Crystallization Of Different Types Research Articles

Topological Isomorphism of Liquid–Vapor, Fusibility, and Solubility Diagrams: Analogues of Gibbs–Konovalov and Gibbs–Roozeboom Laws for Solubility Diagrams

The comprehensive topological isomorphism of liquid–vapor, fusibility, and solubility diagrams in the proper sets of variables is proven with the aid of van der Waals equations of the shift in phase equilibrium. Analogues of Gibbs–Konovalov and Gibbs–Roozeboom laws are demonstrated in solubility diagrams of ternary and quaternary systems under crystallization of different types of solid solutions. For the demonstration, the quaternary reciprocal system K+,NH4+||Cl−,Br−−H2O and its ternary subsystems with modeling of the liquid phase within the framework of the classical Pitzer formalism are mainly used. An algorithm for calculating solubility equilibria in these systems is given.

Inhomogeneous spatial distribution of residual amplitude modulation in optical phase modulation using a bulk electro-optic crystal.

Residual amplitude modulation is one of the major sources of instability in many precision measurements using frequency modulation techniques. Although a transverse and inhomogeneous distribution of residual amplitude modulation has long been observed, the underlying mechanism is not well understood. We perform measurement and analysis of this spatial inhomogeneity using several electro-optic crystals of different types. Two distinct components are identified in the spatial distributions, and their detailed properties, some of which are previously unnoticed, are mapped out and analyzed, showing that the spatial inhomogeneity can be explained by acousto-optic interaction inside the crystal. Moreover, this spatial inhomogeneity can be further suppressed, improving the 1000-s stability of residual amplitude modulation to 3×10-7 (8×10-8) at modulation frequency of 11 MHz (120 kHz), corresponding to a frequency instability of 1×10-17 (3×10-18), estimated for a cavity-stabilized laser using a Pound-Drever-Hall discrimination slope of 1×10-4 V/Hz.

Spectroscopic features of electron-irradiated diamond crystals from the Mir kimberlite pipe, Yakutia

The behavior of characteristic centers in diamond crystals from the Mir pipe (Yakutia) was investigated upon electron irradiation. A series of diamond crystals of different types was chosen for experiments based on the nitrogen content and aggregation parameters. In electron-irradiated diamonds of the IaAB type, a new characteristic photoluminescence system was found with a zero-phonon line (ZPL) at 615 nm together with phonon replicas of 41 and 90 meV. The phonons' energies pointed to multiphonon interactions with a quasilocal vibration of a vacancy. According to our data, the nitrogen-related defect responsible for this phenomenon contains a vacancy and may be accompanied by some other impurity. Conversely, in an almost nitrogen-free crystal, a specific system with the ZPL at 558 nm was noted. The center in question is known to be vacancy-related and was formed in type IIa crystals from the Mir pipe not only by electron irradiation but also by high-pressure high-temperature annealing when vacancies were released as a result of motion or annihilation of dislocations. Regardless of the nitrogen impurity, specific systems with the ZPL at 454, 491, and 492 nm were registered in the irradiated diamond crystals from the Mir pipe. To examine the generated defects, the irradiated diamond crystals were subjected to low-temperature annealing at ≤600 °C. Although the 454 and 491 nm systems persisted, the annealing of the 492 nm system along with well-known 523.6, 489.0, and 503.4 nm (3H) centers indicated the interstitial-vacancy nature of the defect.

Field Emission Properties of Surface-Modified Silicon Crystals of Different Types of Conduction

A new technology of nanostructuring and modification of the surfaces of silicon crystals of different types of conduction, using self-organized carbon mask coatings and highly anisotropic plasma-chemical etching is proposed. It is shown that the structures obtained make it possible to reduce the field emission excitation thresholds by several times and to increase the maximum field emission current densities by more than an order of magnitude in comparison with traditional technologies. It is established that the relation between the morphological and field emission characteristics of the obtained multi-tip cathode arrays is determined by the type of electrical conduction of the semiconductor and the total dipole moment of its surface. It is shown that the interpretation of the relation between them using the representations of the Fowler and Nordheim theory is not sufficient.

Two processes of α-phase formation in polypropylene at high supercooling

The non-isothermal and isothermal crystallization of different types of commercial polypropylenes (PP) are investigated by fast scanning calorimetry and wide-angle X-ray scattering. Typically, PP shows two different crystallization processes: below 55°C the mesophase formation and at higher temperatures the α-phase formation. Here we report the first observation of an additional crystallization process in some PP-types. It is observed between 45°C and 75°C, and is understood as a consequence of an additional nucleation of α-phase crystals.

