Analyses of Rumanová meteorite

Mössbauer spectroscopy was used as an analytical tool in investigation of iron containing compounds of Rumanová meteorite found on Slovak territory and it was classified as chondrite H. The results showed that the Mössbauer spectra consist of magnetic and non-magnetic components related to different iron-bearing phases. In non-magnetic part, olivine, pyroxene, and traces of Fe^3?+? phases have been identified. The magnetically ordered part of the Rumanová meteorite spectrum consists of kamacite, troilite and the third additional component corresponds to hydroxides originating from weathering due to being long time on the Earth surface. The weathering products can be recognised mainly as maghemite, however traces of other weathering components as akagaenite, goethite and magnetite cannot be excluded. On the contrary to Rumanová, no weathering products have been found in the sample of Ko?ice meteorite which fell on the territory of Slovakia in February 2010 and has been investigated a few months after the fall.     

Re-examination of Dronino iron meteorite and its weathering products using Mössbauer spectroscopy with a high velocity resolution

Re-examination of Dronino iron meteorite and products of its weathering in the internal and external surface layers was carried out using Mössbauer spectroscopy with a high velocity resolution. New results showed the presence of α-Fe(Ni, Co), α ₂-Fe(Ni, Co) and γ-Fe(Ni, Co) phases with variations in Ni concentration in Dronino metallic iron alloy. The surface weathering products were supposed as magnetite and/or maghemite, goethite with different particles size and probably ferrihydrite in the internal layer and goethite with different particles size and probably ferrihydrite in the external layer.     

Characterization of initial atmospheric corrosion of conventional weathering steels and a mild steel in a tropical atmosphere

The phases and compositions of the corrosion products of a mild steel (A-36) and two weathering steels (A-588 and COR 420) formed after 3 months exposure to the tropical marine atmosphere of Panama were examined using FTIR and Mössbauer spectroscopy. The results show that amorphous or crystallized iron oxyhydroxides goethite α-FeOOH and lepidocrocite γ-FeOOH are early corrosion products. Maghemite γ-Fe₂O₃ and magnetite Fe₃O₄ have also been identified and found to be prominent components for steels exposed to the most aggressive conditions. The formation of akaganeite β-FeOOH was observed when chlorides were occluded within the rust. FTIR showed the presence of hematite α-Fe₂O₃ in one sample.     

