Ind. Eng. Chem. Res. 2007, 46, 6269-6272
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PROCESS DESIGN AND CONTROL Validation of TiO2 Particle-Size Distribution Measured by Scanning Mobility Particle Sizer Meng-Dawn Cheng,*,† Emory A. Ford,‡ David W. DePaoli,† Edward A. Kenik,† and Peter Angelini† Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6038, and Material Technology Institute, St. Louis, Missouri
In the latest Vision2020 roadmap (http:// www.chemicalvision2020.org/ nanomaterialsroadmap.html), a key need identified across the nanomanufacturing industry is the capability of on-line real-time characterization of nanoparticles smaller than 50 nm. Electron microscopy is the gold standard for quality-assuring designed nanomaterial. However, imaging of a large number of particles needed for statistics, 10 000 per batch for example, is a daunting task and would take a prohibitively long time to complete, eliminating the possibility for using microscopy for practical process monitoring and control. A demonstration project was executed at Oak Ridge National Laboratory (ORNL) to evaluate the feasibility of using a commercial particle measurement system for on-line real-time characterization. Production of titanium nanoparticles in the vapor phase was chosen for the demonstration project. The results showed that the measurement system could be used as a continuous monitor for nanomanufacturing. However, it is noted that, after the completion of this project, a significant maintenance task was required to restore the commercial system to the operation-ready state, because of the corrosive nature of the sample stream. Thus, if the commercial measurement system is to be used on a continuous basis on an industrial process, the system will have to be reconstructed and possibly redesigned to be able to achieve long-term operation stability and reduce maintain cost. Introduction In December 2003, Chemical Industry R&D Roadmap for Nanomaterials by Design was published by the Chemical Industry Vision2020 Technology Partnership (http:// www.ChemicalVision2020.org). This roadmap presents a vision to accelerate commercialization of nanoscale technology for production of nanomaterials of desired properties. The production of designed nanomaterials in a controlled and predictable way will require both a fundamental understanding of nanoscale properties and new paradigms for high-volume synthesis. Since size affects everything about nanoscale materials, it is important to be able to monitor and control particle size during production in a timely fashion. A key need identified across the industry is the capability for real-time characterization of nanoparticles smaller than 50 nm during synthesis. According to the industry experts, the techniques currently used in commercial operations are not on-line or real time; they are not suitable for in-plant operation. In other words, the current ability to monitor and control production processes for nanoscale materials is inadequate, resulting in unreliable product quality. Although not exactly an engineered or designed nanomaterial, titanium dioxide nanoparticles are widely available in commercial applications for decades, and the industry has optimized the production process over the years.1 There are ongoing interests to making these materials even smaller and in a cleaner * To whom correspondence should be addressed. Phone: (865) 241-5918. Fax: (865) 576-8646. E-mail:
[email protected]. † Oak Ridge National Laboratory. ‡ Material Technology Institute.
route such as an aerosol route. Although production optimization has been achieved in the past through tremendous efforts, successful on-line automatic control of an aerosol process that enables consistent production of the titania powder of individual particle size smaller than 50 nm remains problematic. Vaporphase production of TiO2 has been studied in the past by Akhtar et al.1 among many others cited therein. Moody and Collins2 employed direct numerical simulation technique to describe the effects of mixing on the nucleation and growth of titania particles, but no experimental data were available to verify the simulation results. However, these studies did not address the issues of on-line continuous monitoring of produced nanoparticles that are
