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NASA NTRS1985

Electronic readout systems for microchannel plates

The modes of operation of position-sensitive electronic readout systems which use high-gain microchannel plate (MCP) electron multipliers are described, and their performance characteristics, along with those of the MCP, are compared. Among the structures presented are the wedge-and-strip, Codacon, and multilayer coincidence-anode MAMA (Multimode Microchannel Array) arrays. Spatial resolution of 25 x 25 sq microns (coincidence anode arrays) is achieved with an array format of 256 x 1024 pixels. On the basis of the performance data it is concluded that the readout systems using only conducting electrodes offer the best performance characteristics.

Timothy, J. G.↗

NASA NTRS1992

The microstrip proportional counter

Microstrip detectors in which the usual discrete anode and cathode wires are replaced by conducting strips on an insulating or partially insulating substrate are fabricated using integrated circuit-type photolithographic techniques and hence offer very high spatial accuracy and uniformity, together with the capability of producing extremely fine electrode structures. Microstrip proportional counters have now been variously reported having an energy resolution of better than 11 percent FWHM at 5.9 keV. They have been fabricated with anode bars down to 2 microns and on a variety of substrate materials including thin films which can be molded to different shapes. This review will examine the development of the microstrip detector with emphasis on the qualities which make this detector particularly interesting for use in astronomy.

Ramsey, B. D.↗

NASA NTRS2005

Moisture-Induced Spallation and Interfacial Hydrogen Embrittlement of Alumina Scales

Thermal expansion mismatch stresses and interfacial sulfur activity are the major factors producing primary Al2O3 scale spallation on high temperature alloys. However, moisture-induced delayed spallation appears as a secondary, but often dramatic, illustration of an additional mechanistic detail. A historical review of delayed failure of alumina scales and TBC s on superalloys is presented herein. Similarities with metallic phenomena suggest that hydrogen embrittlement from ambient humidity, resulting from the reaction Al+3H2O=Al(OH)3+3H(+)+3e(-), is the operative mechanism. This proposal was tested by standard cathodic hydrogen charging in 1N H2SO4, applied to Rene N5 pre-oxidized at 1150 C for 1000 1-hr cycles, and monitored by weight change, induced current, and microstructure. Here cathodic polarization at -2.0 V abruptly stripped mature Al2O3 scales at the oxide-metal interface. Anodic polarization at +2.0 V, however, produced alloy dissolution. Finally, with no applied voltage, the electrolyte alone produced neither scale spallation nor alloy dissolution. These experiments thus highlight the detrimental effects of hydrogen charging on alumina scale adhesion. It is proposed that interfacial hydrogen embrittlement is produced by moist air and is the root cause of both moisture-induced, delayed scale spallation and desktop TBC failures.

Smialek, James L.↗

NASA NTRS2008

Moisture-Induced Delayed Spallation and Interfacial Hydrogen Embrittlement of Alumina Scales

While interfacial sulfur is the primary chemical factor affecting Al2O3 scale adhesion, moisture-induced delayed spallation appears as a secondary, but impressive, mechanistic detail. Similarities with bulk metallic phenomena suggest that hydrogen embrittlement from ambient humidity, resulting from the reaction Al(sub alloy)+3(H2O)(sub air) = Al(OH)(-) (sub 3) +3H(+) may be the operative mechanism. This proposal was tested on pre-oxidized Rene N5 by standard cathodic hydrogen charging in 1N H2SO4, as monitored by weight change, induced current, and microstructure. Cathodic polarization at -2.0 V abruptly stripped mature Al2O3 scales at the oxide-metal interface. Anodic polarization at +2.0 V, however, produced alloy dissolution. Finally, with no applied voltage, the acid electrolyte produced neither scale spallation nor alloy dissolution. Thus, hydrogen charging was detrimental to alumina scale adhesion. Moisture-induced interfacial hydrogen embrittlement is concluded to be the cause of delayed scale spallation and desktop thermal barrier coating failures.

Smialek, James L.↗

NASA NTRS1965

Short wide angle, 1-1/2 inch electrostatic image dissector with parallel plate resistive strip electronic multiplier Final report, 22 Feb. 1963 - 1 Nov. 1965

Electron optical imaging system and combination anode-deflection cone for electrostatic image dissector tube - testing and calibration

ELECTROSTATIC INSTRUMENT↗

NASA NTRS1986

Operational characteristics of Wedge and Strip image readout systems

Application of the Wedge and Strip readout system in microchannel plate detectors for the Extreme Ultraviolet Explorer and FAUST space astronomy programs is discussed. Anode designs with high resolution (greater than 600 x 600 pixels) in imaging and spectroscopy applications have been developed. Extension of these designs to larger formats (100 mm) with higher resolution (3000 x 3000 pixels) are considered. It is shown that the resolution and imaging are highly stable, and that the flat field performance is essentially limited by photon statistics. Very high speed event response has also been achieved with output pulses having durations of less than 10 nanoseconds.

