共查询到20条相似文献,搜索用时 15 毫秒
1.
The presence of sulfur in radioactive waste to be incorporated in borosilicate glasses entails difficulties mainly due to the relatively low solubility of sulfates in the vitreous phase. In this work a study is presented on the effects of the ratio R = [Na2O]/[B2O3], the type of sulfate added and the addition of V2O5 on the incorporation of sulfates in borosilicate glasses. Glass samples were prepared at the laboratory scale (up to 50-100 g) by melting oxide and sulfate powders under air in Pt/Au crucibles. XRF and ICP/AES chemical analysis, SEM/EDS, microprobe WDS and Raman spectroscopy were employed to characterize the fabricated samples. The main experimental results confirm that the incorporation of sulfates in borosilicate glasses is favored by the network depolymerization, which evolves with the ratio R. The addition of V2O5 seems to accelerate the kinetics of sulfur incorporation in the glass and, probably, increase the sulfate solubility by modifying the borate network and fostering the formation of voids of shape and size compatible with the sulfur coordination polyhedron in the glassy network. The kinetics of X2SO4 incorporation in the glass seems to be slower when X = Cs. 相似文献
2.
Amel Dakhlaoui Mouna Jendoubi Leila Samia Smiri Andrei Kanaev Noureddine Jouini 《Journal of Crystal Growth》2009,311(16):3989-3996
Zinc oxide monodispersed nanoparticles were synthesized using a modified polyol process without any requirement to use a catalyst or calcination step at high temperature. The morphology and the size of the resulting oxide particles were adjusted by using several synthesis parameters (temperature, alkaline ratio, hydrolysis ratio, etc.). The increasing of the alkaline ratio results in a great change of the elaborated particles morphology that evolved from irregular and anisotropic forms (conical, nanorod-like and elliptical) to spherical one. A growth mechanism of these particles was proposed on the basis of zincite crystal structure and the morphology evolution as a function of the synthesis parameters. The photoluminescence spectra show UV-excitonic and visible emission bands. The strongest intensity of the visible emission was observed in nanorod-like particles, which implies an increased fraction of oxygen vacancies in this sample. The rod-like particles with 1 μm length show the dominant UV-emission, which evidences their improved stoichiometry. 相似文献
3.
Synthesis of silver nanoparticles in silica aerogel matrix by sub-critical drying technique is reported in the present article. Physical characterization of silver/silica aerogel nanocomposites with 1, 5 and 25 wt% of silver has been discussed. Physico-optical properties of the composites have been evaluated as a function of the silver particle size crystallized within the silica matrix. The maximum size of the silver grains that could be accommodated in the amorphous matrix was observed to be 25 nm. Silver particles of diameter larger than 25 nm were found segregated out of the silica matrix; such silver particles were single crystalline with dendritic morphology. Optical absorption analysis confirmed the presence of both the oligomeric and nanometallic silver in the samples heat-treated up to 500 °C. With decreasing silver particle size, the surface plasmon resonance was found first to shift towards blue followed then by a red shift. The blue shift is attributed to the chemisorption occurring between the metallic core and the silica matrix. With larger grain size of 25-80 nm in 25 wt% Ag-silica aerogel sample, the diffuseness of electron cloud outside the potential well was observed to cause a red shift in the surface plasmon resonance. 相似文献
4.
Phosphate glasses in the system P2O5-CaO-MgO-Na2O-TiO2 for use as degradable implant materials were produced. In order to classify their solubility behavior, dissolution experiments were performed in deionized water for 60 min at 98 °C. Resulting solutions were analyzed using ICP-OES. In addition, pH measurements were carried out in physiological NaCl solution. With increasing phosphorus oxide content, the glasses showed a higher solubility and gave lower pH values in aqueous solution. This was caused by changes in the glass structure, as long phosphate chains are more susceptible to hydration than smaller phosphate groups. These changes in glass structure were followed by 31P MAS-NMR experiments. Increasing sodium oxide concentrations in exchange for calcium or magnesium oxide also increased the glass solubility by disrupting ionic cross links between chains. By contrast, addition of titania made the glasses more stable towards dissolution by cross linking smaller phosphate groups. The aim of this study was to find a relationship between glass composition and solubility behavior. As classical linear methods of data analysis were unsuitable due to the complexity of the relationship, preliminary artificial neural networks analyses were performed and were found to be an interesting tool for modeling the solubility behavior of phosphate glasses. 相似文献
5.
