JPS585844B2 - Stable β-type alumina slurry - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stabilized slurry of beta alumina powder and a method of spray drying the stabilized slurry to produce a highly flowable and filling powder.

The powder is suitable for use in a machine that automatically fills and presses molds, from which the resulting article can be sintered into dense beta alumina ceramic articles of suitably low electrical resistance. I can do it.

In particular, the present invention provides a method for producing a flowable powder that can be pressed and then fired to form a dense β'' or β-alumina-containing ceramic body useful for use in a variety of electrical conversion devices. Regarding.

More particularly, the present invention provides a polycrystalline β" or
- A method for producing a flowable powder capable of forming an alumina-containing molded body.

Among the polycrystalline binary or multicomponent metal oxides most suitable for use in electrical conversion devices, especially such devices using molten metals and/or molten metal salts as reactants, are:
There are members of the beta-alumina family, all of which exhibit a general crystal structure that is easily identified by X-ray diffraction.

For example, beta alumina (sometimes referred to as sodium-beta alumina) consists of a series of aluminum oxides (Al2
O3) layers and sodium ions occupying the points between those layers and the columns.

A number of beta-alumina polycrystalline materials exhibiting this general crystalline structure are described in the following U.S. patents, which are incorporated herein by reference: 3404035;
4036;3413150;3446677
; 3458356 ; 3468709 ; 34
68719;3475220;3475223
;3475225;3535163;37
19531; . and 3811943.

Among the numerous polycrystalline β-alumina materials described in these patents are those that can be processed according to the method of the present invention as follows.

Standard β-type alumina exhibits a crystal structure consisting of a series of aluminum oxide layers held apart by pillars of linear Al-0 bond chains as described above, with sodium occupying points between the layers and the pillars.

As discussed in the above patents, beta alumina contains at least about 80% by weight, preferably at least about 85% by weight aluminum oxide and about 5 to about 15% by weight, preferably about 8 to about 11% by weight. of sodium oxide.

There are two well-known crystal forms of beta alumina:
Both exhibit the aforementioned general β-type alumina crystal structure, and both can be easily identified by their respective characteristic X-ray diffraction images.

Beta-alumina is a crystalline form that can be represented by the formula Na20.11Al2O3.

The second crystalline form is β”-alumina, with the formula Na20.6A1
It can be expressed as 2O3.

It will be appreciated that the .beta.'' crystalline form of .beta.-alumina contains about twice as much soda (sodium oxide) per unit weight as does .beta.-alumina.

The β''-alumina crystal structure is preferred for forming solid electrolytes or reaction zone separation members for electrical conversion devices.

This is because its specific electrical resistance is low.

2) Boron oxide B203 modified beta alumina in which about 0.1 to about 1% by weight boron oxide is added to the composition.

This modification of β-type alumina is more fully discussed in the aforementioned U.S. Pat. type alumina.

4) β-type alumina modified by adding a small amount of metal ions with a valence of 2 or less;
A type alumina composition consists of mostly aluminum and oxygen and a small proportion of metal ions arranged in a crystal lattice, and is a modified β type alumina with cations that move with respect to the crystal lattice when an electric field is applied. .

A preferred embodiment is one in which the metal ion with a valence of 2 or less is lithium or magnesium or a combination of lithium and magnesium.

Such metals may be present in an amount of about 0.1 to about 5% by weight, preferably about 0.
．． It is included in the composition in an amount ranging from 1 to about 1.5 parts by weight in the form of lithium oxide or magnesium oxide or mixtures thereof.

This type of modified β-alumina is disclosed in the above-mentioned US Pat. No. 3,475.
No. 225 and No. 3,535,163, discussed in more detail.

Such lithia and magnesia stabilized β-aluminas are preferred compositions for producing β-type alumina bodies exhibiting a β” crystal structure.

Energy conversion devices in which objects made from presses made in accordance with the present invention are particularly useful as solid electrolytes are described in some detail in the aforementioned US patents.

When operating such an energy conversion device, cations such as sodium in β''-alumina or some other cations partially or totally replaced with sodium are subject to the effects caused by the electric field. as a result of movement relative to the crystal lattice.

Thus, the solid ceramic electrolyte prepared from the raw dense ceramic press made by the method of the present invention is
Particularly suitable for providing selective cation conduction between the anodic and cathodic reaction zones of an energy conversion device, for fluid reactants used in the device when the reactants are in elemental, compound or anionic states. Essentially opaque.

