Tin

                       Tin is one of the earliest metals known and used. Because of its hardening effect on copper, tin was used in bronze implements as early as 3,500 B.C., although the pure metal was not used until about 600 B.C. About 35 countries mine tin throughout the world. Nearly every continent has an important tin-mining country. Tin is a relatively scarce element with an abundance in the earth's crust of about 2 parts per million (ppm), compared with 94 ppm for zinc, 63 ppm for copper, and 12 ppm for lead. Most of the world's tin is produced from placer deposits; at least one-half comes from Southeast Asia. The only mineral of commercial importance as a source of tin is cassiterite (SnO2), although small quantities of tin are recovered from complex sulfides such as stanite, cylindrite, frankeite, canfieldite, and teallite.

                       Most tin is used as a protective coating or as an alloy with other metals such as lead or zinc. Tin is used in coatings for steel containers, in solders for joining pipes or electrical/electronic circuits, in bearing alloys, in glass-making, and in a wide range of tin chemical applications. Secondary, or scrap, tin is an important source of the tin supply.Ordinary tin is a silvery-white metal, is malleable, somewhat ductile, and has a highly crystalline structure. Due to the breaking of these crystals, a "tin cry" is heard when a bar is bent. The element has two allotropic forms. On warming, grey, or α-tin, with a cubic structure, changes at 13.2°C into white, or β-tin, the ordinary form of the metal. White tin has a tetragonal structure. When tin is cooled below 13.2°C, it changes slowly from white to grey. This change is affected by impurities such as aluminium and zinc, and can be prevented by small additions of antimony or bismuth. The conversion was first noted as growths on organ pipes in European cathedrals, where it was thought to be the devils work. This conversion was also speculated to be caused microorganisms and was called "tin plague" or "tin disease".

                      Tin resists distilled, sea, and soft tap water, but is attacked by strong acids, alkalis, and acid salts. Oxygen in solution accelerates the attack. When heated in air, tin forms SnO2. It is, or was, used to plate steel, making "tin cans". Tin is used as one component in bell metals.

*Name: Tin
*Symbol: Sn
*Atomic number: 50
*Atomic weight: 118.710 (7) [see note g]
*Standard state: solid at 298 K
*CAS Registry ID: 7440-31-5 Group in periodic table: 14
*Group name: (none)
*Period in periodic table: 5
*Block in periodic table: p-block*Colour: silvery lustrous grey
*Classification: Metallic


Physical Properties:

The Physical Properties for Tin are:
*Standard State (phase): Solid
*Density (near room temp.): 7.365g/cm^3
*Liquid Density (at melting point): 6.99g/cm^3
*Melting Point (K): 505K
*Melting Point (°C): 231°C
*Melting Point (°F): 449°F
*Boiling Point (K): 2875K
*Boiling Point (°C): 2602°C
*Boiling Point (°F): 4716°F
*Heat of Fusion: 7.03kJ/mol
*Heat of Vaporization: 296.1kJ/mol
*Specific Heat Capacity: 27.112J/mol·1/K

Chemical Properties:
                       Tin is relatively unaffected by both water and oxygen at room temperatures. It does not rust, corrode, or react in any other way. This explains one of its major uses: as a coating to protect other metals. At higher temperatures, however, the metal reacts with both water (as steam) and oxygen to form tin oxide.

                        Similarly, tin is attacked only slowly by dilute acids such as hydrochloric acid (HCl) and sulfuric acid (H 2 SO 4 ). Dilute acids are mixtures that contain small amounts of acid dissolved in large amounts of water. This property also makes tin a good protective covering. It does not react with acids as rapidly as do many other kinds of metals, such as iron, and can be used, therefore, as a covering for those metals.

                       Tin dissolves easily in concentrated acids, however, and in hot alkaline solutions, such as hot, concentrated potassium hydroxide (KOH). The metal also reacts with the halogens to form compounds such as tin chloride and tin bromide. It also forms compounds with sulfur, selenium, and tellurium.

Health effects of tin:
                  Tin is mainly applied in various organic substances. The organic tin bonds are the most dangerous forms of tin for humans. Despite the dangers they are applied in a great number of industries, such as the paint industry and the plastic industry, and in agriculture through pesticides. The number of applications of organic tin substances is still increasing, despite the fact that we know the consequences of tin poisoning.
The effects of organic tin substances can vary. They depend upon the kind of substance that is present and the organism that is exposed to it. Triethyltin is the most dangerous organic tin substance for humans. It has relatively short hydrogen bonds. When hydrogen bonds grow longer a tin substance will be less dangerous to human health. Humans can absorb tin bonds through food and breathing and through the skin.
The uptake of tin bonds can cause acute effects as well as long-term effects.

Acute effects are:
- Eye and skin irritations
- Headaches
- Stomachaches
- Sickness and dizziness
- Severe sweating
- Breathlessness
- Urination problems

Long-term effects are:
- Depressions
- Liver damage
- Malfunctioning of immune systems
- Chromosomal damage
- Shortage of red blood cells
- Brain damage (causing anger, sleeping disorders, forgetfulness and headaches)

Effects of tin on the environment:
                  Tins as single atoms or molecules are not very toxic to any kind of organism, the toxic form is the organic form. Organic tin components can maintain in the environment for long periods of time. They are very persistent and not fairly biodegradable. Microrganisms have a great deal of trouble breaking down organic tin compounds that have accumulated on water soils for many years. The concentrations of organic tins still rise due to this.

                 Organic tins can spread through the water systems when adsorbed on sludge particles. They are known to cause a great deal of harm to aquatic ecosystems, as they are very toxic to fungi, algae and phytoplankton. Phytoplankton is a very important link in the aquatic ecosystem, as it provides other water organisms with oxygen. It is also an important part of the aquatic food chain.

                   There are many different types of organic tin that can vary greatly in toxicity. Tributyltins are the most toxic tin components to fish and fungi, whereas trifenyltin is much more toxic to phytoplankton.
Organic tins are known to disturb growth, reproduction, enzymatic systems and feeding patterns of aquatic organisms. The exposure mainly takes place in the top layer of the water, as that is where organic tin compounds accumulate.

                                 Published by Ravindra.K(Mechanical Engineerimg)