Date of Graduation
2018
Document Type
Dissertation
Degree Type
PhD
College
Statler College of Engineering and Mineral Resources
Department
Industrial and Managements Systems Engineering
Committee Chair
Edward M Sabolsky
Committee Co-Chair
Xingbo Liu
Committee Member
Konstantinos A Sierros
Committee Member
Charter D Stinespring
Committee Member
Nianqiang Wu
Abstract
Many common electrical materials used in the current sensing applications suffer from structural and functional issues related to high operating temperatures (750°-1600°C), alternating reducing/oxidizing atmospheres, high pressures and corrosive environments. Therefore, there is a need for development of new materials, which are capable to operate under high-temperature and harsh-environments to provide real-time, accurate sensing during industrial processes such as coal gasification and power generation. In this study, electroconductive ceramic composites were fabricated by incorporating the 20-90 vol% of transition metal silicides (MoSi2, WSi2, NbSi2, TaSi 2, CrSi2) within refractory oxides (Al2O 3, ZrO2, Cr2O3), followed by sintering at 1370°-1600°C in argon. The densification, microstructural evolution, phase development and thermal stability of the composites were studied after sintering and further annealing by Archimedes, Scanning electron microscopy (SEM) and X-ray diffraction/Rietveld (XRD) techniques. Their non-isothermal and isothermal oxidation behavior was studied under ambient air using a thermogravimetric analyzer (TGA) at 50°-870°C to understand the key parameters influencing their high-temperature oxidation. The selected composites were also preoxidized at 1000°-1200°C for 10-120 minutes to better understand their high-temperature oxidation kinetics and surface layer formation, and hence, to enhance their oxidation resistance by forming a protective surface layer. XRD, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used for structural and surface characterization. In addition, their 4-point DC electrical conductivities were measured up to 800°-1000°C to study their electrical performance as a function of the composition and processing. A microstructural image analysis method was also developed for quantitatively characterizing the degree of distribution (homogeneity) within the composites. Lastly, thick-film embedded thermocouples (e.g. MoSi2-Al2O3//WSi 2-Al2O3) were fabricated using selected composites by a screen printing technique. Their thermoelectric properties were measured in argon by a typical hot-cold junction temperature measurements, while their structural and microstructural analyses were performed by XPS, XRD and SEM.
Recommended Citation
Yakaboylu, Gunes Alp, "Processing, Stability and High-Temperature Properties of Transition Metal Silicide-Refractory Oxide Composites for Electrical Applications" (2018). Graduate Theses, Dissertations, and Problem Reports. 6993.
https://researchrepository.wvu.edu/etd/6993
