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At least 649 records · Page 36Linked to original sources
PubMed2006

Enthalpy relaxation of freeze concentrated sucrose-water glass.

The enthalpy relaxation of freeze concentrated sucrose-water glass was investigated using 40% sucrose, differential scanning calorimetry (DSC) with isothermal ageing for 1-6 days at various temperatures (-70, -65, -60, and -55 degrees C). The enthalpy relaxation was observed as an endothermic peak superimposed on the endothermic step-wise change due to the glass transition around -47 degrees C. The enthalpy relaxation was found to increase with ageing time and temperature. An 80% sucrose glass was also investigated at ageing temperatures of -60 and -65 degrees C, and this material exhibited a similar glass transition and enthalpy relaxation to that observed with the frozen 40% sucrose solution. The calculated activation energy of the enthalpy relaxation of the sucrose-water glass was smaller than that reported for pure sucrose. These results suggest that the freeze concentrated sucrose-water glass could have a higher molecular mobility and less stability than pure sucrose glass.

Calorimetry, Differential Scanning↗
PubMed2006

Surface characterizations of mono-, di-, and tri-aminosilane treated glass substrates.

The surface properties and structure of mono-, di-, and tri-aminosilane treated glass surfaces were investigated using surface analytical techniques including X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), and streaming potential. An optimized dip-coating process was demonstrated to produce roughly silane monolayer coverage on the glass surface. The surface charge measurements indicated that aminosilanization converts the glass surface from negative to positive potentials at neutral pH values. Higher positive streaming potential was observed for tri-compared with mono- and di-aminosilane treated glass surfaces. For all aminosilane treated glass samples, the high-resolution N 1s XPS spectra indicated a preferential orientation of the protonated amino-groups towards the glass surface whereas the free amino groups were protruding outward. This study aimed to obtain uniform, reproducibly thin, strongly adhering, internally cross-linked, and high positively charged aminosilane-coated glass surfaces for the attachment of DNA fragments used in microarraying experiments.

Journal Article↗
PubMed2005

A high-resolution 19F NMR spectroscopic study of barium fluorozirconate glasses and related crystals.

Fluorozirconate glasses have attracted considerable attention not only for their transparency in the infrared, but also due to their high fluorine ion conductivities and extreme fragility in the viscosity-temperature relationship. We report on structural studies of binary BaF2-ZrF4 glasses with 58-78 mol% ZrF4 using high-resolution magic-angle-spinning 19F NMR. High-speed 19F MAS NMR allows us to resolve at least three unique fluorine environments in these binary glasses. These fluorine environments are attributed to one type of bridging fluorine, between corner-sharing Zr-F coordination polyhedra, and two types of non-bridging fluorine (NBF), one of which is bonded to one Zr and one Ba atom while the other is bonded to one Zr and two Ba atoms. The concentration of the first type of NBF increases with decreasing ZrF4 concentration, while that of the second type is essentially independent of glass composition. These assignments have been made on the basis of detailed 19F NMR studies of a wide variety of crystalline fluorozirconates with known crystal structures. A comparison between the glass and crystal 19F NMR spectra rules out any significant concentration of edge-shared Zr-F polyhedra in these binary glasses. The Zr atoms in all glasses are found to be coordinated to approximately 7.8+/-0.2F atoms.

Journal Article↗
PubMed2005

Combined 17O NMR and 11B-31P double resonance NMR studies of sodium borophosphate glasses.

17O enriched sodium borophosphate glasses were prepared from isotopically enriched NaPO3 and H3BO3. These glasses have been studied by 17O, 11B and 31P NMR including 17O and 11B multiple quantum magic angle sample spinning (MQMAS), 11B-31P heteronuclear correlation (HETCOR) NMR and 11B{31P} rotational echo double resonance (REDOR). For comparison, the crystalline borophosphates BPO4 and Na5B2P3O13 were included in the investigations. The latter compound shows three sharp 31P resonances at -0.2, -2 and -8 ppm and two BO4 sites that can only be resolved by MQMAS. The 17O NMR spectra were recorded using both the static echo method at medium magnetic field (9.4 T) as well as MAS and MQMAS methods at high field (17.6 T). In total, five oxygen sites were identified in these borophosphate glasses: P-O-P, Na...O-P, P-O-B, B-O-B, Na...O-B. However, these five sites are not present simultaneously in any of the glasses. The 17O MQMAS spectra prove that P-O-B links play a major role in borophosphate glasses. These results are confirmed by the complementary 11B MAS spectra that show the presence of asymmetric and symmetric trigonal groups BO3a and BO3s and two tetrahedral BO4 units. 11B{31P} REDOR NMR is used to give independent information to assign the 11B lines to structural units present in the glasses. These REDOR measurements reveal that B-O-P bonds are present for each borate unit, including the BO3 groups. Particularly, a structural proposal for the two different BO4 resonances is given in terms of a different number of bonded phosphate tetrahedra. The 31P MAS spectra are usually broad and not well resolved. It is shown by 11B-31P HETCOR NMR that a possible structural assignment of a 31P signal at about -20 ppm to Q2 units as in binary sodium phosphate glasses is wrong and that the phosphate tetrahedron belonging to this resonance must be connected to borate groups.

