Spontaneous infiltration and wetting behaviors of a Zr-based alloy melt on a porous SiC substrate

The spontaaleous infiltration aald wetting behaviors of a Zr-based alloy melt on porous a SiC ceramic plate were studied using tile sessile drop metilod by continuous heating and holding for 1800 s at different temperatures in a high-vacuum furnace. The results showed that tile Zr-based alloy melt could pastly infiltrate tile porous SiC substrate without pressure due to tile effect of capillary pressure. Wettability and infiltration rates increased witil increasing temperature, and interracial reaction products （ZrC0.7 and TiC） were detected in tile Zr-based alloy/SiC ceramic system, likely because of tile reaction of tile active elements Zr and Ti witil elemental C. Furtilelinore, tile redundant ele- ment Si diffused into tile alloy melt.

Effect of Deposition Temperature on Optical Properties of Porous Amorphous SiC Film

To study the effect of different deposition temperatures on the optical properties of porous SiC films,single crystal Si was used as the substrate,a layer of anodic aluminum oxide(AAO)film was transferred on the Si substrate by chemical method,and then a layer of SiC was deposited on anodic aluminum oxide(AAO)template to prepare porous fluorescent SiC film by magnetron sputtering.The deposition temperature was ranged from 373 to 873 K.The thickness of the porous SiC film coated on the AAO surface was around 283 nm.It is found that the porous SiC with the deposition temperature of 873 K has the strongest photoluminescence(PL)intensity excited by 375 nm laser.The time-resolved PL spectra prove that the PL is mainly from intrinsic light emitting of SiC.With the optimized process,porous amorphous SiC film may have potential applications in the field of warm white LEDs.

A reverse particle grading strategy for design and fabrication of porous SiC ceramic supports with improved strength

Porous ceramics usually require high mechanical strength and maximized porosity simultaneously,while for conventional particle grading strategies,it is highly challenging to meet both demands.To this end,a reverse particle grading strategy was developed based on the linear packing model by unusually introducing coarse particles(d50=16μm)into a fine particle(d50=5μm)matrix.Following the extrusion and sintering process,tubular porous SiC ceramic supports with improved mechanical strength were successfully fabricated.The effects of coarse particles on the rheological properties of the ceramic paste and the macroscopic properties and microstructure of the SiC supports were systematically investigated.With an increase in the content of coarse SiC particles to 30 wt%,the pressure generated during extrusion decreased from 5.5±0.2 to 1.3±0.1 MPa.Notably,the bending strength of the tubular supports increased from 36.6±5.6 to 49.1±4.5 MPa when 20 wt%coarse powder was incorporated.The notably improved mechanical strength was attributed to the distribution of coarse particles that prolonged the route of crack deflection.Additionally,the optimized tubular supports had an average pore size of 1.2±0.1μm,an open porosity of 45.1%±1.6%,and a water permeability of 7163±150 L/(m2·h·bar)as well as good alkali and acid corrosion resistance.Significantly,the strategy was proven to be feasible for the scale-up fabrication of 19-channel SiC tubular porous ceramic supports.

Effect of CeO_(2) on carbon deposition resistance of Ni/CeO_(2) catalyst supported on SiC porous ceramic for ethanol steam reforming

Ni/CeO_(2) catalysts(nCeO_(2):n_(Ni)=0,1,4,7,10)supported on SiC porous ce ramics for ethanol steam reforming(ESR)were investigated with respect to hydrogen production performance and growth of carbon deposition.The oxygen released from CeO_(2) enables the oxidation of CH_(x) species to serve as carbon precursors,thus providing Ni/CeO_(2) catalysts with stronger resistance to carbon deposition compared with Ni catalysts.The Ni/CeO_(2) catalysts prepared by inverse microemulsion and impregnation methods exhibit regular semicircular spherical shape on SiC porous ceramics.Under 500℃for 25 h of ESR reaction,the ethanol conversion rate over Ni/CeO_(2) catalysts(n_(CeO_(2)):n_(Ni)=7)is sustained up to 100%and H_(2) selectivity is essentially kept at 74%.The by-product selectivity declines stepwise with increasing content of CeO_(2),which is attributed to the adsorption and oxidation of CO and of CH_(x) species as CH_4 precursor from CeO_(2).The scanning electron microscopy(SEM)and transform electron microscopy(TEM)results reveal that further loading of CeO_(2) on the surface of Ni catalysts can alleviate both migration and sintering of Ni particles.Furthermore,carbon deposition on Ni/CeO_(2) catalysts preferentially outgrow filamentous rather than amorphous carbon,with a tendency for the latter to be more deactivated.

Foam-gelcasting preparation of porous Si C ceramic for high-temperature thermal insulation and infrared stealth

Porous SiC ceramics(PSCs)are promising lightweight and efficient thermal insulators that can evade infrared detection by reducing the surface temperature of the protected object,which plays a crucial role in the development of new military equipment.However,the controllable synthesis of PSCs with both hierarchical pore structure and thermal/mechanical stability remains challenging.In this work,such PSCs were prepared by a facile foam-gelcasting/solid-state reaction method,using silicon powders and glucose-derived carbon as starting materials.The favorable dispersibility and wettability of hydrophilic carbon microspheres and the in-situ formed SiC guarantee the highly porous structure(92.8%porosity),comparable bulk density(0.20 g·cm^(-3))and reasonable mechanical property of the product.The designed PSCs performed outstanding high-temperature performance,especially thermal insulation in both oxidizing and inert atmospheres.More importantly,the composite architecture of PSCs and low emissivity layer(Al foil)exhibited desirable infrared stealth property(at a temperature up to 1100℃),significantly extending the operating temperature range of thermal camouflage material.The unique combination of excellent properties would make PSCs a potential candidate material for future thermal protection and infrared stealth applications in an extreme environment.

Porous silicon carbide coated with tantalum as potential material for bone implants

Porous silicon carbide(SiC)has a specific biomorphous microstructure similar to the trabecular microstructure of human bone.Compared with that of bioactive ceramics,such as calcium phosphate,SiC does not induce spontaneous interface bonding to living bone.In this study,bioactive tantalum(Ta)metal deposited on porous SiC scaffolds by chemical vapour deposition was investigated to accelerate osseointegration and improve the bonding to bones.Scanning electron microscopy indicated that the Ta coating evenly covered the entire scaffold structure.Energy-dispersive spectroscopy and X-ray diffraction analysis showed that the coating consisted of Ta phases.The bonding strength between the Ta coating and the SiC substrate is 88.4MPa.The yield strength of porous SiC with a Ta coating(pTa)was 45.862.9MPa,the compressive strength was 61.463.2MPa and the elasticmodulus was4.8GPa.When MG-63 human osteoblasts were co-cultured with pTa,osteoblasts showed good adhesion and spreading on the surface of the pTa and its porous structure,which showed that it has excellent bioactivity and cyto-compatibility.To further study the osseointegration properties of pTa.PTa and porous titanium(pTi)were implanted into the femoral neck of goats for 12weeks,respectively.The Van-Gieson staining of histological sections results that the pTa group had better osseointegration than the pTi group.These results indicate that coating bioactive Ta metal on porous SiC scaffolds could be a potential material for bone substitutes.