JP2008064328A - Roasting furnace and manufacturing method of iridium oxide powder using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roasting furnace capable of efficiently roasting fine powder with a simple structure, and to provide a method of efficiently manufacturing iridium oxide powder suitably used for forming a thick film resistor by using the roasting furnace. <P>SOLUTION: This roasting furnace is a tubular furnace of the approximately angular cross-sectional shape, having flat shelf boards for loading materials in multiple stages in the vertical direction in a roasting chamber, atmosphere gas blowing nozzles are disposed to allow the atmosphere gas to evenly flow to each of the stages, and the plurality of atmosphere gas blowing nozzles are disposed in parallel with each other on the same vertical planar position from the shelf boards so that the atmosphere gas flows only in the approximately same direction as the blowing direction on a material surface just after flowing in. Ammonium hexachloroiridate (IV) or potassium hexachloroiridate (IV) is subjected to oxidation roasting at 600-1,050°C by using the roasting furnace, thus iridium oxide powder with stable quality can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a roasting furnace suitable for oxidative roasting of fine powder, and a method for producing iridium oxide powder suitable as a conductive powder for a thick film resistor paste using the same.

  2. Description of the Related Art In recent years, circuit wiring boards in which electronic parts such as conductors, resistors, capacitors, and the like are printed on an insulating substrate using a paste have been widely used in electronic devices. Thick film resistors are widely used in chip resistors, thick film hybrid ICs, resistor networks, and the like. As a method for manufacturing a thick film resistor, a process is generally used in which a paste in which conductive powder is uniformly dispersed is printed on a conductor circuit pattern or an electrode formed on the surface of an insulator substrate, and this is fired. Manufactured.

A paste used for manufacturing a thick film resistor is prepared by uniformly dispersing conductive powder and a glass binder in an organic medium called a vehicle. Of these, conductive powder plays the most important role in determining the electrical characteristics of thick film resistors, and fine powders of ruthenium oxide (RuO ₂ ) and lead ruthenate (Pb ₂ Ru ₂ O ₇ ) are widely used. Yes.
In general, ruthenium oxide is used as a conductor in a wide range from a low resistance value to a high resistance value, and in the high resistance region, lead ruthenate having a smaller variation in the resistance value with respect to the conductor concentration is often used.
However, in recent years, for the purpose of eliminating the use of toxic lead from electronic devices, as a conductive powder for thick film resistors in the high resistance region, a conductive powder containing no lead instead of lead ruthenate powder is desired. Yes. As a solution to this, ruthenium composite oxides such as Bi ₂ Ru ₂ O ₇ , CaRuO ₃ , SrRuO ₃ , BaRuO ₃ , LaRuO ₃ have been proposed, but have not yet been put into practical use.

Iridium oxide (IrO ₂ ) is generally known as a conductive powder that has a higher resistance than a ruthenium oxide powder when a resistor is formed from a paste containing the powder. Therefore, iridium oxide powder is promising as a conductive powder containing no lead in place of lead ruthenate powder.
As an efficient method for producing such iridium oxide powder, chlorinated iridium salts such as ammonium hexachloroiridium (IV) or potassium hexachloroiridium (IV) can be roasted at a high temperature in an oxidizing atmosphere. .

However, in such oxidative roasting of iridium chloride, the thickness of the raw material layer should be about 1 to 2 mm in order to make the properties of the obtained iridium oxide powder uniform, and it must react uniformly with the atmospheric gas. In other words, productivity is low with respect to the hearth area. The low productivity with respect to the hearth area can be improved by extending the effective area of the furnace by placing raw materials on a tray and stacking them vertically. As the roasting furnace, a general firing furnace used for firing ceramics can be used. As such a baking furnace, what is to be fired is accommodated in a plurality of stages in a roasting chamber and the atmosphere is circulated with hot air so that it can be uniformly fired in each part of the roasting chamber (for example, Patent Documents). 1).
When trying to make the atmosphere in the roasting chamber uniform in a hot air circulation furnace, it is necessary to make the air volume extremely large, which is not suitable for roasting fine powder. Further, when the air volume is reduced, stagnation of the atmosphere occurs and uniform roasting cannot be performed.

