Chemicals in Industry

This chapter asks what an alloy and a superconductor alloy are, how glass and ceramic are made, what types of glass there are, and what natural and synthetic polymers are p. 183. Double glazed windows have two glass panels with an empty space in between, which reduces incoming heat and makes the window soundproof p. 183.

9.1 Alloy

Many objects around us are made of alloys p. 184. An alloy is a mixture of several types of metals or a mixture of metal and non-metal by a certain percentage, and common alloys are steel, pewter, bronze, brass and duralumin p. 184. Steel is 99% iron and 1% carbon, hard and strong, and used for buildings, bridges, vehicle frames and railway tracks p. 184. Pewter is 96% tin, 3% copper and 1% antimony, lustrous and resistant to corrosion, and used for decorative items such as photo frames p. 184. Bronze is 88% copper and 12% tin and is used for monuments, metal sculptures, coins and medals p. 184. Brass is 75% copper and 25% zinc, strong, shiny, malleable and gold in colour, and used for keys, door knobs and the trumpet p. 184. Duralumin is 95% aluminium, 3% copper, 1% magnesium and 1% manganese, light, strong and resistant to corrosion p. 184.

Most pure metals are soft and can corrode easily, so alloying is done to improve the properties of pure metal p. 185. The atoms in a pure metal are arranged orderly in layers that slide over each other easily when force is applied p. 185. When other elements are added, the foreign atoms have different sizes and make the layers difficult to slide, so alloys are stronger and harder than pure metals p. 185. The composition of each element in an alloy can be altered based on its use p. 185.

In Experiment 9.1, a 1 kg weight is dropped from 50 cm onto a steel ball on a copper block and then a bronze block, and the diameter of the dent is measured p. 186. In Experiment 9.2, an iron nail and a steel nail are left in water for a week to see which forms a brown layer p. 187.

Steel is used for skyscrapers because of its hardness and resistance to corrosion, and the body of an aeroplane is made of light and strong duralumin p. 188. Some musical instruments are made of brass, which is shiny and resistant to corrosion p. 188. Superconductors are materials that can conduct electricity at high efficiency without resistance, and they resist a magnetic field so that the material floats on a magnet p. 188. Superconductor alloys are used for the railway track of a high-powered train so that it floats without friction and moves at high speed p. 188. Superconductor alloys such as niobium-titanium and niobium-tin are used in the Magnetic Resonance Imaging (MRI) machine p. 188.

9.2 Glass and Ceramic

Glass is believed to have been used since 5000 B.C. and is made of silica, a compound that contains silicon dioxide and exists naturally in sand p. 189. Pure silica melts and liquefies at around 1500°C to form glass p. 189. Fused silica glass is resistant to heat and chemically inert, and soda-lime glass, made with calcium carbonate and sodium carbonate, has a low melting point and is easy to shape p. 189. Borosilicate glass contains boron oxide and has higher resistance to heat and chemicals than soda-lime glass p. 189. Lead crystal glass contains lead(II) oxide and has a low melting point and a high refractive index p. 189.

Ceramic consists of non-metal substance formed by heat at a very high temperature, and it is made from clay whose main component is aluminium silicate p. 190. Ceramic can withstand high temperature and high pressure, is very hard, brittle, chemically inert, does not rust, and is a good insulator of heat and electricity p. 190.

Beakers and conical flasks are made of borosilicate glass because of its high resistance to heat and chemicals, and bulbs are made of soda-lime glass because it resists heat and is easily shaped p. 191. A prism made of lead crystal glass is used to study the dispersion of light because it has a high refractive index p. 191. Tableware is made of ceramic because of its resistance to heat and corrosion, and dentures because of its hardness and inertness to chemicals p. 191.

9.3 Polymer

A polymer is a large molecule formed by chains of smaller molecular units known as monomers, and polymers are classified into natural polymers and synthetic polymers p. 192. Natural polymers exist naturally: starch (monomer glucose), protein (monomer amino acid) and natural rubber (monomer isoprene) p. 193. Synthetic polymers are man-made using chemical substances: polythene from ethene, polystyrene from styrene, Perspex from methyl methacrylate, and synthetic rubber from neoprene p. 193. Polymerisation joins monomers through chemical bonds into a long-chain polymer, and depolymerisation splits the polymer back into its monomers p. 193. Addition polymerisation involves monomers of the same type, breaking a double bond into a single bond, and polythene is produced this way from ethene p. 193.

Latex is the milky fluid from tapped rubber trees, and natural rubber is elastic, soft, cannot withstand heat, is a good electrical insulator and is not permeable to air p. 194. In latex, the rubber molecules are covered with a protein membrane surrounded by negative charges, so they repel each other and latex stays liquid p. 194. When acid is added, hydrogen ions neutralise the negative charges, the rubber molecules collide, the membrane breaks and the rubber coagulates into solid lumps p. 194. Latex left alone also coagulates because bacteria produce acid, and adding alkali keeps latex liquid because hydroxide ions neutralise the hydrogen ions p. 194.

Natural rubber is soft and not resistant to heat, so tyres made of it would become soft and melt on hot road surfaces p. 196. Vulcanisation is a process of heating rubber with sulphur, and Charles Goodyear founded the process in 1839 p. 196. The added sulphur atoms produce cross-links between the rubber polymer chains, so the chains are difficult to slide and the structure is difficult to break when heated p. 196. Vulcanised rubber is hard and more elastic, resistant to heat, a good electrical insulator, not permeable to liquid and air, and does not react with acid and alkali p. 197. It is suitable for tyres, rubber gloves and shoe soles p. 197.

Rubber is one of the major commodities of Malaysia, and the Malaysian Rubber Board carries out research and development on it p. 198. Cuplump Modified Asphalt makes road pavements last longer, and rail pads made of rubber reduce vibration and sound between the railway and the train’s engine p. 198.