Properties of oxide porous ceramics prepared by different additions of fly ash cenosphere

Dong Bo, Deng Chengji, Chen Yufeng, Xie Zhe, Ding Jun, Zhu Qingyou, Zhu Hongxi, Yu Chao

2023, (3): 185-188. doi：10.3969/j.issn.1001-1935.2023.03.001

In order to further expand the application of fly ash cenosphere in the field of porous ceramics,porous ceramics were prepared using fly ash cenosphere,forsterite,sericite powder and bauxite as main raw materials,molding,then heat treating at 1 100 ℃ for 1 h in air atmosphere.The fly ash cenosphere addition varied from 40%,60%,to 80%,by mass.The phase composition,microstructure and conventional physical properties of the porous ceramics were studied.The results show that:(1)with the increase of the fly ash cenosphere addition from 40% to 80%,the interval between fly ash cenosphere and the matrix increases,the porosity rises,the bulk density and the cold compressive strength decrease,but the fractal dimension of the pores does not change significantly;(2)with 60% addition of fly ash cenosphere,the comprehensive performance of the sample is optimal with about (0.90±0.01) g·cm^-3 of the bulk density,(66.9±0.5)% of the porosity,about ( 12.37±0.69) MPa of the cold compressive strength,and 0.201,0.232 and 0.262 W·m^-1·K^-1 of the thermal conductivity at 300,600 and 900 ℃.Therefore,it has a good application prospect in the field of thermal insulation refractories.

Effect of calcium dialuminate addition on properties of corundum castables

Qin Hongbin, Jin Feng, Tang Shiming, Zhou Huijun, Li Hongxia, Shi Shubing, Zhang Sanhua, Cheng Li, Hui Xianlei

2023, (3): 189-193. doi：10.3969/j.issn.1001-1935.2023.03.002

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In order to improve the performance of corundum castables,white corundum,calcium dealuminate (CA₂),active α-Al₂O₃ micropowder and pure calcium aluminate cement were used as main raw materials to prepare corundum castables.The effects of the CA₂ addition (0,20%,30%,40%,by mass) on the properties of corundum castables were studied.The results show that:(1)with the increase of the CA₂ addition,the bulk density of corundum castables decreases significantly,and the cold compressive strength of corundum castables after drying at 110 ℃ and the heat treatment at 800 ℃ is improved obviously,while the cold compressive strength after the heat treatment at 1 200 ℃ changes slightly;(2)with the increase of the CA₂ addition,the average thermal expansion coefficient decreases gradually,the thermal conductivity decreases significantly,and the retention rate of the modulus of rupture of the sample after 800 ℃ water-quenching thermal shock is greatly improved;(3) the introduction of CA₂ greatly improves the permeability,and does not affect the resistance to hydrogen reduction of corundum castables.

Effect of potassium hexafluorozirconate addition on properties of foamed ceramics from fly ash

Chang Xinglan, Gu Yajie, Sun Shengrui, Sun Ke, Liao Dachen, Liu Yangqiao, Xi Shuang, Dong Manjiang

2023, (3): 194-199. doi：10.3969/j.issn.1001-1935.2023.03.003

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In order to achieve the widespread application of high additions of fly ash in low-cost and high-performance foamed ceramics,foamed ceramics were prepared by high temperature calcination,using fly ash,talcum,feldspar and silicon carbide as raw materials,and adding different additions (0,2%,5%,and 7%,by mass) of potassium fluorozirconate (K₂ZrF₆).The effect of the K₂ZrF₆ addition on the phase composition,microstructure and properties of the foamed ceramics was studied.The results show that:with the addition of K₂ZrF₆ increasing from 2% to 7%,the characteristic peaks of zircon and spinel gradually increase,while those of mullite gradually weaken.Meantime,the bulk density and compressive strength decrease,the thermal conductivity shows a trend of first decreasing and then increasing.At the same time,the addition of K₂ZrF₆ improves the pore size,uniformity and roundness.However,when the addition of K₂ZrF₆ reaches 7%,the pore size further increases,the roundness decreases and the pore structure deteriorates.In general,compared with the sample without K₂ZrF₆,the compressive strength of the samples containing K₂ZrF₆ significantly increases,and the bulk density as well as thermal conductivity obviously reduces.When the addition of K₂ZrF₆ is 5%,the sample has the best comprehensive performance.

