STUDY OF THE SUBLIMATION AND VAPORIZATION OF ALKALI

METAL PERTECHNETATES, MTcO4 (M = Na,K, Cs)

Institute of Physical Chemistry Russian Academy of Sciences

German K., Peretroukhin V.

Main reasons for the accumulation of volatility data

on 99Tc(VII) compounds

understanding of Tc behavior in the procedures of radioactive wastes vitrification

basis for estimating of possible environmental contamination during accidental nuclear reactors.

basis for estimating conditions of high - temperature technology procedures (conversion of white inclusions, reprocessing in molten salts)

basis for estimating conditions for high temperature analytical procedures (decarbonization, …)

State of knowledge of volatile Tc species

At < picogram level - TcO3 (Eichler, Domanov, 1975, JINR Steffen, Bachman, 1978), HTcO4

At micro and macro level

Tc2O7, MTcO4 (Boyd, …)

(MTcO4)2, (Kuranov,1986)

Tc2O5, Gibbson,1993)

Fusion temperatures NaTcO4 - 1063 K

KTcO4 - 803 K

CsTcO4 - 863 K

Considerable information is found on volatility of Tc during radioactive wastes vitrification

Evaporation rate for NaTcO4 was reported to be 0.37 mg*cm-

2*min-1 at 700 оС and increased

to 3.2 mg*cm-2*min-1 at 1050 оС

(German, Peretrukhin, 1990) Tc - Carbonyls (Suglobov) Tc - acetate-chloride (German) Tc - fluorides

Experimental

Chemically pure compounds MTcO4 (M= Na, K, Cs) were synthesized in our Laboratory

The high-temperature evaporation/sublimation was studied by thermogravimetry analyses (TGA)

Instrumentation : Q-1500D derivatograph (system F.Paulik-J.Paulik-L.Erday)

300 – 1300 K temperature region Dynamic and quasi-isothermal modes were used

Experimental thermogramms for CsTcO4 and CsI

under identical conditions - Starting sample mass 200 mg

- Controlled evaporation surface

- Nuclearised

instrument

175

180

185

190

195

200

500 600 700 800 900 1000Temperature, oC

M, m

g

CsICsTcO4

Fusion points

Sublimation/Evaporation rates for CsTcO4 and CsI as F(T)

Evaporation rate Wef of CsI and CsTcO4 measured in dynamic TGA mode (T-rate 10 deg/min)

0

2

4

6

500 600 700 800 900 1000

T, oC

Wef (

mg *

min

-1*c

m-2

)

CsICsTcO4

Evaporation rate linearization for fused salt sample of CsI and CsTcO4

in dynamic TGA mode

CsI and CsTcO4

-2

-1.5

-1

-0.5

0

0.5

0.0008 0.0009 0.001 0.0011

1/T, K-1

LOG

10(k

efM

iT1

/2)

CsI

CsTcO4

- pre-fused samples- temperature increase rate 10 deg/min- sample evaporating surface 1 cm2

- initial sample mass 200 mg