An Electron Spin Resonance Study of Evolution of Organic Free Radicals in Irradiated Pepper During Heat Treatment

ABSTRACT: The thermal evolution behavior of the organic free radicals induced in irradiated black pepper was studied by electron spin resonance spectroscopy. To analyze the time-dependent evolution process, we used the theory of transient phenomena, that is, an ordinal differential equation, as well as the nonlinear least squares numerical method. We found that the radical evolution that occurred in the irradiated pepper obeys a single exponential function and yields a unique time constant. The evolution of the organic free radical undergoes a simple reaction process of a single radical species.     

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.     

Reaction control of TiB2 formation from titanium metal and amorphous boron

TiB₂ powder was synthesized by a controlled formation reaction from titanium metal and amorphous boron. Precursory TiB₂ formed by the pretreatment of the mixed powder (mole ratio: B/Ti=2.0) at 600° C for 60 min in an argon stream. Hollow TiB₂ powder with an average grain size of 15m was obtained by subsequent heat treatment above 900° C for more than 60 min in an argon stream. The formation reaction of TiB₂ powder was further controlled by pretreatment of the mixed powder at 600° C for 60 min in a hydrogen and argon stream and subsequent heat treatment at 1000° C for 360 min in an argon stream, when hollow-free TiB₂ powder was formed by a milder formation reaction between amorphous boron and the reformed titanium metal with hydrogen diffused lattice.     

Synthesis of Cubic Boron Nitride from Boron Nitride Synthesized by Pressure Pyrolysis of Borazine

Cubic BN was synthesized under high-temperature and -pressure conditions from BN powder formed by pressure pyrolysis of borazine below 700°C and 100 MPa. The conversion of BN powder to cubic BN was strongly influenced by the residual hydrogen identified by the BH/BN ratio of IR absorption band. The activation energy for cubic BN synthesis from BN powder-20 mol% AIN was 46 kJ/mol, when the starting BN was synthesized at 250°C. A mixture of BN powder and cubic BN particles was converted to cubic BN in a 100% yield by heat treatment at 1800°C and 6.5 GPa without any catalyst. The presence of cubic BN particles does enhance the conversion to cubic BN from BN powder. The energy required for the transformation of starting BN to cubic BN in the presence of cubic BN seed was 355 kJ/mol.     

Strength of spline joints assembled by forming

In this paper, a new assembling method of spline joints that enables tight fitting in a simple manner by allowing slight plastic deformation at the spline teeth was introduced. Experiments were carried out for the spline joints of medium carbon steel varying the overlap zone between the male and the female spline teeth. Axial joining strength was increased with increase in the overlap length due to the residual compressive stress by forming. The joint by the proposed method also showed higher torsional strength than the conventional joint. Improvement in the torsional strength was explained based on the deformation and hardness distribution around the spline teeth. With respect to the shape of overlap zone, better results were obtained when using the specimen having a uniform overlap length along the axial direction.     

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.     

Current status and future prospect of in‐cell‐polarizer technology

Abstract— A thin‐crystalline‐film (TCF) polarizer has been developed which can be used internally in liquid‐crystal‐display cells. Based on this material, a manufacturing process has been developed for the fabrication of monochrome LCDs with internal polarizers. A new TCF polarizer material and coating equipment, developed to realize a high‐performance color TFT‐LCD, are discussed.