Rapid eutectic growth of Sb-24%Cu alloy is realized in the drop tube during the free fall under the con-tainerless condition. Based on the analysis of crystal nuclea-tion and eutectic growth in the free fall condition...Rapid eutectic growth of Sb-24%Cu alloy is realized in the drop tube during the free fall under the con-tainerless condition. Based on the analysis of crystal nuclea-tion and eutectic growth in the free fall condition, it is indicated that, with the increase of undercooling, microstruc-tural transition of Sb-24%Cu eutectic alloy proceeds from lamellar to anomalous eutectic structure. Undercoolings of 0 -154 K have been obtained in experiment. The maximum undercooling exceeds to 0.19TE. Calculated results exhibit that Cu2Sb compound is the primary nucleation phase, and that the primary Sb dendrite will grow more rapidly than the eutectic structure when undercooling is larger than 40 K. The eutectic coupled zone around Sb-24%Cu eutectic alloy leads strongly to the Cu-rich side and covers a composition range from 23.0% to 32.7%Sb.展开更多
A 3m drop-tube was used to investigate the solidification of Fe50Cu50 hypoperitectic alloy. The falling droplets solidified as spheres and splats. The obtained particles range from 1000μm to 80μm in diameter. It was...A 3m drop-tube was used to investigate the solidification of Fe50Cu50 hypoperitectic alloy. The falling droplets solidified as spheres and splats. The obtained particles range from 1000μm to 80μm in diameter. It was found that the phase separation occurred if the Fe-Cu liquid was undercooled to a certain extent before solidification.In the big particles macroscopic separation of Fe-rich phase always appeared in the cented of the particles, and in the small ones the Fe-rich phase usually solidified as little spheres. In the flakes the Fe-rich and Cu-rich layers alternatively displayed from top to bottom.展开更多
Solidification of 0.1―1.0 mm diameter droplets of Fe-66.7 at.%Si alloy was achieved in a 3 m drop tube. The XRD, EDS, and SEM measurements reveal that all the droplets are composed of the primary phase α and the α+...Solidification of 0.1―1.0 mm diameter droplets of Fe-66.7 at.%Si alloy was achieved in a 3 m drop tube. The XRD, EDS, and SEM measurements reveal that all the droplets are composed of the primary phase α and the α+ε eutectic. With decreasing droplet diameter, the growth mode of the primary phase α changes from faceted to nonfaceted growth and the eutectic changes from needle-like to anomalous eutectic. In addition, the width of the primary phase α decreases with decreasing droplet size. The different cooling rates and undercooling levels corresponding to the samples with different sizes are responsible for the morphology changes. The cooling rates of the samples with different diameters during free fall were calculated and their effects on the microstructure formation were discussed. This kind of transition is also found inside the same sample, which is due to the larger cooling rate on the surface than at the center.展开更多
To explore the heat transfer of micro-droplet during free fall in the drop tube, the falling velocity and microgravity level are calculated. The Newtonian heat transfer formulation is coupled with the classical heat c...To explore the heat transfer of micro-droplet during free fall in the drop tube, the falling velocity and microgravity level are calculated. The Newtonian heat transfer formulation is coupled with the classical heat conduction equation to predict the heat transfer process within micro-droplet. Based on the numerical solution by finite difference method with implicit Euler scheme,the temporal evolution of thermal information inside micro-droplet is obtained including the temperature distribution, cooling rate, temperature difference and gradient. To quantitatively reveal the mechanism how the various factors affect the heat transfer of micro-droplet, the effects of physical properties of liquid metal and cooling gas as well as the micro-droplet size are studied.As the important indicators of heat transfer process, the cooling rate and temperature difference are acquired to systematically investigate the relationship between thermophysical properties and heat transfer process of different metallic micro-droplets.展开更多
The solidification microstructure of Al-Ni, Al-Cu, Ag-Cu, Al-Pb and Cu-Co alloys quenched in silicone oil before and after free fall in evacuated 50 m drop tube were investigated contrastively. The effect of micrograv...The solidification microstructure of Al-Ni, Al-Cu, Ag-Cu, Al-Pb and Cu-Co alloys quenched in silicone oil before and after free fall in evacuated 50 m drop tube were investigated contrastively. The effect of microgravity on the solidification process of medium-low-melting-point eutectic, monotectic and peritectic alloys were ana-lyzed and discussed. The results indicated that the effects of microgravity on the eutectic cell shape, the pattern in eutectic cell and the inter-eutectic spacing were different for different types of eutectic systems; the size distribution of Pb particles in Al-5wt% Pb monotectic alloy was significantly changed by microgravity; and the shape of retained primary α-Co phase in Cu-10wt%Co peritectic alloy was also changed by microgravity. These results are beneficial for people to further identify and analyze the solidification behavior of multiphase alloys under microgravity.展开更多
