The effects of the initial framework SiO2/Al2O3 ratio and temperature on the structural changes of NaY zeolites during hydrothermal treatments are studied. Two samples with different framework SiO2/Al2O3 ratios are ...The effects of the initial framework SiO2/Al2O3 ratio and temperature on the structural changes of NaY zeolites during hydrothermal treatments are studied. Two samples with different framework SiO2/Al2O3 ratios are subjected to hydrothermal treatment at four different temperatures. For zeolite with a lower initial SiO2/Al2O3 ratio of 4.2, mesopores are easily formed because more framework aluminum is detached. Moreover, two kinds of mesopores are produced at a higher temperature due to the interconnection of vacancies and smaller mesopores. For zeolite with a higher initial SiO2/Al2O3 ratio of 6.0, there are less mesopores formed as compared with the lower initial SiO2/Al2O3 ratio sample, but there are some macropores formed. This may be attributed to the isolation of vacancies and the different distributions of aluminum in the crystal lattice of the zeolite. The experiment data show that NaY with the SiO2/Al2O3 ratio of 6.0 retains a high relative crystallinity during the hydrothermal treatment. This proves that a high framework SiO2/Al2O3 ratio benefits the stability of zeolite.展开更多
Fine Al（OH）3 crystals were aggregated from supersaturated aluminate solution in the batch reaction tanks. By means of laser particle size analyzer and scanning electron microscopy, the influences of temperature and ...Fine Al（OH）3 crystals were aggregated from supersaturated aluminate solution in the batch reaction tanks. By means of laser particle size analyzer and scanning electron microscopy, the influences of temperature and initial molar ratio of Na2O to Al2O3 （aK） on agglomeration of fine seed in Bayer process were investigated. The results show that agglomeration is almost finished in 8 h, and seeds with size less than 2 μm are easily aggregated together, and almost disappear in 8 h under the optimal process conditions. In the aluminate solution with the same moderate initial aK, when the reaction temperature reaches 75 ℃, the secondary nucleation does not occur, and the effect of agglomeration is better. And at the same reaction temperature, when the initial aK is 1.62, the initial supersaturation of aluminate solution is moderate, the binders on the surfaces of the seed are enough to maintain the agglomeration process, and the agglomeration degree is better. From SEM images, agglomeration mainly occurs in the fine particles, the combinations among the fine particles are loose and the new formed coarse crystal shapes are irregular.展开更多
The flocculation tests of four pure minerals(diaspore,kaolinite,illite,pyrophyllite)and bauxite ore were investigated by the sedimentation.The dispersion behavior of the four pure minerals shows a very good consistenc...The flocculation tests of four pure minerals(diaspore,kaolinite,illite,pyrophyllite)and bauxite ore were investigated by the sedimentation.The dispersion behavior of the four pure minerals shows a very good consistency with the variation of zeta potential.The concentrate with the mass ratio of Al2O3 to SiO2(m(Al2O3)/m(SiO2))8.90 and the recovery of Al2O3 86.98%is obtained from bauxite ore(m(Al2O3)/m(SiO2)=5.68)in pH range of 9.5-10.0 by using sodium carbonate(5 kg/t)and sodium polyacrylate(7 g/t)as dispersant and flocculant respectively.Sodium carbonate acts as both pH modifier and favorable dispersant for aluminosilicates.The high performance of sodium polyacrylate on flocculation for diaspore is contributed to the carboxyl of sodium polyacrylate that interacts with active Al sites on diaspore by chemical absorption,and the hydrogen bond effects between hydroxyl group of macromolecule and surface Al—OH on diaspore to accelerate the sedimentation of diaspore.展开更多
