Naomichi Nakamura

Boron Removal in Molten Silicon with Steam Added Plasma Melting Method

Oxidation and removal of boron from molten silicon by a steam-added plasma melting method was investigated as an important part of a sequential metallurgical process for producing high-purity solar grade silicon (SOG-Si) from commercially available metallurgical grade silicon (MG-Si). Experiments were carried out with the mass of silicon per charge varied in the range from 0.6 to 300 kg, corresponding to the laboratory scale to industrial scale. Boron was removed to ½B� < 0:1 mass ppm, which is the permissible boron content for SOG-Si. The deboronization rate was proportional to the steam content, 3.2th power of the hydrogen content of the plasma gas, boron content of the molten silicon, and area of the dimple formed by the plasma gas jet, and was inversely proportional to the mass of the molten silicon. A thermodynamic study showed that preferential oxidation of boron in molten silicon is positively related to higher temperatures, supporting the conclusion that this plasma method, which causes a local increase in the temperature of the reaction surface, is in principle advantageous.

Growth of YBa2Cu3Ox single crystals by a self-flux method with alkali chlorides as additives

Abstract Single crystals of YBa 2 Cu 3 O x in sizes up to 10 x 5 mm 2 in area and 50 μm in thickness have grown by a BaOCuO self-flux method with alkali chlorides MCl (M=Na, K, and Rb) as additives. T c of a crystal annealed in an oxygen atmosphere is determined magnetically to be 86 K. The X-ray diffractometry for the same sample, however, suggests the structure of orthorhombic-II featured by a lower T c . This discrepancy is probably explained by inhomogeneous oxidation which may divide the crystal into high T c- and low T c- parts. Added MCl is found to evaporate completely during soaking and to be absent when crystal growth is in progress. The role of MCl is presumably to remove impurities from the flux surface thus enhancing the crystal growth.

Influence of Microstructure on Coercive Force of Pure Iron Powder Cores

The recrystallization behavior of pure iron powder cores during the annealing process is visualized as Grain Orientation Spread (GOS) maps with an SEM/EBSD analysis. It is found to be significantly heterogeneous, leading to a heterogeneous dislocation density distribution. Nevertheless, a conventional dislocation pinning model well describes the coercive force behavior if the average dislocation density is applied. The pinning model is modified to separate the influence of the grain boundary pinning, and the relationship between the coercive force and the microstructure is discussed comprehensively. [doi:10.2320/matertrans.Y-M2018821]

Intergranular Flux Creep in Ceramic YBa2Cu3Ox

Magnetic relaxation in crystallographically aligned superconducting ceramics YBa2Cu3O was measured to study the kinetics and anisotropy of flux penetration into intergranular region. With use of a thermally activated flux motion model, the activation energy of the intergranular flux creep was evaluated as 4.0±1.0 meV and 3.7±1.1 meV for external magnetic fields perpendicular and parallel to the ab-plane, respectively. Implications of the apparent isotropy are discussed.

Processing of Dense, Fine Grained YBa2Cu3Ox Ceramics Using a Spray-Drying Technique

High-Tc superconductor YBa2 Cu3 Ox has been synthesized using a spray-drying technique with special reference to the influence or the purity of the starting reagents on microstructures and superconducting properties. Sintering is enhanced and high density is easily obtained with ultrapure reagents of acetic salts. Doping with Sr to examine the impurity effects of reagents of conventional grade has resulted in porous microstructures. Magnetic field dependences of magnetization and critical current density of the ceramics are significantly dependent on the grade of the starting reagents.