Micrometer-sized diamonds were incorporated into silicon nitride(Si_(3)N_(4))matrix to manufacture high-performance Si_(3)N_(4)-based composites using spark plasma sintering at 1500℃under 50 MPa.The effects of the di...Micrometer-sized diamonds were incorporated into silicon nitride(Si_(3)N_(4))matrix to manufacture high-performance Si_(3)N_(4)-based composites using spark plasma sintering at 1500℃under 50 MPa.The effects of the diamond content on the phase composition,microstructure,mechanical properties and thermal conductivity of the composites were investigated.The results showed that the addition of diamond could effectively improve the hardness of the material.The thermal conductivity of Si_(3)N_(4)increased to 52.97 W/m·k at the maximum with the addition of 15 wt%diamond,which was 27.5%higher than that of the monolithic Si_(3)N_(4).At this point,the fracture toughness was 7.54 MPa·m^(1/2).Due to the addition of diamond,the composite material generated a new substance,MgSiN2,which effectively combined Si_(3)N_(4)with diamond.MgSiN2 might improve the hardness and thermal conductivity of the materials.展开更多
Ultrafine grain tungsten heavy alloys (WHAs) were successfully produced from the nano-crystalline powders using spark plasma sintering.The present study mainly discussed the effects of sintering temperature on the den...Ultrafine grain tungsten heavy alloys (WHAs) were successfully produced from the nano-crystalline powders using spark plasma sintering.The present study mainly discussed the effects of sintering temperature on the density,microstructure and mechanical properties of the alloys.The relative density of 98.12% was obtained at 1 050 ℃,and the tungsten grain size is about 871 nm.At 1 000 ℃-1 200 ℃,the mechanical properties of the alloys tend to first rise and then goes down.After SPS,the alloy exhibits improved hardness (84.3 HRA at 1 050 ℃) and bending strength (987.16 MPa at 1 100 ℃),due to the ultrafine-grained microstructure.The fracture mode after bending tests is mainly characterized as intergranular or intragranular fracture of W grains,interfacial debonding of W grains-binding phase and ductile tearing of binding phase.The EDS analysis reveals a certain proportion of solid solution between W and Ni-Fe binding phase.The good mechanical properties of the alloys can be attributed to grain refinement and solid solution strengthening.展开更多
B4C-TiB2-SiC composites with excellent properties were prepared by reactive hot-pressing using B4C,TiC,and Si powders as the raw materials.The phase transition process was investigated by heating the powder mixture to...B4C-TiB2-SiC composites with excellent properties were prepared by reactive hot-pressing using B4C,TiC,and Si powders as the raw materials.The phase transition process was investigated by heating the powder mixture to different temperatures and combined with XRD tests.TiB2 and SiC phases were synthesized through an in situ reaction,and the mechanical and thermal properties were improved simultaneously.Microstructure and mechanical properties were also studied,and the 60wt% B4C-21.6wt% TiB2-18.4wt% SiC composite showed a relative density of 99.1%,Vickers hardness of 34.6 GPa,flexural strength of 582 MPa,and fracture toughness of 5.08 MPa·m1/2.In addition,the values of thermal conductivity and thermal expansion coefficient were investigated,respectively.展开更多
Titanium diboride ceramic was produced via spark plasma sintering(SPS)using finer TiB_(2)powder made by high-speed planetary ball milling.The effects of ball milling parameters on the composites and particle size of T...Titanium diboride ceramic was produced via spark plasma sintering(SPS)using finer TiB_(2)powder made by high-speed planetary ball milling.The effects of ball milling parameters on the composites and particle size of TiB_(2)powder were investigated.It was shown that the average particle size of TiB_(2)powder decreased from 5.8 to 1.59μm and the wear rate of WC balls was 1.58 wt%,when the ball-to-powder weight ratio(BPR),the rotary speed and milling time and were 10:1,600 rpm and 20 min,respectively.The content of WC in TiB_(2)powder can be limited below 4.58 vol%by optimizing the milling conditions.The sintering temperature of TiB_(2)powder milled can be decreased obviously,and the mechanical properties are evidently improved and the microstructure becomes more homogeneous when the powder of TiB_(2)becomes finer.The relative density,hardness,bending strength,and fracture toughness of the TiB_(2)ceramic fabricated at 1700℃reach the optimal values,which are 98.13%,19.14 GPa,756 MPa,and 5.71 MPa·m~(1/2),respectively.The decrease of TiB_(2)particle size and the introduction of WC are the potential reasons for the improvement of TiB_(2)ceramic performance.展开更多
