allows it to be used for the manufacture of resistances in electronic circuits of many modern devices: telephones, televisions, computers, multimedia players, in radio engineering and other similar devices.

It is known that the precious metal completely lacks any smell, and also this material does not have the ability to magnetize. In addition, it has been scientifically proven that gold as an element is part of at least 15 minerals mined in the bowels of the earth. In most of the mined rocks included in this number, gold is included in the atomized composition found at the atomic level.

The metal, called gold (aurum), has a designation - Au, which literally can mean "sunny" or "yellow". In the Mendeleev system, metal is assigned to group 1, it is assigned 79 atomic number. The chemical crystal lattice of Au has a cubic structure.

Metal has special chemical properties.

• Relative inertia. Gold does not change its properties upon contact with sulfur and oxygen, does not interact with nitrogen, carbon, hydrogen and phosphorus. Gold does not react to many alkalis and acids.
• The valency of this chemical element manifests itself as + I or + III.
• At t = 20ºС, the metal enters into a chemical reaction with aqueous solutions of chlorine and bromine. And water-alcohol solutions of iodine, reacting with 585 gold, leave patches of dark spots on it, which does not happen if iodine is added to 750 gold.
• The color spectrum of the metal depends on what size particles it consists of. The smallest particles of gold can have a greenish-gray hue. According to geological exploration, for every 20 mines there is only one, where gold is mined in the form of yellow nuggets.

If you melt a natural gold nugget, then in a liquid state it will look like a substance that has a pale greenish-gray hue, and this hue is also inherent in vapors that rise from a hot molten metal. One has only to heat the substance to a temperature exceeding 1064 ° C, that is, increase the melting rate of the metal by at least 1 ° C, as the vapor of the gold alloy will begin to disappear into the atmosphere. And the higher the melting point of a substance, the higher its volatility index will be. If mercury, arsenic, and antimony or tellurium components are added to the alloy, the evaporation from the surface of the gold alloy will increase even more, since these components will form the so-called volatile compounds.

Jewelers working with various gold alloys have noticed that The chemical, physical and external properties of the material obtained by the smelting of gold are affected by ligature impurities.

Let us consider in more detail how the properties of a precious mineral change when combined with different substances.

In combination with silver, a noble yellow metal lowers its melting point, and also changes the natural initial greenish-yellow color to steel silver shades. This combination has its positive and negative sides. Despite external visual changes, the strength of the finished molten material when combined with silver only increases. But in the course of practical research it was established that with such a composition, a valuable alloy somewhat reduces such important qualities as malleability and ductility. However, this does not mean at all that Au and Ag alloys are not used - on the contrary, this is a fairly common combination that jewelers often use in their work.

Changes in the physical properties of the finished precious alloy will occur if copper is added as a ligature to it. This metal significantly increases the strength of the gold alloy, while maintaining the combination of metals, the plasticity of the obtained material and its good ductility.

If the composition of the precious alloy of copper gold is present from 14.5% or more, then the finished product will have a pronounced reddish tint - this gold is called "pure". But in this case, it was not without drawbacks - using copper ligature, the resulting material loses its anti-corrosion properties, which is due to the increased ability of copper to form oxidative reactions with oxygen. Contacting with a humid environment and even just with air, over time a product from such an alloy will necessarily darken, while losing its original bright colors and luster.

Since copper has a low cost, then alloy from it will not be too expensive in price, which affects the cost of finished products - it is the cheapest. During the Soviet Union, 583 samples of gold were produced for the population, and only in 1995, 585 samples were put into production, which contained 0.2% less copper than the previous analogue, but the gold content increased by the same 0.2%. which immediately led in due time to the rise in price of gold items.

This natural metal is used by jewelers in order to clean the gold alloy from the natural red, and especially often this ligature is used in the manufacture of especially valuable white gold.

When combined in a precious alloy of Au and Ni, the strength of the finished precious material is significantly increased. Products made from such a noble alloy have a steel color with a subtle pale straw hue. To permanently eliminate this weakly manifest yellowness, the surface of finished jewelry is covered with a thin layer of another metal - rhodium. They do this not only for beauty, but also to reduce the allergenicity of precious products.

The fact is that Nickel metal is known for its ability to cause allergic manifestations on the skin.. In 8 out of 10 people, these manifestations will certainly make themselves felt when wearing jewelry. Therefore, from alloys where nickel was used as a ligature, brooches, cufflinks, pendant pendants, key rings are most often made - in a word, something that has little contact with human skin with prolonged contact. Over time, a thin rhodium-plated coating on jewelry is worn away, and approximately once every 6 or 7 years it will need to be updated in a jewelry workshop. After such restoration work, the decoration will again look like brand new, shining with steel bluish-silver tints.

A chemical element called palladium, according to chemists, is a product that appeared as a by-product in the processing of precious metals. This element was obtained by combining platinum, mercury cyanide and aqua regia (its composition: 3 parts of nitric + 1 part of hydrochloric acid). In this way, the discovery of this metal was made when Pd, Au, Pt and Ag were already discovered. Under normal temperature conditions, fluorine does not act on palladium; hydrochloric acid and even aqua regia do not affect it. This metal is absolutely not prone to oxidation in contact with oxygen, it has a very strong structure and does not appear scratches, cracks or chips, and in addition, it is well prone to any machining and welding.

By adding palladium metal as a ligature component to the gold alloy, white gold can be obtained. Due to its unusualness and increased strength, gold products with palladium are superior in quality and cost to other gold alloys that have simpler components in their composition.

Palladium is valued not only in jewelry production, but also finds applications ranging from medicine to aircraft construction. At international market auctions, the value of palladium quotes sometimes exceeds even the cost of gold, and jewelry made from it looks particularly elegant and noble. They are in high demand among connoisseurs of white precious alloys.

Today, natural platinum is the most expensive of all precious metals known to mankind. By its physicochemical properties, platinum has 2 times more density and strength than its precious counterpart - gold. Besides, platinum has the highest resistance to metal corrosion — oxidation does not occur when it comes into contact with oxygen. By its properties, platinum is most similar to palladium metal, the difference between them is most of all in cost - platinum is more expensive than palladium.

When creating a noble alloy, platinum is added to pure gold, and then after smelting, a product of a sparkling silver-white color is obtained, in which any impurities of yellowness are absolutely absent. As part of the gold alloy, platinum significantly increases its value, which affects finished jewelry.However, this alloy is always very popular and has a very good reputation among those who appreciate the purest white alloys created from noble metals.

You can find out below why gold is of great value.