Caustic-based metal battery with seeded recirculating electrolyte

A battery and a method for its operation are described. The battery comprises a caustic-based metal, e.g. aluminum, battery with a cathode adapted to reduce oxygen and a metal anode positioned in spaced juxtaposed relation to the cathode to define therewith an anode-cathode gap for receiving electrolyte to form an anode-cathode pair electrically coupled by electrolyte. The battery contains an alkaline electrolyte and seed particles adapted to decrease passivation of the anode during discharge of the battery. The seed particles are .alpha.-alumina of very fine particle size distribution obtained by calcination of high-purity alum.

BACKGROUND OF THE INVENTION 
The invention relates to caustic-based metal batteries and methods for 
their operation, and particularly aluminum anode batteries having 
recirculating caustic electrolyte containing a particulate seeding agent. 
Caustic-based metal batteries produce electricity by the electrochemical 
coupling of a reactive metallic anode to an air cathode through a suitable 
electrolyte in a cell. The air cathode is typically a sheet-like member, 
having opposite surfaces respectively exposed to the atmosphere and to the 
aqueous electrolyte of the cell. During cell operation oxygen is reduced 
within the cathode while metal of the anode is oxidized, providing a 
usable electric current flow through external circuitry connected between 
the anode and cathode. The air cathode must be permeable to air but 
substantially impermeable to aqueous electrolyte, and must incorporate an 
electrically conductive element to which the external circuitry can be 
connected. Present-day commercial air cathodes are commonly constituted of 
active carbon (with or without an added oxygen-reduction catalyst) in 
association with a finely divided hydrophobic polymeric material and 
incorporating a metal screen as the conductive element A variety of anode 
metals have been used or proposed; among them, zinc, alloys of aluminum 
and alloys of magnesium are considered especially advantageous for 
particular applications, owing to their low cost, light weight, and 
ability to function as anodes in metal/air battery using a variety of 
electrolytes. 
Other caustic-based metal batteries may utilize a cathode comprising a 
nickel surface impregnated with a catalyst. This cathode does not have a 
surface exposed to air or oxygen. Instead, the liquid electrolyte contains 
hydrogen peroxide in solution which is reduced by the cathode while the 
metal of the anode is oxidized, thereby providing a useable electric 
current flow. 
A typical aluminum/air cell comprises a body of aqueous electrolyte, a 
sheet-like air cathode having one surface exposed to the electrolyte and 
the other surface exposed to air or oxygen, and an aluminum alloy anode 
member (e.g. a flat plate) immersed in the electrolyte in facing spaced 
relation to the first-mentioned cathode surface. 
The aqueous electrolyte for caustic-based aluminum batteries typically 
consists of a highly alkaline solution. The highly alkaline electrolyte 
usually consists of NaOH or KOH solution. 
In alkaline electrolyte, the cell discharge reaction may be written: 
EQU 4Al+3O.sub.3 +6H.sub.2 O+4KOH.fwdarw.4Al(OH).sub.4.sup.- +K.sup.+ (liquid 
solution), 
followed, after the dissolved potassium (or sodium) aluminate exceeds 
saturation level, by: 
EQU 4Al(OH).sub.4.sup.- +4K.sup.+ .fwdarw.4Al(OH).sub.3 (solid)+4KOH 
In addition to the above oxygen-reducing reactions, there is also an 
undesirable, non-beneficial reaction of aluminum in both types of 
electrolyte to form hydrogen, as follows: 
EQU 2Al+6H.sub.2 O .fwdarw.2Al(OH).sub.3 +3H.sub.2 (gas) 
There is a need for a caustic-based aluminum battery which can be used as 
an emergency power source at locations where electric supply has been 
temporarily disrupted. Such a battery must have a high energy capacity and 
be capable of running for a long period of time under high load, e.g. 
deliver in excess of 500 watts with an energy density in excess of 365 
Wh/kg. During discharge of a battery containing aluminum anodes and 
caustic electrolyte, the concentration of dissolved aluminum in the 
electrolyte continues to build up until a limiting level of super- 
saturation is reached such that no more aluminum from the anode can enter 
into solution. At this point a film or scale of aluminum hydroxide forms 
on the anode surface causing passivation of the anode and collapse of the 
battery voltage. 
