CA1191018A - Preparation of a precursor solid for the manufacture of a ceramic hydrogen ion conductor - Google Patents

Abstract

ABSTRACT
In a method of making a solid polycrystaliine ceramic, that is a precursor conductor for the hydronium ion (HO3+), feed compounds, which in the preferred embodiment are alkalies in the ratio of 60 wt% Na2CO3 and 40 wt% K2CO3, are mixed with 3 wt% MgCO3 and the balance Al2O3, at the atomic scale whereupon a preferred, intermediate, crystalline powder is achieved with a chemical formula;

(Na0?6K0?4)2O (3 W/o MgO) .beta./.beta."-Al2O3 yielding an ?(.beta.) of approximately 0.37 where;

and .beta. and .beta." are the polymorphs of alumina. This powder can be compressed and sintered, for a very short period of time, so the value of ?(.beta.) does not migrate significantly, yet the surface energy levels of the polycrystals are relieved and a solid polycrystalline ceramic, of any predetermined shape, with the above formula is created. It is shown herein that this preferred solid has a conductivity greater than 10-1 (ohm)-1 (cm)-1 at 300°C.; 10-4 (ohm)-1 (cm)-1 at room tempera-ture; that the conductivity is discontinuous at selected values of ?(.beta.) vis a vis temperature; and, how to select ?(.beta.). Mixing at the atomic scale of the feed compounds may take place either by dissolving the feed compounds in water then freeze drying, or spray drying in a spray dryer;
thereafter, calcine and drive off any H20 residual.

Description

This invention relates to the preparation of, and to, asolid ceramic that is a precursor for a hydroniu~ ion conduc-tor.
While it is known that single crystals of hydronium ~
and ~" aluminas can be formed, the creation of a solid poly-crystalline hydronium ~-" alumina has escaped the creative abi-lity of those skilled in the art.
Such said hydronium polycrystalline ~" aluminas are pos-sible host material for hydrogen fuel cells or for use as a membrane to decompose water - electrolysis cells, since the polycrystalline material could be formed into any desired shape as might be required by the geometric or design para-meters of the cell.
It is known that the ~" alumina phase is the preferred polymorph of ~ alumina as the former has three conductive planes (sometimes referred to in the prior art as three spinel blocks), while the ~ phase possesses only but two.
It is known in the prior art how to create single crys-tals of sodium ~"-A12O3 (sodium beta double prime alumina), and the prior art alleges knowledge of how to replace the so-dium ion with hydronium so as to create a hydronium ion con-ductor. In the prior art, when the ion re~lacement of sodiurn with hydronium takes place, within a single crystal, the crys-tal expands in size (to accommodate the hydronium ion as will be hereafter explained), while within solid polycrystals of sodium ~"-Al~O3, the polycrystal shatters.
We have determined that the reasons for the shattering of the said polycrystals, as will become more apparent in this application, is because the hydronium ion is so much larger than the sodium ion which it replaces, or is begged to rep-lace, by appropriate processes, that the crystal lattice stru-cture of the sodium ~" aluminas will not accommodate its size;
the fracture strength of the polycrystal is not large enough so as to overcome the undue stress placed upon it when the hydronium ion replaces the sodium ion that is, the pressure put on the polycrystal lattice structure by the hydronium ion exceeds its molecular bonding threshold whereby it shatters

2 --The prior art is replete with allegations that the ~"- A12O3 ion would be a good conductor of the hydrogen ion, but the ability to yield defacto such polycrystalline conductors, pre-ferably ~olids, has yet to be achieved.
It is an object of this invention to disclose the opti-mum conductivity of a ~ " alumina polycrystalline solid which is a precursor for such hydronium analogues and to fabricate this solid into any desired shape. The resultant is a high density mechanically strong solid ceramic conductor with high resistance to acidic and alkaline corrosion.
Some of the inventors herein have earlier disclosed in a co-pending application [1], filed in Canada, 28 April, 1981 as Serial No. 376,561-0 now entitled THE PREPARATION OF A PRECUR-SOR POWDER FOR THE MANUFACTURE OF A CERAMIC HYDROGE~ ION CON-DUCTOR, a potassium ~ alumina compound and method of senera-ting the same. The resultant, thereof, is a fine crystalline powder with a high weight density of ~" alumina.
For the convenience and for understanding, it is appro-priate to define the following function:

