.. Chen et al./ Materials Letters 56(2002)279-283 (99.5%)and KCL (99.5%)and NaF (99.5%)were ac were analyzed by X-ray energy dispersive spectrom- ded as precursor of halogenation and Ni (99.5%)pow- eter(EDS, Link IsIS-300)equipped with the SEM der added as catalyst. Furthermore, NaF and sucrose Fig. I shows whiskers prepared via different mate- can also act as additives to decrease the eutectic point rial system under suitable condition. They formed on of the system. Powders of different mole ratios were the original powder bed and around the wall of the mixed in an agate mortar for 45 min, then placed into graphite crucible. When the raw materials have pre covered graphite crucible and housed in a graphite scriptions of Ta2O /C/KCL (NaCI/Ni=1: 7: 0.5: 0.08 resistance furnace which was heated up to the desired and Ta205/C/NaF/C12H22O11(sucrose)=1: 11: 4: 4, the temperature of 1150-1350C in argon atmosphere at yield of whiskers is the highest about 0. 1 MPa pressure. The temperature increasing The powder XrD patterns of the synthesized whis rate is approximately 1000C/h, and these samples kers via different system are shown in Fig. 2. It can be ere held at the synthesis temperature for 2h. seen that they matched the data reported by the JCPDS The composition, structures and the lattice param-(card no. 35-801) very well and so we can consider eters of obtained whiskers were identified by X-ray that these whiskers are mainly Tac phase diffraction(XRD)method (nickel-filtered Cuk a radi- As shown in Fig. 1, whiskers exhibit mainly four ation, scan step 0.25/min). With scanning electron morphologies when synthesized via different material microscopy(SEM, JSM-6301F), their morphologies system. Fig. la and b are the whiskers synthesized via were investigated, and their chemical compositions Ta2O5-C-KCI-Ni system Some whiskers have fair (b) 1303 Fig 1 SEM of whiskers synthesized via different material system.(a, b)Ta205-C-KCl-Ni system(c)Ta2Os-C-NaCl-Ni system (d) Ta2O5-C-NaF-C12H22On1(sucrose) system.(99.5%) and KCL (99.5%) and NaF (99.5%) were ad￾ded as precursor of halogenation and Ni (99.5%) pow￾der added as catalyst. Furthermore, NaF and sucrose can also act as additives to decrease the eutectic point of the system. Powders of different mole ratios were mixed in an agate mortar for 45 min, then placed into covered graphite crucible and housed in a graphite resistance furnace which was heated up to the desired temperature of 1150– 1350 jC in argon atmosphere at about 0.1 MPa pressure. The temperature increasing rate is approximately 1000 jC/h, and these samples were held at the synthesis temperature for 2 h. The composition, structures and the lattice param￾eters of obtained whiskers were identified by X-ray diffraction (XRD) method (nickel-filtered CuK a radi￾ation, scan step 0.25j/min). With scanning electron microscopy (SEM, JSM-6301F), their morphologies were investigated, and their chemical compositions were analyzed by X-ray energy dispersive spectrom￾eter (EDS, Link ISIS-300) equipped with the SEM. Fig. 1 shows whiskers prepared via different mate￾rial system under suitable condition. They formed on the original powder bed and around the wall of the graphite crucible. When the raw materials have pre￾scriptions of Ta2O5/C/KCL (NaCl)/Ni = 1:7:0.5:0.08 and Ta2O5/C/NaF/C12H22O11 (sucrose) = 1:11:4:4, the yield of whiskers is the highest. The powder XRD patterns of the synthesized whis￾kers via different system are shown in Fig. 2. It can be seen that they matched the data reported by the JCPDS (card no. 35-801) very well and so we can consider that these whiskers are mainly TaC phase. As shown in Fig. 1, whiskers exhibit mainly four morphologies when synthesized via different material system. Fig. 1a and b are the whiskers synthesized via Ta2O5 –C –KC1 –Ni system. Some whiskers have fair￾Fig. 1. SEM of whiskers synthesized via different material system. (a, b) Ta2O5 –C – KCl – Ni system. (c) Ta2O5 –C – NaCl – Ni system. (d) Ta2O5 –C – NaF –C12H22O11 (sucrose) system. 280 Y.-J. Chen et al. / Materials Letters 56 (2002) 279–283