Refractory Fibers Research Articles

Thermal insulation refractory materials and products (review)

A literature review of manufacturing technologies, properties, and applications of thermal insulation refractory materials and products was carried out. It was shown that thermal insulation refractory materials are relevant for modern industry and science, as they contribute to solving many problems related to improving the efficiency, safety, and ecology of various technological processes. They are a promising object of research and development, as they are constantly being adapted to different operating conditions. Various methods of porosization (swelling (foaming); evaporation or burning of the pore­forming agent; loose packing; contact monolithization; bulk monolithization; and creation of combined structures) were shown to produce lightweight insulating refractories. A separate part of the review was devoted to fiber refractory materials and products as the most modern and relevant materials. The technologies for obtaining both refractory glass fibers and polycrystalline fibers, their properties, and applications were described. Based on the literature review on the classification, manufacturing technologies, and applications of thermal insulation refractory materials and products, the main directions of further research in the field of refractory fiber thermal insulation were identified.

Praseodymium(III) Removal from Aqueous Solutions Using Living and Non-Living Arthrospira platensis Biomass

Praseodymium, the sixth-most abundant rare-earth element, is widely used in the aircraft industry for the elaboration of refractory substances, coloring materials, lighting equipment, and fiber optical cables. Living and non-living Arthrospira platensis biomass was applied for Pr(III) removal from aqueous solutions. In bioaccumulation experiments, the effect of Pr(III), introduced into the medium in a concentration range of 10–30 mg/L, on biomass productivity, biochemical composition, and antioxidant activity was assessed. The biomass showed high accumulation capacity (more than 99%) toward Pr(III). Supplementation of the cultivation medium with Pr(III) led to a decrease in carbohydrate and lipid content, but it did not significantly influence biomass productivity or the content of proteins and pigments. In experiments with non-living biomass, the effect of pH, Pr(III) concentration, temperature, and contact time on the efficiency of metal removal was investigated. The maximum uptake of Pr(III) was achieved at pH 3.0 after 3.0 min of interaction. The equilibrium data were explained using the Langmuir and Freundlich models, while the kinetics of the process was described by applying pseudo-first-order, pseudo-second-order, and Elovich models. The maximum sorption capacity of Arthrospira platensis biomass calculated from the Langmuir model was 99.3 mg/g. According to the thermodynamic calculations, the process of Pr(III) removal was spontaneous and exothermic in nature. The obtained data can be used for the development of environmentally-friendly technology for Pr(III) recovery from wastewater as well as to understand the effect of Pr(III) on aquatic organisms.

Novel low temperature derived Wf/W–ZrC–Cu composites by reactive infiltration with enhanced mechanical and thermal physical properties

Wf/W–ZrC–Cu composites with densities over 95% have been prepared by infiltrating Zr–Cu binary molten alloys into porous Wf/W + WC preforms at 1200−1400 °C. The hybrid strengthening of in-situ formed ZrC particles, and the addition of continuous Wf have made the composites improved flexure strength and fracture toughness of 612 MPa and 10.41 MPa m1/2, respectively. The residual Cu provided a moderate interface between Wf and W–ZrC matrix, which was beneficial to improved fracture energy of 2–3·103 J m−2 and thermal conductivity of over 80 W (m K)−1. The Wf impeded cracks and new surfaces to the ultra-high temperature air plasma torch. The composites thus possess superior thermal shock resistance, and the linear and mass ablation rates reduced to 0.40 mm s−1 and 0.0112 g s−1, respectively. This study provides a novel approach for the fabrication of refractory fiber reinforced refractory metal/carbide based composites with excellent comprehensive properties at relatively low temperatures.

(Digital Presentation) Creation of Composite Materials “Refractory Metal Carbide – Carbon Fiber” in Molten Salts and Study Their Electrical Double Layer in Hydrogen Peroxide and Sodium Sulfate Solutions

NbC/C, TaC/C, and Mo2C/C composites were synthesized by the electrochemical method of currentless transfer in molten salts containing compounds of these refractory metals. The electrical double layer formed in solutions of sodium sulfate Na2SO4 and hydrogen peroxide H2O2 on the composite material "refractory metal carbide-carbon fiber" has been studied by electrochemical impedance spectroscopy.

