Статті в журналах: "Polymorphic phase transformation kinetic"

1

Spivak L. V., Kirchanov V. S., and Shchepina N. E. "Polymorphic transformations in iodine titanium." Physics of the Solid State 64, no. 11 (2022): 1784. http://dx.doi.org/10.21883/pss.2022.11.54208.400.

Повний текст джерела

Анотація:

Based on the analysis of differential scanning calorimetry data, the possibility of classifying the observed endothermic or exothermic transformations as phase transformations of the first oder is considered. Two approaches have been implemented. The first is based on the correspondence between the temperatures of the maximum conversion rate and the temperatures of the extrema on the second derivative of the differential scanning calorimetry signal with respect to temperature. In the second approach, the phase transformation is considered as a kind of kinetic reaction of a chemical process with the determination of some parameters included in the kinetic equations. In this case, the order parameter of such reaction n is obtained from the analysis of the differential scanning calorimetry signal shape in the region of phase transformation registration temperatures. Using the example of experiments carried out during thermal cycling of titanium iodide samples, it is shown that both the first and second approaches make it possible to fairly adequately attribute the processes that cause calorimetric effects on the dependences of differential scanning calorimetry to first-order phase transitions. In particular, the obtained results of differential scanning calorimetry during heating and cooling of iodide titanium show that polymorphic transformations in it are realized by various mechanisms depending on the rate of thermal cycling and the thermal history of the metal. Keywords: activation energy, titanium, calorimetry, polymorphism, structure, approximation.

Стилі APA, Harvard, Vancouver, ISO та ін.

2

Purba, Elida. "DETERMINATION OF REACTION KINETICS USING ONLINE X-RAY DIFFRACTION." Indonesian Journal of Chemistry 8, no. 3 (June 17, 2010): 337–41. http://dx.doi.org/10.22146/ijc.21588.

Повний текст джерела

Анотація:

X-ray diffraction (XRD) is a powerful technique for the study of polymorphism and polymorphic phase transformations. Monitoring of phase transformation directly has been very limited to-date. The XRD system used in this study was used to determine the rate of transformation of pure glutamic acid a form to b form in a solution mediated phase. On every run starting from the pure a form, the transformation process was monitored continuously at fixed temperature, and separate experiments were performed as a function of temperature. The operating temperature was varied from 36 to 57 °C with 10% w/w solid concentration. Data were taken every 200 seconds until the transformation was completed. This paper is concerned with a study of the transformation of the alpha (a) form of L-glutamic acid (L-GA) to the beta (b) form in order to determine the kinetic reaction. The rate constant (k), activation energy (Ea) and pre-exponential factor (A) were obtained. Sensitivity tests were also carried out to examine minimum detection limit when both a and b present in the mixture. In addition, effect of particle size on XRD patterns was also determined. The results show that XRD gives useful information to observe polymorphism for pharmaceutical industry. Keywords: XRD, polymorphism, glutamic acid, reaction kinetics

Стилі APA, Harvard, Vancouver, ISO та ін.

3

Sadigh, Babak, Luis Zepeda-Ruiz, and Jonathan L. Belof. "Metastable–solid phase diagrams derived from polymorphic solidification kinetics." Proceedings of the National Academy of Sciences 118, no. 9 (February 22, 2021): e2017809118. http://dx.doi.org/10.1073/pnas.2017809118.

Повний текст джерела

Анотація:

Nonequilibrium processes during solidification can lead to kinetic stabilization of metastable crystal phases. A general framework for predicting the solidification conditions that lead to metastable-phase growth is developed and applied to a model face-centered cubic (fcc) metal that undergoes phase transitions to the body-centered cubic (bcc) as well as the hexagonal close-packed phases at high temperatures and pressures. Large-scale molecular dynamics simulations of ultrarapid freezing show that bcc nucleates and grows well outside of the region of its thermodynamic stability. An extensive study of crystal–liquid equilibria confirms that at any given pressure, there is a multitude of metastable solid phases that can coexist with the liquid phase. We define for every crystal phase, a solid cluster in liquid (SCL) basin, which contains all solid clusters of that phase coexisting with the liquid. A rigorous methodology is developed that allows for practical calculations of nucleation rates into arbitrary SCL basins from the undercooled melt. It is demonstrated that at large undercoolings, phase selections made during the nucleation stage can be undone by kinetic instabilities amid the growth stage. On these bases, a solidification–kinetic phase diagram is drawn for the model fcc system that delimits the conditions for macroscopic grains of metastable bcc phase to grow from the melt. We conclude with a study of unconventional interfacial kinetics at special interfaces, which can bring about heterogeneous multiphase crystal growth. A first-order interfacial phase transformation accompanied by a growth-mode transition is examined.

Стилі APA, Harvard, Vancouver, ISO та ін.

4

An, Ji-Hun, Guang Jin Choi, and Woo-Sik Kim. "Polymorphic and kinetic investigation of adefovir dipivoxil during phase transformation." International Journal of Pharmaceutics 422, no. 1-2 (January 2012): 185–93. http://dx.doi.org/10.1016/j.ijpharm.2011.10.049.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

5

Хлебникова, Ю. В., Д. П. Родионов, Л. Ю. Егорова та Т. Р. Суаридзе. "Кристаллографические особенности структуры alpha-фазы гафния и сплавов гафний--титан". Журнал технической физики 89, № 1 (2019): 86. http://dx.doi.org/10.21883/jtf.2019.01.46968.86-18.

Повний текст джерела

Анотація:

AbstractThe structure of a hafnium crystal undergoing β → α (bcc → hcp) polymorphic transformation upon gradual cooling and the structure of Hf_55Ti_45 and Hf_30Ti_70 alloys formed under various kinetic conditions of polymorphic transformation are studied. The structure of the α phase in cast hafnium is shown to consist of lath crystals grouped into packets. The misorientations between separate laths in a packet are less than 1°. The Hf–Ti alloys in the cast state exhibit a mixed structure consisting of α-phase crystals of several morphological types. A structure of packet martensite is observed in the Hf–Ti alloys after quenching. Each packet includes laths of several crystallographic orientations. There is no regular alternation of differently orientated laths in the packet. The same set of α-phase orientations within an initial β-phase grain is observed independently of the cooling rate of the Hf–Ti alloys upon β → α polymorphic transformation. The misorientation of substructural elements within an α-phase crystal in the Hf–Ti alloys is ~5° for the cast state and ~2.2° after quenching.

Стилі APA, Harvard, Vancouver, ISO та ін.

6

Kerschhofer, Ljuba, Catherine Dupas, Ming Liu, Thomas G. Sharp, William B. Durham, and David C. Rubie. "Polymorphic transformations between olivine, wadsleyite and ringwoodite: mechanisms of intracrystalline nucleation and the role of elastic strain." Mineralogical Magazine 62, no. 5 (October 1998): 617–38. http://dx.doi.org/10.1180/002646198548016.

