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SiC fiber-reinforced matrix composites (SiC f /SiC) have limited applications because of the irradiation-induced shrinkage of SiC fibers; the fiber shrinkage mechanism is still not fully understood. In this study, we tried to clarify the effect of annealing temperature on the proportion of fiber shrinkage and swelling. SiC f /SiC was irradiated at 30 °C to 100 dpa, and the deterioration of mechanical properties was evaluated after irradiation. The compressive displacement of > 60% of the fibers before failure increased to more than 1.5 times that of the as-received specimen. Significant swelling was observed, indicating that the proportion of swelling was higher than that of shrinkage after irradiation. This can be attributed to the amorphization of SiC, and its amorphization threshold dose increased with decreasing grain boundary volume fraction. The findings of this study provide insights into the mechanism of irradiation-induced fiber amorphization and can be useful in developing improved SiC f /SiC. • Amorphization was observed in room-temperature-irradiated SiC fibers. • Different amorphization threshold doses were caused by differences in grain boundary volume fraction. • Volume expansion was observed in both the CVIed-SiC and SiC fibers. • The strength of the amorphous SiC fiber degraded. • The compressive displacement before failure significantly increased. [ABSTRACT FROM AUTHOR]

SiC fiber oxidation is a potential factor limiting the operating temperature of SiC f /SiC composites owing to the strength degradation after oxidation. Herein, we fabricated 1-μm-diameter pillars at the core of the fiber cross-sectional surface after SiO 2 removal to eliminate surface effects caused by external oxidation. The fiber strength significantly decreased during the first hour of oxidation in dried air at 1400 °C, but this deterioration became less pronounced after 10 h. Simultaneously, the oxidation lowered the Young's modulus and Weibull modulus. Oxidation considerably increased the porosity and the alterations in the mechanical behavior were primarily caused by the variations in porosity. Oxidation-induced pores were frequently detected at the fiber core and were partially filled with SiO 2. Compared with those of the as-received fibers, O impurities in the oxidized fiber core were significantly reduced. Thus, the fiber strength was potentially degraded by the internal oxidation reaction between residual C and O. • SiC fibers transformed from dense to porous after oxidation. • Significant increase in porosity influenced the mechanical behavior of the fibers. • Strength of SiC fibers was evaluated by micropillar compression tests. • The strength degradation of SiC fibers was potentially caused by internal oxidation. [ABSTRACT FROM AUTHOR]

In this study, nanoscale composite SiC-ZrC ceramic fibres, derived from polyzirconocenecarbosilane (PZCS) via melt spinning, electron beam crosslinking, pyrolysis and sintering were investigated in detail. Compared with several commercial products of second-generation SiC fibres, the produced composite fibres exhibit improved thermal stability, mechanical properties and oxidation resistance. SiC grains in the fibre grew from 9.8 nm to 33.9 nm after annealing in an inert atmosphere at 1800 °C for 1 h, as well as decomposition of the SiC x O y phase and the growth of SiC grains affected the mechanical properties of the fibres, and the mechanical properties of the fibres were maintained at 1.1 GPa, accompanied by an increase in the modulus. After the fibres were oxidized at 1100∼1400 °C for 1 h, a dense oxide layer of SiO 2 -ZrO 2 was formed on the surface of the fibres, which slowed down the rate of further fibre oxidation, thus, the fibres exhibited excellent oxidation resistance. [ABSTRACT FROM AUTHOR]

Presented article summarises preparation of fibre reinforced alumina and alumina laminates containing zirconia micro-fibres. Electrophoretic deposition was performed from concentrated isopropanolic suspensions stabilised by monochloracetic acid containing mixture of alumina powder and certain amount of zirconia micro-fibres. A method for in-situ monitoring the deposition of alumina and zirconia micro-fibres mass was applied to control deposition kinetics. Two different approaches for composite deposition were applied: (i) electrophoretic deposition of powders mixture and (ii) electrophoretic co-deposition from sonicated suspension containing stabilization aid. Applying the optimised procedure the alumina laminates reinforced with zirconia fibres were prepared. The co-deposition of ceramic micro-fibres and powder led to the preparation of microstructures having unique orthogonal fracture properties. Developed laminate with layers created by zirconia micro-fibres in the alumina matrix seems to be the most promising. This type of material exhibited potential of the crack trapping and deflection even when very small amount of micro-fibres was used. [ABSTRACT FROM AUTHOR]

Abstract: Metal core piezoelectric fibres (MCPFs) show strong potential for structural actuator applications. Unfortunately the development of such fibres is problematic because of their fabrication difficulties. In order to obtain the best properties, both aspect ratio and piezoceramic–metal core compatibility have to be considered. For those reasons, fabrication of such fibres by a multi-dip-coating process has been investigated on platinum wires. The multi-coating process is shown to be more versatile and allows to control the aspect ratio. It is shown that decreasing slurry temperature during the dip process is a suitable way to reduce the number of coating steps in order to achieve high aspect ratio. After sintering, coatings exhibit the same behaviour as bulk ceramics in terms of microstructure, crystallography and ferroelectric loops. [Copyright &y& Elsevier]

