Zeolite FAU composites with a macro/meso-microporous hierarchical structure were hydrothermally synthesized using macro-mesoporous γ-Al_2O_3 monolith as the substrate by means of the liquid crystallization directing...Zeolite FAU composites with a macro/meso-microporous hierarchical structure were hydrothermally synthesized using macro-mesoporous γ-Al_2O_3 monolith as the substrate by means of the liquid crystallization directing agent(LCDA) induced method. No template was needed throughout the synthesis processes. The structure and porosity of zeolite composites were analyzed by means of X-ray powder diffraction(XRD), scanning electron microscopy(SEM) and N_2adsorption-desorption isotherms. The results showed that the supported zeolite composites with varied zeolitic crystalline phases and different morphologies can be obtained by adjusting the crystallization parameters, such as the crystallization temperature, the composition and the alkalinity of the precursor solution. The presence of LCDA was defined as a determinant for synthesizing the zeolite composites. The mechanisms for formation of the hierarchically porous FAU zeolite composites in the LCDA induced synthesis process were discussed. The resulting monolithic zeolite with a trimodal-porous hierarchical structure shows potential applicability where facile diffusion is required.展开更多
TiB2-Al2O3 composite powders were produced by self-propagating high-temperature synthesis（SHS） method with reductive process from B2O3-TiO2-AI system. X-ray diffraction（XRD） and scanning electron microscopy（SEM...TiB2-Al2O3 composite powders were produced by self-propagating high-temperature synthesis（SHS） method with reductive process from B2O3-TiO2-AI system. X-ray diffraction（XRD） and scanning electron microscopy（SEM） analyses show the presence of TiB2 and Al2O3 only in the composite powders produced by SHS. The powders are uniform and free-agglomerate. Transmission electron microscopy （TEM） and high resolution electron microscopy （HREM） observation of microstructure of the composite powders indicate that the interfaces of the TiB2-Al2O3 bond well, without any interfacial reaction products. It is proposed that the good interfacial bonding of the composite powders can be resulted from the TiB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.展开更多
Effects of Al2O3 and Ni as the additives on the sinterability, microstructure and mechanical properties were systematic studied. The experimental results show that only a relative density about 96.2% of hot-pressing T...Effects of Al2O3 and Ni as the additives on the sinterability, microstructure and mechanical properties were systematic studied. The experimental results show that only a relative density about 96.2% of hot-pressing TiB2-30%Al2O3 can be attained due to the plate-like TiB2 particle and its random orientation and excessive Al2O3 grain growth. When sintering temperature is higher than 1 700 ℃, TiB2 grain growth can be found, which obvious improves flexural strength of TiB2 matrix but decreases toughness. It seems that mechanical properties of TiB2-Al2O3 composites are mainly depended on relative density besides grain growth. otherwise, they will be determined by relative density and TiB2 matrix strength together. Anyway, Al2O3 addition can weaken the grain boundary and thus improve the toughness of the materials. A flexural strength of 529 MPa, Vickers hardness of 24.8 GPa and indentation toughness of 4.56 MPa·m1/2 can be achieved inTiB2-30vol% Al2O3.展开更多
Open-celled porous （TiB2-Al2O3）/NiAl composites were successfully fabricated by using spherical carbamide as space holders via self-propagating high-temperature synthesis （SHS）. Effects of 10Al-3B2O3-3TiO2 conten...Open-celled porous （TiB2-Al2O3）/NiAl composites were successfully fabricated by using spherical carbamide as space holders via self-propagating high-temperature synthesis （SHS）. Effects of 10Al-3B2O3-3TiO2 contents （0-20 wt%） on the pore structures and the quasi-static compressive behaviors of the resultant materials were investigated. The porous （TiBE-Al2O3）/NiAl composites exhibit composite pore structure consisting of homogeneously distributed and interconnected millimeter pores and micropores. The millimeter pores virtually inherit the shape and size of carbamide particles, while the pore size of micropores increases with increasing the 10Al-3BEO3-3TiO2 content. Depending on the volume fraction of the carbamide, the porosity of the porous materials can be easily controlled in a range of 55%-85%. When the porosity is about 72%, the compressive strengths of porous NiAl and porous （TiBE-Al203）/NiAl composite with 15% 10Al-3B2O3-3TiO2 in green compact are 19 and 32 MPa, and the corresponding strains are 2.9% and 5.7%, respectively. Furthermore, the quasi-static compressive behavior of porous （TiB2-AlEO3）/NiAl composites can be estimated by Gibson-Ashby model.展开更多
The effect of successive washing instead of traditional intermittent washing on the porous structure of pseudoboehmite was investigated by mercury porosimetry, N2 adsorption and thermal analysis, while the stabilities...The effect of successive washing instead of traditional intermittent washing on the porous structure of pseudoboehmite was investigated by mercury porosimetry, N2 adsorption and thermal analysis, while the stabilities of different types of crystals were investigated by X-ray diffractometer. Experimental results show that successive washing is a continuation of the aging process of intermittent washing. After a successive washing, the pore types showed no difference with the intermittent washing. During successive washing, the characteristics of the pores in the range of 2-15 nm changed only very little. However, the distributions of the pore radius for pores of 20-50 and 300-1000 nm were obviously influenced. It was shown that the volume of larger pores decreased only to a smaller extent after the successive washing, as compared with that of the intermittent washing, and the pore size was affected by the condition of the successive washing. The roles of physisorbed water, intermicellar liquid, weakly bonded water, as well as the role of stirring, have been discussed.展开更多
基金the financial support from the National Natural Science Foundation of China(No.20973022 and No.11472048)the State Key Laboratory of Catalytic Materials and Reaction Engineering(RIPP,SINOPEC)(Serial No.33600000-14-ZC0607-0006)
文摘Zeolite FAU composites with a macro/meso-microporous hierarchical structure were hydrothermally synthesized using macro-mesoporous γ-Al_2O_3 monolith as the substrate by means of the liquid crystallization directing agent(LCDA) induced method. No template was needed throughout the synthesis processes. The structure and porosity of zeolite composites were analyzed by means of X-ray powder diffraction(XRD), scanning electron microscopy(SEM) and N_2adsorption-desorption isotherms. The results showed that the supported zeolite composites with varied zeolitic crystalline phases and different morphologies can be obtained by adjusting the crystallization parameters, such as the crystallization temperature, the composition and the alkalinity of the precursor solution. The presence of LCDA was defined as a determinant for synthesizing the zeolite composites. The mechanisms for formation of the hierarchically porous FAU zeolite composites in the LCDA induced synthesis process were discussed. The resulting monolithic zeolite with a trimodal-porous hierarchical structure shows potential applicability where facile diffusion is required.
