Pore Structure Distribution Research Articles

Study on Influence Mechanism of Short-Cut BF Dispersion Morphological Behavior on Concrete Properties Based on Meso Scale.

The orientation, distribution, and contact point density of BF (basalt fiber) in the concrete matrix play significant roles in the mechanical properties of BF concrete, but represent a weak point in current research. It is meaningful to study the morphological characteristics of BF in concrete. In this study, the transparent model test and joint blocking method were innovatively adopted to investigate the correlation of dosage with the BF morphological parameters and concrete mechanical properties. A focus on a BF dosage of 0–7.5 kg/m3 and the contribution index of fibers Cf was defined. Furthermore, NMR and CT techniques were used to observe the changes in the microstructure of BF concrete. The experimental results show that the BF contribution index Cf reaches the largest value when the BF content is around 3 kg/m3, approximately 2.7; in this case, the mechanical properties of BF concrete were also optimal, and the Cf was only 2.34 when the BF content was 7.5 kg/m3. NMR and CT test results show that there is a strong correlation between the BF morphological parameters and the distribution of pore structure in the concrete matrix. The overlapping contact of BF clusters led to the penetration of pores, which led the macro-pore proportion to increase dramatically. The increase in the macro-pore proportion is the main reason for the deterioration in concrete performance. In addition, these macro-pores may have adverse effects on the chloride ion permeability of BF concrete.

Relationship Between Microscopic Pore Structure and Strength of Cement-Based Materials with Low Water-Binder Ratio Under Sulfate Attack Environment

In this paper, the mass loss test, relative dynamic elasticity modulus test, compressive strength test, thermogravimetric analysis (TGA-DTG), and mercury intrusion porosimetry (MIP) were used to study the performance of cement-based materials with low water-binder ratio after sulfate attack, and the influence of microsilica dosage and erosion period on the performance was also investigated. The results indicate that the microsilica mixed can improve the macro-properties of cement-based material with low water-binder ratio after sulfate attack, and as the microsilica dosage is increased, the improvement effect tends to decrease after an increase, while the microsilica dosage is 15%, all performance indexes are the best. This study also demonstrates that the microsilica dosage could affect the mass percent and pore structure distribution of the hydration products of cement-based materials with low water-binder ratio after sulfate attack, and different pore structure distribution may have impact on compressive strength of cement-based materials. Besides, we established relation models for the influence of capillary pores’ and gel pores’ proportion on the compressive strength of cement-based material after sulfate attack, and concluded that there was no interaction between the impacts of two pore types on compressive strength.

Evaluation of Gas Adsorption in Nanoporous Shale by Simplified Local Density Model Integrated with Pore Structure and Pore Size Distribution.

Simplified local density (SLD) model has been widely used to describe the gas adsorption behaviors in porous media. However, the slit pore geometry and constant pore width associated with the SLD model may fail to represent the heterogeneous pore network structure in shale. In this study, a new method to integrate the SLD model with the slit and cylindrical pore structures as well as the pore size distribution (PSD) is proposed and validated by the grand canonical Monte Carlo (GCMC) simulations and the experimentally measured adsorption of methane on shale with complex pore network. Comparison results show that reasonably good agreement is achieved between the SLD model and GCMC simulations for both the gas adsorption isotherms and discrete-density profiles in multiwalled carbon nanoslit and nanotube. The corresponding average absolute percentage deviations (% AADs) are below 0.3 and 9.3 for gas adsorption isotherm and discrete-density profile, respectively. In addition, the SLD model coupled with the PSD of slit and cylindrical pores ranging from micro- to macropores properly characterizes the measured excess adsorption of methane on Wolfcamp shale core sample with % AADs between 1.7 and 3.6. It is found that when the pore volume is fixed, the gas adsorption isotherm and gas density profile are heavily dependent on the pore geometry and pore size. Furthermore, integrating the PSD into the SLD model can guarantee the valid identification of the adsorbed- and free-gas regions in flow channels with different sizes based on the gas density profiles. The findings of this study shed light on the effects of pore structure on gas adsorption in nanopores and enable us to precisely evaluate and predict the gas adsorption behaviors in slit and cylindrical pores over a wide range of pore sizes.

