SiBCN Ceramics Research Articles

Evolution of dielectric properties of SiBCN ceramics and its derived wireless passive temperature sensor application

SiBCN ceramics derived from preceramic polymers are suitable candidates for high-temperature sensors due to their remarkable high-temperature stability and semiconducting properties. However, research into their dielectric performance together with relevant sensors is meaningful but inadequate. In this work, the correlation between dielectric properties and the structure of SiBCN ceramic is identified by studying the evolution trend of the chemical composition, microstructure, and dielectric properties with pyrolysis and environment temperature. SiBCN ceramic was prepared by powder pressing process and pyrolyzed at 1000–1400 °C. As the pyrolysis temperature increased, the dielectric constant and dielectric loss tangent of SiBCN ceramic gradually increased. Within the test temperature range of 500 °C, the dielectric loss was mainly polarization loss. In addition, SiBCN ceramic wireless passive temperature sensors were prepared to test their performance from room temperature to 500 °C. The results showed that the sensitivity increased with the test temperature, and the transmission efficiency of the sensor was closely related to the dielectric properties, indicating that SiBCN ceramic has promising application prospects in the field of high-temperature sensing with good repeatability and stability.

Novel anti-oxidation coating prepared by polymer-derived ceramic for harsh environments up to 1200 °C

Environmental barrier coatings (EBCs) are protective barriers that could prevent internal materials from oxygen and harmful agents. However, the combination between EBCs and polymer-derived ceramics (PDCs) is relatively hard but essential. In this work, an anti-oxidation coating based on PDCs is fabricated on target SiBCN ceramics by spraying. The coating reveals a uniform and continuous structure with an approximate thickness of 11.7 μm. Experiments and characterization such as oxidation, thermal shock, scratch, and electrical resistance tests were carried out to investigate the performance of coating. The results show that during the high-temperature oxidation process, the coating surface undergoes a molten phase transformation that effectively seals pores and cracks, preventing oxygen diffusion into the ceramic interior. Moreover, the coating can withstand 20 thermal shocks without failure, and firmly adheres to the substrate even after prolonged oxidation and repeated thermal cycling. Comparative analysis of temperature-resistance results demonstrates the efficacy of the coatings in protecting against oxidation up to 1200 °C. The developed PDC-EBCs here exhibit remarkable resistance to oxidation and thermal shock, along with high insulation resistivity. This strategy offers a straightforward and efficient solution for protecting electronic materials in harsh environments.

Ablation behavior of Csf/SiC‐BN composites with polyborosilazane as sintering aids: High‐temperature damage mechanism

AbstractMicrostructural evolution and high‐temperature ablative damage mechanism of Csf/SiC‐BN composites with and without polyborosilazane (PBSZ) as sintering aids that can convert to polymer‐derived SiBCN ceramics (PDCs‐SiBCN) by cross‐linking and pyrolysis during sintering were studied. The density of Csf/SiC‐BN composites increases from 2.17 to 2.25 g/cm3 with 10 wt.% sintering aids because PBSZ promotes rearrangement and redistribution of raw materials by pyrolysis during the sintering process. With the increase of carbon fiber content, ablation performance (mass ablation rate: 15.25 mg/s; linear ablation rate: 0.100 mm/s) negligibly decreases, compared to counterparts with lower fiber content (mass ablation rate: 16.53 mg/s; linear ablation rate: 0.072 mm/s) because the presence of PDCs‐SiBCN partially compensates for the detrimental effect of carbon fibers on ablation performance. Csf/SiC‐BN composites with and without PBSZ show similar phase composition mainly containing quartz, amorphous SiO2, and matrix crystallization products and morphology after ablation because of similar phase composition before ablation. The ablation mechanism is oxidative corrosion and mechanical scouring and stripping.

