Precursor-derived Ceramics Research Articles

Evolution of conductive phase in SiCN ceramics for high piezoresistivity performance at high temperatures

Precursor-derived SiCN ceramics have been demonstrated to exhibit outstanding piezoresistivity in their amorphous state, making them suitable for application as high-temperature pressure sensors. This study reveals that partially crystallized SiCN ceramics exhibit an even higher piezoresistive coefficient of almost 11,000. From a microscopic perspective, it was previously believed that the excellent piezoresistive performance of precursor-derived ceramics (PDCs) originated from the pressure sensitivity of free carbon in the structure. However, this study has revealed that in partially-crystallized SiCN PDCs, several phases including free carbon, SiC, and Si can also exhibit conductivity. The critical factor that contributes to high piezoresistivity is the proximity between the concentration of conductive phases and the percolation threshold, leading to exceptional pressure sensitivity of SiCN ceramics.

Precursor-derived SiHfBCN ceramics with ultrahigh temperature stability: Facile preparation, phase evolution behavior, and mechanism of ultrahigh temperature thermal stability

SiHfBCN ceramics are the most promising candidates as ultrahigh temperature ceramics for aerospace applications. In this work, PHSNB precursors were synthesized by hydrosilylation reaction of polyborosilazane (PSNB) and polyhafnocenecarbosilane (PHCS), and then the SiHfBCN ceramics can be obtained from the PHSNB precursors through the precursor-derived ceramics (PDC) strategy. The structure, composition, pyrolysis process, and phase evolution behavior at high temperatures of the SiHfBCN ceramics were systematically investigated. The results show that the optimum SiHfBCN ceramic prepared in this study can remain stable until 1780 °C, and the weight loss at 1800 °C is only 0.8 wt%, demonstrating the excellent high temperature thermal stability of the SiHfBCN ceramics. The outstanding high temperature thermal stability of the SiHfBCN ceramics can be attributed to two reasons. Firstly, the formation of HfCxN1-x solid solution at high temperatures can greatly inhibit the formation of SiNx, so the carbothermal reduction reaction and thermal decomposition reaction of SiNx can be greatly inhibited. Secondly, the generated crystal phases at high temperatures are surrounded by the chaotic layered structures of B–C–N phase, which greatly restricts the decomposition process of the SiHfBCN ceramics. This work presents a convenient strategy in preparing multiphase ceramics (not only SiHfBCN) that can be applicable in various harsh environmental conditions.

Additive Manufacturing of Silicon Oxycarbide Ceramics with Minimal Surface Structures

The traditional ceramic powder sintering forming method severely limits the performance of the fabricated parts. Many new solutions have been achieved by precursor derived ceramics (PDC). Silicon oxycarbide ceramics as one of them has many performance advantages such as excellent mechanical properties, low density, excellent thermal stability, low thermal conductivity, and resistance to thermal shock and corrosion. In this paper, a photosensitive polysiloxane resin (PPR) with excellent light curing properties was prepared, which has high precision in the process of additive manufacturing. In addition, samples with minimal surface features in different porosity were fabricated. The compressive strength of the structure with 85%, 75%, and 65% porosity was about 9.51 MPa, 13.76 MPa, and 21.69 MPa, respectively. These porous silicon oxycarbide ceramics are likely to have a wide range of potential applications in aerospace, aviation, and other fields.

Single source precursor derived SiBCNHf ceramic with enhanced high‐temperature microwave absorption and antioxidation

Electromagnetic (EM) wave-absorbing materials with high-temperature-resistance are urgently desirable to eliminate EM interference in extreme conditions. Precursor derived ceramics (PDC) route is being evolved as an effective strategy to solve the puzzle. Herein, a single source hyperbranched polyborosilazane precursor containing hafnium (hb-PBSZ-Hf) is introduced and the SiBCNHf ceramic is obtained by further pyrolysis. The micro-sized tissues including HfC, SiC, HfB2 nanocrystals and segregated carbons are in situ generated during annealing which not only increase EM wave absorption ability (minimum reflection coefficient (RCmin) is -56.71 dB with a thickness of 2.5 mm, effective absorption bandwidth (EAB) is 3.4 GHz), but also improve antioxidation property (less than 2 wt.% mass fluctuation at 1400 °C in air). Theoretical simulation of complex permittivity suggests that SiBCNHf ceramic has an RCmin of less than -5 dB for the whole X-band even at 1100 °C. Such SiBCNHf ceramic with superior high-temperature-resistance and antioxidation performance derived from single source precursors possesses great potential for EM wave absorbing coatings in high-temperature and harsh environments.

