Aluminosilicate Fibers Research Articles

Effect of sheath material and reaction overpressure on Ag protrusions into the TiO2 insulation coating of Bi-2212 round wire

In order to develop a high current density in coils, Bi-2212 wires must be electrically discrete in tight winding packs. It is vital to use an insulating layer that is thin, fulfils the dielectric requirements, and can survive the heat treatment whose maximum temperature reaches 890 °C in oxygen. A thin (20-30 µm) ceramic coating could be better as the insulating layer compared to alumino-silicate braided fiber insulation, which is about 150 μm thick and reacts with the Ag sheathed Bi-2212 wire during heat treatment. At present, TiO2 seems to be the most viable ceramic material for such a thin insulation because it is chemically compatible with Ag and Bi-2212 and its sintering temperature is lower than the maximum temperature used for the Bi-2212 heat treatment. However, recent tests of a large Bi-2212 coil insulated only with TiO2 showed severe electrical shorting between the wires after over pressure heat treatment (OPHT). The origin of the shorting was frequent silver protrusions into the porous TiO2 layer that electrically connected adjacent Bi-2212 wires. To understand the mechanism of this unexpected behaviour, we investigated the effect of sheath material and hydrostatic pressure on Ag protrusions. We found that Ag protrusions occur only when TiO2-insulated Ag-0.2%Mg sheathed wire (Ag(Mg) wire) undergoes OPHT at 50 bar. No Ag protrusions were observed when the TiO2-insulated Ag(Mg) wire was processed at 1 bar. The TiO2-insulated wires sheathed with pure Ag that underwent 50 bar OPHT were also free from Ag protrusions. A key finding is that the Ag protrusions from the Ag(Mg) sheath actually contain no MgO, suggesting that local depletion of MgO facilitates local, heterogeneous deformation of the sheath under hydrostatic overpressure. Our study also suggests that predensifying the Ag(Mg) wire before insulating it with TiO2 and doing the final OPHT can potentially limit Ag protrusions.

Sol-gel temperature dependent ductile-to-brittle transition of aluminosilicate fiber reinforced silica matrix composite

Abstract A thorough understanding in the micro mechanical properties of the fiber, the fiber/matrix and the matrix of the composite material, especially in response to different processing temperatures, is critical to explore the strengthening and toughening mechanisms of the novel oxide fiber reinforced oxide ceramic matrix composites. This work contributes this by studying the sol-gel temperature dependent micro mechanical properties of an aluminosilicate fiber reinforced silica matrix composite using novel nano-mechanical methods like nanoindentation and push-in techniques. In the sol-gel temperature range of 600–1200 °C, the aluminosilicate fiber was comparably stable in mechanical properties, though a microstructure transition from amorphous SiO2+ γ-Al2O3 to crystallized mullite+γ-Al2O3 was found at 1000 °C. The silica matrix was amorphous in microstructure, but were more crystallized as the sol-gel temperature increased, which subsequently led to an enhanced mechanical property at higher temperature. The interfacial shear strength was small in the temperature range of 600–1000 °C, and was increased slightly from ∼50 MPa at 600 °C to ∼84 MPa at 1000 °C. The interfacial shear strength at 1200 °C was high (∼256 MPa), due to the interfacial reaction occurring at this temperature. Correlating these micro mechanical properties to the macro fracture resistance that was quantified by the three-point bending test, an interface mediated toughening mechanism was finally concluded to explain the sol-gel dependent fracture resistance of the composite and the ductile-to-brittle transition observed in the temperature range.