The solubility of aluminum hydroxide increases with temperature and with 
caustic concentration. In metal-air batteries, caustic concentrations are 
chosen to maximize electrical conductivity and are typically in the range 
of 4-5 molar. At this caustic level the aluminum solubility at the 
prevailing battery temperature of 55.degree.-75.degree. C., corresponds to 
a molar ratio of dissolved Al to KOH or NaOH of roughly 0.40. Aluminum may 
continue to dissolve above this ratio into the supersaturated zone and 
even attain a ratio as high as 0.80. In the supersaturation zone the 
solution is in a metastable state and has a natural tendency to reduce its 
dissolved aluminum concentration by precipitating out solid aluminum-oxide 
trihydrate or bayerite according to the following equation: 
EQU Al(OH).sub.4.sup.- .fwdarw.Al(OH).sub.3 .dwnarw.+OH.sup.- 
EQU or, 
EQU 2Al(OH.sub.4.sup.- .fwdarw.Al.sub.2 O.sub.3.3H.sub.2 O.dwnarw.+2OH.sup.- 
The metastable state possesses great stability, unless a seeding agent is 
present to induce precipitation, and the Al/XOH ratio can go as high as 
0.75-0.80, where anode passivation occurs. High current density and low 
electrolyte turbulence enhance the tendency to passivate. 
Various techniques have been tried to avoid passivation at medium to high 
current densities and one technique has been to use a very large volume of 
electrolyte. However, this greatly increases the battery size and weight, 
thus reducing its energy density and market attractiveness. Another way of 
extending discharge time prior to passivation has been to use higher 
caustic concentrations, but this has the effect of reducing electrolyte 
conductivity and hence battery voltage. Yet another way has been to add 
organic stabilizers to the electrolyte to improve the meta-stability, or 
to use NaOH/KOH mixtures to achieve the same effect, but these methods 
achieve only a relatively small extension of the battery capacity. 
Even if the anode does not passivate, there is a further problem with the 
occurence of very high supersaturation levels corresponding to Al/XOH 
ratios above 0.70 and that is the uncontrolled nucleation of a vast number 
of new particles of solid aluminum hydroxide, probably close to the anode 
surface. These have the effect of increasing the viscosity of the 
electrolyte to that of a thick soup and thereby clogging the cell and 
causing battery failure. 
There remains a need for a seeding agent to induce hydrargillite or 
bayerite precipitation which is insoluble in caustic electrolyte, while 
having a fineness of particle size allowing it to remain suspended in the 
electrolyte with little or no mechanical stirring. 
SUMMARY OF THE INVENTION 
According to the present invention, it has been discovered that a very 
effective seeding agent for caustic based metal, preferably aluminum, 
batteries with alkaline electrolyte is particles of high purity 
(preferably 99.99% pure), ceramic grade .alpha.-alumina powder of very 
fine particle size distribution obtained by calcination of high-purity 
alum. As examples of suitable .alpha.-alumina powder, there may be 
mentioned Baikalox.RTM. CR-15 and CR-10 ceramic alumina powder, 
manufactured by Baikowski International Corporation. 
In the supersaturation zone, the driving force for the precipitating out of 
solid aluminum-oxide trihydrate or bayerite increases with the square of 
the supersaturation level, and the rate of the precipitation reaction is 
directly proportional to the surface area of the seed present. Tests in 
NaOH electrolyte have shown the reaction rate to be: 
##EQU1## 
Where A=Seed surface area in square meters 
R=Moles Al/moles NaOH 
Re=Equilibrium ratio:moles Al/moles NaOH 
The above equation shows that the presence of seed in the electrolyte is 
essential to achieve a precipitation rate that is fast enough to avoid the 
high supersaturation levels that cause anode passivation. 
The seed material has very small particle sizes of less than 1 micron and 
preferably about 0.5 micron. These very small particles move freely 
through the battery with the flow of electrolyte and have been found to be 
highly effective in preventing anode passivation. 
A problem with many seed materials of small particle size is that they tend 
to dissolve in fresh electrolyte. Accordingly, they can safely be added to 
the electrolyte only after several hours of battery discharge when the 
electrolyte is approaching saturation in dissolved aluminum. However, the 
seed material of this invention is insoluble in fresh caustic electrolyte 
and can thus be present and in contact with the electrolyte from the 
initiation of the battery discharge. This greatly reduces the complexity 
and improves the reliability of the system. 
