Ingot. A chunk or bar of cast raw metal, especially iron or a noble metal such as gold, silver or platinum.
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- 1 Types of ingot
- 2 Metallic
- 1 Semiconductor material
- 2 Gold bar
- 3 Crystal structure
- 3 Sources
Metal ingots are made by heating the alloy above its melting point and pouring the liquid metal into molds prepared for this purpose. The primary metal ingots are then used in the industry to produce other metal parts, by casting , extrusion or other technological means.
In the electronics industry, monocrystalline ingots of semiconductor material manufactured using the Czochralski or Bridgeman method are used.
400 troy ounce (12.4 kg) gold bars with a minimum of 99.5% purity constitute the international Good Delivery standard for storage and trade as reserve and other major operations by the central banks that maintain them, as well like other large operators. Due to its high price, bars of 1 kg (kilobar) or, in some cases, 500 grams are used for small-scale trade. In the more retail market, lower weight bars are usually used.
Ingots are generally made with molds in the form of a parallelepiped or a truncated pyramid with a rectangular base, to facilitate stowage. As cooling begins at the surface, a temperature gradient is created where the center of the liquid remains hotter than the edges.
Consequently, solidification begins at the surface and ends at the center, generating a typical three-layered crystal structure: a columnar crystallization at the surface, dendritic at the next layer, and equiaxial at the center. As it solidifies, the metal decreases in volume and the surface of the ingot in contact with the atmosphere generally has a so-called “retraction” concavity. If the casting has been poor, the ingot will show fissures on its surface, and pores on the inside.
There are various techniques to improve and homogenize the crystalline structure of an ingot, including strict control of the solidification speed, the isolation of certain parts of the molds to produce a directed solidification, and the use of flocculation techniques.