Iron Oxide Coatings Research Articles

Photocatalytic Activity of Titanium Oxide – Iron Oxide Coatings Prepared by Plasma Spraying

This study examines the photocatalytic activity of coatings produced by atmospheric plasma spraying (APS). The spraying tool used is a water -stabilized plasma gun WSP. The TiO2 �Fe2O 3powder withand withoutNa 2SiO3additive was agglomerated to build p articles suitable for feeding into the plasma jet and spraying. The coatings are analyzed by scanning electron microscopy, X -ray fluorescence and Xray diffraction. Photocatalytic degradation of acetone as well as the growth kinetics of the products -carbon dioxide and carbon monoxide -is quantified for both coating types and compared with a pure TiO 2 coating. The coatings show a lamellar structure, as is typical for this technological process. Howe ver the porosity is rather high. Anatase titania from the feedstock powder is converted to rutile phase whereas a presence of FeTiO 3is detected in the coating without Na 2SiO3. The coating from powder withNa 2SiO3 admixture is amorphous. Both coatings aremore photocatalytically active than the reference TiO 2coating.

Kinetics and efficiency of H2O2 activation by iron-containing minerals and aquifer materials

To gain insight into factors that control H2O2 persistence and OH yield in H2O2-based in situ chemical oxidation systems, the decomposition of H2O2 and transformation of phenol were investigated in the presence of iron-containing minerals and aquifer materials. Under conditions expected during remediation of soil and groundwater, the stoichiometric efficiency, defined as the amount of phenol transformed per mole of H2O2 decomposed, varied from 0.005 to 0.28%. Among the iron-containing minerals, iron oxides were 2–10 times less efficient in transforming phenol than iron-containing clays and synthetic iron-containing catalysts. In both iron-containing mineral and aquifer materials systems, the stoichiometric efficiency was inversely correlated with the rate of H2O2 decomposition. In aquifer materials systems, the stoichiometric efficiency was also inversely correlated with the Mn content, consistent with the fact that the decomposition of H2O2 on manganese oxides does not produce OH. Removal of iron and manganese oxide coatings from the surface of aquifer materials by extraction with citrate–bicarbonate–dithionite slowed the rate of H2O2 decomposition on aquifer materials and increased the stoichiometric efficiency. In addition, the presence of 2 mM of dissolved SiO2 slowed the rate of H2O2 decomposition on aquifer materials by over 80% without affecting the stoichiometric efficiency.

Bioleaching of clays and iron oxide coatings from quartz sands

Silica sands of low quality contain free iron oxides, clay and silt. These impurities may be removed by biological leaching as well as by industrial washing. The fine fractions obtained from industrial washing of quartz sand from Šastín, Slovakia, with a higher content of iron-bearing minerals and clay minerals were used to study bioleaching of impurities of the quartz sands. The influence of biological leaching by indigenous heterotrophic bacteria and Bacillus spp. bacteria was evaluated by changes in chemical composition of the fine fractions before and after reaction. The bioleaching experiments were performed for 63days at 24°C. The extracted iron and clay products were characterized by XRD, FTIR, Mössbauer spectroscopy, chemical and granulometric analyses, SEM, EDX, and nitrogen adsorption techniques. The bacteria assisted in releasing the poorly ordered clay minerals from the surface of quartz particles via dissolution of amorphous Fe oxyhydroxides.

Sveinbergeite, Ca(Fe2+6 Fe3+)Ti2(Si4O12)2O2(OH)5(H2O)4, a new astrophyllite-group mineral from the Larvik Plutonic Complex, Oslo Region, Norway: description and crystal structure

