SiCp/Cu composites prepared by the dual-directional extrusion process of floating die
SiCp/Cu composites were fabricated by the dual-directional extrusion process of the floating die. The microstructure, wear behavior and conductivity of SiCp/Cu composites were studied by optical microscope, abrasion test and current conductivity instrument. The results show that the SiCp/Cu composites with SiC particle distributed uniformly can be obtained, and the conductivity of composites decreased with the increasing of concentration of SiC particles, the wear resistance behavior of SiCp/Cu composites is evidently better than Cu with the increasing of concentration of SiC particles, the wearing mechanism of composites is a synthetically combined function of micro-cutting wearing and surface peeling off and grain wearing.
Tribological behaviour of SiC particle-reinforced copper matrix composites
Abstract Pure copper and its composites reinforced with SiC particles were prepared by hot isostatic pressing (HIP) process. The tribological behaviour of copper and composites was studied on a pin-on-disc tester. The pins were slid against a hardened steel disc under dry ambient conditions. In two-body abrasive wear measurements, the disc surface was bonded with a SiC abrasive paper of 240 grit size. The abrasive wear measurements showed that soft copper exhibits an extremely high wear loss. However, additions of SiC particles up to 20 vol.% appeared to improve the abrasive wear resistance of copper significantly under the applied loads of 15–55 N. Dry sliding wear tests also indicated that the composite with 20 vol.% SiC exhibits a lower wear loss compared to pure copper. This was due to the reinforcing SiC particles being effective to reduce the extent of wear deformation in the subsurface region during sliding.
l-Phenylalanine dehydrogenase from Brevibacterium sp. for production of l-phenylalanine by reductive amination of phenylpyruvate
SummaryFor production of l-phenylalanine the reductive amination of phenylpyruvate, catalyzed by phenylalanine-dehydrogenase was examined. To reach high levels and a sufficient stability of the inducible intracellular enzyme, growth conditions of Brevibacterium sp. are optimized. For continuous production of l-phenylalanine in an enzyme membrane reactor, the kinetic parameters of the partially purified enzyme are determined.In continuous production a space time yield of 37.4 g l-Phe l-1 d-1 can be reached.By means of the measured kinetic parameters and simultaneous calculation of the mass balances of all reaction components the behaviour of the reactor can be simulated. For certain conditions the multi-enzyme-system shows multiple steady-states.