AU592823B2

AU592823B2 - Zirconia ceramics and a process for production thereof

Info

Publication number: AU592823B2
Application number: AU62136/86A
Authority: AU
Inventors: Nobuo Kimura; Junichi Morishita; Hiromichi Okamura
Original assignee: Nippon Soda Co Ltd
Current assignee: Nippon Soda Co Ltd
Priority date: 1985-07-03
Filing date: 1986-09-01
Publication date: 1990-01-25
Anticipated expiration: 2006-09-01
Also published as: AU6213686A; JPH0553751B2; JPS627667A

Description

l _i COMMONWEALTH OF AU S 8 2 3 PATENT ACT 1952 COMPLETE SPECIFICATION (Original) FOR OFFICE USE Class Int. Class Application Number: Lodged: Complete Specification Lodged: .ait Accepted: Published: ,Priority: Related Art: 8 l rl 44 I 4' 62136 4 Name of Applicant: Address of Applicant: SAddress of Applicant: NIPPON SODA CO., LTD.

2-1, Ohtemachi 2-chome, Chiyoda-ku, Tokyo, Japan.

Actual Inventor(s): Address for Service: Junichi MORISHITA Nobuo KIMURA Hiromichi OKAMURA DAVIES COLLISON, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

Complete Specification for the invention entitled: "ZIRCONIA CERAMICS AND A PROCESS FOR PRODUCTION THEREOF" The following statement is a full description of this invention, including the best method of performing it known to us -1-

I

-i la- Title of Invention ZIRCONIA CERAMICS AND A PROCESS FOR PRODUCTION THEREOF Technical field The present invention relates to zirconia ceramics such as partially-stabilized zirconia, including partially-stabilized zirconia containing alumina.

More particularly, it relates to a process for the production of easy sintering raw material powder to be used for the production of zirconia ceramics as well as to a method for the production of high density zirconia ceramic materials from the above raw particulate material and to the products of these methods.

Background Art There are known two species of zirconia ceramic 15 material, i.e. fully stabilized zirconia ceramics wherein the crystal phase of ZrO 2 constituting the ceramic comprises the cubic phase, with the cubic phase having been stabilized to be stable even at a relatively low 4 temperature range, and partially stabilized zirconia 20 ceramics wherein the crystal phase of ZrO, constituting the ceramic comprises the tetragonal phase, with the tetragonal phase having been stabilized to be stable even at a relatively low temperature range.

As a method for stabilizing the crystal phase of ZrO, 25 constituting the ceramics, there has been widely used the process which comprises adding a stabilizer such as CaO, MgO, Y,0 3 and/or CeO, to the raw material powder or the .ceramics in order to fully stabilize or to partially stabilize the crystal phase of ZrO 2 in the ceramics.

30 Particularly, YO is widely utilized as a stabilizing agent for the production of partially stabilized zirconia ceramics having high strength because ceramics having excellent stability and good mechanical properties are obtained.

The fully stabilized zirconia ceramics have been used as a solid electrolytic media, or as a heat resistant material for a furnace etc., because of this 1'"1 '1.1 l l l l l l l r L2 excellent thermal stability.

On the other hand, the partially stabilized zirconia ceramics have been called a phase transformation toughening type zirconia, wherein it is considered that if an external mechanical stress is applied to the ceramics, the tetragonal phase of ZrO 2 constituting the ceramics will transform martensite-like into a monoclinic phase that is a stable phase at the lower temperature range. Consequently the ceramics may have high tenacity because that the fracture energy is absorbed by said phase transformation.

Accordingly, it is known that the partially stabilized zirconia ceramic is a functional ceramic having high strength and high tenacity, and is expected 15 to be used for structural material such as mechanical material, abrasion resistant material, and cutting material, etc.

Among these stabilized zirconia ceramics, it i3 necessary to produce a dense ceramic having high density 20 and controlled microstructure by suppressing the grain growth in the ceramics to have the desired functions, for example, in the fully stabilized zirconia ceramics, oxygen ion conductivity, thermal stability, mechanical properties and the like, and in the partially stabilized S 25 zirconia ceramics, mechanical properties such as bending strength, tenacity and the like.

There has been produced dense zirconia ceramics having controlled microstructure by special moulding techniques, and high pressure sintering techniques such 30 as hot pressing or the HIP method. However, these methods need complicated operation and special installations, and therefore, the resultant product will be relatively expensive.

On the other hand, there has been proposed a process for the production of ceramics which comprises preparing the raw material powder by using chemical techniques such as co-precipitation or the like and then sintering a ,e f;R;911 i d

I~

I

3 moulding of the obtained raw material powder at a comparatively low temperature range.

However, it is known that in general the more finely divided particulate material has the stronger cohesive force. Therefore, it is difficult to produce ceramics having high density with high reproducibility from the chemically-treated raw powder.

Further, there has been proposed the addition of sintering activator, for example, Japanese Laid Open Gazette No. shou 50-10351 describes a process for the production of ceramics comprising moulding and sintering a raw material powder which is obtained by adding aqueous ammonium to the mixed aqueous solution containing water soluble zirconium salt, water soluble salts of calcium, S 15 magnesium, yttrium and the like as a stabilizing agent(s), and water soluble salt of the transition metal for sintering activator, so as to precipitate the desired co-precipitated hydroxide containing the desired metals, r then, drying and calcining thereof. The raw material 20 powder produced by this method can not provide satisfactory lower temperature sintering characteristics nor enough relative density of the ceramics.

In the above mentioned process, aqueous ammonium is used for precipitation. Some transition metals will form amine complexes with ammonium so that in practice aqueous ammonium can not be used in cases of such transition metal.

SIn order to avoid this shortcoming, there is a process in that the oxides of the transition metals are 30 used in place of the water soluble salt of the transition metals so as to disperse in the mixed solution containing the other components whereas the hydroxides of the other metal components are co-precipitated together with oxides of the transition metals.

However, in this process, the surface of the oxide of the transition metal is coated with the hydroxides of the other components. Therefore, it is difficult to

J

;iir- -4 impart a satisfactory sintering activator action in the ceramics when only small amounts of transition metal are added.

It was reported that the content of Y 2 0 3 in the ceramics can be decreased to 2.0 mol.% in Y 2 O, partially stabilized zirconia ceramics so that the fracture toughness(KIc) of approximately 10 MN/m 312 can be obtained for ceramics having high tenacity.

This means that partially stabilized zirconia ceramics containing Y 2 O, content in the ceramics in the amount ranging nearly to 2 mol.% can produce relatively high tenacity and strength.

F. F. Lange reported in Journal of Materials Science 17, 240-246 (1982) that "There is critical limit of the 15 particle size of tetragonal phase respectively to Y 2 0 3 content, and when the size exceeds the critical limit, t the tetragonal phase can not be present. Though the critical particle size is more than 1 gm at the Y 2 0 3 content of 3 mol.%, it decreases to in order of 0.2 pm at 1 20 the content of 2 molar As described before, the reduction of Y 2 0 3 content in the Y 2 O, partially stabilized zirconia ceramics is important in view of the high tenacity of the ceramics, and can be attained by suppressing the grain growth in 25 the ceramics.