Digital Light Processing 3D-Printed Ceramic Metamaterials for Electromagnetic Wave Absorption

Combining 3D printing with precursor-derived ceramic for fabricating electromagnetic (EM) wave-absorbing metamaterials has attracted great attention. This study presents a novel ultraviolet-curable polysiloxane precursor for digital light processing (DLP) 3D printing to fabricate ceramic parts with complex geometry, no cracks and linear shrinkage. Guiding with the principles of impedance matching, attenuation, and effective-medium theory, we design a cross-helix-array metamaterial model based on the complex permittivity constant of precursor-derived ceramics. The corresponding ceramic metamaterials can be successfully prepared by DLP printing and subsequent pyrolysis process, achieving a low reflection coefficient and a wide effective absorption bandwidth in the X-band even under high temperature. This is a general method that can be extended to other bands, which can be realized by merely adjusting the unit structure of metamaterials. This strategy provides a novel and effective avenue to achieve “target-design-fabricating” ceramic metamaterials, and it exposes the downstream applications of highly efficient and broad EM wave-absorbing materials and structures with great potential applications.

Enhanced Li-Ion Rate Capability and Stable Efficiency Enabled by MoSe2 Nanosheets in Polymer-Derived Silicon Oxycarbide Fiber Electrodes.

Transition metal dichalcogenides (TMDs) such as MoSe2 have continued to generate interest in the engineering community because of their unique layered morphology—the strong in-plane chemical bonding between transition metal atoms sandwiched between two chalcogen atoms and the weak physical attraction between adjacent TMD layers provides them with not only chemical versatility but also a range of electronic, optical, and chemical properties that can be unlocked upon exfoliation into individual TMD layers. Such a layered morphology is particularly suitable for ion intercalation as well as for conversion chemistry with alkali metal ions for electrochemical energy storage applications. Nonetheless, host of issues including fast capacity decay arising due to volume changes and from TMD’s degradation reaction with electrolyte at low discharge potentials have restricted use in commercial batteries. One approach to overcome barriers associated with TMDs’ chemical stability functionalization of TMD surfaces by chemically robust precursor-derived ceramics or PDC materials, such as silicon oxycarbide (SiOC). SiOC-functionalized TMDs have shown to curb capacity degradation in TMD and improve long term cycling as Li-ion battery (LIBs) electrodes. Herein, we report synthesis of such a composite in which MoSe2 nanosheets are in SiOC matrix in a self-standing fiber mat configuration. This was achieved via electrospinning of TMD nanosheets suspended in pre-ceramic polymer followed by high temperature pyrolysis. Morphology and chemical composition of synthesized material was established by use of electron microscopy and spectroscopic technique. When tested as LIB electrode, the SiOC/MoSe2 fiber mats showed improved cycling stability over neat MoSe2 and neat SiOC electrodes. The freestanding composite electrode delivered a high charge capacity of 586 mAh g−1electrode with an initial coulombic efficiency of 58%. The composite electrode also showed good cycling stability over SiOC fiber mat electrode for over 100 cycles.

Mechanical response and thermal expansion characteristics of spark plasma sintered Zr–La–B–C(O)-based precursor-derived ceramics

ABSTRACT In this work, a Zr–La–B–C(O)-based precursor-derived ceramic system is spark plasma sintered at 1600°C for 10 min. Chemical and phase analysis of the sintered ceramic reveals nanocrystalline ultra-high temperature (UHT) phases of ZrB2, ZrC, and La2Zr2O7 embedded in a glassy carbon matrix. A comprehensive evaluation of mechanical properties and thermal expansion characteristics correlates well with the presence of phases. Depth-sensing nanoindentation exemplifies high elastic recovery of 91% typically seen in glassy carbons. The hardness and Young’s modulus measured to be ∼4.5 and ∼29.5 GPa respectively, seem to be governed mainly by the presence of glassy carbon, and secondarily by stiff B–C bonds and the UHT phases. The linear coefficient of thermal expansion measured from 130°C to 1550°C is ∼7.9 × 10−6 K−1 and the thermal expansion behaviour is found to be strongly driven by the constituent UHT phases.

Novel class of precursor-derived Zr–La–B–C(O) based ceramics containing nano-crystalline ultra-high temperature phases stable beyond 1600 °C

In this work, a novel ultra-high temperature resistant precursor-derived ceramic containing Zr, La, B, and C was synthesized through precursor modification of phenol formaldehyde resin. The thermal stability and resistance to crystallization of the ceramic at a temperature of 1600 °C was investigated and was found to be profoundly influenced by the boron content in the starting precursors. The ceramics remained amorphous at 1600 °C for 2 h in argon and upon sustained heat-treatment for up to 16 h resulted in nano-crystalline ultra-high temperature phases such as ZrB 2 , ZrC, LaB 6 and La 2 Zr 2 O 7 . Thermodynamic equilibrium phase calculations show that even longer durations of heat treatment may be required to achieve thermodynamic equilibrium. High-resolution transmission electron microscopy revealed encapsulation of nanocrystals (<5 nm) in an amorphous matrix surrounded by turbostratic layers of carbon inhibiting its growth. Spectrochemical techniques confirmed the presence of boron substituted carbon in the amorphous matrix of the ceramic. The unique nature of the amorphous matrix lends the ceramic resistance to crystallization and chemical degradation that can surpass the likes of classical silicon-based precursor-derived ceramics.

