Colloidal solution peptization

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). 

Positively-charged hydroxide sols can be prepared from many metals. To produce a colloidal solution from the precipitate, a process termed peptization, a solution of the salt, itself, is not... 

F. S. Brown and C. R. Bury 6 obtained colloidal solutions of phosphorus pentoxide in nitrobenzene by stirring the mixture in the presence of alcohols or organic acids. The hydroxy-compound is absorbed and peptizes the pentoxide. Traces of moisture cause coagulation. Cone. soln. set to gels on keeping. 

In the particulate-sol method a metal alkoxide dissolved in alcohol is hydrolyzed by addition of excess water or acid. The precipitate that results is maintained as a hot solution for an extended period during which the precipitate forms a stable colloidal solution. This process is called peptization from the Greek pep—to cook (not a misnomer many descriptions of the sol-gel process have a strong culinary flavor). The colloidal solution is then cooled and coated onto the microporous support membrane. The layer formed must be dried carefully to avoid cracking the coating. In the final step the film is sintered at 500-800 °C. The overall process can be represented as ... 

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. 

A water-soluble blue can be manufactured by adding peptizing agents (the latter improve the water solubility via an emulsifying action). This forms a transparent colloidal solution in water without the use of high shear forces [3.172]. 

Peptization is less important in the formation of natural colloidal solutions, inasmuch as conversion of the coagulant into sol again is characteristic of fresh highly dispersed sediments under the influence of special substances — peptizers. Peptization usually is observed when substances capable of forming sols act on sediments formed by coagulation of colloidal particles. 

At room temperature colloidal solutions of iron hydroxide can be obtained only by way of prolonged dialysis (Glazman et al., 1958). And finally, experiments are known in which sols were obtained by peptization, by treating freshly precipitated, washed Fe(OH)3 sediment with ferric chloride while heating. A dilute solution with a certain amount of HCl acts on freshly precipitated Fe(OH)3 as ferric chloride does. The sols of Fe(OH)3 obtained by peptization are no different in structure from the sols obtained by hydrolysis. 

Colloidal form of transport of ferric iron in the Precambrian, apparently, was less important than in later geologic epochs. On the basis of an examination of the known methods of formation of colloidal solutions, it can be assumed that condensation phenomena predominate in the geochemical processes, and dispersion and peptization play a secondary role. Consequently one of the conditions for obtaining colloidal solutions is the presence of ionic solutions as an obligatory intermediate stage in the cycle weathering transport deposition. 

Preparation of TiO Colloid Solution. Titanium tetraisopropoxide (Aldrich Chemical Company) at a concentration of 5 ml in 25 ml of isopropanol, was added dropwise to 0.1 M aqueous HC1 solution while stirring. After the addition was complete, the solution was stirred for another 10 minutes and then heated slowly to remove the solvent the residue was dried under vacuum at 118°C. The Ti02 powier readily peptized in water. Aqueous colloidal solutions tended to precipitate in basic solutions addition of large amounts of inert salts also precipitated the colloids. Photoplatinization was done as reported earlier (9 ). 

A colloidal solution or sol is a suspension of nanometer size particles in a liquid. Sols can be formed by dispersing ultrafine particles in a liquid or by precipitation of fine particles from a solution followed by peptization. The stability of the sol can simply result from Brownian... 

Peptization n. Process of bringing a solid into a colloidal solution. Becher P (1989) Dictionary of colloid and surface science. Marcel Dekker, New York. 

Typical examples of real physical systems and processes conforming to this approach (r = const) include colloid solutions of micelle-forming surfactants and the dispersion (peptization) of a globular structure with a given strength of contacts between the particles, p, and the work of the contact rupture, u. ... 

The inverse phenomenon of coagulation is peptization. It occurs when the precipitate passes into a colloidal solution. (Recall that the colloidal state of matter is characterized, among other properties, by a certain range of particule sizes 1 nm-0.1 p.m.) This may occur if the electrolyte concentration in the supernatant liquid goes below the coagulation value. These considerations may be summarized by the scheme... 

Nevertheless we know that not only the peptizing electrolytes, but all other electrolytes as well influence the stability of a colloidal solution The question, is, how can they influence the repulsion between particles when the potential difference between the two phases is fixed by the presence of potential-determining ions We have nientio-... 

Hydrolysis of solutions of Ti(IV) salts leads to precipitation of a hydrated titanium dioxide. The composition and properties of this product depend critically on the precipitation conditions, including the reactant concentration, temperature, pH, and choice of the salt (46—49). At room temperature, a voluminous and gelatinous precipitate forms. This has been referred to as orthotitanic acid [20338-08-3] and has been represented by the nominal formula Ti02 2H20 (Ti(OH). The gelatinous precipitate either redissolves or peptizes to a colloidal suspension ia dilute hydrochloric or nitric acids. If the suspension is boiled, or if precipitation is from hot solutions, a less-hydrated oxide forms. This has been referred to as metatitanic acid [12026-28-7] nominal formula Ti02 H2O (TiO(OH)2). The latter precipitate is more difficult to dissolve ia acid and is only soluble ia concentrated sulfuric acid or hydrofluoric acid. 

If unchanged barium methyliminodiacetate remains in solution, it peptizes the barium sulfate and the filtration is likely to be troublesome. If colloidal barium sulfate is encountered, it... 

To peptize means a bulk phase enters solution as a colloid (here, as a micelle). 

Mack (58, 59) points out that asphaltenes from different sources in the same petro-lenes give mixtures of approximately the same rheological type, but sols of the same asphaltenes in different petrolenes differ in flow behavior. Those in aromatic petrolenes show viscous behavior and presumably approach true solution. Those in paraffinic media show complex flow and are considered to be true colloidal systems. Pfeiffer and associates (91) consider that degree of peptization of asphaltene micelles determines the flow behavior. Thus, a low concentration of asphaltenes well peptized by aromatic petrolenes leads to purely viscous flow. High concentrations of asphaltenes and petrolenes of low aromatic content result in gel-type asphalts. All shades of flow behavior between these extremes are observed. 

Solution methods starting with a suspension and producing a colloid (peptization). 

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