ThO2

The thermal linear expansion of ThO2 is well established. Touloukian et al. [61] list more than 34 different experimental determinations which are in excellent agreement and recommended the following equation (150-2,000 K):

% AL/Lo = -0.179 + 5.097 x 10-4(Г/K) + 3.732 x 10-7(Г/K)2-7.594

x 10-11(T/K)3; (25)

Touloukian states that the equation has an accuracy of ±3 % or less. Hoch and Momin [72] showed that their data, obtained by XRD measurements of thermal expansion of ThO2, is in very good agreement with that obtained by Ohnysty and

Temperature (K)

%AL/L0

Expansion coefficient, x10 6 K 1

Mean

Instantaneous

298.15

0.0

8.43

8.43

400

0.087

8.53

8.63

500

0.174

8.63

8.82

600

0.264

8.73

9.01

700

0.355

8.83

9.20

800

0.448

8.93

9.39

1,000

0.641

9.13

9.77

1,200

0.842

9.33

10.2

1,400

1.05

9.53

10.5

1,600

1.27

9.73

10.9

1,800

1.49

9.93

11.3

2,000

1.72

10.1

11.6

2,500

2.34

10.6

12.5

3,000

3.01

11.1

13.4

3,500

3.72

11.6

14.3

Rose [73] by dilatometry. Their data also agreed well with that of Aronson et al. [74] and Hirata et al. [75]. Hoch and Momin [72] recommended the following equation for ThO2 (293-2,373 K):

% AL/L0 = -0.2426 + 7.837 x 10-4(Г/K) + 9.995 x 10^8(Г/K)2 (26)

The results obtained from the above equations are almost identical. Hoch and Momin concluded from their studies that the lattice defects in ThO2 were probably of the Frenkel type.

The extrapolation data to higher temperatures other than those covered by measurements need caution [76]. The equation of Touloukian is valid in the range of 150-2,000 K and that of Hoch and Momin [72] should be used for extrapola­tion. The recommended values of thermal expansion of are shown in Table 10. Thermal expansion curve for ThO2 is shown in Fig. 7.

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