Microtextural Studies Research Articles

Area-preserving colour coding of inverse pole figure domain.

The inverse pole figure (IPF) map is a routinely displayed output in microtexture studies, interpreted using the attached colour legend/diagram. An area-preserving relation between the IPF domain and RGB colour domain has been developed here, and the resultant IPF colour diagrams of different crystal point group symmetries are presented.

Paleoenvironments of a proglacial lake in Schirmacher Oasis, East Antarctica: Insights from quartz grain microtextures

AbstractEighteen sediment samples from a 36 cm long sediment core retrieved from a proglacial lake (namely P 11) situated in the Schirmacher Oasis, East Antarctica, were analysed for the study of quartz grain morphology and microtexture, along with sand percentage, to reconstruct the paleoenvironmental changes in the lake during the Holocene. The age of the core ranges from 3.3 ka BP to 13.9 ka BP. The quartz grain morphology and microtexture reveal significant evidences of glacial transport along with some eolian and aqueous activities. On the basis of predominance of these signatures and the zonation from CONISS Cluster Analysis on the percentages of characteristic grain morphology and microtextures, the entire core has been subdivided into three major zones. From the paleoenvironmental perspective, it can be concluded that there is an onset of interglacial period at the advent of Holocene (12.3 ka BP), which reigned until 5.3 ka BP and thereafter, again a glacial environment prevailed until 3.3 ka BP with some variations in-between. The results indicate probable alternative colder and less colder phases in the study area, which are also well supported by the respective sand percentages in the sediments.

Micro-structure and micro-textural studies of friction stir welded AA6061-T6 subjected to different rotation speeds

The heat-treated AA6061-T6 plate was welded by friction stir butt-welding (FSW) using different rotation speeds. Electron backscattered diffraction (EBSD) results showed the occurrence of geometric dynamic re-crystallization within the stir zone (SZ), and existence of different shear texture components across the weld zone was revealed. It was found that the material flow was asymmetric around the tool in the stir zone. In addition, different rotation speeds also lead to different combinations of heat input and heterogeneous plastic deformation within the stir zone, which influences the mechanical behavior of the different welds during uniaxial tension and micro-hardness tests, due to the variations in the micro-structure.

Quartz surface microtextural studies of Cauvery River sediments, Tamil Nadu, India

The spatially distributed sand samples of the Cauvery River sediments in Tamil Nadu were investigated with respect to their surface microtextural features in north-east (NE) and south-west (SW) monsoon rainfall seasons. The quartz grains show distinct surface microtextures with unique mechanical, chemical and morphological features with respect to the sedimentation process. The mechanical features like conchoidal fractures with arcuate steps indicate that the sand grains were derived from crystalline rocks. The abundance of angular grains supports that the grains were transported long distance by fluvial process. The silica globule, overgrowth and precipitation marks on the grain surfaces decipher the chemical process in silica saturated environment. Similarly, the solution pits in sand grains near Poombugar indicate the influence of sea water. The chatter mark trails suggest the wet tropical climate. The abundance of mechanical features and smooth surface microtextures suggest that the grains were transported in high-energy conditions. The NE monsoon sediments are coarse grained to medium grained and SW monsoon sediments are medium to fine sand size, which are attributed to the high and moderate energy conditions, respectively.

Micro-texture and petrophysical properties of dilation and compaction shear bands in sand

We have studied micro-textural and petrophysical properties of dilation and compaction shear bands (zones) created during deformation of two quartz sands (Ottawa and Hostun sands), differing in angularity, under triaxial compression experiments. Image processing of in-situ CT-scan images taken during the experiments allowed both qualitative study of micro-texture, and quantitative study of porosity and dilatancy. Our results indicate that, in both sands at low confining pressure, i.e. 100 kPa, a zone of enhanced porosity (dilation shear band) is initiated with dilatancy factor ∼0.5–0.6, and towards the end of the tests the porosity continuously increases, especially at the center of the zone (from ∼33% to ∼45% for Ottawa sand and from ∼40% to ∼52% for Hostun sand). However at high confining pressure (7000 kPa), the tested sands reveal different dilatancy and porosity evolution. In rounded Ottawa sand, first a wide dilated zone (dilatancy factor ∼0.26) forms, and by progressive shear loading, a compacted zone is developed inside this dilated zone (dilatancy factor ∼−0.11). For the angular Hostun sand the dilatancy is negative both at the initiation and the final stage, which is reflected by a wide zone of compaction.

