peter mirwald - Academia.edu (original) (raw)

Papers by peter mirwald

Physics of the Earth and Planetary Interiors, 1982

Compression measurements on cordierite, (Mg, Fe) 2A14Si5O18. n (H20, C02, etc.), reveal two volum... more Compression measurements on cordierite, (Mg, Fe) 2A14Si5O18. n (H20, C02, etc.), reveal two volume discontinuities. Room-temperature measurements to 30 kbar located them at 2 and 9 kbar. While the P-T-path of the lower discontinuity has been determined by compression experiments up to 900°C(P (kbar)~0.0075T°C+2),the one of the upper discontinuity relies on indirect evidence from H20-and C02-content data of Mg-cordierite, which suggest a similar positive slope. When interpreted as an abrupt change in specific volume (AV>O), both discontinuities yield a change in volume on the order of 0.002; the calculated changes in the thermodynamic parameters (e.g. ~S ~°°0.4 J K. mol~)are similarily small. X-ray data give no indication of deviation from the orthorhombic space group Cccm of cordierite. The two volume discontinuities are interpreted as displacive, higher order phase transitions. Comparison of the presented compression data with those of other framework silicates and the ring silicate beryl yield an intermediate behavior for cordierite.

Na in cordierite thermometry and garnet-cordierite barometry: Comparison of experimental results with natural data

Physical Chemistry Chemical Physics, 2006

We report in situ density values of amorphous ice obtained between 0.3 and 1.9 GPa and 144 to 183... more 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 B0.8 GPa, with a slope of 0.21 g cm À3 GPa À1 below 0.8 GPa and a slope of 0.10 g cm À3 GPa À1 above 0.8 GPa. Both X-ray diffractograms and Raman spectra of recovered samples show that major structural changes occur up to B0.8 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 B100-116 K, at 1.17 GPa between B121-130 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 B0.8 GPa lead to the pronounced increase in density, whereas above B0.8 GPa the density increase is dominated to a large extent by reversible elastic compression. These results seem consistent with simulation studies by (R. Martonˇa`k, 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 sixmembered to mainly nine-membered rings were observed on pressure increase up to 0.9 GPa and further pressure increase had little effect.

The melting curve of gold, silver, and copper to 60-Kbar pressure: A reinvestigation

Journal of Geophysical Research, Nov 10, 1979

The melting curves of gold, silver, and copper were redetermined by differential thermal analysis... more The melting curves of gold, silver, and copper were redetermined by differential thermal analysis to 60‐kbar pressure. The experiments were carried out with an end‐loaded piston‐cylinder high‐pressure apparatus using a recently developed low‐friction cell. Significant improvements in the precision of the temperature determination above 40 kbar were obtained. We observed a slight lowering of the melting temperature of copper when graphite capsules were used, which is consistent with our past experience and indicates some alloying of the copper and carbon. The following parabolic functions (Tm = a3 + [a2(P − a1)]½ 10 8a2) were fitted to the raw data, and the data corrected for the influence of pressure on the emf of the thermocouples (in parenthesis): gold, Tm = −2439.28 + [0.262850×10−4(P + 322.668)]½ × 2628.50 (Tm = −1773.88 + [0.309303×10−4(P + 249.167)]½ × 3093.03); silver, Tm = −261.759 + [0.661750×10−4 (P + 99.085)]½ × 6617.50 (Tm = −194.145 + [0.668583 × 10−4(P + 89.347)]½ × 6685.83); and copper, Tm = 129.171 + [0.134011×10−3(P + 122.305)]½ × 134.011 (Tm = 199.265 + [0.135218×10−3(P + 105.960)]½ × 135.218). The precision of the pressure measurements at the 90% confidence level is 0.3±0.5 kbar. The precision in the temperature is ±5°C. A revision of a previously made suggestion for a high‐pressure calibration scale based on the melting temperatures of pure elements is proposed.

