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1.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1991,47(2):219-232
Inelastic Electron Tunnelling Spectroscopy (IETs) has been applied to study the adsorption of 2,3-dihydroxynaphthalene, 1,2-dihydroxybenzene, 1,3-dihydroxybenzene and 1,4-dihydroxybenzene onto plasma-grown thin-film partially hydroxylated magnesium and aluminium oxides. For both 2,3-dihydroxynaphthalene and 1,2-dihydroxybenzene on aluminium oxide it is found that adsorbate chemisorption involves reaction of the two hydroxyl groups present in the adsorbate to form a di-anion in the case of the former and both the mono- and di-anion for the latter. The tunnel spectra for both compounds on magnesium oxide indicate that the di-anion is formed. Adsorption at the oxide surfaces for these two adsorbates involves adsorbate deprotonation with the formation, at the oxide surface, of molecular water which is subsequently desorbed and pumped away during sample junction preparation. For the 1,3- and 1,4-dihydroxy systems, on both oxides, the presence of a strong ν(OH) band at ≈3650 cm−1 suggests that only one of the hydroxyl groups present in both systems is involved in adsorbate deprotonation interactions at the respective oxide surfaces, with the second hydroxyl group present contributing to the enhanced substrate oxide ν(OH) envelope observed. 相似文献
2.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1991,47(3-4):387-395
The inelastic electron tunnelling spectra of benzotriazole and benzimidazole suggest that these are adsorbed on thin-film plasma-grown magnesium oxide by deprotonation thus forming an anionic surface species. Conversely, the formation of a cationic adsorbate seems likely for both systems on the corresponding less basic aluminium oxide surface. 相似文献
3.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1990,46(11):1569-1579
Inelastic electron tunnelling spectroscopy (IETS) has been applied to study the adsorption of a series of aminophenols on plasma-grown aluminium and magnesium oxides. Vapour-phase doping of these surfaces was used and spectra recorded for 1,2-aminophenol, 1,3-aminophenol and 1,4-aminophenol. The tunnel spectra of the 1,2- and 1,3-aminophenols show that their chemisorption at both oxide surfaces is via reaction between phenolic and surface hydroxyl groups. For the 1,4-aminophenol example, adsorbate chemisorption involves transfer of surface-bound protons from the oxide in amino-group protonation. Some of these protons are replaced by deprotonation of the phenol at surface oxide ions. Observed band intensities for all three systems on aluminium oxide are held to be indicative of an adsorbate orientation on the surface which is close to the vertical. In contrast, those for magnesium oxide are more consistent with a non-vertical configuration. 相似文献
4.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1992,48(8):1101-1105
The inelastic electron tunnelling spectra of 1,2- and 1,4-diaminobenzene on thin-film plasma-grown aluminium oxide suggests that these molecules are adsorbed on this surface via Lewis acid—Lewis base and hydrogen-bonded interactions, with chelate formation at the surface likely in the case of the 1,2-diamino compound. Protonation of nitrogen in both structures is also considered given the spectral features observed. In both adsorbates the ring plane is believed to be near perpendicular with respect to the local oxide surface. 相似文献
5.
The mass spectra of several fluorohydrocarbons are shown and discussed. The fragmentation of these compounds displays a close correlation with the molecular structure and points to the importance of the charge-stabilisation concept for the ion intensities. The iodo-derivatives show a large abundant molecular ion. 相似文献
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The mass spectra of some tertiary aliphatic nitroaldehydes, nitroketones, nitroesters, nitronitriles and related nitrocarbonyl compounds are discussed and compared with those of some analogous nitro compounds lacking the carbonyl function. The M+˙ ? NO2˙ and in several cases M+˙ ? HNO2 fragmentation seem to be the most characteristic features of all tertiary aliphatic nitro compounds. In the presence of the primary nitro group, the loss of NHO2 is always observed. 相似文献
8.
Studies have been made of the effects of mixtures of aluminium oxides and organic halogen compounds on the flammability of polyethylene and an acrylonitrile-butadiene-styrene copolymer (ABS). There is considerable synergism in the flame-retardant action, particularly when anhydrous alumina and a bromine compound are introduced into ABS. The addition of relatively small amounts of alumina prevents the saturation effects otherwise observed when increasing quantities of halogen compounds on their own are incorporated into the polymers. Chemical interaction between aluminium oxides and the halogens occurs in the condensed phase. 相似文献
9.
Comprehensive kinetic studies on isothermal and non-isothermal reactions of some aluminium compounds
J. Madarász G. Pokol C. Novák H. Moselhy S. Gál 《Journal of Thermal Analysis and Calorimetry》1993,40(3):1367-1378
Residual differences after model fitting were investigated in both isothermal and non-isothermal kinetics in order to make numerical comparisons between several models and various parameter-estimating methods. Data from two independent experimental series were evaluated. A large data set, collected earlier under isothermal conditions from decompositions and hydrothermal reactions of aluminium hydroxides and oxides, was processed first. It showed that mechanical activation of the starting gibbsite affected reactivity of samples in several subsequent reactions for all model equations tried. The relative residual deviation concept is introduced, and statistics were applied to find a model that fits a certain reaction in most of the cases. In the second study, the sulphate decomposition step of aluminium sulphate octadecahydrate was investigated. TG curves were measured using a constant heating rate. Dynamic models were fitted by three mathematical methods, including a new general purpose one. Fitting ability of the methods with various complexity were compared on the basis of residual deviations obtained after integration of the model equations. As well as evaluating the best fit, this new parameter-estimating method provides a statistical analysis of the reliability of the whole model fitting process. 相似文献
10.
