In order to fabricate porous ceramics with good properties and proper production cost,SiC-Al2 O3 porous ceramics were prepared at 1 450 ℃ for 2 h from the powders of commercial silicon carbide and white fused corundu...In order to fabricate porous ceramics with good properties and proper production cost,SiC-Al2 O3 porous ceramics were prepared at 1 450 ℃ for 2 h from the powders of commercial silicon carbide and white fused corundum via a polymeric replication method. Effects of the mass ratio of SiC powder to white fused corundum powder（ 1 ∶ 3,1 ∶ 1 and 3 ∶ 1） on the appearance,phase composition,sintering properties and thermal shock resistance were investigated. The research results indicate that the as-prepared Si C-Al2 O3 porous ceramics have uniform pores,and their linear shrinkage ratio,apparent porosity and bulk density reach 4. 70%,67. 17%and 0. 83 g·cm-3,respectively. The thermal shock cycles from 1 400 ℃ to room temperature reach 23 including 15 cycles in air cooling condition and then 8 cycles in water cooling condition. Their main phases areα-Al2 O3 and Al6 Si2 O13 as well as a small amount of SiC and free SiO2. The as-prepared porous ceramic with the ratio of m（ SiC） ∶ m（ Al2 O3） = 1∶ 1 possesses prior comprehensive properties.展开更多
In this study,functionally graded foam made of Inconel 625 superalloy was successfully produced using the template replication method,with open-cell polyurethane foams as a precursor.The products have a similar pore m...In this study,functionally graded foam made of Inconel 625 superalloy was successfully produced using the template replication method,with open-cell polyurethane foams as a precursor.The products have a similar pore morphology as the templates and adjacent layers were successfully sintered together by particle bonding.Sound absorption experiments on graded metallic foams reveal that the sound absorption at particular frequency ranges can be improved by various permutations of foam layers.For graded foam of two distinct pore sizes,a mathematical equation was proposed to predict the location of the intersection point of the sound absorption curves,thereby aiding in graded foam design.An increase in sound absorption coefficients by resonance-like effects can be introduced before the intersection points by placing the foam layer of smaller pore size nearer to the sound source.The sound absorption performances can be further customized when the thickness proportion of the pore sizes is changed and when the number of distinct pore sizes used is increased.The sound absorption performance at lower frequencies is generally boosted by resonance-like effects when the layer of foam with the largest pore size is placed furthest from the sound source.Given the same composition of foam with a fixed thickness proportion of pore sizes,one can introduce resonance-like effects to improve the sound absorption performance compared to other permutations while possibly satisfying weight requirements in practical applications.This study provides valuable insights and mathematical guidelines in the design and manufacturing of functionally graded metallic foam for specific applications.展开更多
This study aims to evaluate the Silver-to-Gold LEED-NC 2009 (Leadership in Energy and Environmental Design for New Construction and Major Renovations) cross-certification performance and categorize the cross-certifica...This study aims to evaluate the Silver-to-Gold LEED-NC 2009 (Leadership in Energy and Environmental Design for New Construction and Major Renovations) cross-certification performance and categorize the cross-certification performance in eight US states in 2012-2017. The following three statistical analyses were used: (a) pooling LEED projects within a single state and single year in a single-state-year group with the subsequent use of a replication method, (b) pooling the medians of the LEED projects in each state from all years in a state-and-total-years group, and (c) pooling the LEED projects from all states and years in a total states-and-years group. The Silver-to-Gold cross-certification performance has a low propelling effect. Considering the Silver-to-Gold category cross-certification performances, the Energy and Atmosphere (EA) category has a high propelling effect, the Sustainable Sites (SS) and Environmental Quality (EQ) categories have moderate propelling effects, the Water Efficiency (WE), Materials and Resources (MR), and Innovation in Design (ID) categories have low propelling effects. Six of the eight states used an EA-high emphasized strategy, and two of the eight states used a SS/EA/WE/EQ/ID-moderate emphasized strategy. The single-state-year group and state-and-total-years group analyses are more robust than the pooling LEED projects using the total state-and-year group analysis.展开更多
文摘In order to fabricate porous ceramics with good properties and proper production cost,SiC-Al2 O3 porous ceramics were prepared at 1 450 ℃ for 2 h from the powders of commercial silicon carbide and white fused corundum via a polymeric replication method. Effects of the mass ratio of SiC powder to white fused corundum powder（ 1 ∶ 3,1 ∶ 1 and 3 ∶ 1） on the appearance,phase composition,sintering properties and thermal shock resistance were investigated. The research results indicate that the as-prepared Si C-Al2 O3 porous ceramics have uniform pores,and their linear shrinkage ratio,apparent porosity and bulk density reach 4. 70%,67. 17%and 0. 83 g·cm-3,respectively. The thermal shock cycles from 1 400 ℃ to room temperature reach 23 including 15 cycles in air cooling condition and then 8 cycles in water cooling condition. Their main phases areα-Al2 O3 and Al6 Si2 O13 as well as a small amount of SiC and free SiO2. The as-prepared porous ceramic with the ratio of m（ SiC） ∶ m（ Al2 O3） = 1∶ 1 possesses prior comprehensive properties.
基金supported by A*STAR under the AME YIRG Grant(No.A20E6c0099)AME IAF-PP Grant(No.A1896a0034)。
文摘In this study,functionally graded foam made of Inconel 625 superalloy was successfully produced using the template replication method,with open-cell polyurethane foams as a precursor.The products have a similar pore morphology as the templates and adjacent layers were successfully sintered together by particle bonding.Sound absorption experiments on graded metallic foams reveal that the sound absorption at particular frequency ranges can be improved by various permutations of foam layers.For graded foam of two distinct pore sizes,a mathematical equation was proposed to predict the location of the intersection point of the sound absorption curves,thereby aiding in graded foam design.An increase in sound absorption coefficients by resonance-like effects can be introduced before the intersection points by placing the foam layer of smaller pore size nearer to the sound source.The sound absorption performances can be further customized when the thickness proportion of the pore sizes is changed and when the number of distinct pore sizes used is increased.The sound absorption performance at lower frequencies is generally boosted by resonance-like effects when the layer of foam with the largest pore size is placed furthest from the sound source.Given the same composition of foam with a fixed thickness proportion of pore sizes,one can introduce resonance-like effects to improve the sound absorption performance compared to other permutations while possibly satisfying weight requirements in practical applications.This study provides valuable insights and mathematical guidelines in the design and manufacturing of functionally graded metallic foam for specific applications.
文摘This study aims to evaluate the Silver-to-Gold LEED-NC 2009 (Leadership in Energy and Environmental Design for New Construction and Major Renovations) cross-certification performance and categorize the cross-certification performance in eight US states in 2012-2017. The following three statistical analyses were used: (a) pooling LEED projects within a single state and single year in a single-state-year group with the subsequent use of a replication method, (b) pooling the medians of the LEED projects in each state from all years in a state-and-total-years group, and (c) pooling the LEED projects from all states and years in a total states-and-years group. The Silver-to-Gold cross-certification performance has a low propelling effect. Considering the Silver-to-Gold category cross-certification performances, the Energy and Atmosphere (EA) category has a high propelling effect, the Sustainable Sites (SS) and Environmental Quality (EQ) categories have moderate propelling effects, the Water Efficiency (WE), Materials and Resources (MR), and Innovation in Design (ID) categories have low propelling effects. Six of the eight states used an EA-high emphasized strategy, and two of the eight states used a SS/EA/WE/EQ/ID-moderate emphasized strategy. The single-state-year group and state-and-total-years group analyses are more robust than the pooling LEED projects using the total state-and-year group analysis.
