Detection and Imaging with Leak Microstructures

Results obtained with a new, very compact detector for imaging with a matrix of leak microstructures (LM) are reported. Spatial linearity and spatial resolution obtained by scanning and the detection of alpha particles with 100% efficiency, when compared with a silicon detector, are stressed. Preliminary results obtained in detecting single electrons emitted by the heated filament (Ec < 1 eV) at 1–3 mbar of propane are reported.

Preparation and Characterization of Silicon-Metal Fluoride Reactive Composites

Fuel-rich composite powders combining elemental Si with the metal fluoride oxidizers BiF3 and CoF2 were prepared by arrested reactive milling. Reactivity of the composite powders was assessed using thermoanalytical measurements in both inert (Ar) and oxidizing (Ar/O2) environments. Powders were ignited using an electrically heated filament; particle combustion experiments were performed in room air using a CO2 laser as an ignition source. Both composites showed accelerated oxidation of Si when heated in oxidizing environments and ignited readily using the heated filament. Elemental Si, used as a reference, did not exhibit appreciable oxidation when heated under the same conditions and could not be ignited using either a heated filament or laser. Lower-temperature Si fluoride formation and oxidation were observed for the composites with BiF3; respectively, the ignition temperature for these composite powders was also lower. Particle combustion experiments were successful with the Si/BiF3 composite. The statistical distribution of the measured particle burn times was correlated with the measured particle size distribution to establish the effect of particle sizes on their burn times. The measured burn times were close to those measured for similar composites with Al and B serving as fuels.

Heat Transfer in Additive Manufacturing of Glass

The temperature in the molten region is a critical parameter for Additive Manufacturing (AM) of transparent glass using a laser heated filament-fed processing. This paper presents a study of the heat transfer in single track printing of borosilicate glass using the filament-fed process. The incandescent radiation emitted from the melt pool is monitored using a spectrometer. The spectral data indicates the breakdown of materials occurring inside of the glass, and reflects the occurrence of bubble formation due to reboil at high temperatures. A simple numerical model of the filament-fed process based on an energy balance within the melt pool is used to estimate the temperature. By combining the numerical and experimental results, the estimated temperature calculated from this model is suitable for control feedback.

Infrared Fiber Optic Diagnostic for Solid Propellant Combustion

We report on a program to develop and demonstrate a diagnostic technique using infrared fiber optics to probe the decomposition processes in burning gun propellant strands. The present experimental configuration involves measuring the absorption through a small gap between two embedded fibers. The gap can be filled with propellant, or left open to fill with gaseous decomposition products. Spectroscopic detection is presently achieved using pairs of bandpass filters. The absorption record can be correlated with readings from an embedded thermocouple and with a high resolution video recording of the bum. We also report on preliminary experiments in which an electrically heated filament is used to melt the infrared fiber as its transmission and physical appearance are monitored.The goal of this program is to develop a fast-response probe of solid phase processes which can support the development of a predictive modeling capability for gun propellant combustion. We present examples of data for the atmospheric pressure burning now under investigation. A full assessment of the usefulness of this technique will require further observations and analysis.

Formation of AlGaAs by ion beam mixing of Al films on GaAs

There is considerable interest in the use of ion implantation for material synthesis. The synthesis of AlGaAs by dual implants of As+ and Al+ into GaAs followed by rapid thermal annealing (RTA) has been reported recently. In this paper results relating to the formation of AlxGa1-xAs by depositing thin Al films on GaAs substrates and irradiating with arsenic ions followed by RTA are presented.Aluminium layers of 580Å or 650Å in thickness were deposited onto liquid encapsulated Czochralski (LEC) grown samples of semi-insulating <100> GaAs. The deposition was done using pure aluminium on a heated filament at a chamber pressure of ∽10−6 Torr with the thickness being measured using a talystep. Subsquently As+ implants were performed at room temperature using an energy of 150, 200 or 300 keV and a dose of 3x1016 or 1x1017 cm−2. The implantation energy was selected to ensure that the projected depth exceeded the thickness of the Al overlayer employed.

Studies of Diamond Growth Mechanisms in a Hot Filament Reactor

ABSTRACTThe incorporation of methane into low-pressure CVD diamond thin films has been compared to that of acetylene. 13CH4 and 12C2 H2 were used as the hydrocarbon sources in a heated-filament CVD diamond growth process at a total concentration of 0.5% hydrocarbon in 99.5% hydrogen. Results indicated that methane and/or methyl radical is the dominant carbon source for diamond growth in a hot filament reactor under steady state conditions and that acetylene is rapidly hydrogenated to methane. Results also indicated that diamond surface reactions play an important role in determining the relative methane to acetylene ratios.