Synthesis of Hierarchical Porous SAPO-34 and Its Catalytic Activity for 4,6-Dimethyldibenzothiophene.

Zeolite SAPO-34 has been widely used in the industry because of its special pore structure and wide distribution of acid sites in the pore channel. However, traditional SAPO-34 with a small pore size suffers from carbon deposition and deactivation in catalytic reactions, and its inability to catalytically convert bulky organic molecules limits its industrial application. Meanwhile, impurities of SAPO-5, which have weak acidity leading to rapid catalyst deactivation, appear in SAPO-34 zeolite. Therefore, it is of great significance to synthesize SAPO-34 zeolite with a mesoporous pore structure, which can significantly improve the transfer of molecules in zeolites. In this paper, SAPO-34 zeolite with a hierarchical pore structure was synthesized, and its hydrodesulfurization performance for 4,6-dimethyldibenzothiophene (4,6-DMDBT) was studied in a fixed bed reactor. The characteristic results show that BET-specific surface area, micropore volume, and mesoporous volume of synthesized SAPO-34 are 754 m2 g−1, 0.25, and 0.23 cm3 g−1 respectively, and the pore size is mainly concentrated at 4 nm. The catalytic conversion of 4,6-DMDMT with Co- and Mo-supported SAPO-34 is about 83%, which is much higher than the catalytic performance of Al2O3.

A modified nuclear magnetic model for characterizing the fluid signal response in hydrocarbon bearing rocks

The nuclear magnetic resonance (NMR) technique is a crucial means for formation evaluation. It can provide an accurate set of formation parameters in single-phase-flow reservoirs, such as porosity, permeability, and pore structure distribution; however, in most cases, there are hydrocarbon-water two-phase fluids in the reservoirs. The secondary change of the T2 distribution makes the accuracy of the evaluation a challenge. Hence, it is necessary to clarify the impact of changes in hydrocarbon content on the response of NMR signals before using the traditional evaluation methods. In this paper, we analyzed the response mechanism of NMR T2 distribution under different saturation conditions. Based on the theoretical derivation, we established a nuclear magnetic model that describes the relation among the T2 geometric mean value of water signal, hydrocarbon signal, and water saturation. The accuracy of each model part was verified by numerical simulation. In addition, the calculation results in core samples show that the proposed model is more effective and reliable than two existing models (the T2 saturation ratio model and the Xiao empirical model), especially in extreme conditions (irreducible water and hydrocarbon saturated samples). Finally, we applied the proposed model to field application in the Tertiary formation in the Bohai Bay Basin, China, which achieved good effects in the NMR fluid substitution and the NMR saturation evaluation.

Nitrogen-doped hierarchically porous carbon obtained via single step method for high performance supercapacitors

In the present work, nitrogen doped hierarchically activated porous carbon (APC) samples have been synthesized via single step scalable method using ethylene di-amine tetra acetic acid (EDTA) as precursor and KOH as activating agent. Activated porous carbons with different pore sizes have been developed by varying the activation temperature. SEM, TEM and SAXS analysis suggest that with variation of activation temperature, a hierarchical porous structure with interconnected meso-pore and micro pores has been achieved. The sufficiently high surface area of the synthesized materials provides active sites to enhance the diffusion of ions between the electrolyte and the carbon electrodes. The electrode prepared at 800 °C activated sample exhibited highest specific capacitance of 274 Fg-1 in two electrode setup, at a current density of 0.1 Ag-1 in 1 M aqueous H2SO4. Along with this, it showed maximum energy density of 9.5 Whkg−1 at a power density of 64.5 Wkg-1. The remarkable electrochemical performance reveals that the synthesized nitrogen doped activated carbon electrodes derived from EDTA can be tuned to have optimum pore structure and pore size distribution for better electrochemical performance, so it can be considered as a potential electrode material for applications in electrochemical energy storage.

