Development of low-loss lead-germanate glass for mid-infrared fiber optics: I. glass preparation optimization

Reducing the mid-infrared attenuation loss due to absorption of hydroxyl (OH) groups and scattering of metallic Pb species for lead-germanate glass is essential to pave the way for their applications as low-loss mid-infrared fiber optics. In the first part of this study, we report the understanding of the factors that determine dehydration efficiency and metallic Pb formation during the lead-germanate glassmelting process. Combining a dry O₂-rich atmosphere containing ultra-dry N₂ together with the use of chloride dehydration agent and nitrate oxidation agent compound was found to enable efficient dehydration effect and absence of metallic Pb scattering sources in the dehydrated glasses. This glassmelting procedure overcomes previous limitations on the preparation of similar kinds of heavy-metal oxide glasses, where only pure O₂ atmosphere was used and/or use of fluoride dehydration agent deteriorated the glass thermal stability. This work provides guidance for developing other low-loss mid-infrared glasses/fibers containing multivalent heavy-metal ions such as Pb, Bi, Te, Sb, etc     

Review of tellurite glasses purification issues for mid-IR optical fiber applications

We reviewed the tellurite glass purification studies performed over the last 20 years, in particular dealing with the mid-infrared (mid-IR) transmission performances. Best results are obtained under rich O₂ atmosphere with platinum crucibles although Gibbs energy calculations show that other crucibles material are possible such as gold or alumina. From the point of view of the thermodynamics of involved oxidation reactions only, we identified the suitable conditions based on Gibbs energy calculations to be a synthesis temperature set above 900 K and a O₂ pressure around 10⁵ Pa. The performances of the different purification techniques were also compared. Finally, we analyzed the tellurite fibers recently optimized for mid-IR which present low attenuation up to 4 µm allowing supercontinuum generation up to 5 µm.     

Fabrication of glass ceramic sealants with ceramic fiber filler for solid oxide fuel cells

In this study, ceramic fibers are used as a filler material for glass ceramic sealant in solid oxide fuel cells to improve the thermal cycle behavior. Beside the bare glass ceramic sealant for comparison, multilayered sealants with different ceramic fiber contents are fabricated to investigate the effect of ceramic fiber quantity also. The mechanical performances of the samples are measured via tensile tests by placing them between two metallic interconnector plates after the glass formation process as well as after 1, 5 and 10 thermal cycles. The results show that the mechanical strength in general tends to decrease with increasing the ceramic filler content, which can be attributed to poor adhesion due to reduced glass ceramic composition. On the other hand, thermal cycle behavior of the samples with ceramic fibers is found to be improved at some extend. This may be due to the behavior of ceramic filler network and relatively slow crystallization with increasing the amount of the filler as proven by microstructural observations. Especially for the sample including 4 ceramic fiber interlayers each having 0.030 g ceramic fibers, the mechanical strength shows an increasing trend with the number of thermal cycles.     

Potential for the formation of respirable fibers in carbon fiber reinforced plastic materials after combustion

Fundamental aspects for the thermal decomposition and formation of respirable fragments of carbon fibers are investigated to assess the health hazard of carbon fiber reinforced plastic material after a fire. The influence of temperature (600°C‐900°C)/heat flux (30‐80 kW/m²), time of thermal load (up to 20 minutes), and oxygen exposure is analyzed by means of mass loss and fiber diameter of intermediate modulus and high tenacity fibers with initial diameters of 5 to 7 μm. Various types and concentrations of flame retardants were tested with respect to fiber protection. Epoxy‐based composite specimens (RTM6/G0939) additionally containing aluminum or magnesium hydroxide and/or zinc borate (1‐25 wt% per resin) were analyzed by cone calorimetry. Carbon fiber decomposition increases with combustion/irradiation time and temperature/heat flux, after a threshold temperature (ca 600°C) is exceeded. Critical fiber diameters below 3 μm are reached within minutes and are predominantly observed close to the panel surface in contact with air. Effective fiber protection is achieved by flame retardants acting beyond 600°C, forming thermally resistant layers such as zinc borate. A new field of research is opened identifying flame retardants, which protect carbon fibers in carbon fiber reinforced plastic.     

