In recent years,environmental pollution and energy crisis have become increasingly serious issues owing to the burning of fossil fuels.Among the many technologies,decomposition of water to produce hydrogen has attract...In recent years,environmental pollution and energy crisis have become increasingly serious issues owing to the burning of fossil fuels.Among the many technologies,decomposition of water to produce hydrogen has attracted much attention because of its sustainability and non-polluting characteristic.However,highly efficient decomposition of water that is driven by visible light is still a challenge.Herein,we report the large-scale preparation of step-scheme porous graphite carbon nitride/Zn0.2Cd0.8S-diethylenetriamine(Pg-C3N4/Zn0.2Cd0.8S-DETA)composite by a facile solvothermal method.It was found by UV-vis spectroscopy that 15%Pg-C3N4/Zn0.2Cd0.8S-DETA exhibited suitable visible absorption edge and band gap for water decomposition.The hydrogen production rate of 15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite was 6.69 mmol g^-1 h^-1,which was 16.73,1.61,and 1.44 times greater than those of Pg-C3N4,CdS-DETA,and Zn0.2Cd0.8S-DETA,respectively.In addition,15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite displayed excellent photocatalytic stability,which was maintained for seven cycles of photocatalytic water splitting test.We believe that 15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite can be a valuable guide for the development of solar hydrogen production applications in the near future.展开更多
To further improve the charge separation and photocatalytic activities of g-C3N4 and CdMoO4 under visible light irradiation,CdMoO4/g-C3N4 composites were rationally synthesized by a facile precipitation-calcination pr...To further improve the charge separation and photocatalytic activities of g-C3N4 and CdMoO4 under visible light irradiation,CdMoO4/g-C3N4 composites were rationally synthesized by a facile precipitation-calcination procedure.The crystal phases,morphologies,chemical compositions,textural structures,and optical properties of the as-prepared composites were characterized by the corresponding analytical techniques.The photocatalytic activities toward degradation of rhodamine B solution were evaluated under visible light irradiation.The results revealed that integrating CdMoO4 with g-C3N4 could remarkably improve the charge separation and photocatalytic activity,compared with those of pristine g-C3N4 and CdMoO4.This would be because the CdMoO4/g-C3N4 composites could facilitate the transfer and separation of the photoexcited electron-hole pairs,which was confirmed by electrochemical impedance spectroscopy,transient photocurrent responses,and photoluminescence measurements.Moreover,active species trapping experiments demonstrated that holes(h+)and superoxide radicals(?O2?)were the main active species during the photocatalytic reaction.A possible photocatalytic mechanism was proposed on the basis of the energy band structures determined by Mott-Schottky tests.This work would provide further insights into the rational fabrication of composites for organic contaminant removal.展开更多
Pressureless infiltration process to synthesize Si3N4/Al composite was investigated. Al-2%Mg alloy was infiltrated into Si3N4 and Si3N4 containing 10% Al2O3 preforms in the atmosphere of nitrogen. It is possible to in...Pressureless infiltration process to synthesize Si3N4/Al composite was investigated. Al-2%Mg alloy was infiltrated into Si3N4 and Si3N4 containing 10% Al2O3 preforms in the atmosphere of nitrogen. It is possible to infiltrate Al-2%Mg alloy in Si3N4 and Si3N4 containing 10% Al2O3 preforms. The growth of the dense composite of useful thickness was facilitated by the presence of magnesium powder at the interface and by flowing nitrogen. During infiltration Si3N4 reacted with aluminium to form Si and AlN, the growth of composite was found to proceed in two ways, depending on the Al2O3 content in the initial preform. Firstly, preform without Al2O3 content gives rise to AlN, Al3.27Si0.47 and Al type phases after infiltration. Secondly, perform with 10% Al2O3 content gives rise to AlN-Al2O3 solid solution phase (AlON), MgAl2O4, Al and Si type phases. AlON phase was only present in composite, containing 10% Al2O3 in the Si3N4 preforms before infiltration.展开更多
Aluminum-matrix boron carbide (B4Cp/Al) is a kind of neutron absorbing material widely used in nuclear spent fuel storage. In order to improve the tensile property of B4Cp/Al composites, a new type of nano-Al2O3 parti...Aluminum-matrix boron carbide (B4Cp/Al) is a kind of neutron absorbing material widely used in nuclear spent fuel storage. In order to improve the tensile property of B4Cp/Al composites, a new type of nano-Al2O3 particle (Al2O3np) reinforced B4Cp/Al + Al2O3np composites were prepared by powder metallurgy method. The Monte Carlo particle transport program (MCNP) was used to determine the influence of Al2O3np on the thermal neutron absorptivity of composites. The universal material testing machine and scanning electron microscope (SEM) were used to study the mechanical properties, microstructure and fracture morphology of B4Cp/Al composites. The results indicated that the neutron absorption properties of B4Cp/Al composites were not affected by the addition of nano-Al2O3 particles in the range of 1 wt%-15 wt%. The addition of Al2O3np can obviously reduce the grain size of B4Cp/Al matrix metals thus improve the tensile strength of the composites. The addition threshold of Al2O3np is about 2.5 wt%. Both B4Cp and Al2O3np change the fracture characteristics of the composites from toughness to brittleness, and the latter is more important.展开更多
Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN (30%, mass fraction) composite ceramics with La203 as sintering additive wer...Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN (30%, mass fraction) composite ceramics with La203 as sintering additive were prepared by hot-pressing at 1 800 ℃ and subsequently annealed at 1 450 ℃ and 1 850 ℃ for 2 h and 4 h, respectively. The materials were characterized by XRD and SEM. The effect of annealing process on the phase composition, sintering performance, microstructure, bending strength, dielectric loss and thermal conductivity of the materials was investigated. The results showed that both annealing at 1 850 ℃ and 1 450 ℃ promoted the phase transformation of α-Si3N4 to β-Si3N4. After annealing at 1 850 ℃, grain growth to a certain extent occurred in the materials. Especially, the elongated β-Si3N4 grains showed a slight increase in diameter from 0.2 μm to 0.6 μm approximately and a decrease in aspect ratio. As a result, as the annealing time increased to 4 h, the bending strength declined from 456 MPa to 390 MPa, whereas the dielectric loss decreased to 2.15× 10^-3 and the thermal conductivity increased to 16.3 W/(m.K) gradually. When annealed at 1 450 ℃, increasing the annealing time to 4 h significantly promoted the crystallization of glassy phase to La2Si6N803 phase in the materials, which led to the increase in bending strength to 619 MPa and thermal conductivity to 15.9 W/(m·K), respectively, and simultaneously the decrease in dielectric loss to 1.53× 10^-3.展开更多
Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the ...Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the composites were increased by the addition of SiC platelet until the content up to 20 vol pct. A slight decrease in flexural Strength was measured at room temperature with increasing SiC platelet content. The high temperature flexural strength tests at 1150, 1250, and 1350℃ were conducted. It was found that the flexural strength at elevated temperature was degraded with the rising temperature, and the downward trend of flexural strength for the composite containing 10 vol. pct SiC platelet was less. The results indicate that SiC platelet had a positive influence on the high temperature strength. Effects of SiC platelet reinforcement were presented展开更多
Polypyrrole‐modified graphitic carbon nitride composites(PPy/g‐C3N4)are fabricated using an in‐situ polymerization method to improve the visible light photocatalytic activity of g‐C3N4.The PPy/g‐C3N4 is applied t...Polypyrrole‐modified graphitic carbon nitride composites(PPy/g‐C3N4)are fabricated using an in‐situ polymerization method to improve the visible light photocatalytic activity of g‐C3N4.The PPy/g‐C3N4 is applied to the photocatalytic degradation of methylene blue(MB)under visible light irradiation.Various characterization techniques are employed to investigate the relationship between the structural properties and photoactivities of the as‐prepared composites.Results show that the specific surface area of the PPy/g‐C3N4 composites increases upon assembly of the amorphous PPy nanoparticles on the g‐C3N4 surface.Owing to the strong conductivity,the PPy can be used as a transition channel for electrons to move onto the g‐C3N4 surface,thus inhibiting the recombination of photogenerated carriers of g‐C3N4 and improving the photocatalytic performance.The elevated light adsorption of PPy/g‐C3N4 composites is attributed to the strong absorption coefficient of PPy.The composite containing 0.75 wt%PPy exhibits a photocatalytic efficiency that is 3 times higher than that of g‐C3N4 in 2 h.Moreover,the degradation kinetics follow a pseudo‐first‐order model.A detailed photocatalytic mechanism is proposed with·OH and·O2-radicals as the main reactive species.The present work provides new insights into the mechanistic understanding of PPy in PPy/g‐C3N4 composites for environmental applications.展开更多
Si3N4/TiC nanocomposite ceramics have been fabricated by hot pressing technique with Al2O3 and Y2O3 as additives. The results showed that well dispersed composite powder was carried out by adding dispersant and adjust...Si3N4/TiC nanocomposite ceramics have been fabricated by hot pressing technique with Al2O3 and Y2O3 as additives. The results showed that well dispersed composite powder was carried out by adding dispersant and adjusting pH values of suspensions. Remarkable increase in flexural strength at room temperatures was obtained by adding nanoparticles in Si3N4 matrix with 10% (wt pct) of nano-Si3N4 and 15% of nano-TiC. The flexural strength, fracture toughness and hardness were 1025 MPa, 7.5 MPa.m^1/2 and 15.6 GPa, respectively. The microstructures of materials were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which indicated that TiC nanoparticles distribute in the matrix and at the grain boundaries. According to the fracture form, low contents of nano particles could refine matrix grains and lead to the crack deflection as well as crack pinning. The multiplex microstructure was formed by mixing nano-Si3N4 particles. The crack trajectories exhibited crack deflection, rod-like grain bridging and pull-out.展开更多
