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 K-St-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 K-St-values for some nm powders. (C) 2013 Elsevier B.V. All rights reserved.