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A new approach to improving the interfacial compatibility of SiCf/Ti-6Al-4V composites by using fiber coating coupled with subsequent heat treatment was presented. The SiCf/Ti-6Al-4V composites with C-coated and C/Mo-coated fibers were prepared using the foil-fiber-foil method and subsequently heat treated in vacuum at 750 °C to obtain several kinds of the SiCf/Ti-6Al-4V composites with different interfacial characteristics. Interfacial microstructures of these composites were systematically characterized by means of scanning electron microscopy and X-ray energy dispersive spectroscopy to investigate the interfacial microstructure evolution and reaction dynamics. The effects of interfacial microstructures on interfacial mechanical properties were also investigated using thin-slice fiber push-out tests. The results show that the brittle interfacial reaction layer of TiC in the C-coated SiCf/Ti-6Al-4V composites was obviously thickened and some microvoids even formed near the matrix with increasing heat treatment durations, whereas the matrix adjacent to Mo coating in the C/Mo-coated SiCf/Ti-6Al-4V composites gradually transformed into a ductile β-Ti layer. Interfacial shear strengths of the C/Mo-coated composites were slightly increased with increasing the heat treatment time, while those of the C-coated composites were remarkably improved. Critical issues on modifying interfacial compatibility of the SiCf/Ti composites for further improving the mechanical behavior of the composites were discussed.

Fiber coatings for BN/SiC-and BN/Si3N4-bilayer systems were developed for the use in SiC/SiC composites. All coatings were produced with high process velocities of 500 m/h by a continuous roll-to-roll dip-coating process. The fiber surface was fully covered with a homogeneous coating and without fiber bridging. Tensile tests of fiber bundles were used to examine potential degradation of the fiber properties due to the application of the coatings. The coated fiber bundles showed a reduction of the maximum tensile load to 90.0 % for the BN/Si3N4 and to 86.7 % for the BN/SiC coating in comparison to the fiber bundle in the as-received state. A thermal treatment of the coated fiber bundles up to 1650 °C led to no reduction of their maximum tensile load. SiC/SiC composites were fabricated by polymer infiltration and pyrolysis. The flexural strength and strain of composites with BN/SiC fiber coating were improved to 467 MPa and 0.42 % in comparison to the composites without fiber coating. The composites with BN/SiC coating showed toughened fracture behavior with fiber pull-out effects.

Fiber coatings based on BN, BN/SiC and BN/Si3N4 were deposited on Hi Nicalon type S SiC fibers. The coating parameters were optimized using a design of experiments study. With optimized parameter sets, the coatings exhibited a high degree of coverage on the fibers and almost no fiber bridging could be observed. The coated fiber bundles are flexible and can be processed further by techniques such as filament winding. In comparison to a non-processed reference sample, the maximum tensile load of the fiber bundles with BN, BN/SiC and BN/Si3N4 coatings was reduced by only 5 %, 13 % and 10 %, respectively. The coated fiber bundles retained their tensile strength after thermal annealing up to 1650 °C in a nitrogen atmosphere for 0.5 h. SiCf/SiC samples with BN/SiC fiber coatings exhibited higher values of bending strength and strain-to-failure as a reference sample without fiber coating indicating the functionality of the fiber coatings.

Protective fiber coating decides the mechanical strength of an optical fiber as well as its resistance against the influence of environment, especially in some special areas like irradiation atmospheres. According to the experiment in this paper, it was found that the tensile force and peeling force of resistant radiation optical fiber was improved because of the special optical fiber coating.

In order to develop a practical process for the carbon coating on SiC fiber, high-speed and continuous pyrocarbon (PyC) coating process are under development by using a continuous CVD furnace with open-ends structure. The effects of process gas and winding speed have been investigated. It was revealed that the growth rate of PyC is in proportion to winding speed and the flow rate of process gas. PyC growth rate was reached up to 250 nm/min, which is several hundred higher than those of conventional CVI/CVD methods This results indicates that the mass production of PyC coated SiC fiber without unexpected residual deformation (torsion and curvature) is possible. And, the mass production and practical use of SiC/SiC using PyC coated SiC fiber will be largely promoted.

By adding sintering additives (CMS and nanoTiO2), Ni-MF/Al2O3 composites were prepared by pressureless sintering. In order to ameliorate the combination between mullite fiber and alumina matrix, mullite fiber surface was coated with Al2O3 coating. To improve the property of alumina ceramic composite, Ni particles were chosen as toughening phase. For the preparation of composite, the optimum process was 10% MF, 13% Ni, and sintering temperature in 1400°C. The material performance can be effectively improved.

