In order to investigate the effects of oxide particles on the high-temperature resistance and ablation performance of ceramicizable phenolic resin composites, three types of quartz fiber-reinforced ceramicizable phenolic resin composites were prepared using MgO particles or Al2O3 particles as the second-phase oxides and ZrB2 particles as the high-temperature ceramic filler, through a mold pressing process. The enhancement effects and mechanisms of the added second-phase oxides on the high-temperature resistance and ablation performance of the composites were discussed and analyzed through high-temperature testing, phase characterization, oxyacetylene testing, and microstructure characterization. The results show that ZrB2 particles oxidize to form ZrO2 and B2O3 in an oxygen-rich high-temperature environment. The added second-phase oxide particles can react with B2O3 to form corresponding borates, thereby strengthening the matrix. After treatment at 800 °C, the flexural strength of the ZrB2-MgO quartz fiber-reinforced phenolic resin composite (QFPR/ZM) increased by 55.3

This study utilized phosphate composites modified with nano-La2O3. The influences of nano-La2O3 on the thermal stability, phase evolution, and high-temperature load-bearing capacity of phosphate materials were investigated, as well as the high-temperature resistance and flexural strength of alumina/phosphate composites based on nano-La2O3. The results indicate that the incorporation of nano-La2O3 effectively enhances the mass retention of phosphate materials, with the material exhibiting optimal overall performance at a nano-La2O3 loading of 20 wt%. After heat treatment at 1,200 degrees C, the modified composite material retained a flexural strength of 28.1 MPa, which was significantly higher than that of the unmodified composite material. Microstructural characterization confirms that the composite undergoes a phase transformation at high temperatures, yielding a densified structure. This transformation promoted the formation of an effective thermal protection barrier composed of AlPO4 and LaPO4 phases. The formation of this protective layer plays a critical role in significantly improving the high-temperature load-bearing capacity and ablation performance of composite materials.

Lightweight phenolic aerogel composites represent a crucial component of future thermal protection systems in aerospace applications. Multifunctional hybrid modification is considered an effective method to enhance the thermal stability and ablation resistance of phenolic aerogel composites. In this study, silicone and boric acid were crosslinked with phenolic resin (SiBRx) to introduce high-bond-energy Si-O and B-O bonds. Subsequently, the SiBRx can be used to prepare a lightweight aerogel by the sol-gel method. The specific surface area of the SiBRx aerogel reached 180.25 m2 g-1, representing a 59% increase compared to the unmodified phenolic resin (PR) aerogel. Furthermore, the SiBRx aerogel exhibited superior thermal stability, with a maximum decomposition temperature of 603.2 °C, 12% higher than that of the PR aerogel. Quartz fiber-reinforced phenolic aerogel composites (QF/SiBRx) were fabricated by incorporating quartz fiber mats and varying the content of the curing agent hexamethylenetetramine (HMTA). At a HMTA content of 15%, the QF/SiBR15% aerogel composite achieved a bending strength of 14.17 MPa, with compressive strength increasing from 9.99 MPa to 12.26 MPa. Moreover, the QF/SiBRx composites demonstrated outstanding ablation resistance, with a remarkably low linear ablation rate of 0.077 mm s-1. The incorporation of Si and B forms a dense composite ceramic layer (C, SiO2, and B2O3) on the ablated surface, preventing pyrolytic degradation of the material structure and enhancing ablation resistance.

Alumina fiber-reinforced composites represent auspicious thermal protection materials due to their exceptionally high-temperature mechanical properties. This study successfully fabricated alumina fiber-reinforced phenolic resin composites modified with ZrSi2 and TiB2 fillers. The long-term oxidation resistance (20 min), hightemperature load-bearing capacity, and ablation resistance of these composites were systematically evaluated across a broad temperature range of 600 degrees C-1400 degrees C. Experimental results demonstrate a mass retention rate of 91.4 % at 1400 degrees C, while a flexural strength of 35.9 MPa was retained after 20 min of static ablation at this temperature,and the linear ablation rate and mass ablation rate of the composite material incorporating TiB2 were significantly reduced, decreasing by 46.2 % and 60 % respectively. Analysis reveals that the composite undergoes ceramization reactions at elevated temperatures, leading to its in situ transformation into a ceramicrich material. This transformation facilitates the formation of an effective thermal protection barrier composed of TiB2, TiO2, ZrO2, ZrSiO4, ZrB2, and molten B2O3 and SiO2 phases. The establishment of this barrier plays a critical role in significantly enhancing the composite's long-term oxidation resistance, high-temperature load-bearing capacity, and ablation resistance.

