U.S. patent application number 10/546893 was filed with the patent office on 2006-05-18 for process for the produciton of metal oxide and metalloid oxide dispersions.
This patent application is currently assigned to DEGUSSA AG. Invention is credited to Christoph Batz-Sohn, Wolfgang Lortz, Gabriele Perlet, Gerrit Schneider, Werner Will.
Application Number | 20060104881 10/546893 |
Document ID | / |
Family ID | 33154199 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060104881 |
Kind Code |
A1 |
Lortz; Wolfgang ; et
al. |
May 18, 2006 |
Process for the produciton of metal oxide and metalloid oxide
dispersions
Abstract
Process for the production of an aqueous dispersion of
pyrogenically produced metal oxide and metalloid oxide powders with
a BET surface area of between 5 and 600 m.sup.2/g, with a metal
oxide or metalloid oxide content in the dispersion of between 5 and
25 wt. %, comprising the following steps:--water, which is
optionally adjusted to pH values of between 2 and 4 by adding
acids, is circulated from a receiving vessel via a rotor/stator
machine, and--metal oxide or metalloid oxide powder is introduced,
using a feed device, into the shear zone between the slots in the
rotor teeth and the stator slots, continuously or discontinuously
and with the rotor/stator machine running, in a quantity such that
a predispersion with a solids content of between 20 and 40 wt. %
results, and, after all the metal oxide powder or metalloid oxide
powder has been added,--the feed device closes and shearing
continues in such a way that the shear rate is in the range of
between 10000 and 40000 s.sup.-1, and--then, by dilution, the
predispersion is adjusted to the desired solids content of the
dispersion while maintaining the dispersing conditions.
Inventors: |
Lortz; Wolfgang;
(Wachtersbach, DE) ; Batz-Sohn; Christoph; (Hanau,
DE) ; Perlet; Gabriele; (Grobkrotzenburg, DE)
; Will; Werner; (Gelnhausen, DE) ; Schneider;
Gerrit; (Hanau, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
DEGUSSA AG
Benningsenplatz 1
Duesseldorf
DE
40474
|
Family ID: |
33154199 |
Appl. No.: |
10/546893 |
Filed: |
April 1, 2004 |
PCT Filed: |
April 1, 2004 |
PCT NO: |
PCT/EP04/03445 |
371 Date: |
August 24, 2005 |
Current U.S.
Class: |
423/335 ;
423/625 |
Current CPC
Class: |
C01P 2002/50 20130101;
C09K 3/1463 20130101; C01P 2006/12 20130101; C09G 1/02 20130101;
C01B 33/1417 20130101; C03C 1/006 20130101; C01P 2006/22 20130101;
C01F 7/026 20130101; C01B 13/145 20130101 |
Class at
Publication: |
423/335 ;
423/625 |
International
Class: |
C01B 33/12 20060101
C01B033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2003 |
DE |
103 17 066.9 |
Claims
1. A process for the production of an aqueous dispersion of
pyrogenically produced metal oxide and metalloid oxide powders with
a BET surface area of between 5 and 600 m.sup.2/g, with a metal
oxide or metalloid oxide content in the dispersion of between 5 and
25 wt. %, comprising the steps: water, which is optionally adjusted
to pH values of between 2 and 4 by adding acids, is circulated from
a receiving vessel via a rotor/stator machine, and metal oxide or
metalloid oxide powder is introduced, using a feed device, into the
shear zone between the slots in the rotor teeth and the stator
slots, continuously or discontinuously and with the rotor/stator
machine running, in a quantity such that a predispersion with a
solids content of between 20 and 40 wt. % results, and, after all
the metal oxide powder or metalloid oxide powder has been added,
the feed device closes and shearing continues in such a way that
the shear rate is in the range of between 10000 and 40000 s.sup.-1,
and then, by dilution, the predispersion is adjusted to the desired
solids content of the dispersion while maintaining the dispersing
conditions.
2. The process according to claim 1, wherein the metal oxide or
metalloid oxide powder is a silica powder, an alumina powder, a
silica powder doped with alumina or a silicon-aluminium mixed oxide
powder.
3. The process according to claim 1, wherein bases or acids are
added to the dispersion and/or predispersion.
4. The process according to claim 1, wherein cationic polymers
and/or aluminium salts are added to the dispersion and/or
predispersion.
