High technology ceramics with partially stabilized zirconia

A process for making a fully or a partially stabilized zirconia is disclosed. The process comprises making an aqueous solution of zirconium sulfate in admixture with an inorganic or organic water soluble salt of one or more metals selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ra, Sc, Y, La, Ac, Ce, Hf, Th and Al. The aqueous solution is atomized into a solvent at least partially miscible with water with the solvent being agitated during the addition of the solution. The coprecipitated metal salt formed is separated from the solvent, washed with inert solvent or solvents, dried, and calcined.

FIELD 
This invention relates to high technology ceramics. More specifically, this 
invention relates to fully stabilized zirconia (FSZ) and to partially 
stabilized zirconia (PSZ) having very high chemical uniformity. 
BACKGROUND OF THE INVENTION 
Zirconia and mixtures of zirconia with other inorganic oxides are beginning 
to receive a great deal of attention as ceramic materials. These materials 
combine toughness with a high tolerance for rapid temperature changes. 
Because of their unique properties zirconia based materials are already 
finding application as high temperature furnace insulation, casting dies, 
pressure nozzles and thread guides. Potential future applications include 
engine parts, medical prosthesis and electronic materials. 
Zirconia (ZrO.sub.2) exists in three polymorphic crystal structures between 
room temperature and its melting temperature. Pure zirconia is rarely used 
as a ceramic material. The martensitic tetragonal to 
##STR1## 
monoclinic phase transformation at approximately 1100.degree. C. is 
diffusionless, athermal and reversible. The 3.25% volume expansion results 
in catastrophic failure of pure zirconia materials at &gt;1000.degree.C. 
Other oxides are added to zirconia to form either fully stabilized zirconia 
or partially stabilized zirconia. The oxides most commonly used are calcia 
(CaO), magnesia (MgO) and yttria (Y.sub.2 0.sub.3). Stabilized zirconias 
result from the addition of enough of these other oxides to form a solid 
solution with the cubic fluorite structure. Partially stabilized zirconias 
contain less additives than stabilized zirconias resulting in monoclinic 
or tetragonal phase zirconia exclusively or as precipitates in the mixed 
oxide cubic fluorite solid solution. In addition, the temperature of the 
monoclinic-tetragonal phase transition can be raised to a maximum of 
approximately 1230.degree. C. by the addition of hafnia to zirconia. 
Fully stabilized zirconias have good ion conductivity and can be used as 
solid electrolytes. However, their high thermal expansion and low thermal 
conductivity results in poor thermal resistance. 
Partially stabilized zirconia typically contains 15-50% unstabilized 
zirconia crystallites. These materials have good thermal shock resistance. 
They have low thermal conductivity, low coefficient of friction against 
steel and good resistance to damage from machining. They often toughen on 
grinding and sinter to near theoretical density. Unlike fully stabilized 
zirconia, PSZ has low ionic conductivity and electromagnetic 
transmissibility. 
Zirconium dioxide (zirconia) exists as the naturally occurring minerals 
baddeleyite and endialite. Zircon (ZrSiO.sub.4 or ZrO.sub.2.SiO.sub.2) 
also occurs naturally as zirconia silicate (ZrSiO.sub.4) in zircon sand. A 
variety of methods have been developed for processing zircon sand. The 
sand can be chlorinated at 1100.degree. C. to produce zirconium chloride: 
##STR2## 
Zircon sand can be converted to zirconia in a plasma process: 
##STR3## 
Pure zirconia (approximately 99%) can be prepared by caustic leaching of 
silica from the product mixture. Zirconium chloride and zirconium dioxide 
are the most commonly used precursors for partially stabilized zirconias. 
The most energy intensive method of preparing PSZ involves melting and 
cooling a mixture of the appropriate oxides. This route yields the highest 
quality PSZ crystals obtained to date. 
Zirconia and PSZ powders have been prepared by hydrothermal processes. 
Single-phase monoclinic zirconia powders have been prepared by 
hydrothermal treatment of amorphous hydrated zirconia with 8 wt % aqueous 
KF. The reaction is performed at 100 MPa (14,000 psi), 
200.degree.-500.degree. C. for 24 hours to yield 16-22 mm powders. Yttria 
stabilized cubic zirconia crystals have been prepared hydrothermally at 
650.degree.-750.degree. .C and 15,000-22,000 psi. 
Yttria stabilized zirconia has been prepared by the hydrolysis of a mixture 
of zirconium isopropoxide and yttrium isopropoxide. Calcination of the 
mixed oxide powders is required to obtain the PSZ. PSZ layers can also be 
obtained from plasma sprayed powders. 