A type of powder/whisker hybrid phenolic resin adhesive, which could be employed for high-temperature environments in the aerospace industry, was firstly developed by using ZrB2 particles as inorganic fillers and SiCW as reinforcing agents suitable for ceramic structural components. Shear strength testing, flatwise tensile strength testing, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermodynamic theoretical calculations were employed to investigate bonding strength, thermal stability, microstructure, compositional evolution, and bonding mechanisms. The experimental results show that the adhesive with only ZrB2 added exhibited limited improvement in bond strength at high temperatures, which was due to the defects caused by the volatilization of the oxidation product B2O3 at high temperatures. The introduction of SiCW as a second addition significantly improves the bonding performance and toughness of the hybrid adhesive at high temperatures, due to its higher oxidation resistance temperature and unique aspect ratio structure. Even if part of SiCW is oxidized, its oxidation product combines with B2O3 to form a stable borosilicate glass system, thereby effectively solving the volatilization problem of single-component B2O3, significantly improving the strength and toughness of the adhesive at high temperature, and achieving considerable mechanical properties. After treatment at 1200 degrees C, the shear strength of the BPR-ZrB2/SiCW adhesive increased by 125 %, reaching 32.78 MPa, while the flatwise tensile strength improved by 159 %, culminating at 10.49 MPa. The whisker-toughened phenolic adhesive shows potential in future applications for joining high-temperature ceramic structural components.

In this study, two types of high-temperature adhesives were prepared using molybdenum-modified phenolic resin (MoPF) as the matrix and TiB2 or TiB2/ZrSi2 particles as active fillers for bonding Al2O3 ceramic substrates. Shear strength testing, thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to investigate the bonding properties, thermal properties, microstructure, compositional evolution, and bonding mechanism of the adhesives. The results demonstrate that MoPF-TiB2/ZrSi2 adhesive exhibits superior bonding properties than MoPF-TiB2 adhesive. It is noteworthy that the incorporation of ZrSi2 can mitigate the internal stress induced by rapid volume expansion of the adhesive, and ensuring high density and mechanical strength through the generation of ZrB2 and ZrTiO4, which effectively prevents the sudden decline in bonding performance beyond 1200degree celsius. The mechanical strength of the adhesive can still be maintained at 31.5 MPa after treatment at 1400degree celsius.

Phenolic aerogel is one of the most widely used lightweight thermal protective materials at present. With changes in the application environments, higher requirements are put forward for the heat resistance and mechanical properties of phenolic aerogel. In this paper, boric acid was used to modify phenolic resin, and then boron-modified phenolic aerogel was prepared. The chemical structure of modified phenolic resin was studied by infrared spectroscopy (FTIR). The microstructure, thermal stability, heat resistance in air, and compression resistance of phenolic aerogel were studied by volume shrinkage, scanning electron microscope, thermogravimetric analysis, high-temperature combustion test, and mechanical test. The results showed that the modification introduced boron oxygen bonds on the phenolic main chain. The compatibility difference between boron and phenolic resin with different content has a significant impact on the performance of phenolic aerogel. When boron content is 5-10% of phenolic resin, the network structure and thermal stability of phenolic aerogel can be significantly improved, and the maximum compressive strength of phenolic aerogel can also be improved. Boron-modified phenolic aerogel is expected to play an important role in the field of thermal insulation.

The bi-continuous interpenetrating structure of ceramic reinforcement and Al matrix is expected to achieve a breakthrough in the trade-off between strength and toughness of Al-matrix composites. This study reports a promising method using biomimetic design and hybrid technology combining additive manufacturing with melt infiltration to prepare Al-matrix composites with high geometric freedom and superior mechanical properties. The Al2O3/Al interpenetrating phase composites (IPCs) with BCC and Gyroid lattice-based ceramic scaffolds exhibit simultaneously enhanced compressive stress, energy absorption, and specific energy absorption. The highest gain in specific energy absorption of Al2O3/Al IPCs reveals an impressive sixfold increase. These significant improvements are attributed to damage delocalization, interfacial interactions, and geometric effects of ceramic lattices. Overall, this study provides a potential strategy for lightweight Al-matrix composites in automotive and aerospace applications.