Abstract: Non-oxide CMCs based on pyc-coated SiC-fibres (Tyranno SA3™) as well as novel amorphous ceramic fibres in the quaternary system Si–B–C–N (named SiBNC-fibres) were manufactured via polymer infiltration and pyrolysis process. Two different fibre architectures were applied: 0|90° unidirectional (UD) cross-ply and 0|90° plain weave fabric layer. UD cross-ply reinforced CMCs exhibit much more uniformly distributed filaments leading to better infiltration efficiency in resin transfer moulding process. Bending strength and fracture behaviour are strongly influenced by fibre architecture: UD cross-ply reinforced CMCs show higher bending strengths and less non-linear behaviour compared to plain weave fibre reinforcement. In tensile test there is no evidence of an influence of fibre architecture. Mechanical properties of unexposed SiCpyc/SiCN and SiBNCpyc/SiCN strongly correlate with fibre properties. After exposure to air (T =1100°C, 20h), a significant decrease of mechanical properties could be observed, caused by complete oxidation of pyc-fibre coating interfered with silica formation. [Copyright &y& Elsevier]

Abstract: Inspired by nest structure, highly porous fibrous yttria-stabilized zirconia (YSZ) ceramics were fabricated through tert-butyl alcohol (TBA)-based gel-casting process and pressureless sintering by using YSZ fibers as raw material and adding K2SO4 as removable sintering aid. Different sintering temperature and soaking time were investigated to achieve optimal thermal and mechanical properties. The results show that all specimens consist of crystallized t-YSZ phase. Fibers interconnect with good interfacial bonding on junctions. Under higher sintering temperature, porosity drops gradually while compressive strength increases significantly. With prolonged soaking time, there is no obvious change in porosity and compressive strength increases gradually. All specimens have uniformly distributed pores with average size of 30.2μm and show good structural stability at high temperature. Ultra-low thermal conductivity is achieved and ductile fracture mode with high elongation makes it more applicable in high-temperature thermal insulating applications. [Copyright &y& Elsevier]

Abstract: The crystal structure of gallium oxynitride nanowire was investigated by using scanning transmission electron microscopy. Gallium oxynitride nanowire was directly observed to have a biphasic wurtzite and zinc-blende structure. There was a stacking disorder of several atomic layers between the two phases. The new biphasic nanowire formed due to the presence of Ni in starting material because its nitride has a zinc-blende structure whereas gallium oxynitride has the wurtzite structure. Crystal growth of gallium oxynitride nanowires was studied using seed crystals. Seed crystals and amorphous gallium oxide precursors were annealed under different ammonia flow rates to grow gallium oxynitride nanowires. The nanowires grew to length of 150μm but they did not grow laterally when the ammonia flow rate was 50mL/min. [Copyright &y& Elsevier]

Abstract: Borides and carbides of early transition metals are considered a class of promising materials for several applications, the most appealing ones being in the aerospace and energy sectors. The present work is mostly focused on toughening of UHTCs through incorporation of SiC chopped fibers. Mechanical properties of reinforced composites are compared to those of un-reinforced, whisker- and particle-reinforced materials and the effect of different kinds of sintering aids is studied. Addition of fibers allows toughness to be increased from 3–4MPam1/2 (for un-reinforced materials) to 5.0–6.2MPam1/2. The high temperature behavior is also investigated both in air furnace and in arc jet facility. Eventually, a paragraph is dedicated to potential of UHTCs as sunlight absorbers for future solar concentrating systems operating in the high temperature regime. [Copyright &y& Elsevier]

Abstract: The laser floating zone technique was used to grow large 2Al2O3–SiO2 mullite fibres (up to 1.6mm in diameter and 40mm in length). The fibres grown at 10mm/h are single crystalline in nature, while those pulled at higher rates (40 and 100mm/h) are polycrystalline with a cellular microstructure. The crystals are highly [001] textured with respect to the fibre axis, as determined by X-ray diffraction analysis. The Raman spectra taken at different orientations corroborate the strong anisotropy observed by X-ray and SEM on both single crystalline and textured polycrystalline samples. Four point bending tests and ultramicroindentation Vickers experiments were performed at room temperature in order to characterize the mechanical properties. The presence of lamellar inclusions in the single crystalline fibres decreases the flexural strength (431MPa) and the fracture toughness (1.2MPa.m1/2) compared to the polycrystalline ones (631MPa and 1.6MPa.m1/2). However, the absence of grain boundaries in the single crystals leads to higher ultramicrohardness (H V =15.6GPa) and Young''s modulus (E =170GPa) than those of the polycrystalline fibres (14.2 and 145GPa), where a glassy intergranular phase exists. [Copyright &y& Elsevier]

Abstract: The influences of the chemical composition and the heat-treatment conditions on both the crystallisation behaviour and the high-temperature stability (HTS) of three types of amorphous stone wool fibres of iron-bearing alumino-silicate composition are studied by performing thermal, structural, and compositional analyses. The fibres heat-treated under oxidising conditions exhibit outstanding HTS, i.e., the fibres are able to maintain their original geometric shape in a high-temperature environment. This is attributed to the formation of a nano-crystalline layer on the surface of the fibres as a consequence of the oxidation of Fe2+ to Fe3+. The layer remains after the bulk crystallisation process has been completed. The thickness of the layer increases with increasing initial content of Fe2+ and Mg2+ in the fibres. The nanolayer influences the bulk crystallisation in the manner that it lowers the crystallisation onset temperature, the activation energy, and the Avrami parameter. Such influence benefits the enhancement of the HTS. In contrast, the fibres heat-treated under reducing and inert conditions exhibit poor HTS. This is attributed to the early viscous heating of the fibres because of lack of the nano-crystalline surface layer. The HTS does not depend on the identity of the bulk crystalline phases. [Copyright &y& Elsevier]

