Hydration of lanthanum tungstate (La/W = 5.6 and 5.3) studied by TG and simultaneous TG-DSC

详细信息    查看全文

• 作者：Ragnhild Hancke ; Anna Magras&oacute ; Truls Norby ; Reidar Haugsrud ; ^{reidar.haugsrud@smn.uio.no}
• 关键词：Lanthanum tungstate ; Inherently oxygen deficient proton conductor ; Hydration properties ; Thermogravimetry ; TG&ndash ; DSC ; H/D isotope exchange
• 刊名：Solid State Ionics
• 出版年：2013
• 出版时间：4 February, 2013
• 年：2013
• 卷：231
• 期：Complete
• 页码：25-29
• 全文大小：503 K

文摘

The hydration properties of lanthanum tungstate (La/W = 5.6 and 5.3) have been studied by means of thermogravimetry in the temperature range 1100 to 300 ¡ãC. The relative weight was independent of the oxygen partial pressure between oxidizing and reducing conditions over the entire temperature range showing that the oxygen stoichiometry is close to constant. The materials take up water upon decreasing temperature and increasing water vapor partial pressure, eventually reaching saturation. Moreover, there is a significant reversible change in the relative weight upon shifting from H₂O to D₂O containing atmospheres. The results are interpreted based on the most recent defect model for dissolution of protons in lanthanum tungstate yielding standard enthalpy and entropy changes of hydration of ¦¤H_Hydr⁰ ¡Ö -90 kJ mol^? 1 and ¦¤S_Hydr⁰ ¡Ö -115 J (mol K)^? 1. The hydration enthalpy was verified by direct measurements using TG-DSC, yielding - 85 kJ mol^? 1. The thermodynamic parameters obtained herein are in general agreement with literature values from fitting conductivity data, and may be considered an improvement of these.