However, suppressing the grain growth in the ceramics, to control the size of the grain to in order of equal to or less than 0.2 pm, is extremely difficult by the prior art process for the production of the ceramics.

4 30 The characteristics of sintering at the lower temperature such that the grain size is controlled to approximate 0.2 pm or less cannot be attained even by 'i using the raw material powder prepared by the aforementioned co-precipitation process. Therefore, the Y20, content in the Y 2 0 3 partially stabilized zirconia ceramics has the lower limit at about mol.%. There is not known the highly strong Y 2 0 3 partially stabilized ;is~l~

I

5 zirconia ceramics having the Y, 2 0 content of less than 2 mol.%.

The partially stabilized zirconia with Y, 2 0 content approximating 2 mol,% has heat deterioration problems and therefore, the prior art YO, partially stabilized zirconia uses ordinarily the range of about 3 mol.% for the Y 2 0 3 content.

As described above, the known partially stabilized zirconia is not satisfactory in view of improving the mechanical strength and stability, and therefore, ceramics with high tenacity and strength has been highly desired.

There is known in Japanese Patent Laid Open Gazette No. shou 60-86073 (1985) a method to improve the 15 mechanical properties of partially stabilized zirconia .o ceramics by adding of alumina in the composition of the ceramics.

However, such known partially stabilized zirconia rv ceramics containing alumina requires special sintering 20 techniques such as the HIP process, and therefore, the produced ceramics will be relatively expensive as described before.

It is an object of the present invention to alleviate the aforementioned disadvantages of prior 25 proposals.

Disclosures of Invention According to the present invention there is provided a process for the production of an easy-sintering raw material to be used for the production of partially- 30 stabilized zirconia ceramics which comprises suspending a powder of zirconium compound(s) containing stabilizing agent(s) in a solution or slurry containing at least one 'i kind of transition metal compound(s) and subsequently removing a solvent from the suspension and drying the resultant powder to form said easy-sintering raw material.

Further according to the present invention there is

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6 provided a zirconia ceramic raw material which is produced by the process described in the immediately preceding paragraph.

Still further according to the present invention there is provided a process for the production of partially stabilized zirconia ceramic which comprises moulding the zirconia ceramic raw material described in the immediately preceding paragraph and sintering the moulded raw material.

Yet still further according to the present invention, there is provided a partially stabilized zirconia ceramic when produced by the process described in the immediately preceding paragraph.

By the present invention a Y,,0 3 partially stabilized 15 zirconia ceramic may be produced which is characterized by Y 2 0 3 content in a range more than or equal to 1.3 mol.

percent and less than 2.0 mol. percent, and the content of the tetragonal phase being 65% or more. Similarly an alumina containing partially stabilized zirconia ceramic S• 20 may be produced by the present invention which is characterized by the following ranges of composition; partially stabilized zirconia; 99 to 40 mol. percent, a-alumina; 1 to 60 mol. percent, and transition metal oxide; 0.01 to 1 percent of the atomic 25 ratio of transition metals compared to the combination of Zr plus Al, which are produced by the above mentioned process.

C.tT. The transition metal compound(s) used in this invention may be compound(s) of at least one metal 30 selected from the group consisting of Mn, Fe, Co, Ni, Cu, and Zn as well as the compound(s) to generate one or more of the above mentioned metal oxides by thermal decomposition.

As the transition metal compound, there may be used inorganic compounds such as oxides, hydroxides, nitrates, chlorides and the like of the above mentioned metals; organic acid salts such as oxalates, acetates, S y 91101.6 7 propionates, higher fatty acid salt and the like of the above mentioned metals; and organic metal compounds such as alkoxide compounds, chelate compounds and the like of the metals, even if it is not only soluble but also insoluble to the used solvents. Preferably the compound(s) is solvent soluble.

The stabilizing agent may be selected from Y 2 0 3 CaO, MgO and CeO,, as well as yttrium compounds, calcium compounds, magnesium compound, or cerium compounds to generate respectively Y,,0 3 CaO, MgO, or CeO 2 by thermal decomposition.

The powder of zirconium compound(s) may include: zirconia powder containing a stabilizing agent(s) with or without alumina and precursor powder to generate zirconia containing a oo stabilizing agent(s) with or without alumina by thermal decomposition.

The Production of Raw Material Powder 0, For the powder of zirconium compound(s), the above 20 mentioned powders containing stabilizing agent(s) can be used, which may be obtained by conventional processes such as oxide method, co-precipitation method, hydrolysis method, pyrolysis method and the like.

i Particularly, it is preferable to use a precursor 25 powder which is obtained by drying the co-precipitated hydroxides or mixed carbonates prepared by adding as a precipitating agent, aqueous ammonium or ammonium carbonate to the mixed solution containing water soluble zirconium compounds, and water soluble yttrium compounds, S 30 water soluble magnesium compounds, water soluble calcium compounds, or water soluble cerium compounds, and if desired, alumina powder, or water soluble aluminium compounds.

In accordance with this invention, the powder of zirconium compound(s) is added to the solution or slurry containing the transition metal compound(s), and then the objective raw material powder is obtained by removing solvent from the suspended slurry and drying the residue.

The solvent used for dissolving or suspending the transition metal compound may be water and/or organic solvents, organic solvents being preferable because of convenient removal of the solvent by evaporation and because of less evaporation energy at drying.

The usable organic solvent is not limited, but the use of highly viscous solvents is not preferable because homogenous suspension of the powder of zirconium compounds and the transition metal compounds is difficult and further, the removal and drying of the solvent is difficult. Preferably, lower alcohols such as methanol, ethanol, propanol, buthanol and the like can be used.

The unit operation for suspension of the powder of 15 zirconium compounds into the solution or slurry o containing the transition metal compounds can be a simple agitating operation resulting in satisfactory mixture, but when the grinding and mixing operation such as *t milling is applied, the resultant mixing effect will be *e 20 more sure.

The removal of solvent(s) and drying may be carried out by conventional evaporation methods, but when the transition metal compound is insoluble to water or 4. organic solvent(s), or when the precipitation has been already obtained by applying a precipitating agent to the solution containing the soluble transition metal compounds, solvent can be removed by filtration.

Further, spray drying can be used to treat efficiently and effectively in large scale the material powder.

l 30 The resultant raw material powder can be used for production of ceramics as it is. However, it can be calcined at a temperature in a range from 300 to 1200 0 C 1 for further treatment.

In the raw material powder obtained by the above mentioned process, the transition metal compounds are uniformly adhered and/or coated on the surface of the raw material powder, so that it functions effectively as a Iffp 1.8 V~f^ ~yi1 s 1 9 sintering activator.

The Production of Ceramics The raw material powder will produce a dense ceramic by the easy sintering through firing under atmospheric pressure at the relatively lower temperature in a range from 1100 to 1700 0 C, preferably 1100 to 1500°C.

The atomic ratio of transition metal to Zr, or to the combination of Zr and Al if Al is present, may be 0.01 to 1.0 percent, preferably, 0.01 to 0.5 percent.

