Exfoliation

Layered silicate clays are natural crystallites and are well recognized for their structures and industrial applications, but there are very few reports on their structural confinement properties and on the mechanisms that underlie their polymer interactions. In this review, we summarize the recent progress on clay modification via conventional ion exchange reactions, sol-gel linking, atom transfer radical polymerization, and polymer intercalation. The organic interaction of ionic clays involves different noncovalent bonding forces, such as amido acid five-membered ring chelation, carboxylic acid chelation, intermolecular hydrogen bonding, and double-layer hydrophobic alignment in a layered clay confinement. Controlling the organic species, their amounts and their self-assembled conformation in a clay confinement could lead to the tailoring of the silicate platelet interlayer distance and of their organophilic properties.

A polymerizable cationic surfactant, vinylbenzyldimethyldodecylammonium chloride (VDAC) was synthesized for functionalization of montmorillonite (MMT) and preparation of exfoliated polystyrene-clay nanocomposites. Organophilic MMT was prepared by cationic exchange between inorganic ions of MMT and ammonium cations of VDAC in an aqueous medium. Dispersions of intercalated clay (VDAC-MMT) in styrene monomer formed gels. Shear thinning behavior of the gels was observed via rheological measurements. Polystyrene-clay nanocomposites were prepared by free radical polymerization of styrene containing dispersed organophilic MMT. Exfoliation of MMT in polystyrene matrix was achieved as revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The exfoliated nanocomposites have higher dynamic modulus and higher decomposition temperature than pure polystyrene. ᭧

Dust engenders a fear of the unseen, an anxiety and horror at the dissolution of matter to a minute scale; it is amorphous, all pervading, and knows no boundaries. Through the inevitable progress of time the body is transformed and reduced to
dust as the outer layers are shed as dander. In its smallest form the body is grotesque and undelineated. Our dead return to dust but so too do the living. The skins and cells of our moving, breathing bodies disperse into the world, mingling
with foreign matter and waste as we pass through space. Dust forms stagnant veils coating objects of disuse, gathering in corners and floating above our beds. It is an
unsettling and permanent presence, marginal and transitional, without site or bounds.

This paper explores bodies that are decentralised and in a state of dusty disintegration. It addresses the horror of the body in a state of dissipation by asking: where and when does the body begin? Where may it end? And how might the body's transgressed boundaries offer up possibilities for designing wearable artefacts?

Desilication of the medium-pore ferrierite zeolite in sodium hydroxide solutions was conducted to modify the porous structure and to create structural defects, resulting in enhanced accessibility and ultimately improved catalytic performance. Commercial H-ferrierite (Si/Al = 29) with the characteristic plate-like morphology was used as starting material. The attack by NaOH induces deaggregation, exfoliation, fracture, and ultimately perforation of the ferrierite crystals, resulting in mesoporosity of combined inter-and intracrystalline nature. The parent and treated samples were characterized by ICP-OES, XRD, N 2 adsorption, SEM, TEM, 27 Al and 29 Si MAS-NMR, FTIR, and NH 3 -TPD. Optimization of the treatment conditions (NaOH concentration, temperature, and time) is required to introduce substantial mesoporosity without significantly altering the micropore structure due to excessive Si leaching. Compared to other frameworks (e.g. MFI, MTW, MOR, and BEA), FER requires harsher conditions to extract silicon leading to mesoporosity. Under optimal conditions, the mesopore surface area of the NaOH-treated ferrierite increased by a factor of 3-4 with respect to the parent zeolite, while mostly preserving the native crystallinity and acidity. The ability of NaOH to induce porosity changes in FER largely exceeds conventional dealumination post-treatments. The benefit of the introduced porosity was demonstrated in the catalytic pyrolysis of low-density polyethylene.