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

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

Facile synthesis of dense SiBCN coatings with excellent compactness, smoothness, and high-temperature inertness on defective graphite surfaces

SiBCN ceramics possess extreme high-temperature stability among engineering ceramics; however, their application is constrained by the difficulty in achieving large continuous products at low cost. This work exhibits the possibility of fabricating SiBCN continuous coatings on graphite substrates to improve their surface integrity, hardness, and inertness. The ceramic coatings were fabricated simply by spin coating, curing, and pyrolysis. The key innovations are the synthesis of the precursor, polyborosilazane (PBSZ), that derives continuous ceramic films after pyrolysis, and the finding that the xylene solution of PBSZ can achieve a very good spinning performance on various surfaces, especially the low-quality graphite surfaces with holes. The fabricated SiBCN coatings, characterized to be networks of Si–C, Si–N, C–C, and B–N bonds, possessed smooth and hard surfaces with roughness below 9 nm and a hardness of 7.3 GPa. The coating thickness can be well controlled in the range of 1.4 – 2.1 μm as the latter is linearly dependent on the concentration of PBSZ in the solution. Detailed observations of surface morphologies and physisorption experiments reveal that the coating surfaces are crack-free and highly dense, rendering a significant reduction in specific surface areas when a defective graphite face is coated.

Rational design of SiBCN ceramics with excellent attenuation to strong electromagnetic-wave-absorbing properties at low frequency

To achieve strong electromagnetic wave absorbing properties, it is important to have good impedance matching, moderate electrical conductivity, and high polarization loss, particularly at low frequency. However, meeting these requirements for polymer-derived ceramics remains challenging. This paper proposes a simple approach to addressing this challenge by adjusting the crystallinity and defects of SiBCN ceramics. The addition of Sm as a catalyst and tailored heating temperatures were used to create SiBCN ceramics with adjustable crystallinities and defective nanograins. The controlled crystallinity provided good impedance matching, while the tailored defective nanograins offered high polarization loss. The combination of these factors results in high-performance electromagnetic wave absorption, with the SiBCN ceramics achieving a minimum reflection loss of −59.13 dB at 3.6 GHz and an effective attenuation bandwidth of 6.87 GHz with a thickness of 2.22 mm. This study provides an effective strategy for the design and fabrication of strong EMW absorbing materials.

Temperature and frequency dependent conductive behavior study on polymer-derived SiBCN ceramics

Conductive behavior research is vital for in-depth understanding the conductive capabilities of materials as well as promoting the development of their applications in fields such as electronics, energy and sensing. In the article, the AC conductive behavior was systematically evaluated for polymer-derived SiBCN ceramics by complex impedance spectroscopy and electrical modulus methods. The results suggest that SiBCN ceramics have a frequency-independent conductivity at low frequencies, whereas it exhibits a relaxation process with increasing frequency at high frequencies. In addition, the SiBCN ceramics follow the electron hopping conductive mechanism in both low and high-frequency bands over the testing temperature range. By considering the relationship between the prefactor σ0 and T0, the conductive mechanism is revealed to be the band-tailed state hopping instead of the variable range hopping. It is worth noting that although the material has the same conductive mechanism at various testing temperatures, hopping is mainly controlled by the matrix phase at low frequencies; while at high frequencies, hopping is dominated by free carbon phase. Our results provide the underlying insights needed to guide the design of amorphous SiBCN ceramics for applications in electrically relevant fields.

Hyperbranched polyborosilazanes derived SiBCN ceramic for high-temperature wave-transparent performance

Polymer-derived ceramics (PDCs) is a promising way to prepare ceramic-based electromagnetic functional materials, which can conveniently modulate the composition and dielectric properties of the ceramics. In this paper, SiBCN ceramic matrix composites with excellent high-temperature wave-transparent performance were prepared through PDC method. Three hyperbranched polyborosilazanes (PBSZs) were prepared by adjusting the type of chlorosilane monomers containing different numbers of methyl groups. The carbon element of pyrolytic ceramics was tuned by adjusting the molecular structure of the precursor and the pyrolysis temperature. The lower the methyl number and pyrolysis temperature, the lower the dielectric constant of the polymer-derived SiBCN ceramics, which is favorable for electromagnetic wave (EMW) transmittance. The average EMW transmittance of SiBCN-C pyrolyzed from hyperbranched PBSZ using trichlorosilane at 1000 °C was 90.56 % at room temperature. More excitingly, the excellent wave-transparent performance was also maintained in the temperature range of 100–800 °C. At the test temperature of 800 °C, SiBCN-C-1000 still had excellent wave-transparent performance with minimum and average EMW transmittance of 76.13 % and 88.96 %, respectively. This paper provided a new idea for the preparation of high-temperature wave-transparent SiBCN composite ceramics.

