Table of Content

15 June 2021, Volume 40 Issue 6

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3D Printing Cement-Based Materials

Research Progress and Application of 3D Printing Concrete

ZHANG Chao, DENG Zhicong, MA Lei, LIU Chao, CHEN Yuning, WANG Zhibin, JIA Zijian, WANG Xianggang, JIA Lutao, CHEN Chun, SUN Zhengming, ZHANG Yamei

2021, 40(6):  1769-1795. 

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3D printing concrete technology, with the advantages of free formwork, high automation and intellectualization, has attracted more and more concerns, and achieved successful application in the field of construction engineering and other related fields. However, 3D printing technology puts forward higher requirements to the rheological performance of concrete, while the current standards or codes for concrete are no longer applicable to guide the mix design of 3D printing concrete. Meanwhile, due to the effect of the printing process, the hardened properties and reinforcement technology of 3D printing concrete are different from that of conventional concrete. Therefore, this paper reviews 3D printing concrete from four main aspects, i.e., rheological and printable performance, mix design, hardened properties, and reinforcement technology. Besides, for comprehensively presenting the development and application of 3D printing concrete, different types of engineering projects and special types of 3D printing concrete are introduced in this review. This review is expected to provide a reference for the further development and research of 3D printing concrete.

Progress on 3D Printing Construction Technology and Its Cement-Based Materials

ZHANG Yi, ZHU Yanmei, REN Qiang, JIANG Zhengwu

2021, 40(6):  1796-1807. 

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3D printing technology has the characteristics of digitalization, automation, rapid and efficiency, no mold, and material saving. It is a manufacturing technology with low energy consumption and low emission, and it is also the key technology for the upgrading of the manufacturing industry. 3D printing technology has great potential in the construction industry, which can greatly shorten the construction cycle and improve the structural designability of buildings. It is a promising construction technology in some extreme environments as well. Therefore, 3D printing construction technology is not only favored by research workers but also strongly supported by governments. This review summarized the recent development of 3D printing construction technology based on cement-based materials. First, the history and application of 3D printing construction technology based on cement-based materials were introduced. Then the progress of 3D printing cement-based materials was introduced from three aspects of printability, mechanical properties,and durability. Finally, thoughts and suggestions about 3D printing construction technology were proposed. In addition, its developing tendency was pointed out.

A Review of Recent Research Progress of 3D-Printed Concrete in Australia

LIU Junli, REN Jie, TRAN Phuong Jonathan

2021, 40(6):  1808-1813. 

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3D printing, also known as additive manufacturing, is a technology to fabricate three-dimensional objects via layer-by-layer additive deposition process. Over the past few years, 3D printing has been attracting increasingly attention from the building and construction industry. Compared with the traditional concrete casting technique, the application of 3D concrete printing (3DCP) results in higher efficiency with freeform construction and less dependence on labor. Globally, the research work on 3DCP has experienced a substantial increase over the last few years thanks to the active research teams from different universities and institutions, including those in Australia. This review paper aims to provide information in the recent progress on the 3DCP research by two Australian universities, including RMIT University and Swinburne University of Technology. The printing facilities and their printing characteristics in both universities were described at first, followed by the discussion on research area and recent publications. The research team from RMIT University focuses on the effects of fibres on the mechanical performance of 3D-printed concrete. On the other hand, the properties of 3D-printed geopolymer concrete have been widely investigated by the group from Swinburne University of Technology. It is anticipated that this paper can help develop a better understanding in the research progress in 3DCP contributed by Australian research teams.

Quantification, Optimization and Standardization of 3D Printability of Cementitious Composites

WANG Li, LI Danli, YE Kehan, GUAN Jingyuan, FENG Duo

2021, 40(6):  1814-1820. 

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The coordination between the 3D printability of cementitious composites and printing process is crucial to the rapid additive manufacturing. However, due to the variety of raw materials and mix proportion, printing equipment and manufacturing process, etc., the quantification and evaluation of 3D printability have not been unified, which brings barriers to the application and promotion of this technology in engineering practices. The influencing factors of 3D printability are analyzed, the quantitative evaluation methods of concrete 3D printability are summarized, six optimization methods of 3D printability are summarized and analyzed, and suggestions for standardization promotion are provided, which provide practical guidance value for the engineering application of 3D concrete printing technology.

Influencing Factors and Testing Methods of Printability of 3D Printing Concrete Materials

JIAO Zekun, WANG Dongmin, WANG Qibao, HUANG Tianyong, WANG Jixiang, LI Linkun

2021, 40(6):  1821-1831. 

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Concrete 3D printing is a new and high technology developed in recent years, which has attracted extensive attention and achieved many research results. However, there is no unified understanding of the testing method of material properties at present. In this paper, the research progress of 3D printing concrete was reviewed for five aspects: fluidity, setting time, rheological properties, extrudability and buildability. Fluidity test is used to quickly screen out material not suitable for printing. In the long run, materials with short setting time have more potential. The rheological properties of materials are quantitatively analyzed, but the evolution of static yield stress with time is lacking in research. At present, the extrudability is still judged by observation method and quantified by voidage. Due to different collapse modes, buildability should be evaluated by combining the number of printed layers with the deformation of specimens. The printability testing methods in recent years were summarized, their advantages and disadvantages were analyzed. And this paper provides some suggestions for the quantification and evaluation of printability for researchers to use for reference.

Research Progress on Concrete Materials for 3D Printing and 3D Printing Formwork Technology

SUN Kaili, WU Xiangqiang, LIN Xiqiang, LI Guoyou, LI Xinjian, SUN Zhipeng

2021, 40(6):  1832-1843. 

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Concrete 3D printing is a typical representative of modern digital manufacturing, which has attracted wide attention due to its technological advantages of intelligence, personalize and green construction. As a new construction method, concrete 3D printing has had a disruptive effect on the construction industry and has challenged traditional concrete materials. Improving the adaptability of concrete materials and 3D printing technology and realizing the wide application of 3D printing technology in buildings are the focus of general attention. In this paper, the development process of concrete 3D printing technology was summarized and the performance requirements of concrete materials for 3D printing were discussed, including the rheological properties, printability, buildability and mechanical properties. The typical application of 3D printing formwork technology in decoration and special-shaped structures was also introduced, which was expected to provide some reference for the research and engineering development of concrete 3D printing.

Review on Performance Requirements and Related Admixtures of 3D Printed Concrete

WANG Yuling, WANG Chunfu, ZHANG Feiyan

2021, 40(6):  1844-1854. 

