JP6256399B2 - Electropolishing apparatus and electropolishing method - Google Patents

Description

The present invention relates to an electropolishing apparatus for electropolishing a metal sample to be observed with an electron microscope. In particular, the present invention removes deposits that are generated on the surface of a metal sample during electropolishing and hinders polishing, and are extremely smooth. The present invention relates to an electropolishing apparatus capable of obtaining a simple sample surface.
The present invention also relates to an electrolytic polishing method for electrolytic polishing a metal sample observed with an electron microscope.

  In the field of material analysis, surface observation with an electron microscope such as a scanning electron microscope (SEM) has become very important. In particular, observation with an electron microscope is extremely useful and widely used in analyzing metal structures.

  When observing a metal structure with an electron microscope, it is necessary to polish and smooth the surface of a metal sample to be observed in advance. For this purpose, various methods such as electrolytic polishing, chemical polishing, ion milling, and focused ion beam (FIB) are known. Of these, electrolytic polishing is performed in a short time without damaging the surface. Since a wide range can be smoothed, it is generally used.

  However, with the recent development of electron microscopes, observation with low acceleration voltage and observation with high magnification is possible. As a result, slight unevenness on the sample surface affects the observation image, making accurate tissue observation difficult. The problem of becoming. In addition, the accuracy of the material increases the complexity of the sample structure, making it difficult to obtain a smooth material as compared to previous materials. For this reason, in the field of tissue observation using an electron microscope, there is a demand for a technique for further smoothly polishing the surface of a metal sample to be observed.

  On the other hand, in the field of electrolytic polishing, a method of obtaining a smooth polished surface by flowing an electrolytic solution by jet flow or stirring during electrolytic polishing is known. For example, in Patent Document 1, when analyzing the surface of a metal sample using an analysis method such as X-ray photoelectron spectroscopy (XPS), the metal sample is placed in a basket-like anode, and the anode is moved up and down. However, it has been proposed to smooth the surface of a metal sample by performing electropolishing.

JP 2008-184439 A

  However, the smoothness of the polished surface can be improved to some extent by using the method described in Patent Document 1, but sufficient smoothness cannot be obtained as a metal sample to be observed with an electron microscope. was there. In order to perform structure observation with an electron microscope with higher accuracy, development of an electropolishing apparatus capable of further smoothly polishing a metal surface is required.

  The present invention has been developed in view of the above circumstances, and an object thereof is to provide an electrolytic polishing apparatus and an electrolytic polishing method capable of polishing a metal sample observed with an electron microscope very smoothly.

The inventors obtained the following findings (1) to (3) as a result of intensive studies to achieve the above object.
(1) Even if the electropolishing is carried out under conditions that are considered to be optimum, for example, the composition, temperature, voltage, current, etc. of the electrolytic solution used, fine deposits that are considered corrosion products are found during the electropolishing. It forms on the metal surface.
(2) If the electropolishing is continued with the deposit remaining, the final polished surface becomes uneven. If the deposit can be removed quickly during the electropolishing, the smoothness of the polished surface will be improved. Can be improved.
(3) The deposit is difficult to remove by stirring the electrolytic solution or by moving the workpiece (metal sample) up and down, but applying ultrasonic waves to the electrolytic solution during electrolytic polishing This can be removed.

The present invention is based on the above findings, and the gist of the present invention is as follows.
1. An electropolishing apparatus for electropolishing a metal sample to be observed with an electron microscope,
An electropolishing means for electropolishing the metal sample in an electrolytic solution;
An electropolishing apparatus comprising: an ultrasonic wave application means for applying an ultrasonic wave to the electrolytic solution during electropolishing.

2. 2. The electropolishing apparatus according to 1, wherein a temperature adjusting unit for adjusting the temperature of the electrolytic solution is provided.

3. 3. The electropolishing apparatus according to 1 or 2, further comprising a control unit that performs control to apply ultrasonic waves by the ultrasonic wave application unit during electropolishing by the electropolishing unit.

4). An electropolishing method for electropolishing a metal sample to be observed with an electron microscope in an electrolyte solution,
An electrolytic polishing method in which ultrasonic waves are applied to the electrolytic solution during electrolytic polishing.

5. 5. The electrolytic polishing method according to 4, wherein the temperature of the electrolytic solution is maintained at 25 to −40 ° C.

  According to the present invention, the deposit generated on the surface of the metal sample during electropolishing can be removed by an extremely simple method of applying ultrasonic waves to the electrolytic solution, and the metal sample can be polished extremely smoothly. Such an electropolishing apparatus and an electropolishing method are extremely useful in performing final polishing of a metal sample observed with an electron microscope.

