Table of Content

15 October 2021, Volume 40 Issue 10

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Editorials

Introduction for Special Issue

MA Chengliang, HU Junhua, ZHANG Haijun

2021, 40(10):  3189-3190. 

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In Memories of Mentor Professor Zhong Xiangchong

MA Chengliang

2021, 40(10):  3191-3192. 

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Reviews

Research Status of Fired Alumina Carbon Sliding Plate for Continuous Casting

LIU Gengfu, LIAO Ning, JI Zixu, LI Yawei

2021, 40(10):  3193-3199. 

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Fired alumina carbon sliding plate is one of the key functional materials of continuous casting flow control system. In the process, the materials suffer from the scouring of molten steel and slag, rapid and repeated thermal shock, and potential oxidation risk. Therefore, strict requirements are put forward for the mechanical properties, thermal shock stability, and oxidation resistance of materials. In recent years, in order to improve the above properties of fired alumina carbon materials and prolong their service life, the structure and composition of materials were continuously optimized. The main research directions included the reinforcement of in-situ ceramic phase formed by additives (such as aluminum and silicon), the synergistic strengthen and toughen of nanocarbon with in-situ ceramic phase, and the synergistic effects of layered compounds with nanocarbon and in-situ ceramic phase for strengthening, toughening and oxidation resistance.

Research Articles

Effect of Al on Phase and Structure Evolution of SiC-MgAl₂O₄ Composites under Nitrogen Atmosphere

GU Chenwei, WANG Zhanmin, ZHAO Shixian

2021, 40(10):  3200-3205. 

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SiC-MgAl₂O₄ composites were fabricated in flowing nitrogen for 5 h at 1 500 ℃, using SiC and MgAl₂O₄ powders as well as various mass fraction of 1%, 3%, 5%, 7%, 9% and 12% aluminum powders as the raw materials. The sintered samples were analyzed by XRD, SEM and EDS. The results show that a series of reactions occur in the material system after sintering at 1 500 ℃. β-SiC, MgAl₂O₄, nitride and sialon as the main phases are detected in all the sintered samples. Aluminum is partially nitridated at high temperature to form aluminum nitride and participate in the reaction of sialon and MgAlON formation. The spinel is transformed into two phases coexisting with aluminum-rich spinel and MgAlON. With the increase of aluminum content, α-Al₂O₃ can be precipitated when the solid-solute aluminum in spinel reaches to the content limit. Moreover, as the aluminum content increases, the morphology of the Si-Al-O-N phase changes from slab-band shape to slab-columnar shape, and eventually develops a clearer plate layer shape. A certain amount of Mg element is dissolved in the sialon phase by SEM-EDS analysis, which is considered as the sialon polymorph of Mg-sialon phase.

Oxidation Behavior of Al₂O₃-O’-SiAlON-SiC Composite under Thermal Shock Condition

SU Kai, CHEN Xiaoyu, ZHANG Jing, WANG Zihao, LIU Xinhong

2021, 40(10):  3206-3212. 

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Al₂O₃-O’-SiAlON-SiC composite was prepared from tabular corundum (aggregates and fines), ultra-fine α-Al₂O₃ and Si powder as starting materials at 1 500 ℃ for 3 h in carbon embedded condition. The effects of thermal shock and thermal shock cycle on oxidation behavior of the composite were investigated. The results show that the weight gain ratio of the composite increases with temperature increasing from 900 ℃ to 1 300 ℃ with and without thermal shock condition. The weight gain ratio with thermal shock is more than that without thermal shock, and the weight gain ratio increases with the increase of thermal shock cycle, indicating that thermal shock can promote the oxidation of Al₂O₃-O’-SiAlON-SiC composite. The oxidation curves exhibit parabolic-like without thermal shock, and the curves are linear-like with thermal shock. O’-SiAlON and SiC are oxidized on the surface of sample to form a dense protective film which retards oxygen diffusion into the inner of sample without thermal shock. However, the oxidation protective film is broken under thermal shock condition, which provides passages for oxygen to enter the inner part of the samples, accelerating the oxidation of the composite.

Prediction of SiC Oxidation Reaction Behavior Based on Back Propagation Artificial Neural Network

ZHAO Chunyang, WANG Enhui, FANG Zhi, GUO Chunyu, DUAN Xingjun, HOU Xinmei

2021, 40(10):  3213-3218. 

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Non-oxide refractory raw materials represented by SiC are widely used in the metallurgical high-temperature industry as important components of high-temperature structural materials. In practice, the oxidation behavior of SiC accelerates the failure of corresponding refractories at high temperatures, resulting in a significant reduction of their service life. Therefore, it is important to understand the oxidation behavior of non-oxide refractory raw materials at high temperature. Kinetic models are the most common means to analyze the oxidation behavior. However, the establishment of kinetic models often requires a lot of data processing work, and it is difficult to meet the two conditions of high descriptive accuracy and simple model parameters at the same time. With the exploration of artificial intelligence and big data technology in the field of materials, back propagation artificial neural network (BP-ANN) is expected to make a breakthrough in this area. In this paper, a typical non-oxide refractory raw material SiC was taken as an example, and the oxidation behavior of SiC was trained and predicted by building a neural network. The relative errors of the predicted results and experimental data are less than 3%, and the relative errors of the reaction activation energy and reaction rate constant calculated by regression with the predicted data are less than 4% with the results calculated by the experimental data. This shows that BP-ANN has great potential in studying the oxidation behavior of non-oxide refractory raw materials.

Effect of Heat Treatment Temperature on Properties of ZrO₂ Fiber Composite ZrO₂-C Material

CHEN Haijun, XU Enxia, LI Miao, GAO Jinxing, GE Tiezhu

2021, 40(10):  3219-3225. 

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Submersed entry nozzle is critical functional refractories in continuous casting and the slag line parts has the worst working environment. At present, the most suitable slag line material is ZrO₂-C material. In order to improve the performance of submersed entry nozzle, ZrO₂-C material was prepared by using zirconia and flake graphite as the main raw materials, zirconia fiber and metal silica powder as reinforcement materials, and phenolic resin as binder. The effects of three heat treatment temperatures, 1 000 ℃, 1 200 ℃ and 1 500 ℃, were compared on the properties and microstructure of ZrO₂-C material. The results show that when the heat treatment temperature is higher than 1 200 ℃, the silicon powder reacts with carbon to form silicon carbide, and a large number of whisker silicon carbide interleaves with ZrO₂ fiber to form a network structure, which improves the mechanical properties and thermal shock resistance of the material.

Effect of Firing Process on Performance of Granite-Based Lightweight Thermal Insulation Materials

PAN Mengbo, LI Xiang, QI Wenhao, DU Haoran, WU Xiaopeng, ZHAO Fei, MA Chengliang

2021, 40(10):  3226-3231. 

