Pechini method
otherwise
polymerisable complex method; liquid mix technique
(rus. Печини, метод otherwise цитратный метод; метод полимерных комплексов)
—
a method of synthesis of highly homogeneous and finely dispersed oxide materials including formation of complexes and production of polymer gel as an intermediate product.
Description
The Pechini method was proposed in 1967 as a technique of depositing dielectric films of titanates and niobates of lead and alkaline-earth elements in the production of capacitors. Later, the process was customised for the in-lab synthesis of multicomponent finely dispersed oxide materials. The method is based on an intensive blending of positive ions in a solution, controlled transformation of the solution into a polymer gel, removal of the polymer matrix and development of an oxide precursor with a high degree of homogeneity.
During the synthetic process, metal salts or alkoxides are introduced into a citric acid solution with ethylene glycol. The formation of citric complexes is believed to balance the difference in individual behaviour of ions in solution, which results in a better distribution of ions and prevents the separation of components at later process stages. The polycondensation of ethylene glycol and citric acid starts above 100ºС, resulting in polymer citrate gel formation. When the heating temperature exceeds 400ºС, oxidation and pyrolysis of the polymer matrix begin, which lead to the formation of X-ray amorphous oxide and/or carbonate precursor. Further heating of this precursor results in the formation of the required material with a high degree of homogeneity and dispersion.
Today, the Pechini method is widely used in the synthesis of dielectric, fluorescent and magnetic materials, high-temperature superconductors and catalysts, as well as for the deposition of oxide films and coatings. The method’s advantages include its relative simplicity, almost complete independence of the process conditions from the chemistry of positive ions contained in the final material and a relatively low temperature of precursor treatment, due to which the process may occur almost completely without sintering, resulting in the production of nanocrystal powders of refractory oxides. Shortfalls of the Pechini method include the use of toxic ethylene glycol and significant volumes of organic reagents per unit of product mass, a lack of stable citric complexes of some elements (bismuth, silicon, etc.), as well as the partial or complete regeneration of one of the components during pyrolysis of polymer gel (e.g., copper, lead, zinc, ruthenium, etc.).
During the synthetic process, metal salts or alkoxides are introduced into a citric acid solution with ethylene glycol. The formation of citric complexes is believed to balance the difference in individual behaviour of ions in solution, which results in a better distribution of ions and prevents the separation of components at later process stages. The polycondensation of ethylene glycol and citric acid starts above 100ºС, resulting in polymer citrate gel formation. When the heating temperature exceeds 400ºС, oxidation and pyrolysis of the polymer matrix begin, which lead to the formation of X-ray amorphous oxide and/or carbonate precursor. Further heating of this precursor results in the formation of the required material with a high degree of homogeneity and dispersion.
Today, the Pechini method is widely used in the synthesis of dielectric, fluorescent and magnetic materials, high-temperature superconductors and catalysts, as well as for the deposition of oxide films and coatings. The method’s advantages include its relative simplicity, almost complete independence of the process conditions from the chemistry of positive ions contained in the final material and a relatively low temperature of precursor treatment, due to which the process may occur almost completely without sintering, resulting in the production of nanocrystal powders of refractory oxides. Shortfalls of the Pechini method include the use of toxic ethylene glycol and significant volumes of organic reagents per unit of product mass, a lack of stable citric complexes of some elements (bismuth, silicon, etc.), as well as the partial or complete regeneration of one of the components during pyrolysis of polymer gel (e.g., copper, lead, zinc, ruthenium, etc.).
Illustrations
|
Nanopowder BaAl2O4 obtained through annealing of polymer gel at 800 ºС. Author: Valery V. Petrykin, Tohoku University, Japan. From personal files. |
Author
Sources
- Pechini M. P. US Patent 3,3306,97. 1967. — www.google.com/patents/about?id=D3sfAAAAEBAJ&dq=3,330,697 (reference date: 12.12.2011).
- Tai L.W., Lessing P. A. Modified resin-intermediate processing of perovskite powders. Part I. Optimization of polymeric precursors // J. Mater. Res. 1992. V. 7. P. 502–510.
- Tai L.W., Lessing P. A. Modified resin-intermediate processing of perovskite powders. Part II. Processing for fine, nonagglomerated Sr-doped lanthanum chromite powders // J. Mater. Res. 1992. V. 7. P. 511–519.
- Kakihana M., Yoshimura M. Synthesis and characterization of complex multicomponent oxides prepared by polymer complex method // Bull. Chem. Soc. Jpn. 1999. V. 72. P. 1427–1443.