The functional properties of BaTiO_(3)ceramics,produced by using the same pressing/sintering strategy from nanopowders with two distinct morphologies(cuboidal/equiaxed nanoparticles)and similar particle sizes,are comp...The functional properties of BaTiO_(3)ceramics,produced by using the same pressing/sintering strategy from nanopowders with two distinct morphologies(cuboidal/equiaxed nanoparticles)and similar particle sizes,are comparatively investigated.The sintered ceramics exhibit similar nanoscale structures,with faceted crystalline grains and crystalline inclusions,clean grain boundaries and well-defined 90°lamellar domains extending in some entire grains or finer nanodomains inside grain regions.The differences in the functional behavior originating from the different nanopowder morphology are described in terms of the nanoparticle assembly during the pressing step.The numerically simulated green body densification indicated a more efficient assembly resulting in higher density for the cubic particles(0.90 vs.0.84 relative density)and a more homogeneous pore distribution in the spherical-derived ones.As a result of the higher density after sintering,the functional properties are enhanced in cuboid-originated ceramics.For comparison,the ceramic produced from cubic nanoparticles sintered at T_(1)/T_(2)=1250/800℃shows higher permittivity(room temperature value of∼2100-cubic vs.∼1700-rounded),enhanced ferroelectric characteristics(cubic:P_(s)=8.57μC cm^(-2),P_(r)=0.95μC cm^(-2),and E_(c)=2.3 kV cm^(-1),with respect to P_(s)=6.06μC cm^(-2),P_(r)=0.4μC cm^(-2),and E_(c)=1.4 kV cm^(-1),for spherical-derived ones,measured at E_(max)=29.3 kV cm^(-1))and a stronger dc-field dependence of their permittivity of∼12%(cubic)vs.only∼2%(spherical),for a dc-applied field in the range of-15 kV cm^(-1)<Edc<15 kV cm^(-1).In contrast,the spherical particles-derived ceramics contain fewer defects and have a more homogeneous and finer porosity distribution in the ceramic volume and consequently,they are more stable and sustain larger field applications in comparison with the cubic-derived counterparts.展开更多
Silicon nitride (Si3N4) ceramic is an attractive material for dental applications, especially used as a dental core material, due to its unique properties including high fracture toughness, high strength, high wear re...Silicon nitride (Si3N4) ceramic is an attractive material for dental applications, especially used as a dental core material, due to its unique properties including high fracture toughness, high strength, high wear resistance and non-cytotoxicity. In this study, the Si3N4 ceramic was fabricated by a non-pressure sintering technique at a relatively low sintering temperature of 1650℃ in nitrogen atmosphere. Borosilicate glass and 5 wt% ZrO2-added borosilicate glass were used for coating on the Si3N4 core surface because of their compatibility in thermal expansion, high chemical resistance and bio-inert. The specimens were then fired in electric tube furnace at 1100℃. The Vickers microhardness of borosilicate glass and 5 wt% ZrO2-added borosilicate glass veneering materials were measured and compared with the commercial dental veneer porcelain as a control (VITA VMK 95). The cytotoxicity of the Si3N4 ceramic and the veneering materials were tested by MTT assay, using human gingival fibroblasts (HGF) and periodontal ligament fibroblasts (HPDLF). The results indicate that the Si3N4 ceramic and Si3N4 ceramic veneered with borosilicate glass or 5 wt% ZrO2-added borosilicate glass veneering materials tested in this study are not toxic to oral tissue and can be used to produce dental prostheses.展开更多