Some of the energy conversion devices in which β''-alumina-containing ceramics are useful include (1) electrochemically reactive oxidizing agents and reducing agents that are used in contact with both sides of a solid electrolyte or reaction zone separation member; Primary battery; (2) Secondary battery in which an oxidizing agent and a reducing agent with electrochemical reversibility are brought into contact with both sides of a solid electrolyte or reaction zone separation member; (3) Temperature and A pressure difference is maintained between the anode and cathode reaction zones and/or between the anode and the cathode, and the molten alkali metal converted to the ionic state passes through the polycrystalline β''-alumina-containing ceramic wall or inorganic diaphragm. (4) a thermally regenerated fuel cell; and (4) a thermally regenerated fuel cell.

Conventional methods for making green compact shaped ceramic bodies suitable for forming β''-alumina-containing ceramic bodies include at least about 80% by weight aluminum oxide, typically a finely divided powder with poor flow properties; A finely divided powder having a composition of about 5 to about 15 parts by weight of sodium oxide is poured into a suitable mold and heated under high pressure (typically about 600,000 parts by weight).
psi) and includes an isostatic compression operation.

In order to uniformly fill a mold for balanced compression with conventional powder,
It has been found necessary to vibrate the mold either during or after loading the powder, or preferably both.

To fill conventional powders with acceptable density and uniformity, total mold filling times in excess of 5 minutes are typically used.

Filling uniformity typically results in variations in the thickness of the green ceramic body for iso-squeezed solid electrolyte or reaction zone separation elements if the mold is unevenly filled before iso-squeezed. It is necessary because it will wake you up.

Such thickness variations result in a minimum thickness in the sintered solid electrolyte or reaction zone separation member.

The lowest thickness provides a path of low resistance for conduction of sodium ions.

Such a low electrical resistance path results in premature failure of the solid electrolyte or reaction zone separation element under the conditions of use of the energy conversion device.

Conventional methods involving mold vibration, although generally suitable for forming high quality presses, are time consuming and difficult to apply to commercial mass production of presses.

In order to make the cost of the electrical energy conversion devices competitive with other electrical conversion devices, it is necessary, inter alia, to devise a fast and efficient method for producing these compresses.

The walls of the solid electrolyte or reaction zone separation member shall be sufficiently thick to provide reasonable mechanical strength to the part, but sufficiently thin to provide an acceptably low resistance to sodium ion conduction. It should be.

A practical desirable wall thickness has been found to be approximately 1-3 mm.

This wall thickness after sintering means that the corresponding width of the cavities of the isostatic pressing mold will be about 2.5 to about 7.5 mm.

That this mold cavity width is typical can be seen, for example, by consulting US Pat. No. 3,903,225.

The mold cavity width corresponding to the wall thickness after sintering given in the example of U.S. Pat. No. 3,903,225 is 3.1
It is 5m.

The above considerations indicate the need for a flowable powder.

For the purposes of the present invention, a free-flowing powder is defined as a funnel with no legs.
．． It is defined as a powder that flows continuously by gravity through a hole no larger than 5 u, such that the application of other energy, such as vibrating the funnel or adding a gas flow, is unnecessary.

The definition of fluidity is based on the "Metal Powder Industry Federation Standard No. 03" revised in 1972.
oder industriesFederat
ion Standard No. 3 ")".

In particular, it is Degassa Tecnica/l/-Pretain (
Degussa Technical Bulletin
) A31, rAerosil for Improving the Fluidity of Powder Materials
ngthe Flow Behavior of Pow
der Substance).

The latter publication describes a series of footless glass funnels with different outlet hole diameters.

A funnel in the form of what will hereinafter be referred to as an hourglass was used to examine the flowability of powders produced according to the invention and powders produced by conventional methods.

A fluidity test using an hourglass is an indirect measurement test of the frictional force and adhesion force acting between powder particles.

These forces not only inhibit the flowability of the powder, but also the amount of powder per unit volume of the container, which can be achieved by filling a standard powder substance in a standard container and vibrating the container until the powder no longer settles. limit.

The rate at which a powder reaches its final volume per unit volume, and the final volume per unit volume itself, both determine how frictional and adhesive forces between powder particles affect the powder's ability to quickly and effectively fill a container. It is useful as an indirect measure of the power of influence.

Powders that can be rapidly filled in relatively large amounts per unit volume of a container under such conditions are defined as fillable powders for the purposes of the present invention.

Conventional spray drying methods applied to alumina ceramic powders include the use of anti-agglomerating agents to produce a non-agglomerated slurry.

