Boron carbide has unique properties for wide application possibilities;however,poor sinterability limits its applications.One approach to overcome this limitation is the addition of secondary phases into boron carbide...Boron carbide has unique properties for wide application possibilities;however,poor sinterability limits its applications.One approach to overcome this limitation is the addition of secondary phases into boron carbide.Boron carbide based composite ceramics are produced by the direct addition of secondary phases into the structure or via reactive sintering using a sintering additive.The present study investigated the effect of Ti_(3)SiC_(2) addition to boron carbide by reactive spark plasma sintering in the range of 1700-1900℃.Ti_(3)SiC_(2) phase decomposed at high temperatures and reacted with B4C to form secondary phases of TiB2 and SiC.The results demonstrated that the increase of Ti_(3)SiC_(2) addition(up to 15 vol%)effectively promoted the densification of B4C and yielded higher hardness.However,as the amount of Ti_(3)SiC_(2) increased further,the formation of microstructural inhomogeneity and agglomeration of secondary phases caused a decrease in hardness.展开更多
Boron carbide(B_(4)C)has excellent high-temperature oxidation resistance,high hardness,low relative density,high melting point and excellent abrasive resistance,which is widely used in fields such as refractories,wear...Boron carbide(B_(4)C)has excellent high-temperature oxidation resistance,high hardness,low relative density,high melting point and excellent abrasive resistance,which is widely used in fields such as refractories,wear-resistant materials and lightweight protective materials.The research progress and application of B_(4)C materials in China and overseas in recent years were summarized.The influences of sintering processes(pressureless sintering,hot-pressing sintering,hot isostatic pressing sintering,spark plasma sintering and microwave sintering)and sintering additives(simple substances,oxides and carbides)on the B_(4)C densification were analyzed.The development of B_(4)C materials was prospected.展开更多
In this experimental study,magnesium(AZ91D)based boron carbide(B4C)and graphite(Gr)particle reinforced hybrid composite materials were manufactured by stir casting.The tribological and mechanical properties of these c...In this experimental study,magnesium(AZ91D)based boron carbide(B4C)and graphite(Gr)particle reinforced hybrid composite materials were manufactured by stir casting.The tribological and mechanical properties of these composite materials were investigated.The results of the tests revealed that the graphite reinforced hybrid composites exhibited a lower wear loss compared to the unreinforced AZ91D alloy and AZ91D–B4C composites.It was found that with an increase in the B4C content,the wear resistance increased monotonically with hardness and ultimate tensile strength decreased.This study revealed that the addition of both a hard reinforcement(e.g.,B4C)and soft reinforcement(e.g.,graphite)significantly improves the wear resistance of magnesium composites.These entire results designate that the hybrid magnesium composites can be considered as an excellent material where high strength,ultimate tensile strength and wear-resistant components are of major importance,primarily in the aerospace and automotive engineering sectors.展开更多
The sluggish kinetics of Fe(Ⅱ)recovery in Fenton/Fenton-like reactions significantly limits the oxidation efficiency.In this study,we for the first time use boron carbide(BC)as a green and stable promotor to enhance ...The sluggish kinetics of Fe(Ⅱ)recovery in Fenton/Fenton-like reactions significantly limits the oxidation efficiency.In this study,we for the first time use boron carbide(BC)as a green and stable promotor to enhance the reaction of Fe(Ⅲ)/H_(2)O_(2) for degradation of diverse organic pollutants.Electron paramagnetic resonance analysis and chemical quenching/capturing experiments demonstrate that hydroxyl radicals(·OH)are the primary reactive species in the BC/Fe(Ⅲ)/H_(2)O_(2) system.In situ electrochemical analysis indicates that BC remarkably boosts the Fe(Ⅲ)/Fe(Ⅱ)redox cycles,where the adsorbed Fe(Ⅲ)cations were transformed to more active Fe(Ⅲ)species with a higher oxidative potential to react with H_(2)O_(2) to produce Fe(Ⅱ).Thus,the recovery of Fe(Ⅱ)from Fe(Ⅲ)is facilitated over BC surface,which enhancesOH generation via Fenton reactions.Moreover,BC exhibits outstanding reusability and stability in successive cycles and avoids the secondary pollution caused by conventional organic and metalliferous promotors.Therefore,metal-free BC boosting Fe(Ⅲ)/H_(2)O_(2) oxidation of organics provides a green and advanced strategy for water decontamination.展开更多
High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates(FML)has been explored.Both single and multiple projectiles impact conditions were considered.Ti/GFRP FML targets were fabrica...High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates(FML)has been explored.Both single and multiple projectiles impact conditions were considered.Ti/GFRP FML targets were fabricated with addition of 5%and 10%weight percentage of boron carbide(B_(4)C)particles.Mechanical properties of Ti/GFRP FML targets were determined as per ASTM standards.High velocity ballistic experiments were conducted using Armour Piercing Projectile(APP)of diameter 7.62 mm and velocity ranging between 350 and 450 m/s.Depth of penetration of the projectile into the target was measured.The deformation behaviour of Ti/GFRP targets with and without the presence of ceramic powder(B_(4)C)was investigated.“Ductile hole growth”failure mode was observed for pure GFRP target when subjected to single projectile impact whereas“plugging”failure mode was noted for Ti/GFRP targets.The presence of B_(4)C(5%by weight)particles has significantly improved the ballistic resistance of the Ti/GFRP FML target by offering frictional resistance to the projectile penetration.Further addition(10%by weight)of B_(4)C has reduced the ballistic performance due to agglomeration.None of the targets showed‘brittle cracking’or‘fragmentation’failures.When compared to the published results of Aluminium(Al 1100/GFRP and Al 6061/GFRP)FMLs,Ti/GFRP FML showed lesser DoP which increases its potential application to aerospace industry.展开更多
