Peter W. Mirwald

Isobaric annealing of high-density amorphous ice between 0.3 and 1.9 GPa: in situ density values and structural changes

We report in situ density values of amorphous ice obtained between 0.3 and 1.9 GPa and 144 to 183 K. Starting from high-density amorphous ice made by pressure-amorphizing hexagonal ice at 77 K, samples were heated at a constant pressure until crystallization to high-pressure ices occurred. Densities of amorphous ice were calculated from those of high-pressure ice mixtures and the volume change on crystallization. In the density versus pressure plot a pronounced change of slope occurs at approximately 0.8 GPa, with a slope of 0.21 g cm(-3) GPa(-1) below 0.8 GPa and a slope of 0.10 g cm(-3) GPa(-1) above 0.8 GPa. Both X-ray diffractograms and Raman spectra of recovered samples show that major structural changes occur up to approximately 0.8 GPa, developing towards those of very high-density amorphous ice reported by (T. Loerting, C. Salzmann, I. Kohl, E. Mayer and A. Hallbrucker, Phys. Chem. Chem. Phys., 2001, 3, 5355) and that further increase of pressure has only a minor effect. In addition, the effect of annealing temperature (T(A)) at a given pressure on the structural changes was studied by Raman spectra of recovered samples in the coupled O-H and decoupled O-D stretching band region: at 0.5 GPa structural changes are observed between approximately 100-116 K, at 1.17 GPa between approximately 121-130 K. Further increase of T(A) or of annealing time has no effect, thus indicating that the samples are fully relaxed. We conclude that mainly irreversible structural changes between 0.3 to approximately 0.8 GPa lead to the pronounced increase in density, whereas above approximately 0.8 GPa the density increase is dominated to a large extent by reversible elastic compression. These results seem consistent with simulation studies by (R. Martonàk, D. Donadio and M. Parrinello, J. Chem. Phys., 2005, 122, 134501) where substantial reconstruction of the topology of the hydrogen bonded network and changes in the ring statistics from e.g. mainly six-membered to mainly nine-membered rings were observed on pressure increase up to 0.9 GPa and further pressure increase had little effect.

Cordierite under hydrostatic compression: Anomalous elastic behavior as a precursor for a pressure-induced phase transition

Abstract The high-pressure behavior of cordierite was investigated by means of in situ experiments using piston-cylinder press and diamond-anvil cell. Static compression in diamond-anvil cells was conducted with various penetrating and non-penetrating pressure media (H2O up to 2 GPa, argon and 4:1-methanolethanol up to 7 GPa). The measurement of lattice parameters revealed neither a significant influence on the elasticity nor any indication for effects in analogy to over-hydration within the experimental pressure ranges. Volumetric compression experiments at constant rates up to 1.2 GPa in a piston-cylinder apparatus insinuate subtle irregularities in the low-pressure range at around ~0.35 and ~0.85 GPa. The ΔV/V contribution related to the anomalous compression behavior in that pressure range is of the order of 5 × 10-4. The results obtained from single-crystal X-ray diffraction between 10-4 and 7 GPa revealed an unexpected and anomalous linear volume decrease, corresponding to KT,298 = 131±1 GPa for the bulk modulus and K′ = -0.4±0.3 for its pressure derivative for a third-order Birch-Murnaghan equation of state. The compressional behavior of the main axis directions is anisotropic with βa-1 ≈ βb-1 > βc-1 for an initial pressure regime up to ~3 GPa. At pressures above ~4 GPa, the compression of the a- and b-axis starts to differ significantly, with the b-axis showing elastic softening as indicated by negative values for ∂(βb-1)/∂P. The diversification between the a- and b-axis is also expressed by the pressure-depending increase of the distortion parameter Δ. The pronounced elastic softening in both the b-axis and c-axis directions ∂(βb-1)/∂P = -4.3±0.9, ∂(βc-1)/∂P = -1.2±0.8) are responsible for the apparent linear bulk compression, which indicates the structural instability and precedes a so far not reported ferroelastic phase transition to a triclinic polymorph, following a primitive lattice above the critical transition at ~6.9 GPa.

