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1.
Ozao R. Ochiai M. Yoshida H. Ichimura Y. Inada T. 《Journal of Thermal Analysis and Calorimetry》2001,64(3):923-932
Gamma-alumina membrane was prepared from anodic (amorphous) alumina (AA) obtained in a sulphuric acid electrolyte. The transformation
scheme, i.e., the crystallization to form metastable alumina polymorphs and the final transition to α-Al2O3 with heating was studied by TG-DTA and X-ray diffraction (XRD) using fixed time (FT) method. When heating at a constant rate,
the crystallization occurred at 900°C or higher and the final formation of α-Al2O3 occurred at 1250°C or higher, which temperatures were higher than the case of using anodic (amorphous) alumina prepared from
oxalic acid electrolyte. Relative content of S of the products was obtained by transmission electron microscope (TEM)-energy
dispersive spectroscopy (EDS). The proposed thermal change of anodic alumina membrane prepared from sulphuric acid is as follows:
1. At temperatures lower than ca 910°C: Formation of a quasi-crystalline phase or a polycrystalline phase (γ-, δ- and θ-Al2O3);
2. 910–960°C: Progressive crystallization by the migration of S toward the surface within the amorphous or the quasi-crystalline
phase, forming S-rich region near the surface;
3. 960°C: Change of membrane morphology and the quasi-crystalline phase due to the rapid discharge of gaseous SO2;
4. 960–1240°C: Crystallization of γ-Al2O3 accompanying δ-Al2O3; and
5. 1240°C: Transition from γ-Al2O3 (+tr. δ-Al2O3) into the stable α-Al2O3.
The amorphization which occurs by the exothermic and the subsequent endothermic reaction suggests the incorporation of SO3 groups in the quasi-crystalline structure.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
M. A. Ryashentseva 《Chemistry of Heterocyclic Compounds》2006,42(8):1018-1020
In the presence of Pd-and Cr-containing catalysts applied to γ-Al2O3 or sibunite 4,5,6,7-tetrahydroindole is converted into indole. Indole was obtained in quantitative yield on sulfided 0.15–0.5%
Pd/γ-Al2O3 catalyst at 360°C and on catalysts containing 5% Cr2O3, 5% La2O3 (or 5% polirit), 1% K2O/89% γ-Al2O3 at 475–480°C.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1176–1178, August, 2006. 相似文献
3.
R. Cremer M. Witthaut K. Reichert D. Neuschütz 《Analytical and bioanalytical chemistry》1999,365(1-3):158-162
The suitability of PVD films of γ-Al2O3 and of ternary Al-O-N as diffusion barriers between a nickel based superalloy CMSX-4 and NiCoCrAlY for a possible application
in gas turbines was investigated. Therefore, an Al2O3 film and, alternatively, an Al-O-N film were deposited on CMSX-4 at 100 °C substrate temperature by means of reactive magnetron
sputtering ion plating (MSIP). After characterization of composition and structure of the films by X-ray photoelectron spectroscopy
(XPS) and grazing incidence X-ray diffraction (XRD), a NiCoCrAlY coating was deposited onto the diffusion barriers and, for
comparison, directly onto CMSX-4 by MSIP as well. The composites were annealed for 4 h at 1100 °C under inert atmosphere.
Wavelength dispersive X-ray (WDX) element mappings and line-scans of the cross-sectional cut served to evaluate the suitability
of the films as diffusion barriers. After detachment of the coatings from the substrate, the phase stabilities of the two
metastable phases γ-Al2O3 and Al-O-N were determined by means of grazing incidence XRD. Without a diffusion barrier, enhanced interdiffusion was observed.
Analyses of the composite with the γ-Al2O3 interlayer revealed diffusion of Ti and Ta from the substrate into the NiCoCrAlY coating. No interdiffusion of Ni, Ti, Ta,
and Cr could be detected in case of the ternary Al-O-N film. Whereas the ternary Al-O-N film remained in the as-deposited
X-ray amorphous structure after annealing, a phase change from the γ to the α modification could be observed in case of the
Al2O3 film, presumably responsible for its lower efficiency as a diffusion barrier.
