In the present work, passive oxidation kinetics of silicon nitride α-Si3N4 and (α+β)-Si3N4 powders at different temperatures from 1000 to 1200 °C were evaluated. Oxidation these was carried out improve wettability pressureless infiltration AZ91E Mg-alloy. The kinetic constant (kp) values oxide layer depth calculated. constants kp, 9.11e-16 6.35e-16 kg2/m4s 4.25 nm 3.69 nm, for (α+β)-Si3N4, resp...

The catalytic effects of chromium (Cr) on the direct nitridation of silicon (Si) and morphology of nitridation product were investigated. Cr dramatically improved the conversation of Si to silicon nitride (Si3N4). The complete conversion was achieved at 1350 °C upon addition of 1.25 wt% Cr. This temperature was much lower than that required in the case without using a catalyst. Meanwhile, Cr pl...

Recently, a hardness similar to that of diamond has been reported for a quasiternary, nitride-based nanocomposite. The related, quasibinary nanocomposite "nc-TiN/a-Si3N4," which may be regarded as the prototype of the family of superhard nc-metal-N/a-Si3N4 systems, also exhibits a significant hardness enhancement. Extensive density-functional theory calculations indicate that the superhardness ...

We demonstrate that the compressibility of spinel Si3N4 nanocrystals increases when the pressure is raised above ;40 GPa. Si3N4 nanocrystals initially exhibit an extremely high bulk modulus of 685~45! GPa. But, above 40 GPa, the bulk modulus is reduced to 415~10! GPa. Thus, a critical pressure of ;40 GPa was determined that signifies the onset of size-induced weakening of elastic stiffness in n...

Crack deflection and the subsequent growth of delamination cracks can be a potent source of energy dissipation during the fracture of layered ceramics. In this study, multilayered ceramics that consist of silicon nitride (Si3N4) layers separated by boron nitride/silicon nitride (BN/Si3N4) interphases have been manufactured and tested. Flexural tests reveal that the crack path is dependent on th...

Silicon nitride (Si3N4) is a very robust material against oxidation and is typically used as an oxidation mask. Here, we report atomic-force microscope ~AFM!-based local oxidation of Si3N4 and its applications in selective-area epitaxial growth using chemical-vapor deposition. High growth selectivity is accomplished in this work by employing a SiO2 /Si3N4 bilayer mask structure, which is formed...

The aim of this study is to produce highly dense Si3N4 based composites with good mechanical properties and bioactivity. ceramics without using sintering aids, Si3N4-HA Si3N4-HA-GNP have been produced by spark plasma (SPS) at temperatures 1525–1550°C. effect reinforcement type content on the densification behavior, phase analysis, microstructural development, properties, in-vitro bioactivity be...

Tension experiments in vacuum were performed on a monolithic Si3N4 sample at 1375°C and a 20Vol% SiCp-Si3N4 composite sample at 1400°C using the new SMARTS diffractometer at the Los Alamos Neutron Science Center. The deep penetration of neutrons facilitated these in-situ studies. In particular, the hkl-dependent strains were measured and the results interpreted by Eshelby-based modeling for the...

A low-loss, broadband and high fabrication tolerant optical coupler for the monolithic integration of Si3N4 and polymer waveguides is designed and experimentally demonstrated. The coupler is based on the adiabatic vertical tapering of the Si3N4 waveguides. Low-loss operation is experimentally verified at both 976 and 1460-1635 nm wavelengths. Measured losses per coupler are as low as 0.12 and 0...

The etching of silicon nitride (Si3N4) and silicon dioxide (SiO2) in the afterglow of NF3 and NF3 /O2 microwave discharges has been characterized. The etch rates of both materials increase approximately linearly with the flow of NF3 due to the increased availability of F atoms. The etch rate of Si3N4 is enhanced significantly upon O2 injection into the NF3 discharge for O2 /NF3 ratios of 0.3 an...