Thermoelectric Properties of Ceramic Thin Film Thermocouples

摘要

Thin film ceramic thermocouples are being developed to assess temperatures beyond 1400℃ in the hot sections of gas turbine engines. Several promising ceramic materials were systematically investigated as thermoelements including indium-tin oxide (ITO), alumina doped zinc oxide (ZnO) and a NiCrCoAlY/alumina nanocomposite. These ceramic thermoelements were initially tested relative to a platinum reference electrode and the resulting thermoelectric properties were evaluated. Bi-ceramic junctions comprised of the most stable and responsive ceramic thermoelements, I.e. Those thermoelements with the largest and most stable Seebeck coefficients relative to platinum, were fabricated and tested. Bi-ceramic junctions based on nitrogen-doped ITO:oxygen-doped ITO exhibited excellent high temperature stability and reproducibility, however, this thermocouple pair had a relatively low Seebeck coefficient (6μV/℃). Alumina doped ZnO:ITO thermocouples generated a very large electromotive force at low temperatures but lacked high temperature stability. When nitrogen-doped ITO was combined with a NiCoCrAlY/alumina nanocomposite, a very large and stable Seebeck coefficient (375 μV/℃) was realized. Ceramic thermocouples based on these materials were demonstrated at temperatures up to 1200℃ and the potential for temperature sensors and energy harvesting for the production of electrical energy at a remote location with minimal processing is discussed.