We analysed the dehydroxylation of 001, 101, and 111 β-cristobalite surfaces using the periodic density functional theory method and established the OH density stability diagrams of these surfaces as a function of temperature and water partial pressure. Our calculations suggest that important surface reconstructions, involving SiO(2) unit migrations, are required to reach the experimentally mea...

In this paper, we describe a new method based on aerosol-assisted vapor synthesis for making glass materials by pyrolysis of readily available silsesquioxanes CH3Si(OCH3)3 and CH3Si(OC2H5)3. Combined powder X-ray diffraction (XRD) and spectroscopic studies in the far infrared region (FIR) showed that under applied conditions the method yielded amorphous materials. Subsequent structural studies ...

Sugarcane bagasse ash re-utilisation has been advocated as a silica-rich feed for zeolites, pozzolans in cements and concretes, and geopolymers. However, many papers report variable success with the incorporation of such materials in these products as the ash can be inconsistent in nature. Therefore, understanding what variables affect the ash quality in real mills and understanding the process...

We use molecular dynamics computer simulations to calculate the frequency dependence of the specific heat of a SiO2 melt. The ions interact with the BKS potential and the simulations are done in the NVE ensemble. We find that the frequency dependence of the specific heat shows qualitatively the same behavior as the one of structural quantities, in that at high frequencies a microscopic peak is ...

Zn(II) sorption onto Al and Si oxides was studied as a function of pH (5.1-7.52), sorption density, and ionic strength. This study was carried out to determine the role of the various reaction conditions and sorbent phases in Zn complexation at oxide surfaces. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to probe the Zn atomic environment at the metal oxide/aqueous int...

The current carcinogenicity study with female rats focused on the toxicity and carcinogenicity of intratracheally instilled fine and ultrafine granular dusts. The positive control, crystalline silica, elicited the greatest magnitude and progression of pulmonary inflammatory reactions, fibrosis and the highest incidence of primary lung tumors (39.6%). Addition of poly-2-vinylpyridine-N-oxide dec...

Microsilica, or silica fume, is an amorphous type of silica mostly collected as byproduct of the silicon and ferrosilicon alloy production. In this work, low shrinkage alumina-mullite ceramic composites were prepared from mixtures of calcined alumina, silica fume and aluminum metal powder and sintered at 1550 o C for 2 hrs. The influence of silica fume and aluminum powder on the densification p...

The physicochemical characteristics and oral absorption of a poorly water-soluble drug, K-832, adsorbed onto porous silica (Sylysia 350), were compared with those of K-832 adsorbed onto non-porous silica (Aerosil 200). K-832 and silica were treated with supercritical CO(2) (scCO(2)) to produce K-832-Sylysia 350 and K-832-Aerosil 200 formulations. Scanning electron microscopy, polarizing microsc...

We present the results of extensive molecular dynamics computer simulations in which the high frequency dynamics of silica, ν > 0.5 THz, is investigated in the viscous liquid state as well as in the glass state. We characterize the properties of high frequency sound modes by analyzing Jl(q, ν) and Jt(q, ν), the longitudinal and transverse current correlation function, respectively. For wave–vec...

We use molecular dynamics computer simulations to study the equilibrium properties of the surface of amorphous silica. Two types of geometries are investigated: i) clusters with different diameters (13.5Å, 19Å, and 26.5Å) and ii) a thin film with thickness 29Å. We find that the shape of the clusters is independent of temperature and that it becomes more spherical with increasing size. The surfa...