An additional advantage of the seeding agent of this invention is the 
fineness of the particle size. This allows it to remain suspended in the 
electrolyte with little or no mechanical stirring, and prevents it from 
sedimenting at the bottom of the cells where no stirring is possible. 
Also, the finer the particle size, the greater the seed surface area per 
unit weight of seed. 
Thus, one feature of the present invention is a method for operating a 
caustic-based metal battery of the type comprising a cathode adapted to 
reduce oxygen supplied thereto as oxygen or oxidant and a metal anode 
positioned in spaced juxtaposed relation to said cathode to define 
therewith an anode-cathode gap for receiving electrolyte to form an 
anode-cathode pair electrically coupled by electrolyte. According to this 
invention, the above seed particles are added to the electrolyte within 
the battery, preferably at the start of battery discharge. The seeds are 
used in sufficient quantity to prevent passivation of the anode and 
thickening of the electrolyte during discharge of the battery. 
According to one preferred embodiment, the cathode is an air or oxygen 
cathode having opposed surfaces supported for simultaneous exposure of a 
first of said surfaces to air or oxygen and a second of said surfaces to 
liquid electrolyte. Such cathode is referred to hereinafter as an air 
cathode. In another embodiment, the cathode has a nickel surface 
impregnated with catalyst and the electrolyte contains an oxidant, e.g. 
hydrogen peroxide. 
The invention is of particular interest for use in batteries characterized 
by a supply reservoir for the electrolyte enclosed in a housing below a 
plurality of metal-air or oxygen cells mounted in side-by-side 
relationship with air gaps therebetween. Each of the above cells comprises 
a pair of spaced-apart flat side walls joined by edge faces. The flat side 
walls include air cathodes and a metal anode is mounted between the flat 
side walls con- taining the air cathodes in facing spaced relationship to 
the cathode surfaces. Each cell includes an electrolyte inlet connection 
in a lower region below the bottom of the anode and an electrolyte outlet 
connection. The inlet connector is flow connected to pump means for 
pumping electrolyte from the reservoir and the outlet connector is adapted 
to return electrolyte to the reservoir. The battery is normally completed 
by circuit means for connecting the cells in series to each other and to 
an external load. With this battery, the seeds are preferably added to the 
electrolyte in the reservoir. 
The metal-air cells are typically placed on a support panel with 
electrolyte inlet and outlet connectors extending through the panel. The 
electrolyte is pumped upwardly through the inlet connectors and into the 
metal-air cells. 
The outlet connectors extend through the support panel at locations such 
that the returning electrolyte can flow directly into the electrolyte 
reservoir. 
Each metal-air cell preferably includes a vertical divider wall extending 
from the bottom edge face up to a short distance below the top edge face. 
This divider wall provides an electrolyte chamber connected to the 
electrolyte inlet and an overflow chamber connected to the electrolyte 
outlet. The top end of the divider wall forms an electrolyte overflow weir 
and is positioned at or above the top end of the metal anode. With this 
arrangement, the electrolyte flows upwardly through the metal-air cells 
and provides a strong flushing action to remove metal hydroxide reaction 
products formed in the space between the anode and cathode. Thus, metal 
hydroxide product is carried upwardly and over the weir for discharge back 
into the reservoir. This reaction product settles to the bottom of the 
reservoir and the battery can be operated for a considerable period of 
time before it is necessary to remove the collected solid reaction product 
from the bottom of the reservoir. 
The electrolyte reservoir preferably includes a divider wall which extends 
upwardly for part of the height of the reservoir to provide a further 
overflow weir. The electrolyte flowing over the internal weir of the 
reservoir is substantially free of the solid reaction product and pump 
inlets are positioned in the reservoir on the downstream side of the weir. 
The electrolyte pump may be in the form of a single pump or several small 
centrifugal pumps may be used. When a single pump is used, it is 
preferably in the form of a column pump with an impeller submersed in the 
electrolyte in the reservoir on the downstream side of the weir and a 
motor mounted above the electrolyte. When several pumps used, they are 
preferably submersible centrifugal pumps which are mounted in the 
reservoir on the downstream side of the weir. 
