JP2010209412A - Method for producing noble metal powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing noble metal powder in which the concentration of an impurity gas is reduced without changing a grain size distribution before and after heat treatment. <P>SOLUTION: In the method for producing noble metal powder in which the concentration of the impurity gas is reduced, noble metal powder essentially composed of noble metal is fed to a heating furnace, the noble metal powder is heated in a state of being dispersed into a gas, and is further brought into contact with a refrigerant while being kept in the dispersed state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a noble metal powder having a reduced impurity gas concentration, and more particularly to a technique for producing a noble metal powder having a reduced impurity gas concentration without changing the particle size distribution before and after the heat treatment. It is.

  Noble metal powders used as raw materials for sputtering targets and automobile catalysts are required to have a low concentration of impurity gases such as nitrogen N, oxygen O, and chlorine Cl, and a narrow particle size distribution. In order to provide such a noble metal powder, various heat treatment methods have been proposed.

  For example, in Patent Document 1, as a method for producing a highly crystalline platinum powder having a narrow particle size distribution range and capable of obtaining a highly pure platinum powder, platinum black and at least one alkali salt or alkaline earth metal salt are used. A method is disclosed in which the mixture is pulverized after being wet-mixed and then baked to remove the gas, and then the salt is dissolved and removed. However, this method is premised on the use of an alkali salt or an alkaline earth metal salt, and requires a separate step for separating the above components after the heat treatment, which makes the treatment complicated. Further, if the above components are not sufficiently separated, impurities may be mixed into the platinum powder, and the purity of the platinum powder may be reduced.

  Although not intended for precious metal powders, for example, in Patent Document 2, a vertical heating furnace is used, and wet powder of high-purity silica is used while maintaining high purity by minimizing the contamination of impurities. A method of drying and firing in a short time is disclosed. However, the above document only discloses a drying method for ceramics such as silica, and does not consider anything about reducing the impurity gas concentration in the noble metal powder. Actually, this technique was made from the viewpoint of minimizing contamination from the apparatus material constituting the heating furnace and the heat source for drying when the moisture-containing silica powder is dried. It is not intended to reduce the amount of impurity gases such as O, O, and Cl, and in the examples, it was confirmed that the purity of Na, Al, and Zr was not increased after heat treatment and high purity was maintained. It was only done.

  Patent Document 3 discloses a free-fall heat treatment furnace capable of rapidly heating a processed object to a predetermined temperature by heating the processed object such as an aluminum foil piece from the surroundings while freely dropping the processed object in a vacuum. . Patent Document 4 discloses a vertical firing furnace that can be used for calcination firing without contaminating various ceramic powders, etc., and the heated material to be fired is provided below the vertical firing furnace. Collected by the collected collection unit and cooled. However, in the methods disclosed in these documents, since the heat treatment is performed while the particles are in contact with each other, the particles are sintered. In these documents, noble metal powder is not targeted, and no consideration is given to reducing the impurity gas contained in the processed product.

Japanese Patent Laid-Open No. 10-102103 JP-A-6-3050 JP 2003-139469 A JP 2008-14504 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a noble metal powder that can reduce the concentration of impurity gas contained in the noble metal powder without adding an additive such as an alkali component. There is to do. Specifically, an object of the present invention is to provide a method capable of producing a noble metal powder in which the particle size distribution before and after the heat treatment does not change because the sintering of the powder is suppressed and the impurity gas concentration is reduced.

  The method for producing a noble metal powder according to the present invention that has solved the above-mentioned problem is to supply a noble metal powder mainly composed of noble metal to a heating furnace, and after heating the noble metal powder dispersed in a gas, The main point is that it is brought into contact with the refrigerant in a dispersed state.

  In a preferred embodiment of the present invention, a downward gas flow is formed in the heating furnace from the upper part to the lower part of the heating furnace. In preferable embodiment of this invention, the gas in a heating furnace is suck | inhaled by the gas suction part provided in the lower part of the said heating furnace. In a preferred embodiment of the present invention, the heating is performed at 500 to 1200 ° C. In a preferred embodiment of the present invention, the noble metal powder is a powder mainly composed of platinum or palladium.

