Jurnal Nanosains & Nanoteknologi ISSN 1979-0880 Edisi Khusus, Agustus 2009 Induction Time in Formation of Copper nanoparticles M. Abdolkarimi Mahabadi and Mehrdad Manteghian (*) Chemical engineering department, Tarbiat Modares University Jalal-Al-Ahmad Highway, Tehran, Iran (*) E-mail: manteghi@modares.ac.ir Received : 20 May 2009 Accepted for publication : 26 May 2009 Abstract Copper nanoparticles are synthesized by the reaction of cupric chloride with hydrazine in the aqueous cetyltrimetylammonium bromide (CTAB) solution. Induction time is estimated by two ways, one from an absorption-time graph obtained by monitoring the absorption of solution after creation of supersaturation by UV-vis spectrum and by visual observation of color alterations. An analogy test has been performed for comparison of these ways with accuracy of 95% . Whereas experimental data was in concord with classical nucleation theory, this theory is used for calculation of interfacial tension. Correlations related to classical nucleation theory are compared with each other and two equations for calculation of interfacial tension. Keywords: Crystallization, interfacial phenomena, nanoparticles. 1. Introduction In crystallization system, The time between the creation of supersaturation and the first changes in the physical properties of the system due to appearance of new particles is defined as induction time (t ind ) [1]. This means that after the initial moment of reaching supersaturation in the old phase, formation of an detectable amount of the new phase requires a certain time, called the induction time[2]. Induction time is a function of the solution temperature and supersaturation and is also influenced by external factors such as the presence of impurities and seeds [3-7]. Although interfacial tensions evaluated from experimentally measured induction times are somewhat unreliable, measurements of the induction time can provide useful information on other crystallization phenomena, such as kinetics of new phase nucleation, order of nucleation processes and effect of impurities[1-3] In nucleation studies, induction time measurements are commonly made, whereas nucleation rates are seldom measured. The induction time has frequently been used as a measure of the nucleation event, making the simplifying assumption that it can be considered to be inversely proportional to the rate of nucleation. So, induction time depends on supersaturation, temperature and interfacial tension. According to the classical nucleation theory, if there was a linear relationship between ln t ind and 1/(ln S) 2 , it should allow a value of the interfacial tension[3]. Metal nanoparticles have attracted a great deal of attention and have been extensively exploited for their unique optical, magnetic, electric, and catalytic properties [8-10]. Copper nanoprticles have been prepared by various routes. One of them is Chemical reduction method in solution as referred in [11-14]. The basic properties of metal nanoparticles are mainly determined by size, shape, crystallinity and structure. The size of these nanoparticles is controlled by the kinetics of reaction crystallization. Recently, Ghader et al. [15] reported the induction time of reaction crystallization of silver nanoparticles and their interfacial tension. In this paper, copper nanoparticles are produced with a redox reaction in the existence of a stabilizing agent in a batch crystallizer to measure induction time at different temperatures and supersaturations. In this case, classical nucleation theory is used for prediction of induction times. The induction time of copper nanoparticle is determined experimentally at different temperatures and supersaturations and interfacial tension is estimated. 2. Teori The nucleation rate according to the classical theory of homogeneous nucleation is [3]: ) ) (ln ) ( 3 16 exp( 2 3 2 3 0 S kT V B B m πγ − = (1) Where S = C/C* is supersaturation ratio, V m is the molecular volume, k is the Boltzmann constant and T is temperature, and γ is the interfacial tension between the crystal and its surrounding supersaturated fluid. As noted in the introduction, the induction time has inversely proportional to the rate of nucleation t ind ∝ 1/B. So we have: ) ) (ln ) ( 3 16 exp( 2 3 2 3 1 S kT V K t m ind πγ = (2) Thus, for a given temperature, ln t ind against 1/(ln S) 2 should yield a straight line which, if the data truly 32