Corrosion Behavior of Fe-Cr Alloy in Molten (Li-K)_2CO_3 at 650 °C

The corrosion behavior of 0.382,3 mole fraction neutralization air atmosphere. The result is clear. Pure iron. 5, and 0, alloys are subject to faster rot. The addition of the heart below 10 does not help f improve the corrosion resistance of Fe. The addition of Cr to 20 and 25 can improve the corrosion resistance of Fe. On the corrosion mechanism of pure iron and VC alloys.

Molten carbonate fuel cells have attracted much attention due to their advantages such as high power generation efficiency and low pollution, and have made great progress. However, the low life and high cost of batteries currently restricts the commercialization process, which is mainly related to molten carbonic acid. Corrosion of battery materials caused by salt electrolytes involves the dissolution of battery cathode materials, corrosion of anode and bipolar plate materials, and the like. Bipolar plate materials are generally made of stainless steel or Ni-based alloys, but these materials have poor corrosion resistance, especially on the anode side, and cannot meet practical requirements. Around this, we asked about the corrosion behavior of a variety of stainless steels in the 6501 melting 0.62 to 0.382003 mole fraction, the same as in the following. It was found that the corrosion rates of the 33310 and 33446 stainless steels were low, and the inner layer of the alloy surface oxide films formed a dense National Natural Science Foundation of China. 59401012 Received the first draft date 1999102, received the revised draft date 200000 Author brief introduction male. Born in 1965, the researchers, Ph.D., although the corrosion rate of the alloy is low, 30, the corrosion of the alloy is more serious. 161. SpiegelW et al. also studied the corrosion behavior of a high Cr-containing Fe-based alloy in molten 0.6204382003, found high, with deletion alloy. The corrosion rate is significantly lower than that of iron, but in the formation of the alloy surface, 2,3 is gradually converted to a soluble scale.2,4. It is clear that alloying elements have different mechanisms of action for 6, base alloys. This paper studies the corrosion behavior of different alloys in the melting ruler 2003 to improve the mechanism of action.

1 experimental method Corps 25 mass fraction, under the same alloy. The materials were respectively cut into 10mmxl0mmx2mm specimens, and the specimens were ground up to No. 600 sandpaper. The experiment was conducted in a high temperature box resistance furnace. The experimental molten salt was 0.622, 30.382, 3 mole fraction. The experimental temperature was 650. The mixed salt was placed in an alumina crucible and first heated to the experimental temperature after 350 dries treatment 241. The etching product of the corrosion kinetic curve 2.2 of Ming 1 was used, and the phase composition of the corrosion product on the alloy surface was analyzed by ray diffraction. As a result, all sample surfaces were formed. , 2 phases, while the alloy surface also forms the LiFe508 phase. 2 is the cross-sectional morphology of Fe and FVC alloys that were etched 100 in a 650, melting bar 2003. Combined with ray diffraction analysis, it can be seen that the outermost layer of the pure iron surface corrosion product is 0 corpse 6, 2 and the inner layer is an oxide. The outermost layer of the 5,1 alloy surface corrosion product is still. 02, the outer oxide layer. The innermost layer is a mixed oxide of Fe and C. The outermost layer of Ft10C alloy is 2 dark, and the inner layer is a mixed oxide layer of 5, 8 and 6, respectively, without forming a continuous 203 layer. Corpse 20, the outermost layer of the alloy. 2, the oxide in the middle layer is rich in the innermost layer, the outermost layer of the alloy is also 02, the oxides in the outermost layer are mainly small, and the innermost layer is 203 layers. From the above corrosion product analysis results, it can be seen that the better corrosion resistance of the 200 and 25,1 alloys is attributed to the formation of a continuous oxide-rich layer.

The sample is immersed in the molten salt, and the sample is taken out at intervals 6. Boiling distilled water was used to wash away the residual salt from the sample surface. Weigh the sample and change it. Get the alloy corrosion kinetics curve. The corrosion of the samples was observed by ray diffraction, scanning electron microscopy and energy spectrum analysis.

2 Experimental results and discussion 2.1 Corrosion kinetics 1 Corrosion kinetics curves in 1 ft. 20, 3 melt jin. From this set of curves can be cooked out.

Pure iron 5 and Zhi 10 are subject to faster corrosion. The total weight gain of the pure iron after corroding 100 has reached 18.9. 2. The corrosion weight gain of the valence 5 alloy is similar to that of pure iron, but the corrosion rate of 10 is slightly higher than that of pure iron. Obviously, 5 and 10, the Canadians did not increase their corrosion resistance. The corrosion rate of Fe0C and Fe25Cr alloys with higher C content is significantly reduced, and the rot resistance of Ft25C alloy is better than 2.3. Discussion From the above analysis, it can be seen that pure iron and 0, alloy surface turbidity products are the outermost. 13 are 6, 6,620 and 625 alloy surfaces also form a continuous rich oxide layer, while the factory, 5 and 6,100 alloys do not. Corrosion kinetics show that the Fe,C mixed oxide layer formed by the Fe5CrffiFelOCrA gold surface does not provide better protection than the LiFeO2 layer. However, the better corrosion resistance of the 620, and 25 alloys is attributed to the formation of an oxide-rich layer.