~+ ~
It is an object of the invention, therefore, to achieve a solid (alkali) compound (a high density mechanically strong ceramic) possessing alumina and ~" alumina phases where f(~) = 0.01 - > 1, which preferably is in the range of 0.25 --~
0.48 and specifically 0.37 while preferably using mixes of oxides of sodium and potassium (Na2O/K~O). In an alternative embodiment a preferred value for f(~) is in the range of 0.5 - > 0.55. At or about the value of f(~) = 0O37 (within the range 0.25 --~ 0.48) conductivity of the compound is greater than 10-2 (ohm)~1 (cm)~l at 300C. ( 10~3 (ohm)~l (cm)~l at room temperature ). The preferred compound with f(~ = 0.37 is of a chemical formula;
(NaO-6K0-4)2O (3 W/o MgO) ~ A12O3 In order to explain the properties of such compound, a theory has been evolved known as the MAP theory and the same is partially disclosed herein. The theory accurately predicts the experimental results of conductivity for mixes of alkali (Na/K) ~/~" aluminas.
A method of making such polycrystalline solid is also disclosed and consists generally of the steps:
(a) selecting compounds of a least two alkalies, and an aluminum compound soluble in water;
(b) dissolving the same in water;
(c) mixing the components at the atomic level;
(d) removing the water therefrom so as to derive white polycrystalline powder, wherein the aforesaid compounds are now mixed at the atomic level and wherein f(~) is predetermined;
(e) compressing the powder into a predetermined shape;
(f3 sintering the compressed powder so as to relieve . the polycrystals of their high surface energy, but for a short interval of time so as to not alter significantly the aforesaid predetermined value f(~);
The water removal step (d) includes the step of calcina-20 tion.
Specifically the method comprises the steps of:
(a) selecting soluble sodium and potassium compounds, and an aluminum compound;
(b) dissolving said compounds in water to mix the same at the atomic level;
(c) removing the water therefrom so as to derive a plu-rality of crystallites forming a white crystalline pow-der wherein the sodium, potassium and aluminum compounds are mixed in the crystallites at the atomic level;
(d) calcining the powder to obtain a predetermine value of f(~);
(e) compressing the powder into a predetermined shape;
and, (f) sintering the compressed powder, into a solid cer-amic, so as to relieve the polycrystallites of th~ir high surface energy, but for a short interval of time so as to not alter significantly the value f(~);

,".

l~g~18 Specifically the alkalies are in the preferred weight percent ratios 60 Na2O/40 K2O.
In the preferred method, the selecting step (a~ comp-rises selecting feed alkalies in ratios of 60 wt% Na2CO3; 40 wt% K2CO3 (of the total alkali); 3.0 wt% MgO and the balance A12O3 in the form of A12(SO4)3; while the preferred sintering step (d) takes place for approximately 1 minute at a tempera-ture of 1610C.~ 2C.
Figure 1 is a prior art phase diagram for Na2O-A12O3.
Figure 2 plots the density of the resultant material of this invention as a function of Na2O content.
Figure 3 plots ~ f versus Na20 content.
Figure 4 plots density as a function of Na2O content~
Figure 5 plots surface area and particle size vs Na2O
content.
Figure 5 is a flow chart depicting two routes of obtai-ning the preferred product, by two alternative method se-quences.
Figure 7 are x-ray diffraction results of the spacing of the ~" and ~' phases, along the C-axes of the crystal illust-rating, along the dashed line, the calculated results and plots from prior art reports, while the solid line, the exper-imental results of the inventors, all as a function of f(~.
Figure 8 is a conductivity plot as a function of A f, for mixes of two alkalis with ~ ~ " alumina phases (Na/K ~ ~ "
aluminas).
Figure 9 is a plot of the experimental results according to this invention and according to the disclosed MAP Theory.
Figure 10 is a theoretical plot of figure 9, at two tem-peratures, room t~mperature and 300C.Background to the Invention It is now known that the proton conductivity of the ~"
phase is higher than the ~ phase, therefore, one desires to achieve the value of f( ~) = 0. One of the co-inventors herein has earlier noted [2] that the ~" alumina is less stable than the ~ alumina phase because of the defect nature of the crystal structure of ~"A12O3.

