Showing papers on "Hematite published in 1976"

Mineralogic and petrologic implications of viking geochemical results from Mars: interim report.

Abstract: Chemical results from four samples of martian fines delivered to Viking landers 1 and 2 are remarkably similar in that they all have high iron; moderate magnesium, calcium, and sulfur; low aluminum; and apparently very low alkalies and trace elements. This composition is best interpreted as representing the weathering products of mafic igneous rocks. A mineralogic model, derived from computer mixing studies and laboratory analog preparations, suggests that Mars fines could be an intimate mixture of about 80 percent iron-rich clay, about 10 percent magnesium sulfate (kieserite?), about 5 percent carbonate (calcite), and about 5 percent iron oxides (hematite, magnetite, maghemite, goethite?). The mafic nature of the present fines (distributed globally) and their probable source rocks seems to preclude large-scale planetary differentiation of a terrestrial nature.

DTA study of the dehydration of synthetic goethite αFeOOH

Abstract: The shape of DTA endothermic peak, associated with the dehydration of goethite FeOOH into hematite, depends strongly on the size of the goethite particles. With samples of low specific surface, two distinct peaks were observed. The dehydration process of a low-specific surface goethite was followed by X-ray diffraction and lowtemperature nitrogen adsorption. The results are in good agreement with the hypothesis of the formation of an impermeable hematite layer on each grain which temporarily stops the dehydration process of the internal part of the grain.

Selective extraction of amorphous iron oxide by edta from a mixture of amorphous iron oxide, goethite, and hematite

Abstract: Summary Iron (III) was extracted by EDTA and ammonium oxalate from a model substance consisting of amorphous iron oxide, goethite, and hematite precipitated in the presence of quartz sand. Even by varying the EDTA concentration between 0.02 and 0.1 M, pH between 4.40 and 6.00, the solid:solution ratio between I:25 and I:250, and using extraction times up to go days, it was found that EDTA was able to extract only a limited amount of iron. In contrast, 0.2 M ammonium oxalate at pH 3.0 is able to dissolve all the iron compounds if the extraction time is sufficient. Nevertheless, the amount of EDTA-extractable iron is equal to the amount of iron extracted after 4–5 hours with ammonium oxalateat pH 3.0. From X-ray analysis, DTA curves, a solubility product determination, and a kinetic investigation, it is concluded that the EDTA-extractable fraction consists of X-ray amorphous iron oxide, less soluble than polymeric iron hydroxide, and presumably only one compound. Therefore, it is concluded that it may be possible by means of EDTA to carry out a selective extraction of X-ray amorphous iron oxides mixed with goethite and hematite.

Structural changes and kinetics in the gaseous reduction of hematite

Abstract: The mechanism of the gaseous reduction of hematite grains to magnetite was studied. Gravimetric measurements were carried out for the reduction of Carol Lake hematite pellets and grains in CO-CO2 atmospheres over the temperature range 500 to 1100°C. The pore size distribution in the reduced magnetite was measured by mercury porosimetry. Partially reduced grains were examined by optical microscopy. At temperatures below 800°C, the reduction of a hematite grain to magnetite occurred at a well-defined shrinking-core interface. The average pore size in magnetite formed at 600°C was found to be 0.03 μm. An estimate of the rate of CO diffusion through pores of this size indicated that the reaction rate at 600°C was controlled by a step near the hematite-magnetite interface. At temperatures above 800°C, the reaction mechanism became altered due to the preferential growth of magnetite along a single direction in each hematite grain. The reduction rate decreased with an increase in temperature, and no microporosity was present in magnetite formed at 1000°C and above. It was postulated that the reaction rate was controlled by the rate of formation of fresh nuclei and by their rate of subsequent growth.

High Extraction Magnetic Filtration of Kaolin Clay

Abstract: A new magnetic separation technique combines high magnetic fields, extreme gradients, and controlled retention time to separate feebly magnetic mineral contaminants from kaolin. Extraction of pyrite, siderite, hematite, iron stained anatase, and mica by magnetic filtration of kaolin significantly upgrades brightness of many sub-marginal deposits and reduces consumption of reagents in processing.

Kinetic Studies on the Precipitation of Hematite from Iron‐Rich Spinel Solid Solutions

Abstract: The kinetics of hematite precipitation from iron-rich spinel solid solutions has been studied with special emphasis on the effect of divalent cations and iron-oxide concentration. The precipitation kinetics is expressed by the Avrami equation α= 1 – exp [–k(t –t0)n] with n= 1, where α, k, and t are fractional precipitation, proportionality constant, and time, respectively. The process is characterized by an activation energy of 30·0.5 kcal/mol, independent of iron-oxide concentration. Stabilization of spinel solid solutions by the cation is most pronounced for Ni followed by Mg and Zn in the order stated, and the effect of the cation is interpreted in terms of the cation distribution in the spinel lattice.

