Corrosion-Resistant Polymer-Derived SiOC Membrane for Effective Organic Removal via Synergistic Adsorption and Peroxymonosulfate Activation

A major challenge is to construct ceramic membranes with tunable structures and functions for water treatment.Herein,a novel corrosion-resistant polymer-derived silicon oxycarbide(SiOC)ceramic membrane with designed architectures was fabricated by a phase separation method and was applied in organic removal via adsorption and oxidation for the first time.The pore structure of the as-prepared SiOC ceramic membranes was well controlled by changing the sintering temperature and polydimethylsiloxane content,leading to a pore size of 0.84–1.62μm and porosity of 25.0–43.8%.Corrosion resistance test results showed that the SiOC membranes sustained minimal damage during 24 h exposure to high-intensity acid–base conditions,which could be attributed to the chemical inertness of SiOC.With rhodamine 6G(R6G)as the model pollutant,the SiOC membrane demonstrated an initial eff ective removal rate of 99%via adsorption;however,the removal rate decreased as the system approached adsorption saturation.When peroxymonosulfate was added into the system,efficient and continuous degradation of R6G was observed throughout the entire period,indicating the potential of the as-prepared SiOC membrane in oxidation-related processes.Thus,this work provides new insights into the construction of novel polymer-derived ceramic membranes with well-defined structures and functions.

Defects of Polymer-derived Si-C-O Fibers and Their Originations

Defects of polymer-derived Si-C-O fibers were intensively studied by the SEM and TEM techniques and their originations were also discussed on the basis of factors experiments.The defects were found mainly in the form of strumaes,pits and splits on surfaces as well as microflaw networks,porosity clusters and inclusions in the bulk.Factors experiments reveal that a nonuniform or an insufficient curing would result in larger-sized strumaes or interior microflaws.Gas evolution rates due to different firing rates have a great influence on the formation of internal microflaws or porosity clusters and some oxidation-induced pits or splits may be formed on surfaces because of a trace of oxygen or water vapor accumulated from the flowing inert atmosphere during pyrolysis.

Ablation resistance of ZrC coating modified by polymer-derived SiHfOC ceramic microspheres at ultrahigh temperature

Polymer-derived ceramics(PDCs)method opens up new possibilities for the preparation of novel multi-phase ceramic nanocomposites owing to the molecular design of the precursors at the nanoscale level.In the current work,ZrC coatings incorporated with polymer-derived ceramic microspheres(CMS),SiH-fOC_CMS,were deposited to enhance the ablation resistance by supersonic atmosphere plasma spraying.Upon 10.0 MW·m^(-2) plasma ablation at above 3000℃,the linear ablation rate of ZrC-SiHfOC_CMS coat-ing was reduced to 0.20μm·s^(-1),62%lower than that of the pristine ZrC coating.The improvement was ascribed to the presentence of viscous SiO_(2)/HfO_(2) molten mixed phase,rather than HfSiO4,which can ef-fectively seal pinholes and cracks.Moreover,the in-situ generated crystalline SiO_(2) had a lower oxygen diffusion rate than amorphous SiO_(2),meanwhile,m-HfO_(2) could improve the stability of SiO_(2) glassy film,thus further enhancing the ablation resistance.

Structural evolution and high-temperature sensing performance of polymer-derived SiAlBCN ceramics

In situ temperature monitoring has become extremely imperative in high-temperature harsh environments and polymer-derived ceramics(PDCs)as sensing materials have attracted great attention.However,the stability and oxidation/corrosion resistance of PDCs cannot be simultaneously achieved at the moment,limiting their practical application.Herein,polymer-derived SiAlBCN ceramics were synthesized via polymer conversion method under different pyrolysis temperatures.Their microstructure evolution,high temperature sensing properties,and stability were investigated in detail.The results show that the amorphous SiAlBCN phase grows more orderly and the size of the free carbon phase enlarges with the increasing temperature.The defect concentration displays a decreasing tendency.Concurrently,the SiAlBCN ceramics as sensing materials exhibit a good temperature-resistance property from roo temperature to 1100℃.The fabricated SiAlBCN temperature sensor possesses excellent stability,repeatability,and accuracy.Moreover,SiAlBCN ceramics exhibit distinguished oxidation/corrosion resistance after 100 h treatment at 1200℃in a water/oxygen environment,which is attributed to their low corrosive rate constant(0.57 mg/(cm^(2)·h))and oxidative rate constant(3.43 mg^(2)/(cm^(4)·h)).Therefore,polymer-derived SiAlBCN ceramics as sensing materials,which possess outstanding stability and oxidation/corrosion resistance,have great potential for in-situ monitoring of extreme environmental temperatures in the future.

