Y. Chen et al. Materials Letters 56(2002)279-283 indicates that these whiskers grew via VLS process Fig 3 shows the EDS of the whiskers. Fig. 3a shows that Ta element is the principal composition in whisker body and Fig 3b indicates that Ni element is the prin- cipal composition in whisker tip, which means that Ni 1250℃ powder is the catalyst that promotes the VLs pr Actually, carbon is also the predominant element in 350℃ whisker but it can not be detected by the apparatus due to its light mass. From this, we can also draw a con- clusion that the whiskers comprise Tac phase. Their 20 /Degree diameters are about 0.6 um and their lengths are 3 um Many whiskers, however, exhibit a shape of square conical body with zigzag tip. Their length are 1-10 um. Because their tips have no obvious spherical drop- lets, the growth mechanism can not be easily deter- Ic shows the whiskers synthesized via Ta2O5 I-Ni system. They are straight and mostly are pillar-shaped with spherical droplets at their tips. Thi strongly indicates these whiskers formed via VLS pro- cess. The diameters varied in a range of 0.2-0.5 um and the length in a range of 5-10 um. Fig. Id is the whiskers prepared via Ta2O5-NaF-C-C12H22O11 (sucrose)system. They grew in the form of cluster and are fairly straight. The surfaces are very smooth and some tips are capped with spherical droplets, which verified the growth mechanism is VLs. Accord- ing to the whisker diameter, these whiskers can be classified as two types: thin whisker and thick whisker. The thin whiskers have diameters of 0. 1-0.5 um and lengths of 10-50 um. The thick whiskers have diam- eters of 1-9 um. The aspect ratio was in the range of 20-100. Since via different material systems and even the same material systems, the whiskers grown have dif- ferent morphologies, there must be some factors rela- ted to raw material and growth condition which affect whisker morphology. In order to obtain the desired morphology and even control the morphology of whis- Fig. 2. The powder XRD pattems of the synthesized whiskers syn- ker, it is, therefore, necessary to investigate this rela esized via(a) Ta205-C-KCl-Ni system at different temper tionship and growth mechanism, which is the further atures,(b)Ta2O5-C-NaCl-Ni system at 1350C and (c) Ta205- work of our research group C-NaF-C12H22On1(sucrose)system at 1350C, respectively On the other hand, it is well known that metal carbides are always nonstoichiomet ly perfect pillar-shaped bodies with a rectangular pounds, and without exception for tantalum cross-section and spherical droplet at whisker tip, In our work, the whiskers synthesized are TaCx and the and there are striations distributed at equal intervals values of x are smaller than 1. In order to determine the along the lateral surfaces of the whiskers. This also lattice parameter a and the values of x(C/Ta ratio),wely perfect pillar-shaped bodies with a rectangular cross-section and spherical droplet at whisker tip, and there are striations distributed at equal intervals along the lateral surfaces of the whiskers. This also indicates that these whiskers grew via VLS process. Fig. 3 shows the EDS of the whiskers. Fig. 3a shows that Ta element is the principal composition in whisker body and Fig. 3b indicates that Ni element is the prin￾cipal composition in whisker tip, which means that Ni powder is the catalyst that promotes the VLS process. Actually, carbon is also the predominant element in whisker but it can not be detected by the apparatus due to its light mass. From this, we can also draw a con￾clusion that the whiskers comprise TaC phase. Their diameters are about 0.6 Am and their lengths are 3 Am. Many whiskers, however, exhibit a shape of square conical body with zigzag tip. Their length are 1 –10 Am. Because their tips have no obvious spherical drop￾lets, the growth mechanism can not be easily deter￾mined. Fig. 1c shows the whiskers synthesized via Ta2O5 – C–NaC1 –Ni system. They are straight and mostly are pillar-shaped with spherical droplets at their tips. This strongly indicates these whiskers formed via VLS pro￾cess. The diameters varied in a range of 0.2 –0.5 Am and the length in a range of 5– 10 Am. Fig. 1d is the whiskers prepared via Ta2O5 –NaF–C–C12H22O11 (sucrose) system. They grew in the form of cluster and are fairly straight. The surfaces are very smooth and some tips are capped with spherical droplets, which verified the growth mechanism is VLS. Accord￾ing to the whisker diameter, these whiskers can be classified as two types: thin whisker and thick whisker. The thin whiskers have diameters of 0.1 –0.5 Am and lengths of 10 – 50 Am. The thick whiskers have diam￾eters of 1– 9 Am. The aspect ratio was in the range of 20– 100. Since via different material systems and even the same material systems, the whiskers grown have dif￾ferent morphologies, there must be some factors rela￾ted to raw material and growth condition which affect whisker morphology. In order to obtain the desired morphology and even control the morphology of whis￾ker, it is, therefore, necessary to investigate this rela￾tionship and growth mechanism, which is the further work of our research group. On the other hand, it is well known that transition metal carbides are always nonstoichiometric com￾pounds, and without exception for tantalum carbides. In our work, the whiskers synthesized are TaCx and the values of x are smaller than 1. In order to determine the lattice parameter a and the values of x (C/Ta ratio), we Fig. 2. The powder XRD patterns of the synthesized whiskers syn￾thesized via (a) Ta2O5 –C – KCl – Ni system at different temper￾atures, (b) Ta2O5 –C – NaCl –Ni system at 1350 jC and (c) Ta2O5 – C – NaF –C12H22O11 (sucrose) system at 1350 jC, respectively. Y.-J. Chen et al. / Materials Letters 56 (2002) 279–283 281