Such conventional slurry stabilization methods typically involve adjusting the aqueous slurry to between 3 and 9 parts.

Gum Arabic and Darvan No. 7 (
Norwalk, Conn., R. T. Vander
bilt Co. Polymer electrolyte type aggregation inhibitors such as ) are also used.

Such methods are not useful in the case of beta alumina slurries, which can be produced by leaching the basic components from the powder into the aqueous phase during slurry preparation and stabilization, as the pH is relatively high, greater than 13. do not have.

In such highly basic (caustic) conditions, neutralization of the excessive basicity cannot be carried out because large amounts of acid anions are required.

The large amount of acid anions will in turn reduce the density of each spray-dried agglomerated particle by introducing excessive pores therein.

Furthermore, this high degree of neutralization results in a faster rate of further leaching of basic components from the powder and faster regeneration of the initial basic state.

Those skilled in the art to which this invention pertains will appreciate that β-type alumina slurry is chemically different from α-alumina slurry;
- It will be readily appreciated that slurry stabilization methods useful for alumina slurries would not be expected to be useful for β-type alumina slurries as well.

Structurally, the difference between beta alumina and other types of alumina in general is that essentially the sodium ions are
It exists together with the main component of 12O3.

Unfortunately, the system of nomenclature for Al2O3 substances has evolved outside of the framework of a unified nomenclature system.

One compound of the Al2O3 family was initially identified as alpha-alumina, pure Al2O3 with a hexagonal crystal structure.

Another material containing what was thought to be a simple structural modification of the same Al2O3 was later discovered and named β-alumina.

If the discoverer had been aware of the presence of Na within the crystal matrix, the term would have been properly applied to sodium aluminate.

Sodium aluminate is formed by reacting Na2O and Al2O3, Na2O.Al2O3
New compounds are formed whose sodium content varies from Na2O.11Al2O3.

As expected from changes in molecular composition, β-form aluminum can be easily distinguished from common alumina materials by significant and unexpected chemical and physical changes.

Among the most notable differences are the changes that occur in the aqueous phase of the slurry, which consists of water and beta alumina.

A reaction appears to occur between water and calcined beta alumina.

This is because the pH and viscosity increase significantly.

These changes are illustrated in the following summary which also shows the effect of dispersants.

Viscosity was measured as described in this application.

α-Alumina with 0.103M NaOH in Table A
were mixed and measured under the conditions of the corresponding section number.

The viscosity increase over 60 minutes is as follows: 1) 10.9 seconds to 11.6 seconds 2) 11.0 seconds to 11.3 seconds 3) 11.0 seconds to 10.4 seconds α-Alumina slurry In the case of , apart from the minimal increase in viscosity over time, there is almost no difference between the actual pH value and the theoretically calculated value.

Slurries of H20, tartaric acid and HCl (0.103M
Their values after 60 minutes (in NaOH) were:

Actual pH value Calculated pH value 12.6 13.03. 8
3. 81.7
1.1 It is clear that there is a significant change in the viscosity of β-type alumina compared to α-alumina, indicating that the chemistry of these materials is unusual.

Moreover, the unexpected reaction of the β-alumina slurry, which causes large deviations from the calculated pH values, strengthens the conclusion that α and β alumina have different properties.

The chemical differences are also proven by comparing the X-ray diffraction images of the two types.

Flowable and filling powders are necessary for the rapid production of green bodies for solid electrolytes or reaction zone separation elements with uniform wall thickness by isostatic pressing.

The function of an automatic isostatic press involves the flow of powder into the isostatic press mold under the influence of gravity.

The mold must be filled quickly and uniformly with very little or generally no vibration.

β-type alumina powders produced according to conventional methods without the addition of binders or with binders added by means other than spray drying exhibit poor flow and filling properties.

It has been found that such prior art powders have a rough surface texture and contain a large proportion of fine particles.

These surface characteristics, particle size characteristics, etc. are thought to have the function of effectively increasing the adhesion force and frictional force between powder particles. making it unsuitable for

Therefore, a method for producing a highly fluid and filling powder suitable for use in a pressing machine in which the mold cavity is automatically filled, from which the pressed article is sintered and electrically It is believed that the ability to create compact β-type alumina ceramic articles with suitably low resistance and suitably high wall thickness uniformity would advance the art.

It is therefore an object of the present invention to produce a stabilized slurry of β-alumina powder that can be used to produce fine spherical aggregates of β-alumina by spray drying.