High strength-to-weight ratio of non-ferrous alloys, such as aluminium, magnesium and titanium alloys, are considered to be possible replacement of widely accepted steels in transportation and automobile sectors. Amon...High strength-to-weight ratio of non-ferrous alloys, such as aluminium, magnesium and titanium alloys, are considered to be possible replacement of widely accepted steels in transportation and automobile sectors. Among these alloys, magnesium is self explosive and titanium is costlier, and aluminium is most likely to replace steels. Application of aluminium or its alloys is also thought of as an appropriate replacement in defence field, especially to enhance the easiness in mobility of combat vehicles while maintaining the same standard as that of conventional armour grade steels. Hence most of the investigations have been confined to aluminium or its alloys as base material and open an era of developing the newer composite materials to address the major limitation, i.e. tribological properties. The surface composites can be fabricated by incorporating the ceramic carbides like silicon carbide, carbides of transition metals and oxides of aluminium using surface modification techniques, such as high energy laser melt treatment, high energy electron beam irradiation and thermal spray process which are based on fusion route. These techniques yield the fusion related problems, such as interfacial reaction, pin holes, shrinkage cavities or voids and other casting related defects, and pave the way to need of an efficient technique which must be based on solid state. Recently developed friction stir processing technique was used in the present investigation for surface modification of AA7075 aluminum alloy, which is an alternative to steels. In the present investigation, 160 μm sized boron carbide powder was procured and was reduced to 60 μm and 30 μm using high energy ball mill. Subsequently these powders were used to fabricate the surface composites using friction stir processing.Ballistic performance testing as per the military standard(JIS.0108.01) was carried out. In the present work, an analytical method of predicting the ballistic behavior of surface composites was developed. This method was based on energy balance, i.e., the initial energy of impact is same as that of energy absorbed by multi layers. An attempt also has been made to validate the analytical results with the experimental findings. Variation between the analytical and experimental results may be accounted due to the assumptions considering such as isotropic behavior of target and shearing area of contact as cylindrical instead of conical interface As the analytical model yields the ballistic performance in the closer proximity of experimentally obtained, it can be considered to be an approximation to evaluate the ballistic performance of targets.展开更多
Reduced graphene oxide(rGO)enhanced B_(4)C ceramics was prepared by SPS sintering,the enhancement effect of rGO on the microstructure and mechanical properties of composites was studied through experiments and numeric...Reduced graphene oxide(rGO)enhanced B_(4)C ceramics was prepared by SPS sintering,the enhancement effect of rGO on the microstructure and mechanical properties of composites was studied through experiments and numerical simulation.The results show that the composite with 2wt%rGO has the best comprehensive mechanical properties.Compared with pure boron carbide,vickers hardness and bending strength are increased by 4.8%and 21.96%,respectively.The fracture toughness is improved by 25.71%.The microstructure observation shows that the improvement of mechanical properties is mainly attributed to the pullout and bridge mechanism of rGO and the crack deflection.Based on the cohesive force finite element method,the dynamic crack growth process of composites was simulated.The energy dissipation of B_(4)C/rGO multiphase ceramics during crack propagation was calculated and compared with that of pure boron carbide ceramics.The results show that the fracture energy dissipation can be effectively increased by adding graphene.展开更多
Microstructure of plasma spray boron carbide coating was studied by SEM and TEM. its physical, mechanical and electrical properties were measured. The results showed that high microhardness. modulus and low porosity o...Microstructure of plasma spray boron carbide coating was studied by SEM and TEM. its physical, mechanical and electrical properties were measured. The results showed that high microhardness. modulus and low porosity of B4C coating were manufactured by plasma spray. It was lamellar packing and dense. The B4C coating examined here contained two principal structures and two impurity phase besides major phase. The relatively small value of Young’s modulus, comparing with that of the bulk materials, is explained by porosity. The Fe impurity phase could account for the relatively high electrical conductivity of boron carbide coating by comparing with the general boron carbide materials.展开更多
Boron carbide (B4C) is a rhombic structure composed of icosahedra and atomic chains, which has an important application in armored materials. The application of B4C under super high pressure without failure is a hot s...Boron carbide (B4C) is a rhombic structure composed of icosahedra and atomic chains, which has an important application in armored materials. The application of B4C under super high pressure without failure is a hot spot of research. Previous studies have unmasked the essential cause of B4C failure, i.e., its structure will change subjected to impact, especially under the non-hydrostatic pressure and shear stress. However, the change of structure has not been clearly understood nor accurately determined. Here in this paper, we propose several B4C polymorphs including B4C high pressure phases with non-icosahedra, which are denoted as post-B4C and their structures are formed due to icosahedra broken and may be obtained through high pressure and high temperature (HPHT). The research of their physical properties indicates that these B4C polymorphs have outstanding mechanical and electrical properties. For instance, aP10, mC10, mP20, and oP10-B4C are conductive superhard materials. We hope that our research will enrich the cognition of high pressure structural deformation of B4C and broaden the application scope of B4C.展开更多
