Structural Evolution Characteristics Research Articles

The Multitype Pore Structure Evolution Characteristics of Ziliujing Formation Shale from the Northeastern Sichuan Basin in China: Experimental Study Using Small Angle Neutron Scattering Technology

The high complexity and heterogeneity of shale pore compositions and abundant nanopores complicate the multiscale characterization of a shale reservoir pore structure. As the degree of geological evolution changes, the pore structure and connectivity also undergo complex changes and the thermal simulation experiment is a practical method to reveal the evolution characteristics of shale within a relatively short time period using the time–temperature compensation principle. In this study, thermal simulation experiments were used to obtain shale samples of the Ziliujing Formation in Northeastern Sichuan Basin with different evolution degrees. The pore structure of the samples was quantitatively characterized by SANS combined with N2 adsorption and mercury injection capillary pressure (MICP) methods. The pore morphology was qualitatively characterized by the field emission scanning electron microscopy (FE-SEM) experiment. Finally, the influence of thermal evolution on the pore structure of shale samples was investigated. The results show that the pore size distribution of SANS is similar to that of MICP and N2 adsorption methods, and the pore volume is mainly concentrated in 5–100 nm. The porosity and pore specific surface area obtained by the three characterization methods showed the trend of SANS > MICP > N2 adsorption, and the difference in pore structure was mainly affected by fluid accessibility. With the increase in thermally simulated temperature, the total pore volume and pore specific surface area of shale samples show a trend of an increase first and then a decrease. The proportion of >10 nm pores increases gradually, and the fraction of closed pores shows a downward trend as a whole. Basically, with the increase in thermally simulated temperature, the pore connectivity is enhanced, and the sample heterogeneity is weakened, all of which are conducive to the migration of shale reservoir fluid. Overall, clarifying the evolution of closed pores in shale reservoirs is of great significance for estimating original oil and gas reserves more accurately and improving oil and gas recovery.

Spatiotemporal Evolution of County-Level Land Use Structure in the Context of Urban Shrinkage: Evidence from Northeast China

Shrinking cities are a class of cities that show different trajectories in the urbanization process. Although many studies have examined shrinking cities from multi-dimensional perspectives, the spatiotemporal evolution of land use structure is still poorly understood. This study constructed an analysis framework for spatiotemporal evolution characteristics of land use structure over two 10-year periods based on 334 county-level administrative units in the context of northeast China, a region undergoing substantial population loss and urban shrinkage. This study analyses quantitatively measured population loss and land use conversion and investigated the rationality of the expansion mode of newly added construction land in research units. The results demonstrated that, first, the total population in northeast China continued to decline, but the total construction area continued to grow, and the various types of construction land in most shrinking units did not decline with the loss of population. Second, 67.09% of new construction land came from cropland, and compared with 2000–2010, the growth of new construction land in 2010–2020 slowed down. Third, during the study period, more than half of the expansion area for newly added construction land came from sprawling expansion, and areas in a state of shrinking were no exception.

Study on the chloride ion transport mechanism of recycled mixed aggregate concrete based on evolution characteristics of pore structure

• An interface model of RMA concrete considering pore structure characteristics was established. • The evolution characteristics of the microscopic pore structure for RMA concrete were studied. • The chloride ion transport mechanism of RMA concrete was studied based on microstructure parameters. The difference in pore structure characteristics is the fundamental reason that the chloride ion transport mechanism of recycled mixed aggregate (RMA) concrete is different from that of ordinary concrete. In this paper, the chloride ion penetration tests were performed on eight groups of specimens with different water-binder ratios (w/b) and coarse aggregate types. The specimens’ micromorphology, pore structure, fractal dimension, and microhardness were analyzed in detail. The results show that the pore structure of the specimen has an important influence on the chloride ion transfer process. With the increase in curing age, the porosity of new mortar (NM) and mortar attached to the surface of brick aggregate (BM) decreased, while the total fractal dimension increased, and the porosity of BM decreased more than that of NM. The brick aggregate is wrapped in a dense hydration layer, which prevents chloride ions from penetrating the brick aggregate to a certain extent. The anti-chloride ion transport performance of NM is weaker than that of BM due to the NM contains more capillary and large pores. Different pore size distribution ranges of the specimens have similar fractal characteristics. The fractal dimension first increases and then decreases with the change of the pore size range from small to large. The interface pore model of RMA concrete was established to provide a reasonable basis for further research on the durability of the specimens.

