Polymer-derived Ceramics Route Research Articles

Advanced synthesis of highly crystallized hexagonal boron nitride by coupling polymer-derived ceramics and spark plasma sintering processes—influence of the crystallization promoter and sintering temperature

Hexagonal boron nitride nanosheets (BNNSs) are promising 2D materials due to their exceptional chemical and thermal stabilities together with their electrical insulation properties. A combined synthesis method involving the polymer-derived ceramics (PDCs) route and the spark plasma sintering (SPS) process is proposed, leading to well-crystallized and pure layered h-BN crystals, prone to be exfoliated into large BNNSs. Here we focus more specifically on the influence of two key parameters of the process to be optimized: the Li3N concentration (0–10 wt%) and the SPS temperature (1200 °C–1950 °C). The presence of Li3N, added as crystal promoter in the pre-ceramic powder, significantly improves the crystallinity level of the product, as evidenced by XRD, SEM and Raman spectrometry. SPS temperature strongly modifies the size of the resulting h-BN flakes. The influence of SPS temperature on both purity and crystallinity is studied using cathodoluminescence. h-BN flakes larger than 200 μm2 (average flake area) are obtained. Few-layered BNNSs are successfully isolated, through exfoliation process.

Graphene Shield by SiBCN Ceramic: A Promising High-Temperature Electromagnetic Wave-Absorbing Material with Oxidation Resistance.

As cutting-edge emerging electromagnetic (EM) wave-absorbing materials, the Achilles' heel of graphenes is vulnerable to oxidation under high temperature and oxygen atmosphere, particularly at temperatures more than 600 °C. Herein, a graphene@Fe3O4/siliconboron carbonitride (SiBCN) nanocomplex with a hierarchical A/B/C structure, in which SiBCN serves as a "shield" to protect graphene@Fe3O4 from undergoing high-temperature oxidation, was designed and tuned by polymer-derived ceramic route. The nanocomplexes are stable even at 1100-1400 °C in either argon or air atmosphere. Their minimum reflection coefficient (RCmin) and effective absorption bandwidth (EAB) are -43.78 dB and 3.4 GHz at ambient temperature, respectively. After oxidation at 600 °C, they exhibit much better EM wave absorption, where the RCmin decreases to -66.21 dB and EAB increases to 3.69 GHz in X-band. At a high temperature of 600 °C, they also possess excellent and promising EW wave absorption, for which EAB is 3.93 GHz, covering 93.6% range of X-band. In comparison to previous works on graphenes, either the EAB or the RCmin of these nanocomplexes is excellent at high-temperature oxidation. This novel nanomaterial technology may shed light on the downstream applications of graphenes in EM-wave-absorbing devices and smart structures worked in harsh environments.

SiBCN-ZrO2 hybrid ceramic aerogels through the polymer-derived ceramics (PDCs) route

The SiBCN-ZrO2 hybrid ceramic aerogels were fabricated by pyrolysis of preceramic aerogels prepared from Polyborosilane/Zirconium 5n-butoxide /Divinylbenzene (PSNB/ZBO/DVB) combining a simple hydrosilylation reaction with CO2 supercritical drying. The micromorphology and pore structure parameters of the preceramic hybrid aerogels were investigated. Structural evolution of the ceramic hybrid aerogels and the crystallization behavior were studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that all the preceramic hybrid aerogels had a typical mesoporous structure. The neck region between the particles of SiBCN-ZrO2 ceramic hybrid aerogels was gradually increased when the sintering temperatures increased from 750 °C to 1550 °C. After heat treatment at 1550 °C, the specific surface area and pore volume for the samples were drastically reduced down to 108.85 m2 g−1 and 0.49 cm3 g−1, respectively. The ZrO2 nanocrystals were well-distributed in amorphous SiBCN network backbone, the final crystalline phases were composed of hexagonal BN, β-SiC crystals and monoclinic ZrO2.

