JP2017137560A - Method for producing porous nickel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing porous nickel capable of producing production cost in a method for producing porous nickel using a molten salt.SOLUTION: Provided is a method for producing porous nickel comprising: a molten salt preparation step (S1) of preparing an aluminum-containing molten salt containing aluminum fluoride together with sodium chloride and potassium chloride; an aluminum electrodeposition step (S2) of applying a potential electrodepositing aluminum to a nickel base material immersed into the aluminum-containing molten salt to form a nickel aluminide alloy layer; and an aluminum dissolution step (S3) of applying a potential dissolving aluminum and also not dissolving nickel to the nickel base material formed with the nickel aluminide alloy layer, and dissolving aluminum from the nickel aluminide alloy layer to form a porous layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing porous nickel.

  In recent years, hydrogen has been actively produced with the spread of fuel cells. A steam reforming method is used for producing hydrogen. At that time, methane and water vapor are mixed and hydrogen is generated using a nickel catalyst. The nickel catalyst is required to be porous in order to secure a surface area.

  As for the porous nickel, Raney nickel is known. Raney nickel makes nickel porous by dissolving an aluminum with a strong alkaline solution after producing an alloy of nickel and aluminum (for example, Patent Document 1). This method is difficult to handle because hydrogen generated by the reaction between alkali and aluminum is adsorbed by nickel.

  In recent years, research for making nickel porous without using such a strong alkali has been conducted. It has been reported that the intermetallic compound phase of the thin film can be changed to another phase in a short time by performing potential scanning in the anode direction on the electrode on which the Ni—Y intermetallic compound thin film is formed. . In this method, after dissolving yttrium (Y) in a molten salt of LiCl—KCl, flat polycrystalline nickel as a working electrode, glassy carbon as a counter electrode, and a silver / silver chloride electrode as a reference electrode in the molten salt First, a thin film layer of yttrium 20 μm is formed on nickel over 4 hours. Thereafter, the thin film layer portion is made porous by dissolving yttrium from the thin film layer portion made of nickel and yttrium by potential scanning in the anode direction (Non-patent Document 1).

Japanese Patent Laid-Open No. 1-2242148, page 1, lower right column “(Conventional Technology)”

Kenji Tateiwa, Masayuki Tada, Akihiko Ito “Phase Control and Porousization of Ni-Y Intermetallic Compound Thin Films”, Surface Technology, Vol. 46, no. 7, 1995, p. 672-673

Since the method using the molten salt as in Non-Patent Document 1 does not use a strong alkali as in the Raney nickel manufacturing method, a problem caused by the strong alkali does not occur. However, it takes about 4 hours to form a 20 μm nickel-yttrium thin film layer on a nickel substrate. According to Non-Patent Document 1, the nickel-yttrium thin film layer is assumed to be Ni ₂ Y. For this reason, there is much usage-amount of yttrium called rare earth with respect to Ni. For these reasons, the manufacturing method of the conventional porous nickel using the molten salt increases the manufacturing cost.

  Accordingly, an object of the present invention is to provide a method for producing porous nickel that can reduce production costs in a method for producing porous nickel using a molten salt.

  The present invention is achieved by the following means.

(1) a molten salt preparation step of preparing an aluminum-containing molten salt containing sodium chloride, potassium chloride, and aluminum;
An aluminum electrodeposition step of forming a nickel aluminide alloy layer by applying a potential at which aluminum is electrodeposited to a nickel base immersed in the aluminum-containing molten salt;
An aluminum melting step of forming a porous layer by dissolving the aluminum from the nickel aluminide alloy layer by applying a potential that dissolves aluminum and does not dissolve nickel to the nickel base material on which the nickel aluminide alloy layer is formed When,
A method for producing porous nickel, comprising:

(2) In the aluminum electrodeposition step, when a reference electrode and a counter electrode are immersed in the aluminum-containing molten salt and the nickel base is used as a cathode, the cathode potential with respect to the reference electrode is −1.8 V to −1. To be 2V,
In the aluminum dissolution step, when the reference electrode and the counter electrode are immersed in the aluminum-containing molten salt and the nickel base material on which the nickel aluminide alloy layer is formed is used as an anode, the anode potential with respect to the reference electrode is -1. The method for producing porous nickel according to the above (1), wherein 25 V to −0.3 V is set.

  (3) In the molten salt preparation step, the concentration of the aluminum fluoride is set to 1 to 5 mol% with respect to the total amount of the aluminum-containing molten salt using aluminum fluoride as an aluminum source. A method for producing porous nickel.

  (4) The molten salt preparation step according to any one of (1) to (3), wherein the aluminum-containing molten salt further includes at least one element of yttrium, zirconium, and hafnium. Of producing porous nickel.

  (5) In the molten salt preparation step, any one element selected from the group consisting of yttrium fluoride, zirconium fluoride, and hafnium fluoride is used as an element source of at least one of yttrium, zirconium, and hafnium. The method for producing porous nickel according to (4) above, wherein the concentration of any one of the metal fluorides is 0.01 to 0.2 mol% with respect to the total amount of the aluminum-containing molten salt using a metal fluoride. .

  According to the present invention, a nickel aluminide alloy layer is formed by electrodepositing aluminum on the surface of a nickel substrate in an aluminum electrodeposition step, and a porous layer is formed by dissolving aluminum from the nickel aluminide alloy layer in an aluminum melting step. Formed. By using aluminum in this manner, the manufacturing cost can be reduced as compared with the conventional method for producing porous nickel using molten salt.