B

It is also known that one may create sodium ~ " alumina in a powder or solids where f(~) ~ O and these have been des-cribed in the literature.
Further, one would ultimately wish to create H30+ super-ionic conductors by replacing the sodium ion (Na+) with the hydronium ion (H30+) but the success in doing so has been limited because of the "crystal shattering" during the rep-lacement of the Na+ by the H30~. This shattering is known as structural damage.
From measurements, it is known that the dimensional size of the sodium, potassium and hydronium ions are as set forth in the following table:
K+ = 1.4 A
Na+ = 0.9 A
H30~ = 104 A
From the size of each of the aforesaid ions the crystal shattering of the prior art can be explained; when the hydro-nium ion ~H30+) replaces the sodium ion (Na+) in the polycry-stal lattice, s:ince it is almost 50% larger, the polycrystal lattice structure is stretched beyond its polycrystal fracture strength; it thus shatters.
From the foregoing, it would be preferred, therefore, to replace the Na+ partially with K+ and hence, to create a sodium-potassium ~" alumina since the potassium ion is of the exact magnitude as the hydronium ion. Two of the inventors herein have, in fact, created a K-~"A1203 compound (no sodium) where f(~) = O, or is approximately O and have disclosed the same in the aforesaid Canadian Patent Application. Such compound, however, is but a powder.
It is desired to create the aforesaid polycrystalline powder into a solid. On sintering of the aforesaid powder K-~"A1203, the f(~) increases dramatically and the high weight percent of the preferred ~ "A1203 is lost. This can now be explained with reference to figure 1, being a phase diagram for Na20-A1203. (Note: one would prefer a K20-A1203 phase diagram similar to that of figure 1, but none is available.
It is thus assumed that the phase diagram for K20-A1203 is -.,~

similar to that of Na2O A12O3). The dashed line 10 thereof is the stability range for Na~"A12O3 and it becomes destabilized at about 15~03C. Sintering above that temperature, therefore, collapses the ~" crystal structure in a short time and the same is lost.
It is known that Na~"A12O3 powder is more stable than the potassium version thereof and it was conceived, therefore, to mix both potassium and sodium versions thereof.
The Invention Materials were prepared with soda contents of 40, 50 and 50 wt~ of total alkali by three methods, all utilising spray freeze/freeze drying procedures for powder synthesis.
(a) mixing K ~ ~"Al~O3 and Na~"A12O3 powders (series 1).
(b) mixing K-Na~ Al2o3 (Rl-05M9-30A110-3317) with Na~"A1203 powder (series 2).
(c) mixed alkali powder (series 3).
Each composition was made up with 40, 50 and 60 wt%
total alkali as Na2O the balance of the alkali K2O. The re-sults of this series of experiments are summarized in figure 2. The lowest of f(~) values were obtained in series 3. The best sample from the density and f(~) standpoint had a maximum density of 95% theoretical and f(~) = 0.46.
A further decrease in f(~) was explored by inserting MgO
and varying its content. Compositions with 2 and 3 wt% MgO
and 40, 50 and 60 wt% (total alkali) as Na2O (balance K2O) were sprayed, calcined, pressed and sintered. The change of f(~) on sintering (defined as ~f) is shown in figure 3. The

