Submicroscopic Scales Research Articles

(Invited) Multiscale Electrochemical Analysis of Sol-Gel Films Modified with Eco-Friendly Corrosion Inhibitors for Active Corrosion Protection of AZ61 Magnesium Alloy

The use of magnesium and its alloys has increased in recent years due to their low weight, high strength, excellent machinability, and high dimensional durability. Therefore, they have found application in communications, automotive and aerospace industries, among others. However, their high negative reduction potentials, low chemical stability, and the unstable native oxide films have limited their use, particularly in applications that require high corrosion resistance.1 -3 The application of sol-gel coatings has shown to be an effective method to overcome this problem. In this context, the aim of this study was to develop sol-gel thin-films doped with ecological corrosion inhibitors for corrosion protection of AZ61 alloy surfaces. The objective was to determine whether these new systems could provide an alternative to the replacement of chromates, surface pre-treatments and chemical conversion coatings that contain conventional corrosion inhibitors, which are currently being questioned for their harmfulness to health and the environment.4 Methyltriethoxysilane (MTEOS) and tetraethylorthosilicate (TEOS) were used as precursors to produce sols, which were then modified with active corrosion protection dopants. Eco-benign corrosion inhibitors, such as L-cysteine (L-Cys), lanthanum (III) acetate hydrate, and lanthanum (III) isopropoxide were incorporated in the sol-gel matrix as dopants. A set of sol-gel coatings was modified with a common dopant, benzotriazole (BTA), for comparison purposes, as it is a well-known effective corrosion inhibitor. However, this chemical compound is known to be carcinogenic and toxic to flora and fauna, and its use is currently being restricted today in compliance with environmental protection regulations.5,6 The resulting sols were processed and deposited on AZ61 substrates by dip-coating technique, producing transparent sol-gel thin-films. The thickness of the films was evaluated by interference of reflection spectra. Their chemical composition was characterized by X-ray fluorescence (XRF), while surface chemical composition and oxidation state of elements present at the outermost surface nanolayers was also analysed by X-ray photoelectron spectroscopy (XPS). The structural and thermal characterization of the doped thin-films were respectively analysed by Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry and differential thermal analysis (TG/DTA).The corrosion protection behaviour of the sol-gel coatings during immersion tests in 0.006 M and 0.6 M NaCl aqueous solutions was studied using a multiscale electrochemical approach. Global electrochemical impedance spectroscopy (EIS) was used for macroscopic scale characterisation. Localised electrochemical impedance spectroscopy (LEIS and LEIM) was used for the characterisation at micro- and sub-microscopic scales using an electrochemical minicell system and a scanning electrochemical workstation.The texture and microstructure of coated samples before and after corrosion tests were observed by optical and scanning electron microscopies (OM and SEM), while topography and coating roughness were analysed by atomic force microscopy (AFM).In terms of corrosion resistance, similar results were obtained with sol-gel thin-films doped with lanthanum acetate or lanthanum isopropoxide. The synthesis method of the acetate-doped gels is much simpler and cheaper, so from a practical standpoint, these sol-gel thin-films could be more interesting. On the other hand, highly satisfactory results were obtained with gels doped with non-toxic L-Cys compared with those doped with BTA. Finally, it is noteworthy that an interesting synergistic effect was observed in the corrosion protection of the AZ61 alloy in sol-gel coatings that were doped with metal-organic inhibitors and loaded with organic inhibitors (L-Cys or BTA).As a concluding remark, this study has provided an effective and environmentally friendly solution for the active corrosion protection of the AZ61 alloy. Sol-gel thin-films doped with eco-friendly corrosion inhibitors have showed promising results in extending the durability of AZ61 alloy while being sustainable. The multiscale electrochemical approach used has provided a comprehensive understanding of the active corrosion protection behaviour and the self-healing properties of sol-gel coatings, which can be extended to other materials and systems. Funding Sources This work has been supported by the Ministry of Science and Innovation (MCINN, Spain) through the Project PID2019-104717RB-I00. References Feliu Jr., S., Maffiotte, C., Samaniego, A., Galván, J.C., Barranco, V. Acta, 56 (12) (2011) 4554-4565 Stojadinović, S., Vasilić, R., Radić-Perić, J., Perić, M. Coat. Technol., 273 (1) (2015), pp. 1-11 Toorani, M., Aliofkhazraei, M., Naderi, R., Golabadi, M., Sabour Rouhaghdam, A. Ind. Eng. Chem., 53, (2017) pp. 213-227 Vaghefinazari, B., Wierzbicka, E., Visser, P., Posner, R., Arrabal, R., Matykina, E., Mohedano, M., Blawert, C., Zheludkevich, M., Lamaka, S. Materials, 15 (23) (2022), art. no. 8676 Albini, M., Letardi, P., Mathys, L., Brambilla, L., Schröter, J., Junier, P., Joseph, E. Corrosion Sci., 143 (2018), pp. 84-92Tan, L., Sun, Y., Li, J., Han, S., Zhou, X., Tang, Y., Zeng, X. Langmuir, 39 (2023), 2579-2588