PSZ ceramic articles have historically been prepared by sintering mixtures 
of zirconium oxides with the desired stabilizing oxide. This process 
generally results in the formation of inhomogenous products with limited 
strength. It is advantageous to prepare the finished ceramic from a 
specially prepared PSZ powder. 
The usual method of preparing yttria --PSZ powder is the coprecipitation of 
yttria and zirconia using ammonia. Typical reaction proceeds as follows: 
##STR4## 
The major problems with this procedure are that the powder obtained is 
usually not chemically homogeneous and that the powder size is not fine, 
uniform, or of narrow size distribution. 
Partially stabilized zirconias possess a variety of physical properties 
which make them very attractive for demanding, high technology ceramic 
products. Their chemical inertness, high strength, thermal stability and 
tolerance of thermal shocks are responsible for their use in high 
temperature furnace insulation, casting dies, pressure nozzles and thread 
guides. Major potential applications include ceramic engine parts and 
electronic materials. 
One of the most attractive potential applications for partially stabilized 
zirconia is in engine applications. In the conditions of high thermal flux 
in gas turbines, the thermal stress due to the large coefficient of 
thermal expansion restricts the use of zirconia to thin coatings or low 
density insulative parts which can tolerate cracking. The unusual 
toughness and low thermal conductivity of PSZs makes them more attractive 
for diesel engine applications where the temperature does not exceed 
1000.degree. C. 
Zirconia based ceramics are used as sensors in harsh environments such as 
monitoring automobile exhaust. Zirconia based materials are also used as 
thermistors and piezoelectric components. Due to the increasingly high 
demand for partially stabilized zirconias for use in high technology 
ceramic products, there exists a need for PSZ of very high chemical 
uniformity having spherical particles of uniform size and submicron 
diameter. A PSZ having these properties would yield ceramics having a 
highly pure and uniform density wherein the pores between the spherical 
particles close uniformly during ceramic formation. Heretofore, such a PSZ 
has not been readily available. This invention now provides such a PSZ and 
a process for making such PSZ as well as a FSZ.

SUMMARY OF THE INVENTION This invention provides a process for the 
production of a fully or a partially stabilized ZrO.sub.2 comprising: 
(a) making an aqueous solution of zirconium sulfate in admixture with an 
inorganic or organic salt of one or more metals selected from the group 
consisting of Be, Mg, Ca, Sr, Ba, Ra, Sc, Y, La, Ac, Ce, Hf, Th, and Al, 
said organic salt having from about 1 to about 20 carbon atoms; 
(b) atomizing said solution into a solvent at least partially miscible with 
water (e.g., a solvent having a solubility parameter of about 9.5 to about 
14 (cal/cm.sup.3)) present in an amount of at least 3 times the volume of 
said solution such that the ratio of said solution to said solvent is 
about 1:3 to about 1:50, said solvent being agitated during the addition 
of said solution, forming a coprecipitated metal salt; 
(c) separating said coprecipitated metal salt from said solvent; 
(d) washing said separated coprecipitated metal salt with an inert solvent; 
(e) drying said washed coprecipitated salt; and 
(f) calcining said dried coprecipitated salt in a flowing gas or mixture of 
gases. 
This invention also provides a fully or a partially stabilized zirconia 
comprising: 
(a) zirconium dioxide (zirconia, ZrO.sub.2) in an amount of about 75 to 
about 99% by weight, based on the total weight of the PSZ or FSZ, with 
about 80 to about 98 being preferred; and 
(b) an oxide of one or more metals selected from the group consisting of 
Be, Mg, Ca, Sr, Ba, Ra, Sc, Y, La, Ac, Ce, Hf, Th, and Al with Y, Mg and 
Ca being preferred and Y being most preferred, said oxide being present in 
an amount of about 1 to about 25% by weight, based upon the total weight 
of the PSZ or FSZ, with about 2 to about 20 being preferred. 
wherein (a) and (b) are in admixture as a solid solution in individual 
particles with each particle approximating a sphere in shape and each 
particle having a diameter of about 4 to about 1000 nm with about 4 to 
about 200 being preferred; wherein each of said particles have a uniform 
chemical composition of about 75 to about 99% by weight, based on the 
weight of said particle, of (a), with about 80 to about 98 being 
preferred, and about 1 to about 25% by weight, based on the weight of said 
particle, of (b), with about 2 to about 20 being preferred; and wherein 
the PSZ has a green density of about 1.8 to about 3.0 g/cc with greater 
than 2.5 g/cc being preferred. 