Rahul Pal 《Journal of Non》2009,355(1):76-78
An acidic silica sol (35 ± 2 wt% equivalent SiO2) having a gelling time of 9-10 min has been used as an aqueous phase for obtaining a w/o emulsion in CCl4 as oil phase in presence of a surfactant, Tween 80. The silica sol was allowed to form gel at room temperature via polycondensation among the -Si-OH groups forming the porous silica gel microspheres. The surface area of the microspheres heated at 500°, 700° and 900 °C was found to be 227 m2/g, 167 m2/g and 81 m2/g indicating the gradual densification. The decreased surface area and unchanged -Si-O-Si- asymmetric stretching vibration at 1084 cm−1 up to 700 °C probably indicate the formation of extensive cross-linked gel structure in the microsphere. The appearance of the -Si-O-Si- asymmetric stretching vibration at 1104 cm−1 and the absence of porosity while heating at 1000 °C indicate the formation of dense silica glass microspheres. 相似文献
6.
Four ZnO-Bi2O3-TeO2 glasses were prepared from high purity (4N5) oxides. From measurements of the optical transmission on very thin bulk samples the optical gap was determined at around 3.55 eV for the glasses studied. The temperature dependence of the optical gap was also determined from the room temperature close up to 500 K. Preliminary Raman scattering measurements indicate that with a decrease in TeO2 content, TeO4 trigonal bipyramid transformation proceeds into TeO3 trigonal pyramids. 相似文献
7.
Melt-spun ribbon and bulk samples in cylindrical rod form with diameter ranging from 2 mm to 4 mm of Ti40Cu40Zr10Ni10 alloy were prepared by melt-spinning technique and copper mould casting method, respectively. The microstructure, thermal stability and mechanical properties of the bulk samples were investigated. A completely glassy single phase is formed in the 2 mm rod sample. Increasing the diameter of the rod samples resulted in the formation of CuTi crystalline phase in the 3 mm and 4 mm rod samples. The 2 mm single glassy rod sample exhibited a large supercooled liquid region ΔTx = 58 K and γ = Tx/(Tg + Tl) is 0.390, which indicated that the alloy possessed a good glass-forming ability. The bulk samples also exhibited good mechanical properties. The 2 mm rod sample showed the highest yield strength of about 2086 MPa. The 3 mm rod sample not only showed high yield strength of about 2000 MPa, but also enhanced plastic strain of about 0.71%. 相似文献
8.
This paper investigated on the dehydration of Er3+-doped phosphate glasses using O2 + CCl4 bubble flow method. The influence of parameters of dehydration effect was studied systemically. It was found that the dehydration rate was rather rapidly at the initial stage of bubbling. Increasing gas flow rate and temperature could drive the dehydration process toward lower OH concentration in the melts. The dehydration process was carried out in open system and analyzed by thermodynamic theory of open system, which clarified the process of eliminating of OH groups from the glass melts with bubbling time and gas flow rate. A time-dependent empirical equation about reaction rate constant was derived, and the relationships between rate constant and bubbling flow rate, and temperature were also discussed. This analytical method could be applicable to the dehydration of glass melt using other dehydration agents. 相似文献
9.
We show room temperature plasticity in several ZrCu-based bulk metallic glasses (BMG) after dispersions of crystalline nanoparticles were generated prior to mechanical testing. BMGs are heated in synchrotron light in transmission such that annealing can be interrupted at the very first detection of nucleation of the crystallites. Effect of embedded nanocrystals on the mechanical properties of BMG-Composites was investigated by compressive testing. When nanocrystal dispersions were generated, zirconium-copper-based BMGs that initially showed no plastic deformation prior to fracture, exhibited ductile behavior in compression with about 10% deformation. 相似文献
10.
Nobuaki Terakado 《Journal of Non》2008,354(18):1992-1999
Oxy-chalcogenide glasses with compositions of xGeO2-(100 − x)GeS2, where 0 ? x ? 100 mol%, have been prepared and studied in terms of their structures and optical properties. X-ray fluorescence spectroscopy shows that Ge:S ratio can deviate from GeS2 by ∼10 at.%, depending critically upon the preparation conditions. Raman scattering spectroscopy suggests that stoichiometric GeO2-GeS2 glasses have a heterogeneous structure in the scale of 1-100 nm. The optical gaps are nearly constant at 3.0-3.5 eV for glasses with 0 ? x ? 80 mol% and abruptly increase to ∼6 eV in GeO2. This dependence suggests that the optical gap is governed by GeS2 clusters, which are isolated and/or percolated. Composition-deviated glasses appear as orange and brown, and these glasses seem to have more inhomogeneous structures. 相似文献
11.
