2023 Vol.32, No.2 Date of publication: 15 June 2023

In-situ Formation of MgAl₂O₄: A Methodof Tailoring Microstructure and Propertiesfor Development of High-performance Refractories

The in-situ formation mechanism of MgAl₂O₄ was introduced, focusing on the formation process by solid phase reaction and gas phase reaction as well as the phenomenon of secondary spinelization. The influencing factors of the in-situ MgAl₂O₄formation and its effect on the microstructure and the properties of materials were systematically summarized for the Al₂O₃-MgO-MgAl₂O₄ system and the carbon-containing refractories systems. It was pointed out that the in-situ formation of MgAl₂O₄, including secondary spinelization, can regulate the microstructure and the service performance of materials. Its expansion effect can not only offset the shrinkage caused by sintering to improve the corrosion resistance of refractories, but also seriously restrict the reliability of functional refractories. The composition, the particle size, the atmosphere, and the temperature are important factors affecting the in-situ formation of MgAl₂O₄. In the carbon-containing materials systems, the solid-solid reaction and the gas-solid reaction coexist to produce MgAl₂O₄, which provides an effective way to further regulate the microstructure and the properties of materials through the reaction process.

LIU Guoqi, WANG Minghui, LI Hongxia, YU Jianbin, GAN Feifang, GU Qiang, MA Weikui

2023 Vol.32 (2): 1-6. doi:10.19691/j.cnki.1004-4493.2023.02.001

Development and Application of Multi-phase Nitrides Bonded Silicon Carbide Lintel Blocks for Dry Quenching Furnaces

Multi-phase nitrides bonded silicon carbide lintel blocks were prepared using industrial SiC (SiC≥98 mass%, 3-0.5, ≤0.5 and ≤0.044 mm), Si powder (Si ≥98 mass%, ≤0.044 mm), and SiO₂ micropowder (SiO₂≥96 mass%, d₅₀=0.15 μm) as raw materials, and calcium lignosulfonate as the additive, batching, mixing, and molding on a vibration pressure molding machine, drying and then firing at 1 420 ℃ for 10 h in high-purity N₂. The apparent porosity, the bulk density, the cold modulus of rupture, the hot modulus of rupture, and the linear expansion coefficient of the samples were tested. The phase composition and the microstructure of the samples at different nitriding depths (50, 100, and 150 mm) were analyzed by XRD and SEM. The field application effects of the blocks were studied. The results show that: (1) the multi-phase nitrides bonded silicon carbide refractories can dynamically adjust their own phase composition and minimize structural and thermal stresses, improving the service life of key parts of dry quenching furnaces; (2) calcium lignosulfonate can improve the nitriding micro-environment of multi-phase nitrides bonded silicon carbide lintel blocks, successfully increasing the effective nitriding thickness of the blocks to 300 mm; (3) Sinosteel LIRR provides a unique concept in the design of materials and block types as well as the stable and scientific overall structure, promoting the industrialization process of dry quenching furnaces with long service life in China.

CAO Huiyan, FENG Yanbin, ZHANG Xinhua, HUANG Zhigang, LI Jie, WANG Xinhui, WU Jiguang

2023 Vol.32 (2): 7-11. doi:10.19691/j.cnki.1004-4493.2023.02.002

Finite Element Analysis of Large Size Chromium Oxide Green Bodies During Firing

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 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^-1above 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.

ZHANG Yongzhi, WANG Han, ZHANG Tao, FAN Muxu, SHI Pengkun, FENG Zhiyuan, LIANG Zhen

2023 Vol.32 (2): 12-17. doi:10.19691/j.cnki.1004-4493.2023.02.003

Steam Oxidation Resistance Comparison of Several Silicon Carbide Refractories at Elevated Temperatures

The oxidation tests of different SiC refractories including Si₃N₄-SiC bricks, Si₃N₄-Si₂N₂O-SiC bricks from China (SNO-1), Si₃N₄-Si₂N₂O-SiC bricks from overseas (SNO-2), 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 different durations (100, 200, 300, 400 and 500 h). The mass, the volume, the bulk density and the apparent porosity before and after the 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), as the oxidation time increases 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 and SNO-2 have basically the same chemical and phase composition, SNO-2 has the lower mass change rate than SNO-1 during oxidation from 200-500 h, which indicates that SNO-2 has the better steam oxidation resistance than SNO-1.