Journal of Physics and Chemistry of Solids, 1978

vanadium-ion, proposed by previous investigators, is be oxygen vacancies. The diffusivities for f... more vanadium-ion, proposed by previous investigators, is be oxygen vacancies. The diffusivities for faster mode examined, are given by Df = 2.94 exp [-86.6 Kcal/RT] cm 2 sec1 Received 5 July 1977 and, the slower mode,D~= 1.08 x iO~exp [-32.8 Kcal/RTJ cm2 sec'.

Composition of hydrous melts in equilibrium with quartz eclogites

Mineralogy and Petrology, 1996

Summary Compositions of the hydrous melts in equilibrium with garnet, omphacitic clinopyroxene an... more Summary Compositions of the hydrous melts in equilibrium with garnet, omphacitic clinopyroxene and quartz have been investigated experimentally at 28.5 and 35 kbar. They are represented by silica-rich liquids (&amp;gt; 70% SiO2) with low MgO, FeO and CaO contents. The removal of ca 10–15% of the magma of this composition may be sufficient to convert quartz eclogite formed after subduction

Journal of Geophysical Research, 1980

The phase relations of low quartz, high quartz, and coesite were reinvestigated using extremely p... more The phase relations of low quartz, high quartz, and coesite were reinvestigated using extremely pure SiO2. The study was conducted with a piston-cylinder apparatus employing low-friction cells. While the low quartz-coesite transition between 600 ø and 1100øC was determined by conventional quench techniques, the greater portion of this study relied on in situ methods (differential thermal analysis and a volumetric method referred to as differential pressure analysis). The agreement with previous results is good; however, the precision of present data is considerably higher. A comparison of our salt-cell data with the raw data of previous studies shows a pressure loss due to friction of about 10% for talc cells. A discussion of thermochemical aspects of the low quartz-coesite transition indicates improved agreement between thermodynamic and experimental data. Reconnaissance data on the influence of the NaAIO2 component show above 600øC in the absence of H20 a considerable shift of the quartz-coesite boundary toward higher pressure (4 kbar at 1100øC). In the presence of H20 a partial liquid is formed, and the shift is reversed; the transition boundary is reduced 3 kbar and lies between 680 ø and 1000øC at even lower pressure than that of the pure SiO2 modifications.

To arrive at a better understanding of the processes that produce thermal effects on stone object... more To arrive at a better understanding of the processes that produce thermal effects on stone objects, a PhD thesis has been performed at the Institute of Mineralogy and Petrography, University of Innsbruck on regionally important tyrolean and south tyrolean natural stone such as granite, porphyry, sandstone, marble and limestone. The objective was to observe the many processes that occur within a temperature range of 200°C to 1000°C and result in damage or alteration to the various rock types. Some of the methods employed, such as microscopy, spectroscopy, pressure testing and gravimetry have normative characteristics. That made it possible to determine technical, petrophysical and materials science parameters. The results of these temperature experiments showed that the development of cracks and discoloration were the most common macroscopic changes to stone caused by fire. Other physical changes noted included very pronounced changes in the petrophysical characteristics of the rocks...

Mineralogy and Petrology, 2017

The aim of this experimental study was to investigate the incorporation of Na in cordierite in me... more The aim of this experimental study was to investigate the incorporation of Na in cordierite in metapelites as a function of temperature and pressure using natural quartzphyllite rocks as starting materials. The experiments were performed in a hydrothermal apparatus as well as a piston-cylinder apparatus with two natural quartzphyllite samples, which represent the protolith rocks of the hornfelses from the Brixen Granite contact aureole near Franzensfeste. Sample W shows high muscovite contents (57 wt%) and only accessory plagioclase while sample SP5 has high plagioclase (16 wt%) and lower muscovite contents (20 vol%). The experiments were done dry at pressures of 0.15, 0.3 and 0.6 GPa in a temperature range of 550 °C to 780 °C. The Na content of the newly formed cordierites shows a systematic variation and decreases linearly with increasing temperatures and no influence of pressure and melting on the Na contents of cordierite was observed. The experiments also show that the difference in mineral assemblage considerably shifts the obtained Na contents of cordierite. The P-independent temperature correlations for both sets of experiments can be described with the linear relationships: T (°C) = (Na [apfu] -0.4052)/ (-0.000487); R 2 = 0.96; (±20 °C, calibration W) and T (°C) = (Na [apfu] -0.3671)/(-0.000383); R 2 = 0.94; (±15 °C, calibration SP5). The difference between the two temperatures is large and the SP5 experiments yield temperatures that are up to 100 °C higher. This is not unexpected since theoretical phase relations in the system NMASH predict different Na contents depending on the buffering assemblage (plagioclase vs. paragonite). On the other hand these T differences could also reflect disequilibrium behaviour in the SP5 experiments. Detailed micro-Raman spectroscopic investigations reveal that cordierites from both experiments show disordered structures but the SP5 experiments show a much higher degree of Si-Al disorder and the elevated Na contents could reflect this disequilibrium behaviour. Preliminary geothermometric calculations using the data from the W experiments are in very good agreement with T estimates from conventional geothermometry in metapelitic contact aureoles as well as high-grade migmatic gneisses from the literature.

