Method and device for manufacturing porous tungsten needle tip

Abstract

The invention relates to the technical field of micro-nano machining, in particular to a porous tungsten needle tip manufacturing method and device. According to the method, a dynamic alternating current control strategy is combined with dynamic electrochemical etching to prepare the porous tungsten needle tip, firstly, porous tungsten serves as an anode, and anode etching is carried out to enable the anode to gradually form a conical tip; then the porous tungsten is used as a cathode, bubbles are generated at the cathode, and the bubbles are used for washing the etching product adsorbed in pores of the porous tungsten, so that the etching product falls off in time; after anode etching is conducted for a period of time, cathode cleaning is conducted, adsorbed etching products are washed away in time, and cleanliness of the porous tungsten is kept; by means of the method, the etching product adsorbed in the pores of the porous tungsten can be removed in time, the micropore structure is prevented from being blocked in the etching process, the mode does not affect formation of the needle tip or cause damage to the needle tip, and therefore the high-quality second electrode needle tip can be prepared, and the product percent of pass is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-nano processing, and more particularly to a porous tungsten needle tip manufacturing method and device. BACKGROUND

[0002] Porous tungsten is a kind of metal material with unique pore structure, which combines the characteristics of tungsten and the advantages of porous structure, has the advantages of high temperature resistance, corrosion resistance, etc., and the internal interconnected pores can be used for storage and transportation of liquid working medium, so it has wide application in ion source emitting needle, ionic liquid thruster and field emission electric thruster emitter. The raw material of porous tungsten is usually a round bar or block produced by metal powder injection molding technology. In practical application, it needs to be processed into a sharp needle structure, and the needle tip radius needs to be processed to several microns, and the surface pores need to be kept open after processing. Mechanical processing and electric spark processing cannot meet both requirements. Electrochemical etching is a potential solution. In the field of solid tungsten needle preparation, electrochemical etching technology has formed a perfect process system. Through mature process schemes such as static etching and dynamic etching, precise machining of solid tungsten needle with micron-level tip radius and large length-diameter ratio can be realized. However, when the existing electrochemical etching process is applied to porous tungsten material, due to the structural difference between porous tungsten and solid tungsten, the internal interconnected pore structure shows significant adsorption characteristics. The high adsorption of porous material makes it difficult for etching products to diffuse to the solution. This unique material property causes the etching reaction products to easily accumulate in the micro-pore structure during processing, as shown in Figure 6 , causing a chain reaction of reaction interface passivation, electrolyte penetration obstruction, etc., ultimately resulting in ineffective etching process. This key technical bottleneck seriously restricts the reliable preparation and performance optimization of porous tungsten needle. SUMMARY

[0003] The purpose of the present application is to overcome the shortcomings of the prior art that the etching reaction products of the porous tungsten material prepared by electrochemical etching are easily accumulated in the micro-pore structure during processing, causing a chain reaction of reaction interface passivation, electrolyte penetration obstruction, etc. A porous tungsten needle tip manufacturing method and device are provided, which can effectively avoid the blockage of micro-pore structure.

[0004] To solve the above technical problems, the technical scheme adopted by the present application is: A porous tungsten needle tip manufacturing method is provided, comprising: The first electrode is placed in an electrolytic cell containing electrolyte, and the first electrode completely invades the electrolyte; the first electrode is in a ring structure; the second electrode is prepared from porous tungsten material; one end of the second electrode is inserted into the electrolyte and passes through the middle part of the first electrode; Anodic etching: the first electrode and the second electrode are connected with an alternating current power supply respectively, and the first electrode is taken as a cathode and the second electrode is taken as an anode, a +n volt voltage is applied, and multiple anodic dynamic reciprocating etching is carried out to form a conical tip; Cathodic cleaning: the polarity of the power supply is switched, a -n volt voltage is applied, the second electrode is taken as a cathode and the first electrode is taken as an anode, and multiple cathodic dynamic reciprocating etching is carried out; bubbles are generated at the cathode, the bubbles are used to flush the pores of the second electrode, and the etching products adsorbed on the second electrode are detached from the second electrode; Periodic switching: after N1 times of anodic dynamic reciprocating etching, N2 times of cathodic dynamic reciprocating etching is carried out; the tip radius of the second electrode is monitored in real time until the requirement is reached.

