Interlayer Porosity Research Articles

Process parameter interaction effect on the evolving properties of laser metal deposited titanium for biomedical applications

The laser power interaction effects on the evolving properties of commercially pure titanium during Laser Metal Deposition were analyzed. The optimized processing parameters obtained for this research study were, spot size of 4mm, powder flow rate of 2g/min, gas flow rate of 2l/min, and the scanning speed set at 0.002m/s. A total of seven samples were fabricated by depositing titanium powder onto a Ti–6Al–4V base metal; using an Nd-Yag laser by varying the laser power from 400 to 1600W while keeping all the other parameters constant. The deposited samples were characterised through the evolving microstructure, microhardness, wear and the corrosion behaviour. The microstructural evaluation revealed that the ratio of dilution increased with an increase in the laser power. Furthermore, it was found that as the dilution increased, the wear resistance behaviour of the deposits decreased due to the increased foreign elements (Al and V) from the substrate which inhibited smooth fusion as the molten deposit cooled. Also, the microstructural evaluation showed that finer martensitic microstructures were obtained at lower laser power rating which was associated with inter-layer porosity and due to the low laser-material interaction. However, Widmanstätten structures were observed at higher laser power settings together with the presence of intra-layer porosity which is desirable for osteointegration. For biocompatibility, immersion tests in the Hank's solution were conducted for 14days. The atomic absorption spectroscopy analyses showed that no leaching happened during the immersion process for all the samples hence, confirming the desirable properties expected of biomedical implants. An overall overview on the effects of the laser power which has a significant effect on the evolving properties is essential in order to know how this process parameter can be controlled to attain certain properties of the material for specific and tailored functions.

Distorted Graphene Sheet Structure-Derived Latent Nanoporosity.

High surface area graphene monoliths consist mainly of single graphene layers wider than 10 nm. The interlayer porosity of high temperature treated nanoporous graphene monoliths with tuned intergraphene layer structures is evaluated by hybrid analysis of Ar adsorption at 87 K, N2 adsorption at 77 K, high resolution transmission electron microscopic observation, and small-angle X-ray scattering (SAXS) measurements. SAXS analysis results in surface areas that are 1.4 and 4.5 times larger than those evaluated by Ar adsorption for graphene monoliths nontreated and treated at 2273 K, respectively. A distorted graphene sheet structure model is proposed for the high surface area graphene monoliths on the basis of the hybrid analysis.

A novel composite cathode La0.6Sr0.4CoO3−δ–BaZr0.1Ce0.7Y0.1Yb0.1O3−δ for intermediate temperature solid oxide fuel cells

In this study, BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) was incorporated into La0.6Sr0.4CoO3−δ (LSC) to form a composite cathode LSC–BZCYYb. The X-ray diffraction (XRD) results demonstrate that BZCYYb has an extremely desirable chemical compatibility with LSC below 1200°C. The thermal expansion coefficient (TEC) measurements indicate that incorporating 30wt% BZCYYb enables the TEC of the composite cathode to be significantly reduced to 14.7×10−6K−1 from 20×10−6K−1 (LSC). The influence of the sintering temperature, composition and thickness on the microstructure as well as the electrochemical properties of the LSC–BZCYYb cathode were investigated. A Scanning electron microscope (SEM) testing shows that the LSC–BZCYYb cathode sintered at 950°C has an optimum microstructure with good adhesion to the GDC interlayer and higher porosity. Electrochemical measurements reveal that 0.7LSC–0.3BZCYYb sintered at 950°C with a thickness of approximately 20μm possesses the minimum activation energy (Ea=1.32eV) and polarization resistance (Rp), measuring approximately 0.116Ωcm2 at 650°C. This study confirms that the composite 0.7LSC–0.3BZCYYb cathode has the great potential to be a cathode material for intermediate temperature solid oxide fuel cells.

Effets non ciblés (bystander, abscopal) de la radiothérapie externe : potentielles implications pour le clinicien ?