In order to intensify the supply of air to the gaps between the metal-air 
cells, a blower and air distributor are preferably installed adjacent the 
cells to blow air through the gaps. According to a preferred feature, this 
air is used for a secondary purpose of flushing the surface of the 
electrolyte in the reservoir. It has been found that in high load 
batteries of this type, there can be build-up of hydrogen above the 
surface of the electrolyte. To avoid this problem and dilute the hydrogen 
concentration in the reservoir, openings are preferably provided in the 
support panel between the metal-air cells at the side of the cells remote 
from the blower. In this manner, the air passing in one direction through 
the gaps between the cells is forced down through the openings in the 
support panel and across the surface of the electrolyte in the reverse 
direction, thereby diluting the hydrogen. This air can then be discharged 
through a demister and a condenser to the atmosphere. 
Also, to control the temperature of the electrolyte, a heat exchanger may 
be provided through which electrolyte is recirculated from the reservoir. 
When high electrical outputs are required from the battery, the condenser 
can be replaced by a second heat exchanger and the air can be discharged 
directly to the atmosphere.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, a housing 10 with side walls 13 is provided 
comprising a suitable material resistant to caustic solutions at 
temperatures up to 95.degree. C., such as polypropylene or 316 stainless 
steel, and serving as an electrolyte reservoir. Extending across an upper 
region of the interior of housing 10 is a support panel or platform 11. At 
one side of the housing, there are gaps 36 in the support panel, providing 
air openings into the electrolyte reservoir. 
Extending upwardly from and supported by the support panel 11 are a 
plurality of metal-air cells 12 with air gaps therebetween. These cells 12 
have a long, flat rectangular shape with side walls 21 having window 
openings retaining air cathodes 22. 
The air cathodes 22 are generally rectangular sheet members fabricated of 
activated carbon and incorporating an electrically conductive material 
such a wire mesh. Each cathode 22 extends entirely over an opening in wall 
21 with its edges sealingly adhered to the interior surface of the wall 
around the periphery of the opening. The cathodes in the two side walls 
are preferably electrically connected such that they effectively form a 
single cathode surrounding the anode spaced between them. The cathodes are 
susceptible to hydrostatic deformation which affects the gap between the 
anode and cathode. To avoid this problem, a supporting grid 71 is provided 
across the opening in wall 21 and small projections 72 are provided on the 
outer edges of the grid 71. These projections 72 are arranged so that the 
projections of adjacent pairs of cells engage each other, thereby 
providing a rigid structure while permitting free flow of air between the 
cells. 
The side walls 21 are joined by a removable top lid 23, a pair of end walls 
24 and a bottom wall 25, the lid 23 tightly sealing within walls 21 and 
24. The anode 26 has a vertically extending tab 75 projecting upwardly 
through a slot in lid 23, and similarly the cathode has a connector lead 
76 extending from the side of the cell where the two cathodes are joined. 
The tab 75 and lead 76 are connected to suitable circuit means (not shown) 
for connecting the cells in series to each other and to an external load. 
A divider wall 30 is formed between side walls 21 near one end wall 24 to 
form a narrow discharge conduit 32 adjacent the side edge. This divider 
wall 30 terminates at an upper edge 31 a short distance below the cell top 
edge 23, the edge 31 forming an overflow weir. Vertical slots are provided 
in divider wall 30 and side wall 24 to retain an aluminum anode 26. This 
anode terminates slightly below the top edge 31 of divider wall 30. An 
inlet tube 27 connects to bottom edge 25 beneath the anode 26 and an 
outlet tube 33 connects to bottom edge 25 directly below the discharge 
conduit 32. These pass through holes 29 and 29a respectively in support 
panel 11. Preferably the tube 27 is provided with annular grooves 
containing O-rings which snugly seal the tube 27 within hole 29. The 
discharge tube 33 is formed slightly smaller than hole 29a to facilitate 
inserting and withdrawing the metal-air cell 12. To prevent leakage of air 
through holes 29a, a thin foam or rubber pad with small holes may be 
placed on the panel 11 over the holes 29a. The discharge tubes pass 
through the small holes in the pad and then through the larger holes 29a. 
