Silicon Nitride Fibers Research Articles

Predicting density-related mechanical properties of amorphous silicon nitride using molecular dynamics simulations

Silicon nitride fiber is among the most popular candidates for high-temperature wave-transparent ceramic matrix composites (CMC) in aerospace engineering, and the measurement of its mechanical properties has always been the focus of researchers. In this paper, a simple and effective molecular dynamics method is used to generate molecular dynamics models of amorphous silicon nitride (a-Si3N4) materials with different densities, and it is verified that the developed models reflect the microstructure of the fiber. Based on analyzing the effects of size on the results, tensile and shear simulations are carried out to obtain the mechanical properties of the models with different densities. According to the research data obtained, the empirical equation between mechanical properties (Young's modulus, shear modulus, tensile strength, and shear strength) and density of fiber is established, and validated by the published experimental results. The empirical equation can not only predict the mechanical properties of fibers directly from the density but also provide a new way to measure the mechanical properties of fibers nondestructively.

Preparation of C/Si3N4 flexible conductive composite films by coating method

Carbon-based materials are widely used in electrical heaters, resistors, battery electrodes, and other applications. Membranous electronic components, with light weight, small volume, extraordinary mechanical flexibility, can be used in microelectronic devices and flexible electronic devices. The C/Si3N4 composite film was prepared by circulating 16% sucrose solution on the coating machine for 4 times and heat treating with nitrogen at 850 °C for 60min. The composite film has excellent electrical conductivity, and the resistivity is 15 mΩ cm at normal temperature (20 °C), and the minimum resistivity can be less than 1 mΩ cm at high temperature. In addition, the composite film maintains the inherent flexibility of silicon nitride fiber paper, and the minimum bending radius is as low as 3 mm. Compared with polymer flexible membranes, C/Si3N4 composite membranes show excellent long-term stability at high temperatures, and the preparation process is green, low cost, easy to operate, and suitable for large-scale production.

Preparation of silicon nitride fibers by additive-assisted nitridation of polysilicon waste powder

Preparation of silicon nitride fibers by additive-assisted nitridation of polysilicon waste powder

Atomistic Construction of Silicon Nitride Ceramic Fiber Molecular Model and Investigation of Its Mechanical Properties Based on Molecular Dynamics Simulations.

Molecular simulations are currently receiving significant attention for their ability to offer a microscopic perspective that explains macroscopic phenomena. An essential aspect is the accurate characterization of molecular structural parameters and the development of realistic numerical models. This study investigates the surface morphology and elemental distribution of silicon nitride fibers through TEM and EDS, and SEM and EDS analyses. Utilizing a customized molecular dynamics approach, molecular models of amorphous and multi-interface silicon nitride fibers with complex structures were constructed. Tensile simulations were conducted to explore correlations between performance and molecular structural composition. The results demonstrate successful construction of molecular models with amorphous, amorphous-crystalline interface, and mixed crystalline structures. Mechanical property characterization reveal the following findings: (1) The nonuniform and irregular amorphous structure causes stress concentration and crack formation under applied stress. Increased density enhances material strength but leads to higher crack sensitivity. (2) Incorporating a crystalline reinforcement phase without interfacial crosslinking increases free volume and relative tensile strength, improving toughness and reducing crack susceptibility. (3) Crosslinked interfaces effectively enhance load transfer in transitional regions, strengthening the material's tensile strength, while increased density simultaneously reduces crack propagation.

An Innovative Design for the Fabrication of Flexible Composite Films from Si3N4 Fiber Paper

A high‐temperature‐resistant flexible substrate is a critical component of high‐performance flexible electronic components. Herein, a method that does not require flowing gas and which is suitable for volume production is presented for the preparation of several‐millimeter‐long silicon nitride (Si3N4) fibers with a cross‐sectional dimension of 0.1–1.0 μm. Further, a square sheet of paper with a weight of 0.050 g, side lengths of 105 mm each, and thickness of 15 μm is fabricated using the Si3N4 fibers via a conventional laboratory paper‐making method. Subsequently, the Si3N4 paper is coated with an LaNiO3 sol using a blade‐coating machine, dried at 80 °C for 10 min, and then annealed at 650 °C for 60 min to prepare Si3N4 fiber paper/LaNiO3 composite films to evaluate the feasibility of applying the paper as a substrate for fabricating flexible functional films. The experimental results confirm that the Si3N4 fiber paper has excellent high‐temperature resistance during annealing in air, and the Si3N4 paper/LaNiO3 composite film presents excellent flexibility and conductivity. Thus, membranous flexible electronic components can be fabricated from Si3N4 fiber paper/LaNiO3 paper by a regular high‐temperature annealing process.

