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Патент USA US2406465

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Patented Aug. 27, 1946
2,406,465 _
UNITED STATES‘ PATENT OFFICET
2,406,465
TITANIUM OXIDE PIGMEN T PRODUCTION
John Lewis Keats, Wilmington, Del., assignor to
E. I. du Pont de Nemours & Company, Wilming
ton, Del., a corporation of Delaware
No Drawing. Application January 9, 1942,
Serial No. 426,251
I
1
(01. 23-202)
17 Claims.
2.
.
This invention relates to the production of pig
1050° C., or above, the resulting products are in
substantially the rutile crystal form. Many proc
esses contemplating such type of anatase to rutile
conversion by high temperature calcination al
ready exist. In such instances, however, the po
ment-useful titanium compounds, and more par
ticularly to the manufacture of titanium oxide
pigments in substantially the rutile crystalline
form.
More speci?cally, the invention pertains to
tentially higher hiding power and tinting strength
novel methods for obtaining highly improved ru
of the higher refractive-index modi?cation are
tile titanium oxide pigments, by conversion of
not realized. The use of these excessive tempera
anatase, through treatment of said anatase at
tures causes sintering, grit and aggregate forma
elevated calcination temperatures, in the presence 10 tion and this results in objectionable particle size
of a precipitated titanium-oxygen compound
growth which is decidedly disadvantageous to sat
which acts as a rutile conversion promoter.
isfactory TiO2 pigment production. As a conse
Titanium oxide on X-ray analysis reveals three ,
quence, the resulting product is often wholly un?t
TiOz crystalline modi?cations—anatase, brookite
for many intended uses, especially in coating
and rutile, the respective indices of refraction of 15 compositions, such as paints, enamels and lac
which are 2.52, 2.65 and 2.71. Anatase and rutile
quers, wherein the pigment must possess satis
comprise the forms which are mostadaptable and
factory color, brightness and texture, as well as
useful for pigment purposes. Rutile raw pigment
high tinting strength and hiding power.
may be precipitated upon hydrolysis of titanium
chloride solutions while anatase raw pigment pre
cipitates upon hydrolysis of titanium sulfate solu
tions. After being subjected to the usual puri?ca
tion and washing treatments, calcination of the
_
It is among the objects of this invention. to
20 overcome these and other difficulties and disad
vantages characterizing prior rutile pigment pro
duction, and to provide novel procedures for ob
taining an improved form of rutile pigment hav
raw pigment precipitate, at temperatures in ex
ing completely satisfactory color or whiteness
cess of about ‘750° C. (and usually from about 25 characteristics, together with other equally satis
850-1000° 0.), develops its essential pigmentary
factory and essential physical properties such as
properties and provides the ?nal TiOz pigment.
texture and brightness, high tinting strength,
Although anatase has the lowest TiOz refrac
hiding power, and desired smallness and uniform
tive index and rutile the highest refractive index
ity of particle size. Particular objects of the in
(and consequently the greatest potential hiding
power), most present-day commercial T102 pig
30 vention include the provision of a novel method
ments are in the anatase modi?cation. The main
reason for this is that anatase production entails
procedures which are more economical and at
tractive for commercial exploitation. For in 35
stance, titanium sulfate solutions may be readily
obtained from the sulfuric acid attack or dissolu
tion of titaniferous ores, such as ilmenite. These
solutions are less corrosive toward plant equip
for obtaining an improved, relatively insoluble,
durable, weather-resistant rutile pigment, having
the above and othe'r essential characteristics, by
adding to an anatase hydrolysate a separately
prepared precipitated titanium-oxygen compound
adapted to promote or induce the conversion of
said anatase to rutile at a temperature below that
normally required to convert anatase tov rutile.
