Ceramic Precursors Research Articles

Synthesis, pyrolysis of a novel carborane ceramic precursor, and coating on carbon fiber

A novel carborane–carbosilane–(cyclo-silazane) polymer has been synthesized as precursor of ceramic and applied to the surface treatment of carbon fiber (Cf) by precursor infiltration and pyrolysis method. The preparation of carborane precursor was carried out by hydrosilylation of trivinyltrimethylcyclosilazane with dimethylchlorosilane firstly, and then by polycondensation reaction with hydroxylated 1,1′-hydroxysilylene-2,2′-bis(hydroxydimethylsilyl)biscarborane whose −OH was formed by transferring the newly introduced C–H bond via hydroxylation. Chemical structure of the polymer was studied by liquid-nuclear magnetic resonance while evolution of various ceramic phases was studied by Fourier transform infrared spectroscopy and the thermal curing process was studied by thermogravimetric/differential thermal analysis and pyrolysis-gas chromatography/mass spectrometry. The cross-linked polyborosilazane precursor exhibited higher ceramic yield of 65.6% at 1000°C. The coating on the Cf was identified to be uniform, relatively smooth, and continuous with a thickness ranged from 0.1 to 0.5 μm through scanning electron microscope and energy dispersive spectroscopy. Thermogravimetric analysis revealed high temperature stability of the coated Cf in flowing air up to 600°C.

First printing of continuous fibers into ceramics

AbstractThis article reports a novel method for three‐dimensional (3D) printing of continuous fibers into ceramics to improve the mechanical properties of printed ceramics, which is difficult in other 3D printing technologies. The ceramics were derived by pyrolysis of thermoplastic ceramic precursor feedstocks, which were prepared by two methods. One is homogeneously mixing thermoplastic resins and ceramic precursors. The feedstocks prepared by this method exhibit good thermoplastic properties and can be extruded into filaments. Ceramics were obtained by heating the feedstocks to 1100°C in argon atmosphere. The ceramics were amorphous and remained stable during 1100‐1300°C; at 1400°C they decomposed into β–SiC with simultaneous volatile gas generation. Above 1400°C, their quality decreased significantly due to cracking of ceramic skeletons. The other method is directly heating, extruding and printing the ceramic precursor. The precursors showed good printability and complex ceramic structures were printed with continuous carbon fibers inside. The continuous carbon fibers improved the flexural strength of pyrolytic ceramics, which is about 7.6 times better than that of the ceramics without fibers. The novel method unravels the potential of 3D printing of continuous fibers into ceramics with complex lightweight structures to improve the strength.

Residues from Sewage Sludge Incineration for Ceramic Products with Potential for Zinc Stabilization

Serious environmental pollution has been frequently caused by the release of heavy metals from wastes generated from industrial activities. Although some of the heavy metals can be stabilized in ceramic matrix, the replacement of traditional ceramic precursors is needed due to adverse effects caused by clay mining. With abundant contents of aluminum, iron and silicon, the beneficial use of residues from sewage sludge incineration processes has attracted much attention. In this study, ZnO was simulated as zinc-bearing industrial waste, and the stabilization of zinc was achieved in aluminum- and iron-rich ceramic matrix provided by the residues of sewage sludge incineration. Through a 3-h sintering procedure at temperatures ranging from 650 to 1350 °C, zinc was found to be incorporated into a ZnAlxFe2-xO4 spinel solid solution and the incorporation was greatly enhanced by the elevated temperature. The leachability of zinc was found to decline substantially with the continuous formation of the spinel when the samples were extracted in acidic, neutral and basic environments. Besides the effective stabilization of zinc, aluminum and iron can also be well immobilized in the sintered ceramic products. The temperature range of 950-1250 °C was found to be promising to reach the most satisfactory zinc stabilization without extra energy consumption, and to fabricate ceramic products with a variety of microstructures for future application. Therefore, the residues from the sewage sludge incineration can be blended into the existing ceramic sintering processes for making marketable products, which will further alleviate the environmental burden caused by heavy metal release from industrial wastes.

