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A systematic insight into the role of SiO2 as a protective layer in realizing uniform Li-ion deposition is proposed.

Dynamic hazard and coal spontaneous combustion are major potential safety hazards in coal mines with enriched gas and spontaneously inflammable property. However, the initial oxidizability of coal samples after dynamic hazard has yet to be understood. A simplified device for dynamic hazard simulation of coal-and-gas outburst was established. The physical and chemical changes of coal surface, and their effects on initial oxidation were analyzed. Firstly, loose coal was pressurized by gas step-by-step, and the CO content was enhanced with increase in gas pressure. Meanwhile, the specific surface area provides a hotbed for low-temperature oxidation of radicals and functional groups of coal. Finally, the mechanism of mechanical force on the increase of radical and active groups with the homolysis of covalent bond was discussed. The initial oxidizability of coal after dynamic damage was characterized by oxygen absorption. The physicochemical characteristics suitable for coal oxidation, were formed under the mechano–chemical effect. The findings presented in here add to our understanding of the influence of dynamic hazard on coal oxidation.

The spontaneous combustion disaster caused by low-temperature oxidation of coal often leads to mine fire which poses a serious threat to the safe mining of underground coal resources. Due to the co...

Safety and environmental problems caused by coal mining and utilization are becoming increasingly severe. The air leakage and uneven oxygen distribution in goaf seriously affect coal’s natural oxidation. Therefore, an in-depth understanding of the changes of free radicals and functional groups in coal under different oxygen concentrations during low-temperature oxidation is essential for dynamically preventing and controlling the spontaneous combustion of residual coal in goaf, which is of great significance for mine safety and environmental protection. Based on Electron spin resonance (ESR) and Fourier transform infrared (FTIR) spectroscopy, an analysis was made on the influence of different oxygen concentrations on the reaction activity of micro-groups during low-temperature coal oxidation. The results show that with increasing oxidation temperature in a range of 30℃–230℃, the concentration of free radicals Ng improves. When the oxygen concentration exceeds 9 %, the production of free radicals Ng significantly accelerates. The content of −CH2 and −CH3 and −OH, major reaction groups in coal oxidation, declined to various degrees with the gradual increase of temperature. The reaction rate of C O and −COOH was positive in the whole heating range (30℃–230℃), indicating that C O and −COOH are the products. During the entire oxidation heating process, when the oxygen concentration reaches 3% and 21 %, the C O content increases by 38.65 % and 59.71 %, respectively, and the −COOH content increases by 32.74 % and 51.96 %. At low oxygen concentrations (O2≤9 %), the range of each active group’s change is relatively small, which implies that low-oxygen conditions can inhabit the coal-oxygen reaction. At high oxygen concentrations (O2 > 9 %), active groups are more likely to react. The rise of temperature ushers in a rapid oxidation stage of coal. Besides, it is necessary to strengthen the fire extinguishing and cooling efforts in goaf deep low-oxygen area.

A single physical or chemical inhibitor can hardly meet the uttermost requirements for coal spontaneous combustion prevention. Therefore, it has become essential to develop an efficient inhibitor w...

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 combustion-prone coal seams.

Outburst prevention and control measures such as protective seam mining and coal seam gas pre-drainage can cause low-temperature oxidation of coal seam, and there is a lack of research on the changes in coal quality characteristics and outburst comprehensive index during low-temperature oxidation. In this paper, the changes of coal quality characteristic indexes during oxidation of coals with different metamorphic degrees, the initial gas emission velocity and the firmness coefficient were measured, the influence of coal quality characteristics on outburst comprehensive index is studied, and the change of outburst comprehensive index K = Δ p f in the low-temperature oxidation process was analyzed. The results show that for coal with different metamorphic degrees, the coal with a lower metamorphic degree enters the stage of inherent moisture evaporation later and is more likely to undergo decomposition and volatilization of volatile matters. In the midterm of low-temperature oxidation (120–160 °C), the growth rates of △p values and the decline rates of f values of coal samples with higher metamorphic degrees tend to decrease. It can be known that the K value of bituminous coal and anthracite are more than 25 during the whole oxidation heating stage, which shows a serious outburst risk. For these coals, effective outburst prevention measures must be taken to prevent outburst risk and inhibit coal spontaneous combustion. In contrast, for lignite coal, the growth rate of △p value and the decline rate of f value keep increasing in the midterm of low-temperature oxidation, due to the joint action of moisture evaporation and volatile decomposition and volatilization. The K value of Lignite is more than 15 when oxidation temperature rises to 150 °C, which shows a general outburst danger. According to the analysis results in the midterm, appropriate measures must be taken to inhibit coal oxidation when local or overall temperature of coal seam reaches 130 °C.

