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.     

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.     

Synthesis and phosphorescence properties of Dy3+ and (Pr3+–Dy3+) in MgTiO3

Using tetra-n-butyl titanate and magnesium nitrate as raw materials, Dy³⁺ and Pr³⁺ ions in the matrix of magnesium titanate (MgTiO₃) was successfully synthesized by a modified solid-state reaction. The mixtures to achieve a solid-state reaction were heated in porcelain crucibles at 600?°C for 2?h, 900?°C for 6?h, and 1000.0?°C for 2?h. The reaction products obtained in an air atmosphere were characterized by X-ray powder diffractions. The optimization of reaction conditions were carried out by thermal gravimetry and differential thermal analysis methods. Surface and elemental analyses were performed by using on SEM instrument. The excitation and emission spectra were recorded by photoluminescence spectrophotometer.     

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.     

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.     

Basic hydrolysis of glyceryl nitrate esters. III. Trinitroglycerin

Kinetics of the basic hydrolysis of glyceryl trinitrate (TNG) were investigated in CO₂-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N₂ sparging of the reaction mixture. TNG hydrolyzed via second-order reaction at 25°C, 18°C, and 10°C. The activation energy of the hydrolysis reaction of TNG was calculated from the kinetic data and found to be equal to 27.53 kcal/mol. The major products of the hydrolysis of TNG in solution of calcium hydroxide were calcium nitrate and calcium nitrite, accounting for approximately 50% of the degradation products. The minor identified products such as calcium oxalate and nitrate esters amounted to approximatey 6% of the products. The remaining 30% of the isolated products was a mixture of calcium formate, a nitrate ester, and unidentified volatiles, polymerlike substances, and other organic residue.     

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.     

Preparation of aluminas

Aluminium hydroxide was prepared by precipitation from aluminium nitrate solution with ammonia solution. Thermal decomposition of the solid hydroxide was studied by means of TG, DTG and DTA. The sample was thermally treated in the temperature interval between 200 °C and 1000 °C. X-ray phase analysis was used to study the phase compositions of the resulting products, and their surface areas were compared.     

Bench-scale biosynthesis of isonicotinic acid from 4-cyanopyridine by Pseudomonas putida

Pseudomonas putida CGMCC3830 harboring nitrilase was used in isonicotinic acid production from 4-cyanopyridine. This nitrilase showed optimum activities towards 4-cyanopyridine at pH 7.5 and 45°C. The half-life of P. putida nitrilase was 93.3 h, 33.9 h, and 9.5 h at 30°C, 38°C, and 45°C, respectively. 4-Cyanopyridine (100 mM) was fully converted into isonicotinic acid within 20 min. The bench-scale production of isonicotinic acid was carried out using 3 mg of resting cells per mL in a 1 L system at 30°C and finally, 123 g L^?1 of isonicotinic acid were obtained within 200 min without any by-products. The conversion reaction suffered from the product inhibition effect after the tenth feeding. The volumetric productivity was 36.9 g L^?1 h^?1. P. putida shows significant potential in nitrile hydrolysis for isonicotinic acid production. This paper is the first report on isonicotinic acid biosynthesis using Pseudomonas putida and it represents the highest isonicotinic acid production reported so far.     

Thermal decomposition of methylxanthines

The thermal decomposition of theophylline, theobromine, caffeine, diprophylline and aminophylline were evaluated by calorimetrical, thermoanalytical and computational methods. Calorimetrical studies have been performed with aid of a heat flux Mettler Toledo DSC system. 10 mg samples were encapsulated in a 40 μL flat-bottomed aluminium pans. Measurements in the temperature range form 20 to 400°C were carried out at a heating rate of 10 and 20°C min⁻¹ under an air stream. It has been established that the values of melting points, heat of transitions and enthalpy for methylxanthines under study varied with the increasing of heating rate. Thermoanalytical studies have been followed by using of a derivatograph. 50, 100 and 200 mg samples of the studied compounds were heated in a static air atmosphere at a heating rate of 3, 5, 10 and 15°C min⁻¹ up to the final temperature of 800°C. By DTA, TG and DTG methods the influence of heating rate and sample size on thermal destruction of the studied methylxanthines has been determined. For chemometric evaluation of thermoanalytical results the principal component analysis (PCA) was applied. This method revealed that first of all the heating rate influences on the results of thermal decomposition. The most advantageous results can be obtained taking into account sample masses and heating rates located in the central part of the two-dimensional PCA graph. As a result, similar data could be obtained for 100 mg samples heated at 10°C·min⁻¹ and for 200 mg samples heated at 5°C min⁻¹.     

