Polymer Infiltration Pyrolysis Research Articles

The Microstructure and Mechanical Properties of Si3N4f/BN/SiBCN Microcomposites Fabricated by the PIP Process.

SiBCN ceramics based on SiC, BN and Si3N4 structures have good comprehensive properties such as high-temperature resistance, oxidation resistance, creep resistance and long life, which makes it one of the very promising ceramic material systems in military and aerospace fields, etc. In this study, SiBCN ceramics, as well as Si3N4f/BN/SiBCN microcomposites, were prepared by a polymer infiltration pyrolysis method using PBSZ as the polymer precursor. The PBSZ was completely ceramized by pyrolysis at 900 °C. The weight loss and elemental bonding forms of the products after the pyrolysis of the precursors hardly changed from 600 °C to 900 °C. After pyrolysis at 600 °C for 4 h and using the BN coating obtained from twice deposition as the interfacial phase, a more desirable weak interface of fiber/matrix with a binding strength of 21.96 ± 2.01 MPa can be obtained. Si3N4f/BN/SiBCN ceramic matrix microcomposites prepared under the same pyrolysis conditions have a relatively good tensile strength of 111.10 MPa while retaining a weak interface between the fibers and the matrix. The results of the study provide more theoretical and methodological support for the application of new composite structural ceramic material systems.

Effects of polymer-derived ZiC interlayer on mechanical properties and ablation performance of C/C-ZiC-ZrC-SiC composites prepared by RMI

C/C-ZiC-ZrC-SiC composites were prepared by a combination of PIP (polymer infiltration & pyrolysis) and RMI (reactive melt infiltration) processes on porous C/C composites. The PIP is used for preparing a ZrC-SiC interlayer (denoted as ZiC) between the C/C composites and ZrC-SiC matrix prepared by RMI. Mechanical properties and microstructure of the composites with and without ZiC were characterized. The results show that, the increase of both flexural and tensile strength of the composites after RMI can be optimized by adjusting the ZiC and achieves 50.54% and 56.76%, respectively. The mechanisms can be attributed to the facts that the ZiC effectively protects carbon fibers and PyC from serious erosion by high-temperature melt and weakens the interfacial bond between ceramic matrix and carbon fibers, ensuring a series of stress release under external load. Interestingly, the composites with ZiC also exhibit enhanced ablation performance at ca. 2200 °C due to the improved ZrC content.

Effect of high temperature oxidation on mechanical and electromagnetic interference shielding effectiveness of Ti3SiC2 modified SiCf/BN/SiBCN composites

SiCf/BN/SiBCN composites were prepared through the technique of polymer infiltration pyrolysis (PIP). To enhance the electromagnetic interference (EMI) shielding effectiveness (SE), 20 wt% of Ti3SiC2 was incorporated into the composites. The study investigated the influence of different oxidation temperatures (1300 °C, 1400 °C, and 1500 °C) on both the mechanical properties and EMI SE of the composites. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to analyze the phase and microstructure of the composites, while characterizing their mechanical properties and EMI SE. The outcomes revealed a decline in the mechanical properties of the composites following high temperature oxidation, with the formation of SiO2 and TiO2 as the main oxidation products. Notably, an oxide layer formed on the material's surface at 1400 °C acted as a barrier to oxygen diffusion, facilitating self-healing of pores and cracks and thereby enhancing material protection. Moreover, the material oxidized at 1400 °C demonstrated a remarkable synergy between impedance matching and electromagnetic loss, resulting in the optimum EMI SE. The EMI SE of this material was 6.35% higher than the total shielding effectiveness at room temperature and effectively shielded 99.88% of electromagnetic waves.

