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Results for “electrical resistance measurements”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Measuring Electrical Resistivity Of Compacted Powder

Slightly modified micrometer used in conjunction with special cup to measure electrical resistance of specimen of powder as function of packing fraction. Powder pressed between anvils of micrometer, which make electrical contact with specimen. Device used in manufacturing batteries to determine effective electrical conductivities of powders loaded into plastic sheets to make battery substrates. Coupled with good mathematical description of expected conductivity of particulate composite as function of packing density. Also serves as tool for evaluating conductivity of dispersed phase, as well as evaluating electrical resistances of interparticle contacts.

Shlichta, Paul J.↗
NASA NTRS1970

A Study of the Electrotransport in Thin Films: An Advanced Method for the Study of Electrotransport in Thin Films Using Electrical Resistance Measurements

To date, very little is understood about electrotransport in thin films. One reason for this is the lack of methods in which electromigration can be adequately monitored dynamically. In this thesis, a new nondestructive method for the study of the electrotransport phenomenon in thin aluminum films is presented. This method makes use of electrical resistance measurements of various regions along the test sample to monitor changes in resistance resulting from electromigration. The advantage of this method is that resistance changes can be observed long before void formation can be seen using standard microscopy methods. In order to achieve the best efficiency using this method, special consideration must be given to the design of the sample. Design problems and their respective solutions are given. The results of the electrical resistance measurements are interpreted by means of photographs taken with an scanning electron microscope. The increase in resistance of the aluminum samples is interpreted to be due to void formation. The expected decrease in resistance near the anode was never observed. It is shown that mass accumulation takes on the form of hillocks and whiskers on the surface of the aluminum film, which does not contribute appreciably to conductivity.

Hummel, R. E.↗
NASA NTRS2018

Influence of Fiber Content, Thermal Cycles and Creep on Electrical Resistivity Measurements of SiCf/SiC Minicomposites

Fiber-reinforced Ceramic Matrix Composites (CMCs) are currently being used in high-temperature applications such as jet engine components. In such extreme environment applications, materials are exposed to many mechanical and thermal loading cycles during the life of the component. This exposure can degrade the component, and thus, components need to be monitored and inspected during service. The electrical resistivity nondestructive evaluation technique has been shown to be very sensitive to damage in CMCs, and although its performance is highly dependent on temperature, this temperature-dependence is still not well understood. Therefore, this current study aims to establish the influence of thermal cycles, creep, CVI-SiC matrix cracks and fiber volume fraction on the electrical resistance of Hi Nicalon and Hi-Nicalon Type S SiC fiber-reinforced minicomposites with BN interphases. Minicomposites with 97% CVI-SiC matrix volume fraction were used to characterize the electrical resistivity of the CVI-SiC matrix. Next, models were constructed to calculate fiber resistivity and onset and evolution of damage during tensile testing at room-temperature. The thermal cycles were achieved by heating as-received and precracked specimens to 1200°C and then cooling them to room temperature, with or without applied stress on fibers.

creep↗
NASA NTRS1993

Apparatus Measures Seebeck Coefficient And Resistivity

Electrical measurements made by four point probes, two of which double as temperature probes. Laboratory apparatus measures both Seebeck coefficients and electrical resistivities of candidate thermoelectric materials at temperatures from ambient to 1,300 K. Apparatus makes possible to take both measurements alternately and in rapid succession during same heating cycle, thereby reducing distortion.

Zoltan, Leslie D.↗
NASA NTRS1972

Thermal conductivity of austenitic stainless steel, SRM 735, from 5 to 280 K

Thermal conductivity and electrical resistivity measurements were conducted on two lots of an austenitic stainless steel. Electrical resistivity measurements were performed on the second lot, both before and after the material was hot-swaged and reannealed to a size 1/10 the original diameter. These measurements indicate that this steel can be swaged and reannealed without an appreciable change in thermal conductivity. Electrical resistivity measurements as well as direct thermal conductivity measurements on several specimens from both lots indicate a material variability in these lots of less than 1% in thermal conductivity.

Hust, J. G.↗
NASA NTRS1971

Room temperature measurements of electrical resistivity and thermal conductivity of various graphites

Room temperature thermal conductivity measurements were completed on 10 graphite samples selected from the lot of 120 to uniformly span the range of electrical resistivity values. From these data and other measurements a thermal conductivity-electrical conductivity correlation was established to predict room temperature thermal conductivity values for the graphite samples. The correlation, expressed by a parabolic equation, represents available thermal and electrical conductivity data to about + or - 8%.

Mcelroy, D. L.↗
NASA NTRS1992

Automated High-Temperature Hall-Effect Apparatus

Automated apparatus takes Hall-effect measurements of specimens of thermoelectric materials at temperatures from ambient to 1,200 K using computer control to obtain better resolution of data and more data points about three times as fast as before. Four-probe electrical-resistance measurements taken in 12 electrical and 2 magnetic orientations to characterize specimens at each temperature. Computer acquires data, and controls apparatus via three feedback loops: one for temperature, one for magnetic field, and one for electrical-potential data.

Parker, James B.↗
NASA NTRS1996

Constant-Current Source For Measuring Low Resistances

Constant-current source constructed for measuring electrical resistances up to few ohms in power-supply equipment. By setting current at 1 A and measuring resulting voltage drop across item under test, one obtains voltage reading numerically equal to resistance in ohms.

Toomath, Robert L.↗
NASA NTRS1986

Measuring Resistivities of Small Fibers

Technique for measuring electrical resistivities of fibers of graphite, silicon carbide/silicon nitride mixture, and other materials used in composites simple, accurate, and reproducible. Suitable for monofilament fibers with diameters of about 10 to 50 micrometers. Also adapted to two fiber strands.

Daniels, J.↗
NASA NTRS2018

Developing a Novel Platform for Characterizing Thermoelectric Materials for Uncooled Detectors for Land Imaging Applications

Thermal land imaging (imaging at ~8-14 micron optical wavelength) is an essential tool for understanding and managing terrestrial freshwater resources. Current thermal imaging instruments employ low temperature detectors, which require cryocoolers. Consequently, cost-saving reductions in size, weight, and power can be achieved by employing uncooled detectors. One uncooled detector concept, which NASA is pursuing, is a thermopile detector with sub-micron thick doped-Si thermoelectric materials. In order to characterize the thermoelectric properties of the doped silicon, we designed and optimized a novel apparatus. This simple apparatus measures the Seebeck coefficient with thermally isolated stages and LABVIEW automation. We optimized thermal stability using PID tuning and optimized the thermal contact between the thin film samples and stages using electrically conductive springs. Utilizing our apparatus, we measured the Seebeck coefficient of 0.45 micron thick phosphorus-doped single crystal Si samples bonded to alumina substrates. Using these Seebeck coefficient measurements and four-wire electrical resistivity measurements, we determined the relationship between the thermoelectric figure of merit and dopant concentration. These characterization results for doped-Si will guide our thermopile detector design to provide an optimal and competitive detector alternative for future thermal imaging instruments.

Reid, Riley A.↗