Ignition and explosion risks of nanopowders

Inhibition characteristics research of aluminum alloy polishing dust explosion through addition of ultrafine Al(OH)3 inerting agent

Investigations into the deactivation of explosion sensitivity and reduction of flame propagation for aluminium alloy polishing wastes were carried out by the addition of ultrafine Al(OH)3 inerting agent. Meanwhile, high-purity aluminium powders with similar mean diameters were also used as a comparative study. The explosion propagation characteristics of high-purity aluminium dust and aluminium alloy polishing waste dust under different inerting ratios (ε ) were tested and investigated using a standardised Hartmann tester and a developed experimental platform. The results show that the minimum ignition energy of high-purity aluminium powder is between 40 and 45 mJ, and the minimum ignition energy of aluminium alloy polishing waste is between 500 and 550 mJ, which is one order of magnitude higher than that of high-purity aluminium powder. The lower explosion limit concentration of aluminium alloy polishing waste dust is 150 g/m3, which is 53.33% of that of high-purity aluminium powder. According to the analysis of the SEM image, the main reason is that the spherical particles of high-purity aluminium dust have a folded surface and good dispersion. Compared with the smooth fibre surface of aluminium alloy polishing waste dust, the former is easier to contact with air and the contact area is larger. Therefore, in engineering practice, it is not appropriate to use high-purity aluminium dust-related explosion parameters as the basis for the risk assessment of combustion and explosion at aluminium alloy polishing work sites. In addition, as the dust concentration decreases, the combustion intensity of high-purity aluminium dust and aluminium alloy polishing waste dust also decreases, and the flame propagation appears to be a discontinuous phenomenon. The peak flame propagation velocity of aluminium alloy polishing waste is 7.368 m/s at a concentration of 300 g/m3, which is 56.85% of that of high-purity aluminium powder. As the inerting ratio increases, the propagation velocity of the explosion flame slows down. When the inerting ratio reaches 30%, the minimum ignition energy of aluminium alloy polishing waste is inerted to 1 J, and self-sustained flame propagation cannot be formed. The results show that the ultra-fine Al(OH)3 powder has a significant inerting effect and is a realistic possibility in the production of aluminium alloy polishing.

Nanomaterials, a New Challenge in the Workplace

Nanomaterials are a nanotechnological product of increasing importance given the possibilities they offer to improve quality of life and support sustainable development. Safe management of nanomaterials is needed to ensure that this emerging technology has the highest levels of acceptance among different interest groups, including workers. This chapter reviews the current state that presents the different stages of risk management applied to nanomaterials, including standardisation, regulation, risk assessment and risk control. Particularly, the chapter contextualizes the development of nanotechnologies at European level and analyses the scientific evidence available on the risks derived from nanomaterials use. Furthermore, it highlights the required conditions to encourage the responsible development of nanomaterials, as well as reflects on the lack of consensus in terms of approaches and frameworks that could facilitate standardisation adoption, regulatory enforcement and industry intervention concerning nanomaterials.

Safe(r) by design guidelines for the nanotechnology industry

Expectations for safer and sustainable chemicals and products are growing to comply with the United Nations and European strategies for sustainability. The application of Safe(r) by Design (SbD) in nanotechnology implies an iterative process where functionality, human health and safety, environmental and economic impact and cost are assessed and balanced as early as possible in the innovation process and updated at each step. The EU H2020 NanoReg2 project was the first European project to implement SbD in six companies handling and/or manufacturing nanomaterials (NMs) and nano-enabled products (NEP). The results from this experience have been used to develop these guidelines on the practical application of SbD. The SbD approach foresees the identification, estimation, and reduction of human and environmental risks as early as possible in the development of a NM or NEP, and it is based on three pillars: (i) safer NMs and NEP; (ii) safer use and end of life and (iii) safer industrial production. The presented guidelines include a set of information and tools that will help deciding at each step of the innovation process whether to continue, apply SbD measures or carry out further tests to reduce uncertainty. It does not intend to be a prescriptive protocol where all suggested steps have to be followed to achieve a SbD NM/NEP or process. Rather, the guidelines are designed to identify risks at an early state and information to be considered to identify those risks. Each company adapts the approach to its specific needs and circumstances as company decisions influence the way forward.

