Simple and scalable synthesis of super-repellent multilayer nanocomposite coating on Mg alloy with mechanochemical robustness,high-temperature endurance and electric protection

Multi-functionalization is the future development direction for protective coatings on metal surface,but has not yet been explored a lot.The effective integration of multiple functions into one material remains a huge challenge.Herein,a superhydrophobic multilayer coating integrated with multidimensional organic-inorganic components is designed on magnesium alloy via one-step plasma-induced thermal field assisted crosslinking deposition(PTCD)processing followed by after-thermal modification.Hard porous MgO ceramic layer and polytetrafluoroethylene(PTFE)nano-particles work as the bottom layer skeleton and filler components separately,forming an organic-inorganic multilayer structure,in which organic nano-particles can be crosslinked and cured to form a compact polymer-like outer layer with hierarchical surface textures.Remarkably,the chemical robustness after prolonged exposure to aqua regia,strong base and simulated seawater solution profits from polymer-like nanocomposite layer uniformly and compactly across the film bulk.Moreover,the self-similar multilayer structure coating endows it attractive functions of strong mechanical robustness(>100th cyclic rotary abrasion),stable and ultra-low friction coefficient(about 0.084),high-temperature endurance,and robust self-cleaning.The organic-inorganic multilayer coating also exhibits high insulating property with breakdown voltage of 1351.8±42.4 V,dielectric strength of 21.4±0.7 V/μm and resistivity of 3.2×10^(10)Ω·cm.The excellent multifunction benefits from ceramic bottom skeleton,the assembly and deposition of multidimensional nano-particles,and the synergistic effect of organic inorganic components.This study paves the way for designing next generation protective coating on magnesium alloy with great potential for multifunctional applications.

Effects of Fiber Surface Pretreatment and Composite Posttreatment on Mechanical Properties of 2D⁃Cf/Phosphate Geopolymer Matrix Composites

Geopolymers are an important class of materials with potential applications because of their heat resistance,flame resistance,environmental friendliness,and possibilities of being transformed into ceramic matrix composites at low cost.However,the low mechanical properties as well as the intrinsic brittleness limit their technological implementations,and it is necessary to enhance the mechanical properties of geopolymers by adopting various kinds of reinforcements.In this work,therefore,two⁃dimensional continuous carbon fiber(Cf)reinforced phosphate⁃based geopolymer composites(Cf/geopolymer)were prepared through ultrasonic⁃assisted impregnation method.Effects of acetone treatment and high⁃temperature treatment on the properties of Cf/geopolymer composites were studied by X⁃ray photoelectron spectroscopy(XPS),X⁃ray diffraction(XRD),and scanning electron microscopy(SEM).Results of the study proved that acetone treatment plays a key role in ameliorating the interfacial interaction between Cf and phosphate matrix,which can thus enhance the mechanical properties of Cf/geopolymer composites.The Cf/geopolymer composites prepared by acetone⁃treated Cf had a flexural strength of 156.1 MPa and an elastic modulus of 39.7 GPa in Y direction.Moreover,an additional Sol⁃SiO2 re⁃impregnation treatment could further enhance the mechanical properties of the acetone⁃treated Cf/geopolymer composites by repairing the cracks and filling the pores.The results in this paper not only provide insights into the surface modification of Cf,but also report a facile and low⁃cost preparation route for Cf/geopolymer composites with potential applications in aerospace and defense technology.

Effect of SiO_2 Content on the Mechanical and Dielectric Properties of SiBON Composites

A novel composite ceramics with excellen mechanical and dielectric properties was fabricated by means of low temperature hot-pressing using mechanically alloyed SiBON powders as raw materials.The influences of SiO_2 content on phase microstructure,mechanical and dielectric properties of the SiBON ceramics were investigated.

