Research progress on hydration resistance of magnesia-calcia refractories

Huang Ren, Li Kezhuo, Xie Houbo, Gao Ruihong, Huang Zhong, Zhang Haijun, Zhang Shaowei

2022, (4): 277-282. doi：10.3969/j.issn.1001-1935.2022.04.001

Magnesia-calcia refractories are widely used in the iron and steel smelting industry because of their advantages of steel liquid purification,high refractoriness,good thermal shock resistance and high corrosion resistance in basic slag.However,MgO and CaO usually hydrate in the process of manufacturing,storage and use of magnesia-calcia refractories,which seriously restricts the application and the development of magnesia-calcia refractories.In this work,the characteristics and hydration mechanism of magnesia-calcia refractories were reviewed,and the current research status and existing problems of the anti-hydration of magnesia-calcia refractories were summarized from three aspects:sintering densification,surface treatment and sealed packaging.In addition,the development trends and the research emphases of anti-hydration technology of magnesia-calcia refractories in the future were also prospected.

Development of purging plugs for ladles and damaging mechanisms of typical composite structures

Chen Lu, Xu Yuanchao, Guo Peng, Zhang Hui, Wei Changsheng, Jia Qingwei

2022, (4): 283-288. doi：10.3969/j.issn.1001-1935.2022.04.002

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The material replacement and the structure evolution of purging plugs for ladles were briefly reviewed,and the deficiencies of single structure plugs were listed.According to the main gas passage types,composited purging plugs were divided into three categories:dispersive,core-plate and ceramic-tube.Their structural characteristics,service performance and metallurgical efficiency were compared.By analyzing the used purging plugs,the typical damage mechanisms of composited purging plugs were revealed.(1)The chief damage mechanism of dispersive composited purging plugs is that liquid steel slag penetrates and blocks the through pores,then the penetration layer is eroded by the high-pressure argon or ablated by the oxygen lance.(2)CaO from steel slag infiltrates the matrix of corundum-mullite core plate,then reacts with mullite to form low melting point phases.The eroded core plate damage is accelerated under oxygen cleaning.(3)Due to the poor thermal shock resistance of the body material,transverse fracture of the plug occurs under frequent thermal shock,or the steel infiltrates the straight tube,resulting in the failure of bottom blowing or the flow reduction,which are the key damage mechanism of ceramic-tube purging plugs.

Effect of pore-forming agents on properties of microporous mullite aggregates

Jin Zhishang, Shan Zhilin, Zhao Huizhong, Yu Jun, Zhang Han

2022, (4): 289-293. doi：10.3969/j.issn.1001-1935.2022.04.003

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Microporous mullite aggregates were prepared from bauxite by dry pressing and firing at 1 700 ℃ for 3 h with corn starch,PMMA microspheres or rice husk powder as the pore-forming agent.The effects of the pore-forming agents and their addition (mass fraction of 0,5%,10%,15% and 20%,respectively) on the properties of microporous mullite aggregates were analyzed by XRD,SEM and Image-Pro Plus software.The results show that the comprehensive performance of the sample with 10 mass% rice husk powder is the best,the closed porosity is 5.6%,the bulk density is 2.63 g·cm^-3,the compressive strength is 148 MPa,the median pore size is 15.16 μm,and the thermal conductivity at 500 ℃ is 2.30 W·m^-1·K^-1.

Effect of magnesium aluminate spinel types on sintering properties of spinel-periclase composites

Zheng Pei-yu, Zhang Ling, Li Renjun, Chen Lu

2022, (4): 294-298. doi：10.3969/j.issn.1001-1935.2022.04.004

Abstract ( ) PDF (3215KB)( )

Spinel-periclase specimens were prepared using three kinds of spinels (magnesia-rich spinel,alumina-rich spinel and bauxite-based magnesia-rich spinel) and sintered magnesia as main raw materials,adding a small amount of silica fume and firing at 1 550 ℃ for 3 h.The effects of different kinds of spinels on the sintering properties of the spinel-periclase specimens were studied.The results show that:during the sintering of the magnesia-rich spinel and the sintered magnesia,spinel reacts with periclase to form a high melting point forsterite phase,which plays a bridging role to improve the bonding strength of the specimens;the sintering of the alumina-rich spinel and the sintered magnesia is accompanied by the formation of secondary spinel,producing volume expansion,which counteracts the sintering shrinkage and reduces the linear shrinkage.The formation of secondary spinel produces Kirkendall effect,resulting in a large number of connected long and narrow Kirkendall voids,which endows the specimens with low density and strength.Compared with the magnesia-rich spinel,the bauxite-based magnesia-rich spinel contains a small amount of impurities,which act as a sintering promoter in the reaction,making the spinel-periclase specimens dense after sintering.

