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In order to systematically study the suppression effect of Aluminum hydroxide[Al(OH)3] and Magnesium hydroxide[Mg(OH)2] on the explosion of flour, Hartmann experiment system was used to carry out the explosion flame propagation experiment, and the influence of adding different proportions of Al(OH)3 and Mg(OH)2 powder on the morphology and propagation speed of flour combustion flame was studied. Combined with the thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) curves of Al(OH)3 and Mg(OH)2 powder, the inhibition mechanism of Al(OH)3 and Mg(OH)2 powder on flour explosion was analyzed. The results showed that with the increase of Al(OH)3 and Mg(OH)2, the flame propagation speed gradually decreases. After adding 40%wt Mg(OH)2, when t = 182 ms, the flame reaches the top of the glass tube. When 60 wt% Mg(OH)2 and 60 wt% Al(OH)3 powder were added, the maximum flame propagation velocity of flour decreased from 13.86 m/s to 5.78 m/s and 1.62 m/s, respectively, and Al(OH)3 was superior to Mg(OH)2 in inhibiting flame propagation. Both inhibitors can inhibit flour combustion by adsorption of H and OH radicals. [ABSTRACT FROM AUTHOR]

In order to study the explosion of micro‐sized and nanosized iron powder, the explosion overpressure and flame propagation were measured in a 20‐L near‐spherical explosion pressure experiment and a Hartmann tube experiment. The explosion overpressure experiments show that the optimum explosion concentrations of micro‐sized and nanosized iron powder are 750 and 375 g/m3, respectively. The maximum explosion pressure and the maximum explosion pressure rise rate of nanosized iron powder are 0.56 MPa and 46.41 MPa/s, which are 144% and 225% of that of micro‐sized iron powder, respectively. Under the optimum explosion concentration, the explosion flame of nanosized iron powder is brighter, and the propagation time is shorter. The maximum propagation velocity of micro‐sized and nanosized iron powder flame is 0.84 and 6.55 m/s, respectively, and the flame pulsation degree of micro‐sized iron powder is larger. The spherical particles and the cracks on the surface of the product particles were observed in the micro images of the explosion products, and the explosion mechanism model of micro‐sized and nanosized iron powder was obtained. It was observed that the deformation of micro‐sized iron particles intensifies, forming regular and complete spherical iron oxide particles. [ABSTRACT FROM AUTHOR]

• The mechanism of gas phase reaction inhibition of coal dust combustion was revealed. • The changes of free radicals and intermediate substances were quantitatively analyzed. • NaHCO 3 and MPP show different patterns of inhibition and dominance. • HPO 3 ⇔ PO 2 is the central radical reaction that interrupts the combustion chain. In this paper, the flame propagation behavior and free radical reaction mechanism of two powder explosive suppressants, sodium bicarbonate (NaHCO 3) and polyphosphate melamine (MPP), at different additions were investigated using Hartmann experimental system and CHEMKIN-PRO numerical simulation. The results showed that NaHCO 3 and MPP showed different inhibitory advantages. MPP mainly suppressed the propagation of flame during the development and rapid rise stages, while NaHCO 3 had a better suppression effect at the preliminary stage of explosion. The gas phase kinetic analysis also proved that the NaHCO 3 reaction was rapid, and it could decompose and endothermy at the beginning of the explosion, and generate gaseous H 2 O and CO 2 to dilute the concentration of volatile components. Meanwhile, NaOH, NaO, and NaO 2 produced by decomposition consumed free radicals and reduced the initial reaction rate of the explosion. In the process of gas phase reaction, MPP continuously reduced the amount of flame free radicals through a inhibition cycle of HPO 3 ⇔ PO 2 , and generated a large number of inert products for inerting fixed carbon, exhibiting better long-term effectiveness. This study can provide a reference for the selection and design of explosion suppressants. [ABSTRACT FROM AUTHOR]

