Rare-earth silicates are promising environmental barrier coatings(EBCs)that can protect SiC_(f)/Si C_(m)substrates in next-genera tion gas turbine blades.Notably,RE_(2)Si_(2)O_(7)(RE=Yb and Ho)shows potential as an EB...Rare-earth silicates are promising environmental barrier coatings(EBCs)that can protect SiC_(f)/Si C_(m)substrates in next-genera tion gas turbine blades.Notably,RE_(2)Si_(2)O_(7)(RE=Yb and Ho)shows potential as an EBC due to its coefficient of thermal expansion(CTE)compatible with substrates and high resistance to water vapor corrosion.The target operating temperature for next-generation tur bine blades is 1400°C.Corrosion is inevitable during adhesion to molten volcanic ash,and thus,understanding the corrosion behavior o the material is crucial to its reliability.This study investigates the high-temperature corrosion behavior of sintered RE_(2)Si_(2)O_(7)(RE=Yb and Ho).Samples were prepared using a solid-state reaction and hot-press method.They were then exposed to volcanic ash at 1400°C for 224,and 48 h.After 48 h of exposure,volcanic ash did not react with Yb_(2)Si_(2)O_(7)but penetrated its interior,causing damage.Meanwhile Ho_(2)Si_(2)O_(7)was partially dissolved in the molten volcanic ash,forming a reaction zone that prevented volcanic ash melts from penetrating the interior.With increasing heat treatment time,the reaction zone expanded,and the thickness of the acicular apatite grains increased The Ca:Si ratios in the residual volcanic ash were mostly unchanged for Yb_(2)Si_(2)O_(7)but decreased considerably over time for Ho_(2)Si_(2)O_(7).Th Ca in volcanic ash was consumed and formed apatite,indicating that RE^(3+)ions with large ionic radii(Ho>Yb)easily precipitated apatit from the volcanic ash.展开更多
<div style="text-align:justify;"> Environmental barrier coatings (EBCs) play a critical role in mitigating the degradation of SiC<sub>f</sub>/SiC ceramic matrix composites (CMCs) in complex...<div style="text-align:justify;"> Environmental barrier coatings (EBCs) play a critical role in mitigating the degradation of SiC<sub>f</sub>/SiC ceramic matrix composites (CMCs) in complex combustion environment, and improve the service life of thermal engine components. In this paper, by adjusting the parameters of atmospheric plasma spraying (APS), the spraying process of ytterbium disilicate (Yb<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>) under a lower power has been optimized. A two-layer EBC system consisting of ytterbium disilicate and silicon is prepared on the SiC<sub>f</sub>/SiC composite substrate by using optimized technological parameters. The thermal resistance and water oxygen corrosion resistance of such two-layer EBC system are investigated. The results indicate that the current ytterbium disilicate/silicon EBC system exhibits good phase stability, excellent water vapor and oxygen corrosion resistance. However, the exposed silicon bonding layer tends to generate an excessive thermal growth oxide (TGO) layer known as SiO<sub>2</sub>, leading to an early spallation of the coating. </div>展开更多
Most viewpoints in China consider green barrier is one kind of non-tariff barriers imposed by developed countries and is unfair to developing countries. Different from these, this paper points out that green barriers,...Most viewpoints in China consider green barrier is one kind of non-tariff barriers imposed by developed countries and is unfair to developing countries. Different from these, this paper points out that green barriers, evolving from the background of sustainable development theory and the principle of environment protection, have positive effect on ideology, international institutional arrangement and innovation stimulation. Demonstrating the rationality of green barriers, the paper puts forward that green barriers should be regarded as the stimulation for technology innovation and industrial restructure rather than obstacles. The best way to surmount the green barriers for Chinese government and enterprises is to implement circular economy and clean production so as to achieve the harmony of trade, environment and economic development.展开更多
Although many obese patients do not engage in adequate physical activity (PA), little is known about whether physicians discuss environmental barriers in promoting PA. We conducted this study to describe physicians’ ...Although many obese patients do not engage in adequate physical activity (PA), little is known about whether physicians discuss environmental barriers in promoting PA. We conducted this study to describe physicians’ views about discussing environmental barriers in promoting PA with obese patients and determine whether counseling varies by years of practice. We conducted an online survey of family physicians practicing in 17 clinics in Central Texas. We performed descriptive analysis on barriers to PA, counseling on meeting PA recommendation, and