JP2005248192A - Method for manufacturing thin film for separating hydrogen, and palladium plating bath - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a thin film for separating hydrogen, and a palladium plating bath in which a hydrogen separating film to be used for, for example, a modified fuel cell is suitably manufactured, the hydrogen separating film is reduced in film thickness, hydrogen can be separated at high purity, a fuel reformer is reduced in size and weight, the modification reaction is performed with high efficiency and high economical efficiency a palladium thin film can be suitably manufactured by the plating method in the plating bath, the use of plating liquid is reduced, a uniform palladium film can be deposited, and the plating productivity can be improved. <P>SOLUTION: In the method for manufacturing the thin film for separating hydrogen, metal ions in plating liquid 10 stored in a reaction bath 1 are deposited on a work 18 to be plated. Plating liquid 10, supercritical state or substance formed therein, and surfactant 11 are stored in the reaction bath 1. After the super-critical state and the emulsion state are formed in the reaction bath 1, the metal ions are diffused to be deposited on the work 18 to be plated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is suitable, for example, for the production of a hydrogen separation membrane used in a reforming fuel cell. The hydrogen separation membrane can be thinned to separate hydrogen with high purity. High efficiency and economic efficiency are achieved, and a dense and uniform thin film without pinholes can be obtained at a low cost. It is also suitable for a plating bath for producing a palladium thin film by a plating method as a hydrogen separation film. The present invention relates to a method for producing a thin film for hydrogen separation and a palladium plating bath, which can reduce the amount used and deposit a uniform palladium film and improve the productivity of plating.

Recently, from the viewpoint of environmental problems, energy security, and the like, the development, practical application and popularization of fuel cells are strongly expected.
Among the fuel cells, there are solid polymer fuel cells for reforming various hydrocarbons and alcohol fuels, and these cells have a low operating temperature and use platinum or a platinum alloy as an electrode. High-purity hydrogen that does not contain electrode poisoning substances such as carbon oxide is required.

As a means for hydrogen separation / purification in obtaining such high-purity hydrogen, a membrane separation method capable of continuous operation and miniaturization with energy-saving technology without phase transition is attracting attention. Application to hydrogen production is under consideration.
In particular, metal membranes for hydrogen separation, such as palladium, have the fastest hydrogen diffusion in the metal, excellent heat resistance, and can be used in high-temperature reaction fields, so the separation membrane is built into the fuel reformer. However, application to so-called membrane reformers has been attempted.

In particular, a palladium alloy membrane, which is a non-porous metal membrane, has an advantage that the separated hydrogen can be used as it is in a polymer electrolyte fuel cell because the gas separation ability is extremely high and the hydrogen purity can be increased (for example, patent documents). 1).
However, since palladium is an expensive metal and hinders the practical use and spread of fuel cells, when a palladium alloy film is used in a fuel cell, it is necessary to reduce the amount of metal used by reducing the film thickness.
Therefore, in consideration of the mechanical strength of palladium, the thin film of palladium is made of porous film ceramics or porous stainless steel as a support, and the support is covered with the palladium thin film.

As the palladium thinning method, a rolling method, a vacuum deposition method, a sputtering method, a chemical vapor deposition method, an electrolytic plating method, an electroless plating (chemical plating) method, and the like are known.
Among these, the rolling method mechanically thins the metal pieces, so there is a certain limit to thinning the film, and the above-mentioned vapor deposition method and plating method cannot avoid the occurrence of pinholes. There is a problem that the separation selectivity is lowered, and the pinhole is gradually expanded by the thermal cycle during operation, which promotes the reduction of the hydrogen separation selectivity.

  Among them, as a solution to the problem of the plating method, a plating solution, an object to be processed, and a surfactant are contained in a bath, and supercritical carbon dioxide is introduced into the bath to emulsify the bath. There is a supercritical plating method in which an electroplating is performed under good conditions, a uniform and thin metal film can be deposited, and the amount of plating solution used and the amount of waste solution can be reduced (for example, Patent Document 2). ).

However, in the electroplating method, when the shape of an object to be processed is generally complicated, it is difficult to achieve uniformity in the thickness of the plating film, and it is difficult to obtain a thin film and uniformity.
By the way, although the supercritical plating method is suggested to be applied to electroless plating, it is based on the condition that the object to be plated is immersed. In addition, since supercritical carbon dioxide dissolves in the plating solution and becomes acidic, and the pH of the plating solution fluctuates, there is a problem that a homogeneous plating film cannot be obtained with an alkaline plating solution, and there is a problem immediately. It is difficult to adopt.