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Granite waste, clay and feldspar as the main raw materials were used to make granite-based lightweight thermal insulation materials. The effects of different firing process factors (firing temperature, holding time, heating rate) on the performance of the thermal insulation material were investigated. The high-performance thermal insulation materials with low apparent density, high compressive strength and low thermal conductivity at room temperature were prepared at optimal firing process. The results show that the optimal firing process is rising from room temperatureto 1 000 ℃ at 5 ℃/min, and then to 1 200 ℃ at 3 ℃/min for 30 min. The apparent density, the compressive strength at room temperature, and the thermal conductivity at room temperature of the thermal insulation material prepared at optimal firing process is 0.6 g/cm³, 18.11 MPa and 0.2 W/(m·K), respectively. The overall performance is the best.

Effects of Different Aluminum-Based Materials on Properties and Microstructure of MgO-Al-C Materials

HAN Xiaoyuan, SHI Kai, XIA Yi, HONG Siyang, LIU Yang, SHANG Jianzhao

2021, 40(10):  3232-3240. 

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MgO-Al-C materials were fabricated using sintered magnesia aggregates, fused magnesia fine powder, Al powder, N220 carbon black as raw materials, and phenolic resin as a binder. The effects of three aluminum-based raw materials (granulated alumina micro-powder, alumina hollow micro-beads, calcium hexaaluminate) on the cold modulus of rupture, high modulus of rupture, thermal shock resistance and oxidation resistance of samples were investigated, the phase composition and microstructure were analyzed via SEM and XRD. The results show that granulated alumina micro-powder has a porous structure that can absorb thermal stress inside the MgO-Al-C materials. When the granulated alumina micro-powder is added at 1% (mass fraction, the same below), it can increase the cold modulus of rupture and thermal shock resistance of the MgO-Al-C materials, and significantly improve the oxidation resistance. Alumina hollow micro-beads has a hollow structure, which can buffer thermal stress inside the MgO-Al-C materials. When the added amount of alumina hollow micro-beads is 3%, the cold modulus of rupture of the MgO-Al-C materials can be significantly improved, and the material has high thermal shock resistance and oxidation resistance. Calcium hexaaluminate has a lower coefficient of thermal expansion, which can give the MgO-Al-C materials better toughness. When the added amount of calcium hexaaluminate is less than 5%, the MgO-Al-C materials have better thermal shock resistance.

Influences of Different Carbon Materials on Properties of Alumina-Carbon Castables

KUANG Changliu, WANG Xing, LIU Zhenglong, DING Jun, YU Chao, DENG Chengji, ZHU Hongxi

2021, 40(10):  3241-3247. 

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Carbon containing castables have always attracted attention due to the poor water wettability of carbon materials and poor material properties caused by high-temperature oxidation. Thermal oxidized graphite, ZrC coated graphite and biomass carbon materials were added as carbon sources to alumina-carbon castables, and their influences on the apparent porosity, physical properties, phase composition, oxidation resistance and slag corrosion resistance were studied. The results show that the castable with thermal oxide graphite has the highest water addition, its residual pores impart the internal structure of the castable, leading to low mechanical properties. Adding ZrC coated graphite reduces the water addition of the castable, then gets better oxidation resistance and effects slightly the improvement of mechanical properties. Using biomass carbon material as carbon source significantly improves the physical properties of the castable, and compared to the sample with thermal oxidized graphite added, the biomass carbon material does not significantly improve the slag corrosion resistance of the sample.

Crystal Phase and Properties of Hexagonal Columnar Cordierite Synthesized by Forsterite

LI Yin, DONG Bo, DENG Chengji, DING Jun, ZHU Hongxi, WANG Hui, YU Chao

2021, 40(10):  3248-3256. 

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Natural forsterite mineral resources are rich in China. Due to the complex composition of this material, it is underutilized and its products have low added value. Forsterite, industrial alumina and quartz sand were used as raw materials to prepare cordierite at 800 ℃ to 1 380 ℃ for 2 h to 8 h in air atmosphere in order to expand the technology of high-efficiency utilization of forsterite. The influences of raw material composition and firing schedule on the synthesis of hexagonal columnar cordierite were studied. The results show that the best sintering system for cordierite is synthesized at 1 380 ℃ for 8 h. At this time, the synthetic purity of cordierite is the highest, the crystal form of cordierite is well developed and the crystal grains are hexagonal columnar. When the sintering temperature is 1 380 ℃ and the holding time is extended from 2 h to 8 h, the corresponding diffraction peak of quartz sand disappeares while the amount of cordierite precipitation increases and the crystallinity of the material is improved. The type of point defects of cordierite crystal is transition from V^"_Mg to O^"_i After the sample with excessive quartz sand is sintered at 1 380 ℃ for 8 h, the cordierite grains are covered and wrapped by glassy phase much more than before, the spacing between grains is reduced, and the density of cordierite increases, but the synthetic purity of cordierite is not improved.

Effects of Fibers and Opacifiers on Properties of Nanoporous Powder Insulation Material

DU Haoran, XING Yiqiang, LI Xiang, CHEN Kaiyang, WANG Shijie, MA Chengliang

2021, 40(10):  3257-3264. 

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Novel high temperature insulation material has a significant energy efficient effect on the industrial kiln, and it reduces the kiln high temperature radiation thermal conductivity facilitating high temperature insulation performance. In this work, the samples of fibers and opacifiers to add different types and different mass fraction were prepared using a dry method and the compressive strength and thermal conductivity of the samples were tested, and the microstructure and infrared transmittance of the samples were analyzed by SEM, EDS and FTIR. The results show that polycrystalline mullite fiber effectively improves the compressive strength of the insulation material and the thermal conductivity of the 9% (mass fraction) polycrystalline mullite fiber doped the nanoporous powder insulation material is 0.047 W/(m·K) at 800 ℃, which is lower than that of the insulation material added with quartz fiber. Nano-SiC powder and zircon powder effectively inhibit the radiant heat transfer and reduce the high-temperature radiant thermal conductivity as the opacifier. The thermal conductivity of the nanoporous powder insulation material with 10% (mass fraction) nano-SiC powder added is only 0.041 W/(m·K) at 800 ℃.

Effect of Modified SiO₂ Source on Structure and Properties of High-Purity Mullite Materials

LI Keke, ZHU Xianzhong, MAI Haixiang, ZHOU Chaojie, XU Enxia, LIU Xinhong, ZHAO Fei

2021, 40(10):  3265-3272. 

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To assess the effects of modified SiO₂ sources on the structure and properties of high-purity mullite materials by reactive sintering method, the modified SiO₂ source was fabricated by doping 8% (mass fraction) γ-Al₂O₃ into natural quartz and heating at 1 550 ℃. Subsequently, mullite samples were prepared by using different SiO₂ sources and γ-Al₂O₃ as raw materials. The results show thatthe melting temperature of SiO₂ decreases after adding a small amount of γ-Al₂O₃. The modified SiO₂ sources are transformed into a large amount of SiO₂-rich liquid phase in a narrow temperature range (1 570 ℃ to 1 580 ℃). The formation of a large amount of SiO₂-rich liquid phase promotes the mulliteization reaction, accelerates the particle rearrangement, increases the density of materials, and improves the reaction sintering property of high-purity mullite materials. During the calcination process, the SiO₂-rich liquid phase is gradually consumed by the reaction and converted into high-temperature mullite. Meanwhile, the liquid phase environment provided by the melting of modified SiO₂ source promotes the anisotropic crystal growth of mullite. After calcination at 1 700 ℃ for 3 h, the obtained mullite grains morphology exhibits columnar shape and forms a cross network structure, which enhances the degree of bonding between crystals. Therefore, high-purity mullite materials with the modified SiO₂ sources exhibit higher density and better mechanical properties.

