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Ray L Frost - One of the best experts on this subject based on the ideXlab platform.
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surface analysis tem dynamic and controlled rate thermal analysis and infrared emission spectroscopy of gallium doped Boehmite nanofibres and nanosheets
Applied Surface Science, 2009Co-Authors: Jing Yang, Yanyan Zhao, Ray L FrostAbstract:Abstract Ga doped Boehmite nanofibres with varying Ga content have been prepared at low temperatures using hydrothermal treatment in the presence of poly (ethylene oxide) surfactant. The resulting nanofibres were characterized by X-ray diffraction (XRD), dynamic and controlled rate thermal analysis and infrared emission spectroscopy (IES), transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDX), N 2 adsorption/desorption. TEM results show that nanotubes are dominant when the doped gallium percentage is no more than 5%; nanosheets and an amorphous phase are observed in 10% and 20% gallium doped samples. N 2 adsorption/desorption analysis reveals a large amount of micropores and mesopores are present in the resultant samples. Similar to iron and yttrium doped Boehmite nanomaterials, remarkable larger BET specific area was achieved compared to pure Boehmite nanomaterials. Both dynamic and controlled thermal analyses show that the gallium doped Boehmite nanomaterials dehydrate at higher temperature than that of pure Boehmite. Interestingly, the higher the crystallinity of the resultant nanotubes is, the higher the dehydration temperature. The IES spectra show that dehydroxylation of the resultant gallium doped Boehmite nanomaterials starts at 250 °C and is complete by 450 °C, in harmony with the dynamic and controlled rate thermal analysis results.
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growth of Boehmite nanofibers by assembling nanoparticles with surfactant micelles
Journal of Physical Chemistry B, 2004Co-Authors: Huai Zhu, Xueping Gao, D Y Song, Y Bai, Simon Ringer, Z Gao, Wayde N Martens, James D Riches, Ray L FrostAbstract:It is known that Boehmite (AlOOH) nanofibers formed in the presence of nonionic poly(ethylene oxide) (PEO) surfactant at 373 K. A novel approach is proposed in this study for the growth of the Boehmite nanofibers: when fresh aluminum hydrate precipitate was added at regular interval to initial mixture of Boehmite and PEO surfactant at 373 K, the nanofibers grow from 40 to 50 nm long to over 100 nm. It is believed that the surfactant micelles play an important role in the nanofiber growth: directing the assembly of aluminum hydrate particles through hydrogen bonding with the hydroxyls on the surface of aluminum hydrate particles. Meanwhile a gradual improvement in the crystallinity of the fibers during growth is observed and attributed to the Ostwald ripening process. This approach allows us to precisely control the size and morphology of Boehmite nanofibers using soft chemical methods and could be useful for low temperature, aqueous syntheses of other oxide nanomaterials with tailorable structural specificity such as size, dimension and morphology.
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thermal decomposition of bauxite minerals infrared emission spectroscopy of gibbsite Boehmite and diaspore
Journal of Materials Science, 2002Co-Authors: J. Theo Kloprogge, Huada Ruan, Ray L FrostAbstract:Infrared emission spectroscopy has been used to study the dehydroxylation behavior over the temperature range from 200 to 750°C of three major Al-minerals in bauxite: gibbsite (synthetic and natural), Boehmite (synthetic and natural) and diaspore. A good agreement is found with the thermal analysis and differential thermal analysis curves of these minerals. Loss in intensity of especially the hydroxyl-stretching modes of gibbsite, Boehmite and diaspore as function of temperature correspond well with the observed changes in the TGA/DTA patterns. The DTA pattern of gibbsite clearly indicates the formation of Boehmite as an intermediate shown by a endotherm around 500°C. Dehydroxylation of gibbsite is followed by a loss of intensity of the 3620 and 3351 cm−1 OH-stretching bands and the corresponding deformation band around 1024 cm−1. Dehydroxylation starts around 220°C and is complete around 350°C. Similar observations were made for Boehmite and diaspore. For Boehmite dehydroxylation was observed to commence around 250°C and could be followed by especially the loss in intensity of the bands around 3319 and 3129 cm−1. The DTA pattern of diaspore is more complex with overlapping endotherms around 622 and 650°C. The dehydroxylation can be followed by the decrease in intensity of the OH-stretching bands around 3667, 3215 and 2972 cm−1. Above 550°C only a single band is observed that disappears after heating above 600°C corresponding to the two endotherms around 622 and 650°C in the DTA.
