共查询到20条相似文献,搜索用时 15 毫秒
1.
《Journal of Non》2005,351(52-54):3789-3796
Using picosecond stimulated Raman scattering (SRS) in silica-based fibers as a spectroscopic tool, some correlations between medium-range ordering and photosensitivity in silica glasses were experimentally established. Apart from the fundamental Raman-active vibrations attributed to the silica tetrahedra and dopant groups and their overtones, the intense Raman combination bands were observed. Based on the overtone band sequences, the vibrational anharmonicity constants were calculated and analyzed, including the ones corresponding to the 570 cm−1 band. This band is forbidden in Raman scattering in silica crude selection rules are used. However, the transition is activated owing to the tetrahedron distortions by outer shells of the first and second peripheral atoms in a silica network. It is the intensity of the 570 cm−1 Stokes band that grows enormously in the SRS spectra of germanium-doped silica fibers as a result of photoinduced changes in the glass structure resulting in second harmonic generation (SHG). The experimental data are interpreted using a modern glass theory. Practical applications of picosecond SRS spectroscopy for glass microstructural studies are discussed. 相似文献
2.
《Journal of Non》2007,353(5-7):526-529
Formation and destruction of silicon hydride (Si–H) groups in silica by F2 laser irradiation and their vacuum ultraviolet (VUV) optical absorption was examined by infrared (IR) and VUV spectroscopy. Photoinduced creation of Si–H groups in H2-impregnated oxygen deficient silica is accompanied by a growth of infrared absorption band at 2250 cm−1 and by a strong increase of VUV transmission at 7.9 eV. Photolysis of Si–H groups by 7.9 eV photons in this glass was not detected when the irradiation was performed at temperature 80 K. However, a slight destruction of Si–H groups under 7.9 eV irradiation was observed at the room temperature. This finding gives a tentative estimate of VUV absorption cross section of Si–H groups at 7.9 eV as 4 × 10−21 cm2, showing that Si–H groups do not strongly contribute to the absorption at the VUV fundamental absorption edge of silica glass. 相似文献
3.
《Journal of Non》2007,353(16-17):1540-1545
In this study, the failure resistance of soda-lime-silica glass was increased by surface treatment with sol–gel silica. Samples annealed and ion-exchanged in KNO3 for 24 h at 450 °C were considered. Sol–gel silica coating was carried out by dipping the glass samples into a sol suspension prepared by hydrolysis of Si(OEt)4 in ethanol/water solution. The deposited layer was consolidated in air for 24 h and subjected to mild thermal treatment at 300 °C for 1 h. The surface treatment increased the fracture resistance of annealed glass of about 35 MPa; conversely, ion-exchanged specimens showed an average increase of about 90 MPa. The strengthening effect induced by the surface treatment was attributed to the reduction of the effective crack length generated by the silica coating. The different strength increase between annealed and ion-exchanged samples is discussed in terms of fracture toughness which, for ion-exchanged glass, is not constant, due to the presence of the surface residual stresses and thus the reduction of the crack length due to the silica coating determines a higher strength increase than for annealed glass. 相似文献
4.
W. Blanc T.L. Sebastian B. Dussardier C. Michel B. Faure M. Ude G. Monnom 《Journal of Non》2008,354(2-9):435-439
Thulium-doped optical fibre amplifiers (TDFA) are developed to extend the optical telecommunication wavelength division multiplexing (WDM) bandwidth in the so-called S-band (1460–1530 nm). The radiative transition at 1.47 μm (3H4 → 3F4) competes with a non-radiative multi-phonon de-excitation (3H4 → 3H5). The quantum efficiency of the transition of interest is then highly affected by the phonon energy (Ep) of the material. For reliability reasons, oxide glasses are preferred but suffer from high phonon energy. In the case of silica glass, Ep is around 1100 cm?1 and quantum efficiency is as low as 2%. To improve it, phonon energy in the thulium environment must be lowered. For that reason, aluminium is added and we explore three different core compositions: pure silica, and silica slightly modified with germanium or phosphorus. The role of aluminium is studied through fluorescence decay curves, fitted according to the continuous function decay analysis. From this analysis, modification of the thulium local environment due to aluminium is evidenced. 相似文献
5.