Novel visible light-induced Cr-doped Sr Ti O3-g-C3N4 composite photocatalysts were synthesized by introducing polymeric g-C3N4. The composite photocatalyst was characterized by X-ray diffraction(XRD), high-resolutio...Novel visible light-induced Cr-doped Sr Ti O3-g-C3N4 composite photocatalysts were synthesized by introducing polymeric g-C3N4. The composite photocatalyst was characterized by X-ray diffraction(XRD), high-resolution transmission electron microscopy(HRTEM), Fourier transform infrared(FT-IR) spectroscopy, UV-vis diffuse reflection spectroscopy, photoluminescence(PL) spectroscopy and BET surface area measurements. The photocatalytic oxidation ability of the novel composite photocatalyst was evaluated using methyl orange(MO) as a target pollutant. The photocatalysts exhibited a significantly enhanced photocatalytic performance in degrading MO. The optimal g-C3N4 content for the photodegradation activity of the composite photocatalysts was determined. The as-prepared composite photocatalyst exhibits an improved photocatalytic activity due to enhancement of photo-generated electron-hole separation at the interface.展开更多
The novel visible light-induced carbon nitride(g-C3N4) and Bi VO4 composite photocatalysts were obtained through a simple mixing-calcination method. The physical and photophysical properties of the Bi VO4-g-C3N4 com...The novel visible light-induced carbon nitride(g-C3N4) and Bi VO4 composite photocatalysts were obtained through a simple mixing-calcination method. The physical and photophysical properties of the Bi VO4-g-C3N4 composites were investigated by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, UV-vis diffuse reflection spectroscopy, high-resolution transmission electron microscopy(HRTEM), photoluminescent(PL) spectroscopy, and BET surface area measurements. Photocatalytic oxidation ability of the prepared samples was examined by studying the degradation of rhodamine B(Rh B) as a target pollutant under visible-light irradiation. The composite photocatalysts exhibited an enhanced photocatalytic performance in degrading Rh B. The optimal g-C3N4 content of the composite photocatalysts was determined for the photodegradation activity. The improved photocatalytic activity of the as-prepared composite photocatalyst may be attributed to the enhancement of photo-generated electron-hole separation at the interface.展开更多
The photocatalytic reduction of aqueous Cr(VI)to Cr(III)was preliminarily studied using porousg‐C3N4as a photocatalyst under acidic conditions.The observed synergistic photocatalytic effect ofporous g‐C3N4on a Cr(VI...The photocatalytic reduction of aqueous Cr(VI)to Cr(III)was preliminarily studied using porousg‐C3N4as a photocatalyst under acidic conditions.The observed synergistic photocatalytic effect ofporous g‐C3N4on a Cr(VI)/4‐chlorophenol(4‐CP)composite pollution system was further studiedunder different pH conditions.Compared with single‐component photocatalytic systems for Cr(VI)reduction or4‐CP degradation,the Cr(VI)reduction efficiency and4‐CP degradation efficiency weresimultaneously improved in the Cr(VI)/4‐CP composite pollution system.The synergistic photocatalyticeffect in the Cr(VI)/4‐CP composite pollution system can be attributed to the acceleratedredox reaction between dichromate and4‐CP by electron transfer with porous g‐C3N4.展开更多
The tribological behaviour of gravity die stir cast LM6alloy with graphite(Gr)and silicon nitride nanoparticles was investigated.Al?Gr?Si3N4hybrid composite,Al?Si3N4nanocomposite and Al?Gr nanocomposites were separate...The tribological behaviour of gravity die stir cast LM6alloy with graphite(Gr)and silicon nitride nanoparticles was investigated.Al?Gr?Si3N4hybrid composite,Al?Si3N4nanocomposite and Al?Gr nanocomposites were separately fabricated to investigate their frictional and wear characteristics under dry sliding conditions.EDS was used to ensure the uniform presence of nano Si3N4and graphite in the cast.L9orthogonal array method was chosen to conduct the experiments to study the effect of different applied loads(20,30and40N)and sliding distances(1,2and3km).The results showed that the respective wear rate and coefficient of friction(COF)decreased by25%and15%for hybrid composite when compared with those of Al?Si3N4nanocomposite whereas the wear rate and COF of Al?Gr was found to be very minimal.The micro Vickers hardness of the hybrid composite was14%more than that of the simple nanocomposite and there was not much notable variation for Al?Gr and Al?Si3N4nanocomposite materials.Scanning electron microscope was used to analyze the worn surface and subsurface,from which it was noted that the predominant wear mechanisms observed were abrasive for nanocomposite and both abrasive and adhesive mechanism for hybrid composite.Analysis of variance(ANOVA)and F-test were used to check the validity model and to determine the significant parameters affecting the wear rates.展开更多