X Bokhimi - One of the best experts on this subject based on the ideXlab platform.
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crystallization of sol gel Boehmite via hydrothermal annealing
Journal of Solid State Chemistry, 2002Co-Authors: X Bokhimi, J Sanchezvalente, F PedrazaAbstract:Abstract Thin crystallites of Boehmite were synthesized by annealing a sol–gel precursor under hydrothermal conditions. Samples were characterized with X-ray powder diffraction, thermogravimetry, transmission electron microscopy, and by refining the crystalline phases. Fresh samples consisted of Boehmite sheets forming folded paper-like “crystallites,” which were transformed into thin flat crystalline plates perpendicular to crystallographic b -axis when they were annealed under hydrothermal conditions using water as mineralizer. Boehmite's crystallite size increased with the annealing time. The rhombic Boehmite crystallites had their shortest diagonal parallel to crystallographic a -axis, and their lateral faces parallel to {101} planes forming an angle of 104.32° between each other; these planes contained active aluminum atoms responsible for the crystallites growing along them. The hydrogen bonding length, which decreased as crystallite size increased, determined the variation of Boehmite's transition temperature into γ -alumina. Since this transformation is pseudo-morphic, both particle morphology and sample porosity of alumina were determined by the arrangement of crystallites in Boehmite. γ -Alumina crystallite distribution had memory about Boehmite crystallite dimensions and atomic arrangement: crystallites were oriented parallel to Boehmite’s a axis, and were confined by Boehmite's crystallite dimensions.
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dependence of Boehmite thermal evolution on its atom bond lengths and crystallite size
IEEE Journal of Solid-state Circuits, 2001Co-Authors: X Bokhimi, J A Toledoantonio, M L Guzmancastillo, F Hernandezbeltran, B Marmar, J NavarreteAbstract:Abstract The thermal properties of Boehmite with a crystallite size between 1 and 27 nm were analyzed by thermogravimetry and differential thermal analysis, and correlated with its crystallography, crystallite morphology, and the atom bond lengths determined by refining its crystalline structure with the Rietveld method. Boehmite's thermal evolution depended on atom bond lengths: the dehydratation temperature was determined by the interaction between an aluminum atom and the oxygen atom of hydroxyl. After dehydratation, the number of hydroxyls in crystals was larger than expected from stoichiometry, because oxygen atoms on crystal surfaces perpendicular to the (020) plane reacted with hydrogen and hydroxyls in environment. The transition temperature from Boehmite into γ -alumina was determined by the hydrogen bond in Boehmite. The transformation temperature from transitional aluminas into α -Al 2 O 3 also varied with Boehmite's crystallite size; however, it was not determined by the amount of hydroxyls in transitional aluminas, but probably by the aluminum–oxygen bonds in Boehmite.
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relationship between crystallite size and bond lengths in Boehmite
IEEE Journal of Solid-state Circuits, 2001Co-Authors: X Bokhimi, J A Toledoantonio, M L Guzmancastillo, F HernandezbeltranAbstract:Abstract Boehmite with a crystallite size between 1 and 27 nm was prepared by annealing a Boehmite precipitate under hydrothermal conditions at different temperatures. The crystalline structure, measured with X-ray powder diffraction, was refined with the Rietveld method. From the refinement bond lengths and bond angles between oxygen and aluminum atoms were calculated, which revealed that Boehmite bond lengths and local symmetry depended on crystal dimensions. When Boehmite's crystallite size decreased, Al–OH interaction increased, and the local octahedral symmetry tended to be tetrahedral. The hydrogen bond, sustaining Boehmite's crystalline structure, and the bonds between oxygen atoms and hydroxyls inside the octahedra double layers, building the crystalline structure, became weaker as crystallite size decreased, which could explain why Boehmite's transformation temperature into a transitional alumina also decreased with crystallite size. Alumina crystallite size also depended of the corresponding size of Boehmite. It was shown that desorbed water from annealed samples came from the crystal surface and not from the bulk.