Dynamic control on serpentine crystallization in veins: Constraints on hydration processes in oceanic peridotites

Deformation and hydration processes are intimately linked in the oceanic lithosphere, but the feedbacks between them are still poorly understood, especially in ultramafic rocks where serpentinization results in a decrease of rock density that implies a volume increase and/or mass transfer. Serpentinization is accompanied by abundant veining marked by different generations of vein‐filling serpentines with a high variety of morphologies and textures that correspond to different mechanisms and conditions of formation. We use these veins to constrain the role of deformation and mass transfer processes during hydration of oceanic peridotites at slow‐spreading ridges. We have selected a representative set of veins from ocean floor serpentinites of the Mid‐Atlantic Ridge near Kane transform fault (23°N) and characterized these in detail for their microstructures and chemistry by coupling optical and electron microscopy (SEM, TEM) with electron microprobe analyses. Four main veining episodes (V1 to V4) accompany the serpentinization. The first episode, identified as vein generation V1, is interpreted as the tectonically controlled penetration of early seawater‐dominated fluid within peridotites, enhancing thermal cracking and mesh texture initiation at 3–4 km up to 8 km depth and at T <300–350°C. The two following vein stages (V2 and V3) formed in a closed, diffusive system and accommodate volume expansion required to reach almost 50% serpentinization of the protolith. The cracks exploited by these veins were caused by the progressive unroofing at depths of ∼4 to ∼2 km along a detachment fault. Degree and rate of serpentinization seem to be controlled by the capacity of the system to create space and to drive the mass transfer needed for ongoing serpentinization, and this capacity is in turn linked to the exhumation rate and local tectonics. During this period, water consumed by hydration may prevent the establishment of convective hydrothermal cells. The onset of an open hydrothermal system in the shallow lithosphere (<2 km), where brittle fracturing and advective transfer dominate and enable the completion of serpentinization, is marked by the last vein generation (V4). These results show a complete history of alteration, with the crystallization of different types of serpentine recording different tectonic events, chemical conditions, and modes of hydrothermal alteration of the lithosphere.

Optical monitoring of polyesters injection molding

AbstractAn optical fiber sensor similar to the one developed by Thomas and Bur1 was constructed for the monitoring of the crystallization of three polyesters during the injection molding process. The polyesters studied were: polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), and polyethylene terephthalate (PET). With this optical system it was possible to obtain, in real time, some essential parameters of the polyester crystallization kinetics at different processing conditions. Thus, a study of the influence of injection molding variables on the nonisothermal crystallization kinetics of these polyesters was done. The processing variables were: mold wall and injection temperatures, Tw and Ti, respectively; flow rate, Q; and holding pressure, Ph. The experiments were done following a first order central composite design statistical analysis. The morphology of the samples was analyzed by polarized light optical microscopy, PLOM. The signal of the laser beam during the filling and the crystallization stages of the injection molding of these materials was found to be reproducible. The measurements showed that this system was sensitive to variations of the crystallization of different types of polymers under different processing conditions. The system was not able, however, to monitor the crystallization process when the crystallinity degree developed by the sample was very low, as in the PET resin. It was also observed that Tw and Ti were the most influential variables on the crystallization kinetics of PBT and PTT. Due to its slower crystallization kinetics, PTT was found to be more sensitive to changes in these parameters than the PBT. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 563–579, 2006

Diagnostic value of synovial fluid microscopy: a reassessment and rationalisation.

This study is in two parts. In the first synovial fluid from 1892 patients with 14 different arthropathies was examined microscopically. Crystals of different types were identified and the disease distribution of these and various cell types, including several not previously reported in synovial fluid, have been described. These features have been used to derive a series of microscopic diagnostic criteria for each arthropathy. The criteria have been used in the second part of the study to examine synovial fluids from 200 patients without knowledge of any clinical diagnosis. Cytological and clinical diagnoses were compared at the end of the study. Matching diagnoses were made in 71 (35.5%) and a short list of differential diagnoses (based on cytological criteria), which included the clinical diagnosis, was made in a further 43 (21.5%). Of the rest, 63 (31.5%) were correctly described as inflammatory or non-inflammatory and in five (2.5%) no diagnosis could be made. Only in seven cases (3.5%) was an inaccurate (false positive) cytological diagnosis made. The results indicate that synovial fluid microscopy is a potentially more important diagnostic screening test in rheumatological and orthopaedic practice than it would at first appear from published reports.

The Study of the Structure and Properties of Nematic, Smectic and Cholesteric Liquid Crystals by the Molecular Dynamics Method

Abstract Methods of computer experiments which were successfully used to study isotropic liquids are rather promising for the investigation of properties of different liquid crystals. This paper discussed the main results of studying anisotropic systems by methods of computer experiments (the molecular dynamics method and that of Monte Carlo). It gives the description of the molecular dynamic model and the technique of molecular dynamic modeling liquid crystals of different types (nematic, smectic, cholesteric, as well as films of liquid crystals). Special attention is paid to the choice of the pair potential of interaction which takes into account anisotropic of the dispersion attraction and form peculiarities of molecules as well as specific contributions to the interaction energy (which result in the formation of twisted cholesteric structures, smectic layers, etc.) The model of “a molecule in a molecule” is suggested to describe the smectic state.

The Study of the Structure and Properties of Nematic, Smectic and Cholesteric Liquid Crystals by the Molecular Dynamics Method

Abstract Methods of computer experiments which were successfully used to study isotropic liquids are rather promising for the investigation of properties of different liquid crystals. This paper discussed the main results of studying anisotropic systems by methods of computer experiments (the molecular dynamics method and that of Monte Carlo). It gives the description of the molecular dynamic model and the technique of molecular dynamic modeling liquid crystals of different types (nematic, smectic, cholesteric, as well as films of liquid crystals). Special attention is paid to the choice of the pair potential of interaction which takes into account anisotropic of the dispersion attraction and form peculiarities of molecules as well as specific contributions to the interaction energy (which result in the formation of twisted cholesteric structures, smectic layers, etc.) The model of “a molecule in a molecule” is suggested to describe the smectic state.