Chemical vapor deposition is an important method for the preparation of boron carbide.Knowledge of the correlation between the phase composition of the deposit and the deposition conditions (temperature,inlet gas comp...Chemical vapor deposition is an important method for the preparation of boron carbide.Knowledge of the correlation between the phase composition of the deposit and the deposition conditions (temperature,inlet gas composition,total pressure,reactor configuration,and total flow rate) has not been completely determined.In this work,a novel approach to identify the kinetic mechanisms for the deposit composition is presented.Machine leaning (ML) and computational fluid dynamic (CFD) techniques are utilized to identify core factors that influence the deposit composition.It has been shown that ML,combined with CFD,can reduce the prediction error from about 25% to 7%,compared with the ML approach alone.The sensitivity coefficient study shows that BHCl_(2 )and BCl_(3) produce the most boron atoms,while C_(2)H_(4) and CH_(4) are the main sources of carbon atoms.The new approach can accurately predict the deposited boron-carbon ratio and provide a new design solution for other multi-element systems.展开更多
Due to the complex products and irradiation-induced defects, it is hard to understand and even predict the thermal conductivity variation of materials under fast neutron irradiation, such as the abrupt degradation of ...Due to the complex products and irradiation-induced defects, it is hard to understand and even predict the thermal conductivity variation of materials under fast neutron irradiation, such as the abrupt degradation of thermal conductivity of boron carbide (B_(4)C) at the very beginning of the irradiation process. In this work, the contributions of various irradiation-induced defects in B_(4)C primarily consisting of the substitutional defects, Frenkel defect pairs, and helium bubbles were re-evaluated separately and quantitatively in terms of the phonon scattering theory. A theoretical model with an overall consideration of the contributions of all these irradiation-induced defects was proposed without any adjustable parameters, and validated to predict the thermal conductivity variation under irradiation based on the experimental data of the unirradiated, irradiated, and annealed B_(4)C samples. The predicted thermal conductivities by this model show a good agreement with the experimental data after irradiation. The calculation results and theoretical analysis in light of the experimental data demonstrate that the substitutional defects of boron atoms by lithium atoms, and the Frenkel defect pairs due to the collisions with the fast neutrons, rather than the helium bubbles with strain fields surrounding them, play determining roles in the abrupt degradation of thermal conductivity with burnup.展开更多
Carbide boronizing is a promising approach to obtain fine grained boron carbide based ceramics with improved mechanical properties. In this work, reaction process, microstructural characteristics and mechanical proper...Carbide boronizing is a promising approach to obtain fine grained boron carbide based ceramics with improved mechanical properties. In this work, reaction process, microstructural characteristics and mechanical properties of BxC-TaB2(x = 3.7, 4.9, 7.1) ceramics were comprehensively investigated via this method. Dense BxC-TaB2 ceramics with refined microstructure were obtained from submicro tantalum carbide and boron powder mixtures at 1800℃/50 MPa/5 min by spark plasma sintering. The stoichiometry of boron carbide was determined from lattice parameters and Raman shift. It was found that uniformly distributed TaB2 grains in the BxC matrix is favor of the densification process and restricting grain growth.Besides, planar defects with high density were observed from the as-formed B7.1 C grains and transient stress was considered to contribute to the densification involved with plastic deformation. Microstructural observations indicate the dissolution of oxygen in the TaB2 lattice and most of the B7.1 C/TaB2 phase boundaries were clean. Owing to the highly faulted structure and finer grain size, as-obtained BxC-TaB2 ceramics exhibit high Vickers hardness(33.3–34.4 GPa at 9.8 N) and relatively high flexural strength ranging from 440 to 502 MPa.展开更多
The fabrication of boron carbide reinforced aluminum matrix composites(Al-B_(4)C)with various contents of B_(4)C(1wt%,6wt%,15wt%,and 30wt%)was performed by powder metallurgy,and the influence of the content of B_(4)C ...The fabrication of boron carbide reinforced aluminum matrix composites(Al-B_(4)C)with various contents of B_(4)C(1wt%,6wt%,15wt%,and 30wt%)was performed by powder metallurgy,and the influence of the content of B_(4)C on their mechanical and tribological behavior was examined.The Al-30B_(4)C composites recorded the highest density(~2.54 g/cm^(3)),lowest porosity(4%),maximum Vickers hardness(HV~75),lowest weight loss(0.4 mg),and lowest specific wear rate(0.00042 mm^(3)/(N·m))under a load of 7 N,with an enhancement of 167%in hardness,a decrease of 75.8%in weight loss,and a decrease of 76.7%in the specific wear rate compared with pure aluminum.In addition,the scanning electron microscope images of the worn surface revealed that the Al-B_(4)C composite has the narrowest wear groove of 0.85 mm at a load of 7 N,and the main wear mechanism was observed as an abrasive wear mechanism.According to the friction analysis,the coefficient of friction between surfaces increased with increasing boron carbide content and with decreasing applied load.In conclusion,B_(4)C is an effective reinforcement material in terms of tribological and mechanical performance of the Al-B_(4)C composites.展开更多
The significant advantage of proton therapy over other particle-based techniques is in the unique physical characteristics of the Bragg peak.It can achieve a highly conformal dose distribution and maximize the probabi...The significant advantage of proton therapy over other particle-based techniques is in the unique physical characteristics of the Bragg peak.It can achieve a highly conformal dose distribution and maximize the probability of tumor control by varying the irradiation energy.Most proton facilities use cyclotrons for fixed energy beam extraction and are equipped with degrader and collimator systems for energy modulation and emittance suppression.However,interactions between charged particles and degrader materials inevitably cause beam loss and divergence and deteriorate beam performance,which present great challenges for downstream transport and clinical treatment.In this work,we investigate a method of energy reduction by combining boron carbide and graphite in a degrader to obtain greater beam transmission at lower energy.The results demonstrate that the beam size and emittance at the exit of the combined degrader diverge less than those of multi-wedge one in the energy range of 70-160 MeV.Correspondingly,the transmission efficiency after the first dipole also shows improvements of 36.26%at 70 MeV and 70.55%at 110 MeV.As a component with a high activity level,the degrader causes additional ambient radiation during operation.Residual induced radiation even remains several hours after system shutdown.Analysis of material activation and induced radiation based on 1 h irradiation with a 400 nA beam current shows that the combined degrader has a definite advantage in shielding despite producing more secondary particles.Both radioactivity and average ambient dose equivalent are reduced by 50%compared with the multiwedge degrader at the important cooling time of 1 h.After 12 h and 24 h of cooling,the radiation levels of degraders decrease slightly due to the presence of long half-life residual nuclides.The average dose generated from the multi-wedge degrader is still 1.25 times higher than that of the combined one.展开更多
