Large Number Of Pores Research Articles

Investigation on the microscopic damage mechanism of fracturing fluids to low-permeability sandstone oil reservoir by nuclear magnetic resonance

Hydraulic fracturing has become an essential stimulation treatment for improving the development efficiency of low-permeability oil reservoirs. However, fracturing fluid inevitably causes reservoir damage. This study proposed a combined method of microscopic and macroscopic experiments to investigate the nature of formation damage of fracturing fluid by quantifying its influence on porosity, permeability, and pore structure. Nuclear magnetic resonance technology combined with core flooding test and parallel sample comparison method was applied to quantitatively evaluate the damage degree and identify the main damage types of hydroxypropyl guar (HPG) fracturing fluid and slickwater fracturing fluid. The microscopic damage mechanisms of these fracturing fluids were analyzed by thin section petrography, X-ray diffraction, rate-controlled mercury intrusion, scanning electron microscopy, and wettability tests. The results show that the total permeability damage degree of HPG fracturing fluid filtrate is 30.43%, of which water sensitivity, water lock, and macromolecule adsorption account for 6.06%, 23.26%, and 1.11%, respectively. Water lock is the major damage factor. Regarding the damage of slickwater fracturing fluid filtrate, water sensitivity causes the severest damage, corresponding to 39.08% of core permeability loss, whereas macromolecule adsorption and water lock contribute 13.21% and 0.97%, respectively. Water sensitivity damage causes reduced porosity, decreased permeability, and narrower pores, resulting from hydration, swelling, dispersion and migration of clay minerals. Water lock damage increases the movable pore volume, decreases the permeability, increases the pore radius, decreases the throat radius, and increases the pore throat ratio, which increases the flow resistance to the oil phase. The magnitude of water lock damage is closely related to the surfactant content and performance, rock wettability, and pore throat radius ratio. Macromolecule adsorption damage leads to a decrease in permeability, a reduction in the number of large pores, an increase in the number of small throats, and an increase in the pore throat radius ratio due to the absorption and retention of macromolecules on the surfaces of the pores and throats. Increasing the flowback volume of slickwater fracturing fluid can recover part of the macromolecule absorption damage. This research can provide a reliable reference for the optimization of fracturing fluid performance, enhancement of the fracturing effect and reservoir protection of low-permeability reservoirs.

Hydrothermally prepared binary metal hydroxide electrode with a rational design and an innovative structure for electrochemical capacitors

The development of highly effective electrodes with new structures and rational designs is a major challenge for materials researchers in the twenty-first century, as it will aid in the improvement of energy storage device efficiency. Materials having high conductivity, a large surface area, a large number of pores, a network structure, and good stability are usually considered to be suitable for practical usage in modern electrochemical capacitors (ECCs). The ever-increasing need for high-performance ECCs has prompted materials researchers to create and design a new class of materials with integrated features. We manufacture a new honeycomb-like Co/Ni-LDH material in this paper and deposit it directly onto carbon cloth (CC, Co/Ni-LDH@CC) through the hydrothermal process to develop the binder-free and flexible electrode for ECC applications. Chemical composition, texture, thermal stability, shape, surface area, and the nature of atomic and molecular interaction in the produced Co/Ni-LDH@CC sample were all investigated using EDX, PXRD, TGA, FESEM, BET, and TGA techniques, respectively. In terms of application, our self-supporting and flexible electrode has an outstanding gravimetric capacity (C g ) of 1916 F/g and a remarkable preservation of 96.6% at the end of 6000 testing cycles. Our integrated electrode, in addition, has a better rate capability, as shown by the fact that it retains 69.15% of capacitance even after a fifteen-fold rise in the applied current density. The Co/Ni-LDH electrode's excellent electrochemical activity is a result of its self-supporting design, higher electronic conduction, non-resistive current collector, larger surface area, network structure, and very porous bulk.