When the atomic ratio of the transition metal is less than 0.01 percent, the effect for activating sintering is insufficient. Further, when it is more than percent, the properties of the resultant ceramics will be affected and the range of more than 1.0 percent 15 should be avoided.

In accordance with one aspect of the present invention, the zirconia ceramic is produced by moulding the raw material powder obtained by the above process, and then by sintering the moulded body.

20 The moulding may be a press moulding by using the conventional moulding technique, but it is preferable to apply further a hydrostatic compressing after lower pressure moulding, so as to improve the sintered density o and the mechanical strength of the finished ceramics.

25 The sintering may be by any of the known methods.

By sintering under atmospheric pressure, the object of p t sintering is sufficiently achieved.

In order to control the grain growth in the ceramics for the production of dense ceramics, particularly highly strong partially stabilized zirconia ceramics, the lower sintering temperature is better, and therefore, the range of 1200 to 1500°C is most preferable.

In accordance with such method, since the raw material powder has good sintering characteristics, the use of the atmospheric firing at the lower temperature can produce easily dense ceramics having relative density in relative to the theoretical density of more than 99%.

i) Y,0 3 partially stabilized zirconia ceramics YzOa partially stabilized zirconia ceramics having a tetragonal phase content of 65% or more and high tenacity andr high strength can be readily obtained in accordance with the invention. Preferably, by limiting the raw material powder in accordance with the invention comprises zirconia powder containing Y, 2 0 or precursor powder of the above produced by thermal decomposition, in which said powder has a crystal particle size of 400 A or less and BET specific surface area of 2 m 2 /g or more.

In the production of the ceramics, when the crystal particle size of the powder of zirconia compounds exceeds 400 A, or when the BET specific surface is less than 2 m 2 the sinter activating effect by the transition metal compound(s) may be insufficient in which case enough dense ceramics of high density may not be obtained by the atmospheric sintering at the relatively temperature range.

The atomic ratio of the transition metal to Zr in the production of the ceramics may be in a range of from 0.01 to preferably 0.01 to S The sintering temperature is preferably not more than 1400°C. By the above mentioned process for the production of the ceramics, Y 2 0, partially stabilized S 25 zirconia ceramics having Y 2 0 3 content of 1.3 mol.% or more, and less than 2.0 mol.% and having tetragonal phase content of 65% or more, preferably 80% or more, can be produced.

The Y 2 0 3 content is based on the total combination of

S

t 30 YO 3 plus ZrO 2 in the ceramics.

These obtained ceramics may have a sintered density of at least 5.8 g/cm 3 preferably more than 5.9 g/cm 3 and more preferably 6.0 g/cm 3 or more, and fracture tenacity value (KIc) in the range of from 10 MN/m 3 2 to 16 MN/m 3 so that they are of high density, of high tenacity and of high strength.

The grain size in the ceramic may be 0.5 pm or less, S- 11 preferably 0.3 pm or less.

When the Y 2 O, content is less than the content of the monoclinic phase will increase and the tetragonal phase content of 65% or more may be difficult to maintain. On the other hand, the ceramics having the Y,0 3 content of 2.0 mol.% or more have been known, and the fracture tenacity value thereof has not be more than MN/m 3 1 2 When the grain size in the ceramic exceeds 0.5 pm, it is extremely difficult to maintain the content of the tetragonal phase 65% or more. In addition, when the grain size is 0.3 pm or less, the stability of the ceramics under heat stress may be improved and the mechanical strength of the ceramics may be stable.

Further, when the sintering temperature exceeds 1400°C, grain growth in the ceramic may be activated, so that grains larger more than 0.5 pm are produced in which case ceramics having relatively higher content of monoclinic phase may be produced, and further cracks may be caused during firing.

ii) Partially stabilized zirconia ceramics containing Salumina Also by the present invention a novel alumina containing partially stabilized zirconia ceramic can be produced comprising the composition of partially stabilized zirconia of 99 to 40 mol.%.

a-alumina of 1 to 60 mol.% transition metal oxide having an atomic ratio compared to the combination of Zr plus Al ranging 0.01 to 1%.

30 The resultant ceramic has high tenacity and high hardness, in that the fracture tenacity may be 18.5 MN/m 2 and the Vickers hardness may reach 1600 kg/mm', as well as excellent heat shock resistance.

The powder the zirconium compound which can be used 35 for the production of this ceramic imay be the mixed powder comprising zirconia containing a stabilizer, 99 to 40 mol.% and S'89101.11 r i: ii .II-LI;LIII-- i 12 alumina 1 to 60 mol.%; or precursor powder to produce the above powder by its thermal decomposition, and the above oowder is added to the solution or slurry containing the transition metal compound(s) to form the suspension, then followed by removing the solvent therefrom and drying to obtain a raw material powder including transition metal at an atomic ratio of the transition metal(s) to the combination of Zr plus Al ranging from 0.01 to 1%.

This material may be moulded into shape and fired to sinter, resulting in the desired ceramic.

The ceramic may be Y 2 0 3 partially stabilized zirconia, for example, having Y,0 3 content in the range of from 1.3 to 4 mol.%, or Y 2 0 3 partially stabilized zirconia wherein a part or all of Y,0 3 for stabilizer is substituted by CaO, MgO, or CeO,, and the content of the stabilizer is 0.01 to 12 mol.%.

The content of the stabilizing agent such as Y 2 0 3 is based on the total amount of ZrO, and the presumed oxide for the stabilizing agent.

In case of Y 2 0 3 partially stabilized zirconia, when the Y 2 ,O content is less than 1.3 molar%, the ratio of monoclinic phase in the ceramics may increase undesirably 25 even in the presence of Al 2 0 3 and then it is difficult to keep the ratio of tetragonal phase of 65% or more. When the YO, content exceeds 4 mol.%, the fracture tenacity value of the ceramics may decrease undesirably.

If the Al, 2 0 content in the ceramics is less than 1 30 mol.%, insufficient hardness may be obtained. Further, when the A1 2 0 3 content is more than 60 mol.%, it is difficult to produce enough dense ceramic having high 1, 4, 4 4 .4,4e 4 4l I 4 .4 I 44 4 4 4r44 4 4O 4 density.

When the atomic ratio of the transition metal to the combination of Zr plus Al in the ceramics is less than 0.01%, a dense ceramic with high density may not be obtained. Further, when such atomic ratio is more than 101 12 i i

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13- 1 mol.%, the sintering characteristics of the ceramics will be degraded.

The grain size of zirconia in the ceramic may be 2 pm or less, and preferably 0.5 pm or less. The content of the tetragonal phase in the ceramics may be 65% or more, and preferably 80% or more. The grain size of Al 2 0 3 in the ceramics may be 4 pm or less, and preferably 2 pm or less.

The resultant alumina containing partially stabilized zirconia ceramic may have extremely high hardness such as Vickers hardness in the range of from 1100 to 1600 Kg/mm 3 and have good heat resistance, for example a bending strength of 85 Kg/mm 2 or more even after heat treatment at 200°C for 1000 hours.