Molecular dynamics simulation is applied to investigate the mechanism and variation of self-diffusion in calcium aluminosilicate slags. The self-diffusion coefficients are calculated for eleven slag compositions with ...Molecular dynamics simulation is applied to investigate the mechanism and variation of self-diffusion in calcium aluminosilicate slags. The self-diffusion coefficients are calculated for eleven slag compositions with varying Al2O3/SiO2 ratios at a fixed CaO content. In practice, the results of the study are relevant to the significant changes in transport phenomenon caused by the changes in chemical composition during continuous casting of steels containing high amounts of dissolved aluminum. The cooperative movement between O atoms and network formers is discussed since [AlO4] and [SiO4] tetrahedra are the elementary structural units in the CaO-Al2O3-SiO2 (CAS) slag system. The diffusivities for four atomic types are affected by the degree of polymerization (DOP) of slag network characterized by the proportions of non-bridging oxygen (NBO) and Qn species in the system. On the other hand, a sudden increase in 5-coordinated Al as network modifiers in high alumina regions slightly increases the self-diffusion coefficient for Al. As another structural defect, oxygen tricluster plays an important role in the behavior of self-diffusion for O atoms, while the diffusivity for Ca is deeply influenced by its bonding and coordinating conditions.展开更多
The optimum Mo/[H^+] ratio per unit cell of the active precursors in Mo/HZSM-5 catalysts for methane dehydro-aromatization, measured by1H MAS NMR, was found to be about 1 when adjusting the acid sites by altering eith...The optimum Mo/[H^+] ratio per unit cell of the active precursors in Mo/HZSM-5 catalysts for methane dehydro-aromatization, measured by1H MAS NMR, was found to be about 1 when adjusting the acid sites by altering either the SiO2/Al2O3 ratios or the Mo loading. This implies that a concerted interaction between the Mo species and the Bronsted acid sites probably features the bifunctionality of the Mo/HZSM-5 catalyst. On the other hand, it was found that the driving force for Mo species to move into the HSZM-5 zeolite channels and the interaction between the Mo species and the Bronsted acid sites are closely and proportionably related with the amount of Bronsted acid sites per unit cell.展开更多
The effect of alumina content and heat treatment temperature and time, on microstructure and Er3＋ （0.5 mol.%） emission of oxyfluoride glass-ceramics were investigated in this research. Two values of 1.8 （SA1.8Er0....The effect of alumina content and heat treatment temperature and time, on microstructure and Er3＋ （0.5 mol.%） emission of oxyfluoride glass-ceramics were investigated in this research. Two values of 1.8 （SA1.8Er0.5） and 2.18 （SA2.18Er0.5） were selected in this research for SiO2/Al2O3 ratio. According to DTA results, precursor glasses were heat treated at 630, 660 and 690 ℃ for 4 h and some glasses were also heat treated at 630 ℃ for 48 and 72 h. The results indicated that alumina content had significant effect on phase separation and viscosity of the glasses. Therefore the size, size distribution, and volume concentration of nano CaF2 crystals which precipitated during the heat treatment depended on alumina content of the glass. Due to the much smaller size of the precipitated CaF2 crystals in the glasses of low alumina content, these samples maintained excellent transparency and had narrower crystal size distribution than the high alumina glasses. The crystal size was increased markedly with the temperature increasing from 630 to 690 ℃. On the other hand a slight increase was observed in the crystal size by raising the heat treatment time in both glasses. Results indicated that in low alumina content glass （SA2.18Er0.5） the size of CaF2 nanocrystals was controlled in one order of magnitude. The increase of heat treatment time and temperature led to the incorporation of Er3＋ ions into CaF2 crystalline phase, increasing significantly the upconversion intensity. After heat treatment at 690 ℃for 4 h, atomic force microscope （AFM） revealed the development of small crystals with an average size of 80 and 30 nm in SA1.8Er0.5 and SA2.18Er0.5 samples, respectively.展开更多
Grain size of eolian deposits from the Loess Plateau in China has been widely used to reconstruct the history of the East Asian winter monsoon. However, the grain size of bulk samples is only partially indicative to t...Grain size of eolian deposits from the Loess Plateau in China has been widely used to reconstruct the history of the East Asian winter monsoon. However, the grain size of bulk samples is only partially indicative to the strength of the winter monsoon because post-depositional weathering processes have significantly changed the grain size of original eolian particles. Here, non-weathered loess samples were separated into eight different particle fractions, and major chemical elements were determined in order to establish a geochemical indicator of original eolian grain size. The results show that SiO2 and AI2O3 contents and the SiO2/AI2O3 ratio