Comparison of 80-keV D+ Ion Implantation with Thermal D2 Doping in Silica by FTIR and ESR Spectroscopy

Behavior of deuterium atoms in fused silica, which were implanted by 80-keV D⁺ (D₂⁺, D₃⁺) ions or doped thermally by D₂ (or D₂O), was studied by infrared Fourier transform spectroscopy (FTIR) and by ESR spectroscopy. When 80-keV deuteron ions are implanted into fused silica, OD bonds are formed. The OD bonds are also formed by thermal doping with D₂ or D₂O. When the deuterated silica is γ-ray irradiated at 77 K, D atoms are formed by rupture of the OD bonds. The efficiency of the OD bond rupture in the deuteron-implanted silica is much less than that in the D₂-doped silica. It is concluded from the results of thermal annealing that the low efficiency of the OD bond rupture in the deuteron-implanted silica is due to the radiation damage accompanying the implantation process. However, the decay rate and detrapping energy of deuterium atoms, once formed in the silica, are similar in both cases.     

Decomposition of Mullite by Silica Volatilization

Thermal decomposition of mullite into corundum was investigated using a high-temperature X-ray single-crystal camera equipped with a gas-flame furnace and by scanning electron microscopy and electron probe microanalysis (EPMA). When heated to ∼1750°C, mullite decomposed to corundum by the liberation of the SiO₂ component with topotaxial relations of:

• (1) 

  (310)_mull∥(001)_cor; [001]_mull∥[110]_cor
• (2) 

  (130)_mull∥(001)_cor; [001]_mull∥[110]_cor
• (3) 

  (110)_mull∥(001)_cor; [001]_mull∥[110]_cor

Thus, it was considered that, when mullite decomposed into corundum, their oxygen close-packed planes were almost preserved. The SEM photographs showed that the crystals of the developed corundum are prismatic and ∼5 μm wide. The EPMA showed that the phase boundary between mullite and developed corundum is discontinuous.     

Selective O–H Bond Cleavage in the Radiolysis of Quartz

Cleavage of the O–H bond in quartz was studied by Fourier transform infrared spectroscopy and ESR spectroscopy. When quartz single crystals and fused silica glass are γ-irradiated at 77 K, hydrogen atoms are produced by rupture of O–H bonds. The initial efficiency of O–H bond cleavage in quartz single crystals, i.e. the initial yield of H atoms, was three times as great as that in fused silica glass, although the concentration of O–H bonds in quartz single crystals (70 ppm) is much lower than that in fused silica glass (4000 ppm). The efficiency of O–H bond cleavage in quartz single crystals indicates that energy transfer from the irradiated single crystal to the O–H bonds takes place effectively at 77 K. The efficiency of O–H bond cleavage decreases with increasing γ-ray dose, i.e. with increasing amounts of radiation-induced defects in quartz single crystals. When the radiation-induced defects are removed by annealing the irradiated quartz single crystal at 773 K, the O–H bonds are ruptured again as effectively as for a fresh quartz single crystal. The distance of the energy transfer, estimated by a target model, is ∼15 nm.     

Ferroelectric-Paraelectric Phase Transition in Lead Titanate Containing Lattice Defects

A series of lead titanates containing lattice defects was prepared and characterized in terms of inhomogeneously distributed vacancies, □_Pb and □_O•. The tetragonal lattice strain and the Curie temperature varied as functions of the Pb or O deficiency in the crystals. The tetragonal strain for these crystals decreased slowly with increasing temperature as the Curie temperature was approached. The phase transition, which extends over a temperature interval, is interpreted according to a model in which microregions in the crystal differ in composition and therefore have different Curie temperatures.     

Structural Analysis of SiO2-Al2O3 Glasses

The structure of SiO₂-Al₂O₃ glasses with up to 60 wt% Al₂O₃ was investigated using the radial distribution function together with the correlation method based on X-ray scattering intensity data. Radial distribution curves are interpreted on the basis of glass-in-glass separation with the constituents of SiO₂-rich and Al₂O₃-rich glasses. The structure of the Al₂O₃-rich glass has a short-range ordering similar to the crystal structure of mullite. The calculated S- i (S) curve of this model gives good agreement with the observed one.     

Effects of AIN Additions and Atmosphere on the Synthesis of Cubic Boron Nitride

Aluminum nitride was found to act as the catalyst for the synthesis of cubic BN by sealing the mixture of hexagonal BN and AIN in a pressure cell under the inert or reducing atmosphere. No conversion of hexagonal BN to cubic BN was observed under pressures below 7×10⁹ Pa (7 GPa, 70 kbar) without AIN addition. All hexagonal BN could be completely converted to cubic BN under 6.5 GPa at 1600°C by the addition of 20 mol% AIN. The cubic BN thus synthesized was a typical tetrahedron (grain size ≅2 μm). The pressure-temperature diagram for the synthesis of cubic BN was determined at >7 GPa and T <1700°C.     

Sluggish Pansition Between Tetragonal and Rhombohedral Phases of Pb(Zr,Ti)03 Prepared by Application of Electric Field

Tetragonal and rhombohedral phases always coexist in Pb(Zr_xTil_1−x)0₃ near the morphotropic phase boundary compositions (0.52≤x≤0.55) when prepared by solid-solid reaction among the constituent oxides. A special technique was developed to obtain perovskite ceramics exhibiting no co-existence in the boundary compositions, in which no compositional fluctuation occurred in the B site of the perovskite structure. Even these monophasic perovskite ceramics of the morphotropic phase boundary compositions were two-phase with the lapse of time after poling. This phenomenon is interpreted in terms of thermodynamics. It is suggested that this phenomenon may closely relate to the origin of aging in piezoelectrics.     

Synthesis of LiAlO2 Powder by Hydrolysis of Metal Alkoxides

Crystalline fine powders of LiAlO₂ can be prepared by hydrolysis of metal alkoxides for application to the breeder blanket in nuclear fusion. The precipitates were fine crystalline particles of β-LiAlO₂of ∼0.1-μm size under controlled conditions. The transformation from β- to γ-phase was confirmed at temperatures between 700° and 750°C. The microstructure of a sintered body at 1000°C consisted of homogeneous fine particles and pores suitable for the blanket material. A fully dense sintered body could be prepared at 1400°C.     

BUBBLE FORMATION FROM AN ORIFICE SUBMERGED IN LIQUIDS

The phenomena of the bubble formation from an orifice submerged in a liquid is classified according to their formation mechanisms and the estimation expressions of the bubble volume are reviewed

The revised two-stage model of bubble formation accompanied by the pressure fluctuation in the gas chamber is presented and the results computed by this model are compared with the experimental results obtained for relatively wider range of gas chamber volume. Effects of some factors on the bubble volume, such as, gas chamber volume, orifice diameter, physical properties of gas and velocity of surrounding liquid are discussed