Hypoeutectic and hypereutectic Al2O3-ZrO2 multiphase ceramics-lined composite pipes were produced by using the gravitational separation self-propagate high-temperature synthesis （SHS） process. The microstructure of ...Hypoeutectic and hypereutectic Al2O3-ZrO2 multiphase ceramics-lined composite pipes were produced by using the gravitational separation self-propagate high-temperature synthesis （SHS） process. The microstructure of the ceramics was observed by means of SEM and EPMA. The fracture toughness of the multiphase ceramics was tested by using the Vickers indentation method. The fracture toughness of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.96 MPa·m^1/2 and that of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.23 MPa·m^1/2. The toughening mechanisms were systematically investigated by means of SEM and XRD. The results show that the bridging toughening mechanism, stress induced ZrO2 transformation toughening mechanism, and microcrack toughening mechanism are the predominant toughening mechanism.展开更多
Fe–Fe2O3–MnO2–sucrose–epoxy resin and O2 as reaction system and feed gas,separately,were used to prepare micro-nano hollow multiphase ceramic microspheres containing MnFe2O4absorbent by self-reactive quenching met...Fe–Fe2O3–MnO2–sucrose–epoxy resin and O2 as reaction system and feed gas,separately,were used to prepare micro-nano hollow multiphase ceramic microspheres containing MnFe2O4absorbent by self-reactive quenching method which is integrated with flame jet,selfpropagating high-temperature synthesis(SHS),and rapidly solidification.The morphologies and phase compositions of hollow microspheres were studied by scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD),and energy dispersive spectroscopy.The results show that the quenching products are regular spherical substantially with hollow structure,particle size is between few hundreds nanometers and 5 lm.Phase compositions are diphase of Fe3O4,Mn3O4,and MnFe2O4,and the spinel soft magnetic ferrite MnFe2O4 with microwave magnetic properties is in majority.Collisions with each other,burst as well as‘‘refinement’’of agglomerate powders in flame field may be the main reasons for the formation of micro-nano hollow multiphase ceramic microspheres containing MnFeOabsorbent.展开更多
The isothermal oxidation behavior and mechanism of the TiC-TiB2 multiphase ceramics fabricated by self-propagating high temperature synthesis were studied.The result shows that the oxidation kinetics agrees to the par...The isothermal oxidation behavior and mechanism of the TiC-TiB2 multiphase ceramics fabricated by self-propagating high temperature synthesis were studied.The result shows that the oxidation kinetics agrees to the parabolic rule within the temperature rang of RT to 1000℃. First at 600℃ TiB2 was oxidized to be TiO2. Then both TiB2 and TiC were oxidized to be TiO2 when temperature increased to 1000℃. A compact TiO2 film, the oxidation product, formed on the sample surface, which prevented further oxidation and resulted in a very high oxidation resistance of the sample.展开更多
Utilizing SHS Reactive Flame Spraying (RFS) technology, TiC-TiB2-Al2O3 multiphase ceramics coatings were produced on steel substrate. Phase constituents and microstructure of the ceramic coatings were analyzed. The pr...Utilizing SHS Reactive Flame Spraying (RFS) technology, TiC-TiB2-Al2O3 multiphase ceramics coatings were produced on steel substrate. Phase constituents and microstructure of the ceramic coatings were analyzed. The procedure of chemical combustion and structure transformation, reactive mechanism, and solidifying behavior during spaying were emphasized. Reactants which influenced on SHS spraying was discussed. SHS reactive spraying processes were studied. Mechanical properties of the coatings were tested.展开更多
3Y-TZP/3wt%Al_(2)O_(3) powder was coated with varying amounts of BN using the urea and borate reaction sintering method,and then multiphase ceramics were prepared by hot pressing sintering.The micro-topography and the...3Y-TZP/3wt%Al_(2)O_(3) powder was coated with varying amounts of BN using the urea and borate reaction sintering method,and then multiphase ceramics were prepared by hot pressing sintering.The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy,transmission electron microscopy and X-ray diffraction.A mechanical tester was used to analyze the Vickers hardness,fracture toughness,and bending strength of the synthesized ceramics.The results showed that the ceramic with a BN content of 12wt%showed the best processability,but had diminished mechanical properties(such as fracture toughness and bending strength).The ceramic with a BN content of 9wt%showed better processability than those with 3wt%and 6wt%BN.However,the fracture toughness was affected by the addition of 9wt%BN,making this ceramic only usable as a base material for a three-unit fixed bridge.In contrast,the ceramics with a BN content of 3wt%or 6wt%fulfilled the criteria for use in multi-unit restoration,but their low processability made them unsuitable for milling after sintering.展开更多
