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Structural transformations in alkali perchlorates
~qORG.
NUCL.
CHEM. LETTERS
Vol. 9, pp. 1193-1196, 1973.
STEUCTU]~u~L T~',E~)R/,~TIONS
Pergamon .Press. Printed in Great Britain.
II~ AL~L;~LI PERCHLORAT2S
S. K. Syal and $. R. Yoganarasimhan Denartment of Chemistry, Indian Institute of Technology New Delhi 110029 India (Received 11 July 1973)
The all:all uerchlorates
with the exception of lithium perchlorate
transform reversibly from a low temperature orthorhombic high temperature potassium,
form. The transformation
rubidium,
temperatures
and cesium perchlorates
309 °, 3OO °, 278 °, and 2210C respectively.
form to a cubic
for sodium,
are reported(l-4)
The transformations
to be are
oressumed to be brouL~ht about by the onset of rotation of CIO~ ions(3) though no exT~erimental evidence has been presented. on these transformations
The available data
are at best scanty despite the tremendous
importance" of some of these perchlorstes mixtures(5 ). Some preliminary
as oxidiserr, in propellent
results on hysteresis
in these transfor-
mations are reported in this communication. Jhnelytic,,.l reagent grade sodium and notassiunl perchlore.tes ,;:ere rocrystallised
fror,z hot a cueous solutions four times. Rubidium and
cesiuz:~ oerchlorates
were prepared by treating Rb2CO 3 and Cs~!CO~ of
~.Merck (~uaranteed Reagent ,Trade with 60% solution of oerchloric acid. The resulting perchlorste~ water ( solubilities pSrchlorates
~:,ere recrystallised
four times froz hot
of all the~e ~erchlere.tes ale very io~: ). All the
~sere. dried at 180°C for 48 hour~ and were then stored in
vaeUULI. Chemical an~-lyzis(0)
as nitron perchlorate
sho~ved a purity of
hi~;her than )).95~ in all the cases. The differential
ther~,s.l analysis of all the perchlorates
~a.s
co rried out in a mannual thermo analyser e~nloyinc a constant heating
1193
1194
ALKALI PERCHLORATES
Vol. 9, No. U
rate of 5°C per minute. Extreme care had initially been tv.ken to establish the conditions for good reproducibility.
The oarticle size was mai:~.tSined
at -200 + 275 mesh size. Ignited s.lumins of the same mesh size served as reference. The instrument calibration was done with K2SO 4 and AgNO 3 for which enthalpies of transformation are available in the literature(7,8). The results of DTA of the four perchlorstes are presented in the Table. The peak temperatures,
and their variation from sodium to cesium
are in agreement with the idea that as the ~ols,rizing po~.rer of the cation decreases from Na + to Cs +, the metal - oxygen intere.clion becomes weaker with a consequent lowering of transition ter,pereture, The Table shows that the peak temperature for the reverse transformation,
~,
is lower
than the corresoonding temperature for the fozu.~ard transformation, •
T p~ f
in each case. However, the inception temperatures in both the directionsTi'f Trz - are approximately the same suggesting that there should be no hysteresis on purely thermodynamic considerations.
But kinetic factors
such as volume changes affecting the rates of nucles.tion of the product phase in the parent matrix, probably lower T Pr , s.nd give rise to a hysteresis loop(8).
T r should necessarily be lower than T f if the p o
change in enth~ipy, energy of activation snd frequency fsctor are consistent.
Since k f = ,~ e x p
and and also
( - z~l~
)
k r = A exp. ( - Er/RT ) E f - E r = ~ H o,
Tr~
Tf
at isokinetic points. The hysteresis
so developed should be closely related to the volume strain ener~fiy. The trend in the voriation of ~ (
E e + ~e ) with ~ V
in the Table is
very good. The apparent discrepency in the case of sodiun ~erchlor~te is due to the fact that llaClO4 cryst~llize~ in the Cs,;~O4 for~.1 s s against BaSO 4 form of the other perchlorates in the lo~z temperature pha~e.
It
is necessary# to realize that surfsce ener,,~J besides the volu~.~e r~train
300
279
228
286
359
2]6
K=o a
RbCIO 4
CsClO4
12
20
14
?
oc
AV
in the
20@
251
282
307
°C
#urn
]98
2a
2?7
303 6
•
Ioeru
34
24.4
30
40
~
alutie
17?