Uvarovite: Stability of uvarovite-andradite solid solutions at low pressure

Abstract: Uvarovite (Ca3Cr2Si3O12) forms a complete solid solution series with andradite (Ca3Fe 2 +3 Si3O12) below 1,137±5 ° C at a total pressure of 1 atm. Pure uvarovite decomposes to pseudowollastonite (CaSiO3)+eskolaite (Cr2O3) at 1,385 ± 10 ° C. The incorporation of Ca3Fe 2 +3 Si3O12 component in the uvarovite structure lowers the thermal stability of the garnet. The breakdown assemblage is garnetss (Ca3(Cr,Fe+3 2)Si3O12)+pseudowollastonite (CaSiO3)+hemeskolaitess(Cr,Fe+3O3). Pure andradite decomposes to pseudowollastonite (CaSiO3)+hematite (Fe2O3) at 1,137±5 °C. Andradite thermal stability is increased by incorporation of Ca3Cr2Si3O12 component by 248 °C. At 1,264±5 °C pseudowollastonite+hematite react to liquid defining a thermal minimum of the CaSiO3-Cr2O3-Fe2O3 ternary system. This minimum is located at about 64.5 wt.-% CaSiO3, 0.5 wt.-% Cr2O3, and 35.0 wt.-% Fe2O3. Uvarovite and andradite bulk compositions start to melt at 1,420 °C and 1,265 ±5 °C, respectively. The unit-cell parameter for uvarovite is 11.999 (2) A, the refractive index 1.866 (2). The substitution of Cr+3 by Fe+3 increases a and n almost linearly toward the andradite end member which displays a unit-cell parameter of 12.059 (3) A and a refractive index of 1.887 (2).

Characteristics and genesis of nodules and concretions occurring in soils of the r. chinit area, kompong thom province, cambodia

Abstract: Morphological, chemical and mineralogical studies were made on different types of nodules and concretions occurring in Gleysols, Ferralsols and Vertisols of the R. Chinit area, Kompong Thorn Province, Cambodia. The examinations indicated that nodules have developed through impregnation of soil matrix with iron and/or manganese oxides, whilceoncretions have formed through periodical precipitation of iron oxide around ferruginous or manganiferous nuclei to the exclusion of surrounding soil materials. Alternation of wet and dry seasons is believed to play an important part in the localization of iron and manganese into mottles and their subsequent hardening. The proportion of anhydrous iron oxides (hematite, maghemite) to hydrated iron oxide (goethite) appears to be closely related to the degree of desiccation of soils in dry seasons. Decomposition of kaolinite in the nodules and concretions was suggested by their lower kaolinite, and higher amorphous silica and alumina contents as compared to the s...

Über die Koexistenz der Aluminium- und Eisen(III)-hydroxide und Oxide

Abstract: Analysis of the IR spectra reveals that traces of aluminium ions reduce the amount of goethite phase in the products of ageing of amorphous ferric hydroxide. X-ray studies showed that the unit-cell parameters of the hematite decrease during ageing, this decrease ceasing at the composition 0,2 Al2O3· · 0,8 Fe2O3. Electron microscopic examination showed that the hematite grains are always larger in the presence of Al3+. Thermal analysis showed the hydrohematite formed in the presence of 0,03 mole of Al2O3 to be almost anhydrous.

Petrology and Origin of the Red Beds of the Perry Formation New Brunswick, Canada, and Maine, USA

Abstract: Fault trough deposition during the Late Devonian in the Perry Formation of Maine and Canada produced texturally and mineralogically immature red and green sandstones as well as conglomerates and mudstones containing angular clasts and hematite and calcite cement. Deposition occurred in two separate basins, each with different source areas. The origin of the red color of the Perry Formation is two fold. Some of the red pigment is primary, derived from underlying older lithologic units. Secondly, mafic minerals such as magnetite and hornblende, were altered and partially removed by intrastratal solutions providing in situ alteration to form additional hematite. Calcareous crusts associated with these sediments indicate they probably were formed in an arid setting. Once formed, th se crusts impeded upward migrating iron-laden groundwater, trapping some iron in cracks and fractures below the crusts. Migration and deposition of iron in solution by groundwaters is suggested as an agent which aided in the formation of the red beds. The iron in solution might have been derived from an external source in the groundwater recharge area to supplement iron formed by in situ alternation of mafic minerals.