In order to get high-performance low voltage varistors,Cr2O3 doped ZnO ceramic thick films were fabricated by modified sol-gel process. The precursors were fabricated by dispersing doped-ZnO ceramic nano-powders in th...In order to get high-performance low voltage varistors,Cr2O3 doped ZnO ceramic thick films were fabricated by modified sol-gel process. The precursors were fabricated by dispersing doped-ZnO ceramic nano-powders in the sols,which were prepared by dissolving zinc acetate dihydrate into 2-methoxyethanol and stabilized by diethanolamine and glacial acetic acid and doped with a concentrated solution of bismuth nitrate,phenylstibonic acid,cobalt nitrate,manganese acetate and chromium nitrate. The results show that ZnCr2O4 phase can form in ZnO based ceramic films doped 1.0%(mole fraction) Cr2O3. Three secondary phases,such as Bi2O3,Zn7Sb2O12,and ZnCr2O4 phases,are detected in the thick films. The Raman spectra show that the intensity and the position of Raman bands of Zn7Sb2O12 and ZnCr2O4 phases change obviously with increasing Cr2O3 doping. The nonlinearity coefficient α of ZnO thick films is 7.0,the nonlinear voltage is 6 V,and the leakage current density is 0.7 μA/mm2.展开更多
以3.5PbO.96.5B2O3(m o l%)玻璃作为研究对象,着重研究其在不同重力条件下的分相现象。该部分讨论了2个落塔实验试样发生分相的重力条件,同时分析了试样的相组成和试样成分的不均匀性。结果发现,该成分玻璃发生分相后形成的富硼相和富...以3.5PbO.96.5B2O3(m o l%)玻璃作为研究对象,着重研究其在不同重力条件下的分相现象。该部分讨论了2个落塔实验试样发生分相的重力条件,同时分析了试样的相组成和试样成分的不均匀性。结果发现,该成分玻璃发生分相后形成的富硼相和富铅相都是玻璃相。分相在高重力阶段发生的试样其成分均匀性最差,原因在于富硼相和富铅相间存在较大的密度差。展开更多
TiO2-hydroxyapatite （HA） nanostructured coatings were produced by atmospheric plasma spray method. The effects of starting powder composition and grain size on their mechanical properties were investigated. The micr...TiO2-hydroxyapatite （HA） nanostructured coatings were produced by atmospheric plasma spray method. The effects of starting powder composition and grain size on their mechanical properties were investigated. The microstructure and morphology were characterized by X-ray diffraction and scanning electron microscopy （SEM）. It is found that the coating with 10% HA has the best mechanical properties. Based on Rietveld refinement method, the mean grain size of the as-received powder （212 nm） extensively decreases to 66.4 nm after 20 h of high-energy ball milling. In spite of grain growth, the deposited coatings maintain their nanostructures with the mean grain size of 112 nm. SEM images show that there is a lower porosity in the coating with a higher HA content. Optical microscopy images show that uniform thickness is obtained for all the coatings.展开更多
Using coal tar pitch as a matrix precursor to prepare carbon materials is widelyused by impregnation/carbonization processing technology.Four different grades of coaltar pitch and a natural pitch were characterized in...Using coal tar pitch as a matrix precursor to prepare carbon materials is widelyused by impregnation/carbonization processing technology.Four different grades of coaltar pitch and a natural pitch were characterized in terms of carbon yield, density, viscosity,and fractionation with solvents, as well as by thermal analysis methods.The suitability ofthese commercially available matrices for densification of 3 dimensional carbon-carboncomposites was examined.The theoretical results compared with experimental results.The highest density after impregnation was obtained using one of the coal tar pitches.Thepredicted results are in reasonable agreement with experiment data.The significance ofthis research is that a special heat treatment regime was conducted.The effects of modificationtemperature on the densification efficiency of composites were investigated andthen structure and characteristics of the composites were determined by scanning electronmicroscopy (SEM), Transmission electron microscopy (TEM) and X-Ray Diffraction (XRD).展开更多