Polymer-infiltration-pyrolysis (PIP) inspired hydrophobic nano-coatings for improved corrosion resistance

Polymer-infiltration-pyrolysis (PIP) inspired hydrophobic nano-coatings for improved corrosion resistance

Extreme hardness via nanoscale confinement effects in ultra-low density carbon matrix nanocomposites

Polymer-derived pyrolytic carbons (PyCs) are often desirable for low density high-temperature structural applications when they can be reinforced with high stiffness and strength fibers to address brittleness. Nanofibers, such as aligned carbon nanotubes (A-CNTs), can be an ideal reinforcement owing to their high mass-specific properties, and while modeling suggests that properties of A-CNTs at high volume fractions (i.e., 10–30 vol%) could yield significant enhancements, it is unknown how CNT confinement influences processing, as such materials have never been synthesized. Here, we report process development demonstrating the first successful fabrication of fully infused, void-free A-CNT carbon matrix nanocomposites (A/C-NCs) via polymer infiltration pyrolysis (PIP) that establishes a platform to study nanofiber-reinforced polymer-derived ceramics. The size of the average A/C-NC graphitic crystallites increases as CNT vol% increases up to 30 vol%, and the inter-layer separation of the PyC graphitic crystallites decreases, evidencing a nanoscale confinement effect observed in concert with increased mechanical performance. Vickers microhardness testing in the axial CNT direction of A/C-NCs shows agreement with prior data for low vol% CNTs in PyC and mechanical modeling, where specific hardness increases from ∼3.3 GPa/(g/cm3) for PyC to ∼6.7 GPa/(g/cm3) for 30 vol% A/C-NCs, demonstrating A/C-NCs as an advantaged superhard lightweight material.

Matrix cracking of 2D SiC/SiC composite characterized by in situ SEM and nano-CT

Two-dimensional plain-woven silicon carbide (SiC) fiber-reinforced SiC matrix (2D SiC/SiC) composite was prepared by polymer infiltration-pyrolysis (PIP). Matrix cracking mechanisms of the composite were investigated by in situ SEM and nano-CT to grasp tensile damage evolution. Results showed that PIP-SiC matrix possessed low-fracture energy with non-homogeneous distribution, leading to simultaneous initiation of matrix cracking outside transverse fiber bundles and in unreinforced regions. Cracks then got deflected along weak fiber/matrix interface, which accelerated crack proliferation within the composite. With an increase in the stress, cracks subsequently deflected along plain-woven layers and converged to form longitudinal macrocracks. The composite was finally delaminated via sliding.

Sandwich structure SiCf/Si3N4–SiOC–Si3N4 composites for high-temperature oxidation resistance and microwave absorption

SiC fiber reinforced ceramic matrix composites (SiCf-CMCs) have been widely used as structural-functional materials at high temperatures. However, their mechanical and electromagnetic wave (EMW) absorbing properties will deteriorate due to high-temperature oxidation. Therefore, unique sandwich structure, consisting of inner Si3N4 impedance layer, middle porous SiOC loss layer and dense oxidation-resistant Si3N4 layer, was proposed to enhance multiple material properties in oxidation environment. Herein, SiCf/Si3N4–SiOC–Si3N4 composites was fabricated by alternating chemical vapor infiltration (CVI) and polymer infiltration pyrolysis (PIP) methods. For these composites, SiC fiber is used as both reinforcing phase and electromagnetic (EM) absorber. CVI Si3N4 matrix was distributed in inner and outer layer of the SiCf/Si3N4–SiOC–Si3N4 composites. While inner Si3N4 layer between BN interphase and SiOC matrix forms nano-heterogeneous interphase to consume EM energy and enhance mechanical properties of composites, outer dense and oxidation-resistant CVI Si3N4 coating serves to maintain properties. PIP SiOC matrix exhibits porous structure that can effectively deflect cracks and achieve multiple scattering of EMW. SiCf/Si3N4–SiOC–Si3N4 composites with sandwich structure demonstrated excellent EMW absorbing properties and mechanical performance in high-temperature oxidation environments.