Droplets of Cu-20%Sb hypoeutectic alloy has been rapidly solidified in drop tube within the containerless condition. With the decrease of droplet diameter, undercooling increases and the microstructures of primary cop...Droplets of Cu-20%Sb hypoeutectic alloy has been rapidly solidified in drop tube within the containerless condition. With the decrease of droplet diameter, undercooling increases and the microstructures of primary copper dendrite refines. Undercooling up to 207 K (0.17 TL) is obtained in experiment. Theoretic analysis indicated that, because of the broad temperature range of solidification, the rapid growth of primary copper dendrite is controlled by the solutal diffusion. Judging from the calculation of T0 curve in the phase diagram, it is shown that the critical undercooling of segregationless solidification is △T0=474 K. At the maximum undercooling of 207 K, the growth velocity of primary copper phase exceeds to 37 mm/s, and the distinct solute trapping occurs.展开更多
The influence of gravity on the solidification microstructure of Al-Al3Ni eutectic alloy was investigated by using a 50-m-long drop tube. It was found that at different growth rates the average inter-rod spacing was a...The influence of gravity on the solidification microstructure of Al-Al3Ni eutectic alloy was investigated by using a 50-m-long drop tube. It was found that at different growth rates the average inter-rod spacing was always larger under rnicrogravity （μg） than those under normal gravity （lg）. Moreover, with increasing growth rate, the spacing difference between lg samples and μg samples reduced progressively. Based on the experimental results and analysis, a physical model was proposed to describe the effect of gravity on the solidification process of eutectic alloy.展开更多
The steam-gasification reaction characteristics of coal and petroleum coke （PC） were studied in the drop tube furnace （DTF）. The effects of various factors such as types of carbonaceous material, gasification temp...The steam-gasification reaction characteristics of coal and petroleum coke （PC） were studied in the drop tube furnace （DTF）. The effects of various factors such as types of carbonaceous material, gasification temperature （1100- 1400 ℃） and mass ratio of steam to char （0.4：1, 0.6：1 and 1：1 separately） on gasification gas or solid products were investigated. The results showed that for all carbonaceous materials studied, H2 content exhibited the largest part of gasification gaseous products and CH4 had the smallest part. For the two petroleum cokes, CO2 content was higher than CO, which was similar to Zun-yi char. When the steam/char ratio was constant, the carbon con- version of both Shen-fu and PC chars increased with increasing temperature. When the gasification temperature was constant, the carbon conversions of all char samples increased with increasing steam/char ratio. For all the steam/char ratios, compared to water gas shift reaction, char-H2O and char-CO2 reaction were further from the thermodynamic equilibrium due to a much lower char gasification rate than that of water gas shift reaction rate. Therefore, kinetic effects may play a more important role in a char gasification step than thermodynamic effects when the gasification reaction of char was held in DTF, The calculating method for the equilibrium shift in this study will be a worth reference for analysis of the gaseous components in industrial gasifier. The reactivity of residual cokes decreased and the crystal layer （L002/d002） numbers of residual cokes increased with increasing gasification temperature. Therefore, L002/d002, the carbon crystallite structure parameter, can be used to evaluate the reactivity of residual cokes.展开更多
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 59901009, 59876016 and 59871040) Huo Yingdong Education Foundation (Grant No. 71044).
文摘Rapid eutectic growth of Sb-24%Cu alloy is realized in the drop tube during the free fall under the con-tainerless condition. Based on the analysis of crystal nuclea-tion and eutectic growth in the free fall condition, it is indicated that, with the increase of undercooling, microstruc-tural transition of Sb-24%Cu eutectic alloy proceeds from lamellar to anomalous eutectic structure. Undercoolings of 0 -154 K have been obtained in experiment. The maximum undercooling exceeds to 0.19TE. Calculated results exhibit that Cu2Sb compound is the primary nucleation phase, and that the primary Sb dendrite will grow more rapidly than the eutectic structure when undercooling is larger than 40 K. The eutectic coupled zone around Sb-24%Cu eutectic alloy leads strongly to the Cu-rich side and covers a composition range from 23.0% to 32.7%Sb.
文摘A 3m drop-tube was used to investigate the solidification of Fe50Cu50 hypoperitectic alloy. The falling droplets solidified as spheres and splats. The obtained particles range from 1000μm to 80μm in diameter. It was found that the phase separation occurred if the Fe-Cu liquid was undercooled to a certain extent before solidification.In the big particles macroscopic separation of Fe-rich phase always appeared in the cented of the particles, and in the small ones the Fe-rich phase usually solidified as little spheres. In the flakes the Fe-rich and Cu-rich layers alternatively displayed from top to bottom.
基金supported by the National Natural Science Foundation of China(Grant Nos.50325103 and 50171059).
文摘Solidification of 0.1―1.0 mm diameter droplets of Fe-66.7 at.%Si alloy was achieved in a 3 m drop tube. The XRD, EDS, and SEM measurements reveal that all the droplets are composed of the primary phase α and the α+ε eutectic. With decreasing droplet diameter, the growth mode of the primary phase α changes from faceted to nonfaceted growth and the eutectic changes from needle-like to anomalous eutectic. In addition, the width of the primary phase α decreases with decreasing droplet size. The different cooling rates and undercooling levels corresponding to the samples with different sizes are responsible for the morphology changes. The cooling rates of the samples with different diameters during free fall were calculated and their effects on the microstructure formation were discussed. This kind of transition is also found inside the same sample, which is due to the larger cooling rate on the surface than at the center.