Experimental study of the explosion characteristics of isopropyl nitrate aerosol under high-temperature ignition source

Experimental methods and results of aerosol explosion under high-temperature ignition source have not yet been reported. An explosion test system for aerosol explosion at high-temperature source was established in this study. Through a series of experiments carried out in a 20 L confined vessel, explosion characteristics of isopropyl nitrate (IPN) aerosol under high-temperature ignition source were obtained and the results discussed. The explosion pressure-time history of IPN aerosol under high-temperature ignition was found to have a "double peak" structure produced in the first and second explosion respectively. The second peak of the explosion pressure is 3-5 times that of the first. The peak of explosion pressure at electric spark ignition is higher, compared with the second peak of the explosion pressure at high-temperature ignition for the IPN aerosol with the same equivalence ratio, but both are not significantly different. The maximum rate of pressure rise in the first explosion of IPN aerosol at high-temperature ignition is clearly larger than that at electric spark ignition. The maximum rate of explosion pressure rise at electric spark ignition is slightly higher than that in the second explosion at high-temperature ignition for the IPN aerosol with the same equivalence ratio.

Nanometal Dust Explosion in Confined Vessel: Combustion and Kinetic Analysis

Extensive application of metal powder, particularly in nanosize could potentially lead to catastrophic dust explosion, due to their pyrophoric behavior, ignition sensitivity, and explosivity. To assess the appropriate measures preventing accidental metal dust explosions, it is vital to understand the physicochemical properties of the metal dust and their kinetic mechanism. In this work, explosion severity of aluminum and silver powder, which can be encountered in a passivated emitter and rear contact (PERC) solar cell, was explored in a 0.0012 m³ cylindrical vessel, by varying the particle size and powder concentration. The P _max and dP/dt _max values of metal powder were demonstrated to increase with decreasing particle size. Additionally, it was found that the explosion severity of silver powder was lower than that of aluminum powder due to the more apparent agglomeration effect of silver particles. The reduction on the specific surface area attributed to the particles' agglomeration affects the oxidation reaction of the metal powder, as illustrated in the thermogravimetric (TG) curves. A sluggish oxidation reaction was demonstrated in the TG curve of silver powder, which is contradicted with aluminum powder. From the X-ray photoelectron spectroscopy (XPS) analysis, it is inferred that silver powder exhibited two reactions in which the dominant reaction produced Ag and the other reaction formed Ag₂O. Meanwhile, for aluminum powder, explosion products only comprise Al₂O₃.

Influence of Heating Modes of Compacted Samples from Nickel Powders with Nanosized Particles on Their Interaction with Air

Abstract

In this paper, we study compact samples of pyrophoric nickel powders with the average particle size of 85 nm, obtained by the chemical-metallurgical method. For the first time, it is experimentally shown that it is possible to passivate compact samples with a diameter of 3 mm from pyrophoric nickel powders with nanosized particles in air. For a relative density of 0.4 to 0.5, the passivation time is only 3–5 s. According to the X-ray phase analysis data, only the Ni phase is observed in passivated samples. It is found that passivated samples retain their thermal stability in air upon slow (<10 deg/s) heating to ~200°C, which is an important parameter for fire safety when handling nanopowders. The electron microscopic analysis of the passivated samples did not reveal traces of sintering of nickel nanoparticles, including after checking for thermal stability. The uniform distribution of oxygen over the passivated samples according to the data of energy dispersive analysis (the standard deviation is 0.9 at %) indicates the volumetric nature of the interaction of the samples with air during passivation. For the obtained passivated samples, the critical heating conditions were determined, under which self-ignition occurs, which is in agreement with N.N. Semyonov’s classical theory of thermal explosion.