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The special construction technology of 3D printed concrete puts forward new requirements for concrete materials. The reasonable selection of the type and dosage of admixtures effectively adjusts the rheology, setting property, strength and durability of 3D printed concrete, and ensures the constructability and useability of 3D printed concrete. In this paper, the performance requirements of 3D printed concrete were firstly discussed, and then the action mechanism and usage of admixtures were analyzed, and theoretical suggestions for the selection of admixtures for 3D printed concrete were provided. At last, the future development of admixtures for 3D printed concrete were proposed.

Effect of Nano-Silica on Structural Deformation, Rheological and Mechanical Properties of 3D Printed White Portland Cement-Based Materials

JIN Yuan, XU Jiabin, SUN Dengtian, CHEN Mingxu, HUANG Yongbo, LU Lingchao, CHENG Xin

2021, 40(6):  1855-1862. 

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Compared with the traditional building materials, the printed structure build-up of 3D printed building materials proposes higher requirements on the rheological properties. The nano-silica was introduced to control the rheological properties of 3D printed white Portland cement-based materials, aiming to stabilize the paste structure and improve the mechanical properties. The experimental results show that the nano-silica shortens the setting time significantly, and improves the early mechanical properties of 3D printed white Portland cement-based materials. Meanwhile, the addition of nano-silica in 3D printed white Portland cement-based materials improves the yield stress and elastic modulus, which is conducive to resist its own gravity and reduce printed structural deformation. In addition, the 3 d compressive strength and flexural strength reach up to 46.9 MPa and 6.1 MPa, respectively, when the dosage of nano-silica reaches 0.5% (mass fraction). Based on the correlation of multiple rheological parameters, the dynamic yield behaviors present little influence on the deformation of the 3D printed structure, while the static yield stress presents the reverse phenomenon, which influences the structural deformation obviously. In conclusion, the introduction of nano-silica into the 3D printed white Portland cement-based materials can well control the rheological properties, and improve the printed structures and early mechanical properties.

Effect of Iron Oxide Red Pigment on Rheological Property and Printability of 3D Printed White Portland Cement-Based Materials

XU Jiabin, JIN Yuan, ZHAO Zhihui, CHEN Mingxu, LU Lingchao, CHENG Xin

2021, 40(6):  1863-1869. 

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Recently, most of the research on 3D printing technology in the field of architectural decoration focuses on the rheological property of materials and the mechanical properties of materials, while the study of its decorative effect is still few. In this paper, iron oxide red pigment was introduced into 3D printed white Portland cement-based materials for dyeing. The effects of iron oxide red pigment on the rheological property, printability, and mechanical property on 3D printed white Portland cement-based materials were studied. The experimental results show that the low pigment content can reduce the dynamic rheological property of the 3D printed white Portland cement-based materials and improve the extrusion performance of the paste, while the high pigment content is not conducive to the extrusion of the paste. Besides, the addition of iron oxide red pigment can significantly increase the static yield stress of the paste and reduce the structural deformation rate from 11.38% to 4.03%. At the same time, the addition of iron oxide red pigment can improve the early mechanical properties of the paste, and the 3 d maximum compressive strength and flexural strength of the paste can reach 48.56 MPa and 5.07 MPa, respectively. In general, the introduction of iron oxide red pigment can improve the deformation rate of paste through the regulation of rheological properties.

Effects of Fibers on Printing Performance and Mechanical Properties of 3D Printing Concrete

ZHANG Chao, DENG Zhicong, WANG Zhibin, HOU Zeyu, JIA Zijian, WANG Xianggang, JIA Lutao, CHEN Chun, SUN Zhengming, ZHANG Yamei, PAN Jinlong

2021, 40(6):  1870-1878. 

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In order to investigate the effects of fiber on the performance of 3D printing concrete (3DPC), the influence of fiber on the rheological properties, printing properties, mechanical properties, and pore structure of 3DPC were studied by adding PVA fiber, PP fiber, and sisal fiber. The result of the rheological property test shows that the static yield stress of 3DPC increases linearly with the content of three kinds of fiber, but the influence of fiber on the rheological property of 3DPC is different. The results of printing performance test indicate that the addition of PVA fiber reduces the extrudability of 3DPC, but it significantly improves the size uniformity of extruded concrete. The test results of mechanical properties and pore structure point out that PP fiber significantly improves the compressive strength of 3DPC, sisal fiber has the most significant strengthening effect on the flexural strength of 3DPC, and the increase of fiber content will reduce the apparent density of 3DPC and increase the internal porosity, resulting in the reinforcement effect of high fiber content is weaker than that of low fiber content.

Effect of Humidity Evolution on Microstructure and Mechanical Properties of Alternate 3D Printing Specimens

CAO Qianfei, CUI Dong, SHI Xiaohan, WAN Yi, ZUO Xiaobao, LAI Jianzhong

2021, 40(6):  1879-1888. 

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This paper offers a novel alternate 3D printing technique using alkali-activated slag (AAS) and Portland cement (PC), based on which AAS-PC composite specimens were prepared. The microstructures of specimens before and after drying were analyzed separately using X-ray computed tomography (CT), and flexural and compressive strengths for all specimens before and after drying were tested respectively. The experimental results show that the interface between AAS and PC is inclined to crack during humidity reduction, as the shrinkage resistance for both materials varied, and that leads to deterioration of microstructure and decrease of mechanical properties for the printout. Despite that, PC effectively remedies the strength insufficiency of AAS, and the flexural and compressive strengths for AAS-PC composite specimens are thus better as compared to printed specimens using AAS. Comparing between layer-by-layer and line-by-line printing method, the former one produces specimens with better flexural strength, while the latter one produces specimens with better compressive strength. The above results offer guidances for promotion and application of 3D printing technique.

Effect of Alkali-Resistant Glass Fiber Content on Performance of 3D Printed Mortar

XIAO Bofeng, LI Gu, ZHANG Guanghu

2021, 40(6):  1889-1894. 

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As an excellent inorganic nonmetallic fiber material, alkali-resistant glass fiber (ARGF) has a good research value and the application potential in the field of civil engineering. As an emerging technology, 3D printing technology has high matching degree and application prospect in civil engineering. In this study, by adding varied ARGF fiber content and adjusting superplasticizer dosages, a series of 3D printed mortar (3DPM) with good printing performance were made, and the effects of ARGF fiber content on the mechanical properties were explored. The results show that, to achieve good printing performance, the flow spread in jump table test was suggested to be ranging from 180 mm to 220 mm. With the increase of fiber content, the flexural strength of 3DPM significantly increaseds, and the increases rate up to 99.2%. With the increase of fiber content, the compressive strength of 3DPM first increases and then decreases, and the optimum fiber mass content is 0.25%.