《Journal of Non》2007,353(22-23):2301-2305
Water diffusion in fiber reinforced ceramic composites could reduce the flexural strength as a result of weakened fiber/matrix binding. In the paper, the braided silica fiber reinforced silicon nitride and boron nitride amorphous composites (SiO2f/Si3N4–BN) was prepared through repeated infiltration of hybrid preceramic precursor and pyrolysis at high temperature in ammonia atmosphere. The moisture behavior of the SiO2f/Si3N4–BN composites and moist effects on the mechanical properties and the microstructures of composites were studied. The results showed that the water absorption characteristic of amorphous composites could be described by using the Fick’ law. The flexural strength could be adjusted and the maximal value of that reached 161.7 MPa by controlling moderate relative humidity, which is 58.8% higher more than that of the as-received composites. SEM indicated that good mechanical properties is on the ground of the interface structure change between fiber and matrix and more fibers were pulled out which absorbing much more fracture energy. 相似文献
6.
Muhammad Ashfaq Rukhsana Tabassum Muhammad Mahboob Ahmed Karamat Mehmood M. Asghar Tanveer Hussain 《Journal of Non》2012,358(4):847-853
Amorphous anhydrous silica SiO2 (mw) (99.99%) is successfully synthesized through microwave irradiation technique and time of reaction is reduced up to 1 h. The dehydration phase study of Si–water, Si–OH, Si–O–Si networking, elemental analysis and surface morphology was carried out by FTIR, FTNIR, SEM and EDAX spectroscopic techniques. The broad absorption stretching and bending of Si–OH and H2O at 3695.38–2832.96 cm? 1, 1638 cm? 1 and 1191.20–1017.14 cm? 1 completely disappeared and appearance of new bands at 946.93 and 797.63 cm? 1 confirmed the amorphous anhydrous silica with Si–O–Si networking. The SEM images of SiO2 (mwc) described the smooth and fine particle texture and confirmed 99.99% Si–O–Si networking of anhydrous silica. The 99.99% purity was verified by EDAX spectra which exhibited sharp signals only for oxygen and silicon. Toxicity against Monomorium minimum and Tribolium castaneum with 100% mortality and LT50 91 min and 7.5 h respectively is being reported. It can be used for long storage of grains in the future. 相似文献
7.
Slip casting process is usually applied for the forming of fused silica products. Segregation always occurs and it will results in density deviation. By using gel casting process, green is fabricated by means of in situ polymerization with a three-dimensional network, holding the particles together and eliminating the tendency of migration. To prepare gel casting slurries, premix solutions were composed of acrylamide and N,N′-methylenebisacrylamide. Solid loading was kept 60% and the average particle size of silica powder 8–8.5 μm. Lactic acid was introduced as a dispersant to regulate the pH value 3–4. Mechanism of the dispersant was investigated by studying ζ-potential at different pH. Ammonium persulfate (NH4)2S2O4 was added as an initiator. Gelation took place with the help of initiator at 50–60 °C. Nanometer silica was introduced to boost sinterability so that the density and bending strength of fused silica ceramics have been increased to 2.1 g/cm3 and 40 Mpa, respectively. 相似文献
8.
《Journal of Non》2006,352(21-22):2254-2258
The aluminum coordination state in bismuth doped silica glass, which has new broad infrared emission at 1.3 μm regions, was investigated by using 27Al NMR, and it is demonstrated that 6-fold coordinated aluminum ions with corundum structure are dominant in bismuth doped silica glass until Bi2O3 concentrations of 1.0 mol% with Al2O3. The aluminum ion efficiently affects the creation of a Bi luminescent center at an intensity of Bi2O3 (1.0 mol%)–Al2O3 (2.3 mol%)–SiO2 (96.7 mol%); the sample is three orders of magnitude larger than the Bi2O3 (1.0 mol%)–SiO2 (99.0 mol%) sample. Aluminum ions with corundum structure in silica glass have a very important role for the configuration of peculiar Bi luminescent centers. 相似文献
9.