Received: 19 September 1998 / Revised: 14 April 1999 / Accepted: 18 April 1999 相似文献
4.
The structure of freshly prepared Al(OPh)3, its decomposition product, the hydrolyzed products and their structural evolution were investigated employing 27Al MAS NMR spectroscopy, PXRD, TGA/DTA/DSC/FTIR techniques. In the 27Al MAS NMR spectrum of the aluminium phenoxide, three signals with the chemical shift at 3.78, 21 and 45 ppm were observed.
The chemical shift at 3.78 and 45 ppm revealed the presence of four and sixfold coordinated aluminum. The signal at 21 ppm
corresponded to fivefold coordinated aluminium. When the aluminium phenoxide was directly decomposed in air at 600 °C, it
resulted in amorphous product as evidenced from the PXRD pattern. The observed signals with chemical shifts at 10.1, 42, 73.6 ppm
in the 27Al MAS NMR spectrum indicated the presence of 6, 5 and 4 coordination for the aluminium atoms suggesting disordered transitional
γ-alumina to be the product. The hydrolysis studies of Al(OPh)3 with excess of water at 70 °C yielded bohemite (γ-AlOOH). The alumina obtained after dehydration at 600 °C was X-ray amorphous.
The dehydrated product at 600 °C showed the presence of four and six coordinated aluminium atoms in the 27Al MAS NMR spectrum confirming it to be ordered γ-Al2O3. Crystalline γ-Al2O3 was obtained on further heating at 800 °C. 相似文献
5.
Junseo Choi Ji-Young Ban Suk-Jin Choung Jinsoo Kim Haznan Abimanyu Kye Sang Yoo 《Journal of Sol-Gel Science and Technology》2007,44(1):21-28
Mesoporous TiO2/γ-Al2O3 composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules
can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of
the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH3 decomposition, TiO2/γ-Al2O3 granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO2/γ-Al2O3 granules using titania made by hydrothermal method had comparable performance in NH3 decomposition. 相似文献
6.
Barbara Pacewska Olga Kluk-Płoskońska D. Szychowski 《Journal of Thermal Analysis and Calorimetry》2007,87(2):383-393
The process of hydrolysis of
aqueous aluminium sulfate was carried on in ammonia medium at 100°C and
for different time intervals (0, 20, 39 or 59 h). The products thus obtained
were calcined at 550, 900 or 1200°C for 2 h with the aim to obtain aluminium
oxides. The materials were studied with the following methods: thermal analysis,
IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption, adsorption–desorption
of benzene vapours and scanning electron microscopy.
Freshly precipitated
material was an amorphous basic aluminium sulfate which after prolonged refluxing
at elevated temperature in a mother liquor underwent a phase transformation
into highly crystalline NH4Al13(SO4)2(OH)6 containing tridecameric unit Al13. It was accompanied
by a decrease of specific surface area and the formation of a porous structure
less accessible for benzene molecules. Regardless of the duration of the hydrolysis
process, all products were characterised with poorly developed porous structure
and hydrophilic character. Their calcination at the temperature up to 1200°C
resulted in the formation of α-Al2O3
via transition forms of γ/η- and δ-Al2O3.
The samples of aluminium oxides obtained after calcination at 550 and 900°C
had higher values of specific surface area than starting materials due to
processes of dehydroxylation and desulfurization. The process of calcination
up to 900°C was reflected in developing of not only porous structure but
also hydrophobic character of prepared materials. The S
BET
values calculated for the oxide samples obtained from aged products of hydrolysis
at 1200°C were lower than for the analogous sample prepared without the
ageing step. It was concluded that prolonged refluxing at elevated temperature
of the products of hydrolysis of aluminium sulfate decreased thermal stability
of final aluminium oxides. 相似文献
7.
Al(OPh)3 involving sterically hindered phenyl groups on ultrasonic assisted micro hydrolysis yielded a mixture of boehmite and bayerite
as deduced from the FTIR and powder X-ray diffraction pattern. In the thermogravimetric trace, the complete removal of decomposable
moieties of the hydrolyzed gel occurred around 530 °C. Calcining the gel at temperatures 600, 700, 800 and 900 °C showed crystalline
tetragonal δ-Al2O3 to be the product at 900 °C as deduced from FTIR, 27Al NMR and PXRD techniques. δ-Al2O3 showed a surface area of 135 m2/g with rectangular bar like morphology with the sizes below 50 nm in the TEM images. 相似文献
8.
