Vapor Infiltration Method Research Articles

Characterization of the Microstructure of Three-Dimensional-Needled Carbon/Silicon Carbide Composites

Three-dimensional-needled, carbon-fiber-reinforced silicon carbide matrix composites (C/SiC) were prepared by a chemical vapor infiltration and reactive melt infiltration method. It was found that two kinds of SiC existed in the C/SiC composites, that is, micro-β-SiC grains within the range of 5–15 μm and nano-β-SiC grains with a size of about 100 nm. The interface of C/SiC and the distribution of SiC showed evidence for the reaction mechanism of the reactive melt infiltration process.

Preparation of Mesoporous Pt−Ru Alloy Fibers with Tunable Compositions via Evaporation-Mediated Direct Templating (EDIT) Method Utilizing Porous Anodic Alumina Membranes

Synthesis of composition-controlled mesoporous Pt−Ru alloy fibers by a dual-templating method (Yamauchi et al. J. Am. Chem. Soc., 2008, 130, 5426−5427) is demonstrated using lyotropic liquid crystals (LLCs) as mesostructural direct templates and porous anodic alumina membranes (PAAMs) as morphological direct templates. The LLCs, including Pt and Ru species, were formed from diluted precursor solutions inside PAAM channels via the evaporation-mediated direct templating (EDIT) method. For all Pt−Ru compositions, the tubular mesophases in the LLCs were stacked like donuts within the PAAM channels because of the confined effect. After metal deposition by the vapor infiltration method of dimethylamineborane (DMAB) and subsequent removal of both surfactants and PAAM, mesoporous Pt−Ru fibers with various compositions were successfully prepared. Both the alloy state and the mesoporous structures were fully characterized by high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TE...

Fe 2O 3/SBA-15 catalyst synthesized by chemical vapor infiltration for Friedel–Crafts alkylation reaction

Fe/SBA-15/carbon composites were synthesized by chemical vapor infiltration (CVI) method using ferrocene as concurrent iron and carbon precursor. Accordingly, Fe 2O 3 nanoparticles supported on mesoporous SBA-15 silica or metallic Fe homogeneously embedded in mesoporous carbon were selectively obtained either by oxidizing the carbon component in air or by removing the silica template using an aqueous NaOH solution. The Fe 2O 3/SBA-15 and Fe/carbon composites so obtained were thoroughly characterized by N 2 adsorption/desorption isotherm measurements, powder X-ray diffraction (XRD), transmission electron microscopy and H 2-temperature programmed reduction (H 2-TPR). The effects of CVI duration time and temperature on their corresponding reduction states and particle dispersion, and consequently on their catalytic performances during benzylation reaction of benzene with benzyl chloride were examined and discussed.

Development of the tailored SiC/SiC composites by the combined fabrication process of ICVI and NITE methods

In order to improve the thermo-mechanical performances of SiC/SiC composite, process improvement and modification by the combination of nano-infiltration and transient eutectic-phase (NITE) method and chemical vapor infiltration (CVI) method were studied. Multilayered PyC/SiC fiber coating and matrix infiltration within fiber-tows were prepared with isothermal/isobaric CVI (ICVI) method and full-densification of SiC matrix was examined with NITE methods using four kinds of processing options. Applied pressure was useful for nearly-full matrix densification due to the promoting infiltration driving force of SiC nano-powder intra-fiber-tows, but simultaneously caused the sever degradation of fibers and interphase with fracture, resulting in lower strength. Increase of additives amount and additional polymer were effective ways for matrix densification by SiC nano-power infiltration intra-fiber bundles without pressure. Thermal conductivity was greatly improved with the decrease of matrix porosity. The tailoring of thermo-mechanical properties might be easily controlled by the SiC matrix porosity without process-induced fibers and interphases degradations.

Hollowed carbon capsule based Pt–Fe/carbon electrodecatalysts prepared by chemical vapor infiltration method

A new type of hollowed carbon capsule (HCC) material has been fabricated and utilized as a support for Pt–Fe catalyst by means of chemical vapor infiltration (CVI) method. The supported Pt–Fe/HCC catalyst was found to possess cavities with sizes around 20–40 nm and well-dispersed Pt–Fe alloy particles embedded on the internal graphitic carbon walls and hence can be used as potential electrodecatalyst for fuel cells. Preliminary performance tests by cyclic voltammetry revealed that the supported Pt–Fe/HCC catalyst has electrochemical properties compatible to a common commercial catalyst. The formation mechanism of the HCC material is also proposed.

