Characterization of Hierarchical Silica Gels with Positron Annihilation Lifetime SpectroscopyIn this study the results of the characterization of hierarchical silica-gel samples with nitrogen adsorption and positron annihilation lifetime spectroscopy (PALS) were compared. The hierarchical silica-gel samples were synthesized by pseudomorphic transformation of a meso porous silica gel with CTAOH. The results of the PALS measurements clearly indicate the hierarchical pore structure of the materials. Two individual pore systems can be detected with a good resolution. The peak area of the signals can be calculated and compared with the pore volumes determined by nitrogen adsorption.
Calculation of Thermal Processes In Flash Butt WeldingFor the calculation of the thermal processes in flash butt welding the Fourier equation for heat conduction is used paying regard to resistance heating. With a model of calculation the assumptions and simplifications made can be explained. Cooling of the clamps, losses by flashing and heat transfer arc taken into account. The input of heat at the gap can bc treated as a flat heating source. Particularities with respect to preheating, flashing and cooling may be introduced into the calculation by corresponding inital and boundary conditions. As a result we get the dependence of temperature on the welding parameters. Experiment and calculation are in good agreement.
The thermal conduction of a sulphur-doped single crystal plastically deformed by bending at 963 K was measured between 2 and 50 K. The thermal resistivity W at temperatures > 14 K is practically independent on deforniation. At lower temperatures W is found to be proportional to A T F S before and to A ! P 3 + B T -2 after deformation. A is due to boundary scattering, B due t o dislocations.Die Warmeleitung eines schwefeldotierten Einkristalls wurde zwischen 2 und 50 K vermessen, der bei 963 K durch Biegung plastisch verformt worden ist. Der Warmewiderstand W ist bei Temperaturen > 14 K praktisch unabhiingig von der Verformung.Bei tieferen Temperaturen erweist sich W als proportional zu A T -3 vor und zu A T -3 + B T -2 nach der Verformung. A geht auf Grenzflachenstreuung, B auf Versetzungeri zuriick.
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