Abstract: For single piezoelectric ceramic fibres a method was developed to measure the piezoelectric strain loops. In this work we present a measurement method using a capacitive displacement sensor to characterize single fibres with diameters of 100–500 m. The electric field is applied in the length direction of the fibre and the strain parallel to the field is measured. Strain-electric-field loops of PZT fibres were measured at high electric field strength and frequencies up to 100Hz. The sensitivity of the measurement method is high enough to determine the low-voltage piezoelectric coefficient . The results were compared with other results measured on single fibres. The advantages and drawbacks of the method are discussed. [Copyright &y& Elsevier]

Abstract: We report the structural and mechanical characterization of yttrium aluminum garnet fibers obtained with Eu and Nd additions by the melt-extraction method (ME). Powders were synthesized by the modified citrate precursor method. This method produces in a single step of heat treatment the pure YAG phase avoiding the formation of YAlO3, Y4Al2O9 or Y2O3 phases. Rare earth additions delay proportionally to the added quantity of dopant the crystallization temperature of the YAG phase. Using crystalline powders, cylindrical fibers (20–30μm) in an amorphous state irrespective of doping type and amount were obtained by ME. Nanoindentation tests were carried out showing hardness and reduced elastic modulus of 5.8±0.3 and 79.3±4.9GPa for pure YAG fibers, respectively. 2at.% additions of Nd to the YAG phase lead to an increment in hardness and reduced elastic modulus (9.1 and 128.6GPa, respectively). However, further increments of Eu or Nd (5at.%) cause a clear degradation of the mechanical properties respective to the values reached with 2at.% of rare earth additions. This degradation effect seems to be correlated to the atomic interaction due to difference between radii of Eu and Nd, respective to Y. [Copyright &y& Elsevier]

Abstract: The production of lead zirconate titanate (PZT) fibres, 1-3, 3-1 and 2-2 composites for actuator and sensor applications through the thermoplastic co-extrusion process can be achieved by using a macro-scale preform shaped by two different extrudable mixtures. The main challenge of this method is the optimization of materials that can be co-extruded and at the same time maintain the preform geometry in the final product, without axial and cross-sectional deformation. In this work, rheological characterizations of PZT/polyethylene and carbon black/polyethylene feedstocks were carried out to produce monofilament composites by the co-extrusion process. To explore the interface instabilities resulting from the viscosity mismatch between the processed materials, the co-extrusion tests were performed varying the velocity of the piston during extrusion. Successful co-extrusion, with well preserved fibre morphologies and defined interface between the co-extruded materials, was achieved for viscosity ratios between the feedstocks ranging from 0.98 to 1.16. Outside of this range, interface distortions were observed. [Copyright &y& Elsevier]

Abstract: In this paper, results presented concern both the chemical and physical behaviours of hemp fibres in lime-based mineral matrix in order to better understand the role of chemical modifications of cellulosic fibres in the evolution of the macroscopic properties, essentially mechanical ones, of such composite materials. The role of fibres surface treatment has been also studied through various chemical treatments applied on hemp fibres. In a first step, the influence of such treatments on the fibre characteristics has been investigated by several means, such as scanning electron microscopy, thermal analysis, X-ray diffraction and FTIR spectroscopy, in order to evaluate their consequences on the fibre behaviour itself. Secondly, an attempt to characterise the influence of the various chemical treatments of fibres on the mechanical behaviour of hemp reinforced lime-based composites has been completed by a three points bending testing campaign. According to the results, it seems that the modifications induced by specific chemical treatments (EDTA, NaOH) on fibres play a major role in the strengthening of the lime/fibres interface but also in the improvement of the overall stiffness of the composite (with respect to the one reinforced by untreated fibres) most probably related to a specific stiffening process of the fibre itself. [Copyright &y& Elsevier]

Abstract: Mullite fibres with uniform diameter and smooth surface have been synthesized using commercial grade polyvinyl butyral (PVB) as binder. The sol with good spinnablity was obtained at reaction temperature of 60°C for 1h. The results of X-ray diffraction indicated that the Al–Si spinel was obtained before complete mullization, which implied the addition of PVB retarded the phase transformation of mullite. The fibres showed a rough surface and lateral cracks at 800°C. Smooth and dense surface was observed when fibres were sintered at 1200°C and completed transformation to mullite was achieved. This technique offered the possibility of synthesizing mullite fibres at considerably lower cost than at present. [Copyright &y& Elsevier]

Abstract: The mechanisms governing tensile creep and creep fracture are identified for siliconized silicon carbide (Si–SiC) and sintered silicon carbide (SSC), as well as for various SiC-matrix composites reinforced with interwoven bundles of different fibres. With Si–SiC and SSC, creep is controlled by the rate at which intergranular damage development allows grain boundary sliding. Fracture then results from the formation and link up of grain boundary cavities and cracks, unless premature failure occurs by rapid crack propagation from a pre-existing flaw. In contrast, with the woven SiC-matrix composites, immediate failure was never encountered on loading at stresses less than the UTS, despite the presence of macroscopic pores. Instead, the longitudinal fibres control the rates of creep strain accumulation and crack growth. However, the fracture properties are determined by oxidation-assisted fibre failure, because matrix cracking permits oxygen ingress during tests in air. By clarifying the processes limiting the creep capabilities of current product ranges, possible development avenues are suggested for fibre-reinforced composites displaying improved long-term service performance in oxidizing atmospheres. [Copyright &y& Elsevier]