Variations of gas products and reaction characteristics of main functional groups during low-temperature oxidation of coals with different metamorphic degrees were analyzed based on the gas chromatographic analysis of gas products and the FTIR determination of oxidized coal samples. Meanwhile, changes in the microcrystalline structure parameters during the low-temperature oxidation were determined with the aid of the XRD technology. Since gas product contents of coal with different metamorphic degrees grow continuously with the rise of oxidation temperature, a forecast system that adopted CO and C2H4 as indicator gases in the low-temperature oxidation process was established. The content of CH3/ CH2 , the primary participant in the oxidation reaction, gradually falls with the rise of oxidation temperature. During the low-temperature oxidation of coal, the stacking height Lc, ductility La, stacking layer N and graphitization degree P of aromatic layers all increase with the rise of oxidation temperature. Finally, the critical temperature ranges (80–110 °C for RL coal, 110–140 °C for YL coal and 130–170 °C for WY coal) for drastic changes during low-temperature oxidation were proposed by comparatively analyzing the variation laws of gas products, main reaction functional groups and aromatic layers, as well as the corresponding temperature variations.

The gas and coal spontaneous combustion coexisting disasters have become a common mode of major and extraordinarily serious accident of coal mine, so it has important significance to predict the coexistence disaster for prevention and treatment. This study took the gas samples from gas drainage pipeline in the goaf of 1203 working face of Hongyang No. 2 Coal Mine, and then analyzed the chaotic characteristics of coal gas indexes from gas drainage pipeline by using the R/S analysis method. The results show that the Hurst index of time series of gas indicators related to coal spontaneous combustion shows stable statistical characteristics when the oxygen concentration fluctuates smoothly. However, when the oxidation of coal in goaf accelerates, the Hurst index will be smaller than 0.77025. The Hurst index of time series of gas indicators related to gas in the goaf of 1203 working face is greater than 0.5, which indicates that gas has persistent correlation. The Hurst index can quantitatively reflect the inherent tendency characteristics and persistent intensity of the gas concentration variation process. The Hurst index of time series of gas indicators related to coal spontaneous combustion at the monitoring point can be used to judge the time tendency of coal spontaneous combustion in goaf and further judge the spontaneous combustion state of coal. Therefore, methods for judging whether the coal in goaf is in the dangerous stage of spontaneous combustion and for determining the change trend of gas concentration in the goaf were proposed. On this basis, the coexisting disaster were forecasted, moreover, this kind of prediction method can reduce the misinformation of the coexisting disaster. The study provides a meaningful new idea and method for improving the theory of coexisting disaster prediction.

Gas injection displacement technology not only helps to increase gas production, but also serves to store greenhouse gases by reducing CO2 emissions. However, coal seam dynamic disasters caused by gas (CO2) injection displacement are rarely reported. In order to explore the change in coal seam outburst risk after gas injection, the indexes (ΔP) of initial velocity of gas diffusion and the isothermal adsorption curves of coal with different metamorphic degrees were experimentally measured under different concentration ratios of CO2/CH4 mixed gas, and the experimental process of gas injection displacement and the change in pore structure were also investigated. The experiment results indicate that the ΔP of CO2 is nearly three times of that of CH4. Therefore, the accuracy of safety situation judgment of a coal seam would be reduced if outburst risk of the coal seam is only assessed through the ΔP in the pure CH4 environment. The results of isothermal adsorption experiment show that the gas adsorption capacity of three kinds of coal increases with the rise of the CO2 concentration in the mixed gas. The results of gas injection displacement experiment reveal that CO2 plays a significant role in replacing CH4, but a large amount of CO2 has been adsorbed into the coal seam before CH4 can be completely desorbed, which in turn raises outburst risk of the coal seam. After the displacement, the internal pore structures of the three kinds of coal samples become tinier and tinier. Finally, a new comprehensive index K ′ = α B E T × Δ P / f was established to assess the risk of dynamic disasters in a coal seam. Compared with the single index ΔP, the new comprehensive index K ′ can more accurately grasp the possibility of outburst danger in a coal seam subjected to gas injection displacement.

