Table of Content

15 August 2022, Volume 41 Issue 8

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Invited

Research Progress of Mid-Infrared Tellurite Glass and Optical Fibers

WAN Rui, YANG Liqing, HUO Weirong, MA Yuan, LI Shengwu, GUO Chen, WANG Pengfei

2022, 41(8):  2589-2603. 

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Near/mid-infrared (NIR/Mid-IR) lasers and supercontinuum light sources have very important applications in the fields of infrared optoelectronic countermeasure, biomedical technology, telemetry sensing, and light laser detection and ranging (LIDAR), etc. In recent years, researches on the generation and transmission of high-brightness NIR/Mid-IR (especially 2~5 μm) laser based on soft glass fibers have made remarkable progress. Among the soft glass systems, tellurite glass having relative lower phonon energy is particularly attractive for the design of NIR/Mid-IR lasers and amplifiers, as well as passive optical fibers for high-power Mid-IR laser transmission and sensing applications. In this paper, the key preparation technologies of low loss tellurite glass were summarized, and the research progress of Mid-IR luminescence of rare earth doped tellurite glass and optical fibers was reviewed. Finally, the existing problems and development trend of tellurite glass and fibers were summarized and prospected.

Cement and Concrete

Review on Mechanism of Chloride Ion Binding and Its Influencing Factors in Cement-Based Materials

GENG Yuanjie, SUN Congtao, SUN Ming, ZHANG Yuguo, DUAN Jizhou

2022, 41(8):  2604-2617. 

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The chloride ion binding ability of cement-based materials mainly depends on the content and stability of hydrate calcium silicate (C-S-H) gel and Friedel's salt, and the high content and the great stability of both are benefit to improve the chloride ion binding ability. The influences of various factors, such as cement type, mineral admixture type, temperature, chloride ion concentration, cation type, sulfate erosion and carbonization should be considered in the analysis of the chloride ion binding ability of cement-based materials. They will directly affect the production of C-S-H gel and Friedel's salt, or indirectly affect the pH value and ion concentration of pore fluid to change the stability of C-S-H gel and Friedel's salt, thus affecting their physical adsorption ability and chemical binding ability, and promoting the recombination and release of chloride ions, eventually, causing significant change in chloride ions binding ability. In this paper, the changes of C-S-H gel and Friedel's salt content and stability in cement-based materials under the above factors, as well as their influences on chloride ion binding ability were reviewed, and some suggestions for future research were put forward.

Deterioration Mechanism of Supersulfated Cement Paste by Acid Erosion

GAO Fuhao, WANG Lu, LIU Shuhua

2022, 41(8):  2618-2627. 

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The mechanical properties of supersulfated cement (SSC) and Portland cement under hydrochloric acid attack were investigated, and the deterioration mechanism by acid erosion was discussed in this paper. The compressive strength of SSC paste in hydrochloric acid and water were measured and the compressive strength retention rate was calculated. The changes of the types and quantities of hydration products and the evolution of microstructure were analyzed by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TG-DTG). The experiment results show that the main hydration products of SSC are ettringite and calcium silicate hydrate, which are different from Portland cement. Compared with Portland cement, SSC shows better compressive strength retention rate and resistance to acid. The deterioration of SSC in hydrochloric acid can be attributed to the dissolution of main hydration products. There are dihydrate gypsum and a lot of silica gel in SSC system, and silica gel in Portland cement after erosion.

Effect of EVA on Microstructure and Mechanical Properties of Calcium Sulfoaluminate Cement Paste

HE Xiangxiang, MEI Junpeng, JIANG Tianhua, LI Hainan, XU Zhidong, WANG Zhixin, ZHOU Lanlan, ZHOU Zhiyang

2022, 41(8):  2628-2636. 

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The effect of ethylene-vingyl acetate (EVA) on compressive strength, setting time, drying shrinkage, mass loss and internal temperature of calcium sulfoaluminate cement (CSA) paste was studied, and the hydration products and microstructure at the age of 6 h and 28 d were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results show that the setting time of CSA paste decreases significantly with the addition of EVA, and the compressive strength increases at 6 h, but decreases at 1 d, 3 d, and 28 d. The drying shrinkage and mass loss ratio of CSA paste gradually decrease with the increases of EVA. The addition of EVA improves the peak value of the internal temperature curve of CSA paste, and accelerates the appearance time of the peak value. Microscopic analysis shows that EVA could promote the hydration of CSA paste at 6 h, resulting in the formation of more ettringite, while it has inhibitory effect on the hydration of CSA paste at 28 d, and the hydration products reduce.

Effect of SO₄^2-/C₃A Ratio on Formation of Thaumasite in Monomineral C₃S Cement Paste

LI Xiangguo, TIAN Bo, HE Chao, LYU Yang, JIAN Shouwei, JIANG Dongbing, ZHANG Cheng, ZHOU Yang

2022, 41(8):  2637-2643. 

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Thaumasite sulfate attack (TSA) is a sulfate attack with thaumasite as the product, and the formation process of thaumasite is closely related to the aluminum source in cement-based materials and sulfate in the external environment. In this paper,aluminum source tricalcium aluminate (C₃A), erosion medium Na₂SO₄ solution and monomineral tricalcium silicate (C₃S) were used to prepare the cement paste. XRD, FTIR and SEM/EDS were used to characterize the effects of different molar ratios of SO^2-₄ to C₃A (S/Al ratios) on the formation of thaumasite in monomineral C₃S cement paste, so as to reveal the formation mechanism of thaumasite and find the methods to inhibit its formation. The results show that when the S/Al ratio is 3, there is no thaumasite detected in the erosion products after 14 months of attack. When the S/Al ratio is 6 and 9, thaumasite can be detected after 3 months, indicating that the higher external sulfate ion concentration is more beneficial for the formation of thaumasite.

CO₂ Corrosion Kinetics of C₃S in Cement Single Ore under CCUS Environment

GAO Qiang, MEI Kaiyuan, WANG Dekun, ZHANG Liwei, ZHANG Chunmei, CHENG Xiaowei

2022, 41(8):  2644-2653. 

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Under thecarbon capture, utilization and storage (CCUS) well, the oil well cement will be carbonized and corroded due to the long-term action of downhole high temperature, high pressure and highly acidic fluid, resulting in the failure of the cement sheath. In order to simulate the carbonation and corrosion environment of CO₂ geological storage well, the main single ore mineral calcium silicate (C₃S) of oil well cement was placed under different temperatures (30 ℃, 60 ℃, 90 ℃) and sealed 8.0 MPa gas or liquid phase CO₂ carbonization environment. XRD and TGA were used to analyze the influence of C₃S in cement single ore by CO₂ corrosive environment. According to the infiltration theoretical model of unsteady Fick diffusion, a mathematical model of the quantitative analysis results of corrosion products and corrosion age was established, and the product formation coefficient of C₃S after being corroded by CO₂ was obtained by fitting, so as to evaluate the influences of different CO₂ corrosion factors on C₃S. The results show that the increase of temperature significantly aggravates the corrosion of C₃S and leads to the dissolution phenomenonin the gas phase environment of CO₂. While in the liquid phase environment of CO₂, the high temperature (90 ℃) makes the C₃S hydration reaction intensify, forming a retardation layer and slowing down the CO₂ corrosion rate to C₃S.

