Crystallization of nordstrandite in ethylene glycol water solutions: electron microscopic studies

The present work shows the growth of nordstrandile microcrystals observed by transmission and scanning electron microscopy. Nordstrandite was synthesised from non-crystalline aluminium hydroxide reacted in 20% ethylene glycol/water solution, at room temperature. This material was characterized by TEM, SEM, SAED, XRD and EDS/TEM, during six month and revealed the formation and growth of nordstrandite. Fibrillar pseudoboehmite is the only aluminium hydroxide which could be identified during the first two weeks. The nuclei grow, from complete dissolution/recrystallization of pseudoboehmite fibrils, into platy rectangular microscrystals of nordstrandite. Some tabular microcrystals recrystallise, forming after six months only the mufti-point nordstrandite stars. This electron-optical study suggest that the star shape results from the overlapping of rectangular plates, and pseudoboehmite fibrils act as the precursor of nordstrandite crystallisation in ethylene glycol/water solution.

Micro Far-Infrared Reflectivity of CaNb(2)O(6) Single Crystal Fibers Grown by the Laser-Heated Pedestal Growth Technique

CaNb(2)O(6) single crystal fibers were grown by the laser-heated pedestal growth technique, directly from the starting reagents. Optically transparent fibers were obtained in the form of rods with elliptical cross-section, free from cracks, impurities, and secondary phases, with an average diameter of 0.4 mm and about 20 mm of length. The fibers grew within the orthorhombic Pbcn columbite structure, with the growth axis nearly parallel to the crystallographic a-direction. The parameters b and c were parallel to the shorter and larger ellipsis axes. A special setup using a microscope was developed to obtain the far-infrared reflectivity spectra of these micrometer-sized fibers, allowing the identification and assignment of 34 of the 38 polar phonons foreseen for the material. From these phonons, the intrinsic dielectric constant ( = 18.2) and quality factor ( of 185 THz) could be estimated, showing the potential of the material for applications in microwave circuitry. These results, along with previous polarized Raman data (Cryst. Growth Des. 2010, 10, 1569), allow us to present a comprehensive set of optical phonon modes and to discuss the potential use of designed CaNb(2)O(6) microcrystals in compact optical devices.

Triple Structural Transition below Room Temperature in the Antifilarial Drug Diethylcarbamazine Citrate

A very unusual triple structural transition pattern below room temperature was observed for the antifilarial drug diethylcarbamazine citrate. Besides the first thermal, crystallographic, and vibrational investigations of this first-line drug used in clinical treatment for lymphatic filariasis, a noteworthy behavior with three structural transformations as a function of temperature was demonstrated by differential scanning calorimetry, Raman spectroscopy, and single-crystal X-ray diffractometry. Our X-ray data on single crystals allow for a complete featuring and understanding of all transitions, since the four structures associated with the three solid-solid phase transformations were accurately determined. Two of three structural transitions show an order-disorder mechanism and temperature hysteresis with exothermic peaks at 224 K (T(1)`) and 213 K (T(2)`) upon cooling and endothermic ones at 248 K (T(1)) and 226 K (T(2)) upon heating. The other transition occurs at 108 K (T(3)) and it is temperature-rate sensitive. Molecular displacements onto the (010) plane and conformational changes of the diethylcarbamazine backbone as a consequence of the C-H center dot center dot center dot N hydrogen bonding formation/cleavage between drug molecules explain the mechanism of the transitions at T(1)`/T(2). However, such changes are observed only on alternate columns of the drug intercalated by citrate chains, which leads to a doubling of the lattice period along the a axis of the 235 K structure with respect to the 150 and 293 K structures. At T(2)`/T(1), these structural alterations occur in all columns of the drug. At T(3), there is a rotation on the axis of the N-C bond between the carbamoyl moiety and an ethyl group of one crystallographically independent diethylcarbamazine molecule besides molecular shifts and other conformational alterations. The impact of this study is based on the fascinating finding in which the versatile capability of structural adaptation dependent on the thermal history was observed for a relatively simple organic salt, diethylcarbamazine citrate.