On the other hand, as an electroless palladium plating solution, palladium chloride is used as a palladium ion source, ammonium ion or ethylenediamine as a complexing agent for palladium ions, and sodium hypophosphite, sodium borohydride, dimethylamine borane, or sodium formate as reducing agents. There are those using phosphate, tetraborate, phthalate, acetate, citrate and the like as pH adjusters.
Among the above plating solutions, when sodium formate is used as the reducing agent, the plating deposition rate is slowed down. For this reason, formate is used as the reducing agent with excellent plating deposition rate, and a tetraammine palladium compound is used as the palladium ion source ( For example, Patent Document 3).

  However, while the plating solution can eliminate the delay of the plating deposition rate, it suppresses the generation of hydrogen gas that is inevitably generated during electroless plating. There is a problem that it floats inside and adheres to the surface of the object to be plated, which causes uneven plating and pinholes, and a dense and uniform plating film cannot be obtained.

JP 2003-308869 A Japanese Patent Laid-Open No. 2003-321791 JP 2000-129454 A

  The present invention solves such a problem, and is suitable for manufacturing a hydrogen separation membrane used for, for example, a reforming fuel cell. The hydrogen separation membrane can be thinned to separate hydrogen with high purity. Light weight, high efficiency of reforming reaction and economic efficiency, and a precise and uniform thin film without pinholes can be obtained. Also suitable as a plating bath when a palladium thin film is produced by a plating method as a hydrogen separation membrane. Thus, an object of the present invention is to provide a method for producing a thin film for hydrogen separation and a palladium plating bath, which can reduce the amount of plating solution used and deposit a uniform palladium film and improve the productivity of plating.

  According to a first aspect of the present invention, there is provided a method for producing a hydrogen separation thin film in which metal ions in a plating solution stored in a reaction bath are deposited on an object to be plated. Then, after containing a surfactant and forming a supercritical state and an emulsion state in the reaction bath, the metal ions are diffused and deposited on the object to be plated. Dissolve the generated gas in a supercritical material, prevent retention in the plating solution, and crush and compress the generated gas bubbles to make them finer, making the surfactant work efficiently on the bubbles. It is suitable for a method for producing a hydrogen separation membrane for use in a reformed fuel cell, which promotes peeling from the object to be plated and further promotes the dissolution to obtain a dense and uniform thin film without pinholes.

In the invention of claim 2, the plating solution and the reducing agent are separately introduced into the reaction bath at a time, and when producing a thin film by the electroless plating method, the oxidation-reduction reaction is prevented until the time of deposition of metal ions. In the meantime, a supercritical state and an emulsion state of the reaction bath are formed, so that a reasonable thin film can be manufactured.
According to a third aspect of the invention, the object to be plated and the plating solution excluding the reducing agent are always kept in a non-contact state to reduce the amount of the plating solution and prevent the occurrence of displacement plating before the deposition of metal ions. In addition, the adhesion of the plating film is strengthened.

According to a fourth aspect of the present invention, the object to be plated and a plating solution containing a surfactant are always kept in a non-contact state, and metal ions are applied to the object to be plated when a supercritical state and an emulsion state of the reaction bath are formed. The amount of the plating solution containing the surfactant is reduced by bringing them into contact with each other, and the occurrence of displacement plating before the deposition of metal ions is prevented, thereby strengthening the adhesion of the plating film.
In a fifth aspect of the present invention, after the supercritical state and emulsion state of the reaction bath are formed, a reducing agent is introduced into the reaction bath so as to rationally manufacture a thin film by an electroless plating method.

According to a sixth aspect of the present invention, palladium ions are deposited on the object to be plated to realize a rational production method of a palladium thin film, and a palladium thin film for hydrogen separation suitable for a reformed fuel cell can be provided.
In the invention of claim 7, supercritical carbon dioxide is introduced after the alkaline plating solution is contained in the reaction bath, the supercritical carbon dioxide is dissolved in the plating solution, and the plating solution is adjusted to a predetermined acidic acid concentration. The plating solution is prepared to an acid concentration capable of plating with an inexpensive material.

