Thin Zone Research Articles

Depth-direction analysis of nickel depletion in a Ni–gadolinia-doped ceria hydrogen electrode after steam electrolysis operation

We have examined the initial-stage degradation of a Ni–gadolinia-doped ceria (GDC) cermet hydrogen electrode prepared on a GDC buffer layer of a stabilized-zirconia electrolyte supported cell during steam electrolysis operation at 800 °C. With use of an air reference electrode, the IR-free electrode potential E and ohmic resistance of the hydrogen electrode side (RH2-side) were recorded. After a steam electrolysis operation at −1.0 A cm−2 for 211 h, the RH2-side increased appreciably, by 36 %, while the value of E was nearly unchanged. It was found via a depth-direction analysis with use of focused ion beam-scanning ion microscopy that the remaining percentage of Ni decreased to ca. 60 % in the layer between 1 and 3 µm from the top of the GDC buffer layer, followed by a further decrease to 42 % at 0.5 µm. Since this suggests a significant cathodic polarization within the thin reaction zone, an enlargement of the reaction zone, together with a stabilization of Ni contacting with GDC, could be essential to mitigate such a degradation.

Influence of the Thickness of the Reaction Zone in Aluminum/Stainless Steel Brazed Joints on the Mechanical Properties

The study deals with the characterization of the relationship between the microstructure of the reaction zone and the mechanical properties in the brazed joints of aluminum alloy 3003 and stainless steel AISI 304 in order to determine the influence of the intermetallic layers on the tensile shear strength of the joints. The joints were produced by induction brazing using an AlSi10 filler in an argon atmosphere at a temperature of 600 °C. Due to the local heat input into the liquid brazing filler during a short brazing time, a thin reaction zone is formed in the brazed joints (~1 µm), which ensures good mechanical properties of the joints. In order to observe the growth kinetics of the reaction zone in the brazed joints and to investigate the influence of the thickness of the reaction zone on the mechanical properties of the brazed joints, the joints were aged at temperatures of 200 °C and 500 °C for 6, 48 and 120 h. The results have shown that the thickness of this layer increases to a maximum of 2 µm depending on the duration of the thermal aging at a temperature of 200 °C. The results of the tensile shear strength tests have shown that the brazed joints with this thin layer ensure a high strength. The thermal aging at a temperature of 500 °C influences the growth of the reaction zone in the brazed joints significantly. The total thickness of the reaction zone increases to a maximum of 12 µm during the thermal aging. The results of the tensile shear tests of these joints have shown that the thermal aging at a higher temperature leads to a decrease of the tensile shear strength of the brazed joints to 67% due to the growth of the existing intermetallic layer and the formation of a new intermetallic layer in the reaction zone.

Understanding the deformation and fracture mechanisms in backward flow-forming process of Ti-6Al-4V alloy via a shear modified continuous damage model

A shear modified coupled damage criterion based on continuum damage mechanics has been proposed in this study. Khan-Huang-Liang (KHL) model is implemented to predict the constitutive behavior of Ti-6Al-4 V (Ti64) alloy. A VUMAT subroutine has been developed for the damage model using a stress integration algorithm. Multiple simulations with tensile, compression and shear geometries are carried out in Abaqus/Explicit and compared with the experimental results to benchmark the hardening and damage criteria. The flow forming process involves a complex triaxial state of stress. This study is focused on understanding the contribution of triaxiality and shear during deformation and fracture in the flow-forming process with different roller arrangements. For this purpose, the flow-forming processes with three different roller arrangements, single roller, three roller, and wedge roller, are modeled, and their formability is compared by implementing a shear modified continuous damage model. A single roller flow-forming (SRF) arrangement undergoes high triaxiality due to excessive material displacement by the roller and high strain gradient in the axial direction. The fracture occurs near the interface of the reducing and thinning zone. The three-rollers flow-forming (TRF) provided maximum reduction till fracture and material fails due to excessive strain in the thinning zone at a relatively large percentage reduction. The wedge roller flow-forming (WRF) suffers a lack of uniform material softening, and fracture occurs near the interface of the uplift and reducing zone under high triaxiality. 3-D process maps have been developed for predicting fracture strain as a function of stress triaxiality/Lode parameter and stress triaxiality/thermal softening factor (E/σ¯2). Finally, a summary chart correlating the parameters, and flow-formability has been developed.