Rapid temperature response of polymer-derived SiBCN ceramics

Polymer-derived SiBCN ceramics with good high-temperature stability and temperature-sensitive properties can be used in real-time temperature monitoring in the aeronautical industry. However, previous investigations mostly focus on the temperature sensitivity of SiBCN ceramics but neglect the fast temperature conversion of the real operating environment and its effect on the temperature sensitivity, which hinders their further practical application. In this study, the response to rapid temperature changes of polymer-derived SiBCN was studied. SiBCN ceramics maintain excellent high-temperature semiconductor performance under rapid heating, and its direct-current (DC) conductivity increases with increasing temperature. The conductive mechanism conforms to the amorphous semiconductor formula, following three different transition mechanisms in different temperature regions. The resistance of SiBCN increases with the number of cycles during 100 cycles of 500–1200 °C, presenting excellent temperature-sensitivity and relatively good sensing stability. This work demonstrates that SiBCN ceramics can maintain excellent temperature-resistance under extreme environments with rapid heating and cooling, and it is hoped that this work could guide the development of temperature sensors for extreme environments in the future.

Oxidation behavior of amorphous and nanocrystalline SiBCN ceramics – Kinetic consideration and microstructure

Oxidation behavior of amorphous and nanocrystalline SiBCN ceramics – Kinetic consideration and microstructure

Enhanced microwave absorption of refractory SiBCN metamaterials

AbstractSo far, developed microwave absorbers exhibit significant changes in absorption with temperature, which hinder their operation within a wide temperature range. In this paper, a microwave absorber based on SiBCN ceramics was prepared. Due to the excellent high‐temperature stability of SiBCN ceramics, its permittivity changes less with temperature, avoiding the issue of performance deterioration or even failure that traditional refractory absorbers face at high temperatures. The experiment proves the absorption bandwidth for –15 dB of the SiBCN metamaterials absorber (SMA) is 12 GHz at 800°C, with a maximum absorptivity of 99.99%. According to the computed data, the resonance loss contributes 81.9 to 94.5% of the microwave absorption of SMA. This work demonstrates significant potential for applications in radar stealth under harsh conditions.

A competitive reaction strategy toward dielectric phases for enhancing electromagnetic wave absorption of polymer-derived ceramics

HfZrCN forms a cage-like structure around Si3N4, The RLmin reaches −42.7 dB, and the EAB is 4.96 GHz (11.2–16.12 GHz).

Microstructure-electrical conductivity relationship of Si(Ni)BCN ceramics

Wireless passive sensors based on surface acoustic wave (SAW) provide a good solution for the measurement demand under high temperature and harsh conditions. SiBCN ceramics have excellent mechanical properties at high temperature and semiconductor behavior, making them potential for electrode of SAW sensors. To achieve the target conductivity, a series of SiBCN and SiNiBCN coatings are prepared by polymer derived ceramics (PDC) method and the influence of microstructure on the conductivity of the coatings is discussed. The results show that the conductivity of the SiBCN coatings is affected by both the content of free carbon and the degree of graphitization. The introduction of Ni leads to the formation of Ni2Si conductive microcrystals at lower temperatures and catalyzes the graphitization of the carbon phase, so that the SiNiBCN coatings show lower electrical resistivity. The amount of the metal conductive phase and the graphitization degree of the carbon phase increase with the pyrolysis temperature, resulting in decrease of the SiNiBCN coatings resistivity.

