Thermodynamics for chemical vapor synthesis (CVS) of Nb nanopowder in NbCl5-H2-Ar system was investigated by using FactSage software. The validation experiments were conducted to confirm the thermodynamics points. T...Thermodynamics for chemical vapor synthesis (CVS) of Nb nanopowder in NbCl5-H2-Ar system was investigated by using FactSage software. The validation experiments were conducted to confirm the thermodynamics points. The results indicate that under the atmospheric pressure, the reduction approach from NbCl5(g) to Nb(s) is a stage-wise process with the formation of complex sub-chlorides, and is controllable at low hydrogen ratio (mole ratio of n(NbCl5):n(H2)<1:180) and low temperature (<1050 °C). Furthermore, a reasonable amount of inert loading gas is favorable to increase the reduction ratio of NbCl5 and the powder yield. The as-synthesized Nb nanopowder with the homogeneous size of 30-50 nm and the powder yield of 85% (mass fraction) is obtained by the CVS process under n(NbCl5):n(H2):n(Ar)=1:120:1 and 950 °C with the NbCl5 reduction rate of 96.1%.展开更多
Tetragonal zirconia (T-ZrO2) ceramic nanopowders stabilized with 3 mol% Y2O3 were synthesized via polyacrylamide gel method, using ZrOCl2?8H2O and Y(NO3)3?6H2O as raw materials. The effect of temperature on phase comp...Tetragonal zirconia (T-ZrO2) ceramic nanopowders stabilized with 3 mol% Y2O3 were synthesized via polyacrylamide gel method, using ZrOCl2?8H2O and Y(NO3)3?6H2O as raw materials. The effect of temperature on phase composition and morphology of YSZ nanopowders and sintering behavior of YSZ ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers hardness tester. The aging-resistance of YSZ ceramics was measured by means of aging experiments. The results demonstrated that the phase composition of YSZ ceramic nanopowders had no obvious change and it was composed of T-ZrO2. Particle size of well-dispersed YSZ ceramic nanopowders increased from 17 to 35 nm with increasing calcining temperature from 600 to 800 ℃. There was noticeable negative correlation between calcining temperature and the relative density of YSZ ceramic at the same sintering temperature. The aging experiments showed that water vapor facilitated tetragonal to monoclinic phase transformation, and the sample that had smaller grain size exhibited better aging-resistance. It can be concluded that when the calcining temperature is 600 ℃ and sintering temperature is 1550 ℃, the relative density and hardness of YSZ ceramic arrive at the peak of 96.64% and 11.135 GPa respectively, and it has less microcracks and excellent aging-resistance.展开更多
We propose an experimental spectroscopy method for investigating the electrical characteristics of concentrated nanopowder dispersed systems based on compacted ZrO2. The technique is based on measurement of electroche...We propose an experimental spectroscopy method for investigating the electrical characteristics of concentrated nanopowder dispersed systems based on compacted ZrO2. The technique is based on measurement of electrochemical impedance of the compacts. A possibility is shown for using the technique to study the processes of structure formation in nanopowder dispersed systems. It is shown that the technique is quite sensitive to detect subtle effects due to the chemical composition of the reactants from which the dispersed phase has been synthesized and external electromagnetic fields. In particular, it has been determined that the powders produced by chemical deposition possess conductiv-ity by nanoparticle volume which is several order of magnitude lower than that for powders obtained from the chloride feedstock. It has been revealed that exposure to weak (H = 105 A/m - 106 A/m) pulsed magnetic fields leads to a redistribution of free charge carriers between volume and surface of the nanoparticles.展开更多
Citrate-nitrate autocombustion process is a promising synthesis route in the field of nanomaterials. This route involves many controlling parameters which ultimately affect properties of the products. In the present r...Citrate-nitrate autocombustion process is a promising synthesis route in the field of nanomaterials. This route involves many controlling parameters which ultimately affect properties of the products. In the present research work, the effect of concentration of fuel to that of metal nitrates has been studied in a systematic manner. The nature of exothermic reaction was analyzed with DSC-TGA and the powder properties were characterized by XRD, TEM and BET measurement. The properties of the powders have been explained with respect to fuel content, vigorousness of the exothermic reaction, combustion temperature and duration. The most vigorous reaction was found to occur for the composition with FER of 0.50 with the production of the smallest crystallite size of 9 nm.展开更多
High temperature treatment of tungsten alloy of W-5wt.% TM (transition metals, TM = Ni, Fe, Cu, Co) nanopowder was run under different temperatures to cover the oxidation rate at different temperatures. The correlat...High temperature treatment of tungsten alloy of W-5wt.% TM (transition metals, TM = Ni, Fe, Cu, Co) nanopowder was run under different temperatures to cover the oxidation rate at different temperatures. The correlation was developed for certain temperatures to find an equation for the relation between time and weight. The thermal treatment was done for different quantities at certain times. The proposed equation studies the correlation between temperature, time, and weight. For each temperature, a number of points were recorded from the measured oxidation curve. The shape of the curves is well-represented in this paper. The final results will present the highest temperature, the maximum weight, and the maximum time for full oxidation at high and low temperatures.展开更多
In-situ electron irradiation and aging are applied to introduce high-density precipitates in an Mg-10Gd-3Y-1Zn-0.5Zr(GWZ1031K,wt.%)alloy to improve the hardness.The results show that the hardness of the Mg alloy after...In-situ electron irradiation and aging are applied to introduce high-density precipitates in an Mg-10Gd-3Y-1Zn-0.5Zr(GWZ1031K,wt.%)alloy to improve the hardness.The results show that the hardness of the Mg alloy after irradiation for 10 h and aging for 9 h at 250℃ is 1.64 GPa,which is approximately 64% higher than that of the samples before being treated.It is mainly attributed to γ'precipitates on the basal plane after irradiation and the high-density nanoscale β'precipitates on the prismatic plane after aging,which should be closely related to the irradiation-induced homogenous clusters.The latter plays a key role in precipitation hardening.This result paves a way to improve the mechanical properties of metallic materials by tailoring the precipitation through irradiation and aging.展开更多
基金Project(51102015)supported by the National Natural Science Foundation of China
文摘Thermodynamics for chemical vapor synthesis (CVS) of Nb nanopowder in NbCl5-H2-Ar system was investigated by using FactSage software. The validation experiments were conducted to confirm the thermodynamics points. The results indicate that under the atmospheric pressure, the reduction approach from NbCl5(g) to Nb(s) is a stage-wise process with the formation of complex sub-chlorides, and is controllable at low hydrogen ratio (mole ratio of n(NbCl5):n(H2)<1:180) and low temperature (<1050 °C). Furthermore, a reasonable amount of inert loading gas is favorable to increase the reduction ratio of NbCl5 and the powder yield. The as-synthesized Nb nanopowder with the homogeneous size of 30-50 nm and the powder yield of 85% (mass fraction) is obtained by the CVS process under n(NbCl5):n(H2):n(Ar)=1:120:1 and 950 °C with the NbCl5 reduction rate of 96.1%.
