Silicon Nitride Matrix Research Articles

High pressure and high temperature modulation of electrical conductivity in high hardness silicon nitride-carbon composites

Electrically conductive silicon nitride ceramics with both high hardness and electrically conductive properties are promising advancing ceramics. However, ensuring the high hardness while simultaneously enhancing their electrical conductivity poses a great challenge. In this work, Si3N4-carbon composites with different carbon content were synthesized with diamond phase transformation method under high pressure and high temperature (HPHT). The α→β phase transition in silicon nitride enables the coexistence of α/β phases, offering a hardness of up to 23.15 ± 0.08 GPa, comparable to dense silicon nitride ceramics and significantly higher than synthesized silicon nitride-graphite composites. Diamond uniformly distributed in the silicon nitride matrix is graphitized at high temperatures to form conductive channels, reducing resistivity to 2 × 10-⁴ Ω∙m, over a dozen orders of magnitude lower than pristine silicon nitride. This phase transition sinter mechanism provides a method for designing conductive Si₃N₄-based ceramics with high hardness.

Laser-Induced Graphene/h-BN Laminated Structure to Enhance the Self-Lubricating Property of Si3N4 Composite Ceramic

Incorporating graphene as ceramic additives can significantly enhance both the toughness and self-lubricating characteristics of ceramic matrices. However, due to the difficult dispersion and easy agglomeration of graphene, the preparation process of composite ceramics still faces many problems. In this study, a laminated laser-induced reduced graphene oxide/hexagonal boron nitride (L-rGO/h-BN) was introduced as an additive into a silicon nitride matrix, then a silicon nitride/reduced graphene oxide/hexagonal boron nitride (Si3N4/L-rGO/h-BN) ceramic composite was successfully synthesized using Spark Plasma Sintering technology. This approach led to enhancements in both the mechanical and self-lubricating properties of silicon nitride ceramics. This is due to the good monodispersity of the incorporating graphene in the silicon nitride matrix. The flexural strength and fracture toughness of the ceramic composite experienced notable increases of 30.4% and 34.4%, respectively. Tribological experiments demonstrate a significant enhancement in the self-lubricating performance of ceramic composites upon the incorporation of L-rGO/h-BN. The coefficient of friction and wear spot diameter experienced reductions of 26.6% and 21%, respectively. These improvements extend the potential industrial applications of Si3N4/L-rGO/h-BN ceramic composites. Throughout the friction process, the evenly exposed rGO and h-BN demonstrate an effective self-lubricating effect on the wear surface. This research paves the way for a novel approach to fabricating high-performance self-lubricating structural ceramics.

Role of Carbon Nanotube Wetting Transparency in Rapid Water Transport for a Nanopore Membrane.

A carbon nanotube (CNT) may facilitate near-frictionless water transport within it. In this work, we elucidate the slip flow characteristics for a CNT embedded in a silicon nitride matrix using the molecular dynamics (MD) method. We reveal that the wetting transparency of a CNT, the transmission of the membrane matrix wetting property over a CNT, cannot be ignored. Due to the effect of CNT wetting transparency, the orientation flip behavior of water molecules should be the primary cause of the entrance and exit losses, which is a dominant factor influencing the interfacial friction coefficient for the thin CNT membrane. The relationship between the friction coefficient and pore size follows a logarithmic function, which agrees well with the reported experimental data. Our findings bridge the gap between the MD prediction and experimental observation for water transport in a CNT membrane and provide a clear understanding of the mechanism behind its ultrafast flow performance.

Study on a novel Si3N4-based composite with the incorporation of N-GQDs produced from nano-lignin

In order to enhance the mechanical properties of ceramic materials and realize the high value utilization of lignin, the nano-lignin precursor was added into the silicon nitride matrix as the second phase to obtain a novel ceramic composite material with excellent mechanical performance in this study. During the preparation, the nano-lignin was transformed into nitrogen-doped graphene quantum dots(N-GQDs) in the ceramic matrix by the pyrolysis-hot pressing sintering coupling process. Aiming to reveal the pyrolysis conversion process of lignin, the segmented products at the different temperature gradient were prepared, and their phase composition and microstructure were deeply analyzed by various test methods. In addition, the continuous pyrolysis process of nano-lignin was further studied by simultaneous thermal analyzer. The results showed that, nano-lignin was transformed into solid products (amorphous carbon) in the temperature range of room temperature to 800 °C and produced a large number of volatiles. Subsequently, in the temperature range of 800∼1400 °C, part of amorphous carbon began to transform into N-GQDs, and part of α-Si3N4 also began to transform into β-Si3N4. When the temperature rose to the temperature of 1700 °C, all amorphous carbon was transformed into N-GQDs through carbon structure rearrangement and nitrogen doping, and meanwhile the most of α-Si3N4 was transformed into β-Si3N4. At the final stage, β-Si3N4 columnar grains were covered by an overlayer composed of N-GQDs, and a novel ceramic composite with a special “core-shell” microstructure was obtained and exhibited excellent mechanical performance. This study presents a promising approach for the preparation of high-performance ceramic materials, and can also intrigue great interests in lignin graphitization and lignin-derived carbon materials.