Effects of oxygen on the thermal stability of silicon nitride fibers

Two types of Si3N4 fibers with different oxygen contents were annealed in a nitrogen atmosphere at 1500 °C for 1 h. After annealing, the fiber (SN-L) containing 0.5 wt% oxygen crystallized to α-Si3N4 but lost its strength, whereas the fiber (SN-H) containing 4.2 wt% oxygen was amorphous and retained 63.6% of its strength. The phase transition in these fibers was mainly influenced by the oxygen level. The lower oxygen content in the SN-L favored the precipitation of an almost stoichiometric composition of α-Si3N4 initially at ~1450 °C with an activation energy (Ea) of 663.357 kJ/mol. Nanopores existing naturally in the fiber promoted crystallization via heterogeneous nucleation. SN-H precipitated as an amorphous SiNxOy metaphase preferentially at ~1400 °C with an Ea of 440.434 kJ/mol, owing to the higher oxygen content approaching that of Si2N2O. SiNxOy inhibited the crystallization of α-Si3N4, making SN-H more thermally stable than SN-L at temperatures above 1500 °C.

Degradation behavior of amorphous silicon nitride fibers in low atmospheric pressure

Degradation behavior of amorphous silicon nitride fibers in low atmospheric pressure

Effect of Nitriding Process on Phase and Microstructure of Silicon Nitride Fibers Prepared by Direct Nitriding Method

Effect of Nitriding Process on Phase and Microstructure of Silicon Nitride Fibers Prepared by Direct Nitriding Method

Fabrication of Silicon Nitride Fiber Materials by Organic Foam Impregnation Method

In this paper, porous silicon was prepared by organic foam impregnation, and silicon nitride fibers were prepared by direct in-situ nitridation of porous silicon. The effect of pore structure of porous silicon on material properties was studied. The results show that the silicon nitride fiber material with low density, high strength and low thermal conductivity can be obtained by using organic foam impregnation method. The pore size of template has a certain effect on the growth of silicon nitride fibers. The smaller the pore size of the template, the higher the content of silicon nitride in silicon nitride fiber material. This is due to the concentration of gas phase reactants in pore.

Preparation of High-Performance 2D Si3N4f/SiBN Ceramic Matrix Composites by Precursor Infiltration Pyrolysis

Continuous nitride fiber reinforced nitride matrix composite has been recognized as a promising microwave transparent radome material. The preparation of 2D silicon nitride fibers fabric reinforced silicon boronitride ceramic composites through polyborosilazane precursor infiltration pyrolysis routine is reported. The effects of thermal molding process on the properties and microstructure of theSi3N4f/SiBN composites were studied. The results show that the optimal molding pressure was 6 MPa due to the fine interfacial bonding between fiber and matrix. The Si3N4f/SiBN composites exhibits brittle fracture characteristic, the flexural strength and elastic modulus182.7 MPa and 51.1 GPa respectively, and the dielectric constant and dielectric loss are 4.12 and 8.82×10−3, respectively. The Si3N4f/SiBN composites get the best comprehensive performance.

Preparation and interface modification of Si3N4f/SiO2 composites

In order to modify the interface, SiON coating was introduced on the surface of silicon nitride fiber by perhydropolysilazane conversion method. Si3N4f/SiO2 and Si3N4f/SiONc/SiO2 composites were prepared by sol-gel method to explore the influence of SiON coating on the mechanical properties of composites. The results show that with the protection of SiON coating, Si3N4 fiber enjoys a strength increase of up to 24.1% and Si3N4f/SiONc/SiO2 composites have a tensile strength of 170.5 MPa and a modulus of 26.9 GPa, respectively. After 1000 °C annealing in air for 1 h, Si3N4f/SiONc/SiO2 composites retain 65.0% of their original strength and show a better toughness than Si3N4f/SiO2 composites. The improvement of mechanical properties is attributing to the healing effect of SiON coating as well as its intermediate coefficient of thermal expansion between Si3N4 fiber and SiO2 matrix.