基金Funded by the National Natural Science Foundation of China(No.51964035)the Natural Science Foundation of Inner Mongolia Autonomous Region(No.2019MS0520)。
文摘Tetragonal zirconia (T-ZrO2) ceramic nanopowders stabilized with 3 mol% Y2O3 were synthesized via polyacrylamide gel method, using ZrOCl2?8H2O and Y(NO3)3?6H2O as raw materials. The effect of temperature on phase composition and morphology of YSZ nanopowders and sintering behavior of YSZ ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers hardness tester. The aging-resistance of YSZ ceramics was measured by means of aging experiments. The results demonstrated that the phase composition of YSZ ceramic nanopowders had no obvious change and it was composed of T-ZrO2. Particle size of well-dispersed YSZ ceramic nanopowders increased from 17 to 35 nm with increasing calcining temperature from 600 to 800 ℃. There was noticeable negative correlation between calcining temperature and the relative density of YSZ ceramic at the same sintering temperature. The aging experiments showed that water vapor facilitated tetragonal to monoclinic phase transformation, and the sample that had smaller grain size exhibited better aging-resistance. It can be concluded that when the calcining temperature is 600 ℃ and sintering temperature is 1550 ℃, the relative density and hardness of YSZ ceramic arrive at the peak of 96.64% and 11.135 GPa respectively, and it has less microcracks and excellent aging-resistance.
文摘We propose an experimental spectroscopy method for investigating the electrical characteristics of concentrated nanopowder dispersed systems based on compacted ZrO2. The technique is based on measurement of electrochemical impedance of the compacts. A possibility is shown for using the technique to study the processes of structure formation in nanopowder dispersed systems. It is shown that the technique is quite sensitive to detect subtle effects due to the chemical composition of the reactants from which the dispersed phase has been synthesized and external electromagnetic fields. In particular, it has been determined that the powders produced by chemical deposition possess conductiv-ity by nanoparticle volume which is several order of magnitude lower than that for powders obtained from the chloride feedstock. It has been revealed that exposure to weak (H = 105 A/m - 106 A/m) pulsed magnetic fields leads to a redistribution of free charge carriers between volume and surface of the nanoparticles.
文摘Citrate-nitrate autocombustion process is a promising synthesis route in the field of nanomaterials. This route involves many controlling parameters which ultimately affect properties of the products. In the present research work, the effect of concentration of fuel to that of metal nitrates has been studied in a systematic manner. The nature of exothermic reaction was analyzed with DSC-TGA and the powder properties were characterized by XRD, TEM and BET measurement. The properties of the powders have been explained with respect to fuel content, vigorousness of the exothermic reaction, combustion temperature and duration. The most vigorous reaction was found to occur for the composition with FER of 0.50 with the production of the smallest crystallite size of 9 nm.
文摘High temperature treatment of tungsten alloy of W-5wt.% TM (transition metals, TM = Ni, Fe, Cu, Co) nanopowder was run under different temperatures to cover the oxidation rate at different temperatures. The correlation was developed for certain temperatures to find an equation for the relation between time and weight. The thermal treatment was done for different quantities at certain times. The proposed equation studies the correlation between temperature, time, and weight. For each temperature, a number of points were recorded from the measured oxidation curve. The shape of the curves is well-represented in this paper. The final results will present the highest temperature, the maximum weight, and the maximum time for full oxidation at high and low temperatures.
基金supported by the National Natural Science Foundation of China(Grant Nos.51871222,52171021,and 51801214)Liaoning Provincial Natural Science Foundation(2019-MS-335)the research fund of SYNL。
文摘In-situ electron irradiation and aging are applied to introduce high-density precipitates in an Mg-10Gd-3Y-1Zn-0.5Zr(GWZ1031K,wt.%)alloy to improve the hardness.The results show that the hardness of the Mg alloy after irradiation for 10 h and aging for 9 h at 250℃ is 1.64 GPa,which is approximately 64% higher than that of the samples before being treated.It is mainly attributed to γ'precipitates on the basal plane after irradiation and the high-density nanoscale β'precipitates on the prismatic plane after aging,which should be closely related to the irradiation-induced homogenous clusters.The latter plays a key role in precipitation hardening.This result paves a way to improve the mechanical properties of metallic materials by tailoring the precipitation through irradiation and aging.