Gustave C. Fralick

Use of a Multiwavelength Pyrometer in Several Elevated Temperature Aerospace Applications

A multiwavelength pyrometer was developed for applications unique to aerospace environments. It was shown to be a useful and versatile technique for measuring temperature, even when the emissivity is unknown. It has also been used to measure the surface temperatures of ceramic zircornia thermal barrier coatings and alumina. The close agreement between pyrometer and thin film thermocouple temperatures provided an independent check. Other applications of the multiwavelength pyrometer are simultaneous surface and bulk temperature measurements of a transparent material, and combustion gas temperature measurement using a special probe interfaced to the multiwavelength pyrometer via an optical fiber. The multiwavelength pyrometer determined temperature by transforming the radiation spectrum in a broad wavelength region to produce a straight line (in a certain spectral region), whose intercept in the vertical axis gives the temperature. Implicit in a two-color pyrometer is the assumption of wavelength independen...

Thin film TiC/TaC thermocouples

TiC and TaC thin films were investigated, for the first time, for thin film thermocouple applications. Thin films of TaC and TiC were deposited on electronic grade alumina substrates using the r.f. sputter deposition technique. Sheet resistance of the thin films was measured using a four point probe. It was observed that the sheet resistance of the films depends critically on the deposition parameters such as substrate temperature during deposition, sputter gas pressure and r.f. power used. The deposition parameters were optimized to yield the lowest sheet resistance of the thin films at room temperature. The thermoemf of the deposited films was measured as a function of temperature in a vacuum using a home made device. It was observed that thin films of TaC and TiC yield fairly high and stable thermoemf throug hout the temperature range of stability. Under the optimized deposition conditions, thin film thermocouples were fabricated. The thermocouples were calibrated against temperature and the output was measured in vacuum (pressure <10−6 Torr). TiC/TaC thermocouples yield stable output up to 1350 K, temperatures above which breakdown occurs. The thermocouple output was theoretically estimated from the thermoemf measured, and compared. It was observed that these thermocouples yield reproducible output in the temperature range of stability and hold excellent potential for high temperature thin film temperature sensor applications in vacuum or inert atmospheres.

Development and application of high-temperature sensors and electronics for propulsion applications

High temperature sensors and electronics are necessary for a number of aerospace propulsion applications. The Sensors and Electronics Branch at NASA Glenn Research Center (NASA GRC) has been involved in the design, fabrication, and application of a range of sensors and electronics that have use in high temperature, harsh environment propulsion environments. The emphasis is on developing advanced capabilities for measurement and control of aeropropulsion systems as well as monitoring the safety of those systems using Micro/Nano technologies. Specific areas of work include SiC based electronic devices and sensors; thin film thermocouples, strain gauges, and heat flux gauges; chemical sensors; as well as integrated and multifunctional sensor systems. Each sensor type has its own technical challenges related to integration and reliability in a given application. These activities have a common goal of improving the awareness of the state of the propulsion system and moving towards the realization of intelligent engines. This paper will give an overview of the broad range of sensor-related development activities on-going in the NASA GRC Sensors and Electronics Branch as well as their current and potential use in propulsion systems.

Development of Thin Film Ceramic Thermocouples For High Temperature Environments

The maximum use temperature of noble metal thin film thermocouples of 1100 C (2000 F) may not be adequate for use on components in the increasingly harsh conditions of advanced aircraft and next generation launch technology. Ceramic-based thermocouples are known for their high stability and robustness at temperatures exceeding 1500 C, but are typically found in the form of rods or probes. NASA Glenn Research Center is investigating the feasibility of ceramics as thin film thermocouples for extremely high temperature applications to take advantage of the stability and robustness of ceramics and the non-intrusiveness of thin films. This paper will discuss the current state of development in this effort.

A Thin Film Multifunction Sensor for Harsh Environments

ABSTRACT The status of work at NASA Glenn Research Center to develop a minimally intrusive integrated sensor to provide real-time measurement of strain, heat flux and flow in high temperature environments is presented in this paper. The sensor can be beneficial as a single package to characterize multiple stress and strain modes simultaneously on materials and components during engine development and validation. A major technical challenge is to take existing individual gauge designs and modify them into one integrated thin film sensor. Ultimately, the goal is to develop the ability to deposit the sensors directly onto internal engine parts or on a small thin substrate that can be attached to engine components. Several prototype sensors constructed of platinum, platinum-rhodium alloy, and alumina on constant-strain alumina beams have been built and bench-tested. The technical challenges of the design, construction, and testing are discussed. Data from the preliminary testing of the sensor array is presented. The future direction for the sensor development is discussed as well.