Characteristics and phase transformation behavior of quartzites

Mao Shengxiao, Jia Zhenggang, Li Bing, Yuan Wenjie

2022, (4): 299-303. doi：10.3969/j.issn.1001-1935.2022.04.005

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Three kinds of quartzites from different regions were crushed,ground,shaped,dried and fired at different temperatures (1 350,1 450 and 1 550 ℃) for 2 h.The quartzites powders were investigated in terms of the infrared spectrum,the particle size distribution,and the microstructure.The fired specimens were tested in terms of the phase composition,the true density and the linear change rate.The results show that:(1)the grain size distribution of quartzite from different regions is different;there both exist fine grains of more than ten microns and coarse grains of hundreds of microns;(2)under the same crushing and grinding conditions,the quartzite with smaller average size has small particle size and presents a bimodal distribution,while the quartzite with larger average size has large particle size and presents a multi-modal distribution;(3)the phase transformation rate of the quartzites is affected by both the impurity content and the crystal grain size;and the transformation rate of crystalline quartzite is relatively fast.

Preparation and properties of porous MgAl₂O₄ ceramics by low-temperature combustion

Piao Jiasi, Du Qingyang, Bai Jiahai

2022, (4): 304-308. doi：10.3969/j.issn.1001-1935.2022.04.006

Abstract ( ) PDF (1753KB)( )

To lower the synthesis temperature of MgAl₂O₄ and the energy consumption,MgAl₂O₄ powders were synthesized via a low-temperature combustion route using Al(NO₃)₃·9H₂O,Mg(NO₃)₂·6H₂O and NH₄NO₃ as oxidizing agents,C₂H₅NO₂ and CH₄N₂O as reducing agents,and EDTA as the fuel.Then porous MgAl₂O₄ ceramics were prepared with the prepared powders or the prepared powders treated at 800 ℃.The effects of the EDTA addition (0,2.5%,5%,7.5% of the reducing agents,by mole) on the properties of the MgAl₂O₄ powders and the porous MgAl₂O₄ ceramics were studied.The experimental results show that:(1)with the increase of the EDTA addition in the precursors,the ignition loss increases and the specific surface area of the MgAl₂O₄ powders rises significantly;(2) with the increase of the EDTA addition in the precursors,the water absorption and the apparent porosity of the porous MgAl₂O₄ ceramics obviously decrease,the bulk density increases significantly,and the grain size of MgAl₂O₄ decreases slightly;(3)compared with the ceramics prepared from the MgAl₂O₄ powders treated at 800 ℃,the porous MgAl₂O₄ ceramics prepared with the MgAl₂O₄ powders have relatively higher water absorption and apparent porosity,and more uniform microstructure;(4)when the EDTA addition is 2.5% of the reducing agents,the porous ceramic sample prepared with the MgAl₂O₄ powders has the water absorption of 23.8%,the apparent porosity of 46.9%,and the bulk density of 1.9 g·cm^-3,presenting uniform microstructure.

Effect of Si powder on properties of corundum-mullite bricks

Ma Shulong, Wang Zhifeng, Ma Fei, Kang Jian, Zhang Jili, Gao Changhe

2022, (4): 309-311. doi：10.3969/j.issn.1001-1935.2022.04.007

Abstract ( ) PDF (1825KB)( )

The corundum-mullite bricks were prepared using brown corundum,α-Al₂O₃ powder,andalusite powder,and Guangxi white mud as raw materials.In order to improve the iron slag erosion and corrosion resistance of corundum-mullite bricks,2 mass% Si powder was introduced into the corundum-mullite bricks,and the properties of the samples were compared before and after Si powder addition.The results show that compared with the corundum-mullite sample without Si powder,the sample with Si powder has uniform and small pores,and the apparent porosity decreases from 15.8% to 13.5%,the cold compressive strength increases obviously,the hot modulus of rupture increases by 5.6 times,the hot toughness and the iron slag corrosion resistance and the penetration resistance are obviously improved.