This study investigates the diffusion process of calcium cations confined in the interlayer space of 5 mm disks of vermiculite swelling clay minerals during the Na-for-Ca exchange process. Diffusion experiments were performed at four NaCl salinities (3 × 10−3, 5 × 10−2, 0.1 and 1 M) of the exchanger solution. A macroscopic analysis of the diffusion process based on the aqueous calcium concentrations released in the solution and on Ca-profiles obtained in the solid was performed using a pore diffusion model that has been classically used in the literature. The results obtained at the macroscopic scale showed that the apparent diffusion coefficients describing both aqueous and profiles data for Ca depend on the diffusion time and salinity of the aqueous reservoir. Such variations suggested that interlayer diffusion was driven by (1) the gradient of the sorbed species in the interlayer, which depends on the diffusion time due to the ion exchange equilibrium; and (2) the discontinuity, due to Donnan equilibrium, existing at the limit between the “internal disk border” and the “external disk border” in contact with the aqueous reservoir. Then, a set of molecular and Brownian dynamics simulations was used to (1) assess such interpretations and (2) quantitatively predict aqueous and profile data obtained at the macroscopic scale. For an aqueous reservoir with high salinity (1 M NaCl), a good agreement was obtained between the macroscopic data and the predictions obtained from Brownian dynamics simulations, confirming the role played by the gradient of the interlayer species that is suggested at the macroscopic scale and which is at the basis of the “surface diffusion models” published in literature. In addition, for aqueous reservoirs with lower salinity (5 × 10−2 M), the results obtained by Brownian dynamics simulations and normalized to the exchange rate measured at infinite time showed that the diffusion properties of the species in the aqueous reservoir cannot be neglected to correctly interpret macroscopic data. This behavior confirms the role played by the ionic flux that exists at the “disk border”, which can limit the global diffusion process in a low salinity reservoir, even if it is well stirred. Moreover, by assuming a tortuosity equal to 1 for monocrystals, the self-diffusion coefficient issued from molecular dynamics simulations is in good agreement with the apparent diffusion coefficient describing macroscopic data when the gradient of sorbed concentrations within the solid is null; this latter condition is obtained in our case at infinite time (20 days) when the initial Ca-saturated disks are fully exchanged with Na cations. Finally, the use of monocrystals allows us to have only interlayer porosity and then to obtain a self-diffusion coefficient for Ca from Molecular Dynamic simulations, which is in good agreement with Ca-surface mobility, which was defined by some authors to predict the “surface diffusion process” at the macroscopic scale.

Cation diffusion in the interlayer space of swelling clay minerals – A combined macroscopic and microscopic study

This study investigates the diffusion process of calcium cations confined in the interlayer space of 5mm disks of vermiculite swelling clay minerals during the Na-for-Ca exchange process. Diffusion experiments were performed at four NaCl salinities (3×10−3, 5×10−2, 0.1 and 1M) of the exchanger solution. A macroscopic analysis of the diffusion process based on the aqueous calcium concentrations released in the solution and on Ca-profiles obtained in the solid was performed using a pore diffusion model that has been classically used in the literature. The results obtained at the macroscopic scale showed that the apparent diffusion coefficients describing both aqueous and profiles data for Ca depend on the diffusion time and salinity of the aqueous reservoir. Such variations suggested that interlayer diffusion was driven by (1) the gradient of the sorbed species in the interlayer, which depends on the diffusion time due to the ion exchange equilibrium; and (2) the discontinuity, due to Donnan equilibrium, existing at the limit between the “internal disk border” and the “external disk border” in contact with the aqueous reservoir. Then, a set of molecular and Brownian dynamics simulations was used to (1) assess such interpretations and (2) quantitatively predict aqueous and profile data obtained at the macroscopic scale. For an aqueous reservoir with high salinity (1 M NaCl), a good agreement was obtained between the macroscopic data and the predictions obtained from Brownian dynamics simulations, confirming the role played by the gradient of the interlayer species that is suggested at the macroscopic scale and which is at the basis of the “surface diffusion models” published in literature. In addition, for aqueous reservoirs with lower salinity (5×10−2M), the results obtained by Brownian dynamics simulations and normalized to the exchange rate measured at infinite time showed that the diffusion properties of the species in the aqueous reservoir cannot be neglected to correctly interpret macroscopic data. This behavior confirms the role played by the ionic flux that exists at the “disk border”, which can limit the global diffusion process in a low salinity reservoir, even if it is well stirred. Moreover, by assuming a tortuosity equal to 1 for monocrystals, the self-diffusion coefficient issued from molecular dynamics simulations is in good agreement with the apparent diffusion coefficient describing macroscopic data when the gradient of sorbed concentrations within the solid is null; this latter condition is obtained in our case at infinite time (20days) when the initial Ca-saturated disks are fully exchanged with Na cations. Finally, the use of monocrystals allows us to have only interlayer porosity and then to obtain a self-diffusion coefficient for Ca from Molecular Dynamic simulations, which is in good agreement with Ca-surface mobility, which was defined by some authors to predict the “surface diffusion process” at the macroscopic scale.

