U.S. patent application number 10/322565 was filed with the patent office on 2004-06-17 for densification of aerated powders using positive pressure.
Invention is credited to Bates, James William, Brownbridge, Thomas Ian.
Application Number | 20040112456 10/322565 |
Document ID | / |
Family ID | 32507292 |
Filed Date | 2004-06-17 |
United States Patent
Application |
20040112456 |
Kind Code |
A1 |
Bates, James William ; et
al. |
June 17, 2004 |
Densification of aerated powders using positive pressure
Abstract
A process for increasing the bulk density of an aerated powder
is provided. The powder is placed in a container. The container is
then closed and the gas pressure within the container is increased
to a level above atmospheric pressure and at a rate sufficient to
cause the powder to compact before a substantial portion of said
pressurization gas diffuses into said powder. In one embodiment,
the process is utilized to increase the bulk density of an aerated,
free-flowing titanium dioxide pigment. Apparatus for carrying out
the process is also provided.
Inventors: |
Bates, James William;
(Armory, MS) ; Brownbridge, Thomas Ian; (Oklahoma
City, OK) |
Correspondence
Address: |
MCAFEE & TAFT
TENTH FLOOR, TWO LEADERSHIP SQUARE
211 NORTH ROBINSON
OKLAHOMA CITY
OK
73102
US
|
Family ID: |
32507292 |
Appl. No.: |
10/322565 |
Filed: |
December 16, 2002 |
Current U.S.
Class: |
141/12 |
Current CPC
Class: |
C09C 1/3646 20130101;
C09C 3/046 20130101; H01M 10/052 20130101; C01B 13/145 20130101;
H01M 4/5825 20130101; H01M 6/16 20130101; H01M 4/485 20130101; B65B
1/26 20130101; C01P 2004/64 20130101; B82Y 30/00 20130101; Y02E
60/10 20130101; C01P 2006/20 20130101; C01P 2006/10 20130101 |
Class at
Publication: |
141/012 |
International
Class: |
B65B 001/20 |
Claims
What is claimed is:
1. A process for increasing the bulk density of an aerated powder,
comprising: placing said powder in a container; and increasing the
gas pressure in the area of said container containing said powder
to a level above atmospheric pressure at a rate sufficient to cause
said powder to compact before a substantial portion of said
pressurization gas diffuses into said powder.
2. The process of claim 1 further comprising the steps of
depressurizing said container and removing said compacted powder
from said container.
3. The process of claim 1 wherein said gas pressure in the area of
said container containing said powder is increased to a level above
atmospheric pressure by injecting a gas into said container.
4. The process of claim 3 wherein said gas injected into said
container is selected from the group consisting of an inert gas,
air, nitrogen, oxygen, carbon dioxide and chlorine.
5. The process of claim 4 wherein said gas injected into said
container is air.
6. The process of claim 1 wherein said powder is an inorganic metal
oxide.
7. The process of claim 6 wherein said powder is a titanium dioxide
pigment.
8. The process of claim 7 wherein the bulk density of said titanium
dioxide pigment is increased to a level greater than about 35
lbs/ft.sup.3.
9. The process of claim 8 wherein the bulk density of said titanium
dioxide pigment is increased to a level in the range of from about
40 lbs/ft.sup.3 to about 50 lbs/ft.sup.3.
10. The process of claim 7 wherein said gas pressure in the area of
said container containing said powder is increased to a level above
atmospheric pressure by injecting chlorine gas into said
container.
11. The process of claim 6 wherein said powder comprises a
battery-active material.
12. The process of claim 11 wherein said battery-active material is
selected from the group of metal oxides and metal phosphates
wherein said metal is vanadium, manganese, nickel, cobalt, iron or
a combination thereof.
13. The process of claim 11 wherein said battery-active material is
selected from the group of lithium metal oxides and lithium metal
phosphates wherein said metal is vanadium, manganese, nickel,
cobalt, iron or a combination thereof.
14. The process of claim 13 wherein said battery-active material is
a lithium vanadium oxide.
15. The process of claim 13 wherein the bulk density of said
battery material is increased by at least about 10 percent.
16. The process of claim 15 wherein the bulk density of said
battery material is increased by at least about 15 percent.
17. A process for placing a predetermined volume of a powder into a
receptacle, comprising: placing said powder in a container;
increasing the gas pressure in the area of said container
containing said powder to a level above atmospheric pressure at a
rate sufficient to increase the bulk density of said powder to a
predetermined level; and removing a predetermined amount of said
powder from said container and placing it in said receptacle.
18. The process of claim 17 wherein said gas pressure in the area
of said container containing said powder is increased to a level
above atmospheric pressure by injecting a gas into said
container.
19. The process of claim 18 wherein said gas injected into said
container is selected from the group consisting of an inert gas,
air, nitrogen, oxygen, carbon dioxide and chlorine gas.
20. The process of claim 17 wherein said powder is an inorganic
metal oxide.
21. The process of claim 20 wherein said powder is a titanium
dioxide pigment.
22. The process of claim 20 wherein said powder comprises a
battery-active material.
23. The process of claim 22 wherein said battery-active material is
selected from the group of metal oxides and metal phosphates
wherein said metal is vanadium, manganese, nickel, cobalt, iron or
a combination thereof.
24. The process of claim 22 wherein said battery-active material is
selected from the group of lithium metal oxides and lithium metal
phosphates wherein said metal is vanadium, manganese, nickel,
cobalt, iron or a combination thereof.
25. The process of claim 24 wherein said battery-active material is
a lithium vanadium oxide.
26. A process for increasing the bulk density of an aerated powder,
comprising: placing said powder in a container; and injecting a gas
into said container at a rate sufficient to increase the gas
pressure in the area of said container containing said powder to a
level above atmospheric pressure and cause said powder to compact
before a substantial portion of said pressurization gas diffuses
into said powder.
27. The process of claim 26 wherein said gas injected into said
container is selected from the group consisting of an inert gas,
air, nitrogen, oxygen, carbon dioxide and chlorine gas.
28. The process of claim 26 further comprising the steps of
depressurizing said container and removing said compacted powder
from said container.
29. The process of claim 26 wherein said powder is an inorganic
metal oxide.
30. The process of claim 26 wherein said powder is a titanium
dioxide pigment.
31. The process of claim 26 wherein said powder comprises a
battery-active material.
32. The process of claim 31 wherein said battery-active material is
selected from the group of metal oxides and metal phosphates
wherein said metal is vanadium, manganese, nickel, cobalt, iron or
a combination thereof.
33. The process of claim 31 wherein said battery-active material is
selected from the group of lithium metal oxides and lithium metal
phosphates wherein said metal is vanadium, manganese, nickel,
cobalt, iron or a combination thereof.
