Chemical Vapor Infiltration Technique Research Articles

Processing of Biomorphic Porous Ceramics by Chemical Vapor Infiltration and Reaction (CVI-R) Technique

not Available.

Effect of transition metal catalysts on the microstructure of carbide-derived carbon

Carbon materials with different microstructure can be produced by a carbide-derived carbon (CDC) approach varying the carbide precursor and the reaction conditions for the selective etching of the metal. CDC was produced using biomorphic TiC and SiC ceramics derived from paper preforms by a chemical vapor infiltration and reaction technique. In this work the effect of transition metal salt catalysts such as Ru(III), Fe(II), Fe(III) or Ru(III)/Fe(III) on the chlorination process at temperatures in the range 600–1200 °C as well as on the microstructure of the resulting carbon was investigated. The produced CDC was characterized by its degree of order and pore structure using Raman spectroscopy, high resolution transmission electron microscopy and low temperature nitrogen adsorption. A higher etching rate as well as a higher degree of order at lower reaction temperatures was observed if a catalytically active metal was present during the chlorination process. This effect was mostly pronounced in the case of a Ru(III)/Fe(III) bimetallic catalyst. The higher degree of order of the carbon is associated with an increased amount of mesopores and with a decrease in specific surface area. Therefore, the CDC processing in the presence of catalysts offers another way to produce ordered carbon structures at lower temperatures.

Oxidation behavior of silicon carbide based biomorphic ceramics prepared by chemical vapor infiltration and reaction technique

The oxidation behavior of biomorphic SiC based ceramics with different microstructure and composition was studied at 1450 °C in airflow for 50 h by thermal gravimetric analysis (TGA). SiC with amorphous, coarse grain, crystalline and fine grain crystalline microstructures as well as SiC–Si 3N 4 composite ceramics were processed from paper preforms by chemical vapor infiltration and reaction technique. The ceramics were characterized by X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDX) before and after oxidation. The results show that the crystalline SiC with fine grain structure and SiC–Si 3N 4 composite ceramics show very good oxidation resistance at a temperature of 1450 °C.

Modeling the Geometry of Satin Weave Fabric Composites

The focus of this study is aimed at characterizing the weave architecture in orthogonally woven polymer and ceramic—matrix composites. Three-dimensional (3D) geometric models of the unit-cells of four harness (4HS), five harness (5HS), and eight harness (8HS) satin weave morphologies are developed. The fiber bundle and matrix architecture in the 4HS, 5HS, and 8HS morphologies is represented via mathematical shape functions within the domain of the repeating unit-cells of the woven fabrics. This work brings together the non-uniform layer methodology of Kuhn and Charalambides [1] and the sub-cell modeling approach developed by Hewitt et al. [2]. In addition, this article introduces the novel concept of a `middle matrix layer' in capturing the ingress of matrix material away from undulating bundle regions, as documented by Morscher [3]. The geometry models developed herein account for a porous polymer matrix deposited over the woven mat via either resin film infusion (RFI) or resin transfer molding (RTM). This modeling also incorporates micro-structural intricacies observed in woven CMCs fabricated using chemical vapor infiltration (CVI) techniques for the deposition of the ceramic—matrix phase. Finally, results on the overall volumetric composite characteristics are reported.

Preparation and oxidation resistance of 2D C/SiC composites modified by partial boron carbide self-sealing matrix

The C/SiC composites with partial boron carbide (BC x ) self-healing matrix were prepared by isothermal chemical vapor infiltration technique (ICVI). SEM results showed that the multilayer SiC–BC x matrix exist among fiber bundles, nevertheless there were still SiC matrix among monofilaments. The mechanical properties at room temperature were tested and compared with conventional C/SiC composites. The modified composites hold better strain to fracture than the conventional C/SiC composites, although the other mechanical properties of the two kinds of composites were similar. The pull-out of multilayer matrices was the main factor of the increase of strain to fracture. The high residual strengths were demonstrated after oxidized at static air and simulation combustion environments. The improvement for oxidation resistances of the modified composites were contributed to the self-healing of crack and pore during oxidation in static air and simulation combustion environments, compared with conventional C/SiC composites.

