Category Science

               The word ‘ceramics’ has its origin in the Greek word Keramos, which means “potter’s clay”. Today the word refers to all types of pottery, whatever its composition or use. All ceramics are made from various clays, together with materials such as flint, felspar or china clay.

               However, strictly speaking ceramics are compounds of silicon, carbon, oxygen and nitrogen combined with other elements like sodium, potassium, calcium, barium etc. The principal raw material used in the manufacture of ceramics is clay. These clays are formed by decomposing natural rocks which are exposed to the wearing action of air and water. Granite is the rock which provides the bulk of useful clays. It is composed of quartz, mica, felspar etc. These clays are crushed and ground into fine particles. The particles are mixed and moisted with right proportion of water, which makes the particles flexible for shaping. Different methods are used for getting the desired shape.

               After the product has dried, it is heated. This process takes place in a special type of furnace called kiln. Ceramics are heated at temperatures ranging from 650°C to 1650°C. Firing makes the products hard in the desired shape and turns their glaze into a smooth coat. This process also makes the product leak-proof, durable and decorative.

               Clay and shale are used to make building products, such as bricks and drain pipes. Calcium silicates are used in making the cement. Gypsum is used in the manufacture of plaster. Porcelain is used in making bath-tubs, sinks and toilets. Bowls, cups and plates are also made from porcelain. Artificial bone joints and false teeth are made from porcelain.

               Some ceramics such as alumina and porcelain, do not conduct electricity and used as insulators in automobile spark plugs, electric power lines. Some types of capacitors are made from Barium titanate which is a ceramic material. Refractories are another important group of ceramic products used for lining furnaces. They resist heat and chemical action. Alumina, silica and magnesium compounds are used as refractories. Uranium oxide ceramics are used as fuel elements for nuclear reactors. Alumina in the form of ruby is used in the making of lasers, which produce extremely strong light beams.

               It is our common practice to measure our body temperature with the help of a thermometer when we feel feverish. In ordinary thermometers, the lowest temperature is marked as 0°C. Today scientists can produce temperatures well below 0°C. Kelvin William Thomson a British Physicist first pioneered the absolute scale of temperature. The scale which is used to measure low temperatures therefore called ‘Kelvin’ scale or absolute scale of temperature.

               Theoretically the lowest possible temperature which a gas can attain is known as absolute zero. In centigrade scale it is equal to -273.15°C. This is based on the theory that the volume of a gas reduces in correspondence to the fall in temperature. So according to this theory, the gaseous volume would disappear and would loose all its kinetic energy if its temperature was lowered to -273.15°C or absolute zero. The gas molecules would be completely at rest, and it would not possess any heat. In practice, however, all gases change to liquids and then to solids before their temperature reach absolute zero.

               Scientists have never been able to reach absolute zero in their laboratory experiments. The lowest recorded temperature so far was achieved by magnetizing copper nuclei at a low temperature. When the electromagnet was switched off, the copper nuclei became demagnetized; the temperature fall was upto a million part of a degree above absolute zero.

               Materials react strangely when cooled to a temperature near absolute zero. At this temperature, oxygen gas freezes to a bluish white solid, and a rubber ball becomes so brittle that it shatters instead of bouncing. Mercury, normally a liquid, becomes and shines like hard silver. Hydrogen becomes a liquid and begins creeping into the sides of its container. Natural gas is shipped around the world in special containers after being cooled and liquefied at a low temperature.

               The Kelvin scale is used for scientific measurements, e.g. the liquefaction temperature on the Kelvin scale for Hydrogen is 20K and for liquid Helium it is 4.2K.