Refractory Fibers Research Articles

Length-reduction method for man-made mineral fibers for biological experiments.

A simple fiber length-reduction method was developed to obtain a large amount of fiber samples with different length distributions for use in various biological experiments. This press method is only to press a raw fiber sample charged in a stainless cylinder at an adequate pressure, and is effective for man-made mineral fibers (MMMF) such as glass wool, rock wool and wool and refractory fibers (ceramic fibers, mullite fibers) and some brittle natural mineral fibers such as fibrous brucite and wollastonite. The mean fiber-length of man-made mineral fibers became shorter with the increase in the pressure applied without diameter change. We could obtain a length-reduced fiber sample with a suitable length distribution by this method. This press method is therefore a size-selective method able to produce a large amount of pulverized fiber sample depending on the press cylinder size for biological experiments. A very small amount of non-fibrous particles with aspect ratios (length vs. diameter) of under 3 was seen in the pulverized fiber samples. To eliminate such non-fibrous particles as well as too long fibers from the sample, separation by sedimentation in water was somewhat effective.

Does the skeleton of a sponge provide a defense against predatory reef fish?

Sponge tissue often contains two structural components in high concentrations: spicules of silica, and refractory fibers of protein (spongin). Some terrestrial plants contain analogous structures, siliceous inclusions and refractory lignins, that have been demonstrated to deter herbivory. We performed feeding experiments with predatory reef fish to assess the deterrent properties of the structural components of three common Caribbean demosponges, Agelas clathrodes, Ectyoplasia ferox, and Xestospongia muta. The concentrations of spicules and spongin in the tissues varied widely between the three species, but when assayed at their natural volumetric concentrations, neither spicules (all three species assayed) nor the intact spiculated spongin skeleton (A. clathrodes and X. muta assayed) deterred feeding by reef fish in aquarium or field assays using prepared foods of a nutritional quality similar to, or higher than, that of sponge tissue. Spicules deterred feeding in aquarium assays when incorporated into prepared foods of a nutritional quality lower than that of sponge tissue (15-19 times less protein), but spiculated spongin skeleton was still palatable, even in prepared foods devoid of measurable protein, and even though spicules embedded in spongin were oriented in their natural conformation. Based on comparisons of the nutritional qualities of the tissues of the three sponge species and of the prepared foods, sponge tissue would have to be much lower in food value (5 times less protein or lower) for spicules to provide an effective defense, and spicules in combination with the spongin skeleton would be unlikely to provide an effective defense regardless of the nutritional quality of the tissue. Unlike terrestrial plants, marine sponges may use silica and refractory fibers solely for structural purposes.

5456981 Process for the manufacture of a fibrous preform formed of refractory fibers for producing a composite material article

5456981 Process for the manufacture of a fibrous preform formed of refractory fibers for producing a composite material article

5480707 Toughened ceramic composite materials comprising coated refractory fibers in a ceramic matrix wherein the fibers are coated with carbon and an additional coating of ceramix material and carbon mixture

5480707 Toughened ceramic composite materials comprising coated refractory fibers in a ceramic matrix wherein the fibers are coated with carbon and an additional coating of ceramix material and carbon mixture

Theoretical and technological principles of creating lightweight refractories reinforced by fine disperse refractory fibers

Results on raising the quality of lightweight articles due to the synergetic effect of simultaneous reinforcing of interpore bridges by disperse mullite-siliceous fibers and self-compacting of compositions of different components are presented. The conditions for choosing the components for the charge are formulated. Recommendations on the dry distribution of fibers in the lightweight matrix, which unites two operations into one, are presented. The main properties and the microstructure of reinforced lightweight articles are investigated. The material obtained combines such hardly compatible properties as low density and thermal conductivity and high strength and heat resistance.

Special features of the evaluation of the pore structure of ceramic filtering materials

A linear dependence of the gas permeability on the thickness of the specimen in the interval 2 – 10 mm is determined for materials based on clay with charnotte additions, refractory and high-melting fibers with a burning-off addition, and chamotte of grade ShA, which can be used as filtering elements. The intensity of the growth of gas permeability with an increase in the thickness of the specimens depends on the type of addition. It is shown that flat specimens can be used for preliminary evaluation of the permeability of tubular pieces.