Paper derived SiC–Si 3N 4 ceramics for high temperature applications

Biomorphic Si 3N 4–SiC ceramics have been produced by chemical vapour infiltration and reaction technique (CVI-R) using paper preforms as template. The paper consisting mainly of cellulose fibres was first carbonized by pyrolysis in inert atmosphere to obtain carbon bio-template, which was infiltrated with methyltrichlorosilane (MTS) in excess of hydrogen depositing a silicon rich silicon carbide (Si/SiC) layer onto the carbon fibres. Finally, after thermal treatment of this Si/SiC precursor ceramic in nitrogen-containing atmosphere (N 2 or N 2/H 2), in the temperature range of 1300–1450 °C SiC–Si 3N 4 ceramics were obtained by reaction bonding silicon nitride (RBSN) process. They were mainly composed of SiC containing α-Si 3N 4 and/or β-Si 3N 4 phases depending on the nitridation conditions. The SiC–Si 3N 4 ceramics have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and Raman spectroscopy. Thermal gravimetric analysis (TGA) was applied for the determination of the residual carbon as well as for the evaluation of the oxidation behaviour of the ceramics under cyclic conditions. The bending strength of the biomorphic ceramics was related to their different microstructures depending on the nitridation conditions.

Modification of C/SIC Composites using Partial Boron Carbide Self-Sealing Matrix by ICVI

C/SiC composites were modified using partial boron carbide (BCx) as matrix by isothermal chemical vapour infiltration technique (ICVI). SEM results showed that the multilayer SiC-BCx matrix exist among fibre bundles, nevertheless there were still SiC matrix among monofilaments. The modified composites hold better fracture roughness than the conventional C/SiC composites, although the other mechanic properties of the two kinds of composites were similar. The pull-out of multilayer matrix was the main factor of the increase of fracture toughness. Compared with the C/SiC composites coated with SiC/SiC/SiC, SiC/B-C/SiC or SiC/B/SiC coatings, the lower weight loss and higher residual strength of the modified composites were demonstrated. Furthermore, the weight gain and strength increase of the modified composites were found after oxidation at 1000°C and 1300oC due to the self-sealing of the micro-cracks and pores as shown in SEM results.

Structure of carbonized paper coated with pyrolytic carbon and its anode property for lithium-ion battery

Using pressure-pulsed chemical vapor infiltration (PCVI) technique, pyrolytic carbon (pyrocarbon) was infiltrated at 950°C from C3H8 (30%)-H2 gas system into the carbonized paper substrate. Carbon fibers in the carbonized paper were coated with dense pyrocarbon films having a laminar texture oriented parallel to the surface of carbonized fibers. It was revealed from XRD and Raman spectroscopy that the crystallinity of pyrocarbon was higher than that of carbonized fiber. BET surface area was decreased from 210 m2g-1 of the original substrate to 1.9 m2 g-1 of the pyrocarbon-coated sample.Reversible capacity of the sample coated with 8 mass % pyrocarbon was 500 mA h g-1, which were nearly close to that of the original carbonized paper. High irreversible capacity of 180 mA h g-1 was observed in the original carbonized paper, reflecting the disordered structure and high surface area. Irreversible capacity was reduced to 100 mA h g-1 by coating with 8 mass % pyrocarbon, which would be attributed to high crystallinity, laminar structure and low surface area of pyrocar-bon. Irreversible capacity was further decreased with increasing the mass fraction of pyrocarbon, however, reversible capacity was also decreased.