It is a flowchart which shows the manufacturing method of the porous nickel which concerns on embodiment. It is a schematic sectional drawing for demonstrating the state of the nickel base material accompanying the manufacturing method of the porous nickel which concerns on embodiment. It is the schematic for demonstrating the apparatus structure for performing an Al electrodeposition stage and an Al melt | dissolution stage. It is a drawing substitute photograph which shows the SEM observation result of each sample after Al electrodeposition. It is a graph which shows the relationship between time passage and current density in constant potential electrodeposition by cathode potential -1.5V. It is a drawing substitute photograph which shows the SEM observation result of each sample after Al melt | dissolution. It is a graph which shows the relationship between an anode electric potential when changing an anode electric potential, and performing Al melt | dissolution, and a current density. It is explanatory drawing explaining the composition distribution of a depth direction. It is a graph which shows the relationship between an anode electric potential when changing an anode electric potential, and performing Al melt | dissolution, and a current density. It is a graph which shows the relationship between the time passage at the time of Al melt | dissolution, and current density. It is a drawing substitute photograph which shows the SEM observation result of the sample after Al melt | dissolution. It is explanatory drawing explaining the composition distribution of a depth direction. Is a graph showing the mass increment and YF ₃ concentration relationship per unit area in Al Electrodeposition.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the size and ratio of each member in the drawings are exaggerated for convenience of explanation, and may be different from the actual size and ratio.

  FIG. 1 is a flowchart showing a method for producing porous nickel according to an embodiment. FIG. 2 is a schematic cross-sectional view for explaining the state of the nickel base material associated with the method for producing porous nickel according to the embodiment.

<Molten salt preparation stage>
In the method for producing porous nickel, first, an Al-containing NaCl-KCl molten salt is prepared (S1). For this purpose, aluminum fluoride (AlF ₃ ) is prepared as an aluminum (Al) source together with sodium chloride (NaCl) and potassium chloride (KCl). Each of these is placed in a heat-resistant container such as a predetermined amount of crucible and heated to obtain an Al-containing NaCl-KCl molten salt. In this molten salt preparation step, NaCl-KCl may be heated to prepare a molten salt, and aluminum fluoride (AlF ₃ ) may be dissolved in the molten salt.

  NaCl has a melting point of 800 ° C. and KCl has a melting point of 776 ° C. The NaCl-KCl mixed salt (mixing molar ratio 1: 1) has a melting point of 660 ° C. Therefore, when preparing the molten salt, by making the NaCl-KCl an equimolar amount, the melting point is lowered and the molten salt is easily dissolved. From these melting points, the temperature of the molten salt may be about 660 ° C. to 950 ° C., for example. Note that nickel (Ni) has a melting point of 1455 ° C. and aluminum (Al) has a melting point of 660 ° C. For this reason, when the temperature of the molten salt is 660 ° C. to 950 ° C., Al dissolves but Ni does not dissolve. The melting point of NiAl forming the nickel aluminide alloy layer described later is 1638 ° C. Therefore, if the temperature of the molten salt is within this range, the formed nickel aluminide alloy layer does not melt as it is.

The concentration of AlF ₃ in the molten salt is not particularly limited as long as it is a concentration at which an alloy of Ni and Al is formed in the Al electrodeposition step described later. For example, 1 mol% to 5 mol% is sufficient with respect to the total amount (100 mol%) of the molten salt. Preferably it is 3.5 mol% from the Example mentioned later.

In the molten salt preparation stage, at least one rare earth (element) of yttrium (Y), zirconium (Zr), and hafnium (Hf) may be further added to the molten salt. As these element sources, for example, any one metal fluoride selected from the group consisting of yttrium fluoride (YF ₃ ), zirconium fluoride (ZrF ₄ ), and hafnium fluoride (HfF ₄ ) is used. . When these are added, these metal fluorides may be placed in a heat-resistant container and heated and dissolved together with NaCl, KCl, and AlF ₃ .

  The concentration of these metal fluorides is, for example, 0.01 to 0.2 mol% with respect to the total amount of molten salt (100 mol%). The reason for setting the concentration of the metal fluoride in such a range is that the lower limit can be made porous even if rare earth is not added at all from Examples described later. Therefore, the lower limit in the case of adding rare earth may be added exceeding 0 mol%. However, if the amount is too small, the effect of promoting porosity cannot be expected, so the amount is about 0.01 mol%. On the other hand, the upper limit is preferably set to 0.2 mol% or less from the examples described later, since addition of a large amount of rare earth suppresses electrodeposition of Al.

  Even when rare earth is added in this way, the concentration may be low. This is because, unlike the prior art (Non-Patent Document 1), it is not intended to produce an alloy composed of Ni and Y.

<Al electrodeposition stage>
Next, a cathode potential is applied to the Ni substrate immersed in the Al-containing NaCl-KCl molten salt (including cases where rare earth is included; the same applies hereinafter) to deposit Al on the Ni substrate (S2).

  In the Al electrodeposition stage, the Ni base 101 to be made porous as shown in FIG. 2A is set as a working electrode before heating in the molten salt preparation stage in advance. Similarly, a reference electrode and a counter electrode are also set. At this time, each electrode including the Ni base material 101 is set to a position where it is immersed in the molten salt after being converted into a molten salt by heating. Instead of this, each electrode including the Ni base material may be immersed in the molten salt after it has been converted into a molten salt by heating.

  The working electrode (Ni base 101, which is the cathode here), the counter electrode (here, the anode), and the reference electrode are connected to a power supply control device (potentiostat).

  The temperature of the molten salt in the Al electrodeposition step may be the same as when the molten salt is prepared, and is, for example, 660 ° C to 950 ° C.

  A potential is applied between the Ni base 101 as a cathode and the reference electrode. As a result, Al is electrodeposited on the Ni base 101, and as shown in FIG. 2B, a nickel aluminide alloy layer (hereinafter referred to as NiAl layer) 102 is formed.

