Note: Descriptions are shown in the official language in which they were submitted.
~2~3~340
SPECIFICATIO~
Titla of Invention
ZIRCONIA CERAMICS AND A PROCESS FOR PRODUCTIOM THEREOF
The present invention relates to zirconia ceramics including fully
stsbilized zirconia, partially-stabilized zirconia and partially-stabilized
zirconia containing alumina (hereinafter refer generally to "zirconia", unless
otherwise specified).
More particularly, it relates to a process for the production of easy
sintering raw material powder to be used for tbe production of æirconia
ceramics as well as a method of the production of high density zirconia
ceramic materials which comprises moulding the above raw particulate material,
and, then sintering, and ~urther to Y203 partially stabilized zirconia
ceramic material of a novel compos~tion as well as alumina containin~
partially stabilized zirconia ceramic material.
Two species of zirconia ceramic material are known, i.e. fully
stabilized zirconia ceramics wherein all crystal phase of ZrO2 constitutin~
the ceramics is the cubic phase, and the cubic phase has been stabilized even
at the lower temperature range, and partially stabilized zirconia ceramics
wherein the crystal phase of ZrO2 constituting the ceramics is the
tetragonal phase, and the tetragonal phase has been stabilized even at the
lower temperature range.
", . . -] ~
~2~3~340
As a method for stabilizing ths crystal phase of ZrO2 constituting
the ceramics, a process has been widely used which comprises adding a
stabiliæer such a~ CaO, ~gO, Y203, and/or CeOz to the raw matsrial
powder or the ceramics in order to fully stabilize or to partially stabilize
the crystal phase of ZrO2.
Y203 particularly is widely utilized as a stabiliz;ng agent for
the production of partially stabilized zirconia ceramics having high strength
because ceramics having excellent stability and good mechanical properties are
obtained.
Fully stabilized zirconia ceramics have been used as solid
electrolytic media, or as heat resistant materials for furnaces etc., because
of excellent thermal stability.
On the other hand, 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 ths ceramics,
the tetragonal phase of Zro2 constituting the ceramics will transform
martensite-like into the monoclinic phase that is the stable phase at a lower
temperature range, consequently the ceramics may have high tenacity because
the fracture energy is absorbed by the phase transformation.
Accordingly, it is known that partially stabilized zirconia ceramics
are functional ceramics having high strength and high tenacity, and it is
expected to use them for structural material such as mechanical materials,
abrasion resistant materials, and cutting materials, and the like.
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~8~3~
Among these stabilized zirconia ceramics, it is necessary to produce
dense ceramics having high density and controlled microstructure by
suppressing the grain growth in the ceramics to have objective ~unctions, for
example, in the fully stabilized zirconia ceramics, oxygen ion conductivity,
thermal stability, mechanical properties and the like, and in the partially
stabilized zirconia ceramics, such objective functions as mechsnical
properties such as bending strength, tenacity and the like.
Dense zirconia ceramics have been produced having controlled
microstructure by special moulding techniques, and high pressure sintering
techniques such as the hot press technique or HIP method. However, these
methods require complicated operation and special installations, and
therefore, the resultin~ product will be very expensive.
On the other hand, a process has been proposed for the production of
ceramics which comprises preparing a raw mateial powder by using chemical
techniques such as co-precipitation or the like and then sintering a moulding
of the raw material powder at a comparsbly low temperature range.
However, it is known that in general the more finely divided
particulate material has stronger cohesive ~orce. Therefore, it is difficult
to produce ceramics having high density with hi~h reproducibility from the
chemically-treated raw powder.
Further, the addition of sintering activator has been proposed, for
example, Jbpanese Laid Open Gazette ~o. SH0 50-10351 describes a process for
the production of ceramics comprising moulding and sintering a raw material
powder which is obtained by adding aqueous ammonia to an aqueous solution
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~28~L3~LO
containing water~soluble 7irconium salt, water-soluble salts of calcium,
magnesium, yttrium and the like as a stabilizing agentts), and water-soluble
salt of a transition metal as sintering activator, so as to precipitate the
desired co-precipitated hydroxide containing the desired metals, then, drying
and calcining thereof. The raw material powder can not provide satisfactory
lower temperature sintering characteristics nor enough relative density of the
ceramics.
In the above-mentioned process, aqueous ammonia is ussd for
precipitation. Some transition metals will form ammine complexes with ammonia
so that in practice aqueous ammonia can not be used in the cases of such
transition metals.
In order to avoid this shortcoming, there is a process wherein the
oxides of the transition metals are used in place of the water-soluble salts
of the transition metals so as to disperse in the solution containing the
other components wherein the hydroxides of the other metal components are
co-precipitated together with oxides of the transition metals.
~ owever, in this process, the surfacs of the oxide of the transition
metal is coated with the hydroxides of the other components. Therefore, it is
difficult to impart satisfactory effect for the sintering activator by the
transition metal in the ceramics in small amounts.
It was reported that the content of Y203 in the ceramics can be
dacreased to 2.0 mol.% for Y203 partially stabilized zirconia ceramics so
that a fracture toughness(RIc) of approximately 10 M~/m can bs obtained
for the ceramics having high tenacity.
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~ZE~3~
This means that partially stabilized zirconia ceramics containing
Y2O3 in an amount ranging nearly to 2 mol.70 can evidence relatively high
tenacity and strength.
F.F. Lange reported in Journal of ~aterials Science 17, 240-246
(1982) that "Thers is a ~ritical limit of t~e particle size of the tetragonal
phase respectively to Y203 content, and when the size exceeds the critical
limit, the tetragonal phase can not be present. Though the critical particle
size is more than 1 m at a Y203 content of 3 mol.70, it decreases to the
order of 0.2 ~m at a content of 2 molar ~".
