Amounts Of Hematite Research Articles

Leaching behaviour of limonite ores from Lapaopao, Southeast Sulawesi, Indonesia: Effect of mineralogy and acid types

An atmospheric leaching study of limonite ores from Lapaopao, Southeast Sulawesi, using hydrochloric acid (HCl), nitric acid (HNO<sub>3</sub>), and sulfuric acid (H<sub>2</sub>SO<sub>4</sub>) has been performed. The objectives of this study were to analyze the effect of ore mineralogy and acid types on the dissolution behavior of minerals and the leaching rate of Ni and Co at atmospheric pressure conditions. Mineralogical analysis was carried out using optical microscopy, scanning electron microscopy (SEM), and X-ray diffractometry (XRD), while the ore's chemical composition was determined by using X-ray fluorescence spectrometry (XRF) and atomic absorption spectrophotometry (AAS). Mineralogically, the limonite ores are dominated by goethite, followed by gibbsite, talc, and lizardite, with less amounts of hematite and quartz. Analysis results of solid residues revealed that mineral dissolution order was determined as follows: goethite > lizardite > gibbsite> hematite > talc> quartz. The results of the leaching experiment exhibited that the order of leaching rates of Ni in the three ores samples using three different acids were found as follows: Ore-1 > Ore-2 > Ore-3. Comparison of HCl, HNO<sub>3</sub>, and H<sub>2</sub>SO<sub>4</sub> as the lixiviants for the leaching of limonite ores demonstrated that HCl was the most reactive acid, followed by HNO<sub>3</sub> and then H<sub>2</sub>SO<sub>4</sub>. This might be due to the differences in mineralogical nature and reactivities of acids during the leaching process.

GEOQUÍMICA DO PERFIL LATERÍTICO DE OUTEIRO (BELÉM-PARÁ)

The Amazon region has, in all its immensity, abundant occurrences of laterites. These laterites, a product resulting from subaerial tropical weathering processes, keep records and important information about the environmental transformations experienced by the region. The Outeiro Island, inserted in this context, presents in its cliffs, good exposures of this lithological type. In this work these laterites are described as a function of the texture, closely related to the granulometry of the Barreiras Sediments, involved in the lateritization process. In them, the soil horizons, concretionary, mottled and remains of the mother rock and/or substrate are identified. The predominant mineralogy in the horizons in this profile is quartz and kaolinite, occurring in the concretionary horizon a large amount of hematite and goethite and muscovite in the most basal portion. The heavy minerals identified were, in order of abundance, staurolite, tourmaline, kyanite, zircon and rutile. The chemistry is characterized by high levels of SiO2, ranging from top to bottom from 90% to 51% and high levels of Fe and Al in the concretionary horizon and of Fe in the bedrock, not characterizing, however, a complete chemical differentiation, proving the immature nature of the profile. Keywords: Soils; concrecionary; mottled; kaolinite; hematite.

Comparison of Different Synthetic Routes of Hybrid Hematite-TiO2 Nanotubes-Based Electrodes.

Nowadays, green hydrogen is an important niche of interest in which the search for a suitable composite material is indispensable. In this sense, titanium oxide nanotubes (TiO2 nanotube, TNTs) were prepared from double anodic oxidation of Ti foil in ethylene glycol electrolyte. The morphology of the nanotubes was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Once characterized, nanotubes were used as templates for the deposition of hematite. The use of three synthetic procedures was assayed: Chemical Vapor Deposition (CVD), Successive Ionic Layer Adsorption and Reaction (SILAR), and electrochemical synthesis. In the first case, CVD, the deposition of hematite onto TiO2 yielded an uncovered substrate with the oxide and a negative shift of the flat band potential. On the other hand, the SILAR method yielded a considerable amount of hematite on the surface of nanotubes, leading to an obstruction of the tubes in most cases. Finally, with the electrochemical synthesis, the composite material obtained showed great control of the deposition, including the inner surface of the TNT. In addition, the impedance characterization showed a negative shift, indicating the changes of the interface electrode–electrolyte due to the modification with hematite. Finally, the screening of the methods showed the electrochemical synthesis as the best protocol for the desired material.

