Agglomeration silver particle

In Fig. 9.15 are shown SEM images of silver produced with an immersion of niobium substrates into highly alkaline Ag(I) solutions above 90 °C. Agglomerated silver particles are clearly visible from these images. Deposition of silver onto niobium surface via galvanic displacement shows that unavoidably present oxide film at the surface of the substrate can be successfully removed. A production of powdery deposits suggests that oxide film is unevenly removed from the niobium surface. 

Figure 8.12 Mobility diameter of agglomerates composed of 16-nm silver particles decreases as a result of in situ hearing at constant tentperaiure. (After Weber and Friediander, 1997b.)...

A typical silver deposit obtained from the ammonium solution at an overpotential of 650 mV is shown in Fig. 2.3a. From Fig. 2.3a, it can be seen that very branchy dendrites are produced at this overpotential. Silver particles obtained by tapping the silver deposit (Fig. 2.3a) are shown in Fig. 2.3b. The dendritic character of this particle is made of the comcob-like elements as presented by the images in Fig. 2.3c, d. A further analysis of the comcob-like elements at the microlevel showed that they are composed of small agglomerates of silver grains (Fig. 2.3d). Anyway, morphologies of silver particles electrodeposited from ammonium solution were completely different than those formed during silver electrodeposition from nitrate electrolyte. 

It is necessary to note that the shape of the polarization curve for silver electrodeposition from ammonium solutitm (Fig. 2.1) and morphologies of silver particles (Fig. 2.3) were very similar to those obtained by copper electrodeposition from sulfate solutions at overpotentials corresponding to the plateaus of the limiting diffusion current density [4, 7-11] (see also other chapters). The similarity of silver and copper dendrites was observed at both macro- and microlevels, because both copper and silver dendrites were composed of comcob-like forms, while the comcob-like forms were built of small agglomerates of metal grains [4]. 

Adsorption of ions or neutral molecules on the surface of metal particles can lead to a change in optical absorption and chemical reactivity. The optical changes are most strongly produced in the wavelength range of the plasmon absorption band. Most remarkable effects are observed for silver particles whose plasmon absorption is especially intense, i.e. little damped. The adsorption of substances can lead to a destabilization of particles, i.e. to agglomeration. This effect generally is accompanied by a redshift of the plasmon absorption band due to dipole-dipole interaction between near-by... 

Small silver nanoparticles are stabilized by ionic species that adsorb to their surface, much like the citrate ions prevent rapid agglomeration of gold nanoparticles. The ionic repnlsion experienced by the silver particles are likely due to carboxylic acids that form after the oxidation of aldehydes. Upon the addition of o er ionic species, the silver nanoparticles approach each other more easily and grow in size. Stndents observe a change in color from yellow to green as the plasmon resonance band shifts to longer wavelengths. 

Water paints were impregnated with nanosized silver colloids. Most of initial silver nanoparticles agglomerated into up to 200-nm clusters as a result of attractive interaction forces between the particles (Fig. 18.2). 

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