Melt Infiltration Method Research Articles

Oxidation and recession of plain weave carbon fiber reinforced ZrB2-SiC-ZrC in oxygen–hydrogen torch environment

The oxidation and recession of four plain weave carbon fiber reinforced ZrB2-SiC-ZrC composites with different matrix compositions were compared with those of a plain weave carbon fiber reinforced ZrB2-SiC matrix composite. These composites were fabricated using a silicon melt infiltration method. The composite with the higher ZrC content also formed ZrSi2 in the matrix instead of residual silicon. The composites were oxidized at 1700 and 1800 °C in an oxygen–hydrogen torch environment. The oxides consisted of ZrO2 and SiO2, which formed on the surface of all samples. Carbon fiber at the surface was lost due to oxidation. The recession resistance of ZrB2-SiC-ZrC matrix composites remained constant at 1700 °C, even if the matrix composition varied, while the resistance at 1800 °C increased with the matrix of ZrC and ZrSi2. The ZrB2-SiC-ZrC matrix composite with the higher ZrC and ZrSi2 compositions formed a sintered ZrO2-rich layer, which was denser than the ZrO2-SiO2 and improved the recession resistance.

Fabrication and bending behavior of amorphous SiC-fiber-reinforced Si-Co eutectic alloy composites at elevated temperatures

Amorphous SiC-fiber-reinforced Si-CoSi2 and CoSi2–CoSi eutectic alloys composites have been developed by a melt infiltration method, and their mechanical properties were evaluated at elevated temperatures up to 1220 °C. As compared to polycrystalline Si, Si–Co ingots showed a ductile transition at a lower temperature (200–400 °C) due to the ductile transition of CoSi2 and the presence of a debonding interface. Moreover, the composites using Si–Co alloys showed superior bending behavior at elevated temperatures around 1000 °C as compared to composites using Si because of the ductile behavior of the Si–Co alloys and the prevention of the degradation of the SiC fibers.

Processing and Mechanical Properties of Dual-Carbide (B4C, SiC), Dual-Metallic Phases (Al, Si) Infiltrated Composites

Abstract This work is on processing and studying of toughening property of indentation fracture composites. By applying reactive melt infiltration method infiltrated composites were prepared where different Si-Al compositions and as-pressed porous boron carbide were used at various infiltration temperatures. In which the process became feasible within the experimental constrains of this task. Polished sections of infiltrated composites were examined by quantitative methods with standards for the volumetric fractions of B4C, Si, Al, and SiC crystalline phases; and the element distribution in the phases were investigated by SEM/EDS, represented through ternary phase diagram. The distribution of ductile aluminium and brittle phases could determine the means of toughening mechanism and further discussed the de-bonding of interphases.

Enhanced dehydrogenation kinetic properties and hydrogen storage reversibility of LiBH4 confined in activated charcoal

Abstract LiBH4 was confined into activated charcoal (AC) by melt infiltration method (MI), and its effects on the hydrogen sorption properties were investigated. The N2 adsorption results reveal that melt infiltration method can effectively incorporated LiBH4 into AC. It can maintain the structural integrity of the scaffold and ensure the confinement effect. The nano-confined LiBH4/AC starts to release hydrogen at around 190 °C, which is 160 °C lower than that of pure LiBH4, and reaches a hydrogen desorption capacity of 13.6% at 400 °C. When rehydrogenated under the condition of 6 MPa H2 and 350 °C, it has a reversible hydrogen storage capacity of 6%, while pure LiBH4 shows almost no reversible hydrogen storage capacity under the same condition. Mass spectrometry analysis (MS) results suggest that no diborane or other impurity gases are released in the decomposition process. The apparent activation energy of dehydrogenation of LiBH4 after confinement into AC decreases from 156.0 to 121.1 kJ/mol, which leads to the eminent enhancement of dehydrogenation kinetics of LiBH4.