Organosilicon polymer-derived ceramics: An overview

Polymer-derived ceramics(PDCs) strategy shows a great deal of advantages for the fabrication of advanced ceramics. Organosilicon polymers facilitate the shaping process and different silicon-based ceramics with controllable components can be fabricated by modifying organosilicon polymers or adding fillers. It is worth noting that silicate ceramics can also be fabricated from organosilicon polymers by the introduction of active fillers, which could react with the produced silica during pyrolysis. The organosilicon polymer-derived ceramics show many unique properties, which have attracted many attentions in various fields. This review summarizes the typical organosilicon polymers and the processing of organosilicon polymers to fabricate silicon-based ceramics, especially highlights the three-dimensional(3 D) printing technique for shaping the organosilicon polymerderived ceramics, which makes the possibility to fabricate silicon-based ceramics with complex structure. More importantly, the recent studies on fabricating typical non-oxide and silicate ceramics derived from organosilicon polymers and their biomedical applications are highlighted.

Si-based polymer-derived ceramics for energy conversion and storage

Since the 1960s,a new class of Si-based advanced ceramics called polymer-derived ceramics(PDCs)has been widely reported because of their unique capabilities to produce various ceramic materials(e.g.,ceramic fibers,ceramic matrix composites,foams,films,and coatings)and their versatile applications.Particularly,due to their promising structural and functional properties for energy conversion and storage,the applications of PDCs in these fields have attracted much attention in recent years.This review highlights the recent progress in the PDC field with the focus on energy conversion and storage applications.Firstly,a brief introduction of the Si-based polymer-derived ceramics in terms of synthesis,processing,and microstructure characterization is provided,followed by a summary of PDCs used in energy conversion systems(mainly in gas turbine engines),including fundamentals and material issues,ceramic matrix composites,ceramic fibers,thermal and environmental barrier coatings,as well as high-temperature sensors.Subsequently,applications of PDCs in the field of energy storage are reviewed with a strong focus on anode materials for lithium and sodium ion batteries.The possible applications of the PDCs in Li–S batteries,supercapacitors,and fuel cells are discussed as well.Finally,a summary of the reported applications and perspectives for future research with PDCs are presented.

Role of in-situ formed free carbon on electromagnetic absorption properties of polymer-derived SiC ceramics

In order to enhance dielectric properties of polymer-derived SiC ceramics,a novel single-source-precursor was synthesized by the reaction of an allylhydrido polycarbosilane(AHPCS)and divinyl benzene(DVB)to form carbon-rich SiC.As expected,the free carbon contents of resultant SiC ceramics annealed at 1600℃are significantly enhanced from 6.62 wt%to 44.67 wt%.After annealing at 900-1600℃,the obtained carbon-rich SiC ceramics undergo phase separation from amorphous to crystalline feature where superfine SiC nanocrystals and turbostratic carbon networks are dispersed in an amorphous SiC(O)matrix.The dielectric properties and electromagnetic(EM)absorption performance of as-synthesized carbon-rich SiC ceramics are significantly improved by increasing the structural order and content of free carbon.For the 1600℃ ceramics mixed with paraffin wax,the minimum reflection coefficient(RCmin)reaches-56.8 dB at 15.2 GHz with the thickness of 1.51 mm and a relatively broad effective bandwidth(the bandwidth of RC values lower than-10 dB)of 4.43 GHz,indicating the excellent EM absorption performance.The carbon-rich SiC ceramics have to be considered as harsh environmental EM absorbers with excellent chemical stability,high temperature,and oxidation and corrosion resistance.

