Correlations among free radicals, apparent activation energy, and functional groups during lowtemperature oxidation of Jurassic coal in Northern Shaanxi were investigated by examining three coal samples collected from...Correlations among free radicals, apparent activation energy, and functional groups during lowtemperature oxidation of Jurassic coal in Northern Shaanxi were investigated by examining three coal samples collected from the Ningtiaota, Jianxin, and Shigetai coal mines. Free radical concentrations at less than 120 ℃ were investigated by electron spin resonance experiments while the thermogravimetric experiments were conducted to analyze apparent activation energies. In addition, Fourier transform infrared spectroscopy was employed to study the spectrum of functional groups generated in coal. The results indicated that, in decreasing order, the apparent activation energies were Shigetai 〉Jianxin 〉 Ningtiaota, indicating that, from 50 to 120 ℃, the Ningtiaota coal sample most easily absorbed and reacted with oxygen while the most resistant was the Shigetai coal sample. Free radical concentrations and line heights increased with increased temperature, and the line width and Lande factor showed irregular fluctuations. Functional group variations were different among these coals, and the phenol and alcohol-associated OHs, carboxyls, and aromatic ring double bonds might have had a major impact on free radical concentrations. These results were meaningful for better consideration and management of coal oxidation at low temperatures.展开更多
文摘增强激光诱导等离子体的发射光谱强度,对于精确测量微弱光谱信号,改进待测材料中低含量元素的探测灵敏度意义重要。首先对金属样品加热升温,并且在一定温度时利用波长为1 064 nm的Nd:YAG纳秒脉冲激光烧蚀样品,激发产生等离子体,测量了不同样品温度条件下等离子体的发射光谱强度和信噪比。结果表明,采用的激光能量为200 m J时,随着样品温度的升高,等离子体辐射会逐渐增强,并且在温度为150℃时达到最大。计算表明,样品中分析元素Mo、Cr、Ni和Mn在温度为150℃时的光谱线强度比室温条件下的分别提高了54.56%,72.43%,70.29%和54.01%,光谱信噪比分别增大了37.44%,40.74%,38.6%和37.06%。实验还通过观察等离子体的照片,测量等离子体的温度、电子密度和样品蒸发量,讨论了激光诱导金属等离子体辐射增强的原因。可见,升高样品温度是改善激光等离子体光谱质量的一种有效手段。
基金supported by the Key Projects of the National Natural Science Foundation of China (Nos. 51504187, 51774233, and 51704226)Shaanxi Province Industrial Science and Technology Research Project (No. 2016GY-192)the China Postdoctoral Science Foundation (No. 2016-M-590963)
文摘Correlations among free radicals, apparent activation energy, and functional groups during lowtemperature oxidation of Jurassic coal in Northern Shaanxi were investigated by examining three coal samples collected from the Ningtiaota, Jianxin, and Shigetai coal mines. Free radical concentrations at less than 120 ℃ were investigated by electron spin resonance experiments while the thermogravimetric experiments were conducted to analyze apparent activation energies. In addition, Fourier transform infrared spectroscopy was employed to study the spectrum of functional groups generated in coal. The results indicated that, in decreasing order, the apparent activation energies were Shigetai 〉Jianxin 〉 Ningtiaota, indicating that, from 50 to 120 ℃, the Ningtiaota coal sample most easily absorbed and reacted with oxygen while the most resistant was the Shigetai coal sample. Free radical concentrations and line heights increased with increased temperature, and the line width and Lande factor showed irregular fluctuations. Functional group variations were different among these coals, and the phenol and alcohol-associated OHs, carboxyls, and aromatic ring double bonds might have had a major impact on free radical concentrations. These results were meaningful for better consideration and management of coal oxidation at low temperatures.