Genesis of the low sulfide-high-grade PGE mineralization in the W Horizon, Coldwell Complex, Canada: quantitative modeling for PGE reef-style mineralization in syn-magmatic sills

The W Horizon is a thin continuous zone of low sulfide-high-grade platinum group element (PGE) mineralization in the Two Duck Lake gabbro at the Marathon Cu-PGE deposit, Coldwell Complex, Canada, that resembles reef-type PGE deposits found in much larger intrusions. The Marathon deposit was previously shown to have grown by accretion of syn-magmatic, sulfide-bearing sill-like intrusions that formed each of the W Horizon, Main Zone, and Lower Zone mineralization. Each zone can be distinguished by features such as sulfide mineral or platinum group mineral assemblages, or by Cu/Pd, Pd/Se, and Pd/Au values. For example, the W Horizon is defined by the presence of bornite, very high PGE values, low Cu/Pd ( 95% of the original sulfide liquid. In some samples, metal and S abundances indicate that PGE were transported as TABS-PGE phases. This work describes an example of thin PGE-rich sill-like injections that could be of importance to PGE exploration elsewhere.

Mineralogical features of gold of the Permian conglomerates of the Sololiy uplift of the Olenek high (Northeastern Siberian platform)

Typomorphic features of placer gold of conglomerates of the Ortokinskaya formation of the Early Permian age (P1or) of the Sololiy Uplift of the Olenek High and modern channel alluvium of the Ortoku Eekit river, which drains these deposits, are studied. It is found that extremely heterogeneous composition and complex inner structure are typical features of the vast majority of gold of the Permian conglomerates. There are several stages of different fineness (from 251‰ to 999‰) within a single gold particle, as a result, gold has a mosaic-block inner structure. It is proposed that such heterogeneity is formed due to epigenetic transformations of primary medium-grade gold in an intermediate reservoir of the Permian age, and also under influence of superposed hydrothermal mineralization with low-grade gold, related to the processes of the Mesozoic tectonomagmatic activation. The latter is indicated by the discovery of impregnated gold-sulfide mineralization in the Permian conglomerates. Ore mineralization is represented by gold, silver, pyrite, sphalerite, chalcopyrite, galena, argentite, native tin, and barite. Association mineralization to thin tectonic zones of conglomerate fragmentation, suggests that superposed gold-sulfide hydrothermal mineralization of impregnated type was formed as a result of manifestations of the Mesozoic tectonomagmatic activation, when gold-bearing hydrothermal solutions migrated in faults. It is determined that auriferous conglomerates of the Ortokinskaya formation of the Permian age were major sources of placer gold of modern alluvium in the studied part of the Ortoku Eekit.

Barrellite and Pillarrite: A Description and a Mode of Formation of a Novel Post-Sedimentary Twin Structures from As-Subbiyah, North of Kuwait Bay, Kuwait

