Porous Carbon Preforms Research Articles

High strength and self-lubrication graphite/SiC composites

For the reaction-formed graphite/SiC composites, the presence of cracks and poor mechanical properties seriously affect their reliability as wear resistant or sealing materials. In this work, a porous carbon preform was pressure formed first by carbon-composite-powder (PFC@G) and carbon black, impregnated with resin and carbonized subsequently, which can heal the micro-cracks, increased the strength of porous carbon preforms and finally reduce the reactivity of liquid Si and carbon during the reaction forming process. The results show that the modified porous carbon preform has a 4.8 % reduction in porosity and a 3.98 times increase in compressive strength. After reactive melt infiltration, the prepared graphite/SiC composites had a compact and isotropic structure and obtained the highest carbon content of 66.18 vol%. In addition, the coupling effect of the PFC@G size on the carbon content and mechanical properties of composites was studied. With the decreasing of the PFC@G size, the mechanical properties of the composites increased and the carbon content decreased. The sample with a carbon content of 48 vol% and a bending strength of 137 MPa exhibited excellent self-lubrication properties.

SiC-Si composite part fabrication via SiC powder binder jetting additive manufacturing and molten-Si infiltration

High hardness and superior thermal stability of silicon carbide (SiC) are advantageous for engineering parts but they make it difficult to manufacture complex products with full density. Reaction-bonded SiC are effective solutions for the paradox. SiC-Silicon (Si) composite materials are manufactured by molten Si infiltration through porous SiC and/or Carbon (C) preforms owing to superior wetting of molten Si on SiC and reactive wetting of molten Si on C. Cold isostatic pressing of mixed powders feedstock, green machining and joining are a typical manufacturing pathway for green-body parts. Multiple processes with tools and significant materials loss are regarded as wastes from the viewpoint of lean manufacturing principle. In the present study, feasibility of binder jetting additive manufacturing (BJT AM) technology was assessed for green-body part manufacturing stage in the course of SiC/Si parts production. Adoption of BJT AM showed opportunities for process savings, tool savings, materials savings and design freedom. However, strength of brown-body parts as well as density of as-built green-body parts are challenges. To overcome the limitations, phenolic resin solution impregnation through as-built green parts was introduced. It is highlighted that green-body strength, brown-body strength and infiltrated-body strength are modified with evolutionary phase transformations from cured phenolic resin to reaction-synthesized SiC by way of decomposed carbon through the conventional post-AM densification manufacturing pathway.

Hybrid processing of TiC/TiCu/C composites with tailored hardness

This work reports the effect of TiC volume fractions on hardness of TiC/TiCu/C composites synthesized through in situ reactive infiltration of Ti-Cu alloy into porous carbon preforms prepared by 3 D-printing. Reactive melt infiltration of the alloy at 1100 °C under argon into C-preforms with different porosities resulted in materials composed of TiC, Cu-rich intermetallic matrix (Ti3Cu4) and residual carbon. The microstructure consists of TiC grains distributed along the Cu-Ti/C boundary. The hardness of TiC/Ti3Cu4/C composites could be tailored by the TiC volume fraction and the distribution in the composites, which are determined by the processing parameters and the initial porosity of the carbon templates in 3 D-printing stage. The hardness of the produced composites ranges from 350 HV to 570 HV and could be tailored by the TiC volume fraction and distribution in the composites, which are determined by the processing parameters and the initial porosity of the carbon-preforms.

Thermal Protection Performance of Porous Carbon Ablators with Three Different Matrices

A porous carbon material with a three-dimensional network and open-cell structure was applied to preform new lightweight ablators. The materials impregnated into the porous carbon were polyimide, phenol, and poly(methyl methacrylate). To evaluate the performance of the ablators, their thermal response and recession resistance were evaluated using an arc wind tunnel. All the ablators exhibited thermal insulation due to the pyrolysis reaction, and they decreased in the surface temperature due to gas blocking. Poly(methyl methacrylate) was especially found to be the most effective for the thermal responses desired here. Furthermore, the ablators showed stable recession resistance, which was comparable to that of existing lightweight ablators. This was attributed to the fact that the porous carbon preform had high resistance to mechanical erosion, which in turn maximized the effect of blownoff pyrolysis gas in improving recession resistance. Among the materials, the poly(methyl methacrylate) porous carbon ablator achieved the best recession resistance at low heat flux; this was the highest recession resistance measured thus far for a lightweight ablator.

