Erosion characteristics of silicon nitride ceramics
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Distilled water
Silicon oxynitride
Carbon fibers
AES and XPS measurements of silicon nitride films with refractive indices ranging from 1.93 to 2.08 have been made. The films studied were grown on silicon (100) substrates by CVD using varying mixtures of silane and ammonia. Earlier AES studies of similar silicon nitride films have suggested that these films are microscopic mixtures of Si and Si3N4. We present XPS data which show that there is no measurable ’’free’’ silicon (i.e. the level of ’’free’’ silicon is ≲3 at. %) in the silicon nitride films with refractive indices ≲2.02. AES data show an increase in oxygen content corresponding to a decrease in refractive index of the silicon nitride films. These AES measurements agree qualitatively with measurements of the physical properties of silicon oxynitride films.
Silicon oxynitride
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Aluminum nitride whiskers have excellent characteristics, not only can be used in the high heat conductivity for the preparation of a new composite, but also can be used as a reinforcing agent for the preparation of a new composite toughened. Using wet, melamine, and aluminum nitrate as raw material, aluminum nitride whiskers precursor are prepared and pure aluminum nitride whiskers can be obtained by nitrogen and carbon removal processes. This kind of aluminum nitride whiskers possess smooth surface, uniform length, straight whisker, and a long cylindrical structure with a diameter of 4-6 μm and a length diameter ratio of 40-100.
Monocrystalline whisker
Carbon fibers
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Silicon nitride is a typical engineering ceramics as structural materials for high-temperature or functional applications. However, the fabrication of silicon nitride costs a lot because the densification of silicon nitride needs vast energy to get high-temperature of 2073∼2273 K and special apparatus such as a hot-press. Therefore, it is difficult to use silicon nitride in large amount. Consequently, lowering of the fabrication cost is essential to apply silicon nitride to wider fields.We propose a new process of the liquid phase sintering of silicon nitride using an oxynitride sintering aid which consisted of SiO2, MgO and preliminarily added α-Si3N4 and was fired at temperature up to 2073 K. The α-Si3N4 green compacts with the oxynitride sintering aid were sintered at 1873 K for 64-512 min under 0.1 MPa nitrogen pressure, and fully dense β-Si3N4 ceramic was fabricated after 512 min sintering. This sintering temperature is about 200 K lower than that of a conventional method.
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The use of oxynitride glasses in the Y-Si-Al-O-N system to join sintered silicon nitride was investigated. Flexural strength of joined silicon nitride was dependent upon joining temperature, joint morphology, and joining glass composition. Non- brittle behavior was observed at test temperatures of 1100°C or higher with joint morphologies characterized by thick glass layers (40–50 μm). In contrast, brittle behavior was observed to test temperatures of 1300°C with joint morphologies characterized by thin glass layers (<5 μm). Joint strengths comparable to the strength of as-received silicon nitride were observed to test temperatures as high as 1100°C. Oxidation of the fracture surfaces was observed at lest temperatures of 1300°C and higher.
Silicon oxynitride
Brittleness
Brittle fracture
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Abstract Silicon nitride has been prepared by heating pure silicon in purified nitrogen at 1450°. X ‐ray studies showed the presence of two nitrides, and a method was therefore devised to separate them. Although these nitrides differ in their crystal structure, they have the same compositions, corresponding to Si3N4. A few chemical tests were performed on finely divided silicon nitride prepared at or above 145°. Several alloys containing various proportions of silicon were nitrided under different conditions, and the X ‐ray diffraction patterns of the nitrides extracted from these alloys were found to be in complete agreement with that of α‐Si 3 N 4 . The diffraction lines obtained from the nitrided alloy prior to any chemical treatment gave nitride lines which did not correspond to those of the α‐Si 3 N 4 or β‐Si 3 N 4 .
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Silicon nitride ceramics seeded with 3 wt%β‐Si 3 N 4 whiskers of two different sizes were prepared by a modified tape casting and gas pressure sintering. The fine whiskers had a higher aspect ratio than the coarse whiskers. Quantitative texture analysis including calculation of the orientation distribution function (ODF) was used for obtaining the degrees of preferred orientation of sintered samples. The maximum multiples of random distribution (mrd) values of samples seeded with the fine and coarse whiskers were large, greater than 15 and 9, respectively. Meanwhile, the mrd value of a sample seeded with fine whiskers was only 9 when it was prepared by conventional tape casting. The microstructures and the XRD data revealed that the well‐aligned whiskers grew significantly after sintering and dominated the texture. Differences among the degrees of preferred orientation of the samples were explained using Jeffrey's model on rotation of elliptical particles carried by a viscous fluid.
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Texture (cosmology)
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Silicon oxynitride
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Theoretical calculations indicate that the tunneling currents in silicon nitride or oxynitride are greatly reduced compared to those in SiO/sub 2/ for equivalent oxide thicknesses (EOT) below 4 nm. Experimental results obtained on Jet Vapor Deposited (JVD) nitrides/oxynitrides are shown to verify the theoretical trend. These results suggest that extending the scaling limit well below 4 nm of EOT is possible with the JVD nitride.
Silicon oxynitride
Scaling limit
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The oxidation behavior of porous reaction-bonded silicon nitride has been investigated in the temperature range 900-1400℃ for up to 3 hours by the Simultaneous Thermal Analysis technique. The mechanism of oxidation is complex and depends critically on the temperature. At low temperatures in excess oxygen, a protective silica film is formed by passive oxidation. The low P_ in pores beneath the film leads to active oxidation of both the silicon nitride and silicon oxynitride which may be formed during fabrication process. A model for the roles of the silica film and the silicon oxynitride was proposed and discussed.
Silicon oxynitride
Thermal oxidation
Porous Silicon
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ESCA is used to characterize silicon nitride surface oxidation. Si 2p, N 1s, and O 1s binding energies and photoelectron line intensities of oxidized nitride films are compared with the corresponding lines from thick reference films of silicon, silicon nitride, silcon dioxide, and a series of oxynitrides. Rapid initial oxidation of silicon nitride surfaces occurs at room temperature on exposure of nitride films to air. A graded oxidized nitride film forms between the film surface and the nitride. Similarly, oxynitride films with gradations in composition are obtained upon oxidation of nitride films at high temperatures.
Silicon oxynitride
Silicon dioxide
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