Gold is the most popular metal in history, in culture, in the economy. For his possession, rivers of blood were spilled, family strife broke out, and even wars were waged. Its significance for the entire human civilization is based on its unique chemical and physical properties, on the peculiarities of its internal structure.
Gold is the most ductile metal. This quality makes it popular everywhere: from jewelry to microelectronics.
The most "metal" metal
All the most obvious properties that scientists call metallic are concentrated in gold. It is second only to silver, copper and pure palladium in electrical conductivity. By thermal conductivity - the same silver, copper and cobalt. In its ability to absorb thermal energy, gold is second only to exotic bismuth, ahead of mercury and silver. According to other "metallic" properties - malleability and light reflection - it is a champion. Gold is the most ductile metal in the world, and its luster is a legendary concept.
The molecular structure of gold is also very "metallic." It is a geometrically regular crystal lattice with positive ions in the nodes and a dense concentration cloud of "electronic" gas between them. This part of the atom is made up of free electrons located at the external energy level. They create an attractive force between the nodes of the lattice, which ensures the ability of the metal to deform without violating the overall integrity. So the most ductile metal is arranged.
Plasticity determination
From the Greek ฮ ฮปฮฑฯฯฮนฮบฮฎ ("sculpting", "modeling") the word "plastic" came from, giving the root to others related to the change in the shape of a solid. Plasticity is the property of a solid to change its shape and dimensions and maintain permanent deformation after the termination of the action of external forces without changing the volume and integrity violation.
For metals, this is one of the most important characteristics that allows you to use them in practice. Without the ability to shape metal blanks, it would be impossible to create even the simplest household items. Gold is the most ductile metal, and products made of it are an example of what shape can be given to a sufficiently malleable material by forging, pressure, rolling, drawing, drawing, etc. The inherent property of the material is fragility.
Ductility test
The ductility characteristics of metals are usually determined in static tests. The most significant is the tensile test. In order to find out which metal is the most plastic, it is necessary to expose to this effect samples of the same size under similar temperature conditions. The amount of deformation that a metal sample can withstand before failure is an objective indicator of ductility.
The numerical expression of the result of tensile tests are two main factors. Relative elongation is the percentage of the increased length of the specimen after rupture caused by deformation, to the original. The most ductile metal - gold - has an indicator of 65%. For comparison: iron - 40-50, aluminum - 30-40.
The second indicator of ductility is the relative narrowing of the cross section of the sample. Gold has an initial sample cross section 90% larger than what it has before rupture. For aluminum, this figure is 80%, for copper - 75%.
Soft, viscous and durable
According to the Mohs hardness scale for gold, the indicator is 2.5โ3.7. In its pure form, this metal is much softer than many widely used materials and is scratched with a knife or even a fingernail. Therefore, in order to avoid the rapid wear of gold products, special reinforcing ligature elements, usually silver or copper, are added to the metal for their manufacture. Gold also has harmful impurities. The most ductile metal in the periodic table in the presence of lead, platinum, cadmium or sulfur becomes brittle.
The softness of gold is of a special nature, it is complemented by its viscosity and ductility. The convenience of molding and processing of parts is complemented by high tensile strength - 3300 kg / cm 2 . Such a unique combination of physical and mechanical characteristics of gold has been used since ancient times. An example is gold leaf.
Domes in Russia are covered with pure gold ...
Despite the centuries-old history of gold mining, this metal has always been rare and precious. This is the most ductile metal. This quality makes the use of gold foil for decorative decoration of interior elements or even for covering church domes cost-effective. To cover a large area, very little precious metal is required: 1 gram of the plate can be uncoated into a sheet of 1 m 2 .
Even the manual method of obtaining sheets for gilding makes it possible to achieve a thickness of a thousandth of a millimeter. This thickness allows the gold plates to stay on the surface due to molecular attraction. The technology for obtaining tinsel has improved significantly. Robotic lines are now used to flatten gold sheets, but the process is based on the high ductility of the starting material.
Golden thread
The ability of gold to withstand tensile forces without breaking is known from the very beginning of its commercial use. The manufacture of such a wire for jewelry was established in ancient times - ancient craftsmen already knew which metal was the most plastic. In the mid-20th century, a microwire was produced with a gold core, which even with plastic insulation was 7 times thinner than a human hair. A continuous gold thread about 3.5 km long was drawn from 1 gram of metal.
Today's technologies have brought the thickness of the gold wire to several microns, further development of the technological advantages of the metal continues.