CA1089630A - Process for the preparation of pigmentary bright primrose yellow bismuth vanadate - Google Patents

Abstract

ABSTRACT

Process for the preparation of pigmentary primrose yellow bismuth vanadate by reacting bismuth nitrate with an alkali vanadate under controlled conditions to obtain a bis-muth vanadate gel which is then subjected to aqueous digestion to produce pigmentary monoclinic bismuth vanadate.

Description

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BACKGROUND OF THE INVE~TION
Bismuth vanadate occurs in nature in an ortho-rhombic form commonly called pucherite. Pucherite is a dull yellow-brown mineral, which is not useful as a pig-ment. Pucherite is slmilar in color to limonite, a dull yellow-brown iron oxide, which has never been produced as a bright, high intensity pigment despite repeated attempts.
Various references have described the synthetic preparation of bismuth vanadate, for example, I. M. Gottlieb and C. R. Rowe, "Preparation and Thermal Properties of Bismuth Orthovanadate", Thermal Analysis~
Vol. 2, Proceedings Third ICTA DAVOS (1971), pp. 303-311;
R. S. Roth and J. ~. Waring, "Synthesis and~Stability of ~;
Bismutotantalite, Stibiotantalite and Chemically Slmilar AB04 Compounds", The American Mineralogist, Vol. 48 (Nov. - Dec., 1963)g pp. 1348-56; H. E. Swanson et al., "Standard X-Ray Diffraction Powder Patterns", National Bureau of Standards Report, No. 7592 (Aug., 1962);
Eduard Zintl and Ludwig Vanino, "Process For The Manu-facture Of Pure Bismuth Vanadate"; German Patent No. 422,947 (1925). However, as in the case of yellow iron oxide, none of the above references provide a process which is successful for use in the preparation of bis-muth vanadate which is useful as a bright yellow pigment.
SU~ARY OF THE INVENTION
The present invention relates to a process ~or preparing pigmentary bismuth vanadate which process com-prises mixing a solution of Bi(N03)3 5H20 in nitric acld 30 with a solution of alkall vanadate in an aqueous base ~
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selected from sodium hydroxide and potassium hydroxide, :~
to precipitate a bismuth vanadate gel suspended in a solution containing dissolved alkali nitrate, wherein the molar ratio of Bi3 to V043 is from about 0.90:1.00 to about 1.10:1.00 and wherein the normalities of the acid and base solutions are adjusted prior to mixing so that the pH of the mixture will be from about 1.0 to about ~ .
11.0~ preferably from about 1.5 to 4.0; adjusting the pH
of the suspension to about 2.2-6.0 with an aqueous base . ~
10 selected from sodium hydroxide and potassium hydroxide ~ . .
if the pH is less than about 2.2, or with an acid :
selected from nitric acid or sulfuric acid if the pH is greater than about 6.o; removing the gel from the sus- .. ....... ..
pension; washing the gel with water until it contains about 10 percent or less alkali nitrate, based on the theoretical yield of bismuth vanadate; heating the gel in water at about 60-200C. for at least 0.2 hour; holding the pH within the range of from about 2.2 to 6.o with an aqueous base selected from sodium hydroxide and potassium 20 hydroxide if the pH is less than about 2.2 or with an .
acid selected ~rom nitric acid, hydrochloric acid~ hydro- ~ :
bromic ac.id, sul~uric acid or phosphoric acid if the pH
is greater than about 6.3 to convert it to pigmentary monoclinic bismuth vanadate; ad~usting the pH of the . . .
suspension to 8.o to 9.5 with an aq.ueo~base selected .~.
from sodium hydroxide or potassium hydroxide and main~
taining the suspenslon at this pH at a temperature of 50-100C. ~or 15 to 30 minutes; and filtering, washing and drying the pigment. .. .
DETAILED DESCRIPTION OF_T~IE INVENTION

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ThiS ln~entlon rel~tes to ~ proce~ ~or the preparation of pigmentary monoclinic b~gmuth v~nadate.
By "pi~mentary~' iæ meant a bi~muth vanadate ~hich i8 bright prlmr~se yellow, sin~le ph~3e monoclinlc cryætal-line a~ detexmined by X-ray di~fractiony having high intensity, good strength and good light~a~tness. ~-A6 indicated, pigm~nt~ry bi~muth ~anadate i~
en~irely ln the monoclinlc crystal phase a~ determined u~g X-ray dif~raction. ~-ray di~action mea~urement~
are made wlth a Debye~Scherrer* powder camera using C ~
radiation ~rom a Norelco* Type l2045B unit at ~0 kV/~OmA
and a 6-hour exposure.
The bismuth vanadate o~ the present invention exhibits a large increa~e in re~lectance in the range o~
the vislble spectrum ~rom 450 to 525nm which showA th~t it iæ primrose yellow in color and has high intenælty and good strength. Reflectanre iæ used herein as a com-parison of the specular and di~u~e re~lect~nce o~ a kno~n st~n~rd with the sample to be te~ted using Type I
illumin~tionO Re~lectance i8 measured on a Cary* Model l~
spectrophotometer equipped with an lntegrating sphere, palnted with Eastm~n* white re~lectanQe paint No~ 6080.
The sample to be te~ted 15 prepared by mixing lO weight percent of the bismuth vanadate o~ the presen~ lnvention wlth 90 weight pereent o~ barium ~ul~ate~ Eastman Re~lectance Standard No~ 6091, until a uniform powder ls obtained. Then the r~Mectance o~ the known standard Eastman Re~lectance Standard No. 6091, is compared with that o~ the ~ampleO In the range Or the Yi~ible spectrum ` ~ -from 450 to 525nm~ th~ ~ample conta~nlng the biæmuth * denotes trade m~rk . . . , : . .......... .. . . . ....... ~, . .
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~anadate o~ the present lnvention exh1bits an increa~e o~
at least about 65 re~lectance units on a scale in which the Eastman Reflectance Standard No. 6091 exhibitæ a re~lectance of 100 units over the entire vi~ible spectrum~
In ~act, many o~ the sampleæ exhibit increases in re~lec-tance o~ at least about 70 units or greater~ The greater the mag~itude o~ the change in re~lectance within the speci~ied æpectral range, the greater the intensity and ~trength o~ the sample.
The lntensity and light~a~tne~s o~ pigmentary bismuth vanadate in a paint are measured ~rom palnt dr~w-down~ made to complete hiding~ The paint ls made by dis-per~ing the pigment into a binder in a 2:1 ratio by -:
weight of pigment to binder using a Hoover* muller. The binder is compo~ed o~ 98.9 weight percent #2 transparent , varnish made by Superior Varnish and Drler Company, -:
MerchantsvillQ, ~ew Jersey; 1 weight percent~ a~ lead, o~ lead Nuodex~ drier (contain~ 24% lead), and 0~1 weight :
percent, as manganese~ of m~nganese Nuode~ drler (con-tains 6% mangane~e)0 The drawdownæ are dried ~or about ~ ~
72-120 hour~ ~n A well-ventilated room at 25C. and leæs : .:
than about 50% humldlty. ~ .
Intensity i~ determlned by the green ~ilter re~lectanc~ o~ a masstone drawdown. Inten~ity is expres~ed ~ .
as a percent o~ green ~ilter re~lectance me~sured with a ~ : :
Gardinar* Multipurpose Re~lectometerg Ser~al No. 40 (Gardiner Laboratory, Inc., Bethesda, Maryland)l using a white re Msct&nce ~t~ndard at a ~etting o~ 86.1 and light from a General Electric* CVS pro~eetor lamp passed throu~h the green tristimulu~ ~ilter ~upplied with the Gardiner * denote~ trade mark ~, ~

