GB2240336A

GB2240336A - Ceramic composite powders

Info

Publication number: GB2240336A
Application number: GB9101707A
Authority: GB
Inventors: Kunio Ohtsuka; Mitsuru Suda; Johji Koga
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 1990-01-29
Filing date: 1991-01-25
Publication date: 1991-07-31
Anticipated expiration: 2011-01-25
Also published as: FR2657550A1; JPH0773671B2; GB2240336B; DE4102602A1; DE4102602C2; JPH03224629A; GB9101707D0; FR2657550B1

Abstract

A manufacturing method for a ceramic composite powder comprises admixing an inorganic powder having cation- exchange properties with a solution containing one or more metal complex ions to form a suspension and cause ion exchange with the metal ions on the surface of the powder; decomposing the metal complex ion in the suspension to cause precipitation of metal hydroxides, metal oxides, or metal basic salts on the surface of said powder; and drying the powder on the surface of which is precipitated said metal hydroxides, metal oxides or metal basic salts. A ceramic-ceramic composite powder is produced by calcining the dried powder with the above precipitates to convert the precipitates into metal oxides. A metal-ceramic composite powder is manufactured by reducing the above dried or calcined precipitates on the surface of the powder to metal. In the composite powder, any arbitrary amount of metal oxides or metal is supported on the surface of the powder.

Description

BACKGROUND OF THE INVENTION 1) Field of the invention

This invention relates to a method of preparing a ceramic-ceramic composite powder in which ceramic components are combined with other ceramic components, and a metalceramic composite powder in which metal components are combined with ceramic components, and to the ceramic composite powder obtained thereby. More particularly it relates to a method of preparing the composite powder in which any arbitrary amount of metal oxides or metal is supported on the surface of an inorganic powder.

2) Description of the Related Art

One typical method of synthesizing ceramic products includes the steps of weighing ingredients of a ceramic starting material in the respective amounts to obtain the predetermined composition, thoroughly mixing the components to obtain uniform distribution, and calcining the resultant mixture. According to this method, the calcined product must be subjected to repeated pulverizing, mixing and calcining to obtain a sufficiently homogeneous composition.

Metal powders or ultrafine metal particles have conventionally been used extensively as conductive or magnetic materials without being supported on any particular powder. The prior art metal-ceramic composite materials, such as, oxide dispersion strengthened alloys, heat resisting struc

1 tural materials, and damping materials, demonstrate their functions by dispersing the ceramic particles in the metallic matrix.

According to the above conventional method of synthesizing ceramic products, despite thorough mixing, it is difficult to obtain an ideally homogeneous composition of particles because of aggregation of the component powders. In order to obtain a ceramic product having an ideally homogeneous composition, ceramic-ceramic powders having the predetermined composition should be used. However, no method has yet been found for synthesizing such ceramicceramic composite powders as are suitable for the purpose.

Use of metal powders or ultrafine metal particles not supported on any special powder is disadvantageous in that (1) their specific gravity is relatively high, (2) they are hard to disperse, (3) they are hard to handle, and (4) metal particles are easily sintered when exposed to heat. For example, when a metal powder is mixed with an organic binder to obtain a conductive paste, the metal powder tends to become separated from the organic binder because the metal powder has a greater specific gravity than the organic binder. Moreover, when the product is to be used as a paint in the form of powder rather than in flakes, the resultant coating layer tends to become uneven.

In order to solve these problems, use of composite powders in which inorganic powders are coated with metal by 2 i means of electroless plating has been proposed. However, the method is detrimental because electroless plating is expensive and requires a highly complicated process.

Also, the metal-ceramic composite materials, such as, oxide dispersion strengthened alloys, heat resisting structural materials, and damping materials, can be obtained by mixing a ceramic powder with a metal powder and sintering the resultant mixture. Because of the difference in the specific gravity between the ceramic powder and the metal powder, it is extremely difficult to uniformly disperse the ceramic powder in the metal powder. Metal-ceramic composite materials in which the ceramic powder is uniformly dispersed in the metal powder can be obtained, provided that metalceramic composite powders in which metallic and ceramic components have been combined are sintered. As mentioned above, such metal-ceramic composite powders can be obtained by the electroless plating method, which is, however, defectively expensive and complicated in its process.