Abstract: TiO2 nanofibers were prepared by using electrospun TiO2/polyvinylpyrrolidone fibers by drying for 5h in air and subsequent annealing for 3h at 500°C. Uniform and smooth fibers with diameters of 120±10nm were observed at a PVP concentration of 0.09g/ml, a Ti(OCH(CH3)2)4 concentration of 0.14g/ml, a flow rate of 0.5ml/h, and an electric field of 1kV/cm, respectively. TiO2/PVP nanofibers were also electrospun by varying the collector grounding design to improve the axial alignment of fibers. The collector is composed of two pieces of conductive substrates separated by a gap of 1.5mm. In addition, the collector consisting of two sets of substrates placed by 90° are prepared for a grid structure of the fibers. Both collectors show that the charged nanofibers are stretched to span across the gap between the electrodes. [Copyright &y& Elsevier]

Abstract: Toxicology studies have indicated that stone wools with different compositions have different levels of biopersistence. It is however not easy to carry out a large number of in vivo experiments. It is also known that in vitro dissolution rates at two pH values correlate with two dissolution phenomena in lungs. In this work, nonlinear models of in vitro dissolution rates at pH 4.5 and at pH 7.4 have been developed for stone wools of widely different compositions from a limited amount of experimental data. These in vitro dissolution rates, in combination with some other variables, have then been correlated with in vivo retention half times. It is expected that once the models predicting half times are reliable enough, testing on animals could be reduced to a negligible fraction of its amount today. The dissolution rates of stone wools depend on their composition in a complicated manner. Not only are the effects nonlinear, there are strong cross effects of combinations of variables. Therefore, the conventional linear techniques are not effective. Phenomenological modelling is hardly possible since very little is known about the kinetics of the potential surface reactions taking place at different pH values. New techniques of nonlinear modelling have made this kind of model development feasible, as it is illustrated in this paper. These techniques have opened up new possibilities in materials science, including fibre technology and ceramics. [Copyright &y& Elsevier]

Abstract: The product range of bioactive glasses is restricted by their tendency to crystallize at working processes typically performed with high viscosity melts. In this work high-temperature properties viscosity, devitrification temperature and liquidus temperature of seven bioactive glasses are measured. Further, the parameters used to describe glass stability and crystallization tendency are discussed. The results indicate that bioactive glasses can be divided into two groups: (1) glasses which nucleate and crystallize within the whole viscosity range of interest for forming processes, such as sintering and fiber drawing, and (2) glasses with a viscosity range enabling high temperature processing without crystallization. The main difference between these groups is the primary crystalline phase in crystallization. Glasses showing sodium-calcium-silicate crystallization are sensitive to high temperature processing, while glasses showing wollastonite crystallization have better stability at working temperatures. Thus, by adjusting the composition special products, such as fibers and porous implants can be manufactured. [Copyright &y& Elsevier]

Abstract: A new route of gelcasting is applied to prepare Gd2O3 and Gd2O2S as well as Al2O3 ceramic parts, i.e. thin plates and fibres. Cellulose acetate is used as monomer. Instead of a water-based solvent system, ethylenediamine as solvent is employed; therefore, moisture- and air-sensitive ceramic powders can be processed, such as Gd2O2S. The presented work focuses on the characterisation of the slurry by rheological and chemical measurements, the polymerisation process and the first results of the fabrication of ceramic bodies. Both green and sintered parts were investigated using electron microscopy, X-ray diffractometry and physisorption. [Copyright &y& Elsevier]

Abstract: Alumina fibres and alumina–zirconia fibres were prepared by sol–gel process. The starting materials used for the preparation of alumina and zirconia sol were aluminium-tri-isopropoxide and zirconium oxychloride respectively. Alumina sol and zirconia sol were mixed in definite proportions, so that the final composition contains 10wt.% ZrO2. Alumina and alumina–zirconia fibres were prepared from the alumina sol and mixed sol respectively. MgO was introduced in the fibres by adding MgNO3 into the sol. Sintered alumina fibre has α-Al2O3 phase and alumina–zirconia fibre has α-Al2O3 and t-ZrO2 phases. The phase transition to α-Al2O3 takes place at higher temperature in the alumina fibre with MgO, whereas the effect is less in alumina–zirconia fibre. The addition of MgO reduces the grain size and increases the tensile strength. [Copyright &y& Elsevier]

Abstract: We have investigated the setting of binary blends (latex-filled plaster and polyamide fibre-reinforced plaster materials) and ternary blends (polyamide fibre-reinforced latex-filled plaster materials). The influences of the latex (nature and concentration) and the fibres (concentration, length and diameter) were analysed in terms of the setting time, the total swelling and the hydration of the plaster. The association of hydrophilic polyamide fibres with plaster disturbs the hydration, and the setting time of the plaster/latex binary blends depends strongly on the nature of the polymer. The choice of the proper latex to be associated with the plaster was made looking upon its influences on the setting time and the mechanical properties of the blend. The ternary blends were characterised by a drastic increase of the setting time correlated with a reduction of the total swelling. [Copyright &y& Elsevier]

Abstract: Sols of yttria-stabilized zirconia may be used as simple, readily processable and accurate controllable precursors for the ZrO2 interfacial coatings on SiC-based Nicalon™ fibers. The ZrO2 interfacial coatings of predictable crystal phase compositions were obtained in dependence of yttria dopant level. The morphology, composition and oxidation resistance of coated fibers were evaluated by SEM, EDS, XPS, XRD, and Raman analysis. All coatings obtained are uniform, continuous and adherent to substrates. The delamination within the ZrO2 interfacial coating was found. Possible reasons of this phenomenon are discussed. The peculiarities of the behavior of Y-stabilized ZrO2-coated fibers in air at elevated temperature are considered. [Copyright &y& Elsevier]

