Hypergolic or self ignition delays of unsymmetrical dimethylhydrazine (UDMH) and several amine fuels, mixed with three fuming nitric acid oxidizers, have been determined, at room temperature, in a highly sensitive “Cup Test” apparatus. Ignition delay (ID) variations have been studied with respect to the chemical structure of fuel, oxidizer composition, and oxidizer‐to‐fuel (O/F) ratio. Probable preignition reactions and structure‐hypergolicity correlations have been suggested.
Some non‐hypergolic hydrocarbons and petroleum fractions have been hypergolized by addition of UDMH, and ID variations have been studied with respect to UDMH‐content in fuel and catalytic additives (ammonium metavanadate, ammonium dichromate, and cuprous oxide) in the red fuming nitric acid oxidizer (RFNA). Increment in UDMH‐content improves the hypergolicity of fuels towards RFNA. For example, kerosene + UDMH 60:40 blend ignites with RFNA with a remarkably low ID of 6 ms. However, the catalytic effect of the additive in RFNA varies widely with the fuel‐blend composition.
Non‐isothermal TG curves for four samples of polyvinyl nitrate (PVN), having 15.71%, 14.95%, 13.34% and 11.76% nitrogen contents, were obtained at 5°C/min heating rate. The weight loss of PVN samples depends directly on their % N and occurs in three or more temperature zones. For PVN with 15.71% N (max 15.73% N in theory), the main decomposition step results in more rapid and complete weight loss than for PVN with lower % N, probably due to higher oxygen balance of the former. The TG data were subjected to kinetic analysis using a computer programme. For each decomposition step, the kinetic parameters (E and A) and the regression coefficient (r) were calculated on the basis of several kinetic models and equations consistent with the Arrhenius relationship. It was concluded that the thermal decomposition kinetics of all four PVN sample are best expressed by the Random nucleation model (Mampel unimolecular law) first‐order reaction. For the initial and slowest decomposition step, E ranged between 188 kJ/mol − 217 kJ/mol and In A between 46.88 s−1 ‐ 60.13 s−1. The In A versus E plots for all PVN samples exhibited a linear relationship, probably due to the kinetic compensation effect.
Replacement of a large proportion of -Ol;"O2 groups by -N3 groups in polymer chain ('azidation' of I PVN) enhanc~ reactivity, impact sensitivity and energetics, but reduced thennal stability of the products. The thennogravynetric analysis of PVN showed the onset of rapid decomposition at about 171 °C.jThe kinetic analysis of thennogravimetric results indicated the validity of random nucleation first-order reaction model.1A differential scanning calorimetry thennogram of PV AZ showed a peak at 183.9 °c and heat of d~omposition of 2732 JIg, which is lower than that for PVN. I.
EXPERIM~NTAL DETAIUS2.
Polyvinyl nitrate (PVN) is one of the few known polymeric explosives. PVN was prepared by controlled addition of cooled nitric acid to a pre‐cooled suspension of polyvinyl alcohol in acetic anhydride and subsequent processing of the reaction product. Nitrogen content of different PVN samples was in the range 11.76% to 15.71%;, and the molecular weight about 100000. Several properties of PVN have been investigated and correlated with its degree of nitration. Scanning electron micrographs of PVN fibres show a porous surface. Abel heat test values at 82°C indicate that fibrous PVN has a fairly good degree of stability, which decreases with increase in its % N. Addition of small amounts (0.25%; by wt.) of DPA, 2NDPA, carbamite and resorcinol into PVN (15.71%; N)improves its heat stability. With increasing %;N, ignition temperature of PVN decreases and impact as tetryl. With increasing %; N from 11.76%; to 15.71%;, heat of combustion decreases from 3744 cal/g to 3023 cal/g, and heat of explosion increases from 456 cal/g to 987 cal/g, due to increase in oxygen balance.
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