[0005] The porous tungsten needle tip manufacturing method of the application adopts a dynamic alternating current control strategy combined with dynamic electrochemical etching to realize the preparation of the porous tungsten needle tip, the polarity of the alternating current is changed, the second electrode is taken as an anode first to realize the etching of the tip of the second electrode, so that a conical tip is gradually formed; then the second electrode is taken as a cathode, bubbles are generated at the cathode, the bubbles are used to flush the etching products adsorbed in the pores of the porous tungsten, so that the etching products are timely detached; after a period of anodic etching, cathodic cleaning is carried out to timely flush away the adsorbed etching products and keep the porous tungsten clean; anodic etching and cathodic cleaning are alternately carried out to realize the preparation of the porous tungsten needle tip; through the method of the application, the etching products adsorbed in the pores of the porous tungsten can be timely removed, the microporous structure is prevented from being blocked during the etching process, and the method will not affect the formation of the needle tip or cause damage to the needle tip, so that the application can not only prepare a high-quality second electrode needle tip, but also improve the product qualification rate.

[0006] Further, the first electrode is horizontally placed in the electrolyte; when the anodic dynamic reciprocating etching and the cathodic dynamic reciprocating etching are carried out, the second electrode is controlled to move up and down vertically to the plane where the first electrode is located.

[0007] Further, when the anodic dynamic reciprocating etching is carried out, the second electrode is controlled to move up and down between d1 mm above the liquid surface of the electrolyte and d2 mm below the liquid surface; when the cathodic dynamic reciprocating etching is carried out, the second electrode is controlled to move up and down between d1 mm above the liquid surface of the electrolyte and d3 mm below the liquid surface, and the value of d3 is greater than or equal to the value of d2.

[0008] Further, a camera is used to take pictures to record the morphology of the second electrode in the etching process, and the termination time of the etching process is preliminarily determined.

[0009] Further, the material of the first electrode is stainless steel or graphite, and the shape of the second electrode is a cylinder.

[0010] Further, the electrolyte is potassium hydroxide solution or sodium hydroxide solution, and the concentration of the electrolyte is greater than or equal to 0.1 mol / L.

[0011] Further, the etching voltage ranges from -10 V to +10 V.

[0012] Further, when the anodic etching is performed, the electrochemical reaction occurring at the second electrode is: When the cathodic cleaning is performed, the electrochemical reaction occurring at the second electrode is: .

[0013] Further, when the up-and-down reciprocating motion of the second electrode is controlled, the motion rate is 1 mm / s to 5 mm / s.

[0014] The application further provides a second electrode needle tip manufacturing device, which comprises an electric displacement platform for realizing the up-and-down reciprocating motion, an insulating clamping assembly for clamping the electrode, a transparent electrolytic tank for containing the electrolyte, an alternating current power supply, a first electrode, a second electrode, and a camera for observation and recording; the electric displacement platform comprises a vertical support rod and a moving block in vertical sliding connection with the support rod; one end of the insulating clamping assembly is connected with the moving block, the second electrode is vertically clamped at the other end of the insulating clamping assembly, and one end of the second electrode is immersed in the electrolyte and passes through the first electrode; the first electrode is horizontally placed in the electrolytic tank containing the electrolyte; the alternating current power supply is electrically connected with the second electrode and the first electrode respectively; the camera is located outside the electrolytic tank and is used for shooting the topography of the tip of the second electrode.

[0015] Compared with the prior art, the application has the following beneficial effects: The porous tungsten needle tip manufacturing method and device can timely remove the etching products adsorbed in the pores of the porous tungsten, avoid the blockage of the microporous structure in the etching process, and will not affect the formation of the needle tip or cause damage to the needle tip, so that the high-quality porous tungsten needle tip can be prepared, and the product qualification rate is improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is a method flowchart of the application; Figure 2 It is a voltage configuration and first electrode displacement curve correspondence diagram of the application; Figure 3 It is a first electrode topography change and movement diagram in the etching process of the application; Figure 4 It is a topography diagram of the porous tungsten needle tip prepared by the method of the application; Figure 5SEM image of a porous tungsten tip prepared by the method of the present application; Figure 6 SEM image of a porous tungsten tip etched using prior art; Figure 7 Schematic diagram of the device of the present application.

