A detailed description of the devitrification mechanism of d-mannitol

2020 ◽  
Vol 22 (9) ◽  
pp. 5011-5017 ◽  
Author(s):  
Yannick Guinet ◽  
Laurent Paccou ◽  
Alain Hédoux
Keyword(s):  
Amorphous State ◽  
Surface Crystallization ◽  
Bulk Crystallization ◽  
Devitrification Mechanism

The transformation of undercooled d-mannitol into “phase X” previously interpreted as a second amorphous state is actually corresponding to a surface crystallization accompanied by a very slow bulk crystallization into α form.

Decoupled bulk and surface crystallization in Pd85Si15 glassy metallic alloys: Description of isothermal crystallization by a local value of the Avrami exponent

1988 ◽  
Vol 3 (1) ◽  
pp. 59-66 ◽  
Author(s):  
A. Calka ◽  
A. P. Radliński
Keyword(s):  
Amorphous Alloys ◽  
Transition Process ◽  
Avrami Exponent ◽  
Surface Crystallization ◽  
Scanning Calorimetry ◽  
Avrami Model ◽  
X Ray ◽  
Bulk Crystallization ◽  
Phase Transition Process ◽  
Local Value

Isothermal devitrification of Pd85Si15 amorphous alloys has been analyzed using differential scanning calorimetry (DSC) and x-ray diffractometry. Both as-quenched and aged amorphous ribbons were investigated. Crystallization of aged samples starts from the surface and proceeds several micrometers into the bulk. The product of this process is a layer of strongly textured palladium (111) followed by a mixture of Pd2Si, Masumoto MSI phase, and untextured palladium. Next, the crystallization occurs via a different (bulk) mechanism, resulting in a mixture of Masumoto MSII phase and untextured palladium. The bulk mechanism is the only one observed in as-quenched samples. The surface and bulk crystallization mechanisms are spatially decoupled and, therefore, the corresponding DSC data can be analyzed separately. This has been done according to the Kolmogorov–Johnson–Mehl–Avrami model and also using the recently developed concept of local value of Avrami exponent n. For both the surface and bulk crystallization the phase transition process cannot be characterized by a single value of n. Observed variation of n with the crystallized fraction x is explained by a considerable variation of the nucleation rate that takes place during devitrification.

DSC Kinetic Studies on Glass Ceramic System Crystallizing Indialite (Mg2Al4Si5O18)

2006 ◽  
Vol 45 ◽  
pp. 25-29
Author(s):  
Giovanni Baldi ◽  
Valentina Dami ◽  
V. Faso
Keyword(s):  
Mechanical Characteristics ◽  
Kinetic Studies ◽  
Surface Crystallization ◽  
Initial Surface ◽  
Scanning Calorimetry ◽  
Isothermal Method ◽  
Bulk Crystallization ◽  
Dimensional Growth ◽  
Avrami Parameter ◽  
Different Grain Size

A formulation belonging to the CaO-MgO-SiO2-Al2O3 system was characterized in order to found a monophase system based on indialite (Mg2Al4Si5O18), known for its good mechanical characteristics. The classical kinetic studies performed in the muffle kiln show an initial surface crystallization followed from immediate bulk crystallization. The kinetic results obtained via differential scanning calorimetry (DSC) were treated with isothermal method, Kissinger, Ozawa and Matusita and Sakka approaches and compared. These results partially explain the macroscopic behavior, because the studies performed on sample of different grain size show a typical trend for a surface crystallization, while the value of Avrami parameter calculated from the kinetics is 2.3, demonstrating a bi-dimensional crystallization. The value of crystallization energy EC calculated with the isothermal method is 517.8 kJmol-1 and the comparison with nonisothermal studies suggests bulk crystallization to occur with an increasing number of nuclei and a two-dimensional growth of crystals.

Surface Analysis Of The Nanocrystalline Fe-Based Alloys By Conversion Electron Mossbauer Spectroscopy

1999 ◽  
Vol 577 ◽  
Author(s):  
A. Grabias ◽  
M. Kopcewicz ◽  
B. Idzikowski
Keyword(s):  
Mössbauer Spectroscopy ◽  
Surface Analysis ◽  
Conversion Electron ◽  
Annealing Temperature ◽  
Mossbauer Spectroscopy ◽  
Surface Crystallization ◽  
Bulk Crystallization ◽  
Temperature Range ◽  
Mößbauer Spectroscopy ◽  
Transmission Mössbauer Spectroscopy

ABSTRACTA combined conversion electron and γ-transmission Mössbauer spectroscopy is applied to investigate the differences in the surface and bulk crystallization of the amorphous Fe-M-B-Cu (M: Zr, Ti, Nb, Ta) alloys. It is shown that the surface crystallization occurs at an annealing temperature lower than in the bulk. The nanocrystalline bcc Fe phase is significantly more abundant at the surface than in the bulk in the entire annealing temperature range.

