Steel-cemented WC was prepared by ball milling, cold compacting and microwave sintering with Fe powder as the matrix, WC as the hard phase and the addition of rare earth Y2O3. The results show that the interface of th...Steel-cemented WC was prepared by ball milling, cold compacting and microwave sintering with Fe powder as the matrix, WC as the hard phase and the addition of rare earth Y2O3. The results show that the interface of the WC particles and Fe matrix exhibits excellent wettability and liquidity when the microwave sintering temperature reaches 1,280℃. The density and mechanical properties of the steel bonded WC carbides could be greatly improved, the hard phases become finer and more uniform dispersed owing to the addition of Y2O3. With the increase of the Y2O3 contents, the grain becomes uniform and fine first, and then gathers and grows up. The relative density, microhardness and bending strength all rise first, reaching the maximum values of 97.29 %, HV1024 and 1,267.60 MPa at 0.5 % Y2O3, respectively, and then decrease. Moreover, the relative density and mechanical properties of the steel-cemented WC with nano-Y2O3 are higher than that with micron-Y2O3, which indicates that the effect of nano-Y2O3 is better than that of the micron-Y2O3.展开更多
Ultra-fine titanium carbonitride (TiCN) matrix materials with a grain size less than 1μm were successfully prepared by vacuum microwave sintering. The milling process for raw TiCN particles and the microstructure a...Ultra-fine titanium carbonitride (TiCN) matrix materials with a grain size less than 1μm were successfully prepared by vacuum microwave sintering. The milling process for raw TiCN particles and the microstructure and properties of cermets produced with a composition of 15wt.%WC-17wt.%(Co+Ni)-9wt.%Mo2C-59wt.%Ti0.TN0.3 and sintered by vacuum microwave were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that a ball-to-powder mass ratio of 8:1 and a milling time of 50 h provided appropriate conditions for the production of ultra-fine TiCN solid solution powders. The use of vacuum microwave sintering produced cermets with much finer grain and black core structures and higher relative density and hardness than those produced by vacuum sintering technology.展开更多
Despite the importance of aluminum alloys as candidate materials for applications in aerospace and automotive industries, very little work has been published on spark plasma and microwave processing of aluminum alloys...Despite the importance of aluminum alloys as candidate materials for applications in aerospace and automotive industries, very little work has been published on spark plasma and microwave processing of aluminum alloys. In the present work, the possibility was explored to process A12124 and A16061 alloys by spark plasma and microwave sintering techniques, and the microstructures and properties were compared. The alloys were sintered for 20 rain at 400, 450, and 500℃. It is found that compared to microwave sintering, spark plasma sintering is an effective way to obtain homogenous, dense, and hard alloys. Fully dense (100%) A16061 and A12124 alloys were obtained by spark plasma sintering for 20 rain at 450 and 500℃, respectively. Maximum relative densities were achieved for A16061 (92.52%) and A12124 (93.52%) alloys by microwave sintering at 500℃for 20 min. The Vickers microhardness of spark plasma sintered samples increases with the increase of sintering temperature from 400 to 500℃, and reaches the values of Hv 70.16 and Hv 117.10 for A16061 and A12124 alloys, respectively. For microwave siutered samples, the microhardness increases with the increase of sintering temperature from 400 to 450℃, and then decreases with the further increase of sintering temperature to 500~C.展开更多
Ca0.6La0.2667TiO3 ceramics were prepared by conventional and microwave sintering techniques and their sinterability, microstructure, and microwave dielectric properties were investigated in detail for comparison. Dens...Ca0.6La0.2667TiO3 ceramics were prepared by conventional and microwave sintering techniques and their sinterability, microstructure, and microwave dielectric properties were investigated in detail for comparison. Densified Ca0.6La0.E667TiO3 ceramics were obtained by microwave sintering at 1350℃ for 30 min and by conventional sintering at 1450℃ for 4 h. An unusual phenomenon was found that some larger grains (grain size range: 8-10 pan) inclined to assemble in one area but some smaller ones (grain size range: 2-4 μm) inclined to gather in another area in the microwave sintered ceramics. The microwave dielectric properties of Ca0.6La0.2667TiO3 ceramics prepared by micro- wave sintering at 1350℃ were as follows" dielectric constant (er) = 119.6, quality factor (Qf) = 17858.5 GHz, and temperature coefficient of resonant fi'equency (rf)= 155.5 ppm/℃. In contrast, the microwave dielectric properties of the ceramics prepared by conventional sintering at 1450℃ were er = 117.4, Qf= 13375 GHz, and rf= 217.2 ppm/℃.展开更多