Effect of Potassium Hydroxide-Sodium Water Glass Activator on Properties of Alkali-Activated Slag Cementitious Materials

WANG Lingling, SI Chenyu, LI Chang, SUN Xiaowei, ZHOU Honghong, GUO Shimeng

2022, 41(8):  2654-2662. 

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Potassium hydroxide was used to adjust the modulus of sodium water glass to prepare compound alkali activator. Taking sodium water glass modulus and alkali content as variables,the effect of potassium hydroxide on sodium water glass activated slag cementitious material performance was analyzed, and the change law of fluidity, setting time and compressive strength of potassium hydroxide-sodium water glass activated slag cementitious material was studied. The results show that the stimulating effects of potassium hydroxide-sodium water glass compound alkali activator are better than those of single sodium water glass activator. When the sodium water glass modulus is 1.2 and the alkali content is 8% (mass fraction), the fluidity of potassium hydroxide-sodium water glass activated slag cementitious materials reaches up to 240 mm, and the compressive strength of 7 d and 28 d reaches up to 98.88 MPa and 104.59 MPa, which is 16.7% and 22.9% higher than that of the sodium water glass activated slag cementitious materials under the same conditions.

Interface Modification of Water Absorbent Microcapsules to Improve Impermeability of Cement-Based Materials

ZHANG Lu, MAO Qianjin, WU Wenwen, LI Runfeng, HAN Lei, WANG Ziming, CUI Suping

2022, 41(8):  2663-2671. 

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In self-healing cement-based materials, the interface between microcapsules and cement matrix determines the probability of microcapsules triggered by cracks, which affects the self-healing effect. Aiming at the interface bonding problem of water absorbent microcapsules, the surface of epoxy/calcium alginate microcapsules was modified with silane coupling agent KH550 to improve the interface bonding between calcium alginate microcapsules and cement matrix. The X-ray photoelectron spectrometer and inductively coupled plasma emission spectrometer were used to characterize the bonding condition of silane coupling agent on the surface of microcapsules. The pore structure of cement-based materials was analyzed by mercury injection method, and the impermeability and self-healing effect of cement-based materials were tested. The results show that the silane coupling agent forms the chemical bonding with the calcium alginate on the outer wall of the microcapsule. The interface between the microcapsules and the cement matrix is effectively improved. The number of harmful pores in the cement matrix is reduced, and the number of harmless and less harmful pores increases. The impermeability and self-healing effect of cement-based materials are improved.

Influence of Oxygen Concentration on Reinforcement Corrosion in Seawater Sea-Sand Mortar Based onWire Beam Electrode Technique

GAO Yuan, JIN Zuquan, LI Ning

2022, 41(8):  2672-2683. 

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To find out the influence of oxygen concentration on reinforcement corrosion in seawater sea-sand mortar, the wire beam electrode (WBE) technique was introduced. The influences of oxygen concentration (5%, 21%, 85%, volume fraction) and water-binder ratio (W/B) (0.48, 0.18) on time-dependent behavior of corrosion potential and electrochemical impedance spectroscopy (EIS) of WBE were separately investigated. Results show that the polarization resistance of WBE decreases and corrosion current density increases with the increase of corrosion time. The changes are greater with the increase of oxygen concentration and W/B.It can be observed from the experimental results that the corrosion probability of reinforcement increases with the increase of oxygen concentration. At a low oxygen concentration (5%), the reinforcement depassivation induced by chloride can be effectively retarded and thus the reinforcement corrosion is restrained. While at a high oxygen concentration, the reinforcement experiences a nonuniform corrosion process with progressive oxygenation from part to the whole. The anticorrosion capacity of reinforcement in seawater sea-sand cement-based systems can be effectively improved by decreasing W/B.

Tensile Property and Crack Control Mechanism of Basalt Fiber Reinforced Polymer Bar Reinforced ECC

OUYANG Jianxin, GUO Rongxin, WAN Fuxiong, MA Qianmin, YANG Yang

2022, 41(8):  2684-2695. 

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Engineered cementitious composite (ECC) has become a research hotspot because of its high toughness and multiple cracking characteristics. Fiber reinforced polymer (FRP) has attracted extensive attention because of its high tensile strength, low density and good corrosion resistance. In order to study the tensile property of basalt fiber reinforced polymer (BFRP) bar reinforced ECC (BFRP-ECC) and the crack control mechanism of bars on the matrix, considering different types of matrix and reinforcement ratio, an experimental program on ECC dog-bone specimens, BFRP-ECC and BFRP-mortar thin plate specimens was conducted under uniaxial tensile loading. At the same time, the full field strain and cracking state of specimens were obtained by digital image correlation (DIC) technology. Based on Richard's elastic-plastic stress-strain formula, the BFRP-ECC stress-strain constitutive model was proposed. The results show that the ultimate tensile stress of BFRP-ECC increases with the increase of reinforcement ratio. The enhancing effect of ECC matrix on the tensile property of composites is better than that of mortar matrix. At the same time, the composites based on ECC are obviously better than those based on mortar in the control of crack spacing and width. BFRP bar can increase the bridging stress at BFRP-ECC cracks, reduce the crack spacing and width, and increase the number of cracks. The uniaxial tensile stress-strain constitutive model of BFRP-ECC established in this paper is in good agreement with experimental data, which better reflects the tensile stress-strain relationship of BFRP-ECC.

Experimental Study on Electrical Properties of Carbon Fiber-Steel Fiber Cement Matrix Composites

WANG Congcong, DU Hongxiu, SHI Lina, FAN Qi

2022, 41(8):  2696-2705. 

