Glass-like carbons （GCs） were prepared by carbonization of acetone-furfural resin in nitrogen atmosphere at 850℃, followed by heat treatment over a range of 1 200-2 500℃in inert atmosphere. The effect of heat trea...Glass-like carbons （GCs） were prepared by carbonization of acetone-furfural resin in nitrogen atmosphere at 850℃, followed by heat treatment over a range of 1 200-2 500℃in inert atmosphere. The effect of heat treatment temperature （HTT） on the oxidation behavior was investigated by dynamic and isothermal thermogravimetric analyses. The structure of GC was examined by X-ray diffractometry （XRD） and the morphologies of GC before and after oxidation were examined by scanning electron microscopy （SEM）. It is shown that the GC samples present peculiar oxidation behavior. The anti-oxidation behavior increases with increasing the HTT to 1 600 ℃, whereas decreases gradually thereafter. GC sample heat treated at 1 600℃ obtains relatively optimal anti-oxidation properties under this condition. During the oxidation, this material produces grid network matrix surface and numerous nodular residues on the surface, resulting in excellent resistance to the attack of oxygen atoms.展开更多
The dynamic mechanical properties of rock specimens after thermal treatment in the air-filled environment(AE:i.e.,at the free surface)have been extensively investigated,yet they are rarely estimated in the quasi-vacuu...The dynamic mechanical properties of rock specimens after thermal treatment in the air-filled environment(AE:i.e.,at the free surface)have been extensively investigated,yet they are rarely estimated in the quasi-vacuum environment(VE:i.e.,far from free surface),which is of special importance in engineering practice.Several precise laboratory tests(i.e.,split Hopkinson pressure bar test)on marble samples in both AE and VE were performed to investigate physical and dynamic mechanical behaviors of marble after heat treatment(25℃ to 900℃)in AE and VE.The tests results demonstrate that related properties of marble could be divided into three different stages by corresponding critical temperatures of 300℃ and 600℃,at which heat damage factors are 0.29(0.30)and 0.88(0.92)in VE(AE),respectively.The thermal damage developes more fully in AE than in VE.The thermal environment plays an important role,especially in Stage 3.Specifically,a conspicuous difference(greater than 20%)between AE and VE occurs in corresponding dynamic strength and the anti-deformation capacities of tested marble specimen.The influence of heat damage of rock is very important and valuable in engineering practice,particularly when the temperature is very high(greater than 600℃).展开更多
The formation mechanisms and growth kinetics of Al3 Ni and Al3Ni2 in Ni-Al diffusion couple prepared by electrodeposition of Ni on Al substrate were investigated. The nickel coating with 20 μm thickness was applied o...The formation mechanisms and growth kinetics of Al3 Ni and Al3Ni2 in Ni-Al diffusion couple prepared by electrodeposition of Ni on Al substrate were investigated. The nickel coating with 20 μm thickness was applied on 6061 aluminum alloy by direct current electroplating. The samples were then heat-treated for different durations at 450, 500 and 550 °C under argon atmosphere. The intermetallic phases were identified by means of scanning electron microscopy（SEM）, energy dispersive spectrometry（EDS） and X-ray diffraction（XRD）. The results showed that the formation of intermetallic phases consisted of two important steps. The first step was the lateral growth of intermetallic phase from separate sites, resulting in the formation of a continuous layer. The second step was the growth of the continuous intermetallic layer in the direction perpendicular to the interface. However, excessive increase in thickness of intermetallic phases led to the detachment of reaction products, i.e., Al3 Ni and Al3Ni2, from the substrate. It was also observed that aluminum was the dominant diffusing element during Al3 Ni growth, while nickel diffusion was dominant during Al3Ni2 growth. The growth kinetics of both Al3 Ni and Al3Ni2 phases obeyed a parabolic law.展开更多
Transition metal impurities such as chromium(Cr)and vanadium(V)in solution deteriorate electrical conductivity of smelter grade aluminium(Al).These impurities can be removed from solution via boron treatment in which ...Transition metal impurities such as chromium(Cr)and vanadium(V)in solution deteriorate electrical conductivity of smelter grade aluminium(Al).These impurities can be removed from solution via boron treatment in which borides form upon their in-situ reaction with boron(B)-bearing substances.However,Cr removal from smelter grade Al solution is not well understood.A disagreement related to chromium boride(CrB_(2))formation in molten Al in the presence of other transition metals(V,Ti,Zr,Fe)by adding Al−B master alloy has been reported in literatures.This study presents an effort to understand the mechanism of Cr removal from Al−0.50%Cr−0.50%V(mass fraction)alloy by adding Al−B(AlB_(12))master alloy at 1023 K in the Al alloy solution.Results indicate that Cr removal from molten Al−0.50%Cr−0.50%V alloy by forming stable borides cannot be achieved at 1023 K;whereas excess of B in the solution preferentially forms aluminium boride(AlB2)over CrB_(2) during boron treatment of molten Al.The underlying kinetics of V removal from molten Al−0.50%Cr−0.50%V alloy revealed that early reaction stage is controlled by[B]/[V]mass transfer through liquid phase and mass transfer coefficient(km)was measured to be 9.6×10^(−4) m/s.The later reaction stage was controlled by[B]/[V]diffusion through boride(VB_(2))ring.This study,therefore,advocates to investigate alternative ways to remove Cr from molten Al.展开更多
基金Project (2006CB600902) supported by the National Basic Research Program of China
文摘Glass-like carbons （GCs） were prepared by carbonization of acetone-furfural resin in nitrogen atmosphere at 850℃, followed by heat treatment over a range of 1 200-2 500℃in inert atmosphere. The effect of heat treatment temperature （HTT） on the oxidation behavior was investigated by dynamic and isothermal thermogravimetric analyses. The structure of GC was examined by X-ray diffractometry （XRD） and the morphologies of GC before and after oxidation were examined by scanning electron microscopy （SEM）. It is shown that the GC samples present peculiar oxidation behavior. The anti-oxidation behavior increases with increasing the HTT to 1 600 ℃, whereas decreases gradually thereafter. GC sample heat treated at 1 600℃ obtains relatively optimal anti-oxidation properties under this condition. During the oxidation, this material produces grid network matrix surface and numerous nodular residues on the surface, resulting in excellent resistance to the attack of oxygen atoms.