The Influence of CaO and MgO on the Mechanical Properties of Alkali-Activated Blast Furnace Slag Powder.

CaO and MgO are both reported as effective activators for blast furnace slag. However, the synergistic effect of these two components on the mechanical properties of alkali-activated blast furnace slag remains unclear. In this study, the flexural and compressive strengths of alkali-activated blast furnace slag powder with MgO and CaO range from 0% to 30% by the mass ratio of alkali-activated blast furnace slag powder are investigated. Moreover, the dry shrinkage rate of alkali-activated blast furnace slag powder is measured. One percent refractory fibers by volume of binder materials are added in the alkali-activated blast furnace slag. Some refractory fibers are treated with water flushing, meanwhile, some refractory fibers are directly used without any treatment. Finally, the scanning electron microscope, the thermogravimetric analysis curves and the XRD diffraction spectrums are obtained to reflect the inner mechanism of the alkali-activated blast furnace slag powder’s mechanical properties. The water-binder ratios of the alkali-activated blast furnace slag powder are 0.35 and 0.42. The curing ages are 3 d, 7 d and 28 d. The measuring temperature for the specimens ranges from 20 °C to 800 °C. Results show that the flexural and compressive strengths increase with the increased curing age, the decreased water-binder ratio and the addition of refractory fibers. The water-treated refractory fibers can improve the mechanical strengths. The mechanical strengths increase in the form of a quadratic function with the mass ratio of MgO and CaO, when the curing age is 3 d, the increasing effect is the most obvious. A higher water-binder ratio leads to an increasing the drying shrinkage rate. The activated blast furnace slag powder with CaO shows a higher drying shrinkage rate. The mechanical strengths decrease with the increasing testing temperature.

Internal Defects of Multifilament Threads Made of Oxide Refractory Fibers

Internal Defects of Multifilament Threads Made of Oxide Refractory Fibers

ОПРЕДЕЛЕНИЕ ТЕПЛОПРОВОДНОСТИ ТЕПЛОЗАЩИТНОГО МАТЕРИАЛА НА ОСНОВЕ ВОЛОКОН ОКСИДА КРЕМНИЯ

Describes a mathematical model for processing the results of measurements of thermal conductivity of highly porous fibrous materials of thermal protection. The results and some methodological features of measuring the thermal conductivity of rigid thermal insulation based on refractory oxide fibers are presented. The possibility of measurements taking into account the anisotropy of properties is investigated. The stiffness of the thermal insulation at the fiber contacts is provided by the binder. Thermal conductivity was measured by the stationary method on cylindrical samples in a wide temperature range from 20 to 1700 °C in various gaseous media.

High-temperature heat-shielding, ceramic and ceramic-metal composite materials for new-generation aviation equipment

This paper describes achievements of the All-Russian Scientific Research Institute of Aviation Materials in the field of creating high-temperature heat-shielding, ceramic and metal-ceramic composite materials. The advantages and prospects of applying the developed materials in the manufacturing of structural elements of aircraft and friction joints are discussed. The synthesis features and basic properties of metal-ceramic composite materials based on light alloys, refractory metal matrices, ceramic composite materials for use in heavily loaded structural elements of modern aircraft are presented. The main achievements in the field of heat-shielding materials based on refractory oxide fibres are presented, along with their properties and application in new-generation aircrafts.

Improved Sublimation Resistance of Skutterudites by Silane Modified Ceramic-Based Coating

The organic/inorganic hybrid sol was prepared by hydrolysis polymerization of methyl-triethoxysilane (MTES) with acidic silica sol. Zirconium silicate, zircon sand and refractory fiber were respectively added to the hybrid sol to increase the stability of the coating in high temperature service. P-type skutterudite(SKD) protective coating obtained by multi-layer coating and certain pretreatment. Protective effect was studied by observing the diffusion of antimony from the SKD into the coating. The results show that the coating has the advantages of simple process and high strength and high stability after aging. The sublimation of antimony is suppressed and it is expected to be applied to the protection of SKD in vacuum.