Structural evolution, dielectric relaxation, and charge transport characteristics of formamidinium lead iodide (FAPbI3) perovskite

Recently, hybrid halide perovskite solar cells have drawn the researchers’ attention, owing to their high-power conversion efficiency. Among the different compounds, MAPbI3 (MA = Methylammonium CH3NH3) and FAPbI3 (FA = Formamidinium CH(NH2)2) are especially potential candidates since their bandgap suited the energy range of visible light. Here, the hybrid perovskite FAPbI3 is successfully synthesized via the inverse temperature crystallization method. Different characterization techniques such as variable-temperature structural analyses, differential scanning calorimetry (DSC), and impedance spectroscopic analysis show that FAPbI3 presents a phase transition at T = 300 K from the hexagonal to the cubic symmetry. Optical analysis of FAPbI3 shows the direct band-gap value of ∼1.4 eV. FAPbI3 is characterized by impedance spectroscopy technique performed in the 10−1–106 Hz frequency and 210–390 K temperature ranges. The alternating current (AC) conductivity is illustrated in terms of Jonncher's power law. The study on charge transportation within FAPbI3 suggests the presence of the NSPT (non-overlapping small polaron tunneling) and OLPT (overlapping large polaron tunneling) models in the hexagonal and cubic phases, respectively.

An Evaluation and Optimization of the Spatial Pattern of County Rural Settlements: A Case Study of Changshu City in the Yangtze River Delta, China

The development model of rural settlements in economically developed regions has reference and guiding significance for other developing rural settlements. The study was conducted to discuss the spatial distribution and scale structure evolution characteristics, in order to understand the development process and the problems of rural settlements in Changshu City, Jiangsu Province. Then, based on the multi-stage goals of Rural Revitalization of “pole–field–zone–network”, a multi-stage rural settlement spatial structure was revealed to promote the optimization of settlement layout and promote urban–rural integration. The data of rural settlements were extracted from the land use data of nearly 20 years from 2000 to 2020. Different research methods were utilized for the study. The results revealed that the spatial pattern and scale structure of rural settlements in Changshu had experienced two periods of drastic changes and stable adjustment in the past 20 years. The rural settlement density generally presented a spatial pattern of dense in the north, sparse in the South and sparse in the East. The scale system of rural settlements tended to disperse from centralization, but the spatial agglomeration was enhanced. Finally, based on the above research results and problems, a “pole–field–zone–network” multi-stage settlement structure was revealed, which helps to form a reasonable urban and rural network.

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting.

High-pressure air blasting (HPAB) is one of the main feasible technologies to improve the extraction efficiency of unconventional gases. At present, there are few visual studies on the evolution characteristics of pore structure in coal under HPAB, resulting in an unclear understanding of the mesoscopic damage evolution mechanism of coal under HPAB. To study the dynamic response and mesoporous structure evolution characteristics of coal under HPAB, simulated coal specimens were used in HPAB experiments. The pore structure characteristics of coal at different locations away from the blasthole after HPAB were analyzed by using computed tomography scanning and 3D reconstruction technology. The maximum sphere algorithm was used to study the law of pore connectivity and reveal the mesoscopic damage evolution mechanism of coal under HPAB. The results indicate that the stress wave and attenuation and the crack propagation direction are greatly affected by the confining pressure. Compared without confining stress, the radial strain attenuation index decreases by 11.97% and the lateral strain attenuation index increases by 15.36% under confining pressure. Without confining pressure, the crack direction is disordered. On the contrary, the crack expands along the σ1 and σ2 directions with confining pressure, while the expansion along other directions is inhibited. The stress wave has a great influence on the pore structure in the nearby zone. Compared with before HPAB, at 25 mm distance from the blasthole, the number of pores increased by 24.80%, the number of throats increased by 12.96 times, the maximum equivalent radius of throats increased by 52.15%, and the maximum channel length of the throat increased by 56.06%. With the increase of the distance, the stress wave has little influence on the pore structure in the middle and far zones. The porosity of representative elementary volume and the distance from the blasthole decay in a power function trend. The maximum disturbance distance under HPAB can reach nearly 110 times of the blasthole radius. The study results provide a theoretical basis for enhancing the coal seam permeability and gas drainage of low-permeability coal seam by HPAB.