Sol/gel-based precursors for manufacturing refractory oxide fibres

Several kinds of mixed refractory oxide fibres containing the oxides of Zr, Ti, Al, Cr and Ce were produced from sol/gel precursors via a melt spinning process from 50 to 110°C. For the synthesis of precursor sols the n-propoxides of Zr and Ti were reacted with chelating agents acetylacetone, ethyleneglycole, acetic acid and hydrolysis water. The surplus of solvents was distilled off, to adjust the viscosity. The viscosity and spinnability were improved by the use of N,N-dimethylformamide (DMF) as drying control chemical additive (DCCA) and different organic polymers as plastifiers. The elements Al, Cr and Ce were added to the precursor sols as chlorides, basic chlorides or basic acetates. The precursors were spun into bundles of thin gel-fibres with minimum diameters of ca. 45 μm by extrusion though multifilament spinnerets. The gel fibres were cured in air at 105°C and converted into fine grained ceramic fibres by pyrolysis at 1450°C. The decomposition process was investigated by thermogravimetric measurements (TG/DTA) and thermomechanical analysis (TMA).

Diffusion in the nickel-rhenium system

Most Ni-based metal matrix composites (MMC) studied to date were reinforced with ductile refractory metal fibers, mostly W or W-alloys. However, Ni embrittles and weakens cold-drawn W fibers by (1) forming intermetallic phases at the fiber-matrix interface and (2) inducing recrystallization of W at temperatures as low as 950 C by rapid grain-boundary diffusion. To prevent these problems, ceramic coatings with low solubility, reactivity, and diffusion coefficients for both W and Ni can be applied at the interface. However, ceramic coatings are brittle, and typically exhibit a large mismatch of coefficient of thermal expansion with Ni; therefore, these coatings tend to crack when the composite is subjected to thermal cycling. To prevent cracking of the diffusion barrier, ductile, metallic coatings can be used. Rhenium is an attractive candidate for W fibers in a Ni matrix, since it exhibits high-temperature strength significantly higher than W, while retaining excellent ductility at all temperatures, even after recrystallization. Also, its coefficient of thermal expansion is between those of W and Ni. Diffusion in the Re-W system at the potential use temperatures of Ni-based MMC (1,200--1,500 K) is negligible due to the very high melting points of both W and Re (3,695 K and 3,459more » K, respectively). Furthermore, Re additions have been found to improve the mechanical properties of both W and Ni. Finally, the Ni-Re phase diagram shows a simple peritectic system with no intermetallic present. However, one potential drawback is the relatively high solubility of each metal in the other. The authors present an experimental investigation of diffusion phenomena in the Ni-Re system. The parameters controlling diffusion (activation energy and frequency factor) of each metal into the other are determined in order to predict long-term diffusion behavior at elevated temperatures and to assess the suitability of Re diffusion coatings for W fibers in Ni-based matrices.« less

Surface coating of mullite fibres with microporous titanium silicate (TS-1), and alumophosphate (SAPO-5)

Two types of refractory fibres, containing alumina and silica, are known: ceramic fibres and aluminabased fibres [1]. Ceramic fibres are prepared from melt refractory materials containing A1203 and SiO2 (1:1) by weight. In general they are amorphous glasses with a smooth surface. Alumina-based fibres contain over 7 2 w t % A1203. They are actually polycrystalline materials containing mullite and different crystalline modifications of alumina, the latter being dependent on the calcination temperature and silica content. Owing to the thermal and chemical stability and crystalline fine structure, the alumina base fibres are attractive objects for surface modification. Their coating with zeolites allows one to combine the properties of the separate components: fibres and zeolite. The composite material can be subjected to physico-chemical treatments without significant damage to the zeolite coating. Thus, for example, by vacuum forming with an appropriate inorganic binding substance, highly gas permeable monoliths of various shape and size with 0.20-0.35 g/cm 3 density can be prepared from these fibres. Additionally, flameless heaters are offered [2], whose basic elements are planes prepared from fibres. These fibres are modified in such a way as to yield maximum infrared radiation upon burning in natural gas. Recently, it was reported that porous titanium silicates [3] and alumophosphates [4] are suitable materials for catalyst supports in removing waste gases containing CO, NOx, and hydrocarbons. In the field of catalysis, considerable attention has been paid to the preparation of zeolite films on heat resistant materials. After surface modification of the mullite fibres with porous zeolite material, these fibres might be an appropriate catalyst carrier for catalytic removal of waste gases from stationary sources. In view of the above, the present work considers the possibility of coating mullite fibres (80% A1203, 20% SiO2) under hydrothermal conditions with a layer of titanium silicate zeolite, TS-1 and silicoaluminophosphate SAPO-5. Works are known from the literature in which, under hydrothermal conditions, zeolite A has been deposited on alumina-based fibres [5], zeolite Y on magnetic particles [6] or various metal wafers [7], and mordenite on chromium particles [8]. Mullite fibres used in the present work were

INDUSTRIAL FIBRES: A TECHNICAL AND COMMERCIAL REVIEW

Properties, costs and availabilities are reviewed for a number of raw materials in current use, or having potential use, as replacements for asbestos fibre. These include glass fibres and mineral wools; ceramic or refractory fibres; a number of minerals in fibrous or particulate form; and some specific synthetic and natural organic fibres. A tabulation shows the major product groups which may incorporate these various materials.

