Experimental Research And Spectral Diagnosis Of Several Luminous Patterns In Atmospheric Pressure Liquid Electrode Discharge

Being vacuum equipment free,atmospheric pressure discharge with a liquid electrode is easily to be used in assembly line production,which has broad prospects in diversified application fields,such as environmental protection,biomedicine,nanocatalysis,material preparation,surface treatment,and new energy.It has become one of the hot topics in low-temperature research.Up to now,various patterns can be formed in atmospheric pressure discharge with a liquid electrode due to the high nonlinearity of the discharge.It is of great value to investigate pattern structures for the development of pattern dynamics.Aim to this status,atmospheric pressure discharge with a liquid electrode has been employed in this thesis to generate several pattern structures excited with direct-current（DC）,sinusoidal,and square-wave power supplies.With varying experimental parameters,discharge characteristics and evolution behaviors of patterns are experimentally studied.Main contents of the thesis are given as follows.1.Luminous patterns and discharge characteristics with a DC power supply.（1）For air,discharge,the discharge morphology on the liquid cathode evolves with time,which undergoes a scenario from a conical structure,an axisymmetric horn,and finally to a rectangular horn.Fast photography reveals that the axisymmetric horn is formed by the rotation of the rectangular horn,and the rectangular horn results from the swing of a micro-discharge filament.（2）For air discharge with a low current,a conical glow discharge is present above the water anode,which is formed by the rotation of a micro-discharge filament by fast photography.With a high current,a series of self-organized patterns is formed on the surface of the water anode,including patterns of a single-ring with stripes,a double-ring with a disk,and a triple-ring with a disk,which evolve with time.（3）Introducing an axial argon flow into the discharge,a diffuse disk,a single ring,a ring with a disk,spokes,and radial stripes patterns are formed on the water surface.Fast photography reveals that discrete spot is normally born near the central area and moves outward along the radial direction after formation.For radial stripes pattern,the discrete spot disappears immediately when it reaches the end of a radial stripe.However,it will rotate a short distance along a ring in the spokes pattern after reaching the end of a stripe（spoke）.In addition,a honeycomb-like pattern is observed above the water anode in the images with a short exposure time.2.Luminous patterns and discharge characteristics with sinusoidal and square-wave power supplies.（1）With the increase of peak value(U_pp)of applied voltage,patterns are formed on the water surface in turn,including a single ring,a single ring with surrounding corona,a triple ring,and a triple ring with a central spot.（2）With the decrease of duty ratio of square wave,patterns are formed on the water surface,including a bright disk,a bright disk with an outer ring,a concentric triple ring,and a triple ring with a central spot.With the increase of gap width,self-organized patterns are observed,including a concentric triple ring,and a ring with a disk.Fast photography reveals that the above-mentioned patterns are a temporal superposition of honeycomb patterns.3.Plasma activated water research with a DC power supply.Results show that for deionized water or tap water used as liquid electrode,gap voltage between the two electrodes decreases with the increase of discharge current.Under a constant current,gap voltage and output voltage of the power supply are greater when deionized water is used as the liquid electrode.The emission spectra mainly include N₂（C-B）,N₂⁺（B-X）,N₂（B-A）,O I（777.7nm,844.6nm）,NO（A-X）,H_α（656.3 nm）,and OH（A-X）.Line intensities emitted from OH,NO and O increase with the increase of discharge current.In addition,rotational temperature,electron temperature,and vibrational temperature are studied by optical emission spectroscopy,which present a growing trend with the increase of discharge current.With the increase of discharge current or treatment time,pH value decreases,while conductivity increment,concentrations of NO₂^-,NO₃^-,and H₂O₂ increase for the liquid electrode.