WO2017047542A1 - 貴金属粉末の製造方法 - Google Patents
貴金属粉末の製造方法 Download PDFInfo
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- WO2017047542A1 WO2017047542A1 PCT/JP2016/076777 JP2016076777W WO2017047542A1 WO 2017047542 A1 WO2017047542 A1 WO 2017047542A1 JP 2016076777 W JP2016076777 W JP 2016076777W WO 2017047542 A1 WO2017047542 A1 WO 2017047542A1
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- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/14—Treatment of metallic powder
- B22F1/142—Thermal or thermo-mechanical treatment
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/0466—Alloys based on noble metals
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C5/00—Alloys based on noble metals
- C22C5/02—Alloys based on gold
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- C22C—ALLOYS
- C22C5/00—Alloys based on noble metals
- C22C5/04—Alloys based on a platinum group metal
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- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
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- B22F2201/00—Treatment under specific atmosphere
- B22F2201/01—Reducing atmosphere
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- B22F2201/10—Inert gases
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- B22F2301/00—Metallic composition of the powder or its coating
- B22F2301/25—Noble metals, i.e. Ag Au, Ir, Os, Pd, Pt, Rh, Ru
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
- B22F2998/10—Processes characterised by the sequence of their steps
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C5/00—Alloys based on noble metals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/02—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of metals or alloys
Definitions
- the present invention relates to a method for producing a noble metal powder, and more particularly to a method for producing a noble metal powder for a thick film paste mainly used in electronic equipment.
- Such a laminated part is a conductive paste in which a metal powder such as a noble metal powder is dispersed in an organic solvent containing an organic binder, printed on a ceramic green sheet, subjected to a process of laminating, pressing and cutting, It is manufactured by firing and further forming external electrodes.
- the noble metal powder used in such a conductive paste is required to have a narrow particle size distribution range, high purity and high crystallinity.
- Patent Document 1 platinum black and calcium carbonate are wet mixed, dried and pulverized, and then the pulverized body is baked to remove carbon dioxide gas, and then the remaining calcium oxide is diluted with dilute acid. It is described that a high-purity platinum powder having a narrow particle size distribution range can be obtained by a method for producing a highly crystalline platinum powder which is dissolved and removed by washing with water and dried to obtain a platinum powder.
- Patent Document 1 when the method described in Patent Document 1 is used, if there is an abnormality in either the characteristics of platinum black, which is a platinum powder, or the characteristics of calcium carbonate, the characteristics of the resulting highly crystalline platinum powder are greatly changed. There was a problem.
- platinum black which is a platinum powder, is manufactured first, and each process including wet mixing with calcium carbonate is then performed to manufacture a highly crystalline platinum powder, so the platinum powder is manufactured twice in total. There is a problem that the number of manufacturing steps is large and the cost is high.
- Patent Document 2 discloses a method for producing one or more metal fine powders selected from platinum, gold, rhodium, palladium, silver, copper, and nickel, wherein the metal A metal compound aqueous solution preparation step in which an aqueous solution having a pH of 4 or less is prepared; and the aqueous solution having a pH of 4 or less is converted into one or more kinds of periodic table 2A element metal hydroxides selected from calcium hydroxide, magnesium hydroxide and barium hydroxide A reaction step of mixing the product powder and / or its aqueous slurry to a pH of 10 or higher; a first separation step of separating and drying the insoluble solid after completion of the reaction step; Heating in a gas or hydrogen gas atmosphere at a temperature not lower than 800 ° C.
- a process for producing a metal fine powder characterized in that it comprises each of the steps is described.
- an object of the present invention is to provide a method for producing a noble metal powder that can produce a noble metal powder having a narrow particle size distribution range, high purity, and high crystallinity at a low cost.
- the present invention provides a step of preparing an acidic aqueous solution of at least one noble metal compound and a calcium compound, adding the acidic aqueous solution to a basic aqueous solution, and oxidizing the noble metal, hydroxide or a mixture thereof, and hydroxylation.
- Production of noble metal powder including a step of generating calcium, a step of reducing the noble metal oxide, hydroxide or a mixture thereof with a reducing agent, and a step of separating and heat-treating a solid content containing the noble metal reductant Regarding the method.
- the method for producing a noble metal powder of the present invention further includes a step of subjecting the obtained heat-treated product to an acid treatment after the heat treatment step.