DETAILED DESCRIPTION OF THE INVENTION 
In the processes of this invention, FSZ or PSZ is produced from zirconium 
sulfate and inorganic or organic water soluble salts of one or more metals 
selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ra, Sc, Y, La, 
Ac, Ce, Hf, Th, and Al. It is contemplated that the other members of the 
Lanthanum and Actinium series may also be used. The inorganic salts are 
selected from the group consisting of oxides, sulfates, chlorides, 
nitrates, perchlorates, and the like. The organic salts are derived from 
organic acids (e.g. carboxylic acids, hydroxy acids, and the like), 
saturated or unsaturated, substituted or unsubstituted, having about 1 to 
about 40 carbon atoms with about 1 to about 20 being preferred. Examples 
include but are not limited to the following acids: formic (formate); 
acetic (acetate); propionic (propionate); butyric (butyrate); valeric 
(valerate); caproic (caproate); caprylic (caprylate); capric (caprate); 
lauric (laurate); myristic (myristate); palmitic (palmitate); stearic 
(stearate); oleic (oleate); linoleic (linoleate); linolenic (linolenate); 
cyclohexanecarboxylic (cyclohexanecarboxylate); benzoic (benzoate); o-, m- 
and p- toluic (toluate); o-, m- and p- chlorobenzoic (chlorobenzoate); 
terephthalic (terephthalate); glycolic (glycolate); lactic (lactate); 
2-hydroxybutryic (2-hydroxybutryate); mandelic (mandelate); glyceric 
(glycerate); malic (malate); tartaric (tartarate); citric (citrate); 
oxalic (oxalate); malonic (malonate); succinic (succinate); glutaric 
(glutarate); adipic (adipate); pimelic (pimelate); suberic (suberate); 
azelaic (azelate); sebacic (sebacate); maleic (maleate); fumaric 
(fumarate); trimellitic (trimellitate); trimesic (trimesate); and the 
like. 
Of the inorganic salts it is preferred to use the sulfates. Of the organic 
salts it is preferred to use the acetates, formates, and citrates. 
Preferably, the metals that form the salts that are coprecipitated in solid 
solution with the zirconium sulfate are selected from the group consisting 
of Y (yttrium), Mg or Ca. Of these three each has its own advantages and 
range of applications relative to the end use of the PSZ or FSZ produced. 
For example, Y is preferred for high temperature applications. Mg is 
preferred over Ca for other applications because Mg has a lower 
volatility. 
The salts can be dissolved separately to make their own solution and the 
solutions mixed to form one solution or, more conveniently, the salts can 
be dissolved in one solution, without having first dissolved them 
individually in their own solution. Generally, purified water is used to 
make the aqueous solutions to avoid interference or interaction with other 
ions which may be present in the water. Examples of purified water include 
distilled, deionized or millipore filtered (e.g., through a filter having 
a pore size in the range of about 0.2 .mu.m to about 10 .mu.m) water with 
distilled being preferred and millipore filtered being most preferred. 
The individual salt solutions before mixing to form one solution or the 
single solution with all salt components dissolved therein are preferably 
filtered through a millipore filter having a pore size in the range of 
about 0.2 .mu.m to about 10 .mu.m, with about 0.2 to about 3 being 
preferred, to remove unwanted particulate matter and, without wishing to 
be bound by theory, this provides for homogeneous nucleation. The salts 
are mixed together in solution by any suitable means known to those 
skilled in the art for thoroughly dispersing the solutes, including, for 
example, ultrasonic vibration, mechanical stirring, magnetic stirring and 
the like. 
The amounts of the salt in the aqueous solution can vary from about 0.1 to 
about 2.5 molar for the zirconium sulfate, with about 1 to about 2.5 being 
preferred; and from about 0.001 to about 1.3 molar for the coprecipitant, 
with about 0.05 to about 0.5 being preferred. The amount of these salts 
are so chosen in accordance with the amount of each salt desired in the 
FSZ or PSZ product. 
Generally, the amount of zirconium oxide (derived from the zirconium 
sulfate) is from about 75 to about 99% by weight based on the weight of 
product oxide, with about 80 to about 98 being preferred. This corresponds 
to an amount of zirconium sulfate in the mixed salt solution of about 0.1 
to about 2.5 moles/liters with about 1 to about 2.5 being preferred. The 
amount of coprecipitant salt is generally about 1 to about 25% by weight 
based on product oxide, with about 2 to about 20 being preferred. This 
corresponds to an amount of the coprecipitant salt in the mixed salt 
solution of about 0.001 to about 0.8 moles/liters, with about 0.01 to 
about 0.5 being preferred. 
In general the solutions are prepared at a temperature, such as room 
temperature, suitable for dissolving the salt being utilized. If desired 
slightly elevated temperatures (e.g., about 30.degree. to about 80.degree. 
C.) may be used to more conveniently dissolve the salt being utilized. 
