China's Refractories ›› 2022, Vol. 31 ›› Issue (1): 16-23.DOI: 10.19691/j.cnki.1004-4493.2022.01.003
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Sintering Complexity of Magnesia-chrome Refractories
GUO Zongqi1,*(
), MA Ying2, LI Yong3
- 1 School of Materials Science and Engineering, Xi’an University of Architecture and Technology,Xi’an 710055, China
2 RHI Magnesita (Dalian) Co., Ltd., Dalian 116600, China
3 School of Materials Science and Engineering, University of Science and Technology Beijing,Beijing 100083, China
-
Online:2022-03-15Published:2022-04-02 -
Contact:GUO Zongqi -
About author:Dr. Guo Zongqi studied the major of refractories in Xi’an University of Architecture and Technology, China, and received his PhD degree in Ecole Polytechnique, University of Montreal, Canada. For more than 10 years, he has been working on the syntheses of chromia raw materials and pioneering development of high chrome refractories for slagging coal gasifiers, which was awarded with Second Grade Technical Advance Prize by the Ministry of Chemical Industry. Dr. Guo has gained broad research experience on a few of international refractory platforms in Canada, Austria, Poland and China. His recent investigations and industrial practice include a great progress of high purity, high density sintered magnesia from natural magnesite. He has been involving in long-term continuous studies of burnt and unburnt basic bricks for cement rotary kilns, glass-making regenerators and steel-making process.
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GUO Zongqi, MA Ying, LI Yong. Sintering Complexity of Magnesia-chrome Refractories[J]. China's Refractories, 2022, 31(1): 16-23.
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URL: http://www.cnref.cn/EN/10.19691/j.cnki.1004-4493.2022.01.003
Table 1 Typical catalogues of commercial magnesia-chrome bricks
| Catalogue | Type I | Type II | Type III |
|---|---|---|---|
| Bonding mode | Silicate-bonded magnesia-chrome | Direct-bonded magnesia-chrome | Rebonded fused-grain magnesia-chrome |
| Aggregate as main component | Mid-grade sintered magnesia | High grade magnesia | Fused magnesia chrome |
| Chemical composition /mass% | |||
| MgO | 61.12 | 58.90 | 58.45 |
| Cr2O3 | 18.89 | 20.80 | 20.89 |
| Al2O3 | 5.86 | 6.66 | 6.73 |
| Fe2O3 | 11.20 | 12.50 | 12.28 |
| CaO | 1.04 | 0.84 | 0.68 |
| SiO2 | 1.31 | 0.43 | 0.56 |
| Bulk density /(g · cm-3) | 3.20 | 3.27 | 3.31 |
| Apparent porosity /% | 16.5 | 15.5 | 15.0 |
| Cold crushing strength /MPa | 60.0 | 62.5 | 70.0 |
| Thermal expansion at 1 600 °C /% | 1.8 | 1.7 | 1.7 |
| Hot modulus of rupture /MPa | |||
| at 1 250 °C | 17.2 | 14.0 | |
| at 1 400 °C | 3.4 | 5.2 | 9.2 |
| at 1 500 °C | 1.2 | 3.1 | 6.4 |
Table 1 Typical catalogues of commercial magnesia-chrome bricks
| Catalogue | Type I | Type II | Type III |
|---|---|---|---|
