Table of Content

15 June 2023, Volume 42 Issue 6

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Cement and Concrete

Review on CO₂ Mineral Carbonation-Cured Cement-Based Materials

WU Shengkun, HUANG Tianyong, XIE Yan, WANG Zhanpeng, BAO Qi, TIONG Michelle, YE Hang, LIU Qi

2023, 42(6):  1897-1911. 

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CO₂ mineralization curing is considered an effective approach to mitigate the impact of the construction industry on global climate change by reacting CO₂ with cement-based materials (CBM) (e.g. cement clinker, namely tricalcium silicate, β-dicalcium silicate, tricalcium aluminate and its hydration products, namely calcium hydroxide, amorphous calcium silicate hydrates, hydrated aluminate and sulfate phases) to form calcium carbonate mainly composed of calcite and amorphous silica gel with high degree of polymerization, realizing the storage and utilization of CO₂. Attributed to the good stability, filling effect and nucleation effect of the resultant products, the mechanical properties and durability of CBM are effectively improved while better performance is anticipated in a relatively short time compared with other curing technologies. In this paper, the reaction mechanisms and latest research progress of CO₂ mineral carbonation-cured CBM are reviewed. The effect of influencing factors, such as pre-condition, relative humidity, water binder ratio, CO₂ concentration, curing pressure and temperature on the post-mineralization properties, carbon fixation rate and mineralization degree are evaluated. Finally, based on the current research status and existing problems, suggestions and recommendations for a wider application of CO₂ mineralization technology in the future are also provided.

Research and Application Progress of Serpentine Concrete

YANG Zhao, SHI Jianjun, XU Xinchun, ZHANG Zhiheng

2023, 42(6):  1912-1920. 

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Serpentine concrete has excellent neutron shielding property, which has been widely used in the nuclear industry and medical industry to shield neutron radiation in foreign countries. With the rapid development of nuclear industry and rich serpentine minerals in China, it should be a lot of research and application of serpentine concrete, however, in fact, serpentine concrete is not only less studied in China, but also its application is far less than abroad. Therefore, the characteristics of serpentine aggregate were summarized, and the physical properties, particle shape characteristics and chemical composition of three kinds of serpentine subspecies aggregate were compared. The influence of serpentine aggregate on concrete property was described in detail, and the shortcomings of current research on serpentine concrete were analyzed. The application status of serpentine concrete was combed. Finally, in order to promote further research and application of serpentine concrete in China, the future development of this field was prospected.

Carbon Footprint Assessment of Cementitious Materials Prepared from Industrial By-Product Gypsum Based on Life Cycle

LI Ying, DUAN Pengxuan, NI Wen, ZHANG Dajiang

2023, 42(6):  1921-1930. 

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Under the new situation of “Two Mountains” theory and “Dual Carbon” goals, our country has issued a series of policies and preferential conditions to encourage the preparation of gypsum cementitious materials from industrial by-product gypsum, including calcined gypsum, α high-strength gypsum, mixed phase gypsum, et al. So far, there are few carbon footprint calculation reports on gypsum cementitious materials in China. In this paper, the carbon footprint calculation model of gypsum cementitious materials prepared from industrial by-product gypsum was established based on life cycle assessment method, which was demonstrated through the production of α high-strength gypsum from phosphogypsum. The results show that the carbon footprint in three stages of raw material acquisition, production and transportation of α high-strength gypsum product is 3.95, 288.04 and 14.31 kg CO₂ eq/t, respectively, and the total emission is 306.3 kg CO₂ eq/t. The carbon emission in production stage is the largest, which is an important segment to reduce energy consumption, reduce carbon emission and save costs. The carbon footprint calculation model established in this paper is applicable to the carbon footprint calculation for calcined gypsum, α high-strength gypsum, anhydrite, mixed phase gypsum, et al.

Blockage Mechanism Analysis of 3D Printing of High Viscosity Cement

WANG Yibo, REN Changzai, YAN Ming, AO Chenyang

2023, 42(6):  1931-1937. 

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In order to solve the blockage problem of 3D printing of high viscosity cement, physical simulation experiments were carried out by building up a 3D printing platform. The hardened products were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the internal flow field of printhead was analyzed by finite element software Polyflow. Combining with tests results and numerical simulation results, the reasons for the blockage problem were confirmed. The results show that the setting time of high viscosity cement is 10~23 min, which is faster than that of ordinary Portland cement to form prismatic crystals. The internal pressure gradient of printhead reaches a peak value 113.9 kPa at extrusion outlet, and the slurry in the channel is transported in the form of plug flow. During the process of 3D printing, part of the slurry adheres to the surface of the screw, and the product formed by rapid hardening is embedded in the micro-convex surface of the screw. The unadsorbed slurry in the channel is transported in the form of plug flow under the action of high pressure difference in the cylinder, and the liquid phase migration occurs at the variable diameter in the cylinder, which eventually causes the printing blockage problem. The research results can provide theoretical support for the design of 3D printing printhead used for high viscosity cement.

Effect of Composite Thickener on Performance of Large-Flow Thin Layer Mortar and Its Anti-Cracking Mechanism

YANG Wenxiu, ZHAO Qinglin, ZHOU Mingkai, WU Defan, WU Miaomiao, SHEN Weiguo

2023, 42(6):  1938-1949. 

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For the characteristics of the two thickeners, welan gum (WG) and hydroxypropyl methyl cellulose (HPMC), they were added to solve the problem of easy cracking of cement-based large-flow mortar for thin layer construction under harsh environments. By comparing the effects of WG, HPMC, and composite thickener, the influence law of the composite thickener on the workability, mechanical properties and anti-cracking of large-flow mortar was elaborated. The mechanism of anti-cracking action of the composite thickener was also explained by cryo-scanning electron microscopy. The results show that neither WG nor HPMC alone can solve the problem of mortar cracking under harsh environments. The composite thickener performs better in water retention and anti-cracking, and the modulus of elasticity of mortar becomes lower, and the flexibility is improved, so that it will not crack in outdoor exposure in summer. The anti-cracking mechanism is considered as that the composite thickener combines the respective advantages of WG and HPMC. It forms the superposition of three-dimensional network structure and film structure in the system slurry space. The three-dimensional network structure can greatly enhance the stability of slurry, while the film effect again enhances the stability of slurry and greatly improves the water retention of mortar, which in turn significantly reduces water diffusion and evaporation to achieve the purpose of mortar anti-cracking.

Quantitative Characterization Method of Crack Self-Healing Effect of Cement-Based Materials Based on Contact Resistance Theory

ZHANG Xuan, FU Changhao, ZHAN Qiwei, SU Yilin, PAN Zhihong

2023, 42(6):  1950-1959. 