I report on the occurrence of a pair of novel and related post-sedimentary structures that form in the Neogene cross-bedded red sandstones in the As-Subbiyah area, north of Kuwait Bay, Kuwait. I named them barrellite and pillarrite. Barrellite forms as vertical tubes of concentric sheaths of siltstone with partially hollow interior or intervening homogeneous and structure-less sandstone. It stands as barrels above the background sandstone. Pillarrite forms as discrete, vertical and solitary spines of homogeneous sandstone and siltstone, or inside barrellite masses from which successive siltstone sheaths were stripped. The structures range in diameter from one-centimeter poke marks to one-meter-wide barrels and hunks, and their vertical length exceeds two meters. Barrellite, pillarrite and their complex intergrowths develop near thin quartz veins and chaotic zones, and form with them complex geometrical relationships. The dual structures are genetically related and fall within the general class of tubular structures in sedimentary rocks. I consider them as a special type of sand injectites. The mode of formation of these structures is enigmatic. They develop in a geological setting that displays evidence of a widespread and vigorous oil field brine. I suggest a tentative scenario for their formation, involving flushing of the brine through hydraulic fracturing of the sedimentary succession above the Ebharah Oil Field reservoir in the As-Subbiyah area. The brine plucks mineral and rock fragments and mixes with them along its paths, producing a heterogeneous slurry. Ultimately, the slurry solidifies as barrellite and pillarrite, chaotic zones and quartz veins. The vertical nature of the structures, circular and internal concentric arrangements, as well as the homogenous lithology inside their masses mimic characteristics of flow and deposits in vertical and horizontal pipelines.

Principal strain rate evolution within turbulent premixed flames for different combustion regimes

The statistical behaviors of the principal strain rates and its evolution in turbulent premixed flames have been analyzed using a three-dimensional direct numerical simulations dataset of statistically planar turbulent premixed flames with different turbulence intensities spanning from the corrugated flamelet regime to the thin reaction zone regime. It has been found that the scalar gradient predominantly aligns collinearly with the most extensive principal strain rate eigendirection within the flame for large values of Damköhler numbers and small values of turbulence intensities and Karlovitz numbers. However, this tendency weakens with the increasing turbulence intensity, which, for a given integral length scale, amounts to a decrease (an increase) in the Damköhler (Karlovitz) number. Moreover, it has been observed that the terms due to molecular diffusion, pressure Hessian, and the correlation between pressure and density gradients play key roles in the evolution of principal strain rates for flames with large values of Damköhler numbers and small values of Karlovitz numbers. However, the relative importance of the terms arising from the correlation between pressure and density gradients and the pressure Hessian relative to the strain rate and vorticity contributions of the principal strain rate transport diminishes with the increasing Karlovitz number and decreasing Damköhler number. The statistical behaviors of the mean values of the terms of the transport equation of the principal strain rate have been explained based on the relative alignments of principal strain rate eigenvectors with vorticity, pressure gradient, and the eigenvectors of the pressure Hessian tensor. The findings of the current analysis suggest that the pressure gradient and pressure Hessian tensor play key roles in the evolution of principal strain rates within premixed turbulent flames, and their influence needs to be accounted for high fidelity modeling of the tangential strain rate and scalar–turbulence interaction terms of the flame surface density and scalar dissipation rate transport equations, respectively. This provides possible explanations for the modification in the alignment of the reactive scalar gradient with local principal strain rates in premixed flames in comparison to that in non-reacting turbulent flows.

Mechanisms and predictive force models for machining with rake face textured cutting tools under orthogonal cutting conditions

The cutting performance and mechanisms of rake face textured carbide cutting tools in orthogonal machining of a carbon steel are investigated. Micro-grooves at 15.5 μm top width and different depth-to-width ratios are fabricated on the tool rake face using a femtosecond laser. It is found that the textures can significantly enhance the surface wettability of the cutting tools to an emulsified cutting fluid, and a fast liquid infiltration along the micro-grooves takes place. The machining tests show that cutting tools with the rake face grooves can reduce the thrust force by up to 14.68% in comparison with the untextured cutting tools, as a result of the decreased frictional force between the tool and chip. It is shown that the reduced tool-chip actual contact area due to the rake face textures and reduced tool-chip contact length due to the thinning of chip are the main reasons for this frictional force reduction. It is further found that the ploughing action between the groove edges and chip material tends to increase the frictional force while the chip material deposition to the textural structures reduces the functionality of the textures. Plausible trends of the reduction of the cutting forces with respect to the textural parameters are discussed, from which grooves in parallel to the cutting edge at 0.6 depth-to-width ratio and about 90 μm spacing are found to perform the best. A cutting force model for orthogonal machining using rake face textured cutting tools are then developed using the classical thin shear zone theory and the unified mechanics of cutting approach. The model is finally verified experimentally which shows that the model predictions agree well with the corresponding experimental data for cutting with and without a cutting fluid.

