Tin is one of the metals most studied by man. It was discovered in prehistoric times. Already an ancient man knew what the temperature of melting tin, the physical and chemical properties of this metal and the range of its use in everyday life. The alloy of tin and copper is the first human experience in metallurgy, the first artificial metal compound created by human hands.
Tin in the nature
The most important natural compounds are cassiterite, which includes tin oxide, and stannite (tin pyrites). In ancient times, this metal was mined in open mines, but in the modern world there are almost no open deposits of tin. On an industrial scale, it is smelted from ores containing about 1% of this substance. Thus, to get 1 kg of pure tin, you need to process a centner of ore.
Use of tin
One of the best-known applications of tin – soldering. Low melting point allows soldering at home. For soldering this metal is sold in the form of small bars with diameter up to 10 mm. Alloys with various additives are often offered - with lead, silver, copper, indium and others. The melting point of tin and lead is lower than that of pure tin, so the soldering process is faster.
Due to the physical properties of the metal can be stored under normal conditions in a liquid form. Low melting point tin solder allows the metal liquid in glass vials for laboratory or other studies.
Tin is easy enough to melt in large quantities and cast into a mold made of graphite or any other material. The average melting temperature of tin does not exceed 240 ° C. The basic requirements for the material for forms are as follows:
- the substance must not be wetted with liquid tin;
- the material should withstand temperatures of 250°C, without collapsing and without changing its shape.
The molten metal is able to oxidize in the open air, and the solid is fairly resistant to oxygen corrosion. Sometimes this property is used to apply a metal layer to the tin products. But unlike zinc spraying, tin does not give the product electrochemical protection - in the case of a scratch, corrosion will quickly erode the surface with a tin coating, and not with a zinc coating.
Tin for soldering
The melting temperature depends on the amount and composition of impurities in the rod. About what the melting point of the tin, you can see from the table most common alloys.
In electrical engineering well established three-component alloys based on lead, silver and tin. The percentage of impurities in the solder are different: standards for additives is still not developed. All manufacturers agree on one thing – the content of tin in the alloy should not be less than 95 %. The melting point of the tin solder in the composition varies in the range of 217-221° C.
To improve the characteristics of the solder, a small amount of antimony is introduced into it. This composition is used for soldering radio components in the most critical areas.
Alloys with silver content proved to be good. The presence of this noble metal improves the technical characteristics of the finished product and increases the period of its operation. Alloys with a high content of silver are used in various means of communication and in industrial equipment.
Zinc-containing alloys are not very common. The reason for this dislike is the increased chemical activity of zinc. Due to its interaction with the environment, the zinc-containing compounds break down fairly quickly, and active fluxes must be used when working with them. Solder pastes containing this additive are not intended for long-term storage. The melting temperature of tin for soldering with zinc content is quite high. For example, the known compound Sn91Zn9 melts at a temperature of 200 ° C.
Tin and lead
As tin and lead in alloys and additives used by man since time immemorial. This inexpensive and abundant metal has properties that improve the quality of the solder and its performance.
Solders, which include lead, are called lead-containing. Lead compounds are very harmful to health, therefore the use of compounds of this metal is very limited. In the past, the widespread use of lead solders was due to the good performance characteristics of the alloy and its low processing temperature. The melting point of tin and lead does not exceed 190 ° C. Despite stringent restrictions, solders with lead are widely used in certain industries, for example, in the defense industry and in the nuclear power sector.
Use of pure tin
The semiconductor industry uses solders with a high content of pure tin, in which 999,999 atoms of pure metal per one atom of the side metal. The melting temperature of tin in pure form is 240 ° C. But in domestic conditions, such solders are not in demand: the fact is that when the temperature is lowered, this metal transforms its structure, gray spots appear on the surface of the product-the so-called tin plague. Additives of various components change this temperature and give more stability to tin alloys.