Materials propellant inhibition

The mechanical and physical properties of the inhibiting material must be fairly similar to those of the propellant in order to minimize the differential expansion. In this respect the use of several layers with possibly different compositions is favorable. With long burning timers (more than 20 sec) the development of a reliable inhibitor poses a fairly difficult problem, especially with end-burning grains. 

Most of the work on the inhibition of oxidative degradation of HTPB by incorporating anti-oxidants is in the form of patents or classified reports [225-227]. The use of N-phenyl-P-naphthylamine (PBNA) has been extensively studied [226, 228] for this purpose but it is reported to be a carcinogenic material and hence banned for use as a propellant ingredient in developed countries. 

Inert polymeric materials to be suitable for inhibition of rocket propellants must fulfill a number of requirements [279-281] and the important ones are given below ... 

The choice of material for use as inhibitor depends mainly upon the type of propellant, that is, DB, CMDB, Composite and Fuel-rich and also on the ingredients in their formulations. For double-base propellants, cellulosic materials such a cellulose acetate, ethyl cellulose and different filled or unfilled flexible polyesters are used while fuel or binder material filled with inert substances such as asbestos, mica, silica, etc. in fine powder form is used for composite propellants. Since nitroglycerine is present in CMDB propellants also as in DB propellants, the materials used for DB propellants may also be used with minor modifications for the inhibition of CMDB propellants. 

The choice of an inhibiting material or inhibitor depends upon several factors such as the type of propellant, cost-effectiveness, and physical and mechanical properties of an inhibitor with special reference to ballistic requirements. The inhibition of propellants is therefore discussed by category of propellant. 

The force which propels secretory granules along the microtubules is less clear. It is known that the micro tubular system exists in at least two states the fully polymerized form represented by intact microtubules, and the disintegrated form represented by a pool of depolymer-ized globular proteins (tubulin) in the cytoplasm. In order for microtubules to function properly, a dynamic state of equilibrium must exist between the fully-formed tubules and the tubule constituent pool. Thus, colchicine and other antimitotic agents bind to specific sites on the microtubular subunits. It has been proposed that they exert their effect by inactivating the free subunits and thereby shift the equilibrium between the associated and dissociated states of the microtubules so that eventually no intact microtubules remain and secretion is inhibited. Similarly, stabilization of microtubules in the polymerized form with D2O also inhibits cellular secretion of insulin. From this, one can hypothesize that if the secretory vesicles were somehow attached to the microtubules, possibly by way of microfilaments, a constant cycle of depolymerization near the cell periphery, with a repolymerization at the central area of the cell, would advance the secretory vesicle from the cell center to the cell web. In addition, if tubulin actually contains an actin-like contractile protein, then this contractile property may well contribute to the intracellular movement of secretory materials. 

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