Infrared evanescent-absorption spectroscopy with chalcogenide glass fibers

We have used telluride glass fibers fabricated in house to measure the evanescent-absorption spectra of water, methanol, ethanol, isopropanol, acetone, ethanoic acid, hexane, and chloroform. Furthermore, detection limits of less than 2 vol. % solute were obtained for mixtures of water and methanol, ethanol, isopropanol, acetone, and ethanoic acid. Techniques to reduce the detection limits are discussed.     

Photo-induced absorption changes in selenium-based chalcogenide glass films

The random network model for amorphous alloys proposed by White has been developed for some selenium-based amorphous semiconductors (GeSe and AsSe) annealed or irradiated with light. The model suggests that the photo-bleaching and the photo-darkening observed in these systems may be due to changes in the numbers of bonds.     

Effect of fluorine doping on the optical loss in MCVD fibers based on heavily doped germanosilicate glass

We have studied the size distribution of silica glass particles in the fabrication of heavily doped germanosilicate glass fiber preforms by modified chemical vapor deposition (MCVD) at different Freon 113 concentrations in the gas mixture. The addition of Freon 113 to the gas mixture is shown to reduce the particle size in the deposited core glass layer and the optical loss in the fiber. A mechanism is proposed which accounts for the effect of the initial particle size in the core glass layer on the anomalous scattering and total optical loss in heavily doped step- and graded-index fibers.     

冷却方式对硫系玻璃性能的影响

通过DSC、XRD、SEM、FT-IR和显微硬度测试等分析手段,研究了冷却方式对99.75Ge23Se67Sb10-0.25RbI玻璃组织、热稳定性以及光学和力学等性能的影响。结果表明,采用空冷制得的试样在8~12μm波段红外透过率达70%以上,高于水冷试样(64%),但由于空冷冷速慢,氢在硒中的固溶度大,导致杂质吸收也大于水冷试样;空冷试样在280℃热处理20h可从XRD检测发现明显Sb2Se3和GeSe2的结晶峰,而水冷试样在300℃热处理20h后才能检测到结晶峰;经过热处理,水冷试样的最大KIC值可达到0.414 MPa·m1/2,较未热处理值提高了26%,且高于空冷试样的最大KIC(0.368 MPa·m1/2),因此,水冷试样高温稳定性好,断裂韧性较大,更适合用作微晶化硫系红外玻璃。     

Effect of core glass composition on the optical properties of active fibers

We optimized the composition of core glass for active fibers. Using solution doping, we obtained aluminogermanosilicate core fibers containing up to 0.6 mol % Yb₂O₃ with optical losses within 10 dB/km.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 508–512.Original Russian Text Copyright © 2005 by Khopin, Umnikov, Vechkanov, Rozental, Guryanov, Bubnov, Rybaltovskii, Belov, Dianov.Deceased.     

Deformation, stress relaxation, and crystallization of lithium silicate glass fibers below the glass transition temperature

The deformation and crystallization of Li₂O·2SiO₂ and Li₂O·1.6SiO₂ glass fibers subjected to a bending stress were measured as a function of time over the temperature range 50 to 150°C below the glass transition temperature (T _g). The glass fibers can be permanently deformed at temperatures about 100°C below T _g, and they crystallize significantly at temperatures close to, but below T _g, about 150°C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams- Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, E _s, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E (400 kJ/mol) near T _g for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T _g.     

Mechanisms of light absorption in gamma-irradiated blanks for optical fibers based on high-purity quartz glass

The IR optical absorption spectra and the Raman spectra of rods made of high-purity quartz glass of the KU-1 and KS-4V grades have been studied in comparison to those measured for the blanks of optical fibers fabricated from this glass using the plasma outside deposition (POD) technology. Based on these data, a discussion is presented of the most probable mechanisms responsible for an increase in the γ-radiation-induced absorption in high-purity quartz glasses as a result of their processing in the course of optical fiber fabrication using the POD technology.     

Effect of iron oxides on the fabrication and properties of continuous glass fibers

We have studied the effect of iron oxides (0–10 wt % in terms of FeO) on the fabrication conditions and properties of continuous Fe-containing glass fibers and have determined the temperature ranges of fiber fabrication. A relationship between the iron oxide content of glass and the fiber fabrication temperature has been established. Using differential scanning calorimetry and x-ray diffraction, we have investigated the effect of glass composition on the glass transition temperature and temperature range of crystallization of the fibers. At high iron oxide contents (5–10 wt %), the first to crystallize is magnetite, otherwise quartz appears first. Increasing the heat-treatment temperature leads to crystallization of pigeonite, augite, enstatite, anorthite, and labradorite.     

Effect of heat treatment on the infrared absorption spectra of Sr-Na borosilicate glass

Internal modes of vibrations are studied here at different temperatures (27–800°C) and in the frequency range 200–4000 cm^–1 through heat treatment. The baseline method was used. The strong bands of SiO₄ tetrahedra in this glass show an increase in absorbance at high temperature (600–800°C). The deformation of SiO₄ tetrahedra is investigated. This is found to depend on the ionic radius of the divalent metal oxide introduced, and the coordination number of the cation. Also from a study of the temperature dependence of the relative integrated intensity of the modes 600–800 and 850–1450 cm^–1, the relaxation time and rotational energy barrier of the glasses selected indicate that the glassy phases are transformed to crystalline phases at 500°C.     

