Thermal dissociation of basic aluminium ammonium sulfate in vacuum

Investigations were carried out on the kinetics of thermal decomposition of basic aluminium ammonium sulfate in vacuum. The kinetic model of dissociation of the compound was identified. The results of the kinetic studies and the mechanism of the process are discussed.

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Zusammenfassung Es wurde die Kinetik der thermischen Zersetzung von basischem Ammoniumaluminiumsulfat im Vakuum untersucht. Die Parameter für das kinetische Modell der Dissoziation von der Verbindung wurden identifiziert und die Ergebnisse der kinetischen Untersuchungen im Zusammenhang mit dem Verfahrensmechanismus besprochen.

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Résumé La cinétique de la décomposition thermique sous vide du sulfate basique d'aluminium et d'ammonium a été étudiée. On a identifié les paramètres du modèle cinétique de la dissociation de ce composé. Les résultats des études cinétiques et le mécanisme du processus de décomposition sont discutés.

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Properties of aluminium oxides obtained by calcination of the products of reductive roasting of basic aluminium-potassium sulfate

The influence of calcination conditions on changes in phase composition and porous structure was studied for hydrous aluminium oxide, obtained by leaching out potassium salts from the products of roasting basic aluminium-potassium sulfate in hydrogen atmosphere at 600°C. The product of calcination at 350°C in vacuum has the most developed porous structure with most pores of internal radius within 10–60 Å. Calcination in air atmosphere at temperatures 700, 800, 900, or 1000°C resulted in decrease of specific surface of aluminium oxide and increase of the share of pores with internal radius above 60 Å in the overall porosity of the samples. The reconstruction of the porous structure proceeds mainly as a result of coalescent sintering.     

Mineral–Carbon Sorbents Based on Aluminium Hydroxide and Atactic Poly(propylene)

The present work is an attempt to use the waste water stream, containing considerable amounts of aluminium chloride, for the manufacture of mineral–carbon sorbents. The use of the wastewater has given a possibility of obtaining a suitable mineral matrix of aluminium hydroxide for the sorbents. Atactic poly(propylene) (APP) have been used as the necessary carbon raw material. The modification of aluminium hydroxide was attained by preliminary mixing with the organic component, followed by carbonisation. Optimum conditions for obtaining Al(OH)₃ have been determined and the effect of the amount of carbon matter on the properties of the materials obtained has been evaluated. The studies have enabled to trace the changes in the structure and properties of the sorbents obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigations of cement early hydration in the presence of chemically activated fly ash

The paper describes an attempt of chemical activation of fly ash and claims the usefulness of combination of such investigation methods as calorimetry and infrared absorption for investigations of early periods of cement hydration. The research samples were cement pastes made with an addition of fly ash and admixtures of chemical activators, CaCl₂, Na₂SO₄ and NaOH, whereas a cement paste without fly ash addition and a cement-fly ash paste (both without admixtures) were used as reference samples. In order to investigate early periods of cement pastes hydration, the amount and rate of heat release were registered, and IR spectrums were checked at appointed hydration moments. As a result, it was shown that the combination of calorimetric and IR absorption methods in the investigations of early periods of cement hydration was useful. It was confirmed that the use of chemical activators CaCl₂, Na₂SO₄ and NaOH accelerated the hydration of cement pastes containing fly ash additive in early hours after adding water. The action of activators on hydrating cement system is different for each of investigated compounds.     

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

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.     

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

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.     

Studies on the influence of different fly ashes and Portland cement on early hydration of calcium aluminate cement

The influence of three mineral additives, i.e. fly ashes from pulverized combustion and from fluidized combustion of hard coal as well as Portland cement, on early hydration (up to 28th day) of calcium aluminate cement was investigated. Cement pastes containing 0, 5 and 25 wt% of additives were studied by the use of calorimetry, thermal analysis and infrared spectroscopy methods. It was confirmed that hydration of calcium aluminate cement is closely dependent on the type of addition and its amount. The influence of additives of different properties on cement hydration was discussed basing on received results and other literature reports.     

Studies of Thermal Transformations of Petrochemical Wastes For Obtaining Mineral-carbon Sorbents

In the present work an attempt was made to obtain mineral-carbon sorbents by thermal decomposition of solid waste materials containing, besides to mineral components, solid petroleum derivatives. The amount and the homogeneity of distribution of coal product formed in decomposition of organic matter on the surface of the mineral matrix, as well as the porous structure of the sorbents obtained depend largely on the conditions of calcination of the wastes used. The aim of this work was to find optimum conditions of the process. The sorptive properties of the obtained material were checked in the process of reduction of pollutants contained in industrial wastes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Aluminium nitrate as a precursor of mesoporous aluminium oxides

The thermal transformations of the products of hydrous aluminium nitrate hydrolysis in ammonia medium were studied by thermal analysis, mass spectrometry, infrared spectrophotometry, X-ray phase analysis, and sorption methods. Experiments have shown that the hydrolysis of hydrous aluminium nitrate in ammonia medium at pH=6-7 leads to the formation of boehmite. The degree of crystallinity of this product increases, if the hydrolysis is carried out for 264 h at 100°C, with respect the samples separated from the mother liquor just after completing the dosage of the reagents. It has also been found that aluminium oxide, obtained by thermal decomposition of the products of hydrolysis carried out for 264 h at an increased temperature, is characterized by a well developed specific surface, stable at high temperatures, amounting to about 100 m2 g^-1, after calcination for 2 h at 1200°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of different ways of activation of fly ash–cement mixtures

Journal of Thermal Analysis and Calorimetry - Cement industry emits large amount of CO2. One of the ways to reduce this emission is to use cement replacements, such as fly ash, in binding mixtures....