Flash X-ray cinematography analysis of dwell and penetration of smallcaliber projectiles with three types of SiC ceramics

In order to improve the performance of ceramic composite armor it is essential to know the mechanisms during each phase of the projectile–target interaction and their influence on the penetration resistance.Since the view on the crater zone and the tip of a projectile penetrating a ceramic is rapidly getting obscured by damaged material,a flash X-ray technique has to be applied in order to visualize projectile penetration.For this purpose,usually several flash X-ray tubes are arranged around the target and the radiographs are recorded on film.At EMI a flash X-ray imaging method has been developed,which provides up to eight flash radiographs in one experiment.A multi-anode 450 k V flash X-ray tube is utilized with this method.The radiation transmitted through the target is then detected on a fluorescent screen.The fluorescent screen converts the radiograph into an image in the visible wavelength range,which is photographed by means of a high-speed camera.This technique has been applied to visualize and analyze the penetration of 7.62 mm AP projectiles into three different types of Si C ceramics.Two commercial Si C grades and MICASIC(Metal Infiltrated Carbon derived Si C),a C-Si Si C ceramic developed by DLR,have been studied.The influences,not only of the ceramic but also the backing material,on dwell time and projectile erosion have been studied.Penetration curves have been determined and their relevance to the ballistic resistance is discussed.

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.

畸变钙钛矿结构YBa_2Cu_3O_(7-x)晶体中氧含量与高温超导性

本文报道了氧含量对畸变钙钛矿结构 YBa_2Cu_3O_(7-x)晶体高温超导性的影响。发现采用强氧化剂 BaO_2代替 BaCO_3作原料制备的单晶中氧含量有明显提高,超导性能也有较大改善。

Phosphorylated Salicylic Acid as Flame Retardant in Epoxy Resins and Composites

A novel,versatile flame retardant substructure based on phosphorylated salicylic acid(SCP)is described and used in the synthesis of new flame retardants for HexFlow
RTM6,a high-performance epoxy resin used in resin transfer molding processes as composite matrix.The starting material salicylic acid can be obtained from natural sources.SCP as reactive phosphorus chloride is converted with a novolak,a novolak containing 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide(DOPO)substituents or DOPO-hydroquinone to flame retardants with sufficient thermal stability and high char yield.Additionally,these flame retardants are soluble in the resin as well as react into the epoxy network.The determined thermal stability and glass transition temperatures of flame retarded neat resin samples as well as the interlaminar shear strength of corresponding carbon fiber reinforced composite materials showed the applicability of these flame retardants.Neat resin samples and composites were tested for their flammability by UL94 and/or flame-retardant performance by cone calorimetry.All tested flame retardants decrease the peak of heat release rate by up to 54%for neat resin samples.A combination of DOPO and SCP in one flame retardant shows synergistic effects in char formation and the mode of action adapts to neat resin or fiber-reinforced samples,so there is efficient flame retardancy in both cases.Therefore,a tailoring of SCP based flame retardants is possible.Additionally,these flame retardants efficiently reduce fiber degradation during combustion of carbon fiber-reinforced epoxy resins as observed by scanning electron microscopy and energy dispersive X-ray spectroscopy.

Recent advances in self-healing hydrogel composites for flexible wearable electronic devices

Flexible electronic devices with mechanical properties like the soft tissues of human organs have great potential for the next generation of wearable and implantable electronic devices.Self-healing hydrogel composites typically have high tensile strength,high electrical conductivity and damage repair properties and have wide applications in flexible electronics,such as human-computer interaction,health detection and soft robots.Various self-healing hydrogel composites have been developed to produce new stretchable conductive materials with satisfactory mechanical and selfhealing properties.This paper presents the fabrication of self-healing hydrogel composites and their application in flexible electronic devices.Firstly,the repair mechanism of physically cross-linked and chemically cross-linked self-healing hydrogel composites is presented.Secondly,self-healing double network hydrogels,self-healing nanocomposite hydrogels and double crosslinked self-healing hydrogel composites and their applications in flexible sensors,energy harvesting devices,energy storage devices and optical devices are presented and discussed.Finally,the challenges and prospects of self-healing hydrogel composites in flexible electronic devices in the future are presented.

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.

Advancing oxygen separation:insights from experimental and computational analysis of La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)(M=Cu,Zn)oxygen transport membranes

In this study,perovskite-type La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)(M=Cu,Zn)powders were synthesized using a scalable reverse co-precipitation method,presenting them as novel materials for oxygen transport membranes.The comprehensive study covered various aspects including oxygen permeability,crystal structure,conductivity,morphology,CO_(2) tolerance,and long-term regenerative durability with a focus on phase structure and composition.The membrane La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)exhibited high oxygen permeation fluxes,reaching up to 0.88 and 0.64 mL·min^(−1)·cm^(−2) under air/He and air/CO_(2) gradients at 1173 K,respectively.After 1600 h of CO_(2) exposure,the perovskite structure remained intact,showcasing superior CO_(2) resistance.A combination of first principles simulations and experimental measurements was employed to deepen the understanding of Cu/Zn substitution effects on the structure,oxygen vacancy formation,and transport behavior of the membranes.These findings underscore the potential of this highly CO_(2)-tolerant membrane for applications in high-temperature oxygen separation.The enhanced insights into the oxygen transport mechanism contribute to the advancement of next-generation membrane materials.

Tailoring thermoelectric properties of Zr(0.43)Hf(0.57)NiSn half-Heusler compound by defect engineering

The thermoelectric transport properties of Zr0.43Hf0.57 NiSn half-Heusler compounds were investigated for samples sintered with different spark plasma sintering(SPS)periods:8,32 and 72 min.By means of scanning transmission electron microscopy with a highangular annular dark-field detector(STEM-HAADF),it was found that sintering time affected the defect concentration,namely the amount of Ni interstitial atoms,and created locally ordered inclusions of full-Heusler phase.The structural information,phase composition and electrical transport properties could be consistently explained by the assumption that Ni interstitials give rise to an impurity band situated about 100 meV below the bottom of the conduction band via a self-doping behavior.The impurity band was found to merge with the conduction band for the sample with intermediate SPS time.The effect was ascribed to the gradual dissolution of full-Heusler phase inclusions and production of interstitial Ni defects,which eventually vanished for the sample with the longest sintering time.It was demonstrated that the modification of the density of states near the edge of the conduction band and enhanced overall charge carrier concentration provided by defect engineering led to overall 26%increase in the thermoelectric figure of merit(ZT)with respect to the other samples.

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.

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.

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.

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.

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.

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.

Anisotropic magnetoresistance:A 170-year-old puzzle solved

Thomson[1],the later Lord Kelvin,reported an increased electric resistance in iron and nickel when the magnetization is parallel rather than normal to the current direction,an effect now called anisotropic magnetoresistance(AMR).The AMR allows sensing magnetic fields by simply measuring the resistance change when the magnetization realigns.While the magnetoresistance of magnetic tunnel junctions is larger,AMR sensors are attractive by their simplicity and robustness.

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.