N. Ahlen et al. Journal of the European Ceramic Society 20 (2000)2607-2618 from the whiskers. The whiskers themselves have the ondary growth is usually flat(the slab thickness is les same [100 growth direction as the others, and the than the width of the whisker). viewing crystals like secondary growth can be described as <001> termi- those in Fig. 14 perpendicular to the whisker direction nated slabs with <110> edges(see Fig. 14) The sec- and to the viewing direction of this figure would show a whisker"with perfect edges. It is obvious that this growth has taken place after the whisker growth was finished. This secondary growth is always more or less pure TiC and may have formed by precipitation directly from the vapour ph TiCl3(g)+2C0(g)- TiC(s)+Co(g)+3Cl(g)(8) The CO2(g) thus produced can then react with carb CO2(g)+C(s)→2COg) 500nm [100 [100 110 [0101 Fig. Il.(a) Tic(1275.C)whisker with a screw-like shap c Fig 12.(a)Overview of TiC whiskers(1250C) showing the frequent (1250.C)have similar morphology(b) TiC whiskers(12 ft screw-like appearance; (b) close up of one screw-like whisker changing one grown along [100] and the right one along [lll e growth direction. Growth started along [100 and continued along 010]from the whiskers. The whiskers themselves have the same [100] growth direction as the others, and the secondary growth can be described as <001> termi￾nated slabs with <110> edges (see Fig. 14) The sec￾ondary growth is usually ¯at (the slab thickness is less than the width of the whisker). Viewing crystals like those in Fig. 14 perpendicular to the whisker direction and to the viewing direction of this ®gure would show a ``whisker'' with perfect edges. It is obvious that this growth has taken place after the whisker growth was ®nished. This secondary growth is always more or less pure TiC and may have formed by precipitation directly from the vapour phase. TiCl3… †‡ g 2CO g…†! TiC s… †‡ CO2… †‡ g 3Cl g…† …8† The CO2(g) thus produced can then react with carbon to form CO(g) CO2… †‡ g C s…†! 2CO g…† …9† Fig. 11. (a) TiC (1275C) whisker with a screw-like shape. Ta0:5Ti0:5C (1250C) have similar morphology. (b) TiC whiskers (1275C), the left one grown along [100] and the right one along [111] (note that the right one is not perpendicular to the beam). Fig. 12. (a) Overview of TiC whiskers (1250C) showing the frequent screw-like appearance; (b) close up of one screw-like whisker changing growth direction. Growth started along [100] and continued along [010]. 2616 N. AhleÂn et al. / Journal of the European Ceramic Society 20 (2000) 2607±2618