HfC Nanowires Research Articles

Thermal shock resistance of carbon-based composites reinforced by HfC nanowires under extreme conditions

Lightweight composites with excellent thermal shock performance exhibit significant potential for thermal structural components. Herein, HfC nanowires modified carbon/carbon (HfCNWs-C/C) composites are fabricated, establishing a three-dimensional network within the matrix. The microstructure of the composites before and after thermal shock cycles were characterized by SEM, XRD and TEM. Additionally, the flexural strength with varied thermal shock were analyzed, which were initially increasing before subsequently decreasing with the number of thermal shock cycles under Ar atmosphere, exhibiting thermal shock strengthening phenomena. While within oxy-acetylene system, the strength of HfCNWs-C/C exhibit an increasement of 75 % compared with C/C after ablation for 6 cycles, which can be attributed to the sintering and the generation of molten film of partial HfO2 phases that can mitigates oxidation of the matrix, but still lead to a declining trend in the strength following ablative thermal cycles.

Synthesis of HfC nanowires on carbon fibers by a novel catalyst-assisted pyrolysis using HfCl4 as precursor

The synthesis of hafnium carbide nanowires (HfCNWs) on carbon fibers was successfully achieved by employing HfCl4 and furfuryl alcohol as precursor materials, facilitated by Ni-assisted catalytic pyrolysis. In the polymerization and cross-linking processes of furfuryl alcohol, hafnium cations play a crucial role, leading to the atomic-level amalgamation and effectively enhancing the reactivity of the Hf-O-C system. The nucleation of HfCNWs takes place at 1300 °C, followed by growth through a solid-liquid-solid (SLS) mechanism. Carbon fibers were uniformly coated with tens micrometer-long HfCNWs having an approximate diameter of 500 nm. Notably, the tips of these HfCNWs exhibited clean surfaces free of Ni catalyst particles, indicating their root growth model. This novel catalyst-assisted pyrolysis method holds great potential for enabling cost-effective large-scale production of transition metal carbide nanowires.

Ultra-high temperature performance of carbon fiber composite reinforced by HfC nanowires: A promising lightweight composites for aerospace engineering

Lightweight composites with excellent high-temperature performance are attractive as thermal structural components in extreme environment. In general, the excellent properties depend on both their microstructures and intrinsic properties of their counterparts. Herein, we report a lightweight carbon fiber composites reinforced by hafnium carbide nanowires (HfCNWs) and the corresponding high temperature performance. The evolution of the microstructures and compositions after treated at high temperature are analyzed. As suggested from the results, with the presence of HfCNWs, the interlaminar shearing strength (ILSS), out-of plane compression strength (OCS) and flexural strength (FS) increased by 81.36%, 87.96% and 78.38%, respectively. Although the mechanical performance deteriorated after treated at high temperatures, the mechanical strength retention rate (MSR) of HfCNWs reinforced C/C (HfCNWs-C/C) composites is superior to that of pure C/C composites. Besides, the excellent ablative resistance of HfCNWs-C/C composites provide potential possibility to be applied in extreme conditions.

Two birds with one stone: Simultaneous fabrication of HfC nanowires and CNTs through efficient utilization of polymer-derived ceramics

• Carbon nanotubes (CNTs) were fabricated by using the waste gasses when preparing hafnium carbide nanowires (HfC NWs ) through thermal pyrolysis of Hf-containing precursor. • The CO and CH 4 released by Hf-containing precursor are the main carbon source for the growth of CNTs. • The in situ growth of HfC NWs increased the flexural strength of carbon/carbon (C/C) composites, and CNTs/carbon cloth displayed enhanced electrochemical performance. Carbon nanotubes (CNTs) are fabricated in carbon cloth by ultilizing the waste gasses when fabricating hafnium carbide nanowires (HfC NWs ) through thermal pyrolysis of Hf-containing polymer precursor. The formed HfC NWs are distributed uniformly on the surface of the carbon fibers in carbon/carbon (C/C) composites and display perfect single crystal appearance. The pyrolysis of the Hf-containing organic precursor provides hafnium and carbon source for the growth of HfC NWs . The released waste gasses containing CO, CH 4 and CO 2 are the main carbon source for the growth of CNTs. Specifically, the flexural strength of HfC NWs reinforced carbon/carbon (HfC NWs -C/C) composites is enhanced by ∼105% compared with pure C/C, and the CNTs/carbon cloth also displays improved electrochemical performance with respect to capacitor applications. The present study introduces a novel sustainable and eco-friendly process related to polymer-derived ceramics to form advanced ceramic nanocomposites and proposes a deep understanding of the growth mechanism of CNTs.

