Preferred Orientation Of Crystallites Research Articles

Does the preferred orientation of crystallites in tablets affect the intrinsic dissolution?

The aim of this study was to examine the effect of preferred orientation of crystallites, i.e. texture, on the intrinsic dissolution rate of some active pharmaceutical ingredients. Although it has often been speculated that the intrinsic dissolution of pharmaceutical tablets is affected by texture, no experimental evidence of this effect has been reported. The texture of acetylsalicylic acid, tolbutamide, carbamazepine and entacapone tablets was measured using three different methods both before and after the dissolution measurements. To clarify the effect of texture, texturizing and less-texturizing batches of each material were used. The texturizing batches had big needle or plate-like particles and the less-texturizing batches were prepared by grinding the texturizing powders. The USP rotation disc method was used to measure the intrinsic dissolution rate of the samples. The results indicated that the acetylsalicylic acid, tolbutamide and entacapone tablets texturized strongly in compression and the grinding of the texturizing powders decreased the degree of texture. Also the carbamazepine tablets were slightly texturized. All of the texture measurement methods used were found to give acceptable and consistent results and therefore a special texture goniometer is not required to perform these measurements. The intrinsic dissolution rate of all the tablets compacted from the ground powder was slightly higher than the intrinsic dissolution rate of the more texturized samples. However, these differences were not significant on a large scale. After the dissolution tests the degree of texture of the samples was decreased. The intrinsic dissolution rates of the samples were presumably affected by several different parameters such as texture, solubility, pH, surface energetics and crystal strains. Although only small differences were found between the intrinsic dissolution rates of texturized and less texturized samples the effect of texture on the dissolution behavior of the pharmaceuticals should be considered when performing accurate intrinsic dissolution studies.

FABRICATION AND CHARACTERISTICS OF Pb DOPED BST FERROELECTRIC THIN FILMS FOR UNCOOLED INFRARED FOCAL PLANE ARRAYS

ABSTRACT (Ba1-xSrx)TiO3 (BST) ferroelectric thin films with Pb doped from 1 to 10 mol % were fabricated on Pt/Ti/SiO2/Si substrates by sol-gel technique in order to improve the crystallographic properties and decrease the ferroelectric relaxation and the diffuse phase transition. The microstructures, surface morphology, dielectric properties, and ferroelectric properties of BST thin films were studied. The Pb doping increased the BST grain size, lowered the diffusion phase transition, and narrowed the diffuse phase region of BST thin films. We found that 5 mol% Pb doped (Ba0.8Sr0.2)TiO3 thin films show a strong preferential orientation of crystallites in (110), excellent ferroelectric properties, the better crystallographic properties, and low loss tangent, which is basically suitable for the detecting materials of uncooled infrared focal plane arrays (UFPAs). The 5 mol% Pb doped BST thin films with dielectric constant of 402, loss tangent of 0.011, remanent polarization of 3.8 μCcm−2, a coercive field of 45 kVcm−1 have been fabricated by using sol-gel process.

Mechanical Properties of Hydroxyapatite in Bone at the Interface with Implants

We intend to obtain information about crystal growth and orientation close to the bone-implant interface using a non-destructive method. We will compare the results at the interface of cortical bone for hydroxyapatite Ca 10 (PO 4 ) 6 (OH) 2 (HAp) coated and uncoated titanium alloy. At the interface with an implant, bone tends to change its properties, affecting the acceptance of the implant. The preferred orientation of HAp crystallites at the interface bone-implant has been measured with the neutron 2-axis diffractometer D20 at the Institut Max von Laue-Paul Langevin. The implant has two faces, one uncoated and one coated with plasma-sprayed HAp (80 μm). We probed the samples with a spatial resolution of 0.5 mm starting at the interface in order to inspect the distributions of the HAp'crystallite distribution after implantation.