Dual-boron-source-modified Polysilazane as a Novel Precursor for SiBCN Ceramics

Here,we demonstrated a novel synthesis of a polyborosilazane(PBSN)precursor using hydroboration and aminolysis reaction synergies to modify polysilazane(PSN).Specifically,borane tetrahydrofuran and boron trichloride hexane were used as dual boron sources,which not only reacted

Microarc Oxidation/Graphene Duplex Coating Formed on Aluminum Alloy Radiator:Preparation,Microstructure and Thermal Dissipation Properties

The lifetime and luminescenceefficiency o Light emitting diode(LED)tend to drop rapidly with the increasing P-N junction temperature(Tj).To enhancethe heat dissipationofaluminum alloy radiator for LED,a high emissivity and hydrophobic coatingwas fabricated bymicroarc oxidation(MAO)com-

Microstructure Evolution Behavior of Metastable SiBCN Ceramics Prepared by Mechanical Alloying

The fully dense amorphous Si-B-C-N monoliths were fabricated at 1000°-1600°C under5 GPa for 30 min where the mechanically alloyed amorphous Si-B-C-N powders were used as raw material.Crystallization and microstructure evolution of the prepared ceramics were

Fabrication of Amorphous SiBN powders by Mechanical Alloying and its Crystallization Process

Because of the excellent mechanical and dielectric properties,Si BN ceramic was regarded as one of the best comprehensive performance thermal-insulation and wave-transparent material.We prepared amorphous Si BN powders by mechanical alloying using amorphous nano-Si3N4and h-BN

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.

Fabrication of dense SiBCN monolith at a lower temperature and its high-temperature performance

In this study,a crack-free pyrolysis process of partially cured precursor powder compacts was developed to prepare dense silicon boron carbonitride(SiBCN)monoliths at much lower temperatures(1300℃),thereby circumventing the challenges of sintering densification(>1800℃).Unlike the elastic fracture in over-cured precursors or the viscoelastic deformation in under-cured precursors,the partially cured precursor,exhibiting elastic-plastic deformation behavior,facilitates limited nanoscale pore formation in a dense structure,achieving a balance between crack-free pyrolysis and densification.Compared to SiBCN derived from the over-cured precursor(σ=~159 MPa,K_(IC)=1.9 MPa:m^(1/2),Vickers hardness(HV)=7.8 GPa,and E=122 GPa),the resulting SiBCN monolith exhibited significantly improved mechanical properties(σ=~304 MPa,K_(IC)=3.7 MPa-m12,HV=10.6 GPa,and E=161 GPa)and oxidation resistance.In addition,this study investigated the high-temperature performance of SiBCN monoliths,including crystallization and oxidation,and determined the oxidation kinetics induced by pore structure healing and the different oxidation mechanisms of Si-C-N and B-C-N clusters in the amorphous structure.Due to its unique composition and structure,the SiBCN ceramic oxide layer exhibits exceptional self-healing effects on repairing the nanoporous system in the initial stage and shows outstanding high-temperature stability during prolonged oxidation,mitigating adverse effects from bubble formation and crystallization.Due to the nanoporous structure,the oxidation rate is initially controlled by gas diffusion following a linear law before transitioning to oxide layer diffusion characterized by a parabolic law.Finally,due to different valence bond configurations,Si-C-N transforms into an amorphous SiCNO structure after phase separation,unlike the nucleation and growth of residual B-N-C.

Integration of Electrical Properties and Polarization Loss Modulation on Atomic Fe–N‑RGO for Boosting Electromagnetic Wave Absorption

