Study On Preparation And Performance Of BCABS Glass-based Composite Sealing Material For Solid Oxide Fuel Cell

Sealing material is one of the key materials of IT-SOFC.Finding a suitable sealing material is of great significance to promote the rapid development of SOFC.The thermal expansion value of BaO-CaO-Al₂O₃-B₂O₃-SiO₂(BCABS)sealing glass is about 11×10^-6K^-1and its thermal expansion performance can be adjusted,which has attracted wide attention from researchers.However,glass-based sealing materials are brittle at room temperature and easily cause cracks;in addition,glass has a crystallization process at high temperatures,and if the glass crystallization is out of control,it may cause fatal damage to the sealing material.In response to the appeal,in order to further improve the mechanical properties and long-term thermal stability of the BaO-CaO-Al₂O₃-B₂O₃-SiO₂glass system,this paper adjusts the glass composition,and then adds spherical alumina,magnesium oxide and other spine bones to the glass system.Material to prepare glass/ceramic composite sealing material to improve its sealing performance.The research content and conclusions of this article are as follows:(1)Four types of BaO-CaO-Al₂O₃-B₂O₃-SiO₂-x Co₃O₄sealing glass were prepared by the fusion quenching method and named BCABS-1,BCABS-2,BCABS-3 and BCABS-4.Co₃O₄does not change the network structure of the glass,but reduces the Tg temperature of the glass,and has little effect on the softening temperature and thermal expansion coefficient;it can be seen from the wettability experiment that it enhances the use temperature of the glass,and the sealing temperature is set according to the application conditions.It is 850?/1h;Co₃O₄also enhances the mechanical properties of the glass,and the bending strength of BCABS-3 reaches 72MPa after crystallizing.Through the study of chemical compatibility with Crofer22 APU stainless steel interface,it is found that the interface between the four sealing glasses and the adjacent metal connectors is well combined.When the addition of Co₃O₄exceeds 1wt%(BCABS-4),the diffusion of Cr element occurs.An oxide layer containing Cr is formed at the interface,which enhances the chemical compatibility of glass and stainless steel;but SOFC has been operating at600?800?for a long time,and the diffusion of Cr element is detrimental to the long-term thermal stability of SOFC.Comprehensive comparison BCABS-3 is more in line with the requirements of SOFC sealing,and is also used as the next glass matrix for the preparation and research of glass/ceramic composite materials.(2)The thermal properties,crystallization behavior,long-term thermal stability,mechanical properties and interface chemical compatibility of Mg O-glass composite sealing materials are studied.We add Mg O powder to BaO-CaO-Al₂O₃-B₂O₃-SiO₂(BCABS-3)glass system,named BCABS-M00,BCABS-M05,BCABS-M10,BCABS-M15 and BCABS-M20 according to the added amount.The addition of Mg O adjusts the thermal expansion coefficient and thermal conductivity of the base glass within a certain range,and increases with the increase of Mg O content.The CTE value of BCABS-M20 reaches the maximum 12.65×10^-6k^-1,which exceeds the SOFC Maximum CTE requirements;the increase in thermal conductivity makes the sealing material more compatible with the thermal performance of stainless steel,which is beneficial to alleviate the thermal stress of SOFC;through sintering experiments,it is found that Mg O helps to maintain the shape and size of the composite sealing compound when used at high temperatures;Mg O It also improves the mechanical properties of the composite sealant,but the increase is not significant after the addition amount exceeds 10wt%.Among the composite sealing materials,the thermal expansion coefficient of BCABS-M10 after 100h heat treatment is 11.41×10^-6k^-1,which is the closest to the CTE(11.5×10^-6k^-1)of Crofer22APU;the bending strength is 101MPa,which is higher than the glass matrix And the sealing interface of BCABS-M10 and Crofer22 APU is well combined,there is no cracking and no Cr element diffusion.In summary,adding 10wt%Mg O is the best adding ratio for comprehensive sealing performance,and BCABS-M10 seal can be used as a candidate sealing material in SOFC.However,Mg O reacts with glass to form more new phases,and the thermal expansion coefficient changes greatly,which leads to poor thermal stability,which is detrimental to the long-term operation of SOFC.The thermal properties,crystallization behavior,long-term thermal stability,mechanical properties and interface chemical compatibility of Al₂O₃-glass composite sealing materials were studied.We added spherical Al₂O₃powder with better fluidity and thermal properties to the BaO-CaO-Al₂O₃-B₂O₃-SiO₂(BCABS-3)glass system,and named them BCABS-A00,BCABS-A10,BCABS-A20 according to the added amount,BCABS-A30 and BCABS-A40.The spherical Al₂O₃particles are added to the base glass to adjust the thermal expansion coefficient and thermal conductivity of the base glass within a certain range,and with the increase of the spherical Al₂O₃content,the thermal expansion coefficient decreases and the thermal conductivity increases;BCABS-A30 and BCABS-A40 The CTE value is lower than 9.5×10^-6k^-1,which does not meet the CTE matching requirements of SOFC;through sintering experiments,it is found that the spherical Al₂O₃helps maintain the shape and size of the composite sealant when used at high temperatures;the spherical Al₂O₃also improves the composite The thermal stability and mechanical properties of the sealing material,heat treatment at 750?for different times,the standard deviation of the CTE value of the sealing material decreases with the increase of the Al₂O₃content;the flexural strength increases with the increase of the Al₂O₃content.The average long-term thermal expansion coefficient of BCABS-A10 is 10.46×10^-6K^-1,which meets the matching requirements of SOFC thermal expansion coefficient.After 100h heat treatment,the flexural strength of BCABS-A10 can reach 140.6MPa,which is about 60%higher than that of BCABS-A00.The morphology and energy spectrum analysis of the interface between the metal connector with Crofer22APU show that Cr does not diffuse into BCABS-A10,and it has good chemical compatibility with Crofer22APU.Therefore,BCABS-A10 seal can be used as a candidate sealing material in SOFC.