The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when wat...The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when water-binder ratio is lower than 0.40, the cement-based material with limestone powder has insignificant change in appearance after being soaked in 10% magnesium sulfate solution at low temperature for 120 d, and has significant change in appearance after being soaked at the age of 200 d. Expansion damage and exfoliation occur on the surface of concrete test cube at different levels. When limestone powder accounts for about 28 percent of cementitious material, with the decrease of water-binder ratio, the compressive strength loss has gradually decreased after the material is soaked in the magnesium sulfate solution at low temperature at the age of 200 d. After the specimen with the water-binder ratio of less than 0.4 and the limestone powder volume of greater than 20% is soaked in 10% magnesium sulfate solution at low temperature at the age of 200 d, gypsum attack-led destruction is caused to the concrete test cube, without thaumasite sulfate attack.展开更多
By micro- and macro-observations, the deterioration mechanisms of concrete under alternate action between repeated sub-high temperature/cooling by water and sodium sulfate solution attack （TW-SA） were studied; meanw...By micro- and macro-observations, the deterioration mechanisms of concrete under alternate action between repeated sub-high temperature/cooling by water and sodium sulfate solution attack （TW-SA） were studied; meanwhile, the single sodium sulfate solution attack （SA） was also done as comparison. Micro-observations included the analysis of attack products by thermal analysis method and the determination of sulfate-ion content from surface to interior by chemical titrating method （modified barium sulfate gravimetric method）. Macro-observations mainly included the mechanical behaviors such as compressive strength, splitting strength. The experimental results indicate, in both cases, the main attack product is ettringite, only in the first layer of case SA some gypsum is checked; in case SA, the sulfate ions mainly concentrate in the surface layer, so the attack is relatively mild; but in case TW-SA, the repeated sub-high temperature/cooling by water promotes the sulfate ions diffusing inwards, which leads to obvious strength degradation.展开更多
Electrochemical water splitting plays a crucial role in storing sustainable energy into H2 as an ideal fuel,in which the anodic oxygen evolution reaction(OER)is the bottleneck.Currently,Fe-doped NiOOH(Ni_(1−x)Fe_(x)OO...Electrochemical water splitting plays a crucial role in storing sustainable energy into H2 as an ideal fuel,in which the anodic oxygen evolution reaction(OER)is the bottleneck.Currently,Fe-doped NiOOH(Ni_(1−x)Fe_(x)OOH)is a promising OER catalyst under alkaline conditions.However,the specific active sites responsible for their good performances remain debatable.Here,we identify a nickel-oxygen radical(Ni–O·)and an iron-oxo(Fe=O)group as two essential states for adsorbed oxygen.Meanwhile,both thermochemical O–O coupling and electrochemical OER elementary steps are considered on the Ni_(1−x)Fe_(x)OOH catalysts.Sophisticated mechanistic studies with a combined density functional theory simulation and experimental analysis unravel that both the Ni and Fe centers can act as the active sites for the defective Ni_(1−x)Fe_(x)OOH to catalyze OER,depending on the nature of the defect.The presence of Fe can benefit the stabilization of the defective surface and influence the electronic property of the nearby Ni site.This work not only identifies the intrinsic active sites of Ni_(1−x)Fe_(x)OOH,but also illustrates the essential roles of defects in catalysis,which sheds light on the design of more efficient OER catalysts in the future.展开更多
文摘The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when water-binder ratio is lower than 0.40, the cement-based material with limestone powder has insignificant change in appearance after being soaked in 10% magnesium sulfate solution at low temperature for 120 d, and has significant change in appearance after being soaked at the age of 200 d. Expansion damage and exfoliation occur on the surface of concrete test cube at different levels. When limestone powder accounts for about 28 percent of cementitious material, with the decrease of water-binder ratio, the compressive strength loss has gradually decreased after the material is soaked in the magnesium sulfate solution at low temperature at the age of 200 d. After the specimen with the water-binder ratio of less than 0.4 and the limestone powder volume of greater than 20% is soaked in 10% magnesium sulfate solution at low temperature at the age of 200 d, gypsum attack-led destruction is caused to the concrete test cube, without thaumasite sulfate attack.
基金Funded by the National Natural Science Foundation of China(No. 90715041)Outstanding Youth Science Fund of Henan Province(No.04120002300)
文摘By micro- and macro-observations, the deterioration mechanisms of concrete under alternate action between repeated sub-high temperature/cooling by water and sodium sulfate solution attack （TW-SA） were studied; meanwhile, the single sodium sulfate solution attack （SA） was also done as comparison. Micro-observations included the analysis of attack products by thermal analysis method and the determination of sulfate-ion content from surface to interior by chemical titrating method （modified barium sulfate gravimetric method）. Macro-observations mainly included the mechanical behaviors such as compressive strength, splitting strength. The experimental results indicate, in both cases, the main attack product is ettringite, only in the first layer of case SA some gypsum is checked; in case SA, the sulfate ions mainly concentrate in the surface layer, so the attack is relatively mild; but in case TW-SA, the repeated sub-high temperature/cooling by water promotes the sulfate ions diffusing inwards, which leads to obvious strength degradation.
文摘Electrochemical water splitting plays a crucial role in storing sustainable energy into H2 as an ideal fuel,in which the anodic oxygen evolution reaction(OER)is the bottleneck.Currently,Fe-doped NiOOH(Ni_(1−x)Fe_(x)OOH)is a promising OER catalyst under alkaline conditions.However,the specific active sites responsible for their good performances remain debatable.Here,we identify a nickel-oxygen radical(Ni–O·)and an iron-oxo(Fe=O)group as two essential states for adsorbed oxygen.Meanwhile,both thermochemical O–O coupling and electrochemical OER elementary steps are considered on the Ni_(1−x)Fe_(x)OOH catalysts.Sophisticated mechanistic studies with a combined density functional theory simulation and experimental analysis unravel that both the Ni and Fe centers can act as the active sites for the defective Ni_(1−x)Fe_(x)OOH to catalyze OER,depending on the nature of the defect.The presence of Fe can benefit the stabilization of the defective surface and influence the electronic property of the nearby Ni site.This work not only identifies the intrinsic active sites of Ni_(1−x)Fe_(x)OOH,but also illustrates the essential roles of defects in catalysis,which sheds light on the design of more efficient OER catalysts in the future.