Preparation and Properties of Aluminum Borate-Potassium Hexatitanate Whisker Composite Thermal Insulation Materials

SHANG Jiaqi, LIU Hao, WANG Zhoufu, YANG Zhiqian, CHEN Senna, MA Yan, WANG Xitang

2021, 40(10):  3273-3278. 

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Aluminum borate-potassium hexatitanate whisker composite thermal insulation materials were prepared by solid-state sintering with boric acid, aluminum hydroxide and potassium hexatitanate whiskers (PTW) as main raw materials. The effects of pre-synthesized aluminum borate whisker (ABW) on microstructure, mechanical and thermal insulation properties of the materials were studied. The results show that, with the increase of preparation temperature, ABW and PTW change from point contact to whisker through K_1.5(Al_1.5Ti_6.5)O₁₆ bonding phase, resulting in the increase of density and compressive strength of the composite thermal insulation materials. Fine ABW forms smaller pores between PTW, which significantly improves the thermal insulationproperty of the composite thermal insulation materials by reducing convection and radiation heat transfer. As for the composite insulation materials prepared at 1 100 ℃ by controlling PTW, pre-synthesized ABW and carbon black mass ratio of 9∶1∶3, the bulk density, compressive strength and thermal conductivity are 1.11 g/cm³, 3.5 MPa and 0.11 W/(m·K) to0.16 W/(m·K) (from 200 ℃ to 800 ℃), respectively.

Effect of CaCO₃ Micropowder on Properties of Corundum Based Porous Purging Plug

QIU Xin, LI Fangyuan, ZHANG Shiming, LIU Xinhong, JIA Quanli

2021, 40(10):  3279-3284. 

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Porous purging plugs have been widely used due to the advantages of good air supply reliability, high safety and good refining effect. However, its application is limited by the defect such as low strength and short service life caused by its own porous structure. In order to further improve the properties of corundum based porous purging plugs, fused white corundum particles and fine powder, α-Al₂O₃ micropowder and Cr₂O₃ micropowder were used as raw materials, the mass ratio of aggregate to matrix was fixed at 85∶15, and 0%, 1%, 2% and 3% (mass fraction) CaCO₃ were used to replace fused white corundum fine powder, respectively. The effect of the introduction of CaCO₃ micropowder on the properties of porous purging plugs was explored. The results show that the strength at room temperature and high temperature all increase with the amount of CaCO₃ powder (from 0% to 2%). The main reason is that the CaO formed by the decomposition of CaCO₃ reacts with Al₂O₃ in the matrix to form calcium hexaaluminate, which intersperses and connects with each other to increase the bonding degree between the matrix, thus improving the strength of the samples.

Effect of Addition of Cr₂O₃ Micropowder on Properties of Al₂O₃-Cr₂O₃ Refractory

KANG Xin, ZHANG Lixin, DENG Junjie, LIU Ping, XU Enxia, LI Suping

2021, 40(10):  3285-3291. 

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The effect of the addition of Cr₂O₃ micropowder on the normal temperature and high temperature performances, phase composition and microstructure of Al₂O₃-Cr₂O₃ refractories was studied by using fused chromium corundum and white corundum as the main raw materials, and using Cr₂O₃ micropowder to partially replace the fused chromium corundum fine powder. The results show that with the increase of the addition of Cr₂O₃ micropowder, (Al_1-xCr_x)₂O₃ solid solution is in-situ formed, which promotes sintering. And the apparent porosity of the material decreases first and then increases. The lattice constant of (Al_1-xCr_x)₂O₃ solid solution increases linearly with the increase of the addition of Cr₂O₃ micropowder, which conforms to Vegard’s law. The cold modulus of rupture and cold compressive strength increase first and then decrease with the increase of the addition of Cr₂O₃ micropowder. When the addition of Cr₂O₃ micropowder is 15% (mass fraction), the strength of the material reaches the maximum value. When the addition of Cr₂O₃ micropowder is 20% (mass fraction), the apparent porosity of the material increases and the strength decreases due to volatilization. The hot modulus of rupture of the material increases, and the residual strength rate of the material decreases first and then increases with the increase of the addition of Cr₂O₃ micropowder.

Effects of Additives on Gelation Process and Rheological Behavior of Acid Silica Sol and Slurry

YANG Yufei, LIU Hao, WANG Zhoufu, LIU Wenyuan, MA Yan, WANG Xitang, LIU Maolin

2021, 40(10):  3292-3297. 

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Taking acid silica sol and its bonded slurry as the research object, the effects of additives (polyacrylamide, magnesium hydroxide, and triammonium citrate) on the rheological behavior and gelation process of acid silica sol and its bonded slurry were researched by comparing rheological parameters, such as gelation time, viscosity, thixotropic area, and shear stress. The results show that Mg²⁺ ionized by magnesium hydroxide promotes the condensation reaction of acid silica sol, and presents significant effects on the gelation process of acid silica sol. And the increase of magnesium hydroxide addition increases the gelation speed and decreases the stability of acid silica sol.As an anionic surfactant, polyacrylamide associates the hydrogen bonds to form a three-dimensional network structure in the sol through steric hindrance. At the same time, polyacrylamide is hydrolyzed and adsorbed on the surface of the sol micelle particles, which accelerates the flocculation of SiO₂ particles, and increases the viscosity of acid silica sol and its bonded slurry. Addition of triammonium citrate below 10 mg/mL is conductive to the lowered viscosity and enhanced stability of silica sol bonded slurry.

Effect of Novel Binder SioxX-Zero on Microstructure and Properties of No-Cement Castables for Coal Burner Pipe

ZHANG Sisi, WANG Qinghu, PENG Hong, LI Yawei, SHU Xiaomei, DAI Changhao, WANG Danbin, ARINDAM Mukherjee

2021, 40(10):  3298-3304. 

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As the key bearing component of cement kiln, the coal burner pipe is subjected to severe long-term abrasion by high temperature clinker dust and airflow, thus requires better high temperature mechanical properties. In this work, the novel SioxX-Zero and traditional calcium aluminate cement were used as binders to prepare no-cement and low-cement Al₂O₃-SiC castables for coal burner pipe. All castable specimens applied tabular corundum, α-Al₂O₃ powder and SiC as main raw materials, and should be fired at 1 100 ℃ and 1 400 ℃ for 3 h. The effect of SioxX-Zero on microstructure, physical properties and high temperature mechanical properties for castables were investigated. The results show that, compared with traditional calcium aluminate cement, the introduction of SioxX-Zero increases flowability and delays flowability decrease of castables, improving the workability. Moreover, more needle-liked mullite with larger size in-situ forms in Al₂O₃-SiC castables containing SioxX-Zero, which significantly enhances the cold modulus of rupture, cold crushing strength, hot modulus of rupture and high-temperature abrasion resistance.