Coarse graining the dynamics of nano-confined solutes: the case of ions in clays

We investigate the possibility of describing by a continuous solvent model the dynamics of solutes confined down to the molecular scale. We derive a generalised Langevin equation (GLE) for the generic motion of a solute in an external potential using the Mori–Zwanzig formalism. We then compute the corresponding memory function from molecular simulations, in the case of cesium ions confined in the interlayer porosity of montmorillonite clays, with a very low water content (only six solvent molecules per ion). Previous attempts to describe the dynamics of cesium in this system by a simple Langevin equation were unsuccessful. The purpose of this work is not to carry out GLE simulations using the memory function from molecular simulations, but rather to analyse the separation of time scales between the confined ions and solvent. We show that such a separation is not achieved and discuss the relative contribution of the ion–surface, ion–solvent and ion–ion interactions to the dynamics. On the picosecond time scale, the ion oscillates in a surface-and-solvent cage, which relaxes on much longer time scales extending to several nanoseconds. The resulting overall dynamics resembles that of glasses or diffusion inside a solid by site-to-site hopping.

Heteroatom-Tolerant Delamination of Layered Zeolite Precursor Materials

The synthesis of the first delaminated borosilicate layered zeolite precursor is described, along with its aluminosilicate analogue, which consists of Al-containing UCB-3 and B-containing UCB-4 from as-made SSZ-70. In addition, the delamination of PREFER (which is the precursor to ferrierite zeolite) under similar conditions yields delaminated layered zeolite precursors consisting of Al-containing UCB-5 and Ti-containing UCB-6. Multinuclear solid-state NMR spectroscopy (^(11)B and ^(27)Al), diffuse-reflectance UV-vis spectroscopy, and heteroatom/Si ratios measured via elemental analysis are consistent with a lack of heteroatom leaching from the framework following delamination. Such mild delamination conditions are achieved by swelling the zeolite precursor in a fluoride/chloride surfactant mixture in DMF solvent, followed by sonication. Powder X-ray diffraction, argon gas physisorption, and chemisorption of bulky base probes strongly suggest delamination, and demonstrate a 1.5-fold increase in the number density of external acid sites and surface area of calcined UCB-3, relative to calcined Al-SSZ-70. The synthesis of microporous pockets in materials UCB-3–UCB-5 suggests the possibility of interlayer porosity in SSZ-70, which is a layered zeolite precursor material whose structure remains currently unknown. The mildness of the delamination method presented here, as well as the lack of need for acidification in the synthesis procedure, enables the delamination of heteroatom-containing zeolites while preserving the framework integrity of labile heteroatoms, which could otherwise be leached under harsher conditions.

