Ultrathin polymer-derived ultra high temperature ceramic (UHTC) coating

Abstract

Various examples are provided related to ultrathin polymer-derived ultra-high temperature ceramic (UHTC). In one example, a ceramic coating includes a polymer-derived ceramic (PDC); an UHTC; and a ceramic adhesive comprising alumina (Al2O3). For example, the PDC can include silicon carbide and the UHTC can include a titanium carbide. A thickness of the ceramic coating can be less than 1 mm. In another example, a method includes providing the ceramic coating and applying the ceramic coating to a surface of a structure. For example, the structure can be an aircraft, a ship, a missile, or a rocket.

Description

ULTRATHIN POLYMER-DERIVEDULTRA HIGH TEMPERATURE CERAMIC (UHTC) COATINGCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, U.S. provisional application entitled “Ultrathin Polymer-Derived Ultra High Temperature Ceramic (UHTC) Coating” having serial no. 63 / 535,686, filed August 31 , 2023, which is hereby incorporated by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under grant number FA9550- 21-1-0057 awarded by the US Air Force Office of Scientific Research. The government has certain rights in the invention.BACKGROUND

[0003] High performance microwave absorbing materials are highly desired for aerospace applications such as aircraft engine nozzles and their aerodynamically heated parts. These materials are used for aircraft safety and high precision electronic apparatus by converting electromagnetic energy to thermal energy. Designing a material system for such applications is always challenging, because these harsh environment applications require the materials to withstand high-temperature oxidation while maintaining good microwave absorption property. Thus, there is a need to materials to meet these demands.SUMMARY

[0004] Aspects of the present disclosure are related to ultrathin polymer-derived ultra- high temperature ceramic (UHTC) and its associated methods. In one aspect, among others, a ceramic coating comprises a polymer-derived ceramic (PDC); an ultra-high temperature ceramic (UHTC); and a ceramic adhesive for high-temperature survivability, wherein the ceramic adhesive comprises alumina (AI2O3). In one or more aspects, the PDC can comprise silicon carbide (SiC), silicon oxycarbide (SiOxCy), silicon nitride(Si3N4), silicon carbonitride (Si3+xN4Cx+y), silicon oxynitride (SiOxNy), or any combination thereof. The UHTC can comprise HfB2, ZrB2, TiB2, NbB2, TaB2, TaC, HfC, NbC, TiC, ZrC, TaN, HfN, NbN, TiN, ZrN, or any combination thereof. The ceramic adhesive for high-temperature survivability can further comprise silica (SiO2), zirconia (ZrO2), CaO, Fe2O3, or any combination thereof.

[0005] In various aspects, a weight ratio of the ceramic adhesive to a total of the PDC and the UHTC can be in a range from approximately 5 percent (5%) to approximately 80 percent (80%). A thickness of the ceramic coating can be less than 1 mm. The PDC can comprise silicon carbide (SiC) and the UHTC can comprise titanium carbide (TiC). The weight ratio of the AI2O3 to the total of the SiOC and the TiC can be approximately fifty percent (50%). The ceramic coating can have a thickness of approximately 0.60 mm. The weight ratio of the AI2O3 to the total of the SiOC and the TiC can be approximately eighty percent (80%). The ceramic coating can have a thickness of approximately 0.38 mm. In some aspects, the ceramic coating can comprise a plurality of layers. At least one layer of the plurality of layers can comprise a metasurface structure. The ceramic coating can be disposed on a substrate. A thickness of the ceramic coating can be less than 1 mm, 0.9 mm or less, 0.8 mm or less, 0.7 mm or less, 0.6 mm or less, 0.5 mm or less, or 0.4 mm or less. The substrate can comprise carbon fiber reinforced polymer (CFRP).

[0006] In another aspect, a method comprises providing a ceramic coating comprising a PDC, an UHTC, and a ceramic adhesive comprising alumina (AI2O3); and applying the ceramic coating to a surface of a structure. In one or more aspects, the ceramic coating can be a paste disposed on the surface of the structure. The structure can be an aircraft. A thickness of the ceramic coating can be less than 1 mm, less than 0.9 mm, less than 0.8 mm, less than 0.7 mm, less than 0.6 mm, less than 0.5 mm, or less than 0.4 mm.

[0007] Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0009] FIG. 1 illustrates an example of a titanium carbide (TiC) / silicon oxycarbide (SiOC) composite synthesis process, in accordance with various embodiments of the present disclosure.

[0010] FIGS. 2A and 2B illustrate examples of X-ray diffraction (XRD) analysis and surface morphology of SiOC-based composites with different TiC contents, pyrolyzed at 1300 °C and 1400 °C, in accordance with various embodiments of the present disclosure.

[0011] FIGS. 3A-3D include scanning transmission electron microscopy (STEM) images and energy dispersive spectroscopy (EDS) mappings of TiC / SiOC-O.25 heat treated at 1300 °C, and 1400 °C, in accordance with various embodiments of the present disclosure.

[0012] FIGS. 4A and 4B illustrate examples of thermal oxidation stability of TiC / SiOC- 0.25 ceramics pyrolyzed at 1300 °C and 1400 °C (in situ XRD characterization at 25-1150 °C in air, with the ramp rate of 10 °C min-1), in accordance with various embodiments of the present disclosure.

[0013] FIG. 5 is a schematic diagram illustrating an example of an infinite-thickness model, in accordance with various embodiments of the present disclosure.

[0014] FIG. 6 is a schematic diagram illustrating an example of an electromagnetic wave (EMW) signal transmitted through a sample with a metal background, in accordance with various embodiments of the present disclosure.

[0015] FIGS. 7A and 7B illustrate examples of the effects of thickness and pyrolysis temperature on EMW absorption performance of TiC / SiOC-O.25 ceramic composites pyrolyzed at 1300 °C and 1400 °C, in accordance with various embodiments of the present disclosure.

[0016] FIG. 8 illustrates examples of return loss (RL) of the polymer-derived TiC- containing SiOC ceramics pyrolyzed at 1300 °C and 1400 °C, in accordance with various embodiments of the present disclosure.

[0017] FIG. 9A illustrates examples of XRD patterns of TiC / SiOC-O.25, TiC / SiOC-20, 50, 80 wt% of AI2O3 adhesive, in accordance with various embodiments of the present disclosure.

[0018] FIG. 9B illustrates an example of TEM / EDS mapping of TiC / SiOC-O.25, in accordance with various embodiments of the present disclosure.

[0019] FIG. 9C is an image of the apparatus used for erosion testing, in accordance with various embodiments of the present disclosure.

[0020] FIGS. 9D and 9E are SEM images of TiC / SiOC-50 wt% AI2O3paste before and after erosion testing, in accordance with various embodiments of the present disclosure.

[0021] FIG. 9F is an image of images of a TiC / SiOC-AI2O3paste coating a CFRP sample surface, in accordance with various embodiments of the present disclosure.

[0022] FIGS. 10A-10C illustrate examples of reflection loss curves of TiC / SiOC-AI2O3coatings with different AI2O3contents, in accordance with various embodiments of the present disclosure.

