Most studies addressing the specificity of meridians and acupuncture points have focused mainly on the different neural effects of acupuncture at different points in healthy individuals. This study examined the effect...Most studies addressing the specificity of meridians and acupuncture points have focused mainly on the different neural effects of acupuncture at different points in healthy individuals. This study examined the effects of acupuncture on brain function in a pathological context. Sixteen patients with ischemic stroke were randomly assigned to true point group (true acupuncture at right Waiguan (SJ5)) and sham point group (sham acupuncture). Results of functional magnetic resonance imaging revealed activation in right parietal lobe (Brodmann areas 7 and 19), the right temporal lobe (Brodmann area 39), the right limbic lobe (Brodmann area 23) and bilateral oc-cipital lobes (Brodmann area 18). Furthermore, inhibition of bilateral frontal lobes (Brodmann area 4, 6, and 45), right parietal lobe (Brodmann areas 1 and 5) and left temporal lobe (Brodmann area 21 ) were observed in the true point group. Activation in the precuneus of right parietal lobe (Brodmann area 7) and inhibition of the left superior frontal gyrus (Brodmann area 10) was observed in the sham group. Compared with sham acupuncture, acupuncture at Waiguan in stroke patients inhibited Brodmann area 5 on the healthy side. Results indicated that the altered specificity of sensation-associated cortex (Brodmann area 5) is possibly associated with a central mechanism of acupuncture at Waiguan for stroke patients.展开更多
In the present study, 10 patients with ischemic stroke in the left hemisphere and six healthy controls were subjected to acupuncture at right Waiguan (TE5). In ischemic stroke subjects, functional MRI showed enhance...In the present study, 10 patients with ischemic stroke in the left hemisphere and six healthy controls were subjected to acupuncture at right Waiguan (TE5). In ischemic stroke subjects, functional MRI showed enhanced activation in Broadmann areas 5, 6, 7, 18, 19, 24, 32, the hypothalamic inferior lobe, the mamiilary body, and the ventral posterolateral nucleus of the left hemisphere, and Broadmann areas 4, 6, 7, 18, 19 and 32 of the right hemisphere, but attenuated activation of Broadmann area 13, the hypothalamic inferior lobe, the posterior lobe of the tonsil of cerebellum, and the culmen of the anterior lobe of hypophysis, in the left hemisphere and Broadmann area 13 in the right hemisphere. In ischemic stroke subjects, a number of deactivated brain areas were enhanced, including Broadmann areas 6, 11,20, 22, 37, and 47, the culmen of the anterior lobe of hypophysis, alae lingulae cerebella, and the posterior lobe of the tonsil of cerebellum of the left hemisphere, and Broadmann areas 8, 37, 45 and 47, the culmen of the anterior lobe of hypophysis, pars tuberalis adenohypophyseos, inferior border of lentiform nucleus, lateral globus pallidus, inferior temporal gyrus, and the parahippocampal gyrus of the right hemisphere. These subjects also exhibited attenuation of a number of deactivated brain areas, including Broadmann area 7. These data suggest that acupuncture at Waiguan specifically alters brain function in regions associated with sensation, vision, and motion in ischemic stroke patients. By contrast, in normal individuals, acupuncture at Waiguan generally activates brain areas associated with insomnia and other functions.展开更多
Positive activation and negative activation of glucose metabolism can be detected in different brain regions under acupuncture conditions using functional magnetic resonance imaging (fMRI) which reveals acupoint fun...Positive activation and negative activation of glucose metabolism can be detected in different brain regions under acupuncture conditions using functional magnetic resonance imaging (fMRI) which reveals acupoint function and location-acupoint specificity. This study observed the regional cerebral activation of the Waiguan (SJ 5) acupoint following true needling at the true Waiguan acupoint, sham needling at the true Waiguan acupoint and true needling at a sham point using fMRI. The fMRI results demonstrated that compared with sham needling, true needling at Waiguan activated the BA8 area and left cerebellum. Compared with needling at the sham point, needling at Waiguan activated the BA2 area, the left cerebellum and the right inferior semilunar lobule. Thus the activated brain areas caused by needling Waiguan may be the basis for treatment of certain diseases.展开更多
