Mechanical testing, evidence investigation

Methods of the first type have been used for both qualitative and quantitative investigation. An important limitation is that the rates of interconversion of the tautomeric forms must be small as compared with those of the test reaction (s). The method is further complicated since the test reactions are sometimes complex and it is difficult to be certain that only one tautomer is reacting. An even more fundamental objection is that much chemical evidence is based on incorrect reaction mechanisms. Thus, the formation of condensation products (30) with aldehydes has repeatedly been quoted as evidence for structures of type 31 and against type 32,. whereas if 31 does react with an aldehyde it must either first tautomerize to 32 or ionize to 33. 

When chemists investigate the mechanism of a reaction, they are not so lucky. Determining the mechanism of a chemical reaction is a bit like figuring out how a clock works just by looking at its face and hands. For this reason, reaction mechanisms are proposed rather than definitively stated. Much of the experimental evidence that is obtained to support a mechanism is indirect. Researchers need a lot of creativity as they propose and test mechanisms. 

It is remarkable that the initial description of the mechanism, although based on qualitative evidence, has so successfully passed the test of time and of quantitative investigations. The latter have allowed a more precise description of the kinetics and the assignment of the termination steps, but the core of the mechanism, i.e. the propagation loop (103), has essentially remained untouched (see, however, the discussion at the end of this section). 

Composite propellants consist of an oxidizer (AP/AN/ADN), a metallic fuel such as Al, Mg etc and a binder, usually a polymer which also serves as a fuel. Vacuum stability tests (VSTs) suggest that composite propellants are intrinsically more stable than SB, DB and propellants. However, use of more exotic ingredients such as oxidizers (ADN and hydrazinium nitroformate, HNF), binders [poly([NiMMO)] and poly([GlyN)] are likely to introduce severe compatibility-related problems [30, 31]. Some recent research in this direction indicates that stability of such propellants is largely determined by the chemical and mechanical properties of propellants. However, early evidence of deterioration generally comes from a change in their mechanical properties rather than from chemical investigations [32]. 

A laboratory investigation led to the development of a composition consisting of RDX 60, TNT 32 N-octadecylphthalimide 8%. This mixture was found to be much less sensitive to mechanical shock than std Composition B. Its brisance value by sand test is equivalent to Composition B, but its fragmenting power, ballistic mortar and rate of detonation values are lower than the values for Composition B. The composition is castable at the same temp used for std Composition B and shows no evidence of exudation after six months storage at elevated temps (Ref 16) ... 

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