Hussain, M. Raza

Mehdi, Safia

Rao, B. Rama

English

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INDIAN J. CHEM., VOL. ISA, SEPTEMBER 1977High Temperature X-Ray Diffraction Study of.Barium Pyrophosphate+0'2oUU01oo 3X It6Fig. 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.... (3)References1. l'FA~:\", \V. G., Trans. met.all. Sac, AfME,I<J4 (1952). 794.2. VUE, ,\. S., Trans. metall. Soc., AIME, 248 (1970), 19.3. VUE, A. S., Trans. met all . Soc., AIAIE, 212 (1958). 88.4. "VILCOX, \V. R & HERINGTON, Zone ",dling (1 organiccom-pounds (John Wilcv, New York). 1963.S. TI;\lMER~lA:-<S, T, Physicochemical crmslu nls of pllreorganic compounds (Elsevier, Houston, Texas), 1950.6. RASTOGI, R. P. & RAM VERMA, K. T.,]. (/"!III. Soc. (1 (56),7. NIPPON J\'OJDIA, H., Kagaku Zasshi, 91 (1970),810.8. R~STOGI, R. P., SINGH. N. B. & SINGH, l'\ARSIC<"GHBHADUR,j. Cryst. Growth, 37 (1977), 3299. WILCOX, W. R, SEGUNDO, EL., FRIEDENBERG, R &BACK, NATHAN, Chern. Reo., 64 (1964), 187.820SAFJA IVfEHDI, M. RAZA HUSSAIN & B. RAMA RAORegional Research Laboratory, Hyderabad 500009Received 10 May 1976; revised and accepted 6 May 1977Hi~h temperature X-ray diffraction study of bariumhydrogen phosphate has been undertaken in order tofind out whether any phase changes take place in it.It has been observed that this compound ~ets com-pletely converted into barium pyrophosphate at 550°,On heating the latter to further higher temperaturesthere is no change in phase but the d-values decreaseafter 850°. This behaviour is similar to that of UP201'X-ray powder pattern of barium pyrophosphate hasbeen indexed. The system is orthorhombic with thefollowing crystal data: a=9·200 A, b=14·120 A, c=5·420A, %=4, D",=4·45 ~ crrr" and space group symmetry isPmmm or Pmm2 or P222-THE effect o~ heat ,on barium hydrogen phosphatehas been investigated by X-ray methods andthe results are described in this paper.X-ray diffraction patterns were taken o~ a P~ilipsPW 1010 X-ray diffractometer employing nickelfiltered CuK radiation, The samples were heatedby means of a high temperature attachment to thediffractometer. Pure barium hydrogen phosphatewas heated up to 1000° starting from room tempe-rature, and X-ray patterns were taken at intervalsof 100°. The accuracy of temperature measurementann uniformity of temperature have been checkedby known lattice spacing-temperature relation ofsilver. Calibration at room temperature was donefrom the positions of high angle peaks by extra-polation methods. ..It is observed that the conversion of bariumhydrogen phosphate into barium pyroph~sphatebegins at 270° and is complete at about 550, TheX-ray pattern of this pyrophosphate is s~mil~r tothe pattern of a-pyrophosphate reported in litera-ture! (except for the presence of a few extra weakreflections, which could be located by us becausethe patterns were taken on a diffractometer andnot on a camera), But the temperature of for-mation of a-barium pyrophosphate observed hereis much less than that reported. The low tem-perature or a-phase has not been observed at all.The pattern obtained at 550° is completely that ofa-pyrophosphate. It is stable at room temperatureand is unaffected by further heating even up. to1400°. Also, there is no indication of the formationof another phase. However an interesting pheno-menon has been observed. The values of theinterplanar spacings increase when the temperaturereaches about 850° and then start decreasing onheating to higher temperatures. This ~an. be, seenfrom the plots in Fig. 1, ",'here the var iation 111 d-spacings with temperature is shown for four str?ngreflections, This unusual behaviour of banumpyrophosphate is similar to that of uranium pyro-phosphate- which expands up to about 400° andthen contracts till 1200°, Since the structure of35273272-211IV1285€284If)oz~2'63a.If)a:.:( 2·82z~~"~Ir---~~--~----~----~----~----~~a.:::i 356I-z355353II3·953·9439T E MPERATUREoC ~1_~2.?...._:_...J l, ~ L_. .L.__.-J ...L£.00 "iOO 600 700 800 900 1000Fig. 1 - Variation of d-spa.cings with temperature for fourstrong reflections in X-ray pattern of barium pyrophosphatebarium 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.NOTESTABLE 1 - INDEXED X-RAY POWDER PATTERN OF BARIUMPYROPHOSPHATEd in A I 1Ikl d in A I hkl5·331 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. 4801·354 8 004The 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 UniversityBhagalpur 812007Received 23 August 1976; accepted 13 April 1977The 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 aqueousacetic acid giving a clear yellow solution which on*To whom all correspondence should be addressed.[Present address: A. N. S. College. Barh (MagadhUniversity).821

High Temperature X-Ray Diffraction Study of Barium Pyrophosphate

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High Temperature X-Ray Diffraction Study of Barium Pyrophosphate

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