Amphiphilic-triblock-copolymer-derived protective layer for stable-cycling lithium metal anodes

Lithium metal batteries have shown great potential for the development of efficient energy storage devices. However, the uncontrollable growth of lithium metal dendrites results in poor cycling efficiency and severe safety concerns. In this study, amphiphilic triblock copolymers (P123) were used for the direct polymerization of silica precursors, resulting in a well-ordered mesoporous silica structure SBA-15 with a large surface area and excellent absorbent properties for the protective layer. The protective layer consisting of SBA-15 stores Li ions in a large number of pores as an electrolyte reservoir, which exhibits sufficient ionic conductivity. Furthermore, it ensures a spatially uniform Li-ion flux on the anode surface and plays an important role in the physical blocking of dendrite growth. As proof of concept, the SAB-15 protective layer anode demonstrates a high average Coulomb efficiency, rate capability, and cycle stability at 1 mA h cm−2 over 1200 cycles. Moreover, SAB-15 can be cycled stably for more than 750 cycles in symmetric cells. The results provide insights for implementing stable lithium metal anodes in next-generation batteries.

Розробка біокомпозитів, наповнених продуктами переробки вторинної сировини рослинного походження

The article presents the results of the analysis of the composition and forming technology of biocomposite materials based on an adhesive (bone glue K3,5) and disperse fillers obtained by processing of secondary raw materials of plant origin (coffee grounds with high dispersion of particles, mechanically crushed dried leaves, coconut coir and grains stalks. The content of fillers in biocomposite materials varied in the range of 80…130 wt. parts. This is the optimal content of particles in the biopolymer matrix. Samples formed by mechanically mixing a solution of bone glue with the processed filler. Then the resulting biocomposition pressed into a mold. Homogeneity and continuity of the biopolymer matrix is ensured by a step-by-step heat treatment of biocomposite materials. The optimal content of fillers was determined by the results of analysis of experimental studies of the compressive strength of cylindrical samples. The highest values of the compressive strength (78,02 MPa) have biocomposite materials containing 190 wt. parts of particles of grain stalks. The macrostructure of the developed biocomposite materials analyzed. Biocomposite materials filled with particles of crushed dried leaves have the largest number of macroscopic defects after heat treatment. A large number of pores and cracks were found in these samples. The least number of defects have biocomposites filled with particles of crushed grains stalks, which confirmed by the obtained values of the compressive strength. The developed biocomposite materials can use for fabrication elements of furniture and floor, elements of a decor of salon of vehicles, containers and cases of devices.

Effect of self-diverting acid viscosity and the chemical structure of coal under different acid environment

In order to solve the poor water infusion problem for low permeability coal seams, this paper studied the self-diverting acid to uniformly distribute acid. The results show that massive Ca2+ generated by the reaction between HCl and calcite can enhance the crosslinking of micelles. With the increase of HCl concentration, the viscosity increased and then decreased, which could be divided into “low viscosity zone” (0.1%–2%), “viscosity rapid increase zone” (2%–5%) and “viscosity decrease zone” (5%–15%). After treated with self-diverting acid, the fracture width and connectivity of coal was increased. Massive clay minerals were dissolved, the distribution range of pore size and pore volume gradually increased, and a large number of pores caused by corrosion appeared. Due to the influence of viscosity, the wettability of self-diverting acid for the coal was gradually reduced during infusion process. However, compared with distilled water, the overall wettability of coal still increased by 6.91%.

Particle morphology of water atomised iron‑carbon powders

Water atomisation can produce metal powders faster and at lower cost than gas atomisation, but it is well known that the powder particles are irregular and may contain a large number of pores. The current study analyses three iron‑carbon alloys with different superheats, produced as powder by water atomisation and compares the particle shapes and porosity in each. The alloy with the most carbon (4.2 wt%) showed the highest circularity (0.72) for 20–45 μm particles, but the lowest (0.59) for 180-212 μm particles. This is consistent with collisions between droplets affecting particle shape. The lowest-carbon melt (0.22 wt%) solidified fastest, so underwent fewest collisions and showed similar circularity for all particle sizes. The breakdown of water to form hydrogen and the formation of hydrogen bubbles was the most likely cause of porosity. The findings of this study may be used to inform future water atomisation process design to control particle shape and minimise porosity.

