Publication Date

8-2016

Date of Final Oral Examination (Defense)

6-30-2016

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

Major Advisor

Darryl Butt, Ph.D.

Advisor

Yanliang Zhang, Ph.D.

Advisor

Lan Li, Ph.D.

Advisor

Patrick M. Price, Ph.D.

Abstract

Thermoelectric half-Heusler compounds have potential to convert the heat wasted from industrial and transportation processes to useful electricity. Among the highest performing half-Heusler compounds are nano-structured bulk materials which have been arc-melted, pulverized into a nano-powder, and sintered by DC-hot press. High performing n- and p-type half-Heusler compounds with nominal composition of Hf0.25Zr0.75NiSn0.99Sb0.01 and Nb0.75Ti0.25FeSb, respectively, have been provided to us in both dense and powder form by our collaborators at the University of Houston. We consolidate these powders by SPS, refine these powders to improve both particle size and phase-purity, and synthesize these compositions by an alternative mechanical alloying process. In addition to these compositions, we investigate these same base compositions with different doping levels as well as compounds with different base compositions.

Through mechanically alloying processes, we are able to reduce wide distributions of grain sizes in as-received materials ranging from sub-micrometer to larger than 20 μm, to a narrow distribution of grain sizes ranging from 300 – 700 nm. Although single phase, Hf-containing half-Heusler compositions were not successfully synthesized by mechanical alloying, we demonstrate the ability to make useful quantities of single-phase, Hf-free nano-powders in a rapid, single-step process. Finally, the thermoelectric performance for several compositions of half-Heusler compounds, synthesized and consolidated by several processes, are compared.