Experiments and phase-field simulation of counter-current imbibition in porous media with different pore structure

Spontaneous imbibition is relevant to many processes in nature and industry. In this work, the effect of pore structure of porous media on counter-current imbibition is studied. The one-dimensional counter-current imbibition experiments were conducted in packed porous media with different pore structure. Experimental results showed that counter-current imbibition can only proceed for a short time in homogeneous porous media for all fluids. In heterogeneous porous media, counter-current imbibition can only proceed a short time for water–air experiments as well. However, imbibition can proceed continuously until the imbibition front reaches the end of packed porous media for water–oil experiments and the mass of water infiltration is proportional to the square root of time. The efficiency of water infiltration behind the imbibition front decreases with increase in viscosity of non-wetting phase fluid. In addition, the numerical simulation of counter-current imbibition in porous media with different pore structure were conducted using phase-field method. Simulation results showed that very little oil was produced in homogeneous porous media and more oil was produced in heterogeneous porous media. It is indicated that the difference between capillary driving pressure and capillary back pressure, which are closely related to pore structure and pore size distribution of porous media, has important influence on counter-current imbibition. Furthermore, the snap-off of oil or gas production channels in narrow pore throats may lead to termination of imbibition when the water saturation behind the imbibition front is higher.

Electrospun carbon nanofibers from PAN and a loose medium component of coal as binder-free electrodes for supercapacitors

BackgroundDespite the significant progress of co-spinning strategy to prepare 1D hierarchical porous carbon nanofibers, reducing raw material cost and improving specific surface area (SSA) utilization ratio still needs further improvement. MethodsThe binder-free and flexible carbon nanofibers (CNFs) are fabricated using a blend of polyacrylonitrile (PAN) and a loose medium component (LMC) of coal via electrospinning, followed by pre-oxidation and carbonization process. Significant findingsLMC, an effective pore-enhancing modifier for CNFs, can increase pore volume and improve electrochemical performance while retaining the basic characteristics of good pore structure and pore size distribution (PSD). The prepared materials have higher SSA utilization, mainly due to the dominant pore distribution of 0.9 nm and the special fibrous properties, which are different from ordinary porous carbon. The supercapacitor electrodes prepared from LCNF3 possess a high specific capacitance (227.4 F g−1 at 1 A g−1) and outstanding cycling stability (104.3% capacitance retention after 10,000 cycles). This work provides a new perspective for increasing the pore volume of CNFs prepared by electrospinning and realizing coal's high value-added utilization.

Relationship between fractal feature and compressive strength of concrete based on MIP

Concrete is a heterogeneous, multiphase, and multilayer composite system with extremely intricate microscopic pore structure. The structural characteristics of microscopic pore of concrete are closely related to its mechanical properties and durability. The pore structure of concrete with various strength grades (C10-C150) was analyzed by Mercury intrusion porosimetry (MIP) from the aspects of pore diameter distribution, pore volume, pore specific surface area and fractal feature. The Menger sponge model was used to calculate the fractal dimension of different pore regions in each test group, and the most suitable pore fractal region was selected to establish the mathematical model between fractal dimension and compressive strength. The results showed that all fractal curves are divided into four segments according multi-fractal characteristic of concrete, namely Region I, Region II, Region III and Region IV. Region I is macropores fractal region (d = 10 μm ∼ 950 μm), representing the packing patterns of hydrated cement grains, while Region II - Region Ⅳ is micropores fractal region (d = 0.0064 μm ∼ 10 μm), reflecting mainly the microstructure of C-S-H hydrates. Region I and Region Ⅳ exhibit obvious fractal features and the fractal dimension D is between 2 and 3. However, the fractal dimension D > 3 in Region II and Region III, which are nonphysical from the point of view of surface geometry. The fractal dimension can clearly describe the internal pore characteristic, and it is a real good correlation with the most probable pore diameter and the pore specific surface area. Moreover, the mathematical model between the fractal dimension and the compressive strength both accords with the positive power exponential function in Region I and Region IV. The fractal dimension can be viewed as a comprehensive parameter of pore shape and spatial distribution of pore structure, which can more accurately represent the relationship between the microscopic pore structure features and compressive strength of concrete. In practical engineering, it serves to realize the damage detection of concrete on site.

