Incipient Crystallization Research Articles

Incipient crystallization of calcium carbonate on desalination membranes: dead-end filtration with agitation

The development of reliable criteria for determining the onset of scaling on desalination membranes is of high practical value. A novel approach to systematically investigate incipient membrane crystallization and scale-particle evolution was recently reported by this laboratory, involving modeling-relevant phenomena during membrane desalination and experiments, in well-controlled pressure cells operating in dead-end mode with no agitation. However, parallel studies have shown that flow conditions equivalent to those prevailing in real desalination membrane modules are obtained in pressure cells with agitation. Therefore, this work aims to employ the aforementioned approach to the more realistic case of membrane CaCO3 scaling in dead-end desalination with agitation. Detailed data regarding incipient CaCO3 scaling of desalination membranes were obtained, by analyzing scanning electron microscopy (SEM) images, for small bulk supersaturation ratios S = 1 to 4 and short filtration times (~30–90 min). Mean shear stresses at the membrane surface were similar to those prevailing in desalination modules. The data show that concentration polarization due to salt rejection strongly affects scale-particle growth rate, insignificantly influencing particle-number surface density. There is no evidence of a significant induction period in the nucleation and growth of scale-particles on the membrane surface. The initial CaCO3 deposit flux, in mg/(m2 min), exhibits a strong dependence on membrane surface supersaturation. Experimental data on the supersaturation-dependent scale evolution appear to significantly differ from predictions based on classical concepts of heterogeneous nucleation and growth, thus indicating that non-conventional nucleation is the dominant mechanism of the membrane-scale development.

Crystallization Stability of Sb<sub>2</sub>O<sub>3 </sub>-Doped Vanadium Phosphate Sealing Glass Analyzed by XPS

The mechanism of the increased crystallization stability (the difference between glass incipient crystallization temperature and transition temperature) of Sb2O3 —doped vanadium phosphate sealing glass investigated by X-ray photoelectron spectroscopy (XPS) is reported in the present study. Experimental results showed that after doping with Sb2O3, the rate of bridging oxygen increased while the rate of no-bridging oxygen decreased, and the ratio of V4+/Vtotal also increased, too. This two changes led to the break of V=0 bond which is essential for the formation of V2O5 crystalline phase, thus inhibited the formation of that crystalline phase and improved glass crystallization stability.

University Promotion – Key Factor Of The Use Of Marketing Strategies, In The Context Of Improving The Romanian Higher Education. Case Study

AbstractThis scientific approach was triggered by the interest to analyze the ability of Romanian higher education to use the marketing strategies, such as the use of promotion, (as instrument of the marketing mix), as strategies of boosting their competitive advantage. The research final conclusions highlight, however, an incipient crystallization of this ability, standing by the initial statement, according to which the Romanian higher education institutions have not yet reached the maturity level in using the marketing instruments, which calls for, in a fairly foreseeable future, the need to adjust their using manner.

Chemical controls on incipient Mg-silicate crystallization at 25°C: Implications for early and late diagenesis

AbstractMg-silicate minerals (e.g., stevensite, kerolite, talc, sepiolite) play an important role in the construction of facies models in lacustrine and peri-marine environments because they are sensitive to changes in solution chemistry. However, the response of Mg-silicate mineralogy to changing aqueous chemistry is only broadly understood because the mechanisms underpinning the coprecipitation of Mg2+and SiO2(aq) from surface water, and subsequent Mg-silicate crystallization, are unclear. Here we describe the results of experiments designed to systematically examine the effects of pH, Mg/Si and salinity of the parent solution on the nature of initially precipitated products. Structural interrogation of the products with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and thermal analysis (TGA/DTA) allow comparison of synthetic products with naturally occurring crystalline counterparts. In general, Mg2+and SiO2(aq) co-precipitation and nucleation of Mg-silicate layer structures first involves the rapid formation of 2:1 layers with trioctahedral occupancy and a mean coherent X-ray scattering domain between 1–2 unit cells with respect to thecaxis. Well defined but diffusehkreflections indicate two-dimensional growth, turbostratic stacking and highly variable interlayer hydration. Diffuse reflectance FTIR shows numerous structural similarities with stevensite, kerolite and sepiolite. However, TGA/DTA analysis indicates the presence of variable kerolite/stevensite interstratification not readily detectable through XRD analyses, as well as a significant degree of surface and interlayer hydration (e.g. 15–20 wt.%).We observe a number of clear trends in the products with respect to solution chemistry. For example, at low salinity, kerolite-like products dominate at high Mg/Si and high pH, whereas sepiolite-like products are formed at lower pH and lower Mg/Si. At high salinity and high Mg/Si, stevensite-like products are favoured at high pH and kerolite-like products dominate at lower pH, whereas a decrease in Mg/Si of the solution leads to sepiolite-like products at low pH and only stevensite-like products at high pH. Higher pH leads to an increase in octahedral vacancies which favour stevensite-like products; this may result from a higher rate of two-dimensional tetrahedral sheet expansion relative to the octahedral sheet, as inferred from studies of silica oligomerization and brucite growth kinetics.Together, our results indicate that the neoformation of Mg-rich silicates from solution may often begin with the rapid nucleation of hydrated 2:1 layers. Subsequent dehydration leads to progressive layer stacking order and could occur in response to wetting/drying cycles, prolonged exposure to high salinity solutions, or burial and heating. The surface and interlayer water associated with these products is undoubtedly an important source of diagenetic water in Mg-silicate-bearing successions, and the chemistry of this water upon later diagenesis should be a focus of future investigation.