34. The process of claim 33 wherein said battery-active material is
a lithium vanadium oxide.
35. A process for increasing the bulk density of an aerated powder,
comprising: placing said powder in a container, said container
having a first end and a second end opposing said first end;
increasing the gas pressure in the area of said container
containing said powder to a level above atmospheric pressure at a
rate sufficient to cause said powder to compact against said second
end of said container before a substantial portion of said
pressurization gas diffuses into said powder; opening said second
end of said container whereby said container is depressurized and
said powder is expelled from said container through said second end
of said container.
36. The process of claim 35 wherein said gas pressure in the area
of said container containing said powder is increased to a level
above atmospheric pressure by injecting a gas into said
container.
37. A process for preparing a slurry, comprising: processing a
powder; prior to allowing said powder to fully settle, increasing
the bulk density of said powder by deaerating said powder; and
dispersing said densified powder into a liquid medium.
38. The process of claim 37 wherein said powder is deaerated by:
placing said powder in a container; and increasing the gas pressure
in the area of said container containing said powder to a level
above atmospheric pressure at a rate sufficient to cause said
powder to compact before a substantial portion of said
pressurization gas diffuses into said powder; and removing said
compacted powder from said container.
39. The process of claim 38 wherein said powder is titanium dioxide
pigment, and said liquid medium is water.
40. A process for preparing a concentrated titanium dioxide pigment
slurry, comprising: milling a titanium dioxide pigment; prior to
allowing said titanium dioxide pigment to fully settle, increasing
the bulk density of said pigment by: placing said powder in a
container; and increasing the gas pressure in the area of said
container containing said powder to a level above atmospheric
pressure at a rate sufficient to cause said powder to compact
before a substantial portion of said pressurization gas diffuses
into said powder; and removing said compacted powder from said
container; and dispersing said deaerated pigment in a liquid
medium.
41. The process of claim 40 wherein said milling step is carried
out in a fluid energy mill.
42. An apparatus for increasing the bulk density of a powder,
comprising: a container for containing said powder under pressure,
said container having a first end and a second end opposing said
first end; and pressurization means associated with said container
for increasing the gas pressure in the area of said container
containing said powder to a level above atmospheric pressure at a
rate sufficient to cause said powder to compact before a
substantial portion of said pressurization gas diffuses into said
powder.
43. The apparatus of claim 42 wherein said pressurization means
comprise: means for injecting a gas into said container; and a
source of gas.
44. The apparatus of claim 42 wherein: said first end of said
container includes an inlet for allowing said powder to be added to
said container; said second end of said container includes an
outlet for allowing said powder to be removed from said container;
and said container further comprises a first valve for opening and
closing said inlet and a second valve for opening and closing said
outlet.
45. The apparatus of claim 44 wherein said pressurization means
causes said powder to compact against said outlet when said outlet
is closed and eject from said container when said outlet is
opened.
46. An apparatus for increasing the bulk density of a powder,
comprising: a cylinder, said cylinder having a first end and a
second end opposing said first end, said first end containing an
inlet and said second end containing an outlet; a rotary
containment device positioned within said cylinder, said rotary
containment device including: a hub; a pair of opposed blades
attached to said hub and creating two powder containment areas
within said cylinder, said rotary containment device being capable
of turning within said cylinder such that each of said powder
containment areas rotate to a first position within said cylinder
adjacent said inlet whereby powder can be added to said area, a
second position within said cylinder adjacent said wall of said
cylinder whereby powder in said area can be compacted, and a third
position within said cylinder adjacent said outlet whereby powder
in said area can be ejected from said area; and rotating means for
turning said rotary containment device within said cylinder; and
pressurization means associated with said cylinder for increasing
the gas pressure within said each of said powder containment areas
of said rotary contaimnent device to a level above atmospheric
pressure when said area is in said second position at a rate
sufficient to cause the powder within said area to compact before a
substantial portion of the pressurization gas diffuses into the
powder.
47. The apparatus of claim 46 wherein said pressurization means
comprises: means for injecting a gas into said powder containment
areas; and a source of compressed gas.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to methods and apparatus for
increasing the bulk density of aerated powders. By way of example
only, the invention can be utilized to increase the bulk density of
highly aerated, free-flowing inorganic metal oxide powders with
considerable commercial significance, for example, titanium dioxide
pigments, complex metal oxides of the type presently being employed
in primary and secondary rechargeable batteries (typically
comprising lithium metal oxides) and blends of such complex metal
oxides with various other components of a cathode composition of a
battery.
[0002] Handling and containing fine, highly aerated powders can be
problematic in many respects. For example, filling a bag or other
container to capacity with a highly treated titanium dioxide
pigment (for example, one designed for use in water-based latex
paints) can be difficult to accomplish in an efficient manner
without first deaerating the pigment. Due to the relatively low
bulk density of the pigment, the container can generally be filled
to only 80 to 90% of its capacity. On standing, air entrapped in
the pigment will slowly rise through the tortuous pathways defined
between gravitationally settling pigment particles, in the process
increasing the bulk density of the pigment and allowing additional
pigment to be added to the container. However, in a continuous
manufacturing and packaging process, the additional time and
handling required to fill the container to capacity makes the
process inefficient. Further, it can be difficult to impart a
consistent, predetermined amount of pigment to each bag in a
continuous bagging process. Similarly, filling a battery
compartment or shell to capacity or with an exact amount of
battery-active material (e.g., cathode material) can be difficult
to achieve due to air entrapped in the material.
[0003] Various processes have been utilized to deaerate and compact
a free-flowing powder. For example, the powder container has been
placed on top of a device that allows the container to be shaken
and/or vibrated as the container is filled. A similar technique
involves placing a vibrating rod into the container in order to
cause entrapped air to dissipate. Additional methods utilized in
the past include a compression device for compressing the container
and powder therein in order to squeeze out air entrained in the
powder, and placing a porous pipe connected to a vacuum system into
the container during the filling process to evacuate the entrained
air. All of these processes have serious drawbacks. For example,
although removing entrained air with a porous pipe works for a
short time, the pores in the pipe ultimately become blocked due to
the fine particle size of many powders.
[0004] One technique that has been used commercially over the years
is vacuum densification. In a vacuum densification process, the
powder to be deaerated is placed in a container that is connected
to a vacuum source. A vacuum is then pulled to whatever level is
desired. Upon attaining the desired vacuum level, the valve
controlling the vacuum source is closed and a second valve into the
container is opened allowing the pressure within the container to
rapidly equilibrate back to atmospheric pressure. This process
causes the powder to compact.
