Thermal Stability Analysis And Optimization Of CaO-BaO-Al₂O₃-B₂O₃-SiO₂ Sealing Glass Of SOFC

Intermediate temperatures-solid oxide fuel cells?IT-SOFCs?is an all solid-state power generation device that converts chemical energy of fuel and oxidant into electric energy directly,which mainly adopts a planar structure with advantages of simple preparation process,low cost,high power density and short current collection path.Improving the thermal stability of the sealing material is one of the key factors for the commercial application of planar IT-SOFCs.But the sealing material which is widely used is a Ba-rich boron aluminosilicate sealing glass at present.This project focuses on the study of thermal stability of Ba-rich boron aluminosilicate sealing glass under IT-SOFCs working conditions,and optimizes the glass formula from the perspective of inhibiting crystal transformation to obtain a relatively stable sealing material.The main research contents are as follows:?1?Based on the formula of 12.47 CaO-56.13 BaO-4.29 Al₂O₃-8.79 B₂O₃-17.15SiO₂?wt.%?sealing glass,CaO-BaO-Al₂O₃-B₂O₃-SiO₂ sealing glass has been prepared through adjusting the B₂O₃ content to 0,4.4,8.79 and 13.2 wt.%and labeled as SCBA0,SCBA1,SCBA2 and SCBA3,respectively.The effects of B₂O₃ content on the structure and properties of glass were researched by various test methods.Combined with the infrared peak and its quantitative analysis,it can be seen that with the increase of B₂O₃content,the content of[BO₃]in the glass structure keeps increasing and the[SiO₄]keeps decreasing.The introduction of B₂O₃ reduces the densification temperature of glass?about 973¹123 K?and greatly improves the wettability of SCBA powders on the surface of 8YSZ electrolyte.Barium feldspar crystals were precipitated from SCBA glass at the sealing temperature of 1073K.It was further confirmed by SEM that the bonding ability of SCBA1 and SCBA2 glass with 8YSZ electrolyte was good.?2?On the basis of the formula of SCBA2 sealing glass,the content of Al₂O₃ is increased by 0,6.24 and 12.48 wt.%,and the three glasses obtained were labeled as BSCA0,BSCA1 and BSCA2,respectively.Through differential heat and thermal expansion instrument test and analysis,it can be concluded that in BSCA glasses,Al₂O₃,the network formation body involved in glass network bonding,can effectively enhance the network structure of glass,improve the crystallization activation energy of glass,and at the same time reduce the thermal expansion coefficient of sealed glass.The VFT results show that the viscosity of glass increases from 10^6.72dPas to 10^7.43dPas at the operating temperature of IT-SOFCs?973 K?.Combined with XRD and thermal expansion curve analysis,it can be seen that the increase of glass viscosity effectively inhibits the transformation of BaAl₂Si₂O₈ crystal precipitated in BSCA glass from hexagonal phase to monoclastic phase,reduces the decline of thermal expansion coefficient,and improves the thermal stability of BCAS series sealed glass.?3?Based on the results of differential thermal analysis of BSCA1 glass,the crystallization kinetic index n of BSCA1 glass was studied through non-isothermal crystallization kinetics.Two different methods were used to demonstrate each other,and the mean kinetic energy index n value of BSCA1 glass was?1,indicating that the crystal nucleated on the glass surface in the heat treatment process and increased outward by one dimension.SEM results show that a large number of fibrous crystals are formed between sealing glass and electrolyte interface,which is consistent with the calculated results.?4?In order to directly avoid precipitation of barium feldspar from Ba-rich boron aluminosilicate sealing glass,Al₂O₃ content of SCBA1 was reduced to 0 wt.%,and the glass obtained was labeled as BCBS.Ba_1.55Ca_0.45SiO₄ precipitated from BCBS sealed glass did not change after 0,160 and 320 h insulation of 973K.Further analysis by XRD shows that the crystal content in glass is 10.72,12.32 and 16.67 wt.%,respectively.The results of the thermal expansion curve show that the content change of Ba_1.55Ca_0.45SiO₄crystal has no significant effect on the thermal expansion coefficient of the BCBS sealing glass,and the value has been maintained at about 11.15×10-6 k-1,which is within the range of the actual sealing requirements of SOFC.After 973K insulation for 480 h,BCBS sealing glass and SOFC electrolyte have good bonding properties.