Bonding Behavior of Spray-Based 3D Printing Magnesium Phosphate Cement and Concrete

LIU Xiongfei, LI Qi, WANG Li, WANG Nan

2021, 40(6):  1895-1904. 

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In this paper, combining the all-angle intelligent construction of spray-based 3D printing and magnesium phosphate cement (MPC) with fast hardening, high early strength and excellent bonding performance, the bonding behavior of the spray-based 3D printing MPC and concrete was studied. By adding metakaolin (MK) and fly ash (FA) to adjust the setting time, rheological properties and mechanical properties of the MPC, a spray-based 3D printing MPC was developed, and the change rule of the bond strength and microstructure of the interface between the spray-based 3D printing MPC and concrete was investigated. The results show that MK significantly prolongs the setting time of MPC by reducing the hydration heat release rate of MPC, and FA shortens the difference between initial setting time and final setting time of MPC, thus improving the stability of spray-based 3D printing MPC. The flexural strength of MPC increases first and then decreases with the addition of MK. FA further improves the flexural strength of MPC. With the increase of MK content, the static yield stress of MPC gradually increases. The effect of FA on the yield stress of MPC is not obvious, but the plastic viscosity of MPC significantly reduces. When adding 30%MK and 15%FA, the construction and pumping performance of MPC can be ensured. Through high-speed spray extrusion, the spray-based 3D printing improves the bond strength between MPC and concrete, which make the micro interface between MPC and concrete compact.

Discussion on Statics Numerical Simulation of 3D Printed Concrete Hollow Gravity Dam

LIU Xiaopeng, FENG Jingjing, LIU Zhongqiu, ZHOU Jing

2021, 40(6):  1905-1910. 

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There are relatively few applications of 3D printed concrete technology in water conservancy projects, currently. A small hollow gravity dam with a height of 10 m was taken as the research object, based on ANSYS software to simulate and discuss the bearing capacity of 3D printed concrete hollow gravity dam under the action of self-weight pressure and hydrostatic pressure. The impact of weak interlayers on the bearing capacity of hydraulic structures was discussed.The results show that under the action of self-weight pressure and hydrostatic pressure, the 10 m high 3D printed small concrete hollow gravity dam has no major deformation and can perform its normal use function. There is an over-stress zone at the upstream heel of the hollow gravity dam, but the area is extremely small and can be solved by adding steel bars and other measures. A tensile stress value that exceeds the tensile strength of the weak interlayers appears at the position of the hollow part near the upstream surface. Measures must be taken to enhance the bonding ability of weak interlayers or set up steel trusses to offset tensile stress to ensure the safety and reliability of the dam.

Effect of Nano-Alumina on Rheological Property, Hydration and Hardening Strength of Portland Cement Paste

XIE Xiaojie, WANG Shen

2021, 40(6):  1911-1917. 

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The effects of nano-alumina (NA) on the early rheological properties, mid-term hydration rate and long-term mechanical properties of Portland cement pastes were studied, and the correlation of these parameters were analyzed. Results show that the addition of NA increases the yield stress and plastic viscosity of fresh cement paste, and the maximum growth rates of these two parameters are more than 110% when NA content is 3% to 5%. NA significantly changes the hydration heat flow rate and heat release of Portland cement in the early stage, and increases the compressive strength and bending strength of paste at various ages. For this composite paste system, the early hydration heat release and rheological parameters show an exponential growth trend, while the peak rate of heat flow has an approximate linear function relationship with the compressive strength.

3D Printing Ceramics

Research Progress on Slurry System of Ceramic 3D Printing Technology Based on Slurry Morphology

LIU Wenjin, ZHOU Guoxiang, LIN Kunpeng, ZHANG Yanzhao, ZHAO Zhe, YANG Zhihua, JIA Dechang, ZHOU Yu

2021, 40(6):  1918-1926. 

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3D printing technology is widely used in the manufacturing of fine ceramic fields due to its simple operation, rapid molding, and applications in preparation of complex structures. In this paper, the characteristics of different 3D printing technologies in ceramic preparation were reviewed based on the material morphology of 3D printing ceramics. The application and mechanism of binder and dispersant applied in direct ink writing, stereolithography and inkjet printing 3D printing technology of ceramics were introduced, and these additive components of water based and non-water based were summarized and discussed, aiming to provide reference for the preparation of high-performance ceramic samples via 3D printing technology.

Preparation of Fine-Grained Alumina Ceramics by Gel 3D Printing

GUO Jinyu, XIE Hehan, YANG Xiaole, LIU Yueming, MA Zhengyu, YANG Xianfeng, XIE Zhipeng

2021, 40(6):  1927-1936. 

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In this paper, a boehmite gel suitable for direct ink writing was prepared by sol-gel method. Rheological properties of the gel were adjusted by changing the content of boehmite and the content of hydroxyethyl cellulose, the printing properties of the gel were evaluated. Multi-step liquid phase drying method was innovatively proposed to tackle the challenges faced by the drying of gel body. Low molecular weight polyethylene glycol was used as the drying medium and ethyl acetate as the extractant, the gel body with a thickness of 10 mm was dried within 26 h, avoiding the occurrence of drying defects, which is difficult to achieve by the traditional low temperature and high humidity drying method. A dense alumina ceramic part with an average grain size of 1.5 μm, a relative density of 99%, and a bending strength of (351±53) MPa is successfully prepared after normal pressure sintering.

Sintering Characteristics of SiC Ceramics Prepared by Stereolithography 3D Printing

CUI Congcong, LI Shan, LI Wei, BAO Jianxun, ZHANG Ge, WANG Gong

2021, 40(6):  1937-1942. 

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Stereolithography (SLA), as one of the main methods of 3D printing of SiC ceramics materials, has a wide range of applications. In this paper, the experiments of debinding and reactive melt infiltration (RMI) were carried out on the SiC prepared by stereolithography. The sintering characteristics of the SiC were studied through the changes of density, strength, shrinkage,and microstructure. The results show that,the shrinkage of the sample is low after debinding, especially along the additive direction, which is only 0.88%. The strength of the sample after debinding is 0.26 MPa. The residual pyrocarbon (PyC) formed by the UV resin is connected with SiC particles in a network structure. The pyrocarbon locally breaks and microcracks appear along with the printed layers. The residual pyrocarbon reacts with silicon to form β-SiC after reactive infiltration and the silicon fills the pores and microcracks. The density of the sample is 2.79 g/cm³, and the bending strength is 183.99 MPa.

