Category Science & Technology

               Explosives are substances that release a very large amount of energy in a short time when they burn. They all contain a fuel plus an oxidizer, which is a substance containing sufficient oxygen to burn the fuel. Explosives do not need air to explode, because they contain their own oxygen, and so they can burn in confined spaces or even underwater. Some explosives, such as those in a cartridge detonator, explode violently when hit or heated. Others only cause a violent explosion when confined in a gun barrel or a hole drilled in rock for blasting.

               Gunpowder, the first ever explosive, was invented in China over 1,000 years ago. Large amounts of modern explosives are commonly used in quarrying and mining, as well as for munitions.

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               Plastics are synthetic materials that consist of long chains of molecules called polymers. When the chains are positioned in long rows the plastic is rigid. When the polymer molecules are tangled together, the plastic is soft and flexible. All plastics can be moulded under pressure into complicated shapes. Thermoplastics melt when they are heated, and this means that they can be remelted at any time. There are other forms of plastic known as thermosetting plastics, which cannot be remelted.

               The majority of plastics are made from synthetic resins, which are usually derived from oil. Other types come from sources such as coal or wood. As they do not conduct electricity, most plastics are excellent insulators, so are widely used in electrical wiring. The main disadvantage of plastics is that they are very slow to break down, causing serious environmental problems when discarded.

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               Natural rubber comes from a kind of tree that originally grew in South America. Its liquid sap, called latex, is drained from the tree by making cuts in the bark.  The latex is collected and processed into rubber. Natural rubber is very soft and is used for making the soles of shoes and sandals.

               In 1839 Charles Goodyear, an American inventor, found that heating rubber together with sulphur made it much harder. This process, known as vulcanization, made it possible to use rubber for vehicle tyres. Rubber is now used for electrical insulation, motor tyres, cushions, golf balls and many other applications.

               Since World War II most of the rubber we use has been produced synthetically. Rubber’s properties are based on the way its molecules link up into long chains, making giant molecules called polymers.

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            Steel is made from iron, which is usually mined in the form of iron ore. The ore needs to be smelted in order to extract the iron. Smelting is done in a blast furnace, where coke and limestone are added to the iron ore. This mixture is heated to a very high temperature and air is blown through it. The molten iron is drawn off.

            To make steel, iron is mixed with carbon and other metals to give it extra harness. There is about 1.6 percent carbon in most steel. Other forms of steel contain elements such as chromium and nickel to prevent rusting. Ordinary carbon steel rusts as easily as iron, and must be protected with paint or other coatings.

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