Nuclear size corrections to the energy levels of single-electron and -muon atoms

We formulate an analytic method which accounts for the finite size of the nucleus by treating it as a boundary value problem. The method is used to obtain solutions of the Dirac equation for a central potential that is proportional to 1/r only for values of the radial coordinate greater than a given value R. Our results are applied to a non-perturbative calculation of the nuclear size corrections to the energy levels of single-electron and single-muon atoms. For values of the nuclear charge number Z greater than 40 in the case of electronic atoms, and greater than 1 in the case of muonic atoms, we find large discrepancies between our results for the atomic energy levels and those obtained from first-order relativistic perturbation theory.

Steady-State and Frequency Response of a Thin-Film Heat Flux Gauge

Anewand simplerdesign ofthin-e lm heate ux gaugehasbeendeveloped forusein high-heat-e ux environments. Heat e ux gauges of the same design were fabricated on three different substrates and tested. The heat e ux gauge comprises a thermopile and a thermocouple junction, which measures the surface temperature. The thermopile has 40 pairs of S-type thermocouples and is covered by two thermal resistance layers. Calibration and testing of thesegaugesweree rst carriedoutin an arc-lamp calibrationfacility.Sensitivityofthegaugewasdiscussed in terms of the relative conductivity and surface temperature. The heat e ux calculated from the gauge output was in good agreement with the precalibrated standard sensor. The steady-state and the transient response characteristics of the heat e ux gauge were also investigated using a carbon dioxide pulse laser as a heat source. The dynamic frequency response was evaluated in terms of the nondimensional amplitude ratio with respect to the frequency spectrum of a chopped laser beam. The frequency response of the gauge was determined to be about 3 kHz. The temperature proe les in the thin-e lm heat e ux gauge were obtained numerically in steady-state conditions using FLUENT and compared with the experimental results. Nomenclature d = thickness of thermal resistance layer, m Es = thermopile voltage output, mV K = thermal conductivity, W/m C K = relative conductivity, W/m C N = number of thermocouple pairs in the thermopile Q = heat e ux, W/m 2 S T = absolute thermoelectric power at temperature T, mV/ C T = temperature, C t = time, s = absorptivity d = thickness difference in thermal resistance layers between 1 and 2 Subscripts 1, 2 = thermal resistance layers 1 and 2, respectively

An experimental study of a radially arranged thin-film heat-flux gauge

A new thin-film heat-flux gauge was designed and fabricated on three different substrate materials. Forty pairs of Pt - Pt/10% Rh thermocouple junctions were deposited in a circular pattern on the same plane of the substrate. Over the thermocouples, 5 and 10 m thick thermal resistance layers were deposited to create a temperature gradient across those layers. Calibration and testing of these gauges were carried out in an arc-lamp calibration facility. The heat flux calculated from the gauge output is in good agreement with the value obtained from the pre-calibrated standard sensor. A laser was also used to test the steady-state and dynamic responses of the heat-flux gauge. During the steady-state test, the time constant for the heating period was 30 s. The frequency response of the heat-flux gauge was measured in the frequency domain using a laser and a chopper. The responses from an infrared detector and the heat-flux gauge were measured simultaneously and compared. It was found that the thin-film heat-flux gauge has a dynamic frequency response of 3 kHz.

Thermoelectric power factor of In2O3:Pd nanocomposite films

A nanocomposite exhibiting large thermoelectric powers and capable of operating at temperatures as high as 1100 °C in air was fabricated by embedding palladium nanoparticles into an indium oxide matrix via co-sputtering from metal and ceramic targets. Combinatorial chemistry techniques were used to systematically investigate the effect of palladium content in these nanocomposite films on thermoelectric response. Based on these rapid screening experiments, the thermoelectric properties of the most promising nanocomposites were evaluated as a function of post-deposition heat treatment at high temperatures. An n-type nanocomposite film was developed exhibiting a power factor of 4.5 × 10−4 W/m·K2 at 1000 °C in air.

Developing Multilayer Thin Film Strain Sensors With High Thermal Stability

A multilayer thin film strain sensor for large temperature range use is under development using a reactively-sputtered process. The sensor is capable of being fabricated in fine line widths utilizing the sacrificial-layer lift-off process that is used for microfabricated noble-metal sensors. Tantalum nitride films were optimized using reactive sputtering with an unbalanced magnetron source. A first approximation model of multilayer resistance and temperature coefficient of resistance was used to set the film thicknesses in the multilayer film sensor. Two multifunctional sensors were fabricated using multilayered films of tantalum nitride and palladium chromium, and tested for low temperature resistivity, TCR and strain response. The low temperature coefficient of resistance of the films will result in improved stability in thin film sensors for low to high temperature use.