Thin film ceramic thermocouples

Abstract

A thin film ceramic thermocouple (10) having two ceramic thermocouple (12, 14) that are in contact with each other in at least on point to form a junction, and wherein each element was prepared in a different oxygen / nitrogen / argon plasma. Since each element is prepared under different plasma conditions, they have different electrical conductivity and different charge carrier concentration. The thin film thermocouple (10) can be transparent. A versatile ceramic sensor system having an RTD heat flux sensor can be combined with a thermocouple and a strain sensor to yield a multifunctional ceramic sensor array. The transparent ceramic temperature sensor that could ultimately be used for calibration of optical sensors.

Description

PRIORITY INFORMATION [0001] This application claims priority to U.S. Provisional Application No. 60 / 561,393 filed on Apr. 12, 2004.BACKGROUND OF THE INVENTION [0002] The evolutionary development of new engine materials and designs has allowed turbines to be operated at much higher temperature and thus, achieve higher efficiencies. In order to evaluate engine performance, it is necessary to monitor the temperature of all the static and dynamic components in the turbine environment. Several techniques have been used to monitor the surface temperature of blades and vanes, including wire thermocouples, infrared photography, pyrometry and thermal paints. One technique employs imbedded thermocouple wires in the blade wall however this may cause serious structural and aerodynamic problems, disturbing the flow of cooling air. Infrared photography has been used for this purpose but is a non-contact method where the thermal radiation patterns of an object are converted into a visible image. T...

AI Technical Summary

Benefits of technology

[0003] As operating temperatures in gas turbine engines are pushed to higher levels, engine designs must rely on complex cooling systems and ceramic coatings to maintain the structural integrity of the metallic blades and vanes. Embedded wire thermocouples are frequently used for temperature measurement in the gas turbine engine environment but as the blades get thinner, structural integrity can be compromised. A thin film ceramic thermocouple based on indium-tin-oxide (ITO) alloys may be used to measure the surface temperature of both static and rotating engine components employed in propulsion systems that operate at temperatures in excess of 1300° C. By fabricating two different ITO elements, each having substantially different charge carrier concentrations, it is possible to construct a robust ceramic thermocouple. A thermoelectric power of 6.0 μV / ° C., over the temperature range 25-1250° C. has been measured for an unoptimized thin film ceramic thermocouple.

[0004] Testing in a computer controlled burner rig showed that ITO thermocouples exhibited a linear voltage-temperature response over the temperature range 25-1250° C. Not only was the thermoelectric power a critical measure of performance of thermocouples in these applications but the electrical and chemical stability was equally important in these harsh conditions, since these temperature sensors must survive tens of hours of testing at elevated temperatures. To enhance the carrier concentration difference in the different legs of thermocouple, ITO thin films were deposited by r.f. sputtering in different oxygen, nitrogen, and argon plasmas. ITO thin films prepared in nitrogen rich plasmas have survived temperatures in excess of 1575° C. for tens of hours. SEM micrographs revealed that the surfaces of the ITO thin films after high temperature exposure exhibited a partially sintered microstucture with a contiguous network of ITO nanoparticles. In these films, nitrogen was metastably retained in the individual ITO grains during deposition. Nitrogen diffused out of the bulk grains at elevated temperature and eventually became trapped at grain boundaries and triple junctions. Not only are these ceramic thermocouples being considered for propulsion applications, other applications such as glass melting and steel making are also being considered. Thermal cycling of ITO thin films in various oxygen partial pressures showed that the temperature coefficient of resistance (TCR) was nearly independent of oxygen partial pressure, with TCR's ranging from 1320 ppm / ° C. to 1804 ppm / ° C. at temperatures above 800° C., and eventually became independent of oxygen partial pressure after repeated thermal cycling below 800° C.

[0005] It is an object of the present invention to provide a versatile ceramic sensor system having an RTD heat flux sensor which can be combined with a thermocouple and a strain sensor to yield a multifunctional ceramic sensor array.

[0006] It is another object of the invention to provide a ceramic sensor array prepared under different plasma conditions, i.e. different oxygen and nitrogen partial pressures in the argon plasma and having very high temperature stability.

Problems solved by technology

Embedded wire thermocouples are frequently used for temperature measurement in the gas turbine engine environment but as the blades get thinner, structural integrity can be compromised.

Images