Maskless lithography of silazanes for fabrication of ceramic micro-components

Free standing single layer silicon carbonitride components with sub-mm features have been constructed by maskless lithography followed by pyrolysis. In comparison to prior fabrication methods based on molding of ceramic precursors, this work is advantageous as crosslinked polymer green bodies are formed in a direct manner and no mold is needed. The resultant silazane green bodies are pyrolyzed in argon to give SiCN ceramics. Mechanical properties of test samples created via the same process indicate typical flexural strength of 890 MPa and hardness of 1550 HV1.0. This methodology should be of general interest for the production of silicon carbide and silicon carbonitride components for various MEMS applications.

Oxide Ceramic Nano/Microfibers Prepared by Needle-Less Electrospinning - Materials for Fiber Reinforced Composites

Nano/microfibers are already widely used as the reinforcements in various types of advanced composites for reducing weight, improving specific properties like hardness, fracture toughness and other mechanical ones. This contribution describes the preparation of the titanium dioxide nano/microfibers by needle-less electrospinning, along with a detailed characterization of the obtained polycrystalline ceramics. For spinning solutions preparation the polyvinylpyrrolidone (PVP), titanium isopropoxide (TTIP), ethanol and acetic acid were used. Influence of the ceramic precursor concentration in the spinning solution showed that decreasing the concentration of TTIP from 30 to 10 wt.% has no effect on the precursor polymer fibers shape. However, it causes deviation from the fibers oval shape (in the cross-section) up to the formation of solid ribbons or even multilayered porous ribbons. Heat treatment temperature defined the phase composition of the obtained oxide ceramics – stabile polycrystalline rutile fibers were obtained at 600 °C.

Effective and uniform cooling on a porous micro-structured surface with visualization of liquid/vapor interface

This study examines cooling efficiency, uniformity, and bubble dynamics on a porous surface. We use infrared (IR) thermometry to visualize results of temperature fields and liquid/vapor interfacial dynamics. Porous and non-porous micro-structured surfaces are prepared using soft-lithography and a ceramic precursor, allylhydropolycarbosilane (AHPCS). The surface cavities promote nucleation, and the heat transfer coefficient on the porous surface is approximately 30% higher than that on the non-porous surface. Additionally, the porous surface exhibits a more uniform temperature field with lower spatial and temporal variations than the non-porous surface. Bubble dynamics is visualized via an IR camera through the bottom side of the test specimens using the IR transparent characteristics of the substrate and micro-structures. The porous surface reveals higher nucleation site density and contact line density and lower equivalent bubble diameter when compared with those of the non-porous surface, and this is consistent with more effective and uniform cooling on the porous surface.

Antimony-Functionalized Phosphine-Based Photopolymer Networks.

The synthesis of phosphane-ene photopolymer networks, where the networks are composed of crosslinked tertiary alkyl phosphines are reported. Taking advantage of the rich coordination chemistry of alkyl phosphines, stibino-phosphonium and stibino-bis(phosphonium) functionalized polymer networks could be generated. Small-molecule stibino-phosphonium and stibino-bis(phosphonium) compounds have been well characterized previously and were used as models for spectroscopic comparison to the macromolecular analogues by NMR and XANES spectroscopy. This work reveals that the physical and electronic properties of the materials can be tuned depending on the type of coordination environment. These materials can be used as ceramic precursors, where the Sb-functionalized polymers influence the composition of the resulting ceramic.

Antimony‐Functionalized Phosphine‐Based Photopolymer Networks

AbstractThe synthesis of phosphane‐ene photopolymer networks, where the networks are composed of crosslinked tertiary alkyl phosphines are reported. Taking advantage of the rich coordination chemistry of alkyl phosphines, stibino‐phosphonium and stibino‐bis(phosphonium) functionalized polymer networks could be generated. Small‐molecule stibino‐phosphonium and stibino‐bis(phosphonium) compounds have been well characterized previously and were used as models for spectroscopic comparison to the macromolecular analogues by NMR and XANES spectroscopy. This work reveals that the physical and electronic properties of the materials can be tuned depending on the type of coordination environment. These materials can be used as ceramic precursors, where the Sb‐functionalized polymers influence the composition of the resulting ceramic.

