Pyrotechnic material

Details Pyrotechnic material Pyrotechnic material

1997-10-14

2000-01-11

Nelson, Peter A.

Explosive and thermic compositions or charges

Containing free metal or free carbon

149 37, 428113, 102336, C06B 3300

Patent

active

060131446

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a pyrotechnic material and in particular to a pyrotechnic material suitable for use as an infra red (IR) radiation source.
Known material, such as that disclosed in U.S. Pat. No. 4,624,186, comprises thin supports, for example metal foil or paper, on to which is pressed an incendiary paste to form IR emitting flakes. The incendiary paste is constituted with more or less incendiary material in order to speed up or slow down its burn rate and hence control the IR emission characteristics of the flakes. Here it is the paste which, in the main, acts as the IR radiation source. This has the disadvantage that because the pressing process used to coat the thin supports is not accurately controllable the IR emission characteristics of the material so produced is not accurately controllable or reproducible.
It is an aim of the present invention to provide a pyrotechnic material suitable for use as an IR emitter having controllable and reproducible IR emission characteristics.
According to the present invention there is provided a pyrotechnic material characterised in that a fibrous, carbon containing substrate has vapour deposited on substantially all of the surface of one or both faces thereof a combustible material layer, the layer being capable in use of igniting substantially simultaneously the entire surface on which it is deposited.
In use this flash ignition of the surface of the carbon containing substrate by the combustible layer exposes a burning surface of the substrate which then continues to burn to act as a IR radiation source.
The duration of burning of the substrate and hence the emission characteristics, such as wavelength and intensity distributions, of the IR radiation can be controlled to some extent by regulating the carbon content of the substrate. Clearly it is essential that the substrate of the current invention remains for a period of time after the consumption of the combustible layer and it has been found that in order to achieve this the carbon content of the substrate must lie in the range of between 20 g/m.sup.2 and 400 g/m.sup.2 and should preferably lie in the range of between 50 g/m.sup.2 and 150 g/m.sup.2. Suitable substrates may comprise a consolidated layer of fibres, for example as in a felt or a woven carbon cloth such as a carbonised rayon textile. Moreover the high degree of control over the physical characteristics of the combustible layer offered by vapour deposition enables the emission properties of the pyrotechnic material to be reliably reproduced.
A further advantage of vapour deposition is that the combustible material layer is deposited directly onto individual, exposed fibres of the substrate which contain, or are covered with, carbon. This maximises the intermingling of the carbon content of the substrate and the combustible material layer at the interface to provide a large, intimate contact area between the two. The resulting pyrotechnic material exhibits considerable resistance to spontaneous ignition but, largely because of this intimate contact, the controlled ignition of the combustible layer at any selected location spreads substantially simultaneously across the entire layer. Intimate interfacial contact, and consequentially the ignition transfer through the combustible layer, is further enhanced by the nature of vapour deposition processes which are conventionally conducted in essentially oxygen-free environments such as a vacuum or a low pressure inert atmosphere, so preventing any inhibiting film of oxide which may form between the combustible material layer and the carbon containing substrate. Furthermore, vapour deposition ensures that the advantageous properties of the textile type substrate base material (such as flexibility, strength, and toughness) are not substantially degraded during the manufacture of the pyrotechnic product.
The thickness and composition of the combustible material layer is selected to ensure reliable and rapid progression of the ignition through the combustible material layer and to generate s

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