Patented Aug. 19, 1952 2,607,659 UNITED STATES PATENT OFFICE PROCESs FoR PREPARING TITANATE . PGMENTS Frank O. Rummery, Baltimore, Md., assignor to Theporation Glidden of Ohio Company, Cleveland, Ohio, a cor No Drawing. Application December 1, 1948, serial No. 62,965 4 Claims. (CI. 23-51) 2 This invention relates to an improved process As indicated above, I have found that lead for preparing pigmentary lead titanate, and re titanate (PbTiO3) can be prepared directly, and lates more particularly to the use of pigmentary in a pigmentary state of good quality, by calcin dioxide as one of the raw materials ing an intimate mixture of pigmentary titanium used in said process. dioxide and a reactive lead compound, which Heretofore, lead titanate (PbTiO3) pigments liberates lead oxide during the calcination. The have been made by reacting titanium dioxide calcination is carried out in an oxidizing, or at (or a compound capable of yielding this oxide) east non-reducing, atmosphere at a temperature With lead oxide at an elevated temperature, the below about 750 C., and preferably at tempera conditions being such that a crude lead titanate tures between about 600° C. and 750° C. The Was first formed after which the crude product mixture which is to be so calcined should prefer was further treated to convert it to a pigmentary ably be an intimate mixture of the finely-divided state. Usually such processes have involved two ingredients. The lead oxide or reactive lead calcinations, the first being -at a selected low compound particles should preferably be finer temperature suitable for bringing about the s than about 0.5 micron and when lead oxide is formation of the crude product, and the second used it may be in either the rhombic or tetrag being at a higher temperature found suitable for onal modification. The titanium dioxide should developing the desired pigmentary qualities. In also be in particles less than about 0.5 micron in One of the recently issued United States patents size and may be in either the anatase modifica On Such a process, the patentee states that he had tion or the rutile modification. I particularly Sought in vain for a single temperature capable prefer to use titanium dioxide pigment of the of bringing about both of these ends. anatase structure in particles between about 0.15 I have now found that a single calcination and 0.4 micron in size. When rutile titanium can be employed to produce pigmentary pigment is used, I prefer to have the titanates when the titanium dioxide which is 25 particle size between about 0.1 and 0.3 micron. employed as one of the reactants is already in The mixture of titanium dioxide pigment and a pigmentary State. My discovery of this and lead oxide or other reactive lead compound is other benefits flowing from the direct use of made up to contain at least equal molar propor titanium dioxide pigment makes it possible to tions of TiO2 and PbO and preferably should provide a simple process for preparing lead titan contain at least a small excess of titanium di ate pigments. oxide pigment over the one-to-one ratio. I Accordingly, it is an object of this invention prefer a ratio of about 1.2 moles of titanium to provide a process for preparing lead titanate dioxide pigment to each mole of lead oxide, when pigment directly from titanium dioxide pigment pigment of the PbTiO3 type is being prepared, by calcining it with lead oxide or other corn but leaded titanium dioxide pigments may also pound of lead which yields lead oxide during the be prepared in which the molar ratio of TiO2 calcination...... to PbO is up to about 5 to 1 or higher. It is a further object to provide a process in The lead oxide should all be in the reactive Which a single calcination may be used to pre state. That is, when lead oxide per se is used pare lead titanate pigment from titanium dioxide it should not contain metallic lead, and to ensure pigment and a lead oxide-yielding compound 40 freedom of metallic lead, I prefer to treat the of lead...... lead oxide with nitric acid, thereby converting It is another object to prepare a stable, light the metallic lead to lead nitrate which is, in insensitive lead titanate pigment by the direct turn, converted to lead oxide during the calcina calcination of an intimate mixture of titanium tion. Lead compounds which yield lead oxide dioxide pigment with lead oxide or other re 45 during calcination may be similarly or otherwise active lead compound. - . treated to ensure the provision of lead oxide free It is another object to prepare a lead titanate of metallic lead. , pigment having an excess of titanium dioxide By having all the lead oxide in a reactive Over a monomolecular ratio thereof to lead oxide, 50 State, and by having a small excess of titasai II. the excess titanium dioxide being in a pig dioxide over the requimolar proportions, e3,6 mentary condition and useful in developing titanates of the PbTiO3 type which are produces durable pigmented coating compositions. by the calcination are highly stable in color aid These and other objects will be apparent from quality. They are not light-sensitive (that is, do the following description of the invention. 55 not turn dark on prolonged exposure to Sun