- the ratio of the one or more kinds of noble metal compound and the calcium compound is a weight ratio (noble metal atom / calcium atom) in terms of an atomic basis. It is preferably 10: 1 to 0.2: 1.
- the acidic aqueous solution by dropping it into the basic aqueous solution.
- the reaction solution after adding the total amount of the acidic aqueous solution to the basic aqueous solution is basic.
- the heat treatment is performed at a temperature of 800 ° C. or higher.
- the heat treatment is performed in an inert atmosphere or a reducing atmosphere.
- a noble metal powder having a narrow particle size distribution range, high purity and high crystallinity can be produced at a low cost.
- FIG. 1 is an SEM photograph of the platinum powder obtained in Example 1.
- FIG. 2 is an SEM photograph of the platinum powder obtained in Comparative Example 1.
- FIG. 3 is an SEM photograph of the platinum powder obtained in Comparative Example 2.
- 4 is a SEM photograph of the gold powder obtained in Example 2.
- the method for producing a noble metal powder of the present invention may be simply referred to as the production method of the present invention.
- the method for producing a noble metal powder of the present invention includes a step of preparing an acidic aqueous solution of one or more kinds of noble metal compounds and a calcium compound (hereinafter also referred to as an acidic aqueous solution preparation step), adding the acidic aqueous solution to a basic aqueous solution, A step of generating oxide, hydroxide or a mixture thereof, and calcium hydroxide (hereinafter also referred to as a reaction step), a step of reducing the oxide of the noble metal, a hydroxide or a mixture thereof with a reducing agent (hereinafter referred to as “reaction step”) , And a reduction step) and a step of separating and heat-treating a solid content containing a noble metal reductant (hereinafter also referred to as a heat treatment step).
- the manufacturing method of the noble metal of this invention further includes the process (henceforth an acid treatment process) which performs an acid treatment to the obtained heat-treated material after the said heat treatment
- the noble metal contained in the target noble metal powder may be any noble metal. Specifically, for example, one or more selected from gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir) and ruthenium (Ru) can be mentioned. It is done.
- the noble metal compound is not particularly limited, and examples thereof include platinum compounds, gold compounds, rhodium compounds, palladium compounds, iridium compounds, silver compounds, and ruthenium compounds.
- platinum compound examples include hexachloroplatinic (IV) acid, tetrachloroplatinum (II) acid, and tetraammineplatinum (II) acid.
- gold compound examples include chloroauric (III) acid, tetrachloroauric (III) acid, and ammonium tetrachloroaurate (III).
- rhodium compound examples include rhodium (III) nitrate and ammonium hexachlororhodium (III).
- Examples of the palladium compound include palladium nitrate (II) and tetraammine palladium (II) nitrate.
- iridium compound examples include iridium oxide, iridium chloride, and iridium nitrate.
- Examples of the silver compound include silver chloride, silver nitrate, and silver acetate.
- ruthenium compound examples include ruthenium (IV) oxide, ruthenium (III) chloride, and ruthenium (III) nitrate.
- one or more precious metal compounds can be appropriately selected and used in consideration of the type of precious metal contained in the target precious metal powder.
- the calcium compound is a component that functions as a spacer that becomes calcium hydroxide in the reaction step described later, becomes calcium oxide by thermal decomposition in the subsequent heat treatment step, and suppresses the grain growth of the noble metal particles in the heat treatment step.
- the calcium compound is not particularly limited as long as it is soluble in an acidic aqueous solution, and examples thereof include calcium carbonate, calcium hydroxide, calcium oxide, calcium sulfate, calcium chloride, and calcium nitrate.
- examples thereof include calcium carbonate, calcium hydroxide, calcium oxide, calcium sulfate, calcium chloride, and calcium nitrate.
- calcium chloride and calcium nitrate are preferable because they are easily dissolved in water and easy to handle.
- the compounds exemplified other than calcium chloride and calcium nitrate are sparingly soluble in water, but the aqueous solution of the noble metal compound is often a strong acid and can be dissolved in the aqueous solution of the noble metal compound.
- the said calcium compound may be used individually by 1 type, and may be used in combination of 2 or more type.
- the use ratio of the noble metal compound and the calcium compound in preparing the acidic aqueous solution is not particularly limited, but when the ratio of the noble metal compound is excessively large, the ratio of the calcium compound becomes too small, and heat treatment described later. Necking at the time increases, and it tends to be difficult to obtain noble metal particles having a uniform particle diameter.
