Explosivity and Flammability of Nanopowders: New Challenges (original) (raw)
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Ignition and explosion characteristics of four kinds of nanopowders
Journal of Physics: Conference Series
This work is about the study of ignition sensitivity and the explosion violence characteristics of nanoparticles. It was carried out on various nanopowders as part of a project (NANOGRA) that aims at a multidisciplinary assessment of the risks related to nanoparticles. This paper discusses the experimental results for the determination of ignitability and explosion violence characteristics of Thermal Black N990, Corax N550, MWCNTC7000 and partially passivated metallic nanoparticles (Aluminium). The results of the various tests (MIE, Pmax and KSt) led to the conclusion that carbon nanopowders are capable of generating , when airborne, an ATEX with moderate explosion intensity comparable to the ST1 class. They are little sensitive to electrostatic phenomena. The assessment of explosion parameters of carbon nanopowders was generally found similar to their microscopic size analogue. The pyrophoric nature of partially passivated aluminium nanopowder required screening tests (e.g. MIT layer and combustibility) to control the risk of ignition in the stages of the characterization tests.The results show that aluminium nanoparticles are sensitive to the risk of ignition by a phenomenon of electrostatic origin, and explosion violence seems to decrease when BET specific surface area increases.
Potential Explosion Hazard of Carbonaceous Nanoparticles: Explosion Parameters of Selected Materials
Journal of Hazardous Materials, 2015
Following a previous explosion screening study, we have conducted concentration and ignition energy scans on several carbonaceous nanopowders: fullerene, SWCNT, carbon black, MWCNT, graphene, CNF, and graphite. We have measured minimum explosive concentration (MEC), minimum ignition energy (MIE), and minimum ignition temperature (MIT cloud) for these materials. The nanocarbons exhibit MEC ~ 10 1-10 2 g/m 3 , comparable to the MEC for coals and for fine particle carbon blacks and graphites. The nanocarbons are confirmed mainly to be in the St-1 explosion class, with fullerene, at K St ~ 200 bar-m/s, borderline St-1/St-2. We estimate MIE ~ 10 2-10 3 J, an order of magnitude higher than the MIE for coals but an order of magnitude lower than the MIE for fine particle graphites. While the explosion severity of the nanocarbons is comparable to that of the coals, their explosion susceptibility (ease of ignition) is significantly less (i.e. the nanocarbons have higher MIEs than do the coals); by contrast, the nanocarbons exhibit similar explosion severity to the graphites but enhanced explosion susceptibility (i.e. the nanocarbons have lower MIEs than do the graphites). MIT cloud > 550°C, comparable to that of the coals and carbon blacks.
Potential explosion hazard of carbonaceous nanoparticles: screening of allotropes
Combustion and Flame, 2016
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/m 3 , using a 5 kJ ignition source. Time traces of overpressure were recorded. Samples typically exhibited overpressures of 5-7 bar, and deflagration index K St = V 1/3 (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).
Assessment of Explosion Hazards Associated With Nano-Powders
SPE Kingdom of Saudi Arabia Annual Technical Symposium and Exhibition
Nano-powders are composed of particles in size range from about 1 to 100 nano-metres (nm). The growing demand for nano-powders arises from the change in physical, chemical and electrical properties exhibited by such particles when their size falls below 100 nm. Along with the increasing production and use of Nano scale particles, there has been a growing concern over the impact of this new technology on health, safety and environment. This has almost exclusively concentrated on the potential health hazards of nano-powders. One potential hazard that appears to have received little attention to date is their explosivity. Explosive dust clouds can be generated from most organic materials, many metals and even some non-metallic inorganic materials. Dust explosions involving particle sizes ranging from a few microns to hundreds of microns, there is a need for these particles to be extensively studied. This work involves computationally modelling the explosion, and investigation of critical parameters that can enhance the severity of the explosion. These parameters include but are not limited to effect of particle size, dust concentration and composition, ignition strength, degree of dust dispersion, explosion characteristics of nano-particles, operating conditions. Further, the work involved in this paper looks at the impact onto the environment by explosion of such nano-powders. The possibility of dust generation accumulation and explosion in various areas of the facility are investigated. A checklist for adequacy of existing safety measures is prepared, and requirement for additional safeguards is studied, in order to avoid catastrophic effects.
Risk assessment of the ignitability and explosivity of aluminum nanopowders
Process Safety and Environmental Protection, 2012
Previously, an extensive study has been carried out in order to assess the ignition sensitivity and explosivity of aluminum nanopowders. It showed notably that, as the particle size decreases, minimum ignition temperature and minimum ignition energy decrease, indicating higher potential inflammation. However, the explosion severity decreases for diameters lower than 1 m. As a consequence, this study leads to the conclusions that the ignition sensitivity and explosion severity of aluminum nanopowders may be affected by various phenomena, as pre-ignition, agglomeration/aggregation degree and the intrinsic alumina content. The presence of wall-quenching effects and the predominance of radiation compared to conduction in the flame propagation process have to be discussed to ensure the validity of the 20 L sphere and of the results extrapolation. Based on the peculiar behaviours that had been previously highlighted, a specific risk analysis has been developed in order to assess the fire and explosion risks of such materials. It has been applied to an industrial plant of aluminum nanopowders production. The hazard identification and the consequence modelling steps, especially the quantification of the likelihood and consequences, have been designed specifically. The application of this method has led to the definition of the most adequate safety barriers.
