Método de diferenciación de Caolinitas y Cloritas

En el presente trabajo se hace una revision bibliografica de los distintos métodos de identificación de Caolinita y Clorita en mezclas naturales y artificiales, valorando la distinta problematica que presentan cada uno de ellos, y aplicandolos a muestras patrones y mezclas naturales que presentan esta problematica a fin de obtener una mejor valoraci6n de los distintos métodos expuesto

Ceramica gris medieval catalana: caracterizacíon y tecnologia de produccion

En este trabajo se plantean brevemente los resultados cualitativos obtenidos sobre un conjunto de 400 muestras de cerámica gris medieval catalana, con ejemplos de algunas de las conclusiones, que serán publicadas detalladamente más adelante. Asimismo se exponen las conclusiones generales sobre tecnología de producción, referentes a temperatura y atmósfera de los hornos desgrasante y acabados de las cerámicas. Se propone un ensayo de clasificación de las pastas basado en observaciones microscópicas y las correspondientes variantes tecnológicas

Thermal behaviour of kaolinitic raw materials from San José (Oruro, Bolivia)

Kaolin is widespread as a result of the alteration in the San José Sn-Ag deposit located in Oruro, Bolivia. This study presents a chemical, mineralogical and thermal characterization of the San José kaolinitic deposit, which is necessary to determine their optimal applications. Mineral phases of these white silty kaolinitic materials were determined by X-ray diffraction (XRD) and are quartz, kaolinite, K-feldspar, muscovite, illite and minor halloysite, dickite, plagioclase, jarosite, rutile, alunite and gypsum. The fraction < 63 µm contains 20-27 mass% of kaolinite. Differential thermal analysis (DTA) shows an endothermic peak at 520 °C associated with the dehydroxylation of kaolinite and an exothermic peak at ~ 980 °C related to the crystallization of mullite. TG curves show a total mass loss up to 1300 °C of about 8 mass%. The dilatometric curves show a shrinkage at about 890 °C produced by the collapse of metakaolinite into a spinel-like structure, and another shrinkage starts at 1010 °C, at the beginning of the sintering, when the spinel-like phase is transformed to mullite and amorphous SiO2. Lightness L* is 80-92, but only the mined materials have b* < 4, suitable for paper filling applications

Synthesis and crystal phase evaluation of hydroxylapatite using the rietveld-maximum entropy method

Bioceramic systems based on hydroxylapatite (HAP) are an important class of bioactive materials that may promote bone regeneration. The aim of this research was to evaluate how the stoichiometry of HAP influences its microstructural properties when diagnosed using the combined Rietveld method and Maximum entropy method (MEM). The Rietveld Method (RM) is recognizably a powerful tool used to obtain structural and microstructural information of polycrystalline samples analyzed by x-ray diffraction. Latterly have combined the RM with the maximum entropy method (MEM), with the goal of improve structural refinement results. The MEM provides high resolution maps of electron density and their analysis leave the accurate localization of atoms inside of unit cell. Like that, cycles Rietveld-MEM allow an excellent structural refinement In this work, a hydroxylapatite sample obtained by emulsion method had its structure refined using one cycle Rietveld-MEM with x-ray diffraction data. The indices obtained in initial refinement was Rwp = 7.50%, Re = 6.56%, S - 1.14% e RB = 1.03%. After MEM refinement and electron densities maps analysis to correction of atomics positions, the news indicators of Rietveld refinement quality was Rwp = 7.35%, Re = 6.56%, S = 1.12% and RB = 0.75%. The excellent result obtained to RB shows the efficiency of MEM as auxiliary in the refinement of structure of hydroxylapatite by RM