Polymer-Derived Ceramics with engineered mesoporosity: From design to application in catalysis

The scientific and technological challenges of energy-related fields are mainly associated with the emergence of new, advanced knowledge and fundamental understanding of materials. In the different categories of materials, ceramics offer a unique combination of physical and chemical properties making them key contributors for energy production/conversion and storage applications. The Polymer-Derived Ceramics (PDC) route enables the synthesis of such materials with an excellent control of the porosity at mesoscopic length scale offering potentialities as support materials to anchor and disperse active metals or for a direct use as catalysts. This review proposes an overview of the works related to the design of mesoporous PDC in the last 15 years. A particular focus is made on the forming methods which have been associated with the PDC route to engineer the mesoporosity and the shape of ceramics derived from preceramic polymers. The main topics reviewed are related to the processing of tailor-made polymeric precursors to mesoporous components, and to the characterization of the material properties. The two strategies adopted for the development of the catalytic activity of mesoporous PDC, i.e., deposition of metal nanoparticles on the mesoporous network or in-situ generation of the catalytically active phase in the mesoporous PDC matrix, are presented. Their recent application in various catalyst-assisted reactions is then discussed. Additionally, we outline the current challenges on the field of mesoporous PDC and provide perspectives on the need for further advances in mesoporous PDC.

Plasmon enhanced visible light photocatalytic activity in polymer-derived TiN/Si-O-C-N nanocomposites

Herein, we provide a detailed insight into the precursor chemistry, precursor-to-material transformation and characterization of nanocomposites made of a TiN nanophase and a Si-O-C-N ceramic. The polymer-derived ceramics (PDCs) route applied to synthesize these nanocomposites resulted in the formation of nanocrystals less than 4 nm in size and the calculated lattice parameter value for the nanocrystals (a = 0.4239 nm) matched the theoretical value of TiN (a = 0.4241 nm). The Si-O-C-N ceramic served as a platform for anchoring TiN nanocrystals. As a proof of concept, we have attempted to exploit the plasmonic properties of nanocomposites to achieve photocatalytic degradation of organic dyes. The absorption spectra clearly showed plasmonic resonance in the visible region with peak positioned around 670 nm according to the presence of TiN nanocrystals which resulted in the enhancement of dye degradation.

Polymer Derived Si–B–C–N Ceramics: 30 Years of Research

Long term stability of ceramics at high temperatures is one of the great challenges of the contemporary technology developments. Multi‐component ceramics such as Si–B–C–N systems gain a lot of interest for high temperature applications due to the stability of their amorphous inorganic network arising from strong covalent bonding. The polymer derived ceramics (PDC) route enables the synthesis of such materials from preceramic polymers as well as their manufacturing as specific ceramic geometries, which are difficult to obtain otherwise. This review proposes an overview of the works related to the development of Si–B–C–N ceramics through the PDC route in the last 30 years. A particular focus is made on the relation between the chemical structure of the precursors and the properties of the resulting ceramics. The main topics reviewed are related to the synthesis of tailor‐made polymeric precursors, to their processing to ceramic components, and to the characterization of the material properties and functionalities. The various strategies adopted for the development of shaped Si–B–C–N ceramics as functional materials are presented and the trend of nowadays research for future evolution of Si–B–C–N materials is discussed.

Microwave-Assisted Heating of Electrospun SiC Fiber Mats

Flexible silicon carbide fibrous mats were fabricated by a combination of electrospinning and a polymer-derived ceramics route. Polycarbosilane was used as a solute with various solvent mixtures, such as toluene and dimethylformamide. The electrospun PCS fibrous mats were cured under a halogen vapor atmosphere and heat treated at 1300°C. The structure, fiber morphology, thermal behavior, and crystallization of the fabricated SiC fibrous mats were analyzed via scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermal imaging. The prepared SiC fibrous mats were composed of randomly distributed fibers approximately 3 μm in diameter. The heat radiation of the SiC fiber mats reached 1600°C under microwave radiation at a frequency of 2.45 GHz. Key words: Microwave, Electrospinning, Silicon carbide mat, Polycarbosilane, Heat radiation

In-situ synthesis and textural evolution of the novel carbonaceous SiC/mullite aerogel via polymer-derived ceramics route

