Finite element analysis of large size chromium oxide green bodies during firing

Zhang Yongzhi, Zhang Tao, Tan Qinghua, Yang Wengang, Song Yan, Wei Changsheng

2023, (1): 1-5. doi：10.3969/j.issn.1001-1935.2023.01.001

To prevent dense chromium oxide covers from cracking during firing,such as internal cracking,surface cracking and fracture,the firing process of dense chromium oxide products was simulated,and the performance parameters at several specific temperatures before and after densification of chromium oxide green bodies were tested.The temperature difference and the stress difference of the chromium oxide green bodies were calculated by Finite Element Software at heating and cooling rates of 10,20,30 and 40 ℃·h^-1,respectively.The results show that large temperature difference and thermal stress difference are the main causes of internal cracking,surface cracking and fracture of the brick.Suitable heating rates reduce or avoid internal cracking of the brick.When the heating rate is 30 ℃·h^-1 below 1 450 ℃ and 10 ℃·h^-1 above 1 450 ℃,the temperature difference and the thermal stress difference in the brick are below 4 ℃ and 4 MPa,respectively,and there is no internal crack in the brick after firing.The initial cooling stage is the key stage that causes cracking or fracture of bricks.When the cooling rate is 20 ℃·h^-1 above 1 450 ℃,the thermal stress difference in the brick is less than 4 MPa,which can significantly reduce the surface cracks and fracture of the brick.

Effect of ZrO₂ addition on lanthanum aluminate based high emissivity coating materials

Zhang Yifan, Wang Qu, Wang Gang, Lu Keke, Zhang Qi

2023, (1): 6-9. doi：10.3969/j.issn.1001-1935.2023.01.002

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In order to enhance the sintering resistance of lanthanum aluminate based high emissivity coatings,Ca²⁺-Fe³⁺ doped LaAlO₃/ZrO₂ specimens were prepared by solid state sintering using La₂O₃,Al₂O₃,CaCO₃,and Fe₂O₃ (that all have the purity of 99 mass%) as raw materials,extra-adding fused yttria-stabilized ZrO₂ (0,5%,10%,and 15%,by mass),ball milling,pre-calcining,pressing into shapes and sintering at 1 600 ℃ for 2 h.The effect of the ZrO₂ addition on the properties of lanthanum aluminate based high emissivity coatings was explored.It is concluded that ZrO₂ does not react with LaAlO₃,which can inhibit the sintering of the specimens.With the increase of the ZrO₂ addition,the linear shrinkage rate and the thermal conductivity decrease significantly,while the emissivity decreases,but the emissivity of all the specimens is higher than 0.9.The optimal addition of ZrO₂ is 10%.

Effects of sintering temperatures on microstructure and properties of mullite porous ceramics

Guo Huishi, Chen Wenliang, Li Wenfeng, Yang Jialin, Qin Xiaomei, Gui Yanghai, Liu Yingfan

2023, (1): 10-14. doi：10.3969/j.issn.1001-1935.2023.01.003

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Mullite porous ceramics were prepared by in-situ sintering using zirconia-containing sillimanite as the main raw material,α-Al₂O₃ powder as the auxiliary material and modified starch as the pore-forming agent.The effects of the sintering temperature (1 400-1 600 ℃,an interval of 50 ℃) on the phase composition,the microstructure and the properties of the samples were studied.The results show that:(1)with the increase of the sintering temperature,the intensity of the mullite diffraction peaks increases and the mullite crystals gradually grow up;moreover,steps are observed on mullite surfaces,indicating that the mullite grows by two-dimensional nucleation mechanism;(2)with the increase of the sintering temperature,the bulk density of the samples decreases firstly and then increases,while the apparent porosity and the linear change show the opposite trends,but the cold compressive strength increases gradually;(3)when the sintering temperature is 1 550-1 600 ℃,the samples show the optimal comprehensive properties;mullite crystals grow up and combine closely,which makes mullite porous ceramics suitable for application at high temperatures.