Heterogeneous oxidation behavior and kinetic mechanisms of SiBCN ceramic with structure of MA-SiBCN coated by PDCs-SiBCN

In this study, SiBCN ceramics with a structure of three-dimensional PDCs-SBCN network structure coated MA-SiBCN (MA@PDCs-SiBCN) were fabricated, which significantly improved the sintering activity and oxidation performance. The effect of MA@PDCs-SiBCN structure on oxidation behaviors and kinetics of oxide layer growth of the SiBCN ceramics at 1500 ℃ was investigated, indicating that the significantly improved oxidation resistance is attributed to the different heterogeneous oxidation behaviors, especially in the initial stage. Therefore, the heterogeneous oxidation behaviors and kinetic laws of different phases in MA@PDCs-SiBCN ceramics at different temperature ranges and their effects on structural evolution and oxide layer composition were analyzed by comparison with the MA-SiBCN ceramics. The significantly improved oxidation resistance of MA@PDCs-SiBCN ceramics should be attributed to the inhibition of MA@PDCs-SiBCN structure to heterogeneous oxidation, especially the consumption of t-C, and different oxide layer composition generated from microcrystalline structure rather than nanocapsule-like crystalline structure.

DLP–printable hyperbranched polyborosilazane for microwave absorbing SiBCN(O) ceramic metastructure

This work introduces a novel digital light processing (DLP) printable SiBCN(O) ceramic precursor (UV-hPBSZ), derived through a straightforward aminolysis approach. The unique hyperbranched molecular structure of UV-hPBSZ leads to remarkable UV curing efficiency, excellent printability, satisfied ceramic yield, and consistent shrinkage ratio. UV-hPBSZ also exhibits superior resistance against cracking and collapse during the polymer-to-ceramic process, thus enabling the fabrication of intricate SiBCN(O) ceramic structures. Upon pyrolysis at 1200 °C, the resulting SiBCN(O) ceramic demonstrates outstanding electromagnetic wave (EMW) absorption performance, achieving full coverage in the X band (RLmin = -36.68 dB). To showcase the design flexibility, a distinctive metastructure is proposed and successfully fabricated using DLP printing technique. This SiBCN(O) metastructure absorber enables impressive EMW absorption in the Ku band (94.6 % coverage), attributed to surface resonance effects and multiple internal reflections. Moreover, SiBCN(O) ceramics exhibit excellent high-temperature stability, with less than a 1.63 % total mass change from room temperature to 1400 °C. UV-hPBSZ offers a simple but versatile way to control dielectric properties, which opens up new possibilities for multifunctional integrated EMW absorbers suitable for both ambient and high-temperature conditions.

Mechanical and ablation properties of Cf/SiBCN-ZrB2 composites prepared by an in-situ reaction: Effect of carbon source

SiBCN ceramics were prepared by a novel inorganic method: the in situ reaction of amorphous SiBON and C. Differences in the mechanical and ablation properties of composites prepared from flake graphite and carbon black (denoted as Cf/CGZ and Cf/CBZ, respectively) were compared to find a suitable carbon source. The results showed that flake graphite is the optimal carbon source. The fracture toughness of the Cf/CGZ composite was 9.1 ± 0.4 MPa·m1/2, which is 23.0% higher than that of the Cf/CBZ composite. This is because the flake graphite promoted crack deflection. Furthermore, after exposure to a plasma flame with a heat flux of 6.68 MW/m2 for 300 s, the mass and linear ablation rates of the Cf/CGZ composite are 0.39 mg/s and − 0.19 µm/s, respectively, which is a decrease of 22.00% and 64.81%, respectively, as compared to those of the Cf/CBZ composite. This is because of the directional distribution of flake graphite, which improved the thermal conductivity, reduced the ablation surface temperature, and facilitated the formation of a dense ZrO2/SiO2 layer as an anti-ablation barrier.

Effect of Zr on the solid sintering process of SiBCN ceramics: Diffusion couple method experiment and DFT calculation

AbstractThe impact of Zr addition on the solid sintering process of SiBCN multiphase ceramics was investigated under high temperatures. To gain deep insight, SiBCN‐Zr diffusion couple method (sample preparation at 1500–1800°C) was utilized in conjunction with first‐principles calculations. Significantly, the results demonstrated the formation of SiC and BN as well as ZrC/ZrB2 at the interface of the diffusion couples. Possible mechanisms have been analyzed and proposed. On the one hand, the extensive generations of defects are supposed to facilitate the formation of SiC and ZrC during the preparation of SiBCN amorphous powders. On the other hand, the presence of distinctive BN(C) structures in SiBCN hindered the formation of ZrB2, thus causing a delay in its formation. Through first‐principles calculations, remarkable variations in interatomic bonding strengths have been revealed among the different phases at the interface. Specifically, interfaces of ZrC/ZrB2 and SiC exhibit stronger bonding strengths compared to BN and SiC, implying that Zr, and its compounds may act as binding agents.

