High Temperature Ceramic Composites Research Articles

Robust, thermally insulating, and high-temperature resistant phosphate-enhanced mullite fiber porous ceramic composites

Porous mullite ceramics with high porosity and low thermal conductivity are urgently required as high-temperature thermal insulators in harsh environments. How to improve the strength of Porous mullite ceramics dramatically under the premise of no sacrificing its thermal insulating properties has remained an extremely challenging. Inspired by the freezing rain phenomenon in nature, high-strength and high-temperature resistant phosphate coatings were applied to the surface of mullite fibers, which significantly improved the mechanical properties of porous mullite ceramics without significantly increasing their thermal conductivity. The Al(H2PO4)3 solution concentration significantly affected the mechanical and thermal properties of the composite material, where the mechanical performance improved with an increasing Al(H2PO4)3 solution concentration. The phosphate coating phase stabilized with an increasing calcination temperature. The mechanical properties of the ceramics were improved by the excellent interfacial bonding strength between the coating and mullite fiber, and the forms of phosphate in the porous ceramics. The optimum composite preparation process increased its compressive strength by approximately nine-fold to 4.1 MPa and resulted in a thermal conductivity of only approximately 0.09 W/(m·K), demonstrating that the composite exhibited a significantly higher comprehensive performance than other previously reported porous ceramics and aerogels. Such new composites with excellent mechanical and thermal insulation properties exhibit excellent potential for high-strength thermal insulation in the chemical, metallurgical, pharmaceutical, aerospace, and other fields.

Heterogeneous solid solutioning in carbon nanotube reinforced HfB2-ZrB2-SiC ultra high temperature ceramic composites

Heterogeneous solid solutioning in carbon nanotube reinforced HfB2-ZrB2-SiC ultra high temperature ceramic composites

Ultrafast deposition of polydopamine for high-performance fiber-reinforced high-temperature ceramic composites

The low deposition time efficiency and small thickness limit the expansion of polydopamine (PDA) application to fiber-reinforced high-temperature ceramic composites. In this work, the electric field-assisted polymerization (EFAP) route was developed to improve the deposition time efficiency of PDA coating and overcome the thickness limitation. Carbonized polydopamine (C-PDA) coating was used as the interphase of carbon fiber-reinforced ZrB2-based composites (Cf/ZrB2-based composite) to bond rigid fibers and brittle ceramics, where C-PDA coating was prepared by the carbonization of PDA coating. Firstly, uniform and dense PDA coatings were deposited on carbon fibers (Cf) by EFAP. The thickness of PDA coating reached the micron level (over 1800 nm) for the first time. Benefiting from the EFAP route promoting the oxidation process of dopamine (DA) and accelerating the aggregation and in-situ polymerization of DA and its derivatives on the surface of Cf, the deposition rate of PDA coating reached 5589 nm/h, which was 3 orders of magnitude higher than that of the traditional self-polymerization process. By adjusting the EFAP parameters (e.g. DA-concentration, current, and deposition time), the thickness of PDA coating could be conveniently designed from nano-scale to micro-scale. Then, PDA coating was pyrolyzed to obtain C-PDA coating. C-PDA coating was well bonded on Cf without visible cross-sticking among neighboring fibers. C-PDA coating presented a layered structure and the thickness of C-PDA coating could be designed by controlling the thickness of PDA. C-PDA coating was used as the interfacial phase of the Cf/ZrB2-based composite, which ensured that the composite possessed good load-bearing capacity and thermal stability. Moreover, extraordinary damage resistance of the composite was achieved, with work of fracture up to 9936 ± 548 J/m2 at room temperature and 19,082 ± 3458 J/m2 at 1800 °C. The current work provides a high time efficiency processing route for depositing PDA coating on carbon fibers and demonstrates the attractive potential of PDA coating in fiber-reinforced high-temperature ceramic composites.

Densification and Characterization of Pressureless Sintered ZrB2-20 Vol% MoSi2 Ultra High Temperature Ceramic Composites

Densification and Characterization of Pressureless Sintered ZrB2-20 Vol% MoSi2 Ultra High Temperature Ceramic Composites

Processing and characterization of carbon fibres reinforced ZrB2 ultra high temperature ceramic matrix composite

A process technology for the processing of the continuous carbon fibre reinforced ZrB2 (Cf – ZrB2) ultra high temperature ceramic matrix composite (UHTCMC) has been developed. The processing steps are slurry infiltration followed by curing and pyrolysis. The composite was then subjected to high temperature pressureless sintering. The microstrcutural and mechanical properties of Cf – ZrB2 UHTCMC were characterized at the completion of each processing step. The de-lamination between the carbon fibre and the ZrB2 matrix layer in 2D Cf – ZrB2 composite after pressureless sintering was found. However, the problem of de-lamination after sintering was not detected in the 2.5D Cf – ZrB2 composite by stitching the infiltrated layers in the Z-direction. Significant improvements in the sintered density, Young's modulus and flexural strength were achieved through 2.5D Cf – ZrB2 composite.