Another object is to provide a process for prepar
ment than the highly corrosive titanium chloride, 40 ing rutile TiOz pigments which overcomes'the
solutions from which rutile is derived. Further
disadvantages arising by reason of prior high
more, rutile processes require an extremely di?i~
temperature conversion processes. Other objects
cult and carefully controlled type of operation,
and advantages will be evident from the ensuing
which, with its accompanying corrosion and re
description of the invention.
lated problems, presents an extremely expensive, 45 These and other objects are attainable in this
less economical type of process, thereby render
' invention which embodies the discovery that an
ing such processes less attractive for wide com
excellent rutile pigment results from anatase con
mercial adaptation in T102 production.
version, if the anatase, and particularly a pre
When hydrous titanium oxide, such as is pre
cipitated, hydrated form thereof, is subjected to
cipitated in commercial processes from the hy 50 calcination in the presence of an added, sepa
drolysis of titanium sulfate solutions, is calcined
rately prepared titanium-oxygen compound pre
in the temperature range of from about 950° C.
cipitate which may be either in rutile crystal form
to about 1000” C., high quality titanium oxide pig
or in the form of an anatase having a rutile con
ments in the anatase crystal form are usually pro
version temperature below that'of commercially
duced. If the calcination is carried out at a high 55
er temperature, ranging to from, say 1025° C. to
produced anatase.
.
c
In' a more’speci?c‘ and preferred embodiment,
2,406,465
3
ions in solution to the trivalent state. The solu
tion was heated quickly to 95° C. by injection of
rutile titanium oxide pigment by calcining a pre
cipitated, hydrous form of anatase T102 at a tem- ‘ live steam and immersion of the container in a
boiling water bath and was then held at 95° C.
perature within a range which is normally em
to 98° C. for 30 minutes. Sulfuric acid equiv
w.
ployed in producing pigment anatase, after ad
al'ent. to 15% ofthe' weight of. the TiOz was added
mixing with the previously prepared anatase .hy'i
to‘ the suspension as a, 50% solution. After stand
‘ drolysate' a relatively small amount of a rutile ,
ing several hours, the suspension was ?ltered and
, conversion promoter, comprising precipitated, raw ,
' the- cake washed until the washings showed no
rutile titanium oxide.
testv for sulfate. ions with BaClz. The washed
Q the invention comprises obtaining an improved
,
In one practical and preferredadaptation;relai- ;
, precipitate, hereafter designated as raw rutile,
, tively pure, washed anatase raw pigment, such
was sl'urried with water to a concentration of 200
as is prepared from the hydrolysi’sof'a titanium
sulfate solution in accordance with, for‘ example,v "
* the commercial processes described in U". S‘. Re
issue Patents 18,854 or 18,790, admixedwith: a
small amount, say, from about 2% to 10%.‘of’
grams T102 per liter. I
'
Relatively pure anatase raw pigment, produced
'
the hydrolysis of titanium sulfate in accord
. ance- with U. S. Reissue Patent 18,854, was then
mixed with the above raw rutile seeding agent,
in‘the" ratio one part rutile to ten parts anatase
by weightpof 'I'i02. The resulting mixture was
filtered; dried' and calcined in a rotary furnace
at 950°‘ C. for 30'minutes. The calcined product
was substantially alliru‘tile (‘98%). A sample of,
the same anatase raw pigment, but containing
separately prepared titanium oxide which has .
been precipitated in the rutile crystalline‘ form.
Said rutile conversion promoter may comprise
the hydrolysate resulting from the hydrolysis of
a titanium chloride‘ solution, in accordance'with‘,
for‘ example, the procedures outlined‘ in U. S.