A novel chalcohalide fiber with high nonlinearity and low material zero-dispersion via extrusion

High nonlinear fibers with low zero-dispersion wavelength (ZDW), high laser power tolerance and large band-gap are urgent for all-optical-band supercontinuum (SC) generations. Widely used chalcogenide fibers usually have a large ZDW and low laser power tolerance, and thus are not ideal for such purpose. Here, an ultra-low material ZDW chalcohalide (ChH) glass fiber with high nonlinearity as well as high laser power tolerance has been fabricated successfully via a novel peeling-off-extrusion method. The step-index fiber has double-cladding structure, the inner cladding is GeGaSe-CsI glass and the outer one is GeSbS jacket. The core glass has an ultra-low material ZDW of 3.5 μm and large absorption edge of 2.0 eV. The nonlinear refractive index is 6.67 × 10⁻¹⁸ m²/W @1.55 μm. Broadband SC generation covering 1.05-13.0 μm is demonstrated in this novel ChH fiber. Such glass fiber with high nonlinearity, wide transparent range, low ZDW and high laser damage threshold is promising for the applications in the mid-infrared.     

In vitro cytotoxicity of Manville Code 100 glass fibers: Effect of fiber length on human alveolar macrophages

Background  

Synthetic vitreous fibers (SVFs) are inorganic noncrystalline materials widely used in residential and industrial settings for insulation, filtration, and reinforcement purposes. SVFs conventionally include three major categories: fibrous glass, rock/slag/stone (mineral) wool, and ceramic fibers. Previous in vitro studies from our laboratory demonstrated length-dependent cytotoxic effects of glass fibers on rat alveolar macrophages which were possibly associated with incomplete phagocytosis of fibers ≥ 17 μm in length. The purpose of this study was to examine the influence of fiber length on primary human alveolar macrophages, which are larger in diameter than rat macrophages, using length-classified Manville Code 100 glass fibers (8, 10, 16, and 20 μm). It was hypothesized that complete engulfment of fibers by human alveolar macrophages could decrease fiber cytotoxicity; i.e. shorter fibers that can be completely engulfed might not be as cytotoxic as longer fibers. Human alveolar macrophages, obtained by segmental bronchoalveolar lavage of healthy, non-smoking volunteers, were treated with three different concentrations (determined by fiber number) of the sized fibers in vitro. Cytotoxicity was assessed by monitoring cytosolic lactate dehydrogenase release and loss of function as indicated by a decrease in zymosan-stimulated chemiluminescence.     

1.8–13 μm supercontinuum generation by pumping at normal dispersion regime of As–Se–Te glass fiber

Mid-infrared (MIR) band supercontinuum (SC) light source has highly important application prospects in aerospace, biomedicine, MIR sensing, and pollutant monitoring. As–Se–Te glass has high nonlinear refractive index, wide MIR transmission range and weak crystallization ability. As₄₀Se₄₀Te₂₀ glass fiber is suitable for producing wide MIR–SC spectrum. In this study, purified As₄₀Se₄₀Te₂₀ glass was prepared and unclad and step-index fibers were drawn. An unclad As₄₀Se₄₀Te₂₀ glass fiber with minimum loss of 1.7 dB/m at 8.8 μm was obtained. By pumping the unclad fiber in the normal dispersion region at 5 μm, we recorded the broadest SC generation spectrum, which covered 1.8–13 μm with a 30 dB spectral flatness, from a fiber with 15 cm length. Besides, As₄₀Se₄₀Te₂₀/As₄₀Se₄₂Te₁₈ step-index fiber with minimum loss of 5.6 dB/m at 5 μm was drawn from isolation extruded preform. The step-index fiber was pumped in the normal dispersion region at 5 μm, and the SC spectrum, covering 2.1–11.2 μm with a 40 dB spectral flatness, was recorded from a fiber with 15 cm length. The SC spectrum, which was achieved by pumping the As₄₀Se₄₀Te₂₀ fiber, covered almost all the transparent range of material.     