For the electrodeposition of Al, the cathode potential is preferably in the range of −1.8 V to −1.2 V (the potential between the cathode and the reference electrode) which is the Al reduction potential region. The reason is that an electric current flows between the cathode and the anode in such a range of the cathode potential, and Al electrodeposition occurs. The electrodeposition time of Al varies depending on the concentration of Al ions (Al ⁺ ). Further, since it varies depending on the thickness of the NiAl layer 102 to be formed by electrodeposition, it cannot be generally stated. However, when the cathode potential is -1.5 V, for example, from an example described later, the electrodeposition time is constant potential electrodeposition. In this case, the NiAl layer 102 having a thickness of about 10 to 100 μm can be formed at about 1.5 ks to 3.6 ks (however, 1 ks = 1000 seconds, the same applies hereinafter). Even if this time is too long, the electrodeposition reaction itself is saturated (cathode polarization current stops flowing). For this reason, even if the Al electrodeposition time is 3.6 ks or more, it does not make much sense.

  The Al electrodeposition step is preferably performed in an inert gas atmosphere (for example, flowing argon gas). This is to prevent the molten salt from absorbing moisture.

  In the examples, assuming that the reference electrode in the Al-containing NaCl-KCl molten salt is 0 V, the Ni substrate 101 side is set to −1.8 V to −1.2 V so that the Ni substrate 101 and the counter electrode are counter electrodes. The current is controlled to flow between the two.

  These anode potential and electrodeposition time may be the same when rare earth is added.

<Al dissolution stage>
Next, an anode potential that dissolves Al and does not dissolve Ni is applied to the Ni base material on which the NiAl layer is formed, and Al (including rare earth, if any) is dissolved from the NiAl layer to make it porous. A layer is formed (S3).

  In this Al dissolution step, a potential is applied between the Ni substrate 101a with a NiAl layer immersed in a NaCl-KCl molten salt as an anode and a reference electrode. The potential applied at this time is such that Al is dissolved and Ni is not dissolved. Thereby, Al is dissolved from the NiAl layer 102. As a result, as shown in FIG. 2 (c), an Al component is removed from the NiAl layer 102 (alloy), and a Ni porous layer 103 in which the portion from which Al is removed becomes a hole is completed.

  The temperature of the molten salt in the Al melting stage may be the same as when the molten salt is prepared and in the Al electrodeposition stage, for example, 660 ° C. to 950 ° C.

  The anode potential applied in this Al melting stage is set to -1.25V to -0.3V from the examples described later. When the voltage exceeds −0.3 V, Ni is also dissolved, so that it cannot be made porous. On the other hand, even if it is less than -1.25V, since dissolution of Al does not occur, there is no point in making it lower. Moreover, it is preferable that the time for melt | dissolving this Al is 1.0ks-3.6ks, for example.

  In the examples, when the reference electrode in the NaCl-KCl molten salt is set to 0V, the Ni substrate with NiAl layer is set so that the Ni substrate 101a side with NiAl layer becomes -1.25V to -0.3V. Control is performed so that a current flows between 101a and the counter electrode.

  These anode potentials and dissolution times may be the same when rare earth is added.

  Even in the Al dissolution stage, it is preferable to carry out in an inert gas atmosphere (for example, flowing argon gas). This is to prevent the molten salt from absorbing moisture.

  This Al dissolution step may be performed continuously from the Al electrodeposition step. When performing continuously, it may be controlled so that the Ni substrate side becomes the cathode during the Al electrodeposition stage and the anode during the Al dissolution stage. Moreover, when performing continuously, the state in which Al remains in molten salt may be sufficient. Moreover, when it carries out continuously, the temperature of molten salt may be the same throughout each step.

  Of course, the Al dissolution stage may be performed separately from the Al electrodeposition stage. When carried out separately, the molten salt may use an equimolar amount of NaCl-KCl (NaCl: KCl = 1 mol: 1 mol). However, the Al component is dissolved in the NaCl-KCl molten salt as the Al is dissolved. For this reason, the Al component may be contained in the NaCl-KCl molten salt from the beginning. This is because, as described above, the condition for dissolving Al from the NiAl layer 102 is determined by the range of the anode potential and does not depend on the Al concentration in the molten salt. When carried out separately, the temperature of the molten salt may be different at each stage or the same. When performing separately from the Al electrolysis step, NaCl and KCl may be put in a heat-resistant container and each electrode may be set including a Ni base material on which a NiAl layer is formed before heating. At this time, each electrode is set at a position where it is immersed in the molten salt after becoming a molten salt. Moreover, after it becomes molten salt by heating, each electrode including the Ni base material on which the NiAl layer is formed may be immersed in the molten salt.

  As described above, since the porous layer is formed on the nickel base material, the porous layer is taken out from the molten salt, and is sufficiently washed after being cooled.

  Next, the apparatus configuration will be described.

  FIG. 3 is a schematic diagram for explaining an apparatus configuration for performing the Al electrodeposition stage and the Al dissolution stage. In addition, the apparatus (electrodeposition dissolution apparatus) demonstrated here is an example for performing the electrodeposition and melting | dissolving of Al to the last, and an apparatus structure required in order to implement this invention is limited to such an apparatus structure. It is not a thing.

  The electrodeposition melting apparatus 200 includes a quartz tube 202 in an electric furnace 201. An alumina crucible 203 is provided in the quartz tube 202. The molten salt 100 is stored in the alumina crucible 203. A reference electrode 211 (RE), a counter electrode 212 (CE), a working electrode 213 (WE), and a temperature sensor 214 are immersed in the molten salt 100.

