Mössbauer and mineral magnetic studies on archaeological potteries from Adhichanallur, Tamilnadu, India

Megalithic potteries collected from Adhichanallur, Tamilnadu, India (Lat. 8°44′ N; Long. 77°42′ E) have been subjected to various spectroscopic and rock magnetic studies. The type of clay, their origin, level of structural deformation due to firing, firing temperature and atmospheric condition followed during making the potteries are analyzed. The potteries were subjected to Mössbauer and X-ray diffraction studies to analyze the iron phases in them. It is found that the samples were made of local clay (red clay), fired above 600°C under open atmospheric and/or reduced atmospheric conditions and air has been allowed during cooling. The Mössbauer spectra reveal the presence of Fe^3?+?, Fe^2?+? and iron oxides of hematite and magnetite. The firing temperature and firing conditions established from Mössbauer studies are similar to the observation made from FT-IR studies. The magnetic mineral types, the mass fractions and the domain states of the constituent magnetic grains were elucidated from a range of rock magnetic measurements including variation of susceptibility with low field, frequency and temperature, hysteresis parameters and isothermal remanence acquisition data. The magnetic mineralogy of most pottery samples was dominated by magnetite/(titano) magnetite, while magnetic grain size spectrum varies from very fine (super paramagnetic) to fine (stable single domain, pseudo single domain). The reversible thermo magnetic behavior reflects no mineralogical transformations during reheating and all the samples show same Curie temperature 580°C due to magnetite. From the above information it is demonstrated that these samples are suitable for determining the reliable ancient geomagnetic field intensity values existed during that period.     

Evidence for a weakening ‘dead zone’ in Tokyo Bay over the past 30?years

Weakened hypoxia in the past 30?years at a dredged area in Tokyo Bay was proven by the existence of amorphous hematite (α-Fe2O3) in sediments. The chemical states of iron in sediments can become a proxy for the scale of anoxia at the time of sedimentation. In 2009, we collected core sediments from a dredged area off Makuhari in Tokyo Bay that is very strongly anoxic in the summer. Every layer of the sediments was analysed by ⁵⁷Fe M?ssbauer spectroscopy and excess 210Pb dating, and amorphous hematite was identified in the sediments from the 1976–1979, 1986–1989 and 2006–2009 layers. Using an estimate based on the Eh-pH diagram optimized for the sedimental environment, the existence of hematite in the dredged area proves that the scale of hypoxia/anoxia is decreasing, and these results agree well with the observed dissolved oxygen level of the seawater mass.     

Evidence of Impact at the Permian/Triassic Boundary from Mössbauer Spectroscopy

Sediment samples from Spiti valley, India, deposited about 250 Million years ago during the Permian-Triassic transition, have been analysed. ⁵⁷Fe Mössbauer spectroscopic studies show that iron occurs mainly as nanoparticles of hematite and goethite with a broad size distribution. The results show a high degree of resemblance with the Cretaceous-Tertiary boundary (65 My) samples where an asteroidal impact is believed to have caused mass extinction.

     

Morin transition suppression in Polycrystalline 57Hematite (α-Fe2O3) exposed to 56Fe(II)

We used the isotope selectivity of ⁵⁷Fe Mössbauer spectroscopy to investigate changes in the magnetic properties of polycrystalline hematite exposed to ferrous iron (Fe(II)). We found that sorption of ⁵⁶Fe(II), followed by interfacial electron exchange, alters the bulk magnetic properties of ⁵⁷hematite. After reaction with ⁵⁶Fe(II), we observed partial suppression of the Morin transition of ⁵⁷hematite to below 13 K. This is significantly lower than the Morin temperature (T _M) of ～230 K measured for isotopically enriched polycrystalline ⁵⁷hematite, as well as the T _M of 264?±?2 K reported for normal polycrystalline hematite.     

Preparation and mechanism of formation of hematite particles in the Fe-HNO3 system

The mechanism of formation of hematite particles in the Fe-HNO₃ system is investigated by introduction of a small amount of PO₄³⁻ ions to the system. The intermediate species in the reaction, 6-line ferrihydrite, is successfully obtained. The transformation of 6-line ferrihydrite to hematite is investigated. The results show that Fe(II) in the Fe-HNO₃ system can catalyze the dissolution of 6-line ferrihydrite, leading to the rapid formation of hematite.     