The production of poly-α-olefins(PAOs)has attracted attention due to their excellent viscosity-temperature dependence,wear characteristics,oxidative properties,and high thermal stability.In this study,indene extracte...The production of poly-α-olefins(PAOs)has attracted attention due to their excellent viscosity-temperature dependence,wear characteristics,oxidative properties,and high thermal stability.In this study,indene extracted during coal tar refining was used as a raw material to synthesize a bis(indenyl)zirconium dichloride metallocene catalyst.A PAO with low viscosity and a high viscosity index was produced via the oligomerization of 1-decene in the presence of both the prepared metallocene and a methylaluminoxane(MAO)co-catalyst.Notably,the effects of different synthesis reaction parameters,such as Al:Zr ratio,amount of catalyst,and reaction temperature,on the conversion ratio and product selectivity were investigated in detail.The produced PAO was thoroughly characterized using Fourier-transform infrared,^(13)C,and^(1)H nuclear magnetic resonance spectroscopies;gas chromatography;and viscosity measurements.At 70℃,the metallocene catalyst created more stable active sites.In addition,the alkylation effect of MAO was noticeable.Interestingly,the obtained catalysis results demonstrated that a high conversion ratio of~93%was achieved at a low reaction temperature of 70℃,with a catalyst dosage of 0.0848 mmol and Al:Zr ratio of 8.48mmol:0.0848mmol.Moreover,under these optimal conditions,the kinematic viscosity of PAO was 4.25 mm2/s at 100℃,and the viscosity index was 139,indicating good viscosity-temperature properties.展开更多
Hollow silica microspheres （HSMSs） have been successfully fabricated via a facile hydrothermal route using D-glucose as the sacrificial template and sodium silicate powder as the silica precursor. The resulting sili...Hollow silica microspheres （HSMSs） have been successfully fabricated via a facile hydrothermal route using D-glucose as the sacrificial template and sodium silicate powder as the silica precursor. The resulting silica hollow particles were characterized by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）, and infrared spectroscopy （IR）. The surface area was determined using the BET method. SEM and TEM images exhibited micro-sized silica hollow particles with a size of -1.5μm.展开更多
The production of geopolymer binders from low-purity clays was investigated. Three low-purity clays were calcined at 750℃ for 4 h. The calcined clays were chemically activated by the alkaline solutions of NaOH and Na...The production of geopolymer binders from low-purity clays was investigated. Three low-purity clays were calcined at 750℃ for 4 h. The calcined clays were chemically activated by the alkaline solutions of NaOH and Na2SiO3. The compressive strength was measured as a function of curing time at room temperature and 85℃. The results were compared with those of a pure kaolin sample. An amorphous aluminosilicate polymer was formed in all binders at both processing temperatures. The results show that, the mechanical properties depend on the type and amount of active aluminum silicates in the starting clay material, the impurities, and the processing temperature.展开更多
Calcium phosphate cements have received much attention in recent decades owing to their biocompatibility, in situ handling, and shaping abilities. However, their low initial mechanical strength is still a major limita...Calcium phosphate cements have received much attention in recent decades owing to their biocompatibility, in situ handling, and shaping abilities. However, their low initial mechanical strength is still a major limitation. On the other hand, calcium aluminate cements (CACs) set fast and have a high initial strength and good corrosion resistance in contact with body fluids, making them excellent dental restorative materials. Therefore, the chemical, mechanical and biological properties of new-TCP/CA cement after aging in simulated body fluid (SBF) were investigated. The results indicated that the composites have setting times not appropriated for immediate applications and have degradation rates higher than those of the traditional CPCs. Moreover, the compressive strength of composite was lower than 5MPa and did not increase with SBF immersion. However, the α-TCP/CA composites showed a higher bioactivity at early stages and were not only more biocompatible but also more noncytotoxic.展开更多
