Honeycomb Texture Research Articles

Honeycomb Texturing of Silicon Via Nanoimprint Lithography for Solar Cell Applications

A novel texturing method to realize a honeycomb texture on multicrystalline silicon solar cells is presented in this paper. The demonstrated process chain is based on nanoimprint lithography (NIL), where an ultra-violet (UV)-curable polymer layer is structured by mechanical embossing in a high-throughput process. This patterned polymer layer can then be used as an etching mask for plasma or wet chemical etching processes to transfer the defined pattern into the silicon substrates. Within this study, the whole process chain of this novel texturing scheme, using interference lithography, cast moulding, NIL, and plasma etching, is described with a focus on the NIL process. The textured substrates are characterized by reflection measurements, which are compared with standard solar cell textures. Besides optical measurements, first results of honeycomb textured solar cells are presented. Short-circuit current densities above 40 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were achieved on high-quality float zone material. To increase the feasibility of an industrial realization of this process chain, we are developing a roller-NIL tool to structure an etching mask in a continuous in-line process. First results of this novel tool are also shown in this study.

Near Hydrothermal Alteration of Obsidian Glass: Implications for Long Term Performance Assessments

Abstract Obsidian glass alteration experiments under near hydrothermal conditions were performed to study mechanism and conditions of formation of altered minerals. X-ray diffraction patterns and cell dimensions of the specimens treated at 150, 200 and 3000C (pH = 8.03) revealed appearance of three main minerals - illite (9.5-10 Å), chlorite (7.04 Å) and halloysite (10.25Å). Further increase in the pH favours matrix dissolution with the formation of secondary altered layers. SEM-EDS study show that the alteration causes smoothing of the grain surfaces. These surfaces exhibits etch pits and series of depressions, formed by the process of dissolution. SEM - Back Scattered Electron images of obsidian specimens show thin laminae of smectite, with foliated bulky rims and cellular honeycomb texture, formed by precipitation from the solution as well as by direct transformation of glass during alteration. This mechanism is resulting from the alteration of alkalis by ionic inter-diffusion with H3O+ and H+ and inward diffusion of H2 O, leading to free diffusion of silica into solution and then to a local rearrangement of the glass framework. Thus, a direct transformation of glass into clay minerals is the major reaction mechanism as evidenced by the mechanism of glass dissolution and subsequent mineral precipitation.

Homogenization of linearly elastic honeycombs

A continuum model for the in-plane deformations of cellular materials with honeycomb texture is derived by using the tools of homogenization theory via Γ-convergence. It is shown that the effective medium does not develop couple stresses, although it exhibits some mild trait of polarity. General stress–strain relations and the yield domains for various levels of the applied body couples are deduced. The paper is a refinement of a previous one based on a less rich microscopic kinematics, but the analysis confirms most of those results.

Application of the Inkjet-Honeycomb-Texture in Silicon Solar Cell Production

In this work a honeycomb texture (HC-texture), which is created by isotropic wet chemical under-etching of an inkjetted mask, was successfully applied to Floatzone silicon (FZ-Si) wafers with a diameter of 150mm. A nearly perfect HC-texture with 18.2% reflection after texturization was obtained despite printing irregularities in the masking step. Lifetime measurements after emitter diffusion and anti-reflection coating show that the HC-texture is also better passivated than of the 25.8% reflecting acidic texture that was used in the reference group. An overall efficiency gain of 0.6% might be deduced when using a HC-texture instead of the acidic texture.

Formation of a honeycomb texture for multicrystalline silicon solar cells using an inkjetted mask

AbstractAn effective way to reduce the reflection of a multicrystalline solar cell is the use of a honeycomb structure, which can be generated by etching a mask isotropically. In this Letter, a directly printed hexagonal inkjet mask is presented. It results in a honeycomb texture with well developed and defined etch pits at an average distance of 50.1 μm and a weighted reflection of 18.4%. The major advantage of this mask is that the masking process is simple and that it has the potential of being fast and having low costs.magnified imageTopographical image of the texture created with the hexagonal inkjet mask presented in this paper.(© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A Homogenized Model for Honeycomb Cellular Materials

Within the framework of Γ-convergence theory we derive a continuum model for the in-plane deformations of cellular materials with honeycomb texture. At variance with other authors’ results, the effective medium does not develop couple stresses, although it exhibits some mild trait of polarity. General stress–strain relations, yield domain and stability thresholds are deduced.