[0005] Unfortunately, like the other powder deaeration processes
utilized heretofore, vacuum densification has its drawbacks. For
example, vacuum systems require an elaborate filter system and are
generally somewhat expensive to put in place. Many powder
manufacturing plants do not otherwise have vacuum systems in place.
Also, vacuum systems are limited to atmospheric pressure
(approximately 15 psig (1 kg/sq. cm, gauge)).
BRIEF SUMMARY OF THE INVENTION
[0006] In a vacuum densification process, the powder densifies to a
small extent as the pressure within the vacuum chamber decreases.
However, it is the rapid in-flow of air into the evacuated
container achieved by releasing the vacuum that ultimately causes
the deaerated material to compact to a significant degree. If the
vacuum is released at a sufficient rate, the in-rush of air on top
of the pigment is too fast to allow the air to diffuse back between
the particles, thereby forcing the pigment into a smaller
volume.
[0007] It has now been discovered that rapid pressurization of the
gas (e.g., air) in a closed vessel also causes a highly aerated
powder within the vessel to become densified. Accordingly, the
invention provides a process for increasing the bulk density of an
aerated powder based on positive pressure. As discussed below, the
use of a positive pressure system to achieve the desired powder
densification has many advantages.
[0008] In one aspect, the invention provides a process for
increasing the bulk density of an aerated powder. In accordance
with the process, the powder is placed in a container. The gas
pressure in the area of the container containing the powder is then
increased to a level above atmospheric pressure at a rate
sufficient to cause the powder to compact before a substantial
portion of the pressurization gas diffuses into the powder. As
explained below, the level above atmospheric pressure to which the
gas pressure must be increased and the rate of increase required in
order to achieve a significant degree of powder compaction will
vary depending upon the type of powder, the size of the container
and other parameters.
[0009] For example, in one application, the inventive process can
be used to place a predetermined volume of powder into a bag or
other receptacle. The powder is placed in a container. The gas
pressure is then increased in the area of the container containing
the powder to a level above atmospheric pressure at a rate
sufficient to increase the bulk density of the powder to a
predetermined level. A predetermined amount of the compacted powder
is then removed from the container and placed in the receptacle.
This allows, for example, a consistent, predetermined amount of
powder to be placed in each bag in a continuous bagging
process.
[0010] In one embodiment, the gas pressure in the area of the
container containing the powder is increased to a level above
atmospheric pressure by injecting a gas into the container. The gas
is injected into the container at a rate sufficient to cause the
powder to compact before a substantial portion of the gas diffuses
into the powder. A variety of gases, including air, can be used,
provided that the gas selected does not adversely react with the
powder or otherwise negatively affect either the process or the
apparatus used to carry out the process. Preferably, the injection
gas is an inert gas, air, nitrogen, oxygen, carbon dioxide or
chlorine gas.
[0011] Examples of fine, highly aerated powders that can be
densified in accordance with the inventive process include
inorganic metal oxide powders such as inorganic pigments (e.g.,
titanium dioxide pigments) and battery-active materials. Such
battery-active materials include the inorganic metal oxide and
metal phosphate powders used in primary and secondary rechargeable
batteries, for example, lithium metal oxides and lithium metal
phosphates including those wherein the metal is vanadium,
manganese, nickel, cobalt, iron or combinations of such metals.
These battery-active materials may or may not have lithium present
in their crystalline structure. The invention is particularly
suitable for densifying lithium vanadium oxides. Also, blends of
battery-active materials with other components for use in a cathode
composition may also be densified in accordance with the inventive
process, as exemplified below.
[0012] In another embodiment, the inventive process for increasing
the bulk density of an aerated powder comprises placing the powder
in a container, the container having a first end and a second end
opposing the first end. The gas pressure in the area of the
container containing the powder is then increased to a level above
atmospheric pressure at a rate sufficient to cause the powder to
compact against the second end of the container before a
substantial portion of the pressurization gas diffuses into the
powder. Next, the second end of the container is opened thereby
causing the container to depressurize and the powder to be expelled
from the container through the second end of the container.
[0013] The invention also includes a process for preparing a
slurry. In accordance with the process, the powder is first milled
or otherwise processed. The milling or other processing procedure
typically causes the powder to become aerated. Prior to allowing
the powder to fully settle, the bulk density of the powder is
increased by deaerating the powder. After the bulk density of the
powder is increased, the powder is dispersed in a liquid medium.
The deaeration step allows the powder to be quickly dispersed in
the liquid medium (i.e., the powder can be quickly dispersed into
the liquid medium even though it has not been allowed to fully
settle). Unless the powder is deaerated (either naturally over time
or in accordance with the invention), dispersing large amounts of
the powder into a liquid medium in a timely manner can be difficult
to achieve. The powder is preferably deaerated in accordance with
the inventive positive pressure deaeration system described
above.
[0014] For example, the above process can be used to disperse
freshly fluid energy milled titanium dioxide pigment into a
suitable liquid, such as water, to form a concentrated pigment
slurry. The increased bulk density of the pigment speeds up the
slurry dispersion process by increasing the rate at which the
pigment will "wet" into the slurry. The concentrated pigment slurry
can then be admixed into paint formulations and the like in a
relatively quick and easy manner.
[0015] In another aspect, the invention includes apparatus for
carrying out the inventive process. In one embodiment, the
apparatus comprises a container for containing the powder under
pressure, the container having a first end and a second end
opposing the first end. Pressurization means are associated with
the container for increasing the pressure in the area of the
container containing the powder to a level above atmospheric
pressure at a rate sufficient to cause the powder to compact before
a substantial portion of the pressurization gas diffuses into the
powder. In one embodiment, the pressurization means comprises means
for injecting a gas into the container, and a source of compressed
gas.
[0016] In another embodiment, the inventive apparatus comprises: i)
a cylinder with first and second opposing ends defining an inlet
and an outlet, respectively; ii) a rotary containment device
positioned within the cylinder in a hub-and-spoke type arrangement
whereby aerated powder can be added through the inlet to powder
containment areas defined by adjacent "spokes" within the cylinder;
and iii) pressurization means comprising means for injecting a gas
into the container, and a source of compressed gas. The device can
be rotated such that powder in the powder containment areas is
densified by the inputting of a pressurized gas through the
pressurization means. The device can then be further rotated such
that densified powder is removed from the cylinder through the
outlet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1 and 2 are section views of a simple container
illustrating the positive pressure system of the invention.
[0018] FIG. 3 is a side elevation view illustrating one embodiment
of the inventive apparatus.
[0019] FIG. 4 is a top view of the apparatus illustrated by FIG.
3.
[0020] FIG. 5 is a front schematic and partially sectional view
illustrating another embodiment of the inventive apparatus.