The invention of claim 8 is a palladium plating bath containing at least a palladium ion supply source in a plating solution, wherein the plating bath contains a supercritical state or a substance forming the supercritical state, and a surfactant that forms an emulsion state. In the plating method that makes full use of the state, a reliable and stable palladium thin film can be obtained, and the plating solution and the surfactant can be reduced in quantity.
The invention according to claim 9 is characterized in that the palladium plating bath contains palladium chloride as a source of palladium ions, ethylenediamine as a complexing agent, and phosphinic acid, phosphonic acid or trimethylamine borane as a reducing agent. At this time, an optimum reducing agent can be selected according to the working conditions.

The invention of claim 10 is characterized in that the palladium plating bath contains palladium chloride as a source of palladium ions, ethylenediamine as a complexing agent, phosphinic acid as a reducing agent, and thioglycolic acid as an improving agent. A specific plating bath suitable for manufacturing a thin palladium film is provided.
The invention according to claim 11 is characterized in that the palladium plating bath contains palladium chloride as a source of palladium ions, ethylenediamine as a complexing agent, phosphonic acid as a reducing agent, and thioglycolic acid as an improving agent. A specific plating bath suitable for manufacturing a thin palladium film is provided.

The invention of claim 12 is characterized in that the palladium plating bath contains palladium chloride as a source of palladium ions, ethylenediamine as a complexing agent, trimethylamine borane as a reducing agent, and thioglycolic acid as an improving agent. A specific plating bath suitable for manufacturing a thin palladium film is provided.
In the invention of claim 13, the plating solution is alkaline when accommodated in the plating bath, and supercritical carbon dioxide is dissolved in the plating solution to a predetermined acidic concentration, so that the plating solution can be plated with an inexpensive material. Try to prepare.

  According to the first aspect of the present invention, a plating bath, a supercritical state or a substance forming the same, and a surfactant are contained in a reaction bath, and after forming a supercritical state and an emulsion state in the reaction bath, the metal ions are added. Because it diffuses and deposits on the object to be plated, the gas generated during plating is dissolved in the supercritical material by the plating method that makes full use of the supercritical state, and the retention of the gas in the plating solution is prevented. Crushing and compressing the material to make it finer, and using a surfactant efficiently, promotes the exfoliation of the bubbles from the object to be plated, and further promotes the dissolution to obtain a dense and uniform thin film without pinholes. Therefore, there is an effect suitable for a method for producing a hydrogen separation membrane used in a reforming fuel cell.

In the invention of claim 2, since the plating solution and the reducing agent are separately introduced into the reaction bath, when the thin film is produced by the electroless plating method, the oxidation-reduction reaction is performed until the deposition of metal ions. In the meantime, a supercritical state and an emulsion state of the reaction bath are formed, and a reasonable thin film can be manufactured.
In the invention of claim 3, since the object to be plated and the plating solution excluding the reducing agent are always in a non-contact state, the amount of the plating solution can be reduced and the occurrence of displacement plating before the deposition of metal ions. Can be prevented, and the adhesion of the plating film can be strengthened.

According to a fourth aspect of the present invention, the object to be plated and a plating solution containing a surfactant are always kept in a non-contact state, and metal ions are applied to the object to be plated when a supercritical state and an emulsion state of the reaction bath are formed. Since they are brought into contact with each other and deposited, the amount of the plating solution containing the surfactant can be reduced, and the occurrence of displacement plating before the deposition of metal ions can be prevented, and the adhesion of the plating film can be strengthened.
In the invention of claim 5, since a reducing agent is introduced into the reaction bath after the supercritical state and emulsion state of the reaction bath are formed, it is possible to rationally manufacture a thin film by an electroless plating method.

According to the invention of claim 6, since palladium ions are deposited on the object to be plated, it is possible to realize a rational method for producing a palladium thin film and to provide a palladium thin film for hydrogen separation suitable for a reformed fuel cell.
In the invention of claim 7, supercritical carbon dioxide is introduced after the alkaline plating solution is contained in the reaction bath, the supercritical carbon dioxide is dissolved in the plating solution, and the plating solution is adjusted to a predetermined acidic acid concentration. Since it is prepared, the plating solution can be adjusted to an acidic concentration capable of plating with an inexpensive material.