Effect of water vapor pressure on oxidation rate of two types of SiC refractories

Luo Tian, Wang Wenwu, Niu Shicheng, Guo Wenhui

2022, (4): 312-314. doi：10.3969/j.issn.1001-1935.2022.04.008

Abstract ( ) PDF (984KB)( )

In order to improve the oxidation resistance test method for SiC refractories and to save testing time,the oxidation of two kinds of SiC refractories (Si₃N₄-SiC and Si₂N₂O/Si₃N₄-SiC) treated by 1 000 ℃ water vapor with different pressures (0.10,0.11,0.13,0.15,0.17,and 0.19 MPa,respectively) for different periods (20 and 40 h,respectively) was studied.The mass and the apparent porosity of the specimens before and after oxidation were measured,and the mathematical relationship between the mass change rate and the water vapor pressure was analyzed by the mathematical statistics method.The result indicates that the increase of the water vapor pressure accelerates the oxidation progress of Si₃N₄-SiC and Si₂N₂O/Si₃N₄-SiC refractories at 1 000 ℃;the square of the mass change rate has a highly significant linear relationship with the water vapor pressure after being oxidized for 20 or 40 h,which shows that the oxidation basically follows the classical parabolic kinetic equations.

Effect of ZrO₂ isolation layer on phase composition and microstructure of lanthanum aluminate high emissivity coating

Zhang Yifan, Wang Gang, Wang Qu, Zhang Qi, Wang Laiwen, Huang Zhenwu, Zhang Lei

2022, (4): 315-319. doi：10.3969/j.issn.1001-1935.2022.04.009

Abstract ( ) PDF (2347KB)( )

In order to explore the effect of ZrO₂ isolation layer on phase composition and microstructure of lanthanum aluminate high emissivity coating,Ca²⁺ and Fe³⁺ doped lanthanum aluminate (LaAlO₃) powders were prepared using La₂O₃,Al₂O₃,CaCO₃ and Fe₂O₃ (all 99% purity) as raw materials via solid phase sintering method according to the stoichiometric ratio of La_0.8Ca_0.2Al_0.8Fe_0.2O₃.The LaAlO₃ and ZrO₂ composite coating (LCAFO/ZrO₂) were prepared using LaAlO₃ powder as the high emissivity infrared ceramic powder radiation agent and ZrO₂ coatings with different particle sizes as the isolation layer.The developed coating and the LCAFO (LaAlO₃) coating were spread on the surface of bubble Al₂O₃ bricks for the lining of industrial furnaces,respectively.The coatings were analyzed using XRD and SEM.The results show that LCAFO coating does not react with bubble Al₂O₃ bricks at 1 200 ℃,but they react at 1 400 ℃ forming LaAl₁₁O₁₈,and the reaction is more sufficient at 1 600 ℃.The thickness of the LaAl₁₁O₁₈ layer increases with the temperature rising.When the ZrO₂ isolation layer is coated between the LCAFO layer and the bubble Al₂O₃ bricks,no LaAl₁₁O₁₈ phase exists and no reaction layer appears at 1 400 ℃.

Effects of catalyst on microstructure and properties of Al₂O₃-SiC-C castables

Cheng Cuili, Zhao Zijian, Ren Shiyi, Li Lei, Chen Ping'an, Li Xiangcheng, Zhu Boquan

2022, (4): 320-324. doi：10.3969/j.issn.1001-1935.2022.04.010

Abstract ( ) PDF (2048KB)( )

The La₂O₃ doping Ni was prepared by ball-milling method and added into the Al₂O₃-SiC-C castable specimens as the catalyst,which were prepared using tabular corundum,SiC powder,ball pitch,α-Al₂O₃ micropowder,SiO₂ micropowder,Al-Si alloy powder,and calcium aluminate cement as raw materials.Effects of the catalyst and the hot treatment temperatures (500,700,900,1 100,and 1 450 ℃ for 3 h ) on the microstructure and the properties of the castables were investigated.The results reveal that after ball milling,the X-ray diffraction peak intensity of Ni decreases drastically and the angle of Ni shifts,suggesting that the lattice of Ni is distorted due to the La dissolution into Ni.With the temperature rising,the one-dimensional phases (CNTs and SiC whiskers) and two-dimensional phase (gehlenite) in the castables containing catalyst increase,the modulus of rupture and the crushing strength reach the maximum values,respectively.Therefore,the La₂O₃ doping Ni can obviously increase the one-dimensional and two-dimensional strengthening phases in the castables and enhance the strength of the castables.

