Siliconated Pyrolytic Graphite : Part 2. The State of Silicon Present in Siliconated Pyrolytic Graphite

By X-ray diffraction, surface oxidation, X-ray microanalysis, electron diffraction, and electron microscopy, the state of silicon present in siliconated pyrolytic graphite has been examined on several samples prepared under a variety of conditions. In the siliconated pyrolytic graphite prepared at the deposition temperatures below 1730℃, the greater part of the silicon occurs as β-SiC. It does not segregate in the cone boundaries but disperses uniformly. It exists as flake-1ike single crystals, whose size increases with decreasing temperature. The (111) plane of β-SiC is parallel to the (001) planes of graphite

Siliconated Pyrolytic Graphite : Part 4. Electrical Resistivity

Investigations have been made on the electrical resistivity ρ of siliconated pyrolytic graphite (PG(Si), 0.02 to 4 wt % silicon) prepared by pyrolysis of a mixture of propane gas and silicon tetrachloride vapour at various deposition temperatures, total gas pressures, and partial pressures of silicon tetrachloride vapour. With increase in the partial pressure of silicon tetrachloride, ρ_a decreases and ρ_c increases. The electrical anisotropy (ρ_c/ρ_a) of PG(Si) is two orders of magnitude higher than that of PG, at deposition temperatures between 1600 and 1700℃ and a total gas pressure of 50 torr. Effects of the silicon content, density and structural features on the resistivities and the anisotropy have been discussed. The anisotropy is closely related to the preferred orientation, and high values of ρ_c/ρ_a induced by discontinuity in the stacking of crystallites are lowered in silicon-rich PG(Si) by the presence of SiC between the crystallites

Embrittlement in Neutron Irradiated Niobium

This paper discusses the effect of neutron irradiation on the embrittlement of niobium. The irradiation was carried out at about 100℃ to a neutron does of 2.9×10^n/cm^2 (<1 MeV) and measurements were made of the yield stress, fracture stress and fracture strain in the temperature range from liquid nitrogen to room temperature. The interaction of dislocations produced by deformation with irradiation-induced defects was studied by transmission electron microscopy. The fracture surfaces were examined using a scanning electron microscope. The brittle fracture stress was evaluated under theory of the dislocation and by the strain-energy method. Based on the results obtained, a possible mechanism for the fracture in neutron irradiated niobium was discussed

Crystallization of 3Ln_2O_3・5Ga_2O_3 Glasses

The oxide glasses of 3Ln_2O_3・5Ga_2O_3 Were prepared, using Pr, Nd, Sm, Eu or Gd as a lanthanoid element . Crystallization of the glasses was studied by DTA and X-ray diffraction. A metastable phase was found on the way of the crystallization process of 3Pr_2O_3・5Ga_2O_3 and 3Nd_2O_3・5Ga_2O_3 glasses terminating in the transition into garnet. However, the phase transition transforming the amorphous phase directly into garnet not through a metastable phase was observed in case of 3Ln_2O_3・5Ga_2O_3 glasses (Ln=Sm, Eu or Gd)

Syntheses and Properties of Crosslinked Ferrocene Polymers(Chemistry)

The polycondensation reaction of acetylferrocene and furfural was investigated in the presence of concentrated H_2SO_4 as a catalyst without solvent. Stoichiometric reaction took place with 2 mol of acetylferrocene and 5 mol of furfural. Poly-condensation afforded satisfactory results when 1 mol of acetylferrocene was treated with 2-7 mol of furfural. The structural evidence for these products was derived from chemical and infrared analyses. Density, micro Vickers hardness, magnetic susceptibility, and thermal behavior of these products were measured in comparison with those of other resins

Amorphous Phase in Yttrium-Cobalt-Boron System

By rapid quenching of the melt, an amorphous phase of yttrium-cobalt-boron system was obtained. The phase is stable at room temperature, and its crystallization takes place in the vicinity of 700℃ on heating at 10℃/min. Electrical resistivity of the amorphous phase is constant at about 10^Ωcm in the temperature range below 660℃ ; the variation in the resistivity with the transition from the amorphous to the equilibrium state was measured