As described before, the reduction of Y203 content in the
Y203 partially stabilized zirconia ceramics is important in view of the
high tenacity of the ceramics, and can be attained by suppressing the gro~th
of crystal grains in the ceramics.
However, the suppression of the growth of crystal grains in the
ceramics to control the size of the crystal grains to the order of equal to or
less than 0.2~ m is extremely difficult by the prior art process for the
production of the ceramics.
The characteristics of sintering at a lower temperature such that the
grain size is controlled to approximately 0.2~ m or less cannot be attained
even by using the raw material powder prepared by co-precipitation.
Therefore, the Y203 content in the Y203 partially stabilized zirconia
ceramics has a lower limit of about 2 mol.%. A high strength Y203
partially stabilized zirconia ceramics having a Y2O3 content oÇ less than
2 mol.% is not known. Partially stabilized zirconia with a ~23 content
approximating 2 mol.~ has the problem o heat deterioration and therefore, the
prior art Y2O3 partially stabilized zirconia ordinarily uses a range o about 3
L3~
nol.% for the Y2O3 content.
As described above, the known partially stabilized zirconia is not
satisfactory from the point of view of improving the mechanical strength ~nd
stability, and therefore, ceramics wi~h higher tenacity and stren~th have been
highly desired.
Japanese Patent Laid Open application Gazette Mo. SHO 60-86073 (1985)
discloses a method to improve the mechanical properties of partially
stabilized ~irconia ceramics by the addition of alumina to the composition of
the ceramics.
However, such known partially stabilized zirconia ceramics containing
alumina require special sinterin~ techniques such as the HIP process, and
therefore, the ceramics products will be extremely expensive as described
before.
The present invention provides in one aspect a process for the
production of a raw material powder with characteristics of sintering at a
lower temperature, which can be used for the production of dense zirconia
ceramics as well as a process for the production of dense zirconia ceramics
with controlled crystal structure.
ThP invention also provides in a particular embodiment a Y2O3
partially stabilized zirconia ceramics with high fracture tenacity, having a
novel composition as well as a method for the production of the same.
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~L2~3~3~
The present invention still further provides in another embodiment
partially stabilized zirconia ceramics containin~ alumina as well as a process
for the production of the same.
The present invention comprises a process for the productlon of an
easy sintering raw material powder to be used for the production of zirconia
ceramics which process comprises adding powder principally containin~
zirconium compound(s) together with stabiLizing agents, into a solution or
slurry containing at least one species of transition metal co~pound(s) to form
a suspension, then, removin~ the solvent from the slurry and dryin~ to obtain
a powder product, and also a process for the production of high density
zirconia ceramic, which comprises mouldin~ and sinterin~ the raw material
powder prepared by the above-mentioned process.
The present invention also provides a Y203 partially stabilized
zirconia ceramics bein~ characterized by a Y203 content in a ran~e of
greater than or squal to 1.3 mol. percent and less than 2.0 mol. percent, the
content of tetra~onal phase bein~ 6570 or more; and an alumina containing
partially stabilized zirconia ceramics being characterized by the following
ranges of composition: 99 to 40 mol. percent partially stabilized zirconia; 1
to 60 mol. percent ~-alumina; and transition metal oxide in an amount of 0.01
to 1 percent of the atomic ratio of transition metsls to the combination of Zr
plus Al, which are produced by the above-mentioned process.
The transition metal compound(s) for this invention may be the oxides of
at least one metal selected from the ~roup consistin~ of ~n, Fe, Co, ~i, Cu,
and Zn as well as compound(s) which ~enerate the above-mentioned metal oxides
by thermal decomposition.
. /ih~
., , , ~.
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As to the transition metal compounds, there may be used inor~anic
compounds such as oxides, hydroxides, nitrates, chlorides and the like of the
above-mentioned metals; organic acid salts such as oxalates, acetates,
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 matals, if ,either soluble or insoluble in the
solvents used. So1vent-soluble compounds are preferred.
The stabilizing agent for this imvention may include Y203, CaO,
Mg~ or CeO2, as well as yttrium compounds, calcium coumpounds, magnesium
compound, or cerium compounds to generate respectively ~2~3~ CaO, MgO, or
CeO2, on thermal decomposition.
In the present in~ention, the powder principally containg zirconium
compound(s) includes:
(a) fully stabilized zirconia powder, partially stabilized zirconia powder or
stabilized zirconia powder containing alumina, and
(b) precursor powders which generate fully stabilized zirconia, partially
stabilized zirconia or alumina containing partially stabilized zirconia by
thermal decomposition, all of which can be stabilized by adding the
above-mentioned stabilizing agents.
The powder principally containing zirconium compounds can be the
above-mentioned powder containing the stabilizing agents, which ara obtained
by conventional processes such as the oxide method, the co-precipitation
method, the hydrolysis method, the pyrolysis method and the like.
... , . , -
1~8~34
Particularly, it is preferable to use a precursor powder which is
obtained by drying the co-precipitated hydroxides or mixed carbonates prepared
by adding as a precipitating agent, aqueous ammonia or ammonium carbonate to
the mixed solution containing water-soluble zirconium compounds, and
water-soluble yttrium compounds, 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 principally containing
zirconium compounds is added to the solution or slurry containing the
transition metal compound, and ~hen the 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, and the organic solvents are
preferred because of convenient removal of the solvent by evaporation and
because of less evaporation energy on drying.
The usable organic solvents are not limited, but the use of highly
viscous solvents is not preferred because homogeneous suspension of the powder
principally containing zirconium compounds and containing the transition metal
compounds is difficult and further, removal and drying out of the solvent is
then difficult. Preferably, lower alcohols as for example methanol, ethanol,
propanol, buthanol and the like can be used.
