Thermal stability and ablation properties study of aluminum silicate ceramic fiber and acicular wollastonite filled silicone rubber composite

The thermal stability and ablation properties of silicone rubber filled with silica (SiO₂), aluminum silicate ceramic fiber (ASF), and acicular wollastonite (AW) were studied in this article. The morphology, composition, and ablation properties of the composite were analyzed after oxyacetylene torch tests. There were three different ceramic layers found in the ablated composite. In the porous ceramic layer, the rubber was decomposed, producing trimers, tetramers, and SiO₂. ASF and part of AW still remained and formed a dense layer. The SiO₂/SiC filaments in the ceramic layer reduced the permeability of oxygen, improving the ablation properties of the composites. The resultant ceramic layer was the densest, which acted as effective oxygen and heat barriers, and the achieved line ablation rate of the silicone composite were optimum at the proportion of 20 phr/40 phr (ASF/AW). Thermogravimetric analysis (TGA) confirmed that thermal stability of the composites was enhanced by the incorporation of ASF and AW. The formation of the ceramic layer was considered to be responsible for the enhancement of thermal stability and ablation properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39700.     

Ablation and thermo-mechanical investigation of polyarylacetylene impregnated heat vulcanising silicone rubber for ultrahigh temperature applications

Hot vulcanised silicone rubber composites filled with polyarylacetylene (PAA) prepolymer or carbon fibre (CFs) are prepared. The residual weight, mechanical properties and ablation property of the composite are tested. The results show that the incorporation of PAA into silicon rubber can obviously increase the residual weight of the resulting composite. The addition of PAA or CFs has improved the hardness of the composites. The tensile stress and elongation at break of the composite are found increased initially and then decreased with the increasing of the concentration of PAA. PAA and CFs can greatly improve the ablation properties of the composites. The ablated surface contains SiO₂, SiC and/or Si, which hinder the oxygen diffusion and the thermal conduction, and consequently prevent the decomposition and oxidation of the composite. The crack is a crucial factor determining the thermal conduction of the ablation layer when exposed to the oxyacetylene torch.     

Influence of stearic acid treated nano-CaCO3 on the properties of silicone nanocomposites

The aim of the work reported here was to study the influence of treated nano-CaCO₃ on the silicone:dicumyl peroxide system. Thermal degradation was studied using TGA of treated and untreated nano- and commercial CaCO₃:silicone rubber composites. Thermal stability as well as % char yield increased with increasing content of treated nano-CaCO₃ as compared to untreated and commercial CaCO₃. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were performed to study the degree of dispersion of treated and untreated nano-CaCO₃ and commercial CaCO₃ in silicone rubber composites. Moreover, the nanocomposites were subjected to various tests, such as those for tensile strength, % elongation at break, flammability and abrasion resistance. The tensile strength (8.5 kg/cm²) and elongation at break (780%) showed their greatest improvements at 10 wt% loading with treated nano-CaCO₃ in comparison to the untreated nano- and commercial CaCO₃:silicone rubber composites. The improvements in the properties of treated CaCO₃:silicone composites compared to the untreated nano- and commercial CaCO₃ silicone rubber composites were due to the uniform dispersion of nanoparticles in the treated composites and their good compatibility with the rubber chains, as shown by AFM and SEM studies.     

Ablation behaviors and mechanism of ultra-thick anti-oxidation layer coating on carbon-bonded carbon fiber composites

To enhance the oxidation resistance capability of the carbon-bonded carbon fiber composites (CBCFs), a silicide ultra-thick coating as high as 1.6 mm with gradient structure is designed and fabricated via a multi-step rapid sintering method. Compared with other ceramic layers on carbon fiber-based composites, ultra-thick anti-oxidation layer coated-CBCFs have the lowest thermal conductivity. Additionally, ablation behaviors of the ultra-thick ceramics layer coated-CBCFs under the oxyacetylene torch are also investigated. After being exposed to oxyacetylene torch, the ultra-thick ceramics layer coated-CBCFs possess a linear rate range from 0.6 to 1.2 μm/s, while a mass ablation rate ranges from 4.95 × 10⁻⁵ g/m² s to 1.45 × 10⁻³ g/m² s.     

