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The slow dissolution process of zirconium oxide (ZrO 2) limits the efficient and energy-saving production of zirconium-rich basalt fibers with excellent alkali resistance for fiber-reinforced concrete. Therefore, it is necessary to investigate the optimum homogenization conditions to produce high-performance zirconium-rich basalt fibers. In this study, quenched zirconium-rich glasses and zirconium-rich fibers with the addition of 7 wt% ZrO 2 at different homogenization temperatures and time were prepared. The quenched melt structure was characterized by XRD and FTIR, and followed information about the melt structure obtained by Gaussian curve fitting of the FTIR spectra. The results indicated that obvious ZrO 2 crystals appeared in the melts and fibers with homogenization temperature below 1500 °C and time below 4 h. The degree of polymerization of zirconium-rich basalt melt was found to increase with increasing homogenization temperature and time. Meanwhile, the tensile strength and production stability of zirconium-rich fibers increased with increasing the degree of polymerization. The optimum homogenization temperature and time for zirconium-rich basalt fibers were concluded to be 1580 °C and 10 h, and the corresponding tensile strength is 1799 MPa and 1761 MPa, respectively. By diffusion experiment of ZrO 2 in basalt melt with altered major component content, it was found that the Ca, Mg, Na, and Fe significantly facilitated the melting of ZrO 2 into basalt melt by XRD and EDS. It was mainly attributed to the charge-compensating effect of metal cations on the [ZrO 6 ] octahedra, which promoted the homogenization of ZrO 2 in basalt melt. [ABSTRACT FROM AUTHOR]

Understanding the tensile strength properties and damage evolution mechanism in fissured rock is very important to fundamental research and engineering design. The effects of flaw dip angle on the tensile strength, macroscopic crack propagation and failure mode of symmetrical Brazilian discs of rock-like materials were investigated. A parallel bonding model was proposed to examine the damage of pre-flawed discs under splitting the load. The microscopic parameters of particles and bonds in the model that can characterize rock-like materials' mechanical and deformation properties were obtained by calibrating against the laboratory test results. The crack development, energy evolution and damage characteristics of Brazil discs containing a single pre-existing flaw were studied at the microscopic scale. The results show that the flaw significantly weakens the strength of the Brazilian disc, and both the peak load and the initial cracking load decrease with increasing flaw angle. The failure modes of the rock-like specimens are mainly divided into three types: wing crack penetration damage mode, tensile-shear penetration damage mode and radial penetration failure mode. Except for the flaw dip angle 0°, the wing cracks generally sprouted at the tip of the pre-flaw, and the wing cracks at both tips of the pre-flaw are centrosymmetric. Crack coalescence was concentrated in the post-peak stage. Based on the particle flow code (PFC) energy partitions, the damage variables characterized by dissipation energy were proposed. The disc specimen's pre-peak damage variables and peak damage variables decreased with increasing flaw angle, and the damage was concentrated in the post-peak phase. [ABSTRACT FROM AUTHOR]

• The high-sodium coal ash slag has a low viscosity as the Na 2 O can provide O2− ions and break Si-O-Si bonds, leading to decreasing the slag viscosity. • The slag viscosity gradually increases as the phosphorus acts as a network former and enhances the slag viscosity. • The ratio of (Q0(Si) + Q1(Si) + Q2(Si))/(Q3(Si) + Q4(Si)) decreases from 1.45 to 0.32 when the PO 4 3−/Na molar ratio ranges from 0/0 to 2/1. • The content of non-bridging oxygen decreases and enhances the polymerization degree of slag. • With the addition of phosphorus, the viscous flow activation energy of slag increases while reducing the crystallization tendency. Co-gasification of P-rich fuels and coal would reduce the large-scale usage of fossil fuels and pollution emissions, and fit the "carbon neutrality" goal in 2060. However, the effect of phosphorus on the viscosity-temperature behavior and structure of high-sodium coal ash slag is not yet completely characterized. In this work, the effect of phosphorus on the viscosity and structure of slag was investigated, and the crystallization tendency was also elevated. Results indicate that the high-sodium coal ash slag has a low viscosity as the Na 2 O can provide O2− ions and break Si-O-Si bonds, leading to decreasing the slag viscosity. The slag viscosity gradually increases as the PO 4 3−/Na molar ratio increases because the phosphorus acts as a network former and enhances the slag viscosity. The temperature of critical viscosity rises from 1206 °C to 1305 °C and 1127 °C to 1207 °C, respectively, for Group 1 and Group 2 when the PO 4 3−/Na molar ratio rises from 0/0 to 2/1. With the addition of phosphorus, the cations of Na are removed from the silicate network and form Na phosphate complexes and Si-O-Si linkages, and the content of Q3(Si) and Q4(Si) units increases while the contents of Q0(Si), Q1(Si), and Q2(Si) units decrease, increasing the slag viscosity. In addition, the Si-O-P and P-O-P linkages are formed due to the phosphorus atoms being introduced into the slag structure. Resulting in decreases the content of non-bridging oxygen and rises the degree of polymerization of slag. Furthermore, the viscous flow activation energy of slag increases while reducing the crystallization tendency after the application of phosphorus. [ABSTRACT FROM AUTHOR]