The present inventors have completed this invention in the course of their studies on inorganic ion exchangers by noting that a ceramic- ceramic composite powder in which metal oxides are uniformly supported on the surface of an inorganic powder can be obtained by precipitating uniformly metal hydroxides or metal basic salts, etc. on the surface of the inorganic ion exchanger and then calcining the resultant composite powder, and that metal-ceramic composite pow- 3 der in which the inorganic powder is uniformly coated with the metal, can be obtained by reducing the metal oxidea to metal.

SUMMARY OF THE INVENTION

An object of this invention is to provide an inexpensive and simple method of preparing a ceramic-ceramic composite powder and metal-ceramic composite powder in which any arbitrary amount of metal oxides or metal is supported on the surface of an inorganic powder. Another object of this invention is to provide a method of preparing a ceramic-ceramic composite powder suitable as the starting material for production of ceramics, or a ceramic-ceramic composite powder that is useful as a functional ceramic powder, and to provide the powder obtained thereby. Another object of this invention is to provide a method of preparing a metal-ceramic composite powder suitable as a conductive or magnetic material, and the powder obtained thereby. Still another object of this invention is to provide a method of preparing a metal-ceramic composite powder suitable for preparing metal-ceramic composite materials, such as, oxide dispersion strengthened alloys, heat resisting structural materials, and damping materials, and the powder obtained thereby.

In order to achieve these objects of this invention, the present first method for manufacturing a ceramic com- 4 posite powder includes the steps of; admixing an inorganic powder having cation-exchange properties with a solution containing one or more metal complex ions to form a suspension and cause ion exchange with the metal ions on the surface of the inorganic powder; precipitating metal hydroxidgs, metal oxides, or metal basic salts on the surface of said inorganic powder by decomposing the metal complex ion in the suspension; and drying the inorganic powder on the surface of which metal hydroxides, metal oxides, or metal basic salts have been precipitated.

A second embodiment of the present method comprises a step of calcining the inorganic powder dried by the above first method to convert metal hydroxides, metal oxides, or metal basic salts precipitated on the surface of the inorganic powder to metal oxides to thereby synthesize a ceramic-ceramic composite powder.

A third embodiment of the present method comprises a step of reducing metal hydroxides, metal oxides, or metal basic salts on the surface of the inorganic powder precipitated by the above first method to metal to thereby synthesize a metal-ceramic composite powder.

In a fourth embodiment of the present method, by reducing the metal oxides converted by the second embodiment to metal, a metal-ceramic composite powder is obtained.

"Precipitation" as used in this specification means a phenomenon wherein a substance produced by chemical reaction in a solution appears as solids in the solution.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described in further detail. Natural or artificial inorganic powders having a cation-exchange property to be used in this invention may be classified into those that are amorphous, and those that are crystalline. The amorphous inorganic ion-exchangers include various hydrate oxides, such as silica gel and alumina gel. The crystalline inorganic ion-exchangers include natural clay minerals, such as montmorillonite, vermiculite and beidellite, artificial clay minerals, aluminum silicate, sodium titanate, sodium uranate and zirconium phosphate. The inorganic powders to be used in this invention are not specifically limited so long as they are inorganic and have the cationexchange property.

An inorganic powder having cation-exchange properties is added and mixed with a solution containing a metal complex ion to cause ion exchange. One or more metal ions may be contained. The amount of the added powder is in the range from about 0.1 to 80,000 grams against 100 grams of the metal complex ions in terms of the metal amount. To accelerate the ion exchange, treatments, such as, heating or pressurization may be conducted as the needs arises. The heating is conducted at a temperature in the range of from about room temperature to about the boiling point of the 6 solution containing the metal complex ion and pressurizing at a pressure in the range of from about 1 to about 30 atms. This ion exchange treatment fixes the desired metal complex ion at the sites of ion exchange on the surface of the inor ganic powder to thereby form'a suspension.