The creep behaviour of β-Si3N4 whisker reinforced Al-8.5Fe-1.3V-1.7Si composite has been investigated at the temperature 773 and 823 K. The results are characterized by high stress exponent and high apparent creep ac...The creep behaviour of β-Si3N4 whisker reinforced Al-8.5Fe-1.3V-1.7Si composite has been investigated at the temperature 773 and 823 K. The results are characterized by high stress exponent and high apparent creep activation energy The creep data can be interpreted based on the incorporation of a threshold Stress and a load transfer coefficient into the power-law creep equation. A good correlation between the normalized creep rate and normalized effective stress is available which demonstrates that the creep behaviour of both the alloy and the composite is controlled by the matrix lattice self-diffusion in AI. EXamination on microstructure shows that edge dislocations exist at the interfaces between two adjacent whiskers and the intedeces emit edge dislocations in parallel paired-columns.展开更多
Si3N4/SiC nanocomposites are well known and attractive for advanced ceramic applications due to excellent mechanlcal and thermal properties, which make them suitable for use in turbine engines, heat exchangers, and ot...Si3N4/SiC nanocomposites are well known and attractive for advanced ceramic applications due to excellent mechanlcal and thermal properties, which make them suitable for use in turbine engines, heat exchangers, and other sophisticated applications. However, without the presence of additives, the fabrication of Si3N4/SiC composites is difficult. The additives form a liquid phase during sintering and facilitate the densification of the composite. However, the additives present a drawback at high temperatures since they decrease the mechanical properties of the composites. Recently, Si3N4/SiC composites were fabricated via the polymer precursor route without any additives, using electric field assisted sintering (EFAS). In this study, fully densified Si3N4/SiC nanocomposites incorporating hexagonal-BN were successfully fabricated by hot pressing without any additives at 1700 ℃ for 2 h under vacuum at a pressure of 50 MPa (via the amorphous precursor route). Moreover, the incorporation of additives and h-BN is found to decrease the content of SiC. The phase transformation, densification, microstructure, and mechanical properties were discussed and presented.展开更多
The microstructure and tensile properties of Al_4C_3 dispersion strengthened Al composite fabricated by reaction milling technique were investigated.It is indicated that the rod-like Al_4C_3 dispersoids having a diame...The microstructure and tensile properties of Al_4C_3 dispersion strengthened Al composite fabricated by reaction milling technique were investigated.It is indicated that the rod-like Al_4C_3 dispersoids having a diameter of 0.02-0.03 μm and a length of 0.1-0.3μm are formed by reaction of C with Al, and uniformly distributed in the Al matrix.The interface between Al_4C_3 and Al is clean and the interfacial bonding is good.The matrix consists of the subgrains which have the size of 0.3-0.4μm, and most of the Al_4C_3 dispersoids are distributed on the subgrain boundaries.The 11 vol.-% Al_4C_3/Al composite exhibits an UTS (ultimate tensile strength) of 400 MPa and an elongation-to-failure of 8.0%.展开更多
The Si_3N_4 whisker reinforced 6061Al composite with bending strength of 790 MPa was prepared by squeeze casting process.After heat-treatment under T6 regime i.e.530℃, 1 h solutioning and 160℃,24 h aging,an incremen...The Si_3N_4 whisker reinforced 6061Al composite with bending strength of 790 MPa was prepared by squeeze casting process.After heat-treatment under T6 regime i.e.530℃, 1 h solutioning and 160℃,24 h aging,an increment in strength and microhardness may be over 20% and 28% respectively,The microstructures of Si_3N_4 whisker and Si_3N_4/Al interface were observed by meas of HRTEM.The relation between interracial structure and composite properties was discussed.展开更多
icrostructure and mechanical properties of Al_4C_3 and Al_2O_3 dispersion strengthened aluminum composite fabricated by mechanical attrition and hotpressing consolidation method were studied. It was shown that fine we...icrostructure and mechanical properties of Al_4C_3 and Al_2O_3 dispersion strengthened aluminum composite fabricated by mechanical attrition and hotpressing consolidation method were studied. It was shown that fine well developed Al_4C_3 stick and equiaxed γAl_2O_3 dispersoids with total content of about 6.6 v% uniformly distributed within the Al grains or along the grain boundaries. The Al/Al_4C_3 and Al/Al_2O_3 interfaces are very clean and well bonded at atomic level, but have no fixed orientation relationships between the dispersoids and the aluminum matrix exists. At ambient and especially elevated temperatures, strength and stiffness of the composite are much higher than that of P/M Al and even better than that of the 15 v% SiCw/Al composite.展开更多
The equilibrium phases and adiabatic temperature for combustion synthesis and reaction hot pressing of Al 2O 3/B 4C employing ① Al, B 2O 3 and C ② C, B, Al 2O 3 as starting reactants were analyzed by the CALP...The equilibrium phases and adiabatic temperature for combustion synthesis and reaction hot pressing of Al 2O 3/B 4C employing ① Al, B 2O 3 and C ② C, B, Al 2O 3 as starting reactants were analyzed by the CALPHAD technique. It is shown that the equilibrium phases at the adiabatic temperature in the combusion system (1) are not the intended composite Al 2O 3/B 4C but other phases. Good agreement with the experimental data was achieved for the calculated adiabatic temperature. The results were discussed with respect to the elimination of the by product in the combustion synthesis. It also revealed that the reactant mixture (2) is a weak exothermic or endothermic reaction system, which can be employed in the reaction hot pressing.展开更多