Functional brain imaging studies of the specificity of acupoint stimulation have revealed that needling at particular acupoints can induce activation of corresponding brain areas, examined in physiological and patholo...Functional brain imaging studies of the specificity of acupoint stimulation have revealed that needling at particular acupoints can induce activation of corresponding brain areas, examined in physiological and pathological states. The present study examined Waiguan (SJ 5) as the acupoint of interest. We tested five conditions: a true needling at true acupoint group, a sham needling at true acupoint group, a true needling at sham acupoint group, a sham needling at sham acupoint group, and a healthy control group. We examined changes in glucose metabolism in different functional cortical regions to determine the specific brain activation elicited by acupuncture at Waiguan. The results revealed that true and sham acupuncture at the same acupoint activated different brain regions. In addition, applying acupuncture at a genuine acupoint and a neighboring sham acupoint activated different brain regions. These findings suggest that acupuncture at Waiguan causes activation in some brain regions.展开更多
Acupoint combination is a method used for acupoint treatment of patients. Traditionally, acupoints are matched along the meridian distribution, which is a common rule in clinical practice, but the underlying mechanism...Acupoint combination is a method used for acupoint treatment of patients. Traditionally, acupoints are matched along the meridian distribution, which is a common rule in clinical practice, but the underlying mechanism remains unclear. Cerebral scans with functional magnetic resonance imaging (fMRI) have been used in the study of acupuncture and acupoint specifically. In this study, fMRI was used to detect the activation of the brain areas under different acupoints, matched along different meridians, to elucidate the acupoint combination via a modern medical approach. Forty healthy volunteers were randomly divided into the following groups: Waiguan point (SJ 5), Waiguan (SJ 5) + Zhigou (SJ 6) (2 acupoints come from the same meridian), Waiguan (SJ 5) + Neiguan (PC 6) (2 acupoints come from 2 meridians with the relationship of interior-exterior), Waiguan (SJ 5) + Yanglingquan (GB 34) (2 acupoints come from 2 meridians with the same name-Shaoyang Meridian), and sham point groups (needling in different points on the right hand). A real-time cerebral fMRI scan was simultaneously performed. The cerebral activation rate, and the number and strength of different regions of interest were compared among the groups. The fMRI cerebral imaging confirmed that there were some differences in the activation of cerebral areas by the needlings in SJ 5, and in combination with other acupoints. Needling at SJ 5 alone greatly activated the right cerebellum, while needling at both SJ 5 and different co-needling points activated different cerebral functional areas.展开更多
Spatial heterogeneity is an inherent characteristic of natural forest landscapes, therefore estimation of structural variability, including the collection and analyzing of field measurements, is a growing challenge fo...Spatial heterogeneity is an inherent characteristic of natural forest landscapes, therefore estimation of structural variability, including the collection and analyzing of field measurements, is a growing challenge for monitoring wildlife habitat di- versity and ecosystem sustainability. In this study, we investigated the combined influence of plot shape and size on the accuracy of assessment of conventional and rare structural features in two young-growth spruce-dominated forests in northwestern China. We used a series of inventory schemes and analytical approaches. Our data showed that options for sampling protocols, especially the selection of plot size considered in structural attributes measurement, dramatically af- fect the minimum number of plots required to meet a certain accuracy criteria. The degree of influence of plot shape is related to survey objectives; thus, effects of plot shape differ for evaluations of the "mean" or "representative" stand structural conditions from that for the range of habitat (in extreme values). Results of Monte Carlo simulations suggested that plot sizes 〈0.1 ha could be the most efficient way to sample for conventional characteristics (features with relative constancy within a site, such as stem density). Also, 0.25 ha or even larger plots may have a greater likelihood of capturing rare structural attributes (features possessing high randomness and spatial heterogeneity, such as volume of coarse woody debris) in our forest type. These findings have important implications for advisable sampling protocol (plot size and shape) to adequately capture information on forest habitat structure and diversity; such efforts must be based on a clear definition of which types are structural attributes to measure.展开更多