Eu^2+-doped Ba3Si6012N2 green phosphors were prepared by microwave assisted sintering method at 1275℃ for 4 h, while the counterparts using conventional solid-state reaction method were synthesized at temperature hi...Eu^2+-doped Ba3Si6012N2 green phosphors were prepared by microwave assisted sintering method at 1275℃ for 4 h, while the counterparts using conventional solid-state reaction method were synthesized at temperature higher than 1300℃ and for to 10 h. Microwave assisted sintering could reduce the activation energy and enhance the diffu- sion rate, thus greatly improved the sintering. Moreover, the influence of Si3N4 content on phase formation, morphol- ogy, absorption, and quantum efficiency, and photoluminescence properties of phosphors were studied. As a result, the Ba3Si6OI2N2:Eu^2+ samples sintered by microwave assisted sintering method have a higher phase purity and photo- luminescence intensity under ultraviolet excitation as compared with samples sintered in the conventional tube furnace The proposed method is a potential preparation method for the oxynitride phosphors with strong photoluminescence and high phase purity.展开更多
Ti–51at%Ni shape memory alloys(SMAs) were successfully produced via a powder metallurgy and microwave sintering technique.The influence of sintering parameters on porosity reduction,microstructure,phase transformatio...Ti–51at%Ni shape memory alloys(SMAs) were successfully produced via a powder metallurgy and microwave sintering technique.The influence of sintering parameters on porosity reduction,microstructure,phase transformation temperatures,and mechanical properties were investigated by optical microscopy,field-emission scanning electron microscopy(FE-SEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests,and microhardness tests.Varying the microwave temperature and holding time was found to strongly affect the density of porosity,presence of precipitates,transformation temperatures,and mechanical properties.The lowest density and smallest pore size were observed in the Ti–51at%Ni samples sintered at 900°C for 5 min or at 900°C for 30 min.The predominant martensite phases of β2 and β19′ were observed in the microstructure of Ti–51at%Ni,and their existence varied in accordance with the sintering temperature and the holding time.In the DSC thermograms,multi-transformation peaks were observed during heating,whereas a single peak was observed during cooling;these peaks correspond to the presence of the β2,R,and β19′ phases.The maximum strength and strain among the Ti–51at%Ni SMAs were 1376 MPa and 29%,respectively,for the sample sintered at 900°C for 30 min because of this sample's minimal porosity.展开更多
Using the microwave sintering technology, the effects of phosphorus (P) additions on the microstructure and properties of the ultrafine WC-10Co alloys were investigated. The experimental results show that with only ...Using the microwave sintering technology, the effects of phosphorus (P) additions on the microstructure and properties of the ultrafine WC-10Co alloys were investigated. The experimental results show that with only 0.3wt% P additions, full density WC-10Co cermets were obtained at temperature of 1250℃, which is 70 ℃ lower than that of the undoped counterparts. Lower sintering temperature can result in finer WC grain growth; therefore, the P-doped WC-10Co alloys exhibited higher hardness than the undoped ones. But at the same time, P doping could lead to sacrifice of fracture toughness ofWC-10Co cemented carbides.展开更多
Spark plasma sintering (SPS) and conventional vacuum sintering (VS) wereemployed to fabricate ultrafine Ti(C,N)-based cermets. The shrinkage behavior, microstracture, andporosity and mechanical properties of the sampl...Spark plasma sintering (SPS) and conventional vacuum sintering (VS) wereemployed to fabricate ultrafine Ti(C,N)-based cermets. The shrinkage behavior, microstracture, andporosity and mechanical properties of the samples fabricated by SPS were compared with those of thesamples sintered by VS using optical microscopy, scanning electron microscopy, universal testingmachine, and rockwell tester. The results are as follows: (1) The shrinkage process occurred mainlyin the range of 1000-1300 deg C during the VS process, and only a 0.2 percent linear shrinkage ratioappeared below 800 deg C; during the SPS process, a 60 percent dimensional change occurred below800 deg C as a result of pressure action. (2) By utilizing the SPS technique, it is difficult forobtaining fully dense Ti(C,N)-based cermets. Due to the much existence of pores and un-combinedcarbon, the mechanical properties of the sintered samples by SPS are inferior to sintered ones byVS. (3) grain size of the samples sintered by SPS is still below 0.5 urn, but not by VS; because oflow sintering temperature, there are no typical core/rim structures formed in the sintered samplesby SPS1; the main microstructures of the sintered samples by SPS2 are a white core/grey shellstructure, whereas by VS show a typical black core/grey shell structure.展开更多