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The self-healing effect of cracks is an important basis for evaluating the level of functional recovery of materials. To realize the comprehensive evaluation of the full-section repair effect of cracks in cement-based materials, research on crack self-healing evaluation methods based on contact resistance theory had been carried out, including the selection and optimization of conductive materials, the optimization of test parameters, and the derivation of calculation methods. The results show that 0.3% volume dosage carbon fiber can effectively reduce the resistivity of cement-based materials and simultaneously improve mechanical properties. The measured voltage has no significant effect on the resistivity. The resistivity gradually decreases with the increase of contact pressure. The self-healing process of cracks is the process of changing the contact form of crack surface, which is also accompanied by changes in the contact resistance. According to this, a quantitative calculation formula for contact resistance and self-healing effect can be established. This method is only related to the accumulation of repair products on the crack surface, and is not affected by the spatial distribution of the products. The conclusions provide a reference for the quantitative characterization of the self-healing effect of cement-based materials.

Self-Healing and Mechanical Properties of Bacterial ECC

SUN Xichen, CHEN Bingcheng, WANG Yang, FENG Jun

2023, 42(6):  1960-1969. 

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Microbial induced calcium carbonate precipitation (MICP) technology has been widely used in the modification of cement-based materials to achieve self-healing of microcracks.Engineered cementitious composite (ECC) has the characteristic of fine and dense cracks under tension, and Bacillus pasteurii microorganisms were added to obtain self-healing ECC based on MICP technology mechanism. The mechanical properties and self-healing properties of bacterial ECC were studied by uniaxial compressive, uniaxial tension, SEM and XRD tests. The results show that MICP technology makes that bacterial ECC has a good self-healing ability and restores mechanical property in some degree. After 28 d incubation and bioremediation, compressive strength of bacterial ECC recovers by 9.44%, ultimate tensile strength recovers by 15.4%, and tensile strain increases by 21.3%. The crack filler is calcium carbonate with vaterite morphology. This study aims to obtain a new type of bacterial ECC with strong self-healing ability based on the MICP technology mechanism.

Study on Centroplasm Effects of SAP Aggregate Concrete

LIU Yunpeng, PENG Bo, WANG Shaohui, WANG Fazhou

2023, 42(6):  1970-1979. 

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This study quantitatively characterized the positive and negative centroplasm effects of superabsorbent polymer (SAP) aggregate with different particle sizes (6~20 mm) by testing the compressive strength of concrete with single SAP or expanded polystyrene (EPS) aggregate, drawing on the centroplasm hypothesis. The results show that the water release of SAP aggregate exhibits a positive centroplasm effect on cement mortar due to the interfacial enhancement and a negative centroplasm effect due to pore formation. The empirical formula of negative centroplasm effects caused by pores induced by SAP aggregate is proposed. With the increase of SAP aggregate size, its negative centroplasm effect increases, while its positive centroplasm effect increases first and then decreases. The concept of "critical size" of SAP aggregate in mortar with different water-cement ratios is proposed. It is related to the water-cement ratio and the curing age of mortar.

Tests and Numerical Simulation on Compressive Properties of 3D Printing Concrete along Rectangular-Ambulatory-Plane Path

ZHANG Haiyan, TANG Guoming, GUO Minlong, KANG Shengguo

2023, 42(6):  1980-1986. 

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The concrete samples of 3D printing along rectangular-ambulatory-plane (R-a-p) path were cut into three types of test cubes: R-a-p, stripe and corner. Compressive strength tests were conducted on these specimens in X, Y and Z directions, and their compressive behaviors were simulated using the finite element models based on the interface bonding. The strength inhomogeneity, anisotropy and formation mechanism of 3D printing along R-a-p path were investigated. The test results show that the highest compressive strength of the three types specimens is in the X direction (along the printed strip direction), the lowest is in the Z direction (layer-by-layer stacking direction) and the R-a-p specimens exhibit the highest average strength of three directions and the most significant strength anisotropy. Overall, there is no great difference between the average strength of three types cubes. The strength calculation results and damage characteristics from finite element models are basically consistent with the experimental results, implying that the introduction of cohesive element can better simulate the interface behavior of 3D printing concrete. The horizontal interface perpendicular to the loading direction has a great influence on the strength, and the difference in the number and distribution of these interfaces in different loading directions is the main reason for the strength anisotropy of 3D printing concrete. The research provides a reference for the printing path planning of 3D printing concrete.

Experimental Study on Dynamic Compressive Mechanical Properties of Mortar-Concrete Joint Interface

ZHAO Yanfei, ZHANG Shifan, YAN Xingfei, ZHANG Tao, PENG Shuai, WU Bo, YU Zhenpeng, DU Xiaoqing

2023, 42(6):  1987-1995. 

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In order to investigate the dynamic compressive mechanical properties of mortar-concrete joint interface, three different specimens of concrete, mortar and mortar-concrete joint interface were designed, and their static and dynamic mechanical properties were investigated by hydraulic servo machine and split Hopkinson bar (SHPB). The damage morphology and mechanical characteristic parameters of specimens under different joint conditions were obtained from the test. At the same time, the dynamic enhancement effect of three different spcimens was analyzed and its mechanism was revealed from the mesoscopic level by using CT scanning technology. The results show that under static action, the overrall compressive strength of joint specimens is between mortar specimens and concrete specimens. Under dynamic action, the compressive strength of three different specimens increases correspondingly with increasing strain rate. Concrete has stronger sensitivity to strain rate and mortar has the weakest sensitivity. Compared with concrete specimens, the integrity of mortar and mortar-concrete joint specimens after compressive damage is significantly improved. Based on experimental data and CEB formula proposed by ComitÉ Euro-International du BÉton, the dynamic increase factor (DIF) and strain rate mathematical model suitable for three different materials are optimized.

Performance of Ultra-High Performance Lightweight Concrete with Pottery Sand and Its Influencing Factors

WANG Qing, GAO Shuchang, GAO Jiacheng, WEN Changcheng, XU Gang

2023, 42(6):  1996-2006. 

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The effects of water-binder ratio, binder-sand ratio, fly ash content, silica fume content, steel fiber content and density grade of pottery sand on working performance, mechanical properties, apparent density and ratio of strength to density of ultra-high performance lightweight concrete (UHPLC) with pottery sand were studied, and the optimal mix ratio was determined. UHPLC with dry apparent density of 1 950 kg/m³, fluidity of 233 mm (slightly higher than that of ultra-high performance concrete) and 28 d compressive/flexural strength not less than 120/20 MPa was prepared. By means of X-ray diffractometer and scanning electron microscope, the variation laws of UHPLC hydration products and microstructure with time were discussed. From the perspective of microstructure, the characteristics of interface transition zone between pottery sand and matrix, steel fiber and matrix were analyzed, and the change law of ratio of strength to density of UHPLC increasing with the increase of density grade of pottery sand was revealed under the same conditions. Through standardized regression coefficient analysis, the results indicate that steel fiber content has the greatest influence on the strength and density of UHPLC, and the contribution rates are greater than 40%. The most significant influence on the fluidity of UHPLC is the water-binder ratio, and the contribution rate is 38.18%. The binder-sand ratio has a more obvious influence on the fluidity of UHPLC, and the contribution rate is 27.20%.