Journal Article↗
PubMed2005

A 125Te and 23Na NMR investigation of the structure and crystallisation of sodium tellurite glasses.

125Te static nuclear magnetic resonance (NMR) and 23Na and 125Te magic angle spinning (MAS) NMR have been used, in conjunction with X-ray diffraction, to examine the structure and crystallisation behaviour of glasses of composition xNa2O.(1-x)TeO2 (0.075 x 0.4). The MAS NMR 23Na spectra from the glasses are broad and featureless but shift by approximately +5 ppm with increased x, i.e. as the system becomes more ionic. The static 125Te NMR spectra show an increase in axial symmetry with increasing x, indicating a shift from predominantly [TeO4] to [TeO3] structural units. The 23Na and 125Te spectra from the crystallised samples have been fitted to obtain information on the sites in the metastable crystal phases, which are the first to form on heating and which are therefore more closely related to the glass structure than thermodynamically stable crystal phases. New sodium tellurite phases are reported, including a sodium stabilised, face centred cubic phase related to delta-TeO2; a metastable form of Na2Te4O9 containing 3 sodium and 4 tellurium sites; and a metastable form of Na2Te2O5 containing 2 sodium sites. There is evidence of oxidation of TeIV to TeVI occurring in glasses with high values of x and, at x=0.40 and 0.50 (outside the glass forming range), some sodium metatellurate (Na2TeO4) is formed at the same time as sodium metatellurite (Na2TeO3). The 125Te shift is very sensitive to environment within the sodium tellurite system, covering more than 320 ppm, with anisotropies varying from 640 to 1540 ppm. The lack of features in the 125Te spectra of the glass phases, combined with the large shift range and high but variable anisotropy, means than it is not possible to obtain a unique fit to any presumed species present. Furthermore, the chemical shift anisotropy parameters for three of the four Te sites in the Na2Te4O9 phase are found to lie outside the range used for previous simulations of glass spectra.

Journal Article↗
PubMed2004

The perceived direction and speed of global motion in Glass pattern sequences.

Observers indicated the perceived direction of global motion in sequences of noisy Glass patterns containing real motion signals in directions that conflicted with the orientation of signal dipoles in the Glass patterns. Dipole orientation influenced the perceived direction of motion. Observers also judged the apparent speed of sequences of independent noiseless Glass and Glass Line patterns (dipoles replaced by lines). Speed was high and increased with the length of lines in Glass Line patterns but not with dipole separation in Glass patterns. When real motion signals were added to sequences of noisy Glass patterns they exerted an influence on apparent speed that increased with motion signal strength but was independent of pattern signal strength. The results suggest that pattern exerts a global influence on the computation of motion direction and, possibly, on speed.

Humans↗
PubMed2006

Utilization of waste glass in ECO-cement: strength properties and microstructural observations.

Waste glass creates a serious environmental problem, mainly because of the inconsistency of the waste glass streams. The use of waste glass as a finely ground mineral additive (FGMA) in cement is a promising direction for recycling. Based on the method of mechano-chemical activation, a new group of ECO-cements was developed. In ECO-cement, relatively large amounts (up to 70%) of portland cement clinker can be replaced with waste glass. This report examines the effect of waste glass on the microstructure and strength of ECO-cement based materials. Scanning electron microscopy (SEM) investigations were used to observe the changes in the cement hydrates and interface between the cement matrix and waste glass particles. According to the research results, the developed ECO-cement with 50% of waste glass possessed compressive strength properties at a level similar to normal portland cement.