Повний текст джерела

Анотація:

AbstractKinetic models and rate equations for polymorphic reconstructive phase transformations in polycrystalline aggregates are usually based on the assumptions that (a) the product phase nucleates on grain boundaries in the reactant phase and (b) growth rates of the product phase remain constant with time at fixed P-T. Recent observations of experimentally-induced transformations between (Mg,Fe)2SiO4 olivine (α) and its high pressure polymorphs, wadsleyite (β) and ringwoodite (γ), demonstrate that both these assumptions can be invalid, thus complicating the extrapolation of experimental kinetic data. Incoherent grain boundary nucleation appears to have dominated in most previous experimental studies of the α–β–γ transformations because of the use of starting materials with small (<10–20 µm) grain sizes. In contrast, when large (0.6 mm) olivine single crystals are reacted, intracrystalline nucleation of both β and γ becomes the dominant mechanism, particularly when the P-T conditions significantly overstep the equilibrium boundary. At pressures of 18–20 GPa intracrystalline nucleation involves (i) the formation of stacking faults in the olivine, (ii) coherent nucleation of γ-lamellae on these faults and (iii) nucleation of β on γ. In other experiments, intracrystalline nucleation is also observed during the β-γ transformation. In this case coherent nucleation of γ appears to occur at the intersections of dislocations with (010) stacking faults in β, which suggests that the nucleation rate is stress dependent. Reaction rims of β/γ form at the margins of the olivine single crystals by grain boundary nucleation. Measurements of growth distance as a function of time indicate that the growth rate of these rims decreases towards zero as transformation progresses. The growth rate slows because of the decrease in the magnitude of the Gibbs free energy (stored elastic strain energy) that develops as a consequence of the large volume change of transformation. On a longer time scale, growth kinetics may be controlled by viscoelastic relaxation.

Стилі APA, Harvard, Vancouver, ISO та ін.

7

Zeng, Guang, Stuart D. McDonald, Jonathan J. Read, Qinfen Gu, and Kazuhiro Nogita. "Kinetics of the polymorphic phase transformation of Cu6Sn5." Acta Materialia 69 (May 2014): 135–48. http://dx.doi.org/10.1016/j.actamat.2014.01.027.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

8

Спивак, Л. В., В. С. Кирчанов та Н. Е. Щепина. "Полиморфные превращения в йодидном титане". Физика твердого тела 64, № 11 (2022): 1820. http://dx.doi.org/10.21883/ftt.2022.11.53341.400.

Повний текст джерела

Анотація:

Based on the analysis of differential scanning calorimetry data, the possibility of classifying the observed endothermic or exothermic transformations as phase transformations of the first oder is considered. Two approaches have been implemented. The first is based on the correspondence between the temperatures of the maximum conversion rate and the temperatures of the extrema on the second derivative of the differential scanning calorimetry signal with respect to temperature. In the second approach, the phase transformation is considered as a kind of kinetic reaction of a chemical process with the determination of some parameters included in the kinetic equations. In this case, the order parameter of such reaction n is obtained from the analysis of the differential scanning calorimetry signal shape in the region of phase transformation registration temperatures. Using the example of experiments carried out during thermal cycling of titanium iodide samples, it is shown that both the first and second approaches make it possible to fairly adequately attribute the processes that cause calorimetric effects on the dependences of differential scanning calorimetry to first-order phase transitions. In particular, the obtained results of differential scanning calorimetry during heating and cooling of iodide titanium show that polymorphic transformations in it are realized by various mechanisms depending on the rate of thermal cycling and the thermal history of the metal.

Стилі APA, Harvard, Vancouver, ISO та ін.

9

Botoshansky, M., A. Ellern, N. Gasper, J. O. Henck, and F. H. Herbstein. "Structural, Thermodynamic and Kinetic (Hysteresis) Aspects of the Enantiotropic First-Order Phase Transformations of N-Anilinophthalimide and N-(N'-Methylanilino)phthalimide." Acta Crystallographica Section B Structural Science 54, no. 3 (June 1, 1998): 277–90. http://dx.doi.org/10.1107/s0108768197012135.

Повний текст джерела

Анотація:

The crystal structures of the orthorhombic and monoclinic polymorphs of N-anilinophthalimide (m.p. of monoclinic polymorph 457 K) have been determined by X-ray diffraction at 293 K and were found to have only small differences between the molecular conformations in the two phases, but quite different molecular arrangements. There is very weak N—H...O hydrogen bonding in the orthorhombic phase and weak N—H...O hydrogen bonding in the monoclinic phase. The thermal motion in the crystals of both phases has been analyzed and their thermal expansion determined. The enthalpies of solution in a number of solvents have been calculated from the solubility measurements of Chattaway & Lambert [(1915), J. Chem. Soc. 107, 1773–1781], which also give the temperature and enthalpy of the enantiotropic `orthorhombic to monoclinic' phase transformation (Tc = 283 K; ΔH transf = 1.54 kJ mol−1). The phase-transformation endotherm in a DSC (differential scanning calorimetry) trace from the orthorhombic polymorph occurs only at ∼310 K on heating and there is no corresponding exotherm on cooling; the DSC trace gives ΔH transf = 1.62 kJ mol−1 and ΔH fus = 26.9 kJ mol−1. This phase transformation is an example of the common type (occurrence ∼95%) where ΔV transf = (V monoclinic − V orthorhombic) is positive. Analogous (but less complete) results have been obtained for the monoclinic and triclinic polymorphs of N-(N′-methylanilino)phthalimide (m.p. of triclinic polymorph 398 K). There were only minor differences between the molecular conformations in the two phases, but the molecular arrangements were quite different. This `monoclinic to triclinic' phase transformation also has ΔV transf = (V triclinic − V monoclinic) positive. The solubility (and other) measurements of Chattaway & Lambert (1915) gave Tc = 328.43 K and ΔH transf = 4.17 kJ mol−1. A DSC trace for the monoclinic crystals shows a broad endotherm at ∼372–376 K on heating, but there is no corresponding exotherm on cooling; ΔH transf = 3.6 kJ mol−1 and ΔH fus = 21.7 kJ mol−1. These two compounds provide further examples of molecular crystals with a large hysteresis in their first-order enantiotropic solid-state phase transformations, the transformation to the high-temperature phase occurring well above Tc and the low-temperature phase not being recovered on cooling below Tc . Presumably the hysteresis must be ascribed to as-yet unknown features of the nucleation processes.

Стилі APA, Harvard, Vancouver, ISO та ін.

10

An, Ji-Hun, Wonno Youn, Alice Kiyonga, Changjin Lim, Minho Park, Young-Ger Suh, Hyung Ryu, Jae Kim, Chun-Woong Park, and Kiwon Jung. "Kinetics of the Solution-Mediated Polymorphic Transformation of the Novel l-Carnitine Orotate Polymorph, Form-II." Pharmaceutics 10, no. 4 (October 1, 2018): 171. http://dx.doi.org/10.3390/pharmaceutics10040171.