Routine characterization and interpretation of complex alkali feldspar intergrowths

Almost all alkali feldspar crystals contain a rich inventory of exsolution, twin, and domain microtextures that form subsequent to crystal growth and provide a record of the thermal history of the crystal and often of its involvement in replacement reactions, sometimes multiple. Microtextures strongly influence the subsequent behavior of feldspars at low temperatures during diagenesis and weathering. They are central to the retention or exchange of trace elements and of radiogenic and stable isotopes. This review is aimed at petrologists and geochemists who wish to use alkali feldspar microtextures to solve geological problems or who need to understand how microtextures influence a particular process. We suggest a systematic approach that employs methods available in most well founded laboratories. The crystallographic relationships of complex feldspar intergrowths were established by the 1970s, mainly using single-crystal X-ray diffraction, but such methods give limited information on the spatial relationships of the different elements of the microtexture, or of the mode and chronology of their formation, which require the use of microscopy. We suggest a combination of techniques with a range of spatial resolution and strongly recommend the use of orientated sections. Sections cut parallel to the perfect (001) and (010) cleavages are the easiest to locate and most informative. Techniques described are light microscopy; scanning electron microscopy using both backscattered and secondary electrons, including the use of surfaces etched in the laboratory; electron-probe microanalysis and analysis by energy-dispersive spectrometry in a scanning electron microscope; transmission electron microscopy. We discuss the use of cathodoluminescence as an auxiliary technique, but do not recommend electron-backscattered diffraction for feldspar work. We review recent publications that provide examples of the need for great care and attention to pre-existing work in microtextural studies, and suggest several topics for future work.

Study of micro-texture and skid resistance change of granite slabs during the polishing with the Aachen Polishing Machine

In this paper, massive granite slabs were cut from lumps of rock using a diamond saw. The surface of the stone slabs was then retreated so that the slabs were characterized by different degrees of roughness. On the other hand, the slabs had no macro-texture, so that the skid resistance depended exclusively on the micro-texture. The prepared slabs were polished under various polishing conditions using the Aachen Polishing Machine. Changes of the micro-texture were studied on the basis of both texture level measured by spectral analysis and skid resistance measurements measured by the British pendulum tester. The results showed that micro-texture and skid resistance changes of the slabs are related to the applied polishing agent, initial roughness and mineralogical compositions of the granite slabs. The contribution of micro-texture to the skid resistance can be described with a function of the two texture parameters.

Microstructure, texture, property relationship in thermo-mechanically processed ultra-low carbon microalloyed steel for pipeline application

An ultra-low carbon Ti-containing microalloyed steel has been thermo-mechanically controlled rolled and water-quenched. Microstructural characterization of the samples finish rolled in the temperature range of 750–850°C revealed the presence of polygonal ferrite, quasi-polygonal ferrite, acicular ferrite and granular bainite. Micro-texture study showed the dominance of random texture and cube orientation at higher deformation temperatures, whilst, α-fiber and γ-fiber components intensified with the decrease in finish rolling temperature. Characteristic ferrite-bainite microstructure with fine ferrite grain size (<4µm) and a uniform distribution of fine TiC particles (<100nm) offered decent combination of strength (yield strength: 478–497MPa, ultimate tensile strength: 557–571MPa), ductility (total elongation: 20–26%), and impact toughness (110–114J at −40°C). Such a combination of mechanical properties makes the steel a potential choice for pipeline application.

Pyrophanite pseudomorphs after perovskite in Perkupa serpentinites (Hungary): a microtextural study and geological implications