Nanoimprint Lithography for Honeycomb Texturing of Multicrystalline Silicon

Abstract We investigated a novel process chain based on Nanoimprint Lithography (NIL) for realising defined textures. As application we chose the honeycomb texturing of multicrystalline silicon (mc-Si), which so far was applied using elaborate photolithographic processing for reaching the highest efficiencies on this type of substrate material up to now. The developed process chain contains the single steps of interference lithography (master origination of the hexagonal pattern) and cast moulding of silicone (stamp fabrication) as preliminary steps and the repetitive steps of NIL (structuring of the etching mask) and plasma etching (pattern transfer into the mc-Si substrate). First characterization steps of these textured substrates included reflection measurements to evaluate their optical properties as well as determination of emitter saturation current densities to gain information about potential plasma induced damages. These tests were conducted on high-quality float zone monocrystalline silicon to be not affected by material quality issues. Solar cells fabricated out of these test samples showed short circuit current densities exceeding 40 mA/cm 2 , revealing the potential of this texturing scheme. To further increase the feasibility of this process chain we developed a roller-NIL tool, which allows the patterning of UV-curable resists on non transparent, rough and brittle mc-Si substrates in a continuous process flow. Results of imprint quality using this novel tool are also shown in this work.

Mineralogy, Geochemistry, and Origin of Bentonite in Upper Cretaceous Pyroclastic Units of the Tirebolu Area, Giresun, Northeast Turkey

AbstractWidespread alteration in the Upper Cretaceous pyroclastic units of the Tirebolu (Giresun) area, NE Turkey, has resulted in significant occurrences of bentonite with economic potential. No detailed geological, mineralogical, or geochemical characterization of these occurrences has been carried out to date. The aim of this study was to describe the geological background, the mineralogical, chemical, and stable-isotope characteristics of the bentonite, and major aspects of their formation, e.g. type and source of low-temperature alteration, mass balance, chemical evolution of the smectites, and geochemistry of major and trace elements. The bentonite contains abundant smectite with occasional kaolinite and mordenite, volcanogenic feldspar, quartz, biotite, hornblende, glass shards, and pumice fragments, along with the diagenetic minerals, opal-CT, and, in some locations, calcite. X-ray diffraction patterns of the clay fractions exhibit characteristics of pure montmorillonite and beidellite-type smectite. Micromorphologically, the smectite exhibits a honeycomb texture, the kaolinite occurs in both vermiform and irregular platy forms, and the mordenite occurs in fibrous form. All of these minerals are edged with devitrified volcanic glass and resorbed feldspar. Chemically, the smectites are Ca-smectite. Geochemical data indicate that alteration of the pyroclastic units took place under suboxic and anoxic environmental conditions during bentonite formation. Field observations and mineralogical, geochemical, oxygen, and hydrogen isotopic data indicate that the alteration of feldspar and volcanic glass in the pyroclastics by mixed meteoric and sea water in a shallow marine environment under alkaline and acidic conditions, respectively, controlled by environmental Al, Ca, and Na concentrations, resulted in the formation of authigenic smectite, mordenite, and kaolinite. A large Ca content in the smectite originated from surrounding units, which resulted in high alkalinity; Mg originated from seawater.

New Insights into Andesite Genesis: the Role of Mantle-derived Calc-alkalic and Crust-derived Tholeiitic Melts in Magma Differentiation beneath Zao Volcano, NE Japan