Повний текст джерела

Анотація:

Research studies related to the polymorphs of l-Carnitine orotate (CO), a medication used for the treatment and prevention of liver diseases, are insignificant or almost nonexistent. Accordingly, in the present study, l-Carnitine orotate (CO) was prepared for investigating CO polymorphs. Here, a reactive crystallization was induced by reacting 1g of l-Carn (1 equivalent) and 0.97 g of OA (1 equivalent) in methanol (MeOH); as a result, CO form-I and CO form-II polymorphs were obtained after 1 h and 16 h of stirring, respectively. The characterization of CO polymorphs was carried out utilizing Powder X-ray diffraction (PXRD), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and solid-state Nuclear Magnetic Resonance Spectroscopy (solid-state CP/MAS 13C-NMR). The solution-mediated polymorphic transformation (SMPT) of CO polymorphs was investigated in MeOH at controlled temperature and fixed rotational speed. The results revealed that CO form-I is a metastable polymorph while CO form-II is a stable polymorph. From the same results, it was confirmed that CO form-I was converted to CO form-II during the polymorphic phase transformation process. Moreover, it was assessed that the increase in temperature and supersaturation level significantly promotes the rate of nucleation, as well as the rate of mass transfer of CO form-II. In addition, nucleation and mass transfer equations were employed for the quantitative determination of SMPT experimental results. Lastly, it was suggested that CO form-II was more thermodynamically stable than CO form-I and that both polymorphs belong to the monotropic system.

Стилі APA, Harvard, Vancouver, ISO та ін.

11

Zhou, Yanan, Shuyi Zong, Jie Gao, Chunsong Liu, and Ting Wang. "Solution-Mediated Polymorphic Transformation of L-carnosine from Form II to Form I." Crystals 12, no. 7 (July 21, 2022): 1014. http://dx.doi.org/10.3390/cryst12071014.

Повний текст джерела

Анотація:

In this study, L-carnosine was chosen as the model compound to systematically study solution-mediated polymorphic transformation by online experiment and theoretical simulation. Form II, a new polymorph of L-carnosine, was developed using an antisolvent crystallization method. The properties of form I and form II L-carnosine were characterized by powder X-ray diffraction, polarizing microscope, thermal analysis, and Raman spectroscopy. In order to explore the relative stability, the solubility of L-carnosine form I and form II in a (water + DMAC) binary solvent mixture was determined by a dynamic method. During the solution-mediated polymorphic transformation process of L-carnosine in different solvents, Raman spectroscopy was employed to detect the solid-phase composition of suspension in situ, and the gravimetric method was used to measure the liquid concentration. In addition, the effect of the solvent on the transformation process was evaluated and analyzed. Finally, a mathematical model of dissolution–precipitation was established to simulate the kinetics of the polymorphic transformation process based on the experimental data. Taking the simulation results and the experimental data into consideration, the controlling step of solution-mediated polymorphic transformation was discussed.

Стилі APA, Harvard, Vancouver, ISO та ін.

12

Polat, Sevgi, Tuba Nur Ozalp-Sendur, and Perviz Sayan. "Effects of Tryptophan on the Polymorphic Transformation of Calcium Carbonate: Central Composite Design, Characterization, Kinetics, and Thermodynamics." Acta Chimica Slovenica 68, no. 2 (June 15, 2021): 414–25. http://dx.doi.org/10.17344/acsi.2020.6503.

Повний текст джерела

Анотація:

The objectives of this study were to: (i) determine the effects of tryptophan on the polymorphic phase transformation of CaCO3, (ii) investigate the thermal degradation characteristics of CaCO3 in terms of kinetics and thermodynamics using the Coats–Redfern method, and (iii) assess the influence of the experimental conditions on the vaterite composition of CaCO3 using response surface methodology based on central composite design. First, the CaCO3 crystals were prepared and analyzed using XRD, FTIR, SEM, BET, AFM, and zeta potential analysis. Based on the characterization results, the shape of the CaCO3 crystals changed from smooth cubic calcite crystals to porous irregular spherical-like vaterite crystals with increasing tryptophan concentration. Meanwhile, the kinetic results showed that the thermal degradation of CaCO3 followed the shrinkage geometrical spherical mechanism, R3 and the average activation energy was 224.6 kJ/mol. According to the results of the experimental design, the tryptophan concentration was the most influential variable affecting the relative fraction of vaterite in the produced crystals. It can be concluded that tryptophan is important for better understanding and controlling the polymorph, size, and morphology of CaCO3 crystals.

Стилі APA, Harvard, Vancouver, ISO та ін.

13

POLAT, Sevgi, and Perviz SAYAN. "Kinetic analysis and polymorphic phase transformation of glycine in the presence of lauric acid." Journal of Crystal Growth 481 (January 2018): 71–79. http://dx.doi.org/10.1016/j.jcrysgro.2017.10.037.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

14

Kumar, Sujeet, S. J. Burns, and T. N. Blanton. "Growth kinetics, phase transitions, and cracking in cholesterol gallstones." Journal of Materials Research 10, no. 1 (January 1995): 216–24. http://dx.doi.org/10.1557/jmr.1995.0216.

Повний текст джерела

Анотація:

The growth kinetics of cholesterol gallstones have been studied by growing crystals from melted gallstones. The resulting microstructures are spherulitic which is essentially the same as the structures seen in natural gallstones prior to melting. The cholesterol crystals when observed in hot stage microscopy emerge from a unique nucleation center growing radially in the [001] direction with constant rate. The DSC thermograph of a natural gallstone is initially similar to that of cholesterol monohydrate. Upon melting, cholesterol monohydrate changes to anhydrous cholesterol; both forms are crystalline and exhibit polymorphic transformations. Synthetic stones grown from cholesterol were anhydrous and have a phase change at temperatures close to human body temperature. Optical microscopy established that this phase transformation cracks the spherulitic crystals perpendicular to the fast growth direction. Thermal expansion measurements demonstrate that upon heating, the low density, low temperature phase is transformed to a high density phase. This phase transformation and repeated cracking may prove to be useful in destroying natural gallstones, while suppressing this transformation and its associated cracking might aid in securing other solid cholesterol deposits within the human body.

Стилі APA, Harvard, Vancouver, ISO та ін.

15

Trush, Vasyl, Alexander Luk’yanenko, and Viktor Fedirko. "Study of titanium oxidation kinetics at temperature above polymorphic transformation." Technology audit and production reserves 4, no. 1(60) (July 27, 2021): 37–41. http://dx.doi.org/10.15587/2706-5448.2021.237250.