5. The process according to claim 1, wherein a surface-active
substance is added to the dispersion and/or predispersion.
6. The process according to claim 1, wherein a preservative is
added to the dispersion and/or predispersion.
Description
[0001] The invention provides a process for the production of
low-viscosity, highly filled dispersions of pyrogenic metal oxides
and metalloid oxides.
[0002] Low-viscosity, highly filled dispersions of pyrogenic metal
oxides or metalloid oxides are widely used. For example, silica and
aluminium dioxide dispersions are used in polishing processes
(chemical-mechanical polishing) or in the paper industry for the
production of a paper coating. In the glass industry, highly filled
silica dispersions or dispersions of silicon-titanium mixed oxide
are used for the production of shaped glass articles.
[0003] U.S. Pat. No. 5,116,535, U.S. Pat. No. 5,246,624 and U.S.
Pat. No. 6,248,144 all describe processes for the production of
low-viscosity dispersions of pyrogenic silicon dioxide powder
(fumed silica).
[0004] Fumed silica powders are produced like other pyrogenic oxide
powders, e.g. alumina or titanium dioxide, preferably by flame
hydrolysis. In this process, a homogeneous mixture of a vaporous
starting material of the subsequent oxide, e.g. silicon
tetrachloride or aluminium chloride, is burnt with hydrogen, oxygen
and an inert gas using a burner in a cooled combustion chamber. In
a first step of this process, water is produced by the reaction of
hydrogen and oxygen, and in a second step, this water hydrolyses
the starting material with the formation of the pyrogenic
oxide.
[0005] In this process, primary particles are initially formed,
which can coalesce into aggregates as the reaction progresses.
Aggregates here are primary particles that have fused together. The
aggregates can cluster together further to form agglomerates.
During the dispersing of pyrogenic oxide particles, even under the
action of low dispersing energy, the agglomerates are first
separated. With higher dispersing energies, larger aggregates are
also converted to small aggregates.
[0006] The principle on which the documents U.S. Pat. No.
5,116,535, U.S. Pat. No. 5,246,624 and U.S. Pat. No. 6,248,144 are
based is the same, i.e. to achieve as complete as possible a
destructuring of the fumed silica powder by the action of high
shear energies. However, in order to be able to introduce the high
shear energies into the system, this must have a high viscosity.
The high viscosity is achieved in the production processes of the
above documents by a high level of filling of silica powder, which
has to be at least 40 wt. %, and preferably 50 to 60 wt. %. If the
content of silica powder in these processes is reduced to values of
less than 40 wt. %, the effectiveness of the dispersing is reduced
to such an extent that only incomplete destructuring of the silica
powder takes place and larger aggregates remain in dispersion. This
can lead to sedimentation or gelation of the dispersion. The
dispersion is then adjusted to the desired solids content by
dilution.
[0007] A disadvantage of these processes is the time- and
energy-intensive incorporation of the pyrogenically produced silica
powder to achieve the required viscosity.
[0008] In addition, there is a process for the dispersion of
pyrogenically produced metal oxides in an aqueous medium, in which
two predispersed suspension streams under high pressure are
depressurised via two nozzles. These nozzles have to be adjusted in
such a way that the dispersion jets hit one another exactly and the
particles grind one another as a result.
[0009] This process for the production of dispersions containing
pyrogenically produced silica is described e.g. in EP-A-773270.
[0010] In this process, an aqueous predispersion is divided into
two partial streams, which are brought together again under high
pressure. The particles grind one another during this process. In
another embodiment, the predispersion is also placed under high
pressure, but the collision of the particles takes place against
armoured wall regions. Dispersion can take place over the entire pH
range, the alkaline range being preferred. If a dispersion with a
high solids content in the acidic range is desired, it is
advantageous to reduce the viscosity by means of suitable
additives.
[0011] The precise adjustment of the two predispersed suspension
streams is problematic in this process. Only with precise
adjustment can uniform grinding of the silica powder take place. A
further complicating factor is that, under the extreme stress on
the nozzles at pressures of up to 3500 kg/cm.sup.2, these display
marked wear, which has a negative effect on the above-mentioned
adjustment and can lead to impurities entering the dispersion.