[0023] FIG. 1 1 illustrates an example of simulated nanostructure of SiOC (increasing C), in accordance with various embodiments of the present disclosure.

[0024] FIGS. 12A and 12B illustrate examples of coating molds and a coated CRFP plate, in accordance with various embodiments of the present disclosure.

[0025] FIGS. 13A and 13B are images of a humidity test setup and humidity chamber at 99.5% RH, in accordance with various embodiments of the present disclosure.

[0026] FIG. 13C illustrates examples of return loss (dB) as a function of percentage of RH, in accordance with various embodiments of the present disclosure.

[0027] FIG. 14 illustrates examples of return toss (dB) as a function of the environmental temperature, in accordance with various embodiments of the present disclosure.DETAILED DESCRIPTION

[0028] The present disclosure provides examples related to ultrathin polymer-derived ultra-high temperature ceramic (UHTC) and its associated methods. In one aspect, among others, a ceramic coating can comprise a polymer-derived ceramic (PDC), an UHTC, and an adhesive comprising alumina (AI2O3). The PDC can comprise silicon carbide (SiC), silicon oxycarbide (SiOxCy), silicon nitride(Si3N4), silicon carbonitride (Si3+xN4Cx+y), silicon oxynitride (SiOxNy), or any combination thereof. The UHTC can comprise HfB2, ZrB2, TiB2, NbB2, TaB2, TaC, HfC, NbC, TiC, ZrC, TaN, HfN, NbN, TiN, ZrN, or any combination thereof. A weight ratio of the ceramic adhesive to a total of the PDC and the UHTC is in a range from approximately 5 percent (5%) to approximately 80 percent (80%). For example, the weight ratio of the AI2O3to a total of the PDC (e.g., SiOC) and the UHTC (e.g., TiC) can be in a range from approximately five percent (5%) to approximately eighty percent (80%), or approximately twenty percent (20%) to approximately eighty percent (80%), or approximately twenty percent to approximately fifty percent, or approximately fifty percent to approximately eighty percent, or approximately 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80 percent. The ceramic coating can yield exceptional EM absorption performance and high- temperature survivability. This ultrathin coating can be deposited on aircraft, ships, missiles, rockets or other vehicles, to achieve stealth capabilities via electromagnetic shielding and absorption.

[0029] AI2O3exhibits low dielectric parameter, rendering it an effective EM transparent material. A high-performance EM-absorbing material comprising TiC / SiOC ceramic / glass composites derived from polysiloxane and titanium isopropoxide has also been developed.This innovative material exhibits an exceptionally wide absorption bandwidth, spanning the entire Ka-band (26.5-40 GHz), while maintaining a remarkably low thickness of less than 1 mm. The achievement of both broad effective absorption bandwidth (EAB, the frequency bandwidth with RL < -10 dB) and thin thickness addresses an important challenge in designing efficient EM wave absorbers. Reference will now be made in detail to the description of the embodiments as illustrated in the drawings, wherein like reference numbers indicate like parts throughout the several views.

[0030] Electromagnetic wave (EMW) absorption materials are widely used in defense aircraft as structural and functional components. The desired composite structures with optimal EMW-absorbing characteristics, combined with specifically designed dimensions, are essential for achieving low radar cross-section (ROS). In the existing advanced materials systems, microwave-absorbing ceramics can be excellent candidates for high-temperature low-observable aircraft applications due to their lightweight and chemical inertness.

[0031] Unlike traditional ceramics, polymer-derived ceramics (PDCs) can be derived from the pyrolysis of preceramic polymers at lower temperatures. This approach can provide a unique and novel route to thoroughly control the shapes and structures of ceramics by tailoring the precursor’s molecular structure and the processing parameters. With the fast development of advanced electromagnetic applications, the enhancement of EMW absorbing properties exhibited by PDCs capture extensive attention. SiOC ceramics can be prepared by pyrolysis of polysiloxane / FeCI3, and the obtained materials demonstrated a minimum return loss (RL) was -58.37 dB with a thickness of 2.95 mm. Furthermore, more than 99% of the EMW was absorbed due to the interfacial polarization from complex interfaces. Graphene and polysiloxane-derived SiOC ceramic composite can be synthesized with excellent electromagnetic wave absorbing performance, with the minimum reflection coefficient reaching -69.3 dB at 10.55 GHz at a thickness of 2.35 mm. Studies on the design of the conductor / insulator phases to achieve better absorption performances have made noticeable progress. However, there is still much space for improvement in current relevant works, including the effective absorption bandwidth (EAB) and the sample thickness at which the best absorption effect can be achieved. Until now, few studies could raise the EAB above 10 GHz, and most were below 5 GHz with a thickness of around 3 mm. Therefore, it beneficial to develop a high-efficiency EMW absorber with both broad EAB and low thickness.

[0032] Polymer-derived ternary silicon oxycarbide (SiOC) has gained substantial interest due to its exceptional mechanical properties, high-temperature oxidation resistance, and chemical stability. Recently, increasing attention has been paid to exploring the EMW absorbing properties of SiOC glasses. Polymer-derived SiOC has a versatile stoichiometry. It often contains amorphous carbon particles and SiC particles, and the observed EMWabsorbing properties of polymer-derived SiOC are mainly due to the presence of these electrically conductive and semiconductive particles. Incorporating fillers into SiOC can further improve its microwave-absorbing properties. These fillers can include transition metals (iron, cobalt, nickel, etc.) and electrically conductive nanofillers (SIC, TiC, CNTs, etc.). Titanium carbide (TiC), a transition metal boride from one of the classes of ultra-high temperature ceramics (UHTC), has a melting point as high as 3140 °C, low density (4.94 g cm-3), excellent strength larger than 680 MPa, and more importantly an outstanding electrically conductivity of 2 x w6Sm-1. Due to the abovementioned parameters of TiC, nanosized TiC can be promising candidates for EM shielding or absorption functions. The surface chemistry incompatibility between these inorganic additives and the polymer precursor is still difficult to address during processing, and the main challenges have been the significant tendency of filler aggregation and inhomogeneous distribution within the matrix, especially at higher concentrations.

[0033] A novel approach for preparing TiC / SiOC ceramic / glass composites with adjustable and wide-band EMW absorption characteristics suitable for high-temperature applications is described herein. The TiC-containing SiOC composites were successfully synthesized by a simple and feasible method based on thermal pyrolysis of the crosslinked mixture of polysiloxane and titanium isopropoxide (TTIP). These nanocomposites can achieve superbroad EAB with a low thickness requirement (<1 mm) in a harsh environment. Until now, such low-thickness coating material has never been reported.

[0034] Carbon Fiber Reinforced Polymer (CFRP) has attracted significant attention in the aerospace industry due to its exceptional mechanical properties, including high strength- to-weight ratio, stiffness, and corrosion resistance. The high strength-to-weight ratio of CFRP makes it an attractive material for use in aircraft structures, as the lightweight nature of CFRP allows for significant weight savings, which can convert into reduced fuel consumption and emissions. However, one of the key challenges of using CFRP in aerospace applications is its low electromagnetic (EM) absorption capability. The high EM reflection capability of CFRP is due to its high electrical conductivity from significant carbon fibers, which makes it an undesired absorber of electromagnetic waves. This can cause interference with sensitive electronic equipment by creating reflections and standing waves that can distort or disrupt signals. As a result, there is a need for advanced materials to overcome this limitation and ensure that the benefits of CFRP can be fully realized in aerospace applications.

