The oscillatory adsorption of self‐assembled organosilane films on aluminium oxide surfaces

The time‐dependent oscillatory growth mechanism of organosilane film self‐assembly on aluminium oxide has been investigated using X‐ray photoelectron spectroscopy. While this unusual oscillatory process has been reported for the trifunctional silane, propyltrimethoxysilane, we report here, for the first time, that this oscillatory behaviour is also present during the self‐assembly of the difunctional silane propylmethyldimethoxysilane. The presence of multiple oscillations in this growth mechanism is also first reported for propyltrimethoxysilane and propylmethyldimethoxysilane as a function of exposure time. Multiple oscillations indicate that the 3‐component model that is used to describe and fit a single coverage oscillation must be reconsidered and contain additional components to account for the multiple oscillations seen experimentally. The absence of such oscillatory behaviour in the growth of the monofunctional organosilane propyldimethylmethoxysilane, which in fact follows a Langmuir‐type growth mechanism, indicates that this measurable oscillatory behaviour is because of the ability of multifunctional silanes to oligomerise both on the substrate and in solution.     

Chromatographic investigations of adsorption of some aromatic compounds on aluminium oxide and silica gel from solutions

Summary Using adsorption TLC R_M 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 R_M values. The agreement is valid both when the R_M 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 R_M values.     

Metal adsorption on oxide polar ultrathin films

The adsorption of Au and Pd atoms on two nanostructured titania monolayers grown on the Pt(111) surface is investigated via a computational approach. These phases present compact regions (zig-zag-like stripes) with titanium atoms at the oxide-metal interface and oxygen in the top-most overlayer, sometimes intercalated by point defects, i.e. holes exposing the bare metal support, and give rise to very regular patterns extending for large distances. A Pd atom experiences a rather flat energy landscape on the compact regions whereas it is strongly bound to the defects which act as nucleation centers, whence the interest of these substrates as nanotemplates for the growth of metal clusters. The interaction of a Au atom with these phases is peculiarly different: a charge transfer from the underlying Pt(111) support occurs so that Au gets negatively charged and strongly interacts with a titanium atom extracted from the interface in the compact regions, whereas it penetrates less easily than Pd into the defective holes due to its larger size. These results are discussed as paradigmatic examples of the interaction of metals with polar ultrathin films of oxides grown on metal supports, a novel and promising field in materials science.     

Simultaneous DTA and DTG measurements on aluminium oxide monohydroxides

Simultaneous DTA and DTG curves (Mettler TA-2) have been measured for one diaspore and four different boehmites at temperatures up to 750° in a flow of dried argon. The crystallographic structures of the materials were assessed by X-ray diffraction and the degree of clustering of the elementary particles by scanning electron microscopy. To get straight base-lines a calibration curve was used to correct the DTA curves. The usefulness of the correction was established by comparison with DTA curves obtained with a Mettler TA-2000.The diaspore contained occluded water. Expulsion of the water at 300–350° brought about fragmentation of the crystals. The DTA and DTG peaks that correspond to the dehydration to alumina both lie at 560°.There is a noticeable spread in the DTA and DTG peaks for the different boehmites in the temperature range 455–530°. All the DTA peaks lie close to the corresponding DTG peaks. One of the boehmites displayed a double peak (470° and 502°). To trace the origin of the variation in peak temperature, the porous structure of the boehmite having its peak at 530° was varied by ball-milling and by dispersion into water, neither of which markedly affected the crystallographic structure and the crystallite size. Whereas ball-milling did not change the peak temperature much, dispersion into water brought about a transition from a single peak at 530° to a double peak at 450° and 490°. Prolonged storage in air led to a shift of the peaks to 480° and 520°. It is concluded that the porous structure of boehmites can profoundly affect the appearance and the temperature of their dehydration peaks.

