Performance analysis and comparison of methyl-modified Al2O3/SiO2 xerogels fabricated by two methods

Two methyl-modified Al2O3/SiO2 xerogels, i. e. AIP-Al2O3/MSiO2 and ANN-Al2O3/MSiO2 xerogels, were prepared using aluminum isopropoxide and aluminum nitrate nonahydrate as the aluminum precursors, respectively. The appearance, density, viscosity, Gibbs activation energy for viscous flow and reaction rate constant of the sols were analyzed and compared. Their microstructures were characterized by means of powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and nitrogen adsorption–desorption measurements. The results show that the Al–O–Si bond is formed in the AIP-Al2O3/MSiO2 and ANN-Al2O3/MSiO2 xerogels. The ANN-Al2O3/MSiO2 sol has a smaller mean particle size and greater sol stability than the AIP-Al2O3/MSiO2 sol. Meanwhile, the ANN-Al2O3/MSiO2 xerogel has a smaller pore size and higher porosity. The total pore volume and specific surface area of the ANN-Al2O3/MSiO2 xerogel are 27.27% and 29.36% larger than those of the AIP-Al2O3/ MSiO2 sample, respectively. The saturated adsorption capacity of the ANN-Al2O3/MSiO2 xerogel to methylene blue is 7.15% larger than that of the AIP-Al2O3/MSiO2 xerogel.

Properties of humic acids from copper tailings 20 years after reclamation

Part of Cu post flotation tailings of Serbia ZiJin Bor Copper, Serbia, was reclaimed by restoration of top soil with arable soils, and revegetation in 1991. Humic acids isolated from these Technosols were investigated to find out if their properties underwent any changes since reclamation. Two groups of control samples were used. Elemental composition (CHNS analysis) falls within the range of average soil humic acids. Humic acids belong to the type B pointing out to its lower humification degree (UV?Vis). Relative abundances of functional groups are ranged as follows: polysaccharide C ??aromatic C > carboxyl C > OH group > aliphatic C. Aromaticity indexes are low, 1.88? 3.25 (ATR-FTIR). Basic units at pH 10 are in the 11.7?26.8 nm range. Pronounced reaggregation (1462-?5218 nm) at pH 3 points out to less expressed humic acid sol stability, as well as to increase in aromatic condensation degree (dynamic light scattering). No significant changes have occurred in technosol humic acids since the recultivation, confirming stability of their properties over time (PCA). Nevertheless, humic acids from very strongly acidic Technosols show higher humifycation degree possibly originating from arable soils used in reclamation, but more likely from low soil pH and low litter input, results of unsuccessful reclamation.

Research on the Application of Liquid Permeating Method to Silica Sol Stability

The stability of SiO2 sol is an important parameter in the practical applications. But so far the parameter for expressing the stability of SiO2 sol cannot be characterized by a proper measurement. In this paper, a new method, liquid permeating method, was introduced, by which the stability of SiO2 sol was characterized and the effects of additive, such as dimethylformamide (DMF) and MgO were presented. The results show that with the amount of DMF increasing, the gel-time of SiO2 sol became longer; and that with the amount of MgO increasing, the gel-time became shorter. The results obtained by this new method are as same as that from the traditional tedious viscometer measurement method, which indicate that this liquid permeating method is a reliable method for characterizing the stability of SiO2 sol. Besides, this liquid permeating method is also simple, time-saving and low-cost for evaluating SiO2 sol stability.

Experimental taphonomy: silicification of plants in Yellowstone hot-spring environments

ABSTRACTDuring experiments conducted within the vent pool of Medusa Geyser, Norris Geyser Basin, Yellowstone National Park, USA, amorphous opaline silica (opal-A) was deposited on/within plant tissues within 30 days of immersion. Initially, deposition created inter/intra-cellular films which lined cell walls plus intercellular colloid suspensions (sols) of opal-A nano/microspheres. By 330 days, opal-A deposition created a robust external and internal matrix that stabilised tissues against collapse and replicated plant structure. Opal-A films increased to micron-order thicknesses and intracellular sols were created. Systematic variation of opal-A fabric between tissues comprising living/dead cells at the time of deposition indicate that cell function, architecture and shape influence fabric development. Heterogeneity of opal-A fabric within adjacent cells of similar structure/function indicates spatially/temporally fluctuating physicochemical conditions and the presence of intraorganic microenvironments. Early deposition of opal-A films suggests a period of low silica supersaturation and slow opal-A deposition. In contrast, intracellular sols suggest high levels of supersaturation, and rapid opal-A deposition. Shell-like microsphere growth suggests cyclic variation of silica supersaturation, and alternations between rapid and slower opal-A deposition. Microsphere growth to the upper limit of colloidal stability and colloidal crystal structures indicate prolonged sol stability, whilst floc-like microsphere networks indicate localised sol instabi

Hybrid composite materials containing magnetic iron oxide nanoparticles

ABSTRACTHybrid magnetic composites made up of calibrated maghemite nanoparticles well dispersed in an epoxide resin were obtained by polymerization of the resin inside stable organosols of maghemite. The sol stability was ensured by ligand adsorption onto the particle surface. Studies of phenylphosphonic acid adsorption are presented. They show a strong interaction between PPA ions and hydroxyl groups of particle surface and through bridging ≡Fe2O2POΦ species. Infrared and Mössbauer spectroscopies as well as quasi- elastic light scattering and transmission electron microscopy were used to characterize the materials.

Colloidal platinum sols: anion effects on coagulation behaviour

The concentration of added electrolyte required to induce coagulation of a platinum sol has been determined for a range of electrolytes. It has been found that, for electrolytes in which the anion contains lone-electron-pair substituents, sol stability is significantly enhanced compared with that observed when similar but non-electron-pair-containing anions are used. It is proposed that the lone electron pairs enable anion adsorption on negative platinum surfaces despite the Coulombic repulsions present.