- the use ratio of the noble metal compound and the calcium compound is preferably 10: 1 to 0.2: 1 in terms of a weight ratio (noble metal atom: calcium atom) converted to an atomic basis, and is preferably 2: 1 to 0.5. : 1 is more preferable.
- the preparation method for preparing the acidic aqueous solution of the noble metal compound and the calcium compound is not particularly limited.
- an acidic aqueous solution may be prepared by preparing an aqueous solution of a noble metal compound and dissolving a calcium compound therein.
- an acidic aqueous solution may be prepared by preparing an aqueous solution of a calcium compound and dissolving a noble metal compound therein.
- an aqueous acidic solution may be prepared by separately preparing an aqueous solution of a noble metal compound and an aqueous solution of a calcium compound and mixing them.
- noble metal compounds and calcium compounds can be converted into a target acidic aqueous solution only by dissolving in water, but an acid may be added as necessary at any or a plurality of stages of preparing the acidic aqueous solution. May be.
- an acidic aqueous solution of a noble metal compound and a calcium compound it is preferable to prepare an acidic aqueous solution of a noble metal compound and a calcium compound by preparing a noble metal compound in advance as an acidic aqueous solution and dissolving the calcium compound therein or mixing it with an aqueous solution of a calcium compound.
- the acid used may be any acid that can increase the solubility of the noble metal compound or calcium compound in water, or can be adjusted to an acidic solution intended for an aqueous solution, such as hydrochloric acid, nitric acid, acetic acid, Examples include organic acids such as formic acid.
- Sulfuric acid may be used, but depending on the purpose of use of the generated metal fine particles, the possibility of mixing sulfur atoms may be extremely avoided, which may not be preferable from this aspect.
- the pH of the acidic aqueous solution to be prepared is not particularly limited as long as it is acidic. From the viewpoint of preventing the precious metal from being precipitated as an oxide or hydroxide, the pH is preferably 4 or less, more preferably 2 or less, and even more preferably 1 or less.
- reaction process In the production method of the present invention, the acidic aqueous solution prepared as described above is then added to the basic aqueous solution to produce a noble metal oxide, hydroxide or mixture thereof, and calcium hydroxide.
- the basic aqueous solution for example, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, and aqueous ammonia can be used.
- the pH of the basic aqueous solution is not particularly limited as long as it is basic, but from the viewpoint of efficiently and appropriately precipitating the calcium compound as a hydroxide, the pH is preferably 11 or more, and 12 or more. More preferably.
- the addition ratio of the acidic aqueous solution to the basic aqueous solution may be appropriately adjusted in consideration of the pH of the acidic aqueous solution and the pH of the basic aqueous solution. It is preferable to prepare a basic aqueous solution sufficient to neutralize the acidic aqueous solution in which the noble metal compound and the calcium compound are dissolved. That is, it is preferable to use a basic aqueous solution sufficient to precipitate the noble metal oxide, hydroxide or mixture thereof and calcium hydroxide.
- the acidic aqueous solution it is important to add the acidic aqueous solution to the basic aqueous solution.
- a liquid feed pump for example, it is preferable to use a liquid feed pump, a pipette, a dropper, a funnel, or the like as appropriate, and drop the acidic aqueous solution into the basic aqueous solution at once or gradually while stirring.
- an acidic aqueous solution in which noble metal ions and calcium ions are uniformly dispersed is added to a basic, preferably strongly basic aqueous solution. Therefore, the formation of noble metal oxide, hydroxide or a mixture thereof and calcium hydroxide starts almost simultaneously or immediately after the addition, or immediately after the start of the formation of calcium hydroxide Production of the product, hydroxide or mixture thereof is started. That is, since the production of noble metal oxide, hydroxide or a mixture thereof is started before the production of calcium hydroxide is completed, a liquid in which these are uniformly dispersed is obtained.
- noble metal powder having a narrow particle size distribution range and a uniform particle size can be obtained by subsequent steps.
- acidic aqueous solution it is preferable to add acidic aqueous solution to the place where basic aqueous solution is stirring.
- the control of the reaction conditions controls the particle size and mixing ratio of the noble metal particles and calcium hydroxide particles. Therefore, it is possible to control the characteristics of the obtained noble metal powder and to stabilize the quality.