Fe-WC nanocomposites were successfully fabricated by high-frequency induction heated sintering of ball milled nanostructure powders. The ball milled powders were characterized by X-ray diffraction. Density measurement...Fe-WC nanocomposites were successfully fabricated by high-frequency induction heated sintering of ball milled nanostructure powders. The ball milled powders were characterized by X-ray diffraction. Density measurements by the Archimedes method show that all sintered samples have the relative density higher than 95%. Studies on the effects of WC content, milling speed, and milling time indicate that a higher milling speed and a more WC content lead to the improvement of mechanical properties. There is a very good distribution of WC particles in the Fe matrix at the milling speed of 650 r/rain. For the sintered sample 20-5-650 （20wt% WC, milling time of 5 h, and milled speed of 650 r/min）, the maximum Brinell hardness and yield stress are obtained to be 3.25 GPa and 858 MPa, respectively. All sintered samples have brittle fracture during compression test except the sample 20-5-650.展开更多
Magnesium powders were mechanically alloyed with SiO2 powder particles having different particle sizes using nigh-energy ball milling techniques under Ar atmosphere for 1 h. The powders were consolidated with cold pre...Magnesium powders were mechanically alloyed with SiO2 powder particles having different particle sizes using nigh-energy ball milling techniques under Ar atmosphere for 1 h. The powders were consolidated with cold pressing under 560 MPa. They were then sintered at 550℃ for 45 min under Ar atmosphere. The composites obtained on the Mg-SiO2 system were investigated using the Archimedes principle, a differential scanning calorimeter, X-ray diffraction, optic microscopy, and scanning electron microscopy. For the mechanically alloyed powders, the solid-state reaction of the synthesis of Mg2Si and MgO progressed further during sintering of the materials. The results showed that the strengthening mechanisms were dependent on dispersion hardening of fine Mg2Si and MgO particulates dispersed homogeneously in the matrix. Mg-展开更多
A grain boundary diffusion process(GBDP)was adopted to improve magnetic properties of Dy-free highly coercive Nd-Fe-B permanent magnet by coating thin layers of Nd and Cu in grain boundaries.For GBDP of Nd and Cu,Nd a...A grain boundary diffusion process(GBDP)was adopted to improve magnetic properties of Dy-free highly coercive Nd-Fe-B permanent magnet by coating thin layers of Nd and Cu in grain boundaries.For GBDP of Nd and Cu,Nd and Cu were coated by wet process,e.g.,electrochemical and electroless on Nd-Fe-B magnets,which was fabricated by hot-deformed/die-upset with meltspun specimen.Heat treatment was performed for 20 min at 600℃followed by several different cooling conditions.The cooling conditions after heat treatment were varied to understand distribution and micros tructural effects of Nd and Cu species in grain boundaries.The coercivity increased from 1.565 to 1.637 T in oil cooling rate but remanence decreased,while remanence jumped with little decrease in coercivity in furnace cooling.Micros tructure analyses suggested that the coercivity was closely related to the cooling rate as well as distribution of Nd.The mechanism of coercivity enhancement due to the cooling rate was discussed based on the results presented here and those in the literature.展开更多
基金supported by the Romanian Ministry of Education and Research,CNCS-UEFISCDI Research Grant No.PN-Ⅲ-P1-1.1-PD-2021-0531.
