Polydispersity of Primary Particles inAgglomerates made by Coagulation and Sintering

摘要

The polydispersity of primary particles (PP) in agglomerates is important in a number ofapplications, including nanocomposites, quantum dots and even for pigments. A new twodimensionalsectional model for coagulation and sintering is developed conserving the PP numberand size distribution once agglomerates are formed. By balancing the complete PP population as afunction of agglomerate size, physical and numerical narrowing or broadening of the primaryparticle size distribution (PPSD) are investigated systematically. Physical narrowing of the PPSD inagglomerates arises by the faster sintering of smaller PP compared to larger ones. Numericalnarrowing of the PPSD occurs when average PP diameters are employed in the calculation ofagglomerate coagulation and sintering. Numerical broadening of the PPSD by numerical diffusionis caused by the fixed primary particle spacing, similar to aerosol growth by condensation.Agglomerate and primary particle dynamics are elucidated during TiO2 formation by detailed twodimensional(primary and agglomerate) size distributions. It shows that the PPSD can be muchnarrower than the well known self-preserving size distribution of agglomerates by Browniancoagulation, especially when hard-agglomerates are formed.