Various Avenues Taken in Search for Diamonds
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ing pH. At very high pH values (pH = 13), the corrosion rate of the phosphate glass surface was so rapid that the silane could not form a stable bond with the surface and no APS could be detected by x-ray photoelectron spectroscopy (XPS). The researchers also determined that the concentration of silane on the surface of silicate glasses increases with increasing solution concentration until a critical value is reached where the surface concentration then becomes constant, independent of solution concentration. The adsorbed concentration of silane on the surface of the phosphate glass also increased with increasing solution concentration. In contrast though, after forming a monolayer, the concentration of silane on the surface then begins to rise rapidly with increasing solution concentration, due to the formation of multilayers. Additionally, said Barnes, the shape of the high-resolution spectra peak by XPS changes with solution concentration. This peak can provide information concerning the state of the nitrogen in the adsorbed silane layer, showing both a free amine (–NH2) and a protonated amine (–NH3+) at different binding energies. At low concentrations, the nitrogen is almost entirely in the free state, Barnes said, suggesting that APS is adsorbing to the surface through the hydrolyzed alkoxy group (the silane end). As multilayers begin to form, the protonated amine concentration begins to increase. Barnes said that very little literature is available on the surface of phosphate glasses and even less on the factors effecting silane adsorption to phosphate glasses. She said that phosphate glasses are finding ever-increasing uses in both photonics and optics applications and the ability to couple the glass with other materials to form composite or hybrid structures is important in both present and future applications. Understanding how to effectively adsorb a coupling agent to the surface is the first step to expanding the potential applications of multicomponent phosphate glasses, she said. “Applications to join two phosphate glasses, phosphate glass and polymers, or phosphate glass and other organic chemicals are just beginning,” said Barnes. “With a silane coating, these glasses can be used as hybrids rather than standalone materials. We can connect and combine them with dissimilar materials.”
Various Avenues Taken in Search for Diamonds Geological studies are exploring evidence from Venus to several hundred kilometers under the Earth’s surface to determine ways to locate diamonds. Some of southern Africa’s most prof664
itable diamond mines are located near areas where the earth is exceptionally stable and cool up to 250 km below the surface, according to Matt Fouch, assistant professor of geological sciences at Arizona State University; David James and John VanDecar of the Department of Terrestrial Magnetism, Carnegie Institution of Washington; and Suzan van der Lee of the Institute of Geophysics, Zürich, Switzerland. Geologists think diamonds develop up to several hundred kilometers deep within ancient cr
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