The mixed solution of salts is then delivered into a solvent at least 
partially miscible with water in the form of fine droplets. Generally this 
is accomplished by atomizing or spraying the solution into the solvent to 
produce a fine mist. The atomized solution is produced, for example, by 
the interaction of a liquid passing through a nozzle in conjunction with 
pressurized gas or ultrasonic vibrations. Such nozzles are commercially 
available, as for example a Siphon Solid Cone Air Atomizing Nozzle WDA-WDB 
and an Aspirating Type H-lA, which are dual pressure nozzles obtainable 
from Delavan Corporation and Bete Fog respectively; or, for example, Model 
No. 8409-2-35TC or 8308-2-60TC which are utrasonic nozzles obtainable from 
Sono-Tek. The rate of delivery of the salt solution into the solvent is 
not a determinitive factor of the desired product obtained and may vary in 
accordance with the quantity of materials being utilized. Those skilled in 
the art will be able to vary the delivery rate and still obtain the sought 
after results without any undue experimentation. More conveniently, the 
rate of delivery of salt solution into solvent is predetermined by the 
nature and design of the delivery device utilized. 
The droplet size of the delivered salt solution can effect the size of the 
particles and the content of the FSZ or PSZ. For example, in three ethanol 
dehydrations in the production of Y.sub.2 O.sub.3 -PSZ smaller droplets of 
salt solution resulted in smaller particles and a higher Y.sub.2 O.sub.3 
content in the Y.sub.2 O.sub.3 -PSZ. This may be explained, without 
wishing to be bound by theory, by more rapid precipitation of the salts 
from the smaller droplets. Therefore, particle size and salt, e.g., yttria 
(i.e., Y.sub.2 O.sub.3), content can be controlled by the size of the 
droplets and hence the delivery method. Such delivery methods are amply 
exemplified heretofore and any variations in them are well within the 
capabilities of those skilled in the art without undue experimentation. 
The solution, as previously stated, is delivered into a solvent at least 
partially miscible with water. The solvent utilized is capable of drying 
the droplets of salt solution by rapidly removing water while the 
remaining metals coprecipitate forming a dry precipitated powder 
(coprecipitated metal salt). Therefore, the solvent utilized has 
sufficient water miscibility to prevent the separation of the water from 
the delivered salt solution into a second phase, but is not so miscible as 
to adversely effect the precipitation of the FSZ or PSZ. In general, for 
example, solvents which are utilizable have a polarity having a dipole 
moment of about 1.6 to about 4.0 debyes. Examples of utilizable solvents 
include for example: alcohols and mixtures thereof having 1 to about 8 
carbon atoms, with about 2 to about 4 being preferred and mixtures 
thereof; ketones and mixtures thereof having about 3 to about 8 carbon 
atoms, with about 3 to about 5 being preferred; cyclic or acyclic hetero 
atom containing compounds and mixtures thereof having about 2 to about 12 
carbon atoms, with about 2 to about 8 being preferred, and whose hetero 
atoms are selected from the group consisting of oxygen, nitrogen, and 
sulfur. 
Examples of the aforementioned solvents include but are not limited to: 
methanol; ethanol; propanol; isopropanol; n-butanol; sec-butanol; 
isobutanol; amyl alcohol; acetone; methyl ethyl ketone; methyl n-propyl 
ketone; ethyl ketone; methyl isopropyl ketone; methyl isobutyl ketone; 
benzyl methyl ketone; acetophenone; benzophenone; tetrahydrofuran; furan; 
pyrrole; piperazine; morpholine; piperidine; pyrrolidine; 2-picoline; 
thiophene; dimethyl sulfoxide; dimethyl formamide; and the like. 
Amongst the alcohols, ethanol, isopropanol and secbutanol are preferred; 
amongst the ketones, acetone is preferred; and amongst the hetero atom 
containing compounds, tetrahydrofuran is preferred. While alcohols of 8 
carbons can be used, it is preferable that alcohols having from about 6 to 
about 8 carbon atoms be used in admixture with other alcohols having a 
lower carbon number. This is because alcohols with above 6 carbon atoms 
tend to be much less miscible with water than lower carbon alcohols. 
Of the aforementioned solvents, alcohols are preferred with ethanol and 
isopropanol being most preferred. The solvent is rapidly agitated, for 
example, by stirring, mixing, or swirling continuously to insure the most 
advantagous rapid precipitation of metal salts from the solution droplets. 
Such agitation can be done by mechanical stirring, magnetic- sitrring or 
ultrasound. Different techniques of mixing the solvent can result in 
slight variations in the final FSZ or PSZ product. Some mixing techniques 
may not be as efficient as others resulting in some larger particle sizes 
or in a broader particle size distribution in the product. Some techniques 
may produce heat, such as that produced by an ultrasonic probe. The heat 
can cause more of a particular salt to dissolve resulting in a product 
having a lower content of that particular salt. However, such variations 
may be substantially reduced by insurinq rapid stirring of the solvent. 
