China's Refractories ›› 2022, Vol. 31 ›› Issue (1): 16-23.DOI: 10.19691/j.cnki.1004-4493.2022.01.003
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GUO Zongqi1,*(), MA Ying2, LI Yong3
Online:
2022-03-15
Published:
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.
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
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 |
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 |
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% |
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 |
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