In the invention of claim 8, since the plating bath contains a supercritical state or a substance forming the same and a surfactant that forms an emulsion state, a reliable and stable palladium thin film can be obtained in a plating method using the supercritical state. As a result, the plating solution and the surfactant can be reduced in quantity.
In the invention of claim 9, since the palladium plating bath contains palladium chloride as a palladium ion supply source, ethylenediamine as a complexing agent, and phosphinic acid, phosphonic acid or trimethylamine borane as a reducing agent, the electroless plating method is used. At the time of work, an optimum reducing agent can be selected according to work conditions.

Since the palladium plating bath contains palladium chloride as a palladium ion source, ethylenediamine as a complexing agent, phosphinic acid as a reducing agent, and thioglycolic acid as an improving agent, the palladium plating bath is uniform and A specific plating bath suitable for production of a dense palladium thin film can be provided.
Since the palladium plating bath contains palladium chloride as a source of palladium ions, ethylenediamine as a complexing agent, phosphonic acid as a reducing agent, and thioglycolic acid as an improving agent, the palladium plating bath is uniform and A specific plating bath suitable for production of a dense palladium thin film can be provided.

Since the palladium plating bath contains palladium chloride as a palladium ion source, ethylenediamine as a complexing agent, trimethylamine borane as a reducing agent, and thioglycolic acid as an improving agent, the palladium plating bath is uniform and A specific plating bath suitable for production of a dense palladium thin film can be provided.
In the invention of claim 13, the plating solution is alkaline when accommodated in the plating bath, and supercritical carbon dioxide is dissolved in the plating solution to obtain a predetermined acidic concentration. Therefore, the plating solution can be plated with an inexpensive material. The concentration can be adjusted.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will now be given of illustrated embodiments in which the present invention is applied to a case where a palladium thin film is manufactured by an electroless plating (chemical plating) method as a hydrogen separation thin film suitable for a reformed fuel cell. 1 is a sealable reaction bath composed of a pressure vessel, and an open / close lid (not shown) is provided at an appropriate position so that a substrate, which will be described later, can be taken in and out.

First to third conduits 2 to 4 are piped to the reaction bath 1, and the other end of the first conduit 2 is communicated with a pressure vessel 5 filled with a supercritical material, in the embodiment, carbon dioxide. Yes.
A condenser 6 for liquefying the carbon dioxide, a pressure pump 7 and a heater 8, and an on-off valve 9 are inserted in the first conduit 2, and the carbon dioxide is supercritical (7.3 MPa, 31. 1 ° C.), which can be introduced into the reaction bath 1. In the embodiment, the inside of the reaction bath 1 is formed at 10 MPa and 50 ° C.

The other end of the second conduit 3 can be communicated with a storage tank 12 containing a plating solution (excluding a reducing agent) 10 and a predetermined surfactant 11, and the plating solution 10 and the surfactant 11 are connected to each other. It can be introduced into the reaction bath 1 via a liquid feed pump 13 inserted in the second conduit 3.
As shown in FIG. 2, the plating solution 10 of the embodiment includes 0.01 mol / L of palladium chloride (PdCL ₂ ) as a palladium ion supply source, 0.08 mol / L of ethylenediamine as a complexing agent, and thioglycolic acid as an improving agent. Prepare 30 mg / L and make it alkaline with pH 11.7.
In this case, the volume ratio of the plating solution 10 and the surfactant 11 is about 4 to 1 to 3 to 2, and the total amount thereof is a substrate described later as shown in FIG. 6A when the reaction bath 1 is introduced. It is metered so that it can be accommodated in a non-contact state directly underneath.

The other end of the third conduit 4 is allowed to communicate with a storage tank 15 that stores the reducing agent 14, and the reaction bath 1 is connected via a liquid feed pump 16 having the reducing agent 14 inserted into the third conduit 4. It is possible to introduce to. In the figure, reference numeral 17 denotes an on-off valve inserted in the third conduit 4.
The reducing agent 14 of the embodiment uses sodium hypophosphite NaH ₂ PO ₂ (phosphinic acid) 0.06 mol / L, and is adjusted to about 1/5 of the capacity of the plating solution 10.

  In the figure, reference numeral 18 denotes a substrate which is an object to be processed constituting the above-mentioned support. A through-hole 24 is formed in a porous alumina flat plate, which is a conductive film to the extent that the pores are not blocked. An ultra-thin palladium is coated and suspended in the reaction bath 1 during plating so that the surface of the film can be coated with a palladium thin film, in the embodiment, a palladium-phosphorus alloy.

