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Crystallization kinetics studies for six experimental glass formulations in the system Na2O-CaO-SiO2-P2O5 synthesized by wet chemistry were conducted by means of differential thermal analysis. These glasses had CaO/P2O5 and SiO2/ (CaO + Na2O) ratios ranging from 8.74-3.38 and 0.92-3.03, respectively. Samples of each glass (n = 30 were heated from 23 to 1250 degrees C under N2 atmosphere at heating rates ranging from 10 to 50 degrees C/min. Glass-ceramics were obtained after heat treating the initial glasses at temperatures determined from their DTA exotherms. The activation energy of crystallization for each glass composition was calculated from an expression-relating log-heating rate and the reciprocal of the exothermic peak temperature. The compositions of the six glasses were significantly different (p = 0.05). The activation energy of crystallization (Q) values ranged from 196 to 782 kJ/mole. A correlation was obtained between Q and CaO/P2O5 and between Q and the Young's modulus (P < 0.001). Two of the six glasses exhibited bulk crystallization. X-ray diffraction studies showed that four of the six glasses exhibited different proportions of crystalline phases following heat treatment. These phases were wollastonite (CaSiO3), Na2CaSi3O9, combeite [Na4Ca3SI6O16(OH)2], and some unidentifiable phases. Two of the six bioceramic materials had a mixture of unknown crystalline phases.
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PMID:Crystallization of experimental bioactive glass compositions. 886 80

Adsorption isotherms have been determined for the binding of Cd2+ onto the surfaces of hydrophilic A200 SiO2 and hydrophobic R972 SiO2 particles dispersed in ethanol (1>)-cyclohexane (2) mixtures at ethanol mole fractions of x1 = 0.05, 0.10, 0.20, and 0.40. CdS nanoparticles have been generated in situ within the ethanolic nanoreactors at surfaces of SiO2 particles in the different ethanol-cyclohexane binary liquids by the addition of hydrogen sulfide. Absorption spectra of the CdS particles provided information on their quantity, absorption edges, optical band gaps, and mean diameters. Good correlations have been obtained between the adsorption isotherms and size of the CdS particles as well as between the adsorption isotherms and the amount of CdS formed. The smallest CdS particles (ca. 6 nm diameter) have been obtained on the surfaces of SiO2 particles dispersed in ethanol (1>)-cyclohexane (2) mixtures at ethanol mole fractions of x1 = 0.05. More CdS particles have been observed to coat the hydrophilic A200 SiO2 than the hydrophobic R972 particles. In the x1 = 0.10 ethanol (1)-cyclohexane (2) liquid mixtures up to 10% of the SiO2 surface can be covered by CdS nanoparticles. Immersion wetting enthalpy measurements in methanol established the surface of the SiO2 particles to be hydrophilic, which became partially hydrophobic upon and the binding of cadmium ions and hence upon the subsequent formation of CdS. Copyright 1997 Academic Press. Copyright 1997Academic Press
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PMID:The Effect of Cadmium Ion Adsorption on the Growth of CdS Nanoparticles at Colloidal Silica Particle Interfaces in Binary Liquids 944 32

A bonelike apatite layer was formed on organic polymers when sodium silicate was used as a catalyst for the apatite nucleation, and modified simulated body fluid was used as a medium for the apatite growth. The apatite-forming ability was the highest when the SiO2 concentration and SiO2/Na2O mole ratio of the sodium silicate solution were above 2.0 M and 1.0-1.5, respectively. It is assumed that particular silicate oligomers with structures such as dimer, linear trimer and cyclic tetramer contribute to the apatite nucleation the most. The apatite layer was formed not only on limited surfaces but also on the whole surfaces of fine PET fibers constituting a fabric. This method is expected to enable the bonelike apatite coating on various kinds of materials with complex shapes.
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PMID:Bonelike apatite coating on organic polymers: novel nucleation process using sodium silicate solution. 1035 45

A glass with a composition (in mole %) of: SiO2 (70), CaO (26), and P2O5 (4) was obtained using a sol-gel method. The in vitro bioactivity of the glass was assessed by determining the changes in surface morphology and composition after soaking in simulated body fluid (SBF) for periods of up to 14 days at 37 degrees C. X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, and FTIR analyses of the glass surface after different soaking periods in SBF demonstrated the growth of an apatite-like layer on the glass surface. In the first stage, an amorphous calcium phosphate layer was formed; after 7 days this surface consisted of spheres, with diameters ranging between 2 and 15 microm, composed of needle-like apatite crystallites (250 x 100 nm) with a crystallinity similar to that of a biological apatite.
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PMID:XRD, SEM-EDS, and FTIR studies of in vitro growth of an apatite-like layer on sol-gel glasses. 1039 45

In this work an extension of the simplified theory of microwave drying of silicate solutions to arbitrary values of SiO2/M2O mole ratio was introduced, and good agreement between theoretical results and new experimental data for a broad range of values of SiO2/M2O mole ratio was obtained.
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PMID:Simplified theory of microwave drying of alkali metal silicate solutions with arbitrary values of SiO2/M2O mole ratio. 1109 45