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~eflectometer. The Gardiner Multipurpose Reflectometer is described in National Bureau of Standards ~esearch Paper RP 1345, dated Nov., 1940, by Richard S. Hunter, and National Bureau of Standards Circular C429, dated July 30, 1942, by Richard S. Hunter. The higher the percent reflectance of the drawdown, the more intense the color. The intensity of the bismuth vanadate of the present invention is such that it has a green filter reflectance of at least about 60 percent.

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Lightfastness is determined after the dried paint drawdowns have been continuously exposed for 44 hours in an Atlas Color Fade-Ometer~ Type FDA P. A ~ -Gardiner Multipurpose Reflectometer is used as described above to measure green filter reflectance before and after exposure. Measurements are taken within one hour prior to exposure and again within one hour after exposure.
The percent lowering of reflectance after exposure based on initial reflectance is percent Fade-Ometer~ darkening. -The lower the percent Fade-Ometer~ darkening, the better the lightfastness of the pigment. The bismuth vanadate of the present invention will generally exhibit a percent Fade-Ometer~ darkening of about 11 percent or less, preferably about 7 percent or less, after 44 hours of exposure.
The surface area of the bismuth vanadate is about 2-22 m2/g. For use in film forming compositions, ~ -such as paints and inks, a surface area of about a-22 m2/g.
is preferred. For use in plastic compositions, a surface area of about 2-4 m2/g. is preferred because of increased 30 heat stability. The surface area is measured on a ~ ;

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Perkin-Elmer Shell* Model 212C Sorptometer using the technique recommended b~ the manufacturer.
According to the process o~ thi~ in~ention pigmentary bismuth vanadate i5 prepared by mixln~ a solution of up to about 0.8M BitN03)3 5H20 in up to about

4.oN nitric acid, preferably about O.~M Bl(~03)3'5H20 in about l.ON nitric acid, with a ~olution of alkali vana-date (sodium ~anadate or potassium vanadate)~ preferably up to about 0.32M ~a3V04, in up to about 1.6N aqueous baæe selected ~rom sodium hydroxide or potaæ~ium hydro- -xide, more preferably about O.~M Na3V04 in about l.ON
sodium hydroxide. Upper concentration limits for the re~ctant solutions are determined by solubility; however, control o~ equimolar incremental mixing is easier with more dilute solutions. The temperature o~ mlxing is not critic~l and mixing can be carried out at temperatures of ~rom lO to 100C~ but it is preferred that the ~olution~ be mixed at 20 to 30C.
The molar ratio o~ Bi3+ to V043 can be about -;~
0~90:1.00 to 1.10:1.00, preferably about 0~98:1.00 to 1,05:1.00, which indicates that e~ther an eæces~ of B~3~
or ~0~3 i8 allowable. me symbol vo~3 is used herein to denote a pentavalent ~ranadium species in an a~ueou~
~olution, but lt doeæ not mean a speci~ic pentavalent ~nadium ~pecies pre~ent at a glven p~ and vanadium concentrationO
The normalitie~ o~ the acid and base solution~
~re adJu~ted prior to mixing ~o that the p~ o~ the reaction mixture will be about l~O-lloO~ A pH o~ about 1.5-4,0 is preferred because it yield~ a gel ~rom which a * denotes trade m~rk , ~ . .
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plgmentary monoclinic bismuth vanadate product having optimum intensity and/or light~astness can be obtained.
The preferred method of mixing the solutions is in a ~low reactor which gives a very rapid incre-mental combination under high turbulence conditions.
Incremental combination means that small, essentially stoichiometric quantities are reacted at one time.
This prevents relatively large gradients and stoichio-10 metric imbalance that result when large quantities of ~;
reactants are mixed at once. Such imbalance results in undesirable side reactions. Apparatus which conveniently achieve this result are tee mixers or flow reactors.
When the solutions of Bl(N03)3 5H20 and alkallvanadate are mixed under the above conditions, a suspen-sion of bismuth vanadate gel in alkali nitrate (sodium nitrate, potassium nitrate, or both) solution is ~ormed.
Bismuth vanadate gel as used herein means a hydrous, . .
X-ray amorphous bismuth vanadate precipitate containing o~cluded water.
The gel should not be removed from the suspen-slon until the pH o~ the suspension has been stabllized at about ~.2-6.0, pre~erably about 3.0-3.5. Thus, i~ the pH Or the suspension is less than about 2.2, it may be ad~usted upward with aqueous sodium hydroxide or potassium -hydroxide, and if it is greater than about 6.0, it may be ad~usted downward with an acid selected ~rom nitrlc acid or sulfuric acid. Prompt ad~ustment of the pH of the suspension to the final range listed above is advisable, although under certain circumstances the : .