Two distinctive differentiation trends, tholeiitic and calc-alkalic, are recognized in Zao volcano, which is located immediately behind the volcanic front of the NE Japan arc. The genetic relationship between these two magma series is critical for a better understanding of andesite genesis, because they often coexist in close spatial and temporal proximity in arc volcanoes. Petrographic features indicative of ‘disequilibrium’ , such as reversely zoned pyroxene phenocrysts, the wide and bimodal compositional distribution in Ca/(CaþNa) of plagioclase phenocrysts, honeycomb textures and dusty zones that these plagioclase phenocrysts often exhibit, and the presence of olivine^pyroxene pairs with different Mg/Fe, are observed exclusively in calc-alkalic rocks. In tholeiitic rocks the Sr isotopic ratios of plagioclase phenocrysts, determined by both micromilling combined with thermal ionization mass spectrometry, and laser-ablation inductively coupled plasma mass spectrometry techniques, are constant at 0 7042^0 7044. On the other hand, those in calc-alkalic rocks (0 7033^0 7042) show more complex characteristics, which can be best understood if at least three end-member components, a calc-alkalic basaltic melt, a tholeiitic basaltic melt and a tholeiitic felsic melt, contribute to the production of mixed calc-alkalic magmas.The Sr/Sr and trace element compositions of the leastdifferentiated basalt magmas, which are inferred from the composition of the calcic plagioclase [Ca/(CaþNa)40 9], suggest that two types of basaltic magma, calc-alkalic and tholeiitic, exist beneath the volcano. The tholeiitic basalt magma has a higher Sr/Sr than the calc-alkalic magma (0 7042 vs 0 7038) and a characteristic trace element signature consistent with the presence of plagioclase and amphibole as melting residues.This suggests that the tholeiitic magmas are produced via anatexis of amphibolitic crust caused by underplating and/or intrusion of mantle-derived calcalkalic basalt magmas into the sub-Zao crust. The mantle-derived calc-alkalic basalt magma mixes with crust-derived tholeiitic melts to form calc-alkalic andesite magmas.The hypothesis proposed here requires revision (or even abandonment) of the general consensus that calc-alkalic magmas have greater contributions of a crustal component than tholeiitic magmas.

Clay Mineralization Of The Neogene Aged Volcanics Of The Northeastern Sivrihisar (Mülk-Demirci)

The Neogene lacustrine units in the Mulk-Demirci region (NE Sivrihisar) are composed of detrital- evaporitic, volcanic and pyroclastic rocks. The Miocene volcanic rocks consist of lava flows of basalt and andesite composition and pyroclastic rocks are made up of agglomerate, tuff, altered tuff and tuffitic sandstone interbed- ded with altered claystone. These volcanic units change to dolomite, dolomitic limestone, marl and gypsiferous levels to the top. Some alteration zones in tuffs such as iron oxidation, limonitization, carbonatization and argilliza- tion are very noticeable with their yellow and red colors. Smectite is the main clay mineral which was formed as a result of alteration of volcanic and pyroclastic rocks in the study area. In some samples, smectite is accompa- nied mostly by feldspar, dolomite, calcite, opal-CT, quartz and partly by illite, gypsum and analcime. In the elec- tron microscopy (SEM) studies, smectite morphology was distinguished with platy flakes that are developed as a honeycomb texture. In addition, it was also determined in SEM images that smectite mineralization mostly deve- lops in dissolution voids and along fracture and fissures of volcanic glass or on the feldspar minerals. On the basis of field and laboratory studies, formation of smectite was found to be controlled by feldspar and volcanic glass which comprises the main component of tuffaceous units. Under hot and dry climate conditions, alteration of vol- canic material in the lake water had an important role in the formation of smectite. Smectite was formed by hyd- rolysis of volcanic glass and alteration of feldspar.

