Electrochemical removal of oxygen in amorphous Zr55Cu30Al10Ni5

Contamination with oxygen is known to reduce the processability and otherwise affect the properties of Zr-based bulk metallic glasses (BMGs). Due to their affinity for oxygen, however, it is difficult and/or expensive to reduce the oxygen level in these materials. As a result, the glass-forming ability (GFA) of commercial-grade BMGs is significantly lower than that of research-grade materials. We present the application of a novel electrochemical method to this problem. The general principle is to remove oxygen from the material by direct electrochemical reduction in a molten-salt electrolyte. A cathode consisting of a porous metallic phase containing dissolved oxygen is submerged in a molten mixture of chlorides. When a current is applied, oxygen is ionised at the cathode, dissolved in the molten salt and discharged at the anode. We investigate thermodynamic and kinetic limitations to the reduction in oxygen content and the resulting improvement in GFA that can be achieved when this method is applied to glass-forming alloys such as Zr55Cu30Al10Ni5.