Porosity investigation of compacted bentonite using XRD profile modeling

Many countries intend to use compacted bentonite as a barrier in their deep geological repositories for nuclear waste. In order to describe and predict hydraulic conductivity or radionuclide transport through the bentonite barrier, fundamental understanding of the microstructure of compacted bentonite is needed. This study examined the interlayer swelling and overall microstructure of Wyoming Bentonite MX-80 and the corresponding homo-ionic Na + and Ca 2 + forms, using XRD with samples saturated under confined swelling conditions and free swelling conditions. For the samples saturated under confined conditions, the interparticle, or so-called free or external porosity was estimated by comparing the experimental interlayer distances obtained from one-dimensional XRD profile fitting against the maximum interlayer distances possible for the corresponding water content. The results showed that interlayer porosity dominated total porosity, irrespective of water content, and that the interparticle porosity was lower than previously reported in the literature. At compactions relevant for the saturated bentonite barrier (1.4–1.8 g/cm 3), the interparticle porosity was estimated to ≤ 3%.

Microcomputed tomography analysis of intralayer porosity generation in laser direct metal deposition and its causes

Laser direct metal deposition has wide application in the areas of rapid manufacturing, surface coating, and component repair. Defects of interlayer and intralayer porosity are often observed in laser deposited structures and repaired components. Interlayer porosity can be controlled to some extent by adjusting processing parameters, but there is still disagreement as to the source of intralayer porosity and whether process conditions, process parameters, or initial powder materials are the dominant causal factor. In this work, two samples of Ti–6Al–4V powder, prepared using gas-atomization and the plasma rotating electrode (PREP) process, were analyzed using laser diffraction and microcomputed tomography for any initial porosity content. A 1.5 kW diode laser with a coaxial deposition head was then used to deposit a number of thin-wall structures with the different powders at different processing parameters. The deposited structures were characterized using scanning electron microscopy and microcomputed tomography. The results show a clear positive relationship between initial power porosity and intralayer porosity in deposition samples. However, the effect of processing parameters is more complex and analysis reveals that other factors such as strong Marangoni flow, pool instability, and the surrounding atmosphere may have an effect. The main trends found are a reduction in porosity with increased power and high porosity at very low mass flow rates; thus, for high value parts, PREP powder, higher power, and moderate powder mass flow rate, as dictated by other process constraints, appears to be a practical combination.

Modelling approaches for anion-exclusion in compacted Na-bentonite

The accessible porosity for Cl − in bentonite is smaller than the the total porosity due to anion repulsion (exclusion) by the surface of montmorillonite, the main mineral in bentonite. The accessible porosity is a function of the bentonite density and the salt concentration. Anion exclusion data were gathered from the literature, reprocessed in a coherent data set, and modelled using four different models. Very simple models, with or without anion access to the interlayer space, are successful in reproducing trends in anion exclusion in bentonite as a function of ionic strength in the external solution and montmorillonite bulk dry densities in the bentonite. However, a model that considers clay microstructure changes as a function of bentonite compaction and ionic strength is necessary to reproduce observed trends in the data for all experimental conditions within a single model. Our predictive model excludes anions from the interlayer space and relates the interlayer porosity to the ionic strength and the montmorillonite bulk dry density. This presentation offers a good fit for measured anion accessible porosities in bentonites over a wide range of conditions and is also in agreement with microscopic observations.

Comparative study of tracer diffusion of HTO, 22Na + and 36Cl − in compacted kaolinite, illite and montmorillonite