The ratio of the amount (by volume) of solvent used to the solution added 
is about 3:1 to about 50:1 and preferably about 5:1 to about 20:1. 
It is preferred to maintain a nearly constant water (from the aqueous 
solution) to solvent ratio during the addition of the salt solution to the 
solvent. Maintaining a nearly constant water to solvent ratio results in a 
nearly constant polarity of the solvent, which (without wishing to be 
bound by theory) is believed to result in a more uniform particle size and 
chemical distribution. Therefore, it is preferred that fresh solvent be 
added to the solvent receiving the salt solution during the addition of 
the salt solution. The fresh solvent is added at a rate of about 3 to 
about 50 times the rate (based on volume) of the addition of the solution 
with about 5 to about 20 times the rate being preferred. The additional 
solvent can be added by means suitable to deliver the desired volume of 
solvent, e.g., by droplets, driping, injecting, and the like. Addition by 
continuous stream may also prove useful. 
The foregoing steps are conveniently carried out at room temperature, but 
may if desired be carried out at higher or lower temperatures, e.g., about 
-10.degree. C. to about 100.degree. C. and preferably about 0.degree. C. 
about 60.degree. C. without adverse effect on the physical properties of 
the FSZ or PSZ powder. However, as those skilled in the art will 
appreciate, due to the effect of temperature on the solubility of a 
solute, variations in temperatures may cause slight variations in the 
concentration of the coprecipitant, in the FSZ or PSZ, e.g., Y.sub.2 
O.sub.3 in a Y.sub.2 O.sub.3 -PSZ. 
The precipitated powder is then separated from the supernatant, for example 
by filtration or centrifugation. The separated powder is then washed with 
an inert solvent, such as, for example acetone. Other solvents for washing 
the precipitated powder include but are not limited to toluene, n-butanol, 
ethyl acetate, and the like. The solvents may be used individually, 
sequentially or as mixtures. For example, a sequential use of acetone and 
toluene with acetone being used first in the sequence. 
The washed powder is then dried for a time and at a temperature sufficient 
to dry the powder without degrading the powder or causing other adverse 
chemical or physical changes in the powder. For example, the powder can be 
dried for a time period of about 1/2 to about 16 hours at a temperature of 
about 40.degree. to about 150.degree. C.; preferably at 60.degree. to 
120.degree. C. 
The dried powder is then calcined in a flowing gas or mixtures thereof for 
a time period and at a temperature which will calcine the powder without 
causing adverse physical effects. For example, the dried powder can be 
calcined at a temperature of about 700.degree. to about 1100.degree. C., 
preferably about 700.degree. to about 900.degree. C. and most preferrably 
at 750.degree. to 800.degree. C. for a time period of about 1 to about 12 
hours, preferably about 1 to about 5 hours and most preferably about 2 
hours. The flowing gases that can be utilized include for example air, 
oxygen, and the like. Most preferably flowing air is used. 
FSZ and PSZ differ from each other only in the ratio of metals present. 
Thus a FSZ is produced when the ratio of metals present results in 
formation of a solid solution with a cubic fluorite structure whereas a 
PSZ is produced when higher Zr levels are used. The ratio of metals 
utilized to produce a FSZ or PSZ are readily determined by reference to 
phase diagrams for the metals being used. 
The following examples are provided for the purposes of illustration only. 
The examples should not be construed as limiting the invention in any way 
as variations of the invention are possible which do not depart from the 
spirit and scope of the appended claims. 
In general, in the following examples, the monoclinic phase observed by 
x-ray diffraction (XRD) was increased in the preparation of the samples 
for testing. Grinding in a mortar or ultrasonic vibration induces the 
tetragonal to monoclinic transformation. As an example, when the powder 
prepared using the Sono-Tek nozzle was ground, &gt;5-10% monoclinic phase was 
observed. Smearing the unground powder into the sample holder produced 
only 5% monoclinic. No monoclinic phase was detected when the powder was 
sprinkled and gently pressed. 
In the examples that follow PSZ are produced. 
EXAMPLE 1 
To 50 ml water was added 7.1 lg zirconium sulfate tetrahydrate and 0.6 g 
yttrium sulfate octahydrate. This solution was filtered through a 0.2 
.mu.m filter and then sprayed into 0.5 L ethanol using a ceramic nebulizer 
(Beckman #485857) pressurized by compressed air at 5 to 10 psi. The 
ethanol solution was mechanically stirred during this process. A white 
precipitate was formed. The precipitate was collected by filtration and 
was washed with 0.5 L acetone. The precipitate was dried for 1 hour at 
120.degree. C. and then calcined in air at 750.degree. C. for 2 hours. 
