Morphologies of electrochemically formed copper powder particles and their dependence on the quantity of evolved hydrogen N.D. Nikolić a, ⁎ , Lj. J. Pavlović a , M.G. Pavlović a , K.I. Popov a,b a ICTM-Institute of Electrochemistry, University of Belgrade, Njegoševa 12, P.O.B. 473, 11001 Belgrade, Serbia b Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, P.O.B. 3503, 11001 Belgrade, Serbia Received 8 May 2007; received in revised form 1 August 2007; accepted 18 October 2007 Available online 26 October 2007 Abstract Copper powder particles formed by electrolysis under different quantities of evolved hydrogen were analyzed using the scanning electron microscopy (SEM) technique. It was found that the structure of the powder particles strongly depended on the quantity of evolved hydrogen — that is, two types of powder particles were formed, depending on the quantity of evolved hydrogen. One type of particle was formed during the electrodeposition of copper when the quantity of evolved hydrogen was insufficient to change the hydrodynamic conditions in the near-electrode layer. This particle type comprised dendrites constructed of corncob-like structures as the basic element. The other type of particle was cauliflower-like and was formed when the quantity of evolved hydrogen was sufficient to change the hydrodynamic conditions in the near- electrode layer. However, both types of particle consisted of agglomerates of copper grains. The only difference lay in the size of the copper grains of which the agglomerates were constituted. The size of the grains was a function of the electrodeposition overpotential and, consequently, the quantity of evolved hydrogen, with a tendency to attain a steady value when the electrodeposition overpotential was increased. © 2007 Elsevier B.V. All rights reserved. Keywords: Powder particles; Copper; Electrolysis; Scanning electron microscope (SEM); Hydrogen evolution 1. Introduction An electrolytic metal powder represents a disperse electro- deposit removed from the electrode by tapping or some such similar manner [1]. In the potentiostatic regime [1–9], disperse electrodeposits of copper are obtained at overpotentials corresponding to the limiting diffusion current density plateau, as well as at higher overpotentials when simultaneous with copper electrodeposition processes, the hydrogen evolution reaction occurs [6]. In galvanostatic powder deposition, the initial deposition current density must be larger than the limiting diffusion current density [10]. An electrolytic metal powder consists of particles. These may assume various forms and sizes, whereas the powders, as an association of such particles, exhibit, more or less, the same characteristics as if they were deposited under identical condi- tions and if the manipulation of the deposits after removal from the electrode was the same. The most important properties of a metal powder are: the specific surface, the apparent density, the flowability and the particle grain size and distribution [11]. These properties, called decisive properties, characterize the behavior of a metal powder. The specific surface of a powder is determined as the surface per unit mass of powder and can be determined by the method given in the literature [12]. The apparent density or volumetric mass is defined as the mass per unit volume and can also be determined experimentally [13]. The powder particles from the same frac- tion of different powders occupy approximately the same vol- ume, but, depending on the structure of the metallic copper, exhibit different apparent densities [13]. Obviously, the more disperse a deposit is, the larger is the specific surface and the lower is the apparent density of the analyzed powder. The flow rate is the gravitational speed at which a powder flows through an orifice. Standard funnels with a calibrated orifice are used for its determination. A specific quantity of powder is poured into the funnel and the flow time is recorded [14]. Available online at www.sciencedirect.com Powder Technology 185 (2008) 195 – 201 www.elsevier.com/locate/powtec ⁎ Corresponding author. Tel./fax: +381 11 337 03 89. E-mail address: nnikolic@tmf.bg.ac.yu (N.D. Nikolić). 0032-5910/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2007.10.014