To explore the role and reaction mechanism of the natural slow oxidation process in coal spontaneous combustion at critical temperature, this paper simulates the oxidation process of coal in the range of critical temperature from the perspective of isothermal conditions and analyzes the variation law of spontaneous combustion characteristic parameters. It is found that the slow oxidation process at low temperatures plays a key role in the process of coal spontaneous combustion, which promotes the oxidation heat release in the heating process and reduces the reaction energy barrier. The spontaneous combustion characteristics of two kinds of low-rank coal (PZ and LJH) changed abruptly after oxidation at 70 degrees C and 80 degrees C, respectively. A comparative analysis of the variations in reactive oxygen-containing functional groups and their kinetic correlations during isothermal oxidation of two low-rank coal types reveals that hydroxyl (-OH) groups exert a predominant influence on the initial stages of coal spontaneous combustion mechanisms prior to reaching the critical ignition temperature. Beyond the critical temperature, the aliphatic hydrocarbon moieties within the coal matrix predominantly govern the coal-oxygen chain reactions. This finding establishes a theoretical foundation and research framework for elucidating the mechanistic pathways of coal spontaneous combustion and developing effective inertization strategies.

Deep-mine residual coal often undergoes pre-oxidation, thermal disturbance, and tensile damage, altering its pore structure, oxygen transport, and oxidation reactivity. To elucidate the evolution mechanism under thermal-tensile stress coupling, pre-oxidized coking coal samples were studied using thermal analysis, pore characterization, oxygen transport simulation, FTIR, and ESR. Results show that the coupled effect reconstructs the pore-fracture network, enlarging oxygen pathways. As pore size increases from 0.5 to 5 nm, the O2 diffusion coefficient rises from 3.97 to 9.85 Å2/ps, indicating enhanced oxygen transport. The thermal-tensile coupling exerts stage-dependent regulation: the maximum endothermic temperature (TD1) is delayed by 8.97–14.91 °C, enhancing low-temperature physical endothermy; the initial exothermic temperature (TD2) drops by 2.89–9.95 °C; the ignition temperature (TD3) shifts lower; total heat release increases by 9.88–17.15%, intensifying medium-to-high temperature oxidation FTIR and ESR reveal that aliphatic side-chain cleavage, carbonyl/carboxyl formation, and free-radical accumulation promote radical-chain oxidation upon reheating. CRITIC analysis indicates that dominant risk factors shift sequentially from oxygen-containing functional group activation and initial radical generation (before TD1) to aliphatic decomposition, radical accumulation, and enhanced heat release (after TD2). This study reveals a stage-dependent transition from low-temperature inhibition to medium-/high-temperature oxidation promotion in pre-oxidized coal under thermal-tensile stress coupling, offering theoretical support for controlling thermal instability in disturbed deep-mine residual coal.

In deep mining, high temperature and humidity affect coal properties and spontaneous combustion. A closed oxygen consumption experiment was conducted on coal from Hongyang No. 2 mine. GCMC and MD techniques analyzed O2 adsorption/desorption dynamics under varying water injection and temperature conditions. Results indicate that with rising temperature and decreasing water content, oxygen uptake, CO generation, and coal's oxidative heat emission intensity increase exponentially. Molecular simulation shows H2O displaces oxygen by occupying adsorption sites. Water injection promotes oxygen release from coal, with more infusion volume leading to greater promotion. In high-temperature or high-water-content systems, the root-mean-square displacement and diffusion coefficient of O2 are higher than in low-temperature or low-water-content systems. Increased water injection raises the average directional change and diffusion coefficient of O2, enhancing its activity. Rising temperature and reduced water content effectively promote O2 desorption, indicating a stronger coal spontaneous combustion tendency under hygrothermal effects. This study, to explore the reasons for the disparity in the likelihood of spontaneous combustion between raw coal and wet thermal effect from macro and micro perspectives by combining experiment and simulation. The findings of the study can offer a theoretical foundation for the fire prevention technology in goaf.