Deterioration Characteristics of UHPC under Stray Current Environment

GAO Dejun, HUANG Yulong, WANG Qing, WANG Xuan

2023, 42(6):  2007-2014. 

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To study the durability of ultra-high performance concrete (UHPC) under stray current environment, the effects of environmental type, chloride ion concentration and cementing material type on the corrosion morphology, ultrasonic velocity loss rate, damage depth, porosity and strength loss of UHPC under stray current environment were studied by electromigration accelerated corrosion test. The results show that UHPC specimens first generate cracks and spalling on the surface under stray current environment. With the increase of time of impressed current, the damage develops from the surface to the inside, and the internal fibers are seriously corroded and separated from the matrix. Under stray current environment, the damage depth of UHPC increases with the increase of time of impressed current approximately in a quadratic function. In the absence of chloride ion environment or less than 1% (mass fraction) of chloride ion concentration, the effect on the damage depth of UHPC is not significant, but with the increase of chloride ion concentration, the effect gradually becomes significant. The damage depth of UHPC at 3% chloride ion concentration is twice as large as that at 1%. Under the same conditions, the denser the UHPC is, the stronger the ability to resist stray current damage is. Adding phosphorus slag powder or fly ash to UHPC helps to enhance its corrosion resistance.

Frost Resistance of Nano-TiO₂ Concrete Based on Nuclear Magnetic Resonance Method

ZHAO Yanru, ZHANG Jianxin, LI Na, GUAN He

2023, 42(6):  2015-2026. 

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The evolution of pore structure is very important to the frost resistance of concrete. In order to study the effect of nano-TiO₂ on pore structure and frost resistance of concrete, the nano-TiO₂ concrete with substitution rates of 0%, 1%, 3%, 5% (mass fraction, the same below) were selected as research object, and the quick freezing test, compressive strength test, nuclear magnetic resonance test and scanning electron microscope test were carried out. The changes of mass, dynamic elastic modulus, compressive strength, pore structure and micro-morphology of nano-TiO₂ concrete before and after freeze-thaw cycle were analyzed to evaluate the freeze-thaw damage at -18~5 ℃ and to analyze the improvement mechanism of nano-TiO₂ on concrete properties. At the same time, the response models of compressive strength, relative dynamic modulus, free water saturation and crack ratio were established to determine the optimum content of nano-TiO₂. The results show that an appropriate content of nano-TiO₂ effectively improves the micro-morphology of concrete, increases the proportion of micropores and medium pores of concrete, and reduces the proportion of macropores and cracks, while excessive nano-TiO₂ increases the proportion of macropores and cracks in concrete, which is not conducive to the improvement of frost resistance of concrete. When the content of nano-TiO₂ is 1%, the frost resistance of concrete is the best. Based on the frost resistance performance index and pore test results, the response model is established, and the optimal content of nano-TiO₂ is close to 1%, which is consistent with the test results.

Mechanical Behavior and Chloride Penetration Resistance of Internal Curing Concrete

LIU Yutao, GAO Yirong, MA Bicong

2023, 42(6):  2027-2036. 

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With the continuous advancement of China’s infrastructure construction, the requirements for concrete materials are becoming higher and higher. As a new type of internal curing material, super absorbent polymer (SAP) possesses the advantages of good water absorption and water retention, light weight and hard to dehydrate after compression, it has attracted more and more attention from scholars at home and abroad. To explore the mechanical behavior and chloride penetration resistance of SAP internal cured concrete, several groups of concrete with different SAP content and particle size were set up, and the internal micro pore structure of SAP concrete was observed and analyzed by means of nuclear magnetic resonance (NMR) and scanning electron microscope (SEM). The results show that the incorporation of SAP material can significantly reduce the early strength of concrete, and the 3 d strength can be reduced by up to 25% compared with the reference group, but the influence on the strength of the middle and later period is not very great. With the addition of SAP, the volume and number of pores in concrete are significantly reduced, and the pore structure is optimized. The addition of SAP improves the chloride penetration resistance of concrete, the 56 d impermeability is improved by 38% compared with the reference group. The chloride migration coefficient can be well predicted by BP neural network fitting.

Solid Waste and Eco-Materials

Effects of Particle Size and Confining Pressure on Laterally Confined Compression Properties of Coral Sand

XIONG Xuemei, ZHENG Yuxuan, HUANG Junyu, ZHOU Fenghua

2023, 42(6):  2037-2046. 

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Coral sand, as an important building material of ocean reef islands, is widely used in hydraulic reclamation and construction of military and civil facilities such as island foundation, subgrade, airport runway, etc. A series of laterally confined compression tests were conducted on the coral sand from a reef island in the South China Sea. The effects of particle size distribution and passive confining pressure on the laterally confined compression properties of coral sand were studied quantitatively to provide reference for subsequent research on particle size and passive confining pressure effects of coral sand. The experimental results show that the axial engineering stress-strain curves of coral sand under passive confining pressure exhibit increasing hardening. The stress path of coral sand under laterally confined compression is basically independent of the particle size, and the passive confining pressure increases linearly with the increasing axial stress, which is about 35% of the axial stress. This paper calculates accurately the yield strength and compressibility coefficient of coral sand, the following conclusions are drawn: as the mean particle size of coral sand increases, the yield strength decreases exponentially, while the compressibility coefficient increases exponentially. Therefore, the onset stress of particle breakage is lower for the coral sand with a larger mean particle size, which leads to a higher amount of particle breakage, and higher compressibility as well for the coral sand. The yield strength of coral sand is almost independent of passive confining pressure, but depends only on the material characteristics of coral sand. With the increase of passive confining pressure, the compressibility coefficient of coral sand decreases significantly. This is because the high passive confining pressure prohibits particle breakage of coral sand, and leads to a lower compressibility of coral sand.

Solidification Mechanism of Cadmium in Clay Sintering

SHENG Guanghong, WANG Keyi, MA Yan, LUO Shiyu, WANG Shisheng, LIU Ling

2023, 42(6):  2047-2053. 

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The effects of chemical composition and sintering temperature on the solidification rate and leaching concentration of Cd in clay sintering material were studied. And the solidification mechanism of Cd during clay sintering was investigated by XRD, SEM, XPS, FTIR and heavy metal speciation analysis. The results show that the increasing content of Fe₂O₃ is beneficial to the formation of hematite, and the residue proportion of Cd sintering at 750 ℃ is higher than that of other samples. The content of CdAl₂Si₂O₈ increases after increasing the Al/Si ratio. When the Al/Si ratio is 0.3 at the sintering temperature of 1 050 ℃, the solidification rate of Cd can reach 99.64%. When the CaO content increases to 3% (mass fraction), the leaching concentration is lower than 1 mg·L^-1. The formation of anorthite increases the pH value of the leaching solution and inhibits the leaching of Cd. The clay can form a denser structure after sintering, which can wrap Cd in the liquid phase. At the same time, Cd²⁺ can replace Ca²⁺ in the crystal to generate stable CdAl₂Si₂O₈, as a result, Cd is fixed in the sintered clay material.

