A Molecular Dynamics Study on the Constraint Conditions of the Particle Growth Process in Laser Synthesis of Nanopowders

Shiwei Zhang,Wenhui Zhang,Zhijun Zhang,Jun Liu

doi:10.1155/2012/830140

Abstract

Laser-induced chemical vapor deposition (LICVD) is a nanopowder synthesis method in which the nanoparticles of a synthetic product undergo nucleation, growth, and agglomeration. The growth process is crucial because it directly determines the growth rate and final size of nanoparticles. In this paper, the nanoparticle growth process is analyzed through a molecular dynamics study, and the process is divided into five steps. In addition, this study explains the microscopic heat and mass transfer processes that occur in the surrounding space and on the particulate surface. Three constraint conditions that may restrict the growth process, namely, transfer constraint, surface constraint, and temperature constraint conditions, are proposed and modeled. To calculate the final diameter and the nanoparticle growth rate, formulae for the constraint conditions are developed. The behavior of four gases in the particulate growth zone is discussed in detail.

Highlights

Laser-induced chemical vapor deposition (LICVD) is a nanopowder synthesis method which produces nanopowders that have excellent properties such as high purity, small particle size, narrow particle size distribution, good surface cleanliness, and the absence of hard agglomerates [1,2,3,4,5]
During LICVD synthesis of nanopowders, the gaseous precursor is injected into the reaction chamber and pyrolyzed by using a laser beam, and the vapor molecules of the desired solid product as well as gaseous byproducts are generated in the region of the laser beam
This paper details the mechanism of the particle growth process on a molecular scale, and the heat and mass transfers in the process are analyzed as constraint conditions through a molecular dynamics study

Summary

Introduction

Laser-induced chemical vapor deposition (LICVD) is a nanopowder synthesis method which produces nanopowders that have excellent properties such as high purity, small particle size, narrow particle size distribution, good surface cleanliness, and the absence of hard agglomerates [1,2,3,4,5]. The partial pressure and temperature of the vapor decrease along with the gas flow as a result of the diffusion loss and condensation on the core surface. The condensation causes the cores to continue absorbing the colliding vapor molecules and grow into nanoparticles. The particles become visible nanopowder as a result of agglomeration and the flow of the residual exhausted gas towards the collector. During LICVD synthesis, the nanoparticles undergo nucleation (core formation), growth, and agglomeration. These factors are the constraint conditions of the growth process [6,7,8,9]. This paper details the mechanism of the particle growth process on a molecular scale, and the heat and mass transfers in the process are analyzed as constraint conditions through a molecular dynamics study

Growth Process Analysis

Transfer Constraint Condition

Surface Constraint Condition

Temperature Constraint Condition

Conclusions