《Journal of Non》2006,352(26-27):2829-2833
Hollow silica spheres were synthesized by using a chitosan-polyacrylic acid (CS-PAA) template. Polyacrylic acid (PAA) was titrated into the dissolved chitosan solution to form CS-PAA particles. For forming the core-shell particle, colloidal silica which was prepared from homogeneous nucleation was mixed with a solution of CS-PAA particles. Colloidal silica was adsorbed on to the surface of the CS-PAA particles to form a shell structure. CS-PAA could be removed from the core of the core-shell particles by adjusting with HCl to pH < 1 for forming the hollow silica structure. The outside particle size diameter, shell thickness, specific surface, pore diameter and pore volume of the final hollow silica sphere are about 200 nm, 20 nm, 350.95 m2/g, 5.4078 nm and 0.516768 cm3/g, respectively. 相似文献
10.
Zhijian Peng Xiuli Fu Na Zhu Xi Guo Chengbiao Wang Zhiqiang Fu 《Journal of Non》2009,355(43-44):2156-2159
Large-scale synthesis of clustered one-dimensional amorphous silica nanowires was achieved by simple thermal pyrolysis of an amorphous preceramic powder from perhydropolysilazane on alumina wafers coated with catalyst FeCl2. Scanning electron microscopy and transmission electron microscopy observations showed that the silica nanowires had smooth surface, and lengths of hundreds of micrometers and diameters in the range of 30–40 nm. Energy dispersive X-ray spectroscopy revealed that these nanowires consisted of Si and O elements in an atomic ratio of approximately 1:2, consistent with the stoichiometric formula SiO2. The two amorphous bulges in Raman spectrum at the centers of around 260 cm?1 and 800 cm?1 were identified to be those of amorphous silica. The growth mechanism of the as-produced silica nanowires could be attributed to vapor–liquid–solid mechanism. These results provide an alternative and simple preparation procedure for nanostructures with controlled morphology, and it will be helpful to understand the growth mechanism of one-dimensional SiO2 nanostructures. 相似文献
11.
Fast ion conducting (FIC) phosphate glasses and glass ceramic composites have gained considerable importance due to their potential applications in the fabrication of solid-state batteries and other electrochemical devices. We, therefore, present an overview on various types of FIC glasses and glass ceramic composites. Silver phosphate glasses doped with different weight percent of lithium chloride (1, 5, 10 and 15 wt.%) were synthesized by melt quenching technique. The Ag2O–P2O5–(15 wt.%) LiCl glass exhibited the maximum electrical conductivity (σ = 8.91 × 10? 5 S cm? 1 at room temperature and 4.16 × 10? 3 S cm? 1 at 200 °C). Using this glass as an amorphous host material, glass–ceramic composites of Ag2O–P2O5–(15 wt.%) LiCl:xAl2O3 (x = 5–50 wt.%) were prepared. The ionic transference number, electrical conductivity, ionic mobility and carrier ion concentration of the synthesized samples were measured. Ag2O–P2O5–(15 wt.%) LiCl:(25 wt.%) Al2O3 composite system exhibited the maximum σ value (σ = 3.32 × 10? 4 S cm? 1 at room temperature and 2.88 × 10? 2 S cm? 1 at 200 °C ). Solid‐state batteries using undoped Ag2O–P2O5 glass, Ag2O–P2O5–(15 wt.%) LiCl glass and glass ceramic composite containing 25 wt.% Al2O3 as electrolytes were fabricated. The open circuit voltage (OCV) values and discharge time of these cells were measured and compared. It is found that the glass ceramic composites show enhanced ionic conduction, better OCV value and discharge characteristics. 相似文献
12.
The silica aerogels were synthesized by sol–gel method via ambient pressure drying. Tetraethyl orthosilicate (TEOS) was used as a main silica source, methyltriethoxysilane (MTES) as a co-precursor silica source and (3-Glycidoxypropyl)trimethoxysilane (GPTMS) as a silane coupling agent. The silica aerogels obtained were further undergoing cross-linking epoxy from GPTMS with amine from diethylenetriamine (DETA) which played a dual role of base catalyst and reagent. The cumulative volumes for open pores of the cross-linked aerogels were evaluated to be 1.4 cm3/g. The Young's modulus and maximum compression strength were 25.4 MPa and 6.17 MPa, respectively. The addition of MTES accelerated the solvent exchange of alcohol within the pores with n-hexane and reduced the shrinkage of aerogels network during the ambient pressure drying. The formation of organic network enhanced the strength of the cross-linked aerogels to prevent the crack generation and the subsequent failure of the monolith during the ambient drying, therefore, protected the nanoporous structure of aerogels. 相似文献
13.
