Formation and catalytic activity of amorphous Ni 50 Pd 40 Si 10 alloy powder by mechanical alloying
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Formation and catalytic activity of amorphous Ni50 Pd40 Si10 alloy powder by mechanical alloying H. F. Zhang, J. Li, Q. H. Song, and Z. Q. Hu State Key Laboratory of RSA, Institute of Metal Research, Academia Sinica, Shenyang, 110015, China (Received 26 January 1996; accepted 16 June 1998)
Amorphous Ni50 Pd40 Si10 alloy powder was prepared by mechanical alloying. The surface states and catalytic activities of amorphous and crystalline Ni50 Pd40 Si10 alloy powder pretreated with hydrofluoric acid (HF) solution were studied. The results show that amorphous Ni –Pd–Si alloy powder was easily prepared by mechanical alloying. After treating with HF solution, the number of Pd atoms on the surface of amorphous Ni –Pd–Si powder was obviously higher than that of the crystalline alloy and catalytic activity of amorphous Ni –Pd–Si powder was higher than that of the crystalline one by three times.
Amorphous catalysts exhibit high catalytic activity and selectivity. But amorphous alloys prepared by the rapid-quenching method are in the form of ribbon, and the small surface area of ribbon has prevented the development of an alloy with high catalytic activity. Therefore, physical methods, chemical methods, and mechanical pulverization using a vibratory rod mill were used to increase the surface area of alloy.1–5 In this communication, amorphous powder with large surface area was prepared by mechanical alloying. It is suitable to be used as a catalyst. Pure Ni (purity 99.9%), Pd (99.9%), and Si (99.99% single crystal) powders, with a composition of Ni50 Pd40 Si10 , were loaded in a planetary ball mill under the protection of Ar. The ball to powder weight ratio was 20 : 1. Mechanical alloying was discontinuously carried out by milling for 1 h and then stopping for 0.5 h to radiate heat outward. Crystalline Ni50 Pd40 Si10 powder was made from amorphous Ni50 Pd40 Si10 powder which was heat-treated under vacuum at 723 K for 2 h. The formation of amorphous Ni–Pd–Si alloy powder was studied by XRD. The surface states of amorphous and crystalline Ni–Pd–Si alloy powders were studied by Brunauer–Emmett– Teller (B.E.T.), transmission electron microscopy (TEM), Auger electron spectroscopy (AES), and electron spectroscopy for chemical analysis (ESCA) spectra. The amorphous and crystalline Ni–Pd–Si alloy powders were treated with 1 mol dm23 hydrofluoric acid (HF) solution for 3 min. Hydrogen (0.1 MPa) and styrene were introduced into a conventional closedcirculation reaction vessel (1 dm3 ). The reaction was performed at 298 K. The initial hydrogen absorption rate (dm3yh ? g) expressed activity. The initial rate was estimated from the initial pressure change. Three consecutive trials were run (Fig. 7). The catalytic activities of amorphous and crystalline Ni–Pd –Si catalysts pretreated with 1 mol dm23 HF solution were studied and compared, respectively. J. Mater. Res., Vol. 13, No. 10, Oct 1998
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The formation of amorphous Ni–Pd–Si alloy powder
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