Two earth years of Mössbauer studies of the surface of Mars with MIMOS II

The element iron plays a crucial role in the study of the evolution of matter from an interstellar cloud to the formation and evolution of the planets. In the Solar System iron is the most abundant metallic element. It occurs in at least three different oxidation states: Fe(0) (metallic iron), Fe(II) and Fe(III). Fe(IV) and Fe(VI) compounds are well known on Earth, and there is a possibility for their occurrence on Mars. In January 2004 the USA space agency NASA landed two rovers on the surface of Mars, both carrying the Mainz Mössbauer spectrometer MIMOS II. They performed for the first time in-situ measurements of the mineralogy of the Martian surface, at two different places on Mars, Meridiani Planum and Gusev crater, respectively, the landing sites of the Mars-Exploration-Rovers (MER) Opportunity and Spirit. After about two Earth years or one Martian year of operation the Mössbauer (MB) spectrometers on both rovers have acquired data from more than 150 targets (and more than thousand MB spectra) at each landing site. The scientific measurement objectives of the Mössbauer investigation are to obtain for rock, soil, and dust (1) the mineralogical identification of iron-bearing phases (e.g., oxides, silicates, sulfides, sulfates, and carbonates), (2) the quantitative measurement of the distribution of iron among these iron-bearing phases (e.g., the relative proportions of iron in olivine, pyroxenes, ilmenite and magnetite in a basalt), (3) the quantitative measurement of the distribution of iron among its oxidation states (e.g., Fe²⁺, Fe³⁺, and Fe⁶⁺), and (4) the characterization of the size distribution of magnetic particles. Special geologic targets of the Mössbauer investigation are dust collected by the Athena magnets and interior rock and soil surfaces exposed by the Athena Rock Abrasion Tool and by trenching with rover wheels. The Mössbauer spectrometer on Opportunity at Meridiani Planum, identified eight Fe-bearing phases: jarosite (K,Na,H3O)(Fe,Al)(OH)6(SO4)2, hematite, olivine, pyroxene, magnetite, nanophase ferric oxides (npOx), an unassigned ferric phase, and a metallic Fe–Ni alloy (kamacite) in a Fe–Ni-meteorite. Outcrop rocks consist of hematite-rich spherules dispersed throughout S-rich rock that has nearly constant proportions of Fe³⁺ from jarosite, hematite, and npOx (28%, 35%, and 19% of total Fe). Jarosite is mineralogical evidence for aqueous processes under acid–sulfate conditions because it has structural hydroxide and sulfate and it forms at low pH. Hematite-rich spherules, eroded from the outcrop, and their fragments are concentrated as hematite-rich soils (lag deposits) on ripple crests (up to 68% of total Fe from hematite). Olivine, pyroxene, and magnetite are primarily associated with basaltic soils and are present as thin and locally discontinuous cover over outcrop rocks, commonly forming aeolian bedforms. Basaltic soils are more reduced (Fe³⁺/Fe_total ～0.2?0.4), with the fine-grained and bright aeolian deposits being the most oxidized. Basaltic soil at Meridiani Planum and Gusev crater have similar Fe-mineralogical compositions. At Gusev crater, the Mössbauer spectrometer on the MER Spirit rover has identified 8 Fe-bearing phases. Two are Fe²⁺ silicates (olivine and pyroxene), one is a Fe²⁺ oxide (ilmenite), one is a mixed Fe²⁺ and Fe³⁺ oxide (magnetite), two are Fe³⁺ oxides (hematite and goethite), one is a Fe³⁺ sulfate (mineralogically not constrained), and one is a Fe³⁺ alteration product (npOx). The surface material in the plains have a olivine basaltic signature (Morris, et al., Science, 305: 833, 2004; Morris, et al., J. Geophys. Res., 111, 2006, Ming, et al., J. Geophys. Res., 111, 2006) suggesting physical rather than chemical weathering processes present in the plains. The Mössbauer signature for the Columbia Hills surface material is very different ranging from nearly unaltered material to highly altered material. Some of the rocks, in particular a rock named Clovis, contain a significant amount of the Fe oxyhydroxide goethite, α-FeOOH, which is mineralogical evidence for aqueous processes because it is formed only under aqueous conditions.     

On the reaction of iron oxides and oxyhydroxides with tannic and phosphoric acid and their mixtures

The actions of tannic acid, phosphoric acid and their mixture on lepidocrocite, goethite, superparamagnetic goethite, akaganeite, magnetite, hematite and maghemite for 1 day and 1 month were explored. It was found that these acids form iron tannates and phosphates. Lepidocrocite and magnetite were the iron phases more easily transformed with the mixture of the acids after 1 month of reaction, whereas hematite was the most resistant phase. In the case of goethite, our results suggest that in order to understand properly the action of these acids, we have to take into account its stoichiometry, surface area and degree of crystallinity.     

An57Fe Mössbauer study of iron concretions in weathered,nickeliferous Cuban crust

A study of iron concretions of the highest stratum in cuban weathering crust using⁵⁷Fe Mössbauer spectroscopy has been performed. Goethite, hematite and maghemite are reported as main phases of these concretions. The density distribution function of the effective magnetic field in the Fe nuclei,p(H _n) showed a greater reduction of the effective magnetic field in the Fe nuclei of goethite than in the hematite ones and a broadening of Mössbauer lines for goethite spectrum as a consequence of a greater influence of relaxation effects.     

Characterization of Chinese loess and associated palaeosol by Mössbauer spectroscopy

A Mössbauer study of magnetically enriched samples of loess and associated, palaeosol from a section in Jixian (China) reveals that the iron-bearing magnetic components are predominantly hematite and magnetite, exhibiting to a large extent similar features in loess and soil. The only important difference observed is the presence of a substantial amount of maghemite in the soil, indicating an advanced stage of weathering of magnetite in the latter. It is therefore concluded that the enhanced remanence observed in the soil can mainly be explained by a dilution of the primary non-magnetic loess minerals and the acquisition of chemical remanence.     