Reference numeral 19 denotes a stirrer. In the embodiment, a cross stirrer having high stirrability is used. Reference numeral 20 denotes an exhaust pipe capable of communicating with the atmosphere. A back pressure valve 21 and an on-off valve 22 are inserted into the pipe 20. Yes. Reference numeral 23 denotes a heater provided on the outer surface of the reaction bath 1.
In this case, the intended purpose can also be achieved by omitting the heater 23 and installing the reaction bath 1 in a thermostat (not shown).

The present invention configured as described above requires a reaction bath 1 that is a pressure vessel that can be hermetically sealed and a means for forming supercritical carbon dioxide introduced into the bath 1.
These facilities are unique to the conventional electroless plating method. Of these, the reaction bath 1 can be reduced in size and weight compared to the bath of a conventional electroless plating apparatus by reducing the amount of plating solution to be accommodated. Further, the pH adjustment means for the plating solution can be simplified by reducing the amount of the plating solution to be used, and a conventional regeneration tank can be omitted.

Next, when a palladium thin film is obtained using the above equipment, the surface of the substrate 18 is coated with ultra-thin palladium, and the surface is activated and suspended in the reaction bath 1.
The properties of the substrate 18 and the surface and cross section before and after the coating of the ultra-thin palladium film are as shown in FIGS. The substrate 18 is heated to about 50 ° C. through, for example, the heater 23 to promote the subsequent deposition of the palladium film.

Thereafter, a plating solution 10 excluding the reducing agent 14 and a predetermined amount of a predetermined surfactant 11 are sent from the storage tank 12 to the reaction bath 1 via a liquid feed pump 13, and a stirrer 19 is installed. This situation is as shown in FIG.
In the embodiment, the plating solution 10 is 0.01 mol / L of palladium chloride as a palladium ion supply source, 0.08 mol / L of ethylenediamine as a complexing agent, and 30 mg of thioglycolic acid as an improving agent as shown in FIG. / L is adjusted to an alkaline pH of 11.7.
The total amount is about 25 mL, and they are accommodated in the reaction bath 1 in a non-contact state immediately under the substrate 18 as shown in FIG. The volume ratio of the plating solution 10 and the surfactant 11 excluding the reducing agent is about 4 to 1 to 3 to 2.

Thereafter, the carbon dioxide filled in the pressure vessel 5 is led to the first conduit 2 and liquefied by the condenser 6 and pressurized and heated to 10 MPa and 50 ° C. by the pressure pump 7 and the heater 8. Critical carbon dioxide is formed and introduced into reaction bath 1.
After the introduction, the supercritical carbon dioxide is dissolved in the plating solution 10 to adjust the plating solution 10 to an acidic pH of 2 to 4, and mixed with the surfactant 11 to become an emulsion, as shown in FIG. Such an emulsion state is formed. Then, the emulsion state is left for a while, and when the state is stabilized, the stirrer 19 is driven at about 650 rpm to make the emulsion state uniform.

Under such circumstances, a predetermined amount of reducing agent 14 made of phosphinic acid, in the embodiment, 5 mL, that is, 0.06 mol / L is sent from the storage tank 15 to the reaction bath 1 via the liquid feed pump 16.
If it does in this way, the reducing agent 14 will spread | diffuse rapidly in an emulsion state, the said board | substrate 18 will exhibit the condition where it was immersed in the emulsion of the plating solution 10 containing the reducing agent 14, and an electroless-plating reaction will start. This situation is as shown in FIG.

  That is, the electroless plating reaction is performed by the reducing agent 14 made of the metal salt palladium chloride, which is the main component of the substrate 18 and the plating solution 10, and phosphine, phosphine ions are oxidized, palladium ions are reduced, Ions are deposited on the surface of the substrate 18. The precipitation reaction was continued by the catalytic action of palladium chloride. In the embodiment, the plating reaction was performed for 2 hours.

At the time of electroless plating with the phosphinic acid reducing agent, the following reaction is performed in the reaction bath 1.
H ₂ PO ₂ ⁻ + 3OH ⁻ → HPO ₃ ²⁻ + 2H ₂ O + 2e ⁻
Pden ²⁺ + 2e ⁻ → Pd + en

During such electroless plating, palladium ions and phosphine ions are rapidly and accurately diffused into the reaction bath 1 by supercritical carbon dioxide, and exchange of these ions or electrons is performed uniformly and vigorously. Ions are deposited on the surface of the substrate 18.
Therefore, compared to the conventional electroless plating method, the plating is better, it is possible to obtain a uniform plating thickness for the object to be plated in a complicated shape, and the thickness can be reduced, which is suitable for palladium plating which is a noble metal. become. Moreover, due to the excellent diffusivity of the supercritical carbon dioxide, the precipitation is intermittently performed, the crystal of the deposited film is refined, and the densification of the plated film is promoted.