- the reaction solution after adding the entire amount of the acidic aqueous solution to the basic aqueous solution is basic.
- the pH of the reaction solution after adding the entire amount of the acidic aqueous solution to the basic aqueous solution is preferably 11 or more, more preferably 12 or more.
- the pH gradually increases from the acidic region to the basic region.
- the formation of a noble metal hydroxide begins to occur first. Thereafter, the formation of calcium hydroxide occurs. Therefore, in this case, the noble metal hydroxide and calcium hydroxide are not generated simultaneously.
- the noble metal hydroxide that has started to be produced becomes a noble metal-based aggregate in which calcium is not disposed around and becomes a basis of coarse particles, making it difficult to obtain a uniform particle size.
- the noble metal oxide, hydroxide or mixture thereof is reduced by a reducing agent. That is, a reducing agent is added to a liquid containing noble metal oxide, hydroxide or a mixture thereof obtained by the above reaction step, and calcium hydroxide, and the noble metal oxide, hydroxide or them in the liquid is added. The mixture of is reduced.
- the reducing agent used is not particularly limited as long as it can reduce a noble metal oxide, hydroxide, or a mixture thereof.
- examples include hydrazine, formalin, glucose, hydroquinone, hydroxylammonium chloride, and sodium formate. From the viewpoint of precipitation efficiency and particle size uniformity, hydrazine is preferable for platinum, and hydroxylammonium chloride is preferable for gold.
- the amount of the reducing agent used is not particularly limited as long as it can sufficiently reduce the noble metal oxide, hydroxide or mixture thereof.
- the solid content (insoluble matter) containing the reduced form of the noble metal is separated from the liquid after the reduction of the oxide, hydroxide or mixture thereof.
- Heat treatment (firing) is performed.
- the reduction step is performed to obtain a solid content.
- the separated solid content contains the reduced form of noble metal and calcium hydroxide in a uniformly dispersed state.
- the coexisting calcium hydroxide is thermally decomposed into calcium oxide.
- the reductant of the noble metal becomes a semi-molten state and aggregates in the state of zero valence, but is surrounded by calcium oxide, which is a thermally stable solid, preventing aggregation, and around the aggregated noble metal.
- the calcium oxide is placed so as to surround it.
- noble metal particles can be grown in an environment where noble metal particles can grow freely from a state in which the reduced form of noble metal and calcium hydroxide are uniformly dispersed, so that the noble metal particle diameters can be made uniform and the particle size distribution. It is possible to obtain noble metal particles having a narrow range, high purity and high crystallinity.
- a conventionally known solid-liquid separation method such as filtration or centrifugation is appropriately used. You can select and apply. Moreover, you may remove the water
- the drying temperature is not particularly limited, but can be performed at 80 to 200 ° C., for example.
- the heat treatment temperature for heat-treating the separated solid content is not particularly limited. However, in order to further improve the purity and crystallinity of the noble metal powder, it is preferably 800 ° C. or higher, more preferably 900 ° C. or higher. preferable. Further, the upper limit of the heat treatment temperature is not particularly limited. From the viewpoint of uniformly controlling the particle size, it is preferable that the temperature is not higher than the melting point of the noble metal having the lowest melting point by 100 ° C. or more among the noble metals contained in the target noble metal particles.
- the heat treatment time is not particularly limited, but is preferably 0.2 to 5 hours, more preferably 0.5 to 3 hours. It is preferable for the heat treatment time to be 0.2 hours or longer because the grain growth of the noble metal particles is sufficient. Further, it is preferable that the heat treatment time is 5 hours or less because the production efficiency is high.
- the heat treatment atmosphere for performing heat treatment on the separated solid content may be affected by oxidation depending on the type of noble metal, so in an inert atmosphere such as nitrogen, argon and helium, or a reducing atmosphere such as hydrogen. Preferably there is.
- the heat-treated product subjected to the heat treatment contains noble metal particles and calcium oxide, but by acid treatment, only the noble metal particles (powder) are left and only the calcium oxide is dissolved in the acid. Components can be removed.
- the heat-treated product may be immersed and held in an acid aqueous solution.
- the acid used at this time may be any acid that does not dissolve the target noble metal fine particles but can dissolve only calcium oxide in water.
- the noble metal is at least one selected from platinum and gold, it is at least one selected from hydrochloric acid, nitric acid and acetic acid.
