Mullite Fibers Research Articles

Preparation and Properties of SiBCO Aerogel and Its Composites.

To obtain new high-temperature resistant composites that can meet the requirements of aircraft development for thermal insulation and mechanical properties, SiBCO aerogel composites were prepared by sol-gel, supercritical drying and high-temperature pyrolysis with trimethyl borate (TMB) or phenylboronic acid (PBA) as the boron source and mullite fiber as reinforcement. The structure and composition of the SiBCO aerogel and its composites were characterized with SEM, FT-IR, ICP and nitrogen adsorption tests. The specific surface area of the SiBCO aerogel is 293.22 m2/g, and the pore size is concentrated in the range of 10–150 nm. The mechanical properties, the thermal insulation properties and the temperature resistance were also studied. Due to the introduction of boron, the temperature resistance of SiBCO aerogel composites is improved greatly, and the service temperature of composites reached 1773 K. When n (TMB)/n (TEOS) = 1/1, the temperature resistance of the composites is the best. After heating in air at 1773 K for 30 min, the shrinkage of SiBCO aerogel composites is only 2.45%, and the thermal conductivity of the composites is 0.138 W/(m·K) at 1773 K. In addition, the type and amount of catalyst also have certain effects on the mechanical properties and temperature resistance of the composites.

Design and development of sulfonated tetrafunctional epoxy nanocomposites for advanced engineering applications

Attempts were made in the present study to design and develop skeletally modified ether linked tetraglycidyl epoxy resin (TGBAPSB), which is subsequently reinforced with different weight percentages of amine functionalized mullite fiber (F-MF). The F-MF was synthesized by reacting mullite fiber with 3-aminopropyltriethoxysilane (APTES) as coupling agent and the F-MF structure was confirmed by FT-IR. TGBAPSB reinforced with F-MF formulation was cured with 4,4’-diamino diphenyl methane (DDM) to obtain nanocomposite. The surface morphology of TGBAPSB-F-MF epoxy nanocomposites was investigated by XRD, SEM and AFM studies. From the study, it follows that these nanocomposite materials offer enhancement in mechanical, thermal, thermo-mechanical, dielectric properties compared to neat (TGBAPSB) epoxy matrix. Hence we recommend these nanocomposites for a possible use in advanced engineering applications that require both toughness and stiffness.

Mechanical evaluations of mullite fibrous ceramics processed by filtration and in situ pyrolysis of organic precursor

Highly porous mullite fiber-based ceramics with a three-dimensional cross structure were successfully designed and fabricated by filtration method. To address the thermal migration of silica sol, polysiloxane was introduced in the bonding system as high temperature binder to form more stable nods in the skeleton as opposed to silica sol which would migrate to the surface of fibers during the sintering process. Due to the lapped structure of mullite fibers, all products showed high porosity(74.1%∼80.9%), low density(0.554g/cm3∼0.608g/cm3) and relatively low thermal conductivity(<0.14 W/(m*K)). The reaction process of in situ porolysis and fracture mechanisms were illustrated, respectively. Besides, results showed that both sintering temperature and binder content had significant influence on the microstructure and mechanical properties of the products.

Preparation and characterization of the three-dimensional network mullite porous fibrous materials by pressure and freeze-casting method

Porous fibrous materials (PFMs) with three-dimensional networks were prepared by mullite fibers as skeleton and silica sols as binder via pressure and freeze-casting method. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) were used to investigate the microstructures, phase and porous characteristics. The density of PFMs can be controlled by adjusting the pressure and sintering during the synthetic process. With the increase of density, the mechanical and thermal conduction properties were increased due to densification of fibers. Based on their lightweight and low thermal conductivity, the PFMs can be used in the field of high temperature thermal insulation.

