JP6407850B2 - Method for producing platinum powder - Google Patents

Description

  The present invention relates to a method for producing platinum powder, and more particularly to a method for producing platinum powder in which a platinum compound is reduced in a wet form to form powder.

  As an application of the platinum powder, there is an application of manufacturing a conductive film, a heating element circuit, an electrode and the like of various electronic parts using a platinum paste. A general component structure of the platinum paste includes platinum powder, an inorganic oxide such as a metal oxide or glass frit that serves as a binder for the substrate, and an organic vehicle. The platinum paste is coated by means such as screen printing on an insulating substrate such as ceramics or an element, and then the coating layer is baked to form a conductive film, a heating element circuit, an electrode, and the like.

  In recent years, in order to reduce the size and improve the performance of these electronic components, there has been an increasing demand for high precision and thinning of these conductive films, heating element circuits, electrodes, and the like. Accordingly, there is a strong demand for platinum powder not only to have a fine particle size but also to have a uniform particle size.

  As a method for producing the platinum powder, there is a method in which a platinum compound is reduced to a powder by wet processing, that is, a method called a liquid phase reduction method. This is a production method in which platinum present in the form of ions or complex ions is reduced to precipitate platinum fine powder in the liquid. For example, the precipitated powder is washed with water and dried to obtain platinum powder.

  In Patent Document 1, platinum is precipitated by reducing chloroplatinic acid or a salt thereof using a hydrazine chloride as a reducing agent and using a buffering agent such as ammonium acetate or ammonium carbonate in the reduction reaction. A method for producing platinum powder is disclosed in which the powder is separated from the solution and the residual salts are washed away. Further, it is described that a protective colloid such as polyethylene glycol can be applied to the solution in the platinum reduction precipitation reaction.

  Patent Document 2 discloses a platinum powder manufacturing method in which a hydrazine compound is used as a reducing agent for a platinum compound, an ammonia compound is used as an additive, and the platinum compound is reduced to a powder by wet processing. It is described that hydrazine compounds such as hydrazine hydrate, hydrazine hydrochloride and hydrazine sulfate can be used as the hydrazine compound.

JP 55-2766 JP-A-2-294416

  Conventionally, only powder having a small particle size and a non-uniform particle size distribution have been obtained. Or there was a subject that there was much mixing of nonspherical powder.

  An object of the present invention is to provide a production method in which platinum powder having an average particle diameter D50 in the range of 0.1 to 1 μm, a substantially spherical particle shape, and a uniform particle size distribution can be obtained. .

  As a result of intensive studies to achieve the above-mentioned object, the present inventors passed a step of pre-reducing tetravalent platinum to divalent platinum using a platinum compound having a valence of platinum of 4 as a starting material. Later, by reducing to zero-valent platinum, it was found that platinum powder having a substantially spherical particle shape and a narrow particle size distribution was obtained, and the present invention was completed.

  That is, in the method for producing platinum powder by wet reaction of a platinum compound and a reducing agent, the first aqueous solution is obtained by reacting an aqueous solution of a platinum compound having a valence of platinum with a reducing agent. The oxidation-reduction potential of the first aqueous solution is equal to or lower than the oxidation-reduction potential before adding the reducing agent in the aqueous solution of the platinum compound and equal to or higher than plus 0.3 V (vs. SHE: standard hydrogen electrode). Thus, the first step of reducing the tetravalent platinum to divalent platinum, the second aqueous solution containing a reducing agent, and the first aqueous solution are reacted to form a mixed aqueous solution. The divalent platinum is obtained by setting the oxidation-reduction potential to a potential not less than the oxidation-reduction potential before mixing with the first aqueous solution in the second aqueous solution and not more than 0.1 V (vs. SHE). Reduced to zero It is achieved by the method for manufacturing a platinum powder and obtaining a platinum powder by including a second step for precipitating platinum powder, a Te.

  In the manufacturing method, the redox potential before adding the reducing agent in the aqueous solution of the platinum compound in the first step is plus 0.5 to plus 0.7 V (vs. SHE), and in the second step It is preferable that the redox potential of the second aqueous solution before mixing with the first aqueous solution is minus 0.8 to minus 0.6 V (vs. SHE).

  Moreover, it is preferable to include an acid in the aqueous solution of the platinum compound in the first step.

  Moreover, it is preferable to include an alkali in the second aqueous solution in the second step.

  The aqueous solution of the platinum compound is preferably an aqueous solution of chloroplatinic (IV) acid.

  The acid is preferably hydrochloric acid.

  The alkali is preferably ammonia water.

  According to the present invention, it is possible to provide a production method in which platinum powder having an average particle diameter D50 in the range of 0.1 to 1 μm, a substantially spherical particle shape, and a uniform particle size distribution can be obtained.