The low alkali resistance of basalt fiber limits its utilization in the strong alkaline environment such as cement and concrete as the reinforcing material. Adding additive in the basalt rocks is the feasible method to enhance the alkali resistance. However, it is necessary to develop the efficient additive for basalt fiber. In this work, the effect of TiO 2 on the preparation condition, alkali resistance and mechanical properties of basalt fiber was investigated. The preparation conditions were studied by DSC, XRD and high-temperature rotational viscometer. Then the corrosion behavior of TiO 2 -basalt fibers in NaOH solution was studied via SEM/EDX, FIB/SEM and FTIR. The results indicated that the viscosity of basalt melt decreased significantly with the increasing TiO 2 content from 0% to 2%, but the crystallization tendency was not changed with TiO 2 below 2%, the upper limit for TiO 2 addition. The tensile strength increased by 20–60% because Ti4+ promoted Al3+ into the network structure and intensify the polymerization by entering the network structure as network precursor in the form of [TiO 4 ]. Meanwhile, TiO 2 in the basalt fibers formed insoluble titanium hydroxide, so the weight loss of TiO 2 -basalt fibers in NaOH solution was reduced up to 50%. Through FIB/SEM/EDX, the corrosion of basalt fiber in alkali condition is controlled by ion diffusion. The outward diffusion of Fe, Mg and Ti to the surface of fiber formed the insoluble layer, so the rate of substitution reaction between the OH− and basalt fibers was slowed down, but it also leaded to the non-uniform corrosion. • Effect of TiO 2 on alkali resistance of BF was firstly investigated systematically. • TiO 2 -BFs with excellent alkali resistance were obtained. • The tensile strength of TiO 2 -BFs increases by 22–58%. • Non-uniform corrosion of BF in alkaline solution was directly observed by FIB/SEM. [ABSTRACT FROM AUTHOR]

To improve the extraction of coal resources, gob‐side entry driving is gradually being promoted and applied. However, as the thickness of the coal seam increases, the deformation control of the roadway becomes more difficult. Aiming at this problem, a combination of theoretical calculation, numerical simulation, and field test was used to analyze the aspects of the stress environment, surrounding rock properties, and support forms. The phenomenon and mechanization of intensified deformation and failure of roadway with increasing coal seam thickness were revealed. The specific results include: (1) The ratio of principal stress at the excavation position controls the maximum failure depth of roadway, and the direction of principal stress determines the location of the maximum failure depth; (2) As the thickness of the coal seam increases, the properties of the surrounding rock at the excavation position decrease, the principal stress ratio increases, and the deflection angle of the principal stress increases, which lead to an intensification of the deformation and failure of the roadway. Based on the deformation and failure characteristics of the roadway and the shortcomings of the original support form, a control strategy and support scheme based on a new support structure called "Anchor Cable with C‐shaped Tube" is proposed, which has achieved better deformation control effect in on‐site application. [ABSTRACT FROM AUTHOR]

Cement provides zonal isolation and mechanical support, and its integrity is critical to the safety and efficiency of the CO2 injection process for geologic carbon storage. This work focuses on interfacial debonding at wellbore interfaces and radial cracking in cement during CO2 injection. It adopts the definition of the energy release rate (ERR) to characterize the propagation of cracks. Based on the finite element method, the proposed model estimates the ERRs of both types of cracks with practical wellbore configurations and injection parameters. Further parametric studies reveal the effects of cement's mechanical and thermal properties and the crack geometry on crack propagation. Simulation results show that the ERRs of interfacial and radial cracks would surpass 100 J/m2 with typical cement properties. The cement's thermal expansion coefficient is the most influential factor on the ERR, followed by its Young's modulus, Poisson's ratio, and thermal conductivity. The initial sizes and positions of the cracks are also important parameters for controlling crack propagation. Moreover, non-uniform in situ stresses would accelerate crack propagation at the interfaces. These findings are valuable and could help to optimize cement sheath design in order to ensure the long-term integrity of wells for geological carbon storage. [ABSTRACT FROM AUTHOR]