《Journal of Non》2006,352(32-35):3478-3483
In this work a SiO2 matrix with more than 50% porosity was developed and infiltrated with a pure silica sol under isostatic pressure, as a prior step to the immobilization of radioactive waste using this technique. The silica glass was prepared through the acidic leaching of phase-separated and partially-sintered sodium–borosilicate glass powder compacts. Phase separation was promoted at different stages of the sintering process to obtain different total porosity or pore size distributions, which in all cases showed macro, meso and micropores. Infiltration leads to a significant increase in weight, reflecting the initial porosity of the substrates. Porosimetry techniques (Hg porosimetry and N2 adsorption isotherms) show that the silica sol fills practically all the pores with diameters over 3 nm. Preliminary sintering tests show that the infiltration technique lowers the sintering temperature by more than 150 °C. 相似文献
14.
Nicholas Leventis Sudhir Mulik Xiaojiang Wang Amala Dass Vishal U. Patil C. Sotiriou-Leventis Hongbing Lu Gitogo Churu Alex Capecelatro 《Journal of Non》2008,354(2-9):632-644
Macroporous (1–5 μm) monolithic silica aerogels consisting of both random but also ordered mesoporous walls have been synthesized via an acid-catalyzed sol–gel process from tetramethoxysilane (TMOS) using a triblock co-polymer (Pluronic P123) as a structure-directing agent and 1,3,5-trimethylbenzene (TMB) as a micelle-swelling reagent. Pluronic P123 was removed by Soxhlet extraction, and materials in monolithic form were obtained by extracting the pore filling solvent with liquid CO2, which eventually was taken out supercritically. Although these monoliths are more robust than base-catalyzed silica aerogels of similar density, nevertheless, the mechanical properties can be improved dramatically by letting an aliphatic di-isocyanate (Desmodur N3200) react with the silanols on the macro- and mesoporous surfaces. As it turns out, the polymer fills the mesopores and coats conformally the macropores of templated samples, so that BET surface areas decrease dramatically, from 550–620 m2 g?1 to <5 m2 g?1. By comparison, polymer nano-encapsulation of non-templated acid-catalyzed aerogels preserves a large fraction of their mesoporous surface area, and BET values decrease from 714 m2 g?1 to 109 m2 g?1. Finally, since polymer nano-encapsulation preserves the macroscopic physical dimensions of the monoliths before drying, comparative analysis of the physical dimensions against XRD data of native versus polymer nano-encapsulated samples provides evidence that upon drying macropores (micron size regime) shrink less than mesopores (nanometer size regime). 相似文献
15.
《Journal of Non》2007,353(47-51):4344-4352
We report new results on segmental dynamics and glass transition in a series of poly(dimethylsiloxane) networks filled with silica nanoparticles prepared by sol-gel techniques, obtained by differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC), broadband dielectric relaxation spectroscopy (DRS) and dynamic mechanical analysis (DMA). The nanocomposites are characterized by a fine dispersion of 10 nm silica particles and hydrogen bonding polymer/filler interactions. The first three techniques indicate, in agreement with each other, that a fraction of polymer in an interfacial layer around the silica particles with a thickness of 2–3 nm shows modified dynamics. The DSC data, in particular measurements of heat capacity jump at Tg, are analyzed in terms of immobilized polymer in the interfacial layer. The dielectric TSDC and DRS data are analyzed in terms of slower dynamics in the interfacial layer as compared to bulk dynamics. We employ a special version of TSDC, the so-called thermal sampling (TS) technique, and provide experimental evidence for a continuous distribution of glass transition temperatures (Tg) and molecular mobility of the polymer in the interfacial layer, which is consistent with the DRS data. Finally, DMA results show a moderate slowing down of segmental dynamics of the whole polymer matrix (increase of glass transition temperature by about 10 K as compared to the pure matrix). 相似文献
16.
