Table of Content

15 March 2021, Volume 40 Issue 3

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Focus—Chinese Engineering

Development and Application of Intelligent Solar Photovoltaic Industry

GUAN Min, YU Tao, CHANG Zheng, HU Kuangyi, GAI Linlin, AI Xiaojing, SHENG Jiacheng, CHU Jingyuan

2021, 40(3):  693-703. 

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In recent years, China Triumph International Engineering Co., Ltd. (CTIEC) makes full use of its own advantages in the full coverage of the solar photovoltaic industry chain, as well as technological breakthroughs made in basic materials, components, equipment, etc. CTIEC has carried out a comprehensive intelligent upgrade of the company's photovoltaic industry, including research and development (crystalline silicon, CdTe & CIGS thin-films), intelligent equipment manufacturing, design, construction (photovoltaic factory, photovoltaic power station, etc.), operation, maintenance and management. The relevant results have been applied to many key photovoltaic projects in domestic and abroad. This will play a positive role in promoting the high-quality development of my country's photovoltaic industry, especially the technological progress of intelligent photovoltaic industry.

ement and Concrete

Review on Mechanism of Graphene in Cement-Based Materials

LIANG Jiafeng, GUO Jianqiang, LI Yue, ZHU Qiaosi, LI Jiongli, WANG Xudong

2021, 40(3):  704-713. 

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Graphene has excellent mechanical strength, barrier property and large specific surface area. As a result, it can be used to prepare the high-performance graphene cement-based composites by physical or chemical dispersion treatments. Graphene can improve the mechanical strength and durability of cement-based materials by regulating cement hydration reaction, improving pore structure and interfacial bonding, and show great application potential in the field of cement-based materials. The research progress of graphene cement-based composites was reviewed, the dispersion methods and the application effects of graphene were also summarized. At the same time, the mechanism of graphene was discussed and the development trend of graphene cement-based composites was prospected.

Research Progress of Carbon Nanotubes Cement-Based Composites

ZHANG Jixu, WANG Wenguang, LI Jinquan, HAN Jie

2021, 40(3):  714-722. 

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In recent years, more and more attention has been paid to the application of carbon nanotubes (CNTs) in traditional cementitious materials. Some properties of cementitious materials are effectively improved by adding appropriate CNTs. The application of CNTs in cement-based materials was reviewed in this paper. The effects of CNTs on mechanical properties, durability and microstructure of cement-based materials and the addition of active substances on properties of CNTs/cement-based composites were mainly discussed. Some problems existing in the current research were summarized and some suggestions for future research prospects were put forward.

Preparation and Hardening Performance of Ultra-Light Sulphoaluminate Cement-Based Foaming Material

WANG Shang, LIU Songhui, ZHOU Rong, ZHANG Yuehong, ZHANG Haibo

2021, 40(3):  723-730. 

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Aiming at the problems of traditional Portland cement-based foaming materials, such as small expansion ratio, large bulk density and dry density, and long setting time. An ultra-light sulfoaluminate cement-based foaming material (U-SCFM) was prepared using sulfoaluminate cement clinker, lime and hard gypsum as cementitious materials, hydrogen peroxide (H₂O₂) as blowing agent and hydroxypropyl methylcellulose ether (HPMC) as foam stabilizer.The influence of H₂O₂ dosage, HPMC content and water-binder ratio on the expansion ratio, dry density, and hardening strength of U-SCFM were systematically researched. The hydration products and microstructure of U-SCFM hardened body were also characterized by using the ultra-depth-of-field microscope, thermal analysis (TGA), scanning electron microscope (SEM). The results show that when the water-binder ratio is 0.8, H₂O₂ and HPMC content are respectively 10% and 1% of the cementitious materials mass, U-SCFM with an expansion ratio of 4.2, dry density of 265 kg/m³, and 7 d compressive strength of 0.98 MPa is prepared. The thickening effect of HPMC and the rapid setting and hardening of U-SCFM to form ettringite crystals are the main reasons for the formation of the porous structure of the U-SCFM hardened body. The above results provide a green, safe, low-cost filling material for filling the high-collapse area of coal mine tunnels.

Effects of Different Dispersants on Mechanical and Electrical Properties of GO/CNFs Cement-Based Composites

WU Yichen, GUO Rongxin, XIA Haiting, SUO Yuxia, WEI Lihuang, CHEN Jiamin

2021, 40(3):  731-740. 

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Graphene oxide (GO) and carbon nanofibers (CNFs), as two new carbon nanomaterials, can be used to improve the performance of traditional cement-based materials on the premise of good dispersion. Polycarboxylate superplasticizer (PCs), sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) these three different dispersants were used to disperse GO and CNFs in cement-based composites. The effects of dispersants on the mechanical and electrical properties of GO/CNFs cement-based composites were studied. The microstructures of GO/CNFs cement-based composites prepared with different dispersants were analyzed by scanning electron microscope (SEM). The results show that when PCs is used as dispersant alone, the compressive strength of specimen reaches the maximum (70.1 MPa) at the mass fraction of 0.05%GO and 0.5%CNFs. When the mass fraction is 0.05%GO and 0.3%CNFs, the resistivity of specimen is the lowest (112.65 Ω·m) and shows a good resistivity-stress response under loading conditions. When SDS and SDBS are used, a large number of bubbles are generated in the preparation of GO/CNFs mixed dispersion and in the preparation of specimens, which make the internal structure of cement matrix composites loose, reduce compressive strength, increase resistivity and decrease electrical conductivity. In addition, through SEM analysis, it is seen that the hydration products of GO/CNFs cement-based composites dispersed by PCs are compact in structure, while the microstructure of cement-based composites is loose when SDS is used as dispersant, and a large number of pores in the surface is observed only at a factor of 100. Therefore, when PCs is used as dispersant, it has the best performance improvement effect on GO/CNFs cement-based composites.

Solid-Liquid Equilibrium Equation of Cement-Based Materials under Leaching of Ammonium Chloride

TANG Yujuan, ZUO Xiaobao, YIN Guangji, TONG Xiaofang, XU Fei

2021, 40(3):  741-749. 

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The solid-liquid equilibrium curve of Portland cement system in 6 mol/L ammonium chloride solution was experimentally obtained using the dissolving equilibrium between cement paste powders and simulated pore solutions. The obtained equilibrium curve in nitrate solution has a similar three-stage form to that in water. The leaching mechanism of ammonium chloride solution on cement-based materials is similar to that of deionized water solution. In addition, leaching process of ammonium chloride solution is accompanied by the leaching of other solid elements (including sulfur and magnesium). And its dissolution loss has three stages, which is similar to solid phase calcium, but solid phase Al and Fe basically do not dissolve.

Salt Corrosion Resistance of Hardened Slurry of Magnesium Ammonium Phosphate Cement with High Fluidity

LI Tao, ZHANG Jiwen, JIANG Hailou, YANG Jianming

2021, 40(3):  750-757. 

