The Thermodynamic Calculations And Experimental Studies On The Phase Equilibria Of The Au-Pt-TM(TM=Co,Ni) Ternary Systems

Au and Pt of the precious metals have excellent catalytic performance.Adding some transitional elements such as Co and Ni to form bimetallic/trimetallic catalysts has become a research hotspot at present to further improve catalytic activity and reduce cost.Therefore,the study on the thermodynamics and phase equilibria of Au-Pt-TM(TM=Co,Ni)systems has important guiding significance for design and application of the catalytic.In this work,CALPHAD method was used to conduct thermodynamic calculations of Au-Pt-TM(TM=Co,Ni)systems and the results were used to guide the design of alloy composition and diffusion couple.To verify the predicted results,Scanning electron microscope(SEM),Energy Dispersive Spectrometer(EDS)and Electron Probe Micro-Analyzer(EPMA)were used to analyze the morphology and the compositions of the alloys and the diffusion couple.And Xray Diffractometer(XRD)was used in this work to analyze the structure of alloys.The main results are as follows:(1)Based on the thermodynamic assessments of Au-Co,Au-Pt and Pt-Co binary systems,the isothermal sections of the Au-Pt-Co ternary system at 600-1250? were extrapolated in this work.It shows that there is a ternary miscibility gap between(Au)and(Pt.Co)when the temperature is above 850?.Below 750?,in addition to the miscibility gap between(Au)and(Co)and(Pt),there is also ternary order-disordered transitions between(Au)and CoPt and CoPt3 ordered phases.(2)Based on the thermodynamic analysis,the phase diagram of Au-Pt-Co ternary system was efficiently determined by the combination of alloy method and diffusion couple technique.The ternary miscibility gap of Au-Pt-Co system at 850? was measured.And using the same method,the two-phase equilibrium relations between(Au)and(Co),CoPt,CoPt3 and(Pt)of this system at 600? were well determined and the composition ranges of the three-phase regions were extrapolated.The experimental results well verify the predicted results at 850 and 600?.(3)Thermodynamic analysis and calculation of Au-Ni,Au-Pt,Pt-Ni binary phase diagrams were carried out.And combined with a series of experimental data of Au-Pt-Ni system at higher temperatures,the Gibbs free energy of liquid phase and fcc phase in the ternary system was optimized.Based on this,the phase equilibrium relations of Au-Pt-Ni system at 850? and 500? were predicted,which laid a foundation for the experimental study on the lowtemperature phase equilibrium of Au-Pt-Ni ternary system.(4)According to the results of thermodynamic calculations,the composition of the key ternary alloy was determined to be Au10Pt45Ni45.The two-phase equilibrium between(Au)and(Ni,Pt)was measured at 850?,and the experimental results agree well with the calculated prediction.And by combining the alloy with diffusion couple,the phase equilibrium relations among Au,(Ni),Ni3Pt,NiPt,(Pt)and(Pt)in Au-Pt-Ni ternary system at 500? were determined.Except for the rich Pt region,the experimental results are basically consistent with the predicted phase diagram.In the rich Pt region,the solid solubility of(Pt)is larger than that predicted by calculation.