Patent 2,062,133. Seeding‘ of the anatase may
5 no raw rutile seed, showed no conversion to rutile
be- conveniently effected by blending. with the
seed material While in aqueous suspension, fol-1
lowing which agitation of the‘ resulting suspension
even after calcination at l_000° C. The strength
andicolorot the seeded product calcined at 950°
C. were’ distinctly superior to rutile pigments ob
is resorted to in order to effect intimate and"
tained by‘ calcining the unseeded‘ anatase raw
thorough’ admixture of the T102 particles" with
‘pigment
at temperatures above 1000° C‘.
each other, and then. ?ltering to remove excess.
water. The resulting‘ pigment cake then may be’ 30
Example II '
dewatered ‘by drying, if desired‘, or, if preferred;
may‘ be fed as a wet paste into a conventional
type of calciner, suchv as arotary or‘ muffle type.
of ‘furnace, and the seeded? mixture calcined under
Anatase raw pigment from the same: source as‘
that referred to- in Example I was desulfated by
neutralizing a slurry to a pH of 6.8' to 7.0 with
NH‘LOH‘ and washing out the sulfate ions. The
desultated anatase raw pigment was mixed with
substantially atmospheric pressure at tempera
tures ranging‘ from about 900° C‘. to 1000° Ca, or‘
at such temperature that the ?nal calcined
rutile. raw'pigment, prepared under the condi
product, upon X-ray analysis, is substantially
.tions- outlined in. Example I, in the ratio of one
completely in' the rutile crystalline form. Cale
part rutile to three parts anatase. The mixture
cination treatmentv for a time period: ranging 40 wasv then.’ calcined in a rotary furnace at 950° C.
from‘about 1 to 2- or 3 hours at‘ the indicated. tem—
forv 30. minutes.‘ The product was determined to
peratures will‘ usually suf?ce to develop‘ all' es.
be, entirely ‘converted to the rutile crystal form
scntia-I pi'gmentary' properties and substantially:
completely convert the Ti'Oz. to rutile‘. After'com’-~
. and. had tinting strength of 168 compared with
p-leti‘ng' the‘: calcination treatment, the calciner" '
discharge is‘ conventionally‘ cooled. and is then
ground, either in wet or dry condition, to- desired
pigment ?neness.
In order!‘ to" illustrate the invention more para
ti'cul‘arly, the following speci?c examples: are a
150 for commercial anatase. A like“ sample of
the desul-fated anatase raw pigment with no seed
present showed no conversion to rutile even after
calcination. at '1000-° C.
The above tinting strength values were deter
mined in accordance with the method describedv
by’ J... E. Booge and‘ H. E. Eastlack in the Paint,
given, it being’ understood that said examples are
not to be considered as placing any limitations
Oil- and Chemical Review, dated April 16, 1924.
or restrictions upon. the herein-described‘ inven
tion?
tion with certain. speci?c and preferred‘ embodi
The invention has been illustrated in connec
ments, thereof, entailing the use of speci?c tita
nium compounds or hydrolysates and particular
conditions, amounts, ratios and temperatures of
Example I
A raw rutile: product for seeding anatase raw
calcination, etc. Obviously, it is not t@ be con
strued- as limited thereto since variance there»
chloridev solution obtained by dilution of the re
distilled commercial anhydrous product. The hy-r 60 from may be had without departing from its
pigment was prepared by hydrolysis of titanium
underlying spirit and scope.
drolysi's-v was conducted according to the follow
ing conditions. Seed was prepared by precip
itating orthotitanic acid by neutralizing, with
NI’LlQH to: a pH of 6.0, a TiCl4 solution obtained
by diluting the redistilled- commercial. anhydrous
product.- The precipitatewas washed free of elec
trcl-yte and peptized by slurrying to a' concentra
tio‘niof 30 grams‘ Tioz‘per liter and0.3 normal.
with respect to- HCl- and heating the- suspension.
at 80° Cpfor 20 minutes. The sol thus formed
was added to the TiCl4. solution to be hydrolyzed
in an amount equivalent to 3% ‘on the
basis
and' the: concentration of the seededsolutionladr
justed to 110 grams TiO2 per liter. Powdered
zin’c‘ was added“ to reduce 01.5% of the titanium
,
As will. beevident, the invention is generally
applicable to all types of anatase titanium oxide
in order to promote or accelerate its conversion
65
to. substantially rutile during calcination or re
calcination treatment. It is- highly useful for
treating precipitated anatase raw pigment ob
tained. fromv the hydrolysis of titanium sulfate
solutions and/for converting said. anatase to rutile
through calcination by addition, prior to said cal
cination, of a relatively small amount of a dif
ferent form. of titanium hydrate, especially raw .