Mechanochemical synthesis of niobium pentoxide nanoparticles

Acicular α-FeOOH particles are formed through aging of ferric oxyhydroxide colloidal solution formed by the neutralization of FeCl₃ aqueous solution by NaOH. The effect of foreign ion addition to the colloidal solution on the formation and morphology of α-FeOOH particles has been investigated. The magnetic properties of Fe₃O₄ particles made from the obtained particles have also been investigated. The rate constant of the formation of α-FeOOH remarkably decreased, but the crystallite size of α-FeOOH particles increased with increasing the quantity of phosphate ion added even with small amounts. These results have been explained as follows: the phosphate ions are selectively adsorbed on the (a) plane of α-FeOOH, cover the (a) plane, and block the crystal growth of the (a) plane of the α-FeOOH. The quantities of the phosphate ion adsorbed on the b and c planes are relatively small. The complex ion of Fe(OH)₄^- is preferentially deposited on both (b) and (c) planes, and the crystal growth of (b) and (c) planes is greatly accelerated. The relationship between the morphology of the formed α-FeOOH particles and the quantity of phosphate ion added has been investigated. The asterisk type particles: α-FeOOH particles heterogeneously junctioned to α-Fe₂O₃ particles, were formed when a small amount of phosphate was added to the mother liquid. The α-FeOOH crystal epitaxially grew on the junction interface with the α-Fe₂O₃ crystal. In the case of the aging at the temperature as high as 80°C, the cross type junctioned particles were stably formed at pH below 12.0. The Fe₃O₄ particles with screw-like unique three-dimensional morphology were produced from the heterogeneously junctioned particles.

Nonisothermal Crystallization Behavior of Poly(m-xylene adipamide)/Montmorillonite Nanocomposites

This article reports the nonisothermal crystallization behavior of MXD6 and its clay nanocomposite system (MXD6/MMT) using differential scanning calorimetry (DSC). The DSC experimental data were analyzed by theoretical modeling of the crystallization kinetics using the Avrami, Ozawa, Jeziorny, and the combined Avrami―Ozawa semiempirical models. It has been determined that these models adequately described the crystallization behavior of the MXD6 nanocomposite at cooling rates below 20 °C/min, but there was a deviation from linear dependence at higher cooling rates. This was attributed to changes of both the free energy and the cooling crystallization function K(T) over the entire crystallization process, as well as possible relaxation effects leading to structural rearrangements. In addition, the activation energy determined using the differential isoconversional method of Friedman was also found to vary, indicating changes in both the free energy and crystallization mechanism. Despite the lack of a reliable theoretical model, the heterogeneous nucleating activity of the MMT nanoparticles was demonstrated and quantified using Dobreva's method (Φ = 0.71), and the crystallization rate for the nanocomposite system was found to be greater than pure MXD6 by up to 79% at 40 °C/min.

New insight into non-isothermal crystallization of PVA-graphene composites

The melt crystallization of poly(vinyl alcohol) (PVA) and PVA composites has been a controversial subject due to inconclusive evidence and different opinions for its decomposition during crystallization. Using graphene as a model, the melt crystallization of PVA and PVA-graphene composites occurring during single-cycle and multiple-cycle non-isothermal annealing processes was systematically analyzed using different characterization techniques. The results obtained using single-cycle non-isothermal annealing indicated that the entire crystallization process took place through two main stages. The graphene in the PVA matrix regulates the nucleation and crystal growth manner of the PVA, yet resulting in retardation of the entire crystallization. The FTIR and Raman spectroscopic results particularly demonstrated that the annealing process not only improved the crystallinity but also led to clear decomposition in PVA and PVA-graphene composites, such as the elimination of hydroxyl groups and the production of C=C double bonds. The newly produced C=C double bonds were found to be responsible for the retardation of PVA macromolecule crystallization and the breaking of hydrogen bonds among the hydroxyl groups in the PVA chains. In addition, the morphological observation and multi-cycle non-isothermal crystallization further confirmed the existence of decomposition based on the surface damage as well as decreased crystallization enthalpy and crystallization peak temperature. Therefore, the non-isothermal crystallizations of the pure PVA and the PVA-graphene composites were in fact the combination of non-isothermal crystallization and non-isothermal degradation processes.

Crystalline Structures and α → β and γ polymorphs transformation induced by nanoclay in PVDF-based nanocomposite

Poly(vinylidene fluoride) (PVDF) nanocomposites were prepared by melt-mixing. The dispersion of clay platelets and rheology of nanocomposites were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and rheometric mechanical spectrometer (RMS). The transformation of α to β and γ phase in PVDF was induced by the addition of nanoclay and subsequently the isothermal crystallization kinetics of neat PVDF and its nanocomposite have been investigated. The interaction between clay nanofillers and PVDF macromolecular chains induced the change of conformation from trans-gauche to all-trans crystal structure in PVDF segment. The isothermal crystallization of PVDF/clay nanocomposites was carried out by Differential Scanning Calorimetry (DSC) technique. The influence of clay platelets on nucleation crystallization rate and Avrami exponent were studied. PVDF/clay nanocomposite showed higher crystallization rate indicating that nanoclay has acted as an effective nucleation agent. This nucleation effect of nanoclay increased the Avrami exponent and decreased the degree of crystallinity. © 2014 World Scientific Publishing Company.