A novel melt infiltration method promoting porosity development of low-rank coal derived activated carbon as supercapacitor electrode materials

Abstract Focusing on the bottlenecks of traditional physical or chemical activation methods for the preparation of activated carbons, we report a simple and scalable melt infiltration strategy assisted with CO2 activation for the preparation of activated carbons from Chinese large-scale reserve Zhundong coal. The preparation is achieved by the melt infiltration of a small amount of anhydrous FeCl3 (10–20 wt%) into the coal framework and subsequent CO2-assisted physical activation during which the encapsulated iron species play the dual role of pore-forming templates and activating catalysts. The as-obtained MI-AC-2 possesses a partially hierarchical pore structure with a high specific surface area of 1872 m2 g−1, five times more than the activated carbon prepared by solely physical activation, which endows the constructed MI-AC-2 electrode with good supercapacitive performances. Relative to the large consumption of activation agents used in a traditional chemical activation process, such a new method with low-cost resource materials and the low-dose FeCl3 additive paves a scalable way to loading metal precursor into coal/biomass for the preparation of high-porosity activated carbons. This work also provides a simple and efficient strategy to encapsulate active materials into external matrix or substrate.

C/C–SiC composite fabricated via PCS–Si slurry reactive melt infiltration

AbstractThe slurry reactive melt infiltration (RMI) method was used to overcome the shortcomings of the traditional RMI method utilized in preparing the large‐irregular shaped C/C preform. C/C–SiC composite was successfully fabricated via PCS–Si slurry RMI. Results show that it has a favorable physical bonding between the PCS–Si slurry and the C/C preform. After RMI, most of the Si in the PCS–Si slurry coating infiltrated into the C/C preform, the density of the C/C preform increased from 1.24 to 1.52g cm−3, and the open porosity decreased from 27.22% to 18.04%. SiC was formed on the surface as well as in the pores of the C/C preform. The as‐received C/C–SiC composite showed a pseudo‐ductile fracture behavior with a flexural strength of 76.4MPa. The mass ablation rate of the C/C–SiC composite is 0.34 mg s−1, exhibiting much better ablation resistance than the C/C preform with a mass ablation rate of 1.80 mg s−1.

High temperature anti‐oxidation behavior of in situ and ex situ nanostructured C/SiC/ZrB2‐SiC gradient coatings: Thermodynamical evolution, microstructural characterization, and residual stress analysis

AbstractNanostructured C/SiC/ZrB2–SiC oxidation protective gradient coating was prepared by a two‐step reactive melt infiltration method. In order to reduce production cost, ZrB2 phase was synthesized by the in situ reactive that included low‐cost ZrO2 and B2O3 powders as raw materials. High‐temperature oxidation behavior of coatings was evaluated by isothermal oxidation test at 1773 K in air for 10 hours. Thermodynamical behavior of the coatings at various temperatures during oxidation test and coating process was predicted by HSC Chemistry 6.0 software. Compressive residual stresses of 36.9 MPa and 41 MPa were calculated for in situ and ex situ coatings by Williamson‐Hall method. After 10 hours of isothermal oxidation at 1773K, in situ and ex situ coatings showed 12.84% and 15.69% of weight losses with oxidation rates of 1.87 × 10−2 g cm−3 h−1 and 0.91 × 10−2 g cm−3 h−1, respectively. These results indicated that the oxidation protection ability of the coating produced by the in situ method was very close to ex situ coating.

Isothermal sulfur condensation into carbon nanotube/nitrogen-doped graphene composite for high performance lithium–sulfur batteries

Nitrogen-doped graphene (NG) is a promising material for fabricating high-performance lithium–sulfur batteries. Here a facile hydrothermal method was used to synthesize the NG and then the composite of NG and SWCNT (NG/SWCNT) was obtained by mixing with single-walled carbon nanotubes (SWCNT) via a simple ultrasonic method. Finally, the NG/SWCNT-sulfur composite (NG/SWCNT-S) is synthesized via an isothermal method that enables rapid vapor infiltration of sulfur into carbon nanotubes. The resulting sulfur-containing cathode shows a good capacity performance, reaching high initial capacities of 1199.6 mAh g−1 at 0.1 C and 725.2 mAh g−1 at 1 C. The optimized electrochemical performance can be attributed to the NG addition which leads to an effective improvement of sulfur utilization and seizing polysulfides during cycling. Moreover, we show that the vapor infiltration method based on the thermodynamics of capillary condensation on nanoscale surfaces offers a new idea for assembling cathode, compared to the traditional melt infiltration method.