Presented herein is an experimental study on the combustion of B4C/KNO3 binary pyrotechnic system.Combustion products were tested using X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive sp...Presented herein is an experimental study on the combustion of B4C/KNO3 binary pyrotechnic system.Combustion products were tested using X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive spectrometer(EDS).According to the results of tests and CEA calculation,the combustion reaction equation was established.The flames and burning rates were recorded by a high speed camera and a spectrophotometer.The effect of B4C particle size on the thermal sensitivity of B4C/KNO3 was investigated by differential scanning calorimetry(DSC)techniques.In addition,a reliable method for calculating the flame temperature was proposed.Based on the results of experiments,the combustion reaction mechanism was briefly analyzed.The burning rate,flame temperature and thermal sensitivity of B4C/KNO3 increase with the decrease of B4C particle size.The mass ratio of B4C/KNO3 has a great effect on combustion properties.Oxidizer-rich compositions have low flame temperatures,low burning rates,and provide green light emission.The combustion reactions of fuel-rich compositions are vigorous,and the B4C/KNO3 with mass ratio of 25:75 has the highest burning rate and the highest flame temperature.展开更多
By doping titanium hydride(TiH2) into boron carbide(B4C), a series of B4C + x wt% TiH2(x = 0, 5, 10, 15, and 20)composite ceramics were obtained through spark plasma sintering(SPS). The effects of the sintering temper...By doping titanium hydride(TiH2) into boron carbide(B4C), a series of B4C + x wt% TiH2(x = 0, 5, 10, 15, and 20)composite ceramics were obtained through spark plasma sintering(SPS). The effects of the sintering temperature and the amount of TiH2 additive on the microstructure, mechanical and electrical properties of the sintered B4C-TiB2 composite ceramics were investigated. Powder mixtures of B4C with 0–20 wt% TiH2 were heated from 1400℃ to 1800℃ for 20 min under 50 MPa. The results indicated that higher sintering temperatures contributed to greater ceramic density. With increasing TiH2 content, titanium diboride(TiB2) formed between the TiH2 and B4C matrix. This effectively improved Young’s modulus and fracture toughness of the composite ceramics, significantly improving their electrical properties: the electrical conductivity reached 114.9 S·cm-1 at 1800℃ when x = 20. Optimum mechanical properties were obtained for the B4C ceramics sintered with 20 wt% TiH2, which had a relative density of 99.9±0.1%, Vickers hardness of 31.8 GPa,and fracture toughness of 8.5 MPa·m1/2. The results indicated that the doping of fine Ti particles into the B4C matrix increased the conductivity and the fracture toughness of B4C.展开更多
There is a strength and fracture toughness tradeoff in nanoceramic composite. The strength varies reciprocally with the grain size whereas the toughness contributed by compressive residual stress increases with the di...There is a strength and fracture toughness tradeoff in nanoceramic composite. The strength varies reciprocally with the grain size whereas the toughness contributed by compressive residual stress increases with the dimension of the second phase. In this work, a novel duplex microstructure with reinforced clusters composing of nanosized grains was proposed and validated using a model system of B_(4)C-TiB_(2) ceramics densified by carbide boronizing. As-obtained ceramics exhibit excellent combined mechanical properties at room temperature, including Vickers hardness, Young's modulus, flexural strength and fracture toughness(by surface crack in flexure method) of 32.1 ± 2.7 GPa, 506.9 ± 2.0 GPa,1175 ± 71 MPa and 5.1 ± 0.4 MPa m^(0.5), respectively. Both strength and toughness are at least ~30 % higher than the counterparts with similar composition but homogenously distributed TiB_(2) grains. Graphite onion was confirmed to be an intermediate product during reactive sintering, it facilitated the grain pullout during fracture and retained the nanometric TiB_(2) grain in the cluster, both of which also contribute the toughening and strengthening mechanisms in the B_(4)C-TiB_(2) ceramics.展开更多
Cu matrix composite materials reinforced with B4C particle at four different contents(1.5 wt%,3.0 wt%,4.5 wt% and 6.0 wt%) and also CuAl matrix composites with 13 wt% Al reinforced with B4C particle at four different ...Cu matrix composite materials reinforced with B4C particle at four different contents(1.5 wt%,3.0 wt%,4.5 wt% and 6.0 wt%) and also CuAl matrix composites with 13 wt% Al reinforced with B4C particle at four different contents(1.5 wt%,3.0 wt%,4.5 wt% and 6.0 wt%)were fabricated by hot pressing(HP) and a powder metallurgy(PM) process.Experimental samples were produced by keeping them at 880℃ at the constant pressure of 2.3×10~8 Pa for 6 min.The density,microstructure and mechanical properties of the produced samples were examined.The microstructure and phase examinations were carried out by scanning electron microscope(SEM)and optical microscope(OM),energy-dispersive spectrometer(EDS) and X-ray diffractometer(XRD) analysis.The hardness measurements,three-point bending test and impact test were conducted to determine the mechanical properties.As a result of the examinations,it was observed that the relative density values decreased with the increasing content of B4C and provided a relatively effective bonding.Moreover,it was homogeneously distributed in the produced specimens.Consequently,there was a considerable increase in the hardness and the bending strength of CuAl matrix specimens with Al addition.展开更多
基金YOK(MEVLANA 2018-9999-Proj-ect-Based International Exchange Programme)for financial support in inter-national collaboration.