Raman, Infrared, and Chemical Characterization of Fly Ash-Generated Spherules

The majority of studies on silicate glass spherules containing fly ash deal only with the determination of their chemical composition. Nearly 70 vol.% of fly ash is comprised of silicate glass spherules. Here, we report spectroscopic properties of silicate glass spherules using the laser micro-Raman and Fourier transform infrared techniques coupled with refractive index measurements, X-ray diffraction, and electron probe micro-analysis to better ascertain their physical and chemical properties. Glass spherules show similar refractive indices (1.499–1.510) and a bell-shaped diffraction pattern with 5–10 vol.% of crystallites observed on microscopic and submicroscopic scales. The bulk chemical composition of fly ash spherules is predominantly silica-rich (SiO2: 70.96–74.13 wt.%) with a subordinate amount of Al2O3 (0.11–0.69 wt.%), FeO(Total) + MgO (3.6–4.94 wt.%), and CaO + Na2O + K2O (20.83–22.62 wt.%). The infrared spectra suggest the presence of a dissolved –OH– bearing fluid phase in the studied fly ash spherules. The spectra also show symmetric stretching peaks of C–O–C due to the atmospheric CO2 adsorption at 2350 cm–1. The Raman spectra show broad amorphous and/or short-ordered phases.

Feature size reduction in two‐photon polymerization by optimizing resin composition

ABSTRACTIn the last decades, an increasing refinement over submicroscopic scales has played a decisive role in boosting scientific and technological progress. When dealing with miniaturized devices, organic materials have drawn considerable attention, not only for requiring lower energies during processing but also for allowing functionalization with ease, exhibiting biocompatibility and presenting high optical quality. In this scenario, the modification of acrylate polymers by femtosecond lasers has become an important mechanism. Among the main techniques based upon this principle, two‐photon polymerization (2PP) stands out due to its capability of producing fine features. Still, 2PP has often been combined with sophisticated methods devised to further improve spatial resolution and miniaturized devices. However, such measures invariably raise the cost of the experiments by demanding either the addition of other chemical compounds or a second laser system. In this study, we discuss how the relative proportion of acrylate monomers and different concentrations of a photoinitiator influence the final dimension of structures fabricated using polymeric samples, which are widely used in 2PP experiments. Furthermore, we demonstrate that it is possible to produce finer features only by varying the proportion of these constituents, achieving linewidths on the order of 360 nm and heights on order of 300 nm. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1158–1163

New Taxa of Streptophyte Algae (Streptophyta) from Terrestrial Habitats Revealed Using an Integrative Approach