Scratch Test of TiCN Thin Films with Different Preferred Orientation

The purpose of this study is to examine the effect of crystallite preferred orientation on the mechanical strength of TiCN thin films in highly compressive residual stress. TiCN thin films were deposited by PVD on JIS-SKH55 (AISI M35) steel. The applied substrate bias voltages were set for –50, -80, -100, -120 and –150V. Subsequently, residual stress and crystalline preferred orientation of these specimens were investigated by X-ray diffraction methodology. The crystalline preferred orientation in thin films was evaluated by the ODF calculated from pole figures. On the other hand, dynamic hardness test (DH) and scratch test were executed to evaluate the mechanical strength of thin films. In our study, it was observed that negative bias voltages had an effect on the preferred orientation. The orientation density at –120V was the highest of all specimens. In addition, the value of scratch section area at –120V was the largest of all specimens. As a conclusion, the relation between the scratch area and the negative bias voltages corresponded to the relation between the preferred orientation and the bias voltages.

Solid-state synthesis of boron subnitride, B6N: myth or reality?

Abstract Solid-state synthesis of boron subnitride, B 6 N, as a result of chemical interaction between boron and boron nitride at 7.5 GPa and 1700 °C has been previously reported by Hubert et al. However, a critical analysis of the results has shown that the evidence for the formation of boron subnitride with B 6 O-like structure is inconclusive. We have studied in situ the interaction between boron and BN at the same p – T conditions using X-ray diffraction with synchrotron radiation. At 7.4 GPa and 1700 °C the formation of a new phase has not been observed. At the same time, HP–HT treatment has resulted in strong and unpredictable preferred orientation of boron crystallites. This leads to the rise of some weak boron reflections that might be erroneously attributed to the appearance of a new phase. To cite this article: V.L. Solozhenko et al., C. R. Chimie 9 (2006) .

Simple Shear Deformation of Polypropylene via the Equal Channel Angular Extrusion Process

The morphological changes of isotactic polypropylene (iPP) subjected to varying shear strains have been investigated by the equal channel angular extrusion (ECAE) process. Morphological measurements were made by wide- and small-angle X-ray scattering (WAXS and SAXS) using synchrotron radiation, differential scanning calorimetry (DSC), and reflected optical microscopy (ROM) of permanganic etched specimens. ROM results reveal the initially equiaxed spherulites are elongated with increasing shear. The deformation of the spherulite was found to always lag behind the overall macro deformation. This was attributed to the interlocking nature of the α spherulites. WAXS and SAXS results revealed two preferred crystallite and crystalline c-axis orientations at all shear strains investigated. In both orientations the crystalline c-axis was found to be incorporated along the length of the crystallite. It is proposed that the observed scattering was due to the formation of two microfibrillar domains.

Optical characterization of tristructural isotropic fuel particle cross-sections using generalized ellipsometry

One particularly important measure of quality of tristructural isotropic (TRISO) fuel particles is the degree of preferred orientation of crystallites in the polycrystalline pyrolytic carbon coatings. Excessive crystallographic anisotropy leads to unwanted anisotropic dimensional changes during irradiation that can cause the TRISO coatings to fail. Early optical methods were developed in the 60s and 70s to measure this anisotropy by taking advantage of the large optical anisotropy of graphite. Since that time, there have been significant improvements in both the theoretical understanding and experimental techniques in the understanding of optical anisotropy. Here we discuss a new method, based on the two-modulator generalized ellipsometer (2-MGE) to measure the optical anisotropy. This technique has been demonstrated to measure the optical diattenuation to an accuracy from ±0.001 to ±0.005 and the preferred direction of the crystallites to an accuracy of better than ±2° with a spatial resolution of better than 5μm. Diattenuation ‘pictures’ of the nuclear fuel cross-sections reveal that the inner pyrocarbon layer (IPyC) is far from uniform both in the degree of diattenuation and in the direction of the principal axis. The 2-MGE technique is faster, more accurate, and collects considerably more data than previous optical anisotropy measurements of TRISO fuel particles.