Genetic Types of the tp12cx Strike-Slip Fault Segments and Their Role in Controlling Reservoirs in the Tarim Basin

The change of motion mode of multistage active strike-slip faults controls the segmentary types of strike-slip faults, which is seldom studied.Based on high-precision 3D seismic data and the principle of structural analysis, this paper defines the structural evolution characteristics of the tp12cx strike-slip fault in the key structural period and identifies the fault segmentation types. Combined with the statistical results of drilling production data and fault width, and fault width, it is demonstrated that different fault segments display various reservoir architecture and hydrocarbon potential. The tp12cx strike-slip fault experienced two phases of tectonic activity controlling reservoir development: the middle Caledonian and the late Caledonian to early Hercynian. During the middle Caledonian period, a left-lateral and left-step strike-slip fault was formed. The overlapping segments of the left steps were transtension zones, and the rest were pure strike-slip segments. From the late Caledonian to the early Hercynian, the movement mode changed from left-lateral to right-lateral, and the arrangement of left steps remained unchanged, forming right-lateral and left-step strike-slip faults. That is, as a weak zone, the transtension zones of all the preexisting overlapping segments took the lead in moving into many pure strike-slip segments and maintained the transtensional property. During the right-lateral slipping process of all the original pure strike-slip segments along the fault, they were blocked and squeezed by the surrounding rocks on both sides, forming a series of “positive” flower-shaped fault anticlines, which became overlapping segments, and the fault property became transpressional. Under the continuous action of the right-lateral slipping, a regional right-lateral and right-step strike slip fault formed. The interiors of the right-step-arranged faults were composed of the left-step arranged faults. Among them, the right-step overlapping segments were weakly step overlapping segments were weakly transtensional, and the larger the fault width of the internal left step pure strike slip and overlapping segments, the stronger the dissolution. The deformation of the right-step pure strike-slip segments was weak and basically maintained the characteristics of the previous stage. According to the evolution and superposition of pure strike-slipped and overlapped segments and the changes in fault properties, four types of strike-slip fault segments and corresponding reservoir models are divided. Type I: left-step pure strike-slip segment + left-step transpressional segment + right-step transtensional segment; Type II: left-step transtensional segment + left-step pure strike-slip segment + right-step transtensional segment; Type III: left-step pure strike-slip segment + left-step transpressional segment; and Type IV: left-step transtensional segment + left-step pure strike-slip segment. The fault width and oil production of type II and type IV with transtensional properties are much larger than those of type I and type III with transpressional properties.

Spatiotemporal Evolution of Crop Planting Structure in the Black Soil Region of Northeast China: A Case Study in Hailun County

Detailed characteristics of crop planting structure (CPS) evolution can inform the optimization of the crop yield proportion in the black soil region of Northeast China (BSRNC). Choosing Hailun County as an example, this study sought to analyze the geographic characteristics of CPS evolution from 2000 to 2020. Our analysis produced new spatiotemporal information based on the remote-sensing interpretation data, namely, Landsat4-5 TM, Landsat7 ETM+, and Landsat8 OLI images. The study characterized the temporal and spatial dynamics of CPS. Our results showed the following: (1) Soybean and maize were the main crops, with a total land area of 70%; they alternated as the most dominant crop. (2) The distribution breadth and aggregation intensity of soybean and maize were spatially complementary; rice had the smallest distribution range but strong water aggregation. (3) The evolution pattern of CPS was the interconversion between a single type of soybean and maize. Our results indicate that the future CPS adjustment of BSRNC needs to consider the county-level optimization of crop area proportion and crop spatial distribution. This context has excellent implications in geographically informing policymaking to adjust county-level CPS of BSRNC, thus safeguarding food security.