  According to the present invention, the noble metal powder is appropriately dispersed in a heating furnace, heated while maintaining the dispersed state, and then immediately cooled while being dispersed. Sintering is suppressed, and the concentration of impurity gas contained in the noble metal powder can be reduced while the particle size distribution before the heat treatment is maintained after the heat treatment. According to the method of the present invention, since a desired noble metal powder can be obtained without adding an alkali component other than the noble metal powder as in the prior art, there is no risk of contamination due to the addition of the component, Since a process for separating the components is not necessary, the heat treatment process can be simplified. Furthermore, according to the method of the present invention, the impurity gas concentration can be reduced without performing the heat treatment by controlling the atmosphere in the heating furnace under vacuum, which is useful in that the equipment can be simplified.

FIG. 1 is a schematic explanatory view showing an example of a heating / cooling apparatus suitably used in the method of the present invention.

  In the production method of the present invention, a precious metal powder mainly composed of a precious metal is supplied to a heating furnace, the precious metal powder is heated in a state of being dispersed in a gas, and then further brought into contact with the refrigerant in a dispersed state. There are features. According to the method of the present invention, the precious metal powder is maintained in a predetermined dispersion state in all steps of supplying the precious metal powder into the heating furnace, heating the precious metal powder in the heating furnace, and cooling the precious metal powder after heating. The heat treatment is performed in such a manner that the sintering of the noble metal powder due to heating is suppressed, the particle size distribution before the heat treatment is maintained after the heat treatment, and the impurity gas concentration in the noble metal powder is also reduced. Noble metal powder is obtained.

  Specifically, in the present invention, the supply speed when supplying the noble metal powder into the heating furnace is controlled to an appropriate dispersion state, and the heating furnace is heated at an appropriate temperature while maintaining this dispersion state. Therefore, the precious metal powder can be heated uniformly. As a result, the particle size distribution before the heat treatment can be prevented from changing due to aggregation and coarsening of the noble metal powders during heating, and the impurity gas concentration in the noble metal powder can be reduced. That is, in general, preventing coarsening of the particle size (suppression of sintering) and reducing the impurity gas concentration are difficult to achieve at the same time. If the heating temperature is too low to suppress sintering, the impurity gas concentration is reduced. On the other hand, if the heating temperature is too high to reduce the impurity gas concentration, sintering cannot be suppressed and the particle size becomes coarse. In the present invention, as described above, the temperature range (for example, the impurity gas concentration can be reduced without increasing the particle size while maintaining an appropriate dispersion state over the supply to the heating furnace, heating, and subsequent cooling). Since it is heated at 500 to 1200 ° C.), it is thought that both can be achieved.

  Furthermore, in the present invention, since the precious metal powder after heating is immediately brought into contact with the refrigerant and cooling (forced cooling, rapid cooling) is performed while maintaining this appropriate dispersion state, the state after heating (particle size before and after heat treatment) A noble metal powder is obtained in which the distribution change is small and the impurity gas concentration is reduced. In other words, when the product is allowed to cool in the air without forced cooling as described above, a secondary reaction occurs due to the residual heat held in the powder by heating, or noble metal powders adhere to each other during the cooling. However, the problem that the particle diameter increases or the concentration of the impurity gas rises due to the incorporation of gas in the atmosphere during cooling, etc., can be avoided by the method of the present invention.

As described above, in the present invention, it is extremely important to perform heating and cooling in a state where the precious metal powder is appropriately dispersed. Since the dispersion state of the noble metal powder is closely related to the particle size and density of the noble metal powder, it cannot be determined to one, but it can be dispersed by setting the input amount of the noble metal powder in the range of 10 to 1000 g / m ^3. The state is maintained properly. That is, it is only necessary to adjust the powder drop rate (residence time in the furnace) so that the amount of powder input to the heating furnace is 10 to 1000 g / m ³ with respect to the volume in the heating furnace.

If the amount of powder input is too much and exceeds 1000 g / m ³ , the precious metal powder is present in an overly dense state in the heating furnace, so uniform heat treatment cannot be performed, and noble metal powder collides with each other in the heating furnace. Agglomeration increases the particle size of the powder after heat treatment. On the other hand, if the input amount of the powder is too small and falls below 10 g / m ³ , the above problem does not occur and the noble metal powder is heated uniformly, but the productivity is lowered. A more preferable input amount of the noble metal powder is in the range of 40 to 400 g / m ³ of the noble metal powder in the heating furnace.

