Pechini methods

This method is well-known and is used for the synthesis of homogeneous multicomponent metal oxide materials it includes a combined process of metal complex formation and in situ polymerization of organics. It relies on the development of complexes of alkali metals, alkaline earths, transition metals, or even nonmetals with bi- and tridentate organic chelating agents such as citric acid [40], 

The method is normally performed as follows [32,39] an aqueous solution of suitable oxides or salts is mixed with an a-hydroxycarboxylic acid, such as citric acid, and EG is added to the solution. At heating, an esterification process runs in the system leading to the formation of a stable gel in which the metal ions remain fixed. In the modified Pechini process, ethylenediaminetetraacetic acid (EDTA) has been used to replace citric acid due to its stronger chelating power. 

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Example. The Pechini method for fuel cell electrode preparation. La, Ba, Mn niU ates - - CgHgO — citrate complex - - C2FI6O2 — gel. Metal nitrates are complexed with citric acid, and then heated with ethylene glycol to form a transparent gel. This is then heated to 600 K to decompose the organic content and then to temperatures between 1000 and 1300K to produce tire oxide powder. The oxide materials prepared from the liquid metal-organic procedures usually have a more uniform particle size, and under the best circumstances, this can be less than one micron. Hence these particles are much more easily sintered at lower temperatures than for the powders produced by tire other methods. 

The Pechini method was originally developed for preparing lead and alkaline-earth... 

Mori M and Sammes NM. Sintering and thermal expansion characterization of Al-doped and Co-doped lanthanum strontium chromites synthesized by the Pechini method. Solid State Ionics 2002 146 301-312. 

The limitations of the Pechini method, like many techniques, hes in the lack of size and morphological control. With traditional sol-gel methods, the particles are part of the gel structure, in the Pechini method the metal cations are trapped in the polymer gel. This reduces the ability to grow controlled shapes. The size is controlled, to an extent, by the sintering process and the initial concentration of metals in the gel. 

White et al. synthesized nanometric La2Cu04 through three techniques auto-ignition, Pechini method, and coprecipitation (White et al., 2008). The NPs were used to fabricate sensing electrodes for NO, and the effect of electrode microstructure on the sensitivity and response time was studied. The response times of the sensors were exponentially dependent on electrode grain size. Sensors with fine-grained electrodes were able to produce a steady-state and consistent voltage at lower temperatures, which improved their response sensitivity. 

Other synthesis methods have also been developed but may not be practiced on a large commercial scale as compared to those indicated above. Examples of syntheses that begin from liquid phase precursors include the sol-gel, hydrothermal, and Pechini methods. In the course of these reaction schemes, polycondensation or precipitation occurs, and the volatile components are removed, often by thermal methods. Other synthesis routes to ceramic materials include the nitridation of metals to form metal nitrides and the carbothermal reduction of oxides to form carbides and borides. 

RONCONI, C. M. and PEREIRA, E. C. Electrocatalytic properties of Ti/Ti02 electrodes prepared by the Pechini method. J. Appl. Electrochem. 31, 2001, pp. 319-323. 

FIGURE 20.7 Flow chart for preparing SrTiOs powders by the Pechini method. 

In Section 20.6 we described the Pechini method for producing SiTiOs powders. Other multicomponent oxide powders such as YBa2Cu307 (YBCO) have been made by a similar process. Identify suitable reactants to make YBCO powders by the Pechini method. 

In the Pechini method, metal ions from starting materials, such as carbonates, nitrates, and alkoxides, are complexed in an aqueous solution with a-carboxylic acids, such as citric acid. When heated with a polyhydroxy alcohol, such as ethylene glycol, polyesterification takes place. Once excess liquid is removed, a transparent resin is formed. The resin is then heated to decompose the organic constituents. After milling and calcination, oxide powders can be obtained accordingly. Various oxide nanopowders have been synthesized by using Pechini or modified Pechini methods [269-276], although less information is available on the fabrication of transparent ceramics with these powders. 

F. 3.52 Flow chart of synthesis of the Yb Lu203 nanociystals with a modified Pechini method. Reproduced with permission from [277]. Copyright 2008, Elsevier... 

Bhattacharyya D, Hazra C, Gangwar P, Sivakumar S, Mahalingam V (2012) Microstructural, optical and c)notoxicity studies of Eu -doped Y2O3 nanoparticles prepared by simple control of the chain length of cross-linkers via pechini method. Sci Adv Mater 4 656-662... 

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