Experimental study on suppression of magnesium powder deflagration flame with different bimetallic supramolecular compounds

Magnesium powder, as a commonly used metal material, frequently causes combustion and explosion accidents during production processes. To seek efficient explosion suppressants for magnesium powder, six bimetallic supramolecular compounds were synthesized using the co-precipitation and their flame suppression effects on magnesium powder flames were compared based on flame morphology and flame propagation velocity using Hartmann tube, alongside a comparison with the traditional suppressant sodium bicarbonate. In the experiments, magnesium powder was pre-mixed with seven suppressants at a ratio of 1:6 and then ignited in the Hartmann tube. The average flame propagation velocity was calculated using the tube length and the time taken for the flame to reach the top of the tube, and the flame propagation velocity was calculated by measuring the flame height at different times. A larger average velocity and a faster flame front propagation velocity indicate a poorer suppression effect of the suppressant. However, when ranking the suppression performance of the seven suppressants according to these two parameters, the results were not entirely consistent. For example, the average velocity corresponding to MgAl-Cl was lower than that of NaHCO3, whereas the maximum flame propagation velocity showed the opposite trend. This is because some suppressants had a weak inhibitory effect on the magnesium powder flame, leading to rapid flame propagation in the area close to the tube outlet due to sufficient oxygen availability. Based on a comprehensive analysis of the average velocity and the maximum flame propagation velocity, the suppression effectiveness of the seven suppressants was ranked from weakest to strongest as follows: NaHCO3, MgAl-Cl, ZnCr-CO3, CaFe-Cl, MgAl-CO3, CuAl-CO3, CaFe-CO3. Furthermore, the percentage reduction in average velocity for the four bimetallic supramolecular compounds: MgAl-Cl versus MgAl-CO3, and CaFe-Cl versus CaFe-CO3, on the deflagration flame of magnesium powder was calculated to be 17.95%, 27.30%, 23.82%, and 50.76%. Thus, it is concluded that bimetallic supramolecular compounds with carbonate as the interlayer anion have a superior suppression effect on magnesium powder deflagration compared to those with chloride as the interlayer anion. Analysis of the products via SEM, XRD, and the TG-DSC curves of the bimetallic supramolecular compounds revealed that during the decomposition process, bimetallic supramolecular compounds reduce the flame temperature through the desorption of interlayer water molecules and the heat absorption associated with the decomposition of the layered structure. Moreover, the inert gases and metal oxides generated during decomposition can block heat transfer and inhibit the volatilization of combustible gases from the surface of magnesium powder particles. Meanwhile, the metal ions and interlayer anions participate in the combustion reaction, consuming free radicals and interrupting the chain reaction, thereby achieving the explosion suppression effect.