A combustion synthesized AlN powder was studied for its feasibility as a filler for epoxy molding compound (EMC) and effects of various experimental parameters on the thermal conductivity and moisture resistance of the EMC were investigated. The AlN powder was coated with silane both to increase the moisture resistance of the EMC and to enhance the bonding between the filler AlN and the matrix resin. The thermal conductivity could be significantly increased by using AlN powders with large particle sizes and this was considered to be due to a reduction in interface area between the AlN particles and the matrix resin. A thermal conductivity of 14 W/mK was obtained when the EMC was fabricated by a process involving no use of a solvent and a AlN powder with a particle size of 35.3 μm and a filler content of 67 vol % were used. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4734–4740, 2006

High thermal conductivity epoxy molding compound filled with a combustion synthesized AlN powder

Energetic materials are conventionally ignited by the application of heat to some part of an explosive target. This is most often provided by a flame or by electrical heating using a resistive wire. The material responds by thermally heating and starting a burning zone, which spreads out from the ignition point generating gas. In some cases this zone can accelerate (due to the effect of this gas) into a reactive shock wave, termed detonation. Lasers are used in a variety of applications to thermal heat a range of materials, and thus seem an obvious candidate to trigger chemical reaction in energetic ones. A light pulse offers several advantages over an electrical one, since it may be delivered down a path both immune to electrical effects and chemically stable. Thus, the triggering of safety apparatus (such as the firing of bolts on aircraft exits) represents a major thrust in the development of laser–triggered explosive devices. The energy of the pulse may be used in one of two ways to achieve these effects. In the first, the laser is shone directly upon the chemical medium, which absorbs the light at discrete wavelengths. In the second, it is used to vaporize a metallic flyer that is launched to impact on a target creating a high–pressure zone. Either mechanism starts the required reaction. However, when the pulse is delivered directly to the material, detonation is found to proceed immediately with no transition via burning. This makes the process inexplicable using present concepts. This review will address a range of the experiments conducted and theories developed for this novel field. However, it should be emphasized that the fundamental mechanisms remain to be fully explained making the application both academically stimulating as well as industrially important.

On the laser ignition and initiation of explosives

Nanosized hexagonal wurtzite aluminum nitride (AlN) powders have been synthesized by the direct current (DC) arc plasma method using mixed gas of ammonia and nitrogen (NH3−N2). The growth of the cr...

Synthesis and Infrared Study of Nanosized Aluminum Nitride Powders Prepared by Direct Current Arc Plasma

Surface chemistry analysis of nanostructured aluminium nitride powder, obtained by a chemical synthesis method, has been conducted using FTIR spectroscopy. The study compared the spectra of the as-synthesized powder, the activated powder treated at temperatures from 573 to 873 K, the surface-deuteriated powder, and the powder treated under ammonia. Hydroxy and amine functional groups were determined on the surface of the as-synthesized powder. The activity and the types of these groups were examined. The surface analysis results were compared with those of γ-Al2O3. The unique surface characteristics of the nanostructured AlN are discussed.

FTIR analysis of the surface of nanostructured aluminium nitride powder prepared via chemical synthesis

The chemical nature of a nanoparticle surface is of crucial importance in controlling the interparticle forces during powder processing. As a continuation of a FT-IR spectroscopy study on the surface chemical structure of the chemically synthesized aluminum nitride (AlN) nanopowders, the adsorption of two representative cyclic amides, i.e., N-methyl-2-pyrrolidinone (NMP) and 2-pyrrolidinone (NHP), have been investigated. Upon adsorption of these cyclic amides, strong hydrogen bonding between the amide carbonyl oxygen and the surface hydroxyl groups was evident. The unusual thermal stability for the hydrogen bonding observed with NMP was explained as being due to the enhancement by secondary interactions between the NMP amide carbonyl group and the surface Lewis acidic sites, such as Al3+. With the adsorption of NHP at room temperature, besides the formation of strong hydrogen bonding, a striking 100 cm-1 shift to higher wavenumbers was observed for both the carbonyl and amide C−N stretching bands. This ha...

Infrared spectroscopic investigation of chemisorption on chemically synthesized aluminum nitride nanopowders with 2-pyrrolidinones

Laser-ignited : explosive and pyrotechnic components

A hermetic, stand alone, laser-ignited deflagration-to-detonation transition (DDT) detonator has been developed. The detonator uses the secondary explosive HMX (cyclotetramethylenetetranitramine) and was originally developed for use with the US Navy`s Laser Initiated Transfer Energy subsystem (LITES). The design of the new detonator allows for its use with a variety of laser fire sets. A high density blend 6f 830 cm2/g HMX with 3% carbon black by weight was used for the ignition charge. Deflagration-to-detonation transition was achieved with a transition charge of undoped 830 cm2/g HMX. Using a 12-ms ND-YAG laser pulse coupled to the detonator via a 1-mm diameter optical fiber, the ignition threshold was determined to be approximately 30 mJ. Full detonating outputs were demonstrated by function testing in Navy detonation sensitivity fittings. Finally, the detonator was tested in several configurations with shielded mild detonating chord (SNMC) endrips to determine its capability for lighting transfer lines.

D. P. Kramer

Papers

Laser-ignited : explosive and pyrotechnic components

Development of a laser ignited all secondary explosive DDT detonator