Kazuo Adachi

Synthesis of purified AlN nano powder by transferred type arc plasma

Nano powder of aluminium nitride (AlN) is one of the materials necessary for developing solid insulating materials with high thermal conductivities. This paper describes the results of chemical equilibrium composition calculations and the results of experiments in synthesizing AlN nano powder using transferred type arc plasma. In order to increase the AlN content in synthesized powder, ammonia was recommended as a reacting/quenching gas, to be blown into aluminium gas in a temperature range between 2000 and 2400 K. The AlN content increased by more than 99% on passing the synthesized powder through ethanol.

Vaporization Behavior of Cs in Plasma Melting of Simulated Low Level Miscellaneous Solid Wastes.

A DC transfer type plasma with a maximum output of 60 kW was used to melt 10 kg of carbon steel and 3 kg of granular oxide mixtures ( Fe2O3, Al2O3, SiO2 and CaO) containing non-radioactive cesium nitrate, for measuring Cs vaporization. These materials are the main components of low level miscellaneous solid wastes. The vaporization rate constant values obtained by approximating Cs vaporization by a first order reaction rate formula were in the range of (4.01–7.1)×10-6 (m/s). The vaporization rate constant of Cs did not depend on the initial Cs content, and increased with the increase of slag basicity ( %CaO/%SiO2). Since the vaporization rate constant was unaffected by the viscosity of the slag on which the Cs transfer rate in the slag depends, the Cs vaporization phenomenon from the slag can be estimated to be controlled by the vaporization step from the slag surface.

Effects of Copper Vapor on Heat Transfer from Atmospheric Nitrogen Plasma to a Molten Metal Anode

As an object of nitrogen plasma operated with an arc current to 200 A, an arc length about 35 mm, we evaluated heating efficiency from arc plasma to the molten copper anode and the water-cooled solid copper anode. The heating efficiency to the molten anode is smaller than that to the solid anode by about 20%. We focused on copper vapor concentration in plasma as a possible cause for a decrease in heating efficiency, and estimated it by means of the Cu and the N spectral line measurement. Simple numerical analysis, taking into consideration measured copper vapor concentration, suggested that an increase in electrical conductivity due to copper vapor, made the plasma temperature change and consequently caused a decrease in thermal conductivity. We concluded that one of the reasons for a decrease in heating efficiency would be caused by copper vapor contamination.

Influence of atmospheric gases on the treatment of miscellaneous solid wastes by plasma melting technology

The material properties of the treated waste forms and the behavior of radionuclides found in the plasma melting tests of simulated miscellaneous solid wastes (iron, fly ash and wood) with cold tracers were examined by using different heating atmospheric gases. The material properties were changed with increasing iron oxide content in the slag layers by changing atmospheric gases. The results showed a homogeneous distribution of cold tracers and low leaching rate of it from the treated waste forms appropriate for shallow land burial site disposal in every atmospheric gas. The high residual rate of Cs in the slag layers (about 70%) was obtained in the plasma melting process except the extremely high reductive atmospheric conditions.

Investigation of a New Dry Surface Decontamination Technology with Low-Pressure Arc Plasma and Its Application to Pipe-Shaped Test Pieces

We investigated a dry surface decontamination technology using low-pressure arc plasma for radioactive corrosion product films. The low-pressure arc plasma is produced with a transferred-type DC arc discharge that operates under reduced pressure; here, the cathode is the object to be treated. The cathode spots formed inside the low-pressure arc plasma can melt away the metal oxide film on the surface of the object without significantly damaging the metal substrate. One of the major advantages of this technology is its potential to reduce the amount of secondary waste compared with existing technologies, e.g., decontamination with chemical solutions, because it eliminates the need for a medium. In this report, the dependence of the decontamination performance on the type of plasmasource gas was investigated. Argon, hydrogen, chemically active carbon monoxide, and a mixed gas of CF4/O2 were selected. Consequently, a higher Cobalt-60 removal ratio was obtained with smaller electric charges in the hydrogen low-pressure arc plasma. The low-pressure arc plasma was also applied to pipe-shaped test pieces with a corrosion product film. And eventually, a Co removal ratio exceeding 90% was achieved. The applicability of the dry surface decontamination technology with low-pressure arc plasma for radioactive metal waste with a corrosion product film is demonstrated.

High-Speed Observation of Alumina Vapor Progress in DC Arc Plasma for Synthesizing Nanoparticles

Nanoparticles (NPs) are used as smart materials in some industrial areas. The methods that utilize arc plasma are a good choice in terms of raising production rate of NPs. In this paper, alumina NPs are synthesized from alumina bulk by transferred-type dc arc plasma, and a high-speed observation of the alumina vapor in the arc plasma is carried out in order to investigate on the evaporation behavior of the alumina bulk.