Laminar TiZr-based bulk metallic glass composites with improved mechanical properties

A novel strategy to design bulk metallic glass composite is proposed. The foils with the composition of the β phase in the in-situ TiZr-based composite are prepared. The in-situ composite matrix and the β foils are composited at the semi-solid temperature using the modified melt infiltration method. The mechanical properties of the newly prepared laminar composite reinforced with both ex- and in-situ β phases are improved remarkably. The composite shows controllable structure based on the phase equilibrium, and the corresponding mechanism is discussed thermodynamically. The interaction kinetics is studied by the modified liquid-bridge experiments and a dissolution kinetics model is deduced. The laminar composite shows obvious plasticity and work hardening behavior because of the introduction of multiscale ductile β phase. The multiple shear bands in the metallic glass and the β phase, and the phase transformation of β to α" contribute to the high performance of the composite. This study provides a new design approach to manipulate the microstructure and further improve the mechanical properties of the composites.

High temperature ablation-oxidation performance of SiC nanowhisker toughened-SiC/ZrB2-SiC ultra-high temperature multilayer coatings under supersonic flame

Ablation behavior of SiC nanowhisker toughened-SiC/ZrB2-SiC ultra-high temperature multilayer coatings was evaluated under supersonic flame at ∼2173 K for 120s. SiC nanowhisker toughened-SiC/ZrB2-SiC coatings were prepared on graphite substrate by two-step reactive melt infiltration (RMI) method. The ZrB2–SiC outer coating was prepared on the SiC coated graphite surface by in-situ and ex-situ methods. In ex-situ processing, ZrB2 powder was directly introduced into the powder mixture as a raw material. In in-situ processing, ZrB2 phase was formed in the coating by in-situ reaction between ZrO2 and B2O3. The linear and mass ablation rates for the in-situ ZrB2-SiC coating after 120s ablation under supersonic flame were 1.75 μm s−1 and 0.083 × 10−3 g cm−2 s−1 respectively. For the ex-situ ZrB2-SiC coating the linear and mass ablation rates were 1.5 μm s−1 and 0.064 × 10−3 g cm−2 s−1. The results showed that, the ablation resistance of in-situ ZrB2-SiC coating is very close to ex-situ ZrB2-SiC coating which can provide stable protection for the carbon substrate. Moreover, The SiC nanowhisker network structure in both in-situ ans ex-situ ZrB2-SiC coatings not only improved the toughness of the protective film by crack bridging, crack deflection and crack impedance, but also enhanced the bonding ability of protective film by the pinning and framework effects.

Converting biomass waste into microporous carbon with simultaneously high surface area and carbon purity as advanced electrochemical energy storage materials

Developing carbon materials featuring both high accessible surface area and high structure stability are desirable to boost the performance of constructed electrochemical electrodes and devices. Herein, we report a new type of microporous carbon (MPC) derived from biomass waste based on a simple high-temperature chemical activation procedure. The optimized MPC-900 possesses microporous structure, high surface area, partially graphitic structure, and particularly low impurity content, which are critical features for enhancing carbon-based electrochemical process. The constructed MPC-900 symmetric supercapacitor exhibits high performances in commercial organic electrolyte such as widened voltage window up to 3V and thereby high energy/power densities (50.95Whkg−1 at 0.44kWkg−1; 25.3Whkg−1 at 21.5kWkg−1). Furthermore, a simple melt infiltration method has been employed to enclose SnO2 nanocrystals onto the carbon matrix of MPC-900 as a high-performance lithium storage material. The obtained SnO2-MPC composite with ultrafine SnO2 nanocrystals delivers high capacities (1115mAhg−1 at 0.2A g−1; 402mAhg−1 at 10Ag−1) and high-rate cycling lifespan of over 2000 cycles. This work not only develops a microporous carbon with high carbon purity and high surface area, but also provides a general platform for combining electrochemically active materials.