The product was a white powder of 5 mole % Y.sub.2 O.sub.3--ZrO.sub.2. The 
powder was 99% pure, was 90% cubic/tetragonal phase, and was spherical 
with an average particle size of 40 nm as determined by quasielastic light 
scattering. Analysis by analytical electron microscopy indicated a narrow 
yttria distribution of 5.+-.1% on a particle by particle basis. 
EXAMPLES 2-3 
Examples 2 and 3 were performed as in Example 1 except that the reaction 
temperature was maintained at 0.degree. C. or 60.degree. C., respectively, 
instead of room temperature. The product obtained in each of these 
examples was identical to that of Example 1. These examples demonstrate 
that this process can be conducted under a wide range of temperatures. 
EXAMPLE 4 
Example 4 was performed as in Example 1 except the amount of ethanol was 
increased to 1.0L. The product was identical to that obtained in Example 1 
except that the yttria content was 4.6 mole %. 
EXAMPLES 5-7 
Zirconium sulfate (274.01 g, 0.77 moles) and yttrium sulfate (13.51 g, 0.02 
moles) were dissolved in 390 m water. After addition, the solution volume 
was 530 ml. This solution was filtered through a 0.2 .mu.m filter and then 
sprayed, using three different nozzles, into 1 to 1.5 liters of rapidly 
stirred isopropanol. Isopropanol is added at 5 times the rate of the 
sulfate solution. The total volume of alcohol was 3860 ml. Addition 
required 40 to 80 minutes. 
The metal salts immediately coprecipitated. The slurry was filtered and the 
precipitate was washed with 2 liters of acetone. The powder was dried for 
11/2 hours to 2 hours at 120.degree. C. and then calcined in flowing air 
at 750.degree. C. for 2 hours. The results are reported in Table I. 
TABLE I 
______________________________________ 
EFFECT OF SPRAY NOZZLE ON PSZ 
CHEMICAL 
EXAM- MOLE % TICLE HOMO- 
PLE NOZZLE Y.sub.2 O.sub.3 
SIZE GENITY* 
______________________________________ 
5 Air 3.7 20 nm 2.0-7.6 
Pressure 
A** 
6 Air 3.4 6nm 2.0-5.4 
Pressure 
B*** 
7 Ultra- 3.6 12 nm 2.3-4.9 
Sonic 
______________________________________ 
*Mole % Range of Y.sub.2 O.sub.3 
**Bete Fog 
***Delavan 
SonoTek 83082-60TC 
These results demonstrate how a number of commercial nozzles can be used 
for this process. The ultrasonic nozzle provides a low pressure spray and 
results in the best chemical uniformity. 
The results of particle by particle analysis by Analytical Electron 
Microscopy (AEM) of the product produced in accordance with the procedure 
of Example 7 is given in Table II and graphically represented in FIG. I. 
TABLE II 
______________________________________ 
MOLE % Y.sub.2 O.sub.3 ON A TICLE 
BY TICLE BASIS 
POINT MOLE % Y.sub.2 O.sub.3 
______________________________________ 
1 2.4 
2 2.3 
3 3.2 
4 3.6 
5 4.0 
6 3.2 
7 4.0 
8 3.5 
9 3.8 
10 4.7 
11 2.6 
12 2.7 
13 4.4 
14 3.0 
15 4.9 
16 3.6 
17 3.4 
18 2.7 
19 3.0 
20 3.2 
AVERAGE 3.41 
STANDARD 0.73 
DEVIATION 
______________________________________ 
EXAMPLES 8 and 9 
Zirconium sulfate (1261.5 g, 3.55 moles) and yttrium sulfate (61.3 g, 0.10 
moles) were dissolved in 1.75 liters water. This solution was filtered 
through a 0.2 .mu.m filter and then sprayed, utilizing two different 
nozzles, into 3 to 3.5 liters of rapidly mechanically stirred isopropanol. 
Isopropanol was added at 6 times the rate of the aqueous solution. The 
total volume of alcohol was 17.5 liter. Addition required 11/2 to 2 1/2 
hours. The slurry was filtered and the precipitate was washed with 8 
liters of acetone. The powder was dried for 2 hours at 120.degree. C. and 
calcined for 2 hours at 750.degree. C. The results are reported in Table 
III. 
