Bassi, P. S.

Sharma, Indu Bhushan

Sharma, N. K.

English

NOPR

NotesKinetics of Solid State Reaction between Copper& Bromine VapoursP. s. BASSI, INDU BHUSHAN SHARMA & N. K. SHARMADepartment of Chemistry, University of Jammu, Jammu 1Received 5 November 1975; accepted 7 January 1976Kinetics of the reaction between copper (plates) andbromlne (vapour) has ,been studied in the temperaturerange 30-50°. The kinetic data follow a parabolicequation. The reaction product has been identifiedas 1-CuBr by chemical analysis and X-ray diffractionstudies.IN the tarnishing reactions when the productlayer is coherent and thick (above 1000 A)generally a parabolic equation is found to fit thekinetic data1,2. This is attributed to the diffusionof reacting species under a concentration gradient.In some cases, however, deviations have also beenfound, which are due to periodic cracking of theproduct film3•4.Studies of the reaction between silver metal andbromine (vapour) show that the kinetic data followa parabolic equation where quite thick productfilm is formed 5. In the present note kinetics ofthe reaction between copper (plates) and bromine(vapour) have been studied at various temperatures.The product was analysed by chemical and Xvraydiffraction analyses.Copper (plates) of equal size (each 4·00 cm'') werecut from copper metal foil (AR) , a hole was drilledin each plate near the one end to facilitate suspen-sion and rubbed with emery powder by keeping theplates dipped in benzene (AR) so as to absorb anyheat generated due to abrading and ultimatelyto prevent any cold work on the metal plates.Closed reaction vessels made of pyrex glass andprovided with standard joints and platinum wirehangers (provided at the top of the vessel to suspendthe metal plates inside the vessel] were taken, eachfilled with 10 g of bromine (liquid) and placed ina thermostat kept at constant temperature (± 0.1°).The copper plates were taken out of benzene, andweighed. The plates were suspended in the vesselsTABLE 1 - X-RAY DIFFRACTION DATA OF THE REACTIONPRODUCT AND THE KNOWN DATA OF y-CuBrd (A) d (A)Expl. Known Expl. Known3·218 3·285 0·962 0·9621·956 2·012 0·949 0'9481·695 1·716 0·899 0·8991·406 1'423 0·868 0·8681·295 1'306 0·820 0·8211-153 1-162 0·797 0·7961·084 1·095 0·790 0·7891·005 1·006692540480420360""~'52)(300en.•....lJ: 24018012060Fig.ootO--------~4--------~8----~1~2--------1~6------20------~2~4------28------t (II.)1-- Kinetics of bromination of copper (plates) bybromine (vapour) at different temperaturesso th~t the p~ates while not in contact with liquidbromine are In an atmosphere of bromine vapourat saturated pressure at the temperature of theexperiment. Each plate was removed after certainmt~rvals of time and weighed. The increase in:veIght ga,,:e the weight at bromine reacted whichIS proport ional to the thickness of the productlayer: T~e reaction product analysed for CuEr.The identity of the product as Y-CuEr was furtherconfilme.d by X-ray diffraction studies of the pro-duct usrng CuKa. radiation (Table 1).. Plots of ~, weIght. of bromine reacted against~Ime, t, are grven m FIg. 1. The following equationIS found to fit the kinetic data of the reactionw2= Kt+C ... (1)where K aI.1d ~ arc co.nst~~.nts. The applicabilityof t~e equ~tIOn IS shown III Fig, 2 where w2 is plottedagainst time t. Parameters of the equation aregiven in Table 2.TABLE 2 - PARAMETERS OF EQ. (1) FOR THE REACTIONBETWEEN COPPER AND BROMINE (VAPOUR) AT DIFFERENTTEMPERATURESTemp. Kxl05 Cxl06°C (g2jhr) (g2)30 6·92 4·5040 8·09 6,0550 12·30 7·00....•.~sJCI\I~ 200........~1004 8 12 ust (fir)Fig. 2 ~ Plot of Wi versus t at different temperatures forreaction between copper (plates) and bromine (vapour)20 24The average maximum thickness of the productfilm calculated from mass, theoretical density of theproduct Y-CuBr and the dimensions of the metal platec?mes out to be 0·0026 ern. The reaction is a diffu-sion-controlled process. The product film which iscoherent and protective controls the diffusion process.References1. KROGER.F. A.• The chemistry of imperfect crystals (North-Holland. Amsterdam). 1965. 825.2. CABRERA.N. & MOTT.N. F .•Reports on progress in physicsVol. 12 (The Physical Society. London). 1949. 