Understanding the Crystallization Mechanism of a Wollastonite Base Glass Using Isoconversional, IKP Methods and Master Plots

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Avrami exponent of crystallization in tellurite glasses

Nucleation process and crystal growth for three samples of the (20-x)Li(2)O-80TeO(2)-xWO(3) glass system were studied using X-ray diffraction and differential scanning calorimetry techniques. X-ray diffraction data confirmed the amorphous characteristic of the as-quenched samples and indicated the growth of crystalline phases formed due to the thermal treatment for annealed samples. These results reveal the presence of three distinct gamma-TeO(2), alpha-TeO(2) and alpha-Li(2)Te(2)O(5) crystalline phases in the TL sample, and two distinct alpha-TeO(2) and gamma-TeO(2) crystalline phases in the TLW5 and TLW10 samples. The activation energy and the Avrami exponent were determined from DSC measurements. The activation energy values X-ray diffraction data of the TLW10 glass sample suggest that gamma-TeO(2) phase occur before the alpha-TeO(2). The results obtained for the Avrami exponent point to that the nucleation process is volumetric and that the crystal growth is two or three-dimensional.

Crystallization of nordstrandite in ethylene glycol water solutions: electron microscopic studies

The present work shows the growth of nordstrandile microcrystals observed by transmission and scanning electron microscopy. Nordstrandite was synthesised from non-crystalline aluminium hydroxide reacted in 20% ethylene glycol/water solution, at room temperature. This material was characterized by TEM, SEM, SAED, XRD and EDS/TEM, during six month and revealed the formation and growth of nordstrandite. Fibrillar pseudoboehmite is the only aluminium hydroxide which could be identified during the first two weeks. The nuclei grow, from complete dissolution/recrystallization of pseudoboehmite fibrils, into platy rectangular microscrystals of nordstrandite. Some tabular microcrystals recrystallise, forming after six months only the mufti-point nordstrandite stars. This electron-optical study suggest that the star shape results from the overlapping of rectangular plates, and pseudoboehmite fibrils act as the precursor of nordstrandite crystallisation in ethylene glycol/water solution.

Crystallization of ZrF4-LaF3-AlF3 glasses

0.7125ZrF4-0.2375(1 - xLaF3 • xLnF3)-0.05AIF3 with x = 0.01, 0.02 and 0.03 for Ln = Er and x = 0.03 for Ln = Pr, Nd glasses were studied by differential thermal analysis (DTA), X-ray diffraction and optical spectroscopy. Avrami parameters (Ec and n) were obtained from DTA curves. With La3+ substitution a decrease in the stability against crystallization was observed. This decrease follows the order Er3+ > Nd3+ ≈ Pr3+ for 3% molar substitution. n values suggest an interface controlled growth mechanism with grain edge nucleation abler saturation. Two crystalline polymorphs of the LaZr3F15 phase were identified. With the substitution of 3 mol% of Pr3+, Nd3+ or Er3+ for La3+ only the crystallization of the rhombohedral α-LnZr3F15 phase was observed. An increase in Ω6 Judd's intensity parameter occurs with crystallization and also an increase in the 1.04 μm peak emission cross-section for Nd3+ 4I3/2 state suggesting the potential application of these glass ceramics in optical amplification devices. © 1997 Elsevier Science B.V.

Particle growth during calcination of polycation oxides synthesized by the polymeric precursors method

The particle-growth kinetics of sodium niobate and zirconium titanate powders that were processed by the polymeric precursors method were studied. The growth kinetics that were studied for the particle, in the final stage of crystallization, showed that the growth process occurs in two different stages. For temperatures <800°C, the particle-growth mechanism is associated with surface diffusion, with an activation energy in the range of 40-80 KJ/mol. For temprratures >800°C, particle growth is controlled by densification of the nanometric particle cluster and by a neck-size-controlled particle-growth mechanism. The results suggest that this behavior was typical of the synthesis method, because two different polycation oxides presented the same behavior.