Fabrication and oxidation resistance of silicon nitride fiber reinforced silica matrix wave-transparent composites

Wave-transparent ceramic matrix composites for the high temperature use should possess excellent oxidation resistance. In this work, Si3N4f/SiO2 composites with different fiber content were fabricated by filament winding and sol gel method. The oxidation resistance was investigated by tracking the response of flexural strength to the testing temperature. The results show that the flexural strength and toughness of the composites with fiber content of over 37% can reach high levels at around 175.0 MPa and 6.2 MPa m1/2, respectively. After 1 h oxidation at 1100 °C, the flexural strength drops a lot but can still reach 114.4 MPa, which is high enough to ensure the safety of structures. However, when the oxidation temperature rises to 1200–1400 °C, the flexural strengths continue to fall to a relatively low level at 50.0–66.4 MPa. The degradation at high temperatures is caused by the combination of over strong interfacial bonding, the damage of fiber and the crystallization of silica matrix.

Microstructure and mechanical properties of Si3N4f/Si3N4 composites with different coatings

The Si 3 N 4 coating and Si 3 N 4 coating with Si 3 N 4 whiskers as reinforcement (Si 3 N 4w -Si 3 N 4 ) were prepared by chemical vapor deposition (CVD) on two-dimensional silicon nitride fiber reinforced silicon nitride ceramic matrix composites (2D Si 3 N 4f /Si 3 N 4 composites). The effects of process parameters of as-prepared coating including the preparation temperature and volume fraction of Si 3 N 4w on the microstructure and mechanical properties of the composites were investigated. Compared with Si 3 N 4 coating, Si 3 N 4w -Si 3 N 4 coating shows more significant effect on the strength and toughness of the composites, and both strengthening and toughening mechanism were analyzed.

Micro-mechanical properties of a novel silicon nitride fiber reinforced silicon carbide matrix composite via in situ nano-indentation method.

A novel Si3N4 fiber reinforced SiC matrix composite has been prepared and the micro-mechanical properties of the composites in situ have been explored. For the Si3N4 fibers, the micro-mechanical properties in situ remained almost unchanged with the increasing fabrication temperatures. In comparison, for the PCS derived SiC matrix, higher fabrication temperature could trigger more β-SiC formations, which led to enlarging the corresponding micro-mechanical properties. The microstructure analysis of the interfacial zones in the composites revealed strong interfacial reactions existing in the composites fabricated at ≥800 °C. Therefore, the interfacial shear strength of the composite was significantly increased from ∼420 MPa to ∼535 MPa with the fabrication temperature increasing from 800 °C to 1200 °C, thus impeding the toughening mechanisms of the composites. After introducing BN interphase, the interfacial shear strength was significantly reduced to ∼140 MPa and the flexural strength was increased from ∼140 MPa to ∼250 MPa. The work highlights the efficiency of introducing BN interphase to weaken the interfacial interaction, thus to enhance the macro-mechanical properties.

Fabrication and Characterization of Short Silicon Nitride Fibers from Direct Nitridation of Ferrosilicon in N2 Atmosphere

Short silicon nitride fibers were fabricated by direct nitridation of ferrosilicon in N2 atmosphere, and their structure and possible growth mechanism were characterized and investigated. The rod-like fibers which were α-Si3N4 with a low degree of crystallization and a high aspect ratio had a diameter of about 4 μm and a length close to a few millimeters. Belt-like fibers with a width about 5 μm and a thickness about 1 μm were also found in the nitrides. Scanning electron microscope (SEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) investigations indicated that the fibers were single-crystalline α-Si3N4 with few amorphous distributed in the edge region, and the fibers grew by vapor–liquid–solid (VLS) mechanism.

Effect of nitrogen gas pressure during heat treatment on the morphology of silicon nitride fibers synthesized by carbothermal nitridation

ABSTRACTThe effects of N2 gas pressure on the diameter and morphology of Si3N4 fibers obtained via carbothermal nitridation were investigated. Sol–gel-derived precursors containing a silica and carbon mixture were placed in an Al2O3 crucible and heat-treated under various N2 pressures from 0.1 to 0.5 MPa at 1500ºC. The heat-treated samples were characterized by X-ray diffraction (XRD), a scanning electron microscope (SEM) coupled with an energy dispersion X-ray (EDX) spectrometer, and transmission electron microscopy (TEM). Various nitride fibers with α- and β-phase Si3N4 were formed. The fiber diameter decreased with increases in N2 pressure, and nanometer-scale fibers of around 200 nm in diameter were obtained at a N2 pressure of 0.5 MPa. It was found that silicon oxynitride Si2N2O or its Al-doped form, O′-SiAlON, was produced due to high N2 pressure and doping with Al originating from the Al2O3 crucible. This oxynitride was considered to act as a template for Si3N4 fiber growth by the direct phase transformation mechanism. It was shown that the diameter of the Si3N4 fibers decreased for two reasons: decreased partial pressure of SiO gas due to high N2 pressure and increased formation of the silicon oxynitride templates.