Corundum-mullite porous materials printed by direct ink writing

Zhu Kai, Yang Daoyuan, Wang Meijiao, Yang Lianghua, Zhao Xiang, Chen Junhuan, Yuan Huiyu

2023, (3): 200-204. doi：10.3969/j.issn.1001-1935.2023.03.004

Abstract ( ) PDF (1392KB)( )

Sintered corundum micropowder with 10.3 μm of d₅₀,SiO₂ micropowder with 0.2 μm of d₅₀ and chemically pure sodium hexametaphosphate were used as main raw materials.The slurry with the solid content of 63% (φ) was prepared according to 11∶1 of the mass ratio of sintered corundum micropowder to SiO₂ micropowder and 0.15∶100 of the mass ratio of sodium hexametaphosphatate to sintered corundum micropowder.After vacuum defoaming treatment,the through-hole porous materials with regular triangle,square and hexagon cross sections were printed by the direct ink writing technology.The effects of the pore shape,pore size,force direction and heat transfer direction on the cold compressive strength and thermal conductivity of the materials were studied.The results show that:(1)the printed porous material has no visible defects or deformation,the surface is relatively smooth and even,and the extrusion lines are uniform and smooth;the contact between the printing layers is close without the stratification phenomenon;(2)at the same porosity,the cold compressive strength of the material increases gradually in the order of regular triangle pore material,square pore material and hexagonal pore material,while the thermal conductivity decreases gradually in this order;(3)at the same pore shape and porosity,the cold compressive strength decreases and the thermal conductivity increases with the increase of the pore size;at the same pore shape,pore size and porosity,the cold compressive strength and the thermal conductivity parallel to the through-hole direction are greater than those perpendicular to the through-hole direction.

Preparation of lightweight alumina-silica castables by replacing open-pore perlite aggregates with coal gangue ceramsite

Zan Wenyu, Ma Beiyue, Wang Yuqing, Jiang Zhifeng

2023, (3): 205-209. doi：10.3969/j.issn.1001-1935.2023.03.005

Abstract ( ) PDF (1648KB)( )

A new kind of lightweight alumina-silica castables was investigated,which is expected to be used as a lining material for petrochemical tube furnaces,reducing production costs and promoting the sustainable recycling of refractory raw materials.Lightweight alumina-silica castables were synthesized using closed-pore perlite (4-2 mm),open-pore perlite (8-4 mm) and coal gangue ceramsite (5-2 mm) as aggregates,floating beads (0.5-0.3 mm),sinking beads (0.8-0.6 mm),silica micropowder,α-Al₂O₃ micropowder,zirconia and zircon micropowder as the matrix,Secar 71 as the binder.Effects of the addition of coal gangue ceramsite (0,5%,10%,15%,and 20%,by mass) to replace the same amount of open-pore perlite aggregate on the properties of lightweight alumina-silica castables were studied.The results show that:CaO,MgO,and Na₂O in coal gangue ceramsite can act as sintering agents,which are conducive to the densification of the sample.The appropriate addition of coal gangue ceramsite can also facilitate the generation of CaZr₄O₉,accompanied by the formation of internal microcracks,which can increase the cold compressive strength and thermal shock resistance of the sample.However,the excessive coal gangue ceramsite worsens the hydration effect of the cement and decreases the amount of the bonding phase between aggregates,leading to a decrease in the cold compressive strength.Additionally,the excessive coal gangue ceramsite will also increase the amount of the liquid phase,so the linear shrinkage rate increases.The suitable addition of coal gangue ceramsite is 10%.