Microstructures and enhanced flexural properties of single-crystalline HfC nanowires in-situ modified carbon/carbon composites by electrophoresis-thermal evaporation using CNTs as the template

To improve the mechanical properties of carbon/carbon (C/C) composites, in-situ synthetized single-crystalline hafnium carbide nanowires (HfCnws) were introduced into the carbon fiber preforms by electrophoresis-thermal evaporation method. The Multi-walled carbon nanotubes (MWCNTs) were utilized as the carbon source and templates for forming HfCnws. The microstructure, chemical composition and mechanical properties of the HfCnws modified carbon/carbon (HfCnws-C/C) composites were characterized. Results reveal that HfC is produced preferentially in the inner nodular parts and end parts of MWCNTs. The raising heat-treatment temperature would influence the diffusion rate of Hf atoms and then the number of nucleation sites, which further changed the aspect ratio and morphology of HfCnws. The HfCnws have refined the grain size of pyrolytic carbon (PyC), and significantly improve the flexural strength of C/C composites by 79.3%.

Integrative improvement on thermophysical properties and ablation resistance of laminated carbon/carbon composites modified by in situ grown HfC nanowires onto carbon fiber cloths

HfC nanowires modified carbon fiber cloth laminated carbon/carbon (HfCnw-C/C) composites were fabricated by in situ growth of HfC nanowires on carbon cloths via catalytic CVD, followed with lamination of the cloths and densification by pyrolytic carbon (PyC). Morphologies, thermal conductivity, coefficient of thermal expansion (CTE), and ablation resistance of the composites were investigated. Due to the loading of HfC nanowires, the matrix PyC with low texture was obtained; the thermal conductivity of the composites in the Z direction was enhanced from 100℃ to 2500℃; CTE along the X–Y direction also decreased in the range of 2060 ℃ – 2500 ℃, which reaches the maximum of 24 % at 2500℃. Moreover, the 20s-ablation-resistance of HfCnw-C/C composites exhibits mass and linear ablation rates of 5.3 mg/s and 21.0 μm/s, which are 40 % and 37 % lower than those of pure C/C composites, respectively. Our work shows laminated HfCnw-C/C composites are a promising candidate for high-temperature applications.

Issue Information

Cover Photograph: Starting clock wise from upper left hand corner: SEM images of the products synthesized at 1500 °C. HfC ceramic particles were stacked together on the surface of carbon cloth; SEM images of awl‐like HfC nanowires synthesized at 1500 °C. HfC nanowires with length of 5~30 μm were synthesized and distributed evenly between the fiber bundles; Typical high‐magnification SEM images of awl‐like HfC nanowires grown on carbon fiber. The diameter of the obtained HfC nanowires decreases from the bottom to the top; Morphology of single HfC nanowire. The as‐prepared awl‐like HfC nanowires have a prismatic geometry surface morphology instead of showing a smooth surface like a cylindrical morphology. Image credit: Yanqin Fu (Northwestern Polytechnical University). DOI: 10.1111/jace.17073. image 2019 ACerS Ceramographic Exhibit & CompetitionCategory: STEM, 2nd Place image

Effect of HfC nanowires grown on carbon fibers on the microstructure and thermophysical properties of C/C composites

AbstractOne‐dimensional (1D) hafnium carbide nanowires (HfCnws) were grown in situ on carbon fibers (CFs) via a Ni‐assisted pyrolysis method of organometallic polymer precursor. Scanning electron microscopy (SEM), transmission electron microscope (TEM), polarized‐light optical microscopy (PLM), and Raman were used to analyze the effect of HfCnws on the microstructure of pyrolytic carbon (PyC). The specific heat capacity (HC), thermal diffusivity (TD), thermal conductivity (TC), and coefficient of thermal expansion (CTE) of HfCnws‐C/C composites were also investigated. Results show that HfCnws wrapped by carbon nanosheet were successfully synthesized. The diameter of HfCnws is about 30 nm and the thickness of carbon nanosheet is about 10 nm, which could induce the formation of isotropic (ISO) PyC. After introducing HfCnws, the TD and CTE of HfCnws‐C/C composites were increased. Ni2HfCnws‐C/C composites show a higher TC and TD, and the CTE increased with the increasing content of HfCnws.