The desulfurater(BaAl2O4) was successfully synthesized with BaCO3 and Al(OH)3 powders as raw materials by microwave sintering method.The mass loss of raw materials and the characterization of the outcome were investig...The desulfurater(BaAl2O4) was successfully synthesized with BaCO3 and Al(OH)3 powders as raw materials by microwave sintering method.The mass loss of raw materials and the characterization of the outcome were investigated by means of TG-DSC,XRD and optical microscopy.The reaction mechanism was discussed.The experimental results show that synthesized BaAl2O4 by microwave sintering method is feasible.Compared with conventional sintering method,microwave sintering is a better way to synthesize BaAl2O4 with advantages of low temperature sintering,short time sintering and high synthesis rate.展开更多
The microwave absorbing behaviour of Mn-Zn ferrite sintered at 1100,1200,1300,1400 and 1500℃ has been investigated.The phase constitution of the ferrite was analyzed by X-ray diffraction.The results show that the fer...The microwave absorbing behaviour of Mn-Zn ferrite sintered at 1100,1200,1300,1400 and 1500℃ has been investigated.The phase constitution of the ferrite was analyzed by X-ray diffraction.The results show that the ferrite sintered at 1 500℃ has better microwave absorbing prop- erty than those prepared at other temperatures,due to the increase of turbulent loss generated by the formation of excessive Fe^(2+) in deoxidizing of Fe_2O_3 at high temperatures.展开更多
Composite powders of nanocrystalline WC-10Co (15wt%),Y2O3 (8mol%) stabilized nanocrystalline ZrO2 (30wt%),industrial cobalt powder (4.5wt%) and submicron Al2O3 (55wt%) composite powders were fabricated by hi...Composite powders of nanocrystalline WC-10Co (15wt%),Y2O3 (8mol%) stabilized nanocrystalline ZrO2 (30wt%),industrial cobalt powder (4.5wt%) and submicron Al2O3 (55wt%) composite powders were fabricated by high-energy ball-milling process.The nanocomposite powders were consolidated by microwave sintering process at temperature ranged 1300℃-1550℃ for 15min,respectively.The optimum consolidation conditions,such as temperature,were researched during microwave sintering process.Vickers Hardness of the consolidated cermets was measured by using a Vickers indentation test,and density of specimens was also determined by Archimedes' principle.Microwave sintering process could not only increase the density of Al2O3-ZrO2-WC-Co cermets and reduce the porosity,but also inhibit abnormal grain growth.展开更多
Microwave sintering method was carried out to prepare porous mullite composite. An insulation structure based on hybrid heating mode was well designed with the wall of mullite and the aided heaters of SiC. The obtaine...Microwave sintering method was carried out to prepare porous mullite composite. An insulation structure based on hybrid heating mode was well designed with the wall of mullite and the aided heaters of SiC. The obtained samples were characterized by XRD analysis, apparent porosity detection, and bending strength measurement. SEM was used to observe the microstructure of the sample. It is found that the porous mullite composite could be prepared through the microwave sintering within 2 h at relatively low temperatures around 1000 ℃. The lasted samples show comparatively superior properties to the products prepared by conventional processing.展开更多
The effects of microwave sintering and conventional H2 sintering on the microstructure and properties of W-15Cu alloy using ultrafine W-15Cu composite powder fabricated by spray drying & calcining-continuous reductio...The effects of microwave sintering and conventional H2 sintering on the microstructure and properties of W-15Cu alloy using ultrafine W-15Cu composite powder fabricated by spray drying & calcining-continuous reduction technology were investigated. In comparison to the conventional HE sintering processing, microwave sintering to W-15Cu can be achieved at lower sintering temperature and shorter sintering time. Furthermore, higher performances in microwave sintered compacts were obtained, but high microwave sintering temperature or long microwave sintering time could result in coarser microstructures.展开更多
The effects of CuO and H3BO3 additions on the low-temperature sintering,microstructure,and microwave dielectric properties of Ba2Ti3Nb4O18 ceramics were investigated.The addition of less amount of CuO ( 〈1 wt%) con...The effects of CuO and H3BO3 additions on the low-temperature sintering,microstructure,and microwave dielectric properties of Ba2Ti3Nb4O18 ceramics were investigated.The addition of less amount of CuO ( 〈1 wt%) considerably facilitated the densification of Ba2Ti3Nb4O18 ceramics.Appropriate addition of H3BO3 ( 〈3.5 wt%) remarkably improved the microwave dielectric properties of ceramics.The addition of H3BO3 and CuO successfully reduced the sintering temperature of Ba2Ti3Nb4O18 ceramics from 1300 to 1050 ℃.Ba2Ti3Nb4O18 ceramics sintered at 1 050 ℃ for 4 h with the addition of 1.0 wt% CuO and 3.5 wt% H3BO3 exhibited good microwave dielectric properties:er=33.74,Q?f=13 812 GHz,and tf=-5.35 ppm/°C at about 5.0 GHz.展开更多