Ablation mechanism of C/C–SiC and C/C–SiC–ZrC composites in hypersonic oxygen-enriched environment

In this study, C/C–SiC and C/C–SiC–ZrC composites were prepared via chemical vapor infiltration and polymer infiltration pyrolysis, and the ablation mechanism under hypersonic oxygen-rich environmental conditions was investigated. The C/C–SiC composites demonstrate an excellent ablation resistance in a hypersonic oxygen-rich environment with a relatively low temperature and speed of approximately 1800 K and 1100 m/s, respectively. It is only in the ablation center area with higher temperatures that a certain degree of thermochemical ablation was observed. The mass and linear ablation rates of C/C–SiC composites (0.027 g/s and 0.117 mm/s, respectively) showed a significant increase in a hypersonic oxygen-rich environment with a temperature and velocity of approximately 2050 K and 2000 m/s, respectively. The high-temperature ablation resistance of ZrC-modified C/C–SiC–ZrC composites improved significantly. However, the ZrC ceramic component had a considerable impact on the ablation resistance of the material. The structural integrity of C/C–20SiC–30ZrC composites was relatively high in hypersonic oxygen-rich environments with a jet temperature and velocity of 2050 K and 2000 m/s, respectively, and mass and linear ablation rates were 0.012 g/s and 0.015 mm/s, respectively. When the ZrC content increased by 40%, the ablation resistance of the composite reduced significantly, whereas the mass and linear ablation rates increased to 0.043 g/s and 0.130 mm/s, respectively.

The mechanical, thermophysical and electromagnetic properties of UD SiCf/SiC composites in different directions

Unidirectional (UD) silicon carbide (SiC) fiber-reinforced SiC matrix (UD SiCf/SiC) composites with CVI BN interphase were fabricated by polymer infiltration-pyrolysis (PIP) process. The effects of the anisotropic distribution of SiC fibers on the mechanical properties, thermophysical properties and electromagnetic properties of UD SiCf/SiC composites in different directions were studied. In the direction parallel to the axial direction of SiC fibers, SiC fibers bear the load and BN interphase ensures the interface debonding, so the flexural strength and the fracture toughness of the UD SiCf/SiC composites are 813.0 ± 32.4 MPa and 26.1 ± 2.9 MPa·m1/2, respectively. In the direction perpendicular to the axial direction of SiC fibers, SiC fibers cannot bear the load and the low interfacial bonding strengths between SiC fiber/BN interphase (F/I) and BN interphase/SiC matrix (I/M) both decrease the matrix cracking stress, so the corresponding values are 36.6 ± 6.9 MPa and 0.9 ± 0.5 MPa∙m1/2, respectively. The thermal expansion behaviors of UD SiCf/SiC composites are similar to those of SiC fibers in the direction parallel to the axial direction of SiC fibers, and are similiar to those of SiC matrix in the direction perpendicular to the axial direction of SiC fibers. The total electromagnetic shielding effectiveness (EM SET) of UD SiCf/SiC composites attains 32 dB and 29 dB when the axial direction of SiC fibers is perpendicular and parallel to the electric field direction, respectively. The difference of conductivity in different directions is the main reason causing the different SET. And the dominant electromagnetic interference (EMI) shielding mechanism is absorption for both studied directions.

Enhanced mechanical property and tunable dielectric property of SiCf/SiC-SiBCN composites by CVI combined with PIP

The SiBCN matrix via chemical vapor infiltration (CVI) or/and polymer infiltration pyrolysis (PIP) technologies was orderly introduced to SiCf/SiC composites to optimize the mechanical property and electromagnetic (EM) shielding effectiveness simultaneously. The BN interface with the thickness of 350 nm was designed to obtain a little stronger interface bonding. The flexural strength of SiCf/SiC-SiBCN composites reached 545.45±29.59 MPa thanks to the crack deflection between the CVI SiC and CVI SiBCN, as well as CVI SiBCN and PIP SiBCN matrix because of the modulus difference between them. The fracture toughness (KIC) with the value of 16.02±0.94 MPa·m1/2 was obtained owing to the extension of crack propagation path. The adverse effect of stronger interface bonding was eliminated by the design of matrix microstructure for SiCf/SiC-SiBCN composites. The thermal conductivity in the thickness direction was 7.64 W·(m·K)−1 at 1200 °C and the electric resistivity decreased to 1.53×103 Ω·m. The tunable dielectric property was obtained with the coordination of wave-absorption CVI SiBCN matrix and impedance matching PIP SiBCN matrix, and the total shielding effectiveness (SET) attained 30.01 dB. It indicates that the SiCf/SiC-SiBCN composites have great potential to be applied as structural and functional materials.

