The Pechini Method

Somewhat similar to the Pechini method is the combustion synthesis, or autoignition technique, that was presented by Kingsley and Path in 1988 [69]. Here, metal nitrate salts are reacted with an organic fuel (usually urea, glycine or citric acid) in a strongly exothermic reaction to form the crystalline oxides at 

In order to circumvent the calcination treatment that may lead to desorption and decomposition of the organic stabilizers and uncontrolled grain growth, some more elaborate combined approaches were developed. Schmidt et al., for example, 

Alternatively, alcohols can be used as solvents for water-free sol-gel processing and, in contrast to the media mentioned above, they are actively involved in the 

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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. 

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. 

Marin R, Sponchia G, Riello P, Sulcis R, Enrichi F (2012) Photoluminescence properties of YAG Ce, Pr phosphors synthesized via the Pechini method for white LEDs. J Nanoparticle Res 14 1-13... 

To further understand the synthesis mechanism used in this work, which uses gelatin instead of ethylene glycol, it is necessary to review the traditional polymeric precursor method proposed by Pechini (Pechini, 1967). The Pechini method involves the formation of stable metal-chelate complexes with certain alpha-hydroxycarboxyl adds, such as dtric acid, and polyesterification in the presence of a polyhydroxy alcohol, such as ethylene glycol, to form a polymeric resin. The metal cations are homogeneously distributed in the polymeric resin, which is then calcined to yield the desired oxides. The most common materials used as source of cations are nitrate salts since they can be fully removed at low temperatures (400 - 500 °C). The synthesis mechanism of the modified Pechini method used in this work can be explained in three basic steps, as shown in Fig. 2. It stands out by its simplicity and low cost, using only citric acid, gelatin and metal nitrates as reagents. 

Steps in thin film with the Pechini method. 

He H, Fu RL, Wang H, Song X, Pan Z, Zhao X, Zhang X, Cao Y (2008) Li2SrSi04 Eu phosphor prepared by the pechini method and its apphcation in white light emitting diode. 

The Pechini method is a representative example of this approach as it is the most widely used polymer complex method. The original patent [47] describes the formation of a polymeric network by polyesterification of an a-hydroxy-carboxylic acid (e.g., citric add) and a polyhydroxy-alcohol (e.g., ethylene glycol). It is an effective method for the synthesis of multicomponent oxides by dissolving metal nitrates in water, adding an a-hydroxy-carboxyhc acid to chelate the metal cations, and adding ethylene glycol. Upon heating at moderate temperature (100 "C to 1500 °C), a poly-esterificahon reaction occurs that results in an ester which still contains two alco-... 

When compared to the Pechini method, grinding and calcination of the product are not required. The very fine size and crystalline nature of the powder is believed to be a direct result of the short exposure to high temperatures during the ignition step. With adequate process control, the glycine nitrate process offers a relatively inexpensive route to the preparation of very fine, chemically homogeneous powders. It has been used for the preparation of simple oxides as well as complex oxides (e.g., manganites, chromites, ferrites, and oxide superconductors). 

Seldne et al. [78] investigated the WGS reaction at low temperature (300 °C) over Pt and Pd catalysts supported on several LaBOs (B = Cr, Mn, Fe, Co, and Ni) perovskite oxides prepared using the Pechini method. They observed that perovsldte oxides without active metal showed no activity for the WGS reaction, while those loaded with Pt and Pd exhibited good WGS activity. Interaction between Pt or Pd and the support promotes the WGS reaction. They found that both Pt/LaCoOs and Pd/LaCoOs catalysts have high catalytic activity, although Pt/LaCoOs catalyst deactivated immediately, and Pd/LaCoOs, although initially less active, exhibited superior stability. The cause of deactivation of Pt/LaCoOs was attributed to the reduction of Co and Pt cations. 

Several methods are found in the literature for the synthesis of Ce02-based mixed oxides, including the coprecipitation method [7-10], the hydrothermal method [11], the microemulsion method [3,12], the glycothermal method [13,14], the citrate method [6], and the Pechini method [5]. 

In the second part, we aim to study the temperature-programmed superficial reaction of propane oxidation with CO2 on a Cei Fe c02-a mixed oxide. This mixed oxide was prepared by the Pechini method as described in Ref. [27]. In short, solutions of 0.4 M Ce(N03)3-6 H2O, 0.1 M Fe(N03)2-9H20, and 0.5 M citric acid (CA) were mixed at room temperature. Then, the CA solution was added with increasing temperature up to 60 °C, for 30 min. Finally, a solution of ethylene glycol was added with increasing temperature up to 90 °C, forming a polymeric complex, calcined at 500 °C. 

Baythoun M.S.G., Sale F.R. Production of strontium-substituted lanthanum manganite perovskite powder by the amorphous citrate process. J. Mater. Sci. 1982 17 2757-2769 Bernard M.I.B., Soledade L.E., Santos I.A., Leite E.R., Longo E., Varela J.A. Influence of the concentration of 86203 and the viscosity of the precursor solution on the electrical and optical properties of Sn02 thin films produced by the Pechini method. Thin Solid Films 2002 405 228-233... 

Figure 4-3. Effect of CA/EG ratio in the starting solution on the gel properties in the Pechini method.

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