Study On Preparation Of Porous Platinum/Zirconia Composite

With the development of modern technology,people’s requirement of materials is getting higher and higher.Metal/ceramic composite materials have many advantages such as low thermal expansion,chemical stability,corrosion resistance,high hardness,while both excellent metal toughness and impact resistance.The addition of metal platinum to yttrium stabilized zirconia（YSZ）ceramic composites is one of the hot materials,which are widely used.As a catalytic material or biological material,platinum/YSZ sintering process of porous maintenance is very important.In this paper,the evolution of YSZ particles and the influence of the presence of platinum on the growth of YSZ particles were discussed by sol-gel method.The size of ZrO²⁺ and C₂O₄^2-,stability of the sol,the types of zirconium oxide clusters and the crystal form were analyzed by means of light scattering nanoparticle analysis,transmission electron microscopy（TEM）and infrared spectroscopy.The results showed that the reaction temperature was controlled at 45℃,the particle size of the gel was small and the dispersion was stable.The zirconium oxide clusters formed in the sols were composed of four-membered rings,six-membered rings and large octa-rings.They were composed a variety of structures such as symmetrical growth of apices and chain patterns.The presence of yttrium ions in the sol was favorable for the early formation of zirconium oxide clusters in the sol towards the tetragonal structure of zirconia,with preferential zirconia tetragonal or cubic crystals.Thermogravimetry differential thermal analysis（TG-DTA）and X-ray diffraction（XRD）analysis showed that gel dehydration when heated to 160℃,the formation of amorphous ZrO₂ with the temperature in the range between 335 and 340 ℃,and at 500 ℃ can be observed tetragonal crystal structure formation.When sintered to 1450℃,the relative density of ZrO₂ particles was 98.5%.When Pt was added to the sol,the Pt particles would block the dense growth of the YSZ particles.The effects of bismuth and bismuth oxide on the growth of Pt/YSZ were investigated.At low temperature,bismuth and platinum can form fusible alloy.After 500 ℃ liquid phase enrichment growth,Pt/YSZ would form larger spherical mesh particles.The presence of bismuth oxide promoted the growth of YSZ particles,and at 500 ℃ the dispersed YSZ particles can be grown into a network.Under low temperature sintering,the addition of bismuth oxide can obtain the porous structure of porous Pt/YSZ material.In order to obtain the porosity of Pt/YSZ material under high temperature sintering,a spherical poly（methyl methacrylate）（PMMA）was used as a pore-forming agent,and observed the microstructure of porous YSZ materials by scanning electron microscopy（SEM）when sintered at 1450 ℃.The porosity of the YSZ material was obtained by Archimedean drainage method.The flexural strength of YSZ material was tested by the three-point bending test method.The results showed that the spherical pores were well maintained,the pore structure was clear and the porosity was also high when adding 40 wt.%,3 μm spherical PMMA at 1450℃ for 2 h.With the increase of the holding time,when the YSZ partices growth,migration and merging,the pore size changed,the pore structure deformed and gradually disappeared,and the porosity decreased.The results showed that the flexural strength increased with the increase of PMMA particle size at the same content of PMMA,and the particle size was from 3.0 to 5.5 μm.The flexural strength of porous YSZ material was up to 100 MPa.The influence of PMMA on the sintering Pt/YSZ composites was investigated on the basis of the porous YSZ.The results showed that the mass fraction of Pt was between 5 wt.%and 50 wt.%,the holes made by PMMA were uniform and the shape was better.When the mass fraction of Pt was increased from 50 wt.%to 80 wt.%,the number of pores decreased or disappeared.When the mass fraction of Pt increased from 5 wt.%to 80 wt.%,the relative density of Pt/YSZ composites increased from 42%to 90%,the porosity decreased from 60%to 10%,and the porosity did not changed much.The results showed that the growth of Pt particles was mainly at 900℃,and the Pt particles were distributed between the small YSZ particles.The results showed that Pt and YSZ were different from each other at different sintering temperatures.After 900℃,YSZ began to grow obviously.From 900℃ to 1450℃,Pt particles and YSZ were intertwined into three-dimensional porous network.When the Pt content was 70 wt.%,the metal Pt phase and the YSZ phase formed a continuous phase,and had a large phase contact interface,which was favorable for conductivity,catalysis and mechanical properties.The results showed that the peak current and peak area of Pt/YSZ composites were much larger than that of pure Pt electrode,and the peak current value increased with the increase of Pt mass fraction.The results showed that Pt/YSZ composites had good electrochemical catalytic activity.