163. '3. BASSI, P. S. & SHARMA.I. B., Indian J. Chem, 12(1974), 813. '4. EVANS,U. R., Nature, 157 (1946), 732.5. HAUFEE,K., R.eactivity of solids, edited by J. W. Mitchell,R. C. Devries, R. W. Roberts & P. Cannon (WileyInterscience, New York), 1969, 311.6. SMI!H, J. V:' X-ray diffraction data card No. 6-0292 (Arne-rrcan Society for Testing Materials, Philadelphia), 1962.IR Spectrum of Benzoic Acid-NaphthaleneEutecticP. S. BASSI& N. K. SHARMADepartment of Chemistry. University of JammuJammu (Tawi)Received 10 October 1975; accepted 10 December 1975In naphthalene-benzoic acid system, certain C-Hin-plane and out-of-plane frequencies of naphthaleneand also C~C bond srretchtng frequency of aromaticring in be nzoic acid are restricted, when the eutecticis formed. There, thus appears to be a definite orien-tation of naphthalene and benzoic acid with respect toeach other in the eutectic mixture.NOTESRASTOGI and Bassil have made a comprehensivestudy of the growth characteristics and thermo-chemistry of eutectics formed between organiccompounds. The growth kinetics and struc!ureof the liquid eutectics have also been studied-,Savchenkos considers a eutectic to be formed bysome sort of loose molecular or atomic interactionwhich does not involve the formation of a chemicalcompound, i.e. the formation of a eutectic lea~sto some merging of electron ener~y lev~ls, but th~sis not accompanied by the formation of inter-atomicelectrostatic bonds. Investigations have revealedthat the mechanism of eutectic crystallization isquite complex. X-ray examination shows thata binary eutectic is a mixture of two kinds of crystals,favourably oriented with respect to each others.Many eutectic composites have been reported byHogan" to show a unique crystallographic orien-tations relationship both between constituent phasesand their mating planes. After nucleation, manyeutectics grow more or less perpendicular to thesolidification front. Perfect lamellar grains havebeen found in lamellar Sn-Cd eutectic by Gruzleskiand Winegard". But in a number of systems, theeutectic grains do not exhibit a fixed crystal orien-tation with respect to external lines of reference?IR reflectivity measurements of LiF-NaF lamellareutectic by Proux and Racek" revealed that thedifference in peaks may be due to interfacial phonones.In view of these conflicting ideas, it was thoughtnecessarv to ha vs some information regarding thecharacter of eutectic from IR spectroscopy.Naphthalene (USSR) was purified by sublimation(m.p. 80·3°) and benzoic acid (m.p. 121'2°, BDH,Analar) was used as such. Accurately weighednaphthalene and benzoic acid were taken in a tube,which was then sealed to avoid evaporation. Thematerial in the tube was melted and then suddenlychilled in ice cold water 4-5 times, Tube wasbroken and the solid mixture thus formed wastaken in agate crucible and powdered.The phase diagram of naphthalene-benzoic acidsystem was determined by thaw melt method.Eutectic was found to be formed at 0·6670 mole-fraction of naphthalene with its melting point at69·10° (ref. 9).IR spectra (KBr) of the composite cannot beexactly superimposed on the spectra of constituentmaterials, naphthalene and benzoic acid. In theregion 770 to 1030 crrr", a general decrease in inten-sities of the bands of eutectic in comparison withthe parent compounds has been observed, e.g. thebands at 770 (s), 955 (m) and 1005 (m) cm-1 werereduced in intensity and appeared at 775 (m),950 (sh) and 1005 (sh) crrr- in the eutectic. Similarlybands at 800 (m) and 925 (m) crrr+ of benzoic acidappeared at 800 (sh) and 930 (m) cm-1 in the eutectic.Moreover, 978 (w) cm-1 band of naphthalene, whichis due to out-of-plane homocyclic C-H deformation-?was altogether missing in the eutectic. In-planebending of C-H bond ba.nd 1020 (m) crrr" of benzoicacid was diminished in intensity and shifted to1030 (w) cm-l in the eutectic.In-plane bending bands 1237 (w) and 1265 (m)cm~l, which are due to homocyc1ic C-H bond innaphthalene, were totally missing from the spectrum693

Kinetics of Solid State Reaction between Copper & Bromine Vapours

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Kinetics of Solid State Reaction between Copper & Bromine Vapours

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