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Arcjet Synthesis of Diamond
Published in Mark A. Prelas, Galina Popovici, Louis K. Bigelow, Handbook of Industrial Diamonds and Diamond Films, 2018
A plasma jet, or, “arcjet”, is a generic expression for a high pressure direct-current (dc) plasma discharge in which convection plays a significant role in transport processes. The name arcjet stems from the fact that an electric arc discharge is used to dissipate energy, via ohmic heating, into a flowing, high pressure gas, thereby increasing the gas enthalpy and kinetic energy. In a typical arcjet, the arc is confined to a chamber that contains a nozzle from which the plasma issues. The arc chamber itself, or arcjet body, may sit in a second chamber which is maintained at a pressure lower than that of the arc chamber, forcing the issuing plasma to expand. It is this pressure difference which is primarily responsible for the gas dynamic conversion of the thermal energy in the arc to kinetic energy of the flow. Such high-enthalpy arc-heated flows found early applications in fields ranging from the study of high-speed aerodynamics to the vaporization of refractory materials [Giannini 1957]. The temperature in the core of the arc, Tarc, of such a plasma can reach 40,000 K, and the plasma’s conductivity increases with increasing temperature. This behavior leads to a discharge that has a negative impedance, a feature characteristic of an electric arc, and one that poses a significant challenge to those designing high efficiency arc power supplies.
Nonchemical Rocket Engine
Published in D.P. Mishra, Fundamentals of Rocket Propulsion, 2017
As in the case of resistojet, the catalytic decompositions of hydrazine can be used in an arcjet to further augment specific impulse. This is known as chemical arcjet thruster (CAJT). Liquid hydrazine is decomposed catalytically into gaseous products which enters the arc at around 1000 K. Subsequently, the heat transfer to this hydrazine gas can enhance product gas temperature and results in higher specific impulse. Note that hydrazine being a liquid is easy to store in smaller volume space and hence is preferred over other gaseous propellants. The specific impulse in the range of 400–600 s can be easily achieved for a chemically arcjet thruster.
Past, present, and the future of the research and commercialization of CVD diamond in China
Published in Functional Diamond, 2022
Very recently, extra-large diameter diamond thin film coated tube drawing dies with a maximum diameter of 200 mm has been put into the Chinese market by the Hebei Plasma Diamond Technology [27–29]. It is unimaginable that these 200 mm diameter thin diamond film coated ultra-large metal tube drawing dies are produced by the Arc Rotating DC Arc Plasma Jet with Gas Recycling! At present, it is possible to supply diamond thin film coated cemented tungsten carbide tube drawing dies with a diameter from 8 mm to 200 mm (see Figure 5), whilst those made by the Hot Filament CVD are 0.8 mm-35mm only. Besides, the end users seem to be happier with the DC Arcjet dies, as the tool life was reported to be 30 times longer than the uncoated cemented tungsten carbide dies, and 5 times longer than the polycrystalline diamond composite one, when used for the diameter holding and the tube straightening of the large size stainless steel tubes. The better performance of the DC Arcjet dies might be due to the extraordinary high atomic hydrogen concentration produced by the very high gas temperature, which would lead to a better diamond film quality. It might be also due to the fact that the outward diffusion of the cobalt inside the cemented tungsten carbide was depressed efficiently in the process of diamond film deposition by DC Arcjet. Simply because the growth rate was higher than that of the Hot filament CVD, there was no sufficient time for cobalt outward diffusion [30]. This newly emerged technology is still under improvement.