Silica fibers were modified by a specific ratio of SiB6 mixed with silica sol through vacuum impregnation method. The modified fibers were then incorporated into a phenolic resin matrix to prepare fiber-reinforced resin composites. The influences of the SiB6/SiO2 mixed modification on silica fiber properties were analyzed through thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. Additionally, the influence of the SiB6/SiO2 mixed modification on the mechanical properties of phenolic resin matrix composites was evaluated through mechanical testing. The experimeatal results indicate that the SiB6/SiO2 mixed surface modification shows significant improvement in strength at room temperature and high temperatures, and crystallization temperature of silica fiber increases. The SiB6/Silica sol co-modified silica fiber shows potential for future application in thermal protection and other high-temperature conditions.

In this study, a heat-resistant adhesive was prepared using molybdenum-phenolic (Mo-PF) resin as the matrix and TiB2 particle as the ceramizable filler for bonding Al2O3 ceramic substrates. Firstly, Fourier transform infrared (FTIR) was used to characterize the chemical structure of the Mo-PF. Subsequently, thermo gravimetric analysis (TGA) and shear strength testing were employed to investigate the effects of heat treatment in different atmospheres on the thermal stability and residual bonding properties of the adhesive. To further explore the bonding mechanism of the adhesive after heat treatment in different atmospheres, scanning electron microscopy (SEM), compressive strength testing, and X-ray diffraction (XRD) were utilized to analyze the microstructure, mechanical strength, and composition evolution of the adhesive at different temperatures. The bonding strength of Al2O3 joints showed a trend of initially decreasing and then increasing after different temperature heat treatment in air, with the shear strength reaching a maximum value of 25.68 MPa after treatment at 1200 °C. And the bonding strength of Al2O3 joints decreased slowly with the increase of temperature in nitrogen. In air, the ceramicization reaction at a high temperature enabled the mechanical strength of the adhesive to rise despite the continuous pyrolysis of the resin. However, the TiB2 filler in nitrogen did not react, and the properties of the adhesive showed a decreasing tendency with the pyrolysis of the resin.

In this study phenolic resin (Phen)-loaded PCS (Phen-PCS) films were prepared and quartz fiber/Phen-PCS composites based on the resin films were also prepared. The quartz fiber/Phen-PCS composites were prepared by impregnating 2.5 Dimension (2.5D was an arrangement of fibers) quartz fibers using the resin film infusion (RFI) process. The properties of the composites were investigated. The study demonstrated that the density of the composites, after curing gradually increased with the increase in PCS. The flexural strength of the composites exhibited a trend of increasing and then decreasing after curing and pyrolysis at 1100 degrees C under an N2 atmosphere. The flexural strength of the composites reached 13.73 MPa when the addition of PCS was 30% of the phenolic resin, representing an increase of 74.23% compared to that of the composites without PCS. The porosity was found to be as low as 2.3% after curing and 2.1% after pyrolysis. X-ray diffraction (XRD) analysis and infrared spectroscopy tests demonstrated that ceramicization products, such as SiO2 and SiC, were produced after pyrolysis of the composites containing PCS. This transformation significantly enhanced the ablation resistance of the composites. Butane flame tests were performed, and the lowest line and mass ablation rates were 0.026 mm/s and 0.196 mg/s after curing. The results of the study revealed the potential of PCS as a precursor to improve the mechanical properties and heat resistance of composites, which offers promising material options for high-temperature applications.

The resin film infusion (RFI) process is a novel composite molding method for high-fiber content, excellent mechanical properties, low porosity, and adjustable thickness. This review examines two common resin materials used in the RFI process: bismaleimide resin (BMI) and epoxy resin. Furthermore, numerical simulation methods for isothermal and non-isothermal processes in the RFI process are described, focusing on the analysis of the mathematical model of resin flow. Finally, it covers the unique properties of RFI composites and showcases the RFI process's cost-effectiveness and functionality in fabricating composite structures for various applications. The limitations and potential future developments of RFI process molding technology are also summarized.