Lime Mortar with Natural Hydraulic Components: Characterisation of Reaction Rims with FTIR Imaging in ATR-Mode

Reaction rims of natural hydraulic relicts in historic mortars were investigated using a novel technology; a FTIR-spectrometer equipped with a focal plane array detector enabling in ATR-mode IR imaging with a spatial resolution of 1.0 μm. IR spectra show two regions with main absorption bands at 1,280–1,580 cm−1 and 900–1,120 cm−1. Bands at 1,450 and 1,396 cm−1 correspond to the asymmetric stretching of CO 3 2− , indicating two different forms of CaCO3; the 900–1,120 cm−1 group of bands is assigned to Si-O stretching vibrations indicating C–S–H phases. The ratio of the integral absorbance of these two main regions of absorption bands shows an inhomogeneous spatial distribution in the reaction rim. From this variation we conclude that the reaction rims consist of areas containing both calcite and aragonite in addition to C–S–H phases and areas containing aragonite and C–S–H phases, the latter with a lower Ca/Si ratio and a higher degree of polymerization. SiO2 gel is present in both areas.

Pore and hygric properties of porous limestones: a case study from Bratislava, Slovakia

Abstract Most historic stone monuments in Bratislava (Slovakia) are built with various types of porous, light and weakly cemented sedimentary rocks. These Neogene sandstones and limestones, also known as Leitha limestones, were quarried in the Vienna Basin. The various sedimentary environments are reflected in the heterogeneity of lithotypes and their cementation. The distinctly different pore structure of these rocks is reflected in their very variable physical properties and consequently in the distinct durability. Petrographic and petrophysical properties were determined on main ashlar types of the two most important historical monuments of Bratislava, the Castle and St Martins Cathedral. Fresh samples of Leitha limestones were also obtained from the existing or abandoned quarries. The study includes a detailed petrographic examination of major rocks types and an assessment of their mineralogical composition by X-ray diffraction and microscopy. Hygric properties and porosity influence the weathering stability and the chances to apply conservation treatment. Parameters such as pore volume, pore size distribution by mercury porosimetry, specific surface of pores by nitrogen adsorption (BET) analysis as well as water sorption, capillary water uptake and drying behaviour were measured and compared for the six studied lithotypes.

Petrophysical properties of selected Quaternary building stones in western Austria

Abstract In west Austria Quaternary building stones, such as lithic breccias of alluvial fans and talus slopes or calcareous spring tufa, have been frequently used as building stones since Roman times. Spring tufas are a widely used building material of historical objects in west Austria. This porous calcareous rock, formed by carbonate precipitation from calcium carbonate supersaturated spring waters, is an appreciated building stone: easy to quarry, lightweight, easily workable and relatively resistant to weathering. The Hötting Breccia, a lithified talus and alluvial breccia, has only been extracted in a few quarries near Innsbruck/Tyrol, however. Many of the mediaeval buildings of the towns of Innsbruck and Hall are built of this decorative type of stone. Petrography, mineralogical composition, porosity parameters and hygric properties have been investigated in this study from two tufas and one breccia occurrence. The results obtained reveal that these Quaternary stones, being formed at the Earths surface, exhibit pore properties and hygric behaviour which differ considerably from other stone materials which have been subjected to the physical-chemical formation conditions of the upper Earth crust. This has implications for their workability, internal stability and weathering behaviour.

Grödener sandstone, a historical building material in South Tyrol/Italy-the problem of largevariability of stone properties for monument conservation

Publisher Summary This chapter describes Grodener Sandstone, a historical stone material of regional significance in South Tyrol/Italy. Grodener Sandstone has been used predominantly for construction of locally important objects such as churches, monasteries, castles, nobleman houses. The Cathedral of Bozen is the most renowned monument built from this sandstone in the 14th century. This Permian sandstone is characterized by considerable variation in its properties because of its geological condition; and this creates a variety of damages as well as conservatory problems. To elucidate this conservatory problem, a petrographical-mineralogical study was started within the frame of an Italian-Austrian EU-Interreg program. This concentrated on determination of basic petrographical, chemical, and physical parameters— such as sedimentary fabrics, mineralogy, salt content, pore, and hygric properties of the stone. Chemically soluble components are essential because they represent the inherent salt content of the material— in conjunction with its hygric properties— that plays an important role under weathering conditions. Repair works and restoration on Grodener Sandstone objects, where cement-based mortars were applied instead of lime, led to salt damage effects in their next vicinity. Direct consequence of this problem is that good quality materials are needed for repair work, and this can be achieved by geological mapping of all still open quarries.