TABLE III 
______________________________________ 
EFFECT OF SPRAY NOZZLE ON PSZ 
CHEMICAL 
EXAM- Mole % TICLE HOMO- 
PLE NOZZLE Y.sub.2 O.sub.3 
SIZE GENITY* 
______________________________________ 
8 Air** 3.0 12 nm 0-7.0 
Pressure 
9 Ultra- 3.6 20 nm 1.6-4.0 
Sonic*** 
______________________________________ 
*Mole % Range of Y.sub.2 O.sub.3 
**Delavan 
***SonoTek 83082-60TC 
The results of a particle by particle analysis of the product produced in 
accordance with the procedure of Example 9 is given in Table IV and 
graphically represented in Figure II. The analysis was performed by AEM. 
TABLE IV 
______________________________________ 
MOLE % Y.sub.2 O.sub.3 ON A TICLE 
TO TICLE BASIS 
POINT MOLE % Y.sub.2 O.sub.3 
______________________________________ 
1 2.0 
2 2.7 
3 2.5 
4 2.0 
5 2.5 
6 2.1 
7 2.4 
8 3.5 
9 3.2 
10 3.1 
11 4.0 
12 2.3 
13 2.6 
14 2.3 
15 1.6 
16 1.6 
17 2.9 
18 3.2 
19 2.9 
20 2.1 
AVERAGE 2.58 
STANDARD 0.62 
DEVIATION 
______________________________________ 
The Y-PSZ powder, of Example 9, containing about 3.6 mole % of Y.sub.2 
O.sub.3 was pressed at about 10K PSI to yield a pellet. The green density 
of the pellet was about 1.86 g/cc. The pellet was sintered at about 
1500.degree. C. to yield a pellet of fixed density 5.99 g/cc. If the 
powder is milled before use the green density could be increased to 2.99 
g/cc. If the sintering is optimized there should be obtained a fixed 
density of about 6.05 g/cc. 
EXAMPLE 10 
To 50 ml water was added 7.1 g zirconium sulfate tetrahydrate and 0.45 g of 
calcium formate. This solution was filtered through a 0.2 .mu. filter and 
then sprayed into 0.5 L isopropanol using a ceramic nebulizer (Beckman 
#485857) pressurized by compressed air at 5 to 10 psi. The isopropanol 
solution was mechanically stirred during the process. A white precipitate 
was formed. The precipitate was collected by filtration and was washed 
with 0.5 L acetone. The precipitate was dried for 1 hour at 120.degree. C. 
and then calcined in air at 750.degree. C. for 2 hours. The product was a 
white powder of 5.8 weight % CaO. The powder was &gt;90% monoclinic phase 
with the remaining percentage being cubic/tetragonal phase and was 
spherical with an average particle size of 11-15 nm as determined by AEM. 
AEM also indicated a Ca:Zr ratio of 0.01:0.07 on a particle to particle 
basis. 
EXAMPLE 11 
The preparation was the same as in Example 10, except 0.19 g calcium 
citrate tetrahydrate was substituted for calcium formate. The product was 
a white powder of 5.9 weight % CaO. The powder was spherical with a 
submicron particle size as determined by SEM (Scanning Electron 
Microscopy). 
EXAMPLE 12 
To 50 ml water was added 7.1 g zirconium sulfate tetrahydrate and 1.2 g 
magnesium citrate. This solution was filtered through a 0.2 .mu.m filter 
and then sprayed into 0.5 L isopropanol using a ceramic nebulizer (Beckman 
#485857) pressurized by air at 5 to 10 psi. The isopropanol solution was 
mechanically stirred during this process. A white precipitate was formed. 
The precipitate was collected by filtration and was washed with 0.5 L of 
acetone. The precipitate was dried for 1 hour at 120.degree. C. and then 
calcined in air at 750.degree. C. for 2 hours. The product was a white 
powder of 6.9 wt % MgO. The powder was &gt;90% monoclinic phase with the 
remaining percentage being cubic/tetragonal phase and was spherical with 
an average particle size of 18-25 nm as determined by AEM. AEM also 
indicated a Mg:Zr ratio of 0.01:0.23. 
EXAMPLE 13 
The preparation was the same as in Example 12 except 0.31g of magnesium 
formate dihydrate was substituted for magnesium citrate. The product was a 
white powder of 5.8 wt % MgO. The powder was spherical with a submicron 
particle size as determined by SEM. 
EXAMPLE 14 
The preparation was the same as in Example 12 except 0.12 g magnesium 
sulfate was substituted for the citrate. Also, the solvent was 0.5 L 
acetone instead of isopropanol. The product was a white powder of 6.7 wt % 
MgO. The powder was spherical with a submicron particle size as determined 
by SEM. 
EXAMPLE 15 
In a process similiar to Example 9, 25.3 lbs zirconium sulfate and 1.25 
lbs. yttrium sulfate were disolved in 35.1 lbs. millipore filtered water. 
