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

Abstract

The effects of N 2 gas pressure on the diameter and morphology of Si 3 N 4 fibers obtained via carbothermal nitridation were investigated. Sol-gel-derived precursors containing a silica and carbon mixture were placed in an Al 2 O 3 crucible and heat-treated under various N 2 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 αand β-phase Si 3 N 4 were formed. The fiber diameter decreased with increases in N 2 pressure, and nanometer-scale fibers of around 200 nm in diameter were obtained at a N 2 pressure of 0.5 MPa. It was found that silicon oxynitride Si 2 N 2 O or its Al-doped form, O′-SiAlON, was produced due to high N 2 pressure and doping with Al originating from the Al 2 O 3 crucible. This oxynitride was considered to act as a template for Si 3 N 4 fiber growth by the direct phase transformation mechanism. It was shown that the diameter of the Si 3 N 4 fibers decreased for two reasons: decreased partial pressure of SiO gas due to high N 2 pressure and increased formation of the silicon oxynitride templates.

Preparation of poly glycidyl methacrylate (PGMA) chain-grafted boron nitride/epoxy composites and their thermal conductivity properties

“…It is well known that the incorporation of highly thermally conductive ceramic particles such as aluminum nitride (AlN), 6 alumina (Al 2 O 3 ), 7 silicon carbide (SiC), 8 silicon nitride (Si 3 N 4 ) 9 into the polymer matrix can greatly improve the thermal conductivity of composites. However, high thermal conductivity often requires high content fillers to establish a heat conduction network.…”

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

“…The crystal structure in fibers represents a periodic region with long-range ordered structure, and the arrangement of atoms in the crystal lattice plays a crucial role in the mechanical properties of materials [ 11 ], such as tensile strength [ 12 ], compressive strength, and fracture behavior. Moreover, ceramic fibers with high melting points and thermally stable crystal structures tend to maintain their structural and performance stability in high-temperature environments [ 13 ]. Additionally, the arrangement of atoms and the energy band structure in the crystal have a significant impact on thermal conductivity [ 14 ], insulation, and optical properties.…”