Effect of Firing Temperature on Properties of Forsterite Synthesized by Magnesite Tailings

DONG Haoran, NIE Jianhua, LIANG Yonghe, CAI Manfei, JU Maoqi, WEN Lidong, LI Zhou

2023, 42(6):  2054-2061. 

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Forsterite raw material for ceramic proppant was synthesized by solid-phase sintering method with magnesite tailings and silica as raw materials, which is not only beneficial to the secondary resource utilization of magnesite tailings, but also can replace natural forsterite as raw material for ceramic proppant, providing a new direction for the preparation of raw material for ceramide proppant. The effects of different firing temperatures on the properties of synthetic forsterite were investigated by characterization of phase composition, microstructure and cold physical properties. The acid solubility of samples at different firing temperatures was compared. The results show that when the firing temperature are 1 400~1 550 ℃ for 3 h, the main phase of samples is forsterite. With the firing temperature increases, the grain size of forsterite increases continuously, which improves the cold physical properties and acid resistance of samples. However, an excessively high firing temperature lead to an increase of glassy phase content in samples, affecting its performance. When the firing temperature is 1 500 ℃, cold mechanical properties of samples reach the maximum value, and acid solubility is the lowest.

Preparation and Properties of Sintered Ceramsite Prepared by Engineering Slurry Dehydrated Slurry Cake

SHEN Yihang, CHEN Ping, LOU Honghai, SHEN Yunyang, WANG Ziang, ZHAN Liangtong

2023, 42(6):  2062-2070. 

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In order to seek an effective way for the high-value resource utilization of engineering slurry, ceramsite was prepared by adding different proportions of fly ash and steel slag with mechanically dehydrated slurry cake as the main raw material, and the molding equipment and process flow for preparing ceramsite with high water content slurry cake were designed. The influence of chemical composition on the properties of ceramsite was investigated. The workability and strength properties of ceramsite concrete were tested and compared with ordinary concrete. The results show that adding the appropriate amount of steel slag can effectively improve the strength of ceramsite and reduce the water absorption, however fly ash is opposite. The main reason is that the adding of steel slag optimizes the SA/R (mass ratio of refractory component to fluxing component) of clay, while the adding of fly ash deteriorates SA/R. When the content of steel slag is 10% (mass fraction), the compressive strength of the sintered ceramsites is 5.8 MPa, the water absorption rate is 10.4%, the bulk density is 1 076 kg·m^-3, and the apparent density is 2 010 kg·m^-3, which meets the requirements of theTechnical specification for ceramsite concrete (DBJ/T 15-62—2021) for the use of high-strength ceramsite and can be applied to ceramsite concrete. The compressive strength of ceramsite concrete designed according to C45 is 23.49 MPa. The fluidity of ceramsite concrete is good, the apparent density is low, and the self-weight can be reduced by 12.4%, which is suitable for non-load-bearing structures.

Leaching Process and Mechanism of Manganese from Electrolytic Manganese Slag by Citric Acid

ZHANG Huanhuan, FANG Shuangming, FU Juan, CHENG Jinke

2023, 42(6):  2071-2080. 

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The concentration of manganese in electrolytic manganese slag is higher, which not only wastes manganese resources, but also will restrict the comprehensive utilization of manganese residue. The high efficiency leaching of manganese from manganese residue with citric acid as additive can promote the resource utilization of manganese residue and the green and low-carbon development of electrolytic manganese industry. The influence of leaching parameters on the manganese leaching concentration in manganese slag was studied. A manganese leaching model was established by analyzing the phase, structure, valence, morphology and kinetics, and the leaching mechanism was discussed. The results show that when the citric acid content is 25% (mass fraction), the liquid-solid ratio is 5∶1, and the leaching time is 30 min, the manganese leaching effect is better, and the leaching rate is 93.6%. The kinetics of manganese leaching is in accordance with the shrinking core model, which is controlled by the mixture of chemical reaction and solid film. The high valence manganese is reduced to the divalent manganese by citric acid, and then the divalent manganese and citric acid coordinate to form a chelate in the form of 1∶2, in which the carboxyl and hydroxyl groups of citric acid molecules jointly participate in bonding.

Structure and Filtration Performance of Fly Ash-Based Porous Geopolymer

CHEN Xiping, WANG Zhaotian, LUO Hongjie, CHENG Yan, WU Linli, JIANG Hao

2023, 42(6):  2081-2091. 

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At present, the working temperature of industrial dust removal filter bag is not higher than 280 ℃. The high temperature flue gas needs to be cooled before filtration. In order to prepare a new type of filter material with high efficiency and good temperature resistance, porous geopolymer was preparedby polymerization reaction with fly ash as the main raw material and H₂O₂ as foaming agent. The morphology, pore structure, flexural strength and filtration performance were characterized. The results show that the optimum addition of H₂O₂ is 0.98%(mass fraction). The average pore diameters of the lower surface and the interior of the porous geopolymer are 17.3 and 171.5 μm respectively, the porosity is 56.2%, the flexural strength at room temperature is 2.2 MPa, the filtration resistance is 6.2×10^-3 MPa, and the filtration efficiency of PM10 and PM2.5 are 98.2% and 93.3%, respectively. After heat treatment at 800 ℃, the flexural strength increases to 3.4 MPa, and the filtration efficiency of PM10 and PM2.5 remains above 90%. The filtration resistance increases by 1×10^-3 MPa. Therefore, the fly ash-based porous geopolymer has a good application prospect as a high-temperature flue gas filtration material.

Pore Structure and Media Transport Properties of Metakaolin-Slag Geopolymer

XIE Guolun, ZHONG Qingyu, YANG Yiwei, HUANG Dunwen, PENG Hui

2023, 42(6):  2092-2105. 

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Geopolymer is a novel cementitious material with low carbon properties produced by chemical activation, which has great potential to partially replace cement. The pore structure of metakaolin-slag geopolymer paste and mortar was characterized by mercury intrusion porosimetry tests. The effects of liquid-solid ratio and sand volume fraction on pore structure properties were analyzed, the correlation between pore structure properties and surface fractal dimension was clarified, and the permeability resistance of metakaolin-slag geopolymer paste and mortar was investigated using chloride unsteady electromigration test, unsteady natural diffusion test and moisture diffusion test. The correlation between liquid-solid ratio, sand volume fraction, pore surface fractal dimension, and slurry media transport performance was analyzed. The results show that with the increase of liquid-solid ratio, the porosity and the most available pore size of geopolymer paste increase and the permeability resistance decreases. The permeability resistance of geopolymer mortar is superior to that of cement mortar. The most available pore size and media transfer coefficient of geopolymer mortar decrease first and then increase with the increase of sand volume fraction, and the permeability resistance increases first and then decreases. Furthermore, the pore surface fractal dimension can well characterize the pore structure properties of geopolymer slurry and has a good correlation with permeability resistance.