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aluminum local environment and defects in the crystalline structure of sol gel alumina catalyst
Journal of Physical Chemistry B, 1999Co-Authors: J A Wang, X Bokhimi, And A Morales, O Novaro, R GomezAbstract:Nanocrystalline alumina was synthesized by using the sol−gel method with aluminum sec-butoxide as the precursor. FTIR, TG, XRD, and crystalline structure refinement were used to analyze the phase transformations and their crystalline structures. When samples were annealed at 200 °C, they had two nanocrystalline phases γ-Boehmite and γ*-Boehmite, which had the same crystalline structure but different lattice parameters and defect numbers in the structure. After sample annealing above 400 °C, the γ-Boehmite and γ*-Boehmite phases were transformed into nanocrystalline γ-Al2O3 and θ-Al2O3. The γ-alumina crystalline structure contained hydroxyls that brought about cationic defects in aluminum sites, mainly in those of octahedral symmetry. In the 27Al NMR spectra of the samples calcined at 400, 600, and 800 °C, a chemical shift around 33 ppm was observed, which occurred between that of aluminum in oxygen octahedra and aluminum in oxygen tetrahedra. Its origin can be explained by assuming the existence the subst...
Huada Ruan - One of the best experts on this subject based on the ideXlab platform.
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thermal decomposition of bauxite minerals infrared emission spectroscopy of gibbsite Boehmite and diaspore
Journal of Materials Science, 2002Co-Authors: J. Theo Kloprogge, Huada Ruan, Ray L FrostAbstract:Infrared emission spectroscopy has been used to study the dehydroxylation behavior over the temperature range from 200 to 750°C of three major Al-minerals in bauxite: gibbsite (synthetic and natural), Boehmite (synthetic and natural) and diaspore. A good agreement is found with the thermal analysis and differential thermal analysis curves of these minerals. Loss in intensity of especially the hydroxyl-stretching modes of gibbsite, Boehmite and diaspore as function of temperature correspond well with the observed changes in the TGA/DTA patterns. The DTA pattern of gibbsite clearly indicates the formation of Boehmite as an intermediate shown by a endotherm around 500°C. Dehydroxylation of gibbsite is followed by a loss of intensity of the 3620 and 3351 cm−1 OH-stretching bands and the corresponding deformation band around 1024 cm−1. Dehydroxylation starts around 220°C and is complete around 350°C. Similar observations were made for Boehmite and diaspore. For Boehmite dehydroxylation was observed to commence around 250°C and could be followed by especially the loss in intensity of the bands around 3319 and 3129 cm−1. The DTA pattern of diaspore is more complex with overlapping endotherms around 622 and 650°C. The dehydroxylation can be followed by the decrease in intensity of the OH-stretching bands around 3667, 3215 and 2972 cm−1. Above 550°C only a single band is observed that disappears after heating above 600°C corresponding to the two endotherms around 622 and 650°C in the DTA.