Polymer-derived SiBCN ceramic pressure sensor with excellent sensing performance

Pressure measurement with excellent stability and long time durability is highly desired,especially at high temperature and harsh environments.A polymer-derived silicoboron carbonitride(SiBCN)ceramic pressure sensor with excellent stability,accuracy,and repeatability is designed based on the giant piezoresistivity of SiBCN ceramics.The SiBCN ceramic sensor was packaged in a stainless steel case and tested using half Wheatstone bridge with the uniaxial pressure up to 10 MPa.The SiBCN ceramic showed a remarkable piezoresistive effect with the gauge factor(K)as high as 5500.The output voltage of packed SiBCN ceramic sensor changes monotonically and smoothly versus external pressure.The as received SiBCN pressure sensor possesses features of short response time,excellent repeatability,stability,sensitivity,and accuracy.Taking the excellent high temperature thermo-mechanical properties of polymer-derived SiBCN ceramics(e.g.,high temperature stability,oxidation/corrosion resistance)into account,SiBCN ceramic sensor has significant potential for pressure measurement at high temperature and harsh environments.

Formation of nanocrystalline graphite in polymer-derived SiCN by polymer infiltration and pyrolysis at a low temperature

The microstructure of polymer-derived ceramics(PDCs)was closely related to processing.This study demonstrated that SiCN matrix prepared by polymer infiltration and pyrolysis(PIP)at 900℃ inside a Si_(3)N_(4) whisker(Si_(3)N_(4w))preform with submicro-sized pores differed from its powder-consolidated analogue in both the content and structure of free carbon.Chemical analysis showed that PIP process had a higher free carbon yield.Raman spectroscopy and transmission electron microscopy(TEM)observation discovered a higher graphitization degree of free carbon and the existence of nanocrystalline graphite in SiCN matrix.Dielectric properties of Si_(3)N_(4w)/SiCN composites were greatly enhanced when volume fraction of SiCN matrix reached 24.5%due to dielectric percolation caused by highly-lossy free carbon.Reconsolidation of hydrocarbon released during pyrolysis by gas-state carbonization in Si_(3)N_(4) whisker preform was supposed to account for the high yield and graphitization degree of free carbon in PIP process.

Microstructural evolution of polymer-derived hexagonal boron nitride fibres under high-temperature stretching

High-temperature stretching plays a crucial role in enhancing the performance of fibres,while a quantitative investigation into the impacts of tension and stretching duration on the microstructure and performance of hexagonal boron nitride(h-BN)fibres remains absent.In this study,to elucidate the microstructural evolution of the h-BN fibres under thermal stretching,amorphous BN fibres were heated at 2000℃under tension of 30,50,and 70 N for 1,3,and 5 h in a nitrogen atmosphere.Subsequently,the grain size,pore structure,orientation degree,microscopic morphology,and mechanical properties were analysed at room temperature.The results show that high-temperature stretching enhances the orientation degree of the BN fibres,consequently elevating Young’s modulus.The maximum orientation degree of the BN fibres was 86%,aligning with a corresponding Young’s modulus of 206 GPa.Additionally,high-temperature stretching enlarged the sizes of grains and pores,a fact substantiated by the radial cracking of the fibres upon extending thermal stretching time.Owing to the expanded pore structure of the BN fibres and the inability to form a sufficiently strong“card structure”between shorter microfibre bundles,the tensile strength of the BN fibres did not increase continually,reaching a maximum of 1.0 GPa.Microstructural observations revealed that the BN fibres,composed of highly oriented lamellar h-BN grains,tend to form radial textures under high-tensile thermal stretching and onion-skin textures under prolonged thermal stretching.These findings offer a theoretical foundation for the preparation of high-performance h-BN fibres.