Hydration Behavior and Mechanical Properties of Alkaline Excited Slag-Fly Ash-Metakaolin Geopolymer

LIU Gang, DING Mingwei, LIU Jinjun, WAN Huiwen, XUE Yongjie, JIAN Shouwei

2023, 42(6):  2106-2114. 

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By changing the ratio of slag, fly ash and metakaolin, the ternary geopolymer was prepared by alkali excitation with the compound sodium silicate. The setting time, flexural and compressive strength of ternary geopolymer were tested. XRD, SEM, EDS and DTG were used to study the morphology and composition of hydration products in the hardened paste, and the hydration process was analyzed. The results show that the ternary geopolymer is composed of calcium silicate hydrate (C-S-H), calcium aluminate silicate hydrate (C-A-S-H) and sodium aluminate silicate hydrate (N-A-S-H) gels. The higher the slag content is, the shorter the setting time of newly mixed slurry is, the more calcium gel in the hydration products is, and the higher the strength of specimen is. The 3 d compressive strength of 5 groups of specimens with slag content of 10%, 30%, 50%, 70%, 90% (mass fraction) is 2.1, 14.1, 24.2, 29.7, 37.9 MPa, respectively. The longer the curing period is, the more complete the reaction is, the more hydration products are, and the higher the strength of specimen is. When the slag content is 50%, the compressive strength of ternary geopolymer at 1, 3, 7, 28 d is 12.3, 24.2, 27.3, 36.8 MPa, respectively. When the slag content is 90% and the curing age is 28 d, the flexural and compressive strength of specimen are the highest, which are 12.0, 52.0 MPa, respectively. The short setting time of the system makes it have a broad application prospect in the field of road repair materials and 3D printing.

Experimental Study on Hemihydrate Phosphogypsum Modified by Magnesium Oxysulfate Cement

WENG Youfa, LI Moxian, WANG Chaofan, CHEN Bing

2023, 42(6):  2115-2120. 

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Aiming at the problems of low mechanical properties and poor water resistance of hardened hemihydrate phosphogypsum, magnesium oxysulfate cement was used to modify hemihydrate phosphogypsum. The effects of magnesium oxysulfate cement content on setting time, mechanical properties and water resistance of hemihydrate phosphogypsum were investigated. The mechanism of magnesium oxysulfate cement modified hemihydrate phosphogypsum was analyzed from a microscopic point of view. The results show that adding magnesium oxysulfate cement significantly delays the final setting time of hemihydrate phosphogypsum and ensures construction operation time of hemihydrate phosphogypsum. Sulfate ions that dissolved and ionized in hemihydrate phosphogypsum participate in the hydration process of magnesium oxysulfate cement, forming a stable 517 phase filled in dihydrate gypsum, resulting in a great improvement of mechanical properties and water resistance of hemihydrate phosphogypsum.

Research and Application of Cement-Phosphogypsum Stabilized Crushed Stone Pavement Base Material

LIU Chao, ZHAO Deqiang, MA Qian, CHEN Gui, HUANG Ya, SHEN Weiguo

2023, 42(6):  2121-2130. 

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In order to promote the comprehensive utilization of phosphogypsum (PG) and improve the crack resistance of cement stabilized crushed stone, the cement-PG stabilized crushed stone material was prepared by partially replacing fine aggregate with PG. The factors affecting the strength, water stability, and crack resistance of the material were systematically analyzed. The results show that the cement dosage, PG content, and aggregate gradation have a significant impact on the strength of cement-PG stabilized crushed stone material. Properly reducing the mass fraction of fine aggregate by 5%~10% is more conducive to the formation of the framework dense structure. PG has a filling effect offine aggregate and promotes the growth of expansive ettringite (AFt) crystals. When the content of PG is 8% (mass fraction), the strength retention rate of cement-PG stabilized crushed stone after soaking in water for 7 d is 73.4%, showing the fine water stability. Compared with cement stabilized crushed stone, its 7 d strength increases by 26.7% and 28 d dry shrinkage strain is reduced by 40.3%. An engineering application is carried out on a secondary road in Guizhou Province, and the pass rate of the test section is 100%, verifying the feasibility of the mix proportion.

Effects of Retarders on Properties of Phosphogypsum-Sulfoaluminate Cement Composite Cementitious System

WAN Ziheng, JIN Zihao, SU Ying, WANG Liyue, WANG Bin

2023, 42(6):  2131-2039. 

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In this paper, the effects of citric acid (CA) and protein retarder (SC) on the properties of phosphogypsum-sulfoaluminate cement composite cementitious system were investigated. The fluidity, setting time and compressive strength were tested to evaluate the workability and mechanical of composite system, and the change of conductivity, phase composition and microstructure were analyzed to clarify the influence mechanism of different retarders. The results show that the strength loss of composite cementitious system under the action of SC is smaller than that of CA when the same setting time is achieved. The addition of two retarders has a certain inhibitory effect on the dissolution of composite system during the hydration induction and the acceleration period, and CA has a greater inhibitory effect than SC at the same content. CA can cause gypsum dihydrate crystals to show a flat and coarse structure, which has a greater impact on the mechanical properties, while SC increases the overall scale of gypsum dihydrate crystals, with little change in crystal morphology, which has a smaller effect on the deterioration of the mechanical properties of composite system.

Activity and Influence Factors of New Biomass Silicon Admixture

CAO Feng, QIAO Hongxia, ZHANG Ying, LI Shuangying, ZHAO Ziyan

2023, 42(6):  2140-2149. 

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In order to solve the problem of resource disposal of abandoned crop highland barley straw, the abandoned highland barley straw is naturally burned outdoors and then calcined and ground again to prepare new biomass silicon admixture. The preparation conditions and design parameters of highland barley straw ash (HBSA) were preliminarily analyzed and verified by orthogonal test design. The response surface optimization analysis method was used to establish the response surface prediction model, and the preparation conditions of HBSA were further optimized and analyzed, so as to verify the rationality of orthogonal test results. In addition, based on grey entropy correlation analysis, the primary and secondary relationship of the influence factors of HBSA activity was determined. The microstructure of HBSA prepared under the optimum conditions was tested and analyzed by using a variety of microscopic testing techniques, and the reason why HBSA can be used as active admixture was revealed. The results show that the activity of HBSA is the highest when the second calcination temperature is 600 ℃, the calcination time is 2 h, and the grinding time is 2 h. The relative activity index of HBSA is 1.06. The response surface optimization method can be effectively used for the design of HBSA activity preparation parameters. The response surface prediction model has a high prediction accuracy, which better verifies the accuracy of orthogonal test results. The gray entropy correlation of calcination temperature is the largest, which should be the primary control factor in the preparation of HBSA. Because HBSA has finer particle size, larger specific surface area and higher active SiO₂ content, it effectively promotes the active effect of HBSA.