Ablation behavior of single and alternate multilayered ZrC-SiC coatings under oxyacetylene torch

Based on the investigation of ablation behavior and thermal stress of the monolayered ZrC-SiC coatings with different SiC amounts, an alternate coating consisting of 4 sublayers with 10 and 70 vol.% SiC was prepared on SiC-coated carbon/carbon (C/C) composites through plasma spraying technique. Ablation tests were carried out under oxyacetylene torch with a heat flux of 2.38 MW/m². The alternate coating could offer 90 s ablation shield for C/C composites, providing superior ablation properties than all monolayered coatings. The improved ablation resistance is mostly induced by the fact that the outmost scale with abundant ZrO₂ particles was able to better endure the mechanical denudation from the torch. Moreover, due to the indirect contact with torch, the innermost sublayers were placed into relatively mild environment, thereby most of Si-based oxides could be retained and further hinder oxygen transport inward during ablation.     

WSi2 modified HfB2-SiC coating: Microstructure and ablation resistance

To enhance the ablation resistance of carbon/carbon composites, WSi₂ modified HfB₂-SiC coating was prepared by slurry dipping combined with vapor silicon infiltration. The effect of WSi₂ contents on the ablation performance of the coating was investigated. The results showed that the coating with 20 wt% WSi₂ had the best ablation resistance under oxyacetylene torch. During ablation, a dense Hf-Si-W-O oxide layer was covered on the coating surface, inhibiting the diffusion of oxygen. Additionally, WSi₂ with high emissivity and the formed W with good thermal conductivity played a role in reducing the ablation temperature. These effects contributed to the improvement of ablation performance.     

Improving ablation properties of liquid silicone rubber composites by in situ construction of rich-porous char layer

In this article, ammonium polyphosphate (APP) and ammonium pentaborate (APB) were introduced to liquid silicone rubber with an aim of building rich-porous char structure in situ, thereby improving thermal insulation properties. Thermogravimetric analyses indicated that the incorporation of APP greatly increased the char residue of the composites. Oxy-acetylene torch tests showed that the addition of either APP or APB powders effectively enhanced the ablation resistance of the composites, whereas Shore A hardness tests revealed that the APP-containing composites exhibited a higher hardness than APB-filled counterparts. The linear ablation rates of composites with 40 phr APP or APB were reduced by 34.16% and 36.19%, respectively, when compared with the control sample. The maximum back-face temperatures of composites with 40 phr APP or APB was reduced to as low as 73°C. The APP-containing composites exhibited superior ablation resistance, considering both the linear ablation rate and the mechanical properties of char layer. In addition to SiO₂, SiC, and C, B₂O₃ was produced in the APB composites, as characterized by XRD and Raman analysis. Combined with SEM, it was proven that the formation of a firm, continuous, rich-porous and thermal insulation char layer was advantageous to improve the ablation and insulation properties.     

Improving the transient thermal response and ablation properties of epoxy-modified silicone rubber composites by adding fluxing agent

In this work, transient thermal response and ablation behavior of liquid silicone rubber composites containing fluxing/ceramic forming fillers were investigated under different heat flows using an oxyacetylene flame. The results indicated that the introduction of zinc borate (ZB) and aluminum oxide (Al₂O₃) effectively reduced the temperature at various depths of the samples, and they improved the thermal insulation properties and lowered pyrolysis rates. The above finding was attributed to the heat absorption arising from water release and melt filling as well as the vitrified reaction of solid melt due to the decomposition of ZB. Besides, the melting and exfoliation of Al₂O₃ and the formation of aluminum silicate (Al₂SiO₅) caused heat absorption effect. Additionally, the mass ablation rates and line ablation rates increased with rising heat flows coupling with a decrease of compressive strength of the char layers. In a nutshell, the effect of adding ZB/Al₂O₃ on the thermal insulation behavior of epoxy-modified vinyl silicone rubber (EMVSR) composites under different heat flows was elucidtaed. This work served as a reference for the design and preparation of flexible ablative materials for thermal protection applications.     

