Y Chen et al. Materials Letters 56 (2002)279-283 Fig 3. EDS of the rectangular pillar shape whisker synthesized via Ta2O5-C-KCl-Ni system (a) Ta is the principal element in the whisker(b) performed XRD tests for the product prepared via chiometric tantalum carbide, the reaction temperature Ta2O5-C-KCI-Ni system with very slow scan step should be higher. However, the optimal temperature of 0. 25/min. The lattice parameters of the cubic Tac, for preparation of completely stoichiometric Tac is were firstly determined by a least-squares fit of the unknown because the related work is lacking five observed and calculated spacing. Then we can alculate the value of x according to the relationship between x and a [9]. Table I shows the lattice para Acknowledgements eter a and composition x versus synthesis temper atures. From it, we found both parameters increase This work was supported by the Natural Scienc as the synthesis temperature increases from 1150 to Foundation of China(NSFC) and the Chinese Edu- 1350C. This indicates that with the increase of syn- cation Ministry. The authors would like to acknow thesis temperature, the number of defect in the crystal ledge the technical assistance of Xiao-Jun guo decreases. Therefore, if we want to obtain nearly stoi Table 1 References prepared via Ta205-C-NaCl-Ni system at different [Q.-w. Guo, Tantalum cor edia of Chemical temperatures try, vol. 15, Chemical Industry Press, Beijing, 1997 Synthesis Lattice 2]N. Ahlen, M. Johnsson, M. Nygren, Oxidation behaviour of temperature(°C) parameter(nm) TayTil-C and TaxTil-CNI-y whiskers, Thermochim. Acta 336(1999)11 0.44463 3]Y. Yuan, J. Pan, The effect of vapor phase on the growth of TiC 0.4474 hikers prepared by chemical vapor deposition, J. Cryst. Growth193(1998)585performed XRD tests for the product prepared via Ta2O5 –C –KC1 –Ni system with very slow scan step of 0.25j/min. The lattice parameters of the cubic TaC, a, were firstly determined by a least-squares fit of the five observed and calculated spacing. Then we can calculate the value of x according to the relationship between x and a [9]. Table 1 shows the lattice param￾eter a and composition x versus synthesis temper￾atures. From it, we found both parameters increase as the synthesis temperature increases from 1150 to 1350 jC. This indicates that with the increase of syn￾thesis temperature, the number of defect in the crystal decreases. Therefore, if we want to obtain nearly stoi￾chiometric tantalum carbide, the reaction temperature should be higher. However, the optimal temperature for preparation of completely stoichiometric TaC is unknown because the related work is lacking. Acknowledgements This work was supported by the Natural Science Foundation of China (NSFC) and the Chinese Edu￾cation Ministry. The authors would like to acknow￾ledge the technical assistance of Xiao-Jun Guo. References [1] Q.-W. Guo, Tantalum compounds, Encyclopedia of Chemical Industry, vol. 15, Chemical Industry Press, Beijing, 1997. [2] N. Ahlen, M. Johnsson, M. Nygren, Oxidation behaviour of TaxTi1
xC and TaxTi1
xCyN1
y whiskers, Thermochim. Acta 336 (1999) 111. [3] Y. Yuan, J. Pan, The effect of vapor phase on the growth of TiC whiskers prepared by chemical vapor deposition, J. Cryst. Growth 193 (1998) 585. Fig. 3. EDS of the rectangular pillar shape whisker synthesized via Ta2O5 –C – KCl – Ni system. (a) Ta is the principal element in the whisker. (b) Ni is the principal element in the spherical droplet. Table 1 The variation of lattice parameters and values of x in TaCx whiskers prepared via Ta2O5 –C –NaCl – Ni system at different synthesis temperatures Synthesis temperature (jC) Lattice parameter (nm) x in TaCx 1150 0.44425 0.907 1250 0.44463 0.935 1350 0.44474 0.943 282 Y.-J. Chen et al. / Materials Letters 56 (2002) 279–283