Extraction of boron Fe8B2 ribbons by annealing under hydrogen flow

Abstract

Transition metal alloys often are difficult to be prepared as ribbons by conventional methods. If boron is added to these alloys, amorphous ribbons may be prepared by melt spinning. These amorphous ribbons have a better workability than their crystalline counterparts. However, the composition is different from the target composition. Upon annealing treatments in flowing hydrogen the boron may be extracted and the ribbon crystallizes. Thermodynamically the extraction of boron proceeds by the reaction of hydrogen with the borides formed during the crystallization of the ribbons. In order to investigate this extraction in more detail Fe8B2 amorphous ribbons were used. Thermogravimetric measurements were made at three different heating rates which permit to develop a thermokinetic description of the extraction process, which is controlled by chemical reactions and diffusion. The description allows to calculate the degree of boron extraction for various annealing procedures.