The indentation crack initiation behavior of eight vitreous silica specimens containing bulk OH concentrations ranging from 0.2 to 754 wt ppm was investigated. A recording microindentation instrument equipped with optical observation and acoustic emission detection was used to study, in situ, the cracking behavior from indentation with a Vickers diamond. No significant differences in the threshold loads for various types of cracking behavior of the specimens were found. In addition, the polishing medium was found to have little influence on the cracking behavior. The lengths of median-radial cracks around indentations varied little between specimens. The Vickers hardness of the specimens measured at 0.98 N ranged from 6.6 ± 0.3 GPa to 7.5 ± 0.7 GPa, and no trend with the OH concentration was apparent. In addition, the Vickers hardness of the specimens measured while under a 9.81 N maximum load (LVHmax), showed little variation, and no apparent trend with the OH concentration. 相似文献
12.
The transmission of ArF laser pulses in virgin fused silica (type III) samples changes during N = 106 pulses at an incoming fluence Hin = 5 mJ cm−2 pulse−1. The related absorption is determined by the pulse energy absorption coefficient α(N, Hin) using a modified Beer’s law, yielding initial values αini around 0.005 cm−1, a maximum αmax ? 0.02 cm−1 at N = 103-104 and stationary values 0.0045 cm−1 ? αend ? 0.0094 cm−1 after N ≈ 6 × 105 pulses. The development α(N, Hin = const.) is simulated by a rate equation model assuming a pulse number dependent E′ center density E′(N). E′(N) is determined by a dynamic equilibrium between E′ center generation and annealing. Generation occurs photolytically from the precursors ODC II and unstable SiH structures upon single photon absorption and from strained SiO bonds via two-photon excitation. Annealing in the dark periods between the laser pulses is dominated by the reaction of E′ with H2 present in the SiO2 network. The development α(N, Hin = const.) is observed for the very first sample irradiation only (virgin state). The values αend are not accessible by simple spectrophotometer measurements. 相似文献
13.
Claire Pettersen 《Journal of Non》2008,354(27):3194-3206
Wavelength-dispersive X-ray spectroscopy (WDS) was used to characterize the morphology of the reactions between a liquid bronze alloy (Cu-36 at.%Sn) and two magnesium aluminosilicate, glass-ceramic-forming glassmelts, one of which was doped significantly with ZnO. Two suites of experiments were pursued for each glassmelt, an isochronal series (30-min reactions with temperatures ranging from ∼1300 to 1400 °C) and an isothermal series (1350 °C reactions with durations ranging from 5 to 60 min). The reactions are decidedly complex. Transient behavior sees initially rapid incorporation of Cu+,2+ into the glassmelts, effected primarily by a redox couple involving the SiO2 component of the aluminosilicate. This behavior gives way to a more dominant kinetic response in which Sn2+,4+ is incorporated into the glassmelt in a reaction and chemical diffusion process that, in part, pulls the early-incorporated ionic copper back out of the aluminosilicate. In the case of the ZnO-doped glassmelt, coupled redox and interdiffusion of ionic Sn and ionic Zn is important in the longer-time response, giving rise to a Liesegang-band morphology. The extent of metal-silicate reaction diminishes as the temperature is increased, a thermodynamic effect related to the solution thermodynamics of the liquid bronze alloy. The reaction kinetics are interpreted following the Wagner-Schmalzried formalism for diffusion-effected redox reactions. 相似文献
14.
Eun-Sub Lim 《Journal of Non》2006,352(8):821-826
A BaO-B2O3-SiO2 glass system was chosen as a candidate composition for the application to Pb-free low temperature sinterable glass. The effect of BaO content on the crystallization, sintering behavior, and properties of the glasses was examined. Both the glass transition temperature and crystallization temperature decreased as the BaO content increased. Crystallization easily occurred during sintering with a BaO content of more than 50 mol%, which effectively inhibited the over-firing phenomenon. The dielectric characteristics and thermal expansion coefficient of the glasses were examined and the results were explained on the basis of the crystallization and densification of the specimens. 相似文献
15.
Hongxia Lu 《Journal of Non》2007,353(26):2528-2544
Tracer diffusion coefficients of the radioactive isotope Na-22 were measured in glasses of the type (CaO·Al2O3)x(2 SiO2)1−x to study the diffusion of sodium as a function of glass composition, x, temperature and initial water content. The diffusion of Na-22 in glasses diffusion-annealed in dry air can always be well described by a single tracer diffusion coefficient, but sometimes not in samples annealed in common air. It was found that the sodium tracer diffusion coefficient decreases by about six orders of magnitude when the glass composition x changes from 0 to 0.75 at 800 °C. The temperature dependence of the diffusion of sodium seems to decrease as the silica content increases. Variations of the initial water content in some of the glasses investigated did not very significantly influence the rate of the tracer diffusion of sodium. 相似文献
16.