The effect of fiber orientation on failure behavior of 3DN C/SiC torque tube

In this paper, the 3DN C/SiC torque tubes were fabricated by chemical vapor infiltration (CVI) combined with silicon melt infiltration (SMI) method with different fiber orientations (0°/90° and ± 45°) which leads to different density, torsional behaviors and failure behaviors. CT test was implemented to characterize the density heterogeneity. Using the density measured from Archimedes drainage method, FEM software was implemented to simulate the stress distribution of the tubes and calculate the failure stress. A good agreement with analytical model was obtained which helps a lot to failure analysis. Torsional tests were conducted using special attachments to a universal material test machine, the shear strain was calculated from the strain gauge, the shear strength was calculated by simplified formula, different torsional behaviors of two different fiber orientations were represented in the stress-strain curves. The fracture morphologies were observed by SEM, and the predominant factors of failure were analyzed. Torque tubes with fiber orientations of ± 45° have a higher torque capacity, modulus, and reasonable fracture morphologies, which is in good agreement with simulation results.

High-performance Fe5C2@CMK-3 nanocatalyst for selective and high-yield production of gasoline-range hydrocarbons

Highly-loaded and well-dispersed Fe5C2 nanoparticles within ordered mesoporous carbon CMK-3 (Fe5C2@CMK-3) were prepared via a simple melt infiltration method. They were successfully applied to high-temperature Fischer-Tropsch synthesis, and showed high CO conversion (91%) and activity (5.1×10−4molcogFe−1s−1) as well as good selectivity (38wt%) for gasoline-range hydrocarbons (C5–C12). The catalytic property of Fe5C2@CMK-3 was newly interpreted, based on theoretical data obtained by computational simulations.

New Carbon Materials 2016, 31(6): 628–638]. Microstructures and ablation properties of Al-Si modified C/C composites produced by the reactive melt infiltration method

New Carbon Materials 2016, 31(6): 628–638]. Microstructures and ablation properties of Al-Si modified C/C composites produced by the reactive melt infiltration method

Improved dispersion of transition metals in mesoporous materials through a polymer-assisted melt infiltration method

Dispersed metal particles smaller than 2 nm, thermally stable and exhibiting improved catalytic performances are produced by melt infiltration into mesoporous supports.

C/SiC Gradient Oxidation Protective Coating on Graphite by Modified Reactive Melt Infiltration Method: Effects of Processing Parameters on Transition Interface Thickness and High-Temperature Anti-oxidation Behavior

In this research, it was found that the C/SiC transition interface thickness increases without a significant decrease in toughness by modifying the reactive melt infiltration method through the addition of SiC nanoparticles. Also, the effect of the infiltration temperature on the transition interface thickness, isothermal oxidation behavior, and thermal shock resistance of the C/SiC graded coating were investigated. Coatings were characterized by X-ray diffraction, electron probe microanalysis, and scanning electron microscopy with energy-dispersive spectroscopy. Microstructural observations showed that with an increase in the heat treatment temperature, a higher amount of β-SiC (as a product of the infiltration process) is produced, which results in lower surface continuity in the coatings produced at a lower temperature. Moreover, the transition interface thickness increased with a decreasing infiltration temperature. The addition of SiC nanoparticles increased the transition interface thickness and oxidation resistance. After isothermal oxidation at 1773 K (1500 °C) for 10 hours, samples containing 7 wt pct SiC nanoparticles heat treated at 1773 K and 1873 K (1500 °C and 1600 °C) showed 13.3 and 5.03 pct weight loss, respectively.

