Coalescence growth mechanism

The mechanisms of the crystal-building process of Cu on Fe and A1 substrates were studied employing transmission and scanning electron microscopy (1). These studies showed that a nucleation-coalescence growth mechanism (Section 7.10) holds for the Cu/Fe system and that a displacement deposition of Cu on Fe results in a continuous deposit. A different nucleation-growth model was observed for the Cu/Al system. Displacement deposition of Cu on A1 substrate starts with formation of isolated nuclei and clusters of Cu. This mechanism results in the development of dendritic structures. 

Coalescence Growth Mechanism. Following the very early step of the growth represented by Eq. (1), many nuclei exist in the growth zone. Hence Eq. (2) would be a major step for the crystal growth. Since there are many nuclei and embryos with various sizes in the zone, Uy in Eq. (2) can be assumed to be a random variable. Due to mathematical statistics, the fraction of volume approaches a Gaussian after many coalescence steps (3). A lognormal distribution function is defined by... 

In general, analytical solutions are only available for specific initial or inlet size distributions. However, for batch granulation where the only growth mechanism is coalescence, at long times the size distribution may become self-preserving. The size distribution is selfpreserving if the normahzed size distributions

[Pg.1906]

Fig. 10. Four elementary pellet growth mechanisms (a) snowballing (b) crushing and layering (c) coalescence (d) abrasion transfer. [From Sastry and Fuerstenau (S5).]...

The 3D crystallites growth mechanism is discussed in Section 7.10. In this case the structure components are 3D crystallites, and a coherent deposit is built by coalescence (joining) of these crystallites. 

In Chapter 7 various growth models were described layer growth (Section 7.9), nucleation-coalescence growth (Section 7.10), development of texture (Section 7.11), columnar microstructure (Section 7.12), and other structural forms (Section 7.13). In this section we discuss the effects of additives on these growth mechanisms. 

---