Application of CoMn/CoFe layered double hydroxide based on metal-organic frameworks template to activate peroxymonosulfate for 2,4-dichlorophenol degradation.

Metal-organic frameworks (MOFs) have unique properties and stable structures, which have been widely used as templates/precursors to prepare well developed pore structure and high specific surface area materials. In this article, an innovative and facile method of crystal reorganization was designed by using MOFs as sacrificial templates to prepare a layered double hydroxide (LDH) nano-layer sheet structure through a pseudomorphic conversion process under alkaline conditions. The obtained CoMn-LDH and CoFe-LDH catalysts broke the ligand of MOFs and reorganized the structure on the basis of retaining a high specific surface area and a large number of pores, which had higher specific surface area and well developed pore structure compared with LDH catalysts prepared by traditional methods, and thus provide more active sites to activate peroxymonosulfate (PMS). Due to the unique framework structure of MOFs, the MOF-derived CoMn-LDH and CoFe-LDH catalysts could provide more active sites to activate PMS, and achieve a 2,4-dichlorophenol degradation of 99.3% and 99.2% within 20 minutes, respectively. In addition the two LDH catalysts displayed excellent degradation performance for bisphenol A, ciprofloxacin and 2,4-dichlorophenoxyacetic acid (2,4-D). X-ray photoelectron spectroscopy indicated that the valence state transformation of metal elements participated in PMS activation. Electron paramagnetic resonance manifested that sulfate radical (SO4•-) and singlet oxygen (1O2) were the main species for degrading pollutants. In addition, after the three-cycle experiment, the CoMn-LDH and CoFe-LDH catalysts also showed long-term stability with a slight activity decrease in the third cycle. The phytotoxicity assessment determined by the germination of mung beans proved that PMS activation by MOF-derived LDH catalysts can basically eliminate the phytotoxicity of a 2,4-D solution. This research not only developed high-activity LDH catalysts for PMS activation, but also expanded the environmental applications of MOF derivants.

Evolution of tricalcium silicate (C3S) hydration based on image analysis of microstructural observations obtained via Field's metal intrusion

The morphological organisation of cementitious materials greatly affects their mechanical and engineering properties, as well as overall durability. However, detailed image-based characterisation and analysis are challenging due to the complex and multi-scale morphological characteristic of this class of materials. In this study, C3S served as a simplified model of cementitious material. Samples with different hydration times were investigated using Field's metal intrusion to obtain back-scattered electron (BSE) images for detailed microstructural analysis. The degree of hydration was estimated and a metastable barrier surrounding a pack of unhydrated particles was found in the BSE images of C3S microstructure. The length of this barrier correlated well with the hydration rate of C3S. The hydration process was further found to induce a notable change in the pore size and pore profiles of C3S pastes. Generally, the critical pore size limiting C3S hydration was found to be 4 μm, and the hydration process caused both a reduction in the number of large pores and the formation of small pores. The C3S samples were found to reach 80% of hydration at 7 days of hydration and the pore structure developed continuously after 7 days even though the porosity and degree of hydration stayed similar.