CoFe 2O 4 nanowire arrays prepared by template-electrodeposition method and further oxidization

By electrodeposition method and further oxidization, CoFe 2O 4 nanowire arrays within anodic aluminum oxide (AAO) templates were obtained. The XRD result proved that the phase structure of the nanowires is cubic spinel-type, and they exhibit no preferred crystallite orientation. The TEM images showed that, the CoFe 2 nanowires electrodeposited within the templates are loose, while they transformed into compact CoFe 2O 4 nanowires by thermal annealing in open air. When the pore widening time is 40 min, the coercivity of the nanowire arrays reaches the maximum, 1.9 kOe, with the applied field parallel to the nanowires. With further increasing of the pore widening time, the coercivity decreases. When the applied field is vertical to the nanowires, the coercivity decreases with increasing the pore widening time, monotonously. The squareness ratio of the nanowire arrays with parallel applied field decreases from 0.48 to 0.42, monotonously, whereas the squareness ratio with vertical applied field increases from 0.48 to 0.52.

Microstructural characterization and optical properties of ZnSe thin films

Zinc Selenide (ZnSe) thin films (d=0.09–1.25μm) on glass substrates were prepared by physical vapour deposition under vacuum, using the quasi-closed volume technique. X-ray diffraction (XRD) analysis indicated that the samples are polycrystalline, have a cubic (zinc blende) structure and that the crystallites are preferentially oriented with the (111) planes parallel to the substrates. The microstructure of ZnSe films examined by transmission electron microscopy (TEM), including electron diffraction (ED) and high-resolution electron microscopy (HRTEM), confirms the preferential orientation of crystallites. The HRTEM micrographs show that preferred orientation of crystallites, along (111) planes, increases if, after deposition, the samples are subjected to a heat treatment. The spectral dependences of the transmission and absorption coefficients were studied in the range 300–1400nm. The values of the bandgap energy, Eg, calculated from the absorption spectra, ranged between 2.50eV and 2.80eV.

Laboratory coherent-scatter analysis of intact urinary stones with crystalline composition: a tomographic approach

Knowledge of urinary stone composition and structure provides important insights in guiding treatment and preventing recurrence. No current method can successfully provide information relating structure and composition of intact stones. We are developing a tomographic technique that uses measures of coherently scattered diagnostic x-rays to yield stone composition. Coherent-scatter (CS) properties depend on molecular structure and are, therefore, sensitive to material composition. Powdered, amorphous or polycrystalline materials with no significant orientation produce circularly symmetric CS patterns. However, in materials with preferred crystallite orientation, like urinary stones, bright spots in CS patterns are observed. This compromises a composition analysis based on comparing CS measurements from calculi to a library of CS signatures from powdered chemicals. We show that a computed tomographic reconstruction of CS measurements using filtered backprojection (CSCT) effectively eliminates bright spots and yields CS patterns equivalent to powdered materials. This allows for direct comparison with a powdered chemical reference library to establish composition. Validation is achieved through a tomographic CS analysis of an aluminium (Al) rod phantom. Much like calculi, CS patterns from a solid polycrystalline Al rod exhibit diffraction spots, absent in the ring-like Al powder CS pattern. We show that the reconstructed Al CS cross-section is equivalent to its powdered counterpart and results in clearly defined composition images. The potential of CSCT to identify stone composition is demonstrated through images of intact stones deemed chemically pure by infrared spectroscopy. Computed tomographic reconstruction of CS signals allowed the generation of composition maps, showing the distribution of stone components. These images provide strong evidence that current laboratory techniques risk missing critical stone components due to inadequate sampling. This is of particular importance since follow-up treatments are based on these composition analyses. CS analysis can distinguish common stone components and can provide topographic composition maps of intact stones. Such details offer invaluable clinical information regarding stone formation, treatment and follow-up, and thus support the development of CS analysis as a laboratory stone analysis technique.

