JPH0687683A - Production of noble metal coated ceramic powder - Google Patents

Abstract

PURPOSE:To provide a method for producing noble metal coated ceramic powder by which the formation of a flocculated body is inhibited, ceramic components are element prevented from entering a formed noble metal coating layer and a ceramic phase is hardly exposed when ceramic powder, especially fine ceramic powder having <=1mum particle diameter is coated with a noble metal such as Pd by chemical plating. CONSTITUTION:A reducing agent is added to a primary dispersion liq. prepd. by dispersing ceramic powder in an aq. soln. of a noble metal salt and a thin noble metal film is formed on the surface of the ceramic powder. This ceramic powder with the thin noble metal film is dispersed in an aq. soln. contg. a noble metal salt and a water-soluble polymer, a reducing agent is added to the resulting secondary dispersion liq. and a noble metal layer is formed around the thin noble metal film on the surface of the ceramic powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a precious metal-coated ceramic powder. The present invention particularly relates to a method for producing a noble metal-coated ceramic powder in which the noble metal coating layer is substantially free from contamination by the ceramic powder component. Further, the present invention particularly relates to a production method suitable for producing a noble metal-coated ceramic fine powder which is substantially composed of primary particles and has few agglomerates mixed therein.

[0002]

2. Description of the Related Art For electrode layers of multilayer capacitors and various other electronic components, a conductive paste generally composed of a noble metal powder such as silver, platinum, gold, or palladium and an organic binder is applied in a film form on a ceramic substrate. Then, it is formed by firing. The electrode layer thus formed is substantially a continuous layer of noble metal. The noble metal continuous layer has been used for a long time as an electrode material because it has low electric resistance and high conductivity. However, in recent years, it has been studied to reduce the manufacturing cost by reducing the amount of expensive precious metal used. In addition, when the conductive paste is applied to the substrate and fired, the conductive paste is directly applied to an unfired ceramic substrate (also referred to as a green sheet) in order to simplify the manufacturing process. By firing, a method of performing firing of the substrate and firing of the conductive paste (formation of an electrode layer) at the same time (simultaneous firing) is used. Co-firing is a useful method that contributes to the simplification of the process, but if the green sheet and the coating layer of the conductive paste containing the noble metal powder as the main component are co-fired, the noble metal layer and the ceramic substrate are formed. Due to the difference in the coefficient of thermal expansion, there is a problem that cracks and cracks are likely to occur in the ceramic layer. In addition, a peeling phenomenon (delamination) often occurs at the interface between the ceramic sheet and the electrode.

As a measure for avoiding delamination and cracks, and also for reducing the amount of precious metals used, it has already been proposed to introduce a ceramic powder made of the same material as the ceramic substrate into the conductive paste. Has been put into practical use. This method, by introducing a ceramic powder into the conductive paste, to reduce the difference between the coefficient of thermal expansion of the electrode layer formed from the conductive paste and the coefficient of thermal expansion of the ceramic substrate to prevent the occurrence of delamination. It is based on the principle of. At the same time, there is an advantage that the amount of precious metal powder used can be reduced. By using this method, it is possible to suppress the occurrence of delamination. However, since the ceramic powder mixed in the electrode layer adversely affects the electrical characteristics of the electrode layer, particularly the conductivity, there is a problem that it cannot be used for forming the electrode layer requiring high conductivity. For this reason, it has already been studied to coat the ceramic particles with a noble metal layer into a conductive powder using a surface coating method such as a chemical plating method. By preparing a conductive paste using this noble metal-coated ceramic powder as a conductive powder, the conductivity of the electrode layer is significantly improved compared to the conductivity of the electrode layer formed from the noble metal powder and the ceramic powder. To do. However, the particle size of the ceramic powder is 3 μm or less,
In particular, it has been found that it is difficult to obtain a conductive powder having high conductivity by using a conductive powder obtained by using a fine metal powder having a particle size of 1 μm or less and forming a noble metal coating layer on the powder using a chemical plating method. That is, recently, as one of means for downsizing electronic components and electronic devices and cost reduction of electrode materials, thinning of electrode layers (for example, layer thickness 10 μm or less, further layer thickness 3 μm or less, and further layer thickness 1 μm or less). In order to form such a thin film electrode layer, as described above, a conductive fine powder in which the surface of fine particle ceramic powder having a particle diameter of 3 μm or less, particularly 1 μm or less is uniformly coated with a noble metal is used. It is necessary to prepare. However, it is very difficult to stably produce such conductive fine powder uniformly coated with a noble metal by the usual chemical plating method.