The utility of expandable graphite as a flame retardant for PVC, plasticized with 60 phr of a phosphate ester, was investigated. Cone calorimeter results, at a radiant flux of 35 kW m -2 , revealed that adding only 5 wt.% expandable graphite lowered the peak heat release rate from 325 ± 11 kW m -2 to 63 ± 23 kW m -2 and the total heat release from 55 ± 11 MJ m -2 to only 10.7 ± 0.3 MJ m -2 . All samples containing expandable graphite ignited and burned only very briefly before flame out. The remarkable effectiveness of the expandable graphite is attributed to an excellent match between the exfoliation onset temperature of the graphite and the onset of decomposition of the PVC. This means that the exfoliation of the graphite forms a protective barrier layer at the right place at the right time. In addition, the simultaneous release of halogen species by the polymer matrix and the exfoliating graphite prevents the formation of a flammable air fuel mixture.

In recent times, the materials properties of graphene have generated ever-increasing interest across multiple scientifi c disciplines including physics, material science and chemistry. The quantity and quality of graphene produced directly impacts the performance and development of applications related to organic fi eld-effect transistors (OFETs), conductive materials, [ 2b , 5 ] and photovoltaics, not forgetting biological applications. Generally, the techniques used to prepare graphene are based on either physical processes, chemical methodologies [ 3a , 9 ] or a blend of the two. Although physical methods are able to produce high-quality graphene consistently, the amount of processable graphene produced is always limited, as well as being quite costly. Conversely, although chemical oxidation of graphite to graphene oxide (GO), followed by reduction, results in reduced graphene oxide (RGO) in large quantities, this method generates defect-laden RGO to the extent that the resultant graphene is generally of lower quality than that produced by physical methods. Despite the fact that there are some reports relating to the use of wet chemistry to exfoliate graphene from graphite, the exfoliation of graphite to graphene employing noncovalent ππ interactions with π -conjugated molecules in water is relatively unexplored. Herein, we describe the preparation of graphene by direct exfoliation of graphite through the exploitation of ππ interactions between the N,N ′ -dimethyl-2,9-diazaperopyrenium dication ( MP 2 + ) and graphene in aqueous media.

A unique two-step modified Hummers method is developed to unzip and exfoliate multiwalled carbon
nanotubes (MWCNTs) into low-defect graphene oxide nanoribbons (GONRs). From the X-ray diffraction
(XRD), Raman spectroscopic (RS), X-ray photoelectron spectroscopic (XPS), Fourier transform infrared
spectroscopic (FTIR), and transmission electron microscopic (TEM) results, a mechanism involving
multilayer-unzipping followed with rapid local peeing-off (i.e., exfoliation) is proposed for this two-step
Hummers procedure which provides a guide for obtaining high-quality GONRs. In the two-step
procedure, both multilayer-unzipping of MWCNTs and oxidative exfoliation of multilayer GONRs are
accelerated by a freshly prepared, concentrated KMnO4 medium. This action reduces the random
damage on the basal plane of resultant GONRs, which is commonly found in the ineffective, timewasting,
oxidant-consuming, one-step strategy. Consequently, low-defect GONRs can be efficiently
fabricated in this two-step process.

The present paper analyzes the effects of the plasticizer nature on the clay exfoliation process into starchbased nano-biocomposites. The nano-hybrids have been elaborated by melt blending starch with different plasticizers, namely, glycerol, sorbitol and Polysorb Ò . In addition two types of nanofillers, natural montmorillonite (MMT-Na) and montmorillonite organo-modified with cationic starch (OMMT-CS) have been tested. Intercalated/aggregated and exfoliated morphologies were obtained with respectively MMT-Na and OMMT-CS as the nanofillers and glycerol as the plasticizer. Morphological analyses combined with uniaxial tensile tests have shown the negative effect of the sorbitol on the exfoliation extent into such nano-hybrid materials. Besides, thermo-mechanical analyses revealed the occurrence of a phase separation between domains rich and without nanofillers induced by the high plasticizer content of the starch formulations.