[0017] In the drawings: 1, second electrode; 2, first electrode; 3, electrolytic cell; 4, electrolyte; 5, alternating current power supply; 6, motorized displacement platform; 7, clamping assembly; 8, camera. DETAILED DESCRIPTION

[0018] The present application will be further described below in conjunction with specific embodiments. In the drawings, only for exemplary illustration, the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation on the present application; in order to better illustrate the embodiments of the present application, some components in the drawings will be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures in the drawings and their descriptions can be omitted.

[0019] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate the orientation or positional relationship shown in the drawings, only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the positional relationship described in the drawings is only for exemplary illustration, and cannot be understood as a limitation on the present application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0020] Embodiment one This embodiment is a first embodiment of a method for manufacturing a porous tungsten tip, in this embodiment, electrochemical etching is carried out using the following device: Electrolytic cell 3: containing KOH solution (5 mol / L), stainless steel ring-shaped first electrode 2.

[0021] Motion control system: motorized displacement platform 6, controls the vertical reciprocating motion of the second electrode 1 (speed 2 mm / s).

[0022] Power supply system: alternating current power supply 5 (±10 V), adjustable waveform is square wave, voltage amplitude is adjustable, polarity is switchable.

[0023] Monitoring system: real-time camera 8 records the etching morphology, and alternating current power supply 5 monitors the reaction current.

[0024] As shown in the following method steps are implemented: Figure 1 ​ The first electrode 2 is placed in the electrolytic cell 3 containing the electrolyte 4, and the first electrode 2 is completely immersed in the electrolyte 4; the first electrode 2 is in a ring structure; the second electrode 1 is made of porous tungsten material; one end of the second electrode 1 is inserted into the electrolyte 4 and is arranged in the middle of the first electrode 2; Anodic etching: the first electrode 2 and the second electrode 1 are respectively connected with the alternating current power supply 5, and the first electrode 2 is used as the cathode and the second electrode 1 is used as the anode, a +2-volt voltage is applied, and multiple anodic dynamic reciprocating etching is performed to form a conical tip; the movement stroke is 2 mm above the liquid surface and 6 mm below the liquid surface; the reaction occurring is: The second electrode 1 is etched to form a conical tip; Cathodic cleaning: the polarity of the power supply is switched, a -2-volt voltage is applied, the second electrode 1 is used as the cathode and the first electrode 2 is used as the anode, and multiple cathodic dynamic reciprocating etching is performed; H2bubbles are generated at the cathode, the pores of the porous tungsten are flushed by the bubbles, and the etching products adsorbed on the porous tungsten fall off from the porous tungsten; the reaction occurring at the cathode is: H2bubbles flush the pores and remove the adsorbed etching products (such as tungsten oxide and tungstate colloid); the reciprocating etching stroke is 2 mm above the liquid surface and 8 mm below the liquid surface, which is deeper than that in the anodic etching, so as to prevent the etching products from accumulating at the transition between the needle tip and the needle stem.

[0025] Periodic switching: as shown in Figure 2 After 20 times of anodic dynamic reciprocating etching, 10 times of cathodic dynamic reciprocating etching is performed; the tip radius of the second electrode 1 is monitored in real time by the monitoring system until the requirement is met, and the etching cycle is stopped after 500-520 times of etching in this embodiment.

[0026] The porous tungsten needle tip manufacturing method of the embodiment adopts a dynamic alternating current control strategy combined with dynamic electrochemical etching to realize the preparation of the porous tungsten needle tip; by changing the polarity of the alternating current, the second electrode 1 is first used as the anode to realize the etching of the tip of the second electrode 1, so that a conical tip is gradually formed; then the second electrode 1 is used as the cathode, bubbles are generated at the cathode, and the etching products adsorbed in the pores of the second electrode 1 are flushed by the bubbles to make the etching products fall off in time; after a period of anodic etching, cathodic cleaning is performed to flush away the adsorbed etching products in time and keep the second electrode 1 clean; the anodic etching and the cathodic cleaning are alternately performed to realize the preparation of the porous tungsten needle tip; by the method, the etching products adsorbed in the pores of the porous tungsten can be removed in time, the micro-pore structure is prevented from being blocked during the etching process, the method does not affect the formation of the needle tip and does not cause damage to the needle tip, so that high-quality porous tungsten needle tips can be prepared by the method, and the product qualification rate is improved.

