Study On The Preparation Of Sodium Chloride/Nano-Hydrophobic Silica Superfine Powder And Its Extinguishing Performance

Active metals such as potassium,sodium,and magnesium can cause fires when they are exposed to water,acid,or open flame.When fire extinguishing agents such as carbon dioxide and water are used for such fires,further expansion of fire may be caused.As a result,special powders must be needed..In this article,sodium chloride was used as the matrix to prepare superfine dry powder fire extinguishing agent for metal fire.However,because the ultra-fine dry powder is easy to agglomerate and the hygroscopicity of sodium chloride itself is strong,the fire extinguishing performance of the dry powder will be greatly affected.Therefore,an anti-solvent method was applied to modify it,and during this process the nano-hydrophobic silica was adsorbed on the surface of the sodium chloride crystal.PEG-1000 was used as the modifier.Through the measures of scanning electron microscopy(SEM),laser diffraction analysis(XRD),laser particle size analyzer,and hygroscopicity,bulk density,and fluidity,properties of superfine composite dry powder were studied under different modifying conditions(PH value,ultrasonic time,the content of PEG-1000 and nanometer hydrophobic silica).The results showed that 1)the smaller the PH value,the more conducive to the precipitation of sodium chloride crystals and the refinement of particle size,therefore,the PH value should be controlled to be 1.2)The longer the ultrasonic,the smaller and more uniform the particle size,however,when the ultrasonic time exceeded 30 minutes,the refining performance was not obvious,considering time and cost issues,the ultrasonic oscillation time should be controlled to be 30 minutes.3)When PEG-1000 was added,the agglomeration of powders was reduced,and the particles became more regular and refined,when the content reached 0.8wt%,the refinement affect was basically saturated,therefore,the amount of modifier PEG-1000 should be controlled to be about 0.8wt%.4)If the nano-hydrophobic silica was absorbed on the surface of sodium chloride,the powders would be further dispersed and refined,but the excessive addition would be counterprocductive,and the optimum amount is about 3wt%.Therefore,the best preparation solution was to control the solution PH = 1,ultrasonic for 30 minutes,add 0.8wt%of PEG-1000 and 3wt%of nano-hydrophobic silica for modification,in this way,the sodium chloride particles have the advantages of small particle size and uniformity,less agglomeration,high flowability,and low hygroscopicity.In order to study the fire extinguishing performance of composite powders,a magnesium fire test was conducted,using the experimental apparatus of a modified cup burner.Magnesium tablets fire extinguishing experiments were conducted to prove that the fire extinguishing performance of ultrafine composite dry powder was obviously better than that of traditional sodium chloride fire extinguishing agent(commercial D-type fire extinguishing agent L J-MFZD6),and the optimal content of nano-hydrophobic silica is 3%by weight.The fire extinguishing time is only half of the traditional extinguishing agent.Finally,the extinguishing mechanism of the composite dry powder was analyzed.The fire extinguishing effect was due to the synergistic effect of nano-hydrophobic silica and sodium chloride.At the same time,refering to the water mist fire extinguishing method,FDS(ver5.0)was used to simulate the process of dry powder particles and combustion flame,in which the particle properties were changed,setting it as non-evaporable state.The simulation results of change of flame morphology and temperature field distribution showed that the dry powder coverage indeed had a certain inhibitory effect on the flame.