It is the schematic of the electropolishing apparatus in one Embodiment of this invention. It is the schematic of the electropolishing apparatus in other embodiment of this invention. It is the schematic of the electropolishing apparatus in other embodiment of this invention. It is the electron micrograph which observed the sample surface after electropolishing.

Next, a method for carrying out the present invention will be specifically described.
The electropolishing apparatus of the present invention is an electropolishing apparatus for electropolishing a metal sample to be observed with an electron microscope, and an electropolishing means for electropolishing the metal sample in an electrolytic solution, Ultrasonic application means for applying ultrasonic waves to the electrolytic solution. In the electrolytic polishing method of the present invention, ultrasonic waves are applied to the electrolytic solution while the metal sample is electrolytically polished in the electrolytic solution.

[Metal sample]
The electropolishing apparatus and the electropolishing method of the present invention are intended to treat a metal sample observed with an electron microscope. The metal sample is not particularly limited, and any metal material can be used as long as electropolishing is possible. Here, the “metal material” means not only pure metals and alloys, but also metal-based composite materials such as fiber reinforced metals, metal-containing materials such as cermets and cemented carbides in general. Especially, this invention can be used very suitably for preparation of the sample for structure | tissue observation of steel materials.

  The size of the metal sample may be appropriately determined according to the purpose, but if it is excessively large, it becomes difficult to smooth the entire surface by electropolishing. For this reason, the size of the polished surface is preferably 30 × 30 mm or less.

  The metal sample is preferably mirror-polished by mechanical polishing or the like prior to electrolytic polishing. Thereby, the polished surface after electrolytic polishing can be further smoothed. In addition, from the viewpoint of workability such as mechanical polishing, a metal sample may be embedded in a resin in advance, but in the present invention, a metal sample embedded in such a resin can also be used. In this case, an anode terminal of a DC power source, which will be described later, and a metal sample can be connected using a conductive paste, Cu tape, stainless steel chucking, or the like.

[Electrolytic polishing means]
The metal sample is electropolished in an electrolytic solution to smooth the surface. The mode of electropolishing is not particularly limited and can be performed in any mode, but typically, the metal sample becomes an anode in a state where at least a part of the metal sample is immersed in the electrolytic solution. This can be done by energizing. For the energization, a general DC power source can be used. An anode terminal of the power source is connected to the metal sample, a cathode terminal is connected to a cathode separately immersed in an electrolytic solution, and a voltage is applied between the metal sample and the cathode. As the power source, a normal two-electrode type power source can be used, but a three-electrode type power source such as a potentiostat or a galvanostat can be used as necessary. When a three-electrode power source is used, electrolytic polishing can be performed with a reference electrode placed in the vicinity of the metal sample.

  The material of the cathode is not particularly limited, and an electrode made of an arbitrary material can be used. However, from the viewpoint of corrosion resistance, an electrode made of stainless steel, platinum, or platinum-plated titanium is preferably used as the cathode. In order to perform electrolytic polishing uniformly, it is preferable to make the size of the cathode larger than the polishing region of the metal sample.

  The energization at the time of electrolytic polishing may be performed so that the applied potential is constant (constant potential electrolysis) or may be performed so that the current is constant (constant current electrolysis). Electrolysis can also be performed while changing the potential and current continuously or intermittently. Furthermore, from the viewpoint of controlling the amount of electropolishing, the metal polishing is masked to limit the electrolysis region size, and the electropolishing is completed based on the elapsed time from the start of electrolysis or the accumulated current value. It is preferable to use an electropolishing means provided with a quantity control means.

[Electrolyte]
The type of electrolyte used for electropolishing is selected according to the metal sample as the object to be polished. For example, when the metal sample is steel, a mixed solution of perchloric acid and methanol, a mixed solution of perchloric acid, acetic acid, and ethanol can be used. As the composition ratio of the mixed solution of perchloric acid and methanol, it is preferable to use a volume percentage of hydrogen peroxide: 5 to 30% and methanol 95 to 70%. What added 2-n-butoxyethanol further to the mixed solution of perchloric acid and methanol, and the mixed solution of perchloric acid and acetic acid can also be used. When the metal sample is a copper-based material, a solution containing phosphoric acid having a concentration of about 50% by volume can also be used.

  As a container (electrolysis tank) for holding the electrolytic solution, it is preferable to use a material made of a material that is not corroded by the electrolytic solution, and it is more preferable to use a glass container.