  The furnace temperature of the electric furnace 201 is controlled by the electric furnace control device 220. A temperature sensor 214 is connected to the electric furnace control device 220. The electric furnace control device 220 detects the temperature of the molten salt 100 based on the temperature detection signal from the temperature sensor 214, and controls the furnace temperature so that it becomes a desired temperature. The temperature sensor 214 is, for example, a thermocouple. The thermocouple is immersed in the molten salt 100, and an electromotive force (voltage) corresponding to the temperature is transmitted to the electric furnace control device 220 as a signal corresponding to the temperature. The temperature sensor 214 may be other than a thermocouple, for example, an infrared temperature sensor.

  The reference electrode 211, the counter electrode 212, and the working electrode 213 are connected to the potentiostat 210, and control the voltage between the reference electrode working electrode, the current between the counter electrode working electrodes, and the like. As the reference electrode 211, a known reference electrode 211 that can be used for the electrolytic reaction in the molten salt 100 can be used. As the reference electrode 211, for example, a ceramic sheath tube is prepared, and in this sheath tube, an equimolar amount of NaCl-KCl and AgCl of 10 mol% with respect to the total amount are made to form a mixed salt bath, and this mixed salt What immersed the silver (Ag) rod in the bath can be used. That is, it becomes an Ag / AgCl (0.1) reference electrode. For example, tubular graphite can be preferably used as the counter electrode. The Ni base 101 is connected to the potentiostat 210 as the working electrode 213 so as to be electrically connected.

  The quartz tube 202 has a lid portion 204 attached thereto, and the lid portion 204 can seal the quartz tube 202. The lid portion 204 is provided with an opening (not shown) so that various members can be inserted into the quartz tube 202. The opening surrounds the insert by a heat-resistant member (not shown) and seals the lid 204. The inserts here are a reference electrode 211, a counter electrode 212, a working electrode 213, and a temperature sensor 214. The quartz tube 202 is provided with a gas inlet 205 for introducing argon (Ar) into the quartz tube 202 and an exhaust tube 206. Note that the quartz tube 202 is for maintaining the temperature of the molten salt 100 and preventing impurities from entering, so that instead of the quartz tube 202, any impurities or the like that do not enter the molten salt 100 inside during heating can be used. Even materials other than quartz can be used.

  The alumina crucible 203 is a heat-resistant container that holds the molten salt 100 inside the quartz tube 202. The alumina crucible 203 may also be a heat-resistant container made of other materials as long as there is no risk of impurities being mixed into the molten salt 100.

  Using such an electrodeposition dissolution apparatus 200, a process from Al electrodeposition to Al melting can be carried out as a series of processes.

  Operation at each stage using the electrodeposition dissolution apparatus 200 is performed as follows.

First, as a molten salt preparation stage, a required amount of metal fluoride such as NaCl, KCl, AlF ₃ and, if necessary, YF ₃ , ZrF ₄ , HfF ₄ is put in the alumina crucible 203, and this is put in the quartz tube 202. Place. The Ni base 101, the reference electrode 211, and the counter electrode 212 of the working electrode 213 set the molten salt 100 and cover it. The Ni base 101, the reference electrode 211, and the counter electrode 212 of the working electrode 213 are set at a position where the working electrode 213 is surely immersed in the molten salt 100 after becoming the molten salt 100. Thereafter, Ar gas is introduced and the quartz tube 202 is heated while maintaining an Ar atmosphere. Heating is automatically controlled by setting the temperature of the molten salt 100 to a predetermined temperature in the electric furnace controller 220. Of course, the electric furnace 201 may be controlled manually so that the temperature of the molten salt 100 becomes a desired temperature while monitoring the temperature of the molten salt 100.

  After the temperature of the molten salt 100 reaches a desired temperature, the potentiostat 210 controls the working electrode 213 and the reference electrode 211 as the Al electrodeposition stage so as to be at the potential of the Al electrodeposition stage described above. After a predetermined time has elapsed, the Ni substrate 101 is pulled up and washed with water (or a solvent that dissolves salt).

  In the Al melting stage, equimolar amounts of NaCl and KCl are placed in an alumina crucible 203 and placed in the quartz tube 202. Then, the working electrode 213, the reference electrode 211, and the counter electrode 212 of the Ni base material with NiAl layer are set and covered. The working electrode 213, the reference electrode 211, and the counter electrode 212 of the Ni base material with the NiAl layer are set at positions where the molten salt 100 is surely immersed in the molten salt 100 after the molten salt 100 is formed. Thereafter, Ar gas is introduced and the quartz tube 202 is heated while maintaining an Ar atmosphere. Heating is automatically controlled by setting the temperature of the molten salt 100 to a predetermined temperature in the electric furnace controller 220. Of course, the electric furnace 201 may be controlled manually so that the temperature of the molten salt 100 becomes a desired temperature while monitoring the temperature of the molten salt 100. After the temperature of the molten salt 100 reaches a desired temperature, the potentiostat 210 controls the working electrode 213 and the reference electrode 211 as the Al melting stage so as to be at the potential of the Al melting stage described above. After a predetermined time has passed, the Ni substrate with NiAl layer is pulled up and washed with water (or a solvent that dissolves salt).

  In addition, it can also perform continuously from Al electrodeposition to Al fusion | melting. When performing continuously, after the time required for Al electrodeposition, the potentiometer 213 (Ni base material) and the reference electrode 211 are made to have the potential of the above-described Al dissolution stage without pulling up the Ni base material. What is necessary is just to control by the stat 210.

  Using the above-described electrodeposition dissolution apparatus (hereinafter simply referred to as “apparatus”), the following tests were performed by the same operation as described above.