[0021] FIG. 6 is a graph corresponding to Example IV set forth
below.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0022] The invention provides a process for increasing the bulk
density of an aerated powder. As used herein and in the appended
claims, a powder means a solid, dry material of very small particle
size ranging down to colloidal dimensions (e.g., 0.01 microns). As
used herein and in the appended claims, an "aerated" powder means a
powder having air or some other gas entrapped among the particles
forming the powder. The bulk density of a powder means the bulk
density of the powder as determined by the method described and
shown in Example I below.
[0023] Referring now to FIGS. 1 and 2, the general mechanism of the
inventive process is illustrated and described. FIG. 1 illustrates
a container 10 containing an aerated powder 12 prior to
densification. As shown by FIG. 2, rapidly increasing the gas
pressure in the area 14 of the container 10 containing the powder
12 (in this case the area 14 is the whole interior of the container
10) to a level above atmospheric pressure causes the powder to
compact before a substantial portion of the pressurization gas
diffuses into the powder. Without being limiting of the invention
in any way, it is expected in mechanistic terms that a pressure
front or pressure wave (indicated by the dotted line 16) is created
which forces the particles 12 together and forces out the air
entrapped between the powder particles that would otherwise have to
be displaced over time by the gravitational settling of the
particles 12.
[0024] The compacted powder 12 can then be more efficiently
processed. For example, in addition to being easier to handle, the
powder can be more efficiently packaged (e.g., packaging size can
be standardized). The compacted powder 12 can also, for example, be
more efficiently placed into a shell or other vessel (e.g., a
battery shell). In most battery applications, the more densely the
active materials are compacted the greater the charge density of
the battery, i.e., compaction of the battery-active materials
results in a better battery.
[0025] In accordance with the inventive process, the powder is
first placed in a container. The gas pressure in the area of the
container containing the powder is then increased to a level above
atmospheric pressure at a rate sufficient to cause the powder to
compact before a substantial portion of the pressurization gas
diffuses into the powder. The particular level above atmospheric
pressure to which the gas pressure must be increased and the
corresponding rate of increase necessary to achieve a degree of
compaction will vary depending upon the properties of the powder
being densified, the amount of gas entrapped between the powder
particles, and on the container used to carry out the process. Of
course, the amount of gas pressure applied and the rate of increase
in pressure will also depend upon the degree of compaction desired.
Preferably and simply, the process involves increasing the pressure
from an atmospheric pressure wherein the powder can be poured or
flow by gravity into the container to a pressure greater than
atmospheric pressure, which greater-than-atmospheric pressure can
in turn be used to help expel the densified powder cleanly from the
container into packaging, for example.
[0026] For example, as shown by Example I below, in order to
increase the bulk density of a freshly milled, hot (150 to
200.degree. C.) latex paint grade titanium dioxide pigment
("CR-813" marketed by Kerr-McGee Chemical, LLC) from 24.8
lbs/ft.sup.3 (0.40 g/cm.sup.3) to 41.7 lbs/ft.sup.3 (0.67
g/Cm.sup.3) in a 3 liter cylindrical steel vessel having a 15.3 cm
inside diameter and a height of 15.9 cm, the gas pressure in the
area of the container containing the pigment (in this case the
whole interior of the container) was increased from 0 psig to 50
psig (3.5 kg/sq. cm) in approximately 10 to 15 seconds. Similarly,
as shown by Example V below, in order to increase the bulk density
of a freshly dried and vacuum-densified lithium vanadium oxide
battery-active material from 43.6 lbs/ft.sup.3 (0.70 g/cm.sup.3) to
50.5 lbs/ft.sup.3 (0.81 g/cm.sup.3) in the same 3 liter cylindrical
steel vessel, the gas pressure in the area of the container
containing the pigment (in this case the whole interior of the
container) was increased from a full vacuum condition (less than
about 0.1 psia) to 90 psig (6.3 kg/sq. cm) in about 15 seconds.
[0027] Generally, after the desired compaction is obtained, the
container is depressurized and the compacted powder is removed from
the container. In one embodiment, the container in which the powder
is densified also serves as the final or at least interim container
(e.g., packaging) for the product. In this event, of course, the
compacted powder is not removed from the container. In fact
additional powder can be added to the container and compacted in
accordance with the invention, in one or more additional
cycles.
[0028] In one embodiment, the gas pressure in the area of the
container containing the powder is increased to a level above
atmospheric pressure by injecting a gas into the container. For
example, as illustrated above, gas can be injected into the
container at a rate sufficient to increase the overall pressure
within the container as a whole to the desired level within the
desired amount of time in order to achieve compaction of the
powder. The container is then depressurized and the compacted
powder is removed from the container.
[0029] The pressurization gas can be any gas, but should not
adversely react with the powder or otherwise negatively affect
either the process or the apparatus to carry out the process. The
pressurization gas can conceivably be selected to be reactive with
the powder in an advantageous, desired way, in effect combining a
reactive step in the powder's preparation (or treatment) with
densification. However, for most applications it is expected that
the pressurization gas should be non-reactive with the powder and
in the process and apparatus generally. In densifying a lithium
metal oxide battery-active material or like moisture- or
oxygen-sensitive material, for example, an unreactive, dry gas such
as nitrogen is suitably used as the pressurization gas. In the case
of the densification of an aerated titanium dioxide powder,
however, air is simply and preferably used as the pressurization
gas. The gas can also conveniently be a gas that is otherwise
present and readily available (perhaps in an already pressurized
condition) in an associated process for making, treating or
handling the aerated powder. For example, in the production of
titanium dioxide pigment, chlorine gas is commonly utilized,
generated and/or recycled. In an embodiment of the invention, the
chlorine gas is utilized as the gas injected into the container to
increase the gas pressure in the container and compact the
powder.
[0030] A variety of methods can be utilized to depressurize the
container and remove the compacted powder from the container. For
example, in one embodiment, the powder is placed in a container
having a first end and a second end opposing the first end. The
container is configured such that increasing the gas pressure in
the area of the container containing the powder to a level above
atmospheric pressure causes the powder to compact against the
second end of the container. Once the powder is compacted, the
second end of the container is opened whereby the container is
depressurized and the compacted powder is expelled from the
container through the second end of the container.
[0031] Any aerated powder can be densified or compacted in
accordance with the invention. Examples of commercially significant
aerated powders are the titanium dioxide pigments and the complex
metal oxides and metal phosphates used as battery-active materials,
for example, those based on vanadium, manganese, nickel, cobalt,
iron or a combination of such metals. Of particular interest are
the lithium vanadium oxides, lithium cobalt oxides, lithium nickel
and lithium manganese oxides (including the many modified oxides
based on each of these). Examples of applications in which
densification of such aerated powders may be beneficial include
bulk bagging operations and operations to load battery-active
materials into battery compartments of a limited volume.
