Aluminosilicate Fibers Research Articles

Wear behavior of aluminum-based metal matrix composites reinforced with a preform of aluminosilicate fiber

The Al-Si alloys are widely used for applications in the automotive industry as structural components of internal combustion engines. Wear properties are critical to these applications. The reinforcement of alloys with fibers can alter mechanical properties and affect their wear behavior.

Performance of a high concentration Er/sup 3+/-doped alumino silicate fiber amplifier

We report the gain, noise figure, output saturation power, and conversion efficiency of a highly concentrated Er/sup 3+/-doped alumino silicate fiber amplifier. We obtain a gain per unit length of 1.0 dB/cm, which corresponds to the highest gain per unit length obtained in an Er/sup 3+/-doped fiber amplifier. The pump power threshold ranges from 2 to 5 mW, depending on the fiber length.

Mechanical and wear behavior of an Al/Si alloy metal-matrix composite reinforced with aluminosilicate fiber

Aluminum/silicon alloys reinforced with low volume fractions of short aluminosilicate fibers were prepared by the squeeze-casting process. The wear behavior of the metal-matrix composites (MMCs) and that of the monolithic Al/12 wt% Si alloy was investigated in pin-on-disk tests from room temperature to 400 °C under dry conditions. It was found that the additions of 3–7 vol.% of fiber conferred a beneficial effect in reducing the wear rate of the alloy at room temperature. Furthermore, the results of investigations at room temperature also indicated that the MMC with 4.5% fiber exhibited the lowest value of the coefficient of friction. Sliding wear tests at high temperatures revealed that the wear rates of the MMCs were significantly lower than those for the unreinforced alloy, particularly above 300 °C. The worn surfaces and subsurfaces of specimens tested at high temperatures were examined by scanning electron microscopy (SEM). SEM observations revealed that extensive microcracking occurs on the surface of the monolithic alloy tested at lower loads. The growth of these microcracks eventually led to the delamination of debris from the alloy surface. The aluminosilicate fibers tended to reduce the extent of plastic deformation in the surface layer, thereby reducing the occurrence of microcracking in the MMCs.

High temperature behaviour of polycrystalline aluminosilicate fibres with mullite bulk composition. I. Microstructure and strength properties

Temperature-dependent microstructure/strength relations of commercial aluminosilicate fibres with nearstoichometric mullite bulk composition are investigated. As-received Nextel 440 ™ fibres (70 wt% Al 2O 3, 28 wt% SiO 2, 2 wt% B 2O 3), consisting of nanometresized γ-Al 2O 3 and a minor amount of amorphous phase, have tensile strength of 2100 MPa. Heat treatment at 1200 °C causes transformation into fine-grained mullite (mean grain size: 80 nm). The remaining tensile strength is 1600 MPa. Heat treatment at higher temperatures leads to considerable reduction of strength (1100 MPa after firing at 1400 °C) attributed to mullite grain coarsening (mean grain size at 1400 °C: 135 nm). Altex 2K fibres (72 wt% Al 2O 3, 28 wt% SiO 2) consist of single-phase mullite with a mean grain size of 115 nm. Tensile strength is comparatively low (1250 MPa). Annealing at 1000 °C causes a significant increase in strength (1600 MPa). Above 1200 °C mullite coarsening and strength reduction are similar to those of Nextel 440 fibres.

High temperature behaviour of polycrystalline aluminosilicate fibres with mullite bulk composition. II. Kinetics of mullite formation

Kinetics and mechanisms of mullite formation in technical diphasic aluminosilicate fibres (Nextel ™ 440), consisting of transition alumina and a noncrystalline silica-rich phase, were studied by quantitative X-ray phase analysis. The as-received fibres were heat-treated in the temperature and time ranges from 1130 to 1215 °C and from 7·5 min to 32 h. The overall mullitization process can be described by an Avrami reaction law, or alternatively, by a simple exponential reaction law with a temperature-dependent induction period. Early stages of mullite formation with a low mullitization degree (α = 0·02) are characterized by an activation energy of ~650 kJ mol −1, whereas the apparent activation energy of the overall transformation reaction is ~900 kJ mol −1. Both activation energies are significantly lower than those described in the literature for other diphasic aluminosilicate gels. The relatively low activation energies of mullite formation in Nextel 440 fibres are attributed to the small B 2O 3 content of the as-received fibres. The presence of B 2O 3 may be responsible for the decrease of viscosity of the coexisting non-crystalline SiO 2-rich phase, by which diffusion, and mullite nucleation and growth is accelerated.

