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To study the anisotropy of gas seepage in coal seams with low permeability,coal samples were prepared respectively in the parallel bedding direction and the vertical stratification direction of the same coal rock. Tri-axial servo seepage tests on gascontained coal were detected by using a self-developed apparatus. It is found that the permeability of coal samples in the parallel is far greater than that of coal samples in the vertical. With the increase of axial pressure,the permeability of coal samples in the parallel reaches its minimum at the yield point before the peak failure,while the permeability of coal samples in the vertical gets its minimum at the initial period of the elastic stage. The permeability of both the parallel and the vertical nonlinearly increases after the peak failure.

A (Lu1−xScx)0.99Ce0.01BO3 (LSBO:Ce, x = 0–1) material library is successfully prepared via combinatorial materials technology, and the crystal structures are characterized via a high-throughput XRD platform at the Shanghai Synchrotron Radiation Facility (SSRF). The angular distortion increases upon the substitution of Lu3+ with Sc3+, as shown through crystal structure analysis of as-prepared LSBO:Ce, obtained via the Rietveld refinement method. LSBO:Ce shows obvious red shifts in its PLE and PL spectra with increasing Sc concentration because of an increased Stokes shift originating from an increased crystal field splitting effect and angular distortion. Owing to reduced symmetry, increased strain and the nephelauxetic effect will reduce energy transfer from charge carriers to Ce3+ as luminescent centers. Due to greater loss during the energy conversion process, the PL intensity and decay time decrease with an increase in the Sc3+/Lu3+ ratio. Based on high-throughput rapid and efficient screening, the optimized LSBO:Ce (x = 0.2) material was selected to fabricate a scintillation screen with polymethyl methacrylate (PMMA) in order to study its scintillation properties. As the powder concentration increases from 0.5 to 10 wt%, the transmittance of the scintillation screen drops from 86 to 73.5%. It is of note that the integrated XEL intensity of the LSBO:Ce@PMMA scintillation screen is 1.36 times higher than that of a BGO single crystal. The spatial resolution of the scintillation screen can reach as high as 300 μm thanks to the intense XEL intensity and 80% transmittance in the visible light range. This study is of great significance for the potential application of LSBO:Ce in the fields of X-ray detection and imaging. [ABSTRACT FROM AUTHOR]

Gas How in coal seams is a complex coupling process of coal deformation and gas migration. This study investigated the coupling mechanism between coal seam abutment stress and the flow rate of gas drainage based on the field monitoring of the abutment stress and the flow rate of gas drainage at the panel 3211 of Songzao Mine in Chongqing. The results reveal that the change of measured stress experiences a low-high-low process with the distance ahead working face and reaches its peak value around 15-25 m ahead working face. The coal seam can be divided into three stress zones; relief stress zone, abutment stress zone, and recovered stress zone. As the pore and fracture structure is affected by coal seam abutment stress, the flow rate of gas drainage increases in the relief stress zone, decreases in the abutment stress zone and remains stable in the recovered stress zone. A negative exponential formula based on the coupling mechanism between coal seam abutment stress and the flow rate of gas drainage is presented to calculate the flow rate of gas drainage. [ABSTRACT FROM AUTHOR]

To study the change of effective stress impact on permeability dynamic evolution during mining, based on domestic-developed triaxial servo-controlled seepage equipment for thermal-hydrological-mechanical coupling of coal containing methane, the experimental study of permeability properties was performed on raw coal samples under monotonic loading and loading-unloading conditions of different initial stress states. Combined effects of gas mechanism and gas adsorption on the effective stress coefficient, the effective stress calculation and the permeability with effective stress equation under loading-unloading conditions were established, and then according to the initial porosity and the adsorption constants and experimental permeability data under different conditions, the permeability model was verified. The results show that theoretical permeability calculation values and experimental results under loading and loading-unloading conditions are quite high. With the increase of effective stress, permeability of coal samples under different conditions decreases as negative exponential relationship. [ABSTRACT FROM AUTHOR]