The abandoned coal in goaf will adsorb the gases ethylene (C2H4) and acetylene (C2H2) produced by coal oxidation, which makes the concentration data of the indicator gas inaccurate. Therefore, the adsorption law of coal and C2H4 and C2H2 gas is explored. The macromolecular structure model of coal was established and optimized by simulation, and the gas adsorption process was simulated by means of grand canonical Monte Carlo method. The adsorption quantities and adsorption sites of single component and binary component gases C2H4 and C2H2 in coal under different temperatures and pressures were analyzed. The results show that the molecular formula of S7 and W12 coal samples is C136H92O30N2S and C129H87O28N2S, respectively. When C2H4 and C2H2 are adsorbed at the same temperature, the adsorption pressure is positively correlated with the adsorption capacity, and the adsorption capacity increases rapidly with the increase of pressure, and then tends to be flat. With the same pressure, the adsorption capacity of C2H4 and C2H2 is unfavorable with the increase of temperature. The adsorption sites of C2H2 are more than those of C2H4. When C2H4 and C2H2 gas are used as indicator gases alone, they will be adsorbed by the left coal in the goaf, which makes the on-site monitoring gas concentration data inaccurate, resulting in the delay of the early warning time to a certain extent.

To study the effect of microwave thermal radiation on coal structure and features of spontaneous combustion, lean coal (SM) from Shenyang Hongyang No. 2 Mine and anthracite (WYM) from Ordos were used. The experiments involved low-temperature nitrogen adsorption, thermal analysis, Fourier transform infrared (FTIR) testing, and closed oxygen consumption. Results showed that microwave radiation altered the coal's porous architecture, enhancing surface area per unit mass, porosity volume, and peak adsorption capacity. Higher radiation power led to earlier characteristic point temperatures and increased active groups. The rates of oxygen consumption, CO production, and oxidation intensity all exhibited exponential growth. Under 20.9% oxygen and 200–800W radiation, SM and WYM's oxidative heat release intensity was 1.44–3.73 and 1.15–4.13 times higher than raw coal, respectively. This increased spontaneous combustion tendency offers a theoretical foundation for coal fire prevention in mining and gas extraction. Theoretical guidance is offered regarding coal combustion control. This is particularly relevant to post-microwave radiation conditions within mining environments.

The increase of coal seam mining depth leads to the increase of ground temperature stress, which affects the fracture development and spontaneous combustion characteristics of coal samples. Taking anthracite as the research object, scanning electron microscopy, low-temperature N2 adsorption, temperature- programmed experiments and infrared spectroscopy tests were carried out to analyze the mechanism of the influence of pore structure and the number of oxygen-containing functional groups on the spontaneous combustion characteristics of coal samples from the physical and chemical perspectives. The results show that the connection between pores and fractures is enhanced and the scale of micro-fractures is also increased after the thermal and mechanical coupling. After treatment, the oxidation of the coal sample was enhanced, and the overall production rate of the three iconic gases increased. The thermal and mechanical coupling results in the increase of the content of aromatic hydrocarbon, oxygen-containing functional group and aliphatic hydrocarbon in coal. The thermal and mechanical coupling effects promote the occurrence and development of coal spontaneous combustion by changing the structure, temperature and stress state of coal and affecting the reaction process of coal and oxygen. The research results have laid a theoretical foundation for the prevention and control of multi-field coupling CSC.