rutile, which functions as a promoter or acceler
ates-the desired rutile conversion. at- tempera
tures which are normally employed for develop
2,406,465
5
ing essential anatase T102 pigment properties,
e. g., from about 750° C. to 1000° C.
‘
Although my preferred form of seeding agent
comprises precipitated raw rutile pigment, pre
pared from the hydrolysis of titanium chloride or
nitrate solutions, other types of seeding agents,
some of which are not in the rutile but are in
6
. While calcination temperatures ranging from‘
substantially 900-1000° C. have been suggested as
useful herein, these are merely preferred, since
they more readily enable one to obtain optimum
results hereunder. .The use of any particular cal
cination temperature will depend upon the char
’ acter of the titanium oxide under treatment, the
substantially the anatase form when precipitated,
particular pigment properties desired to be devel
may be similarly usefully employed. The impor
oped in the ?nal product, and the extent of rutile
tant feature of any such non-rutile seeding agent 10 crystallinity which such product is to exhibit.
is that when calcined alone, it converts to rutile
As stated, the use of the indicated preferred 900
at temperatures lower than that at which the
1000° C. temperature range will afford optimum
main anatase raw pigment under treatment con
results under the invention for the production
verts when it is calcined alone. That is, because
of a- ?nished product substantially completely in
of its inherent nature or condition, the rutile pro 15 the rutile crystalline form. However, lower tem
moter readily converts to rutile at temperatures
peratures down to, say, I750 or 800° C., may be
below 10000 C. and preferably within a range of
used, if desired, and hence are contemplated. In
from about 600 to about 900° C., as distinguished
such instances, however, the extent of rutile con
from normal anatase raw pigment which usually
version will be found to decrease, especially if
requires temperatures in excess of 1000’ C. and 20 relatively small amounts of the seeding catalyst ,
of the order of above 1100° C. before any substan
are presentduring the heat treatment.
tial or complete conversion to rutile can be de
Again, while the invention has been described
tected upon X-ray examination. Other useful
asadapted particularly for the production of so
forms of rutile promoters comprise the raw pig-'
calledstraight or unextended forms of titanium'
ments resulting from the hydrolysis procedures
oxide pigments, it is also equally applicable to the
disclosed in the co-pending applications Ser.~No.
production of extended forms of such pigments.
283,052, ?led July 6, 1939, and'Ser, No. 283,051,
Thus, I contemplatethe production of titanium
?led July 6, 1939, in which I appear as co-inventor
oxide pigments extended with the various inor
with Henry M. Stark. Such raw pigments, be
ganic compounds, such as barium sulfate, calcium
I cause of their inherent ease of conversion to 30 sulfate, calcium carbonate, magnesium or other'
rutile, may be employed as rutile promoters when
silicates, etc., either precipitated upon or blended
admixed with the usual separately prepared ana
with the titanium oxide during its manufacture,
tase precipitates or already calcined or pigment
processing or ?nishing.
developed anatase. Also utilizable as rutile seed
As will be evident, the invention affords pro
ing agents are the reduced raw TiOz pigment
duction of a ?nished, vfully-developed titanium
products obtained from the mechanical disper
sion of titanium oxide raw pigment to reduce sec
ondary particle size, as contemplated more par_
oxide pigment converted to the desire rutile crys
talline form without the necessity of resorting to
the undesirably high temperatures heretofore re
ticularly in the co-pending application, Ser. No.
quired in obtaining prior converted rutile pig
426,250, ?led January 9, 1942, in which I appear 40 ments. The improved nature of the pigment of
as co-inventor with James H. Peterson.