Comparative study on the microstructure evolution and crystallization behavior of precursor-derived and mechanical alloying derived SiBCN

In this study, the chemical reactions and structural change during the transformation of the precursor into PDCs-SiBCN ceramic were investigated. Besides, the crystallization behaviors of precursor-derived (PDCs-SiBCN) and mechanical alloying derived (MA-SiBCN) SiBCN ceramics at different temperatures (1200–1700 ℃) were compared. Due to different amorphous structures derived from pyrolysis and amorphization processes, the silicon atoms units bonded by sp3 hybridization in PDCs-SiBCN and MA-SiBCN ceramics are SiC4 and SiC(4-x)Nx tetrahedral structure, respectively. Due to the phase separation of SiC(4-x)Nx tetrahedral structure at higher temperatures (>1400 ℃), PDCs-SiBCN ceramic has a higher resistance to crystallization but will suffer obvious carbothermal reduction process of Si3N4 during crystallization. Finally, the crystallization kinetics of SiC in MA-SiBCN ceramic were investigated. The temperature dependence of SiC crystallization in MA-SiBCN ceramic obeys the Arrhenius-type law with different activation energies in the low and high temperature ranges respectively due to the transition of the rate-controlling mechanisms.

Density‐modified structure and mechanical properties of amorphous Si2BC3N by ab initio molecular dynamics calculations

AbstractDensity‐modified structural features and mechanical properties of the amorphous Si2BC3N are studied by ab initio molecular dynamics simulations. The chemical bonds of Si2BC3N are insensitive to the density variation, which is reflected by the negligible changes in bond lengths, peak locations in density of states and Bader charge values under different densities. Instead, the composition of chemical bonds is altered. Meanwhile, high‐density condition induces the transition of polyhedral units from the sp2‐like trigonal configuration to the tetrahedral configuration, especially for B, C, and N. This variation is the main structural responding mechanism of Si2BC3N to increased density, which is different from the stretching and/or shrinkage of bonds as occurred in crystals. The increased tetrahedron content shall further benefit the amorphous structure stability of Si2BC3N by impeding the separation of turbostratic BN(C), and enhance the second‐order elastic constants, elastic moduli and tensile/shear strengths of Si2BC3N. The high density may decrease the debonding capability of the fiber/Si2BC3N interface but will not change the preference for crack deflection at interfaces. These results suggest the promising prospect of mechanical property optimization of SiBCN ceramics through density tailoring in experiments.

Polyborosilazane with Broadly Tunable Boron Content for SiBCN Ceramics.

The high-temperature durability of SiBCN ceramics is significantly influenced by the boron concentration and synthesis methods. Although single-source synthetic routes allow one to obtain homogeneous ceramics at the atomic level, the content of the boron element therein is limited by borane (BH3). In this study, the synthesis of carborane-substituted polyborosilazanes was performed via a simple one-pot reaction of polysilazanes with alkyne bonds on the main chain and decaborododecahydrodiacetonitrile complexes with different molar ratios. This enabled one to vary the boron content from ∼0 to 40.00 wt %. The ceramic yields were in the range of 50.92-90.81 wt %. Independently of the borane concentration, SiBCN ceramics started to crystallize at 1200 °C, and B4C appeared as a new crystalline phase with increasing boron content. The introduction of boron inhibited the crystallization of Si3N4 and increased the crystallization temperature of SiC. The presence of the B4C phase improved both thermal stability and functional properties such as neutron-shielding characteristics of the ceramics. Therefore, this research opens up new prospects for the design of novel polyborosilanzes with great application potential.