Three main influential factors affecting coal seam gas permeability were analyzed and summarized in this study, which were gas pressure, temperature and effective stress. In addition, a BP neural network model of coal seam gas permeability was built based on the coal mechanical properties. A large amount of representative coal gas permeability data under different conditions were used for building training samples and the accuracy of the model was tested. After 11 986 times training, the BP neural network model satisfies the requirements. The results obtained by the BP neural network model show that the maximum absolute error was 0. 049x10-15 m² and the maximum relative error was 4. 298%. The results obtained by the BP neural network model match the measured data well. [ABSTRACT FROM AUTHOR]

An effective stress calculation formula was proposed for coal containing gas with considering the swelling stress of gas adsorption based on the effective stress principles for porous media. Referring to dynamic model of porosity and permeability in coal containing gas, solid-gas coupling model which could describe the skeleton deformability of coal containing gas and the compressibility of gas under the solid-gas interaction condition was built. First we made excavation on the three-dimensional model based on the physical parameters of Pingdingshan tenth coal mine to obtain the stress distribution of coal seam after excavated instead of easy uniform loading. Then we simulated the gas drainage from boreholes based on constructed mathematical model. From the results we got: (1) Negative pressure didn't have a great influence on gas drainage. (2) The porosity of coal seam decreased gradually over time. (3) The effective radius increased gradually to a fixed value over time. [ABSTRACT FROM AUTHOR]

Based on domestic-developed triaxial servo-controlled seepage equipment for thermal-hydrological-mechanical coupling of coal containing methane, the experimental study of unloading confining pressure of coal was performed on coal samples under different gas pressure. The results show that the characteristic of distinct dilatancy is displayed in the process of unloading confining pressure, therefore seepage channels in coal body are extended and seepage velocity increases. The deformation of coal containing methane per unit decreased confining pressure and seepage velocity increases with the increase in gas pressure in the same stress paths. The compressive strength decreases gradually with the increase of gas pressure. In the initial stage of unloading confining pressure, deformation modulus of coal containing methane changes little. After the yielding occurs, it decreases obviously. The deformation modulus decreases 3.71% -7.45% in the process of unloading confining pressure. Meanwhile, the Poisson's ratio turns to increase and a function can be used to describe the relationship between confining pressure and Poisson's ratio. [ABSTRACT FROM AUTHOR]

Coal and gas outburst simulation test device was applied to simulate coal and gas outburst under conditions of different stress in stress-concentrated area in order to study how the stress change in stress concentration zone may influence coal and gas outburst properties. The analysis of experimental results show that the change in stress of stress concentration zone plays an important role in coal and gas outburst, the concrete manifestation of which are as follows : with stress increase in stress concentration zone, the intensity of coal and gas outburst increases, meanwhile, crushing effect of coal thrown out by gas strengthens, and larger total temperature decrease is observed. In addition, concentrated stress has the same impact on the angle between outburst hole and coal seam. [ABSTRACT FROM AUTHOR]

A self-developed device called the gas-bearing coal heat solid coupling servo seepage device was used to conduct the percolation test of two different coal samples (parallel bedding coal and perpendicular bedding coal) under different condition settings to study the differences of deformation and permeability between these two types of coal samples. In the first section of the percolation test, the effective stress and gas pressure remained the same, while the axial pressure and confining pressure were different. In the second section, the gas pressure and hydrostatic pressure remained the same, while the effective stress was different. The result shows that the degree of fracture along the direction of z of parallel bedding sample is bigger than that of vertical bedding sample. The total degree of vertical stratification fractured specimen "φ" is bigger than the parallel bedding sample. In coal, the total fracture of vertical bedding direction is bigger than that of parallel bedding direction. The degree of fracture of parallel bedding sample is bigger than that of vertical bedding sample. Under hydrostatic pressure, the degree of fracture of parallel bedding direction is bigger than that of vertical bedding direction. According to the theory of tablet fluid, quadric relationship between permeability and radial strain can be obtained. The initial crack coefficient of parallel bedding sample is 1 .5-2. 0 times bigger than that of vertical bedding sample in coal. When the flow channel is considered as transfixion crack, the product of the initial crack coefficient and the square of the initial fracture aperture of parallel bedding sample is 1.5-2. 0 times bigger than that of vertical bedding sample. [ABSTRACT FROM AUTHOR]