AbstractSveinbergeite, Ca(Fe2+6Fe3+)Ti2(Si4O12)2O2(OH)5(H2O)4, is a new astrophyllite-group mineral discovered in a syenite pegmatite at Buer on the Vesteroya peninsula, Sandefjord, Oslo Region, Norway. The mineral occurs in pegmatite cavities as 0.01—0.05 mm thick lamellar (0.2—0.5×5—10 mm) crystals forming rosette-like divergent groups and spherical aggregates, which are covered by brown coatings of iron (and possibly manganese) oxides, associated with magnesiokatophorite, aegirine, microcline, albite. calcite, fluorapatite, molybdenite, galena and a hochelagaite-like mineral. Crystals of sveinbergeite are deep green with a pale green streak and a vitreous and pearly lustre. Sveinbergeite has perfect cleavage on ﹛001﹜ and a Mohs hardness of 3. Its calculated density is 3.152 g/cm3. It is biaxial positive with α 1.745(2), β 1.746(2), γ 1.753(2), 2V(meas.) = 20(3)°. The mineral is pleochroic according to the scheme Z > X ∽ Y : Z is deep green, X and Y are brownish green. Orientation is as follows: X ┴ L (001), Y ᶺ b = 12°, Z = a, elongation positive. Sveinbergeite is triclinic, space group P1̄, a = 5.329(4), b = 11.803(8), c = 11.822(8) Å; α = 101.140(8)°, β = 98.224(8)°, γ = 102.442(8)°; V = 699.0(8) Å3; Z = 1. The nine strongest lines in the X-ray powder diffraction pattern [d in Å(I)(hkl)] are: 11.395(100)(001,010). 2.880(38)(004), 2.640(31)(2̄10,l̄41), 1.643(24)(07̄1,072), 2.492(20)(2l̄l), 1.616(15)(070), 1.573(14)(3̄2̄2), 2.270(13)(1̄3̄4) and 2.757(12)(1̄40,1̄3̄2). Chemical analysis by electron microprobe gave Nb2O5 0.55, TiO2 10.76, ZrO2 0.48, SiO2 34.41, A12O3 0.34, Fe2O3 5.57, FeO 29.39, MnO 1.27, CaO 3.87, MgO 0.52, K2O 0.49, Na2O 0.27, F 0.24, H2O 8.05, O=F -0.10, sum 96.11 wt.%, the amount of H2O was determined from structure refinement, and the valence state of Fe was calculated from structure refinement in accord with Mossbauer spectroscopy. The empirical formula, calculated on the basis of eight (Si + Al) p.f.u., is (Ca0.95Na0.12K0.14)Σ1.21(Fe2+5.65Fe3+0.93Mn0.25Mg0.18)Σ7.01(Ti1.86Nb0.06Zr0.05Fe3+)Σ2 (Si7091Al0.09)Σ8O34.61H12.34F0.17, Z = 1. The infrared spectrum of the mineral contains the following absorption frequencies: 3588, ∽3398 (broad), ∽3204 (broad), 1628, 1069, 1009, 942, 702, 655 and 560 cm–1. The crystal structure of the mineral was solved by direct methods and refined to an R1 index of 21.81%. The main structural unit in the sveinbergeite structure is an HOH layer which is topologically identical to that in the astrophyllite structure. Sveinbergeite differs from all other minerals of the astrophyllite group in the composition and topology of the interstitial A and B sites and linkage of adjacent HOH layers. The mineral is named in honour of Svein Arne Berge (b. 1949), a noted Norwegian amateur mineralogist and collector who was the first to observe and record this mineral from its type locality as a potential new species.

Carbonate rocks in the Mojave Desert as an analogue for Martian carbonates

AbstractCarbonate rocks in the Mojave Desert are presented as potential analogues for the carbonates on Mars. Rocks collected from the Little Red Hill site contain iron oxide-bearing coatings that greatly suppress the spectral features due to carbonate of the underlying material and impart a spectral slope. The Mojave Desert was formerly a lush pedogenic soil environment that, over time, transformed into the current arid climate with abundant rock varnish. One niche for microbes in the current desolate environment is inside and underneath the rocks where the microbes profit from solar protection by the iron oxide rock coatings. Carbonates were long predicted to be present on Mars and have recently been detected by instruments on Phoenix and MER and using hyperspectral orbiters such as the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), the Planetary Fourier Spectrometer (PFS) and the Thermal Emission Spectrometer (TES). We describe here the results of a study of carbonate rocks from the Little Red Hill site of the Mojave Desert that includes X-ray diffraction (XRD), chemistry and visible-infrared reflectance spectroscopy. Coatings on the carbonate rocks greatly reduced the strength of the carbonate bands and caused changes in the shape of some bands. We compare these data with a carbonate outcrop at Nili Fossae, Mars. If microbes once inhabited Mars, similar carbonate rocks with iron oxide coatings could have provided a UV-protected niche there as well. Thus, analysis of carbonate-bearing regions on Mars by future landers would be useful sites to search for biosignatures.