文摘TiB2-Al2O3 composite powders were produced by self-propagating high-temperature synthesis（SHS） method with reductive process from B2O3-TiO2-AI system. X-ray diffraction（XRD） and scanning electron microscopy（SEM） analyses show the presence of TiB2 and Al2O3 only in the composite powders produced by SHS. The powders are uniform and free-agglomerate. Transmission electron microscopy （TEM） and high resolution electron microscopy （HREM） observation of microstructure of the composite powders indicate that the interfaces of the TiB2-Al2O3 bond well, without any interfacial reaction products. It is proposed that the good interfacial bonding of the composite powders can be resulted from the TiB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.
文摘Effects of Al2O3 and Ni as the additives on the sinterability, microstructure and mechanical properties were systematic studied. The experimental results show that only a relative density about 96.2% of hot-pressing TiB2-30%Al2O3 can be attained due to the plate-like TiB2 particle and its random orientation and excessive Al2O3 grain growth. When sintering temperature is higher than 1 700 ℃, TiB2 grain growth can be found, which obvious improves flexural strength of TiB2 matrix but decreases toughness. It seems that mechanical properties of TiB2-Al2O3 composites are mainly depended on relative density besides grain growth. otherwise, they will be determined by relative density and TiB2 matrix strength together. Anyway, Al2O3 addition can weaken the grain boundary and thus improve the toughness of the materials. A flexural strength of 529 MPa, Vickers hardness of 24.8 GPa and indentation toughness of 4.56 MPa·m1/2 can be achieved inTiB2-30vol% Al2O3.
基金financially supported by the Natural Science Foundation of Shandong Province (No.ZR2014EMM009)the Public School Visiting Fund of Shandong University of Science and Technology
文摘Open-celled porous （TiB2-Al2O3）/NiAl composites were successfully fabricated by using spherical carbamide as space holders via self-propagating high-temperature synthesis （SHS）. Effects of 10Al-3B2O3-3TiO2 contents （0-20 wt%） on the pore structures and the quasi-static compressive behaviors of the resultant materials were investigated. The porous （TiBE-Al2O3）/NiAl composites exhibit composite pore structure consisting of homogeneously distributed and interconnected millimeter pores and micropores. The millimeter pores virtually inherit the shape and size of carbamide particles, while the pore size of micropores increases with increasing the 10Al-3BEO3-3TiO2 content. Depending on the volume fraction of the carbamide, the porosity of the porous materials can be easily controlled in a range of 55%-85%. When the porosity is about 72%, the compressive strengths of porous NiAl and porous （TiBE-Al203）/NiAl composite with 15% 10Al-3B2O3-3TiO2 in green compact are 19 and 32 MPa, and the corresponding strains are 2.9% and 5.7%, respectively. Furthermore, the quasi-static compressive behavior of porous （TiB2-AlEO3）/NiAl composites can be estimated by Gibson-Ashby model.
文摘The effect of successive washing instead of traditional intermittent washing on the porous structure of pseudoboehmite was investigated by mercury porosimetry, N2 adsorption and thermal analysis, while the stabilities of different types of crystals were investigated by X-ray diffractometer. Experimental results show that successive washing is a continuation of the aging process of intermittent washing. After a successive washing, the pore types showed no difference with the intermittent washing. During successive washing, the characteristics of the pores in the range of 2-15 nm changed only very little. However, the distributions of the pore radius for pores of 20-50 and 300-1000 nm were obviously influenced. It was shown that the volume of larger pores decreased only to a smaller extent after the successive washing, as compared with that of the intermittent washing, and the pore size was affected by the condition of the successive washing. The roles of physisorbed water, intermicellar liquid, weakly bonded water, as well as the role of stirring, have been discussed.
