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Direct Observation of Preceramic and Organic Binder Decomposition in 2‐D Model Microstructures
Author(s) -
Lewis Jennifer A.,
Cima Michael J.,
Rhine Wendell E.
Publication year - 1994
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1994.tb07059.x
Subject(s) - materials science , thermal decomposition , polymer , thermosetting polymer , pyrolysis , microstructure , ceramic , amorphous solid , composite material , polysilane , chemical engineering , silicon carbide , polymer chemistry , organic chemistry , chemistry , engineering
Preceramic and organic binder decomposition processes were studied during thermolysis to determine how the physico‐chemical properties of the binder affected the microstructural development of the ceramic component. Specifically, the behavior of two organic polymers, poly(methyl methacrylate) (PMMA) and a cross‐linked poly(methyl methacrylate) (x‐PMMA), and two preceramic polymers, polycarbosilane (PCS) and vinylic polysilane (VPS) was observed as a function of temperature. Binder‐filled two‐dimensional (2‐D) model microstructures were fabricated to simulate ceramic green bodies whose pores were completely filled with binder. Examination of these 2‐D samples by hot‐stage optical microscopy enabled direct observations of pore development and changes in polymer morphology during binder thermolysis. These observations revealed that the mass transport processes involved during thermolysis as well as the developing microstructural features, depend on the properties of the binder system during thermal decomposition. The organic polymers were investigated because of their chemical similarity and markedly different physical behavior upon heating. It was shown that thermoplastic polymers (e.g., PMMA) are influenced by capillary forces during thermolysis, while thermosetting polymers (e.g., x‐PMMA) do not flow within these porous microstructures. Both of the preceramic polymers displayed a range of physical behavior over the temperatures Studied. The decomposition chemistry and weight loss at a given temperature combined with the associated physical behavior had a dramatic effect on the final distribution of the pyrolyzed product (amorphous silicon carbide and glassy carbon) formed during thermolysis. The pyrolysis product formed from PCS was observed to segregate to the smaller pore channels in the 2‐D microstructures, while the pyrolysis product formed from VPS was observed to be homogeneously distributed in these model microstructures. This work offers guidelines to improve the microstructural homogeneity of ceramic–ceramic composites derived from particulate–preceramic polymer green bodies.