KW-level low photodarkening Yb/Ce codoped aluminosilicate fiber fabricated by the chelate gas phase deposition technique

A Yb/Ce codoped aluminosilicate fiber was successfully fabricated by the chelate gas phase deposition technique. Using the homemade fiber as the amplifier stage in a master oscillator power amplifier configuration laser setup, a near single mode laser output (M2 = 1.55) with an output power of 1026 W and slope efficiency of 84.8% is obtained. In the 100 hour photodarkening experiment, the entire reduced power is less than 14 W, and the ratio, compared to the initial 1026 W output power, is less than 1.4%. The investigation of optical properties indicates that Yb/Ce codoped aluminosilicate fiber fabricated by the chelate gas phase deposition technique shows homogenous distribution, appropriate absorption coefficient, low background attenuation, high optical-to-optical efficiency and a rather low photodarkening loss, making it a promising candidate as an active fiber for a reliable and efficient fiber laser in high-power applications.

Interface controlled micro- and macro- mechanical properties of aluminosilicate fiber reinforced SiC matrix composites

Novel Nextel™ 440 aluminosilicate fiber reinforced SiC matrix composites, with/without chemical vapor deposited carbon interphase were fabricated by polymer derived ceramic process, and they were studied by a combination of micro- and macro- mechanical techniques such as nanoindentation, micropillar splitting, fiber push-in, digital image correction and high temperature three point bend tests. Specifically, micropillar splitting test was firstly employed to measure in-situ the localized fracture toughness. The results revealed that the carbon interphase can effectively hinder the interfacial reactions between Nextel™ 440 fiber and SiC matrix, thus remarkably weakening the composite interfacial shear strength from ∼293MPa to ∼42MPa, and enhance the composite fracture toughness from ∼1.8MPa√m to ∼6.3MPa√m, respectively. This is mainly a consequence of weak interface that triggers crack deflection at the fiber/interphase interface. Finally, this novel composite showed stable mechanical properties in vacuum at temperature range from 25°C to 1000°C.

Identification of Nanocrystalline Inclusions in Bismuth-Doped Silica Fibers and Preforms.

The nature of nanocrystalline inclusions and dopant distribution in bismuth-doped silicate fibers and preforms are studied by scanning and transmission electron microscopy, and energy and wavelength-dispersive X-ray microanalysis. The core compositions are Bi:SiO2, Bi:Al2O3-SiO2, Bi:GeO2-SiO2, Bi:Al2O3-GeO2-SiO2, and Bi:P2O5-Al2O3-GeO2-SiO2. Nanocrystals of metallic Bi, Bi2O3, SiO2, GeO2, and Bi4(GeO4)3 are observed in these glasses. These inclusions can be the reason for the background optical loss in bismuth-doped optical fibers. The bismuth concentration of 0.0048±0.0006 at% is directly measured in aluminosilicate optical fibers with effective laser generation (slope efficiency of 27% at room temperature).

Effects of fluorine on the properties of Yb/Ce co-doped aluminosilicate preforms prepared by MCVD with organic chelate precursor doping technique

Co-doped Yb/Ce aluminosilicate fiber preforms with less than 1Wt% fluorine were prepared by MCVD with organic chelate precursor doping technique at 1400°C. Fluorine content characterized by electron probe microanalysis decreased with increasing SiF4 flow and flow ratio of SiF4/SiCl4. Under maximum SiF4 flow the concentrations of Yb2O3 and CeO2 in the perform core were only as much as 17% and 25% under minimum SiF4 flow, respectively, but smaller refractive index change was only shown in fiber core. The reason was that the reaction of SiF4 with Al2O3,Yb2O3,CeO2 were intensified with increasing flow ratio of SiF4/SiCl4 and then resulted in producing more exhaust gas such as AlF3, YbF3 and CeF4. Raman spectra of core glasses with <0.5Wt% fluorine present different Raman shifts from F doped silica glass with 1–3.3Wt% fluorine: 945cm−1 of SiF stretching bond was not observed, and with growth of fluorine content antisymmetric stretching vibrations of Si-O-Si linkages split from an envelope of 1188cm−1 into two peaks or three peaks shifted higher frequency. At the same time, Boson peak near 125cm−1 shifted to lower frequency. They were attributed to some minor changes of glass's network structure due to introducing lower fluorine into core glasses. On base of bonding energy measured by X-ray photoelectric spectroscopy, the plane graph describing the complex bonding distribution with F in core was supplied to in order to illustrate network structure change.