scholarly journals Entropy-Driven Heterogeneous Crystallization of Hard-Sphere Chains under Unidimensional Confinement

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1352
Author(s):  
Pablo Miguel Ramos ◽  
Miguel Herranz ◽  
Katerina Foteinopoulou ◽  
Nikos Ch. Karayiannis ◽  
Manuel Laso
Keyword(s):  
Phase Transition ◽  
Volume Fraction ◽  
Hard Spheres ◽  
Local Symmetry ◽  
Crystal Nucleation ◽  
Surface Crystallization ◽  
Face Centered Cubic ◽  
Bulk Crystallization ◽  
Wide Range ◽  
Heterogeneous Crystallization

We investigate, through Monte Carlo simulations, the heterogeneous crystallization of linear chains of tangent hard spheres under confinement in one dimension. Confinement is realized through flat, impenetrable, and parallel walls. A wide range of systems is studied with respect to their average chain lengths (N = 12 to 100) and packing densities (ϕ = 0.50 to 0.61). The local structure is quantified through the Characteristic Crystallographic Element (CCE) norm descriptor. Here, we split the phenomenon into the bulk crystallization, far from the walls, and the projected surface crystallization in layers adjacent to the confining surfaces. Once a critical volume fraction is met, the chains show a phase transition, starting from regions near the hard walls. The established crystal morphologies consist of alternating hexagonal close-packed or face-centered cubic layers with a stacking direction perpendicular to the confining walls. Crystal layer perfection is observed with an increasing concentration. As in the case of the unconstrained phase transition of athermal polymers at high densities, crystal nucleation and growth compete with the formation of sites of a fivefold local symmetry. While surface crystallites show perfection with a predominantly triangular character, the morphologies of square crystals or of a mixed type are also formed. The simulation results show that the rate of perfection of the surface crystallization is not significantly faster than that of the bulk crystallization.

Role of boundaries in the crystallization of amorphous films

1988 ◽  
Vol 46 ◽  
pp. 626-627
Author(s):  
D. A. Smith
Keyword(s):  
Low Temperature ◽  
Amorphous State ◽  
Nucleation And Growth ◽  
Amorphous Films ◽  
Island Nucleation ◽  
Surface Steps ◽  
Transmission Electron ◽  
Component Systems ◽  
Temperature Deposition

The nucleation and growth processes which lead to the formation of a thin film are particularly amenable to investigation by transmission electron microscopy either in situ or subsequent to deposition. In situ studies have enabled the observation of island nucleation and growth, together with addition of atoms to surface steps. This paper is concerned with post-deposition crystallization of amorphous alloys. It will be argued that the processes occurring during low temperature deposition of one component systems are related but the evidence is mainly indirect. Amorphous films result when the deposition conditions such as low temperature or the presence of impurities (intentional or unintentional) preclude the atomic mobility necessary for crystallization. Representative examples of this behavior are CVD silicon grown below about 670°C, metalloids, such as antimony deposited at room temperature, binary alloys or compounds such as Cu-Ag or Cr O2, respectively. Elemental metals are not stable in the amorphous state.

Structures and crystallization of vacuum-deposited amorphous Se and Sb films

1990 ◽  
Vol 48 (4) ◽  
pp. 140-141
Author(s):  
Makoto Shiojiri ◽  
Toshiyuki Isshiki ◽  
Tetsuya Fudaba ◽  
Yoshihiro Hirota
Keyword(s):  
Monte Carlo ◽  
Electron Microscope ◽  
Monte Carlo Method ◽  
Computer Program ◽  
Radial Distribution ◽  
Film Formation ◽  
Amorphous State ◽  
Two Dimensional ◽  
Amorphous Films ◽  
Binding Condition

In hexagonal Se crystal each atom is covalently bound to two others to form an endless spiral chain, and in Sb crystal each atom to three others to form an extended puckered sheet. Such chains and sheets may be regarded as one- and two- dimensional molecules, respectively. In this paper we investigate the structures in amorphous state of these elements and the crystallization.HRTEM and ED images of vacuum-deposited amorphous Se and Sb films were taken with a JEM-200CX electron microscope (Cs=1.2 mm). The structure models of amorphous films were constructed on a computer by Monte Carlo method. Generated atoms were subsequently deposited on a space of 2 nm×2 nm as they fulfiled the binding condition, to form a film 5 nm thick (Fig. 1a-1c). An improvement on a previous computer program has been made as to realize the actual film formation. Radial distribution fuction (RDF) curves, ED intensities and HRTEM images for the constructed structure models were calculated, and compared with the observed ones.

