Thermochemical and kinetic studies on CeTe2O6

Thermochemical

and kinetic

studies

on CeTe20,

dvlcrmmethe

1. Introduction The

thcrmochcmia~ry

of uranium. during

01 binary

plutonium

and

fisbion

of oxde

the irradiation

evaluating

their performance

an aggressive

and

chemical states in an irradiated

fuel

corrosive

lission

producls

fuels

producls

oxidr\

evant

to

vicwcd

nuclear

technology

hy Chattopadhyay

1II.It

is one of the

has

recently

and Juncja

and kinetics

been studied

by Krishnan ct al. 141. the lanthanidc elements

Gcncrall;. aqueous

(+3) in trivalent

as well

lanthanide

and

of ThTc,O,,

as solid actinide

hccn

[3]. The

the

rcthcr-

have recently

state. ions

reaction

lanthanum( CcTe,O,,

trivalent Since

have

of tellurium

191 has

compounds.

with

in many isomer

lanthanidc

hecn

oxide

Ln,O:Te

reported.

hut

[6-X1 no

and kinetic data are available

The vaporization

of of and

as and

relevant on these

kinetics of TeO,(g)

due

IO the decomposition of ZrTc,O,(s) were studied by Sorrel1 IlO] under isothermal conditions to evaluate the energy

of activation

In the present work. hehaviour

for ZrTe,O,. the X-ray.

of CeTe,O,

thermal

is reported.

and vapor-

The com-

pound decomposes as

the

similar

CcTe,O,(s)-CeOJs)

+ ZTeO,(g)

The vapour pressures of TeO,(g)

*Corresponding author

relared

is a chemical

111) monotelluroxidrs

thermodynamic

bation are

are closely

The

in faasl hrecdcr

mochcmistry

1.51. Ccrium

hcncc ;I study of the Cc-Te-0 system is relevant to understanding the hchaviour of the Pu-Te-0 system.

in diffcrcnt

cmhrittlcs

they

and also a large yield fission product.

is

cxizts Ihat

potcntlal. propcrlic\

;II

Tcllurimr

reack)rs 121. A thcrmodynamic datababc for lcllurium-hearing systems rcl-

steel cladding

ionic their

plutonium.

lormcd

1s importal)t

in a rcacIor.

producl

highly

lission

and ternary

(1)

over the mixture of CeTe,O,(s) and CeO,(s) were determined by employing the Knudsen effusion mass loss (KEML) technique. In addition, the data on the rate of decomposi-

3. Rebults and discussion

The

l’orm;alion

actton Ilom

and

TcO.

hy the wlid

AI 073 K wa\

powder diflraclion

1I.?].

lilcraturc i\oslructural

2. E~perimcnlrl

ol’ <‘cTc .O,,

of <‘CO. the X-ray

CcTc.O,,

has

hccn

rc-

IO hc

rcportcd

[1.31. Lope/

‘with <‘cSc.O,,

\,a(~

conlirmod

dala IC~OTWC~ in Ihc CI al. 1Yj lound

1ha1 rhc Iargc value of the uni1 cell and ~hc indexing 01 X-ray rcllcction5 wcrc incon\ibtcnl wllh lhc proposed CcTc.O,, ot CeO.

\\;I\ plcp,ircd (anal;~

(YY.Y% March) in a rinlcrcd

by hcding

pdc.

purit

m the molar ralio

alumina

a proud

mi\lure

) and

~W.U.Y%,

TcO,

I:2 a~ 07.7 K for 24 h

boa1 under Ilowing

air. Inlcrmil-

the mixture wrc wilhdrawn. ground ;md rchcatcd. The lorma:ioo ol the product \\.I\ conlirmcd

rcmlp

by the X-ray X-ray

dillraclirm

p.atcrn

diflractomctcr

using

rccordcd

Ni

liltcrcd

on a Diana Cu

KY

\Iruclurc

of

monoclinic

Rolto

and

IYI. the X-ray

rcportcd

rclincd

on

hy Lopu/

&II;I ol’ CcTc,O,,

powder

the prcscnt work wcrc indcvcd wcrc lurlhcr

[I?]. Ba\cd

Baran

cell paramelcrs

the

CI al.

prcparcd

in

and the ccl1 paramctcrs

hy 1hc Icaj!-squares

method

using

the computer programmc I AIIS\K IlJ]. The indcxod X-ray Dada cd CcTc,O,, arc eivcn in Tahlc I.