The effects of doping with CeO2 and calcination temperature on the physicochemical properties of the NiO/Al2O3 system have been investigated using DTA, XRD, nitrogen adsorption measurements at −196°C and decomposition of H2O2 at 30–50°C. The pure and variously doped solids were subjected to heat treatment at 300, 400, 700, 900 and 1000°C. The results
revealed that the specific surface areas increased with increasing calcination temperature from 300 to 400°C and with doping
of the system with CeO2. The pure and variously doped solids calcined at 300 and 400°C consisted of poorly crystalline NiO dispersed on γ-Al2O3. Heating at 700°C resulted in formation of well crystalline NiO and γ-Al2O3 phases beside CeO2 for the doped solids. Crystalline NiAl2O4 phase was formed starting from 900°C. The degree of crystallinity of NiAl2O4 increased with increasing the calcination temperature from 900 to 1000°C. An opposite effect was observed upon doping with
CeO2. The NiO/Al2O3 system calcined at 300 and 400°C has catalytic activity higher than individual NiO obtained at the same calcination temperatures.
The catalytic activity of NiO/Al2O3 system increased, progressively, with increasing the amount of CeO2 dopant and decreased with increasing the calcination temperature. 相似文献
9.
Guoyi Bai Chenfang Zhang Yuecheng Zhang Haijun Yu Fei He Huisen Ning Ligong Chen 《Reaction Kinetics and Catalysis Letters》2007,90(2):373-380
The racemization of R-(-)-2-amino-1-butanol in a reaction using Co/γ-Al2O3 catalysts and catalysts modified by Mg or Ca was investigated in this paper. Complete racemization was achieved with a yield
of over 83% at using the Mg modified Co/γ-Al2O3 catalyst under optimized reaction conditions of 170°C and 2.5 MPa of H2. The catalysts were thoroughly characterized by XRD, XPS, TPR, SEM and TEM. The addition of Mg and Ca may be advantageous
for dispersing and stabilizing the active species of the Co/γ-Al2O3 catalyst, protecting from sintering, significantly improving its catalytic activity and stability. 相似文献
10.
The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al2O3 and Fe2O3/Al2O3 systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure
and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized
using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe2O3 at 350°C and shows thermal stability up to1000°C. Crystalline Fe3O4 and Mn3O4phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al2O3 phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al2O3 phase at1000°C. Crystalline MnAl2O4 and MnFe2O4 phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products
was tested using the decomposition of H2O2 reaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
The phase transitions and thermal effects occurring during annealing in air of material with general formula CrOx (x≥2.4) have been investigated. The investigations were performed with TG, DTA, DSC, EGA, XRD and other spectral techniques.
The formation of an amorphous phase with average composition Cr5O12 in the range 300-400°C has been observed. Further heating leads to partial loss of oxygen, simultaneous decay of Cr2O5 and CrO2 phases and formation of nonstoichiometric Cr2O3+x. The distinct loss of mass is observed in the range 415-428°C, connected with evolving oxygen and small amount of nitric
oxides. Thermal effects accompanying the mass changes depend on the mass of the sample. When the mass decreases, the transition
from exothermic to endothermic effects is observed. This phenomenon can be explained as the competition between two processes:
reconstruction of the crystalline lattice (endothermic effect) and recombination of the evolved atomic oxygen (exothermic
effect).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Chao Song Xiangting Dong 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2013,87(9):1545-1549
Poly(vinyl pyrrolidone) (PVP)/[Ti(SO4)2 + Al(NO3)3] composite nanobelts were prepared via electrospinning technology, and TiO2/Al2O3 nanobelts were fabricated by calcination of the prepared composite nanobelts. The samples were characterized by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). XRD results show that the composite nanobelts were amorphous in structure, and pure phase TiO2/Al2O3 nanobelts were obtained by calcination of the relevant composite nanobelts at 950°C for 8 h. SEM analysis indicates that the surface of as-prepared composite nanobelts was smooth, the widths of the composite fibers were in narrow range, and the mean width was ca. 8.9 ± 2.1 μm, thickness was about 255 nm, and there is no cross-linking among nanobelts. The width of TiO2/Al2O3 nanobelts was ca. 1.3 ± 0.1 μm and the thickness was about 105 nm. TG-DTA analysis reveals that the N,N-dimethylformamide (DMF), organic compounds and inorganic salts in the composite nanobelts were decomposed and volatilized totally, and the weight of the sample kept constant when sintering temperature was above 900°C, and the total weight loss percentage was 81%. FTIR analysis manifests that crystalline TiO2/Al2O3 nanobelts were formed at 950°C. The possible formation mechanism of the TiO2/Al2O3 nanobelts was preliminarily discussed. 相似文献
13.
