Edge Faces Research Articles

Semiempirical model for the description of sorption equilibria on clay mineral surfaces

Based on a review of recent experimental data on heavy metal sorption on clay minerals (montmorillonite, illite, and kaolinite), a method was developed to estimate the unified characteristics of the density of surface sorption sites and constants of reactions occurring on them, such as Meaq ⇄ Mesurf. A model combining the description of ion exchange sorption in the presence of Na electrolytes and pH-dependent chemical adsorption on the amphoteric sites of the edge faces of the three mentioned phases provided a satisfactory approximation of experimental data of various authors and an approach to the understanding of the essence of differences in the properties of sorbents and behavior of metal cations. It was supposed that this approach is helpful as a reconnaissance stage during the analysis of other more complex systems (multicomponent solutions, polymineralic soils, etc.).

Fluidity of highly concentrated kaolin suspensions: Influence of particle concentration and presence of dispersant

This work discusses fluidity of highly concentrated kaolin suspensions prepared by filtration technique in the presence of a dispersant (sodium salt of polyacrylic acid). Two types of rheological tests were carried out on the kaolin aqueous suspensions at different concentrations of kaolin C (12–75 wt.%) and dispersant C d (0–1 wt.% of dispersant/wt. of solid). A classical coaxial viscosimeter was used to measure viscosity of suspension when it was fluid-like. A texture analyser was used for rheological analysis of the thicker kaolin suspensions. A sol–gel (percolation) transition, starting from the kaolin volume fraction φ c = 0.05, was observed in the absence of a dispersant. The addition of a dispersant shifted this percolation transition to higher volume fractions. The rheological data showed that the platelet particles can align in a hydrodynamic flow. A dispersant or kaolin load suppresses the interaction forces between basal and edge faces of the kaolin particles, which bear different charges. As a result, a face-to-face arrangement arises, which is supported by the electron microscopy images. Hence, the loosely packed card-house structure, which is typical for the aqueous kaolin suspensions, undergoes a gradual conversion into an oriented structure under the load of solid particles or dispersant. A maximum of the percolation threshold was reached for a certain optimum dosage of the dispersant ( C d ≈ 0.5 wt.%). The higher filtration efficiency was observed for a loosely packed card-house structure in dispersant-free suspensions at low pH. A dispersant improves fluidity and dryness of the filter cakes, however, produces an oriented face-to-face structure of particles, which causes a rise in resistance to liquid flow during filtration.

Buffer capacities of podzolic and peat gleyic podzolic soils to sulfuric and nitric acids

Soil samples from the main genetic horizons of pale podzolic and peat gleyic podzolic soils from the Central Forest Reserve were subjected to a continuous potentiometric titration by sulfuric and nitric acids. The sulfate sorption capacity was determined in soil mineral horizons. The buffer capacity of mineral horizons of both soils to sulfuric acid was found to be higher than that to the nitric acid. This is explained by the sorption of sulfates via the mechanism of ligand exchange with the release of hydroxyl groups from the surfaces of Fe and Al hydroxide particles and edge faces of clay crystallites. The buffer capacity of organic horizons of the pale podzolic soil to sulfuric acid proved to be higher than that to nitric acid; in organic horizons of the peat gleyic podzolic soil, the buffer capacity to sulfuric acid was lower than that to nitric acid. The reasons for this phenomenon have yet to be investigated.

Phosphate removal from water using lithium intercalated gibbsite

In this study, lithium intercalated gibbsite (LIG) was investigated for its effectiveness at removing phosphate from water and the mechanisms involved. LIG was prepared through intercalating LiCl into gibbsite giving a structure of [LiAl 2(OH) 6] + layers with interlayer Cl − and water. The results of batch adsorption experiments showed that the adsorption isotherms at various pHs exhibited an L-shape and could be fitted well using the Langmuir model. The Langmuir adsorption maximum was determined to be 3.0 mmol g −1 at pH 4.5 and decreased with increasing pH. The adsorption of phosphate was mainly through the displacement of the interlayer Cl − ions in LIG. In conjunction with the anion exchange reaction, the formation of surface complexes or precipitates could also readily occur at lower pH. The adsorption decreased with increasing pH due to decreased H 2PO 4 −/HPO 4 2− molar ratio in solution and positive charges on the edge faces of LIG. Anion exchange is a fast reaction and can be completed within minutes; on the contrary, surface complexation is a slow process and requires days to reach equilibrium. At lower pH, the amount of adsorbed phosphate decreased significantly as the ionic strength was increased from 0.01 to 0.1 M. The adsorption at higher pH showed high selectivity toward divalent HPO 4 2− ions with an increase in ionic strength having no considerable effect on the phosphate adsorption. These results suggest that LIG may be an effective scavenger for removal of phosphate from water.