in different fractions vary regularly with grain size, and that a good linear relation exists between the SiO2/AI2O3 ratio and grain size for the fractions <50μm. Because Al and Si are among the most stable elements and pedogenic processes in the Loess Plateau cannot affect the SiO2/AI2O3 ratio, this index can be used to reflect the grain size of original eolian particles. Application of this index in the Weinan and Luochuan loess sections of the last climatic cycle shows that SiO2/AI2O3 is in good agreement with median grain size (Md) in the loess units. On the contrary, SiO2/AI2O3 has documented a series of fluctuations in the soil units that are not clearly indicated by the grain-size changes of bulk samples.展开更多
Due to the high content of the Al-TRIP steel, Al reacts with SiO2 in the mold slag during the casting process, which results in the increase of ωAl2O3 /ωSiO2 ratio and the Al2O3 content, respectively; the characteri...Due to the high content of the Al-TRIP steel, Al reacts with SiO2 in the mold slag during the casting process, which results in the increase of ωAl2O3 /ωSiO2 ratio and the Al2O3 content, respectively; the characteristic of heat transfer through the slag film is then changed, which influences the smooth operation of the continuous casting process. The heat flux simulator of mold slag film was used to study the change tendency of the heat flux density through slag film and the results were discussed; at the same time, the characteristics of the crystals in the No. 15 mold slag were determined by BSE and XRD. The results obtained show that heat flux density decreases with the increase of ωAl2O3 /ωSiO2 ratio. Heat flux density increases with the increase of Li2O and/or B2O3 content in the mold slag which contains 30 % of Al2 O3. Compared with the heat flux density of common slag of peritectic steel, a suitable mold slag containing 4% of B2O3 and 4% of Li2O is designed. The heat flux density is 0. 645 MW/m^2 when ωAl2O3 /ωSiO2 = 1. 46. Under this experimental condition, the CaF2 crystals precipitate in the mold slag used for Al-TRIP steel.展开更多
文摘The effects of the initial framework SiO2/Al2O3 ratio and temperature on the structural changes of NaY zeolites during hydrothermal treatments are studied. Two samples with different framework SiO2/Al2O3 ratios are subjected to hydrothermal treatment at four different temperatures. For zeolite with a lower initial SiO2/Al2O3 ratio of 4.2, mesopores are easily formed because more framework aluminum is detached. Moreover, two kinds of mesopores are produced at a higher temperature due to the interconnection of vacancies and smaller mesopores. For zeolite with a higher initial SiO2/Al2O3 ratio of 6.0, there are less mesopores formed as compared with the lower initial SiO2/Al2O3 ratio sample, but there are some macropores formed. This may be attributed to the isolation of vacancies and the different distributions of aluminum in the crystal lattice of the zeolite. The experiment data show that NaY with the SiO2/Al2O3 ratio of 6.0 retains a high relative crystallinity during the hydrothermal treatment. This proves that a high framework SiO2/Al2O3 ratio benefits the stability of zeolite.
基金Project(2005CB623702)supported by the Major State Basic Research and Development Program of ChinaProject(20476107) supported by the National Natural Science Foundation of China
文摘Fine Al（OH）3 crystals were aggregated from supersaturated aluminate solution in the batch reaction tanks. By means of laser particle size analyzer and scanning electron microscopy, the influences of temperature and initial molar ratio of Na2O to Al2O3 （aK） on agglomeration of fine seed in Bayer process were investigated. The results show that agglomeration is almost finished in 8 h, and seeds with size less than 2 μm are easily aggregated together, and almost disappear in 8 h under the optimal process conditions. In the aluminate solution with the same moderate initial aK, when the reaction temperature reaches 75 ℃, the secondary nucleation does not occur, and the effect of agglomeration is better. And at the same reaction temperature, when the initial aK is 1.62, the initial supersaturation of aluminate solution is moderate, the binders on the surfaces of the seed are enough to maintain the agglomeration process, and the agglomeration degree is better. From SEM images, agglomeration mainly occurs in the fine particles, the combinations among the fine particles are loose and the new formed coarse crystal shapes are irregular.