Abstract A novel carbonaceous SiC/mullite composite aerogel is derived from catechol-formaldehyde/silica/alumina hybrid aerogel (CF/SiO 2 /AlOOH) via polymer-derived ceramics route (PDCR). The effects of the reactants concentrations on the physicochemical properties of the carbonaceous SiO 2 /Al 2 O 3 aerogel and SiC/mullite aerogel are investigated. The mechanism of the textural and structural evolution for the novel carbonaceous SiC/mullite is further discussed based on the experimental results. Smaller reactants concentration is favorable to formation of mullite. Reactants concentration of 25% is selected as the optimal condition in considering of the mullite formation and bulk densities of the preceramic aerogels. Spherical large silica particles are also produced during heat treatment, and amorphous silica is remained after this reaction. With further heat treatment at 1400 °C, silicon carbide and mullite coexist in the aerogel matrix. The mullite addition decreases the temperature of SiC formation, when compared with the conventional methods. However, after heat treatment at 1450 °C, the amount of mullite begins to decrease due to the further reaction between carbon and mullite, forming more silicon carbide and alumina. The carbonaceous SiC/mullite can be transferred to SiC/mullite binary aerogel after carbon combustion under air atmosphere. The carbonaceous SiC/mullite has a composition of SiC (31%), mullite (19.1%), SiO 2 (14.4%), and carbon (35%). It also possesses a 6.531 nm average pore diameter, high surface area (69.61 m 2 /g), and BJH desorption pore volume (0.1744 cm 3 /g). The oxidation resistance of the carbonaceous SiC/mullite is improved for 85 °C when compared with the carbon based aerogel.

Synthesis and characterization of yttrium and ytterbium silicates from their oxides and an oligosilazane by the PDC route for coating applications to protect Si3N4 in hot gas environments

Environmental barrier coatings are required to protect Si3N4 against hot gas corrosion and enable its application in gas turbines, among which yttrium and ytterbium silicate-coatings stand out. Thus, the polymer-derived ceramic route was used to synthesize these silicates for basic investigations regarding their intrinsic properties from a mixture of Y2O3 or Yb2O3 powders and the oligosilazane Durazane 1800. After pyrolysis above 1200°C in air, the silicates are predominant phases. The corrosion behaviour of the resulting composites was tested at 1400°C for 80h in moist environments. The material containing x2-Yb2SiO5 and Yb2Si2O7 undergoes the lowest corrosion rate (−1.8μgcm−2h−1). Finally, the processing of Y2O3/Durazane 1800 as well-adherent, crack-free and thick (40μm) coatings for Si3N4 was achieved after pyrolysis at 1400°C in air. The coating consisted of an Y2O3/Y2SiO5 top-layer and an Y2O3/Y2Si2O7 interlayer due to the interaction of the coating system with the substrate.

Processing of in situ synthesized polycarbosilane-derived porous SiC using kraft pulp fibers

SiC ceramics were fabricated using the polymer-derived ceramics route with kraft pulp fibers (KPF) and organosilicon monomers as starting materials. For this, KPF or Propargylated Kraft pulp fibers (PKPF) were used as natural templates to be impregnated with a polycarbosilane (PCS), synthesized in situ thanks to a hydrosilylation reaction. Characterizations of the pyrolyzed materials were carried out at different stages by means of TGA coupled with mass spectrometry, XRD and SEM. Depending on the initial template, either KPF or PKPF, SiC ceramics were generated with a porous network and fiber structures, respectively.

Polymer-derived mesoporous Ni/SiOC(H) ceramic nanocomposites for efficient removal of acid fuchsin

In this paper, magnetic porous Ni-modified SiOC(H) ceramic nanocomposites (Ni/SiOC(H)) were successfully prepared via a template-free polymer-derived ceramic route, which involves pyrolysis at 600°C of nickel-modified allylhydridopolycarbosilane (AHPCS-Ni) precursors synthesized by the reaction of allylhydridopolycarbosilane (AHPCS) with nickel(II)acetylacetonate (Ni(acac)2). The resultant Ni/SiOC(H) nanocomposites are comprised of in-situ formed nanoscaled Ni socialized with small amounts of NiO and nickel silicides embedded in the amorphous SiOC(H) matrix. The materials show ferromagnetic behavior and excellent magnetic properties with the saturation magnetization in the range of 1.71–7.08emug−1. Besides, the Ni/SiOC(H) nanocomposites are predominantly mesoporous with a high BET surface area and pore volume in the range of 253–344 and 0.134–0.185cm3g−1, respectively. The measured porosity features cause an excellent adsorption capacity towards a template dye acid fuchsin with the adsorption capacity Qt at 10min of 80.7–85.8mgg−1 and the Qe at equilibrium of 123.8–129.8mgg−1.