基金supported by National Natural Science Foundation of China(Grant Nos.51327901,51474175,51522102 and 51734008)
文摘To explore the heat transfer of micro-droplet during free fall in the drop tube, the falling velocity and microgravity level are calculated. The Newtonian heat transfer formulation is coupled with the classical heat conduction equation to predict the heat transfer process within micro-droplet. Based on the numerical solution by finite difference method with implicit Euler scheme,the temporal evolution of thermal information inside micro-droplet is obtained including the temperature distribution, cooling rate, temperature difference and gradient. To quantitatively reveal the mechanism how the various factors affect the heat transfer of micro-droplet, the effects of physical properties of liquid metal and cooling gas as well as the micro-droplet size are studied.As the important indicators of heat transfer process, the cooling rate and temperature difference are acquired to systematically investigate the relationship between thermophysical properties and heat transfer process of different metallic micro-droplets.
文摘The solidification microstructure of Al-Ni, Al-Cu, Ag-Cu, Al-Pb and Cu-Co alloys quenched in silicone oil before and after free fall in evacuated 50 m drop tube were investigated contrastively. The effect of microgravity on the solidification process of medium-low-melting-point eutectic, monotectic and peritectic alloys were ana-lyzed and discussed. The results indicated that the effects of microgravity on the eutectic cell shape, the pattern in eutectic cell and the inter-eutectic spacing were different for different types of eutectic systems; the size distribution of Pb particles in Al-5wt% Pb monotectic alloy was significantly changed by microgravity; and the shape of retained primary α-Co phase in Cu-10wt%Co peritectic alloy was also changed by microgravity. These results are beneficial for people to further identify and analyze the solidification behavior of multiphase alloys under microgravity.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 59901009 and 50101010) Huo Yingdong Education Foundation (Grant No. 71044).
文摘Droplets of Cu-20%Sb hypoeutectic alloy has been rapidly solidified in drop tube within the containerless condition. With the decrease of droplet diameter, undercooling increases and the microstructures of primary copper dendrite refines. Undercooling up to 207 K (0.17 TL) is obtained in experiment. Theoretic analysis indicated that, because of the broad temperature range of solidification, the rapid growth of primary copper dendrite is controlled by the solutal diffusion. Judging from the calculation of T0 curve in the phase diagram, it is shown that the critical undercooling of segregationless solidification is △T0=474 K. At the maximum undercooling of 207 K, the growth velocity of primary copper phase exceeds to 37 mm/s, and the distinct solute trapping occurs.
基金supported by the National Natural Science Foundation of China(No.51171196)
文摘The influence of gravity on the solidification microstructure of Al-Al3Ni eutectic alloy was investigated by using a 50-m-long drop tube. It was found that at different growth rates the average inter-rod spacing was always larger under rnicrogravity （μg） than those under normal gravity （lg）. Moreover, with increasing growth rate, the spacing difference between lg samples and μg samples reduced progressively. Based on the experimental results and analysis, a physical model was proposed to describe the effect of gravity on the solidification process of eutectic alloy.
基金Supported by the National High Technology Research and Development of China(2012AA053101,2011AA050106)the National Key State Basic Research Development Program of China(2010CB227004)the National Natural Science Foundation of China(21376081)
文摘The steam-gasification reaction characteristics of coal and petroleum coke （PC） were studied in the drop tube furnace （DTF）. The effects of various factors such as types of carbonaceous material, gasification temperature （1100- 1400 ℃） and mass ratio of steam to char （0.4：1, 0.6：1 and 1：1 separately） on gasification gas or solid products were investigated. The results showed that for all carbonaceous materials studied, H2 content exhibited the largest part of gasification gaseous products and CH4 had the smallest part. For the two petroleum cokes, CO2 content was higher than CO, which was similar to Zun-yi char. When the steam/char ratio was constant, the carbon con- version of both Shen-fu and PC chars increased with increasing temperature. When the gasification temperature was constant, the carbon conversions of all char samples increased with increasing steam/char ratio. For all the steam/char ratios, compared to water gas shift reaction, char-H2O and char-CO2 reaction were further from the thermodynamic equilibrium due to a much lower char gasification rate than that of water gas shift reaction rate. Therefore, kinetic effects may play a more important role in a char gasification step than thermodynamic effects when the gasification reaction of char was held in DTF, The calculating method for the equilibrium shift in this study will be a worth reference for analysis of the gaseous components in industrial gasifier. The reactivity of residual cokes decreased and the crystal layer （L002/d002） numbers of residual cokes increased with increasing gasification temperature. Therefore, L002/d002, the carbon crystallite structure parameter, can be used to evaluate the reactivity of residual cokes.
