Impurity controlled diffusion reaction in thorium-vanadium system
Abstract
The effect of ppm level impurities present in the thorium metal on the diffusion reaction in thorium-vanadium system has been investigated by making “sandwich” type diffusion couples and annealing them in the temperature range of 900 to 1200°C. The microstructure of the diffusion zone has been examined by optical and electron microscopy. X-ray powder techniques have been employed to detect the presence of secondary intermetallic phases in thorium metal and in the diffusion zone. The chemical composition of these phases and the elemental distribution in the diffusion zone have been established by using an electron microprobe analyzer. The time and the temperature dependence of the diffusion zone width is used to evaluate the kinetics of layer growth. Present studies have shown that impurities like iron, copper and aluminum form low melting point intermetallic compounds in thorium metal and segregate at the grain boundaries. Further in a diffusion reaction at the elevated temperatures, these thorium rich secondary phases melt and form a liquid film between the thorium and the bonding metal, vanadium in the present case. The rate controlling process appears to be an interfacial chemical reaction involving dissolution of vanadium in the thorium rich liquid.
- Publication:
-
Metallurgical Transactions
- Pub Date:
- May 1974
- DOI:
- 10.1007/BF02644325
- Bibcode:
- 1974MT......5.1141R