Maria Perraki

Raman spectroscopic and microscopic criteria for the distinction of microdiamonds in ultrahigh-pressure metamorphic rocks from diamonds in sample preparation materials

Abstract Natural diamond from three ultrahigh-pressure metamorphic (UHPM) terranes (Erzgebirge Massif, Germany; Kokchetav Massif, Northern Kazakhstan; Rhodope Metamorphic Province, Greece) and synthetic diamond from cutting and polishing materials (paste, spray, saw blade) were studied by means of optical microscopy and Raman microspectroscopy, to constitute a new petrographic and spectroscopic data set that might be a useful tool for identifying and characterizing metamorphic diamond. Several criteria are established for distinguishing natural microdiamond identified in a rock thin section from the externally introduced ones [i.e., diamond as residual particles (contaminants) from the cutting and polishing material] such as the diamond size, the presence of inclusions, coatings, or coexistent phases and two diamond Raman band parameters, i.e., the Raman shift and the full-width at half maximum height (FWHM).

Is quartz a potential indicator of ultrahigh-pressure metamorphism? Laser Raman spectroscopy of quartz inclusions in ultrahigh-pressure garnets

Laser Raman microspectroscopy was applied to quartz inclusions in coesite- and diamond-grade metapelites from the Kokchetav ultrahigh-pressure metamorphic (UHPM) complex, Northern Kazakhstan, and diamond-grade eclogite xenoliths from the Mir kimberlite pipe, Yakutiya, Russia to assess the quantitative correlation between the Raman frequency shift and metamorphic pressure. Quartz crystals sealed in garnets have a higher frequency shift than those in the matrix. Residual pressures retained by quartz inclusions depend on the metamorphic history of the garnet host. The Raman frequency shift of quartz inclusions in garnet from coesite-grade and diamond-grade metamorphic rocks shows no systematic change with increasing peak metamorphic pressures. The highest shifts of the main Raman bands of quartz were documented for monocrystalline quartz inclusions in garnets from a diamond-grade eclogite xenolith. Calibrations based on experimental work suggest that the measured Raman frequency shifts signify residual pressures of 0.1–0.6 GPa for quartz inclusions from coesite-grade metapelites from Kokchetav, 0.1–0.3 GPa for quartz inclusions from diamond-grade metapelites from Kokchetav, and 1.0–1.2 GPa for quartz inclusions from the diamond-grade eclogite xenoliths from the Mir kimberlite pipe. Normal stresses and internal (residual) pressures of quartz inclusions in garnet were numerically simulated with a 3-shell elastic model. Estimated values of residual pressures are inconsistent with the residual pressures estimated from the frequency shifts. Residual pressure slightly depends on P–T conditions at peak metamorphic stage. Laser Raman microspectroscopic analysis of quartz is a potentially powerful method for recovering an ultrahigh pressure metamorphic event. Monocrystalline quartz inclusions yielding a residual pressure greater than 2.5 GPa might indicate the presence of a former coesite.

Aragonite-calcite-dolomite relationships in UHPM polycrystalline carbonate inclusions from the Kokchetav Massif, northern Kazakhstan

The presence of aragonite in polycrystalline carbonate inclusions in garnet in diamond-grade metamorphic rocks from the Kokchetav Massif, N. Kazakhstan was identified for the first time by means of Raman analyses and mapping, cathodoluminescence images and optical and scanning electron microscopy. Aragonite appears within the inclusions as dirty, chaotically oriented materials surrounded by a clean monocrystalline calcite shell; the grain boundary between the host-garnet and the aragonite-bearing inclusions is often characterized by a wavy or amoeboid shape; no cracks occur around the aragonite-bearing inclusions; no significant shift in the main aragonite Raman band was measured. These observations indicate that residual pressure within the inclusion is minor. These features are inconsistent with an origin of aragonite at peak metamorphic conditions (6 GPa) by decomposition of dolomite.

Secondary raw materials in cement industry

The sintering and hydration processes of a modified cement raw mix were examined using thermal analysis techniques. One reference and four modified mixtures, prepared by mixing the reference sample with 0.5, 1.0, 1.5 and 2.0 % w/w of a wolframite-stibnite mineral were studied. The clinkering reactions were recorded and the total enthalpy change during the sintering was determined by means of a differential scanning calorimetry. The combined water and the Ca(OH)2 content in samples hydrated for 1 to 28 days were determined, using thermogravimetry. As it is concluded, the effect of the added mineral on the sintering and hydration reactions can be fully recorded and evaluated using thermal analysis.

First findings of monocrystalline aragonite inclusions in garnet from diamond-grade UHPM rocks (Kokchetav Massif, Northern Kazakhstan)

The presence of aragonite inclusions in garnet from diamond-grade metamorphic rocks from the Kokchetav Massif, Northern Kazakhstan was identified for the first time by means of Raman analyses and mapping. Aragonite appears within the inclusions up to 50 μm in size as a single crystal. These inclusions have rounded shape. The grain boundary between the host-garnet is smooth. No cracks occur around the aragonite inclusions. No significant shift in the main aragonite Raman band was measured. These observations indicate that residual pressure within the inclusion is minor. These findings imply either non-UHPM origin of the host garnet or significant plastic deformation of host minerals during retrograde stage. These features should be taken into account for recovery peak metamorphic conditions and modeling of exhumation processes of UHPM complexes.