  This dispersed state (input amount to the heating furnace) needs to be maintained even in the heating furnace. This is particularly (a) the direction of the gas supplied to the heating furnace, and (b) the heating furnace. This is achieved by controlling the flow rate of the supplied gas as follows. Details are as follows.

[(A) Direction of gas supplied to heating furnace]
The gas supplied to the heating furnace preferably has a downward flow formed from the upper part to the lower part of the heating furnace, and is dispersed by heating in a furnace having a natural fall structure such as a vertical heating furnace. The state can be easily adjusted.

  When the downflow of gas is not sufficiently formed, the noble metal powder is scattered by the influence of the updraft, and the dispersion state is likely to vary. As a result, the particle size distribution of the noble metal powder before and after the heat treatment changes.

[(I) Flow rate of gas supplied to the heating furnace]
In order to disperse the precious metal powder appropriately, it is preferable to form a downward gas flow as described above, but it is also possible to control the flow rate of the gas in the heating furnace to about 0.2 to 5 cm / second. preferable. For example, in the case of a vertical cylindrical heating furnace, the gas flow rate in the heating furnace is a gas velocity when passing through a circular cross-section of the cylinder. The flow rate of the gas is the volume around the room temperature (cm ³ ) per unit time (seconds) of the gas taken into or discharged from the furnace, and the area of the cross-section circle of the furnace ( cm ² ).

  When the gas flow rate is less than 0.2 cm / second, the gas downflow is not sufficiently formed, and the dispersion state tends to vary due to the influence of the ascending airflow, and the residence time of the powder also varies. Sintering occurs. On the other hand, when the gas flow rate exceeds 5 cm / second, the gas suction force becomes too large, and a problem arises in that a part of the noble metal powder is sucked and clogged by the piping of the heating device, the gas suction part, or the like. Specifically, the gas flow rate may be appropriately set within the above range according to the shape of the heating furnace to be used, the component composition of the noble metal powder, the particle size distribution, etc., but more preferably 0. It is 5 cm / sec or more and 3 cm / sec or less.

  In order to form the above-described gas downward flow, for example, as shown in the heating and cooling apparatus of FIG. Alternatively, this can be achieved by providing the gas inlet 2a so that a non-oxidizing gas can be supplied, and (c) providing a gas suction part for sucking the gas at the lower part of the heating furnace and discharging it outside the system. Although not shown in FIG. 1, a device for cooling the gas may be provided in the middle of the path 11.

  That is, depending on the particle size and density of the noble metal powder, the powder is scattered by the rising air flow generated in the heating furnace, and the supply of the noble metal powder to the heating furnace cannot be performed stably or uniformly. There may be a problem that heating cannot be performed uniformly. As a result, the residence time in the heating furnace changes, and there is a possibility that an appropriate dispersion state of the noble metal powder cannot be obtained. This problem may not be sufficiently avoided by using a vertical heating furnace and forming only a downward flow due to the natural fall (free fall) of the powder. On the other hand, if the lower part of the heating furnace is sealed and a gas suction part is provided in the lower part as in (c) above, not only the powder downward flow in the vertical heating furnace but also the gas in the gas suction part Since the forced downward flow is also formed, the formation of the downward flow is promoted, and the generation of the upward airflow can be effectively suppressed.

  Moreover, if generation | occurrence | production of an updraft can be prevented as mentioned above, it can prevent that a fine noble metal powder scatters by an updraft, and can also suppress the loss of noble metal powder. Furthermore, effects such as prevention of adhesion of noble metal powder to the heating furnace wall can be obtained. As a result, the collection efficiency of the noble metal powder is very useful.

  Further, in the present invention, as will be described in detail later, the heated precious metal powder is cooled in contact with a coolant such as water in the cooling tank, but the water vapor generated in the cooling tank is converted into a system by operating the gas suction unit. Efficiently discharges outside. As a result, effects such as prevention of agglomeration of the noble metal powder and prevention of corrosion of the heating furnace can be obtained.

  The noble metal powder used in the present invention includes gold (Au), silver (Ag), platinum group elements [platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru)]. Both precious metal powders; and precious metal powders based on these precious metals are included. Here, the “noble metal powder containing a noble metal as a main component (main component)” contains at least 50% by mass or more of the above noble metal.