A comparison of 2 micron inner diameter open tubular column liquid chromatography with pressure-driven isocratic, slip-flow, and electrochromatographic modes of operation: a theoretical study

Modifications to the flow profile used in open tube capillary liquid chromatography (OT-CLC) include using slip-flow walls and using electroosmosis as a fluid pump as practiced in electrochromatography. These modifications are implemented experimentally by changing the capillary surface and solvent conditions which results in the change of boundary conditions at the capillary wall.In this paper we employ a theory-based study and compare the zone broadening of simple solutes using parabolic flow from a liquid pump, slip-flow from a highly hydrophobic inner surface with water eluent, and electroosmosis for the conditions of pure water and dilute salt utilizing 2 µm inner diameter OT capillaries. In general, the two types of flow other than parabolic exhibit thin zones in the early part of the chromatogram, consistent with previous studies of slip-flow and electroosmotic flow used in electrochromatography. Electrochromatography is shown to yield higher efficiency and less zone broadening than parabolic and slip-flow conditions used in this study. Nonetheless, it is found that the zone standard deviations are shown to be similar for these flow profiles as is the number of plates for these different flow profiles under the conditions utilized here. It is revealed that these modifications do not warrant the effort to maintain the special solvent conditions when compared to gradient elution OT-CLC, which gives a nearly constant peak width throughout the chromatogram, is easiest to implement, and is the method of choice for complex analysis.

Local Anatomic Precursors to New-Onset Geographic Atrophy in Age-Related Macular Degeneration as Defined on OCT

In macula-wide analyses, spectral-domain (SD) optical coherence tomography (OCT) features including drusen volume, hyperreflective foci, and OCT-reflective drusen substructures independently predict geographic atrophy (GA) onset secondary to age-related macular degeneration (AMD). We sought to identify SD OCT features in the location of new GA before its onset. Retrospective study. Age-Related Eye Disease Study 2 Ancillary SD OCT Study participants. We analyzed longitudinally captured SD OCT images and color photographs from 488 eyes of 488 participants with intermediate AMD at baseline. Sixty-two eyes with sufficient image quality demonstrated new-onset GA on color photographs during study years 2 through 7. The area of new-onset GA and one size-matched control region in the same eye were segmented separately, and corresponding spatial volumes on registered SD OCT images at the GA incident year and at 2, 3, and 4 years previously were defined. Differences in SD OCT features between paired precursor regions were evaluated through matched-pairs analyses. Localized SD OCT features 2 years before GA onset. Compared with paired control regions, GA precursor regions at 2, 3, and 4 years before (n= 54, 33, and 25, respectively) showed greater drusen volume (P= 0.01, P= 0.003, and P= 0.003, respectively). At 2 and 3 years before GA onset, they were associated with the presence of hypertransmission (P < 0.001 and P= 0.03, respectively), hyperreflective foci (P < 0.001 and P= 0.045, respectively), OCT-reflective drusen substructures (P= 0.004 and P= 0.03, respectively), and loss or disruption of the photoreceptor zone, ellipsoid zone, and retinal pigment epithelium (RPE, P < 0.001 and P= 0.005-0.045, respectively). At 4 years before GA onset, precursor regions were associated with photoreceptor zone thinning (P= 0.007) and interdigitation zone loss (P= 0.045). Evolution to GA is heralded by early local photoreceptor changes and drusen accumulation, detectable4 years before GA onset. These precede other anatomic heralds such as RPE changes and drusen substructure emergence detectable1 to 2 years before GA. This study thus identified earlier end points for GA as potential therapeutic targets in clinical trials.