Development of a Cellulose-Based Freshness Sensor (II) : Manufacture of Multilayer Freshness Sensor Using Cellulose-based Materials and Evaluation of Its Color Expression

Lately, the increase in consumers’ demand for food packaging safety standards to be followed has spurred a general interest in intelligent packaging technology that can monitor the status of the products in the packaging system. Commercialized sensors can indicate the freshness of food by expressing the colors based on the concentration levels of carbon dioxide (CO₂) in the food item. However, most of the freshness sensors are manufactured from synthetic polymer materials; therefore, it is necessary to develop an eco-friendly freshness sensor that uses biodegradable and recyclable cellulose-based materials.<BR>In this study, a multilayer freshness sensor was manufactured using cellulose-based materials such as commercial filter papers and cellulose nanofibers (CNFs) prepared in a laboratory. The filter paper with small pore size and large number of pores (No. 3) was selected by observing the color change of the immersed filter paper in a pH-sensitive dye, and used as a matrix expressing the specific color according to the CO₂ concentration. The top layer was prepared using enzyme-pretreated CNF (EN-CNF) to make a transparent film, and the middle and bottom layers were prepared using the biowax-coated filter papers with the lowest air permeability due to the largest pore size (No. 4). Finally, a eco-friendly freshness sensor was assembled using the matrix, CNF film, and biowax-coated filter papers, whose color expressions clearly differed based on their CO₂ concentration levels.

Effect of Composition on Engineering Behavior of Clay Tills

Glacial geology, marine environment, and arid climate govern the composition of clay tills. The main purpose of this work is to develop a clear understanding of the engineering behavior of compacted clay till under soil suction and applied stress. The results indicate moderate water adsorption due to the presence of clay minerals (26% corrensite, 10% illite, and 8% kaolinite) with Ca2+ as the dominant cation and a flocculated fabric in a slightly basic (pH = 7.5) pore water. The water retention curve comprised four transition points that are associated with capillary water drainage from large pores (air entry value of 2 kPa and residual suction value of 20 kPa) and small pores (air entry value of 700 kPa and residual suction value of 5 × 104 kPa). Beyond the last value, vapor flow is dominant and removes the adsorbed water by evaporation. The ratio of soil volume change to water volume change best described the s-shaped shrinkage path that also comprised four stages, namely: from most large pores with low volume change; from remaining large and most small pores along with almost equal volume change; from some small pores with low volume change; and from the rest of the small pores with no volume change. Likewise, the s-shaped swelling potential curve comprised three stages and correlated well with bimodal hydraulic conductivity curve, that is, slow initial swelling (unsaturated hydraulic conductivity around 10−14 m/s) due to expansion of peripheral clay in lumps; high primary swelling (unsaturated hydraulic conductivity of up to 10−11 m/s) due to thickened double layer of most colloids; and slow secondary swelling (albeit unsaturated hydraulic conductivity around 10−10 m/s) due to expansion of remaining particles. Soil compression (compression index of 0.164) was due to a gradual reduction in number of large pores, whereas rebound (swelling index of 0.047) was due to water adsorption on clay with part of the deformations recovered. Finally, the consolidation rate was related to saturated hydraulic conductivity, which varied by three orders of magnitude.

Evaluation of Surfactant Mixture for Supercritical Carbon Dioxide Foamed Acid in Carbonate Matrix Acidizing

The effectiveness of matrix acidizing using CO2 foamed acid is dependent on the duration of foam stability. This paper presents a supercritical CO2 foamed acid with a surfactant mixture to improve the foam stability in carbonate matrix acidizing. The experimental apparatus was developed to conduct foam-stability and wormhole-propagation tests under high-pressure and high-temperature (HPHT) conditions. The foam decay times of five types of surfactants were measured under atmospheric conditions. Trimax (blend of cocamidopropyl betaine, disodium cocoamphodiacetate, and amine oxide) and Aromox C/12W (coco bis-(2-hydroxyethyl) amine oxide) had a high foam decay time. The surfactant mixture was prepared using these two surfactants. The foam stability tests of the surfactant mixture were performed according to the HCl concentration, surfactant mixing ratio, and injection rate of HCl under HPHT conditions. As a result, the foam stability could be improved by adding an HCl concentration of 20% to the surfactant mixture. Wormhole-propagation tests were performed using Indiana and Indonesian limestones. Because of the supercritical CO2 foamed acid injection, dominant wormholes were formed in all the core samples; thus, the absolute permeabilities significantly increased. The results of the scanning electron microscopy/energy-dispersive X-ray spectroscopy and thin-section analyses revealed that the number of large pores with pore sizes of ≥0.5 mm increased by the injection of CO2 foamed acid. Therefore, the supercritical CO2 foamed acid with the surfactant mixture exhibited a high efficiency of matrix acidizing in carbonate reservoirs.