Chlorinated polyethylene (CPE)/organophilic-montmorillonite (Cloisite Ò 30B (CL30B)) nanocomposites have been prepared by melt intercalation using (poly(e-caprolactone), (PCL)) as CPE/clay compatibilizer. Actually, a high clay content masterbatch-based on PCL was first produced and then dispersed by melt blending within CPE. CPE/CL30B nanocomposites was also prepared by direct blending of CPE with CL30B for sake of comparison. All the composites were characterized by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). The thermal stability of the nanocomposites was analyzed by thermogravimetric analysis (TGA) while the mechanical properties were assessed by tensile testing. When using low molecular mass PCL chains as compatibilizer, the nanocomposites displayed a rather intercalated structure but their ultimate properties remained unchanged whereas with high molecular weight PCL chains, clay delamination was favoured and led to an increase of both thermal and mechanical properties of the resulting nanocomposites.

Inland notches, are elongated concave-shape indentations that develop on the carbonate rocky cliffs of mountainous zones, down to the desert fringe. These rock shelters form as a result of the interaction between specific petrologic characteristics and climatic controls, emphasizing the importance of environment upon rock decay. Inland notches are shaped due to slight differences (1–15%) in the porosity of the visor and cavity bed: the cavity bed is more porous, so more likely to erode by exfoliation and dissolution. Thus, the cavity bed retreats at a faster rate compared to the slower subaerial dissolution of the visor bed, until a critical point is reached where the visor collapses. In Israel, inland notches inhabit the same lithostratigraphic units as do large caves. The vast majority (71%) of inland notches are formed in hard, dense, and crystalline limestone deposited throughout the Turonian age. Another 27% are cut into the dolomitic sequence of the upper Albian and lower Cenomanian. The rest (2%) are dispersed in the various formations of the Cenomanian and Eocene eras. Notches are most common in semi-arid and in Mediterranean climates but mainly in areas with annual rainfall of between 400 mm and 850 mm. In more humid areas (> 900 mm/yr) notches are negligible or completely absent, due to the rapid rate of chemical dissolution of carbonate rocks. In the desert fringe (200–300 mm/yr), mechanical decay is accelerated and notches exhibit disintegration processes, visor collapse, and rock falls. In the desert area (< 200 mm/yr), salt decay replaces the chemical decay characteristic of inland notches, encouraging tafoni formation. In addition, notches form through fluvial activity or on account of greater petrophysical differences between consecutive beds; i.e. elongated cavities may form in soft rocks, shaded by harder visors or crusts.

The effect of high energy ball milling under different conditions on the structure of Na + -montmorillonite (Na-MMT), and the organo-montmorillonite (Cloisite 30B) was investigated. Ball milling increased the structural disorder: peeling off of layers from the particles was observed, followed by the exfoliation of the particles, indicated by the disappearance of the (001) reflection. X-ray diffraction and infrared spectra revealed that the exfoliated layers did not show deteriorated structures. The presence of the alkylammonium ions seemed to stabilize the structure by reducing exfoliation.

The technological exploitation of the extraordinary properties of graphene relies on the ability to achieve full control over the production of a high-quality material and its processing by up-scalable approaches in order to fabricate large-area films with single-layer or a few atomic-layer thickness, which might be integrated in working devices. A simple method is reported for producing homogenous dispersions of unfunctionalized and non-oxidized graphene nanosheets in Nmethyl-2-pyrrolidone (NMP) by using simple molecular modules, which act as dispersion-stabilizing compounds during the liquid-phase exfoliation (LPE) process, leading to an increase in the concentration of graphene in dispersions. The LPE-processed graphene dispersion was shown to be a conductive ink. This approach opens up new avenues for the technological applications of this graphene ink as low-cost electrodes and conducting nanocomposite for electronics.

Stoichoimetric graphene fluoride monolayers are obtained in a single step by the liquid-phase exfoliation of graphite fluoride with sulfolane. Comparative quantum-mechanical calculations reveal that graphene fluoride is the most thermodynamically stable of five studied hypothetical graphene derivatives; graphane, graphene fluoride, bromide, chloride, and iodide. The graphene fluoride is transformed into graphene via graphene iodide, a spontaneously decomposing intermediate. The calculated bandgaps of graphene halides vary from zero for graphene bromide to 3.1 eV for graphene fluoride. It is possible to design the electronic properties of such two-dimensional crystals.