Exosomes are extracellular vesicles secreted by most eukaryotic cells and participate in intercellular communication.The components of exosomes,including proteins,DNA,mRNA,microRNA,long noncoding RNA,circular RNA,etc....Exosomes are extracellular vesicles secreted by most eukaryotic cells and participate in intercellular communication.The components of exosomes,including proteins,DNA,mRNA,microRNA,long noncoding RNA,circular RNA,etc.,which play a crucial role in regulating tumor growth,metastasis,and angiogenesis in the process of cancer development,and can be used as a prognostic marker and/or grading basis for tumor patients.Hereby,we mainly summarized as followed:the role of exosome contents in cancer,focusing on proteins and noncoding RNA;the interaction between exosomes and tumor microenvironment;the mechanisms that epithelial-mesenchymal transition,invasion and migration of tumor affected by exosomes;and tumor suppression strategies based on exosomes.Finally,the application potential of exosomes in clinical tumor diagnosis and therapy is prospected,which providing theoretical supports for using exosomes to serve precise tumor treatment in the clinic.展开更多
In this study, the influences of La_(2)O_(3) added on the phase, morphology and reduction process of tungsten oxide prepared by solution combustion synthesis(SCS) were investigated for the first time. And tungsten nan...In this study, the influences of La_(2)O_(3) added on the phase, morphology and reduction process of tungsten oxide prepared by solution combustion synthesis(SCS) were investigated for the first time. And tungsten nanopowders with different La_(2)O_(3) doping amount(0.5~5.0 wt%) were successfully prepared by SCS and followed hydrogen reduction. The results showed that with the increase of La_(2)O_(3) addition,the product synthesized by SCS changed from needle-like W_(18) O_(49) to irregularly granulated H0.53 WO3 and the complete reduction temperature also increased form 700°C to 850°C. The densification behavior of as-prepared W nanopowders revealed that the densification inhibitory effect of La_(2)O_(3) was enhanced as the La_2O_3 addition increased. Nevertheless, due to the optimal size and distribution of La_(2)O_(3) particles,the sample with 2.0 wt% La_(2)O_(3) addition has a smallest grain size of 0.47 μm and a highest microhardness value of 739.3 Hv0.2, which are the best compared with the literature.展开更多
Intra-articular injection of mesenchymal stem cells(MSCs)is a promising strategy for osteoarthritis(OA)treatment.However,more and more studies reveal that the injected MSCs have poor adhesion,migration,and survival in...Intra-articular injection of mesenchymal stem cells(MSCs)is a promising strategy for osteoarthritis(OA)treatment.However,more and more studies reveal that the injected MSCs have poor adhesion,migration,and survival in the joint cavity.A recent study shows that tropoelastin(TE)regulates adhesion,proliferation and phenotypic maintenance of MSCs as a soluble additive,indicating that TE could promote MSCs-homing in regenerative medicine.In this study,we used TE as injection medium,and compared it with classic media in MSCs intra-articular injection such as normal saline(NS),hyaluronic acid(HA),and platelet-rich plasma(PRP).We found that TE could effectively improve adhesion,migration,chondrogenic differentiation of infrapatellar fat pad MSCs(IPFP-MSCs)and enhance matrix synthesis of osteoarthritic chondrocytes(OACs)in indirect-coculture system.Moreover,TE could significantly enhance IPFP-MSCs adhesion via activation of integrin β1,ERK1/2 and vinculin(VCL)in vitro.In addition,intra-articular injection of TE-IPFP MSCs suspension resulted in a short-term increase in survival rate of IPFP-MSCs and better histology scores of rat joint tissues.Inhibition of integrin β1 or ERK1/2 attenuated the protective effect of TE-IPFP MSCs suspension in vivo.In conclusion,TE promotes performance of IPFP-MSCs and protects knee cartilage from damage in OA through enhancement of cell adhesion and activation of integrin β1/ERK/VCL pathway.Our findings may provide new insights in MSCs intra-articular injection for OA treatment.展开更多
The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed ...The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed nano powders(~50 nm average particle size), we are able to sinter W-10Re alloy to 98.4% density below 1200 ℃ while maintaining a fine grain size of 260 nm, and sinter molybdenum to 98.3% density below 1120 ℃ while maintaining a fine grain size of 290 nm. Compared to normal sintering,two-step sintering offers record-fine grain sizes and better microstructural uniformity, which translates to better mechanical properties with higher hardness(6.3 GPa for tungsten-rhenium and 4.0 GPa for molybdenum, both being the highest in all pressurelessly sintered samples of the respective material system)and larger Weibull modulus. Together with our previous demonstration in tungsten, we believe that twostep sintering is a general effective method to produce high-quality fine-grained refractory metals and alloys, and the lessons learned here are transferable to other materials for powder metallurgy.展开更多