Immunocytochemical study of Ki-67 as a prognostic marker in canine mammary neoplasia

Background: Canine mammary tumors are challenging for clinicians and pathologists because of complex histologic classification, low specificity of cytologic diagnosis, and unpredictable biological behavior. In histologic specimens, expression of tumor proliferation marker Ki-67, a nuclear nonhistone protein, has been shown to have prognostic value for canine mammary tumors and to correlate with malignancy and low survival rates. Objective: The objective of this study was to measure the proliferation index of canine mammary tumors by immunochemical detection of Ki-67 in cytologic specimens and to determine its relationship to clinical and pathologic variables and patient outcome. Methods: Spontaneous mammary tumors from 31 female dogs were surgically excised. Imprint specimens for cytologic evaluation were wet-fixed in ethanol; histologic specimens were prepared routinely. Immunostaining was performed with the PH 177 monoclonal antibody against Ki-67; proliferation index was graded from negative to +++. Dogs were followed for 18 months. Multivariate logistic regression analysis was used to determine correlations between immunocytochemical results, tumor and clinical variables, and patient outcome. Results: Ki-67 proliferation indices in cytologic specimens were significantly lower for nonmalignant tumors than for malignant tumors. High index values of Ki-67 were positively correlated with metastasis, death from neoplasia, low disease-free survival rates, and low overall survival rate. With the exception of 4 specimens for which cellularity was insufficient, positive expression of Ki-67 in cytologic specimens correlated with that of histologic specimens. Conclusions: The prognostic value of the Ki-67 index in canine mammary tumors by using wet-fixed cytology imprint specimens was similar to that observed previously for histologic specimens. Immunocytochemical detection of Ki-67 could improve the accuracy and value of cytology by providing safe and rapid information about malignancy and patient outcome. © 2004 American Society for Veterinary Clinical Pathology.

Upland rice growth and mineral nutrition as affected by cultivars and sulfur availability

A better understanding of the differential growth of upland rice (Oryza sativa L.) cultivars with increasing soil S availability could help improve rice yield under upland conditions. The objective of this study was to evaluate root and shoot growth and nutrition of upland traditional and modern rice cultivars as affected by S availability. The experimental design was completely randomized in a 3 (rates of S) × 3 (cultivars) factorial with four replications. Low availability of S in the soil reduces root and shoot development and the efficiency of N, P, and S uptake, as well as the concentration and content of these nutrients in rice cultivars. At 0 mg dm-3 of S, rice cultivars prioritize root growth over shoots, and the traditional cultivar does so with greater intensity. Our results suggested that more development of traditional cultivars under low S availability facilitates its adaptation in soils under this condition. On the other hand, the intermediate and modern cultivars are more responsive to S fertilization. Moreover, S fertilization allows significant increases in upland rice growth and must be considered in cropping systems aiming for high yields. © Soil Science Society of America.

Electro-oxidation of ethanol on Pt/C, Rh/C, and Pt/Rh/C-based electrocatalysts investigated by on-line DEMS

The ethanol electro-oxidation reaction was studied on carbon-supported Pt, Rh, and on Pt overlayers deposited on Rh nanoparticles. The synthesized electrocatalysts were characterized by TEM and XRD. The reaction products were monitored by on-line DEMS experiments. Potentiodynamic curves showed higher overall reaction rate for Pt/C when compared to that for Rh/C. However, on-line DEMS measurements revealed higher average current efficiencies for complete ethanol electro-oxidation to CO2 on Rh/C. The average current efficiencies for CO2 formation increased with temperature and with the decrease in the ethanol concentration. The total amount of CO2, on the other hand, was slightly affected by the temperature and ethanol concentration. Additionally, the CO2 signal was observed only in the positive-going scan, none being observed in the negative-going scan, evidencing that the C-C bond breaking occurs only at lower potentials. Thus, the formation of CO2 mainly resulted from oxidative removal of adsorbed CO and CHx,ad species generated at the lower potentials, instead of the electrochemical oxidation of bulk ethanol molecules. The acetaldehyde mass signal, however, was greatly favored after increasing the ethanol concentration from 0.01 to 0.1 mol L-1, on both electrocatalysts, indicating that it is the major reaction product. For the Pt/Rh/C-based electrocatalysts, the Faradaic current and the conversion efficiency for CO2 formation was increased by adjusting the amount of Pt on the surface of the Rh/C nanoparticles. The higher conversion efficiency for CO2 formation on the Pt1Rh/C material was ascribed to its faster and more extensive ethanol deprotonation on the Pt-Rh sites, producing adsorbed intermediates in which the C-C bond cleavage is facilitated. (C) 2012 Elsevier B.V. All rights reserved.