Abstract: Aligned YAG fine fibres had been made previously from an aqueous sol–gel process, but it was suspected that sodium contamination in one of the starting materials lessened the creep resistance of the final product. Therefore, sodium-free gel precursor fibres were made using the same process, and upon firing in air at 900°C these formed pure phase YAG fibres, of 4μm diameter. When steamed over 200–500°C for 3h, the amorphous gel fibre formed single phase nanocrystalline YAG between 400 and 500°C, an extraordinarily low temperature for this material to crystallise. Upon postfiring up to 1550°C, grains averaging 0.5μm and pores of 0.17μm had formed, but despite this porosity and smaller grain size, the sodium-free fibre exhibited superior creep resistance than the sodium contaminated fibres reported previously by the authors, typically creeping at temperatures 50°C higher. This demonstrates that even small levels of sodium contamination are harmful to creep resistance in YAG. [Copyright &y& Elsevier]

Abstract: A porcelain body traditionally used to produce ceramic art and design objects was re-formulated using additional waste paper. The aim of this study was to develop knowledge into the technological properties of paper-composite porcelain in its green state, for use within the traditional practices of ceramic art and design production. Characterisation was made by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Two different production methods used by potters, slip casting and free-hand pressing, were used. The presence of the paper fibre, the paper type and the content amount are the important factors in strengthening development. Significant differences were found in relation to the content amount of paper fibre, between the mother porcelain body and the different content amount of paper fibre in the paper-composite porcelain body. [Copyright &y& Elsevier]

Abstract: Calcium-deficient apatite fibres were successfully synthesized by a homogeneous precipitation method using starting solutions with a Ca/P ratio of 1.00–1.67. In the case of the Ca/P ratio of 1.67, the resulting apatite fibre had long-axes of about 60–100μm and contained 5.2 mass % of carbonate ions. The Ca/P ratio of apatite fibres could be controlled in the range of 1.53–1.68 by changing the Ca/P ratio of the starting solutions from 1.00 to 1.67. The long-axes and the carbonate contents of the resulting calcium-deficient apatite fibres increased with Ca/P ratio of the starting solutions. These apatite fibres were of single crystal and had a preferred orientation in the c-axis direction. [Copyright &y& Elsevier]

Abstract: Mullite grain size characteristics of four different alumino silicate fibres heat-treated between 1400 and 1700°C in a time frame of 0.5–100h have been determined. Mullite grain sizes show little change up to 1500°C though the grain microstructure develops from mosaic-type to facetted. Above 1500°C grain growth kinetics follow the empirical law D 1/n − = kt (D 0 =initial grain size, D =grain size after annealing, 1/n =grain growth exponent, k =reaction constant, and t =firing time). Between 1500 and 1600°C the grain growth exponent is remarkably low (1/n =1/12) but above 1600°C grain growth exponents reach normal values of ≈1/3. The vacancy drag model has been used to explain the complex grain growth behaviour of mullite. [Copyright &y& Elsevier]

Abstract: The availability of fine scale lead zirconate titanate (PZT) fibres has enabled advances in actuator and sensor applications, including devices for structural control such as the active fibre composite (AFC). Since PZT fibres form active elements within a functional device, fibre characterisation and optimisation is essential. Several commercially available fibres have been studied, which are representative of two dominant processing routes currently utilised: extrusion and suspension spinning. Fibres have been characterised in terms of morphology (shape factor and diameter variability), microstructure (grain size and porosity), and phase composition (XRD). Certain fibres were found to exhibit properties unsuitable for AFC applications, which suggests that commercial production of fine scale PZT fibres may not yet be fully optimised. [Copyright &y& Elsevier]

Abstract: The chemical, structural and thermomechanical properties of SiC and diamond CVD-monofilaments have been investigated. Electron and Raman microprobe analyses showed graded radial atomic and phase distributions in the SiC filaments. Thermomechanical investigations (tensile/bending elastic modulus/creep tests) were carried out on single filaments and these properties were correlated with the physicochemical features. The thermal behaviour of the CVD-SiC filaments is strongly related to the nature and the amounts of intergranular secondary phases (free carbon or silicon). The strong covalent bonds and the microcrystalline state of the CVD-diamond filaments give rise to an outstanding thermal behaviour. [Copyright &y& Elsevier]

Abstract: Tensile fracture properties of directionally solidified chromia-doped c-axis sapphire fibers have been studied in a range of temperature (room temperature up to 1400°C) and dopant content (0, 300ppm and 1% of Cr2O3). Delayed failure of the fibers was studied by measuring the dependence of the tensile strength on the loading rate and by fractographic studies on the fracture surfaces of the fibers. In all the temperature range, the fibers doped with 300ppm of Cr2O3 are slightly stronger than the pure sapphire fibers. The least strong fibers are those containing 1% of Cr2O3. For this badge of material, the beneficial effect of solution hardening is counterweighted by increasing amount of defects caused by a faster fabrication. Slow crack growth appears to be the process controlling delayed failure at higher temperature. Little contribution of slow crack growth to delayed failure is found at the lower temperature. [Copyright &y& Elsevier]

