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Investigation of the mechanism of sol-gel formation in the Sr(NO3)2/citric acid/ethylene glycol system by solution state 87 Sr nuclear magnetic resonance spectroscopy

Published online by Cambridge University Press:  31 January 2011

Xiaohua Li
Affiliation:
School of Chemistry and Biochemistry, and Molecular Design Institute, Georgia Institute of Technology, Atlanta, Georgia 30332-0400
Vishal Agarwal
Affiliation:
School of Materials Science and Engineering, and Molecular Design Institute, Georgia Institute of Technology, Atlanta, Georgia 30332-0245
Meilin Liu*
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245
William S. Rees Jr*
Affiliation:
School of Chemistry and Biochemistry, and School of Materials Science and Engineering, and Molecular Design Institute, Georgia Institute of Technology, Atlanta, Georgia 30332-0400
*
a)Address all correspondence to this author. e-mail: will.rees@chemistry.gatech.edu e-mail: meilin.liu@mse.gatech.edu
a)Address all correspondence to this author. e-mail: will.rees@chemistry.gatech.edu e-mail: meilin.liu@mse.gatech.edu
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Abstract

The polymerization mechanism of a modified Pechini process was investigated by 87Sr nuclear magnetic resonance spectroscopy for the mixed solution of strontium nitrate, citric acid, and ethylene glycol. The C-ratio (the ratio of citric acid to metal ions in the polymer complex) is suggested to have a strong influence on the quality of the derived film. An analysis of the chemical shift variation, as a function of C-ratio, indicates the presence in the solution of two species: solvated strontium ions and strontium ions bound to the polymer complex, with a stoichiometry of 1:7. A polymeric precursor model based on this stoichiometry is proposed. Through a relaxation rate study of the strontium sites, it was found that the polymerization mechanism is predominantly bimolecular within the concentration region being studied. The equilibrium rate constant for the polymerization was calculated to be 104 s−1. A kinetic study of the fast cation exchange between the two identified strontium sites indicates that the inhomogeneity of the polymeric network leads to film cracking during pyrolysis.

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Articles
Copyright
Copyright © Materials Research Society 2000

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