文摘The functional properties of BaTiO_(3)ceramics,produced by using the same pressing/sintering strategy from nanopowders with two distinct morphologies(cuboidal/equiaxed nanoparticles)and similar particle sizes,are comparatively investigated.The sintered ceramics exhibit similar nanoscale structures,with faceted crystalline grains and crystalline inclusions,clean grain boundaries and well-defined 90°lamellar domains extending in some entire grains or finer nanodomains inside grain regions.The differences in the functional behavior originating from the different nanopowder morphology are described in terms of the nanoparticle assembly during the pressing step.The numerically simulated green body densification indicated a more efficient assembly resulting in higher density for the cubic particles(0.90 vs.0.84 relative density)and a more homogeneous pore distribution in the spherical-derived ones.As a result of the higher density after sintering,the functional properties are enhanced in cuboid-originated ceramics.For comparison,the ceramic produced from cubic nanoparticles sintered at T_(1)/T_(2)=1250/800℃shows higher permittivity(room temperature value of∼2100-cubic vs.∼1700-rounded),enhanced ferroelectric characteristics(cubic:P_(s)=8.57μC cm^(-2),P_(r)=0.95μC cm^(-2),and E_(c)=2.3 kV cm^(-1),with respect to P_(s)=6.06μC cm^(-2),P_(r)=0.4μC cm^(-2),and E_(c)=1.4 kV cm^(-1),for spherical-derived ones,measured at E_(max)=29.3 kV cm^(-1))and a stronger dc-field dependence of their permittivity of∼12%(cubic)vs.only∼2%(spherical),for a dc-applied field in the range of-15 kV cm^(-1)<Edc<15 kV cm^(-1).In contrast,the spherical particles-derived ceramics contain fewer defects and have a more homogeneous and finer porosity distribution in the ceramic volume and consequently,they are more stable and sustain larger field applications in comparison with the cubic-derived counterparts.
文摘Silicon nitride (Si3N4) ceramic is an attractive material for dental applications, especially used as a dental core material, due to its unique properties including high fracture toughness, high strength, high wear resistance and non-cytotoxicity. In this study, the Si3N4 ceramic was fabricated by a non-pressure sintering technique at a relatively low sintering temperature of 1650℃ in nitrogen atmosphere. Borosilicate glass and 5 wt% ZrO2-added borosilicate glass were used for coating on the Si3N4 core surface because of their compatibility in thermal expansion, high chemical resistance and bio-inert. The specimens were then fired in electric tube furnace at 1100℃. The Vickers microhardness of borosilicate glass and 5 wt% ZrO2-added borosilicate glass veneering materials were measured and compared with the commercial dental veneer porcelain as a control (VITA VMK 95). The cytotoxicity of the Si3N4 ceramic and the veneering materials were tested by MTT assay, using human gingival fibroblasts (HGF) and periodontal ligament fibroblasts (HPDLF). The results indicate that the Si3N4 ceramic and Si3N4 ceramic veneered with borosilicate glass or 5 wt% ZrO2-added borosilicate glass veneering materials tested in this study are not toxic to oral tissue and can be used to produce dental prostheses.
基金Project(2004CB619300) supported by the Basic Research Development Program of ChinaProject(NCET-04-0703) supported by the Program for New Century Excellent Talents in University
文摘In order to get high-performance low voltage varistors,Cr2O3 doped ZnO ceramic thick films were fabricated by modified sol-gel process. The precursors were fabricated by dispersing doped-ZnO ceramic nano-powders in the sols,which were prepared by dissolving zinc acetate dihydrate into 2-methoxyethanol and stabilized by diethanolamine and glacial acetic acid and doped with a concentrated solution of bismuth nitrate,phenylstibonic acid,cobalt nitrate,manganese acetate and chromium nitrate. The results show that ZnCr2O4 phase can form in ZnO based ceramic films doped 1.0%(mole fraction) Cr2O3. Three secondary phases,such as Bi2O3,Zn7Sb2O12,and ZnCr2O4 phases,are detected in the thick films. The Raman spectra show that the intensity and the position of Raman bands of Zn7Sb2O12 and ZnCr2O4 phases change obviously with increasing Cr2O3 doping. The nonlinearity coefficient α of ZnO thick films is 7.0,the nonlinear voltage is 6 V,and the leakage current density is 0.7 μA/mm2.