Introduction to the Ultrasound Guided Regional Anesthesia

The author introduces the ultrasound technique and the description of the sonoanatomy of brachial nerve block different blocks For one year ultrasound was introduced in our department as a tool for regional anesthesia and pain management. We would like to share our limited experience with our colleagues. The author introduces the ultrasound technique and the description of the sonoanatomy of brachial nerve block different blocks.. For peripheral blocks, the commonly used techniques at present are peripheral nerve stimulation and paraesthesia. These technique are essentially blinded techniques relying on anatomical landmarks to identify a needle entry point and guide the needle close enough to the nerve (within 0.5 cm) to allow either paraesthesia or electrical stimulation to confirm nerve location and identity.(1) Many techniques have been tried in the past including fluoroscopy (2), CT and MRI, although useful as a tool for research to investigate and modify existing techniques, they have impractical limitations for routine clinical application (3). Newer techniques such as percutaneous electrical guidance (PEG) and ultrasound may offer a real advance in both nerve location and identification. The use of ultrasound allows real time visualization of the nerves and the surrounding structures with real time guidance of the needle to the nerve and visual confirmation of the local anesthetic spreading around the nerve. Initial studies and results suggest that ultrasound guidance may decrease latency, improve success rates, eliminating or reducing serious complications (4,5). Any technique should ideally be able to fulfill the following criteria: Give information about the location of the target nerve and its relationship to neighboring structures (vascular structures, lung) Estimate or measure skin to nerve distance (depth of needle insertion) Help to determine angle and path that the needle needs to take. Supply real time visual and/or audio signals to show needle and guide to target nerve. Offer some indication of success of technique – ideally visualization of spread of local anesthesia. The principle of ultrasound imaging: US is sound wave with frequency greater than 20,000 cycles per second (20 kHz). US can direct as a beam, obeys the laws of reflection and refraction and is reflected by objects of small size. However, the amount of ultrasound reflected depends on the acoustic mismatch. Propagation through dense objects e.g. bone is poor with nearly the entire ultrasound beam reflected. As a result, bone generates a hyper echoic (bright) image as strong signal is returned to the emitting transducer. On the contrary, fat and tendon have low reflectivity thus they form hypo echoic (dark) images. The outline of an object is generally best delineated when the ultrasound beam is at 90 degrees. Generally speaking, nerves appear in the transverse (cross sectional) view as round to oval shaped structures that are nodular and they can be hypo echoic or hyper echoic depending on location. On the transverse view, peripheral nerves in cross section often appear to have an internal Introduction to the Ultrasound Guided Regional Anesthesia 2 of 5 honey comb texture. This corresponds to the parallel fascicular pattern noted on the longitudinal view. Figure 1 Figure 1a: Axillary approache to Brachial regional block The Probe and Needle. Figure 2 Figure 1b: Axillary sonography with mapping. Figure 3 Figure 2a: Supraclavicular Probe Introduction to the Ultrasound Guided Regional Anesthesia 3 of 5 Figure 4 Figure 2b: Supraclavicular sonogram. Figure 5 Figure 2c: Supraclavicular anesthetic spread. Figure 6 Figure 3a: Infraclavicular Probe and Needle placement Figure 7 Figure 3b: Infraclavicular sonography Introduction to the Ultrasound Guided Regional Anesthesia 4 of 5 CORRESPONDENCE TO Prof. Kamel Romdhane Consultant Anesthetist, ICU Pain Management Anesthesia Department Security Forces Hospital Program Email: kamelromdhane@hotmail.com Mobile # 0502892391

Clay Minerals in Early Amphibole Weathering: Tri- to Dioctahedral Sequence as a Function of Crystallization Sites in the Amphibole

AbstractThe early stages of amphibole weathering result in the crystallization of several clay mineral species: tri- and dioctahedral smectites, interstratified dioctahedral kaolinite-smectite (K-S), and halloysite. Each clay mineral crystallizes into specific microsites which develop from etch pits along specific crystallographic directions in the host amphibole. Two types of microsites are recognized according to their location in the amphibole crystal and their clay mineral crystallizations. The first type is a plane surface related to the (110) amphibole cleavages where saponite particles crystallize in a characteristic honeycomb texture. The second type is a ‘sawtooth’ (001) fracture surface generated by etch-pit coalescence where (1) platy K-S particles crystallize directly in contact with the amphibole at the top of ‘teeth’, (2) halloysite particles with tubular habits crystallize directly in contact with the amphibole on the side of the ‘teeth’, and/or on the K-S particles, and (3) montmorillonite crystallizes in the central part of the (001) fracture as a layer with honeycomb texture in contact with the K-S platelets located at the top of ‘teeth’. The microtextural relationships between the clay minerals and their host mineral suggest the following crystallization sequence: (1) saponite and montmorillonite crystallize first on the (110) and (001) surfaces, respectively; (2) as amphibole dissolution proceeds perpendicular to the (001) fracture planes, montmorillonites continue to form in the middle part of the widening fracture whereas K-S crystallizes on the ‘sawtooth’ termination; (3) in the last stage of weathering, tubular halloysite crystallizes on the side of the ‘teeth’, and/or on the K-S.

A lithofacies terrain model for the Blantyre Region: Implications for the interpretation of palaeosavanna depositional systems and for environmental geology and economic geology in southern Malawi