The metal complex ion in the suspension is then decomposed. As a method for decomposing, various methods can be employed methods, such as (a) heating the suspension at a temperature ranging from about room temperature to about 4000C, (b) pressurizing under about 1 to about 200 atms., (c) raising pH of the suspension by adding an alkali solution thereto, (d) adding an oxidizing agent to the suspension, or (e) combining these methods.

If an organic compound, inorganic compound, oxidizing agent, or reducing agent is added to the above suspension prior to decomposing the metal complex ion in the suspension, it is possible to control the precipitation rate, the composition, particle form, or oxidation degree of precipitates. An oxidizing agent used to decompose the metal complex ion and that used to change the oxidation degree of precipitates may be the same or different.

For example, silver (I), copper (II), nickel (II), cobalt (II), cobalt (III), zinc (II), cadmium (II), etc. react with ammonia to form an ammine complex. This type of ammine complex is known to be easily decomposed to form metal hydroxides by heating, pressurizing, raising pH of the 7 solution, adding an oxidizing agent to the solution, or combining these treatments as described above. Co-presence of an inorganic or organic substance, etc. at that time can control the composition or particle form of metal hydroxides. If an oxidizing agent or reducing agent is added in advance, it is possible to control the oxidation degree of precipitates. For example, addition of a reducing agent prior to decomposition of cobalt (III)-ammine complex by heating, will obtain cobalt (II) hydroxide.

Metal ions react with various chelating agents to form metal complex (metal chelates). For example, EDTA reacts with metal ions to form a metal complex, the metal complex is decomposed uniformly in a solution by heating, pressurizing, raising pH of the solution, adding an oxidizing agent, or combining these treatments. If an inorganic substance, such as phosphate anion, or an alkali, such as sodium hydroxide or potassium hydroxide is present in advance, phosphates or hydroxides become precipitated. Co-presence of an oxidizing or reducing agent at that time can control the oxidation degree of precipitates.

The method of making homogeneous precipitates from the above solution is known as a homogeneous precipitation method and is described in the following references: New Experimental Chemistry 1, Basic manipulation (I), page 309, Maruzen 1975 (in Japanese); (2) F.H. Firsching: Advanced Anal. Chem. Inst. 4, page 1, 1965, (3) L. Gordon, 8 M.L. Salutsky and H.H. Willard: Precipitation from Homogeneous Solution, 1959, John Wiley, (4) E. Matijevi6: Acc. Chem. Res. 14, page 22, 1981.

When a metal complex ion in the suspension is uniformly decomposed in the solution, metal hydroxides, metal oxides or metal basic salts gradually precipitate on the surface of inorganic powder, that is to say, nuclei of the precipitates grow on the metal ions which are introduced on the surface of the inorganic powder by ion exchange, which is followed by the precipitation at the nucleation sites. The inorganic powder with precipitated metal hydroxides, metal oxides, or metal basic salts is extracted from the suspension by filtration or centrifugal separation. Upon drying it at a temperature in the range of from about room temperature to about 2000C under atmospheric pressure, a ceramic-ceramic composite powder is obtained.

When the thus obtained ceramic-ceramic composite powder is calcined at a temperature in the range of from about 100 to about 2,000"C under atmospheric pressure, a ceramicceramic composite powder in which metal hydroxides, metal oxides or metal basic salts are converted to metal oxides, may be obtained.

Alternatively, upon reducing metal hydroxides, metal oxides or metal basic salts of the ceramic-ceramic composite powder obtained by drying the inorganic powder, or metal oxides of the ceramic-ceramic composite powder obtained by 9 calcining the inorganic powder, to metal in the gas phase-or in the liquid phase, a metal-ceramic composite powder may be. obtained. A typical method of reduction in the gas phase comprises calcining in the hydrogen gas atmosphere at a temperature ranging from about 100 to about 2,OOOOC. As for the method in the liquid phase, a ceramic-ceramic composite powder may be reduced in the liquid phase comprising hydrazine or sodium boron hydride.