Microstructure of YBa2Cu3O7-x thin films deposited by dc sputtering

1989 ◽  
Vol 47 ◽  
pp. 172-173
Author(s):  
O. Eibl ◽  
G. Gieres ◽  
H. Behner
Keyword(s):  
Thin Films ◽  
Cross Sections ◽  
Intermediate Layer ◽  
Amorphous State ◽  
Critical Currents ◽  
Dc Sputtering ◽  
State Process ◽  
Diffraction Patterns ◽  
Film Substrate ◽  
Substrate Temperatures

The microstructure of high-Tc YBa2Cu3O7-X thin films deposited by DC-sputtering on SrTiO3 substrates was analysed by TEM. Films were either (i) deposited in the amorphous state at substrate temperatures < 450°C and crystallised by a heat treatment at 900°C (process 1) or (ii) deposited at around 740°C in the crystalline state (process 2). Cross sections were prepared for TEM analyses and are especially useful for studying film substrate interdiffusion (fig.1). Films deposited in process 1 were polycristalline and the grain size was approximately 200 nm. Films were porous and the size of voids was approximately 100 nm. Between the SrTiO3 substrate and the YBa2Cu3Ox film a densly grown crystalline intermediate layer approximately 150 nm thick covered the SrTiO3 substrate. EDX microanalyses showed that the layer consisted of Sr, Ba and Ti, however, did not contain Y and Cu. Crystallites of the layer were carefully tilted in the microscope and diffraction patterns were obtained in five different poles for every crystallite. These patterns were consistent with the phase (Ba1-XSrx)2TiO4. The intermediate layer was most likely formed during the annealing at 900°C. Its formation can be understood as a diffusion of Ba from the amorphously deposited film into the substrate and diffusion of Sr from the substrate into the film. Between the intermediate layer and the surface of the film the film consisted of YBa2Cu3O7-x grains. Films prepared in process 1 had Tc(R=0) close to 90 K, however, critical currents were as low as jc = 104A/cm2 at 77 K.

Formation, Physicochemical Characterization, and Thermodynamic Stability of the Amorphous State of Drugs and Excipients

2016 ◽  
Vol 22 (32) ◽  
pp. 4959-4974 ◽  
Author(s):  
Piera Di Martino ◽  
Federico Magnoni ◽  
Dolores Vargas Peregrina ◽  
Maria Rosa Gigliobianco ◽  
Roberta Censi ◽  
...  
Keyword(s):  
Thermodynamic Stability ◽  
Physicochemical Characterization ◽  
Amorphous State

Enhanced oral bioavailability of Etodolac by liquisolid compact technique: optimisation, in-vitro and in-vivo evaluation

2020 ◽  
Vol 17 ◽  
Author(s):  
Bhumin K. Pathak ◽  
Meenakshi Raghav ◽  
Arti R. Thakkar ◽  
Bhavin A. Vyas ◽  
Pranav J. Shah
Keyword(s):  
Dissolution Rate ◽  
Amorphous State ◽  
Immediate Release ◽  
Angle Of Repose ◽  
Oral Suspension ◽  
Load Factor ◽  
In Vivo Evaluation ◽  
Rate Of Dissolution ◽  
Q 30

Background: Poor dissolution of Etodolac is one of the major challenges in achieving the desired therapeutic effect in oral therapy. Objective: This study aimed to assess the potential of liquisolid compact technique in increasing the rate of dissolution of Etodolac and thus its bioavailability. Methods: Liquisolid compacts were prepared using PEG 400, Avicel PH-200 and Aerosil 200 as non-volatile liquid, carrier and coating material respectively. Optimisation was carried out by applying a 32 full factorial design using Design expert software 11.0.3.0 to examine the effects of independent variables (load factor and carrier: coating ratio) on dependent variables (angle of repose and % cumulative drug release at 30 min [Q 30 min]).Assessment of bioavailability was based on pharmacokinetic study in rabbits and pharmacodynamics evaluation in rats respectively. Results: The formulation M3 was identified as the optimised formulation based on the better flow (lower angle of repose) and a higher rate of dissolution (Q 30 min >95%). The higher dissolution rate could be due to conversion of Etodolac into an amorphous molecularly dispersed state, availability of larger surface area, enhancement of aqueous solubility and enhanced wetting of drug particles. Studies with DSC, XRD, and SEM verified the transformation of Etodolac from crystalline to amorphous state, a key factor responsible for improving the dissolution rate. Pharmacokinetic profile of M3 was prominent, demonstrating higher absorption of Etodolac in comparison of oral suspension and immediate-release conventional tablets in rabbits. Liquisolid formulation exhibited 27% increment in paw thickness as compared to 57% and 46% increments for oral suspension and immediate-release conventional tablets respectively, after 7 hrs in carrageenan-induced paw model in rats. Conclusion: The results indicated liquisolid compact technique to be a promising strategy to enhance the bioavailability of Etodolac.

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