Rapid Preparation of Thick-Walled 3D Printing Silica Ceramics

WANG Shouxing, LI Ling, BI Lunan, LIU Shihao, WANG Yingying, BAO Xiaoyun, HAN Zhuoqun, QU Zhongbao, LYU Jiaqi

2021, 40(6):  1943-1949. 

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A composite dispersant was selected to prepare low-viscosity ceramic slurry, and the thick-walled (>3 mm) SiO₂ hollow hexagonal ceramic part was prepared by the self-developed ceramic 3D printer and DLP (digital light processing) process. The accuracy of the green body was all within 50 μm in three dimensional directions. The thermal decomposition process of 3D printing ceramic green bodies in air atmosphere or argon atmosphere was analyzed, and the influence of atmosphere on the degreasing and sintering of thick-walled (>3 mm) SiO₂ ceramic parts was analyzed. The process of rapid degreasing and sintering of thick-walled (>3 mm) 3D printing SiO₂ ceramic body was analyzed by SEM. The argon atmosphere is conducive to the rapid degreasing and sintering of the thick-walled SiO₂ ceramics. The thick-walled (>3 mm) SiO₂ ceramic part was prepared rapidly by controlling the gas flow in argon atmosphere. The period of degreasing and sintering is greatly shortened to 21.8 h. Compared with the preparation period of the slurry and its process imported from a foreign company (The preparation period of the company’s slurry and process to prepare the same product is 283 h), it is shortened by 92.3%. And it is more than 82% shorter than the preparation period of the SiO₂ ceramic hollow blade prepared by the same process in public reports, which reflects the advantages of 3D printing formless rapid prototyping technology, and has great significance for the practical application of SiO₂ ceramic 3D printing technology.

Effect of Epoxy Resin Content on Properties of Porous Coal Series Kaolin Ceramics Prepared by Selective Laser Sintering

HE Yining, DAI Gaoshang, WU Jiamin, ZHANG Jie, PAN Mingzhu, CHEN Jingyan, CHEN Ying, WANG Yongjun, ZHANG Hongxing

2021, 40(6):  1950-1956. 

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At present, the low level of kaolin resources deep processing technology in China leads to the resources waste and environmental pollution. In this paper, epoxy resin and coal series kaolin powder were used as the binder and raw materials, respectively, and porous coal series kaolin ceramics were prepared by selective laser sintering (SLS). The effect of epoxy resin content on the properties of porous coal series kaolin ceramics were investigated. The results show that the main phases of porous coal series kaolin ceramicswith evenly distributed pores are mullite and cristobalite. With a increase of epoxy resin mass content from 10% to 25%, it is found that the bending strength of porous coal series kaolin ceramic green parts increases continuously from 0.17 MPa to 0.32 MPa, the bending strength of porous coal series kaolin ceramics decreases from 2.81 MPa to 0.82 MPa, and the porosity increases from 50.37% to 59.69%. The preparation of porous ceramics from coal series kaolin by SLS is of great significance to the development and utilization of coal series kaolin resources.

Surface Modification of Si₃N₄ Powder and Its Effect on Digital Light Processing

CHEN Rufei, DUAN Wenyan, WANG Gong, LIU Bingshan, LIU Xiaodong, LI Xin

2021, 40(6):  1957-1964. 

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Traditional ceramic processing technology has high cost, long cycle and many defects, which makes it difficult to produce high-performance ceramics. The refractive index (n=2.1) of pure Si₃N₄ powder is quite different from that of resin (n=1.49), and the light scattering is serious, which leads to the lower curing depth of the ceramic paste. It is difficult to directly use stereolithography technology to form Si₃N₄ ceramic parts. In order to solve the problem that Si₃N₄ powder is difficult to be cured, two methods of surface coating and surface oxidation were used to modify Si₃N₄ powder, and the influence of the two methods on the light curing characteristics of Si₃N₄ powder was compared. The results show that the organic monomer uniformly attaches to the surface of Si₃N₄ powder after a certain reaction time; after being oxidized at 800 ℃ for 4 h, amorphous SiO₂ layer is formed on the surface of Si₃N₄ powder, which is uniformly attached to the surface of Si₃N₄ powder. The curing depth of original Si₃N₄ powder is merely 20 μm, and the curing depth of Si₃N₄ powder after coating modification and oxidation modification increase to 40 μm and 50 μm, respectively. Both methods effectively improve the curing depth of original Si₃N₄ powder.

Research on Rheological Properties of Stereolithography ZrO₂ Ceramic Slurry

HAN Zhuoqun, LI Ling, LIU Shihao, QIU Kun, WANG Shouxing, LIU Futian

2021, 40(6):  1965-1971. 

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This paper focuses on the dispersion of ceramic powder in photosensitive resin. The effects of powder properties, dispersant type and dosage, and solid content on the rheological properties of stereolithography ZrO₂ ceramic slurry were studied. The result shows that the properties of the powder have a significant impact on the rheological properties of the slurry, the use of ZrO₂ powder with a smaller specific surface area and higher sphericity is more conducive to the preparation of low viscosity and high solid content slurry. The rheological properties and stability of the slurry are mainly controlled by the type and dosage of dispersant, using X-100 with a relative powder mass of 4% as a dispersant, the rheological properties and stability of the prepared ceramic slurry are better. The experimental result of the solid content of the slurry shows that the relationship between the solid content of the slurry and the viscosity satisfies the Krieger-Dougherty model. And the dispersion mechanism of the dispersant has been studied. By the research of this experiment, the foundation has been laid for the high-precision molding of the light-cured ZrO₂ ceramic slurry.

3D Printing of Ferrite with High Magnetic Performance and Its Applications

WEI Xiangxia, XIE Yanan

2021, 40(6):  1972-1978. 

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It is difficult or even unable for traditional ceramic processing methods to prepare complex structures with high performance. To overcome this, a direct ink writing based three-dimensional (3D) printing technology was used to near net-shape ceramic structures by the preparation of printable ceramic pastes. In this work, the influence of zinc content on the properties of nickel zinc ferrite was investigated in terms of microstructures, crystal structures, and magnetic properties. The results show that the saturation magnetization (M_s) of nickel zinc ferrite reaches 76.3 emu/g, when zinc content x is 0.4 in Ni_1-xZn_xFe₂O₄, because Zn²⁺ occupies the tetrahedral (A) position due to the cation distribution effect. Moreover, through the preparation of ceramic pastes, nickel zinc ferrite with complex mesh structures can be shaped using the direct writing 3D printing approach. The results show that 3D printed soft magnetic nickel zinc ferrite with a dense mesh structure is obtained after sintering. In the following, the 3D printed magnetic mesh is used to separate magnetic particles under a relatively low magnetic field. Overall, the ferrite mesh structures can be served as a magnetic medium to significantly enhance the magnetic flux density and magnetic field gradient, and therefore is capable of effectively improving the separation efficiency of magnetic particles. Finally, the high gradient magnetic separation is simulated and verified by finite element numerical COMSOL simulation.