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To optimize the electrical properties of cement matrix composites, carbon fiber (CF) and steel fiber (SF) were added into the composites as conductive materials, and the influence of the volume content of carbon fiber and steel fiber on the compressive strength and electrical properties of cement matrix composites were studied through compressive strength test, AC impedance test, scanning electron microscopy test and heating test. The results show that the compressive strength of carbon fiber-steel fiber cement matrix composites increases first and then decreases with the increase of the content of carbon fiber. The percolation threshold of carbon fiber and steel fiber is 0.35% and 0.6% (both are volume fraction). The electrical conductivity of cement matrix composites is greatly enhanced by adding carbon fiber and steel fiber, and an obvious positive hybrid effect is produced. The continuous increase of fiber content has little effect on the improvement of electrical conductivity after the volume content of carbon fiber and steel fiber reaches the percolation threshold. The values of each circuit element of the equivalent circuit are fitted by ZSimp Win software, and the conductive mechanism is analyzed combined with SEM images. Carbon fiber-steel fiber cement matrix composites have good electrothermal performance, when the input power is 7.9 W, the average temperature reaches 33 ℃, 43 ℃ and 50 ℃ after energizing for 30 min, 60 min and 90 min. The regression equation of temperature with time is obtained by curve fitting.

Chloride Penetration Resistance of Ultra-High Performance Concrete under Hydrostatic Pressure

WEI Jiangang, CHEN Rong, HUANG Wei, CHEN Zhendong, CHEN Baochun, CHEN Peibiao, ZHU Weidong

2022, 41(8):  2706-2715. 

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The pore structure of ultra-high performance concrete (UHPC) was analyzed by nitrogen adsorption and desorption (NAD) test in this paper. The influence of steel fiber and mineral admixture on the chloride ion transport behavior of UHPC under different hydrostatic pressures were investigated.Scanning electron microscope and energy dispersive spectrometer analysis were conducted to examine the microstructure of UHPC. The results show that the addition of steel fiber increases the porosity of UHPC matrix, while the variation is not obvious. The addition of slag reduces the porosity of matrix. When the early steam curing is followced by standard curing to 28 d,a large amount of fly ash increases total porosity. The chloride ion concentration and apparent chloride diffusion coefficient at the same depth increase with the increment of hydrostatic pressure, which is more significant under the pressure of 2 MPa. It is found that the linear relationship exist in the content of free chloride ions and the content of total chloride ions. The incorporation of steel fiber reduces the chloride binding ability, while the incorporation of slag and fly ash effectively improves the binding rate of chloride ion,and the maximum chloride binding rate reaches 46.29%. Scanning electron microscope and energy dispersive spectrometer observation suggest that the corrosion of steel fiber only occurs on the surface of UHPC.

Relationship Between Pore Structure, Fractal Dimension and Chloride Diffusion Performance of Concrete

ZHANG Qingzhang, FANG Yan, SONG Li, XU Ning, KANG Zihan

2022, 41(8):  2716-2727. 

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Chloride diffusion coefficient is one of the important parameters to study the durability of concrete structures in marine environment. Through mercury intrusion test and salt spray diffusion test of concrete with different water-binder ratios, the influences of porosity, pore size distribution and critical pore size on chloride diffusion coefficient in concrete were studied. The relationship between the fractal dimension of pore volume and thechloride diffusion coefficient was established based on Menger sponge model. The results show that the porosity and critical pore size are highly correlated with the dimensionless chloride diffusion coefficient, which can be used as important parameters to reflect the chloride diffusion performance of concrete. The distribution of fractal dimension of pore surface calculated by mathematical analysis is 2.56~3.86, and that of pore volume is 2.85~2.98. The fractal dimension of pore volume calculated by mercury intrusion test and fractal theory can be used as an index to evaluate the chloride diffusion coefficient. Thechloride diffusion coefficient decreases with the increase of the fractal dimension of pore volume in four ranges of pore size less than 10 nm, 10~100 nm, 100~1 000 nm and more than 1 000 nm.

Damage Properties of Fiber Concrete under Coupling Effect of Continuous Loading and Freeze-Thaw Cycles

SUN Jie, FENG Chuan, WU Shuang, MA Wen, SUN Mingxing

2022, 41(8):  2728-2738. 

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In order to study the damage performance offiber concrete under the coupling effect of continuous loading and freeze-thaw cycles, the freeze-thaw cycle experiment of fiber concrete was performed under the effect of different compressive stress levels (0, 0.3, 0.5), some parameters, such as test mass loss, relative dynamic elastic modulus and compressive strength loss and so on, were studied with the number of freeze-thaw cycles.Combined with damage mechanics, taking ultrasonic wave velocity as damage variable, the relationship between freeze-thaw damage and load coupling action were analyzed. The freeze-thaw damage prediction model was established according to the Weibull and the evolution equation of freeze-thaw damage and compressive strength was obtained. The results show that, with the increase of the number of freeze-thaw cycles, the freeze-thaw damage of fiber concrete is reduced under the coupling of stress level of 0.3, and the freeze-thaw damage of fiber concrete is further aggravated under stress level of 0.5. The damage prediction model has high feasibility and it accurately predicts the different damage after freeze-thaw cycles. The evolution equation derived has better correlation, and it flexibly realizes the transformation between freeze-thaw damage and compressive strength.

Deflection and Ductility of FRP Bars Reinforced Concrete Superposed Beams

ZHANG Jianbo, CHEN Shengping, LU Yingfa

2022, 41(8):  2739-2747. 

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In order to improve the flexural behavior and ductility of fiber reinforced polymer (FRP) bars reinforced concrete superposed beams, the effects of steel fiber content and thickness of steel fiber reinforced concrete superposed layer on the FRP bars reinforced concrete beams were studied. The volume content of steel fiber (0%, 0.5%, 1.0%, 1.5%) and thickness of steel fiber reinforced concrete superposed layer (0 mm, 180 mm, 210 mm, 300 mm) were taken as variables. The failure process, failure mode, crack width and mid-span deflection of six FRP bars reinforced concrete superposed beams were analyzed by three-point loading test. The results show that the addition of steel fiber improves the mechanical properties of tested beams and makes failure mode of tested beams develop from brittle failure to ductile failure. With the increase of the ratio of steel fiber and thickness of steel fiber reinforced concrete superposed layer, the ultimate bearing capacity, flexural resistance and ductility evaluation index of FRP bars reinforced concrete superposed beams increase by 9%~33%, 4%~18% and 22%~89%, respectively. Based on the experimental and theoretical analysis, the deflection calculation formula and ductility evaluation method of the FRP bars reinforced concrete superposed beams on the factor of steel fiber are established.

Experimental Study on Performance Optimization of Pervious Recycled Concrete Based on Orthogonal Test

XIA Dongtao, LI Xiangyang, HU Jun'an

2022, 41(8):  2748-2758. 