Research Progress of Zirconia All-Ceramic Crowns via Stereolithography 3D Printing

ZHOU Yuanheng, CHEN Caijun, GE Junxian, WANG Jiaxin, WEI Ruiyong, XING Zhanwen

2023, 42(6):  2150-2160. 

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Dental diseases such as dental caries and periodontitis often lead to tooth loss, which is common in China. Clinically, oral restoration is mainly used for treatment. Zirconia, with excellent mechanical properties, good biocompatibility and better aesthetic performance, has become an ideal restorative material in the field of dental restoration. Traditional computer aided design/computer aided manufacturing (CAD/CAM) subtractive manufacturing has the high processing accuracy and good marginal adaptation, but it has shortcomings such as material waste, tool wear and insufficient accuracy in the production of occlusal grooves. As a typical representative of rapid prototyping technology, additive manufacturing (3D printing) meets basic requirements for building precision, personalization and structural complexity all-ceramic crowns, and is expected to be a potential technology for the preparation of all-ceramic crowns. The progress of domestic and foreign research teams in the development and application of zirconia all-ceramic crowns using stereolithography 3D printing were reviewed. The ceramic slurry composition, design of printing process support structure, optimization of printing parameters, post treatment process route and evaluation of the performance of the printed products were reviewed and analyzed accompanying by a large number of examples for explanation. Finally, the challenges that will be faced in the future in the field of zirconia all-ceramic crowns via stereolithography 3D printing have been pointed out, and some suggestions have been provided.

Interfacial Reaction Mechanism of Silicon Carbide and Heat Resistant Steel in High-Temperature Vacuum

XIE Yingying, CHEN Mao, SONG Zijie, FAN Bingbing, ZHANG Rui, CHEN Yongqiang

2023, 42(6):  2161-2171. 

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Silicon carbide (SiC) ceramics can be used as inner lining of reduction tank for magnesium smelting. The interfacial reaction between SiC and heat resistant steel was systematically investigated by diffusion couple experiment under vacuum and 1 200 ℃. The results show that at the early stage of reaction, the main products of interfacial reaction are metal silicide and graphite, and the lamellar graphite distributing at the interface hinders the interfacial reaction. However, due to the melting of silicon-nickel compounds with low melting point at interface, the lamellar graphite is transformed into fibrous graphite under the catalysis of Ni, losing its protective effect on silicon carbide. In addition, the interface reaction changes from solid-solid reaction to solid-liquid reaction, and the interfacial reaction process is accelerated, which accelerates the corrosion of silicon carbide by steel. Compared with heat resistant steel, the interfacial reaction rate between SiC and pure iron is obviously decreased, and the temperature required for the reaction is obviously increased. Reducing Ni content in heat resistant steel can effectively prevent the reaction between heat resistant steel and SiC.

Phase Composition Evolution and Properties of Proto-Enstatite-Base Microcrystalline Ceramics Prepared by Asbestos Tailings

LI Xiang, SUN Hongjuan, PENG Tongjiang, CHEN Tao, WANG Can

2023, 42(6):  2172-2181. 

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The proto-enstatite-base microcrystalline ceramics were prepared by one-time method, taking asbestos tailings and quartz sand tailings as main raw materials. The effects of different m(SiO₂)/m(MgO)mass ratios and sintering temperatures on the crystal phase composition, microstructure and physical-chemical properties of microcrystalline ceramic materials were investigated by X-ray diffraction, field emission scanning electron microscopy and other testing methods. The results show that with the increase of m(SiO₂)/m(MgO) mass ratio and sintering temperature, the content of enstatite formed by the reaction of SiO₂ and forsterite in microcrystalline ceramics increases.After sintering at 1 240~1 280 ℃, enstatite is transformed into its high-temperature stable form, proto-enstatite, and the quartz phase that does not participate in the reaction gradually transforms into cristobalite phase. When the m(SiO₂)/m(MgO) mass ratio is 1.43~3.56 and the sintering temperature is 1 280 ℃, the water absorption, bulk density, linear shrinkage and flexural strength are 0.67%~0.15%, 2.74~2.16 g·cm^-3, 10.29%~1.37%, 107.51~40.35 MPa respectively, and the acid and alkali corrosion amount is less than 1.36% and 0.13%, respectively. Each performance index is superior to the standard of Class Ib low water absorption stoneware brick in Ceramic tiles (GB/T 4100—2015).

Effect of Sintering Process on Structure and Properties of Microcrystalline Ceramic Corundum Abrasive with Nano-Seed

2023, 42(6):  2182-2189. 

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Al₂O₃ corundum precursor was synthesized by sol-gel technology, and microcrystalline ceramic corundum (SG) abrasive was prepared by traditional sintering technology with SiO₂-MgO-CaO as sintering aids and α-Al₂O₃ nano-powder as crystal seed. The characteristics of seed and thermal properties of gel precursor were analyzed by means of transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric-calorimetric scanning (TG-DSC). The effects of sintering temperature and holding time on microstructure and mechanical properties of SG abrasive were studied. The results show that α-Al₂O₃ nano-seed makes the transition temperature of θ-Al₂O₃→α-Al₂O₃ decrease by 250 ℃. With increasing sintering temperature and holding time, the single particle compressive strength and density increase first and then decrease, and the grain morphology changes from equiaxed crystal to platelike crystal. Sintering at 1 320 ℃ for 45 min, the single particle compressive strength and density of SG abrasives reach 40.2 N and 3.88 g/cm³, respectively, and the average particle size is 0.56 μm, which is superior to micron seed abrasive samples prepared by traditional sintering technology.

Preparation of High Density LiNbO₃ Ceramics by Spark Plasma Sintering

HOU Junfeng, ZHANG Mingzhe, TIAN Shaohua, WU Jisi, JIANG Wenli

2023, 42(6):  2190-2196. 