In Examples and Comparative Examples, NaCl, KCl, AlF ₃ , and a rare earth (YF ₃ or ZrF ₄ ) were prepared as molten salts having concentrations shown in Table 1 (the total molten salt was 100 mol%).

  In the molten salt, an Ag / AgCl (0.1) reference electrode, a counter electrode of tubular graphite, and a Ni substrate as a sample were immersed as a working electrode (the reference electrode and the counter electrode are the same in all tests). The Ni substrate was 10 mm long, 10 mm wide, and 1 mm thick. This Ni substrate was electrically connected to the potentiostat wiring so as to be a working electrode. In addition, the magnitude | size of said Ni base material is a magnitude | size of the sample used in order to perform each test, Comprising: If it is the magnitude | size which can enter a crucible, there will be no restriction | limiting in particular.

(Test 1)
Al electrodeposition was performed using the molten salts of Examples 1 and 2. For Example 1, three tests were performed using cathode samples of -1.4V, -1.5V, and -1.6V, respectively, using samples made of different Ni substrates. In Example 2, the cathode potential was set to -1.5V. Both are constant potential electrodepositions with a constant cathode potential. Each Al electrodeposition time was 3.6 ks. The molten salt temperature during Al electrodeposition was 900 ° C.

  Each sample after Al electrodeposition was cut in the depth direction with an automatic precision cutting machine, and the cross-section of the sample was polished with abrasive paper. A scanning electron microscope (SEM) (JXA-8230 manufactured by JEOL Ltd., acceleration voltage 15 kV, Observation by backscattered electron detection).

  FIG. 4 is a drawing-substituting photograph showing SEM observation results of each sample after Al electrodeposition. 4A is a cross section after Al electrodeposition at a cathode potential of −1.4 V in Example 1, and FIG. 4B is a cross section after Al electrodeposition at a cathode potential of −1.5 V in Example 1. FIG. 4 (c) is a cross section after Al electrodeposition at a cathode potential of −1.6V in Example 1, and FIG. 4 (d) is a cross section after Al electrodeposition at a cathode potential of −1.5V in Example 2. It is a cross section.

  The thickness of the NiAl layer in the case where Al was electrodeposited at a cathode potential of −1.4 V using the molten salt of Example 1 shown in FIG. 4A was 36.8 μm.

  The thickness of the NiAl layer in the case where Al was electrodeposited at a cathode potential of −1.5 V using the molten salt of Example 1 shown in FIG. 4B was 88.0 μm.

  The thickness of the NiAl layer was 127.2 μm when Al electrodeposition was performed at a cathode potential of −1.6 V using the molten salt of Example 1 shown in FIG.

  The thickness of the NiAl layer in the case where Al was electrodeposited at a cathode potential of −1.5 V using the molten salt of Example 2 shown in FIG. 4D was 70.2 μm.

  The thickness of each NiAl layer is a value obtained by measuring the thickness of the NiAl layer portion on each SEM photograph of FIGS. 4A to 4D and converting it based on the scale bar on the SEM photograph. Is the average value.

From this result, it can be seen that when the Al deposition time is the same, the thickness of the NiAl layer can be changed by changing the cathode potential. Further, when comparing the cathode potential of -1.5 V of Example 1 and Example 2, if the cathode potential and time of Al deposition are the same even if the concentration of YF ₃ is changed, each cathode potential of Example 1 is It can be seen that the difference in thickness is less than that when changing. Therefore, it is more effective to control the NiAl layer by changing the cathode potential than by changing the concentration of YF ₃ .

  Moreover, when the surface was observed visually after Al electrodeposition, the completed NiAl layer was formed on all surfaces of the Ni substrate. This indicates that whatever the shape of the Ni substrate, the surface can be made porous if the Ni substrate can be brought into contact with the molten salt.

(Test 2)
Using the molten salts of Examples 1 to 3 and Comparative Example 1, changes in current density over time in constant potential electrodeposition with a cathode potential of −1.5 V were observed. The current density is the density of current flowing between the working electrode (cathode) and the counter electrode (anode) of the potentiostat. The molten salt temperature was 900 ° C.

  FIG. 5 is a graph showing the relationship between the passage of time and the current density in constant potential electrodeposition with a cathode potential of −1.5V.

  From FIG. 5, it can be seen that in all of Examples 1 to 3, almost no current flows when the Al electrodeposition time is about 1.5 ks. On the other hand, in the molten salt containing no Al in Comparative Example 1, the current density is almost zero. This means that almost no current flows between the working electrode (Ni base) and the counter electrode. In the first place, Comparative Example 1 is a natural result because there is no substance to be electrodeposited in the NaCl-KCl molten salt. When this Comparative Example 1 is compared with Examples 1 to 3, in Examples 1 to 3, the current density is nearly zero after about 1.5 ks. Therefore, it is shown that the electrodeposition of Al does not proceed after about 1.5 ks. From this, the electrodeposition time in the Al electrodeposition stage may be longer than 1.5 ks and 3.6 ks (1 hour) with a margin. Moreover, in order to reduce process cost (especially tact time), you may make it stop in about 1.5-2ks (about 25-35 minutes) when the current density fell to almost 0.

(Test 3)
After the Al electrodeposition in Examples 1 to 3 and Comparative Example 1, Al dissolution was performed using a sample of a Ni substrate (Ni substrate with a NiAl layer) on which a NiAl layer was formed.

  The sample used here was a cathode potential of −1.5 V and a molten salt temperature of 900 ° C. using the molten salts of Examples 1 to 3 and Comparative Example 1. It was produced by performing constant potential electrodeposition with a time of 3.6 ks.