In the production of the raw material powder, the powder of zirconium compounds may be; the mixture of partially stabilized zirconia powder having a crystal particle size of 400 A or less, and BET specific surface area of 2 m 2 /g or more; or the precursor powder to generate such partially stabilized zirconia by its thermal decomposition, and: S* a-alumina powder having grain size of 1.0 pm or less, and BET specific surface of 2 m2/g or more, or the precursor powder to generate alumina by its thermal decomposition.

S 25 When partially stabilized zirconia powder or the precursor powder has crystal particle size of more than 400 A, or when BET specific surface thereof is less than 2 m 2 the sinter activating effect by the transition metal will be decreased so that the atmospheric sintering at less than 1500°C can not produce enough dense ceramics with high density.

Best Mode for Carrying out the Invention The best mode for carrying out the invention may be illustrated by the following examples.

However, the following examples are not given for limitation of the scope of the invention.

Example 1: Production of Easy Sintering Raw Material S 891101.13 '4 S -14- Powder and Ceramics Production of Raw Material Powder in use for production of ceramic.

Sample (1-1) To the combined solution containing ZrOC 2 1, and YCl 3 in the ratio of Y,0 3

(Y

2 0 3 +ZRO,)=0.03 by oxide molar base calculation, was aqueous ammonia added to regulate the pH of the solution in order to produce co precipitation of the combined hydroxides. The resultant co precipitation hydroxides was filtered and dried, and then the precursor powder of zirconia containing Y 2 0 3 was obtained. By calcining a part of the obtained precursor powder at 800 0 C for one hour, powder of zirconia containing Y 2 0 3 was obtained. For the transition metal compounds, the following compounds were dissolved or dispersed in ethanol to prepare respectively solution or slurry of the transition metal compounds.

Solution Slurry 20 Mn: MN(CH 3 CHOO),.4H 2 0 MnO, I2 *.Ot Fe:Fe(NO 3 2 .9H 2 0 Fe(OH), Co: Co(CH 3 COO),. 4H0 CoO Ni: Ni(N0 3 ),6H,0 Ni(OH), Cu:Cu(CH 3

COO)

2 CuO Zn: Zn(CH 3

COO)

2 .2H 2 0 ZnO To the prepared solution or slurry of the transition metal compounds, the zirconia powder containing Y 2 0 3 as before prepared was added to form the suspension, then, distilling away ethanol, and drying to obtain raw material powder adhering the transition metal compounds which are in use for the production of Y 2 0 3 partially stabilized zirconia ceramics.

Sample (1-2) SIn accordance with the same conditions for the 35 production of Sample except for using

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precursor powder of zirconia containing YO0 3 in place of the powder of zirconia, containing Y,O, the

MPWPI

15 adhering treatment of the transition metal compound(s) was carried out, and then, the resultant material was calcined at 800 0 C for one hour, yielding zirconia raw material powder containing Y,0 3 in use for the production of the zirconia ceramics.

Sample (1-3) The pH of the mixed solution containing ZrOC1 2 and CaCl 2 in the ratio of CaO/(CaO+ZrO 2 )=0.12 by oxide molar calculation for the oxides was adjusted by adding aqueous ammonia to co precipitate mixed hydroxides. The co precipitated mixed hydroxides were filtered, dried and then calcined at 800 0 C for one hour to obtain zirconia powder containing CaO.

The prepared zirconia powder containing CaO was treated under the same condition as for Sample (1-1) with the transition metal compound, obtaining MgO partially stabilized zirconia raw material powder for use in the production of the zirconia ceramics.

Sample (1-4) The pH of the mixed solution containing ZrOC1, and MgC1, in the ratio of MgO/(MgO+ZrO 2 )=0.081 by molar t, calculation for the oxides was adjusted by adding aqueous ammonia to co precipitate mixed hydroxides.

The co precipitated mixed hydroxides were filtered, dried and then calcined at 800°C for one hour to obtain zirconia powder containing MgO.

The prepared zirconia powder containing MgO was treated under the same condition for Sample (1-1) with the transition metal compound, obtaining MgO partially stabilized zirconia raw material powder for use in the production of the zirconia ceramics.

Sample 4t The mixed solution containing ZrOC1, and CeCl, in the ratio of CeO,/(CeO,+ZrO,)=0.08 by oxide molar S891101.15 1 V j -16calculation for the oxides was adjusted by adding aqueous ammonia to precipitate mixed hydroxides.

The precipitated mixed hydroxides were filtered, dried and then calcined at 800 0 C for one hour to obtain zirconia powder containing C:eO 2 The prepared zirconia powder containing CeO, was treated under the same condition for Sample (1-1) with the transition metal compound, obtaining CeO 2 partially stabilized zirconia raw material powder for use in the production of the zirconia ceramics.

Reference Sample (C1-1) To the starting mixed aqueous solution used for the production of the precursor powder as in Sample (1was the transition metal compound added and treated to precipitate mixed hydroxides containing the transition metal compound and then the precipitated mixed hydroxides were filtbred, and dried, obtaining the raw particulate material (Cl-1) for reference.

4' Reference Sample (Cl-2) The treatment for preparation of Sample but omitting the deposition of the transition metal compound was carried out to prepare zirconia precursor powder containing Y 2 0 3 which was referred as the raw material powder (C1-2) for reference (hereinafter refer to "untreated powder").

Reference Sample (C1-3) S"Untreated powder" of zirconia powder containing CaO produced by the process for production of Sample (1- S,3) was used as the raw powder (Cl-3) for reference.

Reference Sample (C1-4) "Untreated powder" of zirconia powder containing MgO prepared by omitting the deposition of the transition metal compound from the preparation process for Sample was used as the raw powder (C1-4) for reference.

SO 5111.16 17- Reference Sample "Untreated powder" of zirconia powder containing CeO 2 prepared by omitting the deposition of the transition metal compound from the preparation method of Sample was used as the raw powder for reference.

Production of Ceramics By pressure moulding the raw material powder as before obtained under pressure of 200 Kg/cm 2 using a mould, and then further hydrostatic compressing the obtained mouldings under pressure of 2 ton/cm 2 mouldings having the desired shape were obtained. The obtained mouldings were fired under atmospheric pressure at the given temperature for three hours, producing zirconia ceramics.

Evaluation Test The density of the resultant ceramics was measured and the three point bending test of the portion thereof based on JIS (Japan Industrial Standard) R 1601 (1981) was carried out.

The Table 1 indicates the results of the following test; on raw material powder; Samples and reference Samples in atomic ratio of the transition metal to Zr, the density and relative density S 25 to the theoretical density of the resultant Y 2 0 3 partially 4 t' stabilized zirconia ceramics produced from each raw material and bending strength (average from 5 points) of the resultant ceramics.

Table 2 indicates the results of the tests on raw 30 material powder; Samples and reference Samples (C1-3) to in atomic ratio of the transition metal to Zr, the density and relative 'i density to the theoretical density of the resultant YO, partially stabilized zirconia ceramics produced from each raw material and bending strength (average from 5 points) '"141 of the resultant ceramics.