Correlation of defect centers with photoinduced second-harmonic generation in Er- and Sm-doped aluminosilicate fibers

The spectral dependence of photoinduced optical losses after chi((2)) writing have been obtained in Sm- and Er-doped fibers. The results show that Sm(2+) and Er(2+) can be a source of photoelectrons during fiber preparation.

Structure and properties of fibre reinforced zn-27% al alloy based cast MMCs

Metal matrix composites (MMCs) based on a zinc-27% aluminium alloy (ZA-27) were produced using a pressure infiltration technique. Preforms of alumina fibres and aluminosilicate fibres were used for reinforcement. Uniform distribution of fibres and satisfactory interfacial bonding were achieved. UTS, specific strength, hardness and wear resistance were improved significantly by the alumina fibre reinforcement, but UTS decreased when using aluminosilicate fibres for reinforcement mainly due to unavoidable clustering of particles in the fibre preforms. Structure-property relations have been analysed in all cases.

Group II Tris(glycolato)silicates as Precursors to Silicate Glasses and Ceramics

Group II tris(glycolato)silicates, MSi(OCH2CH2O)3 (where M = Ba, Ca, Mg), can be synthesized directly by reaction of silica with ethylene glycol and alkaline‐earth (group II) oxides at 200°C. These hexa‐alkoxy silicates serve as precursors to silicate glass and ceramic powders. They are readily modified by exchange with longer‐chain diols into processable polymer precursors. These Theologically useful precursors may provide access to silicate or aluminosilicate powders, thin fllms, fibers, and coatings. Thus, we have examined the utility of hexacoordinate glycolatosilicates as model precursors. Pyrolysis of the compounds, MSi(OCH2‐CH2O)3, in air transforms them to their anticipated ceramic products, MO‐SiO2. The phase transformations and chemical changes that occur during pyrolysis were characterized using X‐ray powder diffractometry (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), and scanning electron microscopy (SEM). The hexacoordinate glycolatosilicates oxidatively decompose at ∼300°C to form amorphous materials. Moderate to significant quantities of the group II carbonates, MCO3 (15–50 wt%), form coincidentally as the amorphous intermediates trap CO2 generated by ligand oxidation. At ∼900°C, the amorphous materials crystallize into the expected, phase‐pure, MO‐SiO2.

Passive selective filter for flattening the erbium-dopedfibre amplifier gainspectrum based on a feature of the silicon oxynitride fibre absorption spectrum

A newly developed nitrogen doped silica fibre was used as a filter in an erbium doped aluminosilicate fibre amplifier. A 30 dB gain was flattened within the 1530 – 1560 nm spectral band, the gain variations being no more than 5 dB.

Effect of applied pressure on mechanical properties of squeeze cast mg matrix composites

The present study aims at investigating the correlation of microstructure and fracture properties of two AZ91 Mg matrix composites fabricated by squeeze casting technique with a variation of the applied pressure. The composites were reinforced with Kaowool alumino-silicate short fibers and Saffil alumina short fibers, respectively. Microstructural observation, fractographic observation, andin situ fracture tests were conducted on these composites to identify the microfracture process. From thein situ fracture observation of the Kaowool reinforced composites, microcracks were initiated at the short fiber/matrix interfaces for the composite processed with the lower applied pressure, whereas microcracks were initiated easily at short fibers already cracked during squeeze casting at the very low stress intensity level for the composite processed with the higher applied pressure. Thus in this case. the effect of the applied pressure on mechanical properties could be explained using a competing mechanism; the detrimental effect of fiber breakage might override the beneficial effect of the grain refinement and the densification as the applied pressure was increased. On the other hand, for the composites reinforced with Saffil short fibers, microcracks were initiated mainly at the fiber/matrix interfaces at the considerably high stress intensity factor level while the degradation of fibers was hardly observed even in the case of the highest applied pressure. This finding indicated that the higher applied pressure yielded the better mechanical properties on the basis of the reinforcing effect of Saffil short fibers having excellent resistance to cracking.