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Pervious concrete has wide application prospects in alleviating urban waterlogging, noise effect and heat island effect, but its low strength due to porosity limits its further application. The recycled coarse aggregate and polypropylene fiber were used to formulate high performance pervious concrete. A five-factor, four-level orthogonal test was designed to analyse the effects of water-binder ratio, target porosity, recycled coarse aggregate replacement rate, fly ash content and polypropylene fiber content on the performances of pervious recycled concrete in terms of compressive strength, effective porosity and permeability coefficient using the extreme difference method. The results show that the main factors affecting the compressive strength of pervious recycled concrete are: target porosity>recycled coarse aggregate replacement rate>water-binder ratio>polypropylene fiber content>fly ash content. The maximum compressive strength of pervious recycled concrete is 48.26 MPa and the permeability coefficient is 1.96 mm/s. The compressive strength decreases linearly with the increase of target porosity. The compressive strength of pervious recycled concrete increases by 119.08% to 28.7 MPa and the permeability coefficient increases by 9.44% when 40% of recycled coarse aggregate replaces the natural coarse aggregate by the same amount. The addition of 0.11% by volume of polypropylene fiber increases the compressive strength of pervious recycled concrete by 10.48% to 27.4 MPa, and does not reduce the permeability performance. The results of this study can provide a basis for the preparation of high performance pervious recycled concrete.

Effects of Chopped Carbon Fibers on Pore Structure and Characteristics of Concrete

WANG Huizi, NIE Liangxue, LUO Xin, LIU Pengcheng

2022, 41(8):  2759-2766. 

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For the purpose of explore the effects of chopped carbon fibers (CFs) on the microscopic characteristics of the internal pore structure of concrete, chopped carbon fibers reinforced concrete (CFC) specimens with volume content of 0%, 0.1%, 0.2%, 0.3% and 0.5% of CFs were prepared. The internal pore structure characteristics of each group of specimens were analyzed by means of mercury intrusion porosimetry (MIP), and the fractal law of pore size was further discussed by introducing fractal theory. The results show that adding an appropriate amount of CFs can effectively reduce the total porosity and average pore size of concrete, and the improvement effect reaches the best when the content of CFs is 0.1%. The inner pore size shows remarkable fractal characteristics, and the fitting correlation coefficient R² of ln(W_n/r²_n) and ln Q_n of each group specimens of concrete is more than 0.996, which means the slopes can be used as pore surface fractal dimension (D_p). The D_p decreases firstly and then increases with the increase of CFs content, and the larger the D_p is, the larger the average pore size is, which further verifies the improvement law of CFs on the internal structure of concrete.

Experimental Study on Bond-Slip Mechanical Properties of Concrete with Different Admixtures and Corroded Reinforcement

ZHUANG Binbin, XIAO Chaoxiong, LIU Qiang, DENG Jiahui, WANG Dayang

2022, 41(8):  2767-2773. 

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The center-drawing method was used to conduct bond-slip tests on plain concrete (PC), cementitious capillary crystalline water-proofing concrete (CCCW), and polypropylene fiber reinforced concrete (PFRC) with hot-rolled ribbed steel reinforcement. To investigate the bonding capability of the reinforcement with concrete after rusting, the electrochemical corrosion method was used to accelerate the rusting of the reinforcement. The results show that introducing an appropriate amount of polypropylene fiber and capillary crystallinewater-proofing material into the concrete increase the ultimate bond strength of reinforced steel by 20.8% and 6.8%, respectively. The ultimate bond strength of reinforcement-concrete pull-out specimens with and without admixture shows a linear decreasing trend with the increase of corrosion rate. The formula of ultimate bond strength of concrete with different internal admixtures and corrosion rate is fitted based on the results of the pull-out test, and it is discovered that polypropylene fiber and capillary crystalline water-proofing material could slow down the decrease of ultimate bond strength of reinforced-concrete with the increase of corrosion rate.

Study on Steel Wire Grid Tile Insulation Roof Panel and Its Bending Resistance

SUN Shibing, LI Dayun, LYU Feng, WANG Wanfu, TIAN Yingliang, JIN Xiaodong, WANG Yingshun, WANG Shuyuan, XIN Zhubin, JIANG Lisong

2022, 41(8):  2774-2784. 

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The roof system of traditional houses in villages and towns is mostly slope roof system. The traditional slope roof system has complex construction, poor safety and insufficient thermal insulation, which can not meet the needs of building a new countryside. A new type of steel wire gride tile insulation roof panel was designed to replace the traditional slope roof system. Starting from the raw materials, tile type and structure of roof panel, this paper selected fiber cement-based materials as the base material and steel wire grid insulation composite board as the insulation layer. According to the existing tile type modeling, Abaqus software was used to design the scale tile roof panel, wave tile roof panel and tubular tile roof panel. The three tile roof panels were simulated and calculated, and the tile type with the best mechanical properties was selected to make the steel wire gride tile insulation roof panel. The size of roof panel is 4 500 mm×835 mm×185 mm, self weight is 159 kg/m², heat transfer coefficient is 0.45 W/(m²·K). Through the three-point bending performance test, under the span of 4 020 mm, the roof panel bear maximum load is 8.70 kN and the bending moment is 8.74 kN·m. The new steel wire grid tile insulation roof panel based on the assembly idea has excellent mechanical and thermal insulation properties, which provides a reference for the research of characteristic traditional village slope roof system.

Solid Waste and EcoMaterials

Adsorption of F^- on Calcite Surface and Its Effect on Calcite Surface Properties

YIN Yulan, CHEN Junhong, XIE Yan, AO Xianquan

2022, 41(8):  2785-2791. 

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Fluoride mainly exists in minerals such as phosphate rock and fluorite, which are associated with calcite gangue minerals. Under the condition of the flotation separation of the weak acid, mineral surface of F^- will be partically dissolved and adsorbed to the mineral surface, thus affecting the mineral surface properties. The adsorption behavior of F^- on calcite surface and the effect of F^- on calcite surface properties were studied in this paper. The results show that F^- is adsorbed on calcite surface by chemisorption at 5.5 pH value of calcite pulp, and the adsorption amount increases gradually with the increase of time, and F^- adsorption by calcite reaches equilibrium at 90 min. When sodium oleate (NaOL) is used as collector, the presence of F^- weakens the hydrophobicity of calcite surface. Zeta potential test, solution chemistry calculation and X-ray photoelectron spectroscopy (XPS) analysis show that the F^- reacts with Ca²⁺on calcite surface to form CaF₂ precipitation, which occupies Ca sites on calcite surface and reduces the adsorption of NaOL on calcite surface.

Effect of Ferronickel Slag Sand on Pore Structure and Shrinkage Cracking of Foamed Concrete

XIONG Yuanliang, ZHU Yu, LI Baoliang, CHEN Chun, ZHANG Yamei

2022, 41(8):  2792-2799. 