Two new genera (Streptosarcina and Streptofilum) and three new species (Streptosarcina arenaria, S. costaricana and Streptofilum capillatum) of streptophyte algae were detected in cultures isolated from terrestrial habitats of Europe and Central America and described using an integrative approach. Additionally, a strain isolated from soil in North America was identified as Hormidiella parvula and proposed as an epitype of this species. The molecular phylogeny based on 18S rRNA and rbcL genes, secondary structure of ITS-2, as well as the morphology of vegetative and reproductive stages, cell ultrastructure, ecology and distribution of the investigated strains were assessed. The new genus Streptosarcina forms a sister lineage to the genus Hormidiella (Klebsormidiophyceae). Streptosarcina is characterized by packet-like (sarcinoid) and filamentous thalli with true branching and a cell organization typical for Klebsormidiophyceae. Streptofilum forms a separate lineage within Streptophyta. This genus represents an easily disintegrating filamentous alga which exhibits a cell coverage of unique structure: layers of submicroscopic scales of piliform shape covering the plasmalemma and exfoliate inside the mucilage envelope surrounding cells. The implications of the discovery of the new taxa for understanding evolutionary tendencies in the Streptophyta, a group of great evolutionary interest, are discussed.

Foragers, tropical forests and the formation of archaeological evidences: An ethnoarchaeological view from South India

Foraging societies present unique ways of livings and sociality which are manifested by distinctive practices and use of space. From an archaeological point of view, understanding forager sociality and studying their practices and the resulted material deposition patterns is crucial to reconstruct archaeological site formation processes. When studying archaeological sites in tropical environments, such as rainforests, one must take into account and study the role of the tropics in the formation of the archaeological record. Human adaptation to tropical environment influences people's practices, use of space and materiality. In addition, the environmental setting plays a significant role in post-depositional processes which may alter, preserve or disrupt archaeological materials. This study involve a long term ethnographic research among a contemporary forager group in South India, which allowed us to associate the social aspects of forager ways of living – such as mobility, immediacy and adaptation to the tropical forest - with patterns of use of apace and material deposition. Excavations of an abandoned open-air site and a rock-shelter of the same group, included field observations and sediment sampling followed by laboratory analyses which enabled the investigation of post-depositional processes at both the visible and invisible (microscopic and sub-microscopic) scales. Overall, although forager ways of living and the environmental conditions in tropical forests challenge the formation of a well preserved archaeological evidence, an integrated approach examining the different scales of the archaeological record can successfully reconstruct the formation processes of archaeological sites in tropical forests and associate the archaeological evidence with social aspects of forager ways of living.

Developing an Understanding of Chemistry: A case study of one Swedish student's rich conceptualisation for making sense of upper secondary school chemistry

In this paper, we report a case study of a 16-year-old Swedish upper secondary student's developing understanding of key concept areas studied in his upper secondary school chemistry course. This study illustrates how the thinking of an individual learner, Jesper, evolves over a school year in response to formal instruction in a particular educational context. Jesper presented a range of ideas, some of which matched intended teaching whilst others were quite inconsistent with canonical chemistry. Of particular interest, research data suggest that his initial alternative conceptions influenced his thinking about subsequent teaching of chemistry subject matter, illustrating how students' alternative conceptions interact with formal instruction. Our findings support the claims of some researchers that alternative conceptions may be stable and tenacious in the context of instruction. Jesper's rich conceptualisation of matter at submicroscopic scales drew upon intuitions about the world that led to teaching being misinterpreted to develop further alternative conceptions. Yet his intuitive thinking also offered clear potential links with canonical scientific concepts that could have been harnessed to channel his developing thinking. These findings support the argument that identifying students' intuitive thinking and how it develops in different instructional contexts can support the development of more effective science pedagogy.