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In order to study the salt corrosion resistance of hardened slurry of magnesium ammonium phosphate cement with high fluidity. The compressive strength, flexural strength, deformation, water absorption, fluidity, hydration temperature curve and microstructure of MAPC cement with high fluidity were tested. The properties of MAPC hardened slurry of the blank group M0 and single mixing water glass M1 immersed in water, sodium chloride and sodium sulfate solutions for a long time were studied. The experimental results show that the early hydration reaction rate and fluidity of MAPC hardened slurry are improved by single mixing water glass. The strength, deformation and water absorption of MAPC hardened slurry are improved by single mixing water glass. In addition, no matter under any solution, the performance of M1 slurry sample of single mixing water glass is better than that of the blank group M0, and the performance is the best under sulfate solution.

Effect of Starch-Based Water Reducer on Properties ofCement and Concrete

MIAO Fangli, YAO Zhihui, ZHANG Ding

2021, 40(3):  758-764. 

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A new green starch-based water reducer (SWR) was prepared by oxidation-etherification reaction using corn starch as biological raw material, hydrogen peroxide (H₂O₂) as green oxidant and cationic quaternary ammonium salt as etherifying agent. In order to evaluate the effect of SWR on cement hydration performance, the change of functional groups in the process of SWR preparation was analyzed by FT-IR. The effects of SWR, PWR and NWR on water reducing ratio, zeta potential, fluidity of cement paste, strength of mortar and compressive strength of concrete were compared. The results show that carboxyl group and ether bond are introduced into SWR molecular chain. With the increase of water reducer content, the water reducing rate of SWR increases gradually, and it has a better water reducing effect than PWR and NWR. Based on the cement quality, when the mass fraction of SWR is 1.0%, the water reducing rate reaches 33%. Zeta potential analysis shows that the three have similar absolute potential values, but SWR has the largest absolute potential over time. When the mass fraction of water reducer is lower than 0.6%, the fluidity of cement paste of the three is similar, but the fluidity of NWR cement paste is more prominent when the content of water reducer continues to increase. The flexural strength and compressive strength of SWR sand specimens at 7 d and 28 d are basically between PWR and NWR sand specimens, the compressive strength of SWR concrete at 7 d is the lowest, and the compressive strength at 28 d is highest, up to 49.6 MPa, indicating that SWR plays a role in retarding setting. Comprehensive analysis shows that SWR water reducer has better water reducing and retarding effects, and guarantee the strength performance of concrete. The recommended mass fraction of SWR is 1.0%.

Effect of Attached Mortar Content of Recycled Coarse Aggregate on Frost Resistance Durability of Recycled Aggregate Concrete

WEI Da, ZHU Pinghua, WANG Xinjie, LIU Hui, LIU Shaofeng, JIA Xuejun

2021, 40(3):  765-774. 

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Five kinds of commercial recycled coarse aggregate (RCA) with different attached mortar content were selected to prepare C40 recycled aggregate concrete under the condition of full substitution for natural coarse aggregate. The effect of attached mortar content of RCA on the frost resistance durability of recycled aggregate concrete under 30% of ultimate tensile stress level was discussed, and the mortar limit content based on relative dynamic elastic modulus and frost resistance durability factor was determined by mathematical fitting. The results show that there is a strong linear relationship between the loss rate of compressive strength of recycled aggregate concrete and the attached mortar content after freeze-thaw cycles. The mass loss rate, relative dynamic elastic modulus and frost resistance durability factor of recycled aggregate concrete have a quadratic function relation with the attached mortar content of recycled coarse aggregate. The relative dynamic elastic modulus of recycled aggregate concrete after 300 freeze-thaw cycles is reduced to 60% as the limit value, and the corresponding mortar limit content is obtained to be 49.52% (mass fraction). Taking the durability factor specified by different design service life and freeze-thaw working conditions as the defining conditions, the mortar limit content satisfying the corresponding durability factor under tensile stress is obtained. Finally, the rationality of the research results is verified by collecting literature data.

Effect of Stone Powder Content on Properties of C45 Tuff Manufactured Sand Concrete

WANG Xuhao, GAN Long, YU Haiyang, LI Cheng, GAO Xinmin, ZHANG Yagang, LI Lianwei, BIAN Qinghua

2021, 40(3):  775-783. 

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The effect of stone powder content on the workability, mechanical properties and chloride ion penetration resistance of C45 tuff manufactured sand concrete (MSC) were assessed by applying the slump test,Vkelly test, compressive strength, elastic modulus, splitting tensile strength and surface resistivity tests. In accordance with the fitting analysis of quadratic formula and the comparative study of MSC and natural sand concrete (NSC), the suggested stone powder content of C45 tuff MSC was established. The results indicate that the slump, Vkelly index compressive strength, elastic modulus, splitting tensile strength andchloride ion penetration resistance of C45 tuff MSC increase first and then start to decrease with the increase of stone powder content in a certain range. In engineering applications, if the specific required slump is greater than 100 mm and elastic modulus is higher than 44 GPa, the suggested stone powder content of C45 tuff MSC is between 2% (mass fraction, the same below) and 5%. Otherwise, the suggested stone powder content between 5% and 8% is accepted. Reasonable control of the stone powder content of manufactured sand can yield a better engineering performance of C45 tuff MSC compared with C45 NSC.

Influence of Corrosion Inhibitor on Durability of Reinforced Concrete in Golmud Salt Lake Area

WANG Chengping, ZHANG Jiasheng

2021, 40(3):  784-791. 

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Corrosion inhibitors are usually used to alleviate steel corrosion in concrete, and whether the types of corrosion inhibitors have a certain impact on the concrete durability needs further research. Therefore, concrete mixed with Ca(NO₂)₂ (also known as CAN) and C₄H₁₁NO (also known as CN) were prepared, and field exposure tests were conducted on the two specimens in the Golmud salt lake area. The electrochemical experiment, ultrasonic testing and quality testing were conducted respectively every three months. The durability was analyzed from three aspects: steel corrosion in concrete, crack formation of concrete and quality loss of concrete. The results show that the internal steel of two groups reaches to a low corrosion state at 180 d, and the internal steel of groups A and B reach to a medium corrosion state and a low corrosion state at 810 d. At 810 d, the ω₁ (relative quality evaluation parametes) values of groups A and B are 0.42 and 0.46, and the ω₂ (relative dynamic modulus of elasticity evaluation parametes) values are 0.47 and 0.53, respectively. After 180 d of exposure, ω₁ and ω₂ values of group A are smaller than those of group B. At 810 d, the maximum cracks on the surface of groups A and B reach about 0.15 mm and 0.11 mm, respectively. Corrosion inhibitor CN improves the durability of concrete better than CAN。

Mechanical Properties of UHPC with Zeolite Powder Replacing Part Silica Fume

LAN Bo, HE Zhihai, HU Haibo, WOLDERUFAEL Yirgalemfissiha, YANG Ying, HAN Xudong

2021, 40(3):  792-800. 

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Compared with silica fume, zeolite powder is a local mineral admixture with the low price. Zeolite powder was used to replace silica fume to prepare ultra-high performance concrete (UHPC). The effects of zeolite powder content, water to binder ratio and volume content of steel fiber on the mechanical properties of UHPC were studied. The results show that when part silica fume is replaced by zeolite powder, the 3 d strength are reduced. And with the increase of ages, zeolite powder with the replacement rate of 15% (mass fraction) increases the strength of UHPC, while zeolite powder with the replacement rate of 30% (mass fraction) has little effect on the strength. Zeolite powder improves the toughness of UHPC at the later ages. Although the increased water to binder ratio decreases the strength, there is no the significant increase of strength between UHPC with water to binder ratio of 0.16 and 0.14. The utilization of steel fiber with appropriate amount is helpful to improve the strength of UHPC with zeolite powder, and the optimal percentage range of volume content of steel fiber is 2.5%~3.0%.