文摘Boron carbide has unique properties for wide application possibilities;however,poor sinterability limits its applications.One approach to overcome this limitation is the addition of secondary phases into boron carbide.Boron carbide based composite ceramics are produced by the direct addition of secondary phases into the structure or via reactive sintering using a sintering additive.The present study investigated the effect of Ti_(3)SiC_(2) addition to boron carbide by reactive spark plasma sintering in the range of 1700-1900℃.Ti_(3)SiC_(2) phase decomposed at high temperatures and reacted with B4C to form secondary phases of TiB2 and SiC.The results demonstrated that the increase of Ti_(3)SiC_(2) addition(up to 15 vol%)effectively promoted the densification of B4C and yielded higher hardness.However,as the amount of Ti_(3)SiC_(2) increased further,the formation of microstructural inhomogeneity and agglomeration of secondary phases caused a decrease in hardness.
文摘Boron carbide(B_(4)C)has excellent high-temperature oxidation resistance,high hardness,low relative density,high melting point and excellent abrasive resistance,which is widely used in fields such as refractories,wear-resistant materials and lightweight protective materials.The research progress and application of B_(4)C materials in China and overseas in recent years were summarized.The influences of sintering processes(pressureless sintering,hot-pressing sintering,hot isostatic pressing sintering,spark plasma sintering and microwave sintering)and sintering additives(simple substances,oxides and carbides)on the B_(4)C densification were analyzed.The development of B_(4)C materials was prospected.
文摘In this experimental study,magnesium(AZ91D)based boron carbide(B4C)and graphite(Gr)particle reinforced hybrid composite materials were manufactured by stir casting.The tribological and mechanical properties of these composite materials were investigated.The results of the tests revealed that the graphite reinforced hybrid composites exhibited a lower wear loss compared to the unreinforced AZ91D alloy and AZ91D–B4C composites.It was found that with an increase in the B4C content,the wear resistance increased monotonically with hardness and ultimate tensile strength decreased.This study revealed that the addition of both a hard reinforcement(e.g.,B4C)and soft reinforcement(e.g.,graphite)significantly improves the wear resistance of magnesium composites.These entire results designate that the hybrid magnesium composites can be considered as an excellent material where high strength,ultimate tensile strength and wear-resistant components are of major importance,primarily in the aerospace and automotive engineering sectors.
基金support to visit The University of Adelaide from the China Scholarship Council(No.201906240037).
文摘The sluggish kinetics of Fe(Ⅱ)recovery in Fenton/Fenton-like reactions significantly limits the oxidation efficiency.In this study,we for the first time use boron carbide(BC)as a green and stable promotor to enhance the reaction of Fe(Ⅲ)/H_(2)O_(2) for degradation of diverse organic pollutants.Electron paramagnetic resonance analysis and chemical quenching/capturing experiments demonstrate that hydroxyl radicals(·OH)are the primary reactive species in the BC/Fe(Ⅲ)/H_(2)O_(2) system.In situ electrochemical analysis indicates that BC remarkably boosts the Fe(Ⅲ)/Fe(Ⅱ)redox cycles,where the adsorbed Fe(Ⅲ)cations were transformed to more active Fe(Ⅲ)species with a higher oxidative potential to react with H_(2)O_(2) to produce Fe(Ⅱ).Thus,the recovery of Fe(Ⅱ)from Fe(Ⅲ)is facilitated over BC surface,which enhancesOH generation via Fenton reactions.Moreover,BC exhibits outstanding reusability and stability in successive cycles and avoids the secondary pollution caused by conventional organic and metalliferous promotors.Therefore,metal-free BC boosting Fe(Ⅲ)/H_(2)O_(2) oxidation of organics provides a green and advanced strategy for water decontamination.
基金the financial support received from the management of SSN。
文摘High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates(FML)has been explored.Both single and multiple projectiles impact conditions were considered.Ti/GFRP FML targets were fabricated with addition of 5%and 10%weight percentage of boron carbide(B_(4)C)particles.Mechanical properties of Ti/GFRP FML targets were determined as per ASTM standards.High velocity ballistic experiments were conducted using Armour Piercing Projectile(APP)of diameter 7.62 mm and velocity ranging between 350 and 450 m/s.Depth of penetration of the projectile into the target was measured.The deformation behaviour of Ti/GFRP targets with and without the presence of ceramic powder(B_(4)C)was investigated.“Ductile hole growth”failure mode was observed for pure GFRP target when subjected to single projectile impact whereas“plugging”failure mode was noted for Ti/GFRP targets.The presence of B_(4)C(5%by weight)particles has significantly improved the ballistic resistance of the Ti/GFRP FML target by offering frictional resistance to the projectile penetration.Further addition(10%by weight)of B_(4)C has reduced the ballistic performance due to agglomeration.None of the targets showed‘brittle cracking’or‘fragmentation’failures.When compared to the published results of Aluminium(Al 1100/GFRP and Al 6061/GFRP)FMLs,Ti/GFRP FML showed lesser DoP which increases its potential application to aerospace industry.
