Polymer-derived Ceramics Route Research Articles

Synthesis of hexagonal boron nitride graphene-like few layers.

Self-standing highly crystallized hexagonal boron nitride (h-BN) mono-, bi- and few-layers have been obtained for the first time via the Polymer Derived Ceramics (PDCs) route by adding lithium nitride (Li₃N) micropowders to liquid-state polyborazylene (PBN). Incorporation of Li₃N as a crystallization promoter allows the onset of crystallization of h-BN at a lower temperature (1200 °C) than under classical conditions (1800 °C). The hexagonal structure was confirmed by both electron and X-ray diffraction.

Image-analytical evaluation of the spatial distribution of particulate fillers in ceramic composites prepared via the polymer-derived ceramics route

A robust and versatile image analysis routine is presented for the quantitative evaluation of the spatial distribution of a recently developed ceramic composite system prepared by using preceramic polymers as both low-loss binder and reagent in combination with particulate fillers, yielding particulate zirconia-strengthened mullite. Micrographs of polished cross-sections were used as a base for binarization, noise-reduction and Voronoi-based tessellation operations, employing open-source software. The resulting cell area distributions were used to evaluate the microstructural homogeneity by calculating a defined factor of homogeneity. Furthermore, the skewness of the cell area distributions was introduced as a novel characteristic number for the characterization of the filler distribution. The resulting values of the experimentally determined microstructural descriptors were compared to values calculated from theoretical distributions following a Poisson Voronoi model, including a hard-core model approach, to determine the quality of spatial dispersion. Significant differences in the spatial distribution of zirconia particulates in the mullite matrix were found depending on the method of introduction of fillers into the precursor material, spray-coating being identified as the superior compounding method. The comparison to a conventional nearest-neighbor metric demonstrates the potential of the developed tessellation-based image-analysis routine, yielding additional information about the nature of the microstructural setup of the material.

Oxidation behavior of spark plasma sintered ZrC–SiC composites obtained from the polymer-derived ceramics route

ZrCm/SiCp composites were elaborated using the polymer derived ceramics route and the spark plasma sintering process. The results of mechanical and microstructural characterization of composites were undertaken, and indicated an improvement by adding the SiC phase. The oxidation resistance of composites was evaluated at very high temperatures, and a better behavior was observed whatever the SiC content compared to ZrC monoliths. By adjusting the composition of the final composite, two main ranges of stability were determined as a function of the heat treatment.

From click to ceramic: An efficient way to generate multielement Si/Zr/C clicked-polymer-derived ceramics (cPDC)

Clicked-polymer-derived ceramics (cPDC) were elaborated using no chromatographic purification steps. Starting from suitable monomers, three original silicon-contained clicked-polymers P1–3 were synthesized in good yields, using the copper-catalyzed azide-alkyne cycloaddition (CuAAC). Then, the thermal behaviors of the organic materials were investigated until 1400°C. Thanks to XRD analysis, an α-SiC was unusually observed for materials obtained from P1 and P2. Thereby, pyrolysis of polymer P3 led to a composite α-SiC–ZrC. The free carbon, initially observed after pyrolytic treatment of P1 and P2, was removed in the final material C3. A structure for P3 was then proposed on the evidence of IR and NMR spectroscopic data. Hence, the polymer-derived ceramics route was synergistically associated to the CuAAC to generate high performance materials.

Multi-walled carbon nanotube-reinforced silicon carbide fibers prepared by polymer-derived ceramic route

Multi-walled carbon nanotube (MWNT)-reinforced silicon carbide (SiC) ceramic fibers were successfully prepared by blending MWNTs (0–0.5wt.%) with polycarbosilane, followed by melt spinning, curing, and pyrolysis. The MWNTs used in this study were modified with a chemical treatment. It was found that the MWNTs were well-dispersed in the matrix and aligned with the axis of the fibers after ultrasonic dispersion combined with melt spinning. Mechanical measurements revealed that significant improvement in Young’s modulus and tensile strength was achieved by incorporating MWNTs into the ceramic fibers. The addition of 0.5wt.% MWNTs led to a 93.6% increase in the Young’s modulus and a 38.5% increase in the tensile strength.