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In order to solve the problem of low sintering density caused by low sintering activity of LiNbO₃ powders and loss on ignition of Li element at high temperature, LiNbO₃ powders with stoichiometric ratio were synthesized by solid phase reaction method. The oxygen vacancy concentration of LiNbO₃ powders increased by reduction treatment, and then high density LiNbO₃ ceramics were prepared by spark plasma sintering (SPS) technology. The phase composition, oxygen vacancy concentration and surface morphology of LiNbO₃ powders and the sintered body were characterized and analyzed by XRD, EPR, XPS, Raman spectroscopy and SEM. The results show that the oxygen vacancy concentration of LiNbO₃ powders increases significantly after 700 ℃ reduction treatment, and the oxygen vacancies generate at the lattice position of O atom in Nb—O octahedron. With the increase of SPS temperature, the relative density of LiNbO₃ ceramics shows a trend of increasing first and then decreasing. The relative density of sintered body reaches a maximum of 98.19% at 900 ℃. After annealing and oxygen increasing treatment at 800 ℃, the color of LiNbO₃ ceramics changes from black to white. At the same time, the oxygen vacancy defect of LiNbO₃ ceramics is eliminated and the relative density is 98.32%. This study provides a new idea for the preparation of high density alkali metal niobate ceramics.

Dry Spinning of Polysilazane and Ultraviolet Irradiation Cross-Linking of Fibers

LUO Xiaoyu, LI Xiaohong, ZHANG Mengna, CHEN Hao, BAO Zhihao, CHEN Jianjun

2023, 42(6):  2197-2205. 

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The precursors of polysilazane (PSZ) with different weights were dissolved in xylene to obtain the spinning solution with different concentration. PSZ spinning solution was converted to SiCN(O) fibers by dry spinning, ultraviolet (UV) irradiation cross-linking, and pyrolysis at 1 100 ℃. The rheological property of PSZ spinning solution and the UV irradiation cross-linking process of PSZ fibers were investigated by rotational rheometer, FTIR, XPS, SEM and TG. The composition, structure and properties of PSZ fibers and SiCN(O) fibers before and after irradiation were also characterized. The results show that the PSZ spinning solution with the mass fraction of 87% has shear thinning behavior at room temperature, which belongs to the pseudoplastic fluid and has excellent dry spinning performance. The ceramic yield of PSZ fibers increases by 30.8% compared with the green fibers after 7 h cross-linking under UV irradiation with wavelength of 185 nm. This research has certain exploration significance for the new spinning process of PSZ and the curing treatment of PSZ fibers.

Comparative Study on Composition, Structure and Mechanical Properties of Three Typical Alumina Insulator for UHVDC

--, 修订日期:--

2023, 42(6):  2206-2214. 

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Composition and structure are the two most essential factors for insulator materials performance. In this paper, the differences in composition, structure and mechanical properties of three typical alumina insulator for ultra high voltage direct current (UHVDC) were systematically studied, and the reasons were analyzed. The results show that compared with NGK, two domestic manufacturers have added more calcined industrial alumina, less potash feldspar and quartz into the formula, and have not properly raised the sintering temperature according to the formula, the porcelains of two domestic manufacturers show the following characteristic: 1) the content of Al₂O₃ are 47.22% and 45.24%, respectively, 7.31% and 5.33% higher than that of NGK, the content of SiO₂ are 46.32% and 48.44%, respectively, 7.09% and 4.97% lower than that of NGK, and the total content of K₂O+Na₂O are 3.21% and 3.14%, respectively, 0.41% and 0.48% lower than that of NGK; 2) the true porosity are 5.24% and 4.18%, respectively, 3.46% and 4.52% lower than that of NGK. The internal pores are basically less than 5 μm, and the pore size is generally smaller. There are many flat, slender, crack like pores, as well as annular pores and cracks surrounding the particles; 3) the content of internal crystalline phase is 48.10% and 49.04%, respectively, which is nearly 10% higher than NGK, with corundum phase being 10% higher, quartz phase being 4% higher, mullite phase being 4% less. The mullite phase is thinner and shorter, and the degree of crosslinking is lower; 4) the average value of the three-point bending strength of the porcelain head test strip are 155 and 158 MPa, respectively, which are higher than NGK, but the dispersion strength of the two domestic manufacturers is higher than NGK.

Glass

Effects of Zirconia Content and Heating Rate on Crystallization Behavior of LAS Transparent Glass Ceramics

HU Wei, YIN Yongming, MENG Hong

2023, 42(6):  2215-2222. 

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Li₂O-Al₂O₃-SiO₂ (LAS) system high crystallinity transparent glass ceramics with different ZrO₂ content were prepared by conventional melt quenching and two-step crystallization approaches. The crystallization kinetics, phase evolution, structure and light transmittance of LAS glass ceramics were studied. The results show that when the content of ZrO₂ increases to a certain amount, the crystallization mode of glass gradually changes from one-dimensional growth to two-dimensional growth, and its crystallization exothermic peak T_p value gradually increases, while its crystallization activation energy gradually decreases. In the process of crystal phase transformation, the glass precipitated crystal phases include lithium silicate (Li₂SiO₃) crystal, lithium permeating feldspar (LiAlSi₄O₁₀) crystal and lithium disilicate (Li₂Si₂O₅) crystal. It is found that when lithium silicate (Li₂SiO₃) crystal is transformed into lithium disilicate (Li₂Si₂O₅) crystal, the transmittance of glass increases. In additions, SEM results show that with the decrease of heating rate, the crystal size of glass precipitation gradually increases, and the crystal morphology is mainly spherical.

Effects of Fe₂O₃ Content and Crystallization Process on Elastic Modulus of Alkali-Free Aluminosilicate Glass

ZHAN Lingli, TAN Hao, MA Shiyu, HAN Lixiong, XIE Jun, XIONG Dehua

2023, 42(6):  2223-2232. 

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In this work, CaO-MgO-Al₂O₃-SiO₂ (CMAS) system alkali-free aluminosilicate glass was selected as the research object. Eight groups of Fe₂O₃ component variables were designed, and the experimental samples were prepared by high temperature melting method. XRD, SEM, TG-DSC and other test methods were used to tested and analyzed the phase, crystallization kinetics, crystallization behavior and elastic modulus of alkali-free glass samples, and then the effects of Fe₂O₃ content and crystallization treatment on the elastic modulus of alkali-free glass were discussed. The results show that the appropriate addition of Fe₂O₃ improves the elastic modulus of CMAS system alkali-free glass. When the mass fraction of Fe₂O₃ is 1.50% (F-6#), the maximum elastic modulus of F-6# alkali-free glass is 97.87 GPa, the crystallization activation energy is 347.1 kJ/mol, and the crystallization index n is 1.383 4, which is surface crystallization.After crystallization treatment by bulk crystallization method, the main crystalline phase precipitated from F-6# glass-ceramics is anorthite phase (CaAl₂Si₂O₈), and the crystal size is 200~400 nm. After crystallization treatment by sintering method, the main crystalline phase precipitated from F-6# glass-ceramics is anorthite phase (CaAl₂Si₂O₈), and the crystal size is 300~500 nm. With the increase of heat treatment temperature, the number and size of the precipitated main crystal phase increase, but the type of the main crystalline phase keeps unchanged. However, because the elastic modulus of anorthite is smaller than that of the base glass, the elastic modulus of the glass-ceramics obtained after crystallization of F-6# alkali-free glass decreases.