For organically modified montmorillonite (OMM)–epoxy nanocomposites, maximal montmorillonite dispersion is found to depend synergistically on the mechanical processing history of the resin mixture and the chemistry at the OMM surface. Specifically, Cloisite 30A (quaternary ammonium OMM) and I30.E (primary ammonium OMM), each containing surfactants with different catalytic effects on the curing chemistry of Epon 862, are compared. Irrespective of the OMM, conventional solvent-free processing methodologies, including sonication, result in an inhomogeneous distribution of OMM on the micron scale. Even though the primary ammonium alkyls within I30.E enhance intragallery reactivity, this only results in extensive swelling of tactoids (interlayer distance ∼10–20 nm), and thus retention of layer–layer correlations, leading to ‘hybrid’ micron scale reinforcing particles, not nanoscale dispersion of individual layers. In contrast, sub-ambient temperature (cryo) compounding had substantial impact on the ability to reduce tactoid and agglomerate size and increase homogeneity of dispersion for Cloisite 30A. The reactivity near Cloisite 30A is similar to that in the bulk and thus localized gelation around the layer-stacks does not retard particulate refinement. In all cases, alteration of the global epoxy network structure was ruled out by FTIR and NMR measurements. For nanocomposites with similar OMM content, however, the final thermal–mechanical properties does not coherently relate to one characteristic of the morphology. The coefficient of thermal expansion (T>Tg) and hardness (T<Tg) depend only weakly on morphology, where as the glass transition temperature depends strongly on the extent of OMM dispersion and interfacial chemistry. In general, the inter-relationships between mechanical processing, OMM surface chemistry and the desired property enhancements are not linear and thus must be considered in light of a final application to evaluate the optimal ‘nanocomposite’ fabrication methodology to achieve maximal benefit.

Achievement of exfoliated structure of polymer/ Clay nanocomposites is of particular interest for the improvement of mechanical properties. In this work, the morphology and mechanical properties of epoxy/ clay nanocomposites has been investigated. Diglycidyl ether of bisphenol A (DGEBA) epoxy resin (EPON828) and Jeffamine D400 curing agent was used. To obtain perfect dispersion, nanoclay (Cloisite 30B) was sonicated in acetone. The mixture was then mixed with polymer. Afterwards, the curing process was performed by addition of curing agent and degassing. Disappearing of peaks in X-Ray diffraction patterns of nanocomposites containing less than 5wt% nanoclay, is a good evidence of perfect dispersion of layered silicates in matrix, i.e. formation of exfoliated morphology. Based on tensile test results, it is deduced that as the amount of nanoclay increases, the elastic modulus and elongation at break of the nanocomposites containing 1wt% and 5wt% nanoclay increases by 12% and 31%, respectively. Therefore, obtaining perfect dispersion of layered silicates in epoxy matrix and exfoliated morphology, results in better mechanical properties of the nanocomposites.

The microcrystalline flaked graphites SFG6 and SFG44 were evaluated with regard to their compatibility with propylene carbonate (PC) by in situ Raman microscopy and postmortem scanning electron microscopy (SEM) study. PC is employed as electrolyte component in lithium-ion batteries. However, when used with certain types of graphitic materials, exfoliation occurs. To compare the effects of exfoliation, the first lithium insertion properties of these graphitic materials were measured with in situ Raman microscopy. Lithium half-cells containing either 1 M LiClO 4 1:1 (w/w) ethylene carbonate (EC):dimethyl carbonate (DMC) or 1:1 (w/w) EC:PC were investigated. The commencement of the exfoliation process was detected in SFG44 EC:PC by the appearance of a shoulder band at 1597 cm −1 on the G-band (1584 cm −1 ) below 0.9 V versus Li/Li + . The band (assigned as the exfoliation or E-band) at higher wavenumbers (1597 cm −1 ) corresponded to solvated lithium ions intercalated into graphite. The in situ Raman spectra of SFG6 in EC:DMC or EC:PC and SFG44 in EC:DMC did not show the E-band and instead displayed regular lithium intercalation spectra.