To study the spontaneous combustion characteristics of preheated coal treated by liquid nitrogen (LN2), surface structure test, thermal analysis experiment and chemical characteristic analysis experiment were used to study the change characteristics of surface structure, oxidation characteristic and chemical structure of coal under the action of LN2 quenching. The results showed that with the increase of preheating temperature, the fractal dimension, specific surface area, pore volume and average pore diameter of the LN2 treated coal (quenched-coal) increase. With the increase of preheating temperature, under the oxidation condition, the CO and CO2 produced at ST of 230 ℃ are 1.19 times and 1.21 times higher than those at ST of 70 ℃. The CO/CO2 emission of quenched-coal is significantly increased, and the secondary oxidation capacity is stronger. Due to the more developed pore cracks of coal under pyrolysis and quenching conditions, the natural characteristics of coal are stronger. The oxygen adsorption capacity and apparent activation energy of pyrolysis coal in the stageⅠ affected by LN2 are stronger. Oxidized coal shows stronger oxidation and heat release ability in the stageⅡ under the action of LN2, resulting in higher apparent activation energy in this endothermic stage. The addition of LN2 blocked the oxidation reaction of preheated coal and sealed the structure of -C = O, –COOH and –OH. The bridge bond –CH2- structure of pyrolysis coal is further destroyed, and the ratio of –CH2/–CH3 is reduced. The increase of alkyl free radicals in pyrolysis coal and alkyl oxygen free radicals in oxidation coal accelerates the spontaneous combustion oxidation of coal. The research results have important guiding significance for the occurrence and prevention of coal reignition disaster after LN2 fire quenching.

To investigate the impact of stratified mining on the spontaneous combustion characteristics of lower coal in thick coal seams, an analysis was conducted on the macro pore structure, temperature rise, oxygen consumption characteristics, chemical structure, surface chemical properties, and functional group distribution of the upper and lower stratified coal samples (LSC, LSR) from the LinSheng Mine 1202 re-mining face. Post re-mining, the specific surface area, average pore diameter for adsorption, micropore volume, and mesopore volume of LSR showed a significant increase compared to LSC. The maximum mass loss rate for LSR was approximately three times that of LSC, and the characteristic temperature of LSR was lower. When the volumetric fraction of oxygen exceeded 12%, the oxygen consumption rate and CO generation rate of LSR surpassed those of LSC. The alkyl carbon content in LSR was 2% lower compared to LSC, while the oxygenated carbon content was higher by 4.37%. The oxygen content in LSR and the O/C ratio were higher than those in LSC. The structural order of LSR was lower by 11.3%, and the oxygen-containing functional groups were higher by 1.15%. These findings suggest that stratified mining increases the spontaneous combustion risk of lower coal layers. This study underscores the need for careful consideration of mining strategies to mitigate potential risks.

To investigate the desorption behavior of O2 through CO2/N2 injection in the gob of a gassing mine, we focused on the adsorption configuration of coal containing O2–CH4. The mechanism underlying the enhancement of O2 desorption in coal due to CO2/N2 injection was elucidated using the Grand Canonical Ensemble Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. Furthermore, the impact of CH4 on O2 desorption was unveiled by detailed calculations and studies of energy variation, concentration distribution, and diffusion coefficients of oxygen.Our findings indicate the following: (1) CO2 and N2 facilitate the displacement of oxygen primarily by occupying adsorption sites. The CO2–O2 model exhibits a significantly higher concentration of free O2 molecules compared to the N2–O2 model, and the CO2–O2–CH4 model surpasses the N2–O2–CH4 model in free O2 molecules. (2) The total energy of the CO2–O2 model is lower than that of the N2–O2 model, indicating greater stability in the former. Similarly, the total energy of the CO2–O2–CH4 model is lower than that of the N2–O2–CH4 model, highlighting its superior stability. It is concluded that CO2 injection is more effective in promoting oxygen desorption than N2, regardless of the presence of methane. (3) Under equivalent injection pressure, the root mean square displacement of O2 in the CO2–O2 system surpasses that in the N2–O2 system. Furthermore, compared to the N2–O2–CH4 system, the CO2–O2–CH4 system exhibits a larger root mean square displacement of O2, signifying higher O2 molecule activity. The diffusion coefficient of O2 in the CO2–O2 system is higher, underscoring the superior effectiveness of CO2 in promoting O2 desorption.In summary, our research outcomes offer valuable theoretical insights for fire prevention technology in goaf.