Si2N2O ceramics were prepared using amorphous Si3N4 as the raw material and Li2CO3 as the sintering additive through vacuum multi-stage sintering.The influence of the Li2CO3 addition(0%,1%,2%,3%,and 5%,by mass)on the ...Si2N2O ceramics were prepared using amorphous Si3N4 as the raw material and Li2CO3 as the sintering additive through vacuum multi-stage sintering.The influence of the Li2CO3 addition(0%,1%,2%,3%,and 5%,by mass)on the phase composition,the microstructure,the porosity,the mechanical properties,the dielectric constant and the tangent of the dielectric loss angle of the porous Si2N2O ceramics was investigated.The results reveal that a suitable addition of Li2CO3 can promote the generation of Si2N2O but excessive or inadequate Li2CO3 causes decomposition of Si2N2O ceramics.The prepared porous Si2N2O ceramics have good mechanical properties,good thermal shock resistance,and low dielectric properties,which have excellent potential for application in microwave sintering furnaces.展开更多
The low-temperature sintered NiZn and NiCuZn ferrites with the composition of Ni0.40Zn0.60Fe2O4 and Ni0.35Cu0.05Zn0.60 Fe2O4 were respectively synthesized by the microwave sintering method. These powders were calcined...The low-temperature sintered NiZn and NiCuZn ferrites with the composition of Ni0.40Zn0.60Fe2O4 and Ni0.35Cu0.05Zn0.60 Fe2O4 were respectively synthesized by the microwave sintering method. These powders were calcined, compacted and sintered at 950℃ for 30 min. X-ray diffraction (XRD) patterns of the samples indicate the formation of single-phase cubic spinel structure. The grain size was estimated from SEM images which increase with CuO addition. The X-ray density is higher than the bulk density in both the ferrites. The temperature variation of the initial permeability of these samples was carried out from 30℃ to 250℃. The NiCuZn ferrite had higher initial permeability than that of the NiZn ferrite, which could be attributed to the microstructure. Saturation magnetization increases from 40 emug/g (NiZn) to 47 emug/g (NiCuZn). The dielectric constant and dielectric loss tangent of NiZn and NiCuZn ferrite samples decreases with increase in frequency exhibiting normal ferrimagnetic behavior. The NiCuZn ferrite had better electro- magnetic properties than the NiZn ferrite.展开更多
MA W-Ni-Fe alloyed powder compact was sintered by microwave technology, and the influence of microwave sintering on consolidation of W-Ni-Fe alloy was studied. The fracture morphology and microstructure of alloys were...MA W-Ni-Fe alloyed powder compact was sintered by microwave technology, and the influence of microwave sintering on consolidation of W-Ni-Fe alloy was studied. The fracture morphology and microstructure of alloys were measured by SEM and metallurgical microscope. The experimental results showed that microwave sintering promoted the densification of MA W-Ni-Fe alloyed powder quickly with the higher heating rate. The density of the sintered samples increased with the increase of sintering temperature, and significant densification shrinkage occured at 1300 ~ 1400°C. The tungsten grain grew rapidly at 1450°C. When the alloy was microwave sintered at 1550°C, the inner structure of alloy is more homogeneous, the average W grain size is about 15 μm, and the relative density of sintered specimen is 99%.展开更多
The kinetics of free-radical crosslinking co-polymerization(FRCCP)of acrylic acid(AA)with both methacrylic acid(MA)(PAMA hydrogel)and maleic acid(MAL)(PAMAL hydrogel)was investigated under the conditions of isothermal...The kinetics of free-radical crosslinking co-polymerization(FRCCP)of acrylic acid(AA)with both methacrylic acid(MA)(PAMA hydrogel)and maleic acid(MAL)(PAMAL hydrogel)was investigated under the conditions of isothermal conventional heating(CH)and under the conditions of microwave heating(MWH)with controlled cooling.The kinetics curves of FRCCP of PAMA and PAMAL hydrogels under the conditions of CH are described with the kinetics model of second order chemical reaction,whereas the kinetics curves under the conditions of CH are described with the kinetics model of Polany-Winger.It is proved that MWH leads to the changes in the rate of FRCCP and to the changes in the values of the kinetic parameters activation energy(Ea)and pre-exponential factor(lnA).It was found the existence of relationship between the values of the kinetic parameters calculated for MWH and CH for PAMA and PAMAL hydrogel synthesis process,which is well-known as compensation effect.The effect of MWH on the kinetics of FRCCP for PAMA and PAMAL hydrogel formation were explained by applying the model of activation by selective energy transfer(SET).The changes in kinetics model,rate of FRCCP and kinetics parameters,caused with the MWH can found wide application in designing novel technologies for obtaining polymers and for synthesis of polymers with novel physico-chemical properties.The suggested mechanism of activation for polymerisation under the conditions of MWH also enables development of novel reaction systems and technologies for polymers productions.展开更多
