Herstellung und Eigenschaften von geformtem Aluminiumoxid. II. Einfluß der mechanischen Zerkleinerung gefällten Böhmithydrogels auf die Porenstruktur und die Abriebfestigkeit des geformten Aluminumoxids

Preparation and Properties of Formed Aluminium Oxide. II. Influence of the Mechanical Comminution of Precipitated Boehmite Hydrogel on the Pore Structure and Abrasion Resistance of the Aluminium Oxide A report is given on the physical-chemical characteristics of formed aluminium oxide on the basis of boehmite which had been continuously precipitated with nitric acid from sodium aluminate solution, subsequently filtrated, dried at 110°C and ground prior to moulding. In double dependence on the grinding intensity (type of mill, grinding time) and on the precipitation conditions (pH value, temperature) the changes of the morphology and the texture of the boehmite hydrogel are investigated. According to the particles constituting the precipitated boehmite hydrogel is made in two stages. In dependence on the grinding intensity a maximum correlation is observed for the abrasion resistance.     

Herstellung und Eigenschaften von Aluminiumaquoxid. I. Böhmit aus Aluminiumnitrat und Ammoniakwasser

Preparation and Properties of Aluminium Hydroxide. I. Boehmite from Aluminium Nitrate and Ammonia The physical-chemical properties of mainly boehmite containing aluminium hydroxide are studied which were made by continuous precipitation from aluminium nitrate solution with ammonia liquor using technical raw materials and test conditions being very similar to those applied in production. The influence of the precipitation conditions (pH value, temperature, concentration and residence time in the precipitation solution) on the composition, structure and texture of the precipitation products is investigated and information about their effect on the filtration behaviour are given. In the case of a continuous precipitation it is possible to obtain phase-pure boehmite being relatively well crystallised. The crystallinity and dispersity of the precipitated hydroxide determine their filterability and the cavity structure.     

Herstellung und Eigenschaften von Aluminiumaquoxid. II. Böhmit aus Natriumaluminat und Salpetersäure

Preparation and Properties of Aluminium Hydroxide. II. Boehmite from Sodium Aluminate and Nitric Acid A report is given on the physical-chemical characteristics of aluminium hydroxide which contain mainly boehmite, having been obtained by continuous precipitation from sodium aluminate solution with nitric acid using technical raw materials and conditions being very similar to those applied in production. The influence of the reaction conditions (pH value, temperature, concentration and residence time in the precipitation suspension) on the chemical composition, structure and texture of the hydrogels is studied. With rising precipitation temperature the pH range extends, within which already after short residence times pure-phase, relatively well crystalline boehmite hydrogels are obtained in the precipitated solution.     

Herstellung und Eigenschaften von Aluminiumaquoxid. III. Peptisierung von Böhmit mit Salpetersäure

Preparation and Properties of Aluminium Hydroxide. III. Peptization of Boehmite with Nitric Acid A reaction of the aluminium oxide hydroxide boehmite with nitric acid in dependence on the temperature and the molar ratio HNO₃/Al₂O₃ is studied. The effect of the acid results in the formation of basic aluminium nitrates, which can change the rheological properties of the boehmite hydrogel due to redispersion or desaggregation up to its ?liquefaction”? to boehmite hydrosol. For the dependence of the flow velocity of the boehmite hydrosol on the molar ration HNO₃ Al₂O₃ a maximum correlation is characteristic. It can also be interpreted from the colloid-chemical point of view and it is a technically relevant indicator for the optimization of the peptization. By the peptization conditions of the boehmite hydrogel the pore structure of the Al₂O₃ can be varied in a carefully directed way.     

Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides

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     

Thermal transformations of the products of partial hydrolysis of hydrous aluminium nitrate

Thermal analysis, mass spectrometry, infrared spectrophotometry, X-ray phase analysis, scanning electron microscopy, and sorption methods were used in the study of thermal transformations of the products of partial hydrolysis of hydrous aluminium nitrate in ammonia medium. It has been found that the process of aluminium nitrate hydrolysis under the conditions applied and in the presence of ammonia gives boehmite as the main product, with some admixture of a basic salt.Aluminium oxide obtained from the products of partial hydrolysis of hydrous aluminium nitrate in ammonia medium at 550°C has a crystalline -Al₂O₃ structure. Its specific surface, as determined by low-temperature adsorption of nitrogen, exceeds 200 m²g^–1. Features of the products are well developed mesopore structure and considerable ability of benzene adsorption. Calcination of the obtained aluminium oxide for 2 h at 900°C reduces its specific surface to about 110 m² g^–1.This revised version was published online in November 2005 with corrections to the Cover Date.     

