Development of a Simple Sintering Law for Fractal Aggregates Composed of Unequal Sized Primary Particles
- PDF / 551,261 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 3 Downloads / 184 Views
1056-HH11-25
Development of a Simple Sintering Law for Fractal Aggregates Composed of Unequal Sized Primary Particles Takumi Hawa1,2, and Michael R Zachariah1,2 1 Department of Mechanical Engineering and Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 20742 2 National Institute of Standards and Technology, Gaithersburg, MD, 20899 ABSTRACT Sintering of silicon nanoparticle chain aggregates composed of unequal sized primary particles are investigated using molecular dynamics (MD) simulations at 1500 K. We consider straight chain aggregates consisting of up to 40 2.5 and 5.4 nm primary particles. The sintering time increases with increase in the total volume of the chain aggregate or with increase in the exposed initial surface area of the chain. A mathematical model was developed to describe the dynamics of sintering of such chain aggregates. The model is a power law modification of the Frenkel sintering equation with the Koch-Friedlander model to include primary particle size dependence. We found that the particle size effect is a local process, and important only at the initial stage of the sintering. Thus, the effect is not significant when the aggregate becomes large. The model is amenable for use in aerosol models that might include sintering effects. INTRODUCTION Fabrication of the desired size with a narrow size distribution, and desired structure, is seen as one of the major challenge in robust implementation of nanoscience to a nanotechnology. The two most obvious ways to control the size of primary particles grown from the vapor are to either change the characteristic collision time by dilution or change the coalescence time by changing particle temperature. For large scale production or for ultraclean materials, a gas phase production method is generally the method of choice [1-4]. However, high volume fraction aerosol synthesis typically results in highly aggregated structures. The size of the spherical primary particles and the growth of agglomerates are determined by the rate of collision and subsequent sintering of particles. To understand the dynamics it would be useful to understand how aggregates sinter. Several researchers have approached the problem of aggregate sintering using Monte-Carlo [5, 6] or Brownian dynamics methods [7]. However, all previous methods make assumptions on the mechanism of aggregate sintering, and then apply a standard sintering approach to map the evolution of the morphology. Our recent studies have focused on developing a sintering model based on a priori atomistic simulation, from which we developed a phenomenological model of aggregate particle sintering as a function of the aggregate size and fractal dimension [8]. The model was able to predict the sintering time with excellent agreement with the results of MD simulations.
In this paper we extend our previous work to the problem of unequal sized primaries and limit ourselves to the simplest geometric representation of an aggregate, that of a chain of particles of unequal primary par
Data Loading...