Magnetic field and chromospheric activity evolution of HD 75332: a rapid magnetic cycle in an F star without a hot Jupiter

ABSTRACT Studying cool star magnetic activity gives an important insight into the stellar dynamo and its relationship with stellar properties, as well as allowing us to place the Sun’s magnetism in the context of other stars. Only 61 Cyg A (K5V) and τ Boo (F8V) are currently known to have magnetic cycles like the Sun’s, where the large-scale magnetic field polarity reverses in phase with the star’s chromospheric activity cycles. τ Boo has a rapid ∼240 d magnetic cycle, and it is not yet clear whether this is related to the star’s thin convection zone or if the dynamo is accelerated by interactions between τ Boo and its hot Jupiter. To shed light on this, we studied the magnetic activity of HD 75332 (F7V) which has similar physical properties to τ Boo and does not appear to host a hot Jupiter. We characterized its long-term chromospheric activity variability over 53 yr and used Zeeman Doppler Imaging to reconstruct the large-scale surface magnetic field for 12 epochs between 2007 and 2019. Although we observe only one reversal of the large-scale magnetic dipole, our results suggest that HD 75332 has a rapid ∼1.06 yr solar-like magnetic cycle where the magnetic field evolves in phase with its chromospheric activity. If a solar-like cycle is present, reversals of the large-scale radial field polarity are expected to occur at around activity cycle maxima. This would be similar to the rapid magnetic cycle observed for τ Boo, suggesting that rapid magnetic cycles may be intrinsic to late-F stars and related to their shallow convection zones.

Early silicification of the Cyrenaican chert, Libya: The importance of moganite as a transitional silicon dioxide phase

AbstractThe Messinian lagoonal carbonate–evaporite sequence of Cyrenaica, north‐east Libya, hosts: (i) opaline nodules in gypsiferous microbial‐rich mudstone; (ii) nodules replacing poikilotopic gypsum cementing bioclastic carbonates; and (iii) bedded porcelanite with large lenticular gypsum pseudomorphs intercalated with recrystallized microbial mats. Optical microscopy, scanning electron microscopy, backscattered electron images – secondary electron images, X‐ray fluorescence, X‐ray diffraction and cathodoluminescence techniques were employed to elucidate on the early stages of chert diagenesis and demonstrate the role of moganite in the formation of varieties of chalcedony during silicification. The opaline nodules composed of opal‐A, exhibit shrinkage cracks lined by isopachous fibrous quartzine underlain by a thin birefringent zone. This suggests that quartzine may develop by crystallization and conversion of opal‐A through a transitional moganite. The quartzine is followed by amorphous silica gel that converts into length‐fast chalcedony. By contrast, lutecite evolved by silica replacement of gypsum through a transitional moganite phase, which forms an amorphous zone in apparent optical continuity with the fibrous lutecite; as moganite advances by pseudo‐crystalline terminations controlled by the gypsum cleavage. In gypsified oyster shells, intercrystalline organic matter enveloping pseudomorphed shell microstructures enabled moganite nucleation that merges syntaxially around the gypsum crystal rim. The associated lutecite occurs as radial‐fibrous beekite aggregates that are consistent with early shell silicification. The bedded porcelanite consists of opal‐CT groundmass undergoing recrystallization and enclosing micro‐cavities lined by quartzine. The associated pseudomorphs display phases of gypsum replacement by moganite and lutecite at the outer margin, followed by dissolution and cavity filling by quartz varieties in response to fluid flushing. In all cases, organic matter and microbes played a vital role in the silicification process.

Secondary Recrystallization of Nickel-Base Superalloy CM 247 LC After Processing by Metal Injection Molding

Fabrication of parts by metal injection molding (MIM) results in very fine grain sizes. In the present investigation, heat treatments were employed to gain a larger grain size that is more creep resistant. The alloy under investigation was CM 247 LC. The composition was slightly modified to facilitate grain growth. Secondary recrystallization was observed to occur during post-sintering annealing treatments approximately 50 °C below the sintering temperature. The grain size increased from 25 µm to > 2 mm. The increase of grain size was found to improve creep strength significantly. The samples in the as-sintered condition exhibited a bimodal grain size distribution. The grain size in a thin surface zone after sintering was slightly increased because of a lower C and O content in this zone that promoted normal grain growth. Secondary recrystallization did not occur in the surface zone. This is attributed to a lack of driving force in this area.

