Modeling nanotechnology processes, Gas-phase carbon nanotube production methods, high -pressure carbon monoxide (HiPco) process, Simulation of Rice University HiPco reactor flowfield.
HiPco Project: (In Collaboration with Dr. Christopher E. Dateo)
Single-walled carbon nanotubes (SWNT) exhibit many unique and useful physical and electronic properties. Therefore, researchers have so far demonstrated several methods for producing SWNT. These methods include laser vaporization of metal-doped graphite targets, arc evaporation of metal-doped carbon electrodes, and decomposition of carbon-containing molecules on supported nanometer size metal particles that serve as catalysts for SWNT growth. All these methods not only produce SWNT in small amounts (milligram to gram in a few hours), but they also produce graphitic deposits and amorphous carbon along with SWNT.
Recently, Professor Richard E. Smalley's group at Rice University developed a high-pressure carbon monoxide (HiPco) process to produce SWNT from gas-phase reactions of iron carbonyl in carbon monoxide at high pressures (10 - 100 atm). The HiPco process is a relatively clean process, i.e., SWNT is obtained without the graphitic deposits and amorphous carbon; and more importantly, the process has the potential for producing SWNT in large quantities since it is from a gas-phase reaction (currently 10 gram a day). In the HiPco process, carbon monoxide mixed with a small amount of iron pentacarbonyl -Fe(CO)5- is heated to produce SWNT. The products of thermal decomposition of Fe(CO)5 react to produce iron clusters in gas phase. These metal clusters serve as nuclei upon which SWNT nucleate and grow.
In the modeling effort so far, we have focused on HiPco process for carbon nanotube production. We have developed two kinetic models for HiPco process. One is a detailed 0-D model to do kinetic studies without flowfield coupling, the other one is the reduced kinetic model coupled to the axisymmetric flow code. In both models, three building blocks of HiPco process are addressed: decomposition of the precursor, metal cluster formation and growth, and carbon nanotube growth. Decomposition of precursor molecules (e.g., iron pentacarbonyl) is necessary to initiate metal cluster formation. The metal clusters serve as catalysts for carbon nanotube growth. Diameter of metal clusters and number of atoms in these clusters are some of the essential information for predicting carbon nanotube formation and growth, which is then modeled by Boudouard reaction (2CO ---> C(s) + CO2) with metal catalysts. The reduced model is formulated based on simulations with the detailed kinetic model.
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