The through-diffusion of HTO, 22Na + and 36Cl − in kaolinite, homo-ionic Na–illite and homo-ionic Na–montmorillonite was measured at a high degree of compaction as a function of the salt concentration in the ‘external solution’, i.e. in the solution in contact with the clay sample. The clays were chosen for this study because of their differences in the number and nature of ion exchange sites leading to different proportions of interlayer-, inter-particle and free pore water. It was found that the diffusive mass transfer of Na + in Na–montmorillonite and Na–illite increased with decreasing external salt concentration, while the opposite trend was observed for the diffusion of Cl −. These trends are more pronounced in the case of Na–montmorillonite than in Na–illite, while almost no salt effect was observed for kaolinite. Similarly no salt effect was observed for the diffusion of HTO through all of the clays tested. These observations are in agreement with a conceptual model where it is assumed that cations diffuse preferentially in the interlayer or diffuse double-layer porosity, while anions are almost completely excluded from these regions. In the case of Na + diffusion, the salt effects can be explained by an influence on the concentration gradient of diffusing cations, while in the case of Cl − the external salt concentration has an effect on the accessible porosity. Effective diffusion coefficients of Cl − fulfil the same relationship to porosity as those of the uncharged HTO, when using accessible porosities for such a comparison. Furthermore it is shown that pore diffusion coefficients for the three tracers are fairly well correlated with the respective diffusion coefficients in bulk water, if the effective diffusion coefficients for Na + are derived from calculated tracer concentration gradients in the interlayer or diffuse double-layer porosities.

The effect of organic cation content on the interlayer spacing, surface area and porosity of methyltributylammonium-smectite

Abstract To examine the effect of the organic cation content on the porous structure of an organosmectite, a sodium-rich smectite (NaS) with a cation exchange capacity (CEC) of 1.08 mol kg−1 was intercalated with methyltributylammonium cations (MTBA+) equivalent to 0.2, 0.4, 0.6, 0.8, and 1.0 times the CEC. The prepared methyltributylammonium smectite (MTBAS) samples were examined by the X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and low temperature nitrogen adsorption–desorption techniques. The basal spacing of the MTBASs, d(0 0 1), obtained from the XRD data, widens from 1.21 to 1.58 nm as the content of MTBA+ increase from 0 to 1.0 time the CEC. The FTIR spectra of the MTBASs display the typical bands related to NaS plus extra bands attributable to the presence of MTBA+. As the extent of intercalation increases the specific surface area (S) increases from 61 to 106 m2 g−1 and specific micro–mesopore volume (V) from 0.11 to 0.25 cm3 g−1. The increase in the S and V values shows that the intercalated MTBA+ cations simply act as pillars to hold the 2:1 layers of the NaS permanently apart, and therefore, the intercalation ends up with the formation an adsorptive-type organosmectite. Otherwise, it would be formed an organic partition nanophase and also a sorptive-type organosmectite.

Anion exclusion effects in compacted bentonites: Towards a better understanding of anion diffusion

Diffusion of 36Cl − in compacted bentonite was studied using through-diffusion, out-diffusion and profile analysis techniques. Both the bulk dry density of the bentonite and the composition of the external solution were varied. Increasing the bulk dry density of the bentonite resulted in a decrease of both the effective diffusion coefficient and the Cl-accessible porosity. Increasing the ionic strength of the external solutions resulted in an increase of both the effective diffusion coefficient and the Cl-accessible porosity. This can be explained by anion exclusion effects (Donnan exclusion). At high ionic strength values (I ⩾ 1 M NaCl) the Cl-accessible porosity approaches the interparticle porosity. This interparticle porosity is the difference between the total and interlayer porosity of the bentonite. The interlayer porosity was found to depend on the degree of compaction. Up to a bulk dry density of 1300 kg m −3 the interlayer is built up of 3 water layers. Between 1300 and 1800 kg m −3 the interlayer water is reduced from 3 to 2 layers of water. Above 1800 kg m −3 evidence for a further decrease to 1 layer of water was found. These findings are in agreement with X-ray data found in the literature showing a decrease of the basal spacing of montmorillonite (the main clay mineral in bentonite) with increasing degree of compaction. The relationship between the effective diffusion coefficient of Cl − and the diffusion-accessible porosity can be described by an empirical relationship analogous to Archie’s law. To predict the effective diffusion coefficient of Cl − in compacted bentonite, the diffusion coefficient of Cl − in water, the bulk dry density and the ionic strength of the pore water have to be known.