Recent advances in precursor-derived ceramics integrated with two-dimensional materials.

The ceramization of polymeric precursors via thermal treatment represents a simple, fast and highly efficient method for producing polymer-derived ceramics (PDCs). PDCs integrating two-dimensional (2D) materials attracted special interest because they combine the diverse functionalities of 2D materials (electrical conductivity and catalytic performance) with the excellent intrinsic properties of PDCs, such as high-temperature stability, oxidation and corrosion resistance. This review focuses on recent development of the composites integrating PDC and 2D materials (PDC-2D composites). The methods used to prepare those materials and the relationship between as-prepared structures and property or functionality are discussed in detail. Then, the applications of PDC-2D composites in electromagnetic wave absorption and shielding, energy storage, hydrogen evolution, and electrothermal devices are also addressed.

Effect of Sic Whiskers On Properties of Precursor-Derived Ceramics Prepared by Additive Manufacturing with Vat Photopolymerization

Effect of Sic Whiskers On Properties of Precursor-Derived Ceramics Prepared by Additive Manufacturing with Vat Photopolymerization

Effect of Nano-Sized SiC Powder Filler on Additive Manufactured Properties of Precursor-Derived Ceramics

Effect of Nano-Sized SiC Powder Filler on Additive Manufactured Properties of Precursor-Derived Ceramics

Fast fabrication of SiC particulate-reinforced SiC composites by modified PIP process using spark plasma sintering – effects of green density and heating rate

SiC particulate-reinforced SiC ceramic matrix composites (SiCp/SiC) were fabricated by a modified polymer infiltration and pyrolysis (PIP) process using spark plasma sintering (SPS). The effects of pyrolysis conditions, green density, and polymer infiltration method on the densification and properties of the SiCp/SiC were investigated. SiCp/SiC with high relative density up to 88.06 % was fabricated after 4 PIP cycles by adopting high green density of SiC pellet (76.5 %) provided from drying the high solid loaded (70 vol. %) SiC slurry and fast SPS pyrolysis. The highest hardness of 21.05 ± 2.4 GPa was achieved for the as-fabricated SiCp/SiC, and the hardness value increased up to 23.99 ± 1.8 GPa after heat treatment at 2000℃. The improvement was attributed to the thermally stable SiC fillers, and partial sintering between the fillers and precursor derived ceramics (PDC) matrix. The excellent mechanical property, thermal stability, and short processing time render the SiCp/SiC composite a challenging candidate for high-temperature application.

Synthesis and Ceramic Conversion of a New Organodecaborane Preceramic Polymer with High-Ceramic-Yield.

Boron carbide is one of the hardest materials known, with diamond-like mechanical properties and excellent chemical stability. It is wildly used in military defense area, nuclear industry, aerospace technology, etc. Precursor-derived ceramics have made it easier to produce pure boron carbide in processed forms and expand its applications. The challenge of this method is the synthesis of precursor polymer with high-ceramic-yield. The aim of the present work is to develop a new poly(6-norbornenyldecaborane-co-decaborane) [P(ND-co-D)] copolymer, which was successfully synthesized via ring-opening metathesis polymerization of 6-norbornenyldecaborane and tandem hydroboration with decaborane. The obtained light-yellow powder displayed good solubility, and was fully characterized by NMR, FT-IR and GPC analysis. Thermogravimetric analysis demonstrated that the char yield was up to 79%. The polymer-to-ceramic transformation process and pyrolysis mechanism has shown that the rearrangement of carbon chains of P(ND-co-D) mainly occurred in the temperature range of 350 °C~470 °C. Furthermore, the crystallization behavior and microstructures of derived ceramics were studied by XRD and SEM. Nano-sized boron carbide powders were prepared by pyrolysis of P(ND-co-D) under argon at 1400 °C for 2 h, while the structure and morphologies of the obtained rhombohedral B4C were investigated.

Ceramic nanocomposites reinforced with a high volume fraction of carbon nanotubes

Multi-walled carbon nanotubes (MWNTs) were incorporated into precursor-derived ceramics made from a polysilazane. A ceramic nanocomposite reinforced with about 35 vol% of carbon nanotubes (CNTs) was fabricated by infiltrating CNT-preform with liquid-phased polymeric precursor followed by pyrolysis. The nanocomposite has a dense structure without micro-cracks. The results reveal that the nanocomposite has lower indentation hardness but higher fracture energy than non-reinforced ceramic from the microindentation tests results. The effect of the CNTs on the mechanical properties of the nanocomposite should be discussed accordingly.