3 wt~ MgO sinters are superior with respect to low /\f values, and in the case of the 60 wt% Na2O samples, 3 wt% MgO also gave the maximum densities. The possibility of further reduc-tion in f(~) was investigated by reducing the sintering tempe-ratures. /\ f versus the Na20 fraction is plotted in figure 3 for 2 and 3 wt~ MgO compositions for these lower tempera-tures. The 3 wt~ MgO compositions are again superior with the lowest /\f values while satisfactory densities are achieved at 1609C. ' 2C~, eg. 1610C. in the case of 60 wt~ Na2O samples ,~,, (figure 4). The increased Na2O probably leads to the form~
ation of liquid phases at the sintering temperature which catalyze sintering.
These results, therefore, show that a satisfactory Na/K
~ ~" alumina with respect to density and f(~) can be prepared by method 3 having the composition of the total alkali 60 wt%
as Na2O, 40 wt% as K2O (of the alkali mix); 3.0 wt~ MgO, and the balance A12O3. The optimum sintering-- temperature is 1610~C., ~ 2C. and optimum sintering time is 1 minute. The product i5 (Na0 6 Ko-4)2 (3 W/o Mgo)~ "Al2o3 sub nom 6N3.
Having determined the increased sinterability of the 6N3 composition, the surface area, lattice parameters and sintered densities of the powders and sinters were measured. The change in surface area with wt% Na2O is shown in figure 5.
Close to the K~ " A12O3 composition, the surface area dec-lines markedly (shown by the dotted line in figure 5~.
6N3 can thus be made by series 1 or series 2 procedures as aforesaid, but the preferred method is that of series 3r apd referring to figure 6, the following are the steps:
~ The feed chemicals contain Na+, K+, A13+, Mg2+ prefer-ably as Na2CO3, X2CO3, A12(SO4)3-16H2O and MgCO3 and are dissolved in water and then sprayed into liquid nitro~en which freezes the constituent materials and they form a very fine powder. In fact, what happens, a "mixing" takes place of the feed materials at the atomic level. Thus, a white powder is formed and it is placed in a freeze dryer and freeze dried for approximately 4 days. Alternatively, the dissolved feed mat-erials can be spray dried in a spray dryer and the same very very fine powder achieved (see figure 6).
The freeze drying or alternatively the spray drying has the effect of driving off the liquid water. The resultant is then calcined, for about 2 hours and a fine crystalline white powder is stabilized thereby and has the general chemical structure Na(K)-3/~"-A12O3 and the preferred chemical composi-tion (Nao.6Ko~4)2o (3 W/o MgO) ~ A12O3 sub nom 6N3 with an f(~) = 0.0 The powder then is packed into a mold which con-sists essentially of an inner metal mandrel and a flexible La;18 outer sleeve which fits over the mandrel, and defines therebe-tween a space whose shape is the shape of the desired solid form, which in our preferred embodiment is a closed end tube (of the approximate size of a test tube, but it should be noted any size appears possible). The powder is loaded into the space through an aperture defined in the sleeve and when fully loaded, a plug is seated in the aperture to close the same. The filled mold is then placed in an oil press and the hydraulic press is driven to pressures of 50,000 lbs. whereup-on the powder is compressed into a solid of the desiredshape. The solid then is removed and sintered quickly for 1 minute at 1610C. me solid precursor for the manufacture of the ceramic hydrogen ion conductor is achieved as all that needs to be done is to replace the sodium and the potassium ions therein with hydronium ions.
me reason for sintering at 1 minute is to relieve the crystals of their high surface energy and to produce a high density mechanically strong ceramic; while, the short time in-terval has the effect of not changing significantly, the value of f( ~) which has already been achieved as a result of the calcination.
It is preferred that the ratios of the feed chemicals, in order to achieve sintered product 6N3, be with a total 60 wt% Na2O; 40 wt~ K2O of the total alkali; 3.0 wt% MgO and the balance A12O3. The face analysis of this composition, 6N3, is 60% ~"-A12O3 and 40% ~-A12O3 (f(~) = 0.4). This suggests that the K+ ion resides in the ~ -alumina phase [as its fraction is equal to that of f(~)] and that the Na+ ion resides in the ~" phase. Proof of this hypothesis is shown in figure 7. In this figure, the lattice parameters of ~/~ "-A12O3 of the composition 6N3 are plotted as a function of f(~). When f(~) is less than 0.4 and K+ ions are forced into the ~"-A12O3 phase, the lattice parameter of this phase increases, whereas that of the ~-A12O3 phase remains constant. On the other hand, for 6N3 with f(~) greater than 0.4, Na+ ions are forced into the ~-A12O3 phase causing its lattice parameter to shrink, while that of the ~"-A12O3 phase remains constant.

The experimental points on this graph support this hypothesis.
m is 6N3 product, f(~) = 0.4/ has a maximum conductivity for the Na20 K20-3/~" alumina system (greater than 10-4 (ohm)~l (cm~~l at room temperature).
This conductivity has been demonstrated and may be cal-culated from what will be known as the Mixed Alkali Percola-tion Theory (MAP), a theory developed by several of the co-in-ventors, yet unreported [33, which takes into-account two exi-sting theories and combines the same in order explain the aforesaid phenomenon. It takes into account the Effective Media Percolation Theory (EMPT) in a polycrystalline system, and the Ion Distribution Theory For Mixed Alkalies sometimes called the Mixed Alkali Effect (MAE).
As a background to MAP and referring to EMPT, it is known that in practical situations, conductivity measurements are carried out on materials which contain a mixture of two phases with different conductivities~ If the two phases are intimately mixed, the measured conductivity will be a func-tion, related to the ratio of the separate conductivities of components of the mixture, and thus be an average of the two constant conductivities al and ~2 where ~1 and a2 are the con-ductivities of the first and second materials. The "average"
conductivity ~m is explained by EMPT by am = k2-klX + [(k2-klX)2 + gala2]_1 (1) where kl = 3tal _ a~)~ k2 = 25l a2 and X = the volume fraction of phase 2 and a m is the conductivity of the mix.
From equation (1), the solid curve plot in figure 8 is derived; while the experimental result taken trace out the dash curve. Thus the theoretical curve for EMPT must be shif-ted to the left which is the anisotropic effect and the two-dimensional nature of the ~-A1203 lattice effectively increa-ses the proportion of the resistive phase, for it is recog-nized that conduction is taking place in a polycrystalline material in which the conductivity in each crystallite is two-dimensional, that is, takes place along the conduction planes between the spinel blocks. It is clear that when many 119~