[Ultrasonic application means]
In the present invention, it is important to apply ultrasonic waves to the electrolytic solution while electrolytic polishing the metal sample in the electrolytic solution. By applying ultrasonic waves during the electropolishing, fine deposits generated on the surface of the metal sample by electrolysis can be quickly removed, and the smoothness of the surface of the metal sample can be prevented from being lowered. Here, “applying ultrasonic waves to the electrolytic solution during electrolytic polishing” means applying ultrasonic waves to the electrolytic solution during at least part of the time (electrolytic time) from the start to the end of electrolytic polishing. . The time for applying the ultrasonic wave is not particularly limited, but from the viewpoint of obtaining a sufficient smoothing effect, the ultrasonic wave application time is 50% or more of the electrolytic polishing time (for example, if the electrolytic polishing time is 10 seconds, The application time of the sonic wave is preferably 5 seconds or more), more preferably 80% or more of the electropolishing time, and further preferably 100% of the electropolishing time. Further, application of ultrasonic waves may be started before electropolishing is started, and similarly, application of ultrasonic waves may be continued after electropolishing is completed.

  As the ultrasonic wave application means for applying the ultrasonic wave, any means can be used as long as it can apply ultrasonic waves to the electrolytic solution. For example, a throwing type (probe type) ultrasonic transducer can be used by directly immersing it in an electrolytic solution, or an electrolytic cell containing the electrolytic solution can be installed on the ultrasonic transducer. Further, a medium such as water is accommodated in a tank to which an ultrasonic vibrator is attached, and an electrolytic tank is installed in a state where the medium is immersed in the medium. Can also be applied. What is necessary is just to determine the output of an ultrasonic application means according to the size of the metal sample which is a process target, the quantity of electrolyte solution, etc., for example, can be 10 W or more.

  In the present invention, in addition to applying ultrasonic waves, the electrolytic solution can be further stirred by an arbitrary method. Examples of the method of stirring the electrolytic solution include a stirrer (stirring bar) installed in the electrolytic cell, stirring by a stirring means such as a screw, stirring by vibrating and swinging the metal sample itself in the electrolytic solution, and the like. Can be mentioned. By stirring the electrolytic solution during electrolytic polishing, the composition and temperature of the electrolytic solution in the electrolytic cell can be made uniform, and a better polished surface can be obtained.

[Temperature adjustment means]
Furthermore, in the electrolysis apparatus of the present invention, it is preferable to provide a temperature adjusting means for adjusting the temperature of the electrolytic solution. As a result, it is possible to suppress fluctuations in the electrolyte temperature due to heat generation caused by application of ultrasonic waves, and to obtain a smoother polished surface. As the temperature adjusting means, one or both of a heating means and a cooling means may be used, or a heat exchange type temperature adjusting device that adjusts the temperature by circulating a constant temperature heat medium may be used.

  The temperature of the electrolytic solution may be determined according to the metal sample to be treated, the composition of the electrolytic solution, the electrolysis conditions (potential, current), and the like. If the temperature of the electrolytic solution becomes too high, dissolution of the metal by electrolysis is excessively promoted, and as a result, smoothness may be lowered. Therefore, the electrolytic solution temperature is preferably 25 to -40 ° C, and more preferably 20 to -30 ° C. In particular, when smoothness is required, the electrolyte temperature is more preferably 0 ° C. or lower.

[Control device]
Furthermore, in the electrolysis apparatus of the present invention, it is preferable to provide a control means for performing control so that the ultrasonic wave is applied by the ultrasonic wave application means during the electropolishing by the electropolishing means. This makes it possible to improve the smoothness of the polished surface by reliably applying ultrasonic waves during electropolishing. The control method is not particularly limited. For example, the control unit that starts the electrolytic polishing and the application of ultrasonic generation at a predetermined timing, or the ultrasonic application unit is operated in conjunction with the power source for electrolytic polishing. A device or the like can be used.

  As described above, electrolytic polishing is performed using the electrolytic polishing apparatus of the present invention. The optimal electropolishing conditions differ depending on the material and structure of the metal sample. Therefore, the electrolyte composition, electrolyte temperature, voltage (for constant potential electrolysis), current (for constant current electrolysis), Adjust the charge polishing time. For example, when the metal sample is a steel material having a carbon content of 0.040% or less, an 8% perchloric acid-10% acetic acid-ethanol mixed solution is used as the electrolytic solution, and the electrolytic solution temperature is room temperature, 60V, 60 seconds. Constant potential electrolysis can be performed. For other materials as well, it is generally desirable to find optimum polishing conditions in the range of electrolyte temperature of 20 to -40 ° C., voltage of 10 V to 70 V, and polishing time of about 2 to 120 seconds.