Anti-Cracking Effects of Expansion Agent and Shrinkage-Reducing Agent on Precast Box Girder Concrete

ZHANG Feng, BAI Yin, ZHANG Jinkang, ZHU Yeran, NING Fengwei, LYU Lele, HU Haiming

2021, 40(3):  801-811. 

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On the basis of testing the mechanical, crack resistance, deformation and thermal properties of box girder concrete (C50), B4Cast software was used to simulate and analyze the temperature, stress development law and cracking trend of concrete, and the anti-cracking effects of expansion agent and shrinkage-reducing agent on the box girder concrete were also studied. The results show that, the box girder concrete (C50) has poor crack resistance, and the total cracking area of the early slab is 310 mm²/m², and the crack time of ring is about 52 h. The maximum temperature difference between the box girder concrete and the external environment is 16 ℃ to 18 ℃, and the tensile stress of concrete surface layer reaches the maximum at both sides of the wing or the corner of bottom plate, which is about 0.8 MPa and 0.9 MPa. The addition of expansion agent or shrinkage-reducing agent has little effect on the workability, mechanical properties and thermal properties of C50 concrete. The mechanical properties of C50 concrete are slightly reduced by only adding shrinkage-reducing agent. The incorporation of expansion agent and shrinkage-reducing agent reduces the total cracking area of slab by 68% to 95% and delay the cracking time of ring by 105.5 h to 227.5 h. The combined mixing of expansion agent and shrinkage reducing agent reduces the shrinkage deformation of concrete by 63% to 78% and dry shrinkage by 38%. With the addition of expansion agent and shrinkage-reducing agent, the temperature peak of box girder concrete structure is reduced by 4 ℃, the maximum tensile stress is reduced by 52%, and the anti-cracking safety factor of concrete reaches 3.05, which significantly reduces the risk of cracking.

Damage of Mechanical Properties of Basalt Fiber Reinforced Concrete under Salt Freezing

XU Cundong, HUANG Song, LI Hongfei, LI Zhen, LIAN Haidong, LI Zhirui

2021, 40(3):  812-820. 

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Aiming at the problem that the concrete structure is easy to crack and the durability is reduced in the cold and dry areas of Northwest China, basalt fiber with excellent mechanical properties was selected as concrete reinforcement material. The volume fraction of fiber was taken as the variable. The dynamic elastic modulus, compressive strength and flexural strength of concrete specimens with different fiber volume content (0.05%, 0.1%, 0.15% and 0.2%) under freeze-thaw action of clean water, 3%NaCl solution and 5%Na₂SO₄ solution were studied. It is found that basalt fiber effectively improves the initial flexural strength and salt frost resistance of concrete, when the fiber volume content is between 0.15% and 0.2%, the attenuation rate of dynamic elastic modulus, compressive strength and flexural strength of concrete specimens under salt frost action slow down obviously. The descending rate of mechanical properties of basalt fiber reinforced concrete in three kinds of freeze-thaw media is clean water<5%Na₂SO₄<3%NaCl. Taking the dynamic elastic modulus as the damage variable, the correlation model of concrete relative compressive strength and relative flexural strength are fitted, and the correlation of the models are good. The research results provide theoretical basis and reference for the practical application and building maintenance of basalt fiber reinforced concrete.

Influence of Low Temperature Freeze-Thaw Cycle on Dynamic Mechanical Properties of Ceramsite Concrete

XUE Wen, WANG Teng, CHENG Wenjie, SHEN Hongru, LI Yi, CHEN Jiangying, ZHU Yaohong

2021, 40(3):  821-828. 

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With the purpose of studying the influences of the freeze-thaw cycle temperature and cycle times on the dynamic mechanical properties of ceramsite concrete, the freeze-thaw cycle test and the Hopkinson pressure bar compression test were performed. The upper limit of the freeze-thaw cycle temperature was +10 ℃ and its lower limit was -20 ℃ to -60 ℃ with the interval of -10 ℃. The sample size used in the tests is 150 mm×150 mm×100 mm, the dynamic compression test on samples after freeze-thaw cycle were carried out. The results show that either increasing the freeze-thaw cycle times or decreasing the freeze-thaw cycle temperature deepens on the damage of ceramsite concrete, reduces its dynamic compressive strength. When the cycle times reach 30 times, the elastic modulus of ceramsite concrete drops to approximately 60% of that prior to freeze-thaw cycle. Basically,the concrete elastic modulus follows a linear decreasing trend with the decrease of the minimum freeze-thaw cycle temperature. In addition, the compressive strength of ceramsite concrete declines with either the increase of the freeze-thaw cycle times or the reduction of the lowest freeze-thaw cycle temperature. Moreover, the strain corresponding to the maximum stress increases when the compressive strength decreases.

Prediction of Impermeability of Concrete Based on Random Forest and Support Vector Machine

WU Xianguo, LIU Xi, WANG Hongtao, CHEN Hongyu, GAO Fei, HUANG Hanyang

2021, 40(3):  829-835. 

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In order to predict the impermeability of concrete quickly and accurately, a RF-SVM prediction model based on random forest (RF) and support vector machine (SVM) was proposed. At first, the permeability coefficient of chloride ion was taken as the evaluation index of impermeability, the initial index system of concrete impermeability was determined based on the ratio of raw materials.Then, the random forest algorithm combined with backward elimination method was used to screen the indexes, and the redundant indexes were eliminated, and the optimal set of indexes for support vector machine modeling was obtained. Finally, a prediction model of concrete impermeability based on support vector machine was established, and a RF-SVM algorithm was developed. Based on a highway project in northeast China, the results show that the proposed RF-SVM model effectively screens out the redundant factors and obtains high precision prediction results, which meets the requirements of engineering practice, and provides a fast and effective method for predicting the impermeability of concrete.

Macro and Meso Multi-Scale Nonlinear Finite Element Analysis of Shear-Flexural Beam

HU Biao, WANG Xianjie, WANG Siwen, LI Chengyue, WANG Zhaoyi, WENG Zhenjiang

2021, 40(3):  836-844. 

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In order to further study the influence of the mesoscopic coarse aggregate gradation on the nonlinear mechanical properties of concrete macroscopic components, the aggregate size satisfying Fuller grading was generated, and the aggregate overlap was judged by the RGB (red, green, bule) value of the placement area pixels, so as to realize the random distribution of aggregate in concrete. On this basis, the equivalent elastic modulus and stiffness matrix of two-dimensional mesoscopic random polygonal aggregate model were solved by homogenization method, and the damage factor of concrete material was introduced to simulate the crack expansion of shear-flexural beam, so a multi-scale nonlinear mechanical model of concrete was established. The results show that when the concrete enters the plastic stage, the correlation between the maximum aggregate size and the damage factor under tension and compression can not be ignored, which directly affects the crack development and the maximum plastic strain of the macroscopic shear-flexural beam. It may also change the failure mode of shear-flexural beam.