Pyrophanite in serpentinite at Perkupa (Hungary) is described in detail for the first time as a replacement product of perovskite. It occurs as a 20- to 30-μm-wide rim, mantling a remnant core composed of perovskite or its alteration products. The pyrophanite rim consists of an inner zone, representing a pseudomorph after perovskite, and an outer overgrowth zone. Raman mapping and electron backscatter diffraction data show that the pyrophanite rims typically represent single crystals rather than being composed of multiple domains in different crystallographic orientations. Perovskite occurs exclusively in the core of pyrophanite and was identified as the orthorhombic CaTiO3 phase, based on Raman spectra. Heterogeneous, polyphase mineral cores, consisting of calcite, anatase and/or brookite, kassite, and Mn-bearing kassite, in some cases in association with relict perovskite, are typical in the larger pyrophanite-rimmed grains. The crystallographically coherent pyrophanite rims could have formed through a process where the precursor perovskite crystal acted as a structural template for the newly forming phase, that is, by interface-coupled dissolution reprecipitation during serpentinization of the precursor rock. This alteration of perovskite to pyrophanite was not complete, resulting in the presence of perovskite fragments enclosed in pyrophanite. During the metamorphic evolution of the rock, some of the remnant perovskite cores further altered to TiO2 polymorphs (anatase and brookite) and calcite, via transitional alteration products.

Insights into the geotectonic evolution of the southern Rhodope as inferred from a combined AMS, microtextural and paleomagnetic study of the Tertiary Symvolon and Vrondou plutons

The present study focuses on the Tertiary granitoids of the Rhodope Massif, Northern Greece, namely the Early Miocene Symvolon pluton and the composite Miocene–Oligocene Vrondou pluton. In this paper we provide new anisotropy of magnetic susceptibility (AMS) data from Symvolon pluton, discussed along with previously published ones from Vrondou, as well as new paleomagnetic data from samples widely distributed over both studied regions, combined with macroscopic observations and microtextural examinations. The magnetic fabric study pointed out anisotropic bodies with strong preferred orientations of the magnetic grains; however, the paleomagnetic vectors, corrected for anisotropy effect, remain unchanged. Two groups of magnetic lineations were identified: a prevailing NE-SW-trending linear fabric, visible mainly in the Early Miocene plutons, and a second NW-SE-trending fabric, clearly imprinted in the Mid-Oligocene eastern part of the Vrondou pluton. Macro- and microtextural study revealed the presence of magmatic textures, mainly in eastern Vrondou, and sub-solidus plastic deformation textures in Symvolon and western Vrondou. Paleomagnetic results displayed a complex pattern with prevailing clockwise rotations reinforcing the existing pattern for N. Greece and supporting the capacity of granitic bodies to reliably record the Earth's magnetic field independently of their anisotropy.

Geochemical diagenetic trends during phosphorite formation – economic implications: The case of the Negev Campanian phosphorites, Southern Israel

AbstractResearch on the Upper Campanian (Upper Cretaceous) Negev phosphorites (Mishash Formation), based on microprobe analyses, Fourier Transform Infrared spectroscopy, wet chemistry, microtextural (Scanning Electron Microscopy) studies and mineralogical analyses, together with quantified rates of sedimentation and P accumulation, enables the chemistry of these rocks to be better constrained across the Negev area and allows their suitability for the manufacture of P fertilizers to be better determined. Two phosphorite facies are differentiated: (i) a pristine phosphorite facies of low P content, more typical of basinal sections and (ii) a reworked, granular phosphorite facies commonly enriched in P, found predominantly near palaeo‐highs and forming most of the economic phosphates. The distribution of F/P2O5, CO2/F, U(IV), Cd, Zn and other trace metals (Mo, Ni, Cr, Cu, V and Y), rare‐earth elements concentration, Ce and Eu anomalies and heavy rare earth elements enrichment, are controlled by these two facies. F/P2O5 in carbonate‐fluorapatite is much lower (0·090 to 0·107) in the pristine than in the reworked facies (0·107 to 0·120); in addition, the lower F/P2O5 in the pristine facies is coupled with: (i) higher Cd, Zn, Mo, Ni, Cr, Cu and V concentrations; (ii) a considerably reduced (&lt; 10%) U(IV) fraction of total U; (iii) lower rare earth elements/P2O5 and Y/P2O5 ratios; (iv) less negative Ce and Eu anomalies and lower heavy rare earth elements (Lu/La) enrichment; (v) an increase in Fe‐rich smectites in the clay fraction; and (vi) presence of OH in the carbonate‐fluorapatite structure. Sedimentary reworking of previously formed pristine phosphate, together with its redeposition near structural highs in more oxic bottom conditions, results in considerable diagenetic changes in the chemistry of the phosphorites, making them more suitable for economic exploitation. The results presented here provide geochemical criteria for identifying pristine phosphate in other phosphorite sequences and may help to better locate phosphate strata chemically suitable for the phosphate industry elsewhere.

