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The codeposition characteristics of Si–B–N ceramics from the SiCl4–NH3–BCl3–H2–Ar system at lower temperatures and phase transformation of as-prepared Si–B–N ceramics at temperatures from 1200 to 1800 °C were investigated. Thermodynamic analysis results indicated that the BN + Si3N4 dual phase region existed from 800 to 1200 °C and that 800 °C was an optimum deposition temperature to deposit Si–B–N ceramic coating. Deposition efficiencies at equilibrium for Si3N4 and BN were high, particularly at temperatures below 1000 °C. Pressure and dilution ratio of H2 had little influence on deposition efficiencies of BN and Si3N4 at 800 °C. The amorphous Si–B–N ceramic coatings were successfully deposited at 800 °C from the same precursor system and contained N–B and N–Si bonds by XPS analysis. It kept amorphous below 1600 °C in N2 and partly transformed to α/β-Si3N4 when heat treated at 1600 °C in N2 for 2 h. These results demonstrated that the composite Si–B–N ceramics could be fabricated at 800 °C and used below 1600 °C.
The infrared emissivity properties of carbon fibers with different treatments were investigated in the wave length range 6–15 μm from 1273 to 1873 K. The heat treatment affected the infrared emissivity of carbon fibers through the microstructure evolution. The Raman investigation about the microstructure indicated that the increase of the graphitization degree in carbon fibers degenerated the infrared emissivity of carbon fibers, especially under high temperatures. For the coated carbon fibers, the infrared emissivity properties were decreased for carbon fibers coated pyrolytic carbon (PyC) due to the lamellar structure of PyC and increased for carbon fibers deposited carbon nanotubes (CNTs) owing to the skeleton-like structure of CNTs. The study also illustrated that the PyC coating thickness from 0.5 to 1.0 μm had few effects on the infrared emissivity properties of carbon fibers.
Ultrafine preceramic Si/C/N composite powders have been prepared from hexamethyldisilazane (HMDS) by laser-induced gas phase reaction, using a new kind of tworeaction-zone reactor which could efficiently increase laser efficiency and production yield compared with a one-reaction-zone reactor. The as-formed products were nanosized (50–80 nm), amorphous powders containing Si–C and Si–N bonds homogeneously mixed with some excess carbon. The production yield was in the range of 88–120 g/h. Changes of chemical composition and crystallization of the powders during heat treatment at 1350 and 1550 °C under nitrogen for 1 h were studied.
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