Immediately below the inlet tubes 27 is mounted a manifold or manifolds 15 
extending across beneath support panel 11. Preferably there is a divider 
wall 50 providing two manifolds, one for each aligned row of metal-air 
cells. As shown in FIG. 4, four inlet tubes 16 feed into the manifold 15, 
two of these tubes feeding into one half of the manifold and two into the 
other half. The inlet end of the four tubes 16 connect to a second 
manifold 17 which in turn connects to three submersible centrifugal pumps 
19 by way of outlet lines 18. Two of the three outlet lines 18 are 
provided with reverse flow check valves 49. The pumps 19 have inlets 20 
which are preferably positioned well above the bottom of the electrolyte 
reservoir. All tubing, connectors and manifold are preferably made of a 
non-conducting material in order to reduce possible shunt currents. 
The electrolyte reservoir preferably has a divider wall 14 with an upper 
edge 14a forming an overflow weir. As can be seen from FIG. 1, the 
electrolyte will, after some discharge time has elapsed, have a higher 
level to the right of the weir and a lower level to the left of the weir. 
Partially clarified electrolyte overflows from the right side to the left 
side of the weir. 
Inlets 20 for pumps 19 are positioned in the downstream side of the 
reservoir for pumping partially clarified electrolyte up through manifolds 
17 and 15 and through the metal-air cells 12. The electrolyte travels from 
the manifold 15 in an upward direction through the gaps between the anode 
and cathodes simultaneously flushing any reaction product formed in the 
gaps. The electrolyte with reaction product is carried over the weir 31 
and down discharge conduit 32 and outlet 33 back into the upstream side of 
the electrolyte reservoir. The reaction product S settles to the bottom of 
the upstream side with the partially clarified electrolyte flowing over 
the weir for recycle through the metal-air cells. 
An air distributor wall 35 is provided adjacent the metal-air cells 12 with 
openings 66 opposite the gaps between the cells for discharge of air 
through the gaps. A blower 34 feeds air to the distributor wall 35, this 
blower being powered by electricity generated by the battery. In 
operation, the compartment containing the metal-air cells is sealed within 
a cover 55 as shown in FIG. 2 except for the air inlets 66 and the gaps 36 
in the support panel 11. This compartment cover includes the air 
distributor wall 35, a pair of side walls 56, an end wall 57 opposite wall 
35 and a removable lid 58. The walls 35, 56 and 57 are tightly sealed 
together and the bottom edges of the four walls are tightly sealed to the 
top of the housing 10, while the lid 58 is tightly connected to the top 
edges of the four walls. Alternatively, the lid 58 may be sealed to the 
walls and the entire compartment cover may be removable. Thus, when the 
blower 34 is in operation, air is blown across through the gaps between 
the metal-air cells 12 and down through the support panel openings 36 into 
the reservoir. The air then travels in the reverse direction across the 
surface of the electrolyte in the reservoir, picking up hydrogen, then 
through demister curtain 70 and fiber demisting pads 40 and is discharged 
to the atmosphere upwardly through a plurality of metal tubes 38 of 
condenser 37. Heat exchange in the condenser is enhanced by means of a 
plurality of mechanically bonded metal fins 39 through which air is blown 
from fans 41. Alternatively, the condenser may be water cooled. 
The electrolyte may be cooled by means of a heat exchanger 42, the heat 
exchange taking place between metal tubes 43 and metal fins 44 by way of 
air fans 48. The electrolyte is pumped by way of pump 45 upwardly through 
tube 46, through the heat exchanger and is discharged back into the 
reservoir via discharge line 47. The operation of the heat exchanger fans 
is controlled by a thermal switch set to a predetermined temperature. 
The condenser and heat exchanger may be protected by a cover 60 as shown in 
FIG. 3 and consisting of two sides 61, one end wall 63 and a top wall 64. 
Side walls 61 contain openings 62 to permit free flow of air around the 
condenser, heat exchanger and circulating air blower. The top wall 64 has 
an outlet 65 serving as an exhaust from condenser tubes 38. This outlet 65 
may be connected to an exhaust vent. 