To study the effects of the anisotropic matrix and structural planes on the splitting strength and failure mode of rocks, Brazilian splitting tests were carried out with seven different loading angles on specimens of rock-like materials with rough structural planes. The surface strains of the samples during the failure process were monitored and analysed with the help of a high-speed camera and digital image correlation (DIC) technology. The test results showed that the Brazilian splitting strength (BSS) decreased gradually with an increased loading angle. According to the crack morphology, the samples showed three failure modes, and the structural plane and the loading angle (θ) had an important effect on the failure mode. When θ < 75°, the sample failure was mainly affected by the matrix, and when θ > 75°, the sample failure was mainly controlled by the structural plane. The numerical simulation of the sample with a structural plane was carried out by the PFC2D particle flow program, the micro parameters were calibrated using a back propagation (BP) neural network model. The internal cracks of the sample under a splitting load were mainly matrix tensile microcracks and structural plane shear microcracks, and the tensile microcracks in the side with the weak matrix appeared significantly earlier than those in the side with the strong matrix. With increasing loading angle, the proportion of tensile microcracks in the matrix increased, while the proportion of shear microcracks in the matrix decreased, especially in the weak matrix. The microcracks at the structural plane mainly changed from tensile microcracks to shear microcracks, and the development degree of microcracks along the structural plane was more significant than that on the weak matrix with increasing loading angle. The results of the study can provide a reference for rock stability evaluation and utilization. [ABSTRACT FROM AUTHOR]

• A novel multiband fusion artificial neural network (MFANN) was proposed for gas radiative properties prediction. • MFANN enables the prediction of gas absorption coefficient in a sub-band selectable manner. • The detailed datasets building strategies for MFANN were discussed. • MFANN achieves an error of less than 1.83 % compared with the line-by-line method. • MFANN spends about 1.33 s to predict the k -distributions for the gas mixture of CO, CO2, and H 2 O of 40 equidistant sub-bands in a wavelength range of 1.5–5.5 μm. Gas radiation exhibits strong selectivity in the spectrum, with its radiation and absorption capabilities only present at distinct wavelength bands. This implies that calculating gas radiative property across the entire wavelength range is unnecessary. In contrast, a computing strategy oriented to the radiative properties for the wavelength band of interest is of great importance for radiative transfer studies of gases. On one hand, this strategy enables researchers to avoid interference caused by noise from non-interest bands, thereby increasing the signal-to-noise ratio and improving computational accuracy. On the other hand, it reduces the computational burden by curtailing calculations in unnecessary bands. In light of these significances, this study proposed the multiband fusion artificial neural network (MFANN) model to predict the radiation property of CO, CO 2 , and H 2 O mixture at a pressure range of 0.5–4.0 atm, a temperature range of 300–3000 K, and a wavelength range of 1.5–5.5 μm. The distinctive feature of this model lies in its division of the target wavelength band into multiple contiguous sub-bands. A single-layer network is trained on each sub-band, afterword the network obtained from each sub-band is fused to emerge a compact big model which enables fast prediction of the gas absorption coefficient, in a correlated k -distribution format, for the mixture within all sub-bands. This study compared the prediction results of the fusion model with benchmarks calculated by the line-by-line (LBL) and full spectral correlated k -distribution (FSCK) methods under different cases to evaluate the model's performance. The results show that the Symmetric Mean Absolute Percentage Error (SMAPE) of MFANN is less than 1.83 %, and MFANN only spends about 1.33 s to predict the k -distribution absorption coefficient at the wavelength range of 1.5–5.5 μm with a sub-band interval of 0.1 μm. [ABSTRACT FROM AUTHOR]