Synthesis of SiC–TiO2 hybrid aerogel via supercritical drying combined PDCs route

The SiC-TiO2 hybrid aerogels were obtained from polycarbosilane (PCS) and tetrabutyltitanate (TBT) as precursors using supercritical drying and polymer derived ceramics route. The polymer to ceramic conversion and the crystallization behavior were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM), suggesting the preceramic aerogels converted to the SiC-TiO2 ceramic aerogels through pyrolysis process at different temperatures. At 1200°C, the ceramic aerogels were homogeneous with well-distributed element components, composed of rutile TiO2 and the β-SiC crystalline phases. The results show that the SiC-TiO2 ceramic aerogels with netwoks structure have 23.36nm average pore size, high surface area (58m2/g) and pore volume (0.22cm3/g).

How to Increase the h-BN Crystallinity of Microfilms and Self-Standing Nanosheets: A Review of the Different Strategies Using the PDCs Route

Hexagonal boron nitride (h-BN) is a well-known material whose use is almost restricted to lubricating applications in domains ranging from metallurgy to cosmetics. Howover, h-BN displays many other interesting properties, opening new perspectives for other engineering applications, such as as a solid lubricant in aeronautics, as the perfect substrate to graphene for electronic devices, etc. However, all these promising developments require tailored h-BN shapes displaying a high level of crystallization, ensuring its properties for the long term. Here, we developed three strategies, all associated with the Polymer Derived Ceramics (PDCs) route, to prepare highly crystallized supported thick coatings and self-standing nanosheets. The first strategy concerns the innovative implementation of a Rapid Thermal Annealing to prepare micrometric h-BN coatings on thermal sensitive substrates. Compared to conventional treatment the crystallization of h-BN has successfully lowered to about 300 °C. The second strategy consists of an additivation of the used polymer precursor. Effect of lithium nitride as a crystallization promoter was investigated lowering the onset crystallization temperature from 1400 °C (traditionally) to 1000 °C. This novel synthetic route allows preparing self-standing highly crystallized h-BN nanolayers. Finally, the third strategy is based on a unique combination of the PDCs route with Spark Plasma Sintering to profit of both approaches. This original method leads to large and well-crystallized flakes available for a subsequent exfoliation.

Template‐Free Synthesis of Porous Fe3O4/SiOC(H) Nanocomposites with Enhanced Catalytic Activity

We present a template‐free synthesis of Fe3O4/SiOC(H) nanocomposites with in situ formed Fe3O4 nanoparticles with a size of about 50 nm embedded in a nanoporous SiOC(H) matrix obtained via a polymer‐derived ceramic route. Firstly, a single‐source precursor (SSP) was synthesized by the reaction of allylhydridopolycarbosilane (AHPCS) with Fe‐acetylacetonate [Fe(acac)3] at 140°C. The SSP was heat‐treated at 170°C to generate Fe3O4 nanocrystals in the cross‐linked polymeric matrix. Subsequently, the SSP was pyrolyzed at 600°C–700°C in argon atmosphere to yield porous Fe3O4/SiOC(H) nanocomposites with the high BET surface area up to 390 m2/g, a high micropore surface area of 301 m2/g, and a high micropore volume of 0.142 cm3/g. The Fe‐free SiOC(H) ceramic matrix derived from original AHPCS is nonporous. The in situ formation of Fe3O4 nanoparticles embedded homogeneously within a nanoporous SiOC(H) matrix shows significantly enhanced catalytic degradation of xylene orange in aqueous solution with H2O2 as oxidant as compared with pure commercial Fe3O4 nanoparticles.

Polymer-Derived Silicoboron Carbonitride Foams for CO2 Capture: From Design to Application as Scaffolds for the in Situ Growth of Metal-Organic Frameworks.

A template-assisted polymer-derived ceramic route is investigated for preparing a series of silicoboron carbonitride (Si/B/C/N) foams with a hierarchical pore size distribution and tailorable interconnected porosity. A boron-modified polycarbosilazane was selected to impregnate monolithic silica and carbonaceous templates and form after pyrolysis and template removal Si/B/C/N foams. By changing the hard template nature and controlling the quantity of polymer to be impregnated, controlled micropore/macropore distributions with mesoscopic cell windows are generated. Specific surface areas from 29 to 239 m(2) g(-1) and porosities from 51 to 77 % are achieved. These foams combine a low density with a thermal insulation and a relatively good thermostructural stability. Their particular structure allowed the in situ growth of metal-organic frameworks (MOFs) directly within the open-cell structure. MOFs offered a microporosity feature to the resulting Si/B/C/N@MOF composite foams that allowed increasing the specific surface area to provide CO2 uptake of 2.2 %.