Effect of hydratable alumina additions on strength and microstructure of corundum castables after medium temperature treatment

Li Yaozheng, Zhang Ju, Wang Saixin, Zhou Wenying, Mu Yuandong, Chen Liugang, Ye Guotian

2023, (1): 15-19. doi：10.3969/j.issn.1001-1935.2023.01.004

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In order to find out the reason for the low strength of HA-bonded castables at intermediate temperatures,corundum castables were prepared using tabular corundum,active alumina powder,and hydratable alumina (HA) as raw materials.The effects of different HA additions (1%,3%,6%,and 9%,by mass) and the heat treatment temperature (drying at 110 ℃ for 24 h,heat treatment at 400,600,800,1 000,1 100 or 1 250 ℃ for 5 h) on the strength and the microstructure of the castables were studied.The results show that:(1)during the curing and drying process,HA generates honeycomb products boehmite and bayerite through hydration,which act as the structural skeleton and provide strength for castables;(2)HA-bonded castables have the lowest strength after the heat treatment at 1 000 ℃;with the increase of the heat treatment temperature below 1 000 ℃,the structure of hydrates is damaged gradually,thus reducing the strength of the castables;when the heat treatment temperature is higher than 1 000 ℃,partial sintering occurs in the castable matrix,enhancing the strength a little bit;(3)the strength of castables at intermediate temperatures cannot be improved by increasing the addition of HA,indicating that the hydration product structure of HA collapses completely due to the thermal treatment at intermediate temperatures,which could not play the role of structural support.

Preparation of porous zirconia ceramics by fused deposition 3D printing

Niu Furong, Zhang Li, Guo Jinyu, Liu Peng, Yang Xianfeng, Xie Zhipeng

2023, (1): 20-26. doi：10.3969/j.issn.1001-1935.2023.01.005

Abstract ( ) PDF (3161KB)( )

Porous zirconia ceramics with the porosity of 15%,25%,35% and 45% were prepared by 3D printing in four printing paths (single line,grid,single line+rectangle,and grid+rectangle) using zirconia as the main raw material and the fused deposition modeling method based on screw extrusion.The microstructure of the pore wall,the interlayer bonding and the pore structure of the porous ceramics was observed,and their crushing strength was measured.The results show that:(1)porous ceramics with dense pore wall structure and good pore shape can be prepared by fused deposition 3D printing;(2)when the porosity is low,the stress-strain curve of the porous zirconia ceramics shows an elastic stage without a collapse stage;with the increase of the porosity,an obvious collapse stage appears;(3)with the same porosity,the crushing strengths of the porous ceramics prepared in the mixed paths are higher than those of in the single paths;when the porosity is 15%,the crushing strength of the porous ceramics printed in the single line+rectangle path is the highest,reaching 271 MPa.

Synthesis and hydration resistance of α-Si₃N₄-AlN composite powder by molten salt method

Wang Sen, Liang Feng, Wang Xiaohan, Gu Haohui, Wu Shuaibing, Lyu Gongye, Zhang Haijun

2023, (1): 27-30. doi：10.3969/j.issn.1001-1935.2023.01.006

Abstract ( ) PDF (2198KB)( )

α-silicon nitride-aluminum nitride (α-Si₃N₄-AlN) composite powders were successfully synthesized by the molten salt method,using silicon powder,melamine (C₃H₆N₆) and aluminum nitride (AlN) powders as raw materials,and NaCl-NaBr as the molten salt medium.The effects of the AlN powder addition,namely m(Si powder)∶m(C₃H₆N₆)∶m(AlN powder) (1∶2∶0,1∶2∶0.2,1∶2∶0.4,1∶2∶0.6 and 1∶2∶1) and the reaction temperature (1 100,1 150 and 1 200 ℃) on the phase composition,the microstructure and the hydration resistance of the synthesized α-Si₃N₄-AlN composite powders were investigated.The results show that at the mass ratio of 1∶2∶0.6,Si powder is completely nitridized to α-Si₃N₄ after firing at 1 200 ℃ for 2 h.The hydration resistance of the α-Si₃N₄-AlN composite powder is significantly improved compared with that of the raw material AlN powder.

