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Nuclear and Hydro Power
Published in Anco S. Blazev, Energy Security for The 21st Century, 2021
If too many neutrons are absorbed by other uranium-235 nuclei, a nuclear chain reaction occurs. If not controlled, the chain reaction could result in a burst of heat, and under some special circumstances it gets so violent it that could end with an explosion. The size of the explosion would depend on the type and quantity of nuclear material involved.
Chlorinated Solvents and Solvent Stabilizers
Published in Thomas K.G. Mohr, William H. DiGuiseppi, Janet K. Anderson, James W. Hatton, Jeremy Bishop, Barrie Selcoe, William B. Kappleman, Environmental Investigation and Remediation, 2020
The mechanics of solvent breakdown are profiled in a study by Arthur Tarrer of Auburn University, with researchers from Tyndall Air Force Base and from the U.S. Army Construction Engineering Research Laboratory (Tarrer et al., 1989; Howell and Tarrer, 1994). An initiator, such as heat or ultraviolet light, removes hydrogen from an unsaturated molecule, RH, forming a free radical, R. Oxygen then combines with the free radical to form a peroxide radical, ROO−, and that then removes hydrogen from a new unsaturated molecule, R'H, thereby propagating the chain reaction (Tarrer et al., 1989).
Insulating Liquids
Published in Mazen Abdel-Salam, Hussein Anis, Ahdab El-Morshedy, Roshdy Radwan, High-Voltage Engineering, 2018
Oxidation inhibitors react with the free radicals and peroxides produced by the oxidation process and thus break their chain reaction mechanism, which would otherwise give momentum to the oxidation process (Dawoud, 1986). By reacting with peroxides of radicals, passivators prevent the formation of naphthanates of copper and iron which are the usual catalysts for the oxidation reaction. For example, for petroleum oils, established additives include di-tert-butyl-para-cresol (DBPC), dimethylaniline (DMA), quinones, anthracenes, and phenyls, whereas for askarels, anthraquinone acts as a scavenger for the hydrogen chloride, which is the most chemically aggressive decomposition product.
Thermal analysis of the styrene bulk polymerization and characterization of polystyrene initiated by two methods
Published in Chemical Engineering Communications, 2019
Xin-Miao Liang, Hui-Chun Jiang, Jiang-Lai Fang, Min- Hua, Xu-Hai Pan, Jun-Cheng Jiang
Conversely, the low molecular weight of the initiator-initiated polystyrene could be explained through the following reaction mechanism. The initiator decomposed and produced large amounts of free radicals, which increased the number of chain reaction units. With an increase in the initiator concentration, the growth rate of free radicals increased, and the instantaneous growth rate of the reaction system increased, which led to a decrease in the molecular weight of the products. Finally, the stirring system was disabled in the experimental conditions, which led to nonuniform distribution of the initiator in the polymerization system. The thermoinitiated process could have occurred simultaneously with the initiator-initiated polymerization process and generated thermoinitiated products. In conclusion, the peak in the GPC spectrum of the initiator-initiated polystyrene that corresponded to the macromolecules was close to that in the spectrum of the thermoinitiated polystyrene. The appearance times of the two types of initiated polystyrene were close. This further demonstrated the conjecture of DSC characterization that the thermoinitiated process occurred along with the initiator-initiated polymerization process.
