Element attribute
Tin is a carbon group element with atomic number 50 and atomic weight 1 18.7 1. Element names come from Latin. Around 2000 BC, humans began to use tin. The content of tin in the earth's crust is 0.004%, almost all of which exists in the form of cassiterite (tin oxide), in addition to a very small amount of tin sulfide ore. There are 14 isotopes in tin, among which 10 is a stable isotope, namely: tin 1 12,1/4, 1 16.
Tin is soft and flexible, with a melting point of 23 1.89℃ and a boiling point of 2260℃. There are three kinds of allotropes:
White tin is tetragonal, and its unit cell parameters are: a=0.5832nm, c=0.3 18 1nm. The unit cell contains four tin atoms, the density is 7.28 g/cm3, the hardness is 2, and the ductility is good.
Gray tin is a rhombic cubic crystal system, and its unit cell parameter is: a=0.6489nm, and the unit cell contains 8 Sn atoms with a density of 5.75 g/cm3.
Brittle tin is orthorhombic with a density of 6.54 g/cm3.
The tin dioxide protective film is stable on the tin surface in the air, and the oxidation reaction is accelerated by heating; Tin reacts with halogen under heating to generate tin tetrahalide; It can also react with sulfur; Tin is stable to water, and can be dissolved slowly in dilute acid and rapidly in concentrated acid. Tin can be dissolved in strong alkali solution; It will be corroded in acidic solution of ferric chloride, zinc chloride and other salts.
Tin is a silvery white soft metal with a specific gravity of 7.3 and a low melting point of only 232℃. If you put it in a briquette furnace, it will melt into liquid like mercury. Tin is so soft that you can cut it with a knife. The chemical properties of tin are very stable, and it is not easy to be oxidized by oxygen at room temperature, so it often keeps shiny silver. Tin is non-toxic, so people often plate it on the inner wall of copper pot to prevent copper and warm water from forming toxic copper rust (basic copper carbonate). Toothpaste shells are often made of tin (toothpaste shells are made of two layers of tin with a layer of lead in the middle). In recent years, China has gradually replaced tin with aluminum to make toothpaste shells. Solder also contains tin, generally containing 6 1% tin, some of which are half lead and half tin, and some of which are composed of 90% lead, 6% tin and 4% antimony.
forgeability
Tin is malleable at room temperature. Especially at the temperature of 100℃, it has very good ductility and can be developed into extremely thin tin foil. Usually, people pack cigarettes and sweets with tin foil to prevent them from getting wet (in recent years, China has gradually replaced tin foil with aluminum foil. Aluminum foil and tin foil are easy to distinguish-tin foil is much brighter than aluminum foil). However, the ductility of tin is very poor. When it is pulled, it will break and cannot be drawn into filaments.
In fact, tin is malleable only at room temperature. If the temperature drops below-13.2℃, it will gradually become loose powder like coal ash. Especially at -33℃ or in the presence of alcohol solution with red salt (sncl 4·2 NH 4 cl), the speed of this change is greatly accelerated. A good tin pot will automatically turn into a pile of powder. This tin "disease" can also be transmitted to other "healthy" tin utensils, which is called "tin epidemic". The reason of tin plague is that the crystal lattice of tin has changed: at room temperature, tin has a tetragonal crystal structure, which is called white tin. When you bend a tin bar, you can often hear a crack. This is because the square white tin crystals rub against each other when bending and make a sound. When the temperature is lower than-13.2℃, white tin is transformed into amorphous gray tin. As a result, the tin turned into a mass of powder.
Since tin is afraid of cold, special attention should be paid not to freeze tin in winter. There are many ironware that are usually soldered with tin and won't freeze. 19 12 years, a foreign Antarctic expedition went to explore the Antarctic, and the petrol tanks used were all soldered. In the Antarctic ice and snow, solder turned into powdered gray tin, and gasoline leaked out.
Tin is not only afraid of cold, but also of heat. Above 16 1℃, white tin is transformed into rhombohedral tin with rhombohedral crystal structure. Oblique tin is brittle, it will break when knocked, and its ductility is poor. It is called "brittle tin". White tin, gray tin and brittle tin are three allotropes of tin.
Tin is inert and does not react with air and water. React with concentrated hydrochloric acid to generate stannous chloride; It does not react with dilute sulfuric acid, but with concentrated hot sulfuric acid to produce tin sulfate (ⅳ); Using concentrated hot nitric acid to produce β-stannic acid.
source
Tin is a famous "hardware"-one of gold, silver, copper, iron and tin. As early as ancient times, people discovered and used tin. In some ancient tombs in China, tin pots, tin candlesticks and other tin utensils are often excavated. According to research, during the Zhou Dynasty in China, the use of tin ware was very common. Tin daily necessities were also found in ancient tombs in Egypt.
China is rich in tin resources, especially Gejiu, a world-famous "tin capital". In addition, Guangxi, Guangdong and Jiangxi provinces also produce tin. 1800 The annual output of tin in the world was only 4,000 tons, 1900 was 85,000 tons, and 1940 was 250,000 tons. Now it has exceeded 600,000 tons.
But arsenic is associated with tin, and its compound is the main component of arsenic.
According to the paper published by the Environmental Restoration Research Center of Institute of Geographical Sciences and Resources, Chinese Academy of Sciences, arsenic, as an associated ore of tin, has become abandoned tailings because of its low utilization value. By 2008, at least 1 167000 tons of arsenic remained in the environment in China, which is equivalent to millions of tons of arsenic scattered in the wilderness, washed by rain, injected into rivers and infiltrated into soil.
use
Metal tin is mainly used to make alloys.
Tin sulfide is a compound of tin and sulfur, which is similar in color to gold and is often used as a gold pigment.
Tin dioxide, compounds of tin and oxygen. Tin is not oxidized in air at room temperature, but becomes tin dioxide when heated strongly. Tin dioxide is a white powder insoluble in water, which can be used to make enamel, white glaze and opalescent glass. Since 1970, people have used it to prevent air pollution-automobile exhaust often contains toxic carbon monoxide gas, but most of it can be converted into carbon dioxide at 300℃ under the catalysis of tin dioxide.