  For Al dissolution, an equimolar amount of NaCl-KCl was used as a molten salt. The temperature of the molten salt was 750 ° C., the anode potential was kept constant at −0.5 V, and the time was 3.6 ks.

  Each sample after dissolution of Al was cut in the depth direction with an automatic precision cutting machine, and the sample whose cross section was polished with abrasive paper was scanned electron microscope (SEM) (JXA-8230 manufactured by JEOL Ltd., acceleration voltage 15 kV, reflection) Observation by electron detection).

  FIG. 6 is a drawing-substituting photograph showing SEM observation results of each sample after dissolution of Al. 6 (a) is a cross section after the Al dissolution of Example 1, FIG. 6 (b) is a cross section after the Al dissolution of Example 2, and FIG. 6 (c) is a cross section after the Al dissolution of Example 3. FIG. 6D is a cross section of the comparative example 1 after dissolution of Al.

Comparing Examples 1 and 2, towards the concentration of YF ₃ is high it can be seen that the hole is large. Moreover, although Example 3 does not add Y, it turns out that it is porous. On the other hand, it can be seen that Comparative Example 1 in which the NiAl layer is not formed does not have a porous layer even if an Al melting operation is performed.

  From these, it can be seen that the Al electrodeposition stage can dissolve Al and form a porous layer even if it is a NaCl-KCl molten salt containing Al. And if Y is added, porosity-ization will be accelerated | stimulated (a hole will increase). Increasing the amount of Y further promotes porosity.

(Test 4)
Next, using the Ni base material with the NiAl layer produced from Examples 1 to 3 and Comparative Example 1, Al was dissolved by changing the anode potential, and the polarization current was observed. The sample used here was the same as in Test 3, using the molten salts of Examples 1 to 3 and Comparative Example 1, with a cathode potential of −1.5 V and a molten salt temperature of 900 ° C. It was produced by performing constant potential electrodeposition with a time of 3.6 ks.

  For Al dissolution, an equimolar amount of NaCl-KCl was used as a molten salt. The temperature of the molten salt was 750 ° C.

  FIG. 7 is a graph showing the relationship between the anode potential and the current density when Al dissolution is performed by changing the anode potential. The current density is the density of current flowing between the working electrode (anode) and the counter electrode (cathode) of the potentiostat.

  From FIG. 7, the current density rises when the anode potential exceeds −0.4 V in the comparative example 1 without the NiAl layer. From this, it can be seen that when the anode potential is applied above -0.4 V, Ni is melted. Conversely, if the anode potential is −0.4 V or less, Ni will not melt.

  On the other hand, Examples 1-3 are samples with a NiAl layer. In these, the current density increases when the anode potential is −1.25 V or more. From this, it can be seen that Al is dissolved when an anode potential of −1.25 V or more is applied.

  From these facts, it can be seen that when the anode potential is −1.25 V or more and −0.4 V or less, Al dissolves but Ni does not dissolve. Therefore, by setting the anode potential in the Al melting stage to −1.25 V to −0.4 V, it is possible to dissolve Al and not dissolve Ni. The anode potential that reliably dissolves Al and does not dissolve Ni is preferably set to −1.25 V or more and −0.5 V or less.

(Test 5)
Next, Al electrodeposition was performed using the molten salts of Examples 4 and 5. In either case, the cathode potential is a constant potential electrodeposition of -1.5V. The Al electrodeposition time was 3.6 ks, and the molten salt temperature was 900 ° C.

  Each sample after Al electrodeposition was cut in the depth direction with an automatic precision cutting machine, and the cross-section of the sample was polished with abrasive paper. A scanning electron microscope (SEM) (JXA-8230 manufactured by JEOL Ltd., acceleration voltage 15 kV, Observation by backscattered electron detection). The sample was subjected to line analysis in the depth direction by energy dispersive X-ray spectroscopy (EDS) to calculate the composition distribution.

  FIG. 8 is an explanatory diagram for explaining the composition distribution in the depth direction, and shows a graph of the composition distribution together with a photograph of the SEM observation result. 8A shows a cross section after Al electrodeposition in Example 4, and FIG. 8B shows a cross section after Al electrodeposition in Example 5. FIG.

FIG. 8 shows that the composition of the NiAl layer formed by Al electrodeposition varies depending on the concentration of ZrF ₄ . In Example 4, the concentration of ZrF ₄ is 0.05 mol%. As a result of the composition analysis, the composition of the NiAl layer in this case was Ni ₂ Al ₃ . In Example 5, the concentration of ZrF ₄ is 0.1 mol%. As a result of composition analysis, the composition of the NiAl layer in this case was NiAl.

  On the other hand, Zr contained in the NiAl layer is extremely small in both Examples 4 and 5, as can be seen from FIG. This result shows that, even when Zr is added, Al is more easily electrodeposited than Zr at a cathode potential of −1.5 V, and thus is hardly taken into the NiAl layer.

  Therefore, rare earth is electrodeposited on the surface of the Ni base together with Al in the Al electrodeposition stage, but the amount taken in is rare. Therefore, it can be seen that a very small amount of rare earth may be added.

(Test 6)
Next, using the Ni base material with the NiAl layer produced with the molten salt of Example 5 and Comparative Example 1, Al was dissolved by changing the anode potential, and the polarization current was observed. The production of the Ni substrate with the NiAl layer (Al electrodeposition stage) was carried out in the same manner as in Test 5, at a cathode potential of −1.5 V, a molten salt temperature of 900 ° C., and a time of 3.6 ks.

  Al dissolution was performed by changing the anode potential at an equimolar amount of NaCl-KCl molten salt at a molten salt temperature of 750 ° C.