[0032] One class of material to which the invention is particularly
applicable is inorganic pigments. For example, due in part to a
final fluid energy milling step, the bulk density of highly treated
titanium dioxide pigment (for example, of a type designed for use
in water-based latex paints) is so low that it is not uncommon that
the container can only be filled to 80-90 percent capacity.
Typically, the bulk density of highly treated, aerated titanium
dioxide pigment is less than about 21.9 lbs/ft.sup.3 (0.35
g/cm.sup.3). In accordance with the invention, the bulk density of
such a pigment can efficiently be increased to a level greater than
about 49.9 lbs/ft.sup.3 (0.8 g/cm.sup.3).
[0033] The inventive densification process is particularly useful
in connection with titanium dioxide pigments having bulk densities
less than about 21.9 lbs/ft.sup.3 (0.35 g/cm.sup.3). Preferably, in
accordance with the present invention, the bulk density of a
titanium dioxide pigment is increased to a level greater than about
35 lbs/ft.sup.3 (0.56 g/Cm.sup.3). More preferably, the bulk
density of a titanium dioxide pigment is increased in accordance
with the invention to a level in the range of from about 35
lbs/ft.sup.3 (0.56 g/cm.sup.3) to about 50 lbs/ft.sup.3 (0.80
g/cm.sup.3), even more preferably from about 40 lbs/ft.sup.3 (0.64
g/cm.sup.3) to about 50 lbs/ft.sup.3 (0.80 g/cm.sup.3).
[0034] In another aspect, the invention includes a process for
preparing a slurry from an aerated powder. Due to the increased
time required to "wet in" the powder into a liquid medium,
preparing slurry from an aerated powder (and in particular, from a
highly aerated powder) can be very time consuming. Although aerated
powders naturally gravitationally settle over time, this adds
another step between the final powder processing step and the
slurry preparation process. In accordance with the invention, the
powder is first processed. For example, this may entail a final
powder milling (e.g., fluid energy milling) step which typically
aerates the powder. Prior to allowing the powder to fully settle,
the bulk density of the powder is increased by deaerating the
powder. The densified powder is then wet in (dispersed) into the
slurry. The resulting slurry can then be effectively and
efficiently added to yet another medium such as a paint
formulation.
[0035] Preferably, the powder is deaerated in accordance with the
invention, namely placing the powder in a container under
atmospheric conditions, increasing the gas pressure in the area of
the container containing the powder to a level above atmospheric
pressure at a rate sufficient to cause the powder to compact before
a substantial portion of the pressurization gas diffuses into the
powder and removing the compacted powder from the container.
[0036] In the titanium dioxide pigment industry, significant
amounts of pigment are sold in a slurry format. These slurries are
typically made at solids levels ranging from about 65% to about 76%
by weight. To achieve these high solids levels, various dispersants
are added to facilitate both rapid "wet-in" and to form a stable
dispersion. The term "wet-in" refers to the displacement of the air
surrounding the particles with a liquid. In highly aerated powders,
occluded air can significantly increase the overall time required
to complete the "wet-in" step. By densifying the pigment prior to
initiating the dispersion process, the "wet-in" time can be
significantly reduced. For example, the "wet-in" time associated
with dispersing a titanium dioxide pigment into water to form a
slurry is, by the present process, preferably reduced by at least
10 percent, more preferably at least 20 percent and most preferably
by at least 30 percent in comparison to the amount of "wet-in" time
required for the same pigment under the same conditions but wherein
the pigment has only been allowed to deaerate naturally and with
settling of the pigment.
[0037] The invention is also particularly useful for increasing the
bulk density of battery-active materials and of compositions
containing such materials, as used for making the cathode of a
primary or secondary rechargeable battery, for example. It will be
appreciated in this regard that with the advent of increasingly
smaller yet more sophisticated hand-held electronic devices, the
batteries used in such devices must be capable of delivering a
correspondingly greater amount of electrical energy yet occupy a
smaller space than in earlier such devices. The present invention
addresses this need and helpfully enables a greater amount of a
given battery-active material to be employed in the increasingly
smaller, fixed volume battery containers or shells that are
required. Preferably, by the process of the present invention, the
bulk density of a battery-useful composition containing a
battery-active material (or mixture of such materials) can be
increased by at least about 10 percent, more preferably by at least
about 15 percent and most preferably by at least about 30 percent
from the bulk density of the same composition without any positive
pressure densification or deaeration having been used.
[0038] The inventive process does not necessarily require
sophisticated apparatus; any closed container should work provided
the materials of construction are capable of sustaining both the
desired operating pressures and a corrosive environment if
corrosive materials are involved.
[0039] Referring now to the drawings, and particularly to FIGS. 3
and 4, one preferred embodiment of the inventive apparatus,
generally designated by the reference numeral 20, is described. The
apparatus 20, an air-lock assembly, can be utilized to increase the
bulk density of any powder. The particular form of the apparatus 20
is not critical. In fact, there are a variety of spherical disk
valves and air lock assemblies that are commercially available and
can be modified for use in connection with the invention. The
particular apparatus shown by FIGS. 3 and 4 is a GEMCO.RTM.
Spherical Disc Valve or Airlock that has been modified in
accordance with the invention.
[0040] The apparatus 20 is positioned in the vertical mode and
comprises a container 22 for containing a powder under pressure.
For example, in a continuous titanium dioxide manufacturing
process, titanium dioxide pigment can be fed directly into the
container 22 from a titanium dioxide separator (not shown).
[0041] The container 22 includes a first end 30 and an opposing
second end 32. Pressurization means 34 are associated with the
container 22 for increasing the gas pressure in the area 36 of the
container 22 containing the powder to a level above atmospheric
pressure and at a rate sufficient to cause the powder to compact
before a substantial portion of the pressurization gas diffuses
into the powder.
[0042] In one embodiment, pressurization means 34 comprise
injection means 38 for injecting a gas into the container 22, and a
source of gas 40 (e.g., compressed gas). The injection means 38
includes a conduit 42 extending from the source 40 into the
container 22 and a corresponding valve 44. The source 40 of
compressed gas includes a suitable container 46. The pressure of
the gas in the container 46 is sufficient to force the gas through
the conduit 42 into the container 22 at a rate sufficient to
increase the gas pressure in the container 22 to the desired level
and within the desired amount of time.
