Yasutaka Ando

Plasma and heat flux characteristics of a supersonic ammonia or nitrogen/hydrogen-mixture direct-current plasma jet impinging on a flat plate

Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics with or without a titanium plate under nitriding for a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle in a low-pressure environment. Heat fluxes into the plate from the plasma were also evaluated with a Nickel slug and thermocouple arrangement. Ammonia and mixtures of nitrogen and hydrogen were used as a working gas. The NH/sub 3/ and N/sub 2/+3H/sub 2/ plasmas in the nozzle and in the downstream plume without a substrate plate were in thermodynamical nonequilibrium states. As a result, the H-atom electronic excitation temperature and the N/sub 2/ molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. Each temperature was kept in a small range in the plume without a substrate plate except for the NH rotational temperature for NH/sub 3/ working gas. On the other hand, as approaching the titanium plate, the thermodynamical nonequilibrium plasma came to be a temperature-equilibrium one because the plasma flow tended to stagnate in front of the plate. The electron temperature had a small radial variation near the plate. Both the electron number density and the heat flux decreased radially outward, and an increase in H/sub 2/ mole fraction raised them at a constant radial position. In cases with NH/sub 3/ and N/sub 2/+3H/sub 2/, a radical of NH with a radially wide distribution was considered to contribute to the better nitriding as a chemically active and non heating process.

Preparation of Carbon-Doped TiO2 Nanopowder Synthesized by Droplet Injection of Solution Precursor in a DC-RF Hybrid Plasma Flow System

Carbon-doped titanium dioxide nanopowder has received much attention because of its higher photocatalytic performance, which is practically activated not only by UV, but also by visible light irradiation. In the present study, C-TiO2 nanopowder was synthesized by droplet injection of solution precursor in a DC-RF hybrid plasma flow system, resulting in higher photocatalytic performance even under visible light irradiation. In-flight C-TiO2 nanoparticles reacted with the high concentration of carbon in plasma flow and were then deposited on the surfaces of two quartz tubes in the upstream and downstream regions of this system. The collected C-TiO2 nanopowder contained anatase-rutile mixed-phase TiO2 and TiC, the contents of which depended on the location of the powder collection, the temperature, and the duration of plasma treatment. Highly functional C-TiO2 nanopowder collected in the downstream region exhibited a higher degradation rate of methylene blue than that of single-phase anatase TiO2, even under visible light irradiation, in spite of being TiC.

Nitriding of aluminum by using supersonic expanding plasma jets

Abstract For the purpose of developing a rapid direct nitriding process to produce aluminum nitride layer without melting or vaporizing of aluminum during operation, nitridings of aluminum and aluminum alloy by using supersonic expanding nitrogen plasma jets were carried out. Nitride layer could not be formed on the substrate in the case of nitrogen gas, though the supersonic expanding plasma jets had enough reactivity to form rapidly titanium nitride layer on the surface of the substrate. Many fibers were formed on the substrate in the case of hydrogen/nitrogen mixture gas. However, the fibers could not be confirmed as aluminum nitride and the surface of the substrate came to be rough during operation in this case. Since the same phenomenon occurred in the case of hydrogen/argon mixture working gas, it was thought that the roughness of the substrate during operation was due to hydrogen infiltration into the substrate. In the case of nitriding of aluminum–magnesium alloy, unlike the case of aluminum substrate use, nitride layer was formed on the substrate even on the condition that pure nitrogen was used as working gas. From these results, this process was found to have a high potential for nitriding to produce aluminum nitride.

Material Spraying Using Electromagnetically Accelerated Plasma

In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. The MPD arcjet generator can produce higher-velocity, higher-temperature, higher-density and larger-area plasmas than those of conventional thermal plasma torches. Two types of MPD arcjet generator were developed for applications to ceramic spray coatings. One generator was installed with a cathode covered with mullite or zirconia ceramics and the other with a titanium cathode. The former was operated with Ar for mullite or zirconia coating by an ablation process of the cathode cover and the latter with N2 for titanium nitride coating by a reactive process between ablated titanium particles and nitrogen plasma. The MPD spray process could successfully form dense, uniform and hard ceramic coatings. In titanium nitride reactive spraying, plasma diagnostic measurement and flowfield analysis were also carried out. A large amount of N and N+ was expected to be exhausted with a high velocity from the MPD generator. Both the electron temperature and the electron number density were kept high at a substrate position compared with those for conventional low-pressure thermal sprayings. A chemically active plasma with excited particles of N+, Ti, Ti+ and Ti2+ was expected to contribute to better titanium nitride coatings. All coating characteristics showed that the MPD arcjet generators had high potentials for ceramic spray coatings.