Effect of B₄C addition on properties of silica sol bonded mullite-corundum castables

Cai Wei, Chen Jinfeng, Ju Maoqi, Cong Peiyuan

2022, (4): 325-328. doi：10.3969/j.issn.1001-1935.2022.04.011

Abstract ( ) PDF (1358KB)( )

Mullite-corundum castable specimens were prepared using sintered mullite,α-Al₂O₃ micropowder,tabular corundum,and imported kyanite as raw materials,silica sol as the biner,adding different amounts of B₄C (0,0.2%,0.4%,0.6%,and 0.8%,by mass),firing at 1 450 ℃ for 3 h.Effect of the B₄C addition on properties of the castables was researched.The result shows that with the increase of the B₄C addition,the bulk density of the specimens hot treated at 1 450 ℃ changes a little,the apparent porosity decreases gradually,the cold strength increases a little,the HMOR increases obviously,the expansion decreases firstly and then increases,and the thermal shock resistance firstly increases and then decreases.The addition of B₄C promotes the formation of boron-rich liquid phases,wetting the grains of Al₂O₃ and SiO₂,resulting in small nucleation barriers,high nucleation rates and high migration rates.It is beneficial to the growth of mullite phases,leading to volume expansion and formation of a certain amount of microcracks,which improves the thermal shock resistance of the specimens.The optimal B₄C addition is 0.4%.

Influence of solid loading on properties and microstructure of lightweight calcium hexaluminate materials prepared by foaming-gel casting

Cao Yimin, Wei Yaowu, Sun Huayun, Zhou Hui

2022, (4): 329-333. doi：10.3969/j.issn.1001-1935.2022.04.012

Abstract ( ) PDF (3018KB)( )

To study the effect of the slurry solid loading on their properties,lightweight calcium hexaluminate materials were prepared using active alumina (d₅₀=1.9 μm) and calcium hydroxide (d₅₀=4.3 μm) as starting materials by foaming-gel casting.The effects of the solid loading in the slurry (50%,52.5%,55%,57.5% and 60%,by volume,respectively) on the phase composition,the microstructure and the properties of the fired samples were studied.The results show that after high temperature treatment,flake calcium hexaluminate crystals in the samples prepared by foaming-gel casting are interwoven to form a large number of micropores smaller than 5 μm,accounting for more than 50% of total pores.In this study,with the solid loading of 57.5%,the sample has the best properties,performing the cold compressive strength of 9.4 MPa.

Effects of different silicon-based raw materials on properties and microstructure of MgO-Al-C materials

Han Xiaoyuan, Shi Kai, Xia Yi, Wang Peixun, Liu Yang, Shang Jianzhao

2022, (4): 334-338. doi：10.3969/j.issn.1001-1935.2022.04.013

Abstract ( ) PDF (2683KB)( )

In order to improve the thermal shock resistance of MgO-Al-C materials,three low-expansion coefficient silicon-based raw materials such as silicon,fused quartz,and SiC were introduced,and their influences on the properties of MgO-Al-C materials were studied by XRD and SEM.The results show that:(1)at high temperatures,Si transforms into SiC and SiO₂,and SiO₂ reacts with magnesia forming forsterite,improving the hot strength,the thermal shock resistance and the oxidation resistance of the materials;(2)fused quartz can significantly improve the thermal shock resistance of the materials,but the softening at high temperatures and the crystal transformation of fused quartz are not conducive to the hot strength and the oxidation resistance;(3)the addition of SiC can improve the thermal shock resistance,the hot strength and the oxidation resistance of the materials;when the addition of SiC exceeds 10 mass%,there are many microcracks in the material due to thermal mismatching,which affects its thermal shock resistance and oxidation resistance.