基金the State Plan for Development of Basic Research in Key Areas(973 Program)in China,No.2006CB504505,2012CB518504the Key Subject Construction Project of"211 Engineering"III Stage of Guangdong Province in Chinathe Guangdong Provincial"College Students’Innovative Experiment Plan"Project in China,No.1212112038
文摘Most studies addressing the specificity of meridians and acupuncture points have focused mainly on the different neural effects of acupuncture at different points in healthy individuals. This study examined the effects of acupuncture on brain function in a pathological context. Sixteen patients with ischemic stroke were randomly assigned to true point group (true acupuncture at right Waiguan (SJ5)) and sham point group (sham acupuncture). Results of functional magnetic resonance imaging revealed activation in right parietal lobe (Brodmann areas 7 and 19), the right temporal lobe (Brodmann area 39), the right limbic lobe (Brodmann area 23) and bilateral oc-cipital lobes (Brodmann area 18). Furthermore, inhibition of bilateral frontal lobes (Brodmann area 4, 6, and 45), right parietal lobe (Brodmann areas 1 and 5) and left temporal lobe (Brodmann area 21 ) were observed in the true point group. Activation in the precuneus of right parietal lobe (Brodmann area 7) and inhibition of the left superior frontal gyrus (Brodmann area 10) was observed in the sham group. Compared with sham acupuncture, acupuncture at Waiguan in stroke patients inhibited Brodmann area 5 on the healthy side. Results indicated that the altered specificity of sensation-associated cortex (Brodmann area 5) is possibly associated with a central mechanism of acupuncture at Waiguan for stroke patients.
基金supported by the National Basic Research Program of China(973 Program),No.2006CB504505,2012CB518504the Third Key Construction Program of "211 Project" of Guangdong Province
文摘In the present study, 10 patients with ischemic stroke in the left hemisphere and six healthy controls were subjected to acupuncture at right Waiguan (TE5). In ischemic stroke subjects, functional MRI showed enhanced activation in Broadmann areas 5, 6, 7, 18, 19, 24, 32, the hypothalamic inferior lobe, the mamiilary body, and the ventral posterolateral nucleus of the left hemisphere, and Broadmann areas 4, 6, 7, 18, 19 and 32 of the right hemisphere, but attenuated activation of Broadmann area 13, the hypothalamic inferior lobe, the posterior lobe of the tonsil of cerebellum, and the culmen of the anterior lobe of hypophysis, in the left hemisphere and Broadmann area 13 in the right hemisphere. In ischemic stroke subjects, a number of deactivated brain areas were enhanced, including Broadmann areas 6, 11,20, 22, 37, and 47, the culmen of the anterior lobe of hypophysis, alae lingulae cerebella, and the posterior lobe of the tonsil of cerebellum of the left hemisphere, and Broadmann areas 8, 37, 45 and 47, the culmen of the anterior lobe of hypophysis, pars tuberalis adenohypophyseos, inferior border of lentiform nucleus, lateral globus pallidus, inferior temporal gyrus, and the parahippocampal gyrus of the right hemisphere. These subjects also exhibited attenuation of a number of deactivated brain areas, including Broadmann area 7. These data suggest that acupuncture at Waiguan specifically alters brain function in regions associated with sensation, vision, and motion in ischemic stroke patients. By contrast, in normal individuals, acupuncture at Waiguan generally activates brain areas associated with insomnia and other functions.
基金the National 973 Program of China,No.2006CB504505the National Natural Science Foundation of China,No.90709027
文摘Positive activation and negative activation of glucose metabolism can be detected in different brain regions under acupuncture conditions using functional magnetic resonance imaging (fMRI) which reveals acupoint function and location-acupoint specificity. This study observed the regional cerebral activation of the Waiguan (SJ 5) acupoint following true needling at the true Waiguan acupoint, sham needling at the true Waiguan acupoint and true needling at a sham point using fMRI. The fMRI results demonstrated that compared with sham needling, true needling at Waiguan activated the BA8 area and left cerebellum. Compared with needling at the sham point, needling at Waiguan activated the BA2 area, the left cerebellum and the right inferior semilunar lobule. Thus the activated brain areas caused by needling Waiguan may be the basis for treatment of certain diseases.
