Procedimiento de obtención de borato de aluminio de fórmula 2Al2O3.B2O3

Referencia OEPM: P0413159.-- Fecha de solicitud: 29/03/1973.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Peer reviewe

Thermal behavior in air of iron oxyhydroxides obtained from the method of homogeneous precipitation. Part I. Goethite samples of varying crystallinity

Differential scanning calorimetry (DSC), thermogravimetry (TG) together with X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been employed to follow the structural and morphological changes in the thermal decomposition in air of goethite (α-FeOOH) samples of varying crystallinity. A clear relationship is noted between the starting goethite and hematite crystallinities. In the 280-600 °C temperature range, the acicular hematite shows a nonuniform broadening process of the (104) and (110) X-ray lines, this process increased as the starting goethite crystallinity increased. Between 600 and 700 ° C a marked increase of the hematite crystallinity was observed, together with a change of acicular to spherical hematite particles

Thermal behaviour in air of iron oxyhydroxides obtained from the method of homogeneous precipitation. Part II. Akaganeite sample

Differential scanning calorimetry (DSC), thermogravimetry (TG), infrared spectroscopy (IR) together with X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) have been employed to follow the structural and morphological changes happening in the thermal decomposition, in air, of a synthetic akaganeite sample (β-FeOOH). It has been stated that both the water molecules and chloride ions adsorbed within the structural tunnels have an important role in the stability of structure of akaganeite. At 300 °C, after the dehydroxylation, two broad reflections can be detected only in the X-ray diffraction pattern, which shows traces of both akaganeite and haematite. The sharp exothermic peak appearing in the DSC curve at 360 °C is related to both the loss of chloride ions as HC1 and the formation of haematite. At this point there is a change in crystallite shape, and the porosity almost disappears indicating that a sintering process is occurring. From 430 to 700 °C the haematite crystallinity increases. At 700 °C two kinds of crystals, rhombic and hexagonal, can be observed

Characterization studies of goethite samples of varying crystallinity obtained by the homogeneous precipitation method

X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and thermogravimetry were used to study the solid phase obtained from sulfuric acid solution of Fe(III) hydrolyzed with urea. The influence of solution factors (temperature, pH, hydrolysis rate, urea and iron concentration, and aging time) on the solid phase is discussed. Hematite (α-Fe2O3) with impurities of goethite (α-FeOOH) was obtained at rapid hydrolysis rate, whereas goethite was formed at a slow hydrolysis rate. As the pH and aging time increased, so did the crystallinity of goethite

Mechanism of akaganeite-hematite transformation via solution

Electron microscopy, IR spectroscopy and X-ray powder diffraction were used to study the solid phases obtained from hydrochloric acid solutions of Fe(III) by precipitation with urea. The results indicated that the transformation mechanism, via solution, of akaganeite into hematite involves two separate steps: (i) dissolution of akaganeite crystals and (ii) appearance of the hematite phase by Fe(III) precipitation. The hematite phase, which is formed more slowly, is more stable; well crystallized akaganeite is obtained in 30 min, whereas well crystallized hematite requires 90 min

Treatment of CDO at room temperature and 150 °c in a water-vapour-saturated atmosphere. Part I

The behaviour of different CdO samples in a water-vapour-saturated atmosphere was studied by X-ray powder diffraction (XRD), IR spectroscopy and thermogravimetry (TG, DTG). The results indicate three steps during the course of the CdO hydration process at room temperature: (i) γ-Cd(OH) is formed initially; its concentration (67%) does not change over a period of 5-31 days, indicating that the hydration reaction has reached equilibrium; (ii) after 31 days, the unhydrated CdO and γ-Cd(OH) are carbonated; (iii) the carbonation increases with time; CdCO is formed at the end of the process. When the temperature of treatment is 150°C, β-Cd(OH) is mainly formed together with γ-Cd(OH) and CdCO. The carbonation does not increase with time and the γ-hydroxide is transformed into β-Cd(OH)

Obtention of meta and pyro vanadates of cadmium from an unusual low energy process. I. α-metavanadate

The behaviour of CdCo3-V2O5 (1:1) mixture in a saturated water-vapour atmosphere, has been studied at room temperature by means of X-ray diffraction (XRD), infrared spectroscopy (IR) and thermal analysis (TG) and (DSC). The results showed a dramatic change in V2O5 crystalline structure due to adsorption process of water molecules and formation of highly reactive V2O5 gels. An acid-base mechanism is proposed in order to explain the CdCO3 decomposition at room temperature by acid attack of V2O5 gels, and posterior α-CdV2O6 formation

Behaviour of CdCO3-V2O5 (1:1M)system in a saturated atmosphere of water vapor at different temperatures

The behaviour of an equimolecular CdCO3-V2O5-system in a saturat ed atmosphere of water vapor has been studied at different temperatures. It was found by means of IR spectroscopy and X-ray data,that the β-Cd(VO3)2,is obtained at 150°C. The beginning of reaction ia stated for an increase of intensity of(001)X-ray line of V2O5. On the other hand, the adsorbed water molecules might cause the transformation crystalline → amorphous of V2O5, and an increase of acid properties at the V2O5surface

α-Cadmium metavanadate preparation at room temperature. Part I

In this paper we propose a method of obtaining α-CdVO at room temperature from equimolecular CdO-VO mixtures kept in a water-saturated atmosphere. Characterization has been carried out by X-ray powder diffraction, infrared spectroscopy and TG analysis. These studies show the instability of α-CdVO and its evolution with time at room temperature towards the β-form. We propose a α-CdVO formation mechanism based on the acid-basic reactivity of VO and CdO, which is considerably increased by a humid atmosphere

Obtention of meta and pyro-vanadates of cadmium from an unusual low energy process. II. Pyro-vanadate

Pyro-vanadate of cadmium has been obtained at 150°C from both CdCO3-V2O5 (2:1) and CdCO3-NH4VO3 (1:1) mixtures, which were heated in a saturated water-vapour atmosphere. In this way, reactivity of V2O5 strongly increased due to the acid sites formed on the surface by means of adsorption process of water molecules. The evolution of the mixtures has been studied by X-ray diffraction (XRD), infrared spectroscopy (IR) and thermal analysis (TG) and (DTA). Different mechanisms of reaction in function of the mixture employed are proposed