Curing kinetics of a siloxane pre-ceramic prepreg resin

Ceramic matrix composites are being investigated as new material of choice for aeronautic and aerospace applications, because of their higher thermal resistance. Among the different ways to manufacture these materials, the polymer infiltration pyrolysis (PIP) is the most versatile. This route uses preceramic resins that present the benefit to be processed like thermosets. However, there is a lack of information available regarding the curing kinetics of preceramic resins and their detailed chemical composition. This limits the possibility for the end user to freely operate the resin, with sufficient accuracy to manufacture components. Dynamic Differential Scanning Calorimetry (DSC) were carried out at 1, 3, 5, 10, 15 and 20°C/min, to plot a Time-Temperature-Transformation (TTT) diagram for a commercial polysiloxane resin, the SPR-688. The activation energy and kinetic parameters were estimated using Kinetics Neo. The glass transition temperature of SPR-688 was modelled using the Di Benedetto's equation. The gelation point was investigated by chemorheology using a Dynamic Mechanical Analysis (DMA) apparatus, by plotting tan δ vs time. The degree of cure was thereafter estimated. The curing mechanism was shown to be a single step reaction (A→B). The cure kinetic was successfully described by numerical optimization, which is based on the analytical Friedman method. The proposed model showed a good agreement between predicted and experimental data. This suggests that the curing kinetics of preceramic resins can be approximated using models that are well accepted for thermosetting polymers. This general strategy is key to manufacturing prepregs made of preceramic resins.

Oxidation behavior of 3D SiCf/SiBCN composites at 800–1200 °C

3D SiCf/BN–SiC/SiBCN composites were fabricated via precursor impregnation and polymer infiltration pyrolysis (PIP). Oxidation behavior of the composites heated in air at 800 °C, 1000 °C and 1200 °C for 50 h was investigated. Following the oxidation treatment, it was found that the bending strength of the composites at different oxidation temperatures was degraded. The weight loss of the composites decreased gradually over the range of oxidation times of 1–50 h. In order to clarify the oxidation mechanism of the composites, reconstructed images, microstructures, phase compositions, the oxide layer formed on the composites and main chemical reactions were all analyzed. It was revealed that the degradation in the fracture strength of the composites was closely related to the oxidation of SiBCN matrix and BN-SiC interphase, whereas there was no signs of oxidation products about SiC fiber, which indicated that SiC fiber could be protected from oxygen by SiBCN matrix at 800−1200 °C in air.

Carbon Nanotube Reinforced Strong Carbon Matrix Composites.

As an excellent candidate for lightweight structural materials and nonmetal electrical conductors, carbon nanotube reinforced carbon matrix (CNT/C) composites have potential use in technologies employed in aerospace, military, and defense endeavors, where the combinations of light weight, high strength, and excellent conductivity are required. Both polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods have been widely studied for CNT/C composite fabrications with diverse focuses and various modifications. Progress has been reported to optimize the performance of CNT/C composites from broad aspects, including matrix densification, CNT alignment, microstructure control, and interface engineering, etc. Recent approaches, such as using resistance heating for PIP or CVI, contribute to the development of CNT/C composites. To deliver a timely and up-to-date overview of CNT/C composites, we have reviewed the most recent trends in fabrication processes, summarized the mechanical reinforcement mechanism, and discussed the electrical and thermal properties, as well as relevant case studies for high-temperature applications. Conclusions and perspectives addressing future routes for performance optimization are also presented. Hence, this review serves as a rundown of recent advances in CNT/C composites and will be a valuable resource to aid future developments in this field.