SiOC Glass–Diamond Composites

New types of bulk SiOC glass matrix composites reinforced with diamond particles were successfully fabricated. Diamond particles were introduced into the SiOC matrix by the polymer‐derived ceramics (PDC) route using polysiloxane and two different sized diamond particles, 2 and 30 μm as starting precursors. Dense bulk specimens were prepared by warm pressing at 150°C–160°C followed by pyrolization at 1100°C for 2 h. The composites were characterized by means of SEM, TEM, optical observation, X‐ray diffraction, and Vickers indentation. Elastic properties were determined by means of ultrasonic echography, and Young's modulus was found to increase from 96 to 154 GPa when diamond content increased from 0 to 25 vol%. Reinforcement results in significant improvement, nearly 100%, in hardness compared to pristine SiOC glass sample. The size of the diamond particles has an influence on density and microstructure of the composites. The TEM investigations reveal that SiOC glass matrix and 2 μm diamond particles have excellent bonding. The present study demonstrates the possibility of fabricating bulk SiOC glass–diamond composites via the polymer‐processing route, resulting in composites with promising mechanical properties.

Novel processable precursor for BN by the polymer-derived ceramics route

Novel precursors polymerized from (alkylamino)borazines (AAB) were synthesized and transformation of processable poly-AAB to boron nitride (BN) was researched. The AAB monomers of the type (BNH) 3(NHR) 3 were synthesized via ammolysis of 2,4,6-trichloroborazine (TCB) with different propylamines under mild conditions. The specially designed monomers served as molecular precursors for BN by the polymer-derived ceramics route. The processability of the polymeric precursors varied with propylamino-groups of AAB linked with boron atoms on (BNH) 3. The good processability of the poly[2,4,6-tris( iso-propylamino)borazine] (PTP iAB) was proven by melt-spinning it into polymer fiber. Furthermore, the PTP iAB gave a ceramic yield of about 53 wt% in Ar at 1200 °C by TGA. Based on FTIR, Raman, XRD, XPS and elemental analysis, the pyrolytic product of PTP iAB showed a composition of BN 1.07. In addition, the BN illustrated excellent oxygen resistance in air.

Preparation of Polyborazylene-Derived Bulk Boron Nitride with Tunable Properties by Warm-Pressing and Pressureless Pyrolysis

The polymer-derived ceramics (PDCs) route has been combined with a warm-pressing process to synthesize for the first time boron nitride workpieces avoiding the conventional sintering process. A polyborazylene was synthesized with a controlled degree of cross-linking suitable to be warm-pressed into cylindrical green bodies which were pressureless pyrolyzed into disk-shaped boron nitride workpieces. On the basis of elemental analyses, differential scanning calorimetry (DSC), and thermomechanical analyses (TMA), the best polyborazylene candidates are those prepared by self-condensation of borazine (B3N3H6) at 60 °C under static argon in an autoclave. They displayed a chemical formula of [B3.0N3.5H4.5]n, a glass transition in the temperature range 88−120 °C, a controlled dimensional change upon heating under load and a high ceramic yield. Such properties provided (i) adjusted viscoelastic properties and sufficient plasticity to be warm-pressed under 74 MPa at 60 °C into disk-shaped bodies with 13 mm in diame...

A new class of boron nitride fibers with tunable properties by combining an electrospinning process and the polymer-derived ceramics route

Novel boron nitride (BN) fibers have been developed with diameters ranging from the nano- to microscale by thermal conversion of as-electrospun fibers from polyacrylonitrile and poly[B-(methylamino)borazine] blend solutions. Such a new class of ceramic fibers is seen as potential candidate for thermal management applications and filtration systems in harsh environments.

A facile synthesis of 2,4,6-trichloroborazine from boron trichloride–dimethylsulfide complex and ammonium chloride

2,4,6-Trichloroborazine has been recognized as a desirable monomer for the preparation of high-performance boron nitride fibers through polymer derived ceramics route. So a high yield and facile synthesis of 2,4,6-trichloroborazine is essential in practice. Using boron trichloride–dimethylsulfide complex ((CH 3) 2S·BCl 3) and ammonium chloride (NH 4Cl) as starting materials and toluene (C 6H 5CH 3) as solvent, the synthesis of 2,4,6-trichloroborazine to give high yield is reported.

Kinetic Modeling of the Polymer-Derived Ceramics Route: Investigation of the Thermal Decomposition Kinetics of Poly[B-(methylamino)borazine] Precursors into Boron Nitride

