scholarly journals Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4075
Author(s):  
Casey Sugie ◽  
Alexandra Navrotsky ◽  
Stefan Lauterbach ◽  
Hans-Joachim Kleebe ◽  
Gabriela Mera
Keyword(s):  
Phenyl Group ◽  
Silicon Oxycarbide ◽  
Enthalpies Of Formation ◽  
Hydroxyl Groups ◽  
Preceramic Polymers ◽  
Calorimetric Measurements ◽  
Polymer Derived Ceramic ◽  
Carbon Nanoscrolls ◽  
Carbon Substitution ◽  
Heat Of Dissolution

Silicon oxycarbides synthesized through a conventional polymeric route show characteristic nanodomains that consist of sp2 hybridized carbon, tetrahedrally coordinated SiO4, and tetrahedrally coordinated silicon with carbon substitution for oxygen, called “mixed bonds.” Here we synthesize two preceramic polymers possessing both phenyl substituents as unique organic groups. In one precursor, the phenyl group is directly bonded to silicon, resulting in a SiOC polymer-derived ceramic (PDC) with mixed bonding. In the other precursor, the phenyl group is bonded to the silicon through Si-O-C bridges, which results in a SiOC PDC without mixed bonding. Radial breathing-like mode bands in the Raman spectra reveal that SiOC PDCs contain carbon nanoscrolls with spiral-like rolled-up geometry and open edges at the ends of their structure. Calorimetric measurements of the heat of dissolution in a molten salt solvent show that the SiOC PDCs with mixed bonding have negative enthalpies of formation with respect to crystalline components (silicon carbide, cristobalite, and graphite) and are more thermodynamically stable than those without. The heats of formation from crystalline SiO2, SiC, and C of SiOC PDCs without mixed bonding are close to zero and depend on the pyrolysis temperature. Solid state MAS NMR confirms the presence or absence of mixed bonding and further shows that, without mixed bonding, terminal hydroxyls are bound to some of the Si-O tetrahedra. This study indicates that mixed bonding, along with additional factors, such as the presence of terminal hydroxyl groups, contributes to the thermodynamic stability of SiOC PDCs.

Microcrystalline Ceramic Composites by Active Filler Controlled Reaction Pyrolysis of Polymers

1992 ◽  
Vol 274 ◽  
Author(s):  
Peter Greil ◽  
Michael Seibold ◽  
Tobias Erny
Keyword(s):  
Composite Materials ◽  
Dimensional Change ◽  
Ceramic Composites ◽  
Silicon Oxycarbide ◽  
Preceramic Polymers ◽  
Active Filler ◽  
Polymer Derived Ceramic ◽  
Property Changes ◽  
Low Dimensional ◽  
Carbide Inclusions

ABSTRACTPyrolytic conversion of preceramic polymers such as polysilanes, -silazanes, or -siloxanes to ceramics may be significantly influenced by the resence of active filler dispersoids. Based on thermodynamic and microstructural considerations a variety of suitable polymer-filler systems can be found which allow the fabrication of microcrystalline composite materials with low dimensional change upon polymer- ceramic conversion. As an example the active filler controlled reaction pyrolysis of polysiloxane with addition of titanium powder was investigated. A composite material with microcrystalline titanium carbide inclusions embedded in an amorphous (< 1000 °C) or nanocrystalline (>1000 °C) silicon oxycarbide matrix was formed. Property changes with increasing pyrolysis temperature can be attributed to various microstructural transformations. Thus, a variety of potential fillers may be used to tailor the microstructure of polymer-derived ceramic composite materials in order to fabricate bulk materials and components with a broad range of compositions and properties.

scholarly journals Insights into the Microstructural Evolution Occurring during Pyrolysis of Metal-Modified Ceramers Studied through Selective SiO2 Removal

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3276
Author(s):  
Aitana Tamayo ◽  
Juan Rubio ◽  
Fausto Rubio ◽  
Mᵃ Angeles Rodriguez
Keyword(s):  
Structural Characteristics ◽  
Domain Size ◽  
Ceramic Composites ◽  
Silicon Oxycarbide ◽  
Crosslinking Degree ◽  
Molecular Precursors ◽  
Textural Characterization ◽  
Polymer Derived Ceramic ◽  
Ultimate Properties ◽  
Lower Carbon

Silicon oxycarbide ceramers containing 5% aluminum, zirconium, and cobalt with respect to the total Si amount are prepared from a commercial polysiloxane and molecular precursors and pyrolyzed at temperatures ranging from 500 to 1000 °C. HF etching is carried out to partially digest the silica phase, thus revealing structural characteristics of the materials, which depend upon the incorporated heteroatom. From the structural and textural characterization, it was deduced that when Al enters into the ceramer structure, the crosslinking degree is increased, leading to lower carbon domain size and carbon incorporation as well. On the contrary, the substitution by Zr induced a phase-separated SiO2-ZrO2 network with some degree of mesoporosity even at high pyrolysis temperatures. Co, however, forms small carbidic crystallites, which strongly modifies the carbonaceous phase in such a way that even when it is added in a small amount and in combination with other heteroatoms, this transient metal dominates the structural characteristics of the ceramer material. This systematic study of the ceramer compounds allows the identification of the ultimate properties of the polymer-derived ceramic composites.

