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Published in Michael L. Madigan, HAZMAT Guide for First Responders, 2017
The following factors affect the stability of an explosive:Chemical constitution. In the strictest technical sense, the word “stability” is a thermodynamic term referring to the energy of a substance relative to a reference state or to some other substance. However, in the context of explosives, stability commonly refers to ease of detonation, which is concerned with kinetics (i.e., rate of decomposition). It is perhaps best, then, to differentiate between the terms thermodynamically stable and kinetically stable by referring to the former as “inert.” Contrarily, a kinetically unstable substance is said to be “labile.” It is generally recognized that certain groups like nitro (–NO2), nitrate (–ONO2), and azide (–N3), are intrinsically labile.Kinetically. There exists a low activation barrier to the decomposition reaction. Consequently, these compounds exhibit high sensitivity to flame or mechanical shock. The chemical bonding in these compounds is characterized as predominantly covalent, and thus they are not thermodynamically stabilized by a high ionic-lattice energy. Furthermore, they generally have positive enthalpies of formation, and there is a little mechanistic hindrance to internal molecular rearrangement to yield the more thermodynamically stable (more strongly bonded) decomposition products. For example, in lead azide, Pb (N3)2, the nitrogen atoms are already bonded to one another, so decomposition into Pb and N2 is relatively easy.Temperature of storage. The rate of decomposition of explosives increases at higher temperatures. All standard military explosives may be considered to have a high degree of stability at temperatures from –10°C to +35°C, but each has a high temperature at which its rate of decomposition rapidly accelerates, and stability is reduced. As a rule of thumb, most explosives become dangerously unstable at temperatures above 70°C.Exposure to sunlight. When exposed to the ultraviolet rays of sunlight, many explosive compounds containing nitrogen groups rapidly decompose, affecting their stability.Electrical discharge. Electrostatic or spark sensitivity to initiation is common in a number of explosives. Static or other electrical discharge may be sufficient to cause a reaction, even detonation, under some circumstances. As a result, safe handling of explosives and pyrotechnics usually requires proper electrical grounding of the operator.
Roles of Soil Organic Matter and Humic Substance Structure in Cu and Pb Adsorption in Histosols
Published in Soil and Sediment Contamination: An International Journal, 2021
Izabella Bezerra Coutinho, Camila daCosta Barros de Souza, Erica Souto Abreu Lima, Andrés Calderín García, Marcos Gervasio Pereira, Gustavo Souza Valladares, Nelson Moura Brasil do Amaral Sobrinho
According to the Freundlich model, Histosols have a higher affinity for Pb than for Cu. However, the experimental data showed that most Cu sorption was specific while Pb sorption was nonspecific. Cu mainly forms irreversible bonds with Histosol colloids, while Pb forms more reversible bonds. Nonetheless, the Pb adsorption coefficient (Q0) presented a positive and significant correlation with the most labile fraction of soil organic matter, FA (Ružičić 2019). Principal component analysis of the soil attributes in the different horizons (Figure 3a) showed that horizons RJ3-Hdo1 and RJ3-Hdp, which presented the highest proportions of specific adsorption of Pb in soil colloids compared with nonspecific adsorption (Figure 2), had the highest FA and total N contents. Moreover, the FA contents in the studied horizons were highly correlated with the N contents, which indicated that N enrichment mainly took place through the amidic nitrogen structures in the FA of this soil. These results explain the positive and significant correlation between the Pb adsorption coefficients and the organic matter, nitrogen, and fulvic acid contents of the histic horizons.
Humus composition and humic acid-like structural characteristics of corn straw culture products treated by three fungi
Published in Chemistry and Ecology, 2021
Yifeng Zhang, Sen Dou, Shufen Ye, Dandan Zhang, Batande Sinovuyo Ndzelu, Xiaowei Zhang, Manjiao Shao
Many scholars have conducted experiments and found that fungi can effectively degrade lignin and cellulose [1,2], and further form quinone compounds [14–17]. Thus, playing an important role in mineralisation and decomposition of corn straw. In soil organic matter, fungi, as the microorganisms in the K strategy, mainly decompose the refractory organic matter [18], organic matter that is difficult to decompose [19] and utilises simple and labile compounds as a source of C and energy [20]. Moreover, fungi contribute more to the soil’s organic matter hangar because they are harder to break down. Therefore, using fungi to pre-treat corn straw to encourage humification is a worthy practice to maximise the utilisation benefit of plant residues [15,21–24], while reducing the time needed to degrade/decompose crop straw residues by indigenous microbiota [25].
Optimization of dynamic-microwave assisted enzymatic hydrolysis extraction of total ginsenosides from stems and leaves of panax ginseng by response surface methodology
Published in Preparative Biochemistry & Biotechnology, 2019
All the time, the orchard workers only pick ginseng, a large number of GSAL were discarded, resulting in waste of resources and environmental pollution. Thus, the products of GSAL processing have attracted much interest. Over the centuries, many methods have been applied to extract the ginsenoside ingredients from the roots, the leaves, the flower-buds, and the fruits of ginseng, such as soxhlet and heat reflux extraction,[18] microwave-assisted extraction (MAE),[19] ultrasonic-assisted extraction,[20] commercial enzyme extraction[5] and so on. However, these conventional methods usually require relatively large volumes of organic solvents, high extraction temperature, long extraction times and high risk of degradation of thermo-labile components with low extraction efficiency. In general, these methods utilized methanol or ethanol as solvent or with alcohol-water solutions to extract ginsenosides. Nevertheless, many thermally labile or perhaps thermally unstable natural products may degrade and lose their biological activity during thermal extraction. Furthermore, the extraction of ginsenoside by hot methanol could lead to the formation of methyl derivatives, which interfered with the extraction of saponins and could not effectively extract the target components.[1,21]