High-temperature properties and interface evolution of silicon nitride fiber reinforced silica matrix wave-transparent composite materials

In order to improve the high-temperature performance of wave-transparent materials especially for the high-speed aircrafts application, filament winding combined with sol-gel method was adopted to the fabrication of unidirectional silicon nitride fiber reinforced silica matrix composites. The mechanical properties and the interface evolution at high temperatures were investigated. The results show that the composite sintered in N2 maintains a flexural strength of 210MPa at up to 1200°C, while its counterpart prepared in air experiences a dramatic reduction to about 73MPa. The degradation is due to the partial oxidation of silicon nitride fibers at the fiber matrix interface. Besides, it is also notable that the bending strength of these two composites undergoes a similar growth from about 160 to 210MPa when tested under 900°C, which can be explained by the release of thermal stress on the silicon nitride fibers.

Mechanical and Dielectric Properties of Two Types of Si₃N₄ Fibers Annealed at Elevated Temperatures.

The mechanical and dielectric properties of two types of amorphous silicon nitride (Si3N4) fibers prior to and following annealing at 800 °C were studied. The tensile strengths of the Si3N4 fiber bundles were measured using unidirectional tensile experimentation at room temperature, whereas the permittivity values were measured at 8.2–12.4 GHz using the waveguide method. The results demonstrated that the tensile strength and dielectric properties of Si3N4 fibers were correlated to the corresponding composition, microstructure, and intrinsic performance of electrical resistance. The Si3N4 fibers with a lower content of amorphous SiNxOy presented an improved thermal stability, a higher tensile strength, a higher conductivity, and a significantly stable wave-transparent property. These were mainly attributed to the highly pure composition and decomposition of less amorphous SiNxOy.

Ablation behavior and mechanism of SiO2f/SiO2, SiO2f/BN and Si3N4f/BN radar wave transparent composites

The ablation behavior and mechanism of SiO2f/SiO2, SiO2f/BN and Si3N4f/BN wave-transparent composites have been comparatively investigated by an oxyacetylene torch test. Viscous SiO2 formed during ablation improves the ablation resistance, while BN undergoes complex ablative oxidizing and absorbs heat via oxidants vaporization. The refractory BN matrix also acts as an tough frame that decreases the scouring of oxygen-resistant SiO2 glass. The reinforcing silicon nitride fiber in the Si3N4f/BN composite suffers from active oxidation under ablation conditions, which degrades its anti-oxidation resistance. The heterogeneous reactions during ablation are analyzed and the ablation mechanisms of the different composites are proposed.

Synthesis of Silicon Nitride Ceramic Fibers and the Effect of Nitrogen Atmosphere on their Morphology

The effect of nitrogen gas flow rate on the morphology of silicon nitride fibers obtained via carbothermal nitridation heat treatment method was investigated. A precursor containing silicon, oxygen and carbon was obtained by a sol-gel method from a mixture of tetraethyl orthosilicate, polyvinyl alcohol, H2O and ethanol. A white wool-like product was obtained by heat treating the precursor placed in an alumina crucible under a 0.5 MPa nitrogen gas pressure at 1500oC with different nitrogen gas flow rates. The mass-based production rates of the samples obtained from the precursor powder were 20-30% for the different nitrogen gas flow rates. X-ray diffraction analysis revealed that the samples contained α-Si3N4 as the major phase along with β-Si3N4, Si2N2O and a small amount of amorphous product as minor phases. Unique twisted fibers with diameters of several hundreds of nanometers were found among the straight fibers by SEM observation. Elemental analysis using energy dispersive X-ray spectroscopy indicated that silicon and nitrogen were contained in the twisted fibers along with approximately 68 at.% of oxygen and several at.% of aluminum, which might have come from the crucible material. The SiAlON-like structures might have been formed by the partial dissolution of Al and O in the Si3N4 fibers. It was considered that the twisted morphology of some fibers might be formed by co-existing of β-SiAlON and/or amorphous phase regions in the Si3N4 fiber and resultant distortion of the fibers.