  After the electrolytic polishing is completed, the metal sample is taken out from the electrolytic solution, and the sample is immediately cleaned in order to prevent dirt and corrosion due to adhesion of the electrolytic solution. For the washing, alcohol, organic solvent, distilled water or the like can be used. After washing, the metal sample is dried. A dryer or a dryer may be used for the drying.

<First Embodiment>
Next, embodiments of the present invention will be specifically described with reference to the drawings. In the following description, the same numbers are assigned to common devices and members.
FIG. 1 is a schematic view of an electropolishing apparatus 1 according to the first embodiment of the present invention. In the figure, reference numeral 2 denotes an electropolishing means, which includes an electrolytic cell 4 for accommodating an electrolytic solution 3, a cathode 5, and a DC power source 6. The metal sample 7 is immersed in the electrolytic solution 3 while being connected to a DC power source 6 so as to serve as an anode.

  On the other hand, 8 is an ultrasonic wave application means, which includes an ultrasonic oscillator 9 and an ultrasonic transducer 10 connected to the ultrasonic oscillator 9. The electrolytic cell 4 is installed on the ultrasonic vibrator 10, and ultrasonic waves are applied to the electrolytic solution through the electrolytic cell 4. In this example, the ultrasonic transducer 10 is provided in the lower part of the electrolytic cell 4, but it may be provided at other positions such as a side surface.

  In this embodiment, since it is only necessary to install the electrolytic bath 4 on the ultrasonic transducer 10, for example, an existing electrolytic polishing apparatus is installed on a generally available ultrasonic transducer. An electropolishing process using ultrasonic waves can be performed by a simple method.

<Second Embodiment>
FIG. 2 is a schematic view of an electropolishing apparatus 1 according to the second embodiment of the present invention. In the present embodiment, a tank 12 filled with water 11 as a medium is installed on the ultrasonic vibrator 10, and the electrolytic tank 4 is immersed in the water 11. Accordingly, the ultrasonic wave is applied to the electrolytic solution 3 inside the electrolytic cell 4 through the water 11. In this example, the ultrasonic transducer 10 is provided in the lower part of the tank 12, but it may be provided at other positions such as a side surface of the tank 12.

  In the case of the present embodiment, a generally available ultrasonic cleaner can be used as the ultrasonic application means 8 and the tank 12. In that case, an electrolytic polishing process using ultrasonic waves can be performed by an extremely simple method of installing an existing electrolytic device in an ultrasonic cleaning machine. Moreover, in this embodiment, the temperature of the electrolyte solution 3 can also be adjusted indirectly using the water 11 in the tank 12 as a heat medium.

<Third Embodiment>
FIG. 3 is a schematic view of an electropolishing apparatus 1 according to the third embodiment of the present invention. In this embodiment, instead of installing a tank on the ultrasonic oscillator, an ultrasonic vibrator 10 is installed inside the electrolytic cell 4. In this case, a throw-in type ultrasonic transducer can be used as the ultrasonic transducer 10. In FIG. 3, the ultrasonic vibrator 10 is installed at the approximate center of the electrolytic cell 4, between the cathode 5 and the metal sample 7, but installed at another position, for example, in contact with the inner wall of the electrolytic cell 4. You can also

  Next, the present invention will be specifically described based on examples. The following examples show preferred examples of the present invention, and the present invention is not limited to the examples. Modifications can be made within the scope that can meet the spirit of the present invention, and such embodiments are also included in the technical scope of the present invention.

  Electropolishing was carried out using a 10 × 10 × 5 mmt stainless steel plate as the metal sample. The electrolytic polishing conditions were: electrolytic solution: 10% perchloric acid-90% methanol mixed solution, electrolytic solution temperature: room temperature, electrolytic method: constant potential electrolysis, applied voltage: 25 V, and electrolytic polishing time: 10 seconds. During the electropolishing, an ultrasonic wave was applied at a frequency of 38 kHz using an ultrasonic cleaner (manufactured by SND, UK-3KS). After completion of the electropolishing, a metal sample was taken out of the electrolytic solution, subjected to primary cleaning with methanol, followed by secondary cleaning and tertiary cleaning using ethanol, and then hot air drying.

