Growing deposit, adsorbates

Adsorbates that do not segregate to the surface during deposition may be incorporated into the growing deposit, thereby affecting the micro structure and physical properties of the solid. Mass balance on the moving planar interface requires that ... 

Decolorisation by Animal Charcoal. It sometimes hap pens (particularly with aromatic and heterocyclic compounds) that a crude product may contain a coloured impurity, which on recrystallisation dissolves in the boiling solvent, but is then partly occluded by crystals as they form and grow in the cooling solution. Sometimes a very tenacious occlusion may thus occur, and repeated and very wasteful recrystallisation may be necessary to eliminate the impurity. Moreover, the amount of the impurity present may be so small that the melting-point and analytical values of the compound are not sensibly affected, yet the appearance of the sample is ruined. Such impurities can usually be readily removed by boiling the substance in solution with a small quantity of finely powdered animal charcoal for a short time, and then filtering the solution while hot. The animal charcoal adsorbs the coloured impurity, and the filtrate is usually almost free from extraneous colour and deposits therefore pure crystals. This decolorisation by animal charcoal occurs most readily in aqueous solution, but can be performed in almost any organic solvent. Care should be taken not to use an excessive quantity... 

Sample Preparation. The methods of sample preparation affect the chemical and physical properties of the sample molecules and hence can profoundly influence the secondary ion formation/ emission process. In earlier molecular SIMS studies the samples were prepared by placing a dilute solution of the compound onto an acid-etched Ag foil [87, 88]. The acid etched surface provides, a substrate onto which thin layers of the compound can be deposited from solutions with extended concentration ranges. If on the other hand, the substrate was not etched and the concentration of the solution was too high, the adsorbed molecular film would grow too thick and consequently quench the secondary ion emission. 

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