Thermally stable boron-containing mullite fibers derived from a monophasic mullite sol

In this work, we reported the synthesis of monophasic boron-containing mullite (MBM) fibers using basic aluminum acetate (BAA) and tetraethyl orthosilicate (TEOS) as starting materials and performed a comparative study between our newly synthesized MBM and commercial Nextel™ 312 fibers. The morphology and the tensile strength are investigated for the new MBM fibers. Continuous and uniform green fibers with a smooth surface were produced via hand drawing method. After the pyrolysis process, amorphous inorganic MBM fibers with a tensile strength of 1.18 ± 0.17 GPa were obtained. After various heat treatment processes (1000–1400 °C for 1.5 h), we found the mullite formation temperature is within the temperature range from 1050 to 1075 °C for both MBM and Nextel™ 312 fibers. However, the results show that the MBM fibers fabricated in this study have a better thermal stability than Nextel™ 312 fibers despite the fact both have the same chemical composition. The improved stability of our MBM fibers is owing to their higher Al4B2O9 formation temperature and lower Al18B4O33 decomposition rate in comparison to those of Nextel™ 312 fibers. Moreover, the newly synthesized MBM fibers have more stable microstructure and less loss in tensile strength at elevated temperatures.

Sintering Behavior and Mechanical Properties of Mullite Fibers/Hydroxyapatite Ceramic.

The effect of fiber content and sintering temperature on sintering behavior and mechanical properties of mullite fibers/hydroxyapatite composites was studied. The composites were fabricated by hydrothermal synthesis and pressureless sintering. The amount of fibers was varied from 5 wt % to 15 wt % through hydrothermal synthesis, mullite fibers and hydroxyapatite composite powders were subsequently sintered at temperatures of 1150, 1250, and 1350 °C. The composites presented a more perturbed structure by increasing fiber content. Moreover, the composites experienced pore coalescence and exhibited a dense microstructure at elevated temperature. X-ray diffraction indicated that the composites underwent various chemical reactions and generated silicate glasses. The generation of silicate glasses increased the driving force of particle rearrangement and decreased the number of pores, which promoted densification of the composites. Densification typically leads to increased hardness and bending strength. The study proposes a densification mechanism and opens new insights into the sintering properties of these materials.

Opacifier embedded and fiber reinforced alumina-based aerogel composites for ultra-high temperature thermal insulation

A novel method was developed to uniformly disperse sub-micron TiO2 opacifier into fiber reinforcements using agar and silica as binders via freeze drying. TiO2 opacifier/ fiber/ alumina-based aerogel ternary (TFA) composites with high strength and excellent high-temperature thermal insulation were successfully prepared by sol-gel route, impregnation process and supercritical fluid drying. The microstructure, mechanical and thermal insulation properties of TFA composites were investigated comprehensively. The results show that the mechanical property of TFA composites can be significantly enhanced by mullite fiber felt and the incorporation of SiO2 binder. The effect of TiO2 opacifier on the high-temperature thermal conductivity was studied by adjusting the content of TiO2 from 0 to 15 wt%. The obtained TFA composites exhibit high Young's modulus of up to 3.58 MPa and low high-temperature thermal conductivities of 0.129 W/m·K at 800 °C and 0.168 W/m·K at 1000 °C, respectively. The mechanism of heat transfer in TFA composites at high-temperature was also analyzed.

Mullite fiber cloth-reinforced mullite composite fabricated via an optimized layer-by-layer assembly method

This article reports the fabrication of fiber cloth-reinforced mullite composite via an optimized layer-by-layer (LbL) assembly method involving the infiltration and pyrolysis of fiber cloth with mullite precursor (PIP) followed by brushing matrix onto the treated fiber cloth and hot pressing. The influence of fiber content on the microstructure and mechanical properties of composite are investigated and the crack propagation is discussed to explain the toughening mechanisms. The composite with 30 vol% fiber content exhibited a high density 2.89 g/cm3, flexural strength 135.5 MPa and fracture toughness 4.13 MPa m1/2. After PIP pretreatment, the gaps existed in the fiber bundle are filled with mullite matrix which transform from mullite precursor, improving the density from 2.89 g/cm3 to 2.94 g/cm3, flexural strength from 135.5 MPa to 163.2 MPa and fracture toughness from 4.13 MPa m1/2 to 4.55 MPa m1/2. The optimized LbL assembly method realizes the creation of fiber cloth-reinforced mullite composites with high density and excellent mechanical properties.