The resulting solution was filtered and then atomized through an 
ultrasonic nozzle into a total of 276 lbs. isopropanol. The solution was 
stirred mechanically. The product was collected by filtration and washed 
with 7.5 gallons acetone, 3 gallons toluene and then 5 gallons acetone. 
The product was dried at 60.degree. C. overnight and then calcined at 
750.degree. C. for 3 hours to yield 25-75 nm spherical particles with 
excellent chemical uniformity. The yttria distribution on a particle by 
particle basis was 2.4.+-.0.7 mole % was for 20 particles as determined by 
AEM. The results of the particle by particle analysis is given in Table V 
and graphically represented in Figure III. 
TABLE V 
______________________________________ 
MOLE % Y.sub.2 O.sub.3 ON A TICLE 
BY TICLE BASIS 
POINT MOLE % Y.sub.2 O.sub.3 
______________________________________ 
1 1.80 
2 1.83 
3 1.91 
4 2.05 
5 2.01 
6 2.67 
7 1.47 
8 4.42 
9 2.07 
10 2.31 
11 1.58 
12 2.96 
13 2.93 
14 2.81 
15 3.01 
16 2.13 
17 2.02 
18 3.26 
19 2.02 
20 2.39 
AVERAGE 2.38 
STANDARD 0.70 
DEVIATION 
______________________________________ 
COMATIVE EXAMPLES 
EXAMPLES 16-19 
Comparative Examples 16-19 were conducted as described in Example 1 with 
the exceptions that solvents other than ethanol were used. The aqueous 
salt solution was added dropwise and the mixing was by ultrasonication. 
The results obtained are reported in Table VI. 
These results show the effects of differing solvent polarity on the yttria 
and the zirconia contant of a PSZ powder, e.g., as the solvent polarity 
increases more zirconium sulfate remains in solution. 
TABLE VI 
__________________________________________________________________________ 
EFFECT OF DIFFERENT SOLVENTS ON PSZ TICLE SIZE 
BULK MOLE % 
Y LEVEL Zr LEVEL 
Y.sub.2 O.sub.3 IN 
IN SOLVENT 
IN SOVENT 
TICLE 
EXAMPLE 
SOLVENT 
POWDER (.mu.m/ml) 
(.mu.m/ml) 
MORPHOLOGY 
__________________________________________________________________________ 
1 Ethanol 
5.0 0.4 128 Submicron Spheres 
16 Methanol 
6.5 -- -- Submicron Spheres 
17 Isopropanol 
4.9 0.3 90 Submicron Spheres 
18 n-Butanol 
4.8 0.5 34 Caked Powder 
19 Acetone 
6.0 -- 222 1-4 .mu.m Fused Masses 
__________________________________________________________________________ 
COMATIVE EXAMPLE 
EXAMPLE 20 
To 50 ml water was added 7. lg zirconium sulfate tetrahydrate and 0.6g 
yttrium sulfate octahydrate. This solution was filtered through a 0.2 
.mu.m filter and then added rapid dropwise into 0.5 L ethanol. The ethanol 
solution was mechanically stirred during this process. A white precipiate 
was formed. The precipitate was collected by filtration and was washed 
with 0.5 L acetone. The precipitate was dried for 1 hour at 120.degree. C. 
and then calcined in air at 750.degree. C. for 2 hours. The product was a 
white powder of 1 mole % Y.sub.2 O.sub.3 --ZrO.sub.2. The powder was 
spherical with an average particle size of 214 nm as determined by 
quasielastic light scattering. 
COMATIVE EXAMPLE 
EXAMPLE 21 
To 35 ml methanol was added 8.6 g zirconium nitrate pentahydrate and 0.8 g 
yttrium hexahydrate. This solution was added dropwise into 0.4 L 
chloroform. The chloroform was ultrasonicated during the process. A white 
precipitate was formed. The precipitate was collected by filtration and 
dried for 1 hour at 120.degree. C. and then calcined for 2 hours at 
750.degree. C. The product was a white powder of 1 to 5 .mu.m size 
particles as determined by SEM. 
COMATIVE EXAMPLE 
EXAMPLE 22 
To 15 ml water was added 11.1 g zirconium acetate and 0.7 g yttrium 
acetate. This solution was added dropwise into 0.3 L acetone. The acetone 
was ultrasonicated during the process. A white precipitate was formed. The 
precipitate was collected by filtration and washed with 0.3 L acetone. The 
precipitate was dried for 1 hour and 120.degree. C. and then calcined for 
2 hours at 750.degree. C. The product was a white powder of 1 to 10 .mu.m 
size particles as determined by SEM.