Colloidal and Amorphous Materials

L2. Lewis, W. K., Squires, L., and Broughton, G., Industrial Chemistry of Colloidal and Amorphous Materials. Macmillan, New York, 1942. 

There are also colloidal "sols in which dispersed and dispersion mediums are solids (Eg alloys, plastics, glass, some minerals, etc) Refs 1)J. Alexander, "Colloid Chemistry, Theoretical and Applied , 6 volumes, Van Nostrand, NY (1926-1946) 2)W.K.Lewis, L.Squires G.Broughton, "Industrial Chemistry of Colloidal and Amorphous Materials , Macmillan, NY (1943) 3)H.B.Weiser, "Colloid Chemistry , A Textbook, Wiley, NY (1949) 4)A.E. Alexander St P.John-... 

G.Broughton, "Industrial Chemistry of Colloidal and Amorphous Materials , Macmillan, NY (1943) 3)H.B.Weiset, "Colloid Chemistry , A Textbook, Wiley, NY (1949) 4)A,E.Alexander P.John-... 

Lewis, Squires, and Broughton, Industrial Chemistry of Colloidal and Amorphous Materials, ... 

In addition to some one hundred papers in broadly diverse areas of chemical engineering, he was coauthor of Industrial Stoichiometry in 1926 and Industrial Chemistry of Colloidal and Amorphous Materials in... 

Colloidal and amorphous materials Process control and instrumentation (Swanson)... 

Langmuir and Whittemore (33) point out that oxyhydroxide precipitates formed in the laboratory at low temperatures are usually mixtures of colloidal-sized amorphous material and crystalline phases, with individual crystal dimensions ranging from 50 to 2000 A. In such mixtures, the most soluble phase, usually amorphous, determines the pQ, the value calculated for pKj, for non-equilibrium phases. Although the crystalline phases grow at the expense of the amorphous material and each other, colloidal-sized crystalline phases can persist indefinitely in dilute waters low in dissolved Fe(II) or Fe(III). 

Over the decades that have passed since La Mer s work numerous examples of monodispersed particles of various composition, morphologies and properties, as well as methods for their preparation (not limited to condensational formation), were described in the literature. Extensive studies in this area were carried out by E. Matijevic and T. Sugimoto. Examples of monodisperse systems formed by precipitation from homogeneous solutions include dispersions of uniform particles of simple composition having different morphologies, such as metal halides, sulfides, phosphates, (hydrous) oxides, etc, various composite particles, including particles of internally mixed composition and coated particles. Both crystalline and amorphous materials can be obtained. Electron micrographs of some characteristic examples of monodispersed colloids are shown in Fig. IV-14. 

Plutonium solubility in marine and natural waters is limited by the formation of Pu(OH)4(am) (for amorphous) or Pu02(c) (for crystalline). The K q of these species is difficult to measure, in part due to the problems of the polymer formation. A measured value for Pu(OH)4(am) is log = -56. This value puts a limit on the amoimt of plutonium present, even if Pu(V) or Pu(IV) are the more stable states in the solution phase. Moreover, hydrolyzed Pu(IV) sorbs on colloidal and suspended material, both inorganic and biological. 

Colloidal offretite crystals with a maximum size of up to 250 nm were prepared by hydrothermal synthesis at 100°C. The system is unusual in the sense that colloidal crystals form from a gel and that the yield sometimes is very high. The effects of the duration of hydrothermal treatment and the composition of the synthesis mixture on the product were investigated using XRD, DLS and SEM. Some syntheses resulted in mixtures of offretite and amorphous material or colloidal sodalite, whereas others resulted in a pure and colloidal offretite product. 

Differences in the absorption spectra of colloidal and macrocrystalline semiconductors were first recognized for CdS and AgBr The absorption of 3 nm particles of CdS in aqueous solution begins close to 515 nm, the wavelength at which bulk CdS starts to absorb however, the increase in absorption at shorter wavelengths is much less steep than for the macrocrystalline material (Fig. 6). The effect was first explained by a possible amorphous structure of the colloidal particles However, after it was shown by Brus and co-workers that the particles had an ordered struc-... 

A variation of the CD process for PbSe involved deposition of a basic lead carbonate followed by selenization of this film with selenosulphate [64]. White films of what was identified by XRD as 6PbC03-3Pb(0H)2-Pb0 (denoted here as Pb—OH—C) were slowly formed over a few days from selenosulphate-free solutions that contained a colloidal phase and that were open to air (they did not form in closed, degassed solutions). CO2 was necessary for film formation—other than sparse deposits, no film formation occurred of hydrated lead oxide under any conditions attempted in this study. Treatment of these films with selenosulphate solution resulted in complete conversion to PbSe at room temperature after 6 min. The selenization process of this film was followed by XRD, and it was seen to proceed by a breakdown of the large Pb—OH—C crystals to an essentially amorphous phase of PbSe with crystallization of this phase to give finally large (ca. 200 nm) PbSe crystals covered with smaller (15-20 nm) ones as well as some amorphous material. 

A source of error in chemical analyses of montmorillonites (and in other clays) that is not commonly checked is the presence of amorphous material, particularly Si and Al. Table XXXII lists structural formulas given by Osthaus (1955) for montmorillonites which were purified by size fraction and by extraction with 0.5 N NaOH to remove amorphous Si and Al. In six analyses dissolved silica ranged from 3.6 to 8.4% and alumina from 0.6 to 2.25%. Amorphous silicon dioxide should be expected in most montmorillonites derived from volcanic material. The source glass has more Si than is required for the 2 1 layer and the excess must be leached from the glass. Much of the Si is deposited in the sediments underlying the bentonite bed in the form of chert but it is to be expected that the extraction would not be complete and a portion of the colloidal Si would remain in the bentonite bed. 

Silica is one of the most abundant chemical substances on earth. It can be both crystalline or amorphous. The crystalline forms of silica are quartz, cristobalite, and tridymite [51,52]. The amorphous forms, which are normally porous [149] are precipitated silica, silica gel, colloidal silica sols, and pyrogenic silica [150-156], According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), porous materials can be classified as follows microporous materials are those with pore diameters from 3 to 20 A mesoporous materials are those that have pore diameters between 20 and 500 A and macroporous materials are those with pores bigger than 500 A [149],... 

Oxyhydroxide precipitates are generally mixtures of different phases. The apparent thermodynamic stability or solubility of such mixtures depends in large part on the solubility of the least stable phase present. This phase is of course often amorphous. Oxyhydroxide precipitates usually contain substantial amounts of collodial-sized material. Sizes from molecular Fe(OH)3° to micron-size crystals or crystal aggregates are possible (8). Both crystalline and amorphous precipitates remain colloidal indefinitely in some solutions. Particle size is probably the major control on the thermodynamic stability of the oxyhydroxides. Other important controls on stability are mineralogy, crystallinity, the degree of hydration of the precipitate, and the presence of impurities. 

During the first part of the induction period (section 6. /), the different components of the reaction interact with one another, moving towards a pseudo-equilibrium under the prevailing conditions of temperature and pressure. In many cases, a visible gel phase is present. In other cases, the same type of material is present as colloidal particles, invisible to the naked eye. A fragment or domain of this amorphous component is shown in Fig. 4(a) as a random network of linked tetrahedra [36]. This amorphous material equilibrates with the cations and anions of the solution phase in such a way that local areas of increased order are created in which the structure begins to resemble that of the eventual product (Fig. 4(b)). 

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