Effect of different manganese sources and aluminum sources on synthesis of manganese aluminate spinel

Shang Jianzhao, Liu Baoliang, Xu Tengteng, Liu Yang, Shi Kai

2023, (3): 210-214. doi：10.3969/j.issn.1001-1935.2023.03.006

Abstract ( ) PDF (2171KB)( )

The preparation key of periclase-manganese aluminate spinel bricks for the cement kiln firing zone is the synthesis of manganese aluminate spinel.Manganese aluminate spinel (MnAl₂O₄) was synthesized at 1 550 and 1 600 ℃ for 3 h,using MnO,MnO₂ and MnCO₃ as manganese sources and α-Al₂O₃ and Al(OH)₃ as aluminum sources.The effects of different manganese and aluminum sources on the properties of manganese aluminate spinel were investigated.The results show that:(1)compared with MnO₂ and MnCO₃,manganese aluminate spinel synthesized with MnO as the manganese source has the higher synthesis rate,lower apparent porosity,higher bulk density,larger grain size of 50 μm and denser structure;(2)compared with Al(OH)₃,manganese aluminate spinel synthesized with α-Al₂O₃ as the aluminum source has less cracks,lower apparent porosity and denser structure.Therefore,dense manganese aluminate spinel with high purity and good crystal development was synthesized by sintering at 1 600 ℃ with α-Al₂O₃ as the aluminum source and MnO as the manganese source.

Effect of zircon addition on properties of corundum porous materials

Liu Xin, Zhang Shiming, Li Ying, Wang Di, Jia Quanli

2023, (3): 215-219. doi：10.3969/j.issn.1001-1935.2023.03.007

Abstract ( ) PDF (2153KB)( )

This paper aims to improve the corrosion resistance of dispersive purging plugs.White fused corundum particles and fine powder,α-Al₂O₃ micropowder,Cr₂O₃ micropowder,Guangxi clay and zircon powder were used as the main raw materials.The mass ratio of white fused corundum particles and fine powder was fixed at 85∶15,and 0,1%,2% or 3% (by mass) of zircon powder was added to replace the same amount of white corundum fine powder.The corundum porous material was prepared by the particle stacking pore-forming method at 1 650 ℃ for 3 h.The effect of the zircon addition on the properties and microstructure of porous materials was investigated.The results show that:after adding zircon,the permeability of the porous material increases,the cold and hot strengths increase obviously,and the expansion rate after firing decreases.When the addition of zircon is 2%,the comprehensive performance of the sample is optimal with the smallest linear change rate and the biggest permeability.

Effect of binder type on corrosion resistance to nickel-based superalloy of corundum-spinel castables

Pan Yuanshuai, Wang Gang, Feng Haixia, Liu Jun, Tian Pengdan, Han Yihui, Wang Jianbin

2023, (3): 220-225. doi：10.3969/j.issn.1001-1935.2023.03.008

Abstract ( ) PDF (3338KB)( )

In order to expand the application of corundum-spinel materials in superalloy smelting,corundum-spinel strip specimens and crucible specimens were prepared using white fused corundum with particle sizes of 5-3,3-1,≤1 and ≤0.074 mm and sintered spinel with particle sizes of ≤1 and ≤0.044 mm as the main raw materials,active α-Al₂O₃ micropowder as the sintering aid,Secar 71 cement,ρ-Al₂O₃ micropowder or magnesium phosphate cement as the binder.The effects of different binders on the conventional properties and corrosion resistance to nickel-based superalloy of the specimens were researched.Among the three kinds of binders,the strip specimen with Secar 71 cement as the binder has optimal conventional performance and the lowest linear shrinkage rate after firing at 1 600 ℃.After the corrosion resistance test,the crucible specimen with Secar 71 cement as binder has the smallest macroscopic corrosion penetration area,the shallowest microscopic penetration depth,and the best corrosion resistance to nickel-based superalloy.The penetration of Cr into the crucible is shallow,and the penetration of Nb and Ti is obviously deeper than that of Cr,while the main components Ni and Fe hardly penetrate into the crucible specimens.