This research aims to explore the influence mechanism of coal oxidation on the outburst risk of coal seams after a magmatic rock invasion. Hence, the possibility of an outburst risk in coal seams caused by coal oxidation under different oxygen concentrations was evaluated by utilizing multiple indices to predict the outburst risk of coal and gas. By applying the BEL-MAX automatic analyzer for specific surface area (SSA), the change laws of the Brunauer–Emmett–Teller (BET) SSA and pore volume during coal oxidation were analyzed. Moreover, the change in multiple physical parameters during coal oxidation was measured by employing an industrial measurement instrument, gas chromatograph, initial velocity (△P) tester, and hardness tester. The results indicate that with the increasing oxidizing temperature of coal, the contents of moisture and volatiles in the coal declined constantly while the BET SSA and pore volume increased, thus strengthening the capability of coal mass for adsorbing gas. Moreover, the coal strength reduced with the constant development of pores, as shown by the Protodyakonov’s coefficient (f value) of coal mass that decreased constantly and △P of gas diffusion for reflecting the diffusion capability of coal for the gas to increase gradually with increasing oxidizing temperature. With the increasing oxygen concentration in an oxidizing atmosphere, the required oxidizing temperature at which the comprehensive index reflecting the outburst risk of coal mass was larger than the critical value reduced gradually. Thus, the coupling effect of magmatic rock invasion into coal mass, thermal metamorphism, and oxidation reaction led to the increase in gas content and SSA of coal mass, thus improving the capability of coal for adsorbing and storing gas. Correspondingly, the mechanical strength of coal mass reduced and the initial velocity of gas diffusion from coal mass increased significantly. Additionally, owing to the sealing effect of magmatic rock inhibiting the migration of gas in coal mass in the area, the risk level of coal and gas dynamic disasters in the area increased significantly.

To analyze the low-temperature oxidation of coal in an air flow containing coalbed methane (CBM), the low-temperature oxidation of coal under different CH4 concentrations was analyzed based on the oxidation reaction of free radicals and functional groups. Based on the experimental platform for simulating the low-temperature oxidation of coal in different atmospheres, the experimental process was carried out by using the electron spin resonance (ESR) and Fourier transform infrared (FTIR) technologies. Furthermore, the influences of CH4 on the activity of coal during low-temperature oxidation and the oxidation reaction of functional groups on the surface of coal were explored. The results showed that, at different oxidization temperatures from 20 °C to 200 °C, the concentration of free radicals decreased with increasing CH4 concentration (0%–45%), and CH4 inhibited the oxidation activity of coal. Under the condition that the CH4 concentration was lower than 30%, CH4 showed a large inhibitory effect on the oxidation activity of coal. After the oxidization temperature was higher than 80 °C, the promotion effect of the oxidization temperature on the oxidation activity of coal was significant. Moreover, –CH2 and –CH3 exhibited high activities during low-temperature oxidation and were the major reactive groups. When the coal was oxidized in dry air, the contents of –CH2 and –CH3 constantly decreased at temperatures of 40 °C–110 °C until the CH4 concentration was higher than 25%. This finding implied that CH4 inhibited the consumptions of –CH2 and –CH3 in the oxidation process of coal. The –OH content generally decreased at first and then increased, showing high activity during low-temperature oxidation, and was considered the major reactive group. With increasing CH4 concentration in the oxidation atmosphere, the reduction amplitude of –OH decreased, indicating that CH4 can inhibit the consumption of –OH in the oxidation process. When the CH4 concentration was higher than 35%, CH4 influenced both the consumption and production processes of –OH, such that the consumption rate of –OH was gradually equal to its production rate. The content of –C–O increased overall, which implied that –C–O was the main product of low-temperature oxidation. As a relatively stable group, the –C–O group was not produced below a certain temperature in the oxidation process. Additionally, the unchanged stage disappeared when the CH4 concentration was higher than 25%, which indicated that CH4 promoted the production process of the –C–O functional group. –COOH showed high activity during low-temperature oxidation, and its content rapidly decreased at first and then increased quickly during coal oxidation in dry air, indicating that it was the main reactive group during low-temperature oxidation. With increasing CH4 concentration in the oxidation atmosphere, the reduction in the –COOH content gradually decreased, and then the –COOH content remained unchanged after the CH4 concentration was higher than 25%. This result indicated that CH4 inhibited the consumption of –COOH in the oxidation process.