基金Financial assistance from Armament research board,New Delhi,India
文摘High strength-to-weight ratio of non-ferrous alloys, such as aluminium, magnesium and titanium alloys, are considered to be possible replacement of widely accepted steels in transportation and automobile sectors. Among these alloys, magnesium is self explosive and titanium is costlier, and aluminium is most likely to replace steels. Application of aluminium or its alloys is also thought of as an appropriate replacement in defence field, especially to enhance the easiness in mobility of combat vehicles while maintaining the same standard as that of conventional armour grade steels. Hence most of the investigations have been confined to aluminium or its alloys as base material and open an era of developing the newer composite materials to address the major limitation, i.e. tribological properties. The surface composites can be fabricated by incorporating the ceramic carbides like silicon carbide, carbides of transition metals and oxides of aluminium using surface modification techniques, such as high energy laser melt treatment, high energy electron beam irradiation and thermal spray process which are based on fusion route. These techniques yield the fusion related problems, such as interfacial reaction, pin holes, shrinkage cavities or voids and other casting related defects, and pave the way to need of an efficient technique which must be based on solid state. Recently developed friction stir processing technique was used in the present investigation for surface modification of AA7075 aluminum alloy, which is an alternative to steels. In the present investigation, 160 μm sized boron carbide powder was procured and was reduced to 60 μm and 30 μm using high energy ball mill. Subsequently these powders were used to fabricate the surface composites using friction stir processing.Ballistic performance testing as per the military standard(JIS.0108.01) was carried out. In the present work, an analytical method of predicting the ballistic behavior of surface composites was developed. This method was based on energy balance, i.e., the initial energy of impact is same as that of energy absorbed by multi layers. An attempt also has been made to validate the analytical results with the experimental findings. Variation between the analytical and experimental results may be accounted due to the assumptions considering such as isotropic behavior of target and shearing area of contact as cylindrical instead of conical interface As the analytical model yields the ballistic performance in the closer proximity of experimentally obtained, it can be considered to be an approximation to evaluate the ballistic performance of targets.
基金by the National Natural Science Foundation of China(52002299)。
文摘Reduced graphene oxide(rGO)enhanced B_(4)C ceramics was prepared by SPS sintering,the enhancement effect of rGO on the microstructure and mechanical properties of composites was studied through experiments and numerical simulation.The results show that the composite with 2wt%rGO has the best comprehensive mechanical properties.Compared with pure boron carbide,vickers hardness and bending strength are increased by 4.8%and 21.96%,respectively.The fracture toughness is improved by 25.71%.The microstructure observation shows that the improvement of mechanical properties is mainly attributed to the pullout and bridge mechanism of rGO and the crack deflection.Based on the cohesive force finite element method,the dynamic crack growth process of composites was simulated.The energy dissipation of B_(4)C/rGO multiphase ceramics during crack propagation was calculated and compared with that of pure boron carbide ceramics.The results show that the fracture energy dissipation can be effectively increased by adding graphene.
文摘Microstructure of plasma spray boron carbide coating was studied by SEM and TEM. its physical, mechanical and electrical properties were measured. The results showed that high microhardness. modulus and low porosity of B4C coating were manufactured by plasma spray. It was lamellar packing and dense. The B4C coating examined here contained two principal structures and two impurity phase besides major phase. The relatively small value of Young’s modulus, comparing with that of the bulk materials, is explained by porosity. The Fe impurity phase could account for the relatively high electrical conductivity of boron carbide coating by comparing with the general boron carbide materials.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 51871114 and 12064013)the Natural Science Foundation of Jiangxi Province, China (Grant No. 20202BAB214010)+3 种基金the Research Foundation of the Education Department of Jiangxi Province, China (Grant Nos. GJJ180433 and GJJ180477)the Open Funds of the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, China (Grant No. 201906)the Ganzhou Science and Technology Innovation Project, China (Grant No. 201960)the Jiangxi University of Science and Technology Scientific Research Starting Foundation, China (Grant No. jxxjbs17053).
文摘Boron carbide (B4C) is a rhombic structure composed of icosahedra and atomic chains, which has an important application in armored materials. The application of B4C under super high pressure without failure is a hot spot of research. Previous studies have unmasked the essential cause of B4C failure, i.e., its structure will change subjected to impact, especially under the non-hydrostatic pressure and shear stress. However, the change of structure has not been clearly understood nor accurately determined. Here in this paper, we propose several B4C polymorphs including B4C high pressure phases with non-icosahedra, which are denoted as post-B4C and their structures are formed due to icosahedra broken and may be obtained through high pressure and high temperature (HPHT). The research of their physical properties indicates that these B4C polymorphs have outstanding mechanical and electrical properties. For instance, aP10, mC10, mP20, and oP10-B4C are conductive superhard materials. We hope that our research will enrich the cognition of high pressure structural deformation of B4C and broaden the application scope of B4C.
基金the National Key R&D Program of China(Grant No.2017YFB0703200)National Natural Science Foundation of China(Grant Nos.51702100 and 51972268)China Postdoctoral Science Foundation(Grant No.2018M643075)for the financial support.