Si_(3)N_(4p)/2024Al composite was fabricated by squeeze casting method and treated by extrusion deformation.Microstructure analyses indicate that Si_(3)N_(4) particles in the composite are in cylindrical polyhedron sh...Si_(3)N_(4p)/2024Al composite was fabricated by squeeze casting method and treated by extrusion deformation.Microstructure analyses indicate that Si_(3)N_(4) particles in the composite are in cylindrical polyhedron shape.Extrusion deformation is beneficial to uniform distribution of Si_(3)N_(4) particles and improves the relative density of Si_(3)N_(4p)/2024Al composite.Tensile strength of Si_(3)N_(4p)/2024Al composite increases by 76.6%after T6 treatment,and after extrusion and T6 treatment it is by 57.6%more than T6 treatment only.Elastic modulus of Si_(3)N_(4p)/2024Al composite increases a little after T6 treatment but increases by 33.5%after extrusion deformation.展开更多
基金supported by the National Natural Science Foundation of China(51572103,51502106)the Distinguished Young Scholar of Anhui Province(1808085J14)+2 种基金the Foundation for Young Talents in College of Anhui Province(gxyqZD2017051)the Key Foundation of Educational Commission of Anhui Province(KJ2016SD53)Innovation Team of Design and Application of Advanced Energetic Materials(KJ2015TD003)~~
文摘In recent years,environmental pollution and energy crisis have become increasingly serious issues owing to the burning of fossil fuels.Among the many technologies,decomposition of water to produce hydrogen has attracted much attention because of its sustainability and non-polluting characteristic.However,highly efficient decomposition of water that is driven by visible light is still a challenge.Herein,we report the large-scale preparation of step-scheme porous graphite carbon nitride/Zn0.2Cd0.8S-diethylenetriamine(Pg-C3N4/Zn0.2Cd0.8S-DETA)composite by a facile solvothermal method.It was found by UV-vis spectroscopy that 15%Pg-C3N4/Zn0.2Cd0.8S-DETA exhibited suitable visible absorption edge and band gap for water decomposition.The hydrogen production rate of 15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite was 6.69 mmol g^-1 h^-1,which was 16.73,1.61,and 1.44 times greater than those of Pg-C3N4,CdS-DETA,and Zn0.2Cd0.8S-DETA,respectively.In addition,15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite displayed excellent photocatalytic stability,which was maintained for seven cycles of photocatalytic water splitting test.We believe that 15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite can be a valuable guide for the development of solar hydrogen production applications in the near future.
基金supported by the Open Project Program of Hubei Key Laboratory of Animal Nutrition and Feed Science,Wuhan Polytechnic University(No.201808)Hubei Important Project of Technological Innovation(2018ABA094)~~
文摘To further improve the charge separation and photocatalytic activities of g-C3N4 and CdMoO4 under visible light irradiation,CdMoO4/g-C3N4 composites were rationally synthesized by a facile precipitation-calcination procedure.The crystal phases,morphologies,chemical compositions,textural structures,and optical properties of the as-prepared composites were characterized by the corresponding analytical techniques.The photocatalytic activities toward degradation of rhodamine B solution were evaluated under visible light irradiation.The results revealed that integrating CdMoO4 with g-C3N4 could remarkably improve the charge separation and photocatalytic activity,compared with those of pristine g-C3N4 and CdMoO4.This would be because the CdMoO4/g-C3N4 composites could facilitate the transfer and separation of the photoexcited electron-hole pairs,which was confirmed by electrochemical impedance spectroscopy,transient photocurrent responses,and photoluminescence measurements.Moreover,active species trapping experiments demonstrated that holes(h+)and superoxide radicals(?O2?)were the main active species during the photocatalytic reaction.A possible photocatalytic mechanism was proposed on the basis of the energy band structures determined by Mott-Schottky tests.This work would provide further insights into the rational fabrication of composites for organic contaminant removal.
文摘Pressureless infiltration process to synthesize Si3N4/Al composite was investigated. Al-2%Mg alloy was infiltrated into Si3N4 and Si3N4 containing 10% Al2O3 preforms in the atmosphere of nitrogen. It is possible to infiltrate Al-2%Mg alloy in Si3N4 and Si3N4 containing 10% Al2O3 preforms. The growth of the dense composite of useful thickness was facilitated by the presence of magnesium powder at the interface and by flowing nitrogen. During infiltration Si3N4 reacted with aluminium to form Si and AlN, the growth of composite was found to proceed in two ways, depending on the Al2O3 content in the initial preform. Firstly, preform without Al2O3 content gives rise to AlN, Al3.27Si0.47 and Al type phases after infiltration. Secondly, perform with 10% Al2O3 content gives rise to AlN-Al2O3 solid solution phase (AlON), MgAl2O4, Al and Si type phases. AlON phase was only present in composite, containing 10% Al2O3 in the Si3N4 preforms before infiltration.