written prescription for exercise and bivariate analysis by years of practice. Statistical significance was set at p < 0.05. Of 96 physicians invited, 57 (59.4%) completed the survey. Majority reported their obese patients brought up the environment as a barrier to walking (89.3%) or PA (91.2%). Majority (80.7%) also reported asking about environmental barriers to walking, with 84.2% giving specific examples to overcome these barriers. While 96.5% reported advising their obese patients about meeting the PA recommendation, only 26.3% reported giving them a written prescription for exercise. These did not vary significantly by years of practice. Physicians felt having more time with their patients and knowing specific strategies to overcome environmental barriers, safe places in patients’ neighborhoods, and what environmental factors influence PA may help discuss environmental issues with their obese patients. Physicians want and counsel their obese patients to be physically active, but do not generally give prescriptions for exercise irrespective of years of practice. They also want tools to enhance their abilities to better assist these patients.展开更多
This paper begins by analysing the mutual influence between international trade and the environment, and then proceeds to explore the environment and trade conflicts. On the basis of sustainable development theories a...This paper begins by analysing the mutual influence between international trade and the environment, and then proceeds to explore the environment and trade conflicts. On the basis of sustainable development theories and the above discussion, the article suggests taking sustainable trade as a solution to the existing conflicts. This paper aims to find the way to strike a balance between international trade and environment based on the present situation in China.展开更多
The lifetime of Si-based environmental barrier coatings(EBCs)is constrained by thermally grown SiO_(2)oxidelayer(SiO_(2)-TGO),which can cause premature cracking and spalling.To address this issue,a new approach for su...The lifetime of Si-based environmental barrier coatings(EBCs)is constrained by thermally grown SiO_(2)oxidelayer(SiO_(2)-TGO),which can cause premature cracking and spalling.To address this issue,a new approach for surfacemodification using aluminum is proposed.The oxidation performance was examined in a 50 vol%H_(2)O-50 vol%O_(2)environment at 1350℃for up to 300 h.The results indicate that a dense ytterbium aluminum garnet(YbAG)layer wasformed after modification,decreasing the porosity by 80%.Due to the elimination of fast diffusion channels and the lowoxygen permeability of YbAG,aluminum modification significantly reduced the growth rate of SiO_(2)-TGO by nearly twoorders of magnitude.Consequently,its thickness decreased by more than 70%after 300 h of exposure.A diffusioncontrolled oxidation mechanism indicates that the modified dense surface is equivalent to an initial SiO_(2)layer with a specificthickness,causing a shift in the oxidation time and increasing the oxidation resistance.This research provides valuableinsights for designing Si-based EBC with improved lifetimes.展开更多
基金supported by JSPS KAKENHI(No.23K19087)“Dynamic Alliance for Open Innovation Bridging Human,Environment and Materials”from the Ministry of Education,Culture,Sports,Science and Technology o f Japan(MEXT).
文摘Rare-earth silicates are promising environmental barrier coatings(EBCs)that can protect SiC_(f)/Si C_(m)substrates in next-genera tion gas turbine blades.Notably,RE_(2)Si_(2)O_(7)(RE=Yb and Ho)shows potential as an EBC due to its coefficient of thermal expansion(CTE)compatible with substrates and high resistance to water vapor corrosion.The target operating temperature for next-generation tur bine blades is 1400°C.Corrosion is inevitable during adhesion to molten volcanic ash,and thus,understanding the corrosion behavior o the material is crucial to its reliability.This study investigates the high-temperature corrosion behavior of sintered RE_(2)Si_(2)O_(7)(RE=Yb and Ho).Samples were prepared using a solid-state reaction and hot-press method.They were then exposed to volcanic ash at 1400°C for 224,and 48 h.After 48 h of exposure,volcanic ash did not react with Yb_(2)Si_(2)O_(7)but penetrated its interior,causing damage.Meanwhile Ho_(2)Si_(2)O_(7)was partially dissolved in the molten volcanic ash,forming a reaction zone that prevented volcanic ash melts from penetrating the interior.With increasing heat treatment time,the reaction zone expanded,and the thickness of the acicular apatite grains increased The Ca:Si ratios in the residual volcanic ash were mostly unchanged for Yb_(2)Si_(2)O_(7)but decreased considerably over time for Ho_(2)Si_(2)O_(7).Th Ca in volcanic ash was consumed and formed apatite,indicating that RE^(3+)ions with large ionic radii(Ho>Yb)easily precipitated apatit from the volcanic ash.