Combined kinetic analysis of multistep processes of thermal decomposition of polydimethylsiloxane silicone

In this work, we studied the thermal decomposition of a widely employed silicone elastomer, polydimethylsiloxane, in an inert atmosphere. This silicone elastomer has several applications due to its high thermal stability such as MEMS (microelectromechanical systems) precursors, microfluidic components, adhesives, lubricants, and precursors for non-porous ceramics. Therefore, a reliable description of the thermal decomposition kinetics is important to prevent or control the decomposition in such applications. While the decomposition has been amply reported as a complex process, most kinetic studies published on this system use simplified methods that avoid the fact that the entire process cannot be described by a single kinetic triplet. Here, we have studied the decomposition process by first separating the overall reaction into its three constituent steps which were subsequently analysed independently. The deconvolution was carried out using Fraser-Suzuki function that is capable of fitting an asymmetric peak fitting function. The resulting kinetic parameters proved to be able to reconstruct the original experimental curves but are also capable of producing accurate predictions of curves recorded at heating schedules different from those employed to record the experimental data used in the kinetic analysis. Finally, it was found that the rate limiting step of all stages is the diffusion of the gases released during the polymer decomposition through the transforming polymeric matrix.

Photoacoustic Spectroscopy Investigation of Zinc Oxide/Diatom Frustules Hybrid Powders

Photoacoustic spectroscopy investigation was carried out on ZnO nanoparticles grown at 80 °C on porous surface of diatomite (DE) by sol–gel technique, using zinc acetate dihydrate as ceramic precursor and triethanolamine to mediate the surface growth of the nanoparticles. Absorption and scattering characteristics of hybrid ZnO/DE powder in the UV–Vis range were inferred by photoacoustic spectroscopy, and results were analyzed based on Helander’s theory. In particular, we discussed in detail the procedure to calculate the absorption and scattering spectra of the hybrid powder showing how from the scattering coefficient in the 300–450 nm range it is possible to obtain information on the size distribution of the ZnO nanospheres. By applying photoacoustic spectroscopy for different modulation frequencies, we showed that is also possible to perform a size distribution depth profile of the ZnO aggregates, opening the way to interesting developments in this research field.

Quartz Fibers Reinforced SiNB Ceramic Matrix Composites Prepared by PIP

The 2.5D quartz fibers reinforced SiNB ceramic matrix composites (2.5D SiO2f /SiNB) were prepared through polyborosilazane infiltration and pyrolysis (PIP) method. The SiNB ceramic precursors and their pyrolytic products were characterized and the mechanical properties, dielectric properties, micro-structures and fracture mechanism of the composites were investigated. The results of FT-IR spectra and XRD patterns show that when the pyrolytic temperature reached 900°C, the pyrolytic products are essentially inorganic. The tensile strength and the tensile modulus are 65MPa and 30GPa respectively, the tensile strength at 800°C is 35MPa,and the dielectric constant is 3.2, the dielectric loss angle is smaller than 6 ´ 10-3. And the composites are ductile fracture, whose fracture faces have distinct fibers pull-out.

The Microstructure and Shear Properties of SiC/SiC Composite Pins with Designed SiC Fiber Preform

In order to obtain the near net shaped SiC/SiC composite pins without the processing cost, four kinds of SiC fiber pin preforms including the knitting yarn and core yarn with two dimension braided structure were designed. The SiC/SiC composite pins were fabricated by precursor infiltration pyrolysis (PIP) process used a liquid SiC ceramic precursor. The results showed that, the near net shaped SiC/SiC composite pins could be obtained by using the designed SiC fiber preform and the graphite mould with curved groove. The macrostructure and microstructure of the SiC/SiC composite pins were observed by scanning electron microscope. Both the single shear stress-displacement curves and the double shear stress-displacement curves of the different kinds of SiC/SiC composite pins showed the saddle-shaped, which indicated the fracture model of the SiC/SiC composites pins was non-catastrophic, and the SiC/SiC composite pins in this paper possessed the secondary bearing capacity. This paper may provide some new ideas for fiber reinforced SiC ceramic matrix composites components designers.