Solid Waste and Eco-Materials

Research Progress and Utilization Status Analysis of Concrete Prepared by Tailings

SHEN Yanjun, BAI Zhipeng, HAO Jianshuai, LIAO Taichang, LI Shuguang, XU Hanhua

2021, 40(3):  845-857. 

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At present, the use of tailings to prepare concrete has become a better way to realize the comprehensive recycling and utilization of tailings resource. The current situation of tailing slag discharge and comprehensive utilization was analysed to explore the resource utilization status of tailings as aggregates for concrete preparation. In addition, the research progress of different types of tailing slag for concrete gel materials, coarse and fine aggregates, and modified admixture sand was specifically clarified. Finally, the later development direction of tailings to replace natural building materials was prospected. The current research shows that when tailings partially replace concrete materials, the “volcanic ash effect” and “micro-aggregate effect” exerted by the secondary hydration of fine powder are the main reasons why the strength of tailings concrete is higher than that of ordinary concrete. Because of the small particles, tailings have a limited range of applications as concrete fine aggregates, but they have great potential as micro-powder filling materials or alternative gel materials. Tailings concrete takes advantages of the angularity and hydrophilicity of fine-grained tailings to increase the viscosity of concrete and facilitate the preparation of synthetic aggregates or tunnel shotcrete. The preparation of concrete from tailings greatly alleviates the shortage of building materials and solves the environmental problems caused by tailings stacking, providing a new idea for the development of green building materials in the future.

Review on Influencing Factors of Mechanical Properties of Fly Ash Geopolymer

PENG Yuqing, GUO Rongxin, LIN Zhiwei, ZHANG Min

2021, 40(3):  858-866. 

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Fly ash geopolymer is prepared by using fly ash as a silico-alumina raw material. It has the advantages of high strength, high-temperature resistance, corrosion resistance, and effective sealing of metal ions. However, its inherent brittleness and the need for high-temperature curing to quickly obtain high strength limits its scope of application, and the use of fiber as a reinforcing material for fly ash geopolymer can not only increase its strength, but also improve its ductility and toughness. Starting from four aspects: the characteristics of fly ash raw materials, alkali activator, curing system and reinforcing materials, the effects of the particle size and chemical composition of fly ash, the type, dosage and modulus of alkali activator, the heating curing time and initial curing temperature on the compressive strength, and the effect of fiber on the compressive strength and flexural performance of fly ash geopolymers were reviewed. Finally, based on the existing research results, how the four influencing factors affect the mechanical properties of fly ash geopolymers were summarized.

Research Development on Influencing Factors of Performances and Gel Products in Fly Ash-Based Geopolymer Material

ZHAO Xianhui, WANG Haoyu, ZHOU Boyu, GAO Han

2021, 40(3):  867-876. 

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Fly ash-based geopolymer materials are favored in the building material industry owing to the advantages of green and low-carbon. Silica-aluminum precursors, alkali-activators and water are the basic components for geopolymeric reaction. However, the gel products in fly ash-based geopolymer material are changing with additional calcium content in system. In this paper, based on the formation and advantage of geopolymer, the advantage of fly ash was analyzed as silica-aluminum precursor. Also, the influences of activator ions, curing conditions and calcium-components were emphasized on the performances of modified fly ash-based geopolymer material. Furthermore, the research developments of gel products and reaction mechanisms were reviewed for fly ash-based geopolymer materials. Currently, the calcium-containing solid wastes tend to be utilized as the inorganic additives to improve the performances of modified fly ash-based geopolymer materials. Therefore, clarifying gel products and reaction mechanisms will provide the theoretical guidance for the performance optimization of fly ash-based geopolymer materials.

Research Status of Properties and Utilization of Lepidolite Lithium Slag

CHEN Zhiyou, SU Xiaoqiong, YANG Zhiwen, XIAO Hongxu

2021, 40(3):  877-882. 

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Lithium slag is the solid waste produced in the process of extracting lithium and its compounds from lithium-containing ore. The sodium salt and alkali remaining in the lithium slag of the lepidolite ore using the method of salt pressuring and autoclaving affect the safety of the environment. This article introduces the production, composition and physical and chemical properties of the lepidolite lithium slag, reviews its latest research progress in the field of building materials and functional materials, and analyzes the main factors restricting the use of lepidolite lithium slag and common problems in its applications. Finally, the application and development directions of the lepidolite lithium slag are prospected for the future drew lessons from the research of fly ash.

Effect of Calcination Temperature on Physical and Mechanical Properties of Natural Hydraulic Lime

LIU Guangying, GUO Xiangyu, DAI Shibing, DAI Shibao, MAN Xiaolei

2021, 40(3):  883-888. 

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Effect of calcination temperature from 900 ℃ to 1 150 ℃ on the physical and mechanical properties of natural hydraulic lime prepared from cambrian limestone was investigated. The calcined products were characterized by X-ray diffractometer, scanning electron microscopy and slaking reactivity, and the wind slaked lime was characterized by setting time, flexural strength and compressive strength. The test results show that free-CaO and β-Ca₂SiO₄ are detected and the compressive strength values at 28 d allows for the classification of the natural hydraulic lime as NHL2 for all calcination temperatures from 900 ℃ to 1 150 ℃. The free-CaO content and slaking reactivity of the calcined products first increase and then decrease with the increase of calcination temperature, and reach the peak values where the calcination temperature is 950 ℃. The setting time of natural hydraulic lime gradually decreases with the increase of calcination temperature, and the exception is at 950 ℃ where the setting time is lower than at 1 000 ℃. The mechanical properties of natural hydraulic lime does not demonstrate a clear relation to the calcination temperature, and the lime binder calcined at 1 150 ℃ reaches the highest flexural and compressive strengths at 28 d.

Preparation and Performance Influencing Factors of Silt-Based Non-Sintered Ceramsite

GAO Peng, XU Yueqing, CAO Yun, HAN Yan, LIU Rong

2021, 40(3):  889-899. 

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Using dredged silt as the main raw material to prepare non-sintered ceramsite, realize the resource utilization of silt. Compared with traditional silt treatment methods, it reduces land occupation and secondary environmental pollution caused by silt stacking, and has significant advantages. The effects of silt/cement ratio, binder addition, gypsum addition and curing time on the performance of ceramsite were explored through experimental analysis. The results show that the best raw material ratio and curing process for silt-based non-sintered ceramsite is silt/cement ratio 2.5 (mass ratio), gypsum addition 10% (mass fraction), binder addition 1% (mass fraction), and curing time 28 d. The compressive strength of ceramsite prepared under these condition is 4.49 MPa, the particle density is 1.3 g·cm^-3, and the 1 h water absorption is 9.78%. Meet the performance indicators of ordinary lightweight aggregate in GB/T 17431.1—2010 "Lightweight aggregate and its test method". SEM and XRD analyses show that the internal pores of ceramsite are closed under the optimal condition, and the crystal grains are tightly combined. The C-S-H and anorthite-like crystalline structure formed by the hydration and hardening reaction are beneficial to improve the comprehensive physical properties of ceramsite.

Activated Oyster Shell for Solidification of Residual Soil and Its Mechanism Analysis

XU Ying, CHEN Rui, WEI Qiying, XU Tingting

2021, 40(3):  900-906. 