[0012] In the embodiment in which the collision of the particles
takes place against armoured wall regions, it has been shown that
the wall regions are subject to marked wear and this embodiment is
not suitable for the dispersing of fumed silica.
[0013] It is true of both high-pressure processes that the
dimensions of the equipment available do not allow larger
quantities of dispersion to be produced inexpensively.
[0014] The object of the invention is to provide a process for the
production of finely dispersed dispersions containing pyrogenically
produced metal oxides as the solid phase, which avoids the
disadvantages of the prior art. In particular, it should be
possible to incorporate pyrogenically produced metal oxides or
metalloid oxides into an aqueous phase as rapidly as possible, the
introduction of impurities should be minimal and it should be
possible to implement the process economically.
[0015] The object is achieved by a process for the production of an
aqueous dispersion of pyrogenically produced metal oxide or
metalloid oxide powders with a BET surface area of between 5 and
600 m.sup.2/g, with a metal oxide or metalloid oxide content in the
dispersion of between 5 and 25 wt. %, which comprises the following
steps: [0016] water, which is optionally adjusted to pH values of
between 2 and 4 by adding acids, is circulated from a receiving
vessel via a rotor/stator machine, and [0017] metal oxide powder or
metalloid oxide powder is introduced, using a feed-device, into the
shear zone between the slots in the rotor teeth and the stator
slots, continuously or discontinuously and with the rotor/stator
machine running, in a quantity such that a predispersion with a
solids content of between 20 and 40 wt. % results, and, after all
the metal oxide powder or metalloid oxide powder has been added,
[0018] the feed device closes and shearing continues in such a way
that the shear rate is in the range of between 10000 and 40000
s.sup.-1, and [0019] then, by dilution, the predispersion is
adjusted to the desired solids content of the dispersion while
maintaining the dispersing conditions.
[0020] In a preferred embodiment, the shear rate can be between
20000 and 30000 s.sup.-1.
[0021] The process according to the invention can preferably be
carried out with silica powder, alumina powder, doped silica
powder, described e.g. in DE-A-19847161 or DE-A-10065028, or with
silicon-aluminium mixed oxide powder, described e.g. in
DE-A-4226711, DE-A-10135452, DE-A19919635 or US-A-2003/22081.
[0022] Furthermore, in the process according to the invention,
bases and/or acids may be added to the dispersion and/or
predispersion. As bases, for example ammonia, ammonium hydroxide,
tetramethylammonium hydroxide, primary, secondary or tertiary
organic amines, sodium hydroxide solution or potassium hydroxide
solution may be used. As acids, for example phosphoric acid,
sulfuric acid, hydrochloric acid, nitric acid or carboxylic acids
may be used.
[0023] Furthermore, in the process according to the invention,
cationic polymers and/or aluminium salts may be added to the
dispersion and/or predispersion. Suitable cationic polymers may be
those with at least one quaternary ammonium group, a phosphonium
group, an acid adduct of a primary, secondary or tertiary amine
group, polyethylene imines, polydiallylamines or polyallylamines,
polyvinylamines, dicyandiamide condensates, dicyandiamide-polyamine
co-condensates or polyamide-formaldehyde condensates. Suitable
aluminium salts may be aluminium chloride, aluminium
hydroxychlorides of the general formula Al(OH).sub.xCl with x=2-8,
aluminium chlorate, aluminium sulfate, aluminium nitrate, aluminium
hydroxynitrates of the general formula Al(OH).sub.xNO.sub.3 with
x=2-8, aluminium acetate, alums such as aluminium potassium sulfate
or aluminium ammonium sulfate, aluminium formates, aluminium
lactate, aluminium oxide, aluminium hydroxide acetate, aluminium
isopropylate, aluminium hydroxide, aluminium silicates and mixtures
of the above compounds. The use of these aluminium compounds in the
production of silica dispersions is already described in the German
patent application with application number DE10238463.0.
[0024] It can also be advantageous to add to the dispersion and/or
predispersion a surface-active substances, which is of a non-ionic,
cationic, anionic or amphoteric nature.
[0025] Finally, one or more preservatives can also be added to the
process according to the invention. These can, for example, be
compounds that are available under the trade names Preventol.RTM.
from Bayer or Acticide.RTM. from Thor.