A small auxilliary battery is used to start the battery of the invention, 
this auxilliary battery being connected to the pumps 19. Thus, when the 
pumps 19 are activated, they commence pumping electrolyte upwardly through 
manifolds 17 and 15. Since gas may accumulate in the manifolds, it is 
desirable to provide a means for venting gas before it passes upwardly 
through the metal-air cells by providing small holes in the upper regions 
of the side walls of manifold 15. After the gas is fully eliminated from 
the manifold, there continues to be a slight flow of electrolyte through 
the holes. As soon as the electrolyte makes contact between the anode and 
cathode, electricity generation commences and the auxilliary battery is no 
longer required. The pumps 19 and 45, the blower 34 and the fans 41 and 48 
are all driven by excess power from the battery of the invention. It is 
also possible to provide a manual pumping device to start the battery, 
thereby avoiding the need for the auxilliary battery. 
The three pumps 19 provide a sufficiently excess flow capacity that two of 
the three pumps can fail and sufficient electrolyte will still be pumped 
to fill the metal-air cells with electrolyte and keep the battery 
operational. In order to prevent a flow short circuit through a failed 
pump, reverse flow check valves 49 are provided on all except one pump. 
When it is desired to stop the battery for any reason, such as replacing 
the metal-air cells, it is simply a matter of stopping the pumps whereby 
the electrolyte drains out of the metal-air cells and the cells can be 
replaced. Thus, the battery can be placed back into immediate operation 
and individual cells can be opened and the anodes replaced at a convenient 
time. 
In order to flush the system, a one-way discharge valve outlet may be 
provided in a side wall 13 of housing 10 at a level above the highest 
permissible accumulation of reaction product solids 5 and below the level 
of weir 14a. Thus, with the one-way valve in the open position, water can 
be fed into the pump side of the electrolyte reservoir and then circulated 
through the pumps and cells into the upstream side of the electrolyte 
reservoir. Simultaneously, liquid flows from the reservoir out through the 
one-way valve. In this manner, all caustic except for that held within the 
solids deposit S may be flushed out of the battery. 
A battery of the design shown in FIGS. 1-6 was produced with 20 
aluminum-air cells. Each aluminum anode had a thickness of 13 mm, a height 
of 18.2 cm and a width of 11.1 cm. The cathodes used were type AE-20 
gas-diffusion cathodes made by Electromedia Inc. The cells each had a 
thickness of 1.7 cm, a height of 23.0 cm and a width of 13.0 cm. 
The electrolyte was 5M KOH with 0.005M sodium stannate and it was pumped 
through the aluminum-air cells at a flow rate of 15 l/min. Air was 
circulated between the cells and through the reservoir at a rate of about 
28 l/min. This battery provided over 500 watts continuously for more than 
60 hours with an output current of approximately 19 amps. The battery also 
had a net energy output of over 300 watt-hours per kg of battery weight. 
In order to determine how the Al/KOH ratio behaves as a function of 
discharge time, a computer simulation was carried out based on the 
equation shown on page 4 at 72.5 watts per cell and seed additions of 3.30 
and 60 grams. The results are shown in FIG. 7 and it can be seen that the 
higher the seed charge and the earlier it is added, the lower the maximum 
Al/KOH ratio attained. Because the electrical conductivity of the solution 
diminishes as the Al/KOH ratio increases, the effect of the seed additions 
is reflected in the cell voltage as represented by the family of full line 
curves in FIG. 7. 
It has been determined that if sufficient seed is added to keep the Al/XOH 
ratio below 0.60, current densities as high as 180 mA/cm.sup.2 are 
possible without anode passivation and that to maintain a current density 
of 60 mA/cm.sup.2, sufficient seed to maintain the ratio below 0.70 is all 
that is required. Also, with sufficient seed present to avoid an 
excessively high supersaturation level, crystal growth and secondary 
nucleation are the precipitation mechanisms, solution viscosity is kept 
low and the solid material can settle out in the sedimentation zone off 
the battery, thereby avoiding cell clogging and resultant battery failure. 
As can be seen from the dashed lines in FIG. 7, once the peak value of the 
Al/XOH ratio has been passed, the ratio becomes constant, striking a 
balance between the rate of aluminum dissolution and precipitation and 
seed sedimentation rate. In this way no further passivation is threatened 
and the lifetime or discharge time of the battery is extended by a factor 
of 4 to 5 times that which can be obtained in the absence of added seed. 