Preparation of calcium hexaaluminate/gehlenite composite from industrial magnesium slag

Bai Pinbo, Xing Li, Kong Xiangchen, Tian Yuming

2023, (3): 226-230. doi：10.3969/j.issn.1001-1935.2023.03.009

Abstract ( ) PDF (1925KB)( )

In order to realize the effective utilization of industrial waste slag,industrial magnesium slag and alumina were used as the main raw materials,and 4 mass% PVA plasticizer was added,the calcium hexaaluminate/gehlenite (CA₆/C₂AS) composite was obtained by high temperature pressureless sintering at 1 300,1 400,1 500 and 1 600 ℃ for 3 h,respectively.The effects of the heat treatment temperature on the phase composition and the physical properties of the samples were studied.The comprehensive properties of the samples after heat treatment at 1 500 ℃ for 3 h are optimal:1.59 g·cm^-3 bulk density,52.7% apparent porosity,30.8 MPa modulus of rupture,1 544 ℃ refractoriness-under-load,lower than 0.22% mass gain rate after hydration for 36 h,and 52.7% modulus of rupture retention ratio after thermal shock at 800 ℃.The samples show good structural stability,hydration resistance and thermal shock resistance.

Service behavior of α-SiC bonded SiC dome bricks for movable roof kilns

Dong Jiancun, Wan Longgang, Zheng Han, Xiang Yubo, Zhang Xinhua, Ma Zhaoyang, Wang Jianbo, Wu Jiguang

2023, (3): 231-235. doi：10.3969/j.issn.1001-1935.2023.03.010

Abstract ( ) PDF (1558KB)( )

In order to solve the problem of pollution and expansion of refractories for the dome of gas-fired movable roof kilns,a piece of α-SiC bonded SiC brick was prepared using silicon carbide particles and fine powder as the main raw materials,and water-soluble resin as the binder with the mass ratio of 65∶35∶4.5,forming a 240 mm×170 mm×140 mm green body by mechanical pressing,and holding at 2 400 ℃ for 3 h in vacuum.The brick was used in the dome of a gas-fired movable roof kiln of an alumina ceramic stick company in China.After 46 heats (276 h in total),the brick fractured seriously.The used brick was sampled,and the properties at different distances from the hot surface were tested and thermodynamically analyzed.The phase composition and the microstructure were analyzed and compared with those of the original brick.The used α-SiC bonded SiC brick has lower apparent porosity and higher bulk density than the original brick,because 12%-14.2% cristobalite is formed in the used brick,transforming from α-SiC bonding to cristobalite bonding,and decreasing the pore size.Compared with the original brick,the cold modulus of rupture and the refractoriness-under-load do not change much.It is speculated that the fracture of the material is not caused by the failure of its own mechanical properties,but by the shear force due to the temperature fluctuation.

Development and application of zirconia slide plates for slag skimming of converters

Yu Tongshu, Li Hong-xia, Li Yong, Li Hongyu, Zhao Chenrui, Wang Dongdong, Zhao Hongbo, Zhang Hui

2023, (3): 236-240. doi：10.3969/j.issn.1001-1935.2023.03.011

Abstract ( ) PDF (2109KB)( )