WANG Jiaping, WU Jiguang, HUANG Zhigang, LYU Chunjiang, WANG Wenwu

2023 Vol.32 (2): 18-23. doi:10.19691/j.cnki.1004-4493.2023.02.004

Alkali Vapor Corrosion of Different Refractories at High Temperatures

Commercial high purity corundum brick, corundum-mullite brick, mullite brick, calcium hexaaluminate brick and calcium hexaaluminate-corundum brick were studied to investigate their reaction state and alkali vapor corrosion mechanism at 1 370 and 1 500 ℃. The results show that: (1) served in hot alkali vapor, the high-purity corundum brick has no obvious slag layer but expands dramatically; (2) the corundum-mullite brick shows obvious reactive expansion at 1 370 ℃ and melting corrosion happens at 1 500 ℃; (3) at 1 370 ℃, alkali vapor and mullite brick react and form a slag layer without volume effect; when the temperature increases to 1 500 ℃, the reaction melting corrosion intensifies; (4) the calcium hexaaluminate brick and the calcium hexaaluminate-corundum brick form a thin slag layer in alkali vapor, and the sample surface absorbs Na⁺ to form a dense layer with small volume effect.

FAN Muxu, HOU Xiaojing, FENG Zhiyuan, WANG Han, LIU Pengcheng, SHI Gan

2023 Vol.32 (2): 24-30. doi:10.19691/j.cnki.1004-4493.2023.02.005

Effect of Different Silica Fumes on Properties of Al₂O₃-SiC-C Castables for Iron Trough

In order to improve the performance of Al₂O₃-SiC-C castables for iron trough, samples were prepared using brown corundum, dense corundum, activated alumina micropowder, ball pitch, and silicon as main raw materials, calcium aluminate cement as the binder. Several kinds of silica fumes (93SiO₂, 96SiO₂, and 99SiO₂) with different particle size distributions and chemical composition were added to research the effects on the properties of castables. The results show that the sample with 99SiO₂ fume has high water requirement for molding, but the bulk density is the lowest, the apparent porosity is the highest, the oxidation resistance is the worst, and the permanent linear change on heating is low after firing at 1 450 ℃ for 3 h. The bulk density and the apparent porosity of the sample with 93SiO₂ fume or 96SiO₂ fume are equivalent, the hot modulus of rupture of the sample with 93SiO₂ fume is the lowest, and the slag resistance of the sample with 96SiO₂ fume is the best. The comprehensive performance of the sample with 96SiO₂ fume is the best.

CAO Zhuang, JIA Qingwei, ZHANG Jun, ZHOU Huijun, LI Jinfeng, HUN Xianlei, YAN Leixin, QIN Hongbin, ZHANG Sanhua

2023 Vol.32 (2): 31-36. doi:10.19691/j.cnki.1004-4493.2023.02.006

Strengthening Mullite Ceramic Materials by Gas Infiltration

In order to improve the high-temperature performance of mullite ceramic materials, mullite ceramic bodies were placed in closed containers with AlF₃ · 3H₂O powder and kept at 1 600 ℃ for 6 h. AlF₃ · 3H₂O reacts with O₂ to produce gaseous compounds AlOF and F, which penetrate into the bodies, promote Al₂O₃ and SiO₂ to form mullite whiskers, and strengthen the mullite ceramic materials. The results show that the mullite ceramics have enhanced hot strength, increased bulk density and declined apparent porosity by adding a certain amount of AlF₃ · 3H₂O in a closed container. When the addition of AlF₃ · 3H₂O is 6%, the bulk density of the ceramic material reaches the maximum and the apparent porosity is the lowest; and when the addition of AlF₃ · 3H₂O is 8%, the hot strength of the material is the highest.