Electrochemical performance of LiFePO 4 modified by pressure-pulsed chemical vapor infiltration in lithium-ion batteries

Using the pressure-pulsed chemical vapor infiltration (PCVI) technique, pyrolytic carbon (pyrocarbon) films were deposited on the surface of LiFePO 4 particles for cathode material of lithium-ion batteries. The electrochemical performance of the original LiFePO 4 and PCVIed LiFePO 4 materials was evaluated using a three electrodes cell by galvanostatic charging/discharging at 25, 40 and 55 °C, respectively. Morphology and structure of LiFePO 4 were analyzed by SEM, XRD and Raman. The resulting carbon contents at 500, 1000, 2000, 3000 and 5000 pulses were 2.7, 4.7, 9.5, 15.1 and 19.4%, respectively and these samples were abbreviated as 500P, 1000P, 2000P, 3000P and 5000P, respectively. All the PCVIed samples exhibited excellent rate performance. The tendency was more and more obvious with the increase of the current densities. The specific capacities of 500P, 1000P and 2000P were maintained at 117, 124 and 132 mAh g −1, respectively, which were 120.8, 264.7 and 29.47% larger than those of corresponding original LiFePO 4, respectively, at a 5 C rate at 55 °C. The EIS measurement showed that electrochemical reaction resistance ( R ct) of PCVIed LiFePO 4 were obviously decreased, indicating a fast kinetics compared to the original LiFePO 4. The cycle ability of the 2000P sample was tested at 25 °C and C/2 rate. The cell was cycled for 150 cycles and no obviously capacity fade was observed. Its specific capacity of 115 mAh g −1 at 150th cycle is 1.7 times higher than that of original LiFePO 4.

Microstructure and properties of particle reinforced silicon carbide and silicon nitride ceramic matrix composites prepared by chemical vapor infiltration

Introduction Particle reinforced silicon carbide and silicon nitride ceramic matrix composites were fabricated using designed particle agglomeration and chemical vapor infiltration (CVI) technique. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) were employed to observe the microstructures of the preforms and as-infiltrated composites. In the preform, the inter-agglomeration and intra-agglomeration pores had an approximate size of 500–800 μm and 5–10 μm, respectively. After infiltrated, a large amount of silicon carbide and silicon nitride matrix were infiltrated in the preform, the sizes of inter-agglomeration and intra-agglomeration pores were 200–400 μm and 2–4 μm, respectively. The SiC and Si 3N 4 whiskers were observed in the residual intra-agglomeration pores. The flexural strength of SiC (p)/SiC composites changed with first-step pressure and second-step pressure. The maximum of the strength was 284 MPa, and the ratio of the retained strength was 95.4% at 1600 °C. The fracture toughness of SiC (p)/SiC composites was around 7 Mpa m 1/2. The Si 3N 4(p)/Si 3N 4 composite attained an acceptable strength, 113.4 MPa and low dielectric constant, about 4.2–4.3.

Carbon/Silicon Carbide Composites with Interphases Processed by Temperature-pulsing Chemical Vapor Infiltration Technique

Carbon/Silicon Carbide Composites with Interphases Processed by Temperature-pulsing Chemical Vapor Infiltration Technique

Growth of SiC nanowires within stacked SiC fiber fabrics by a noncatalytic chemical vapor infiltration technique

An atmospheric pressure chemical vapor infiltration (CVI) process without metallic catalysts was applied for the growth of SiC nanowires within stacked SiC fiber fabrics. We investigated the effect of the concentration of a reactant gas (CH 3SiCl 3, MTS) on the growth behavior and microstructure of the SiC nanowires. At high concentration of MTS in a H 2+MTS mixture gas, one-dimensional (1D) SiC deposits with diameters of several hundreds of nanometers were formed. Microstructures of the 1D SiC deposits exhibited a strong positional dependency throughout the thickness direction of the stacked fabric due to a depletion of the MTS gas. On the other hand, single-crystalline SiC nanowires with average diameters of 50–60 nm could be obtained at a low concentration of MTS. The SiC nanowires also exhibited a homogeneous growth both in the plane of each fabric layer and throughout the thickness of the sample.