A versatile and environmentally friendly method for α,α’-bis(substituted ben-zylidene) cycloalkanones has been developed using a heterogeneous catalysis technology. We have synthesized a series of the α,α’-bis(s...A versatile and environmentally friendly method for α,α’-bis(substituted ben-zylidene) cycloalkanones has been developed using a heterogeneous catalysis technology. We have synthesized a series of the α,α’-bis(substituted benzylidene) cycloalkanones, a biologically important class of compounds, via the cross aldol condensation between arylaldehydes and cycloketones using sodium-modified fluorapatite (Na/FAP) as a highly efficient solid catalyst under conventional heating in aqueous media and solventless conditions under microwave. Catalyst reuse, ease of separation of the pure product, and high yields are some of the unique features of this process. Shorter reaction times (4 - 7 min) and higher yields (80% - 94%) were achieved under microwave irradiation conditions.展开更多
This paper introduces the characteristic of microwave sintering,introduces and analyses the process of microwave sintering of thealumina ceramics, moreover, compared with the experiments ofconventional sintering metho...This paper introduces the characteristic of microwave sintering,introduces and analyses the process of microwave sintering of thealumina ceramics, moreover, compared with the experiments ofconventional sintering method. Based on the research, some resultsare obtained, and experimental basis for microwave sintering ofceramics is put forward.展开更多
基金supported by the Science and Technology Plan Projects of Jiangxi Province (No. 2011BBE50010)the Project from the Jiangxi Province Key Laboratory of Copper Tungsten New Materials (No. 2011-TW-08)
文摘Steel-cemented WC was prepared by ball milling, cold compacting and microwave sintering with Fe powder as the matrix, WC as the hard phase and the addition of rare earth Y2O3. The results show that the interface of the WC particles and Fe matrix exhibits excellent wettability and liquidity when the microwave sintering temperature reaches 1,280℃. The density and mechanical properties of the steel bonded WC carbides could be greatly improved, the hard phases become finer and more uniform dispersed owing to the addition of Y2O3. With the increase of the Y2O3 contents, the grain becomes uniform and fine first, and then gathers and grows up. The relative density, microhardness and bending strength all rise first, reaching the maximum values of 97.29 %, HV1024 and 1,267.60 MPa at 0.5 % Y2O3, respectively, and then decrease. Moreover, the relative density and mechanical properties of the steel-cemented WC with nano-Y2O3 are higher than that with micron-Y2O3, which indicates that the effect of nano-Y2O3 is better than that of the micron-Y2O3.
基金supported by the Hunan Provincial Natural Science Fund for Distinguished Young Scholars of China(No.08JJ1007)the Hunan Provincial Key Science Research Program of China(No.2008GK2009)the Scientific Research Fund of Fujian Provincial Education Department of China(No.JK2009029)
文摘Ultra-fine titanium carbonitride (TiCN) matrix materials with a grain size less than 1μm were successfully prepared by vacuum microwave sintering. The milling process for raw TiCN particles and the microstructure and properties of cermets produced with a composition of 15wt.%WC-17wt.%(Co+Ni)-9wt.%Mo2C-59wt.%Ti0.TN0.3 and sintered by vacuum microwave were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that a ball-to-powder mass ratio of 8:1 and a milling time of 50 h provided appropriate conditions for the production of ultra-fine TiCN solid solution powders. The use of vacuum microwave sintering produced cermets with much finer grain and black core structures and higher relative density and hardness than those produced by vacuum sintering technology.
基金supported by the King Abdul Aziz City for Science and Technology (KACST) (No. ARP-28-122)
文摘Despite the importance of aluminum alloys as candidate materials for applications in aerospace and automotive industries, very little work has been published on spark plasma and microwave processing of aluminum alloys. In the present work, the possibility was explored to process A12124 and A16061 alloys by spark plasma and microwave sintering techniques, and the microstructures and properties were compared. The alloys were sintered for 20 rain at 400, 450, and 500℃. It is found that compared to microwave sintering, spark plasma sintering is an effective way to obtain homogenous, dense, and hard alloys. Fully dense (100%) A16061 and A12124 alloys were obtained by spark plasma sintering for 20 rain at 450 and 500℃, respectively. Maximum relative densities were achieved for A16061 (92.52%) and A12124 (93.52%) alloys by microwave sintering at 500℃for 20 min. The Vickers microhardness of spark plasma sintered samples increases with the increase of sintering temperature from 400 to 500℃, and reaches the values of Hv 70.16 and Hv 117.10 for A16061 and A12124 alloys, respectively. For microwave siutered samples, the microhardness increases with the increase of sintering temperature from 400 to 450℃, and then decreases with the further increase of sintering temperature to 500~C.
