Tin is a silver-white metal with a melting point of 231.9°C and a density of 7.3 g/cm3. There are three allotropes of tin, namely gray tin (α-tin), white tin (β-tin) and brittle tin (γ-tin). The most common one is white tin, a silver-white metal that is stable between 13.2-161°C. Below 13.2°C, white tin begins to transform into powdery gray tin, and its transformation speed accelerates as the temperature drops. The maximum transformation rate is reached when cooled to -30°C. When the temperature is higher than 161°C, white tin turns into brittle tin and becomes liquid until it reaches the melting point (231.9°C). The density of gray tin is 5.85 g/cm3, that of white tin is 7.2 g/cm3, and that of liquid tin foil is 6.98 g/cm3. Tin is stable in the air at room temperature. The reason is that a dense oxide film is formed on the tin surface to prevent further oxidation. Tin has good malleability but poor ductility, so it can be made into very thin tin foil but cannot be drawn into tin wire. At present, the raw material for tin smelting is mainly cassiterite (SnO2). Metal tin can be obtained from cassiterite through reduction smelting, refining and other processes. Uses of tin: Tin is malleable and has good plasticity, and can be rolled into tin foil with a thickness of less than 0.04 mm. Pure tin reacts slowly with weak organic acids and has good corrosion resistance. Even if it is corroded, the compounds generated are generally non-toxic. Therefore, hot-dip tin plating is used in large quantities to produce tinplate, which is used for anti-corrosion or in the food industry. Tin-based bearing alloy (Babbitt) is an excellent wear-resistant material. It has a low friction coefficient and good toughness, thermal conductivity and corrosion resistance. Tin can also be formulated into fusible alloys, solders, printing alloys, tin bronze and tin-containing brass. Tin-containing titanium-based alloys are used in industrial sectors such as aviation, shipbuilding, atomic energy, chemicals and medical devices. Tin-niobium intermetallic compounds can be used as superconductors. The important compounds of tin, tin dioxide, tin tetrachloride and organic compounds of tin, are used respectively as raw materials for ceramic glazes, coal dyes for printing and dyeing silk fabrics, and can also be used as pesticides, antifouling agents, wood preservatives and flame arresters. wait. Tin's "Frostbite" In winter, when the weather is cold and the ground freezes, people's hands and feet suffer from frostbite. However, tin can also cause "frostbites". The reason for "frostbites" on tin is that metal tin breaks into powder at low temperatures and spreads like a disease, causing the entire tin product to be destroyed. Therefore, people call this phenomenon "tin epidemic", and also say that tin causes "frostbites". "Frostbites" on tin can also cause heavy losses! More than seventy years ago, someone took an airplane to explore Antarctica. Because the fuel tank of the airplane was welded with tin, in the freezing cold of Antarctica for thousands of miles, the solder turned into powdery gray tin, causing the gasoline in the fuel tank to leak. As a result, the airplane Lost fuel and unfortunately fell and crashed. The way to inhibit tin "frostbites" is to add impurities such as bismuth, lead, antimony, silver, gold, etc. to tin. When the impurity content reaches a certain level, "frostbites" can be prevented. Tin Capital - Gejiu is located in Gejiu, the central part of the Honghe Hani and Yi Autonomous Prefecture in Yunnan Province. It has abundant tin ore reserves and can be mined in the open. It is the largest tin production base in my country and is known as the "Tin Capital". Gejiu tin mine has a mining history of more than 2,000 years. "Hanshu Geography" records that "Xin comes out of Caishan in the north of Ben and Wushan in the south". These two mountains are now the Gejiu mining area. Although it was continuously developed in the past dynasties, it did not flourish until the Qing Dynasty. Before liberation, more than 90% of tin was produced by small private mines, with the highest annual output exceeding 10,000 tons. After the Opium War in 1840, the imperialist powers poured into China one after another and plundered Gejiu's tin, causing serious damage to Gejiu's mineral resources. By 1949, the annual tin output was only 610 tons, and the Gejiu tin industry was dying. In the 47 years since liberation, Gejiu tin industry has made great progress. Up to now, the large tin produced by Yunnan Tin Industry Company alone accounts for 55% of the national tin output. Including the output of local processing, it accounts for 65% of the national tin output. The products include 8 series and 60 varieties and are honored as "Xindu". The world's largest tin ore belt is in Southeast Asia. It extends from Belitung Island and Bangka Island in Indonesia, through the western part of the Malay Peninsula and the Tanah Sarin coast of Myanmar, to Yeungan in the western Shan State Plateau of Myanmar. The tin reserves in this tin ore belt are about 4 million tons, ranking first in the world. Southeast Asian countries have an earlier history of tin mining (but about two thousand years later than China). In the 9th century AD, there were already famous tin-producing ports on the west coast of the Malay Peninsula. At the end of the 16th century, Myanmar sold tin to India. The tin mining industry in Thailand and Indonesia also has a history of 200-300 years. Southeast Asia's tin production has ranked first in the world since this century, accounting for about 60% of the world's total tin production. my country's tin chloride metallurgical technology Yunnan Tin Company, Kunming Metallurgical Research Institute and Beijing Mining and Metallurgical Research Institute and other units jointly researched the rotary kiln high-temperature chlorination method for the refractory tin ore of low-tin high-speed rail. Comprehensive recovery of valuable metals such as tin and lead can increase the current recovery rate of Yunnan tin by 6%-7%, and recover a large amount of tin and other metals from the tailings accumulated over the years. Abroad, this technology is still a cutting-edge research topic in the tin metallurgical community, and my country has taken a leading position in the world in the chloride metallurgy of tin. The position of nickel in the periodic table of elements determines a series of physical and chemical properties of nickel and its compounds. Many of the physical and chemical properties of nickel are similar to those of cobalt and iron. Because it is adjacent to copper, it is closer to copper in terms of sulfur affinity and oxygen affinity, and will lose its metallic luster and become dark.