- the noble metal contains one or more selected from rhodium, palladium, silver, ruthenium and iridium, it is acetic acid.
- the amount of the acid used for the acid treatment may be an amount sufficient to react with calcium oxide, but in practice, the acid treatment is performed so as to maintain the acidity by immersing in an acid aqueous solution in which the acid is excessive.
- the acid treatment step is preferably performed while stirring.
- the target noble metal powder can be obtained by performing washing
- the drying temperature is not particularly limited, but can be performed at 80 to 200 ° C., for example.
- the production method of the present invention can produce a noble metal powder that has a small number of production steps, is low in cost, has a narrow particle size distribution range (having a uniform particle size), and is highly pure and highly crystalline.
- Example 1 A calcium chloride aqueous solution was prepared by dissolving 55.5 g of calcium chloride in 200 g of pure water. Next, 243.9 g of chloroplatinic acid solution (platinum content 16.4% by weight) was added to the prepared calcium chloride aqueous solution and sufficiently stirred to prepare an acidic aqueous solution containing platinum ions and calcium ions. While stirring 500 g of 40% potassium hydroxide aqueous solution heated to 50 ° C., the acidic aqueous solution was added dropwise over 10 minutes. Next, 200 g of 5% hydrazine was added, and the mixture was further stirred for 1 hour and then cooled to room temperature.
- chloroplatinic acid solution platinum content 16.4% by weight
- Example 1 The insoluble matter separated by filtration was washed, dried at 120 ° C., and heat-treated at 1200 ° C. for 1 hour in a nitrogen atmosphere. Subsequently, 1 L of a 3 mol / L nitric acid solution was prepared, and heat treatment was added to the solution to perform acid treatment. After dissolving and removing the calcium component, washing and drying at 120 ° C. gave 39.4 g of platinum powder. . In FIG. 1, the SEM photograph of the platinum powder obtained in Example 1 is shown.
- a calcium chloride aqueous solution was prepared by dissolving 55.5 g of calcium chloride in 200 g of pure water. Next, 243.9 g of chloroplatinic acid solution (platinum content 16.4% by weight) was added to the prepared calcium chloride aqueous solution and sufficiently stirred to prepare an acidic aqueous solution containing platinum ions and calcium ions. While stirring the acidic aqueous solution while heating to 50 ° C., 500 g of 40% aqueous potassium hydroxide solution was added dropwise over 10 minutes. Next, 200 g of 5% hydrazine was added, and the mixture was further stirred for 1 hour and then cooled to room temperature.
- chloroplatinic acid solution platinum content 16.4% by weight
- Example 1 the particle size distribution of each platinum powder obtained in Example 1 and Comparative Examples 1 and 2 was measured using a laser diffraction particle size distribution measuring device (product name: MT3000, manufactured by Nikkiso Co., Ltd.). Table 1 shows the measurement results of the obtained 10 volume% average particle diameter, 50 volume% average particle diameter, 90 volume% average particle diameter, and maximum particle diameter.
- Example 1 and Comparative Examples 1 and 2 the element content ratio (weight ratio) of platinum and calcium in the dried product (platinum calcium mixed powder) of the insoluble matter filtered off before heat treatment as the reaction product are also shown in Table 1.
- Example 1 in which the acidic aqueous solution was dropped into the 40% aqueous potassium hydroxide solution, the particle diameters were uniform throughout and no coarse particles were contained.
- Comparative Example 1 in which a 40% potassium hydroxide aqueous solution was dropped into an acidic aqueous solution and Comparative Example 2 in which a chloroplatinic acid aqueous solution was added to a calcium hydroxide slurry had a wide particle size distribution and contained coarse particles. It was confirmed that
- Example 2 A calcium nitrate aqueous solution was prepared by dissolving 36.1 g of calcium nitrate in 36 g of pure water. Next, 35.3 g of chloroauric acid solution (gold content: 17.0% by weight) was added to the prepared calcium nitrate aqueous solution and stirred sufficiently to prepare an acidic aqueous solution containing gold ions and calcium ions. While stirring 248 g of 40% calcium hydroxide aqueous solution heated to 50 ° C., the acidic aqueous solution was added dropwise over 80 minutes. Next, 17.1 g of 10% hydrazine hydrochloride was added, and the mixture was further stirred for 1 hour and then cooled to room temperature.