As an improvement measure for the homogenization of the atmosphere in the roasting chamber, the flow rate of the atmospheric gas supplied to each of the mounting surfaces of the heat treatment objects installed in multiple stages in the roasting chamber is set to a specific value, and the mounting surface is An atmosphere gas supply method of a heat treatment apparatus that can perform uniform firing by moving in the horizontal direction is disclosed (for example, see Patent Document 2).
However, continuous furnaces that move heat by moving the loading surface are expensive and unsuitable for production of products with a relatively small production volume. It is complicated to move the loading surface even in a batch furnace. It becomes a structure. Further, the atmospheric gas flow rate required for the homogenization of the disclosed atmosphere is too large for fine powder roasting, and is not suitable for fine powder roasting.

In addition, as a furnace that can homogenize the atmosphere in the roasting chamber, it has a structure in which firewood is stacked in multiple stages in the roasting chamber, and the atmosphere gas flow can be switched by switching the atmosphere gas supply pipe and exhaust pipe. A firing furnace that can supply gas uniformly to the raw material in the roasting chamber has been proposed (see, for example, Patent Document 3).
In addition, heat treatment that makes it possible to keep the atmosphere in the roasting chamber uniform by changing the shape of the outlet of the atmosphere gas supply pipe and rotating or moving at least one of the object to be heat-treated and the atmosphere gas supply pipe A furnace has also been proposed (see, for example, Patent Document 4).
All of the above roasting furnaces have movable parts, and the apparatus has a complicated structure. In addition, there is no description about the atmospheric gas flow rate that needs to be fully considered for the roasting of fine powders, and there is a problem that the atmospheric gas flow rate must be increased in order to forcibly circulate the atmospheric gas. is there.
Under such circumstances, an efficient industrial production method of iridium oxide powder having good powder characteristics as a conductive powder not containing lead as a thick film resistor forming paste instead of lead ruthenate powder is desired. Therefore, it is desired to provide a furnace suitable for roasting fine powders necessary for the production thereof.
JP 05-172464 A JP-A-2005-50849 Japanese Patent Laid-Open No. 04-273388 JP 2002-39691 A

  In view of such circumstances, the present invention provides a roasting furnace suitable for the production of oxide powder that has a simple structure and can efficiently perform fine powder roasting, and uses it to form a thick film resistor. It is an object to provide an industrially efficient method for producing iridium oxide powder as a conductive powder suitable for a paste for use.

As a result of researches on the roasting of fine powders, the present inventors have found that the influence of the flow of the atmospheric gas flowing on the surface of the raw material is large in the roasting of the fine powder, and the atmospheric gas flow is blown into the atmospheric gas flow. It came to the conclusion that the influence of the arrangement | positioning of a nozzle and the space which mounts a raw material is large, and came to complete this invention.
That is, the roasting furnace of the present invention is a tubular furnace having a substantially square cross-sectional shape, and has a plurality of shelves in the vertical direction in the roasting chamber, and an atmosphere in one of the axial directions in the roasting chamber. A roasting furnace having a gas blowing nozzle and an atmosphere gas discharge port on the other side and configured so that the atmosphere gas flows on the surface of the raw material only in substantially the same direction as the blowing direction.
By making the cross-sectional shape into a substantially square shape, a plurality of shelf boards can be installed without creating a useless space in the roasting chamber. In addition, by installing a plurality of shelves in the vertical direction, the amount of raw materials that can be placed in the roasting chamber can be greatly increased even if the thickness of the raw materials placed on each shelf is reduced. .

In the roasting furnace of the present invention, each stage of the shelf on which the raw material is placed is provided with a plurality of nozzles for blowing atmospheric gas, and the nozzles for blowing atmospheric gas are arranged horizontally at the same position in the vertical direction. It is preferable to install.
In order to allow the atmospheric gas to uniformly flow into each stage on which the raw material is placed, it is preferable to provide an atmospheric gas blowing nozzle at each stage, and further, a plurality of atmospheric gas blowing nozzles are provided at each stage. It is preferable.
By installing multiple atmospheric gas injection nozzles at each stage, it is easy to adjust the atmospheric gas flow rate at each stage, preventing partial backflow in each stage and providing a uniform layer of atmospheric gas flow. It becomes possible to make it flow.

The atmospheric gas blowing nozzle is preferably extended to the inside of the shelf board.
By extending the atmospheric gas blowing nozzle to the inside of the shelf board, the gas flow rate can be adjusted for each stage, and the atmospheric gas can be made to flow evenly.