This paper is concerned with restrictions on Left-Branch Extraction (LBE) in
Bulgarian and Macedonian, the only two Slavic languages with articles. The
data indicate that the availability of LBE is related to the number of modiers,
and thus require a revision of the generalisation that all languages with articles
disallow LBE. Following Martinović (2019), Calabrese & Pescarini (2014), a
solution based on the order of operations is proposed, connecting the availability
of LBE to the idea that projections can be removed via syntactic operations
such as Exfoliation (Pesetsky 2019). The application of Exfoliation depends
on the relative timing of article placement, which in turn is performed via a (revised)
post-syntactic operation of Generalised Lowering (Embick & Noyer 2001).
Exfoliation and subsequently LBE are fed by an early application of Lowering,
assumed to be able to interleave narrow syntax (Martinović 2019), but if applied
late, Lowering counter-feeds these two operations.

Layered double hydroxides (LDH) are a class of readily synthesizable layered crystals that can be used as an alternative to the commonly used silicate crystals for the preparation of polymeric nanocomposites. In this work layered double hydroxide/polyamide 6 nanocomposites (LDH/PA6) were prepared from organo-modified LDH by melt processing. The anionic exchange capacity of LDH was varied in order to investigate its influence on the degree of exfoliation. LDH were dispersed by a twin screw micro-extruder at a variety of processing conditions. The nanocomposites were characterized by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), transmission electron microscopy, dynamic scanning calorimetry, and thermogravimetric analysis. It was found that exfoliated nanocomposites were successfully prepared by melt processing with a low exchange capacity LDH, whereas residue tactoids were observed with a high exchange capacity LDH. Shear, together with the exchange capacity, seems to be the key factor for the delamination in LDH/PA6. No major change in the crystalline phase or in the rate of crystallization was observed in the nanocomposite as compared to the neat polymer. A reduction in the onset of thermal decomposition temperature was observed in PA6/LDH compared to neat PA6, likely due to a nucleophilic attack mechanism. The properties of this nanocomposite system are discussed with connections to the current understanding within the broader nanocomposite field. q

The preparation of processable graphene oxide colloids called chemically converted graphene (CCG) involves the following steps: oxidation of graphite to form graphite oxide; exfoliation of graphite oxide to form graphene oxide (GO); and reduction of GO to form CCG. In this work, the exfoliation and reduction steps were monitored by capillary zone electrophoresis (CZE). CZE was performed in fused silica capillaries with UV absorbance at 230 nm (GO) and 270 nm (CCG) using 250 M tetrapropylammonium hydroxide (pH 10.4). The results indicate that almost complete exfoliation of graphite oxide (0.05 wt%) and higher recovery of CCG were obtained by sonication at 50% power for more than 15 h. CZE is considered a valuable tool for the fractionation and analysis of GO nanoparticles and, hence, for the control of different steps in preparation of CCG.

A polymerizable cationic surfactant, vinylbenzyldimethyldodecylammonium chloride (VDAC) was synthesized for functionalization of montmorillonite (MMT) and preparation of exfoliated polystyrene-clay nanocomposites. Organophilic MMT was prepared by cationic exchange between inorganic ions of MMT and ammonium cations of VDAC in an aqueous medium. Dispersions of intercalated clay (VDAC-MMT) in styrene monomer formed gels. Shear thinning behavior of the gels was observed via rheological measurements. Polystyrene-clay nanocomposites were prepared by free radical polymerization of styrene containing dispersed organophilic MMT. Exfoliation of MMT in polystyrene matrix was achieved as revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The exfoliated nanocomposites have higher dynamic modulus and higher decomposition temperature than pure polystyrene. ᭧