EXAMPLES
Analytical Determinations
[0026] Determination of the viscosity of the dispersions: the
viscosity of the dispersions produced was determined using a rotary
rheometer from Physica, model 300, and the CC 27 measuring cup at
25.degree. C. The viscosity value was determined at a shear rate of
10 s.sup.-1 and 100 s.sup.-1.
[0027] Determination of the particle size present in the
dispersion: the particle size present in the dispersion is
determined by dynamic light scattering. The instrument used is the
Zetasizer 3000 HSa (Malvern Instruments, UK). The median value of
the volume distribution d.sub.50(V) is given.
[0028] Determination of the shear rate: the shear rate in the
process according to the invention is expressed as the peripheral
speed divided by the distance between the surfaces.
[0029] The peripheral speeds can be calculated from the speed of
the rotor and the rotor diameter. The distance between rotor and
stator is approx. 1 mm in the dispersing devices used.
[0030] Dispersing devices used: the rotor/stator machines Conti-TDS
3 and Conti-TDS 4 from Ystral are used for dispersing.
[0031] Silica powders used: AEROSIL.RTM. 90 (approx. 90 m.sup.2/g),
AEROSIL.RTM. 130 (approx. 130 m.sup.2/g), AEROSIL.RTM. 200 (approx.
200 m.sup.2/g) and AEROSIL.RTM. 300 (approx. 300 m.sup.2/g), all
DEGUSSA AG, are used.
[0032] Examples: the pH of the predispersion can be between 2 and
4.5, as a result of the acidic nature of the pyrogenically produced
silica and depending on the quality of the raw materials. If
desired, the pH can be adjusted to be constant throughout the
different silica batches by adding acid, e.g. aqueous hydrochloric
acid, or base, e.g. aqueous ammonia solution, in order to achieve a
constant grinding output.
[0033] During the grinding, a pH value of the predispersion close
to the isoelectric point is advantageous, since the particles to be
ground can be more readily ground in this case without having to
overcome reciprocal electrostatic repelling forces. When alkaline
pH values are being adjusted, it can be useful to pass through the
area around pH 7 by rapid addition of the alkaline component.
[0034] In all the examples, a heating of the dispersion by the high
energy input is countered by a heat exchanger, which limits the
temperature increase to no more than 40.degree. C.
Examples 1-3
Production of Acidic AEROSIL.RTM. 200 Dispersions at a Shear Rate
of Approx. 20000 s.sup.-1
[0035] 32.5 kg of deionised water are initially charged into a 60 l
stainless steel mixing tank. Then, with the aid of the suction tube
of the Ystral Conti-TDS 3 (stator slot: 4 mm 25' ring and 1 mm
ring, rotor/stator spacing approx. 1 mm) under shear conditions,
the quantity of AEROSIL.RTM. 200 required for a predispersion of
13.0 wt. % (Example 1, comparative example), 24.0 wt. % (Example 2)
and 28.5 wt. % (Example 3), corresponding to Table 1, is added.
[0036] Once the intake is complete, the suction nozzle is closed
and shearing continues at 3000 rpm for a further 10 min. When the
grinding is complete, deionised water is used to dilute to a
concentration slightly higher than the desired end concentration to
be able to take into account the quantities of additives still to
be added.
[0037] The pH is adjusted to 5.3 with ammonia solution. On reaching
the desired pH, the remainder of the water needed is metered in to
achieve the exact silica end concentration of the dispersion of 12
wt. %. Using the Conti TDS 3, homogenisation is performed for a few
more minutes.
Example 4
Production of an Acidic AEROSIL.RTM. 200 Dispersion at a Shear Rate
of Approx. 25000 s.sup.-1
[0038] 475 kg of deionised water are initially charged into a 1600
l stainless steel mixing tank. Then, with the aid of the suction
tube of the Ystral Conti-TDS 4 (stator slot: 6 mm ring and 1 mm
ring, rotor/stator spacing approx. 1 mm) under shear conditions,
190 kg of AEROSIL.RTM. 200 are taken in. Once the intake is
complete, the suction nozzle is closed and the 28.5 wt. %
predispersion is sheared at 3000 rpm for a further 10 min. The pH
of the predispersion is approx. pH 3.7. When the grinding is
complete, deionised water is used to dilute to a concentration
slightly higher than the desired end concentration of the
dispersion of 12 wt. % to be able to take into account the
quantities of additives still to be added.