ASSESSMENT OF VADOSE ZONE CHARACTERISTICS FOR ENVIRONMENTAL IMPACT AUDIT OF SELECTED CEMETERIES AROUND OSUN STATE, SOUTH-WESTERN PART OF NIGERIA

Cemeteries have been identified as a possible source of groundwater and environmental pollution. This may be due to wrong siting of cemeteries, poor soil selection and very thin vadose zone. Over the years, most communities around Osun State experience a number of communicable diseases like dysentery, diarrhea and typhoid, especially after episodes of flash floods. Therefore, this study was carried out to audit the impact of burial practices on the immediate environment viz-a-viz their interaction with both surface and groundwater which forms the main source of potable water for the communities. Method of approach include; assessing possible water contamination, studying the vadose hydrological characteristics as well as studying the geotechnical properties of soils within the vadose zone. Water samples from the vicinity of both cemeteries shows probable contamination with an average pH of 6.19 for Ede and 6.57 for Iragbiji, EC with an average 480μS for Ede and 1210μS for Iragbiji. Biological constituents found within the area include; enterobacteriaceae (salmonella spp., serratia spp., proteus spp., shigella spp.), suggesting likely contamination of both surface and groundwater around the vicinity of the cemeteries. Most cations and anions analysed for (Mg2+, NO3-, SO42-, and PO43-) comply with the WHO standards based on their maximum permissible limits (MPL). Geotechnical investigations revealed that soils within the study areas are largely unsuitable for a standard cemetery due to their high moisture content, poor grading characteristics, low compaction value, poor hydraulic characteristics and shallow water level. The study concluded that cemeteries from both towns have a negative impact on their immediate environment due to poor selection of soil materials (porous and permeable sandy soil) as reflected in the quality of surface and groundwater.

Intrusion fracturing and quartz sand-rich injections in thrust-related fault rocks within the basal shear zone of the Esla Nappe (Cantabrian Zone, NW Iberia)

The Esla Nappe, located in the Cantabrian Zone (Variscan Orogen, NW Iberia), has an estimated 19 km displacement to the NE accommodated in a thin (<2–3 m) shear zone (ENSZ) at least 4 km depth. Fault-rock assemblages record different deformation processes operating in the hangingwall and footwall. While the hangingwall was largely deformed through cataclastic flow localised in a <50 cm band, hangingwall-footwall intervening ultracataclasites and footwall lithologies preserve evidence for an interplay of cataclastic flow and pressure solution. Final hydrofracturing and calcite vein precipitation has contributed to the vertical dilation of the fault rock assemblages.In the late stages of emplacement, the ENSZ was breached through intrusion fracturing and associated clastic sills and dykes injected along re-opened previous discontinuities and anisotropies. Together, they conform an interconnected network of quartz sand-rich lithosomes reaching structural heights of 20 m over the ENSZ. Injections are formed by a mixture of injected quartz grains and host-derived fragments. Dyke orientations suggest that the injection process occurred under large fluid overpressure conditions exceeding lithostatic values in the footwall. Fluid overpressure may have been caused by progressive fluid accumulation beneath a low-permeability ultracataclasite layer at the base of the nappe. Breaching through the shear zone was favoured by a change in the stress regime following the Esla Nappe emplacement.

