Synthesis of crystal-phase and color tunable mixed anion co-doped titanium oxides and their controllable photocatalytic activity

B and N mixed anions co-doped titania with various crystal phases such as anatase,brookite,and rutile were successfully synthesized by a hydrothermal synthesis followed by heat treatment in an ammonia gas atmosphere at 550-650℃(denoted as BN-Ana_x,BN-Bro_x,and BN-Rut_x,x is the treatment temperature).The colors of as-prepared BN-Ana,BN-Bro,and BN-Rut are red,yellow-green,and cyangreen,respectively.The color changing mechanism of titania was related to their various band gap structure and the existence of B-N bonding.The nitridation temperature exhibits effective color changing compared to that of nitridation time.The different phases of the mixed anion codoped titania possess different photocatalytic deNO_(x) activity.The BN-Ana and BN-Rut show poor photocatalytic deNO_(x) activity,while the BN-Bro shows excellent photocatalytic deNO_(x) activity,better than that of standard titania photocatalyst Degussa P25.The colorful titania with low-photocatalytic activity is heavy metal elements free,indicating their possible applications as nontoxic color pigments or novel cosmetic raw materials.

Surface flashover in 50 years:Theoretical models and competing mechanisms

Surface flashover is a devastating electronic avalanche along the gas–solid interface when a high electric field is applied,which is a potential issue that threatens the safe operations of advanced power electronic,electrical,and spacecraft applications.However,the underlying physical mechanisms for surface flashover development are still under investigation owing to the complex charge transport processes through the gas phase,solid phase,and gas–solid interface.In this study,the history of surface flashover theory in the last 50 years is introduced,and several key questions are reviewed from the perspective of the competing mechanisms of charge transport:the role of each phase in a surface flashover,the origin of surface charging,and effects of traps in solid on surface flashover.Then,some suggestions involve charge transport processes in each phase,and their correlations are put forward,and a predictable‘charge transport competitive flashover model’is proposed by clarifying the competing mechanisms of charge transport processes through multiple phases.This study summarises the history and hot topics of physical mechanisms of surface flashover proposed based on classic and recent progress and offers promising routes for developing a more precise surface flashover theory and improving surface flashover performances.

Thermal ageing of soft and hard epoxy resins

Two kinds of epoxy resin,a soft one with rubber-based additives and an ordinary hard one,are used as electrical insulators and airtight sealants in electrical penetrations in nuclear power plants(NPPs).Knowing how they behave under adverse environments is important for the safe operation of NPPs.In this regard,we gave artificial thermal ageing treatment to the two resins by heating them in air at various temperatures.The resins were then subjected to mechanical,thermal,and dielectric tests.As a result,it has become clear that the soft epoxy resin becomes hard,while its permittivity and loss factor decrease as the heating becomes longer.The glass transition tends to occur at a high temperature in the soft epoxy resin when it was heated.With these changes,the soft resin tends to exhibit similar behaviour in various properties to that of the unaged hard one.On the other hand,the hard one is hardly affected by the simulated thermal ageing.Therefore,both resins can be useable in NPPs.

Synthesis of Fe-doped carbon hybrid composed of CNT/flake-like carbon for catalyzing oxygen reduction

Carbon-based materials with tunable properties have emerged as promising candidates to replace Pt-based catalysts for accelerating oxygen reduction reaction(ORR)in fuel cells or metal-air batteries.In this work,we constructed a carbon hybrid which consists of one-dimensional(1D)carbon nanotubes and flake-like carbons by pyrolysis of leaf-like metal-organic frameworks.The optimal hybrid electrocatalyst of Fe_(7%)-L-CNT-900 possesses the desired features for ORR,including active Fe species,high degree of graphitization,large specific surface area,and hierarchical porous structures.Consequently,Fe_(7%)-L-CNT900 performs a high electrocatalytic activity for ORR with a half-wave potential of 0.88 V,which is comparable to that of Pt/C(20 wt.%).This strategy provides an insight into the investigation of highly efficient and low-cost composite electrocatalyst for oxygen reduction reaction.

Experimental investigation of the degradation mechanism of silicone rubber exposed to heat and gamma rays

Cable-grade silicone rubber was aged thermally or by combining heat and gamma-ray radiation,and resultant changes in chemical,thermal,mechanical and electrical properties were examined.The experimental results obtained in these analyses are clearly consistent with the mechanism that silicone rubber is degraded by forming cross-linked structures via formation of abundant siloxane bonds.With further progress of degradation,decomposition becomes dominant.Reflecting these mechanisms,mechanical properties deteriorate dramatically by losing elasticity.Both the real and imaginary parts of complex permittivity decrease,which is a contrastive difference from typical ageing behaviour of organic insulating polymers.In addition,both the elongation at break and indenter modulus are good indicators of degradation of silicone rubber.