Sergio Cava Renata Benincá Sergio M. Tebcherani Iedo A. Souza Carlos A. Paskocimas Elson Longo José A. Varela 《Journal of Sol-Gel Science and Technology》2007,43(1):131-136
Al2O3 and Al2−x
Cr
x
O3 (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution
of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy
(reflectance spectra and CIEL*a*b* color data). The obtained results allow to identify the γ-Al2O3 to α-Al2O3 phase transition. The single-phase α-Al2O3 powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and
ruby luminescence lines observed for the powders of Al2−x
Cr
x
O3 are related to the γ to α-Al2O3 phase transition and the temperature and time range for such transition depends on the chromium content. 相似文献
14.
N. Pistofidis G. Vourlias D. Chaliampalias E. Pavlidou K. Chrissafis G. Stergioudis E. K. Polychroniadis D. Tsipas 《Journal of Thermal Analysis and Calorimetry》2006,84(1):191-194
Zn
pack coating formation takes place in three steps as differential scanning
calorimetry shows. The initial step (at 193.9°C) is endothermic and involves
the transformation of α-NH4Cl to β-NH4Cl
and the NH4Cl decomposition to NH3
and HCl. During the second step (at 248.6°C), which is exothermic, Zn2+
salts are formed and most probably ZnCl2. Finally at
264.1°C (endothermic reaction) it seems that ZnCl2 is decomposed to form
Zn that is deposited on the ferrous substrate. The as-cast Zn diffuses in
the iron substrate forming the gamma and delta phase of the Fe–Zn phase
diagram. Al2O3 is not involved
in the above-mentioned mechanism and acts only as filler. 相似文献
15.
Barbara Pacewska Olga Kluk-Płoskońska Dariusz Szychowski 《Journal of Thermal Analysis and Calorimetry》2007,90(3):783-793
The paper concerns aluminium hydroxides precipitated during hydrolysis of aluminium acetate in ammonia medium, as well as
aluminium oxides obtained through their calcination at 550, 900 or 1200°C for 2 h. The following techniques were used for
analysing of obtained materials: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption,
adsorption-desorption of benzene vapours and scanning electron microscopy.
Freshly precipitated boehmite/pseudoboehmite had high value of S
BET, very good sorption capacity for benzene vapours, developed mesoporous structure and hydrophilic character. After prolonged
refluxing at elevated temperature its crystallinity increased which was accompanied by a decrease of specific surface determined
from nitrogen adsorption, decrease of sorption capacity for benzene vapours and weakening of the hydrophilic character. Calcination
of all hydroxides at the temperature up to 1200°C resulted in the formation of α-Al2O3 via transition forms of γ-, δ-and θ-Al2O3. The samples of aluminium oxides obtained after calcination at 550 and 900°C were characterised with high values of specific
surface area and displayed quite high heat resistance, probably due to a specific morphology of starting hydroxides. The process
of ageing at elevated temperature developed thermal stability of aluminium oxides. 相似文献
16.
I. Jaymes A. Douy M. Gervais J.P. Coutures 《Journal of Sol-Gel Science and Technology》1997,8(1-3):415-418
The crystallization of amorphous chemically homogeneous powders in the SiO2.Al2O3 system has been studied by differential scanning calorimetry and X-ray diffraction. Up to 1300°C only one exotherm has been
observed. Only mullite crystallizes for compositions ≤69 mol% Al2O3 and spinel for those ≤80%. The crystallizations into mullite and spinel are sharp and exothermic, with an enthalpy of 250–300
J/g. The chemical composition of the crystallized mullite regularly increases from 68 to 76 mol% Al2O3 with increasing bulk composition from 60 to 75 mol% Al2O3. 相似文献
17.