of these crystals are incorporated into a ceramic, the conduc-tion planes of some neighbouring cystals may be oriented per-pendicular to the other. Under these conditions, no current flows across the boundary. The theory assumes that such crys-tals form part of the non-conducting phase and an effective volume fraction of the ion conducting phase may be defined as Xeff = f(~) + b[l - f(~)]
where b is the fraction of the ~ n phase particles which are misalligned. Use of this theory reveals that ~ = 0.3, that is 30% of the particles are misalligned, a finding which is rea-sonable to those skilled in the art. However, theoretically the predicted conductivity to (~ 1 is much lower than what might be expected. This must be explained as the effect of presence of both X+ and Na+ ions.
The so-called MEA is well known in glasses, and can be observed for ~ alumina and its isomorph ~ gallate. Associated with this effect is a large decrease in the conductivity and an increase in activation energy at some intermediate composi-tion. The MEA effect kas been explained in terms of preferen-tial site occupation and ion pair formation. From site energycalculations, it has been suggested that the larger ions pre-fer Beevers-Ross sites in the ~-A1203 and ~"-A1203 lattices and displace the smaller ions to paired interstitial mid-oxy-gen sites. In any event, it is assumed that the Mixed Alkali Effect is responsible for the very low conductivity at the percolation threshold, it should be possible, therefore f to simulate the experimental data if the ion distribution between the two phases is known. Suffice it to say, it can be shown that Na-~" alumina and K-~" alumina mixes are equivalent to a mechanical mixture of K- ~alumina in a matrix of Na ~" alumina whereupon the conductivity according to MEA is readily calcu-lated. Ion exchange experiments with NaNO2/KNO3 melts ha~e shown that potassium ions prefer to reside in the ~ phase.
Considering this marked stability of K-~ alumina, one could propose, as a first approximation, that, when the mole frac-tion of potassium ions (N) in the total system (~+~") equals the proportion of ~ phase [i.e. N - f(~)], the potassium ions '~3 ~ .~

will primarily reside in the ~ phase. Thus, as the proportion of ~ phase decreases, i.e. N>f(~), more and more potassium ions are forced to reside in the ~" phase and we can write for the mole fraction of potassium ions in this phase:
X3" = N ~ fl~' (2) X~ = N

These equations can be inserted into that of equation (1) and plotted as in figure 9. See how close they come to the actual conductivity measurements on 6N3, at room temperature. The curve of figure 9 is at room temperature, while that of figure 10 illustrates the conductivity plots (according to MAP) at room temperature (curve C~T~) and at 3Q0C.( curve o 300).
The conductivity peaks are observed at both temperatures when f(~) = 0.37, the theoretical value of f(~) for 6N3, and this value which is within the error measurement of the experimen~
tal results. ~eferring to figure 10, at room temperature, notice the discontinuity of the curve where f(~ ) - 0.50 to 0.55; the absolute minimum conductivity at room temperature of around when f(~) exceeds approximately 0.5. The discontinuous properties of the conductivity at room temperature have inte-resting applications.
Returning now to a review of figures 10, 3 and 4, spec-fically as to figure 3, note that ~f is lowest when the sodium content versus potassium content as at 0.6 to 0.4. Thus, the preferred alkali mix is the ratio 0.6 sodium oxide/0.~ potas-sium oxide . From figure 4, the maximum density, which is well above 95~ of that of the ceramic solid, is achieved as well when the alkali mix is 0.6 Na20 and 0.4 K20 - the point indicated as 6N3. Also note that in these two figures, figur2 3 and 4, this value is achieved with the magnesium content at 3 wt%. Hence, the nomenclature 6N3 stands for 60 wt~ of sodium in the (sodium oxide - potassium oxide~ alkali mix and 3 wt~ magnesium oxide for stabiliziny the ~ " alumina ~, ~19~ 8 phase~ It is with this ceramic solid that f(~) = 0.37 for which the maximum conductivity is illustrated in figure lOo Referring to figure 5, note the change in the surface area which declines when the sodium oxide content of the alkali exceeds 60% wt. Vi5 a vis potassium oxide.