Compressive Strength↗
PubMed2003

Comparison of the effect of video glasses and nitrous oxide analgesia on the perceived intensity of pain and unpleasantness evoked by dental scaling.

The aim of this study was to evaluate whether distraction induced by video glasses had an effect on the perceived intensity of pain and unpleasantness during dental scaling compared with the effect of nitrous oxide (N(2)O) analgesia. The pain stimulus was dental scaling (removal of dental calculus) with an ultrasonic scaler. As a standardised, non-dental painful stimulus, Von Frey filaments were used. A total of 26 patients with superficial chronic periodontitis were enrolled in this randomised, controlled clinical study. The effect of video glasses was compared with N(2)O in one session and the effect of video glasses versus a control situation in another. The patients rated the intensity of pain and unpleasantness evoked by dental scaling and Von Frey filament stimulation on 100-mm visual analogue scales (VAS). For dental scaling, there was no effect of video glasses on the perceived pain (p=0.85) or unpleasantness (p=0.73) nor of N(2)O (p=0.69 and p=0.51, respectively) compared with the control situation. Similarly, no significant difference was found between VAS scores in the video glasses and N(2)O session (p=0.48, p=0.58). A significant effect of video glasses and N(2)O(p<0.008) was found on the perceived pain intensity produced by Von Frey filament stimulation compared with the control situation, but no significant difference was seen between these methods (p=0.07). Post-treatment interviews of the patients revealed that 81% of the patients in the video and 65% in the N(2)O session stated that the method had some beneficial effect on their overall experience of the treatment situation. In conclusion, administration of video glasses or N(2)O did not affect the perceived intensity of pain and unpleasantness evoked by dental scaling.

Adult↗
PubMedDate not supplied

Spatial variation of refractive index in a pane of float glass.

In the statistical interpretation of forensic glass evidence it is standard practice to make the assumption of homogeneity of the refractive index (RI) of the source glass, or of localized homogeneity. However, the work of Locke and Hayes showed that, for toughened windscreen glass, this assumption might not be true. This work is well cited, but there appears to have been little follow-on published research. Furthermore, the toughening process is something known to affect the refractive index, and is a process that float glass does not undergo. Float glass is a major component of casework in New Zealand and for that reason it would be interesting to know whether the findings of Locke and Hayes apply when dealing with float glass. In this paper we describe an experiment similar to that of Locke and Hayes, systematically examining the variation of RI in a pane of float window glass. It was found that, although there were no systematic differences in refractive index, there were observable differences across the pane.

Journal Article↗
PubMed2006

Molecular orientation analysis of a single-monolayer Langmuir-Blodgett film on a thin glass plate by infrared multiple-angle incidence resolution spectrometry.

Molecular orientation analysis in a single monolayer deposited on a glass substrate has been a difficult matter, since the glass substrate absorbs infrared rays so strongly that the measurements of infrared spectra are difficult to perform, and the single monolayer is not suitable for X-ray diffraction analysis because no periodical structure is available. When a thin glass is used as the substrate, in particular, the infrared analysis becomes more difficult, since optical fringes appear strongly on the absorption spectra due to the multiple reflections in the glass. In the present study, infrared multiple-angle incidence resolution spectrometry (MAIRS) has been employed to remove the fringes from the spectra of single- and five-monolayer Langmuir-Blodgett (LB) films of cadmium stearate deposited on a thin glass plate. The MAIRS in-plane spectra gave quantitatively reliable infrared transmission spectra for both films with little fringes, which made it possible for the first time to analyze the molecular orientation in the single-monolayer LB film on glass. As a result, it has been revealed that the molecule in the single-monolayer LB film on thin glass exhibits a significantly larger molecular tilt angle than those prepared on other substrates such as gold and germanium.

Journal Article↗
PubMed2005

First-principles calculation of the 17O NMR parameters of a calcium aluminosilicate glass.