基金Projects(51579239,42077240,51979280)supported by the National Natural Science Foundation of China。
文摘The dynamic mechanical properties of rock specimens after thermal treatment in the air-filled environment(AE:i.e.,at the free surface)have been extensively investigated,yet they are rarely estimated in the quasi-vacuum environment(VE:i.e.,far from free surface),which is of special importance in engineering practice.Several precise laboratory tests(i.e.,split Hopkinson pressure bar test)on marble samples in both AE and VE were performed to investigate physical and dynamic mechanical behaviors of marble after heat treatment(25℃ to 900℃)in AE and VE.The tests results demonstrate that related properties of marble could be divided into three different stages by corresponding critical temperatures of 300℃ and 600℃,at which heat damage factors are 0.29(0.30)and 0.88(0.92)in VE(AE),respectively.The thermal damage developes more fully in AE than in VE.The thermal environment plays an important role,especially in Stage 3.Specifically,a conspicuous difference(greater than 20%)between AE and VE occurs in corresponding dynamic strength and the anti-deformation capacities of tested marble specimen.The influence of heat damage of rock is very important and valuable in engineering practice,particularly when the temperature is very high(greater than 600℃).
文摘The formation mechanisms and growth kinetics of Al3 Ni and Al3Ni2 in Ni-Al diffusion couple prepared by electrodeposition of Ni on Al substrate were investigated. The nickel coating with 20 μm thickness was applied on 6061 aluminum alloy by direct current electroplating. The samples were then heat-treated for different durations at 450, 500 and 550 °C under argon atmosphere. The intermetallic phases were identified by means of scanning electron microscopy（SEM）, energy dispersive spectrometry（EDS） and X-ray diffraction（XRD）. The results showed that the formation of intermetallic phases consisted of two important steps. The first step was the lateral growth of intermetallic phase from separate sites, resulting in the formation of a continuous layer. The second step was the growth of the continuous intermetallic layer in the direction perpendicular to the interface. However, excessive increase in thickness of intermetallic phases led to the detachment of reaction products, i.e., Al3 Ni and Al3Ni2, from the substrate. It was also observed that aluminum was the dominant diffusing element during Al3 Ni growth, while nickel diffusion was dominant during Al3Ni2 growth. The growth kinetics of both Al3 Ni and Al3Ni2 phases obeyed a parabolic law.
基金Taif University Researchers Supporting Project(No.TURSP-2020/293)Taif University,Taif,Saudi Arabia.
文摘Transition metal impurities such as chromium(Cr)and vanadium(V)in solution deteriorate electrical conductivity of smelter grade aluminium(Al).These impurities can be removed from solution via boron treatment in which borides form upon their in-situ reaction with boron(B)-bearing substances.However,Cr removal from smelter grade Al solution is not well understood.A disagreement related to chromium boride(CrB_(2))formation in molten Al in the presence of other transition metals(V,Ti,Zr,Fe)by adding Al−B master alloy has been reported in literatures.This study presents an effort to understand the mechanism of Cr removal from Al−0.50%Cr−0.50%V(mass fraction)alloy by adding Al−B(AlB_(12))master alloy at 1023 K in the Al alloy solution.Results indicate that Cr removal from molten Al−0.50%Cr−0.50%V alloy by forming stable borides cannot be achieved at 1023 K;whereas excess of B in the solution preferentially forms aluminium boride(AlB2)over CrB_(2) during boron treatment of molten Al.The underlying kinetics of V removal from molten Al−0.50%Cr−0.50%V alloy revealed that early reaction stage is controlled by[B]/[V]mass transfer through liquid phase and mass transfer coefficient(km)was measured to be 9.6×10^(−4) m/s.The later reaction stage was controlled by[B]/[V]diffusion through boride(VB_(2))ring.This study,therefore,advocates to investigate alternative ways to remove Cr from molten Al.