  The impurity gas to be removed in the present invention means oxygen O, nitrogen N, chlorine Cl, etc. (especially oxygen) contained in the noble metal powder. According to the present invention, a noble metal powder in which oxygen is reduced to, for example, 0.1% by mass or less can be produced.

  The average particle size (50% particle size) of the noble metal powder supplied to the heating furnace is preferably about 1 to 500 μm, more preferably 5 to 50 μm. That is, the method of the present invention is a suitable method for heat-treating noble metal powder having such a particle size. In addition, the particle size of the noble metal powder is measured by a microtrack particle size distribution measuring device (MT-3300exII manufactured by Nikkiso). According to this method, a particle is irradiated with laser light, and the particle diameter and particle size distribution are obtained by calculation from the scattered light intensity pattern.

  Hereinafter, the manufacturing method of the present invention will be described in detail with reference to the heating and cooling apparatus of FIG. FIG. 1 shows an example of an apparatus preferably used in the present invention, and the method of the present invention is not intended to be limited to this.

  The apparatus of FIG. 1 includes a vertical heating furnace (falling type heating furnace) in which precious metal powder freely falls in the heating furnace. Thereby, a downward flow of gas is formed from the upper part to the lower part of the heating furnace, and it becomes easy to adjust the dispersion state of the noble metal powder.

  In detail, the heating and cooling apparatus of FIG. 1 includes a supply unit 1 for supplying noble metal powder to the heating furnace 2, a heating furnace 2 for heating the supplied noble metal powder, and the heated noble metal powder as a refrigerant. The cooling part 3 for making it contact 3a, the gas suction part 4 which attracts | sucks gas to the lower part of the heating furnace 2, and the gas inlet 2a for introducing gas into the upper part of the heating furnace 2 are provided. The gas suction unit 4 is connected between the heating furnace 2 and the cooling unit 3 via a path 11. The gas supplied into the heating furnace 2 from the gas introduction port 2a is forced to form a downward flow 2b from the upper part to the lower part of the heating furnace 2 by the gas suction part 4, and passes through the path 11 to the outside of the system. Discharged.

  First, the noble metal powder is supplied to the supply unit 1. The supply unit 1 preferably uses a feeder. By using the feeder, the noble metal powder can be put into the heating furnace 2 at a uniform speed. As the feeder, it is preferable to use a multistage feeder, and the noble metal powder can be introduced into the heating furnace 2 at a constant speed by keeping the amount of the noble metal powder supplied to the hopper of the final stage feeder constant. Specifically, for example, a two-stage feeder including a screw feeder and a vibration feeder, a two-stage feeder equipped with two vibration feeders, and the like are preferably used. In particular, if the noble metal powder is introduced using the former two-stage feeder, it is most preferable because the secondary particles can be crushed by the screw feeder and the powder can be dispersed by the vibration feeder.

  Further, gas is introduced into the heating furnace 2 from the gas inlet 2a. The kind of gas used in the present invention is not particularly limited, and may be air, non-oxidizing gas (for example, nitrogen gas or argon gas) or reducing gas (for example, hydrogen gas). Alternatively, a mixed gas of these may be used.

  Next, the noble metal powder charged into the supply unit 1 is charged into the heating furnace 2.

  In order to appropriately control the dispersion state of the noble metal powder, it is preferable to control the charging speed of the noble metal powder into the heating furnace 2 or the gas flow rate as described above.

  The temperature of the heating furnace 2 is preferably 500 to 1200 ° C. When the heating temperature is less than 500 ° C., the impurity gas in the noble metal powder cannot be sufficiently reduced. On the other hand, if the heating temperature exceeds 1200 ° C, there is a correlation with the heating rate, but it is necessary to set a special heater or to take new measures against heat shock. Become. The preferable temperature of the heating furnace 2 is 700 ° C. or higher and 1150 ° C. or lower, and more preferably 800 ° C. or higher and 1100 ° C. or lower.

  The heating time differs depending on the amount of precious metal powder to be processed, the impurity gas concentration, the size of the heating furnace, and the like, and it is difficult to define it uniformly, but it is generally controlled within the range of several seconds to several tens of seconds. Is preferred.

  Moreover, it is preferable to appropriately control the average rate of temperature rise (° C./second) from the entrance of the heating furnace 2 to the above-mentioned heating furnace temperature (500 to 1200 ° C.).