  FIG. 9 is a graph showing the relationship between the anode potential and the current density when Al dissolution is performed by changing the anode potential. The current density is the density of current flowing between the working electrode (anode) and the counter electrode (cathode) of the potentiostat.

  From FIG. 9, in the sample without the NiAl layer of Comparative Example 1, the current density increases when the anode potential exceeds −0.3V. From this, it can be seen that when the anode potential is applied above -0.3 V, Ni melts. Conversely, if the anode potential is −0.3 V or less, Ni will not melt.

  On the other hand, Example 5 is a sample with a NiAl layer. In Example 5, the current density is increased when the anode potential is −1.25 V or higher. From this, it can be seen that when an anode potential of −1.25 V or more is applied, Al is dissolved.

  From these facts, it can be seen that when the anode potential is −1.25 V or more and −0.3 V or less, Al dissolves but Ni does not dissolve. Therefore, by setting the anode potential in the Al melting stage to −1.25 V to −0.3 V, it is possible to dissolve Al and not dissolve Ni. The anode potential that reliably dissolves Al and does not dissolve Ni is preferably set to −1.25 V or more and −0.5 V or less.

(Test 7)
Next, using the Ni base material with a NiAl layer produced from the molten salt of Example 5, Al dissolution was performed, and the change in current density over time was observed. The current density is the density of current flowing between the working electrode (anode) and the counter electrode (cathode) of the potentiostat. The production of the Ni substrate with the NiAl layer (Al electrodeposition stage) was carried out at a cathode potential of −1.5 V, 900 ° C., and 3.6 ks as in Test 5. Al dissolution was carried out with an equimolar amount of NaCl-KCl molten salt, a molten salt temperature of 750 ° C., and a constant anode potential of −0.3 V.

  FIG. 10 is a graph showing the relationship between the passage of time and the current density during Al dissolution.

  From FIG. 10, it can be seen that almost no current flows when the Al dissolution time is about 1.5 ks. Therefore, even when Zr is added, the dissolution of Al does not proceed after about 1.5 ks. Therefore, the melting time in the Al melting stage may be longer than 1.5 ks and 3.6 ks (1 hour) with a margin. Moreover, in order to reduce process cost (especially tact time), you may make it stop in about 1.5-2ks (about 25-35 minutes) when the current density fell to almost 0.

(Test 8)
Next, using the Ni substrate with NiAl layer produced from the molten salt of Example 5, Al was dissolved to form a porous layer. The production of the Ni substrate with the NiAl layer (Al electrodeposition stage) was performed in the same manner as in Test 5 at a cathode potential of −1.5 V, a molten salt temperature of 900 ° C., and a time of 3.6 ks. The dissolution of Al was carried out for 3.6 ks with an equimolar amount of NaCl-KCl molten salt, a molten salt temperature of 750 ° C., and an anode potential of −0.3 V constant.

  A sample obtained by cutting the Al-dissolved sample in the depth direction with an automatic precision cutting machine and polishing the cross section with abrasive paper was used for a scanning electron microscope (SEM) (JXA-8230 manufactured by JEOL Ltd., acceleration voltage 15 kV, reflected electron Detection).

  FIG. 11 is a drawing-substituting photograph showing the SEM observation result of the sample after dissolution of Al.

  As shown in FIG. 11, it can be seen that a porous layer is formed. The composition of this sample was analyzed by energy dispersive X-ray spectroscopy (EDS). As shown in FIG. 11, the measurement point is generally the intermediate portion in the depth direction of the porous layer.

  As a result of the analysis, they were 99.9 atomic% Ni, 0.1 atomic% Al, and 0 atomic% Zr. From this result, it can be seen that after the Al dissolution step, only a slight amount of Al component remains in the completed porous layer portion, and Zr is not detected at all. From this, it can be seen that when a rare earth such as Zr was added during Al electrodeposition for forming the NiAl layer, Zr contained in the NiAl layer together with Al was completely dissolved in the Al melting stage.

(Test 9)
Next, Al electrolysis was performed using the molten salt of Example 6 to produce a Ni substrate with a NiAl layer. That is, Al electrodeposition was performed using a molten salt containing 3.5 mol% Al and 0.1 mol% Hf in an equimolar amount of NaCl-KCl. Al electrodeposition is a constant potential electrodeposition at a molten salt temperature of 900 ° C., a constant anode potential of −1.5 V, and a time of 3.6 ks.

  About the sample which cut | disconnected the sample after Al electrodeposition in the depth direction with the automatic precision cutter, and grind-processed the cross section with the abrasive paper, it is a scanning electron microscope (SEM) (JXA-8230 by JEOL Ltd., acceleration voltage 15kV, reflection) Observation by electron detection). The sample was subjected to line analysis in the depth direction by energy dispersive X-ray spectroscopy (EDS) to calculate the composition distribution.

  FIG. 12 is an explanatory diagram for explaining the composition distribution in the depth direction, and shows a graph of the composition distribution together with a photograph of the SEM observation result.

From FIG. 12, it can be seen that even when HfF ₄ is added, a NiAl layer is formed by Al electrodeposition. As a result of composition analysis, the composition of the NiAl layer in this case was NiAl. Further, as shown in FIG. 12, Hf contained in the NiAl layer is extremely small.

  This result shows that there is almost no difference from the case where Y or Zr is added. Therefore, it can be seen that even when Hf is added, a porous layer can be formed by applying the same anode potential as when Y or Zr is added as the Al dissolution stage.

(Test 10)
Next, the Al electrodeposited with varying concentrations of YF _3, was measured mass increase before and after Al electrodeposition.