Yet another object of the present invention is to produce a highly flowable and fillable powder consisting primarily of β and/or β”-alumina suitable for use in extrusion machines in which the mold cavity is automatically filled. The goal is to give you a way to do it.

The product obtained by squeezing from the machine is a compact β-type alumina ceramic article with low electrical resistance and a high degree of wall thickness uniformity suitable for use as a solid electrolyte or reaction zone separation member in energy conversion devices. Can be sintered.

These and various other objects, features and advantages of the present invention will be better understood from the following description, taken in conjunction with the accompanying drawings and photographs.

The present invention resides, in part, in a stabilized slurry of β-type alumina material and a method for stabilizing the same, wherein the stabilized slurry has a viscosity of a conventional β-type alumina slurry that is effective for a specific method. If it is too high to produce viscosity, it can have a low to moderate viscosity for an extended period of time, meeting ceramic forming requirements in methods such as spray drying.

The slurry according to the invention (a) does not have a substantially adverse effect on the chemical utility of the β-type alumina powder as a β-type alumina ceramic forming material;
a liquid phase component suitable for suspending type alumina powder; (b) calcined and suitably disaggregated β-type alumina powder, mixed with the liquid phase, in a range of about 30 to about 70% by weight; β-type alumina powder (c) so as to form a finely dispersed slurry having a powder concentration of a dispersant selected from polymeric carboxylic acids having three or more carbon atoms and capable of chelating aluminum ions;

The beta-alumina included in the slurry has the composition generally discussed above.

That is, the composition generally comprises about 0.1 to about 5 parts by weight of lithium oxide, about 5 to about 15 parts by weight of sodium oxide, and the balance aluminum oxide.

Another embodiment of the present invention relates to spray drying the β-type alumina slurry described above to form a highly flowable, filling powder consisting mostly of smooth spherical particles.

When preparing the β-alumina slurry according to the present invention, a polycarboxylic acid containing at least 3 carbon atoms and capable of chelating aluminum ions is added with at least 0.010 mol of acid functional groups per ceramic powder 1002; Preferably the amount ranges from about 0.010 to about 0.200, more preferably 0.02 per 1001 ceramic powder.
It has been found that when used in amounts ranging from 5 to 0.100 moles of acid functionality, it suppresses slurry viscosity by a factor of 2 to 3 for 1 to 3 hours.

Polycarboxylic acids useful as stabilizers in the slurries of the present invention, as described above, contain at least 3 carbon atoms;
Must be able to chelate aluminum ions.

It should be appreciated that the chelating nature of the polycarboxylic acid is simply a parameter that defines the stabilizing agent and that such chelating function does not necessarily have to occur in the stabilized slurry of the present invention.

Polycarboxylic acids found to be useful in the present invention include
Aluminum ion chelators having 3 to 15, preferably 3 to 8 carbon atoms.

These polycarboxylic acids include aliphatic polycarboxylic acids,
Like olefins, they can be saturated or unsaturated, preferably hydroxy-functional, ie with at least one hydroxy group, most preferably mono- or di-hydroxy-functional polycarboxylic acids.

Among the polycarboxylic acids that fall within this general range are tartaric acid, citric acid, tartronic acid, malic acid and α, β, γ
-There is trihydroxyglutaric acid.

Examples of polycarboxylic acid chelators larger than 15 carbon atoms useful in the present invention include number average molecular weights (Mn) of 4000 to 6.
000 polyacrylic acid.

The most preferred polycarboxylic acids within the above range are hydroxy-functional (preferably mono- or di-hydroxy) saturated aliphatic carboxylic acids that are capable of chelating aluminum.

The most preferred of these acids are citric acid and tartaric acid.

The acid chelating agents described act to reduce viscosity;
If the same amount of non-chelating acid, such as hydrochloric acid or acetic acid, is added, the viscosity will not be significantly suppressed for several hours as required.

This difference between chelating and non-chelating agents was unexpected, especially considering that the amount added is generally only sufficient to lower the pH of the slurry to about 11.

Those skilled in the art will recognize that adding other reagents to the slurry also helps to control viscosity.

However, it is unexpected that such special aluminum chelating acids, such as tartaric acid and citric acid, have the dramatic effect of reducing slurry viscosity, thereby allowing for thicker slurries. Met.

Such thick slurries are advantageous in at least three respects.

1) Reduce the cost of spray drying a given amount of powder.

This is because such costs depend on the amount of water that has to be evaporated per unit weight of powder.