基金financially supported by A Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Ca0.6La0.2667TiO3 ceramics were prepared by conventional and microwave sintering techniques and their sinterability, microstructure, and microwave dielectric properties were investigated in detail for comparison. Densified Ca0.6La0.E667TiO3 ceramics were obtained by microwave sintering at 1350℃ for 30 min and by conventional sintering at 1450℃ for 4 h. An unusual phenomenon was found that some larger grains (grain size range: 8-10 pan) inclined to assemble in one area but some smaller ones (grain size range: 2-4 μm) inclined to gather in another area in the microwave sintered ceramics. The microwave dielectric properties of Ca0.6La0.2667TiO3 ceramics prepared by micro- wave sintering at 1350℃ were as follows" dielectric constant (er) = 119.6, quality factor (Qf) = 17858.5 GHz, and temperature coefficient of resonant fi'equency (rf)= 155.5 ppm/℃. In contrast, the microwave dielectric properties of the ceramics prepared by conventional sintering at 1450℃ were er = 117.4, Qf= 13375 GHz, and rf= 217.2 ppm/℃.
文摘Eu^2+-doped Ba3Si6012N2 green phosphors were prepared by microwave assisted sintering method at 1275℃ for 4 h, while the counterparts using conventional solid-state reaction method were synthesized at temperature higher than 1300℃ and for to 10 h. Microwave assisted sintering could reduce the activation energy and enhance the diffu- sion rate, thus greatly improved the sintering. Moreover, the influence of Si3N4 content on phase formation, morphol- ogy, absorption, and quantum efficiency, and photoluminescence properties of phosphors were studied. As a result, the Ba3Si6OI2N2:Eu^2+ samples sintered by microwave assisted sintering method have a higher phase purity and photo- luminescence intensity under ultraviolet excitation as compared with samples sintered in the conventional tube furnace The proposed method is a potential preparation method for the oxynitride phosphors with strong photoluminescence and high phase purity.
基金financial support under the University Research Grant No.Q.J130000.3024.00M57
文摘Ti–51at%Ni shape memory alloys(SMAs) were successfully produced via a powder metallurgy and microwave sintering technique.The influence of sintering parameters on porosity reduction,microstructure,phase transformation temperatures,and mechanical properties were investigated by optical microscopy,field-emission scanning electron microscopy(FE-SEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests,and microhardness tests.Varying the microwave temperature and holding time was found to strongly affect the density of porosity,presence of precipitates,transformation temperatures,and mechanical properties.The lowest density and smallest pore size were observed in the Ti–51at%Ni samples sintered at 900°C for 5 min or at 900°C for 30 min.The predominant martensite phases of β2 and β19′ were observed in the microstructure of Ti–51at%Ni,and their existence varied in accordance with the sintering temperature and the holding time.In the DSC thermograms,multi-transformation peaks were observed during heating,whereas a single peak was observed during cooling;these peaks correspond to the presence of the β2,R,and β19′ phases.The maximum strength and strain among the Ti–51at%Ni SMAs were 1376 MPa and 29%,respectively,for the sample sintered at 900°C for 30 min because of this sample's minimal porosity.
基金the National Key Technology R&D Program of MOST,China(2003BA328C)the National Natural Science Foundation of China(50472043)Natural Science Foundation of Hubei Province(2006ABA312,2006ABA316)
文摘Using the microwave sintering technology, the effects of phosphorus (P) additions on the microstructure and properties of the ultrafine WC-10Co alloys were investigated. The experimental results show that with only 0.3wt% P additions, full density WC-10Co cermets were obtained at temperature of 1250℃, which is 70 ℃ lower than that of the undoped counterparts. Lower sintering temperature can result in finer WC grain growth; therefore, the P-doped WC-10Co alloys exhibited higher hardness than the undoped ones. But at the same time, P doping could lead to sacrifice of fracture toughness ofWC-10Co cemented carbides.
基金This work was financially supported by the National Natural Science Foundation of China (No.50074017), the Natural Sci-ence Foundation of Hubei Province (No.2003ABA092) and the Doctoral Education Fundation of China (No.1999048714).
文摘Spark plasma sintering (SPS) and conventional vacuum sintering (VS) wereemployed to fabricate ultrafine Ti(C,N)-based cermets. The shrinkage behavior, microstracture, andporosity and mechanical properties of the samples fabricated by SPS were compared with those of thesamples sintered by VS using optical microscopy, scanning electron microscopy, universal testingmachine, and rockwell tester. The results are as follows: (1) The shrinkage process occurred mainlyin the range of 1000-1300 deg C during the VS process, and only a 0.2 percent linear shrinkage ratioappeared below 800 deg C; during the SPS process, a 60 percent dimensional change occurred below800 deg C as a result of pressure action. (2) By utilizing the SPS technique, it is difficult forobtaining fully dense Ti(C,N)-based cermets. Due to the much existence of pores and un-combinedcarbon, the mechanical properties of the sintered samples by SPS are inferior to sintered ones byVS. (3) grain size of the samples sintered by SPS is still below 0.5 urn, but not by VS; because oflow sintering temperature, there are no typical core/rim structures formed in the sintered samplesby SPS1; the main microstructures of the sintered samples by SPS2 are a white core/grey shellstructure, whereas by VS show a typical black core/grey shell structure.