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Zusammenfassung Simultane DTA- und DTG-Kurven (Mettler TA-2) wurden für ein Diaspor und vier verschiedene Boehmite bei Temperaturen bis zu 750° in einem Strom von getrocknetem Argon aufgenommen. Die kristallographische Struktur der Substanzen wurde mittels Röntgendiffraktion und der Anhäufungsgrad der Elementarpartikel mittels Raster-Elektronenmikroskopie bestimmt. Um gerade Grundlinien zu erhalten wurde eine Eichkurve zur Korrektur der DTA-Kurven verwendet. Die Nützlichkeit der Korrektur wurde durch Vergleiche der in einem Mettler TA-2000 Gerät erhaltenen DTA-Kurven festgestellt.Der Diaspor enthielt eingeschlossenes Wasser. Das bei 300 bis 350° erfolgte Abspalten des Wassers brachte eine Fragmentierung der Kristalle mit sich. Die DTA- und DTG-Peaks, welche der Dehydratisierung zu Aluminiumoxid entsprechen, liegen beide bei 560°.Im Temperaturbereich von 455 bis 530° läßt sich ein Verbreitern der DTA- und DTG-Peaks der verschiedenen Boehmite wahrnehmen. Einer der Boehmite zeigte einen Doppel-peak (470° und 502°). Um dem Ursprung der Änderungen der Peak-Temperaturen festzustellen wurde die poröse Struktur des Boehmits mit einem Peak bei 530° mit Hilfe einer Kugelmühle und durch Dispersion in Wasser verändert. Keine dieser Behandlungen änderte merklich die kristallographische Struktur und die Kristallgröße. Während das Vermählen in der Kugelmühle die Peak-Temperatur nicht wesentlich änderte, erbrachte die Dispergierung in Wasser einen Übergang von einem einzigen Peak bei 530° zu einem Doppelpeak bei 450 und 490°. Längeres Lagern an der Luft führte zu einer Verschiebung der Peaks nach 480° und 520°. Es wird gefolgert, daß die Porösstruktur von Boehmiten das Erscheinen und die Temperatur ihrer Dehydratisierungspeaks stark beeinflussen kann.

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Résumé Les courbes ATD et TGD d'une diaspore et de quatre boehmites différentes ont été enregistrées simultanément (Mettler TA-2) jusqu'à 750°, sous circulation d'argon desséché. La structure cristallographique de ces composés a été examinée par diffraction des rayons X et le degré de compacité a été évalué par microscopie électronique à balayage. Une courbe d'étalonnage a été utilisée pour corriger les courbes ATD et obtenir des lignes de base droites. L'utilité de cette correction est démontrée en comparant avec les courbes ATD obtenues à l'aide d'un appareil Mettler-TA-2000.La diaspore contenait de l'eau d'inclusion. L'élimination de l'eau à 300–350° a entraîné la fragmentation des cristaux. Les pics ATD et TGD qui correspondent à la déshydratation en oxyde d'aluminium se trouvent tous deux à 560°.Un étalement des pics ATD et TGD est perceptible pour les différentes boehmites dans l'intervalle de température 455–530°. Tous les pics ATD sont proches des pics TGD correspondants. L'une des boehmites a donné un pic double (470 et 502°). Afin de trouver l'origine de la différence de température entre les deux pics, la structure poreuse de la boehmite dont le pic se situait à 530° a été modifiée par traitement dans un broyeur à boulets et par dispersion dans de l'eau; ni l'un ni l'autre de ces deux traitements n'influence de façon apparente la structure cristallographique et la taille des cristaux. Alors que le traitement au broyeur à boulets ne change pas beaucoup la température du pic, la dispersion dans de l'eau fait apparaitre le passage d'un pic unique à 530° à un pic double à 450 et 490°. Le stockage prolongé dans l'air provoque un déplacement des pics à 480 et 520°. On en conclut que la structure poreuse des boehmites peut influer profondément sur l'apparition et la température de leurs pics de déshydratation.

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— ( TA-2) 750° . - , — . . , TA-2000. . 300–350°C, . — , , 560°. - 455–530°. . (470° 502°). , 530°C . . , — 530° — 450° 490°. 480° 520°. , , .

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The authors are indebted to Dr. P. F. Elbers for placing the electron microscopic facilities of the University of Utrecht at their disposal. We especially wish to acknowledge the time and energy spent by Mr. J. Pieters in the preparation of samples and the investigation with the scanning electron microscope. The assistance given by Dr. A. Duisenberg in the measurement of the line-broadening is also gratefully acknowledged.     

Separation of metal ions on a modified aluminium oxide

The possibility of application of a sulpho-derivative of an aromatic organic complexing agent for separation of cations on aluminium oxide has been investigated. Alumina modified with Nitroso-R salt is used for recovery of cobalt from a tap water and for selective separation of palladium from rhodium.     