Dynamic Model for Friction-Induced Oxidation of Metals in Dry Sliding Processes

Abstract Oxidative mechanisms in tribological processes are commonly related with temperature and the real contact area. In this article, a lumped parameter dynamic model was developed to predict friction-generated oxide thicknesses in dry sliding conditions. The proposed model is based on conservative principles and causal equations applied to a pin-on-disk configuration in order to calculate the flash temperature with base on the heat transfer phenomena. Also, a mass balance was proposed to estimate the amount of hematite (Fe2O3), magnetite (Fe3O4), and wüstite (FeO) formed by friction heat. A new equation was proposed to predict the thicknesses of the oxides generated, and the model was validated based on experimental data available in specialized literature.

Synthesis of an Anticorrosive Pigment by Thermal Treatment of Iron Oxides from Steel Industry Wastes

This work reports the obtaining of an anticorrosive pigment composed mainly of hematite (ɑ-Fe2O3) from a powder steel industry waste from rust scale of rebar steel. This residue is mainly composed of Fe2O3 (87.97 %), SiO2 (6.13 %), CaO (1.88 %), Al2O3 (1.30%) and MnO (0.77 %). The total iron oxide of the residue is constituted by the following crystalline phases: magnetite, maghemita, lepidocrocita, wüstite, goethite and hematite. The production of a pigment with a high content of hematite was possible thanks to the high content of precursor iron oxides, which were calcined at different temperatures (750-850 °C) and holding times (0.5-1.50 h). For characterizing the iron content chemically and to identify their iron oxides phases, it was used X-ray fluorescence (XRF) and X-ray diffraction (XRD). The results showed that the pigment with the highest amount of hematite (ɑ-Fe2O3) was obtained at a calcination temperature of 850 °C and a holding time of 1.00 h.

Changes in phase composition of soderites of the bakal deposit at heating

The article presents the results of a study of formation mechanism of magnesia-ferrite when heated siderites of the Bakal deposit with different iron oxide content in an inert and oxidizing atmosphere. It was established that in the case of firing in an inert atmosphere, the decomposition of siderite with high iron content begins at a lower temperature and the enthalpy of such decomposition is less. This effect can be explained by the different phase composition of the samples. The main phases formed under conditions of oxidative firing are hematite and magnesia-ferrite. The amount of hematite and magnesia-ferrite produced in the samples with different iron oxide content during firing in an oxidizing atmosphere is different. Siderite with high content of iron oxides contains more hematite in the firing products than magnesia-ferrite, and siderite with a low content of iron oxides contains more magnesia-ferrite in the firing products than hematite. Formed under conditions of oxidative firing magnesia-ferrites are solid solutions and differ in the degree of substitution of iron and magnesium ions. In siderites with high content of iron oxides, the degree of substitution of magnesium ions with iron ions is greater than in samples with a low content of iron oxides. Since the siderites of the Bakal deposit are poor ore formations, the considerable amount of magnesia-ferrite formed in them during firing makes it difficult to separate silicate and iron-oxide firing products by traditional enrichment methods. Wustite in the products of oxidative firing is not detected, because under these conditions it is in a metastable state and in the presence of a weakly oxidizing atmosphere is converted into magnetite. The scientific novelty is the explanation of the mechanism of siderite decomposition and the description of products of such decomposition. Understanding of the mechanism of decomposition of siderite from the Bakal deposit made it possible to develop the technology of reductive firing of siderite to facilitate separation of its products, and which consists in the regulation of the phase composition of silicate products of reductive firing, ensuring the collapse of magnesia-ferrite and output of iron oxide in a separate phase. The developed technology can be used to provide high-quality enrichment of siderite from the Bakal deposit.