2) Increase powder production rate. 3) Increasing the density of the individual spray-dried agglomerated particles, which results in a more packed powder as defined above.

Those skilled in the art will appreciate that the slurry viscosity is high enough to retard settling of suspended particles during pumping from the supply tank to the atomizer, but sufficient to conveniently pump from the supply tank to the atomizer. It will be understood that this should be adjusted to some convenient value which is as low as possible.

It will also be appreciated that slurry viscosity and surface tension can be varied to obtain spherical spray-dried powder particles with optimal spray-dried powder particle size distribution and optimal smooth surface.

Embodiments of the invention relating to obtaining stable slurries of beta alumina powder suitable for spray drying are further described by way of examples.

Example 1 β-type alumina powder, Li20 (using LiNO3) -0.7%Na
20 (using Na2CO3) -8.7%At203
- The well-mixed mixture consisting of the remainder was baked at 1255°C for 2 hours and placed in a point shaker.
1 with Lucalox ball in )
It was prepared by breaking up the clumps by dry milling for hours.

Several samples of this β-alumina preparation were prepared at 52% by weight.
slurry with water at a concentration of

Other components of each slurry were 2.8% polyvinyl alcohol and trace amounts of 2-octanol in amounts expressed as percentages based on the weight of the beta alumina powder.

In addition to the above components, various acids were added in amounts equal to 0.025 mol of acid functionality per 100 g of powder.

Each 4 slurry has a binder component (polyvinyl alcohol)
was added at the end and made as quickly as possible.

The viscosity and pH values of each slurry were obtained periodically.

The viscosity is recorded as the time (in seconds) it takes for a standard volume of slurry, about 10-, to flow down under the influence of gravity from a standard container with holes of about 1 mm.

The results are shown in Table 1.

The viscosity results obtained at 50 minutes remained essentially the same up to 3 hours.

The results clearly show the beneficial effects of tartaric acid,
In contrast, no acid was added or the non-chelating acids, hydrochloric acid and acetic acid.

Example 2 The results of a similar series of experiments conducted using a slurry concentration of 57% by weight of β-alumina prepared as in Example 1 are shown below.
Shown below.

The benefits of the chelating acids tartaric acid and citric acid have been clearly demonstrated.

To further illustrate the invention, the following detailed examples of preferred embodiments are included.

All percentages are weight percentages of β-type alumina powder as in previous examples.
is the weight percent based on the total slurry weight.

All other percentages are weight percentages based on total weight.

Example 3 β-type alumina powder was mixed with Li20 (using LiNO3) -0.7% Na
20 (using Na2 CO3) -8.7%
It was prepared by firing a well-mixed mixture consisting of A403 and the remainder.

The mixture was calcined at 1250° C. for 2 hours and then de-clumped by shaking the calcined mixture 5002 with 50 1 cm diameter high purity aluminum oxide balls.

The fluidity of the powder after this was determined as described above with <18.12,8,
Hourglasses with various pore sizes of 5 and 2.5 mm were measured to determine if the powder flowed.

The minimum pore diameter (mm) through which a given powder flows is defined as the flow characteristic index.

If the powder does not circulate in any of the aforementioned hourglasses,
The flow characteristic index is defined as "no flow".

The calcined mixed powder after pulverization has the following characteristics: - Shape - Irregular particle surface - Coarse Rough average particle size - 6 μm [by weight, Coulter (
[Coulter Counter]] Flow property index - 54.5% of the non-flowing fired mixed powder, 2.84% of the fired mixed powder
It was spray dried from an aqueous slurry of polyvinyl alcohol, 1.2% polyethylene glycol, 2.1% tartaric acid, and a trace of 2-octanol.

The spray dryer used was a two-fluid type that flowed in the same direction.

The resulting spray dried powder is shown in FIG.

This powder has the following properties. Shape - Predominantly spherical surface - Smooth Roughly average particle size - 100 μm (according to microscopic readings) Flow property index - 2.5 As a control, powder slurry with 1% polyvinyl petral binder in acetone binder solution The fired powder samples coated by evaporation had the following properties:

Shape - irregular Surface – rough Approximate average particle size - 15 μm (according to numerical values obtained using a microscope) Flow characteristic index -18 The last mentioned powder is typical of the conventional process.

The filling properties of the powders according to the prior art and the powders made according to the invention, as previously defined, were determined by placing 4.0 g of powder in a graduated volumetric cylinder with a total volume of 10 cm3 and calculating the volume of the layer after filling and It was determined by measuring after applying vibrations of reproducible frequency and amplitude to the cylinder.