Towards a link between the energetic heterogeneities of the edge faces of smectites and their stability in the context of metallic corrosion

In the context of the potential confinement of high-level radioactive wastes (HLW) within the clay engineered barrier system (EBS) in deep geological formations, the evolution of the retention properties of smectite when interacting with Fe(0) needs to be assessed. If some potential natural analogues describing iron–clay reactivity are easily found, metallic iron–clay interactions are poorly described in studies regarding the Earth. Therefore, experimental investigations are needed. Several parameters influence Fe(0)–clay interactions, such as temperature, the interlayer composition of swelling clays, and the presence of octahedral Fe 3+, etc. From a geometrical point of view, it is thought that clay destabilization is mainly controlled by phenomena starting at the edge faces of the particles. In the present work, the rates of the smectite–Fe(0) reaction at 80 °C were assessed by XRD, Mössbauer, and CEC analyses for three smectites. The investigations show marked differences in the degree of stability, which cannot be explained by the crystal-chemistry rules established in previous studies. Therefore, the Fe(0)-smectite interactions were studied in view of textural and energetic surface quantitative analyses. The studied smectites have equivalent nitrogen BET-specific surface areas, equivalent argon edge surface areas and slightly different basal surface areas. This similarity in particle shape indicates that the edge surface area cannot be accounted for when explaining the observed differences in reactivity. However, a correlation is obtained between smectite reactivity and the energetic heterogeneity of its edge faces. This is interpreted in terms of a multiplication of the number of sites on the edge faces, where the electron transfer between Fe(0) and the smectite structure can occur.

Improved Physical Theory of Diffraction: Removal of the Grazing Singularity

Physical theory of diffraction based on the concept of elementary edge waves [P. Ya. Ufimtsev, Electromagnetics, vol. 11, no. 2, pp. 125-160, 1991] is well suited for analysis of backscattering from perfectly conducting objects with edges. However, it needs to be improved for the investigation of forward scattering, especially in the directions grazing to the edge faces, where it predicts infinite values. The present paper removes this singularity by introducing a new definition for the uniform component of the surface current. This component is defined here as the current induced on the half-plane tangential to the illuminated face of the scattering edge (and to the edge itself). The improved theory of elementary edge waves is developed, which is valid for all scattering directions, including forward scattering

Improved theory of acoustic elementary edge waves

The high-frequency asymptotic theory of acoustic edge waves [P. Ya. Ufimtsev, J. Acoust. Soc. Am. 86, 463–74 (1989)] is well suited for investigation of backscattering from perfectly reflecting (soft or hard) three-dimensional objects with edges. However, it needs to be improved for calculation of forward scattering, especially in the directions grazing to the edge faces, where it predicts infinite values. The present paper removes this singularity by the appropriate choice of the so-called uniform component of the surface field. It is defined here as the field induced on the half-plane tangential to the illuminated face of the scattering edge (and to the edge itself). An improved theory of elementary edge waves is proposed, which is valid for all directions of scattering, including the forward grazing directions.