Since the introduction of solid-phase microextraction (SPME) in the 1990s, different types of coating have shown their crucial role in extraction efficiency. In the past decade, unique properties of nanostructured materials (e.g., large surface area, and remarkable thermal, mechanical and chemical stability) led to their application as desirable coatings in SPME. The current review classifies nanomaterial–based SPME coatings as based on carbon, polymer, silica or metal nanoparticles. It also briefly discusses new developments and methods in preparing nanomaterial-based SPME coatings.

Continuous SiC fiber reinforced copper matrix (SiCf/Cu) composites were prepared by fiber coating method, and Ti6Al4V interlayer was introduced as an interfacial modification coating to improve the interfacial bonding strength. The interfacial reaction characteristics were investigated by transmission electron microscopy (TEM). The results show that nearly all the titanium atoms reacted with the carbon coating of SiC fibers to form two layers of TiC. Also, a thin copper layer that is sandwiched between these two layers was detected. No Ti-Cu interfacial reaction product was observed. The formation process of the interfacial reaction along with its mechanism was discussed.

A rhabdophane (LaPO4·nH2O) sol with fine spherical particles was used to coat Nextel™ 720 fiber tows continuously with monazite (LaPO4). The coatings are compared with those made previously from rod-shaped particles. The coated fibers were heat-treated at 1000°–1300°C for 1, 10, and 100 h. The effect of heat treatment temperature and time on coating microstructure was characterized by scanning electron microscopy and transmission electron microscopy, and the strengths of the coated fibers were measured after coating and heat treatment. Grain shapes and grain growth rates were measured. Coating thickness uniformity was quantified by a fit to a truncated extreme-value distribution. Coating hermeticity was evaluated by analysis of grain growth rates. The spherical particles promote more rapid coating densification and local hermeticity, but introduce problems with sintering shrinkage cracking that are not present in coatings derived from rod-shaped particles.

Alumina fibers as a form of fabric cloth are slurry coated by a vacuum enhanced dipcoating (VEDC) method for the reinforcement of an alumina matrix. Three kinds of precursors including YPO4, CePO4 and LaPO4 are prepared and applied to the coating of alumina cloth. SEM observation shows that the fibers in the bundle are uniformly coated by this method. The coated fibers are debonded from the matrix during fracture of the composites. Mechanical properties of these composites using the vacuum enhanced dip-coated fibers are affected by the properties of coating slurry, including concentration and pH value. The three kinds of coating have shown no significant difference when they are coated under the same conditions. Increase of the concentration of the coating slurry causes increase of the bulk density of the composites, while the optimum coating thickness corresponding to the highest maximum fracture strength is obtained by the medium slurry concentration. When pH of the coating slurry is nearly neutral, the...

Several approaches for fiber-optic evanescent-wave detection of small amounts of liquid hydrocarbons are investigated in the paper. These approaches use polydimethylsiloxane-coated silica (PCS) fibres and detect changes of the fiber attenuation induced by the penetration of hydrocarbons into the fiber coating. The detection ability of bent PCS fibres both in the spectral region from 400 to 600 nm and near-infrared region from 900 to 1700 nm is studied by using available commercial or laboratory spectroscopic techniques. Straight sensing fibres coated with a thin high-refractive index layer and selective excitation of the fibres at 670 nm are investigated as well. A novel approach employing straight fibres coated with a thin siloxane coating and an output mode filter is described as a promising technique for increasing the detection sensitivity of fiber-optic evanescent-wave sensors to petrol fuels.

Polypropylene/wood fiber composites were prepared at three different temperatures: 170°C, 180°C, and 190°C. The surface of wood fibers was modified through the use of silane coupling agents and/or coating with polypropylene or maleated polypropylene. The fiber coating was performed by propylene polymerization in the presence of wood fibers or by immersion in an o-dichlorobenzene polypropylene (or maleated polypropylene) solution. Tensile and three-point bending tests were performed in order to evaluate the adhesion between matrix and wood fibers. Evidence shows that 180°C is the best mixing temperature, while the use of vinyl-tris (2-methoxy ethoxy) silane with or without maleated polypropylene coating is the best surface treatment. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1227–1235, 1997

Trace analysis of fatty acids in water and/or air was enhanced by coupling solid-phase microextraction (SPME) with derivatization of the target analytes to less polar and more volatile species prior to GC analysis. Derivatization was performed in three ways: in the sample matrix, in the SPME fiber coating, and in the GC injector port. Derivatization converts polar analytes into less polar analogues, therefore increasing their coating/water or coating/gas partition coefficients and improving SPME efficiency and method sensitivity. Derivatization changes analytes with low volatilities into more volatile derivatives, thus improving their GC separations, detection, and quantitation. Pentafluorobenzyl bromide and (pentafluorophenyl)diazoethane (PFPDE) were used to derivatize short-chain fatty acids directly in sample matrices for selective and sensitive ECD detection. Diazomethane and pyrenyldiazomethane (PDAM) were used for effective in-fiber derivatization of long-chain and short-chain fatty acids, respecti...