Thermal shock resistance of nextel/silica—zirconia ceramic-matrix composites manufactured by freeze-gelation

Ceramic-matrix composites consisting of a silica—zirconia matrix reinforced by 25% by volume continuous Nextel alumino-silicate fibres have been manufactured by a sol-gel route incorporating freeze-gelation and subjected to thermal shock by water quenching from temperatures up to 800 °C. Although it was demonstrated that the Nextel fibres exhibited significant degradation of properties during composite processing, they still had a significant reinforcing effect. The material showed a critical temperature of approximately 550 °C, below which it was unaffected by water quenching. Above this level there was a 40 and 50% step reduction in modulus and strength respectively. Acoustic emission monitoring showed a significant difference in materials subject to quenching from beyond the critical temperature. There was a lower initial yet higher final AE event rate for a monotonically increasing flexural load, and a bimodal amplitude distribution. This indicated that the material responds in general terms in the manner corresponding to the well-known Hasselmann model of thermal shock of monolithic ceramics, but the presence of fibres appears to improve the thermal shock resistance by raising the predicted critical temperature somewhat.

Phase transition in, thermal history and expansion of NASICON, solid solution and lithium derivative ceramics and of SiC (mullite) fibers-NASICON composites

The thermal expansion of NASICON ceramics has been examined as a function of the composition (phosphate to silicate solid solution, sodium and lithium derivatives) and as a function of the thermal history. Results are discussed at the light of structural changes (monoclinic to rhombohedral transition, water traces, etc.). Comparison is made between monolithic ceramics and SiC and/or aluminosilicate fiber, NASICON matrix composites.

Non-radiative relaxation in Ta-doped silica fibers

We describe the properties of tantalum-doped silica fibers which have been doped with thulium and produced by a normal solution doping technique. In silica fibers, non-radiative decay almost quenches luminescence from several of the Tm levels, notably the 3 F 4 level at 800 nm, and the 3 H 4 level at 2 μm. The properties of these levels are a sensitive test of multiphonon decay rates in the host. We observe fluorescence decay components from these levels in Tm-doped tantalosilicate fibers which are significantly longer than those observed in Tm-doped germanosilicate or aluminosilicate fibers. This is interpreted as the formation of a low-vibrational-energy microenvironment around the rare earth.

Chemical interaction during the chemical vapour deposition of silicon carbide on aluminosilicate fibres from halogenated precursors

Preliminary studies on the coating of silicon carbide (β-SiC) on aluminosilicate fibres of the type Nextel by chemical vapour deposition (CVD), at atmospheric pressure, are reported. Classical CVD experiments were performed by using various precursor gases, such as silicon tetrachloride-methane-hydrogen, methyltrichlorosilane (MTS)-hydrogen and dimethyl dichlorosilane (DDS)-hydrogen mixtures. The deposition processes were studied by thermodynamic calculations. The SiC texture is dependent on the precursor used. It is shown that the best results are obtained from DDS-H2 mixture; the deposit covers the filaments, but has a columnar growth commonly found in CVD materials. The mechanical properties of the different fibres, such as tensile strength and Young's modulus, were monitored at each stage before and after every coating. The decrease of σ R is attributed to the high temperatures which modify the structure of the fibre and to attack the silicoaluminate substrate by the gas mixture with 1σSS of AlCl3, rather than the SiC coating.

