OXIDIZED NANOCRYSTALLINE FE-CU PSEUDOALLOY SUBJECTED TO HIGH-PRESSUREAND ELECTRODISCHARGE PULSES - MOSSBAUER AND X-RAY-INVESTIGATIONS

Nanocrystalline Fe15Cu85 pseudoalloy has been subjected to pulsed heat ing up to 1500 K at high pressure (8 GPa). Two regimes were studied: t he direct heating using electrodischarge through the sample and indire ct heating with the use of cylindrical heater around the sample. The t emperature and time conditions in both types of experiments were adjus ted to be equivalent. The discharge parameters (stored energy, dischar ge time, and magnitude of current pulse) were sufficient to move defec ts by conduction electrons, but insufficient to melt the sample. The p roperties of treated samples were studied using Mossbauer absorption s pectra and x-ray diffraction for three types of samples: (a) primary p owder treated by high pressure up to 8 GPa, (b) powder subjected to in direct pulsed heating at 8 GPa, (c) powder treated by electrical pulse s at 8 GPa. The x-ray diffraction pattern of primary powder exhibits p eaks of copper, iron, and copper oxide (CuO). The Mossbauer spectrum o f primary powder exhibits six peaks of alpha iron and some peaks near zero velocity due to the small iron clusters in the copper matrix and ultrafine clusters of paramagnetic phase x-Fe2O3. The transformation o f CuO to Cu2O takes place in the course of indirect heating, the Mossb auer spectrum being almost unchanged. The direct electrodischarge heat ing causes the appearance of new magnetic phase with the magnetic fiel d on iron nucleus 505 kOe, which corresponds to alpha-Fe2O3. The forma tion of alpha-Fe2O3 was confirmed by x-ray diffraction. At the same ti me the transformation of CuO to Cu2O is incomplete. These experiments demonstrate that high density current pulses, causing the electron win d, can be a useful tool to influence the structure of nanocrystalline powder. (C) 1998 American Institute of Physics.