1.1 Physical properties of nickel Nickel is a silver-white metal. Its physical properties are quite consistent with those of metal cobalt and iron. The main manifestations are: A. The specific gravity of nickel: 8.908 at 20°C, and the reliable value is 8.9~ 8.908, the specific gravity of liquid nickel at the melting point is 7.9. B. The specific heat of nickel: varies from 420 to 620 Joules/kg·K in the temperature range of 0 to 1000°C, with a significant peak at the Curie point or its attachment, and the ferromagnetism is lost at this temperature. C. The resistance of nickel: at 20°C, it varies from 6.8 to 9.9 microohm centimeters (10 to 8Ωm) according to its purity of 99.99 to 99.8%. Although nickel-based alloys are widely used in thermoelectric elements, pure nickel has virtually no such use due to oxidation. D. The thermoelectricity of nickel is different from that of iron, copper, silver, gold and other metals. It is more negative than that of platinum, so the current at the cold end flows from platinum to nickel. Therefore, when nickel is used as a thermoelectric element, a high electromotive force can be generated. E. Nickel is magnetic and is the main component of many magnetic materials (from soft magnetic alloys with high magnetic permeability to permanent magnet alloys with high coercivity), and its content is usually 10 to 20%. 1.2 Chemical properties of nickel Metal nickel is one of the ferromagnetic metals in Group 8 of the periodic table of elements. It has an atomic number of 28, an atomic weight of 58.71, a melting point of 1453±1°C, and a boiling point of 2800°C. Naturally occurring metallic nickel has five stable isotopes: Ni5867.7%, Ni6026.2%, Ni611.25%, Ni623.66%, and Ni641.66%. Its main chemical properties are: A. Dilute sulfuric acid and hydrochloric acid can slowly dissolve nickel, while dilute nitric acid and nickel react quickly, but concentrated nitric acid passivates nickel, and nickel and alkali have no effect. Nickel is resistant to all organic compounds. B. Pure nickel has a silvery white luster. When it interacts with water vapor and oxygen in the air, a NiO film is formed on the nickel surface to prevent further oxidation. Sulfur-containing gases severely corrode nickel, especially when the crystallization temperature of nickel and nickel sulfide Ni3S2 is above 643oC. Nickel has no significant effect on chlorine below 500°C. C. The electrode potential of nickel is -0.227 volts at 20°C and -0.231 volts at 25°C. If there are a small amount of impurities in the solution, especially when sulfur is present, nickel will be significantly passivated. D. Since the surface of nickel can form a dense nickel oxide film, it dissolves very slowly in dilute acid and is easily passivated in strong oxidizing media. It also has good corrosion resistance to alkali solutions, salt water and organic matter.

Tin-nickel can also be made into an alloy, which has very good properties. It combines the properties of both and is better than both.

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