83D
1148
64S
26.7
35.9
16.8
6.6
ll.aS
10.88
13.87
14 • 27
ee.le
eal/ga. '~3/ nmle-
#traim
Cml.aole-1
/Ja a l k . 1 4 pe~nhl,~l, ak_~
Keal .l(o]'e 1
strain
488
828
887
878
of volum
10
12
• c
Tz--~ox~st~ta.
8 (:halsge lm t h e Imlume ~o~ m01eo~le ~l~Jal~ t h e tr an~oz~atten o
/ ~ ( Bs + Bo ) • C h ~ p
310
•C
'I,
303
samite
T J I ~ E - D a t a on 8 t ~ n n t ~ r a l
rq
r
>
>
=
Z P
o<
1196
ALKALI PERCHLORATES
Vol. 9, No. 11
ener~y is ir~portsnt during nucleetion orocess as pointed out by Jackson(9). The nucleation of a phase of higher density in a matrix of lower density during the reverse transformation contributes a negative strain ener~D, causing a further lowering of T r p • Thanks are due to CSIR, India for finsncial support.
R~EREHCES iS.Gordon sad C.Csmobell, Ansi. Chem. 2_/, Ii0~ (1955). ].i.i~arkowitz, D.A.Boryta and ~q.F.Harri~, J.Fhys. Chem. 65, 261 (1961). ][.A.Bredig, J. Phys.Chem. L~9, 537 (1915). A.~.Harvey, l.T.Edmison, E.D.Jones,R.A.Seybert and K.A.Cato, J.Am.Chem.Soc., 76, 3270 (1954). S.H.Dole and K.A.~argolis in "The Chemistry of i~ropellants '' ed. by S.S.Penner and J.Ducarme, (Pergamon Press, London) 1960. R.Belcher and A.J.Nutten, Quantitative Inorganic Analysis (Butterworths Scientific Publications, London) 1960, Pa4~e 138. A.J.1~jumdar and R.Roy, J. Phys. Chem., 6_~, 168% (1965). K.J.Rao and C.N.R.Rao, J.r~terials Sci., l, 238 (1966). K.A.Jackson in "Progress in Solid Stere Chemistry" ed. by H. Reiss (Pergamon Press, London), vol.4, 1967.
NUCL.
CHEM. LETTERS
Vol. 9, pp. 1193-1196, 1973.
STEUCTU]~u~L T~',E~)R/,~TIONS
Pergamon .Press. Printed in Great Britain.
II~ AL~L;~LI PERCHLORAT2S
S. K. Syal and $. R. Yoganarasimhan Denartment of Chemistry, Indian Institute of Technology New Delhi 110029 India (Received 11 July 1973)
The all:all uerchlorates
with the exception of lithium perchlorate
transform reversibly from a low temperature orthorhombic high temperature potassium,
form. The transformation
rubidium,
temperatures
and cesium perchlorates
309 °, 3OO °, 278 °, and 2210C respectively.
form to a cubic
for sodium,
are reported(l-4)
The transformations
to be are
oressumed to be brouL~ht about by the onset of rotation of CIO~ ions(3) though no exT~erimental evidence has been presented. on these transformations
The available data
are at best scanty despite the tremendous
importance" of some of these perchlorstes mixtures(5 ). Some preliminary
as oxidiserr, in propellent
results on hysteresis
in these transfor-
mations are reported in this communication. Jhnelytic,,.l reagent grade sodium and notassiunl perchlore.tes ,;:ere rocrystallised
fror,z hot a cueous solutions four times. Rubidium and
cesiuz:~ oerchlorates
were prepared by treating Rb2CO 3 and Cs~!CO~ of
~.Merck (~uaranteed Reagent ,Trade with 60% solution of oerchloric acid. The resulting perchlorste~ water ( solubilities pSrchlorates
~:,ere recrystallised
four times froz hot
of all the~e ~erchlere.tes ale very io~: ). All the
~sere. dried at 180°C for 48 hour~ and were then stored in
vaeUULI. Chemical an~-lyzis(0)
as nitron perchlorate
sho~ved a purity of
hi~;her than )).95~ in all the cases. The differential
ther~,s.l analysis of all the perchlorates
~a.s
co rried out in a mannual thermo analyser e~nloyinc a constant heating
1193
1194
ALKALI PERCHLORATES
Vol. 9, No. U
rate of 5°C per minute. Extreme care had initially been tv.ken to establish the conditions for good reproducibility.