Certain preferred embodiments of the invention are shown in the following 
non-limiting examples. 
The properties and specification of the various Baikalox aluminas produced 
by a deagglomeration process are given in the following table: 
______________________________________ 
Baikalox Baikalox Baikalox 
Baikalox 
Powder Name CR30 CR15 CR10 CR1 
______________________________________ 
Purity, % Al.sub.2 O.sub.3 
99.99 99.99 99.99 99.99 
Major Phase alpha alpha alpha alpha 
% Major Phase 
65% 85% 90% 97% 
Crystal Density, 
3.98 3.98 3.98 3.98 
gm/cm.sup.3 
Bulk Density, 
0.32 0.46 0.51 0.70 
gm/cm.sup.3 
Pressed Density, 
1.04 1.32 1.45 1.62 
2000 PSI gm/cc 
Ultimate particle 
0.05 0.1 0.15 &lt;1.5 
size, microns 
Mean Agglomerate 
&lt;0.5 &lt;0.5 &lt;0.6 &lt;1.5 
size, microns 
Specific surface area, 
30 .+-. 1 
15 .+-. 1 
10 .+-. 1 
1 
B.E.T., m.sup.2 /gm 
Loss of ignition, % 
1.0 .65 .25 -- 
Agglomerate size 
Cumulative Weight Percent 
distribution by sedigraph 
&lt;0.3 .mu.m 34 31 13 -- 
&lt;0.4 .mu.m 44 45 24 -- 
&lt;0.5 .mu.m 53 56 38 -- 
&lt;0.6 .mu.m 59 68 52 9 
&lt; 1.0 .mu.m 78 88 82 45 
&lt;2.0 .mu.m 93 99 95 88 
&lt;5.0 .mu.m 97 100 98 97 
&lt;10.0 .mu.m 100 -- 100 100 
______________________________________ 
EXAMPLE 1 
A supersaturated solution of caustic potassium aluminate was prepared using 
4.1M KOH and 3.0M Al. Three separate containers holding this solution were 
placed in a constant temperature bath at 50.degree. C. To one solution was 
added 20 g/l of regular hydrargillite seed, to a second solution was added 
20 g/l of Baikalox CR-15 and no seed was added to the third solution. The 
solution conductivities were monitored with in-situ sensors, with an 
increase in electrical conductivity being symptomatic of hydragillite 
precipitation according to the reaction: 
EQU Al(OH).sub.4.sup.- .fwdarw.Al(OH).sub.3 .dwnarw.+OH.sup.- 
The results in FIG. 8 show that Baikalox CR-15 is an effective seed. 
EXAMPLE 2 
The procedure of Example 1 was repeated using a solution prepared from 4.5M 
KOH and 3.3M Al. Four different .alpha.-alumina seeds were tested, 
including 40 g/l of Baikalox CR-15, 40 g/l of laboratory-calcined alumina, 
80 g/l of Alcoa A-16 and Baco RA-107LS. The results in FIG. 9 show the 
ineffectiveness of the .alpha.-alumina other than Baikalcx CR-15. 
EXAMPLE 3 
The procedure of Example 1 was again followed using a solution prepared 
from 4.5M KOH and 3.27M Al. Three different Baikalox alumina seeds were 
tested, including 20 g/l Baikalox CR-15, 20 g/l Baikalox CR-30 and 40 g/l 
Baikalox CR-1. The results in FIG. 10 show the superiority of Baikalox 
CR-15. 
EXAMPLE 4 
The procedure of Example 1 was following using a solution prepared from 
5.0M KOH and 3.6M Al. Tests were conducted using 40 g/l Baikalox CR-15 and 
40 g/l Baikalox CR-10. The results in FIG. 11 show these to be equally 
effective. 
EXAMPLE 5 
The procedure of Example 1 was followed using a solution prepared from 4.5M 
KOH and 3.3M Al. The tests were conducted using 10 g/l hydrargillite seed 
and different concentrations of Baikalox CR-15. The results in FIG. 12 
show the relative effectiveness of different dosages of Baikalox CR-15 
compared with the hydrargillite.