Increase In Silica Concentration Research Articles

Transport and optical properties of SiO 2–polypyrrole nanocomposites

Conducting polypyrrole-wide band gap semiconducting silica (SiO 2) nanocomposites are prepared by polymerizing pyrrole in the presence of colloidal silicon oxide sol. The nanocomposites are characterized by Fourier transform infrared spectrometer and scanning electron microscope. Three dimensional variable range hopping conduction process is involved in electric conduction. The current density ( J ) satisfies the power law, J ∝ V m , with 1 < m < 2 at voltage V > 0.5 V . Optical absorption spectra reveal that the π – π ∗ transition of polypyrrole shifts from 3.9 eV to 4.58 eV with increase of silica concentration.

Silica xerogels from rice hull ash: structure, density and mechanical strength as affected by gelation pH and silica concentration

Silica xerogels were produced from rice hull ash (RHA), and the structure, density and mechanical strength of the gels were investigated. Silica was extracted as sodium silicate from RHA using 1M NaOH. This silicate solution was concentrated by volume reduction and used to obtain silica concentrations of 0.04, 0.06, 0.08, 0.10, and 0.12 g cm−3. The pH values of these silicate solutions were adjusted to 9.0, 10.0, 10.5, or 11.0 to produce silica gels. The silica gels produced were then dried at 80 °C for 24 h. X-ray diffraction demonstrated the amorphous nature of silica gels. Diffuse reflectance Fourier Transform Infrared (FTIR) spectroscopy was used to investigate the effect of gelation pH, and silica concentration on the chemical structure of the xerogel and concomitant effect on density and mechanical strength of the xerogel. The FTIR spectra demonstrated that at higher pH of gelation, siloxane bonding was the primary network in the xerogel. As the pH of gelation decreased, the structural silica gel network became the major interaction in the silica xerogel. At each gelation pH, the silica gel network increased with increase in silica concentration. The higher pH led to condensed glassy solids, while higher silica concentration produced highly porous silica xerogel. Hence, gelation pH and silica concentration of gel-forming solution had significant effects on the density and the mechanical strength of xerogels produced from rice hull silica. © 2000 Society of Chemical Industry

Phytoplankton Population Succession in Hyper-Eutrophic Stabilization Ponds Located at a Sea Based Dredged Sludge Disposal Site.

Field studies of water quality and phytoplankton community at the stabilization ponds of Osaka North Port Solid Waste Disposal Site (ONPSWDS) were carried out to analyze the relationship between eutrophication and the succession of phytoplankton of the red tide.Water temperature of the stabilization ponds varied from 6.5°C in winter to 30.0°C in summer. Its water salinity ranged from 27.2 to 29.2. The ponds were found to be hyper-eutrophic because they contained much total nitrogen (5 to 15mg/l) and total phosphorous (0.5 to 2mg/l) .Chlorophyll a concentrations showed a stepwise increase and decrease pattern with values varying at about 20, above 90 and 50, μg/l in the first, second and last step, respectively. pCOD variation followed the same pattern as chlorophyll a concentration with values varying at about 5, above 10 and 10 mg/l. Phytoplankton cell number varied from 103cells/ml level in the first twenty months of reclamation to 105cells/ml level in the advanced stage of reclamation.The flora of Bacillariophyceae species was abundant and diversified at the earlier stage of reclamation. Other groups such as Flagellata and Chlorophyceae became dominant as reclamation and eutrophication proceeded. It was also observed that when Bacillariophyceae occurred in abundance, Flagellata or Chlorophyceae disappeared or appeared in low number conversely.The increase in Bacillariophyceae cell number was followed by the increase in silica concentration. These findings indicate that silica plays important roles as a thriving compound for Bacillariophyceae.