Amorphous self-glazed,chopped basalt fiber reinforced,geopolymer-based composites

Geopolymer composites reinforced with refractory, chopped basalt fibers, and low melting glass were fabricated and heat treated at higher temperatures. K₂O·Al₂O₃·4SiO₂·11H₂O was the stoichiometric composition of the potassium-based geopolymer which was produced from water glass (fumed silica, deionized water, potassium hydroxide), and metakaolin. Addition of low melting glass (T_m ~815°C) increased the flexure strength of the composites to ~5 MPa after heat treatment above 1000°C to 1200°C. A Weibull statistical analysis was performed exhibiting how the amorphous self-healing and self-glazing effect of the glass frit significantly improved the flexure strength of the geopolymer and ceramic composites after exposure for 1 hour to high temperatures. At 950-1000°C, the K-based geopolymer converted to primarily a crystalline leucite ceramic, but the basalt fiber remained intact, and the melted glass frit flowed out of the surface cracks and sealed them. 1150℃ was determined to be the optimum heat treatment temperature, as at ≤1200°C, the basalt fibers melt and the strength of the reinforcement in the composites is significantly reduced. The amorphous self-healing and amorphous self-glazing effects of the glass frit significantly improved the room temperature flexure strength of the heat-treated geopolymer and ceramic composites.     

Resolved-detrimental surface crystallization in yttrium lanthanum gallate glasses for optical fiber applications

Gallium-rich heavy metal oxide glasses have become highly attractive optical materials since they exhibit a wide transparency window spanning from the ultraviolet ∼270 nm up to the mid-infrared (IR) region ∼6 μm making them promising for a future integration in optical fiber devices. Nonetheless, in most composition, surface crystallization is a key limiting factor for optical fiber drawing using the classical preform-to-fiber method. Herein, taking advantage of structural information from vibrational spectroscopies (Raman/IR) and ⁷¹Ga Solid-State Nuclear Magnetic Resonance, we describe the key role of lanthanum and yttrium rare—earth elements on the glass structure and their impact on the capability to draw those new glass compositions into optical fibers. This approach emphasizes that yttrium ions as compared with lanthanum ones favor the glass disorder, increasing significantly the fraction of GaO₅ units with respect to GaO₄. That, combined with thermal analysis and examination of the crystallization behaviors, highlights that Y₂O₃ prevents the glass devitrification during the glass shaping. The smaller yttrium radius is believed to be the key physical parameter preventing the precipitation of the Ba_yGa_5-yGe_y+1La_3-yO₁₄ (y = 0, 1, 2, 3) langasite-type crystal phase. This study remains particularly relevant and opens up the way for the development of highly robust power scaled fiber devices operating from the visible up to the challenging mid-IR domain.     

Cage-like structured flexible hybrid fiber/SiO2 aerogel composite for noise reduction

The fiber/aerogel material prepared by the traditional method of sol-gel has a serious powder shedding phenomenon, and has serious environmental pollution and health hazards. In this study, an environmentally friendly porous sound absorption material with a cage-like structure, which used flexible ultrafine glass/quartz hybrid fibers (HFs) as the carrier and SiO₂ aerogel as the pore filler, was produced using the wet manufacturing process. The addition of aerogel enhanced the internal reflection of sound waves, reduced the propagation speed, increased the acoustic energy loss and improved the sound absorption coefficient (SAC). The noise reduction coefficient (NRC) reaches 0.49 in the range of 250–6300 Hz. The obtained composite presented a low density (73.5 mg/cm³) and heat resistance up to 500 °C.     

Study of SiC fiber axial compressive behavior using tensile recoil measurement

SiC fibers have been widely investigated as reinforcements for advanced ceramic matrix composites owing to their excellent high-temperature properties. However, the axial compressive strength of SiC fibers has not been thoroughly studied. In this study, the compressive behavior of two SiC fiber types containing different compositions and thermal degradation were characterized by tensile recoil measurements. Results illustrated that the SiC fiber compressive strength was 30%–50% of its tensile strength, after heat treatment at 1200℃–1800℃ for 0.5 h in argon. The fiber compressive failure mechanism was studied, and a “shear-bending-cleavage” model was proposed for the recoil compression fracture of pristine SiC fibers. The average compressive and tensile strengths of the pristine SiC-II fiber were 1.37 and 3.08 GPa, respectively. After treatment at 1800℃ for 0.5 h in argon, the SiC-II fiber compressive strength decreased to 0.42 GPa, whereas the tensile strength reduced to 1.47 GPa. The mechanical properties of the fibers degraded after high-temperature treatment. This could be attributed to SiC grain coarsening and SiC_xO_y phase decomposition.     