Electrical conductivity of calcite between 300 and 1200/sup 0/C

Eos Trans Am Geophys Union, Dec 1, 1976

Recent high-pressure work on the phase relations of CaCO/sub 3/ revealed two high-temperature tra... more Recent high-pressure work on the phase relations of CaCO/sub 3/ revealed two high-temperature transitions of calcite located at one atmosphere at 800 and 990/sup 0/C resp. Extending Bridgman's terminology (1939) these high-temperature phases are referred to as calcite IV and calcite V. Structural considerations suggest anion disorder as the transition mechanism. The experiments were conducted with a conventional two Pt-electrode arrangement under some 50 atm CO/sub 2/ pressure, employing dc (10 V) as well as ac (10 to 60 V/50 Hz). Cleavage fragments of calcite single crystals served as samples. According to the relation delta = delta/sub 0/ exp -E/kT the conductivities and activation energies for different temperature intervals were calculated. These data, additionally supported by measurements of the emf-polarity, suggest that the intrinsic conduction of calcite above 800/sup 0/K may rely mainly on anionic disorder. The almost pressure independent conductivity interval between 1075 to 1175/sup 0/K insinuates a critical disorder state of the calcite IV phase. This tentative interpretation seems to be supported by the behavior of the unit cell parameters and the intensity of reflections specific for CO/sub 3/-groups obtained from high-temperature x-ray powder photographs.

Determination of Melting Entropy by the Measurement of the Volume Change of Melting at High Pressure

High-Pressure Science and Technology, 1979

The determination of phase transitions at high pressures and high temperatures represents an area... more The determination of phase transitions at high pressures and high temperatures represents an area of major interest in highpressure research. To date such investigations have been mostly confined to locating the p-T coordinates of the phase boundary studied. Quantitative assessments of changes in the properties of State associated with the transition have been very rare.

Physics and Chemistry of Minerals, 1981

Thermal expansion measurements on synthetic orthorhombic Mg-cordierite ("low cordierite"), Mg2A14... more Thermal expansion measurements on synthetic orthorhombic Mg-cordierite ("low cordierite"), Mg2A14SisO1 s, were carried out with a high-temperature X-ray Guinier camera. The measurements confirm previous studies reporting low thermal expansion and suggesting a closer relationship with ring rather than framework silicates. No indication for structural modifications correlated with symmetry changes was observed. However, two discontinuities in the thermal expansion function at 275 _+ 25 ° and 600+50°C were detected and are assumed to represent higher-order phase transitions. The first discontinuity is related to a minimum in specific volume, implying unusual expansion behavior (negativ thermal coefficient) at low temperatures. An estimate of the dP/dT-slope of the established discontiniuties yields a positive sign for the one at 275 ° C and a negative one for that at 600 ° C.