Corrosion Products Formed on Mild Steel Samples Submerged in Various Aqueous Solutions

Corroded samples, from the steel shell of an industrial evaporator system were investigated. A protective magnetite layer had formed, which subsequently dissolved in localised areas, resulting in failure of the shell. To clarify the mechanisms involved, mild steel samples of similar composition to the steel shell were submerged in the condensate and experiments were performed at room temperature and at 90°C under both static and dynamic conditions for exposure times up to 30 days. Control samples were submerged in deionised water under similar conditions. The dynamic corrosion rates in the industrial condensate were a factor of 2 higher than the rates for the deionised water, whilst static corrosion rates, measured in both media, were lower by a factor of 3 to 4 found for the dynamic experiments. The corrosion products were identified by means of CEMS analyses. The main components were magnetite and oxyhydroxides of iron. Additional to the species mentioned, -Fe₂O₃, goethite and hematite formed.     

A Comparative Study of Iron Concentrates by Mössbauer Spectroscopy and Optical Microscopy

Five samples of iron-ore concentrates used for the production of pellets were heated at different temperatures under air atmosphere and characterised by chemical analysis, optical microscopy and Mössbauer spectroscopy. In all samples it was observed the presence of specular hematite, martite, and goethite in different proportions, whereas one sample also contains 15% (w/w) of magnetite. The presence of residual goethite was observed in the samples heated at 300°C, whereas the magnetite was only converted to hematite after heating at 900°C. However, the results of the optical microscopy pointed to the existence of large amounts of goethite even in the samples heated at 900°C, which is obviously incorrect. Therefore, it can be concluded that the reflectance of hematite derived from goethite is similar to that of the original goethite, limiting the use of optical microscopy for these types of samples.     

Hematite from a mining area in the east border of Quadrilátero Ferrífero, Minas Gerais, Brazil

Iron oxides are dominant minerals in many geo-domains of economical interest, as iron ore mines. Knowing the main mineral transformation pathways is a fundamental step to plan prospecting new mineral deposits. This study aimed at contributing to a better understanding of the chemical and mineralogical processes related to the genesis and transformations of iron oxides involving hematite in an iron-ore mine of the east border of Quadrilátero Ferrífero, Minas Gerais, Brazil. Two representative geo-samples were analyzed with synchrotron radiation X-ray diffraction (XRD), ⁵⁷Fe Mössbauer spectroscopy, X-ray fluorescence and saturation magnetization (σ) measurements. The iron content varied from 65 to 69 mass% Fe. From XRD data, hematite is indeed the major mineral for all samples but characteristic reflections of goethite and magnetite also appear. For the magnetic sample, σ = 6.9 J T^???1 kg^???1. 298 K- and 110 K-Mössbauer data allow characterizing hematite in these iron-rich geo-materials.     

The growth of the passive film on iron in 0.05 M NaOH studied in situ by Raman micro‐spectroscopy and electrochemical polarisation. Part I: near‐resonance enhancement of the Raman spectra of iron oxide and oxyhydroxide compounds

Raman spectroscopy, in principle, is an excellent technique for the study of molecular species developed on metal surfaces during electrochemical investigations. However, the use of the more common laser wavelengths such as the 514.5‐nm line results in spectra of less than optimal intensity, particularly for iron oxide compounds. In the present work, near‐resonance enhancement of the Raman spectra was investigated for the iron oxide and iron oxyhydroxide compounds previously reported to be present in the passive film on iron, using a tuneable dye laser producing excitation wavelengths between 560 and 637 nm. These compounds were hematite (α‐Fe₂O₃), maghemite (γ‐Fe₂O₃), magnetite (Fe₃O₄), goethite (α‐FeOOH), akaganeite (β‐FeOOH), lepidocrocite (γ‐FeOOH) and feroxyhyte (δ‐FeOOH). Optimum enhancement, when compared to that with the 514.5‐nm line, was obtained for all the iron oxide and oxyhydroxide standard samples in the low wavenumber region (<1000 cm⁻¹) using an excitation wavelength of 636.4 nm. Particularly significant enhancement was obtained for lepidocrocite, hematite and goethite. Copyright © 2010 John Wiley & Sons, Ltd.     