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In order to realize the utilization of the two solid waste resources of oyster shell and residual soil, it was proposed that the pretreated oyster shell was activated by phosphoric acid or diammonium hydrogen phosphate (DAP) to obtain the oyster shell solidified soil. The mechanical properties of oyster shell solidified soil with different ratios were measured and the scouring resistance of slope was studied. The scanning electron microscope and X-ray diffraction were used to observe the microstructure of solidified soil and analyze its solidification mechanism. The results show that the addition of phosphoric acid or DAP improves the compressive strength of oyster shell solidified soil, and the effect of adding DAP is better. The best ratio (mass fraction) of materials is: 73.6% soil, 18.4% oyster shell (particle size ≤1 mm), 8% DAP. Under the optimum ratio condition, the drying compressive strength reaches 2.14 MPa, which is 2.43 times of the compressive strength of oyster shell stabilized residual soil, and the softening coefficient reaches 0.5, which changes the disintegration characteristics of the original soil when exposes to water.In indoor slope scour test, the oyster shell solidified soil mixed with DAP effectively reduces the amount of sand produced by the erosion of slope compared with the plain soil. Microstructure analysis shows that phosphoric acid or DAP interacts with oyster shell to form calcium phosphate crystals and hydroxyapatite. The new products can cement soil particles and solidify the soil.

Experimental Research on Decarbonization of High-CarbonFly Ash by Flotation

HU Zhenwen, GUO Yuanxin, LIN Xiangling, LI Qiuyi, ZHENG Shidong

2021, 40(3):  907-913. 

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High-carbon fly ash is a kind of solid waste that can not be used directly. In order to reduce the loss on ignition of high-carbon fly ash, the decarbonization test of high-carbon fly ash was carried out. Through grinding test, the best grinding time of high-carbon fly ash is 1.25 min. Through the flotation reagent system test, it is determined that the best reagent system is the dosage of Sec-octyl alcohol 4 kg/t and kerosene 12 kg/t. Through the flotation process test, it is determined that the best flotation process of pulverized high-carbon fly ash is turbine speed of 2 000 r/min, scraping time of 8 min, mineral pulp concentration of 120 g/L and air volume per unit area of 0.30 m³/(m²·min). Through the above tests, the loss on ignition of the decarbonized fly ash is 0.63% and the productivity is 60.64%, which meets the grade I ash loss on ignition requirement.

Preparation and Properties of Activated Coal Gangue Geopolymer

WANG Fei, LIU Ze, HAN Le, XIE Fuzhu

2021, 40(3):  914-920. 

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The original coal gangue was analyzed both qualitatively and quantitatively, the calcination temperature of activated coal gangue was optimized, and the effects of sodium-aluminum ratio (n(Na)/n(Al)=0.52, 0.57, 0.62) and the activator modulus (M=0.66, 0.69, 1.32, 1.65) on the compressive strength and microstructure of activated coal gangue geopolymer were investigated. The microstructure of activated coal gangue geopolymer was characterized by XRD, FT-IR and SEM. The results show that activated coal gangue at high temperature is helpful to activate the active components in coal gangue. When the calcination temperature is 600 ℃, the kaolinite facies disappears completely and “the bulge peak” area is relatively large, which can be used to prepare activated coal gangue geopolymer. The increase of n(Na)/n(Al) promots the geopolymer reaction, and the compressive strength is also increased. Meanwhile, the compressive strength is also increased with the increase of the excitation modulus. When n(Na)/n(Al) is 0.62 and the activator modulus is 1.65, the compressive strength of the sample on 7 d reaches to 52 MPa. The product of activated coal gangue geopolymer is sodium silicate hydrate (N-A-S-H) gel, the hydration product is compact and has good performance.

Preparation and Performance Characterization of Magnesium-Rich Nickel Slag-Fly Ash-Based Geopolymer

LIU Yang, WU Jinxiu, FENG Chunfu, YANG Shengwei, FENG Fushan, WANG Mitang

2021, 40(3):  921-928. 

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A series of magnesium-rich nickel slag-fly ash-based geopolymers were prepared from industrial solid waste magnesium-rich nickel slag and fly ash with sodium silicate and NaOH as alkali activators. The effect of different fly ash content on the mechanical properties of geopolymers was studied, and the linear shrinkage and alkali dissolution of geopolymers were measured. The geopolymers were characterized by XRD, IR, DTA, etc. Results show that the strength of the magnesium-rich nickel slag-fly ash-based geopolymer increases first and then decreases with the increase of fly ash content. When the content of fly ash is 30% (mass fraction), the compressive strength of the geopolymer reaches the maximum strength with 22.15 MPa, which is 42.2% higher than that of nickel slag-based geopolymer. XRD result shows that the state of MgO in magnesium-rich nickel slag is forsterite phase, instead of free state, which ensures the good volume stability of geopolymer.

Preparation and Performance Analysis of Iron Tailings Ceramsite Concrete

LI Xiaoguang, HOU Xinxin, LIANG Baozhen, WANG Panqi, ALI Saddam

2021, 40(3):  929-935. 

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Iron tailings ceramsite concrete (from LC30 to LC40) was prepared according to “Technical specification for lightweight aggregate concrete” (JGJ/T 12—2019) by replacing natural coarse aggregate with iron tailings ceramsite. The mechanical properties, durability and economy of the concrete were measured and compared with ordinary concrete. The results show that iron tailings ceramsite concrete meets the requirements of “Technical specification for lightweight aggregate concrete” (JGJ/T 12—2019) LC30 strength. The correlation between strength and water binder ratio is lower than that of ordinary concrete. The flexural strength and elastic modulus are only about 60% and 65% of that of ordinary concrete, respectively. But the chloride ion permeability and frost resistance are significantly better than ordinary concrete. The feasibility of iron tailings ceramsite used in the preparation of lightweight aggregate concrete and the comprehensive performance of the concrete are obtained, which provides data support for the next step of prefabricated component design, and the problem of iron tailings recycling in southern Shaanxi is indirectly solved.

Effect of Adding Amount of Calcined Coal Gangue with High Pozzolanic Reactivity on Cement Compressive Strength

LIU Qian, GUO Yusen, ZHONG Tao, HUANG Qingyun

2021, 40(3):  936-942. 

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Comprehensive utilization of coal gangue is the fundamental method to solve the environmental and social problems caused by coal gangue. Coal gangue can be used as a gel material, which is an important mode for coal gangue comprehensive utilization. High reactivity is an essential characteristic for gel materials. Therefore, it is necessary to analyze the influence of high reactivity coal gangue on cement strength, especially the quantitative law. The gangue from Cuipingshan coal mine in Longyan was taken as the research object, and the calcined activation of coal gangue under different calcination temperatures was tested by pozzolanic reactivity evaluation method. The calcined coal gangue with high pozzolanic reactivity was used to make cement specimens, and the influence of coal gangue adding amount on cement compressive strength was analyzed. The results show that with the increase of calcination temperature, the loss on ignition of coal gangue increased gradually, and there is a power function relationship between the loss on ignition and the calcination temperature. With the increase of calcination temperature, the reactivity of coal gangue increases at first and then decreases. The relationship between calcium absorption and calcination temperature is quadratic polynomial. It is inferred that the optimal calcination temperature of experimental coal gangue is 750 ℃. With the increase of coal gangue adding amount, the compressive strength of cement specimens shows a downward trend, and the compressive strengths of specimens have an exponential relationship with the adding amount of coal gangue. With the increase of curing age, the compressive strengths of cement specimens have an increasing trend. The influence of coal gangue adding amount on cement compressive strength and the relationship between coal gangue adding amount and cement strength through data fitting, which provide a reference for coal gangue as cement admixture in other areas, and are of great significance in guiding the application of coal gangue in gel materials.