Metallocarbosilanes and elementoxanealuminoxanes as precursors of components of nanostructured ceramic composites

Methods for the synthesis of ceramic-forming organoelement poly(oligo)mers, metallocarbosilanes and organoelement oxanealuminoxanes, as precursors of components (matrices, coatings, fibers, etc.) for the development of high-temperature, high-strength, and oxidation-resistant nanostructured carbide and oxide ceramic composites are presented.

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.

Wide-Band Tunable Microwave-Absorbing Ceramic Composites Made of Polymer-Derived SiOC Ceramic and in Situ Partially Surface-Oxidized Ultra-High-Temperature Ceramics.

Microwave-absorbing materials in a high-temperature harsh environment are highly desired for electronics and aerospace applications. This study reports a novel high-temperature microwave-absorbing ceramic composites made of polymer-derived SiOC ceramic and in situ partially surface-oxidized ultra-high-temperature ceramic (UHTC) ZrB2 nanoparticles. The fabricated composites with a normalized weight fraction of ZrB2 nanoparticles at 40% has a significantly wide microwave absorption bandwidth of 13.5 GHz (26.5-40 GHz) covering the entire Ka-band. This is attributed to the extensive nanointerfaces introduced in the composites, attenuation induced by the interference of electromagnetic wave, attenuation from the formed current loops, and the electronic conduction loss provided by the partially surface-oxidized ZrB2 nanoparticles. The minimum reflection coefficient (RC) was -29.30 dB at 29.47 GHz for a thickness of 1.26 mm for the composites with a normalized weight fraction of ZrB2 nanoparticles at 32.5%. The direct current (dc) conductivity of the nanocomposites showed a clear percolation phenomenon as the normalized weight fraction of ZrB2 nanoparticles increases to 30.49%. The results provide new insights in designing microwave-absorbing materials with a wide absorption frequency range and strong absorption loss for high-temperature harsh environment applications.

Nanometallocarbosilanes and organoelementoxanes as precursors of components of promising ceramic composites

Nanometallocarbosilanes and organoelementoxanes represent a new class of unequaled precursors of components of promising ceramic composites. Ceramic-forming polymers (oligomers) have been synthesized in GNIICHTEOS. They can be used to obtain components of carbide and oxide CCM: nanometallocarbosilanes - precursors of SiC ceramics, modified by mixed carbides (TaxZryCz or TaxHfyCz). Organoelementoxane oligomers represent a new class of precursors for components (binders; coatings; fibers, etc.) of corundum (α-Al2O3), aluminosilicate (xAl2O3·ySiO2), yttrium aluminum (xY2O3·yAl2O3), yttrium-aluminosilicate (xY2O3·yAl2O3·zSiO2), magnesium aluminum (xMgO·yAl2O3). yttrium-aluminum-magnesium (xY2O3·yAl2O3·zMgO) and high-temperature binary ceramics based on aluminum and yttrium oxides modified by oxides of refractory metals (zirconium, hafnium or chromium) compositions for the preparing high-strength high-temperature and oxidative-resistant ceramic composites.

Characterization of AlN-based Ceramic Composites for Use as Millimeter Wave Susceptor Materials at High Temperature: High Temperature Thermal Properties of AlN:Mo with 0.25% to 4.0% Mo by Volume

In order to begin to evaluate and model the suitability of high temperature ceramic composites, such as AlN:Mo, as susceptor materials for power beaming applications, the electromagnetic, thermal, and mechanical properties of the material must be known at elevated temperatures. Work reported here focuses on the development of thermal property datasets for AlN:Mo composites ranging from 0.25% to 4.0% Mo by volume. To calculate thermal conductivity of the AlN:Mo composite series, specific heat capacity, thermal diffusivity, and density data were acquired. The calculated specific heat capacity, Cp, of the set of AlN:Mo composites was, on average, found to be approximately 803 J/kgK at 100 °C and to increase to approximately 1133 J/kgK at 1000 °C, with all values to be within +/- 32 J/kgK of the average at a given temperature. These calculated specific heat capacity values matched values derived from DSC measurements to within the expected error of the measurements. Measured thermal diffusivity, α, of the set of AlN:Mo composites was, on average, found to be approximately 3.93 × 10-1 cm2/s at 100 °C and to increase to approximately 9.80 × 10-2 cm2/s at 1000 °C, with all values within +/- 1.84 × 10-2 cm2/s of the average at a given temperature. Thermal conductivity, k, for the set of AlN:Mo composites was found to be approximately 108 W/mK at 100 °C and to decrease to approximately 38 W/mK at 1000 °C, with all values within +/- 5.3 W/mK of the average at a given temperature. Data trends show that increasing Mo content correlates to lower values of of Cp, α, and k at a given temperature.