ZHANG Qi, WANG Gang, WANG Qu, YUAN Bo, LI Hongxia

2023 Vol.32 (2): 37-40. doi:10.19691/j.cnki.1004-4493.2023.02.007

Effect of Zirconia Corundum Addition on Properties of Chrome Corundum Castables

In order to investigate the effect of zirconia corundum on the preparation of chrome corundum castables, samples were prepared using tabular corundum, white fused corundum, active alumina micropowder, chromium oxide micropowder and fused ziconia corundum particles as the main raw materials, and pure calcium aluminate cement as the binder. The effects of the fused zirconia corundum particles addition (1-0.5 mm, 0, 4.5%, 9%, and 18%, by mass) on the linear change rate, the apparent porosity, the cold modulus of rupture, and the thermal shock resistance of chrome corundum castables were studied, and the microstructure of the samples was analyzed. The results show that: (1) with the zirconia corundum addition increasing, the permanent linear change on heating of the samples gradually increases, the apparent porosity gradually increases, the cold modulus of rupture gradually decreases, and the thermal shock resistance gradually increases; (2) according to SEM, it can be found that the phase transformation of ZrO₂ after heat treatment leads to a large number of microcracks in the material. On one hand, the cold modulus of rupture of the material is reduced; on the other hand, the thermal shock resistance of the material is improved.

GUO Peng, CHEN Lu, YU Tongshu, ZHANG Hui, WANG Dongdong

2023 Vol.32 (2): 41-44. doi:10.19691/j.cnki.1004-4493.2023.02.008

Formation of Polytypoids (12H and 21R) in High Temperature Nitrogen Atmosphere and Their Effects on SiC-MgAl₂O₄ Composites

SiC-MgAl₂O₄ composites with SiAlON polytypoids (12H and 21R) as the bonding phases were prepared using SiC fine powder, MgAl₂O₄ fine powder and Al powder as raw materials. The effects of the firing temperature and the mass ratio of SiC to MgAl₂O₄ on the formation of SiAlON polytypoids as well as on the properties of samples were studied. The formation mechanism of SiAlON polytypoids was discussed. The results show that firing at 1 650 ℃ in the nitrogen atmosphere, SiC-MgAl₂O₄ composites with SiAlON polytypoids can be obtained. With the gradual increase of the mass ratio of SiC to MgAl₂O₄ in the raw materials, 12H forms first, and then coexists with 21H, finally, all 12H converts into 21R in samples. Both phases are plate crystals with flat and smooth edges. Compared with 21R, 12H is conducive to improving the density and the cold mechanical properties of materials. After firing at 1 650 ℃ in the nitrogen atmosphere, with the mass ratio of SiC to MgAl₂O₄ of 6:4, the sample has the cold modulus of rupture of 27 MPa, showing the optimal performance.

GU Chenwei, WANG Zhanmin, ZHAO Shixian, SI Yaochen, XIA Miao

2023 Vol.32 (2): 45-50. doi:10.19691/j.cnki.1004-4493.2023.02.009

Abstracts from Naihuo Cailiao (Refractories)

2023 Vol.32 (2): 51-53.

China's Refractories

In-situ Formation of MgAl₂O₄: A Methodof Tailoring Microstructure and Propertiesfor Development of High-performance Refractories

Development and Application of Multi-phase Nitrides Bonded Silicon Carbide Lintel Blocks for Dry Quenching Furnaces

Finite Element Analysis of Large Size Chromium Oxide Green Bodies During Firing

Steam Oxidation Resistance Comparison of Several Silicon Carbide Refractories at Elevated Temperatures

Alkali Vapor Corrosion of Different Refractories at High Temperatures

Effect of Different Silica Fumes on Properties of Al₂O₃-SiC-C Castables for Iron Trough

Strengthening Mullite Ceramic Materials by Gas Infiltration

Effect of Zirconia Corundum Addition on Properties of Chrome Corundum Castables

Formation of Polytypoids (12H and 21R) in High Temperature Nitrogen Atmosphere and Their Effects on SiC-MgAl₂O₄ Composites

Abstracts from Naihuo Cailiao (Refractories)

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