3Gd_2O_3・5Fe_2O_3 Glass Obtained by Rapid Quenching Apparatus Using Laser Beam

The oxide glass of 3Gd_2O_3・5Fe_2O_3 (GIG) was prepared using the piston and anvil technique incorporated into a laser melting furnace. The quenching apparatus provides higher quenching rates than an impact quenching apparatus already made. Crystallization and magnetization of the GIG glass have been examined by means of DTA method and magnetic balance

The Crystal Data of Ternary Rare Earth Borides, RCo_2B_2

Compounds with the composition of RCo_2B_2 (R=La, Nd, Sm, Gd, Tb, Dy, and Y) were prepared by arc-melting methods. Their crystal structure was investigated by means of X-ray diffraction. These ternary rare earth borides crystallize in the tetragonal lattice. The lattice parameters are a=3.616±0.003 A and c=10.215±0.005 A for LaCo_2B_2 and a=3.561±0.002 A and c=9.358±0.005 A for YCo_2B_2. The good agreement between the X-ray diffraction intensities observed and those calculated shows that the ternary borides, LaCo_2B_2 and YCo_2-B_2, crystallize in the ThCr_2Si_2-type structure. The crystallographic data obtained for LaCo_2B_2 and YCo_2B_2 are as follows : space group 14/mmm (D^_); R in 2(a), 4Co in 4(d), and 4B in 4(e) with z～3/8. The boron atoms in this structure are situated at the center of a trigonal prism formed by four rare earth atoms and two cobalt atoms. We also found the RCo_2B_2 compounds to be isostructural with LaCo_2B_2 and YCo_2B_2, where R=Nd, Sm, Gd, Tb, and Dy. However, efforts to prepare CeCo_2B_2 and ErCo_2B_2 by arc-melting were unsuccessful

The Electrical Anisotropies of Pyrolytic Graphite and Its Compounds

The electrical resistivities and the electrical anisotropy of the pyrolytic graphite compounds containing silicon (0.02-4wt% Si ; PG(Si) ) or bromine (0.1-12 wt% Br ; PG(Br) ) have been examined at room temperature. The anisotropy of PG(Si) was closely related to its preferred orientation which depends on the deposition temperature. The anisotropies of PG and PG(Si) are attributed to discontinuity in the stacking of the crystallites, as proposed by Guentert and Klein ; the discontinuity increases with preferred orientation. Low values of the anisotropy for PG(Si), containing large amounts of silicon and having the considerably high preferred orientation, result from the disappearance in the discontinuity because of the presence of SiC between the crystallites. The anisotropy of PG(Br) increases with the amount of bromine. Almost all the bromine atoms may be ionized in PG(Br) according to Blackman et al. The effect of ionization on the anisotropy is not clear

The Preparation and Crystal Structure of Ternary Rare Earth Borides, RCo_3B_2

In the ternary system of rare earth-cobalt-boron, RCo_3B_2 compounds (R=rare earth elements) were prepared by arc-melting methods. Their crystal structure was investigated by X-ray diffraction methods. These ternary borides, RCo_3B_2, crystallize in a hexagonal lattice. The lattice parameters are a=5.020±0.002A and c=3.027±0.002 A for YCo_3B_2 and a=5.066±0.003 A and c=3.022±0.002 A for GdCo_3B_2. The good agreement between the X-ray diffraction intensities observed and calculated shows that the ternary borides, YCo_3B_2 and GdCo_3B_2, crystallize in the CaZn_5-type structure. The space group and atomic positions are as follows : P6/mmm (D^1_), 1R in 1(a), 3Co in 3(g), and 2B in 2(c). It can be seen from these results that the ternary borides, RCo_3B_2, have a superstructure in which two Co atoms in the 2(c) site of intermetallic compounds, RCo_5, with the CaZn_5-type structure are replaced by two B atoms. The B atoms in this structure are situated at the center of a trigonal prism formed by six Co atoms. The interatomic distances between B and the six Co atoms are 2.11-2.10 A and are fairly constant, although the radii of the rare earth atoms are changed according to the lanthanide contraction. We have also found RCo_3B_2 compounds to be isostructural with YCo_3B_2 and GdCo_3B_2, where R=Ce, Sm, Tb, Dy, Ho, and Er. Efforts to prepare LaCo_3B_2, PrCo_3B_2, and NdCo_3B_2 by arc-melting were unsuccessful