基金Funded by Natural National Science Foundation of China(NSFC)(No.11305149)National High-Tech R&D Program(863 Program)(No.2013AA030704)。
文摘Aluminum-matrix boron carbide (B4Cp/Al) is a kind of neutron absorbing material widely used in nuclear spent fuel storage. In order to improve the tensile property of B4Cp/Al composites, a new type of nano-Al2O3 particle (Al2O3np) reinforced B4Cp/Al + Al2O3np composites were prepared by powder metallurgy method. The Monte Carlo particle transport program (MCNP) was used to determine the influence of Al2O3np on the thermal neutron absorptivity of composites. The universal material testing machine and scanning electron microscope (SEM) were used to study the mechanical properties, microstructure and fracture morphology of B4Cp/Al composites. The results indicated that the neutron absorption properties of B4Cp/Al composites were not affected by the addition of nano-Al2O3 particles in the range of 1 wt%-15 wt%. The addition of Al2O3np can obviously reduce the grain size of B4Cp/Al matrix metals thus improve the tensile strength of the composites. The addition threshold of Al2O3np is about 2.5 wt%. Both B4Cp and Al2O3np change the fracture characteristics of the composites from toughness to brittleness, and the latter is more important.
基金Project(50872052) supported by the National Natural Science Foundation of ChinaProject(2009AA05Z313) supported by the National High Technology Research and Development Program of ChinaProject supported by the Commission of Science,Technology and Industry for National Defence,China
文摘Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN (30%, mass fraction) composite ceramics with La203 as sintering additive were prepared by hot-pressing at 1 800 ℃ and subsequently annealed at 1 450 ℃ and 1 850 ℃ for 2 h and 4 h, respectively. The materials were characterized by XRD and SEM. The effect of annealing process on the phase composition, sintering performance, microstructure, bending strength, dielectric loss and thermal conductivity of the materials was investigated. The results showed that both annealing at 1 850 ℃ and 1 450 ℃ promoted the phase transformation of α-Si3N4 to β-Si3N4. After annealing at 1 850 ℃, grain growth to a certain extent occurred in the materials. Especially, the elongated β-Si3N4 grains showed a slight increase in diameter from 0.2 μm to 0.6 μm approximately and a decrease in aspect ratio. As a result, as the annealing time increased to 4 h, the bending strength declined from 456 MPa to 390 MPa, whereas the dielectric loss decreased to 2.15× 10^-3 and the thermal conductivity increased to 16.3 W/(m.K) gradually. When annealed at 1 450 ℃, increasing the annealing time to 4 h significantly promoted the crystallization of glassy phase to La2Si6N803 phase in the materials, which led to the increase in bending strength to 619 MPa and thermal conductivity to 15.9 W/(m·K), respectively, and simultaneously the decrease in dielectric loss to 1.53× 10^-3.
文摘Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the composites were increased by the addition of SiC platelet until the content up to 20 vol pct. A slight decrease in flexural Strength was measured at room temperature with increasing SiC platelet content. The high temperature flexural strength tests at 1150, 1250, and 1350℃ were conducted. It was found that the flexural strength at elevated temperature was degraded with the rising temperature, and the downward trend of flexural strength for the composite containing 10 vol. pct SiC platelet was less. The results indicate that SiC platelet had a positive influence on the high temperature strength. Effects of SiC platelet reinforcement were presented
文摘Polypyrrole‐modified graphitic carbon nitride composites(PPy/g‐C3N4)are fabricated using an in‐situ polymerization method to improve the visible light photocatalytic activity of g‐C3N4.The PPy/g‐C3N4 is applied to the photocatalytic degradation of methylene blue(MB)under visible light irradiation.Various characterization techniques are employed to investigate the relationship between the structural properties and photoactivities of the as‐prepared composites.Results show that the specific surface area of the PPy/g‐C3N4 composites increases upon assembly of the amorphous PPy nanoparticles on the g‐C3N4 surface.Owing to the strong conductivity,the PPy can be used as a transition channel for electrons to move onto the g‐C3N4 surface,thus inhibiting the recombination of photogenerated carriers of g‐C3N4 and improving the photocatalytic performance.The elevated light adsorption of PPy/g‐C3N4 composites is attributed to the strong absorption coefficient of PPy.The composite containing 0.75 wt%PPy exhibits a photocatalytic efficiency that is 3 times higher than that of g‐C3N4 in 2 h.Moreover,the degradation kinetics follow a pseudo‐first‐order model.A detailed photocatalytic mechanism is proposed with·OH and·O2-radicals as the main reactive species.The present work provides new insights into the mechanistic understanding of PPy in PPy/g‐C3N4 composites for environmental applications.
基金supported by the National Natural Sci ence Foundation of China(No.50105011)the Foundation for the author by the National Excellent Doctoral Disserta tion of China(200231)+2 种基金the Natural Science Foundation of Shandong Province(Y2004F14)the SRF for ROCS([2002]247),MOE,Chinathe SRF for ROCS(2002[247]),SEM.