Laboratory-prepared iron oxide coatings on sands: Submicron-scale small-strain stiffness

Chemical weathering of iron-bearing rock minerals results in the formation of iron oxides, which can chemically adsorb onto soil surfaces, and/or absorb into their molecular structure. The objective of this paper is to use laboratory-prepared, iron oxide-coated sand to study the role of iron oxide coatings on the small-strain stiffness of coarse-grained soil. Ottawa sands were geochemically coated with iron oxides of goethite and hematite via a heterogeneous suspension reaction in the laboratory. Specimen preparation techniques were chosen to ensure that the soils were not cemented during preparation. SEM images, ICP analysis, and geotechnical index tests were used to characterize the submicron-scaled iron oxide coatings, and the bender element method was used to measure the shear wave velocities of uncoated and the two iron oxide coated sands. Contact mechanics and submicron scale mechanistic approaches were explored to interpret the experimental data, and results indicated that small-strain stiffness of iron oxide coated sands was higher than that of uncoated sands. Results also suggested that a small-strain stiffness behavioral hierarchy associated with iron oxide thermodynamic stability may exist. This study demonstrated that iron oxide coatings significantly influence sand grain-to-grain behavior, even in the absence of cementation or augmented contact area effects, due to an increase in the number of particle contacts present in the iron oxide coated sands.

ChemInform Abstract: Sonochemical Synthesis and Characterization of Iron Oxide Coated on Submicrospherical Alumina: A Direct Observation of Interaction Between Iron Oxide and Alumina.

Coating of iron oxides on submicrospheres of alumina was carried out by the sonochemical method. Three kinds of alumina were used, namely, the as-prepared, 700 and 1000 °C heated-alumina. TEM results reveal various coating effects on different heat-treated substrates. The optimum coating is obtained on as-prepared amorphous alumina, in which most of the iron oxide particles are adhered to alumina spheres tightly, while in the sample coated on crystallized alumina heated at 1000 °C, most of the iron oxide particles remain separate from the alumina spheres. The strong interaction between iron oxides and alumina substrate was directly observed by XRD, TEM, and IR and magnetic measurements. Owing to the strong interaction between adhered iron particles and alumina substrate, the complete transformation of γ-Fe2O3 to α-Fe2O3 was retarded to higher than 700 °C; conversely, the presence of haematite can induce the formation of α-Al2O3 at the high temperatures. TEM images clearly show the changes of particle size...

Paraquat and Diquat Sorption on Iron Oxide Coated Quartz Particles and the Effect of Phosphates

The covering of quartz particles (Q) with Fe oxides provides high capacity sorption and immobilization of both paraquat (PQ) and diquat (DQ) as well as phosphates (P), that can be used to remediate contaminated environments due to their persistence. Both PQ and DQ have higher sorption strength on crystalline iron oxide coated quartz particles (QFec) than on amorphous iron oxides (QFea), but the highest is for PQ, which might be due to its strongest interaction. The increasing addition of P contributes to the increase of quat maximum sorption on iron oxide coated quartz particles, because the cosorption of P causes the surface charge to become more negative, facilitating the sorption of positively charged quats, but this happens in a different way for both quats. It was also seen that the formation of phosphate−quat complexes has a lower affinity than P by the coated quartz particles. The characteristics of the coated quartz particles would allow increased sorption of these quaternary ammonium herbicide contaminants.

Eolian Transport of Geogenic Hexavalent Chromium to Ground Water

A conceptual model of eolian transport is proposed to address the widely distributed, high concentrations of hexavalent chromium (Cr(+6)) observed in ground water in the Emirate of Abu Dhabi, United Arab Emirates. Concentrations (30 to more than 1000 microg/L Cr(+6)) extend over thousands of square kilometers of ground water systems. It is hypothesized that the Cr is derived from weathering of chromium-rich pyroxenes and olivines present in ophiolite sequence of the adjacent Oman (Hajar) Mountains. Cr(+3) in the minerals is oxidized to Cr(+6) by reduction of manganese and is subsequently sorbed on iron and manganese oxide coatings of particles. When the surfaces of these particles are abraded in this arid environment, they release fine, micrometer-sized, coated particles that are easily transported over large distances by wind and subsequently deposited on the surface. During ground water recharge events, the readily soluble Cr(+6) is mobilized by rain water and transported by advective flow into the underlying aquifer. Chromium analyses of ground water, rain, dust, and surface (soil) deposits are consistent with this model, as are electron probe analyses of clasts derived from the eroding Oman ophiolite sequence. Ground water recharge flux is proposed to exercise some control over Cr(+6) concentration in the aquifer.