Inhibiting coal–oxygen reactions during the heating of coal is an effective means to prevent spontaneous coal combustion. Therefore, it is necessary to investigate the influence of the latent-period slow reaction on the temperature rise of coal oxidation and the microscopic reaction mechanism. Experiments were conducted to simulate the slow oxidation and pyrolysis reactions of coal in the latent period, and characteristic parameters of the spontaneous combustion after the constant-temperature reaction were analyzed. The results showed that the latent period process promotes the oxidation and heat release of coal and reduce the energy barrier of the coal–oxygen reaction. In situ FTIR and EPR experiments were performed to analyze the changes in the active structure. The results indicated that the self-reaction of active groups during pyrolysis at 50 °C and 60 °C is crucial to the oxidation of coal, providing adsorption sites of free radicals centered on a carbon atom for oxygen adsorption. The Pearson correlation analysis showed that the continuous formation and participation of the hydroxyl structure during the oxidation at 70 °C is an important step affecting the coal–oxygen chain reaction, and it is a key group for making the coal–oxygen reaction inert.

To investigate the influence of the collapse column structure on the oxidation characteristics of coal, with the aim of preventing mine fires and ensuring the safety of life and property,low-temperature N2 adsorption, synchronous thermal analysis and enclosed coal oxidation experiments were carried out to analyze the pore structure and macroscopic oxidation characteristics of 3 coal samples (XL1, XL2, XL3) from different affected areas of the collapse column structure in the 1202 working face of Duanwang Mine. 13C-NMR and XPS experiments were conducted to explore the microscopic differences in chemical structure, surface chemical properties, etc. among them. Meanwhile, coal macromolecular models were constructed for ReaxFF pyrolysis simulation. The results show that compared with the original coal XL2, the pores in coal sample XL3 are more developed. The ignition temperatures for XL1, XL2, and XL3 are 510.74 °C, 492.81 °C, and 482.43 °C, respectively. The initial oxygen consumption rate of coal sample XL3 increased by 150% compared to XL2, while that of XL1 decreased by 37.5%. The O/C atomic ratio of XL3 is about 2.0 times that of XL2, and about 2.4 times that of XL1. The A/C ratios (The ratio of aromatic carbon content to alkyl carbon content) of XL1, XL2 and XL3 are 4.866, 3.367 and 3.522, respectively. The molecular formulas for XL1, XL2, and XL3 are C154H80O17N2S2, C156H97O30N2S1, and C156H87O33N2S1, respectively. In the ReaxFF pyrolysis simulation, the occurrence order of indicator gases CO, C2H4, C2H2 is XL3, XL2, XL1, respectively.

To provide a theoretical basis for predicting spontaneous combustion in Linsheng coal mine, the pyrolysis characteristics of coal were investigated from both macroscopic laws and microscopic mechanisms. Programmed-temperature gas chromatography was utilised to test the generation and evolution laws of critical indicator gases (CO, C2H4, C2H2). XPS, 13C NMR and FT-IR were employed to elucidate the microscopic compositional and structural changes of coal samples. ReaxFF simulations revealed the product transformations of coal molecules during pyrolysis. The generation mechanisms of indicator gases were examined by FT-IR analysis. The results showed that the detected temperatures for CO, C2H4 and C2H2 generation from coal were approximately 60 degrees C, 165 degrees C and 308 degrees C. Linsheng coal exhibited a low degree of aromatic condensation with the molecular formula of C148H100O11N2S. During pyrolysis, the content of reactive -OH groups in coal increased, while substituted ar-omatics first increased and then decreased. The carbon content was elevated with a lowered H/C ratio, indicating progressive aromatisation and simplification of the coal structure. Gasification reactions persisted throughout the entire process, leading to continuous cleavage of small molecules to form gases. The formation of indicator gases is closely related to reactive functional groups including ester, ether, alcohol, carbonyl, phenol, alicyclic and substituted aromatics.

