In order to solve the reserve stability problem of pyrotechnic explosives containing magnesium powder, a coating method named rapid expansion of supercritical fluid is studied. Continuous coating film of paraffin can ...In order to solve the reserve stability problem of pyrotechnic explosives containing magnesium powder, a coating method named rapid expansion of supercritical fluid is studied. Continuous coating film of paraffin can be formed on the surface of magnesium powder when paraffin content is about 1.5%. Humidity resistance property of the coated magnesium is promoted obviously. The flame sensitivity of the coated magnesium is 4.8% lower than that of the original magnesium powder after mixed with oxidant. The burning velocity of the coated magnesium is 4.7% lower than that of the contrastive sample. This method may be used to enhance the reserve stability problem of pyrotechnic explosives and the safety of magnesium powder modifying process.展开更多
Tungsten powder was fabricated from the system CaWO4-Mg by self-propagating high-temperature synthesis (SHS) with a magnesium thermit stage. The physic-chemical change during heating and the effects of pressure of sam...Tungsten powder was fabricated from the system CaWO4-Mg by self-propagating high-temperature synthesis (SHS) with a magnesium thermit stage. The physic-chemical change during heating and the effects of pressure of sample and diluents (W powder) on product have been studied. The experimental results show that the porosity of combustion product and the particle size of final tungsten powder decrease with increasing pressure of sample. Addition of diluents could increase the particle size of final tungsten powder. The purity of tungsten is improved by leaching in NaOH solution. The results of spectral analysis and particle size distribution of final tungsten powder show that the final Tungsten powder has a median diameter of 0.87μm,specific surface area of 1.09m2/g and purity of above 99.0%.展开更多
Magnesium aluminum alloy materials were fabricated via powder metallurgy. Microstructural evolution, thermal stability, tensile properties and fracture mechanism of the hot extruded magnesium alloys were investigated....Magnesium aluminum alloy materials were fabricated via powder metallurgy. Microstructural evolution, thermal stability, tensile properties and fracture mechanism of the hot extruded magnesium alloys were investigated. Microstructural observation revealed that all alloys have fine equiaxed grains due to dynamic recrystallization during hot extrusion with Mg 17 Al 12 precipitating along grain boundaries. The DSC analyses exhibited that because diffusion rate of Al into Mg is slow in solid state sintering process, Al concentration in localized region after sintering is still high enough to cause eutectic reaction. The tensile test showed that 0.2% yield strength, ultimate tensile strength and elastic modulus increase and elongation decrease with increasing Al content. Mg 9%Al obtains the best combination of mechanical properties among the investigated alloys. Fracture surface observation showed ductile fracture to be a dominant failure mode. Abundant dimples and tear ridges are found in the fracture surfaces. Grain boundary weakening results from the precipitate Mg 17 Al 12 caused intergranular cracks during tensile test. [展开更多
The effect of limestone powder and fly ash on magnesium sulfate resistance of mortar was studied by testing on the strength, expansion and hydration products of the specimens stored in MgSO4 solution at certain period...The effect of limestone powder and fly ash on magnesium sulfate resistance of mortar was studied by testing on the strength, expansion and hydration products of the specimens stored in MgSO4 solution at certain periods. The experimental results show that the strength of mortar stored in MgSO4 solution increases a little before 28 d, but decreases fast subsequently. The more the contents of limestone powder and fly ash, the less the strength losses. Mortar swells in the MgSO4 solution with the soaking time. And the more the contents of limestone powder and fly ash, the less the expansion rate is. The expansion or strength loss of mortars results from the expansion of gypsum, as well as the loss of Ca（OH）2 and other hydration products of cement. The magnesium sulfate resistance of the mortars containing limestone powder and fly ash is high.展开更多
A high-pressure laser ignition and combustion system with adjustable oxidizer gas atmosphere is established to investigate the ignition and combustion characteristics of boron-magnesium(BM)com-posite powders.An igniti...A high-pressure laser ignition and combustion system with adjustable oxidizer gas atmosphere is established to investigate the ignition and combustion characteristics of boron-magnesium(BM)com-posite powders.An ignition and combustion model of BM powders is established and validated in the present study.The results show that increasing water content,O_(2) content and Mg content all result in shorter ignition delay time of BM powders,among which the effect of water content is the most obvious.However,ignition delay time increases as pressure increases.The combustion time decreases with increasing Mg content and ambient pressure but increases with water content.With the increase of O_(2) content,combustion time of BM powders first increases and then decreases,which means a critical O_(2) content exists above which combustion time decreases.The results show that there exists a trade-off between ignition and combustion performance of BM composite powders.展开更多