Organoelementoxanealumoxanes — precursors of ceramic fibers of oxide composition

Researches of ICTOEC have developed efficient methods for the synthesis of ceramic-forming organoelementoxanealumoxane oligomers with fibre-forming properties which are promising precursors of refractory oxide fibers: α-Al2O3 modified by Y and Mg oxides, spinel MgAl2O4, garnet Y3Al5O12) as well as blend composition fibers MgAl2O4+Y3Al5O12 to produce conceptually new high-temperature ceramic composites for structural purposes.

Novel ceramic matrix composites with tungsten and molybdenum fiber reinforcement

Ceramic matrix composites usually utilize carbon or ceramic fibers as reinforcements. However, such fibers often expose a low ductility during failure. In this work, we follow the idea of a reinforcement concept of a ceramic matrix reinforced by refractory metal fibers to reach pseudo ductile behavior during failure. Tungsten and molybdenum fibers were chosen as reinforcement in SiCN ceramic matrix composites manufactured by polymer infiltration and pyrolysis process. The composites were investigated with respect to microstructure, flexural- and tensile strength. The single fiber strengths for both tungsten and molybdenum were investigated and compared to the strength of the composites. Tensile strengths of 206 and 156 MPa as well as bending strengths of 427 and 312 MPa were achieved for W/SiCN and Mo/SiCN composites, respectively. The W fiber became brittle across the entire cross section, while the Mo fiber showed a superficial, brittle reaction zone but kept ductile on the inside.

Cyclic plastic behavior of unidirectional SiC fibre-reinforced copper composites under uniaxial loads: An experimental and computational study

Silicon carbide continuous fiber-reinforced copper matrix composites (Cu/SiCf) offer huge potential as heat sink material for high-heat-flux applications at elevated temperatures (>300 °C) owing to the beneficial combination of strong, stiff and refractory SiC fibers with a highly conductive and ductile copper matrix. As high-heat-flux components are normally subjected to large temperature fluctuations combined with thermal strain variations, degradation of the Cu/SiCf composites caused by fatigue damages under cyclic loads may affect the structural integrity of the component. In this study, the robustness of the Cu/SiCf composites under cyclic loads at different temperatures was evaluated by means of uniaxial cyclic loading tests. The stability of the cyclic deformation hysteresis curves was used as a measure of material’s durability. The experimentally observed global deformation behavior was interpreted with the help of a micromechanics-based theoretical model. It was shown that the Mori-Tanaka type mean field theory could describe the cyclic loading behavior of the composite quite well with a good fitting quality between the measured and simulated saturated cyclic curves. The effects of fiber content, applied strain range and test temperature are discussed.

Glass formation and short-range order structures in the BaS + La2S3 + GeS2 system

Infrared (IR) optical materials have enabled a broad range of optical sensing and measurement applications in the mid-wave and long-wave IR. Many IR transmitting glasses are based on covalently-bonded selenides and tellurides, such as As2Se3 and GeTe2, which typically have relatively low glass transition temperatures (Tg) on the order of 200 to 350 °C. Many applications have working temperatures above the Tg of these materials, which compels the development of new IR materials. This work studies the underlying short-range order (SRO) structure and glass formability of a new family of ionically-bonded sulfide glasses, xBaS + yLa2S3 + (1 − x − y)GeS2, to develop high Tg optical materials with a broad IR transmission range. These sulfide glasses were produced by melting sulfide materials inside evacuated and sealed carbon-coated silica ampoules at 1150 °C for 12 h and quenching to room temperature to form glass. Glass samples were then characterized by IR and Raman spectroscopies and differential thermal analysis (DTA). It was found that by increasing the modifier concentration, the predominantly Ge4 SRO units, the superscript defines the number of bridging sulfur (BS) ions in the tetrahedral network found in GeS2 glasses, are ultimately converted to Ge0 units at >40 mol% network modifier content through the generation of non-bridging sulfur (NBS) ions. These molecular ionic units still form a glassy network, with some of the highest reported Tg values to date for a pure sulfide glass. This suggests that this composition has strong ionic bonds between negatively-charged tetrahedral SRO units and the positively-charged modifier cations. While the glass network is depolymerized in the high modifier content glasses though the formation of a high concentration of molecular ionic Ge0 SRO groups, they are, nevertheless, homogeneous glassy materials that exhibit the largest Tg and ΔT (difference between crystallization temperature, Tc, and Tg) values of glasses in this system, making them the optimal glasses for high Tg IR optical components, including, potentially, refractory IR optical fibers.