Ionic liquid assisted fabrication of high performance SWNTs reinforced ceramic matrix nano-composites

A Novel approach to fabricate high performance SiCN ceramic nanocomposites containing well dispersed single-walled carbon nanotubes (SWNTs) assisted by room temperature ionic liquids (RTILs) is developed. This method is straightforward, environment-friendly and overcome the typical challenges in the synthesis procedures of SWNTs reinforced precursor derived ceramics (PDCs). The microstructural and elemental characteristics of these ceramic matrix nanocomposites present highly-dispersed SWNTs were introduced and a profitably BN(C) interlayer could be formed in situ between the SWNTs and the ceramic matrix, which resulting in a high performance and a crack free ceramic product. Compared to the pure monolithic SiCN ceramic, the Young's modulus enhanced by ~11% and the electrical conductivities increased up to 0.06Scm−1 for ceramic composite in the case of the 1wt% SWNTs was containing. Furthermore, the electrochemical investigation shows the potential application of these SWNTs-IL/Ceramics composites in electrochemical hydrogen storage.

ChemInform Abstract: Polymer‐Derived Non‐Oxide Ceramics Modified with Late Transition Metals

AbstractReview: 66 refs.

Effects of SiC particles on mechanical properties of SiCN-based composite by atomistic simulation

The design of SiCN reinforced by SiC nanoparticles is attractive because it can improve high temperature properties and decrease the number of the processing cycles by minimizing the free space where precursor-derived ceramics should be filled. However, the high temperature mechanical behaviors of these composites are difficult to be investigated because it is hard to measure these structural changes in the mechanical test. In this paper, molecular dynamics simulations are used to generate amorphous SiCN, then the SiC particles are added and the effects of its size and quantity on mechanical properties of SiCN composites are studied. The results show the participation of β-SiC particles increase the Young’s modulus of SiCN. The quantity of SiC particles does not have too much influence on Young’s modulus, however, the Young’s modulus increases when the diameter of SiC reach 3.2nm.

Polymer derived non-oxide ceramics modified with late transition metals

This tutorial review highlights the methods for the preparation of metal modified precursor derived ceramics (PDCs) and concentrates on the rare non-oxide systems enhanced with late transition metals. In addition to the main synthetic strategies for modified SiC and SiCN ceramics, an overview of the morphologies, structures and compositions of both, ceramic materials and metal (nano) particles, is presented. Potential magnetic and catalytic applications have been discussed for the so manufactured metal containing non-oxide ceramics.

Crystallisation kinetics of amorphous Si–C–N ceramics: Dependence on nitrogen partial pressure

The crystallisation kinetics of amorphous precursor-derived ceramics of composition Si26C41N33 is investigated as a function of temperature and nitrogen partial pressure using X-ray diffractometry. Isothermal annealing at a pressure of 1 bar leads to simultaneous crystallisation of Si3N4 and SiC, while only crystalline SiC is formed with annealing at a reduced pressure of 1 mbar. Rate constants of crystallisation are determined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) formalism. For temperatures below 1700°C, crystallisation rates are significantly higher for annealing at 1 mbar compared to 1 bar. For an explanation of the results, a model is proposed, which is based on diffusion-controlled nucleation and growth of crystalline Si3N4 and SiC in an amorphous matrix combined with thermal decomposition of Si3N4 at high temperatures.

Fracture toughness evaluation of precursor-derived Si–C–N ceramics using the crack opening displacement approach

Difficulties in the fabrication of representative test specimens and in the application of suitable test procedures e.g., in the measurement of the test parameters viz., load, crack length etc., have so far limited the intrinsic fracture mechanical characterization of the precursor-derived ceramics (PDC). The present work reports the evaluation of the crack tip toughness ( K I 0) of Si–C–N ceramics, using the novel crack opening displacement (COD) approach. The fully dense PDC test specimens synthesized from a poly(ureamethylvinyl)silazane precursor covered material structures ranging from partly organic amorphous to inorganic nano-crystalline states. Critically loaded cracks were achieved using either a special loading fixture or with Vickers indentation. Crack tip CODs were measured with the atomic force microscopy (AFM). Fractography of the fracture surfaces were performed using topographic, frictional and phase contrast AFM. The measured K I 0 values ranged from 0.6 to 1.2 MPa m 1/2. The net change in crack resistance was affected by the stripping of OFC-hydrogen atoms in the amorphous materials and by the segregated turbostratic graphite phase in the phase-separated materials. Nano-scale crack deflection observed even in the amorphous materials indicated the presence of structural and compositional inhomogeneities within the amorphous network.