3D Fabric Analysis in Fault Rock Using Synchrotron μ-CT: A Statistical Approach to SPO (Shape Preferred Orientation) for Estimation of Fault Motion

This study provides information about fault motion by statistically presenting shape and orientation information for tens of thousands of grains. The recently developed shape preferred orientation (SPO) measurement method using synchrotron micro-computed tomography was used. In addition, various factors that were not considered in previous SPO analysis were analyzed in-depth. The study area included the Yangsan and Ulsan fault zones, which are the largest fault zones in the southeastern part of the Korean Peninsula. Samples were collected from five outcrops in two regions. According to the field observation results, the samples in the area were largely divided into fault gouge and cataclasite, and as a result of SPO analysis, we succeeded in restoring the three-dimensional fault motion direction for each outcrop and identified the fault type. In addition, the analysis results of the fault gouge and cataclasite samples collected from the thin fault zone were interpreted using the focal mechanism solution. As a result, the statistical SPO analysis approach supplements the shortcomings of previous research methods on two-dimensional planes and can quantitatively infer the three-dimensional fault motion for various fault rock samples in the same sequence, thus, presenting useful evidence for structural analysis.

The Role of Premagmatic Rifting in Shaping a Volcanic Continental Margin: An Example From the Eastern North American Margin

AbstractBoth magmatic and tectonic processes contribute to the formation of volcanic continental margins. Such margins are thought to undergo extension across a narrow zone of lithospheric thinning (~100 km). New observations based on existing and reprocessed data from the Eastern North American Margin contradict this hypothesis. With ~64,000 km of 2‐D seismic data tied to 40 wells combined with published refraction, deep reflection, receiver function, and onshore drilling efforts, we quantified along‐strike variations in the distribution of rift structures, magmatism, crustal thickness, and early post‐rift sedimentation under the shelf of Baltimore Canyon Trough (BCT), Long Island Platform, and Georges Bank Basin (GBB). Results indicate that BCT is narrow (80–120 km) with a sharp basement hinge and few rift basins. The seaward dipping reflectors (SDR) there extend ~50 km seaward of the hinge line. In contrast, the GBB is wide (~200 km), has many syn‐rift structures, and the SDR there extend ~200 km seaward of the hinge line. Early post‐rift depocenters at the GBB coincide with thinner crust suggesting “uniform” thinning of the entire lithosphere. Models for the formation of volcanic margins do not explain the wide structure of the GBB. We argue that crustal thinning of the BCT was closely associated with late syn‐rift magmatism, whereas the broad thinning of the GBB segment predated magmatism. Correlation of these variations to crustal terranes of different compositions suggests that the inherited rheology determined the premagmatic response of the lithosphere to extension.

Crystal structure and Raman spectroscopic studies of OH stretching vibrations in Zn-rich fluor-elbaite