  The above average heating rate is the difference (° C.) between the temperature in the soaking area (heating furnace temperature ± 10 ° C.) in the heating furnace and the temperature at the inlet of the heating furnace from the entrance of the heating furnace. It is a calculated value calculated by dividing by the time t (seconds) required to pass through the distance to reach the soaking area. Preferably, it is 100 to 2000 ° C./second.

  If the average heating rate is controlled to exceed 2000 ° C./second, the distance from the furnace inlet to the soaking temperature region must be shortened, and a special speed is required to achieve the speed. The equipment becomes complicated, such as the need to set a heater and take new measures against heat shock. On the other hand, if it is attempted to control the above average heating rate to less than 100 ° C./second, the furnace length of the heating furnace 2 must be increased, resulting in an increase in equipment costs and a problem in installation location.

  Specifically, the range of the average rate of temperature increase is appropriately considered in terms of the simplicity and economy of the apparatus, and from the above range, depending on the type and particle size distribution of the noble metal powder, the impurity gas concentration, An appropriate speed may be set as appropriate.

  The heat-treated noble metal powder has no change in particle size distribution before and after the heat treatment, and the impurity gas concentration in the powder is also reduced.

  Next, the precious metal powder after the heat treatment is immediately put into the cooling unit 3 and rapidly cooled by being brought into contact with the refrigerant 3a. As a result, the precious metal powder is cooled at once while maintaining the above dispersion state, so that the state of the precious metal powder after heating is maintained as it is, and a desired powder is obtained. That is, if the cooling is performed in the air without using the refrigerant 3a, the powders are fixed to each other during the cooling or the powder is sintered by the residual heat, and the particle size distribution of the noble metal powder is changed. Oxygen increases the amount of oxygen in the noble metal powder (see Examples below), but according to the method of the present invention, these problems are not observed.

  What is necessary is just to set the temperature of the refrigerant | coolant 3a in the cooling unit 3 to about 5-40 degreeC, for example.

  Water is preferably used as the refrigerant 3a used in the cooling unit 3. This is because if a refrigerant other than water is used, excess elements contained in the refrigerant may be mixed into the noble metal powder during the cooling process, and the impurity concentration may increase. For example, when oil is used as the refrigerant 3a, C (carbon) contained in the oil may be mixed into the noble metal powder as an impurity. In addition, when oil is used, a separate cleaning step is required. However, when water is used, the cleaning process is unnecessary, and the productivity can be improved by drying it as it is.

  In drying, care must be taken so that the impurity gas concentration does not increase during drying. Specifically, avoiding excessive heating, for example, drying at 150 ° C. or lower is preferable. Moreover, it is more preferable to dry in an inert gas atmosphere depending on the kind of noble metal powder.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. All of these are possible within the scope of the present invention.

  In the following Experimental Examples 1 to 6, experiments were performed using the heating and cooling apparatus of FIG.

  In detail, the heating and cooling apparatus used in the following experimental examples includes a two-stage feeder having a screw feeder in the first stage and a vibration feeder in the second stage as the supply section 1, and a water tank as the cooling section 3. Is used. The temperature of the water tank is about 10-30 ° C.

  Of Experimental Examples 1 to 6, Experimental Examples 1 and 5 are examples using Pt powder, Experimental Examples 2 and 4 are Pd powder, and Experimental Examples 3 and 6 are Ag-Pd alloy powders. Experimental Example 4 is an example in which a water tank is not used as the cooling unit 3, Experimental Example 5 is an example in which the gas suction unit 4 is not used, and Experimental Example 6 has an excessive amount of noble metal powder supplied to the heating furnace 2. It is an example.

[Experimental Example 1 (Invention Example: Pt powder)]
The details of the noble metal powder (Pt powder) used in Experimental Example 1 are as follows.
Particle size distribution: 10% particle size 3.4 μm, 50% particle size 13 μm, 90% particle size 23 μm
(The above is the measurement result by the microtrack particle size distribution measuring device.)
Impurity gas concentration: O (oxygen) 0.9 mass%, N (nitrogen) 0.3 mass%, Cl (chlorine) 0.06 mass%
(O and N are measurement results using “EMGA-620W” manufactured by HORIBA, Ltd., and Cl is measured by combining “Automatic Sample Baking Device AQF-100” manufactured by Dia Instruments with “Ion Chromatograph ICS-1500” manufactured by Nippon Dionex. Is the result.