Microstructure and mechanical properties of three dimensional Cf/SiC-ZrC-ZrB2 composites prepared by reactive melt infiltration method

Three-dimensional Cf/SiC-ZrC-ZrB2 composites were fabricated by reactive melt infiltration of ZrSi2 alloys into porous Cf/B4C-C preforms prepared through a sol-gel process. The influence of pore structure of the Cf/B4C-C preforms on microstructure and mechanical performances of the Cf/SiC-ZrC-ZrB2 composites was studied. It was found that the microstructure and mechanical performances of the composites showed a strong dependence on the pore structure of the preforms. Residual ZrSi2 content in the composites was significantly reduced with the decreases in the porosity and pore size of the Cf/B4C-C preforms. At the same time, fiber erosion in the composites was also gradually mitigated, which led to a significant improvement in the fracture behaviors of the composite, as failure mode of the composites changed from brittle to pseudo-plastic. When the porosity of the preforms decreased from 53.7% to 31.3%, the flexural strength of the composites increased from 53MPa to 184MPa.

3D Cf/SiC-ZrC-ZrB2 composites fabricated via sol-gel process combined with reactive melt infiltration

Three-dimensional (3D) Cf/SiC-ZrC-ZrB2 composites were successfully fabricated by sol-gel process combined with reactive melt infiltration (RMI) method. With H3BO3 and PVA as raw materials for gel precursor, a porous C-B4C matrix was first introduced into the 3D carbon fiber preform by impregnation of the gel precursor, followed by heat-treatments of pyrolysis and carbothermal processes at 1500°C in Ar atmosphere. Then molten ZrSi2 alloys were infiltrated into the 3D Cf/C-B4C preform to obtain 3D Cf/SiC-ZrC-ZrB2 composites. Based on thermodynamic analysis, the formation mechanism of SiC-ZrC-ZrB2 matrix was revealed. Oxidation resistance and ablation resistance properties of the fabricated 3D Cf/SiC-ZrC-ZrB2 composites were tested using a muffle furnace and a plasma wind tunnel equipment, respectively. The flexural strength of the as prepared composites and its strength retention after oxidation were evaluated. It is revealed that the 3D Cf/SiC-ZrC-ZrB2 composites showed superior flexural strength, good oxidation resistance and excellent anti-ablation properties.

Ablation behavior of C/SiC-HfC composites in the plasma wind tunnel

In order to satisfy the requirements for the thermal protection system to serve at ultrahigh temperatures, carbon fiber reinforced silicon carbide-hafnium carbide (C/SiC-HfC) composites were fabricated by reactive melt infiltration method. The ablation behaviors of C/SiC-HfC composites were examined in plasma wind tunnel. The results indicated that ablation was controlled by the oxidation of HfC-SiC under dissociated oxygen conditions at low heat flux and stagnation pressure. However, a sudden temperature jump caused by the change in the catalytic surface from silica to hafnia was observed at high heat flux and stagnation pressure during ablation. The increase in surface temperature was further accelerated by the burning of carbon fiber and recombination of carbon and nitrogen on it.

Effect of pyrolytic carbon interface on the properties of 3D C/ZrC–SiC composites fabricated by reactive melt infiltration

3D C/ZrC–SiC composites have been fabricated by slurry infiltration combined with reaction melt infiltration method. In order to clarify the effect of fiber/matrix (F/M) interface on properties on 3D C/ZrC–SiC, pyrocarbon (PyC) interface with various thickness (160–1100nm) was introduced by chemical vapor infiltration. The microstructure, mechanical properties and ablation properties were investigated systematically. Results showed that thicker PyC could protect fiber bundles from the erosion caused by the melt, leading to the as-prepared 3D C/ZrC–SiC with more excellent mechanical properties. The flexural strength and fracture toughness of C/ZrC–SiC composites with 850nm PyC was 125.67±2.49MPa and 4.82±0.48MPam1/2, respectively, which obtained 181% and 81% improvement compared with that of C/ZrC–SiC with 160nm PyC. However, as the thickness of PyC rised from 850nm to 1100nm, mechanical properties of C/ZrC–SiC decreased obviously. Also, after the ablation test, it was found that C/ZrC–SiC with 470nm PyC showed the best ablation resistance as SiC content was improved and porosity was lower in contrast with that of other composites.