Real-time semantic segmentation plays an important role in intelligent industrial scenarios like autonomous driving, and the core challenge is to consider both performance and efficiency. In this paper, we present a quick network called QNet to address this problem. The overall design of the proposed network is an asymmetric encoder-decoder architecture. The encoder is based on a new Bottleneck architecture that combines channel split and channel shuffle, which reduces network parameters while improving the level of extracting features. An improved spatial pyramid multi-feature fusion module is adopted to the decoder, which can enlarge the receptive field and make up for the loss of spatial information, with only a small computational complexity. Experiments on Camvid and Cityscapes datasets show that without using any pre-trained model, the proposed QNet achieves a state-of-the-art trade-off between performance and efficiency, better than other methods. Specifically, in a single GTX 1080Ti GPU, it can run at over 38 FPS on the Camvid test dataset with 51.8% mean IoU, and 37 FPS with 75.28% category IoU on the Cityscapes test dataset.

As coal reservoirs containing high methane content are more prone to spontaneous combustion, disasters caused by the combined effects of methane and coal spontaneous combustion have been in...

To explore the reaction mechanism of spontaneous coal combustion and the indicators for forecasting this risk, reaction characteristics of free radicals and functional groups during low-temperature oxidation of coal with different ranks were analyzed by electron spin resonance (ESR) and Fourier transform infrared (FTIR) spectroscopy. Combined with gas chromatography of CO, other indicators besides the main indicator gas CO were researched to forecast spontaneous coal combustion. The results showed that with increasing oxidizing temperature in the range of 30 °C–230 °C, the production of free radicals changed from slow to rapid after being oxidized and heated above characteristic temperatures, depending on the coal grade. The oxygen-containing functional groups in coal of all ranks mainly include OH, C O, C O and COOH, whose reaction trends varied widely. The concentration and production rate of free radicals and the C O functional group in coal can be regarded as the leading indicators.

To achieve multiple and highly effective inhibition of coal spontaneous combustion, a novel composite inhibitor was developed by mixing a superabsorbent polymer (SAP) hydrogel with a synergistic antioxidant. Temperature-programmed oxidation, differential scanning calorimetry, and electron spin resonance were used to examine the inhibitor-treated coal samples to investigate the slowing effect of the composite inhibitor by comparing the inhibitions of the SAP hydrogel, synergistic antioxidant, and composite inhibitor on coal oxidation. The SAP hydrogel physically suppresses coal oxidation during the low-temperature phase, while the synergistic antioxidant chemically inhibits the oxidation during the high-temperature stage. Nevertheless, the composite inhibitor provides stable physicochemical inhibition for coal oxidation throughout the oxidation process by the synergistic effect of physical and chemical inhibition; the composite inhibitor provides a better overall effect for suppressing coal spontaneous combustion by combining the inhibiting characteristics of the SAP hydrogel and synergistic antioxidant. This study combines physical and chemical inhibitions of coal oxidation and provides a new method to efficiently prevent coal spontaneous combustion.

This research is aimed at studying the different effects and mechanisms of CO2 and N2 on inhibiting coal spontaneous combustion (CSC) and providing theoretical guidance for the prevention and control of CSC in the goaf. The variations of free radicals and functional groups and the generation of indicator gas CO during low-temperature oxidation of coal under the conditions of dry air (DA), dry air-nitrogen mixture (DA + N2) and dry air-carbon dioxide mixture (DA + CO2) were investigated based on electron spin resonance spectrometer, Fourier transform infrared spectroscopy and gas chromatograph. The experimental results reveal that the reaction of free radicals and the transformation of functional groups occur in the low-temperature oxidation process. In the whole oxidation heating process (30–230 °C), the concentrations of free radicals (Ng) increase by 4.04 × 1017 spin/g, 2.24 × 1017 spin/g and 1.90 × 1017 spin/g under the conditions of DA, DA + N2 and DA + CO2, respectively. The variation ranges of peak areas of active functional groups (–C-O–, –C O, –CH2–, –CH3 and –OH) under the action of inert gases (CO2 and N2) are notably smaller than those in the DA environment. The time and amount of CO generation both exhibit an obvious “hysteresis effect”, indicating that the presence of N2 and CO2 inhibits coal oxidation and conduces to CSC prevention. A comparison between the values of inhibition effect parameters R (RCO, RNg, R-C-O- and R-C O) and P (P-CH2-, –CH3, P-OH) discloses that CO2 boasts a superior ability to inhibit CSC than N2. This study presents a comparison between N2 and CO2 in CSC prevention and control based on the variation characteristics of indicator gas and active groups. It provides an experimental and theoretical basis for developing and improving the technology of fire prevention and extinguishing by inert gases.

To explore the reaction mechanism of the low-temperature oxidation of coal and the law of active groups producing CO through oxygenolysis, this article analyzed the reaction characteristics of free...

