N. Ahlen et al. Journal of the European Ceramic Society 20(2000)2607-2618 reactions were completed after 4 h at the respective composition and the phase composition changes during optimum synthesis temperature. Three series with synthesis; one series with Tac whisker synthesis at experiments interrupted after different times from o to 960 1220C and two series with Tic whisker synthesis at min were performed in order to study how the chemical 1250 and 1400 C, respectively. Only a few whiskers terminated with a catalyst dro- (a)1.0 plet after completed reaction, indicating that there is a rapid redistribution of Ni in the reactor after a whisker has grown to full length. The search for droplets in experiments interrupted before completed whisker growth was a time-consuming task. It was observed that 1400°C small additions of red phosphorus to the starting mix- --1250C ture increased the occurrence of nickel droplets. After 0.4 solidification of the droplets small nickel phosphide particles were found to have precipitated on the droplet surface. No effect on the whisker yield was observed however. Therefore, experiments were done where red 0200060800010 phosphorous was added to the starting mixture in order to increase the possibility to find whiskers terminated lyst dre 22. characterisation The products were characterised by their X-ray powder diffraction patterns(XRD), obtained with a Guinier 806 Hagg focusing camera. CuKaI radiation (=1.54060 A) sed. and fine ed silicon a=5. 430880(35)AI were evaluated in an automatic film scanner Orded films was added as an internal standard. The reco The morphology and composition of the whiskers and catalyst droplets were investigated using a high-resolu tion scanning electron microscope(SEM, JEOL 880) equipped with an energy-dispersive spectrometer 200 (LINK ISIS), which allows detection of boron and heavier elements. A high-resolution transmission elec tron microscope (TEM, JEOL 3010)and a TEM JEOL 2000FX) equipped with EDS (LINK AN10000) were used for the electron diffraction work to determine whisker growth directions and for studies of the catalyst droplets 806/ 0.4 Table 7 0.2 Phases present, according to powder X-ray diffraction data (XRD) after different reaction times for the 1250C series of interrupted TiC whisker synthesis experiments 0 Starting03060120180240 mixture time(min) Fig. 5.(a)Observed weight change as a fraction of the expected vs TiO,(rutile) eaction time for the two temperature series(1250 and 1400oC)of TiO,(anatase) nterrupted TiC whisker synthesis experiments; (b)observed weight ange of the different elements as a fraction of the expected vs reac. ion time for TiC whisker synthesis at 1250C. Based on the assump- ion that the starting mixture transforms to TiC and that all O, Na, CL. and Ni disappear from the reactor during synthesis; (c)same as(b)but The experiments were interrupted after different holding times for TiC whisker synthesis at 1400oC. from o to 240 min. Ni and c could not be detected from Xrd datareactions were completed after 4 h at the respective optimum synthesis temperature. Three series with experiments interrupted after di€erent times from 0 to 960 min were performed in order to study how the chemical composition and the phase composition changes during synthesis; one series with TaC whisker synthesis at 1220C and two series with TiC whisker synthesis at 1250 and 1400C, respectively. Only a few whiskers terminated with a catalyst dro￾plet after completed reaction, indicating that there is a rapid redistribution of Ni in the reactor after a whisker has grown to full length. The search for droplets in experiments interrupted before completed whisker growth was a time-consuming task. It was observed that small additions of red phosphorus to the starting mix￾ture increased the occurrence of nickel droplets. After solidi®cation of the droplets small nickel phosphide particles were found to have precipitated on the droplet surface. No e€ect on the whisker yield was observed, however. Therefore, experiments were done where red phosphorous was added to the starting mixture in order to increase the possibility to ®nd whiskers terminated with a catalyst droplet. 2.2. Characterisation The products were characterised by their X-ray powder di€raction patterns (XRD), obtained with a Guinier￾HaÈgg focusing camera. CuKa1 radiation (l=1.54060 AÊ ) was used, and ®nely powdered silicon [a=5.430880(35) AÊ ] was added as an internal standard. The recorded ®lms were evaluated in an automatic ®lm scanner.8 The morphology and composition of the whiskers and catalyst droplets were investigated using a high-resolu￾tion scanning electron microscope (SEM, JEOL 880) equipped with an energy-dispersive spectrometer (LINK ISIS), which allows detection of boron and heavier elements. A high-resolution transmission elec￾tron microscope (TEM, JEOL 3010) and a TEM (JEOL 2000FX) equipped with EDS (LINK AN10000) were used for the electron di€raction work to determine whisker growth directions and for studies of the catalyst droplets. Fig. 5. (a) Observed weight change as a fraction of the expected vs. reaction time for the two temperature series (1250 and 1400C) of interrupted TiC whisker synthesis experiments; (b) observed weight change of the di€erent elements as a fraction of the expected vs. reac￾tion time for TiC whisker synthesis at 1250C. Based on the assump￾tion that the starting mixture transforms to TiC and that all O, Na, Cl, and Ni disappear from the reactor during synthesis; (c) same as (b) but for TiC whisker synthesis at 1400C. Table 7 Phases present, according to powder X-ray di€raction data (XRD), after di€erent reaction times for the 1250C series of interrupted TiC whisker synthesis experimentsa Starting mixture 0 30 60 120 180 240 TiC ± TiO2 (rutile) ± ± TiO2 (anatase) ± Ti2O3 ± ±±± Ti3O5 ± ±± ± ± NaCl ±±± a The experiments were interrupted after di€erent holding times from 0 to 240 min. Ni and C could not be detected from XRD data. N. AhleÂn et al. / Journal of the European Ceramic Society 20 (2000) 2607±2618 2611