On the other hand, during the electroless plating reaction, hydrogen gas is mainly generated, and the bubbles may stay on the surface of the substrate 18 or move on the surface, which may cause uneven plating or chipped pinholes. However, the reaction bath 1 is placed under a supercritical high pressure, and under this high pressure, dissolution of the generated gas into the supercritical carbon dioxide or the plating solution 10 is promoted, and the bubbles are compressed and refined. Further, the surfactant works efficiently on the finer bubbles, and the bubbles adhering to the surface of the substrate 18 are quickly peeled off to promote dissolution in the supercritical carbon dioxide and the plating solution 10.
Therefore, the occurrence of the plating unevenness, chipped pinholes and the like can be prevented, and a uniform and dense plating film can be obtained.

The palladium film on the substrate 18 thus obtained is as shown in FIG. 7, and it is as follows when compared with the conventional electroless plating method shown in FIG.
That is, in the precipitated crystal according to the present invention, as shown in FIG. 7A, the cracks generated by the conventional plating method of FIG. 8A disappeared, and a fine and dense precipitated crystal was obtained. Further, as shown in FIG. 8B, the deposited film according to the present invention has a uniform film thickness as compared with the conventional electroless plating method, and the average film thickness is 4.10 μm, which is slightly thicker than the conventional 3.50 μm. The standard deviation was 0.38, which was smaller than the conventional 0.46, and it was confirmed that the film thickness was improved.
These results are all due to the reasons described above. The gas generated during plating dissolves in supercritical carbon dioxide, and its generation is suppressed or prevented, and it is based on the excellent diffusivity of supercritical carbon dioxide. confirmed.

After completion of the plating time, the driving of the pressurizing pump 7 and the stirring bar 19 is stopped, the on-off valve 22 is opened to reduce the pressure in the reaction bath 1, and the substrate 18 is taken out from the reaction bath 1.
In this way, the supercritical carbon dioxide is depressurized and shifts to a state below the critical point, and is rapidly vaporized or liquefied to generate a flow in the system, which is quickly discharged to the outside.
At that time, the plating solution adhering to the substrate 18 is blown off, and drying of the substrate 18 is promoted, and the plating solution 10 and the surfactant 11 remain in the reaction bath 1 in two layers. This situation is as shown in FIG.

Thereafter, when the plating solution 10 and the surfactant 11 remaining in the reaction bath 1 are used, it is necessary to replenish those shortages and adjust the pH. However, as described above, the present invention has a small amount. Since the plating solution 10 and the surfactant 11 are used, the replenishment amount or pH adjustment amount is small, and each can be handled with appropriate dropping means, so that it requires large-scale facilities and complicated work as in the past. do not do.
Further, since supercritical carbon dioxide is dissolved in the plating solution 10 to obtain a predetermined acidic concentration necessary for plating, it is cheaper and safer than when using an expensive and toxic acidic chemical solution as in the past. Can work.

9 to 14 show other embodiments of the present invention, and the same reference numerals are used for portions corresponding to the above-described configuration. In addition, since the electroless plating method in these embodiments is substantially the same as the above-mentioned embodiment, the description is abbreviate | omitted and the structure of the different plating solution and the obtained plating film are demonstrated.
9 to 11 show a second embodiment of the present invention. In this embodiment, 0.02 mol / L of phosphonic acid is used as the reducing agent 14 instead of phosphinic acid, and the plating solution is shown in FIG. As described above, palladium chloride was used as a source of palladium ion at 0.01 mol / L, ethylenediamine as a complexing agent was used as 0.08 mol / L, and thioglycolic acid was used as an improving agent at a pH of 10.6. Yes.