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bismuth vanadate gel is stable for up to several hours at room temperature prior to pH adjustment.
The gel is then removed ~rom the suspension, -preferably by filtration. The gel is collected and, if it contains more than about 10 percent alkali nitrate based on the theoretical yield of bismuth vanadate, the gel must be washed with water until it contains about 10 percent or less.
When an excess of vanadium is used in the forma- -tion of the gel, the gel must be washed prior to the above aqueous digestion to remove any alkali nitrate in excess of 10 percent by weight based on the theoretical yield of bismuth vanadate. The suspension containing the gel is then heated at a temperature of ~rom about 60C. to about 200C. for at least 0.2 hour, and preferably at a temperature of ~rom 90C. to about 100C. ~or about one to two hours to convert the gel to pigmentary mono-clinic bismuth vanadate. Durlng the aqueous digestion the pH of the suspension must be maintalned at a pH
of from 2.2 to 6.o, and pre~erably ~rom a pH of 3.0 to 3.5, by adding a suitable acid or base as needed. Acids suitable ror use lnclude nitric, sulfuric, hydrochloric, hydrobromic or phosphoric. Bases sultable for use include aqueous sodium hydroxide or potassium hydroxide.
It wlll be understood that if temperatures above about 100C. are used, the heating must Oe carried out undçr pressure. In additlont when the ratio of Bi to V04 is 0.9:1 to 1.0:1.0, the digested pigment must be washed a~ter the heatln~ step by suspending it in water for 15 to 30 minutes at 50C. to 100C. while holdlng the pH

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6~ -at 8.o to 9.5 with an aqueous base selected from sodium hydroxide and potassium hydroxide. Pre~erably the digested pigment will be washed in wa~er for 15 minutes at 70C.
while holding the pH at 9.0 with an aqueous base selected from sodium h~droxide and potassium hydroxlde. When a molar excess of bismuth is used in the formation of the -~
gel, it is not necessary to reduce the alkali nitrate~ -content of the gel prior to digestion, although removal or reduction of the alkali nitrate from the gel prior to digestion is ~ermissible.
After digestion is complete the pigment is filtered, washed and dried, e.g., at about 130C. The product is bright primrose yellow bismuth vanadate which is entirely in the monoclinic phase as identified by X-ray dif~raction.
In the process as described above the pH
adJustment can be made a~ter the gel has been removed from the suspension. However, in order to easily adJust the pH of the gel, the gel should be resuspended in water. Once the pH of the gel has been properly ad~usted, the gel under certain circumstances is stable for up to about a week at room temperature.
It is possible to prepare the alkali vanadate solution by dissolving a pentavalent vanadium compound ;

25' Na3vo4~ Na4V2O7~ NaVO3, or K VO4 in an aqueous base selected from sodium hydroxide and potassium hydroxide.
After the bismuth vanadate pigment has been prepared by the process of this inventlon, its light-3 fastness may be improved by encapsulation in a dense ~. ..:, .- :' ,.

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amorphous coating of silica or a treatment with aluminum p~rophosphate. Coatings can be applied in accordance with known processes, such as those taught in Re 27`,818 (reissue of U. S. Patent 3,437,502) to Werner; U. S.
3,639,133 to Linton; U. S. 3,370,971 to Linton; and of u. s. 3,885,366 to Iler.

A mixture is prepared by combining the following -ingredients in a mixing tee:
(i) Bi(NO3)3.5H2O (10.93 lb.) dissolved in 12.78 1. of 4 .ON HN03, then diluted to 51.1 1. with water, and (ii) V2O5 (2.05 lb.) dissolved ln ~1.94 1. of water containing 7.210 lb. NaOH, then diluted to 51.1 1. with water to give a solution of sodium vanadate plus sodium hydrDxide.
The mixing tee has inside diameters of 0.118 in. for the bismuth nitrate opening, 0.192 in. for the sodium vanadate openlng, and 0.1~2 in. for the exit. The bismuth nitrate enters on the leg. The solutions are mixed in about 15 minutes when a pressure of about 15 psi is applied across the tee. Sufficient HNO3 is added to ingredient (i) or aqueous NaOH to ingredient (ii) so that the pH of the mix-ture of the two will be about 1.5 to 2Ø The mixture ~-~
is squlrted into a 45 gal. tank containing 7 gal. of water which has been ad~usted to a pH of 2.2 with HN03. The ~;
contents of the tank are stirred ~or several minutes, and the pH is ad~usted to 3.2 with 2.0N NaOH. The contents 3n are then stirred for 15 minutes,filtered, and washed with , ', . .
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20 gal. o~ water and re~iltered. me bismuth vanadate gel .

is collected ~rom the ~ilter cloth, and is stirred into a tank containing 70 lb. of water, which ha~ been adjusted to a pH o~ 3.1 with HN03. The contents of the tank are heated to 95C. in about 40 minutes and held at that temperature and a p~ o~ 3.1 ~or 120 minutes. The product~ pigmentary bismuth vanadate, is isolated by ~iltration, washed twice with 20 gal. o~ water, and dried ~ -.
~t 1~0~.
The above procedure is repeated four times to -~
yield about 28 lb. o~ pigment, Twenty-five pound~ o~ the -pi~ment are dispersed in 104 lb. o~ ~ater containing 567 g.
o~ Fi~cher* 28% ~odium silicate æolution (~0-42 ~aume~ by passing it through a Gaulin* Submicron Homogenizerg first at 2000 p~i, and again at 5000 psi. me mixture i~ then heated to ~nd held at 90C. and adJusted to a pH o~ 9.6 w~th 2.0N NaOH. A solution of 14.~97 lb. o~ eher 28%
~odium sllicate in 62.5 lb. o~ water is added to the mixture over a ~our-hour pcriod. At the same time, a ~
20dilute sulfuric acid solution (2.299 lb. of ~oncentrated -~ -8ul~uric acld in 71~25 lb. o~ water) iæ added to the mixture at a rate such that the pH o~ the mixture drops .
to 9~4 in about 45 mlnutes. The pH o~ the mixture i~
immediately raised to 9.6 wlth 2.0N MaOH. mis pH control procedure i~ continued over the ~our-hour ~ilicate ;j ~-addition period.
A~ter the ~our-hour addition period, the pH
i~ reduced to 9.0 wlth H2S04, held ther~ ~or 60 minutes, and then reduced to 7Ø Then, while the mixture i~
still at 90C~, a solutlon o~ 3.75 lb, of A12(S04~3.18H20 * denotes trade mark ,:: ,,' ,.

