**1.1. Annealing**

Based on Kalpakjian's Manufacturing Engineering and Technology, annealing is a general term used to describe the restoration of a cold-worked or heat-treated metal or alloy to its original properties, such as to increase elongation rate and reduce hardness and strength, or

© 2012 Tran et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

to modify the microstructure. The traditional thin metallic wire annealing is using external heating source or Joule heating as shown in Figure 2.

Effect of Dielectric in a Plasma Annealing System at Atmospheric Pressure 183

recrystallization) and grow crystal (recrystallization). After annealing, if the crystal size is enlarged and in good orientation, the elongation rate increases. At the first state, the recovery process, some the crystals are not fully rearranged therefore the elongation rate is still low. At primary recrystallization process, a number of crystals in the wire are born and this process strongly depends on the temperature but not duration. However, when the temperature is so high, the number of formed crystal increases then crystal size is small. Small size crystal means elongation rate is low. Therefore, choosing temperature in this process is important to get good orientation of crystal. At the recrystallization process, the crystals were born from the previous process will grow up. The crystal growth depends on duration. No noteworthy crystal growth will occur in the short annealing period then crystal size remains the same. Therefore, the duration of annealing in this process is important to get good orientation of crystal. For continuously thin wire annealing, to have good period annealing, applied voltage and the velocity of thin wire moved through or the length of chamber along the thin wire of plasma reactor have to be considered. If annealing duration is long, the annealing temperature at the end of the process is high and it is the cause of some disadvantages like increasing surface roughness. Moreover, during annealing at high temperature, the presence of hydrogen in air can increase the roughening effect of thin wire.

In order to solve the environmental harm of traditional annealing method, the plasma annealing is replaced. At low pressure such as in vacuum, the temperature generated by the ion bombarding on a target was studied for using in plasma immersion ion implantation (PIII) [15, 16]. This phenomenon was generally applied in modifying the target surface [16, 17] or heating the target [18, 19]. However, these systems operate under expensive vacuum systems. Recently, the atmospheric pressure dielectric barrier discharge (APDBD) for wire annealing has become greatly interesting [20, 21] because of its low-cost system and being

**Outer Electrode Dielectric Barrier**

**Carrier speed**

**Inner Electrode Plasma Zone**

At atmospheric pressure dielectric barrier discharge, the thin metallic wire is annealed by moved through the plasma reactor as shown in Figure 3. The dielectric is used to prevent the arc and the gas is fed into reactor to assist plasma discharge. The conceptual layout of

**Figure 3.** Annealing thin wire at atmospheric pressure dielectric barrier discharge

**1.2. Plasma annealing** 

environmentally friendly.

The purpose of annealing thin metallic wire is using heat to increase elongation rate in short duration. The temperature and duration of annealing affect the crystal size and crystal texture of thin wire. And elongation rate depends on the size and orientation of crystal. In addition, the annealing temperature is configured by drawing process; generally lower than 2/3 melting point of the wire material. With assuming that the drawing process is stable then deformation degree is constant. Therefore, in order to reach the required elongation rate, the temperature, and duration of annealing need to be properly chosen.

**Figure 1.** Mechanism of drawing process

**Figure 2.** Traditional mechanism of annealing and cleaning process

Heating thin metallic wire at annealing temperature is a thermodynamic process, which is used to rearrange or eliminate of dislocations (recovery), create new crystal (primary recrystallization) and grow crystal (recrystallization). After annealing, if the crystal size is enlarged and in good orientation, the elongation rate increases. At the first state, the recovery process, some the crystals are not fully rearranged therefore the elongation rate is still low. At primary recrystallization process, a number of crystals in the wire are born and this process strongly depends on the temperature but not duration. However, when the temperature is so high, the number of formed crystal increases then crystal size is small. Small size crystal means elongation rate is low. Therefore, choosing temperature in this process is important to get good orientation of crystal. At the recrystallization process, the crystals were born from the previous process will grow up. The crystal growth depends on duration. No noteworthy crystal growth will occur in the short annealing period then crystal size remains the same. Therefore, the duration of annealing in this process is important to get good orientation of crystal. For continuously thin wire annealing, to have good period annealing, applied voltage and the velocity of thin wire moved through or the length of chamber along the thin wire of plasma reactor have to be considered. If annealing duration is long, the annealing temperature at the end of the process is high and it is the cause of some disadvantages like increasing surface roughness. Moreover, during annealing at high temperature, the presence of hydrogen in air can increase the roughening effect of thin wire.

#### **1.2. Plasma annealing**

182 Dielectric Material

to modify the microstructure. The traditional thin metallic wire annealing is using external

The purpose of annealing thin metallic wire is using heat to increase elongation rate in short duration. The temperature and duration of annealing affect the crystal size and crystal texture of thin wire. And elongation rate depends on the size and orientation of crystal. In addition, the annealing temperature is configured by drawing process; generally lower than 2/3 melting point of the wire material. With assuming that the drawing process is stable then deformation degree is constant. Therefore, in order to reach the required elongation rate, the

heating source or Joule heating as shown in Figure 2.

