Preparation of Size and Aggregation Controlled Nickel Oxalate Dihydrate Particles from Nickel Hydroxide

Abstract. Nickel oxalate nanoparticles as nickel precursor were synthesized from nickel hydroxide (Ni(OH) 2 ) slurry by mixing H 2 C 2 O 4 solution. Precipitates of nickel oxalate dihydrate (NiC 2 O 4 ·2H 2 O) were formed by adding H 2 C 2 O 4 solution of pH 1. The NiC 2 O 4 ·2H 2 O particles with rectangular parallelepiped shape of ca. 440 nm sizes were prepared from the Ni(OH) 2 slurry at 298 K by dropping H 2 C 2 O 4 solution at a rate of 1 ml min -1 . The NiC 2 O 4 ·2H 2 O particles of rectangular parallelepiped shape were formed at 298-333 K, and was finely dispersed without aggregation. The size of the particle was controllable by preparation temperature. Introduction Interest in synthesizing nickel nanoparticles has increased considerably in recent years, largely in line with its growing applications such as magnetic recording medium, battery, internal electrodes of multi-layer ceramic capacitors and so on. The size and morphology control of nanoparticles is very important for their use in nanotechnology applications. A number of methods are considered for preparing nickel particle. Main methods of preparation, however, have so far been chemical reduction procedures and decomposition of metal carbonyl nickel compounds. In particular, the chemical reduction in aqueous system can prepare only a spherical nanoparticle, but the aggregation of particles is often serious [1-6]. We developed fabrication process of nickel nanoparticle to control the morphology and size. The process consists of two-step, i.e., synthesis of nickel oxalate as nickel precursor by precipitation reaction between nickel ammoniate ion, and oxalate ion and thermal decomposition of the nickel oxalate precursor. The morphology of the precursor is controllable as rectangular parallelepiped shape, rod-like, and needle-like by controlling coordination number of nickel ammoniate ion [7]. Then, needle-like nickel particle is obtained by the heat treatment of the needle-like precursor under inert atmosphere [8]. The main part of this process is morphology and size controls of nickel oxalate precursor, because those of the precursor determine the morphology and size of final products. In the preparation of nickel oxalate precursor in aqueous solution, aggregation of the