Macroscopic behavior and kinetic mechanism of ammonium dihydrogen phosphate for suppressing polyethylene dust deflagration

In this paper, the inhibition effect of ammonium dihydrogen phosphate (NH4H2PO4) on the deflagration of polyethylene dust (C100H202) is studied by combining experimental tests with reaction molecular dynamics simulation (ReaxFF MD). The mechanism by which NH4H2PO4 inhibits C100H202 deflagration is revealed at the microscopic level. The experimental results demonstrate that the inhibition effect of NH4H2PO4 on C100H202 deflagration is positively correlated with its concentration, and the addition of NH4H2PO4 equivalent to 50 % of the mass of C100H202 can completely suppress the deflagration. The apparent activation energies for the decomposition of C100H202 and C100H202/50 %NH4H2PO4 are calculated using ReaxFF MD to be 97.11 kJ/mol and 124.78 kJ/mol, respectively, which are in agreement with the results obtained from thermogravimetric tests. Furthermore, ReaxFF MD is employed to calculate the types and quantities of deflagration products and free radicals before and after the addition of NH4H2PO4. The results indicate that the number of the main intermediate C2H4 decreases with the increasing addition of NH4H2PO4. Based on this, the generation and consumption pathways of C2H4 are traced. It is found that phosphorous groups such as HOPO and PO2 scavenge active free radicals like <middle dot>O and <middle dot>OH, thereby altering the formation and consumption pathways of C2H4, leading to a reduction in both its formation and consumption. Additionally, H2O and inert gases produced by the thermal decomposition of NH4H2PO4 also contribute to inhibiting the progression of C100H202 deflagration.