Furthermore, in the roasting furnace of this invention, it is preferable that a shelf board is flat except for the side wall part which makes a spacer.
This is for bringing the surface of the raw material layer into contact with the atmospheric gas as uniformly as possible.
In order to prevent scattering of the raw material, it is conceivable to install a shielding plate between the tip of the atmospheric gas blowing nozzle and the raw material. However, if the shielding plate is installed, the atmospheric gas flow collides with the shielding plate, resulting in a vortex. It is not preferable. Therefore, it is preferable to completely open the atmosphere gas discharge port side of the shelf board. If an obstacle such as a partition plate is installed on the atmosphere gas discharge port side, there is a risk of reverse flow of the gas flow.

  Furthermore, the manufacturing method of the iridium oxide powder of the present invention uses the roasting furnace of the present invention and contains ammonium hexachloroiridium (IV) or potassium hexachloroiridium (IV) at a roasting temperature of 600 to 1050 ° C. and contains oxygen. A method of roasting in a gas atmosphere was adopted.

  In the manufacturing method of the iridium oxide powder of the present invention, potassium can be added to ammonium hexachloroiridium (IV) or potassium hexachloroiridium (IV) and roasted.

  According to the present invention, since the fine powder raw material can be efficiently roasted using the atmospheric gas that has become a laminar flow, there is provided a roasting furnace suitable for the production of an oxide powder with little particle size variation. In addition to being obtained, iridium oxide powder as a conductive powder suitable for a thick film resistor forming paste can be produced industrially and efficiently, and the effect of contributing to the industry is very large.

First, the structure of the roasting furnace of the present invention will be described. FIG. 1 is a view for explaining the internal structure of a roasting furnace according to the present invention. FIG. 1 (a) is a perspective view, and FIG. 1 (b) is a sectional view taken along line AA ′ in FIG. Show.
The roasting furnace 10 of the present invention is a tubular furnace having a substantially square cross section with the roasting chamber 1 in the center. A plurality of atmospheric gas blowing nozzles 9 are attached to the side wall 2 at one end of the roasting chamber 1, and predetermined atmospheric gases are introduced into the roasting chamber 1 by these atmospheric gas blowing nozzles 9. be introduced. The atmospheric gas used for the roasting is discharged out of the system by the atmospheric gas discharge pipe 8 attached to the side wall 3 at the other end of the roasting chamber 1 and also serves as a spacer in the vertical direction in the roasting chamber 1. A plurality of shelf boards 6 (three-stage examples are shown in the figure) for placing raw materials are installed. By making the cross-sectional shape in the furnace substantially square, a plurality of shelf boards 6 can be installed without creating a useless space in the roasting chamber. In addition, by installing a plurality of shelf boards 6 in the vertical direction, the amount of raw materials that can be placed in the roasting chamber 1 is greatly increased even if the thickness of the raw materials placed on each shelf board 6 is reduced. Can be made.

As shown in FIG. 1B, the shelf board 6 has side walls 6a and 6a having appropriate heights on both sides along the longitudinal direction of the roasting chamber 1, and a plurality of shelf boards 6 are stacked and placed. It plays the role of spacer when doing. The top plate 6b of the shelf board 6 is flat and plays the role of a tray (dish) for placing the thinly spread raw material 15 to be processed. However, a separate tray is prepared and the raw material to be processed is placed on the tray. After thinly spreading, it may be placed on the top board.
A plurality of shelves 6 on which the raw material 15 to be treated is placed are placed in the roasting chamber 1, and the atmosphere gas for roasting is unidirectionally placed in the space of the tunnel portion formed below the shelf 6. The roasting process is performed by pouring gently.
The shelf board 6 is made of a heat-resistant material such as ceramics such as alumina or stainless steel.