The unit operation for suspension of the powder principally
containing zirconium compounds into the solution or slurry containing the
~-~z~
transition metal compounds can be a simple agitating operation resultin~ in a
satisfactory mixture, but when a grinding and mixing operation such as milling
is used, a complete mixing effect is more certain.
The removal of solvent(s) and drying are carried out by conventional
evaporation methods, but when the transition metal compound is insoluble in
water or organic solvent(s), or when the precipitation has been obtained by
applying a precipitating a~ent to the solution containing the soluble
transition metal compounds, the solvent can be removed by filtration.
Further, spray drying can be used to treat efficiently and effectively the
material powder on a large scale.
The resulting raw material powder can be used for the productlon of
ceramics as it is, but, it can be calcined at a temperature in the range Prom
300 to 1200C for further treatment.
In the raw material powder obtained by the above-mentioned process,
the transition metal compounds uniformly adhere and/or coat the surface of the
raw material powder, so that it functions effectively as a sintering activator.
The raw material powder will produce dense ceramics by the easy
sintering through firing at atmospheric pressure at the relatively lower
temperature in the range of 1100 to 1500C.
The atomic ratio of transition metal to Zr, or to the combination of
Zr plus Al, when the raw material powder contains alumina, 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 as sintering activator is insufPicient. Further, when it
is more than 1.0 percent, the properties of the resultant ceramics will be
affected and a range o~ ~reater than 1.0 percent should be avoided.
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8~L3~C~
In accordance with the present invention, the zirconia ceramics are
produced by moulding the raw material powder obtained by the above process,
and then by sintering the moulded body.
The moulding may be press mouldin~ by using conventional moulding
techniques, but it is preferable to further apply a hydrostatic compression
after low pressure moulding, so as to improve the sintered density and the
mechanical strength of the finished ceramics.
The sintering may be any of the known methods, and by atmospheric
sintering under atmospheric pressure, the object of sintering is sufficiently
improved.
Generally, the sintering temperature can be in the range of from 1100
to 1700C.
In order to control the growth of crystal grains in the ceramics for
the production of dense ceramics, particularly high strength partially
stabilized zirconia ceramics, a lower sintering temperature is better, and
therefore, the range of 1200 to 1500C is preferable.
In accordance with such method, since the raw material powder has
good sintering characteristics, the use of the atmospheric firing at a lower
temperature can easily produce dense ceramics having relative density in
relation to the theoretical density of more than 99qO.
In accordance with the present invention~ Y2O3 partially
stabilized zirconia ceramics havinG a tetragonal phase content of 65% or more
and high tenacity and high strength can be obtained by limiting the raw
material powder to a powder of Y203 partially stabilized zirconia or
~.~8~3~)
precursor powder which produces Y203 partially stabilized zirconia on
thermal decomposition, in which said powder has a crystal particle size of 400
or less and B~T specific surface of 2 m /g or more.
In the production of the ceramics, when the particle si~e of the
powder principally containing zirconia compounds e~ceeds 400 A, or when the
~ET specific surface is less than 2 m /g, the sinter activating effect by
the transition metal compound(s) is insuf~icient and then ceramics of high
enou~h density can not be obtained by atmospheric sintering at the lower
temperature.
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 1.0%, preferably 0.01 to 0.57O.
The sintering temperature is preferably not more than 1400C.
In accordance with the present invention, by the above-mentioned process
for the production of the ceramics, novel Y203 partially stabilized
zirconia ceramics having a Y203 content of 1.3 mol.~ or more, but less
than 2.0 mol.~ and having a tetragonal phase content of 6570 or more can be
produced.
The Y2O3 content is based on the total combination of Y203
plus ZrO2 in the ceramics.
The ceramics products have sintered density of at least 5.8 g/cm ,
preferably more than 5.9 g~cm , and more preferably 6.0 g~cm or more, and
fracture tenacity value (KIc) in the range of from 10 MN~m to 16
MN~m and therefore, are of high density, of high tenacity and of hi~h
strength.
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L3~
The size of crystal grains in the ceramics may be 0.5 m or less,
preferably 0.3 ~m or less, and the content of the tetragonal phase in the
ceramics is 65qo or more.
When the Y203 content is less than 1.3%, the content of the
monoclinic phase will increase and the tetragonal phase content of 65% or more
is maintained with difficulty. On the other hand, ceramics having a Y203
content of 2.0 mol.% or more, have been known, and the fracture tenacity value
theraof can not be more than 10 MN/m
When the size of the crystal graLns in the ceramics exceeds 0.5~ m,
it is extremely difficult to keep the content of the tetragonal phase 65~ or
more. In addition, when the grain size is 0.3 ~m or less, the stability of
the ceramics under heat stress will be improved and the mechanical strength of
the ceramics will be stabilized.
Further, when the sinterin~ temperature exceeds 1400C, the grain
growth in the ceramics will be activated, and the grain size becomes more than
0.5 ~m, and then, only the ceramics having a relatively higher content of
monoclinic phase will be produced, and further cracks may be caused during
firing.
The atomic ratio of the transition metal to '~r in the particulate raw
material powder may range from 0.01 to 1.0~. When the atomic ratio exceeds
1.0%, the characteristics of the ceramics will be undesirably affected.
. .
~Z8~34~)
In accordance with the present invention, the novel alumina
containing partially stabiliæed zirconia ceramics comprising the composition
of 99 to 40 mol.~ partially stabilized zirconia, 1 to 60 mol.7J~-alumina, and
transition metal oxide havin~ the atomic ratio thereof to the combination of
Zr plus A1 ranging from 0.01 to 170 can be produced.