A complete kinetic modeling of the polymer-derived ceramics (PDCs) route is achieved for the first time through the investigation of the solid-state decomposition of a typical melt-spinnable poly[B-(methylamino)borazine] into boron nitride fibers at various heating rates. Through the use of the Lorentz fitting approach, it is shown that the two-step weight loss associated with the polymer-to-ceramic conversion is governed by a complex interplay of five diffusion-type transport mechanisms that are independent of the applied heating schedule. The application of the Friedman method to dynamic thermogravimetry data yields Ea and ln A values that are seen to increase with the extent of the ceramic conversion from region one (Ea = 38.73 kJ mol(-1)) to region five (Ea = 146.64 kJ mol(-1)). This fact indicates that both the mechanisms within those regions are parallel routes to the formation of the final solid-state material and their complexity increases with the conversion progress. The cross-linking process (first weight loss) of the polymer is governed by three dependent poorly energetic mechanisms. The first weight loss is activated by ammonolysis reactions that provide a modified polymer capable of undergoing condensation reactions in regions two and three to yield a highly cross-linked polymer. A large evolution of methylamine is identified during this process. Mineralization (region four) and ceramization (region five) steps are represented by two highly energetic multistep mechanisms. The mineralization step is associated with a large evolution of methylamine and occurs during the transition between the cross-linking and ceramization processes through the cleavage of the inter-ring B-N bonds. Ceramization represents the end of the polymer-to-ceramic conversion in which the planar consolidation of BN hexagons occurs through complex structural rearrangements of the borazine units (cleavage of the intraring B-N bonds) accompanied with an ammonia evolution. Finally, the simulation of the polymer-to-ceramic conversion was demonstrated through a simplified model that appropriately predicted experimental data.

ポリマーから誘導されたケイ素系セラミックス<br>─合成・性質・応用に関する総説─

This review presents the synthesis, characterization techniques, processing and potential applications of silicon-based ceramic materials derived from organosilicon polymers. The Si-ceramics are prepared by thermolysis of molecular precursors. The influence of the initial molecular structure of the precursor on the properties of the final ceramic material and its applications is discussed. The thermolytic decomposition of suitable Si-based polymers provides materials which are denoted as polymer-derived ceramics (PDCs). In particular, this procedure is a promising method for the preparation of ternary and multinary silicon-based ceramics in the system SiCNO. There is no other synthetic approach known to produce e.g. SiCO or SiCN based ceramics. In the case of PDCs route, common preceramic polymers are poly(organosilazanes), poly(organosilylcarbodiimides) and poly(organosiloxanes). One basic advantage of the PDC route is that the materials can be easily shaped in form of fibers, layers or bulk composite materials by applying processing techniques established in the plastic industry. The PDCs in general exhibit enhanced thermomechanical properties, i.e., temperature stabilities up to approximately 1500°C. Recent investigations have shown that in some cases the high temperature stability in terms of decomposition and/or crystallization can be increased even up to 2000°C if the preceramic polymer contains some amount of boron. The composition and microstructure of the PDC are a result of the molecular structure of the preceramic polymer. Therefore, the observed differences in the macroscopic properties are also closely related to the variation of composition and solid state structure of these materials.

Preparation of high-temperature stable Si [sbnd]B [sbnd]C [sbnd]N fibers from tailored single source polyborosilazanes

Bulk Si B C N ceramics derived from polyborosilazanes of the type [B(C 2H 4SiRNH) 3] n ( 1a, R = CH 3; 2a, R = H; C 2H 4 = CHCH 3, CH 2CH 2) exhibit an exceptional structural stability at high temperature. Therefore, such quaternary systems are of great scientific and technical interest as fibrous reinforcements intended for high-temperature applications. In this context, the design of novel polyborosilazanes, which display properties tailored for the preparation of Si B C N fibers, is studied. Boron-modified polysilazanes of the type [B(C 2H 4SiRNCH 3) 3] n ( 1b, R = CH 3; 2b, R = H) are prepared via aminolysis of the tris(dichlorosilylethyl)boranes B(C 2H 4SiRCl 2) 3 ( 1, R = CH 3; 2, R = H). It is shown that the functionalisation of the precursors with N CH 3 units improves their processability (i.e. solubility) compared to that of their ammonolysed analogs [B(C 2H 4SiRNH) 3] n ( 1a, R = CH 3; 2a, R = H). In addition to the influence of the N CH 3 units, the presence of the Si CH 3 functions in such polymers offers the best potential for the preparation of fibers by melt-spinning. As-spun fibers are then converted under controlled atmosphere into high-temperature stable Si B C N fibers according to the polymer-derived ceramic route.

Alkylaminoborazine-based precursors for the preparation of boron nitride fibers by the polymer-derived ceramics (PDCs) route

Various borazine-based polymeric precursors can be prepared from tris(alkylamino)boranes and B-tri(chloro)borazine. Their chemical structures are described and compared in this review, along with their melt-spinnability. After polymer-to-ceramic conversion, the mechanical performances of the ensuing BN fibers are analyzed in relation with the structure of the corresponding thermoplastic polymers. The most promising results were obtained with B-tri(methylamino)borazine, which appears, at the present time, as the best candidate for a potential industrialization of the process. However, promising results were also obtained with borylborazines. This comparative study clearly emphasizes that the synthesis of tailored polyborazines is one of the key point for the preparation of high-performance BN fibers.