Effect of ZnO-B₂O₃ Glass on Low Temperature Sintering and Properties of Li₂Zn₃Ti₄O₁₂-CaTiO₃ Composite Ceramics

SHU Guojin, YUAN Shifeng, PANG Jinbiao, DOU Zhanming, YANG Jun, LIU Kai, HAN Guangxue

2021, 40(10):  3305-3310. 

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The 0.94Li₂Zn₃Ti₄O₁₂-0.06CaTiO₃ (LZT-CT) composite ceramics were prepared by the traditional solid-state reaction method, and ZnO-B₂O₃(ZB) glass was synthesized by high temperature melting method. The sintering characteristics, phase compositions, microstructures and microwave dielectric properties of LZT-CT composite ceramics with different mass fraction (x=0.5%, 1.0%, 1.5%, 2.0% and 2.5%) of ZB glass were investigated in detail. The results indicate that, the ZB glass effectively decreases the sintering temperature of the LZT-CT composite ceramics from 1 175 ℃ to 875 ℃ and also promotes the densifiction. There are no new phases in addition to the LZT and CT phase when ZB glass addition x≤2.5%. With the increase of ZB glass addition, the densification temperature of composite ceramics decreases gradually, the bulk density, relative permittivity (ε_r), quality factor (Q×f) initially increase and then decrease, and the temperature coefficient of resonance frequency (τ_f) is stable, fluctuated between -2.25×10^-6/℃ and 4.51×10⁶/℃. When added 2.0%ZB glass, LZT-CT composite ceramics sintered at 875 ℃ for 2 h obtained maximun bulk density of 4.22 g/cm³, and excellent microwave dielectric properties: ε_r=23.9, Q×f=58 595 GHz, τ_f=-0.14×10^-6/℃.

Research Letter

Improving the Performance of Artificial Sand Concrete with Chemical Composition Detection

ZHUANG Kaiqun, MA Yongsheng, SONG Shaomin, LIU Ruichao, GUO Yuxuan, JIANG Zeyu

2021, 40(10):  3311-3315. 

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Based on the chemical composition detection of artificial sand, the artificial sand can be divided into high calcareous artificial sand, high siliceous artificial sand, high aluminum artificial sand and high iron artificial sand. The four artificial sand have their own characteristics in adsorption and compatibility with additives. According to the characteristics of each artificial sand, the concrete additive components are adjusted to improve the workability of concrete and make it meet the engineering quality requirements.

Cement and Concrete

An Overview on Subsequent Hydration of Cement-Based Materials with Low Water-to-Binder Ratio

LI Ganglai, SHI Caijun, WU Zemei, LI Ning, LIU Yiwei

2021, 40(10):  3316-3325. 

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Cement-based materials with low water-to-binder (W/B) ratio have low porosity, excellent mechanical properties, durability, and impact resistance. The hydration of cement particles are restrained by the limited free water and the confined space for the precipitation of hydration products, leading to a high amount of unhydrated cementitious materials. This paper illustrated the process and mechanism of subsequent hydration of cement, reviewed the effects of subsequent hydration on microstructure, volume stability and strength of cement-based materials with low W/B ratio. Finally, some issues associated with subsequent hydration were addressed and the prospects for future researches were put forward. It aims to lay a theoretical information for the study and application of long-term stability of cement-based materials with low W/B ratio.

Research Status and Development Trend of Concrete Vibration Technology

WEN Jiaxin, HUANG Fali, WANG Zhen, YI Zhonglai, XIE Yongjiang, LI Huajian, CHENG Huan

2021, 40(10):  3326-3336. 

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Vibration is a key step of concrete construction. Appropriate vibration equipments and methods help improve the efficiency and quality of concrete construction. Since the interior of the concrete is not visible, the evaluation and quality control of concrete vibrating compaction mainly rely on human experience and judgment, which restricts the further improvement of vibrating technology. In this paper, in order to further improve the construction quality of vibration, the mechanism of concrete vibration is summarized, the compaction process and its influence on vibration are analyzed, the evaluation methods of concrete vibration compaction effect are compared, the current research on concrete vibration technology is expounded, and the development direction of intelligent vibration technology is put forward.

Effect of High Temperature Carbonation Curing on Strength and Microstructure of Dry-Mixed Cement Pastes

LING Tungchai, ZHU Fangping, WANG Min

2021, 40(10):  3337-3344. 

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Carbonation curing has attracted lots of research interests for the ability to improve early compressive strength and storage CO₂. However, the effect of high temperature on the carbonation process has been barely investigated. In the present study, 20 ℃, 100 ℃, 120 ℃, 140 ℃ and 160 ℃ were chosen for carbonation curing, the variation of compressive strength was investigated and the microstructural properties of carbonated dry-mixed cement pastes were evaluated by thermogravimetric analysis (TG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM). The results show that compressive strength and carbonation degree firstly increase with the increase of carbonation temperature and then became constant. The compressive strength of the sample cured at 20 ℃ is 14.8 MPa, while achieved about 4 times higher strength at 140 ℃ with recorded values of 71.2 MPa, which means that high temperature speeded the carbonation process. At such temperatures, part of the free water can be evaporated to enhance the CO₂ diffusion thus beneficial for a more complete carbonation reaction. Polymorphs of CaCO₃ are varied in samples carbonated with different carbonation temperatures. Compared to sample carbonated at 20 ℃, sample carbonated at 140 ℃ presented a higher proportion of aragonite and vaterite. Also, calcium silicate hydrate (C-S-H) generated from the sample carbonated at 140 ℃ is identified higher polymerization degree than that of sample carbonated at 20 ℃.

Physical and Mechanical Properties and Hydration of High Belite Sulphoaluminate Cement Modified White Cement

LAN Mingzhang, WANG Hao, CHEN Zhifeng, GE Zhongxi, WANG Jianfeng, PEI Tianrui

2021, 40(10):  3345-3351. 

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White Portland cement (white cement) has good whiteness and it is a cementing material with decorative effects. Aiming at the problems of long setting time, slow early strength development and large shrinkage deformation of this kind of cement, the high belite sulphoaluminate cement was used to modify the white cement. The effect of high belite sulphoaluminate cement mixed with 10% to 30% (mass fraction) on the setting time, mortar strength and free expansion rate of white cement was systematically studied. Hydration microcalorimeter, XRD, TGA, SEM, and other methods were used to analyze the hydration process, hydration products and microscopic morphology of the composite cementitious system. The results show that high belite sulphoaluminate cement increases the hydration heat release rate of white cement, and significantly shortens the setting time of white cement. The modified white cement hydration product generates a large amount of AFt, which grows interspersedly in the C-S-H gel, consuming part of the Ca(OH)₂, making the structure more compact, strength higher, and expansion performance better.

Effects of Nano-Silica/Graphene Oxide Composite on Mechanical Properties of Ordinary Portland Cement

YIN Yujiao, WU Fei

2021, 40(10):  3352-3358. 