Developing effective strategies to regulate graphene’s conduction loss and polarization has become a key to expanding its application in the electromagnetic wave absorption(EMWA)field.Based on the unique energy band structure of graphene,regulating its bandgap and electrical properties by introducing heteroatoms is considered a feasible solution.Herein,metal-nitrogen doping reduced graphene oxide(M–N-RGO)was prepared by embedding a series of single metal atoms M–N_(4) sites(M=Mn,Fe,Co,Ni,Cu,Zn,Nb,Cd,and Sn)in RGO using an N-coordination atom-assisted strategy.These composites had adjustable conductivity and polarization to optimize dielectric loss and impedance matching for efficient EMWA performance.The results showed that the minimum reflection loss(RL_(min))of Fe–N-RGO reaches−74.05 dB(2.0 mm)and the maximum effective absorption bandwidth(EAB_(max))is 7.05 GHz(1.89 mm)even with a low filler loading of only 1 wt%.Combined with X-ray absorption spectra(XAFS),atomic force microscopy,and density functional theory calculation analysis,the Fe–N_(4) can be used as the polarization center to increase dipole polarization,interface polarization and defect-induced polarization due to d-p orbital hybridization and structural distortion.Moreover,electron migration within the Fe further leads to conduction loss,thereby synergistically promoting energy attenuation.This study demonstrates the effectiveness of metal-nitrogen doping in regulating the graphene′s dielectric properties,which provides an important basis for further investigation of the loss mechanism.

Oxidation behavior of amorphous and nanocrystalline SiBCN ceramics–Kinetic consideration and microstructure

In this study,the structural evolution of SiBCN ceramics during crystallization and its effects on oxidation behavior involving different atomic units or formed phases in amorphous or crystalline SiBCN ceramics were analyzed.The amorphous structure has exceptionally high oxidation activity but presents much better oxidation resistance due to its synchronous oxidation of atomic units and homogeneous composition in the generated oxide layer.However,the oxidation resistance of SiBCN ceramic will degrade during the continual crystallization process,especially for the formation of the nanocapsule-like structure,due to heterogeneous oxidation caused by the phase separation.Besides,the activation energy and rate-controlling mechanism of the atomic units and phases in SiBCN ceramics were obtained.The BNCx(Ea=145 kJ/mol)and SiC(2-x)(Ea=364 kJ/mol)atomic units in amorphous SiBCN structure can be oxidized at relatively lower temperatures with much lower activation energy than the corresponding BN(C)(Ea=209 kJ/mol)and SiC(Ea=533 kJ/mol)phases in crystalline structure,and the synchronous oxidation of the SiC(2-x)and BNCx units above 750C changes the oxidation activation energy of BNCx(Ea=332 kJ/mol)to that similar to SiC(2-x).The heterogeneous oxide layer formed from the nanocapsule-like structure will decrease the activation energy SiC(Ea=445 kJ/mol)and t-BN(Ea=198 kJ/mol).

Preparation and anisotropic properties of textured structural ceramics: A review

Ceramics are usually composed of randomly oriented grains and intergranular phases, so their properties are the statistical average along each direction and show isotropy corresponding to the uniform microstructures. Some methods have been developed to achieve directional grain arrangement and preferred orientation growth during ceramic preparation, and then textured ceramics with anisotropic properties are obtained. Texture microstructures give particular properties to ceramics along specific directions, which can effectively expand their application fields. In this review, typical texturing techniques suitable for ceramic materials, such as hot working, magnetic alignment, and templated grain growth(TGG), are discussed. Several typical textured structural ceramics including α-Al2O3 and related nacre bioinspired ceramics, Si3N4 and SiAlON, h-BN, MB2 matrix ultra-high temperature ceramics, MAX phases and their anisotropic properties are presented.

Progress of a novel non-oxide Si-B-C-N ceramic and its matrix composites

In the past twenty years,Si-B-C-N ceramic has attracted wide attention due to its special structure and outstanding properties.The ceramic generally has an amorphous or a nano-crystalline structure,and has excellent structural stability,oxidation resistance,creep resistance and high-temperature mechanical properties,etc.Thus,Si-B-C-N ceramic attracts many researchers and finds potential applications in transportation,aerocraft,energy,information,microelectronics and environment,etc.Much work has been carried out on its raw materials,preparation processes,structural evolution,phase equilibrium and high-temperature properties.In recent years,many researchers focus on its new preparation methods,the preparation of dense ceramic sample with large dimensions,ceramic matrix composites reinforced by carbon fiber or SiC whisker,or components with various applications.Research on Si-B-C-N ceramic will develop our insight into the relationship between structures and properties of ceramics,and will be helpful to the development of novel high-performance ceramics.This paper reviews the preparation processes,general microstructures,mechanical,chemical,electrical and optical properties,and potential applications of Si-B-C-N ceramic,as well as its matrix composites.