Wherein when electroless plating using a reducing agent phosphonic acid, HPO ₃ ^2- + 2OH following reaction takes place in the reaction bath within ^{_{1 - → HPO 4 2- + H}} 2 O + 2e -
HPO ₃ ²⁻ + H ₂ O → H ₂ PO ₄ ⁻ + H ⁺ + 2e ⁻
Pden ²⁺ + 2e ⁻ → Pd + en

The palladium film on the substrate 18 thus obtained is as shown in FIG. 10, and is compared with the conventional electroless plating method shown in FIG. 11 as follows.
That is, the precipitated crystal according to the present invention is finer and denser than the precipitated crystal formed by the conventional plating method of FIG. 8A, as shown in FIG. 10A, and the film thickness is as shown in FIG. Compared with the conventional electroless plating method shown in FIG. 11B, the film thickness is uniform and the average film thickness is 7.03 μm, which is slightly thicker than the conventional 5.70 μm, but its standard deviation is 0.39, which is It was smaller than 0.46, and the improvement in film thickness uniformity was confirmed.
These results are all due to the reasons described above. The gas generated during plating dissolves in supercritical carbon dioxide, and its generation is suppressed or prevented, and it is based on the excellent diffusivity of supercritical carbon dioxide. confirmed.

  FIGS. 12 to 14 show a third embodiment of the present invention. In this embodiment, 0.06 mol / L of trimethylamine borane is used as the reducing agent 14 instead of phosphinic acid and phosphonic acid, and the plating solution is as shown in FIG. As described above, the pH was adjusted to 10.6 using 0.01 mol / L of palladium chloride as the source of palladium ions, 0.08 mol / L of ethylenediamine as the complexing agent, and 50 mg / L of thioglycolic acid as the improving agent. ing.

At the time of electroless plating with the reducing agent of trimethylamine borane, the following reaction is performed in the reaction bath 1.
(CH ₃ ) ₃ BH ₃ + 7OH ⁻ → (CH ₃ ) ₂ + BO ₂ + 5H ₂ O + 6e ⁻
Pden ²⁺ + 2e ⁻ → Pd + en

The palladium film on the substrate 18 thus obtained is as shown in FIG. 13 and is compared with the conventional electroless plating method shown in FIG. 14 as follows.
That is, the precipitated crystal according to the present invention is finer and denser than the precipitated crystal by the conventional plating method of FIG. 14A as shown in FIG. 13A, and the film thickness is as shown in FIG. Compared to the conventional electroless plating method shown in FIG. 14B, the film thickness is uniform and the average film thickness is 5.03 μm, which is slightly thicker than the conventional 3.85 μm, but its standard deviation is 0.39, which is Although slightly larger than 0.30, the uniformity of the film thickness was confirmed.
These results are all due to the reasons described above. The gas generated during plating dissolves in supercritical carbon dioxide, and its generation is suppressed or prevented, and it is based on the excellent diffusivity of supercritical carbon dioxide. confirmed.

  As described above, the method for producing a thin film for hydrogen separation and the palladium plating bath of the present invention can reduce the hydrogen separation membrane to a high purity, reduce the size and weight of the fuel reformer, and improve the efficiency of the reforming reaction. In addition, it is possible to obtain a dense and uniform thin film without pinholes, and it is suitable for a plating bath when a palladium thin film is produced by a plating method as a hydrogen separation film, reducing the amount of plating solution used. A uniform palladium film can be deposited, and the productivity of plating can be improved. For example, it is suitable for producing a hydrogen separation membrane used in a reformed fuel cell.

It is a schematic diagram which shows the condition of the thin film manufacture by the electroless plating (chemical plating) method applied to the thin film manufacture of this invention. It is a table | surface which shows the composition of the plating solution which uses the phosphinic acid applied to the thin film manufacture of this invention as a reducing agent. It is a table | surface which shows the shape of the board | substrate applied to the thin film manufacture of this invention. It is a photograph figure which shows the surface condition (a) and cross-sectional condition (b) before the coating | cover in the preparation process of the board | substrate applied to the thin film manufacture of this invention. It is a photograph figure which shows the surface condition (a) and cross-sectional condition (b) after the coating | coated in the preparation process of the board | substrate applied to the thin film manufacture of this invention.

It is explanatory drawing which shows in order the thin film manufacturing process by the electroless-plating method applied to the thin film manufacture of this invention, (a) is before plating, (b) is at the time of plating, (c) has shown the condition after plating. In the supercritical electroless plating method applied to the production of the thin film of the present invention, the surface state (a) and the cross-sectional state (b) of the thin film deposited on the substrate surface using a plating solution containing phosphinic acid as a reducing agent are shown. FIG. In the conventional electroless-plating method applied to thin film manufacture, it is the photograph figure which shows the surface condition (a) and the cross-sectional condition (b) of the thin film which deposited on the substrate surface using the plating solution which uses phosphinic acid as a reducing agent. is there. It is a table | surface which shows the composition of the plating solution which uses the phosphonic acid applied to the thin film manufacture of the 2nd Embodiment of this invention as a reducing agent.