漫反射光谱法对闽粤沿海花斑粘土沉积环境及成因的指示

赤铁矿和针铁矿是自然界最常见的两种铁氧化物,广泛分布于沉积物中,其相对含量关系不仅可以反映沉积环境,同时也为成因判别提供依据。由于传统测试方法操作复杂、效率低下,因此难以快速而准确的测定铁氧化物的种属及含量。近年来,基于紫外-可见光-近红外分光光度计的漫反射光谱分析法因操作简单、测试速度快、检测限低等优势,被广泛地应用于沉积物的研究中。在我国闽粤沿海的晚第四纪盆地中,广泛发育一套末次盛冰期的黄色粉土层,有时混杂红、灰色,也被称为“花斑粘土”。对于该套花斑粘土层,前人多将其归因于海进期的水下沉积物在全球低海面时期,顶部因暴露地表风化所致。而研究发现,大部分花斑粘土与下伏沉积在岩性上没有过渡,截然相交,“风化”难以解释该现象;花斑粘土中也并无发现其下伏沉积层所富含的海相生物化石,表明两者在沉积环境及物源上存在较大差异。为了进一步判定花斑粘土的沉积环境及成因,在以往研究的基础上,使用漫反射光谱分析法,从铁矿物特征的角度对珠江三角洲第四纪钻孔进行研究。结果表明,花斑粘土的赤铁矿特征峰峰高>针铁矿特征峰峰高,而其下伏沉积层的赤铁矿特征峰峰高<针铁矿特征峰峰高。赤铁矿是干燥温暖、陆上氧...     

漫反射光谱测定云南元谋盆地古红土铁氧化物

铁氧化物矿物是现代土壤和古土壤的重要组成,其数量和形态是反映土壤成土条件和土壤风化发育程度的重要指标。鉴于其粒度细小、结晶度差、含量低、与粘土矿物密切共生, 加之基体效应的影响,难以快速准确测定其含量;鉴于某些测试方法自身的限制,能用于铁氧化物矿物定量分析的方法也很少。在分析目前常用测量方法的基础上,选择漫反射光谱法（DRS）对云南元谋盆地所采古红土样品中的铁氧化物进行定量研究,结果表明：漫反射光谱法测得土壤样品在400~2 500 nm之间,间隔2 nm共1 061个波段的光谱反射率最高45%左右,各样品反射率特征较为一致;漫反射光谱一阶导数显示,光谱主峰位于575 nm处,为赤铁矿的指示波谱段,次级峰位于435 nm处,为针铁矿的指示波谱段;确定云南元谋古红土存在赤铁矿和针铁矿,其含量范围3~5和5~10 g·kg-1,此结果获得XRD方法分析方法的佐证。     

A new method for preparation of magnetite from iron oxyhydroxide or iron oxide and ferrous salt in aqueous solution

In this study, a new method is proposed for the preparation of Fe₃O₄ from iron oxyhydroxides (goethite, akaganeite, lepidocrocite, feroxyhyte and ferrihydrite) or iron oxide (hematite) and ferrous salt in aqueous solution. The product is magnetite with various particle sizes. Products are characterized by X-ray powder diffraction, IR spectra and vibrating sample magnetometery.     

Influence of Cu and Ni on the morphology and composition of the rust layer of steels exposed to industrial environment

Four samples of steels with alloying elements were exposed to an industrial environment during 1,955 days, aiming to elucidate the effect of the alloying elements Cu and Ni on the resistance of weathering steels to corrosion processes. The samples were characterized with optical microscopy, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), saturation magnetization measurements and with energy dispersive (EDS), infrared, Mössbauer and Raman spectroscopies. All the steels originated orange and dark corrosion layers; their thicknesses were determined from the SEM images. EDS data of such rust layers showed that the alloying element content decreases from the steel core towards the outer part of the rust layer. Moreover, in the dark rust layer some light-gray regions were identified in the W and Cu-alloy steel, where relatively higher Cr and Cu contents were found. XRD patterns, infrared, Raman and Mössbauer spectra (298, 110 and 4 K) indicated that the corrosion products are qualitatively the same, containing lepidocrocite (γFeOOH; hereinafter, it may be referred to as simply L), goethite (αFeOOH; G), feroxyhite (δ′FeOOH; F), hematite (αFe₂O₃; H) and magnetite (Fe₃O₄; M) in all samples; this composition does not depend upon the steel type, but their relative concentrations is related to the alloying element. Mössbauer data reveal the presence of (super)paramagnetic iron oxides in the corrosion products. Saturation magnetization measurements suggest that feroxyhite may be an occurring ferrimagnetic phase in the rust layer.     