Structure and properties of squeeze infiltrated zirconia grade-aluminosilicate short fiber reinforced aluminum composites

Squeeze infiltration process is successfully adopted to develop Al6061 metal matrix composite reinforced with zirconia grade aluminosilicate fiber using 15 and 20 vol% preforms. Composites microstructure depicts uniform distribution of fiber throughout the matrix with the elimination of preform breakage, porosities, and shrinkage. TEM observation shows the formation of Al2O3 at the interface, which controls the chemical interaction between the matrix and the fiber. Infiltrated composite shows enhanced wear resistance behavior compared to that of base alloy, and it improves with the increase in volume fraction of the reinforcement. However, sliding speed overcomes the volume fraction concept in improving the wear resistance of the composite by the quick formation of mechanically mixed layer (MML) at increased sliding speed. The tensile and impact strength of the base alloy is slightly higher than that of the composite due to its ductile nature. Incorporation of fiber in the matrix improves the CTE, hardness, compression and corrosion properties of the composite.

A comparative study of the performance of graded index perfluorinated plastic and alumino silicate optical fibers in internal optical interconnections

This paper theoretically investigates a comparative analysis of the performance of both graded index perfluorinated plastic optical fiber and alumino-silicate optical fiber in internal optical interconnections operation, where these materials have low dispersion at the operating wavelength 1.3μm. Temperature dependence of total dispersion coefficient is deeply investigated for these fibers. The temperature variations range from −50°C to 100°C. The obtained results show the dramatic effects of increasing ambient temperature variations on the signal quality degradation. The effects of increasing optical fiber length on optical interconnections performance efficiency and operation speed. A comparative study shows that, perfluorinated plastic optical fiber overcomes the alumino- silicate in operation performance efficiency and installation flexibility.

Steady photodarkening of thulium alumino-silicate fibers pumped at 1.07 μm: quantitative effect of lanthanum, cerium, and thulium.

By pumping thulium-doped silica-based fibers at 1.07 μm, rapid generation of absorbing centers leads to photoinduced attenuation (PIA). This detrimental effect prevents exploiting laser emissions in the visible and near infrared. We report on the characterization of the PIA versus the fiber core composition, particularly the concentration of thulium (Tm), lanthanum (La), and cerium (Ce) ions. We show that UV emission induced by Tm-Tm energy transfers is the source of photodarkening and that lanthanum and cerium are efficient hardeners against PIA.

Er3+-doped nano-engineered yttria stabilized zirconia–alumino silicate fiber for efficient CW and mode-locked laser operation

We report on the development of efficient continuous wave (CW) and mode-locked ring fiber lasers utilizing an $\text{Er}^{3+}$ - doped nanoengineered yttria-stabilized zirconia alumino (YSZA)-silicate fiber as the gain element. With the proper design of the material composition, the YSZA fiber host presents superior features to eliminate the $\text{Er}^{3+}$ cluster effects and enhance the radiative emission over commercial silica fibers, thus significantly increasing the fiber laser efficiencies. Through cavity analysis and optimization, we successfully demonstrate a 975-nm pumped single-mode $\text{Er}^{3+}$ - doped CW YSZA-silicate fiber laser with a slope efficiency of 43%, which is corresponding to the quantum efficiency of 69%. Because of the special dispersion property of the $\text{Er}^{3+}$ - doped YSZA-silicate fiber, we are able to build a stable soliton mode-locked 1565-nm fiber laser with 3.2-nJ pulse energy, 644-fs pulsewidth, and 4.96-kW peak power.