Direct ink writing of continuous SiO2 fiber reinforced wave-transparent ceramics

This article reports the first example of 3D printed continuous SiO2 fiber reinforced wave-transparent ceramic composites via an adaptation of direct ink writing technology to improve the mechanical and dielectric properties of ceramics.The ceramic inks showed good printability by adding nano-SiO2 powder.The effective continuous fiber-reinforced printing progress was achieved through the design and optimization of the coaxial needle structures by finite element simulation.After printing,the continuous fibers were evenly and continuously distributed in the matrix ceramics and the high molding precision for fiber reinforced composite was kept.It is demonstrated that 10 vol%continuous SiO2 fiber improved the bending strength of ceramics by about 27%better than that of the ceramics without fiber and the dielectric performance has also been greatly improved.The novel method unravels the potential of direct ink writing of continuous fiber reinforced wave-transparent ceramics with complex structures and improved properties.

Advanced lanthanide doped upconversion nanomaterials for lasing emission

Microlasers are narrow-band and coherent light from small cavities,which have been widely applied in biomedicine,optical interconnection,integration devices,etc.Lanthanide doped upconversion materials are potential gain media for microlasers from near infrared(NIR)to visible and UV regimes due to their multi ladder-like metastable energy levels and superior optical frequency conversion capability.The optical feedback from photon scattering of the porous upconversion nanoparticles clusters has been reported to produce upconversion random lasers.The light bouncing back and forth between two reflective surfaces or internal surface has been utilized to achieve modulated upconversion lasing emission.In addition,photon lattices and plasmonic cavities with enhanced electromagnetic fields can amplify the upconversion process within the sub-diffraction volumes and produce highly efficient upconverting lasers.In this review,the recent advances on using lanthanide doped upconversion materials for random,whispering gallery mode(WGM)/Fabry-Perot(FP)cavity and photon lattice/plasmonic cavity modulated upconversion microlasers are overviewed.Current challenges and future directions of the upconverting lasers are also discussed.

Microstructural evolution of h-BN matrix composite ceramics with La-Al-Si-O glass phase during hot-pressed sintering

BN/La-Al-Si-O composite ceramics were fabricated by hot-pressed sintering using hexagonal boron nitride(h-BN),lanthanum oxide(La_(2)O_(3)),aluminia(Al_(2)O_(3)),and amorphous silica(SiO_(2))as the raw materials.The effects of sintering temperature on microstructural evolution,bulk density,apparent porosity,and mechanical properties of the h-BN composite ceramics were investigated.The results indicated that La-Al-Si-O liquid phase was formed during sintering process,which provided an environment for the growth of h-BN grains.With increasing sintering temperature,the cristobalite phase precipitation and h-BN grain growth occurred at the same time,which had a significant influence on the densification and mechanical properties of h-BN composite ceramics.The best mechanical properties of BN/La-Al-Si-O composite ceramics were obtained under the sintering temperature of 1700℃.The elastic modulus,flexural strength,and fracture toughness were 80.5 GPa,266.4 MPa,and 3.25 MPa·m^(1/2),respectively.

