High speed propulsion: Performance advantage of advanced materials

High-speed air breathing propulsion systems have many attractive military and civil applications. The high propulsive efficiency of these systems allows the exploitation of speed, distance, and bigger payloads, or any combination of the three. The severe operating conditions of these systems require particular attention to overall thermal management of the engine/air-frame. Fuel-cooling the engine structure is a viable way of maintaining thermal balance over a range of flight conditions. Air Force applications have focused on using endothermic hydrocarbon fuels to address this issue because of their compatibility with the military operations. Recent ground tests of scramjet engines have demonstrated adequate performance utilizing state-of-the-art technology in materials. This progress has paved the way for an expendable flight test vehicle in the near future. In order to take full advantage of the capabilities of this propulsion system, advances in fuel-cooled structures, high temperature un-cooled materials, and increased heat capacity of hydrocarbon fuels will be needed to enable expendable systems to reach higher Mach numbers. An additional benefit would be realized in future reusable systems.     

Synthesis of new sulphides of transition metal ions in presence of sun light

New sulphides of transition metal ions [M⁺ⁿ = Cu⁺¹, Cu⁺² and Zn⁺²] have been synthesised in sunlight. XRD patterns show that these compounds are not MxSy but are mercaptyl, hydroxyl metal sulphides [M(SH)(OH)(H₂O)₂] which is further ascertained by I.R. spectra showing bands due to T _d-symmetry. ESCA of compound of copper in solid state shows presence of Cu¹⁺ and Cu²⁺ ion. The presence of hydroxyl, mercaptyl, aqua and S^–2 groups has finally been confirmed with TGA, DTA and ESCA. Conductivity and Seebeck coefficient measurements show that compound of copper is p-type semiconductor and compound of zinc is n-type semiconductor. The production of these low cost materials opens an interesting area of research and development for their use in solar cell devices.     

Negative thermal expansion of laminates

Measurements have been carried out on the in-plane and through the thickness thermal expansion coefficients of glass polypropylene fibre composites of 50% volume fraction between room temperature and 120°C. Only in the temperature range 20° to 75°C are reproducible results obtained. It is confirmed that in-plane negative values may be obtained in specific directions. The physical reason for this and its connection with the necessary appearance of a large Poisson ratio is pointed out. The expansivity of the matrix material depends strongly on temperature. Very good agreement between the experimental values and those predicted from the properties of the two constituents is found provided that the value for the expansivity of the polyoropylene is that within the temperature range considered. It is shown that the polypropylene matrix does not provide a matrix which is stable enough in its properties to enable the system to yield consistent negative values of expansivity. An alternative system is proposed and a single experiment confirms that a negative value of the thermal expansivity of as large as –50 × 10^–6 K^–1 may be obtained.     

Feasibility study of absolute activity measurement with metallic magnetic microcalorimeters

We report on a feasibility study on precise determination of mass-specific activity of low-energy emitting radioisotopes. Conventional methods of activity measurement suffer from source self-absorption and a strong decrease in detection efficiency for low-energy electrons and photons. We propose a new method based on metallic magnetic microcalorimeters with the source embedded in the detector target in a 4π geometry. First results with a ⁵⁵Fe source show that electrons and photons are detected with a detection efficiency close to unity and with little loss of energy for electrons. The aim of this study is to provide standards of activity with very low uncertainties in the framework of radiation metrology.     

Using ion implantation to adjust the transition temperature of superconducting films

We summarize a continuing investigation into using ion implantation to alter the transition temperature of superconducting thin films. The primary motivation for the work presented here was to study the feasibility of using magnetic ion doping to replace the bi-layer T_c control process currently used for certain cryogenic detector applications at National Institute for Standards and Technology. The results from work with various ion species implanted into aluminum, molybdenum, titanium and tungsten host films are presented.     

Fine Purification of Monoisotopic Silanes 28SiH4 , 29SiH4 , and 30SiH4 via Distillation

High-purity isotopically enriched (99.98% ²⁸Si, 99.57% ²⁹Si, and 99.83% ³⁰Si) silane samples are prepared for the first time. The total hydrocarbon content of the samples is no higher than 0.1–0.3 ppm. The concentration of electroactive impurities in the silicon prepared from the purified monoisotopic silane is below 10¹⁵ cm^–3.