Porous aluminum titanate‒strontium feldspar‒mullite fiber composite ceramics with enhanced pore structures and mechanical properties

This study demonstrates the pore structures and mechanical properties of porous aluminum titanate‒strontium feldspar‒mullite fiber (ASM) composite ceramics. Samples were prepared using two different processes. A traditional reactive sintering method, with Al2O3 and TiO2 as raw materials, was used to prepare one group of samples, and an improved method, using aluminum titanate (AT) clinkers, was used to prepare another group of samples. The effects of the processes and raw materials on the pore structure and mechanical properties of the composite ceramics were investigated. The properties of the sintered porous ceramics, including the microstructure, density, porosity, pore size, and mechanical properties, were analyzed. After sintered at 1400 °C, the ASM ceramics that were prepared using the improved method had a porosity level of 70% and a pore size of 24 µm, which were twice that of the traditional ASM ceramics, while both samples had identical flexural strength values of 2.27 MPa. The improved process endowed the porous ASM ceramics with excellent pore structures and mechanical properties, promoting their potential use in filter applications.

One step co-sintering process for low-cost fly ash based ceramic microfiltration membrane in oil-in-water emulsion treatment

Ceramic membranes with higher chemical stabilities and organic solvent resistances are indispensable for water purification. The fabrication of low-cost ceramic membranes (lower sintering consumption and cheaper membrane materials) facilitates practical water treatment applications. In this study, a novel process for the fabrication of a low-cost fly ash based microfiltration (MF) membrane via a co-sintering process was proposed. In the novel process, the MF layer was sprayed on a “green” fly ash support and co-sintered. The mullite fibers with excellent heat resistance and stability were proposed to alleviate the shrinkage difference in the co-sintering process, and improve the porosity and bending strength of the support. The raw material cost, energy consumption, and preparation period of the ceramic membrane could be significantly reduced. The prepared ceramic MF membrane had an average pore size of 100 nm with a high permeability of 450 Lm−2 h−1 bar−1. Moreover, it exhibited a high total organic carbon (TOC) removal efficiency (>99%) for oil-in-water (O/W) emulsion, and a high stable permeability of 165 Lm−2 h−1 bar−1 was maintained. This technique, combining low-cost materials and the co-sintering process, can serve as a cost-effective method for the production of high-performance ceramic membranes for water purification.

The formation mechanism of mullite whisker in the mullite fiber network

The formation mechanism of mullite whisker in the mullite fiber network

Mechanical and interfacial behavior of single mullite fiber and mullite fiber-based porous ceramics

The mechanical behaviors of single mullite fiber and binder/mullite fiber interface were experimentally investigated. The growth of the mullite grains of the fiber with the increasing calcination temperature greatly affected the tensile and compression strengths of the mullite fibers. As the calcination temperature went up from 1000 °C to 1500 °C, the average tensile strength decreased from 0.954 GPa to 0.191 GPa, and the Weibull modulus decreased from 5.1 to 1.8. The compressive strength was 50–60% of the average tensile strength under the same calcination temperature. The bonding strength of the binder/fiber interface increased with the increase of the calcination temperature. The mechanical properties and fracture mechanism of the mullite fiber-based porous ceramics with different binder contents were comprehensively analyzed based on the mechanical behavior of the single mullite fiber and the binder/fiber interface.