Abstract: Submicron diameter ZrB2, TiB2 and HfB2 fibers were produced in single crystal form. Directional solidification of diboride eutectics followed by matrix phase removal was utilized to fabricate single crystal fibers. LaB6 was utilized as the matrix phase for crystal growth. Fiber diameter ranged from 0.4 to 0.8μm for all compositions investigated. The length-to diameter aspect ratio exceeded 500 for all compositions. Fibers were uniform and had smooth surfaces along the entire length. Transmission electron microscopy characterization showed that the fibers were single crystals with a high degree of perfection and preferential growth direction along the 〈111〉 orientation of the diboride lattice. Porous structures were formed by pressing the diboride fibers and sintering at temperatures up to 2200K in vacuum. The level of porosity, average pore size distribution, and specific surface area could be controlled to some extent by mechanical pressing. The diborides in small fiber form may have technical applications in structural components and functional devices, i.e., industrial filters, thermal protection systems, and possibly for reinforcement. [Copyright &y& Elsevier]

The distributions of fibre strength, pullout length, and fibre/matrix interface shear strength within a single fibre bundle were investigated for a 3-D woven SiC/SiC composite tensile tested at 1100 °C in air. Fibre pullout lengths were largest at the fibre bundle centre with an embrittled region of approximate width 15 μm at the perimeter. Whereas the fibre strength varied by less than a factor of 2 across the fibre bundle, the fibre/matrix interface shear strength varied by a factor of ∼23 with a minimum (100±16 MPa) at the centre and a maximum (2.25±0.21 GPa) close to the embrittled region. The minimum fibre/matrix interface shear strength required for the transition between pseudo-ductile and brittle behaviour was thus estimated to be 2.25±0.21 GPa for this composite system. [Copyright &y& Elsevier]

A new polymer was prepared at room temperature from a di-chloroborazine and a reactive aminoborane. It displays borazine rings unambiguously linked through three atoms N–B–N bridges. This connecting mode was evidence by 15N solid state NMR. This polyborazine was processed into a continuous polymer fibre of about 21μm diameter, which was subsequently heat-treated under NH3/N2 up to 1800°C for conversion into BN fibres. The achievement of hexagonal boron nitride was confirmed by X-ray diffraction and Raman spectroscopy. Tensile tests were carried out on the ceramic fibres. The average tensile strength is about 1000MPa and the Young''s modulus is close to 200GPa. Structural characterisation of the BN fibres was undertaken by polarised light and transmission electronic microscopies. [Copyright &y& Elsevier]

In this paper, needlelike and dispersible hillebrandite (Ca2(SiO3)(OH)2) and β-dicalcium silicate (β-Ca2SiO4) fibers, 1.0–1.5 μm in diameter and 15–25 μm in length were prepared by a modified hydrothermal method. In vitro bioactivity and dissolution of the two types of fibers were evaluated by soaking in the simulated body fluid (SBF) for various periods. Hydroxyapatite-like aggregates appeared on the fibers after soaking for 7 days, and uniform lathlike agglomerates with typical morphology of hydroxyapatite (HAp) formed after 14 days. It was observed that the fibers after soaking still kept stability in fibrous morphology with an aspect ratio in the range of 6–9. The Ca2(SiO3)(OH)2 and β-Ca2SiO4 fibers dissolved about 30.91 and 30.42%, respectively, within 14 days. The two types of fibers exhibited certain desirable characteristics including bioactivity, degradability and stability in morphology, and they are promising candidates as reinforcement reagents to develop novel bioactive composites for biomedical applications. [Copyright &y& Elsevier]

Continuous alumina fiber-reinforced alumina-matrix composites were fabricated by hot-pressing. Fibers were coated by La-monazite, and matrix was prepared using the mean size of 7 nm and/or 180 nm alumina raw powders. It was observed that the powder size of matrix affected the properties of the composites. Composites using the nano-sized powder (7 nm) as matrix showed higher pseudo-ductility, but lower maximum strength and density than those of the composite using the submicron-sized powder (180 nm) as matrix, regardless of the sintering temperature. Woody-type fracture due to fiber pull-out from matrix could be observed for all composites regardless of the size of powder for matrix after sintering at relatively lower temperatures. Nano-sized powder supplies a looser matrix than submicron powder, therefore, it should be corresponded to higher pseudo-ductility of the composites. Combination of the nano-sized and submicron-sized powder as matrix gives composites with highest strength as well as enough ductility. [Copyright &y& Elsevier]

The effect of the addition of borosilicate glass powder in the matrix on tensile mechanical behavior in an unidirectional Si-Ti-C-O fiber-reinforced SiC matrix minicomposite fabricated by the polymer infiltration pyrolysis (PIP) process has been studied. Tensile test of the minicomposite is carried out in an argon atmosphere at 298, 1273 and 1573 K. The Si-Ti-C-O/SiC shows a nearly linear tensile load–displacement curve which is similar to a dry fiber bundle independent of test temperature; conversely, the glass-powder-containing Si-Ti-C-O/SiC(g) exhibits a pronounced tensile load–displacement curve with a large nonlinear domain of deformation; however, this nonlinear domain became smaller at 1573 K. The matrix cracking load of Si-Ti-C-O/SiC(g) remained nearly constant at and below 1273 K, and it decreased at 1573 K. The tensile fracture load of the minicomposite is increased remarkably by the addition of a borosilicate glass powder in the matrix, but the increase was larger at and below 1273 K than at 1573 K. This increase of the tensile fracture load was attributed to more effective load transfer at the fiber/matrix interface for the Si-Ti-C-O/SiC(g) than for the Si-Ti-C-O/SiC. Degradation of the increase at 1573 K is due to the interface degradation decreasing interfacial load transfer capacity. [Copyright &y& Elsevier]