[0043] The first end 30 of the container 22 includes an inlet 48
for allowing the powder to be added to the container (the inlet
includes a flange 48a for connection to the feed supply). The
second end 32 of the container 22 includes an outlet 50 for
allowing the powder to be discharged from the container into a bag
or other receptacle (not shown) (the outlet includes a flange 50a
for connection to the receptacle). The container further includes a
first valve 54 for opening and closing the inlet 48 and a second
valve 56 for opening and closing the outlet 50. As illustrated, the
valves 54 and 56 are conventional sliding knife gate valves, which
are automatically operated by corresponding valve motors 58a and
58b as known to those skilled in the art (e.g., the motors can be
electrically or pneumatically operated; a programmable logic
controller can be included to control cycle time). The valves 54
and 56 open and close very quickly allowing rapid filling and
discharge from the container. One or more pressure valves 60 can be
associated with the container 22 for indicating the pressure within
the container 22.
[0044] In operation of the apparatus illustrated by FIGS. 3 and 4,
the first valve 54 is opened and the powder to be densified is
gravity fed into the container 22 through the inlet 48. The valve
56 remains fully closed. The powder falls and piles up against the
valve 56. Once the container 22 is filled to the desired level, the
valve 54 is closed. The valve 44 is then opened to inject
pressurization gas from the source of gas 40 into the container 22.
The pressurization gas within the source of gas 40 is compressed
such that it is injected into the container 22 at a rate sufficient
to increase the gas pressure in the container to the desired level,
i.e., to a level above atmospheric pressure at a rate sufficient to
cause the powder to compact whereby the powder is compacted or
densified against the valve 56 of the container 22 before a
substantial portion of the pressurization gas diffuses into the
powder. Once the powder has been compacted as desired, the valve 56
is opened whereby gravity together with the increased gas pressure
within the container 22 causes the powder to completely eject from
the container 22. This is an added benefit of the invention,
particularly in circumstances where the cohesive characteristics of
some powders may cause these powders to tend to stick to the walls
of the container 22 and not be easily removed to a separate
package, for example. The increased gas pressure in the container
22 can help overcome the tendency of such powders to stick to the
walls of the container 22. The compacted powder is directly ejected
into a bag or other type of product receptacle (not shown).
Preferably, no additional mechanical device is required to effect
the discharge.
[0045] Referring now to FIG. 5, yet another embodiment of the
inventive apparatus for increasing the bulk density of a powder is
illustrated. The apparatus in this embodiment, which is generally
designated by the reference numeral 70, includes a cylinder 72, a
rotary containment device 74, rotating means 76 (represented by
dotted lines) for turning the rotary containment device within the
cylinder, and pressurization means 78 associated with the cylinder.
A powder 80 is fed from a feed container 82 into the cylinder 72
and ultimately from the cylinder into an end-container (e.g., a
bag) 84.
[0046] The cylinder 72 includes a first end 90 containing an inlet
92, a second end 94 opposing the first end and containing an outlet
96 and a wall 98. The inlet 92 includes a first valve 100. The
outlet 96 includes a second valve 102. The rotary containment
device 74 is positioned within the cylinder 72. The rotary
containment device includes a hub 110 and three pairs of opposed
blades, 112A and 112B, 114A and 114B and 116A and 116B,
respectively, attached to the hub. The blades 112A and 112B, 114A
and 114B and 116A and 116B create six powder containment areas 120A
through 120F within the cylinder 72. The rotary containment device
74 is capable of turning within the cylinder 72 such that each of
the powder containment areas 120A through 120F rotate to a first
position 122 within the cylinder adjacent the inlet 92 whereby
non-compacted powder 80 can be added to the area, a second position
124 within the cylinder adjacent the wall 98 of the cylinder
whereby powder 80 in the area can be compacted, and a third
position 126 adjacent the outlet 96 whereby compacted powder 80 can
be ejected from the area into the end-container 84.
[0047] The rotating means 76 includes a motor 130 (represented by
dotted lines) and shaft 132. The shaft 132 is attached at one end
to the motor 130 and the other end to the hub 110. The motor 130
rotates the shaft 132, which in turns rotates the rotary
containment device 74.
[0048] The pressurization means 78 associated with the cylinder 72
function to increase the gas pressure within each of the powder
containment areas 120A through 120F of the rotary containment
device 74 so that the powder within the area is compacted or
densified when the area is in the second position 124. The gas
pressure within each of the powder containment areas 120A through
120F is increased to a level above atmospheric pressure and at a
rate sufficient to cause the powder within the area to compact
before a substantial portion of the pressurization gas diffuses
into the area. The pressurization means 78 include a pulsed air
pressure control system 140, a main gas conduit 142, a filter and
vent system 144 and a cleanout system 146. A first end 148 of the
main gas conduit 142 is attached to the pulsed air pressure control
system 140. A second end 150 of the main gas conduit 142 extends
through the wall 98 of the cylinder 72 and is positioned in each of
the powder containment areas 120A through 120F when the area is in
the second position 124.
[0049] The filter and vent system 144 includes a valve 154,
pressure gauge 156 and a bag-type filter 158. A first branch 160 of
the main gas conduit 142 extends into the filter 158. The filter
and vent system 144 allows gas to be vented from the pressurization
means 78 as necessary.
[0050] A second branch 164 of the main gas conduit 142 extends into
the cleanout system 146. The cleanout system 146 includes a valve
166 and allows any particles that become entrapped in the
pressurization means 78 to be removed from the pressurization
means.
[0051] In operation, powder 80 to be compacted is placed in the
feed container 82. The rotating means 76 is operated to rotate the
rotary containment device 74 in a counterclockwise direction within
the cylinder 72 at the desired rate; i.e., a rate such that a
proper amount of powder 80 will be fed into each of the powder
containment areas 120A through 120F when the area is in the first
position 122, and to allow the powder 80 in the area to be
sufficiently compacted when the area is in the second position 124.
The first valve 100 is then opened allowing non-compacted powder 80
to fill each of the powder containment areas 120A through 120F when
the area is in the first position 122. As the rotary containment
device rotates, each of the powder containment areas 120A through
120F moves from the first position 122 to the second position 124.
When in the second position 124, the pressurization means 78
operates to increase the gas pressure within the corresponding
powder containment area to the desired level above atmospheric
pressure at a rate sufficient to cause the powder in the area to
compact before a substantial portion of the pressurization gas
diffuses into the powder. Rotation of the rotary containment device
74 causes each of the powder containment areas 120A through 120F to
also rotate from the second position 124 to the third position 126.
When a powder containment area is in the third position 126, the
compacted powder therein falls from the area through the second
valve 102 and outlet 96 into the end container or bag 84.
Continuous operation of the device allows powder to be continuously
densified in accordance with the invention.