Conventionally, various methods have been known as a method for forming a noble metal coating layer on the surface of ceramic powder, and a typical method thereof is an electroless plating method. This electroless plating method is also called an electrodeless plating method or a chemical plating method. Generally, ceramic powder is dispersed in an aqueous solution of a noble metal salt, and a reducing agent is added to this dispersion liquid so that the noble metal is coated on the surface of the ceramic powder. It is a method of precipitating. This method can be carried out without much problems when the ceramic powder consisting of relatively large particles is coated with the noble metal, but it can be carried out as fine particle ceramic powder, for example, ultrafine particles having a diameter of 3 μm or less, particularly 1 μm or less. When it is desired to coat the surface of the ceramic powder with the noble metal, it is difficult to uniformly form the noble metal coating layer on the surface of the ceramic fine particles. This is because fine-grained ceramic powder tends to aggregate in an aqueous solution of a noble metal salt, and particularly when a reduction reaction occurs, and a noble metal coating layer is formed on the surface of the ceramic powder aggregate (secondary particles). Is. Aggregates whose surface is covered with a noble metal coating layer are disintegrated when a conductive paste is prepared later to form a thin film electrode layer and become primary particles, but the surface of the primary particles is a part of Has a noble metal coated surface in the area,
The ceramic phase is exposed in the region that was in contact with other particles when the aggregate was formed. Therefore, when the electrode layer is formed by using the conductive particles in which the ceramic phase is exposed and the surface is inhomogeneous as described above, the electrical characteristics of the electrode layer, particularly the electrical conductivity, are difficult to reach a sufficient level. Further, in the conventional chemical plating method as described above, the noble metal produced by the reduction reaction does not always deposit only on the surface of the ceramic particles, and a part of the produced noble metal itself forms fine particles, so the noble metal fine particles are formed. Will be mixed in the obtained coating powder.

In view of the above circumstances, when the fine ceramic powder is coated with the noble metal by using the chemical plating method in order to obtain the conductive fine particles, the noble metal coating is performed while suppressing the formation of aggregates as much as possible. However, at present, there is no known method that is practically sufficiently satisfactory in the reagents and procedures to be used.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of coating a noble metal while using a chemical plating method to coat a fine ceramic powder with a noble metal while suppressing the formation of aggregates. To provide.
Further, according to the present invention, a ceramic fine particle powder having a particle diameter (meaning an average particle diameter unless otherwise specified) of 3 μm or less, particularly 1 μm or less is coated with a noble metal, and the ceramic phase is hardly exposed and the purity is high. That is, it is also an object to provide a method of forming a noble metal coating layer in which the mixture of ceramic components is small.

[0007]

According to the present invention, a reducing agent is added to a dispersion liquid (primary dispersion liquid) in which ceramic powder is dispersed in an aqueous solution of a precious metal salt to form a precious metal thin film layer on the surface of the ceramic powder. Step, and disperse the ceramic powder having the noble metal thin film layer in an aqueous solution containing a noble metal salt and a water-soluble polymer, and then add a reducing agent to the dispersion (secondary dispersion) to make the noble metal layer ceramic. There is a method for producing a ceramic powder coated with a noble metal, which comprises forming around the noble metal thin film layer on the surface of the powder.

The present invention can be said to be an improved method of conventional chemical plating. That is, a known chemical plating method in which a reducing agent is added to a dispersion liquid containing a ceramic powder dispersed in an aqueous solution of a noble metal salt to reduce the noble metal salt, and the noble metal is deposited on the surface of the ceramic powder to form a noble metal coating layer. Method of utilizing the method, but an improved method of suppressing the agglomeration of ceramic powder or noble metal-coated particles to form a noble metal coating layer that has almost no exposure of the ceramic phase and is high in purity, that is, contains less ceramic components. Is.

The material components of the ceramic powder used in the present invention are not particularly limited, but those formed from materials arbitrarily selected from the materials of various ceramic substrates used in the production of ordinary electronic parts are used. . Such a ceramic material, barium titanate, aluminum oxide, titanium dioxide, zirconium oxide, oxide powder such as silicon oxide, and PbTi0 _3, PZT (P
b (Zr, Ti) O ₃ abbreviation), PLZT ((Pb, L
a) (Zr, Ti) O ₃ abbreviation) or PMN (P
a piezoelectric or electrostrictive ceramic particle powder such as a metal oxide represented by b (Mg _1/3 Nb _2/3 ) O ₃ or particles of a metal oxide containing these metal oxides as a main component. Can be mentioned.