Process Mineralogy of Iranian High Sulfur Iron Ore

Processing of Iranian high sulfur iron ore is problematic in minerals industry. The iron ores were studied by the means of polarizing microscopy, chemical analysis, X-ray diffraction. The study shows that the iron ores have high grade of iron, and complex structures. XRD showed that the iron ore consists of metallic minerals such as magnetite with a small amount of hematite and limonite and non-metallic minerals as serpentine, chlorite, and talc. The average particle size of magnetite crystals is 0.182 mm. The ore contains 1.62% sulfur as harmful impurity in form of pyrite mineral. Due to the isomorphism of magnesium and iron, magnetite mono crystal grade is lower than 68%, and difficult to be physically upgraded to a higher-grade iron concentrate using the available mineral processing technologies.

Heat impact and soil colors beneath hearths in northern Sweden

The archaeological remains of Sami hearths in boreal and subarctic areas of northern Sweden are common finds. Greater understanding of the effects of heat on soil coloration will facilitate interpretation of the main purpose of these hearths, for example as heat sources or for cooking or other processing, and whether they were used seasonally for long or short periods of time. We therefore studied effects of heat on the coloration of natural B-horizons beneath traditional Sami hearths using three approaches: firing with dry pine wood in experimental hearths and measuring the temperature at various levels beneath the hearths; laboratory heating of B-horizon soils at different temperatures (200–900 °C) in a muffle oven and; measuring soil color changes in terms of RGB-values, and comparing the experimental results with soil profiles beneath real hearths used by nomadic Sami reindeer herders in northern Sweden. The study shows that the temperature reached beneath hearths strongly depends on the type of fuel used and the length of firing. The temperature can rise rapidly in upper layers of the soil but it takes considerable time for heat to penetrate 20 cm below the hearth surface. Our experimental firings, for 10 h on three consecutive days and for 72 consecutive hours, resulted in bowl-shaped areas of discoloration, with strong red coloration (rubification) towards the edges and dark grey/brown discoloration in the middle of the hearths in both tests. After laboratory heating, soil samples darkened during temperatures of 200–300 °C, and rubification at 250–350 °C depending on the amount of humus in the soil. The RGB analysis showed a steady increase in rubification from 300 °C, peaking at 750–800 °C. We believe that the rubification is caused mainly by transformation of iron compounds to maghemite and hematite and that the quantity of hematite is determined by temperature and not by time.Excavations of ancient hearths also revealed examples of bowl-shaped discoloration in B-horizons deeper than 20 cm. These discolorations had a rather uniform red tone with no dark areas. This suggests that the darker areas, probably colored by reduced iron and not by charred particles, could have been altered over time. The main conclusion is that rubification in B-horizons beneath hearths can arise after a relatively short period of firing but-bowl shaped areas of deep coloration can only arise, in boreal and subarctic areas, when hearths have been fired heavily and continuously for long periods of time, indicating winter use.

Converting Fe-rich magnetic wastes into active photocatalysts for environmental remediation processes

Abstract Hematite/magnetite photocatalysts were prepared by thermal treatment at 500 and 1000 °C of a Fe-rich waste obtained from a niobium mining. Rietveld analysis of XRD data and 57 Fe Mossbauer spectroscopy indicated that during the heat treatment magnetite is partially converted into hematite, which was the active photocatalytic phase in the samples. The remaining magnetite in the composites was useful to retard the fast electron-hole recombination in hematite. Zeta potential measurements revealed that the point of zero charge (pzc) of the iron oxides increased due to the thermal treatment, which favored the adsorption of negatively charged dye molecules. Diffuse reflectance measurements indicated that the band gap energies of iron oxides increased after the heat treatment due to a higher amount of hematite in those samples. Moreover, the valence band edges of hematite were more positive after the treatment of samples, which increased its dye photo-oxidation power. The photo-oxidation of neat methylene blue and Congo red in the presence of all samples was more efficient than that of neat methyl orange. On the other hand, it was verified from the competitive studies using the three dyes simultaneously that the photo-oxidation of methyl orange was favored, while the methylene blue and Congo red photo-oxidation decreased due to the methyl orange is replacing Congo red in the active photocatalytic sites of hematite. The proposed mechanism of dyes degradation was based on two main processes: (i) direct electron transfer from the dyes to the valence band of hematite, and (ii) dye oxidation by photogenerated OOH radicals on the hematite surface.