The influence of the heat treatment temperature in the magnetic characteristics of a SiO2–Li2O–Fe2O3 glass prepared by sol-gel

The glass with the molar composition 88SiO2–2Li2O–10Fe2O3 (mole %) was prepared by the sol-gel route and after heat-treated at temperatures between 250 and 1000°C under oxidizing conditions. Crystalline phases (LiFe5O8, SiO2, Fe2O3 and LiFe(Si2O6)) were observed by X-ray powder diffraction in the glasses treated at temperatures above 800°C. Scanning electron micrographs reveal the presence of particles in the samples heat-treated up to 800°C, which are essentially amorphous or with an incipient crystallization. The increase of the heat-treatment temperature promotes the coarsening of particles.The magnetic characteristics of the prepared glasses and glass ceramics were performed using a vibrating sample magnetometer in function of the magnetic field amplitude (−10T≤B≤10T) and in function of temperature (5K–300K). The samples heat-treated at 900 and 1000°C present a ferrimagnetic behavior accompanied by the appearance of peaks corresponding to the lithium ferrite phase (LiFe5O8). A curious aspect is the saturation magnetization of the sample heat-treated at 800°C is the highest of all samples, indicating the highest amount of LiFe5O8 crystals. The Mossbauer results are in accordance with the magnetization and magnetic susceptibility measurements.

In situ observations of bubble growth in basaltic, andesitic and rhyodacitic melts

Bubble growth strongly affects the physical properties of degassing magmas and their eruption dynamics. Natural samples and products from quench experiments provide only a snapshot of the final state of volatile exsolution, leaving the processes occurring during its early stages unconstrained. In order to fill this gap, we present in situ high-temperature observations of bubble growth in magmas of different compositions (basalt, andesite and rhyodacite) at 1,100 to 1,240 °C and 0.1 MPa (1 bar), obtained using a moissanite cell apparatus. The data show that nucleation occurs at very small degrees of supersaturaturation (<60 MPa in basalt and andesite, 200 MPa in rhyodacite), probably due to heterogeneous nucleation of bubbles occurring simultaneously with the nucleation of crystals. During the early stages of exsolution, melt degassing is the driving mechanism of bubble growth, with coalescence becoming increasingly important as exsolution progresses. Ostwald ripening occurs only at the end of the process and only in basaltic melt. The average bubble growth rate (G R) ranges from 3.4 × 10−6 to 5.2 × 10−7 mm/s, with basalt and andesite showing faster growth rates than rhyodacite. The bubble number density (N B) at nucleation ranges from 7.9 × 104 mm−3 to 1.8 × 105 mm−3 and decreases exponentially over time. While the rhyodacite melt maintained a well-sorted bubble size distribution (BSD) through time, the BSDs of basalt and andesite are much more inhomogeneous. Our experimental observations demonstrate that bubble growth cannot be ascribed to a single mechanism but is rather a combination of many processes, which depend on the physical properties of the melt. Depending on coalescence rate, annealing of bubbles following a single nucleation event can produce complex bubble size distributions. In natural samples, such BSDs may be misinterpreted as resulting from several separate nucleation events. Incipient crystallization upon cooling of a magma may allow bubble nucleation already at very small degrees of supersaturation and could therefore be an important trigger for volatile release and explosive eruptions.