Electro-conductive porous ceramics prepared by chemical vapor infiltration of TiN

Using pressure-pulsed chemical vapor infiltration (PCVI) method, TiN was partially infiltrated at 850 °C from gas system of TiCl4 (1%)–N2 (10%)–H2 into the highly porous carbon substrates prepared by the carbonization of cotton-wool, filter paper, and wood at 1,000 °C in Ar for 4 h. After 10,000 pulses of PCVI, electro-conductive porous ceramics having the three-dimensionally continuous current paths were obtained, which had the porosity of 80% and more, the resistivity of 10−5–10−6 Ω m, and the average pore sizes of 10–40 μm. The geometric surface area per unit volume of the sample was higher than that of the conventional foil-type current collector for lithium-ion battery. The surface area showed the highest value for the sample obtained from carbonized wood substrate.

Effects of Interphase Thickness on Damping Behavior of 2D C/SiC Composites

Internal friction of 2D C/SiC composites fabricated by chemical vapor infiltration (CVI) method was measured by dynamical mechanical analysis (DMA) at different frequencies from room temperature (RT) to 400°C in air atmosphere. Internal friction of 2D C/SiC composites increased gradually with increasing temperature and then decreased after damping peak appeared in the temperature range of 250°C to 300°C. Damping capacity and peak value decreased gradually with increasing frequency, accompanied with a shift of damping peak towards lower temperatures. Moreover, the effect of interphase thickness on damping behavior of 2D C/SiC composites was investigated. The results showed that damping peak of the composites increased gradually and the temperature of the peak shifted to the lower temperature with increasing PyC interphase thickness, when the interphase thickness is in the range of 90~296nm. The influence of interphase thickness on interfacial bonding strength, sliding resistance and the microstructure of SiC matrix was discussed, which was considered to be responsible for the results.

Acoustic Emission Research on Thermal Shock Behaviors of Three-Dimensional C/SiC Composites in Different Environments

Three-dimensional (3D) carbon fiber reinforced silicon carbide matrix composites (C/SiC) were prepared by a low-pressure chemical vapor infiltration method. The thermal shock behaviors of the composites in different environments were researched using an advanced acoustic emission (AE) system. Damage initiation and propagation were easily detected and evaluated by AE. The thermal shock damage to C/SiC composites mainly occurred at the process of cooling and was limited at argon but unlimited at wet oxygen atmosphere. Also correlations have been established between the different damage mechanisms and the characteristics of acoustic emission signals obtained during thermal shock tests. In this way, the paper contributes to the development of the acoustic emission technique for monitoring of damage development in ceramic-matrix composites.

Stressed oxidation behaviors of SiC matrix composites in combustion environments

Performance of three kinds of continuous fiber reinforced SiC matrix composites prepared by chemical vapor infiltration (CVI) method, i.e. 2D C/SiC, 3D C/SiC and 3D SiC/SiC composites, have been investigated in the high temperature combustion environment gas with various creep stresses. The relationship between the life time of composite and the normalized peak strength, defined by the ratio of the test stress to the material strength, was studied. The life time of composites decreased with increasing the normalized peak strength following an exponential relationship. The oxidation resistance of the SiC/SiC composite was the best and that of the 2D C/SiC composite was the worst in the high temperature combustion environment with an applied stress. The experimental results suggested that there was a critical normalized peak strength which controls the oxidation mechanism of C/SiC. Below the critical normalized peak strength, the degradation of C/SiC in the combustion environment was controlled by the diffusion of oxygen and water vapor through the cracks in the composite. Above the critical normalized peak strength, the degradation was controlled by the oxidation of C fibers.

Yttria-stabilized zirconia thin films deposited on NiO–(Sm 2O 3) 0.1(CeO 2) 0.8 substrates by chemical vapor infiltration

Fabrication of YSZ films deposited on NiO–samaria-doped ceria (SDC) substrate was studied by the chemical vapor infiltration method (CVI). A NiO–SDC substrate was used as oxygen source. The main mechanism of YSZ growth was electrochemical vapor deposition (EVD), while the contribution of oxygen in the carrier gas increased with increasing NiO content of the substrate above 60.6 mol%. The YSZ film on SDC used as the anode proved effective in obtaining high cell performance. In particular, a YSZ film thickness of 1 μm yielded the highest cell performance in the temperature range from 973 to 1073 K. The CVI method was useful for preparing a dense and strong YSZ film on the complex-shaped NiO–SDC substrate.