Taking three kinds of micron aluminum powder as the research object, taking the deflagration characteristics and dynamic mechanism of aluminum dust as the main line of research, using high‐speed camera system and temperature measurement system to study the dust cloud of three kinds of aluminum powder with different concentration in the transparent pipe dust flame The flame shape, propagation speed, and temperature change law of the propagation device, the flame propagation speed and temperature increase with the increase of dust cloud concentration, and decrease with the increase of particle size; through the experiment of 20 L spherical explosive device, the empirical regression equation of maximum explosion pressure Pmax and maximum pressure rise rate (dP/dt)max is obtained, the explosion pressure (Pmax) will first increase and then decrease with the dust concentration, (dP/dt)max increases with the increase of dust concentration, while Pmax and (dP/dt)max increase with the decrease of particle size; The explosion products of aluminum powder were analyzed by XPS and surface energy spectrum, and the main substances of the explosion products were Al2O3, Al(OH)3, and unburned Al, and the deflagration mechanism model of micron aluminum powder was obtained; at the same time, the simultaneous thermal analyzer (TG‐DSC) was used to conduct microscopic thermal analysis kinetics experimental research on micron aluminum powder with different particle sizes. The combustion process of aluminum powder in the air was divided into three stages. Fit the curve by analyzing and calculate the reaction kinetic parameters of the aluminum dust combustion process. The smaller the particle size of the micron aluminum powder, the more aluminum particles involved in the oxidation reaction, the more intense the combustion reaction, the faster the flame propagation speed, the greater the height of the flame front, the greater the explosion pressure, the exothermic phenomenon is significant, and the activation energy required for the oxidation reaction to occur is smaller. [ABSTRACT FROM AUTHOR]

[Display omitted] • The in-situ synthesis was adopted in the preparation of novel ATH/SBA-15 firstly. • The ATH nanoparticles in ATH/SBA-15 suppressant are well dispersed. • The apparent activation energy increased significantly after adding ATH/SBA-15. • The ATH/SBA-15 shows efficient inhibition effect by physicochemical synergy. Recently, polyethylene (PE) dust explosions have become a serious threat to the petrochemical industry. In order to prevent the occurrence of PE dust explosion, a novel aluminum hydroxide (ATH)/Santa Barbara Amorphous type 15 (SBA-15) powder explosion suppressant with the uniform dispersion of ATH was prepared by in-situ synthesis method. For ATH/SBA-15 inhibitor, SBA-15 molecular sieve and ATH was used as the carrier and active component of explosion inhibition, respectively. The inhibition effect on PE dust deflagration was studied by flame propagation experiment. The results showed that when the addition amount of ATH/SBA-15 exceeded 40 wt%, PE dust deflagration flame was almost completely inhibited. Furthermore, the Coats-Redfern method was used to study the thermal decomposition kinetics model. It was found that the thermal decomposition kinetics model of PE before and after the addition of explosion suppressants followed the random nucleation and growth reaction mechanism (A3 model). Further fitting analysis showed the apparent activation energy of PE increased significantly after adding ATH/SBA-15 inhibitor, confirming that ATH/SBA-15 had a significant inhibitory effect on PE deflagration in thermodynamics. Finally, combining with a series of characterization results, it was founded that the ATH/SBA-15 suppressant played the efficient synergy of physics and chemistry, which was efficient in inhibiting PE deflagration. The physical inhibition mainly includes: the free radicals adsorption by SBA-15 molecular sieve, the coating effect of ATH, the endothermic effect and the reduction in O 2 concentration by H 2 O decomposed from ATH. Meanwhile, the chemical inhibition mainly lies in the elimination of the free radicals O· and H· in the explosion process by ATH. [ABSTRACT FROM AUTHOR]

[Display omitted] The properties of a green waste molecular sieve-based powder suppressor in inhibiting the flame propagation of coal dust were studied. Waste molecular sieve (S) was pretreated and selected as the carrier, potassium oxalate (K) and ferric citrate (T) as the active components. The reverse dissolution crystallization method was adopted and S@K/T, S@T/K, S@ T -K suppressors with different core–shell structure were prepared by different loading sequences. Their particle size, morphology and thermal pyrolysis behavior were compared. The results showed that the particle distribution of three powders is uniform and the dispersity of them is good. The active components of explosion suppression are evenly loaded on the waste molecular sieve carrier and they have different coating structure. The thermal desorption heat of them is 44.64 J/ g, 66.95 J/g and 92.9 J/g, respectively. Furthermore, the flame propagation characteristics of coal dust were tested by the Hartmann flame propagation device. The results showed that all powders had the effect of inhibiting the flame propagation of coal dust and the inhibition effect is S@ T -K, S@T/K and S@K/T from strong to weak. Combined with characterization results, the influence mechanism of the difference in the flame propagation inhibition effect of three suppressants was investigated. [ABSTRACT FROM AUTHOR]