2,607,659 3 4. light); and are quite stable when employed in so that there were present 43 pounds of TiO2 and their ultimate intended uses as pigment in a 100 pounds of PbO. The rutile pigment had a Surface-coating film. Similar properties, and tinting strength of 1650 and an average particle characteristics obtain in the leaded titanium diameter of 0.15 micron. The litharge contained dioxide pigments. I attribute these characteris Only trace quantities of impurities and Only ticS and properties, at least in part, to the use traces of metallic lead. Its mean particle size of titanium dioxide pigment as one of the re was 0.3 micron. The slurry was treated with actants. The titanium dioxide which reacts With mixed acid containing 1.4 pounds H2SO4 and 2.0 the lead oxide during calcination is already in a pounds HNO3, and heated moderately to convert Stable crystalline modification before reaction. 0. any possible free lead to lead nitrate or lead Sul OCCurs and is not required to undergo at that fate. The slurry was deWatered, dried, and pull time as great a change in its basic crystallization verized, then placed in a calciner and heated for to produce a stable lead titanate as would be one and one-half hours in the temperature range necessary if the titanium dioxide raw material : from 675 to 725° C. The materials Were con Were in a form of hydrated Ortho- or meta-titanic 5 verted to a form of high quality lead titanate acid Such as has been used in other prior meth pigment which had high tinting strength, good Ods of manufacture. Furthermore, the exceSS color quality, and contained a Small amount of titanium dioxide is also in a stable pigmentary lead sulfate. Crystal form initially and its conversion to a Eacample 3 pigmentary state is not a consideration which 20 Finely ground lead nitrate Was mixed enters into the Selection of the calcining ten thoroughly with calcined anatase pigment which perature. In other words, by - starting with had an average particle size of 0.35 micron and titanium dioxide which is already in either of a tinting strength of 1300. There were present the stable forms which experience has shown in the mixed powder 164 pounds of Pb(NO3)2 to exist in pigmentary titanium dioxide, the low 25 and 40 pounds of TiO2. The mixture was heated temperature calcination to Which I. Subject the in a rotary calciner for one-hour between 600° mixture has only to serve the function of bring and 700° C. A lead titanate pigment Was formed, ing about chemical combination of the titanium of high tinting strength and good color quality. dioxide and the lead oxide. In this respect my treatment differs from prior treatments where 30 Eacd.imple 4 tWO calcinations Were used since my single cal Calcined rutile pigment having a mean particle cination brings the lead titanate reaction prod diameter of 0.20 micron and a tinting strength uct directly to a stable crystalline structure which of 1635 was slurried in so that there was manifests desirable pigment characteristics. To present 37 pounds of TiO2 in 22.5 gallons of the best of my knowledge, this result has never Water. To this slurry Was added a slurry of basic previously been obtained in a single calcination. lead carbonate which contained 100 pounds of It is already known that for Some ultimate uses 2PbCO3Pb(OH)2 in 60 gallons of water. To this of lead titanate pigment, it is beneficial to in was added 12.5 pounds of a 10% solution of clude minor proportions of lead sulfate. When H2SO4. The slurry was mixed thoroughly and I desire to introduce lead sulfate into a lead 40 filtered. The moist filter cake Was placed in titanate or a leaded titanium dioxide calcination a rotary kiln and heated in the temperature range mixture, I may omit the treatment of the lead 720°,-750° C. for one hour, during which time the Oxide With nitric acid and add Sulfuric acid to pigmentary titanium dioxide reacted with the the mixture in an amount sufficient to convert basic lead carbonate and Sulfuric acid to form a all of the metallic lead to lead sulfate and to 45 PbTiO3-PbSO4 pigment. The product was of Convert any additionally desired amount of lead good color and high tinting strength. Oxide to lead Sulfate. Any reactive lead compound which liberates Eacample 5 lead oxide during the calcination may be used A dry mechanical mixture was made from 75 in place of or in combination with lead oxide 50 pounds of high grade commercial lead oxide, free per Se. For instance, lead nitrate or basic lead of metallic lead, of average particle diameter carbonate I2RbCO3Fb(OH)2] may be employed 0.15 micron, and 135 pounds of pigmentary ana to provide Some or all of the requisite quantity tase titanium dioxide of average particle diameter of lead oxide. 