The particle size of the ceramic powder used in the present invention is not particularly limited, but as described above, when the method of the present invention is used, the ceramic fine particle powder having a particle size of 3 μm or less, particularly 1 μm or less is increased with a noble metal. It is advantageous to select such a finely divided ceramic powder when carrying out the coating method of the present invention, since the coating can be performed with a high degree of purity. In addition, according to the coating method of the present invention, the particle diameter is 0.
A uniform noble metal coating of ultrafine powder having a particle size of 8 μm or less and further a particle size of 0.5 μm or less is realized.

As the noble metal with which the surface of the ceramic powder is coated, a noble metal having a high electric conductivity such as silver, platinum, palladium or gold is selected.

Next, the operation of the method for producing the noble metal-coated ceramic powder of the present invention will be described in detail. In the method for producing a ceramic powder coated with a noble metal of the present invention, first, a salt of a noble metal is dissolved in water to prepare an aqueous solution of the noble metal, and then the ceramic powder is uniformly dispersed in this to obtain a primary dispersion liquid. It is also possible to use a method in which an aqueous dispersion of ceramic powder is first prepared and then a water-soluble noble metal salt is dissolved therein. As the water-soluble noble metal salt, various noble metal salts (or complexes) such as tetrachloropalladate ammonium salt, tetraamminepalladium chloride, tetrachloroplatinum ammonium salt, and tetraammineplatinic chloride can be used. It should be noted that a substance other than the water-soluble noble metal salt and the ceramic powder (for example, a water-soluble polymer) may be added to the primary dispersion liquid in a small amount. However, for example, when the water-soluble polymer is added, the addition amount needs to be smaller than the addition amount of the water-soluble polymer to the secondary dispersion liquid described later.

Next, a ceramic dispersion liquid (primary dispersion liquid) obtained by dispersing ceramic powder in the above-mentioned precious metal salt aqueous solution.
A reducing agent is added to this dispersion while stirring. As the reducing agent, a reducing agent such as hydrazine, hydrazine hydrochloride, formic acid, formalin, hypophosphorous acid and the like used in a known chemical plating method is generally used. The reducing agent is usually added as an aqueous solution to the above primary dispersion. Alternatively, the above primary dispersion may be added to the aqueous reducing agent solution. By mixing the primary dispersion and the reducing agent aqueous solution, a noble metal thin film (a monoatomic film or a thin film similar thereto) is formed on the surface of the ceramic powder.

Then, the above-mentioned ceramic powder having a noble metal thin film layer formed on the surface (referred to as primary coating ceramic powder) is taken out from the dispersion liquid, and this primary coating ceramic powder is then mixed with a noble metal salt and a water-soluble polymer. To prepare a secondary dispersion liquid. However,
The primary coating ceramic powder does not necessarily have to be separated from the primary dispersion, and the noble metal salt and the water-soluble polymer may be added to the primary dispersion containing the primary coating ceramic powder to prepare the secondary dispersion.

The noble metal salt (water-soluble noble metal) used in preparing the secondary dispersion may be the same as the water-soluble noble metal salt used in preparing the primary dispersion, or may be another water-soluble noble metal salt. It may be.

The water-soluble polymer used for preparing the secondary dispersion is not particularly limited, but as the water-soluble polymer, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, hydroxyethyl methyl cellulose, which has good dispersibility of ceramic fine powder, can be used. It is desirable to use water-soluble cellulose derivatives such as, hydroxypropylmethyl cellulose, carboxymethyl cellulose and the like. However, water-soluble natural product polymers such as gelatin and casein, and water-soluble synthetic polymer compounds such as polyvinyl alcohol and polyvinylpyrrolidone may be used.

Next, a reducing agent is added to this dispersion while stirring the secondary dispersion prepared by dispersing the primary coating ceramic powder in the aqueous solution containing the above-mentioned noble metal salt and water-soluble polymer. As the reducing agent, in principle, the reducing agent used for producing the primary coating ceramic powder is used, but it is not necessary to be the same. By mixing the secondary dispersion and the reducing agent (reducing agent aqueous solution), a noble metal layer much thicker than the primary coating layer is formed on the surface of the primary coating ceramic powder.