• Oxidation performance of stearic acid coated aluminum dust. • Influence of stearic acid coating on MEC of aluminum dust. • Effect of stearic acid coating on explosion characteristics of aluminum dust. • Analysis of explosion products of stearic acid coated aluminum dust. • Physical model of stearic acid coated aluminum dust explosion. To explore the effect of stearic acid coating on the explosion characteristics of aluminum dust, the flame propagation characteristics, minimum explosion concentration and explosion overpressure characteristics of aluminum (Al) and stearic acid coated aluminum dust (SA-Al) were studied by using the synchronous thermal analyzer, the improved Hartmann tube explosion test device, and 20 L explosion test device. Then micro morphology and composition of the explosion products were determined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), and a physical model of stearic acid coated aluminum dust explosion was established. The results showed that the combustion intensity and flame propagation velocity of SA-Al dust cloud in the semi-closed pipe were lower than that of Al dust cloud, and the flame propagation was weak in the initial stage of explosion. The minimum explosion concentration (MEC), the optimal explosion concentration, the maximum explosion pressure (P max) and the maximum explosion pressure rise rate ((d P /d t) max) of SA-Al dust cloud were greater than that of Al dust cloud, and its products contained the incomplete combustion products AlO 2 , indicating that the stearic acid coating could abate the explosion sensitivity of Al dust cloud, and weaken the degree of oxidation of Al dust. In case of explosion, stearic acid coating could significantly enhance the explosion hazard of Al dust, resulting in a higher explosion risk. [ABSTRACT FROM AUTHOR]

• The overpressure and flame propagation of oil shale dust. • Studying in a 20-L square closed vessel and Hartmann experimental device. • When 70% NaHCO 3 is added, the speed drops by 81%, and the Pmax drops by 50.1%. • The flame propagation velocity of oil shale/NaHCO 3 dust hybrid has three stages. • The explosion mechanism of oil shale are established. The overpressure and flame propagation of oil shale dust explosions suppression by sodium bicarbonate (NaHCO 3) are studied in a 20-L square closed vessel and Hartmann experimental device. oil shale dust was mixed with sodium bicarbonate (NaHCO 3) with concentrations of 0%–70%. The results show that by increasing the mass percentage of sodium bicarbonate (NaHCO 3), the flame propagation height, flame propagation speed and explosion pressure can be effectively reduced. The inhibition mechanism of sodium bicarbonate (NaHCO3) is proposed: on the one hand, the efficient decomposition of sodium bicarbonate (NaHCO 3) in the flame can absorb the heat released during the combustion process, thereby cooling the flame, and the generated sodium carbonate can be adsorbed on the surface of the oil shale. Prevent the reaction from continuing; on the other hand, in a gas-phase explosion, free radicals such as sodium and gas-phase intermediate products such as sodium oxide (Na 2 O) react uniformly with free radicals and reactant oxygen (O 2). Sodium-containing species act as oxygen species scavengers, and the chain reaction of oil shale explosion is interrupted. [ABSTRACT FROM AUTHOR]

The polyethylene (PE) industry is in a stage of rapid development. However, PE dust floating in the air is frequently associated with unexpected explosions. To find a proper way of preventing and mitigating the potential of PE dust explosion, a study was carried out in which (NH 4) 2 CO 3 and SiC were used for the first time to suppress PE deflagration flames. In a Hartmann tube apparatus, PE deflagration flame propagation in the presence of (NH 4) 2 CO 3 and SiC powders as the suppressant was observed. The suppression effects of these two powders at different mass fractions were compared. The results showed that flame propagation velocity and acceleration decrease with increasing mass fraction of (NH 4) 2 CO 3 and SiC. Through XRD, FIRT, TG-DSC, GC–MS and sensitivity test, explosion products and combustion reactions were characterized and the PE explosion suppression mechanisms of (NH 4) 2 CO 3 and SiC for PE were compared and investigated. PE explosion is suppressed by SiC physically by reducing temperature and pressure of explosion combustion, while the explosion combustion of PE was suppressed by physical and chemical effect of (NH 4) 2 CO 3. As a result, (NH 4) 2 CO 3 is better able to suppress explosion flames. The study provides a theoretical and practical basis for the prevention and control of explosion fire accidents in the polyethylene industry. [Display omitted] • (NH 4) 2 CO 3 and SiC were used for the first time to suppress PE deflagration flames • The advantages of synergistic inhibition were illustrated by comparative study • The inhibition mechanism of PE deflagration for two novel inhibitors was revealed [ABSTRACT FROM AUTHOR]