基金Project(50264001) supported by the National Natural Science Foundation of ChinaProject(QKH-J-2008-2009) supported by Guizhou Science and Technology Department, China
文摘The desulfurater(BaAl2O4) was successfully synthesized with BaCO3 and Al(OH)3 powders as raw materials by microwave sintering method.The mass loss of raw materials and the characterization of the outcome were investigated by means of TG-DSC,XRD and optical microscopy.The reaction mechanism was discussed.The experimental results show that synthesized BaAl2O4 by microwave sintering method is feasible.Compared with conventional sintering method,microwave sintering is a better way to synthesize BaAl2O4 with advantages of low temperature sintering,short time sintering and high synthesis rate.
文摘The microwave absorbing behaviour of Mn-Zn ferrite sintered at 1100,1200,1300,1400 and 1500℃ has been investigated.The phase constitution of the ferrite was analyzed by X-ray diffraction.The results show that the ferrite sintered at 1 500℃ has better microwave absorbing prop- erty than those prepared at other temperatures,due to the increase of turbulent loss generated by the formation of excessive Fe^(2+) in deoxidizing of Fe_2O_3 at high temperatures.
基金Funded by the Youth Science Plan for Light of the Morning Sun of Wuhan City (200750731270)
文摘Composite powders of nanocrystalline WC-10Co (15wt%),Y2O3 (8mol%) stabilized nanocrystalline ZrO2 (30wt%),industrial cobalt powder (4.5wt%) and submicron Al2O3 (55wt%) composite powders were fabricated by high-energy ball-milling process.The nanocomposite powders were consolidated by microwave sintering process at temperature ranged 1300℃-1550℃ for 15min,respectively.The optimum consolidation conditions,such as temperature,were researched during microwave sintering process.Vickers Hardness of the consolidated cermets was measured by using a Vickers indentation test,and density of specimens was also determined by Archimedes' principle.Microwave sintering process could not only increase the density of Al2O3-ZrO2-WC-Co cermets and reduce the porosity,but also inhibit abnormal grain growth.
基金Funded by the National Natural Science Foundation of China( Nos.50972132 and 51172213)
文摘Microwave sintering method was carried out to prepare porous mullite composite. An insulation structure based on hybrid heating mode was well designed with the wall of mullite and the aided heaters of SiC. The obtained samples were characterized by XRD analysis, apparent porosity detection, and bending strength measurement. SEM was used to observe the microstructure of the sample. It is found that the porous mullite composite could be prepared through the microwave sintering within 2 h at relatively low temperatures around 1000 ℃. The lasted samples show comparatively superior properties to the products prepared by conventional processing.
基金Funded by the Project for Science and Technology Plan of Wuhan City(200910321092)the Youth Science Plan for Light of the Morning Sun of Wuhan City (200750731270)
文摘The effects of microwave sintering and conventional H2 sintering on the microstructure and properties of W-15Cu alloy using ultrafine W-15Cu composite powder fabricated by spray drying & calcining-continuous reduction technology were investigated. In comparison to the conventional HE sintering processing, microwave sintering to W-15Cu can be achieved at lower sintering temperature and shorter sintering time. Furthermore, higher performances in microwave sintered compacts were obtained, but high microwave sintering temperature or long microwave sintering time could result in coarser microstructures.
文摘The effects of CuO and H3BO3 additions on the low-temperature sintering,microstructure,and microwave dielectric properties of Ba2Ti3Nb4O18 ceramics were investigated.The addition of less amount of CuO ( 〈1 wt%) considerably facilitated the densification of Ba2Ti3Nb4O18 ceramics.Appropriate addition of H3BO3 ( 〈3.5 wt%) remarkably improved the microwave dielectric properties of ceramics.The addition of H3BO3 and CuO successfully reduced the sintering temperature of Ba2Ti3Nb4O18 ceramics from 1300 to 1050 ℃.Ba2Ti3Nb4O18 ceramics sintered at 1 050 ℃ for 4 h with the addition of 1.0 wt% CuO and 3.5 wt% H3BO3 exhibited good microwave dielectric properties:er=33.74,Q?f=13 812 GHz,and tf=-5.35 ppm/°C at about 5.0 GHz.
基金The authors would like to thank the National Key R&D Program of China(2017YFB0304000)National Natural Science Foundation of China(51932008,51772277)Central China Thousand Talents Project(2042005100111).