Mössbauer study of superparamagnetic δ-FeOOH and its transformation into α-Fe2O3

Abstract: Mossbauer spectra of δ-FeOOH are obtained at 23°C after heating in air in the range 80 to 600°C. The spectra were run with external magnetic fields of H0 = 20 kOe and H0 = 0. From a comparison of the spectra the formation of the intermediate phase δ-Fe2O3 after heating at 125 to 200°C seems to be followed by an increase of the quantity of defects and an equilibration of the sublattice population. A collinear ferromagnetic structure, but not canted as in ordinary hematite, is shown to grow in the initial stages of hematite formation (after heating at 225°C). [Russian Text Ignored].

M73246ssbauer spectroscopic evidence for akaganéite ( β -FeOOH) in New Zealand soils

Abstract: 57Fe Mossbauer spectroscopy and computer-based data reduction procedures have been used to study quantitatively, the various secondary iron-containing minerals in a selection of New Zealand soils and iron-manganese soil concretions The results indicate that akagankite (â-FeOOH), previously considered a rare mineral, is a major form of iron in these samples Lepidocrocite (a-FeOOH), and/or goethite (a-FeOOH) with a particle size less than approximately 70 A also appear to be present in all samples Distinction between these two latter forms was not possible, because of the super-paramagnetic effects associated with fine particles of goethite Hematite (a-Fe2O3 with a suitably large particle size (greater than approximately 180 A) was positively identified in two of the soil samples studied The ratios of the concentrations of the various forms of iron are given

Is the history of an ancient pottery ware correlated with its mössbauer spectrum

Abstract: This investigation refers to the existence of aging effects in ancient pottery wares. The dependence of the size of iron oxides in modern pottery samples prepared under various firing conditions, data from refiring ancient sherds and data from the chemical removal of their iron oxides strongly indicate that the presence of very fine oxide particles in the ancient ware is partially due to aging. This indication is further supported from results from the artificial (( aging >) of modern pottery samples via a fatigue treatment based on thermal cycling. 1 . Introduction. Since the first exploratory application [l] of Mossbauer effect as a tool to answer archaeological questions on ancient pottery wares, few more investigations have been performed towards this aim. Their results indicate the possible existence of correlations between Mossbauer parameters from spectra of ancient pottery sherds and their provenance [l , 21, their colours [3, 41 and their age 151. These findings although they are quite encouraging for the potential usefullness of Mossbauer Spectroscopy to disentangle archaeological problems in the important field of pottery, they have to be ultimately understood on the basis of the physicochemical transformations occuring to iron along the history of an ancient pottery ware i. e. from its production until today. Only few detailed and systematic studies towards this aim exist up to now and their results have been recently reviewed by Kostikas et al. 161 and Coey [7]. In this work we present part of the results of our investigation mainly via Mossbauer Spectroscopy of the transformations occuring in the iron present in modern clay upon firing, in ancient pottery wares upon refiring and in modern ceramic samples upon artificial erosion. The aim of this investigation is to elucidate the existence of aging eflects in the ancient pottery wares. Although, the existence of such effects has been indicated by a correlation of the size of the iron oxides and the age of only few ancient Greek pottery sherds [5] and of a group of Brasilian pottery wares studied by Danon (l), it deserves special attention because of its great importance to Archaelogy and Ceramic Technology, if eventually such a correlation would be established. The next section refers to the size of the iron oxide particles present in modern clays upon different firing conditions and to the difference observed in the size of these oxides between ancient and modern pottery. Experimental evidence supporting the view that ancient pottery wares have aged is presented in section 3. In section 4 we present results on artificially eroding modern pottery wares before and after they have been subjected to a fatigue treatment based on thermal cycling. * The last section comprises concluding remarks on the problems which deserve further investigation. 2. Size of Iron Oxides. In the studies of the form of iron present in an Attic clay [g] and of the transformations occuring to iron upon firing this clay in air [g] it was found that : a) in the clay, iron is present in the lattice of the clay mineral platelets (structural iron) as well as in the form of fine oxide or hydroxide particles of about 100 A in diameter, b) firing the clay to pottery results to an increase in size of the iron oxide particles, c) this increase occurs at two different regions of the firing temperature. The one around 300 OC is related to the transformation of the hydroxides to haematite, while the other bet(1) Private communication 1976 and C6-19.. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19766183 C6-868 N. H. J. GANGAS, I. SIGALAS AND A. MOUKARIKA ween 800 OC and 900 OC is related to the migration of the structural iron out of the clay mineral platelets. Similar results were also obtained by Hess and Perman [4] in experiments with clays from Cyprus and Israel. However, the published [2, 3, 4, 10, 11, 121 or measured by us Mossbauer spectra of many ancient pottery sherds of different styles, texture, fineness, provenance and age show in about 80 % of the cases that the size of their iron oxides is significantly smaller than that found upon firing modern clays in air. Due to the importance of this difference in the size of the iron oxides between ancient and modern pottery samples and since ancient potters varried the firing conditions in their kilns from oxidizing to reducing and vice versa [13], we investigated the dependence of the size of the iron oxides upon different firing temperatures and also upon different firing armospheres. Samples of Attic clay were fired according to the step firing scheme used in a previous work [g] under the following firing conditions : (i) up to 600 0C in air, (ii) up to 800 OC in air, (iii) up to 900 OC in air, (iv) up to 900 OC in vacuum and (v) up to 800 OC in air, then up to 950 OC and down to 800 OC in a reducing atmosphere produced by the oxygen deficient burning of saw dust and carbon powder and finally cooled below 800 OC in air. This last firing cycle simulated the firing :of ancient Attic potters [13]. Mossbauer spectra of 150 mg of the above samples were obtained at temperatures ranging from 4.2 K up to 573 K. These spectra were analysed via a computer program enabling the use of up to four iron sites. The results from this analysis are presented in brief below. Comparing the values of the hyperfine paramenters and the fractions of the absorption areas at different measuring temperatures (Table I presents part of these data) we deduced that : (i) the transformation of the hydroxides to hematite occurs independently of the firing atmosphere, as no oxygen is needed for this process and (ii) the increase of the iron oxide particles due to the migration of structural iron out of the clay lattice is controlled by the reducing character of the firing atmosphere. Furthermore, we note that for the sample fired under conditions simulating those of the ancient Attic potters the size of iron oxide particles is between those of the samples fired in vacuum and in air at 900 OC. Mossbauer data .for clay samples $red under various conditions : (i) in air up to 600 OC (600) and 900 OC (900), (ii) in vacuum up to 900 OC (900-V) and (iii) in a j r i n g cycle simulating ancient kiln conditions (950-S). Isomer shifts are given relative to a 57Co in Cu source at 4.2 K and T, is the temperature of measurement. Number in parentheses give estimated errors in the last digit. T m Sample (K) HWHM (mmls) 0.27 0.30 (3) 0.37 (3) 0.25 (2) 0.48 (2) 0.40 (2) 0.27 (3) 0.26 (2) 0.23 (2) 0.25 0.32 (3) 0.40 0.59 0.25 0.4 0.4 0.3 0.22 0.25 0.31 0.25 Fraction ( %l -