Coal and oil shale are often mined and utilized together, and mixed dust is easily formed in these processes. In order to ensure safe production in these processes, the explosion characteristics of mixed dust were studied. Using a Godbert-Greenwold (G-G) Furnace experimental device, Hartmann tube experimental device, and 20 L explosion vessel, the oil shale and coal mixed dust ignition sensitivity experiment, flame propagation experiment, and explosion characteristics experiment were carried out. The minimum ignition temperature (MIT), minimum ignition energy (MIE), maximum explosion pressure (Pmax), maximum rate of pressure rise ((dp/dt)max), and explosibility index (KSt) parameters and the flame propagation behavior of the mixed dust were analyzed in detail. A scanning electron microscope (SEM) analysis of the coal and oil shale dust before and after the explosion was carried out to study the changes in the microscopic morphology of the dust particles. The results show that due to the oil shale having a high volatile content and low moisture content, in the mixture, the greater the percentage of oil shale, the more likely the dust cloud is to be ignited and the faster the explosion flame is propagated; the greater the percentage of oil shale, the greater the (dP/dt)max and KSt will be and, under a high dust concentration, a greater Pmax will be produced. During explosion, coal dust will experience particle pyrolysis and the gas phase combustion of the volatile matter, followed by solid phase combustion of coal char, whereas oil shale dust will only experience particle pyrolysis and the gas phase combustion of the volatile matter. [ABSTRACT FROM AUTHOR]

[Display omitted] • The influence of OA-Mt inhibitor on the 5%, 7% and 9% methane–coal flame propagation was studied. • The optimum K 2 C 2 O 4 loading concentration for explosion flame inhibition was 80%. • The inhibitory effects became enhanced with an increase of OA-Mt. • The OA-Mt inhibited 7% methane–coal explosion flame most significantly. • The explosion inhibition mechanism of OA-Mt on methane–coal dust flame zones was discussed. To enrich the methane–coal dust explosion inhibition theory at different methane concentrations, the influence of the potassium oxalate-montmorillonite (OA-Mt) nanocomposite inhibitor on the flame propagation characteristics of 5%, 7% and 9% methane–coal dust explosion was studied experimentally and its explosion inhibition mechanism was revealed. Results showed that the optimum K 2 C 2 O 4 loading concentration for explosion flame inhibition was 80%. The flame brightness was weakened, the flame instantaneous peak velocity v m was decreased, and the flame average velocity inhibition ratio φ was enhanced, proving that OA-Mt could be adopted as an excellent inhibitor for the methane–coal dust explosion. Additionally, OA-Mt had the most significant inhibition on 7% methane–coal explosion. Finally, an inhibition physical model of OA-Mt on methane–coal dust flame zones was established and the suppression mechanism was discussed. The physical-dominated inhibition effect in the flame preheating zone and the chemical-dominated inhibition effect in the combustion reaction zone co-mitigated the methane–coal flame propagation. [ABSTRACT FROM AUTHOR]

Experiments of nano-scale polymethyl methacrylate dust explosions were conducted to reveal the flame propagation characteristics and evolution mechanism. The results showed that the flame preheat zone front was approximately smooth. The average pulsating flame propagation velocity and maximum temperature both increased with an increase in dust concentration. The thermal heat transfer rate and pyrolysis rate dominated the propagating flame. A transition from pyrolysis rate control to combustion reaction rate control occurred as the dust concentration increased during the combustion process. Speculating from the physical model of nano dust flame propagation including a post-flame zone, a luminous spot-flame reaction zone, a combustible premixed-gas reaction zone, a preheat zone, an unburnt particle stagnation zone, and an unburnt zone away from the flame front, the propagating flame was macroscopically analogous to the kinetic combustion of premixed gas. In addition, it was microscopically coupled with the localised diffusion combustion of luminous spot flames. Unlabelled Image • A physical model of the nano PMMA dust flame propagation is established. • A nano PMMA dust flame propagation mechanism is proposed. • A time-scale analysis reveals the controlling regime during the flame propagation. • The agglomeration significantly affects the nano dust flame propagation mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Suppression mechanism based on thermal characteristic and flame propagation behavior of micron/nano dust explosion. • Effect of NaHCO 3 on pyrolysis oxidation characteristic of micron/nano PMMA dust. • Flame propagation of micron/nano PMMA dust cloud under intervention of NaHCO 3. • Effect of nano-aggregates on 100 nm PMMA explosion suppression mechanism. The suppression mechanism of NaHCO 3 on micron/nano PMMA dust cloud flame based on thermal analysis was investigated. The results showed that the pyrolysis oxidation processes of 30 μm and 100 nm PMMA dusts were suppressed by NaHCO 3 , and the apparent activation energy E and pre-exponential factor A were increased. The flame combustion intensity and propagation velocity of both micro and nano PMMA dusts were decreased obviously. Compared with 30 μm PMMA, NaHCO 3 maintained an efficient suppression on 100 nm PMMA with the mass ratio of NaHCO 3 increased with no suppression saturation phenomenon appeared. And 100 nm PMMA were more sensitive to particle size of NaHCO 3. In the flame preheat zone, the suppression effect of NaHCO 3 was mainly dominated by physical suppression, including the cooling effect of both pyrolysis reaction and products and the dilution effect on the concentration of combustible reactant. In the combustion reaction zone, the suppression effect of NaHCO 3 was mainly dominated by chemical suppression. The free radicals were absorbed by the active groups NaOH, forming the Na⇔NaOH suppression cycle. The E of nano PMMA dust flame was sustainably increased in both preheat and combustion reaction zones, contributing to the continuous high efficiency suppression and the sensitiveness to the particle size of explosion suppressant. [ABSTRACT FROM AUTHOR]