On the toughness and creep behavior of fiber reinforced MoSi 2 intermetallics

The strength and creep behavior of an MoSi 2/SiC matrix reinforced with continuous undirectional molybdenum fibers, coated with Al 2O 3, has been investigated. The results demonstrate that the ductility and interfacial debonding of the coated molybdenum fibers promote a high undirectional fracture resistance. In addition the molybdenum fibers substantially improve the creep resistance at 1100 °C, when the composite is again loaded parallel to the fiber direction. This work verifies the concept of using high strength, ductile, refractory fibers for the dual purpose of enhancing both fracture resistance and creep strength.

Human epidemiology: a review of fiber type and characteristics in the development of malignant and nonmalignant disease.

Consideration of the human epidemiology of diseases arising from exposure to naturally occurring and man-made mineral fibers encompasses the several forms of asbestos (chrysotile, crocidolite, amosite, anthophyllite, tremolite-actinolite), other naturally occurring silicates (talc, sepiolite, erionite, attapulgite, vermiculite, and wollastonite), and man-made mineral fibers (glass continuous filament, glass/rock/slag insulation wools, ceramic and other refractory fibers, and glass microfibers). The diseases arising from exposures to some of these fibers include pleural thickening (plaques, diffuse pleural thickening, and calcification), pulmonary fibrosis, lung cancers, mesothelioma of the pleura and peritoneum, and other cancers). Risk factors important in assessing these diseases include assessment of latency, duration of exposure, cumulative exposure, fiber origin and characteristics (length and diameter), other possible confounding occupational or environmental exposures, and smoking. Methodological issues commonly presenting problems in evaluation of these data include assessment of the adequacy of environmental exposures, particularly in regard to fiber identification, distribution, and concentration over the duration of exposure, and the adequacy of study design to detect health effects (disease frequency, latency, and cohort size). Research priorities include further assessment and standardization of pleural thickening relative to fiber exposure, uniform mesothelioma surveillance, further epidemiological assessment of certain silicate and man-made mineral fiber cohorts with emphasis given to assessment of tremolite and small diameter glass and ceramic fibers. Further assessment of possible health risks of the general public should await improved definition of relevant fiber exposure in ambient air.

Human Epidemiology: A Review of Fiber Type and Characteristics in the Development of Malignant and Nonmalignant Disease

Consideration of the human epidemiology of diseases arising from exposure to naturally occurring and man-made mineral fibers encompasses the several forms of asbestos (chrysotile, crocidolite, amosite, anthophyllite, tremolite-actinolite), other naturally occurring silicates (talc, sepiolite, erionite, attapulgite, vermiculite, and wollastonite), and man-made mineral fibers (glass continuous filament, glass/rock/slag insulation wools, ceramic and other refractory fibers, and glass microfibers). The diseases arising from exposures to some of these fibers include pleural thickening (plaques, diffuse pleural thickening, and calcification), pulmonary fibrosis, lung cancers, mesothelioma of the pleura and peritoneum, and other cancers). Risk factors important in assessing these diseases include assessment of latency, duration of exposure, cumulative exposure, fiber origin and characteristics (length and diameter), other possible confounding occupational or environmental exposures, and smoking. Methodological issues commonly presenting problems in evaluation of these data include assessment of the adequacy of environmental exposures, particularly in regard to fiber identification, distribution, and concentration over the duration of exposure, and the adequacy of study design to detect health effects (disease frequency, latency, and cohort size). Research priorities include further assessment and standardization of pleural thickening relative to fiber exposure, uniform mesothelioma surveillance, further epidemiological assessment of certain silicate and man-made mineral fiber cohorts with emphasis given to assessment of tremolite and small diameter glass and ceramic fibers. Further assessment of possible health risks of the general public should await improved definition of relevant fiber exposure in ambient air.