Chemical vapor infiltration method for deposition of gold nanoparticles on porous alumina supports

Knudsen’s effusion method with mass spectral analysis of the composition of the gas phase was used to measure the temperature dependence of the saturated vapor of several (CH3)2AuL chelate complexes and to determine the thermodynamic parameters of their sublimation. Based on the results of this study, conditions for chemical vapor deposition of gold using dimethylgold(III) chelates were chosen. Gold nanoparticles were synthesized by chemical vapor deposition (infiltration) of (CH3)2Au(acac) on porous granules of γ-Al2O3 with subsequent calcination in air at 325°C. Particle size and the chemical state of gold in Au/γ-Al2O3 systems were evaluated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A vapor infiltration procedure is suggested to prepare metallic gold particles ≤5 nm in diameter from Au/γ-Al2O3. It is shown that Au/γ-Al2O3 systems obtained by chemical vapor infiltration and containing small gold crystallites possess high catalytic activity in CO oxidation reactions at 40°C.

A rapid fabrication of C/C composites by a thermal gradient chemical vapor infiltration method with vaporized kerosene as a precursor

A thermal gradient, atmospheric pressure chemical vapor infiltration method with simultaneous vaporized kerosene as a precursor for rapid fabrication of C/C composites was studied. By this method, carbon felts (bulk density ∼0.2 g cm −3) were densified to C/C composites with density of 1.67 and 1.71 g cm −3 when prepared at 1050 and 1150 °C for 6 h, respectively. X-ray diffraction result indicates that the composites have a strong ability to graphitize and the higher deposition temperature leads to the increased graphitization degree. Polarized light microscope and scanning electron microscope images reveal that fibers of the composites prepared for 6 h are surrounded by ring-shaped pyrocarbon matrix with a thickness of ∼20 μm, and that the matrix is delaminated to 4–6 layer-like regions. The deposition process is analyzed by dividing the reactor into four regions associated with specific functions and the reasons for the rapid fabrication are proposed as the short convection and diffusion path for the precursor and the existing of thermal gradient across the preform.

Microstructure of C/C composites prepared by chemical vapor infiltration method with vaporized kerosene as a precursor

The microstructures of two types of C/C composites prepared from different carbon felts by a rapid densification method, thermal gradient chemical vapor infiltration with vaporized kerosene as a precursor, at 1080–1120 °C for 6 h were characterized by polarized light microscopy (PLM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman micro-spectrometry techniques. The experimental results show that the fibers in the two composites are both surrounded by ring-shaped pyrocarbons with rough laminar texture, but the thickness, the surface morphology of the pyrocarbons and the graphitizability of the composites depend much on the configurations of carbon felts. The C/C composite fabricated from a higher porosity carbon felt possesses larger thickness and rougher surface of pyrocarbon, and has a lower graphitizability after heat treatment at 2300 °C for 2 h.

Template-assisted synthesis of mesoporous tubular carbon nanostructure by chemical vapor infiltration method

A novel synthesis route for fabrication of tubule mesoporous carbon by chemical vapor infiltration method using a mesoporous silica template is reported. Powder X-ray diffraction and pore size analysis revealed that the nano-sized carbon material consists of three-dimensional framework structure and possesses a bimodal pore distribution with average pore diameters of 1.5 and 3.3 nm. The formation of the former pore is ascribed due to removal of the silica template, whereas the latter represents pore size of tubule carbon with ordered structure having an average wall thickness corresponding to about 1.3 layers of graphitic sheets, as verified by Raman spectroscopy and electron microscopy.

Tribological properties of carbon nanotube-doped carbon/carbon composites

Carbon nanotube (CNT)-doped carbon/carbon (C/C) composites were fabricated by the chemical vapor infiltration (CVI) method to investigate the effect of CNTs on tribological properties of C/C composites. CNTs, which had been synthesized by catalytic pyrolysis of hydrocarbons, were added to carbon fiber formed preforms before CVI process. Ring-on-block-type wear tests were performed to evaluate the frictional properties of CNT-doped C/C composites. Results show that CNTs can not only increase wear resistance of C/C composites but also maintain stable friction coefficients under different loads. Polarized light microscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy analyses demonstrate that favorable effects of CNTs on tribological properties of C/C composites have been achieved indirectly by altering microstructure of pyrocarbons and directly by serving as high-strength lubricative frictional media at the same time. Electron dispersive spectroscopy (EDS) analyses verify the existence of adhesive wear mechanism in both pure C/C composites and CNT-doped C/C composites albeit the two-body abrasive mechanism dominates in pure C/C composites.

