Banerjee, B K

Srinivasa, V K

IACS Institutional Repository

Indtan J. Pfvya., 50, 1018-1022 (1976)T em perature variation  o f the lattice constant and the coefficient o f  therm al expansion  o f  am m onium  ch lorideV. K. Srinivasa  and B. K. B anerjeeJHamdny c(j Development Division,The Fertilizer Corporation of India Limited, Sindri, Bihar{Received 29 December 1975, revised 19 June 1979)Using an ftxiaapolatiou leohnjqiio as well as (bhens least square method, preeision determination of the lattice constant oi ammonium Chloride has boon made at different temporatui'os bet'woon 20-245°C. From these, b}?^  a graphit^al treatment, the coefficients of thermal expansion at various temperatures have boon evaluated. The trans­formation oharactoristic of ammonium chloride from a-/6f form around 185°C has been studied by high temperature X-ray diffraction techni­ques.1 I ntroductionThe effect of tomporaturo of ammmrium chloride has been the subjeerti of numerous (liscussitms According to Wallaen (1910) there is a maikod change in the heat effect of ammonium chloride (NH4CI) at 159°C. Scheffer (1916) finds that Wallace’s result is too low, for the transifiion temperature is 184-5°C. Hachraoister (1919) gave ]74°C for tlu' tiansition tempiuature of NH4t'I from a —>/y and Bridgman (1916) gav'c 184-3°C Wegscheidei (1908, 1911) postulated that NH4CI is stable and is transformed at ]84-5°C into /? NH4CI m the presence of moisture but that sometimes a labile a' torm is produeed which evaporated Avithout dissociation. In view of the discripencies m those results an accurate redetormination of transition I.emperatiu’c Avas thought to be worthAvhile.Ammonium chloride belongs to the cubic system. Further, XBS circular (1953) rox>orted the length of the unit cell of NH4CI as 3-8756 A at 26°C. Bartlett & Langmuir (1921) gave the lattice constant as 6'533 A at 250°C. Data on the linear coefficient of thermal expansion of this salt has been reported by Fizeau (1867) as 62-546 X 10“® at 40°C. Nevertheless, extensive X-ray determinatiop o f the coefficient of thermal expansion over a wide range of temperature has not so far been reported. The present paper reports an accurate redetermination of the transition temperature of NH4CI from a—> p  form and the coefficient of thermal expansion over the range of temperature 20-165°G. It was felt that such an investigation might throw some light on the physical characteristics such as caking, of the complex mixed fertilizers containing N H 4 C I .1018Lattice constant and thermal expansion2. Expertmental1019Transition temperaturp.Phase transformation studies of NH^Cl lias been done over the range oi‘ temperature 20-245°C, by X-ray powder diffraction method in Guinior-Lemie High Temperature X-ray Camera. The special feature of this (camera is that by means of a synchronously moving film cassette with (^ oiiliinuous monitoring of the temperature, structural changes of a system ax’e investigated by recording the chai'aotoristic X-ray diffraction linesFrom the X-ray diffraction pattern obtained by the above technique, it has been found that the translormation of NH^Cl from a to fi form takes place around 185”0. This corroborates the results obtained by Scheffer (1910) and Smith ef ill (1915, 1919) who repotted that the i.runsfonnation cxr-fi form ocem’S at this temperature However, m one of the diffraction photographs (Figure 1) taken in GiimicM-Lenne High Temporaturf  ^X-ray Camera, the sample being kept under vacuum and heated from room temperature to 250°C, it has been observed Uvtt a NH4CI did not inansform to (i ibrin. fnstead, an additional phase started appearing at 50°0 and the formation of this new phase completed at 125‘'C with 1he disappearance of a-XH l^ l^ (X-ray data is given in table J). According toTable 1 . X-ray diffraction data for a, ji and supposed a' forms of ammoniumchlorideaNH,Cl a'NH^ Clc l A S c lA I d A 187(1 8 3-286 vs 2-48 w2-747 V.S 2-319 H 2-24 ms1-9:^ m 1-9S ms 2 -20 in] ‘721 rnw 1-896 m 1 936 m1-677 ms 1-643 vvw 1-78 w1 366 w 1-508 WAV J-04 vw1-284 vw 1-46 AV 1 -376 inw1 -222 mw 1-343 vw M75 in1-116 w w 1-263 vvw1-0723 w w 1-176 11-0334 m etc0-9384 vvwWegsoheidor (1908, 1911) ordinary a-NH^Ol being a labile form which changes to a'-NH4Cl at a higher temperature in the presence of moisture, and it is the transition a'- to ^-NH^Cl which occurs at 184‘5°C, while dry a-NH4Cl docs not change. Further, he also postulated that possibly a-NH4Cl is stable and is transformed at 184-5°C into NH4CI, but that sometimes a labile a'-form is produced in the preparation of the salt, and it is this form which evaporates with-liable 2 . Lattico Constant of NH^Cl at varioiiK temperaturos1020 V. K. Srinivasa and B. K. BanerjeePhase Temperature a(A)2 0 “C 3*876640" C :V877665“ C 3*879385“ C! 3*8849I05“C 3-9889125“P 3*8965145^ 1^^ 3 90303*90962 0 0 'C 6-5375225“ 6-5423245“ r 6-5485out cliHRooiatJoii. Tho prosent exponmeiiial ovidont'o loi' the existence of this unknown phase may bo the onlj^  proof wlii(.