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In this study, ferronickel slag artificial sand (ferronickel slag sand) was used to produce foamed concrete. Effect of ferronickel slag sand on the compressive strength, deformation and shrinkage cracking of foamed concrete was investigated. Meanwhile, SEM and X-CT were used to investigate the microstructure. Experimental results reveal that the foamed concrete with 5% (mass fraction, the same below) ferronickel slag sand possesses the highest compressive strength. However, too many interfacial defects can be introduced with the addition of ferronickel slag sand above 10%, thus decreasing the compressive strength of the foamed concrete. The ferronickel slag sand can restrict the deformation of the matrix, decrease the usage of cement, mitigate the drying shrinkage of the foamed concrete, and enhance its crack resistance. When the content of ferronickel slag sand increased from 0% to 20%, the crack resistance grade of the foam concrete increases from V to II. Overall, ferronickel slag sand has potential to be used as a raw material in producing foamed concrete.

Characteristics of Yunfu Pyrite Tailings and Performance Analysis as Auxiliary Cementitious Materials

YIN Suhong, ZENG Shaohong, CAO Wenxiang, WU Huanxun

2022, 41(8):  2800-2809. 

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Yunfu pyrite tailings have a huge storage capacity, which affects the surrounding environment and wastes resources. In this paper, the feasibility of high absorption utilization of tailings used as auxiliary cementitious materials was discussed, the mineral and chemical composition of tailings and the occurrence state and content of sulfur were analyzed, and the properties of tailings as auxiliary cementitious materials and the evolution of gypsum and pyrite contained in tailings and their influence on the properties were studied. The results show that Yunfu pyrite tailings belong to high sulfur pyrite tailings, and the sulfur in the tailings exists in the form of pyrite (FeS₂), pyrrhotite (Fe_1-xS) and gypsum. In the hardened cement paste, most of the gypsum in the tailings reacts to form ettringite (AFt) at 28 d, which is the main factor affecting the performance, and the oxidation degree of FeS₂ is still low at 180 d. The 28 d activity index of cement mortar mixed with 30% (mass fraction) pyrite tailings can reach 74%, but compared with 3 d and 7 d, the 28 d activity index does not increase or even decrease, and the compressive strength at 180 d is inverted. It may be a better way to use tailings as cement mixture and coagulant at the same time.

Mechanical Activation of High Silicon Iron Tailings and Its Mechanism

LIANG Zhipeng, SUN Chang, BI Wanli, ZHAO Mingze, GUAN Yan

2022, 41(8):  2810-2818. 

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In order to promote engineering application of iron tailings, taking Benxi high silicon iron tailings in Liaoning Province as an example, the effects of different mechanical activation methods and time on the activity and morphology of iron tailings were studied. The effect of mechanical activation on the particle size distribution, specific surface area, activity index and pozzolanic activity of iron tailings were detected by grading analysis, mortar test, lime adsorption test and so on. The hydration reaction mechanism of cementitious system was explored by X-ray diffraction and scanning electron microscopy analysis. The results show that mechanical activation can refine the partical size of iron tailings, increase the particle roundness and reduce surface crystallinity. Grinding for 40~60 min has the best effect. The activity index is up to 96.6% after wet grinding for 50 min, and the pozzolanic activity is significantly enhanced. The activation effect of wet grinding is better than that of dry grinding. Mechanical activation promotes the secondary hydration reaction between iron tailings and cement, and improves the performance of cementitious system.

Manufacture and Microstructural Characterization of Fly Ash-Muck Artificial Aggregates with High Strength

ZHANG Rihong, MING Wei, WAN Wenhao, LIU Yunpeng

2022, 41(8):  2819-2827. 

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The effect of different proportion of engineering muck and fly ash on the physical properties of artificial aggregates with high strength and low water absorption was studied. Moreover, the mineral composition, microstructure and porosity of artificial aggregates were characterized by X-ray diffractometer, X-ray computed tomography (X-CT), mercury intrusion porosimetry and scanning electron microscope. The results indicate that the density and strength of artificial aggregates increase firstly and then decrease with the increase of fly ash content. However, the water absorption variation shows the opposite trend. When the fly ash content is 50% (mass fraction), thehigh strength and low water absorption artificial aggregates with an apparent density of 2.17 g/cm³, compressive strength of 22.88 MPa, and water absorption rate of 0.055% are prepared. The decrease in the strength of artificial aggregates and the increase in water absorption is mainly due to the increased porosity caused by the insufficient liquid phase. High Al₂O₃ content in the raw material hinders the formation of a liquid phase, which degrades the physical properties of artificial aggregates.

Whiskers Growth and Mechanism Analysis by Titanium Gypsum under Alkaline Conditions

HUANG Jia, JIN Yingrong, YANG Hualin, CHEN Wei, LI Yuling, WANG Zhijie

2022, 41(8):  2828-2835. 

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The α-calcium sulfate hemihydrate whiskers were prepared by hydrothermal method with titanium gypsum as raw material, calcium hydroxide saturated solution as solvent and magnesium sulfate heptahydrate as crystal promoter. The effects of reaction temperature, reaction time, solid-liquid ratio of slurry, content of crystal promoter and volume of calcium hydroxide solution on the yield and morphology of α-calcium sulfate hemihydrate whiskers were investigated, the growth mechanism of whiskers was clarified, too. The results show that in alkaline hydrothermal environment, titanium gypsum first transforms into α-calcium sulfate hemihydrate and then grows into whiskers. Adhering to the existing whiskers is an important way of whisker growth. When the solid-liquid ratio of slurry is 1∶12, the temperature is 120 ℃, the reaction time is 8 h, and the content of crystal promoter is 6%, the α-calcium sulfate hemihydrate whisker has high yield and excellent performance. The whiskers yield with smooth surface can reach 71.6%, and the mean aspect ratio is 70.

Influence of Phosphogypsum Particle Size on Properties and Microstructure of Wet-Mixed Mortar

ZHANG Yue, WANG Hongjie, YANG Lin, CHEN Hong, CAO Jianxin

2022, 41(8):  2836-2843. 

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Four kinds of phosphogypsum with different particle sizes were selected and mixed with mechanical sand, cement and admixtures to prepare wet-mixed mortar. The effects of phosphogypsum particle size on the workability and mechanical properties of mortar were investigated, and the mechanism of phosphogypsum particle size on the hydration products and microstructure of wet-mixed mortar was investigated by XRD, TG-DSC, MIP and SEM test. The results show that with the increase of phosphogypsum particle size, the workability and mechanical properties of wet-mixed mortar show a trend of increase first and then decrease. When 30% (mass fraction) phosphogypsum with particle size of 53~106 μm is added, the wet-mixed mortar consistency loss is 19%, water retention rate is 90%, 28 d compressive strength is 10.7 MPa, 14 d tensile bond strength is 0.25 MPa, which can meet the requirements of compressive strength greater than 10 MPa. With the increase of phosphogypsum particle size, the eutectic phosphorus content in phosphogypsum decreases, the hydration process of cement is inhibited to a lesser extent, the calcium silicate hydrate (C-S-H) generated in mortar increases, and a large amount of C-S-H appears in the region away from CaSO₄·2H₂O particles.However, the pore volume of mortar hardening body shows a trend of decrease first and then increase, when 30% (mass fraction) phosphogypsum with particle size of 53~106 μm is added, the pore volume of mortar is the smallest, only 0.130 9 mL/g. Phosphogypsum particle size range is suitable to be controlled in 53~106 μm, at this time, the wet-mixed mortar has good workability and mechanical properties.