Effect of zirconia addition on properties of magnesia refractories

Gao Yongjun, Wu Feng, Li Xinwei, Su Yuxi, Feng Yu, Luo Xudong, Chen Weimin, Wang Qiong

2022, (4): 339-341. doi：10.3969/j.issn.1001-1935.2022.04.014

Abstract ( ) PDF (1250KB)( )

Light burned magnesia powder (≤0.074 mm) was prepared with Xiuyan grade Ⅱ magnesite firing at 900 ℃ for 3 h.Samples were prepared by the obtained powder and desiliconized zirconia with different additions (0,4%,8%,12% and 16%,by mass),grinding,mixing,forming,drying,and calcining at 1 500,1 600 and 1 700 ℃ for 3 h,respectively.The bulk density,the relative density,the cold compressive strength and the thermal shock resistance of the fired samples were tested.The phase composition and the microstructure were analyzed.The results show that the cold compressive strength,the relative density and the thermal shock resistance of the samples basically increase first and then decrease with the increase of the desiliconized zirconia addition,achieving the maximum with 8% desiliconized zirconia.The sample added with 8% desiliconized zirconia and sintered at 1 700 ℃ for 3 h has the relative density of 86.21%,the cold compressive strength of 201 MPa and the thermal shock resistance of 6 cycles.

Effect of SiO₂ particle size and reaction temperature on synthesis of mullite whiskers by molten salt method

Su Yuxi, Li Xinwei, Wu Feng, Gao Yongjun, Luo Xudong, Feng Yu, Chen Weimin

2022, (4): 342-345. doi：10.3969/j.issn.1001-1935.2022.04.015

Abstract ( ) PDF (2599KB)( )

To study the effect of the particle size and the reaction temperature of SiO₂ raw material on the synthesis of mullite whiskers by the molten salt method,mullite whisker samples were synthesized using Al₂(SO₄)₃·18H₂O and SiO₂ (d₅₀=80.25,45.16,0.91,and 0.02 μm,respectively) as starting materials,and Na₂SO₄ as the molten salt media,firing at 800,900,1 000,and 1 100 ℃ for 3 h,respectively,soaking in distilled water,sucking filtering,washing,and drying.The phase composition and the microstructure of the samples were analyzed.The results show that the optimal preparation conditions are adopting SiO₂ of d₅₀=0.02 μm and firing at 900 ℃.The obtained mullite whisker performs good crystallization,high purity and large length-diameter ratios.

Structure simulation and discussion on practical problems of ladle capacity expansion

Xu Guotao, Zhang Meijie, Wu Jie, Kong Yongjiang, Qin Shimin, Wang Zhiqiang, Xiao Tongda, Zhang Honglei

2022, (4): 346-350. doi：10.3969/j.issn.1001-1935.2022.04.016

Abstract ( ) PDF (3065KB)( )

The ladle capacity expansion schemes with thinned permanent layers and working layers were numerically simulated and analyzed,and the temperature field change was researched.Thinning the permanent layer increases the heat dissipation loss of ladles,which has little effect on the temperature field and slag corrosion of refractories for the working layer of ladle walls.When thinning both the permanent layer and the working layer,the temperature of the working layer in the ladle wall area changes slightly,which has no significant impact on the service life;in the slag line area of ladles,the temperature rises and the slag corrosion intensifies in the steel holding stage;and the temperature has a large gradient during cooling,sharpening the thermal shock,thus easily leading to spalling.For ladle capacity expansion,to give consideration to both the heat dissipation and the ladle lining life,the thickness of precast blocks for the permanent layer and the working layer of ladle walls is reduced by 30 mm respectively,and the magnesia carbon bricks for slag line are subject to minor repairs,medium repairs and timely maintenance to achieve the overhaul cycle.The industrial test results show that:after ladle capacity expansion,the average molten steel capacity of ladles increases from 200 to 218 t;and under the smelting requirements of a high steel scrap ratio,the molten steel capacity of ladles can reach 220 t.