Numerical Modelling of Swelling Pressure in Unsaturated Expansive Elasto-Plastic Porous Media

The focus of this work is to provide a new concept for accessing the swelling stress in expansive porous media, especially in highly compacted bentonite. The key to the new approach is the simulation with a chemical swelling model of an infinitesimal volume change followed by a back compaction Process. Free extension is allowed in the first step, to calculate the interlayer porosity change (micro) and the induced volume change potential (macro). The object-oriented FEM simulator GeoSys/RockFlow allows the combination of different processes. The hydro-mechanic/chemical (H2M/C) model takes into consideration two phase flow and deformation, as well as chemical swelling effects. The negative displacements on each boundary after the free extension simulation are taken as Dirichlet boundary conditions of the back compaction problem. The deformation step is simulated in the context of elasto-plasticity using the modified Cam-Clay model. The stresses obtained by back compaction represent the swelling pressure. A 2D example of compacted bentonite is analyzed with the new H2M/C model.

Oxidation of SiC/Porous Al2O3 Laminated Ceramic Composites

The oxidation behavior of SiC/porous Al2O3 interphase laminated composites was studied using oxidation experiments and mathematical modeling of the reaction/porous diffusion kinetics in this system. Oxidation at 800°C produced both closure of the interlayer porosity at the lateral ends of the laminate and a limited penetration of the oxidation product layer front from the laminate edges to its interior. Oxidation at 800°C resulted in a persistent product layer of nearly uniform thickness that is more suited to test the effects of oxidation on laminate properties. The modeling approach, which explicitly considers the porous microstructure of the interphase and its evolution upon oxidation, reproduces these experimental observations successfully. The model was extended to study the effect that the mixing of SiC grains with Al2O3 grains to form a two‐phase porous interphase has on pore closure at the interface and oxide product front penetration into the interior of the laminate. Pore closure was found to be accelerated considerably with increasing SiC content, and was not accompanied by any significant decrease in the distance from the laminate edges upto which an oxidation product layer was formed.

An upscaling method and a numerical analysis of swelling/shrinking processes in a compacted bentonite/sand mixture

AbstractThis paper presents an upscaling concept of swelling/shrinking processes of a compacted bentonite/sand mixture, which also applies to swelling of porous media in general. A constitutive approach for highly compacted bentonite/sand mixture is developed accordingly. The concept is based on the diffuse double layer theory and connects microstructural properties of the bentonite as well as chemical properties of the pore fluid with swelling potential. Main factors influencing the swelling potential of bentonite, i.e. variation of water content, dry density, chemical composition of pore fluid, as well as the microstructures and the amount of swelling minerals are taken into account. According to the proposed model, porosity is divided into interparticle and interlayer porosity. Swelling is the potential of interlayer porosity increase, which reveals itself as volume change in the case of free expansion, or turns to be swelling pressure in the case of constrained swelling. The constitutive equations for swelling/shrinking are implemented in the software GeoSys/RockFlow as a new chemo‐hydro‐mechanical model, which is able to simulate isothermal multiphase flow in bentonite. Details of the mathematical and numerical multiphase flow formulations, as well as the code implementation are described. The proposed model is verified using experimental data of tests on a highly compacted bentonite/sand mixture. Comparison of the 1D modelling results with the experimental data evidences the capability of the proposed model to satisfactorily predict free swelling of the material under investigation. Copyright © 2004 John Wiley & Sons, Ltd.

Modeling the Transverse Thermal Conductivity of 2-D SiCf/SiC Composites Made with Woven Fabric