Improved test method for convection heat transfer characteristics of carbonate fractures after acidizing etching

Understanding of convection heat transfer characteristics of fractures is of great significance to improve the heat extraction efficiency of carbonate reservoir. Previous studies on convection heat transfer of fluid flowing through rock fractures are on either granite or sandstone. Limited experimental research has been performed on carbonate fractures after acidizing etching. In this work, an improved test method is developed to analyze the convection heat transfer characteristics of carbonate fractures after acidizing etching under real-time high temperature and high confining pressure. In this method, the traditional test method of convection heat transfer coefficient is improved by monitoring the temperature of inner fracture surface and flowing water. Two thermocouples are especially arranged inside the sample to monitor the temperature of inner fracture surface along the flow direction, and two other thermocouples for the inlet and outlet water temperatures. The results show that the temperature differences between the fracture surface and the flowing water are significantly dependent on confining pressure, fracture roughness and flow rate, and the maximum temperature difference could be reached 2.2 ◦C, which leads to a significant difference in the convection heat transfer coefficient between the traditional and improved test methods. A larger number of pores, caves, and micro-fractures caused by acid etching are observed on the fracture surface by scanning electron microscopy. The special fracture morphology of carbonate is totally different from those of granite and sandstone in previous studies, and can increase the convection channel and increase the contact area with flowing fluid and results in the inapplicability of the hypothesis to carbonate fractures after acidizing etching. The present work could improve the knowledge of convection heat transfer characteristics of carbonate fractures. Cited as: Zhan, H., Dong, W., Chen, S., Hu, D., Zhou, H., Luo, J. Improved test method for convection heat transfer characteristics of carbonate fractures after acidizing etching. Advances in Geo-Energy Research, 2021, 5(4): 376-385, doi: 10.46690/ager.2021.04.04

WITHDRAWN: Evaluation of Surfactant Mixture for Supercritical Carbon Dioxide Foamed Acid in Carbonate Matrix Acidizing

Abstract The effectiveness of matrix acidizing using CO2 foamed acid is dependent on the duration of foam stability. This paper presents a supercritical CO2 foamed acid with a surfactant mixture to improve the foam stability in carbonate matrix acidizing. The experimental apparatus was developed to conduct foam stability and wormhole propagation tests under high-pressure and high-temperature (HPHT) conditions. The foam decay times of five types of surfactants were measured under atmospheric conditions. Trimax (blend of cocamidopropyl betaine, disodium cocoamphodiacetate, and amine oxide) and Aromox C/12 W (coco bis-(2-hydroxyethyl) amine oxide) have a high foam decay time. The surfactant mixture was prepared using these two surfactants. The foam stability tests of the surfactant mixture were performed according to the HCl concentration, surfactant mixing ratio, and injection rate of HCl under HPHT conditions. As a result, the foam stability could be improved by adding an HCl concentration of 20% to the surfactant mixture. Wormhole propagation tests were performed using Indiana and Indonesian limestones. Because of the supercritical CO2 foamed acid injection, dominant wormholes were formed in all the core samples; thus, the absolute permeabilities significantly increased. The results of the scanning electron microscopy/energy-dispersive x-ray spectroscopy and thin-section analyses revealed that the number of large pores with pore sizes of ≥0.5 mm increased by the injection of CO2 foamed acid. Therefore, the supercritical CO2 foamed acid with the surfactant mixture exhibited a high efficiency of matrix acidizing in carbonate reservoirs.