Nanosafety by design: risks from nanocomposite/nanowaste combustion
Risks associated with the end-of-life of nanomaterials are an issue that needs to be addressed so that the public perception and opinion, with regard to these emerging technological products, can effectively be supported by experimental evidences. In order to find new ecological ways to treat nanoproducts at their end-of-life, a new home-made demonstrator system was setup at INERIS, specifically designed to perform burning tests, coupled to a differential thermal analyzer to monitor the combustion kinetics. To assess nanoobject release during combustion, a high-performance nanocomposite polymer commonly used in the automotive industry, namely the polymeric compound acrylonitrile butadiene styrene matrix mixed with 3 wt% of multiwalled carbon nanotubes (MWCNTs) was tested. To assess the potential release of carbon nanotubes (CNTs) during the combustion with this tool, the particle size distribution in the fumes was measured using an electrical low pressure impactor, and CNTs were collected using an aspiration-based transmission electron microscopy grid sampler. One of primary objective of these preliminary tests described in this study consisted in validating whether CNT fibers can be released in the gas phase during the combustion of a polymeric matrix filled with CNTs. It was found indeed that MWCNT of about 12-nm diameter and 600-nm length can be released in the ambient environment during combustion of 3 % MWCNT ABS. Such information is critical to assess whether a nanoproduct can be deemed to be considered as “nanosafe by design” in its risk assessment.
The Explosion and Dispersion Potential of Engineered Nanoparticles
2016
This work investigates the explosion and dispersion potential of engineered nanoparticles (ENP). The European Union (EU) sponsored this investigation, firstly to predict or estimate risks posed by the use of engineered nanomaterials (ENM), and secondly to implement procedures for the purpose of risk mitigation. These include establishing exposure control limits and controlling and monitoring exposure, including the accidental explosive or massive release of ENP into the environment. To this end, the release of ENP originating from specific nanopowders was simulated in a 31 m3 airtight chamber of controllable environment. Their loss and dispersion characteristics were studied under ventilated and unventilated conditions. The explosion characteristics of specific ENP in lean hybrid blends of nanoparticles with methane and air, were studied in a 23 L cylindrical combustion vessel providing the adjustment of isotropic turbulence induced by specially designed fans. The influence of ENP o...
Chemical Engineering Transactions, 2016
The influence of carbon blacks nanoparticles addition to methane/air mixture explosions has been studied. Low concentrations of carbon black nanoparticles ranging from 20 to 300 nm average diameter have been mixed with methane. Explosion tests have been performed in the 20 L sphere and in a flame propagation tube at different initial degrees of turbulence. The burnt gases have been analysed by micro gas-chromatography. The influence of carbon black nanoparticles on the explosion severity and on the velocity of the front flame has been appreciated by comparing the results obtained for pure methane explosions. It appears that the maximum explosion overpressure can slightly increase when a few percent of carbon blacks are introduced for lean mixtures but decrease for rich mixtures. This trend can be explained by using an analogy and assuming that carbon nanoparticles are soot nuclei, which enhance the physical and/or chemical condensation of combustion products. Furthermore, the explos...
Influence of carbon black nanoparticles on the front flame velocity of methane/air explosions
Journal of Loss Prevention in the Process Industries, 2017
This work aims to study the influence of low concentrations of carbon black nanoparticles in gas mixtures on the front flame velocity. Due to their low settling velocity, nanoparticles offer the opportunity to study the hybrid mixture explosion at low turbulence levels of dispersion. They can also be used as particles to model the presence of soot. The flame velocity of carbon black nanoparticles/methane/air mixtures was measured in a vertical 1 m long tube with a square crosssection connected to a gas mixing system. Dust clouds are generated by a pulse of methane/air mixture at 5 barg from the bottom of the tube, where the mixture is also ignited. A high-speed video camera is used to record the flame propagation. An estimation of the laminar burning velocity is obtained using the method proposed by Andrews and Bradley. Although this method may not be precise for laminar flame velocity estimations, it offers a first approximation for hybrid systems explosions. The influence of the initial turbulence was also studied by varying the ignition delay. The influence of low concentrations of carbon black nanoparticles on the front flame velocity has been appreciated by comparing the results obtained for gaseous mixtures explosions at different turbulence levels. The burning velocity of gaseous mixture seems to increase when the initial turbulence of the system is augmented. However, when the initial turbulence is significant, the front flame velocity seems to decrease, suggesting that the flame kernel can be strongly destabilized by turbulent vortices. Moreover, it appears that the flame burning velocity can slightly decrease when carbon black nanoparticles concentration is increased. The unstretched burning velocity is decreased by 43% when 20 mg of carbon black nanoparticles are added to the system. This trend could be explained by the enhancement of the heat radiation transfer of the system. The results are then compared to the explosions trends in a 20 L spherical vessel.
Modified Setup of 20-L-Sphere for the Determination of Safety Characteristics of Nano Powders
This paper describes a modified experimental setup for the test apparatus 20-L-Sphere (also known as 20-L Siwek Chamber), that enables the test samples to be kept under inert atmospheric conditions nearly until ignition. This setup was designed to allow the determination of safety characteristics of nanopowders under most critical circumstances (e.g. minimisation of the influence of oxidation before the test itself). The aim of this modification was to determine, whether or not the current setup and procedures underestimate the explosion violence and ignitability of nanopowders. The work includes experimental results of micrometer dusts to validate the modified setup. Moreover first results of nanometer iron and aluminium dusts are presented, which were kept at inert conditions until shortly before the ignition. The tested nano iron was found to react pyrophoric, as soon as it gets in contact with air, while the tested nano aluminium did not generally show such behaviour.