Water absorption spectroscopy has been successfully demonstrated as a sensitive and accurate means for in situ determination of temperature and H2O mole fraction in silica (SiO2) particle-forming flames. Frequency modulation of near-infrared emission from a semiconductor diode laser was used to obtain multiple line-shape profiles of H2O rovibrational (v1 + v3) transitions in the 7170-7185-cm(-1) region. Temperature was determined by the relative peak height ratios, and XH2O was determined by use of the line-shape profiles. Measurements were made in the multiphase regions of silane/hydrogen/oxygen/ argon flames to verify the applicability of the diagnostic approach to combustion synthesis systems with high particle loadings. A range of equivalence ratios was studied (phi = 0.47 - 2.15). The results were compared with flames where no silane was present and with adiabatic equilibrium calculations. The spectroscopic results for temperature were in good agreement with thermocouple measurements, and the qualitative trends as a function of the equivalence ratio were in good agreement with the equilibrium predictions. The determinations for water mole fraction were in good agreement with theoretical predictions but were sensitive to the spectroscopic model parameters used to describe collisional broadening. Water absorption spectroscopy has substantial potential as a valuable and practical technology for both research and production combustion synthesis facilities.
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PMID:H2O absorption spectroscopy for determination of temperature and H2O mole fraction in high-temperature particle synthesis systems. 1200 20

Sulfur hexafluoride (SFd)-contained gas is a common pollutant emitted during the etching process used in the semiconductor industry. This study demonstrated the application of radio-frequency (RF) plasma in the decomposition of SF6. The decomposition fraction of SF6 [etaSF6 (C(in)-C(out))/C(in) x 100%] and the mole fraction profile of the products were investigated as functions of input power and feed O2/SF6 ratio in an SiO2 reactor. The species detected in both SF6/Ar and SF6/O2/ Ar RF plasmas were SiF4, SO2, Fe2, SO2F2, SOF2, SOF4, S2F10, S2OF10, S2O2F10, and SF4. The results revealed that at 40 W, etaSF6 exceeded 99%, and the reaction products were almost all converted into stable compounds such as SiF4, SO2, and F2 with or without the addition of oxygen. Sulfur oxyfluorides such as SO2F2, SOF2, SOF4, S2OF10, and S2O2F10 were produced only below 40 W. The results of this work can be used to design a plasma/chemical system for online use in a series of a manufacturing process to treat SF6-containing exhaust gases.
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PMID:Decomposition of SF6 in an RF plasma environment. 1246 13

A new nanometer complex heteropoly acid with Keggin structure, H3PW12O40/SiO2, were prepared by sol-gel method, and were characterized with IR, UV, XRD and TEM techniques. By means of this nanometer catalytic materials, the optimum conditions of the n-butyl acrylate synthesis have been studied. The results show that the complex heteropoly acid H3PW12O40/SiO2 nanoparticles have the mean grain size of 40 nm and they are typical amorphous. A strong chemical interaction exists between H3PW12O40 and silica surface. The nanoparticles have high catalytic activity for synthesizing n-butyl acrylate. The optimum catalytic conditions are as follows: the mole ratio of acrylic acid and n-butyl alcohol is 1:1.2, the reaction temperature is approximately 90-96 degrees C, and the catalyst quantity in the reaction is 10% of the acid mass. The conversion proportion is 94.37% and product yield 91.2% in 5 h. Apparently, the unique structure of the Keggin anions and surface acid center and the high specific surface area and the pseudoliquid phase of H3PW12O40/SiO2 play an important role in the esterification reactions with the acid catalyst.
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PMID:[Catalytic application of synthesizing n-butyl acrylate by a new type nanometer complex heteropoly acid catalyst H3PW12O40/SiO2]. 1576 24

ZnO nanoparticles embedded into SiO(2) by an ex situ method were shown to result in stable green emission with a peak at 510 nm compared to the normal peak at 495 nm from micron-sized ZnO powders. Green emission from ZnO nanoparticles was completely suppressed when they were embedded in SiO2 doped with Eu3+. Instead, the f-f emissions from Eu3+ were enhanced 5-10 times by energy transfer from the embedded ZnO nanoparticles to Eu3+. The Eu3+ luminescence increased as the Eu3+ concentration increased from 1 vs 5 mole % (for 10 mole % ZnO). In addition, the intensity increased as the embedded ZnO nanoparticles concentration increased up to 10 mole % (for 5 mole % Eu3+). The effects of phonon mediated energy transfer, quenching by activator interactions between Eu3+ ions, and energy back-transfer from Eu3+ ions to ZnO nanoparticles were discussed.
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PMID:Enhanced luminescence of SiO2:Eu3+ by energy transfer from ZnO nanoparticles. 1616 23

CaMgSiOs6 : Eu samples were synthesized by a normal solid state reaction using CaCO3, MgO, SiO2 and Eu2O3 as starting materials. The properties of structure, VUV excitation and luminescence under VUV excitation were studied. CaMgSi2O6 : Eu belongs to the monoclinic space group, and the crystal structure does not change as the crystal lattice is doped with Eu ions. The emission spectra of CaMgSi2O6 : Eu3+ have revealed an intense and sharp (611 nm) red color emission from Eu3+ ((5)D0-->(7)F2) transition under 147 nm VUV excitation. The correlative data shows that the concentration quenching occurs when the Eu3+ mole concentration ranges from 0.02 to 0.10 mol. The emission spectra of CaMgSi2O6 : Eu2+ have revealed an intense and sharp (452 nm) blue color emission from Eu2+ (5d-->4f) transition under 172 nm VUV excitation. It can be seen that the intensity of the emission peak increases with increasing H3BO3 concentration.
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PMID:[VUV spectral properties of CaMgSi2O6 : Eu]. 1765 18


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