Nd3+-doped glass-ceramic fiber fabricated by drawing precursor ceramic and successive heat treatment

Optical fibers have been formed by replacing precursor glass core with precursor ceramic core, in which drawing process, the precursor ceramic melted to fill the space of the core region while the clad glass was softened. Nd³⁺ doped LaNbO₄ nanocrystals were precipitated in the core after heat treatment. X-ray diffraction, Raman spectra, high-resolution transmission electron microscopy, electron paramagnetic resonance, optical microscope, and photoluminescence were used to characterize the obtained fiber. No crystallization, cracking, bubble, or undissolved substance is observed in the core region of precursor fiber. Nd³⁺ doped LaNbO₄ nanocrystals are precipitated in the core region after thermal treatment. Under the pumping source of 808 nm, three emission bands located at ～887 nm, ～1064 nm, and ～1337 nm are observed, which makes this GC fiber a promising material for the NIR fiber amplifier.     

Scheelite coatings on SiC fiber: Effect of coating temperature and atmosphere

Scheelite coating was deposited on SiC fiber tows from various liquid-phase precursors followed by heat treatments between 900 °C and 1100 °C in different atmospheres. The tensile strength was fully retained for the coated fibers treated at 900 °C in vacuum. Subsequent heat treatment at 1100 °C in Ar had little effect on the fiber strength, which is explained by the excepted good thermal stability between the scheelite coating and SiC fiber. However, larger strength degradation and poor spool ability of coated fibers prepared in Ar/air were found. Assisted oxidation of SiC fiber by calcium salts is suggested to be responsible for the much larger strength degradation of fibers prepared in Ar/air.     

Observation and practical implications of nano-scale phase separation in aluminosilicate glass optical fibers

This communication provides direct experimental evidence of nano-scale phase separation in as-fabricated high-alumina content (>25 mole percent) optical fibers, experimentally corroborating recent molecular dynamic simulations. In addition, previously incorrect assumptions of glass homogeneity in low-loss binary aluminosilicate optical fibers are corrected and practical implications for such intrinsically low nonlinearity glass optical fiber amplifiers and lasers are discussed.     

Zero stress aging in notched multi-component glass fibers

Degradation of glass under zero applied load in the presence of humidity at ambient temperature is of great interest to the container and fiber glass industries. The phenomenon is well documented for fused silica used in optical fibers, but has not been studied in detail for multi-component glasses. In this work notches of varying length (500-1500 nm) were placed with a focused ion beam into two types of multi-component glass fibers, E-glass (48 μm diameter) and soda-lime-silicate (35 μm diameter). Notched specimens were exposed to dry and humid conditions for up to 32 days. Transmission electron microscopy revealed the presence of extensive reaction products within the root of the notch, even after only 1 day of aging in the nominally dry environment for the soda-lime-silicate glass. Surprisingly, the extensive reactions have no measurable effect on the fiber strength. The uniaxial tensile strength of the notched glass fibers, measured with the fracture surface mirror radius method, does not follow a classic fracture mechanics prediction, implying that the notches are not classic Griffith flaws. Fracture mechanics is applied to show that sharpness at the notch base may be important, especially when subcritical crack growth is present during the strength measurement.     

The dual effect of zirconia fiber on the insulation and mechanical performance of the fumed silica-based thermal insulation material

Inorganic fibers and opacifiers are indispensable for improving the strength and high temperature insulation performance of the fumed silica-based thermal insulation material. However, zirconia fiber enhances the strength of the fumed silica-based thermal insulation material and reduces the radiative heat transfer to replace the opacifier. The sample of fumed SiO₂/Al₂O₃ doped with 7% zirconia fiber (FZ7) has a lower density of 0.70 g/cm³ and a high porosity of 75.0%. In addition, the thermal conductivity of FZ7 at 800 °C is 0.077 W/(m·K), which is lower than the sample of fumed SiO₂/Al₂O₃ doped with 7% glass fiber (FG7) and 0.089 W/(m·K) at 800 °C. The effective extinction coefficient of the thermal insulation material containing zirconia fiber is larger than that of the glass fiber by Fourier transform infrared spectroscopy analysis and calculation, indicating that the zirconia fiber has a distinct absorption and scattering effect on infrared radiation to reduce the radiative heat transfer. Therefore, zirconia fiber enhances the strength and decreases the high temperature thermal conductivity of the composites with the dual effect on the insulation and mechanical performance of the fumed silica-based thermal insulation material.     

