水热法制备环境障涂层用硅酸镱粉体的性能研究

Properties of Ytterbium Silicate Powder for Environmental Barrier Coating with Hydrothermal Method

采用水热法,以九水硅酸钠和六水氯化镱为原料,以去离子水为介质,以NaF为矿化剂,一步制备出高纯硅酸镱粉体.采用XRD、SEM等手段,研究了水热温度、水热时间等水热条件对硅酸镱粉体的晶相结构以及微观形貌的影响,并对水热法合成硅酸镱粉体的机理进行了分析,最后将粉体压制成块,表征了所制备粉体的热胀系数。结果表明,在230℃-250℃保温24 h以上可获得高纯、均匀的硅酸镱粉体。当镱硅摩尔比例分别为0.95和1.90时,可分别获得高纯相的焦硅酸镱(Yb_(2)Si_(2)O_(7))和单硅酸镱(Yb_(2)SiO_(5)),在1200℃的平均热胀系数分别为3.0×10^(-6)/K和4.3×10^(-6)/K,导热系数在1300℃以下均低于4.8W/(m·K),对SiC_(f)/SiC复合材料具有良好的热匹配性能和隔热性能,满足环境障涂层对粉体材料的应用要求。

Ytterbium silicate powders were prepared by using hydrothermal method,with Na2SiO_(3)·9H_(2)O and YbCl_(3)·6H_(2)O as raw materials,water as solvent and NaF as mineralizer.The effects of hydrothermal conditions,including temperature and time,on phase structure and microstructure of the ytterbium silicate powders were studied,by using XRD and SEM.The hydrothermal reaction mechanism of the ytterbium silicate was elucidated.Finally,the powders were pressed into blocks to characterize th eir coefficients of thermal expansion.Ytterbium silicate powders with uniform morphology and high dispersion behavior could be obtained after hydrothermal reaction at 230-250℃for 24 h.When the molar ratios of Yb/Si were 0.95 and 1.90,high purity ytterbium pyrosilicate(Yb_(2)Si_(2)O_(7))and ytterbium monosilicate(Yb2SiO5)were formed,with coefficients of thermal expansion to be 3.0×10^(-6)/K and 4.3×10^(-6)/K,respectively,at 1200℃,while their thermal conductivity were both below 4.8 W/(m·K)at 1300℃.The powders exhibited properties comparable with those of SiC_(f)/SiC composite in thermal matching and heat-insulating characteristics,which meet the application requirements as environment barrier coatings.