Investigation on the evolution characteristics of bed porous structure during iron ore sintering

To better understand the evolution characteristics of bed porous structure during iron ore sintering, X-ray computed tomography scanning technology was used to analyze the pore parameters in different areas of the sintering bed. A pore skeleton structure model was established to study the characteristics of the airflow channels in different zones. The absolute permeability of different areas was calculated through simulation, and the corresponding streamline and pressure drop distribution were analyzed. The results show that the porosity of raw material zone, high-temperature zone, and sintered zone increases gradually, which are 37.69%, 46.41%, and 55.57%, respectively. The absolute permeability calculation results of the raw material zone and sintered zones are 792.49 μm2 and 20560.80 μm2, while the tortuosity is 1.77 and 1.45, respectively. Compared with the raw material zone, the flow streamline in the sintered zone is thicker and denser, the airflow resistance and the pressure drop are minor.

Origin of large piezoelectricity in BF-BT based multiphase ferroelectrics

Bismuth ferrite-barium titanate (BF-BT) based ferroelectrics with multi-phase coexistence exhibit promising piezoelectricity, while whose physical mechanism of property enhancement is poorly understood. In the present work, the Rayleigh law, in-situ electric field dependent synchrotron X-ray diffraction and ex-situ piezo-response force microscopy were utilized to gain insight into the property and structure evolution characteristics under electric fields. Extrinsic contribution from domain wall motion was regarded as the major determiner in piezoelectricity of the 0.69Bi1.05Fe0.99Sc0.01O3-0.3BaTiO3-0.01Bi1.05(Zn0.5Hf0.5)O3 ferroelectrics with rhombohedral and pseudo-cubic phase coexistence, different from those proposed structural origins in BF-BT based relaxor ferroelectrics (with high BT content) with large strain response. By analyzing the property discrepancy between unpoled and poled samples, the enhanced polarization and electro-strain in poled ceramics were attributed to the activated domain state induced by the direct current pre-poling.

Fatigue Test on Heavy Haul Railway Tunnel Bottom Structure With Base Cavity

The presence of a base cavity will degrade the bearing capacity of tunnel bottom structures, and will also have a noteworthy impact on its fatigue performance. In order to study the fatigue performance and cumulative damage to tunnel bottom structure, a series of bending fatigue tests are conducted by reference to a heavy haul railway tunnel with a base cavity. Through the tests, fatigue evolution characteristics of tunnel bottom structure with cavity are obtained, then based on the expression of S-N curves, a non-linear fatigue cumulative damage model is therefore proposed, the deflection evolution and cumulative damage evolution can be divided into three stages, and characterized with an “s-shaped” curve. The tests results reveal that the damage to the tunnel bottom structure develops rapidly when a cavity exists in the base rock, fatigue occurs more easily, and the fatigue life of specimens decreases with the increase of the stress level and cavity width.

Sequential surface passivation for enhanced stability of vapor-deposited methylammonium lead iodide thin films

Understanding the correlation between surface passivation and degradation kinetics in vapor-deposited organic–inorganic hybrid perovskite thin films is crucial for developing strategies to enhance their structural integrity for long-term operational stability. Here, we demonstrate that the sequential introduction of vapor-phase phenethylammonium iodide (PEAI) and methylammonium (MAI) into methylammonium lead iodide (MAPbI3) thin films, which is obtained from PbI2, suppresses their degradation and enhances the ambient stability. Compared with the simultaneous PEAI introduction during the conversion of PbI2 to MAPbI3, the MAPbI3 films with sequential treatment exhibited higher PEAI surface coverage, which imparts superior resistance to degradation. Combined analyses of the exposure-time-dependent crystal structure evolution, photoemission profiles, and photocurrent generation characteristics of the films reveal that conformal PEAI passivation suppresses the volatile release of methylammonium (MA) species and the inclusion of O2/H2O molecules. This study highlights the importance of developing a vapor-phase passivation strategy for innate polycrystalline perovskite thin films and their optoelectronic applications with long-term stability.