The Pt powder was put into a two-stage feeder, air was introduced from the gas introduction part 2a to the heating furnace 2, and heating and cooling were performed under the following conditions.
Pt powder amount in the heating furnace: 300 g / m ³
Heating temperature in the heating furnace: 900 ° C
Average heating rate during heating: 300 ° C./second Air flow rate: 0.8 cm / second

  The Pt powder cooled in the water bath was filtered and solid-liquid separated, and the obtained Pt powder was dried at 120 ° C. for 3 hours in an air atmosphere. The recovery rate of Pt powder was 98%.

The details of the Pt powder after the heat treatment are as follows (measurement conditions are the same as before the heat treatment). When the heat treatment method of the present invention was used, the concentration of all impurity gases of oxygen, nitrogen and chlorine was reduced as compared with that before the heat treatment, and almost no change in the particle size distribution was observed before and after the heat treatment.
Particle size distribution: 10% particle size 4.1 μm, 50% particle size 13 μm, 90% particle size 25 μm
Impurity gas concentration: O (oxygen) 0.07 mass%, N (nitrogen) 0.03 mass%, Cl (chlorine) 0.02 mass%

[Experimental example 2 (Invention example: Pd powder)]
The details of the noble metal powder (Pd powder) used in Experimental Example 2 are as follows. The measurement conditions are the same as in Experimental Example 1.
Particle size distribution: 10% particle size 2.5 μm, 50% particle size 10 μm, 90% particle size 75 μm
Impurity gas concentration: O (oxygen) 0.2% by mass

The Pd powder was put into a two-stage feeder, air was introduced from the gas introduction part 2a to the heating furnace 2, and heating and cooling were performed under the following conditions.
Pd powder amount in heating furnace: 150 g / m ³
Heating temperature in the heating furnace: 1100 ° C
Average heating rate during heating: 800 ° C./second Air flow rate: 2 cm / second

  The Pd powder cooled in the water bath was filtered and solid-liquid separated, and the obtained Pd powder was dried at 100 ° C. for 5 hours in an argon atmosphere. The recovery rate of Pd powder was 99%.

The details of the Pd powder after the heat treatment are as follows (measurement conditions are the same as before the heat treatment). When the heat treatment method of the present invention was used, the oxygen concentration was reduced as compared with that before the heat treatment, and almost no change in the particle size distribution was observed before and after the heat treatment.
Particle size distribution: 10% particle size 2.7 μm, 50% particle size 10 μm, 90% particle size 75 μm
Impurity gas concentration: O (oxygen) <0.05% by mass

[Experimental Example 3 (Invention Example: Ag-Pd Alloy Powder)]
The details of the noble metal powder (Ag 20 wt%, Pd 80 wt% Ag—Pd alloy powder) used in Experimental Example 3 are as follows. The measurement conditions are the same as in Experimental Example 1.
Particle size distribution: 10% particle size 1.2 μm, 50% particle size 3.7 μm, 90% particle size 7.0 μm
Impurity gas concentration: O (oxygen) 0.5% by mass

The above Ag—Pd alloy powder was put into a two-stage feeder, air was introduced into the heating furnace 2 from the gas introduction part 2a, and heating and cooling were performed under the following conditions.
Ag—Pd alloy powder amount in heating furnace: 40 g / m ³
Heating temperature in the heating furnace: 1000 ° C
Average heating rate during heating: 1200 ° C./sec Air flow rate: 3 cm / sec

  The Ag—Pd alloy powder cooled in the water bath was filtered and solid-liquid separated, and the obtained powder was dried in the same manner as in Experimental Example 1. The recovery rate of the Ag—Pd alloy powder was 98%.

The details of the Ag—Pd alloy powder after the heat treatment are as follows (the measurement conditions are the same as before the heat treatment). When the heat treatment method of the present invention was used, the oxygen concentration was reduced as compared with that before the heat treatment, and almost no change in the particle size distribution was observed before and after the heat treatment.
Particle size distribution: 10% particle size 1.5 μm, 50% particle size 4.0 μm, 90% particle size 8.2 μm
Impurity gas concentration: O (oxygen) <0.05% by mass

[Experimental Example 4 (Comparative Example: Pd powder)]
In Experimental Example 4, the same Pd powder as in Experimental Example 2 was used, and the Pd powder after heating was collected in a deposition tank provided at the lower part of the heating furnace without using a water tank as the cooling unit 3. Heat treatment was performed in the same manner as described above. The recovery rate of Pd powder was 98%.