Silver Mesoporous Silica Nanoparticles: Fabrication to Combination Therapies for Cancer and Infection.

The integration of silver nanoparticles (Ag NPs) with mesoporous silica nanoparticles (MSNs) protects the former from aggregation and promotes the controlled release of silver ions, resulting in therapeutic significance on cancer and infection. The unique size, shape, pore structure and silver distribution of silver mesoporous silica nanoparticles (Ag-MSNs) embellish them with the potential to perform combined imaging and therapeutic actions via modulating optical and drug release properties. Here, we comprehensively review the recent progress in the fabrication and application of Ag-MSNs for combination therapies for cancer and infection. We first elaborate on the fabrication of star-shaped structure, core-shell structure, and Janus structure Ag-MSNs. We then highlight Ag-MSNs as a multifunctional nanoplatform to surface-enhanced Raman scattering-based detection, non-photo-based cancer theranostics and photo-based cancer theranostics. In addition, we detail Ag-MSNs for combined antibacterial therapy via drug delivery and phototherapy. Overall, we summarize the challenges and future perspectives of Ag-MSNs that make them promising for diagnosis and therapy of cancer and infection.

Coupling mechanism and parameter optimization of sewage sludge dewatering jointly assisted by electric field and mechanical pressure

Pressurized electro-dewatering technology is considered to be one of the most effective methods for improving dewatering performance of sewage sludge. In this paper, four dewatering protocols were developed to further explore the coupling mechanism of sludge dewatering through mechanical pressure, electric field and their joint. The results showed that the dewatering performance of the four dewatering protocols were as follows: pressurized electro-dewatering with constant voltage gradient mode (G-PEDW) > first mechanical dewatering then electro-dewatering > mechanical dewatering > electro-dewatering. The coupling mechanism was revealed from the perspectives of pore structure and moisture distribution of sludge cakes. The pore structure was discussed in detail from the whole pore size distribution and fractal dimension. The fractal dimension could quantitatively describe the change of pore structure. The moisture distribution was analyzed by the thermogravimetric differential scanning calorimetry test. The results showed that the electric field could reduce bound strength of moisture and produce new micro-pores to build more water flow paths, the water was discharged through interior capillary channels, and mechanical pressure could accelerate the water removing process. Response surface method was used to establish an empirical prediction model of G-PEDW, and discussed the selection of optimal parameters. The R-square values of mathematical models of moisture content and energy consumption were as high as 0.9863 and 0.9838, respectively, which was more advanced than other mathematical models. Experiments showed that G-PEDW could reduce the time to 20 min or reduce the energy consumption to 7.1 Wh/kg•H2O when the target moisture content was set to 41.7%.

The Law and Mechanism of the Sample Size Effect of Imbibition Oil Recovery of Tight Sedimentary Tuff.