Formation of Micro and Mesoporous Amorphous Silica-Based Materials from Single Source Precursors

Polysilazanes functionalized with alkoxy groups were designed and synthesized as single source precursors for fabrication of micro and mesoporous amorphous silica-based materials. The pyrolytic behaviors during the polymer to ceramic conversion were studied by the simultaneous thermogravimetry-mass spectrometry (TG-MS) analysis. The porosity of the resulting ceramics was characterized by the N2 adsorption/desorption isotherm measurements. The Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopic analyses as well as elemental composition analysis were performed on the polymer-derived amorphous silica-based materials, and the role of the alkoxy group as a sacrificial template for the micro and mesopore formations was discussed from a viewpoint to establish novel micro and mesoporous structure controlling technologies through the polymer-derived ceramics (PDCs) route.

Polymer-derived ceramics route toward SiCN and SiBCN fibers: from chemistry of polycarbosilazanes to the design and characterization of ceramic fibers

Polymer-derived ceramics route toward SiCN and SiBCN fibers: from chemistry of polycarbosilazanes to the design and characterization of ceramic fibers

Tailoring of Porous Structure in Macro-Meso-Microporous SiC Ultrathin Fibers via Electrospinning Combined with Polymer-Derived Ceramics Route

Porous SiC has attracted extensive attention for its wide applications, especially in harsh environment, due to its unique properties. In the present paper, novel macro-meso-microporous SiC ultrathin fibers (MMM-SFs) were synthesized through electrospinning process associated with polymer-derived ceramics route, and the porous structure in the SFs can be conveniently tailored by tuning the composition of the spinning solvents and the concentration of the precursor (polycarbosilane). The surface features and microstructures of the resultant MMM-SFs were characterized in detail. These fibers presented a high specific surface area of 86.1–128.2 m2 g−1. The formation mechanism of hierarchically porous structure was discussed as well. N,N′-dimethylformamide (DMF) played a critical role in forming macropores, while the decomposition of SiOxCy phase was responsible for the meso-/micropores. Our method utilized to synthesize hierarchically porous SFs is easily capable of designing other ceramic fibers.

Single-source-precursor Synthesis and High-temperature Behavior of SiC Ceramics Containing Boron

AbstractIn this paper, a hyperbranched polyborocarbosilane (HPBCS) was prepared by a one-pot synthesis with Cl2Si(CH3)CH2Cl, Cl3SiCH2Cl and BCl3 as the starting materials. The obtained HPBCS was characterized by GPC, FT-IR and NMR, and was confirmed to have hyperbranched structures. The thermal property of the resulting HPBCS was investigated by TGA. The ceramic yield of the HPBCS is about 84% and that of the counterpart hyperbranched hydridopolycarbosilane is only 45%, indicating that the introduction of boron into the preceramic polymer significantly improved the ceramic yield. With the polymer-derived ceramic route, the final ceramics were annealed at 1800 °C in argon atmosphere for 2 h in order to characterize the microstructure and to evaluate the high-temperature behavior. The final ceramic microstructure was studied by XRD and SEM, indicating that the introduction of boron dramatically inhibits SiC crystallization. The boron-containing SiC ceramic shows excellent high-temperature behavior against decomposition and crystallization at 1800 °C.

Polymer-Derived Boron Nitride: A Review on the Chemistry, Shaping and Ceramic Conversion of Borazine Derivatives.

Boron nitride (BN) is a III-V compound which is the focus of important research since its discovery in the early 19th century. BN is electronic to carbon and thus, in the same way that carbon exists as graphite, BN exists in the hexagonal phase. The latter offers an unusual combination of properties that cannot be found in any other ceramics. However, these properties closely depend on the synthesis processes. This review states the recent developments in the preparation of BN through the chemistry, shaping and ceramic conversion of borazine derivatives. This concept denoted as Polymer-Derived Ceramics (PDCs) route allows tailoring the chemistry of precursors to elaborate complex BN shapes which cannot be obtained by conventional process. The effect of the chemistry of the molecular precursors, i.e., borazine and trichloroborazine, and their polymeric derivatives i.e., polyborazylene and poly[tri(methylamino)borazine], in which the specific functional groups and structural motifs determine the shaping potential by conventional liquid-phase process and plastic-forming techniques is discussed. Nanotubes, nano-fibers, coatings, monoliths and fiber-reinforced matrix composites are especially described. This leads to materials which are of significant engineering interest.