The details of the Pd powder after the heat treatment are as follows (measurement conditions are the same as before the heat treatment). In Experimental Example 4 in which cooling with water was not performed, the oxygen concentration after the heat treatment did not change. This is considered to be because oxygen in the air was taken in while the powder stayed in the deposition tank after the heating even though the amount of oxygen was reduced by the heat treatment. The reason why the particle size of the powder increased after the heat treatment is presumed to be that the powder aggregated due to residual heat while the powder stayed in the deposition tank after heating.
Particle size distribution: 10% particle size 20 μm, 50% particle size 100 μm, 90% particle size 450 μm
Impurity gas concentration: O (oxygen) 0.2% by mass

[Experimental Example 5 (Comparative Example: Pt powder)]
In Experimental Example 5, the same Pt powder as in Experimental Example 1 was used, and heat treatment was performed in the same manner as in Experimental Example 1 except that the Pt powder was recovered using a heating and cooling device that did not have the gas suction unit 4. The recovery rate of Pt powder was 95%.

The details of the Pt powder after the heat treatment are as follows (measurement conditions are the same as before the heat treatment). In Experimental Example 5 in which the suction by the gas suction unit 4 was not performed, the impurity gas concentration was reduced, but the particle size after the heat treatment was increased. In addition, the recovery rate of Pt powder was lower than that in Experimental Example 1. The reason why the particle size distribution before and after the heat treatment is changed and the recovery rate of the Pt powder is thus reduced is that some fine powder components are discharged out of the system along with the upward flow generated in the heating furnace 2. Conceivable. In addition, it is considered that the particle size of the powder increased after the heat treatment because the residence time in the heating furnace 2 varied and the powder retained for a long time was sintered.
Particle size distribution: 10% particle size 14 μm, 50% particle size 30 μm, 90% particle size 50 μm
Impurity gas concentration: O (oxygen) <0.05 mass%, N (nitrogen) 0.02 mass%, Cl (chlorine) 0.01 mass%

[Experimental Example 6 (Comparative Example: Ag—Pd Alloy Powder)]
In Experimental Example 6, the same Ag—Pd alloy powder as in Experimental Example 3 was used, and the amount of Ag—Pd alloy powder supplied to the heating furnace 2 was adjusted to 1200 g / m ³ to collect the Ag—Pd alloy powder. Except that, heat treatment was performed in the same manner as in Experimental Example 3. The recovery rate of the Ag—Pd alloy powder was 98%.

The details of the Ag—Pd alloy powder after the heat treatment are as follows (measurement conditions are the same as before the heat treatment). In Experimental Example 6 in which the amount of Ag—Pd alloy powder charged into the heating furnace 2 was large, the impurity gas concentration was reduced, but the particle size after the heat treatment was increased. This is presumably because the amount of powder charged into the heating furnace 2 was large, so that the powders contacted each other in the heating furnace 2 and sintered.
Particle size distribution: 10% particle size 3.5 μm, 50% particle size 10 μm, 90% particle size 21 μm
Impurity gas concentration: O (oxygen) 0.1% by mass

DESCRIPTION OF SYMBOLS 1 Supply part 2 Heating furnace 2a Gas inlet 2b Downflow 3 Cooling part 3a Refrigerant 4 Gas suction part 11 Path | route

Claims (5)

A method for producing a noble metal powder with reduced impurity gas concentration,
Supplying a precious metal powder mainly composed of a precious metal to a heating furnace, heating the precious metal powder in a state of being dispersed in a gas, and then bringing the precious metal powder into contact with a refrigerant in a dispersed state. Method.   The manufacturing method according to claim 1, wherein a gas downward flow is formed in the heating furnace from the upper part to the lower part of the heating furnace.   The manufacturing method of Claim 2 which attracts | sucks the gas in the said heating furnace with the gas suction part provided in the lower part of the said heating furnace.   The manufacturing method in any one of Claims 1-3 which heat the said noble metal powder at 500-1200 degreeC.   The manufacturing method according to claim 1, wherein the noble metal powder is a powder mainly composed of platinum or palladium.

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