Повний текст джерела

Анотація:

The object of research is the analytical description of the phenomena in the near-surface layer, which are caused by the interaction of titanium with oxygen at high temperatures. These are temperatures that exceed the polymorphic transformation of the metal. High-temperature oxidation gives titanium products unique performance properties. Of course, such characteristics are determined, first of all, by the state of the near-surface layer. Therefore, an understanding of oxidation processes will make it possible to predict the state of the near-surface layer after heat treatment. However, to date, no unified approach has been created to describe the mechanism and kinetics of high-temperature oxidation of titanium in the near-surface layer. Indeed, most of the existing approaches make it possible to predict the nature of oxidation in the bulk of the metal. Some scientific papers describe the kinetics of oxidation, taking into account only the formation and growth of oxide layers. However, simultaneously with oxide formation, a diffusion zone is formed, which significantly affects the kinetics. Therefore, today one of the most problematic areas of high-temperature titanium oxidation is the description of the processes that take place in the near-surface layer. In this work, to describe the kinetics of high-temperature oxidation of titanium, in addition to the formation and growth of the oxide layer, the formation and growth of the diffusion zone is taken into account. In the diffusion zone, under the influence of structural phase transformations, solid solutions of oxygen are formed in the alpha and beta phases. This approach made it possible to take into account additional factors and thereby more accurately describe the processes of high-temperature oxidation of titanium. As a result of the calculations, the thickness of the oxide layer of the diffusion zone is given depending on the oxygen concentration and the duration of treatment. And also the dependences of the kinetics of displacement of the boundary of the oxide-diffusion layer are given and a system of equations for calculating the ratio of the formed phase components is developed. Thanks to the proposed analytical approach, it will be possible to calculate the sizes of interphase boundaries on the basis of temperature-time parameters and oxygen concentration and thereby form a hardened near-surface layer with certain functional properties

Стилі APA, Harvard, Vancouver, ISO та ін.

16

Fosu, Allen Yushark, Ndue Kanari, Danièle Bartier, Harrison Hodge, James Vaughan, and Alexandre Chagnes. "Physico-Chemical Characteristics of Spodumene Concentrate and Its Thermal Transformations." Materials 14, no. 23 (December 3, 2021): 7423. http://dx.doi.org/10.3390/ma14237423.

Повний текст джерела

Анотація:

Spodumene concentrate from the Pilbara region in Western Australia was characterized by X-ray diffraction (XRD), Scanning Electron Microscope Energy Dispersive Spectroscopy (SEM-EDS) and Mineral Liberation Analysis (MLA) to identify and quantify major minerals in the concentrate. Particle diameters ranged from 10 to 200 microns and the degree of liberation of major minerals was found to be more than 90%. The thermal behavior of spodumene and the concentration of its polymorphs were studied by heat treatments in the range of 900 to 1050 °C. All three polymorphs of the mineral (α, γ and β) were identified. Full transformation of the α-phase was achieved at 975 °C and 1000 °C after 240 and 60 min treatments, respectively. SEM images of thermally treated concentrate revealed fracturing of spodumene grains, producing minor cracks initially which became more prominent with increasing temperature. Material disintegration, melting and agglomeration with gangue minerals were also observed at higher temperatures. The metastable γ-phase achieved a peak concentration of 23% after 120 min at 975 °C. We suggest 1050 °C to be the threshold temperature for the process where even a short residence time causes appreciable transformation, however, 1000 °C may be the ideal temperature for processing the concentrate due to the degree of material disintegration and α-phase transformation observed. The application of a first-order kinetic model yields kinetic parameters which fit the experimental data well. The resultant apparent activation energies of 655 and 731 kJ mol−1 obtained for α- and γ-decay, respectively, confirm the strong temperature dependence for the spodumene polymorph transformations.

Стилі APA, Harvard, Vancouver, ISO та ін.

17

Tumanov, Nickolay A., Elena V. Boldyreva та Hans Ahsbahs. "Structure solution and refinement from powder or single-crystal diffraction data? Pros and cons: An example of the high-pressure β′-polymorph of glycine". Powder Diffraction 23, № 4 (грудень 2008): 307–16. http://dx.doi.org/10.1154/1.2999248.

Повний текст джерела

Анотація:

The structure of a high-pressure polymorph of glycine (the β′-polymorph formed reversibly at 0.8 GPa from the β-polymorph) was determined from high-resolution X-ray powder diffraction data collected in situ in a diamond anvil cell at nine pressure points up to 2.6 GPa. X-ray powder diffraction study gave a structural model of at least the same quality as that obtained from a single-crystal diffraction experiment. The difference between the powder-diffraction and the single-crystal models is related to the orientation of the NH3-tails and the structure of the hydrogen-bonds network. The phase transition between the β- and β′-polymorphs is reversible and preserves a single crystal intact. No transformations were observed between the β-, α-, and β′-polymorphs on compression and decompression, although the α- and β′-polymorphs belong to the same space group (P21/c). The instability of the β- and γ-forms with pressure can be predicted easily when considering the densities of their structures versus pressure. The direction of the transformation (i.e., which of the high-pressure polymorphs is formed) is determined by structural filiation between the parent and the high-pressure phases because of the kinetic control of the transformations.

Стилі APA, Harvard, Vancouver, ISO та ін.

18

Aufrecht, J., A. Leineweber, and E. J. Mittemeijer. "Polytypic transformations of the HfCr2 Laves phase – Part II: Kinetics of the polymorphic C14 → C15 transformation." Intermetallics 19, no. 10 (October 2011): 1442–47. http://dx.doi.org/10.1016/j.intermet.2011.05.010.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

19

Shi, Genpei, Si Li, Peng Shi, Junbo Gong, Mingtao Zhang, and Weiwei Tang. "Distinct pathways of solid-to-solid phase transitions induced by defects: the case of DL-methionine." IUCrJ 8, no. 4 (May 8, 2021): 584–94. http://dx.doi.org/10.1107/s2052252521004401.

Повний текст джерела

Анотація:

Understanding of solid-to-solid phase transition mechanisms in polymorphic systems is of critical importance for rigorous control over polymorph purity in the pharmaceutical industry to achieve the desired bioavailability and efficacy of drugs. Ubiquitous defects in crystals may play an important role in the pathways of phase transitions. However, such effects remain poorly understood. Here, the effects of crystal defects on the solid-to-solid phase transformations between DL-methionine polymorphs α and β are investigated by means of experimental and computational approaches. Thermal analyses of polycrystalline powders show two endothermic peaks in the α-to-β phase transition (and two exothermic peaks for the reverse transition), in contrast with one thermal event observed for single crystals. Variable-temperature 1D and 2D Raman spectra, as well as powder X-ray diffraction patterns, reveal the appearance of two peaks that can attributed to a two-step phase transition, and the extent of the second-step phase transition increases with milling time (or defect density). Quantification of transition kinetics unveils a remarkably higher energy barrier in the second-step phase transition than in the first, proceeding by the cooperative molecular motion pathway. The good linear fitting on the kinetic data by the Jeziorny model suggests that the second-step transition follows the nucleation and growth mechanism. Molecular dynamics simulations were also conducted to understand the role of crystal defects in the solid-state phase transition by tracking the atomic distribution and hydrogen bond lifetime during the transition. It was found that the increasing defect density hinders the propagation of cooperative molecular motion, leading to a combined transition mechanism involving both cooperative motion and nucleation and growth. This study highlights the significant impact of crystal defects on solid-state phase transitions, and the two-step transition mechanism postulated may be universal given the ubiquitous presence of defects in crystalline materials.