Geochemical fates and unusual distribution of arsenic in natural ferromanganese duricrust

Preferential enrichment of arsenic in iron oxides relative to manganese oxides has been well documented. In this study, however, a distinct arsenic enrichment is revealed in natural ferromanganese duricrusts, which are commonly found in natural weathering profiles of manganese-bearing carbonate rocks. In the studied ferromanganese duricrust covering Carboniferous carbonates at Qixia Mountain in eastern China, stromotalite-like structures composed by hematite, goethite, pyrolusite and hetaerolite have been observed. Electron microprobe analysis (EMPA) mapping and synchrotron-based micro-scanning X-ray fluorescence (μ-XRF) analyses reveal that the arsenic content in manganese oxides is elevated with respect to iron oxide phases. For example, the arsenic content of pyrolusite is approximately 5 times as much as that of hematite or hetaerolite. However, the highest arsenic content (0.58 wt% As2O5) occurs in 2.75 (±0.96, ±σ) μm micro-bands of hematite ((FexMnIII1-x)2O3, 0.75 < x < 0.83). Although arsenic contents in the Mn-rich hematite micro-bands are extraordinarily high, the amount of hematite with a high Mn content is very low in the duricrust. Hence manganese oxides are suggested to be the major arsenic sink in the ferromanganese duricrust. Extended X-ray absorption fine structure spectra (EXAFS) further shows that all arsenic is present as oxidized As(V) and are bound to Fe/Mn oxides in bidentate binuclear bridging complexes with AsFe and AsMn bond distances of 3.24 Å and 3.23 Å, respectively. In addition, it is found that zinc is also more enriched in Mn oxides (besides hetaerolite) than in Fe oxides. The fine hematite crust with low contents of heavy metals could act as a protective seal to separate Mn oxides core with high Zn and As from environmental fluids. This separation could reduce the interaction between them and decrease the release of Zn and As from this ferromanganese duricrusts, which ensures long-term sequestration of heavy metals. The unique structural and mineralogical constraints on the distribution of heavy metals can provide insights into novel strategies for environmental remediation of heavy metals contaminations.

Assessment of firing conditions in old fired-clay bricks: The contribution of X-ray powder diffraction with the Rietveld method and small angle neutron scattering

Full characterization of fired-clay bricks is crucial for the improvement of process variables in manufacturing and, in case of old bricks, for restoration/replacement purposes. To this aim, five bricks produced in a plant in Czech Republic in the past have been investigated with a combination of analytical techniques in order to derive information on the firing process. An additional old brick from another brickyard was also used to study the influence of different raw materials on sample microstructure. The potential of X-ray diffraction with the Rietveld method and small angle neutron scattering technique has been exploited to describe the phase transformations taking place during firing and characterize the brick microstructure. Unit-cell parameter of spinel and amount of hematite are proposed as indicators of the maximum firing temperature, although for the latter, limited to bricks produced from the same raw material. The fractal quality of the surface area of pores obtained from small angle neutron scattering is also suggested as a method to distinguish between bricks produced from different raw clays.

Validity of archaeomagnetic field recording: an experimental pottery kiln at Coppengrave, Germany.