Synthesis and characterization of onion-like carbon /TiN0.3 enhanced Si3N4 composites

Research on how to obtain Si3N4 composites with high hardness and toughness at lower temperatures is important. Si3N4 composites with onion-like carbon (OLC)-TiN0.3 were prepared using high pressure and high temperature techniques. The effects of TiN0.3 and OLC additives on the mechanical properties and microstructure of the silicon nitride ceramics were analyzed. During the sintering process, the vacancies in TiN0.3 promoted the formation of the TiC0·3N0.7 interface between the three compositions, whose particles were homogeneously dispersed in the silicon nitride matrix with strong bonding to the substrate. OLC (10 vol%)-TiN0.3 (10 vol%)-Si3N4 composites were prepared at 5 GPa, 1500 °C and held for 15 min. The Vickers hardness and fracture toughness were determined to be 18.6 GPa and 6.6 MPa m1/2, flexural strength of 531 MPa, and showed higher high-temperature hardness. This was higher than the typical values reported for Si3N4 ceramics (15–17 GPa). This work provides a new strategy for low-temperature of Si3N4 composites with both high hardness and high toughness.

Optimizing CO2 laser beam welding parameters for magnesium hybrid metal matrix composites (ZE41A)

ABSTRACT The current work is the investigation of optimizing input welding parameters of CO2 laser welding of two stir squeeze casted magnesium (ZE41A) matrix silicon nitride and alumina-reinforced hybrid metal matrix composites (MMCs). Two similar hybrid MMC plates were joined by the CO2 laser beam welding process and were investigated for input welding parameters influencing the metallurgical and mechanical properties. The identified parameters were subjected to optimization by Box-Behnken experimental design of Response Surface Methodology (RSM) and the experimental trials were validated by Analysis of Variance (ANOVA). With increases of 16% and 23%, the microhardness and tensile strength peaked at 207 MPa and 78 HV, respectively. The ideal input welding settings were 3500W of laser power, 4 mm/minute welding speed, and a focus length of 1.5 mm.

Downshift of the Ni d band center over Ni nanoparticles in situ confined within an amorphous silicon nitride matrix.

Herein, nanocomposites made of Ni nanoparticles in situ distributed in an amorphous silicon nitride (Ni/a-Si3N4) matrix, on the one hand, and within an amorphous silicon dioxide (Ni/a-SiO2) matrix, on the other hand, were synthesized from the same Ni-modified polysilazane precursor. In both compounds, the Ni/Si atomic ratio (0.06-0.07), average Ni nanocrystallite size (7.0-7.6 nm) and micro/mesoporosity of the matrix were rigorously fixed. Hydrogen (H2)-temperature-programmed desorption (TPD) profile analysis revealed that the activation energy for H2 desorption at about 100-130 °C evaluated for the Ni/a-Si3N4 sample (47.4 kJ mol-1) was lower than that for the Ni/a-SiO2 sample (68.0 kJ mol-1). Mechanistic study with X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations revealed that, at Ni nanoparticle/matrix heterointerfaces, Ni becomes more covalently bonded to N atoms in the a-Si3N4 matrix compared to O atoms in the a-SiO2 matrix. Therefore, based on experimental and theoretical studies, we elucidated that nickel-nitrogen (Ni-N) interactions at the heterointerface lead to remarkable Ni d band broadening and downshifting of the d band center relative to those generated by Ni-oxygen (Ni-O) interactions at the heterointerface. This facilitates H2 desorption, as experimentally observed in the Ni/a-Si3N4 sample.

Tuning LSPR of Thermal Spike-Induced Shape-Engineered Au Nanoparticles Embedded in Si3N4 Thin-Film Matrix for SERS Applications.