Occupational exposure during handling and loading of halloysite nanotubes – A case study of counting nanofibers

Halloysite nanotubes (HNTs) are abundant naturally-occurring hollow aluminosilicate clay mineral fibers with a typical diameter < 100 nm and an aspect ratio of up to 200. Here we assessed the potential inhalation exposure to HNTs in an industrial research laboratory. Inside a fume hood, ten times 100 g of HNTs were poured at rate of 0.5 kg min−1, which increased concentrations from the background level up to 2900 cm−3 and 6.4 μm2 cm−3. Inside the fume hood, the respirable mass concentration was 143 μg m−3 including background particles. Outside the fume hood we did not measure elevated concentrations. We classified 1895 particles according to their length and aspect ratio. Five particles were in aspect ratio > 3 and in length > 2 μm. These particles were agglomerated and/or aggregated particles where the longest individual fiber was 2 μm in length. The occupational exposure limits for refractory mineral fibers vary from 0.1 to 2 fibers cm−3. Following standard protocols for fiber analysis, detection of 0.1 fibers cm−3 would require analysis on 4 × 104 images when the filter loading is good. Thus, the fiber sampling and quantification procedures needs to be improved significantly if nanofibers <100 nm in diameter are included in regulatory exposure assessment. Due to very limited toxicological information of HNTs we recommend avoiding inhalation exposure.

Lytic xylan oxidases from wood-decay fungi unlock biomass degradation.

Wood biomass is the most abundant feedstock envisioned for the development of modern biorefineries. However, the cost-effective conversion of this form of biomass into commodity products is limited by its resistance to enzymatic degradation. Here we describe a new family of fungal lytic polysaccharide monooxygenases (LPMOs) prevalent among white-rot and brown-rot basidiomycetes that is active on xylans-a recalcitrant polysaccharide abundant in wood biomass. Two AA14 LPMO members from the white-rot fungus Pycnoporus coccineus substantially increase the efficiency of wood saccharification through oxidative cleavage of highly refractory xylan-coated cellulose fibers. The discovery of this unique enzyme activity advances our knowledge on the degradation of woody biomass in nature and offers an innovative solution for improving enzyme cocktails for biorefinery applications.

Lightweight Preheating Stands and Lids Used in Steelwork Trinec

In a wide range of metallurgical operations, steel casting or filling ladles and tundishes must be dried or preheated. Many types of preheating and covering lids are used in these processes. Technological facilities of this type are used in the Trinec melt shops for production and processing of steel. Refractory castables, dense or lightweight refractory bricks, or refractory fibre module systems can be used to line various types of lids. The article focuses on the particular advantages of fibre module systems applied in the construction of these types of linings. Fibre ensures low weight, easy maintenance and satisfactory service lifetime, which enables streamlined usage under busy steel production conditions. Indeed, fibre can be envisioned as a solution for an even larger range of lining systems.

Thermal conductivity of refractory glass fibres

In the present study, the current international standards and corresponding apparatus for measuring the thermal conductivity of refractory glass fibre products have been reviewed. Refractory glass fibres are normally produced in the form of low-density needled mats. A major issue with thermal conductivity measurements of these materials is lack of reproducibility in the test results due to transformation of the test material during the test. Also needled mats are inherently inhomogeneous, and this poses additional problems. To be able to compare the various methods of thermal conductivity measurement, a refractory reference material was designed which is capable of withstanding maximum test temperatures (1673 K) with minimum transformation. The thermal conductivity of this reference material was then measured using various methods according to the different standards surveyed. In order to compare different materials, samples have been acquired from major refractory glass fibre manufacturers and the results have been compared against the newly introduced reference material. Materials manufactured by melt spinning, melt blowing and sol–gel have been studied, and results compared with literature values.