Palaeomagnetic data obtained from archaeological materials are used for reconstructions of the Earth's magnetic field of the past millennia. While many studies tested the reliability of this recorder for palaeointensity only a few studies did this for direction. The study presents an archaeomagnetic and rock magnetic investigation applied to an experimental pottery kiln, which was operated in 2003 to produce stone ware. This kind of high-quality pottery needs a temperature of at least 1160 °C. Shortly before heating of the kiln direct absolute measurements of the absolute geomagnetic field vector have been carried out close to it. After cooling of the kiln 24 oriented palaeomagnetic samples have been taken. Although Curie temperatures are about 580 °C, that is the typical temperature for magnetite, thermal as well as alternating field demagnetisations reveal also a considerable amount of hematite as magnetic carrier. This mixture of magnetite and hematite is dominated by pseudo-single domain grains. Demagnetisation removed in some cases weak secondary components, but in most cases the specimens carried a single component thermoremanent magnetisation. The mean characteristic remanent magnetisation direction agrees on 95per cent confidence level with the directly measured field direction. Archaeointensity was obtained from five specimens with the Thellier-Coe method and with the multiple-specimen palaeointensity domain-state corrected method. Six of these specimens also provided a result of the Dekkers-Böhnel method, which overestimated the archaeointensity by about 9per cent compared to the direct value, while after correction for fraction the value agrees very well. For the multiple-specimen palaeointensity domain-state corrected method only fractions between 25 and 75per cent have been used and specimens showing alteration have been excluded. Above 450 °C many specimens showed alteration of the magnetic grains. Because median destructive temperatures were often above this value in most cases the fraction was less than 50per cent. Nevertheless the obtained intensity (48.48± 0.24 μ) is on 95per cent confidence level in agreement with the direct observation. Behaviour of the specimens during the Thellier-experiments was not ideal because of narrow unblocking temperature spectra and alteration. Nevertheless, the obtained mean archaeointensity is also in agreement with the direct field observation. Here the relative palaeointensity error is about 6per cent and very high compared the multiple-specimen palaeointensity domain-state corrected method. The investigation demonstrates that a pottery kiln can provide a very precise estimate of the ancient geomagnetic field vector.

A Comparison of Texture Development in an Experimental and Industrial Tertiary Oxide Scale in a Hot Strip Mill

Electron backscatter diffraction (EBSD) has been used to investigate the microstructure and texture-based features of an industrial tertiary oxide scale formed on a micro-alloyed low-carbon steel from a hot strip mill. EBSD-derived maps demonstrate that the oxide scale consists primarily of magnetite (Fe3O4) with a small amount of hematite (α-Fe2O3) which scatters near the surface, at the oxide/steel interface and at the cracking edges. The results extracted from these maps reveal that there is a significant difference between the industrial and the laboratory oxide scales in their grain boundaries, phase boundaries, and texture evolutions. There are high proportions of special coincidence site lattice boundaries Σ3 and Σ13b in the magnetite of the industrial oxide scale, rather than the lower orders of Σ5, Σ7, and Σ17b, which develop in the experimental oxide scale. Within the phase boundaries, the orientation relationships between the magnetite and the hematite correspond to the matching planes and directions {111}Fe3O4||{0001}α-Fe2O3 and {110}Fe3O4||{110}α-Fe2O3. Magnetite in both of these oxide scales develops a relatively weak {001} fiber texture component including a strong {001}〈100〉 cube and a slightly strong {100}〈210〉 texture components. Unlike the {001}〈110〉 rotated cube component in the experimental oxide scale, the magnetite in the industrial tertiary oxide scale develops a strong {112}〈110〉 and a relatively strong {113}〈110〉 and {111}〈110〉 texture components. These findings have the potential to provide a convincing step forward for oxidation research.

Magnetic characteristics and its environmental implications of core YSJD-86GC sediments from the southern South China Sea

Sediments of core YSJD-86GC (referred to as 86GC) collected from the southern South China Sea were selected for environmental magnetic studies. Combined with the published chronological framework, sediment magnetic properties were revealed for the study area since the MIS3 stage. The rock magnetic results indicate that low-coercivity magnetite is the main magnetic mineral within the sediments. Also, a certain amounts of hematite are present. The King plot and Day plot, which reflect the magnetic particle size, show that fine-grained pseudo-single-domain phase magnetic particles dominate the magnetic minerals in the sediments. Comparison of magnetic parameters and geochemical indicators show that magnetic properties of core 86GC sediments reflect a terrigenous input. Simultaneously, magnetic characteristics of the studied sediment are influenced by the quantity of terrigenous sediment input, oxidation-reduction conditions of the provenance area, and the transportation environment and distance. Sea level fluctuation caused by global climate change was the main factor for variation in concentration of magnetic minerals and magnetic particle size of the studied core sediments. Thus, variation of sediment magnetic properties in the study area can be used as an indirect indicator of sea level fluctuation.