[0035] To address the issue of high EM reflection capability, the use of advanced EM absorbing coatings that can be applied to the surface of substrates has been explored. Numerous types of materials have been used recently in the design and utilization, including metallic compounds, ceramics, and polymer-based coatings, such as AI2O3, p(HEMA-co-BA)-Fe3O4, carbonyl iron / carbon fiber-filled epoxy / silicone resin, Ti3SiC2 / AgNWs, TiC / epoxy, AI2O3 / FeCrAI, and so on. These coatings are typically made of conductive or magnetic materials and an insulator matrix that protects the absorbent while keeping the shape of the coatings. The EM wave absorption application of plasma-sprayed AI2O3 / FeCrAI composite coatings has been studied at the lower frequency region from 8.2 to 12.4 GHz, however, the reflection loss values below -10 dB can only be obtained at 9.2-10.7 GHz within the X band representing a narrow microwave absorption, and the coating thickness is over 1 mm.

[0036] Graphene or carbon nanotube-filled polymer materials have been studied, and the microwave absorption performance with strong absorption was shown at a thickness of 1 .9 mm and limited bandwidth of 5.38 GHz. While carbon fibers exhibit excellent thermal stability, the organic epoxy matrix has a lower thermal resistance. Several significant challenges still exist, impeding the further advancement and widespread implementation of EM-absorbing materials, including the limited EM-absorbing bandwidth and excessive thickness, both of which considerably restrict their broader and large-scale applications. Table 1 provides a comparison of the EM absorption characteristics of other material systems in open literature. Additionally, the complex fabrication processes associated with these materials contribute to their relatively lower applicability and diminished economic effectiveness.

[0037] Therefore, a novel EM absorbing coating was developed using a simplified and cost-effective manufacturing approach to achieve a wide effective absorption bandwidth and reduced thickness for enabling more practical applications. In ceramic-based EM absorbing composites, AI2O3exhibits low dielectric parameters, rendering it an effective EM transparent material. On the other hand, the development of a high-performance EM- absorbing material comprising TiC / SiOC ceramic / glass composites derived from polysiloxane and titanium isopropoxide has been demonstrated. This innovative material exhibits an exceptionally wide absorption bandwidth, spanning the entire Ka-band (26.5-40 GHz), while maintaining a remarkably low thickness of less than 1 mm. The achievement of both broad effective absorption bandwidth (EAB, the frequency bandwidth with RL < -10 dB) and thin thickness addresses an important challenge in designing efficient EM wave absorbers. However, despite these advancements, the current structural bulk of this material imposes limitations on its further practical applications, and the ongoing challenge remains in finding effective solutions to further reduce the material's thickness.

[0038] Consequently, the design of TiC / SiOC-AI2O3ceramic with precise structural configurations is anticipated to yield exceptional EM absorption performance. Such advancements hold significant potential for enhancing EM absorption capabilities in domains like aerospace and military applications. The development of a low-cost and ultra-thin high- performance EM absorbing coating derived from TiC nanoparticles (NPs)ZSiOC and AI2O3ceramic adhesive is investigated. The performance of this EM-absorbing paste was evaluated and found to be excellent over the entire Ka band with a thickness of only 0.6 mm and 0.38 mm. The results of this study demonstrate that the incorporation of EM-absorbing paste on CFRP and other substrates can significantly mitigate EM interference, particularly in high-frequency bands, and effectively enhance the overall performance of electronic equipment.TABLE 1Material Types EAB Thickness Maximum Maximum Reference (GHz) (mm) RL Absorption (dB) (%)3D hierarchical i 3.94 2.75 - 58.2 > 99.9 Mao, F., et al., CeramicsCNTSA / O2I International, 2023. 49(11 , Part A): p. 16924-16931V3Si2C25.44 2.64 - 16.97 > 90 Zhou, W., et al., Ceramics International, 2022. 48(2): p. 1908-1915AI2O3MRAC 8 1.5 - 5 > 70 Zhao, S., et al., Journal of Alloys and Compounds, 2021. 874: p. 159822TiC / epoxy 15.1 1.8 - 5 > 70 Wang, Y., et al., Ceramics International, 2014. 40(7, Part B): p. 10749-10754AhOs / FeCrAI 1.5 1.3 - 10 > 90 Zhou, L, et al., Applied Surface Science, 2012. 258(7): p. 2691-2696Honeycomb 4.2 3.5 - 63.65 > 99.9 Mei, H., et al., ChemicalAI2OVSiCwEngineering Journal, 2019. 372: p. 940-945SiCN(Fe) / AI2O3i 4 3.5 - 18 > 90 Lin, X., et al., Ceramics International, 2023. 49(14, Part A): p. 23851-23863AI2O- / TiC i 3.45 1.6 - 8 > 70 Shao, T., et al., Journal of the European Ceramic Society, 2020. 40(5): p. 2013-2019TiC / SiOC- 13.5 0.6 - 18.5 > 90 Current workAI2O3(50wt%)TiC / SiOC- 10.74 0.38 - 58.26 > 99.9 Current workAI2O3(80wt%)Experimental Section

[0039] Chemicals. Polycarbosiloxane liquid resin (MS-154, EEMS, NY, USA) was used as the precursor for SiOC. CLC-PB058 (EEMS, NY, USA), a combination of platinum and peroxide liquid catalyst, was used for crosslinking the polycarbosiloxane resin. Titanium(IV) isopropoxide, also referred to as titanium tetraisopropoxide (TTIP, 98p%, Acros, NJ, USA), acted as the titanium-containing precursor.

[0040] Synthesis of the Ceramic Composites. FIG. 1 is a schematic diagram showing an example of the TiC / SiOC composite synthesis process used for the preparation of the samples. Mixtures with different weight ratios of TTIP and polycarbosiloxane (0, 0.10, 0.20, 0.25, and 0.30) were stirred (at 103) at 250 rpm for 3 h after the addition of 0.5 wt% catalyst solution, and labeled as TiC / SiOC-0, TiC / SiOC-0.10, TiC / SiOC-0.20, TiC / SiOC-O.25, and TiC / SiOC-0.30, respectively. The resultant homogeneous viscous solutions were poured into alumina crucibles and cured at 140 °C in an oven overnight (at 106) to become cross-linked solids. Subsequently, the solids were ball-milled (at 109) in an 8000D Mixer / Mill-Dual High- Energy Ball Mill for 1 h. For each composition, 0.5 g of ball-milled powder was placed in a 25mm diameter die and pressed under a uniaxial pressure of 3.4 MPa at room temperature, with a holding time of 10 min (at 112). The particle size and morphology of the ball-milled powders after curing were between 2 and 16 pm as shown in the scanning electron microscope (SEM) image 115. All the samples were finally placed into a crucible in a zirconia tube furnace (CARBOLITE GERO 30-3000 °C, Germany) and heated (at 118) to 1300 and 1400 °C with a holding time of 2 h under high-purity 4.8-grade argon. The heating / cooling rate was 2 °C min-1.