o in 15 lb. of water is added over a ten-minute period and the pH falls to 2.0-3Ø The pH is then raised to 6.o with 2.ON NaOH in about 20 minutes. The product is filtered hot, washed twice with 30 gal. of water and dried at 140C. Chemical analysis and electron micrographs show that the pigment particles have been coated with silica. Intensity and lightfastness measurements on the pigment before and after coating are shown in Table I.

TABLE I

1 0 - _Befor~ Coatin~ 1~ After Coatin~ lJ

Intensity ~ightfastness Intensity Lightfastnes~

X Green Filter ~ Fade-Omete~D . % Green Filter % Fade-Omete~

Re~lec~ance Darkening Reflectance Darkenin~ :

67.9 6.0 67.4 2.4 )Pcrcent reflectance change after ~4 hours of Fade-Ometer~ exposure ~

This example shows that encapsulating bismuth ' vanadate pigment with silica improves its lightfastness as determined by Fade-Ometer~ exposures.

A mixture is prepared by combining the following ingredients in a 1 mm ID mixing tee at 40 psi over a period of about two minutes:
(1) Bi(N03~3.5H20 (166.0 g.) dissolved in 800 ml. of 2.ON HN03 and diluted to 1610 ml. with water, and (li) Na3V04 (60.66 g.) dissolved in 1610 ml.
of l.ON NaOH.
Sufficient HN03 is added to ingredient (i) or aqueous NaOH to ingredient (ii) so that the pH of the mixture o~
the two will be about 1.5-2Ø The mixture is squirted 3n into a large beaker containing 1200 ml. o~ water adJusted to a pH of 2.7 with HN03. The contents of the beaker are stirred and the pH is adjusted to 3.4 with 0.5N NaOH. The contents are then stirred for 10 minutes, filtered, washed with 1000 ml. of water, and refiltered. A bismuth vanadate gel is collected from the filter paper, is stirred into a beaker containing 3000 ml. of water, is brought to a boil, is adJusted to a pH of 3.0-3.5 using HN03 or NaOH and is held at that temperature and pH for 120 minutes. The product, bismuth vanadate pigment, is isolated by ~iltration, washed by suspendin~ in 1000 ml.
.
of water, refiltering, and ~inally suspended in 2400 ml.
of water.
The suspension is then heated to 85C. and ~ `~
aluminum sulfate (18.0 g. A12(SO4)3.18H2O in 240 ml. water) ~ ~ -is added. The pH of the suspension is adjusted to 4.0 ~ith 1.0N NaOH, and sodillm pyroph~sphate (6.0 g. in 120 ml.
;
of water) and aluminum sulfate (6.o g. A12(SO4)3.18H20 in ~ -120 ml. of water) are added to the suspension. The pH ;~
is adjusted to 7.0 with aqueous NaOH over a thirty-minute period. The suspension is filtered, washed and dried at 110C. to yield an aluminum phosphate coated yellow pigment. Intensit~ and li~htfastness before and after . : .
coating are shown in Table II. ~`

~ABLE II
_ , Befcre Coatin~ Ir After Coatin~
Intensity LightfastnessIntensity Lightfastness ) Z Green Filter Y. Fade-Ometer~% Green Filter Y Fade-Omete~ -Reflectance Darkenin~Reflectance Darkenin~
66.1 6.7 64.g 3.9 `~

l)Percent r,eflectance change after : 44 hours of Fade-Ometer~ exposure This example shows that treatment o~ bismuth :;' '`

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A mixture is prepared by combining the following ingredients in a 1 mm ID mixing tee at 40 psi over a period of about two minutes: -(i) Bi(NO3)3.5H2O (40.0 g.) dissolved in 200 ml.of 2.0N HNO3, then diluted to 405 ml. with water,and (ii) Na3VO4 (15.16 g.) dissolved in 200 ml. of 2.0N NaOH, then diluted to 400 ml. with water.
Sufficient HNO3 is added to ingredient (i) or aqueous NaOH to ingredient (ii) so that the pH of the mixture of the two will be about 1.5 to 2Ø The mixture is squirted into a 4 liter beaker containing 1200 ml. of water which has been ad~usted to a pH of 3.0 with HN03.
The contents of the beaker are stirred for one minute and the pH is adjusted to 3.4 with 0.5N NaOH. The mixture is than stirred for 15 minutes, filtered, washed with 500 ml.
of water, and refiltered. A bismuth vanadate gel (Samp].e A) is collected from the filter paper, and is stir~red into a beaker containing 1600 ml. of water and the pH o~ the mixture is ad~usted to 3.3 to 3.4 wlth HBr or NaOH. The mixture is boiled for 90 minutes while the pH is held at ~
3.3 to 3.4. A bismuth vanadate plgment is isolated by ~;
filtration, washed with 1000 ml.of water, and heated to 130C. until dry.
Sample B is prepared according to the procedure ~0 used for Sam~le A except that 42.0 g., instead of 40.0 g., .~-, , 3(~