The effect of applied voltages on the structure,apatite-inducing ability and antibacterial ability of micro arc oxidation coating formed on titanium surface

The micro arc oxidation(MAO)coatings with different concentrations of Ca,P and Zn elements are successfully formed on the titanium substrate at the different applied voltages.After MAO treatment,the MAO coating exhibits the porous surface structure and composed of anatase and rutile TiO2 phases.Meanwhile,the average size and density of micro-pores on the MAO coatings have been modified via the adjusting the applied voltages.In addition,the contents of the incorporated elements such as Zn,Ca and P elements in the MAO coatings have been optimized.The bonding strength test results reveal that the MAO coating shows higher bonding strength,which is up to 45±5 MPa.Compared to the pure Ti plate,the MAO coating formed at 350 and 400 V show good apatite-inducing ability.Meanwhile,the MAO coating containing Zn,Ca and P elements have better antibacterial ability for E.coli and S.aureus.Thus,the incorporation of Zn,Ca and P elements was an effective method to improve the antibacterial ability.Moreover,the concentrations of Zn,Ca and P elements could be adjusted with the changing of the applied voltages.As a result,the enhancement of the antibacterial ability on the MAO coating surfaces was depended on the comprehensive effect of the incorporated elements and the surface property of MAO coatings.

Enhanced mechanical properties and thermal shock resistance of Si_2BC_3N ceramics with SiC coated MWCNTs

Bulk Si_2 BC_3 N ceramics were reinforced with SiC coated multi-walled carbon nanotubes(MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si_2 BC_3 N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength(532.1 MPa) and fracture toughness(6.66 MPa m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si_2 BC_3 N ceramics maintains much higher residual strength(193.0 MPa) after thermal shock test at 1000 ℃.The enhanced properties should be attributed to:(1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation;(2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the "pull out" of MWCNTs.

Enhanced thermal shock and oxidation resistance of Si_2BC_3N ceramics through MWCNTs incorporation

Multi-walled carbon nanotubes(MWCNTs)reinforced Si_2BC_3N ceramics were prepared through mechanical alloying(MA)and following spark plasma sintering(SPS).The thermal shock resistance of Si_2BC_3N ceramics was evaluated comparatively through ice water quenching test and theoretical prediction.Furthermore,the oxidation resistance of MWCNTs incorporated Si_2BC_3N ceramics was evaluated under high temperature.The results show that the calculated parameters such as the critical thermal shock temperature(R)and the thermal stresses resistance(R_(st)),as well as the toughness(R"")are improved with addition of 1 vol%MWCNTs.In addition,the crack propagation resistance of 1 vol%MWCNTs incorporated Si_2BC_3N ceramics is obviously improved through generating more tortuous crack propagation paths attributing to the"crack bridging","pull-out",and"crack deflection"mechanisms of MWCNTs.Therefore,the residual strengths of 1 vol%MWCNTs containing specimens remained the highest after the thermal shock tests.Besides,the present work also reveals that the oxidation resistance is more sensitive to relative density than MWCNTs addition.

3D-printed Lunar regolith simulant-based geopolymer composites with bio-inspired sandwich architectures

Over time,natural materials have evolved to be lightweight,high-strength,tough,and damage-tolerant due to their unique biological structures.Therefore,combining biological inspiration and structural design would provide traditional materials with a broader range of performance and applications.Here,the application of an ink-based three-dimensional(3D)printing strategy to the structural design of a Lunar regolith simulant-based geopolymer(HIT-LRS-1 GP)was first reported,and high-precision carbon fiber/quartz sand-reinforced biomimetic patterns inspired by the cellular sandwich structure of plant stems were fabricated.This study demonstrated how different cellular sandwich structures can balance the structure–property relationship and how to achieve unprecedented damage tolerance for a geopolymer composite.The results presented that components based on these biomimetic architectures exhibited stable non-catastrophic fracture characteristics regardless of the compression direction,and each structure possessed effective damage tolerance and anisotropy of mechanical properties.The results showed that the compressive strengths of honeycomb sandwich patterns,triangular sandwich patterns,wave sandwich patterns,and rectangular sandwich patterns in the Y-axis(Z-axis)direction were 15.6,17.9,11.3,and 20.1 MPa(46.7,26.5,23.8,and 34.4 MPa),respectively,and the maximum fracture strain corresponding to the above four structures could reach 10.2%,6.7%,5.8%,and 5.9%(12.1%,13.7%,13.6%,and 13.9%),respectively.