Abstract Zinc-rich fluor-elbaite from Piława Górna, Poland, was studied by electron microprobe (EPMA), single-crystal X-ray diffraction (SREF), and Raman spectroscopy (RS) to check the possibility of the application of RS to draw crystal-chemical conclusions for Al-rich and Li-bearing tourmalines on basis of the O–H stretching vibrations in the spectral range 3400–3800 cm–1. This tourmaline, forming a thin metasomatic zone around gahnite, features varying compositions with a ZnO content reaching in the studied fragment of 5.70(12) wt%. The crystal structure of this Zn-rich fluor-elbaite [a = 15.921(1), c = 7.127(1) Å] was refined with a R1 value of 1.67%. Its formula was determined on the basis of electron-microprobe and structure refinement as (Na0.84☐0.14Ca0.01)XΣ1.00(Al1.06Li0.84Zn0.69Fe0.322+Mn0.09)YΣ3.00AlZ6(BO3)3(Si6TO18)(OH)3V(F0.65OH0.26O0.09)W. The deconvolution of the O–H stretching vibration bands, performed by fitting of an input model of component bands with Gaussian function shapes for the empirical spectrum, indicates that each of the three maxima assigned for VOH bonded to YAl3+, Y2+, and YLi+ and with the total integral intensity of at least 75% of the total OH content could be resolved into 1 to 3 bands, depending on the X-site occupation (vacancies, Na+, and Ca2+). The deconvolution indicates further that several low intense bands of WO–H modes above a Raman shift of 3600 cm–1, totally reaching ≤25%, are dependent on the occupation of triplets of YYY cations bonded to the hydroxyl. These WO–H modes are also influenced by the X-site occupation. Due to ordering of all octahedral cations (except Al) at the Y site and a complete occupation of the Z site by Al and the V site by OH, it seems possible to evaluate the Li and OH contents in a Al-rich and Li-bearing tourmaline directly from the Raman spectrum. By using the ratio VOHIYAlZAlZAl/(VOHIYZZ + WOHIYYY) as evaluated from RS, corresponding to the ratio YAl/V+WOH in the crystal, the formula of the Zn-rich fluor-elbaite can be calculated as (Na0.85☐0.14Ca0.01)XΣ1.00(Al1.11Y1.112+Li0.78)YΣ3.00AlZ6(BO3)3(Si6O18)(OH)3(F0.65OH0.13O0.22), where Y 2+ = Zn + Fe + Mn. The formula, determined only on basis of EPMA and deconvolution of RS in the O–H stretching bands, corresponds very well (≤1 SD range of EPMA) to the formula determined on basis of EPMA and SREF. This result implicates that the O–H stretching vibrations, measured by Raman spectroscopy, could be applied for Al-rich and Li-bearing tourmalines as a useful tool for providing additional information for determining the crystal-chemical formula. It is also very helpful when crystal structural data are not available.

Destruction electrospark deposits during Joule heating of base metal

Electrospark coating deposited on the surfaces of machine parts is a common surface hardening method. Hard materials are normally used for depositing to improve wear resistance or other properties. In this investigation electrospark deposition intended for use as micro-alloying of welds by deposition on to the surface of the base metal and in this case it remelts completely. Intense heating and destruction occurs before remelting, which changes the chemical composition of the melt. The aluminum and titanium coatings is shown to deteriorate at 500 to 650 °C generating a liquid phase due to eutectic available in both metals in this temperature range. Most of titanium and aluminum oxidized at that. It is found that a solid layer, appears after electrospark depositing using both coatings. For aluminum coating, after high-temperature heating, a thicker white layer appears with the same microhardness level as that of the base metal, and a thin layer of partial decarburizing. Fusion sectors are detected in the titanium coating that are harder than the base metal and have a dendritic structure, followed by a thin zone of complete decarburization and quite an extended zone of partial decarburization.

On the validity of Damköhler's second hypothesis in statistically planar turbulent premixed flames in the thin reaction zones regime

The validity of Damköhler's second hypothesis, which was originally proposed for premixed combustion for conditions where the large scale turbulent timescale remains smaller than the chemical timescale and the integral length scale remains smaller than the flame thickness, has been assessed for a range of Damköhler and Karlovitz numbers (i.e. 0.2≤Da≤3.0 and 0.58≤Ka≤33.34) using a three-dimensional DNS database of statistically planar turbulent premixed flames subjected to forced unburned gas turbulence. It has been found that Damköhler's first hypothesis remains valid for all cases considered in this work irrespective of the combustion regime. By contrast, Damköhler's second hypothesis does not hold in the strict sense for the thin reaction zones regime flames with small values of Damköhler number. However, the ratio of the turbulent flame speed normalised by laminar burning velocity and the square root of the ratio of turbulent diffusivity to mass diffusivity converges to a value of the order of unity for the flames with high turbulence intensity and low Damköhler number in the thin reaction zones regime. Under this condition, Damköhler's second hypothesis, in an order of magnitude sense, can be considered to be valid alongside Damköhler's first hypothesis. A scaling analysis has been carried out using the equilibrium of the tangential strain rate and curvature terms in the Flame Surface Density transport equation to demonstrate that Damköhler's second hypothesis can be expected to be valid only in an order of magnitude sense for the thin reaction zones regime flames with small values of Damköhler number.