Mineralogy and Petrology, 2009

The Ordovician Kellerjochgneiss (Schwaz Augengneiss) is a polymetamorphic orthogneiss-bearing uni... more The Ordovician Kellerjochgneiss (Schwaz Augengneiss) is a polymetamorphic orthogneiss-bearing unit and is part of the Austroalpine basement nappes north of the Tauern Window. Within the Kellerjochgneiss a small, strongly deformed metapegmatite dike occurs. The pegmatite crosscuts the gneiss discordantly and contains the mineral assemblage muscovite 1,2+plagioclase+ K-feldspar+chlorite+quartz+garnet 1 (Alm 67-76 Andr 0.9- 2 Sps 17-28 Prp 0.4-5 )+garnet 2 (Grs 36-46 Alm 24-32 Andr 8- 21 Sps 15-17 Prp 0-1 )±stilpnomelane±biotite±clinozoisite. The magmatic protolith assemblage is comprised of relict K-feldspar, quartz and garnet 1. Textural observations indicate that biotite and muscovite cores (muscovite 1) are either part of the magmatic-or an earlier (Variscan?) metamorphic assemblage. Geothermobarometry of the metapegmatite was done on the latest-stage (Eo-Alpine) mineral assemblage garnet 2+muscovite 2+chlorite+stilpnomelane+ plagioclase+quartz. Calculations of H 2 O-absent intersections in the system [KCNFMAS] with the multi-equilibrium program THERMOCALC v.3.1 yielded P-T estimates of 4.4 to 6.7 kbar and 321°C to 376°C. Calculations of the P-T conditions by using the assemblage muscovite 2+ chlorite+stilpnomelane+quartz yielded slightly higher pressures of 6.4 to 7.2 kbar at temperatures of 310-325°C. Correlating these P-T data with geochronological data from the neighbouring lithologies (Kellerjochgneiss, Innsbruck Quartzphyllite, Wildschönau Schists) and with structural investigations from these units indicate that the P-T estimates obtained in this investigation represent the Eo-Alpine metamorphic overprint. Hence, these unusual rocks provide important information on the Eo-Alpine P-T conditions since most samples studied from the investigated Austroalpine basement nappes north of the Tauern Window rarely contain mineral assemblages suitable for geothermobarometry.

Journal of Physics and Chemistry of Solids, 1976

ABST-RACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLiDS vii ionic crystals together with an illus... more ABST-RACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLiDS vii ionic crystals together with an illustrative application, optical rotation in mixed crystals of NaC1O 3--NaBrO3 of Frequency splittings originating from Coulomb inter-different compositions. actions between induced dipoles are explained satis-Received 21 August 1975 factorily by the calculations. Important discrepancies remaining in rigid-ion treatments are considerably 11. MELTING TEMPERATURE OF LEAD AND reduced by taking into account the electronic polariz-SODIUM AT HIGH PRESSURES abilities. Some effects of anisotropy of the ionic polarizabilities on crystal vibrations are discussed briefly.

The Journal of Chemical Physics, 2008

The system CaSO4–H2O, characterized by the three dehydration reactions gypsum-anhydrite, gypsum-b... more The system CaSO4–H2O, characterized by the three dehydration reactions gypsum-anhydrite, gypsum-bassanite, and bassanite-anhydrite, was reexamined by in situ differential pressure analysis in the temperature range of 60–350°C up to 3.5GPa pressure. The investigation revealed a fine structure in the dehydration boundaries of gypsum-bassanite and bassanite-anhydrite, each characterized by three inflections at 0.9–1.0, 1.9–2.0, and 2.6–28GPa. In addition, the phase transition of anhydrite high pressure anhydrite (monazite structure) was established for the first time at high P-T conditions intersecting the bassanite-anhydrite dehydration boundary at 2.15GPa∕250°C. Furthermore, the triple point gypsum-bassanite-anhydrite was redetermined with 235MPa∕80.5°C. The evaluation of the gypsum-bassanite dehydration boundary with respect to the volume and entropy change of the reaction, ΔVreact and ΔSreact, by means of the Clausius–Clapeyron relation yields for the entropy parameter an unusually...