Basic hydrolysis of glyceryl nitrate esters. II. 1,2-glyceryl and 1, 3-glyceryl dinitrate esters

Kinetics of the basic hydrolysis of 1,2-glyceryl dinitrate (1,2-DNG) and 1,3-glyceryl dinitrate (1,3-DNG) esters were investigated in CO₂-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N₂ sparging of the reaction mixture. Both glyceryl dinitrate esters hydrolyzed via second-order reaction at 25°C. 1,2-DNG in basic solutions isomerized to 1,3-DNG which subsequently hydrolyzed to yield products. The main hydrolysis product of 1,3-DNG was identified as glycidyl nitrate. Other products formed during the basic hydrolysis of DNGs were nitrites and nitrates.     

Fibers and fiber cocktails to improve fire resistance of concrete

Hybrid organic–inorganic resin matrix, i.e., hexa[3,4-dicyano]-phenyl phosphonitrile trimer (HPPT) has been prepared by the reaction of hexachlorophosphonitrile and 4-hydroxyphthalonitrile in the presence of sodium hydride which on heating at 300 °C yielded a high-temperature-stable highly crosslinked hybrid resin (C-HPPT). The elemental analysis (C, H, and N), FTIR, and ¹H and ¹³C-NMR studies were used to characterize the synthesized hybrid resin. The thermal analysis studies viz. TG and DSC were also carried out to determine the thermal stability and glass transition temperature of the cured resin. The isothermal study of the cured resin after 300 h at 300 °C showed only a mass loss of 4.36%.     

Thermal Degradation of Polymers. IV. Poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole

The thermal decomposition of poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole has been investigated at temperatures to 916°C. Mass-spectrometric thermal analysis (MTA), supported by elemental analysis of residues at various stages of a thermogravimetric analysis, was used to determine product distribution as a function of temperature. Below 550°C, the major product is water. Above 550°C, degradation of the heterocyclic structure to hydrogen cyanide, ammonia, carbon monoxide, and water begins. Hydrogen and methane probably are formed from decomposition and condensation of the carbocyclic structure. Activation energies for the formation of each major product were derived from the MTA data. The average of these is somewhat temperature-dependent but agrees within experimental error with the value of 44 ± 11 kcal obtained from isothermal kinetics. A mechanism involving initial hydrolysis of the polymer to an amine-substituted polyamide is postulated. Subsequent homolytic reactions account for formation of the major products.     

Effect of phenyl group on the structure and formation of transitional alumina from Al (OPh)<Subscript>3</Subscript>

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.     

The use of thermal analysis in the study of Ca<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>6</Subscript> formation by the polymeric precursor method

Single-phase Ca₃Al₂O₆ was prepared via polymeric precursor method. The influence of the reactants nature in the Ca₃Al₂O₆ synthesis was investigated. For this purpose, citric acid and soluble salts of calcium (nitrate, chloride, carbonate) and aluminium (nitrate, chloride, acetate) were used as starting materials, in the presence and, respectively, in the absence of ethylene glycol. Ca₃Al₂O₆ resulted as single-phase after annealing at 1050 °C for 1 h only starting from calcium nitrate or carbonate and aluminium nitrate or acetate as salts precursor for Ca²⁺ and Al³⁺ cations. The formation of Ca₃Al₂O₆ is not conditioned by the ethylene glycol presence in these mixtures. Using calcium and aluminium chlorides, the phases present at 1050 °C are Ca₁₂Al₁₄O₃₃ and unreacted CaO.     