Improving the flexural property and long-lasting anti-ablation performance of the CVD-HfC coating by in-situ growing HfC nanowires

HfC nanowires (HfCNWs) were in-situ synthesized via CVD technique and acted as the reinforcement in the CVD-HfC coating for C/C composites. The morphology, flexural property and long-lasting anti-ablation performance of the HfC coating were researched. The deposition efficiency and compactness of the HfC coating were both elevated by virtue of in-situ growing HfCNWs. The flexural property of the coated C/C exhibited a pronounced increment on account of incorporating HfCNWs. HfCNWs formed an interlocking network in the oxide layer and inhibited the coating delamination or spalling in harsh ablation condition, so the long-lasting anti-ablation performance of the HfCNWs-reinforced HfC coating improved. After exposure to the oxyacetylene flame for 120 s, the mass and linear ablation rates of the HfCNWs-HfC-coated C/C were only 0.57 mg/s and -0.35 μm/s, which were 54.03% and 117.77% reduction in comparison with those of the HfC-coated C/C (1.24 mg/s and 1.97 μm/s).

Influence of HfC nanowires on the growth behavior, microstructure and ablation resistance of CVD-HfC coating

HfC nanowire-toughened HfC ablation resistant coating was prepared on carbon/carbon composites by two steps of chemical vapor deposition. Effects of HfC nanowires on the growth behavior, microstructure and ablation resistance of the HfC coating were researched. Due to the incorporation of HfC nanowires, the deposition rate of the HfC coating was improved, the HfC coating was composed of particle-stacked crystals. After incorporating HfC nanowires, the bonding strength and fracture toughness of the HfC coating increased. HfC nanowires could restrain the crack propagation of HfC coating during ablation, contributing to improving the ablation resistance of HfC coating. After ablation for 60 s, the mass ablation rate of the HfC-coated C/C sample reduced from 0.44 to 0.26 mg/s because of the incorporation of HfC nanowires.

Large‐scale synthesis of hafnium carbide nanowires via a Ni‐assisted polymer infiltration and pyrolysis

AbstractHafnium carbide (HfC) nanowires were successfully synthesized on C/C composites via a Ni‐assisted polymer infiltration and pyrolysis. Before synthesizing HfC nanowires, the composition and microstructure of the organic HfC precursor and its pyrolyzed products were characterized by Fourier transform infrared spectra, X‐ray photoelectron spectroscopy, and X‐ray diffraction. The effect of heat‐treatment temperature on the morphology and microstructure of HfC nanowires were investigated by scanning electron microscopy and transmission electron microscopy. Results show that HfC nanowires exhibits three‐layer core‐shell structure, including HfC core, HfO2 inner shell (~2 nm) and carbon nanosheet outer shell (~1 nm). The obtained HfC nanowire is typically grown along <01> with the diameters of ~100 nm and the length of several micrometers. The growth of HfC nanowire follows the combination of top‐type vapor‐liquid‐solid and solid‐liquid‐solid mechanism.

Effects of HfC nanowire amount on the microstructure and ablation resistance of CVD-HfC coating

To improve the ablation resistance of HfC coating for carbon/carbon (C/C) composites, various fractions of HfC nanowires were incorporated into the HfC coating by chemical vapor deposition (CVD). Effects of HfC nanowire amount on the microstructure and ablation resistance of the CVD-HfC coating were investigated. Results indicated that the HfC nanowire layer became thicker and denser with the deposition time extending. HfC nanowires could inhibit the formation of cracks and interlaminar gaps in the HfC coating. With the increase of HfC nanowire amount, the HfC coating became thicker, while its porosity and roughness firstly decreased and then increased. Ablation tests indicated that the incorporation of HfC nanowires could effectively improve the ablation resistance of the HfC coating, which could be ascribed to the decreasing surface temperature of the coated samples and the effective alleviation of cracking and delamination of the coating during ablation. The HfC coating with HfC nanowires deposited for 1 h exhibited better ablation resistance owing to its compact microstructure, and its mass and linear ablation rates were only 0.41 mg/s and − 1.53 µm/s after ablation for 120 s.

Ablation resistance of HfC coating reinforced by HfC nanowires in cyclic ablation environment

To improve the ablation resistance of carbon/carbon composites in cyclic ablation environment, SiC/HfC ceramic coating reinforced by HfC nanowires was prepared. The microstructure, bonding strength, coefficient of thermal expansion and cyclic ablation resistance of the as-prepared coating were investigated. After incorporating HfC nanowires, the bonding strength between inner SiC coating and outer HfC coating was increased. HfC nanowires could relieve the coefficient of thermal expansion mismatch between inner and outer coating and improve the toughness of the outer coating. By introducing HfC nanowires, the coated sample’s cyclic ablation resistance was improved. After cyclic ablation under oxyacetylene flame for 60s×3, the mass and linear ablation rates of the coated sample with HfC nanowires were only 0.444mg/s and −0.767μm/s, respectively.

