Arc furnace

Arc furnace is used for high degrees of heating. When an air gap is subjected to a very high voltage, the air gets ionized due to electrostatic force. This basic idea is employed in arc furnaces. The ionized air has conducting nature. Due to this, a current starts flowing through the air gap in the form of continuous spark. This spark is known as arc. As electrodes, either graphite or carbon is used. There are two varieties in this category. They are direct arc furnace and indirect arc furnace. In a direct arc furnace, charge acts as another electrode. Very high temperature can be achieved here since the arc is directly in contact with the charge. Usually size of this type of furnace ranges from 5 to 10 tonnes and power factor is around 0.8. This type of furnace is commonly used in steel production industry but not all recommended for melting processes. In an indirect arc furnace, arc is produced between two electrodes and the heat is transmitted to the charge by radiation. Here one single-phase supply is enough since only two electrodes are used. It’s difficult to attain very high temperature in an indirect arc furnace.

Shapes of nanomaterials

Nanomaterials are classified as quantum wells, quantum wires and quantum dots. In a three dimensional structure, if one dimension, say thickness, is of nanosize, then the structure is called quantum well. If two dimensions are of nanosize, then it is called a quantum wire and if all the three dimensions are of nanosize, then it is called quantum dot. The word quantum is associated with the structures because the properties exhibited by them are described by quantum mechanics. The density of states for the various quantum structures can be explained. For quantum dots, permitted energy values are almost discrete. But chance for a slight broadening exists due to the size effect. In a quantum wire, density of states has peaks. For a quantum well, density of states varies as a step function.

Carbon nanotubes

Carbon nanotubes are cylindrical fullerene. Its novel properties find potential applications in different areas like nanotechnology, optics, electronics, material science etc. They are good conductors of heat and exhibit enormous strength. There exist two types of carbon nanotubes-single walled nanotubes and multi walled nanotubes. Single walled carbon nanotubes exhibit superlative electrical properties and is widely used now in modern electronics. The major application of single walled carbon nanotubes is in intramolecular field effect transistors. Multi walled carbon nanotubes exist in two models. They are Russian doll model and parchment model. In the Russian doll model, graphite sheets are arranged in concentric cylinders and in parchment model, a single graphite sheet rolled in around itself.

Different laser systems

Laser is light amplification by stimulated emission of radiation. He-Ne laser, carbon dioxide laser and Argon laser are examples of gas lasers. In He-Ne laser a mixture of He and Ne gas is taken in a discharge tube. Pumping mechanism employed is direct electron excitation and inelastic atom-atom collisions. The wavelength in this case is 632.8 nm. Ruby laser and Nd:YAG laser are exadmples of solid state lasers. Ruby rod is used in ruby laser with optical pumping. Wavelength of laser light is around 694.3 nm. Nd:YAG laser emit light in the near infrared region. Semiconductor laser is another laser system which is very economical. Some other laser systems are ion and metal vapour laser, excimer laser, liquid dye laser, free electron laser, chemical laser and heater laser.

Bomb Calorimeter

Calorific value of a fuel is defined as the quantity of heat evolved by the complete combustion of unit quantity of the fuel in air. Bomb calorimeter is a device used to determine the caloric value of a solid fuel. First step here is burning a known mass of the solid fuel completely in the presence of oxygen. Brass calorimeter and the surrounding water absorb the heat liberated. By using a sensitive thermometer, note the increase in temperature of water and the calorimeter. Now the calorific value of the solid fuel can be calculated by using the principle that the heat lost by the burning fuel is equal to the heat gained by the water and the brass calorimeter. The main components of a bomb calorimeter are steel bomb, graphite sample, ignition coil, sealing ring, water tank, gas inlet, needle valve, insulated jacket, stirrer, power supply and a thermometer.