Next, the ceramic powder having a noble metal layer laminated on the surface (referred to as secondary coated ceramic powder) is taken out from the dispersion and dried to obtain the target noble metal coated ceramic powder.

When the noble metal-coated ceramic powder is obtained by the production method of the present invention, the ratio of the ceramic part which becomes the core (nucleus or core) and the noble metal part which becomes the coating layer (shell) can be arbitrarily selected. However, the ratio of ceramic: noble metal is usually 5:95 to 80:20 (weight ratio).
Especially, ceramic: precious metal is 10:90 to 50:50
(Weight ratio) is preferable.

The noble metal-coated ceramic powder obtained by the production method of the present invention can be used alone as a conductive paint (paste) by mixing it with an ordinary binder or the like by a conventional method. The powder may be used as a mixture with a pure precious metal powder.

A method of manufacturing an electrode by applying a conductive paste to a substrate is generally used. When the conductive paste using the noble metal-coated ceramic powder of the present invention is used, the same treatment is performed to form an electrode. can do.

[0022]

【Example】

Example 1 Production of Palladium-Coated Barium Titanate Fine Powder (1) Production of Palladium Primary-Coated Barium Titanate Fine Powder 2.0 g Barium Titanate Fine Powder (BaTiO ₃ , Average Particle Size 0.2 μm, Ratio) Surface area 12.7 m ² / g) and 3.2
ml of an aqueous solution of ammonium tetrachloropalladate (an aqueous solution having a concentration of 1 g / 100 ml in terms of metal palladium) was added to 200 ml of pure water, and barium titanate fine powder was dispersed in the aqueous solution of ammonium tetrachloropalladate. A primary dispersion was prepared. While stirring this primary dispersion at room temperature, 1.2 ml of an aqueous hydrazine hydrate solution (1 ml of 100% hydrazine hydrate diluted with 100 ml of pure water) was added. By adding this hydrazine hydrate aqueous solution, a trace amount of metallic palladium is uniformly deposited on the surface of the barium titanate fine powder,
Palladium primary coated barium titanate fine powder was produced.

(2) Production of Palladium Secondary-Coated Barium Titanate Fine Powder The palladium primary-coated barium titanate fine powder was taken out and dried, and then uniformly added to a hydroxyethyl cellulose aqueous solution (0.2 g / 500 ml). It was well dispersed and suspended. Next, an aqueous solution of tetraamminepalladium chloride (containing 18.0 g of metal palladium (Pd) was added) was added to this dispersion to prepare a secondary dispersion. Then, while stirring the secondary dispersion, an aqueous hydrazine hydrate solution (100%
Hydrazine hydrate (containing 5.4 ml) was slowly added. By adding this hydrazine hydrate aqueous solution, barium titanate fine powder having a blackish gray coating layer was obtained. This was separated by filtration, washed with water, and then dried to obtain a dry fine powder. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles consisted of 90% by weight of metallic palladium and 10% by weight of barium titanate.

Example 2 Production of Palladium-Coated Barium Titanate Fine Powder (1) Production of Palladium Primary-Coated Barium Titanate Fine Powder Example 1 except that the amount of each material used was changed as follows.
Palladium primary-coated barium titanate fine powder was produced in the same manner as in (1) above. Barium titanate fine powder (same as in Example 1): 4.0 g Ammonium tetrachloropalladate aqueous solution (same as above): 6.4 ml Pure water: 200 ml (same as above) Hydrazine hydrate aqueous solution (same as above): 2.4 ml (2) Production of Palladium Secondary Coated Barium Titanate Fine Powder Example 1 except that the amount of each material used was changed as follows:
Palladium secondary-coated barium titanate fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraamminepalladium chloride aqueous solution: 16 g
(Metal Pd equivalent) Aqueous hydrazine hydrate solution: 4.8 ml (100% hydrazine hydrate equivalent) The obtained barium titanate fine powder having a black gray coating layer was filtered off, washed with water, and then dried and dried. A fine powder was obtained. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles are 8
It consisted of 0% by weight metallic palladium and 20% by weight barium titanate.