The resultant ceramics have high tenacity and high hardness, in that
the fracture tenacity is of the order of 18.5 U~Jm ~ and the Vickers
hardness reaches to 1600 kg/mm3, as well as excellent heat shock resistance.
In accordance with the process of the invention, the powder
principally containing the zirconium compound material which can be used for
the production of the ceramics may be
(a) a mixed powder comprising partia~ly stabilized zirconia of 99 to ~0 mol.%
and alumina of 1 to 60 mol.~; or
(b) precursor powdsr to produce the above powder on thermal decomposition~
and the above powder is added to a solution or slurry containing the
transition metal compounds to form a suspension, then followed by removing the
solvent therefrom and drying to obtain a raw material powder having the
transition metal in an atomic ratio of the transition metal(s) to the
combination of Zr plus Al ranging from 0.01 to 1%, and then, the material is
moulded and sintered, resulting in the desired ceramics.
The ceramics may be Y203 partially stabilized zirconia ha~ing a
Y2O3 content in the range of from 1.3 to 4 mol.~, or Y2O3 partially
stabilized zirconia wherein a part or all of the Y2O3 stabilizer is
substituted by CaO, MgO, or CeO2, and the content of the stabilizer is 0.01
to 12 mol.%
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L3~
The content of the stabilizin~ agent such as Y203 is based on the
total amount of Zro2 and the presumed oxide for the stabilizing agent.
In the case of Y203 partially stabilized zirconia, when the
Y203 content is less than 1.~ molar70, the ratio of monoclinic phase will
increase even in the presence of Al203, and then it is difficult to keep
the amount of tetragonal phase to 65% or ~nore. When the Y203 content
exceeds 4 mol.%, the fracture tenacity va'Lue of the ceramics will decrease.
When the Al203 content in the ceramics is less than 1 mol.%, high
enough hardness can not be obtained. Further, when tbe Al203 content is
more than 60 mol.%, it is difficult to produce ceramics having high enough
density.
When the atomic ratio of the transition metal to the combination of
Zr plus A1 in the ceramics is less than 0.01~, ceramics with high enough
density can not be obtained. Further, when such atomic ratio is more than 1
mol.%, the sintering chara~teristics of the ceramics will be degraded.
The grain size of zirconia in the ceramics may be 2~ m or less, and
preferably 0.5~ m or less. The content of the tetragonal phase in the
ceramics may be 65~ or more, and preferably 8070 or more. The ~rain size of
Al203 in the ceramics may be 4 ~m or less, and preferably 2~ m or less.
The resultant alumina containing partially stabilized zirconia
ceramics has extremely hi~h hardness such as Vickers hardness in the range of
from 1100 to 1600 Kg/mm , and particularly excellent heat resistan~e such as
a bending strength of 85 Kg/mm or more, even after heat treatment at 200C
for 1000 hours.
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~L~8~L3~0
In the production of the raw material powder, the powder principally
containing zirconium compounds may be: a mixture of partially stabilized
zirconia powder having ~rain size of ~00 A or less, and BET specific surface
of 2 m /g or more; or a precursor powder which generates partially
stabilized zirconia on thermal decomposition; and-4-alumina powder having
Brain size of 1.0~ m or less, and BET s~ecific surface of 2 m /g or more9 or
a precursor powder ~hich generates alumina on thermal decomposition.
When partially stabilized zirconia powder or precursor powder has a
grain size of more than 400 A, or when the BET specific surface thereof is
less than 2 M /g, the sinter activating effect of the transition metal wilL
be decreased so that atmospheric sinterine at less than 1500C can not produce
ceramics with high enough density.
The invention is illustrated by the following examples but these are
not limiting to the scope of the invention.
Example 1: Production of Easy Sintering Raw Material Powder and Ceramics
(1) Production of Raw Material Powder for production of ceramics.
Sample (1-1)
To a solution containing ZrOCl2, and YC13 in a ratio of
Y~03(Y2O3+ZrO2)=0.03 by oxide molar base calculation, was added
aqueous ammonia to regulate the pH of the solution in order to produce
co-precipitation of the combined hydroxides. The resultant co-precipitated
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L3~0
hydroxides were filtered and dried, and then the precursor powder of Y203
partially stabilized zirconia was obtained. By calcining a part of the
obtained precursor powder at 800C for one hour, a powder of Y203
partially stabilized zirconia was obtained. For the transition metal
compounds, the following compounds were dissolved or dispersed in ethanol to
prepare, respectively, a solution or slurry of the transition metal compounds.
Solution Slurry
Mn:MN(CH3CH00)2 4H2o MnO2
pe Fe(N03)2 9H2 ~e(OH)3
Co:Co(CH3Coo)2 4H2o CoO
Ni:Ni(No3)26H2o N'i(O'~)2
Cu:Cu(CH3CO0)2 CuO
Zn:Zn( CH3CO0)2.2H20 ZnO
To the prepared solution or slurry of the transition metal compounds,
the partially stabilized zirconia powder was added to form a suspension, then,
the ethanol distilled off and the residue dried to obtain a raw material
powder for use in the production of Y203 partially stabilized zirconia
ceramics.
Sample (1-2)
In accordance with the same conditions for the production of Sample
(1-1) except for using a precursor powder for Y~03 partially stabilized
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34~
zirconia in placs of the powder of Y203 partially stabilized zirconia, the
adhering treat~ent of the transition metal compound(s) was carried out, and
then, the resultant material was calcined at 800C for one hour, yielding
Y203 partially stabilized zirconia raw material powder for the production
of zirconia ceramics.