Crystallites of magnetic charges in artificial spin ice

Artificial spin ice is a class of lithographically created arrays of interacting ferromagnetic nanometre-scale islands. It was introduced to investigate many-body phenomena related to frustration and disorder in a material that could be tailored to precise specifications and imaged directly. Because of the large magnetic energy scales of these nanoscale islands, it has so far been impossible to thermally anneal artificial spin ice into desired thermodynamic ensembles; nearly all studies of artificial spin ice have either treated it as a granular material activated by alternating fields or focused on the as-grown state of the arrays. This limitation has prevented experimental investigation of novel phases that can emerge from the nominal ground states of frustrated lattices. For example, artificial kagome spin ice, in which the islands are arranged on the edges of a hexagonal net, is predicted to support states with monopolar charge order at entropies below that of the previously observed pseudo-ice manifold. Here we demonstrate a method for thermalizing artificial spin ices with square and kagome lattices by heating above the Curie temperature of the constituent material. In this manner, artificial square spin ice achieves unprecedented thermal ordering of the moments. In artificial kagome spin ice, we observe incipient crystallization of the magnetic charges embedded in pseudo-ice, with crystallites of magnetic charges whose size can be controlled by tuning the lattice constant. We find excellent agreement between experimental data and Monte Carlo simulations of emergent charge-charge interactions.

Extensive Development of Precursory Helical Pairs Prior to Formation of Stereocomplex Crystals in Racemic Polylactide Melt Mixture

Melt crystallization of racemic polylactide (equimolar PLLA/PDLA) blend upon slow cooling (1 °C/min from 270 °C) was studied via a combination of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FTIR). Results indicated extensive development of racemic (32/31) helical pairs below 220 °C, followed by emergence of a broad mesomorphic peak in the WAXS profile below 190 °C; the intensity of this mesophase peak started to decrease at 150 °C, with concomitant emergence of WAXS- or DSC-discernible formation of stereocomplex (βc) crystals. Isothermal measurements at 200 vs 170 °C revealed the presence of low vs high populations of helical pairs; βc crystals were observed to develop only at 170 °C but not at 200 °C, indicating the need for adequate population of racemic helical pairs for formation of their mesomorphic clusters in the melt matrix as precursors of βc nuclei. The clear change in the melt structure well before the formation of incipient βc crystals reflects strong driving force under large supercooling toward transformation, but the transformation process is kinetically suppressed: only after extensive development of racemic helices and emergence of mesomorphic clusters in the melt matrix may nucleation occur. These observations suggest that the nucleation process proceeds in elementary units of preformed helical pairs in the melt matrix, with an intermediate stage of clustered helical pairs before incipience of βc crystals.

On modeling incipient crystallization of sparingly soluble salts in frontal membrane filtration

Modeling incipient crystallization (“scaling”) in desalination membrane modules is a very difficult task due to several complications arising from the interplay of physico-chemical solution conditions (leading to supersaturation) with the flow field and related transport processes, including solid phase generation phenomena and membrane surface geometrical changes caused by the developing discrete particles. Although eventually all these aspects must be included in a comprehensive process model, it is fruitful to isolate and tackle them separately, thereby improving our understanding and developing techniques which will facilitate the ensuing synthesis of an integrated modeling framework. The focus in this work is on solid phase generation phenomena accounting for the membrane surface geometrical changes. A mean field model is developed that includes bulk and surface particle nucleation and growth processes. The relative importance of the two types of processes is analyzed. It is shown that, if thick concentration boundary layers exist around surface particles, the mean field theory—although not strictly valid—can be approximately used to estimate the transport coefficients, in conjunction with a unit cell problem for transport processes around a single surface particle. The unit cell problem is formulated and typical results for the flow and concentration field therein are presented as well as the corresponding mass transfer coefficients.

An optical and dielectric spectroscopy study of Er3+ -doped KTaO3

We report the results of a multifaceted study of optical and dielectric properties of erbium-doped (500 ppm) potassium tantalate incipient ferroelectric single crystals. Studies of optical absorption and photoluminescence spectra allowed us to determine the system of energy levels that control the main internal optical transitions in the 4f electronic shell of Er3+ in KTaO3. It was found that at least two types of Er3+ centres, major and minor ones, are present. The major centres are non-cubic, formed by Er3+ substituting for K+ sites; these are responsible for the n-type conductivity of KTaO3:Er crystals. Wideband optical absorption with a maximum at 1.13 eV (λ = 1097 nm) was observed in the near-IR range and was attributed to polaron formation. Low-temperature far-infrared reflectivity studies revealed an increase in the frequency of the lowest transverse optical mode and a decrease in the dielectric permittivity in comparison with undoped KTaO3 crystals. This stiffening means the suppression of the ferroelectric instability in the system.