Low-temperature formation of nanocrystalline β-SiC with high surface area and mesoporosity via reaction of mesoporous carbon and silicon powder

We report here a new route to prepare nanocrystalline β-silicon carbide with high specific surface areas and mesoporosity. The preparation method was via the reaction of ordered mesoporous carbons (OMCs, carbon replicas of MCM-48, SBA-15 and KIT-6) with silicon powder at the temperature of 1200–1300 °C, which is below the melting point of silicon, 1420 °C. The SiC samples were characterized by XRD, SEM, TEM, N 2 adsorption and other techniques, which showed that the SiC samples were nanocrystalline and had a high surface area of up to 147 m 2 g −1 and a mesoporosity in the range of 5–40 nm. In addition, the silicon vapor infiltration method at a temperature beyond 1420 °C was also brought into comparison.

Braking Behavior of C/SiC Composites Prepared by Chemical Vapor Infiltration

Carbon fiber‐reinforced silicon carbide matrix composites have the potential to overcome the shortcoming of the currently used carbon/carbon friction materials in aircraft brakes. In this article, the carbon/silicon carbide (C/SiC) composites were prepared by chemical vapor infiltration method, and the brake disks with different densities and component content were finally obtained. The friction coefficient and friction stability can be significantly improved by increasing both material density and carbon content. When the density of C/SiC composite is 2.3 g/cm3, the coefficient of friction measured is 0.23, the coefficient of friction stability remains about 0.43, the liner wear rate is less than 9.3 μm/cycle, and the weight wear rate is less than 9.1 μm/cycle. The rapid increase of friction coefficient approaching the end of braking is mainly related to the increasing of surface temperature in a short time and the enhanced adhesion and abrasion of contact conjunctions and asperities. The C/SiC composites exhibited a good stability of braking against fading versus the braking number and surface temperature. The surfaces of C/SiC brake disks were covered with wear debris including the fragment of carbon fibers after the braking tests. The wear on the surfaces is significantly determined by cyclic mechanical and thermal stresses, which result in the micro‐cracks in the SiC matrix, the thin flakes of the surface materials as well as the grooves.

Fabrication of Silicon Carbide Whisker/Alumina Composite by Thermal-Gradient Chemical Vapor Infiltration

SiC(w)/Al2O3 composites were made from an AlCl3-H2-CO2 mixture by a thermal-gradient chemical vapor infiltration (CVI) method. Al2O3 was deposited from the reaction of AlCl3 and H2O, which was produced from the oxidation of H2 by CO2. The densification rate was measured at various reactant compositions and total pressures. When the reaction rate or total pressure increased, the rate-controling step shifted from H2O production to AlCl3 diffusion, which led to premature pore closing. To obtain dense composites in a short infiltration time, the diffusion rate of AlCl3 had to be increased by decreasing the total pressure.

On Ultrasonic Characteristics in Carbon/Phenolic Matrix Composite Materials

In order to assess material properties and part homogeneity in carbon matrix composite (CMC) brake disks we have performed nondestructive evaluation, which are originally developed for aerospace applications. In this paper we have adopted several ultrasonic techniques to evaluate carbon matrix composites for the material properties that are attributable to the manufacturing process. In a carbon matrix composite manufactured by chemical vapor infiltration (CVI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CVI process in order to increase the density of the CMC composites. Ultrasonic velocity and attenuation depend on a density variation of materials. Low frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. Optical micrograph had been examined on the surface of the CMCs using a destructive way. Also a motorized system was adopted to measure ultrasonic velocity on the point of the CMC materials under the same coupling conditions. Manual results were compared with those obtained by the motorized system with using dry-coupling ultrasonics and through transmission method in immersion.

Mechanical Properties of High Purity SiC Fiber-Reinforced CVI-SiC Matrix Composites

Mechanical properties of silicon carbide composites reinforced with highly crystalline fibers and fabricated by the chemical vapor infiltration method were evaluated. Materials used were SiC/SiC composites reinforced with unidirectional Hi-Nicalon Type-S fibers and unidirectional Tyranno SA fibers with various fiber/matrix interphase. Also, SiC/SiC composites reinforced with plain weave Tyranno SA fibers with carbon or multilayers of silicon carbide and carbon interphase were evaluated. In-plane tensile, transthickness tensile and interlaminar shear properties were evaluated by the in-plane tensile test, the transthickness tensile test, the diametral compression test and the compression test of double-notched specimens.The elastic modulus and proportional limit stress were improved by using high purity silicon carbide fibers. The in-plane tensile properties were insensitive to carbon interphase thickness for a range of thicknesses between 30 and 230 nm. It was found that the in-plane tensile strength of composites containing multilayers of silicon carbide and carbon coating of fibers and fiber bundles was superior to that of composites with carbon alone. Transthickness tensile strength and shear strength of high purity silicon carbide composites were successfully evaluated.