文摘Si2N2O ceramics were prepared using amorphous Si3N4 as the raw material and Li2CO3 as the sintering additive through vacuum multi-stage sintering.The influence of the Li2CO3 addition(0%,1%,2%,3%,and 5%,by mass)on the phase composition,the microstructure,the porosity,the mechanical properties,the dielectric constant and the tangent of the dielectric loss angle of the porous Si2N2O ceramics was investigated.The results reveal that a suitable addition of Li2CO3 can promote the generation of Si2N2O but excessive or inadequate Li2CO3 causes decomposition of Si2N2O ceramics.The prepared porous Si2N2O ceramics have good mechanical properties,good thermal shock resistance,and low dielectric properties,which have excellent potential for application in microwave sintering furnaces.
文摘The low-temperature sintered NiZn and NiCuZn ferrites with the composition of Ni0.40Zn0.60Fe2O4 and Ni0.35Cu0.05Zn0.60 Fe2O4 were respectively synthesized by the microwave sintering method. These powders were calcined, compacted and sintered at 950℃ for 30 min. X-ray diffraction (XRD) patterns of the samples indicate the formation of single-phase cubic spinel structure. The grain size was estimated from SEM images which increase with CuO addition. The X-ray density is higher than the bulk density in both the ferrites. The temperature variation of the initial permeability of these samples was carried out from 30℃ to 250℃. The NiCuZn ferrite had higher initial permeability than that of the NiZn ferrite, which could be attributed to the microstructure. Saturation magnetization increases from 40 emug/g (NiZn) to 47 emug/g (NiCuZn). The dielectric constant and dielectric loss tangent of NiZn and NiCuZn ferrite samples decreases with increase in frequency exhibiting normal ferrimagnetic behavior. The NiCuZn ferrite had better electro- magnetic properties than the NiZn ferrite.
文摘MA W-Ni-Fe alloyed powder compact was sintered by microwave technology, and the influence of microwave sintering on consolidation of W-Ni-Fe alloy was studied. The fracture morphology and microstructure of alloys were measured by SEM and metallurgical microscope. The experimental results showed that microwave sintering promoted the densification of MA W-Ni-Fe alloyed powder quickly with the higher heating rate. The density of the sintered samples increased with the increase of sintering temperature, and significant densification shrinkage occured at 1300 ~ 1400°C. The tungsten grain grew rapidly at 1450°C. When the alloy was microwave sintered at 1550°C, the inner structure of alloy is more homogeneous, the average W grain size is about 15 μm, and the relative density of sintered specimen is 99%.
基金the Ministry of Science and Technical Development of the Republic of Serbia,through Project No.172015 OI.
文摘The kinetics of free-radical crosslinking co-polymerization(FRCCP)of acrylic acid(AA)with both methacrylic acid(MA)(PAMA hydrogel)and maleic acid(MAL)(PAMAL hydrogel)was investigated under the conditions of isothermal conventional heating(CH)and under the conditions of microwave heating(MWH)with controlled cooling.The kinetics curves of FRCCP of PAMA and PAMAL hydrogels under the conditions of CH are described with the kinetics model of second order chemical reaction,whereas the kinetics curves under the conditions of CH are described with the kinetics model of Polany-Winger.It is proved that MWH leads to the changes in the rate of FRCCP and to the changes in the values of the kinetic parameters activation energy(Ea)and pre-exponential factor(lnA).It was found the existence of relationship between the values of the kinetic parameters calculated for MWH and CH for PAMA and PAMAL hydrogel synthesis process,which is well-known as compensation effect.The effect of MWH on the kinetics of FRCCP for PAMA and PAMAL hydrogel formation were explained by applying the model of activation by selective energy transfer(SET).The changes in kinetics model,rate of FRCCP and kinetics parameters,caused with the MWH can found wide application in designing novel technologies for obtaining polymers and for synthesis of polymers with novel physico-chemical properties.The suggested mechanism of activation for polymerisation under the conditions of MWH also enables development of novel reaction systems and technologies for polymers productions.
文摘A versatile and environmentally friendly method for α,α’-bis(substituted ben-zylidene) cycloalkanones has been developed using a heterogeneous catalysis technology. We have synthesized a series of the α,α’-bis(substituted benzylidene) cycloalkanones, a biologically important class of compounds, via the cross aldol condensation between arylaldehydes and cycloketones using sodium-modified fluorapatite (Na/FAP) as a highly efficient solid catalyst under conventional heating in aqueous media and solventless conditions under microwave. Catalyst reuse, ease of separation of the pure product, and high yields are some of the unique features of this process. Shorter reaction times (4 - 7 min) and higher yields (80% - 94%) were achieved under microwave irradiation conditions.
基金the National Advanced Manerale Commotee China 563 Plan
文摘This paper introduces the characteristic of microwave sintering,introduces and analyses the process of microwave sintering of thealumina ceramics, moreover, compared with the experiments ofconventional sintering method. Based on the research, some resultsare obtained, and experimental basis for microwave sintering ofceramics is put forward.