Synthesis of boron nitride from triammoniadecaborane and hydrazine under pressure

Boron nitride (BN) of low crystallinity was synthesized from triammoniadecaborane (TAD) and hydrazine at 125 MPa below 650° C. TAD itself was pyrolysed at 600° C and 125 MPa to form a mixture of amorphous boron and boron nitride containing BH and NH bonds. The infrared spectrum of the pyrolysed product of TAD itself at 600° C and 125 MPa showed the BNB absorption at 800cm^–1 due to the formation of B₃N₃ structures. The X-ray diffraction (XRD) of the reaction product from TAD and hydrazine at 600° C had broad diffractions centred at 2=25.5° and 43.0° (CuK). The BH absorption at 2500cm^–1 decreased in intensity on increasing the N/B ratio from 0.3 to 0.85, and disappeared finally at a ratio of N/B=1.3. The reaction product at 125 MPa had a porous structure. The electron diffraction of the specimen changed from faint rings to spots on circular rings after heat treatment at 800° C for 10 h. The heat-treated specimen, however, did not give sharp reflections corresponding to hexagonal BN in the XRD profile. BN of low crystallinity was transferred to cubic BN at 1200° C and 6.5 GPa in a 90% yield, which was higher than that of well-crystallized BN in the presence of AIN.     

Preparation of TiB2 sintered compacts by hot pressing

A sintered compact of titanium diboride (TiB₂) was prepared by hot pressing of the synthesized TiB₂ powder, which was obtained by a solid-state reaction between TiN and amorphous boron. Densification of the sintered compact occurred at 20 MPa and 1800° C for 5 to 60 min with the aid of a reaction sintering, including the TiB₂ formation reaction between excess 20 at % amorphous boron in the as-synthesized powder (TiB₂ + 0.2B) and intentionally added 10 at % titanium metal. A homogeneous sintered compact of a single phase of TiB₂, which was prepared by hot pressing for 30 min from the starting powder composition [(TiB₂ + 0.2B) + 0.1 Ti], had a fine-grained microstructure composed of TiB₂ grains with diameters of 2 to 3 m. The bulk density was 4.47 g cm^–3, i.e. 98% of the theoretical density. The microhardness, transverse rupture strength and fracture toughness of the TiB₂ sintered compact were 2850 kg mm^–2, 48 kg mm^–2 and 2.4 MN m^–3/2, respectively. The thermal expansion coefficient increased with increasing temperature up to 400° C and had a constant value of 8.8 x 10^–6 deg^–1 above 500° C.     

FORMATION AND FLOW OF GAS BUBBLES IN A PRESSURIZED BUBBLE COLUMN WITH A SINGLE ORIFICE OR NOZZLE GAS DISTRIBUTOR

The characteristics of gas bubbles in a 5 cm diameter bubble column equipped with a single orifice of 1,3 or 5 mm diameter were investigated under system pressure of 0.1-15 MPa. The formation of gas bubbles was strongly affected by the system pressure. Under high pressures a dispersed gas jet was formed at gas velocities where spherical gas bubbles would have been formed at atmospheric pressure. The critical gas velocity between the bubbling regime and the jetting regime was correlated with the liquid phase Weber number and the gas phase Reynolds number based on the gas velocity at the orifice. Bubble size and gas holdup in the main part of the bubble column were also affected by the bubble formation pattern at the distributor     

Mechanism of Magnetite Seam Formation and its Role for FeO Scale Transformation

The phase transformation behavior of a thermally grown oxide scale of FeO on pure-Fe and an Fe–2wt%Au alloy was investigated. Particular attention was paid to formation of a magnetite seam, which is the Fe₃O₄ layer formed at the FeO/alloy interface at an initial stage of the phase transformation, since it has important effects on the overall phase transformation of FeO scale. A thin Au(Fe) layer was found to develop on the Fe–Au alloy at the FeO/alloy interface after 32 min of oxidation at 750 °C in air. This Au(Fe) layer prevented formation of a magnetite seam and accelerated the FeO eutectoid reaction. The Au(Fe) layer acted as a “chemical diffusion barrier” for inward diffusion of Fe from the FeO to the alloy substrate across the FeO/alloy interface and prevented magnetite seam formation.     