Magnetically aligning multilayer graphene to enhance thermal conductivity of silicone rubber composites

The increasing demand for packaging materials calls for new technologies to achieve excellent thermal conductivity of polymer composites with low content of thermal conductive filler. This article prepared a kind of magnetically functionalized multilayer graphene (Fe₃O₄@MG) via electrostatic interactions, which efficiently enhanced the thermal conductivity of silicone rubber (SR) composites by the alignment of Fe₃O₄@MG in an external magnetic field. The morphology and structure of the Fe₃O₄@MG together with the thermal conductivity of corresponding Fe₃O₄@MG/SR composites were systematically investigated by SEM, TEM, XRD, elemental mapping, and thermal conductivity tester. The obtained results showed that Fe₃O₄@MG was induced to form chain-like bundles in silicone rubber matrix under the applied magnetic field, which enhanced the MG–MG interaction, and formed effective thermal pathways in the alignment direction. Furthermore, as coating mass ratio of Fe₃O₄@MG increased, the thermal conductivity of randomly oriented Fe₃O₄@MG/silicone rubber composites (R-Fe₃O₄@MG/SR) decreased gradually, whereas the through-plane thermal conductivity of vertically aligned Fe₃O₄@MG/silicone rubber composites (V-Fe₃O₄@MG/SR) increased even filled with same contents of thermal conductive filler. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47951.     

Ablation behavior of laminated Graphite/ZrB2-SiC ceramics in two different directions

Laminated Graphite/ZrB₂-SiC ceramics were fabricated by tape casting and hot pressing. The ablation properties of the ceramics in the parallel and the perpendicular directions were studied using an oxyacetylene torch. The mass ablation rates were 8.1?±?0.4?mg/s in the parallel direction and 0.2?±?0.1?mg/s in the perpendicular direction. The linear ablation rates were 3.1?±?0.2?µm/s in the parallel direction and 1.2?±?0.1?µm/s in the perpendicular direction. Thus, the ablation resistance of the laminated Graphite/ZrB₂-SiC ceramics in the perpendicular direction was higher than that in the parallel direction. This anisotropy was mainly attributed to the lower surface temperature in the perpendicular direction resulted from higher thermal conductivity, as well as the orientation of the weak graphite interface layer perpendicular to the ablation surface.     

Ultra-high temperature ceramic coating for carbon/carbon composites against ablation above 2000 K

To improve the ablation resistance of carbon/carbon composites at the temperature above 2000 K, a ZrB₂-SiC-ZrC ultra-high temperature ceramic coating was prepared by combination of supersonic atmosphere plasma spray (SAPS) and reaction melt infiltration. The micro-holes in ZrB₂-Si-ZrC coating prepared by SAPS were effectively filled and the compactness and interface compatibility between the coating and C/C composites was improved through the reaction melt infiltration process. The ultra-high temperature ceramic coating exhibited good ablation resistance under oxyacetylene torch ablation above 2000 K. After ablation for 120 s, the mass and linear ablation rates of the ZrB₂-SiC-ZrC coated C/C samples were only ?0.016 × 10^?3 g/s and 1.30 µm/s, respectively. Good ablation resistance of the ultra-high temperature ceramic coating is mainly attributed to the dense coating structure and the improvement of interface compatibility between the coating and C/C composites.     

Effect of zirconia on ablation mechanism of asbestos fiber/phenolic composites in oxyacetylene torch environment

Micron-size zirconium oxide (ZrO₂) was used to improve the thermal stability and ablation properties of asbestos fiber/phenolic composites and to reduce their final cost. ZrO₂/asbestos/phenolic composites were prepared in an autoclave by the curing cycle process. The densities of the composites were in the range of 1.64–1.82 g/cm³. The ablation properties of composites were determined by oxyacetylene torch environment and burn-through time, erosion rates and back surface temperature in the first required 20 s. To understand the ablation mechanism, the morphology and phase composition of the composites were studied by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Thermal stability of the produced materials was estimated by means of thermal gravimetric analysis, in air which consisted of dynamic scans at a heating rate of 10 °C/min from 30 to 1000 °C with bulk samples of about 23±2 mg. The thermal stability of the composites was enhanced by adding ZrO₂. The results showed that the linear and mass ablation rates of the composites after adding 14 wt% ZrO₂ decreased by 58% and 92%, respectively. The back surface temperature of a sample with 14% zirconia was 49% lower than that of pure composite. The SEM studies showed that, modified composites displayed much lower porosity than that of non-modified composite and the destruction of asbestos fibers was very low. On the other hand, it appeared that a thin melted layer of ZrO₂ covered the surfaces of zirconia-containing composites.     