[0041] Characterization. Phase compositions of the pyrolyzed samples were examined using a Rigaku SmartLab X-ray diffractometer (Ou KQiKa2)-Bragg-Brentano to observe the crystalline properties. The scan range was between 10° and 90° 29, with a step size of 0.05° and duration of 2 s step-1. High-temperature X-ray diffraction (XRD) measurements were carried out using P Analytical Empyrean diffractometer with Anton Paar HTK 1200. The sample was heated from 25 to 1150 °C while scanned within a 29 range of 10°-80°. The transmission electron microscopy (TEM) samples were prepared by grinding the pyrolyzed samples in a mortar and then dispersing them in absolute methanol. The size distribution and composition of TiC / SiOC-20 composites were identified using TEM-energy dispersive spectroscopy (EDS) (Talos F200X, FEI). Microstructural characterizations were carried out on an FEI Verios 460 field emission gun scanning electron microscope (FEG-SEM).

[0042] Thermogravimetric Analysis (TGA) was conducted in the air using TA Discovery TGA 550 with a heating profile from 25 to 950 °C, and typical heating rates of 10 °C min-1, for evaluating the thermal stability of the samples after pyrolysis. A thermal shock test of the composites was conducted by quenching in a water bath at room temperature. The samples were completely dried in an oven at 100 °C overnight before the experiment. The thermal shock behavior of the composites was evaluated as a function of sample temperature and quenching cycles. The samples were heated at a rate of 10 °C min-1to a preset temperature (1000 °C) in a tube furnace (GSL-1600X, MTI Corporation, USA) in air, and were then held at this temperature for 10 min. Then, the heated samples were dropped by free fall into the water bath. Each sample was tested 5 times. Raman spectra were conducted on a Horibaspectrometer (JY Horiba HR 800) with an excitation wavelength of 633.15 nm produced by an Ar laser in the spectral range of 500-3500 cm-1.

[0043] Electromagnetic properties were examined by the waveguide method according to ASTM D 5568-08 on a vector network analyzer (Keysight, N5225A PNA, 10 MHz to 50 GHz). Before measurement, the system was calibrated by calibration kits (R11644A). Microwave scattering parameters were measured by the PNA. Permittivity was calculated according to the Nicolson-Ross-Weir (NRW) algorithm. Samples with dimensions of 7.112mm x 3.556mm x (0.90-3.06) mm were measured in Ka-band (26.5-40 GHz).

[0044] To enhance the adhesive strength and enable performance under challenging conditions, a laboratory-produced AI2O3-based adhesive was used as a unique catalytic curing and insulator matrix within the coating. The raw carbon fiber epoxy prepreg, specifically the Aldila AF254 Resin System with Tg of 135 °C from Aldila Composite Materials, was utilized for the preparation of the CFRP laminate. Mixtures containing varying weight ratios (20, 50, and 80 wt%) of the AI2O3adhesive to the total of TiC / SiOC were prepared and applied to the CFRP surface, resulting in coatings with different thicknesses. Subsequently, the composites were cured at 120 °C in an oven.

[0045] Characterization of the pyrolyzed samples involved examining their phase compositions using a Rigaku SmartLab X-ray diffractometer (Cu KaiKa2)-Bragg-Brentano setup to analyze the crystalline properties. Furthermore, the size distribution and composition of the composites were identified using transmission electron microscopy (TEM) combined with energy-dispersive spectroscopy (EDS) on a Talos F200X instrument from FEI. Microstructural investigations were conducted using a field emission gun scanning electron microscope (FEG-SEM) model FEI Verios 460. Electromagnetic properties were assessed using the waveguide method, as per ASTM D 5568-08, employing a vector network analyzer (Keysight, N5225A PNA). Before conducting measurements, calibration was performed using suitable calibration kits (R11644A) to ensure accurate characterization of the EM properties. The sandblasting was conducted by the experimental setup (Siphonfeed abrasive blaster, ECONOLINE, Grand Haven, Michigan) in the lab.

[0046] To gain deeper insights into the polymer-derived silicon oxycarbide (SiOC) material and the interactions among Si, O, and C constituents, a ReaxFF energy potential in combination with LAMMPS (Large-scale Atomic / Molecular Massively Parallel Simulator) was employed to conduct molecular dynamics (MD) simulations. ReaxFF is a robust MD simulation method extensively utilized in this study. In the simulations, the polymer chains were subjected to the NPT ensemble, allowing for relaxation throughout 80,000 timesteps at a timestep of 0.2 femtoseconds (fs) per timestep. The deletion interval between consecutive steps was set at 5 picoseconds (ps). Throughout the simulation, the types of molecules thatwere deleted remained consistent, ensuring consistency and accuracy in the analysis of the simulation results.Results and discussion

[0047] It is believed that the formation of pyrolyzed TiC composition results from the carbothermal reaction between free carbon and titanium dioxide. FIGS. 2A and 2B depict the phase patterns of the SiOC matrix with different amounts of in-situ formed TiC at 1300 and 1400 °C, respectively. At 1300 °C (FIG. 2A), the diffraction peaks are broader as compared to all of the samples at 1400 °C. It can be explained by the Debye-Scherrer formula that a smaller crystalline size causes a broader peak at half the maximum intensity (full width at half maximum). More specifically, the diffraction peaks are formed by the constructive interference of X-ray reflected by crystal planes, and the restricted number of reflection planes from smaller crystallites results in wider diffraction peaks. Sharper peaks are observed at higher temperatures in FIG. 2B due to the substantial reflection planes from larger crystallites.

[0048] In regard to the phase identification in FIGS. 2A-2B, the sharp Bragg diffraction peaks at 30°-80° are from two different ceramic carbide phases (SiC and TiC), which have no distinguishable difference between them based on similar lattice parameters. But with the pyrolysis at 1300 °C, it is seen that no peaks except the amorphous SiO2are exhibited in undoped SiOC samples. Crystalline SiO2was not observed due to the limited dwelling time during the pyrolysis, although the reaction temperature was above 1200 °C. After doping with Ti, the formation of SiC from the SiOC phase separation is facilitated, along with TiC. Besides, it is worth noting that stacking faults exist extensively in SiC and TiC due to their low formation energies. A stacking fault results from any error in the regular sequence of layers, and the (111) and (110) slip systems are most likely to occur in the SiC and TiC, respectively. Thus, the experimental XRD data shows that two additional peaks not associated with the TiC / SiC structures at 32.99° and 38.29° are due to the occurrence of the stacking faults.

