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The Measurements of High Temperature Thermochemical Properties of Rare Earth Manganites with Electrical Conductivity

稀土导电锰矿高温热化学性质的测定

基本信息

批准号：
62550486
负责人：
OHGUSHI Tatsuo
金额：
$ 1.15万
依托单位：
TOYOHASHI UNIVERSITY OF TECHNOLOGY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

项目摘要

The aim of this project is to obtain the high temperature thermochemical properties of rare earth manganites. We could obtain these quantities from the measurements of isothermal electrical conductivity and thermogravimetric analysis as a function of oxygen partial pressure. When these manganite phases is annealed under low oxygen partial pressure at high temperature, they decompose into rare earth sesqui oxides and manganese monoxide. Both results from thermogravimetric analysis and electrical conductivity measurements were in good agreement for the temperature and oxygen partial pressure at the decomposition. Therefore the chemical potential diagram for the equilibria between rare earth manganites and the decomposed oxides could be obtained in satisfactory precision. By using these results at several temperatures (900 - 1200 C of temperature and 1 - 10^<-22> atm of oxygen partial pressures), the free energies, enthalpy and entropy changes for LnMnO_3 phases could be obtained from the second law treatment of thermodynamics.Also heat capacities of several manganites at high temperatures and enthalpy changes of phase transitions of some of these manganites and another type of rare earth manganites with higher structure, e.g. BaLn_2Mn_2O_7, were measured by DSC method. After these measurements are accomplished with a satisfactory precision, the thermochemical properties of these rare earth manganites are to be obtained with more precise from by using the third law treatment of thermodynamics.

本项目的目的是获得稀土锰氧化物的高温热化学性质。我们可以从等温电导率和热重分析的测量中获得这些量作为氧分压的函数。当这些锰氧化物相在高温下在低氧分压下退火时，它们分解成稀土倍半氧化物和一氧化锰。热重分析和电导率测量的结果与分解时的温度和氧分压非常一致。因此，可以获得精确的稀土锰氧化物与分解氧化物平衡的化学势图。利用这些结果，在900 - 1200 ℃和1 - 10 μ atm氧分压下，由热力学第二定律处理，可以得到LnMnO_3相的自由能、焓变和熵变，并用DSC法测定了几种锰氧化物的高温热容和其中一些锰氧化物以及另一种具有更高结构的稀土锰氧化物如BaLn_2Mn_2O_7的相变焓变。<-22>在这些测量以令人满意的精度完成后，这些稀土锰氧化物的热化学性质将由热力学第三定律处理得到更精确的结果。