New Functional Materials

Preparation of Superhydrophobic SiO₂ Aerogel by Liquid-Liquid Solvent Replacement Method

LIU Weihai, XIA Chenkang, ZHANG Xinyuan, HAO Mingyuan, MIAO Yang, GAO Feng

2023, 42(6):  2233-2241. 

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In the field of thermal insulation, SiO₂ aerogel has attracted much attention because of its outstanding performance, but the high cost of organosilicon source limits its popularization and application. In order to reduce production cost, researchers have turned their attention to inorganic silicon source, but the preparation of SiO₂ aerogel using inorganic silicon source requires complicated solvent replacement. To solve the problem of solvent replacement, using coal gangue as raw material, the new type of liquid-liquid solvent displacement method combining with low temperature activation method were adopted to prepare super hydrophobic SiO₂ aerogel. The results show that when the activation temperature is 200 ℃, the gangue acid ratio is 1.0∶1.0 (ratio of solid mass to liquid volume), residue and NaOH solution ratio is 1.0∶1.0 (ratio of solid mass to liquid volume), activation conditions are the best. The prepared SiO₂ aerogel has unique three-dimensional network structure, high specific surface area (687.7 m²/g), super hydrophobicity (161.9°) and low density (0.034 g/cm³). This method provides a new idea for preparing SiO₂ aerogel from inorganic silicon source and significantly reduces the cost of preparing SiO₂ aerogel.

Preparation and Adsorption Properties of Boron-Nitrogen Co-Doped Biochar Materials

XU Meng, GUO Yucheng, LIN Guoqiang, LI Jianbao, CHEN Yongjun, LUO Lijie

2023, 42(6):  2242-2250. 

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Boron-nitrogen co-doped biochar material was prepared by high temperature reaction under ammonia (NH₃) atmosphere, using kapok, boric acid (HBO₃), and urea (CO(NH₂)₂) as raw materials. The PEI-BCN material was obtained by treating boron-carbon-nitrogen (BCN) material with polyethyleneimine (PEI), and the adsorption properties of PEI-BCN material were studied. The results show that the prepared BCN material has a porous structure with an average pore size of 11.0 nm when the reaction temperature is 1 100 ℃. The adsorption property of BCN material is better than that of biochar, and after PEI modification, the adsorption property of BCN material is greatly improved. The adsorption amount of organic dye malachite green (MG)by PEI-BCN material is up to 710.0 mg/g, showing excellent adsorption property. The adsorption of PEI-BCN material is consistent with the pseudo-first-order adsorption kinetics model, and the adsorption of MG by PEI-BCN material belongs to Langmuir isothermal adsorption.

Preparation of 4A Molecular Sieve from Coal Gasification Slag and Its Adsorption Performance

XU Qibin, NIU Xiangli, CHEN Tingting, CHEN Yuxin, LI Yang, ZHANG Hua, NI Hongwei

2023, 42(6):  2251-2261. 

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In order to solve the difficult problem of comprehensive utilization of coal gasification slag (CGFS), 4A molecular sieve was synthesized with CGFS as raw material by an alkali fusion-water leaching-hydrothermal method. Under the conditions that the molar ratio of water to sodium (n(H₂O)/n(Na₂O)) is 80 and the molar ratio of silicon to aluminum (n(SiO₂)/n(Al₂O₃)) is 2, the effects of reaction time, hydrothermal temperature and precursor aging time on the phase structure and microstructure of prepared 4A molecular sieve were investigated. The phase transformation and synthesis mechanism for activated CGFS-P1 molecular sieve-4A molecular sieve were proposed. Meanwhile, the adsorption performance of the prepared 4A molecular sieve for Cu²⁺ in the solution was tested by using copper sulfate solution to simulate industrial wastewater containing heavy metal ions. The results show that 4A molecular sieve with uniform size and well crystallization could be prepared at 100 ℃ for 12 h. The adsorption of Cu²⁺ by 4A molecular sieve mainly occurrs in the initial 10 min and the adsorption rate reaches 69.7%. The saturated adsorption rate reaches 97.3% in 90 min and the saturated adsorption capacity is 196.4 mg/g. It is indicated that the prepared 4A molecular sieve exhibits good adsorption performance, which provides the theoretical and experimental foundation for the high value-added utilization of CGFS.

Contact Characteristics of G/FTO Bilayer Films Based on Atomic Force Microscopy

WANG Min, CAI Wenhao, YU Jianyuan, WANG Zhihao, ZHOU Haozhe, ZHAO Hongli

2023, 42(6):  2262-2272. 

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Single layer graphene (G) and fluoride doped tin dioxide(FTO) thin film were compounded together by wet etching method. The structure, surface and interface topography and elemental distribution of G/FTO bilayer film were investigated by Raman spectroscopy, focused ion beam (FIB) and transmission electron microscopy (TEM). The topography, contact potential difference (CPD), work function and contact barrier of FTO film and G/FTO bilayer film were investigated using Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM) based on atomic force microscopy (AFM). The results show that the contact potential difference of FTO film and G/FTO bilayer film is -0.474 and -0.441 V, respectively, and the work function of the two films is 5.329 and 5.296 eV, respectively. Compared with FTO film, the mobility of G/FTO bilayer film increases from 21.26 cm²·V^-1·s^-1 to 23.82 cm²·V^-1·s^-1. The corresponding barrier height of FTO film and G/FTO bilayer film is (0.39±0.06) V and (0.33±0.05) V, respectively, and the barrier height of G/FTO bilayer film is smaller.

Controllable Preparation and Properties of Layered Al₂O₃/EP Composites

HOU Junfeng, TANG Pengcheng, TIAN Shaohua, ZHANG Mingzhe, WU Jisi

2023, 42(6):  2273-2280. 

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The Al₂O₃ 3D network skeletons with layered structure were constructed by ice template method. The epoxy (EP) was successfully infiltrated into the pores of porous Al₂O₃ material by vacuum impregnation process, and finally the Al₂O₃/EP composites were prepared. The influences of wedge silicone rubber angle, slurry solid content and freezing temperature on the microstructure of layered Al₂O₃ 3D network skeleton were investigated. And the influence of the lamellar spacing on the thermal, dielectric and insulation properties of Al₂O₃/EP composites was analyzed. The results show that the order of layered Al₂O₃ 3D network skeleton is the best with the wedge silicone rubber angle of 10° and 15°. Simultaneously, the lamellar spacing in the Al₂O₃ 3D network skeleton decreases with the increase of solid content and the decrease of freezing temperature. The thermal conductivity and dielectric constant of Al₂O₃/EP composites increase with the decrease of the lamellar spacing, but the volume resistivity shows a decreasing trend. When the lamellar spacing is 45 μm, the thermal conductivity reaches 0.52 W/(m·K) and the volume resistivity is 10¹² Ω·cm.