(A =

0.1541X nm) redialion. The

mas, loas mcasurcmcnt\

ol

1.0 ,: with

contamcd hcisht

a scnsitivlty

01 I pe.

in it machimblc

and

diamctcr

X mm

of

were carried

out in a

having a loading

C’ahn vacuum microbalancc.

horon

diamctcr

The

capacity

nilridc

ccl1 ol Y mm

:I central

with

1.0 mm on the iid. The

furnace

to within

+

I K.

whore temperature The Icmpcraturc

CcO,(\)

and CcTc,O,,(s)

was maintained by a

was mcasurcd

/J( Pa) = (dn,/dr)[ whcrc

cross-sectional

tcrmining

The Clausing

Au

[I II. The

conlinuously isothermal Knudsen vapour

ma

trmpcraturc. ccl1 were

prcsburc\

of In. Zn.

as a Iunction The

01 Tc,(g)

of lime al an

microhalancc

calibrated

by

Ag and

was monilorc:l

loss of the sample

on u recorder

and

dctcrmining

over Tc(s)

I l(~A)l(?.2X

x IO’)1

TIM

(2)

dwtldr is the rate of mass loss (g s ‘). A is the

tcmpcraturc

tcmpcralurcs

from the ralc

/one of a

chromcl-alumcl thcrmocouplc placed near fhc cell. The thormocouplc was previously calibrated by de the mcltmg

wcrc mcasurcd

ol mass loss using the relation

orilicc

cell was hcalcd

under vacuum (6x IO ’ Pa) in an isothermal re&tancc

was

\amplc

arca (K).

factor

as 0.524:! ~0.017X of Te,(g)

the the

Using

over TcO,(s).

orifice

(cm’).

T

in the prcscnl

hy dctcrmining

lhis

values reported

Clausing

factor.

is the

mas5 of the vaporil-

k is the Clausing

[IS].

lactor

study was derived

the rate of mass loss

over Tc(s) at various temperatures

vapc\ur prcssurc

and TeO,(g)

~,f the

M is rhc molar

(gmol ’) and

ing spccics

and using

[161.

in the litcraturc partial

wcrc mcasurcd

pressures

TcO,(g)

over TcO,(s)

prcbsurc

values agreed well with the Eltcrature

of

and the vapour values

1171. The over arc The

sampls

thermal S K min lyrcr

was hcatcd

conditions

’in

(model

in dry air

under

up to 1473 K at a constant

a SINKU-RICO TGD-7000)

(ULVAC) equipped

gold image heating

furnace.

was independently

monitored

non-isorate of

thermal

ana-

with

an infrared

The sample

temperature

by a calihratcd

Pt to

mcasurud

in Tablo

is good agrccmcnl lit values. perature

The

log I>(TeO,)(

Alumina

expressed

cups were

ment.

Isothermal

carried

out at 1173, 1193. 1213 and 1233 K in the n:,,ne

balance

heating

for evaluating

measurements

the kinetic

were

parameters.

kPa) + 0.07 = Gihhs

values of TcO,(g)

a~ various

tcmporalurcs

the corresponding

Isast-

the cxpcri::umtal 01 p(TcO,.g)

11213/7’(K)

energy change

tcm-

+X.78

for reaction (I)

(3) is

+ 2A,G=Te02(g)

- A,G”CeTe,O,,(s) A,G”

and the with

hy the cquation

hy the equation

A,G” = A,G”CeO,(s)

also

hetwccn

dependence

can hc reprcsentcd

The standard

sintercd alumina was used as the refcrencc material. A sample size of around ho mg was used in each experi-

pressure

2 and

squares lit is shown in Fig. I. It can hc !:c:en that there

PI + IO’% Rh thcrmocouplc

touching the sample holder. used as container material and

vapour

CcTc,O,,(s)+C’cO,(s) given

for CeTezO,,(s)

can be written

(4)

L,G”CcTe,O,,(s)

= L,G”CeO,(s)

+RTln whcrc

K is an cquilihrium

K =p’(TcO,)

+ U,<;“TcO,(g)

K

(5)

constant

t’or reaction

(I

).

given hy K = p?TeO:)cc, ro.‘ll<

(6)

c,<.
Assuming no interaction hetwccn condensed pha$cs which ale in equilibrium with TcO,(g). K can hc cxprcsscd a>

YW

IoilI 1016 10.11 lo43 IO.52

Thcrcforc 1,CXeTe,O,

(7) can bc evaluated as

A,G”CcTc,O,, =A,G”CeO,(s) +24C”TeO,(g) +2RTln p(Te0,)

(8)

Values of L\,G”TeO,(g) are taken from the literalure. assuming TeO:(I) as standard state. as our

I x07

4X7-1

3Y53

13.llto

4.447

IV155

7.027

'7706

li7Yfl

369.35

IZ.YuY

JS.h?X

Io6X

2O.lYh

IO80

2.5 IYY

X6.llO

IW2

31.567

III.XY6

6S.W

1104

38.340

I44h46

Ill6

47.872

IXS.YR7

mca\urcd

tempcraturc

tempcraturc

studies

of TcOI(s).