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The poor dispersion of graphene oxide (GO) in cement matrix hinders its effective improvement of performance of cement-based composites. SiO₂/GO (GOS) nanosheets were synthesized via a sol-gel process. The dispersion stability of GOS was compared to that of GO in a simulated cement pore solution. Then, cement pastes with the addition of nanosheets were produced and the effects of GO and GOS on its mechanical properties were investigated. The results show that GOS has significantly greater dispersion stability than GO. Compared with the control, the flexural and compressive strength of GO/cement-based composites at 28 d increase by 20.48% and 13.14%, while GOS/cement-based composites increase by 35.42% and 23.90%, respectively.Microscopic analysis shows that flower-like hydration crystals formed in GO/cement-based composites. The hydrated crystals inside GOS/cement-based composites were cross-linked with each other, and the structure was dense, which reduced the brittleness of the cement and improved the toughness.

Improving Early Crack Resistance of Concrete by Shrinkage-Reducing Polycarboxylate Superplasticizer

ZHANG Jian, MAO Qianjin, WANG Ziming, HUANG Lina, CUI Suping

2021, 40(10):  3359-3365. 

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Shrinkage-reducing polycarboxylate superplasticizer (SRPC) is a new type of concrete admixture with both shrinkage-reducing and water-reducing effects.Its early crack resistance to concrete will affect its application in engineering. In this paper, the effect of SRPC on the early crack resistance of concrete was investigated and compared with polycarboxylate superplasticizer (PCE) and shrinkage reducing agent of low molecular weight (SRA) by using a flat crack resistance tester. Moreover, surface tension of solution, shrinkage of concrete, pore structure of cement slurry, and cement hydration heat were analyzed to discuss the anti-cracking mechanism of SRPC. Experimental results show that SRPC improved the early crack resistance of concrete. When 0.15% (mass fraction) SRPC and 1.5% (mass fraction) SRA are added to the concrete, although the former’s shrinkage effect is not as good as SRA, SRPC still show better early crack resistance. Compared with PCE, the cracked areas of SRPC and SRA are reduced by 39.33% and 21.34%, respectively. Mechanism analysis show that SRPC reduce the shrinkage of concrete by reducing the surface tension of the pore solution and changing the pore structure, which is similar to SRA. Furthermore, compared with SRA, SRPC also delay the rate of cement hydration, reduce the heat of early hydration, inhibit the evaporation of water inside the concrete, thereby improving the early crack resistance of concrete.

Synthesis and Characterization of Polyether Type Polycarboxylate Superplasticizer and Its Microscopic Action Mechanism on Cement

ZHANG Xiaoyu, ZHEN Weijun, GUAN Shoulu, CHEN Jun

2021, 40(10):  3366-3375. 

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In this paper, polycarboxylate superplasticizers JS-PCE and BT-PCE were synthesized by free radical polymerization using polyether, acrylic acid and hydroxyethyl acrylate as raw materials. JS-PCE synthesis condition is optimized by orthogonal design as follows: the polymerization temperature is 25 ℃, the dripping time of ascorbic acid-mercaptopropionic acid mixture and acrylic acid is 3 h and 2.5 h, respectively, the ratio of acid to ether is 4.25∶1, and the initiator dosage is 1.10% of polyether total mass. The fluidity of the cement slurry with JS-PCE is up to 230 mm, which shows good fluidity. Interfacial chemistry and electrochemical methods were used to explore the micro-mechanism of superplasticizer on Xinjiang cement. The results show that the polycarboxylate superplasticizers have saturated adsorption capacity on the surface of cement particles, and there was strong adsorption between the polycarboxylate superplasticizers and cement particles, which contributed to dispersion and water reduction effect. The rheological behavior analysis shows that the optimal content of JS-PCE and BT-PCE is 0.3% and 0.4%, respectively.

Microscopic Homogenization of Steel Fiber Lightweight Aggregate Concrete and Ultimate Bearing Capacity of Torsion Components

WANG Huiming, HE Zhengbo, ZHU Wen

2021, 40(10):  3376-3384. 

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Due to the advantages of light weight and excellent heat resistance, steel fiber lightweight aggregate concrete (SFLWC) is increasingly used in civil engineering. Considering the SFLWC is a multiphase composite material in nature, and the mechanical performance test results are highly discrete and the test is time-consuming and labor-intensive, the application of microscopic homogenization theory to predict its mechanical properties is considered to be one of the effective methods. Based on the Mori-Tanaka homogenization theory, this paper predicted the elastic modulus of steel fiber lightweight aggregate concrete when the steel fiber volume content is 0%, 0.5%, 1%, and 1.5%. And on that basis, it carried out torsion finite element calculations on steel fiber lightweight aggregate concrete beams, and proposed amendments to the empirical calculation formula for the ultimate bearing capacity of torsion components. The results show that the predicted value of elastic modulus obtained by the homogenization theory had little error with the calculation result of the empirical formula in the specification, and it is in good agreement with the test results. The torsion curve of steel fiber lightweight aggregate concrete beam obtained by finite element calculation accorded with the relevant test results to a high degree. The calculation and correction formula of the limit torque proposed in this paper is relatively consistent with the test results. Therefore, the proposed correction formula has been verified to be of certain practical reference value for engineering calculation and application.

Experimental Study on Compressive Strength of Ultra-High Performance Concrete with Hooked Steel Fiber

CHANG Yafeng, SHI Junping, HOU Yapeng

2021, 40(10):  3385-3395. 

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In order to study the influence of the content of hooked steel fibers on the compression performance of ultra-high performance concrete (UHPC), five groups UHPC cube specimens were tested under axial compression. The failure process and failure modes of UHPC specimens with different fiber volume fraction were recorded, and the load-displacement curves of them were compared. Then the fiber constraint coefficient and the influence of the constraint coefficient of end-hooked steel fiber on the compressive strength and compression energy consumption of UHPC cube specimens were analyzed. Based on the experimental data in this paper, a prediction model of UHPC cube specimens compressive strength was established. The results show that compared with the normal UHPC, when the hooked steel fiber is added to the test piece, the specimen starts to be damaged when the load is about 40% of the ultimate load. A continuous rapid fracture sound occurs inside the specimen when the load is close to the ultimate load. The UHPC specimens with end-hook type steel fibers finally failed and showed multiple diagonal cracks, and they can still remain as complete shape in the final failure, showing the phenomenon of "cracked but not broken". With the increase of the volume content of the hooked steel fiber, the compressive strength and the deformation of the specimen increase. Compared with the prime UHPC specimen, with the increase of fiber content, the influence of size effect on UHPC gradually decreases. Considering the fiber constraint index, a prediction model of UHPC cube compressive strength is established, which match well with the test results.

Bonding Properties of Steel Fiber Modified Crumb Rubber Concrete and Deformed Bar

WANG Yihong, CHEN Chao, HUANG Menglong

2021, 40(10):  3396-3404. 