Mechanism of Adsorption of Water Vapor by Muscovite: A Model Based on Adsorption Calorimetry

AbstractAdsorption isotherms and differential heats of adsorption of water vapor by muscovite were measured at 303 K. The heats of adsorption are stepwise and each step corresponds to the stoichiometric formation of adsorption complexes of H2O molecules with K+ ions, (H2O)n/K+, (n = 1–6), which are located on the basal and lateral (edge) faces. At saturation, the ditrigonal cavities of the basal faces are fully occupied by hexameric clusters. It is suggested that half of the K+ ions on the basal faces come from neighboring layers by migration under the influence of the adsorbed H2O at the initial stage of adsorption. Similar migration of K+ to the edges was also hypothesized, suggesting that only every second site can be occupied by a cluster. At the final stage of adsorption, H2O molecules are believed to form H-bonded bridges between the hexameric water/cation clusters on the basal faces, whereas on the edge faces no such effect is believed to occur. The mean molar integral adsorption entropy of water is ∼−7 J/mol K less than the molar entropy of the bulk liquid. The mobility of H2O on muscovite is slightly less than in bulk water. Migration of K+ cations under the influence of adsorbed H2O both on the basal and lateral faces of muscovite is reversible.

Role of Exchangeable Cations on Geometrical and Energetic Surface Heterogeneity of Kaolinites

Textural and energetic proprieties of kaolinite were studied by low-pressure argon adsorption at 77 K. The heterogeneity of four kaolinites (two low-defect and two high-defect samples) modified on their surface by cation exchange with Li+, Na+, or K+ was studied by DIS analysis of the derivative argon adsorption isotherms. The comparison between the derivative adsorption isotherms shows that the nature of the surface cation influences the adsorption phenomena on edge and basal faces. In the case of basal faces, two adsorption domains are observed: for the first one, argon adsorption is slightly sensitive to the nature of the surface cation; for the second one, argon adsorption energy depends on the nature of surface cation suggesting their presence on theoretically uncharged basal faces. This study also shows that the shape of elementary particles, as derived from basal and edge surface areas, changes with the nature of cation. This anomalous result is due to the decrease of edge surface area with increasing the size of the cation. This surface cation dependence can be accounted for the area occupied by the edge surface cations in the first argon monolayer.

Collision cascade containment in classical dynamics simulations of sputtering

Classical dynamics simulations of sputtering have been carried out for 3 keV Ar projectiles incident on Cu(1 0 0) crystallite targets with a range of lateral and vertical dimensions. The purpose of the simulations was to document the effects of containment failure on the predicted sputter yields and to establish criteria for convergence of the predicted sputtering properties to asymptotic values. Failure of lateral containment produces sputter yield errors due to both lateral truncation of the target (which understates yields) and to sputtering from the edge faces of the target crystallite (which overstates yields). Failure of vertical containment understates sputter yields. For practical purposes, sputter yield containment can be achieved using a 12-layer Cu(1 0 0) target with 441 atoms per layer, provided that the contribution from atoms originating from the crystallite edge faces is excluded from the sputter yield estimates.

Adsorption of Carboxylic Acids on Submicrocrystalline Aluminum Hydroxides in Aqueous Solution. Part I: Qualitative Study by Infrared and Raman Spectroscopy

Adsorption of acetic, oleic, benzoic, and salicylic acids on submicrocrystalline aluminum hydroxide samples is investigated in aqueous solutions. Experimental infrared and Raman spectroscopic data are analyzed to determine the reactivity of the monocoordinated hydroxyl groups located on the edge faces of bayerite or gibbsite crystals. Two key parameters were (1) the effect of concentration of aqueous solutions of the acids, and (2) the variation in specific surface areas of different samples of bayerite and gibbsite powders. Strong preferential adsorption to bayerite was observed over the whole pH range. No adsorption to gibbsite was detected. Data from the literature indicate that acetate, oleate, and benzoate form bidentate complexes on bayerite while salicylate forms a monodentate complex. The infrared spectra show that only monocoordinated hydroxyl groups are reactive, in the bayerite samples, and the band at 1020 cm−1 corresponds to the deformation mode of the monocoordinated hydroxyl groups whose stretching vibration was at 3465 cm−1. It is suggested that the specific surface areas given by the adsorption isotherms is a condition necessary for adsorption, but not sufficient in itself. Adsorption requires the presence of Al-OH2+1/2 species as well as the presence of steps or of a packaging sequence ABABABA rather than a packaging sequence ABBAABBA of the hydroxyl planes. The gibbsite impurity present in the bayerite sample reacted completely, while the lateral OH in the gibbsite sample did not, reflecting the lower reactivity in gibbsite relative to extended domains of bayerite.