Preparation of Siliconized Graphite by Liquid Silicon Infiltration of Porous Carbon Materials

Siliconized graphite was prepared by liquid silicon infiltration (LSI) of carbon preforms composed of mesocarbon microbeads (MCMBs), petroleum coke and graphite powder as the carbon source with binder of phenolic resin. Effects of the carbon source, binder contents, ball-milling time and moulding pressure on the properties of the porous carbon preforms and the siliconized graphite were investigated. The results showed that the moulding pressure was the main factor influencing the open porosity of the carbon preforms. The carbon preforms with porosity of above 45% could be infiltrated completely with Si, and maximum open porosity of 56% could be reached for the carbon preforms. For the siliconized graphite, high MCMBs contents contributed to high density, while high graphite content led to increased carbon remaining. The densities, open porosities, and the highest bending strength of the siliconized graphite were ranged between 2.90-3.01g·cm-3, less than 1.5%, and 317 MPa, respectively.

Fabrication and Properties of Porous Carbon Preforms for Making Reaction Formed SiC

This paper describes a proper low cost way to fabricate defects free porous carbon preforms with interconnect pore structure for making reaction formed SiC (RFSC). Taking charcoal , poplar powder, camphene and polymer dispersant together, making slurries by milling under 55 °C for several hours, controlling the content of charcoal and poplar powder, after casting, sublimating and carbonizing, the porous carbon performs with a series density (0.66 g/cm3-0.78 g/cm3) and porosity (62.9 vol.%-68.6 vol.%) were prepared; through the Si infiltrating process under a vacuum condition (~5.0 Pa) at 1500°C for about 0.5 hour, the RFSCs with fine mechanic performance were fabricated, one RFSC sample has the density, Weibull modulus, and the max three points flexural strength is 2.91 g/cm3, 9.5 and 505.0 MPa respectively.

A low cost preparation of C/SiC composites by infiltrating molten Si into gelcasted pure porous carbon preform

C/SiC composites were prepared by infiltrating molten Si into gelcasted pure porous carbon preforms derived from mesocarbon microbeads (MCMBs). First large size flaw-free carbon preforms with smooth surfaces were produced by gelcasting method. The porosity and pore size of the carbonized preforms can be adjusted by changing the solid loading (MCMBs) ranging from 40 to 65wt%. Subsequently, C/SiC composites were fabricated by liquid silicon infiltration of the porous carbon preforms. The results show that the preforms with solid loading from 40 to 50wt% were completely infiltrated with Si and formed a C/SiC with homogeneous microstructure. While “SiC shell—black carbon core” structures were observed for the C/SiC composites with solid loading above 50wt%, indicating that the Si infiltrating process was stopped in the surface of the preform. Reaction and infiltration mechanism analysis reveals that the siliconization process of porous carbon preform and the microstructures of the C/SiC samples were mainly affected by the reaction activity of carbon materials and pore structures of carbon preforms.

Microstructural analysis of a C/SiC ceramic based on the segmentation of X-ray phase contrast tomographic data

Abstract This paper is dedicated to the analysis of 3D data of carbon fiber reinforced silicon carbide ceramics. In the production process of C/SiC, a porous carbon preform reinforced with bundles of carbon fibers is infiltrated with liquid silicon at approximately 1 500 °C. The reaction between liquid silicon and carbon creates a layer of silicon carbide while the silicon vanishes almost completely. This material is able to withstand extremely high temperatures and it is extremely tough with respect to fracture. To increase the efficiency of the costly and time consuming production process, methods for monitoring the quality of the material are helpful. For instance, the thickness of the silicon carbide layer is a valuable measure. Moreover, due to different coefficients of thermal expansion of the components, typically cracks appear during the production process. For effective analysis 3D high resolution image data are necessary that can be acquired by synchrotron computed tomography. In a first image processing step, we segment the 3D image data with a convex optimization approach incorporating spatial regularity. Further, we work on the detection of cracks using an eigenvalue analysis of the 3D Hessian matrix determined in each pixel.

Conductive TiC/Ti–Cu/C composites fabricated by Ti–Cu alloy reactive infiltration into 3D-printed carbon performs

The microstructure and electrical properties of dense TiC/Ti–Cu/C composites fabricated by pressureless reactive infiltration of Ti–Cu alloy into porous starch-derived carbon preforms prepared by 3D printing was evaluated. Porosities in the range of 65–78 vol% were varied by post-isostatic pressing the as-printed preforms at pressures of 50–400 MPa. The reactive melt infiltration was carried out at 1100℃ in a flowing Ar atmosphere and resulted in formation of a composite comprised predominantly of substoichiometric TiC, binary intermetallic Ti–Cu phases and residual carbon. Scanning electron microscopy analyses revealed a microstructure consisting of dispersed fine-grained TiC in a Ti–Cu matrix surrounded by a continuous carbon phase. Electrical resistivity measurements using the four-probe method were carried out and correlated to the composite microstructure. The electrical resistivity was evaluated in terms of carbon and TiC volume fractions.