3D Printing Other Materials

Preparation and Properties of α-Hemihydrate Gypsum 3D Printing Slurry Material

HUANG Yanmin, MAO Yanpeng, WANG Xujiang, LI Jingwei, WANG Wenlong, MA Yidi

2021, 40(6):  1979-1986. 

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The process of using pre-mixed α-hemihydrate gypsum slurry material for 3D printing has the advantages of high product strength and short printing cycle. However, there are problems such as short initial setting time of the gypsum and insufficient buildability of the slurry. On this basis, the effects of plant protein retarder and polyphosphate retarder on the compressive strength, fluidity and printable time of the material were studied. And the effect of the hydroxypropyl methylcellulose ether (HPMC) on the rheological properties of the slurry and the volume stability of 3D printed components was also studied. The results show that the two kinds of retarders have different mechanisms for retarding gypsum hydration. Plant protein retarders can extend the stable period of fluidity, while polyphosphate retarders cannot increase the printable time well. The slurry with polyphosphate retarder has lost its fluidity before the initial setting 8 min to 12 min. The addition of HPMC significantly increases the apparent viscosity and yield stress of the slurry material and eliminates the bleeding caused by the retarder, but it has little effect on the plastic viscosity and it reduces the compressive strength of the material. The α-hemihydrate gypsum 3D printed component with high HPMC content has good volume stability, and the volume deformation rate of the 3D printing component with 0.020% (mass fraction) plant protein retarder and 0.60% (mass fraction) HPMC is 0.09.

Effects of Attapulgite and Nano-Silica on 3D Printability of High Strength Gypsum Plaster

YU Yue, JIA Junhong, DUAN Bin, WANG Kuan, HONG Zhengdong, CAO Ruoyu, HUANG Jian

2021, 40(6):  1987-1996. 

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In this paper, the effects of attapulgite (ATP) and nano-silica (NS) on printability such as pumpability, rheology, buildability as well as solidified sample strength of α-hemihydrate gypsum plaster for 3D printing were investigated. Results show that the pumping force of plaster with ATP remains at (0.57±0.02) kN. The shear stress against strain rate curve does not change much with ATP addition. The 0 h and 4 h collapse angles of the printed plaster with 2.8% (mass fraction, the same below) ATP decrease from 24° and 32° to 8° and 11°, respectively. In comparison to ATP, the pumping force increases by the addition of NS. The pumping force of the plaster is nearly doubled with 2.8% NS in comparison with the plaster with ATP of the same additive content. Meanwhile, the initial shear stress of the plaster with the increase of NS addition also increases. Although the addition of NS leads to the increase of the pumping force, the buildability of the plaster with NS is better than the plaster with ATP. 0 h and 4 h printed plasters with 2.8% NS both show little slump. The solidified plaster with ATP or NS addition amount 1% to 2% is printable, and its compressive strength is strengthened, but the interlaminar bonding strength is weakened by 2/3 compared with the control sample.

Preparation and Properties of a 3D Printing Photosensitive Resin Based on Double Oligomer

YOU Xiaoping, YU Xian, LIANG Wen

2021, 40(6):  1997-2002. 

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With the development of UV curing 3D printing technology, it is very important to prepare photosensitive resin with low shrinkage and high gel content. The photosensitive resin was prepared by using pure acrylate (2 functionality, 2-AE) and urthane acrylate (6 functionality, 6-PUA) as prepolymer, tri (propylene glycol) diacrylate (TPGDA) and 2,4,6-trimethylbenzoyl diphenylphosphine oxide was as diluent and photoinitator, respectively. Shrinkage rate, gel content, viscosity and hardness were evaluating indicator.The photosensitive resin solution was prepared by orthogonal experiment and the sample was prepared by 3D printing. Taking shrinkage ratio, gel content, viscosity and hardness as evaluation indexes, the test results were analyzed by comprehensive balance method. The experiment results show that, the best combination is that ratio of two oligomers is 2∶1, the mass ratio of diluent is 57.6%, the mass ratio of photosensitizer is 3%. The performance parameters are: shrinkage rate 4.7%, gel content 96.6% (mass fraction), viscosity 105 mPa·s, Shore hardness 80 HD.

Cement and Concrete

Effect of Al₂O₃ Doping on Carbonation Performance of γ-C₂S

MING Xinzhao, LIU Zhichao, WANG Fazhou, HU Shuguang, HU Chuanlin

2021, 40(6):  2003-2010. 

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The effect of Al₂O₃ doping on the particle size, microstructure and mechanical properties of calcined γ-C₂S clinker was investigated. Results indicate that Al₂O₃ doping has no influence on the crystal form of γ-C₂S, but significantly changes its morphology. The undoped γ-C₂S grains exhibit wrinkly surface morphology and the particle size is larger. After Al₂O₃ doping, the grain surface becomes smooth. The compressive strength and the degree of carbonation of γ-C₂S carbonated for 24 h gradually increase with the increasing content of Al₂O₃. Based on the carbonation temperature rise, full width at half maximum of the diffraction peaks of calcium carbonate and the quantitative XRD analysis, Al₂O₃ doping retards the heat release of carbonation, which is beneficial for a more sustained carbonation reaction. Al₂O₃ doping also promotes the growth and the number of calcium carbonate crystals, which increases the degree of carbonation, densifies the carbonated matrix and increases the compressive strength.

Quantitative Study of Concrete Mesostructure Based on Two-Phase Composition of Aggregate and Paste

XU Haiming, XU Xiaoming, NIU Heyang, XU Gelong, CAI Jiwei, TIAN Qing

2021, 40(6):  2011-2018. 

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Paste thickness or distance between aggregates is an important parameter in the study of concrete properties and the mix design of concrete, and its quantitative methods generally include two types of paste thickness models, the mean free path model and the image processing method. In this paper, the paste thickness and the mean free path of 24 concrete specimens were calculated and measured by the quantitative methods above, by comparing the differences and relationships of the quantitative results, the applicability of these methods was illustrated. The results show that the power functions can be regressed between the paste thickness obtained by different methods and the volume fraction of aggregate, and the linear relationships are observed between the paste thickness calculated and measured by different methods, which implies that all of these methods can be used to qualitatively analyze the relationship between concrete performance and mesostructure. By comparing the derivation process of the different quantitative models, a modified paste thickness model (MAPT_Ⅱ) is obtained, which has better convenience and precision than the maximum/average paste thickness (MPT/APT_Ⅰ) models.

