ELECTRICAL CHARACTERIZATION OF A PLANAR MICRO ...
ELECTRICAL CHARACTERIZATION OF A PLANAR MICRO-DISCHARGE OPERATING AT ATMOSPHERIC PRESSURE A. C. de Almeida1, M. Mafra2, R. P. Cardoso1* 1
Laboratório de Tecnologia de Pós e Plasma, Departamento de Engenharia Mecânica, Universidade Federal do Paraná, Centro Politécnico, 81531-980, Curitiba, PR, Brazil. 2 Departamento Acadêmico de Mecânica, Universidade Tecnológica Federal do Paraná, 80230-901, Curitiba, PR, Brazil. E-mail: [email protected] In the last decades the research on atmospheric pressures plasma was intensified motivated by its potential industrial applications. Micro-discharges are very promising low-cost atmospheric plasmas that can potentially be applied for materials and surface treatment. In the present work the development and characterization of a micro-discharge generated in a planar parallel electrodes configuration, focusing in future applications for materials surface treatments, is presented. The electrodes were constructed in stainless steel with 2mm in diameter. The discharge was generated in pure nitrogen, applying up to 2000 V, with a DC power supply. The electrical characterization of the discharge was performed using multimeters and a 100MHz digital oscilloscope. Different inter-electrode gap, from 30 to 300μm, and different values of the ballast resistance, up to 1.2M Ω, were studied. The Paschen curve and the VxI characteristics of the discharge were measured. The discharge operation regime is very sensitive to the electrode surface finishing and ballast resistance. The Paschen curve is in good accordance with the literature. The VxI curves are more difficult to be studied since the normal/abnormal regime easily changes to arc if the correct ballast is not chosen or if the electrode surface is eroded by previous arcing phenomena.
Keywords: Atmospheric pressure plasma, Micro-discharge, Paschen curves
Introduction Atmospheric pressure plasma were the first studied gas discharge, but, with the advent of vacuum technologies and microelectronics, low-pressure plasma became the most important studied topic on this area. Recently, motivated mainly by potential industrial application, atmospheric pressure plasmas have gained attention of the industrial and scientific communities, being nowadays one of the key topics of study on the domain of plasma applications. Different technologies were developed depending on the intended application, and, as it can be observed for low-pressure plasmas, different excitation sources can be applied [1]. Micro-discharges (or micro-plasmas) appear as one of the easier way to generate an atmospheric pressure discharge, requiring the application of only feel hundreds do volts to reach the breakdown. It can be very interesting from and industrial point of view, but one important limitation is the very low inter-electrode distance. In this context, this work aims to studied a planar micro-discharge operating at atmospheric pressure looking forward for overcame its limitations and apply it for material surface treatments. Experimental setup In the present work, the micro-discharge is generated between the planar surface of two cylindrical stainless steel electrodes of 2 mm in diameter, placed inside a 3 mm controlled atmosphere gas channel. The plasma is generated by a DC power supply and a ballast resistance (Rb) is introduced in the system to prevent arcing. The voltage
applied between electrodes (Vp) is measured by using a resistive potential voltage divider and a voltmeter. An electrical scheme of the micro-discharge reactor is presented in Fig. 1. Experiments were carried out in pure nitrogen at a flow rate of 1.7 Nl/min. The inter electrode distance (d) was measured using a portable microscope and typical studied values for d range between 30 and 300 m. Results and discussion The minimal voltage to sustain the discharge (Voff) versus pd (pressure x inter-electrode distance) and the experimental Paschen curve (breakdown voltage (Vb) versus pd) are presented in Fig. 2. Both curves present the expected behavior and, for the case of the Paschen curve, the breakdown voltage values are in reasonable accordance with curves presented by [2]. It is to be noted that this curve is sensitive to the electrode material, what can explain the observed differences. 2000 1800 1600 1400 1200
Vp
Vb Voff
d Electrode Gap
Vp (V)
1000 800 600
Rb 400
power supply Fig. 1 – Electrical scheme of the experimental setup.
2
4
6
8
10 12 14 16
pd (cm.Torr) Fig. 2 – Discharge breakdown voltage (Vb) versus pd (pressure x inter-electrode distance) and minimum voltage for sustaining the discharge (Voff).
Measurements of V x I curves of the discharge were also performed, but the very low current and discharge stability problems induced relatively high measurement errors, so results are difficult to be interpreted. Two different electrode finishing (roughness) were also tested showing that surface roughness can play an important role in this kind of micro-discharge.
Conclusions After conducting the electrical characterization of the planar micro-discharge in the presented experimental setup it is possible concluded that the obtained Paschen curve is in good agreement with data presented in the literature and the Voff x pd present the expected behavior. From experiments not reported in this extend abstract it can be concluded also that the stability of the discharge is very sensitive to the value of Rb, pd and the electrode surface finishing (roughness).
References [1] Tendero, C., Tixier, C., Tristant, P., Desmaison, J., Leprince, P., 2006 Atmospheric pressure plasmas: a review, Spectrochimica Acta B 61, 2–30. [2] Raizer, Y.P., Gas Discharge Physics, 1997, Springer-Verlang: Berlin. Acknowledgement: This work was supported by CNPq, CAPES-COFECUB and Programa Interdisciplinar de Petróleo e Gás Natural da UFPR (PRH24).