文摘Chemical vapor deposition is an important method for the preparation of boron carbide.Knowledge of the correlation between the phase composition of the deposit and the deposition conditions (temperature,inlet gas composition,total pressure,reactor configuration,and total flow rate) has not been completely determined.In this work,a novel approach to identify the kinetic mechanisms for the deposit composition is presented.Machine leaning (ML) and computational fluid dynamic (CFD) techniques are utilized to identify core factors that influence the deposit composition.It has been shown that ML,combined with CFD,can reduce the prediction error from about 25% to 7%,compared with the ML approach alone.The sensitivity coefficient study shows that BHCl_(2 )and BCl_(3) produce the most boron atoms,while C_(2)H_(4) and CH_(4) are the main sources of carbon atoms.The new approach can accurately predict the deposited boron-carbon ratio and provide a new design solution for other multi-element systems.
基金This work was supported by the National Natural Science Foundation of China(Grant No.52172062)the Beijing Natural Science Foundation(Grant No.2182007).
文摘Due to the complex products and irradiation-induced defects, it is hard to understand and even predict the thermal conductivity variation of materials under fast neutron irradiation, such as the abrupt degradation of thermal conductivity of boron carbide (B_(4)C) at the very beginning of the irradiation process. In this work, the contributions of various irradiation-induced defects in B_(4)C primarily consisting of the substitutional defects, Frenkel defect pairs, and helium bubbles were re-evaluated separately and quantitatively in terms of the phonon scattering theory. A theoretical model with an overall consideration of the contributions of all these irradiation-induced defects was proposed without any adjustable parameters, and validated to predict the thermal conductivity variation under irradiation based on the experimental data of the unirradiated, irradiated, and annealed B_(4)C samples. The predicted thermal conductivities by this model show a good agreement with the experimental data after irradiation. The calculation results and theoretical analysis in light of the experimental data demonstrate that the substitutional defects of boron atoms by lithium atoms, and the Frenkel defect pairs due to the collisions with the fast neutrons, rather than the helium bubbles with strain fields surrounding them, play determining roles in the abrupt degradation of thermal conductivity with burnup.
基金financially supported by the National Natural Science Foundation of China (Nos. 51521001 and 51832003)
文摘Carbide boronizing is a promising approach to obtain fine grained boron carbide based ceramics with improved mechanical properties. In this work, reaction process, microstructural characteristics and mechanical properties of BxC-TaB2(x = 3.7, 4.9, 7.1) ceramics were comprehensively investigated via this method. Dense BxC-TaB2 ceramics with refined microstructure were obtained from submicro tantalum carbide and boron powder mixtures at 1800℃/50 MPa/5 min by spark plasma sintering. The stoichiometry of boron carbide was determined from lattice parameters and Raman shift. It was found that uniformly distributed TaB2 grains in the BxC matrix is favor of the densification process and restricting grain growth.Besides, planar defects with high density were observed from the as-formed B7.1 C grains and transient stress was considered to contribute to the densification involved with plastic deformation. Microstructural observations indicate the dissolution of oxygen in the TaB2 lattice and most of the B7.1 C/TaB2 phase boundaries were clean. Owing to the highly faulted structure and finer grain size, as-obtained BxC-TaB2 ceramics exhibit high Vickers hardness(33.3–34.4 GPa at 9.8 N) and relatively high flexural strength ranging from 440 to 502 MPa.
基金financially supported by the Scientific Researched Project Department of Ondokuz Mayιs University(No.PYO.MUH.1901.20.001)。
文摘The fabrication of boron carbide reinforced aluminum matrix composites(Al-B_(4)C)with various contents of B_(4)C(1wt%,6wt%,15wt%,and 30wt%)was performed by powder metallurgy,and the influence of the content of B_(4)C on their mechanical and tribological behavior was examined.The Al-30B_(4)C composites recorded the highest density(~2.54 g/cm^(3)),lowest porosity(4%),maximum Vickers hardness(HV~75),lowest weight loss(0.4 mg),and lowest specific wear rate(0.00042 mm^(3)/(N·m))under a load of 7 N,with an enhancement of 167%in hardness,a decrease of 75.8%in weight loss,and a decrease of 76.7%in the specific wear rate compared with pure aluminum.In addition,the scanning electron microscope images of the worn surface revealed that the Al-B_(4)C composite has the narrowest wear groove of 0.85 mm at a load of 7 N,and the main wear mechanism was observed as an abrasive wear mechanism.According to the friction analysis,the coefficient of friction between surfaces increased with increasing boron carbide content and with decreasing applied load.In conclusion,B_(4)C is an effective reinforcement material in terms of tribological and mechanical performance of the Al-B_(4)C composites.
基金supported in part by the National Natural Science Foundation of China (No. 52077211)
文摘The significant advantage of proton therapy over other particle-based techniques is in the unique physical characteristics of the Bragg peak.It can achieve a highly conformal dose distribution and maximize the probability of tumor control by varying the irradiation energy.Most proton facilities use cyclotrons for fixed energy beam extraction and are equipped with degrader and collimator systems for energy modulation and emittance suppression.However,interactions between charged particles and degrader materials inevitably cause beam loss and divergence and deteriorate beam performance,which present great challenges for downstream transport and clinical treatment.In this work,we investigate a method of energy reduction by combining boron carbide and graphite in a degrader to obtain greater beam transmission at lower energy.The results demonstrate that the beam size and emittance at the exit of the combined degrader diverge less than those of multi-wedge one in the energy range of 70-160 MeV.Correspondingly,the transmission efficiency after the first dipole also shows improvements of 36.26%at 70 MeV and 70.55%at 110 MeV.As a component with a high activity level,the degrader causes additional ambient radiation during operation.Residual induced radiation even remains several hours after system shutdown.Analysis of material activation and induced radiation based on 1 h irradiation with a 400 nA beam current shows that the combined degrader has a definite advantage in shielding despite producing more secondary particles.Both radioactivity and average ambient dose equivalent are reduced by 50%compared with the multiwedge degrader at the important cooling time of 1 h.After 12 h and 24 h of cooling,the radiation levels of degraders decrease slightly due to the presence of long half-life residual nuclides.The average dose generated from the multi-wedge degrader is still 1.25 times higher than that of the combined one.