基金Project(2005CB623701)supported by the Major State Basic Research Development Program of China
文摘The flocculation tests of four pure minerals(diaspore,kaolinite,illite,pyrophyllite)and bauxite ore were investigated by the sedimentation.The dispersion behavior of the four pure minerals shows a very good consistency with the variation of zeta potential.The concentrate with the mass ratio of Al2O3 to SiO2(m(Al2O3)/m(SiO2))8.90 and the recovery of Al2O3 86.98%is obtained from bauxite ore(m(Al2O3)/m(SiO2)=5.68)in pH range of 9.5-10.0 by using sodium carbonate(5 kg/t)and sodium polyacrylate(7 g/t)as dispersant and flocculant respectively.Sodium carbonate acts as both pH modifier and favorable dispersant for aluminosilicates.The high performance of sodium polyacrylate on flocculation for diaspore is contributed to the carboxyl of sodium polyacrylate that interacts with active Al sites on diaspore by chemical absorption,and the hydrogen bond effects between hydroxyl group of macromolecule and surface Al—OH on diaspore to accelerate the sedimentation of diaspore.
文摘Molecular dynamics simulation is applied to investigate the mechanism and variation of self-diffusion in calcium aluminosilicate slags. The self-diffusion coefficients are calculated for eleven slag compositions with varying Al2O3/SiO2 ratios at a fixed CaO content. In practice, the results of the study are relevant to the significant changes in transport phenomenon caused by the changes in chemical composition during continuous casting of steels containing high amounts of dissolved aluminum. The cooperative movement between O atoms and network formers is discussed since [AlO4] and [SiO4] tetrahedra are the elementary structural units in the CaO-Al2O3-SiO2 (CAS) slag system. The diffusivities for four atomic types are affected by the degree of polymerization (DOP) of slag network characterized by the proportions of non-bridging oxygen (NBO) and Qn species in the system. On the other hand, a sudden increase in 5-coordinated Al as network modifiers in high alumina regions slightly increases the self-diffusion coefficient for Al. As another structural defect, oxygen tricluster plays an important role in the behavior of self-diffusion for O atoms, while the diffusivity for Ca is deeply influenced by its bonding and coordinating conditions.
文摘The optimum Mo/[H^+] ratio per unit cell of the active precursors in Mo/HZSM-5 catalysts for methane dehydro-aromatization, measured by1H MAS NMR, was found to be about 1 when adjusting the acid sites by altering either the SiO2/Al2O3 ratios or the Mo loading. This implies that a concerted interaction between the Mo species and the Bronsted acid sites probably features the bifunctionality of the Mo/HZSM-5 catalyst. On the other hand, it was found that the driving force for Mo species to move into the HSZM-5 zeolite channels and the interaction between the Mo species and the Bronsted acid sites are closely and proportionably related with the amount of Bronsted acid sites per unit cell.
