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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
Since ceramics have high melting temperatures (for example >2500 °C for SiC) and are insoluble and very hard, machining of such materials is difficult and expensive. One primary advantage of the preceramic polymer route over the conventional powder processing technology is the ease of fabrication of useful forms such as coatings, fibers, and complex shapes. Other advantages of the polymer pyrolysis technology include: ability to purify precursors at low cost; lower processing temperatures; opportunity to prepare novel materials such as ceramic–ceramic and ceramic–metal composites and to modify chemical, physical, optical, mechanical, and electrical properties; at least some ability to control grain size, microstructure, and crystallinity thereby allowing densification at temperatures lower than traditional processing temperatures.
Ceramic Fabrication Processes: An Introductory Overview
Published in M. N. Rahaman, Ceramic Processing and Sintering, 2017
Polymer pyrolysis refers to the pyrolytic decomposition of metal-organic polymeric compounds to produce ceramics. The polymers used in this way are commonly referred to as preceramic polymers in that they form the precursors to ceramics. Unlike conventional organic polymers (e.g., polyethylene), which contain a chain of carbon atoms, the chain backbone in preceramic polymers contains elements other than carbon (e.g., Si, B, and N) or in addition to carbon. The pyrolysis of the polymer produces a ceramic containing some of the elements present in the chain. Polymer pyrolysis is an extension of the well-known route for the production of carbon materials (e.g., fibers from pitch or polyacrylonitrile) by the pyrolysis of carbon-based polymers (54). It is also related to the solution sol–gel process described in the previous section where a metal-organic polymeric gel is synthesized and converted to an oxide.
Ceramic Fabrication Methods for Specific Shapes and Architectures
Published in Mohamed N. Rahaman, Ceramic Processing, 2017
Polymer pyrolysis refers to the pyrolytic decomposition of metal–organic polymeric compounds to produce ceramics. The polymers used in this way are sometimes referred to as preceramic polymers, in that they form the precursors to ceramics. Unlike conventional organic polymers (e.g., polyethylene), which contain a chain of C atoms, the chain backbone in preceramic polymers contains elements other than C (e.g., Si, B, or N), or in addition to C. The pyrolysis of the polymer produces a ceramic containing some of the elements present in the chain. The overall fabrication process is summarized in Figure 16.9. In practice, the process typically involves the following steps: (1) purchasing the desired preceramic polymer commercially, (2) forming it into the desired shape (e.g., fiber drawing; casting; injection molding), (3) curing the as-formed green article, by heating at ~150°C–250°C in an oxidizing atmosphere or by electron beam irradiation, to cross-link the polymer—the more rigid cross-linked structure allows better shape retention on subsequent heating—and (4) pyrolysis at temperatures up to 1000°C–1500°C, to convert the organic polymer to an inorganic material and to form a crystalline ceramic product.
Additive manufacturing of flexible polymer-derived ceramic matrix composites
Published in Virtual and Physical Prototyping, 2023
Jun Ou, Minzhong Huang, Yangyang Wu, Shengwu Huang, Jian Lu, Shanghua Wu
Polymer-derived ceramics (PDCs) are a class of ceramic materials that can be formed directly from precursors by pyrolysis, without the need for sintering (Colombo et al. 2010; Xia et al. 2020). For instance, polycarbosilane, polysiloxane, polysilazane, and polyborosilazane can be pyrolyzed to silicon carbide (SiC), silicon oxycarbide (SiOC), silicon carbon nitride (SiCN), and silicon boron carbon nitride (SiBCN), respectively. Moreover, the pyrolysis of PDCs is completed at relatively low temperatures (typically 800–1300°C) (He et al. 2020; Zanchetta et al. 2016), and PDCs are resistant to oxidation, creep, and phase separation at temperatures up to 1500°C and higher (Colombo et al. 2010; Zanchetta et al. 2016). Furthermore, preceramic polymers can be modified such that they can be converted to ceramic parts with the compositions and microstructures necessary to exhibit desired performances and functionalities (Riedel et al. 2006; Zhou et al. 2020). In particular, flexible preceramic polymer materials can be easily designed to meet the demand for 3D-printed and deformable green ceramic parts, which provides the opportunity to realise the 4D printing of deformable ceramic structures that can be stably transformed into various shapes.
Metal-doped polymer-derived SiOC composites with inorganic metal salt as the metal source by digital light processing 3D printing
Published in Virtual and Physical Prototyping, 2020
Cong Ma, Chong He, Weilin Wang, Xiaoyan Yao, Liwen Yan, Feng Hou, Jiachen Liu, Anran Guo
The electrical conductivity of the Cu/SiOC ceramics can be attributed to the interaction of the alloy phase and the percolating carbon network. On one hand, the preceramic polymer would transform into a free carbon-rich ceramic matrix after pyrolysis, in which percolating carbon networks formed (Ionescu, Kleebe, and Riedel 2012; Lu, Erb, and Liu 2016). On the other hand, copper-tin alloy generated during the pyrolysis process was incorporated in the percolating carbon network in the matrix, forming an electrically conductive system (Colombo et al. 2004; Ionescu, Kleebe, and Riedel 2012), exhibiting a semiconducting behaviour. In this article, the conductivity of the Cu-doped SiOC ceramic lattice obtained by DLP printing is in a relative high level, indicating that it may have potential application in some electrical structural parts. Other kinds of inorganic metal salts such as Zr(NO3)4, Fe2(SO4)3 can be also introduce into the preceramic polymer as metal source for modifying specific properties (such as catalytic or magnetism characteristics), to fabricate multifunctional metal-doped SiOC ceramics via DLP method, which have potential applications in several functional fields. It should be noted that the metal salts containing silver ion were not suitable for this method because such mixtures would turn into black grey under UV the irradiation and exert negative influence on the 3D printing process.
Solution based freeze cast polymer derived ceramics for isothermal wicking - relationship between pore structure and imbibition
Published in Science and Technology of Advanced Materials, 2019
Daniel Schumacher, Dawid Zimnik, Michaela Wilhelm, Michael Dreyer, Kurosch Rezwan
Compared to conventional ceramics such as Al2O3, TiO2 and mullite polymer-derived ceramics offer some advantages. Significantly reduced thermal conductivity ensures benefits in capillary transport at cryogenic conditions and lower pyrolysis/sintering temperatures provide advantages in terms of environment and costs [20]. Furthermore, incomplete decomposition of the organic groups at low pyrolysis temperatures results in the creation of micropores and allows for the adjustment of the surface characteristic, e.g. hydrophilicity. The unique adjustment of micropores and hydrophilicity by pyrolysis temperature enables additional possibilities to adapt the material to specific capillary transport applications. In contrast to conventional powder-based fabrication methods, preceramic polymers offer a great versatility in shaping techniques. Also, shaping methods assigned to polymers such as solution-based freeze-casting can be used [21].