0.25 micron. The tinting strength of the anatase My process is illustrated by, but not restricted 55 pigment was 1300 as determined by the Reynolds to, the following examples: - constant volume method. The mixture was Eacample 1 calcined in a rotary kiln between 700° and 735° C. for one hour in an oxidizing atmosphere. A 111.5 pounds of high grade commercial lead very high quality pigment resulted. oxide constituting essentially 100% PbO and 80 In summary, it will be understood that in ac having an average particle size of 0.5 micron, cordance with the principles of my invention, lead Was mixed thoroughly in the dry state with 48 titanate pigment is prepared by calcining to pounds of calcined anatase pigment having an gether lead Oxide as one ultimate reagent, all average particle diameter of 0.25 micron and a of which is in a reactive condition, and pigmen tinting strength of 1300 as determined by the 65 tary titanium dioxide. The proportions of tita Reynolds Constant Volume Method. The mix nium dioxide to lead oxide may be in a molar ture Was calcined in a rotary kiln between 700° ratio of one to One (preferably 1.2 to one) to and 735 C. for one hour in an oxidizing atmos form PbTiO3, or may be in any higher ratio to phere, and the materials reacted to form a pig form What I term leaded titanium dioxide pig mentary grade of lead titanate which was 70 ments. In the case of such higher ratios, the eminently Suited to the manufacture of outdoor lead oxide becomes combined with titanium di metal finishes. oxide just as completely as when a 1.2 to one Eacample 2 ratio prevails, and is equally effective in propor A mixed slurry was made of a pigmentary tion to its concentration in the final product. grade of rutile titanium dioxide and pure litharge 75 The advantages flowing from my use of pigmen 2,607,659 5 6 tary titanium dioxide are various, as here in the lead oxide is free of elemental or metallic dicated: lead and hence is all in a reactive state. A. Chemical reaction between the lead oxide Having described my invention, What I claim and titanium dioxide can be effected at low cal S. cining temperatures (below 750 C.) to produce 5 1. The method of preparing lead titanate pig pigmentary lead titanate in a single direct Step. ment directly in a single calcination from pig B. Any excess titanium dioxide present beyond mentary titanium dioxide and reactive lead oxide the amount required to react with all of the lead which consists of: providing an intimate mixture oxide is in a stable pigmentary condition and composed essentially of calcined, pigmentary ti thereby avoids the difficulties, which arose in prior O tanium dioxide having a particle size below about processes and products from incompletely cal 0.5 micron and reactive lead oxide having a par cined or non-pigmentary titanium dioxide. ticle size below about 0.5 micron, Said nixture C. The chemical reaction between the lead being free of metallic lead and being proportioned oxide and titanium dioxide goes to completion so as to have therein at least one and not more readily at the low calcining temperatures and than about 1.2 mols of TiO2 per mol of lead oxide, ensures complete conversion of the lead oxide and calcining said mixture directly to lead tita to lead titanate. nate pigment by heating it between about 600 C. D. A simple treatment of the lead oxide With and 750° C. in a non-reducing to oxidizing at nitric acid ensures that all of the lead oxide is mosphere until all of the lead oxide has become in a reactive state. combined chemically with the titanium dioxide E. Lead titanate pigment free of lead Sulfate and the resulting lead titanate has a particle size can be produced directly, or if the presence of of desired pigmentary dimensions below about lead sulfate is desired, it can be incorporated 0.5 micron. without impairing the completeness of the lead 2. The method as claimed in claim 1 wherein titanate reaction. the pigmentary titanium dioxide is in the anataSe Typical pigment properties of lead titanate modification and has a particle size between about . pigments of the PbTiO3 type prepared in ac 0.15 and 0.4 micron, Cordance With this invention are: 3. The method as claimed in claim 1 wherein Reynolds tinting strength.------Approx. 650 said mixture includes a minor amount of lead 30 Sulfate. Average particle size (microns).-- 0.25-0.50 4. The method as claimed in claim 1 Wherein Refractive indeX------2.7 the pigmentary titanium dioxide is in the rutile In the foregoing description of my invention, modification and has a particle size between and in the following claims, the terms "titanium about 0.1 and 0.3 micron. dioxide pigment' and "pigmentary titanium di Oxide' are synonymous and are used to identify FRANK O. RUMMERY. titanium dioxide which has been completely processed. So as to manifest the high-hiding pig REFERENCES CEO mentary qualities which have heretofore been The following references are of record in the recognized as obtainable from rutile and anatase 40 file of this patent: modifications of titanium dioxide, typical char acteristics of which are as indicated here: UNITED STATES PATENTS Number Nae Date Anatase Rutile 2,140,222 EspenSchied ------Dec. 13, 1938 2,166,221 Patterson ------July 19, 1939 Reynolds Tinting Strength.------,300 i. 650 2,213,542 Booge ------Sept. 3, 1940 Average particle diameter (microns).------0.5-0.40 0.10-0, 30 Refractive index------2.55 2.72 2,419,246 Barton ------Apr. 22, 1947 FOREIGN PATENTS The term "lead oxide' is used in the claims in a Number Country Date generic sense to mean lead oxide per se, or lead 405,340 Great Britain ------Feb. 5, 1934 Oxide produced in Situ from an appropriate lead 416,615 Great Britain ------Sept. 18, 1934 Compound. 765,833 France ------Mar. 31, 1934 The term “reactive lead oxide' is used in the 308,908 Italy ------June 20, 1933 same generic sense, but connotes additionally that 5 5 31,005 Norway ------Aug. 16, 1920