Diagnóstico del deterioro de la piedra en el patrimonio construido. Datos y perspectivas

Stone and other materials used for the construction of historic buildings, memorial statues, gravestones and similar are exposed to weathering and polluting agents and, therefore, progressive decay. Such deterioration, whether physical, chemical or biological, involves mineral phases and their interrelationships (structure and texture).A review of the analytical procedures applied in scientific research on stone damage has revealed the need for appropriate tools and tests (each with a specific scope, depending on the extant damage) to identify decay processes and apply the correct “therapy”, i.e. temporary and/or permanent protection (cleaning, protection, reinforcement, repair and/or replacement). A number of case histories of famous components of the Italian built heritage are discussed in the context of the use of integrated methodologies for researching decay in different kinds of stone.La piedra y otros materiales utilizados para construir edificios históricos, estatuas conmemorativas, lápidas, etc. sufren la acción de los agentes atmosféricos y contaminantes y, por tanto, a una degradación progresiva. En dicha degradación, ya sea física, química o biológica, intervienen las fases minerales de la piedra y sus correspondientes interrelaciones (estructura y textura).Un análisis de los procedimientos analíticos aplicados en la investigación científica sobre los daños en la piedra ha puesto de manifiesto la necesidad de herramientas y pruebas adecuadas (cada una con un objetivo concreto, según el daño existente) para identificar los procesos de degradación y aplicar la «terapia» adecuada; es decir, una protección provisional o definitiva (limpieza, protección, refuerzo, reparación o sustitución).Se comentan varios casos prácticos relacionados con conocidos elementos del patrimonio construido italiano en el contexto del empleo de metodologías integradas para la investigación de la degradación en distintos tipos de piedra

Uses and applications of clays and clay minerals. State-of-the-art and perspectives

The use of clays is growing at an enormous rate in a great variety of industries. Moreover, clay science has also many applications in soil mechanics, agriculture and plays a role in environmental problems. Last but not least, clay minerals may have a critical part in the origin, migration and trapping of hydrocarbons, and in petroleum cracking. High-quality products require high technology and high-grade raw materials. However, many good materials are used for low-grade products and large quantities of useful raw materials are wasted. On other hand, in many instances insufficient information is available about the potentialities of alternative materials. Inadequate understanding the true nature of raw clay materials prevents fully defining and characterizing their properties, and predicting their behaviour in the formulated products. Modifications of physical and chemical properties, or mixing may allow clays to be used for benefication and manufacturing. The "communication gap" sometimes inhibits interaction between the generators and users of basic research. Areas of incomplete knowledge and the need for new commercial applications should stimulate further investigations. Industrial innovation, technological and processing optimization, and the development of new products should promote interdisciplinary cooperation linking basic science and technology.Veniale Fernando. Uses and applications of clays and clay minerals. State-of-the-art and perspectives. In: Proceedings of the 9th international Clay Conference, Strasbourg, 1989. Vol V : Industrial applications of clays. Analytical techniques and teaching of clay mineralogy. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1990. pp. 81-90. (Sciences Géologiques. Mémoire, 89

Uses and applications of clays and clay minerals. State-of-the-art and perspectives

The use of clays is growing at an enormous rate in a great variety of industries. Moreover, clay science has also many applications in soil mechanics, agriculture and plays a role in environmental problems. Last but not least, clay minerals may have a critical part in the origin, migration and trapping of hydrocarbons, and in petroleum cracking. High-quality products require high technology and high-grade raw materials. However, many good materials are used for low-grade products and large quantities of useful raw materials are wasted. On other hand, in many instances insufficient information is available about the potentialities of alternative materials. Inadequate understanding the true nature of raw clay materials prevents fully defining and characterizing their properties, and predicting their behaviour in the formulated products. Modifications of physical and chemical properties, or mixing may allow clays to be used for benefication and manufacturing. The "communication gap" sometimes inhibits interaction between the generators and users of basic research. Areas of incomplete knowledge and the need for new commercial applications should stimulate further investigations. Industrial innovation, technological and processing optimization, and the development of new products should promote interdisciplinary cooperation linking basic science and technology.Veniale Fernando. Uses and applications of clays and clay minerals. State-of-the-art and perspectives. In: Proceedings of the 9th international Clay Conference, Strasbourg, 1989. Vol V : Industrial applications of clays. Analytical techniques and teaching of clay mineralogy. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1990. pp. 81-90. (Sciences Géologiques. Mémoire, 89

Influence du traitement par le dithionite de sodium sur les hydroxydes libres d'une smectite

The effect of Na-dithionite pretreatment -widely used for the removal of free iron from clays -on a smectite with low Fe-content has been investigated by means of several methods : chemical analysis, C.E.C., specific surface, thermal analyses (D.T.A., T.G. and D.T.G.), X-ray diffraction, IR and Mössbauer spectra. The treatment affects the interlay er components decreasing the degree of collapse of the lattice upon heating (12,2 Â again 9.6 Â) and K-saturation. Inverlayer islands of hydrated Fe2+ (.VI) become stable, and they transform into Fe3+ tetrahedrons by heating at 350°C , These tetrahedrons are presumably inverted, like it occurs in the structure of stilpnomelane or of montmorillonite as suggested by EDELMAN and FAVEJEE .On a étudié les modifications apportées sur une smectite à faible teneur en fer par le traitement avec le Na-dithionite , communément utilisé pour l'élimination des hydroxydes libres. On a analysé la fraction < 2 µ soit de la smectite naturelle, soit de la même smectite après traitement avec le Na-dithionite, en utilisant les méthodes suivantes : analyse chimique, C.E.C., surface spécifique, analyses thermiques (D.T.A., T. G, et D.T.G .), diffraction des rayons X, spectrométrie infrarouge et Mössbauer . A la suite des diverses observations, on a été conduit à conclure que le traitement appliqué aboutit à la stabilisation d'îlots interfoliaires constitués par Fe3+ hydraté à coordination octaédrique , qui est mis en évidence par une fermeture partielle à 12.2 Â, plutôt qu'à 9.6 Â. Ces îlots inter foliaires, après chauffage à 350°C, se transforment en tétraèdres stables centrés sur Fe3+, probablement inversés par rapport à la couche tétraédrique de la smectite, comme il arrive dans la structure du stilpnomélane ou même dans la structure de la montmorillonite, selon l'hypothèse de EDELMAN et FAVEJEE . On conclut que pour identifier les propriétés et les caractéristiques in situ des minéraux argileux dans les sédiments et les sols, il vaudrait mieux éviter tout prétraitement.Veniale Fernando, Pace S. Influence du traitement par le dithionite de sodium sur les hydroxydes libres d'une smectite. In: Bulletin du Groupe français des argiles. Tome 22, fascicule 2, 1970. pp. 127-137