The Matrix Cracking Stress and Residual Thermal Stress of 2D SiC/SiC Composite Fabricated by PIP Process

A two dimensional silicon carbide fiber reinforced SiC matrix (2D SiC/SiC) composite fabricated by precursor infiltration pyrolysis (PIP) process used a liquid SiC ceramic precursor was obtained. Two key properties including matrix cracking stress and thermal residual stress were investigated for this PIP 2D SiC/SiC composites. Three methods were applied to determine the matrix cracking stress in order to obtained a trusted value, and the value of matrix cracking stress for SiC/SiC composite was 75±4 MPa. The thermal residual stress of the composites was calculated by linear regression line according to the loading-unloading-reloading stress-strain curve of the 2D SiC/SiC composite, and the result showed that the value of thermal residual stress of SiC matrix in composite was 20MPa, which means the PIP SiC matrix in the 2D SiC/SiC composite was under the compressive stress when the composite cooling down from the fabrication temperature to the room temperature.

Tape casting of polysiloxane-derived ceramic with controlled porosity and surface properties

Tape casting has been applied to produce porous hybrid and SiOC ceramic tapes using ceramic precursors and commercially available polysiloxanes as polymeric binders. SiC particles of two different mean sizes (4.5 or 6.5 μm) were used as inert fillers to prevent shrinkage and increase mechanical stability. Macroporosity was adjusted by varying the azodicarbonamide (ADA) content from 0 to 30 wt.%. Decomposition of the polysiloxanes at 600 °C resulted in the generation of micropores with high specific surface area (187–267 m2 g−1) and a predominant hydrophobic behavior. At 1000 °C mainly meso/macroporosity were observed (SSA: 32–162 m2 g−1) accompanied by increased hydrophilicity. The influence of ADA content, SiC size, and pyrolysis temperature on open porosity (2.5–37%), average pore size (<0.01–1.76 μm), surface characteristics, and flexural strength (10.5–121 MPa) were investigated. The porous tapes with different surface characteristics and controlled structure are highly promising for applications involving membrane processes, particularly microfiltration systems (0.1–10 μm).

A novel carborane-containing ceramic precursor: Synthesis, characterization, and ceramic conversion mechanism

Linear carborane-carbosilane-phenylacetylene polymers have been synthesized as precursors for ceramic and characterized by Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H-NMR), and carbon-nuclear magnetic resonance (13C-NMR). Novel linear polymers have the advantage of being extremely easy to process and convert into ceramics, since they are either viscous liquids or low melting solids at room temperature and are soluble in most organic solvents. Ceramic conversion reaction of the polymers was studied, and the conversion mechanism using thermogravimetric analyzer, FT-IR, and pyrolysis-gas chromatography-mass spectrometry was proposed. During the early heating period in the mechanism, the precursor polymer is cured and oligomer is formed. Then the degradation of oligomer takes place at higher temperatures with the weak bond cleaved and cross-linked simultaneously. Ceramic yield of the polymer after heating up to 1000°C in nitrogen (N2) was 77.6%. The derived ceramics exhibit excellent thermal and thermo-oxidative stability, whose 5% mass loss temperature was identified to be 650°C in N2 and 665°C in air, respectively. Boron appears to be the key element to achieve the outstanding thermo-oxidative stability. The relevant kinetic data were obtained by two kinds of model-free-kinetic algorithms, differential Friedman and integral Kissinger–Akahira–Sunose. These two methods were combined to give the energy profile, which has been identified to be a function of the transformation degree ( α), since the energy demand at each degradation stage is different depending on α.

SiBCN-precursor-derived gradient oxidation protective ceramic coating for C/C composites

This paper reports a gradient anti-oxidation ceramic coating for carbon/carbon (C/C) composites, which was prepared via dip-coating the mixed slurry of polyborosilazane (denoted as PSNB, a polymer precursor for SiBCN ceramics), ZrB2 and SiC powders, followed by pyrolysis and low-temperature densification process. By controlling of the solid content of PSNB based slurry, a crack-free coating with thickness of approximately 200 μm was achieved with only one coating-pyrolysis cycle. The micro-morphology, elemental composition and distribution, crystalline phase, anti-oxidation property, as well as anti-oxidation mechanism of the coating were investigated. The coated C/C composite showed excellent oxidation resistance with no obvious weight change after oxidation at 900 °C for 5 h and only 0.06% weight loss after oxidation at 1500 °C for 30 min. The formed dense ZrO2-B2O3 layer affords the low-temperature oxidation protection, while the ZrO2-SiO2 layer formed above 930 °C endows the coating with high-temperature anti-oxidation property. Besides, the gradient coating possessed superior thermal-shocking resistance with no large-area peeling off or detachment of coating from C/C composite after 12 cycles-air quenching from 1500 °C to room temperature.