Mechanical and microwave absorbing properties of Tyranno® ZMI fiber annealed at elevated temperatures

The tensile strength and microwave absorbing properties of the amorphous silicon carbide fiber (Tyranno-ZMI) annealed at different temperatures were studied. The tensile strength of the as-received ZMI fiber tows was 1.1 GPa; and the average real and imaginary parts of permittivities of the as-received ZMI/resin samples were 11.3 and 10.5 respectively. The major dielectric loss mechanism of the fibers was conduction loss, which was due to high electrical conductivity of the enriched carbon in ZMI fibers. The 2.0 mm thick ZMI/resin composites could absorb 80% microwave energy in X band, indicating good microwave absorbing property. After heat treatment, fibers degraded gradually and permittivities increased, which were mainly attributed to the decomposition of amorphous SiC_xO_y and the growth of the SiC nanocrystals and free carbon nanodomains.     

Short fiber reinforced thermoplastic polyurethane elastomer composites

Mechanical properties of thermoplastic polyurethane elastomer (TPE) reinforced with short fibers were studied. Two types of fibers were used as the discontinuous phase: an aromatic polyamide (Twaron, diameter: 12 μm) and carbon fiber (FCI 140/90-R33—diameter: 8–10 μm). Because of processing limitations, the maximum length of both fibers, after incorporation in the composites, was reduced to 3 mm. The TPE (continuous phase) was a polyol-polyester type [Elastollan—glass transition of short fiber segments: −42°C (1)]. Both types of composites had fiber concentration of 10, 20, and 30 phr. Component interaction is discussed, as well as the application of a third power polynomial to establish a relationship between the amount of fiber added and stress at break data. Stress-strength, tear resistance, shore A and B hardness, abrasion resistance, and compression set tests were performed. Composites reinforced with aromatic polyamides showed higher values in most of the tests, except in the abrasion resistance test, in which a smaller material loss was observed.     

Surface Analysis and Treatment of Extruded Fluoride Phosphate Glass Preforms for Optical Fiber Fabrication

Fabrication of fluoride phosphate glass optical fibers using the extrusion method for preform fabrication has been studied using the commercial Schott N‐FK51A glass. The extrusion step was found to create a surface layer of differing composition from the bulk glass material, leading to defects drawn down onto the optical fiber surface during fiber fabrication, resulting in high loss and fragile fibers. Similar phenomena have also been observed in other fluoride‐based glasses. Removal of this surface layer from preforms prior to fiber drawing was shown to improve optical fiber loss from >5 dB/m to 0.5–1.0 dB/m. The removal of this surface layer is therefore necessary to produce low‐loss fluoride phosphate optical fibers.     

Study on effects of short glass fiber reinforcement on the mechanical and thermal properties of PC/ABS composites

This article mainly investigated the length distributions of the alkali‐free short glass fibers in specimens and their effect on the mechanical and thermal properties of the composites. The results show that the initial length, addition level and feed way of the fibers have obvious effects on the length distributions of fibers in specimens, and thereby the mechanical and thermal properties of the composites. The main‐direction feed way has an intense shear action on the fibers in specimens. With the increase of the fiber content, the reinforcing effect of fibers on the tensile strength, flexural strength and flexural modulus of the composites is increased, while the impact strength is decreased first and then tends to be stable, and the strength factor (F) of the tensile strength to weld line is significantly reduced. The longer the fiber lengths in specimens are, the more obvious the reinforcing and toughening effects are. To some extent, with the increase of the fiber content, the storage modulus (E′) and loss modulus (E′′) of the specimens are increased, but the loss factor (Tan δ) is reduced. The effect of the fiber initial lengths on the heat‐degradation of composites is smaller than that of the fiber content. Meanwhile, adding fibers can improve the thermal stability of the composites, and this law is also confirmed by the heat deflection temperature (HDT) test. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40697.