Initiation delay

High set instantaneous overcun-ent through the positive sequence network. An initial delay of a few cycles is introduced to avoid a trip during a start, whereas it will trip instantly on a phase fault, cable fault or a short-circuit. 

Related to both DDT and initiation by shock is the initiation of solid expls by gas detonations. Weiss et al (Ref 61) found that PETN at 0.7g/cc could be initiated by a gas detonation of 21 atm initial pressure, which produced an initial (presumably in the PETN) pressure of 2kbar. Under these conditions initiation delay in the PETN was less than one microsecond... 

A delay element is a self-contained pyrotechnic device consisting of an initiator, delay column and an output charge or relay, ail assembled into a specially designed inert housing. It provides a predetermined inter/al between initiation and functioning of a device... 

The characteristic feature of solid—solid reactions which controls, to some extent, the methods which can be applied to the investigation of their kinetics, is that the continuation of product formation requires the transportation of one or both reactants to a zone of interaction, perhaps through a coherent barrier layer of the product phase or as a monomolec-ular layer across surfaces. Since diffusion at phase boundaries may occur at temperatures appreciably below those required for bulk diffusion, the initial step in product formation may be rapidly completed on the attainment of reaction temperature. In such systems, there is no initial delay during nucleation and the initial processes, perhaps involving monomolec-ular films, are not readily identified. The subsequent growth of the product phase, the main reaction, is thereafter controlled by the diffusion of one or more species through the barrier layer. Microscopic observation is of little value where the phases present cannot be unambiguously identified and X-ray diffraction techniques are more fruitful. More recently, the considerable potential of electron microprobe analyses has been developed and exploited. 

There is a small fall in plasma glucose upon starvation, then little change as starvation progresses (Table 27-2 Figure 27-2). Plasma free fatty acids increase with onset of starvation but then plateau. There is an initial delay in ketone body production, but as starvation progresses the plasma concentration of ketone bodies increases markedly. 

The initiation delay has been also measured for several solid expls when sub-j ected to a relatively weak shock stimulus generated by an HE and attenuated by a rubber barrier. The delay was found to be dependent on the barrier thickness, at least for the geometry employed. For a zero gap... 

When a shock wave is transmitted from a metal to a solid expl a pure shock wave is transmitted into the expl. The shock generally builds up to a complete detonation wave but in some cases it fails to initiate the expl. In the former case an effective delay time is abserved. Initiation delay times have been measured in 2-inch diam chges of 60/40 RDX/TNT... 

The writer (unpublished results) was able to initiate Lead Azide pellets of ca 2.5 g/cc density with oxy-acetylene detonations. However ca 1.2 g/cc PETN pellet could not be initiated under these conditions. Gordeev et al [Nauchn-Tekhn Probl Goreniya Vzryva (1965) p 12 CA 64 1894 (1966)] succeeded in initiating liquid mixtures of tetranitromethane (TNM) and benzene with stoichiometric methane-oxygen detonations. For 1.5 vol parts of TNM 1 vol p of benz the initial pressure, P0, of the detonating gas mixture had to be greater than 2 atm to initiate the liquid. Initiation delays decreased as P0 increased delays were 350, 10 0 psec for P0 of 2, 12 24 atm. For 4 1 by vol TNM/benz initiation of the liquid was observed for Po>0.7 atm. At Po 0.7 atm the initiation delay for this liquid mixture was 70 jusec... 

Studies on the kinetics of carbon black dispersion in various rubbers have been reported using a Brabender mixer fitted with cam-type rotors [110]. Dispersion rating, determined by visual inspection of photomicrographs, was found to depend strongly on mixing time. For an SBR emulsion, it was observed that there was an initial delay period where the carbon black agglomerates were thought to be fractured and incorporated into the rubber. Subsequently, the process of dispersion continued for a considerable time thereafter. 

The effect of crystal size on the critical light energy or initiation delay was reported by Bowden and Yoffe (Ref 57) for Ag azide and by Roth (Ref 132) for Pb azide. Each found that crystal size had no effect. Roth pursued this further and reported that the packing density range 1,6 to 3.2 gm/cc, and the particle size range 0.5 to 10 y had no effect on the initiation... 

Brish et al (Ref 189) continued their expts with secondary expls including RDX and HMX, as well as Pb azide and PETN. With Pb azide the data indicates that over a broad interval of variation of the ignition lag (or initiation delay), approx from 10"8 to 1Cf4 secs, the energy required to expld the Pb azide is almost constant, above 10-4 secs it increases (see Meerkamper (Ref 36). This is not true for PETN... 

The writer studied the initiation of Pb Azide by high-intensity light (Ref 9b). He found that the process of initiation was thermal, with thermal expln occurring in a thin layer that was heated by absorbing most of the incident light. He was able to make estimates of the kinetic parameters of Pb Azide based on observed initiation delays and thermal expln theory... 

Scan 20mV seer Figure 6. Effect of initial delay time on... 

The initial delay in the development of the chemistry of fluorine and its compounds compared with the chemistry of other halogens was soon erased by very intensive work in fluorine chemistry. Hundreds of thousands of fluorine compounds have been prepared over the last century, and the number of fluorine chemistry monographs exceeds by many times that of other halogens. 

Comment Cond Tine Cuiid Put. Initial Delay Equil. Ting DC Potential... 

In the case of solid fuel rockets, the delay in inflammation, which is determined on a test stand, is understood to mean the time which elapsed between the moment of application of the initiation voltage to the electric inflammation element and the moment when about 10% of the maximum pressure has been attained. Clearly, the magnitude of this parameter depends both on the nature of the firing charge employed and on the ease with which the solid propellant can be initiated. The permitted initiation delay will depend on the objective of the firing. 

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