**Figure 1.** Mechanism of drawing process

DC power supply 10kVA

Copper Wire

**Figure 2.** Traditional mechanism of annealing and cleaning process

Joule Heating in N2

Heating thin metallic wire at annealing temperature is a thermodynamic process, which is used to rearrange or eliminate of dislocations (recovery), create new crystal (primary

Electrode Poller

Joule Heating to dry H2 O

N2 H2O

Cleaning in H2

O

temperature, and duration of annealing need to be properly chosen.

In order to solve the environmental harm of traditional annealing method, the plasma annealing is replaced. At low pressure such as in vacuum, the temperature generated by the ion bombarding on a target was studied for using in plasma immersion ion implantation (PIII) [15, 16]. This phenomenon was generally applied in modifying the target surface [16, 17] or heating the target [18, 19]. However, these systems operate under expensive vacuum systems. Recently, the atmospheric pressure dielectric barrier discharge (APDBD) for wire annealing has become greatly interesting [20, 21] because of its low-cost system and being environmentally friendly.

**Figure 3.** Annealing thin wire at atmospheric pressure dielectric barrier discharge

At atmospheric pressure dielectric barrier discharge, the thin metallic wire is annealed by moved through the plasma reactor as shown in Figure 3. The dielectric is used to prevent the arc and the gas is fed into reactor to assist plasma discharge. The conceptual layout of plasma annealing is shown in Figure 4. In the plasma reactor, the discharge gas is ionized into electron and ion. Under a strong electric field, ion and electron bombard the thin wire surface. The essence of the generated temperature is the impact energy of electrons and ions on thin wire surface as shown in Figure 5. Furthermore, the electron-neutral particle collisions in streamers also assist generating temperature. The total temperature generated by the charged particle bombarding (ions and electrons) and the electron-neutral collision continuously heats the wire surface to annealing temperature.

Effect of Dielectric in a Plasma Annealing System at Atmospheric Pressure 185

Electron bombarding on the target was studied for melting target [22-25]. The electrons bombard the anode (thin wire) and then convert their kinetic energy into thermal energy. Heat transfer occurs from the plasma to the anode in several ways. Firstly, the electrons have thermal energy, which they release upon contact with the anode. Secondly, the electrons also have kinetic energy, which partially gets converted to thermal energy as it passes through the anode. It is important to note that the transfer kinetic energy from

The ion bombarding on a target was studied for using in plasma immersion ion implantation (PIII) [15, 16]. When the negative high-voltage pulse is applied to the target, the electrons near the cathode are driven away on the time scale of inverse electron plasma frequency, which is relatively shorter than the time scale of inverse ion plasma frequency, leaving the ions behind to form an ionic space charge sheath. On the time scale of inverse ion plasma frequency, the ions within this sheath are accelerated and then bombard the target surface under the sheath electric field. This phenomenon was generally applied in modifying the target surface [16, 17] or heating the target [17, 18] using low-pressure plasma. It is known that the treatment effect depends on ion bombarding energy, i.e., sheath thickness, ion current, and sheath electric field. On the basis of the fluid model [26] or kinetic model [27-29], it is possible to calculate dynamic sheath thickness, ion current, or ion bombarding energy. Recently, the atmospheric pressure dielectric barrier discharge (APDBD) for annealing thin wire has become greatly interesting [21, 30]. Also, our previous studies showed that annealing using APDBD is possible for thin copper wire [31]. However, the generated temperature by ion bombarding was not estimated. In this study, an analysis model using helium, argon or nitrogen gases and low-frequency (35 – 45 kHz) applied

The system consists of a gas tank, a power supply, a plasma reactor, a spectrometer sensor and a temperature sensor, as shown in Figure 6. The connecting power to the cylindrical reactor is shown in Figure 7. The design parameters of the reactor shown in Figure 8 are shown in Table 1. The thin cylindrical aluminum electrode (outer electrode) is covered with a dielectric to prevent arcing and it is connected to a power supply (20 kVp-p, 2 Ap-p, and 45 kHz). The thin copper wire (inner electrode) is driven through the reactor by carriers and connected to the ground. Before annealing, the reactor is filled up with discharge gas; helium, argon or nitrogen (purity > 99.9%). During annealing, purified discharge gas is continuously fed into the plasma reactor under a control ow rate to assist the plasma discharge. The applied voltage and current waveform are recorded using a digital oscilloscope (Yokogawa SL1000) with a high voltage probe (Iwatsu HV-P30), and a Rogowski coil (PEARSONTM current monitor 4997), respectively. The elongation rate of

*1.2.1. Electron bombarding* 

*1.2.2. Ion bombarding* 

**2. Experiment setup** 

electron to anode depends on the current density.

voltage is proposed to analyze the annealing result in APDBD.