While gold nanoparticles (Au NPs) are widely used as surface-enhanced Raman spectroscopy (SERS) substrates, their agglomeration and dynamic movement under laser irradiation result in the major drawback in SERS applications, viz., the repeatability of SERS signals. We tune the optical and structural properties of size- and shape-modified Au NPs embedded in a thin silicon nitride (Si3N4) matrix by intense electronic excitation with swift heavy ion (SHI) irradiation with the aim of overcoming this classical SERS disadvantage. We demonstrate the shape evolution of a single layer of Au NPs inserted between amorphous Si3N4 thin films under fluences of 120 MeV Au9+ ions ranging between 1 × 1011 and 1 × 1013 ions cm-2. This shape modification results in the gradual blue shift of the localized surface plasmon resonance (LSPR) dip until 1 × 1012 ions/cm2 and then a sudden diminishment at 1 × 1013 ions/cm2. Finite domain time difference (FDTD) simulations further justify our experimental optical spectra. The dynamical NP aggregation and dissolution, in addition to NP elongation and deformation at different fluences, are noted from 2D grazing incidence small-angle X-ray scattering (GISAXS) profiles, as well as cross-sectional transmission electron microscopy (X-TEM). The systematic shape evolution of metal NPs embedded in the insulating matrix is shown to be due to thermal spike-induced localized melting and a localized pressure hike upon SHI irradiation. Utilizing this specific control over the characteristics of Au NPs, viz., shape, size, interparticle gap, and corresponding optical response via SHI irradiation, we demonstrate their applications as very stable SERS substrates, where the separation between NPs and analyte does not alter under laser illumination. Thus, these irradiated SERS active substrates with controlled NP size and gap provide the optimal conditions for creating localized electromagnetic hotspots that amplify the SERS signals, which do not alter with time or laser exposure. We found that the film irradiated with 1 × 1011 exhibits the highest SERS intensity due to its optimal NP size distribution and shape. Thus, not only our study provides a SERS substrate for stable and repeatable signals but also the understanding depicted here opens new research avenues in designing SERS substrates, photovoltaics, optoelectronic devices, etc. with ion beam irradiation.

Colored Si3N4 ceramics via constructing Nd3+ doped core‐shell structures

AbstractSi3N4 ceramics have been attractive casing materials for electronics devices under the 5th generation mobile communication technology because of its outstanding comprehensive properties. However, single color cannot meet the needs of most consumers. Here, a typical strategy, involving forming core‐shell structures by utilizing Nd2O3‐MgO‐YAG system, is proposed to rich color. Scanning transmission electron microscope‐energy dispersive X‐ray spectrometry results confirm the presence of core‐shell structures in the silicon nitride matrix, and the core is pore and the shell is Nd‐enriched liquid phase. The Nd‐rich core‐shell structure as the color center makes the silicon nitride appear cyan or blue.

From polysilazanes to highly micro-/mesoporous Si3N4 containing in situ immobilized Co or Ni-based nanoparticles

The in-situ immobilization of cobalt (Co) or nickel (Ni) nanoparticles (NPs) in a polymer-derived silicon nitride (Si3N4) matrix is firstly reported. It is accomplished by the coordination of a polysilazane with metal chlorides (CoCl2 or NiCl2) followed by the subsequent pyrolysis of the metal:organosilicon polymer coordination complex in the temperature range 700–1000 °C in flowing ammonia. By coupling X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) on powders, it has been shown that the phase composition and crystallinity (NPs and matrix) as well as the crystal size of the NPs can be finely tuned through the synthesis parameters including the type of metals, the Si:metal ratio, the reaction time, the self-crosslinking ability of the considered polysilazane in the presence of the metal salts and the heat-treatment temperature. Then, the micro-/mesoporosity of the Si3N4 matrix has been developed using a nano-casting approach to exploit the catalytic activity of NPs towards the hydrolysis of sodium borohydride (NaBH4). Hence, compounds with a matrix delivering BET specific surface areas (SSA) as high as 921.5 m2 g and supporting the NPs have been investigated to evaluate their potential for catalysis.