Tensile strength and morphological investigation of SiC-coated carbon fibers

SiC-coated film onto carbon fibers as a barrier of oxidation resistance and reaction between carbon fibers and metals was investigated. The chemical vapor deposition of silicon carbide onto carbon fibers was performed at various temperatures ranging from 700 to 1000°C using triisopropylsilane vapor carried by hydrogen gas. The strength of the SiC-coated carbon fibers was decreased due to deterioration of fibers and chemical attack of hydrogen on the surface of carbon fibers during the coating process. The oxidation and the thermal resistance of the SiC-coated carbon fibers compared to the uncoated carbon fibers were improved at temperature range of 600–800°C and 1000–1200°C, respectively. Morphological change by air oxidation at temperature range of 500–800‡C was also investigated for the SiC-coated and the uncoated carbon fibers, respectively. The SiC-coated film between carbon fiber and aluminum was sufficient as a barrier of reaction on carbon fiber reinforced aluminum at temperature of above 1000°C.     

On the formation of solid solution in Co3−xMnxO4 system

The formation of solid solution in the Co_3−xMn_xO₄ system in atmospheres of oxygen, air and argon was examined at a constant temperature of 1000 °C. In oxygen, a small amount of the NaCl-type compound was found to co-exist with the cubic spinel in the composition rangex≤0.1. A single phase of the cubic spinel was found in the range 0.1 to 1.3 and the tetragonal spinel above 1.9. In the rangex=1.3 to 1.9 where the cubic and tetragonal spinels co-exist they both have very broadened diffraction line profiles. In air, the identified phases and the changes in their lattice constants with composition were very similar to those in oxygen, except that the NaCl-type compound and the cubic spinel co-existed over a larger range. In argon, the cubic spinel was not observed over any of the composition range and the NaCI-type compound and the tetragonal spinel co-existed in the wide range of 1.1 to 2.3. The experimental results are discussed with regard to the cation distribution in the spinel and also to the relative stability of Co³⁺- and Mn³⁺-ions under the low partial pressure of oxygen.     

Liquid holdup and heat transfer coefficient between bed and wall in liquid solid and gas-liquid-solid fluidized beds

In fluidized beds of 0.052 and 0.12 m i.d. air, water and aqueous solutions of carboxymethyl cellulose (viscosity = 9.0 X 10^-4- 52 X 10^-2 Pa s), and glass beads were used as gas, liquid and solid phase, respectively. The diameters of the glass beads were 4.2 X 10^-4 6.6 X 10^-4 1.2 X l0^-3, and 2.2 X 10^-3 m.The liquid holdup in the gas-liquid-solid fluidized bed was well correlated by modifying the Garside and Al-Dibouni's equation with the gas phase Froude number.The wall heat transfer coefficient of the gas-liquid-solid fluidized beds in the range of stable fluidization state runs correlated as a function of modified Nusselt number, modified Reynolds number and gas phase Froude number.     

Radial compression of sugi wood (Cryptomeria japonica D. Don)

This paper deals with the heat fixation of compressive deformation of sugi wood (Cryptomeria japonica D. Don) which is a typical Japanese coniferous wood with a low density. After wet specimens were compressed in the radial direction to about 50% of their original thickness and dried under restraint, they were subjected to heat treatment by three methods: beneath the surface of molten metal, and in the presence or absence of air. The relationship between the recovery of deformation and the weight loss was expressed by a hyperbolic equation regardless of heating methods. The retentions of the MOE and the MOR of compressed specimens at the perfect fixation were 89% and 81%, respectively. The perfect fixation of deformation was speculated to have resulted from the release of stresses stored in the cell wall polymers by their degradation as well as the reduction of hygroscopicity of the cell wall polymers.     

Source-synchronization and timing vernier techniques for 1.2-GB/sSLDRAM interface

This paper describes a validation system for an SLDRAM interface. The SLDRAM system utilizes two techniques to achieve a high data-transfer rate with a conventional module mounting style. The first technique is a source-synchronization scheme. Since the chip that transmits data also supplies the data clock, the clock and data are completely synchronous. The second is the timing vernier technique. A wait time for output data is programmable in each SLDRAM. Therefore, the time at which data arrive at the controller from any SLDRAM can be set by the controller with a 200-ps step size. The validation chip is designed to emulate these operations. The chip is fabricated using a 0.35-μm CMOS process technology and packaged in a conventional 0.65-mm pitch thin small out-line package, mounted on a single-chip module, and put into an eight-module system. A stub series terminated logic (SSTL)-like interface is adopted for high-speed signals. From system-level measurements, the data eye width of 600 ps is obtained at a data rate of 600 Mbps. Errorless data transmission is observed in both read and write operations in a bit-error rate testing. The validation system has successfully demonstrated a data-transmission rate of 1.2 GB/s (600 Mbit/s/pin) using source-synchronization and timing vernier techniques at the supply voltage of 2.5 V