The preparation of processable graphene oxide colloids called chemically converted graphene (CCG) involves the following steps: oxidation of graphite to form graphite oxide; exfoliation of graphite oxide to form graphene oxide (GO); and reduction of GO to form CCG. In this work, the exfoliation and reduction steps were monitored by capillary zone electrophoresis (CZE). CZE was performed in fused silica capillaries with UV absorbance at 230 nm (GO) and 270 nm (CCG) using 250 M tetrapropylammonium hydroxide (pH 10.4). The results indicate that almost complete exfoliation of graphite oxide (0.05 wt%) and higher recovery of CCG were obtained by sonication at 50% power for more than 15 h. CZE is considered a valuable tool for the fractionation and analysis of GO nanoparticles and, hence, for the control of different steps in preparation of CCG.

Medium chain length polyhydroxyalkanoates (mcl-PHA) have been produced by fed-batch cultivation of Pseudomonas oleovorans. Using octanoic acid as the sole carbon substrate, a copolymer of 3-hydroxyoctanoate and 3-hydroxyhexanoate monomer units was accumulated up to 38 wt. % of cell mass. Mcl-PHA based nanocomposites have then been prepared using Cloisite 15A as nanofiller and characterized. Wide angle X-ray diffraction and rheological analysis of the nanocomposites highlighted their morphologies, which can be considered as well-intercalated structures. The thermal characteristics of mcl-PHA are not significantly affected by the nanofiller incorporation. On the contrary, the storage moduli of nanocomposites are greatly enhanced with increasing clay fraction due to the degree of dispersion of the nanoplatelets in the polymer matrix.

A synthetic Li-fluorohectorite with typical aspect ratios around 1000 shows superior thermal, fire and mechanical properties. A comparison between Li-fluorohectorite and MMT underlines the crucial role of the aspect ratio in particular for flame retardancy. Furthermore, solution blending yields a better dispersion of the filler, as compared to melt compounding, which directly transforms into superior properties. Quite surprisingly, the homogenous clay surface layer built during burning of the PS fluorohectorite nanocomposite has such a high gas barrier that an intumescent-like behavior of the char is detectable.

New type of film-forming electrolyte additive (functional co-solvent) for rechargeable lithium batteries has been demonstrated. The additive prevents solvent co-intercalation and graphite exfoliation in propylene carbonate based electrolytes. The additive performs best at 15% w/w ratio and is a mixture of homologous disiloxanes functionalized with polyether side chains of variable length. Galvanostatic and potentiodynamic charge/discharge characteristics are presented. SEM/EDX analysis has been carried out to evidence the suppression of PC co-intercalation.

Zeolites-microporous crystalline aluminosilicates-are widely used in petrochemistry and fine-chemical synthesis 1-3 because strong acid sites within their uniform micropores enable size-and shape-selective catalysis. But the very presence of the micropores, with aperture diameters below 1 nm, often goes hand-in-hand with diffusion limitations 3-5 that adversely affect catalytic activity. The problem can be overcome by reducing the thickness of the zeolite crystals, which reduces diffusion path lengths and thus improves molecular diffusion 4,5 . This has been realized by synthesizing zeolite nanocrystals 6 , by exfoliating layered zeolites 7-9 , and by introducing mesopores in the microporous material through templating strategies 10-17 or demetallation processes . But except for the exfoliation, none of these strategies has produced 'ultrathin' zeolites with thicknesses below 5 nm. Here we show that appropriately designed bifunctional surfactants can direct the formation of zeolite structures on the mesoporous and microporous length scales simultaneously and thus yield MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolite nanosheets that are only 2 nm thick, which corresponds to the b-axis dimension of a single MFI unit cell. The large number of acid sites on the external surface of these zeolites renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-togasoline conversion. We expect that our synthesis approach could be applied to other zeolites to improve their performance in a range of important catalytic applications.