| Bonding mode | Silicate-bonded magnesia-chrome | Direct-bonded magnesia-chrome | Rebonded fused-grain magnesia-chrome |
| Aggregate as main component | Mid-grade sintered magnesia | High grade magnesia | Fused magnesia chrome |
| Chemical composition /mass% | |||
| MgO | 61.12 | 58.90 | 58.45 |
| Cr2O3 | 18.89 | 20.80 | 20.89 |
| Al2O3 | 5.86 | 6.66 | 6.73 |
| Fe2O3 | 11.20 | 12.50 | 12.28 |
| CaO | 1.04 | 0.84 | 0.68 |
| SiO2 | 1.31 | 0.43 | 0.56 |
| Bulk density /(g · cm-3) | 3.20 | 3.27 | 3.31 |
| Apparent porosity /% | 16.5 | 15.5 | 15.0 |
| Cold crushing strength /MPa | 60.0 | 62.5 | 70.0 |
| Thermal expansion at 1 600 °C /% | 1.8 | 1.7 | 1.7 |
| Hot modulus of rupture /MPa | |||
| at 1 250 °C | 17.2 | 14.0 | |
| at 1 400 °C | 3.4 | 5.2 | 9.2 |
| at 1 500 °C | 1.2 | 3.1 | 6.4 |
Fig. 1 Microstructure of silicate-bonded magnesia-chrome brick 1. Periclase; 2. Chromite; 3. Secondary chromite
Fig. 1 Microstructure of silicate-bonded magnesia-chrome brick 1. Periclase; 2. Chromite; 3. Secondary chromite
Fig. 2 Direct bond between magnesia particles in magnesia-chrome brick
Fig. 2 Direct bond between magnesia particles in magnesia-chrome brick
Fig. 3 Microstructure of direct-bonded magnesia-chrome brick
Fig. 3 Microstructure of direct-bonded magnesia-chrome brick
Fig. 4 Microstructure of rebonded fused-grain magnesia-chrome brick
Fig. 4 Microstructure of rebonded fused-grain magnesia-chrome brick
Table 2 Chemical composition of common chrome ores /mass%
| Source of chrome ore | South Africa | India |
|---|---|---|
| SiO2 | 0.31 | 0.83 |
| Al2O3 | 14.66 | 10.54 |
| Fe2O3 | 27.87 | 16.71 |
| CaO | 0 | 0.36 |
| MgO | 10.28 | 12.67 |
| Cr2O3 | 46.12 | 58.71 |
| LOI | 0.76 | 0.18 |
Table 2 Chemical composition of common chrome ores /mass%
| Source of chrome ore | South Africa | India |
|---|---|---|
| SiO2 | 0.31 | 0.83 |
| Al2O3 | 14.66 | 10.54 |
| Fe2O3 | 27.87 | 16.71 |
| CaO | 0 | 0.36 |
| MgO | 10.28 | 12.67 |
| Cr2O3 | 46.12 | 58.71 |
| LOI | 0.76 | 0.18 |
Table 3 XRD semi-quantitative S-Q compounds in chrome ores of South Africa and India
| Compounds in chrome ore | Formula | Iron valence | S-Q of South Africa | S-Q of India |
|---|---|---|---|---|
| Chromite, magnesian | (Fe0.51Mg0.49)(Cr0.73Al0.27)2O4 | Fe2+ | 34.8% | 31.6% |
| Iron silicon spinel | (Fe0.324Si0.676)(Fe0.963Si0.037)2O4 | Fe2+ + Fe3+ | 1.6% | 5.2% |
| Magnesium aluminum chromium spinel | (Al0.32Cr1.68)MgO4 | 3.2% | 16.8% | |
| Iron alumochromate | Fe(AlCrO4) | Fe2+ | 10.9% | 20.6% |
| Iron chromium trioxide | FeCrO3 | Fe3+ | 11.4% | |
| Magnesium aluminum iron spinel | MgAl0.8Fe1.2O4 | Fe3+ | 7.2% | 23.3% |
| Magnesioferrite, aluminian | (Mg0.32Fe0.68)(Al0.70Mg0.68Fe0.62)O4 | Fe2+ + Fe3+ | 22.5% | |
| Maghemite-Q, syn | Fe2O3 | Fe3+ | 6.9% | |
| Gibbsite, syn | Al(OH)3 | 0.6% | 2.0% | |
| Chlorite-serpentine | (Mg,Al)6(Si,Al)4O10(OH)8 | 0.9% | 0.5% |
Table 3 XRD semi-quantitative S-Q compounds in chrome ores of South Africa and India