Release characteristics of AAEMs and physicochemical structural evolution of char during rapid coal pyrolysis

Rapid pyrolysis experiment of Zhundong coal was conducted in a high-frequency furnace to investigate release characteristics of alkali and alkaline earth metals (AAEMs) and its correlation with changes of physical and chemical properties of char. Residence time and atmosphere during pyrolysis were important process parameters that affected the migration characteristics of AAEMs and physicochemical structural evolution of char. Experimental results show that the release of AAEMs in coal char increases over time. The maximum release rate of Na, Mg and Ca is 61.05%, 64.47%, and 44.01%, respectively. Promoting effect of CO2 on release of Na mainly occurs in the initial stage of rapid pyrolysis, nevertheless the promoting effect on release of Mg and Ca mainly is in the middle and late stage. CO2 accelerates release of AAEMs by promoting release of volatiles, facilitating decomposition of oxygen-containing functional groups and aliphatic functional groups, and promoting formation of cracks on surface of coal char.

Study on the stability of foamed gel and its structural evolution characteristics

ABSTRACT Foamed gel is an efficient material for coal spontaneous combustion prevention and control, which effectively combines the fire prevention and extinguishing properties of foam and gel. In this paper, the formation principle, structural evolution, stability, and fluidity of foamed gel are elaborated. Foamed gel is mainly formed by foaming agent, cross-linking agent and water through physical foaming and gelling reaction, and its formation process is divided into two stages: the first stage is physical foaming and forming foam; the second stage is adding cross-linking agent to foam and generating foamed gel through gelling reaction. The first stage of foamed gel mainly reflects the fluidity and stacking of foam, and in the second stage, with the increase of gel amount, foamed gel reflects the temperature resistance of gel. The basic structure of the foamed gel is the same as that of the water-based foam, and the gel particles constitute the basic skeleton of the foamed gel, which slows down the gravitational drainage and foam disproportionation rate. The evolution process of foamed gel structure includes liquid film rupture, gel formation and skeleton collapse, which eventually forms a gel layer to fill the residual coal fissure. The flow of foamed gel in the mining area is subject to the combined effect of grouting pressure, gravity and resistance, and the lateral flow velocity is larger than the longitudinal flow velocity, and the contour line of its diffusion front peak is ellipsoidal.

Evolution of Microstructure during Rapid Solidification of SiC under High Pressure

The microstructure evolution of liquid silicon carbide (SiC) during rapid solidification under different pressure values is simulated with the Tersoff potential using molecular dynamics. The structure evolution characteristics of SiC are analyzed by considering the pair distribution function, bond angle distribution, coordination number, and the diagrams of the microstructure during rapid solidification. The results show that the average energy of atoms gradually increases with pressure. When the pressure reaches 100 GPa, the average energy of the atom is greater than the average energy of the atom in the initial liquid state. Under different pressures, the diffusion of atoms tends to remain stable at a temperature of about 3700 K. The application of pressure has a major impact on the arrangement of atoms, except on the third-nearest neighbor, while the impact on the nearest neighbor and the second-nearest neighbor is relatively small. The pressure increases the medium-range order of the system. The coordination numbers of Si and C atoms gradually decrease with the decrease in temperature and increase in pressure. Pressure changes the microstructure of the SiC amorphous system after solidification, and the density can be increased by adjusting the coordination number of atoms. As the pressure increases, the SiC amorphous system exhibits a dense structure with coordination numbers of 4, 5, 6, and 7.

Structural Evolution and Motion Characteristics of a Hard Roof During Thickening Coal Seam Mining

This study combined theoretical analysis, physical simulation, and numerical simulation to discuss the influences of the structural evolution and motion characteristics of a hard roof during thickening coal seam mining on working face pressure. Results showed that during the mining of the thickening coal seam with a hard roof, the settlement curve of low-level strata was a stepwise wave slope, and the settlement curve of high-level strata shifted from a “V-shaped” distribution pattern to a parabola under the full mining of the coal seam. When the mining thickness was relatively small, the mining space expanded with the increase in mining thickness due to the “masonry beam” structure formed by the low-level, sub-critical overlying strata. The low-level critical strata formed a “composite cantilever beam” structure with a hard immediate roof after advancing into the caving zone. After complete recovery, the overlying strata were in a steady-movement state, and the plastic failure zone of the overlying strata of the thickening coal seam presented obvious distribution characteristics of longitudinal and transverse partitions. This study provides theoretical reference for coal seam mining under similar geological conditions.