文摘Si3N4/TiC nanocomposite ceramics have been fabricated by hot pressing technique with Al2O3 and Y2O3 as additives. The results showed that well dispersed composite powder was carried out by adding dispersant and adjusting pH values of suspensions. Remarkable increase in flexural strength at room temperatures was obtained by adding nanoparticles in Si3N4 matrix with 10% (wt pct) of nano-Si3N4 and 15% of nano-TiC. The flexural strength, fracture toughness and hardness were 1025 MPa, 7.5 MPa.m^1/2 and 15.6 GPa, respectively. The microstructures of materials were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which indicated that TiC nanoparticles distribute in the matrix and at the grain boundaries. According to the fracture form, low contents of nano particles could refine matrix grains and lead to the crack deflection as well as crack pinning. The multiplex microstructure was formed by mixing nano-Si3N4 particles. The crack trajectories exhibited crack deflection, rod-like grain bridging and pull-out.
基金Funded by the National Natural Science Foundation of China(No.51208102)
文摘Novel visible light-induced Cr-doped Sr Ti O3-g-C3N4 composite photocatalysts were synthesized by introducing polymeric g-C3N4. The composite photocatalyst was characterized by X-ray diffraction(XRD), high-resolution transmission electron microscopy(HRTEM), Fourier transform infrared(FT-IR) spectroscopy, UV-vis diffuse reflection spectroscopy, photoluminescence(PL) spectroscopy and BET surface area measurements. The photocatalytic oxidation ability of the novel composite photocatalyst was evaluated using methyl orange(MO) as a target pollutant. The photocatalysts exhibited a significantly enhanced photocatalytic performance in degrading MO. The optimal g-C3N4 content for the photodegradation activity of the composite photocatalysts was determined. The as-prepared composite photocatalyst exhibits an improved photocatalytic activity due to enhancement of photo-generated electron-hole separation at the interface.
基金Funded by the National Natural Science Foundation of China(No.51208102)
文摘The novel visible light-induced carbon nitride(g-C3N4) and Bi VO4 composite photocatalysts were obtained through a simple mixing-calcination method. The physical and photophysical properties of the Bi VO4-g-C3N4 composites were investigated by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, UV-vis diffuse reflection spectroscopy, high-resolution transmission electron microscopy(HRTEM), photoluminescent(PL) spectroscopy, and BET surface area measurements. Photocatalytic oxidation ability of the prepared samples was examined by studying the degradation of rhodamine B(Rh B) as a target pollutant under visible-light irradiation. The composite photocatalysts exhibited an enhanced photocatalytic performance in degrading Rh B. The optimal g-C3N4 content of the composite photocatalysts was determined for the photodegradation activity. The improved photocatalytic activity of the as-prepared composite photocatalyst may be attributed to the enhancement of photo-generated electron-hole separation at the interface.
基金supported by the National Natural Science Foundation of China(51568049,51468043,21366024,21665018)the National Science Fund for Excellent Young Scholars(51422807)+2 种基金the Natural Science Foundation of Jiangxi Province,China(20161BAB206118,20171ACB21035)the Distinguished Youth Science Fund of Jiangxi Province(20162BCB23043)the Natural Science Foundation of Jiangxi Provincial Department of Education,China(GJJ14515)~~
文摘The photocatalytic reduction of aqueous Cr(VI)to Cr(III)was preliminarily studied using porousg‐C3N4as a photocatalyst under acidic conditions.The observed synergistic photocatalytic effect ofporous g‐C3N4on a Cr(VI)/4‐chlorophenol(4‐CP)composite pollution system was further studiedunder different pH conditions.Compared with single‐component photocatalytic systems for Cr(VI)reduction or4‐CP degradation,the Cr(VI)reduction efficiency and4‐CP degradation efficiency weresimultaneously improved in the Cr(VI)/4‐CP composite pollution system.The synergistic photocatalyticeffect in the Cr(VI)/4‐CP composite pollution system can be attributed to the acceleratedredox reaction between dichromate and4‐CP by electron transfer with porous g‐C3N4.
文摘The tribological behaviour of gravity die stir cast LM6alloy with graphite(Gr)and silicon nitride nanoparticles was investigated.Al?Gr?Si3N4hybrid composite,Al?Si3N4nanocomposite and Al?Gr nanocomposites were separately fabricated to investigate their frictional and wear characteristics under dry sliding conditions.EDS was used to ensure the uniform presence of nano Si3N4and graphite in the cast.L9orthogonal array method was chosen to conduct the experiments to study the effect of different applied loads(20,30and40N)and sliding distances(1,2and3km).The results showed that the respective wear rate and coefficient of friction(COF)decreased by25%and15%for hybrid composite when compared with those of Al?Si3N4nanocomposite whereas the wear rate and COF of Al?Gr was found to be very minimal.The micro Vickers hardness of the hybrid composite was14%more than that of the simple nanocomposite and there was not much notable variation for Al?Gr and Al?Si3N4nanocomposite materials.Scanning electron microscope was used to analyze the worn surface and subsurface,from which it was noted that the predominant wear mechanisms observed were abrasive for nanocomposite and both abrasive and adhesive mechanism for hybrid composite.Analysis of variance(ANOVA)and F-test were used to check the validity model and to determine the significant parameters affecting the wear rates.