Effect of gas temperature on the gas loss from ventilated cavities

Summary. The theory for gas loss from ventilated cavities under isothermal conditions is extended to the non isothermal case, where the gas inside the cavity has a temperature different from the water temperature.     

Quantitative evaluation of chalcogenide glass fiber evanescent wave spectroscopy

A quantitative theoretical model that describes the amount of evanescent field that is absorbed by an infinite cladding has been developed. The validity of this model has been confirmed by a series of experiments to determine the typical dependence of the abosrption on each parameter (fiber length, fiber diameter, light beam launching condition, and wavelength) separately, and the total amount of absorption as a function of all the parameters combined. The results show that this model can predict the amount of absorbed radiation with an error range of 5%. It is therefore possible to analyze the infrared spectrum by quantitative data such as the ratio between two absorption lines or by deriving the absorbance coefficient of the absorption curve.     

Effect of short glass fibers on the mechanical properties of cast ZA-27 alloy composites

This paper aims to study the effects of short glass fiber reinforcement on the mechanical properties of cast ZA-27 zinc alloy composites containing glass fibers of content ranging from 0% to 5% by weight. The composites were fabricated using the ‘compocasting’ method in which the short glass fibers were introduced into the vortex created in the molten alloy through an impeller rotated at 500 rev./min. The molten mass was thoroughly stirred, poured into permanent moulds and squeeze-cast under pressure. The results of this study revealed that as glass fiber composition was increased, there were significant increases in the ultimate tensile strength (UTS), hardness and Young's modulus, accompanied by a reduction in its ductility and impact strength. An attempt is made in this article to provide explanations for these phenomena.     

温度场对PAN预氧纤维中类萘啶结构的影响

采用固体13 C核磁共振(13 C Solid-NMR)、差示扫描量热分析(DSC)研究了不同温度场对聚丙烯腈纤维预氧过程中类萘啶结构生成的影响。研究结果表明:提高预氧化温度纤维中易于形成类萘啶的梯形含氮芳杂环结构,预氧化热处理温度高于230℃时,类萘啶结构生成速度较快。梯度升温方式影响类萘啶结构的生成,三温区温度场条件下(210-230-245℃),在高温区(245℃)停留时间较长时有利于类萘啶结构的形成和发展;四温区温度场中(210-230-245-260℃),均匀分配各温区的热处理时间更有利于类萘啶结构的生成。     

Effect of high pressure on chalcogenide glasses

The effect of high pressures on the various properties of the chalcogenide glasses is reviewed. The properties discussed include the mechanical, electrical, optical and magnetic properties. The phenomena of the crystallization of the chalcogenide glasses under high pressure is also discussed. This article is dedicated to the memory of late Dr N S Satya Murthy who had been intimately associated directly and indirectly with the development of condensed matter physics in India.     

Effect of RF-plasma deposition parameters on the composition and properties of organic layers deposited on glass fibers

Thin films were deposited from vinyltriethoxysilane (VTES) and tetravinylsilane (TVS) by radio frequency (RF) cold plasma operated in a pulsed mode on the surface of E-glass fibers. Film thickness and molecular structure was controlled by the length of plasma cycle expressed as ratio of time on/time off (t_on/t_off). It was found that t_on as short as 1 ms was long enough for vinylsilane precursor gas fragmentation. Time t_off was the main parameter controlling structural variables of the deposited films. Short t_off led to apparently disordered and cross-linked structure. Increased t_off led to more uniform films with enhanced properties compared to the short t_off deposited films. Only films prepared under long t_off improved adhesion between the glass fiber and polyester resin as measured employing the micro-droplet test. Strong effect of the molecular structure of the vinylsilane precursor has also been observed under the conditions used. VTES film deposited under t_on/t_off = 1:999 increased interfacial adhesion only by 20%, TVS film deposited at 1:99 improved adhesion by 48%, compared to the solution deposited coating of the VTES used commercially.     

Effect of water on the fatigue behaviour of a pa66/glass fibers composite material

The aim of this study is to evaluate the effect of the humidity on the long term behaviour of glass fiber reinforced thermoplastic in fatigue. Two sets of samples were studied, one set contained 0.2 wt% of water, the second 3.5 wt%. The fatigue tests are performed at a 10 Hz frequency, at room temperature and two various relative humidity ratios, 50% RH and 96% RH. The S–N curve of dried samples (0.2%) is above the one of humid samples (3.5%), the endurance limit at 10⁷ cycles for dried samples is equal to 40 MPa against 35 MPa for the second set. For a given strain, the fatigue life is higher for humid samples because the induced stress is much lower due to the plasticizing effect of water. Though the tests are carried out at room temperature (23 °C), the sample temperature at the surface reaches values higher than Tg and whatever the applied strain, the matrix is in a rubbery state when the fracture occurs. On the basis of S.E.M. examinations, the following scenario is proposed: crack initiation at the fiber end, crack propagation along the fiber sides going with debonding, then crack propagation in the rubbery matrix.