A Spectrophotometric Study of the Oxidation of Tantalum

Collateral spectrophotometric and gravimetric studies of the air oxidation of tantalum have been conducted over the range of 220° to 350°C. Good reproducibility of data was observed. This metal obeys a logarithmic law up to 320°C and a parabolic law above. Arrhenius plots of the logarithmic rate law data give temperature dependences of 12.57 kcal/mole on the basis of the microgravimetric method and 12.0 kcal/mole from the spectrophotometric method. The Arrhenius plot of initial parabolic rate law data gives 27.2 kcal/mole in good agreement with a previous value obtained by Gulbransen and Andrew. The two methods have been used to estimate the ratio of true to apparent surface area to be 10.