Authors:Giancarlo Angelini, Ornella Ursini, and Franco Cataldo
Fullerene/silica hybrid materials were obtained by radiation grafting on silica surface of toluene or decalin solutions of
C60. As determined by thermogravimetric analysis, the amount of C60 grafted on silica surface was dependent from the radiation dose administered and independent from the C60 concentration and the nature of the organic solvent. In absence of air, a dose of 48 kGy was sufficient to ensure a grafting
level of 30% by weight of C60 in the hybrid material. The fullerene/silica hybrid material shows a remarkable thermal stability, since the early decomposition
starts above 300 °C as measured by DTG and DTA. The chemical structure of the fullerene/silica hybrid material was determined
by FT-IR spectroscopy and with solid state 13C CP-MAS NMR. The potential application of such materials has been outlined.
. This necessitated the utilization of micro filler silica fume (SF) as a supplementary cementitious material that fills up the voids in the concrete thereby enhancing its performance [ 2 ]. Various researches on the utilization of SF have shown improved
The use of ionizing radiation to achieve some desired effect on silica gel, applicable to the adsorption of radionuclides
has been investigated as a function of the dose-rate over a wide range of doses, in experiments with strongly alkaline aqueous
solutions containing an excess of UO
relative to trace concentrations of88Y,103Ru,134Cs and141Ce. The results obtained revealed that γ-irradiation of silica gel was reproduced with an uptake comparable to that measured
for the unirradiated-silica gel. Radiation resistance is strongly influenced by the basic macromolecular structure, the presence
of water, and the particular environmental exposure conditions.
Authors:S. A. Abo-El-Enein, Z. M. Abou-Gamra, F. I. El-Hosiny, and S. M. A. El-Gamal
The hydration of two calcium hydroxide-silica fume mixtures was studied at 25°C. The mixtures were prepared at lime/silica molar ratios of 1.0 and 1.7. The free lime, free silica and chemically combined water contents were determined after various periods of hydration (0.5 h-90 days). Thus, the molar ratios CaO/SiO2 and H2O/SiO2 molar in the calcium silicate hydrates (C-S-H) formed could be derived. The hydrates formed were identified by using differential thermal analysis. The mechanism of the hydration-gardening thermal analysis. The mechanism of the hydration-hardening reaction between lime and silica fumes was suggested. The changes in the molar ratios CaO/SiO2 and H2O/SiO2 in the C-S-H formed with the time of hydration were found to follow the same trends as observed during the hydration course for the suggested mechanism.
Authors:Quan Wan, Christopher Ramsey, and George Baran
Three different silica filler materials were thermally treated in order to effect dehydration, dehydroxylation, and rehydroxylation.
Samples were characterized by thermogravimetry (TG), pycnometry, elemental analysis, and scanning electron microscopy (SEM).
For all fillers, our results indicate incremental removal of silanol groups at higher heating temperatures and irreversible
dehydroxylation at over 673 K. To remove the organic content and maintain adequate silanol density for subsequent silanization
on Stöber-type silica, we suggest heating at 673 K followed by overnight boiling in water.
Authors:K. Chrissafis, E. Pavlidou, K. M. Paraskevopoulos, T. Beslikas, N. Nianias, and D. Bikiaris
, strength, and moduli values commensurate with bone replacement implants [ 11 , 12 ]. Fumed silica (SiO 2 ) has, also, been widely used as a nanofiller for the preparation of polyester/SiO 2 nanocomposites [ 13 , 14 ]. It possesses advantages of a light
Authors:Marcela Stoia, Mircea Stefanescu, Mirela Barbu, Paul Barvinschi, and Lucian Barbu-Tudoran
systems NiM 2 III O 4 , where M III = Fe III and Cr III , inside a silica matrix. In order to obtain 50% NiFe 2 O 4 /50% SiO 2 and 50% NiCr 2 O 4 /50% SiO 2 nanocomposites, we have used a versatile route based on the thermal decomposition inside the
The heat capacities of unirradiated silica glass and three samples of fast neutron-irradiated silica glass were measured between 6 and 340 K. For the glass samples irradiated with fast neutrons, a decrease in heat capacity was observed in comparison with the starting silica glass. This agrees with the assumption that at higher doses the silica glass is converted into the metamict phase, which has a different local structure.
Three samples of silicon dioxide were syhthesized and their surface areas were measured. A thermo-chemical cycle was designed
to calculate the molar formation enthalpy. The molar formation enthalpy, ΔfHmΦ, for three amorphous silica with the Langmuir surface area 198.0854, 25.1108 and 11.9821 m2 g−1 gave −895.52, −910.86 and −915.67 kJ mol−1, respectively. With the increasing surface area, the values of ΔfHmΦ increased accordingly.
The results suggest that the silica with larger surface area is more unstable. The wetting heat was also measured by adding
the silica powder into water. With the rehydration of the more SiOH groups on the surface, the larger surface areas of silica
lead to the more wetting heat. A smaller particle has the more unstable hydroxyl groups and surface energy.
Authors:K. Venkatesan, N. Sasidharan, and P. Wattal
Laboratory experiments were performed on the sorption of cesium on gamma-irradiated silica-titania gel. The detrimental effects
of absorbed dose on the affinity of the sorbent towards cesium was discussed. Data obtained from sorption studies were fit
into heterogeneity based Freundlich isotherm. The empirical parameters, thus obtained were used to arrive at the site distribution
function. The potential of site distribution function in foreseeing, the reusability and long-term residence of radionuclides
in the sorbent has been highlighted.