[0027] Embodiment two This embodiment is an embodiment of a device for manufacturing a porous tungsten needle tip. In this embodiment, as shown in FIG. 1, the device comprises the following structures: Figure 7 First electrode 2: The first electrode 2 is a porous tungsten material produced by metal injection molding technology. Specifically, it has a cylindrical shape, a diameter of 0.5 mm to 3 mm, and a length of 1.5 cm to 10 cm. The porosity can be between 10% and 60%.

[0028] Second electrode 1: It can be a graphite or stainless steel conductor. It has a ring shape with an inner diameter of 3 cm to 6 cm.

[0029] Electrolytic cell 3 is a glass beaker with a volume of 250 mL to 500 mL, used to hold electrolyte 4 and can accommodate second electrode 1, which is the place where the first electrode 2 is electrochemically etched. The electrolyte 4 is a potassium hydroxide (KOH) or sodium hydroxide (NaOH) solution. The concentration of the electrolyte is not less than 0.1 mol / L. In some embodiments, the concentration of the electrolyte is up to 10 mol / L. Electrolytes with higher concentrations are used to reduce manufacturing time due to faster etching rates of the first electrode 2.

[0030] Electric displacement platform 6 has a stroke range of more than 3 cm, realizes vertical up and down movement, and the movement rate is adjustable at 1 mm / s to 5 mm / s. Its movement scheme can be controlled by software or instructions to realize the function of continuous reciprocating motion at a specified speed within the set stroke range. During processing, the first electrode 2 is continuously reciprocated up and down in the electrolyte 4 under the control of the electric displacement platform 6, and gradually etched into a conical shape under the action of anodic electrochemical reaction.

[0031] Among them, the electric displacement platform 6 includes a vertically arranged support rod and a moving block vertically slidingly connected with the support rod; the insulation clamping assembly 7 includes a connecting screw and a clamp; the connecting screw is an insulator with threads. It can be made of ceramic or plastic materials. It is used to connect the second electrode 1 and the clamp with the moving block of the electric displacement platform 6 to realize the function of controlling the movement of the second electrode 1 through the electric displacement platform 6; the clamp is a three-jaw chuck with a clamping diameter range of 0.5 mm to 3 mm, and a screw hole is opened on the side, which can be fixed by bolts.

[0032] ​AC power supply 5 is a programmable power supply with positive and negative output, voltage output range is -10 V to +10 V, the upper limit of current output is 5 A, AC power supply 5 is connected with first electrode 2 and second electrode 1, when the loading voltage of second electrode 1 is positive, second electrode 1 will occur anodic electrochemical reaction and be gradually etched, when the loading voltage of second electrode 1 is negative, second electrode 1 will occur cathodic electrochemical reaction and generate hydrogen bubbles, the etching products in the microporous structure of second electrode 1 are carried away under the scouring of the bubbles, so that second electrode 1 is restored to clean. The configuration of loading voltage and the exchange of polarity are matched with the motion configuration of second electrode 1, which is controlled by software or instructions, and the Figure 2 The matching schematic diagram of voltage configuration and tungsten needle displacement curve is given, when AC power supply 5 outputs etching voltage with positive polarity, motorized displacement platform 6 controls second electrode 1 to reciprocate between the initial position and the etching depth m times, when AC power supply 5 outputs cleaning voltage with negative polarity, motorized displacement platform 6 controls second electrode 1 to reciprocate between the initial position and the cleaning depth n times. The polarity of the output voltage of AC power supply 5 is changed alternately, and second electrode 1 will be gradually processed into the required needle tip under the dynamic reciprocating etching and cleaning effect.

[0033] Camera 8 is used to take pictures to record the morphology of second electrode 1 in the etching process, and the termination of the processing process is preliminarily judged by monitoring the etching degree of second electrode 1 in real time.

[0034] The base is used to fix motorized displacement platform 6 and place electrolytic cell 3.