• A systematic study of the crystallization properties of mullite in slag. • The kinetic characterization parameters of mullite were obtained. • Provided optimized conditions for smooth slagging of slag with high SiO 2 and Al 2 O 3 content. Mullite crystallization leading to poor slag discharge, is the bottleneck of solid fuel gasification. In order to quantify the crystallization behavior and prevent slag blocking, the crystallization thermodynamics and kinetics of slags in the main crystalline phase region of mullite were studied using FactSage, XRD, SEM-EDS and DSC. Mullite crystallization temperatures ranged from 1189 °C to 1325 °C, and an increase in the cooling rate reduced the mullite onset crystallization temperature as detected by DSC. Kinetic analysis showed that mullite possesses strong nucleation capacity and crystallize tendency, and the minimum activation energy of crystallization of slags was 304.4 kJ/mol. The Si-O-Al structure was regarded as the key short-range ordered structure for mullite crystallization ability, and its concentration was reduced by increasing SiO 2 /Al 2 O 3. Then the crystallization tendency could be weakened by adjustment of SiO 2 /Al 2 O 3. Meanwhile, slags with SiO 2 /Al 2 O 3 = 2.0 or Fe 2 O 3 ≤ 15 wt% showed weak crystallization tendency or glassy slag, which was favorable for slagging operation. The results of this study can provide theoretical guidance for the smooth slagging of ash slag in the main crystalline phase of mullite. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-situ Py-TOF-MS reveals interactions between coal and mixed plastic. • H-rich radicals from PP react with phenoxy radicals from coal to form diphenols. • The further addition of LDPE enhances the inhibitory effect on HM pyrolysis. • The co-pyrolysis of HM with PP/LDPE/PS generates more aromatic products. Online detection of pyrolysis volatiles is essential for exploring the mechanism of coal and plastics co-pyrolysis. In-situ pyrolysis time-of-flight mass spectrometry (Py-TOF-MS) equipped with double ionization sources, vacuum ultraviolet photoionization (VUVPI) and electron ionization (EI), was used to analyze the release of primary volatiles during the pyrolysis and co-pyrolysis of Hami coal (HM) with mixed plastic (PP/LDPE and PP/LDPE/PS, with ratios of 3:2 and 12:8:1, respectively). Meanwhile, the interaction mechanism was discussed at the molecular level. According to the thermogravimetric (TG) results and the total ion currents (TIC) of primary volatiles with temperature, the inclusion of plastic shortens the overall reaction time. In-situ Py-TOF-MS results indicate that the volatiles produced from HM pyrolysis at lower temperatures induce the decomposition of PP and promote further dehydrogenation of long-chain C–C. Besides, the addition of PP visibly facilitates the transportation of hydrogen, which reacts with phenoxy from HM pyrolysis to produce diphenol. The further addition of LDPE after PP enhances the inhibitory effect of molten plastic on HM pyrolysis, resulting in a decrease in the content of diphenol, such as benzenediol (from 1.34% to 0.71%), methyl-benzenediol (from 1.12% to 0.68%) and dimethyl benzenediol/ethyl benzenediol (from 0.68% to 0.50%). The co-pyrolysis of HM with PP/LDPE/PS generates more aromatic products compared to that of theoretical value, such as styrene (from 0.29% to 3.16%), 1-ethenyl-3-methyl benzene (from 0.07% to 0.31%) and 1-butene-2,4-diphenyl (from 0.19% to 0.65%). This indicates that co-pyrolysis strengthens the breakage of C ar -C β bond in the PS backbone. The addition of PS to the mixture plastic also promotes intramolecular and intermolecular hydrogen transfer in the system. For the evolution of inorganic gases, the addition of mixed plastics promotes the decomposition of aliphatic and aromatic carboxylic acids in coal at lower temperatures, resulting in a decrease in CO 2. [ABSTRACT FROM AUTHOR]