In reactive-hot-pressed ZrB_(2)-SiC-ZrC ceramics,ZrO_(2) was found to replace ZrC phase,hence leading to confusion in designing ultra-high-temperature ceramics(UHTCs).We employ high-precision X-ray diffraction and ele...In reactive-hot-pressed ZrB_(2)-SiC-ZrC ceramics,ZrO_(2) was found to replace ZrC phase,hence leading to confusion in designing ultra-high-temperature ceramics(UHTCs).We employ high-precision X-ray diffraction and electron microscopies to reassess the phase behavior during entire reaction and densification and to reveal the evolution of multiphase relationship at different stages before reaching the final ZrB2-SiC-ZrO_(2) composition.Frozen from transient liquid-phase,bulk glassy phase of 15 vol% was found to be constituted of Zr-Si-B-C-O with stable Zr:O ratio,which starts as early as in the intermediate stage to suppress ZrC in favor of SiC nucleation.Inhomogeneity in phase relations and microstructures results from variation in local transient liquid-phase to develop SiC phase in various modes and rates.As inferred from the earlier report of phase formation,competing reactions for ZrC and ZrB_(2) phases in the initial stage below 1000℃ were mediated via Zr-O-B-C liquid phase.Such liquid phase was moderated by stable B-O components,as initiated from surface oxides of starting powders.This picture under a continuous mother liquid phase can unify the reactions and sintering into a collective meltingenucleationegrowth process,which enables and guides the evolution of multiphase relationship through several stages to reach final densification at relatively low temperature with the help of residual oxides.展开更多
Pressure hulls play an important role in deep-sea underwater vehicles.However,in the ultra-high pressure environment,a highly destructive phenomenon could occur to them which is called implosion.To study the character...Pressure hulls play an important role in deep-sea underwater vehicles.However,in the ultra-high pressure environment,a highly destructive phenomenon could occur to them which is called implosion.To study the characteristics of the flow field of the underwater implosion of hollow ceramic pressure hulls,the compressible multiphase flow theory,direct numerical simulation,and adaptive mesh refinement are used to numerically simulate the underwater implosion of a single ceramic pressure hull and multiple linearly arranged ceramic pressure hulls.Firstly,the feasibility of the numerical simulation method is verified.Then,the results of the flow field of the underwater implosion of hollow ceramic pressure hulls in 11000 m depth is analyzed.There are the compression-rebound processes of the internal air cavity in the implosion.In the rebound stage,a shock wave that is several times the ambient pressure is generated outside the pressure hull,and the propagation speed is close to the speed of sound.The pressure peak of the shock wave has a negative exponential power function relationship with the distance to the center of the sphere.Finally,it is found that the obvious superimposed effect between spheres exists in the chain-reaction implosion which enhances the implosion shock wave.展开更多
文摘Hypoeutectic and hypereutectic Al2O3-ZrO2 multiphase ceramics-lined composite pipes were produced by using the gravitational separation self-propagate high-temperature synthesis （SHS） process. The microstructure of the ceramics was observed by means of SEM and EPMA. The fracture toughness of the multiphase ceramics was tested by using the Vickers indentation method. The fracture toughness of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.96 MPa·m^1/2 and that of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.23 MPa·m^1/2. The toughening mechanisms were systematically investigated by means of SEM and XRD. The results show that the bridging toughening mechanism, stress induced ZrO2 transformation toughening mechanism, and microcrack toughening mechanism are the predominant toughening mechanism.
基金supported by the ational Natural Science Foundation of China (No. 51172282)
文摘Fe–Fe2O3–MnO2–sucrose–epoxy resin and O2 as reaction system and feed gas,separately,were used to prepare micro-nano hollow multiphase ceramic microspheres containing MnFe2O4absorbent by self-reactive quenching method which is integrated with flame jet,selfpropagating high-temperature synthesis(SHS),and rapidly solidification.The morphologies and phase compositions of hollow microspheres were studied by scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD),and energy dispersive spectroscopy.The results show that the quenching products are regular spherical substantially with hollow structure,particle size is between few hundreds nanometers and 5 lm.Phase compositions are diphase of Fe3O4,Mn3O4,and MnFe2O4,and the spinel soft magnetic ferrite MnFe2O4 with microwave magnetic properties is in majority.Collisions with each other,burst as well as‘‘refinement’’of agglomerate powders in flame field may be the main reasons for the formation of micro-nano hollow multiphase ceramic microspheres containing MnFeOabsorbent.