Стилі APA, Harvard, Vancouver, ISO та ін.

20

Taran, Yu А., М. К. Zakharov, А. L. Тaran, and R. N. Ivanov. "EXPERIMENTAL DETERMINATION OF THE RATES OF NUCLEATION AND OF GROWTH OF PHASE TRANSFORMATION CENTERS." Fine Chemical Technologies 11, no. 6 (December 28, 2016): 43–54. http://dx.doi.org/10.32362/2410-6593-2016-11-43-54.

Повний текст джерела

Анотація:

The processes of granulation by crystallization of molten droplets in the flow of a cooling agent (prilling) and on the cooled surfaces of the granulators are widely used in the chemical and allied industries. The process of granulation (crystallization) of melts and qualitative indicators of granular products, their marketability is determined by the transfer phenomena in the phases and by the kinetics of crystallization and enantiotropic polymorphic transformations in the crystalline phase. Quantitatively the latter are given in the form of dependences of the rate of nucleation and growth of centers of transformation. The processes kinetics is usually less studied, but it determines the structure of the formed crystal phase and the maximum rate of the process. Therefore, most attention is focused on its study. The description of the scheme, of developed experimental laboratory facilities for the study of the rates of nucleation and growth of crystallization centers in the polycrystalline front of the growing group of crystals, as is the case when crystallization occurs in devices in real conditions (constrained growth of crystals) and single crystals in a thin layer (unrestricted growth of crystals) is given. The transfer of heat in the measuring cell and the sample and possible errors of experimental results were estimated using the natural scale method.

Стилі APA, Harvard, Vancouver, ISO та ін.

21

Zeuch, David H., Stephen T. Montgomery, and Jeffrey D. Keck. "Hydrostatic and triaxial compression experiments on unpoled PZT 95/5–2Nb ceramic: The effects of shear stress on the FR1 → AO polymorphic phase transformation." Journal of Materials Research 7, no. 12 (December 1992): 3314–32. http://dx.doi.org/10.1557/jmr.1992.3314.

Повний текст джерела

Анотація:

We conducted a series of hydrostatic and constant shear stress experiments at room temperature on three different sintering runs of unpoled, niobium-doped lead-zirconate-titanate ceramic (PZT 95/5–2Nb) in order to quantify the influence of shear stress on the displacive (possibly martensitic), first-order, rhombohedral → orthorhombic phase transformation. Inter- and intra-batch variations were detected, but some generalizations can be made. In hydrostatic compression at room temperature, the transformation began at approximately 260 MPa, and was usually incompletely reversed upon return to ambient conditions. Strains associated with the transformation were isotropic, both on the first and subsequent hydrostatic cycles. Results for the constant shear stress tests were very different. First, the confining pressure and mean stress at which the transition begins decreased systematically with increasing shear stress. Second, we observed that the rate of transformation decreased with increasing shear stress and the associated elastic shear strain. This result contrasts with the typical observation that shear stresses increase reaction and transformation kinetics. Third, strain was not isotropic during the transformation: axial strains were greater and lateral strains smaller than for the hydrostatic case, though volumetric strain behavior was comparable for the two types of tests. However, this effect does not appear to be an example of transformational plasticity: no additional unexpected strains accumulated during subsequent cycles through the transition under deviatoric loading. If subsequent hydrostatic cycles were performed on samples previously subjected to shear stress, strain anisotropy was again observed, indicating that the earlier superimposed shear stress produced a permanent mechanical anisotropy in the material. The mechanical anisotropy probably resulted from a crystallographic preferred orientation that developed during the transformation under shear stress. Finally, in a few experiments on specimens from one particular sintering run, volume strain was often completely recovered and sporadic evidence for a shape memory effect was observed.

Стилі APA, Harvard, Vancouver, ISO та ін.

22

Ni, Hai, Hoo-Jeong Lee, and Ainissa G. Ramirez. "Compositional Effects on the Crystallization Kinetics of Nickel Titanium Thin Films." Journal of Materials Research 20, no. 7 (July 1, 2005): 1728–34. http://dx.doi.org/10.1557/jmr.2005.0215.

Повний текст джерела

Анотація:

The crystallization and phase transformations of amorphous NiTi thin films were studied using in situ transmission electron microscopy (TEM). These films were sputter-deposited onto micromachined silicon-nitride membranes and subjected to heating and cooling conditions. The microstructural evolution was monitored and recorded. Kinetic parameters such as the nucleation rate, growth rate, and area-fraction transformed were independently determined by noting the number of grains per frame and their change in size. Using the Johnson–Mehl–Avrami–Kolmogorov analysis, fitted kinetic parameters were determined and found to be consistent with TEM observations. To explore the compositional sensitivity of crystallization, samples near-equiatomic and slightly Ti-rich were studied with these methods. TEM micrographs show that equiatomic films exhibit polymorphic crystallization while samples that are slightly off-stoichiometry showed more complicated behavior.

Стилі APA, Harvard, Vancouver, ISO та ін.

23

Tang, Weiwei, Arthur D. Sima, Junbo Gong, Jingkang Wang, and Tonglei Li. "Kinetic Difference between Concomitant Polymorphism and Solvent-Mediated Phase Transformation: A Case of Tolfenamic Acid." Crystal Growth & Design 20, no. 3 (January 22, 2020): 1779–88. http://dx.doi.org/10.1021/acs.cgd.9b01503.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

24

Tang, C. C., S. P. Thompson, J. E. Parker, A. R. Lennie, F. Azough, and K. Kato. "The ikaite-to-vaterite transformation: new evidence from diffraction and imaging." Journal of Applied Crystallography 42, no. 2 (February 27, 2009): 225–33. http://dx.doi.org/10.1107/s0021889809005810.

Повний текст джерела

Анотація:

Vaterite is one of three polymorphs of calcium carbonate (CaCO3) found in nature, the others being calcite and aragonite. Here the formation of vaterite from decomposition of ikaite (CaCO3·6H2O) was investigated using synchrotron powder diffraction and scanning electron microscopy. The crystallite sizes of vaterite (∼40 nm) were found to be much smaller than those of the precursor ikaite (∼0.5–1.0 µm) as a result of vaterite nucleating as ikaite dehydrates. The rate of decomposition to vaterite increases with temperature, indicating kinetic control of this transformation. It is postulated that the structural arrangement of the hydration sphere around Ca2+in ikaite determines the orientation of Ca2+and CO32−ions such that vaterite nucleates upon dehydration. This implies that the dehydration of a precursor hydrated phase such as ikaite is required for vaterite nucleation.

Стилі APA, Harvard, Vancouver, ISO та ін.

25

Wetzel, Marius Holger, Tina Trixy Rabending, Martin Friák, Monika Všianská, Mojmír Šob, and Andreas Leineweber. "Phase Stability of Iron Nitride Fe4N at High Pressure—Pressure-Dependent Evolution of Phase Equilibria in the Fe–N System." Materials 14, no. 14 (July 15, 2021): 3963. http://dx.doi.org/10.3390/ma14143963.