To explore the mechanism of low-temperature oxidation of residual coal at different depths in goaf, the oxygen concentration of airflow was dynamically adjusted to simulate the natural oxidation of coal at different depths in goaf with the aid of a self-built simulation experiment system of low-temperature coal oxidation. Based on electron spin resonance (ESR), analyses were made on the variation of free radicals during coal oxidation at low temperatures in different concentrations (volume fraction) of O2. Besides, an industrial analyzer and a gas chromatograph were also applied to the determination of the change of volatile matter and the emission of gaseous products. The results show that line height, the free radical concentration, volatile matter, and CO concentration change in stages with the increase of oxidation temperature. At about 130 °C, they shift from slow-varying to rapid-changing, reflecting that the coal steps out of a slow oxidation stage and enters a rapid one. The variation trend of line height and free radical concentration is basically the same, and g values are always in the range of 2.00141–2.002034, with little change. As O2 concentration rises, the tendency of each parameter with the oxidation temperature remains unchanged, but the overall variation gradually increases. When O2 concentration is lower than or equal to 9%, free radicals undergo reaction at a low speed and CO generation delays in the low-temperature stage. When it is higher than 9%, there is a growing possibility of coal-oxygen reaction. The increase in temperature improves the excitation of free radical reaction, so that CO concentration rises exponentially. Since different O2 concentrations have varying effects on coal oxidation, it is of great importance to adopt prediction and prevention technology in different-depth areas of goaf to ensure the safe mining of coal seam.

To explore the optimum oxidation temperature of coalbed for promoting methane desorption, this paper carried out the experiments based on the self-built coal oxidation heating system in different gaseous environments and the high-temperature and high-pressure gas adsorption instrument. Besides, the effect of methane on free radicals and surface functional groups at the optimum oxidation temperature was studied by using electron spin resonance (ESR) spectrum and Fourier transform infrared spectroscopy (FTIR). The results show that the residual methane is the lowest at the oxidation temperature of 80 °C, indicating that 80 °C is the optimum oxidation temperature for CBM extraction. At 80 °C, the inhibitory effect of methane on the reactivity of coal is stronger and the reactivity can also increase. At low concentration (

Anticorrosive coatings prepared by sol-gel derived approaches have become an emergent research area in the field of corrosion prevention materials. Furthermore, enhanced coating thickness can greatly improve the barrier effect of the sol-gel coatings, thus influencing their service life in industrial applications. Here, we propose the preparation of a two-layer coating system using a low-cost sol-gel derived method. The coating structure was composed of first an underlying layer incorporated with silica and titania powder as filler and pigment materials, and a second translucent topcoat containing a colloidal silica sol-gel matrix crosslinked by methyltrimethoxysilane (MTMS). This coating system was applied on Q235 carbon steel substrate by a two-step spray deposition method, resulting in an enhanced coating thickness of around 35 &mu, m. The physical and morphological properties of the coatings were characterized using multiple techniques, including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). The anticorrosion performance of the sol-gel coatings was studied by a salt spray test, outdoor exposure test and electrochemical impedance spectroscopy (EIS). Results revealed that this two-layer coating system exhibited excellent physical and anticorrosion properties, and that the topcoat played a crucial role in maintaining the barrier effect and preventing water leakage.

The hydrogen production from an easily transported liquid feedstock can be an efficient alternative for fuel cells application. The steam-oxidative reforming of bio-ethanol by a novel gliding arc discharge named Laval nozzle arc discharge (LNAD) was investigated in this paper at low temperature and atmospheric pressure. The conversion efficiency and product distributions, mainly of H2 and CO, were studied as functions of O/C ratio, S/C ratio, the ethanol flow rate and input power. The voltage–ampere (V–I) characteristic is also discussed here concerning the non-thermal plasma effect on the bio-ethanol reforming. A high conversion rate and fair H2 yield have been achieved, 90% and 40% respectively. When the ethanol flow rate (Gethanol) was 0.15 g s−1 and S/C = 2.0, the minimum specific energy requirement of H2 and CO were achieved at O/C = 1.4 with the specific energy input of 55.44 kJ per ethanol mole, 72.92 kJ mol−1 and 80.20 kJ mol−1 respectively. The optimal conditions for ethanol reforming seem to be S/C = 2.0 and O/C = 1.4–1.6, which are higher than those of the reaction's stoichiometry. This paper shows interesting results in comparison with the ethanol reforming assisted by other discharges. Compared with others, it features good conversion rate, low energy consumption and significantly reduced nitrogen oxide emission.