文摘以3.5PbO.96.5B2O3(m o l%)玻璃作为研究对象,着重研究其在不同重力条件下的分相现象。该部分讨论了2个落塔实验试样发生分相的重力条件,同时分析了试样的相组成和试样成分的不均匀性。结果发现,该成分玻璃发生分相后形成的富硼相和富铅相都是玻璃相。分相在高重力阶段发生的试样其成分均匀性最差,原因在于富硼相和富铅相间存在较大的密度差。
文摘TiO2-hydroxyapatite （HA） nanostructured coatings were produced by atmospheric plasma spray method. The effects of starting powder composition and grain size on their mechanical properties were investigated. The microstructure and morphology were characterized by X-ray diffraction and scanning electron microscopy （SEM）. It is found that the coating with 10% HA has the best mechanical properties. Based on Rietveld refinement method, the mean grain size of the as-received powder （212 nm） extensively decreases to 66.4 nm after 20 h of high-energy ball milling. In spite of grain growth, the deposited coatings maintain their nanostructures with the mean grain size of 112 nm. SEM images show that there is a lower porosity in the coating with a higher HA content. Optical microscopy images show that uniform thickness is obtained for all the coatings.
文摘Using coal tar pitch as a matrix precursor to prepare carbon materials is widelyused by impregnation/carbonization processing technology.Four different grades of coaltar pitch and a natural pitch were characterized in terms of carbon yield, density, viscosity,and fractionation with solvents, as well as by thermal analysis methods.The suitability ofthese commercially available matrices for densification of 3 dimensional carbon-carboncomposites was examined.The theoretical results compared with experimental results.The highest density after impregnation was obtained using one of the coal tar pitches.Thepredicted results are in reasonable agreement with experiment data.The significance ofthis research is that a special heat treatment regime was conducted.The effects of modificationtemperature on the densification efficiency of composites were investigated andthen structure and characteristics of the composites were determined by scanning electronmicroscopy (SEM), Transmission electron microscopy (TEM) and X-Ray Diffraction (XRD).
基金supported by the Chinese Academy of Sciences Strategic Pilot Science and Technology Special (Class A)(XDA21020000)the National Natural Science Foundation of China (22072175,21673272)support from the Ulam program,awarded by the Polish National Agency for Academic Exchange (NAWA),Poland,under project No.PPN/ULM/2020/1/00006/DEC/1
文摘The production of poly-α-olefins(PAOs)has attracted attention due to their excellent viscosity-temperature dependence,wear characteristics,oxidative properties,and high thermal stability.In this study,indene extracted during coal tar refining was used as a raw material to synthesize a bis(indenyl)zirconium dichloride metallocene catalyst.A PAO with low viscosity and a high viscosity index was produced via the oligomerization of 1-decene in the presence of both the prepared metallocene and a methylaluminoxane(MAO)co-catalyst.Notably,the effects of different synthesis reaction parameters,such as Al:Zr ratio,amount of catalyst,and reaction temperature,on the conversion ratio and product selectivity were investigated in detail.The produced PAO was thoroughly characterized using Fourier-transform infrared,^(13)C,and^(1)H nuclear magnetic resonance spectroscopies;gas chromatography;and viscosity measurements.At 70℃,the metallocene catalyst created more stable active sites.In addition,the alkylation effect of MAO was noticeable.Interestingly,the obtained catalysis results demonstrated that a high conversion ratio of~93%was achieved at a low reaction temperature of 70℃,with a catalyst dosage of 0.0848 mmol and Al:Zr ratio of 8.48mmol:0.0848mmol.Moreover,under these optimal conditions,the kinematic viscosity of PAO was 4.25 mm2/s at 100℃,and the viscosity index was 139,indicating good viscosity-temperature properties.
基金the National Research Center of Egypt for the partial support of this work
文摘Hollow silica microspheres （HSMSs） have been successfully fabricated via a facile hydrothermal route using D-glucose as the sacrificial template and sodium silicate powder as the silica precursor. The resulting silica hollow particles were characterized by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）, and infrared spectroscopy （IR）. The surface area was determined using the BET method. SEM and TEM images exhibited micro-sized silica hollow particles with a size of -1.5μm.
