Nucleation and growth mechanisms

Nucleation and growth mechanisms are described in detail in texts on precipitation (Sohnel and Garside, 1992), and crystallization (Mullin, 2001 Mersmann, 2001 and Myerson, 2001). Granulation is considered in Sherrington and Oliver (1981), Stanley-Wood (1990) and Pietsch (1991) whilst comminution is dealt with in Prior etal. (1990). 

An initial deceleratory process ( 1%) in KN3 decomposition is ascribed to reaction at superficial imperfections [712]. The subsequent constant rate of product evolution corresponds to an interface process but this is not a nucleation and growth mechanism since the product metal is volatile (as in NaN3). The catalytic properties of potassium vapour are attributed... 

G6mez H, Henriquez R, Schrebler R, Cordova R, Ramirez D, Riveros G, Dalchiele EA (2005) Electrodeposition of CdTe thin films onto n-Si(lOO) nucleation and growth mechanisms. Electrochim Acta 50 1299-1305... 

Introduction. After we have discussed examples of uncorrelated but polydisperse particle systems we now turn to materials in which there is more structure - discrete scattering indicates correlation among the domains. In order to establish such correlation, various structure evolution mechanisms are possible. They range from a stochastic volume-filling mechanism over spinodal decomposition, nucleation-and-growth mechanisms to more complex interplays that may become palpable as experimental and evaluation technique is advancing. 

Stranski-Krastanov growth has been documented for copper on Au(lll) [101, 102], Pt(100) and Pt(lll) [103], for silver on Au(lll) [104, 105], for cadmium on Cu(lll) [106] and for lead on Ag(100) and Ag(lll) [107-109]. In all of these examples, an active metal is deposited onto a low-index plane of a more noble metal. Since the substrate does not undergo electrochemical transformations at the deposition potential, a reproducible surface can be presented to the solution. At the same time, the substrate metal must be carefully prepared and characterized so that the nucleation and growth mechanisms can be clearly identified, and information can be obtained by variation of the density of surface features, including steps, defects and dislocations. 

The previous discussion has shown that the CIPS technique allows one to produce macroporous epoxy networks with either a narrow or bimodal size distribution. However, no indication has been given on the type of phase separation mechanism to yield these morphologies. As discussed earlier, the formation of a closed cell morphology can result either from a nucleation and growth mechanism or from spinodal decomposition. 

Since the start of modern interpenetrating polymer network (IPN) research in the late sixties, the features of their two-phased morphologies, such as the size, shape, and dual phase continuity have been a central subject. Research in the 1970 s focused on the effect of chemical and physical properties on the morphology, as well as the development of new synthetic techniques. More recently, studies on the detailed processes of domain formation with the aid of new neutron scattering techniques and phase diagram concepts has attracted much attention. The best evidence points to the development first of domains via a nucleation and growth mechanism, followed by a modified spinodal decomposition mechanism. This paper will review recent morphological studies on IPN s and related materials. 

The co-occurrence of nucleation and spinodal decomposition had been observed in the temperature quench experiment of poly(2,6-dimethyl-l,4-phenylene oxide)-toluene-caprolactam system, [64,65], in which the typical morphology formed by nucleation and growth mechanism was observed with electron-microscopy when the quench of temperature is slightly above the spinodal boundary. On the other hand, if the quench temperature is somewhat lower than the spinodal boundary, they observed interconnected structures as well as small droplets. 

K is positive, representing the "surface free energy at the boundary between emergent phases. Thus, if (3 f/3c ) > 0 the solution is stable to the small fluctuations applicable to eqn. 9 and phase separation by a random nucleation and growth mechanism can only be initiated by a finite, thermally driven fluctuation. The limit of this metastability (i.e., the spinodal) occurs at (3 f/3c ) 0 and the solution becomes unstable whenever (3 f/3c ) is negative. The... 

Apart from the development in photography, most of nucleation and growth mechanisms based on a chemical reduction (Section 20.4.4) behave as development processes, and are likewise controlled by the nuclearity dependence of the cluster redox potential and by the potential of the electron donor. 

The nucleation and growth mechanism of CdTe thin films at polycrystalline gold surface [203] and on the rough face side of a Si(lOO) were studied as a function of different potential steps. Schematic representation of CdTe formation is shown in [204]. 

Allongue etal. [464] have studied nucleation and growth mechanisms of Co and Ni on Au(lll) using in situ STM and electrochemical methods. 

Lowenhaupt and Hellmann (1991) have determined whether microphase separation or macrophase separation occurs in blends of a PS-PMMA diblock with PMMA homopolymer with a < 1 and a > 1 using TEM. They found that the transition between purely microphase separation and macrophase separation occurs for a lower diblock content for blends with a smaller a, as supported by calculations of the instability limit using the random phase approximation. Blends with a < 1.4 were always initially microphase separated, although in a blend with a - 1.4 this was followed by macrophase separation. However, the macrophase-separated structure took the form of aggregates of micelles (see Fig. 6.1), suggesting a nucleation and growth mechanism for the secondary... 

MPa, and 81.5% only at 4.8 MPa [16], In absorption process, the reaction of magnesium with hydrogen is a nucleation and growth mechanism where the nucle-ation rate is pressure dependent. They estimated the enthalpy and corresponding entropy of MgH2 formation as -70.0 kJ/mol and -126 J/mol K, respectively. 

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