基金the National Basic Research Program of China (973 program), No.2006CB504505the National Natural Science Foundation of China, No.90709027
文摘Functional brain imaging studies of the specificity of acupoint stimulation have revealed that needling at particular acupoints can induce activation of corresponding brain areas, examined in physiological and pathological states. The present study examined Waiguan (SJ 5) as the acupoint of interest. We tested five conditions: a true needling at true acupoint group, a sham needling at true acupoint group, a true needling at sham acupoint group, a sham needling at sham acupoint group, and a healthy control group. We examined changes in glucose metabolism in different functional cortical regions to determine the specific brain activation elicited by acupuncture at Waiguan. The results revealed that true and sham acupuncture at the same acupoint activated different brain regions. In addition, applying acupuncture at a genuine acupoint and a neighboring sham acupoint activated different brain regions. These findings suggest that acupuncture at Waiguan causes activation in some brain regions.
基金the National 973 Program of China, No. 2006CB504505the National Nature Science Foundation of China, No. 90709027
文摘Acupoint combination is a method used for acupoint treatment of patients. Traditionally, acupoints are matched along the meridian distribution, which is a common rule in clinical practice, but the underlying mechanism remains unclear. Cerebral scans with functional magnetic resonance imaging (fMRI) have been used in the study of acupuncture and acupoint specifically. In this study, fMRI was used to detect the activation of the brain areas under different acupoints, matched along different meridians, to elucidate the acupoint combination via a modern medical approach. Forty healthy volunteers were randomly divided into the following groups: Waiguan point (SJ 5), Waiguan (SJ 5) + Zhigou (SJ 6) (2 acupoints come from the same meridian), Waiguan (SJ 5) + Neiguan (PC 6) (2 acupoints come from 2 meridians with the relationship of interior-exterior), Waiguan (SJ 5) + Yanglingquan (GB 34) (2 acupoints come from 2 meridians with the same name-Shaoyang Meridian), and sham point groups (needling in different points on the right hand). A real-time cerebral fMRI scan was simultaneously performed. The cerebral activation rate, and the number and strength of different regions of interest were compared among the groups. The fMRI cerebral imaging confirmed that there were some differences in the activation of cerebral areas by the needlings in SJ 5, and in combination with other acupoints. Needling at SJ 5 alone greatly activated the right cerebellum, while needling at both SJ 5 and different co-needling points activated different cerebral functional areas.
基金supported by the Hundred Talents Program of the Chinese Academy of Sciences(No.29Y127D11)the National Natural Science Foundation of China(No.41271524)+1 种基金Natural Science Foundation of Gansu Province(No.1210RJDA015)Forestry Industry Research Special Funds for Public Welfare Projects(No.201104009-08)
文摘Spatial heterogeneity is an inherent characteristic of natural forest landscapes, therefore estimation of structural variability, including the collection and analyzing of field measurements, is a growing challenge for monitoring wildlife habitat di- versity and ecosystem sustainability. In this study, we investigated the combined influence of plot shape and size on the accuracy of assessment of conventional and rare structural features in two young-growth spruce-dominated forests in northwestern China. We used a series of inventory schemes and analytical approaches. Our data showed that options for sampling protocols, especially the selection of plot size considered in structural attributes measurement, dramatically af- fect the minimum number of plots required to meet a certain accuracy criteria. The degree of influence of plot shape is related to survey objectives; thus, effects of plot shape differ for evaluations of the "mean" or "representative" stand structural conditions from that for the range of habitat (in extreme values). Results of Monte Carlo simulations suggested that plot sizes 〈0.1 ha could be the most efficient way to sample for conventional characteristics (features with relative constancy within a site, such as stem density). Also, 0.25 ha or even larger plots may have a greater likelihood of capturing rare structural attributes (features possessing high randomness and spatial heterogeneity, such as volume of coarse woody debris) in our forest type. These findings have important implications for advisable sampling protocol (plot size and shape) to adequately capture information on forest habitat structure and diversity; such efforts must be based on a clear definition of which types are structural attributes to measure.
基金supported by the National Natural Science Foundation of China(81802785[Y.J.])Hunan Provincial Natural Science Foundation of China(2020JJ5382[Y.J.],2020JJ5381[L.C.]).
文摘Exosomes are extracellular vesicles secreted by most eukaryotic cells and participate in intercellular communication.The components of exosomes,including proteins,DNA,mRNA,microRNA,long noncoding RNA,circular RNA,etc.,which play a crucial role in regulating tumor growth,metastasis,and angiogenesis in the process of cancer development,and can be used as a prognostic marker and/or grading basis for tumor patients.Hereby,we mainly summarized as followed:the role of exosome contents in cancer,focusing on proteins and noncoding RNA;the interaction between exosomes and tumor microenvironment;the mechanisms that epithelial-mesenchymal transition,invasion and migration of tumor affected by exosomes;and tumor suppression strategies based on exosomes.Finally,the application potential of exosomes in clinical tumor diagnosis and therapy is prospected,which providing theoretical supports for using exosomes to serve precise tumor treatment in the clinic.
