| Proton ceramic fuel cell(PCFC)is a kind of solid state fuel cell with proton as the conductive load particle.It can be used for power supply at the medium and low temperature of 400?700?.Compared with other fuel cells,it has the advantages of high operational reliability,long life and high fuel efficiency.However,the further application of PCFC is restricted by two problems:the electrolyte material is difficult to prepare because of its high melting point.When the connectors are used to assemble the PCFC cell stack,the connectors are affected by high temperature wet oxygen and high temperature reducing atmosphere,which puts forward higher requirements for the connection of the connectors/PCFC functional components.Therefore,the high-temperature proton conductor BaCe0.7Zr0.1Y0.1Yb0.1O3-?(denoted as BCZY-Yb)was firstly prepared by solid-state reaction sintering method(SSRS)in one step,and Crofer22 APU stainless steel was used as the connecting body.After the protective layer of manganese cobalt spinel(Mn,Co)3O4 was prepared on the surface,Ag-CuO solder was used to connect the electrolyte sheet BCZY-Yb and the surface modified Crofer22 APU stainless steel to realize the study of PCFC cell stacked assembly.Firstly,the SSRS method was used to prepare PCFC electrolyte sheet BCZY-Yb ceramics by one-step sintering under air condition.The ceramic density was 98.424%,and the grain size was 7?10um.The effect of sintering process on the phase structure,microstructure morphology and density of BCZY-Yb ceramics is a typical cubic perovskite structure.As the sintering temperature increases from 1300?to 1500?,the density of ceramics increases,but the grain size also increases,which affects the mechanical properties.Finally,the sintering parameters of 1400?/24h were selected and used in the following research.In order to improve the Cr volatilization of ferrite stainless steel joints under PCFC service conditions,the(Mn,Co)3O4 spinel protective layer with excellent high temperature conductivity and CTE matching was sintered in Crofer22 APU by air heating sintering method,microwave heating sintering method and pre-oxidization-microwave heating sintering method.It is found that the coating density of MnO and Co precursor powders obtained by air heating sintering is very low,and the bonding interface cracks due to the excessive stress of the coating during sintering.MnO and Co are strong wave-absorbing media,which are rapidly densified due to the combined effect of arc discharge loss,magnetic loss and electrical conduction loss in the heating process,so that the air can not enter the inner coating to participate in the reaction and spinel components can not be obtained;MnO and Co are strong wave-absorbing media,which are rapidly densified due to the combined effect of arc discharge loss,magnetic loss and electrical conduction loss in the heating process,so that the air can not enter the inner coating to participate in the reaction and spinel components can not be obtained.Only the precursor powder was pre-oxidized to spinel powder by air heating sintering method,then brushed on the surface of stainless steel and then sintered by microwave heating,the coating with good bonding with stainless steel matrix was obtained,and the coating density reached 98.187%.The effect of microwave heating temperature on the microstructure of(Mn,Co)3O4 spinel coating was studied.It was found that with the microwave heating temperature increasing from 900?to 1200?,the coating density first increased and then decreased,and the composition of the coating changed at 1200?.BCZY-Yb/Crofer22APU stainless steel(coated with manganese cobalt spinel)was bonded by Ag-CuO solder.The microstructure and phase composition of the joint interface and fracture were analyzed by SEM/EDS,XRD and transmission electron microscopy(TEM).The effects of solder composition and process parameters on microstructure,mechanical properties and linear expansion coefficient(CTE)of the joint were investigated.The optimal process parameters were determined as CuO content 2mol.%,1050°C/30min,The typical interface structure of the joint is Fe-Cr/(Mn,Co,Cu)3O4/CuO/Ag(CuO)/CuO/(Ba-Cu-O)+(Ce-Cu-O)/BCCZY-Yb.The Cu in the filler metal is dissolved in the(Mn,Co)3O4 spinel coating to form a more compact(Mn,Co,Cu)3O4 spinel phase,which improves the high temperature conductivity and CTe matching properties.The reaction mechanism at the side interface of stainless steel was analyzed by TEM,and the bonding relationship between CuO and Ag solder and(Mn,Co,Cu)3O4 spinel phase was discussed.In order to improve the CTE difference of the joint,the arc grooves were machined on the ceramic side,and the influence of the width and spacing of the arc grooves on the residual stress distribution of the joint under tension and compression and the improvement of the joint strength were analyzed.Finally,glass G18 was used to connect BCZY-Yb/Crofer22APu stainless steel(coated with manganese cobalt spinel).After holding at 900?for 1h,the glass-crystal mixed joint structure was obtained,and the crystal phase was mainly Ba2Si3O8 and black rod-like Bam GSi2O5.The structural structure of the joint was Fe-Cr/(Fe,Cr)2O3/Mn1.5Co1.5O4/Poor Ba phase/BCAS/Ba2Si3O8/Ba Si2O5/Ba2Si3O8/BaCe O3/BCZY-Yb.The influence of connection temperature and time on the mechanical properties of the joint was studied.With the increase of connection temperature from 800?to 950?,the fluidity of G18 was improved,the pores were reduced,and dispersed-distributed crystals were precipitated.When the temperature was higher than 950?,the sealing material flowed seriously and the crystal continued to grow,which had a serious impact on the joint performance.When the connection time is less than 40min,the fluidity of the sealing material is poor and the joint defects are more.Only when the connection time is up to 1h,the good match between the viscosity of the sealing material and the crystallization rate can be achieved and the excellent joint can be obtained. |
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