According to this invention method, an arbitrary amount of metal oxide or metal may be supported on the inorganic powder surface by utilizing ionexchange capacities of the. powder. This enables production of a ceramicceramic composite powder and metal-ceramic composite powder simply and at a low cost.

This invention method further enables production of a ceramic-ceramic composite powder that is suitable as starting materials for production of ceramics, or of a ceramicceramic composite powder that is useful as various functional ceramic powders. This method also achieves the synthesis of a metal-ceramic composite powder that is useful as conductive paints, toners, magnetic materials, and catalysts, etc. A metal-ceramic composite powder suitable for the production of metal- ceramic composite materials, such as, oxide dispersion strengthened alloys, damping materials, and heat resisting structural materials may also be synthesized.

1 i R:

This invention will be described more specifically referring to the following examples. Example 1 To 230 ml of 14.8 M (mol/1) of an ammonium hydroxide solution was added 1, 704 ml of a nickel nitrate solution containing 49.3 g of Ni(N03)26H20 to obtain a nickel-ammine complex solution.

To this solution was added 0.2 g of sodium fluoride tetrasilicic mica (NaM92.5S'4010F2), which is a crystalline ion exchanger. The resultant mixture was stirred for 2 days to cause ion exchange. By heating the suspension at 98'C for 24 hours, the nickel-ammine complex was decomposed and precipitated as nickel hydroxide. The suspension was then filtered to extract the resultant powder. The powder was dried at room temperature under atmospheric pressure, and observed with an electron microscope to reveal nickel hydroxide uniformly formed on the surface of sodium fluoride tetrasilicic mica. Chemical analysis revealed that the weight ratio of Ni/mica in the composite powder was 47.

By calcining the composite powder at 7000C for 2 hours under atmospheric pressure, NiO-artificial mica (ceramicceramic) composite powder was obtained. By further heating the resultant composite powder at 400'C for 2 hours in a hydrogen gas atmosphere, NiO was reduced to a Ni-artificial mica (metal-ceramic) composite powder in which the mica surface was uniformly coated with Ni.

X Example 2

The Ni-artificial mica (metal-ceramic) composite powder obtained in Example 1 was subjected to compression molding at 8 tons/cm 2, and the molded body was calcined at 7000C for 2 hours in a hydrogen gas stream to obtain a sintered body in pellet form. The cross section of the sintered body was electrolytically etched and observed with an electron microscope to reveal a nano-composite in which ceramics (sodium fluoride tetrasilicic mica having a thickness of about 0 several 10 A) were uniformly dispersed in Ni.

Example 3

The metal-ceramic composite powder obtained in Example 1 was kneaded with an acrylic resin coating base (Kansai Paint Co., Ltd., No. 2026) to form a paint wherein the powder constituted 30 vol. %. This paint was spread on an ABS substrate with a thickness of 30 pm. The electrical resistance of the substrate surface was 0.5 Q/0, indicating an excellent conductivity. The thus obtained composite powder was revealed to be flakes with excellent coating performance and conductivity.

Example 4

To 230 mi of 14.8 M (mol/1) of an ammonium hydroxide solution was added 1, 800 ml of a cobalt nitrate solution containing 49.5 g of Co(N03)26H20 to obtain a cobalt-ammine 12 complex solution.

To this solution was added 0.5 g of Na-montmorillonite powder (Aterazawa Mine, Yamagata Pref.), which is a natural ion exchanger. The resultant mixture was stirred for 2 days to cause ion exchange. By heating the suspension at 90'C for 24 hours, the cobalt-ammine complex was decomposed and precipitated as cobalt hydroxide. These operations were conducted under N2 atmosphere.

The suspension was then filtered to extract the resultant powder. The powder was dried at room temperature under atmospheric pressure, and observed with an electron microscope to reveal cobalt hydroxides uniformly formed on the montmorillonite surface. Chemical analysis revealed that the weight ratio of Co to montmorillonite (Co/montmorillonite) in this composite powder was 20.

By calcining the composite powder at 700C for 2 hours under atmospheric pressure, a cobalt (II, III) oxidemontmorillonite composite powder was obtained.