While I prefer to incorporate the rutile seed
ing agent into the original raw pigment by inter
this invention is evident when the fact is con
sidered that the avoidance of the high conversion
temperatures previously required prevents any
objectionable sintering from occurring and ad
mate association of the two TiOz components re 45 versely affecting the color, uniformity, particle
sults by mixing hydrolysates which remain sub
size, texture, tinting strength and hiding power
stantially wet from the time of precipitation to
of the ultimate pigment. Pigments obtained by
admixture, dry mixing of the seeding agent with
calcining at an excessively high temperature are
the anatase may be resorted to.
characteristically coarse and gritty in nature and,
Although I preferably employ in my preferred 50 prior to use, must be subjected to prolonged
procedure rutile and anatase mixed in the ratio
grinding treatments in an effort to reduce to some
of from about 2-10 parts of rutile per 100 parts of
degree the aggregates formed during such sin
anatase, this range may be extended, and if de- ’
tering. By this invention, this additional dis
sired may comprise from about 1-25 parts of ru
advantage is completely eliminated and a direct
tile per 100 parts of anatase,
55 process is provided in lieu thereof for obtaining
From the foregoing, it will be apparent that the
‘an inherently soft and smooth-textured pigment
invention is especially suitable for promoting con
having excellent tinting strength, hiding power
version of anatase TiOz hydrolysates obtained
and color, together with complete freedom from
mixing aqueous slurries of each, whereby inti
from the commercial process described in U. S.
objectionable sintered aggregates or coarse par
Reissue Patent 18,854, and that it is equally ap 60 ticles.
‘
plicable to the treatment and conversion of raw
The titanium oxide products prepared accord
pigment anatase generally resulting from the hy
ing to my invention will be usefulin all ?elds in
drolysis or neutralization of titanium salts, espe
which white titanium oxide pigments are em—
cially titanium sulfate solutions. Similarly, it
ployed, as, for instance, in interior and exterior
may be applied to the treatment and conversion 65 coating compositions, such as paints, enamels,
of the hydrolysate resulting from the processes
lacquers, etc., in linoleum and ‘similar products,
described in U. S. Reissue Patent 18,790. Al
in paper, rubber compounding, in delustering
though precipitated anatase, obtained from the
rayon and other arti?cial silk materials, and in
hydrolysis of titanium salt solutions, comprises a
various other ?elds. Because of its relatively
preferred form of product for treatment and con
high hiding power and pigment density, my rutile
version in accordance with my invention, treat
product will be found to be particularly useful
ment is also contemplated of a previously cal
‘wherever formulations are required which employ
cined or pigment-developed anatase, in accord
relatively low pigment volume.
'
1
ance with my invention, to obtain a converted
I claim as my invention:
,
form of rutile T102.
.
75. 1. A process for obtaining a rutile titanium
2,406,465
.
7
.
8.
oxide pigment through calcination and wconven
sion of anatase; whichcomprises admixing with
9. A process for producing an improved rutile
titanium oxide pigment which comprises calcin
previously prepared anatase TiO2 av minor ‘
amount?'of asep'arately prepared titanium-oxy
C.-1000° C. an anatase hydrolysate after admix
ing at a temperature ranging from‘ about'75'0°
ing with a separately prepared minor amount of
gen compound rutile promoter which when cal
a rutile conversion promoter, comprising a sepa
cined' alone at a temperature not in excess of
rately precipitated raw pigment titanium oxide
compound which exhibits the rutile crystalline
substantially 900° C.,' exhibits substantially the
' X-ray- diffraction pattern of rutile, and then cal
pattern when calcined'a'lone at a substantially‘
lower temperature than the major titanium ox
cining the resulting mixture. at a temperature
sufficient to develop the pigment properties there-'
of but not exceeding about l000°‘C.