Micromorphological evidence for mineral weathering pathways in a coastal acid sulfate soil sequence with Mediterranean-type climate, South Australia

Soil micromorphology, using light microscopy and scanning electron microscopy (SEM), was used to describe detailed soil morphological and compositional changes and determine mineral weathering pathways in acid sulfate soils (ASS) from the following 2 contrasting coastal environments in Barker Inlet, South Australia: (i) a tidal mangrove forest with sulfidic material at St Kilda, and (ii) a former supratidal samphire area at Gillman that was drained in 1954 causing sulfuric material to form from sulfidic material. Pyrite framboids and cubes were identified in sulfidic material from both sites and are associated with sapric and hemic materials. Gypsum crystals, interpreted as a product of sulfide oxidation, were observed to have formed in lenticular voids within organic matter in the tidal mangrove soils at St Kilda. Sulfide oxidation was extensive in the drained soil at Gillman, evidenced by the formation of iron oxyhydroxide pseudomorphs (goethite crystallites and framboids) after pyrite and jarosite, and of gypsum crystals. Gypsum crystals occur where a local source of calcium such as shells or calcareous sand is present. Sporadic oxidation episodes are indicated by the formation of iron oxide and jarosite coatings around coarse biogenic voids. These observations indicate that mineral transformation pathways are strongly influenced by soil physico-chemical characteristics (i.e. oxidation rate, Eh, pH, soil solution chemistry, mineralogy, and spatial distribution of sulfides). This information has been used to illustrate the interrelationships of pyrite, carbonate, gypsum, jarosite, and organic matter and help predict soil evolution under changing hydro-geochemical, redoximorphic, and thermal conditions in soils from coastal environments.

Genesis of light-colored acid eluvial horizons in soil profiles

General ideas concerning the formation of light-colored acid eluvial horizons in soil profiles are considered. In Russia, the current concept is related to the polygenetic origin of these horizons due to processes of acid hydrolysis, lessivage, and gley. Based on the original and literature data summarized by the author, the conclusion was drawn that the acid hydrolysis cannot provide the reduction of Fe (III) to Fe (II) under aerobic conditions or its further transfer to the soil solution. Lessivage, which governs the formation of light-colored acid eluvial horizons, is not an obligatory factor, as its features are often absent in the profile of these soils. Under conditions of a stagnant-percolative water regime, gley may be considered to be the only process responsible for the eluviation of Fe, Mn, and Al and removal of iron hydroxide and iron oxide coatings from mineral grains, resulting in an increase in the relative Si content and the appearance of a whitish color. This factor is the only cause for the formation of light-colored eluvial (podzolic) horizons. Therefore, they are monogenetic in origin.

The staining of blue stone limestones petrographically unraveled

This paper deals with the first results of a comparative petrographical study of un-aesthetically stained blue stone limestones, including Lower Carboniferous crinoidal limestones and Middle Cambrian oolitic limestones. Although it was commonly accepted that this staining resulted from weathering of ferroan dolomite, our study proved that it rather resulted from weathering of framboidal pyrite and subsequent dissolution of partially dedolomitized dolomite. Meteoric weathering resulted in a chemical reaction chain including oxidation of pyrite, formation of sulphate-rich water, dissolution of dedolomitized dolomite rhombs and precipitation of iron (hydr)oxide coatings in the intercrystalline dissolution voids. Weathering was probably accelerated by an increased permeability, related to the presence of open stylolites and/or by initial secondary dolomitization of the host limestone. Optical microscopy of fluorescent epoxy impregnated thin sections and of polished slabs proved to be particularly useful in elucidating the above staining mechanism, especially in combination with SEM and BSEM with on-line WDS/EDS.