The freezing method is widely used in the construction of vertical shafts in water-rich strata. The formed frozen rock wall is often involved in the creep process, and in particular, the creep behavior of frozen fissured rock mass poses a great threat to construction safety. To better understand the creep instability law of ice-filled, fractured red sandstone under freezing and triaxial stress conditions, a series of triaxial creep tests on frozen red sandstone specimens containing a single, pre-existing flaw at −10°C and under a confining pressure of 4 MPa were carried out with a self-developed DRTS-500 subzero rock triaxial testing system. The multistage loading creep curves were obtained, and the evolution laws of deformation and damage for the frozen specimens in the primary (instantaneous), secondary (steady-state) and tertiary (accelerating) phases were analyzed. The nonlinear visco-elastoplastic constitutive model of red sandstone with a single ice-filled flaw was established according to the fractional calculus theory and the Kachanov damage theory. The results show that the initial creep property, unstable creep property and creep failure mode of frozen single-flaw red sandstone are significantly affected by the flaw dip angle. The proposed creep damage model can accurately describe the complete creep curves of frozen red sandstone with a single ice-filled flaw, especially in the unstable creep stage. The influences of the stress level and flaw dip angle on the creep parameters were analyzed, and sensitivity analyses of the characteristic creep parameters were carried out to verify the reliability and rationality of our creep model. This research can be applied to the assessment of collapse, cracking and other long-term failures and hence can be used as a theoretical basis of design in the freezing engineering of coal mine shafts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different feedstock configurations are designed to deconvolute synergy during co-pyrolysis. • The interaction between volatiles is found to be a major contributor to tar lightening. • The unreacted-HM and PS-volatiles interaction is the main contribution to char aromatization. • The unreacted-HM and PS-melt interaction is unfavorable to the production of gas. Co-pyrolysis with low rank coal is an important way to treat waste plastics and recycle them into valuable materials. Complex interactions between volatiles-feedstock, volatiles-volatiles, and volatiles-char co-exist during co-pyrolysis, which will influence the synergistic effects and have not been extensively understood. In this work, some new feedstock configurations were conducted in a fixed-bed reactor to explore the contribution of these complicated interactions between different sources to the synergy effect observed during co-pyrolysis of Hami coal (HM) and polystyrene (PS). Results show that the interaction between PS-volatiles and HM-volatiles is found to be a dominant contributor to tar lightening in co-pyrolysis, which accounts for 5.67 wt% increase in the content of gasoline fractions (<180 °C) compared to the theoretical calculated value. Meanwhile, the content of gasoline fractions in tar increases with the enhancement of the interaction between volatiles and unreacted-HM. The volatiles and unreacted-HM interaction is the main contributions to synergy in aromatization of char, while the PS-volatiles and HM-char interaction plays an opposite role. The co-pyrolysis of HM-char locating on the top of PS also reveals the catalytic activity of HM-char on PS decomposition. Furthermore, the interaction between unreacted-HM and PS-melt is not conducive to the production of gas, but favorable to the production of char with high aromaticity. These results provide a valuable supplement for the understanding of the interaction mechanisms during co-pyrolysis, and also help to enhance synergistic pathways of the target products while simultaneously reducing inhibitory interactions. [ABSTRACT FROM AUTHOR]

The artificial freezing method is an effective method of shaft construction in water-rich soft rock beds. Engineering frozen walls involves the use of intact rock material, flaws and ice. To better understand the mechanical properties of frozen walls, explore the failure laws of frozen fractured rock, and solve the problem of complex ice-rock coupling, it is necessary to carry out laboratory triaxial tests on frozen fractured rock. Herein, X-ray diffraction and mesostructure observations are used to analyse the mineral composition and microstructural characteristics of red sandstone specimens taken from the Shilawusu coal mine. Then, the strength, deformation and crack evolution behaviour of red sandstone containing two pre-existing ice-filled fissures are obtained under triaxial compression using the self-developed DRTS−500 subzero rock triaxial testing system. The experimental results show that the peak strength and elastic modulus of the specimens with pre-existing flaws are all much lower than those of the intact specimens, and the strength parameters are distinctly related to the flaw combinations. For the frozen red sandstone containing two intermittent ice-filled fissures, the peak strength, elastic modulus and shear strength parameters all have a linear relationship with the confining pressure and temperature, whereas the shear strength (σ 1 − σ 3) has a nonlinear relationship with the confining pressure. The deviatoric stress-strain curve of the samples is divided by four characteristic stresses (compacting stress, crack initiation stress, dilatancy stress and peak stress) into five stages from loading to failure. The lower the confining pressure or temperature is, the faster the curve falls after reaching the stress-strain peak value, indicating that the sample exhibits increasingly brittle characteristics. The ultimate failure modes of the specimens containing two pre-existing ice-filled flaws include mixtures of several types of cracks (shear cracks, main cracks, secondary cracks, tensile cracks, coplanar cracks, slip cracks and wing cracks), which depend on the flaw combinations. An obvious crack coalescence failure mode can be observed in the GG and GS specimens, but no obvious crack coalescence phenomenon can be observed in the SS specimens. • Triaxial tests are conducted under different confining pressure and temperature. • The strength of pre-flawed specimens were much lower than those of intact specimens. • The relationships between the strength parameters and flaw combinations were studied. • The crack growth is affected by the combination of pre-existing flaws. [ABSTRACT FROM AUTHOR]