Effects of Yb ion concentration on the spectral properties of lead silica glasses

The spectral properties in different concentration of Yb ions (0.5-5 mol%)-doped silica glasses are explored in this paper. The glasses are prepared by traditional melting method. The absorption spectra and the fluorescent lifetime (tau(f)) are measured at room temperature and low temperature (18 K). The stimulated cross-section (sigma(emi)) and potential laser properties (beta(min), I-sat, I-min) are calculated based on the absorption spectra. The absorption cross-section (sigma(abs)) are in the range 1.08 x 10(-20) - 1.18 x 10(-20) cm(2) in different glasses, the fluorescence lifetime (tau(f)) change from 1.9 to 1.2 ms with the increase of Yb3+ concentration. The potential laser properties indicate that lead silica glass is a good host for highly Yb ion doping glass. (c) 2005 Elsevier B.V. All rights reserved.

The influence of particle shape on the stress-strain and creep response of a fine silica sand

The influence of particle shape on the stress-strain response of fine silica sand is investigated experimentally. Two sands from the same source and with the same particle size distribution were examined using Fourier descriptor analysis for particle shape. Their grains were, on average, found to have similar angularity but different elongation. During triaxial stress path testing, the stress-strain behavior of the sands for both loading and creep stages were found to be influenced by particle elongation. In particular, the behavior of the sand with less elongated grains was more like that of rounded glass beads during creep. The results highlight the role of particle shape in stress transmission in granular packings and suggest that shape should be taken more rigorously into consideration in characterizing geomaterials. © 2005 Taylor & Francis Group.

Thermogravimetric study on the hydration of reactive magnesia and silica mixture at room temperature

The synthesis of magnesium silicate hydrate (MSH), which has wide applications in both construction and environmental fields, has been studied for decades. However, it is known that the characteristics of magnesia (MgO) vary significantly depending on their calcination conditions, which is expected to affect their performance in the MgO-SiO2-H2O system. This paper investigated the effect of different MgO and silica sources on the formation of magnesium silicate hydrate (MSH) at room temperature. The hydration process was studied by mixing commercial reactive MgO and silica powders with water and curing for 1, 7 and 28 days. The hydration products were analysed with the help of X-ray diffraction (XRD) and thermogravimatric analysis (TGA). The results showed the continuous consumption of MgO and the existence of MSH and brucite and other minor phases such as magnesite and calcite. It is found that the Mg and Si sources have significant effect on the hydration process of MgO-SiO2-H2O system. The reaction degree is controlled by the availability of dissolved Mg and Si in the solution. The former is determined by the reactivity of MgO and the latter is related to the reactivity of the silica as well as the pH of the system. © 2013 Elsevier B.V. All rights reserved.

Unilamellar liposomes covalently coupled on silica gel for liquid chromatography

Silica gel was used as a support for the covalent coupling of liposomes, which could overcome drawbacks of soft gel beads in column efficiency and separation speed. The influences of the concentration of added dimethylaminopyridine and reaction time on the chloroformate activation reaction of silica gel were investigated. Temperature and pH for covalent coupling of liposomes on the activated silica gel were also optimized. Experimental results indicated that the stability of the covalently coupled liposome columns was obviously superior to that of the noncovalently coated liposome columns but the selectivity of both columns was basically identical. Separation and analysis of a crude extract of a traditional Chinese medicine Ligusticum Wallichii and a mixture of small peptides on both columns further support this conclusion.

Studies on the magnetism of cobalt ferrite nanocrystals synthesized by hydrothermal method

Fe-Co/CoFe2O4 nanocomposite and CoFe2O4 nanopowders were prepared by the hydrothermal method. The structure of magnetic powders were characterized by X-ray diffraction diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermal gravity analysis (TGA) and differential thermal analysis (DTA) analysis, X-ray photoelectron spectrometry (XPS), and Fourier transform infrared spectra (FTIR) techniques, while magnetic properties were determined by using a vibrating sample magnetometer (VSM) at room temperature.

Direct electrochemistry and electrocatalysis of glucose oxidase immobilized on glassy carbon electrode modified by Nafion and ordered mesoporous silica-SBA-15

In this paper, it was found that glucose oxidase (GOD) has been stably immobilized on glassy carbon electrode modified by ordered mesoporous silica-SBA-15 and Nafion. The sorption behavior of GOD immobilized on SBA-15 matrix was characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-vis), FTIR, respectively, which demonstrated that SBA-15 can facilitate the electron exchange between the electroactive center of GOD and electrode. The direct electrochemistry and electrocatalysis behavior of GOD on modified electrode were characterized by cyclic voltammogram (CV) which indicated that GOD immobilized on Nafion and SBA-15 matrices displays direct, nearly reversible and surface-controlled redox reaction with an enhanced electron transfer rate constant of 3.89 s(-1) in 0.1 M phosphate buffer solution (PBS) (pH 7.12).