Hydrazine-controlled hydrothermal synthesis of Co 9 S 8 from a homogeneous solution
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Hydrazine-controlled hydrothermal synthesis of Co9S8 from a homogeneous solution J.H. Zhan, X.G. Yang, Y. Xie,a) D.W. Wang, Y.T. Qian, and X.M. Liu Structure Research Laboratory and Department of Chemistry, University of Science & Technology of China, Hefei, Anhui 230026, People’s Republic of China (Received 10 February 1999; accepted 26 August 1999)
Single-phase nanocrystalline Co9S8 was prepared by hydrothermal treatment of Co(Ac)2 and NH2CSNH2 in hydrazine solution at 170 °C. The products were characterized by x-ray powder diffraction (XRD) technique, transmission electron microscope (TEM), and wet chemical analysis. XRD indicated the product was the cubic Co9S8 phase. The relative crystallite size was 6.3 nm as determined by the Scherrer method. TEM images showed the particles were agglomerative. The electron diffraction pattern also revealed their nanocrystalline nature. In this hydrothermal formation process of Co9S8, hydrazine was a critical factor. The formation process is discussed.
I. INTRODUCTION
Cobalt sulfides including CoS, Co4S3, Co9S8, Co3S4, and CoS2 have been prepared by various routes. The most direct method is combining a stoichiometric amount of the elemental cobalt and sulfur in evacuated silica tube at high temperature.1,2 Repeated grinding and heating are necessary to obtain a single-phase product. A higher firing temperature is essential to overcome the long diffusion path lengths. But the higher temperature leads to a larger particle size and inhomogeneity. As for these cobalt sulfides, temperature has a considerable effect on the formation of various phases. The phase diagram for the Co–S system has been determined.3 Cobalt sulfides could be also prepared by the reaction of cobalt or cobalt monoxide (CoO) with hydrogen sulfide.4,5 Moreover, there have been several reports on formation of cobalt sulfide using sulfur dioxide (SO2) as a sulfuring agent.6,7 Among these cobalt sulfides, Co9S8 has important applications in hydrodesulfurization catalysis and magnetic devices.8 It has been shown that Co9S8 permits little variation from ideal stoichiometry.9,10 Although many routes have been shown to prepare cobalt sulfides, the conditions for obtaining Co9S8 were not very specified. A midtemperature synthesis route of Co9S8 was reported involving the treatment of anhydrous cobalt sulfates in a controlled H2/H2S atmosphere at 520 °C.11 As we know, there are few reports about formation of Co9S8 by lowtemperature hydrothermal method. Hydrothermal synthesis is one of the most promising solution chemical methods, by which the particle size and phase homogea)
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J. Mater. Res., Vol. 14, No. 11, Nov 1999 Downloaded: 14 Mar 2015
neity could be well controlled.12,13 In this paper we report a low-temperature hydrothermal synthesis of Co9S8 involving the reaction between cobalt acetate and thiourea in hydrazine aqueous solution. II. EXPERIMENTAL
Analytical acetate [Co(Ac)2 䡠 4H2O,
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