A simple question with complex answers; is nitroglycerine compatible with boron potassium nitrate or not?

摘要

It was previously thought that the incompatibility reactions between a nitrate ester based propellant and a material known as SR44, which is a simple mixture of boron and potassium nitrate, was due to the oxidation and hydrolysis products of boron causing decomposition of the nitrate esters such as nitroglycerine [1]. In order to investigate the specific reactions of nitroglycerine with boron potassium nitrate (BPN) some additional experiments have been conducted using accelerating rate calorimetry (ARC), heat flow calorimetry (HFC) and differential scanning calorimetry (DSC). It should be noted that BPN is the US equivalent of SR44 but in addition to boron and potassium nitrate, it also contains a polyester- based binder. The HFC experiments have involved heating NG and BPN in close proximity to each other whereas in DSC and ARC, the two components were in direct contact with each other. Following the HFC experiments, the NG was subjected to high performance liquid chromatography and liquid chromatography / mass spectrometry to determine the concentration of NG remaining and if any NG degradation products had formed. Despite testing five replicates of samples under each condition the results were complicated by a surprising variability in the data. Further investigations revealed that the BPN pellets were contaminated with magnesium. This was established using atomic absorption spectroscopy and it is known that one of the common contaminants of boron is magnesium. Also, even though the NG was all from the same batch, there might have been slight differences in the residual acid and water content in this liquid. Additionally, the data revealed that ascertaining the compatibility of two materials is not always clear cut, as in the case of NG and BPN, it was not always unequivocal if NG was incompatible with BPN or not. As a result, some of the issues surrounding compatibility testing of energetic materials using thermal analysis techniques as described in STANAG 4147 [2] and the draft version of AOP-4147 [3] will be discussed in more detail.