基金financially supported by the National Key R&D Program of China (2017YFB0306000 and 2017YFB0305600)the National Natural Science Foundation Program of China (51574031,51604239,51604240 and 51674095)+2 种基金the Natural Science Foundation Program of Beijing (2162027)the General Project of the Education Department of Hunan Province (15C1308)the Fundamental Research Funds for the Central Universities(JZ2017HGBZ0920)。
文摘In this study, the influences of La_(2)O_(3) added on the phase, morphology and reduction process of tungsten oxide prepared by solution combustion synthesis(SCS) were investigated for the first time. And tungsten nanopowders with different La_(2)O_(3) doping amount(0.5~5.0 wt%) were successfully prepared by SCS and followed hydrogen reduction. The results showed that with the increase of La_(2)O_(3) addition,the product synthesized by SCS changed from needle-like W_(18) O_(49) to irregularly granulated H0.53 WO3 and the complete reduction temperature also increased form 700°C to 850°C. The densification behavior of as-prepared W nanopowders revealed that the densification inhibitory effect of La_(2)O_(3) was enhanced as the La_2O_3 addition increased. Nevertheless, due to the optimal size and distribution of La_(2)O_(3) particles,the sample with 2.0 wt% La_(2)O_(3) addition has a smallest grain size of 0.47 μm and a highest microhardness value of 739.3 Hv0.2, which are the best compared with the literature.
基金supported by CHONGQING TALENTS PROJECT(4246ZJ1)Science and technology projects of Chongqing Education Commission(KJQN202000427).
文摘Intra-articular injection of mesenchymal stem cells(MSCs)is a promising strategy for osteoarthritis(OA)treatment.However,more and more studies reveal that the injected MSCs have poor adhesion,migration,and survival in the joint cavity.A recent study shows that tropoelastin(TE)regulates adhesion,proliferation and phenotypic maintenance of MSCs as a soluble additive,indicating that TE could promote MSCs-homing in regenerative medicine.In this study,we used TE as injection medium,and compared it with classic media in MSCs intra-articular injection such as normal saline(NS),hyaluronic acid(HA),and platelet-rich plasma(PRP).We found that TE could effectively improve adhesion,migration,chondrogenic differentiation of infrapatellar fat pad MSCs(IPFP-MSCs)and enhance matrix synthesis of osteoarthritic chondrocytes(OACs)in indirect-coculture system.Moreover,TE could significantly enhance IPFP-MSCs adhesion via activation of integrin β1,ERK1/2 and vinculin(VCL)in vitro.In addition,intra-articular injection of TE-IPFP MSCs suspension resulted in a short-term increase in survival rate of IPFP-MSCs and better histology scores of rat joint tissues.Inhibition of integrin β1 or ERK1/2 attenuated the protective effect of TE-IPFP MSCs suspension in vivo.In conclusion,TE promotes performance of IPFP-MSCs and protects knee cartilage from damage in OA through enhancement of cell adhesion and activation of integrin β1/ERK/VCL pathway.Our findings may provide new insights in MSCs intra-articular injection for OA treatment.
基金supports by the Natural Science Foundation of China(52074032,51974029,52131307,52071013)and“111”Project(No.B170003).Y.D.and J.L.acknowledge the support by Eni S.p.A.through the MIT Energy Initiative.
文摘The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed nano powders(~50 nm average particle size), we are able to sinter W-10Re alloy to 98.4% density below 1200 ℃ while maintaining a fine grain size of 260 nm, and sinter molybdenum to 98.3% density below 1120 ℃ while maintaining a fine grain size of 290 nm. Compared to normal sintering,two-step sintering offers record-fine grain sizes and better microstructural uniformity, which translates to better mechanical properties with higher hardness(6.3 GPa for tungsten-rhenium and 4.0 GPa for molybdenum, both being the highest in all pressurelessly sintered samples of the respective material system)and larger Weibull modulus. Together with our previous demonstration in tungsten, we believe that twostep sintering is a general effective method to produce high-quality fine-grained refractory metals and alloys, and the lessons learned here are transferable to other materials for powder metallurgy.