[0049] In FIG. 2B, the peaks from TIC formation become invisible due to the limited sizes and numbers. More detailed observations can be depicted in the following two aspects: first, the relative intensity of peaks from 40° to 43° is increasing with an increase of TiC content at 1400 °C; second, the right-side shoulder peaks at 60° also follow the aforementioned trend. These two observations both result from more and more TiC being formed at higher temperatures according to Equation (1). At higher pyrolysis temperatures, the carbothermal reduction between TiO2and C to TiC proceeds to a greater extent, potentially due to a higher probability of contact between SiO2, free C domains in the matrix, and the presence of better refined TiC nucleation sites.Ti(O iC3H7)4TiO;, (thermal decomposition of TUP)(1)-r C (phase — separated of SiOC) TiC

[0050] The aforementioned results are also consistent with the findings in FIGS. 3A-3D. The specific crystalline sizes of the TiC nanoparticles in detail are shown in the scanning transmission electron microscopy (STEM) image and EDS mapping. FIGS. 3A and 3B reveal that the TiC nanosized phases within the spherical-like shape are uniformly dispersed in the SiOC matrix, where individuals are not aggregated in certain areas of the sampled space. From this, the sizes of TiC nanoparticles span from 3 to 20 nm. When increasing the pyrolysis temperature to 1400 °C (FIGS. 3C and 3D), the situation of homogeneous TiC formation is unchanged, but its sizes keep growing and reach the range of 13-38 nm in the selected areas. The presence of conductive TiC phases inside the SiOC matrix will have a positive effect on the electrical and EMW properties of the corresponding composite material, and the size of TiC formation can be finely controlled by the designation of pyrolysis temperatures.

[0051] The surface morphology of the ceramic composites is also described in FIGS. 2A and 2B. Based on the featureless SEM observation, an important microstructure change can be found. From the un-doped SiOC to TiC / SiOC-0.1 , 0.2, and 0.25, the porous surface morphology is unchanged / slightly changed. However, the sample becomes denser when the TiC achieves the highest amount (TiC / SiOC-0.30) at both 1300 and 1400 °C pyrolysis temperatures. This means that some transient pores collapse or are fulfilled by the massive formation of the in situ formed TiC phase. It is particularly beneficial to investigate and explain the influence of porosity changes on the EMW absorbing performance, as the porous structure controls not only the degree of impedance matching but also the multiple scattering absorptions in the pores. Meanwhile, the situation of another conductive factor, carbon, is also investigated to fully explore the capacity of this material system for EMW absorbing application. Raman spectroscopy can explain the order degree of carbon structure in ceramic materials. The characteristics of short-range order and long-range order result in the sharply increasing complex permeability, thus enhancing the electromagnetic wave absorbing property.

[0052] High-temperature resistance of resultant materials was also considered and investigated by TGA and in situ XRD characterization (FIGS. 4A and 4B at 25-1150 °C in air, with the ramp rate of 10 °C min-1). TiC / SiOC-O.25 samples with the pyrolysis of 1300 and 1400 °C were particularly selected based on their excellent performance in EMW absorbing measurement and are used to compare with the un-doped SiOC. For the TiC / SiOC-O.25 sample (1300 °C) in FIG. 4A, the XRD characteristic shows the extensive 22.9° hump corresponds to the (022) plane of amorphous SiO2when the oxidation temperature reaches850 °C. At a higher annealing temperature of 1400 °C, the SiOC matrix has further evolved and becomes more stable against oxidation, thus no obvious silica formation is detected. However, the peaks for Ti3Os and TiO3centered at 25.5° and 27.7° show up separately with the air-oxidation temperature over 400 °C, and the intensity of the TiC / SiC peak weakens only after 1000 °C in the air. In conclusion, the TiC / SiOC-O.25 sample (1400 °C) possesses better thermal resistance to the air, although some titanium intermediate oxides were detected. The functional TiC / SiC phases can still survive largely in harsh conditions.

[0053] Microwave Absorption Analysis. For the characterization of microwave absorption performance of the PDCs, the relative complex permittivityand dielectric loss tangentare two dominating parameters that were investigated. The room temperature permittivity of un-doped SiOC and SiOC composites with different normalized weight fractions of TiC (TiC / SiOC-0.10, 0.20, 0.25, and 0.30) pyrolyzed at 1300 and 1400 °C were considered. The real part (E / ) of the relative complex permittivity is related to the stored energy within the medium, and the imaginary part (er") is associated with the dissipation (or loss) of energy within the medium. Based on a previous study, SiOC derived from the pyrolysis of polycarbosiloxane at 1000 °C can be considered as an EMW transmitting material with ET' and ET" values of 4.24 and 0.06 in Ka-band (26.5-40 GHz), respectively. In this study, SiOC derived from pyrolysis of polycarbosiloxane at 1300 and 1400 °C have similar ET' values and slightly higher ET" values. The larger values of ET" from TiC-containing SiOC composites may be explained by the contribution of TiC and graphitized carbon. The addition of the transition metal Ti can catalyze the formation of graphitic along with turbostratic carbons via the carbide formation-decomposition or carbon dissolution-precipitation mechanisms.

[0054] Dielectric tangent 6, described as E / ' / e / -isone of the most important factors for estimating the microwave-absorbing property of materials. In general, higher dielectric loss results in better microwave-absorbing performance. To further explain the EMW absorption performance of TiC / SiOC ceramic composites, the Debye permittivity equations are introduced. According to Debye’s theory, the relationship between the real and imaginary parts of permittivity is shown by Equations (2-4):and the Cole-Cole equation can be summarized as:where ■mis the permittivity at infinite frequency, ESis the static permittivity, co is the angular frequency, T is the relaxation time, and j is the imaginary unit.

[0055] Based on Equation (5), the plots of the real and imaginary parts of the permittivity are Cole-Cole semicircles. Each semicircle corresponds to a different relaxation process. The TiC / SiOC composites exhibit the Cole-Cole semicircles more evidently than the undoped SiOC. Interfacial polarization occurs at the interfaces between the electrically conductive TiC nanoparticles and the carbon particles. The TiC / SiOC-0.30 composite has the largest semicircle radius compared to the other samples, suggesting the highest interface polarization in the composite. According to the Maxwell-Wagner effect, the charge accumulated at the heterogeneous interfaces under microwave irradiation can produce interfacial polarization and related relaxation, thereby improving the microwave absorption.

[0056] The quarter wavelength model was introduced and discussed in the study. This model elucidates that the reflection of microwaves is minimized when the thickness of theTIA. material equals where n is an odd integer and X is the wavelength within the material.This can be calculated by Equation (6) as:where dmis the quarter wavelength thickness, X is the wavelength, c is the speed of light, and and eTare the relative permeability and permittivity of the material.