Surface-modification of anode carbons for lithium-ion battery using chemical vapor deposition / chemical vapor infiltration technique

Recently, surface-modification by coating with pyrolytic carbon (pyrocarbon) using chemical vapor deposition (CVD) has been applied to graphite-based anodes of lithium-ion secondary battery (LIB) to restrain the decomposition of propylene carbonate based solvent. For non-graphitizing carbon coated with thin pyrocarbon film using chemical vapor infiltration (CVI), the irreversible capacity was significantly reduced without the decrease of reversible capacity, reflecting the laminar texture, high crystallinity and low surface area of pyrocarbon. Thus, pyrocarbon-coating by CVD/CVI technique is effective in improving the electrochemical properties of anode carbons. In present paper, recent works were summarized on synthesis and modification of anode carbons for LIB using CVD, especially CVI technique.

Processing of biomorphic porous TiO 2 ceramics by chemical vapor infiltration and reaction (CVI-R) technique

Porous biomorphic TiO 2 ceramics were manufactured from paper preforms by chemical vapor infiltration and reaction (CVI-R) in a three-steps process. First, the cellulose fibers of the paper were converted into carbon (C b) by pyrolysis in an inert atmosphere. Then, C b-template was infiltrated with a precursor system consisting of TiCl 4, CH 4 and H 2 to produce porous TiC ceramics, which were oxidized in a final step with air at temperatures in the range of 400–1200 °C. Depending on the conversion degree, TiC/TiO 2 or TiO 2 ceramics were obtained. The kinetics of the oxidation process was studied by thermal gravimetric analysis (TGA) and activation energies of 63 and 174 kJ mol −1 were estimated for the lower (400–800 °C) and higher (950–1200 °C) temperature regions, respectively. The TiO 2 ceramics were characterized by Raman spectroscopy (anatase/rutile ratio), SEM/EDX (morphology, composition) and nitrogen gas adsorption (pore structure). It was shown, that the anatase/rutile ratio as well as the pore structure of the resulting TiO 2 ceramics could be controlled varying the oxidation temperature. The TiO 2 samples obtained by oxidation of TiC biomorphic porous ceramics are lightweight but nevertheless have very good mechanical performances. Their bending strength varies between 30 and 40 MPa at a porosity of 65–70%. These structures have many potential applications, e.g. light structured materials, implants because of their bio-compatibility, catalyst support or catalyst for photo catalytic applications.

Low-temperature synthesis of graphite particles by chemical vapor infiltration and their electrochemical properties for lithium-ion battery

Using pressure-pulsed chemical vapor infiltration technique, pyrolytic carbon (pyrocarbon) was deposited at low temperature below 1100°C from the source gases of C6H6 (6%)-H2 into Ni-foam as catalyst. Pyrocarbon could be deposited at 650 °C or higher. The crystallinity was increased with the temperature elevation up to 900°C. It was found by XRD and Raman spectroscopy that high crystalline pyrocarbon particles having mainly graphite phase were deposited at 800-900°C. However, low crystalline carbon was co-deposited under the condition of temperature above 900 °C. For the samples obtained at 900°C or lower, the charge-discharge behaviors were similar to that of high crystalline natural graphite. On the other hand, “sloping region” in charge-discharge curves were observed for the sample obtained at 1000 and 1100 °C, resulting from the co-deposition of low crystalline carbon. The sample obtained at 850 t showed the highest reversible capacity of 352 mAhg-1 at a current density of 30 mAg-1, and 8 % of the capacity was maintained even at 3000 mAg-1.

Fabrication and Microstructure of C/SiC Composites Using a Novel Heaterless Chemical Vapor Infiltration Technique

Fabrication of C/SiC composites by using the heaterless chemical vapor infiltration (HCVI) technique, which is an improved technology based on the conventional chemical vapor infiltration, is reported for the first time in this paper. In the HCVI process, a gradient temperature field formed in the fiber preform overcomes the problems of slow diffusion and restricted permeability of gaseous reactant species to some extent, and the electro‐deposition is necessary to accelerate the SiC deposition rates. The highest linear deposition rates of SiC matrix within inter‐fiber pores are 0.33 μm/h. Microstructures of the C/SiC composites are uniform, and the inter‐fiber and inter‐ply pores can be well infiltrated. The longitudinal and circumferential microcracks are found in the composites.

