Tin
Next week, we will be demonstrating the melting points of
tin and lead. We will also be discussing alloys. To teach our peer’s about
this, we need to know a bit more about tin ourselves.
A bit about tin
Tin (Sn) is a silvery/white metal. It is malleable and slightly
ductile, with a crystalline structure. When a bar of tin is bent, a “tin cry”
is heard due to the breaking of these crystals. (4) There are twenty-two known
isotopes of tin, with nine of these being stable isotopes. Tin has a melting
point of 231.9681˚C and a boiling point of 2270˚C. (5)
(4)
(7)
How long has tin been around?
Tin has been
around since the formation of the Earth. It began to be used during the Bronze
Age, starting around 3000 B.C. The first metals to be discovered and used by
ancient men were gold, silver, copper and lead. Following these, tin, iron and
mercury were then discovered and used. (1)
Where is tin found?
During ancient times, Europe obtained
most of its tin from the British Isles. The major producers of tin today are
China, Indonesia, Peru, Brazil and Bolivia. (2) The primary source of
tin is found in cassiterite (tin dioxide). (1) Cassiterite is found in vein
deposits, granitic rocks, and pegmatites.
Tin can be extracted from the ore through smelting, which is heating to extract the ore. (1) An ore is a compound from which an element can be extracted.
Smelting: Cassiterite is reduced with carbon in a reverberatory furnace. A temperature of over 1200˚C is required. Cassiterite is hardly ever produced entirely free from other minerals. Many minerals are reduced to metals at the same time, forming alloys with tin. The tin therefore needs to be refined in order to become commercially useful. Iron is removed by passing steam through the metal when it is molten. Arsenic and antimony are removed by adding aluminium alloy. Copper is removed with sulphur. Very impure tin can be refined using electrolysis. (4)
Tin can be extracted from cassiterite by heating cassiterite with charcoal. The carbon reacts with and removes the oxygen from the cassiterite, leaving behind pure tin. Iron also occurs in very small amounts in cassiterite. If this is not removed, a very hard, useless form of tin is produced. Cassiterite is heated with oxygen to oxidize any iron. The iron is converted to iron (III) oxide and tin is left. (2)
(8)
Uses of tin
Tin is not easily oxidized, or easily affected by the sea,
water, soft tap water or weak acids. Therefore, it is used to protect other
metals from rusting or corroding. (1) Metals can be plated with tin in two
ways. The metal can simply be dipped in molten tin and then pulled out. A thin
layer of molten tin sticks to the metal and then cools to form a coating. The
second method is electroplating. The base metal is suspended into tin sulphate solution,
or a similar compound. An electric current is passed through the solution,
causing the tin to be deposited on the surface of the base metal. (2)
Tin can be made into bronze. The earliest bronze had a small amount of tin in it. It was soon found that tin added to metals, especially copper, making them stronger and easier to cast. Combing tin and copper made bronze. This brought metalworking from the Copper Age to the Bronze Age. Gold, copper, silver, lead, tin, iron and mercury were used by the Egyptians, Mesopotamians, Romans and Greeks.
Tin is easily mixed with other metals, so it is a good alloy. Tin chloride is used in the manufacture of dyes, textiles and polymers; in the silvering of mirrors; as a food preservative; as an additive of the perfumes used in soap; and as an anti-gumming agent used in lubricating oil. Tin oxide is used in the manufacture of special types of glass, glazes and colours, perfumes, cosmetics, in textiles, and as a polishing material for glass, steel and other materials. Tin fluoride is used as an additive in toothpaste to help protect against cavities. (2) Amalgams in dentistry are made of tin, silver, mercury and sometimes zinc. (1)
Tin is widely used for soldering because it bonds with many metals below their melting points. (1)
One application of tin is that of tin foil. Tin foil is a very thin sheet of tin used to wrap foods. The tin protected the products from spoiling through exposure to the air. Today, most tin foil is made of aluminium as this metal is less expensive.
The majority of today’s toys are made from plastic. However, beginning in the 1800s and during World War Two, many of the best toys were made from tin-plated metal. (2)
Tin is also used in paint, plastics and pesticides. (1) Tin has many uses, due to this, not all of them have been discussed above.
Tin can be made into bronze. The earliest bronze had a small amount of tin in it. It was soon found that tin added to metals, especially copper, making them stronger and easier to cast. Combing tin and copper made bronze. This brought metalworking from the Copper Age to the Bronze Age. Gold, copper, silver, lead, tin, iron and mercury were used by the Egyptians, Mesopotamians, Romans and Greeks.
Tin is easily mixed with other metals, so it is a good alloy. Tin chloride is used in the manufacture of dyes, textiles and polymers; in the silvering of mirrors; as a food preservative; as an additive of the perfumes used in soap; and as an anti-gumming agent used in lubricating oil. Tin oxide is used in the manufacture of special types of glass, glazes and colours, perfumes, cosmetics, in textiles, and as a polishing material for glass, steel and other materials. Tin fluoride is used as an additive in toothpaste to help protect against cavities. (2) Amalgams in dentistry are made of tin, silver, mercury and sometimes zinc. (1)
Tin is widely used for soldering because it bonds with many metals below their melting points. (1)
One application of tin is that of tin foil. Tin foil is a very thin sheet of tin used to wrap foods. The tin protected the products from spoiling through exposure to the air. Today, most tin foil is made of aluminium as this metal is less expensive.
The majority of today’s toys are made from plastic. However, beginning in the 1800s and during World War Two, many of the best toys were made from tin-plated metal. (2)
Tin is also used in paint, plastics and pesticides. (1) Tin has many uses, due to this, not all of them have been discussed above.
Health effects of tin
Tin bonds with organic substances. This is bad for our
bodies. Humans can absorb tin through the skin, by breathing and through eating.
The effects of tin include:
- Breathlessness
- Eye and skin irritations
- Urination problems
- Dizziness
- Stomach aches
- Severe sweating
- Headaches
More severe effects include:
- Liver damage
- Damage to chromosomes
- Brain damage
- Red blood cells shortage
- Depression
- Weakening of the immune system (1)
Tin in the environment
Tin is pretty much non-biodegradable. It is toxic to living
things and damages aquatic ecosystems by interfering with reproduction, growth
and feeding patterns. Organic tin compounds build up in the upper part of the
ocean. (1)
By Lauren Watmough
Lauren, this is interesting. You say "Tin can be extracted from cassiterite by heating cassiterite with charcoal. The carbon reacts with and removes the oxygen from the cassiterite, leaving behind pure tin". Sounds really interesting. Would this be feasible to do on our own charcoal fire???
ReplyDeleteYes, we would be able to do this. This process first came about in ancient times. Ancient people found that heating cassiterite in a charcoal fire produced tin. Therefore, by using our own charcoal fire, we could carry out this process. (http://www.scienceviews.com/geology/tin.html)
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