Reversible adsorption of carbon monoxide on cupric oxide

Conclusions A gas chromatographic study of the reaction of CO with CuO enabled us to observe that, besides chemisorption, the reversible physical adsorption of CO on CuO occurs.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1626–1627, July, 1981.     

NO adsorption on tin(IV) oxide

The adsorption of NO on SnO₂ has been studied in the temperature range from 0 to 86°C, at pressures from 0.4 to 3.5 Torr. The adsorption isotherms are described by the Freundlich equation. The rate of adsorption obeys the Roginskii-Zeldovitch equation and decreases with increasing temperature. The reduction of SnO₂ with carbon monoxide results in a drop in the adsorption rate and in the amount of adsorbed NO.

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NO SnO₂ 0°–86°C 0,4–3,5 . . - . SnO₂ NO.

     

EPR studies of aluminium oxide phase compositions

EPR method of radiation probes is suggested for use to identify Al oxide-hydroxide phase composition in catalysts. A possibility to determine mixture components is exemplified by a heterogeneous mixture -Al₂O₃+Al(OH)₃ (bayerite). Parameters for the hole centers formed in Al₂O₃ and Al(OH)₃ are given.

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- . Al₂O₃ (-) Al(OH)₃ () . Al₂O₃ Al(OH)₃.

     

Reaction of ammonium sulphate with aluminium oxide

The reaction between ammonium sulphate with aluminium oxide was studied. It was confirmed by X-ray diffraction and chemical analysis that three intermediate reaction products, (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ and Al₂(SO₄)₃, are formed. The thermal decompositions of these three compounds were carried out. It has been shown that the same rate law is valid for them. The activation energies for (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ and Al₂(SO₄)₃ are 95.9, 177.9 and 291.0 kj/mol, respectively.

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Zusammenfassung Die Reaktion von Ammoniumsulfat mit Aluminiumoxid wurde untersucht. Durch Röntgendiffraktion und chemische Analyse wurde bestätigt, daß drei Zwischenprodukte (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ und Al₂(SO₄)₃ gebildet werden. Die thermische Zersetzung der drei Verbindungen wurde durchgeführt. Es wurde gezeigt, daß für alle drei dasselbe Geschwindigkeitsgesetz Gültigkeit hat. Die Aktivierungsenergien für (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ und Al₂(SO₄)₃ sind 95.9, 177.9 und 291.0 kJ/Mol.

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. - : (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ Al₂(SO₄)₃. , , . (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ Al₂(SO₄)₃, , 95.9; 177.9 291.0 . ^–1.

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The authors are grateful to Dr. H. Osada and Mr. H. Nakamura, Department of Environmental Engineering, Kyushu Institute of Technology, for their helpful discussions.     

Microwave assisted dissolution of aluminium oxide samples

The dependence on time of the efficiency of microwave assisted digestion of Al₂O₃ samples with various physico-chemical properties in H₂SO₄ solution (1 + 1) at a temperature of 170 °C and a pressure of 207 kPa has been investigated. Therefore, the concentrations of Al and that of the impurities in the solutions obtained, as well as the masses of residues after different times have been measured. The efficiency of the dissolution was shown to depend on the specific surface area and on the phase-state of the Al₂O₃. The time demand for total dissolution of the samples ranged from 0.1 to 7 hours.     

Knoevenagel condensation catalysed by aluminium oxide.

The Knoevenagel condensation of carbonyl compounds with active methylene compounds was readily carried out with aluminium oxide as catalyst.     

The influence of aluminium and aluminium oxide on the effects of mechanical activation of nickel hydroxocarbonate

The chemical and physical processes occurring during the grinding of nickel hydroxocarbonate and mixtures of nickel hydroxocarbonate with aluminium and aluminium oxide were discussed. For mechanical treatment a planetary ball mill was used. The phase analyses of ground products were carried out using thermogravimetry and X-ray diffraction methods. The amount of Ni₂(OH)₂CO₃ undecomposed and Al₂O₃xH₂O, xNiO, Ni⁰, Ni_xAl_y alloys and remained Al⁰ in the systems strongly depends on the proportion of components and on the duration of grinding in a mill which was used in the study. The comparative results are presented.This revised version was published online in November 2005 with corrections to the Cover Date.     

The fluorimetric detection of pesticides on aluminium oxide layers.