In order to improve the thermal shock resistance of zirconia slide plates for slag skimming of converters,zirconia materials were prepared using monoclinic zirconia powder,fused magnesia stabilized zirconia (PMD) as main raw materials and magnesia powder (or magnesium hydroxide) as the stabilizer.The effects of the magnesia powder addition,substitution amount of PMD and stabilizer types on the properties,phase composition and microstructure of zirconia materials were studied.Based on the optimal formulation of 86% monoclinic zirconia powder,14% PMD and 3.12% magnesium hydroxide,the dense zirconia plates with the bulk density of 5.26 g·cm^-3,the apparent porosity of 7.9%,the high m-ZrO₂ content of 75% and excellent thermal shock resistance can be prepared after fine powder granulation,200 MPa high pressure molding and 1 720 ℃ high temperature firing.The developed zirconia plates were embedded in slag skimming slide plates of 150 t and 260 t converters in batches.The average service life reached 25 heats,which was 5 heats higher than before,and there were no accidents such as steel leakage and burning through of the slide plates during service.The zirconia slide plate surface was smooth and complete after offline,without cracks and cold steel adhesion.

Effect of microsilica addition on properties of Al₂O₃-SiO₂ spraying mix

Cai Wei, Ju Maoqi, Chen Jinfeng, Cong Peiyuan

2023, (3): 241-244. doi：10.3969/j.issn.1001-1935.2023.03.012

Abstract ( ) PDF (1739KB)( )

Electric porcelain waste,high alumina bauxite,Guangxi white clay,CA50 cement and microsilica were used as raw materials to prepare Al₂O₃-SiO₂ spraying mix.The effects of the microsilica addition (0,1.5%,3% and 4.5%,by mass) on the apparent porosity,cold modulus of rupture,phase composition and microstructure of the samples after drying and heat treatment at different temperatures were studied.With the increase of the microsilica addition,the apparent porosity of the samples after drying at 110 ℃ gradually decreases,and the cold modulus of rupture gradually increases.With the increase of the microsilica addition,the apparent porosity of the samples after heat treatment at 1 100 and 1 300 ℃,respectively,decreases first and then increases,and reaches the lowest when the microsilica addition is 1.5%.The cold modulus of rupture of the spraying mix after heat treatment at 1 100 and 1 300 ℃ increases first and then decreases,and reaches the maximum when the microsilica addition is 3.0%.By comprehensive consideration,the optimum addition of microsilica is 3.0%.

Variable temperature damage of refractories based on multi-scale generalized self-consistent model

Tian Fucheng, Wang Zhigang, Liu Changming

2023, (3): 245-249. doi：10.3969/j.issn.1001-1935.2023.03.013

Abstract ( ) PDF (1599KB)( )

The damage caused by the mismatch of the thermal expansion between the particle phase and the matrix phase during the temperature change was numerically analyzed with the aid of the micromechanical model,and the hot pressed glass-spherical alumina material was used as the research object.A nonlinear damage behavior simulation method was proposed for the whole reheating-cooling process of the material.The simulation results are in good agreement with the experiments.The degree of the thermal damage of a material is influenced by the absolute value of Δα and the volume fraction of the particle phase.The larger the absolute value of Δα and the higher the volume fraction of the particle phase,the severer the thermal damage of the material.

Effect of MgO addition on properties of zirconia sizing nozzle material

Lin Siqi, Liu Xinggang, Liu Tao, Li Yuqing, Yu Jingkun

2023, (3): 250-252. doi：10.3969/j.issn.1001-1935.2023.03.014

Abstract ( ) PDF (1823KB)( )

In order to improve the performance of sizing nozzles,MgO stabilized zirconia sizing nozzle material was prepared using ZrO₂ fine powder(d₅₀=3,5 and 8 μm) as the raw material,polyvinyl alcohol aqueous solution as the binder,extra adding different mass fractions (2.0%,2.5%,2.8%,3.0% and 3.5%) of MgO,and heat treating at 1 700 ℃ for 2 h.The effects of the MgO addition on the phase composition,microstructure and properties were studied.The bulk density,the cold compressive strength and the strength retention ratio after 3 cycles of thermal shock of the samples increase first and then decrease with the increase of the MgO addition.When the MgO addition is 2.5%,the comprehensive performance of the sample is the best with 0.75% apparent porosity,5.51 g·cm^-3 bulk density,980 MPa cold compressive strength,and 1 025 MPa cold compressive strength after three thermal shocks.

