High temperature plasma jets

K. The arcs are often coupled with a gas flow to form high-temperature plasma jets. The arc discharges ate well known not only to scientists and engineers but also to the general public because of their wide applications in welding devices. The arc discharge can be considered a major example of thermal plasma sources (see Fig. 1-7). 

In the past few decades, plasma spray-coating techniques have been developed to cover orthopedic implants with protective and/or bioactive coatings. As introduced in Chapter 1, the plasma spray-coating method employs high temperature plasma jet to melt and spray a feedstock material onto a substrate to form a coating. The feedstock materials for plasma spray can be in the forms of solid, liquid or suspension [29,30]. For the fabrication of nanocoating on orthopedic implants, the commonly used solid... 

A non-linear wall-stabilized non-transferred arc is shown in Fig. 4 8. It consists of a cylindrical hollow cathode and coaxial hollow anode located in a water-cooled chamber and separated by an insulator. Gas flow blows the arc column out of the anode opening to heat a downstream material, which is supposed to be treated. In contrast to transferred arcs, the treated material is not supposed to operate as an anode. Magnetic 7x5 forces cause the arc roots to rotate around electrodes (Fig. 4-48), which provides longer electrode lifetime. The generation of electrons on the cathode is provided in this case by field emission. An axisymmetric version of the non-transferred arc, usually referred to as the plasma torch or the arc jet, is illustrated in Fig. 4-49. The arc is generated in a conical gap in the anode and pushed out of this opening by gas flow. The heated gas flow forms a very-high-temperature arc jet, sometimes at supersonic velocities. 

Plasma Plating—deposition on critical areas of metal coatings resistant to wear and abrasion normally this is done by means of a high velocity and high-temperature ionized inert gas jet. 

Some workers have correlated experimental data in terms of k at the arithmetic mean temperature, and some at the temperature of the bulk plasma. Experimental validation of the true effective thermal conductivity is difficult because of the high temperatures, small particle sizes and variations in velocity and temperature in plasma jets. 

In recent years there has been renewed interest in treating coal at high temperatures both by rapid processing in the more conventional type of carbonization apparatus (I) and by using such devices as flash tubes (5, 12, 13), lasers (13), arc image furnaces (9, 11), and plasma jets (3). All these methods produce conditions whereby the coal can be heated rapidly to a temperature well in excess of 1000°C. followed by quenching of the products. The work described here is an investigation into the reactions of coal in a plasma jet and has been reported briefly elsewhere (3). 

Lasers and plasma provide means for investigating the rapid carbonization of coal at high temperatures. Owing to the short residence time of coal particles in a plasma jet, it is unlikely that thermodynamic equilibrium or even thermal equilibrium will be attained. Moreover the gaseous products will be heavily diluted by the carrier gas. Nevertheless the thermodynamics presented here provide a useful guide to the type of products which may be expected at various temperatures and their relative yields. 

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