  The shelf board 6 forming each step has side walls 6a, 6a that also serve as spacers extending in the vertical direction for stacking the shelf boards. The shelf board 6 is preferably flat except for the side walls 6a, 6a which also serve as spacers. In order to prevent the raw material from scattering, it is not preferable to install a shielding plate between the end of the atmospheric gas blowing nozzle and the raw material because the atmospheric gas flow is generated by the shielding plate. When necessary, it is preferable to reduce the height as much as possible when a shielding plate is inevitably installed. Moreover, it is preferable that the atmosphere gas discharge side of the shelf board 6 is completely opened. If a partition plate or the like is installed on the atmosphere gas discharge side, the atmosphere gas flow is reversed. For this reason, it is desirable that the side walls 6 a, 6 a serving also as spacers provided on the respective shelf boards 6 are provided with only columnar protrusions extending in the vertical direction on both sides along the length direction of the roasting chamber 1.

A side wall 2 at one end of the tubular roasting chamber 1 is provided with a penetrating nozzle 9 for blowing atmospheric gas. It is preferable that a plurality of the atmosphere gas blowing nozzles 9 are arranged in a particularly upper portion of the shelf board 6 and are arranged horizontally at the same vertical position.
In the roasting furnace of the present invention, it is important that the atmospheric gas is made into a laminar flow and flows uniformly into each stage. Further, it is preferable that the flow rate is made uniform between the atmosphere gas supply nozzles installed in each stage. By laminar flow, even fine powder raw material can be uniformly roasted without being scattered. Moreover, it is because the raw material in a roasting chamber can be roasted without variation in quality by equalizing the amount of inflow.
In the present invention, an oxygen-containing gas such as air or oxygen gas is used as the atmosphere gas. In order to obtain a laminar flow using these oxygen-containing gases, the flow rate of the atmosphere gas is suitably 100 cm / sec or less.

Evenly adjusting the flow rate of the atmospheric gas can be easily performed by installing a simple flow rate adjusting device for each stage or for each nozzle for blowing atmospheric gas.
The flow rate of the atmospheric gas that becomes a laminar flow is made possible by the arrangement of the nozzle for blowing the atmospheric gas. The arrangement of the atmospheric gas blowing nozzle for flowing the atmospheric gas in only one direction can be easily obtained by performing numerical calculation using commercially available software (for example, general-purpose fluid analysis software CFX). Conditions changed by the roasting scale, that is, the number, interval and shape of the shelves, the amount of space between the shelves in the roasting chamber and the inlet and outlet sides, the number and interval of the nozzles for blowing atmospheric gas, and the roasting temperature What is necessary is just to input and calculate conditions.

In the roasting furnace of the present invention, the atmospheric gas blowing nozzle 9 is preferably extended to the inside of the shelf board 6.
The extending position is not particularly limited, but the raw material to be processed placed inside the tunnel part formed by the shelf and on the shelf so that all the atmospheric gas that flows in flows through each stage of the shelf. What is necessary is just to enter to the position of the gas inflow side rather than.
By extending the atmospheric gas blowing nozzle to the inside of the shelf board, the gas flow rate can be adjusted for each stage, and the atmospheric gas can flow more evenly.

  After the atmospheric gas is introduced, it is necessary that the atmospheric gas flows on the surface of the raw material only in substantially the same direction as the blowing direction. When the atmospheric gas partially flows backward, the reaction between the raw material and the atmospheric gas is not uniformly performed, and unevenness occurs in baking in the shelf board, resulting in variations in the quality of the product obtained. In order to flow the atmospheric gas in only one direction without backflow, it is necessary to slow down the flow velocity of the atmospheric gas to make it laminar. If the laminar flow is used, the atmosphere gas flows in parallel along the raw material layer to be processed, and even if the raw material to be processed is a fine powder, it is not scattered and a uniform roasted product can be obtained.

  The roasting furnace of the present invention can also be used for the production of other fine metal oxide powders, and can be suitably used particularly for the production of conductive powders for thick film resistor pastes such as ruthenium oxide powders.

In the case of producing iridium oxide powder using the roasting furnace of the present invention, ammonium hexachloroiridium (IV) or potassium hexachloroiridium (IV) is used as a raw material, and the atmospheric gas used for roasting is oxygen. Contained gas. A roasting temperature shall be 600-1050 degreeC.
When ammonium hexachloroiridium (IV) is used as a raw material, the potassium component is preferably contained in an amount of 0.02 to 0.3% by weight based on the total amount. By including potassium, potassium chloride is generated during roasting and abnormal grain growth of iridium oxide can be suppressed. When the roasting temperature is less than 600 ° C., unoxidized iridium metal remains, and when it exceeds 1050 ° C., volatilization of iridium oxide increases and the yield decreases.