Magnetic ordering of monoclinic FeNaP2O7 studied by Mössbauer spectroscopy

Several perlites of different colours originating from east Rhodope (Bulgaria) have been studied by Mössbauer spectroscopy. Several types of iron are revealed (i) paramagnetic Fe²⁺ and Fe³⁺ down 4.2K which correspond to iron dispersed into the glass matrix (ii) small aggregates of Fe²⁺ and hematite in colloidal type phase with superparamagnetic properties (iii) large aggregates and microlites of hematite and magnetite. Alteration effects and colour problem are discussed.     

Al‐for‐Fe substitution in hematite: the effect of low Al concentrations in the Raman spectrum of Fe2O3

Five different mixed Al‐hematites with an aluminium molar content varying from 0 to 10% were investigated by micro‐Raman spectroscopy to study the effect of Al‐for‐Fe substitution on the hematite lattice. A red shift of hematite vibrational wavenumbers and a line broadening were observed; also a shoulder located near 430 cm⁻¹ and a broad band at 670 cm⁻¹ developed. The variation of the spectral features is discussed in terms of a local disorder correlated to the insertion of Al³⁺ ions into the Fe(O)₆ octahedra constituting hematite structure. A multivariate analysis was also carried out on the spectral data to distinguish between the doped samples analysed. Copyright © 2007 John Wiley & Sons, Ltd.     

Mössbauer study of the firing technology of the moon-white Jun porcelain in Chinese Yuan Dynasty

The moon-white Jun porcelain glaze contains Fe₂O₃, Fe₃O₄ and structural iron. The firing atmosphere of ancient Jun kilns was modestly reductive. The firing temperature was slightly above 1250 C. The glaze color appears moon-white, and is related to the low concentration of Fe²⁺. The coordination numbers of Fe²⁺ and Fe³⁺ are both 4.     

X-ray photoelectron spectroscopy of fast-frozen hematite colloids in aqueous solutions. 4. Coexistence of alkali metal (Na+, K+, Rb+, Cs+) and chloride ions

Colloidal suspensions of hematite in contact with aqueous solutions of 50 mM alkali metal chloride electrolytes (NaCl, KCl, RbCl, CsCl) were investigated by cryogenic X-ray photoelectron spectroscopy (XPS) and electrophoretic mobility. Suspension pH values were varied from 2 to 11 in order to evaluate effects of positively- and negatively-charged hematite surfaces. XPS revealed coexisting cations and chloride ions both below and above the point of zero charge. Concentration profiles of adsorbed cations point to a Hofmeister series in the order of Na⁺ > K⁺ > Rb⁺ ≈ Cs⁺. Binding energies of photoelectrons emitted from electrolyte ions increased with pH at roughly 0.04 eV per pH unit. This shift was attributed to variations in the surface electric potential of hematite. This effect, compounded by rises in aliphatic carbon signals with pH, called for referencing of all spectra to the 530.0 eV oxide component of the hematite O1s spectrum. This departure from the traditional use of the external C 1s 285.0 eV peak is hereby proposed for cryogenic XPS studies of interfacial reactions involving hematite.     

Firing-Induced Microstructural Properties of Quasi-Diamagnetic Carbonate-Based Porous Ceramics: a <Superscript>1</Superscript>H NMR Relaxation Correlation Study

This study deals with the application of two-dimensional proton nuclear magnetic resonance relaxometry (2D ¹H NMR-R) to the characterization of porous ceramics nearly free of magnetic compounds. Different microstructural properties were obtained by firing a diamagnetic mixture of kaolin, calcium, and magnesium carbonate over a wide range of maximum temperatures (600–1100 °C) and firing times at the maximum temperature (soaking times) (0–10 h). The 2D ¹H NMR-R method relies on the correlated measurement of ¹H longitudinal (T ₁) and transverse (T ₂) relaxation times of pore-filling water by which the properties of the interconnected pore space may be investigated. In the absence of significant magnetic susceptibility effect due to para- and ferro-magnetic compounds, the 2D ¹H NMR-R maps allow studying the conjoint effects on pore size distribution and inter-pore coupling due to the variations in both time and temperature of firing. The NMR experiments were performed with a low-field ¹H NMR sensor, which allows non-destructive and in situ analysis. For ceramic specimens fired at 600 and 700 °C, the fraction of smallest pores increases with firing time at the expenses of those with intermediate size. The pore shrinkage occurring at this stage, and likely associated with the transformation of kaolinite in metakaolinite, is affected in a similar way by soaking time and firing temperature, in line with the concept of equivalent firing temperature. At temperatures from 800 to 1100 °C, the structural modifications involving interconnectivity and average pore size are driven primarily by firing temperature and, secondarily, by soaking time. The 2D ¹H NMR-R results are confirmed by more traditional, but destructive, mineralogical, and structural analyses like X-ray powder diffraction, helium pycnometry, mercury intrusion porosimetry, and nitrogen adsorption/desorption method.     

