No abstract

Single-crystal sapphire is utilized as a high-performance engineering material, especially in extreme and harsh environments. However, due to its extreme hardness and brittleness, the machinability of sapphire is still a challenge. By means of nanoindentation and plunge-cut experiments, the anisotropic brittle-ductile transition of the prismatic M-plane and rhombohedral R-plane is examined by analyzing crack morphologies and the critical depth-of-cut (CDC). The experimental results of the nanoindentation tests are correlated to the plunge-cut experiment. Both the prism plane and the rhombohedral crystal plane exhibit a two-fold symmetry of ductility with various crack patterns along the machined grooves. The direction-dependent plasticity of the hexagonal sapphire crystal is mainly connected to a twinning process accompanied by slip dislocation.

No abstract

The vulcanization of ENBH (C9H14), a model for vulcanization of EPDM containing ENB, was studied (140°, 1 h) using four different vulcanization systems (conventional, sulfur free, low-sulfur and high-sulfur). The influence of the system on the total yield of crosslinked products (C9H13—Sn—C9H13) is considerable, low-sulfur giving the lowest and high-sulfur giving the highest yield. The influence of the system on the composition of the crosslinked products as determined by HPLC is surprisingly small. By using 1H-NMR it was shown that formation of monosulfides is almost negligible under our conditions with all four vulcanization systems.