Imbibition is an important mechanism to improve the recovery factor (RF) of a tight oil reservoir. Accurately evaluating the oil production capacity of tight oil reservoirs by imbibition is of great significance for the formulation of oilfield production plans and productivity prediction. However, there is currently no unified regulation on the selection of rock sample size in tight oil reservoir imbibition evaluation experiments, resulting in great differences in reservoir imbibition oil production capacity obtained from rock samples of different sizes, which brings great challenges to the efficient development of tight oil reservoirs. To clarify the law and mechanism of the rock sample size effect of tight core imbibition oil recovery, this paper takes the newly discovered tight sedimentary tuff (TST) oil reservoir as an example. First, several representative real cores were collected. Then, their wettability and pore structure characteristics were analyzed. Finally, physical simulation experiments of imbibition under different rock sample sizes were conducted. The results show that the TST has very favorable imbibition conditions, which are manifested in the following: (i) the wettability is weakly hydrophilic to hydrophilic; (ii) the mineral composition is tuffaceous minerals, calcite, and quartz, without clay minerals; (iii) micro-nanoscale pores are developed; and (iv) the pore throats are evenly distributed. In the imbibition experiments of rock samples of different sizes, the oil production characteristics of the core surface, the variation form of imbibition rate, pore production characteristics, and the influence mode of imbibition pressure on imbibition do not have the sample size effect. However, the RF of the spontaneous imbibition has an obvious sample size effect, and there is a good exponential function relationship between the imbibition RF and the specific surface area (SSA) of cores. The fundamental reason why the rock sample size effect of the TST imbibition oil recovery is relatively stable and has strong regularity is that its pore structure and wettability are relatively homogeneous and stable. The change of rock sample size does not have a great impact on the distribution of the core pore structure and wettability, resulting in no significant change in its imbibition power, resistance, and distance. Therefore, the main factor determining the imbibition RF of rock samples with different sizes is their SSA. The research results of this work can provide an important theoretical basis for understanding the law and mechanism of TST imbibition oil recovery and unifying the imbibition experimental results of small-sized rock samples.

Pore structure and fluid distribution of tight sandstone by the combined use of SEM, MICP and X-ray micro-CT

Tight reservoirs contain considerable hydrocarbon resources, which are characterized by complicated pore structure and heterogeneous fluid distribution in the pore network. In this study, a tight sandstone sample from the Lucaogou Formation in the Jimsar Sag was selected for the characterization of pore structure and two-phase (brine and oil) flow experiment. Interparticle and intraparticle pores were identified and quantified by direct image analyses. Intraparticle pores, commonly smaller than 1 μm, were the dominant contributor of surface area, whereas interparticle pores contributed considerably to pore volume with minor quantity. Pore network model of the selected sample was featured by large pore throat ratio, which was also verified by low efficiency of mercury ejection (≈1.66%). The flow potential of tight reservoir was dominantly controlled by pore-throats with a diameter larger than 2 μm. Based on the results of pore-scale micro-CT flow experiments, the configuration of oil clusters in the pore space was categorized into singlet, multiple, branched and network. The size of oil clusters ranged over five orders of magnitude (10 μm3 – 106 μm3), which followed a power-law distribution. The displacement process of water by oil in the pore space of tight sandstone was controlled by pore structure and external driving force. The well-connected pore network mainly composed of large interparticle pores was the preferential flow path, and a high proportion of singlet oil clusters was attributed to high aspect ratios of the pore network. As the external driving force increased, convergence and divergence of oil flow occurred simultaneously in the pore network. The displacement process of water by oil was suggested as a cooperative pore-filling event.

Dynamic characteristics and microstructural study of nano calcium carbonate modified cemented soil under different salt water solutions

Cemented soil is a cement slurry mixed with soil to form a solidified body, which is usually used in the foundation treatment of large projects such as coastal ports and terminals, airport runways, artificial islands around the sea etc. These infrastructures are commonly exposed to seawater environment, which usually has high corrosive environment and may pose severe deterioration of the cemented foundation. To address these issues, in the present study, nano calcium carbonate (CaCO3) is proposed to improve the engineering properties of cement soil. Nano CaCO3 is an ultrafine solid powder material with particle size between 0.01 and 0.1 μm. To verify the improvement effect of nano-CaCO3 on the dynamic properties and corrosion resistance of nano-CaCO3 modified cemented soil, a series of dynamic triaxial tests were conducted on a medium-scale true triaxial apparatus equipped with a cyclic loading device. In addition, nuclear magnetic resonance (NMR) tests and scanning electron microscopy (SEM) tests were conducted to reveal the microstructural mechanism of CaCO3 nanoparticles on the improved cemented soil. The results of the dynamic triaxial tests showed that the small strain elastic modulus of nano-CaCO3-modified cemented soil increased by 14.3–16.5% compared to the control specimens at the same salt content and cured for 28 days. NMR study confirmed that C-S-H gel grew with nano-CaCO3 at the nucleus, number of small and large pores of the nano-CaCO3-modified cemented soil were reduced as compared to the controlled specimens. The photographs obtained from the SEM test of the nano-CaCO3 modified cemented soil matches with the pore structure distribution measured by NMR test. The present study provides very conclusive evidence that nano CaCO3 is a very useful ingredient to improve the dynamic characteristics of the clay soil exposed to sea water environment.