[0057] Infinite Sample Thickness Model. To further explain, a model with an infinite sample thickness was assumed so that the transmitted signal would not be reflected by the termination metal. A schematic diagram of the model used in the study is shown in FIG. 5. Under such hypothetical conditions, the return loss (RL) can be calculated by Equations (7 and 8):7 ■ ■V (8)

[0058] Finite Sample Thickness Model. Different from the infinite-thickness model, the finite sample thickness was also considered and is illustrated in FIG. 6 with the electromagnetic wave (EMW) signal transmitted through the sample with a metalbackground. VRI and VR2are the power reflected by the first surface of the material and the termination metal, respectively; and Vn and VT2were the power transmitted from the freespace to the material, and back from the material to the freespace, respectively. The reflection power (VR2) exists between the material and the termination metal. When the material thickness d equals a quarter wavelength of microwave, the power reflected at the first surface of the nanocomposite (VRI) and the power reflected at the second surface (VR2) have a 180° phase difference. Thus, the energies of these two parts were completely offset. The input impedance of this model can be calculated by Equation (9): fr*** 4- Zy(9) where rLis the reflection coefficient between the material and the termination metal. The return loss (RL) can be calculated by Equations (10 and 11).FIG. 7 shows the effect of thickness on the EMW absorption property of the TiC / SiOC-O.25 composites pyrolyzed at 1300 and 1400 °C, respectively. It can be seen that the return loss (RL) values are lower than -10 dB at a thickness of around 1 mm. The first notch of both materials was between 0.7 and 1.1 mm, and the second notch occurred in the range of 2.1- 3.3 mm. The depth of the notch becomes smaller with the increasing sample thickness, suggesting that about 1 mm was the optimal thickness for achieving the best EMW absorbing performance.

[0059] FIG. 8 shows the RL values of the TiC / SiOC ceramic composites (802-820) with various normalized weight fractions of in situ synthesized TiC nanofillers. The un-doped SiOC sample and the TiC / SiOC-0.10 composites pyrolyzed at 1300 °C exhibited the smallest absolute values of the RL parameters and therefore they have undesirable microwave absorption performance. The best performance is achieved for the sample pyrolyzed at 1300 °C with a 0.95mm thickness and the sample pyrolyzed at 1400 °C with a 0.85mm thickness. The TiC / SiOC-O.25 sample pyrolyzed at 1300 °C with a 0.95mm thickness shows the maximum absorption at 32.24 GHz (-14.32 dB) which is about 96.3% microwave absorption at the full effective bandwidth of about 13.5 GHz. The TiC / SiOC-O.25 sample pyrolyzed at 1400 °C with a 0.85mm thickness shows the best absorption value, at 30.2 GHz (-32.29 dB), which is about 99.94% absorption.

[0060] When compared to others, the disclosed material has a thinner thickness and a wider EAB than typical PDCs composites in the recent literature. Samples at thicknesses of 0.95 and 0.85mm can achieve about 96.3% and about 99.94% maximum EMW absorption, respectively. This is the first time that more than 99.9% EMW absorption has been reported for ceramic materials with a thickness of less than 1 mm, along with a super broad EAB (13.5 GHz), has been reported. Compared to other existing work, ceramic samples with a limited EAB and thickness constrain their practical applications as effective coating materials. The unique properties of the presented TiC / SiOC composites demonstrate a significant advantage over other reported EMW absorbing ceramic materials for harsh conditions applications.

[0061] FIG. 9A illustrates the phase composition of the TiC / SiOC-O.25 absorbing coatings with varying AI2O3contents. The TiC / SiOC-O.25 sample is the ceramic resulting from the pyrolysis of titanium isopropoxide and polycarbosiloxane, with a corresponding weight ratio of 25 wt%. XRD analysis revealed the clear presence of SiC and TiC phases in the pattern of TiC / SiOC-O.25 pyrolyzed at 1400 °C. However, based on similar lattice parameters, distinguishing between the SiC (Moissanite 3C, Cubic, PDF reference code: 98- 001-1866) and TiC (Titanium Carbide, Cubic, PDF reference code: 98-009-3029) phases was challenging. TEM / EDS analysis in FIG. 9B provides insights into the nanoscale characteristics of the TiC phase. The TiC crystallites exhibited an average size of approximately 20 nm, displaying a spherical-like shape and a uniform dispersion within the ceramic matrix. Notably, individual crystallites did not exhibit aggregation in specific regions of the sample space.

[0062] In comparison to the well-defined diffraction peaks originating from the crystalline AI2O3(Aluminium Oxide-Alpha, Hexagonal, PDF reference code: 98-003-2973), the diffraction peaks arising from the nano-sized TiC crystallites exhibit increased broadening. On the other hand, the TiC / SiOC-AI2O3pastes display sharper peaks due to the substantial reflection planes contributed by larger crystallites. The presence of a regular arrangement of atoms within the crystal lattice results in the distinct and well-defined diffraction peaks observed in the XRD pattern. The diffraction peaks from the nanosized TiC are less noticeable and relatively weaker compared to the intense diffraction peaks of AI2O3. This can be attributed to the influence of crystal plane orientation in the NPs, which affects the intensity and visibility of the diffraction peaks. In this study, the TiC NPs exhibit a predominant alignment that reduces the intensity of their diffraction peaks. Additionally, nanoparticles often exhibit a broadening of the diffraction peaks due to the finite size of the crystalline domains.

[0063] FIGS. 9C-9E illustrate the experimental setup employed for a sandblasting measurement, along with SEM images of coated TiC / SiOC-50wt% AI2O3CFRP samplesbefore and after erosion testing. In aggressive and harsh environments, the ability to maintain structural integrity and other properties over an extended period is important. Therefore, a comprehensive understanding of the wear resistance exhibited by the coating material can ensure prolonged durability. The images of FIG. 9C show the experimental setup. In the experiment, the aim was to adhere to the ASTM C418-12 standard as closely as possible. This standard is commonly used for measuring the sandblasting property of concrete. The experimental set-up for the measurement and the sandblasting parameters is given in Table 2.Table 2Description Experimental Parameters Standard for cement (ASTM C418-12)Sample size 1” by 1” At least 8" by 8” to get eight spotsAir pressure i 50 psi 59.5 ± 1 psiDistance from the nozzle § 3” 3 ± 0.1 inch to sample surface Duration Up to 1.5 mins 1 minProjecting angle 90° 90° Flowing rate ~ 800 g / min Require flow of abrasives as 600 ± 25 g / minAbrasives Silica Silica

[0064] The coating adhering to the CFRP surface as shown in FIG. 9F demonstrates prolonged resistance against erosive wear. No significant damage was observed, indicating that the stresses within the contact zone did not exceed the material's yield strength. However, minor brittle cracks (about 4 pm) were detected after the erosion test, in contrast to the intricate crack networks reported in the related literature, where combined cone and radial cracks longer than 7 pm were observed. Notably, no radial cracking was found in the experimental results, indicated in FIGS. 9D and 9E, and no mass loss was detected during erosion under normal impact conditions. Overall, the coating's thickness, which is less than 1 mm, still provides commendable resistance against erosion.