Sample (1-3)
The pH of a solution containing ZrOCl2 and CaCl2 in the ratio of
CaO/(CaO+ZrO2)=0.12 by oxide molar calculation for the oxides was adjusted
by adding aqueous ammonia to co-pracipitate mixed hydroxidas. The
co-precipitated mixed hydroxides were filtered, dried and then calcined at
800C for one hour to obtain CaO fully stabilized zirconia powder.
The prepared CaO fully stabilized zirconia powder was treated under
the same conditions as for Sample (1-1) with transition metal compounds,
obtaining CaO fully stabilized zirconia raw particulate material (1-3) for the
production of the zirconia ceramics.
Sample (1-4)
The pH of a solution containing ZrOCl2 and MgCl2 in the ratio of
MgO/(MgO+ZrO2)=0.081 by 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
800C for one hour to obtain M~O partially stabilized zirconia powder.
~.
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' '
341:~
The prepared M~O partially stabilized zirconia powder was treated
under the same conditions as for Sample (1-1) with the transition metal
compounds, obtainin~ MgO partially stabilized zirconia raw material powder
(1-4) for the production of zirconia cer~mics.
Sample (1~5)
A solution containing ZrOC12 and CeC14 in the ratio o~
CeO2~(CeO2+ZrO2)=0.08 by oxide molar calc~lation for the oxides was
adjusted by adding aqueous ammonia to precipitate mixed hydroxides. The
precipitated mixed hydroxides were filtered, dried and then calcined at 800C
for one hour to obtain CeO2 partially stabilized zirconia powder.
The prepared CeO2 partially stabilized zirconia powder was treated
under the ssme conditions as for Sample (1-1) with the transition metal
compounds obtainin~ CeO2 partially stabilized zirconia raw particulate
material (1-5) for the production of zirconia ceramics.
Reference Sample (Cl-1)
To the starting aqueous solution used for the production of the
precursor powder as in Sample (1-1), was added the transition metal compound
and then it was treated to precipitate mixed hydroxides containin~ the
transition metal compound. The precipitated mixed hydroxides were filtered,
and dried, obtaining raw particulate material tCl-1) for reference.
~8~4C9
Reference Sample (C2-2)
The treatment for preparation of Sample (1-1) was carried out but
omitting the deposition of the transition metal compound, in order to prepare
Y203 partially stabilized zirconia precursor powder which was referred as
raw material powder (Cl-2) for reference (hereinafter referred to as
"untreated powder").
Reference Sample (Cl-3)
"Untreated powder" of CaO fully stabilized zirconia produced by the
process for production of Sample (1-3) was used as raw powder (Cl-3) for
reference.
Reference Sample (Cl-4)
"Untreated powder" of NgO partially stabilized zirconia powder
prepared by omitting the deposition of the transition metal com~ound from the
preparation process for Sample (1-4) was used as raw powder (Cl-4) for
reference.
.,
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' ,.
~28~L3~
Reference Sample (C1-5)
"Untreated powder" of CeO2 partially stabilized zirconia powder
prepared by omitting the deposition of the transition metal co~pound from the
preparation method of Sample (1-5) was used as raw powder (C1-5) for reference.
(2) Production of Ceramics
The raw material powder as before obtained was pressure molded under
2 pressure of 200 Kg/cm , and then hydrostatic compression applied to the
product mouldings under a pressure of 2 ton/cm2, and mouldin~s having the
desired shape were obtained. The obtained mouldings were fired under
atmospheric pressure at the given temperature for three hours, producing
zirconia ceramics.
(4) Evaluation Test
The density of the resultant ceramics was measured and the three
point bending test of a portion thereof based on JIS (Japan Industrial
Standard) R 1601 (1981) was carried out.
Table 1 indicates the results of the following tests: on raw
material powder; Samples (1-1), (1-2) and reference Samples (Cl-1)-(C1-2), in
atomic ratio of the transition metal to Zr, the density and relative density
. 1~
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~8~3''L~
to the theoretical density of the resultant Y2O3 partially 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 material powder;
(Samples (1-3~, (1-4), (1-5) and reference Samples (Cl-3) to (Cl-5), in atomic
ratio of the transition metal to Zr, the density and relative density to the
theoretical density of the resultant Y2O3 partially stabilized zirconia
ceramics produced from each ra~l material, and bending strength ~average from 5
points) of the resultant ceramics.
The theoretical density of the ceramics are as follows:
Y203 partially stabilized zirconia ceramics: 6.10 ~/cm
CaO fully stabilized zirconia ceramics: 5.68 g/cm
MgO partially stabilized zirconia ceramics: 5.80 g/cm
CeO2 partially stabilized zirconia ceramics: 6.23 g/cm
In the following tables, (A) means that the transition metal
compound(s) was adhered by the solution method, and (B) means that the
transition metal compound(s) was adhered by the slurry method.
-22-
,, .
.