To investigate the desorption behavior of O-2 through CO2/N-2 injection in the gob of a gassing mine, we focused on the adsorption configuration of coal containing O-2-CH4. The mechanism underlying the enhancement of O-2 desorption in coal due to CO2/N-2 injection was elucidated using the Grand Canonical Ensemble Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. Furthermore, the impact of CH4 on O-2 desorption was unveiled by detailed calculations and studies of energy variation, concentration distribution, and diffusion coefficients of oxygen.Our findings indicate the following: (1) CO2 and N-2 facilitate the displacement of oxygen primarily by occupying adsorption sites. The CO2-O-2 model exhibits a significantly higher concentration of free O-2 molecules compared to the N-2-O-2 model, and the CO2-O-2-CH4 model surpasses the N-2-O-2-CH4 model in free O-2 molecules. (2) The total energy of the CO2-O-2 model is lower than that of the N-2-O-2 model, indicating greater stability in the former. Similarly, the total energy of the CO2-O-2-CH4 model is lower than that of the N-2-O-2-CH4 model, highlighting its superior stability. It is concluded that CO2 injection is more effective in promoting oxygen desorption than N-2, regardless of the presence of methane. (3) Under equivalent injection pressure, the root mean square displacement of O-2 in the CO2-O-2 system surpasses that in the N-2-O-2 system. Furthermore, compared to the N-2-O-2-CH4 system, the CO2-O-2-CH4 system exhibits a larger root mean square displacement of O-2, signifying higher O-2 molecule activity. The diffusion coefficient of O-2 in the CO2-O-2 system is higher, underscoring the superior effectiveness of CO2 in promoting O-2 desorption.In summary, our research outcomes offer valuable theoretical insights for fire prevention technology in goaf.

In order to explore the influence of fault tectonism on the characteristics of the chemical structure of coal and the characteristics of the microcrystalline structure. The primary coal and fault tectonic coal of the Hongqingliang mine and Duanwang mine were analyzed by Fourier Transform Infrared Spectroscopy FTIR and X-ray diffraction XRD. The following results showed that because of the influence of fault tectonism, the contents of benzene ring disubstituted and benzene ring tetrasubstitution in Hongqingliang and Duanwang fault tectonic of coal were significantly higher than those in primary coal, the contents of benzene ring trisubstitution and benzene ring pentasubstitution were lower than those in primary coal, and the contents of ether bond C-O-C stretching vibration, methylene -CH2 antisymmetric bending vibration, both methyl, methylene and aromatic ring substituted by hydroxyl -CH3 and -CH2 in fault tectonic of coal were higher than those in primary coal. In comparison, the contents of the polar bond of ether vibration, carbon-carbon double bond, methine and phenol of aromatic hydrocarbon in fault tectonic of coal were lower than those in primary coal. The aromaticity f(a) of fault tectonic of coal in Hongqingliang and Duanwang mine was 1.01 and 1.03 times that of primary coal, the aromatic cyclocondensation DOC was 1.01 and 3.7 times that of primary coal, the ratio of CH2 to CH3 was 0.933 and 0.94 times that of primary coal, and the aromaticity I was 1.01 and 1.34 times that of primary coal, respectively. The conclusions showed that fault tectonism influenced promoting the shedding of functional groups and fat chains, increasing the degree of polycondensation of coal, reducing the length of fat side chains in coal and increasing the content of aromatic structure. The XRD test results showed that the primary coal and the fault tectonic coal had similar mineral components, and the fault tectonism did not significantly change the types of mineral components in coal. There was a (002) characteristic band near the diffraction angle 2 theta=26 degrees, which indicated the presence of a small amount of layered graphite structure, while there was no displayed zone, which indicated the basal low growth level of graphite structure in coal. Compared with the primary coal, the value of the variation range of intergranular spacing d(002) of the fault tectonic of coal in Hongqingliang and Duanwang mine was very small. The value of the microcrystalline stacking height L-c was 0.904 5 times and 0.902 7 times of the primary coal respectively, the value of the aromaticity f(a-XRD) was 1.143 9 times and 1.066 9 times of the primary coal respectively, and the value of the average layer Nave of the crystal stacking was 0.909 45 times and 0.923 56 times of the primary coal respectively. Because of the fault tectonism, the stacking degree of aromatic lamellae of coal reduced, the aromaticity of coal increased, and the stacking layers of coal microcrystalline structural units reduced, indicating that the fault tectonism promoted the transformation from non-aromatic compounds to aromatic compounds in coal. The aromaticity and maturity of the fault tectonic coal were higher, but the combustion reactivity of fault tectonic coal was weaker than that of primary coal.