Design and fabrication of Al2O3f/SiCN composite with excellent microwave absorbing and mechanical properties

AbstractA new kind of structural and functional integration ceramic matrix composite material was prepared from high‐performance alumina (Al2O3) fibers and absorbing silicon carbonitride (SiCN) ceramics via a combination of polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods. The Al2O3 fiber annealed at its cracked temperature had enhanced permittivity, because the sizing agent on the Al2O3 fiber surface was cracked into pyrolysis carbon. For PIP + CVI Al2O3f/SiCN composites, PIP SiCN matrix with low conductivity was used as the matching phase, while CVI SiCN matrix with medium permittivity and dielectric loss was regarded as the reinforcing phase distributed in porous PIP SiCN matrix and inter‐bundles of Al2O3 fiber to improve their mechanical and microwave absorption properties. The fracture toughness and flexural strength of Al2O3f/SiCN composite were determined to be 9.4 ± 0.5 MPa m1/2 and 279 ± 28 MPa, respectively. Based on the design principles for impedance matching, the Al2O3f/SiCN composites before and after oxidation were used as loss and impedance layers, respectively. It was found that the optimized composite had the lowest reflection coefficient (RC) of −70 dB and the effective absorption bandwidth covering the whole X‐band. In conclusion, Al2O3f/SiCN composite can serve as a high‐temperature structural material with excellent microwave absorption properties for aerospace applications.

A large-pressure-range, large-sensing-distance wireless passive pressure sensor based on polymer infiltration pyrolysis-enhanced polymer-derived ceramic films

Large-pressure-range, large-sensing-distance evanescent-mode resonator wireless passive pressure sensors were fabricated from silicon carbonitride polymer-derived ceramic (PDC-SiCN) films enhanced by the polymer-infiltration-pyrolysis (PIP) process. The properties of PIP enhanced PDC films ensure a large pressure range for the sensor. To increase the sensing distance between the interrogation antenna and the sensor, the size or position of the resonator and slot antenna were optimized by High Frequency Structure Simulator simulations. The experimental results show that the resonant microwave signal can be wirelessly detected at distances up to 30 mm. The pressure sensor has a large pressure range (0–850 kPa) and high pressure sensitivity (211.8 kHz kPa−1) in pressure environments at room temperature.

Fabrication of high‐fracture‐strength and gas‐tightness PDC films via PIP process for pressure sensor application

AbstractHigh‐fracture‐strength and high‐gas‐tightness thin‐film gas‐pressure sensors were fabricated using a silicon oxycarbonitride polymer‐derived‐ceramic (SiCNO‐PDC) material via a multiple polymer‐infiltration‐pyrolysis (PIP) process. To obtain dense SiCNO ceramic films, two types of liquid polyvinylsilazane (PVSZ) precursors were chosen; a high‐ceramic‐yield precursor with high viscosity (PVSZ‐1) was designed to construct the skeleton of ceramic film, whereas a relatively high‐ceramic‐yield precursor with low viscosity (PVSZ‐2) was designed to infiltrate in ceramic defects. The results confirmed that the PVSZ‐2 can effectively fill both intergranular and intragranular defects of ceramic films pyrolyzed by the PVSZ‐1, and produce the sponge‐like structures with nanosized pores. Although the density of the ceramic films only increased by 2.2%‐5.2% after PIP process, the gas tightness was fundamentally improved, and all ceramic films after PIP process could keep gas‐tight condition without loss of pressure after 72 hours. Similarly, the fracture strengths of the ceramic films after PIP cycles have also been improved, and the value could reach 108 MPa after only three PIP cycles. In addition, because a linear relationship among the load, resonant frequency, and deflection was detected in our ceramic films, the wireless passive gas‐pressure sensors with high‐sensitivity and high‐temperature resistance have been fabricated. It strongly indicates that the ceramic films obtained by our PIP process have real potential to be used as thin‐film gas‐pressure sensing elements in high‐temperature and high‐pressure fields.