[0035] Example three This embodiment is a second embodiment of a method for manufacturing a porous tungsten needle tip, which is similar to example one, in this embodiment, the device provided in example two is used, which specifically includes the following steps: Device installation and debugging: the porous tungsten rod with a diameter of 2 mm and a porosity of 30% is clamped by a clamp and installed on motorized displacement platform 6 through a connecting screw. The electrolytic cell 3 containing 200 mL of KOH solution with a concentration of 5 mol / L and the first electrode 2 made of stainless steel with a diameter of 50 mm is placed on the base and adjusted to be directly below second electrode 1. Second electrode 1 and first electrode 2 are connected to the positive and negative electrodes of AC power supply 5 through wires. The position of camera 8 is adjusted to focus on second electrode 1. The initial position of second electrode 1 is adjusted to be 2 mm above the surface of electrolyte 4 by motorized displacement platform 6.

[0036] Anodic etching process: AC source outputs +2 V, motorized displacement platform 6 is started to control second electrode 1 to reciprocate 20 times (speed: 2 mm / s, stroke: 2 mm above the surface to 6 mm immersed in the surface), when second electrode 1 with positive loading voltage gradually immerses in electrolyte 4, anodic reaction occurs on the surface of second electrode 1 , the second electrode 1 gradually dissolves. Since the bottom end of the second electrode 1 is immersed in the electrolyte 4 earlier and removed later than other parts, the etching time is longer and the etching degree is deeper, the part of the second electrode 1 immersed in the electrolyte 4 in the up-down reciprocating motion will be gradually etched into a conical shape, thereby processing the needle tip.

[0037] Cathode cleaning process: switch the polarity of the alternating current power supply 5, the alternating current power supply 5 outputs -2 V, and the second electrode 1 is controlled to move up and down 10 times by the motorized displacement platform 6 (speed 2 mm / s, stroke: 2 mm above the liquid surface to 8 mm immersed in the liquid surface); when the second electrode 1 loaded with negative voltage gradually immerses in the electrolyte 4, the surface of the second electrode 1 will undergo a cathodic reaction , the generated hydrogen H2 bubbles will scour the surface of the second electrode 1, and drive the flow of the solution around the second electrode 1, so that the etching products adsorbed in the microporous structure of the second electrode 1 are carried away, thereby restoring the cleanliness of the second electrode 1. The up-down reciprocating motion of the second electrode 1 during the reaction process helps to accelerate the flow of the solution and promote the removal of the products in the pores, improving the cleaning effect. During the cleaning process, the immersion depth of the second electrode 1 is slightly larger than that during the etching process, which can prevent the accumulation of etching products at the transition between the needle tip and the needle shaft, ensuring the overall cleaning effect of the needle tip.

[0038] Periodic repetition: 20 times of anodic reciprocating etching and 10 times of cathodic reciprocating cleaning are completed as one cycle. Continuous processing, the tip morphology is monitored by the camera 8, and the processing is terminated after 25 cycles (500 times of etching in total). The above parameters have been optimized by comparison. As shown in Figure 3 , the behavior and morphology of the first few points at different price stages are shown in the figure, a is the initial state, b is the anodic etching process at an intermediate stage; c is the cathodic cleaning process at an intermediate stage; d is the end of etching.

[0039] As shown in Figure 4 and Figure 5 , the porous tungsten needle tip processed by the method of the present application has a vertex radius of less than 5 μm, the pores remain open, and the needle tip has high quality.

[0040] In the specific content of the above specific embodiments, any combination of technical features can be combined arbitrarily without contradiction, and in order to make the description concise, not all possible combinations of the above technical features are described, however, as long as the combination of technical features does not exist contradiction, it should be considered as the scope disclosed in the specification.

[0041] Obviously, the above embodiments of the present application are merely exemplary but not intended to limit the embodiments of the present application. Based on the above description, any other variations or changes can be made by those skilled in the art without departing from the spirit and principles of the present application. It is not necessary to list all the embodiments here. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall fall within the scope of the claims of the present application.

