synonymHydrogen reduction(The method of preparing metal by reducing metal oxide with hydrogen at high temperature) Generally refers to hydrogen reduction
Hydrogen reduction means that hydrogen is used tometallic oxideThe process of making metal by reduction.And other methods (such asCarbon reduction, zinc reduction method, etc.).It is widely used in the production of tungsten, molybdenum, cobalt, iron and other metal powders as well as germanium and silicon.
Chinese name
Hydrogen reduction
Foreign name
hydrogen reduction process
Interpretation
Reduction of metal oxides with hydrogen to produce metals
With the global impact on COtwoAs greenhouse gas emissions are increasingly restricted, the traditional carbon metallurgy process is facing great challenges.Therefore, in recent years, Europe and Japan have successively launched the "ultra-low COtwoSteel making "(ULCOS) and" COURSE50 "plans, in which it is proposed that partial oxidation of natural gas and transformation of coke oven gas to obtain high HtwoThe content of direct reduction and blast furnace reduction ironmaking with concentrated reducing gas, in order to significantly reduce CO in metallurgical industrytwoDischarge of.However, to realize the practical application of hydrogen reduction in metallurgy, it is necessary to further understand the reaction characteristics and control methods of hydrogen reduction.
althoughIron oxideThere have been many studies on the hydrogen reduction of C, but there are still no exact explanations for some special reaction behaviors.Abnormal temperature effect in the reduction process of magnetite, that is, at a certain reduction temperature, the reduction rate does not increase with the increase of temperature, but decreases with the increase of temperature[1]。
Hydrogen reduction process of ferrous oxide particles
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At 773K, the product maintained its appearance, but there were many small holes on the surface;At 873K, the original appearance was basically maintained, but the surface became rough and uneven, with a large number of holes and small protrusions;At 973K, the aggregation of surface protrusions became larger;At 1023K, there is obvious sintering phenomenon, and there are many large holes on the surface;At 1073K and 1173K, the dendritic structure appeared on the surface, and at 1173K, there was more obvious sintering phenomenon.
The local surface began to generate holes and expand inward, and some small protrusions appeared;A large number of micropores appeared on the surface and the number of small protrusions increased at 4-8 min;When the reaction is completed, the surface void becomes smaller and there is obvious sintering phenomenon.The reduction process at 1023K showed a similar process of product structure change. Compared with the product morphology at 973K, the characteristics of the reaction stage appeared earlier, a large number of micropores appeared at 2min, and the sintering characteristics were more obvious when the reaction was completed.As the reduction temperature rises and the reaction rate accelerates, a large number of dendritic products appear from the beginning of the reaction, and these dendritic products are continuously sintered and densified in the reaction process, showing different product morphology characteristics from low-temperature reduction.
According to the above observed changes in the surface morphology of the product under different temperature conditions, the following hydrogen reduction process can be inferred: at the beginning of the reactionIron oxideLocal points on the surface (such as cracks, crystal defects and other active points) undergo hydrogen reduction, and expand inward to form small holes. At the same time, the generated active iron generates protrusions through surface diffusion and gradually develops into iron whiskers. Because of these porous product structures, the reduction gas and product gas can diffuse smoothly, and the interface chemical reaction can be carried out smoothly;However, as the reaction proceeds, the product layer continues to thicken, and the reduction products begin to appear sintering and densification. The diffusion of reduction gas and product gas is affected, and gradually becomes the limiting link of the reaction[2]。
Hydrogen reduction at low temperature
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At low temperature, the sintering process is relatively slow. In most of the reduction time, the product structure will not affect the gas diffusion, so the low-temperature hydrogen reduction process is the interface reaction speed control.With the increase of temperature, the sintering process continues to accelerate, and the effect of product sintering on the reaction gradually increases. At 973 ～ 1073K, when the reaction fraction is not too high, the surface sintering starts to hinder the diffusion of gas, which shows that the reduction fraction increases rapidly to a certain extent and then suddenly flattens,In the later reduction process, the reduction fraction is lower than that at low temperature.With the further increase of temperature, the rate of early chemical reaction also increases rapidly, and the reduction degree reached before the formation of dense structure affecting gas diffusion also increases continuously, even at 1273K, the reduction process has ended before the formation of dense product structure[3]。
summary
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773 ～ 1273 K was studied by thermogravimetryFerrous oxideThe isothermal hydrogen reduction kinetics showed an abnormal temperature effect in the temperature range of 973 ～ 1073 K.The morphology of the products under different reaction conditions was observed.The results showed that with the increase of reaction temperature, the pores on the surface of the reduction products increased, and the dendritic characteristics increased significantly, while the surface sintering phenomenon was obvious at 973K and 1023K.The sintering and densification of reduction products are important factors affecting hydrogen reduction.With the sintering of the product, the diffusion of the reducing gas and the product gas is hindered, making the speed control link of the reaction gradually change from the interface chemical reaction speed control to the diffusion speed control.With the increase of temperature, this transition is gradually advanced, which is the main reason for the abnormal temperature effect.At higher temperature, the reduction process is over before the formation of dense product structure, so there is no impact on the reduction process[2]。
