Int J Adv Manuf Technol (2004) 24: 879–885 DOI 10.1007/s00170-003-1816-6
ORIGINAL ARTICLE
Tsing-Tshih Tsung · Ho Chang · Liang-Chia Chen · Ming-Kun Liu · Hong-Ming Lin · Chung-Kwei Lin
Process development of a novel arc spray nanoparticle synthesis system (ASNSS) for preparation of a TiO2 nanoparticle suspension
Received: 27 September 2002 / Accepted: 9 December 2002 / Published online: 19 May 2004 Springer-Verlag London Limited 2004 Abstract This article presents the development of an innovative technology to manufacture TiO2 nanoparticles. Manufacturing nanoparticles is considered as a crucial step towards product and process innovation. In our proposed process, a titanium rod, as the electrode, is melted and vaporised in deionised water, which is used as an insulating liquid. The vaporised metal particles are then rapidly quenched by the designed cooling system, and thus nanocrystalline powders are nucleated and formed. By implementing the system, we have successfully developed the processing equipment of the arc spray nanoparticle synthesis system (ASNSS). The experimental results indicate that uniformly distributed and well-controlled TiO2 nanoparticle size can be manufactured by ASNSS. Keywords Nanoparticle suspension · Nanoparticle synthesis · Nanotechnology · Submerged arc · Titanium dioxide
T.-T. Tsung (u) · H. Chang · M.-K. Liu Department of Mechanical Engineering, National Taipei University of Technology, Taiwan, R.O.C. Email:
[email protected] L.-C. Chen Department of Automation Technology, National Taipei University of Technology, Taiwan, R.O.C. E-mail:
[email protected] H.-M. Lin Department of Materials Engineering, Tatung University, Taiwan, R.O.C. E-mail:
[email protected] C.-K. Lin Department of Material Science, Feng Chia University, Taiwan, R.O.C. E-mail:
[email protected]
1 Introduction and motivation The essence of nanotechnology is the ability to work at the molecular level, atom by atom, to create large structures with fundamentally new molecular organisation. Nanotechnology is one method to create useful materials, devices and systems through the control of matter on the nanometre scale. It also represents a type of exploitation of novel properties and phenomena developed at that scale [1–4]. The features of these materials in the range of about 1 to 100 nm, which is a typical dimension (1 nm is 10,000 times smaller than the diameter of a human hair) exhibit important property changes. It has been widely recognised that nanomaterials (both crystalline and non-crystalline) possess different atomic structures, resulting in significant differences in their physical and chemical characteristics such as photo, electric and magnetic properties. There are currently many existing methods used to prepare nanoparticles of which sputtering, thermal evaporation and laser methods are the most common. In these processes, the nanoparticles produced often aggregate during their condensing processes and some important characteristics of the particles that only exit on the nanoscale vanish. The aim of this article is to develop a novel nanoparticle manufacturing system, called the arc spray nanoparticle synthesis system (ASNSS) to avoid the disadvantages described above to produce uniformly distributed nanoparticles of well-controlled size dispersed in deionised water suspension [5].
2 Literature review Two main preparing mechanisms, namely melting and evaporation, are applied in the ASNSS [6]. A titanium rod, used as raw material, is melted under both liquid and gaseous state during the nanoparticle preparation stage. The change of the pulse-duration of an electrical discharge arc heating system (EDAHS) has a direct influence on the radius of crater, the temperature distribution of the arc, and the melting depth at the end surface of Ti rod.
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The dimension of the craters remained at the end surface of Ti rod affects the size of nanoparticles produced. The detailed relationship between craters and applied electric pulse-duration is described in Eq. 1 [7]: 3
4 r g = 0.788t ON
(1)
where r g (µm) is the crater radius and t ON (µs) is the pulseduration. Eubank and Mukund simulated the temperature distribution of arc by their proposed variable-mass-cylindrical-plasma-model (VMCPM) [8]. To verify the simulation, Pillans and Erensen further measured the temperature of the arc by optical fibres [9]. In general, the temperature of the arc changes with the pulseduration t ON (µs) and the temperature of the arc can be modulated by the pulse-duration t ON (µs). When a Titanium (Ti) rod is heated by an intermittent arc, it was found that the heat affected zone (HAZ) is only distributed around the end surface of the Ti rod. The relationship between the pulse-duration and the melted and vaporised depth of the Ti rod can be expressed in Eq. 2 [9]: x = 1.15 4αt ON (2) where x is the melted and vaporised depth, αis the thermal diffusion coefficient and t ON is the pulse-duration. In the proposed ASNSS, the vaporised metal is processed through three stages, namely nucleation, growth and condensation, in order to generate nanoparticles. According to the nucleation theory, the nucleating rate of unit volume (I) can be described in Eq. 3 [7, 8]: − (∆G + ∆g) kT I = Nv exp . (3) h kT Fig. 1. Schematic diagram of the ASNSS
where Nv is the number of atoms in row material, G is the change of free energy when new phase formed, g is the required activation energy when atoms pass through interfaces, T is the absolute temperature, h is the Planck constant and k is the Boltzmann constant. According to Eq. 3, G is a critical parameter to influence I when the temperature is kept constant. In addition, G affects the saturation during material transformation from solid to gaseous state. High saturation depends on the temperature difference between arc and dielectric liquid. In other words, high nucleation rate can be obtained when the metal is vaporised at high temperature and rapidly condensed at low temperature. If the saturation rate is not sufficient, uniform nanoparticles cannot be obtained by the ASNSS. Controlling adequate radiuses of condensation nuclei is essential during the nucleating process because the properties of the particles are mainly determined by this factor. In order to obtain nanoparticles, decreasing the critical radiuses of condensation nuclei is important.
3 System design of the ASNSS The schematic diagram of ASNSS is depicted in Fig. 1. The system consists of four subsystems described as a heating unit, a parameter control system, a constant pressure system and an isothermal system. The heating unit provides a heating process with stable arc to vaporise metals. Important parameters, such as applied electrical current, voltage, pulse-duration, off time, velocity of serve feed, gap and machining time are modulated by the parameter control system. The constant pressure system is used to maintain a set vacuum pressure in the chamber. The dielectric liquid in the chamber is deionised water. A Titanium metallic rod with a diameter of 8 mm is submerged in de-lionised water and positioned at the bottom of chamber. An adequate gap between