文摘The isothermal oxidation behavior and mechanism of the TiC-TiB2 multiphase ceramics fabricated by self-propagating high temperature synthesis were studied.The result shows that the oxidation kinetics agrees to the parabolic rule within the temperature rang of RT to 1000℃. First at 600℃ TiB2 was oxidized to be TiO2. Then both TiB2 and TiC were oxidized to be TiO2 when temperature increased to 1000℃. A compact TiO2 film, the oxidation product, formed on the sample surface, which prevented further oxidation and resulted in a very high oxidation resistance of the sample.
基金Supported by national natural science fund of P.R.China,No.50272084.
文摘Utilizing SHS Reactive Flame Spraying (RFS) technology, TiC-TiB2-Al2O3 multiphase ceramics coatings were produced on steel substrate. Phase constituents and microstructure of the ceramic coatings were analyzed. The procedure of chemical combustion and structure transformation, reactive mechanism, and solidifying behavior during spaying were emphasized. Reactants which influenced on SHS spraying was discussed. SHS reactive spraying processes were studied. Mechanical properties of the coatings were tested.
基金financially supported by the National Natural Science Foundation of China(No.81371183).
文摘3Y-TZP/3wt%Al_(2)O_(3) powder was coated with varying amounts of BN using the urea and borate reaction sintering method,and then multiphase ceramics were prepared by hot pressing sintering.The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy,transmission electron microscopy and X-ray diffraction.A mechanical tester was used to analyze the Vickers hardness,fracture toughness,and bending strength of the synthesized ceramics.The results showed that the ceramic with a BN content of 12wt%showed the best processability,but had diminished mechanical properties(such as fracture toughness and bending strength).The ceramic with a BN content of 9wt%showed better processability than those with 3wt%and 6wt%BN.However,the fracture toughness was affected by the addition of 9wt%BN,making this ceramic only usable as a base material for a three-unit fixed bridge.In contrast,the ceramics with a BN content of 3wt%or 6wt%fulfilled the criteria for use in multi-unit restoration,but their low processability made them unsuitable for milling after sintering.
基金financially supported by the National Natural Science Foundation of China(No.51532006)the Shanghai Municipal Science and Technology Commission(No.16DZ2260600)the 111 Project of the Ministry of Education and the National Bureau of Foreign Experts(No.D16002).
文摘In reactive-hot-pressed ZrB_(2)-SiC-ZrC ceramics,ZrO_(2) was found to replace ZrC phase,hence leading to confusion in designing ultra-high-temperature ceramics(UHTCs).We employ high-precision X-ray diffraction and electron microscopies to reassess the phase behavior during entire reaction and densification and to reveal the evolution of multiphase relationship at different stages before reaching the final ZrB2-SiC-ZrO_(2) composition.Frozen from transient liquid-phase,bulk glassy phase of 15 vol% was found to be constituted of Zr-Si-B-C-O with stable Zr:O ratio,which starts as early as in the intermediate stage to suppress ZrC in favor of SiC nucleation.Inhomogeneity in phase relations and microstructures results from variation in local transient liquid-phase to develop SiC phase in various modes and rates.As inferred from the earlier report of phase formation,competing reactions for ZrC and ZrB_(2) phases in the initial stage below 1000℃ were mediated via Zr-O-B-C liquid phase.Such liquid phase was moderated by stable B-O components,as initiated from surface oxides of starting powders.This picture under a continuous mother liquid phase can unify the reactions and sintering into a collective meltingenucleationegrowth process,which enables and guides the evolution of multiphase relationship through several stages to reach final densification at relatively low temperature with the help of residual oxides.
基金the support from the National Natural Sciences Foundation of China(51779139,U2067220)the National Key Research and Development Program of China(Grant No.2016YFC0300700)+1 种基金Shanghai Talent Development Funding(2018029)the Young Talent Project of China National Nuclear Corporation.
文摘Pressure hulls play an important role in deep-sea underwater vehicles.However,in the ultra-high pressure environment,a highly destructive phenomenon could occur to them which is called implosion.To study the characteristics of the flow field of the underwater implosion of hollow ceramic pressure hulls,the compressible multiphase flow theory,direct numerical simulation,and adaptive mesh refinement are used to numerically simulate the underwater implosion of a single ceramic pressure hull and multiple linearly arranged ceramic pressure hulls.Firstly,the feasibility of the numerical simulation method is verified.Then,the results of the flow field of the underwater implosion of hollow ceramic pressure hulls in 11000 m depth is analyzed.There are the compression-rebound processes of the internal air cavity in the implosion.In the rebound stage,a shock wave that is several times the ambient pressure is generated outside the pressure hull,and the propagation speed is close to the speed of sound.The pressure peak of the shock wave has a negative exponential power function relationship with the distance to the center of the sphere.Finally,it is found that the obvious superimposed effect between spheres exists in the chain-reaction implosion which enhances the implosion shock wave.
