Calcined Mixtures of Litharge and Titanium Dioxide X-RAY DIFFRACTION STUDY DOUGLAS G. NICHOLSON University of Illinois, Urbana, Ill
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HE matitifacture of lead titanate on a commercial scale has made available a new pigment characteriaed by tire advantageous durahilit,? characteristics t,lrat it imparts t,o t,he resulting paint film (Z). It is rmpared hy calciuat.ion of inixturcs of litharge and titanium dioxide. 111 view of the fact that both titaniiuii dioxide and litharge c r y s t a l l i a r i i i more t,lran one crystalline form, it seemed desirai)le to determine what, effect excess quantities of either cow sbit,uent have upon the structurr of the resrilting calcined mass, and to aseert,ain whet,lier compounds o t l w than that required by the fonnoln I’bTiO, can exist. An x-ray diffract,ion study of rarious synthetic mixtures, tioth calcined and uncalcineil. was therefore undertaken. Accordirrgly, inolecular blends of litharge and commercial titanium dioxide (anatase modification) were pre-
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FIGURE 2. C H h N O E S I S D I F F K I C T l O S PA-RNS OF CALCINEDMATERIALA B THE LITHARGE-TITANISM D I O X I DCEO N T E N TIs VARIED
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until the ratio of litharge to titanium dioxide was 8 to 1, a n e w s e t of diffraction lines began to appear. With further d e c r e a s e i n the amount of litharge present, the intensity of tlie new lines increased; a t the same time the lines attributable to tetragonal lead oxide became less and less pronounced. At a niolecular ratio of 1 to 1, this new set of lines had attained a maximum intensity, while the tetragonal litharge pattern had disappeared completely.
were oiitained. A similar diffraction picture was taken of each unealcined control mixture. The diffraction camera was of the cyliiidrical type (Figure I). All exposures lasted 3 hours. The x-ray beam was obtained by means of a Philips Metalix tube with a copper target. Tlrc voltage across the tuhe was 27 kilovolts with an average current of 23 milliamperes. .Uthough the uncalcined litharge used in this study showed orthorhombic structure in a control p.ttern, a calcined sample of the same material shored a structure not iuilike that of tetragonal lead oxide. Calcined hlerids which were relat,irely Iiigli in lit,liarge content also showed this characteristic stnictiire. A s t,he mo1w:ular percrntagr of lead oxide as decreased
An x-ray diffraction study of calcined samples of mixtures of litharge and titanium dioxide shows conclusively that a definite chemical compound is formed when the molecular proportion of the two substances is in the ratio of 1 to 1 . Any deviation from the 1 to 1 ratio results in a physical mixture of this compound with the constituent present in excess. The x-ray diffraction patterns produced by calcined, 1 to 1 mixtures of (a)litharge and commercial titanium dioxide, ( b ) lead nitrate and hydrous titanium oxide, and (c) lead hydroxide and hydrous titanium oxide, are identical with that produced by a sample of commercial lead titanate.
With continued increase in the relative titanium dioxide content, the prominent lines in the 1 to 1 pattern became less iiitense, until at, tlie 1 to 10 ratio of litharge to titanium dioxide they had become quite faint. Meanwhile a new set of diffraction lines began to sppcar at a litharge-titanium dioride ratio ol 1to 2 or 1 to 3. This nerr- set of lines increased in intensity as t>horelative titanium dioxide contcnt increased and was shown to bo due t o titanium dioxide. Figure 2 depicts the patterns in rather complete detail. These data are in accord with statement,s made hy Cole and Espenschied ( 1 ) . In Figure 3 the pat,t,ernsof a representative numbcr of nncalciiicd control samples are shown. In samples containing B relatively liiglr litharge content, the pattern of this mat,erial predominates. Those high in t,itaniuiii dioxide content sliorv a different pat.trm. Iriteniiediate inistiires shoTt- a composite pattern. For cwiiparison Figure 4 presents paattorns of a calcined 1 to I blend of ht,harge and titaninni dioxide and a sample of coirimercial lead titanate pigmcnt. The diffraction patterns 01,taincd from calcined 1 to 1 mixtures of lead nitrate and l y droos titaniiim oxide as ~ e las l 1 to 1 mixtures of lead hydroaide arid 1iydn:iis titanium oxide are also included. Upon , tlie Eiiiier and Amend "c. P. quality" hydrous titanium oxide was foinid t o lip approsiniately titanyl hydroxide, TiO(OH),. j
Acknowledgment The author wishes to thank the Krebs Pigment and Color Corporation for the samples of coinmercial pigments used in this st.udy.
Literature Cited (1) Cole and Eapenschied, J . Phys. Chent. [t.o he publiahed) (2) Robert,son. IND EN^. CHEM.. 28, 2lG (1936).
RECEWED Janusiy 22, 1837