Example 3 Production of Palladium-Coated Barium Titanate Fine Powder (1) Production of Palladium Primary-Coated Barium Titanate Fine Powder Example 1 except that the amount of each material used was changed as follows.
Palladium primary-coated barium titanate fine powder was produced in the same manner as in (1) above. Barium titanate fine powder (same as that of Example 1): 5.0 g Ammonium tetrachloropalladate aqueous solution (same as above): 8.0 ml Pure water: 200 ml (same as above) Hydrazine hydrate aqueous solution (same as above): 3.0 ml (2) Production of Palladium Secondary Coated Barium Titanate Fine Powder Example 1 except that the amount of each material used was changed as follows:
Palladium secondary-coated barium titanate fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraamminepalladium chloride aqueous solution: 15 g
(Metal Pd equivalent) Aqueous hydrazine hydrate solution: 4.5 ml (100% hydrazine hydrate equivalent) The obtained barium titanate fine powder having a black gray coating layer was filtered off, washed with water, and then dried and dried. A fine powder was obtained. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles are 7
It consisted of 5% by weight metallic palladium and 25% by weight barium titanate.

Comparative Example 1-Production of Palladium-Coated Barium Titanate Fine Powder 5.0 g of the same barium titanate fine powder used in Example 1 was added to an aqueous solution of tetraamminepalladium chloride (metal palladium (Pd)). (Contains 15g when converted)
And dispersed in 300 ml of a mixed solution of isopropyl alcohol. Then, while stirring this dispersion, an aqueous hydrazine hydrate solution (containing 4.5 ml of 100% hydrazine hydrate) was slowly added thereto at room temperature. By adding this hydrazine hydrate aqueous solution, barium titanate fine powder having a black coating layer was obtained. This was separated by filtration, washed with water, and then dried to obtain a dry fine powder. When the dried fine powder (coated particles) was observed with a scanning electron microscope,
It was confirmed to be a powder containing a large amount of palladium metal particles and a large amount of aggregates. The entire powder containing the palladium metal particles and the agglomerates was composed of 75% by weight of metallic palladium and 25% by weight of barium titanate.

[Evaluation of Palladium Secondary-Coated Barium Titanate Fine Powder as Electrode Material] 100 parts by weight of the palladium-coated barium titanate fine powder obtained in each of Examples 1 to 3, 5 parts by weight of ethyl cellulose, and terpineol. 75 parts by weight were kneaded using a three-roll mill to obtain a conductive paste. A conductive paste was obtained in the same manner by using the powder containing the palladium metal particles and the aggregate obtained in Comparative Example 1. Further, a palladium metal powder was used instead of the palladium-coated barium titanate fine powder, and a conductive paste was obtained in the same manner. The obtained conductive paste was printed on a barium titanate green sheet (unbaked substrate) by screen printing, dried at 100 ° C. for 10 minutes, and then baked at 1300 ° C. for 1 hour. 1300 ° C from room temperature
Up to 200 ° C./hour. The surface appearance and electrical characteristics (resistance value) of the electrode thus obtained are
Shown in the table.

Table 1 ──────────────────────────────────── BiTiO ₃ : Pd Resistance (mΩ / Sq.) External appearance ──────────────────────────────────── Example 1 10:90 50. 6 Good Good Example 2 20:80 54.6 Good Good Example 3 25:70 69.0 Good Good Comparative Example 1 25:70 540 Good Good Reference Example 0: 100 44.0 Partial peeling occurrence ─── ──────────────────────────────────

Example 4 Production of Palladium-Coated Barium Titanate Fine Powder (1) Production of Palladium Primary-Coated Barium Titanate Fine Powder Example 1 except that the amount of each material used was changed as follows.
Palladium primary-coated barium titanate fine powder was produced in the same manner as in (1) above. Barium titanate fine powder (same as in Example 1): 10.0
g Ammonium tetrachloropalladate aqueous solution (same as above): 16 ml Pure water: 200 ml (same as above) Aqueous hydrazine hydrate solution (same as above): 3 ml (2) Palladium secondary coated barium titanate Fine powder production Example 1 except that
Palladium secondary-coated barium titanate fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraamminepalladium chloride aqueous solution: 10 g
(Metal Pd equivalent) Aqueous hydrazine hydrate solution: 3.0 ml (100% hydrazine hydrate equivalent) The obtained barium titanate fine powder having a black gray coating layer was filtered off, washed with water, and then dried and dried. A fine powder was obtained. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles are 5
It consisted of 0% by weight metallic palladium and 50% by weight barium titanate. 50 parts by weight of the above palladium-coated barium titanate fine powder, 50 parts by weight of palladium metal powder, 5 parts by weight of ethyl cellulose, and 75 parts by weight of terpineol were kneaded using a three-roll mill, and a conductive paste (barium titanate: metallic palladium = 25:
75, weight ratio). An electrode was produced from the obtained conductive paste by the method described above, and the appearance and electrical characteristics (resistance value) of the surface of this electrode were examined. The appearance was good and the resistance value was 55.0 mΩ / sq. ． And a value similar to that of an electrode manufactured from a conductive paste using only palladium metal powder.