The composites were prepared by modifying silicon carbide fiber with particles of zirconium carbide (ZrC) and boron carbide (B4C) and incorporating them into a phenolic resin matrix. The influence of ZrC and B4C on the mechanical performance of SiCf/phenolic composites after high-temperature pyrolysis was studied through flexural performance test. The results show that the composite material has good thermal stability and high-temperature mechanical properties. After static ablation at 1 400 degrees C for 15 minutes, the flexural strength of the composite material reaches 286 MPa, which is still 7.3% higher than at room temperature, indicating that the composite material still has good mechanical properties even after heat treatment at 1 400 degrees C.

Phenolic aerogel is a type of nanoporous resin-based material with low density, high specific surface area, excellent thermal insulation performance, and a high carbon residue rate which has been widely used in the field of thermal protection. However, the development of phenolic aerogel is limited by the complex and expensive preparation technique, inadequate oxidation/ablation resistance, and excessive brittleness. As a result, academic research is constantly concentrated on low-cost preparation methods and efficient modification of phenolic aerogel. This review gives a description of the preparation technology, modification techniques, and application fields of phenolic aerogel and summarizes the limitations. Now, phenolic aerogel is not applied widely due to its complex and expensive preparation technique. Moreover, phenolic aerogel shows greater brittleness and insufficient mechanical property. The prospective future developments of the materials were prospected, and the phenolic aerogel with environmental protection, efficient thermal protection, and low cost will be the mainstream research direction.

In this work, two ceramizable phenolic adhesives were prepared using ZrSi2 particles or ZrSi2/B4C mix particles as the inorganic fillers. The thermal stability, bonding strength, microstructure and phase composition of the adhesives were investigated by TGA, shear strength of Al2O3 joints, SEM, EDS, XRD and XPS. The results show that these two adhesives have different bonding performances and ceramicization evolutions above 600 degrees C in air due to the addition of the second phase particles B4C. The bonding strength of ZrSi2/B4C modified phenolic adhesive after treatment at 1200 celcius can be as high as 36.6 MPa, while the bonding strength of ZrSi2 modified phenolic adhesive under the same conditions is only 17.5 MPa. B4C undergoes oxidation reaction before ZrSi2, and the oxidation product B2O3 liquid phase not only reacts with ZrSi2 to form oxidation-resistant ZrB2, but also can dissolve the high temperatures defects of the adhesive and chemically bond with the Al2O3 substrates at the interface.

The large-scale application of phenolic aerogel is limited by its complex and lengthy production process as well as its expensive cost. Herein a simultaneous drying-curing method for phenolic aerogels was designed based on the sol–gel process, and a series of phenolic aerogels with different hexamethylenetetramine (HMTA) contents were prepared. The material parameters such as microstructure, pore structure, mechanical properties, shrinkage, and density of the aerogel were characterized. The results show that compared with the conventional full-sealing method, the simultaneous drying-curing method shortens the preparation time of aerogels by nearly half and improves the safety of the preparation process. The prepared phenolic aerogels still maintain the nanoporous microscopic morphology. When the HMTA content is 1/6 of the phenolic mass, the linear shrinkage rates of the aerogels prepared by this method and the conventional full-sealing method are 9.8 and 9.4%, respectively. The densities are 0.25 and 0.22 g·cm−3, and the BET specific surface areas are 54.42 and 54.31 m2·g−1, and the compressive yield strengths are 1.76 and 1.16 MPa. At the same time, the thermal conductivity of the phenolic aerogels prepared by the simultaneous drying-curing method is less than 0.06 W·(m·K)–1 at room temperature. These results indicate that the properties of the aerogels prepared by the simultaneous drying-curing method are close to those prepared by the conventional method, which proves that this method has guiding significance for the large-scale, low-cost, and rapid production of nanoporous phenolic aerogels.

