Melting of materials

Different types of furnaces can be used for melting, among which electric resistance furnace is the most commonly used one in industry. Electrical resistance furnace is several meters long with open roof and its inner space is loaded with a layer of catalyst powder. Two iron electrodes are inserted into the both ends of the furnace. The raw materials are put into the furnace and the two electrodes are connected by an iron bar. After that, the material is heated to the operating 

Induction furnace is a refractory crucible, in which copper tube cooled by water is used as the primary coffer and the molten material as a secondary coffer. There is no iron core in the magnetic circuit and the magnetic flux is completely emanative, which leads to a waste of current. To overcome this weakness, capacitors and primary coilers are parallel coimected. Intermediate frequency (500 Hz-1,000 Hz) is used in large-capacity induction furnace. Stoves are usually diagonal, and therefore the molten material can easily be poured out. It is also operated in batches as the resistance furnace. 

Induction furnace has many advantages compared with the resistance furnace. Since the current can be very large, the temperatme can reach above 2,000°C and is easy to be controlled. As a result, the melting time can be shortened. It also means that the oxidation degree of Fe +/Fe + can be accmately adjusted. In addition, the magnetic field formed by the primary coffer can maintain a continuous rotation of the melt, and the powerful magnetic line can play the role of automatic mix round, which helps the diffusion and distribution of promoters. This leads to the 

In the electric arc furnace method, the raw material is melted by a three-phase arc in a container lined with MgO or AI2O3 (available Si02). The wiring voltage between two electrodes (electrodes introduced vertically into the container and almost touching the material) is generally 75V-180 V. To maintain a constant current, the distance between the electrodes and molten material must be adjusted automatically. 

It is difficult to compare the preponderance of the three methods mentioned. The reasons are the difference of ratio between the investment cost and running cost because their relative income changes with the production capacity. Undoubtedly, the induction method is the preferred way to secure the best quality of catalyst, especially when the promoters are dispersed as molecular in the melt magnetite and the oxidation degree is close to the stoichiometric magnetite. 

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Determination of melting of materials with certain melting point [87]... 

The melting of materials due to short laser pulses is an extremely nonequilibrium phenomenon. In a heterogeneous system, such processes as intermixing, interdiffusion and segregation are added. This makes the situation quite unpredictable and lets expect novel phenomena. 

Volcanic activity is a surface manifestation of a disordered state within the Earth s interior that has led to the melting of material and the consequent formation of magma. This magma travels to the surface, where it is extravasated either from a fissure or a central vent. In some cases, instead of flowing from the volcano as lava, the magma is exploded into the air by the rapid escape of the gases from within it. The fragments produced by explosive activity are known collectively as pyroclasts. 

While it is clear that granite-like rocks or mixtures of granite-like rocks and basalts can account for the lanthanide distribution of the NASC, the origin of continental material is still obscure. Some granites seem clearly to be products of extreme metamorphism of previously existing sediments. Others seem to be products of partial melting of material deep within the crust, or even the upper mantle, possibly of older volcanics. If volcanic, onto what sort of crust did the precursors to the granites extrude ... 

An appreciation of phase diagrams greatly aids the imderstanding of the principles of freeze-drying and the hterature on mixtures and melting of materials such as fats. Figure 1.18a represents a trivial phase diagram and shows the condition of perfect mixtures of... 

During the production of mineral oils from vacuum distillates, one of the process steps, dewaxing , removes the high melting point materials in order to improve the oil s pour point. Dewaixing produces paraffins and waxes, the first coming from light distillates, and the second from medium or heavy distillates. 

The thennal evaporation source was the earliest used to produce metal clusters in the gas phase [H, 12 and 13], mostly for clusters of the alkalis and other low melting point materials. In this technique, a bulk sample is simply... 

Hydrolysis of methyl m-nitrobenzoate to m-nitrobenzoic acid. Place 90 -5 g. of methyl m-nitrobenzoate and a solution of 40 g. of sodium hydroxide in 160 ml. of water in a 1-htre round-bottomed flask equipped with a reflux condenser. Heat the mixture to boiling during 5-10 minutes or until the ester has disappeared. Dilute the reaction mixture with an equal volume of water. When cold pour the diluted reaction product, with vigorous stirring, into 125 ml. of concentrated hydrochloric acid. Allow to cool to room temperature, filter the crude acid at the pump and wash it with a httle water. Upon drying at 100°, the crude m-nitrobenzoic acid, which has a pale brownish colour, weighs 80 g. and melts at 140°, Recrystalhsation from 1 per cent, hydrochloric acid afibrds the pure acid, m.p. 141°, as a pale cream sohd the loss of material is about 5 per cent. 

Material Properties. The properties of materials are ultimately deterrnined by the physics of their microstmcture. For engineering appHcations, however, materials are characterized by various macroscopic physical and mechanical properties. Among the former, the thermal properties of materials, including melting temperature, thermal conductivity, specific heat, and coefficient of thermal expansion, are particularly important in welding. 

Environmental Aspects. More than two-thirds of aluminum cans are recaptured and returned for recycling into more cans. Because of the heat of melting, the use of post-consumer recycled cans is safe for beverage contents. Not only does recycling save on mass of materials, it also saves the energy of manufacture from aluminum ore (see Recycling, nonferrous metals). 

Refractory Linings. The refractory linings (2,3) for the hearth and lower wads of furnaces designed for melting ferrous materials may be acidic, basic, or neutral (see Refractories). Sdica has been widely used in the past, and is stid being used in a number of iron and steel foundries. Alumina, a neutral refractory, is normally used for furnace roofs and in the wads for iron foundries, but basic brick can also be used in roofs (4). 

There are large-scale operations using direct-heat resistance furnaces. These are mainly in melting bulk materials where the Hquid material serves as a uniform resistor. The material is contained in a cmcible of fixed dimensions which, coupled with a given resistivity of the material, fixes the total resistance within reasonable limits. The most common appHcation for this type of direct-heat electric resistance furnace is the melting of glass (qv) and arc furnaces for the melting of steel (qv). 

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