Effect of CrSi2 on the ablation resistance of a ZrSi2-Y2O3/SiC coating prepared by SAPS

To improve the ablation resistance of carbon/carbon (C/C) composites, a proportional amount of ZrSi₂-CrSi₂-Y₂O₃ mixed particles were deposited on the surface of SiC-coated C/C composites by supersonic air plasma spraying (SAPS) to form a ZrSi₂-CrSi₂-Y₂O₃/SiC coating. The microstructure and phase compositions of the coating were studied by SEM, EDS, XRD and its anti-ablation performance was tested by oxyacetylene torch. The experimental results showed that the ZrSi₂-CrSi₂-Y₂O₃ outer coating had a dense microstructure without obvious pores and microcracks, and the thickness reached approximately 150 μm. In the process of being eroded and scoured by the oxyacetylene flame, the coating exhibited excellent anti-ablation property, which was attributed to the mosaic microstructure formed by ZrO₂ and a Si-O-Cr liquid film on the coating surface. After experiencing an ablation time of 80 s, the linear ablation rate and the mass ablation rate of the coating were -1.0 ± 0.03 μm s^-1 and -0.16 ± 0.014 mg s^-1, respectively.     

Novel heat‐conductive composite silicone rubber

The silicone rubber with good thermal conductivity and electrical insulation was obtained by taking vinyl endblocked polymethylsiloxane as basic gum and thermally conductive, but electrically insulating hybrid Al₂O₃ powder as fillers. The effects of the amount of Al₂O₃ on the thermal conductivity, coefficient of thermal expansion (CTE), heat stability, and mechanical properties of the silicone rubber were investigated, and it was found that the thermal conductivity and heat stability increased, but the CTE decreased with increasing Al₂O₃ fillers content. The silicone rubber filled with hybrid Al₂O₃ fillers exhibited higher thermal conductivity compared with that filled with single particle size. Furthermore, a new type of thermally conductive silicone rubber composites, possessing thermal conductivity of 0.92 W/mK, good electrical insulation, and mechanical properties, was developed using electrical glass cloth as reinforcement. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2478–2483, 2007     

Cyclic ablation behavior of C/C–ZrC–SiC composites under oxyacetylene torch

Cyclic ablation behavior of C/C–ZrC–SiC composites prepared by precursor infiltration and pyrolysis process was studied using oxyacetylene torch. After repeated 30 s ablation for four times, the composites exhibited better ablation properties than those under single ablation for 120 s because of the lower surface temperature, and their linear and mass ablation rates were −3×10^–4 mm/s and −2.29×10^–3 g/s, respectively. A continuous ZrO₂–SiO₂ layer formed on the surface of center ablation region and acted as an effective barrier to the transfer of heat and oxidative gases into the inner material. Thermal stress induced by repeated impact of oxyacetylene led to some cracks on the ZrO₂–SiO₂ layer; however its destructive power was weaker than that of higher temperature. Stick like silica as grown silica nanowires were generated in the transition ablation region due to the evaporation of silicon oxide at appropriate temperature.     

Ablation properties and mechanisms of BN-coated Cf-reinforced SiBCNZr ceramic composites under an oxyacetylene combustion torch

The ablation properties andmechanisms of BN-coated C_f-reinforced SiBCNZr composites under an oxyacetylene combustion torch were investigated. The mass and linear ablation rates of the C_f/SiBCNZr ceramic matrix composites were lower than those of C_f/SiBCN and SiC_f/SiBCN composites, reaching 0.0022 mg/s and 0.0136 mm/s, respectively. The ablation resistance of the SiBCN ceramics was enhanced by the addition of Zr, whereas the BN-coated C_f increased the thermal shock resistance of the SiBCNZr ceramics. No macrocracks were found on the ablation surface of the C_f/SiBCNZr specimen. The ablation mechanisms based on different ablation temperatures, phase evolution during ablation, and ablation morphologies in the different ablation regions consisted of oxidation of the carbon fibre and ceramic matrix, emission of various gases, the flow of high-viscosity SiO₂, and denudation of C_f under the erosion of the ablation flame.     

