HYDROGEN TRAPPING AND PERMEATION IN NICKEL THORIA

A series of modulated permeation experiments have been performed on fo ils of cold-worked nickel and nickel thoria (NITD). The parameters of the measurements include modulation frequency and base pressure togeth er with the thickness, specimen temperature, and pretreatment of the f oil. Experiments were carried out between 373 and 920 K. The frequency response of the permeation flux shows a characteristic form which has been modeled satisfactorily. Permeation and trapping data are derived from the fitting of the model to experimental characteristics. The de gree of trapping diminishes as the extent of the annealing increases, and as the base pressure (driving) increases, the degree of trapping d ecreases. These effects suggest that the trapping sites had been intro duced by cold working, but that they are not directly associated with accumulation of hydrogen gas in the microvoids. It is suggested that d islocation networks formed around thoria particles are responsible for the trapping of hydrogen in NITD with a depth of 40 kJ/mole. Trapping has also been detected for cold-worked nickel, at much lower temperat ures than in NITD. Transmission electron microscopy (TEM) studies have also been correlated with measurements of hardness and resistivity to monitor the annealing process.