Based on the measurement standards of rock burst tendency of coal samples, it has been measured under different gas pressures. The methods of energy accumulation and dissipation were applied to analyze the relationship between energy accumulation and dissipation of coal samples under the conditions of uniaxial compression and uniaxial cyclic loading and unloading in different gas pressures. The results show that with the increase of gas pressure, the indexes of every rock burst tendency are constantly reduced, and their outburst-proneness are decreased. Before destruction, the elastic energy stored is reduced, while the gaining rate of dissipated energy decreases rapidly in the form of nonlinear relationship during destruction. Under cyclic loading, the dissipated energy of coal samples in each cycle increases along with the increase of gas pressure. Gas reduces the destructive impact of coalbed rockburst, but when considering the expansion energy of gas, the overall destruction can be more serious. Therefore, gas should be considered when the rockburst tendency is evaluated in high gassy coal mines. [ABSTRACT FROM AUTHOR]

Rased on die analysis method from seepage mechanics, the coupling effect of coal-seam mining fissure, stress and methane flow was studied. The fissure of coal-seam and overlying rock, as well as mining stress and gas pressure were measured on site. Also, the interaction of these three parameters was comparatively analyzed. The results show that the permeability of cracked coal mass under mining is related to fissure width, connect situation, unevenness, spacing, normal stiffness and mining stress; methane flow in cracked coal mass is intimate to fissure development; and methane permeability is positively correlated to fissure width and negative to fissure spacing. Based on the coupling effect of mining fissure, stress and methane flow in front of working face, a mechanic model of cracked coal mass' mining stress and methane seepage was built. The model can provide the coupling effect of mining fissure, mining stress and methane flow in fractured coal-rock mass. [ABSTRACT FROM AUTHOR]

The application of LuBO 3 :Ce 3+ (LBO:Ce) crystal as an excellent scintillation material has been limited due to its poor phase stability at high temperature or high pressure, so improving the phase stability is essential for promoting its development. Ga stabilized LuBO 3 :Ce 3+ (LGBO:Ce) is synthesized by solid-state reaction at 1200 °C. Powder X-ray diffraction patterns and Raman spectra at ambient pressure show that all the samples are pure calcite phase. In situ high-pressure synchrotron radiation XRD patterns illustrate that calcite phase LGBO:Ce exhibits more excellent phase stability than that of LBO:Ce under high pressure due to the superior compressibility of the [GaO 6 ] octahedral unit. The optical band gap of LGBO decreases from 5.58 to 4.64 eV after introducing 10% Ga, which leads to the decreased nonradiative transition and about double luminescence intensity as expected. More interestingly, the charge transition from O 2- to Ce 4+ is observed at about 290 nm in the absorption spectra. The X-ray photoelectron spectroscopy spectra indicate the ratio of Ce 4+ /Ce 3+ increases with increasing concentration of Ga 3+ , which can be attributed to the variation of energy separation between the 4f ground state of Ce 3+ and the Fermi energy level position. In contrast to the enhancement of PL intensity, the integrated X-ray excited luminescence intensity decreases after Ga 3+ incorporation attributing to the result of both decreased effective atomic number and ionization energy between 5d 1 level and conduction band. The thermal luminescence spectra show that after the incorporation of Ga 3+ the oxygen vacancy and intrinsic defects in LBO remain unchanged but that the concentration of oxygen vacancy significantly reduces. The mechanism of Ga 3+ incorporation on phase stability and luminescence properties of LBO:Ce has been proposed and discussed systematically.