Influence of tin impurities
In the application of tin is of great importance impurities of antimony, copper, bismuth, zinc, aluminum, iron, arsenic and lead. These elements not only affect the physico-chemical properties, but also have the ability to speed up or delay the development of so-called tin plague.
Small amounts of lead does not reduce the mechanical properties. Tin, used in the manufacture of white tin sheets, contains up to 0.04% Pb. In the production of vysokohromistyh, consisting of more than 83% of tin, to avoid the formation of noticeable amount of low-melting eutectic, the proportion of lead should not exceed 0.25%.
Reduces plastic properties of the alloy and increases the hardness. Normal iron content in the tin does not contribute to the violation of its basic properties.
Zinc and aluminium
These impurities in tin fall in the refining process. Due to the formation of thin films consisting of oxides of zinc and aluminum, which are held on the surface of the tin, hampered the fusion of drops of metal. This significantly hinders the use of this type of tin is in soldering and tinning. Impurity of metallic zinc, and aluminum greatly reduce the overall corrosion resistance. In this connection, the contents in the tin these metals is strictly limited (no more than 0,002%).
Small amounts of copper forms with tin eutectic (from 0.7 to 1% Cu) with a melting point of 227 °C. the Production of most alloys, the minimum admixture of copper do not harm. But in high concentrations the supplements of copper to tin greatly reduce the overall corrosion resistance.
Arsenic contributes to a significant deterioration of the plastic properties of the metal, reducing its fluidity. It is especially harmful in the tin, which is intended for the production of tin tin, and the limit of arsenic content in the layer of tinning shall not exceed 0,015%, otherwise it can affect both the appearance and the nature of his fracture, because the brittleness and hardness of tin is significantly greater.
In many cases bismuth is a deleterious impurity for tin, the contents were severely limited, despite the fact that bismuth has a valuable property. With its low content in the tin (less than 0,035%) prevented the transition of white to gray tin at low temperature.
The presence of tin to 9% of Sb promotes the formation of solid solutions. Tin, retains the ability easily rolled and hammered. Many alloys of tin do not accept the presence of a significant amount of antimony that makes adjusting its content in the relevant standards.
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