Generation Of Atmospheric Pressure Radio Frequency Plasma And Study On Its Application Of Coating Fabrication

Coating technology is used widely in industrial field.Coating workpiece surface is beneficial for improving workpiece functional performance,extending workpiece service life and reducing workpiece manufacturing cost.Some devices are directly coated,such as printed circuit board.With the development of science and technology,the requirement of coating preparation is becoming increasingly high,and the requirement of technology of coating preparation is also becoming increasingly high.Atmospheric pressure radio frequency(RF)plasma technology has the advantages of simple structure and environmental friendliness,and it has been attracted more and more attention in the field of coating preparation.Atmospheric RF plasma has two discharge mode,one is the capacitive coupling discharge mode(E mode)caused by axial electrostatic electric field,and another one is inductive coupling discharge mode(H mode)caused by toroidal inductive electric field in coil.In this work,we used E mode discharge to fabricate copper film and used H mode discharge to fabricate boron carbide coating.The generation of plasma,the dynamics of E-H mode transition process,the plasma characteristics at different experiment conditions and the characteristics of fabricated coatings at different experiment conditions were studied.The works and main experimental results as follow:(1)High speed camera was used to analyze the RF plasma E-H mode transition process and the ring to volume discharge transition process at H mode.The results show that the E-H mode transition time is about 0.5-1 ms at argon discharge and input power 300-1000 W.After ring shape H mode discharge forming,the discharge will develop from the discharge tube boundary to tube center and forming volume H mode discharge.Increasing input power and sheath gas flow rate and adding a small quantity hydrogen to argon is beneficial for lessen the transition time of ring to volume discharge at H mode.(2)A RF E mode discharge with a copper wire in discharge tube is diagnosed by optical emission spectroscopy and the ignition process is investigated by high speed camera.The results show that the discharge start at copper wire tip and develop to plasma jet at the effect of gas flow.And the discharge is filamentary.In the experiment condition,the effective voltage value is at the range of 650-850 V,and the effective discharge current value of pure argon is at the range 4-6.5 A.Adding a little hydrogen to argon discharge leading to the effective discharge current value dropping to 2.5-5 A.And the discharge current phase is about 90 degrees ahead of the voltage phase.The introduction of a small amount of hydrogen into argon discharge will leading to the increase of plasma gas temperature and electron number density,but leading to the decrease of electron excitation temperature.The plasma gas temperature is approximately 600-1400 K.The electron excitation temperature is about 8000-11000 K.The electron density is about 3.1×1020-8.2×1020 m-3.(3)The effects of input power,gas flow rate and hydrogen concentration on the process of copper film deposition by rf E mode discharge at atmospheric pressure were studied.The results show that the temperature of plasma gas and discharge current through copper wire are the main causes of copper wire erosion.With the increase of input power,the plasma gas temperature and the discharge current increases,which is conducive to the erosion of copper wire tip,thus increasing the evaporation of copper atoms,accelerating the deposition rate of copper film,and increasing the roughness of the film and the particle size on the film.When the gas flow rate is increased,the plasma gas temperature drops,resulting in a decrease in the evaporation of copper atoms and a decrease in the deposition rate,particle size and surface roughness of copper film.As hydrogen concentration increases,plasma gas temperature increases and discharge current decreases.When the hydrogen concentration is less than 1.6‰,with the increase of hydrogen concentration,the evaporation of copper atoms increases,and the deposition rate and particle size on the film increases.When the hydrogen concentration is higher than 1.6‰,as the hydrogen concentration increases,the evaporation of copper atoms decreases,and the deposition rate and the particle size on the film decreases.In addition,increasing the hydrogen concentration is beneficial for reducing the surface roughness of thin films.(4)Pure boron carbide coating and boron carbide/copper gradient coating were prepared on copper substrate by inductively coupled thermal plasma(H mode discharge).The XRD results show that the phase of boron carbide does not change after plasma spraying.Boron carbide/copper gradient coating materials were successfully prepared.The test results show that the binding force of boron carbide coating on copper substrate can be effectively improved.In addition,with the increase of hydrogen concentration introduced into the sheath gas,the compactness of the pure boron carbide coating prepared on the copper substrate increases and the porosity of it decreases.The change of the characteristic parameters of the inductively coupled thermal plasma with hydrogen concentration at sheath gas was studied by optical emission spectrometry and high speed camera.The results show that the plasma shrinks in both axial and radial direction when hydrogen is introduced into the sheath gas.With the increase of hydrogen flow rate,the volume shrinkage of plasma increases.The electron excitation temperature and electron number density increase with the increase of hydrogen content.