*h can bo aseribed to the assumed a'-NH4Cl because repeated expiuiiueuts on heatmg the sample both undoi’ vacuum as well as in atmf>sphere (allowing the sample to absorb moisture) did not give any consistent results The exact conditions ol formation or preparation of this compound is yet to be probed.3 Thermal ExpisnsionLattice constants at room tiemporatiiro and at elevated temporn-tnros wore obtained with the help of 19 cm. dia. cylindrical camera (Unicam) The films recorded six well resolved an doublets with CuKu radiation (Radon House X-ray Unit, 30 KV 16 inA rating). The films were measured on a Philips Com­parator with an accuracy of 0  005 cms. Random errors were minimized by repeated measurements. Precision determination of lattice constants were done by Cohens least square method as well as by extrapolation against cos'-^ l^ /sin 0 -|-cos“^ / .^ The differences in the values obtained by these two different methods were within the experimental errors Table 2 gives the values ol tlie lattice constants obtained at different temperatures foi* a-NH4Cl and its variation corres­ponding to different temperature, is shown in figure 2 . From the graph of tem­perature vs lattice constant. valuciS of a were read at regular intervals of 20“C. From those, the coefficients of expansion at the moan temperature of the interval were derived using the definition__ 1 (Aa)By a least squares treatment of the data obtained the following equation was derived for the curve giving the temperature variation of the coe£6cients of expansion over the range 20-165°C.olt =  1647xl0-«-f8-243xl0-»T+14-77xl0-i®T2 (1)Lattice constant and thermal expansion 1021The values o£ the coefficient of expansion obtained by using the above equa­tion are compared with the values derived using the definition (Table 3), The uncertainties in the evaluation of coefficients of expansion (a7i) is very much reduced in the higher range of temperature,RT- ■’ ’ ^I t lF ig . 1. Q u in ie r -L o n n o  H ig h  1om]>oraturiv X - r a y  P h o to g r a p h  o f  a n m iom u n i o h lo n d e .Fig. 2. Plot of lattice constant ageonst temper^ lture.Table 3. Coefficient of expansion of NH4CI at various temperatures1022 V. K. Srinivasa and B. K. BanerjeeTemperature a from the “C definition4000SO100liiOJ4010020-63x10-" 24-48x10-" 32-51 V 10-"30-22 V 1 0-" 18 27); 1 0"" 5 5  96 X 1 0 - " "  0 5 - 7 7  X  1 0  ■ "a from equation (1)20-13x10-® 26-13x10-® 31-52x10-® 38-48 X 10 ® 40-63 X 10-® 55 96/ 10-" 66-47 \ 10 ®+ 2-42 -2-60 + 3-35 -1 1-87 + 3-39-1-06Jjattjcc constants obtained at difftu’ont teinporatures varies from ,H'8756A at 20"C 1,0 3-9096A at 165"C for a-NH^Cl and in the case of /i-NH^Cl it varies from (V5375A at 200''0 to 6-548riA at 245°C. By inspection of X-ray diffraction data (table 1) it is easily recognizable that a-phase is simple cubic lattice and ytf-phase is FCC. The measuiod values for the linear coefficient of expansion for /y-phase (FCC) in the range 200-245”C is 37-33x10“® j^ or °C. A rough check of the values of lait.ice expansion (table 2 ) shows that- the lattice expansion is comparatively grc^ ator in /?-phase than a-phaso suggesting that in a general way, the weakonnig of the binding foices with the rise of temperature. Further, i-he fact that expansion coeffiiuent of a-phase is smaller than the expansion co­efficient ol yff-phase may also he underst ood in terms of the strong iut.ralayer binding in a-phase. •R e v e b e n o e bBartleU G. & Langmuir 1921 Journ. Am&r. Chem . Sor 43, 84.Bridgman W. 1916 /Voc A m er . A ca d . 52, 89 Fizeau H 1867 C om 2Jt. B en d  64, 314.Haohmoiater K. 1919 Z eil. A n org . Ohem . 109, 145.NBS Circular 539. 1953 (ASTM. 7-7) I, 69Scheffer F. E. C. 1916, Proo A k a d . A m sterd a m  18, 446, 1498.Smith A. & Lombard R. K 1915 J ou rn  A m er . Chem  Soc. 37, 48.Smith A , Raablack H & Scatchard G. 1919 Jou rn, A m er . Chem . S oc. 41, 1961.Wallace R . C 1910 Genti' M i n  33.WegHcheider R. 1908 Zeit Phys Chem . 65, 97.Wegsoheider R. 1911 Zeit. Phya. Chem . 75 , 269. _

Temperature Variation of the Lattice Constant and the Coefficient of Thermal Expansion of Ammonium Chloride

http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/4647/1/Temperature%20Variation%20of%20the%20Lattice_V%20K%20Srinivasa.pdf

Temperature Variation of the Lattice Constant and the Coefficient of Thermal Expansion of Ammonium Chloride

Abstract

Similar works

Full text

Available Versions

IACS Institutional Repository