INDIAN J. CHEM., VOL. ISA, SEPTEMBER 1977

High Temperature X-Ray Diffraction Study of.Barium Pyrophosphate

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Fig. 2 --- l'lcts of lug CIC., against xlll.x naphthalene-catecholsystem; 0 Ilapl;thaklle-p-chlordllltn,bellzenc system]

For the case of non-mixing, Eq. (3) is followed:

C = Co[1+ (~~ -1) exp (-;Vp:s)]where D is the diffusion coefficient and v is thevelocity of zone movement. . .

From Eq. (2) it follows that for complete rruxingthere should not be any change in the concentrationwith change in the value of x. This is. ~ot v=in the present case. Hence, complete mixmg uoesnot take place in the zone melting of the samplesstudied in the present case. In order to test Eg.(3), log (1- CICu) was plotted agai~lst x. Straightlines were not obtained. Hence It follows thatthe equation for non-mixing is also not applicable.Since the rate of zone movement is large and Eqs.(2) and (3) do not fit the da ta, it app.ears that partialmixing occurs in the prcse.nt e~tec.tJc ~ystems. .

Since the value of effective distribution coefficientis less than unity in both the systems, the impuritiesare preferentially rejected by the solid and pile upin the liquid close to the interface. Further, greaterthe deviation from unity in the value of It, ~hegreater is the separation efficiency. The. separationefficiency in the naphthalene-p-chlorol1ltrobenzenesystem is greater than in the naphthalene-catecholsystem.

The financial assistance from COSIP scheme isgratefully acknowledged.

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References

1. l'FA~:\", \V. G., Trans. met.all. Sac, AfME,I

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£.00 "iOO 600 700 800 900 1000Fig. 1 - Variation of d-spa.cings with temperature for fourstrong reflections in X-ray pattern of barium pyrophosphate

barium pyrophosphate is not yet known, it isnot possible to give a conclusive explanation forthis phenomenon. However, if its structure consistsof P04 tetrahedra linked together to form P207groups, then the decrease in the cell dimensionscould perhaps be explained on the basis of thetilting theory", because tilting is probable in struc-tures where polyhedra are linked by their cornersonly.

The peculiar behaviour of barium pyrophosphateas well as its diffraction pattern suggest that thissubstance is not isomorphous with calcium andstrontium pyrophosphates, This is in agreementwith the observations of Ranby ct aU who havementioned that the o-form has no isomorphs at all.Therefore, the general statement that barium pyro-phosphate is -isomorphous with strontium andcalcium pyrophosphates- is not wholly correct.

NOTES

TABLE 1 - INDEXED X-RAY POWDER PATTERN OF BARIUMPYROPHOSPHATE

d in A I 1Ikl d in A I hkl

5·331 6 001 2·153 31 0424·334 3 210 2·108 27 1613·915 100 121 2·037 4 3023·529 25 040 1·956 11 0523·354 6 211 1·909 4 1523·254 6 131 1'865 8 332. 3603·223 3 230 1·832 4 5003'(l70 11 300 1·805 4 0033·011 3 310 1·769 4 080, 3612·')67 4 041 1·722 5 1232·828 55 050 1·668 4 2132·708 39 002 1·586 7 233, 1432·351 5 202. 060 1·538 6 6002·318 27 340 1·482 9 5512·265 11 410 1·411 12 4132·219 18 222 1·402 7 516. 480

1·354 8 004

The powder pattern of barium pyrophosphatehas been indexed and is given in Table 1. Thesystem is orthorhombic with Pmmm, Pmm2 or P222as the probable space group. The crystal datais as follows:

a = 9·200 A, b = 14·120 A, c = 5·420 A, z = 4and Pm=4·45 g crrr".

The authors thank Drs E. R. Saxena and RaziaFarooqi for the sample of barium hydrogen phos-phate, Dr V. S. Subrahmanyam for measuring thedensity and to the Director, RRL, Hyderabad,for his keen interest in the work.

References1. RANBY. 1'. W., MASH. D. H. & HENDERSON. S. T .• Brit.

f. appl. Phys., Supplement 4 (1955), 18.2. KIRCHNER, H. P., MERZ, K. M. & BROWN, W. R., f. Am.

ceram. Soc .• 40 (1963). 137.3. MEGAW. H. D .• Mat. Res. Bull .• 6 (1971), 1007.4. PLUMIER, R, Bull. Classe. Sci. A cad. ray Belg, (1957).43.

Thermochemical Studies ofDiaquodiacetatodioxouranium(VI)

LAMBODAR THAKUR*. MD FAIZ AHMAD & RAJENDRA PRASADtDepartment of Chemistry. Bhagalpur University

Bhagalpur 812007

Received 23 August 1976; accepted 13 April 1977

The heats of solution of anhydrous diacetatodioxo-uranium(VI) and diaquodiacetatodioxouranium(VI) inwater and 2N acetic acid at 300oK, are -1l·3±0·6,-22'4±0'5; 22·6±0·4, and 10·7±0'2 KJ mol-! respec-tively. The standard heat of formation of anhydrousU02Ac2 is -1991·9 KJ mol-t, The gas phase enthalpyof reaction between U02Ac2 and one mole of wateris -60·6 KJ mol-I, commensurate with the dativeuranium-oxygen bond strength.

ANHYDROUS diacetatodioxouranium(VI) in thecrystalline state, dissolves in water or in aqueous

acetic acid giving a clear yellow solution which on

*To whom all correspondence should be addressed.[Present address: A. N. S. College. Barh (Magadh

University).

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