Use of rumen–reticulum fill to examine nutrient transfer and factors influencing food intake in white-tailed deer (Odocoileusvirginianus)

Estimating relationships of gut fill in mammalian herbivores is useful to understanding digestive functions. Large animals might have more fluid in the gut to facilitate nutrient transfer between the gut lumen and the gut wall. Furthermore, relationships between concentrations of dietary refractory and indigestible fiber (CRIF) and gut fill might indicate whether chemostatic factors or physical distension of the gut affects food intake. We collected white-tailed deer (Odocoileus virginianus (Zimmermann, 1780); 122 males, 152 females) from three sites in central and south Texas that varied in diet quality as indexed by rumen–reticulum crude protein concentrations. Large animals did not have more fluid in their rumina–reticula than small animals because the scalar between body mass and wet mass of rumen–reticulum contents was not greater than the scalar estimated for dry mass of rumen–reticulum contents. We expected a positive or an inverse relationship when rates of forage comminution, digestion, and particle passage were high or low, respectively. At the site where deer had access to a high-quality pelleted diet, we detected a positive relationship between CRIF and dry mass. At sites with free-ranging deer and lower quality diets, relationships between CRIF and dry fill were inversely related. Food intake of deer was probably influenced by chemostatic factors at the site with a high-quality pelleted diet and by physical distension of the gut at the other two sites.

Simultaneous organic carbon and nitrogen removal from refractory petrochemical dry-spun acrylic fiber wastewater by hybrid A/O-MBR process

To improve the efficiency of the existing plant for refractory petrochemical dry-spun acrylic fiber (DAF) wastewater treatment, a pilot-scale hybrid anoxic/oxic-membrane bioreactor (A/O-MBR) system with multi-cell section was designed and tested. The operation parameters, alkalinity and carbon source demands in nitrification/denitrification and removal performance of typical pollutants were investigated, and the results were compared with those from the existing wastewater treatment plant (WWTP) of DAF factory. It showed that at hydraulic retention time >32 h, recycle ratio of 80 % and pH 7.2–7.8 in nitrification stage, the average removal efficiency of COD, NH4 +–N and TN in the hybrid A/O-MBR could reach 56.5, 86.6 and 45.9 %, respectively, which had been significantly higher than those of the existing WWTP. The deficiency of alkalinities and carbon sources hindered further nitrogen removal; therefore, Na2CO3 and NaAc were supplemented to improve the performance of nitrification and denitrification, and the recycle ratio was optimized from 80 to 200 %. Then, under the conditions of 200 % recycle ratio, 97.8–148.5 mg/L of alkalinity addition to oxic tank and 107.4–149.6 mg/L of carbon source addition to anoxic tank, the nitrification and denitrification performance in the hybrid A/O-MBR was clearly enhanced, and the NH4 +–N and TN removal efficiency could be improved from 64.3 and 45.9 to 86.9 and 60.5 %, respectively. Meanwhile, the removal efficiency of typical pollutants SO3 2−, CN−, AN, DMF, BOD and TOC reached 99.3, 91.3, 100, 100, 92.5 and 53.5 %, respectively. Compared with the existing WWPT, the tested hybrid A/O-MBR process had a better treatment performance for nitrification and denitrification, and the effluent could meet the Grade I requirements of the National Discharge Standard of Acrylic Fiber Industry.

Experimental Analysis of Hydrothermal Curing Influence on Properties of Fiber-Cement Composite

Special industrial application of fiber-cement composites is currently one important issue of concrete industry and research activity. The field of refractory and high-temperature resistance materials is very large and contains the cement composites too. Hydrothermal curing together with using aluminous cement with refractory basalt aggregates and fibers shows high potential for its applications in high temperature. These composite is characterized by compressive strength over 140 MPa and tensile strength in bending 12 MPa (investigated on specimens 40 x 40 x 160 mm). After exposure to temperature 1000 °C these parameters are 60 MPa in compression respective 6 MPa in bending. Achieved values are significantly higher than in the case of laboratory curing condition and there are suitable especially for prefabricated fire resistance cladding or other special application in the industry.