We have computed the (17)O NMR parameters of an amorphous calcium aluminosilicate (CAS) from first-principles. The atomic coordinates of a CAS glass of composition (CaO)(0.21)(Al(2)O (3))(0.12)(SiO (2))(0.67) were obtained by quenching a liquid to room temperature by the means of ab initio molecular-dynamics simulations of the Car-Parrinello type. The structure of the glass is found to be overall in good agreement with diffraction experiments. Some excess nonbridging O (NBO) atoms are found and are compensated by tricluster O atoms, i.e., by 3-fold coordinated O atoms to 4-fold coordinated Al or Si atoms. The glass coordinates were used to compute the (17)O NMR parameters using GGA-DFT and a correction of the Ca 3d orbital energy. The chemical shifts and the electric field gradients were obtained with the gauge including projector augmented-wave (GIPAW) and the projector augmented-wave (PAW) methods, respectively. The simulated 2D-3QMAS NMR spectrum of the CAS glass is in very good agreement with the available experimental data, notably because it takes into account the disorder present in the glass. This agreement further validates our CAS glass model. We show that the oxygen triclusters are not visible in a 2D-3QMAS NMR (17)O spectrum since their NMR parameters overlap with those of the Al-O-Si, Si-O-Si, or Al-O-Al sites. Finally, correlations between the structural characteristics and the values of the NMR parameters are extracted from the calculation with the aim of helping the interpretation of NMR spectra of glasses of similar compositions.

Journal Article↗
PubMed1998

Determination of the glass properties of D-mannitol using sorbitol as an impurity.

Due to its strong tendency to crystallize, the glass properties of mannitol cannot be measured directly. However, because mannitol can exist in a fully or partially amorphous state in drug formulations, it is important to determine the glass properties of mannitol. We obtained the glass properties of mannitol by introducing a small amount of sorbitol, an isomer of mannitol, to delay the onset of crystallization. Extrapolation to zero sorbitol concentration yielded the following properties for the mannitol glass: Tg onset = 10.7(o)C, Tg midpoint= 12.6( o)C, Tg end = 18.4 degreesC and DeltaCp = 1.27 J/g/K. In addition, we estimated the following parameters of the mannitol glass from the width of glass transition using the results of Moynihan (J. Am. Ceram. Soc. 1993, 76, 1081) and Angell (J. Phys. Chem. 1994, 98, 13780): DeltaH (at Tg onset) = 103 kcal/mol, D = 11, and T0 = 222 K. The value of T0 is consistent with the Kauzmann temperature TK (236 K) obtained calorimetrically. The properties of the mannitol glass may be useful for predicting the behavior of amorphous mixtures containing mannitol.

Calorimetry, Differential Scanning↗
PubMed2002

Fluoride release from model glass ionomer cements.

Glass ionomer cements (GICs) are an important class of biomedical material used extensively for color matched mercury free, dental restorations. GICs can release clinically beneficial amounts of fluoride and have acceptable handling properties which make them suitable as dental restoratives. The fluoride release of model GICs produced from specially synthesized fluoro-alumino-silicate glasses was studied. Nine glasses of varying fluoride content based on 4.5SiO(2)-3Al(2)O(3)-1.5P(2)O(5)-(5-Z)CaO-ZCaF(2) were synthesized and cement disks were prepared from them. The glass transition temperature reduced with increasing fluorine content of the glass. Fluoride ion release was measured into distilled water as a function of time for up to 140 days using a fluoride ion selective electrode. The quantity of fluoride released was found to be proportional to the fluorine content of the glass at all intervals time. The cumulative fluoride release was proportional to square root time. Substituting strontium for calcium in the glass had little influence on the fluoride release behavior of the cements.

Journal Article↗
PubMed1994

Measurement of glass transition temperatures of freeze-concentrated solutes by differential scanning calorimetry.

Thermal analysis of aqueous solutions in which the solute does not crystallize immediately upon freezing was carried out to define the effects of experimental parameters on thermograms in the glass transition region. The intensity of enthalpy relaxations in the glass transition region is related to both the rate of cooling and the rate of heating through the glass transition region--slow cooling or slow heating increases the extent of structural relaxation in the glassy state and increases the intensity of the endotherm. Plots of the logarithm of heating rate versus 1/Tg' are linear, and activation enthalpies for structural relaxation are in the range of 210-350 kJ/mol. For polymeric solutes, both the activation enthalpies for structural relaxation and the heat capacity change accompanying the glass transition increase with increasing molecular weight of the solute. Molecular weight dependence of the observed midpoint of the glass transition agrees with the Fox-Flory relationship. Results are compared and contrasted with glass transitions in solid polymers and with the glass transition of hyperquenched water. Practical implications for characterization of formulations intended for freeze-drying are discussed.

Calorimetry, Differential Scanning↗
PubMed2003

Apatite-forming ability of glass-ceramic apatite-wollastonite - polyethylene composites: effect of filler content.