Study of microstructure and microtexture of modified 9Cr–1Mo steel subjected to high deformation

The Nb–V modified 9Cr–1Mo ferritic steel is an extremely important structural material in the power industry. Present work is focused on how the microstructure, microchemistry and microtexture of this steel evolve during high degree of deformation, starting from the normalized and tempered condition. While the microstructure and microchemistry are analyzed using analytical transmission electron microscopy, the microtexture analysis is carried out using the electron back-scatter diffraction (EBSD) technique. High degree of cold rolling leads to the formation of forests of dislocations and cellular structure of ferritic matrix. The carbides were found to retain their morphology and chemistry after 88% cold work. Analysis of misorientation angles was used to derive the grain boundary character of the normalized and tempered steel and the deformed steel. Analysis of fiber texture reveals that deformation in the material does not lead to predominance of any particular fiber which is useful from fabrication point of view.

Study of Micro-Texture during Recovery and Recrystallisation in Folded BCC and FCC Sheet Samples

The sheet folding process generates both tensile and compressive strains across the folded section, producing systematic strain and texture gradients. In this investigation the EBSD technique has been used to gain insight into this phenomenon in folded ferritic steel and nickel alloys, both in the as folded and after annealing conditions. As expected in the fcc material the {111} and {110} fibre texture components get reinforced in the tensile and compressive regions respectively, while the {110} and {111} components are reinforced in the bcc material during folding. After annealing at 600oC for 40 minutes the texture components formed during the folding process are retained despite the formation of new strain free grains. The new grains were found to be slightly larger in the tensile regions than in the compressed regions this was the case for both materials. However, in the mid-region of the section in the nickel alloy abnormal grain growth took place, while only recovery was observed in the ferritic alloy.

Effect of Uni-Axial Tensile Deformation on Microstructure and Magnetic Properties of 3.2% Si Grain Oriented Electrical Steel

Cold rolled grain oriented (CRGO) steel was deformed by uni-axial tensile loading in three different directions: Rolling Direction (RD) (110) , Transverse Direction (TD) (110) and 45° to RD (110) . Deformation behavior was found to be different for the different directions of loading. Such differences were biased by the heat flattening coating and could be captured, effectively, through discrete dislocation dynamics simulations. Results from texture and micro-texture studies, mechanical tests and magnetic measurements show a clear relationship between strain hardening exponent (n) and degradation in magnetic properties (watt loss and permeability). These were also related to misorientation developments, relative recovery and deviations from ideal Goss orientation.

Evolution of texture and grain boundary microstructure in two-phase (α + β) brass during recrystallization

The evolution of texture and microstructure during recrystallization is studied for two-phase copper alloy (Cu–40Zn) with a variation of the initial texture and microstructure (hot rolled and solution treated) as well as the mode of rolling (deformation path: uni-directional rolling and cross rolling). The results of bulk texture have been supported by micro-texture and microstructure studies carried out using electron back scatter diffraction (EBSD). The initial microstructural condition as well as the mode of rolling has been found to alter the recrystallization texture and microstructure. The uni-directionally rolled samples showed a strong Goss and BR {236}⟨385⟩ component while a weaker texture similar to that of rolling evolved for the cross-rolled samples in the α phase on recrystallization. The recrystallization texture of the β phase was similar to that of the rolling texture with discontinuous ⟨101⟩ α and {111} γ fiber with high intensity at {111}⟨101⟩. For a given microstructure, the cross-rolled samples showed a higher fraction of coincident site lattice Σ3 twin boundaries in the α phase. The higher fraction of Σ3 boundaries is explained on the basis of the higher propensity of growth accidents during annealing of the cross-rolled samples. The present investigation demonstrates that change in strain path, as introduced during cross-rolling, could be a viable tool for grain boundary engineering of low SFE fcc materials.

Facial conditions of the formation of oxide ores in the World Ocean

This work is an analysis of the layered structure of ferromanganese concretions (FMC) from the Clarion-Clipperton ore province and Co-rich manganese from guyots of the Magellan seamounts, study of microtextures, detection and interpretation of accessory minerals, which allowed us to establish that the formation of deposits of oxide ores, was accompanied by active intraplate volcanism and the formation of sulfide structures, such as black smokers.

