Voltage-carrying states in superconducting microstrips

Summary in DutchApplied SciencesApplied Science

The double explosive layer cylindrical compaction method

The standard cylindrical configuration for shock compaction is useful for the compaction of composite materials which have some plastic behavior. It can also be used to densify hard ceramics up to about 85% of the theoretical density (TMD), when low detonation velocity explosives (2-4 km s-1) are used. In order to attain higher densities, higher pressures will be needed. With the aid of computer simulations, it is shown that this can be realized without the risk of tensile rarefaction waves, by using two layers of explosives having different detonation velocities. This method has already resulted in a homogeneous B4C compact (87% TMD). After infiltration with Al, a B4C composite having a hardness ranging from 15 to 18 GPa could be obtained with this method. © 1999 Elsevier Science S.A. All rights reserved

Functionally graded TiC-based cermets via combustion synthesis and quasi-isostatic pressing

Experimental results on the preparation of functionally graded TiC-based cermets obtained by combustion synthesis (also known as Self-Propagating High-Temperature Synthesis, SHS) followed by quasi-isostatic (QIP) pressing in a granulate medium are presented. Pellets of TiC-Fe graded cermets are produced by stacking layers of Ti and C powder mixtures in which the content of a NiFe alloy (50 wt% Ni and 50 wt% Fe) is varied from 5 up to 25 vol %. X-ray diffraction showed that the NiFe alloy did not react with the TiC, thus preserving its special properties. Scanning electron microscopy results show a graded material with pores increasing in size towards the side with the highest ceramic fraction

Shock wave fabricated ceramic-metal nozzles

Shock compaction was used in the fabrication of high temperature ceramic-based materials. The materials' development was geared towards the fabrication of nozzles for rocket engines using solid propellants, for which the following metal-ceramic (cermet) materials were fabricated and tested: B4C-Ti (15 vol.-%). B4C-Al, and TiB2-Al, with an Al content typically between 15-20 vol.-%. Here, the B4C-Ti was only shock-compacted, while the other two cermets were shock compacted followed by melt infiltration with Al. The materials were subjected to gradually more severe testing conditions. Slabs of the materials were first tested for thermal shock resistance in an acetylene flame, followed by testing in the exhaust gas stream of a rocket propellant, and thereafter as a cylindrical insert in a nozzle of TZM alloy. The B4C-Ti composite showed erosion and cracking after the first test in the propellant flame, while the B4C-Al composite failed the insert tests. The TiB2-Al composite performed well under all conditions. A venturi nozzle of that material was formed during compaction. This real, shaped nozzle was shown to function well, even during repeated 3-6 s tests. This could be explained by the resistance of TiB2 to molten Al, the high thermal conductivity of the TiB2-Al cermet and the in situ formation of a protective layer, consisting mainly of Al2O3

Spectroscopic studies of dynamically compacted monoclinic ZrO2

The properties of dynamically compacted monoclinic zirconia have been studied by X-ray powder diffraction, IR, Raman, EPR and luminescence spectroscopy. Compaction introduces a large number of defects into the sample, which leads to a broadening of the X-ray lines, and IR and Raman bands. Besides, Raman spectra of compacted samples recorded with both 1064 and 488 nm excitation show additional bands in comparison with original monoclinic zirconia. The bands in the region 540-730 nm with 488 nm excitation are ascribed to electronic transitions of Sm3+ ions. The nature of the extra bands in the 3000-1830 cm-1 region observed with 1064 nm excitation is unknown. Their intensity depends on the concentration of defects, but these bands are still observed for a sample containing no paramagnetic defects. In contrast to uncompacted zirconia, the EPR spectrum of the dynamically compacted material shows defects, most likely related to V′o (oxygen vacancies), which might be an indication for ionic conduction. As monoclinic zirconia is not an ionic conductor, it could be that shock-compaction introduces sample conductivity, e.g. ionic conduction, which can be important for the development of new applications such as batteries. © 1999 Published by Elsevier Science Ltd. All rights reserved