Ion, peptizing

Potential Determining Ions Ions whose equilibrium between two phases, frequently between an aqueous solution and a surface or interface, determines the difference in electrical potential between the phases, or at the surface. Example For the Agl surface in water, both Ag+ and I- would be potential-determining ions. If such ions are responsible for the stabilization of a colloidal dispersion, then they are sometimes referred to as peptizing ions. See also Indifferent Electrolyte. 

Hydrated Stannic Oxide. Hydrated stannic oxide of variable water content is obtained by the hydrolysis of stannates. Acidification of a sodium stannate solution precipitates the hydrate as a flocculent white mass. The colloidal solution, which is obtained by washing the mass free of water-soluble ions and peptization with potassium hydroxide, is stable below 50°C and forms the basis for the patented Tin Sol process for replenishing tin in staimate tin-plating baths. A similar type of solution (Staimasol A and B) is prepared by the direct electrolysis of concentrated potassium staimate solutions (26). 

At lower pH values, hydrogen ions are discharged, whereas at higher pH values, the magnetite layer thickens coarsely, becomes porous, and may peptize. Hydrogen blistering also may occur. 

Cathodic protection is a useful supplement to other forms of water treatment, as a general corrosion inhibiting device in HW boilers, or where specific design configurations can lead to inadequately protected localized metal in steam boilers. Where BW makeup demands are minimal and boiler output is fairly constant, cathodic protection devices can also provide some measure of protection against hardness scales. Calcium carbonate salt is formed as a floc-culant or soft sludge rather than a hard scale, due to the peptizing effects of a zinc hydroxide complex formed from zinc ions in alkaline BW. 

In the literature the term soluble Prussian blue introduced by Keggin and Miles [5] to determine the KFeFe(CN)6 compound is still widely used. However, it is important to note, that the term soluble refers to the ease with which the potassium ion can be peptized rather than to the real solubility of Prussian blue. Indeed, it can be easily shown by means of cyclic voltammetry that the stability of Prussian blue films on electrode supports is nearly independent of their saturation by potassium cations. Moreover, Itaya and coworkers [9] have not found any appreciable amount of potassium ions in Prussian blue, which makes doubtful structures like KFeFe(CN)6. Thus, the above equation fully describes the Prussian blue/Prussian white redox reaction. 

Rare-earth elements have been largely used in these studies. Among them, europium (III) was considered owing to its unusual electronic structure. Eu3+-ion-modified TiOz samples were prepared by a chemical coprecipitation-peptization method [156], which consists of prehydrolysis of TiCl4 by frozen distilled water. The Eu203 powder was added to the above solution to produce a transparent aqueous solution according to the required Eu3+ modifying content (Eu3+ ion equivalent to 3.0 at% of Ti in bulk solution). 

It seemed wise, therefore, to make preliminary experiments with sodium thiocyanate, NaCNS, because the sodium ion is not especially toxic and the thiocyanate ion is very effective in causing the peptization of proteins. The difference in action between sodium and potassium thiocyanate is apparently very great. We have injected 30 cc. of a 20% sodium thio-... 

Peptization also occurs naturally, such as when flowing water acts to convert unconsolidated particulate rock material into colloidal suspensions [49]. In this case peptization can be due to both the dilution effect and also to ion exchange reactions (such as the exchange of coagulating calcium ions for peptizing sodium ions). 

The principle of the sol-gel process is as follows. A sol is prepared by peptizing a well suited alumina powder with an acid. The powder particles or agglomerates are stabilized by a positively charged layer on the surface of these particles. An increase in pH allows the hydroxyl ions to neutralize the positive ions on the surface of the particles. These particles will grow together to larger particles and gelation will occur. The sol-gel process can be carried out in several ways ... 

Washing the precipitates It is essential to wash all precipitates in order to remove the small amount of solution present in the precipitate, otherwise it will be contaminated with the ions present in the centrifugate. It is best to wash the precipitate at least twice, and to combine the first washing with the centrifugate. The wash liquid is a solvent which does not dissolve the precipitate but dilutes the quantity of mother liquor adhering to it. The wash liquid is usually water, but may be water containing a small amount of the precipitant (common ion effect) or a dilute solution of an electrolyte (such as an ammonium salt) since water sometimes tends to produce colloidal solutions, i.e. to peptize the precipitate. 

To obtain pure sols, dialysis or electrodialysis, ion exchange, and peptization at high temperatures are used (Her, 1959). 

Many productive methods have been developed for the preparation of silica sol including acidification/121 electrolysation-electrodialysis,[13] ion-exchange,[14] peptization/111 and hydrolysis of silicon compounds/101 which can be grouped into two main types. One is called the aggregation method that contains two steps the polymerization of silicate ions and the aggregation of these polysilicate anions via condensation reaction between the hydroxy groups of the particles. The other one is called the peptization method, i.e., dispersal of a precipitate of Si02 to form colloid. The acidification method will be discussed in detail below. 

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