Footnotes:
.

[1) Also correspondingly filed as European Patent Applica-tion SN. 82103395.8 filed 22 April, 1982, Published 10 November, 1982, Bulletin 82/45, as Publication No.
Al-0,064,226; sub nom: Ceramic Hydrogen Ion Conductor and its Preparation.

[2] Nicholson et al; The Relative Stability of Spray -Frozen/Freeze-Dried ~ "-A12O3 Powder, Matts. Res. Bull., Vol~ 15, pp. 1517-1524, 1980.

[3] Bell et al; A Percolation Model for the Conductivity of Mixed Phase, Mixed Ion Aluminas to be published in Stockholm Sweden 9 July, 1983.

., ,, ~.

Claims (35)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A high density mechanically strong polycrystalline solid ceramic compound of sodium and potassium possessing .beta. alumina and .beta." alumina wherein;
where;

2. A high density mechanically strong polycrystalline solid ceramic compound of sodium, potassium and magnesium of the following chemical formula:
(Na/K)2O (MgO) .beta./.beta."-Al2O3 wherein;
where;

3. A high density mechanically strong polycrystalline solid ceramic compound of sodium, potassium and magnesium of the following chemical formula:
(Na/K)2O (3W/o MgO) .beta./.beta."-Al2O3 wherein;
where;

4. The compound as claimed in claim 1, 2 or 3, wherein;

5. The compound as claimed in claim 1, 2 or 3, wherein;
?(.beta.) = 0.37

6. The compound as claimed in claim 1, 2 or 3, wherein;

7. The compound as claimed in claim 1, 2 or 3 wherein the conductivity is greater than 10-1(ohm)-1 (cm)-1 at 300°C.

8. The compound as claimed in claim 1, 2 or 3, wherein the conductivity at room temperature is greater than 10-4(ohm)-1 (cm)-1.

9. The compound as claimed in claim 1, 2 or 3, wherein the conductivity is less than 10-5(ohm)-1 (cm)-1 at room temper-ature.

10. A high density mechanically strong polycrystalline solid ceramic of sodium, potassium and magnesium alumina having the following chemical formula:
(Na0?6K0?4)2O (3 W/o MgO) .beta./.beta."-Al2O3

11. A method of making a high density mechanically strong polycrystalline solid ceramic from alkali and aluminum com-pounds, comprising the steps of;
(a) selecting compounds of a least two alkalies and so-luable aluminum;
(b) mixing the compounds at the atomic level so as to derive a plurality of crystallites forming white poly-crystalline powder, wherein metalic oxides of the afore-said alkalies, are now mixed with alumina, at the atomic scale within each crystallite and wherein ?(.beta.) is pre-determined;
(c) compressing the powder into a predetermined shape;
(d) sintering the compressed powder so as to relieve the polycrystals of their high surface energy, but for a short interval of time so as to not alter significantly the aforesaid predetermined value of ?(.beta.);
where;

12. A method of making, as a precursor for a high density mechanically strong polycrystalline ceramic powder from com-pounds of sodium and potassium and aluminum so that the pre-cursor powder has a predetermined value of ?(.beta.) comprising the steps of;
(a) selecting soluble compounds from the group of sol-uble compounds comprising sodium, potassium and alumi-num;
(b) mixing said compounds at the atomic level; to de-rive, a plurality of crystallites forming a white crys-talline powder wherein sodium, potassium and alumina, both in its .beta. and .beta." phases are mixed, at the atomic level, within each crystallite with a predetermined value of ?(.beta.);
where;