[0065] The absorption mechanism in the SiOC / AI2O3matrix, involving nano-sized TiC and SiC particles, is a complex interplay of multiple factors that contribute to the enhanced EM absorption properties. In the SiOC / AI2O3matrix, the small size of TiC and SiC phases allows for better dispersion within the matrix, preventing aggregation and ensuring a uniform distribution throughout the material. This specific morphology contributes to their efficient scattering properties, enabling multiple scattering events with electromagnetic waves and enhancing absorption. Nano-sized absorbents play an important role in enhancing EM absorption capabilities. TiC NPs offer a significantly higher surface area-to-volume ratiocompared to larger-sized absorbents, enabling more interaction sites and repeated scattering events with EM waves. The size and shape of these nano-sized absorbents can be precisely engineered to match specific resonance frequencies of EM waves. Notably, TiC NPs exhibit efficient EM absorption even at reduced thicknesses while maintaining high absorption performance. This phenomenon can be attributed to nanoscale effects. The nanoscale size of TiC nanoparticles introduces unique electromagnetic properties. The high surface area-to-volume ratio of nanoparticles enhances their interaction with incident electromagnetic waves, allowing for increased EM absorption efficiency, even with a lower material thickness.

[0066] FIGS. 10A-10C illustrate the impact of different AI2O3content on the absorption performance of TiC / SiOC-AI2O3coatings, as measured by reflection loss (RL) versus frequency. FIGS. 10A-10C show the reflection loss curves of TiC / SiOC-AI2O3coatings with different AI2O3contents of (a) 20 wt%, (b) 50 wt%, and (c) 80 wt%, respectively, at various thicknesses that less than 1 mm. When the absorbing materials are applied to a metal substrate, the theoretical RL values of the materials can be determined using the transmission line theory:where Zoand Zinare characteristic impedance and the normalized input impedance, respectively; p.Tand eTare the relative permeability and permittivity of the absorber; d is the thickness, and c stands for the propagation speed of EM wave. The optimal performance was achieved with TiC / SiOC-50 wt% AI2O3at an optimal thickness (dm) of only 0.60 mm. This configuration exhibits RL values below -10 dB (corresponding to >90% absorption) and covers the entire Ka band from 26.5 to 40 GHz, providing an effective absorption bandwidth (EAB) of 13.5 GHz. The lowest observed RL value (RLmin) is -58.26 dB for the TiC / SiOC-80 wt% AI2O3coating at 34.62 GHz, with a dmof 0.38 mm. The TiC / SiOC-80wt% AI2O3coating exhibits an RL value of smaller than -10 dB (corresponding to > 90% EM absorption) over a bandwidth of 10.74 GHz, spanning the frequency range of 29.26 GHz to 40 GHz.Additionally, the coating demonstrates an RL value smaller than -20 dB (indicative of > 99% EM absorption) within a bandwidth of 3.5 GHz, encompassing the frequency range from 33 GHz to 36.5 GHz. While TiC / SiOC-20 wt% AI2O3coatings exhibit relatively weaker performance compared to the optimal configuration, they still cover an EAB of approximately 8 GHz at thicknesses of 0.29 mm and 0.82 mm.

[0067] Based on the findings, the absorbing properties (RLminand EAB) of TiC / SiOC- AI2O3coatings can be easily adjusted by varying the AI2O3content and coating thickness,allowing customization to meet specific application requirements. All other reported ceramicbased coatings exceed 1 mm in thickness (as listed in Table 1), and this work represents the first report of achieving EABs of 10.74 GHz and 13.5 GHz, even with coatings as thin as 0.38 mm and 0.60 mm, respectively.

[0068] The presence of SiC and C in the SiOC matrix can have a significant impact on the EM properties of TiC / SiOC-AbOs composites. SiC and C from the polymer-decomposed SiOC, as well as interactions of the constituting Si, O, and C, are complex, but a new reactive force field (ReaxFF) for simulations of SiOC ceramics can be conducted. The ReaxFF reactive force-field interatomic potential is an invaluable computational technique for investigating the nanostructure of novel materials. ReaxFF, a reactive force field, has been designed to describe the stability and geometry of nonconjugated, conjugated, and radicalcontaining compounds and, additionally, to describe the dissociation and formation of chemical bonds in compounds.

[0069] FIG. 11 illustrates the simulated atomic changes during the simulation of the SiOC system at an experimental temperature of approximately 1400 °C. Previous studies have demonstrated that transition metals, including Ti, can catalyze the formation of various carbon structures, including graphitic and turbostratic carbons, through mechanisms such as carbide formation-decomposition or carbon dissolution-precipitation. The addition of Ti into the SiOC system promotes increased carbon formation. In the simulation, the effect of carbon on the phase evolution was investigated. Initially, all atoms (Si, O, and C) were randomly distributed, but as the temperature increased, atom clusters and free carbon emerged. Larger SiO2clusters formed, connecting to create a Si-rich environment. With the increasing C content, the formation of graphite rings comprising six carbon atoms was observed, alongside the coexistence of SiO2and C. Additionally, greater diffusion of carbon into the Si-0 clusters / regions was observed, facilitating carbothermal reduction for the formation of SiC. The incorporation of SiC into the coating enhances its absorption capability due to its inherent conductivity, providing additional pathways for EM energy dissipation and leading to improved absorption efficiency. Moreover, the presence of SiC contributes to enhanced electromagnetic scattering within the coating, further enhancing its absorption properties.

[0070] The ceramic coating can comprise a plurality of layers to further enhance its effectiveness. At least one layer can comprise a metasurface structure. A metasurface structure provides a macroscopic three-dimensional, periodic structure that exhibits special properties not normally found in nature such as, e.g., a negative index of refraction (n<0), negative permittivity (E<0), and negative permeability (|i<0) in its interaction with electromagnetic radiation, sound, or other waves. The described ceramic coating can provide a metasurface structure with varying properties based upon the ceramic adhesive.Experimental Description

[0071] The TiC-SiOC ceramic material has been prepared for EM absorption performance. First, the chemical TTIP was mixed with liquid polymer-derived ceramic precursor, crosslinked at 120 °C, then sintered at 1300 °C. The sintered material was milled to prepare powder. A slurry of 10 wt% of TiC-SiOC powder was mixed with AI2O3 ceramic adhesive along with thinner to apply onto a carbon-fiber-reinforced polymer (CFRP) substrate.

[0072] Achievement 1 - Application of an ultra-thin TiC-SiOC / A^Ch layer (thickness < 1 mm) on a CFRP substrate. For the free space tests of the EM absorption performance, 6" x 6” specimens were prepared with a uniform material coating. For that, a new coating applicator tool was modeled for 6" x 6" sheets. This tool applies coatings evenly by guiding the metal tool along a flat surface of CFRP. The model (left) and final mold (right) are shown in FIG. 12A. At the same time, the flowability of the coating material was checked by adding different compositions of AI2O3 ceramic adhesive (wt% - weight percentage) and thinner. The composition that was used comprised 85.5 wt% AI2O3 ceramic adhesive, 4.5 wt% thinner, 10 wt% TiC / SiOC powder. Finally, the slurry composition was applied on a 6” x 6” CFRP sheet using the mold and a coating applicator. The final product is shown in FIG. 12B. Images of a 6” x 6” CFRP plate and a CFRP plate coated with the TiC-SiOC / AI2O3coating (coating thickness: 0.67 mm) is shown on the left and right, respectively.