Siegmund, O. H. W.↗

NASA NTRS2003

Electrodeposition of High Quality Nickel Phosphorous Alloys for Pollution Reduction and Energy Conservation

NASA and the University of Alabama in Huntsville have developed ecologically friendly, versatile nickel and nickel cobalt phosphorous electroplating processes. Solutions show excellent performance with high efficiency for vastly extended throughput. Properties include, clean, low temperature operation (40 - 60 C), high Faradaic efficiency, low stress and high hardness. A variety of alloy and plating speed options are easily achieved from the same chemistry using soluble anodes for metal replacement with only 25% of the phosphorous additions required for electroless nickel. Thick deposits are easily achieved unattended, for electroforming freestanding shapes without buildup of excess orthophosphate or stripping of equipment.

Engelhaupt, Darell↗

NASA NTRS2004

Electrodeposition of High Quality Nickel Phosphorous Alloys for Pollution Reduction and Energy Conservation

Engelhaupt, Darell↗

NASA NTRS1983

A basic design fault in ceramic flat packs

Recent moisture resistance tests of various multilayer top brazed ceramic flat packs and leaded and unleaded chip carriers has revealed a serious design defect. These packages, which utilize a tungsten interconnect system, in the presence of high humidity, suffer a galvanic corrosion which anodically consumes the tungsten. This process can continue until the package suffers an open circuit. The test results indicate that the lead plating system does not adequately seal off the interface area where the tungsten strips egresses from the inside of the package.

Drotman, B.↗

NASA NTRS1973

Pitting of titanium. I - Titanium-foil experiments. II - One-dimensional pit experiments.

Pitting experiments were conducted with strips of titanium foil in beakers containing chloride, bromide, or iodide solutions. The potentials were determined in reference to the saturated calomel electrode. Corrosion occurred at the edge of a foil specimen when it was maintained at a potential between the steady-state pitting potential of about 0.9 V and a potential of about 1.4 V in neutral bromide solution. A model is discussed to account for the complex relationships observed in the experiments. Conclusions based on experiments conducted with one-dimensional pits at the ends of insulated titanium pencils in the anode-facing-up position are also presented.

Beck, T. R.↗

NASA NTRS1990

Dry compliant seal for phosphoric acid fuel cell

A dry compliant overlapping seal for a phosphoric acid fuel cell preformed f non-compliant Teflon to make an anode seal frame that encircles an anode assembly, a cathode seal frame that encircles a cathode assembly and a compliant seal frame made of expanded Teflon, generally encircling a matrix assembly. Each frame has a thickness selected to accommodate various tolerances of the fuel cell elements and are either bonded to one of the other frames or to a bipolar or end plate. One of the non-compliant frames is wider than the other frames forming an overlap of the matrix over the wider seal frame, which cooperates with electrolyte permeating the matrix to form a wet seal within the fuel cell that prevents process gases from intermixing at the periphery of the fuel cell and a dry seal surrounding the cell to keep electrolyte from the periphery thereof. The frames may be made in one piece, in L-shaped portions or in strips and have an outer perimeter which registers with the outer perimeter of bipolar or end plates to form surfaces upon which flanges of pan shaped, gas manifolds can be sealed.

Granata, Jr., Samuel J.↗

NASA NTRS2008

Chemical Passivation of Li(exp +)-Conducting Solid Electrolytes

Plates of a solid electrolyte that exhibits high conductivity for positive lithium ions can now be passivated to prevent them from reacting with metallic lithium. Such passivation could enable the construction and operation of high-performance, long-life lithium-based rechargeable electrochemical cells containing metallic lithium anodes. The advantage of this approach, in comparison with a possible alternative approach utilizing lithium-ion graphitic anodes, is that metallic lithium anodes could afford significantly greater energy-storage densities. A major impediment to the development of such cells has been the fact that the available solid electrolytes having the requisite high Li(exp +)-ion conductivity are too highly chemically reactive with metallic lithium to be useful, while those solid electrolytes that do not react excessively with metallic lithium have conductivities too low to be useful. The present passivation method exploits the best features of both extremes of the solid-electrolyte spectrum. The basic idea is to coat a higher-conductivity, higher-reactivity solid electrolyte with a lower-conductivity, lower-reactivity solid electrolyte. One can then safely deposit metallic lithium in contact with the lower-reactivity solid electrolyte without incurring the undesired chemical reactions. The thickness of the lower-reactivity electrolyte must be great enough to afford the desired passivation but not so great as to contribute excessively to the electrical resistance of the cell. The feasibility of this method was demonstrated in experiments on plates of a commercial high-performance solid Li(exp +)- conducting electrolyte. Lithium phosphorous oxynitride (LiPON) was the solid electrolyte used for passivation. LiPON-coated solid-electrolyte plates were found to support electrochemical plating and stripping of Li metal. The electrical resistance contributed by the LiPON layers were found to be small relative to overall cell impedances.

West, William↗