Y. Kogure

Two-site model analysis of 13C n.m.r. of polypropylene polymerized by Ziegler-Natta catalyst with external alkoxysilane donors

Abstract Two-site model analysis was carried out for 13 C n.m.r. of polypropylene polymerized by Ziegler-Natta catalyst with external alkoxysilane donors. Four effects of the external donors were found: selective poisoning of symmetric site; transformation of a symmetric to an asymmetric (but fluctuating) site; increase of whole isotacticity due to that of polymers obtained by the fluctuating site; and increase of isotacticity of the polymers obtained by the fluctuating site when the concentration of external donor is high enough.

External silane donors in Ziegler-Natta catalysis : a two-site model simulation of the effects of various alkoxysilane compounds

Abstract The results of experiments with a supported Ziegler-Natta catalyst were interpreted by a two-site model of the active sites, in order to enhance the understanding of multiple types of catalyst active sites and in particular the role of the external donor. The applicability of the two-site model is discussed and the stochastic parameters of the model are correlated with both the experimental and molecular modelling data. The two-site model satisfactorily explains the major part of the active sites of this highly isospecific catalyst and is a suitable tool for analysing the effects of the donors on catalyst active sites. Nevertheless, it does not completely describe the behaviour of Mg-supported Ziegler-Natta Ti catalyst. There is probably more than one kind of active site producing the part of polypropylene that is soluble in boiling heptane. This study also supports the earlier suggestion that some of the changes in the population of active sites can be explained only through the formation of new sites, and more specifically through the existence of fluctuating sites that can be stabilized by external donors. The stability of these new sites depends on both the structural and electronic properties of the external donors.

An improved transient hot‐wire method for studying thermal transport in condensed matter

The transient hot‐wire method for simultaneously measuring the thermal conductivity and thermal diffusivity of materials has been modified to improve the accuracy of the measurements. In this new experimental method, called the multicurrent method, several constant current values are used for heating the hot wire in order to determine accurately the thermal transport quantities. The details of the multicurrent method are precisely described, and examples of experiments using the method with pure water, electrolytic solution, and ionic conducting glasses are given. It is shown that this method can be used both for liquid and solid materials; a relatively small amount of the specimen material is sufficient for each experiment; the material can be insulating as well as highly ionic‐conductive; the accuracies of the determined thermal conductivity and the thermal diffusivity values are, respectively, around ±1% and ±5%.

Ultrasonic attenuation in glasses of SiO2GeO2 mixture

Ultrasonic absorption on SiO2-5 mole% GeO2 and SiO2-10 mole% GeO2 glasses between 1.6–250 K shows that the most probable origin of the structural relaxation of SiO2 glass is the transverse motion of the oxygen atom in SiOSi bridge among existing models. In addition it is also suggested that the same structure is the origin of two-level system (TLS) phenomena below 10 K.

Internal friction of SiO2 glasses with excessive and deficient oxygen

The lack of stoichiometry in SiO2 glass causes optical absorption, luminescence and so on. The internal friction of SiO2 glasses with excessive and deficient oxygen was measured in the temperature range of 1.6–250 K. At 35 K excessive oxygen enhanced the intensity of the internal friction of the glass, and deficient oxygen reduced this intensity. These changes of internal friction are analyzed by the bending model related to bridging oxygens in SiOSi bonds. Densitues of both the excessive and deficient oxygen are in the order of 1017/cm3. It is supposed tha the changes in Youngs modulus of these glasses are due to the OH contents.

Distribution of double-well potentials in SiO2 and SiO2: Ge glasses

Abstract The temperature dependence of the internal friction and the elastic modulus of pure SiO 2 and SiO 2 : Ge glasses measured by 50 kHz composite oscillator method have been analyzed on the basis of the double-well potential model. The density of relaxation strength and the distribution of the asymmetry parameter have been determined uniquely for pure SiO 2 , SiO 2 5% GeO 2 , and SiO 2 10%GeO 2 specimens by fitting the asymmetry potential model to the internal friction and elastic modulus data. The asymmetry parameter is found to increase with the doping of Ge atoms.

Study of the thermal transport properties of superionic conducting glasses

Abstract The thermal conductivity and the thermal diffusivity of AgPO 3 and (AgI) 0.5 (AgPO 3 ) 0.5 glasses have been measured simultaneously in the temperature ranges below and above the glass transitions by using an improved transient hot-wire (multicurrent) method. Using this method, both of the thermal transport properties could be measured accurately. Special care was taken in the measurement concerning the high ionic conductivity of the materials. The temperature dependences of the two transport properties were especially noted, and apparent differences in them could be seen between two glassy materials. The experimental results were discussed on the basis of a simple phonon transport theory with special consideration of the present superionic conducting glasses.

Internal friction of SiO2 glass with excessive oxygen

Abstract The internal friction (ultrasonic attenuation at 51 kHz) of a SiO 2 single crystal, pure SiO 2 glass and SiO 2 glass with excessive oxygen (10 17 /cm 3 ) was measured within the temperature range of 1.6–250 K. No original peak related to the excessive oxygen was recognized, although the doping of oxygen to the glass showed a slight increment of the internal friction at the same temperature. The doped oxygen probably enhances the internal friction caused by the bridging oxygen atoms; in other words, the doped oxygen molecules thought to exist in the gas phase slightly alter the potential acting on the bridging oxygen atoms in the random network.

Elastic and Lattice Dynamical Properties of Metals Studied by N-Body Potential

Higher order elastic constants and phonon dispersion relation have been calculated by using the n-body potential based on the embedded atom method. Results of second- and third-order elastic constants for Cu, Ag, and Au crystal were compared with the experimental data and the Cauchy discrepancy was discussed. A result of phonon dispersion relation for Cu crystal was also shown.

Molecular dynamics simulation of dislocations in fee metals

The molecular dynamics simulations of a screw dislocation in copper and aluminum have been made on the basis of embedded atom method. The configuration and the motion of dislocations under the applied stress were investigated by means of the Burgers vector density. The Peierls stress for a dislocation in copper was estimated to be τ P ∼ 3 × 10 −5 μ, where μ is the shear modulus.