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Electroceramic Actuators for Operation at Low Temperatures

Relatively large strokes are produced at temperatures between 30 and 60 K. Electrostrictive ceramic actuators that can function at low temperatures have been developed for controlling the shapes of mirrors in the Next Generation Space Telescope (NGST). On Earth, electrostrictive ceramic actuators may be useful for fine control of the positions of objects in cryogenic laboratory apparatuses and in industrial cryogenic (including superconducting) systems.

Posted in: Briefs, Materials

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Refrigerant Blends Containing Trifluoroiodomethane

Some of these non-ozone-depleting refrigerants can supplant older ozone-depleting ones. Blends of refrigerant fluids have been developed as improved alternatives to conventional chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants, which contribute to depletion of stratosphere ozone. Each blend of this type is a zeotropic or nearly azeotropic mixture of trifluoroiodo-methane (CF3I) with two or three hydro-fluorocarbon (HFC) refrigerant compounds. In addition to having zero ozone-depletion potential, these CF3I-containing refrigerant blends are nonflammable, and have low toxicity, low global-warming potential (GWP), and low total equivalent warming impact (TEWI). [GWP and TEWI are two measures that quantify different aspects of contributions to global warming.]

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Heat-Exchanger Rocket Engine

Engine heat is used to prevaporize liquid oxygen. The proposed rocket engine includes a combustion chamber actively cooled by liquid oxygen: Heat from the combustion chamber vaporizes the flowing liquid oxygen, and the absorption of latent heat of vaporization contributes to cooling of the combustion-chamber wall. The resulting high-vapor-quality (mostly vapor) two-phase flow of oxygen is then injected into the combustion chamber to burn with the fuel. Vaporization of the majority of the oxygen prior to injection renders the engine insensitive to wide variations of inlet conditions.

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Stable Ohmic Contacts on SiC Devices for High Temperatures

The candidate material — Ti3SiC2 — is thermodynamically stable in contact with SiC. Ti3SiC2 has been proposed as a mate- rial for ohmic contacts on SiC-based electronic and microelectromechanical devices intended to operate at temperatures >600 °C and/or in corrosive environments. Although SiC is stable and devices made of SiC are capable of functioning at elevated temperatures and in corrosive environments, the lack of stable ohmic contacts has been a barrier to the realization of SiC-based devices. Most metals react with SiC at high temperatures, forming metal silicides and/or carbides. At a minimum, these reactions cause contact resistances to change over time, affecting the performances of devices; in extreme cases, entire contact layers can deteriorate through oxidation, melting, evaporation, or balling up on surfaces.

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Development of Alternatives to Hydrazines as Propellants

A brief report summarizes an investigation of less-toxic alternatives to toxic monopropellant fluids used in launch vehicles, upper stages, and spacecraft propulsion. The toxic fluids in question are (1) hydrazine and its derivatives, used, variously, as fuels or by themselves as catalytically decomposable monopropellants; and (2) nitrogen dioxide, used as an oxidizer for such fuels.

Posted in: Briefs, TSP, Materials

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Relatively Simple Atmospheric-CO2 Controller

Temperature of an alkanolamine solution is controlled to make it absorb or desorb CO2. An apparatus has been developed as a means of controlling the partial pressure of CO2 (pCO2) in air in a closed or semiclosed environmental system. The apparatus takes CO2 from the air in a source chamber and supplies the CO2, at a regulated partial pressure, to the air in a sink chamber. In the original intended application, the chambers would be located aboard a spacecraft: the source chamber would be inhabited by crewmembers, and the sink chamber would be a plant-growth chamber. Apparatuses like this one could also be used to control pCO2 in research plant-growth chambers on Earth.

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A Technique for Injecting Ag+ Ions as Biocide into H2O

A simple and reliable technique facilitates the addition of silver ions to water supplies to suppress bacterial contamination. In the original application for which the technique was devised, there is a need for Ag+-ion concentrations at a biocidal levels (0.5 mg/L) in 44-L batches of drinking water. The technique involves the preparation of a solution of concentrated biocide by dissolving 0.66 g of AgF and 1.04 g of NaF in 0.5 L deionized water. Batches of the solution are put into plastic syringes that have volumes of 20 cm3 each and are equipped with fittings for connection to the water supplies to be treated. The syringes are capped and placed in plastic bags for transport and storage. The shelf life of the syringes stored at room temperature is at least two years. When needed, a syringe is simply unpacked and connected to a mating fitting on a water supply. The concentrated solution is then injected into the flowing water, wherein the solution becomes diluted to the desired final concentration.

Posted in: Briefs, TSP, Materials

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