Abnormal Graphitization Behavior in Near‐Surface/Interface Region of Polymer‐Derived Ceramics

Abstract

A free carbon phase has been proven to be beneficial for many structural and functional properties of PDCs, such as electrical conductivity, [8][9][10][11][12][13][14] electromagnetic properties, [15][16][17] electrochemical properties, [18,19] piezoelectricity, [20,21] corrosion resistance, [22] and oxidation resistance. [23] In high-temperature sensing applications, the concentration and morphology of free carbon strongly affect the electrical properties of devices and the selectivity/sensitivity of sensors. [4] In energy applications, PDCs are considered promising for electrical energy storage in devices ranging from cell phones to electric cars. [24] The electrical conductivity or free carbon morphology of PDC-based anode materials for lithium ion batteries plays an important role in achieving high reversible capacity, good rate performance, and reliable cycle stability. [25] In electromagnetic wave absorbing and shielding applications, an increase in the free carbon concentration of PDCs leads to an increase in the dielectric loss and, in turn, improves the total shielding effectiveness in terms of both absorption and reflection shielding effectiveness. [26] Therefore, the microstructural evolution of carbon and the properties resulting from the same are of great interest in this research area.This leads to the fundamental and common question of how to effectively regulate the structural evolution of carbon to further enhance the performance of PDCs. The polymer-toceramic transformation process of most PDCs mainly includes the synthesis of a preceramic precursor, shaping, cross-linking, and pyrolysis. [2,27] Amorphous PDCs undergo a devitrification process to form an amorphous multiphase system through a redistribution reaction of chemical bonds under hightemperature conditions. [2,27] The separated free carbon phase undergoes a graphitization process that plays an important role in the microstructural evolution of PDCs. [4] Many studies have claimed that the amount of free carbon within PDCs strongly depends on the thermal stability of the hydrocarbon linkages rather than on the percentage of the total carbon content of the polymer; therefore, a large number of new precursor solutions (e.g., polysiloxane or polysilazane, carbon-rich or carbonpoor polymers) and optimized heat-treatment parameters (e.g., temperature, atmosphere, and holding time) have been designed and explored to improve the graphitization level of The in situ free carbon generated in polymer-derived ceramics (PDCs) plays a crucial role in their unique microstructure and resultant properties. This study advances a new phenomenon of graphitization of PDCs. Specifically, whether in micro-/nanoscale films or millimeter-scale bulks, the surface/interface radically changes the fate of carbon and the evolution of PDC nanodomains, promotes the graphitization of carbon, and evolves a free carbon enriched layer in the near-surface/interface region. Affected by the enrichment behavior of free carbon in the near-surface/interface region, PDCs exhibit h...

In Situ Investigation of Thermally Induced Surface Graphenization of Polymer-Derived Ceramic (PDC) Coatings from Molecular Layer (MLD) Deposited Silicon-Based Preceramic Thin Films

“…Interestingly, the graphene shell is formed only in those regions of the SiAlCO PDCs that were exposed to the e-beam, indicating the need for high energy input. Similar graphenization of the near-surface/interface region and the formation of graphene-like layers was also observed in silicon based PDCs obtained from different deposition techniques, such as direct ink writing (DIW) additive manufacturing or spark plasma sintering of powders. , However, the literature reported formation of graphene-like layers in silicon-based PDCs only at pyrolysis temperatures above 1200 °C, while in this work, the layers grew at considerably lower temperatures, starting at 800 °C, which confirms that the e-beam plays a role in the transformation. It is likely that the e-beam provides an additional energy increment needed for the conversion of the decomposed organic groups to graphene.…”

“…This is in good agreement with the TEM investigations that did not show graphene in the PDC bulk. In addition to that, the Raman signals of the locations (7,9,13,17,19) of SiAlCO PDCs showed fluorescence, suppressing the second-order wavenumber range of the Raman spectrum, which is correlated with the presence of sp 2 -carbon clusters in the amorphous matrix of the film.…”

“…methyl groups) after annealing. The heatmaps of the 2D and D + G band distributions in Figure 3e show that for the Raman signal of some locations (7,9,13,17,19) 2D and D + G bands are missing. These are regions with ZrO 2 agglomerates that were not exposed to the e-beam and consequently show strong disorder of the amorphous sp 2 carbon in the PDC film.…”

“…The typical polymer-to-ceramic transformation process for most PDCs consists of the synthesis of a suitable preceramic precursor, followed by shaping, cross-linking, and pyrolysis. , If amorphous, the PDCs will typically undergo a devitrification process at elevated temperatures, where chemical bonds are redistributed, resulting in the formation of an amorphous multiphase system . The generation of carbon within the Si-based ceramic matrix during the transformation process has been extensively described in the relevant literature. – Research over the past decades established that the formation of free carbon is a common denominator for all PDCs . The free carbon in PDCs originates from the hydrocarbons incorporated into the preceramic precursors and is formed upon pyrolysis.…”

Bioinspired High Tolerant Vein–Membrane Al2O3 Coating

“…The strain sensing properties of C/SiCN thin-film strain gauge were tested by deflection method. [71] Its gauge factor (GF) was determined as 23. The stable signal output of 5000 fatigue tests of the C/SiCN thin-film strain gauge indicated that the insulation layer had good fatigue tolerance.…”