of Bi(N03)3.5H20 is used.
Sample C is prepared by combining the following ingredients in a 1 mm ID mixing tee at 40 psi over a period of about 2 minutes:
(iii) Bi(N~)3 5H2o (88.o g.) dissolved in 52 ml.
of concentrated HNO3 and 400 ml. of water, then diluted to 800 ml. with water, and (iv) V2O5 (15.0 g.) dissolved in 600 ml. of water containing 53.0 g. of NaOH, then diluted to 800 ml. with water to give a solution of sodium vanadate plus sodium hydroxide.
Sufficient HNO3 is added to ingredient (iii) of aqueous NaOH to ingredient (iv) so that the pH of the mixture of the two will be about 1.5 to 2Ø The mixture is squirted into a 4-liter beaker containing 1200 ml. of water which has been adjusted to a pH of 2.2 with HN03. ; ~ ;
The contents of the beaker are stirred for one minute and the pH is ad~usted to 3.3 with 0.5N NaOH. The mixture 20 is then stirred for 15 minutes, filtered, washed with -~;-500 ml. of water, and refiltered. A bismuth vanadate gel is collected from the filter paper and is stirred into a beaker containing 500 ml. of water. The pH of the mixture is ad~usted to 3.3 to 3.4 with HNO3 or NaOH and is boiled for 90 minutes while the pH is kept constant at 3.3 to 3.4. A bismuth vanadate pigment is isolated by filtration, washed with 500 ml. of water, and heated at 130C. until dry.
Sample D is prepared according to the procedure 30 used for Sample A, except that 46.o g., instead of 40.0 g., ., . . . . ,................ ,.. ,, . .. . .............. :- .
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~U~630 of Bi(N03)3.5H20 is used.
Sample E is prepared by combining the following ingredients in a 1 mm ID mixing tee at 40 psi over a period of 2 minutes.
(v) Bi(N03)3.5H20 (72.0 g.) dissolved in 56 ml. concentrated HN03 and 400 ml.
water, then diluted to 800 ml. with water, and (vi) V205 (15.0 g.) dissolved in 600 ml.
water containing 53.30 g. NaOH, then diluted to 800 ml. with water to give a solution of sodium vanadate plus sodium hydroxide.
Sufficient HN03 is added to ingredient (v) or aqueous NaOH to ingredient (vi) so that the pH of the mixture o~ the two will be about 1.5 to 2Ø The mixture is squirted into a 4-liter beaker containing 1200 ml. of water whlch has been ad;usted to a pH of 2.2 with HN03.
The contents of the beaker are stirred for one minute and .
20 ~ the pH is ad~usted to 3.3 with 0.5N NaOH. The mixture is then stirred for 15 minutes and ~iltered. A bismuth vanadate gel is collected ~rom the filter paper. The gel is stirred into a beaker containing 500 ml. of water and the pH o~ the mixture is ad~usted to 3.1 with HN03 or NaOH. The mixture 1s boiled for 120 minutes while its pH is held at 3.1. The bismuth vanadate pigment is .. . .
lsolated by ~iltration and resuspended ln 400 ml.
of water. The temperature is then raised to 50C. and ; the pH raised to 8 . o and held there for 10 minutes. A
.

3 bismuth vanadate pigment is isolated by filtration, .
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1~18~t~30 washed with 500 ml. of water9 and heated to 130C. until dried.
TABLE III

3~ 3_ Intensity Lightfastness Bi ~o VO4 Z Green Fi.].ter % Fade-Om~te~
Samples Molar R~tio Reflect~nceDarlccning Aq~eous .

A 1.00/1.00 71.2 4.5 B 1.05/1.00 69.0 . 6.4 C 1.10/1.00. 73.9 8.0 : :
D 1.15/1.00 74.2 l4.5 .:
E 0.90/].. 00 61.7 4.7 -~:

1 0 , ~ ,, reflectance chan~e after ;
44 hour3 of Fade-Ometer~ exposure A mixture is prepared by combining the ~ollowing-~
ingredients in a mixing tee: -(i) Bi(N03)3.5H20 (10.731 lbs.) dissolved in 12.78 liters of 4.oN HN03, then diluted to 51.1 liters with water, and (ii) V205 (2.049 lb.) dissolved in 31.94 liters of water containing 7.210 lb. NaOH, then diluted to 51.1 liters with water, to give -a solution of sodium vanadate plus sodium hydroxide.

The mixing tee has inside diameters of 0.118 in. ~or the bismuth nitrate opening, 0.192 in. ~or the sodium vanadate opening, and 0.192 in. for the exit. The bismuth nitrate enters on the leg. The solutions are mixed in about 15 minutes when a pressure of about 15 psi is applied across the tee. Su~ficient HN03 is added to ingredient (i) or aqueous NaOH to ingredient (ii) so that the pH of the mixkure of the two will be about '~ ' ' ' '': ', ':, '~,.,' .

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1.5 to 2Ø The mixture is squirted into a 45 gal. tank containing 7 gal. of water which has been ad;usted to a pH of 2.2 with HNO3. The contents of the tank are stirred for several minutes, and the pH is adjusted to 3.2 with 2.ON NaOH. The contents are then stirred for 15 minutes, filtered and washed with 20 gal. of water and refiltered.
Seven 100 g. samples of the gel are respectively suspended in seven 300 ml. portions of water. The suspensions are heated to a boil and held at that temperature for two hours. The pHs of the suspensions are brought to the values shown in Table IV for samples A to G by additions of HNO3 or aqueous NaOH, as necessary, and held there during the two-hour boiling period. All the samples are then filtered, resuspended in 200 ml.
of water, re~iltered and dried at 130C.
The crystal phase, intensity and lightfastness for the samples are given in Table IV.