Compound effects of water immersion and pyritic sulfur on the microstructure and spontaneous combustion of non-caking coal

In order to reveal the compound effects of water immersion and pyrite on the microstructure and spontaneous combustion characteristics of non-caking coal, three coal samples from two neighboring mines were selected and prepared. The SEM observation, CO2 and N2 adsorption, XRD, XRF, FTIR tests and low temperature oxidation experiment were carried out on raw coal and soaked coal (S30). Showing that a large number of pores and fissures developed after waterlogging, especially M2 sample, the oxidation of its pyrite content (FeS2) leads to the promotion of pore development in coal matrix. Simultaneously, the presence of pyrite was more favorable for the generation of various functional groups and the maintenance of long chain aliphatic hydrocarbons during soaking. In conclusion, the presence of pyrite contributes to the micro-physical and chemical changes in the coal body during the water immersion, which further promotes the propensity for spontaneous combustion (combining data on oxygen consumption, gas products and CPT changes) of soaked coal.

Service damage mechanism and performance attenuation of nickel-based alloy turbine blades

Multi-scale morphology observations and fatigue performance tests were carried out to study the damage evolution mechanism and fatigue performance attenuation behavior of K403 turbine blades in service. During service in field, the dendrite separation and breakage, γ' phase polymerization and rafting, MC carbide decomposition, harmful phase precipitation and grain boundary weakening are having adverse effects on the fatigue performance of turbine blades. Meanwhile, the loss of alloying elements in matrix causes the alloy matrix to soften. In addition, a large number of pores and microcracks formed in the process of service further deteriorate the service performance of turbine blades. Therefore, after long-term operations, the solid solution strengthening, precipitation strengthening, dispersion strengthening and grain boundary strengthening effects of K403 turbine blades are all weakened, which led to serious degradation of the fatigue performance of these turbine blades with the fatigue life reduced. Besides, the crack initiation source of turbine blade is gradually transformed from subsurface metallic pore initiation to carbide initiation.

Effect of La2O3 particle size on the microstructure and properties of Al Si alloys deposited via wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) of AlSi alloy deposits exhibits the advantages of a high deposition rate and easy operability, while being suitable for fabricating large-sized metal parts. However, the alloy deposits suffer from various problems such as a large number of pores, coarse and uneven microstructures, and poor mechanical properties. Herein, we added La2O3 powders with different particles sizes (nano-sized, micron-sized, and ordinary-sized particles) to AlSi alloy deposits for optimizing the properties of the specimens. The results show that the surface roughness of the specimens increased with the addition of micron-sized or ordinary-sized particles. However, the addition of nano-sized La2O3 powder improved the forming quality of the alloy deposit, eliminated the slender columnar grains near the fusion line and the central region of the coating, and refined the grains. The addition of La2O3 powder also reduced the maximum texture intensity in the specimen, for which adding nano-sized La2O3 powder had the most obvious effects. In addition, the microhardness and tensile strength of the specimens with nano-sized La2O3 powder were improved, while the average microhardness increased by 13% from 55.2 HV to 62.4 HV. The average tensile strength in the horizontal direction increased by 28% from 172 MPa to 221 MPa, and that in the vertical direction increased by 13% from 135 to 152 MPa. The addition of La2O3 powder was effective in improving the properties of the AlSi alloy deposit. The nano-sized La2O3 powder was the most suitable powder for the WAAM of AlSi alloy.

Foam Concrete: A Review

Foam concrete has the potential of being an alternative to ordinary concrete, as it reduces dead loads on the structure and foundation, contributes to energy conservation, and lowers the cost of production and labour cost during the construction and transportation. Presently the emerging trend is the use of foam concrete, which is a lightweight concrete having more strength-to-weight ratio with density varying from 300 to 2000 kg/m3. This reduces the dead load on the structure, cost of production and labour cost involved during the construction and transportation. Also, the large number of pores in the foamed concrete reduces the thermal and sound absorption, thus making the structure appropriate for all climatic conditions. The paper outlines a review of foamed concrete in terms of its definitions &amp; classifications, materials, mix design, production of foamed concrete, properties of foamed concrete such as workability, density, compressive strength, porosity, fire resistance, shrinkage, water absorption, permeability. Apart from this, the paper outlines various applications of foam concrete.