Sodium Sulfate Corrosion Resistance of Gypsum Slag Cement Concrete

KONG Yaning, ZHOU Jianwei, GAO Yuxin, YANG Wen, YU Baoying, CHENG Baojun

2022, 41(8):  2844-2850. 

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Gypsum slag cement with low hydration heat and good chemical erosion resistance is a low carbon dioxide emission green cementitious material. To clearify to the effect of raw materials on the resistance of gypsum slag cement concrete to sulfate attack, the strength development and sodium sulfate corrosion resistance of gypsum slag cement concrete prepared with different chemical composition and active granulated blast furnace slag (GBFS) were studied. The results show that increasing the content of Al₂O₃ in GBFS effectively improves the early 3 d strength of gypsum slag cement concrete. The strength of gypsum slag cement concrete increases first and then decreases in sodium sulfate environment, showing strength softening disadvantage. Increasing the amount of cement and reducing the water to cement ratio effectively improves the sodium sulfate corrosion resistance of gypsum slag cement concrete prepared with low active GBFS, but it is not conducive to the sodium sulfate corrosion resistance of gypsum slag cement concrete prepared with high active GBFS. The research provides experimental data supporting for the preparation of gypsum slag cement concrete with low active GBFS and predicting for its life.

Effect of Regenerated Micropowder on Properties of Dry Mixed Mortar

GAO Min, GUO Qilong, DU Lei, HUA Liang, LIU Ronghao, WANG Chunya, MA Zhitong

2022, 41(8):  2851-2859. 

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In order to promote the recycling and utilization of construction waste, the dry mixed mortar was prepared by replacing part of cement with regenerated micropowder, and the effects of the fineness, content and compounding ratio of the regenerated micropowder on the consistency, compressive strength, flexural strength and microstructure of the mortar were explored. The results show that the consistency of mortar decreases with the decrease ofregenerated micropowder particle fineness, the compressive strength and flexural strength of mortar at 28 d increase, and the strength reaches the maximum value after grinding for 40 h. With the increase of the content of regenerated micropowder, the consistency of mortar shows a downward trend, and the compressive strength and flexural strength of mortar at 28 d show a trend of increase first and then decrease. When the content of regenerated micropowder is 10% (mass fraction), the compressive strength reaches the maximum value. With the increase of the compounding ratio (mass ratio) of regenerated micropowder, the consistency of mortar shows a downward trend, and the compressive strength and flexural strength of mortar show a trend of increase first and then decrease. When the compounding ratio of micropowder milled for 20 h to unmilled micropowder is 6∶4, its compressive strength reaches the maximum value.

Ceramics

Research Progress on Control and Preparation of Vaterite-Type Calcium Carbonate

WANG Xin, WEI Ming, LIU Kun

2022, 41(8):  2860-2870. 

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Vaterite-type calcium carbonate has unique physical, chemical, biological and mechanical properties, and has great application prospects in the fields of daily use, biological medicine, building materials and new materials. However, vaterite-type calcium carbonate is the most unstable thermodynamically stable one among the three anhydrous calcium carbonate crystals, and it is easily converted into aragonite-type or calcite-type calcium carbonate, especially in humid environments or aqueous solutions, this conversion is more likely to occur. This results in many difficulties in the production, processing and application of vaterite-type calcium carbonate. Therefore, the stable preparation method of vaterite-type calcium carbonate has always been one of the research hotspots in the field of calcium carbonate. In this paper, the research methods for the stable regulation and preparation of vaterite-type calcium carbonate in recent years are reviewed, including carbonization method, complex decomposition method, biomineralization method, template method and so on. According to the preparation principle and implementation process, these methods are classified and summarized, their advantages, disadvantages and application prospects are expounded, and the influence laws of various technological factors in the control and preparation process are analyzed. The purpose of this article is to provide practical and theoretical references for the realization of the stable preparation of vaterite-type calcium carbonate in industry.

Recent Progress on Modification of Garnet Li₇La₃Zr₂O₁₂ Solid-State Electrolyte

LI Jinyao, DONG Shengde, MA Luxiang, ZHOU Yuan

2022, 41(8):  2871-2878. 

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Solid-state electrolyte is the core component of all-solid-state lithium battery with the characteristics of high safety and high energy density. The typical representative Li₇La₃Zr₂O₁₂ (LLZO) has been paid extensive attention by researchers due to its high ionic conductivity, high mechanical strength, high electrochemical stability, low interfacial impedance, and good stability for lithium metal anodes. However, compared to liquid-state electrolytes, problems such as lower ionic conductivity and less contact with the solid-solid interface of electrodes in LLZO still exist. This research mainly introduced effects of the crystal structure and modification method of LLZO on its performances of ionic conductivity and interface impedance. Existing problems of LLZO were summarized, and future development directions were prospected. This research provides theoretical guidance for the practical production and application of all-solid-state lithium batteries.

Preparation of Boron Carbonitride Porous Material and Its Adsorption and Regeneration Performance

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

2022, 41(8):  2879-2888. 

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Boron carbonitride (BCN)porous material is considered as an excellent adsorption material due to its high specific surface area and excellent chemical stability. In this paper, porous embryos were prepared by freeze-drying method and BCN porous material was synthesized by high-temperature solid-phase reaction method under NH₃ atmosphere at different reaction temperatures with waste coconut shells, boric acid (H₃BO₃) and urea (CO(NH₂)₂) as raw materials. The results show that with the increase of reaction temperature, the pore size of BCN porous material gradually increases, and the average pore size is 2.1 nm when the reaction temperature is 950 ℃. The as-prepared BCN porous material is applied to adsorb malachite green (MG), an organic dye pollution in water, and its maximum adsorption capacity can reach 1 239.8 mg·g^-1. After five cycles of regeneration, the average adsorption capacity is still as high as 1 138.6 mg·g^-1, indicating that BCN porous material has excellent cyclic adsorption performance. Langmuir and Freundlich isothermal adsorption models, pseudo-first-order and pseudo-second-order adsorption kinetic models were used to study the relationship among concentration, adsorption time and equilibrium adsorption capacity. The results show that the adsorption of BCN porous material is consistent with the pseudo-second-order adsorption kinetic model, and the adsorption on MG belongs to the Langmuir isotherm adsorption of uniform surface monolayer molecules. The as-prepared BCN porous material exhibits excellent adsorption capacity and is expected to be a very promising adsorbent.