Carbon film coated refractory fiber cloth: Doljack, F. A., Rogers, D. Z., Rickborn, S. F. and Matlow, S. L. (Northrop Corporation, Hawthorne, CA, USA) US Pat 4 732 860 (2 February 1988)

Carbon film coated refractory fiber cloth: Doljack, F. A., Rogers, D. Z., Rickborn, S. F. and Matlow, S. L. (Northrop Corporation, Hawthorne, CA, USA) US Pat 4 732 860 (2 February 1988)

Refractory-fiber formation processes

Treating the main element of the production line of refractory fibers (namely, processing of the melt into fibers) as a set of three interrelated processes made it possible to use the methods of continuum mechanics for carrying out a theoretical study of the mechanism of fiber formation. At the given parameters characerizing the flow of the energy carrier and the physical properties of the melt, one can determine the parameters of the obtainable staple fibers. Therefore, the geometry of the flowing part of the fiber-forming device can be determined by solving the reverse problem. Practical studies showed that when designing the fiber-forming device, the error of the suggested approximation was found to be 13.7%.

Features of formation of refractory magnesium-aluminosilicate fiber

Features of formation of refractory magnesium-aluminosilicate fiber

Health-related aspects of the devitrification of aluminosilicate refractory fibres during use as a high-temperature furnace insulant.

On etudie la formation de cristobalite et de mullite dans des refractaires fibreux d'aluminosilicate dans des conditions reelles et simulees d'utilisation dans des fours, ce processus pouvant provoquer des risques de silicose

Effects of the calcium antagonist gallopamil (D600) upon excitation-contraction coupling in toe muscle fibres of the frog.

1. The effects of the Ca2+ antagonist gallopamil (D600) upon force development in short skeletal muscle fibres (m. lumbricalis digiti IV) of the frog were investigated under voltage-clamp control, using two flexible internal micro-electrodes (temperature = 6-7 degrees C). 2. In the presence of 5-100 microM-gallopamil muscle fibres developed one normal phasic contracture when they were depolarized from a holding potential of -90 to 0 mV. Subsequent depolarizations caused no mechanical response (paralysis). However, the ability to contract could be restored by hyperpolarizing the membrane to potentials between -120 and -150 mV. 3. In the absence of gallopamil, mechanical refractoriness could be fully reversed within 5-7 s by repolarizing the fibre from 0 to -120 mV. In the presence of 100 microM-gallopamil, no detectable restoration occurred within the first minute at -120 mV, and 45 to 100% of maximum force was eventually reached after 6 min of restoration. 4. The potential V at which the 'steady state' 50% of maximum force of a refractory fibre was restored shifted from -51 mV under normal conditions to -83 and -90 mV in the presence of 5 and 100 microM-gallopamil, respectively. 5. Paralysis in the presence of gallopamil and recovery from paralysis during hyperpolarization could also be observed when 2 mM-Cd2+ was applied to the external solution, i.e. when most Ca2+ channels in the T-tubular system were blocked. 6. Gallopamil shifted the threshold for activation of force to more negative potentials. Fibres developed force when they were depolarized to membrane potentials between -60 and -80 mV, whereby a fast phase of activation was followed by a slower one. Upon repolarization relaxation likewise occurred in a fast and a slow phase. 7. High concentrations of gallopamil (greater than 500 microM) caused a slowly developing contracture, independent of membrane potential (-90 or 0 mV). 8. It is proposed that gallopamil binds to a receptor at the force-controlling system in the T-tubular membrane (potential sensor) with a high affinity in the depolarized state and a lower affinity at negative potentials. Therefore association of gallopamil mainly leads to stabilization of the inactive state (paralysis) but can also stabilize the active state.

Shaped blocks of refractory fibers

The use of fiber refractories makes it possible to significantly reduce the material consumption for linings and to increase their life with a simultaneous reduction in heat losses. This paper presents monolithic burner blocks similar to those produced abroad and thermal insulation semicircular blocks for lining the production furnaces. The method of production of the shaped fibrous lining blocks is explained. An experimental lot of monolithic burner blocks and fiber lining blocks were produced from using the method. The temperature of use of the lining blocks may be increased to 1350 C by the use of aluminochromium silicate or similar fibers as the fiber component.

Highly refractory heat-insulating articles based on polycrystalline oxide fibers (Review)

The authors discuss the production of polycrystalline fibers from highly refractory oxides, mainly alumina and zirconium dioxide which are the most readily available and the cheapest materials, but highly refractory fibers may be obtained also from other oxides. The fibers are obtained in the monoand polycrystalline forms and the preparation methods for polycrystalline highly refractory fibers are described in some detail. The properties for the main types are given. An addition of small amounts of alumina, polycrystalline fibers to mullite-siliceous glass fiber has a significant influence on the reduction in the shrinkage.