Magnesium matrix composites （MMC） reinforced with 5wt% tricalcium phosphate （TCP） particles were prepared by powder metallurgy. Pure magnesium （CP-Mg） was fabricated by the same procedure for comparison. Scannin...Magnesium matrix composites （MMC） reinforced with 5wt% tricalcium phosphate （TCP） particles were prepared by powder metallurgy. Pure magnesium （CP-Mg） was fabricated by the same procedure for comparison. Scanning electron microscopy and en- ergy-dispersive X-ray spectroscopy analyses revealed that TCP particles were distributed homogeneously in the MMC. In order to investi- gate the corrosion properties, MMC samples were immersed in a simulated body fluid （SBF） at 310~0.5 K for 72 h. The mass loss of the samples in SBF and the pH values of the SBF were evaluated. Moreover, electrochemical measurements were conducted in the SBF. It was shown that the corrosion rate of the MMC decreased with the addition of TCP compared with CP-Mg. Hydroxyapatite was formed on the surface of MMC samples after immersion in the SBF for 72 h but not on the surface of CP-Mg.展开更多
The proper spacer material and the preparation technology for biological compatible porous magnesium materials were explored by the powder metallurgy method, and microstructures, porosity and mechanical properties of ...The proper spacer material and the preparation technology for biological compatible porous magnesium materials were explored by the powder metallurgy method, and microstructures, porosity and mechanical properties of sintered porous magnesium were investigated. The results show that compared with spacer materials of NH4CO3, NH3Cl and carbamide, NH4CO3 is the best one for preparation of sintered porous magnesium,and the worst one is NH3Cl.The isolated blind pores are formed mainly by the particle interval of the magnesium powders. Adding spacer material favors the formation of open pores, while has little contribution to the formation of blind pores. The overall porosity and porosity of open pore of the sintered porous magnesium increase with the increase of added spacer material, while decrease with the increase of the molding stress. The mechanical properties of sintered porous magnesium increase with decreasing addition of spacer material and increasing molding stress.展开更多
Magnesium oxysulfate (MgSO4·5Mg(OH)2·2H2O) flake powders with an average diameter of 2 μm and a thickness of 0.052 μm were prepared using magnesium sulfate and sodium hydroxide as raw materials by hydrothe...Magnesium oxysulfate (MgSO4·5Mg(OH)2·2H2O) flake powders with an average diameter of 2 μm and a thickness of 0.052 μm were prepared using magnesium sulfate and sodium hydroxide as raw materials by hydrothermal synthesis process. The composition, morphology and structural features of the hydrothermal products were examined with X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The experimental results indicate that in the conditions of n(NaOH)/n(MgSO4) of 1.25, the dosage of w(Na3PO4) crystal additives of 1.0% w(MgSO4), stirring for 5 h at 180 °C, the morphology of MgSO4·5Mg(OH)2·2H2O products is flaky and laminar, which is a kind of complex magnesium single- crystal. The recycling of MgSO4 mother liquor was also investigated to make a full use of the materials and reduce disposal. The results prove that there is no adverse effect on the yield and purity of the products.展开更多
基金Project (20031013) supported by Youth Science and Technology Foundation of Shanxi Province of China
文摘In order to solve the reserve stability problem of pyrotechnic explosives containing magnesium powder, a coating method named rapid expansion of supercritical fluid is studied. Continuous coating film of paraffin can be formed on the surface of magnesium powder when paraffin content is about 1.5%. Humidity resistance property of the coated magnesium is promoted obviously. The flame sensitivity of the coated magnesium is 4.8% lower than that of the original magnesium powder after mixed with oxidant. The burning velocity of the coated magnesium is 4.7% lower than that of the contrastive sample. This method may be used to enhance the reserve stability problem of pyrotechnic explosives and the safety of magnesium powder modifying process.
文摘Tungsten powder was fabricated from the system CaWO4-Mg by self-propagating high-temperature synthesis (SHS) with a magnesium thermit stage. The physic-chemical change during heating and the effects of pressure of sample and diluents (W powder) on product have been studied. The experimental results show that the porosity of combustion product and the particle size of final tungsten powder decrease with increasing pressure of sample. Addition of diluents could increase the particle size of final tungsten powder. The purity of tungsten is improved by leaching in NaOH solution. The results of spectral analysis and particle size distribution of final tungsten powder show that the final Tungsten powder has a median diameter of 0.87μm,specific surface area of 1.09m2/g and purity of above 99.0%.
