Colloids of metals

FIGURE 8.45 The stability of colloids is illustrated by this violet liquid, which is a colloid of metallic gold that has survived since it was prepared by Michael Faraday in 1857... 

Colloids of metals with practically zero overpotential for Hj evolution such as platinum and iridium are very efficient at catalysing production. The transferred electrons are immediately converted into adsorbed H atoms which then undergo the Heyrovsky reaction to form Hj e + H -h H2. The gold microelectrode... 

When colloids of metal sulfides, selenides, phosphides and arsenides are illxuninated in the presence of air, decomposition takes place. Metal ions migrate into solution and sulfate, selenite, phosphate or arsenate are formed. The process was first investigated in the case of colloidal CdS... 

Table 3.2 Tenside-Stabilized Colloid of Metals of Groups 8-11 of the Periodic Table by Reduction with Hydrogen in H20...

Preparation and Application of Aqueous Colloids of Metal Oxide and Multimetal Oxide Nanoparticles... 

The neutral silver is formed by this reaction. During the subsequent heat treatment of the glass at approximately 600 C, colloids of metallic silver are formed (Beall 1992). This colloidal silver forms heterogeneous nuclei of approximately 80 A for the subsequent crystallization of a lithium metasilicate primary crystal phase, Li2Si03. Lithium metasilicate possesses a chain silicate structure. The crystallization of this compound proceeds dendritically. The dentritic growth of crystals in glass-ceramics is discussed in Section 3.2.4. 

Clusters of metal atoms can form colloidal suspensions. Colloidal clusters of copper, silver, and gold in glass are responsible for some of the vivid colors of stained glass in medieval cathedrals. Even aqueous suspensions of metal clusters are known (Fig. 8.45). 

The decomposition is significantly accelerated and the temperature of the first decomposition reaction is lowered to 120°C (Fig. 19.7). The decomposition rate is relatively low compared with other titanium-based dopants. The highest activity of a titanium catalyst used in alanate decomposition was observed for ligand-stabilized colloidal titanium metal [42]. 

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]. 

The alcohol reduction process invented by Hirai and Toshima is widely applicable for the preparation of colloidal precious metals stabilized by organic pol5mers such... 

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