基金Project supported by ACIISI of Gobierno de Canarias (ID20100152)Ministerio de Economíay Competitividad of Spain(MINECO)within the National Program of Materials(MAT2010-21270-C04-02/-03/-04)+2 种基金the Consol-ider-Ingenio 2010 Program(MALTACSD2007-0045,www.malta-consolider.com)ACIISI(Gobierno de canarias)project ID20100152governments of Spainand India for the award of a project within the indo-Spanish Joint Programme of Cooperation in Science and Technology(PRI-PIBIN-2011-1153/DST-INT-Spain-P-38-11)
文摘The effect of alumina content and heat treatment temperature and time, on microstructure and Er3＋ （0.5 mol.%） emission of oxyfluoride glass-ceramics were investigated in this research. Two values of 1.8 （SA1.8Er0.5） and 2.18 （SA2.18Er0.5） were selected in this research for SiO2/Al2O3 ratio. According to DTA results, precursor glasses were heat treated at 630, 660 and 690 ℃ for 4 h and some glasses were also heat treated at 630 ℃ for 48 and 72 h. The results indicated that alumina content had significant effect on phase separation and viscosity of the glasses. Therefore the size, size distribution, and volume concentration of nano CaF2 crystals which precipitated during the heat treatment depended on alumina content of the glass. Due to the much smaller size of the precipitated CaF2 crystals in the glasses of low alumina content, these samples maintained excellent transparency and had narrower crystal size distribution than the high alumina glasses. The crystal size was increased markedly with the temperature increasing from 630 to 690 ℃. On the other hand a slight increase was observed in the crystal size by raising the heat treatment time in both glasses. Results indicated that in low alumina content glass （SA2.18Er0.5） the size of CaF2 nanocrystals was controlled in one order of magnitude. The increase of heat treatment time and temperature led to the incorporation of Er3＋ ions into CaF2 crystalline phase, increasing significantly the upconversion intensity. After heat treatment at 690 ℃for 4 h, atomic force microscope （AFM） revealed the development of small crystals with an average size of 80 and 30 nm in SA1.8Er0.5 and SA2.18Er0.5 samples, respectively.
基金the National Basic Research Project (GrantNo. 1998040800), the National Natural Science Foundation of China (Grant Nos. 49725206, 49894170-06 and 40024202) and the Chinese Academy of Sciences (Grant No. KZCX2-108).
文摘Grain size of eolian deposits from the Loess Plateau in China has been widely used to reconstruct the history of the East Asian winter monsoon. However, the grain size of bulk samples is only partially indicative to the strength of the winter monsoon because post-depositional weathering processes have significantly changed the grain size of original eolian particles. Here, non-weathered loess samples were separated into eight different particle fractions, and major chemical elements were determined in order to establish a geochemical indicator of original eolian grain size. The results show that SiO2 and AI2O3 contents and the SiO2/AI2O3 ratio in different fractions vary regularly with grain size, and that a good linear relation exists between the SiO2/AI2O3 ratio and grain size for the fractions <50μm. Because Al and Si are among the most stable elements and pedogenic processes in the Loess Plateau cannot affect the SiO2/AI2O3 ratio, this index can be used to reflect the grain size of original eolian particles. Application of this index in the Weinan and Luochuan loess sections of the last climatic cycle shows that SiO2/AI2O3 is in good agreement with median grain size (Md) in the loess units. On the contrary, SiO2/AI2O3 has documented a series of fluctuations in the soil units that are not clearly indicated by the grain-size changes of bulk samples.
基金Item Sponsored by National Natural Science Foundation of China (50874125)
文摘Due to the high content of the Al-TRIP steel, Al reacts with SiO2 in the mold slag during the casting process, which results in the increase of ωAl2O3 /ωSiO2 ratio and the Al2O3 content, respectively; the characteristic of heat transfer through the slag film is then changed, which influences the smooth operation of the continuous casting process. The heat flux simulator of mold slag film was used to study the change tendency of the heat flux density through slag film and the results were discussed; at the same time, the characteristics of the crystals in the No. 15 mold slag were determined by BSE and XRD. The results obtained show that heat flux density decreases with the increase of ωAl2O3 /ωSiO2 ratio. Heat flux density increases with the increase of Li2O and/or B2O3 content in the mold slag which contains 30 % of Al2 O3. Compared with the heat flux density of common slag of peritectic steel, a suitable mold slag containing 4% of B2O3 and 4% of Li2O is designed. The heat flux density is 0. 645 MW/m^2 when ωAl2O3 /ωSiO2 = 1. 46. Under this experimental condition, the CaF2 crystals precipitate in the mold slag used for Al-TRIP steel.
