Title

Transient Liquid Phase Sintering and Joining of Lanthanum Calcium Ferrite

Publication Date

4-2008

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

Major Advisor

Darryl P. Butt

Abstract

Lanthanum calcium ferrite (La1-xCaxFeO3) is a perovskite-type oxide that is used as an oxygen separation membrane and in Syngas production, processes which require them to operate in environments with high temperatures and pressures. A novel transient liquid phase (TLP) method has been applied to sintering and joining La1-xCaxFeO3. The sintering behavior of cold pressed pellets with compositions La0.9Ca0.lFeO3 and La0.75Ca0.25FeO3 was studied using an isothermal method at temperatures up to 1400°C. Sintering had three distinct regions which were dependant on the density that had been achieved. The rate limiting mechanism for sintering was particle rearrangement in the presence of a liquid phase until approximately 65-70% theoretical density was reached. From approximately 65-90% theoretical density, sintering was rate limited by a combination of particle rearrangement in the presence of a liquid phase and solution reprecipitation. After approximately 90% theoretical density was reached, sintering was rate limited by solution reprecipitation. For La0.9Ca0.lFeO3 the apparent activation energy for sintering controlled by particle rearrangement in the presence of a liquid phase was 200±50 kJ/mol. The apparent activation energy for solution reprecipitation was 700±180 kJ/mol. For La0.75Ca0.25FeO3the apparent activation energy for sintering controlled by particle rearrangement in the presence of a liquid phase was 230±60 kJ/mol. The apparent activation energy for solution reprecipitation was 630±160 kJ/mol.

The TLP method was also used to successfully join La0.9Ca0.lFeO3 to itself resulting in a single phase joint interface. The joined assemblies were characterized using scanning electron microscopy. The joint interfaces tended to contain some residual porosity after joining.

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