The electrical behavior of backgate graphene field effect (GFET) transistor was studied at different ambient conditions. Backgate p-channel GFET transistors were fabricated on oxidized silicon wafers by exfoliation of graphite. The carrier mobilities were determined from the measured transconductance. For all ambients investigated (N 2 , Ar, and air), the graphene transistors show enhanced mobilities at elevated temperatures. This behavior can be explained by a stronger screening of scattering centers, i.e., defects in graphene and at the graphene oxide interface, with increasing temperature. For operation in air the transistors showed a higher transconductance compared to the operation in nitrogen and argon due to the strong acceptor-like behavior of gases adsorbed on the graphene surface.

Siliceous MCM-41-supported nickel phosphides from a precursor with a Ni/P atomic ratio of 3, 2, 1.25, 1, 0.5, or 1/3 were prepared by in situ reduction. A high heating rate and a multistep program were used to prepare the supported nickel phosphides. The in situ reduction method proved superior to the traditional reduction-passivation-rereduction method. The timely removal of local moisture from the surface during reduction is crucial to obtaining a high hydrodesulfurization (HDS) performance of the phosphide catalysts. The precursors were characterized by TPR to investigate the reactions involved in phosphide preparation, and the structures of the resulting nickel phosphides were characterized by means of 31 P NMR and XRD. Nickel phosphide formation may start with the reduction of NiO to Ni, and the Ni metal may assist phosphide formation in the reduction of nickel-rich precursors. Nickel-rich phosphides exhibited much higher HDS activity than phosphorus-rich phosphides prepared by the in situ reduction method. Reduction of the precursor with Ni/P = 2 yielded Ni 12 P 5 / MCM-41, whereas reduction of the precursor with Ni/P = 1.25 produced Ni 2 P/MCM-41. As in the traditional reduction-passivationrereduction method, a small excess of phosphorus in the precursors is also needed to obtain the desired nickel-rich phosphides by the in situ reduction method. Ni 2 P/MCM-41 was the most active catalyst in the HDS of dibenzothiophene among all of the supported nickel phosphides prepared by the in situ reduction method.

Siliceous MCM-41-supported nickel phosphides from a precursor with a Ni/P atomic ratio of 3, 2, 1.25, 1, 0.5, or 1/3 were prepared by in situ reduction. A high heating rate and a multistep program were used to prepare the supported nickel phosphides. The in situ reduction method proved superior to the traditional reduction-passivation-rereduction method. The timely removal of local moisture from the surface during reduction is crucial to obtaining a high hydrodesulfurization (HDS) performance of the phosphide catalysts. The precursors were characterized by TPR to investigate the reactions involved in phosphide preparation, and the structures of the resulting nickel phosphides were characterized by means of 31 P NMR and XRD. Nickel phosphide formation may start with the reduction of NiO to Ni, and the Ni metal may assist phosphide formation in the reduction of nickel-rich precursors. Nickel-rich phosphides exhibited much higher HDS activity than phosphorus-rich phosphides prepared by the in situ reduction method. Reduction of the precursor with Ni/P = 2 yielded Ni 12 P 5 / MCM-41, whereas reduction of the precursor with Ni/P = 1.25 produced Ni 2 P/MCM-41. As in the traditional reduction-passivationrereduction method, a small excess of phosphorus in the precursors is also needed to obtain the desired nickel-rich phosphides by the in situ reduction method. Ni 2 P/MCM-41 was the most active catalyst in the HDS of dibenzothiophene among all of the supported nickel phosphides prepared by the in situ reduction method.

An improved, safer and mild method was proposed for the exfoliation of graphene like sheets from graphite to be used in fuel cells. The major aim in the proposed method is to reduce the number of layers in the graphite material and to produce large quantities of graphene bundles to be used as catalyst support in polymer electrolyte membrane fuel cells. Graphite oxide was prepared using potassium dichromate/sulfuric acid as oxidant and acetic anhydride as intercalating agent. The oxidation process seemed to create expanded and leafy structures of graphite oxide layers. Heat treatment of samples led to the thermal decomposition of acetic anhydride into carbondioxide and water vapor which further swelled the layered graphitic structure. Sonication of graphite oxide samples created more separated structures. Morphology of the sonicated graphite oxide samples exhibited expanded the layer structures and formed some tulle-like translucent and crumpled graphite oxide sheets. The mild procedure applied was capable of reducing the average number of graphene sheets from 86 in the raw graphite to nine in graphene-based nanosheets. Raman spectroscopy analysis showed the significant reduction in size of the in-plane sp2 domains of graphene nanosheets obtained after the reduction of graphite oxide.

