| The nano-scale MnCo2O4 powder was prepared by means of Sol-Gel. High temperature oxidation resistance of metallic interconnect and the electrical conductivity under high temperature environment were improved by adding MnCo2O4 coating on the surface of SUS430 with the method of screen printing. The special contents of research and the related conclusions are as follows.(1) MnCo2O4 powder was prepared by means of Sol-Gel. The stability of the formed gel was compared. XRD and TEM are employed to analyze the phase composition of the MnCo2O4 powder and and the microstructure, as well as the particle size of the MnCo2O4 powder. The effect of different complex agent (citric acid, EDTA and EDTA-citric acid), pH value (weak acidic, neutral and weak alkaline) and sintering temperature (600℃, 700℃,800℃ and 900℃) on the performance of MnCo2O4 powders were studied. The best technology conditions are found.The results indicate that the effect of complex agent with EDTA-citric as the complex agent is better than citric acid or EDTA alone. Effect of complex agent under the weak alkaline is more ideal than weak acid or neutral, when the sintering temperature is lower than 700℃, MnCo2O4 powder has small size but with poor crystallity. When the sintering temperature is higher than 800℃, powder has a good crystallinity, but the grain sizes is too big. Nano-scale MnCo2O4 powders which have single phase, uniform size, and high crystallinity is obtained at 750℃ with the preservation time of 2h.(2) MnCo2O4 coating was prepared by the screen printing method. The adhesive strength of the coating was tested by pencil scratching. SEM was employed to observe the surface and cross-section morphology of the coating, the oxidation resistance of the coating was characterized by oxided at 750℃ under the air atmosphere to oxidatie 1000 hours. ASR value of the products was tested to characterize the electrical conductivity of the products during which the temperature range is from 600℃ to 800℃ after oxided at 750℃ under the air to oxidatie 1000 hours.Effect of the sintering atmosphere (the oxidizing atmosphere, neutral atmosphere and the oxidizing atmosphere before heat treatment in reducing atmosphere), the sintering temperature (800℃,900℃ and 1000℃) and the addition amount of binder (lwt%,3wt%,5wt%) on the performance of the coating. The best technology conditions are found. The results show that the coating which was sintered in oxidizing atmosphere before heat treatment in reduced atmosphere is more beneficial to get a high density and has a good adhesion between the alloy. Its oxidation resistance is high and the ASR value is low under high temperature environment, when the sintered temperature is at 800℃,the coating has a poor incorporation with the alloy. When the sintered temperature is 1000℃, the alloy can not withstand high temperature, thus causing the deformation. When the sintered temperature is 900℃, density of the coating is high and with a good incorporation with the coating and the alloy. When the content of EC is 1 wt%, the adhesion between the coating and the alloy is too bad with which the content of EC is 5 wt%. When the add content of EC is 3wt%, effect of the conglutination is fine with a high consistency. The product is obtained with the adding amount of EC being 3wt% which was sintered under the atmosphere with 95%N2+5%H2 at 900℃ and kept 3 h. Then sintered at 800℃ under the air to keep 10h, the weight gain of the product is 0.14mg/cm2 after oxided at 750℃ under the air and kept 1 OOOh. Its weight increased one-sixth compared with the uncoated sample. The ASR value is 0.026Ωcm2 after oxided at 750℃ which kept 1000h under the air, its magnitude is two levels of lower than the uncoated sample. The MnCo2O4 coating can effectively reduce the oxidation rate and degree of oxidation of SUS430 alloy, and also can improve the conductivity of SUS430 alloy significantly at high temperature. |
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