Research On Vertical Liquid Membrane Electrochemical Etching Method

Micro electrodes have important applications in biomedicine,sample detection,precision instruments and other fields.Micro electrode is an indispensable part in micro electrochemical machining,which directly affects the surface quality and machining accuracy.At present,the preparation methods of micro electrodes including focused-ion-beam milling method,micro-mechanical machining method,wire electro-discharge grinding method,electrochemical machining method and so on.The FIB machining method is much too expensive,the mechanical force in micro-mechanical machining will cause electrode bending,the surface quality of electrode prepared by WEDG method is much too poor,which exists heat affected zone and recast layer.Electrochemical machining is based on the principle of anodic dissolution.It has great advantages than other electrodes preparation methods in principle.It can produce various kinds of micro electrodes with good surface quality and small size with high efficiency and low cost.Compared with other methods,liquid membrane electrochemical etching method has better controllability and stability.Metallic glass materials have excellent physical,chemical and mechanical properties due to its unique amorphous structure.Meanwhile,the absence of grain size limitations in these materials means that differences in grain size,grain boundaries,and grain dissolution speed are eliminated in the process of electrochemical etching.It is an ideal material for preparing micro electrodes.In this paper,the preparation of tungsten and Fe-based metal glass(Fe_77.5B₁₅Si_7.5)micro electrodes by vertical liquid membrane electrochemical etching method were studied.The main research contents are as follows:(1)In order to solve the problem of large taper caused by the diffusion layer that deposited at the lower part of the electrode in the traditional transverse liquid membrane electrochemical etching method,the vertical liquid membrane electrochemical etching method was proposed,and the corresponding special fixtures were designed.The current density distribution on the electrode surface was studied by COMSOL simulation software.The difference between the transverse liquid membrane method and the vertical liquid membrane method in the current density distribution on the electrode surface and the thickness distribution of the diffusion layer was compared.The machining mechanism of the vertical liquid membrane electrochemical etching method of preparing micro electrode was analyzed.(2)By using the vertical liquid membrane electrochemical etching method,the effects of offset,electrolyte concentration and electrode reciprocating motion on the preparation of tungsten micro tool-electrode were studied through experiments;the effects of electrolyte concentration,reciprocating velocity and initial diameter of electrode on the preparation of tungsten wire-electrode were further studied.The tungsten micro tool-electrode and wire electrode with large aspect ratio were prepared.And the correctness of simulation analysis results is verified experimentally.(3)Based on the preparation of tungsten micro electrodes,the fabrication of Fe-based metallic glass micro electrodes using vertical liquid membrane electrochemical etching method was studied.The passivation characteristics of materials in H₂SO₄ and H₃PO₄ electrolyte were compared.The influences of electrolyte concentration and processing voltage on electrode morphology and surface quality were studied.Needle tip electrode with good tip size was prepared in H₂SO₄ solution,micro tool electrode and wire electrode with large-aspect-ratio were prepared in H₃PO₄ solution.