In the case of carbonate, there is the following equilibrium at 650, and the scale of the standard, 1 free energy based on these values ​​can be calculated. In this experimental condition, the activity of Li2O and 20 are respectively, melting. The alkalinity of 20,3 is much greater than that of molten alloys 20,3, so the surface oxide film of the alloy may be mainly formed by the reaction in the course of corrosion. The product is not a ruled product. The experimental results also confirmed this. In the early stage of corrosion, the outermost layer of the pure iron surface corrosion product is Fe203, and 6, the outermost layer of the alloy corrosion product is still mainly 6203, but the inner layer is the mixed oxide layer or the rich oxide layer. Studies have been conducted but chemically dissolved in molten carbonates. Formation, 2 and 1, participate in the cathodic reaction. Formed, 7 and, widely separated + diffused to the oxide film at the interface of the molten salt is reduced to 2 parts can contribute to the long side of the alloy surface oxide film. At the same time, the concentration of 2 tends to increase at the molten salt interface of the oxide film. Therefore, there is a negative gradient of 2 concentration from the semi-molten salt air interface at the molten salt interface of the oxide film. 2 and 3 of the alloy surface can form a solid state reaction with 2, along the 62, 3 molten salt interface. 6,2.

With the progress of corrosion. Fei+p diffuses through the alloy surface oxide layer. In the oxide film, the following reactions occur at the 6,2 molten salt interface to maintain. Corpse; 02 due to growth. 6,2 is almost insoluble in molten carbonate. Therefore, the molten salt interface of the film can gradually form stable 6 and 2 layers. Therefore, in a definite sense, it can be considered that the 6th and 2nd layers have a certain protective effect. Although there is a negative gradient of ion concentration from the molten salt interface of the oxide film to the molten salt air interface, the alkali oxide film of the alloy does not undergo alkaline dissolution and reprecipitation reaction of the oxygen ratio film. Therefore, under the conditions of this article, the traditional mechanism of alkaline dissolution is negligible. In the supply and demand system. Sexual dissolution can also be performed in the form of Equation 4, but due to the presence of the interface from the oxidized peritoneal molten salt to the molten salt air interface, the concentration is positive and negative. Therefore, it will not happen that the decomposing and re-precipitating reactions of Daihuamiao are for 100 alloys. In addition to the formation of 02, the following reactions are also formed from the reaction thermodynamically. Other alloys are held in pure iron. 5, and 2, also 6 to form. The valences of 5,6 phases in the experiment were not related to the fact that the formation of 1508 phases in these alloys may differ from the alloy composition and lead to different stages of their formation. The increase in gold-containing rots is greater than that in pure iron and 5,1 alloys may be related to the formation of 5,8 for Dingwei 150, phase growth. The + must be extended inward. In the 82,3 interface, the crystal structure of the reaction-response oxides is generated. Defect structure and yin. The cation expansion and other factors determine the growth mechanism of yttrium oxide. The growth of 1303 can be carried out by the diffusion of 1 and ytterbium, but the rate of increase and decrease is very low. The growth of spinel oxides can also be carried out by the mutual expansion of metal ion oxygen ions. The rate of oxygen expansion is 1 small dry gold. The diffusivity of the dices 8!02 is cubic oxide 0 and 5 8 is a spinel oxide, although the defect structure and ion expansion of 102 and 1504 are not clear at present, but according to the growth of oxides other than telluride, it can be inferred that the out diffusion of iron is significantly faster. Intrinsic diffusion of oxygen, which has been confirmed by experimental facts 4. Intra-diffusion of another 1 is also possible, otherwise. 5, 8 will not be formed. Although not yet clear. 2 and. 5,8 defect structure and ion diffusion, but can be inferred from corrosion product analysis and corrosion kinetic measurements. For low-zero-content, 50,100 alloys, the corrosion product inner layer and mixed oxides do not provide better corrosion resistance than 6,6.

Content, so in the corrosion process can form a continuous rich oxide layer FeCr2O4, Cr2O3. Compared with 6,2, this rich oxide layer has better compactness, so the corrosion rate of FV20C and Fe25Cr alloys is significantly reduced. The corrosion resistance of the 250 alloy is better than that of the 200 alloy because the alloy has a higher 0 content and a continuous rich 203 protective layer is formed.

3 Conclusions The 650, C molten Li2.03 suffers faster corrosion, while the 200 and 25 alloys have better corrosion resistance. A stable LiFC02 layer exists on the outermost layers of pure iron and FtCr alloy face corrosion products. The corrosion resistance of Fe5Cr and Fe alloys is not better than that of pure iron, which is the formation of protective properties of the alloy surface. The better corrosion resistance of alloys 20 and 25 is due to the formation of a continuous, rich oxide layer with good protection inside the oxide layer.

Du Senlin, Lu Hongde, Lu Lianqing Chemical Progress, 1994;129