Shu Usuba

Onion-like carbon deposition by plasma spraying of nanodiamonds

Abstract A deposit of carbon nanoparticles based on an onion-like structure was fabricated from detonation nanodiamond powders by a novel plasma spraying process, electromagnetically accelerated plasma spraying (EMAPS). EMAPS was able to transform nanodiamonds to onion-like structured carbon within 300 μs through a thermal graphitization process in which the temperature of the particles would be in the range of 2700–4500 K. Synthesized onion-like carbon nanoparticles were spherical or polyhedral. The G-band in the UV–Raman spectra of the produced deposits was found to be a superposition of a characteristic band of well-formed carbon onions at 1571 cm −1 and the G-band of defective carbon onions at 1592 cm −1 . The availability of a plasma spraying process for developing solid lubricant coatings incorporating nanodiamond and onion-like carbon was demonstrated.

Sonochemical polymerization of benzene derivatives: the site of the reaction.

Sonochemical polymerization of benzene and halogen-substituted benzenes has been studied. The difference of absorption spectra of polymerization products can be explained qualitatively using bond energies of the primary products. The relative rate constant of the polymerization reaction is apparently proportional to the inverse of the vapour pressure of the liquids. Using this relation, we analysed the relative rate constant of the polymerization in benzene/chrolobenzene mixtures. From this, we conclude that sonochemical polymerization proceeds in the vapour phase of a bubble.

Possible new route for the production of C60 by ultrasound

The production of C60 by ultrasonic irradiation of liquid benzene has been studied. After irradiating 150 ml of liquid benzene for 1 h (600 W, 20 kHz), approximately 1 microgram of C60 is produced.

Pressure effect on magneto-optical properties in CdTe/(Cd, Mn)Te single quantum wells with high Mn concentration

The pressure effect on the magnetic field induced type I–type II transition is studied in a CdTe/Cd1−xMnxTe (x=0.24) single quantum well. Photoluminescence measurements under hydrostatic pressures up to 1.07 GPa and long pulsed magnetic fields up to 60 T with a pulse duration of 2 s are reported. The pressures were generated in a plastic diamond anvil cell. A bend toward lower energies (additional red shift) is observed above 28.5 T in magnetic field dependence of the exciton energy for a 13 A thick quantum well. We attribute this red shift to a phenomenon preceding the type I–type II transition after a comparison with a simple quantum mechanical calculation. The onset field of the additional red shift increases by 3.4 T by applying a pressure of 1.07 GPa. Spin–spin coupling between the exciton and the Mn ion in the interface region is also investigated and found to be enhanced by pressure.

Diamond Powders Less Than 100 nm in Diameter as Effective Solid Lubricants in Vacuum

The frictional behavior of detonation nanodiamond and single-crystal fine diamond powders were studied to determine the effect of particle diameter on their lubricative and abrasive characteristics. In vacuum, nanodiamond with an average aggregate size of 75 nm and mechanically crushed single-crystal diamond powders with an average diameter of 50 nm formed a uniform lubricating layer while sliding against a SiC ball and showed very low friction coefficients of 0.03 and less than 0.01, respectively, under moderate conditions of 0.5 N applied load and 3.5 mm/s sliding speed. A clear tendency was observed for both the friction coefficient and specific wear rates to decrease with decreasing particle/aggregate size.

Formation of boron carbide coating by electromagnetically accelerated plasma spraying

Abstract Boron carbide (B 4 C) coating formation is investigated using an electromagnetically accelerated plasma spraying, which can generate a dense and a high velocity plasma jet of 1 MPa and 2.0–2.5 km/s by applying a pulsed high-current arc-discharge to accelerate and heat powders. Highly crystalline B 4 C coatings with roughened coating-substrate interfaces were formed on mirror-polished stainless (SUS304) substrates without a binder material. The density and uniformity of the coating are improved by changing the source powder size from 30 to 10 μm, where the estimated porosity is decreased from 9 to 4%.

Excitation density effect on the decomposition of liquid benzene by ArF excimer laser (193 nm) irradiation

Abstract The excitation density effect on the decomposition of liquid benzene has been studied using an ArF excimer laser ( λ =193 nm). At low excitation density, biphenyl was primarily produced. At higher laser fluence, large-size aromatic molecules and graphitic carbon were produced. The apparent production yield of biphenyl increases steeply with laser fluence. From the dilution effect of benzene by cyclohexane, we conclude that the steep increase is due to the thermal decomposition induced by the non-radiative decay of optically excited molecules.

Boron carbide coating by electromagnetically accelerated plasma spraying

A new system of electromagnetically accelerated plasma spraying (EMAPS) consisting of a pulsed high-current arc-plasma gun and a large flow rate pulsed powder injector has been developed to synthesize a hard and dense coating of boron carbide (B4C) with a high adhesion. The plasma gun with a co-axial cylindrical electrode configuration generates electromagnetically accelerated arc plasma with a typical velocity and maximum pressure of 1.5–3.0 km/s and 1 MPa, respectively, by discharging a pulsed high current of about 100 kA in peak and about 300 µsec of duration. The heating and accelerating of source powder are accomplished by injecting it into the inter-electrode space of the gun prior to the plasma generation using a newly developed pulsed powder injector that enables a gram of powder to be injected within 1 ms with precisely controlled time delay. With this system, hard B4C coatings with a high adhesion and crystallinity were successfully formed on mirror-polished stainless (SUS304) substrates without a binder.

High-pressure Raman study of a polar molecule, acetonitrile

Abstract Liquid acetonitrile underwent phase transitions to a molecular crystalline β phase at 0.4 GPa and further to an α phase at 0.6 GPa. The α phase appeared to be stable up to 15 GPa, where polymerization reaction was induced. The Raman spectra of the α phase showed that the lattice frequencies increased largely with pressure, whereas the internal frequencies changed little. In addition, significant decreases in Raman intensity were observed for the librational lattice and internal bending modes. These frequency and intensity changes may be interpreted as a result of pressure change in intermolecular interactions, particularly, in the charge transfer between the methyl and nitrile groups.

Infrared study of phase transition and chemical reaction in tetracyanoethylene under high pressure

Infrared spectra of the cubic and the monoclinic phases of tetracyanoethylene have been investigated as a function of pressure at room temperature. The cubic phase, a low-temperature phase stable below 318 K at ambient pressure, appeared to be stable up to 6 GPa. The high-temperature monoclinic form metastably obtained at room temperature showed a structural transformation near 3 GPa. This high-pressure phase, showing an infrared spectrum different from that of the cubic phase, transformed reversibly to the monoclinie phase on unloading. Polymerization occurred in both the cubic and high-pressure molecular phases near 6 GPa.