Pigments and enamelling/gilding technology of Mamluk mosque lamps and bottle

On‐site Raman spectroscopy is used to investigate four mosque lamps and a bottle dating back to the 13–14th centuries (Syria and/or Egypt, Mamluk period) from the Department of Islamic Art, Musée du Louvre, Paris. The pigments and the enamelled glass matrix have been identified in order to discuss their technology. A comparison is made with one masterpiece from the 19th century made by Brocard. The results obtained for blue (lapis lazuli or Co‐coloured glass), yellow (Naples yellows or zinc/chrome yellow), green (mixture of the aforementioned blue and yellow pigments or lead chromate for restorated foot) red (hematite), white (cassiterite or arsenate) and pink (hematite and cassiterite) pigments are presented. The consistency of the pigments period of use/technology with the datation proposed for each artefact is evaluated. For one lamp, the detection of quartz in some places of the hematite‐rich glassy layer supporting the gold is related to the search of a physical bonding with the artefact body. Carbon residues in such enamel are consistent with the use of an organic medium to place the enamel powder before the firing. Copyright © 2012 John Wiley & Sons, Ltd.     

Mössbauer Spectroscopy, NAA and PIXE Study on Some Archeological Problems of Ancient Chinese Ru Celadon

By Mössbauer spectroscopy, NAA and optical spectroscopy, the coloring and the firing technology of ancient Ru celadon were studied. Also, the relationship between Ru Kuan celadon from Qingliang Temple and Ru celadon from Zhanggongxiang was studied by PIXE. The glaze color of Ru celadon depends on the ratio of the structural iron ions, i.e. the Fe²⁺/Fe³⁺ ratio. Further, it depends on the firing conditions. As the Fe²⁺/Fe³⁺ ratio gradually increases, the glaze color of Ru celadon will gradually change from pea green to sky green. All the Ru celadons were fired in a reducing atmosphere. The sky green Ru celadon was fired in the most reducing atmosphere and at the highest temperature, the powder green in a more reducing atmosphere and at a lower temperature and the pea green in a lightly reducing atmosphere and at the lowest temperature. The PIXE experimental results showed that Ru Kuan celadon from Qingliang Temple and Ru celadon from Zhanggongxiang were incompletely identical in the recipe of glaze and they could be differentiated by the cluster analysis of the major element concentration of glaze.     

Micro‐structural characterization of red decorations of red and green color porcelain (Honglvcai) in China

Red and green color porcelain (Honglvcai) is an important type of polychrome porcelains invented in North China during Song and Jin Dynasties. One of its great successes is its red decoration painted on the surface of glaze and fired at low temperature. Raman spectroscopy and X‐ray absorption fine structure (XAFS) at Fe K‐edge, were used to characterize the microstructure of red decorations from Song and Jin Dynasties to Ming Dynasty. The analyzing results on eight samples showed that hematite (α‐Fe₂O₃) was the main chromogenic substance in red decorations from different dynasties, which indicated a similar technological skill among the investigated samples. The oxidation state of iron in red decorations was determined to be mainly trivalent, indicating that red decorations were fired under oxidizing atmosphere. Besides, it was found that the hematite (α‐Fe₂O₃) in red decorations had a distorted structure, which was presumed to be an important factor influencing the color of red decorations. Copyright © 2009 John Wiley & Sons, Ltd.     