Chromium vaporization of bare and of coated iron–chromium alloys at 1073 K

Suppression of chromium vaporization from oxidation scales formed on ferritic stainless steel, when used on the cathode side of Solid Oxide Fuel Cells (SOFC), is a most important issue, since gaseous chromium species cause deposition of chromium oxide on electrolyte or electrode materials. This phenomenon leads to deterioration of the cell performance. The chromium vaporization rates of bare and of coated iron–chromium alloys were measured at 1073 K. The effect of ceramic coating layers, deposited by low-cost aerosol spraying or by dip coating, was evaluated and the morphology of the coating layer was observed. Lanthanum strontium manganese oxide (LSM: La 0.65Sr 0.3MnO 3), lanthanum strontium cobalt iron oxide (LSCF: La 0.6Sr 0.4Co 0.8Fe 0.2O 3) and manganese cobalt oxide (MCO: MnCo 2O 4) coatings, formed from submicron powders, decreased chromium vaporization by a factor of as much as 21–40 at 1073 K. Manganese cobalt oxide and lanthanum strontium chromium oxide (La 0.7Sr 0.3CrO 3) coating, formed from powders prepared by a glycine nitrate combustion synthesis, reduced chromium vaporization by factors of only 2–3 because the coating layers were porous.

Quantitative detection of aqueous arsenic and other oxoanions using attenuated total reflectance infrared spectroscopy utilizing iron oxide coated internal reflection elements to enhance the limits of detection

An attenuated total reflectance Fourier transform infrared spectroscopy technique has been developed utilizing an oxide coated internal reflection element to quantitatively evaluate the concentrations of three inorganic oxoanions, arsenate, sulfate, and selenate, at environmentally significant levels. Two iron oxide coatings, goethite and an iron sol–gel, were used and compared to an uncoated internal reflection element which typically has a limit of detection around 1.0 mM. The goethite coating improved the limits of detection by factors of 45.6 and 137.0 for arsenate and sulfate as compared to an uncoated cell. The iron sol coating improved the limits of detection by factors of 481.2, 156.2, and 114.0 for arsenate, sulfate, and selenate, respectively.

Coating carbon nanotubes with iron oxide using methanol–thermal reaction

Based on a methanol–thermal reaction method, coating carbon nanotubes (CNTs) with needle-like iron oxide has been achieved. The structure, composition and morphology of the coatings were characterized by using transmission electron microscopy, X-ray energy dispersive spectrum and X-ray photoelectron spectroscopy. The experimental results indicate that the pre-oxidation of CNTs and the acid-based methanol–thermal environment are very important points to obtain dense and uniform coatings on CNTs. Magnetic measurement for the iron oxide coatings indicates that the coercivity has been enhanced after coating.

The impact of additives found in industrial formulations of TCE on the wettability of sandstone

The wettability of aquifer rocks is a key physical parameter which exerts an important control on the transport, residual trapping, distribution and eventual fate of chlorinated hydrocarbon solvents (CHSs) released into the subsurface. Typically chlorinated solvents are assumed to be non-wetting in water saturated rocks and unconsolidated sediments. However industrially formulated solvent products are often combined with basic additives such as alkylamines to improve their performance; and the mineral surfaces of aquifer rocks and sediments usually possess a range of acid and hydrogen-bonding adsorption sites. The presence of these sites provides a mechanism whereby the basic additives in CHSs can be adsorbed at the solvent phase/solid phase interface. Given the amphiphilic molecular structure of these additives, this may result in changes in the wetting conditions of the solid phase. The aim of this study was therefore to test this conjecture for two classes of additives (alkylamines and quaternary ammonium salts) that are often encountered in industrial solvent formulations. Wettability assessments were made on sandstone cores by means of measurements of spontaneous and forced water drainage and spontaneous and forced water imbibition and through contact angle measurements on a smooth quartz surface. No solvent/additive combination produced solvent wetting conditions, though dodecylamine and octadecylamine significantly reduced the water wetting preference of sandstone which frequently resulted in neutral wetting conditions. The large volume of spontaneous water drainage observed in wettability experiments involving cetyltrimethylammonium bromide and octadecyltrimethylammonium bromide, suggested that the sandstone cores in these tests remained strongly water wetting. However equilibrium static contact angles of around 60° were measured on quartz suggesting that the sandstone surfaces should be close to neutral wetting conditions. This paradox was finally resolved by noting that contact between the solvent mixture and water in the sandstone core resulted in a final solvent phase which had an extremely low interfacial tension. It is therefore suspected that the observed spontaneous drainage of solvent from the core was driven by gravitational and buoyancy forces rather than strong water wetting conditions. Finally it was noted that the mobilisation of iron oxide coatings from the sandstone surface had a considerable influence in reducing the interfacial tension and in the formation and stabilisation of TCE/water emulsions.