The Blantyre City Area is part of the African savanna in southern Malawi. Sedimentological, geomorphological, chemical and mineralogical studies were conducted to create a lithofacies terrain model. The project involves mapping, cross-sectioning, grain size, heavy mineral analysis, XRD and the study of sedimentary textures under the petrographic microscope. These classical techniques were combined with GIS-based field and office works. The combined efforts led to 2-D maps and 3-D block diagrams that illustrate the geomorphological and sedimentological evolution of the landscape in southern Malawi during the late Mesozoic and Cenozoic. The results obtained through integrated geomorphological–sedimentological studies form the basis for land management (planning of residential areas, waste disposal sites, assessment of bearing capacity of rocks), geohazard prediction (delineation of high risk zones in terms of mass flow and inundation) and the evaluation of high-place (ceramic raw materials) and high-unit value (placers of precious metals and gemstones) mineral commodities in the study area. The study addresses regional and general aspects alike. In regional terms, the study aimed at unraveling the evolution of landforms at the southern end of the East African Rift System during the most recent parts of the geological past. Four stages of peneplanation were established in the working area. Planation was active from the Cretaceous to the Quaternary (stage I: early to mid-Cretaceous, stage II: early Tertiary, stage III: early to mid-Tertiary, stage IV: mid- to late Tertiary). During the most recent parts of the Quaternary, strong fluvial incision was triggered by the base-level lowering of the Shire River. Geomorphological alteration of the landscape goes along with a phyllosilicate–sesquioxide transformation from minerals indicative of more acidic meteoric fluids (e.g., gibbsite, kaolinite) to those typical of more alkaline conditions (e.g. smectite, vermiculite, hydrobiotite). In addition, the investigation is to provide some characteristic features suitable for the recognition and interpretation of terrestrial environments resembling the present-day savanna in the ancient sedimentary record: (1) Conspicuous bimodality in the grain-size distribution. (2) High degree of gravel roundness. (3) Boulder fields (basal conglomerates) with fitting breccias and no rotation of structural elements. (4) Poor to very poor sorting of siliciclastics. (5) Stratification is rare; if present only in sandy beds with antidune and tabular cross-bedding at low angle prevailing over cross-bedding at high angle. (6) Grading rare; in arenaceous deposits poorly developed FU sequences, in rudites poorly developed CU sequences, locally with surface armoring. (7) Directional sedimentary structures in coarse-grained deposits are unimodal. Fabric types: a(t)b(i) and a(p)b(i); shear planes indicative of slide may be present. (8) Ribbon-shaped architectural elements prevail over channel-like types. Bounding surfaces/unconformities are uneven to wavy and more widespread than scour-and-pool structures. (9) Fine-grained carbonaceous interbeds are restricted to shallow depressions. (10) Etch marks such as tafonis, flutes, honeycomb textures are common. (11) Placer deposits of metallic and non-metallic mineral commodities are abundant. (12) Alucretes and ferricretes of bog iron (ferrihydrite > goethite) and lateritic (goethite > ferrihydrite) types are common, calcitic freshwater limestones and gypcretes are scarce. (13) Kandite-group minerals “in” (relic), smectite-group minerals “in”, vermiculite “in” (recent), mica-group minerals “out”.

Cordierite-anorthoclase hornfels xenoliths in Stromboli lavas (Aeolian Islands, Sicily): an example of a fast cooled contact aureole

High-grade hornfels xenoliths in the 60 ka old calcalkaline basaltic andesite lava flows of Stromboli (Omo lavas; Paleostromboli II period) consist of fine- to medium-grained holocrystalline rocks. Feldspar (mainly anorthoclase) and cordierite represent ca . 85 vol% of the modal mineralogy. Aluminiferous spinel (hercynite), sillimanite, ± corundum, ± ilmenite, ± chlorapatite are also present. Major and trace element compositions, together with Sr, Nd and Pb isotopic data, indicate that the source rocks are metapelites compatible with upper continental crust-derived materials. According to common petrogenetic grids for pelitic rocks ( e.g. NaKFMASH), a pressure range of 2–3.5 kbar and a peak temperature close to 800° C can be inferred for the mineral assemblage. A honeycomb texture and wide, high-T compositional range of the ternary feldspars (Ab 35–70 Or 3–63 An 2–49 ) suggest incipient melting followed by quenching. Accordingly, the xenoliths may well represent contact metamorphosed rocks (contact aureole), compatible with metapelites belonging to the continental crust basement of Stromboli. TEM (Transmission Electron Microscopy) observations of alkali-feldspar showed the presence of a cross-hatched pattern oriented parallel to (010) and (001), and of albite twinning in the orthoclase-enriched and -depleted samples, respectively. Both textures are related to a monoclinic to triclinic phase transition in a highly disordered feldspar. A highly disordered Al-Si configuration is also corroborated by cell parameters. Incipient decomposition textures, but no exsolution lamellae, are present in the intermediate alkali-feldspars. These results support a fast cooling of the hornfels xenoliths, of the order of degrees per hour. The high-T feldspar textures were preserved because the xenoliths, stoped into the uprising basaltic andesite host magma, were rapidly transported to the surface shortly after they reached the contact aureole peak temperature.