On the preferred orientation in Ti1 –xAlxN and Ti1–x–yAlxSiyN thin films

Abstract The influence of the deposition geometry and the chemical composition on the form and degree of the preferred orientation of crystallites was investigated in TiN, Ti1–xAlxN, and Ti1–x–yAlxSiyN thin films deposited by cathodic arc evaporation. The deposition geometry was varied by changing the angle between the cathodes and the substrates. The chemical composition of the thin films was modified by the choice of the cathodic materials. In TiN thin films, the crystallites were preferentially oriented with the {111} direction perpendicular to the sample surface, independent of the deposition geometry. Besides, a well-pronounced in-plane texture was observed. Co-deposition of Ti, Al, and Si in nitrogen atmosphere stimulated inclination of the texture direction towards the sample surface, which can be described as a change of the texture direction related to the sample surface perpendicular direction, and reduced the amount of the in-plane texture in the coatings (the preferred orientation of crystalli...

Sci‐YIS Fri ‐ 10: Tomographic composition analysis of intact urinary calculi by x‐ray coherent scatter

Knowledge of urinary stone composition and structure provides important insights in guiding treatment and preventing recurrence. No present method can successfully provide information relating structure and composition of intact stones. We are developing a tomographic technique that uses measures of coherently scattered diagnostic x rays to yield stone composition and structure. Coherent‐scatter (CS) properties depend on molecular structure and are, therefore, sensitive to material composition. For powdered, amorphous or polycrystalline materials with no significant parallel crystal orientation, CS patterns are azimuthally symmetric. In materials with preferred crystallite orientation, such as urinary stones, bright spots appear in their CS patterns. This may compromise a composition analysis based on comparing CS measurements from urinary calculi to a library of CS signatures from powdered chemicals. We show that a tomographic reconstruction of CS measurements (CSCT) effectively eliminates bright spots and yields CS patterns equivalent to powders. This allows for direct comparison with a powdered chemical reference library and provides more accurate material identification. Validation was achieved using an aluminium rod phantom, which exhibits bright spots much like calculi. CSCT composition analysis was performed on intact stones deemed chemically pure by infrared spectroscopy. Computed tomographic reconstruction of CS signals allowed the generation of composition maps, showing the distribution of components. These images provide strong evidence that current laboratory techniques risk missing critical stone components in their analysis due to inadequate sampling. This supports the development of CS analysis as a stone analysis technique both in the laboratory and possibly in situ.

Investigating the role of anionic surfactant and polymer morphology on the environmental stress cracking (ESC) of high-density polyethylene

The influence of a commercial grade and a pure anionic surfactant (dodecylbenzenesulfonic acid sodium salt, DBS) in aqueous solutions on the environmental stress cracking (ESC) of high-density polyethylene (HDPE) has been investigated. Injection moulded HDPE samples in “dog-bone” shape were exposed to the aqueous solutions of surfactant (0.14 M) at 80 °C under strain ( ɛ = 1.2%) for 5 days. Both the commercial and pure surfactants caused cracks under the experimental conditions. The change in surface chemistry of the HDPE was followed using attenuated total reflectance Fourier transform infrared (ATR-FTIR) and Raman spectroscopy. The thermogravimetric analysis (TGA) did not show any significant differences in thermal stability of the samples studied. Differential scanning calorimetry (DSC) analysis, however, revealed an increase in crystallinity of the exposed samples. Wide Angle X-ray Scattering (WAXS) indicated that the HDPE sample has a boundary of both preferred and random (isotropic) crystallite orientations close and far away from the injection moulding inlet, respectively. The structure of the surfactants in solution was investigated by light scattering (LS). This showed that the commercial grade surfactant forms large aggregates (e.g., 500 nm) both at room temperature and at the exposure temperature of 80 °C, whereas the pure surfactant has a critical micelle temperature (CMT) of around 45 °C. Below the CMT aggregates are formed, and above the CMT the surfactants are unimeric. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) analysis revealed that the commercial surfactant has a wide distribution of hydrocarbon chains from C-10 to C-13, whereas the pure one contains predominantly hydrocarbon dodecyl (chain of C-12).