Untersuchungen an oxidischen Katalysatoren. XIV. Die katalytische Aktivität verschiedener Übergangsformen des Aluminiumoxids bei der Dehydratisierung von Isopropanol

Studies on Oxide Catalysts. XIV. The catalytic Activity of some transient Forms of Alumina in the Dehydration of Isopropanol In order to give statements about the influence of the method of preparation of aluminum hydroxides and oxide hydroxides on the catalytic properties of alumina obtained from these compounds in the dehydration of ispropanol, bayerite, nordstrandite, and boehmite were prepared by several methods, carefully excluding impurity ions. Also, hydrargillite containing alkali was included in the investigations. By calcination in oxygen at 550 and 950°C, respectively, two groups of alumina were obtained. The catalytic properties of the oxides in the dehydration of isopropanol were examined by an apparatus working according to the dynamic principle. The specific activities of the different transient forms of alumina were found to vary according to the sequence η-;≈γ->?-≈δ->??(>??-)Al₂O₃.     

X-ray photoelectron spectroscopic studies of the oxidation of aluminium by liquid water monitored in an anaerobic cell

The oxidation of clean polycrystalline aluminium foil was performed in a previously described anaerobic cell and studied by core level and valence band X-ray photoelectron spectroscopy. Oxide free sample surfaces were exposed under inert atmosphere at room temperature to increasingly oxidative environments of water vapor and liquid water beginning with an oxide free metal foil each time. Minor oxidative environments were found to produce a film of boehmite with a thinner outer film of gibbsite. Harsher oxidation in liquid water resulted in an oxide film much thicker than that found on the as received sample which contained an inner composition of gamma alumina with an outer film of gibbsite. As expected, the oxide film observed for ultra high purity polycrystalline aluminium foil in the as received state was gibbsite. The valence band of the cleaned metal is discussed in terms of residual surface species. The evaluation and determination of these residual surface species is evaluated following an analysis of two different band structure calculations which use different d orbital exponents. It is found that while the density of states is almost unaltered by changes in the d exponent, the predicted spectrum is substantially changed. The work makes extensive use of valence band X-ray photoelectron spectroscopy.     

X-ray photoelectron spectroscopic studies of the oxidation of aluminium by liquid water monitored in an anaerobic cell

The oxidation of clean polycrystalline aluminium foil was performed in a previously described anaerobic cell and studied by core level and valence band X-ray photoelectron spectroscopy. Oxide free sample surfaces were exposed under inert atmosphere at room temperature to increasingly oxidative environments of water vapor and liquid water beginning with an oxide free metal foil each time. Minor oxidative environments were found to produce a film of boehmite with a thinner outer film of gibbsite. Harsher oxidation in liquid water resulted in an oxide film much thicker than that found on the as received sample which contained an inner composition of gamma alumina with an outer film of gibbsite. As expected, the oxide film observed for ultra high purity polycrystalline aluminiurm foil in the as received state was gibbsite. The valence band of the cleaned metal is discussed in terms of residual surface species. The evaluation and determination of these residual surface species is evaluated following an analysis of two different band structure calculations which use different d orbital exponents. It is found that while the density of states is almost unaltered by changes in the d exponent, the predicted spectrum is substantially changed. The work makes extensive use of valence band X-ray photoelectron spectroscopy.     

Calibration of sputtering yields for AES depth profiling of oxide layers on aluminium by means of carrier-gas heat extraction analysis

Summary For the purpose of obtaining suitable reference materials for technical coatings on aluminium, the feasibility of calibration of oxide layers by means of heat extraction was studied. Oxide layers were prepared on aluminium sheets by immersion in water of 50 or 80 ° C and annealing at 500 or 600 °C in argon atmosphere. The layer thickness was calculated from the oxygen content of the sample as measured by carrier-gas heat extraction analysis.The total sputtering yield of aluminium oxide layers was obtained via the correlation of AES depth profiling with heat extraction analysis results. This was demonstrated for high purity (99.9%) and technical purity (98.5%) aluminium with its original roughness from the rolling process, on which 20 to 1,000 nm thick oxide layers had been grown.The sputtering yields for the oxide layers prepared were found to be 3.9±0.8 atoms/ion, i.e., about four times higher than that for -Al₂O₃. Calibration of depth profiling on such technical quality oxide layers on aluminium was found to be feasible with a relative precision of 10 to 20%.