| Compounds in chrome ore | Formula | Iron valence | S-Q of South Africa | S-Q of India |
|---|---|---|---|---|
| Chromite, magnesian | (Fe0.51Mg0.49)(Cr0.73Al0.27)2O4 | Fe2+ | 34.8% | 31.6% |
| Iron silicon spinel | (Fe0.324Si0.676)(Fe0.963Si0.037)2O4 | Fe2+ + Fe3+ | 1.6% | 5.2% |
| Magnesium aluminum chromium spinel | (Al0.32Cr1.68)MgO4 | 3.2% | 16.8% | |
| Iron alumochromate | Fe(AlCrO4) | Fe2+ | 10.9% | 20.6% |
| Iron chromium trioxide | FeCrO3 | Fe3+ | 11.4% | |
| Magnesium aluminum iron spinel | MgAl0.8Fe1.2O4 | Fe3+ | 7.2% | 23.3% |
| Magnesioferrite, aluminian | (Mg0.32Fe0.68)(Al0.70Mg0.68Fe0.62)O4 | Fe2+ + Fe3+ | 22.5% | |
| Maghemite-Q, syn | Fe2O3 | Fe3+ | 6.9% | |
| Gibbsite, syn | Al(OH)3 | 0.6% | 2.0% | |
| Chlorite-serpentine | (Mg,Al)6(Si,Al)4O10(OH)8 | 0.9% | 0.5% |
Fig. 5 Various types of chromite spinels in magnesia-chrome brick 1) Ex-solved spinel; 2) Euhedral spinel; 3) Intergranular spinel
Fig. 5 Various types of chromite spinels in magnesia-chrome brick 1) Ex-solved spinel; 2) Euhedral spinel; 3) Intergranular spinel
Fig. 6 Change of major phases with sintering temperature in magnesia-chrome brick
Fig. 6 Change of major phases with sintering temperature in magnesia-chrome brick
Fig. 7 Hot modulus of rupture as a function of secondary chromite spinel
Fig. 7 Hot modulus of rupture as a function of secondary chromite spinel
Table 4 Influence of firing atmosphere on physical properties of magnesia-chrome brick
| Firing atmosphere from 800 °C to 1 650 °C | 3.0% to 5.6% O2 content (Fuel to air ratio < 1:1) | 0.5% O2 content (Fuel to air ratio > 1:1) | |||
|---|---|---|---|---|---|
| Grade of magnesia-chrome compaction | Low | High | Low | High | |
| Unfired density /(g · cm-3) | 3.08 | 3.22 | 3.08 | 3.23 | |
| Fired density /(g · cm-3) | 2.95 | 3.09 | 3.03 | 3.20 | |
| Firing expansion rate /% | 1.40 | 0.73 | 0.47 | 0.33 | |
| Apparent porosity /% | 19.5 | 18.0 | 16.5 | 16.0 | |
| Hot module of rupture /MPa | at 1 260 °C | 9.7 | 10.5 | 20.0 | 14.6 |
| at 1 482 °C | -- | 1.0 | 2.4 | 2.3 | |
Table 4 Influence of firing atmosphere on physical properties of magnesia-chrome brick
| Firing atmosphere from 800 °C to 1 650 °C | 3.0% to 5.6% O2 content (Fuel to air ratio < 1:1) | 0.5% O2 content (Fuel to air ratio > 1:1) | |||
|---|---|---|---|---|---|
| Grade of magnesia-chrome compaction | Low | High | Low | High | |
| Unfired density /(g · cm-3) | 3.08 | 3.22 | 3.08 | 3.23 | |
| Fired density /(g · cm-3) | 2.95 | 3.09 | 3.03 | 3.20 | |
| Firing expansion rate /% | 1.40 | 0.73 | 0.47 | 0.33 | |
| Apparent porosity /% | 19.5 | 18.0 | 16.5 | 16.0 | |
| Hot module of rupture /MPa | at 1 260 °C | 9.7 | 10.5 | 20.0 | 14.6 |
| at 1 482 °C | -- | 1.0 | 2.4 | 2.3 | |
Fig. 8 Inner cracks of magnesia-chrome brick caused by burning atmosphere
Fig. 8 Inner cracks of magnesia-chrome brick caused by burning atmosphere
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