The theoretical density of each ceramics are as 8; I L17 gni i> r Baf' 17 a follows; Y,0 3 partially stabilized zirconia ceramics: 6.10 g/cm CaO partially stabilized zirconia ceramics: 5.68 g/cm MgO partially stabilized zirconia ceramics: 5.80 g/cm CeO 2 partially stabilized zirconia ceramics: 6.23 g/cm In the following tables, means that the transition metal compound(s) was adhered by the solution method, and means that the transition metal compound(s) was adhered by the slurry method.

I 4 4 441 L 4I I

II

ClI i

I

f' ctc Scl I I

AI

Table 1 raw material 1200* 0 firing 130000 firing transition metal sintered relative bend sintered relative bend adhere adhered density density strength density density strength method atom g9/cm3 kcr/mm2 g/cm3 kg/mm2 1-2 Mn 0.3 5.90 96.7 5.98 98.0 1-1 Mn 0.05 5.90 96.7 6.00 98.4 Mn 0.1 5.95 97.5 6.01 98.5 Mn 0.2 5.97 97.9 6.02 98.7 UMn 0.3 5.96 97.6 6.02 98.7 100 Mn 1.0 5.914 97.14 6.02 98.7 4 1Mn 0.05 5.82 95.14 5.93 97.

It M (B 0. 5.8 9.7 5.97 97.9 Mn 0.2 5.90 96.7 5.99 98.2 Mn() 02 59 67 59 82 Mn 0.3 5.91 96.9 95 6.00 98.4 100 Mn 1.0 5.90 96.7 6.00 98.4 Fe 0.05 5.72 93.9 5.92 97.0 Fe 0.1 5.73 93.9 5.94 97.4 Fe 0,2 5.814 95.7 6.02 98.7 Fe 0.3 5.814 95.7 6.03 98.9 101 Fe 0.3 5.80 95.1 814 5.98 98.0 98 Co 0.05 5.89 96.6 5.99 98.2 Co 0.1 5.95 97.5 6.00 98.14 Co 0.2 5.89 96.6 6.02 98.7 Co 0.3 5.87 96.2 6.02 98.7 100 Co 0.3 5.814 95.7 88 5.98 98.0 r. (to be cont'd) raw material 1200'C firing 1300'C firing transition metal sintered relative bend sintered relative bend adhere adhered density density strength density density strength method atom g/cm3 kg/mm2 g/cm3 kg/mm2 1-1 Ni 0.05 5.89 96.6 90 5.99 98.2 Ni 0.1 5.92 97.0 90 5.99 98.2 Ni 0.2 5.99 98.2 93 6.02 98.7 98 Ni 0.3 6.02 98.7 96 6.07 99.5 110 Ni 1.0 6.01 98.5 86 6.07 99.5 I Ni 0.3 5.94 97.4 90 5.98 98.0 98 9 99 1-2 Zn 0.3 5.90 96.7 85 6.02 98.7 100 S- 1-1 Zn 0.05 5.88 96.4 80 6.05 99.2 105 Zn 0.1 5.90 96.7 80 6.07 99.5 113 Zn 0.2 5.99 98.2 90 6.08 99.7 115 Zn 0.3 5.99 98.2 90 6.07 99.5 115 Zn 1.0 5.98 98.0 74 6.07 99.'5 Zn 0.3 5.94 97.4 87 6.01 98.5 100 1-2 Cu 0.3 6.01 98.5 88 6.03 98.9 99 1-1 Cu 0.05 5.96 97.7 92 6.05 99.2 108 Cu 0.1 5.99 98.2 95 6.07 99.5 115 Cu 0.2 6.02 98.7 99 6.09 99.8 120 Cu 0.3 6.05 99.2 105 6.07 99.5 113 Cu 1.0 6.05 99.2 90 6.05 99.2 90 '1 Cu 0.05 5.92 97.0 6.01 98.5 Cu 0.1 5.96 97.7 6.01 98.5 Cu 0.2 5.96 97.7 6.02 98.7 Cu 0.3 5.98 98.0 95 6.02 98.7 98 19 (to be cont'd) raw material 1200*C firing 1300'C firing transition metal sintered relative bend sintered relative bend adhere adhered density density strength density density strength method atom g/cm3 g/cm3 kg/mm2 Cl-i Mn 0.3 5.33 8'4.'4 5.50 90.2 Mn 0.3 5.25 86.1 38 5.50 90.2 Fe 0.3 5.38 88.2 5.70 93.4 Fe 0.3 5.30 86.9 '43 5.55 91.0 68 Zn k.A) 0.3 5.38 88.2 43 5.60 91.8 52 *Zn 0.3 5.28 86.6 40 5.48 89.8 69 ~.Cu 0.3 5.30 86.9 42 5.52 90.5 12 5.28 86.6 '40 5.'48 89.8 69 Table 2 raw material l200*C firing 1300*C firing transition metal sintered relative bend sintered relative bend adhere adhered density density strength density density strength method atom g/cm3 kg/mm2 g/cm3 kg/mnm2 El-3 Mn 0.3 5.214 95.5 5.56 97.9 Fe 0.3 5.56 96.1 5.63 99.1 Co 0.3 5.141 95.5 5.61 98.8 Ni 0.3 5.23 97.14 5.67 99.8 Zn 0.3 5.23 97.1 5.57 98.1 Cu 0.3 5.55 97.7 5.67 99.8 1-14 Mn 0.3 5.73 98.8 te"Fe 0.3 5.76 99.3 Co 0.3 5.69 98.1 Ni 0.3 5.69 98.1 t Zn 0.3 5.71 98.14 tCu 0.3 5.69 98.1 Mn 0.3 6.20 99.5 6.21 99.7 4 1 tiSlt Ni 0.3 6.18 99.1 6.20 99.5 Cu 0.3 6.22 99.8 6.22 99.8 01-3 4.85 85.14 5.30 93.

01-4 5.143 93.6 01-5 5.80 93.1 5.98 96.0 21 22 Example 2: Y,0 3 Partially Stabilized Zirconia Ceramic and Its Production Preparation of raw material powder The same procedure as that for the production of Sample in Example 1 is carried out in changing the mixture ratio of ZrOCl and YCl 3 to produce coprecipitates of hydroxide.

The obtained co-precipitates of hydroxide were treated under the same condition to those of example 1 to produce zirconia powders with different Y,0 3 contents.

Sample (2-1) The resultant zirconia powders containing Y 2 0, were treated with the solution used in example 1 under the similar condition to produce raw particulate material in use for production of ceramics.

Sample (2-2) The dried co-precipitates of hydroxide were treated in the similar way to that for sample and further, calcined at 800 0 C for one hour to produce the raw material powder in use for production Sof ceramics.

S, Sample (2-3) The zirconia powders containing Y,0 3 as before produced were treated with the slurry used in S 25 example 1 under the similar condition to produce the raw material powder Production of ceramics The raw materials to were moulded under the similar condition to that of Example 1 and then fired 30 in atmosphere for 3 hours at the given temperature to 0, result in Y, 2 0 partially stabilized zirconia ceramics.

