Effects Of Microstructures Of Raw Materials And The Oxides Additives On The Preparation Of Cementite

In this paper, the introduction about iron carbide's fundamental properties, application, and the research history and recent status is given. And the effects of reacting temperature and atmosphere, sulfur-contained mixtures, gangue, basic metal oxidation and alloy elements on the formation and properties of iron carbide are summarized elaborately. In order to settle the problem of low conversion rat, low reaction rate and the unclear effect of ore structure in the process of the iron carbide production, the study of influence of oxidation addition and microstructure of ore on the iron carbide formation is carried out. The conclusions are summed up as following:1. The thermodynamics of the reaction between ore and CH4-H2 gas mixtureThe process of the reaction between ore and CH4-H2 gas mixture consists of reduction and carbonization. With the thermal data of all the reactants, the free energyΔG for different reacting function can be calculated out, furthermore the equilibrium diagram of Fe-C-H-O can be made out. Through the diagram, some conclusions come out: at the same temperature and total pressure, the formation of iron carbide become hard with the increase of H2O partial pressure; the region of iron carbide formation shrinks with the temperature increase; it is confirmed by experiment that the condition of 105Pa, 1023K and CH4/H2=30/70 is reasonable to make iron carbide.2. The effects of microstructure of the ore and reduced iron on the formation of iron carbide At the 1023K, the experiment of the reaction between the three different ore and CH4/H2=30/70 gas mixture is taken out. After the analysis of TG and XRD, it is found that the ore with spongy structure is easy to be reduced and carbonized. After the measurements of SEM, EDS and aperture degree to the original ore and the partial-carbonized or no-carbonized samples, the following conclusions can be gotten: the reduction and carbonization of ore happen from exterior into interior; the ore with sponge structure is easy to be reduced completely and the reduced iron is spongier, which are beneficial for iron carbide formation.3. The influence of the oxides additives on the formation of iron carbide Brazilian ore is selected as raw ore. Different contain of Cr2O3,MnO2,TiO2,V2O5 is added into the raw ore powder. These samples are reacted with CH4/H2=30/70 gas mixture at 1023K. And all the samples are measured by TG, XRD and M?ssbauer spectroscopy. Then some conclusions can be summarized as following: the reduction and carbonization of ore have no effect after Cr2O3,MnO2 added into the ore; the reaction can be retarded by TiO2, but the reaction can be promoted by V2O5. At the present experiment condition, 96% iron carbide exists stably in the sample with 1%V2O5 after reacting 30 minutes.4. The kinetics of the reaction between CH4-H2 gas mixture and the ore with V2O5 It is found that the model of shrinking of un-reacted core can be utilized at present experiment condition. The function between reacting time and the rate of progress can be...