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Materials Chemistry and Physics 109 (2008) 404–410
Soft solution synthesis, non-isothermal decomposition kinetics and characterization of manganese dihydrogen phosphate dihydrate Mn(H2PO4)2·2H2O and its thermal transformation products Banjong Boonchom a,b , Chanaiporn Danvirutai b,∗ , Santi Maensiri c a b
King Mongkut’s Institute of Technology Ladkrabang Chumphon Campus, 17/1 M. 6 Pha Thiew District, Chumphon 86160, Thailand Department of Chemistry, Faculty of Science, Khon Kaen University, Mitraparp Road, Muang District, Khon Kaen 40002, Thailand c Integrated Nanotechnology Research Center (INRC) and Small & Strong Materials Group (SSMG), Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand Received 9 July 2007; received in revised form 14 November 2007; accepted 1 December 2007
Abstract Manganese dihydrogen phosphate dihydrate (Mn(H2 PO4 )2 ·2H2 O) was synthesized by a simple, rapid and cost-effective method using Mn(c) and H3 PO4 in water–acetone medium at ambient temperature. The thermal stability of the Mn(H2 PO4 )2 ·2H2 O was studied by means of the nonisothermal kinetic (Kissinger method). The specificity of thermal decomposition was characterized by identification of the bonds to be selectively activated due to energy absorption at vibrational level, which was assigned by comparison of the calculated wavenumbers with the observed wavenumbers in FTIR spectra. These results were used to identify the molecules or ions that were eliminated in each thermal transition step. The thermal transformation products from the synthesized Mn(H2 PO4 )2 ·2H2 O according to the thermal treatments at 243, 773 and 1073 K were obtained to be Mn(H2 PO4 )2 , Mn2 P4 O12 and Mn2 P2 O7 , respectively. The synthesized Mn(H2 PO4 )2 ·2H2 O and its thermal transformation products were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and FTIR spectroscopy. The SEM micrographs of the obtained products show the different morphologies, which are important for specific applications. © 2007 Elsevier B.V. All rights reserved. Keywords: Manganese dihydrogen phosphate dihydrate; Manganese cyclotetrametaphosphate; Manganese pyrophosphate; Thermal analysis; Non-isothermal kinetics
1. Introduction Manganese phosphates considerably possess industrial interesting properties nowadays because of their wide applications in laser host [1], ceramic [2], dielectric [3], electric [4], magnetic [5], and catalytic [6] processes. Manganese phosphates are transformed to other phosphates by hydrolysis and dehydration reactions at elevated temperatures [7–9]. A group of condensed phosphates consists of polyphosphate, cyclo-phosphate, and ultraphosphate. Polyphosphate has a chain structure in which PO4 unit shares two oxygen atoms. Cyclo-phosphate has a cyclic structure, whereas ultraphosphate has a network structure [10]. However, the successful applications of the required material depend on the morphology and purity. The preparation methods for obtaining well-defined chemical microstructure, depends
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[email protected] (C. Danvirutai).
0254-0584/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2007.12.018
mainly on the synthesis conditions. The preparation of some transition metal phosphates by different synthesis conditions had been reported, giving rise to final metal phosphates with costeffective method [11]. However, disadvantages of most general preparation methods are inhomogeneity, lack of stoichiometry control and larger particle size. These can be avoided when the material is synthesized using a solution-based method [12]. The main advantage of the solution-based method is that the process concerns the molecular level mixing which facilitates the formation of polycrystalline homogeneous particles with improved properties. Mn(H2 PO4 )2 ·2H2 O, Mn2 P4 O12 and Mn2 P2 O7 have been found to have a wide range of applications and can be used as catalysts, ion exchangers, reactants in ionic conditions, intercalation reactions, superphosphate fertilizers, and as inorganic pigment in ceramics [13–19]. Few studies on the synthesis and structure of Mn(H2 PO4 )2 ·2H2 O using manganese(II) carbonate and phosphoric acid at low temperature (333–353 K) with a long time period (>2 day) were reported [20,21]. Bagieu-Beucher
B. Boonchom et al. / Materials Chemistry and Physics 109 (2008) 404–410
reported on the synthesized Mn2 P4 O12 from manganese chloride and 85% (w/w) phosphoric acid by hydrothermal or high-temperature (573–773 K) method with a long time period (∼20 h) [22]. While Mn2 P2 O7 was obtained by heating mixtures of MnCO3 or MnO2 and P2 O5 at high temperature (>873 K) with long time consuming (>15 h) [23,24]. These previously reported synthetic methods to obtain three manganese phosphates were time consuming and carried out at high temperature. Most recently, our group reported the synthesis of Mn(H2 PO4 )2 ·2H2 O and its decomposition product Mn2 P4 O12 from different manganese sources (Mn(c) and MnCO3 ) and phosphoric acid at ambient temperature with a short time period (