Colloidal metals stabilization problems

A strategy to solve this problem is to separate the core formation process from the reduction of metal ions in the cores as shown in Scheme 1, and use solvent (EG) and simple ions (OH , etc.) as the stabilizers [11]. In the first step of this process, metal salts hydrolyzed in the alkaline solution of EG to give rise to metal hydroxide or oxide colloids, which were then reduced by EG at elevated temperature to produce colloidal metal nanoclusters in the... 

A review of preparative methods for metal sols (colloidal metal particles) suspended in solution is given. The problems involved with the preparation and stabilization of non-aqueous metal colloidal particles are noted. A new method is described for preparing non-aqueous metal sols based on the clustering of solvated metal atoms (from metal vaporization) in cold organic solvents. Gold-acetone colloidal solutions are discussed in detail, especially their preparation, control of particle size (2-9 nm), electrophoresis measurements, electron microscopy, GC-MS, resistivity, and related studies. Particle stabilization involves both electrostatic and steric mechanisms and these are discussed in comparison with aqueous systems. 

The major disadvantages of colloidal catalysts studied so far can be attributed to problems in controlling the metal colloid formation (control of particle size, particle size distribution, structure of metal colloids) and stabilization of the prepared particles, which are not yet completely solved. But it is exactly the stability of the nanoparticles, that is decisive for long-term usage during catalytic processes. Moreover for catalytic application, it is extremely important to preserve the large surface of such colloidal systems. 

When two metal nanoparticles covered by a layer of adsorbed soluble polymer chains approach to a distance less the total thickness of adsorption layers, the polymer layers start to interact (Fig. 1). The interaction brings about steric stabilization and leads, in a majority of cases, to repulsion between the colloidal particles. It was repeatedly attempted to clarify its nature and determine its magnitude. Most frequently the problem is studied in terms of changing the Gibbs s energy when two particles are covered by an adsorbed polymer that are approaching one another from irffinity. 

In zinc-rich paints some early patents indicate the importance of a silica component. Colloidal silica was reacted with finely divided zinc to form a colloidal zinc silicate in which the excess zinc metal was suspended (654). A water-insoluble binder for zinc-containing coatings was produced by mixing alkali-stabilized colloidal silica with lithium hydroxide in suitable proportions (655). Evolution of gas from mixtures of colloidal silica with zinc powder is prevented by adding an indigoid compounds (656). Another formulation involves quaternary ammonium polysilicate solution milled with lead oxide as the binder for zinc (657). Some of the problems stem from the impurities in the zinc powder which promote reaction with the medium (658). Adhesion. of paints of this type of steel is improved by adding up to 2% of a styrene-acrylic resin dispersion (659). 

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