Study on mechanical and tribological behaviors of GQDs @ Si3N4 composite ceramics

Aiming to improve the mechanical and tribological performance of silicon nitride ceramic, one biomass material - nanoscale lignin as precursor was added into silicon nitride matrix. Through pyrolysis and hot pressing sintering, an overlayer (composed of the derivatives of nanoscale lignin – graphene quantum dots) was formed around the silicon nitride grains with a doping amount of 2 wt. %. The special core-shell microstructure refined the ceramic grains, and improved the mechanical properties of the composite by hindering the crack propagation and absorbing the fracture energy. When the composite with doping amount of 2 wt. % lignin slid against GH4169 in air, a lower friction coefficient of 0.22 and a lower pin wear rate of 1.74 × 10−6 mm3/(N·m) were fulfilled, which was attributed to the formation of surface layer containing GQDs and tribochemical products SiO2. In this study, a high performance green ceramic composite was prepared, and the composite possessed a very good application potential in industry such as cutting tools.

Ceramic nanocomposites prepared via the in situ formation of a novel TiZrN2 nanophase in a polymer-derived Si3N4 matrix

The first demonstration of a nanoscaled titanium zirconium nitride (TiZrN2) single-phase isolated during the preparation of polymer-derived silicon nitride (Si3N4) matrix nanocomposites is discussed. We employed a polysilazane, which was chemically modified with Zr[N(CH2CH3)2]4 and Ti[N(CH3)2]4 then ammonolyzed before a pyrolysis step under ammonia (1000 °C) and a heat-treatment in flowing nitrogen (1000–1700 °C). Based on a careful control of the precursor chemistry in the early stage of the process and nano-/microstructural investigations of the material performed during its preparation, we were able to identify TiZrN2 nanocrystals with a size as low as 9 nm distributed in α- and β-Si3N4 phases at a temperature as low as 1500 °C. We particularly proved that the TiZrN2 nanophase could be generated because of the use of the polysilazane evoluting towards a covalently-bonded Si3N4 matrix . This unique nanostructure is expected to provide particular functionality to Si3N4 as noble metal-free catalysts and components with high plasmonic quality.

Microstructure and mechanical properties of Si3N4f/BN/Si3N4 composites by joint processes of PIP and CVI

The three-dimensional silicon nitride (Si3N4) fiber-reinforced silicon nitride matrix (3D Si3N4f/BN/Si3N4) composites with boron nitride (BN) interphase were fabricated by joint processes of precursor infiltration and pyrolysis (PIP) and chemical vapor infiltration (CVI). The fracture morphologies and mechanical properties of Si3N4f/BN/Si3N4 composites with different PIP and CVI Si3N4 matrix content were studied. The composites with 50 vol% PIP matrix and 50 vol.% CVI matrix show the most optimal mechanical properties, especially the highest fracture toughness reported so far, whose flexural strength and fracture toughness are 198 ± 15 MPa and 7.5 ± 0.9 MPa·m1/2, respectively. Meanwhile, the fracture characteristics were analyzed, and the strengthening and toughening mechanisms dominated by the fibers and high/low modulus matrices, corresponding to CVI/PIP matrices respectively, were also discussed. It is concluded that the multi-step fiber pull-out is conducive to improving both the strength and toughness, where the strengthening and toughening mechanisms include: (Ⅰ) relieving stress and resisting crack propagation by high/low modulus matrices; (Ⅱ) strengthening by short debonded fibers and toughening by long debonded fibers.

Large Faraday effect in nanogranular films with a high refractive index matrix

Nanogranular films consisting of a complex of nanometer-sized magnetic granules and a dielectric insulator matrix exhibit a large Faraday rotation. In this study, the dielectric tensor of the nanogranular films with high refractive silicon nitride matrix are measured, and the effect of refractive index of the matrix and magnetic granules on the dielectric tensor is analyzed. Compared with the fluoride (low refractive index) matrix nanogranular films, the Faraday rotation angle is approximately two times higher in the nanogranular FeCo-SiN film, which exhibits a high refractive index effect on the Faraday rotation angle.

Application in segments for diamond tools of a composite bond based on a silicon nitride matrix instead of tungsten carbide

Application in segments for diamond tools of a composite bond based on a silicon nitride matrix instead of tungsten carbide

Basic Bio-Tribological Performance of Insulating Si3N4-Based Ceramic as Human Body Replacement Joints

The paper presents an in-depth study of the bio-tribological performance on silicon nitride matrix ceramic composites containing hexagonal boron nitride (hBN) with different content. Ultra-high molecular weight polyethylene (UHMWPE) under simulated body fluid lubrication, and the simulated body fluid-lubricated sliding tests were performed on a universal friction and wear tester. The results showed that the incorporation of hBN into silicon nitride matrix reduced the friction coefficients from 0.27 for Si3N4/UHMWPE pair to 0.16 for Si3N4-20%hBN/UHMWPE with full immersion in simulated body fluid lubrication. Scanning electron microscopy (SEM), laser scanning microscope, X-ray photoelectron spectroscopy (XPS) were utilized to characterize the wear surface. The analysis results indicated that, with simulated body fluid lubrication, the interfacial between hBN and Si3N4 facilitated the wear pits to form on the wear surface, and the residual wear particles deposited in the pits. Then, tribochemical products were formed on the wear surface, which protected and smoothed the wear surface of the sliding pair in the simulated body fluid.