基金The support for this work was provided by the National Natural Science Foundation of China(Project No.51676100).
文摘Presented herein is an experimental study on the combustion of B4C/KNO3 binary pyrotechnic system.Combustion products were tested using X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive spectrometer(EDS).According to the results of tests and CEA calculation,the combustion reaction equation was established.The flames and burning rates were recorded by a high speed camera and a spectrophotometer.The effect of B4C particle size on the thermal sensitivity of B4C/KNO3 was investigated by differential scanning calorimetry(DSC)techniques.In addition,a reliable method for calculating the flame temperature was proposed.Based on the results of experiments,the combustion reaction mechanism was briefly analyzed.The burning rate,flame temperature and thermal sensitivity of B4C/KNO3 increase with the decrease of B4C particle size.The mass ratio of B4C/KNO3 has a great effect on combustion properties.Oxidizer-rich compositions have low flame temperatures,low burning rates,and provide green light emission.The combustion reactions of fuel-rich compositions are vigorous,and the B4C/KNO3 with mass ratio of 25:75 has the highest burning rate and the highest flame temperature.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11704340 and 11804305)the Scientific and Technology Project in Henan Province,China(Grant No.202102210198).
文摘By doping titanium hydride(TiH2) into boron carbide(B4C), a series of B4C + x wt% TiH2(x = 0, 5, 10, 15, and 20)composite ceramics were obtained through spark plasma sintering(SPS). The effects of the sintering temperature and the amount of TiH2 additive on the microstructure, mechanical and electrical properties of the sintered B4C-TiB2 composite ceramics were investigated. Powder mixtures of B4C with 0–20 wt% TiH2 were heated from 1400℃ to 1800℃ for 20 min under 50 MPa. The results indicated that higher sintering temperatures contributed to greater ceramic density. With increasing TiH2 content, titanium diboride(TiB2) formed between the TiH2 and B4C matrix. This effectively improved Young’s modulus and fracture toughness of the composite ceramics, significantly improving their electrical properties: the electrical conductivity reached 114.9 S·cm-1 at 1800℃ when x = 20. Optimum mechanical properties were obtained for the B4C ceramics sintered with 20 wt% TiH2, which had a relative density of 99.9±0.1%, Vickers hardness of 31.8 GPa,and fracture toughness of 8.5 MPa·m1/2. The results indicated that the doping of fine Ti particles into the B4C matrix increased the conductivity and the fracture toughness of B4C.
基金supported financially by grants from the National Natural Science Foundation of China (NSFC)(No. 51972243 and51521001)。
文摘There is a strength and fracture toughness tradeoff in nanoceramic composite. The strength varies reciprocally with the grain size whereas the toughness contributed by compressive residual stress increases with the dimension of the second phase. In this work, a novel duplex microstructure with reinforced clusters composing of nanosized grains was proposed and validated using a model system of B_(4)C-TiB_(2) ceramics densified by carbide boronizing. As-obtained ceramics exhibit excellent combined mechanical properties at room temperature, including Vickers hardness, Young's modulus, flexural strength and fracture toughness(by surface crack in flexure method) of 32.1 ± 2.7 GPa, 506.9 ± 2.0 GPa,1175 ± 71 MPa and 5.1 ± 0.4 MPa m^(0.5), respectively. Both strength and toughness are at least ~30 % higher than the counterparts with similar composition but homogenously distributed TiB_(2) grains. Graphite onion was confirmed to be an intermediate product during reactive sintering, it facilitated the grain pullout during fracture and retained the nanometric TiB_(2) grain in the cluster, both of which also contribute the toughening and strengthening mechanisms in the B_(4)C-TiB_(2) ceramics.
基金financially supported by the Bingol University Scientific Research Projects Coordination Unit (No.BAP-SBF.2017.00.001)
文摘Cu matrix composite materials reinforced with B4C particle at four different contents(1.5 wt%,3.0 wt%,4.5 wt% and 6.0 wt%) and also CuAl matrix composites with 13 wt% Al reinforced with B4C particle at four different contents(1.5 wt%,3.0 wt%,4.5 wt% and 6.0 wt%)were fabricated by hot pressing(HP) and a powder metallurgy(PM) process.Experimental samples were produced by keeping them at 880℃ at the constant pressure of 2.3×10~8 Pa for 6 min.The density,microstructure and mechanical properties of the produced samples were examined.The microstructure and phase examinations were carried out by scanning electron microscope(SEM)and optical microscope(OM),energy-dispersive spectrometer(EDS) and X-ray diffractometer(XRD) analysis.The hardness measurements,three-point bending test and impact test were conducted to determine the mechanical properties.As a result of the examinations,it was observed that the relative density values decreased with the increasing content of B4C and provided a relatively effective bonding.Moreover,it was homogeneously distributed in the produced specimens.Consequently,there was a considerable increase in the hardness and the bending strength of CuAl matrix specimens with Al addition.