The ignition sensitivity and explosion hazard of Al Mg alloy dust were systematically studied in this paper. The flame propagation and explosion characteristics of Al Mg alloy were studied experimentally. Then the activation energy of the reaction was studied and the explosive products were analysed. The experimental results show that. Smaller particle sizes of Al Mg alloy dusts are more sensitive to ignition and are more likely to explosion. The explosion flame propagation velocity gradually decreases with increasing particle size, and the flame propagation acceleration of small particle size of Al Mg alloy dust gradually increases. Smaller particle size Al Mg alloy dusts have higher explosion pressure and higher explosion risk. Due to the smaller particle size the activation energy of the Al Mg alloy dust is smaller. Therefore, Al Mg alloy dust with small particle size has a faster chemical reaction rate, is more prone to explosive reactions and is more dangerous. [Display omitted] • The MIE increases and then decreases with increasing dust cloud concentration. • P ex and (dP/dt) ex reach a maximum at a dust concentration of 750 g/m3. • The activation energy decreases with decreasing particle size. • The smaller the particle size the greater the ignition sensitivity and the higher the risk. • Three things can happen when Al Mg alloy particles enter a high temperature gas environment. [ABSTRACT FROM AUTHOR]

In this paper, the Hartmann experimental system was used to study the effect of different proportions of micron and nano Al(OH) 3 powders on the deflagration flame propagation of poplar dust. In the course of the experiment, a high-speed camera was used to record the flame shape and characteristic parameters in the process of poplar dust deflagration flame propagation. Combined with the SEM images of poplar dust explosion products under different conditions, the pyrolysis characteristic curves of poplar dust, micron and nano Al(OH) 3 powders, the inhibition mechanism of micron and nano Al(OH) 3 powders on poplar dust deflagration was analyzed. The experimental results show that micron and nano Al(OH) 3 powders have obvious inhibition effect on poplar dust deflagration flame, and better inhibition effect can be achieved when 35% nano Al(OH) 3 powder is added. And under the condition of adding the same proportion of micron and nano Al(OH) 3 powders, the inhibition effect of nano Al(OH) 3 powder is better than that of micron Al(OH) 3 powder. [ABSTRACT FROM AUTHOR]

[Display omitted] To explore ways of further guaranteeing the production safety of coal processing, novel powder suppressors with core–shell structure were prepared through anti-solvent crystallization method by loading potassium oxalate (K) and ferric citrate (T) on treated waste molecular sieve. Flame propagation experiments were performed to investigate the effects of suppressors prepared under different conditions on coal dust flame propagation. The results showed that when K and T were added simultaneously at the loading of 30 wt%, the suppressor S@T-K showed best suppression performance. The pyrolysis-oxidation mechanism of coal dust with and without suppressor S@T-K was analyzed using Coats-Redfern (C-R) method. After the suppressor was added, the activation energy increased by 11.55 kJ/mol and 15.37 kJ/mol in the rapid and slow pyrolysis stages, respectively. The activation energy values of the coal sample with and without the suppressor under different conversion ratios were further calculated using Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. The average activation energy values during the rapid and slow pyrolysis stages both agree well with the C-R calculation, which verifies the appropriateness of using C-R method to identify the reaction mechanism. By combining the coal dust flame propagation behaviors with the pre- and post-explosion characterization results, it is proposed that waste molecular sieve composite powders with core–shell structure suppress flame propagation through the synergy of physical and chemical reactions. [ABSTRACT FROM AUTHOR]