3 is an SEM photograph of platinum powder obtained in Example 1. 4 is an SEM photograph of platinum powder obtained in Example 2. FIG. 4 is an SEM photograph of platinum powder obtained in Comparative Example 1. 4 is an SEM photograph of platinum powder obtained in Comparative Example 2.

  Hereinafter, the method for producing platinum powder of the present invention will be described in more detail.

  The present invention provides a first aqueous solution by reacting an aqueous solution of a platinum compound having a valence of platinum of 4 with a reducing agent, and the oxidation-reduction potential of the first aqueous solution is reduced to the reducing agent in the aqueous solution of the platinum compound. The first step of reducing the tetravalent platinum to divalent platinum by setting the potential to be equal to or lower than the oxidation-reduction potential before addition of 0.3 and plus 0.3 V (vs. SHE: standard hydrogen electrode) including. The reaction in the first step is referred to as a first reduction reaction (or preliminary reduction).

  The platinum compound that can be used in the present invention is a platinum compound in which the valence of platinum is tetravalent. An example of a platinum compound in which the valence of platinum is tetravalent is platinum (IV) chloride. Platinum (IV) chloroacid is preferable as a starting material of the present invention because platinum has a valence of 4 and is inexpensive and easily available.

  When a platinum compound having a valence of platinum is reduced to zero at a time to obtain platinum powder, non-uniform platinum particle powder is likely to precipitate. The uniformity of the powder can be improved.

  On the other hand, it is conceivable that a platinum compound having a valence of platinum is a starting material, but a platinum compound having a valence of platinum is very expensive even if stable, or Since it is unstable, it is difficult to use as a reaction starting material. Therefore, it is economical by reducing the valence of platinum of a stable and inexpensive tetravalent platinum compound from tetravalent to bivalent once, and reducing the divalent platinum to zero in a series of reduction operations. Thus, it is possible to stably obtain a fine, uniform and highly spherical platinum powder.

  As the reducing agent, hydrazine monohydrate, sodium borohydride (SBH), hydrazine sulfate, hydrazine monohydrochloride, or hydrazine dihydrochloride can be used.

  In the first step, first, an aqueous solution containing a platinum compound is prepared. For example, a predetermined amount of pure water and hydrochloric acid are added to a platinum chloride (IV) acid aqueous solution, and the hydrogen ion index (pH) of the aqueous solution is adjusted to a predetermined value on the acidic side, for example, pH = 0 to 1. The oxidation-reduction potential of platinum in the aqueous solution has a value of plus 0.5 to plus 0.7 V (vs. SHE). When the pH value is decreased (acidic side), the redox potential of the reducing agent increases and the reducing power decreases, and when the pH value is increased (alkaline side), the redox potential of the reducing agent decreases and the reducing power increases. Acids such as hydrochloric acid, sulfuric acid and nitric acid can be used for adjusting the hydrogen ion index (pH). The temperature of the aqueous solution is adjusted to 0 ° C. to 50 ° C., for example.

  Next, the aqueous solution containing the platinum compound is reacted with a reducing agent. Specifically, hydrazine sulfate (reducing agent) is added to the aqueous solution and stirred well to completely dissolve the hydrazine sulfate, which is used as the first aqueous solution. The reaction temperature is more preferably 15 ° C to 35 ° C. The oxidation-reduction potential of the first aqueous solution falls below the initial oxidation-reduction potential of platinum and plus 0.3 V (vs. SHE) or more by adding predetermined hydrochloric acid to the aqueous solution containing the platinum compound.

  The aqueous solution containing chloroplatinic (IV) acid exhibits a reddish orange color reflecting that the valence of platinum is tetravalent. When, for example, a predetermined hydrazine sulfate is added to the aqueous solution, the color of the aqueous solution changes to blackish red, and it can be seen that the valence of platinum is reduced to two.

  In the present invention, a second aqueous solution containing a reducing agent is reacted with the first aqueous solution to form a mixed aqueous solution, and the oxidation-reduction potential of the mixed aqueous solution is mixed with the first aqueous solution in the second aqueous solution. A second step of precipitating platinum powder by reducing the divalent platinum to zero valence by setting it to a potential not less than 0.1V (vs. SHE).

  In the second step, first, a second aqueous solution containing a reducing agent is prepared.

  As the reducing agent in the second step, hydrazine monohydrate, sodium borohydride (SBH), hydrazine sulfate, hydrazine monohydrochloride, or hydrazine dihydrochloride can be used. Here, the reducing agent in the second step may be the same as or different from the reducing agent in the first step. If the reducing agent has a strong reducing power in the second step, the resulting platinum powder tends to have a smaller particle size. Sodium borohydride (SBH) and hydrazine monohydrate have relatively strong reducing power, and hydrazine sulfate, hydrazine monohydrochloride or hydrazine dihydrochloride has relatively low reducing power. The reducing agent in the second step can be selected and used according to the particle size of the platinum powder to be obtained.