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comparison of the raman spectra of bayerite Boehmite diaspore and gibbsite
Journal of Raman Spectroscopy, 2001Co-Authors: Huada Ruan, Theo J KloproggeAbstract:Gibbsite and bayerite are alumina trihydrate (Al(OH) 3). Gibbsite occurs abundantly in nature, usually as a major mineral component in bauxite whereas bayerite is rarely found in nature. Boehmite and diaspore are alumina oxohydroxide (AlOOH) and are two other important minerals in bauxite. The Raman spectra of these four minerals were obtained using a Fourier transform Raman spectrometer operating at 1064 nm. Bayerite spectrum shows five absorption bands, 3652, 3542, 3449, 3438, and 3421 cm-1 and the gibbsite spectrum shows four strong and sharp absorption bands, 3619, 3523, 3433 and 3363 cm-1 in the hydroxyl stretching region. Four broad bands, 3426, 3365, 3229 and 2935 cm-1 and three weak bands, 3420, 3216 and 3090 cm-1 are present in this region for diaspore and Boehmite, respectively. The Raman bands correspond well with the infrared absorption bands at 3620, 3525 cm-1 for gibbsite, 3365 cm-1 for diaspore and 3423, 3096 cm-1 for Boehmite and these bands are assigned to be Raman and infrared active. The spectra of bayerite, gibbsite and diaspore are complex while the spectrum of Boehmite only illustrates four absorption bands in the low frequency region. Common bands of RT-Raman spectra at 1019, 892, 816, 710, 568, 539, 506, 429, 395, 379, 321, 306, 255 and 242 cm-1 were observed for gibbsite, 1079, 1068, 898, 866, 545, 434, 388, 322, 292, 250 and 239 cm-1 for bayerite, 705, 608, 446, 260 and 216 cm-1 for diaspore, and 674, 495 and 360 cm-1 for Boehmite. The differences in the vibrational spectra of bayerite, gibbsite, diaspore and Boehmite are interpreted as being due to the differences in the molecular structure of these minerals.
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comparison of raman spectra in characterizing gibbsite bayerite diaspore and Boehmite
Journal of Raman Spectroscopy, 2001Co-Authors: Huada Ruan, J. Theo KloproggeAbstract:High-quality Raman spectra were used for the characterization of alumina phases of gibbsite, bayerite, diaspore and Boehmite. The Raman spectrum of gibbsite shows four strong, sharp bands at 3617, 3522, 3433 and 3364 cm in the hydroxyl stretching region. The spectrum of bayerite shows seven bands at 3664, 3652, 3552, 3542, 3450, 3438 and 3420 cm. Five broad bands at 3445, 3363, 3226, 3119 and 2936 cm and four broad and weak bands at 3371, 3220, 3085 and 2989 cm-1 are present in the Raman spectrum of the hydroxyl stretching region of diaspore and Boehmite. The hydroxyl stretching bands are related to the surface structure of the minerals. The Raman spectra of bayerite, gibbsite and diaspore are complex whereas the Raman spectrum of Boehmite shows only four bands in the low-wavenumber region. These bands are assigned to deformation and translational modes of the alumina phases. A comparison of the Raman spectrum of bauxite with those of Boehmite and gibbsite showed the possibility of using Raman spectroscopy for on-line processing of bauxites that contain a mixture of alumina phases.
J. Theo Kloprogge - One of the best experts on this subject based on the ideXlab platform.
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thermal decomposition of bauxite minerals infrared emission spectroscopy of gibbsite Boehmite and diaspore
Journal of Materials Science, 2002Co-Authors: J. Theo Kloprogge, Huada Ruan, Ray L FrostAbstract:Infrared emission spectroscopy has been used to study the dehydroxylation behavior over the temperature range from 200 to 750°C of three major Al-minerals in bauxite: gibbsite (synthetic and natural), Boehmite (synthetic and natural) and diaspore. A good agreement is found with the thermal analysis and differential thermal analysis curves of these minerals. Loss in intensity of especially the hydroxyl-stretching modes of gibbsite, Boehmite and diaspore as function of temperature correspond well with the observed changes in the TGA/DTA patterns. The DTA pattern of gibbsite clearly indicates the formation of Boehmite as an intermediate shown by a endotherm around 500°C. Dehydroxylation of gibbsite is followed by a loss of intensity of the 3620 and 3351 cm−1 OH-stretching bands and the corresponding deformation band around 1024 cm−1. Dehydroxylation starts around 220°C and is complete around 350°C. Similar observations were made for Boehmite and diaspore. For Boehmite dehydroxylation was observed to commence around 250°C and could be followed by especially the loss in intensity of the bands around 3319 and 3129 cm−1. The DTA pattern of diaspore is more complex with overlapping endotherms around 622 and 650°C. The dehydroxylation can be followed by the decrease in intensity of the OH-stretching bands around 3667, 3215 and 2972 cm−1. Above 550°C only a single band is observed that disappears after heating above 600°C corresponding to the two endotherms around 622 and 650°C in the DTA.