文摘The creep behaviour of β-Si3N4 whisker reinforced Al-8.5Fe-1.3V-1.7Si composite has been investigated at the temperature 773 and 823 K. The results are characterized by high stress exponent and high apparent creep activation energy The creep data can be interpreted based on the incorporation of a threshold Stress and a load transfer coefficient into the power-law creep equation. A good correlation between the normalized creep rate and normalized effective stress is available which demonstrates that the creep behaviour of both the alloy and the composite is controlled by the matrix lattice self-diffusion in AI. EXamination on microstructure shows that edge dislocations exist at the interfaces between two adjacent whiskers and the intedeces emit edge dislocations in parallel paired-columns.
基金supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012000858)
文摘Si3N4/SiC nanocomposites are well known and attractive for advanced ceramic applications due to excellent mechanlcal and thermal properties, which make them suitable for use in turbine engines, heat exchangers, and other sophisticated applications. However, without the presence of additives, the fabrication of Si3N4/SiC composites is difficult. The additives form a liquid phase during sintering and facilitate the densification of the composite. However, the additives present a drawback at high temperatures since they decrease the mechanical properties of the composites. Recently, Si3N4/SiC composites were fabricated via the polymer precursor route without any additives, using electric field assisted sintering (EFAS). In this study, fully densified Si3N4/SiC nanocomposites incorporating hexagonal-BN were successfully fabricated by hot pressing without any additives at 1700 ℃ for 2 h under vacuum at a pressure of 50 MPa (via the amorphous precursor route). Moreover, the incorporation of additives and h-BN is found to decrease the content of SiC. The phase transformation, densification, microstructure, and mechanical properties were discussed and presented.
文摘The microstructure and tensile properties of Al_4C_3 dispersion strengthened Al composite fabricated by reaction milling technique were investigated.It is indicated that the rod-like Al_4C_3 dispersoids having a diameter of 0.02-0.03 μm and a length of 0.1-0.3μm are formed by reaction of C with Al, and uniformly distributed in the Al matrix.The interface between Al_4C_3 and Al is clean and the interfacial bonding is good.The matrix consists of the subgrains which have the size of 0.3-0.4μm, and most of the Al_4C_3 dispersoids are distributed on the subgrain boundaries.The 11 vol.-% Al_4C_3/Al composite exhibits an UTS (ultimate tensile strength) of 400 MPa and an elongation-to-failure of 8.0%.
文摘The Si_3N_4 whisker reinforced 6061Al composite with bending strength of 790 MPa was prepared by squeeze casting process.After heat-treatment under T6 regime i.e.530℃, 1 h solutioning and 160℃,24 h aging,an increment in strength and microhardness may be over 20% and 28% respectively,The microstructures of Si_3N_4 whisker and Si_3N_4/Al interface were observed by meas of HRTEM.The relation between interracial structure and composite properties was discussed.
文摘icrostructure and mechanical properties of Al_4C_3 and Al_2O_3 dispersion strengthened aluminum composite fabricated by mechanical attrition and hotpressing consolidation method were studied. It was shown that fine well developed Al_4C_3 stick and equiaxed γAl_2O_3 dispersoids with total content of about 6.6 v% uniformly distributed within the Al grains or along the grain boundaries. The Al/Al_4C_3 and Al/Al_2O_3 interfaces are very clean and well bonded at atomic level, but have no fixed orientation relationships between the dispersoids and the aluminum matrix exists. At ambient and especially elevated temperatures, strength and stiffness of the composite are much higher than that of P/M Al and even better than that of the 15 v% SiCw/Al composite.
文摘The equilibrium phases and adiabatic temperature for combustion synthesis and reaction hot pressing of Al 2O 3/B 4C employing ① Al, B 2O 3 and C ② C, B, Al 2O 3 as starting reactants were analyzed by the CALPHAD technique. It is shown that the equilibrium phases at the adiabatic temperature in the combusion system (1) are not the intended composite Al 2O 3/B 4C but other phases. Good agreement with the experimental data was achieved for the calculated adiabatic temperature. The results were discussed with respect to the elimination of the by product in the combustion synthesis. It also revealed that the reactant mixture (2) is a weak exothermic or endothermic reaction system, which can be employed in the reaction hot pressing.
基金Project(HITQNJS.2008.057)Supported by Development Program for Outstanding Young Teachers in Harbin Institute of Technology,China。
文摘Si_(3)N_(4p)/2024Al composite was fabricated by squeeze casting method and treated by extrusion deformation.Microstructure analyses indicate that Si_(3)N_(4) particles in the composite are in cylindrical polyhedron shape.Extrusion deformation is beneficial to uniform distribution of Si_(3)N_(4) particles and improves the relative density of Si_(3)N_(4p)/2024Al composite.Tensile strength of Si_(3)N_(4p)/2024Al composite increases by 76.6%after T6 treatment,and after extrusion and T6 treatment it is by 57.6%more than T6 treatment only.Elastic modulus of Si_(3)N_(4p)/2024Al composite increases a little after T6 treatment but increases by 33.5%after extrusion deformation.