13. A method of making a high density mechanically strong polycrystalline solid ceramic from compounds of sodium, potas-sium and aluminum so as to have a predetermined value of ?(.beta.) comprising the steps of;
(a) selecting soluble compounds from the group of sol-uble compounds comprising sodium, potassium and alumi-num;
(b) mixing said compounds at the atomic level; to de-rive, a plurality of crystallites forming a white crys-talline powder wherein sodium, potassium and alumina, both in its .beta. and .beta." phases are mixed, at the atomic level, within each crystallite with a predetermined value of ?(.beta.);
(c) compressing the powder into a predetermined shape;
and, (d) sintering the compressed powder so as to relieve the polycrystals of their high surface energy, but for a short interval of time so as to not alter significantly the value ?(.beta.) of step (b);
where;

14. The method as claimed in claim 11, 12 or 13, wherein the selecting step (a) includes as a feed compound a compound of magnesium and selecting a predetermined weight percent of a magnesium compound vis a vis the total mix.

15. The method as claimed in claim 11, 12 or 13, wherein in the selecting step (a) there is additionally selected a magne-sium compound at 3 wt% of the total mix.

16. The method as claimed in claim 11, 12 or 13, wherein in the selecting step (a) there is additionally selected an oxide of magnesium at 3 wt% of the total mix.

17. The method as claimed in claim 11, 12 or 13, wherein in the selecting step (a) there is additionally selected a prede-termined weight percent of MgO vis a vis the total mix.

18. The method as claimed in claim 11, 12 or 13, wherein in the selecting step (a) there is additionally selected a MgO of 3 wt% of the total mix, and the alkali consists of oxides of sodium and potassium.

19. The method as claimed in claim 11, 12 or 13, wherein in the selecting step (a) there is additionally selected an oxide of magnesium at 3 wt% of the total mix, and the alkali con-sists of Na2CO3 and K2CO3.

20. The method as claimed in claim 11, 12 or 13, wherein in the selecting step (a) there is additionally selected an oxide of magnesium at 3 wt% of the total mix, and the alkali con-sists of Na2CO3 and K2CO3, wherein the alkali W/o ratios are in the range of 30% to 60% Na2CO3, the balance K2CO3 of the total alkali.

21. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed components at the atomic level;
(ii) removing any water therefrom so as to derive a white crystalline powder wherein the alkali oxides and alumina of the selecting step (a) are mixed at the atomic level and each of the crystallites of the powder have a predetermined value of ?(.beta.).

22. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing water therefrom by (1) spraying the dissolved feed material into liquid nitrogen until a residual white powder is formed;
(2) freeze drying the same to remove any free water in the white powder;
(3) calcining the white powder to drive off the residual H2O therein whereby to form crys-talline powder of the general formula:

(Na/K)2O .beta./.beta." A12O3

23. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
ii) removing the water therefrom by (1) spraying the dissolved feed materials in-to a spray-dryer and drying the same of its unbonded water so that a crystalline powder is formed;
(2) calcining the powder to drive off H2O the bonded water so as to create a crystalline powder of alkali metal and alumina mixed at the atomic level in each crystallite with a predetermined value of ?(.beta.).

24. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing water therefrom by (1) spraying the dissolved feed material into liquid nitrogen until a residual white powder is formed;
(2) freeze drying the same to remove any free water in the white powder;
(3) calcining the white powder to drive off the residual H2O therein whereby to form crys-talline powder of the general formula:
(Na/K)2O .beta./.beta." Al2O3 wherein the selecting step (a) includes as a feed compound a compound of magnesium and selecting a predetermined weight percent of a magnesium compound vis a vis the total mix.

25. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing water therefrom by (1) spraying the dissolved feed material with liquid nitrogen until a residual white powder is formed;
(2) freeze drying the same to remove any free water in the white powder;
(3) calcining the white powder to drive off the residual H2O therein whereby to form crys-talline powder of the general formula:
(Na/K)2O .beta./.beta." Al2O3 wherein in the selecting step (a) there is additionally selec-ted a magnesium compound at 3 wt% of the total mix.

26. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing water therefrom by (1) spraying the dissolved feed material with liquid nitrogen until a residual white powder is formed;
(2) freeze drying the same to remove any free water in the white powder;
(3) calcining the white powder to drive off the residual H2O therein whereby to form crys-talline powder of the general formula:
(Na/K)2O .beta./.beta." Al2O3 wherein in the selecting step (a) there is additionally sel-ected an oxide of magnesium at 3 wt% of the total mix.

27. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing water therefrom by (1) spraying the dissolved feed material into liquid nitrogen until a residual white powder is formed;
(2) freeze drying the same to remove any free water in the white powder;
(3) calcining the white powder to drive off the residual H2O therein whereby to form crys-talline powder of the general formula:
(Na/K)2O .beta./.beta." Al2O3 wherein in the selecting step (a) there is additionally selec-ted a predetermined weight percent of MgO vis a vis the total mix.

28. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing water therefrom by (1) spraying the dissolved feed material into liquid nitrogen until a residual white powder is formed;
(2) freeze drying the same to remove any free water in the white powder;
(3) calcining the white powder to drive off the residual H2O therein whereby to form crys-talline powder of the general formula:
(Na/K)2O .beta./.beta." Al2O3 wherein in the selecting step (a) there is additionally selec-ted a MgO of 3 wt% of the total mix, and the alkali consists of oxides of sodium and potassium.

29. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing water therefrom by (1) spraying the dissolved feed material into liquid nitrogen until a residual white powder is formed;
(2) freeze drying the same to remove any free water in the white powder;
(3) calcining the white powder to drive off the residual H2O therein whereby to form crys-talline powder of the general formula:

(Na/K)2O .beta./.beta." Al2O3 wherein in the selecting step (a) there is additionally selec-ted an oxide of magnesium at 3 wt% of the total mix, and the alkali consists of Na2CO3 and K2CO3.

30. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing the water therefrom by (1) spraying the dissolved feed materials in-to a spray-dryer and drying the same of its unbonded water so that a crystalline powder is formed;
(2) calcining the powder to drive off H2O the bonded water so as to create a crystalline powder of alkali metal and alumina mixed at the atomic level in each crystallite with a predetermined value of ?(.beta.).
wherein the selecting step (a) includes as a feed compound a compound of magnesium and selecting a predetermined weight percent of a magnesium compound vis a vis the total mix.

31. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing the water therefrom by (1) spraying the dissolved feed materials in-to a spray-dryer and drying the same of its unbonded water so that a crystalline powder is formed;
(2) calcining the powder to drive off H2O the bonded water so as to create a crystalline powder of alkali metal and alumina mixed at the atomic level in each crystallite with a predetermined value of ?(.beta.).
wherein in the selecting step (a) there is additionally selec-ted a magnesium compound at 3 wt% of the total mix.

32. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing the water therefrom by (1) spraying the dissolved feed materials in-to a spray-dryer and drying the same of its unbonded water so that a crystalline powder is formed;
(2) calcining the powder to drive off H2O the bonded water so as to create a crystalline powder of alkali metal and alumina mixed at the atomic level in each crystallite with a predetermined value of ?(.beta.).
wherein in the selecting step (a) there is additionally selec-ted an oxide of magnesium at 3 wt% of the total mix.

33. me method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing the water therefrom by (1) spraying the dissolved feed materials in-to a spray-dryer and drying the same of its unbonded water so that a crystalline powder is formed;
(2) calcining the powder to drive off H2O the bonded water so as to create a crystalline powder of alkali metal and alumina mixed at the atomic level in each crystallite with a predetermined value of ?(.beta.).
wherein in the selecting step (a) there is additionally selec-ted a predetermined weight percent of MgO vis a vis the total mix.

34. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing the water therefrom by (1) spraying the dissolved feed materials in-to a spray-dryer and drying the same of its unbonded water so that a crystalline powder is formed;
(2) calcining the powder to drive off H20 the bonded water so as to create a crystalline powder of alkali metal and alumina mixed at the atomic level in each crystallite with a predetermined value of ?(.beta.).
wherein in the selecting step (a) there is additionally selec-ted a MgO of 3 wt% of the total mix, and the alkali consists of oxides of sodium and potassium.

35. The method as claimed in claim 11, 12 or 13, wherein the mixing step (b) includes;
(i) dissolving the selected compounds of step (a) in water so as to mix the feed materials at the atomic level;
(ii) removing the water therefrom by (1) spraying the dissolved feed materials in-to a spray-dryer and drying the same of its unbonded water so that a crystalline powder is formed;
(2) calcining the powder to drive off H2O the bonded water so as to create a crystalline powder of alkali metal and alumina mixed at the atomic level in each crystallite with a predetermined value of f(.beta.).
wherein in the selecting step (a) there is additionally selec-ted an oxide of magnesium at 3 wt% of the total mix, and the alkali consists of Na2CO3 and K2CO3.