The oarticle size was mai:~.tSined
at -200 + 275 mesh size. Ignited s.lumins of the same mesh size served as reference. The instrument calibration was done with K2SO 4 and AgNO 3 for which enthalpies of transformation are available in the literature(7,8). The results of DTA of the four perchlorstes are presented in the Table. The peak temperatures,
and their variation from sodium to cesium
are in agreement with the idea that as the ~ols,rizing po~.rer of the cation decreases from Na + to Cs +, the metal - oxygen intere.clion becomes weaker with a consequent lowering of transition ter,pereture, The Table shows that the peak temperature for the reverse transformation,
~,
is lower
than the corresoonding temperature for the fozu.~ard transformation, •
T p~ f
in each case. However, the inception temperatures in both the directionsTi'f Trz - are approximately the same suggesting that there should be no hysteresis on purely thermodynamic considerations.
But kinetic factors
such as volume changes affecting the rates of nucles.tion of the product phase in the parent matrix, probably lower T Pr , s.nd give rise to a hysteresis loop(8).
T r should necessarily be lower than T f if the p o
change in enth~ipy, energy of activation snd frequency fsctor are consistent.
Since k f = ,~ e x p
and and also
( - z~l~
)
k r = A exp. ( - Er/RT ) E f - E r = ~ H o,
Tr~
Tf
at isokinetic points. The hysteresis
so developed should be closely related to the volume strain ener~fiy. The trend in the voriation of ~ (
E e + ~e ) with ~ V
in the Table is
very good. The apparent discrepency in the case of sodiun ~erchlor~te is due to the fact that llaClO4 cryst~llize~ in the Cs,;~O4 for~.1 s s against BaSO 4 form of the other perchlorates in the lo~z temperature pha~e.
It
is necessary# to realize that surfsce ener,,~J besides the volu~.~e r~train
300
279
228
286
359
2]6
K=o a
RbCIO 4
CsClO4
12
20
14
?
oc
AV
in the
20@
251
282
307
°C
#urn
]98
2a
2?7
303 6
•
Ioeru
34
24.4
30
40
~
alutie
17?
83D
1148
64S
26.7
35.9
16.8
6.6
ll.aS
10.88
13.87
14 • 27
ee.le
eal/ga. '~3/ nmle-
#traim
Cml.aole-1
/Ja a l k . 1 4 pe~nhl,~l, ak_~
Keal .l(o]'e 1
strain
488
828
887
878
of volum
10
12
• c
Tz--~ox~st~ta.
8 (:halsge lm t h e Imlume ~o~ m01eo~le ~l~Jal~ t h e tr an~oz~atten o
/ ~ ( Bs + Bo ) • C h ~ p
310
•C
'I,
303
samite
T J I ~ E - D a t a on 8 t ~ n n t ~ r a l
rq
r
>
>
=
Z P
o<
1196
ALKALI PERCHLORATES
Vol. 9, No. 11
ener~y is ir~portsnt during nucleetion orocess as pointed out by Jackson(9). The nucleation of a phase of higher density in a matrix of lower density during the reverse transformation contributes a negative strain ener~D, causing a further lowering of T r p • Thanks are due to CSIR, India for finsncial support.
R~EREHCES iS.Gordon sad C.Csmobell, Ansi. Chem. 2_/, Ii0~ (1955). ].i.i~arkowitz, D.A.Boryta and ~q.F.Harri~, J.Fhys. Chem. 65, 261 (1961). ][.A.Bredig, J. Phys.Chem. L~9, 537 (1915). A.~.Harvey, l.T.Edmison, E.D.Jones,R.A.Seybert and K.A.Cato, J.Am.Chem.Soc., 76, 3270 (1954). S.H.Dole and K.A.~argolis in "The Chemistry of i~ropellants '' ed. by S.S.Penner and J.Ducarme, (Pergamon Press, London) 1960. R.Belcher and A.J.Nutten, Quantitative Inorganic Analysis (Butterworths Scientific Publications, London) 1960, Pa4~e 138. A.J.1~jumdar and R.Roy, J. Phys. Chem., 6_~, 168% (1965). K.J.Rao and C.N.R.Rao, J.r~terials Sci., l, 238 (1966). K.A.Jackson in "Progress in Solid Stere Chemistry" ed. by H. Reiss (Pergamon Press, London), vol.4, 1967.