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-~(3~9~30 A mixture is prepared by combining the following ingredients in a mixing tee:
(i) Bi(NO3)3 5H2O (277.5 g) dissolved in 694.3 ml of 4.lN HNO3 and diluted to 2750 ml with water.
(ii) V2O5 (51.6 g) dissolved in 1718 ml of water containing 178 g of NaOH, then diluted to 2750 ml to give a solution of sodium vanadate plus sodium hydroxide. ~ -Sufficient HNO3 is added to ingredient (i) or aqueous NaOH to ingredient (ii) so that the pH o~ the mix-ture of the two will be about 1.5-2Ø The mixture is squirted into a strike jar containing 1500 ml of water which has been ad~usted to a pH of 2.2 with HNO3. The mixture is stirred and the pH adjusted to 3.2 with O.5N
NaOH. The stirring is continued for 15 minutes. The pH is adjusted to 3.1 with lN HNO3 and heated to 95C for 3 hrs.
with pH kept between 2.8 and 3.5 using 0.5N NaOH or l.ON
HNO3. The bismuth vanadate precipitate is filtered, washed to 2000Q resistance and dried. The product has 66.2% green ~ ~
fllter reflectance and 4.5% Fade-Ometer darkening. ~-, .
A mixture is prepared by combining the following ~ -ingredients in a 1 mm ID mixing tee at a pressure of 40 p5i .
; over about a 2-minute period. - -(i) Bi(NO3)3 5H2O (82.0g) dissolved in 400 ml of 2N HNO3 then diluted with 400 ml of dis-tilled water.

3o (ii) Na3VO4 (30.3g) dissolved in 400 ml of 2N NaOH

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and diluted with 400 ml of distilled water.
These components give a molar ratio of Bi3 to V043- of 1.025:1.00.
Sufficient HNO3 is added to ingredient (i) or NaOH to ingredient (ii) so that the pH of the mixture of the two will be between 1.5 and 2Ø The mixture is squirted into a 4Q beaker containing 1200 ml of distilled water which had been adjusted to a pH of 2.7 with HNO3.
The mixture is stirred and adjusted to pH = 3.4 with 0.5N
NaOH and stirred at room temperature for 10 minutes. The suspension is filtered and washed. The bismuth vanadate gel is converted to monoclinic bismuth vanadate by hydro-thermal digestion at pH 3.0 to 3.5 at 100C. Twelve-month Florida exposure ln thermosetting acrylic lacquer showed good performance versus commerclal yellow pigment.

A mixture is prepared by combining the following ingredients in a 1 mm ID mixing tee at a pressure of 40 psi over about a 2-minute period.
(i) Bi(NO3~3-5H2O (80.5g) dissolved in 203 ml of ;
4.1N HNO3 and diluted to 800 ml with dis- :-tilled water.
(ii) V2O5 (14.8g) dissolved in 345 ml of 2.3N -(NaOH) and diluted to 800 ml with distilled water.
Sufficient HNO3 is added to ingredient (1) or NaOH to ingredient (ii) so that the pH of the final mixture is 3.2. The mlxture is squirted into a 4Q beaker c~n-taining 1200 ml of distilled water which had a pH = 5.8.
3 The suspension is stirred and pH monitored at 4.o-6.o during ,' ~, ,.

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most of the strike. Final pH is 3.2. The pH is adjusted immediately to 3.0 with HN03 and stirred at room tempera-ture for 30 minutes. The suspension is filtered and washed. The gel is resuspended at pH = 3.1 and converted to monoclinic bismuth vanadate at 100C.
Intensity of the product as measured by green ~ilter reflectance is 67.3% and % darkening after 44 hr.
Fade-Ometer exposure is 5.8%.

A mixture is prepared by combining the following ingredients in a 1 mm ID mixing tee at 15 psi to give a molar ratio of Bi3 to V043 of 0.95:1.00.
(i) ~i(NO3)3-5H2O (76.0 g) dissolved in 400 ml of 2N HN03 and diluted to 800 ml.
(ii) V205 (15.0 g) dissolved in 600 ml of dis-tilled water containing 52.0 g NaOH and diluted to 800 ml to give a solution of sodium vanadate and sodium hydroxide.
Suf~icient HNO3 is added to ingredient (i) or ~ ~;
NaOH to ingredient (ii) so that the pH o~ mixture will be between 1,5 and 2.5. The mixture is squirted under 15 psi ~ -pressure into a LIQ beaker containing 1200 ml of distilled water adjusted to pH 2.2 with dilute HN03. The contents -o~ the beaker are stirred, a~ter 2 minutes the pH is ad~usted to 3.2 with 2N NaOH and stirred 15 minutes.
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About 1/3 o~ the suspended gel is removed and is designated Sample A (See Table V). The remainder ls ~ -~
filtered and divided into 2 parts identi~ied as Samples B
and D, respectively. Sample B is filtered only and Sample D is washed once in 200 ml o~ distilled water.

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~9 Sample A's pH is ad~usted to 3.2 and it is heated to 90-100C with pH maintained between 2.8 and 3.5 at a volume of 700-800 ml for 2-3 hours. After conversion of gel to crystalline material the pH is raised to 8.5 for 15 minutes with temperature ~60C. Bismuth vanadate is then filtered, washed twice and dried at 110C.
Samples B and D are resuspended, respectively, in 700-800 ml of distilled water and pH adjusted to 3.2.
Samples B and D are converted at the same temperature, time and pH as Sample A. After conversion, Sample B is divided in half. One half retains identification as Sample B, is filtered, washed and dried at 110C. The other half is identified as Sample C,has pH adjusted to 9.0 at tempera-ture >60C for 15 minutes, is filtered, washed and dried at 110C. -~
After conversion, Sample D is divided in half.
One half retains identification as Sample D, is filtered, washed and dried. The other half is identif~ed as Sample E and is treated in the same fashion as Sample C.
Sample F is prepared according to the procedure of Sample A except that 78.5 g of Bi(N03)3-5H20 is used, givlng a molar ratio of Bi3 to ~043 of 0.98: 1.00. The gel suspension is filtered and divided in half. One half retains identification Sample F and the other half is identi~ied as Sample G and is washed once in 250 ml of dis-tllled water. i Sample F is converted according to the procedureof Sample A, is filtered, washed and dried at 110C.
Sample G is converted according to the procedure of Sample A, is filtered, washed and dried at 110C.

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This example shows that where the molar ratio Or Bi3 to V043 is less than 1.00:1.00, NaN03 concentra-tion must be reduced below 44% and excess vanadium must be removed by washing the pigmentary bismuth vanadate with a baslc solution.