Synthesis and Characterization of Silicon Oxycarbide Derived Nanocomposites Obtained through Ceramic Processing of TEOS/PDMS Preceramic Materials

Bulk silicon oxycarbide derived ceramic nanocomposites have been prepared by the application of the conventional ceramic processing to preceramic materials. Tetraethylortosilicate/ polydimethylsiloxane preceramic materials obtained by sol-gel process were thermally treated and attrition milled to 4 micrometers. Subsequently, the preceramic powders were pyrolized at 1100 °C to obtain silicon oxycarbide powders that were pressed and sintered at 1550 °C up to 16 hours. Silicon oxycarbide glasses obtained at 1100 °C from pyrolysis of preceramic materials consist of a Si-O-C network and a carbon like graphite phase well dispersed. At annealing temperatures higher than 1100°C silicon oxycarbide glasses undergo a rearrangement which involves a phase separation to silica and silicon carbide and a segregation of carbon like graphite phase. At these temperatures the material can be considered as a glassy matrix nanocomposite. At temperatures higher than 1500 °C the carbothermal reduction occurs with the consumption of both silica and free carbon phase. However, the nanocomposite structure is maintained but with different constituents. The silicon oxycarbide glasses obtained at 1100 °C are amorphous. However, as a result of all involving processes taken place during the ceramic process, the nanocomposites formed at 1550 °C comprise a silica matrix and nanodomains of carbon like graphite and silicon carbide both of them displaying an incipient crystallization. Structure and crystalline size evolution, from preceramic materials to silicon oxycarbide derived nanocomposites, have been determined by FT-IR and Raman spectroscopies, XRD and 29Si-MASNMR.

Incipient crystallization of transition-metal tungstates under microwaves probed by Raman scattering and transmission electron microscopy

Microwave synthesis was used to produce nanosized transition-metal tungstates in environmentally friendly conditions not yet reported by the literature: 110 and 150 °C, for times of 10 and 20 min. X-ray diffraction evidenced incipient crystallized materials, while transmission electron microscopy indicates nanostructured regions of about 2–5 nm inside an amorphous matrix. Raman spectroscopy was used to probe short-range ordering in the achieved samples and also to obtain a reliable set of spectra containing all the Raman-active bands predicted by group-theory calculations. The vibrational spectra showed no extra feature, indicating that the microwave processing was able to produce short-range ordered materials without tetrahedral distortions. These distortions are frequently reported when commercially modified kitchen microwave units are employed. In this work, the syntheses were conducted in a commercial apparatus especially designed for fully controlled temperature–time–pressure conditions.

Incipient crystallization of sparingly soluble salts on membrane surfaces: The case of dead-end filtration with no agitation

This paper aims at contributing to development of reliable criteria for determining the onset of scaling on desalination membranes. A novel approach is proposed to investigate incipient crystallization on membranes through modeling and RO filtration experiments. The evolution of membrane surface concentration of rejected ionic species (e.g. Ca 2+, CO 3 2−) is theoretically determined, and coupled with a detailed kinetic model for nucleation and growth of particles on the membrane. Model results contribute to our understanding of this problem and are in general accord with experimental data on membrane surface crystal density and mean size. Experimental data and model results show that incipient crystallization on RO membrane surfaces, when the bulk supersaturation ratio is maintained near its critical value (S ~ 1), is controlled by fluid permeation, and that the “induction time” may be insignificant under typical RO conditions. This work also suggests that the ability to determine the onset of crystallization on membranes is dependent on the combined sensitivity and adequate spatial resolution of the experimental technique employed, which explains the significant uncertainty associated with the reported in literature “induction period” data of different origin. Directions for future research are discussed.