Modeling description and spectroscopic evidence of surface acid–base properties of natural illites

The acid–base properties of natural illites from different areas were studied by potentiometric titrations. The acidimetric supernatant was regarded as the system blank to calculate the surface site concentration due to consideration of substrate dissolution during the prolonged acidic titration. The following surface complexation model could give a good interpretation of the surface acid–base reactions of the aqueous illites: >SOH↔> SO − +H + , p K a int =3.73∼ 4.06, Al 3+ +H 4 SiO 4 +2H 2 O↔ Al(OH) 2 (OSi(OH) 3 )+3H + , p K f2 =9.85∼ 10.71, >SOH+Al 3+ +H 4 SiO 4 ↔ >SOAl(OSi(OH) 3 ) + +2H + ,pK SC =3.31∼ 3.40. Both experimental and optimized data revealed some similarities in the acid–base behaviors of the different illites. Based on matching results with the standard XRD patterns, the changes in intensities of the diagnostic 0 0 l diffraction lines indicated that the formation of surface Al–Si complexes or precipitates appeared preferable to the bulk deposition of Al(OH) 3 solid. Similar features were also reflected in the microscopic Raman spectra, where the vibrational peaks of Si–O and Al–O bonds diminished following acid attack, then rose again after hydroxide back titration. The varied ratio of signal intensity between IVAl and VIAl species present in 27Al MAS NMR spectra, together with the nearly stable BET surface areas after acidic titration, showed that the basal planes in the layer structure of natural illite contributed to the dissociation of structural components as well as the edge faces. The combined spectroscopic evidence plus the acid–base titration results suggested that the interactions of illite surface sites with silicic acid and aluminum species, released from illite substrate, should be considered in the modeling description.

In situ atomic force microscopy study of hectorite and nontronite dissolution: Implications for phyllosilicate edge surface structures and dissolution mechanisms

The dissolution behavior of two smectite minerals, hectorite (trioctahedral) and nontronite (dioctahedral), was observed in situ, in acid solutions, using atomic force microscopy. As expected, the crystallites dissolved inward from the edges, and the basal surfaces appeared to be unreactive during the timescale of the experiments. The hectorite (010) faces appeared to dissolve about 6 × more slowly than the lath ends, usually broken edges. The edges visibly dissolved on all sides, and appeared to roughen somewhat. On the other hand, the (010), (110), and (11 ‐ 0) faces on nontronite crystals were exceptionally stable, so that any dissolution fronts originating at broken edges or defects would quickly become pinned along these faces, after which no more dissolution was observable. These observations can be explained by using periodic bond chain theory to predict the topology of the surface functional groups on the edge faces of these minerals. If a certain amount of predicted surface relaxation is allowed on the (110) and (11 ‐ 0) faces of nontronite, an important difference between the exceptionally stable faces and the others becomes apparent. That is, the oxygen sites connecting the octahedral and tetrahedral sheets are all fully bonded on the nontronite (010), (110), and (11 ‐ 0) edge faces, whereas all hectorite edge faces and nontronite broken edges would have coordinatively unsaturated connecting O atoms. This explanation for the differential reactivity of these crystal faces implies that the rate limiting step of the dissolution process is the breaking of bonds to connecting O atoms.

Relation between the Infrared Spectra and the Lateral Specific Surface Areas of Gibbsite Samples

The chemical behavior of crystalline Al(OH)3 samples is governed by the lateral-to-basal surface ratio. For well-crystallized gibbsite samples possessing the two types of surfaces clearly spatially separated, a vibrational component at ∼3460 cm-1 in the infrared absorption spectra, not displayed in the Raman spectra, increases linearly with the lateral specific area determined by a gas adsorption isotherm. This intense and broad line is related to hydroxyl stretching modes of AlOH21/2+ or AlOH1/2- species present on the edge faces. However, it is too simplistic to assign this band to a mode of one or the other of these species. More complex structures combining both species should also be considered. When an evacuated sample is submitted during a short time to a D2O vapor injection, the OD spectral region displays essentially one broad component at 2563 cm-1, corresponding to the 3460 cm-1 band in the OH region and not to the other modes of the bulk hydroxyls. This experimental observation is also in agre...