Microscopic and microchemical study of iron sulphide weathering in a chronosequence of technogenic and natural soils

Sulphide alterations are among the most important mineralogical aspects of the functioning of soils developed from sulphide-bearing parent materials. In the present study, the processes of iron sulphide weathering were investigated in a system including sulphide crystals and secondary minerals adjacent to oxidised sulphides. Light microscope observations and scanning electron microscope–energy dispersive spectrometry (SEM–EDS) analyses were used in order to examine evidences of iron sulphide decay at a microscopic and submicroscopic scales, as well as to determine the modes and effects of sulphide weathering on an example of a chronosequence of technogenic soils (Technosols) and naturally developed soils (Leptosols and Cambisols) in Poland. The study covered (1) several years old Technosols developed on the dump of the abandoned hard coal mine in Trzebinia town, (2) several dozen of years old Technosols developed on mine spoils of the abandoned pyrite mine in Rudki village, (3) 100–200years old Technosols developed on dumps of the abandoned pyrite mine in Wieściszowice village, as well as (4) Leptosols and Cambisols developed on natural outcrops of pyrite-bearing schists in the vicinity of the mine in Wieściszowice. Chemical weathering was the most important process involved in the alteration of iron sulphides in the soils studied. The process is expressed by (1) the oxidation of sulphides resulting in a subsequent crystallisation of iron oxides and sulphates from Fe and sulphate ions released to the soil solution, as well as by (2) the development of pseudomorphs after sulphides due to the gradual in-situ transformation of sulphides into secondary minerals (iron oxides mainly). Porous (poorly crystalline) iron oxides predominated across the products of iron sulphide oxidation in “young” technogenic soils from Rudki, in contrast to “old” technogenic and natural soils from Wieściszowice, where massive (well crystallised) iron oxides prevailed. This suggests that the degree of crystallinity of iron oxides increases along with the age of soils. Microstratification was a typical feature of secondary iron oxides occurring in “old” soils from Wieściszowice. The EDS analyses performed along the lines perpendicular to stratified oxides showed that the alternating microlayers differed from each other in terms of contents of oxygen (O-poor layers were alternated with layers rich in this element). This suggests that temporal changes of oxygen concentration in soils may affect the process of iron sulphide transformation. The content of most trace elements (including heavy metals such as Cu, Zn, and Pb) in the examined iron sulphides, analysed by EDS, was low. Furthermore, amounts of these elements in secondary oxide rims were reported to be slightly elevated in comparison with the adjacent sulphides. This suggests that the rims did not constitute places of concentration of high amounts of trace elements in the soils investigated.

The promoter-search mechanism of Escherichia coli RNA polymerase is dominated by three-dimensional diffusion

Gene expression, DNA replication, and genome maintenance are all initiated by proteins that must recognize specific targets from among a vast excess of nonspecific DNA. For example, to initiate transcription, E. coli RNA polymerase must locate promoter sequences, which comprise <2% of the bacterial genome. This search problem remains one of the least understood aspects of gene expression, largely due to the transient nature of search intermediates. Here we visualize RNAP in real time as it searches for promoters, and we develop a theoretical framework for analyzing target searches at the submicroscopic scale based upon single–molecule target association rates. Contrary to long–held assumptions, we demonstrate that the promoter search is dominated by three–dimensional diffusion at both the microscopic and submicroscopic scales in vitro, which has direct implications for understanding how promoters are located within physiological settings.

Petrography of the impact breccias of the Enkingen (SUBO 18) drill core, southern Ries crater, Germany: New estimate of impact melt volume