Lv,G’CcTc,O,,(s)

lit

Hcncc

= ~,G”CcO,(s)

i

ahovc

the melting

Eq. (X) hecomcs t ?A,GTeO,(l)

followed

2RTln p(TcO,)/p”(TcO,)

(Y)

with

composed

rcspcct

to

was calculated

time

The

from

mass

ments with respect to time (min) whcrc

/r’(TcO,)

is the partial

over liquid TcO,.

p”(Tc0,)

formation

of TeO,(g)

using the relation

data [IX]. The free encrgics of and TeO,(l) [ IY] arc values of CcO,(s)

from

the

d,G”CeTc,O, the following

[Ih]

The

data.

reported

arc given in T&k

values

2 and cxpresscd

for hy

relation:

A,(;” < CcTc,O,,.s.T

o = (u’: - W,,,l( w, - W,,)

at time

I and

the

> rt 20.0 kJ mol

’

controlled

hy Our

either

The thcrmogravimctric

curve in Fig. 2 indicates

the

suggests

decomposition

ing equation

with

sample

was idcntitied

tellurile. Based

thermal

CeOz

on

and

the cxpccted pattern

indicated the

from

the

data

X-ray

observed

loss for 2mol of the

the presence

decomposition

obtained

partly

of CeOz during

of the compound.

diffraction weight

loss

TcO,.

The

decomposed and the

cerium non-iso-

four tem-

peratures were chosen, 1173, 1193. 1213 ar,d 1233 K, to carry out the isothermal heating experiments IO eualuale the kinetic

The

parameters

(Y

(Y

such as rate constants

and

studies

or

phase

houndary

on the reaction

showed phase boundary

mecha-

control.

The

observed linearity in the rate of evaporation at each temperature as sbown in Fig. 3 in the present study

initiation of weight loss at I I73 K and the weight becomes constant at 1323 K. The product ZII the end of

diffraction

respectively.

kinetic models [20] to choose

diffusion

earlier

nism of ThTe,O,,

as pure

weight

the weight

The mechanism of the decomposition reactions resulting in solid/so!id and gaseous products may he

(YO2
reaction.

X-ray

linal

values were tit to various

weight.

yielding the best linear fit for the entire range for all the four tcmpcrstures.

(I())

data

(11)

W$,. W, and W, arc the initial

whcrc

the model

= -IhMX+().44Xh7‘(K)

agreed

(Y dc-

loss measurc-

data used in this study are

taken from the reported taken

pressure

fraction

at each temperature

constant

that

the

surface

throughout

ary controlled

area

of

the

reactant

hy the phase hound-

mechanism:

g(o) = I - (I - o)” = krlr,, where l/2

u is the fraction and

1

symmetries: the function the

reactant

dimensional (12)

is

the a range. and the rate govern-

can he represented

for

(12)

reacted

three-.

IWO-

and 11 is equal IO 113. and

one-dimensional

r,. is the radius of the reactanl and x(a) is of ~1. Assuming that the change in radii of to

the

symmetry

product

is negligible,

for

the value of n &comes

oneI: Eq.

reduces tc

energy of activation. The weight

loss at each isothermal

temperature

was

(13)

I lT( K) m ,m Arrhcnius

nlot as shown in Fig. 4 gave

4. Cunclnsion CcTe.0,. TeO.(

p)

i\

found

as the

pressure\

ol’ TcO,(S)

wcrc dctcrmincd The CYvalues calcu!ated

at lo-n isothermal

tcmpera-

lures. 1173. 1193. 1213 and 123.1 K. wcrc lit IO Eq.

(13)

and hcsl lit linear plots wcrc ohlai!icd in each cast as shown in Fig. 3. The rate constants k derived from the slopes of the linear given

in Tahlc

plots

3. The

at Ihesl: tcmpcralures

rcprescntation

of

arc k and

-In

techniqus. lion

inu air

were

diiions action

and

CeTe,O,(s)

IO

the vapour and CeO,(s)

&fusion

mass loss

free cncrav of the forrna-

was ohtaincd

f&m

the TeO.(g)

pressure for the first time.

The kinetics

of the dccomuosition studied

and achvation

cvalualcd. I

over

incongrucntly

spccics

bv the Knudsen

The molar Gibbs

or: CcTc.O,(s)

vapour

IO vaporize

vapori@

The

reaction

under ‘isothermal

in llow-

heating

con-

energy and rate constants

were

mechanism

of the decomnosition

was fc und IO he phase boundary

re-

controlled.

*ooj 3 80

*

1

Acknowledgments The authors

360 i

5

are thankful

tor. Radiochemistry

Jam. Head. Fuel Chemistry interest in this work.

3404

3 20

to Dr.

D.D.

and ~solope Group Division

Sood.

Direc-

and Dr.

H.C.

for their

keen

J

300!I (I 80

,

011

, 0 82 IIT

Fig. 4. Arrheniw CeTe>O.(\).

/ 0 03

I

/ 0 84

0 85

11, . 1000

References

086

III M.G

Adamwn. E.A. Auken and T.R. Lmdemer. 1. Nd.

the I_‘] H. Klcvldmp. 1. Nd

~f~urr.. 1.31(IYXS) 121.

s-(

h

hn\hr,,

1.1 r,,

I J
_‘I-, (,W/T,

7%.VJ