The roasting temperature may be adjusted by the desired primary particle diameter of the iridium oxide powder. A preferable primary particle diameter is 30 to 100 nm, and by setting the particle diameter within this range, an iridium oxide powder having preferable characteristics as a conductive powder of the thick film resistor paste can be obtained.
If the roasting temperature is 760 ° C. or higher, the amount of potassium chloride evaporated increases, but potassium chloride may remain depending on the roasting conditions. In this case, single-phase iridium oxide powder can be easily obtained by washing with water.
During roasting, the raw material of each stage preferably has a layer thickness of 3 mm or less. If the layer thickness is thicker than 3 mm, unreacted chloroiridate or iridium metal remains inside. Although there is no problem even if the layer thickness is reduced, the raw materials that can be placed in the roasting chamber are reduced, and the productivity is lowered. Even when it is desired to shorten the roasting time, it is sufficient to make the layer thickness about 1 mm.

[Example]
Hereinafter, the present invention will be described in more detail with reference to comparative examples and examples of the present invention, but the present invention is not limited to these examples.
(Comparative Example 1)
As the starting material, ammonium hexachloroindium (IV) acid (made of (NH ₄ ) ₂ IrCl ₆ (Furuya Metal Co., Ltd.)) having an iridium concentration of 43.6% by weight was used. 140 g of this ammonium hexachloroindium (IV) is equally divided and placed on six 150 mm square alumina plates at a layer thickness of 2 mm, and this alumina plate 16 is roasted in the rectangular tube furnace shown in FIG. 1 (inner dimensions: 190 mmH × 440 mmW × 1500 mmL) were arranged in three rows along the long axis direction of the roasting furnace. Further, a shielding plate 13 of 25 mmH × 280 mmW was installed across the entire width of the bottom of the roasting chamber between the atmosphere gas (oxygen gas) blowing nozzle 9 and the raw material. The oxygen gas blowing nozzle 9 was a cylindrical alumina tube having an inner diameter of 6 mm, and four nozzles were uniformly attached to a surface perpendicular to the gas traveling direction at the end of the tubular furnace. Then, oxygen gas was supplied from each oxygen gas blowing nozzle 9 at a rate of 10 liters / minute for a total of 40 liters / minute. As a result, the average flow rate of oxygen gas in the roasting chamber was about 48 cm / min.

  The roasting temperature was kept at 900 ° C. and roasted for 4 hours. When the obtained roasted product was evaluated, the average primary particle size was 34 nm, the dispersion of the particle size depending on the raw material placement position was 0.9, and the iridium oxide powder was suitable for the conductive powder of the thick film resistor paste. However, the amount produced was as small as 70 g.

(Comparative Example 2)
Using a roasting furnace in which the height of the roasting furnace of Comparative Example 1 was about three times, ammonium hexachloroiridium (IV) having an iridium concentration of 43.6% by weight was roasted. As shown in FIGS. 3 (a) and 3 (b), shelves 6 serving as three spacers are stacked and placed in the roasting chamber, and a shielding plate 13 is installed on the inflow side of each shelf. The shielding plate 14 was also installed at the end of the shelf on the discharge side.

The raw material to be processed is placed on an alumina plate with a layer thickness of 2 mm, and the shelf plate 6 is used to arrange the raw materials to be processed in two rows of three, six in each stage, and stacked in three stages, for a total of 18 grams, 420 g Roasted raw materials.
Also, two oxygen gas injection nozzles 9 made of alumina with an inner diameter of 6 mm are arranged in each stage symmetrically with the center line of the furnace, for a total of six, and 10 liters / minute from each of the oxygen gas injection nozzles 9. Then, oxygen gas was flown at a total of 60 liters / minute to create an oxidizing atmosphere during roasting. The average oxygen gas flow rate in the tunnel portion of each shelf 6 was 20 cm / min. The numerical analysis results of the atmospheric gas flow are shown in FIG. As shown in the figure, the occurrence of vortex is observed in the rear portion of the shielding plate 13 near the oxygen gas blowing nozzle.