Pristine and Al-doped hematite printed films as photoanodes of <Emphasis Type="Italic">p</Emphasis>-type dye-sensitized solar cells

We hereby propose a non-expensive method for the deposition of pure and Al-doped hematite photoanodes in the configuration of thin films for the application of dye-sensitized solar cells (DSSC). The electrodes have been prepared from hematite nanoparticles that were obtained by thermal degradation of a chemical precursor. The particles have been used in the preparation of a paste, suitable for both screen printing and doctor blade deposition. The paste was then spread on fluorine-doped tin oxide (FTO) to obtain porous hematite electrodes. The electrodes have been sensitized using N3 and D5 dyes and were characterized through current/voltage curves under simulated sun light (1 sun, AM 1.5) with a Pt counter electrode. Al-doping of hematite showed interesting changes in the physical and electrochemical characteristics of sensitized photoanodes since we could notice the growth of AlFe₂O₄ (hercynite) as a secondary crystal phase into the oxides obtained by firing the mixtures of two chemical precursors at different molar ratios. Pure and Al-doped hematite electrodes have been used in a complete n-type DSSCs. The kinetics of charge transfer through the interface dye/electrolyte was studied and compared to that of a typical p-type DSSC based on NiO photocathodes sensitized with erythrosine B. The results suggest a potential application of both Fe₂O₃ and Fe₂O₃/AlFe₂O₄ as photoanodes of a tandem DSSC.     

Directed transverse flow and its disappearance for asymmetric reactions

We study the directed transverse flow for mass asymmetry reactions. This is done by keeping the target fixed and varying the projectile mass from ⁴He to ¹³¹Xe. We find that directed transverse flow is sensitive to the mass of the projectile. We also study the disappearance of flow at a particular impact parameter called Geometry of Vanishing Flow (GVF) for such mass asymmetry reactions. Our results indicate that GVF is sensitive to the beam energy as well as to the mass of the projectile.     

Specific Features of the Structural State of Iron Ions in Iron-Containing Composites Irradiated by Fast Electrons

The present paper analyzes the valence-coordination state of iron atoms in polymer composite materials fabricated from polystyrene and iron-ore concentrates – magnetite and hematite – upon exposure to fast electrons with energy of 6.2 MeV and fluence of 10¹⁸ electrons/cm². Changes in the phase content and valence-coordination and magnetic states of iron atoms are established. After irradiation, the hematite phase is transformed into the magnetite phase with a predominance of Fe³⁺ ions with [FeO₄] coordination, and the magnetite phase forms the wüstite-type (FeO) phase in which Fe²⁺ ions are arranged in [FeO₆] coordination.     

Mössbauer study of iron ore from El Hobo,Huila, Colombia

Iron ore from the El Hobo municipality located in the Huila department in Colombia (2^°35^′7^″N 75^°13^′27^″E) was studied by Mössbauer spectroscopy. The material was quite inhomogeneous, consisting of light brown and dark brown concretions of up to about a centimeter in size, and a sandy fraction. Mössbauer spectra at ambient temperature and at 4.2 K were taken of the two kinds of concretions and the sandy fraction. The concretions contain iron mainly as goethite with only a few percent of hematite. The sandy fraction contains goethite and hematite in roughly equal amounts and a minor fraction of divalent iron that splits magnetically at 4.2 K and may be an impure kind of siderite.     

<Emphasis Type="Italic">In-situ</Emphasis><Superscript>57</Superscript>Fe Mössbauer characterization of iron oxides in pigments of a rupestrian painting from the Serra da Capivara National Park,in Brazil,with the backscattering Mössbauer spectrometer MIMOS II

It is reported the use of the miniaturized portable ⁵⁷Fe Mössbauer backscattering spectrometer MIMOS II to perform in situ measurements in the archaeological site known as Toca do Boqueirão do Sítio da Pedra Furada (BPF), in Serra da Capivara National Park, in order to specifically examine shades of dark red pigments and compare their differences relatively to the light red part of the same painting. The hyperfine Mössbauer parameters reveal that the dark red area of the rupestrian painting is composed of three populations of hematite and of a small proportion of maghemite, whereas the light red are of the same painting contain hematite mixed with a small proportion of maghemite and a (super)paramagnetic Fe ³⁺. The Fe content in the dark red area from the rupestrian painting is of approximately twice the amount in the light red of the same prehistoric graphism. The corresponding analysis of red ochre sample collected in the excavation of these archaeological site exhibited two populations of hematite and also a small proportion of maghemite.