Optimization on the gradually varied pore structure distribution for the irradiated absorber

An optimization method for the gradually varied porous absorber is proposed. The Monte Carlo Ray Tracing method based on the acceptance-rejection sampling is established to obtain the absorption distribution of irradiation in the gradually varied porous absorber. The fluid flow, convection, and thermal radiation in the porous absorber are evaluated. Combined with the genetic algorithms, the distribution of porosity and pore size of the porous absorber could automatically adjust to match the non-uniform radiation flux in both radial and axial directions. Moreover, the internal flow layout could be regulated by an optimized radial pore distribution that directs more fluid enters the high heat flux zone. The optimization results demonstrate that the gradually varied porous absorber with porosity ranging from 0.95 to 0.90 and pore size ranging from 2.5 mm to 1.5 mm could achieve high thermal efficiency and low flow resistance. Compared with the standard model of the uniform porous absorber, the thermal efficiency of the optimal gradually varied porous absorbers could be further increased by 1.23%–9.76%, while the pressure drop could be reduced by 7.88%–55.73%.

The Effect of Density on the Delicate Balance between Structural Requirements and Environmental Issues for AAC Blocks: An Experimental Investigation

Among other construction materials, Autoclaved Aerated Concrete (AAC) offers several advantages to face the pressing need to build more sustainable and energy-efficient buildings. From the building side, the low thermal conductivity of AAC allows the realization of energy-efficient building envelopes, with interesting savings in terms of heating and cooling processes. The equilibrium between structural performances (related to safety issues) and energy efficiency requirements is, however, very delicate since it is strictly related to the search for an “optimum” material density. Within this context, this work discusses the results of wide experimental research, showing the dependency of the most important mechanical properties (compressive strength, elastic modulus, flexural strength and fracture energy) from density, as well as the corresponding variation in thermal conductivity. In order to identify the better compromise solution, a sort of eco-mechanical index is also defined. The big challenge for future researches will be the improvement of this eco-mechanical index by working on pore structure and pore distribution within the material without significantly reducing the density and/or by improving the strength of the skeleton material.

Moduli variations in two-phase fluid rocks considering squirt flow and patchy saturation

The complex pore structure and fluid distribution in underground rocks bring difficulties to rock physics modeling and reservoir interpretation. The existence of cracks and ellipsoidal pores will cause squirt flow during wave propagation, and the fluid may be present as patchy saturation. By considering the effects of both squirt flow and patchy saturation, a new rock physics model is proposed. The fluids in inclusions include a soft fluid such as gas and a stiff fluid such as water. The novelty is that an explicit expression of patch saturation with frequency is introduced. Thus, the proposed model is helpful to analyze the variations of moduli with frequency caused by squirt flow and patchy saturation simultaneously. By comparison, the proposed model matches well with existed boundary models and covers all possible behavior of the moduli. Then, variations in moduli with water saturation and frequency are analyzed in detail, as well as the impact of patchy saturation on the attenuation induced by the squirt flow. The analysis shows that a small amount of gas contained in inclusions can cause a large change in moduli, especially the bulk modulus. The effect of patchy saturation on the moduli increases with the increasing frequency and when the frequency is low, the effect only occurs at very high water saturation. Besides, at high water saturation, the squirt flow can cause a sharp change in bulk modulus. The proposed model is helpful for understanding wave propagation in partially saturated rock with cracks.

