Properties of metals and its use

A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal (Ancient Greek métallon, μέταλλον) is an element, compound, or alloy characterised by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions. Those ions are surrounded by delocalised electrons, which are responsible for the conductivity. The solid thus produced is held by electrostatic interactions between the ions and the electron cloud, which are called metallic bonds. Currently, there are 86 known metals. Before the 19th century, only 24 of these metals had been discovered and of these 24 metals, 12 were discovered in the 18th century. Therefore, from the discovery of the first metals - gold and copper until the end of the 17th century, some 7700 years, only 12 metals were known. Four of these metals, arsenic, antimony, zinc and bismuth, were discovered in the thirteenth and fourteenth centuries, while platinum was discovered in the 16th century. The other seven metals, known as the metals of antiquity, were the metals upon, which civilisation was based. Mechanical properties of metals The mechanical properties of metals determine the range of usefulness of the metal and establish the service that can be expected. Mechanical properties are also used to help specify and identify metals. The most common properties considered are strength, hardness, ductility, and impact resistance. The strength of a metal is its ability to withstand the action of external forces without breaking. Tensile strength, also called, ultimate strength, is the maximum strength developed in a metal tension test. The tension test is a method for determining the behaviour of a metal under an actual stretch loading. This test provides the elastic limit, elongation, yield point, yield strength, tensile strength, and the reduction in an area. Tensile tests are normally taken at standardised room temperatures but may also be made at elevated temperatures. The ductility of a metal is the property that allows it to be stretched or otherwise changed in shape without breaking and to retain the changed shape after the load has been removed. The ductility of a metal can be determined from the tensile test. Reduction of area is another measure of ductility and is obtained from the tensile test by measuring the original cross-sectional area of the specimen and relating it to the cross-sectional area after failure. The tensile test specimen also provides another property of metal known as its modulus of elasticity, also called Young's modulus. This is the ratio of the stress to the elastic strain. It relates to the slope of the curve to the yield point. The modulus of elasticity is important to the designers and is incorporated in many design formulas. The hardness of a metal is defined as the resistance of a metal to local penetration by harder substance. The hardness of metals is measured by forcing a hardened steel ball or diamond into the surface of the specimen, under a definite weight, in a hardness testing machine. Reactive, refractory metals The reactive and refractory metals were originally used in the aerospace industry and are now being welded for more requirements. Reactive metals have a strong affinity for oxygen and nitrogen at elevated temperatures, and when combined, form very stable compounds. At lower temperatures they are highly resistant to corrosion. Refractory metals have extremely high melting points. They may also exhibit some of the same characteristics of reactive metals. The refractory metals all have extremely high melting points, relatively high density, and thermal conductivity. The reactive metals have lower melting points, lower densities, and, except for zirconium, have higher coefficient of therMen's Shorts - Shop Men's Shorts Online