Design and development of sulfonated tetrafunctional epoxy nanocomposites for advanced engineering applications

Attempts were made in the present study to design and develop skeletally modified ether linked tetraglycidyl epoxy resin (TGBAPSB), which is subsequently reinforced with different weight percentages of amine functionalized mullite fiber (F-MF). The F-MF was synthesized by reacting mullite fiber with 3-aminopropyltriethoxysilane (APTES) as coupling agent and the F-MF structure was confirmed by FT-IR. TGBAPSB reinforced with F-MF formulation was cured with 4,4’-diamino diphenyl methane (DDM) to obtain nanocomposite. The surface morphology of TGBAPSB-F-MF epoxy nanocomposites was investigated by XRD, SEM and AFM studies. From the study, it follows that these nanocomposite materials offer enhancement in mechanical, thermal, thermo-mechanical, dielectric properties compared to neat (TGBAPSB) epoxy matrix. Hence we recommend these nanocomposites for a possible use in advanced engineering applications that require both toughness and stiffness.

Fabrication of unidirectional continuous fiber-reinforced mullite matrix composite with excellent mechanical property

This article reports the fabrication of continuous fiber reinforced mullite matrix composite via layer-by-layer assembly method, involving the coating of mullite fiber with BN coating, followed by compositing the coated fibers with mullite matrix and hot pressing. The influences of the fiber coating, fiber content and sintering temperature on the microstructure and mechanical properties of the composite are investigated. By optimizing the sintering temperature and fiber content, the damage of fiber could be avoided and the microstructure and mechanical properties could be improved. The composite containing 30 vol% fibers coated by BN layer sintered at 1300 °C exhibits 90.9% theoretical density with flexural strength value of 203.2 MPa and fracture toughness value of 4.74 MPa•m1/2. Fracture behavior is investigated to explain the toughening mechanisms. The layer-by-layer assembly method realizes the achievement of an individual architecture featuring fibers distribution and weak interfaces.

Porous fibrous ZrO2-mullite ceramics prepared via tert-butyl alcohol-based gel-casting

Mullite fiber was used to fabricate ZrO2-mullite based porous ceramic via tert-butyl alcohol (TBA)-based gel-casting process using zirconite and bauxite as raw materials. Phase compositions, microstructure, pore size distribution, linear shrinkage, bulk density, apparent porosity, thermal conductivity, and compressive strength were analyzed to investigate influences of mullite fiber content and added Y2O3 on prepared porous ceramics. Results show that bird nest-like three-dimensional fibrous reticular skeleton structure was constructed with mullite fibers that evenly enwrapped rod-like mullite and ZrO2 grains. Prepared porous fibrous ZrO2-mullite ceramics had narrow pore size distribution that consisted of mullite and m-ZrO2. With an increase in mullite fiber content, linear shrinkage and bulk density decreased, apparent porosity increased, and relatively good thermal conductivity was obtained. In addition, added Y2O3 reacted with Al2O3 and SiO2 to form Y-Al-Si-O glass phase, which promoted sintering and densification of the ceramic, thus improving its compressive strength.

A novel way to fabricate fibrous mullite ceramic using sol-gel vacuum impregnation

Inspired by bird's nest structure, fibrous mullite ceramic was fabricated by vacuum impregnation with mullite fibers as raw material and zirconia sol-gel as inorganic binder. The effect of impregnation times on the properties of the fibrous mullite ceramic, such as porosity, microstructure, compressive strength and room-temperature thermal conductivity were investigated. The results showed that low density (0.45–0.66 g/cm3), relative high compressive strength (0.62–3.34 MPa) and low thermal conductivity (0.037–0.125 W/mk) were exhibited for the sample. The toughness of fibrous mullite ceramic was enhanced due to the micro-creaks caused by transformation of zirconia. From the experimental results, it is suggested that it was an optimal method which have the potential use in high-temperature thermal insulation materials to produce fibrous mullite ceramics.

