| In this study, firstly the mineral phase distribution in representative steel slags was observed by the back scattered electron images and the energy dispersive analysis of a scanning electron microscop, the compositions of different mineral phase were determined by statistics, and combined with the existing knowledge of mineral phase in steel slag and the analysis in this study, the mineral phases were classified; secondly, since the system of steel slag is very complex, with an aim to deeply understand why the hydration activity of f-CaO in steel slag is low and provide theoretical support to deal with its volume expansion caused by f-CaO, taking the formation process and the compositions of f-CaO into consideration, mono-component f-CaO was prepared from calcinating analytical grade CaO for different times to explore the influence mechanisms of the calcination time on the hydration activity of mono-component f-CaO, and thermodynamic theory was applied to prove the hydration activity of solid solution of FeO, MnO and CaO was lower than that of mono-component f-CaO; finally, bi-component f-CaO of CaO·aFeO1.5 system and tri-component f-CaO of CaO·aFeO1.5·bMnO2 system, which were not same but similar to bi-component f-CaO of CaO·aFeO system and tri-component f-CaO of CaO·aFeO·bMnO system in steel slag, were originated from calcinating the mixture of CaO, Fe2O3 and MnO2 with a certain proportion to explore the influence mechanisms of Fe2O3 on the hydration activity and expansion of bi-component f-CaO of CaO·aFeO1.5 system and Fe2O3 and MnO2 on the hydration activity and expansion of tri-component f-CaO of CaO·aFeO1.5·bMnO2 system, in order to provide useful and fundamental knowledge for complex system through studying simplified systems.In steel slags, the morphology and distribution of mineral phases was not uniform, the black calcium silicate phase was in round or leaf shape, the white calcium iron aluminium phase was crosslinking shape, the iron magnesium phase was black in center and light white in edge, the iron magnesium manganese calcium phase was light gray and irregular or striation shape, the calcium iron phase was in large particle shape, the gathering calcium iron manganese phase was in gray small particle shape, and there were little amount of f-MgO with gathering black small particle shape and Fe particles with light and round shape; the calcium silicate phase, the calcium iron aluminium phase and the iron magnesium phase were in the representive form of C2S and C3S, Ca2?Fe,Al?2O5 and FeO·0.5MgO, and the compositions of the iron magnesium manganese calcium phase, the calcium iron phase and the calcium iron manganese phase were varied; the iron magnesium phase and the iron magnesium manganese calcium phase can be classified into the complex RO phase, and f-CaO included the calcium iron phase and the calcium iron manganese phase.The crystallinities and microstructures of mono-component f-CaO calcinated for different times were different. Compared with mono-component f-CaO calcinated for 1,5 and 7 h, its crystal linitie was more complete, its microstructure was denser, and the hydration ratio in the first 8 h was lower when mono-component f-CaO was calcinated for 3 h. The difference of the hydration ratios of mono-component f-CaO calcinated for different times was mainly shown in the first 8 h in the hydration process, and all samples hydrated fully after 8 h. The high temperature calcination could restrain the hydration activity of f-CaO, but the restrained degree was limited. Based on this, FeO and MnO may dissolve in f-CaO during the steelmaking process, so thermodynamic theory was applied to further prove the hydration activity of solid solution of FeO, MnO and CaO was lower than that of mono-component f-CaO.The sequence of the hydration activity of the components in f-CaO was as follow:Ca2Fe2O5; Ca3Fe1.5Mn1.5O8<CaO in tri-component f-CaO<CaO in bi-component f-CaO< mono-component f-CaO; due to the hydration reactions of CaO, Ca2Fe2O5 and Ca3Fe1.5Mn1.5O8, the volumes of the solid phases increased by 97.88%,43.44% and 52.02%, respectively; even CaO in simulative f-CaO underwent calcination at 1600?, it can hydrated obviously at normal temperature within a short period, but the hydration activity of Ca2Fe2O5 and Ca3Fe1.5Mn1.5O8 was so weak that they hydrated slightly even under the condition of autoclave hydration at P=2.0 MP, T=216? for 3 h, and they cannot hydrate obviously at normal temperature within a short period. It can be speculated that in steel slag the sequence of the hydration activity of the components in f-CaO was as follow:solid solutions CaO-FeO and CaO-FeO-MnO<CaO in tri-component f-CaO<CaO in bi-component f-CaO <mono-component f-CaO, and the volume expansion rates of the different components in f-CaO were different; if f-CaO can contact with H2O completely in the hydration process of blended cement containing steel slag, CaO in f-CaO will fully take part in hydration reaction within a short time and not lead to the volume expansion of steel slag after cement hardens, but solid solutions CaO-FeO and CaO-FeO-MnO in f-CaO cannot hydrate obviously at normal temperature within a short period and will continue to hydrate after cement hardens, which must result in the volume expansion. |
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