TmF3 doped TeO2–ZnO–La2O3 (TZL) glasses and fibers have been prepared by the conventional melt-quenching and suction casting methods, respectively. 2 μm emission properties and energy transfer mechanisms of the TZL glasses and fibers have been analyzed and discussed. The oscillator strength, Judd–Ofelt parameters, radiative transition probability and radiative lifetime of Tm3+ have been calculated based on the absorption spectra and Judd–Ofelt theory. The maximum emission cross-section of Tm3+ is 6.9 × 10?21 cm2 near 2 μm. Emission spectra have been obtained from both TZL fibers and bulk glass when excited with a 794 nm pump. The results of 2 μm emission spectra indicate that the line width of Tm3+ measured in fibers is narrower than that in the bulk glass sample. The peak position of the emission spectra shifts to longer wavelength with increment of the fiber length. 相似文献
17.
《Journal of Non》2006,352(6-7):488-493
Thulium-doped fiber amplifiers (TDFAs) have been proposed as practical devices for the amplification of light signals in the so-called S-band (1460–1530 nm) of the transparency window of standard telecommunications fiber. As the quantum efficiency of the desired 3H4 → 3F4 luminescence of Tm3+ is adversely affected by non-radiative decay when high maximum phonon energy (MPE) host glasses are used, a practical TDFA requires an active fiber made from a glass with intermediate to low MPE. We have explored the possibility of using aluminate fibers for this application, as bulk samples of Tm-doped alkaline earth aluminate glass are characterized by a MPE of 780 cm−1 and a quantum efficiency for the 1460 nm fluorescence of ∼35%. Despite the high devitrification tendency of aluminate glass, pure aluminate core fibers with minimum losses of ∼0.5 dB/m have been successfully fabricated by the rod-in-tube technique using viscosity- and expansion-matched alkaline earth aluminosilicate cladding glasses. 相似文献
18.
Wet and dry silica oxide layers have been treated thermally up to Ta = 1300 °C and were investigated by cathodoluminescence (CL) spectroscopy. Whereas the dry oxides after high temperature treatment show an increase of the yellow–red spectra region, contrary, in wet oxides the UV–blue region is enhanced. Even a new strong band in the near-UV region (NV) at 330 nm (3.76 eV) is found for wet oxides at liquid nitrogen temperature (LNT), but much broader and with lower intensity for room temperature (RT) in a triple band structure UV: 290 nm, NV: 330 nm, and V: 400 nm. These violet bands should be associated with a thermally decomposed and rapidly cooled-down silica network in presence of OH groups or even dissociated oxygen. Additional oxygen implantation into dry silica with high doses up to 1017 ions/cm2 and high thermal treatment T > 1100 °C leads as well to enhanced UV–NV–V luminescence emission bands supporting the fact that oxygen and structural decomposition play a decisive role in formation of near-UV luminescent defects in silica. 相似文献
19.
Danping Chen Jinan Xia Mingying Peng Lvyun Yang Xiangeng Meng Ning Da Jianrong Qiu Congshan Zhu 《Journal of Non》2008,354(12-13):1226-1229
Porous glass with high-SiO2 content was impregnated with Nd ions, and subsequently sintered at 1100 °C into a compact non-porous glass in air or reducing atmosphere. Sintering in a reducing atmosphere produced an intense violet–blue fluorescence at 394 nm. However, the sintering atmospheres almost did not affect the fluorescence properties in the infrared range. A good performance Nd3+-doped silica microchip laser operating at 1064 nm was demonstrated. The Nd-doped sintering glasses with high-SiO2 content are potential host materials for high power solid-state lasers and new transparent fluorescence materials. 相似文献
20.
《Journal of Non》2007,353(13-15):1407-1413
We report the results of emission and amplification in Tm3+- and Er3+-fibers for signal gain in the 1460–1600 nm region, which covers a large part of S-, C- and L-bands of silica fiber optical communication networks. The paper explains the mechanism for alleviating the pump-excited absorption in Er3+-doped and Tm3+-doped tellurite fibers for maximizing the pump inversion efficiency at 980 nm using the co-dopants and via the structural modification of TeO2 glass by incorporating a high phonon energy oxide namely, B2O3. The spectroscopic data and gain bandwidth of Er-doped fibers are reported in the C- and L-bands. To date the measured maximum relative gain in short fibers of 5–10 cm in length in C- and L-bands are: 30 dB and 15 dB, respectively. By comparison the internal gain in a 20 cm long Tm/Yb ion co-doped fiber pumped with a 980 nm source was 7 dB. 相似文献