Tin is one of the most studied metals by man. It was discovered in prehistoric times. Already the ancient man knew what the melting point of tin, the physicochemical properties of this metal and the range of its application 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 nature
The most important natural compounds are cassiterite, which includes tin oxide, and stannine (tin pyrites). In antiquity, this metal was mined in open mines, but in the modern world there are almost no open tin deposits. On an industrial scale, it is smelted from ores containing about 1% of this substance. Thus, in order to get 1 kg of pure tin, you need to recycle a centner of ore.
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. Quite often offered alloys with various additives - with lead, silver, copper, indium and others. The melting point of tin and lead is lower than 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 mold into a form of graphite or any other material. The average melting point of tin does not exceed 240 ° C. The basic material requirements for forms are as follows:
- the substance should not be wetted with liquid tin;
- the material should withstand temperatures of 250°C, without collapsing and without changing its shape.
Molten metal can oxidize in the open air, and the solid is quite resistant to oxygen corrosion. Sometimes this property is used to apply a metal layer to tin products. But unlike zinc plating, tin does not give the product electrochemical protection - in the case of scratches, corrosion will corrode the surface with tin coating rather than zinc.
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 performance of the solder, a small amount of antimony is injected into it. This composition is used for soldering radio components in the most critical areas.
Silver alloys have proven themselves well. The presence of this noble metal improves the technical characteristics of the finished product and increases its service life. Alloys with a high content of silver are used in various means of communication and in industrial engineering.
Zinc-containing alloys are not well distributed. The reason for this dislike is the increased chemical activity of zinc. Because of its interaction with the environment, zinc-containing compounds are quite rapidly destroyed, moreover, when working with them, it is necessary to use active fluxes. Solder pastes containing this additive are not intended for long-term storage. The melting point of tin for soldering with zinc content is quite high. For example, the well-known compound Sn91Zn9 melts at 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. Lead compounds are very harmful to health, so the use of compounds of this metal is very limited. In the past, the wide distribution 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 strict restrictions, lead-based solders are widely used in particular industries, for example, in defense industry and in the nuclear power sector.
Use pure tin
The semiconductor industry uses solders with a high content of pure tin, in which 999999 atoms of pure metal fall on one atom of an external metal. The melting point of tin in pure form is 240 ° C. But in everyday life such solders are not in demand: the fact is that when the temperature drops, this metal transforms its structure, gray spots appear on the surface of the product, so-called tin plague. Additives of various components alter this temperature and make tin alloys more resistant.