Ti-Bearing Phases in the Huber Formation, an East Georgia Kaolin Deposit

AbstractSix kaolin samples from the Lower Tertiary Huber Formation near Wrens, Georgia were analyzed using transmission electron microscopy (TEM), electron diffraction (ED), powder X-ray diffraction (XRD), chemical analysis, and magnetic susceptibility to characterize the Ti-bearing phases. Selected samples were treated with 5 M NaOH to remove kaolinite and concentrate the Ti-bearing phases for additional analysis. TiO2 content in the bulk fraction ranges from 1.2 to 5.4 wt. %. There are at least three Ti-bearing phases, including anatase, rutile, and a poorly defined nanocrystalline form. Anatase is most abundant and is commonly found with {010} faces in association with kaolinite edge and basal faces. The nanocrystalline form occurs at 0–1 wt. %, and rutile occurs in trace amounts. Bulk XRD analysis correlates well with the bulk TiO2 chemical measurements. Average anatase unit-cell parameters are a = 0.37908 ± 0.0002 nm and c = 0.951 ± 0.001 nm. These parameters indicate an approximate chemical formula of Fe3+0.05Ti4+0.95O1.95(OH)0.05.The distribution of TiO2 content as a function of depth may be useful to obtain original grain-size variations associated with relative sea-level changes responsible for the deposition of the Huber Formation. Evidence for original depositional sediment properties can be seen in the occurrence of pseudomorphic replacement of micas and fecal pellets by kaolinite. Additional evidence for post-depositional changes includes the sub-micrometer euhedral character and low Fe content of the anatase (relative to soil-derived anatase). These observations for the Huber Formation are consistent with a previously published theory for kaolin genesis that includes biomineralization of originally coarser-grained aluminosilicates into a kaolinite-rich ore body.

Initial steps of ligand-promoted dissolution of gibbsite

The initial steps of dissolution of gibbsite by salicylate were examined using adsorption isotherms, electrophoresis, infrared spectroscopy, and controlled rate thermal analysis. A contact time of 24 h was chosen to avoid alteration of the gibbsite platelets. The results clearly show that adsorption of salicylate takes place only on the edge faces of the gibbsite platelets, where the OH groups are monocoordinated to Al atoms and bear a half charge. Monodentate and binuclear complexes are formed. The consequence is charge reversal on the solid surface. The dissolution rate is linearly correlated to the surface density of salicylate. These observations demonstrate that dissolution occurs from the edge faces of the gibbsite platelets. Normalized dissolution rates should therefore be calculated using the surface area of the edges of gibbsite and not the total surface area.

Layer charge and electrophoretic mobility of smectites

The aim of this study is to determine the effect of the layer charge of smectites on their electrophoretic mobility (EM), using electrophoresis measurements. In order to cover the charge domain from 0 to 2 charges per unit structural cell, two clay series were used: thermally treated Cu-montmorillonite (0–0.7) and synthetic saponites (0.7–2). All the studied samples are negatively charged in a pH range from 2 to 12. Neither layer charge nor ionic strength influences the EM of smectites at neutral to alkaline pH. At acidic pH, the EM of smectites ranges from −3 to −0.4 10 −8 m 2 s −1 V −1 when the layer charge ranges from 0.8 to 2. High charge and low charge smectites, which are not expandable, tend to aggregate in aqueous suspension, and the measured EM corresponds then to the amphoteric sites of the edge faces of the layer stacks. These sites are negatively charged at pH values above 3.