A new drill core (SUBO 18) that intersects a continuous sequence of impact breccias has been obtained at the town of Enkingen at the southern edge of the Ries inner crater. Detailed petrographic analysis of this core provides important new information regarding the nature and origin of within-crater suevite, which is not only relevant for the understanding of the formation of the Ries impact structure but has strong implications for impact breccia deposition in general. In the Enkingen core, below 21 m of crater sediment, ∼90 m of impact breccia have been sampled. Most of this material is what in the past has been referred to as suevite—defined as groundmass of clastic material entraining cogenetic melt fragments and target rock clasts. Only the bottommost 10 m of core are melt-dominated impact breccia. Any relatively thick melt rock intersection along this core is revealed to be composed of individual centimeter- to decimeter-sized melt bodies best described as agglomerate due to its close resemblance to volcaniclastics of that type. Detailed macro-, meso-, and microscopic petrographic analysis has established that the SUBO 18 impact breccias cannot be divided into distinct units. The groundmass is extensively altered to phyllosilicate (smectite or chlorite) or carbonate minerals. Results of a detailed scanning electron microscopic investigation of the groundmasses of samples from all parts of this sequence emphatically support the traditional definition of suevite, irrespective of scale. Modal analysis at macroscopic to submicroscopic scales has shown that the overall, average melt content of Enkingen suevite is on the order of 48 vol%. This exceeds by far previous estimates and brings the Ries crater melt volume in line with values traditionally suggested from crater and melt volume scaling for similar-sized impact structures in crystalline and mixed targets.

Role of Reversibility in Viral Capsid Growth: A Paradigm for Self-Assembly

Self-assembly at submicroscopic scales is an important but little understood phenomenon. A prominent example is virus capsid growth, whose underlying behavior can be modeled using simple particles that assemble into polyhedral shells. Molecular dynamics simulation of shell formation in the presence of an atomistic solvent provides new insight into the self-assembly mechanism, notably that growth proceeds via a cascade of strongly reversible steps and, despite the large variety of possible intermediates, only a small fraction of highly bonded forms appear on the pathway.

On the limiting minimum size of grains formed in metallic materials produced by high-pressure torsion

-Results are presented concerning the experimental studies of the limiting minimum grain size dmin in nanostructured metallic materials produced by high-pressure torsion in Bridgman anvils. It is shown that important factors that determine dmin in the process of severe plastic deformation are the critical stresses for dislocation shear and the mobility of point defects, which control the paths of these defects in stress fields, the characteristic scales of the microvolumes involved into reorientation processes, and therefore the sizes of grains and subgrains of submicroscopic and nanoscopic scales.

Increasing Conceptual Understanding of Glycolysis &amp; the Krebs Cycle Using Role-Play

Role-play is one way to give students a visual overview of glycolysis and the Krebs cycle, with the aim of helping them construct their own mental images. Students have reported that this technique has made it easier for them to understand the detailed biochemical reactions in their subsequent private study. The strategy of a choreographed dance as described in this article could also be considered a blueprint for teachers if they wish to construct a similar activity in a different topic which may be more relevant to their own students. Cellular respiration and metabolism are topics that are reportedly poorly understood by students and judged to be difficult by many teachers (Songer & Mintzes, 1994). Although these topics may not be required learning areas in some high school biology curricula, a grasp of fundamental concepts of cellular metabolic processes is advantageous for students undertaking (or intending to undertake) college-level studies in any biology-related course. There are three common difficulties in teaching cellular respiration: Students have a wide array of misconceptions which have developed from prior learning experiences (Driver & Bell, 1986); these misconceptions often persist after instruction perhaps due to the students' level of abstract or concrete operational cognition (Piaget, 1929); these misconceptions often remain intact throughout the undergraduate years despite repeated instruction at successively more advanced levels (Alparsian et al., 2003; Mann & Treagust, 1998; Seymour et al., 1991; Songer & Mintzes, 1994; Wandersee, 1983; Wandersee et al., 1994). Despite the acknowledged prevalence of students' misconceptions, particularly in the areas of photosynthesis and cellular metabolism or respiration (Wandersee et al., 1994), most instructors use lecture-plus-wet-lab as a teaching and learning strategy (Hodson, 1998). Although this dual role of a lecture/laboratory session where students develop their own learning skills and conceptual understanding is well established (Gunstone, 1995), laboratory sessions that are in character may not be effective in dealing with concepts that are molecular or submicroscopic and unable to be seen, but only imagined (Ross unpublished data). Compounding the problem, traditional laboratory exercises in these concept areas require students to also have skills which they have not yet developed--in observation, data analysis, equipment manipulation, and communication (Ragsdale & Pedretti, 2004). Even the most innovative of wet labs (Bolduc et al., 2002; Bullerwell & Hagar, 2003; Buttner, 2000; Korn & Tausch, 2001; Yip, 1998a) may not always provide the students with a link between what they observed at the macroscopic scale and molecular or submicroscopic scale (Lin & Hu, 2003; Ragsdale & Pedretti, 2004). Unhelpfully, teachers may be unable to make this link themselves (Yip, 1998b; Songer & Mintzes, 1994). If we are to assist students, and in some instances teachers, to overcome their misconceptions, there is a need to develop teaching and learning strategies that link these macroscopic and molecular (submicroscopic) scales (Lin & Hu, 2003; Ragsdale & Pedretti, 2004; Songer & Mintzes, 1994). It is also noted by Songer & Mintzes (1994) and Ragsdale & Pedretti (2004) that models and analogies are often effective methods to facilitate students' learning in difficult conceptual areas, thereby allowing them to make the links between the molecular and macroscopic levels. As one type of model, role-play has been found to be an effective method of facilitating learning experiences because this technique uses the student's creative and cognitive input at a number of levels (e.g., Lovejoy, 1995; Cherif & Somervill, 1995; Duveen & Solomon, 1994). This article is a description of a role-play where students act out some major parts of cell metabolism to gain greater conceptual understanding of glycolysis and the Krebs cycle by being a molecule or a key part in a dynamic cellular process. …