[0039] The pH is adjusted to 5.0 with ammonia solution. More
deionised water is used to adjust the concentration of the
dispersion to 12 wt. % silica and, using the Conti TDS 4,
homogenisation is performed for a few more minutes. The thorough
mixing/homogenisation is additionally supported by a jetstream
mixer from Ystral installed in the mixing tank.
Example 5
Production of an Alkaline AEROSIL.RTM. 300 Dispersion at a Shear
Rate of Approx. 25000 s.sup.-1
[0040] 475 kg of deionised water are initially charged into a 1600
l stainless steel mixing tank. Then, with the aid of the suction
tube of the Ystral Conti-TDS 4 (stator slot: 6 mm ring and 1 mm
ring, rotor/stator spacing approx. 1 mm) under shear conditions,
190 kg of AEROSIL.RTM. 300 (or a smaller quantity according to the
Table) are taken in. Once the intake is complete, the suction
nozzle is closed and the 28.5 wt. % predispersion is sheared at
3000 rpm for a further 10 min. The pH of the predispersion is
approx. 3.6. When the grinding is complete, deionised water is used
to dilute to a concentration slightly higher than the desired end
concentration of 15% to be able to take into account the quantities
of additives still to be added.
[0041] The pH is adjusted to 9.5 by rapidly adding ammonia
solution. The thorough mixing/homogenisation is additionally
supported by a jetstream mixer from Ystral installed in the mixing
tank. On reaching the desired pH of 9.5, more deionised water is
used to adjust the concentration of the dispersion to 15 wt. %
silica and, using the Conti TDS 4, homogenisation is performed for
a few more minutes.
Examples 6-15
Production of AEROSIL.RTM. Dispersions Starting from a
Predispersion of 35 wt. % and a Shear Rate of Approx. 20000
s.sup.-1
[0042] 32.5 kg of deionised water are initially charged into a 60 l
stainless steel mixing tank. Then, with the aid of the suction tube
of the Ystral Conti-TDS 3 (stator slot: 4 mm ring and 1 mm ring,
rotor/stator spacing approx. 1 mm) under shear conditions, 17.5 kg
of pyrogenically produced silica according to Table 1 are taken
in.
[0043] Once the intake is complete, the suction nozzle is closed
and the 35 wt. %-predispersion is sheared at 3000 rpm for a further
10 min (Example 14: 30 min). When the grinding is complete,
deionised water is used to dilute to a concentration slightly
higher than the desired end concentration to be able to take into
account the quantities of additives still to be added.
[0044] The pH is adjusted to the desired level using sodium
hydroxide or ammonia solution. On reaching the desired pH, the
remainder of the water needed is metered in to achieve the exact
silica end concentration.
Example 16
Production of an Acidic AEROSIL.RTM. 200 Dispersion Starting from a
Predispersion with 21 wt. % in the Presence of an Aluminium
Salt
[0045] 43.5 kg of deionised water are initially charged into a 60 l
stainless steel mixing tank. Then, with the aid of the suction tube
of the Ystral Conti-TDS 3 (stator slot: 4 mm ring and 1 mm ring)
under shear conditions, 11.6 kg of, AEROSIL.RTM. 200 are sucked in.
Once the intake is complete, the suction nozzle is closed and the
21 wt. % predispersion is sheared at 3000 rpm for a further 10
min.
[0046] After the grinding, an aqueous aluminium chloride solution
is added (10 wt. %, based on Al.sub.2O.sub.3), so that, based on
the quantity of AEROSIL.RTM. 200 used, a concentration of 0.01 mg
Al.sub.2O.sub.3 per m.sup.2 silica surface area is obtained. The pH
of the dispersion is kept at a pH of between 3.8 and 4.5 by
simultaneously adding 25 wt. % sodium hydroxide solution. After
adding the required aluminium chloride solution, the pH is adjusted
to 5.0 with the sodium hydroxide solution, the remainder of the
deionised water needed is added to adjust the concentration of the
dispersion to 20 wt. % and dispersing is continued for a further 5
minutes.