Several pesticides have been investigated for their fluorigenic properties on acidic and basic aluminium oxide layers. Fluorescence was obtained in several instances and the relative intensities were observed. Fluorescence spectra were recorded for the best fluorescence obtained before and after heat treatment of the chromatogram. The results are compared with those already reported for silica gel layers.     

Area-selective microscale metallization on porous anodic oxide film of aluminium

A new method for micropatterning of metallic patterns on porous anodic oxide film of aluminium is described. The porous anodic oxide film was impregnated with organic dye and palladium ions before the hydrothermal pore-sealing. The surface layers formed during the pore-sealing, i.e. outer acicular hydroxide layer and a compact intermediate sub-layer trap the palladium ion underneath the layers. Exposing the palladium enriched area by the help of laser beam followed by electroless nickel deposition results the deposition of nickel on the laser-exposed part. Thickness of the deposits can be up to about 2–3 μm, after about the 20 min of immersion in electroless nickel plating bath. The metallic micropatterns, formed by the method are crack free, smooth and uniform over extended length.     

Prepolymer film growth by adsorption out of solution on silicon and aluminium

A cyanurate prepolymer has been applied to smooth silicon wafers or to distinctly structured aluminium coatings. The surface composition of the substrates has been investigated by X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and ellipsometry. The application methods, spin coating and dip coating represent adsorption by a technical process exerting significant shear stresses or nearly equilibrated conditions, respectively. The mean tickness of the prepolymer film has been adjusted by variation of the concentration of the solution and checked by ellipsometry. Atomic Force Microscopy (AFM) monitored the development of the respective film morphologies of all 4 systems (silicon/aluminium, spin/dip coating) in the mean film thickness range from 1 to 50 nm.     

Prepolymer film growth by adsorption out of solution on silicon and aluminium

A cyanurate prepolymer has been applied to smooth silicon wafers or to distinctly structured aluminium coatings. The surface composition of the substrates has been investigated by X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and ellipsometry. The application methods, spin coating and dip coating represent adsorption by a technical process exerting significant shear stresses or nearly equilibrated conditions, respectively. The mean tickness of the prepolymer film has been adjusted by variation of the concentration of the solution and checked by ellipsometry. Atomic Force Microscopy (AFM) monitored the development of the respective film morphologies of all 4 systems (silicon/aluminium, spin/dip coating) in the mean film thickness range from 1 to 50 nm.     

The effect of aluminium oxide on the reduction of cobalt oxide and thermostabillity of cobalt and cobalt oxide

During precipitation and calcination at 200°C nanocrystalline Co₃O₄ was obtained with average size crystallites of 13 nm and a well developed specific surface area of 44 m² g^?1. A small addition of a structural promoter, e.g. Al₂O₃, increases the specific surface area of the cobalt oxide (54 m² g^?1) and decreases the average size of crystallites (7 nm). Al₂O₃ inhibits the reduction process of Co₃O₄ by hydrogen. Reduction of cobalt oxide with aluminium oxide addition runs by equilibrium state at all the respective temperatures. The apparent activation energy of the recrystallization process of the nanocrystalline cobalt promoted by the aluminium oxide is 85 kJ mol^?1. Aluminium oxide improves the thermostability of both cobalt oxide and the cobalt obtained as a result of oxide phase reduction.      

Thermochemical studies on the formation and constitution of the zinc oxide—aluminium oxide system

This study is based on thermogravimetric (TG), differential thermal analysis (DTA) and chemical analysis of the ZnOAl₂O₃ system. The coprecipitation from mixed nitrate salt solutions of zinc and aluminium results in the formation of zinc basic carbonate and aluminium hydroxide, and is also a precursor to aluminate spinel (2ZnO·3Al₂O₃) only in the samples in which aluminium is present in near or above stoichiometric quantities. Grinding of the mixtures of individual precipitates maintains the similarity with coprecipitates in forming a “precursor”, but to a lesser extent. The endothermic peak in DTA at 275°C in some coprecipitated and mixed samples hints at the formation of a precursor since the individual precipitate does not have a peak at this temperature. The “precursor” to spinel obtained in the precipitation stage in some coprecipitated samples is freely soluble in 1 M HCl, and that obtained at 450°C is partially soluble which cannot be detected by the usual X-ray technique due to its highly disordered structure in amorphous state. The “precursor” is converted around 800°C to an actual spinel structure, which is almost insoluble in M HCl and is detectable by X-rays.