  Further, for comparison, those in which ultrasonic waves were not applied during the above-described electropolishing, those in which stirring was performed by a stirrer instead of ultrasonic waves, and metal samples were vertically moved in place of ultrasonic waves. Those that were vibrated and those that were subjected to ultrasonic treatment in an electrolytic solution for 10 seconds after electropolishing without applying ultrasonic waves were prepared. The photograph obtained by observing the surface of the metal sample obtained by each method with SEM is shown in FIG.

  As a result of the experiment, a stirrer was used instead of applying ultrasonic waves (B), a metal sample was vibrated vertically instead of applying ultrasonic waves (C), and ultrasonic waves were applied after electropolishing. In the applied sample (D), fine powdery deposits remained on the surface of the metal sample, whereas in Example (A) in which ultrasonic waves were applied during electrolytic polishing, a smooth polished surface was obtained. It was obtained. The deposits are formed by reacting the components of the metal sample eluted by electropolishing with the electrolytic solution, the residual precipitates in the steel, and the surface irregularities generated by the presence of the deposits and precipitates. it is conceivable that.

  Moreover, since the deposits remained even in (D) where ultrasonic treatment was performed in an electrolytic solution after electrolytic polishing without applying ultrasonic waves, it was not necessary to simply perform ultrasonic treatment. At the same time, it can be seen that a smooth polished surface can be obtained only by applying ultrasonic waves.

  In the above examples, a stainless steel plate was used as the metal sample, and a 10% perchloric acid-90% methanol mixed solution was used as the electrolytic solution. However, similar deposits were generated even in the combination of other metals and the electrolytic solution. It was confirmed that the deposits could be removed by electropolishing combined with the ultrasonic wave of the present invention.

  The reason why deposits can be removed from the sample surface by applying ultrasonic waves during electropolishing is considered as follows. Since the electrolytic solution used for electrolytic polishing is usually an acid diluted with a solvent such as water or alcohol, the electrolytic solution contains a large amount of hydrogen and oxygen. In addition, when the electrolytic solution is repeatedly used, metal oxides, hydroxides, and the like that have been generated by electrolytic polishing so far exist in the electrolytic solution. When electropolishing is performed in such an electrolytic solution, the eluted metal reacts with oxygen and hydrogen in the electrolytic solution to form metal oxides and hydroxides near the surface of the metal sample. The formation and growth of these corrosion products are performed in the vicinity of the sample surface having a high concentration of eluted metal ions, but it is considered that the ultrasonic waves crush these corrosion products and suppress the growth. Furthermore, since the concentration of metal ions becomes uniform due to the stirring effect of the electrolytic solution by ultrasonic waves, it is considered that the formation of corrosion products is also suppressed. These effects can be expected regardless of the type and conditions of the electrolytic polishing liquid. When electropolishing is performed without applying ultrasonic waves, a large amount of corrosion products are formed and adsorbed on the surface of the metal sample. And even if an ultrasonic wave is applied after electropolishing is finished, the corrosion product remains without being removed.

  As described above, according to the present invention, it is possible to remove deposits generated on the surface of a metal sample during electrolytic polishing by an extremely simple method of applying ultrasonic waves to the electrolytic solution and polish the metal sample extremely smoothly. . Such an electropolishing apparatus and an electropolishing method are extremely useful for observing a metal structure with high accuracy by an electron microscope.

DESCRIPTION OF SYMBOLS 1 Electropolishing apparatus 2 Electropolishing means 3 Electrolytic solution 4 Electrolytic tank 5 Cathode 6 DC power supply 7 Metal sample 8 Ultrasonic application means 9 Ultrasonic transmitter 10 Ultrasonic vibrator 11 Water 12 tank

Claims (3)

An electropolishing apparatus for electropolishing a steel material as a metal sample to be observed with an electron microscope,
An electropolishing means for electropolishing the metal sample in an electrolytic solution;
Ultrasonic application means for applying ultrasonic waves to the electrolyte during electropolishing;
An electropolishing apparatus comprising temperature adjusting means for adjusting the temperature of the electrolytic solution to 0 ° C. or lower . The electropolishing apparatus according to claim 1, further comprising a control unit that performs control to apply ultrasonic waves by the ultrasonic wave application unit during electropolishing by the electropolishing unit. An electropolishing method for electropolishing a steel material as a metal sample to be observed with an electron microscope in an electrolyte solution,
Holding the temperature of the electrolyte at 0 ° C. or lower, −40 ° C. or higher,
An electrolytic polishing method in which ultrasonic waves are applied to the electrolytic solution during electrolytic polishing.