A mixture is prepared by combining the following ingredients in a 1 mm ID mixing tee at 15 psi to give a molar ratio of Bi3 to V043 of 1.00:1.00.
(i) Bi(N03)3 5H20 (80.0g) dissolved in 400 ml of 2N HN03 and diluted to 800 ml with distilled water.
(ii) Na3V04 (30.3 g) dissolved in 400 ml of 2N NaOH and diluted to 800 ml with distilled water.
Suf~icient HN03 is added to ingredient (i) or NaOH to ingredient (ii) so that the pH of the mixture will be between 1.5 and 2.5. The mixture is squirted under 40 psi pressure into a 4Q beaker containing 1000 ml o~
distilled water which had been adjusted to pH 3.3 with 2N HN03. The gel suspension is stirred for a minute and the pH adJusted to 3.3 with 0.5N NaOH. The mixture is stirred for 10 minutes at pH = 3.3. About 1300 ml of the mixture is removed and identified as Sample H in Table V.
The remainder of the mixture, identified as Sample J~is filtered and washed twlce with ~500 ml of distilled water.
Sample H is diluted to 2000 ml, pH is adjusted to 3.3, heated at 100C for 4 hrs. to convert the gel to crystalline material, ~iltered, washed and dried at 110C.
Sample J is converted according to procedure of .:.

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, . , , . , :.. , Sample H except for 3 hrs. instead of 4. The crystalline material is filtered, washed and dried at 110C.
Sample K is prepared by the procedure of Sample H except 88.o g Bi(N03)3 5H20 is used and Na3V04 is prepared from V205 and NaOH. This gives a molar ratio of Bi3 to V043 of 1.10:1.00. The gel suspension is divided in half. One-half retains identification Sample K;
the other half is identified Sample L.
Sample K gel suspension pH is adjusted to 3.2, :
lOtemperature is raised to 98-100C for 2-1/2 hours, pH is ~-maintained at 3.3. Product is filtered, washed and dried at 140C.
Sample L is filtered and resuspended in distilled water to give 700 ml volume. Sample L is converted, filtered 3 washed and dried by the procedure of Sample K.
This example shows that where the molar ratio ~;
of Bi3 to V043 is equal to or greater than 1.00:1.00, NaN03 need not be removed and a basic wash is not required. ~ ;

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Claims (26)

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

1. A process for preparing a pigmentary bright primrose yellow monoclinic bismuth vanadate comprising:
A. mixing a solution o* Bi(N03)3.5H20 in nitric acid with a solution of alkali vanadate in an aqueous base selected from sodium hydroxide and potassium hydroxide, to precipitate a bismuth vanadate gel suspended in a solution containing dissolved alkali nitrate, wherein the molar ratio of Bi3+ to VO43- is from about 0.90:1.00 to 1.10:1.00, and wherein the normalities of the acid and base solutions are adjusted prior to mixing so that the pH of the mixture will be from about 1.0 to 11.0;
B. adjusting the pH of the suspension to about 2.2-6.0 with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 2.2, or with an acid selected from nitric acid and sulfuric acid if the pH is greater than about 6.0, C. removing the gel from the suspension;
D. washing the gel with water until it contains about 10 percent or less alkali nitrate, based on the theoretical yield of bismuth vanadate, E. heating the gel in water at about 60-200°C.
for at least about 0.2 hour adjusting the pH of the sus-pension, if required, to about 2.2-6.0 with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 2,2, or with an acid selected from nitric acid, hydrochloric acid, hydrobromic acid, sulfuric acid, and phosphoric acid if the pH is greater than 6.0 to convert it to monoclinic bismuth vanadate pigment;

F. adjusting the pH of the suspension on to 8.0 to 9.5 with an aqueous base selected from sodium hydroxide and potassium hydroxide and holding at this pH at a tempera-ture of 50-100°C for fifteen to thirty minutes, and G. filtering, washing and drying the pigment.

2, The process of Claim 1 wherein the molar ratio of Bi3+ to V043- is from about 0.90:1.00 to 1.00:1.00.

3. The process of Claim 1 wherein the molar ratio of Bi3+ to V043- is from about 0.98:1.00 to 1.00:1.00.

4. The process of Claim 2 wherein the pH in Step B is adjusted to about 3.0-3.5 and maintaining the pH
at 3.0-3.5 in Step E.

5. The process of Claim 4 wherein the gel is heated in water at about 90-100°C for about 1-2 hours.

6. The process of Claim 4 wherein the pH of the suspension i adjusted to 9.0 and the suspension held at 70°C for fifteen minutes in Step F.

7. The process of Claim 4 wherein the normali-ties of the acid and base solutions in Step A are adjusted prior to mixing so that the pH of the mixture will be from about 1.5 to 4.

8. A process for preparing a pigmentary bright primrose yellow monoclinic bismuth vanadate comprising:
A. mixing a solution of Bi(N03)3.5H20 in nitric acid with a solution of alkali vanadate in an aqueous base selected from sodium hydroxide and potassium hydroxide, to precipitate a bismuth vanadate gel suspended in a solution containing dissolved alkali nitrate, wherein the molar ratio of Bi3+ to V043- is from about 0098:1.00 to 1.00;1.00, and wherein the normalities of the acid and base solutions are adjusted prior to mixing so that the pH of the mixture will be from about 105 to 4;
B. adjusting the pH of the suspension to about 3.0-3.5 with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 3.0, or with an acid selected from nitric acid and sulfuric acid if the pH is greater than about 3.5;
C. removing the gel from the suspension, D. washing the gel with water until it contains about 10 percent or less alkali nitrate, based on the theoretical yield of bismuth vanadate;
E. heating the gel in water at about 90-100°C
for about one to two hours adjusting the pH of the sus-pension, if required, to about 3.0-3.5 with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 3.0, or with an acid selected from nitric acid, hydrochloric acid, hydrobromic acid, sulfuric acid, and phosphoric acid if the pH is greater than 3.5 to convert it to monoclinic bismuth vanadate pigment;
F. adjusting the pH of the suspension to 9.0 with an aqueous base selected from sodium hydroxide and potassium hydroxide and holding at this pH at a temperature of 70°C.
for fifteen to thirty minutes, and G. filtering, washing and drying the pigment.

