Preparation of Oxalate by Precipitation Method with Polyethylene Glycol and Formation Process of the Precipitate

Naofumi UEKAWA*, Hiroyuki ICHIKAWA, Akira ITSUKI, Sayaka ISHII, Kazuyuki KAKEGAWA† and Yoshinori SASAKI

Faculty of Engineering, Department of Materials Technology, Chiba University; 1-33 Yayoi-cho Inage-ku, Chiba-shi 263-8522 Japan
† Department of Materials Technology, Graduate School of Natural Science, Chiba University; 1-33 Yayoi-cho Inage-ku, Chiba-shi 263-8522 Japan

Multicomponent oxalate consisted of Fe3+ and M2+(M=Ni, Cu, Co, Zn) was prepared by heating the polyethylene glycol (PEG) solution of metal nitrate hydrate at 358 K for 3 h. The PEG-cation complex in the solution was oxidized by the nitrate ion so that the oxalate was obtained. The structure and the composition of the cations in the obtained oxalate depended on not only the composition of the PEG solution but also the molecular weight of PEG. The crystallinity and the particle size of the oxalate increased with an increase of the molecular weight of PEG. The relation between the cation composition in the PEG solution and that in the obtained oxalate also depended on the molecular weight of PEG. The two models that describe the formation process of the PEG-cation complex and the oxalate was examined. In the first model, it is assumed that the coordination of Fe3+ ions and that of M2+ occurs independently. In the second model, it is assumed that the coordination of Fe3+ and that of M2+ occurs cooperatively. The relation between the cation composition in the PEG solution and that of the obtained oxalate was derived from these models. According to the comparison between the experimental result and the consequences derived from the models, it is shown that the coordination of M2+ to PEG always occurs near the site where the coordination of Fe3+ occurred. The PEG-cation complex was formed under the cooperative process.


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