[Example 5] Palladium-coated PZT
(Pb (Zr, Ti) O ₃ ) Fine Powder Production (1) Palladium Primary-Coated PZT Fine Powder Production 5.0 g of PZT fine powder (Pb (Zr, Ti) O ₃ , average particle size 0.5 μm, ratio Surface area 2.1 m ² / g) and 4 ml ammonium tetrachloropalladate aqueous solution (concentration of 1 g / 100 ml in terms of metallic palladium)
And were added to 200 ml of pure water to prepare a primary dispersion liquid in which PZT fine powder was dispersed in an aqueous solution of ammonium tetrachloropalladate. While stirring the primary dispersion at room temperature, 3 ml of an aqueous hydrazine hydrate solution (1
1 ml of 00% hydrazine hydrate diluted with 100 ml of pure water) was added. By the addition of this aqueous hydrazine hydrate solution, a trace amount of metallic palladium was uniformly deposited on the surface of the PZT fine powder, and palladium primary-coated PZT fine powder was produced.

(2) Production of PZT fine powder coated with palladium secondary coating The above-mentioned PZT fine powder coated with palladium primary was taken out and dried, and then uniformly dispersed in an aqueous solution of hydroxyethyl cellulose (0.2 g / 500 ml). ,
Suspended. This dispersion was then mixed with an aqueous solution of tetraamminepalladium chloride (metal palladium (Pd)
(15 g in terms of) was added to prepare a secondary dispersion. Then, while stirring the secondary dispersion, at room temperature,
To this, an aqueous hydrazine hydrate solution (containing 4.5 ml of 100% hydrazine hydrate) was slowly added. By adding this hydrazine hydrate aqueous solution, PZ having a black gray coating layer
T fine powder was obtained. This was separated by filtration, washed with water, and then dried to obtain a dry fine powder. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles consisted of 75 wt% metallic palladium and 25 wt% PZT.

[Example 6] -Production of palladium-coated PZT fine powder (1) Production of palladium primary-coated PZT fine powder Example 5 was repeated except that the amounts of the respective materials used were changed as follows.
PdT-coated PZT fine powder was prepared in the same manner as in (1). PZT fine powder (same as in Example 5): 4.0 g Ammonium tetrachloropalladate aqueous solution (same as above): 3.2 ml Pure water: 200 ml (same as above) Hydrazine hydrate aqueous solution (same as above): 1.5 ml (2) Palladium di Production of Next Coated PZT Fine Powder Example 5 except that the amount of each material used was changed as follows.
PdT secondary-coated PZT fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 5) Tetraamminepalladium chloride aqueous solution: 16 g
(Metal Pd equivalent) Aqueous hydrazine hydrate solution: 4.8 ml (100% hydrazine hydrate equivalent) The obtained PZT fine powder having a black gray coating layer was filtered off, washed with water, and then dried to obtain a dry fine powder. Got When the dried fine powder (secondary coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles consisted of 80% by weight metallic palladium and 20% by weight PZT.

[Example 7] -Production of palladium PZT fine powder (1) Production of palladium primary-coated PZT fine powder Example 5 except that the amount of each material used was changed as follows.
PdT-coated PZT fine powder was prepared in the same manner as in (1). PZT fine powder (same as in Example 5): 3.0 g Ammonium tetrachloropalladate aqueous solution (same as above): 2.4 ml Pure water: 200 ml (same as above) Hydrazine hydrate aqueous solution (same as above): 1.0 ml (2) Palladium di Production of Next Coated PZT Fine Powder Example 5 except that the amount of each material used was changed as follows.
PdT secondary-coated PZT fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 5) Tetraamminepalladium chloride aqueous solution: 17 g
(Metal Pd conversion value) Aqueous hydrazine hydrate aqueous solution: 5.1 ml (100% hydrazine hydration conversion) The obtained PZT fine powder having a black gray coating layer was separated by filtration, washed with water, and then dried to obtain dried fine powder. Got When the dried fine powder (secondary coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles consisted of 85% by weight metallic palladium and 15% by weight PZT.