Petrology of titanian clinohumite and olivine at the high-pressure breakdown of antigorite serpentinite to chlorite harzburgite (Almirez Massif, S. Spain)

Rocks of the Cerro del Almirez ultramafic massif (Sierra Nevada, Betic Cordillera, S. Spain) record the high-pressure dehydration of antigorite–olivine serpentinite to form chlorite harzburgite (ol + opx + chl). In the field, these two rock types are separated by a well-defined isograd. Titanian clinohumite (TiCl) and olivine show textural and compositional differences depending on the rock type. OH–TiCl occurs in the serpentinite as disseminated grains and in veins. F–OH–TiCl is observed exclusively in the chlorite harzburgite, where it occurs as porphyroblastic grains and within prograde olivine as irregular and lamellar, planar intergrowths at microscopic and submicroscopic scales. Petrological evidence of partial to complete breakdown of TiCl to olivine + ilmenite is preserved in both rock types. Chlorite harzburgite is characterized by a brown pleochroic olivine with abundantally oriented microscopic to submicroscopic oxide particles. The mean Ti-content of the brown olivine is 144 ppm. The brown olivine preserves TiCl lamellae that sometimes grade into ghost lamellae outlined by the oxide trails. This observation suggests that some of the oxide inclusions in the brown olivine are derived from the breakdown of TiCl intergrowths. Thermodynamic modelling of selected Almirez bulk rock compositions indicates a temperature increase from 635°C to 695°C, at pressures ranging from 1.7 GPa to 2.0 GPa, as the cause for the compositional adjustment of TiCl between the Almirez antigorite serpentinite and chlorite harzburgite. These P–T estimates are in good agreement with the sequence of phase relations observed in the field. The computed phase diagrams in conjunction with the geothermal conditions envisaged for different subduction settings indicate that TiCl is stable in the vicinity of the antigorite serpentinite/chlorite harzburgite phase boundary in some subduction settings. In these circumstances, clinohumite–olivine intergrowths in chlorite harzburgite may act as a sink for high field strength elements, and probably other elements, that are present in the mantle–wedge fluids.