- chloroauric acid solution gold content: 17.0% by weight
- Example 2 The insoluble matter separated by filtration was washed, dried at 120 ° C., and heat-treated at 800 ° C. for 1 hour in a nitrogen atmosphere. Subsequently, 1 L of a 3 mol / L nitric acid solution was prepared, and a heat treatment was added thereto, followed by acid treatment to dissolve and remove the calcium component, followed by washing and drying at 120 ° C. to obtain 6.0 g of gold powder. . In FIG. 4, the SEM photograph of the gold powder obtained in Example 2 is shown.
- the specific surface area of the gold powder obtained in Example 2 was measured by the BET method. The measurement results are shown in Table 2.
- Example 2 the particle size distribution of the gold powder obtained in Example 2 was measured using a laser diffraction particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., product name: MT3000). Table 2 shows the measurement results of the obtained 10 volume% average particle diameter, 50 volume% average particle diameter, 90 volume% average particle diameter, and maximum particle diameter.
- Example 2 the element content ratio (weight ratio) of the gold
- Example 2 in which an acidic aqueous solution was dropped into a 40% potassium hydroxide aqueous solution in the same manner as in Example 1, the particle diameter was uniform overall and almost no coarse particles were contained. It was done.
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Abstract
Description
本発明の製造方法においては、まず、1種以上の貴金属化合物(以下、単に貴金属化合物ともいう)とカルシウム化合物の酸性水溶液を調製する。
本発明の製造方法においては、次に、上記のようにして調製した酸性水溶液を塩基性水溶液に添加して、貴金属の酸化物、水酸化物又はそれらの混合物、及び水酸化カルシウムを生成させる。
本発明の製造方法においては、上記反応工程につづいて、還元剤により前記貴金属の酸化物、水酸化物又はそれらの混合物を還元する。すなわち、上記反応工程により得られた貴金属の酸化物、水酸化物又はそれらの混合物、及び水酸化カルシウムを含む液体に還元剤を添加して、液体中の貴金属の酸化物、水酸化物又はそれらの混合物を還元させる。
つづいて、本発明の製造方法においては、貴金属の酸化物、水酸化物又はそれらの混合物を還元した後の液体から、貴金属の還元体を含む固形分(不溶解物)を分離し、これを熱処理(焼成)する。ここで、本発明の製造方法においては、上記反応工程において貴金属の酸化物、水酸化物又はそれらの混合物と水酸化カルシウムとが均一に分散した液体を得た後、還元工程を経て、固形分(不溶解物)を分離している。したがって、分離された固形分においては、貴金属の還元体と水酸化カルシウムが均一に分散された状態で含まれている。この固形分に熱処理を施すことにより、貴金属の還元体は原子価0の状態で半融状態となり凝集していく。
本発明の製造方法においては、前記熱処理工程の後に、熱処理に供した熱処理物に対して酸処理をさらに施すことが好ましい。ここで、上記熱処理に供した熱処理物には、貴金属粒子と酸化カルシウムが含まれるが、酸処理によって、貴金属粒子(粉末)のみを残して、酸化カルシウムのみを酸に溶解させ、貴金属粉末以外の成分を除去することができる。