Influence of prefiring temperature on preparation of CA₆ materials by two-step sintering

Jin Yao, Wen Tianpeng, Yu Jingkun, Yuan Lei

2023, (1): 31-34. doi：10.3969/j.issn.1001-1935.2023.01.007

Abstract ( ) PDF (1881KB)( )

CA₆ materials were prepared by the two-step sintering method using alumina and calcium carbonate as raw materials,prefiring,crushing,press shaping,and high temperature sintering.Effects of prefiring temperatures (1 100,1 200,1 300,and 1 400 ℃) on the properties and the microstructure of CA₆ materials were mainly studied.The results show that:(1)preheating and crushing damage partial pores in the materials and reduce the pore formation during high temperature sintering,the prepared CA₆ material performs higher density and cold compressive strength than the CA₆ material prepared by the conventional sintering process;(2)the optimum prefiring temperature is 1 200 ℃;the prepared CA₆ material has the apparent porosity of 28.2%,the bulk density of 2.52 g·cm^-3,and the cold compressive strength of 330 MPa.

Preparation and properties of Si-SiC-TaB₂ anti-ablation composite coatings on graphite surface

Tian Yuan, Jiang Yan, Fu Wanlu

2023, (1): 35-40. doi：10.3969/j.issn.1001-1935.2023.01.008

Abstract ( ) PDF (3022KB)( )

In order to improve the ablation resistance of carbon materials,Si-SiC and Si-SiC-TaB₂ coatings were prepared on the surface of graphite materials using graphite block as the matrix,SiC (d₅₀=10 μm),B₄C (d₅₀=50 μm) and TaC (d₅₀=3 μm) as main raw materials,by the slurry method combined with reactive melt infiltration of Si.The phase composition,the microstructure,and the element distribution of the coatings were studied,the thermal shock resistance of the Si-SiC-TaB₂ composite coating from room temperature to 1 600 ℃ was investigated,and the ablation resistance of the coating on graphite at high temperatures was tested by the plasma flame ablation test (120 and 1 980 s at 2 350 ℃,respectively).The results show that:the structure of Si-SiC-TaB₂ composite coating is dense,and there is no obvious interface among SiC,TaB₂ ceramic particles and Si in the coating.After 20 cycles of thermal shock from 1 600 ℃ to room temperature,the mass of the coating sample basically increases gradually,and the sample performs good thermal shock resistance.The mass of the Si-SiC-TaB₂ composite coated sample increases after 1 980 s of ablation,and the surface is covered with a Ta-Si-O oxidation protective layer containing Ta₂O₅ and SiO₂,which effectively prevents the corrosion of high temperature flame to the interior of the graphite.The mass of the Si-SiC coated sample decreases after ablation,and a damaged SiO₂ oxide layer is formed on the surface,and there are clearly visible ablation pits.

Effect of Y₂O₃ addition on CMS in CaO-MgO-SiO₂ system

Ren Longyu, Cui Yan, Qu Dianli, Xu Ruhui

2023, (1): 41-44. doi：10.3969/j.issn.1001-1935.2023.01.009

Abstract ( ) PDF (1923KB)( )

In order to improve the high temperature performance of magnesia refractories,the effects of the Y₂O₃ addition on the formation and the transformation of (monticellite CMS) in CaO-MgO-SiO₂ system were researched using analytically pure chemical reagents MgO,CaO,SiO₂ and Y₂O₃ as main raw materials,and the refractoriness of the forming product Ca₄Y₆O(SiO₄)₆ was studied.The results show that:(1)the addition of Y₂O₃ can not only significantly reduce the production of low melting point phase CMS in the MgO-CaO-SiO₂ system,but also capture CaO and SiO₂ to convert CMS into high-melting point phases Ca₄Y₆O(SiO₄)₆,MgO and Y₂Si₂O₇,which is beneficial to improving the high temperature performance of magnesia materials;(2)and the refractoriness of Ca₄Y₆O(SiO₄)₆ is higher than 1 800 ℃.