[Palladium secondary coating P as electrode material
Evaluation of ZT fine powder] 100 parts by weight of the palladium-coated PZT fine powder obtained in each of Examples 5 to 7, 5 parts by weight of ethyl cellulose, and 75 parts by weight of terpineol were kneaded using a three-roll mill to obtain a conductive paste. Got The obtained conductive paste was screen-printed on a PZT green sheet and baked at 1150 ° C. for 1 hour to manufacture an electrode, and the appearance and electrical characteristics (resistance value) of the surface of this electrode were examined. Table 2 shows the appearance and electrical characteristics (resistance value) of the surface of the electrode thus obtained.

Table 2 ──────────────────────────────────── PZT: Pd Resistance value (mΩ / sq.) Outside ──────────────────────────────────── Example 5 25:75 182.9 Good Good Example 6 20:80 141.6 Good Good Example 7 15:80 106.5 Good Good ─────────────────────────── ──────────

[Example 8] -Production of platinum-coated PZT fine powder (1) Production of platinum primary-coated PZT fine powder Example 1 (1) of Example 5 except that the materials and the amounts used were changed as follows. Platinum primary-coated PZT fine powder was produced in the same manner as in. PZT fine powder (same as Example 5): 3.0 g Ammonium tetrachloroplatinate aqueous solution (aqueous solution having a concentration of 1 g / 100 ml in terms of metal Pt): 1.5 ml Pure water: 200 ml (same as Example 5) Aqueous hydrazine hydrate solution (the same as above): 1.0 ml (2) Production of platinum secondary-coated PZT fine powder Example 5 except that the amount of each material used was changed as follows:
A platinum secondary coated PZT fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraammineplatinum chloride aqueous dispersion: 17 g (metal Pt conversion value) Hydrazine hydrate aqueous solution: 4.5 ml (100% hydrazine hydration conversion) PZT fine powder having the obtained black gray coating layer The powder was filtered off, washed with water and then dried to obtain a dry fine powder. When the dried fine powder (secondary coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles consisted of 85% by weight platinum and 15% by weight PZT. Using the platinum-coated PZT fine powder described above, a conductive paste was prepared according to the method described in Example 5, and then an electrode was produced from this conductive paste by the method described above, and the appearance of the surface of the electrode and When the electrical characteristics (resistance value) were examined, the appearance was good and the resistance value was 368.0 mΩ / sq. And showed good results.

Example 9 Production of Palladium-Coated Titanium Dioxide Fine Powder (1) Production of Palladium Primary-Coated Titanium Dioxide Fine Powder In Example 1 except that the materials and the amounts used were changed as follows: Palladium primary-coated titanium dioxide fine powder was produced in the same manner as in 1). Titanium dioxide fine powder (TiO ₂ , average particle size 0.3 μm,
Specific surface area: 7.14 m ^{2 /} g): 10.0 g Ammonium tetrachloropalladate aqueous solution (same as in Example 1): 8.0 ml Pure water: 200 ml (same as above) Hydrazine hydrate aqueous solution (same as above): 3.0 ml ( 2) Production of Palladium Secondary Coated Titanium Dioxide Fine Powder Example 1 except that the amount of each material used was changed as follows:
Palladium secondary coated titanium dioxide fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraamminepalladium chloride aqueous solution: 10 g
(Metallic Pd conversion value) Aqueous hydrazine hydrate aqueous solution: 3.0 ml (100% hydrazine hydration conversion) The obtained titanium dioxide fine powder having a black gray coating layer was filtered off, washed with water, and then dried to dryness. A powder was obtained. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles consisted of 50% by weight metallic palladium and 50% by weight titanium dioxide.

Example 10 Production of Palladium-Coated Aluminum Oxide Fine Powder (1) Production of Palladium Primary-Coated Aluminum Oxide Fine Powder In Example 1 except that the respective materials and the amounts used were changed as follows: Palladium primary-coated aluminum oxide fine powder was produced in the same manner as in 1). Aluminum oxide fine powder (Al ₂ O ₃ , average particle size 0.3
μm, specific surface area 7.26 m ^{2 /} g): 10.0 g Ammonium tetrachloropalladate aqueous solution (same as in Example 1): 5.0 ml Pure water: 200 ml (same as above) Hydrazine hydrate aqueous solution (same as above): 2.0 ml (2) Production of Palladium Secondary Coated Aluminum Oxide Fine Powder Example 1 except that the amount of each material used was changed as follows:
Palladium secondary-coated aluminum oxide fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraamminepalladium chloride aqueous solution: 10 g
(Metallic Pd conversion value) Aqueous hydrazine hydrate solution: 3.0 ml (100% hydrazine hydration conversion) The obtained aluminum oxide fine powder having a black gray coating layer was filtered off, washed with water, and then dried and dried to a fine powder. A powder was obtained. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles are 5
It consisted of 0% by weight metallic palladium and 50% by weight aluminum oxide.