Electrical and optical properties of r.f. co‐sputtered ZnTe–Cu thin films

ZnTe–Cu thin films with Cu concentration in the range 3–9 at% were prepared using r.f. magnetron co-sputtering. XRD results showed that the films were amorphous below 250 °C, while above that temperature a polycrystalline phase with strong preferential orientation of crystallites appears. For undoped films, the XRD spectrum shows the enhancement of the 100 peak of orthorhombic ZnTe polycrystals while for the ZnTe–Cu films evidence was obtained for the presence of CuxZn1–xTe phase with x near 0.20. The results of electrical measurements supports the view that the majority of Cu is in the CuxZn1–xTe phase. The room temperature transmission and reflectivity were measured in the wavelength range 300 nm ≤ λ ≤ 3000 nm. The energy band gap was determined and found to vary significantly with substrate temperature. This was attributed to the appearance of band tails at the principle bands edges produced by perturbation in the local potential associated with the amorphous modification. For Cu-doped samples, further reduction in Eg is brought about through merging of the Cu acceptor density-of-states with the valence band. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of γ radiation on chromate immobilization by calcined hydrotalcites

AbstractThe ability of hydrotalcites to retain anionic wastes was studied. In particular, Cr(VI)-adsorbed hydrotalcites were heated to immobilize Cr(VI) in the solid sample. When the heating temperature increased up to 500°C, the lamellar structure of hydrotalcite was lost. At high temperatures (1200°C), the solids were recrystallized in the form of a spinel. Lixiviation with 1 N and 5 N NaCl solutions were utilized to simulate the effect of sea water and of concentrated NaCl solutions in salt mines on the immobilization of Cr. Radiation damage on the solid containing the immobilized Cr was studied by γ-irradiating with a 60Co source at 1000 and 6000 kGy. The Cr-containing samples heated at 1200°C, whether irradiated or not, safely immobilized Cr in the hydrotalcite mainly in the form of MgCr2O4 spinel. Irradiation of hydrotalcites revealed two different effects: (1) samples heated up to 1200°C evolved as a solid in which chromium was retained more firmly than in the non-irradiated material, irradiation enhancing the spinel formation; (2) the structure of samples heated at 1200°C developed a preferential crystallite orientation rather than a purely random one or new location of chromium ions, this effect did not affect Cr immobilization in the solid. Chromium lixiviation with 5 N NaCl solution was always less than the corresponding value with 1 N NaCl solution, probably due to the poor mobility of Cl− ions in the highly concentrated NaCl solution.

Characterization of the preferred orientation of δ-mannitol crystallites in tablets

The crystallographic texture, i.e. the preferred orientation of crystallites of δ-mannitol samples, has been experimentally determined by pole figure analysis. The pole figures were measured with an X-ray diffraction texture goniometer. It was found that already the uncompressed δ-mannitol powder sample was slightly texturized so that the (0 2 0) plane was parallel to the upper surface of the sample. The degree of preferred orientation was found to significantly increase when the powder was compressed to a tablet with the minimum (74 MPa) compression pressure. Nevertheless, the direction of the texture remained parallel to the tablet surface. Maximum compression (740 MPa) did not increase the degree of preferred orientation further. The compression time (0 or 60 s) was not found to noticeably affect the strength or direction of the texture. The extent of the texture inside the tablet was determined with a tablet surface grinding experiment. The degree of preferred orientation was found to decrease under the surface while the orientation remained the same. The results were confirmed with orientation distribution function (ODF) calculations.