Metal Oxide Coating on Carbon Nanotubes by a Methanol-Thermal Method

A methanol-thermal method has been developed to fabricate one-dimensional composite nanowires by coating multiwalled carbon nanotubes with lanthanum oxide and iron oxide, respectively. The coating structure and composition have been investigated by transmission electron microscopy and the X-ray energy dispersive spectrum. Magnetic measurement for the iron oxide coatings indicated that the coercivity has been enhanced after coating. The method reported here provides a novel procedure for the fabrication of one-dimensional composite nanostructures.

Synthesis and characterization of iron oxide-coated silica and its effect on metal adsorption

To accurately model metal mobility and bioavailability in soils and sediments, systematic adsorption studies are needed in considering heterogeneous, well characterized minerals. Two important surfaces are iron oxide and silica, which are ubiquitous and associated with one another in the environment playing important roles in metal distribution. This study focuses on the synthesis and characterization of such a system, iron oxide-coated silica. A three-level fractional factorial study was used to determine the optimum conditions for producing goethite-coated silica. The amount of coating achieved was between 0.59 and 21.36 mg Fe g −1 solid. The most significant factor in coating using either adsorption or precipitation was the particle size of silica, where Fe increased from an average of 0.85 to 9.6 mg Fe g −1 solid as silica size decreased from 1.5 to 0.2 mm. Other factors investigated, including coating temperature, initial iron concentration, and contact time, were of less importance. The iron oxide coatings were observed to be non-uniform, concentrated in rough concave areas. FTIR revealed a band shift as well as a new band indicating changes in the chemical environment of Fe O and Si O bonds; these results along with abrasion studies suggest that the interaction between the oxide coating and silica surface potentially involves chemical forces. Because the nano-sized iron oxide coatings increased surface area, introduced small pores, and changed the surface charge distribution of silica, the coated system demonstrates a greater affinity for Ni compared to that of uncoated silica.

Optical and thermoluminescence dating of Middle Stone Age and Kintampo bearing sediments at Birimi, a multi-component archaeological site in Ghana

We report the first luminescence ages for the archeological and geological sediments forming the substrate of the Birimi archaeological site in the Northern Region of Ghana. The site's significance rests on the fact that it contains a rich collection of artifact assemblages representative of three distinct cultures, and that, on the basis of artifact typology, the earliest assemblage is diagnostic of the Middle Stone Age (MSA) . In situ occurrences of MSA artifacts are found at over 1 m below today's surface. They are overlain by a ceramic-rich complex of a sedentary or semi-sendentary Later Stone Age culture known as the Kintampo. The western half of the site is dominated by the industrial remains of Iron Age smelting activity. Elemental, mineralogical, and sedimentological analysis of the cultural and sub-cultural sedimentary horizons at the site revealed at least three distinct lithostratigraphic units. The quartz sediments are derived from the sandstone of the Gambaga escarpment, mass wasted and accreted fluvially at a rate of 3.2 cm/ka, forming a wide terrace at Birimi. Silts and finer fractions derive from windblown dust, likely from White Volta River and granitic sources to the north. Soil forming processes and wide fluctuations in moisture have progressively reduced the sediments at depth to the resistant quartz and kaolinite, with rich iron oxide coatings, and created two ironstone horizons composed of goethite-cemented quartz nodules. Multiple aliquot green-light stimulated optical ages for 125–150 μm quartz grains yielded ages of 23.6±2.9 and 40.8±11.8 ka for the MSA-bearing sediments, and 58.4±15.3 ka for the base of the terrace. Radiocarbon ages on charcoal from Kintampo-bearing units are 3.36–3.83 ka cal BP, and are supported by thermoluminescence (TL) ages on pottery sherds and burnt house daub fragments of this cultural complex. A 0.4 ka age on sediment from the site's surface confirms that the quartz zeroes well when exposed to natural light. Sediments bearing the Kintampo artifacts, however, yielded ages of 7.8–16.9 ka. These ages were obtained on sediments from large pits, some over 50 cm deep, and they deviate only slightly from the ages expected for naturally aggraded sediments at these depths. We conclude, therefore, that extensive digging of pits by the Kintampo dwellers was followed by rapid refilling, and that the bulk mobilization of the matrix did not permit the sedimentary quartz grains to experience any appreciable zeroing at that time.

2628 酸化鉄の摩擦・摩耗特性

2628 酸化鉄の摩擦・摩耗特性