Critical issues of interface modifications in ceramicmatrix composites have been investigated. Minimal interaction between the fiber and the matrix is essential to achieving good toughness in ceramic-fiber-reinforced SiCO composites. Introduction of a thin barrier coating on the fiber surface has been utilized to minimize such interaction. The flexural strength of a SiCO composite containing CVD carbon-coated Nicalon fibers was found to be five times higher than that of the composite containing uncoated Nicalon fibers. Chemical reactions between the barrier coating and the matrix and those between the coating and the fiber must be avoided in such a three-phase material. A methodology for selecting candidate fiber coating materials by the use of chemical compatibility calculations is presented.

Powder impregnation techniques have been developed to increase design and manufacturing flexibility with thermoplastic composites. This paper presents an experimentally based analytical investigation of the coating and consolidation processes of powder impregnated tows. Polymer flow during towpreg manufacture was studied and the various stages of fiber coating were identified. A coalescence model was developed to predict the degree of coalescence of the powder as a function of the processing parameters. The stiffness of the final towpreg was found to be related to the extent of coating of the fibers with the powder. A consolidation apparatus was fabricated to determine the effect of key processing variables upon the degree of consolidation of the towpreg. The plaques produced from the consolidation experiments were evaluated using 3-point flexure tests and image analysis. The influence of each parameter and parameter interaction was determined.

Measurement of the coating geometry of optical fibers is important in maintaining the optical and mechanical integrity of fibers and in the control of splice loss in multiple-fiber ribbons. A method of measuring coating geometry using a side-view system with a novel dark-field illumination technique is presented. A high contrast image is produced with this system from which the coating diameter noncircularity and concentricity error of a fiber can be determined. The measurement repeatabilities of coating diameter and concentricity error are typically 0.20 /spl mu/m and 0.25 /spl mu/m respectively. A means of calibrating the side-view system using a glass rod has been developed and comparison with an interferometric method has shown that a total uncertainty on outer coating diameter of 0.5 /spl mu/m has been achieved. >

Publisher Summary This chapter focuses on the types and properties of the various commercially available solid-phase microextraction (SPME) coatings and devices. It provides a guide on how to select the appropriate fiber for application needs. There are several important criteria that are fundamental for the acceptance of SPME as an extraction technique. These criteria include ease of use and solvent-free extraction capability. The performance of SPME is critically dependent on the availability and selection of appropriate coating. The SPME fiber coating is primarily responsible for the extraction of analytes. Because SPME is capable of extracting a wide range of analytes from volatile to non-volatile and from polar to non-polar, it is important to have fiber coatings that can extract this range of analytes. To accomplish this, different coating types have been developed which enable extraction of a variety of analytes with enhanced selectivity. The reproducibility between fibers and the durability of the coatings are very important for SPME to be widely accepted as a qualitative and quantitative extraction technique. These two criteria allow the analyst to use one fiber for multiple extractions and to obtain similar results when multiple fibers are used. If the coating maintains its integrity, the repeated extractions of some samples should yield reproducible results. If the preparation of the fibers is reproducible, the new fiber should produce similar results compared to the replaced fiber.

Continuous fiber, high-performance composites have found increased use in the design of a large number of civilian and military aircraft. However, the brittle nature of the carbon fiber and the resins used as matrices have restricted the full utilization of these materials in aerospace application. Hence, the development of toughened composites has a great potential for expanding the use of current materials, and a major effort is being undertaken in order to develop toughened composites. Due to several advantages of introducing a ductile or flexible material between the fiber and matrix, coating the fiber with polymers has recently received considerable interest and much effort has been done to understand the effect of the interlayer on composite properties. This paper reviews the technology of toughening composites by fiber coating, showing the composite systems, coating materials, fiber coating methods and toughness mechanisms which have been studied. Finally, a separate section is dedicated to reviewi...

The fiber-matrix interaction in mullite fiber-mullite matrix composites was investigated with the composites fabricated using a commercial mullite powder and a mullite powder synthesized in our laboratory (via a diphasic gel route) as the matrix with uncoated and BN-coated fibers. Two different BN-coating thicknesses, 0.3 μm and 1 μm, were used. The composites made from the mullite powder synthesized in our laboratory showed less interaction between the fiber and matrix as well as no fiber deformation owing to a lower processing temperature, compared with the composite made from the commercial mullite powder. However, the fiber-matrix bonding in both the uncoated and even 0.3 μm BN-coated cases was still strong so that no fiber pullout was observed on the fracture surfaces. In the case of the 0.3 μm BN-coated fiber, the strong interfacial bonding resulted because the coating thickness was too thin to survive during processing. With 1 μm BN-coated fiber, however, extensive pullout could be obtained because the coating survived and prevented bonding between the fiber and matrix.