Integration of NMR and NMRC in the Investigation of the Pore Size Distribution of Tight Sandstone Reservoirs: A Case Study in the Upper Paleozoic of Dongpu Depression

Exploring appropriate methods to understanding the pore structure and overall pore size distribution (PSD) of tight sandstone reservoir is important for evaluating the quality of the reservoir. An integration analysis comprising X-ray diffraction (XRD), three beams of argon ion (TIB) polishing approach, scanning electron microscopy (SEM), high-pressure mercury intrusion (HPMI), nuclear magnetic resonance (NMR), and nuclear magnetic resonance cryoporometry (NMRC) was applied to determine the pore structure of the tight sandstone reservoirs in the Upper Paleozoic of Dongpu Depression as well as their relationship with the physical properties of the reservoirs. NMRC offered the possibility to obtain the nanoscale (4-1400 nm) pore structure of the reservoirs directly and accurately. Therefore, an attempt by combining NMRC and NMR can reveal the PSD of tight sandstone reservoirs with different pore structures. The results showed that the tight sandstone reservoirs consisted of intergranular, intragranular, and intercrystalline (clay mineral) pores. The full PSD intelligibly showed pore structure characteristics of four different types of reservoirs, with pore sizes ranging from 2 nm to dozens of microns. Specifically, the overall PSD of type I reservoirs showed a broad unimodal distribution pattern with the peaks in the range 0.1–2 μm, indicating an association with dissolution intergranular pores, and for type II reservoirs, the overall PSD showed a bimodal distribution pattern, with their left and right peaks, in the ranges 0.004–0.01 μm and 0.15–0.4 μm, respectively, showing similar amplitudes, implying the predominance of both intergranular (mesopores) and intergranular (macropores) pores. The full PSDs of type III and IV reservoirs showed much lower amplitudes than type I and II reservoirs, indicating a lower pore number and a complex pore structure. Furthermore, NMRC also demonstrated that different diagenesis resulted in a correlation between pore structure and reservoir physical properties.

Design and Preparation of Lotus Root Knot Hierarchical Porous Carbon by Highly Efficient Chemistry Activation for Electric Double Layer Capacitors

AbstractIn this work, utilizing lotus root knot as raw material, nitrogen and oxygen co‐doped hierarchical porous carbon with appropriate heteroatom doping, multi‐connected 3D pore structure and suitable pore size distribution were produced by carbonization and chemical activation step. The maximum specific surface area the biochar material reached was 3659 m2 g−1. These physical properties exhibit ultrahigh specific capacitance of up to 454.3 F g−1 in a supercapacitor of the three‐electrode system under the current density of 1 A g−1 and a capacitance retention rate of 81.5 % within the range of 1∼10 A g−1. Furthermore, the specific capacitance is maintained at 91.5 % of the initial value in a two‐electrode system after 10,000 cycles. In a two‐electrode system with tetraethylammonium tetrafluoroborate (TEABF4)/acetonitrile (ACN) solution as the electrolyte. The voltage window attained was 3 V with high energy density of 51.4 Wh kg−1 under the power density of 750 W kg−1. These results show that the assembled supercapacitors provide excellent energy and power density at the same time.

Effect of meso-structure on thermal conductivity of deep granite

In order to study the correlation between meso-structure and thermal conductivity of deep rocks at high geo-temperature, the thermal physical tests were carried out on the granite samples in the depth of 1500m to 2000m in Sanshandao, firstly, the polarizing microscope was used to test the micro characteristics, the nuclear magnetic resonance was used to test the distribution of pore structure, finally, the heat transfer characteristics of dry and wet rock in medium and high temperature environment are obtained by using transient plane source method, The influence of external environment and meso-structure of rocks on thermal conductivity was discussed. The results show that the denseness, porosity, pore size distribution, the way of connection, quartz content between mineral particles and the degree of claying directly will affect the thermal conductivity of rock, among which the denseness and claying have the greatest influence on the thermal conductivity compared to other factors. The results of drying and watering cycle at 60°C test show that the damage of rock internal structure caused by temperature cyclic load can not to be ignored, which can change the thermal conductivity of rock, the increase of pore water content after water saturation treatment enhances the heat transfer performance of rock. The research results provide a data basis and new insights on the thermal conductivity of deep fragmented granite under high geo-temperature and high hydraulic conditions.