Date of Award

Spring 2018

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Metallurgical Engineering

Committee Chair

Hsin-Hsiung Huang

First Advisor

Jerome Downey

Second Advisor

Douglas Cameron

Third Advisor

Prabhat Tripathy

Abstract

Refractory metals are commonly alloyed for improved corrosion resistance, thermal stability, and strength. In service, these alloys form highly stable oxides under mildly oxidizing conditions at relatively low temperatures. In order to recycle these materials, high temperature electrochemical processing is required to reduce the refractory metal oxides. To abet experimental evaluation of the electrochemical reduction process under development at the Idaho National Laboratory, binary mixtures of selected refractory metal oxide powders were sintered to produce cathode pellets, which could be suspended in the molten salt electrolyte during reduction experiments. Preparatory literature review revealed a paucity of published information relative to the formation of intermediate oxides in these binary systems, and particularly so for the tantalum oxide/hafnium oxide system. The subject research was undertaken to begin to fill the data void.

Binary oxide mixtures were prepared to approximate the composition of known intermediate compounds in the Ta2O5 – WO3, Ta2O5 – Nb2O5, Ta2O5 – HfO2, and Ta2O5 – TiO2 systems. Differential thermal analysis was employed to identify heat flow inflections that could be associated with sintering in the subject systems. Based on the resultant data, each of the various binary oxide mixtures was sintered at two temperatures, one below and one above each significant thermal event. Each experimental product was characterized by scanning electron microscopy and x-ray diffraction to evaluate the degree of sintering. The characterization results firmly established that the minimum sintering temperatures corresponded to the DTA inflections identified in the Ta2O5 – WO3, Ta2O5 – Nb2O5, and Ta2O5 – TiO2 systems. However, the information obtained for the Ta2O5 – HfO2 system is inconclusive and warrants further study.

Comments

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Metallurgical & Materials Engineering

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