Determination of solid surface tension from particle–substrate pull-off forces measured with the atomic force microscope

Atomic force microscopy (AFM) is capable of solid surface characterization at the microscopic and submicroscopic scales. It can also be used for the determination of surface tension of solids (gamma) from pull-off force (F) measurements, followed by analysis of the measured F values using contact mechanics theoretical models. Although a majority of the literature gamma results was obtained using either Johnson-Kendall-Roberts (JKR) or Derjaguin-Muller-Toporov (DMT) models, re-analysis of the published experimental data presented in this paper indicates that these models are regularly misused. Additional complication in determination of gamma values using the AFM technique is that the measured pull-off forces have poor reproducibility. Reproducible and meaningful F values can be obtained with strict control over AFM experimental conditions during the pull-off force measurements (low humidity level, controlled and known loads) for high quality substrates and probes (surfaces should be free of heterogeneity, roughness, and contamination). Any probe or substrate imperfections complicate the interpretation of experimental results and often reduce the quality of the generated data. In this review, surface imperfection in terms of roughness and heterogeneity that influence the pull-off force are analyzed based upon the contact mechanics models. Simple correlations are proposed that could guide in selection and preparation of AFM probes and substrates for gamma determination and selection of loading conditions during the pull-off force measurements. Finally, the possibility of AFM measurements of solid surface tension using materials with rough surfaces is discussed.

A transmission electron microscopy study of silica and kerogen biosignatures in approximately 1.9 Ga gunflint microfossils.

Microfossils preserved in chert from the;1.9 Ga Gunflint Formation (Schreiber Beach, Ontario, Canada) were studied with transmission electron microscopy (TEM) and analytical TEM (ATEM). Our goals were to uncover the style of silicification relative to the distribution of organic matter, and to evaluate the distribution and evolution of organic matter, at submicroscopic spatial scales. Petrographically the microfossils typically display filamentous or coccoidal morphologies, and consist of quartz crystals surrounded by kerogen along grain boundaries. ATEM analysis revealed that quartz associated with kerogen consists of 200-500nm-sized, round crystallites, whereas the chert matrix is comprised of randomly oriented, polygonal microquartz (5-10 microm). Silica spheroids found within some fossils consist of quartz subgrains in an amorphous to poorly crystalline matrix, suggesting that precipitation of opaline silica on organic matter occurred with subsequent but incomplete transformation to quartz. Some coccoidal microfossils surround large euhedral quartz crystals (up to 5 microm in diameter) that appeared to have influenced the distribution of kerogen during crystal growth. These euhedral quartz crystals commonly contain elongated (50-100 nm) iron-rich crystallites. Energy-loss, near-edge structure analysis of kerogen associated with a coccoidal microfossil showed that it is composed of amorphous carbon with no evidence of graphitization. TEM results revealed significant differences in the style of silicification between microbe-shaped microfossils and their surrounding chert matrix, as well as the presence of amorphous kerogen.

Assessment of Concrete in Sulfate Soils

An investigation of concrete exposed to sulfate soils is used to illustrate a methodology for the systematic study of the condition of concrete in service. Condition surveys of the site and tests of engineering properties of the concrete were supplemented by examination of concrete cores using the stereomicroscope, the optical microscope, the electron microscope, analysis by wet chemistry, thermal analysis, and X-ray diffraction. Step-by-step progression from large scale (tens of meters) to submicroscopic scales (tens of nanometers) gave continuity to detailed test methods. It also allowed for the selection of specimens appropriately representing the concrete as a whole, and ensured reliable interpretation of the results. In many cases, more than one test method provided the same or similar information. The writers believe the methodology employed will be of value to other investigators.