For reference, omitting the treatment with the transition metal compounds, the raw materials wherein Y 2 0 3 Ir content is less than 1.3 mol.%, the crystal particle size is more than 400 A, and the atomic ratio of the transition metal to Zr is more than 1.0% were used to mould and produce the sintered ceramics. The firing 8 9?101.22 r w 23 temperature was 1500 0

C.

Characteristics of Zirconia Powder containing Y,O, and The Ceramics made therefrom The following characteristics were measured on zircon.ia powder containing Y, 2 0 and ceramics obtained in the above items and Table 3 shows the characteristics of raw material powder and the ceramics produced from that material.

Table 4 shows the characteristics of raw material powder and and the ceramics produced from those materials.

Crystal Particle Size of zirconia powder containing Y,0 3

D

The size D can be calculated from the width at the half value of the peak of X ray diffraction by the following Schellar's formula: D=09A/ cos e A: the wave length of X ray p: the width at the half value 20 of the diffraction peak e: the diffraction angle BET relative surface area of zirconia powder containing YO, 3 was measured by using micromeritics (machine manufactured by Shimazu Works.) Fracture tenacity of partially stabilized zirconia ceramics: KIc was measured by Vickers indent test.

The Vickers indenter was pressed to the polished surface of the samples, and the resulting indentation St size and the resulting length of the generated crack were measured and KIc was calculated from the following formula which Niihara et al proposed. The applied indentation load was 50 kgf.

(Kict/Ha 1 2 (H/E )o4=0. 035 (1/a) /2 resistant moduras 35 H: Vickers hardness E: modulus of elasticity a: half value of diagonal length of indentation 89 01,23 1: length of crack generated from indentation.

Bending strength of partially stabilized zirconia ceramics; was measured in accordance with JIS R 1601 (1981) rule.

The sample of 3x4x40 mm in size was used, and measurement was carried out on span length of 30 mm under crosshead speed of 0.5 mm/min. and the value was determined by average from five samples.

Content of tetragonal phase in the partially stabilized zirconia ceramics.

The surface of the sample was polished by diamond slurry containing 3 m in size of diamond particles, and then, X ray diffraction measurement was carried out on that surface followed by the calculation of the following formula.

(lll)t Tetragonal phase content x 100 (111)t+(lll)m+(lll)m (lll)t: tetragonal (111) face diffraction intensity (lll)m: monoclinic (111) case diffraction intensity (lll)m: monoclinic (111) face diffraction intensity ,(11 (ll)t diffraction peak includes cubic (lll)c diffraction peak, but the I. calculation was carried out presuming that that peak is entirely by tetragonal diffraction.

Grain size in the partially stabilized zirconia ceramics The grain size was measured by observing the fracture face of the ceramics through scanning type electron microscope. It was confirmed that all samples except of reference samples have grain size ranging 0.1 to 3 Umi 24

I

Table 3 tra. metal adhered raw material powder partici. specific Y 203 f iring tern- sintered fracture bending tetragonal kind, atom, content size surface perature density tenacity strength content mol.% A m 2/g .C g/cm3 MN/n3/ Kg/mm2 Mn 0.05 0.1 0.3 Cu 0.05 0.1 0.3 28.5 28.5 25.6 28.8 28.5 28.5 6.4 29.5 5.6 30.5 28.5 27.6 28.5 28.5 25.6 28.8 1200 1200 1200 1100 1200 1300 1300 1300 1300 1300 1300 1300 1200 1200 1200 1100 5.92 5.95 5.01 5.93 6.01 6.03 6.03 6.04 6.04 6.02 6.03 6.03 5.96 5.99 6.01 5.98 15.3 15.2 13.8 14.8 16.0 15.7 11.2 9.4 13.2 14.7 14.9 9.6 14.5 .1 Z Ii

I

le, o be cont'd) tra. me'al adhered y2 03 kind, atom. conti mol raw material powder firing particl. specific tern- sintered fracture bending tetragonal size

A

surface m 2/g perature

.C

density g/cm 3 tenacity r4N/m 3/2 strength Kg/mm2 content Cu 0.3 Fe 0.3 Co 1.1.3 NI 0.3 Zn 0.3 1.7 230 230 380 1.9 238 2.2 226 1.7 230 222 1.7 230 2.2 226 1.7 230 2.2 226 .7 230 2.2 226 1.7 230 2.2 226 1. 7 230 1.9 238 28.5 28.5 6.4 29.5 30.5 28.5 27.6 28.5 30.5 28.5 30.5 28.6 30.5 28.5 30.5 28.5 29.5 1200 1300 1300 1300 1300 1200 1300 1200 1300 1200 1300 1200 1300 1200 1300 1200 1300 6.02 6.05 6.05 6.o6 6.07 6.05 6.05 5.88 6.01 5.91 6.02 6.03 6.07 6.01 6.07 5.148 5.53 15.3 165 15.6 170 16. 1 139 10.9 135 8.6 1314 13.6 1140 7.8 120 15.0 1140 8.6 1214 14.8 145 8.5 128 15.3 168 8.7 131 15.5 16o 8.5 133 Reference C. CC C C C C .4 C 6 S C St C 4' 9 eeC t C CC a S 4 e.0 ii (to be cont'd) tra. metal adhered y2 03 raw material powder firing partici. specific ten- sintered fracture bending tetragonal kind, atom, content size surface perature. density tenacity strength content mol.% A m /g Cg/cm 3 MN/m3 Kg/mm 2 Zn 0.3 Mn 0.3 CU 0.3 25.6 5.6 1.3 30.5 27.6 30.5 28.5 1.2 30.5 30..5 28.5 1.2 30.5 1200 1300 1300 1300 1300 1100 1500 1300 1300 1300 1500 1300 1300 5.48 5.66 4.88 5.70 5.68 crack crack 5.65 6.01 crack crack 5.58 6.01

V

ii~

V

Li j S SO S S 55 0 S S S .9 C Ow

~OR

Table 14 tra. metal raw material powder firing deposit Y2 03 particl. specific tern- sintered fracture bending tetragonal spec. atom. content size surface perature density tenacity strength content mol.% A mn 2 /g C g/cm 3 MN/m 3/2 Kg/mm 2 S Mn 0.3 1.7 230 28.5 1200 5.98 114.8 155 (2-2) Cu 0.3 1.7 230 28.5 1200 6.01 141.9 156 Fe 0.3 1.7 230 28.5 1200 5.88 16.1 139 92 Co 0.3 1.7 230 28.5 1200 5.88 15.8 140 914 Ni 0.3 1.7 230 28.5 1200 5.99 14.5 1149 Zn 0.3 1.7 230 28.5 1200 5.92 114814 >95

CO

S 1.7 23028 1200 5.48 48 Mn 0.3 1.7 230 28.5 1300 5.991.8509 Cu 0.3 1.7 230 28.5 1300 6.02 114.7 156 Fe 0.3 1.7 230 28.5 1300 6.00 15.1 150 92 CO 0.3 1.7 230 28.5 1300 5.98 14.7 1140 Ni 0.3 1.7 230 28.5 1300 6.02 13.9 155 89 Zn 0.3 1.7 230 28.5 1300 6.00 114.1 145 86 Refe- 1.7 230 28.5 1300 5.56 52 140 rence 29 Example 3: Alumina Containing Zirconia Ceramics and Method of Production of the Same Preparation of raw material powder in use for production of ceramics Sample (3-1) The procedures of Example 1 to produce the powder principally containing zirconium compounds was repeated under the same condition as in Example i, except of changing the amount of YCI 3 MgCl 2 CaCI 2 and CeCl 3 to be added, to prepare raw material zirconia powder containing stabilizing agent.