Preparation of Porous Carbon Preform by Casting Camphene Based Charcoal Slurry

This paper describes the process of fabricating porous carbon preform by casting the camphene based charcoal slurry. Five kinds of slurry with different solid content varied from 20vol% to 40vol% has been prepared, we have studied the rheological behavior of slurries and the sublimation behavior of casted bodies. Porous carbon preform with negligible linear shrinkage (<0.6%), high porosity (>67vol%) and interconnected pore structure has prepared.

213 CNFとメゾフェーズピッチによる多孔質炭素プリフォームの作製

213 CNFとメゾフェーズピッチによる多孔質炭素プリフォームの作製

Fabricating hollow turbine blades using short carbon fiber-reinforced SiC composite

The development of hollow turbine blades fabricated by nickel-base superalloy is limited by its high density and low operating temperature (<1,100 °C). A new technology for fabricating hollow turbine blades of fiber-reinforced SiC composite was put forward. The chemical corrosion process of DSM Somos 19120 resin mold was investigated, and the pyrolysis of phenolic resin and the infiltration of liquid silicon were analyzed by using scanning electron microscope and X-ray diffraction. The influence of carbon fiber content on fracture strength and fracture toughness of fiber-reinforced SiC composite was investigated using the measurement of three-point flexural strength test. Results showed that stereolithography molds of photosensitive resin were corroded perfectly using KOH alcohol water solution. The porous carbon preforms were obtained after phenolic resin was pyrolyzed from 400 to 800 °C, which were then infiltrated with molten silicon to gain SiC matrix at the temperature of 1,450 °C in 1 h. The fracture strength and fracture toughness of SiC ceramic matrix were enhanced with the increase of short carbon fiber content. The maximum fracture strength and fracture toughness of samples were about 270 MPa and 5.1 MPa m1/2, respectively. Finally, hollow turbine blades were successfully fabricated using short carbon fiber-reinforced SiC composite.

Reaction Formed SiC Prepared by Room Temperature Freezing Casting

The porous carbon preforms with fine pore structure has been successfully fabricated by room temperature freezing casting, and the reaction formed SiC with fine mechanical property has prepared successfully by liquid silicon infiltration process. Charcoal powder was used as carbon resource, camphene was used as sublimate vehicle, methyl cellulose was used as pore maker and bonder. The result shows that the homogeneity of the porous carbon preform has been improved largely by adding methyl cellulose ,and the defects of reaction formed silicon carbide has reduced largely also. The density, average flexural strength and Weibull modulus of the best reaction formed silicon carbide prepared in this paper is 2.86 g/cm3, 430.75MPa and 9.29 respectively.

Fabrication of Complex-Shaped SiC Parts Based on Polymerization -Induced Phase Separation and Pyrolysis Technique

A route based on a technique of polymerization - induced phase separation and pyrolysis (PIPSP) has been developed to fabricate complex-shaped SiC parts. The capability of this process to produce complex component shapes has been demonstrated, and corresponding reactive mechanisms have been also discussed. Three types of porous carbon preforms, i.e. mesoporous carbon monoliths (MCMs), hierarchical porous carbon monoliths (HCMs) and porous carbon foam (PCFs) were obtained, which has different pore size distributions. The pore structures of the preforms can be controlled through changing starting mixture composition and polymerizing conditions. The apparent porosity of the preform was changed from 19.9 to 60%, which was a key parameter to obtain dense SiC parts. After reactive infiltration of the preform with Si, the SiC parts were obtained. Geometry of SiC parts were controlled by molds. The dimension shrinkage of SiC parts was less than 3% before/after siliconization and no distortion occurred. Compared with other molds assistance route, the wax mold assistance route was a most potential technique to fabricate SiC parts industrially because of its suitable forming precision, recycled mold materials and low-cost. The mechanism of the reactive infiltration of MCMs was different from that of the reactive infiltration of preforms with bigger pore size, i.e. the pore channels of MCMs were restructured at transitional stage of reaction.

A wax-mold route to fabricate polymer-derived SiC scaffold

A wax-mold route was developed to fabricate phenolic resin-derived SiC scaffold. Firstly, a wax-mold with the desired structure of the scaffold was obtained. Then resin mixtures were poured into the mold. After curing and pyrolyzing, porous carbon preform was obtained. The wax-mold was removed through being melted during curing, and the pattern material could be recycled. Finally, the SiC scaffold was fabricated by infiltrating liquid silicon into the preform. The dimension shrinkage of SiC scaffold was between 1.3 and 3 % before/after infiltration, which was affected by the infiltrating temperature and the starting components in resin mixtures, and there is no distortion. When the preform with apparent porosity of 45.5% was employed, the flexural strength and the density of SiC scaffold were 445 MPa and 3.07 g/cm 3, respectively.