Characteristics of the hydrous titanium dioxide-anatase phase transformation during hydrothermal treatment in aqueous solutions

The transformations of hydrous titanium dioxide, prepared by thermal hydrolysis of titanium(IV) compounds in sulfuric acid solutions, during hydrothermal treatment (150–240°C) in water were studied. The dispersivity and the chemical compositions of the samples obtained determined depending on the synthesis conditions (the composition) of hydrous titanium dioxide and the heat treatment temperature.     

Formation of mullite,topaz and corundum

The influence of aluminium fluoride on the thermal behavior of quartz and the formation of topaz, mullite and corundum have been examined in the present work using the derivatograph. The products of sintering were identified microscopically and by using a Siemens Crystalloflex diffractometer. The DTA curves indicate the formation of topaz at 760°C and the formation of mullite at 1000°C using the theoretical amount of aluminium fluoride. The reaction between quartz and aluminium fluoride takes place in two distinct steps using 50% excess of aluminium fluoride. The first is marked by a large endothermic peak at 780°C, representing the formation of topaz and the second by a sharp endothermic peak at 960°C, representing its subsequent dissociation with the formation of corundum or alpha-aluminium oxide.     

The Esterification of Sodium Lignosulfonate with Maleic Anhydride in Water Solution

The esterification of sodium lignosulfonate (LS) with maleic anhydride (MA), which is a by-product of the papermaking industry, was successfully carried out in water solution under mild conditions. The esterification percentage was influenced by many factors including the concentration of LS and the weight ratio of LS/MA, temperature, pH, and reaction time. Optimum conditions of the factors studied obtained after a series of single-factor experiments for lignosulfonate reacted with maleic anhydride were weight ratio of 1.2 to 1.0 under vigorous stirring at 55°C in alkaline solution for 4 h. The products were characterized by FT-IR, thermogravimetric (TG) analysis, and differential scanning calorimetry (DSC). The emergence of a 1717 cm^?1 peak of the FT-IR curves indicated that the esterification reaction was successfully carried out. Moreover, the TG results showed an increase in thermal stability of esterified lignosulfonate compared to unmodified lignosulfonate.     

Thermo- and photooxidation of polyisobutylene. I. Evolutions at temperatures above 50°C

Polyisobutylene films (PIB) were submitted to a thermal oxidation at 100°C and to a photooxidation by exposure to long-wavelength radiations (λ ≥ 300 nm) at 60°C. The modifications of the chemical structure resulting from the oxidation were determined by FT-IR analysis of the polymer films, coupled to chemical treatments that converted specifically the oxidation products. Dissolution of oxidized samples permitted analysis of the polymer by ¹³C- and ¹H-NMR. The structure of the volatile products was determined by mass spectroscopy analysis of the gas phase. Identification of the numerous products formed permitted the proposal of a scheme that accounts for the oxidation of PIB. When the irradiations are carried out at a temperature above 50°C, the depolymerization is favored and the mechanism involves two main routes of oxidation. A direct oxidation starts with the oxidation of radicals obtained by homolysis of the C C bonds on the main chain, and an induced oxidation involves hydrogen abstraction on the methylene and methyl groups by radicals formed by the direct oxidation of the polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1689–1701, 1997     

La matrice eau de mer et le signal du cuivre en spectrometrie d'adsorption atomique sans flamme : Partie 1: Etude de l'influence des principaux composants

(Copper signals from seawater matrices in electrothermal atomic absorption spectrometry. Part 1: study of the effects of principal inorganic ions.)The effects of the main inorganic ions of seawater (Na⁺, Mg²⁺, Ca²⁺, Cl^?, SO^2?₄), and of nitrate as modifier, on the electrothermal atomic absorption spectrometric signal of copper are studied. Sodium chloride, sulfate or nitrate, magnesium chloride or nitrate, and calcium chloride can cause serious interferences. Thermal treatment at about 700°C prevents the interference of MgCl₂ by its hydrolysis. Ashing can be done without loss of copper at higher temperatures in the presence of sulfate salts (1300°C) and nitrate salts (1200°C) than in the presence of chloride salts (1100°C). This is ascribed to the stabilising effect of oxides and sulfides. A study of the influence of two-component matrices, MCl-MNO₃ or MCl-MSO₄, on the atomization signal of copper confirms this stabilizing effect which adds to the decrease in interference connected with removal of chloride in acidic medium.