Hiroyuki Kagi

Changes in the structure of water deduced from the pressure dependence of the Raman OH frequency.

We report on the Raman spectra of water under high temperature and pressure conditions and show a discontinuity in the pressure dependence of the OH stretching frequency. As pressure increases, the strength of hydrogen bonding increases rapidly in the pressure ranges up to 0.4+/-0.1 GPa at 25 degrees C, 1.0+/-0.1 GPa at 100 degrees C, and 1.3+/-0.1 GPa at 300 degrees C and slowly above these pressures. This finding clearly demonstrates the existence of discontinuities in the pressure response of the hydrogen bonds of water, which suggests a possible structural change under these conditions.

Direct observation of tetravalent cerium in ferromanganese nodules and crusts by X-ray-absorption near-edge structure (XANES)

Abstract X-ray-absorption near-edge structure (XANES) was successfully applied for the direct determination of Ce valence in hydrogenetic ferromanganese nodules (two samples) and crust (one sample). Rare earth element (REE) patterns of the hydrogenetic ferromanganese nodules and crust recovered from the Pacific Ocean show large positive Ce anomalies, especially when normalized to seawater. Despite some disadvantages in the spectroscopic analysis of Ce in natural samples (e.g., low concentration and interference from other elements), intense synchrotron radiation and measurement of fluorescent XANES with semiconductor detectors having high energy resolution enabled us to detect XANES at Ce L III edge in the ferromanganese nodule or crust. In the XANES spectra of the nodule or crust, large double peaks were observed, showing that the oxidation state of Ce in the nodule or crust is predominantly tetravalent with little contribution from Ce(III). This is the first in-situ quantitative analysis of Ce(IV) among total Ce in natural samples as a trace element as far as we know. The results obtained by XANES seem to be consistent with the percentage of Ce(IV) estimated from seawater-normalized REE patterns, suggesting that seawater is a precursor of REE in the marine deposits. The present results also confirm that Ce enrichment relative to other REEs in hydrogenetic ferromanganese deposits is due to oxidative removal of Ce from seawater to the ferromanganese nodules and crust in the marine environment. Comparison of XANES spectra of Ce sorbed on synthetic manganese oxide and CeO 2 vs. those of the ferromanganese nodules and crust suggests that the initial reaction of Ce with the ferromanganese nodules and crust is the sorption of dissolved Ce(III) to the manganese oxide surface.

Carbonatitic melts in cuboid diamonds from Udachnaya kimberlite pipe (Yakutia): evidence from vibrational spectroscopy

Abstract Micro-inclusions (1 −10 μm) in 55 diamonds of cubic habit from the Udachnaya kimberlite pipe have been studied using vibrational spectroscopy. This has revealed a multiphase assemblage in cuboid diamonds from the Udachnaya kimberlite pipe. This assemblage includes carbonates, olivine, apatite, graphite, water and silicate glasses. The micro-inclusions preserve the high internal pressure and give confidence that the original materials were trapped during growth of the host diamond. The internal pressures, extrapolated to mantle temperatures, lie within the stability field of diamond and the relatively low temperatures are typical for the formation of cuboid diamonds. In contrast to previously reported data for African diamonds, the micro-inclusions in the cuboids from Udachnaya are extremely carbonatitic in composition (H2O/(H2O+CO2) ≈5−20%) with the observed assemblage of microinclusions similar to some types of carbonatites. The low water and silica content testify that the material in the micro-inclusions of the Udachnaya diamonds was near-solidus carbonatitic melt. Vibrational spectroscopy has provided the evidence of carbonatitic melts in cuboid diamonds.

Micro-Raman Densimeter for CO2 Inclusions in Mantle-Derived Minerals

We investigated the applicability of Raman microprobe spectroscopy for determining the density of CO2 in fluid inclusions in minerals of mantle-derived xenolith samples. A separation (Δ) between two Raman bands of CO2 due to Fermi resonance can be a reliable densimeter for CO2 fluid. The relationship between the density of CO2 (g/cm3) and Δ(cm−1) can be expressed as: d = −0.03238697Δ3 + 10.08428Δ2 – 1046.189Δ + 36163.67. This equation was obtained from the Raman data on CO2 fluid with densities from 0.1 to 1.21 g/cm3, including super critical fluids at 58–59 °C. The Δ value was constant with increasing temperature from room temperature to 200 °C. This indicates that the Raman densimeter is not affected by a possible rise in temperature, an artifact induced by the high flux of the incident laser. The minimum size of measurable inclusions is 1 μm, and the precision in the determination of Δ is 0.1 cm−1, corresponding to 0.02 g/cm3 for inclusions of 1 μm in size. The precision can be better for larger inclusions. The micro-Raman densimeter can determine the density of CO2 fluid inclusions over a wide range. In particular, densities of gas and mixtures of gas and liquid phases, which cannot be measured by microthermometry, can be determined.