By further heating the resultant composite powder at 600'C for 2 hours in a hydrogen gas atmosphere, the cobalt oxide was reduced to a Comontmorillonite (metal-ceramic) composite powder in which the montmorillonite surface was uniformly coated with Co.

Example 5

To 1,600 ml of 0.1 M (mol/1) of an Fe(N03)3 solution 13 was added 0.8 mol of TEA (triethanolamine) to synthesize a Fe (III) - TEA complex ion. Silica gel for chromatography, (Wako Pure Chemical Industries Ltd.) was immersed in 1 N hydrochloric acid for 24 hours to remove iron, washed with water for many hours and then dried by air to obtain an amorphous silica gel having cation-exchange properties.

To the above mentioned Fe (III) - TEA complex ion was added 0.5 g (based on S'02) of the thus obtained silica gel. The resultant mixture was stirred for 2 days to obtain a suspension. To this suspension were added 4,800 ml of 1 M (mol/1) of a NaOH solution and 92 ml of a H202 aqueous solution (60%). The suspension was placed in an autoclave, heated at 260'C for 24 hours at 46 atmospheric pressure to decompose a Fe (III) - TEA complex ion and precipitate it as hematite (a-Fe203)' The suspension was then filtered to extract the resultant powder. The powder was dried at room temperature under atmospheric pressure and observed with an electron microscope to reveal hematites uniformly formed on the silica gel surface.

When the composite powder was calcined at 500C for 2 hours under atmospheric pressure, Fe203-S'02 (ceramicceramic) composite powder was obtained. The weight ratio of Fe to S'02 (FeIS'02) in the composite powder was 14.5.

When the composite powder was further heated at 5000C for 3 hours in a hydrogen gas atmosphere, Fe-S'02 (metal- 14 i i -1 Z ceramic) composite powder in which the S'02 surface was uniformly coated with Fe was obtained.

Claims

WHAT IS CLAIMED IS: 1. A method of preparing a ceramic composite powder

comprising the steps of; admixing an inorganic powder having cationexchange properties with a solution containing one or more metal complex ions to form a suspension and cause ion exchange with the metal ions on the surface of the inorganic powder; decomposing the metal complex ions in the suspension to cause precipitation of metal hydroxides, metal oxides, or metal basic salts on the surface of said inorganic powder; and drying the inorganic powder on the surface of which is precipitated said metal hydroxides, metal oxides or metal basic salts.
2. The method of claim 1 wherein the metal complex ion in the suspension is decomposed by heating or pressurizing the suspension, raising pH of the suspension, adding an oxidizing agent to the suspension, or combining these treatments.
3. The method of claim 1 wherein an organic compound, inorganic compound, oxidizing agent, or reducing agent is added to the suspension prior to decomposing the metal complex ion.

16 1 1 i
4. A method of preparing a ceramic-ceramic composite powder wherein metal hydroxides, metal oxides or metal basic salts precipitated on the surface of the inorganic powder are converted to metal oxides by calcining the dried inorganic powder as claimed in claim 1.
5. A method of preparing a metal-ceramic composite powder wherein metal hydroxides, metal oxides or metal basic salts precipitated on the surface of the inorganic powder as claimed in claim 1 are reduced to metal.
6. A method of preparing a metal-ceramic composite powder wherein metal oxides on the surface of the inorganic powder as claimed in claim 4 are reduced to metal.
7. A ceramic-ceramic composite powder according to the method claim 4 wherein metal oxides are uniformly formed on the surface of the inorganic powder.
8. A metal-ceramic composite powder according to the method claim 5 or 6 wherein metal is uniformly formed on the surface of the inorganic powder.

17 Published 1991 atThe Patent Office. State House. 66/71 HighHolborn, L4DndonWCIR47?. Further copies maybe obtained from Saks Branch. Unit 6. Nine Mile Point, Cwinfelinfach. Cross Keys. Newport. NPI 7RZ. Printed by Multiplex techniques ltd. St Mary Cmy. Kent.