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Four groups of steel fiber(steel fiber volume fraction is 0%, 0.5%, 1.0%, 1.5%, respectively) modified crumb rubber concrete(SFCRC) bond specimens were designed and made in this experiment. The influence of steel fiber volume fraction on bond failure mode, initial bond strength, ultimate bond strength and bond-slip curve was systematically studied by central pull-out test. The results show that with the increase of the steel fiber volume fraction, the initial bond strength is increased by 5.37%, 8.35%, 0.89%, and the ultimate bond strength is increased by 9.44%, 16.49%, 12.91%, respectively, compared with crumb rubber concrete. Adding appropriate amount of steel fiber significantly improves the failure form of bond specimens. The rising section, the descending section and the residual section together constitute the bond slip curve of steel fiber modified crumb rubber concrete. The fullness extent and rising section’s slope of the bond-slip curve increase with the increase of steel fiber volume fraction. Based on the experimental results, the bond-slip constitutive equation of steel fiber modified crumb rubber concrete and deformed steel bar is established, which provides a certain reference for its structural design.

Evolution Behavior of Tensile Properties and Microstructure of New Cementitious Materials at Cryogenic Temperatures

ZHANG Chao, YANG Haitao, DUAN Pinjia, HUANG Huan, LIU Juanhong

2021, 40(10):  3405-3413. 

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The tensile property of concrete at cryogenic temperatures is an important factor affecting the long-term safe service of "all-concrete" liquified natural gas storage tanks. A new type of cryogenic temperature resistant high-performance cementitious materials (CHC) was developed in this paper. The tensile properties of CHC before and after cryogenic temperature cycles (20 ℃ to -165 ℃) were studied using tensile testing machine. The pore structure characteristics of CHC were analyzed with mercury intrusion porosimetry test and nuclear magnetic resonance test. The results show that the total porosity of CHC is lower than that of C60 concrete, while the tensile strength and post-peak deformation ability of CHC are stronger than that of C60 concrete. After cryogenic temperature cycles, the appearance of microcracks and the increase of the total porosity lead to the decrease of the peak stress of CHC and C60 concrete. Moreover, the crack widths and the increase ratio of the total porosity of CHC are both smaller than that of C60 concrete. Thus the decrease of the peak stress of CHC is lower than that of C60 concrete. This study confirms that the tensile properties of CHC before and after cryogenic temperature cycles are both stronger than that of C60 concrete, which is due to the excellent pore structure and the incorporation of steel fibers in CHC.

Solid Waste and Eco-Materials

Research Progress on Dealkaliation Methods and Mechanism of Red Mud

CHEN Shan, CHEN Yunjian, XIE Xin, DONG Zejing, ZHANG Qin, FU Jiangli, HUANG Jianhong

2021, 40(10):  3414-3426. 

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Red mud is a strong alkaline waste produced during the production of alumina, and its high alkaline is an important factor restricting its large-scale comprehensive utilization. Therefore, it is extremely necessary to dealkalize red mud in order to achieve its comprehensive utilization and ensure the sustainable development of the aluminum industry. In this paper, the domestic and foreign red mud dealkaliation methods are reviewed, such as water washing, acid leaching, lime leaching, salt leaching, CO₂ method, biological method, etc. At the same time, the characteristics of various dealkalization methods and the main dealkalization mechanism are analyzed from the perspective of free alkali and chemical combined alkali. It is concluded that the principle of red mud dealkalization is mainly neutralization reaction, precipitation reaction and sodium replacement reaction. At last, the existing problems of various dealkaliation methods are analyzed, and the current suggestions for the study of red mud dealkalization are put forward. This provides a reference for the progress of red mud dealkalization technology and the comprehensive utilization of red mud.

Effect of pH Value on Mechanical Properties and Microstructure of Yunnan Laterite

PAN Tai, ZHAO Guitao, HUANG Ying

2021, 40(10):  3427-3434. 

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In order to explore the evolution law of mechanical properties and microstructure of soil under acid and alkali pollution, the Yunnan laterite polluted by different concentrations of hydrochloric acid (HCl) and sodium hydroxide (NaOH) was investigated. Then, the effects of full range of pH values and their action duration time on the shear strength of the Yunnan laterite were studied. The microstructure changes were detected by scanning electron microscopy (SEM). The test results show that the shear strength (τ_f) and the strength parameters (cohesion (c) and internal friction angle ()) all decrease with the decrease or increase of pH values compared with pH=8.2. The τ_f, c and  all decrease with extension of action duration time and come into stable after 7 d. SEM images and characteristic parameters of laterite polluted by acid and alkali were analyzed. The results show that the degradation of shear strength is caused by the corroded soil structure resulted from the acid and alkali pollution. The worse of engineering properties is most significant in alkali soils. This research can give guiding significance for the understanding and prevention of water environment deterioration engineering hazards in Yunnan laterite regions.

Effect of Internal Curing of SAP on Properties of Alkali-Activated Slag Cementitious Materials

LI Xiangguo, XU Jinsheng, JIANG Dongbing, LYU Yang, HE Chenhao, ZHANG Cheng, FU Qiuyan

2021, 40(10):  3435-3441. 

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Alkali-activated slag (AAS) cementitious materials have the problems of large early shrinkage and high cracking risk, which limit their engineering applications. In this study, superabsorbent polymer (SAP) was used as internal curing material to investigate its influence on the hydration heat, hydration products and pore structure of AAS cementitious materials by means of TAM, TGA and MIP, respectively. Moreover, the effect of SAP on the compressive strength and autogenous shrinkage of AAS cementitious materials were also studied. The results show that the addition of SAP increases the porosity of the matrix, and thus results in the decrease of compressive strength of AAS pastes. With the extension of hydration time, the internal curing effect of SAP promotes the hydration of slag, and the strength reduction is slightly compensated. The addition of SAP has a delay effect on the hydration exothermic process, which prolongs the induction period and leads to the lagging of the second exothermic peak. Furthermore, internal curing of SAP increases the content of hydration products, particularly for AAS pastes with higher modulus. The autogenous shrinkage of AAS pastes with SAP are obviously reduced compared with that of reference samples, and the maximum autogenous shrinkage reduction rate is reached up to 81%.

Effects of Temperature and Activator Concentration on Rheological Properties of Alkali Activated Slag Paste

TAO Jun, TANG Jianhui, LI Ping, BAI Yin, LIU Jian, WEN Donghui

2021, 40(10):  3442-3449. 

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In order to obtain the effects of temperature and activator concentration on the rheological properties of alkali activated slag paste, NaOH was used as the activator and S95 granulated blast furnace slag was used as the activated component. The variation characteristics of yield stress and apparent viscosity of slag paste during setting and hardening were discussed at different activator concentrations (1 mol/L, 2 mol/L and 3 mol/L) and temperatures (20 ℃, 30 ℃ and 40 ℃). The results show that the slag paste with NaOH as the activator shows non-Newtonian characteristy, and the yield stress development conforms to the Bingham fluid model. The higher the concentration and temperature of the activator, the faster the alkali activated slag paste yield stress develops, but the duration of the yield stress stability period and growth period are shortened with the increase of the concentration and temperature of the activator. The time-varying model of apparent viscosity can be represented by η=η₀+e-btⁿ, and the initial apparent viscosity η₀, b and n values all increase with the increase of temperature and the concentration of activator.