UHTC coating reinforced by HfC nanowires against ablation for C/C composites

To improve the ablation resistance of the coated carbon/carbon composites, HfC nanowires acting as reinforcement materials were introduced into ZrB2-SiC/SiC multilayer coating. Synthesis, morphology, mechanical properties and ablation resistance of the coating were researched. A porous HfC nanowire layer was uniformly covered on SiC coating. Both of the toughness and interface bonding strength of ZrB2-SiC coating with HfC nanowires were higher than those of the coating without HfC nanowires. HfC nanowires could effectively inhibit the cracking and peeling of outer coating during ablation. After oxyacetylene torch ablation for 90s, the mass ablation rate of the coated sample without and with HfC nanowires was 0.20mg/s and −0.12mg/s, respectively.

HfC nanowires to improve the toughness and oxidation resistance of Si-Mo-Cr/SiC coating for C/C composites

To improve the oxidation resistance of carbon/carbon (C/C) composites, a dense HfC nanowire-toughened Si-Mo-Cr/SiC multilayer coating was prepared by chemical vapor deposition (CVD) and pack cementation. The microstructure, thermal shock and isothermal oxidation resistance of the coating were investigated. HfC nanowires could improve the toughness of the coating and suppress the coating cracking. After incorporating HfC nanowires in the coating, both of the thermal shock and isothermal oxidation resistance of the coating were obviously improved. The multilayer coating with HfC nanowires could effectively protect C/C composites at 1773K for 270h, whose weight loss is only 0.19%. The good oxidation resistance is mainly attributed to the formation of a compound glass layer containing SiO2 and Cr2O3.

Effects of deposition temperature and time on HfC nanowires synthesized by CVD on SiC-coated C/C composites

HfC nanowires were synthesized on SiC-coated carbon/carbon composites via a catalyst-assisted chemical vapor deposition (CVD) process from the HfCl4–CH4–H2 system. The effects of deposition temperature (1273, 1323, 1373 and 1423K) and time (20, 40, 60 and 90min) on the formation and microstructure of HfC nanowires were investigated. The results showed that the diameter of HfC nanowires increased with the deposition temperature increasing; both the density and thickness of HfC nanowire films increased with the deposition time prolonging. The growth of HfC nanowires followed the bottom-type vapor–liquid–solid (VLS) mechanism.

Oxidation resistance and mechanical properties of HfC nanowire-toughened ultra-high temperature ceramic coating for SiC-coated C/C composites

To improve the oxidation resistance of carbon/carbon (C/C) composites, a dense HfC nanowire-toughened ultra-high temperature ceramic multiphase coating was prepared on SiC-coated C/C composites by chemical vapor deposition (CVD) and pack cementation. The microstructure, mechanical and oxidation resistance properties of the coating were investigated. The results show that the HfC nanowires in the coating could suppress the cracking of the coating and then improve the toughness of the coating. The flexural property, thermal shock and isothermal oxidation resistance of the coating were all improved due to the incorporation of HfC nanowires.

HfC nanowire-toughened TaSi2–TaC–SiC–Si multiphase coating for C/C composites against oxidation

To prevent carbon/carbon (C/C) composites from oxidation at high temperature, a HfC nanowire-toughened TaSi2–TaC–SiC–Si multiphase coating was prepared by a two-step technique including chemical vapor deposition (CVD) and pack cementation. The microstructure and oxidation resistance of the coating were investigated. The HfC nanowires can effectively reduce the size of microcracks and avoid the formation of through-thickness microcracks in the multiphase coating. Due to the toughening mechanisms including nanowire pullout and debonding, the cyclic and isothermal oxidation resistance of the coating are both improved.

SiC coating toughened by HfC nanowires to protect C/C composites against oxidation

Abstract To prevent carbon/carbon (C/C) composites from oxidation at high temperature, a dense SiC coating toughened by HfC nanowires was prepared by a two-step technique of chemical vapor deposition (CVD) and pack cementation. The microstructure, mechanical properties and oxidation resistance of the coating were investigated. The HfC nanowires can effectively reduce the size of microcracks and avoid the formation of through-thickness microcracks in the SiC coating. Due to the toughening mechanisms including microcrack bridging by nanowire and nanowire pullout, the mechanical properties and oxidation resistance of the coating are improved.

Field emission from single-crystalline HfC nanowires

Single HfC nanowire field emitter/electrode structures have been fabricated using nano-assembling and electron beam induced deposition. Field ion microscopy has been applied to study the atomic arrangement of facets formed on a field evaporation-modified HfC nanowire tip. Field evaporation and crystal form studies suggest that the {111} and {110} crystal planes have lower work functions, while the {100}, {210}, and {311} planes have higher work functions. Field emission measurement permits us to obtain that the work function of the {111} crystal plane is about 3.4 eV.