Microstructural evolution during silicon carbide (SiC) formation by liquid silicon infiltration using optical microscopy

Abstract Optical microscopy and quantitative digital image analysis were used to examine the formation of fully dense, net shape silicon carbide by liquid silicon infiltration (LSI) of porous carbon preforms. By examining the phase distribution and structural changes during the reaction, we identified six reaction stages (I–VI) that describe reaction mechanisms and their time scales. The initial stages (0–15 min) of the LSI reaction include (I) liquid silicon infiltration of the carbon preform, (II) dissolution of carbon, and (III) formation of silicon carbide at the liquid–solid interfacial regions. These initial stages occur simultaneously and very rapidly, and culminate in (IV) the completion of a continuous silicon carbide layer of about 10 μm at every liquid–solid interface. Further reaction can only be achieved by (V) carbon diffusion through this layer. The reaction is essentially complete after ∼120 min. Longer reaction times should be avoided because over-reacting causes (VI) long, thin silicon-filled cracks to develop within the continuous silicon carbide matrix.

Rapid manufacture of net-shape SiC components

Stereolithography was introduced into the net-shape SiC components fabrication process to produce the molds for the preparation of porous carbon preforms. The mixed resin was cast into the molds and then pyrolyzed to produce the porous carbon preforms which had a high porosity of 40.93% and were infiltrated and reacted with molten silicon to get reaction-formed silicon carbide (RFSC) components. To realize the complete infiltration of the thick wall parts, pipelines as the channels for the molten silicon were added into the components. The hierarchical structures of the porous carbon had been attained to realize the controllability of the microstructure and properties of RFSC. The samples had a high linear and volume shrinkage, 24.7% and 57.3%, respectively, during the pyrolysis process. Phase composition had been investigated by optical microscopy and X-ray diffraction analysis. The results indicate that no residual carbon was available in the final RFSC. The net-shape fabrication process for the RFSC components could promote the industry applications where SiC components with complex surface and inner structure were needed.

The combined effect of porosity and reactivity of the carbon preforms on the properties of SiC produced by reactive infiltration with liquid Si

This study is focused on the effect of the porosity and chemical reactivity with silicon of the carbon preforms on the properties of SiC pieces produced by reactive infiltration. Petroleum residues were selected as carbon precursor because of their unique combination of properties. On the one hand, semicoke powders with optimum self-sinterability can be obtained from them to develop a wide range of porous carbon preforms without addition of binder to carry out the porosity study. On the other hand, reactivity of the carbon material with silicon can be modified by employing semicokes with different mesophase microstructure obtained from petroleum residues with different chemical composition. SiC yield was strongly affected by the degree of anisotropy of the carbon material, the most ordered carbon being more reactive. SiC pieces made from the optimum carbon preforms (made up by combining the most graphitic carbon and 40% of open porosity) achieved bending strength values of around 260 MPa. Chemical reactivity of carbon substrates was also modified by graphitization treatment. An improvement in the mechanical properties of SiC pieces up to 66% was achieved due to the structural modification caused by graphitization of the carbon preforms. Bending strengths twice the value of commercially available ones were achieved.

Reaction forming of silicon carbide ceramic using phenolic resin derived porous carbon preform

SiC ceramics were prepared with porous carbon preforms derived from phenolic resin by a reaction-forming method. The effects of the structure of the preform pores and the infiltration process on the properties of SiC ceramics were investigated, and components with complex shapes were fabricated by combining this process with stereolithography (SLA). Dense SiC ceramics were obtained from carbon preforms with high apparent porosities, but SiC ceramics with many macrodefects resulted from a carbon preform with an apparent porosity of 39%. The infiltration of molten silicon into the preform pore channel was accelerated under vacuum pressure, resulting in an increase in the depth of the Si infiltration. The growth of SiC was predominantly controlled by carbon diffusion at the last stage of the reaction. The extended grain growth caused the SiC grains to coalesce and some free Si was enveloped in the SiC grains. SiC components with complex geometries were fabricated by combining reaction forming with SLA. The geometry was controlled by SLA.

Synthesis of biomorphic Si-based ceramics

Tilia wood was transformed by pyrolysis into carbon preform. This porous carbon preform was infiltrated with TEOS (Si(OC2H5)4), as a source of silica. In situ reaction between the silica and the carbon template occurred in the cellular wall at a hight temperature. Depending on the applied atmosphere, non-oxide (SiC) or oxide (SiO2) ceramics were obtained. Scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared (IR) spectroscopy, mercury porosimetry and BET measurements were employed to characterize the phases and crystal structure of biomorphic ceramics. The experimental results showed that the biomorphic cellular morphology of the wood maintained in both the SiC and SiO2 ceramics, wich consisted of ?-SiC with trace of ?-SiC and SiO2, respectively. .