X-ray diffraction on nanocrystalline Ti 1−xAl xN thin films

Microstructure of titanium aluminium nitride thin films deposited using arc evaporation was investigated for different aluminium contents. From Ti 0.96Al 0.04N to Ti 0.38Al 0.62N, the dominant phase in the coatings was the fcc Ti 1− x Al x N. In this concentration range, the compressive residual stress as well as the hardness of the coatings increased with increasing aluminium contents. Crystallites of Ti 1− x Al x N were strongly textured; the preferred orientation was found to be related to the deposition geometry, not to the composition of the coatings. Concurrently, preferred orientation of crystallites was found to be a very important parameter influencing the crystal anisotropy of lattice deformation and the coherence of neighbouring crystallites. At higher aluminium contents ( x>0.8), the dominant phase was the hexagonal AlN; the hardness of the films decreased.

A Quantitative Basis for Rocking Curve Measurement of Highly Oriented Polycrystalline Thin Films

A quantitative basis for rocking curve measurements of preferentially oriented polycrystalline thin films is presented. The Gaussian function is used for modeling the preferred orientation of crystallites around the plane normal of the specimen surface. A theoretical rocking curve is fitted to the observed curve by the least-squares method, and the degree of preferred orientation, given in volume fraction, can be derived from a refined preferred orientation parameter of the distribution function even when the preferred orientation is very small. Uses of diffractometers equipped with parallel-beam optics and the integrated intensity rather than peak intensity are important for reliable rocking curve measurement.

Influence of pH on structural and electrical properties of sol–gel derived (Ba, Sr)TiO 3 thin films under humid conditions

Polycrystalline (Ba, Sr)TiO 3 (BST) thin films were prepared by the sol–gel technique using titanium isopropoxide and 2-ethyl hexanoate precursors for barium and strontium. The pH value of the precursor sol was adjusted by adding ammonium hydroxide. These films were studied at 7.4 and 9.0 pH and at different molarities ranging from 0.15 to 0.30 M. The films were porous and adsorb water vapour when exposed to a humid environment. The glancing angle X-ray diffraction (GAXRD) pattern clearly shows a preferential orientation of crystallites in (110) direction with increase of pH. Atomic force microscopy (AFM) shows that grain size decreases from 67 to 38 nm with the increase of pH from 7.4 to 9.5, while surface roughness decreases from 0.81 to 0.74 nm. We have found that sensitivity, linearity and response time of the humidity sensor utilizing these films can be improved by tailoring the process parameters such as pH and molarity of the precursor sol. The calculated sensitivity is found to be 46 at 0.30 M, which is higher as compared to the values 40 and 15 at 0.15 M and 0.20 M, respectively, for a given 7.4 pH of sol. As we increase the pH of sol, it was observed that sensitivity of the deposited films increases and reaches to the maximum value (approx. 189) at 9.0 pH.

Structure-function relationship between preferred orientation of crystallites and electrical resistivity in thin polycrystalline ZnO:Al films

Thin polycrystalline films are often observed to develop a preferred orientation or texture that may have significant effects on film properties, especially in the case of anisotropic crystal structures. We report on a x-ray diffraction study of texture evolution in hexagonal ZnO:Al films, which were performed with a highly sensitive large-area detector enabling the investigation of films with thicknesses of some 10 nm only. In a set of magnetron-sputtered ZnO:Al films with thicknesses between 20 and 500 nm the resistivity was found to decrease with increasing thickness. A comprehensive texture analysis was performed within the framework of the series expansion method of the orientation distribution function (ODF). The investigations reveal a clear correlation between preferred grain orientation and electrical properties in ZnO:Al films. A general model is presented which relates the electronic mobility in polycrystalline films with the ODF by assuming the mobility to be composed of an intra-grain and an inter-grain fraction. It turns out that intra-grain anisotropy in ZnO:Al films cannot account for the observed variations in resistivity. Regarding the charge carrier scattering at grain boundaries the model relates the resistivity to the degree of grain alignment and makes use of the texture index $J.$ On the basis of these assumptions it is shown that the resistivity scales with $1/J.$ The model also predicts the attainable minimum resistivity of thin ZnO:Al films with perfectly aligned crystallites which is in accordance with previously published results.