基金financial support by Taif University(No.1-428-58)
文摘The production of geopolymer binders from low-purity clays was investigated. Three low-purity clays were calcined at 750℃ for 4 h. The calcined clays were chemically activated by the alkaline solutions of NaOH and Na2SiO3. The compressive strength was measured as a function of curing time at room temperature and 85℃. The results were compared with those of a pure kaolin sample. An amorphous aluminosilicate polymer was formed in all binders at both processing temperatures. The results show that, the mechanical properties depend on the type and amount of active aluminum silicates in the starting clay material, the impurities, and the processing temperature.
文摘Calcium phosphate cements have received much attention in recent decades owing to their biocompatibility, in situ handling, and shaping abilities. However, their low initial mechanical strength is still a major limitation. On the other hand, calcium aluminate cements (CACs) set fast and have a high initial strength and good corrosion resistance in contact with body fluids, making them excellent dental restorative materials. Therefore, the chemical, mechanical and biological properties of new-TCP/CA cement after aging in simulated body fluid (SBF) were investigated. The results indicated that the composites have setting times not appropriated for immediate applications and have degradation rates higher than those of the traditional CPCs. Moreover, the compressive strength of composite was lower than 5MPa and did not increase with SBF immersion. However, the α-TCP/CA composites showed a higher bioactivity at early stages and were not only more biocompatible but also more noncytotoxic.
文摘Fe-WC nanocomposites were successfully fabricated by high-frequency induction heated sintering of ball milled nanostructure powders. The ball milled powders were characterized by X-ray diffraction. Density measurements by the Archimedes method show that all sintered samples have the relative density higher than 95%. Studies on the effects of WC content, milling speed, and milling time indicate that a higher milling speed and a more WC content lead to the improvement of mechanical properties. There is a very good distribution of WC particles in the Fe matrix at the milling speed of 650 r/rain. For the sintered sample 20-5-650 （20wt% WC, milling time of 5 h, and milled speed of 650 r/min）, the maximum Brinell hardness and yield stress are obtained to be 3.25 GPa and 858 MPa, respectively. All sintered samples have brittle fracture during compression test except the sample 20-5-650.
文摘Magnesium powders were mechanically alloyed with SiO2 powder particles having different particle sizes using nigh-energy ball milling techniques under Ar atmosphere for 1 h. The powders were consolidated with cold pressing under 560 MPa. They were then sintered at 550℃ for 45 min under Ar atmosphere. The composites obtained on the Mg-SiO2 system were investigated using the Archimedes principle, a differential scanning calorimeter, X-ray diffraction, optic microscopy, and scanning electron microscopy. For the mechanically alloyed powders, the solid-state reaction of the synthesis of Mg2Si and MgO progressed further during sintering of the materials. The results showed that the strengthening mechanisms were dependent on dispersion hardening of fine Mg2Si and MgO particulates dispersed homogeneously in the matrix. Mg-
基金financially supported by the National Research Foundation of Korea(No.2015R1A2A2A01002795)the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Trade,Industry,and Energy,Republic of Korea(No.10080382)the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(No.2018R1D1A1B07041358).
文摘A grain boundary diffusion process(GBDP)was adopted to improve magnetic properties of Dy-free highly coercive Nd-Fe-B permanent magnet by coating thin layers of Nd and Cu in grain boundaries.For GBDP of Nd and Cu,Nd and Cu were coated by wet process,e.g.,electrochemical and electroless on Nd-Fe-B magnets,which was fabricated by hot-deformed/die-upset with meltspun specimen.Heat treatment was performed for 20 min at 600℃followed by several different cooling conditions.The cooling conditions after heat treatment were varied to understand distribution and micros tructural effects of Nd and Cu species in grain boundaries.The coercivity increased from 1.565 to 1.637 T in oil cooling rate but remanence decreased,while remanence jumped with little decrease in coercivity in furnace cooling.Micros tructure analyses suggested that the coercivity was closely related to the cooling rate as well as distribution of Nd.The mechanism of coercivity enhancement due to the cooling rate was discussed based on the results presented here and those in the literature.
