A STUDY OF HYDROGEN TRAPPING IN COLD-WORKED PURE NICKEL AND NICKEL-THORIA BY A PRESSURE MODULATION TECHNIQUE

Comparative experiments are reported investigating hydrogen trapping i n pure nickel and nickel-2% volume thoria. Both materials are studied in a heavily cold-worked condition and after subsequent annealing. The experimental data are phase and amplitude ratios of pressure signals observed during slowly modulated permeation through thin foils. Data f itting to a model involving both surface reactions and bulk diffusion gives diffusivity and permeability values. It is found that trapping c an be induced by cold working of either material and that it effective ly reduces the measured diffusivity. Annealing tends to diminish the e ffective trapping. In nickel-thoria the need to identify the nature of traps is highlighted.