[0052] The pressurization means 78 operates to increase the gas
pressure within each of the powder containment areas 120A through
120F as follows: Air is injected into the main gas conduit 142 by
the pulsed air pressure control system 140. The air is conducted by
the main gas conduit 142 into the powder containment area in the
second position 124. The air flows from the second end 150 of the
main gas conduit 142 into the area in the second position. The
pulsed air pressure control system 140 causes the air to be
conducted through the main gas conduit 142 at a rate sufficient to
increase the gas pressure in the powder containment area in the
second position 124 to the desired level above atmospheric pressure
and at the desired level and at the desired rate, i.e., a rate
sufficient to cause the powder within the area to compact before a
substantial portion of the pressurization gas diffuses into the
powder.
[0053] The filter and vent system 144 allows air to be vented from
the system when the pressure in the system, as indicated by the
pressure gauge 156, exceeds the desired limit. The valve 154 is
opened allowing excess air to travel through the first branch 160
of the conduit 142 into the filter 158 and ultimately into the
atmosphere. The filter 158 catches any particles present in the
vent gas.
[0054] The cleanout system 146 allows any powder that accumulates
in the main gas conduit 142 or other parts of the pressurization
means 78 to be removed from the system. The valve 146 is opened
allowing air and particles in the main gas conduit 142 to enter the
second branch 164 of the conduit where it is conducted through the
valve and collected in an appropriate manner.
[0055] The following examples are provided to further illustrate
the effectiveness of the inventive method and composition.
EXAMPLE I
[0056] A set of experiments was carried out to verify that rapid
pressurization of a closed vessel containing a highly aerated
powder causes the powder to densify or compact (i.e., forces the
powder into a smaller volume). All four combinations of rapid and
slow pressurization and rapid and slow depressurization were
evaluated. Bulk density values were determined in a conventional
manner using a "HOSOKAWA Micron Powder Tester, Model PT-E," by
filling and leveling a 100 cubic centimeter cup with the powder,
attaching an extension piece on top of the cup and filling the
extension piece as well. The filled cup and extension piece were
tapped for 180 seconds at a 60 cycle frequency, with the addition
of powder as necessary to keep the level of the powder above the
top of the cup. At the conclusion of the tapping cycle, the
extension was carefully removed and the cup leveled to remove
excess powder. The weight difference between the filled, tapped and
leveled cup and the empty cup in grams, divided by the 100 cubic
centimeter volume of the cup, provided the sample bulk density in
grams per cubic centimeter.
[0057] The powder used in the tests was a highly aerated, latex
paint grade titanium dioxide pigment ("CR-813" pigment sold by
Kerr-McGee Chemical, LLC). First, the pigment was milled in a fluid
energy mill using superheated steam which aerated the pigment and
raised the temperature of the pigment to approximately
150-200.degree. C. The bulk density of this pigment, prior to
testing, was 24.8 lbs/ft.sup.3 (0.40 g/cm.sup.3). Approximately 500
grams of the hot pigment were then placed into a 3 liter,
cylindrical steel vessel (15.3 cm inside diameter, 15.9 cm in
height) having a removable top. The top of the vessel was then
attached securely. A first valve attached to the top of the vessel
and connected to a compressed air line was opened thereby causing
the vessel to pressurize from zero psig to approximately 50 psig
(3.5 kg/sq. cm, gauge) within 10 to 15 seconds. Once the pressure
reached the level of approximately 50 psig, the first valve was
closed and a second valve, also attached to the top of the vessel,
was opened. Opening of the second valve allowed the vessel to
equilibrate back to atmospheric pressure in approximately 10 to 15
seconds. The top of the vessel was then removed and the pigment was
recovered from the vessel. The bulk density of the recovered
pigment (Sample 1A) was determined to be 41.7 lbs/ft.sup.3 (0.67
g/cm.sup.3). Thus, the bulk density of the pigment substantially
increased, specifically by 68 percent.
[0058] Next, the experiment described above was repeated using the
same procedure and a fresh sample of the same hot pigment. The only
exception was that the pressure in the vessel was allowed to climb
to 50 psig over 3 minutes, as opposed to 10 to 15 seconds, and was
allowed to equilibrate back to atmospheric pressure over a one
minute time frame, as opposed to a 10 to 15 second time frame. The
bulk density of the recovered pigment (Sample 1B) was determined to
be 26.6. Ibs/ft.sup.3 (0.43 g/cm.sup.3), almost the same as the
starting material.
[0059] A third test was carried out, also utilizing the same
equipment and procedure and a fresh sample of the same hot pigment.
In this test, however, the vessel was pressurized rapidly but
depressurized slowly. Specifically, the pressure in the vessel was
allowed to climb to approximately 50 psig over 10 to 15 seconds and
then allowed to equilibrate back to atmospheric pressure over
approximately a one-minute time frame. The bulk density of the
recovered pigment (Sample IC) was determined to be 41.7
Ibs/ft.sup.3 (0.67 g/cm.sup.3), which is equal to the level
achieved in connection with Sample 1A.
[0060] A fourth example was carried out to illustrate the effect of
initially pressurizing the vessel slowly but depressurizing the
vessel rapidly. Again, the test was carried out using the same
equipment and procedure as above and a fresh sample of the hot
pigment. In this test, however, the pressure was allowed to climb
to approximately 50 psig over three minutes and to then dissipate
over a 30-second time frame. The bulk density of the recovered
pigment (Sample ID) was determined to be 29.7 lbs/ft.sup.3 (0.47
g/cm.sup.3), which was only slightly higher than the starting
material.
[0061] The results of the above experiments unequivocally show that
it is rapid pressurization of the vessel that is responsible for
significantly densifying the pigments.
EXAMPLE II
[0062] The pigment densified in accordance with Example I (Sample
1A) was tested in paint formulations to verify that densification
accomplished by means of the present invention does not negatively
impact the optical properties of the pigment. A paint formulation
containing pigment Sample 1A (having a bulk density of
approximately 41.7 lbs/ft.sup.3 (0.67 g/cm.sup.3)) and a paint
formulation including the pigment prior to being treated in
accordance with the inventive process (having a bulk density of
24.8 lbs/ft.sup.3 (0.40 g/cm.sup.3)) (the "untreated pigment
sample") were tested.
[0063] The paint formulations were standard latex paint
formulations, designed for interior architectural applications. The
formulations were formed by incorporating the pigment samples in
portions of a freshly prepared polyvinyl acetate latex emulsion. In
each formulation, the amount of the pigment sample incorporated
into the emulsion was 60% by volume based on the total volume of
the emulsion.
[0064] The resulting paint formulations were first applied to black
glass plates and white cards. The Y reflectance values of the dried
paint films were measured with a HunterLab Color Difference Meter
as known to those skilled in the art. These readings, in
combination with measured film weights, were used to calculate the
scatter value, expressed as hiding power in square feet per pound
of pigment.