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
11.
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
12.
Barbara Pacewska Olga Kluk-Płoskońska D. Szychowski 《Journal of Thermal Analysis and Calorimetry》2006,85(2):351-359
An attempt
to obtain aluminium hydroxide that could give aluminium oxides of increased
thermal stability was made. Aluminium hydroxide was precipitated during a
hydrolysis of aluminium chloride in ammonia medium. The influence of preparative
conditions, such as a dosing rate of aluminium precursor, pH, duration of
the precipitate refluxing and temperature of calcination, on the properties
of obtained hydroxides and oxides was investigated. The materials were studied
with the following methods: thermal analysis, IR spectroscopy, low-temperature
nitrogen adsorption and adsorption–desorption of benzene vapours.
Precipitated boehmites had high values of S
BET
determined from nitrogen adsorption (220–300 m2g–1),
good sorption capacity for benzene vapours, developed mesoporous structure
and hydrophilic character. It has been proved that a high pH value during
the precipitation of aluminium hydroxide favoured better crystallisation of
boehmite structure, higher temperature of its dehydroxylation into γ-Al2O3,
and delayed transformation of γ phase into α-Al2O3.
Aluminium oxides derived from the hydroxides precipitated at a high pH were
the most stable at high temperatures, and were characterised with the best
surface properties.
The online version of the original
article can be found
at 相似文献
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Summary The unusual fluorescence X-ray intensity variation in some aluminium and magnesium alloys was investigated. It was confirmed that the phenomenon occured when the primary crystals having differences in mass absorption coefficients for the fluorescence X-ray of the elements to be analyzed precipitate on both sides of the eutectic point. A simple model of an eutectic alloy was employed for the calculation. The phenomenon should be considered in the fluorescence X-ray analysis of alloys such as silicon in silmine, aluminium in alnico and others.
The authors express their deep graditude to Prof. Dr. H. Gotô for his guidance to carry out this study. 相似文献
Zusammenfassung Es wurden Untersuchungen vorgenommen zur Aufklärung der ungewöhnlichen Veränderung der Linienintensität bei der Röntgenfluorescenzanalyse einiger Aluminium- und Magnesiumlegierungen. Dabei wurde festgestellt, daß diese Erscheinung dann auftritt, wenn primäre Kristalle, die stark unterschiedliche Massenabsorptionskoeffizienten für die Röntgenfluorescenz-Linien der zu analysierenden Elemente aufweisen, sich auf beiden Seiten des eutektischen Punktes abscheiden. Zur Berechnung der Intensitätsveränderungen wurde ein einfaches Modell aufgestellt. Die beschriebene Erscheinung muß bei der Röntgenfluorescenzanalyse von Legierungen (z.B. Bestimmung von Silicium in Silmin oder von Aluminium in Alnico u.a.) beachtet werden.
The authors express their deep graditude to Prof. Dr. H. Gotô for his guidance to carry out this study. 相似文献
16.
Studies on the reactions of aluminium oxides and hydroxides 总被引:1,自引:0,他引:1
C. Novák G. Pokol V. Izvekov T. Gál 《Journal of Thermal Analysis and Calorimetry》1990,36(5):1895-1909
The hydrothermal and decomposition reactions of differently ground gibbsite and its reaction products were studied. The samples were treated isothermally under hydrothermal conditions or in air, and the products were characterized by thermogravimetry and IR spectroscopy. It was found that the method and duration of grinding and the particle size of the starting gibbsite influenced the reactivity of the gibbsite itself and that of the primary reaction products. In a later step of the reaction sequence (hydrothermal rehydration of-alumina), the effects of the differences in the properties of the starting gibbsites were insignificant.
Zusammenfassung Es wurden die hydrothermischen und Zersetzungsreaktionen verschiedener Gibbsitproben und deren Reaktionsprodukten untersucht. Die Proben wurden unter hydrothermischen Bedingungen oder in Luft isothermisch behandelt, die Produkte mittels TG und IR beschrieben. Es wurde festgestellt, da\ Art und Weise der Zerkleinerung und Korngrö\e des Gibbsit-Ausgangsmateriales die ReaktivitÄt von Gibbsit selbst, aber auch die der primÄren Reaktionsprodukte beeinflu\t. In spÄteren Schritten des Reaktionsverlaufes (hydrothermische Rehydratation von-Aluminiumoxid) besitzen Unterschiede in den Eigenschaften des Gibbsit-Ausgangsmateriales keinen Einflu\.相似文献
17.
Henning Lund 《Talanta》1965,12(12):1065-1079
A review of the polarography of aliphatic compounds is presented. 相似文献
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Summary Using adsorption TLC RM values were measured for a number of aromatic compounds on aluminium oxide and silica gels having different specific surface areas, using the following binary mobile phases: benzene+toluene, benzene+carbon tetrachloride and chloroform+carbon tetrachloride. The results are graphically presented and compared with theoretically calculated values. Generally, a good agreement was found between the calculated and measured RM values. The agreement is valid both when the RM values were calculated using experimentally (indirectly) determined partition coefficients or when the coefficients are obtained with help of Ocik's equation [cf. Roczn. Chem.34, 745 (1960) and Chromatographia4, 516 (1971)]. One can assume that in the case of systems in which strong intermolecular interactions are absent, the statically determined partition coefficients of the compounds may be used for the calculation of their RM values. 相似文献