Nano-Structures and Interactions of Alkali Metals within Silica Gel

Citations Over TimeTop 16% of 2011 papers

Abstract

Liquid alkali metals and their alloys can be absorbed into the 15 nm diameter pores of nanostructured silica gel (SG) at loadings up to 40 wt %. Characterization of the resultant materials was done by measuring the amount of hydrogen produced by addition of alcohols and/or water, by differential scanning calorimetry, and by static 23Na NMR spectroscopy. While sodium must be heated above 100 °C to form Na in SG, absorption of Na–K alloys at ambient temperatures yields nanoscale metallic clusters in the pores (Stage 0). In both cases, some of the encapsulated metal may dissolve in the silica and ionize to produce highly mobile M+ ions with reversible electron transfer to the silica. This presumption is consistent with literature observations that sodium is soluble in silica films at ambient temperatures at levels up to 35 mol percent and is presumed to form highly mobile Na+-O– species (Lagarde, P.; Flank, A.-M.; Mazzara, C.; Jupille, J. Surf. Sci.2001, 482–485, 376–380). Heating M-SG materials leads to reduction of SiO2 to form material that contains localized M+-O– species and Si–Si bonds in increased proportion as the temperature and time of heating are increased. Above 350 °C, elemental silicon, alkali metal silicides, and alkali metal silicates are formed. The dissolution and reaction of potassium from encapsulated Na–K alloys occurs preferentially over that of sodium. Irreversible reaction even occurs at room temperature over a period of months. The temperature dependence of solid state 23Na NMR spectra indicates the presence of rapid exchange between Na0 in the metal clusters and Na+ at the walls (and perhaps within the silica).

Related Papers

• → Evidence for auto-catalytic mineral dissolution from surface-specific vibrational spectroscopy(2018)49 cited
• → The role of pores in dissolution processes(1979)9 cited
• → Transmission electron microscopic confirmation of the morphological predictions of the two-site model for hydroxyapatite dissolution(1978)10 cited
• → Differential Scanning Calorimetry (DSC)(2008)201 cited
• → Implications of Global and Local Mobility in Amorphous Excipients as Determined by DSC and TM DSC(2009)