In the order of concentration of YF _3, Example 3 (YF ₃ concentration 0 mol%), Example 1 (YF ₃ concentration 0.05 mol%), Example 2 (YF ₃ concentration 0.1 mol%), Example 7 (YF ₃ Each molten salt of Example 8 (YF ₃ concentration 0.3 mol%) was used. All of the AlF ₃ concentrations are 3.5 mol%. All the Al electrodepositions are constant potential electrodepositions at 900 ° C., a constant anode potential of −1.5 V, and a time of 3.6 ks.

The mass increase is the mass increase per unit area, which is a value obtained by measuring the mass before and after Al electrodeposition, subtracting the mass before Al electrodeposition from the mass after Al electrodeposition, and dividing the result by the surface area of the Ni substrate. It calculated | required as quantity (DELTA) W (g / m < ² >).

FIG. 13 is a graph showing the relationship between the mass increase amount ΔW per unit area and the YF ₃ concentration in Al electrodeposition.

From the graph of FIG. 13, it can be seen that the mass increases most when Y is not added. As the concentration of YF ₃ increases, the amount of increase in mass decreases. This result, in Test 2, and the cathode potential -1.5V Example 1 in FIG. 4 (b), in comparison with the cathode potential -1.5V Example 2 in FIG. 4 (d), the YF ₃ The higher concentration is consistent with the thinner NiAl layer.

From the graph of FIG. 13, it can be seen that when the concentration of YF ₃ exceeds 0.2 mol%, the amount of mass increase is reduced to half or less compared to the case where YF ₃ is not added. This indicates that the electrodeposition of Al is suppressed when the concentration of YF ₃ is increased too much. For this reason, it is preferable that the rare earth concentration when adding rare earth is 0.2 mol% or less.

  According to the present embodiment and examples described above, the following effects are obtained.

  A nickel aluminide alloy layer was formed by electrodepositing Al on the surface of the Ni substrate in the Al electrodeposition stage, and a Ni porous layer was formed by dissolving Al from the nickel aluminide alloy layer in the Al melting stage. . Thereby, porous nickel can be manufactured without using a strong alkali. Therefore, since no strong alkali is used, the finished porous nickel is easy to handle because there is no hydrogen adsorption. Moreover, since it is produced at high temperature, the finished porous nickel is stable at high temperature. Furthermore, there is no problem of waste liquid because no acid or alkali is used. Furthermore, in Al electrodeposition, any shape can be deposited by changing the shape of Ni as a base material in various ways, so that it is possible to produce porous nickel having a complicated shape.

  And since Al is electrodeposited, it is not necessary to use a lot of expensive rare earths. Even if it is used, a very small amount is sufficient. For this reason, material cost is cheap compared with a prior art (nonpatent literature 1). In addition, since the molten salt is NaCl-KCl, the material cost is low. Further, as can be seen from the examples, even if the Al electrodeposition stage is long, it is 3.6 ks, and the Al dissolution stage is similarly long, it is 3.6 ks. . In addition, since the NiAl layer obtained by electrodeposition can have a thickness close to 100 μm, the thickness of the porous layer is also close to that. This makes it possible to reduce the entire manufacturing cost.

  Although the embodiments and examples to which the present invention is applied have been described above, the present invention is not limited to the above-described embodiments and examples. The present invention can be implemented in various forms based on the technical idea described in the claims, and these are also within the scope of the present invention.

100 molten salt,
101 Ni substrate,
101a Ni base material with NiAl layer,
102 NiAl layer,
103 porous layer,
200 Electrolytic dissolution apparatus,
201 electric furnace,
202 quartz tube,
203 alumina crucible,
204 lid,
206 exhaust pipe,
210 potentiostat,
211 reference electrode,
212 counter electrode,
213 working electrode,
214 temperature sensor,
220 Electric furnace control device.

Claims (5)

A molten salt preparation step of preparing an aluminum-containing molten salt comprising sodium chloride, potassium chloride, and aluminum;
An aluminum electrodeposition step of forming a nickel aluminide alloy layer by applying a potential at which aluminum is electrodeposited to a nickel base immersed in the aluminum-containing molten salt;
An aluminum melting step of forming a porous layer by dissolving the aluminum from the nickel aluminide alloy layer by applying a potential that dissolves aluminum and does not dissolve nickel to the nickel base material on which the nickel aluminide alloy layer is formed When,
A method for producing porous nickel, comprising: In the aluminum electrodeposition step, when a reference electrode and a counter electrode are immersed in the aluminum-containing molten salt and the nickel base material is used as a cathode, the cathode potential with respect to the reference electrode becomes −1.8 V to −1.2 V. And
In the aluminum dissolution step, when the reference electrode and the counter electrode are immersed in the aluminum-containing molten salt and the nickel base material on which the nickel aluminide alloy layer is formed is used as an anode, the anode potential with respect to the reference electrode is -1. The method for producing porous nickel according to claim 1, wherein 25 V to −0.3 V is set.   The porous salt according to claim 1 or 2, wherein the molten salt preparation step uses aluminum fluoride as an aluminum source, and makes the concentration of the aluminum fluoride 1-5 mol% with respect to the total amount of the aluminum-containing molten salt. Nickel manufacturing method.   The production of porous nickel according to any one of claims 1 to 3, wherein the molten salt preparation step further includes at least one element of yttrium, zirconium, and hafnium in the aluminum-containing molten salt. Method.   The molten salt preparation step includes any one metal element selected from the group consisting of yttrium fluoride, zirconium fluoride, and hafnium fluoride as an element source of at least one of yttrium, zirconium, and hafnium. The manufacturing method of the porous nickel of Claim 4 which makes the density | concentration of any one said metal fluoride 0.01-0.2 mol% with respect to the whole quantity of the said aluminum containing molten salt.