Claims

1. A method for manufacturing a porous tungsten needle tip, characterized in that: include: The first electrode (2) is placed in an electrolytic cell (3) containing an electrolyte (4), and the first electrode (2) is completely immersed in the electrolyte (4); one end of the second electrode (1) is inserted into the electrolyte (4), and is arranged to penetrate the middle of the first electrode (2); the first electrode (2) is a ring structure; the second electrode (1) is made of a porous tungsten material; Anodic etching: connecting the first electrode (2) and the second electrode (1) to an AC power supply (5) respectively, and making the first electrode (2) serve as a cathode and the second electrode (1) serve as an anode, applying a voltage of +n volts, and performing multiple dynamic reciprocating anode etching to form a tapered tip; Cathode cleaning: switching the power supply polarity, applying a -n volt voltage, making the second electrode (1) act as a cathode and the first electrode (2) act as an anode, and performing multiple cathode dynamic reciprocating etchings; generating bubbles at the cathode, and using the bubbles to flush the pores of the porous tungsten, so that the etching products adsorbed on the second electrode (1) fall off from the second electrode (1); Cycle switching: After performing N1 dynamic reciprocating etching of the anode, perform N2 dynamic reciprocating etching of the cathode; The tip radius of the second electrode (1) is monitored in real time until the requirement is met.

2. The method for manufacturing a porous tungsten needle tip according to claim 1, wherein: The first electrode (2) is placed horizontally in the electrolyte (4); when performing anode dynamic reciprocating etching and cathode dynamic reciprocating etching, the second electrode (1) is controlled to perform up and down reciprocating motion perpendicular to the plane where the first electrode (2) is located.

3. The method for manufacturing a porous tungsten needle tip according to claim 2, wherein: When performing dynamic reciprocating etching of the anode, the second electrode (1) is controlled to reciprocate up and down between a distance d1 mm above the liquid surface of the electrolyte (4) and a distance d2 mm below the liquid surface; when performing dynamic reciprocating etching of the cathode, the second electrode (1) is controlled to reciprocate up and down between a distance d1 mm above the liquid surface of the electrolyte (4) and a distance d3 mm below the liquid surface, and the value of d3 is greater than or equal to the value of d2.

4. The method for manufacturing a porous tungsten needle tip according to claim 3, wherein: The camera (8) is used to shoot and record the morphology of the second electrode (1) during the etching process, and the termination time of the etching process is preliminarily determined.

5. The method for manufacturing a porous tungsten needle tip according to claim 3, wherein: The first electrode (2) is made of stainless steel or graphite, and the second electrode (1) is cylindrical in shape.

6. The method for manufacturing a porous tungsten needle tip according to claim 5, wherein: The electrolyte (4) is a potassium hydroxide solution or a sodium hydroxide solution, and the concentration of the electrolyte is greater than or equal to 0.1 mol / L.

7. The method for manufacturing a porous tungsten needle tip according to claim 5, wherein: The voltage range is –10 V to +10 V.

8. The method for manufacturing a porous tungsten needle tip according to any one of claims 1 to 7, characterized in that: During anodic etching, the electrochemical reaction occurring at the second electrode (1) is: ; During cathode cleaning, the electrochemical reaction occurring at the second electrode (1) is: .

9. The method for manufacturing a porous tungsten needle tip according to any one of claims 2 to 7, wherein: When the second electrode (1) is controlled to move up and down, the movement rate is 1 mm / s to 5 mm / s.

10. A porous tungsten needle tip manufacturing device, characterized in that: The invention comprises an electric displacement platform (6) for realizing up and down reciprocating motion, an insulating clamping assembly (7) for clamping an electrode, a transparent electrolytic cell (3) for containing an electrolyte (4), an AC power supply (5), a first electrode (2), a second electrode (1), and a camera (8) for observing and recording; the electric displacement platform (6) comprises a vertically arranged support rod and a moving block vertically slidably connected to the support rod; one end of the insulating clamping assembly (7) is connected to the moving block, the second electrode (1) is vertically clamped at the other end of the insulating clamping assembly (7), and one end of the second electrode (1) is immersed in the electrolyte (4) and is inserted into the first electrode (2); the first electrode (2) is horizontally placed in the electrolytic cell (3) containing the electrolyte (4); the AC power supply (5) is electrically connected to the second electrode (1) and the first electrode (2) respectively; the camera (8) is located outside the electrolytic cell (3) and is used to photograph the tip morphology of the second electrode (1).

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