Transparent and Scratch-Resistant C:ZrOx Coatings on Polymer and Glass by Plasma-Enhanced Chemical Vapor Deposition

Transparent and scratch-resistant zirconium oxide thin films were deposited in radio-frequency plasma-enhanced chemical vapor deposition process on glass and polycarbonate substrates using zirconium-tetra-tert-butoxide, [Zr(OtBu)4], as the precursor. Investigations on film morphology (AFM), thickness (cross-sectional SEM), phase structure (X-ray diffraction), chemical composition (X-ray photoelectron spectroscopy), and optical properties (UV/Vis, ellipsometry) revealed the interplay of process parameters (plasma power, gas composition, deposition time, and precursor flux) on the composition and properties of the coatings. High-quality transparent coatings (>90%) with a tunable refractive index (n=1.7–2.1) and abrasion-resistant properties were deposited on both polymer and glass substrates. Despite low deposition temperatures (<100°C), the coatings showed good adherence to the substrate and extraordinary barrier properties that were further improved by depositing intermediary SiOx-layers. Phase analysis of the predominantly amorphous films showed the incipient crystallization of ZrO2.

Gas hydrates in shallow deposits of the Amsterdam mud volcano, Anaximander Mountains, Northeastern Mediterranean Sea

We investigated gas hydrate in situ inventories as well as the composition and principal transport mechanisms of fluids expelled at the Amsterdam mud volcano (AMV; 2,025 m water depth) in the Eastern Mediterranean Sea. Pressure coring (the only technique preventing hydrates from decomposition during recovery) was used for the quantification of light hydrocarbons in near-surface deposits. The cores (up to 2.5 m in length) were retrieved with an autoclave piston corer, and served for analyses of gas quantities and compositions, and pore-water chemistry. For comparison, gravity cores from sites at the summit and beyond the AMV were analyzed. A prevalence of thermogenic light hydrocarbons was inferred from average C1/C2+ ratios <35 and δ13C-CH4 values of −50.6‰. Gas venting from the seafloor indicated methane oversaturation, and volumetric gas–sediment ratios of up to 17.0 in pressure cores taken from the center demonstrated hydrate presence at the time of sampling. Relative enrichments in ethane, propane, and iso-butane in gas released from pressure cores, and from an intact hydrate piece compared to venting gas suggest incipient crystallization of hydrate structure II (sII). Nonetheless, the co-existence of sI hydrate can not be excluded from our dataset. Hydrates fill up to 16.7% of pore volume within the sediment interval between the base of the sulfate zone and the maximum sampling depth at the summit. The concave-down shapes of pore-water concentration profiles recorded in the center indicate the influence of upward-directed advection of low-salinity fluids/fluidized mud. Furthermore, the SO42− and Ba2+ pore-water profiles in the central part of the AMV demonstrate that sulfate reduction driven by the anaerobic oxidation of methane is complete at depths between 30 cm and 70 cm below seafloor. Our results indicate that methane oversaturation, high hydrostatic pressure, and elevated pore-water activity caused by low salinity promote fixing of considerable proportions of light hydrocarbons in shallow hydrates even at the summit of the AMV, and possibly also of other MVs in the region. Depending on their crystallographic structure, however, hydrates will already decompose and release hydrocarbon masses if sediment temperatures exceed ca. 19.3°C and 21.0°C, respectively. Based on observations from other mud volcanoes, the common occurrence of such temperatures induced by heat flux from below into the immediate subsurface appears likely for the AMV.

Study of the thermal transformations of Co- and Fe-exchanged zeolites A and X by “in situ” XRD under reducing atmosphere

“In situ” high temperature X-ray diffraction under reducing atmosphere is used for the first time to study the thermal stability and transformations of Co- and Fe-exchanged A and X zeolites. TG-DTA and “ex situ” XRD characterization were also carried out. The temperature of incipient crystallization of metallic phase was found to be 700 °C in Fe-zeolites and 800 °C in Co-zeolites. Moreover, ex situ X-ray experiments, after thermal treatment both under inert and reducing atmosphere, revealed the formation of ceramic phases upon the thermal collapse of the zeolitic framework. Metal nanoparticles were obtained by reduction and the size of metal clusters was found to range between 24 and 40 nm.