A micromechanical model for prediction of the elastic modulus of polymer/layered silicate nanocomposites was developed based on the conventional Halpin-Tsai model. The model considers near realistic intercalated and exfoliated structures of nanocomposites. The dependence of exfoliation ratio (the ratio of exfoliated filler content to the total filler content) on the filler concentration has been studied from different viewpoints and an exfoliation ratio function has been proposed. The predictions of the proposed model with variable exfoliation ratio functions were compared with the predictions of the same model with constant exfoliation ratio and the predictions of the Halpin-Tsai model using experimentally obtained results. The results of the proposed model with variable exfoliation ratio functions are in very good agreement with experimental data, particularly taking their nonlinearities into account.

The dispersion of clay in a polymer matrix is influenced by two factors: the choice of organic treatment for the clay and the processing or mixing method. Maximum benefits are achieved when the platelets are well dispersed or exfoliated. Exfoliated nanocomposites are formed when the individual clay layers break off the agglomerated particles or tactoids and are either randomly dispersed in the polymer (a disordered nanocomposite) or left in an ordered array. It is suggested that size reduction of clay particles and platelet delamination occur by erosion or surface peeling. A model based on the classical theories of interparticle interactions was formulated for the exfoliation of the clay platelets in a polymer matrix. The model involves the estimation of the binding energy and the adhesive force between the platelets in a clay particle, which indicate the forces required for breaking apart or delamination of clay particles. Then, the shear force required for breakup or delamination of the tactoids is estimated and compared to the hydrodynamic shear forces available during processing. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

This paper presents the results of an application of Ground Penetrating Radar (GPR) method for localizing fractures, unloading or exfoliation joints, massive blocks, and identifying the top of fresh granite. The reason for this work was to orient the mining operation in a way to optimize the extraction costs of large blocks of ornamental granite from a quarry in Capão Bonito region of São Paulo State, southern Brazil. Five GPR profiles using antennae of 25, 50, and 100 MHz were made, as well as six velocity soundings. The work was done in three distinct locations in the quarry: on the land surface above the quarry, along a road crossing the quarry, and in front or below the active quarry face. The results led to the definition of planes of structural discontinuity extending to 25 m depth, including inclined fractures and low-angle unloading joints; as well as the localization of massive blocks surrounded by weathered material. The inclined fractures and unloading joints appear as strong reflectors (high energy), and constitute excellent basal planes for the cutting and removal of standard-sized blocks. The location of these planes is important in the exploration process, as designing the quarrying to take advantage of these structural breaks can minimize the use of explosives and greatly facilitate the extraction of commercial-sized blocks. In addition, it was possible to delineate the regions of the quarry, where high-quality homogeneous granite was located, by the absence of strong internal radar reflectors. Knowledge of the spatial distribution of the joints and structural discontinuities, and mapping the localities of high-quality granite were fundamental for the mining engineer. This information served as the basis, and as a guide for planning the advance of the quarry front to minimize the extraction costs, resulting in significant economies for the company.

Palabora represents an interstratified vermiculite-biotite containing less than 50% vermiculite. The sodium-exchanged form was prepared by immersion in saturated brine at ambient conditions. The sodium content reached the equilibrium level within the first month of exposure. However, XRD spectra continued to evolve and sharpen over a six month period. The thermal-activated exfoliation was studied using thermo-mechanical analysis. The expansion of the neat "vermiculite" commenced at temperatures above 420 C. In some applications a lower exfoliation temperature is desirable, i.e. in the range 200 to 350°C. This study revealed that simple sodium exchange is effective towards this goal as it lowered the onset temperature by about 120 C. The linear expansion reached a maximum of about eight-fold at temperatures around 700 C and decreased again at higher temperatures.