The Thermal Expansion Coefficients of Selected Slovenian Building Stone

Ana Mladenovic (ana.mladenovic@zag.si)¹ & Breda Mirtic (breda.mirtic@guest.arnes.si)²

¹ Slovenian National Building and Civil Engineering Institute, Dimiceva 12, 1000 Ljubljana, Slovenia

² Dept. og Geology, Faculty of Natural Sciences and Engineering, University of Ljubljana, Askerceva 12, 1000 Ljubljana, Slovenia

The usefulness of natural stone for building purposes is significantly affected by the stone's thermal expansion coefficient. This is because the behaviour of such stone after installation depends, under changing weather conditions, on its petrographic and physical characteristics. Linear expansion coefficients were determined for six types of natural stone from different deposits in Slovenia (limestone, sandstone, breccia, travertine, granodiorite and gabbro). Measurements were performed, according to the RILEM method P.E.M. 25, within the temperature range from -20 to +50°C, which is seldom found in the literature but corresponds well to the range which is the most applicable for climatic conditions in Slovenia. Several hypotheses concerning the influence of various physical and petrographic parameters on the thermal expansion coefficient were evaluated. The results obtained when measuring the thermal expansion coefficients of the selected Slovenian natural stones were in good agreement with results given in the available literature, even though a different measuring method was used. Mineral composition, the dimensions of mineral grains, the elastic properties of the stones, and the temperature range over which the thermal expansion coefficient is measured, are, in the case of dense and texturally homogeneous stones, the properties which have the most influence on the thermal expansion coefficient. The results of the investigation proved the existence of a non-linear relationship between temperature and the thermal expansion coefficient, the latter having higher values at higher temperatures. The limestone specimens with a biosparite structure had higher thermal expansion coefficients than those with a biomicrite structure. Young's modulus of elasticity varied inversely with the thermal expansion coefficient. No correlation was observed between the linear expansion coefficient and mineral composition, and in particular quartz content, although, according to the literature, mineral composition has an important influence on this coefficient.

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A new Radiative Microfurnace for Single-crystal Diffractometer

Gianmario Molin (gmario@dmp.unipd.it), Fedora Martignago (fedora@dmp.unipd.it) & Alberto Dal Negro (alberto@dmp.unipd.it)

Dipartimento di Mineralogia e Petrologia, Corso Garibaldi 37 I-35100 Padova, Italy

Structural modifications and phase transitions with temperature are goals peculiar to experimental mineralogy. Microfurnaces available today for X-ray single-crystal investigation (radiative, gas-flame, gas-flow) are generally temperature-monitored by a thermocouple placed in a different site with respect to the crystal. The effective experimental temperature is based on the relationship with the cell-edge expansion of a standard crystal commonly sealed close to the crystal in an evacuated glass capillary. The new microfurnace thereafter referred as F1 aimed at achieving the following goals: fast crystal mounting; access to a large portion of reciprocal lattice; low absorption of direct beam; efficient in-situ temperature measurement; fast power supply regulation; high temperature stability; controlled atmosphere. The F1 is composed of two main parts: modified goniometer head, which hosts the crystal, directly glued by refractory cement on to a small rounded thermocouple and a heating body, fixed on the (chi) circle and radially shiftable along the ø axis. The heating body hosts the Pt winding and connections of both gas flow and power-supply and is enclosed in a thin pyrolitic boron nitride (PBN) shield. The precision achieved in the temperature measurement was about ± 4°C. Calibration of the microfurnace was carried out collecting X-ray data from a single-crystal synthetic periclase. Its thermal expansion and structural parameters at temperatures of 28, 150, 300, 450, 600, 700, 900 and 1000°C were measured using a SIEMENS AEDII four-circle diffractometer using graphite-monochromatized Mok(alpha) radiation. Structural refinements were carried out in space group F m 3 m using the SHELXL-93 refinement program. The mean coefficient of linear expansion up to 1000°C was 14.3x 10^-6 °C. A least-squares fit of the data collected using the new F1 microfurnace gave:

a= 0.0000625 (7) [T(K) -273)] + 4.2083 (4).

Solubility in Fluids at Eclogite Facies Conditions: Experimental and Natural Constraints

J. F. Molina (j.f.m.palma@toyen.uio.no)¹, H. Austrheim (hakon.austrheim@toyen.uio.no)¹ & S. Poli (stefano@biko.terra.unimi.it)²

¹ Mineralogisk-Geologisk Museum, Sarsgate 1, N-0562, Oslo, Norway

² Dipartimento Scienze della Terra, Università di Milano, Via Botticelli 23, 20133 Milano, Italy

Field data, phase equilibria and fluid inclusion studies suggest that eclogite facies metamorphism may take place in equilibrium with a fluid phase. In the Marun-Keu complex (Polar Urals, Russia), eclogites form around a net of leucocratic veins. Such net leads to boudin-like structures where a core of dark amphibolite is separated from the vein by centimeter to decimenter thick zones of eclogite facies assemblages. Quartz, white mica or carbonates usually fill these veins, but other phases like garnet, omphacite, amphibole, kyanite, apatite and rutile can also occur, suggesting large amounts of solute in high-pressure fluids. Cl-rich apatite and amphibole occur in some veins and boudins suggesting the presence of Cl-rich fluids. To evaluate the importance of pressure and fluid composition on the solubility of mineral phases in mafic systems, synthesis experiments were performed in the system Na₂O-K₂O-CaO-FeO-MgO-Al₂O₃-Si₂O-H₂O-Cl. Experiments were performed in a piston-cylinder apparatus at 10 kbar and 16 kbar, and 650°C, at fO₂ buffered by NNO. 0, 1 and 5 molar HCl aqueous solutions were used as starting fluids at a fluid/solid ratio of ca. 0.1. Three mafic compositions from Marun-Keu eclogites, ranging from Mg-basalt to Fe-basalt were studied. Most runs contain drop-like tiny aggregates interpreted as deposits from the fluid phase after quenching. The dissolution process changed the effective bulk compositions and produced an assemblage consisting of amphibole + plagioclase + quartz + biotite. At 16 kbar, both H₂O- and Cl-bearing experiments show abundant quench material, amphibole and minor plagioclase and quartz, whereas at 10 kbar, the abundance of plagioclase increases, and quench deposit decreases. Preliminary results of these experiments suggest that under relatively high fluid/rock ratios and high-pressure conditions, mineral phases in mafic systems can dissolve significantly in both H₂O- and Cl-bearing fluids.