ide component undergoing calcination treatment;
'
10. A process for obtaining a rutile: titanium
2. A process for obtaining a rutile titanium
oxide pigment by conversion of vanatase com
prising calcining at temperatures ranging vfrom
oxide pigment through conversion of anatase by
calcinationvat a relatively low conversion tem
about 800 to 1000° C. an anatase hydrolysate
after mixing with a minor amount of an added
perature, comprising calcining said anatase after
separate preparation, in the presence of a minor
separately precipitated titanium-oxygen‘ com
amountuof separately prepared hydrous raw ru
tile promoter, and eii'ecting saidcalcination at a
temperature ranging from about 750° C. to not
exceeding about 1000” C.‘
pound, which when calcinedalone at tempera-p
turesv ranging from about 600-900° C. exhibits
substantially the X-ray diffraction pattern of
,A process forobtaining a rutile titanium
rutile.
7
11. In a process for the production of rutile ti
oxide pigment which comprises subjecting a
tanium dioxide pigment from anatase titanium
dioxide, the'steps comprising calcining at tem
peratures ranging from about '750—1000° C. an
' separately precipitated raw anatase, titanium ox
ide to calcination at a temperature ranging from
about 750° C. to not exceeding substantially 1000°
C‘. after admixture with an added, minor amount
intimate‘mixture of separately prepared titanium
oxides, the major component of the T102 mixture
being in the anatase crystal form and making
precipitated titanium-oxygen compound which
up the larger percentage of said mixture, while
exhibits the rutile VX-raydiifraction pattern when
the minor component present in a lesser percent
calcined alone at temperatures/not in excess of 30
age is added thereto in the uncalcined condition
substantially 1000” C.
r
V
_
and is characterized by showing the rutile X-ray
4. A process for obtaining a rutile titanium
diffraction pattern upon calcination alone at a
oxide pigment through calcination conversioniof
substantially lower temperature than is required
anatase which comprises subjecting a mixture of
to develop the rutile X-ray diffraction pattern
raw pigment anatase and a minor amount of
for the major component.
‘ '
added, precipitated raw pigment rutile to calci
12. A process for obtaining an improved rutile
nation at ,a temperature ranging from substan—
titanium oxide pigment through conversioniof
of a rutile conversion promoter, comprising a
tially '750-1000° C. until the pigment properties
thereof become developed and said anatase be
anatase which comprises intimately mixing in .
comes c-onvertedto rutile.,
raw pigment anatase recovered from the hydroly
_
_
7
‘
7
'
'
aqueous suspension previously-washed purl?ed'
~:
5. Aprocess. for obtaining an improved rutile
titanium oxide pigment which comprises convert
ing precipitated raw'anatase to rutile by calcin
sis of a titanium sulfate solution, with separately- >
prepared raw pigment rutile recovered from the
hydrolysis ‘of a titanium chloride solution, em
ploying in said mixture from about 2-10 parts of
rutile per 100 parts of anatase, ?ltering said sus
pension to remove excess water therefrom, and
then calcining the recovered raw pigment mixture
at temperatures ranging from about 900-1000° C‘.
. ing the same at atemperat'ure ranging from sub
stantially 900~1000° C. after mixing therewith a
separately prepared rutile conversion catalyst,
comprising a small amount of an added, precip
itated and uncalcined, raw rutile pigment.
6. A process for obtaining an improved rutile
titanium oxide pigment which comprises ,con- .'
verting precipitated raw pigment anatase recov
ered from the hydrolysis of a titanium sulfate
solution to‘ rutile by calcining said anatase at a
temperature ranging from about 900—1000° 0., in
to develop the pigment properties thereof and
effect complete conversion of said anatase to
rutile.