Proper understanding of down-shifted Raman spectra of natural graphite: Direct estimation of laser-induced rise in sample temperature

Laser-induced heating during micro-Raman spectroscopy, in some cases, gives rise to considerable down-shifts in Raman spectra of powder graphite samples. Employing the most typical experimental condition for graphitic matter of geochemical and/or cosmochemical interest, 10 mW laser power at the sample surface and ~2 μm laser beam, powdered artificial graphite samples revealed the E2g mode in low Raman peak position ranging from 1567 to 1576 cm−1. The energy range agrees very well with the previously reported frequency range for anomalously down-shifted Raman spectra of natural graphites. In order to extract spectroscopic information inherent in samples from the E2g frequency, it is essential to remove the laser-induced down-shift and to know the temperature of sample surface. We showed that the intensity ratio of the Stokes line to the anti-Stokes line for the E2g Raman band of graphite is potential to monitor the temperature of graphite surface. Furthermore, our measurement employing enough low laser power without laser-heating showed that natural graphite sample containing the rhombohedral polymorph exhibited the same G-band frequency as the E2g (1582 cm−1) frequency of hexagonal graphite. Thus, stacking sequences of graphite did not affect the intralayer vibrational energy.

Fossil pressures of fluid inclusions in mantle xenoliths exhibiting rheology of mantle minerals: implications for the geobarometry of mantle minerals using micro-Raman spectroscopy

Abstract Micro-Raman spectroscopic analysis allows us to estimate the internal pressure of small fluid inclusions. We applied this method to CO2-dominated fluid inclusions in mantle-derived xenoliths. The pressures estimated from the equilibration temperature and density of the fluid range from 0.96 to 1.04 GPa corresponding to depths of up to 30 km, which confirms that these rocks and fluids are of uppermost mantle origin. Furthermore, the inclusions show pressures specific to the individual host minerals (spinel≥orthopyroxene≈clinopyroxene≫olivine). In particular, the densities of CO2 in pyroxenes are 10% higher than in olivine. Such an enormous difference cannot be explained by elastic deformation of the minerals during ascent of the xenoliths, although the process may explain the slightly higher density of CO2 in spinel. During the ascent, the strain rate of orthopyroxene calculated using the ‘constitutive equation’ is several orders of magnitude lower than that of olivine. The difference in densities of CO2 among the host mineral species is therefore attributable to the rheological properties of the minerals. Present internal pressures of fluid inclusions can be a sensitive strength marker of mantle minerals. Conversely, the density of CO2 inclusions in pyroxene (and spinel) may be a useful geobarometer.

Infrared study of human serum very-low-density and low-density lipoproteins. Implication of esterified lipid CO stretching bands for characterizing lipoproteins

Fourier-transform infrared (FT-IR) spectroscopy was applied to examine human serum very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) in aqueous solution and in solid film for characterizing lipid components. On the basis of the FT-IR second-derivative spectra for standard samples of triglycerides, cholesterol esters and phospholipids, it was found that the band at 1746 cm(-1) for VLDL and the band at 1738 cm(-1) for LDL were mainly due to the unsaturated triglycerides and unsaturated cholesterol esters, respectively. The implications of ester C=O stretching bands are discussed.

Change in compressibility of δ-AlOOH and δ-AlOOD at high pressure: A study of isotope effect and hydrogen-bond symmetrization

Abstract The compression behaviors of δ-AlOOH and δ-AlOOD were investigated under quasi-hydrostatic conditions at pressures up to 63.5 and 34.9 GPa, respectively, using results from synchrotron X-ray diffraction experiments conducted at ambient temperature. Because of the geometric isotope effect, at ambient pressure, the a and b axes of δ-AlOOD, which define the plane in which the hydrogen bond lies, are longer than those of δ-AOOH. Under increasing pressure, the a and b axes of δ-AlOOH stiffen at 10 GPa, although the c axis shows no marked change. Identical behavior was found in δ-AlOOD, but the change in compressibility was observed at a slightly higher pressure of 12 GPa. Axial ratios a/c and b/c first decrease rapidly with increasing pressure, then begin to increase at pressures >10 GPa in δ-AlOOH and >12 GPa in δ-AlOOD. At these pressures, the pressure dependence of a/b also changes from increasing to decreasing. The unit-cell volumes of δ-AlOOH and δ-AlOOD become slightly less compressible at high pressures. Assuming K0′ = 4, the calculated bulk moduli of δ-AlOOH below and above 10 GPa are 152(2) and 219(3) GPa, respectively. Those of δ-AlOOD below and above 12 GPa are 151(1) and 207(2) GPa, respectively.