Silicon carbide ceramics with different thicknesses/diameter ratios were prepared by using ultra-fine silicon carbide powder with the sintering additives of 1.0 wt% boron and 1.5 wt% carbon. The influence of thickness...Silicon carbide ceramics with different thicknesses/diameter ratios were prepared by using ultra-fine silicon carbide powder with the sintering additives of 1.0 wt% boron and 1.5 wt% carbon. The influence of thickness/diameter ratio on the microstructure and density of SiC ceramics was investigated in detail. The experimental results show that the addition of boron and carbon sintering aids can promote the densification process of SiC ceramic, leading to the low sintering temperature and improve mechanical properties. At 1950 ℃, SiC ceramic with a density of 99% exhibits Young's modulus, hardness, and flexural strength of 476 MPa, 28.3 GPa, and 334 MPa, respectively. It is found that long holding time has a positive effect on the uniformity of the microstructure and density distribution of SiC ceramics with large thickness/diameter ratios. Additionally, the sintering additive of boron can solid-solve into SiC, and then facilitate the phase transformation of SiC to form 6H-SiC and 4H-SiC composite ceramics.展开更多
BiVO4 photocatalysts were synthesized by a surfactant free hydrothermal method without any further treatments,and characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron mic...BiVO4 photocatalysts were synthesized by a surfactant free hydrothermal method without any further treatments,and characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,ultraviolet-visible diffuse reflectance spectroscopy（UV-vis DRS）,Raman spectroscopy,and Brunauer-Emmett-Teller（BET） surface area techniques.The photocatalytic activity was evaluated for the degradation of the methylene blue（MB） under visible light irradiation.Seen from the structural and morphological characterization,it is stated that the obtained samples present monoclinic phase,and the pH value has significant influence on the morphologies.The enhanced photocatalytic performance was associated with its crystallinity,unique morphology,band gap energy,BET specific surface area,surface charge and adsorption capacity.The recycle experiments results show that the BiVO4 photocatalysts have excellent photo-stability,and we deduced a possible mechanism by examining the effects of the active species involved in the photocatalytic process for MB photocatalytic degradation.展开更多
基金Funded by the Key Research and Development Plan of Jiangxi Province(No.2020ZDYFB0017)the National Key Research and Development Plan(No.2021YFB3701400)the National Natural Science Foundation of China((No.92163208)。
文摘Micrometer-sized diamonds were incorporated into silicon nitride(Si_(3)N_(4))matrix to manufacture high-performance Si_(3)N_(4)-based composites using spark plasma sintering at 1500℃under 50 MPa.The effects of the diamond content on the phase composition,microstructure,mechanical properties and thermal conductivity of the composites were investigated.The results showed that the addition of diamond could effectively improve the hardness of the material.The thermal conductivity of Si_(3)N_(4)increased to 52.97 W/m·k at the maximum with the addition of 15 wt%diamond,which was 27.5%higher than that of the monolithic Si_(3)N_(4).At this point,the fracture toughness was 7.54 MPa·m^(1/2).Due to the addition of diamond,the composite material generated a new substance,MgSiN2,which effectively combined Si_(3)N_(4)with diamond.MgSiN2 might improve the hardness and thermal conductivity of the materials.
基金the National Key Research and Development Plan of China(2017YFB0310400)the National Natural Science Foundation of China(Nos.5167020705 and 51902233)the Self-determined and Innovative Research Funds of WHUT(2019III059XZ)。
文摘Ultrafine grain tungsten heavy alloys (WHAs) were successfully produced from the nano-crystalline powders using spark plasma sintering.The present study mainly discussed the effects of sintering temperature on the density,microstructure and mechanical properties of the alloys.The relative density of 98.12% was obtained at 1 050 ℃,and the tungsten grain size is about 871 nm.At 1 000 ℃-1 200 ℃,the mechanical properties of the alloys tend to first rise and then goes down.After SPS,the alloy exhibits improved hardness (84.3 HRA at 1 050 ℃) and bending strength (987.16 MPa at 1 100 ℃),due to the ultrafine-grained microstructure.The fracture mode after bending tests is mainly characterized as intergranular or intragranular fracture of W grains,interfacial debonding of W grains-binding phase and ductile tearing of binding phase.The EDS analysis reveals a certain proportion of solid solution between W and Ni-Fe binding phase.The good mechanical properties of the alloys can be attributed to grain refinement and solid solution strengthening.
