阳离子场强对BaO-SiO_(2)-Ln_(2)O_(3)微晶玻璃结构及高温性能影响

Effect of Cation Field Strength on Structure and High-temperature Properties of BaO-SiO_(2)-Ln_(2)O_(3)Glass-ceramic

SiO_(2)-BaO基微晶玻璃以其膨胀系数高、耐高性能优异而成为耐高密封领域研究的热点,但稀土氧化物对该类封接玻璃改性的影响研究尚不多见。本工作研究不同高阳离子场强(Cation field strength,CFS)的稀土氧化物取代传统碱土氧化物BaO对新型富稀土—SiO_(2)-BaO-Ln_(2)O_(3)(SBLn,Ln=La、Sm、Er、Yb)系列玻璃的网络结构、结晶行为、微观结构和高温性能的影响。随着稀土阳离子场强由2.82(La^(3+))增大到3.98(Yb^(3+)),SBLn玻璃的玻璃转变温度(T_(g))、析晶起始温度(T_(x))、析晶峰值温度(T_(p))均逐渐增加,说明高稀土阳离子场强有利于提高SBLn玻璃的热稳定性。四类富稀土SBLn玻璃的结晶相均由BaSiO_(3)和BaSi2O5相组成,随稀土阳离子场强增大,BaSiO_(3)相减少、BaSi2O5相增多,稀土元素只存在于玻璃相中,不参与晶相析出。随着稀土阳离子场强增加,SBLn微晶玻璃的热膨胀系数(Coefficient of thermal expansion,CTE)由12.52×10^(–6)/℃增大到13.13×10^(–6)/℃(30~800℃),但析晶量下降导致软化温度从1313.5℃降至1174.1℃。总之,富稀微晶玻璃材料高热膨胀系数大于12×10^(–6)/℃、软化温度均高于1150℃,且在700℃高温下的直流电阻率大于106Ω·cm,说明富稀土微晶玻璃密封材料具有在固体氧化物燃料电池、氧传感器、铂薄膜热敏电阻器等高温场景下的应用前景。

The SiO_(2)-BaO-based glass-ceramics have become the focus of research in the field of high sealing resistance due to their high expansion coefficient and excellent high resistance,but the effect of rare earth oxide on modification of this kind of sealing glass-ceramics is rarely reported.Here,the effects of rare earth elements with different cation field strength(CFS)replacing traditional alkaline-earth oxide BaO on the network structure,crystallization properties,microstructures,and high-temperature resistivity of a new type of rare-earth rich-SiO_(2)-BaO-Ln_(2)O_(3)(SBLn,Ln=La,Sm,Er,Yb)series glass were studied.With the increase of rare earth cation field from 2.82 in La3+to 3.98 in Yb^(3+),the glass transition temperature(T_(g)),crystallization initiation temperature(T_(x))and crystallization peak temperature(T_(p))of SBLn glass are increased,implying that the SBLn glass with higher rare earth cation field strength is more stable.Crystalline phases of the four SBLn glasses are composed of BaSiO_(3)and BaSi2O5 phases.When rare-earth cation field strength increases,the BaSiO_(3)phase decreases while the BaSi2O5 phase increases.Rare-earth elements only exist in the glass phase and do not participate the crystal phase precipitation.The crystallization amount decreases with the increase of rare earth cation field,coefficient of thermal expansion(CTE)of SBLn glass-ceramic increases from 12.52×10^(–6)/℃to 13.13×10^(–6)/℃(30-800℃),but softening temperature decreases from 1313.5℃to 1174.1℃.In short,the CTE,softening temperature and DC resistivity at 700℃of the SiO_(2)-BaO-Ln_(2)O_(3)glass-ceramics are greater than 12×10^(–6)/℃,1150℃and 106Ω·cm,respectively,indicating that the rare-earth-rich glass-ceramic sealant has a promising application prospect in the field of high sealing resistance,such as solid oxide fuel cell,oxygen sensors,platinum thin-film thermistor under elevated temperature.