Reaction process of graphene and silicon powder under carbon embedded condition

Yu Baisong, Zhu Yening, Xi Zijian, Su Yuqing, Sun Miaomiao, Wei Juncong, Tu Junbo, Wang Yilong

2023, (1): 45-49. doi：10.3969/j.issn.1001-1935.2023.01.010

Abstract ( ) PDF (2908KB)( )

In order to explore the reaction process of graphene and silicon powder under carbon embedded condition,the multi-layer graphene (layer number＜30) and silicon powder (99.47% by mass) were heat treated at different temperatures (1 000,1 100,1 200,1 300,1 400,1 500,and 1 600 ℃) for 3 h.Combined with the phase composition and the microstructure of the samples,the thermodynamic analysis and the mechanism investigation were conducted.The results show that:(1)when the sample is heat treated at 1 000 ℃,amorphous SiO₂ microspheres with SiC crystal nucleus appear;(2)at 1 200 ℃,bead-like whiskers form,which are made of SiC nanowires bridge and the amorphous SiO₂ spheres on the bridge;(3)when the hot treatment temperature is lower than 1 400 ℃,the content and the diameter of SiO₂ microspheres and bead-like whiskers gradually increase with temperature rising;(4)at 1 500 ℃,carbothermic reduction reaction occurs,amorphous SiO₂ gradually decreases,and the SiC nanowire content increase;(5)at 1 600 ℃,there are all SiC nanowires in the samples,and the growth of SiC nanowires mainly follows the gas-solid reaction mechanism.

Corrosion of basic refractories for glass tanks using petrol coke and countermeasures

Wang Jiezeng, Liu Zhao, Xu Linlin, Chen Songlin, Liu Xijun

2023, (1): 50-54. doi：10.3969/j.issn.1001-1935.2023.01.011

Abstract ( ) PDF (2190KB)( )

Replacing heavy oil with petrol coke can greatly reduce the cost of glass production,but obviously shorten the service life of refractories used in the regenerator checker body of glass tanks.In order to prolong the service life of regenerator checker body,the chemical composition and the alkali-sulfur ratio of glass tank slag after using petrol coke,the damage mechanism of residual magnesia bricks in the regenerator checker body were studied,as well as the corrosion resistance of three magnesia based bricks (direct bonded magnesia chrome bricks,fused rebounded magnesia chrome bricks,and fused rebonded high purity magnesium aluminate spinel bricks).On this basis,a series of targeted countermeasures were adopted to optimize the configuration of refractories,significantly improving the service life of checker bricks and meeting the requirements of glass industry development.

Effect of chromium addition on properties of corundum refractories

Li Jian, Yu Jingkun, Wen Tianpeng, Liu Zhaoyang

2023, (1): 55-58. doi：10.3969/j.issn.1001-1935.2023.01.012

Abstract ( ) PDF (1251KB)( )

In order to obtain corundum refractories with good thermal shock resistance and long service life,the samples were prepared using white corundum (5-3,3-1,≤1,and ≤0.044 mm) as the main raw material,and chromium (≤0.074 mm) as the additive.Effects of the chromium addition (0,1%,3%,and 5%,by mass) on the physical properties,the thermal shock resistance and the slag corrosion resistance were studied.The results show that:(1)with the chromium addition increasing,the bulk density,the compressive strength and the thermal shock resistance of the samples increase and reach the maximum with 3% chromium addition;(2)the oxidation of chromium at high temperatures produces Cr₂O₃,causing volume expansion,filling partial pores among corundum particles in the sample,and increasing the bulk density;the generated Cr₂O₃ reacts with Al₂O₃ to form alumina chromia solid solution,improving the bonding strength between the matrix and the corundum particles;(3)the addition of chromium can also effectively inhibit the immersion of slag into the refractories and reduce the corrosion depth;when the addition increases from 0 to 3%,the corrosion depth decreases from 6.4 mm to 4.1 mm.