The bioactivity of a range of glass-ceramic apatite-wollastonite (A-W) - polyethylene composites (AWPEXs) with glass-ceramic A-W volume percentages ranging from 10 to 50, has been investigated in an acellular simulated body fluid (SBF) with ion concentrations similar to those of human blood plasma. The formation of a biologically active apatite layer on the composite surface after immersion in SBF was demonstrated by thin-film X-ray diffraction (TF-XRD) and field-emission scanning electron microscopy (FE-SEM). An apatite layer was formed on all the composites, with the rate of formation increasing with an increase in glass-ceramic A-W percentage. For composites with glass-ceramic A-W filler contents >or=30 vol %, the apatite layer was formed within 12 h of immersion, which is a comparable time for apatite formation on monolithic glass-ceramic A-W. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) demonstrated that the apatite formation on AWPEX samples with 50 vol % filler content occurred in a manner similar to that seen on pure glass-ceramic A-W, in that the calcium, silicon, and magnesium ion concentrations increased and, conversely, a decrease was observed in the phosphate ion concentration. These results indicate that a suitable in vitro response was achieved on a composite incorporating particulate glass-ceramic A-W with a particularly favorable response being observed on the AWPEX sample with 50 vol % filler content.

Journal Article↗
PubMed2003

Effect of glass-ceramic microstructure on its in vitro bioactivity.

Two routes were used to obtain a glass-ceramic composed of 43.5 wt % SiO(2) - 43.5 wt % CaO - 13 wt % ZrO(2). Heat treatment of a glass monolith produced a glass-ceramic (WZ1) containing wollastonite-2M and tetragonal zirconia as crystalline phases. The WZ1 did not display bioactivity in vitro. Ceramizing the glass via powder technology routes formed a bioactive glass-ceramic (WZ2). The two glass-ceramics, WZ1 and WZ2, were composed of the same crystalline phases, but differed in microstructure. The in vitro studies carried out on WZ2 showed the formation of an apatite-like layer on its surface during exposure to a simulated body fluid. This paper examined the influence of both chemical and morphological factors on the in vitro bioactivitity. The interfacial reaction product was examined by scanning and transmission electron microscopy. Both instruments were fitted with energy-dispersive X-ray analyzers. Measurements of the pH made directly at the interface of the two glass-ceramics were important in understanding their different behavior during exposure to the same physiological environment.

Journal Article↗
PubMed2003

Crystallization modifies osteoconductivity in an apatite-mullite glass-ceramic.

The response to implantation of novel apatite glass-ceramics was evaluated using a weight bearing in vivo bone implant model. Five novel glasses with varying calcium to phosphate ratios were cast as short rods and heat-treated to crystallize principally apatite. One glass ceramic had an apatite stoichiometry (Ca : P=1.67); three were phosphate-rich and one calcium-rich. One of the phosphate-rich glasses was also tested in its glassy state to determine the effect of crystallization on the biological response. Rods were implanted into the midshaft of rat femurs and left for 28 days. The femurs were then harvested and processed for scanning electron microscopy, energy dispersive X-ray microanalysis and conventional histology as ground and polished sections. Four of the materials exhibited evidence of osseointegration and osteoconduction. However, there was a marked inflammatory response to one of the phosphate-rich glass-ceramics, and to the non-crystallized glass. Crystallization of the latter significantly improved the bone tissue response. The glass-ceramic with an apatite stoichiometry elicited the most favorable response and merited further study as an osteoconductive bone substitute in maxillofacial and orthopedic surgery.

Journal Article↗
PubMed2006

Glass behaviour: Poisson's ratio and liquid's fragility.

The lack of a reliable theory of glass physics has led to the pursuit of correlations between various glass or viscous liquid parameters, one of which is the slope m of the plot of log(viscosity) against Tg/T, extrapolated at the glass-transition temperature, Tg, also termed 'fragility'. Novikov and Sokolov conclude that the value of m for a liquid varies linearly with the ratio of the instantaneous bulk and shear moduli, K infinity/G infinity, of its glass according to the relation m=29(K infinity/G infinity -0.41). Because of the obvious importance of the elastic properties of a glass, we have investigated the basis for this relation and find that its premise is flawed because of the unjustifiable preference for an empirical variation of m with elastic properties, and because of the selected use of glasses. When more glasses are considered in the same way, m does not seem to be linearly related to K infinity/G infinity.

Comment↗