The fine-structure of the dehydration boundary of brucite (Mg(OH)2) up to 3.5 GPa - indication of anomalous PVT behaviour of supercritical H2O

European Journal of Mineralogy, 2005

ABSTRACT Liquid and supercritical H2O, the most abundant and important non-crystalline component ... more ABSTRACT Liquid and supercritical H2O, the most abundant and important non-crystalline component in rock forming processes, is assumed to exhibit continuous PVT behaviour at high pressures and temperatures. However, a number of experimental observations at high pressure and temperatures challenges this concept. Direct measurements of PVT properties of H2O at supercritical conditions are very difficult. Information on the PVT behaviour at these P-T conditions may be gained by certain dehydration reactions. An experimental re-examination of the reaction Mg(OH)(2) (brucite)=MgO (periclase)+H2O has been conducted between 0.4 to 3.5 GPa and 650 to 1200 degrees C. The study was performed with a piston cylinder apparatus using the in-situ differential pressure analysis (DPA)-technique. The data reveal that the P-T slope of the equilibrium boundary is not continuous but exhibit a fine-structure which is characterised by three inflections at 1.1 GPa/830 degrees C, 1.9 GPa/945 degrees C and 2.7 GPa/1040 degrees C. Because the solid phases, Mg(OH)(2) and MgO, exhibit no structural changes at these conditions, these effects are thought to be due to anomalous PVT behaviour of supercritical H2O.

Isothermal compression of low-cordierite to 30 kbar (25� C)

Physics and Chemistry of Minerals, 1984

ABSTRACT

The study presents a re-examination of the dehydration reaction diaspore to corundum + H2O betwee... more The study presents a re-examination of the dehydration reaction diaspore to corundum + H2O between 450° − 600° C in the pressure range 1 to 3 GPa. The high-pressure study bases on differential pressure analysis and simultaneous monitoring of piston displacement performed in a piston-cylinder apparatus. In quasi-isobaric runs the reaction of dehydration and re-hydration is documented by a temperature interval of about 30° width indicating that the reaction is affected by kinetics. In contrast to previous studies which explored the pressure range up to 5 GPa, the re-examined boundary is not presented by a smooth curve, but is structured by pressure anomalies at 1.0, 1.8 and 2.75 GPa. Literature data suggest further anomalies in the pressure range below 1.0 GPa, at 200 and 400 MPa. Comparison with earlier dehydration studies shows a striking similarity in this respect, and suggest a largely temperature independent general system of high-pressure anomalies. Literature examples show that...

Journal of Geophysical Research, 1979

We have completed a study of the ferromagnetic-paramagnetic phase transition (Curie transition) a... more We have completed a study of the ferromagnetic-paramagnetic phase transition (Curie transition) and the •-¾ phase transition in iron by differential thermal analysis. The investigation was carried out in a pistoncylinder apparatus to 53 kbar. A low-friction cell was employed that allowed the phase transitions to be detected by monitoring the change in compressibility. The f erromagnetic-paramagnet ic phase boundary was found to have a small negative slope and to intersect the •-¾ phase boundary in a triple point at 20 * 1.2 kbar. The precision of the measurements is discussed.

Historic Mortars, 2012

Reaction rims of natural hydraulic relicts in historic mortars were investigated using a novel te... more 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 1.0μm. IR spectra show two regions with main absorption bands at 1280-1580cm-1 and 900-1120cm-1. Bands at 1450cm-1 and 1396cm-1 correspond to the asymmetric stretching of CO 3 2-, indicating two different forms of CaCO 3 ; the 900-1120cm-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. Our investigation shows that the reaction rims consist of CaCO 3 , C-S-H phases and SiO 2 gel in variable proportions. In areas with low carbonate-to-C-S-H phase ratios, carbonate is mainly present as metastable aragonite. The associated C-S-H phases show a comparatively low Ca/Si ratio and a high degree of polymerization. In areas with high carbonate-to-C-S-H phase ratios, both, aragonite and calcite are present. The C-S-H phases show a comparatively higher Ca/Si ratio combined with a lower degree of polymerization. The presence of SiO 2 gel and aragonite indicate carbonation of C-S-H phases. The matrix outside of the cloudy reaction rim consists mainly of calcite. FTIR imaging measured in ATR-mode is a promising method to gain information on the hydraulicity of natural hydraulic mortars in its spatial distribution on a micrometer scale and to characterize the hydration and carbonation products as well.