Susceptibility of the Oxide Film Formed on Steel in Air at 100 to 400 C to Local Breakdown in Borate Buffer Solutions Containing Cl− Anions

Abstract: The susceptibility of steel to pitting corrosion (determined by the depth of the pits) and the susceptibility of oxides of different composition and thickness to local breakdown (determined by the number of pits) were studied. It was found that oxide films consisting of magnetite and hematite are more susceptible to local breakdown but less susceptible to pitting corrosion than magnetite films.

Thermomagnetic study of coal and associated roof shale

Abstract: Thermomagnetic studies of Pennsylvanian coals and associated roof shales indicate that hematite and minor goethite are present as ferrimagnetic phases, in addition to the paramagnetic mineral pyrite. Laboratory studies show that the carrier of the stable natural magnetic remanence (NRM) is mainly single domain hematite. X-ray diffraction studies of the samples has directly identified illite, kaolinite and minor amounts of chlorite as the natural suite of clay minerals typical in coal and overclay. Mossbauer spectroscopy identifies hematite and geothite as ferrimagnetic phases within the clay structures. Thermomagnetic studies at higher temperatures show that paramagnetic pyrite is converted to ferrimagnetic hematite through a strongly ferromagnetic phase maghemite. This transition occurs within the 400-500°C temperature interval and results in a significant increase in the ferrimagnetic polarization and paramagnetic susceptibility of the samples.

Influence of magnetic field on the reduction of hematite by hydrogen

Abstract: Measurements are reported which show that a magnetic field has very little effect on the reduction of hematite by hydrogen. Determinations of water loss indicate that the reduction rate increases by 9% in the presence of a field of 500 G. There is no further increase between 500 and 5000 G. The magnetization reflects this field dependence. Mossbauer spectra of the reduced samples clearly show the different reduction products Fe, Fe3O4, Fe2O3.

Magnetite Lamellae in Reduced Hematites

Abstract: A lamellar texture in natural and synthetic oxidized magnetites and reduced hematites has been observed for many years. Hematite (Fe2O3, R3c) and magnetite (Fe3O4, Fd3m) lamellae were found in sinters and burden pellets made by oxidizing magnetite ores at T> 1000 °C (Schwartz, 1929; Cooke and Ban, 1952; Tigerschiold, 1954; Ponghis et al., 1967). Greig et al. (1935) and Gruner (1926) used light optical and X-ray techniques to identify the {111} m ||{0001} h relationship in oxidized magnetites.