Comparison of effects of nitrogen sources on the structures and properties of SiBNC ceramic fiber precursors

Polyborosilazane synthesized from trichlorosilane (SiHCl3), boron trichloride (BCl3) and methylamine (MeNH2) is highly sensitive to moisture for hydrolysis of -NHMe unites and is easy to cross-link for dehydrogenation of Si-H, N-H, which affected the industrial scale production of SiBNC ceramic fibers. In this paper,a new nitrogen source(n-propylamine, C3H7NH2) was used instead of MeNH2 to synthesis polyborosilazane precursor. The influences of nitrogen sources on the structures and properties of SiBNC ceramic fiber precursors were investigated. As compared to SiHCl3/BCl3/CH3NH2 system, polyborosilazane precursor synthesized from the SiHCl3/BCl3/C3H7NH2 system exhibited lower crosslink density, lower sensitivity to moisture and good melt spinnability, and the obtained ceramic fibers showed higher tensile strength (1.03 GPa, an increase of about 37.3%). This synthesis route (SiHCl3/BCl3/C3H7NH2) may serve as a suitable synthetic route for a large-scale production of SiBNC ceramic fibers.

Evaluation of poly(methylsilane‐carbosilane) synthesized from methyl‐dichlorosilane and chloromethyldichloromethylsilane as a precursor for SiC

ABSTRACTA new poly(methylsilane‐carbosilane) (PMSCS) for silicon carbide precursor was synthesized by Wurtz‐type copolycondensation of methyldichlorosilane (MeHSiCl2) with chloromethyldichloromethylsilane (ClCH2MeSiCl2) and terminated with vinylmagnesium chloride (ViMgCl). The use of insufficient sodium made the reaction more economic and safe. By changing the ratios of two monomers and the end‐block agent, the properties of the obtained PMSCS and the C/Si ratio of its derived ceramic could be tuned. Upon pyrolysis at 1000 °C under argon, silicon carbide with nearly stoichiometric C/Si ratio and low oxygen content was obtained in 64% of ceramic yield. PMSCS showed high potential as an economical SiC ceramic precursor for the fabrication of SiC matrix, coating, and adhesives. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46610.

Additive Manufacturing of Transparent Silica Glass from Solutions.

A sol, aqueous solution-based ink is presented for fabrication of 3D transparent silica glass objects with complex geometries, by a simple 3D printing process conducted at room temperature. The ink combines a hybrid ceramic precursor that can undergo both the photopolymerization reaction and a sol-gel process, both in the solution form, without any particles. The printing is conducted by localized photopolymerization with the use of a low-cost 3D printer. Following printing, upon aging and densifying, the resulting objects convert from a gel to a xerogel and then to a fused silica. The printed objects, which are composed of fused silica, are transparent and have tunable density and refractive indices.

Using macroporous graphene networks to toughen ZrC–SiC ceramic

Graphene is one of the important candidates in ceramic toughening due to its outstanding physical and chemical properties. For the weak interface toughening of large-diameter graphene sheet and alleviation of the interfacial reaction between ceramic precursors and graphene sheets during high-temperature pyrolysis, ZrC–SiC‒Graphene composite was synthesized via a facile technology of infiltrating ceramic slurry instead of ceramic precursor into macroporous graphene network and spark plasma sintering. The incorporation of the graphene network improved fracture toughness, critical crack size, and fracture energy of ZrC–SiC ceramic. The multiple length-scale toughening mechanisms of ZrC–SiC‒Graphene composite include the macroscopic toughening mechanism of crack deflection and bifurcation and the micro toughening mechanism of graphene bridging, ceramic micro zone tearing, graphene pull-out, graphene and ceramic brick slipping.