ANFIS based model to forecast the Wire-EDM parameters for machining an Ultra High Temperature Ceramic composite

In this work, a ZrB2 based ceramic composites with 25 wt. % B4C sintered in spark plasma sintering furnace at 2000°C for 10 min under 50 MPa pressure has been machined with Wire electrical discharge machine (WEDM) and can readily be cut to intricate shapes to meet the requirements of industry. The adaptive neuro fuzzy inference systems (ANFIS) has been used to generate mapping relation between input parameters and output responses. ANFIS is a neuro fuzzy technique where the fusion is made between the neural network and the fuzzy inference system. Also the ANFIS models have been tested by a confirmative test and the results shows minimum root mean square error (RMSE) as 0.0416 for kerf width and 0.9605 for machining speed. This verification indicates that ANFIS modeling can be used to forecast the responses.

Large scale synthesis of α-Si3N4 nanowires through a kinetically favored chemical vapour deposition process

Understanding the kinetic barrier and driving force for crystal nucleation and growth is decisive for the synthesis of nanowires with controllable yield and morphology. In this research, we developed an effective reaction system to synthesize very large scale α-Si3N4 nanowires (hundreds of milligrams) and carried out a comparative study to characterize the kinetic influence of gas precursor supersaturation and liquid metal catalyst. The phase composition, morphology, microstructure and photoluminescence properties of the as-synthesized products were characterized by X-ray diffraction, fourier-transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and room temperature photoluminescence measurement. The yield of the products not only relates to the reaction temperature (thermodynamic condition) but also to the distribution of gas precursors (kinetic condition). As revealed in this research, by controlling the gas diffusion process, the yield of the nanowire products could be greatly improved. The experimental results indicate that the supersaturation is the dominant factor in the as-designed system rather than the catalyst. With excellent non-flammability and high thermal stability, the large scale α-Si3N4 products would have potential applications to the improvement of strength of high temperature ceramic composites. The photoluminescence spectrum of the α-Si3N4 shows a blue shift which could be valued for future applications in blue-green emitting devices. There is no doubt that the large scale products are the base of these applications.

Temperature dependence of elastic properties of ZrB2–SiC composites

Elastic properties (Young׳s modulus, shear modulus, and Poisson׳s ratio) of ZrB2, SiC ceramics and ZrB2–SiC ultra high temperature ceramic composites were measured by the Impulse Excitation technique in the RT–1173K temperature range. Two compositions of ZrB2 with 17vol% and 32vol% of SiC strengthening phase were hot pressed to almost full density, followed by machining before the measurements took place. The temperature dependences of elastic properties have shown the expected softening behavior, where only small 4% and 5% linear reduction in Young׳s and shear moduli were detected, respectively, for ZrB2–17vol% SiC and ZrB2–32vol% SiC ceramic composites. The reported decrease in elastic moduli brings the respective linear increase of Poisson׳s ratio up to ~9% in the temperature of interest. Such high temperature behavior corresponds well to the upper and lower bounds of elastic moduli of two ZrB2–SiC ceramic composites calculated by Voigt and Reuss estimations using properties of pure ZrB2 and pure SiC ceramics, as published in the literature.

Gas tungsten arc welding of ZrB2–SiC based ultra high temperature ceramic composites

Abstract The difficulty in fabricating the large size or complex shape limits the application of ZrB 2 –SiC composites. Joining them by fusion welding without or with preheating, controlled cooling under protective gas shield leads to thermal shock failure or porosity at the weld interface. In the present work, a filler material of (ZrB 2 –SiC–B 4 C–YAG) composite with oxidation resistance and thermal shock resistance was produced in the form of welding wire. Using the filler, gas tungsten arc welding (GTAW) was performed without employing preheating, post controlled cooling and extraneous protective gas shield to join hot pressed ZrB 2 –SiC (ZS), and pressureless sintered ZrB 2 –SiC–B 4 C–YAG (ZSBY) composites to themselves. The fusion welding resulted in cracking and non-uniform joining without any filler material. The weld interfaces of the composites were very clean and coherent. The Vickers micro-hardness across the weld interface was found to increase due to the increase in the volume % of both SiC and B 4 C in the filler material. The shear strength of the weld was about 50% of the flextural strength of the parent composite.

Highly flexible, nonflammable and free-standing SiC nanowire paper.

