Microwave-assisted polyol synthesis of Ag powders
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Microwave-assisted polyol synthesis of Ag powders Hiroaki Katsuki Saga Ceramics Research Laboratory 3037-7, Arita-machi, Saga 844-0024, Japan
Sridhar Komarneni Materials Research Institute and Department of Crop and Soil Sciences, 205 Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 29 October 2002; accepted 23 December 2002)
Silver metal powders were prepared through reduction of AgNO3 in ethylene glycol using microwave-polyol (M-P) and conventional-polyol (C-P) reactions at 100–200 °C. Powders of Ag were rapidly produced by microwave-assisted reaction at temperatures above 160 °C. The formation yield of Ag powders from AgNO3 reached 97.8% after treatment for 135 min at 140 °C and 98.6% after treatment for 23 min at 160 °C. Compared to the formation of Ag powders using a C-P reaction, a M-P reaction led to increased rate of formation by 6.5 times at 160 °C, 5.2 times at 140 °C, and 3 times at 130 °C. Silver particles of 0.3–2 m in diameter were produced using M-P and C-P reactions at 100–120 °C. The particle size of Ag powders increased with increasing reaction temperatures and times, and particles strongly aggregated at 160 °C using C-P and M-P reactions.
A novel microwave-hydrothermal reaction was developed recently by us for the synthesis of a wide variety of ceramic powders, for example, unary oxides such as TiO2, Fe2O3, and ZrO2 and binary oxides such as BaTiO3, SrTiO3, PbTiO3, KNbO3, and Ca10(PO4)6(OH)2 at 100–194 °C.1–10 The microwave-hydrothermal process has been shown to be superior to the conventionalhydrothermal process, and the former leads to (i) very rapid heating to the temperature of treatment, (ii) crystallization kinetics increased by 1–2 orders of magnitude over the conventional-hydrothermal process, (iii) selective formation of phases, and (iv) new phases.1–4,7–10 A method known as the “polyol process” was proposed to produce monodisperse Ni, Co, Pd, Pt, Ag, and Au11–14 powders and alloys such as Ag–Pd, Co–Ni, Fe– Co, and Fe–Ni15 particles by using the conventional heating method. In this process, the metal precursor is suspended or dissolved in a polyol such as ethylene glycol, which acts as a reducing agent.16 A new process that combines the microwave field with polyol process was developed to prepare rapidly nanometer-sized to micrometer-sized metal particles from metal salts or hydroxides.17–21 The combination of the microwave field with solvothermal and polyol processes is termed by us as “microwave-solvothermal” (M-S) and “microwavepolyol” (M-P) processes, respectively.20 However, the J. Mater. Res., Vol. 18, No. 4, Apr 2003
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effects of microwave radiation during M-S or M-P reactions on the formation rate and properties of metal powders were not determined in detail. In this study, the effect of microwave radiation on the formation rate and morphologies of Ag particles from AgNO3 and ethylene glycol at 100–200 °C was investigated, and the results were compared with th
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