The results for the two types of powder are shown in Figure 2.

The powders made according to the invention clearly have better filling properties, both initially and after a period of vibration.

The powder made according to the present invention was filled into an isostatic press mold within 10 seconds, wasostatically pressed at 55,000 psi, and at 650°C.
Pre-calcined to remove volatile organic components and heated to 1620℃
for 30 minutes to yield a uniformly thick body with a density of 96.7% of theoretical density and an electrical resistance (for sodium ion conduction) of 3.5 ohm-cm.

Example 4 Slurry spray drying method was applied to zeta (lithium) alumina (Li20.5Al2O3).
It was also used in the powder used in place of LiNO3 as a 20 source.

The stabilized slurry has a lithium-alumina ratio of 1:6 (i.e. Li2 0.5 A403 + some excess A403).
)+Na2 0.5A403 Soda component, nominally 9.0% Na2O- 0. 8%Li2,0-90.2
40% of the powder in a ratio giving a weight composition of 403%
It contained 6.5% by weight.

Slurry is 2.1% tartaric acid, 1.2% based on powder
of polyethylene glycol and 2.8% polyvinyl alcohol.

The spray-dried powder had excellent flow properties (index -2.8) suitable for isostatic pressing.

This material after isostatic pressing at 55 Kpsi can be sintered to a density of 97% (1620°C - 30 minutes)4.
It had an electrical resistance to sodium ion conduction of 3 Ω-cm (300° C.).

Although what is presently considered to be the preferred embodiment of the invention has been shown and described, those skilled in the art will recognize that various changes can be made without departing from the scope of the invention.

Similarly, the slurry applications described herein are merely representative of the many conventional methods that require viscosity controlled within defined ranges.

[Brief explanation of the drawing]

FIG. 1 is a photograph of spray-dried spherical powder particles of the present invention. FIG. 2 is a plot of volume versus time for each of two powders 42 illustrating the improved packing properties of powders prepared according to the present invention as compared to those prepared by conventional methods.

Claims (1)

[Claims] 1 In a stabilized slurry of β-type alumina material, a β
A liquid phase component suitable for suspending the β-type alumina powder without substantially adversely affecting the chemical usefulness of the β-type alumina powder as a ceramic-forming material, b. Calcined and suitably agglomerated. 3. Grind and mix with the liquid phase.
β-type alumina powder made into a finely dispersed slurry with the powder concentration ranging from 0 to 70 wt. a dispersing agent selected from polycarboxylic acids having atoms capable of chelating aluminum ions and contained in an amount of at least about 0.010 moles of acid functionality per 100 1 of said beta alumina powder; β-type alumina slurry. 2. The stabilized slurry according to claim 1, wherein the liquid phase is water. 3. The stabilized slurry of claim 1, wherein the polycarboxylic acid dispersant is included in an amount corresponding to about 0.010 to about 0.200 moles of acid functional groups per 1002 of beta alumina powder in the slurry. . 4. The stabilized slurry of claim 1, wherein the polycarboxylic acid dispersant has 3 to 15 carbon atoms. 5. The stabilized slurry of claim 1, wherein the polycarboxylic acid dispersant has 3 to 8 carbon atoms. 6. Claim No. 6, wherein the polycarboxylic acid dispersant is selected from the group consisting of (1) saturated aliphatic polycarboxylic acids, (ii) olefinic unsaturated aliphatic polycarboxylic acids, and (iii) aromatic polycarboxylic acids. Stabilized slurry according to item 1. 7. The stabilized slurry according to item 6 above, wherein the polycarboxylic acid has a hydroxy functional group. 8. The stabilized slurry according to item 7 above, wherein the polycarboxylic acid dispersant has a mono- or dihydroxy functional group. 9. The stabilized slurry according to item 8 above, wherein the polycarboxylic acid dispersant is selected from the group consisting of tartaric acid and citric acid. 10 Polycarboxylic acid dispersant is β-type alumina powder 1
0.025 to about 0.100 moles of acid functional groups per 00 g, and is selected from the group consisting of saturated aliphatic polycarboxylic acids having hydroxy functional groups. Stabilized slurry as described. 11. The stabilized slurry according to item 10 above, wherein the polycarboxylic acid dispersant is selected from the group consisting of tartaric acid and citric acid. 12. The stabilized slurry of claim 1, wherein the slurry comprises a binder.