The origin and source of heavy oil and its control on oil and gas accumulation

ABSTRACT A large amount of heavy oil have been found in the eastern section of Dinan uplift, Junggar basin. Previous studies on heavy oil mainly focused on the origin and source, and few studies have been conducted on the influence of heavy oil on reservoir physical properties and the control of oil and gas enrichment. Based on this, through the analysis of oil and gas geochemical characteristics and the comparison of reservoir physical properties before and after oil washing, the genesis of heavy oil in this area and the control effect of heavy oil on oil and gas accumulation are systematically studied. The results show that: (1) The carbon isotope of crude oil in this area is lower than −30‰, Pr/Ph is less than 2, C28 and C29 sterane content is high, which is a typical Permian source rock product. (2) Due to the incompleteness of saturated hydrocarbon chromatogram, low maturity of heavy oil isassociated with bacterial decomposition gas, which indicates that the heavy oil is formed by biodegradation of early products of Permian source rock. (3) Heavy oil fills the pores and fractures of the reservoir and occupies a large number of pores and throats, which affects the physical properties and pore structure. After the heavy oil was dissolved, the average increase in sample porosity and permeability is 3.79% and 0.435 × 10−3μm2. (4) The heavy oil formed in the high part of the structure has a certain plugging effect on the reservoir, which leads to the high mature oil and gas in the deep part of the depression did not migrate to the high part of the structure to form an oil reservoir. Therefore, the next step of the exploration for products in the high maturity stage of the depression should be extended to the depression slope area.

3D printing of PDC-SiOC@SiC twins with high permittivity and electromagnetic interference shielding effectiveness

Effective electromagnetic interference (EMI) shielding requires materials with high permittivity. The current study reports 3D printed polymer-derived SiOC ceramics (PDC) modified with SiC nanowires (SiCnw) exhibiting both high real and imaginary parts of permittivity within X-band. SEM results indicated that a large number of pores and cracks exist in the SiOC, and twinned SiCnw were uniformly grown among them along with the existence of graphite microcrystals when the sintering temperature was 1500 ℃. The real part of permittivity ranged from 16.6 to 28.9 while the imaginary part from 31.7 to 34.2 in X-band. The EMI total shielding effectiveness (SET) of the ceramics could reach 34.7 dB with absorption loss (SEA) of 29.3 dB and reflection loss (SER) of 5.4 dB. Meanwhile, the 3D printed PDC-SiOC ceramics at 900 ℃ sintering temperature possess certain mechanical properties with the magnitude of compressive strength being 12.57 MPa.

Study on Mechanical Properties of the Expansive Soil Treated with Iron Tailings Sand

Aiming at researching shear strength parameters of expansive soil modified by industrial waste iron tailings sand, the enhancement of expansive soil is explored from macroscopic and microscopic aspects. After characterization and testing by various means, the results show that expansive soil modified by iron tailings sand will increase the maximum dry density of the improved soil and reduce its optimal moisture content, which is beneficial in tuning the moisture content at the construction site. In addition, iron tailings sand can improve the shear strength of expansive soils. The influence of iron tailings sand on cohesion increases first, then decreases, and reaches the peak value at 30%, while the effect on internal friction angle exhibits a continuously increasing trend. Furthermore, according to mercury intrusion tests and microangle analysis, the addition of iron tailings sand can reduce the tiny pores and enhance the occlusal force of the soil. Simultaneously, it increases the number of large pores, maximizing the macroscopic strengthening of iron tailings sand towards the expansive soil.