A solution of the resultant zirconia powder containing stabilizing agent, alumina powder, and nitrates of each transition metal compound in ethanol was put in a milling pot, and agitated and ground, then removing solvent therefrom and drying to obtain the raw material powder in use for production of ceramics.

Sample (3-2) 20 The procedure for Sample to prepare the material principally containing zirconium compound were repeated under the similar condition except of 1 3 adding alumina powder to the mixed solution of 0.zirconium compounds and stabilizer, to prepare zirconia powder containing alumina and stabilizing agent.

The obtained zirconia powder containing alumina and stabilizing agent and a solution of nitrate of each Stransition metal compound in ethanol were put in the 30 milling pot, agitated and ground followed by removing solvent therefrom and drying to obtain the raw material powder in use for the production of ceramics.

Sample (3-3) The procedures for Sample to prepare the material consisting essentially of zirconium compound were repeated under the similar condition di2 d t t i s l 30 except of adding AidC, powder to the mixed solution of zirconium compound and stabilizing agents so as to form homogeneous mixture, to prepare zirconia powder containing alumina and stabilizing agent.

The obtained zirconia powder containing alumina and stabilizing agent and a solution of nitrate of each transition metal compound in ethanol were put in the milling pot, agitated and ground followed by removing solvent therefrom and drying to obtain the raw material powder in use for production of ceramics.

Production of ceramics The raw material powders to were moulded under the similar condition to that of Example 1 into a desired shape, then fired at the given temperature for 3 hours under atmosphere, obtaining alumina containing partially stabilized zirconia ceramics.

For reference, using the raw material powder 4t tt prepared without the treatment by the transition metal 20 compound the same procedure was repeated under the same condition to sinter, obtaining the ceramics.

Further, in comparison with raw material the ceramics was produced under the same condition by using the raw material with 1.0% of Y, 2 0 content.

Characteristics of raw material powder and ceramics The same properties as those of Example 2 were measured for the raw particulate materials as prepared and the ceramics as produced.

Further, Vickers hardness and bending strength after thermal treatment at 200 0 C and for 100 hours, of the resultant ceramics were measured.

Table 5 shows the properties of Sample and the ceramics made therefrom.

I

The contents of tetragonal phase in all the ceramics except the Reference Samples were 95% or more.

It can be confirmed that grain size of ZrO 2 in the ceramics as produced of all Samples except the Reference i r 1 i o 1101 31 Samples is 2 pm or less, and the particle size of AlO0 3 is 4 pm or less.

Table 6 shows the properties of Sample and the ceramics made therefrom.

The proportion of tetragonal phase in all the ceramics except the Reference Samples was 95% or more.

It can be confirmed that grain size of ZrO, in the ceramics as produced for all Samples except the Reference Samples is 2 pm or less, and the grain size of A1 2 0 is 4 pm or less.

Table 7 shows the properties of Sample and the ceramics made therefrom.

The proportion of tetragonal phase in all the ceramics except the Reference Sample was 95% or more.

It can be confirmed that grain size of ZrO 2 in the ceramics as produced for all Samples except the Reference Samples is 2 pm or less, and the grain size of A1 2 0 3 is 4 pm or less.

St I

I

t i a t 4 4 44! 4 -E t I T^ 1 I ,f A\ 1 i 891101,31 r.-j

J

Table partially stabil. zir. pow. alumina powder stabilizer particl. spec. particl. spec.

kind cont. size surface size surface Al 0 co203 conten.

raw powder tran. metal kind adheri.

atom.% fracture firing sintered tenacity temp. density (KIc) °C g/cm 3 MN/m 3 2 bending strength aftet t.

Kg/mm 2 bending strength vickers after t. hardness Kg/mm 2 kg/mm 2 mol. Iml m2/g pm m2/g mol.% Y203 1.3 190 1.7 230 320 230 230 0.2 0.5 0.1 0.1 0.5 0.1 0.3 0.5 0.5 0.5 0.2 20 10 20 59 30 1.0 40 20 10 10 20 20 30 Mn 0:2 1300 Mn 0.1 1300 Cu 0.3 1400 Mn 0.2 1400 Ni 0.01 1300 Cu 0.2 1400 Fe 0.9 1400 Zn 0.3 1300 Cu 0.3 1300 Co 0.3 1400 Mn 0.3 1400 Cu 0.2 1300 1300 5.58 5.82 5.57 4.70 5.32 5.95 5.10 5.57 5.52 5.45 5.66 5.07 4.74 14.0 15.3 18.5 12.3 10.5 13.0 8.3 9.7 10.2 7.2 10.0 4.8 4.2 132 146 150 138 131 125 135 130 132 125 90 53 65 1260 110 1250 105 1360 1600 1420 1150 1530 1260 95 1230 1430 90 1200 920 47 810 MgO CaO CeO Y203 p p p o

C.

CYCL

(s r *rr4 I .ir u* r v ri ur n **U cr- Y+ 61i Table 6 alumina Powder alumina contain. zirconia powder raw powder zirconia component tran. metal fracture bending grain specific stabilizer partic. 2 3 spec. firing sintered tenacity bending strength vickers size surface kind content size cont. sur. kind deposit temp. density (Kic) strength after t. hardness m m /g mol.% pa mol.% m2/g atom.% °C g/cm MN/m 3 2 Kg/mm 2 Kg/mm 2 Kg/mm 1- 3 Y203 1.3 1.7 40 10 20 1.0 50 20 Mn 0.9 1400 Mn 0.2 1200 Cu 0.3 1300 Fe 0.5 1300 Ni 0.3 1400 Cu 0.05 1400 Cu 0.2 1400 Mn 0.3 1400 1300 5.11 5.82 5.57 5.56 5.56 5.33 5.76 4.74 4.63 10.5 12.5 15.0 9.0 8.8 11.3 10.0 8.5 4.3 1530 1230 100 1350 1340 1330 1420 1130 1580 42 860 1i m MgO Cao 7 Y203 S. 4, 4 uru u r c Table 7 alumina contain. zirconia powder raw powder tran. metal zirconia component stabilizer Al 20 fracture bending bending firing sintered tenacity strength strength vickers spec.

kind cont. cont. surf. spec. deposit temp. density (Kic) after t. after t. hardness mol.% mol.% m 2/g atom.% C g/cm3 YN/m 32 Kg/mm 2 Kg/mm 2 Kg/mm2 -,Io -203 (Ref) .2 1300 .2 1300 .2 1400 .2 1300 .2 1300 .2 1300 1300 6.00 5.57 5.10 5.53 5.08 4.66 4.56 9.5 13.5 11.0 10.3 10.6 4.5 4.5 1150 110 1350 1530 1250 1420 750 750 4 SC 9 99 9 9 0 C 9 9 9 t 9 9 9 Or 0 9 9 9*9 9. 99.9 a 99 99 r Industrial Applicability The first invention in this application is a process for preparation of easy sintering raw material powder for use in the production of zirconia ceramic materials.