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.     

Evidence from Mössbauer spectroscopy of neo-formation of magnetite/maghemite in the soils of loess/paleosol sequences in China

Samples of four different loess/paleosol couplets of a loess sequence in Huangling (China) have been studied with ⁵⁷Fe Mössbauer spectroscopy. Each sample was separated into strongly, weakly and very weakly magnetic fractions. The iron mineralogy of the strongly magnetic fractions of both loess and soils consists of magnetite/maghemite and hematite together with some silicates. The soils contain some additional small-particle maghemite. From the spectral behaviour a similarity in terms of morphology and crystal chemistry for hematite throughout the whole section could be inferred. The ratio of iron in magnetite and maghemite to that in hematite differentiates well between the loess and soil samples. These results strongly suggest the neo-formation of magnetite/maghemite in the soils.     

Portable Raman study on the conservation state of four CorTen steel‐based sculptures by Eduardo Chillida impacted by urban atmospheres

Weathering steel, and particularly CorTen steel, is a very used material for modern artworks exhibited outdoors. One of the characteristic that makes this material so attractive to artists is the property to develop a protective rust layer composed by iron oxides which preserves its metallic core from atmospheric corrosion. This study was conducted to evaluate the conservation state of four CorTen sculptures by Eduardo Chillida, located in different places of Bilbao city (north of Spain) and affected by different factors (environmental among others) by using Raman spectroscopy. Measurements were performed in situ with a handheld Raman spectrometer mounted on a tripod with x–y–z axes motorization at the micron level. The most common oxyhydroxides detected were lepidocrocite (γ‐FeO(OH)), goethite (α‐FeO(OH)), hematite ( ‐Fe₂O₃) and magnetite (Fe₃O₄), being goethite the most stable phase. All the iron oxyhydroxides were identified in all of the studied sculptures but their relative amounts were different for each sculpture. The consequences of the marine aerosols exposure in the steel surface were also studied, detecting limonite (FeO(OH)·nH₂O) and akaganeite (β‐FeO(OH)). The results confirmed that the evolution of the rust layer present on the analyzed weathering steels is different, depending both on the exposure and the particular type of the steel. Copyright © 2012 John Wiley & Sons, Ltd.     

FT-IR、XPS和DFT研究乙酰氧肟酸钠在针铁矿或赤铁矿表面的吸附机理

采用FT-IR、X射线光电子能谱以及基于周期平面波的DFT方法分别研究了乙酰氧肟酸钠(aHA)在针铁矿或赤铁矿表面上的吸附结构,并将计算得到的光电子能谱移动和电荷转移实验得到的XPS结果进行对比.红外结果显示aHA可能以五元环螯合物形式吸附于针铁矿或赤铁矿表面,DFT计算结果表明aHA中氧肟酸基团的两个氧原子与针铁矿(101)或(100)表面上的一个铁原子形成五元环结构,同时氧肟酸基团中的两个氧还相应的与针铁矿表面邻近两个铁原子成键,但氧肟酸基团中的两个氧原子却只与赤铁矿(001)表面上的一个铁原子形成五元环结构.对于针铁矿(101)、(100)和赤铁矿(001)表面上吸附位点对应的铁原子,计算得到的光电子能谱移动与实验得到的光电子能谱移动基本相等,说明了计算结果的可靠性和所得吸附结构的合理性.     

Mössbauer study of corrosion products in the nuclear power plants

Corrosion products formed in the different parts of nuclear power plants are identified using Mössbauer spectroscopy. Both, compact and powder samples were investigated. Mössbauer experiments at room temperature identified corrosion products as predominantly nonstoichiometric ferrous, cation deficient magnetite and lepidocrocite. In some samples small quantities of goethite and hematite were found.