Peptization, of colloids

The soil pH considerably affects soil characteristics. It is important for many soil-forming processes and it also affects the biological activity of soil organisms. The soil pH directly affects particularly the solubility of many substances, ion adsorption and desorption, coagulation and peptization of colloids and chemical reactions. By its action on the soil structure it also affects most of the physical properties of the soil. Thus, the soil pH is an important parameter of the soil fertility. 

The cold frit is crushed in equipment which is preferably totally enclosed to prevent personal contact with the irritant alkaline dust. Leaching is then carried out with water to remove sodium silicate and excess sodium hydroxide. About 7 tons of water per ton of zircon are appropriate, this quantity being divided between several successive leaching operations. Solid-liquid separation is by decantation between each leach. The sodium zirconate is finally filtered off in a fairly dry condition. It is advisable not to use a larger excess of water or peptization of colloidal zirconium com-... 

Ono S., Yamada N., Hirano S. Pottasium lithium niobate films derived from aqueous precursor solution. J. Am. Ceram. Soc. 2001 84 1415-1420 Panda A.B., Pathak A., NandagoswamiM., PramanikP. Preparation and characterization ofnanocrys-talline Sri j Bi2+jTa209 powders. Mater. Sci. Eng. 2003 B97 275-282 Perez-Maqueda L.A., Wang L., Matijevic E. Nanosize indium hydroxide by peptization of colloidal precipitates. Langumuir 1998 14 4397-4401... 

Colloidal State. The principal outcome of many of the composition studies has been the delineation of the asphalt system as a colloidal system at ambient or normal service conditions. This particular concept was proposed in 1924 and described the system as an oil medium in which the asphaltene fraction was dispersed. The transition from a coUoid to a Newtonian Hquid is dependent on temperature, hardness, shear rate, chemical nature, etc. At normal service temperatures asphalt is viscoelastic, and viscous at higher temperatures. The disperse phase is a micelle composed of the molecular species that make up the asphaltenes and the higher molecular weight aromatic components of the petrolenes or the maltenes (ie, the nonasphaltene components). Complete peptization of the micelle seems probable if the system contains sufficient aromatic constituents, in relation to the concentration of asphaltenes, to allow the asphaltenes to remain in the dispersed phase. 

Yonezawa Y, Sato T, Kuroda S, Kuge KJ (1991) Photochemical formation of colloidal silver peptizing action of acetone ketyl radical. J Chem Soc Faraday Trans 87 1905-1910... 

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. 

IN PEPTIZATION, URGE PARTICLES ARE BROKEN DOWN INTO SMALLER PARTICLES OF COLLOIDAL SIZE. 

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. 

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. 

The reverse of the coagulation process is peptization. It is well known from analytical chemistry that fresh precipitates are easier to disperse than old ones, which indicates qualitatively that an aggregate of colloidal particles is not in equillibrium and that irreversible, time-dependent processes occur in coagulation. As pointed out Frens and Overbeek (1971) the interpretation of peptization phenomena with aggregated systems is not possible unless the data are obtained in experiments with a shorter time scale than the aging time of the aggregate. They demonstrated that it was possible to follow the kinetics of peptization by suddenly diluting the sol... 

There are two types of insanity which have not hitherto been differentiated properly by medical men. In one the mental disorder is due to over-coagulation of the brain colloids and in the other to over-peptization of them. 

Peptization will occur only if and when the concentration of colloid is sufficient to form a blanket around the particles to be solubilized. This is known as the critical concentration level. 

A finely powdered carbon is usually preferable for the complete removal of traces of colloids from a crystalline product such as sugar but the finely powdered carbons are less suitable when the main ingredient is a colloid. Then, to avoid peptization, a coarser carbon is desirable and in some cases it is necessary to use a hard granular carbon. 

Besides hydrolysis, one can also utilize other exchange reactions in the preparation of disperse systems. It is, however, important to remember that a substantial amount of electrolyte, which is often present in the solution, may result in a loss of colloidal stability. One can sometimes remove excess electrolyte by washing and subsequent peptization of the precipitate. It is advantageous to prepare disperse systems at high supersaturations, which can be reached upon mixing concentrated solutions of reactants. The sols of Prussian Blue, various sulfides, stannic acid and its compound with colloidal gold (Cassian Purple) are all made by this method. 

In the case when the depth of potential minimum is smaller than several kT, the coagulation (i.e., the combination of two particles) becomes thermodynamically unfavorable even at low height of the potential barrier (Chapter VII, 1), and the stability of colloidal system towards coagulation is of thermodynamic nature. This is confirmed by observed peptization of coagulated precipitates upon washing out the excess of coagulating electrolyte and by stabilization of sols by specifically adsorbed ions. 

The peptization capabilities of polyphosphates depend on their sorption on aluminosilicates and colloidal particles of hydrated oxides of iron, aluminium and manganese. In practice, this causes problems in water treatment by coagulation when already rather low concentrations of polyphosphates can cause improper agglomeration of colloidal particles into sedimentable floccules. 

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