Macrokinetic investigation of the interaction mechanism of the pyrophoric iron nanopowder compacts with air

It is shown that self-heating of a compacted sample made of nonpassivated iron nanopowder is not uniform, although it begins simultaneously within the entire surface of the sample. It is found that the maximum temperature of self-heating decreases with an increase in relative density of samples, which indicates that the oxidation process is limited by the diffusion supply of oxidant. It is shown that the process of interaction of samples with the air occurs in a superficial mode. A qualitative agreement of the results of the theoretical analysis with experimental data is obtained. The possibility of passivation of compacted samples made of iron nanopowder is experimentally established.

Course of explosion behaviour of metallic powders - From micron to nanosize

This work presents an overview about the explosion behaviour of metallic powders from micron to nanosize. Aluminium, magnesium, titanium, iron and zinc were considered and their explosion safety parameters were analysed as a function of their mean primary particle size either determined by BET measurements, particle size distribution. To depict the course of explosion behaviour for these metals, extensive literature review has been performed and additional experimental tests were also performed. Generally, decreasing the particle size in a metallic powder leads to a higher explosion severity. It appears that this statement is true till a critical diameter below which the explosion severity (p_max, dp/dt_max) decreases for all the considered powders. This critical size can be explained by theoretical considerations on the nature of thermal transfer in the flame, namely by analysing the Cassel model. Finally, semi-empirical models were also developed for aluminium to highlight the specific micrometre and nanometre behaviour and the influence of turbulence, particle burning time, diameter and concentration. The influence of these key parameters needs to be further assessed in a future work in order to better understand the mechanisms involved and to extend the scope to other powdered materials.

Combustion Inhibition of Aluminum–Methane–Air Flames by Fine NaCl Particles

The effect of NaCl as an extinguishing agent on metal dust fires require further exploration. This paper reports the results of an experimental study on the performance of micron-sized NaCl powders on hybrid aluminum–methane–air flames. NaCl particles with sub-10 μm sizes were newly fabricated via a simple solution/anti-solvent method. The combustion characteristics of aluminum combustion in a methane-air flame were investigated prior to the particle inhibition study to verify the critical aluminum concentration that enables conical aluminum-powder flame formation. To study the inhibition effectiveness, the laminar burning velocity was measured for the established aluminum–methane–air flames with the added NaCl using a modified nozzle burner over a range of dust concentrations. The results were also compared to flames with quartz sand and SiC particles. It is shown that the inhibition performance of NaCl considerably outperformed the sand and SiC particles by more rapidly decreasing the burning velocity. The improved performance can be attributed to contributions from both dilution and thermal effects. In addition, the dynamic behavior of the NaCl particles in the laminar aluminum–methane–air flame was investigated based on experimental observations. The experimental data provided quantified the capabilities of NaCl for metal fire suppression on a fundamental level.

Inhibition of aluminum dust explosion by NaHCO3 with different particle size distributions

NaHCO₃ with three particle size distributions was employed to determine the minimum inerting concentration (MIC, g/m³) for the explosion of 5μm and 30μm aluminum dust in a standard 20L spherical chamber and thus examine the effect of particle size on the inhibition efficiency. Results showed that the MIC significantly increases as the aluminum particle size decreases from 30μm to 5μm. For 30μm aluminum, the MIC dramatically decreased with the reduction in the NaHCO₃ particle size. By contrast, for 5μm aluminum, the MIC was nearly independent of the particle size of NaHCO₃ in the range studied. Time-scale analysis indicated that the decomposition of NaHCO₃ must be faster than the aluminum combustion reaction for effective chemical inhibition. Scanning electron microscopy showed that the particles of the explosion residues of a NaHCO₃/Al mixture were considerably larger than those of pure aluminum explosion residues. A diameter ratio β_mix was defined to evaluate the degree of incomplete reaction promoted by NaHCO₃. The composition of the explosion products was analyzed by X-ray photoelectron spectroscopy, and the data revealed that Na₂CO₃ and Al₂O₃ are the major species of the products. An inhibition mechanism was proposed based on these results.