9. A process for preparing a pigmentary bright primrose yellow monoclinic bismuth vanadate comprising:
A. mixing a solution of Bi(N03)3'5H20 in nitric acid with a solution of alkali vanadate in an aqueous base selected from sodium hydroxide and potassium hydroxide, to precipitate a bismuth vanadate gel suspended in a solution containing dissolved alkali nitrate, wherein the molar ratio of Bi3+ to VO43- is from about 1.00:1.00 to 1.10:1.00, and wherein the normalities of the acid and base solutions are adjusted prior to mixing so that the pH of the mixture will be from about 1.0 to 11.0;
B. adjusting the pH of the suspension to about 2.2-6.0 with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 2.2, or with an acid selected from nitric acid and sulfuric acid if the pH is greater than about 6.0;
C. removing at least a portion of the clear solu-tion from the suspended gel;
D. heating the gel in water at about 60-200°C.
for at least about 0.2 hour adjusting the pH of the sus-pension, if required, to about 2.2-6.0 with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 2.2, or with an acid selected from nitric acid, hydrochloric acid, hydrobromic acid, sulfuric acid, and phosphoric acid if the pH is greater than 6.0 to convert it to monoclinic bismuth vanadate pigment; and E. adjusting the pH of the suspension to 8.0 to 9.5 with an aqueous base selected from sodium hydroxide and potassium hydroxide and holding at this pH at a tempera-ture of about 50-100°C. for about fifteen to thirty minutes;
and F. filtering, washing and drying the pigment.

10. The process of Claim 9 wherein the molar ratio of Bi3+ to VO43- is from about 1.00:1.00 to 1.05:1.00.

11. The process of Claim 9 wherein the pH in Step B is adjusted to about 3.0-3.5 and maintaining the pH
at 3.0-3.5 in Step D.

12. The process of Claim 9 wherein the gel is heated in water at about 90-100°C. for about 1-2 hours.

13. The process Or Claim 9 wherein the normalities of the acid and the base solutions are adjusted prior to mixing 80 that the pH of the mixture will be from about 1.5 to 4.

14. The process of Claim 9, 10 or 11 in which the gel removed in Step C is washed prior to heating according to Step D.

15. The process of Claim 12 or 13 in which the gel removed in Step C is washed prior to heating according to Step D.

16. A process for preparing a pigmentary bright primrose yellow monoclinic bismuth vanadate comprising:
A. mixing a solution of Bi(N03)3.5H20 in nitric acid with a solution of alkali vanadate in an aqueous base selected from sodium hydroxide and potassium hydroxide, to precipitate a bismuth vanadate gel suspended in a solution containing dissolved alkali nitrate, wherein the molar ratio of Bi3+ to V043- is from about 1.00:1.00 to 1.1:1.00, and wherein the normalities of the acid and base solutions are adjusted prior to mixing so that the pH of the mixture will be from about 1.5 to 11.
B, adjusting the pH of the suspension to about 2.2-6.0-with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 2.2 or with an acid selected from nitric acid and sulfuric acid if the pH is greater than about 6.0;

C. removing the gel from the suspension;
D. washing the gel with water;
E. heating the gel in water at about 60-200°C. for greater than about 0.2 hour, adjusting the pH of the sus-pension, if required, to about 2.2-6.0 with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 2.2, or with an acid selected from nitric acid, hydrochloric acid, hydrobromic acid, sul-furic acid, and phosphoric acid if the pH is greater than 6.0 to convert it to monoclinic bismuth vanadate pigment; and F. filtering, washing and drying the pigment.

17. The process of Claim 16 wherein the amount of alkali nitrate retained in the gel is less than 10%
based on the theoretical yield of bismuth vanadate.

18. The process of Claim 17 wherein the molar ratio of Bi3+ to V043- is from about 1.00:1.00 to 1.05:1.00.

19. The process of Claim 17 wherein the pH in Step B is adjusted to about 3.0-3.5 and maintaining the pH
at 3.0-3.5 in Step E.

20. The process of Claim 17 wherein the gel is heated in water at about 90-100°C. for about one to two hours.

21. The process of Claim 17 wherein the nor-malities of the acid and the base solutions are adjusted prior to mixing so that the pH of the mixture will be from about 1.5-4.

22. A process for preparing a pigmentary bright primrose yellow monoclinic bismuth vanadate comprising:
A. mixing a solution of Bi(NO3)3.5H2O in nitric acid with a solution of alkali vanadate in an aqueous base selected from sodium hydroxide and potassium hydroxide, to precipitate a bismuth vanadate gel suspended in a solution containing dissolved alkali nitrate, wherein the molar ratio of Bi3+ to V043- is from about 1,00:1.00 to 1.10:1.00, and wherein the normalities of the acid and base solutions are adjusted prior to mixing so that the pH of the mixture will be from about 1.0 to 11.0:
B. adjusting the pH of the suspension to about 2.2-6.0 with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 2.2, or with an acid selected from nitric acid and sulfuric acid if the pH is greater than about 6.0;
C. heating the suspension at about 60-200°C.
for at least about 0.2 hour, adjusting the pH of the suspension, if required, to about 2.2-6.0 with an aqueous base selected from sodium hydroxide and potassium hydroxide if the pH is less than about 2.2 or with an acid selected from nitric acid, hydrochloric acid, hydrobromic acid, sulfuric acid, and phosphoric acid if the pH is greater than 6.0 to convert it to monoclinic bismuth vanadate pigment, and D. filtering, washing, and drying the pigment.

23. The process of Claim 22 wherein the molar ratio of Bi3+ to V043- is from about 1.00:1.00 to 1.05:1.00.

24. The process of Claim 23 wherein the pH in Step B is adjusted to about 3.0-3.5 and maintaining the pH
at 3.0-3.5 in Step C.

25. The process of Claim 23 wherein the gel is heated in water at about 90-100°C. for about one to two hours.

26. The process of Claim 23 wherein the normalities of the acid and base solutions are adjusted prior to mixing so that the pH of the mixture will be from about 1.5-4.