A dynamical theory of structures solids. I Basic developments

Based on the well-accepted notion of a Bravais lattice of a crystal at the atomic scale and with particular reference to inelastic behaviour of materials, this paper is concerned with the construction of a macroscopic dynamical theory of solids which incorporates the effect of the presence of the atoms and their arrangements. The theory incorporates a wide variety of microstructural processes occurring at various physical scales and has a range approaching the atomic scale. These processes include theeffectof the motion of individual dislocations, which are modeled here as continuous distributions at the macroscopic scale. The formulation of the basic theory, apart from the kinematical and kinetical variables employed in classical continuum mechanics, utilizes a triad of independent vector-valued variables — called directors — (or an equivalent tensor-valued variable) which represent the lattice vectors and are determined by additional momentum -like balance laws associated with the rate of change of lattice deformation in the spirit of a Cosserat (or directed) continuum. A suitable composition of the triad of directors and the ordinary deformation gradient is identified as a measure of perm anent orplasticdeformation, the referential gradient of which plays a significant role in the kinematics of lattice defects. In particular, a uniquely defined skew-symmetric part of the gradient of plastic deformation is identified as a measure of the density of dislocations in the crystal. The additional momentum -like balance laws associated with the rate of lattice deformation include the effect of forces necessary to maintain the motion of dislocations, as well as the inertia effects on the microscopic and submicroscopic scales arising from the director fields. The basic theoretical developments also provide important clarifications pertaining to the structure of the constitutive response functions for both viscoplasticity and (the more usual) rate independent plasticity.

Micromorphology of soil structure - Description, quantification, application

Micromorphological observation can provide insights into soil structure and aid interpretation of soil behaviour. Undisturbed samples are taken in the field and impregnated. They are used to prepare thin sections or images of the macropore structure using fluorescent photography. Sections can also be obtained at macro, meso and submicroscopic scales. The various elements of soil structure observed micromorphologically can be classified into pore space, physical, distribution and orientation fabrics, and associated structures. Examples of the importance of features in each category are given. Image analysis, especially when computerized, provides a way of parameterizing micromorphological observations. To date it has been used primarily on images of macropore space at the meso and microscopic scales. Such images can be digitized and segmented to show pore space and solid. The pore space can be allocated to pore types. This aids the estimation of 3-D parameters from I-D and 2-D measurements made on the image using stereology. Various ways of using structural parameters to compare structures are discussed. Applications for micromorphological observations, especially when quantitative, include comparison of structures formed by different management techniques. Structural measurements can aid interpretation of soil behaviour as described by physical measurements. They also have a role in estimating the representative elementary volume, on which physical measurements should be made, and in calibrating field estimates of soil structure.

Textures and Geochemistry of Authigenic Albite from Miocene Sandstones, Louisiana Gulf Coast

Feldspars in Louisiana Miocene sandstones, at depths of 2,400 to 6,000 m (80 to 150 degrees C), show progresssive reaction with increasing burial. Plagioclase undergoes both dissolution and replacement by albite, whereas K-feldspar undergoes only dissolution. Reactions do not reach completion by 6,000 m (150 degrees C), where a small amount of oligoclase and K-feldspar remain within an assemblage of nearly pure authigenic albite. Dissolution of plagioclase gradually becomes volumetrically important near 3,600 m (100 degrees C) and for the most part ends by 5,000 m (130 degrees C). Albite replacement of plagioclase also occurs primarily between 3,600 and 5,000 m (100 to 130 degrees C) but continues to the limit of sample control at 6,000 m (150 degrees C). K-feldspar dissolution is negligible until 4,800 to 5,600 m (125 to 140 degrees C). Below 5,600 m, K-feldspar is nearly absent in the rocks. Discontinuous zones of blocky to tabular extinction characterize grains of partially albitized plagioclase. Backscattered electron images of these grains, coupled with electron microprobe analyses, indicate that these zones represent domains of unreacted calcic plagioclase (An (sub 10-30) ) interspersed with domains of nearly pure authigenic albite (An (sub 0-2) ). SEM images show that some albite domains form from precipitation of small albite overgrowths on nucleation sites within secondary intragranular megascopic pores. In thin section, the overgrowths are optically clear. Other highly vacuolized albite domains may develop from direct replacement of calcic domains by dissolution-reprecipitation in submicroscopic pores without the formation of megascopic pores. Here, pore fluid may have been trapped between large numbers of subcrystals that grew together with imperfect boundaries. Operating on both megascopic and submicroscopic scales, albite replacement of plagioclase grains can be completed.