PREPARATION AND CHARACTERIZATION OF Ni/NiO COMPOSITE USING MICROWAVE IRRADIATION AND SONICATION O. Palchik, S. Avivi, D. Pinkert and A. Gedanken* Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel, 52900 (Received February 1, 1999) (Accepted March 31, 1999) Abstract—The Ni/NiO composite was prepared by using the fast method of microwave- assisted oxidation. Amorphous Ni nanoparticles were used as a precursor, and the oxidizing agent was oxygen. By using vapors of H 2 O 2 , almost complete oxidation of nickel was achieved. The products were characterized using XRD, TEM, and EDX as crystalline materials. ©1999 Acta Metallurgica Inc. Introduction Nickel oxide, NiO, has received a considerable amount of attention over the last few years because of the many applications it has found in various fields. Its importance is manifested in the many patents that have been issued for its synthesis. This compound has found applications in areas such as catalysis [1– 4], electrochromic films [5–7], fuel cell electrodes [8 –12], gas sensors [13–15], and others [16]. Recent publications have reported that Ni/NiO composite also shows promising properties, especially in the field of electrochemical capacitors [17a]. In nature, NiO occurs as mineral bunsenite, with a cubic rock-salt structure. Because it has a defect structure, Ni 1-y O, nickel oxide is a p-type semiconductor. Nickel oxide is available in two different forms: green or black. There are a few methods for producing nickel oxide. The most widespread is based on the calcination of almost any nickel compound in air, for example, the nitrate, oxalate, or hydroxide, at ca. 1000°C. The methods of preparation, and especially the temperature, have a profound influence on the properties of NiO [17b]. One of the main targets in modern materials chemistry is the preparation of nanostructured materials. This target creates a demand for new synthetic methods. Other requirements include operation at lower temperatures and shorter reaction times, as compared with the classical ceramic synthesis. If these requirements are not met, grain growth and aggregation would prevent the fabrication of nano- dimensional products. One of these new processes is the microwave-assisted chemical reaction method. Microwave heating has been a known phenomenon since the early 40’s and has been successfully used in the food industry for decades. In the last few years it has been used frequently in chemistry as well [24]. It is based on the interaction of electromagnetic radiation with the dipole moment of the molecule, and it brings about rapid heating. Only recently has it been noticed that metallic powders can also be heated to considerably high temperature in an MW oven without arcing [25]. The mechanism of heating metallic powders is still unknown, but probably arises from microsparking on the surface of * Corresponding author: Dr. A. Gedanken, Bar-Ilan University, Department of Chemistry, 52900 Ramat-Gran, Israel. Tel: 03-531809/10; Fax: 972-3-5351250; Email: gedanken@mail.biu.ac.il Pergamon NanoStructured Materials, Vol. 11, No. 3, pp. 415– 420, 1999 Elsevier Science Ltd Copyright © 1999 Acta Metallurgica Inc. Printed in the USA. All rights reserved. 0965-9773/99/$–see front matter PII S0965-9773(99)00321-9 415