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comparison of raman spectra in characterizing gibbsite bayerite diaspore and Boehmite
Journal of Raman Spectroscopy, 2001Co-Authors: Huada Ruan, J. Theo KloproggeAbstract:High-quality Raman spectra were used for the characterization of alumina phases of gibbsite, bayerite, diaspore and Boehmite. The Raman spectrum of gibbsite shows four strong, sharp bands at 3617, 3522, 3433 and 3364 cm in the hydroxyl stretching region. The spectrum of bayerite shows seven bands at 3664, 3652, 3552, 3542, 3450, 3438 and 3420 cm. Five broad bands at 3445, 3363, 3226, 3119 and 2936 cm and four broad and weak bands at 3371, 3220, 3085 and 2989 cm-1 are present in the Raman spectrum of the hydroxyl stretching region of diaspore and Boehmite. The hydroxyl stretching bands are related to the surface structure of the minerals. The Raman spectra of bayerite, gibbsite and diaspore are complex whereas the Raman spectrum of Boehmite shows only four bands in the low-wavenumber region. These bands are assigned to deformation and translational modes of the alumina phases. A comparison of the Raman spectrum of bauxite with those of Boehmite and gibbsite showed the possibility of using Raman spectroscopy for on-line processing of bauxites that contain a mixture of alumina phases.
Lin Zhao - One of the best experts on this subject based on the ideXlab platform.
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enhanced hydrogen generation by methanolysis of sodium borohydride in the presence of phosphorus modified Boehmite
Fuel, 2014Co-Authors: Dongyan Xu, Yusong Zhang, Fei Cheng, Lin ZhaoAbstract:Abstract Phosphorus (P) modified Boehmite catalysts were prepared with wet impregnation method using phosphoric acid (H 3 PO 4 ) as the P source. The P/Boehmite catalysts with different P loadings ranging from 0 to 6.4 wt% were obtained by regulating the concentration of H 3 PO 4 . These catalysts were characterized by BET surface area and FTIR spectroscopy measurements and their catalytic performance for hydrogen generation by methanolysis of sodium borohydride at 0 °C was evaluated. The results show that the as-prepared non-metallic P/Boehmite catalyst exhibited high catalytic activity toward the methanolysis reaction under the circumstance of low environmental temperature. Appropriate calcination treatment can enhance the catalytic activity of P/Boehmite catalyst to some extent. To understand the kinetic behavior of the methanolysis reaction in the presence of these catalysts, the experimental data were fitted to both zero-order and first-order kinetic models using the integral method.
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enhanced hydrogen generation by methanolysis of sodium borohydride in the presence of phosphorus modified Boehmite
Fuel, 2014Co-Authors: Dongyan Xu, Yusong Zhang, Fei Cheng, Lin ZhaoAbstract:Abstract Phosphorus (P) modified Boehmite catalysts were prepared with wet impregnation method using phosphoric acid (H 3 PO 4 ) as the P source. The P/Boehmite catalysts with different P loadings ranging from 0 to 6.4 wt% were obtained by regulating the concentration of H 3 PO 4 . These catalysts were characterized by BET surface area and FTIR spectroscopy measurements and their catalytic performance for hydrogen generation by methanolysis of sodium borohydride at 0 °C was evaluated. The results show that the as-prepared non-metallic P/Boehmite catalyst exhibited high catalytic activity toward the methanolysis reaction under the circumstance of low environmental temperature. Appropriate calcination treatment can enhance the catalytic activity of P/Boehmite catalyst to some extent. To understand the kinetic behavior of the methanolysis reaction in the presence of these catalysts, the experimental data were fitted to both zero-order and first-order kinetic models using the integral method.