Effect of partial substitution of Mn and Ni for Fe in FeTi on hydriding kinetics

Hydriding kinetics of FeTi containing either Ni or Mn are compared with those of FeTi. The mixture of the specimen and Mn or Ni powder was put in a highly heat conductive Cu tube reactor for the hydriding reaction in order to reduce the effect of temperature excursion of the sample during the reaction. For FeTi and Fe_0.85Mn_0.15Ti, the rate is proportional to (P_H2 - P_eq) at high temperatures and at early stages of reaction, and to (√P_H2 - √P_eq) at low temperatures and at later stages of reaction. A characteristic feature of the nucleation and growth mechanism becomes visible at higher temperatures. For Fe_0.9Ni_0.1Ti, the rate is proportional to (√P_H2 - √P_eq) over the whole experimental range and the characteristic feature of the nucleation and growth mechanism is not observed at all. The kinetic mechanisms of the hydrogenation reaction of three alloys are discussed on the basis of the observed dependence of the rate on the hydrogen pressure and the extent of reaction.     

Synthesis of highly-oriented polyacetylene film in a liquid crystal solvent

The synthesis of oriented polyacetylene films is investigated by using a nematic liquid crystal as polymerization solvent. Highly-oriented thin films are obtained under a flow of catalyst solution in which a nematic liquid crystal is used instead of common solvents such as hexane and toluene. Nematic liquid crystals that could be used as solvents for the Ziegler-Natta catalysts are limited due to their reactive substituents with the active species and/or the components of the catalyst. Among the available nematic liquid crystals, phenylcyclohexane type is stable in the presence of Ziegler-Natta catalysts. Since fibril alignment in the oriented films is found to be along the flow direction of the catalyst solution, it appears that the direction of fibril growth coincides with that of the liquid crystal orientation, which is caused by an alignment effect of the liquid crystal molecules under a flow of the solution.This new and simple method allows quite large highly-oriented films to be synthesized, which makes it possible to investigate various kinds of anisotropic properties of polyacetylene.     

The chemistry of structural defects in CuInSe2

The composition of CuinSe₂ can be described by two parameters, non-stoichiometry and non-molecularity. The concentration variation of the structural defects on thermal annealing is predicted as a function of two component activities. Even though the electrical properties can be interpreted within the model of vacancy defects, the establishment of any defect model must await their identification by structure-sensitive techniques.     

D.C. conductivity versus temperature of a metallic complex of (CH)x with potassium

We have measured the electrical conductivity σ of heavily K-doped cis-(CH)_x as a function of temperature between 300 K and 4.2 K. A semiconductor-like behaviour of σ is observed and the attempt to explain our data led us to examine a conduction model involving tunnelling between potential barriers. Two activation energies are observed and the transition that occurs in the conductivity behaviour could arise from inhomogeneous doping.     

Thermally stimulated discharge currents in poly(vinyl formal) films

Thermally stimulated discharge currents (t.s.d.c.) of pure poly(vinyl formal) films of thickness 42.5 μm grown by the solution growth technique have been studied as a function of polarizing field and polarizing temperature. The temperature corresponding to a peak in t.s.d.c. is found to be independent of polarizing field but dependent on the polarizing temperature. Activation energies and relaxation parameters are evaluated.     

Low-temperature synthesis and magnetic properties of the mixed-valence lanthanide intercalation compounds EuxTiS2 and YbxTiS2

The lanthanide (L) intercalation compounds Eu_xTiS₂ (x=0.007,0.014, and 0.066) and Yb_xTiS₂ (x=0.060) have been synthesized by thermal deintercalation of NH₄⁺ and NH₃ from the corresponding L-NH₃ precursors at 270°C and characterized by thermogravimetric analysis, powder X-ray diffraction, and SQUID magnetometry. Both L²⁺ and L³⁺ are present in the van der Waals gap, and the deintercalation process is accompanied by the conversion of some of the L³⁺ to L²⁺. The resulting compounds contain comparable concentrations of L²⁺ and L³⁺. Magnetic exchange interactions are negligible due to the low concentrations of lanthanide cations.     

On the strength of discontinuous silicon carbide reinforced aluminum composites

The incorporation of dSiC into aluminum matrices results in substantial improvements in yield strength relative to the matrix material, but little change in the proportional limit. The Orowan strengthening mechanism was shown to be insufficient to account for the increase in yield strength of the composite. An increased dislocation density of the matrix due to a difference in the thermal expansion of the SiC and the matrix does predict an increase in composite strength, but is unable to explain why the proportional limit of the composite remains similar to that of the matrix or why the strength of the SiCw/6061Al is anisotropic. The conventional shear lag theory predicts yield strength values that are less than those observed. This is particularly so for the SiCp/Al composites, where the yield strength of the composite is predicted to be equal to that of the matrix independent of SiC volume fraction. If, however, the shear lag theory is modified to take into account the tensile transfer of load, the predicted composite strength is of sufficient magnitude to explain the strengthening effect of both the SiC whisker and platelet material. In addition, the modified shear lag theory can be used to rationalize why the proportional limit of the composite is similar to that of the matrix.