**Figure 4.** Plasma annealing phenomenon

**Figure 5.** Annealing mechanism

#### *1.2.1. Electron bombarding*

184 Dielectric Material

plasma annealing is shown in Figure 4. In the plasma reactor, the discharge gas is ionized into electron and ion. Under a strong electric field, ion and electron bombard the thin wire surface. The essence of the generated temperature is the impact energy of electrons and ions on thin wire surface as shown in Figure 5. Furthermore, the electron-neutral particle collisions in streamers also assist generating temperature. The total temperature generated by the charged particle bombarding (ions and electrons) and the electron-neutral collision

continuously heats the wire surface to annealing temperature.

**Figure 4.** Plasma annealing phenomenon

**Figure 5.** Annealing mechanism

Electron bombarding on the target was studied for melting target [22-25]. The electrons bombard the anode (thin wire) and then convert their kinetic energy into thermal energy. Heat transfer occurs from the plasma to the anode in several ways. Firstly, the electrons have thermal energy, which they release upon contact with the anode. Secondly, the electrons also have kinetic energy, which partially gets converted to thermal energy as it passes through the anode. It is important to note that the transfer kinetic energy from electron to anode depends on the current density.

#### *1.2.2. Ion bombarding*

The ion bombarding on a target was studied for using in plasma immersion ion implantation (PIII) [15, 16]. When the negative high-voltage pulse is applied to the target, the electrons near the cathode are driven away on the time scale of inverse electron plasma frequency, which is relatively shorter than the time scale of inverse ion plasma frequency, leaving the ions behind to form an ionic space charge sheath. On the time scale of inverse ion plasma frequency, the ions within this sheath are accelerated and then bombard the target surface under the sheath electric field. This phenomenon was generally applied in modifying the target surface [16, 17] or heating the target [17, 18] using low-pressure plasma. It is known that the treatment effect depends on ion bombarding energy, i.e., sheath thickness, ion current, and sheath electric field. On the basis of the fluid model [26] or kinetic model [27-29], it is possible to calculate dynamic sheath thickness, ion current, or ion bombarding energy. Recently, the atmospheric pressure dielectric barrier discharge (APDBD) for annealing thin wire has become greatly interesting [21, 30]. Also, our previous studies showed that annealing using APDBD is possible for thin copper wire [31]. However, the generated temperature by ion bombarding was not estimated. In this study, an analysis model using helium, argon or nitrogen gases and low-frequency (35 – 45 kHz) applied voltage is proposed to analyze the annealing result in APDBD.

#### **2. Experiment setup**

The system consists of a gas tank, a power supply, a plasma reactor, a spectrometer sensor and a temperature sensor, as shown in Figure 6. The connecting power to the cylindrical reactor is shown in Figure 7. The design parameters of the reactor shown in Figure 8 are shown in Table 1. The thin cylindrical aluminum electrode (outer electrode) is covered with a dielectric to prevent arcing and it is connected to a power supply (20 kVp-p, 2 Ap-p, and 45 kHz). The thin copper wire (inner electrode) is driven through the reactor by carriers and connected to the ground. Before annealing, the reactor is filled up with discharge gas; helium, argon or nitrogen (purity > 99.9%). During annealing, purified discharge gas is continuously fed into the plasma reactor under a control ow rate to assist the plasma discharge. The applied voltage and current waveform are recorded using a digital oscilloscope (Yokogawa SL1000) with a high voltage probe (Iwatsu HV-P30), and a Rogowski coil (PEARSONTM current monitor 4997), respectively. The elongation rate of three samples is measured by SAIKAWA ET-100. The industrial required elongation rate is higher 20%.

Effect of Dielectric in a Plasma Annealing System at Atmospheric Pressure 187

Gas

**Figure 8.** Cylindrical DBD reactor with design parameters

Responding time 2ms

**Table 2.** IGAR12-LO MB10's specifications parameters.

**3.1. Dielectric permittivity measurement** 

**3. Results and discussions** 

expressed via capacitance C as

where parallel capacitor C is expressed by

Temperature range 300 °C~1000 °C

Accuracy 0.5% of measurement value +1°

The dependence of the dielectric permittivity on the frequency in APDBD annealing system is measured by electrode contact and CLR as shown in Figure 9. Dielectric material is placed sandwich in two aluminum electrodes, high voltage, high frequency function generator is used as power supply. Table 3 shows the experiment equipment be used in this study.

As shown in Figure 9, the dependence of dielectric permittivity on the dielectric voltage V is

(1)

(2)

*<sup>I</sup> <sup>V</sup> j C* 

<sup>0</sup> , *<sup>r</sup> <sup>S</sup> <sup>C</sup> d* 

Distance and area measurement 88mm/φ0.45~4500mm/φ22

**Figure 6.** The schematic diagram of the thin wire plasma annealing system

**Figure 7.** Cylindrical DBD reactor


**Table 1.** Experimental setup parameters

**Figure 8.** Cylindrical DBD reactor with design parameters


**Table 2.** IGAR12-LO MB10's specifications parameters.