Effects of different zirconia-based raw materials on properties of MgO-Al-C materials

Liu Yang, Liu Baoliang, Shi Kai, Han Xiaoyuan, Xia Yi, Shang Jianzhao

2023, (1): 59-64. doi：10.3969/j.issn.1001-1935.2023.01.013

Abstract ( ) PDF (1859KB)( )

To improve their thermal shock resistance,MgO-Al-C materials were prepared using sintered magnesia 98,fused magnesia 98,Al powder,carbon black N220 (25-20 nm),granulated zirconia micropowder,and zirconia hollow cenosphere as raw materials and phenolic resin as the binder.The effects of the granulated zirconia micropowder addition (0,1%,2%,3% and 4%,by mass) and the zirconia hollow cenosphere addition (0,2%,4% and 6%,by mass) on the cold and the hot properties,the phase composition and the microstructure of the samples were researched.The results show that:(1)the granulated zirconia micropowder is agglomerates with porous structure and compressibility,which can absorb thermal stress; with the addition of 2%,the thermal shock resistance of the sample is improved,the strength retention ratio increases by 3.9% compared with that of the original sample Z0,and other properties are almost the same as those of sample Z0;(2)the zirconia cenosphere has a hollow structure with elasticity,which can also absorb thermal stress; with the addition of 4%,the thermal shock resistance of the sample significantly improves with the strength retention ratio increasing by 8% compared with that of sample Z0;the apparent porosity is 12.4%,the bulk density is 2.87 g·cm^-3,the density is higher than that of sample Z0;the oxidation resistance improves to a certain extent with the thickness of the oxidation layer decreasing by 0.15 mm compared with that of sample Z0,and other properties do not significantly change compared with those of sample Z0.

Preparation of mullite whisker in-situ reinforced cordierite-mullite porous ceramics

Lian Xiaoqing, Chen Zhangle, Wang Boyang, Huang Juhua

2023, (1): 65-69. doi：10.3969/j.issn.1001-1935.2023.01.014

Abstract ( ) PDF (2046KB)( )

To realize the resource utilization of coal gangue,mullite whisker in-situ reinforced cordierite-mullite porous ceramics were synthesized using kaolin powder,coal gangue powder,talc powder,and aluminum hydroxide powder as main raw materials.Effects of the coal gangue addition (0,9%,17%,26% and 33%,by mass) and the AlF₃ addition (0,1.5%,2.0%,2.5% and 3.0%,by mass) on the phase composition,the microstructure and the properties of the porous ceramics were studied.The results show that (1)the main mineral compositions of the samples are cordierite and mullite with the coal gangue addition ≤17% and the AlF₃ addition ≤2.5%;(2)raising the coal gangue addition obviously increases the bulk density and the cold compressive strength,but it is unfavorable to maintain the apparent porosity;raising the AlF₃ addition reduces the bulk density and the cold compressive strength,but increases the apparent porosity;(3)with the increase of the coal gangue and the AlF₃ additions,mullite whiskers have increased diameter and length to diameter ratio,showing square column-like or needle-like shapes;(4)added with 17% coal gangue and 2.5% AlF₃,the porous ceramic fired at 1 350 ℃ for 2 h has the bulk density of 1.86 g·cm^-3,the apparent porosity of 31.0% and the cold compressive strength of 27.8 MPa;the needle-like mullite whiskers in the porous ceramic form an interlocking structure and they have an average diameter of 0.5 μm and the length to diameter ratio ＞20.

Effect of B₄C on thermal shock resistance of Si₃N₄/Si₂N₂O bonded SiC materials

Cao Huiyan, Wu Jiguang, Cheng Zhu, Li Jie, Huang Zhigang

2023, (1): 70-73. doi：10.3969/j.issn.1001-1935.2023.01.015

Abstract ( ) PDF (1597KB)( )