文摘<div style="text-align:justify;"> Environmental barrier coatings (EBCs) play a critical role in mitigating the degradation of SiC<sub>f</sub>/SiC ceramic matrix composites (CMCs) in complex combustion environment, and improve the service life of thermal engine components. In this paper, by adjusting the parameters of atmospheric plasma spraying (APS), the spraying process of ytterbium disilicate (Yb<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>) under a lower power has been optimized. A two-layer EBC system consisting of ytterbium disilicate and silicon is prepared on the SiC<sub>f</sub>/SiC composite substrate by using optimized technological parameters. The thermal resistance and water oxygen corrosion resistance of such two-layer EBC system are investigated. The results indicate that the current ytterbium disilicate/silicon EBC system exhibits good phase stability, excellent water vapor and oxygen corrosion resistance. However, the exposed silicon bonding layer tends to generate an excessive thermal growth oxide (TGO) layer known as SiO<sub>2</sub>, leading to an early spallation of the coating. </div>
文摘Most viewpoints in China consider green barrier is one kind of non-tariff barriers imposed by developed countries and is unfair to developing countries. Different from these, this paper points out that green barriers, evolving from the background of sustainable development theory and the principle of environment protection, have positive effect on ideology, international institutional arrangement and innovation stimulation. Demonstrating the rationality of green barriers, the paper puts forward that green barriers should be regarded as the stimulation for technology innovation and industrial restructure rather than obstacles. The best way to surmount the green barriers for Chinese government and enterprises is to implement circular economy and clean production so as to achieve the harmony of trade, environment and economic development.
文摘Although many obese patients do not engage in adequate physical activity (PA), little is known about whether physicians discuss environmental barriers in promoting PA. We conducted this study to describe physicians’ views about discussing environmental barriers in promoting PA with obese patients and determine whether counseling varies by years of practice. We conducted an online survey of family physicians practicing in 17 clinics in Central Texas. We performed descriptive analysis on barriers to PA, counseling on meeting PA recommendation, and written prescription for exercise and bivariate analysis by years of practice. Statistical significance was set at p < 0.05. Of 96 physicians invited, 57 (59.4%) completed the survey. Majority reported their obese patients brought up the environment as a barrier to walking (89.3%) or PA (91.2%). Majority (80.7%) also reported asking about environmental barriers to walking, with 84.2% giving specific examples to overcome these barriers. While 96.5% reported advising their obese patients about meeting the PA recommendation, only 26.3% reported giving them a written prescription for exercise. These did not vary significantly by years of practice. Physicians felt having more time with their patients and knowing specific strategies to overcome environmental barriers, safe places in patients’ neighborhoods, and what environmental factors influence PA may help discuss environmental issues with their obese patients. Physicians want and counsel their obese patients to be physically active, but do not generally give prescriptions for exercise irrespective of years of practice. They also want tools to enhance their abilities to better assist these patients.
基金Youth Science Fund of Chengdu University of Technology, No. 2005QJ10
文摘This paper begins by analysing the mutual influence between international trade and the environment, and then proceeds to explore the environment and trade conflicts. On the basis of sustainable development theories and the above discussion, the article suggests taking sustainable trade as a solution to the existing conflicts. This paper aims to find the way to strike a balance between international trade and environment based on the present situation in China.
基金supported by the Postdoctoral Innovative Talent Support Program(No.BX2021238)the National Natural Science Foundation of China(Nos.U22A20110 and 52301102).
文摘The lifetime of Si-based environmental barrier coatings(EBCs)is constrained by thermally grown SiO_(2)oxidelayer(SiO_(2)-TGO),which can cause premature cracking and spalling.To address this issue,a new approach for surfacemodification using aluminum is proposed.The oxidation performance was examined in a 50 vol%H_(2)O-50 vol%O_(2)environment at 1350℃for up to 300 h.The results indicate that a dense ytterbium aluminum garnet(YbAG)layer wasformed after modification,decreasing the porosity by 80%.Due to the elimination of fast diffusion channels and the lowoxygen permeability of YbAG,aluminum modification significantly reduced the growth rate of SiO_(2)-TGO by nearly twoorders of magnitude.Consequently,its thickness decreased by more than 70%after 300 h of exposure.A diffusioncontrolled oxidation mechanism indicates that the modified dense surface is equivalent to an initial SiO_(2)layer with a specificthickness,causing a shift in the oxidation time and increasing the oxidation resistance.This research provides valuableinsights for designing Si-based EBC with improved lifetimes.