Single and multiphase inclusions in metapelitic garnets of the Rhodope Metamorphic Province, NE Greece.

Single and multiphase inclusions in garnet porphyroblasts from the diamond-bearing pelitic gneisses were studied by means of combined Raman Spectroscopy and Electron Scanning Microscopy (SEM/EDX). They are either randomly distributed or with preferred orientation within the garnet host and their dimensions vary from less than 5 up to 60 microm. In the single-phase inclusions quartz, rutile, kyanite and graphite dominate. Biotite, zircon, apatite, monazite and allanite are also common. Two types of multiphase inclusions were recognized, hydrous silicate (Type I) and silicate-carbonate (Type II) ones. The carbon-bearing multiphase inclusions predominantly consist of Mg-siderite+graphite+CO(2)+muscovite+quartz formed by a high density carboniferous fluid rich in Fe, Mg, Si and less Ca, Mn, Al and K trapped in the growing garnet in a prograde stage of metamorphism at high-pressure (HP) conditions. The carbon-free multiphase inclusions predominantly consist of biotite+quartz+rutile+/-kyanite+muscovite formed through decompression-dehydration/melting reactions of pre-existing phengite. Single and multiphase inclusions are characterized by polygonal to negative crystal shape formed by dissolution-reprecipitation mechanism between the garnet host and the inclusions during the long lasting cooling period (>100 Ma) of the Kimi Complex.

Brown diamonds from an eclogite xenolith from Udachnaya kimberlite, Yakutia, Russia.

We have performed petrographic and spectroscopic studies of brown diamonds from an eclogite xenolith from the Udachnaya pipe (Yakutia, Russia). Brown diamonds are randomly intermixed with colorless ones in the rock and often located at the grain boundaries of clinopyroxene and garnet. Brown diamonds can be characterized by a set of defects (H4, N2D and a line at 490.7 nm) which are absent in colorless diamonds. This set of defects is typical for plastically deformed diamonds and indicates that diamonds were likely annealed for a relatively short period after deformation had occurred. Excitation of brown colored zones with a 632.8 nm He-Ne laser produced the typical diamond band plus two additional bands at 1730 cm(-1) and 3350 cm(-1). These spectral features are not genuine Raman bands, and can be attributed to photoluminescence at ∼710 nm (1.75 eV) and ∼802 nm (1.54 eV). No Raman peak corresponding to graphite was observed in regions of brown coloration. Comparison with previous reports of brown diamonds from eclogites showed our eclogitic sample to have a typical structure without signs of apparent deformation. Two mechanisms with regard to diamond deformation are proposed: deformation of eclogite by external forces followed by subsequent recrystallization of silicates or, alternatively, deformation by local stress arising due to decompression and expansion of silicates during ascent of the xenolith to surface conditions.

Synthesis and Characterization of Nitrogen Doped Carbon Nanotubes

The present work describes the synthesis of nitrogen doped multi-walled carbon nanotubes (CNx CNT). The chosen production method was the catalytic pyrolysis of a solid mixture containing [Ni(DMG)2] and melamine (C3H6N6), under an Αr atmosphere. A series of various experiments were performed, using different proportions of the reaction mixture, in order to optimize the production conditions of nitrogen doped carbon nanotubes. Finally, the produced materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), Raman spectroscopy as well as thermogravimetric analysis (TGA). The obtained data from all the above analyses, showed the formation of nitrogen doped carbon nanotubes of various diameters as well as nanofibers surrounded by byproducts such as aggregations of amorphous carbon and metallic catalyst, depending on the proportion of the reaction mixture.

The Effect of Synthesis Parameters on the Structure and Properties of Metakaolin Based Geopolymers

In the present work the geopolymerisation of metakaolin under varying conditions is investigated.The experimental part comprises the following parts: i) the synthesis of metakaolin based geopolymers and the investigation of the effect of the Si/Al ratio and the kind of alkali ion on the development of the compressive strength and ii) the characterization of the geopolymers by means of XRD, FTIR and SEM. As it is found the development of the compressive strength is strongly affected by the Si/Al ratio in the starting material and the kind of alkali metal, with the maximum being 70.1 MPa for a Si/Al ratio equal to 2.00. The Na- geopolymers show higher compressive strength compared to the NaK-geopolymers. Finally, low Si/Al ratios favour the formation of crystalline compounds (mainly zeolites), while Si/Al ratios higher than 1.5 lead to the formation of amorphous materials.

Synthesis and Characterisation of Slag Based Geopolymers

In the present work the geopolymerisation of blast furnace slag (GGBS) under varying conditions is being investigated. The experimental comprises the following parts: i) dissolution of slag in alkaline media and the investigation of the effect of the alkali ion (K or Na) on the dissolution of Al+3 and Si4+, ii) synthesis of slag based geopolymers and the investigation of the effect of the Si/Al ratio and the kind of alkaline ion on the development of the compressive strength and iii) characterization of geopolymers by means of XRD, FTIR and SEM/EDS measurements. As it is concluded, blast furnace slag geopolymers exhibit high compressive strength, with the maximum being 112.7±2 MPa. The Si/Al ratio of the starting material is found to affect strongly the development of the geopolymer compressive strength. The microstructure of slag–based geopolymers and the incorporation of Ca in the geopolymer matrix are also discussed.