Precipitated iron Fischer–Tropsch catalyst manufacturing: impact of Hematite

This study found that promoted precipitated iron catalysts, containing large quantities of Hematite, demonstrated adequate activity, selectivity, and attrition resistance operating under commercial Fischer–Tropsch synthesis conditions in a product demonstration slurry bed reactor run over an approximately 170-day period. While small quantities of Hematite ( 0.30 cm3/g) and pore size (60–80 A) can be induced if larger quantities of about 30–40 wt % Hematite are present in the fresh calcined unreduced catalyst. The catalyst demonstrated exceptional attrition resistance.

Geochemical characteristics of the coal gangues from the Du’erping coal mine, Xishan coalfield, North China

Inductively coupled plasma mass spectrometry, inductively coupled plasma optical emission spectroscopy, hydride generation-atomic fluorescence spectrometry, emission spectrometry, X fluorescence spectrometry, and X-ray diffraction were employed to study the geochemistry and mineralogy of coal gangues from Nos. 2, 3, and 8 coal seams of the Du’erping coal mine, Xishan coalfield, Taiyuan, Shanxi Province. The study revealed that compared with the sedimentary cover, upper continent crust, Carboniferous-Permian coal from North China, as well as most coal in China, coal gangues from Nos. 2 and 3 coal seams are rich in Li, Be, Sc, Cr, Cu, Ga, Ba, Th, Nb, Cd, Pb, Ta and rare-earth elements, and coal gangues from No. 8 coal seam are rich in Li, Sc, V, Cr, Ga, U, and rare-earth elements. Compared with the Carboniferous-Permian coal from North China and most coal in China, coal gangues from Nos. 2, 3 and 8 seams are rich in Rb, V, Cs and Sr. Therefore, The Du’erping coal gangues in the Xishan coalfield are rich in most hazardous trace elements and rare-earth elements, wherein the contents of Ga and Li reach the industrial grade and have significance for industrial utilization. On the whole, coal gangues of the Shanxi Formation from the Permian are rich in more trace elements than those of the Carboniferous Taiyuan Formation. The distributions of REE show obviously dipping rightwards with negative Eu anomalies. The contents of rare-earth elements in the three seams are quite different. All of the above indicate that the source of the rare-earth elements is terrigenous debris. Minerals in No. 2 seam identified by X-ray diffraction mainly include quartz, kaolinite, in addition to calcite, pyrite, apatite, epidote, and epsomite. No. 3 seam mainly contains quartz, kaolinite, in addition to a small amount of sodium feldspar, calcium nitrate, iron ore, gypsum, and vivianite. No. 8 seam mainly contains kaolinite, dickite, quartz, illite, and a small amount of hematite and U. The correlations between major elements and trace elements in coal gangues of the Du’erping coal mine analyzed by using SPSS (Statistical Product and Service Solutions) indicate that the trace alkali elements and rare-earth elements occur mainly in such clay minerals as kaolinite.

Characterisation of oxide scales developed on high temperature resistant alloys in pure steam environments

Steam oxidation of heat exchanger tubes and pipe work is of growing interest as research into the improvement of power plant efficiencies shows the need for much higher steam temperatures and pressures. This paper reports on the characterisation of the oxide scales grown during the steam oxidation of four alloys (T23, T92, TP347HFG and Inconel 740) in atmospheric pressure steam at four temperatures (600, 650, 700 and 750°C) for periods of 250, 500 and 1000 h. Three methods have been employed in analysing these scales: reflected light optical microscopy, scanning electron microscopy with energy dispersive X-ray analysis and X-ray diffraction.The thickness, composition, morphology and spalling behaviour of the oxides differed with alloy composition, exposure times/temperatures and sample shapes. The ferritic steels exhibited the most severe oxidation, with the scales formed on these typically being triple-layered: an inner layer of Fe – Cr spinel, central layer of magnetite and outermost layer of haematite. However, the amount of haematite formed changed with the exposure time/temperature, alloy and sample orientation. In comparison TP347HFG and Inconel 740 showed significantly slower oxidation, with generally thin oxide scales (<5 µm) developing even at the highest exposure temperatures, though TP347HFG started to form some nodular growths after 1000 h exposure at the two higher temperatures.

