Colloid, hydrated

For low selenosulphate concentrations, only the small crystals were formed, even in thicker films, and this was rationalized by the lower steady-state selenide concentration, which would favor cluster growth over ion-by-ion formation (the product of free lead and selenide ions needs to be larger than the solubility product of PbSe for ion-by-ion deposition to occur). An important difference between the citrate depositions and the NTA or hydroxide ones is that, even in the ion-by-ion citrate deposition, some low concentration of colloidal hydrated oxide was present, due to the relatively low complexing strength of citrate. The pH of the hydroxide baths (> 13) was much higher than that of the citrate or NT A baths (10.8). 

White films of 6PbC03-3Pb(0H)2-Pb0 (from XRD analysis) were slowly formed over a few days from aUcaline-complexed Pb solntions that contained a colloidal hydrated oxide phase and that were exposed to air [31]. This was due to reaction with CO2 in the air (see Sec. 5.3.3). 

With small quantities of water tin (IV) chloride eventually forms a 5-hydrate, but when it is dissolved in large amounts it hydrolyzes with evolution of heat to form colloidal hydrated Sn02. The product must be preserved in tightly stoppered vessels corks used for the preparation or storage of the material must be coated with paraffin wax. It is freely soluble In numerous organic solvents. 

Bentonite occurs commercially as powders ranging in colors and tints from off white to pale brown to gray depending on the cations present in natural deposits. It comprises natural smectite clays consisting primarily of colloidal hydrated aluminum silicates of the montmorillonite or hectorite type of minerals with varying quantities of alkalies, alkaline earths, and iron. It is insoluble in water, in alcohol, in dilute acids, and in alkalies. 

Trivalent iron usually is precipitated from solution in the form of X-ray-amorphous brown precipitates, called amorphous, precipitated, or colloidal hydrate of Fe oxide. The freshly precipitated hydroxide contains a large amount of water, part of which forms hydroxyl groups, but the rest of the water may retain a certain independence, being bound to the hydroxide by adsorption, capillary, or osmotic phenomena. 

Bentonite is a native colloidal hydrated aluminum silicate consisting mainly of montmorillonite, Al203-4Si02-H20 it may also contain calcium, magnesium, and iron. The average chemical analysis is expressed as oxides, see Table I, in comparison with magnesium aluminum silicate. 

The USPNF 23 describes bentonite, purified benonite, and bentonite magma in three separate monographs. Bentonite is described as a native, colloidal, hydrated aluminum silicate and purified bentonite is described as a colloidal montmorillonite that has been processed to remove grit and nonswellable ore compounds. 

Bentonite is a native, colloidal, hydrated aluminum silicate, found in regions of Canada and the USA. The mined ore is processed to remove grit and nonswelling materials so that it is suitable for pharmaceutical applications. 

The products are silicic acid (H4Si04 see below) and colloidal hydrated iron oxide (Fe(OH)3), a weak alkali, which dehydrates to yield a variety of iron oxides, for example Fe203 (haematite—dull red colour) and FeOOH (goethite and lepi-docrocite—yellow or orange-brown colour). The common occurrence of these iron oxides reflects their insolubility under oxidizing Earth surface conditions. 

If the normal hydrate bo dried in vacuo it is converted into (Fe, ).jH,0, and this, when boiled for some hours with H,0, is converted into the colloid, or modified hydrate (Fe,)H,0, ( ), which brick-red in color almost insoluble in HNO, and HCl ves no Prussian blue reaction, and forms a turbid solution with acetic acid. If recently precipitated ferric hydrate be dissolved in solution of ferric chloride or acetate, and subjected to dialysis, almost all the acid passes out, leaving in the dialyzer a dark-red solution, which probably contains this colloid hydrate, and which is instantly coagulated by a trace of H,SO, by alkalies, many salts, and by heat dialyzed iron). 

The tendency toward hydroly of some of these elements can be used to advantage in separation processes. For example, in the Redox process for separating uranium and plutonium from fission products, the aqueous feed to the separation plant is made acid-deficient to promote hydrolysis of zirconium to a less extractable species, probably a colloidal hydrate [B5]. 

By acidification of the silicate solutions colloid polymer forms, colloidal hydrated Si02, are slowly separated. Absorbed silicate anions give the colloidal particles a negative charge. Silicates can form complexes with Fe(III) and Mn(II) their importance was mentioned in the section dealing with iron. 

The colloidal nature of biopolymers has been overlooked. In waterlogged wood, lignin must be in the form of a colloidal hydrated gel, which on drying must cause some dimensional changes. We should be looking into colloidal chemistry for answers to dimensional stability of this colloid (9). 

The terms gelatinous alumina or alumina gel covet a range of products in which colloidal hydrated alumina is the predominant sohd phase. 

Iso- and Hetero-polyanions. Potentiometric titrations of H against WO ions have shown that the product formed in the first 0.01 s of reaction is not paratungstate A, [HW Oji] ", nor any other discrete ion intermediate between this and WO , but is a mixture of a number of ill-defined products. These may be colloidal hydrated W oxides formed very rapidly in local regions of high acidity before complete mixing can occur and which are converted into [HW602i] in ca. 1 s. Steps in the aggregation of [M04] (M = Mo or W) ions have also been studied by cryoscopy, spectrophotometry, and pH measurements. ... 

The weak side of the Itypothesis of crystalhzation pressure is the well known phenomenon that crystals growing in the supersaturated solution carmot exert a pressure when the other crystals can grow free, with no obstacles. To elucidate this discrepancy the hypothesis explaining the expansion as the effect of in situ hydration of anhydrous phases was proposed. It is assumed that the crystals of anhydrous phase are surrounded by the colloidal hydration products. The solution of electrolyte can migrate through the pores in colloidal gel to the surface of anhydrous phase, but there is no empty space for the crystallization of l drates formed. The... 

In the presence of iron, for instance, the rate of decomposition increases markedly between pH 3 and 4, due to the formation of very active colloidal hydrated iron oxide. At pH greater than 5 most catalytic ions are almost insoluble and because of this the pH is normally adjusted to 4.5-6.0. The pH also influences the rate of decomposition of uncontaminated solutions of hydrogen peroxide. In alkaline solution the rate of decomposition increases rapidly as the pH is increased. 

The ability of bentonite to effectively overcome feed refusal due to T-2 toxin is not likely due to ion exchange since this product is a colloidal hydrated aluminum silicate. It has the property, however, of forming highly viscous gels when mixed with water. Absorption of toxin may therefore be reduced as bentonite traps molecules. This property likely accounts for the observation that bentonite can bind aflatoxin in vitro (Masimango et al., 1979). 

Bentonite is a native colloidal hydrated aluminum silicate or clay found in the midwest United States, Wyoming, and Canada. Consisting mainly of montmorillonite, a smectite clay, it is a very fine, odorless, pale buff or cream colored to grayish powder. It consists of particles in the range of 50 to 150 microns, but also has numerous particles in the 1 to 2 micron range. 

---