The wear properties of an alumina-aluminosilicate fibre hybrid reinforced Al-Si alloy in a lubricated condition

The wear and friction behaviour of squeeze cast Al-Si alloy and hybrid composites reinforced with alumina and aluminosilicate fibre was investigated by means of a block-on-ring (bearing steel) type wear rig. Volume loss and coefficients of friction of the hybrid metal matrix composites with 12% reinforcements were measured over a load range of 200–500 N. The experimental results show that the alumina-aluminosilicate fibre ratio exhibited a marked effect on the wear resistance of the hybrid composites. If the alumina-aluminosilicate fibre ratio is above 2:3 the hybrid composites exhibit a fairly good wear resistance, especially for higher loads in the test. However, if the ratio is below 2:3 there is a sudden increase in the volume loss at the load above 300 N. That is to say, the costly alumina fibre can be partially replaced by inexpensive aluminosilicate fibre for the production of Al-Si matrix composites with excellent wear resistance. Also discovered experimently is that the coefficient of friction for the hybrid composites was higher than that of the unreinforced Al-Si alloy, and that it illustrated little variation with alumina-aluminosilicate fibre ratio.

Breakaway strength of fiber glass in the three principal directions

The article presents results of experimental investigations of strength and breaking-away failure in the three principal directions of widely used high-modulus magnesia aluminosilicate fiber and epoxy binder-based winding fiber glass under impact-wave loading at ∼10 4–105 sec deformation velocities and ∼10 6-sec duration. Maximum tensile stresses corresponding to break-away macrofailure of fiber glass along and across the reinforcing layers are determined. It is shown that, under high-speed loading conditions, strength characteristics of the fiber composite depend on the strength of its components, their quantitative relations, and orientation relative to the effective load.

Aluminosilicate fibre mats fired with alumina/silica sol binders containing 1% and 2% K 2O

Aluminosilicate fibre mats fired with alumina/silica sol binders containing 1% and 2% K 2O

Time resolved and site selective spectroscopy of thulium doped into germano- and alumino-silicate optical fibres and preforms

Optical properties of thulium ions doped in varying concentrations into germano- and alumino-silicate glass fibres and their preforms are studied. Absorption and fluorescence spectra are shown to vary little with thulium concentrations up to 12 000 ppm, but vary drastically with germanium or aluminium codopant. Resonant fluorescence studies of Tm 3+ show correlations in the movements of the Stark levels of the ground state, indicating systematic correlations between the ion site and Stark level position. An upper limit of 10 cm -1 for the homogeneous line width of thulium in alumino-silicate glass is established at 9 K. The lifetimes of the 1G 4 and 3F 4 levels are studied and are related to codopant influence and cross-relaxation which are linked to fibre drawing and Tm 3+ concentration. A significant lifetime shortening is observed on drawing preform to fibre. A model is presented for non-exponential decay of the 3F 4 level. Three- and four-level rate equations have been successfully used to simulate the observed rise of the 3F 4 fluorescence and decay of the 1D 2 fluorescence, excited resonantly and by up-conversion processes, respectively. These models yield both the excitation pump rate and cross-relaxation rates.

Photoinduced second-harmonic generation in rare-earth-doped aluminosilicate optical fibers

The presence of defect states in the band gap is an essential ingredient of recent models of photoinduced second-harmonic generation (SHG) in fibers. We have created such states by doping aluminosilicate glass fibers that do not contain Ge with Ce or Eu and observed SHG from 1.06-microm light after preparation of the fibers with 0.532- and 1.06-microm light. In an aluminosilicate fiber doped with 0.008 wt. % Ce, the SHG conversion efficiency is as high as 1.5% at infrared (1.06-microm) peak powers of 200 W.

Characterisation of frequency doubling in Eu 2+ doped aluminosilicate fibres

The results of a series of experiments on efficient second-harmonic generation in a fiber with a Eu(2+)-doped aluminosilicate core are reported. The fiber was prepared by the seeding method with CW mode-locked radiation at 1.06 micron and produced ultrastable peak conversion efficiencies of 0.001 during mode-locked readout. Experiments were performed to determine the IR preparation intensity dependence, the stability of the output, and the type of erasure mechanisms which occur. The results are compared with those of germanosilicate fibers and some similarities and differences are discussed.