Steam oxidation resistance comparison of several silicon carbide refractories at elevated temperatures

Wang Jiaping, Zhu Chong, Wu Jiguang, Huang Zhigang, Lyu Chunjiang

2022, (4): 351-355. doi：10.3969/j.issn.1001-1935.2022.04.017

Abstract ( ) PDF (3501KB)( )

The oxidation tests of different SiC refractories including Si₃N₄-SiC bricks,Si₃N₄-Si₂N₂O-SiC bricks from domestic and abroad,SiAlON-SiC bricks,oxides bonded SiC bricks,self-bonded SiC bricks as well as SiC castables were carried out in the steam atmosphere (1 000 ℃,32 kg·m^-3·h^-1) for 100,200,300,400 and 500 h,respectively.The mass,the volume,the bulk density and the apparent porosity before and after oxidation were tested.The XRD and SEM analyses were conducted.The results indicate that:(1)under the steam atmosphere condition (1 000 ℃,32 kg·m^-3·h^-1),along the oxidation time from 0 to 500 h,the volume and the mass of the silicon carbide refractories increase,while the bulk density decreases;in terms of the apparent porosity,oxides bonded SiC bricks and SiC castables present an increasing trend,Si₃N₄-SiC bricks,SiAlON-SiC bricks and self-bonded SiC bricks present an increasing trend first,and then a decreasing trend,and Si₃N₄-Si₂N₂O-SiC bricks present a decreasing trend or a trend of decreasing first and then increasing.(2)As for Si₃N₄-Si₂N₂O-SiC bricks,SNO-1 from domestic and SNO-2 from abroad with basically the same chemical and phase composition,the mass change rate of SNO-2 is less than that of SNO-1 during the 200-500 h oxidation,which indicates that the steam oxidation resistance of SNO-2 is better than that of SNO-1.

Technological exploration on longevity of ladle refractories

Huang Dongping, Zhang Yanheng, Yang Xiao-dong, Bai Hongyu

2022, (4): 356-360. doi：10.3969/j.issn.1001-1935.2022.04.018

Abstract ( ) PDF (1809KB)( )

The main influencing factors of ladle life were analyzed and discussed,such as materials,masonry methods,slag composition,refining process,steel holding time,and temperature control.The optimization of the ladle bottom masonry methods,the improvement of materials of ladle bricks,slag line bricks and seat blocks,and the improvement of the slag refining process were summarized.Compared with that in 2015,the ladle overhaul life increases from 102 to 201 heats at present,the ladle minor repair life increases from 51 to 100 heats,the average corrosion rate of ladle wall bricks reduces from 1.47 to 0.67 mm per heat,and that of slag line bricks reduces from 3.27 to 1.75 mm per heat,realizing the longevity of ladle refractories.

Process optimization and application for tundish repair quality

Zhang Wenxiang, Wang Ziran, Liu Shanxi, Wu Xiaoyang

2022, (4): 361-363. doi：10.3969/j.issn.1001-1935.2022.04.019

Abstract ( ) PDF (1263KB)( )

The distribution operation of dry mixes for tundish working layers was standardized,the vibration and baking processes of tundish were optimized,and special nozzle foam plugs for tundish repair were designed to ensure the regular shape of nozzles,significantly improving the tundish repair quality.The qualified rate of tundish repair increases from 92.5% to 99.6%,which reduces the production costs,achieves the high efficiency of continuous casting production,and improves the tundish safety in application.

Development of a comprehensive tester for hot mechanical properties of refractories and its experimental teaching application

Yin Yucheng, Zhu Qingyou, Zhou Shuangqing, Xia Zhongfeng, Li Yiwei, Liu Zhiqiang

2022, (4): 364-368. doi：10.3969/j.issn.1001-1935.2022.04.020

Abstract ( ) PDF (2176KB)( )

To conduct the comprehensive experimental teaching and improve the experimental teaching effect,a comprehensive tester for hot mechanical properties of refractories was developed through integrating different loading and heating technologies,designing an open furnace structure,and developing a friendly measurement and control system.The tester has the maximum heating rate of 200 ℃·min^-1 and the maximum test temperature of 1 800 ℃,which can realize one-stop measurement of hot mechanical parameters such as the hot compressive strength,the hot tensile strength and the hot torsional strength.The experimental teaching application shows that with the characteristics of visible teaching process,vivid result display and integrated functions,the tester significantly mobilizes the enthusiasm of students to practice and to think about problems,and strengthens their understanding and mastery about theoretical knowledge,significantly improving the experimental teaching effect.

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