基金Funded by the National Key Research and Development Plan of China(2017YFB0310400)the National Natural Science Foundation of China(5167020705)。
文摘B4C-TiB2-SiC composites with excellent properties were prepared by reactive hot-pressing using B4C,TiC,and Si powders as the raw materials.The phase transition process was investigated by heating the powder mixture to different temperatures and combined with XRD tests.TiB2 and SiC phases were synthesized through an in situ reaction,and the mechanical and thermal properties were improved simultaneously.Microstructure and mechanical properties were also studied,and the 60wt% B4C-21.6wt% TiB2-18.4wt% SiC composite showed a relative density of 99.1%,Vickers hardness of 34.6 GPa,flexural strength of 582 MPa,and fracture toughness of 5.08 MPa·m1/2.In addition,the values of thermal conductivity and thermal expansion coefficient were investigated,respectively.
基金Funded by the National Key Research and Development Plan of China(No.2017YFB0310400)the National Natural Science Foundation of China(No.5167020705)。
文摘Titanium diboride ceramic was produced via spark plasma sintering(SPS)using finer TiB_(2)powder made by high-speed planetary ball milling.The effects of ball milling parameters on the composites and particle size of TiB_(2)powder were investigated.It was shown that the average particle size of TiB_(2)powder decreased from 5.8 to 1.59μm and the wear rate of WC balls was 1.58 wt%,when the ball-to-powder weight ratio(BPR),the rotary speed and milling time and were 10:1,600 rpm and 20 min,respectively.The content of WC in TiB_(2)powder can be limited below 4.58 vol%by optimizing the milling conditions.The sintering temperature of TiB_(2)powder milled can be decreased obviously,and the mechanical properties are evidently improved and the microstructure becomes more homogeneous when the powder of TiB_(2)becomes finer.The relative density,hardness,bending strength,and fracture toughness of the TiB_(2)ceramic fabricated at 1700℃reach the optimal values,which are 98.13%,19.14 GPa,756 MPa,and 5.71 MPa·m~(1/2),respectively.The decrease of TiB_(2)particle size and the introduction of WC are the potential reasons for the improvement of TiB_(2)ceramic performance.
基金Funded by the National Key Research and Development Plan of China (No.2017YFB0310400)the National Natural Science Foundation of China (No.5167020705)
文摘Silicon carbide ceramics with different thicknesses/diameter ratios were prepared by using ultra-fine silicon carbide powder with the sintering additives of 1.0 wt% boron and 1.5 wt% carbon. The influence of thickness/diameter ratio on the microstructure and density of SiC ceramics was investigated in detail. The experimental results show that the addition of boron and carbon sintering aids can promote the densification process of SiC ceramic, leading to the low sintering temperature and improve mechanical properties. At 1950 ℃, SiC ceramic with a density of 99% exhibits Young's modulus, hardness, and flexural strength of 476 MPa, 28.3 GPa, and 334 MPa, respectively. It is found that long holding time has a positive effect on the uniformity of the microstructure and density distribution of SiC ceramics with large thickness/diameter ratios. Additionally, the sintering additive of boron can solid-solve into SiC, and then facilitate the phase transformation of SiC to form 6H-SiC and 4H-SiC composite ceramics.
基金Funded by the National Science Foundation of China(U12301013)the National Science Foundation of China(51521001)
文摘BiVO4 photocatalysts were synthesized by a surfactant free hydrothermal method without any further treatments,and characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,ultraviolet-visible diffuse reflectance spectroscopy（UV-vis DRS）,Raman spectroscopy,and Brunauer-Emmett-Teller（BET） surface area techniques.The photocatalytic activity was evaluated for the degradation of the methylene blue（MB） under visible light irradiation.Seen from the structural and morphological characterization,it is stated that the obtained samples present monoclinic phase,and the pH value has significant influence on the morphologies.The enhanced photocatalytic performance was associated with its crystallinity,unique morphology,band gap energy,BET specific surface area,surface charge and adsorption capacity.The recycle experiments results show that the BiVO4 photocatalysts have excellent photo-stability,and we deduced a possible mechanism by examining the effects of the active species involved in the photocatalytic process for MB photocatalytic degradation.