Shear-influenced partial melting in the Western Tatra metamorphic complex: Geochemistry and geochronology

The geochemical and isotopic characteristics as well as the age relationship between the migmatites and leucogranites, present in the metamorphic basement of the Western Tatra Mts. (Tatric Superunit – Central Western Carpathians), were studied. The suggested process for their formation was the progressive melting of the same metapelitic source under differing P–T–a H2O conditions during shearing. The migmatitic leucosomes started to form by vapour-present partial melting. As the melting developed, with increasing temperature and stress, muscovite dehydration–melting under both vapour-present and vapour-absent conditions was continued, giving rise to the formation of leucogranite melt pockets of different size. Coupled feldspar-governed fractionation and restite removal influenced the chemical and mineralogical zonation in leucogranite bodies, accumulated in the pressure shadows. No fractionation was observed in migmatitic leucosomes. U–Pb TIMS and LA-MC-ICP-MS zircon and monazite ages obtained from anatectic leucosome and leucogranite indicate that the partial melts crystallized at ca. 360–365 Ma. The zircon U–Pb ages reflect the span of time encompassing partial melting, melt separation and crystallization. The effect of the incipient crystallization of the partial melt is recorded by the inner part of the isometric zircons (Th/U < 0.1) which yielded an age of 365.1 ± 2.4 Ma (2 σ). Their growth continued until the metamorphic climax at ca. 750 °C and 8 kbar. Elongate zircons (Th/U > 0.1) yielding an age of 360.5 ± 1.9 Ma (2 σ) crystallized during initial cooling accompanied by melt crystallization. The two zircon populations bracket the time interval during which the analyzed monazite-(Ce) crystallized (ca. 365–360 Ma). The U–Pb age of the leucogranite zircons (359.1 ± 1.2 Ma) supports the thesis that the leucogranites crystallized from melt expelled from the migmatised metapelites.

Petrogenetic characteristics of molten slag from the pyrolysis/melting treatment of MSW

MSW slag materials derived from four pyrolysis melting plants in Japan were studied from the viewpoint of petrology in order to discriminate the glass and mineral phases and to propose a petrogenetic model for the formation process of molten slag. Slag material is composed of two major components: melt and refractory products. The melt products that formed during the melting process comprise silicate glass, and a suite of minerals as major constituents. The silicate glass is essentially composed of low and high silica glass members (typically 30% and 50% of SiO(2), respectively), from which minerals such as spinels, melilite, pseudowollastonite, and metallic inclusions have been precipitated. The refractory products consist mainly of pieces of metals, minerals and lithic fragments that survived through the melting process. Investigations demonstrated that the low silica melts (higher Ca and Al contents) were produced at upper levels of high temperature combustion chamber HTCC, at narrower temperature ranges (1250-1350 degrees C), while the high silica melts formed at broader temperature ranges (1250-1450 degrees C), at the lower levels of HTCC. The recent temperature ranges were estimated by using CaOAl(2)O(3)SiO(2) (CAS) ternary liquidus diagram that are reasonably consistent with those reported for a typical combustor. It was also understood that the samples with a higher CaO/SiO(2) ratio (>0.74-0.75) have undergone improved melting, incipient crystallization of minerals, and extensive homogenization. The combined mineralogical and geochemical examinations provided evidence to accept the concept of stepwise generation of different melt phases within the HTCC. The petrogenesis of the melt products may therefore be described as a two-phase melt system with immiscible characteristics that have been successively generated during the melting process of MSW.

Computational Study on the Antifreeze Glycoproteins as Inhibitors of Clathrate‐Hydrate Formation

The ability of antifreeze glycoproteins to inhibit clathrate-hydrate formation is studied using DFT. A 5(12) cavity, dodecahedral (H(2)O)(20), and the AATA peptide are used to model the inhibitor-clathrate interaction. The presence of AATA in the vicinity of the water cavities not only leads to the formation of complexes, with different peptide/cavity ratios, but also to the deformation of the cavity and to the elongation of several of the hydrogen bonds responsible for keeping the dodecahedral (H(2)O)(20) together. The complexes are formed through hydrogen bonding between the peptides and the water cavities. The glycoproteins are expected to anchor onto the clathrate surface, blocking the access of new water molecules and preventing the incipient crystals from growing. They are also expected to weaken the clathrate structure. Amide IR bands are associated with the complexes' formation. They are significantly red-shifted in the hydrogen-bonded systems compared to isolated AATA. The amide A band is the most sensitive to hydrogen bonding. In addition a distinctive band around 3100 cm(-1) is proposed for the identification of clathrate-peptide hydrogen-bonded complexes.

Structure and dielectric properties of HfO2 films prepared by a sol–gel route

Mono- and multilayer HfO2 sol–gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 °C for 0.5 h (after drying at 100 °C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 °C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 °C the films are totally crystallized. The HfO2 grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO2 layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.