Influence of Potassium-Based Alkaline Electrolyzed Water on Performance of Fly Ash Concrete

XIE Zixi, LIU Guibin, ZHANG Tianyu, LI Qiuyi, WANG Liang

2021, 40(3):  943-950. 

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Alkaline electrolyzed water has the advantages of high activity, strong alkalinity, ionicity and adsorption. Alkaline electrolyzed water was used as mixing water of concrete to prepare fly ash concrete with different replacement ratios. The influence of alkaline electrolyzed water on the workability, mechanical properties and anti-chloride ion permeability performance was studied systemically. Combined with X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and differential thermal analysis experiments (TG/DTA), the hydration products and microstructure morphology of alkaline electrolyzed water fly ash concrete were analyzed. The results show that alkaline electrolyzed water promotes the early hydration reaction of cement in concrete and improves the workability of concrete. In addition to more C-S-H gels, Ca(OH)₂ and other hydration products, the potassium feldspars are also observed, which reduce porosity and improve the compactness of the structure, enhancing the mechanical properties and anti-permeability of concrete. Meanwhile, alkaline electrolyzed water stimulates the pozzolanic effect of fly ash at the early age to a certain extent, which accelerates the fracture of the glass network structure of fly ash in concrete. A large amount of SiO₂ and Al₂O₃ in fly ash dissolve and react with Ca(OH)₂ in concrete to produce more cementitious products such as calcium silicate and calcium aluminate. Compared with ordinary tap water concrete, when the replacement ratio of fly ash is 20% and 30% (mass fraction), the 56 d compressive strength of alkaline electrolyzed water concrete increase by 8.7% and 3.5%, respectively.

Preparation of Silicon Carbide Whiskers from Tire Semicoke

LU Pengfei, XU Guangwen, CUI Yanbin, WU Rongcheng

2021, 40(3):  951-956. 

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Using tire semicoke and silica sand as raw materials, silicon carbide whiskers were prepared by the carbothermal reduction method. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the phase composition and morphology of the prepared product, and the influence laws of reaction temperature (1 300 ℃ to 1 500 ℃), reaction time (120 min to 300 min), heating procedure and semicoke particle size on the synthesis of silicon carbide whiskers were explored. The results show that the whisker growth is best when the temperature is controlled at about 1 350 ℃, and the heating method that first rises to 1 500 ℃ for nucleation and then drops to 1 350 ℃ for holding growth. The particle size of the raw material simultaneously affects the formation rate of silicon carbide. And the whisker as the semicoke particle size decreases, the yield and quality of silicon carbide whiskers increase first and then decrease. When the tire semicoke particle size is 100 mesh to 120 mesh (150 μm to 120 μm), the reaction temperature is 1 350 ℃, and the reaction time is 240 min, under the best conditions, the prepared whiskers have a diameter of 50 nm to 120 nm and a length of 50 μm to 80 μm, with uniform distribution and high yield 95.36%.

Classification of Recycled Brick and Concrete Coarse Aggregate Based on Brick Content

TAO Hangyu, CHEN Ping, GONG Yifan, ZHAN Jingfang, ZHANG Li

2021, 40(3):  957-963. 

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The existing recycled aggregate classification standard in China is inapplicable to guide the comprehensive utilization of recycled aggregate with high brick content. The influence of brick content on water absorption, apparent density and crushing index of recycled brick and concrete aggregate was studied. Based on data analysis, a general linear relationship formula between brick content and water absorption, crushing index was established. A new classification method of recycled brick and concrete aggregate was proposed, which took brick content as main control index, as well as apparent density, water absorption and crushing index as technical control index. This method can effectively improve the existing standards and make it adapt the properties of recycled brick and concrete aggregate. Moreover, it can guide the resource utilization of recycled brick and concrete aggregate in concrete engineering more effectively.

Ceramics

Research Progress of Lithium Zinc Titanate Microwave Dielectric Ceramics

LIU Yuzhao, CAI Zongying, CAO Weigang, LIU Yang

2021, 40(3):  964-969. 

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Li₂ZnTi₃O₈ ceramics has attracted much attention due to its low sintering temperature and good microwave dielectric property, which is expected to be one of the candidate materials for low temperature co-fired ceramics (LTCC). This article mainly introduces several preparation methods of Li₂ZnTi₃O₈ ceramics and its advantages and disadvantages. The effects of ion replacement modification, oxide doping modification and low-temperature co-firing on the overall dielectric properties of microwave dielectric ceramics are also analyzed. The research and application of Li₂ZnTi₃O₈ microwave dielectric ceramics in the next stage are prospected.

Effect of Ionic Pair (Nb⁵⁺-Cr³⁺) Doping on Microstructure and Electrical Properties of 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃ Ceramics

CHEN Pei, ZHOU Changrong

2021, 40(3):  970-977. 

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A new promising lead-free piezoelectric ceramics (Bi_0.5Na_0.5)_0.93Ba_0.07Ti_1-x(Nb_0.5Cr_0.5)_xO₃ (mole fraction x=0%, 0.5%, 1%, 2%, 2.5%, 5%) (abbreviated as BNBT-xNC) were prepared by the conventional solid-phase synthesis method. The effect of ionic pair (Nb⁵⁺-Cr³⁺) on microstructures, dielectric properties, and ferroelectric properties as well as strain properties of 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃ (abbreviated as BNT-7BT) ceramics was systematically investigated. The results show that all composition exhibits a single pseudo-cubic structure. The electrical properties reveal that the ferroelectric relaxor characteristics of BNBT-xNC ceramics change significantly with different ionic pair (Nb⁵⁺-Cr³⁺) substitution. The increasing ionic pair (Nb⁵⁺-Cr³⁺) modification induces two transitions from non-ergodic relaxor state (0%≤x≤1%) to coexistence of non-ergodic-ergodic relaxor state (1%≤x≤2%), and finally to ergodic relaxor state (2.5%≤x≤5%). The ionic pair (Nb⁵⁺-Cr³⁺) modification induces BNBT-xNC ceramics transition from ferroelectric state to relaxor state, and strain properties first increase and then decrease. A low dose of ionic pair (Nb⁵⁺-Cr³⁺) substitution enhances the strain propertites of BNBT-xNC ceramics, and the BNBT-xNC ceramics with x=2% exhibits the maximum strain (S_max=0.22%) and inverse piezoelectric constant (d^*₃₃=431 pm/V). The evolution of electrical properties associates with micostucture, which provides a new sight to investigate the effect of the ionic pair doping on BNT-BT ceramics.

Effect of Alkali Metal Oxide Na₂O on Performance of Vitrified Bond Diamond Abrasive Tools

MEI Tao, HUANG Qizhong, WANG Shaobin, PAN Fuqiang, FENG Xiupeng, LI Hongxue

2021, 40(3):  978-983. 