To deeply understand the mechanism of inert gases in inhibiting coal spontaneous combustion, the effects of dry air, CO2, and N2 on coal spontaneous combustion were analyzed experimentally. To this end, bituminous coal prepared from Dongrong No. 2 Coal Mine was considered the research object. Based on the adsorption configuration of the oxygen-containing coal, the displacement behavior of O2 by CO2 /N2 was studied using the grand canonical Monte-Carlo (GCMC) and molecular dynamics (MD) methods. The obtained results show that the injection of CO2 and N2 reduces the ability of spontaneous combustion of coal. It is found that among the studied gases, CO2 has a stronger inhibition effect on coal spontaneous combustion, which increases the temperature of CO occurrence by 5℃, decreases the concentration of CO by 29.91%, and inhibits low-temperature oxidation of coal. From the microscopic point of view, CO2 /N2 gases can effectively displace O2 by diffusion and occupying adsorption sites. It is found that after the injection of CO2, the concentration of O2 molecules increases significantly in the vacuum layer. Compared with N2, injection of CO2 increases the diffusion activation of O2 by 5.89%. This indicates that the injection of an inert gas significantly reduces the oxygen absorption capacity of coal, thereby decreasing the coal-oxygen combination reaction and preventing the spontaneous combustion of coal. The performed analyses demonstrate that CO2 outperforms N2 in restraining the spontaneous combustion of coal.

This study investigated the influence of OH free radicals on the reactivity of aromatic rings and their side chain active groups. Quantum chemistry theory and in situ diffuse reflectance infrared Fourier transform spectroscopy were applied to perform simulations and experiments. Density functional theory was used to calculate the electrophilic substitution of aromatic hydrocarbons of six model structures by OH free radicals. The reactivities of the key elementary reaction of the side chain active group before and after the reaction were compared. The results showed that the reaction energy barriers of the addition and elimination of OH radicals of aromatic hydrocarbons were lower than 40 kJ/mol, indicating that the reactions can occur at room temperature and emit large amounts of heat. The electronic effect of phenolic hydroxyl and benzene rings further improved the reactivity of the aromatic ring C-H. Combining these results with the change rule of the phenolic hydroxyl structure in coal under isothermal oxidation conditions, we conclude that OH radicals participate in the for-mation of the phenolic hydroxyl structure and further catalyze the oxidation reaction of coal at low tempera-tures. This finding is significant for the heat storage stage of low-temperature oxidation in coal.