塩化カルシウム55.5gを200gの純水に溶解させて、塩化カルシウム水溶液を調製した。次に、塩化白金酸溶液(白金含有率16.4重量%)243.9gを、調製した塩化カルシウム水溶液に加えて十分に撹拌し、白金イオンとカルシウムイオンを含む酸性水溶液を調製した。50℃に加熱した500gの40%水酸化カリウム水溶液を撹拌しているところに、当該酸性水溶液を10分間かけて滴下した。次に、5%ヒドラジンを200g添加し、さらに1時間攪拌してから室温に冷却した後、不溶解物を濾別した。濾別された不溶解物を洗浄した後、120℃で乾燥させ、窒素雰囲気下1200℃で1時間熱処理を施した。つづいて、3mol/Lの硝酸溶液を1L用意し、これに熱処理物を加えて酸処理し、カルシウム成分を溶解除去した後、洗浄及び120℃で乾燥させて、白金粉末39.4gを得た。図1に、実施例1で得られた白金粉末のSEM写真を示す。
塩化カルシウム55.5gを200gの純水に溶解させて、塩化カルシウム水溶液を調製した。次に、塩化白金酸溶液(白金含有率16.4重量%)243.9gを、調製した塩化カルシウム水溶液に加えて十分に撹拌し、白金イオンとカルシウムイオンを含む酸性水溶液を調製した。前記酸性水溶液を50℃に加熱しながら攪拌しているところに、500gの40%水酸化カリウム水溶液を10分間かけて滴下した。次に、5%ヒドラジンを200g添加し、さらに1時間攪拌してから室温に冷却した後、不溶解物を濾別した。濾別された不溶解物を洗浄した後、120℃で乾燥させ、窒素雰囲気下1200℃で1時間熱処理を施した。つづいて、3mol/Lの硝酸溶液を1L用意し、これに熱処理物を加えて酸処理し、カルシウム成分を溶解除去した後、洗浄及び120℃で乾燥させて、白金粉末39.4gを得た。図2に、比較例1で得られた白金粉末のSEM写真を示す。
水酸化カルシウム148.2gを500gの純水に分散させ、水酸化カルシウムスラリーを調製した。この水酸化カルシウムスラリーに対して、塩化白金酸溶液(白金含有率16.4重量%)243.9gに純水を200g加えて混合した溶液を10分間かけて滴下した。次に、5%ヒドラジンを200g添加し、さらに1時間攪拌してから室温に冷却した後、不溶解物を濾別した。濾別された不溶解物を洗浄した後、120℃で乾燥させ、窒素雰囲気下1200℃で1時間熱処理を施した。つづいて、3mol/Lの硝酸溶液を1L用意し、これに熱処理物を加えて酸処理し、カルシウム成分を溶解除去した後、洗浄及び120℃で乾燥させて、白金粉末39.4gを得た。図3に、比較例2で得られた白金粉末のSEM写真を示す。
硝酸カルシウム36.1gを36gの純水に溶解させて、硝酸カルシウム水溶液を調製した。次に、塩化金酸溶液(金含有率17.0重量%)35.3gを、調製した硝酸カルシウム水溶液に加えて十分に撹拌し、金イオンとカルシウムイオンを含む酸性水溶液を調製した。50℃に加熱した248gの40%水酸化カルシウム水溶液を撹拌しているところに、当該酸性水溶液を80分間かけて滴下した。次に、10%塩酸ヒドラジンを17.1g添加し、さらに1時間攪拌してから室温に冷却した後、不溶解物を濾別した。濾別された不溶解物を洗浄した後、120℃で乾燥させ、窒素雰囲気下800℃で1時間熱処理を施した。つづいて、3mol/Lの硝酸溶液を1L用意し、これに熱処理物を加えて酸処理し、カルシウム成分を溶解除去した後、洗浄及び120℃で乾燥させて、金粉末6.0gを得た。図4に、実施例2で得られた金粉末のSEM写真を示す。
Claims (7)
- 1種以上の貴金属化合物とカルシウム化合物の酸性水溶液を調製する工程、
前記酸性水溶液を塩基性水溶液に添加し、貴金属の酸化物、水酸化物又はそれらの混合物、及び水酸化カルシウムを生成させる工程、
還元剤により前記貴金属の酸化物、水酸化物又はそれらの混合物を還元する工程、及び、
貴金属の還元体を含む固形分を分離して熱処理する工程
を含む貴金属粉末の製造方法。 - 前記熱処理する工程の後、得られた熱処理物に酸処理を施す工程をさらに含む、請求項1に記載の貴金属粉末の製造方法。
- 前記酸性水溶液を調製する際の、前記1種以上の貴金属化合物と前記カルシウム化合物の割合が、原子基準に換算した重量比(貴金属原子:カルシウム原子)で、10:1~0.2:1である、請求項1または2に記載の貴金属粉末の製造方法。
- 前記酸性水溶液を前記塩基性水溶液に滴下することにより添加する、請求項1から3のいずれか1項に記載の貴金属粉末の製造方法。
- 前記酸性水溶液の全量を前記塩基性水溶液に添加した後の反応液が塩基性である、請求項1から4のいずれか1項に記載の貴金属粉末の製造方法。
- 前記熱処理が800℃以上の温度で行われる、請求項1から5のいずれか1項に記載の貴金属粉末の製造方法。
- 前記熱処理が不活性雰囲気下又は還元性雰囲気下で行われる、請求項1から6のいずれか1項に記載の貴金属粉末の製造方法。
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