Two birds with one stone: Simultaneous fabrication of HfC nanowires and CNTs through efficient utilization of polymer-derived ceramics

Carbon nanotubes(CNTs) are fabricated in carbon cloth by ultilizing the waste gasses when fabricating hafnium carbide nanowires(HfC_(NWS)) through thermal pyrolysis of Hf-containing polymer precursor.The formed HfC_(NWS) are distributed uniformly on the surface of the carbon fibers in carbon/carbon(C/C) composites and display perfect single crystal appearance.The pyrolysis of the Hf-containing organic precursor provides hafnium and carbon source for the growth of HfC_(NWS).The released waste gasses containing CO,CH4and CO_(2)are the main carbon source for the growth of CNTs.Specifically,the flexural strength of HfC_(NWS) reinforced carbon/carbon(HfC_(NWS)-C/C) composites is enhanced by ~105% compared with pure C/C,and the CNTs/carbon cloth also displays improved electrochemical performance with respect to capacitor applications.The present study introduces a novel sustainable and eco-friendly process related to polymer-derived ceramics to form advanced ceramic nanocomposites and proposes a deep understanding of the growth mechanism of CNTs.

Enhanced electromagnetic wave absorption properties of ZIF-67 modified polymer-derived SiCN ceramics by in situ construction of multiple heterointerfaces

Multiphase polymer-derived ceramics have the advantages of thermal stability and adjustable dielectric properties,which exhibit significant potential for use in high-temperature microwave absorbing materials.Herein,Co-containing polymer-derived SiCN(Co-SiCN)ceramics were successfully synthesized by the physical mixing of zeolitic imidazolate framework(ZIF)-67 and polysilazane precursors and subsequent pyrolysis.The phase and chemical compositions,microstructures,dielectric properties,electromagnetic wave absorption(EWA)performance,and mechanism of the ceramics were investigated.The results showed that the introduction of ZIF-67 promoted the in situ formation of dielectric loss phases,including SiC nanocrystals,CoSi nanocrystals,and free carbon.The phase composition can be regulated by controlling the pyrolysis temperature to achieve ideal EWA properties.The Co-SiCN ceramic pyrolyzed at 1500℃demonstrated excellent EWA performance,with a maximum effective absorption band(EAB_(max))of 3.0 GHz at an ultralow thickness of 1.05 mm and minimum reflection loss(RL_(min))of-46.4 dB at a low frequency of 6 GHz.Compared with other reported SiCN-based ceramics containing magnetic metals,the ceramics prepared in this study stand out because of their low RL and high EAB at low thicknesses.The superior microwave absorption performance of the Co-SiCN ceramics is attributed to the heterointerface polarization,and impedance matching induced by the synergistic effects of their co-existing electromagnetic transparent/absorption phases.This study provides new insights into the development of high-performance SiCNbased microwave absorbers.

Temperature-mediated structural evolution of vapor–phase deposited cyclosiloxane polymer thin films for enhanced mechanical properties and thermal conductivity

Polymer-derived ceramic(PDC) thin films are promising wear-resistant coatings for protecting metals and carbon-carbon composites from corrosion and oxidation.However,the high pyrolysis temperature hinders the applications on substrate materials with low melting points.We report a new synthesis route for PDC coatings using initiated chemical vapor deposited poly(1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane)(pV_3D_3) as the precurs or.We investigated the changes in siloxane moieties and the network topology,and proposed a three-stage mechanism for the thermal annealing process.The rise of the connectivity number for the structures obtained at increased annealing temperatures was found with strong correlation to the enhanced mechanical properties and thermal conductivity.Our PDC films obtained via annealing at 850℃ exhibit at least 14.6% higher hardness than prior reports for PDCs synthesized below 1100℃.Furthermore,thermal conductivity up to 1.02 W(mK)^(-1) was achieved at the annealing temperature as low as 700℃,which is on the same order of magnitude as PDCs obtained above 1100℃.Using minimum thermal conductivity models,we found that the thermal transport is dominated by diffusons in the films below the percolation of rigidity,while ultra-short mean-free path phonons contribute to the thermal conductivity of the films above the percolation threshold.The findings of this work provide new insights for the development of wear-resistant and thermally conductive PDC thin films for durable protection coatings.