Thermal,mechanical, and dielectric properties of aluminum silicate fiber reinforced aluminum phosphate–poly(ether sulfone) layered composites

In this study, a novel aluminum phosphate (AlPO₄) heat‐resistant layer reinforced with aluminum silicate fiber (ASF) was successfully compounded on a poly(ether sulfone) (PES) matrix via the preparation process of high‐temperature heat treatment and vacuum hot‐pressing sintering technique. The influence of the ASF content on the morphology, thermal, mechanical, and dielectric properties of the as‐fabricated aluminum silicate fiber reinforced aluminum phosphate–poly(ether sulfone) (ASF/AlPO₄–PES) layered composite was investigated. The results reveal that the incorporation of aluminum silicate fiber/aluminum phosphate (ASF/AlPO₄) heat‐resistant layer can significantly improve the thermal stability and mechanical performances of the PES matrix composites. Compared with the pristine PES, the ASF/AlPO₄–PES layered composite containing 8.0 wt % ASF exhibited better high‐temperature resistance properties (300 °C) and a lower thermal conductivity (0.16 W m^?1 K^?1). Furthermore, the dielectric constant and dielectric loss tangent of this PES matrix composite decreased to 2.16 and 0.007, respectively. Meanwhile, the frequency stability of the dielectric properties for the ASF/AlPO₄–PES layered composites was remarkably enhanced with increasing ASF addition at frequencies ranging from 10² Hz to 5 MHz. This was attributed to the existence of microscopic pores within the ASF/AlPO₄ layer and the strong interfacial bonding between the ASF/AlPO₄ layer and the PES matrix. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45542.     

CaCO3/natural rubber latex nanometer composite and its properties

Calcium carbonate/natural rubber (NR) latex nanometer composites were prepared by adding nanometer CaCO₃ whose surface had been treated to natural rubber latex (NRL) before sulfuration. The physical, thermooxidative aging, and thermal degradation properties and the ultra‐microstructure were analyzed with a multipurpose material testing meter, a thermal analysis meter and a Philips XL‐30 SEM, respectively. The results showed that the structures and properties of nanometer composites could be clearly improved by NRL mixed with surface‐treated nanometer CaCO₃. The physical properties of the nanometer composites were best when the content of surface treatment agent was 2.5% (to nanometer CaCO₃), the nanometer CaCO₃/NRL content was 3:100, and the stirring time for treating the surface of the nanometer CaCO₃ was 20 min. Simultaneously, the thermooxidative aging resistance of the nanometer composites also was significantly improved. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3442–3447, 2006     

Ablation behaviour of a TaC coating on SiC coated C/C composites at different temperatures

To improve the ablation resistance of carbon/carbon (C/C) composites, a TaC coating was prepared by supersonic plasma spraying on SiC coated C/C composites. The microstructure and morphology of the coatings were characterised by Scanning Electron Microscopy and X-ray diffraction. The ablation properties were studied at different temperatures under oxyacetylene torch. At 2100 °C, the oxides were blown away and resulted in high ablation rates: 1.2×10^?2 mm/s and 3.9×10^?3 g/s. However, most oxides can remain in ablation centre and serve as a coating at low temperature (1900 and 1800 °C). Therefore, the TaC/SiC coated samples exhibited zero linear ablation rate and lower mass ablation rate.     

The ablation behavior and mechanical property of C/C-SiC-ZrB2 composites fabricated by reactive melt infiltration

In order to improve the ablation resistance of carbon/carbon (C/C) composites, SiC-ZrB₂ di-phase ceramic were introduced by reactive melt infiltration. The ablation properties of these composites were evaluated by oxyacetylene torch with a heat flux of 2.38 MW/m² for 60 s. Compared with the pure C/C composites, the C/C-SiC-ZrB₂ composites show a significant improvement in the ablation resistance, and the linear and mass ablation rates decreased from 10.28×10⁻³ mm/s to 6.72×10⁻³ mm/s and from 3.08×10⁻³ g/s to 0.61×10⁻³ g/s, respectively. After ablation test, the flexural strength retentions of the C/C and C/C-SiC-ZrB₂ composites near the ablated center region are 39.7% and 81.6%, respectively. The higher strength retention rate of C/C-SiC-ZrB₂ composites was attributed to the introduction of SiC-ZrB₂ ceramic phases, which have excellent ablation resistant property. During ablation test, an ‘embedding structure’ of Zr-O-Si glass layer was formed, which could act as an effective barrier for oxygen and heat. The oxide ceramic coating could protect the C/C-SiC-ZrB₂ composites from further ablation, and thus contribute to retaining the mechanical property of C/C-SiC-ZrB₂ composites after ablation.