Flexible paper-like semiconductor nanowire materials are expected to meet the criteria for some emerging applications, such as components of flexible solar cells, electrical batteries, supercapacitors, nanocomposites, bendable or wearable electronic or optoelectronic components, and so on. As a new generation of wide-bandgap semiconductors and reinforcements in composites, SiC nanowires have advantages in power electronic applications and nanofiber reinforced ceramic composites. Herein, free-standing SiC nanowire paper consisting of ultralong single-crystalline SiC nanowires was prepared through a facile vacuum filtration approach. The ultralong SiC nanowires were synthesized by a sol-gel and carbothermal reduction method. The flexible paper composed of SiC nanowires is ∼100 nm in width and up to several hundreds of micrometers in length. The nanowires are intertwisted with each other to form a three-dimensional network-like structure. SiC nanowire paper exhibits high flexibility and strong mechanical stability. The refractory performance and thermal stability of SiC nanowire paper were also investigated. The paper not only exhibits excellent nonflammability in fire, but also remains well preserved without visible damage when it is heated in an electric oven at a high temperature (1000 °C) for 3 h. With its high flexibility, excellent nonflammability, and high thermal stability, the free-standing SiC nanowire paper may have the potential to improve the ablation resistance of high temperature ceramic composites.

High temperature fracture behavior of ZrB2–SiC–graphite composite in vacuum and air

Hot pressed ZrB2–SiC–graphite ultra high temperature ceramic composites were prepared for the fracture toughness tests in vacuum up to 1800°C and in air up to 1300°C. Measured results show that a brittle–ductile transition temperature of ZrB2–SiC–graphite composite is deduced to be 1300°C, and ZrB2–SiC–graphite composite exhibits a linear behavior below 1300°C. Fracture toughness in vacuum linearly decreases with the increase of temperature below 1300°C, increases from 1300°C to 1600°C, and has a rapid reduction at 1800°C. The phenomenon can be attributed to the relaxation of thermal residual stress under 1300°C, the existence of plastic flow from 1300°C to 1600°C, and the degeneration of graphite flakes and cavitation formation at 1800°C. In comparison to vacuum, the fracture toughness in air improves by the healing effect of pre-oxidation below 1300°C. The microstructure observations further reveal the great effects of temperature and pre-oxidation on the fracture behavior of ZrB2–SiC–graphite composite.

SPS densification and microstructure of ZrB2 composites derived from sol–gel ZrC coating

A technique for densifying ultra high temperature ceramic composites while minimising grain growth is reported. As-purchased ZrB2 powder was treated with a zirconia-carbon sol–gel coating. Carbothermal reduction at 1450 ◦ C produced 100–200 nm crystalline ZrC particles attached on the surface of ZrB2 powders. The densification behaviour of the sol–gel coated powder was compared with both the as-purchased ZrB2 and a compositionally similar ZrB2–ZrC mixture. All three samples were densified by spark plasma sintering (SPS). The ZrB2 reference sample was slow to densify until 1800 ◦ C and was not fully dense even at 2000 ◦ C, while the sol–gel modified ZrB2 powder completed densification by 1800 ◦ C. The process was studied by ram displacement data, gas evolution, SEM, and XRD. The sol–gel coated nanoparticles on the ZrB2 powder played a number of important roles in sintering, facilitating superior densification by carbothermal reduction, nanoparticle coalescence and solid-state diffusion, and controlling grain growth and pore removal by Zener pinning. The sol–gel surface modification is a promising technique to develop ultra-high temperature ceramic composites with high density and minimum grain growth. © 2014 Elsevier Ltd. All rights reserved.

Bonding and Structure of Ceramic-Ceramic Interfaces

Quantum molecular dynamics simulations of α-Al2O3(0001)/3C-SiC(111) interfaces reveal profound effects of thermal annealing for producing strong interfaces consisting solely of cation-anion bonds and their consequence on interfacial structures. A Si-terminated SiC surface and Al2O3 form a stronger interface (Si-interface) with a Si-O bond density of 12.2 nm(-2), whereas the C interface has an Al-C bond density of 9.46 nm(-2). The interfacial bond strengthening is accompanied by the formation of an Al2O3 interphase with a thickness of 2-8 Å. Such atomistic understanding may help rational interfacial design of high-temperature ceramic composites for broad applications such as power generation systems.

Characterization of Structure-Thermo-Mechanical Properties of Ultra High Temperature Ceramic Composites (UHTCCS) By Nondestructive Testing (NDT)

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Flexural creep of zirconium diboride–silicon carbide up to 2200°C in minutes with non-contact electromagnetic testing

Abstract Flexural creep of ZrB 2 –30 vol% SiC ultra high temperature ceramic composite was studied at 1700–2200 °C and 20–50 MPa using the novel method of electromagnetic Lorentz force loading of electrically heated specimens. Experiments were conducted in air and in non-oxidizing atmospheres. The apparent activation energy for creep was 344 ± 35 kJ/mol for non-oxidizing conditions. The stress exponent was 1.4 ± 0.4. The creep rate was slightly higher in air due to a decrease in the size of the load bearing substrate because of oxidation. There was no evidence of electric field effects. Creep experiments could be performed up to 2200 °C very quickly, with experiments conducted in a few minutes.