Chloride Ion Transport in Polypropylene Fiber Concrete under Dry-Wet Cycle

XIE Guoliang, SHEN Xiangdong, JIANG Wei, ZHANG Bin

2021, 40(6):  2019-2025. 

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In order to explore the transmission law of chloride ions in polypropylene fiber concrete under the action ofdry-wet cycles, four types of polypropylene fiber concrete were designed for experiments, and the free chloride ion content and total chloride ion content were measured under different dry-wet cycles. Measure and analyze the influence of polypropylene fiber incorporation on the chloride ion binding performance and chloride ion diffusion coefficient of concrete. The results show that the incorporation of 0.15% (volume fraction, same below) polypropylene fiber increases the compactness of concrete and reduces the content of free chloride ion. While the incorporation of a large number of fibers (<0.45%) leads to an increase in the content of free chloride ion in the concrete and increases the chloride ion content of the concrete. Ion binding capacity. In the range of 0% to 0.45% of polypropylene fiber content, the chloride ion binding capacity has a quadratic function relationship with the fiber content. The incorporation of polypropylene fiber reduces the chloride ion diffusion coefficient in the later stage of the dry-wet cycle and increases the time-dependent coefficient m, which is beneficial to improve the resistance of concrete to chloride ion erosion.

Experimental Study on Stress-Strain of Concrete Damaged by Early Freezing

LIAN Haidong, TIAN Qingqing, XU Cundong, GAO Yiwei

2021, 40(6):  2026-2033. 

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During the winter construction of concrete in northern areas, the newly poured concrete often suffers damage due to sudden temperature drop. In order to study the effect of early freezing on the mechanical properties of concrete under uniaxial compression,the uniaxial compression tests of concrete under the curing conditions of different freezing temperatures (-5 ℃, -10 ℃) and different freezing moments (1.0 h, 3.5 h, 8.0 h, 24.0 h) were carried out, the full stress-strain curve under uniaxial compression was obtained, and the constitutive equation suitable for uniaxial compression of early frozen concrete was obtained by fitting. The results show that the change trend of the stress-strain curve of concrete after early freezing is basically similar to that of normal cured concrete, but in the descending section, the early frozen concrete is steeper, and the ductility and plastic deformation ability are reduced. The freezing temperature has no obvious effect on the peak stress and peak strain. With the delay of the freezing time, the peak stress first drops and then rises, and the peak strain first rises and then drops. The mechanical properties of frozen concrete after the initial setting and before the final setting are the most severely damaged. The stress-strain curve equation of early frozen concrete based on the fitting of Professor Guo Zhenhai’s model is in good agreement with the experimental curve. The most unfavorable freezing point for the peak stress, peak strain, ductility and plastic deformation ability of the early frozen concrete is around 4 h after curing.

Influence of Disturbance During Setting and Hardening Period on Acoustic Emission Characteristics of Concrete under Compression

SI Xiuyong, HU Weihua, PAN Huimin

2021, 40(6):  2034-2041. 

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In order to understand the influence of the disturbance during setting and hardening period on concrete damage, the simulated disturbance test was carried out on the concrete in the initial setting stage to the final setting stage, and the acoustic emission signals generated during the compression failure process of the disturbed concrete were collected. By comparing the acoustic emission characteristic parameters of different specimens, the acoustic emission characteristics of concrete with different disturbed ages under the uniaxial compression were studied. Based on the formation dynamics of cement concrete structure, the damage mechanism of disturbed concrete was analyzed. The results show that the disturbance causes damage to concrete in different degrees. The disturbance in the middle stage of setting and hardening has a great influence on the performance of concrete, which reduces the peak stress of concrete by 25.1%, and the damage degree reaches 14.2%. The disturbance near initial setting and final setting has little effect on concrete. Compared with the reference concrete, the acoustic emission energy release rate of the disturbed specimen is smaller at the initial stage of loading, and the active range of acoustic emission appears in the later stage of loading. When the relative stress level is less than 50%, there is no obvious emission signal. The acoustic emission rate parameter a is the smallest and the process parameter b is the largest.

Solid Waste and Eco-Materials

Research Progress on Remediation of Heavy Metal Contaminated Soil

REN Zhisheng, LIU Shuhua

2021, 40(6):  2042-2051. 

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Heavy metals (arsenic, cadmium, chromium, mercury, lead, etc.) are widely polluted in the world. Correct understanding of the forms of heavy metals in the soil is conducive to adopting appropriate methods for soil remediation. The existing remediation technologies can be divided into physical, chemical, biological, electrical and thermal remediation according to the principle of remediation, and the specific methods include capping, encapsulation, landfill, soil washing, electric extraction, stabilization/solidification, vitrification, phytoremediation and bioremediation. These technologies have specific advantages and disadvantages and applicability. Capping, encapsulation and landfill are suitable for areas with serious pollution and small area. Because of the large amount of soil washing, it is necessary to treat the chelating agent. Electric extraction is suitable for shallow and low concentration contaminated sites, and the treatment time is long. Stabilization/solidification is widely used but does not remove heavy metals from the soil. Phytoremediation needs to be more efficient. Appropriate remediation technology is crucial for the reuse of heavy metal contaminated soil, which should be combined with the type and degree of pollution, remediation objectives, site characteristics, cost-effectiveness, and remediation time.

Review on Characteristics of Fluidized Bed Combustion Ashes and Key Issues in Their Application as Cement Admixtures

LIU Hulin, WANG Zhao, WU Yuanting, REN Siqian, WANG Wei, HAN Guiying

2021, 40(6):  2052-2061. 

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Fluidized bed combustion (FBC) ash is an effective technology for burning the fuels containing sulphur with low SO₂ emissions. It is an important issue that how to utilize the FBC ashes in an efficient and clean way. In this paper, the major characteristics of FBC ashes in terms of chemical and mineral compositions, microstructures, properties were reviewed. Compared with fly ashes and other by-products from coal burning, FBC ashes with porous structure contain free CaO, CaSO₄ and amorphous aluminosilicate, which leads to the obvious pozzolanic activity, self-hardening and hydration expansion. At the same time, several key issues in the application of FBC ashes as cement admixtures base on their composition, microstructure and properties were discussed. The results show that suitable activators should be used to enhance the activity of ashes. The stability needs to be improved by adjusting the curing process, water-cement ratio and other conditions. Adding water reducing agents controls the water requirement and increases cement strength. This provides some guidances for effective utilization of the building materials with FBC ashes.