Experimental alteration of molybdenite: evaluation of the Re–Os system, infrared spectroscopic profile and polytype

Experiments have been carried out to clarify the effect of alteration on Re–Os system, near infrared (NIR)–infrared (IR) spectroscopic characteristics and polytype of a natural molybdenite mineral (MoS2). The molybdenite sample was placed in H2O and various media of 0.1 mol/L NaCl, NaHCO3, CaCl2, and AlCl3 solutions, and heated in a sealed quartz tube at a temperature of 180°C for 20 d. The unaltered and altered samples were subsequently used for analysis of Re and Os, NIR microscopic observation, and NIR–IR spectroscopy, and microfocus X-ray diffraction (XRD). Molybdenites subjected to NaCl and NaHCO3 solutions give younger Re–Os ages than that of the original unaltered molybdenite. No significant changes in d spacing and width of micro-XRD patterns can be found in these altered molybdenite, indicating the possibility of Re–Os fractionation without significant structural conversion of molybdenite mineral. These results strongly suggest that the Re–Os system in molybdenite would be frequently disturbed if it has experienced alteration, because alteration by the low salinity (<1%), low temperature (∼180°C) hydrothermal solution containing NaCl and/or CO2 is commonly found in the natural environment. We maintain, therefore, that one set of analyses of Re and Os in a sample is not enough to determine whether the obtained Re–Os age has been affected by postdepositional alteration, but systematic replicate analyses are indispensable. Additionally, pulverizing all the collected molybdenite in a sample might give misleading results because portions, which have been altered and experienced Re–Os fractionation, may possibly mix into the undisturbed sample and be homogenized. The molybdenite used for the experiment was originally opaque under NIR light. Infrared microscopic and spectroscopic profiles show that some parts of the molybdenite subjected to CaCl2 and AlCl3 solutions become transparent to NIR. Increased NIR transmittance is possibly attributed to the removal of the impurity band in molybdenite. It was also found in this study, however, that change in IR profile does not correlate with the Re–Os fractionation and, therefore, IR measurement solely is not useful to detect disturbance of Re–Os systematics of molybdenite in alteration.

Chemical properties of Central African carbonado and its genetic implications

Abstract Carbonado diamonds from Central African Republic exhibit very intense laser-induced photoluminescence due to the presence of the radiation damages. From the spectral profiles of photoluminescence obtained for these samples, the carbonado stones were grouped into three groups depending on a variation in the structure of radiation-damage products; Group-A carbonado with 504 nm band (3H band), Group-B carbonado with 575 nm band in addition to weak background peaks centered at 512 and 580 nm, and the Group-AB carbonado with features intermediate between Group-A and Group-B. When heating Group-A carbonado, Group-A was found to transform to Group-B at temperatures higher than 400°C. Thermogravimetry and Differential Thermal Analysis (TG-DTA) clarified the difference in thermal properties between Group-A and Group-B. While Group-A carbonado yields one intense and narrow exothermic peak at 800°C, Group-B carbonado exhibits a broad exothermic peak at 785°C. The distinct difference in the oxidation rate could be attributed to the difference in the density of micropores in carbonado. Chondrite-normalized rare earth element (REE) patterns for the bulk carbonado samples show negative Eu anomalies, and the inclinations of the patterns are similar to those of kimberlites and much steeper than that of continental crust as represented by continental shales. In the chondrite-normalized value, La/Lu ratios were of the order of 10 2 and the light REE abundances were as high as 10 3 relative to chondrite. Further, 1384 cm −1 absorption band was observed in IR (infrared) spectra of both Group-A and Group-B, which suggests the presence of nitrogen platelet in carbonado. These REE and IR results imply that the seed crystal of carbonado was formed at high pressure and high temperature and was subjected to the annealing process to generate nitrogen platelets. The genesis of Central African carbonado is discussed as a reconciliation of these experimental results.