. Can. J. Chem. 72,600 (1994).The reaction: H + CH, + CH3 + Hz has been investigated in a flow system between 348 and 421 K. Hydrogen atoms were generated in a microwave discharge, introduced to the reactor through a movable injector, and monitored by electron spin resonance. After an initial decay attributed to reaction with impurity, the hydrogen atom concentration decayed in a pseudo-first-order manner. Ethane was detected by gas chromatography, consistent with its formation by the following reaction: 2CH3 -t C2H6. The amount of ethane formed at 421 K was only 0.015 times the amount of hydrogen atoms reacting. Most methyl radicals were assumed to have been removed by the process: H + CH3 + M + CH, + M. Because of this process, two hydrogen atoms were removed each time the title reaction occurred. Applying this stoichiometric factor, the rate constant for the elementary reaction was calculated to be 2.5 x lo3 L mol-' s-I at 348 K, increasing to 2.0 x lo4 L mol-I ss-' at 421 K. Most of the previous discrepancy between kinetics and thermochemistry has been eliminated; the exothermicity at 0 K was reduced to 0.8 t 0.4 kJ mol-', which corresponds to a standard heat of formation of the methyl radical of 145 kJ mol-I. Properties of the activation barrier have been inferred from the experimental data with the aid of transition state theory. The fitted barrier height was 63 + 1 kJ mol-I, the average of five low-frequency vibrational term values was 640 t 30 cm-I, and the characteristic tunnelling temperature was 500 t 30 K.

There is a concern that engineered carbon nanoparticles, when manufactured on an industrial scale, will pose an explosion hazard. Explosion testing has been performed on 20 codes of carbonaceous powders. These include several different codes of SWCNTs (single-walled carbon nanotubes), MWCNTs (multi-walled carbon nanotubes) and CNFs (carbon nanofibers), graphene, diamond, fullerene, as well as several different control carbon blacks and graphites. Explosion screening was performed in a 20 L explosion chamber (ASTM E1226 protocol), at a concentration of 500 g/m3, using a 5 kJ ignition source. Time traces of overpressure were recorded. Samples typically exhibited overpressures of 5–7 bar, and deflagration index KSt = V1/3 (dP/dt)max ~ 10 – 80 bar-m/s, which places these materials in European Dust Explosion Class St-1. There is minimal variation between these different materials. The explosive characteristics of these carbonaceous powders are uncorrelated with primary particle size (BET specific surface area).

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This paper explores the explosion characteristics of three nontraditional dusts: nanomaterials, flocculent materials, and hybrid mixtures. Nanomaterials have a high likelihood of explosion with minimum ignition energies potentially less than 1 mJ. These low ignition energies may therefore allow nanomaterials to ignite due to electrostatic sparks, collision, or mechanical friction. The severity of nanomaterial explosions is affected by agglomeration and coagulation of the particles. Flocculent materials with a high length-to-diameter ratio exhibit explosion behavior patterns similar to those for spherical dusts. The length of flocculent particles plays a role in explosion likelihood which is not yet fully understood. High voltage discharge during the electrostatic flocking process is a common flocculent ignition hazard. Hybrid mixtures of a combustible dust and a flammable gas/vapor display a higher explosion severity and a lower minimum explosible concentration than that of the dust alone. Violent hybrid explosions may occur even if the dust and the gas/vapor are below their respective lean limit concentrations.