Interaction in polysilazane/SiC powder systems
Consolidation of ceramic precursor ceramic powder systems upon heating is investigated. A polysilazane (silicon nitride precursor) is chosen as ceramic precursor with a filler of a sub-micron SiC powder. A scheme to optimize the volume fraction of precursor is developed in order to maximize the density of the compacted samples in the green state. Different techniques are presented to improve the homogeneity of precursor distribution in the mixture. A microencapsulation technique is developed that leads to a uniform coating of precursor on individual SiC particles. Upon pyrolysis of systems with 20 wt% polysilazane, little shrinkage occurs. The SiC particles do not coarsen during the heat treatment. The precursor, upon pyrolysis, transforms into an amorphous ceramic phase that acts as a cement between SiC particles. This cement phase can remain amorphous up to 1500{degrees}C; and is best described as a siliconoxycarbide with or without traces of nitrogen. Elimination of nitrogen in the amorphous phase indicates that the filler material (SiC) has a strong influence on the pyrolysis behavior of the chosen polysilazane. The amorphous ceramic phase may crystallize between 1400 and 1500{degrees}C, and depending on the nature of the gas environment, the crystalline phases are SiC, Si or Si{sub 3}N{sub 4}. Mechanisms explaining the strength increase upon heat treatment are proposed. Redistribution of the precursor occurs by capillary forces or vapor phase diffusion and recondensation of volatile monomers. The confined pyrolysis of the precursor results in an increase of residual ceramic matter being decomposed inside the sample. Interfacial reaction between the native silica-rich surface layer on SiC particles and the precursor derived phase explains the high strength of the materials.
- Research Organization:
- Lawrence Berkeley Lab., CA (United States)
- Sponsoring Organization:
- DOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 7000107
- Report Number(s):
- LBL-32689; ON: DE92041178
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360201* -- Ceramics
Cermets
& Refractories-- Preparation & Fabrication
AMORPHOUS STATE
CARBIDES
CARBON COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
COHERENT SCATTERING
CRYSTAL STRUCTURE
CRYSTALLIZATION
CRYSTALS
DECOMPOSITION
DENSITY
DIFFRACTION
ELECTRON MICROSCOPY
ELECTRON SPECTROSCOPY
ENCAPSULATION
FLEXURAL STRENGTH
HEAT TREATMENTS
INTERFACES
MECHANICAL PROPERTIES
MICROSCOPY
MICROSTRUCTURE
MONOCRYSTALS
NITRIDES
NITROGEN COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC SILICON COMPOUNDS
OXIDES
OXYCARBIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PNICTIDES
POLYMERS
POWDERS
PRECURSOR
PROCESSING
PYROLYSIS
SCATTERING
SILICON CARBIDES
SILICON COMPOUNDS
SILICON NITRIDES
SILICON OXIDES
SPECTROSCOPY
SYNTHESIS
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
THERMOCHEMICAL PROCESSES
TRANSMISSION ELECTRON MICROSCOPY
WHISKERS
X-RAY DIFFRACTION