  The second aqueous solution preferably contains a dispersant. Any dispersing agent may be used as long as it has an effect of preventing the aggregation of the produced platinum powder and maintaining good dispersibility in the solvent to be used. Specifically, a compound having a capability as a surfactant or a dispersant (including a polymer compound), for example, methylcellulose can be used.

  The hydrogen ion exponent (PH) before mixing with the first aqueous solution in the second aqueous solution containing the reducing agent is adjusted to about 11-12. When the pH value is small, the size of the obtained platinum particle size is large, and when the pH value is large, the particle size tends to be small. As a method for adjusting the pH value of the second aqueous solution, an alkali may be included in the second aqueous solution containing a reducing agent. As the alkali, ammonia water can be used. In addition, it is not necessary to add an alkali when the second aqueous solution shows a target pH value before adding the alkali.

  The redox potential of the second aqueous solution is minus 0.8 to minus 0.6 V (vs. SHE).

  Next, the 2nd aqueous solution and the 1st aqueous solution are mixed on the conditions of 50 to 90 degreeC. Specifically, the second aqueous solution heated to 50 ° C. to 90 ° C. is added to the first aqueous solution and stirred. This reaction is referred to as a second reduction reaction. The oxidation-reduction potential in the mixed aqueous solution (the mixture of the second aqueous solution and the first aqueous solution) after the reaction can be obtained by adding a predetermined amount of aqueous ammonia to the second aqueous solution, for example. It falls within a value that is not less than the oxidation-reduction potential and not more than plus 0.1 V (vs. SHE).

  By setting the reaction temperature to 50 ° C. or higher, platinum powder can be stably deposited. The reaction does not proceed satisfactorily at a reaction temperature of less than 50 ° C. When it exceeds 90 ° C., the reaction is too early and the uniformity of the particle size distribution is deteriorated.

  Thereafter, an aqueous solution containing zero-valent platinum is filtered, washed, and dried to obtain platinum powder.

  Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1
At room temperature, 60 ml of pure water and 30 ml of 12N hydrochloric acid are added to 30 ml of an aqueous solution of platinum (IV) chloride (IV) containing 6 g of Pt. The pH of this aqueous solution was 0.6 when measured with a pH meter (manufactured by Toa DKK). Further, when the oxidation-reduction potential was measured by an ORP meter (manufactured by Toa DKK), it was plus 0.6 V (vs. SHE).

  This is reacted with hydrazine sulfate (reducing agent in the first step). Specifically, 0.18 g of hydrazine sulfate is added to this aqueous solution and stirred well to completely dissolve the hydrazine sulfate. The pH after the reaction was 0.5, and the redox potential was plus 0.4 V (vs. SHE). This is the first aqueous solution. In this way, platinum of the platinum compound having a valence of platinum of 4 is reduced to divalent.

  To 1,650 ml of pure water, add 10 g of methyl cellulose, 12 ml of 97% hydrazine monohydrate (reducing agent in the second step), and 30 ml of 28% aqueous ammonia, and then heat to 80 ° C. Is the second aqueous solution. The pH of this second aqueous solution was 11.4, and the redox potential was minus 0.7 V (vs. SHE).

  Next, the second aqueous solution was added to the first aqueous solution and stirred. The pH of the mixed aqueous solution after the reaction was 9.2, and the redox potential was plus 0.0 V (vs. SHE). Thereafter, the obtained aqueous solution was filtered, washed and dried.

  The platinum powder thus obtained was a spherical powder with a uniform particle size having an average particle size of 0.11 μm and a span of 0.77.

(Example 2)
The first step was performed under the same conditions as in Example 1 to obtain a first aqueous solution. The pH after the reaction was 0.5, and the redox potential was plus 0.4 V (vs. SHE).

  To 1,650 ml of pure water, 10 g of methyl cellulose and 12 ml of 97% hydrazine monohydrate (reducing agent in the second step) are added, and then heated to 80 ° C. to obtain a second aqueous solution. The pH of this second aqueous solution was 10.9, and the oxidation-reduction potential was minus 0.65 V (vs. SHE).

  Next, the second aqueous solution was added to the first aqueous solution and stirred. The pH of the mixed aqueous solution after the reaction was 1.2, and the oxidation-reduction potential was plus 0.1 V (vs. SHE). Thereafter, the obtained aqueous solution was filtered, washed and dried.

  The platinum powder thus obtained was a spherical powder having a uniform particle size with an average particle size of 0.33 μm and a span of 0.26.