Strength and Acoustic Emission Damage Characteristics of Tailing Sand Modified Concrete

WANG Wenjie, MO Jiyun

2021, 40(10):  3450-3456. 

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In order to study the compression damage characteristics of tailing sand modified concrete, uniaxial compression-acoustic emission monitoring tests were carried out on four groups of concrete with different replacement rates of phosphate tailing sand. According to the acoustic emission (AE) signal released by the concrete under compression, the damage degree of the material was quantitatively discussed, and the evolution characteristics of the concrete damage were analyzed based on the AE index. The results show that the stress-strain curve of concrete is divided into four deformation stages: elastic deformation, plastic deformation, fracture failure and residual deformation. With the increase of the content of tailing sand, the compressive strength of concrete increases first and then becomes stable. The peak compressive strength of concrete with tailing replacement rate of 30% (mass fraction) is the highest. Damage factors were obtained from AE signals, and the damage factor-strain curves show that the damage of ordinary concrete structure is mainly in the plastic deformation stage, while the structural damage of tailing sand modified concrete is concentrated in the fracture failure stage. A certain proportion of phosphate tailing sand helps to improve the compactness of cement mortar, thus enhancing the compressive strength and deformation properties. The research results provides an important reference for the modification of concrete with tailing sand.

Research on Material and Environmental Properties of Gold Tailings

ZHU Jianping, YUE Hongzhi, ZHU Junge, BAI Rong, LI Hongda

2021, 40(10):  3457-3463. 

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Gold tailings are common solid wastes in the process of gold mining. Most of the tailings are directly accumulated in the tailing pond and cannot be recycled, which brings a series of social and environmental problems. The research of resource utilization is becoming more and more urgent. The material properties of gold tailings were investigated by XRD, XRF, SEM, laser particle sizer, TG and DSC. The environmental properties of gold tailings were studied by ICP, low background multi-channel gamma spectrometer and pH value determination. The leaching content, radioactivity specific activity and acid-base property of heavy metals were discussed, the environmental hazards by gold tailings and the feasibility of secondary utilization were analyzed. The results show that the 30 d heavy metal leaching content is less than the surface water class Ⅲ limit, and the index I_Ra=0.1 and I_γ=0.4 are all less than the national radioactive restriction standards, which provides a reference for the comprehensive application of gold tailings in the construction industry.

Heavy Metal Pollution Characteristics and Risk Evaluation of Soil Around Coal Gangue Stockpile Area

WANG Yandong, LI Xiaoguang, LI Jiaxi, LI Wei, ZHANG Mingtian, ZHAO Chen, ZHANG Lieyu, LI Weiping

2021, 40(10):  3464-3471. 

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In order to explore the distribution characteristics and potential risks of heavy metals in long-term storage of coal gangue in the surrounding soil. This study selected the prevailing wind direction soil around the coal gangue stockpile area of the Ningxia Zaoquan coal mine as the research object. The total concentrations and speciation characteristics of 5 kinds of heavy metals (Cu, Zn, Pb, Cr, Mn) in the object soil were analyzed. Meanwhile, the bioactivity of heavy metals was also analyzed and evaluated. The result shows that the concentrations of heavy metals (Zn, Pb and Mn) are high at the edge of the stockpile area due to the long-term storage of coal gangue, wind and rainwater leaching, and decrease with the increase of distance from the stockpile area. The soil pH value has an extremely significant negative correlation with the concentration of total content of Zn and Pb, the commuting states of Pb and Cr, the organic matter binding states of TN and Cu, and the extremely significant positive correlation with the residue state of TN and Cu, respectively. Meanwhile, there is a significant negative correlation between the concentration of total Mn and pH value. The RAC evaluation results show that all the heavy metals except Pb have a low potential risk for soil.

Ceramics

Preparation and Mechanical Properties of Zirconia Fiber Reinforced Ultra-Thin Ceramic Plate

ZHONG Xinzi, CAO Liyun, HUANG Jianfeng, LIU Yijun, OUYANG Haibo, WANG Qinggang

2021, 40(10):  3472-3478. 

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As a kind of light, thin and low energy consumption home decoration products, building ceramic sheet has gradually become the development trend of the market and how to further thinning and strengthen it has also become a research hotspot. In this article, the building ceramics powder with high aluminum content was used as the matrix, a secondary ball milling method was designed and the zirconia fiber with the length-diameter ratio of 70 to 82 was used as the reinforcing phase into the matrix. With the help of KH570 which was as the surface modifier to improve the interface bonding of fiber/matrix (F/M), the zirconia fiber reinforced ultra-thin ceramic plate was prepared. The results show that the secondary ball milling process can effectively influence the fiber dispersion in the matrix. When the doping amount of zirconia fiber is 3% (by mass), the bending strength of the ultra-thin ceramic plate reaches 106.4 MPa which is 9.92% higher than the blank sample of 96.8 MPa. In the high temperature solid phase reaction, the permeation of Na⁺ and K⁺ in the ceramic melt phase to the zirconia lattice causes the transformation of the tetragonal zirconia phase to the zirconite phase. Many positive strengthening mechanisms in the tetragonal zirconia phase, such as micro-crack expansion, particle diffusion enhancement and fiber bridge-pull out, may be responsible for inhibiting cracks’ propagation.

Synthesis and Catalytic Cracking Performance of Small-Sized NaY Zeolite/Kaolin Composites with High Framework SiO₂/Al₂O₃ Ratio

WANG Wenkai, TAN Juan, WANG Shihan, QIU Xin

2021, 40(10):  3479-3489. 

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Small-sized NaY zeolite/kaolin composites with high framework SiO₂/Al₂O₃ ratio were hydrothermally synthesized from two kaolins with different particle sizes. The structure and morphology of composites were characterized by XRD, SEM, grain size analysis and N₂ physical adsorption techniques. The results show that compared with commercial NaY, the structure stability and hydrothermal stability of samples synthesized from kaolin are significantly improved. The grain size of the sample synthesized from fine kaolin is 310 nm, and the specific surface area is 807 m²·g^-1. The catalytic cracking catalysts were prepared by using modified NaY zeolite/kaolin composite as active component. The acidity of the catalysts was characterized by NH₃-TPD, and the heavy oil catalytic cracking performance was evaluated on microreactor. The results show that the acid center strength of sites on catalysts increases with the increase of framework SiO₂/Al₂O₃ ratio, while the acid center amount decreases. The grain size of NaY zeolite/kaolin composites synthesized from fine kaolin is smaller. The number of acid centers and catalytic cracking performance of catalysts prepared by small-sized NaY zeolite/kaolin composites are greatly improved. With the increase of m(calcined kaolin)/m(metakaolin), the content of substrate in NaY zeolite/kaolin composites increases, while the acid center strength of catalysts decreases. The catalyst prepared by the sample with framework SiO₂/Al₂O₃ molar ratio of 6.1 and m(calcined kaolin)/m(metakaolin) of 0.5 presents excellent catalytic cracking performance of heavy oil. And the conversion rate of heavy oil (diesel excluded) is as high as 85.4%, and the gasoline yield is up to 64.2%.