Yb-doped Pedestal Silica Fiber through Vapor Phase Doping for Pulsed Laser Applications

This letter describes successful fabrication and detail characterization of ytterbium (Yb)-doped pedestal aluminosilicate fibers through vapor phase doping technique using modified chemical vapor deposition system (MCVD). Fabricated preforms have uniform step-index profiles devoid of any profile ripples, central dip, and/or core-clad interface defects, which are very common to the preforms made by a solution doping method. Fibers with a pedestal design exhibit good optical properties, low photodarkening-induced losses, high SNR values, and higher efficiencies making them suitable for high-power pulsed laser applications as compared with normal Yb-doped fibers. One of the pedestal fibers has demonstrated the output energy of 186 $\mu \text{J}$ with the 1.86-W average power. The pulse has a width of 100 ns at a 10-kHz repetition rate, which provides a peak power of 1.86 kW.

Distribution of Bismuth and Bismuth-Related Centers in Core Area of Y-Al-SiO2:Bi Fibers

Analysis of the experimental data on microscopic, absorptive, fluorescent, and Raman-scattering properties of Bismuth (Bi)-doped yttria-alumino-silicate glass (Y-Al-SiO 2 :Bi)-based nanoengineered optical fibers, exhibiting broadband near-infrared fluorescence, is presented. Among the other well-established characteristics, inherent to Bi-doped silica fibers codoped with Aluminum (Al), a trend of spatial distributions of Bi atoms and Bi-related fluorescence-active centers is determined, being their concentrating in ring-like areas around the core's center, at approximately a half-distance to core/cladding interface. At the same time, the formation in this region of nanosized Bi clusters, supposedly weakly or nonfluorescing, is revealed for the fibers. These phenomena are argued to underlie worsening of the pump-to-signal overlap factor, which deteriorates efficiency of lasers and amplifiers based on such or similar Bi-doped alumino-silicate fibers.

1120 nm diode-pumped Bi-doped fiber amplifier.

Bismuth-doped aluminosilicate fiber has been fabricated by the MCVD-solution doping method and characterized for its unsaturable loss and gain. The amplifier performance has been compared for a novel pumping wavelength of 1120 nm with the conventional pumping wavelength region of 1047 nm. Unsaturable loss was 65% and 35% at 1047 and 1120 nm, pump wavelengths, respectively. A maximum gain of about 8 dB at 1180 nm for a fiber length of 100 m was observed with 1120 nm pumping. Gain enhancement of 70% was achieved with the 1120 nm pump as compared to the 1047 nm pump. A further 3.5 dB gain was obtained on simultaneous pumping at 1047 and 1120 nm.

Type I and II Bragg gratings made with infrared femtosecond radiation in high and low alumina content aluminosilicate optical fibers

Aluminosilicate fibers have very low Brillouin scattering gain coefficients, making them interesting fibers for nonlinear optical applications. We manufactured Bragg gratings in high (30 mol.%) and low (4 mol.%) alumina content optical fiber using 800 nm femtosecond pulse duration radiation and a phase mask. Grating spectral characteristics and thermal behavior are presented. Index modulations >10−3 were generated for fundamental pitched Bragg gratings, and >10−4 for higher-order gratings. Gratings were annealed at temperatures up to 900°C. Type II gratings written in fibers with lower alumina content showed better thermal stability than gratings written in fibers with higher alumina content. Bragg gratings in these fibers would be well suited as laser cavity mirrors in high-energy laser systems, as well as in telecommunication and sensor systems where Brillouin scattering restricts power scaling.

Numerical simulation and combination optimization of aluminum holding furnace linings based on simulated annealing

To reduce heat loss and save cost, a combination decision model of reverb aluminum holding furnace linings in aluminum casting industry was established based on economic thickness method, and was resolved using simulated annealing. Meanwhile, a three-dimensional mathematical model of aluminum holding furnace linings was developed and integrated with user-defined heat load distribution regime model. The optimal combination was as follows: side wall with 80mm alumino-silicate fiber felts, 232mm diatomite brick and 116mm chamotte brick; top wall with 50mm clay castables, 110mm alumino-silicate fiber felts and 200mm refractory concrete; and bottom wall with 232mm high-alumina brick, 60mm clay castables and 68mm diatomite brick. Lining temperature from high to low was successively bottom wall, side wall, and top wall. Lining temperature gradient in increasing order of magnitude was refractory layer and insulation layer. It was indicated that the results of combination optimization of aluminum holding furnace linings were valid and feasible, and its thermo-physical mechanism and cost characteristics were reasonably revealed.