The Er3+-doped Al2O3 nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC3H7)3]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO3)3·5H2O]. The five phases of γ-(Al,Er)2O3, θ-(Al,Er)2O3, α-(Al,Er)2O3, ErAlO3, and Al10Er6O24 were detected with the 0–20 mol% Er3+-doped Al2O3 nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm
for phase transformation of undoped γ-Al2O3→α-Al2O3 at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with
increase of the Er3+ doping concentration. Infrared absorption spectra of γ-Al2O3 and θ-Al2O3 nanopowders showed the two broad bands of 830–870 and 550–600 cm−1, the three broad bands of 830–870, 750–760, and 550–600 cm−1, respectively. The infrared absorption spectra for the α-Al2O3 nanopowder showed three characteristic bands, 640, 602, and 453 cm−1. The two characteristic bands of 669 and 418 cm−1 for Er2O3 clusters were observed for the Er3+-doped Al2O3 nanopowders when Er3+ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm−1 are the characteristic bands of Al10Er6O24 phase. 相似文献
18.
A. S. Rodriguez B. E. M. Lopez 《Journal of Radioanalytical and Nuclear Chemistry》1998,237(1-2):129-132
Irradiation of α-Al2O3 (Corundum) was carried out in contact with acidic media and with different doses (100-to-2500 kGy) and dose-rates (0.9, 2.6
and 6.1 kGy·h−1) of γ-rays. Simultaneously parallel experiments were carried out using the same procedure, but preheated at 150°C for two
days and then irradiated without acidic media. The solid thus obtained was used to determine the effect of γ-irradiation on
the sorption capacities of microamounts of fission products from strongly alkaline aqueous solutions of uranium. The results
revealed that the effect of γ-irradiation of α-Al2O3 and the acidic media in which it is immersed, is associated with a stable matrix resistant to significant changes in the
composition of the surface layer; whilst it seems that the effect of γ-irradiation of preheated α-Al2O3, is connected with changes of surface-OH groups strongly affected by heat treatment and irradiation dose. 相似文献
19.
A. A. Shutilov G. A. Zenkovets S. V. Tsybulya V. Yu. Gavrilov 《Kinetics and Catalysis》2012,53(1):125-136
The effect of the modification of aluminum oxide with silicon oxide on the stability of fine-particle Γ- and δ-Al2O3 phases upon heat treatment in the wide temperature range of 550–1500°C was studied. It was found that the Γ- and δ-Al2O3 phases modified with silica are thermally stable up to higher temperatures than pure aluminum oxide. This is due to changes
in the real structure of the modified samples, specifically, an increase in the concentration of extensive defects stabilized
by hydroxyl groups bound to not only aluminum atoms but also silicon atoms. It is likely that Si-OH groups, which are thermally
more stable than Al-OH groups, stabilize the microstructure of Γ- and δ-Al2O3 to higher temperatures, as compared with aluminum oxide containing no additives. Simultaneously, an increase in the thermal
stability of the modified samples is accompanied by the retention of a high specific surface area and a developed pore structure
at higher treatment temperatures. 相似文献
20.
A. S. Ivanova G. S. Litvak G. N. Kryukova S. V. Tsybulya E. A. Paukshtis 《Kinetics and Catalysis》2000,41(1):122-126
Differences in the real structure of γ-Al2O3 samples obtained by the thermal decomposition of pseudoboehmite and boehmite prepared by the hydrothermal treatment of bayerite
were found. The transformations of these structures during their conversion to δ-Al2O3 as the treatment temperature increased were studied. The rate of conversion of metastable alumina species into the stable
α-Al2O3 phase significantly depends on the real structure of samples. The rate of this transformation is drastically retarded in
the presence of extended defects in the oxides originated from boehmite, and the stability of metastable alumina species increased
as the degree of surface dehydroxylation increased. 相似文献