Showing 4 results for Silicon Nitride
M. Kalantar and G. Fantozzi,
Volume 22, Issue 1 (7-2003)
Abstract
Dense Silicon nitride was investigated to determine the effect of its microstructural parameters and densification on thermo-mechanical properties and thermal stress resistance to fracture initiation during a hot or cold mechanical and thermal shock testing. The different materials and microstructures were obtained by changing the parameters such as the type of the powder, additive, forming process and sintering condition. Maximum crack growth and thermal shock resistance of dense Si3N4 are achieved after complete conversion of the aàB transformation, and after the change in grain morphology towards elongated
grain and the relative crystallization of the second phases have been obtained. The characteristics are obtained by a high a phase content of the starting powder, high Y2O3, and sintering condition of higher temperature (2000ْC), longer soaking times (1h) and load application at the beginning of the thermal cycle.
Keywords: Silicon nitride, Thermo- mechanical properties, Thermal shock resistance, Crack propagation resistance
Zahra Omidi, Saeed Reza Bakhshi, Ali Ghasemi,
Volume 33, Issue 3 (3-2015)
Abstract
Silicon nitride has attracted a considerable attention because of its excellent properties such as high-temperature strength, good oxidation resistance, high corrosion resistance, good thermal shock resistance, high creep resistance and good thermal and chemical stability. There are several different fabrication methods for synthesizing Si3N4 particles. Such methods are mostly costly and kinetically slow and require lengthy heat treatment. In this study, Si3N4 compounds were synthesized by means
of mechanical milling. In the mechanical milling route,Si powder (≤99.0%) was milled under nitrogen gas for 25 h and heated at various temperatures 1100-1200-1300 and 1400 C for 1 h at the nitrogen atmosphere at a rate of 200 ml/min. Silicon powder was also annealed under a similar condition in order to evaluate the impact of milling process on the low temperature synthesizing of Si3N4. Phase identification and microstructural characteristics of products were evaluated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The Fourier transform infrared spectroscopy and thermal analysis were used for characterization of the formed bands and thermal treatment of the sample, respectively. The obtained results exhibited that Si3N4 powder was fully formed with two kinds of morphologies including globular particles and wire with a width of 100–300 nm and length of several microns at sintering temperature of 1300 C. This was confirmed by the Si–N absorption bonds in the FTIR trace. Based on XRD results, 25 h milling reduced temperature of reaction remarkably in comparison with direct nitridation of Si powders for 1 h. With an increase in the reaction temperature, the Si3N4 samples had a phase transformation 𝛂→𝛃, and variation of the morphology followed the vapor–liquid -solid mechanism.
M. Khajelakzay, S. R. Bakhshi, G.h. Borhani,
Volume 34, Issue 4 (3-2016)
Abstract
In this study, synthesis of silicon nitride by mechanical alloying and the effects of important parameters of milling time and heat treatment temperature, time and rate are presented. Silicon micro powder and nitrogen gas were used as precursor materials. Synthesized phases, morphology and particle size were investigated by X-ray diffraction pattern (XRD) and Field emission scanning electron microscopy (FE-SEM), respectively. X-ray fluorescence analysis (XRF) was used for silicon nitride purity investigation.The optimum sample was produced at 30 h milling time, heat treatment at 1300 ℃ and 22 ℃/min heating rate conditions. X-ray fluorescence analysis showed more than 98% purity.
M. Haghshenas Gorgani, M. Mirkazemi, F. Golestanifard,
Volume 37, Issue 4 (3-2019)
Abstract
In this research, the rheological behavior and stability of suspensions containing Si3N4, Al2O3, Y2O3 and starch were investigated in order to use them in the starch consolidation casting of porous silicon nitride. Dolapix CE64 was used as the dispersant. Then, the effect of some parameters such as Si3N4 surface oxidation, dispersant content, solid loading and starch content on the viscosity and rheological behavior of Si3N4-starch slurry was determined. Surface oxidation of Si3N4 powder at 800°C for 2 hours reduced the viscosity of the slurry, effectively. The best dispersant content was 0.4 wt. %, relative to ceramic powders. Slurries containing 30 to 40 vol. % and 7.5 to 25 vol. % starch, relative to total solid loading, had the suitable viscosity and the sufficient stability for casting by the starch consolidation method.