Ceramic Nanocomposites Reinforced with a High Volume Fraction of Carbon Nanotubes

Multi-walled carbon nanotubes（MWNTs） were incorporated into precursor-derived ceramics made from a polysilazane.A ceramic nanocomposite reinforced with about 35 vol%of carbon nanotubes（CNTs）was fabricated by infiltrating CNT-preform with liquid-phased polymeric precursor followed by pyrolysis.The nanocomposite has a dense structure without micro-cracks.The results reveal that the nanocomposite has lower indentation hardness but higher fracture energy than non-reinforced ceramic from the microindentation tests results.The effect of the CNTs on the mechanical properties of the nanocomposite should be discussed accordingly.

Evolution of microstructure and electromagnetic interference shielding performance during the ZrC precursor thermal decomposition process

A polymer-derived ZrC ceramic with excellent electromagnetic interference(EMI)shielding performance was developed to meet ultra-high temperature requirements.The thermal decomposition process of ZrC organic precursor was studied to reveal the evolution of phase composition,microstructure,and EMI shielding performance.Furthermore,the carbothermal reduction reaction occurred at 1300℃,and the transition from ZrO_(2) to ZrC was completed at 1700℃.With the increase in the annealing temperature,the tetragonal zirconia gradually transformed into monoclinic zirconia,and the transition was completed at the annealing temperature of 1500℃ due to the consumption of a large amount of the carbon phase.The average total shielding effectiveness values were 11.63,22.67,22.91,22.81,and 34.73 dB when the polymerderived ZrC was annealed at 900,1100,1300,1500,and 1700℃,respectively.During the thermal decomposition process,the graphitization degree and phase distribution of free carbon played a dominant role in the shielding performance.The typical core–shell structure composed of carbon and ZrC can be formed at the annealing temperature of 1700℃,which results in excellent shielding performance.

Single-source-precursor synthesis and phase evolution of NbC-SiC-C ceramic nanocomposites with core−shell structured NbC@C and SiC@C nanoparticles

In the present work,novel NbC-SiC-C ceramic nanocomposite powders were successfully synthesized by a polymer-derived ceramic approach with the allylhydridopolycarbosilane(AHPCS)and niobium pentachloride(NbCl5)as starting materials.A single-source-precursor was first synthesized by chemical reaction between AHPCS and NbCl5 and then pyrolyzed at 900​℃ to obtain amorphous ceramic powders.After further annealing amorphous ceramics at higher temperatures in the range of 1100-1500​℃,the NbC-SiC-C ceramic nanocomposite powders were finally obtained.The single-source-precursor synthesis and polymer-to-ceramic transformation were characterized by Fourier transform infrared spectra(FT-IR)and thermal gravimetric analysis(TGA).The phase evolution of resulting ceramics was investigated by X-ray diffraction(XRD)and transmission electron microscopy(TEM).Interestingly,both the NbC@C and SiC@C core−shell structured nanoparticles were in-situ formed at 1300​℃ to form NbC-SiC-C ceramic nanocomposites.With the highest NbCl5 content in the feed,the contents of NbC andβ-SiC obtained by Rietveld refinement of the XRD patterns from the 1500​℃ ceramics are 68.41​wt.%and 31.59​wt.%,respectively,indicating that the ultra-high temperature resistant NbC is the main phase.In general,the resultant NbC-SiC-C nanocomposite with NbC as main phase can be considered as candidate material for structure−function integrated applications in harsh environment.

