| Intermediate-temperature Solid Oxide Fuel Cells(IT-SOFCs)have become one of the hotspots in the field of energy research due to its green and efficient advantages.In recent years,planar-type IT-SOFCs are gradually moving towards commercialization.In order to obtain a SOFC stack with high output power density and long-term stability,the dense and stable sealing materials are essential.At present,the barium boron aluminum silicate(BaO-CaO-B2O3-Al2O3-SiO2)glass system are commonly used for the SOFC sealing glass materials,but under the long-term SOFC operating condition,some crystals would present in the sealing glass system with crystal structure transformation after a certain heat treatment,which would reduce the thermal expansion coefficient of glass,and then result in the seal failure.In addition,over-burning may occur during the sealing process of the glass,and a large number of irregular holes would appear,which would destroy the density of the sealing material and affect the sealing performance.In response to the above two problems,this topic mainly uses three methods to optimize the performance of BaO-CaO-Al2O3-B2O3-SiO2(BCABS)based sealing glass.(1)Based on the basic formula of the BaO-CaO-Al2O3-B2O3-SiO2(BCABS)series sealing glass studied in the previous laboratory,According to the molar ratio of Ba/Sr=3:0,2:1,1:2 and 0:3,SrO is used to gradually replace the BaO in the formula,denoted as Sr0,Sr1,Sr2 and Sr3 sample.Test results of Raman spectrum,thermal expansion coefficient,viscosity,etc.show that the introduction of SrO reduces the CTE(9.86×10-6?-1)of SrO glass to 9.5×10-6,9.57×10-6 and 9.75×10-6?-1,its Tg,Ts and viscosity are obviously increased,which improves the network structure of the glass;XRD results show that the introduction of SrO could inhibit the crystal transformation of hexagonal barium feldspar to a certain extent.The Sr3 sample without barium oxide remained amorphous before and after the heat treatment,which improved the stability of the sealing glass,indicating that the mixed alkaline earth metal effect is conducive to inhibiting the crystallization of the glass and its crystal transformation.According to the high-temperature microscope and SEM images,Sr3 basically avoids the over-burning phenomenon of SrO during the sealing process,which is relatively dense and has good bonding performance with Ni-YSZ and 8YSZ electrolytes.(2)Based on the BCABS series sealing glass formulations studied in the laboratory,the content of Al2O3 in the raw materials was adjusted.When the Al2O3 content is increased from 0 to 9 wt.%,Al2O3 participates in glass network bonding as a network intermediate,improving the connection of the glass network,so that the CTE of glass before glass heat treatment are increased with the increase of Al2O3 content,and the high temperature viscosity increased as the content of Al2O3 increases.when the content of Al2O3 increases from 9 to 12 wt.%,a part of Al2O3 as a network modifier changes the network structure of the glass,which leads to a decrease in high-temperature viscosity.XRD results showed that,when the content of Al2O3 was 0 wt.%,Bai.55Ca0.45SiO4 crystals were precipitated out of the glass after heat treatment.When the content of Al2O3 is 3 wt.%,barium feldspar and Ba1.55Ca0.45SiO4 crystals are mainly precipitated.Combined with XRD and CTE results,it can be seen that the precipitation of crystals in the process of heat treatment reduces the expansion coefficient of glass.When the content of alumina is ?6 wt.%,it still remains amorphous after heat treatment.Therefore,when the content of Al2O3 is 6?12 wt.%,the thermal stability of the glass is improved to a certain extent,but the SEM shows that there are a few pores,which will increase the thermal expansion coefficient of the glass after heat treatment.(3)The sol-gel method is used for improving the characteristics of chemical uniformity and improve the unevenness of RO-Al2O3-B2O3-SiO2 glass.The experiment in this chapter is based on the four groups of glass in the above experiment(Sr0,Sr1,Sr2,Sr3),to change the preparation process and compare the performance differences of different process samples.In the early exploratory experiment,it was found that when R=2.5(R complex ratio=[CH3COOH]/[TEOS]),W=60(W hydrolysis rate=[H2O]/[TEOS]),and pH is less than 2,good process parameters provide a theoretical basis for the preparation of sealing glass with excellent performance.The results show that after heat treatment,crystalline phases are precipitated in S-SrO and S-Sr1;crystalline phases are not precipitated in S-Sr2,however,the crystalline phases are precipitated by the solid phase method,which shows that the sol-gel method could improve the stability of glass;S-Sr3 has always been amorphous.The CTE results show that the sol-gel method promotes the connection of the glass network.The CTE of the four glasses before and after heat treatment are less than that of the glass prepared by the corresponding solid phase method.Among them,only the CTE of the S-SrO sample meets the sealing material before and after heat treatment,which is 9.32 ×10-6?-1 before heat treatment and 9.17×10-6?-1 after heat treatment.Compared with the solid phase method,the thermal stability of sealing glass is improved. |
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