Glassy carbon cladding structure with elongated SiCnw reinforced carbon foam insert

In this study, glassy carbon cladding structure with elongated SiCnw reinforced carbon foam insert (GC-CF/SiCnw) is prepared by slow Polymer Infiltration Pyrolysis (PIP) method. It is tested that the density of the structure reaches 0.6362 g cm−3 while the open porosity reaches 0.8% and total porosity reaches 52.6%. The SEM images show the obvious boundary between the inner and outer parts. In addition, the structure exhibits excellent mechanical properties, its compressive strength reaches 6.6 MPa, and the specific strength reaches 10.3877 MPa g−1 cm−3. Considering the fracture mechanism, the four-stage different force composition in the fracture process is significantly different from the traditional material, reflecting the influence of the excellent structural design of the material on the mechanical properties. Moreover, the structure exhibits excellent high temperature insulation properties. As the temperature increases from 293 K to 1273 K, the effective thermal conductivity increases from 0.215 W m−1K−1 to 0.587 W m−1K−1. Considering the thermal insulation mechanism, the reflection of thermal radiation from the dense and smooth GC shell and the scattering of thermal radiation from the SiC nanowires greatly reduces the transmission of thermal radiation. Besides, the temperature field index diagram under steady-state heat conduction as a heat-source temperature of 1200 K is obtained by thermal resistance network method.

Mechanical and dielectric properties of SiCf/BN/SiBCN composites via different synthesis technologies

SiC fibers reinforced SiBCN ceramic matrix composites (SiCf/BN/SiBCN composites) were synthesized by direct chemical vapor infiltration (CVI), polymer infiltration pyrolysis (PIP) or chemical vapor infiltration combined with polymer infiltration pyrolysis (CVI + PIP). It is shown that the insertion of a continuous and dense SiBCN matrix via the CVI process improves the flexural strength and modulus. Interface debonding and fiber pullout happened with 50–100 nm BN interface in CVI and CVI + PIP SiCf/BN/SiBCN composites. The relative complex permittivity was measured in X-band. Higher ε′′ values in CVI-containing composites can be observed, which can be attributed to the accumulation of C and SiC phases and a multilayer matrix. Strong electromagnetic wave attenuation ability was obtained with high dielectric loss.

The fabrication and mechanical properties of SiC/SiC composites prepared by SLS combined with PIP

Traditionally, SiC components with complex shapes are very difficult or even impossible to fabricate. This paper aims to develop a new manufacturing process, combining selective laser sintering (SLS), cold isostatic pressing (CIP) and polymer infiltration pyrolysis (PIP), to manufacture complex silicon carbide parts and improve the mechanical properties of silicon carbide ceramic parts. The density and porosity of SiC/SiC composites were measured. Furthermore, the mechanical properties of the specimens with cold isostatic pressing and the specimens without cold isostatic pressing were compared. The bending strength of the specimens with cold isostatic pressing was 201 MPa, and the elastic modulus was 1.27 GPa. And, the bending strength of the specimens without cold isostatic pressing was 142 MPa, and the elastic modulus was 0.88 GPa. Increasing the density of SiC/SiC can enhance the mechanical properties of SiC/SiC composites.

Oxidation behavior and high-temperature flexural property of CVD-SiC-coated PIP-C/SiC composites

Polymer infiltration pyrolysis (PIP) was used to prepare carbon fiber-reinforced silicon carbide (C/SiC) composites, and chemical vapor deposition (CVD) was employed to fabricate SiC coating. The oxidation behavior at 1700 °C and the flexural property at 1200 °C were tested. SiC coating exerted remarkable oxidation effects on PIP-C/SiC composites. In the absence of coating, PIP-C/SiC composites lost 29.2% of its mass, with merely 6.74% of the original flexural strength retained. In contrast, CVD-SiC coated PIP-C/SiC composites had the mass loss of 10.2% and the flexural strength retention ratio of 23.4%. In high-temperature tests, SiC coating played an important role in the flexural strength of PIP-C/SiC composites. The flexural strength of uncoated composites became 330.7 MPa, and that of coated ones reduced from 655.3 to 531.2 MPa.