Повний текст джерела

Анотація:

Although the general instability of the iron nitride γ′-Fe4N with respect to other phases at high pressure is well established, the actual type of phase transitions and equilibrium conditions of their occurrence are, as of yet, poorly investigated. In the present study, samples of γ′-Fe4N and mixtures of α Fe and γ′-Fe4N powders have been heat-treated at temperatures between 250 and 1000 °C and pressures between 2 and 8 GPa in a multi-anvil press, in order to investigate phase equilibria involving the γ′ phase. Samples heat-treated at high-pressure conditions, were quenched, subsequently decompressed, and then analysed ex situ. Microstructure analysis is used to derive implications on the phase transformations during the heat treatments. Further, it is confirmed that the Fe–N phases in the target composition range are quenchable. Thus, phase proportions and chemical composition of the phases, determined from ex situ X-ray diffraction data, allowed conclusions about the phase equilibria at high-pressure conditions. Further, evidence for the low-temperature eutectoid decomposition γ′→α+ε′ is presented for the first time. From the observed equilibria, a P–T projection of the univariant equilibria in the Fe-rich portion of the Fe–N system is derived, which features a quadruple point at 5 GPa and 375 °C, above which γ′-Fe4N is thermodynamically unstable. The experimental work is supplemented by ab initio calculations in order to discuss the relative phase stability and energy landscape in the Fe–N system, from the ground state to conditions accessible in the multi-anvil experiments. It is concluded that γ′-Fe4N, which is unstable with respect to other phases at 0 K (at any pressure), has to be entropically stabilised in order to occur as stable phase in the system. In view of the frequently reported metastable retention of the γ′ phase during room temperature compression experiments, energetic and kinetic aspects of the polymorphic transition γ′⇌ε′ are discussed.

Стилі APA, Harvard, Vancouver, ISO та ін.

26

Grzmil, Barbara, Marta Gleń, Bogumił Kic, and K. Lubkowski. "Study of the anatase to rutile transformation kinetics of the modified TiO2." Polish Journal of Chemical Technology 15, no. 2 (July 1, 2013): 73–80. http://dx.doi.org/10.2478/pjct-2013-0026.

Повний текст джерела

Анотація:

TiO2 attracts much interest because of its many potential applications. The use of titanium dioxide strongly depends on its polymorphic form: brookite, anatase, or rutile. Only rutile and anatase play an important role in industry. Anatase as a metastable form undergoes a non-reversible transformation into rutile. Understanding the kinetics of phase transformation and the processes of crystal growth of a material is essential for controlling its structure and, thus, its specific properties. The main purpose of this paper is to explain the anatase to rutile recrystallization kinetics in the modified TiO2 calcined from industrial hydrated titanium dioxide. The apparent activation energy of anatase to rutile transformation and the average size of titanium dioxide crystallites were determined for the unmodified TiO2 and TiO2 modified with P, K, Al, B, Zn, Zr, Ce, Sn, or Sb introduced in the amount of 0.5 mol% and 1.0 mol% when recalculated for their oxides. The growth of TiO2 crystallites during calcination was strongly inhibited by P, Ce and Zr, and inhibited to a lesser degree by Al, Sn and Sb. B and Zn did not affect the investigated process and K accelerated crystallites growth. The values of apparent activation energy depending on a modifier formed a relationship: Al<Sb<Sn<P<B<Ce<0=Zn=K<Zr. The observed dependencies can be explained by reactions occurring between the modifiers and titanium dioxide.

Стилі APA, Harvard, Vancouver, ISO та ін.

27

Manik, S. K., H. Dutta, and S. K. Pradhan. "Microstructure characterization and phase transformation kinetics of polymorphic transformed ball milled a-TiO2–10 mol% m-ZrO2 mixture by Rietveld method." Materials Chemistry and Physics 82, no. 3 (December 2003): 848–59. http://dx.doi.org/10.1016/j.matchemphys.2003.07.014.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

28

Dey, G. K., R. T. Savalia, E. G. Baburaj, and S. Banerjee. "Crystallization of ternary Zr-based glasses—Kinetics and microstructure." Journal of Materials Research 13, no. 2 (February 1998): 504–17. http://dx.doi.org/10.1557/jmr.1998.0065.

Повний текст джерела

Анотація:

The effect of ternary addition on the thermal stability and the sequence and the kinetics of crystallization of metallic glasses Zr76Fe(24−x)Nix (x = 0, 4, 8, 12, 16, 20, 24) have been examined. It has been found that the surface crystallization occurs in the composition range 16 < x < 20, leading to the formation of an ordered Fe-rich (Fe, Ni)3Zr cubic phase, followed by the transformation of the bulk to a mixture of α−Zr and Zr2Ni. Crystallization of alloys containing 12 to 20% Fe occurs at lower temperatures by primary crystallization of Zr3(Fe, Ni), followed by decomposition of the remaining amorphous matrix by eutectic crystallization giving rise to α−Zr + Zr2Ni. At higher temperatures these alloys transform polymorphically to Zr3(Fe, Ni) in which Ni partially substitutes Fe in the Zr3Fe lattice. Copious nucleation of Zr3(Fe, Ni) phase in these alloys, leading to the formation of a nanophase structure, has been observed. This is consistent with the prediction of increasing nucleation rate for Fe-rich compositions. The crystal nucleation and growth kinetics have been examined for primary, eutectic, and polymorphic crystallization processes. The observed nucleation and growth behaviors have been rationalized by considering the role of the quenched in nuclei and the activation energies of nucleation and growth.

Стилі APA, Harvard, Vancouver, ISO та ін.

29

Porporati, Alessandro Alan, Maria Chiara Munisso, Kristina Lessnau, and Giuseppe Pezzotti. "Stoichiometry and Surface Stress Analyses in Advanced Alumina/Zirconia Composites for Hip Arthroplasty Applications." Advances in Science and Technology 76 (October 2010): 240–46. http://dx.doi.org/10.4028/www.scientific.net/ast.76.240.

Повний текст джерела

Анотація:

A spatially resolved cathodoluminescence (CL) analysis is used as a means for chemical and mechanical analyses of the composite surface after environmental exposure. CL emission proves extremely efficient in concurrently monitoring the concentration of point defects (e.g., oxygen vacancies) on the material surface. Using CL, averaging effects from sub-surface parts of the material can be minimized, and the actual chemical state of the material surface is revealed. As a result, information about the stoichiometry of the material surface can be obtained directly from the lattices of the constituent phases, this enabling one to pattern relevant connections to the environmental resistance of oxide-based bioceramics. A highly fracture resistant alumina/zirconia composite represents the latest trend in ceramics for arthroplastic applications in alternative to monolithic alumina or zirconia ceramics. This composite material is designed from both chemical and microstructural viewpoints in order to prevent environmental degradation and fracture events in vivo, an important step forward in the full exploitation of ceramic materials in the field of arthroplasty. Systematically monitoring the optical activity of oxygen vacancies in both alumina and zirconia phase reveals the distinct role on the kinetics of polymorphic transformation. From the presented data an explicit role is evinced for oxygen vacancy formation in the alumina matrix in the complex cascade of mechanochemical events determining the environmental resistance of the composite.

