The non-isothermal reduction kinetics and mechanism of Fe2O3-NiO composites with different Fe2O3-NiO compacts using carbon monoxide as reductant were investigated. The results show that the reduction degree increases ...The non-isothermal reduction kinetics and mechanism of Fe2O3-NiO composites with different Fe2O3-NiO compacts using carbon monoxide as reductant were investigated. The results show that the reduction degree increases rapidly with increasing the content of NiO, and the presence of NiO also improves the reduction rate of iron oxides. It is found that NiO is preferentially reduced at the beginning of the reactions, and then the metallic Ni acts as a catalyst promoting the reduction rate of iron oxides. It is also observed that the increase of the Ni O content enhances the formation of awaruite(FeNi3) but decreases the percentage of kamacite(Fe,Ni) and taenite(Fe,Ni). The particle size of the materials tends to be uniform during the reduction process due to the presence of metallic nickel, metallic iron and the formation of Fe-Ni alloy. The concentration of CO in the product gas is greater than that of CO2 at the beginning of the reaction and then slows down. The fastest reduction rate of Fe2O3-NiO composites with CO appears at 400-500 °C, and nucleation growth model can be used to elucidate the reduction mechanism. Nucleation growth process is found to be the rate controlling step when the temperature is lower than 1000 °C.展开更多
Isothermal experiments on the reduction of Fe_2O_3-Cr_2O_3-NiO(molar ratio of Fe-to-Cr-to-Ni is 3:2:2)by graphite were carried out at 1350–1550°C,and effects of various factors on reduction degree were studied.T...Isothermal experiments on the reduction of Fe_2O_3-Cr_2O_3-NiO(molar ratio of Fe-to-Cr-to-Ni is 3:2:2)by graphite were carried out at 1350–1550°C,and effects of various factors on reduction degree were studied.The results show that the reaction rate of the Fe_2O_3-Cr_2O_3-NiO system is fast during the initial period(reduction degree,α<38%),and then the rate decreases until the end of the reduction.Factors such as temperature,carbon content,sample size have a more significant effect during the final stage(α>38%).The metallic product formed at the initial stage(a Fe-Ni alloy)greatly promotes the reduction of Cr2O3 at the final stage.Further,during the reduction of Fe_2O_3-Cr_2O_3-NiO by carbon,interfacial reaction is the rate-controlling step and g(α)=1-(1-α)0.5 is the reaction mechanism for the initial stage,whereas two-dimensional diffusion is the rate-controlling step and f(α)=α+(1-α)ln(1-α)is the reaction mechanism for the final stage.The apparent activation energies are 55.43 k J/mol and 174.54 k J/mol for the initial and the final stages,respectively.展开更多
基金Projects(51304091,U1302274)supported by the National Natural Science Foundation of ChinaProjects(2013FD009,2013FZ007)supported by Applied Basic Research Program of Yunnan Province,ChinaProject(2012HB009)supported by the Candidate Talents Training Fund of Yunnan Province,China
文摘The non-isothermal reduction kinetics and mechanism of Fe2O3-NiO composites with different Fe2O3-NiO compacts using carbon monoxide as reductant were investigated. The results show that the reduction degree increases rapidly with increasing the content of NiO, and the presence of NiO also improves the reduction rate of iron oxides. It is found that NiO is preferentially reduced at the beginning of the reactions, and then the metallic Ni acts as a catalyst promoting the reduction rate of iron oxides. It is also observed that the increase of the Ni O content enhances the formation of awaruite(FeNi3) but decreases the percentage of kamacite(Fe,Ni) and taenite(Fe,Ni). The particle size of the materials tends to be uniform during the reduction process due to the presence of metallic nickel, metallic iron and the formation of Fe-Ni alloy. The concentration of CO in the product gas is greater than that of CO2 at the beginning of the reaction and then slows down. The fastest reduction rate of Fe2O3-NiO composites with CO appears at 400-500 °C, and nucleation growth model can be used to elucidate the reduction mechanism. Nucleation growth process is found to be the rate controlling step when the temperature is lower than 1000 °C.
基金supported by the National Natural Science Foundation of China(20976162,21103149,20906079)Natural Science Foundation of Zhejiang Province,China(R5100266)Significant Science and Technology Project of Zhejiang Province,China(2010C13001)~~
基金Project(51074025) supported by the National Natural Science Foundation of ChinaProject(FRF-SD-12-009A) supported by the Fundamental Research Funds for the Central Universities,China
文摘Isothermal experiments on the reduction of Fe_2O_3-Cr_2O_3-NiO(molar ratio of Fe-to-Cr-to-Ni is 3:2:2)by graphite were carried out at 1350–1550°C,and effects of various factors on reduction degree were studied.The results show that the reaction rate of the Fe_2O_3-Cr_2O_3-NiO system is fast during the initial period(reduction degree,α<38%),and then the rate decreases until the end of the reduction.Factors such as temperature,carbon content,sample size have a more significant effect during the final stage(α>38%).The metallic product formed at the initial stage(a Fe-Ni alloy)greatly promotes the reduction of Cr2O3 at the final stage.Further,during the reduction of Fe_2O_3-Cr_2O_3-NiO by carbon,interfacial reaction is the rate-controlling step and g(α)=1-(1-α)0.5 is the reaction mechanism for the initial stage,whereas two-dimensional diffusion is the rate-controlling step and f(α)=α+(1-α)ln(1-α)is the reaction mechanism for the final stage.The apparent activation energies are 55.43 k J/mol and 174.54 k J/mol for the initial and the final stages,respectively.