Research status and prospect of energy-saving measures for shuttle kilns

Meng Qingxin, Tang Zan, Gong Xintai, Liang Ruihan, Wang Jinpeng, Liu Zhipeng, Tan Gongliang, Cai Jiaqi

2023, (3): 253-258. doi：10.3969/j.issn.1001-1935.2023.03.015

Abstract ( ) PDF (2005KB)( )

Based on many advantages such as flexible operation and high production efficiency,shuttle kilns have been widely used in refractory and ceramic industries.However,due to intermittent operation,low thermal efficiency and high energy consumption are their main disadvantages.In order to reduce their energy consumption further,the existing energy conservation measures of shuttle kilns were summarized,such as recovering waste heat of flue gas and reducing thermal loss of the kiln body.It was suggested that dual effects of energy saving and environmental protection should be taken into account,and the energy saving of shuttle kilns should be continued from recovering waste heat of products,reducing the thermal storage of kiln cars,lightening the kiln body,using infrared radiation energy saving coatings,strengthening automatic control and improving kiln types.

Research progress on effect of raw material characteristics on sintering densification of magnesium aluminate spinel

Wang Jianbin, Wang Zhanmin, Feng Haixia, Liu Jun, Han Yihui, Pan Yuanshuai

2023, (3): 259-264. doi：10.3969/j.issn.1001-1935.2023.03.016

Abstract ( ) PDF (959KB)( )

According to the different properties of raw materials and the sintering mechanism affecting the densification of magnesium aluminate spinel,the effects of raw material characteristics on the sintering densification of magnesium aluminate spinel were reviewed from the aspects of the raw material type,chemical composition,particle size distribution and pretreatment.It was pointed out that the future research focus is how to quantify the relationship between the properties of magnesium aluminate spinel raw materials and the properties of prepared materials,so as to realize the low-temperature pressureless sintering of raw materials,which is conducive to further energy saving and environmental friendliness with the satisfied performance in the industrial manufacturing process.

Research progress on preparation of silicon nitride by catalytic nitridation

Wang Xin, Wang Junkai, Huang Zhen-xia, Meng Hao, Wang Yifei, Wen Yanke

2023, (3): 265-269. doi：10.3969/j.issn.1001-1935.2023.03.017

Abstract ( ) PDF (1012KB)( )

Silicon nitride is widely used in refractories,metallurgy,aerospace and other fields due to its excellent properties,such as high strength and good resistance to high-temperature,corrosion,wear,thermal shock and oxidation.The introduction of catalyst into the nitriding process of silicon powder by the catalytic nitriding method can not only realize the rapid nitriding of silicon powder at low temperatures,but also change the morphology of the products,promote the formation of silicon nitride whiskers,improve the microstructure of the products,and enhance the mechanical properties.The research progress on the preparation of silicon nitride by catalytic nitriding with metals and metallic oxides as catalysts was reviewed,and the future development direction was prospected.

Progress in preparation,growth mechanism,and application of mullite whiskers

Liu Zhaoyang, Pan Song-yang, Dong Zeming, Wen Jun, Wang Junyang, Yu Jingkun

2023, (3): 270-276. doi：10.3969/j.issn.1001-1935.2023.03.018

Abstract ( ) PDF (981KB)( )

Mullite whiskers have the properties of high temperature resistance,good wear resistance,good oxidation resistance,low thermal expansion coefficient,and good thermal shock resistance,which are an excellent reinforcing agent for composite materials.Preparation methods of mullite whiskers,including solid-state methods,molten salt methods,and sol-gel methods,were introduced.Meanwhile,the vapor-solid (VS) and liquid-solid (LS) growth mechanisms of mullite whiskers were analyzed.The applications of mullite whiskers in ceramic toughening,thermal insulation,separation and filtration,and polymer performance optimization were summarized.Combined with the current problems of the preparation and application of mullite whiskers,the future development of mullite whiskers was prospected.

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