Pore Structure Evolution and Seepage Characteristics in Unclassified Tailing Thickening Process

The tailing paste thickening technology was investigated to achieve goaf reduction treatment and tailing resource utilization of metal mines and reach the effect of controlling two hazards with one waste. However, superfine tailing particles could easily form suspended water-locking flocs in the thickening process, which seriously affected the increase in the underflow concentration in the thickener. Undisturbed compression-stage bed samples were extracted using an in situ sampling method through a continuous dynamic thickening experiment. Then, the morphologies and geometrical structures of micropores were analyzed through high-precision computed tomography scanning. Subsequently, the influences of the shear evolution of pore structure and seepage channel on the dewaterability of underflow slurry were explored by combining Avizo software and 3D reconstruction technology. The thickening and dewatering mechanism of underflow slurry was also revealed. Results showed that under the shear action, the flocs were deformed and compacted, forming a high-concentration underflow. On this basis, the original micropores were extruded, deformed and segmented. Moreover, many loose micropores were formed, the connectivity became poor and the total porosity declined. The diameter of the water-conducting channel in the sample was enlarged because of the shear force and the seepage effect improved. The maximum flow velocity inside the pores was 1.537 μm/s, which was 5.49% higher than that under the non-shear state.

Superconductivity in In2Te3 under Compression Induced by Electronic and Structural Phase Transitions.

Indium telluride (In2Te3) is a typical layered material among III-IV families that are extremely sensitive to pressure and strain. Here, we use a combination of high-pressure electric transport, Raman, XRD, and first-principles calculations to study the electronic properties and structural evolution characteristics of In2Te3 under high pressure. Our results reveal the evidence of isostructure electronic transitions. First-principle calculations demonstrate that the evolution of phonon modes is associated with the transition from semiconductor to metal due to the increase in the density of states near the Fermi level. The pressure-induced metalization as a precursor monitors the structural phase transition, and then the superconductivity is produced. Further, in decompression, Tc slightly increased and remained at 3.0 GPa, and then the disorder is present and the superconductivity is suppressed. Our work not only perfects the superconducting phase of the In-Te system under pressure but also provides a reference for further superconducting research and applications.

Experimental Study on the Effect of Large Temperature Difference on Compressive Strength and Pore Structure of Semirigid Base

Understanding the evolution of mechanical properties and pore structure of semirigid base under large temperature difference is of great significance for evaluating the durability and safety of semirigid base structure and studying the damage cracking mechanism and prevention technology of semirigid base induced by large temperature difference climate. This paper studies the variation law of peak stress and dynamic modulus, the evolution characteristics of pore structure, and the pore size distribution of semirigid base after different cycles at different temperature intervals. Based on the analysis of peak stress and dynamic modulus test results, the degradation effect of freeze‐thaw environment (−20°C∼20°C) on semirigid base is far greater than that of high‐temperature environment (20°C∼60°C) and low‐temperature environment (−5°C∼−30°C). There are significant decreases in peak stress and dynamic modulus of semirigid base in the late cycle (12 to 15 cycles). Under low‐temperature and freeze‐thaw environments, the axial load resistance of semirigid base is significantly correlated with the deformation resistance, and the correlation between the two is not significant under high‐temperature environment. The variability of the thermal expansion and contraction characteristics of the internal microscopic phases of the semirigid base and the force characteristics of the pore interface phases are the root causes of the damage and cracking of the pavement base in a large temperature difference climate.

Characteristics of Pore Structure Evolution of Spent Fcc Catalyst and its Effect Mechanism on Regeneration at Different Atmospheres

Characteristics of Pore Structure Evolution of Spent Fcc Catalyst and its Effect Mechanism on Regeneration at Different Atmospheres