Influence of dispersibility and coagulation on the dust explosion risk presented by powders consisting of nm-particles

At the outset it may seem reasonable to expect that dust clouds from combustible nm-particle powders will exhibit extreme ignition sensitivities (very low MIEs) and extreme explosion rates (very high KSt-values). However, there are two basic reasons why this is not necessarily the case. Firstly, complete transformation of bulk nm-particle powders into dust clouds consisting of well-dispersed primary particles is extremely difficult to accomplish, due to very strong inter-particle forces. Secondly, the extremely fast coagulation process in nm particle clouds of explosive mass concentrations would transform the primary particles in a well-dispersed cloud into much larger agglomerates within fractions of a second. The paper discusses these aspects in relation to recent published MIE data and KSt-values for some nm powders.

Dust clouds in air consisting of well-dispersed nm size particles cannot be realized in practice due to extremely strong inter-particle forces, which make complete dispersion almost impossible. Furthermore, if perfect dispersion had been achieved, extremely fast coagulation (re-agglomeration) of the particles in the cloud would result.Figure optionsDownload as PowerPoint slideHighlights
► Well-dispersed explosive nm-particle clouds in air cannot be generated in practice.
► There are two main reasons: very poor dispersibility and extremely fast coagulation.
► Therefore, explosion rates of nm-particle clouds are not higher than of µm-particle clouds.
► But clouds of some nm metal particles in air have lower MIEs than µm-particle clouds.