Constraints on eruption dynamics of basaltic explosive activity derived from chemical and microtextural study: The example of the Fontana Lapilli Plinian eruption, Nicaragua

The Fontana Lapilli deposit is one of very few examples of basaltic Plinian eruptions discovered so far. Juvenile clasts have uniform chemical composition and moderate ranges of density and bulk vesicularity. However, clast populations include two textural varieties which are microlite-poor and microlite-rich respectively. These two clast types have the same clast density range, making a distinction impossible on that base alone. The high bubble number density (∼ 10 7 cm − 3 ) and small bubble population of the Fontana clasts suggest that the magma underwent coupled degassing following rapid decompression and fast ascent rate, leading to non-equilibrium degassing with continuous nucleation as it is common for silicic analogues. The Fontana products have lower microlite contents (10–60 vol.%) with respect to the other documented basaltic Plinian eruptions suggesting that the brittle fragmentation, implied for the other basaltic Plinian deposits, does not apply to the Fontana products and another fragmentation mechanism led the basaltic magma to erupt in a Plinian fashion.

Electro-Optic and Thermo-Optic Properties of Phase Separated Polymer Dispersed Liquid Crystal Films

Polymer dispersed liquid crystal (PDLC) and guest host polymer dispersed liquid crystal (GHPDLC) films were prepared by phase separated polymerization induced phase separation (PIPS) technique. Micro-texture studies shows that the liquid crystal droplets of varying size (∼ 5–40 μm) consists mainly of bipolar configurations at lower field (∼ < 1V/μm). They develop into maltese type configuration at higher field (∼ 8V/μm, 10V/μm for PDLC and GHPDLC). It was seen that the optical transmission increases in both cases with increasing temperature. A higher threshold voltage for GHPDLC relative to PDLC films with temperature was noticed. GHPDLC film shows faster switching time (∼ 340 μsec) over PDLC (∼ 510 μsec).

Study of texture and microtexture during β to α + β transformation in a Ti–5Ta–1.8Nb alloy

This paper discusses the evolution of texture in a Ti–5Ta–1.8Nb alloy during the transformation of ‘deformed α + β → β → α + β’, characterized using X-ray diffraction and Electron Back Scattered Diffraction techniques. It exhibited a deformation texture of type—[1 0 −1 0]//axial direction (AD) for the wire, and a [0 0 0 2]//normal direction (ND) for the cold rolled sheet sample. On subsequent β-homogenization treatment and cooling, the initial deformation texture was replaced with a transformation texture of [1 1 −2 0]//ND for the sheet sample. The wire sample exhibited a transformation texture with (1 1 −2 2) aligned near to the wire cross-section. A deformation texture was found to be essential to introduce transformation texture.

Clay mineral genesis and chemical evolution in the Miocene sediments of Somosaguas, Madrid Basin, Spain

AbstractA mineralogical and microtextural study of Somosaguas Miocene deposits, located in the Madrid Basin (western Madrid, Spain), was carried out using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and optical microscopy, whereas crystal chemistry data were obtained by analytical electron microscopy-transmission electron microscopy and electron icroprobe analysis. Four stratigraphic sections were studied, compising detrital rocks representing intermediate and distal facies from alluvial fan deposits. The predominant source area of these sediments was the granitic rocks of the Spanish Central System with a lesser contribution of metamorphic rocks. Clayey arkoses are the most abundant rocks of these sections, typical of granite alteration under warm, semi-arid climates. The mineralogy is characterized by phyllosilicates, followed by feldspars and quartz. The data obtained reveal mineral mixtures of detrital (quartz, feldspars, kaolinite, micas and chlorite), transformed (illite and beidellite) and neoformed (montmorillonite) origin. Clay minerals resulted from interactions between detrital minerals and meteoric waters. Two trends of degradation of micas are detected. The first shows a transition from muscovites and dioctahedral illites, to beidellites. The other trend is defined by the biotite degradation to beidellites with different layer charge and octahedral Fe content. Montmorillonites were neoformed from the hydrolysis and weathering of primary minerals (feldspars and muscovite). Magnesian clay minerals such as sepiolite, palygorskite and trioctahedral smectites, extremely abundant in the centre of the basin, were not detected in Somosaguas sediments.