Behavior of two-dimensional C/SiC composites subjected to thermal cycling in controlled environments

Thermal fatigue behavior of two-dimensional carbon fiber reinforced SiC matrix composites fabricated by chemical vapor infiltration technique was investigated using an on-line quench method in controlled environments which simulated an aero-engine gas. A system of damage information acquisition (SDIA) was developed to study changes in electrical resistance of the C/SiC composites during their damage in dynamic testing. Damage to composites was assessed by the ultimate tensile strength (UTS) and SEM characterization. The results showed that: (1) under different atmosphere, the 2D-C/SiC composites subjected to thermal cycling behaved very differently and the most sensitive atmosphere was the wet oxygen; (2) external load could accelerate the degradation of the composites and changed the oxidation regimes of fibers; (3) the electrical resistance of the specimen could be detected on-line, stored in real time and analyzed reliably by the newly-developed SDIA; (4) 2D-C/SiC composites had an excellent thermal fatigue resistance in different environments.

Thermal shock behavior of two-dimensional C/SiC composites in controlled atmospheres

The thermal shock behavior of a two-dimensional carbon fiber reinforced SiC matrix composite fabricated by chemical vapor infiltration technique was investigated using a quenched method. Damage to composites was assessed by fracture strength, real-time damage energy and SEM characterization. The results showed that: (1) 2D-C/SiC composites had an excellent thermal shock resistance in different atmospheres which were simulated for an aero-engine gas. After 50 quenches from 700 to 1200∘C, the residual strength of the composite still retained 88.92% of the original strength in the wet oxygen atmosphere, and retained 98.90%, 96.46%, 95.82% in the argon, dry oxygen and water vapor atmosphere, respectively. (2) The real-time System of Damage Information Acquisition forecasted that the critical cycle number of thermal shock for 2D-C/SiC composite in the wet oxygen atmosphere was about 40 times, which was consistent with experimental statistical results. (3) Different atmospheres under the thermal shock affected mechanical properties of composites differently.

Pyrocarbon-coating on powdery hard-carbon using chemical vapor infiltration and its electrochemical characteristics

Using the pressure-pulsed chemical vapor infiltration technique, thin pyrocarbon films were coated on the surface of the hard-carbon particles. The crystallinity of pyrocarbon shell was higher than that of the core carbon. The BET surface area and the pores with the diameter of 1.5–5 nm were extremely decreased after coating with 7 wt.% pyrocarbon. These changes in the nano-scaled structure of carbon surface could lead to the reduction of irreversible capacity. The cycleability was improved by pyrocarbon-coating, which would be attributed to the increase of the surface roughness on sub-micron scale by coating with the pebble-like pyrocarbon film to increase the adhesion among the particles by the organic binders.

Structures and electrochemical properties of pyrolytic carbon films infiltrated from gas phase into electro-conductive substrates derived from wood

Using the pressure-pulsed chemical vapor infiltration technique, pyrolytic carbon (pyrocarbon) films were deposited into two sorts of conductive porous substrates, that is, the carbonized wood (A) and the TiN-coated wood (B). Structures and electrochemical properties were investigated as the negative electrodes of lithium-ion secondary battery. The electrodes had the three-dimensionally continuous current paths in the pyrocarbon-based anodes without the organic binders and the additional conductive fillers. The pyrocarbon films adhered tightly to the carbonized wood or TiN as current collector. These macro-structures of electrodes were effective in improving the high rate property. The sort of substrates affected the nano-structure of pyrocarbon. The pyrocarbon in sample (A) had the relatively high crystallinity, whereas the pyrocarbon in sample (B) was disordered. The capacity of pyrocarbon in sample (B) was higher than that of sample (A), reflecting the disordered microstructure of pyrocarbon film (B). However, sample (A) showed higher Coulombic efficiency at first cycle (i.e. 87%) than that of sample (B), which would result from the high crystallinity, laminar microstructure and low surface area of pyrocarbon in sample (A).