Thermite reaction driven pyrotechnic formulation with promising functional performance and reduced emissions

Exploration of the reactivities of homemade binary pyrotechnics

Understanding the properties of explosives is the basis for investigating and analyzing explosion cases. To date, due to the strict legal control of standard explosives and initiators, homemade pyrotechnics composed of oxidizers and fuels have become popular explosive sources of improvised explosive devices (IEDs) threatening greatly social stability and personal safety. The reactivity of pyrotechnics strongly depends on their intrinsic characteristics and operating conditions, which determine the efficiencies of heat and mass transfer between the reaction zone and the unreacted zone. Herein, the tests of thermodynamics, pressurization characteristics, and combustion propagation behaviors are conducted to explore the effects of oxidizer species, particle size, and loading density on the reactivity of homemade binary aluminum-based pyrotechnics. The results show that the pyrotechnics with potassium chlorate (KClO3) have the strongest reactivity with the highest pressurization rate (dp/dt) and the shortest combustion duration. Compared with their counterparts based on aluminum microparticles(mAl), pyrotechnics consisting of Al nanoparticles (nAl) possess superior reactivity as expected, which results from the relatively short heat and mass transfer distances. The nAl-based pyrotechnics have a low reaction exothermic peak temperature, great heat release, great aluminothermic reaction completeness, and high produced peak pressure with several orders of magnitude higher pressurization rate. Increasing the loading density of the pyrotechnics over a certain value can change the dominant mode of heat transfer from convective to conduction, sharply decreasing the pressurization characteristics and combustion front propagation velocities (vp). The results of theoretical calculations using the NASA-CEA codes show that loading density can alter the reaction process of the pyrotechnics, leading to a decrease in the predicted pressure per unit mass for Al/KNO3 or Al/AP, and an increase for Al/KClO3. For nAl/potassium nitrate (KNO3), the density is between 1.0 and 1.25 g cm-3, across which dp/dt decreases by one order of magnitude from 0.148 to 0.014 MPa ms-1. In addition, vp decreases by three orders of magnitude from 0.040 to 0.078 m s-1. Distinct pressurization behaviors of nAl/AP are observed at a density of 1.5 g cm-3, while the variation in nAl/KClO3 reactivity fluctuates. These results are beneficial for the damage assessment of scenes caused by an explosion and for inversely calculating charge parameters.

'Green firecrackers' with reduced barium emissions in particulate matter

Ambient air quality is affected due to the emission of pollutants on a large scale after the bursting of firecrackers. Traditionally in all firecrackers, barium (Ba) compounds are used as oxidizers and also to impart green colour flame. Combustion products of barium compounds are water soluble and readily absorbed by the body affecting human health. Thus, the inherent risk of Ba pollution due to the bursting of firecrackers has consequent health effects. To reduce the ambient air pollution caused due to burning of conventional firecrackers, CSIR NEERI has developed reduced emission firecrackers (green crackers). This is achieved by reducing the amount of chemicals, barium nitrate, shell size and addition of additives such as zeolite and iron oxide. This study aims to specifically investigate the influence of additives on the level of barium in reduced emission firecrackers. Four types of conventional and reduced emission firecrackers were selected and tested inside a firecracker emission testing facility to check the levels of barium in PM₁₀ and PM_2.5. The measured mean concentrations of all types of reduced emission crackers (green crackers) provided by fireworks manufacturers show significantly reduced barium concentration by 30-60% compared to conventional crackers depending on the type of firecrackers, shell size and amount of chemicals used. The possible reason for reduced Ba level is attributed to i) reduced usage of Ba(NO₃)₂ and ii) formation of heavy density compounds, leading to soil fallout.

Chemical characterization of PM10 and PM2.5 combusted firecracker particles during Diwali of Lucknow City, India: air-quality deterioration and health implications

Urban air pollution is a growing menace leading to human discomfort, increased hospitalizations, morbidity, and mortality. This study deals with deteriorated air quality due to firecracker bursting during Diwali in Lucknow. Inhalable particulates and gaseous pollutants were monitored during Diwali 2020 using air samplers. Elements, ions, and surface morphology of particles were analyzed using ICP-MS, ion chromatograph, and SEM-EDX, respectively. PM₁₀, PM_2.5, SO₂, and NO₂ were 558, 352, 44, and 86 μg/m³ during Diwali night and 233, 101, 17, and 40 μg/m³ on pre-Diwali night while 241, 122, 24, and 43 μg/m³ on Diwali day. Concentrations surged for PM₁₀: 139% and 132%, PM_2.5: 249% and 189%, SO₂: 159% and 83%, and NO₂: 115% and 100% on Diwali night compared to pre-Diwali night and corresponding Diwali day, respectively. Al, K, Ba, and B showed dominance in PM₁₀ whereas Zn, Al, Ba, and K in PM_2.5 on Diwali night. The order of metal abundance in PM_2.5 was Cd < Co < Ag < As < Cr < Ni < Cu < Bi < Pb < Mn < Sr < Fe < B < Zn < Al < Ba < K. Cations NH₄⁺, K⁺, Mg²⁺, Ca²⁺, and anions F^-, Cl^-, NO₃^-, Br^-, NO₂^-, SO₄^-2, PO₄^3- showed a 2-8 fold increase on Diwali night relative to pre-Diwali night. Average metal concentrations varied by 2.2, 1.6, and 0.09 times on Diwali than pre-Diwali in residential, commercial, and industrial areas, respectively. PM₁₀ concentration increased by 458% and 1140% while PM_2.5, 487%, and 2247% than respective NAAQS and WHO standards. Tiny firecracker particles vary in toxicity as compared to vehicular emissions and have enhanced bioavailability leading to severe threat in terms of LRI, COPD, and atherosclerosis for city dwellers. It is imperative to recognize the present status of ambient air quality and implement regulatory strategies for emission reduction.