Interfacial Charging Phenomena of Aluminum (Hydr)oxides

The interfacial charging of Al(OH)3 (gibbsite and bayerite) and Al2O3 has been studied. For Al(OH)3 it can be shown that the very strong variation in charging behavior for different preparations is related to the relative presence of differently reacting crystal planes. The edge faces of the hexagonal gibbsite crystals are proton reactive over the whole pH range, in contrast to the 001 plane, which is mainly uncharged below pH = 10. On this 001 face only doubly coordinated surface groups are found, in contrast to the edges which also have singly coordinated surface groups. The results are fully in agreement with the predictions of the Multi site complexation (MUSIC) model. The proton adsorption, electrolyte ion adsorption, and shift of the IEP of gibbsite and aluminum oxide have been modeled simultaneously. For gibbsite, the ion pair formation of Na is larger than that of Cl, as is evidenced by modeling the experimentally observed upward shift of the IEP and charge reversal at high electrolyte concentrati...

129Xe NMR study of carbonaceous materials: effects of surface chemistry and nanotexture

Some aspects of the relationship between the physicochemical state of microcrystalline carbons and the 129Xe NMR parameters of adsorbed xenon have been investigated. No correlation between the values of the 129Xe chemical shift (δ0) and the substructural characteristics of the carbons (interlayer spacing, crystallite size, content of ordered or amorphous carbon of the samples), micropore volume and specific surface area was revealed. The δ0 values increase linearly with the surface concentrations of `strong' adsorption sites for H2PdCl4, and chemisorbed heteroatoms (O, Cl) as well. HREM studies of carbon surface microstructure revealed δ0 to be nanotexture-dependent. The lowest δ0 value (∼14 ppm) was detected for a graphitized carbon black, the surface of which consists primarily of exposed basal planes of carbon crystallites, and the highest δ0 value (∼100 ppm) for a carbon sample with exposed edge faces. Medium δ0 values (50±10 ppm) were found for carbons the surface of which was roughened by steps formed by carbon layers of different size. The 129Xe NMR technique, in combination with the common procedures for the determination of the surface area of solids, may open a way to estimate the contribution of the edge faces of carbon crystallites to the total surface area of unoxidized carbons.

Single-crystal Raman spectroscopy study of dickite

Other| February 01, 1998 Single-crystal Raman spectroscopy study of dickite Clifford T. Johnston; Clifford T. Johnston Purdue University, Crop, Soil and Environmental Sciences, West Lafayette, IN, United States Search for other works by this author on: GSW Google Scholar Jozef Helsen; Jozef Helsen Search for other works by this author on: GSW Google Scholar Robert A. Schoonheydt; Robert A. Schoonheydt Search for other works by this author on: GSW Google Scholar David L. Bish; David L. Bish Search for other works by this author on: GSW Google Scholar Stephen F. Agnew Stephen F. Agnew Search for other works by this author on: GSW Google Scholar American Mineralogist (1998) 83 (1-2): 75–84. https://doi.org/10.2138/am-1998-1-208 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Clifford T. Johnston, Jozef Helsen, Robert A. Schoonheydt, David L. Bish, Stephen F. Agnew; Single-crystal Raman spectroscopy study of dickite. American Mineralogist 1998;; 83 (1-2): 75–84. doi: https://doi.org/10.2138/am-1998-1-208 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Raman spectra were obtained from the (001), (010), and (100) faces of a St. Claire dickite specimen of known orientation. Raman spectra collected from the (010) and (100) faces of dickite are reported for the first time and reveal vibrational features significantly different from the (001) spectra. Variations in intensities of the v(OH) bands in polarized spectra were used to confirm previous band assignments, to determine the shape and orientation of the local Raman tensors for the OH1 and OH3 groups. The most striking polarization effect observed in the v(OH) region of dickite was the behavior of the a(c'c')a spectrum relative to Raman and IR spectra of other orientations. Unlike previously reported spectra, the dominant feature in this spectrum was the 3643 cm (super -1) band. This large increase in intensity of the 3643 cm (super -1) band in comparison with the other v(OH) bands was related to the fact that Raman spectra were recorded from the edge faces of dickite with the electric vector of the incident laser polarized along the c axis. This permitted observation of vibrational modes polarized along the c axis. Raman frequencies of the v(OH) bands assigned to the OH2 and OH4 groups differ from their IR counterparts by 12 cm (super -1) , suggesting that these groups may be related by a center of symmetry. For comparison, Raman spectra in the v(OH) region were also obtained from individual micro-crystals of kaolinite that were approximately 5 mu m across the (001) face. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.