0
raw material 1200 C riring 1300 C riring
transition metal sintered relative bend sintered relative bcnd
adhere adhered density density strength density density strength
method atom % g/cm3 % kg/mm2 g/cm3 % kg~mm2
_____________________________________ ._________________ _________________ __
1-2 Mn (A) 0.3 5.90 96.7 - ____5.98 98.0 ----
1-1 Mn (A) 0.05 5.90 96.7 ____6.00 98.11 ----
Mn ~A) 0.1 5.95 97.5 ---- 6.01 9805 ----
Mn (A) 0.2 5.97 97.9 ---- 6.0Z 98.7 _~__
Mn (A) 3 5.96 97.6 ____6.02 98.7 100
Mn (A) 1.0 5.94 97.4 ---- 6.02 98.7 ____
Mn (8) 0.05 5.82 95.4 ---- 5.93 97.2 ____
Mn (8) 0.1 5.88 96.7 ---- 5 97 97 9 ~~~~
Mn (8) 0.2 5.90 96.7 ---- 5.99 98.~ ____
Mn (B) 3 5.91 96.9 956.00 98.4 100
Mn (8) 1.0 5.90 96.~ ____6.00 o8.4 ____
____________________________________________________________________________
Fe (A) 0.05 5.72 93.9 ____5.92 97 0 ____
Fe (A) 0.1 5.73 93.9 ---- 5.94 97.4 ----
Fe (A) 0.2 5.84 95.7 ____6.02 98.7 ___
Fe (A) 0.3 5.84 95.7 ___6.03 98.9 101
Fe (8) 0.3 5.80 95.1 845.98 98.0 98
____________________________________________________________________________
Co (A) 5 5.89 96.6 ---- 5.99 98.2 ----
Co (A) 0.1 5.95 97.5 ---- 6.oo 98.4 ___
Co (A3 0.2 5.89 96.6 ---- 6.02 98.~ ____
Co (A) 0.3 5.87 96.2 ---- 5.02 98.7 100
I Co (13) 0.3 5.~1l95.7 885.98 ~8.(~ 9~
~,
-23-
(t.o ~)c co~
raw matcrial 1200 C ril~ing 1300'C riring
transition metal sintered relative l~end sintcred relative bend
adhere adhered density density stren~th density density Strength
method atom ~ g/cm3 % ~g/mm2 g/cm3 % kg/mm2
______________________________________ _ __ ____ ____ ________ ________
1-1 Ni lA) 5 5.8996.6 90 5.99 98.2 90
Ni (A) 0.1 5.9297.0 90 5.99 98.2 95
Ni (A) 0.2 5.9998.2 93 6.02 98.7 98
Ni (A) 0.3 6.0298.7 96 6.o7 99.5 110
Ni (A) 1.0 6.0198.5 86 6.07 99.5 90
Ni (B) 0.3 5.9497.4 9 5.98 98.o 98
____________________________________________________________________________
1-2 Zn (A) 0.3 5.9096.7 85 6.02 98.7 100
1-1 Zn (A) ~5 5.8896~4 80 6.05 99.2 105
Zn (A) 0.1 5.9096.7 80 6.07 99.5 113
., Zn tA) 0.2 5.9998.2 go 6.o8 99.7 115
Zn (A) 0.3 5~9998.2 90 6.o, 99.5 115
Zn (A) 1.0 5.9898.o 7~ 5.07 99.5 90
Zn (B) 0.3 5-9497 4 87 6.01 98.5 100
____________________________________________________________________________
1-2 Cu (A) 0.3 6~0198.5 88 6.o3 98.9 99
1-1 Cu (A) 0.05 5.9697.7 92 6.o5 99.2 108
Cu (A) 0.1 5.9998.2 95 6.07 99.5 115
Cu (A) 0.2 6.0298.7 99 6.09 99.8 120
Cu (A) 0.3 6.0599.2 ln5 6.o7 99.5 113
Cu (A) 1.0 6.o599.2 90 6.05 99.2 go
Cu (B) 0.05 5.9297.0 ____ G.ol 98.5 ___
Cu (B) 0.1 5.9697.7 ---- 6.ol 98.5 ____
Cu (~) 0.2 5.9~~/.7 ---- fi.~)2 98.
C~l t~) 0.3 5.98')~.r) '~'>
-24-
~8~L3~
( () I)c~ conL ~1~
raw matcrial _ 1200 C riring 1300 C riring
transition mctal sintered relative bend sintered relative bend
adhere adhered density density strength density density strength
method atom % g/cm3 Z kg/mm2 g/cm3 S kg/mm2
___________________ ________________________________________________________
C1-1Mn (A) 0.3 5.3384.4 ---- 5-5090.2 ----
Mn (B) 0,3 5.25 86.138 5.50 90.265
Fe (A) 0.3 5-38 88.2 ---- 5.7 93-4~~~~
Fe (B) 0.3 5.30 86.943 5.55 91.068
Zn (A) 0.3 5-38 88.2113 5.60 91.852
Zn tB) 0.3 5.28 86.640 5.48 89.869
Cu (B) 0.3 5.30 86.942 5.52 90.560
C1-2 ---- ---- 5.28 86.640 5.48 89.869
-25-
raw material 1200'C firing 1300 C firing
transitioo metal sintered relative bend sintered relative bend
adhere adhered density density strength density density strength
method atom % ~/cm3 ~ kg/mm2 g/cm3 ~ _g/mm2
____________________________________________________________________________
El-3 Mn (A) 0.3 5.24 95.5 __~ 5.56 97 9 ____
Fe (A) 0.3 5.56 96.1 ---- 5-63 99.1 ____
Co (A) 0.3 5.14 95.5 ____ 5.61 98.8 ----
Ni (A) 0.3 5.23 97,4 ____ 5.67 99.8 ____
Zn (A) 0,3 5.23 97.1 ---- 5.57 98.1 ----
Cu (A) 0.3 5~55 97~7 ~~~~ 5.67 99.8 ____
_______________________________________________________________________._____
1-4 Mn (A) 0.3 5~73 98.8 ---- ---- -___ ____
Fe (A) 0.3 5-76 99.3 ---- ---- ____ ____
Co (A) 3 5.69 98.1 ---- ---- ____ _ __
Ni (A) ~3 5.69 98.1 ---- ---- -___ ____
~n [A) 0.3 5.7i 98.4 ---- ---- ____ __ _
Cu (A) '3 5.69 98.1 ---- ---~ ~~~~ ~~~~
____________________________________________________________________________
1-5 Mn (A) 0.3 6.20 99.5 ---- 6.21 99.7 ----
Ni (A) 0.3 6.18 9~.1 ____ 6.20 99.5 ----
Cu (A) 0.3 6.22 99.8 -___ 6.22 99.8 ____
____________________________________________________________________________
C1-3 ---- ---- 4.85 85.4 ---- 5.30 93.8 ____
C1-4 ---- ---- 5.43 93.6 ---- ---- -___ ____
Cl-5 _--- -_.-- 5.80 93.1 ____ 5.98 96.0 ----
-26--
~313~
Example 2: Y203 Partially Stabilized Zirconia Ceramics and Its Production
(1) Preparation of raw particulate material
The same procedure as that for the production of Sample (1-1) in
Example 1 was carried out but chan~ing the mixture ratio of ZrOC12 and
YC13 to produce co-precipitates of hydroxide.