When the obtained roasted product was evaluated, the average primary particle diameter was 33 nm, but the dispersion due to the raw material placement position was large with a variation of 18, and it was an iridium oxide powder that was not suitable for the conductive powder of the thick film resistor paste. there were.
The atmospheric gas flow in the roasting chamber was numerically analyzed using commercially available software (CFX, ANSYS Co., Ltd.). The results are shown in FIG. As shown in FIG. 4, there were many partial vortices and starches in the roasting chamber, and a uniform flow velocity distribution was not obtained on the raw material surface.

Using the roasting furnace of the present invention shown in FIG. 1, numerical analysis was performed for the case where the same amount of raw material as in Comparative Example 2 was made into two rows, three sheets, and three layers, and the raw material surface was inflow side to discharge side. The condition that the atmospheric gas flows uniformly was derived. The inner dimensions of the roasting chamber are three times the height of Comparative Example 1 as in Comparative Example 2. While maintaining the oxygen gas flow rate at 10 liters / minute for each oxygen gas blowing nozzle, the number of oxygen gas blowing nozzles is increased from 2 to 4 in each stage to a total of 12 nozzles. Was changed to 8 mm. As a result, the average flow rate of oxygen gas flowing through the tunnel portion of the shelf plate was 40 cm / min. In addition, the shielding plate installed on the inflow side of each stage was removed, and the end of the shelf plate was changed to a completely open state on the discharge side.
The numerical analysis result of the atmosphere gas flow after the change is shown in FIG. It can be seen that the partial vortex and stagnation generated in the roasting chamber are eliminated, and a uniform flow velocity distribution is obtained on the surface of the raw material.
When the obtained roasted product was evaluated, the average primary particle diameter was 33 nm, the dispersion due to the raw material placement position was 2, and the variation could be eliminated, and iridium oxide suitable for the conductive powder of the thick film resistor paste A powder was obtained. Moreover, the production amount per batch was 210 g.

  As described above, it can be seen that in Example 1, compared to Comparative Example 2, the dispersion of the obtained iridium oxide powder depending on the raw material placement position is small, and the quality is stable. Moreover, compared with the comparative example 1, the Example can use the roasting chamber effectively and can improve productivity significantly, and it turns out that iridium oxide powder with stable quality can be produced efficiently by the present invention.

It is a figure explaining the internal structure of the roasting furnace of this invention, Comprising: (a) is a perspective view, (b) is sectional drawing along line A-A '. It is a see-through | perspective perspective view explaining the internal structure of the roasting furnace used in the comparative example 1. FIG. It is a figure which shows the raw material loading method of the comparative example 2, Comprising: (a) is a top view, (b) is a longitudinal cross-sectional view. It is a figure which shows the atmospheric gas distribution in the roasting chamber in the comparative example 2. It is a figure which shows the atmospheric gas distribution in the roasting chamber in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Roasting chamber 2, 3 Side wall 6 Shelf board 8 Atmospheric gas discharge pipe 9 Atmospheric gas blowing nozzle 10 Roasting furnace 13, 14 Shield plate 15 Raw material to be processed 16 Alumina plate

Claims (6)

  It is a tubular furnace having a substantially square cross-sectional shape, and has a plurality of shelves in the vertical direction in the roasting chamber, and has an atmosphere gas blowing nozzle in one of the axial directions in the roasting chamber, and the other A roasting furnace for producing oxide powder, characterized in that the atmospheric gas is provided with an atmospheric gas discharge port so that the atmospheric gas flows on the surface of the raw material only in substantially the same direction as the blowing direction.   A plurality of atmospheric gas blowing nozzles are provided on each stage of the shelf on which the raw material is placed, and the atmospheric gas blowing nozzles are horizontally arranged at the same position in the vertical direction. The roasting furnace according to claim 1.   The roasting furnace according to claim 1 or 2, wherein the atmospheric gas blowing nozzle extends to the inside of the shelf board.   The roasting furnace according to any one of claims 1 to 3, wherein the shelf plate is flat except for a side wall portion forming a spacer.   Using the roasting furnace according to claim 1, roasting ammonium hexachloroiridium (IV) or potassium hexachloroiridium (IV) at 600 to 1050 ° C. in an oxygen-containing gas atmosphere. A method for producing iridium oxide powder characterized by the above.   6. The method for producing iridium oxide powder according to claim 5, wherein potassium is added to ammonium hexachloroiridium (IV) or potassium hexachloroiridium (IV) and roasted.