Broadband FIR absorption spectra of lowdensity polyethylene sheets containing six different antioxidants and estimation of their contents by chemometric analysis

Antioxidants are usually added to polymeric insulating materials to suppress oxidative degradation.However,the details of antioxidant added to a polymer are often not disclosed.On the other hand,compared to mid-infrared absorption spectroscopy,terahertz(THz)absorption spectroscopy,and far-infrared(FIR)absorption spectroscopy have not been performed so often.Based on the above backgrounds,six different kinds of antioxidants were added into low-density polyethylene sheets with four different contents,and their THz and FIR absorption spectra were measured.As a result,it has become clear that each antioxidant shows its specific absorption peaks,by which the antioxidants can be identified.Furthermore,the antioxidant content can be estimated by the absorption intensity of the specific peak.A chemometric analysis can make the estimation more accurately than a simple comparison of absorption intensity.

Effect of chemical corrosion on charge transport behaviour in epoxy/Al_(2)O_(3)nanocomposite irradiated by gamma ray

Chemical corrosion and gamma‐ray irradiation appeared with the loss of coolant accident may seriously threaten the safe operation of a nuclear power plant,where epoxy resin(ER)‐based materials are widely used.It is urgent to study the effects of the corrosion and the irradiation on the electrical performance in an ER‐based nanocomposite.In this work,ER/Al_(2)O_(3)nanocomposite samples with 0,1,3,5‐wt%nano Al2O3 filler content were prepared at the thickness of 2 mm,and the total gamma irradiation dose was 0,500,and 1000 kGy.The samples were chemically corroded in a boric acid solution(pH=4.7)and a trisodium phosphate alkaline solution(pH=11)at 60℃and 100℃for 48 h.Charge transport behaviour in the samples was derived from the surface potential decay method.In addition,the sample structures were characterised to analyse the corrosion mechanism in the solutions.The results indicated that the depth and the density of the trap showed a temperature‐dependent manner associated with the corrosion.With the addition of appropriate content of the filler,the trap centre was deepened and the carrier mobility was limited even after the corrosion.It is found that the appearance of hydroxyl and carboxyl groups during corrosion,the interaction between the nanoparticle and the matrix and the crosslinking reaction caused by the irradiation are responsible for the variation in charge transport behaviour.

Influence of the sintering temperature on ferroelectric properties of potassium-sodium niobate piezoelectric ceramics

The effect of sintering condition on structure,microstructure,and ferroelectric properties of(K_(0.44)Na_(0.52)Li_(0.04))(Nb_(0.86)Ta_(0.10)Sb_(0.04))-O_(3)(KNL-NTS)has been investigated.Ceramic powders have been synthesized by the solid-state reaction method and sintered at different temperatures(1115℃,1125℃,and 1140℃).Then,samples were characterized by thermogravimetric analysis,X-ray diffraction,scanning electron microscopy,and impedance spectroscopy.Through XRD results,the perovskite structure and small peaks corresponding to a secondary phase were detected.Ceramics processed at the highest temperatures showed higher densities and good piezoelectric properties(d_(33),K_(p),and K_(t)),particularly specimens sintered at 1125℃ presented the highest piezoelectric performance.

Charge transport behavior in gamma‐ray irradiated poly(ethylene terephthalate)estimated by surface potential decay

This study reports on the variation in charge transport behaviour of poly(ethylene terephthalate)(PET)caused by gamma‐ray irradiation estimated by means of surface potential decay(SPD)measurement.The 100μm‐thick PET specimens were exposed to 60Co gamma rays to a maximum total dose of 1000 kGy.The SPD test was carried out to obtain charge transport related parameters via various models,and the effect of gamma‐ray on the transport behaviour was examined.Furthermore,Fourier trans-form infrared spectrum,gel content,ultraviolet‐visible spectroscopy,X‐ray photo-electron spectroscopy,differential scanning calorimetry and polarized optical microscope were employed to characterize the change in material structure induced by the irradiation.The test results indicated that with the growth in the total dose,the deep trap centre was basically unchanged,whereas the shallow trap centre became shallower.In addition,the trap density tended to decrease.The carrier mobility in PET increased with the total dose,and the charge transport manner conformed well to the hopping model.It is suggested that the formation of oxygen‐based groups from the irradiation induced oxidation reaction tends to encourage the charge transport,while the decrease of amorphous region gives rise to the reduction in trap density.