13. The method of producing rutile titanium
the presence of from about 2-10 parts of added, ' K
dioxide pigment which comprises hydrolyzing a
titanium salt solution normally yielding anatase
titanium dioxide upon hydrolysis under such con
ditions that the hydrolysate formed can be con
rutile per 1000 parts of the anatase.
verted to rutile titanium dioxide upon calcina
'7. A process for obtaining an improved rutile
tion at a temperature not exceeding 1000"v C.,
titaniumvoxide pigment which comprises con
verting precipitated raw pigment anatase recov 60 admixing at least 1 part of said uncalcined hydrolysate with 100 parts of a second titanium salt
ered from the hydrolysis of a titanium salt so-‘
solution hydrolysate consisting of anatase ti-e
lution to rutile by calcining said anatase at a
tanium dioxide, and calcining the resulting mix
temperature ranging from about 800~1000° C'. in
ture at a temperature not exceeding 1000” C.
the presence of‘ from about 1-25 parts of added,
separately prepared uncalcined, precipitated raw
is. A method for the conversion of precipitated
titanium dioxide having the crystal structure of,
anatase, and normally calcining to anatase, to‘
titanium dioxide having the crystal structure of
rutile, which comprises calcining‘ the titanium
dioxide having the crystal structure of anatase in
the presence of separately prepared titanium vdi
oxide having the crystal structure of rutile, added
after precipitation, the calcination beingv carried
separately prepared uncalcined, precipitated raw
rutile per'lOO parts of anatase.
,
8; A process for producing an improved rutile
titanium oxide pigment which comprises subject
ing a T102 mixture, comprising from about 2 to
10 parts of added, separately prepared uncal
cined, precipitated raw rutilej pigment per 100
parts of precipitated raw anatase pigment‘ re
covered from the hydrolysis of a titanium sul
fate solution, to .calcination at a temperature
of substantially 950°‘ C‘. for about 30‘ minutes.
. out at a temperature not exceeding about 1000*"0;
is
15. A method for the conversion ofprecipitatedw
9
2,406,465
titanium dioxide having the crystal structure of
anatase, and ‘normally calcining to anatase, to
titanium dioxide having the crystal structure of
rutile, which comprises calcining the titanium
dioxide having the crystal structure of anatase
in the presence of separately prepared hydrated
titanium dioxide precipitate having the crystal
structure of rutile, added after precipitation, the
calcination being carried out at a temperature not
exceeding about 1000° C.
16. A method for the conversion of precipitated
titanium dioxide having the crystal structure of -
10
low temperature, added after precipitation, the
calcination being carried out at a temperature
not exceeding about 1000° C.
17. A method for the conversion of precipitated
titanium dioxide having the crystal structure of
anatase, and normally calcining to anatase, to
titanium dioxide having the crystal structure of
rutile, which comprises calcining the titanium
dioxide having the crystal structure of anatase
10 in the presence of a raw pigment substance se
lected from the group consisting of separately
prepared titanium dioxide having the crystal
anatase, and normally calcining to anatase, to
structure of rutile and separately-prepared hy
titanium dioxide having the crystal structure of
drated titanium dioxide which shows a de?nite
rutile, which comprises calcining the titanium 15 rutile crystal structure upon calcination at a rel
dioxide having the crystal structure of anatase in
atively low temperature, added after precipita
the presence of separately prepared hydrated ti-_
tion, the calcination being carried out at a tem
tanium dioxide which shows a. de?nite rutile
perature not exceeding about 1000° C.
crystal structure upon calcination at a relatively
JOHN LEWIS KEATS.
Certi?cate of Correction
August 27, 1946. I
Patent No. 2,406,465.
Q
I
'
JOHN LEWIS KEATS
It is hereby certi?ed that errorappears in the printed speci?cation of the above
numbered patent requiring correction as follows: Column 7, line 57, claim 6, for
1“ 1000 parts” read 100 parts ; and that the said Letters Patent should be read with this
(éofli'irection therein that the same may conform to the record of the case in the Patent
ce.
Signed and sealed this 29th day of October, A. D. 1946. ‘
[um]
LESLIE FRAZER,
First Assistant Commissioner 0 f Patents,
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