Effect of Pre-Oxidation on Microstructure and Flexural Strength of Reaction Boned Silicon Carbide

HAO Hongjian, LI Haiyan, WAN Detian, BAO Yiwang, LI Yueming

2022, 41(8):  2889-2895. 

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In this paper, a simple and effective pre-oxidation treatment method is proposed to strengthen reaction boned silicon carbide (RBSC). The effects of different temperature oxidation treatments from 800 ℃ to 1 300 ℃ on its microstructure and mechanical properties were investigated. Changes of residual flexural strength of materials with different sizes of pre-cracks before and after oxidation were also investigated. The results show that with the increment of the oxidation temperature, the strength and Weibull modulus of RBSC have a tend to first decrease, then increase, and then decrease again, mainly due to the different surface morphologies after oxidized at different temperatures. The flexural strength and Weibull modulus of RBSC increase significantly after pre-oxidized at 1 200 ℃ for 2 h, the strength increase by 19.9%, and the Weibull modulus increase from 7.3 to 11.8. However, both the incomplete oxidation at low temperature of 800 ℃ and the excessively strong oxidation reaction at high temperature of 1 300 ℃ lead to the decrease of flexural strength and Weibull modulus. Under the optimal pre-oxidation condition at 1 200 ℃ for 2 h, the residual flexural strength of RBSC specimen with indentation cracks (load of 20 N) increase from 201.1 MPa to 324.2 MPa after oxidation. The strengthening mechanism is that the SiO₂ generated by high temperature oxidation eliminates the microcracks and defects of the material on the surface.

Effect of PyC Coating on Properties of SiC Nanofiber Reinforced SiC Ceramic Matrix Composites

XIONG Yilian, TAO Jiyu, YANG Jiahao, CHEN Jianjun, ZHENG Junyi

2022, 41(8):  2896-2903. 

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In this work, SiC nanofiber reinforced SiC (SiC_nf/SiC) ceramic matrix composites with 10% (mass fraction) of nanofiber were fabricated by the hot pressing (HP) using SiC nanofiber as reinforcement, which were coated with pyrolysis carbon (PyC) via chemical vapor deposition, SiC powders as matrix and Al₂O₃-Y₂O₃ as sintering aids. The effects of deposition time of the PyC coating on density, fracture surface morphology and mechanical properties of SiC_nf/SiC ceramic matrix composites were investigated. The results show that PyC layer has a layered graphite structure with good crystallinity, and the coating thickness of PyC prepared by deposition at 1 100 ℃ for 60 min is 10 nm. The fracture toughness of SiC_nf/SiC ceramic matrix composites with the SiC_nf content of 10% is (19.35±1.17) MPa·m^1/2, which is 35% higher than that of composites without PyC coating, with the bending strength of (375.5±8.5) MPa and relative density of 96.68%. In addition, the phenomenon of nanofiber pulling out is observed in the fracture section of the composites. However, the SiC_nf/SiC ceramic matrix composites exhibit brittle fracture due to the strong interfacial bond between the nanofiber and matrix and short pull-out length of nanofiber. This work can be used as a reference for the interface design of SiC_nf/SiC ceramic matix composites.

Experimental Study on Crystallization of Anhydrous Magnesium Carbonate Crystals Regulated by Amino Acids

CUI Wanshun, WEN Weixiang, YAN Pingke, GAO Yujuan, BAI Yang

2022, 41(8):  2904-2909. 

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Anhydrous magnesium carbonate crystal as a new inorganic functional material has attracted the attention of researchers. In this paper, anhydrous magnesium carbonate crystal was synthesized by using magnesium chloride as raw material and sodium carbonate as precipitant. And four different kinds of amino acids, named glycine, histidine, alanine, and L-aspartate, were used as additives to regulate the particle size and crystalline morphology of anhydrous magnesium carbonate crystals. The synthesized products were characterized by X-ray diffractometer, scanning electron microscope, and laser particle size analyzer, and the effects of different amino acids on the physical structure and morphology ofanhydrous magnesium carbonate powder were analyzed. The results show that the anhydrous magnesium carbonate regulated by histidine has highly degree of crystallinity, and the n(Mg²⁺)∶n(CO^2-₃) of the synthesized product is 1∶0.94. The purity of crystals regulated by L-aspartate is second. Partial magnesium carbonate hydroxides are grown in the crystals synthesized under the requlation of glycine and alanine. The crystalline morphologies of anhydrous magnesium carbonate crystals under the regulation of histidine, L-aspartate, glycine, and alanine are convex spherical triangular shape, ellipsoidal shape, spherical shape, and irregular shape, respectively. The particle size distribution of anhydrous magnesium carbonate crystals shows a trend of rising first and then oscillating down and trailing slightly particle size. These results provide reference to the bionic synthesis of anhydrous magnesium carbonate crystal.

Glass

Research Progress in MgO-Al₂O₃-SiO₂ Transparent Glass Ceramics

FU Zhe, YAO Bin, LI Hao, ZHANG Meirong, DENG Leibo

2022, 41(8):  2910-2917. 

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Transparent glass ceramics is a kind of new functional materials, which have adjustable thermal expansion coefficient, high strength, good chemical stability, as well as transparent/luminous characteristics. They have widely applied in optical information, biotechnology, laser technology, infrared remote sensing technology and civil lighting. The light transmission mechanism of glass ceramics is briefly summarized. The research progress of crystallization and transparent/luminous properties of nucleating agent doping, transition metal ion doping and rare earth ion doping MgO-Al₂O₃-SiO₂ (MAS) transparent glass ceramics is introduced in this paper. Additionally, the problems in the development of MAS transparent glass ceramics with high crystallinity and transparent/luminescent properties are briefly analyzed. Finally, the development trend of transparent glass ceramics is also prospected.

Action Mechanism and Research Progress of Flux and Adhesive on Glass Lining

ZHENG Jiexi, GONG Kuiyuan, ZHANG Hongyang, XUE Hongxi, XU Kunshan, LIU Jie

2022, 41(8):  2918-2926. 

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Glass lining is a composite material that is sprayed with glass-lined glaze on the metal surface and adhered by high-temperature glass-lined glaze. It has the chemical stability of glass, and the excellent characteristics of high hardness and high strength of metal materials. At the same time, the surface is smooth and easy to clean. Therefore, it is widely used in chemical, pharmaceutical and other industries. The performance of glass lining depends on the composition of glass-lined glaze. Glass-lined glaze includes matrix agent, opacifier, flux, adhesive, etc. The flux contains low-melting substances, which can reduce the melting temperature and destroy the continuous network structure of the glass-lined glaze to formed new molecular bonds, and then improve the enameling process. The adhesive can chemically react with the metal matrix to enhance the bonding strength of the glass-lined glaze and the metal matrix, thereby improving the mechanical properties. This paper briefly introduced various additives in glass-lined glaze, and focused on the composition and action mechanism of the flux and adhesive. The review provides a reference for designing glass-lined glazes and improving the performance of glass-lined equipment in the future.