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By adjusting the content of alkali metal oxide Na₂O in the vitrified bond, the effect of alkali metal oxide Na₂O on the performance of the vitrified bond diamond abrasive tool was explored. When n(Na₂O)/n(SiO₂)=0.1, the strength (57.7 MPa) and hardness (117HRB) of the abrasive sample are the maximum. With the increase of the alkali metal oxide Na₂O, the refractoriness of the vitrified bond decreases significantly, and the fluidity significant increases. The SEM image of the fracture surface of the abrasive tool sample shows that a proper amount of alkali metal oxide Na₂O reduces the voids and porosity of the abrasive tool section, the distribution of vitrified bond and abrasive material is more uniform, and the bonding interface between vitrified bond and abrasive material is closer. XRD analysis show that the abrasive sample is sintered at 720 ℃. In addition to the glass phase, a crystal phase is produced in the bond. The content of alkali metal oxide Na₂O in the bond has no effect on the type of crystal phase produced after sintering.

Composites by Semi-Solid Stirring During Preparation Process

ZHANG Fulong, LIANG Xiaowen

2021, 40(3):  984-989. 

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Particle reinforced magnesium matrix composites have various advantages, such as high specific strength, stable size and low production cost. In particular, magnesium matrix composites reinforced by silicon carbide (SiC) has higher wear resistance and temperature resistance. Stirring method is one of the major methods to prepare SiC particle reinforced magnesium matrix composites, but excessive porosity and uneven particle distribution and other problems often occur in practical operation, so it is necessary to accurately control the stirring process. In this paper, the stirring process of SiC particle reinforced magnesium matrix composites was dynamically simulated by commercial computational fluid dynamics (CFD) software Fluent. The effects of different stirring speed, stirring time and temperature on the microstructure of SiCp/AZ91 (SiC particle reinforced magnesium alloy AZ91) were studied. The results show that the stirring time and speed have an obvious impact on the quality of the finished SiCp/AZ91 material. The increase of the stirring speed is helpful for the SiC particles to disperse better, but excessive speed causes the liquid level to fluctuate and then a large amount of gas to enter into the magnesium liquid, thereby leading to more pores in the finished products. In terms of stirring time, when the stirring time is short, SiC particles can not be fully mixed with the alloy liquid, so a large number of SiC particles agglomerate. With the prolonging of the stirring time, the agglomerated particles gradually disperse into the magnesium alloy liquid, it is observed that when the stirring time is 15 min, the mixed phase composed of SiC solid particles and liquid magnesium is the most uniform, and the macroscopic uniformity of the solid particles does not change further when the stirring time is prolonged. According to the simulation and experimental results, the optimal stirring time is 15 min and the stirring speed is 300 r/min.

Glass

A Diffractive Optical Element with Gradient Refractive Index Micro-Structure Imprinted in Chalcohalide Glasses

HE Xiaoyan

2021, 40(3):  990-998. 

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A diffractive optical element (DOE) with a gradient refractive index (GRIN) micro-structure which was imprinted in the chalcohalide glass covering a range of visible to mid-infrared wavelengths, was prepared by an efficient and inexpensive micro-thermal poling process. The influence laws of polarization parameter (polarization voltage U) of micro-thermal poling on the morphology, micro-structure, diffraction effect and diffractive optical element of chalcohalide glass were investigated. The effective imprinting of GRIN micro-structure on chalcohalide glass was found to be in a range of 0.75 kV to 1.00 kV for U. The depths of surface morphology and the number of the diffraction orders increase with the increment of U, but the micro-thermal poling has little effect on optical transmission and doesn’t affect the practical applications. After the micro-thermal poling process, GRIN micro-structure with a period length of 25 μm and a maximum phase difference of up to 0.60λ (λ=632.8 nm) are observed on the surface of the chalcohalide glass. The main sources of its diffraction performance are the migration of K⁺ on the subsurface near the anode side and the periodic GRIN micro-structure formed by the rearrangement of glass structure.

New Functional Materials

Research and Development on Graphene Doped ZnO Composites

SHENG Hao, LIU Lin, XU Jian, LU Huanming

2021, 40(3):  999-1006. 

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Nanomaterials have excellent anomalous, abnormal electrical, optical, mechanical and catalytic properties, opening up new research and application fields for the research of new materials. Zinc oxide has the advantages of low cost, non-toxic and harmless, large band gap width and high electronic excitation energy, and has been widely used in the development of functional devices. However, ZnO has some defects, such as oxygen vacancies (V_o) and zinc deficiency (Zn_i), rapid recombination rate of photoelectron-hole pairs and low adsorption properties. Doping can change the structure of the material and improve its performance. Graphene is a two-dimensional planar structure material with a thickness of only one atomic layer. Its microstructure is a sp² hexagonal atomic network with allotropes of G, GO and rGO. It has a special structure and good properties. Its excellent stability and large specific surface area make it easy to mix with other materials. These properties all help to improve the performance of ZnO nanoparticles. Recent applications of graphene/zinc oxide composite materials in the fields of photocatalysis, sensing, transparent conductive films, optical detection, and electrodes were introduced. The addition of graphene can control defects. The best defects of ZnO/rGO not only increase the surface and carrier concentration of ZnO/rGO but also provide auxiliary carrier paths, supplemented by rGO flakes for electron-hole separation and extended carrier recombination. These characteristics are very suitable for light detection and photocatalysis applications. Due to the high surface area of graphene, a p-n junction is formed between rGO and ZnO nanoparticles. ZnO/rGO composite material has excellent responsiveness and selectivity to gases, and the combination of rGO nanocrystals and ZnO plays a vital role in enhancing detection performance. Adding metal ions and graphene to ZnO can effectively reduce the square resistance of the film. Vacuum annealing and annealing in Ar+H₂ can make electrical properties more excellent because annealing reduces internal defects and disorder. The carrier mobility of graphene at room temperature is about 15 000 cm²/(V·s). Unlike many materials, the electron mobility of graphene is less affected by temperature changes. The optical and electrical parameters of the ZnO/graphene composite film increase the possibility of becoming a transparent conductive electrode. In addition, it can also be used as a photodetector, diode, etc. The composite of ZnO and graphene has a good influence on the development of many fields in the future, and it is still a hot spot and trend of research.

Research Progress of Ultra-Precision Surface Grinding and Polishing Abrasive Particles

ZHOU Zhaofeng, HONG Juan, HUANG Chuanjin

2021, 40(3):  1007-1015. 

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Ultra-precision processing of semiconductor materials is a technology that achieves high surface quality and surface integrity. Grinding and polishing abrasive particles are one of the key consumables for achieving ultra-precision processing of semiconductor materials. The research status and development trend of grinding and polishing abrasive particles based on their composition and structural characteristics were summarized. Firstly, the contact model between the workpiece, abrasive particles and pad in the grinding and polishing interface was constructed, and the influences of the material, shape, concentration, and particle size of abrasive particles on the quality and efficiency of the grinding and polishing were discussed. Secondly, the grinding and polishing performance and the corresponding mechanism of mixed abrasive particles were introduced from the aspects of material and particle size. Thirdly, the application of composite abrasive particles in ultra-precision processing technology was summarized from the perspective of material structure and chemical action. Finally, the future research direction of grinding and polishing abrasive particles was prospected.

Preparation and Performance of Boron-Labeled Fracturing Fracture Tracer

LI Xianghui, TI Yongzhou, LI Canran, ZHANG Feng, CHEN Qian, WANG Xiaohui, YUAN Suhua, ZHU Yukun

2021, 40(3):  1016-1021. 