Study on the Synergistic Antioxidant Effect of Coal Inhibitors and the DFT Calculation
Published in Combustion Science and Technology, 2023
Yichao Yin, Yinghua Zhang, Zhian Huang, Hao Ding, Xiangming hu, Yukun gao, Yifu Yang
Figure 5a shows the variation of the amount of – CH2 in raw coal and inhibited coal samples as a function of temperature. The – CH2 concentration of raw coal samples at the initial temperature was higher than that of the inhibited coal samples. With the increase of temperature, the content of – CH2 in the inhibited coal gradually became higher than that in the raw coal. On the one hand, the chemical inhibitor slowed down the combination of aliphatic hydrocarbon dehydrogenation and hydroxyl radicals, delaying the chain reaction. On the other hand, the aliphatic hydrocarbon of the chemical inhibitor is relatively stable. The variation trend of – OH content in different coal samples is shown in Figure 5b. With the increase of temperature, the -OH content of all coal samples showed a trend of slowly increasing. In the initial stage, there was slightly more -OH in the inhibited coal sample than in the raw coal because the water retention of the gel prevented -OH from binding to hydrogen radicals, and the inhibition of the chemical inhibitor slowed down the consumption of – OH in the chain reaction. As shown in Figure 5c, the carboxyl content of the inhibited coal sample was significantly higher than that of the raw coal. Carbonyl groups (–C=O) exist mainly in the form of esters and anhydrides in coal structures. In the oxidation process of coal, carbonyl groups decompose to form CO or CO2. Figure 5c shows that the – C=O of the coal samples treated with the compound inhibitor was more stable, indicating that the compound inhibitor had good oxidation resistance. Figure 5d shows that the ether bond (–C – O – C–) content of raw coal and inhibited coal samples showed a slow upward trend because the – C–O – C – structure is the most stable oxygen-containing functional group in coal (Dou et al. 2014). Coal samples treated with the compound inhibitor showed a higher content of – C–O – C–. The results indicated that the compound inhibitor had a good inhibitory effect and ability. The oxidation of coal was inhibited by converting the active groups into relatively stable – C–O–C–.
Effect of the sudden change of ambient atmosphere on free radicals in coal body by CO2 fire prevention gas injection
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Jinrui Miao, Shengqiang Yang, Xiaoyuan Jiang, Zhenshan Hou, Huadi Shao
The apparent activation energy required for the low-temperature oxidation process of coal in an oxygen atmosphere was shown to be smaller and increased with the oxygen concentration by solving the apparent activation energy for various atmospheres (Gao, Chang, and Shen 2017; Li et al. 2016). The inert gases are capable of reducing the oxygen concentration to below the concentration that allows combustion. The continuous decreases of oxygen concentration and temperature are accompanied by the gradual decline of heat production rate of combustible (Deng et al. 2018; Kus, Misz-Kennan, and Iccp 2017). CO and CO2 are the products of sufficient and insufficient oxidation of coal, respectively (Su et al. 2017; Zhu et al. 2020). Compared with the condition in pure air, coal combustion in inert gases corresponds to faster oxygen consumption and lower CO and CH4 production rates during low-temperature oxidation (Zhang et al. 2018). The alterations in free radical functional groups in the coal bodies directly impact macroscopic characteristics like the emission of gaseous products during the oxidation of the coal bodies (Ma et al. 2020). Researches on the mechanism of CSC have went further from the macroscopic characteristics to the micro-structure through the use of many experiments like small-angle X-ray diffraction (XRD) (Wang et al. 2021) Fourier transform infrared spectroscopy (FTIR) (Yang et al. 2023) and electronic energy spectrum analysis (XPS) (Levi et al. 2015). The CSC process involves progressive chain reactions of different active functional group structural units and free radicals with oxygen (Cai et al. 2021) non-free functional group structural units and free radicals, and between free radicals themselves (Lei et al. 2020; Wu et al. 2018). Free radical reactions take place as soon as after contact between coal and oxygen at room temperature (Qi et al. 2019, 2020). The reaction between oxygen and the reactive groups in coal produces new free radicals, increasing the number of free radicals in the coal (Xi et al. 2023). The free radical reaction is highly temperature sensitive, and the presence of oxygen intensifies the free radical reaction in coal (Li et al. 2018; Liu et al. 2014). Active radicals can unite to produce stable chemical structures, whereas stable radicals can go for a long time without reacting (He et al. 2017; Zhou et al. 2017). The main reaction in low-temperature oxidation is the reaction between newly activated radicals and oxygen. After that, stable radicals join the reaction to produce more free radicals as the free radical chain reaction and chain excitation quicken with the temperature rise (Chen et al. 2021; Li et al. 2016).