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Kalibrierung der Ionenzerstäubung zur AES-Tiefenprofilanalyse von Oxidschichten auf Aluminium durch Trägergas-Heißextraktion

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On leave from the Institute of Photographic Chemistry, Academia Sinica, Beijing, People's Republic of China     

Untersuchungen an oxidischen Katalysatoren. XXXVII. Zum Einfluß der Herstellungsbedingungen auf die Eigenschaften röntgenamorpher Al2O3?SiO2-Festkörper

Studies on Oxide Catalysts. XXXVII. On the Influence of Preparation Conditions on the Properties of Silica-Alumina Silica-alumina samples of different composition were prepared by coprecipitation from aqueous solutions at pH = 6 and pH = 9, respectively. Structures and properties of the solids were characterized (i.r., DTA, X-ray, molybdato method, surface acidity, catalytic activity in the cracking reaction of cumene). Solid composition and pH value of the precipitation medium equally exhibit influence on the structure of the silica-alumina (kind of incorporation of the aluminium) and thereby on the acidic and catalytic properties of the solids. Silica-alumina of equal composition but precipitated at different pH values may widely differ in their properties including activity-composition dependency.     

Electron microscope investigations on the morphology of aluminium hydroxides

Summary The results are given of an investigation by means of the electron microscope and electron diffraction of the morphology of amorphous aluminium hydroxide and boehmite. The ageing process of amorphous aluminium hydroxide prepared from aluminium nitrate, ammonium alum and amalgamated aluminium was studied.

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Zusammenfassung Untersuchungen im Elektronenmikroskop und mit Elektronenbeugung über die Morphologie vom amorphen Aluminiumhydroxyd und B?hmit werden beschrieben. Die Alterung von amorphem Aluminiumhydroxyd, hergestellt aus Aluminiumnitrat, Ammoniumalaun und amalgamiertem Aluminium wurde untersucht.

     

Physicochemical properties of the products of basic aluminium-potassium sulfate decomposition in hydrogen atmosphere

Low-temperature modifications of aluminium oxide were obtained by thermal decomposition of basic aluminium-potassium sulfate at temperatures 550, 600, and 650°C. Physicochemical properties of the obtained oxides were studied with particular consideration to phase composition and porous structure. It has been shown how the decomposition parameters of the basic salt used determine the porous structure of the obtained oxides.

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Zusammenfassung Durch thermische Zersetzung von basischem Aluminiumkaliumsulfat bei Temperaturen von 550, 600 und 650°C wurden Niedrigtemperaturmodifizierungen von Aluminiumoxid hergestellt. Die physikochemischen Eigenschaften der erhaltenen Oxide wurden in besonderer Hinsicht auf Phasenzusammensetzung und Porenstruktur untersucht. Es wurde gezeigt, wie die Parameter der Zersetzung des eingesetzten basischen Salzes die Porenstruktur der erhaltenen Oxide beeinflussen.

     

In Situ High‐Energy Synchrotron Radiation Study of Boehmite Formation,Growth, and Phase Transformation to Alumina in Sub‐ and Supercritical Water

Boehmite (AlOOH) nanoparticles have been synthesized in subcritical (300 bar, 350 °C) and supercritical (300 bar, 400 °C) water. The formation and growth of AlOOH nanoparticles were studied in situ by small‐ and wide‐angle X‐ray scattering (SAXS and WAXS) using 80 keV synchrotron radiation. The SAXS/WAXS data were measured simultaneously with a time resolution greater than 10 s and revealed the initial nucleation of amorphous particles takes place within 10 s with subsequent crystallization after 30 s. No diffraction signals were observed from Al(OH)₃ within the time resolution of the experiment, which shows that the dehydration step of the reaction is fast and the hydrolysis step rate‐determining. The sizes of the crystalline particles were determined as a function of time. The overall size evolution patterns are similar in sub‐ and supercritical water, but the growth is faster and the final particle size larger under supercritical conditions. After approximately 5 min, the rate of particle growth decreases in both sub‐ and supercritical water. Heating of the boehmite nanoparticle suspension allowed an in situ X‐ray investigation of the phase transformation of boehmite to aluminium oxide. Under the wet conditions used in this work, the transition starts at 530 °C and gives a two‐phase product of hydrated and non‐hydrated aluminium oxide.     

Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides Part II. Al(ClO4)3·9H2O

Aluminium hydroxide was precipitated during a hydrolysis of aluminium perchlorate in ammonia medium. The materials were studied with the following methods: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption and adsorption–desorption of benzene vapours. Freshly precipitated boehmite had a high value of S_BET=211 m² g^–1 determined from nitrogen adsorption, good sorption capacity for benzene vapours, developed mesoporous structure and hydrophobic character. After prolonged refluxing at elevated temperature its crystallinity increased which was accompanied by an increase of specific surface determined from nitrogen adsorption up to 262m²g^–1 , decrease of sorption capacity for benzene vapours and stronger hydrophobic character. The calcinations of all boehmites at temperature up to 1200°C resulted in formation of à-Al₂O₃ via transition form 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 of 205–220 and 138–153 m² g^–1 , respectively. The SBET values calculated for the oxide samples derived from aged hydroxides and calcined at 1200°C are higher than for the analogous sample prepared without the ageing step. It was concluded that the process of ageing at elevated temperature developed thermal stability of aluminium oxides.     

Über basische Aluminiumsalze und ihre Lösungen. VII. Zum Einfluß der Herstellungsbedingungen,der Konzentration und der Alterungszeit auf die Zusammensetzung von Lösungen basischer Aluminiumsalze

Basic Aluminium Salts and their Solutions. VII. Influence of Preparation, Concentration, and Aging on the Constitution of Solutions of Basic Aluminium Salts 0.1 to 4 molar basic aluminium chloride solutions – prepared by dissolving aluminium metal in substoichiometric quantities of hydrochloric acid and 10^?4 to 0.2 molar basic solutions of aluminium chloride and perchlorate – prepared by adding alkali to the solutions of the neutral salts were investigated for the kinetics of their reactions with ferrone and by ²⁷Al NMR spectroscopy. In all solutions the contents of polymeric species decreases at equal basicity with increasing aluminium concentration. On the other hand the Al₁₃O₄₀ complex is only formed in solutions prepared by addition of alkali. The differences of composition are confirmed by the aging behaviour of the solutions.     

Analytical applications of condensed phosphoric acid-II: determination of aluminium, iron and titanium in bauxites after decomposition with condensed phosphoric acid

Bauxites can be decomposed by condensed phosphoric acid (CPA) very rapidly without the need for subsequent manipulations such as elimination of silica, digestion of fused products and filtration. It is best to heat the samples at about 700 degrees prior to the decomposition, to prevent them from floating on the surface of the CPA. Under the proposed conditions (100 mg of sample, 10 g of CPA, heating at 300 degrees for 30 min), aluminium, iron and titanium are dissolved quantitatively. Iron is determined by photometry with 1,10-phenanthroline after solvent extraction with MIBK, while titanium is determined with N-benzoyl-N-phenylhydroxylamine (BPHA). The effect of phosphate on the determination of titanium is reduced to a minimum at a BPHA concentration of 0.3% and a hydrochloric acid concentration of 7.2M. Aluminium and iron are precipitated quantitatively as the oxinates at pH 5.5 in the presence of orthophosphoric acid or hydrolysed CPA, while the precipitation of titanium oxinate is completely suppressed by the addition of hydrogen peroxide. The total amount of aluminium and iron is obtained by determining the amount of oxine by bromination method. The amount of aluminium is obtained by subtracting the amount of iron from the sum of the two.     

Aluminiumalkyle mit Heteroatomen. III. Über Reaktionen von Titan(IV)-chlorid mit Tris(trimethylsilylalkyl)-aluminium-Verbindungen

Aluminium Alkyls with Heteroatoms. III. On Reactions of Titanium(IV) Chloride with Trimethylsilylmethyl Aluminium Compounds Trimethylsilylmethyl titanium trichloride can be obtained by reaction of titanium(IV) chloride with tris(trimethylsilylmethyl)aluminium diethyl ether (1:1). Its catalytic activity for polymerisation of butadiene has been investigated.     

Über basische Aluminiumsalze und ihre Lösungen. XIX. Zur Art der Al-Kationen in hochbasischen,hochkonzentrierten Aluminiumchloridlösungen

Basic Aluminium Salts and their Solutions. XIX. Nature of Aluminium Cations in Highly Basic Highly Concentrated Aluminium Chloride Solutions It is shown that in highly concentrated basic aluminium chloride solutions (c_Al ≈ 7.7 mol · l^?1; r = OH/Al = 2.48), prepared by dissolving aluminium metal in substoichiometric quantities of hydrochloric acid, polymeric aluminium cations (Al_poly) dominate. By dilution of these solutions also increasing amounts of monomeric cations (Al_mono) occur. On aging Al_mono reacts with Al_poly forming small portions of tridecameric Al₁₃O₄₀ cations (Al₁₃). On the basis of these results literature data, after which corresponding commercial basic aluminium chloride solutions contain essentially Al₁₃ cations, are critically discussed.     

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.