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

Magnesium powder, a commonly utilized metallic material, frequently gives rise to combustion and explosion incidents during its production. To identify efficient suppressants for magnesium dust explosions, six bimetallic supramolecular compounds were synthesized via co-precipitation, and their flame-suppression performance on magnesium dust flames was compared by means of flame morphology and flame-propagation velocity in a Hartmann tube; sodium bicarbonate, a traditional suppressant, served as the reference. In the tests, magnesium powder was premixed with each of the seven suppressants at a mass ratio of 1∶6 and then ignited in the Hartmann tube. The average flame-propagation velocity was derived from the tube length and the time required for the flame to reach the tube top, whereas the instantaneous flame-propagation velocity was obtained by recording flame height at successive instants. A higher average velocity and a faster flame-front propagation velocity signify a weaker suppressant efficacy. When the seven suppressants were ranked according to these two indicators, however, the orders were not fully consistent. For instance, MgAl-Cl yielded a lower average velocity than NaHCO₃, yet its maximum flame-propagation velocity exhibited the opposite trend. This discrepancy arises because certain suppressants only weakly inhibit the magnesium flame, allowing rapid flame acceleration near the tube outlet where oxygen is abundant. Integrating both the average and the maximum flame-propagation velocities, the suppressants can be arranged from the least to the most effective as follows: NaHCO₃, MgAl-Cl, ZnCr-CO₃, CaFe-Cl, MgAl-CO₃, CuAl-CO₃, CaFe-CO₃. Moreover, the percentage reductions in average velocity imparted by the four bimetallic supramolecular compounds (MgAl-Cl versus MgAl-CO₃, and CaFe-Cl versus CaFe-CO₃) were 17.95%, 27.30%, 23.82%, and 50.76%, respectively, evidencing that carbonate as the interlayer anion have a superior suppression effect on magnesium powder deflagration compared to those with chloride as the interlayer anion. Scanning electron microscopy and X-ray diffraction analyses of the reaction products, together with TG-DSC traces of the bimetallic supramolecular compounds, revealed that during the decomposition process, bimetallic supramolecular compounds lower the flame temperature via 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.