**3.5. Dependence of annealing temperature on dielectric size**

Figure 14 shows the relation of the elongation rate and the diameter of dielectric. The size of dielectric is weakly affects elongation rate. It is noteworthy that when the copper wire is driven through the reactor, the chatter motion changes the discharge gap length and heating point on the wire surface and consequently, the annealing result. Moreover, when the thin copper wire is annealed in a wide reactor, discoloration and unevenness occur on the wire surface due to the streamer length density reduction. To obtain a steady discharge state, it is usually necessary to reduce discharge gap length. However, decreasing the reactor gap reduces the discharge volume and consequently, the annealing temperature.

**Figure 13.** The dependence of elongation rate on dielectric thickness

190 Dielectric Material

BN is higher rate than using SiO2. According to a comparison of properties of some dielectric materials (SiO2, Al2O3, BN and glass), we acknowledge that dielectric with higher dielectric constants is more effective to reach the annealing temperature as shown in Table 5. Physical characteristics of the dielectric, such as thermal expansion and melting point, are also important. For example, from our experiment the alumina can be suddenly broken with long duration annealing using a water-cooled electrode due to its large thermal expansion. For the

best annealing result, boron nitride is an excellent choice for the dielectric material.

**Figure 12.** The dependence of elongation rate on dielectric material

**Table 5.** Material properties of dielectric

Material properties SiO2 BN Al2O3 Pyrex Glass

Maximum Temperature (°C) 1713 850 1500 821 Permittivity (F/m) 4.0 6.7 9.5 4.7 Bending strength (Mpa) 105 60.2 310 59.3 Thermal conductivity (W/mK) 1.9 30.98 24 1.005 Thermal expansion (K-1) 8×10-6 0.87×10-6 6.4×10-6 3×10-6

**3.4. Dependence of annealing temperature on the thickness of dielectric** 

**3.5. Dependence of annealing temperature on dielectric size** 

Figure 13 shows the dependence of elongation rate on dielectric thickness. This result shows that the annealing effect strongly depends on the dielectric thickness. Compared to the elongation rate, the elongation rate using thin dielectric is higher rate than that using thick ones.

Figure 14 shows the relation of the elongation rate and the diameter of dielectric. The size of dielectric is weakly affects elongation rate. It is noteworthy that when the copper wire is

**Figure 14.** The dependence of elongation rate on dielectric size