[0073] Achievement 2 - Testing the EM absorption performance in a humidity chamber. A humidity test on EM absorption was conducted at room temperature using a humidity chamber. FIGS. 13A and 138 are images showing the humidity test setup and humidity chamber at 99.5% relative humidity (RH), respectively. The RH percentage was measured as 50.6% in the ambient environment. Free space measurement is a reliable source for understanding the EM absorption behavior in humidity. A Ridged Horn Antenna (DRH0844), 8-44 GHz, was used. The calibrated return loss was obtained after subtracting the surrounding environment effect and calculating the reflection ratio from the sample and from a metal plate (i.e., a perfect reflector). The initial EM absorption (resonance) occurred at 31.8 GHz (50.6% RH), as shown in FIG. 13B.

[0074] FIG. 13C illustrates the return loss (dB) as a function of percentage of RH. The data depicts the EM absorption performance with an increase in RH%. As RH increased from 50.6% to 90.4%, no shift in resonance frequency was observed. The absorptivity exhibited a gradual decrease of 5%. Beyond 90.4% RH, a second resonance occurred at 27.4 GHz (at 92.9% RH). With a subsequent increase in RH from 92.9% to 95%, the EM performance demonstrated a gradual improvement, showing an enhanced absorption. The last measurement was carried out after 14 h at 99.5% RH. Although the absorption remainedwithin the Ka-band, it shifted towards a lower frequency (23.9 GHz). This shift is attributed to the presence of water droplets everywhere inside the chamber and on the sample.

[0075] Achievement 3 - Testing the EM absorption performance from room-temperature to 200 °C. For this test, a free space measurement - the CTG (Compass Technology Group, LLC) test was performed where the antenna used was Quad Ridged Horn Antenna (QRH50E) 5-50 GHz. FIG. 14 shows the return loss (dB) as a function of the environmental temperature. The free space measurement of the sample was taken from room temperature up to 200 °C. The maximum absorption of this sample occurs around 34.4 GHz. As the temperature increased, the change in the EM absorption was the bare minimum, which means that the performance is maintained pretty much the same in practical applications.

[0076] This disclosure has presented the use of a polymer-derived route to synthesize superior thermal resistant and excellent EMW absorbing TiC / SiOC ceramic composites, which are suitable for applications in harsh conditions. TiC nanophases (3-20 nm at 1300 °C and 13-38 nm at 1400 °C) and SiC nanophases were in situ formed within the SiOC matrices. Stacking faults were detected extensively in TiC and SiC due to their low formation energies. All of the samples show good oxidation resistance at high temperature. The weight percentage remains more than 99.70 wt% after heating in the air up to 1000 °C. The evenly crystallized TiC across the matrix not only increased the nanointerfaces but also provided the polarization loss attenuation of electromagnetic waves. Dielectric and microwave absorption properties of the ceramic composites were systemically investigated. Two different models (infinite sample thickness model or finite sample thickness model) were applied to our material system and the model’s accuracy was compared. The conclusion is that the finite sample thickness model is accurate in the RL calculation.

[0077] The highest RL of the 1300 °C TiC / SiOC-O.25 sample with a thickness of 0.95mm and the 1400 °C TiC / SiOC-O.25 sample with a thickness of 0.85mm was 14.32 dB (>96.30% absorption) and -32.29 dB (>99.94% absorption), respectively. The maximum EAB of our materials for >90% absorption is 13.5 GHz (26.5-40 GHz), covering the entire Ka-band. This work was compared to other reported values in recent literature, and our presented materials possess the widest EAB and the thinnest thickness as far as we know. The TiC / SiOC-O.25 composites provide a promising material solution for achieving integrated structural and microwave-absorbing performance suitable for harsh environments.

[0078] The experimental outcomes present compelling evidence of the coating system's remarkable EM performance, with the TiC / SiOC-50 wt% AI2O3 variant showcasing an exceptionally wide EAB of 13.5 GHz, effectively spanning the entire Ka-band at a thin thickness of 0.60 mm. Additionally, the TiC / SiOC-80 wt% AI2O3 system exhibits excellent EM characteristics, exemplified by a RLminof -58.26 dB, an EAB of 10.74 GHz, and an ultrathin thickness of 0.38 mm. Remarkably, this marks the first reported instance of a coating with athickness below 0.5 mm demonstrating such exceptional EM properties. The erosion testing results unveil the coating's notable resistance to erosion, notwithstanding the presence of minor cracks. This resilience contributes to improved absorption efficiency and heightened EM scattering mechanisms within the coating structure.

[0079] It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

[0080] The term "substantially" is meant to permit deviations from the descriptive term that don't negatively impact the intended purpose. Descriptive terms are implicitly understood to be modified by the word substantially, even if the term is not explicitly modified by the word substantially.

[0081] It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. The term “about” can include traditional rounding according to significant figures of numerical values. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.

Claims

CLAIMSTherefore, at least the following is claimed:

1. A ceramic coating, comprising:(a) a polymer-derived ceramic (PDC);(b) an ultra-high temperature ceramic (UHTC); and(c) a ceramic adhesive for high-temperature survivability, wherein the ceramic adhesive comprises alumina (AI2O3).

2. The ceramic coating of claim 1 , wherein the PDC comprises silicon carbide (SiC), silicon oxycarbide (SiOxCy), silicon nitridetSislSL), silicon carbonitride (Si3+xN4Cx+y), silicon oxynitride (SiOxNy), or any combination thereof.

3. The ceramic coating of claim 1 , wherein the UHTC comprises HfB2, ZrB2, TiB2, NbB2, TaB2, TaC, HfC, NbC, TiC, ZrC, TaN, HfN, NbN, TiN, ZrN, or any combination thereof.

4. The ceramic coating of claim 1 , wherein the ceramic adhesive for high-temperature survivability further comprises silica (SiO2), zirconia (ZrO2), CaO, Fe2O3, or any combination thereof.

5. The ceramic coating of claim 1 , wherein a weight ratio of the ceramic adhesive to a total of the PDC and the UHTC is in a range from approximately 5 percent (5%) to approximately 80 percent (80%).

6. The ceramic coating of claim 5, wherein a thickness of the ceramic coating is less than 1 mm.

7. The ceramic coating of claim 2, wherein the PDC comprises SiC, the UHTC comprises titanium carbide (TiC), and the weight ratio of the AI2O3to the total of the SiOC and the TiC is approximately fifty percent (50%).

8. The ceramic coating of claim 7, wherein the ceramic coating has a thickness of approximately 0.60 mm.

9. The ceramic coating of claim 1 , wherein the ceramic coating comprises a plurality of layers.

10. The ceramic coating of claim 9, wherein at least one layer of the plurality of layers comprises a metasurface structure.

11. The ceramic coating of claim 1 , wherein the ceramic coating is disposed on a substrate.

12. The ceramic coating of claim 9, wherein the substrate comprises carbon fiber reinforced polymer (CFRP).

13. A method, comprising: providing a ceramic coating of any of claims 1-10; and applying the ceramic coating to a surface of a structure.

14. The method of claim 13, wherein the ceramic coating is a paste disposed on the surface of the structure.

15. The method of claim 13, wherein the structure is an aircraft, a ship, a missile, or a rocket.

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