The obtained co-precipitates of hydroxide were treated under the same
conditions as those of examyle 1 to produce partially stabilized zirconia
powders with different Y203 contsnts.
Sample (2-1)
The resultant partially stabilized zirconia powders were treated with
the solution used in example 1 under similar conditions to produce raw
particulate material for the production of ceramics.
Sample (2-2)
The dried co-precipitates of hydroxide were treated in a similar way
to that for sample (2-1) and further, calcined at 800C for one hour to
produce the raw material powder (2-2) for the production of ceramics.
-27-
.
3~
Sample (2-3)
Partially stabilized zirconia powders as before produced were treated
with the slurry used in example 1 under similar conditions to produce raw
material powder (2-3).
(2) Production of ceramics
Raw materials (2-l) to ~2-3) were moulded under similar conditions to
that of Example 1 and then fired at atmospheric pressure for 3 hours at a
given temperature to result in Y203 partially stabilized zirconia ceramics.
For reference, omitting the treatment with the transition metal
compounds, raw materials wherein the Y203 content was less than 1.3 mol.%,
the particle size was greater than 400 A, and the atomic ratio of the
transition metal to Zr was greater than 1.0~ were used to mould and produce
sintered ceramics. The firing temperature was 1500 C.
(3~ Characteristics of Partially Stabilized zirconia Powder and The Ceramics
Hade Therefrom
The following characteristics were meas~red on partially stabilized
zirconia powder and ceramics obtained in the above items (1) and (2).
Table 3 shows the characteristics of raw material powder (Z-l) and
the ceramics produced from that material.
-28-
~2~ 4~
Table 4 shows the characteristics of raw material powder (2-2) and
(2-3~ and the ceramics produced from those materials.
(A) Size of partially stabilized zirconia particle: D
The size D can be calculated from the wiclth at the half value of the
peak of X ray diffraction by the following Schellar's formula:
D=o.9 ~/s cos ~ ~: the wave l~ngth Or X ray
B: the width at the halr value Or the
dirfraction peak
~: the dirfractionangle
(B) BET relative surface area of partially stabilized zirconia powder was
measured by using micromeritics (machine manufactured by Shimazu Works).
(C) Fracture tenarity of partially stabilized zirconia caramics: KIc was
measured by VicXers indent test.
The Vickers indenter was pressed against the polished surface of the
samples, and the resultin~ indentation size and the resultin~ len~th of the
generated cracX were measurad and RIc was calculated from the followin~
formula which ~iihara et al proposed. The applied indentation load was 50 k~f.
(~Ic~/Hal/2)(H/e~)O 4 o o3s (1~ )-1/2
~: restraint moduras
H: Vickers hardness
E: modulus Or elasticity
a: halr Yaluc Or dia~onal Icn~th Or indcllt.ltion
-29-
3~
(D) Bending strength of partially stabilized zirconia ceramics was measured
in accordance with JIS R 1601 (lg81) rule.
A sample of 3x4x40 mm in size was used, and the measurement was
carried out on a span length of 30 mm under crosshead speed of 0.5 mm/min. and
the value was determined by average from five samples.
(E) Content of tetragonal phase in the partially stabili~ed zirconia ceramics.
The surface of the sample was polished by a diamond slurry containing
3 m size of diamond particles, and then, X ray diffraction measurement was
carried out on that surface followed by the calculation of the following
formula.
1 t
Tetragonal phase content (%) = - - x loO
(lll)tf(lll)m+(lll~m
~lll)t: tetrasonal (111) face diffraction intensity
(lll)m: monoclinic tlll) case diffraction intensity
(lll)~: monoclinic (lll) face diffraction intensity
(iiijt diffraction pcaf~ inciudes CUDiC ~iil k diffraction pea~, but tne
calculation was carried out presuming that that peak is entirely by
tetragonal difrraction.
(F) Graln size in the partially stabilized zirconia cersmics
The grain size was measured by observing the ~racture face of the
ceramics through a scanning type electron microscope. It was confimed that
all samples except the reference sam*les had grain sizes rangin~ from 0.1 to
3~ m.
. ~ .
-30-
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Example 3: Alumina Containing Zirconia Ceramics ancl ~ethod of Production of
the Same
(1) Preparation of raw material powder for production of ceramics
Sample (3-1)
The procedures of Example 1 to produce a powder principally
containin~ zirconium compounds was repeated under the same conditions as in
Example 1, except for chan~in~ the amount of YC13, M~C12, CaC12, and
CeC13, to be added, to prepare partially stabilized zirconia raw particulate
materials.
A solution of tha resultant partially stabilized zirconia material,
alumina powder, and nitrates of each transit`ion metal compound in ethanol were
milled, then solvent removed therefrom and the residue dried to obtain raw
material powder for the production of ceramics.
