Accession Number : ADA264925
Title : Dielectric Breakdown and its Influence on Ignition
Descriptive Note : Final rept.
Corporate Author : CAMBRIDGE UNIV (UNITED KINGDOM) CAVENDISH LAB
Personal Author(s) : Chaudhri, M M ; Al-Ramadhan, F A ; Haq, I U
Report Date : Mar 1993
Pagination or Media Count : 75
Abstract : Electrical conduction, dielectric breakdown and the consequent ignition of small pellets, 0.2 to 5 mm in thickness and 5 to 7 mm in diameter, of MTV compositions SR886B, SR886E and SR886E have been investigated. The investigations were made using d.c fields and high-speed photography at framing rates of up to one million frames per second was employed to follow the breakdown and ignition behaviour. It was found that under suitable conditions, the dielectric breakdown of the samples led to their ignition and the delay time between the breakdown and ignition could be as small as 20 - 25 microseconds. Furthermore, a special circuit was designed and constructed for determining the minimum ignition energies of samples of different thicknesses. It was found that for samples of thickness of approx. 0.2 mm the minimum electrostatic energy which could cause ignition was as low as approx. 1 mJ. Moreover, the minimum ignition energy was found to increase with the sample thickness. A model, based on our previous model for the electrical ignition of silver azide, has been proposed. According to this, the dielectric breakdown leads to the formation of high conductivity filaments in which Joule heating-results in the formation of high temperature hot spots. Ignition initiates at these hot spots. An essential feature of this model is that the dielectric breakdown is a prerequisite for electrical ignition.
Descriptors : *DIELECTRICS , *IGNITION , VELOCITY , DIAMETERS , TEMPERATURE , THICKNESS , RATES , HEATING , DELAY , PELLETS , UNITED KINGDOM , AZIDES , HIGH SPEED PHOTOGRAPHY , SILVER , ELECTROSTATICS , CIRCUITS , FRAMES , HOT SPOTS , FILAMENTS , PHOTOGRAPHY , TIME , MODELS , CONDUCTIVITY , HIGH TEMPERATURE , ENERGY
Subject Categories : Combustion and Ignition
Distribution Statement : APPROVED FOR PUBLIC RELEASE