Стилі APA, Harvard, Vancouver, ISO та ін.

30

Sovago, Ioana, Andrew Bond, Jacco van de Streek, and Diana Thomas. "Parametric Rietveld refinement applied to dehydration of sodium naproxen." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C503. http://dx.doi.org/10.1107/s2053273314094960.

Повний текст джерела

Анотація:

The identification of the hydration and dehydration transformations of drugs is vital to establish stable pharmaceutical components. Our aim is to monitor the kinetics of hydration and dehydration processes in pharmaceutical solids, and to relate these to the molecular-level crystal structures. One of the primary tools to achieve this is parametric Rietveld refinement. The dehydration of two dihydrate polymorphs of the non-steroidal anti-inflammatory drug (NSAID) sodium naproxen was monitored using synchrotron powder X-ray diffraction measurements at Beamline I711, MAX IV Laboratory, Lund University. Diffraction patterns were measured in the range 300-400 K at 1 K increments. Both polymorphs dehydrate to form identical monohydrate then anhydrous phases. Independent Rietveld refinements were initially performed for each unique phase in order to establish initial values for the parametric refinement. The refinements were performed using TOPAS-Academic [1]. The structures are molecular and both dihydrate polymorphs display pseudosymmetry, thereby requiring an extensive set of restraints. One of the key advantages of the parametric Rietveld refinement is the possibility to introduce algebraic equations that describe the evolution of various parameters [2]. The kinetics of the dehydration processes were monitored using a sigmoid function applied to the scale factors of the various phases (see Figure). The evolution of the unit-cell parameters and atomic displacement parameters were also treated parametrically, and the influence of using multiple coordinate sets (one model per temperature) or a single common coordinate set for each phase was examined. One dihydrate polymorph shows a smooth and continuous transition to the monohydrate, whereas the other polymorph shows an abrupt transition. These differences are linked to the existence of topotactic or non-topotactic chemical transformations between the dihydrate polymorphs and the monohydrate phase.

Стилі APA, Harvard, Vancouver, ISO та ін.

31

Dharmayat, Spoorthi, Robert B. Hammond, Xiaojun Lai, Caiyun Ma, Elida Purba, Kevin J. Roberts, Zeng-Ping Chen, Elaine Martin, Julian Morris та Richard Bytheway. "An Examination of the Kinetics of the Solution-Mediated Polymorphic Phase Transformation between α- and β-Forms ofl-Glutamic Acid as Determined Using Online Powder X-ray Diffraction†". Crystal Growth & Design 8, № 7 (липень 2008): 2205–16. http://dx.doi.org/10.1021/cg0706215.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

32

Bond, Andrew, Dhara Raijada, Jukka Rantanen, Ioana Sovago, Jacco van de Streek, Flemming Larsen, and Diana Thomas. "In situ monitoring of hydration and dehydration in pharmaceutical solids." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C906. http://dx.doi.org/10.1107/s2053273314090937.

Повний текст джерела

Анотація:

This talk will describe a multi-technique study of hydration and dehydration in pharmaceutical solids, using sodium naproxen as a case study. The aim of the work is to establish molecular-level structural understanding of the chemical changes that take place in the solid state as a function of temperature and relative humidity. Dynamic vapour sorption (DVS) analysis on the anhydrous compound carried out as a function of temperature provides a preliminary overview of the solid-form landscape and identifies static conditions to obtain four different hydrate forms [1]. Differences in the sorption and desorption cycles indicates the existence of a polymorphic dihydrate, and the two polymorphs show significant differences in their dehydration behaviour. Crystal structures are established for all phases in the system using either single-crystal or powder X-ray diffraction data, supplemented by dispersion-corrected density functional theory (DFT-D) calculations. The hydration and dehydration processes are monitored by powder X-ray diffraction (PXRD), as a function of relative humidity and temperature, and by variable-temperature solid-state 13C and 23Na NMR. Synchrotron PXRD is applied to the two dihydrate polymorphs to monitor the dehydration processes in approximately real time. The kinetic and structural details of dehydration are established by applying parametric Rietveld refinement [2] to the synchrotron data. This approach adds a structural picture to the kinetic processes. The PXRD studies indicate an essentially continuous dehydration pathway from one of the dihydrate polymorphs to the monohydrate, but a stepped dehydration pathway for the other dihydrate polymorph. The different mechanisms are linked to different degrees of structural similarity, and in particular to the existence of topotactic or non-topotactic transformations between the dihydrate polymorphs and the unique monohydrate and anhydrate phases.

Стилі APA, Harvard, Vancouver, ISO та ін.

33

Thoeny, Alexander V., Iside S. Parrichini, Tobias M. Gasser, and Thomas Loerting. "Raman spectroscopy study of the slow order–order transformation of deuterium atoms: Ice XIX decay and ice XV formation." Journal of Chemical Physics 156, no. 15 (April 21, 2022): 154507. http://dx.doi.org/10.1063/5.0087592.

Повний текст джерела

Анотація:

The nature of the hydrogen substructure of a deuterated and deuterium chloride (DCI)-doped ice VI sample after cooling at 1.8 GPa has been a topic of recent interest—especially because the novel ice polymorph ice XIX was discovered in the course of such studies. We here investigate deuterated samples containing 5% H2O using Raman spectroscopy to probe for transitions associated with rearrangement of D-atoms in ice XIX. The protocol involving heating at subambient pressure (10 mbar) in this study follows closely the one used in our earlier neutron diffraction study. Heating of ice XIX induces a complex cascade of processes involving both ordering and disordering of D atoms. Our Raman spectra demonstrate that the transition sequence is ice XIX → ice VI‡ → ice XV, in accordance with our earlier neutron diffraction result. First signs for ice XIX decay are evident at 100 K, while ice XV build-up is seen only at 108 K and above. Between 100 and 108 K, a transiently disordered D-substructure appears, where at 108 K, ice VI‡ forms from ice XIX and simultaneously decays to produce ice XV—thereby establishing a dynamic equilibrium. Using isothermal, time-resolved Raman spectroscopy in real time, we here determine rate constants, Avrami exponents, and activation energies for both slow processes, ice XIX decay and ice XV build-up. The first transition in this sequence, ice XIX decay, is faster than the second transition, ice XV build-up, so that ice VI‡ accumulates. On the basis of the Johnson–Mehl–Avrami–Kolmogorov data obtained from the isothermal Raman experiment, we additionally report kinetic models for the development of fractions of ices XIX, XV, and VI‡ in non-isothermal heating experiments at different heating rates. These models consider the two coupled first-order transitions as separated processes, where the phase fractions are calculated for incrementally small temperature (or time) steps. These models compare favorably with our previous observations for slowly or rapidly heated ice XIX samples, such as in calorimetry or neutron diffraction experiments.

