The preforms with high SiC volume fraction （〉50%） were successfully fabricated by two bonding methods. Moreover, the dimensional change, compressive strength, and microstructure of SiC preforms were investigated, a...The preforms with high SiC volume fraction （〉50%） were successfully fabricated by two bonding methods. Moreover, the dimensional change, compressive strength, and microstructure of SiC preforms were investigated, and the bonding mechanism among SiC particulates in preforms was also discussed. Results show that, after heating to 1 100 ~C and holding for 2 h, a uniform and interconnected structure in the SiC preforms can be obtained by using starch, stearic acid, and graphite respectively as the pore-forming agents, which benefits the subsequent infiltration by the molten metals. More neck-like-jointing among SiC particulate by using graphite as the pore-forming agent improves the dimensional accuracy and compressive strength of the preform. Besides, the properties of the preforms by the binder bonding are better than those by the oxidation bonding, which is mainly because the mixed neck-like-jointing and binder at high temperature provide effective bonding together.展开更多
Thermal insulation materials play an increasingly important role in protecting mechanical parts functioning at high temperatures.In this study,a new porous high-entropy(La_(1/6)Ce_(1/6)Pr_(1/6)Sm_(1/6)Eu_(1/6)Gd_(1/6)...Thermal insulation materials play an increasingly important role in protecting mechanical parts functioning at high temperatures.In this study,a new porous high-entropy(La_(1/6)Ce_(1/6)Pr_(1/6)Sm_(1/6)Eu_(1/6)Gd_(1/6))PO_(4)(HE(6RE_(1/6))PO_(4))ceramics was prepared by combining the high-entropy method with the pore-forming agent method and the effect of different starch contents(0–60vol%)on this ceramic properties was systematically investigated.The results show that the porous HE(6RE_(1/6))PO_(4)ceramics with 60vol%starch exhibit the lowest thermal conductivity of 0.061 W·m^(-1)·K^(-1)at room temperature and good pore structure stability with a linear shrinkage of approximately1.67%.Moreover,the effect of large regular spherical pores(>10μm)on its thermal insulation performance was discussed,and an optimal thermal conductivity prediction model was screened.The superior properties of the prepared porous HE(6RE_(1/6))PO_(4)ceramics allow them to be promising insulation materials in the future.展开更多
The pore structure of spherical alumina supports is closely related to the dispersion of catalytically active components and the diffusion of reactants.Maintaining excellent pore structure under strict reaction condit...The pore structure of spherical alumina supports is closely related to the dispersion of catalytically active components and the diffusion of reactants.Maintaining excellent pore structure under strict reaction conditions is of utmost importance.In this work,sphericalγ-Al_(2)O_(3)support with a bimodal pore structure,composed of macropores and mesopores,was successfully synthesized using dodecane as the pore-forming agent through the oil–ammonia column-shaping method.The morphology and internal pore structure of the alumina were found to be influenced by the amount of surfactant added and ultrasound treatment conditions.Notably,when concentration of surfactant was 4‰and ultrasound voltage of 20 V was applied,the resultingγ-Al_(2)O_(3)-4‰-20 displayed a highly concentrated distribution of macropores with an average pore size of 100 nm,resulting in an impressive porosity of 69.21%.In contrast,the untreated sample ofγ-Al_(2)O_(3)-0-0 only exhibited a mesoporous distribution with a porosity of 54.03%.Moreover,after being subjected to a hydrothermal treatment in a high temperature(600°C)and high humidity(water vapor)environment for 120 h,theγ-Al_(2)O_(3)-4‰-20 sample maintained a high BET specific surface area of 170.9 m^(2)g^(−1)and mercury intrusion porosimetry specific surface area of 263.3 m^(2)g^(−1).展开更多
基金Funded by the National Natural Science Foundation of China(No.51166011)Aviation Science Foundation(No.2012ZF56024)Key Laboratory for Microstructural Control of Metallic Materials of Jiangxi Province(Nanchang Hangkong University)(No.JW201423003)
文摘The preforms with high SiC volume fraction （〉50%） were successfully fabricated by two bonding methods. Moreover, the dimensional change, compressive strength, and microstructure of SiC preforms were investigated, and the bonding mechanism among SiC particulates in preforms was also discussed. Results show that, after heating to 1 100 ~C and holding for 2 h, a uniform and interconnected structure in the SiC preforms can be obtained by using starch, stearic acid, and graphite respectively as the pore-forming agents, which benefits the subsequent infiltration by the molten metals. More neck-like-jointing among SiC particulate by using graphite as the pore-forming agent improves the dimensional accuracy and compressive strength of the preform. Besides, the properties of the preforms by the binder bonding are better than those by the oxidation bonding, which is mainly because the mixed neck-like-jointing and binder at high temperature provide effective bonding together.
基金the National Key R&D Program of China(No.2021YFB3701404)the National Natural Science Fund for Distinguished Young Scholars(No.52025041)+1 种基金the National Natural Science Foundation of China(Nos.52250091,51904021,and 52174294)the Fundamental Research Funds for the Central Universities(Nos.FRF-TP-20-02C2 and FRF-BD-22-05).
文摘Thermal insulation materials play an increasingly important role in protecting mechanical parts functioning at high temperatures.In this study,a new porous high-entropy(La_(1/6)Ce_(1/6)Pr_(1/6)Sm_(1/6)Eu_(1/6)Gd_(1/6))PO_(4)(HE(6RE_(1/6))PO_(4))ceramics was prepared by combining the high-entropy method with the pore-forming agent method and the effect of different starch contents(0–60vol%)on this ceramic properties was systematically investigated.The results show that the porous HE(6RE_(1/6))PO_(4)ceramics with 60vol%starch exhibit the lowest thermal conductivity of 0.061 W·m^(-1)·K^(-1)at room temperature and good pore structure stability with a linear shrinkage of approximately1.67%.Moreover,the effect of large regular spherical pores(>10μm)on its thermal insulation performance was discussed,and an optimal thermal conductivity prediction model was screened.The superior properties of the prepared porous HE(6RE_(1/6))PO_(4)ceramics allow them to be promising insulation materials in the future.
基金National Key R&D Program of China(grant No.2022YFA1503400)Lanzhou Petrochemical Research Center project,and Programs for Foreign Talent(grant No.G2021106012L).
文摘The pore structure of spherical alumina supports is closely related to the dispersion of catalytically active components and the diffusion of reactants.Maintaining excellent pore structure under strict reaction conditions is of utmost importance.In this work,sphericalγ-Al_(2)O_(3)support with a bimodal pore structure,composed of macropores and mesopores,was successfully synthesized using dodecane as the pore-forming agent through the oil–ammonia column-shaping method.The morphology and internal pore structure of the alumina were found to be influenced by the amount of surfactant added and ultrasound treatment conditions.Notably,when concentration of surfactant was 4‰and ultrasound voltage of 20 V was applied,the resultingγ-Al_(2)O_(3)-4‰-20 displayed a highly concentrated distribution of macropores with an average pore size of 100 nm,resulting in an impressive porosity of 69.21%.In contrast,the untreated sample ofγ-Al_(2)O_(3)-0-0 only exhibited a mesoporous distribution with a porosity of 54.03%.Moreover,after being subjected to a hydrothermal treatment in a high temperature(600°C)and high humidity(water vapor)environment for 120 h,theγ-Al_(2)O_(3)-4‰-20 sample maintained a high BET specific surface area of 170.9 m^(2)g^(−1)and mercury intrusion porosimetry specific surface area of 263.3 m^(2)g^(−1).
