Metal nucleation kinetics

K.C. Russell. Grain boundary nucleation kinetics. Acta Metall., 17(8) 1123—1131, 1969. 

H.I. Aaronson and F.K. LeGoues. An assessment of studies on homogeneous diffusional nucleation kinetics in binary metallic alloys. Metall. Trans. A, 23(7) 1915—1945, 1992. 

Scanning probe microscopies are now able to study in situ the growth of metal clusters. These studies are performed sequentially after deposition. On metal/metal systems it has been possible to follow the nucleation kinetics and to derive the elementary energies like adsorption and diffusion energies (see the excellent review by Brune [68]). On oxide surfaces only recently such studies have been undertaken. STM can be only used on conducting samples, however it is possible to use as a support an ultrathin film of oxide grown on a metal. By this way it has been possible to study the nucleation of several... 

Hillig WB (1966) A derivation of classical two-dimensional nucleation kinetics and the associated crystal growth laws. Acta Metall 14 1868-1969... 

Void swelling occurs because the vacancies and interstitials created by radiation are absorbed preferentially at different sinks (cf. Allen, 2004). Preferentially, interstitials are absorbed at dislocations due to stress fields excess vacancies cluster together to form voids. The kinetics of formation of such clusters are controlled by the physical and chemical nature of the material. In pure metals, the kinetics of cluster nucleation and growth are determined in terms of the mobility of interstitials (vacancies), the irradiation time, radiation flux, and the mobility of the defects. In the... 

Galvanostatic reduction is another alternative for metal electrocrystallization in CPs. The metal nucleation and growth occurs at a continuously varying overpotential and therefore it is not suitable for gaining insight into the kinetics of the metal electrodeposition. Nevertheless, this approach provides a helpful opportunity to assess the involvement of CP reduction in the overall process, and to explore fine differences in the reductive behavior of CP materials synthesized under various electrochemical conditions [180-183,185,189]. 

Bruemmer et al. (55) studied Ni, Zn, and Cd sorption on goethite, a porous iron oxide known to have defects within the structure in which metals can be incorporated to satisfy charge imbalances. At pH 6, as reaction time increased from 2 hours to 42 days (at 293K), sorbed Ni increased from 12 to 70% of Ni removed from solution, and total increases in Zn and Cd sorption over this period increased 33 and 21%, respectively. The kinetics of Cd, Zn, and Ni were described well with a solution to Pick s second law (a linear relation with the square root of time). Bruemmer et al. (55) proposed that the uptake of the metal follows three-steps (i) adsorption of metals on external surfaces (ii) solid-state diffusion of metals from external to internal sites and (iii) metal binding and fixation at positions inside the goethite particle. They suggest that the second step is the rate-limiting step. However, they did not conduct microscopic level experiments to confirm the proposed mechanism. In view of more recent studies, it is likely that the formation of metal-nucleation products could have caused the slow metal sorption reactions observed by Bruemmer et al. (55). 

On a foreign metal substrate and in most of the cases on a substrate of the like metal, the first step of metal deposition is the formation of nuclei of the depositing metal. The kinetics of nucleation of the new metallic phase and its forms and rate of growth, in many cases play a dominant role in determining the overall deposition kinetics as well as the properties of the metal deposit. 

Whatever polymerization method is used, a new phase, the polymer, begins to grow on the electrode. The electrode surface rises due to the increase in roughness, and monomeric oxidation takes place at lower overpotentials on polymer than on metal. As a consequence, the nucleation of the new phase gives a loop of current in voltammograms, a minimum on chronoamperograms and a maximum on chronopoten-tiograms [50,67]. From those responses the influence on physical and chemical parameters on the nucleation kinetics or nucleation processes can be quantified [68]. 

Enol] Enomoto, M., Aaronson H.I., Nucleation Kinetics of Proeutectoid Ferrite at Austenite Grain Boundaries in Fe-C-X Alloys , Metall Trans. A, 17A(8), 1385-1397, (1986) (Phase Relations, Thermodyn., Calculation, Experimental, Kinetics, 53)... 

Tellurium and cadmium Electrodeposition of Te has been reported [33] in basic chloroaluminates the element is formed from the [TeCl ] complex in one four-electron reduction step, furthermore, metallic Te can be reduced to Te species. Electrodeposition of the element on glassy carbon involves three-dimensional nucleation. A systematic study of the electrodeposition in different ionic liquids would be of interest because - as with InSb - a defined codeposition with cadmium could produce the direct semiconductor CdTe. Although this semiconductor can be deposited from aqueous solutions in a layer-by-layer process [34], variation of the temperature over a wide range would be interesting since the grain sizes and the kinetics of the reaction would be influenced. 

Principles The reduction reaction is controlled essentially by the usual kinetic factors such as concentration of reactants, temperature, agitation, catalysts, etc. Where the reaction is vigorous, as, for example, when a powerful reducing agent like hydrazine is used, wasteful precipitation of A/, may occur throughout the whole plating solution followed by deposition on all exposed metallic and non-metallic surfaces which can provide favourable nucleation sites. In order to restrict deposition and aid adhesion, the selected areas are pre-sensitised after cleaning the sensitisers used are often based on noble metal salts. 

Kinetic data for the decompositions of several metal hydrides are summarized in Table 12 to which the following information can be added. The acceleratory period in the decomposition of BeH2 (a < 0.35) is ascribed [673] to the random formation of metal nuclei followed by linear growth. The increase in rate consequent upon exposure to X-irradia-tion is attributed to enhanced nucleation. Grinding similarly increased the... 

Figure 18 shows the dependence of the activation barrier for film nucleation on the electrode potential. The activation barrier, which at the equilibrium film-formation potential E, depends only on the surface tension and electric field, is seen to decrease with increasing anodic potential, and an overpotential of a few tenths of a volt is required for the activation energy to decrease to the order of kBT. However, for some metals such as iron,30,31 in the passivation process metal dissolution takes place simultaneously with film formation, and kinetic factors such as the rate of metal dissolution and the accumulation of ions in the diffusion layer of the electrolyte on the metal surface have to be taken into account, requiring a more refined treatment. 

A quantitative analysis of the kinetics of CdSe deposition from selenosulfate, Cd(II)-EDTA baths in terms of a mechanism involving nucleation and electrode kinetics has been given by Kutzmutz et al. [65], Note also that selenosulfate-containing baths have been used for the anodic selenization of vacuum-deposited metal films in order to synthesize CdSe and other binary selenide semiconductor thin films such as CuSe and InSe [66],... 

Our conclusion then for the oxygen interactions with metals is that because of the specific association of cluster ion intensities with particular types of oxygen rather than total coverage, the technique is not suitable for monitoring coverages or kinetics in an independent manner. Once it is established which type of oxygen a particular cluster ion is representative of, then that ion may, in favorable circumstances, be used for quantification. In the case of Ni, it seems that the negative ions are very sensitive to the initiation of oxide nucleation. In the case of W(IOO), the WOj, WO+ and WOj ions may fill a similar role. 

Turkevich who established the first reproducible standard procedure for the preparation of metal colloids [44] also proposed a mechanism for the stepwise formation of nanoclusters based on nucleation, growth, and agglomeration [45,46]. This model, refined by data from modern analydical techniques and results from thermodynamic and kinetic studies, is in essence stiU valid today (Figure 2) [82]. 

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