Effect of Basalt Fiber by Alkali Etching on Bonding Properties of Geopolymer-Based Wood Adhesives

DENG Muling, ZHANG Yang, PAN Dawei, YE Hanzhou, ZHANG Na

2021, 40(6):  2062-2069. 

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As a new environment-friendly inorganic cementitious material, the geopolymer has great application potential in wood-based panel industry. However, the high brittleness limits its bonding property with wood. In order to improve the brittleness of geopolymer matrix and enhance its bonding property, alkali etching modification on the basalt fiber (BF) was used in this study. The basalt fiber was first etched by NaOH solution with different concentrations under different temperatures, and then the basalt fiber etched by alkali (HAF) was mixed with alkali activator, after which the geopolymer modified by basalt fiber (HAFMG) was prepared by adding metakaolin. The effect of alkali etching method on the mechanical property of HAFMG as well as bonding strength between HAFMG and wood was explored. The results show that alkali etching dissolves the silicon and aluminum components on the surface of BF, improves the surface roughness of BF and its interface combination with geopolymer matrix, and finally improves the bonding strength between the geopolymer and wood. Compared with the pure geopolymer, the geopolymer with the addition of HAF (100 ℃, 0.5 mol/L NaOH) has greater toughness. Its flexural strength increases by 154%, and the compression-flexure ratio is reduced by 41%. In addition, the shear strength of the geopolymer modified by HAF (100 ℃, 0.5 mol/L NaOH) is 121% higher than that of the pure geopolymer.

Influencing Factors of Si Phase Separation from Ilmenite by Gravity Concentration Method

LIN Yinhe, LI Jingwei, WANG Zhe, TANG Yong, CHENG Xiangkui, HUANG Xiaoli

2021, 40(6):  2070-2074. 

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High content of Si phase is a critical problem in the ilmenite for the upgrade of titanium slag from Sichuan. The gravity concentration method was proposed to separate the SiO₂ phase from the ilmenite. Particles with different size were prepared by ball milling process, then the particles were treated by heavy machine. The separation effects of different factors (such as particle size, particle proportion and stroke) on the Si phase from ilmenite were investigated. These results indicate that the proportion of particles with less than -200 mesh (＜75 μm) increases with the grinding time extension. When the grinding time is 8 min, the proportion of particles with less than -200 mesh reaches 83.0% (mass fraction). With the increasing of the stroke, the content of SiO₂ and the recovery rate of TiO₂ increase. When the stroke is 15 mm, the content of SiO₂ decreases to 1.07% (mass fraction) from 2.46%. Three different parties are divided after gravity concentration treatment, the content relation of TiO₂ is ilmenite>middling product>tailing, and the content relation of SiO₂ is ilmenite<middling product<tailing. The minimum content of SiO₂ reaches 0.93% (mass fraction) when the proportion of particles with less than -200 mesh is 85.5% (mass fraction).

Glass

Changes in Structure of Borosilicate Glass in Leaching Condition

ZHANG Xiaoyang, MAO Jiangjiang, CHEN Liting, MAO Yanan, WANG Tiantian, SUN Mengli, PENG Haibo, WANG Tieshan

2021, 40(6):  2075-2082. 

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Borosilicate glass is one of the most possible candidates for the immobilization of high-level radioactive nuclear waste and leaching is the main way that radionuclides inside the vitrification (borosilicate glass form) enter the biosphere. The leaching properties of borosilicate glass by deionized water were investigated using the MCC-1 static leaching method at 90 ℃ for 28 d. With the static leaching method developed by American Nuclear Waste Material Characterization Center, the leaching behavior and the corresponding micro-structures of the borosilicate glass were investigated, adopting a variety of spectral characterization methods including inductively coupled plasma optical emission spectrometry (ICP-OES), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (Raman), and the grazing incident X-ray diffraction (GIXRD). All of the data from FTIR, Raman and GIXRD indicate that, with corrosion in water, the proportion of Si-O-Si structures in glass increases while the B-related structures disappear, and the micro-structures in the layer near the surface are similar to fused silica. After being immersed for 7 d, a corrosion layer and cracks between the corrosion layer and glass base are observed in the surface of samples, which is identified by scanning electron microscope. The formation of the cracks led to a increase in surface area of glass samples. That finally led to an abnormal increase in the leaching rates of Na and Si elements.

Effect of MgO Content on Crystallization Behavior of RSCAF System Glass-Ceramics

XU Guoliang, LUO Yunlong, WANG Fu, LIU Laibao, LIAO Qilong

2021, 40(6):  2083-2089. 

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The glass-ceramics were prepared by using MgO to replace part of CaO in the R₂O-SiO₂-CaO-Al₂O₃-F (RSCAF) system, and the effect of MgO content on the crystallization behavior of the glass-ceramics was investigated systematically. The results show that the main crystalline phase of the glass-ceramics is canasite after heat treatment when the RSCAF system without MgO (CaO content is 16.5%, mass fraction, the same below). Then, the crystalline phase in the microscopic morphology of the glass-ceramics presents a indented appearance and the density of the glass-ceramics is less than that of the basic glass. As the content of MgO in the RSCAF system is in the range of 0% to 3%, the crystallinity of the glass-ceramics reduces with the decrease of CaO content. Along with the further increase of MgO content and the decrease of CaO content in the system, the main crystalline phase of the glass-ceramics transforms gradually from canasite into diopside, and the crystalline diopside phase with columnar and flake-shaped appearance increases in the microscopic morphology and the density of glass-ceramics increases gradually. When the content of MgO in the system increases to 4% (CaO content decreases to 12.5%), the main crystalline phase of the glass-ceramics completely changes to diopside, and the crystallinity of diopside increases compared with that of the main crystalline canasite phase glass-ceramics, and the density of the glass-ceramics is higher than that of the basic glass.

New Functional Materials

Preparation and Coloration of Fe₂O₃/SiO₂ Coated Pigments Doped with Zinc Ions

FENG Jinyang, ZHAO Kenan, FAN Yijun, LI Ningfang

2021, 40(6):  2090-2095. 

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Due to the incomplete coating of Fe₂O₃/SiO₂ pigment, the color of the pigment turns black and dark over 800 ℃. In this paper, the Fe₂O₃/SiO₂ coated pigments were prepared by sol-gel method, and then the effects of catalyst concentration, reaction temperature, mass ratio of silicon/iron and other factors on the coloration of pigments were investigated. On this basis, the coloration of the Fe₂O₃/SiO₂ coated pigments were studied by doping with zinc ions. The results show that the proper condition of synthetic reaction is the catalyst (ammonia) concentration 0.75 mol/L, the reaction temperature 40 ℃, the silicon/iron mass ratio m(SiO₂)/m(Fe₂O₃)=0.20, iron/zinc molar ratio n(Fe)/n(Zn)=4. The heat resistance of the Fe₂O₃/SiO₂ coated pigments doped with zinc ions is significantly improved, and the sample shows a bright orange red tone after 850 ℃ calcination.

