Theoretical And Experimental Study On Explosibility Parameters Of Micro And Nano Titanium Powders

The frequent occurrance of very serious and major dust explosion accidents limited the normal development of powder process industry in China.Paying more attention to the study on explosibility characteristics of very hazardous metal powder,especially nano-sized metal powder is internationally new subject in the dust explosion research area.Statistic data shows that hot surface and electrical spark are the common ignition sources of dust explosion.The ignition process and subsequent pressure development of metal dust explosion induced by them are still hot and difficult issues in dust explosion prevention and protection.Therefore,some theoretical models are systematically provided and validated for the minimum ignition temperature(MIT),minimum ignition energy(MIE),explosion violence of titanium powder,and inerting effect of nano titanium dioxide.The MIT model of micro and nano titanium powders in BAM oven based on ASTM was firstly proposed and validated.Being different with the previous MIT model in GG oven based on IEC,the new model can calculate temperature of floatable particles heated by hot surface,and then to determine MIT and its sensitive parameters.Especially,the physical structure of agglomerated nano powder and its effects on MIT were taken into consideration in this model.The calculated MIT of micron and nano Ti mixture was more close to experimental results than the current harmonic model.Secondly,The MIE model of micro and nano titanium powders was given and validated with test results from MIE III.Spark discharge time is short as little as several micro-second.The temperature history in the spark area cannot determine currently by experimental methods.The new model can determine temperature distribution of dust cloud around electrical spark,and then analyze its sensitive parameters,such as spark energy,discharge time,spark size,and turbulence.The calculated effect of micron particle size on MIE is consistent with Kalkert&Schecker theory.The effect is the same to nano particle size.Finally,the pressure history model of dust explosion in closed vessel was provided and validated by test result of 20L sphere.The explosion pressure history of micro titanium powder in 20L sphere was simulated well with the new model.The calculated pmax and(dp/dt)max of micro titanium powder were agreed with the experimental results.By considering self-ignition of nano Ti powder during dispersion,the initial condition and rate of chemical reaction of Ti powder was modified.The modified model can simulate explosion pressure history of nano titanium powder in 20L sphere,and calculate pmax&(dp/dt)max well.Thus,the modified model is new tool to evaluate the consequence of dust explosion induced by self-ignition during dispersion.The research results also show that nano-sized solid inert mediums would not only absorb reaction heat as micro-sized ones,but also decrease reaction rate of micro-sized Ti powders at the same time.However,nano-sized s?lid inert mediums will enhance the dispersion of nano-sized Ti powders mixed,and then result in higher ignition sensitivity and(dp/dt)max.The classical scientific ideas about solid inerting would be changed by current research.The paper expatiate the comparison of explosion characteristics between micro and nano titanium powder in detail,especially the new models,which was of universal significance for other metal powders.The findings,such as ignition&explosion parameters,inert effect of nano titanium powder and so on,were instructive to the dust explosion prevention and protection for metal powders,especially for nano metal powder.