Example 17
Production of an Acidic AEROSIL.RTM. 200 Dispersion Starting from a
Predispersion with 35 wt. % in the Presence of an Aluminium
Salt
[0047] 35.75 kg of deionised water are initially charged into a 60
l stainless steel mixing tank. Then, with the aid of the suction
tube of the Ystral Conti-TDS 3 (stator slot: 4 mm ring and 1 mm
ring) under shear conditions, 19.25 kg of AEROSIL.RTM. 200 are
sucked in. Once the intake is complete, the suction nozzle is
closed and the 35 wt. % predispersion is sheared at 3000 rpm for a
further 10 min.
[0048] After the grinding, an aqueous aluminium chloride solution
is added (10 wt. %, based on Al.sub.2O.sub.3), so that, based on
the quantity of AEROSIL.RTM. 200 used, a concentration of 0.01 mg
Al.sub.2O.sub.3 per m.sup.2 silica surface area is obtained. The pH
of the dispersion is kept at a pH of between 3.8 and 4.5 by
simultaneously adding 25% sodium hydroxide solution. After adding
the required aluminium chloride solution, the pH is adjusted to 5.0
with the sodium hydroxide solution, the remainder of the deionised
water needed is added to adjust the concentration of the dispersion
to 20 wt. % and dispersing is continued for a further 5
minutes.
[0049] Examples 1, 2, 3 and 6 show the importance of a high filling
level during grinding. A high filling level during grinding with a
rotor/stator set leads to a reduction in the viscosity of the
dispersion.
[0050] Examples 3, 4 and 6 show the importance of the shear rate
for successful grinding. At a higher shear rate, even with a low
concentration of the predispersion, an equivalent product, or even
a product with a slightly lower viscosity, can be achieved.
[0051] Examples 10, 11 and 12 show that, with a higher
concentration of the silica, a higher viscosity is obtained.
[0052] Examples 13, 14 and 15 show that, in addition to the shear
rate and the filling level during grinding, the period of grinding
and the pH of the predispersion also have an influence. A longer
grinding period brings about a lower viscosity of the dispersion. A
reduction from pH 4.4 to 3.5 brings about a marked reduction in
viscosity for the same grinding period.
[0053] Examples 16 and 17 show that the addition of aluminium salts
clearly reduces the viscosity of dispersions containing silica.
When the process according to the invention is applied with high
shear rates, the viscosity of the dispersion can be reduced
surprisingly markedly. This can be seen particularly clearly from
Example 17. TABLE-US-00001 TAB. 1 Dispersing parameters and
physico-chemical data of the silica dispersions Predispersion
Predispersion Shear rate (approx.) Dispersion d.sub.50(v) Visc. 10
s.sup.-1 Visc. 100 s.sup.-1 Ex. AEROSIL wt. % pH s.sup.-1 wt. %
Additive pH nm mPas mPas 1 200 13.0 4.0 20000 12 NH.sub.4OH 5.3 130
1615 320 2 200 24.0 3.8 20000 12 NH.sub.4OH 5.3 130 50 32 3 200
28.5 3.7 20000 12 NH.sub.4OH 5.3 137 35 24 4 200 28.5 3.7 25000 12
NH.sub.4OH 5.0 128 9 8 5 300 28.5 3.6 25000 15 NH.sub.4OH 9.5 131 9
9 6 200 35.0 3.5 20000 12 NH.sub.4OH 5.3 104 12 11 7 200 35.0 3.5
20000 20 NaOH 10.0 81 40 35 8 200 35.0 3.5 20000 20 NH.sub.4OH 10.0
86 38 32 9 300 35.0 3.3 20000 22 NH.sub.4OH 10.3 91 70 53 10 90
35.0 4.0 20000 15 NH.sub.4OH 5.3 154 6 5 11 90 35.0 4.0 20000 20
NH.sub.4OH 5.3 155 26 15 12 90 35.0 4.0 20000 25 NH.sub.4OH 5.3 160
40 23 13 130 35.0 4.4 20000 15 NH.sub.4OH 5.3 165 39 20 14 130 35.0
4.4 20000 15 NH.sub.4OH 5.3 158 21 14 15 130 35.0 3.5* 20000 15
NH.sub.4OH 5.3 155 7 6 16 200 21.0 3.9 20000 20 NaOH, AlCl.sub.3
5.0 108 385 164 17 200 35.0 3.5 20000 20 NaOH, AlCl.sub.3 5.0 88 8
8 *Predispersion adjusted to 3.5 with dilute HCl
* * * * *