Aqueous silicate solutions hydroxides

Harris, R.K, and Knight, C.T.G. (1982) Silicon-29 NMR Studies of Aqueous Silicate Solutions. Part, IV. Tetraalkylammonium hydroxide solutions, J. Mol. Struct, 78,273-278. 

With chemical treatment, the natural surfactants in crude oil can be activated [1384]. This method has been shown to be effective for highly viscous crude oil from the Orinoco Belt that has been traditionally transported either by heating or diluting. The precursors to the surfactants are preferably the carboxylic acids that occur in the crude oil. The activation occurs by adding an aqueous buffer solution [1382,1383]. The buffer additive is either sodium hydroxide in combination with sodium bicarbonate or sodium silicate. Water-soluble amines also have been found to be suitable [1506]. 

Aqueous surfactant solutions were prepared at room temperature. The experiments were performed at a fixed concentration of 0 1M CTAB or CTAC by decreasing the pH (by addition of HC1 or replacing OH" by Cl" with NaCl) of clear basic 0.5M silicate solutions (sodium silicate (T SisCb) solution (waterglass) or D4R species stabilized in an aqueous tetramethylammonium hydroxide/methanol solution [10]). 

Silicates in Solutions. The distribution of silicate species in aqueous sodium silicate solutions has long been of interest because of the wide variations in properties that these solutions exhibit with different moduli (23—25). Early work led to a dual-nature description of silicates as solutions composed of hydroxide ions, sodium ions, colloidal silicic acid, and so-called crystalloidal silica (26). Crystalloidal silica was assumed to be analogous to the simple species then thought to be the components of crystalline silicate compounds. These include charged aggregates of unit silicate structures and silica... 

In a study [6] of the dissolution of amorphous silica gels in aqueous alkali metal hydroxides, the rate of dissolution was found to depend on the cation used in the dissolution reaction. A maximum in dissolution rate was found for potassium hydroxide solutions, whereas both intrinsically smaller and larger cations (lithium-sodium and rubidium-cesium) showed slower dissolution rates, as can be concluded from the concentration of dissolved silicate species (normalized peak areas) as a function of alkali metal cation (Figure 45.2). This result is contradictory to the expectation that a monotonic increase or decrease in dissolution rate is to be observed for the different cations used. One major effect that occurs at the high pH values of this study is that the majority of silanol... 

If an acid solution of a fluorosilicate is rendered faintly alkaline with aqueous sodium hydroxide and then shaken with freshly precipitated cadmium oxide, all the silicic acid is adsorbed by the suspension. The alkali fluoride is then determined in the filtrate. 

Isolation of toxins. The digestive glands of shellfish were extracted with acetone at room temperature. After removal of the acetone by evaporation, the aqueous suspension was extracted with diethyl ether. The ether soluble residue was successively chromatographed twice over silicic acid columns with following solvents benzene to benzene-methanol (9 1), and diethyl ether to diethyl ether-methanol (1 1). To avoid degradation of dinophysistoxin-3 by contaminant acid, the silicic acid was washed with dilute sodium hydroxide solution and then with water prior to activation at 110 C. Toxic residue obtained in the second eluates was separated into two fractions... 

Fortnum (4, 5), in his Raman spectrum study of aqueous ions, observed four distinct lines at 448, 607, 777, and 935 cm-1 which he attributed to the silicate ion. He adds that a fifth line is observed at 1040 cm 1 in solutions having little or no added sodium hydroxide however, this line disappears in solutions having large amounts of sodium hydroxide with an increase in sharpness and intensity of the 777- and 935-cm-1 lines. He says that there are two species which could have been present to give rise to the 1040-cm 1 lines either hydrolyzed silicate ion, SiO(OH)3 , or a dimer, H4Si2072. ... 

Smectite-type materials were synthesized with a hydrothermal method [5]. The aqueous solution of sodium silicate (Si02 / NajO= 3.22) and sodium hydroxide was mixed with the aqueous solution of metal chloride to precipitate Si-M (M divalent metal cation, Si M = 8 6) hydroxides. The precipitation pH of Si-M hydroxide was controlled by changing the molar ratio of sodium hydroxide to sodium silicate. After separating and washing of Si-M hydroxide, slurries were prepared from Si-M hydroxide and water. The Si-M slurries were treated hydrothermally in an autoclave at 473 K under autogaseous water vapor pressure for 2 h. The resultant samples were dried at 353 K then we obtained smectite samples. The smectite-type materials are denoted by the divalent species in octahedral sheets and BET surface area, e.g., Ni-481 for the Ni2+ substituted smectite-type material with a surface area of 481 m2g. ... 

In general, polycarbonate resins have fair chemical resistance to aqueous solutions of acids or bases, as well as to fats and oils. Chemical attack by amines or ammonium hydroxide occurs, however, and aliphatic and aromatic hydrocarbons promote crazing of stressed molded samples. For these reasons, care must be exercised in the choice of solvents for painting and coating operations. For sheet applications, polycarbonate is commonly coated with a silicone—silicate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

The polymerization of basic metal ions will also interfere with crystallization. When a metal salt is mixed with a silicate, the increase in pH in the environment of the metal ion causes the formation of polymeric basic metal ions of colloidal metal hydroxides which are not likely to fit into a silicate crystal. Thus, the precipitation of a metal silicate from aqueous solution at normal temperature tends to produce a coagulation of positively charged colloidal metal hydroxide and negatively charged colloidal silica. 

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