New Functional Materials

Preparation of ZSM-5@t-ZrO₂ and Its Influence Mechanism on Catalytic Synthesis of Methanethiol

PEI Lijie, LIU Fei, CAO Jianxin, YANG Anjie, YAO Mengqin, LIU Piao

2022, 41(8):  2927-2934. 

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The composite catalysts of ZSM-5@t-ZrO₂ and ZSM-5/t-ZrO₂ were prepared by hydrothermal coating method and physical blending method, respectively. Taking catalysts of t-ZrO₂ and ZSM-5 as reference, catalytic performance, physical and chemical properties of the composite catalysts with different structures were studied. On this basis, the effects of reaction temperature and presulfurization operation on the adsorption and conversion characteristics of methanol and hydrogen sulfide on ZSM-5@t-ZrO₂ composite catalyst were studied by means of diffuse reflectance Fourier transform infrared spectroscopy. The results show that hydrothermal coating process modified the physical and chemical properties of ZSM-5@t-ZrO₂ composite catalyst, thus improves the catalytic performance and deactivation resistance of carbon and sulfur deposition of methanol thiolation reaction. Under the conditions of reaction pressure of 1.0 MPa, reaction temperature of 380 ℃, presulfurization for 1 h and N₂ flow rate of 100 mL/min, the methanol conversion, methanethiol selectivity and methanethiol yield are 92.02%, 90.56% and 82.76%, respectively. The rate control step of the thiolation reaction is the adsorption and dissociation of hydrogen sulfide molecules on the base sites of of ZSM-5@t-ZrO₂ catalyst into sulfhydryl groups and then attacking methoxy groups. The reaction temperature of 380 ℃ and presulfurization operation are helpful to build the matching formation rate of sulfhydryl groups and methoxy groups, which not only enhances the catalytic performance but also reduces the formation rate of carbon and sulfur deposition effectively.

Synthesis and Photocatalytic Properties of Polyhydroxylated Fullerenes Modified Nitrogen-Doped Titanium Dioxide Composites

CHEN Yifan, TANG Guoqin, ZHAO Chunxia, CHEN Yekai

2022, 41(8):  2935-2942. 

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Polyhydroxylated fullerenes (PHF) were prepared bythe reaction of fullerene with NaOH in the presence oftetrabutylammonium hydroxide (TBAH) catalytic alkali method. PHF modified nitrogen doped titanium dioxide (PHF-N-TiO₂) was synthesized by a sol-gel method using the PHF as-prepared. The morphology and composition of the PHF-N-TiO₂ have been characterized. The photocatalytic performance of the PHF-N-TiO₂ for catalytic reduction of CO₂ was investigated. The results show that the PHF-N-TiO₂ performs enhanced absorption in the visible light region, leading to improved visible photocatalytic activity for the catalytic reduction of CO₂ at room temperature. The average production rate of CO is up to 5.560 μmol·g^-1·h^-1. The average production rate of CH₄ is 0.789 μmol·g^-1·h^-1. It is believed that the combination of PHF modification and nitrogen doping improves the visible photocatalytic activity of TiO₂.

Preparation and Electrochemical Properties of Rigid Skeleton COS-NMC Material

HE Shunwu, TIAN Hongsong, LI Ying, YE Entong, ZHANG Li, LIN Qian, PAN Hongyan

2022, 41(8):  2943-2953. 

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An in-situ nitrogen-doped mesoporous carbon material (COS-NMC-x) for supercapacitors was prepared by sol-gel method using chitosan oligosac charide (COS) as carbon precursor, triblock copolymer (F127) and ethyl orthosilicate (TEOs) as templating agent. The material was characterized by means of mass spectrometer, TG-DTG, XRD, Raman spectra, N₂ adsorption/desorption, XPS, FT-IR, hydrophilic and electrochemical evaluation to study the physical and chemical properties and electrochemical performance of the material. The results show that the performance parameters (specific surface area, pore volume and nitrogen atomic number fraction) of COS-NMC-x material tend to increase first and then decrease with the increase of ultrasound time, when the ultrasound time is 15 min,the specific surface area, pore volume and nitrogen atomic number fractionof sample reach the maximum, and the contact angle is the minimum, which are 144.94 m²·g^-1, 0.19 cm³·g^-1, 7.59% and 23.16°, respectively. At the same time, the electrochemical performance of COS-NMC-x was evaluated. The results show that, at a current density of 0.5 A·g^-1, the specific capacitance of sample is 189 F·g^-1, which is much higher than other materials in the same group, indicating that the larger pore structure and nitrogen atomic number fraction are beneficial to the improvement electrochemical performance of the material. After 5 000 cycles at 10 A·g^-1, the capacitance retention rate of sample reaches 114%, exhibiting good electrochemical performance and showing great application potential in supercapacitor applications.

Preparation of KBaB₅O₉ by Two-Step Method and Its Process Kinetics

QUAN Zhilin, LI Zhixiang, JIAO Bin, ZHOU Xianwei, XIANG Dexing, FENG Xiaoqin, HUANG Hongsheng

2022, 41(8):  2954-2962. 

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In this paper, K₂Ba[B₄O₅(OH)₄]₂·8H₂O was prepared by solution method, and KBaB₅O₉ was prepared by heat treatment of K₂Ba[B₄O₅(OH)₄]₂·8H₂O. The samples were characterized by XRD, FT-IR, and TG-DTA-DTG. The phase change process in the preparation of KBaB₅O₉ by heat treatment of K₂Ba[B₄O₅(OH)₄]₂·8H₂O was analyzed and studied. The phase change experiences five stages: the loss of crystal water, the loss of hydroxyl, recrystallization, redecomposition, and recrystallization after melting. The loss of crystal water is divided into two steps. The kinetic parameters of the second step loss process of crystal water in K₂Ba[B₄O₅(OH)₄]₂·8H₂O were calculated by Kissinger method, Flynn-Wall-Ozawa method, and Šatava-Šesták method. The activation energy E_s of the second-step loss process of crystal water in K₂Ba[B₄O₅(OH)₄]₂·8H₂O is 151.94 kJ/mol, the logarithm of pre-exponential factor lg A_s is 21.25 min^-1, and the mechanism function is G(α)=(1-2α/3)-(1-α)^2/3 (α is conversion rate).