[0065] Next, a fixed amount of a carbon black tint was added to a
portion of each paint formulation to form a tinted paint sample for
each formulation. The four paint samples were mixed thoroughly.
Drawdowns of all four paint samples and of corresponding controls
were then made on standard LENETATM charts. From these drawdowns
readings from the HunterLab Color Difference Meter were obtained to
enable tint strength calculations to be made. All methods and
calculations were carried out in accordance with ASTM D2805 and
D2745, respectively. The results are shown in Table 1 below.
1TABLE 1 Optical Properties of Paint Formulations Paint with
Untreated Paint with Pigment Test Method Pigment Sample Sample A
Hiding Power (sq. ft/lb of 221 222 pigment) Tint Strength (% of
Standard) 106.6 108.6
[0066] The results of the tests show that there was no
deterioration in the performance of the pigment densified in
Example I whether in terms of hiding power (dryhide) or tint
strength.
EXAMPLE III
[0067] The effect of varying the densification pressure on the bulk
density of the pigment was demonstrated. The pigment used in this
series of tests was a highly aerated, latex paint grade titanium
dioxide pigment ("CR-813" sold by Kerr-McGee Chemical, LLC). Six
samples of the pigment, including a control, were tested.
[0068] First, five of the six samples of the pigment were densified
utilizing the same process, apparatus and equipment described in
Example I. Except for the densification pressure utilized, the test
parameters in each experiment were the same. In each test, the
vessel was rapidly pressurized to the target pressure level within
approximately 3-5 seconds. Upon obtaining the target pressure
level, the vessel was allowed to equilibrate back to atmospheric
pressure over approximately 10-15 seconds. The densification
pressures used in the densification process ranged from 15 psig (1
kg/sq. cm) to 72 psig (5 kg/sq. crn). The bulk density of each
pigment sample, including the control sample, was determined as in
Example I.
[0069] Paint formulations utilizing the control sample as well as
the five samples densified in accordance with the inventive process
were then made. The same formulations, equipment and procedure
described in Example II were utilized. The hiding power and tint
strength of the samples were then measured utilizing the same
procedure described in Example II. The results of the tests are
shown in Table 2 below.
2TABLE 2 Effective of Densification Pressure on Optical Properties
of Paint Formulations Pressure Bulk Density Hiding Power Tint
Strength Sample psig lbs/ft.sup.3 (sq. ft./lb Pigment) (% of
Standard) 3A 0 24.9 213 106.8 3B 15 27.7 213 105.4 3C 30 35.4 213
106.9 3D 45 39.0 214 106.4 3E 60 40.0 213 104.6 3F 72 42.8 213
104.9
[0070] The bulk density measurements demonstrate that the bulk
density of the pigment increases with increasing densification
pressure. Optical properties as measured by hiding power and
tinting strength show no change over the range of densification
pressures evaluated. The tests show that the pigment can be
densified very significantly (from 24.9 to 42.8 lbs/ft.sup.3, which
represents an increase of almost 72%) without affecting the optical
properties of paint formulations formed therewith.
EXAMPLE IV
[0071] A test was carried out to illustrate the beneficial effects
that the inventive densification process and apparatus have on the
rate that a powder can be dispersed into an aqueous medium. The
pigment used in the test was the same pigment described in Example
III above. The pigment was fresh from a fluid energy milling step
of the pigment manufacturing process. Bulk density values were
determined as in Example I.
[0072] Two samples were made, the first to be used as a control.
The second sample was densified utilizing the same procedure and
apparatus described in Example I; in this case pressurization was
to approximately 50 psig within 3-5 seconds and depressurization
was carried out over a time period of 10-15 seconds. Bulk density
measurements showed that the control had a value of 27.1
lbs/ft.sup.3 (0.43 g/cm.sup.3) and the densified sample had a value
of 40.0 lbs/ft.sup.3 (0.64 g/cm.sup.3, for an increase of almost
48%).
[0073] Next, using a DISPERMATTM Model AE3C available from
Byk-Gardner, U.S.A., equipped with torque sensing capability,
slurries were made from each of the two pigment samples. The
technique involved adding 775 grams of the pigment sample being
tested to 370 grams of water and a proprietary blend of
dispersants. All operational parameters such as speed and
temperature were maintained at a constant level. The method of
addition of the pigment to the aqueous medium was such that the
only rate limiting factor was the ability of the titanium dioxide
to "wet-in" to the slurry.
[0074] The results are demonstrated by FIG. 6 of the drawings of
this application. FIG. 6 includes time-torque plots showing both
the sample densified in accordance with the invention and the
control sample. As shown, the pigment sample densified in
accordance with the invention reached a steady state torque 50 to
52 seconds before the control. Thus, the ability of a powder to be
dispersed in an aqueous medium can be substantially enhanced by
densifying the powder in accordance with the invention.
EXAMPLE V
[0075] A pressure densification test was run on a cathode
composition comprised of a lithium vanadium oxide battery-active
material and about 5 percent by weight of a combination of graphite
and carbon black, which composition had been previously dried and
densified under vacuum only. A sample was placed into the same 3
liter steel test cylinder described in Example I and full vacuum
(to less than 0.1 psia) was applied. The cylinder was then
pressurized to 90 psig (6.3 kg/sq. cm) in about 15 seconds with
nitrogen. The packed bulk (tap) density increased from a nominal
43.6 lbs/ft.sup.3 (0.70 g/cm.sup.3) to 50.5 lbs/ft.sup.3 (0.81
g/cm.sup.3), about a 15% increase in density.
EXAMPLES VI through VIII
[0076] For Examples VI through VIII, similar pressure densification
tests were conducted on two samples each of three additional
battery-useful, cathode compositions, all comprised of lithium
vanadium oxide battery-active material, carbon black and graphite.
The compositions of the samples used for Examples VI and VII were
the same, while the composition for Example VIII used a somewhat
greater proportion of graphite as compared to carbon black.
[0077] In contrast to Example V, a vacuum was not applied
initially, so that pressurization took place with nitrogen from
atmospheric pressure to 90 psig over about 15 seconds. The valve to
the container was then opened, and the pressure rapidly released
over a span of about 5 seconds. Also in contrast to previous
examples, in Examples VI through VIII the samples were subjected to
the same densification procedure twice more to achieve maximum
densification, before the packed bulk (tap) density was determined.
Results are presented below in Table 3, with the densities being
expressed in grams per cubic centimeter:
3TABLE 3 Density after Sample Density Densification Avg. Percent
Densification 1A 0.72 0.77 10.2 1B 0.67 0.76 2A 0.59 0.70 16.8 2B
0.60 0.69 3A 0.61 0.84 33.9 3B 0.63 0.82 Thus, significant
improvements in the bulk densities of the samples were
achieved.
* * * * *