In the supercritical electroless plating method applied to the thin film production of the second embodiment, the surface condition (a) and the cross-sectional condition (a) of the thin film deposited on the substrate surface using a plating solution containing phosphonic acid as a reducing agent ( It is a photograph figure which shows b). In the conventional electroless-plating method applied to thin film manufacture, it is the photograph figure which shows the surface condition (a) and cross-sectional condition (b) of the thin film which deposited on the substrate surface using the plating solution which uses phosphonic acid as a reducing agent. is there. It is a table | surface which shows the composition of the plating solution which uses the trimethylamine borane applied to the thin film manufacture of the 3rd Embodiment of this invention as a reducing agent.

In the supercritical electroless plating method applied to the thin film production of the second embodiment, the surface condition (a) and the cross-sectional condition (a) of the thin film deposited on the substrate surface using a plating solution containing phosphonic acid as a reducing agent ( It is a photograph figure which shows b). In the conventional electroless-plating method applied to thin film manufacture, it is the photograph figure which shows the surface condition (a) and cross-sectional condition (b) of the thin film which deposited on the substrate surface using the plating solution which uses phosphonic acid as a reducing agent. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction bath 10 Plating solution 11 Surfactant 14 Reducing agent 18 To-be-plated object (board | substrate)

Claims (13)

  In the method for producing a hydrogen separation thin film in which metal ions in a plating solution stored in a reaction bath are deposited on an object to be plated, the plating solution, a supercritical state or a forming material thereof, and a surfactant are stored in the reaction bath. And forming a supercritical state and an emulsion state in the reaction bath, and then diffusing the metal ions to deposit on the object to be plated.   The method for producing a thin film for hydrogen separation according to claim 1, wherein the plating solution and the reducing agent are separately introduced into the reaction bath at intervals.   The method for producing a thin film for hydrogen separation according to claim 1, wherein the object to be plated and the plating solution excluding the reducing agent are always in a non-contact state.   2. The plating object and a plating solution containing a surfactant are always kept in a non-contact state, and metal ions are brought into contact with the object to be plated when forming a supercritical state and an emulsion state of the reaction bath. The manufacturing method of the thin film for hydrogen separation of description.   The method for producing a thin film for hydrogen separation according to claim 1 or 2, wherein a reducing agent is introduced into the reaction bath after the supercritical state and emulsion state of the reaction bath are formed.   The method for producing a thin film for hydrogen separation according to claim 1, wherein palladium ions are deposited on the object to be plated.   2. The hydrogen separation according to claim 1, wherein supercritical carbon dioxide is introduced after the alkaline plating solution is contained in the reaction bath, the supercritical carbon dioxide is dissolved in the plating solution, and the plating solution is adjusted to a predetermined acidic concentration. Thin film manufacturing method.   A palladium plating bath characterized in that, in a palladium plating bath containing at least a palladium ion supply source in a plating solution, the plating bath contains a supercritical state or a substance forming the same and a surfactant that forms an emulsion state.   The palladium plating bath according to claim 8, wherein the palladium plating bath contains palladium chloride as a palladium ion supply source, ethylenediamine as a complexing agent, and phosphinic acid, phosphonic acid, or trimethylamine borane as a reducing agent.   The palladium plating bath according to claim 8, wherein the palladium plating bath contains palladium chloride as a source of palladium ions, ethylenediamine as a complexing agent, phosphinic acid as a reducing agent, and thioglycolic acid as an improving agent.   The palladium plating bath according to claim 8, wherein the palladium plating bath contains palladium chloride as a source of palladium ions, ethylenediamine as a complexing agent, phosphonic acid as a reducing agent, and thioglycolic acid as an improving agent.   The palladium plating bath according to claim 8, wherein the palladium plating bath contains palladium chloride as a source of palladium ions, ethylenediamine as a complexing agent, trimethylamine borane as a reducing agent, and thioglycolic acid as an improving agent.   The palladium plating bath according to claim 8, wherein the plating solution is alkaline when accommodated in the plating bath, and supercritical carbon dioxide is dissolved in the plating solution to have a predetermined acidic concentration.