Preparation of Copper Aluminate Pigment by Combustion Method

CHENG Zhipeng, LIU Kun, XU Yinan, FANG Yuan, JIANG Caishui, LI Hao, YU Huan, BAO Qifu, ZHOU Jian’er

2021, 40(10):  3490-3496. 

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In this paper, copper nitrate trihydrate, aluminum nitrate nonahydrate and glycine were used as raw materials to prepare CuAl₂O₄ brown pigment by combustion method. The effects of calcination system and Cu/Al molar ratio on phase composition, microstructure, and color performance of the pigment were investigated by means of XRD, FT-IR, TG-DTA and UV-Vis. The results show that when the the calcination temperature is 1 100 ℃ (without heat preservation) and the Cu/Al molar ratio is 1∶2.4, the CuAl₂O₄ pigment with the best color performance is obtained and its chromatic value is L^*=46.22, a^*=24.43, b^*=27.09.

Glass

Effect of MgO Content on Structure and Properties of Glass-Ceramics

PENG Ruixin, HAN Han, LIN Hongjian, LI Xiaofan, JIANG Hong

2021, 40(10):  3497-3503. 

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Li₂O-Al₂O₃-SiO₂ glass-ceramics have excellent optical and mechanical properties. In this paper, the Li₂O-Al₂O₃-SiO₂ transparent glass-ceramics with diorthite and lithium disilicate as the main crystal phase were prepared. The influence of MgO content on the crystallization behavior and structure of glass-ceramics was studied by DSC, XRD and SEM, and the influence of MgO content on the mechanical properties of glass-ceramics was studied by Vickers hardness, bending strength and other test methods. The results show that when the MgO content (mass fraction) increases from 0% to 3%, the crystallization temperature of the basic glass decreases from 771 ℃ to 729 ℃, and the crystallization ability is enhanced, basides, the crystallinity increases from 62% to 72%, and the grain size increases from 29 nm to 33 nm. With the increase of MgO content, β-quartz solid solution precipitates out of the glass-ceramics and the bending strength increases.

Structural Origin Revealing of Dependence of Hardness and Crack Resistance on Composition in CaO-Al₂O₃ Pseudo-Binary Glass System

WANG Yan, GAO Yunzhou, TAO Haizheng, GU Shaoxuan

2021, 40(10):  3504-3510. 

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Understanding the relationship between structure and performances such as hardness and crack resistance has guiding significance for the development of the hard and highly crack resistant glass. To study the structural dependence of hardness and crack resistance on composition in the CaO-Al₂O₃ pseudo-binary glass system, utilizing the laser-heated aerodynamic levitation method, a series of xCaO·(100-x)Al₂O₃ glasses were prepared with x=42.3, 50.0, 63.1, and 75.0, mole fraction. The Vickers hardness (H_V) and crack resistance (C_R) were studied by using a micro-hardness Vicker tester. The structure of these glasses was characterized by Raman spectra, X-ray diffraction (XRD) patterns and magic angle spinning nuclear magnetic resonance (MAS-NMR). The results indicate that with the increase of the CaO content, the H_V values of these glasses decrease whereas the C_R values show a non-linear and non-exponential change. The 42.3CaO·57.7Al₂O₃ glass exhibits the maximum values of H_V (8.09 GPa) and C_R (11.8 N). The decrease of H_V values upon the addition of CaO is attributed to the decrease of average bond energy. The maximum C_R value of the 42.3CaO·57.7Al₂O₃ glass is ascribed to the existence of five coordinated Al, which dissipates the energy in the indentation process through changing the coordination number.

Effect of End-Face Friction on Compression Strength of Glass

LU Huacheng, XIONG Xuemei, ZHONG Donghai, ZHENG Yuxuan, ZHOU Fenghua

2021, 40(10):  3511-3515. 

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In order to study the effect of end-face friction on the compression strength of glass, copper foil and vaseline were used to reduce friction on the compression contact face. Quasi-static compression tests at the strain-rate of 10^-4 s^-1 were carried out on soda-lime-silica samples using the MTS testing machine. High-speed photography was used to record the failure process of the glass samples. The statistical distribution of glass strength was further analyzed. The experimental results show that when the contact surface of the glass sample is only lubricated by vaseline, the significant cracks and surface fragments fall off during the compression process. After the copper foil is added to the contact surface of the glass sample, the force is uniform throughout the compression process, and no significant cracks or fragments fall off. The decrease of the friction force of the end-face will lead to a significant decrease in the compression strength of the glass, mainly because reducing the friction force weakens the lateral restraint on the end of the specimen, and the specimen is in a state closer to uniaxial stress, which largely avoids the strengthening effect caused by confining pressure.

Crystallization Performance of Simulated High-Level Waste Glasses

MENG Baojian, ZHU Yongchang, JIAO Yunjie, ZHAO Chong, WAN Wei, HAN Xu, CUI Zhu, YANG Debo

2021, 40(10):  3516-3522. 

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The simulated high-level waste (HLW) glass containing 16% (mass fraction) nuclear waste was prepared by the Joule-heated, ceramic-lined melter. In this work, the crystallization behavior and thermal stability of waste glass under different heating temperatures were investigated. The results show that some of the waste glass in the actual production and storage process has appeared diopside phase, and the crystallization activation energy of the crystal glass is lower than the waste glass 40 kJ/mol to 60 kJ/mol. Upon heat treatment the glass at 700 ℃ to 900 ℃ develops diopside phase and the apparent color of nuclear waste glass also changes with the increase of crystallinity. Correlation between crystallization and thermal history can facilitate a more realistic prediction of crystallization in waste glass. The results of this initial study provide a theoretical guidance for the operational plant parameters for HLW glass manufacture.

Road Materials

Temperature Reduction and Performance of Asphalt Pavement with Stomatal Basalt Ultra-Thin Overlay

ZHANG Nan, FAN Qunbao, ZHENG Nanxiang

2021, 40(10):  3523-3532. 

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To mitigate the effect of the urban heat island and lower asphalt pavement temperature, the stomatal basalt was added into the NovaChip type ultra-thin overlay asphalt mixture in the current study. The indoor simulation thermal radiation system was used to irradiate the specimen, the temperature variance was collected at different layers, and the cooling effect of the asphalt mixture with different basalt content was compared. The results show that the upper surface temperature of the test specimen increase with an increase in the volume content of stomatal basalt. Compare with 0% mixing amount, the cooling effect of asphalt mixtures with 25％, 50％ and 75％ content of stomatal basalt is relatively good, their temperatures at 2 cm inside dorp are 2.0 ℃, 4.2 ℃ and 5.9 ℃, their temperatures under the bottom dorp are 2.4 ℃, 5.1 ℃ and 6.6 ℃, respectively. The thermal conductivity decrease 39.1％, 50.7％and 61.8％. As the proportion of stomatal basalt increases, the high temperature stability of the asphalt mixture improves, the low-temperature performance is almost invariable, the water stability decreases, and the sliding resistance increases first and then decreases. Overall, considering cooling effect and pavement performance variance, the proportion of stomatal basalt in the asphalt volume content is proposed as 25% to 30%.