Si₂N₂O was synthesized using Si powder and SiO₂ micropowder as raw materials and treating at 700 ℃ in the air atmosphere and then at 1 400 ℃ in the nitrogen atmosphere.The effect of the B₄C addition (0,1.0%,2.0%,3.0% and 4.0%,extra adding,by mass) on the synthesis of Si₂N₂O was studied.With the optimal B₄C addition,Si₃N₄/Si₂N₂O bonded SiC samples were prepared after firing at 700 ℃ for 5 h in the air atmosphere and then at 1 400 ℃ for 5 h in the nitrogen atmosphere.The thermal shock resistance of the samples was evaluated by the retention ratio of the modulus of rupture after 5 cycles of thermal shock(1 300 ℃,air quenching).The phase composition and the microstructure of the samples before and after thermal shock were analyzed.The results show that:(1)the optimal B₄C addition is 3%;B₄C preferentially reacts with O₂ to generate B₂O₃ at 700 ℃ in the air atmosphere,which provides sufficient liquid phase for the formation of plate-like Si₂N₂O at 1 400 ℃ in the nitrogen atmosphere;(2)after thermal shock,the sample added with B₄C has complete Si₂N₂O bonding phase and increased strength retention ratio from 67.5% to 88.5% compared with the sample without B₄C;at the same time,B₂O₃ transforms to BN of good thermal conductivity and self-lubricating property through the carbothermal reduction nitridation reaction,which improves the thermal shock resistance and continues to protect Si₃N₄/Si₂N₂O bonded SiC materials during service.

Thermal insulation optimization and application of torpedo ladle lining in Nanjing Iron & Steel

Li Quanhui, Liu Guili, Ma Weikui, Li Xiang, Yang Wengang, Liu Guoqi

2023, (1): 74-77. doi：10.3969/j.issn.1001-1935.2023.01.016

Abstract ( ) PDF (1578KB)( )

To improve the thermal insulation effect of torpedo ladles and reduce the temperature drop of hot iron,the effect of adding vermiculite plates as the thermal insulation layer to the torpedo ladle lining was analyzed by finite element software ANSYS,and the field application was carried out.The results show that:the temperature drop of hot iron decreases by 5.6 ℃ after adding a layer of vermiculite plates;and the field application indicates that the maximum temperature of the cone section decreases from 307.1 ℃ to 242.9 ℃ with the structure optimization of the ladle lining,presenting an obvious energy-saving effect.

Development of twin-structure slit purging plugs and their application in 120 t refining ladles

Chao Xia, Li Fei, Guo Chaoyang, Sheng Guoxiang

2023, (1): 78-81. doi：10.3969/j.issn.1001-1935.2023.01.017

Abstract ( ) PDF (1550KB)( )

Based on the analysis of the field application of 120 t ladles and purging plugs in No.1 Steelmaking Plant of Henan Jiyuan Iron & Steel (Group) Co.,Ltd.,the materials and the structure of the purging plugs were optimized,and twin-structure slit purging plugs were developed.At the same time,the masonry method and the systems of application,hot repair and maintenance of the ladle lining were improved.The field test shows that the service life of a ladle adopting the developed purging plugs is close to 80 heats after a minor repair,which fulfills the practical application requirements and increases the thermal turnover rate of ladles,thus significantly enhancing the overall economic benefits.

Research progress on hydration resistance of magnesia-calcia refractories

Wang Xin, Wang Junkai, Huang Zhenxia, Wang Yifei, Zhao Chenhang, Ma Shuailing

2023, (1): 82-86. doi：10.3969/j.issn.1001-1935.2023.01.018

Abstract ( ) PDF (930KB)( )

The research achievements on hydration resistance of magnesia-calcia refractories in recent years were summarized,emphasizing the research progress of calcination,surface treatment and additives methods to improve the hydration resistance.The future development direction and the research focus were prospected.

Research progress on oxidation behavior of SiAlON-based materials

Chen Xiaoyu, Feng Desheng, Wang Ye, Ouyang Deze, Liu Xinhong

2023, (1): 87-92. doi：10.3969/j.issn.1001-1935.2023.01.019

Abstract ( ) PDF (937KB)( )

The influences of the oxidation temperature,the oxidation time,the impurities,the particle size and the additive type on the oxidation behavior of SiAlON-based materials in China and abroad were summarized.It was pointed out that each factor had obvious effects on the phase composition,the microstructure,and the oxidation rate of the oxidation products,expecting to provide references for improving the service life of SiAlON-based materials.The future research direction was also indicated.

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