Laboratório de Tecnologia de Pós e Plasma, Departamento de Engenharia Mecânica, Universidade Federal do Paraná, Centro Politécnico, 81531-980, Curitiba, PR, Brazil. 2 Departamento Acadêmico de Mecânica, Universidade Tecnológica Federal do Paraná, 80230-901, Curitiba, PR, Brazil. E-mail: [email protected] In the last decades the research on atmospheric pressures plasma was intensified motivated by its potential industrial applications. Micro-discharges are very promising low-cost atmospheric plasmas that can potentially be applied for materials and surface treatment. In the present work the development and characterization of a micro-discharge generated in a planar parallel electrodes configuration, focusing in future applications for materials surface treatments, is presented. The electrodes were constructed in stainless steel with 2mm in diameter. The discharge was generated in pure nitrogen, applying up to 2000 V, with a DC power supply. The electrical characterization of the discharge was performed using multimeters and a 100MHz digital oscilloscope. Different inter-electrode gap, from 30 to 300μm, and different values of the ballast resistance, up to 1.2M Ω, were studied. The Paschen curve and the VxI characteristics of the discharge were measured. The discharge operation regime is very sensitive to the electrode surface finishing and ballast resistance. The Paschen curve is in good accordance with the literature. The VxI curves are more difficult to be studied since the normal/abnormal regime easily changes to arc if the correct ballast is not chosen or if the electrode surface is eroded by previous arcing phenomena.
Keywords: Atmospheric pressure plasma, Micro-discharge, Paschen curves
Introduction Atmospheric pressure plasma were the first studied gas discharge, but, with the advent of vacuum technologies and microelectronics, low-pressure plasma became the most important studied topic on this area. Recently, motivated mainly by potential industrial application, atmospheric pressure plasmas have gained attention of the industrial and scientific communities, being nowadays one of the key topics of study on the domain of plasma applications. Different technologies were developed depending on the intended application, and, as it can be observed for low-pressure plasmas, different excitation sources can be applied [1]. Micro-discharges (or micro-plasmas) appear as one of the easier way to generate an atmospheric pressure discharge, requiring the application of only feel hundreds do volts to reach the breakdown. It can be very interesting from and industrial point of view, but one important limitation is the very low inter-electrode distance. In this context, this work aims to studied a planar micro-discharge operating at atmospheric pressure looking forward for overcame its limitations and apply it for material surface treatments. Experimental setup In the present work, the micro-discharge is generated between the planar surface of two cylindrical stainless steel electrodes of 2 mm in diameter, placed inside a 3 mm controlled atmosphere gas channel. The plasma is generated by a DC power supply and a ballast resistance (Rb) is introduced in the system to prevent arcing. The voltage
applied between electrodes (Vp) is measured by using a resistive potential voltage divider and a voltmeter. An electrical scheme of the micro-discharge reactor is presented in Fig. 1. Experiments were carried out in pure nitrogen at a flow rate of 1.7 Nl/min. The inter electrode distance (d) was measured using a portable microscope and typical studied values for d range between 30 and 300 m. Results and discussion The minimal voltage to sustain the discharge (Voff) versus pd (pressure x inter-electrode distance) and the experimental Paschen curve (breakdown voltage (Vb) versus pd) are presented in Fig. 2. Both curves present the expected behavior and, for the case of the Paschen curve, the breakdown voltage values are in reasonable accordance with curves presented by [2]. It is to be noted that this curve is sensitive to the electrode material, what can explain the observed differences. 2000 1800 1600 1400 1200
Vp
Vb Voff
d Electrode Gap
Vp (V)
1000 800 600
Rb 400
power supply Fig. 1 – Electrical scheme of the experimental setup.
2
4
6
8
10 12 14 16
pd (cm.Torr) Fig. 2 – Discharge breakdown voltage (Vb) versus pd (pressure x inter-electrode distance) and minimum voltage for sustaining the discharge (Voff).
Measurements of V x I curves of the discharge were also performed, but the very low current and discharge stability problems induced relatively high measurement errors, so results are difficult to be interpreted. Two different electrode finishing (roughness) were also tested showing that surface roughness can play an important role in this kind of micro-discharge.
Conclusions After conducting the electrical characterization of the planar micro-discharge in the presented experimental setup it is possible concluded that the obtained Paschen curve is in good agreement with data presented in the literature and the Voff x pd present the expected behavior. From experiments not reported in this extend abstract it can be concluded also that the stability of the discharge is very sensitive to the value of Rb, pd and the electrode surface finishing (roughness).
References [1] Tendero, C., Tixier, C., Tristant, P., Desmaison, J., Leprince, P., 2006 Atmospheric pressure plasmas: a review, Spectrochimica Acta B 61, 2–30. [2] Raizer, Y.P., Gas Discharge Physics, 1997, Springer-Verlang: Berlin. Acknowledgement: This work was supported by CNPq, CAPES-COFECUB and Programa Interdisciplinar de Petróleo e Gás Natural da UFPR (PRH24).