Composites Obtained from Alumina and Polymer Derived Ceramic

2018 ◽  
Vol 912 ◽  
pp. 141-146 ◽  
Author(s):  
Glauson Aparecido Ferreira Machado ◽  
Rosa Maria Rocha ◽  
Ana Helena Almeida Bressiani
Keyword(s):  
Heat Treatment ◽  
Silicon Carbide ◽  
Linear Shrinkage ◽  
Density Variation ◽  
Silicon Oxycarbide ◽  
Alternative Route ◽  
Preceramic Polymer ◽  
Pure Alumina ◽  
Polymer Derived Ceramic ◽  
Alumina Composites

Alumina-mullite composites with low shrinkage can be made by reaction bond using mixtures of alumina, aluminum and silicon carbide. In this work, an alternative route is used to produce alumina composites with low shrinkage. Here alumina samples containing additions of 10 and 20 wt% of a preceramic polymer were warm-pressed and treated in the range of 900 -1500°C to produce alumina based composites. The obtained composites were analyzed by linear shrinkage and compared to pure alumina samples sintered at the same temperature range. It were also evaluated the density variation and crystalline phases formed during heat treatment of alumina composites. Results showed that alumina-silicon oxycarbide and alumina-mullite composites were obtained with lower shrinkage than pure alumina samples.

Calorimetric study of the digestion of gibbsite, Al(OH)3(cr), and thermodynamics of aqueous aluminate ion, Al(OH)4−(aq)

1991 ◽  
Vol 69 (11) ◽  
pp. 1685-1690 ◽  
Author(s):  
Qiyuan Chen ◽  
Yuming Xu ◽  
Loren G. Hepler
Keyword(s):  
Thermodynamic Properties ◽  
Aqueous Sodium Hydroxide ◽  
Sodium Aluminate ◽  
Heat Capacities ◽  
Enthalpies Of Formation ◽  
Calorimetric Study ◽  
Enthalpies Of Solution ◽  
Calorimetric Measurements ◽  
Wide Range ◽  
Standard Enthalpies Of Formation

We have made calorimetric measurements of the enthalpies of solution of gibbsite, Al(OH)3(cr), in aqueous sodium hydroxide solutions at five temperatures from 100 to 150 °C. Results of these measurements have been used to obtain the standard enthalpies of formation of Na+(aq) + Al(OH)4−(aq) at the experimental temperatures. These results have also led to values of ΔCp0 for the reaction represented concisely by Al(OH)3(cr) + OH−(aq) = Al(OH)4−(aq), from which we have obtained standard state partial molar heat capacities of Na+(aq) + Al(OH)4−(aq). Combination of our results with those from earlier investigations has permitted calculation of thermodynamic properties of Na+(aq) + Al(OH)4−(aq) over a wide range of temperature and thence some generalizations about the usefulness of various equations for representing or predicting these thermodynamic properties. Key words: gibbsite, enthalpy of solution; sodium aluminate (aqueous), thermodynamic properties; heat capacities, Na+(aq) + Al(OH)4−(aq).

Enthalpies of formation of Cr3+(aq) and the inner sphere complexes CrF2+(aq), CrCl2+(aq), CrBr2+(aq), and CrSO4+(aq)

1976 ◽  
Vol 54 (9) ◽  
pp. 1383-1387 ◽  
Author(s):  
Ingemar Dellien ◽  
Loren G. Hepler
Keyword(s):  
Enthalpies Of Formation ◽  
Calorimetric Measurements ◽  
Inner Sphere ◽  
Inner Sphere Complexes

We have carried out calorimetric measurements leading to ΔHf0 = −60 kcal mol−1 for Cr3+(aq). Further calorimetric measurements have led to enthalpies of reaction of Cr3+(aq) with HF(aq), Cl−(aq), Br−(aq), and SO42−(aq) to form the 'inner sphere' complexes CrF2+(aq), CrCl2+(aq), CrBr2+(aq), and CrSO4+(aq). Results of our measurements lead to ΔHf0 = (−60.0 ± 1.5) kcal mol−1 for Cr3+(aq), ΔHf0 = −136.8 kcal mol−1 for CrF2+(aq), ΔHf0 = −93.7 kcal mol−1 for CrCl2+(aq), ΔHf0 = −80.1 kcal mol−1 for CrBr2+(aq), and ΔHf0 = −269.7 kcal mol−1 for CrSO4+(aq).

scholarly journals Synthesis and electrochemical performance of a polymer-derived silicon oxycarbide/boron nitride nanotube composite

RSC Advances ◽  
2017 ◽  
Vol 7 (35) ◽  
pp. 21576-21584 ◽  
Author(s):  
M. A. Abass ◽  
A. A. Syed ◽  
C. Gervais ◽  
G. Singh
Keyword(s):  
Boron Nitride ◽  
Electrochemical Performance ◽  
Boron Nitride Nanotubes ◽  
Silicon Oxycarbide ◽  
Boron Nitride Nanotube ◽  
Electrochemical Applications ◽  
Polymer Derived Ceramic ◽  
New Type

Synthesis of a new type of composite consisting of boron nitride nanotubes (BNNTs) filler in polymer-derived ceramic silicon oxycarbide (SiOC) for electrochemical applications is demonstrated.

Comparison of Microwave Hybrid and Conventional Heating of Preceramic Polymers to Form Silicon Carbide and Silicon Oxycarbide Ceramics

2004 ◽  
Vol 83 (7) ◽  
pp. 1617-1625 ◽  
Author(s):  
Gene A. Danko ◽  
Richard Silberglitt ◽  
Paolo Colombo ◽  
Eckhard Pippel ◽  
Jörg Woltersdorf
Keyword(s):  
Silicon Carbide ◽  
Silicon Oxycarbide ◽  
Conventional Heating ◽  
Preceramic Polymers
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