Sols of alumina, zirconia, titania and their mixes may be used as simple and readily processable precursors for ceramic interfacial coatings on SiC-based Nicalon™ fibers. The morphology, composition and tensile properties of coated fibers were evaluated for different systems in dependence of processing conditions by SEM, XPS, XRD analysis. All coatings obtained are uniform, continuous and adherent to substrates. They are distinguished by their morphological features, tensile strength, thermal resistance and compatibility with fiber. The peculiarities of the behavior of oxide-coated fibers are governed by the properties of initial sols, procedure for coating fabrication, chemical and nanostructural factors. [Copyright &y& Elsevier]

A two-phase alumina–zirconia fibre, the Nextel 650 fibre (3M), has been studied in tension and creep up to 1300 °C. Microstructural investigations on as-received and tested fibres have been conducted in parallel. Compared to current commercially available fine oxide fibres (alumina and alumina–zirconia based), the fibre shows good creep resistance despite a smaller alumina grain size. High temperature deformation of the fibre is achieved by grain-boundary sliding and is accompanied by oriented alumina grain growth. Sensitivity to alkaline contamination is shown by fast α-alumina grain growth at the fibre surface. [Copyright &y& Elsevier]

Si3N4–Cfiber composites using waste-Si sludge were fabricated by hot pressing at 1850 °C for 2 h with and without the addition of carbon powder. The composites were composed of small amounts of β-Si3N4, O′SiAlON, SiC and Y2SiO5 regardless of carbon powder addition. In the composite without the addition of carbon powder, most of the carbon fibers were graphitized with fine particles. Furthermore, many cavities were observed in the interior regions of C-fibers as well as at the interfaces of Si3N4/Cfiber caused by the decomposition of them. However, in the composite with 3 wt.%C powder added, the core regions of C-fibers still existed in an amorphous. The average size of a matrix grain in the composite using 3 wt.%C powder was slightly finer than that of composite fabricated without using carbon powder, which was caused by the existence of nanometer-sized SiC particles. [Copyright &y& Elsevier]

The single fibre test was used to determine the stress–strain behaviour and the strength distribution of three commercially available PZT-5A fibres with an approximate diameter of 250 μm. One of the fibres was manufactured via an extrusion process, whereas the others were produced via similar spinning processes. All the fibres presented a non-linear stress–strain behaviour, which is apparently linked to their piezoelectric nature. The Young''s modulus of the fibres varied between 38 and 40 GPa. The strength distribution analysis (i.e. Weibull analysis) indicated large differences between the fibres with scale parameters varying between 49 and 68 MPa, and shape parameters situated between 4 and 12. These results were well correlated with the presence of defects in the fibres observed under a microscope. The fibres with the lowest scale and shape parameters, manufactured via a spinning process, contained large porosities and their diameter was varying along their length. In contrast, the two other fibres produced via different manufacturing processes (extrusion and spinning) presented better strength properties and a more homogeneous microstructure. [Copyright &y& Elsevier]

Si3N4/carbon fibre composites have been fabricated, and the effect of fibre content on the tribological properties was investigated under dry sliding conditions. The friction coefficient of the composites was around 30% of that of a monolithic Si3N4 composite. A fibre content of 5 vol.% was sufficient to maintain a graphite interface during the sliding tests, such that the friction coefficient did not decrease further with increasing graphite fibre content above this level. The carbon fibre content was effective for maintaining a low friction coefficient throughout the duration of the experiment. [Copyright &y& Elsevier]

The effect of thermal exposure on the microstructure and tensile stress–strain behaviour has been investigated for composites of woven continuous oxide fibres (Nextel 720) in a porous aluminosilicate matrix. The tensile tests were carried out on straight-sided, centre hole notched plates with 0/90° and ±45° orientations. The as-received material was slightly notch sensitive in that the net section fracture stress decreased somewhat with increasing hole diameter but much less than predicted for an ideally elastic, fully notch-sensitive material. After exposure at 1100 °C and for long time at 1000 °C in air the composite was embrittled. In the 0/90 composite this resulted in a reduced fracture strength, a reduced strain to failure as well as a reduced fracture toughness and damage zone size. After exposure for 100 h at 1100 °C (the most extreme exposure applied) the material also became significantly more notch sensitive and had failure characteristics similar to those of a monolithic ceramic. The ±45 composite was also embrittled which resulted in a reduced strain to failure but an increase in fracture strength. Density measurements and observations on the microstructure and fracture surfaces indicated that the embrittlement was due mainly to localised densification of the matrix and an increase in fibre/matrix bonding. [Copyright &y& Elsevier]

Vapor-grown carbon nanofibers (CNFs) were synthesized from a Fe2O3-Al2O3 composite ceramic catalyst. It was revealed that the CNF constructions and structures depended on the catalyst phase. Fe2O3 solid solution and FeAlO3 catalysts synthesized fine CNFs with diameter of 10–15 nm. These CNF structures were similar to those of MW-CNTs. Notably, the FeAlO3 catalyst could synthesize aligned CNF structures. The secondary phase precipitated from FeAlO3 in the specific crystal direction and this precipitation induced the cleavage fracture of FeAlO3 grain during CNF synthesis. As a result, CNFs grew on the specific plane and aligned in one direction. [Copyright &y& Elsevier]

