Restraining effect of nitrogen on coal oxidation in different stages:Non-isothermal TG-DSC and EPR research

Nitrogen is widely used to prevent the spontaneous combustion of coal in underground coal mines. A spontaneous combustion-prone coal seam was studied to investigate the restraining effect of nitrogen on coal oxidation in different oxidation stages, based on non-isothermal thermogravimetry-differential scanning calorimetry(TG-DSC) and electron paramagnetic resonance(EPR) experiments. We found that the key feature temperatures grow steadily with increasing nitrogen in the oxidation environment,resulting in longer oxidation stages. The most significant finding is that there is a stagnation of the inhibitory effect of nitrogen on coal oxidation in the range of 85.0–95.0% nitrogen in the slow and the rapid oxidation stages, owing to the competitive adsorption of coal by nitrogen and oxygen. However, the restraining effect cannot be reflected by the kinetic parameters of the coal before it reaches the thermal decomposition and combustion stage. Nitrogen can also affect free radical types and free radical concentrations during coal oxidation: the higher the concentration of nitrogen in the oxidation environment, the greater the number of free radical types and the lower the free radical concentration. This experimental study improves the understanding of the restraining effect of nitrogen on coal oxidation in different oxidation stages and provides an important reference for coal fire prevention in spontaneous combustionprone coal seams.

Spontaneous combustion influenced by surface methane drainage and its prediction by rescaled range analysis

This study established numerical modeling using COMSOLTMto examine the influence of horizontal location and drainage ability of surface borehole on spontaneous combustion in longwall working face gob. Rescaled Range Analysis(R/S analysis) was employed to investigate the chaos characteristic of N_2/O_2 ratio from a surface borehole in 10416 working face gob, Yangliu Colliery, China. The simulation results show that there is always a circular ‘‘dissipation zone" around the drainage borehole and an elliptic ‘‘spontaneous combustion zone" in deep gob. Little influence was found on spontaneous combustion zone on the intake side of the gob but the width of spontaneous combustion zone in middle gob is enlarged, while the depth of spontaneous combustion zone near the return side is reduced. The R/S analysis indicates that the influence of surface borehole on spontaneous combustion can be divided into two stages by the chaos feature of N_2/O_2: safety drainage stage and spontaneous combustion initiating stage. It can be concluded that the methane drainage from gob through surface borehole can intervene in the distribution of spontaneous combustion zone in gob and the chaos feature of N_2/O_2 from surface borehole can effectively reflect coal spontaneous combustion condition in gob.

Advances in flexible lithium metal batteries

Flexible energy storage devices are becoming indispensable new elements of wearable electronics to improve our living qualities.As the main energy storage devices,lithium-ion batteries(LIBs)are gradually approaching their theoretical limit in terms of energy density.In recent years,lithium metal batteries(LMBs)with metallic Li as the anode are revived due to the extremely high energy density,and are considered to be one of the ideal alternatives for the next generation of flexible power supply.In this review,key technologies and scientific problems to be overcome for flexible LMBs are discussed.Then,the recent advances in flexible LMBs,including the design of flexible Li metal anodes,electrolytes,cathodes and interlayers,are summarized.In addition,we have summed up the research progress of flexible device configurations,and emphasized the importance of flexibility evaluation and functionality integration to ensure the wearing safety in complex environment.Finally,the challenges and future development of flexible LMBs are summarized and prospected.

A review on hydrogen production from ammonia borane:Experimental and theoretical studies

Ammonia borane(NHsBH3,AB)is an ideal raw material of hydrogen production with higher hydrogen storage capacity.In this paper,the catalytic processes of AB dehydrogenation were described from different ways,including thermal dehydrogenation,hydrolysis,methanolysis,photocatalysis and photopiezoelectric synergy catalysis with experimental research and theoretical calculations.Catalyst models include bulk materials,two-dimensional materials,nanocluster particles and single/diatomic structures.Among them,the proportion of H2 released is different,and the reaction conditions are also different,which are suitable for different application scenarios.Through this review,we could have a preliminary comprehensive understanding of AB dehydrogenation reaction.