Mechanical properties and thermal stability of carbon fiber cloth reinforced sol-derived mullite composites

Abstract

For the wide application as thermal protection materials, it is very necessary for mullite ceramics to improve fracture toughness. In this paper, the laminated and stitched carbon fiber cloth preform reinforced mullite (C/mullite) composites were prepared through the route of sol impregnation and heat treatment using the Al 2 O 3 −SiO 2 sol with a high solid content as raw materials. The C/mullite composites showed a flexural strength of 228.9 MPa that was comparable to that of dense monolithic mullite although the total porosity reached 13.4%. Especially, a fracture toughness of 11.2 MPa•m 1/2 that was 4-5 times that of dense monolithic mullite was obtained. Strength deterioration due to the carbothermal reduction between carbon fiber and the residual SiO 2 in matrix was found above 1200 ℃. A pyrolytic C (PyC) coating was deposited on carbon fibers as interfacial coating. The chemical damage to carbon fibers was obviously alleviated by the sacrifice of PyC coating. Accordingly, the C/PyC/mullite composites kept strength unchanged up to 1500 ℃, and showed much higher strength retention ratio than C/mullite composites after annealing at 1600 ℃.

Phase formation, microstructure development, and mechanical properties of kaolin‐based mullite ceramics added with Fe2O3

“…Svetlana et al 37 found that, with increasing temperature, solid solubility of Fe 2 O 3 in mullite was gradually increased, and solubility of up to 7.6 wt% at 1300°C. It is also reported that Fe 3+ ions could enter the crystal lattice of mullite, forming stable solid‐solutions at high temperatures 4,12,38 …”

“…Mullite is an excellent ceramic material due to the unique properties, such as low coefficient of thermal expansion, high corrosion resistance to acid and alkali, high‐temperature creep resistance, strong thermal shock resistance, high chemical and thermal stability, high permeability, and excellent mechanical properties 1–3 . Mullite ceramics have been widely utilized as metallurgical, glass, ceramic, and other industrial refractory materials 4–6 . They are also widely used as heat‐resistant materials, such as crucibles, protective tubes, and thermocouple tubes for electronic packaging 7–9 .…”

“…[1][2][3] Mullite ceramics have been widely utilized as metallurgical, glass, ceramic, and other industrial refractory materials. [4][5][6] They are also widely used as heatresistant materials, such as crucibles, protective tubes, and thermocouple tubes for electronic packaging. [7][8][9] Other applications include window materials under harsh chemical conditions and mechanical stress at high temperatures.…”

“…It is also reported that Fe 3+ ions could enter the crystal lattice of mullite, forming stable solid-solutions at high temperatures. 4,12,38 In this work, we proposed to produce low-cost mullite ceramics from natural kaolin and effectively control the grain growth of the mullite ceramics through the doping of Fe 2 O 3 . Specifically, the effects of the content of Fe 2 O 3 and sintering temperature on phase formation and microstructure development of mullite ceramics from kaolin and Al 2 O 3 were studied in detail.…”

Effects of Composite Sintering Additives: Al(OH)3+Y2O3+CaF2 on the Performance of Porous Mullite Oxide-Bonded SiC Ceramics

“…Since mullite (3Al2O3•2SiO2) exhibits a similar thermal expansion coefficient to SiC [24], better mechanical properties, good oxidation/corrosion resistance and thermal stability [25,26], aluminium sources are introduced to react with the oxidation-derived SiO2 and form mullite phase. Aluminium source includes alumina [27][28][29], Kaolin [30], aluminium hydroxide [31,32], bauxite [33], fly ash [22,34] and aluminium isopropoxide [35].…”