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Boron with high thermal neutron capture cross section can be used to detect fracturing fractures in oil and gas downhole. The effects of different amounts of B₄C (mass fraction of 1%, 5%, and 10%, respectively) on the structure and performance of the fracturing proppant were investigated by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction analysis (XRD), energy spectrum analysis (EDS), scanning electron microscope (SEM) and inductively coupled atomic emission spectroscopy (ICP-AES). The results show that when the adding amount of B₄C is 1%, its main phase is corundum. The breakage ratio and volume density under the 69 MPa pressure are 5.4% and 1.66 g·cm^-3, respectively. When the B₄C adding amount of is at 5% or 10%, the boron oxide generated by oxidation of B₄C reacts with alumina to form aluminum borate whiskers, and the corundum phase is reduced. Carbon dioxide and boron oxide from the oxidation of B₄C evaporated, form a porous structure of the proppant, and result in an increase of the breakage ratio and a decrease in bulk density.

Effect of Reaction Time on Preparation and Adsorption Properties of Mg-Al Hydrotalcite

HU Sheng, ZHANG Minghao, HU Weibing

2021, 40(3):  1022-1028. 

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Tetracycline hydrochloride is not completely absorbed in the organism and is discharged from the body, which is toxic to the soil and threatening the ecological environment. Tetracycline hydrochloride residue in the soil environment is not easy to be biodegraded because of its structure containing naphthol ring. Adsorption method has excellent characteristics like simple, economical, efficient and cheap, which is an effective way to treat tetracycline hydrochloride wastewater. Magnesium-aluminum hydrotalcite was prepared by uniform co-precipitation method. The products were characterized by X-ray diffraction (XRD), fourier transform infrared spectra (FT-IR) and scanning electron microscope (SEM). The effects of the different time on the microstructure of Mg-Al hydrotalcite were studied. The effects of reaction conditions on the adsorption properties of Mg-Al hydrotalcite were investigated by using tetracycline hydrochloride as adsorbent. It has important practical significance for soil pollution control and remediation. The results show that when the reaction time is 12 h, the maximum adsorption rate of tetracycline hydrochloride on Mg-Al hydrotalcite is 70.82%. The adsorption behavior of Mg-Al hydrotalcite for tetracycline hydrochloride is in accordance with Langmuir isothermal equation and quasi first-order kinetic model. The results show that the thermodynamic parameter of ΔH^O is 7.40 kJ/mol, and ΔG^O is less than 0, ΔS^O is 40.82 J/(mol·K), respectively, indicate that the adsorption process is endothermic, spontaneous and entropy increasing process in this study temperature range.

Photocatalytic Degradation Characteristics of ZIF-8 Synergistically Enhanced with TiO₂

XU Hang, DU Huiling, DU Xian, RAN Hongpei, WU Liang, LI Zhuo

2021, 40(3):  1029-1037. 

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Industrial organic wastewater pollution endangers human health and hinders economic development, which is an urgent problem to be solved. Metal-organic framework (MOFs) material is expected to be a potential new material for industrial organic wastewater treatment because of its unique pore structure, large specific surface area and excellent adsorption performance. Due to its complex SOD topological structure and high stability, ZIF-8 (zeolite imidazole ester skeleton-8) has attracted more and more attention to its application value in industrial wastewater adsorption. In this paper, the optimal phase ratio of anatase/rutile mixed phase TiO₂ nanoparticles were firstly prepared by the sol-gel method and temperature regulation, and the coated type ZIF-8 composite material was prepared by in-situ growth on the surface of the TiO₂ particles by the solvent method. The results show that the degradation rate and reaction rate of methylene blue (MB) pollutants in the composite material constructed by introducing 10% (mass fraction) TiO₂ and ZIF-8 follow the first-order kinetic model, which are 1.27 times and 2.3 times that of pure ZIF-8, respectively. The controlled preparation of the uniformly distributed Zn/ZnO_x nano-heterojunctions in the pores of the ZIF-8 organic framework materials served as the activation site, which increases the contact area with MB molecules and the capture number of carriers. At the same time, TiO₂ and the exposed highly active heterojunction interface formed a synergistic enhancement effect and a stereoscopic catalytic degradation complex system, which enhances the catalytic degradation ability.

Refractory Materials

Influence of Alumina Source on Phase Composition and Microstructure of CA₆ Porous Materials

KANG Guowei, LIU Xin, WU Ran, WANG Di, LI Ying, LIU Xinhong, JIA Quanli

2021, 40(3):  1038-1045. 

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CA₆ materials have been synthesized by high temperature solid state reaction using CaCO₃ as calcium source combined with Al(OH)₃, uf-Al₂O₃ and industrial Al₂O₃ as alumina sources. Effects of alumina sources on phase composition, microstructure and properties of CA₆ materials were studied. The results show that CA₆ forms at 1 300 ℃ using Al(OH)₃ and uf-Al₂O₃ as alumina sources. Solid state reaction temperature of samples finishes at 1 500 ℃. Further increasing of firing temperature has no effect on the phase composition. The microstructure of CA₆ produced by the reaction is changed with different alumina sources. When Al(OH)₃ is used as the alumia source, the microstructure of CA₆ is mostly platy. However, as used industrial Al₂O₃ as the alumia source, the microstructure of CA₆ is mostly plate-like and granular, but the microstructure of CA₆ is mostly equiaxed grains by using uf-Al₂O₃ as precursor. When used uf-Al₂O₃ as the source, the compressive strength and bulk density of the materials are the highest, and the porosity is the lowest. As used Al(OH)₃ as alumina source, the compressive strength and bulk density of the materials are the lowest, and the porosity is the highest.

Effect of MgO Source on Preparation of Magnesium Aluminate Spinel by Nano-η-Al₂O₃

ZHENG Peiyu, ZHANG Ling, ZHANG Xiaoxu, LI Renjun

2021, 40(3):  1046-1051. 

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Magnesium aluminate spinel was prepared by solid-state reaction method with light burned magnesia powder, MgCO₃ or analytically pure Mg(OH)₂ as MgO source and nano-η-Al₂O₃ with molar ratio of 1∶1. The effects of different MgO sources on the apparent porosity, bulk density, phase composition, unit cell parameters and microstructure of magnesium aluminate spinel prepared by nano-η-Al₂O₃ were studied. The results show that with the increase of sintering temperature, the compactness of the magnesium aluminate spinel samples prepared by three kinds of MgO sources and nano-η-Al₂O₃ becomes better and better. At 1 600 ℃, the maximum bulk density of spinel samples prepared by using Mg(OH)₂ as MgO source and nano-η-Al₂O₃ is 3.296 g/cm³, the lowest apparent porosity is 1.9%, and the grain size is about between 3 μm and 5 μm. At 1 300 ℃, all the three MgO sources and nano-η-Al₂O₃ form magnesium aluminate spinel. Compared with the traditional solid-phase method, for preparing magnesium aluminate spinel with α-Al₂O₃ as Al₂O₃ source, the synthesis temperature of magnesium aluminate spinel is reduced by 100 ℃. It reduces the cost of magnesium aluminate spinel, which has practical significance for the application of magnesia alumina spinel.