Rare-earth orthoferrite, LnFeO3 (Ln=La, Sm, Gd, Dy, Er and Yb) ceramic fibres were produced by aqueous sol-gel blow spinning process at low-temperatures. Stable, charge stabilised, colloidal precursor sols of orthoferrites were prepared by room temperature processing of inexpensive and commercially available metal salts. The average diameter (Zav) of the colloidal sol particles was in the range 4–7 nm and had a narrow size distribution. The sols were concentrated, combined with spinning aids, and processed further to a viscous ‘spinning solution’. The gel fibres of about 6 μm diameter were blow spun, collected as random fibres, dried and heated to increasingly higher temperatures at a rate of 50 °C/h. The gel fibres converted to flexible ceramic fibres, and single-phase perovskite structure crystallised directly for all the LnFeO3 (Ln=La, Sm, Gd, Dy, Er and Yb ) fibres on heating them to 700 °C. The ceramic fibres had mean diameter of about 3–4 μm, and consisted of randomly oriented submicron sized grains. [Copyright &y& Elsevier]

Optically clear, inclusion-free mullite fibers up to 80 mm in length and 80×70 μm2 in cross-section were grown from an alumino silicate melt by the internal crystallization method (ICM). Microprobe analysis reveals a high chemical homogeneity at 76.5±0.5 wt.% Al2O3 and 23.5±0.5 wt.% SiO2, which is close to the 2/1-mullite composition. Areas of slightly decreased Al2O3 content (≈74.5 wt.%) occur rarely, whereas areas of increased Al2O3 content were not observed. Polarized infrared-reflection micro-spectroscopy using spot sizes of 60 μm diameter on sections cut parallel and perpendicular to the fiber axis show the single crystal character of the fibers. Optical microscopy shows that the fibers consist of a mosaic of single crystal areas up to about 5 mm in length. The c axis of the single crystal individuals are misalligned up to θ ≈±3° with respect to the fiber axis. These orientational misfits are believed to be the reason for the development of the mosaic type microstructure during the growth process. [Copyright &y& Elsevier]

Transparent forsterite fibrous gels were prepared from the hydrolysis of alkoxide precursor sols with acetic acid and water, and the crystallization process of gel fibers was studied after heat treatments up to 1500 °C. Appropriate amount of acetic acid not only promoted the formation of spinnable linear-type polymeric species, but also enhanced the chemical homogeneity and reduced the crystallization temperature of the resultant gels. On heating, fibrous gels started to crystallize into forsterite at 550 °C as investigated by infrared spectrum, X-ray diffraction and thermal analysis. Single phase forsterite fiber thus could be obtained up to 1500 °C when the amount of hydrolysis water was limited. However, fibrous gel derived from the high-water-content sol displayed a few secondary phases of the magnesia (MgO) and protoenstatite (MgSiO3) following heating at 1000 and 1400 °C, respectively; similarly, xerogels derived from without or with insufficient amount of acetic acid also revealed the segregation of second phases on heating. The synthesized forsterite fibers displayed nanocrystalline structure up to 1100 °C. On heating to 1300 °C, fired fibers exhibited grain growth into around 0.3–0.5 μm in size, with the room temperature dielectric constants of around 6.8–7.2 (at 1 MHz). [Copyright &y& Elsevier]

The incorporation of nylon fibres in a water based silica binder to replace the costly liquid polymer addition in investment casting mould were investigated in this work. Ceramic moulds produced with fiber modified binder were found to be 13% thicker at flat section and 40% thicker at sharp edges and radii than polymer modified system. The firing strength after fiber and polymer burn out was comparable for both systems. The extra shell thickness in the fibre system, especially at edges, gives a higher load bear capacity. This has the advantage of resisting cracking during de-wax and mould wall movement during alloy casting which lead to costly defects. A much higher mould permeability at casting temperature of fibre modified system also proves advantageous to complete mould filling. The unique properties of fibre modified system lead to a promising alternative for the standard investment casting industry. [Copyright &y& Elsevier]

This paper deals with the creep mechanism for ceramic matrix composites reinforced by long ceramic fibers in a ceramic or glass-ceramic matrix, tested at low stresses (<400 MPa) and low temperatures, respectively <1673 K for the former and <1373 K for the latter. The macroscopic results give few ideas on the mechanism, but observations at different scales until high resolution evidence brittle damages which lead the authors to use the damage mechanics approach and to demonstrate that a damage creep mechanism is operating for these CMCs in two steps: (1) matrix microcrack development until its saturation, (2) followed by the opening of some of these microcracks enabling under certain conditions creep of the SiC fibers which bridge the microcracks. This was enlightened by precise damage observations on stepping creep tests and by their quantification with automatic image analysis. [Copyright &y& Elsevier]

The present work is devoted to a TEM (transmission electron microscopy) study of the texture, structure and chemistry of a boron nitride (BN) fibre. The general structure of the fibre consists of two concentric parts; the near surface region is finely nano-crystallised, while the bulk of the fibre exhibits larger crystallites, although still of nanometric sizes. All grains appear to be randomly oriented with respect to the fibre axis, which makes the mechanical properties of this material remain modest. From a crystallographic point of view, both hexagonal and rhombohedral BN forms have clearly been identified by high resolution TEM (HRTEM). From a chemical point of view, EELS (electron energy loss spectroscopy) analysis shows that the N/B atomic ratio remains close to one, although it tends to decrease slightly from the outer surface to the ‘core’. No significant amount of impurities (e.g. carbon and oxygen) has been detected. The study of the B–K and N–K edges reveals a great similarity between the hexagonal and the rhombohedral forms. [ABSTRACT FROM AUTHOR]