The hierarchical two-layer (H2L) model describes the effective transverse thermal conductivity (keff) of a two-dimensional (2-D) SiCf /SiC composite plate made from stacked and infiltrated woven fabric layers in terms of constituent properties and microstructural and architectural variables. The H2L model includes the effects of fiber-matrix interfacial conductance, high-fiber packing fractions within individual tows, and the nonuniform nature of 2-D fabric/matrix layers that usually include a significant amount of interlayer porosity. Previously, H2L model keff predictions were compared to measured values for two versions of 2-D Hi-NicalonTM/pyrocarbon (PyC)/isothermal chemical vapor infiltration (ICVI)-SiC composite, one with a “thin” (0.11-μm) and the other with a “thick” (1.04-μm) PyC fiber coating, and for a 2-D TyrannoTM SA/thin PyC/forced flow chemical vapor infiltration SiC composite. In this study, H2L model keff predictions were compared to measured values for a 2-D SiCf /SiC composite made using the ICVI process with Hi-Nicalon type S fabric and a thin PyC fiber coating. The values of keff determined for the latter composite were significantly greater than the keff values determined for the composites made with either the Hi-Nicalon or the Tyranno SA fabrics. Differences in keff values were expected for the different fiber types, but major differences also were due to observed microstructural and architectural variations between the composite systems, and as predicted by the H2L model.

Host–guest Complementarity and Crystal Packing of Intercalated Layered Structures

Intercalated layered structures are analyzed in order to estimate the rules governing their crystal packing. An overview is given on structural types of layered intercalates based on various types of host structures and guest species. The factors describing the host–guest complementarity in intercalated layered structures like: the character of active sites, the host–guest and guest–guest interactions, the size of guests and topology of layers are investigated and their effect on crystal packing is illustrated on examples. Special attention will be paid to the conditions for the regular ordering of guests in the interlayer space, as the requirement of structure ordering is of great importance in design of intercalates for special applications, where one has to control the interlayer porosity or electronic properties of guest molecules etc. A method of structure analysis based on a combination of molecular modeling and experiments has been worked out for intercalates. Molecular modeling (force field calculations) in conjunction with experiments (diffraction methods and vibration spectroscopy) enables us to analyze the disordered intercalated structures, where the conventional diffraction analysis fails.

Texture Development in Modified Lead Titanate Thin Films Obtained by Chemical Solution Deposition on Silicon‐Based Substrates

An advanced method of X‐ray diffractometry analysis, the quantitative texture analysis, is used in this work to study the preferential orientations of ferroelectric lanthanum‐modified lead titanate thin films, to establish the factors affecting their development. The new, more reliable, texture data obtained allows us to discuss previous models of texture development in chemical‐solution‐deposited films. The results show that a fiber type, mixed <100>,<001> preferential orientation, is obtained when high heating rates are used during crystallization. The degree of texture of these films decreases when successive layers are deposited before a simultaneous crystallization of the ensemble is conducted. This undesirable effect is avoided through layer‐by‐layer crystallization, because of the preferential nucleation of <100>,<001> crystals at the interface between layers. The use of a titanium layer on the platinized silicon‐based substrate leads to the development of an additional fiber <111> texture component. In this case, the layer‐by‐layer crystallization process cannot avoid the loss of the degree of orientation (texture index) with the increase of film thickness. This is mainly caused by the appearance of interlayer porosity, which disrupts the growth of <111>‐oriented grains into upper layers.

Combination of modeling and experiment in structure analysis of intercalated layer silicates.

A strategy for the structure analysis of intercalated layer silicates based on a combination of modeling (i.e. force field calculations) and experiment is presented. Modeling in conjunction with experiment enables us to analyze the disordered intercalated structures of layer silicates where conventional diffraction analysis fails. Experiment plays a key role in the modeling strategy and in corroboration of the modeling results. X-ray powder diffraction and IR spectroscopy were found to be very useful complementary experiments to molecular modeling. Molecular mechanics and molecular dynamics simulations were carried out in the Cerius2 and Materials Studio modeling environments. An overview is given of the structures of layer silicates, especially smectites intercalated with various inorganic and organic guest species. Special attention is paid to the ordering of guests in the interlayer space, as it is important for the practical applications of these intercalates, where the interlayer porosity, photofunctions, etc. must be controlled. Figure Structure of montmorillonite intercalated with octadecylamine via ion-dipole interaction with the maximum concentration of guests corresponding to the monolayer arrangement of guests with basal spacing 33.3 A. The Na cations remaining in the interlayer are visualized as pink balls