Murthy, Krishna V G

Rao, Krishna K V

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TEMPERATURE VARIATION OF THE PHOTOELASTIC CONSTANTS OF AMMONIUM CHLORIDEK. V. KKI8HNA RAO and V. G. KRISHNA MURTYI’llYHICS DEPAHTMUNT, OSMANIA U nIVEKSITY, H yDEKAHAU,-?.{licerived November 10, J966).Jri i i  iiajjer (l^ao and Murty, 19(H)) from this laboratory, the tompora-tur('. dopondonc(  ^ of the photoelastii* behaviour of a number of cubic crystals of NaCl type has been described. As ammonium chloride belongs to CiJsOl type and is found to ahoAV a behaviour diffonmt from NaCI tyi)e crystals with regard to variation of elastic constants with temperature (Bhagavantam, 1955), it is thought worthwhile to study the temperature dependence of its photoelastie constants also.Using the same procedure as described earli(‘r (Rao and Murty, 19(H)), i\u) photoelastic constants of ammonium chloride have bc(‘n determined a t varioUvS temperatures in the range 35''C to I t  was not possible to make observa­tions above 100"C, as the crystal became translucent beyond lOC^C, probably due to tlu' onset of sublimation. The data on the thermal expansion and the thermoolastic behaviour, needed for evaluating the photoelestic constants at various temperatures, have been taken from literature (Sharma, 1950 and Subrah- inanyam, 1954). As tlu  ^ data on the thermoelastic behaviour is not availabli', the value oidtijdl is calculated using Ramachandran's theory (1947) on the thermo­optic behaviour of solids.Table J shows the values of the photoelastic constants obtained at different temperatures. The stress and the strain optical constants are found to increase numerically with temperature, in  the temperature range studied, the variation in is only 14.0%, whereas tliev ariation in is much larger, being24.7%. Thus the behaviour of ammonium chloride, with respect to photoelasti-TABLE 1Tomnerature C.O.fcJ. l \ x Pix (Ut X 1013 O.G.S.35 2.95 0.J61 0.251 4.28 0.03260 3.H 0.263 4.70 0.03480 3.25 0.176 0.274 5.03 0.036100 3.38 U.J82 0.284 6.35 0.036160LeUers to the Editor 161city also, is different from NaCl type crystals, in which the variation in (?n—3 12 ) is larger than in q^ .^ It will bo interesting to stody whether other CsCl type crystals also behave in the same manner.R E F E R E N O E lBhagavantam, S. 1955, Proc. Ind, Acad. Sci* A41, 72;Kamachandran, O. M. 1947, Proc. Ivd. Acad. Sci. ASit, 206.Bao, K. V. K. and Murty, V. G. K. 1966, Proc, Ind. jAcad. Set. A64, 24.Sharroa, S. S. lOSO, P,oe. hid. Acad. Sci. A32, 208.f Subrahmanyam, S. V. 1954, P/i. 1), Thesix, Osmanii Univeraity.10

Temperature Variation of the Photoelastic Constants of Ammonium Chloride

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Temperature Variation of the Photoelastic Constants of Ammonium Chloride

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