Performance of Ceramizable Silicon Rubber Composite Tape for Cable

WANG Xingu, SUN Guanghua, CHANG Jintao, LI Xiufeng

2021, 40(6):  2096-2103. 

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Ceramizable silicone rubber composites were prepared by the melting blending method. The tensile properties, flame retardant property, and volume resistivity of the silicone rubber composites were tested. The results show that the tensile property of composites decline with the increasing flux amount. The introduction of more impurity ions improves the conductivity of the composites. The addition of SiO₂ enhances the compactness of the filler network structure, and the elastic deformation and the tensile strength of the composites are also increased. The migration of carriers is hindered, which promotes the increase of volume resistivity of composites. Because of the synergistic effect of a variety of inorganic fillers, composite materials have a better flame retardant property. When the part of weight of glass powder and SiO₂ is 40∶40, the oxygen index of the composites is the highest, meanwhile, the peak heat release rate and the peak smoke production rate are the lowest, and the fire risk is smaller. The blending of EVA and silicone rubber improves the rigidity and plastic deformation of the composites, and also changes the dispersion state of the fillers. The partially stacked fillers act as impurity ions, which causing the resistivity of the materials to decrease.

Effect of TiO₂ Addition on Sintering Kinetics of Aluminum and Chromium Solid Solution

LI Renjun, ZHANG Ling, ZHANG Xiaoxu, WANG Zhigang, HU Yujiang

2021, 40(6):  2104-2109. 

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Aluminum chromium solid solution is widely used in refractory materials, but it’s hard to achieve sintering and densification. Adding a certain amount of sintering additives can effectively improve its density, but the rule of grain growth in the densification process is still unclear. In this experiment, nano η-Al₂O₃ and industrial chromium green were used as raw materials, with TiO₂ as sintering aid and PVA as the binder, after being formed by cold isostatic pressing, the sintered aluminum chromium solid solution with the mole ratio of 1∶1 was prepared by solid phase sintering at 1 400 ℃ to 1 700 ℃ under normal pressure. The density, phase composition, microstructure, and average grain size of the sintered samples were analyzed by Archimedes method, XRD, SEM, and Nano measurer. On this basis, the effect of TiO₂ on sintering kinetics of aluminum chromium solid solution was further calculated and studied. The results show that during the sintering process, the grain growth index and activation energy of Al₂O₃-Cr₂O₃ and Al₂O₃-Cr₂O₃-2%TiO₂ sintered systems decrease with the increase of temperature. The grain growth of Al₂O₃-Cr₂O₃ system is mainly controlled by atoms crossing grain boundaries randomly and volume diffusion, the grain growth of the Al₂O₃-Cr₂O₃-2%TiO₂ system is mainly controlled by volume diffusion. Compared with the two systems, it is found that the addition of TiO₂ can decrease the grain growth index and activation energy of grain growth, and promote the grain growth and its development.

Preparation and Modification of Quaternary Phase Change Material

XIAO Liguang, SHANG Xiaoyue

2021, 40(6):  2110-2117. 

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In order to make hydrated salt phase change materials more suitable for solar energy heat storage, Na₂HPO₄·12H₂O was used as the main heat storage agent, Na₂SO₄·10H₂O, Na₂CO₃·10H₂O, Na₂S₂O₃·5H₂O and CH₃COONa·3H₂O were used as auxiliary heat storage agents, and any three of the four auxiliary heat storage agents were mixed with the main heat storage agent according to the designed ratio, nano-TiO₂, ZnO, Al₂O₃, Na₂SiO₃ and Na₂B₄O₇·10H₂O were selected as nucleating agents to modify the quaternary phase change materials. The data of the samples were analyzed by step cooling curve, DSC, SEM, IR and XRD. The results show that Na₂HPO₄·12H₂O/Na₂CO₃·10H₂O/Na₂SO₄·10H₂O/Na₂S₂O₃·5H₂O is the best combination of PCMs,in which the optimal ratio (mass fraction) is 60%, 10%, 20%, 10% (60/10/20/10), respectively. Among the nucleating agents, zinc oxide has the best effect. When the content of zinc oxide is 10% (mass fraction), the supercooling degree of quaternary PCMs decreases from 3.0 ℃ to 0.2 ℃, the phase change enthalpy increases from 95.11 J/g to 472.39 J/g, the phase transition temperature ranges from 15.44 ℃ to 39.90 ℃ to 50.79 ℃ to 129.64 ℃, and there is no phase separation.

Preparation of Amino Modified NCR-MCM-48 Molecular Sieve by Ethanol Assisting and Its Adsorption Performance of Cr(VI)

CUI Yanhong, SUN Peng, WANG Yingjun, SUO Yanhua, ZHANG Wei, WANG Yanhong

2021, 40(6):  2118-2128. 

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CR-MCM-48 molecular sieve was prepared through hydrothermal synthesis method with the silica gel purified from rice husk ash as the source of inorganic assembled silicon and the ethanol as the assisted reagent, and then NCR-MCM-48 mesoporous molecular sieve was synthesized by amino grafting to CR-MCM-48. The effects of the molar ratio of Si and Na, crystallization temperature, crystallization time and the addition of the organic assisted reagent ethanol on the mesoporous structure and the morphology of CR-MCM-48 were investigated. X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), N₂ adsorption-desorption curves and infrared spectroscopy (FT-IR) were used to characterize the structure and the morphology of the synthesized materials. The adsorption performance of Cr(VI) in aqueous solution by NCR-MCM-48 mesoporous material was evaluated. The results show that when n(Si)∶n (CTAB)∶n(H₂O)∶n(NaOH)∶n(C₂H₅OH) is 1.0∶0.65∶62∶0.625∶0.25, the crystallization temperature is 393 K, the crystallization time is 72 h, and the calcination temperature is 823 K, the assembled and synthesized CR-MCM-48 mesoporous material exhibits the best degree of order. The results of thermodynamic analysis show that the adsorption of Cr(VI) by NCR-MCM-48 is a spontaneous and endothermic reaction. The maximum adsorption capacity of NCR-MCM-48 for Cr(VI) is 88.9 mg·g^-1 when the adsorption temperature is 308 K, pH is 2.0, and the adsorption time is 150 min.