Diffusion of Carbon in Niobium and Molybdenum

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Diffusion coefficients of carbon in niobium and molybdenum have been determined by the residual activity method with radioactive tracer ¹⁴C in the temperature ranges between 1168 and 1567 K for niobium and between 1271 and 1669 K for molybdenum. The temperature dependences of the diffusion coefficient of carbon in niobium and molybdenum are expressed by D/m² s⁻¹ = 2.2 × 10⁻⁶ exp(−152 kJ mol⁻¹/RT) and D/m² s⁻¹ = 5.2 × 10⁻⁶ exp(−163 kJ mol⁻¹/RT), respectively. Since the solubility of carbon in molybdenum is very small, the diffusion of carbon in molybdenum is strongly influenced by carbide precipitation at lower temperatures.