The said process is, as suggested by the above mentioned examples, an extremely simple process wherein the transition metal is deposited on the powder of zirconium compound.

In the process, the transition metal compounds may be deposited uniformly on the surface of the powder particles of zirconium compounds so that the sinter activating effect may be obtained even with a small amount, and, as suggested in the examples the prepared particulate material can be easily sintered.

Accordingly, the said process can be accepted widely for the process of the preparation of the raw powder material in use for the production of partially stabilized zirconia ceramics, alumina containing partially stabilized zirconia ceramics, and special ir zirconia ceramics.

The second invention is a method for the production 1 of high density zirconia ceramics.

1 .This method is characterized by using the easy sintering raw particulate material prepared in accordance with the first invention.

In this method, as suggested by the above mentioned examples, the atmospheric firing to sinter can be enabled, and any special equipment or operation is 3 unnecessary to produce enough high density and enough acceptable mechanical properties of the desired specific zirconia ceramics.

In the preceding examples, only atmospheric firing to sinter was used, but other technique such as hot press technique and HIP method can be used to produce such high density zirconia ceramics.

A third feature is a method of the production of high density and high toughness Y, 2 0 3 partially stabilized 36 zirconia ceramics.

In accordance with this method, the raw powder material can have lower temperature sintering ability in addition to easy sinter, whereas the grain growth during sintering treatment of ceramics is restricted so as to produce high density and high toughness Y, 2 0 partially stabilized zirconia ceramics having microstructure, and high content of tetragonal phase.

A fourth feature is a Y, 2 0 partially stabilized zirconia ceramics having novel composition.

The said ceramics are characterized by having Y 2

O,

content of more than 1.3 mol.%, and less than 2.0 mol.%, and further the content of tetragonal phase being more than The inventive ceramics is expected to function as a structural member of high density and high toughness.

A fifth feature is alumina containing partially stabilized zirconia ceramics having novel composition.

These ceramics may have high density and high hardness imparted by containing alumina, as suggested by the above mentioned examples, and further evidence high strength and excellent thermal stability.

Particularly, when the Y, 2 0 partially stabilized t" zirconia ceramics incorporates alumina, high toighness can be imparted as set forth in the above example.

Therefore, such ceramics can be expected to be utilized as a structural member of high hardness and high thermal stability such as a cutting material.

(c C t 891101.36

Claims

1. A process for the production of an easy-sintering raw material to be used for the production of partially- stabilized zirconia ceramics which comprises suspending a powder of zirconium compound(s) containing stabilizing agent(s) in a solution or slurry containing at least one kind of transition metal compound(s) and subsequently removing a solvent from the suspension and drying the resultant powder to form said easy-sintering raw material.

2. A process according to Claim 1, wherein the or each transition metal compound is a compound of at least one kind of metal selected from the group consisting of Mn, Fe, Co, Ni, Cu, and Zn.

3. A process according to Claim 1 or Claim 2, wherein the stabilizing agent(s) is selected from at least one of Y, 2 0, CaO, MgO, CeO 2 and yttrium compound, calcium compound, magnesium compound, and cerium compound which by thermal decomposition produce Y,0 3 CaO, MgO, or CeO 2 respectively.

4. A process according to Claim 3 wherein the amount of yttrium compound is between 1.3 mol.% and 2.0 mol.% as Y,0 3 based on the total amount of zirconium compound as ZrO 2 and yttrium compound as Y 2 0 3 A process according to any one of Claims 1 to 4 wherein the atomic ratio of the transition metal(s) to Zr is in the range of from 0.01 to

6. A process according to any one of Claims 1 to 3, wherein the powder of zirconium compound(s) containing stabilizing agent also comprises aluminium compound(s).

91101.37 'I W. 38- 7. A process according to Claim 6, wherein the atomic ratio of the transition metal(s) compared to zircon plus aluminium is in the range from 0.01 to 8. A process according to any one of the preceding claims wherein the powder of zirconium compound(s) containing stabilizing agent comprises a precursor powder which by thermal degradation produces partially stabilized zirconia or partially stabilized zirconia with alumina. 9. A process according to Claim 8, wherein the precursor powder is co-precipitation precipitated from a solution containing zirconium compound(s) and stabilizing agent. A process according to claim 8, wherein the precursor powder is co-precipitation precipitated from a solution or slurry containing; j a-alumina powder or aluminium compounds which by their thermal decomposition may produce alumina, zirconium compounds, and S(c) a stabilizing agent. S e i. 11. A process according to any one of the preceding claims wherein the powder of zirconium compound(s) containing stabilizing agent(s) comprises a partially 14 t stabilized zirconia powder having a crystal particle size S of less than 400 A and a BET specific surface area of less than 2 m 2 /g or more. 12. A process according to Claim 11 when dependent from 4 Claim 10 wherein the a-alumina powder has a crystal particle size of 1.0 Mm or less and a BET specific |0 surface area of 2m 2 /g or more. 13. A process according to Claim 1 and substantially as

891101.38 1 (w 4 39- herein described with reference to the Examples. 14. A zirconia ceramic raw material when produced by the process of any one of the preceding claims. A process for the production of partially-stabilized zirconia ceramic which comprises moulding the zirconia ceramic raw material of claim 14 and sintering said moulded raw material. 16. A process according to Claim 15, wherein sintering is conducted under atmospheric pressure at a temperature in the range from 1100*C to 1700 0 C. 17. A process according to Claim 15 or Claim 16 wherein the sintering is conducted under atmospheric pressure at a temperature of 1500 0 C or lower. 18. A partially stabilized zirconia ceramic when Sproduced by the process of any one of Claims 14 to 17. 19. A partially stabilized zirconia ceramic according to Claim 18 wherein the content of tetragonal phase is or more. A partially stabilized zirconia ceramic according to Claim 18 or 19 wherein the grain size of ZrO, in the t f ceramic is 0.5 gm or less. St 21. A partially stabilized zirconia ceramic according to any one of Claims 18 to 20, wherein the density of said zirconia ceramic is 5.8 g/cm 3 or more. 22. A partially stabilized zirconia ceramic according to any one of Claims 18 to 21 and containing alumina, which is characterized by the following ratio in the composition: 891101,39 1~-11~ ~ln T~ N 40 partially stabilized zirconia a-alumina transition metal oxide having an atomic ratio compared to to 40 mol.% to 60 mol.% the combination of Zr and Al, of: 0.01 to 1%. 23. A partially stabilized zirconia ceramic according to Claim 22, wherein the grain size of ZrO 2 in the ceramic is 2 pm or less, and the grain size of A1,0 3 is 4 pm or less. DATED this 1st day of November, 1989. NIPPON SODA CO., LTD. By its Patent Attorneys DAVIES COLLISON trs I I 4r 111 (C I I I t 891101-46