Online preparation of high-quality BN coatings with atomic diffusion based on carbon-free water-soluble precursor

Efficient and environmentally friendly production of high-quality continuous fiber coatings using current preparation methods is highly challenging due to issues such as scale and batch processing restrictions,low deposition rate,high energy consumption,and utilization of multiple environmentally hazardous steps.To address these challenges,we propose a stable and efficient wet chemical deposition coating method for high-throughput online continuous preparation of boron nitride(BN)coatings on ceramic fibers under an ambient environment.Our process involves surface modification,in-situ wet chemical deposition,and heat treatment,and all seamlessly connecting with the ceramic fiber preparation process through continuous stretching.Hydrophilic groups were introduced via surface modification enhancing wettability of the fiber surface with impregnating solution.An in-situ reaction and atom migration improve uniformity and binding of the coating.As a result,outstanding impregnation and adhesion properties are achieved.A comprehensive analysis to evaluate the impact of the BN coatings was conducted,which demonstrates that the BN-coated fibers exhibit a remarkable 36%increase in tensile strength,a 133%increase in fracture toughness,and enhanced temperature resistance of up to 1600℃.It provides a secure and efficient platform for cost-effective production of functional and high-quality coatings through targeted surface modification and rapid stretching impregnation.

Heat dissipation of carbon shell in ZrC-SiC/TaC coating to improve protective ability against ultrahigh temperature ablation

To efficiently decrease ablation heat accumulation and improve the ability of ZrC-SiC/TaC coatings to protect carbon/carbon(C/C)composites,a thermally conductive nanonetwork with a ceramic@carbon core-shell structure was designed and constructed.Polymer-derived SiC/TaC with a graphene carbon shell was synthesized and introduced into a ZrC coating by supersonic atmospheric plasma spraying(SAPS).Graphene shell paths increased the heat transfer capability by lowering the surface temperature to approximately 200℃during oxyacetylene ablation.The heat dissipation of the graphene shell in the ZrC-SiC/TaC@C coating reduced the volatilization of low-melting-point phases and delayed the sintering of ZrO_(2) particles.Thus,the graphene shell in ZrC-SiC/TaC@C coating decreased the mass and linear ablation rates by 91.4%and 93.7%compared to ZrC-SiC/TaC coating,respectively.This work provided a constructive idea for improving the ablation resistance of the coatings by incorporating carbon nanomaterials as a function of heat dissipation.

Synthesis of SiOC@C ceramic nanospheres with tunable electromagnetic wave absorption performance

SiOC-based ceramics are considered promising electromagnetic wave-absorbing materials because of their lightweight,high-temperature resistance,and heat insulation properties.Herein,SiOC@C ceramic nanospheres were prepared using a liquid-phase method combined with a polymer-derived ceramic(PDC)method,followed by heat treatment in N_(2) and Ar atmospheres at different temperatures.The morphology,microstructure,phase composition,and electromagnetic wave absorption performance of the SiOC@C ceramic nanospheres were investigated in detail.The SiOC@C ceramic nanospheres obtained in the Ar atmosphere showed a minimum reflection loss(RL_(min))of−67.03 dB,whereas the SiOC@C ceramic nanospheres obtained in the N_(2) atmosphere exhibited an RLmin value of−63.76 dB.The outstanding electromagnetic wave absorption performance of the SiOC@C ceramic nanospheres was attributed to the synergistic effect between conductive loss,interfacial/defect polarization loss,multiple reflections,and scattering.Therefore,this research provides valuable insights into the design and fabrication of SiOC ceramic-based electromagnetic wave absorbers.

Novel C_(sf)/SiBCN composites prepared by densifying C_(sf)/MA-SiBCN with the PIP process:Oxidation behavior and damage mechanism

To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN(PDCs-SiBCN)were prepared by repeated polymer infiltration and pyrolysis(PIP)of layered C_(sf)/MA-SiBCN composites at 1100℃,and the oxidation behavior and damage mechanism of the as-prepared C_(sf)/SiBCN at 1300–1600℃ were compared and discussed with those of C_(sf)/MA-SiBCN.The C_(sf)/MA-SiBCN composites resist oxidation attack up to 1400℃ but fail at 1500℃ due to the collapse of the porous framework,while the PIP-densified C_(sf)/SiBCN composites are resistant to static air up to 1600℃.During oxidation,oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon(PyC)to the interior of the matrix.Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices,a relatively continuous and dense oxide layer is formed on the sample surface,and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix,which is primarily responsible for improving the oxidation resistance.