Sampla (3-2~
The procedure for Sample (3-1) to prepsre a material principally
containin~ zirconiu~ compound was repeated under similar condâtions except to
add alumina powder to the mixed solution of zirconium compounds and
stabilizer, to prepare partially stabili7ed zirconia powder containing alumina.
-35-
12~3~L34~3
The alumina containing partially stabilized zirconia particulate
material and a solution of nitrate of each transition metal compound in
sthanol were milled, followed by removal of solvent therefrom and drying to
obtain tha raw material powder (3-2) for the production of ceramics.
Sample (3-3)
The procedures for Sample (3-1) to prepare a material consisting
essentially of zirconium compound were repeated under similar conditions
except for the addition of AlC13 powder to the mixed solution of zirconium
compound and stabilizing agents so as to form a homogeneous mixture, in order
to prepare partially stabilized zirconia powder containing alumina.
The partially s~abilized zirconia powder containing alumina and a
solution of the nitrate of each transition metal compound in Pthanol were
milled followed by removal of solvent therefrom and drying to obtain raw
material powder (3-3) for the production of ceramics.
(2) Production of ceramics
The raw material powders ~3-1) to ~3-3) were moulded under similar
conditions to that of Example 1 into a desired shape, then fired at a given
temperature for 3 hours under atmospheric pressure, thus oStaining alumina
containing partially stabilized zirconia ceramics.
For reference, using the raw material powder prepared without
treatment by the transition metal compounds the same procedure was repeated
under the same conditions to sinter, obtaining reference ceramics.
Further, in comparison with raw material (3-1), the ceramics were
produced under the same conditions by using a raw material with 1.0~ of
Y203 content.
(3) 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, ~ickers hardness and bending strength after thermal
treatment at 200C and for 100 hours, of the resultant ceramics were measured.
Table 5 shows the properties of Sample t3-1) and the ceramics made
therefrom.
The content of the tetrazonal phase in all the ceramics except for
Reference Samples was 95% or more.
It can be confirmed that the grain size of ZrO2 in the ceramics as
produced of all Samples except the Reference Samples was 2 ~m or less, and the
particle size of the A1203 was 4 ~m or less.
Table 6 shows the properties of Sample ~3-2) and the cersmics made
therefrom.
The content of tetragonal phase in all the ceramics except for the
Reference Samples was 95~ or more.
It can be confirmed that the ~rain size of ZrO2 in the ceramics as
produced of all Samples except for the Reference Samples was 2~ m or less, and
the particle size of the A1203 was 4~ m or less.
Table 7 shows the properties of Sample S3-3) snd the ceramics made
therefrom.
The content of tetragonal phase in all the ceramics except for the
Reference Sample was 95~ or more.
It can be confirmed that the grain size of ZrO2 in the ceramics as
produced of all Samples except for the Reference Samples was 2 ~m or le~ss, and
the particle size of the A12O3 ~as 4~ m or less.
1~,
-~7-
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3~
The first aspect of the 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, as set forth in the above-mentioned examples, is an
extremely simple process wherein the transition matal is deposited on the
powder consisting essentially of zirconium compound.
In the process of the invention, the transition metal compounds are
deposited uniformly on the surface of the powder particles consisting
essentially of zirconium compounds so that the sinter activating effect can be
obtained even at a lesser amount, and, as set forth in the examples, the
prepared particulate material can be easily sintered.
Accordingly, the said process can be accepted widely for the
preparation of particulate raw materials for use in the production of fully
stabilized zirconia ceramics, partially stabilized zirconia ceramics, alumina
containing partially stabilized zirconia ceramics, and-special zirconia
ceramics.
A second aspect of the invention is a method for the production of
high density zirconia ceramics.
This method is characterized by using the easy sintering raw
particulate material prepared as described.
In this method, as set forth in the above-mentioned examples,
sintering at atmospheric pressure is possible, and any special equipment of
operation is unnecessary to produce high enough density and a~ceptable enough
mechanical properties of the desired specified zirconia ceramics.
L3~
In the preceding examples, only sintering at atmospheric pressure was
used, but other techniques such as the hot press technique and the HIP method
can be used to produce such high density zirconia ceramics.
A third aspect of the invention is a method for the production of
high density and high toughness Y2~3 partially stabilized zirconia
ceramics.
This method is characterized by limiting the starting material to a
powder consisting essentially of zirconium compound.
In accordance with this method, the particulate raw 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 tou~hnsss Y203 partially stabilized zirconia
ceramics having a microstructure, and high tetragonal phase content.
A fourth aspect of the invention is a Y203 partially stabilized
zirconia ceramics having a novel composition.
The said ceramics are characterized by having a Y203 content of
greater than 1.3 mol.70, and less than 2.~ mol.~, and also the tetragonal phase
content is greater than 65~.
The ceramics of the invention are expected to function as structural
members of high density and high toughness.
A ifth aspect of the invention is alumina containing partially
stabilized zirconia ceramics having a novel composition.
These ceramics have high density and high hardness imparted by the
alumina content, as set forth in the above-mentioned examples, and, further,
evidence high strength and excellent thermal stability.
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Particularly when the Y203 partially stabilized zirconia ceramics
of the invention incorporate alumina, high toughness can be imparted as set
forth in the above examples. Therefore, such ceramics can be expected to be
utilized as structural members of high hardness and high thermal stability
such as cutting materials.
The present invention provides a process for the preparation of easy
sintering raw particulate material and zirconia ceramics made thereÇrom that
have high density, high strength, high toughness, high hardness and excellent
thermal stability as well as an economical method for the production of the
same. Therefore, the present invention can provide industrial significance.
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