Effects of heat treatment on mechanical properties of 3D Si3N4f/BN/Si3N4 composites by PIP

The fabrication of three-dimensional silicon nitride (Si3N4) fiber-reinforced silicon nitride matrix (3D Si3N4f/BN/Si3N4) composites with a boron nitride (BN) interphase through precursor infiltration and pyrolysis (PIP) process was reported. Heat treatment at 1000–1200 °C was used to analyze the thermal stability of the Si3N4f/BN/Si3N4 composites. It was found after heat treatment the flexural strength and fracture toughness change with a pattern that decrease first and then increase, which are 191 ± 13 MPa and 5.8 ± 0.5 MPa·m1/2 respectively for as-fabricated composites, and reach the minimum values of 138 ± 6 MPa and 3.9 ± 0.4 MPa·m1/2 respectively for composites annealed at 1100 °C. The influence mechanisms of the heat treatment on the Si3N4f/BN/Si3N4 composites include: (Ⅰ) matrix shrinkage by further ceramization that causes defects such as pores and cracks in composites, and (Ⅱ) prestress relaxation, thermal residual stress (TRS) redistribution and a better wetting at the fiber/matrix (F/M) surface that increase the interfacial bonding strength (IBS). Thus, heat treatment affects the mechanical properties of composites by changing the properties of the matrix and IBS, where the load transfer efficiency onto the fibers is fluctuating by the microstructural evolution of matrix and gradually increasing IBS.

Low temperature in situ formation of cobalt in silicon nitride toward functional nitride nanocomposites.

This work highlights the first demonstration of a low-temperature in situ formation of Co nanocrystallites embedded within an amorphous silicon nitride matrix through careful control of the chemistry behind material design using perhydropolysilazane (PHPS) as a Si3N4 precursor further coordinated with CoCl2 and ammonia as a pyrolysis atmosphere. The Co nucleation was allowed to proceed at temperatures as low as 400 °C via thermal decomposition of Co2N pre-formed in situ by the reaction of CoCl2 with the Si centers of PHPS at the early stage of pyrolysis (220-350 °C).

Targeted design and analysis of microwave absorbing properties in iron-doped SiCN/Si3N4 composite ceramics

The SiCN(Fe)/Si3N4 composite ceramics containing C, β-SiC and α-Fe were designed by impregnating polysilazane followed by pyrolysis at 1–5 times with porous silicon nitride matrix. After the heat treatment, these new phases gradually formed and filled in the pores of the matrix to form a large whole. They bond together to facilitate the formation of conductive networks, which can improve the storage and transport capacity of the charge, thus improving the dielectric properties of the material. In this way, the highest dielectric and magnetic loss tangent values were achieved as 0.49 and 0.29 after third and fourth cycles, respectively. The electromagnetic wave can be absorbed ~80–90% in the range of 8–18 GHz with the thickness of 2 mm. The minimum reflectivity was −12.5 dB at 16 GHz with the thickness of 5 mm, showing >90% electromagnetic wave absorption at this frequency.

The control of interfacial bonding state and optimization of mechanical properties of Si3N4f/BN/Si3N4 composites via different synthesis technologies

Silicon nitride fibers-reinforced silicon nitride matrix (Si3N4f/BN/Si3N4) composites with a BN interphase were fabricated by chemical vapor infiltration (CVI) and precursor infiltration pyrolysis (PIP). It is shown that PIP Si3N4f/BN/Si3N4 composites possessed better mechanical properties and achieved effectively interface debonding and fiber pull-out, whose flexural strength and fracture toughness can achieve 189 ± 17 MPa and 5.6 ± 0.6 MPa·m1/2, about twice and 1.5 times as much as those of CVI Si3N4f/BN/Si3N4 composites, respectively. Combining the micro-nano mechanical and macro-mechanical properties investigations, it is revealed that weakening the interfacial bond and achieving proper modulus matching relationship between fibers and matrix by PIP process could remarkably increase the mechanical properties of the Si3N4f/BN/Si3N4 composites, compared with CVI process.