Fanqing Zeng Guozhong Ren Xiannian Qiu Qibin Yang Jingwu Chen 《Journal of Non》2008,354(29):3428-3432
The Er3+ doped transparent oxyfluoride glass ceramics were obtained by appropriate heat treatment of the precursor glasses with composition (mol%) 50SiO2-xPbF2-(50 − x)PbO-0.5ErF3. The microstructure and optical properties of the glasses and glass ceramics were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), absorption spectra and luminescence spectra. The intensity of upconversion luminescence significantly increased in glass ceramics compared to that in precursor glass. The emission bands centered around 660 nm (4F9/2 → 4I15/2) and 410 nm (2H9/2 → 4I15/2) were simultaneously observed in glass ceramics but cannot be seen in the corresponding precursor glass. The influence of different PbF2 content on the microstructure and upconversion luminescence of the samples was analyzed in detail. The results indicated that with the increase of PbF2 content, the Ω2 was almost the same and the ratios of red to green upconversion luminescence decreased in glass ceramics. 相似文献
17.
A. Koike 《Journal of Non》2008,354(28):3246-3253
Glass samples with same composition and properties but different thermal histories can exhibit different behavior upon a subsequent heat-treatment, a phenomenon known as the memory effect. Generally, it is considered that the memory effect is due to nanoscale density fluctuation, which exists in all glasses and causes non-exponential relaxation with more than one relaxation time. Earlier, we studied the memory effect of various silica glasses and found that some pure silica glasses did not exhibit the memory effect while some silica glasses with higher impurity contents exhibited the memory effect. Based upon this finding, we suggested that the phenomenon originated from concentration fluctuation rather than density fluctuation. In this study, the memory effect in 6 mol% K2O-94 mol% SiO2 glass was investigated. The K2O-SiO2 glass system has a metastable immiscibility below the glass transition temperature and the chosen glass composition is the critical composition corresponding to the estimated critical temperature of the immiscibility boundary. Thus, it is expected that this glass composition would exhibit large super-critical concentration fluctuation, which increases with decreasing heat-treatment temperature. Density fluctuation, on the other hand, increases with increasing heat-treatment temperature. A much larger memory effect was observed at the lower heat-treatment temperature for the present glass. This result supports our earlier contention that the origin of the memory effect is composition fluctuation rather than density fluctuation. 相似文献
18.
We have investigated a series of glasses and melts along the GeO2-SiO2 join using insitu Raman spectroscopy. The results for both the glasses and melts are consistent with a continuous random network in which there are ‘regions’ that are SiO2-like, GeO2-like and mixed GeO2-SiO2-like. Incorporation of GeO2 into the SiO2 network is initially accommodated via the 3- and 4-membered SiO4 rings which are lost as they convert to larger mixed Ge/Si rings. The LO-TO mode behavior is also consistent with a network that is composed of different ‘regions’ and is similar to that expected from the Bruggeman effective media model. At the highest temperatures there are indications that the mixed Ge/Si rings convert back to small 3-membered GeO4 rings and large SiO4 rings; the small 3- and 4-membered SiO4 rings are not reformed. 相似文献
19.
Daniela Carta Dong Qiu Ifty Ahmed Ensanya A. Abou Neel Mark E. Smith 《Journal of Non》2008,354(31):3671-3677
Glasses in the system 40(P2O5)-x(B2O3)-(60 − x)(Na2O) (10 ? x ? 30 mol%) have been prepared by the melt-quenching technique. Thermal properties were studied using differential thermal analysis and the relationship between composition and thermal stability was obtained. Structural characterization was achieved by a combination of experimental data (infrared and Raman spectroscopy, 11B and 31P solid state NMR). In particular, variations in the phosphate network structure upon addition of B2O3 and Na2O were investigated. Analysis of the data indicates that with increasing B2O3 content and decreasing Na2O, the glass network shows increasing levels of cross-linking between phosphate and borate units. Evidence of direct B-O-P bonds was observed. In the compositional range investigated, borate groups contain boron almost exclusively in four-fold coordination. 相似文献
20.
X-ray absorption spectroscopy (XAS) was used to characterize the tin (Sn) environments in four borosilicate glass nuclear waste formulations, two silicate float glasses, and three potassium aluminosilicate glasses. Sn K-edge XAS data of most glasses investigated indicate Sn4+O6 units with average Sn-O distances near 2.03 Å. XAS data for a float glass fabricated under reducing conditions show a mixture of Sn4+O6 and Sn2+O4 sites. XAS data for three glasses indicate Sn-Sn distances ranging from 3.43 to 3.53 Å, that suggest Sn4+O6 units linking with each other, while the 4.96 Å Sn-Sn distance for one waste glass suggests clustering of unlinked Sn4+O6 units. 相似文献