Evaluation of Highly Functional TiO2 Synthesized by Solution Precursor Spraying in a DC-RF Hybrid Plasma Flow System

Carbon doped TiO2 synthesized in a DC-RF hybrid plasma flow system by the solution precursor spraying method was evaluated. The effects of mass fraction of TTB in solution precursor on contents and photocatalytic activity of carbon doped TiO2 were investigated. Highly functional carbon doped TiO2 at 11 wt% TTB had higher UV-visible absorption characteristics, which showed higher degradation rate of methylene blue solution under visible light irradiation.

TiO2 Film Deposition by Atmospheric Thermal Plasma CVD Using Laminar and Turbulence Plasma Jets

In this study, to provide continuous plasma atmosphere on the substrate surface in the case of atmospheric thermal plasma CVD, TiO2 film deposition by thermal plasma CVD using laminar plasma jet was carried out. For comparison, the film deposition using turbulence plasma jet was conducted as well. Consequently, transition of the plasma jet from laminar to turbulent occurred on the condition of over 3.5 1/min in Ar working gas flow rate and the plasma jet became turbulent on the condition of over 10 1/min. In the case of the turbulent plasma jet use, anatase rich titanium oxide film could be obtained though plasma jet could not contact with the surface of the substrate continuously even on the condition that feedstock material was injected into the plasma jet. On the other hand,, in the case of laminar gas flow rate, the plasma jet could contact with the substrate continuously without melt down of the substrate during film deposition. Besides, titanium oxide film could be obtained even in the case of the l...

Creation of Diamond/Molybdenum Composite Coating in Open Air

In order to improve wear resistance of atmospheric thermal plasma sprayed molybdenum (Mo) coating, diamond deposition on the atmospheric plasma sprayed molybdenum coating by the combustion flame chemical vapor deposition (CFCVD) has been operated. Although diamond particles could be deposited on the molybdenum coating, the coating was fractured and peeling off due to thermal influencesin our previous study. In this study, to diminish the thermal damage of the substrate during operation, a thermal insulator was equipped between substrate and water-cooled substrate holder. Consequently, diamond particles could be created on the Mo coating without fracture and peeling off. From these results, it was found that this process had a high potential in order to improve wear resistance of thermal sprayed coating.

Plasma Characteristics of Supersonic Nitrogen/Hydrogen-Mixture and Ammonia Plasma Jets and Nitrided Material Properties

Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics under nitriding for a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle in a low pressure environment. Heat fluxes into the plate from the plasma were also evaluated. Ammonia and mixtures of nitrogen and hydrogen were used as the working gas. The H-atom electronic excitation temperature and the N2 molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. As approaching the titanium plate, the thermodynamical nonequilibrium plasma came to be a temperature-equilibrium one. Both the electron number density near the plate and the heat flux increased with H2 mole fraction for mixtures gases. In cases with mixtures of N2 and H2, a radical of NH with a radially wide distribution is considered to contribute to the better nitriding as a chemically active and non heating process.

Material Processing Using Supersonic Reactive Plasma Jets in Thermodynamical and Chemical Nonequilibrium State

Nitriding of metals and reactive spraying for nitride ceramics are planned using a 10-kW-class direct-current nitrogen or H2/N2-mixture arc plasma jet generator with a supersonic expansion nozzle in a low pressure environment. The H-atom electronic excitation temperature and the N2 molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. As approaching the titanium plate for nitriding, the thermodynamical nonequilibrium plasma came to be a temperature-equilibrium one. Both the electron number density near the plate and the heat flux into the plate increased with H2 mole fraction for mixtures gases. In cases with H2/N2-mixtures, a radical of NH with a radially wide distribution is considered to contribute to the better nitriding as a chemically active and non heating process. Numerical simulation was carried out to examine interactions between injected ceramic particles and the nitrogen plasma flow. When plasma was accelerated to supersonic flow through the nozzle, ceramic particles were smoothly accelerated by the aerodynamic drag force and heated in the highly-reactive plasma flow. The calculated results showed that the supersonic plasma jet in thermodynamical and chemical nonequilibrium state might have some potentials for material processing, even for spraying, because of its high reactivity.