The effect of fiber-coating thickness on retained in-situ fiber strength and the resulting mechanical properties of composites was investigated. Flexure tests in a four-point-bend mode were used to evaluate ultimate strength and work-of-fracture of the composites with various fiber-coating thicknesses. Retained in-situ fiber strength in the fractured composites was evaluated by fractographic techniques. Retained in-situ fiber strength, ultimate strength, and work-of-fracture of the composites increased with increasing fiber-coating thickness, reaching a peak value at a coating thickness of {approximately}0.3{mu}m. Further increases in coating thickness did not improve the mechanical properties of either the fibers or the composites. A direct correlation between retained in-situ fiber strength and mechanical properties of the composites suggests that retained in-situ fiber strength has a significant influence on the mechanical properties of composites.

International audience; Optical fibers are key components in telecommunication technologies. Apart from optical specifications, optical fibers are expected to keep most of their physical properties for 10-20 years in current operating conditions. The reliability and the expected lifetime of optical links are closely related to action of the chemical environment on the silica network. However, the coating also contributes largely to the mechanical properties of the fibers. The aim of this work was to study the strength and the mechanical behavior of the silica optical fibers in an acid environment and with a permanent deformation. A container with ammonium bifluoride acid salt was plunged into hot water at different temperatures (55 and 75 °C). This emitted acid vapors which attacked the optical fibers for a period of 1-18 days. An aging study was performed on silica optical fibers with standard polyacrylate coating and with hermetic carbon coating. A dynamic two-point bending bench at different faceplate velocities (100, 200, 400 and 800 μm/s) was used. For comparison, the same dynamic measurements were also carried out on non-aged fibers. After acid vapor condensation, salt crystal deposits on the fibers were displayed using an electron scanning microscope. These crystals became visible to the naked eye from the seventh day.

The key technological challenge to the use of ceramic composites in high temperature structural applications is oxidation resistant control of fiber/matrix interface properties. A number of approaches based on oxide coatings are being investigated (for a brief review and current references, see Refs. 1 and 2, respectively) and, while the principle role of these coatings is to promote debonding, the actual material and geometric requirements they must satisfy have been poorly understood. As the level of understanding of composite behavior has been increasing, so has appreciation for the potential complexities of fiber coating design. This has led to recognition of several potential design parameters; characteristics that must be controlled in the design of the coating or accommodated in the design of the overall composite. A good deal of our awareness of these coating design parameters stems from the study of the role and importance of surface topography.

The interfacial chemical behavior of two candidate coating systems for use on fine diameter (∼10 μm) Al2O3 in TiAl is presented. The performance of the Nb/Y2O3 system appears to be related to the transport rate of Ti through the Y2O3 layer. Interfacial reaction is then observed at points where the Y2O3 thickness is less than about 1 μm. The main reaction product formed appears to be an oxygen saturated TiAl phase. An alternative system, C/TiN/Y2O3 is then presented as a solution to the Ti transport problem and may offer more desirable interfacial mechanical properties.

Adhesiveless mechanical fiber optic splices may provide pullout resistance by gripping onto the bare fiber or by gripping onto the fiber coating. The possibility of creep and thermal expansion mismatch in the plastic coating makes gripping onto the stripped fiber attractive. We have determined that damage to the fiber by a gripping mechanism is measurable but not severe, particularly by comparison to mechanical stripping damage and handling damage. We have also observed fiber failures within such splices when using 900 micron diameter, tight buffered fiber. Torque, generated when the fiber is arranged into loops in an organizer tray, propagates into the bare fiber inside the splice. This torque can cause a fiber to break in torsion after a period of time.

Significant degradation of the fiber coatings occurred in an optical fiber cable that was aged for five days at 85°C. Incompatibility between the coating and the surrounding buffer tube gel was the suspected cause. To investigate this problem, fiber samples were aged in several gels, the compositions of which were determined using a variety of analytical techniques. Coating degradation occurred as cracking or discoloration in all but one of the gels. These degradations were found to have a strong temperature dependence and to be closely related to the molecular weight distributions of the gel components. Compatibility screening was identified as a necessary procedure to avoid future recurrences of this problem

A technique has been implemented to measure and control the eccentricity of lightguide fiber in transparent polymer coating materials. It is based upon a model which describes the characteristics of a forward-scattered light pattern generated by transversely illuminating coated fiber with a laser beam. The model predicts the behavior of the principal characteristics of the pattern as a function of fiber eccentricity within the coating. The implementation automatically detects and controls the position of the dominant pattern feature to maintain an average fiber-coating concentricity within 2 μn over multikilometer lengths of fiber.