Corrosion behaviors of porous reaction-bonded silicon carbide ceramics incorporated with CaO

Reaction-bonded SiC (RBSC) porous ceramics were fabricated at 1450 °C in air by incorporating CaO using ZrO2 as sintering aids, activated carbon as pore-forming agent, and mullite fibers as reinforcing agent. The effects of CaO content on the properties of the porous RBSC ceramics were studied. Corrosion behaviors of the prepared RBSC porous ceramics in different environments were also investigated. The optimal open porosity, bending strength, average pore size and gas permeability of the ceramics with 0.5% CaO were 40%, 22.5 MPa, 42.9 µm, and 2100 m3/m2 h kPa, respectively. A well-developed neck reaction-bonded by calcium zirconium silicate (Ca3ZrSi2O9) was identified. The porous RBSC ceramics exhibited excellent corrosion resistance in acid and basic solutions. The anti-oxidation temperature of the porous RBSC ceramics could reach 1200 °C in air. The RBSC ceramics maintained the bending strength of 17.5 MPa after 60 cold-hot cycles in air (0–800 °C). The porous RBSC ceramics also exhibited relatively good corrosion resistance in molten salts (NaCl, Na2SO4 and CaCl2). Melten NaOH can aggravate the reaction by breaking the SiO2 layers on the SiC surface. Overall, these findings offer significant insights into expanding the applications porous RBSC ceramics incorporated with CaO.

Effect of glass powder on the technological properties and microstructure of clay mixture for porcelain stoneware tiles manufacture

The present study focused on the use of waste glass powder with clay mixture, for manufacturing of porcelain stoneware wall and floor tiles. The raw materials were characterized in terms of mineralogical and chemical composition. Different mixtures with various amounts of glass were prepared and fired in the temperature range of 1000–1200 °C, for 2 h. The influences of waste glass content on the technological properties (linear shrinkage, water absorption, bulk density and flexural strength) were determined. Microstructural analysis of the fired samples was carried out by X-ray diffraction and SEM. The experimental results revealed that waste glass contributes to improve physico-mechanical properties of samples up to 30 wt% of glass content at 1150 °C. The final product (R50G20C30) showed weak absorbed water value (0.4%) and higher flexural strength (39.06 MPa). Thus, according to the ISO 13006 standard, it can be classified as porcelain stoneware tile, since it satisfies the standard requirements. The addition of high amounts of glass (>30 wt%) into the ceramic bodies is undesirable due to its adverse action on the physical properties of products. Moreover, the SEM micrographs of tiles specimens fired at 1150 °C and with 30 wt% of glass showed a very compact texture and dense microstructure with a mullite fibre. As a consequence, tiles exhibited noteworthy mechanical properties.

Preparation and Characterization of Mullite-Silica Aerogel Composite Material

Silica aerogel due to the high specific surface area, nanometer level pores and low density of the micro structure, had excellent heat-insulating properties. But the characteristics of silica aerogel with low density and high voidage resulted in poor mechanical properties. In order to improve the strength of materials and meet the actual needs, in this paper the heat-insulating composite material was made from the silica aerogel and mullite fiber. This kind of composite material mainly contented of mullite fiber, formed macro block structure, that gas gel is coated and filled with mullite fiber. Furthermore, the composite material had good strength and kept excellent thermal stability at 600°C. In addition the density of composite decreased with the increasing of the gas gel content.

Ablation behavior of advanced TaSi2-based coating on carbon-bonded carbon fiber composite/ceramic insulation tile in plasma wind tunnel

Novel hybrid thermal protection material (TPM), consisting of TaSi2-based coating on carbon-bonded fiber (CBCF) composites and mullite fiber insulation tiles, is investigated using a plasma wind tunnel. Mullite fiber insulation tile is ceramically bonded to coated-CBCF composites. Results show that surface temperatures range from 400°C°C to 1200°C°C at low heat flux and dynamic pressure. However, at high heat flux and dynamic pressure, the surface temperature rapidly reaches 1400°C°C, and the damage to the TaSi2-based coating is also observed. The cold-wall temperature of the hybrid structure remains at room temperature during ablation. In addition, TPM is invalid because of the consumption of the TaSi2-based coating.