Fundamental Studies of Particle Growth and Structure During Powder Synthesis

Publication Reference: 
Author Last Name: 
R C Flagan
Report Type: 
ARR - Annual Report
Research Area: 
Particle Formation
Publication Year: 
United States

Executive Summary

The primary objective of the Caltech program supported by IFPRI is to understand the dynamics of particles which do not coalesce immediately upon coagulation and, through that understanding, to guide the development of processes for production of particles with particular properties. Theoretical and experimental investigations of the dynamics of aggre- gate aerosols have been undertaken with IFPRI support. Following on our studies of the properties of agglomerate particles, we have developed models to describe the kinetics of agglomeration. The kinetics of agglomeration are determined by the mobilities of the ag- glomerate particles and by their collision cross sections. The lower density of agglomerates has competing effects on the coagulation kinetics as compared with dense particles of equal mass: (i) the aerodynamic drag on the particles is increased due to the larger size of the particle of the same mass; (ii) the low density tends to increase the collision cross section of the agglomerate over that of the dense sphere. We have used fractal scaling concepts to evaluate the relationship between these measures of particle size and the particle structure. Our theoretical investigations suggest that the collision frequency of aggregate particles is enhanced over that of dense spheres of equal mass.

This report describes experiments that are being undertaken (i) to probe the structural rearrangements that take place when aggregate particles sinter and (ii) to measure the col- lision frequency for aggregate particles as a function of particle size and structure. The ex- periments are performed using model particles: bispheres for idealized sintering experiments and aggregates produced by low temperature aerosol coagulation for studies of aggregate sintering and aggregation kinetics.