Siliceous surface, variable-temperature

Variable-temperature Si H CP/MAS-NMR spectroscopy was used to study the effect of molecular oxygen on the location of sorbate molecules in highly-siliceous zeolite framework, e.g. ZSM-5 with adsorbed />-dibromoben-zene.662 13C MAS-NMR spectra were used to follow the conversion of methanol on weakly-dealuminated zeolite H-ZSM-5 - showing the formation of cyclic compounds and carbonium ions.663 There is 13C CP/MAS-NMR evidence for surface ra-alkoxyl groups formed by the modification of the proton-ated perovskite HCa2Nb3Oi0 by w-alcohols.664 13C CP/MAS-NMR spectra... 

Variable-Temperature Diffuse Reflectance Fourier Transform Infrared Spectroscopic Studies of Amine Desorption from a Siliceous Surface... 

Variable-temperature diffuse reflectance infrared Fourier transform spectroscopy was used in conjunction with pyridine desorption studies to assess the acidity of a siliceous surface. An amorphous, porous silica substrate was investigated. The results contribute to an understanding of the acidic strength and the distribution of acidic sites on this material. A hydrogen-bonding interaction was observed between pyridine and the surface. Isothermal rate constants and an activation energy for the desorption process are reported and can be used as direct measures of surface site acidity. 

See Silicon-aluminum interactions in biology Alzheimer s disease, role of aluminum, 606 Amine desorption, variable-temperature diffuse reflectance Fourier transform infrared (FTIR) spectroscopy from siliceous surface, 257-266 Amine-stabilized sol, manufacturing... 

K.G. Proctor and D.E. Leyden, Surface Acidity Characterization of Siliceous Materials by Variable Temperature Diffuse Reflectance FTIR, Chemically Modified Oxide Surfaces, Vol. 3, D.E. Leyden and W.T. Collins Eds., Gordon and Breach Science Publishers, New York, pp. 137-149, 1990. 

D.E. Leyden and K.G. Proctor, Variable-Temperature Diffuse Reflectance Fourier Transform Infrared Spectroscopic Studies of Amine Desorption from a Siliceous Surface, The Colloid Chemistry of Silica, ACS Advances in Chemistry Series No. 234, H. Bergna Ed., pp. 257-267, 1994. 

Solubility data were very confusing until it was found that traces of certain metal impurities and especially the presence of an amorphous or at least disturbed layer on the crystal surface caused variable results, especially at temperatures below 150 C. In 1952, Dempster and Ritchie (117) reported that siliceous dusts have a layer of high solubility that gradually blends into the solid core, which adsorbs basic dyestuffs (118). Alexanian (119) found by electron diffraction that quartz possesses a surface layer of amorphous silica about 100 A thick, which is removed by HF but is re-formed in ambient humidity. Waddams found that the quartz surface in water released mosaic silica, presumably as particles of colloidal size, since they scattered light (120). This was confirmed by Sakabe et al. (121), who found that in neutral or alkaline aqueous suspension, quartz released both soluble silica and colloidal particles of crystalline nature, 0.01-0.3 microns in size. Stober and Arnold (122) found that the amount of silica released was much more than a monomolecular layer, and that it decreased with successive changes of water. When quartz was intensively pulverized in water, the disturbed surface layer can amount to as high as 35%, with a specific surface area of 70 m g, and the solubility is increased from less than 10 to 70 ppm at 25 C (123). Paterson and Wheatley (124) made similar observations. 

Harrison and Watson [48] found that the saturation surface of apatite for silicate liquids was relatively insensitive to variables other than temperature and silica activity. The experimental data are well fitted by... 

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