Once the powder particles and air are mixed homogeneously as well asthe powder particles are suspended in the dust cloud (slow deposition), theexplosion will be spread. In addition, leafing aluminum powdersand magnesium powders are easy to break into fine powders and have intensivequadratic effect, in which many crisp metal particles (powders) will generatefine particles that can form the dust cloud, thus the quadratic effect willoccur under this condition.
The dust cloud appearance will influence theexplosive forceDustcloud that exists in the small container will have high explosion pressure riserate due to the multiple reflections of pressure output wave (the reflectionwill enhance the strength of pressure wave and accelerate the reaction). When the particle sizeis reduced, the metal dust cloud will be easy to ignite and has fast reactionrate at the same time. Generally, when the particle size is reduced to lessthan 149m (100 meshes), the metal powder is easy to ignite andthe pressure rise rate will become fast when the blast occurs.
In conclusion, the chemical and physical parameters of powders will bothinfluence its sensitivity to ignition, the rising of powders and the trend offorming dust cloud as well as the possibility of generating secondaryexplosion. Generally speaking, when the disturbance increases,the explosion pressure and pressure rise rate will both increase. Regardingthe electrostatic property of atomized aluminum powders, it tends to remainneutral and will deposit fast.Influence of metal powder particle shapeAs the surface-to-volumeratios of leafing aluminum powders andmagnesium powders are both biggerthan other particle shapes, they are much easier to burn than other shapes of atomizedaluminum powders and magnesium powders. According to the feature ofmaterials, the electrostatic force that generated when the dust cloud riseswill hinder or help the dispersion of dust in the air.
NONE MicrosoftInternetExplorer4 Influence of metal powder particle amorphous polyester resins size andsurface areaThe particlesize and surface area of dust cloud can determine whether it will ignite ornot, or determine whether it will spread the combustion. Electrostatic force can also influence the ability ofparticle retention in the symmetric suspension. Thesize of dust cloud will have effect on the expanding scope of explosion, whilethe shape of dust cloud will have effect on the main direction of explosionextension. Thedisturbance of dust may start from the explosion initiation of the inside dustcloud, or may be caused by the processing equipments that provide large energyfor the particles from the external.
Due tothe disturbance of dust cloud, the spreading rate of explosion will beaccelerated as well as the total destructiveness will be intensified. While the residualdust cloud will have much larger explosibility than the original powdermixture. Forexample, after coating stearic acid on the surface of aluminum particle, freeions will be generated on the surface, which will repulse mutually in thesuspension and look for the irons that have opposite charges in the gas area.Influence of gathered static chargeThecomposition of particle surface will determine whether the particle is gatheredinto static charge or inherently has free ions on the particle surface. Provided thatthe small particle size of metal powder compounds is easy to cause explosion,the large and heavy particles may deposit in the dust cloud