(Comparative Example 1)
Comparative Example 1 is an example in which preliminary reduction is not performed.

  60 ml of pure water and 30 ml of 12N hydrochloric acid are added to 30 ml of an aqueous platinum chloride (IV) acid solution containing 6 g of Pt, and this is used as the first aqueous solution.

  After adding 10 g of methyl cellulose, 12 ml of 97% hydrazine monohydrate (reducing agent in the process corresponding to the second step), and 30 ml of 28% aqueous ammonia to 1,650 ml of pure water Heat to make the second solution.

  Next, the second aqueous solution was added to the first aqueous solution and stirred. Thereafter, the obtained mixed aqueous solution was washed, filtered, and dried. The platinum powder thus obtained was a spherical powder with an average particle size of 0.13 μm and a span of 1.01, which is not very uniform in particle size distribution.

(Comparative Example 2)
Comparative Example 2 is an example in which preliminary reduction is not performed.

  An aqueous solution obtained by adding 12 g of ammonium chloride Pt (IV) to 48 ml of pure water is heated to 30 ° C. This is the first aqueous solution.

  Add 26 ml of 40% aqueous sodium hydroxide and 2 ml of 80% hydrazine monohydrate (reducing agent in the step corresponding to the second step) to 26 ml of pure water, then heat to 30 ° C. This is the second solution.

  Next, the second aqueous solution was added to the first aqueous solution and stirred. Thereafter, the obtained aqueous solution was washed, filtered, and dried. The platinum powder thus obtained had a mean particle size of 0.24 μm and a span of 0.83, and was a non-spherical powder.

About the obtained platinum powder, the scanning microscope (SEM) photograph was image | photographed and the particle size distribution was measured. Specifically, a scanning microscope (SEM) photograph was taken, and the size of each particle (100 particles) of the platinum particles was visually measured using a scale. Then, particle diameters D90, D10, and D50 corresponding to an integrated value of the particle size distribution corresponding to 90%, 10%, and 50% were obtained. D50 was defined as the average particle size. Span was obtained as an index of particle size distribution. Here, the span refers to a value obtained by calculating from D90, D10, and D50 according to the following formula, and is an index of particle size variation. A smaller span indicates a narrower particle size distribution and a uniform particle size.
Span = (D90-D10) / D50

  Scanning electron microscope (SEM) images of platinum powders of Examples and Comparative Examples are shown in FIGS. 1 to 4, and average particle diameters and span values are shown in Table 1. In Examples 1 and 2, it can be seen that platinum powder having an average particle size of about 0.1 μm, a narrow particle size distribution, and a substantially spherical particle shape is obtained. On the other hand, it can be seen that in Comparative Example 1, the particle size distribution is wide, and in Comparative Example 2, the sphericity of the particle shape is poor.

Claims (7)

In a method for producing platinum powder by wet reaction of a platinum compound and a reducing agent,
A platinum compound aqueous solution having a valence of platinum of 4 is reacted with a reducing agent to form a first aqueous solution, and the oxidation-reduction potential of the first aqueous solution is set before the reducing agent in the aqueous platinum compound solution is added. A first step of reducing the tetravalent platinum to divalent platinum by setting the potential to be equal to or lower than a redox potential and plus 0.3 V (vs. SHE: standard hydrogen electrode);
A second aqueous solution containing a reducing agent and the first aqueous solution are reacted to form a mixed aqueous solution, and the redox potential of the mixed aqueous solution is the redox potential before mixing with the first aqueous solution in the second aqueous solution. A second step in which platinum powder is precipitated by reducing the divalent platinum to zero valence by setting the potential to plus 0.1 V (vs. SHE) or less;
A method for producing platinum powder, comprising obtaining platinum powder.   The redox potential before adding the reducing agent in the platinum compound aqueous solution in the first step is plus 0.5 to plus 0.7 V (vs. SHE), and the second aqueous solution in the second step. 2. The method for producing platinum powder according to claim 1, wherein the oxidation-reduction potential before mixing with the first aqueous solution is from minus 0.8 to minus 0.6 V (vs. SHE).   The method for producing platinum powder according to claim 1 or 2, wherein an acid is included in the aqueous solution of the platinum compound in the first step.   3. The method for producing platinum powder according to claim 1, wherein an alkali is contained in the second aqueous solution in the second step.   The method for producing a platinum powder according to any one of claims 1 to 4, wherein the aqueous solution of the platinum compound is an aqueous solution of platinum chloride (IV) acid.   The method for producing platinum powder according to claim 3, wherein the acid is hydrochloric acid.   The said alkali is ammonia water, The manufacturing method of the platinum powder of Claim 4 characterized by the above-mentioned.