Computer Modeling and Description of Nonstoichiometric Apatites Cd5−η/2(VO4)3I1−η and Cd5−η/2(PO4)3Br1−η as Modified Chimney–Ladder Structures with Ladder–Ladder and Chimney–Ladder Coupling

Diffraction patterns from apatite-structure compounds Cd5−η/2(TO4)3X1−η with T=P, V and X=Br, I show sheets of diffuse scattering normal to c* at incommensurate l=q (q=1.63 for Cd–V–I apatite and q=1.78 for Cd–P–Br apatite), because the c repeat of the average unit cell is shorter than two X diameters. The equilibrium X..X spacing along c defines the incommensurate periodicity c/q and stoichiometry (1−η)=q/2. The layers show a honeycomb texture for the Cd–V–I apatite, which is condensed into discrete spots for the Cd–P–Br compound. In both phases, X..X repulsions along 〈100〉 force neighboring rods of X atoms out of phase. In the Cd–P–Br phase, additional 〈210〉 attractions drive incipient formation of a rhombohedral superstructure. Average structure site occupancies and the observation of second-order diffuse layers at both l=2q and l=q+2 imply the existence of strong Cd..X in addition to X..X interactions. A three-dimensional computer model was used to produce finite-temperature structure simulations as a function of X..X interactions along 〈001〉, 〈100〉, and 〈210〉, and X..Cd interactions, from which diffraction patterns were calculated. The experimental patterns were fit and approximate values for the interaction energies obtained (hundreds to thousands of joules per mole). It was apparent that lock-in to commensurability caused by the X..Cd term and the formation of nonprimitive incommensurate modulated structures driven by X..X interactions were mutually antagonistic, and the actual structures are compromises between the two.

Characterization of interstratified minerals associated with argillic alteration in steam-heated environment at Solo, Mabini, Philippines.

Intersratified minerals are significant component of alumina-rich clays in the alteration halo formed by hydrothermal argillization of andesitic rocks at Solo, Mabini, Philippines. The observed argillic alteration lies above the zone of chloride reservoir in steam-heated acid environment within a low-sulphidation hydrothermal system. The assemblage of interstratified minerals includes abundant illite/smectite (I/S) associated with fine-grained crystals of kaolinite and jarosite, and minor amount of dioctahedral chlorite/smectite (C/S). These minerals occupy a specific zone that is transitional between the kaolinite-smectite inner zone and the chlorite-illite fringe zone in the alteration halo. Aluminous illite and smectite interstratifications show a wide range of ratio of component layers and display some distinct variations in chemical composition, structure, and morphology. Such variations can be ascribed to the conversion of early-formed smectite to illite through interstratified illite/smectites. The reaction sequence in the conversion series takes place discontinuously in terms of the degree of ordering of interstratifications from Reichweite R=0 (>55% smectite) to R=1 (50-20% smectite) and finally to R=2 (<20% smectite). This decreasing trend in the proportion of smectite layers in I/S occurs primarily with increasing distance from the kaolinite-smectite inner zone and is accompanied by progressive increase in the K2O content of the mineral towards the chlorite-illite fringe zone. The corresponding crystal morphology changes from poorly developed honeycomb texture of smectite to dominantly pseudohexagonal flakes of illite. Aluminous chlorite/smectite minerals occur sporadically near the chlorite-illite zone in the alteration halo and usually show regular to partially regular type interstratifications. They contain about 40-50% smectite and exhibit structural similarities with the completely ordered interstratification of tosudite. The mechanism of smectite to illite conversion series identified in this study is related to the effect of cation composition of hydrothermal solution and the K+ fixation in interlayers. The illite/smectite and associated aluminian chlorite/smectite is interpreted to have been formed in response to substantial influx of Al and K from leaching the andesite rock or the precursor smectite.