In order to investigate the influence law of fault tectonic on coal structure and spontaneous combustion characteristics, the fault tectonic coal and primary coal in No. 11301 working face of Hongqingliang coal mine were taken as study samples. The FT-IR experiment of infrared spectrum, thermogravimetric analysis experiment, low temperature nitrogen adsorption experiment and closed coal oxidation experiment were used to analyze the active group content, combustion characteristic temperature, pore structure characteristics, oxygen consumption rate, and oxidation heat release intensity of coal samples from a micro perspective and a macro perspective separately. The results of the FT-IR experiment of infrared spectrum showed that the active groups of the fault tectonic coal were more than those of the native coal, and the oxidation activity of the fault tectonic coal was high. The results of the thermogravimetric analysis experiment showed that the cracking temperature, critical temperature, ignition temperature, peak temperature and combustion temperature of the fault tectonic coal were lower than those of the native coal, and the fault tectonic coal showed a stronger tendency of spontaneous combustion. The results of the low temperature nitrogen adsorption experiment showed that the fault tectonism changed the pore structure of the coal, and compared with the native coal, the specific surface area of the fault tectonic coal increased by 2.5 times, and the average increase of pore size was 2.36 times, the increase of micropore volume and mesopore volume were 2.71 times and 1.69 times respectively. The influence of fault tectonism on the pore structure characteristics of coal was facilitated the oxidation reaction between oxygen and active groups in the pores. The results of the closed coal oxidation experiment showed that under the condition of temperature of 25-70 ℃,oxygen consumption rate, CO release rate, CO 2 release rate and oxidative exothermic intensity of coal increased exponentially with the increasing temperature. Under the condition of oxygen concentration of 20% and temperature of 25-70 ℃,the oxidation exothermic intensity of the fault tectonic coal in No.11301 working face of Hongqingliang coal mine was 1.37-2.00 times of the native coal. The tendency of spontaneous combustion was stronger for the fault tectonic coal compared with the native coal of the seam. The whole studies revealed from micro and macro perspectives that the reason why the fault tectonic coal was more prone to spontaneous combustion in the actual mining environment was that the coal’s own structure and spontaneous combustion environment factors were changed to make it more favorable for spontaneous combustion.

The corrosion behavior of rare earth (RE) low-alloy steel in soil simulation solution was investigated by immersion test, electrochemical experiment, scanning electron microscopy, and X-ray diffraction, compared with Q450 weathering steel. The kinetics model of all steels in soil simulation solution was established. The pitting corrosion mechanism of nonmetallic and RE inclusions was discussed. The results revealed that the RE improved the corrosion resistance of low-alloy steel by modifying inclusions and promoting the formation of a dense protective film. The steel containing 0.0047% RE achieved the best corrosion resistance. The corrosion product layers were mainly composed of gamma-FeOOH, alpha-FeOOH, Fe3O4, and Fe(OH)(3). The results of the kinetic model showed that the dissolution of the anode was the restricted link of the whole process. The lowest apparent corrosion rate constant k of the sample containing 0.0047% RE was 2.359 x 10(-4) mu m/h in the soil simulation solution. The kinetic model could serve as a method to predict the service life of steel parts.

The influence of hydroxyl groups in coal on low-temperature oxidation of other active groups was studied by analyzing the reactivity of six small molecule models under various conditions by using the reactive force field molecular dynamics method. Fourier-transform infrared spectroscopy was performed to investigate the influence of hydroxyl on the coal self-reaction process at low temperatures. Finally, the electrostatic potential, bond length, and frontier orbital energy level of each reaction model were calculated using density functional theory. The calculation results revealed that the reactivity of the alcohol hydroxyl structure was the strongest without and with oxygen, and numerous hydroxyl radicals were generated during the reaction process. Hydroxyl radicals accelerated the reaction rate of the active group to be faster than O2. Hydroxyl radicals can affect the reaction of the active group through two routes, one route is the hydrogen abstraction reaction, and the other route is electrophilic substitution. The amount of the OH-OH structure in coal decreased by 3 % under the oxygen-free condition at 343 K compared with that under the normal temperature (298 K). This phenomenon played a crucial role in the self-reaction process of coal and promoted -COOH and -CH2- reactions. Quantum chemical calcu-lations revealed that the energy gap value of each reaction structure decreased, and the reaction activity increased. Hydroxyl radicals affect the electron cloud density of the active group. The nucleophilic reaction sites of ethyl and methyl structures increased, the C-C bond between carboxyl and aldehyde structures and benzene ring was long, and the ability of decarboxylation and dealdehyde was enhanced. Furthermore, the benzene ring of the phenolic hydroxyl group was activated, and the nucleophilic reaction ability of the alcohol hydroxyl group was enhanced.