文摘Magnesium aluminum alloy materials were fabricated via powder metallurgy. Microstructural evolution, thermal stability, tensile properties and fracture mechanism of the hot extruded magnesium alloys were investigated. Microstructural observation revealed that all alloys have fine equiaxed grains due to dynamic recrystallization during hot extrusion with Mg 17 Al 12 precipitating along grain boundaries. The DSC analyses exhibited that because diffusion rate of Al into Mg is slow in solid state sintering process, Al concentration in localized region after sintering is still high enough to cause eutectic reaction. The tensile test showed that 0.2% yield strength, ultimate tensile strength and elastic modulus increase and elongation decrease with increasing Al content. Mg 9%Al obtains the best combination of mechanical properties among the investigated alloys. Fracture surface observation showed ductile fracture to be a dominant failure mode. Abundant dimples and tear ridges are found in the fracture surfaces. Grain boundary weakening results from the precipitate Mg 17 Al 12 caused intergranular cracks during tensile test. [
基金Funded by the Specialized Research Fund for the Doctoral Program of Higher Education of China (No.200804861060)
文摘The effect of limestone powder and fly ash on magnesium sulfate resistance of mortar was studied by testing on the strength, expansion and hydration products of the specimens stored in MgSO4 solution at certain periods. The experimental results show that the strength of mortar stored in MgSO4 solution increases a little before 28 d, but decreases fast subsequently. The more the contents of limestone powder and fly ash, the less the strength losses. Mortar swells in the MgSO4 solution with the soaking time. And the more the contents of limestone powder and fly ash, the less the expansion rate is. The expansion or strength loss of mortars results from the expansion of gypsum, as well as the loss of Ca（OH）2 and other hydration products of cement. The magnesium sulfate resistance of the mortars containing limestone powder and fly ash is high.
基金the supports from National Natural Science Foundation of China(grant Nos.52276087,51806048,51776175)the Fundamental Research Funds for the Central Universities(grant No.D5000210602)+2 种基金the Key Fundamental Strengthening Project(grant Nos.2019-JCJQ-ZD-083-05,2021-JCJQ-J-0401)the Foundation of Key Laboratory(grant No.6142701190106),Natural Science Foundation of Jiangsu Province(grant No.BK20210854)Natural Science Foundation of Jiangsu Universities(grant No.20KJB470009).
文摘A high-pressure laser ignition and combustion system with adjustable oxidizer gas atmosphere is established to investigate the ignition and combustion characteristics of boron-magnesium(BM)com-posite powders.An ignition and combustion model of BM powders is established and validated in the present study.The results show that increasing water content,O_(2) content and Mg content all result in shorter ignition delay time of BM powders,among which the effect of water content is the most obvious.However,ignition delay time increases as pressure increases.The combustion time decreases with increasing Mg content and ambient pressure but increases with water content.With the increase of O_(2) content,combustion time of BM powders first increases and then decreases,which means a critical O_(2) content exists above which combustion time decreases.The results show that there exists a trade-off between ignition and combustion performance of BM composite powders.
基金the National Key Technologies R&D Program(No.2011BAE22B04)Chong qing Science and Technology Commission(No.2008BB4055)
文摘Magnesium matrix composites （MMC） reinforced with 5wt% tricalcium phosphate （TCP） particles were prepared by powder metallurgy. Pure magnesium （CP-Mg） was fabricated by the same procedure for comparison. Scanning electron microscopy and en- ergy-dispersive X-ray spectroscopy analyses revealed that TCP particles were distributed homogeneously in the MMC. In order to investi- gate the corrosion properties, MMC samples were immersed in a simulated body fluid （SBF） at 310~0.5 K for 72 h. The mass loss of the samples in SBF and the pH values of the SBF were evaluated. Moreover, electrochemical measurements were conducted in the SBF. It was shown that the corrosion rate of the MMC decreased with the addition of TCP compared with CP-Mg. Hydroxyapatite was formed on the surface of MMC samples after immersion in the SBF for 72 h but not on the surface of CP-Mg.
文摘The proper spacer material and the preparation technology for biological compatible porous magnesium materials were explored by the powder metallurgy method, and microstructures, porosity and mechanical properties of sintered porous magnesium were investigated. The results show that compared with spacer materials of NH4CO3, NH3Cl and carbamide, NH4CO3 is the best one for preparation of sintered porous magnesium,and the worst one is NH3Cl.The isolated blind pores are formed mainly by the particle interval of the magnesium powders. Adding spacer material favors the formation of open pores, while has little contribution to the formation of blind pores. The overall porosity and porosity of open pore of the sintered porous magnesium increase with the increase of added spacer material, while decrease with the increase of the molding stress. The mechanical properties of sintered porous magnesium increase with decreasing addition of spacer material and increasing molding stress.
基金Project(50704036) supported by the National Natural Science Foundation of ChinaProject(08JJ3027) supported by the Natural Science Foundation of Hunan Province, China
文摘Magnesium oxysulfate (MgSO4·5Mg(OH)2·2H2O) flake powders with an average diameter of 2 μm and a thickness of 0.052 μm were prepared using magnesium sulfate and sodium hydroxide as raw materials by hydrothermal synthesis process. The composition, morphology and structural features of the hydrothermal products were examined with X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The experimental results indicate that in the conditions of n(NaOH)/n(MgSO4) of 1.25, the dosage of w(Na3PO4) crystal additives of 1.0% w(MgSO4), stirring for 5 h at 180 °C, the morphology of MgSO4·5Mg(OH)2·2H2O products is flaky and laminar, which is a kind of complex magnesium single- crystal. The recycling of MgSO4 mother liquor was also investigated to make a full use of the materials and reduce disposal. The results prove that there is no adverse effect on the yield and purity of the products.