Mineralogical responses of siliciclastic carbonate-cemented reservoirs to steamflood enhanced oil recovery

Rock–fluid interactions induced by steamflood enhanced oil recovery were investigated in laboratory simulations to determine the geochemical reactions and the effects of these reactions on reservoir permeability. Flow-through laboratory experiments using mixtures of quartz, kaolinite, and siderite were performed in a high temperature/high pressure permeameter at a confining pressure of 1200 psi and temperatures between 150–250°C. Fluid compositions used in the experiments simulated the vapor and residual liquid phases encountered in steamflood operations as well as an intermediate fluid composition. Effects of fluid pH, fluid salinity and flow rate were systematically investigated in the experiments. The most extensive fluid–rock interactions were observed in the vapor phase simulations and high temperature/high pH condition simulations. Smectite, chlorite, illite, mixed-layer clays, greenalite, analcime, and K-feldspar were all identified as products of rock fluid interaction in the experiments. Smectite was the dominant authigenic phase to reduce permeability in the experiments. The experiments showed that the formation of smectite in Fe-rich environments does not require a clay precursor. Smectite is likely the most damaging neoformed mineral to reservoir permeability under different hydrogeochemical conditions for several reasons including: (1) its relatively high surface area (including microporosity in the “honeycomb texture”), (2) its propensity to migrate and block pore throats during fluid flow in porous media because of its small particle size, pore-lining texture, and electrochemical surface properties, and (3) the wide range of stability of smectites in the physical and chemical conditions that exist in reservoirs undergoing steamflood EOR. The rapid precipitation of authigenic minerals in these experiments suggests that the period required for fluids and rock to reach equilibrium in diagenetic environments are extremely short when considering geologic time scales. The armoring of pre-existing minerals by grain-coating authigenic minerals appears to result in the attainment of local equilibrium conditions prior to when one would predict assuming a continuous supply of reactant minerals was present.

Formation of Organic Derivatives of Boehmite by the Reaction of Gibbsite with Glycols and Aminoalcohols

AbstractThe reaction of gibbsite in various organic solvents at 250°–300°C under spontaneous vapor pressure of the solvents was examined. Glycols and aminoalcohols afforded the organic derivatives of boehmite in which one of the oxygen atoms of the glycol molecule or the alcoholic oxygen atom of aminoalcohol was incorporated into the boehmite layers. By increasing the molecular size of the solvent, the yield of the boehmite derivative decreased, and, at the same time, the basal spacing of the boehmite derivative increased. The product had a honeycomb texture on the surface of the particle, which suggests a dissolution-recrystallization mechanism for the formation of the boehmite derivatives. A hydroxyl group and a functional group, such as hydroxyl, methoxyl, or amino group having the ability to donate its lone pair electrons, were apparently necessary for the organic solvent molecules to form the boehmite derivative by this mechanism.

Thermal Reaction of Aluminum Alkoxide in Glycols

Thermal reaction of aluminum isopropoxide in glycols at 300°C yielded the glycol derivatives of boehmite. The physical properties of the products and the aluminas obtained by calcination strongly depended on the crystallite size of the boehmite derivatives, which seems to be controlled by the heterolytic cleavage of the C‐O bond of HO(CH2)nOAI = formed by alkoxide exchange between aluminum alkoxide and glycol. The product had a unique honeycomb texture, which was preserved on calcination to form a transition alumina.

Textural Variation and Composition of Bentonite Derived from Basaltic Ash

The Rokle bentonite deposit is part of an accumulation of argillized volcanoclastic rocks in the Tertiary stratovolcanic complex of the Doupovske Mountains east of Karlovy Vary (Carlsbad), about 100 km westnorthwest of Prague, Czechoslovakia. The arenite basalt ash was originally composed of hyaloclasts and subordinate biotite. The following types of montmorillonite aggregates were produced during the alteration of the ash in a stagnant, lacustrine environment: (1) extremely fine-grained micro-crystalline aggregates that have honeycomb textures and that replace the original hyaloclasts, and (2) coarse crystalline aggregates that have more open honeycomb textures and that fill pores and cracks in altered hyaloclasts and in pumice vesicles. Both types of aggregates have the same chemical composition according to energy dispersive X-ray analysis. Montmorillonite, separated as the <1-¼m size fraction from olive gray bentonite, has the following crystallochemical formula: (K0.09Na0.02Ca0.29Mg0.10) (Al2.43Fe3+1.05Fe2+0.005Mn2+0.005Mg0.50) (Si7.62Al0.38) O20(OH)4. Biotite was apparently stable during the alteration of the hyaloclasts. Anatase and possible accessory heulandite-clinoptilolite were also formed in small amounts, but were not observed by scanning electron microscopy. Goethite is the youngest oxidation product in some parts of the bentonite. Minute fragments of sodium-rich plagioclase, potassium feldspar, quartz, and muscovite are ubiquitous accessories of the original hyaloclasts. Together with kaolinite, they formed from the underlying fresh or kaolinized orthogneiss.