Effect of Nucleators and Intermediates on the Magnetic Properties of Nanosized Magnetite Obtained by Glass Crystallization

We investigate the role of chromium and phosphorous oxides on the growth and magnetic properties of crystallized Fe-containing borosilicate glasses as well as their evolution under different thermal processing. The glasses have the ratio between SiO2 and Fe2O3 in the range 1.49 to 2.68 and Al2O3 / MgO as intermediate/modifier oxides. X-ray diffraction and Mossbauer spectroscopy data revealed the presence of magnetite as the major crystalline phase in all asprepared samples but additional amounts of hematite and of Fe-rich paramagnetic phases are also visible in some samples. The magnetic response is correlated with the disorder observed in the different sites (tetrahedral and octahedral) of the magnetite.

Sintering Behavior and Machinability of Phlogopite Glass Ceramics Containing Fe2O3

Mica-based glasses in the SiO2-Al2O3-MgO-K2O-F system were prepared by a sintering method to investigate the effects of different amounts of hematite (Fe2O3) on thermal and sintering behaviors besides machinability of the glasses by means of differential thermal analysis (DTA), X-ray diffraction, and scanning electron microscope techniques. DTA analysis on fine and coarse glass powders indicated that the main crystallization mechanism in this system occurred in the bulk rather than the surface. Increasing Fe2O3 content to 5 wt.% improved machinability of the glass ceramic. Fe2O3 led to the disruption of the glass matrix and facilitated the nucleation of the crystalline phase. Precipitation of sellite (MgF2) crystals as heterogeneous nucleating sites for potassium phlogopite crystals acted as a second contribution to the machinability of the 5 wt.% Fe2O3-containing sample. However, introducing more than 5 wt.% Fe2O3 to the base glass prohibited the nucleation of MgF2, and as a result, large micas formed within the glass. This together with precipitation of cordierite aggregates in highly doped glass with Fe2O3 led to lower machinability in these samples.

Mineral magnetic investigation of the Talede loess-palaeosol sequence since the last interglacial in the Yili Basin in the Asian interior

SUMMARY The loess–palaeosol deposit in the Asian interior is sensitive to the evolution of the Westerlies, thus providing a good opportunity to investigate regional palaeoenvironmental evolution and its relationship with global climatic changes. Multiparameter mineral magnetic investigations have been conducted on the Talede section in the Yili Basin, Asian interior. Our study finds that: (1) loess samples have higher concentration magnetic minerals than palaeosols, though the magnetic mineral composition is similar (ferrimagnetic magnetite, antiferromagnetic hematite and lepidocrocite). (2) Large pseudo-single domain (PSD) and multidomain (MD)-like grains dominate both in loess and palaeosols. However, magnetic mineral grains in loess are much coarser than those in the palaeosols. (3) Palaeosols contain approx 30 per cent more amount of hematite than the loess samples. The frequency-dependent susceptibility of both loess and palaeosols is very low, indicating the small amount of super-paramagnetic grains. And the higher χfd per cent values of palaeosols also reveal that palaeosols have more amounts of ultrafine magnetic grains than loess. The magnetic variations in part (1) and (2) can be well explained by the wind vigour model, but the observed enrichment of hematite and ultrafine magnetic grains in palaeosols also reveals the first onset of pedogenic enhancement. Therefore, the Talede section could be seen as an end-member of the classic Chinese Loess Plateau (CLP) magnetic enhancement model.