Example 11 Production of Palladium-Coated Zirconium Oxide Fine Powder (1) Production of Palladium Primary-Coated Zirconium Oxide Fine Powder In Example 1 except that the respective materials and the amounts used were changed as follows: Palladium primary-coated zirconium oxide fine powder was produced in the same manner as in 1). Zirconium oxide fine powder (ZrO ₂ , average particle size 0.2μ
m, specific surface area 12.26 m ^{2 /} g): 10.0 g ammonium tetrachloropalladate aqueous solution (same as in Example 1): 14.0 ml pure water: 200 ml (same as above) hydrazine hydrate aqueous solution (same as above): 5.0 ml (2) Production of Palladium Secondary Coated Zirconium Oxide Fine Powder Example 1 except that the amount of each material used was changed as follows.
Palladium secondary-coated zirconium oxide fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraamminepalladium chloride aqueous solution: 10 g
(Metal Pd conversion value) Aqueous hydrazine hydrate solution: 3.0 ml (100% hydrazine hydration conversion) The obtained zirconium oxide fine powder having a black-grey coating layer was filtered off, washed with water, and then dried to dryness. A powder was obtained. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles are 5
It consisted of 0% by weight metallic palladium and 50% by weight zirconium oxide.

Example 12 Production of Palladium-Coated Silicon Oxide Fine Powder (1) Production of Palladium Primary-Coated Silicon Oxide Fine Powder In Example 1 except that the respective materials and the amounts used were changed as follows: Palladium primary-coated silicon oxide fine powder was produced in the same manner as in 1). Silicon oxide fine powder (SiO ₂ , average particle size 0.3 μm, specific surface area: 49.05 m ^{2 /} g): 10.0 g Ammonium tetrachloropalladate aqueous solution (same as in Example 1): 8.0 ml Pure water: 200 ml (Same as above) Aqueous hydrazine hydrate solution (Same as above): 3.0 ml (2) Production of Palladium Secondary Coated Silicon Oxide Fine Powder Example 1 except that the amount of each material used was changed as follows:
Palladium secondary-coated silicon oxide fine powder was produced in the same manner as in (2). Hydroxyethyl cellulose: 0.2 g / 500 ml
(Same as Example 1) Tetraamminepalladium chloride aqueous solution: 10 g
(Metallic Pd conversion value) Aqueous hydrazine hydrate solution: 3.0 ml (100% hydrazine hydration conversion) The obtained silicon oxide fine powder having a black gray coating layer was filtered off, washed with water, and then dried to dryness. A powder was obtained. When the dried fine powder (secondarily coated particles) was observed with a scanning electron microscope, it was confirmed that the powder was a homogeneous powder with almost no aggregation. The secondary coated particles are 50% by weight.
Of palladium metal and 50% by weight of silicon oxide.

[0041]

Industrial Applicability By coating the ceramic powder with the noble metal using the method of the present invention, the noble metal coating can be realized while highly suppressing the formation of aggregates. In particular, by utilizing the production method of the present invention, a ceramic fine particle powder having a particle diameter of 1 μm or less (further, 0.5 μm or less) is coated with a noble metal so that the ceramic phase is hardly exposed and the purity is high. That is, it is possible to form the noble metal coating layer in which the mixture of the ceramic components is small. The noble metal-coated ceramic particles obtained according to the present invention can be used particularly advantageously in the production of thin-film electrodes.

Claims (1)

[Claims] 1. A step of forming a precious metal thin film layer on the surface of ceramic powder by adding a reducing agent to a dispersion liquid in which ceramic powder is dispersed in an aqueous solution of a precious metal salt, and a ceramic powder having this precious metal thin film layer. , A noble metal-coated ceramic powder, which comprises dispersing in an aqueous solution containing a noble metal salt and a water-soluble polymer, and then adding a reducing agent to the dispersion to form a noble metal layer around the noble metal thin film layer on the surface of the ceramic powder. Manufacturing method.