The effect of residual carbon on the phase stability of LaPO4 at high temperatures

Samples containing LaPO4 and polymeric binders were heated or hot-pressed in oxygen-poor environments to temperatures as high as 1585 C. Carbon analysis, powder XRD and TGA revealed that the residual carbon from the binders caused the LaPO4 to decompose into a lanthanum-rich phosphate compound, La3P...

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Bibliographic Details
Published inJournal of the European Ceramic Society Vol. 21; no. 6; pp. 751 - 757
Main Authors MAWDSLEY, Jennifer R, HALLORAN, John W
Format Journal Article
LanguageEnglish
Published Oxford Elsevier 01.06.2001
Subjects
Applied sciences
Building materials. Ceramics. Glasses
Ceramic industries
Chemical industry and chemicals
Exact sciences and technology
Miscellaneous
Technical ceramics
Fibrous material
Pyrolysis
Lanthanum Phosphates
Monazite
Polymer
High temperature
Experimental study
Binders
Carbon
Oxide ceramics
Hot pressing
Residue
Sintering
Phase stability
Manufacturing
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Summary:Samples containing LaPO4 and polymeric binders were heated or hot-pressed in oxygen-poor environments to temperatures as high as 1585 C. Carbon analysis, powder XRD and TGA revealed that the residual carbon from the binders caused the LaPO4 to decompose into a lanthanum-rich phosphate compound, La3PO7, or a lanthanum oxide, La2O3, at temperatures above 750 C. These results agree with thermodynamic data, indicating that the driving force responsible for this carbothermic reduction reaction is the free energy of formation of P2O5, which is higher than the free energy of formation of CO above 750 C. It was also observed that this phenomenon would be detrimental to composites of LaPO4 and Al2O3, because LaAl11O18 and LaAlO3 were found to form at the interface, unless the samples were annealed in air after binder burnout. 23 refs.
Bibliography:ObjectType-Article-2
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ISSN:0955-2219
1873-619X
DOI:10.1016/S0955-2219(00)00263-6