Photodarkening and photobleaching impact on 1030 nm fiber laser emission

In this paper, photodarkening (PD) and photobleaching (PB) impact on 1030 nm ytterbium doped fiber laser emission are presented. In comparison with 1070 nm fiber laser built from the same kind of aluminosilicate fiber, the 1030 nm fiber laser shows less PD loss as the consequence of lower inversion and the possibility of almost complete efficiency recovery obtained by 633 nm PB. The results indicate the importance of inversion in PD process rather than photons interplay with the phenomenon as well as the occurrences of lower energy de-activation defects.

Absorption and luminescence characteristics of transitions of the holmium ion in -doped aluminosilicate preforms and fibres

We have obtained the spectral dependences of the absorption cross sections for the and transitions in -doped aluminosilicate fibres and the spectral dependence of the stimulated emission cross section for the laser transition in -doped aluminosilicate fibre preforms. The lifetime of the upper laser level in the preforms has been determined.

Charge-transfer state excitation as the main mechanism of the photodarkening process in ytterbium-doped aluminosilicate fibres

We have studied photodarkening in ytterbium-doped fibre preforms with an aluminosilicate glass core. Analysis of their absorption and luminescence spectra indicates the formation of stable ions in the glass network under IR laser pumping at a wavelength and under UV irradiation with an excimer laser . We have performed comparative studies of the luminescence spectra of the preforms and crystals under excitation at a wavelength of . The mechanism behind the formation of ions and aluminium – oxygen hole centres (Al-OHCs), common to ytterbium-doped YAG crystals and aluminosilicate glass, has been identified: photoinduced charge-transfer state excitation.

Thermal stability of mineral-wool heat-insulating materials

When mineral wool articles are heated, organic compounds are released into the gas phase due to the pyrolysis of the polymer binder beginning at 240°C. There are two temperature ranges of pyrolysis: mostly oxygen-free hydrocarbons are observed in the products below 400°C, and oxygen-containing hydrocarbons, above this temperature, in the case of an oxidizing atmosphere. Mineral wool articles contain more than 5 wt % polymer binder. Aluminosilicate fibers have amorphous structure and crystallize into the augite phase when heated to above 850°C.

Gamma-Ray Irradiation-Induced Optical Attenuation in Co/Fe Co-Doped Alumino-Silicate Optical Fiber for Dosimeter Application

Dose dependence of radiation-induced optical attenuation (RIA) at 1310 nm of the Co/Fe co-doped alumino-silicate optical fiber was investigated under gamma-ray irradiation at dose rates from 6.7 to 78.3 Gy/min. From the measured RIA, radiation dose sensitivity (ΔRIA/ΔDose) and rate of RIA change with irradiation time (ΔRIA/ΔTime) at the different dose rates were estimated. RIAs at various wavelengths (800 to 1600 nm) of the optical fiber were also measured and the RIA characteristics at 800 and 1310 nm under discrete gamma-ray irradiation were investigated. The measured RIA of the Co/Fe co-doped fiber showed very high dose sensitivity regardless of the dose rates and the ΔRIA/ΔTime was found to show linear response with respect to the dose rate. The significantly large RIA was attributed to Co, Fe, and Al-related defects in the fiber core which were formed by the irradiation, and it became larger at shorter wavelength. The high radiation dose sensitivity, linear response of the ΔRIA/ΔTime with respect to dose rate, and the high reproducibility of the dose dependence of RIA under the discrete irradiation clearly indicate that the Co/Fe co-doped fiber is able to provide highly accurate information of not only total accumulated dose but also dose rate of the radiation with irradiation time.