In this article, nano-ZrSi2-modified phenolic (Ph) resin and nano-ZrSi2-modified quartz–phenolic (Q–Ph) composites are, respectively, prepared by resin casting and compression molding. The effect of nano-ZrSi2 on the thermal stability of Ph resin and the role of nano-ZrSi2 on the thermal reusability of Q–Ph composites are investigated by multiple thermal gravimetric analyses and mechanical tests. The strengthening mechanism of nano-ZrSi2 modification is investigated by the evolution of microstructure. The results show that the addition of nano-ZrSi2 enhances the thermal stability of Ph resin under repeated heating at 1,200°C in air. The enhancement in thermal stability of resin exhibits a positive effect on improving the thermal reusability of composites. Within the range of 20 repeated heating times, the flexural strength of nano-ZrSi2-modified composites is above 16.01 MPa, which is 163.8% higher than that of unmodified composites. The strengthening mechanism of nano-ZrSi2 is mainly in the inhibition of thermal oxidation and the reduction of microstructural defects during the repeated thermal environment.

Thermal protection system (TPS) is of great significance to launch hypersonic flight and landing process of hypersonic vehicles, which can effectively shield the hypersonic vehicle from severe aerodynamic heating encountered. Phenolic aerogels play an important role in TPS due to their characteristics of low density, high porosity, and low thermal conductivity. However, phenolic aerogel is easy to be oxidized at elevated temperatures under oxidizing environments, which severely limits its large-scale application as thermal insulation materials in TPS. In this study, a novel TiB2–B4C/carbon (TB/C) aerogel composite was synthesized by introducing TiB2 and B4C particles into phenolic aerogels through quick-gelation and mechanical mixing. The developed aerogel composites were characterized by scanning electron microscopy, Fourier transform infrared, thermal analysis, etc., to evaluate their microstructure, oxidation resistance, and mechanical properties. Experimental evidence showed that TiB2 and B4C particles reacted with the oxygen-containing molecules to form TiO2–B2O3 layer, which effectively improved oxidation resistance and mechanical properties of phenolic aerogel composites.

Abstract In this work, octamercapto polyhedral oligomeric silsesquioxane (POSS-8SH) and octaphenol polyhedral oligomeric silsesquioxane (POSS-8Phenol) were successfully synthetized. POSS-8Phenol was added into the synthesis process of liquid thermoset phenolic resin (PR) to obtain POSS-modified phenolic resin (POSS-PR). Chemical structures of POSS-8SH, POSS-8Phenol, and POSS-PR were confirmed by FTIR and 1H-NMR. TG and DTG analysis under different atmosphere showed that char yield of POSS-PR at 1,000°C increased from 58.6% to 65.2% in N2, which in air increased from 2.3% to 26.9% at 700°C. The maximum pyrolysis temperature in air increased from 543°C to 680°C, which meant better anti-oxidation properties. XRD results confirmed both POSS-8Phenol and POSS-PR-generated crystalline SiO2 in air, which could explain the improvement of anti-oxidation properties. SEM showed that the POSS-PR had phase separation during curing process. Finally, carbon fiber fabric-reinforced POSS-PR (C-POSS-PR) was prepared to verify the anti-oxidation properties of POSS-PR.

In this paper, a new polyhedral oligomeric silsesquioxane containing a phenol group (POSS-Phenol) is prepared through the Michael addition reaction, which is added to the synthesis of phenolic resin as a functional monomer. Infrared spectroscopy (IR) is used to demonstrate the chemistry structure of the synthesized POSS modified phenolic resin. After introducing POSS into the resole, a comprehensive study is conducted to reveal the effects of POSS on the thermal degradation of phenolic resin. First, thermal degradation behaviors of neat phenolic resin and modified phenolic resin are carried out by thermogravimetric analysis (TGA). Then, the gas volatiles from thermal degradation are investigated by thermogravimetric mass spectrometry (TG-MS). Finally, the residues after thermal degradation are characterized by X-ray diffraction (XRD). The research indicates that POSS modified phenolic resin shows a better thermal stability than neat phenolic resin, especially at high temperatures under air atmosphere. On the one hand, the introduction of the POSS group can effectively improve the release temperature of oxygen containing volatiles. On the other hand, the POSS group forms silica at high temperatures under air, which can effectively inhibit the thermal oxidation of phenolic resin and make phenolic resin show a better high-temperature oxidation resistance.