Стилі APA, Harvard, Vancouver, ISO та ін.

34

Shakibania, R. "Kinetic Model for Nanocrystalline Anatase to Rutile Polymorphic Transformation." Chemical and Biochemical Engineering Quarterly 31, no. 3 (October 7, 2017): 353–59. http://dx.doi.org/10.15255/cabeq.2017.1094.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

35

Nieuwenhuis, Egbert R., Aurélie Favrot, Li Kang, Matthew O. Zacate, and Gary S. Collins. "Polymorphic Phase Transformation in In2La and CeIn2." Hyperfine Interactions 158, no. 1-4 (November 2004): 305–8. http://dx.doi.org/10.1007/s10751-005-9056-9.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

36

Zhang, Keke, Noalle Fellah, Vilmalí López-Mejías, and Michael D. Ward. "Polymorphic Phase Transformation Pathways under Nanoconfinement: Flufenamic Acid." Crystal Growth & Design 20, no. 11 (October 15, 2020): 7098–103. http://dx.doi.org/10.1021/acs.cgd.0c01207.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

37

Park, Sun-Ah, Sun Lee, and Woo-Sik Kim. "Polymorphic Crystallization of Sulfamerazine in Taylor Vortex Flow: Polymorphic Nucleation and Phase Transformation." Crystal Growth & Design 15, no. 8 (July 10, 2015): 3617–27. http://dx.doi.org/10.1021/acs.cgd.5b00002.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

38

Lin, Shan-Yang, Wen-Ting Cheng, and Shun-Li Wang. "Thermodynamic and kinetic characterization of polymorphic transformation of famotidine during grinding." International Journal of Pharmaceutics 318, no. 1-2 (August 2006): 86–91. http://dx.doi.org/10.1016/j.ijpharm.2006.03.021.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

39

Rezaee, M., and S. M. Mousavi Khoie. "Mechanically induced polymorphic phase transformation in nanocrystalline TiO2 powder." Journal of Alloys and Compounds 507, no. 2 (October 2010): 484–88. http://dx.doi.org/10.1016/j.jallcom.2010.07.213.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

40

Moura Ramos, Joaquim J., and Hermínio P. Diogo. "Thermal behavior and molecular mobility in the glassy state of three anti-hypertensive pharmaceutical ingredients." RSC Advances 7, no. 18 (2017): 10831–40. http://dx.doi.org/10.1039/c7ra00298j.

Повний текст джерела

Анотація:

Good agreement was found between the thermodynamic and kinetic fragilities of these APIs. DSC analysis of irbesartan showed the possibility of transformation A → B between the two monotropic polymorphic forms.

Стилі APA, Harvard, Vancouver, ISO та ін.

41

Trunov, Mikhaylo A., Mirko Schoenitz, Xiaoying Zhu, and Edward L. Dreizin. "Effect of polymorphic phase transformations in Al2O3 film on oxidation kinetics of aluminum powders." Combustion and Flame 140, no. 4 (March 2005): 310–18. http://dx.doi.org/10.1016/j.combustflame.2004.10.010.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

42

Bansal, Narottam P., and Mark J. Hyatt. "Crystallization kinetics of BaO–Al2O3–SiO2 glasses." Journal of Materials Research 4, no. 5 (October 1989): 1257–65. http://dx.doi.org/10.1557/jmr.1989.1257.

Повний текст джерела

Анотація:

Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system have been studied by differential thermal analysis (DTA), x-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt. %) 10BaO–38Al2O3–51SiO2–1MoO3 (glass A) and 39BaO–25Al2O3–35SiO2–1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3 · 2SiO2) and hexacelsian (BaO · Al2O3 · 2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 °C. It undergoes structural transformation into the orthorhombic form at ∼300 °C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

Стилі APA, Harvard, Vancouver, ISO та ін.

43

Braun, Doris, and Ulrich Griesser. "Insights into hydrate formation and stability of morphinanes." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C991. http://dx.doi.org/10.1107/s2053273314090081.

Повний текст джерела

Анотація:

The formation of multi-component crystals with water (hydrates) is a widespread phenomenon among organic molecules. Hydrate formation is of high practical relevance for industrially used materials, as it affects their physicochemical properties. [1,2] To exclude water or moisture in industrial processes is often difficult. Therefore knowledge about the existence and stability of hydrates and the understanding and control of the anhydrate/hydrate balance is mandatory for avoiding manufacturing problems. In order to improve our understanding of hydrate formation we selected representative substances (morphine, codeine, ethylmorphine) from a class of molecules (morphinanes), which are prone to crystallize along with water. Stable hydrates of both, free bases and HCl salts, have been observed in this important class of drug compounds. This allowed us to investigate the influence of different functional groups, the role of water and the Cl– counterion on the structure and properties of these morphinanes. A crystallization screen on the six compounds considerably extended the total number of known solid forms from twelve [3] to 17 and the number of crystal structures from five to twelve. Anhydrous polymorphs were detected for all compounds except ethylmorphine (one anhydrate) and its HCl salt (no anhydrate). The relative stabilities of the hydrated and anhydrous forms differ considerably, which was evaluated by moisture sorption studies and thermal analytical experiments. Two different hydrates, a tri- and dihydrate, were found for morphine HCl. In the free bases, the substituents define the number of hydrogen bond donor groups and lead to differences in the sterical hindrance around polar groups, influencing the intermolecular interactions, packing and stability. Hydrate formation results in higher dimensional hydrogen bond networks, whereas salt formation decreases the packing variability of the structures among the different compounds. Calorimetric measurements and lattice energy calculations were employed to estimate the heat of hydrate/anhydrate phase transformation, showing an enthalpic stabilization of the hydrates over the anhydrates. The combination of a variety of experimental techniques with computational modelling allowed us to generate sufficient kinetic, thermodynamic and structural information to understand the principles of hydrate formation of morphinanes.

Стилі APA, Harvard, Vancouver, ISO та ін.

44

Zavartsev, Nikita A., and Nadezhda T. Kareva. "Determination of Polymorphic Transformation Temperature for Alloy VT8." Materials Science Forum 946 (February 2019): 42–46. http://dx.doi.org/10.4028/www.scientific.net/msf.946.42.

Повний текст джерела

Анотація:

The temperature of polymorphic transformation (Tpt) has been determined for accurate composition of two-phase titanium alloy which has been marked like VT8 through different ways: the method of trial quench and with the help of dilatometric and differential thermal analyzes. The close values of Tpt have been received. Herewith the phase composition has been estimated qualitatively and quantitatively for the hardened samples of alloy VT8 using optical and scanning electron microscopes and the chemical composition with the help of the micro X-ray spectral analysis. The influence of the quenching temperature on the hardness has been investigated. Also, the hardness of the individual structural components and alloy VT8 as a whole unit has been measured. Hardness curves are based depending of the quenching temperature; the results are displayed in tabular and graphical form. The coefficientkhas been found for the calculation of allotropic transformation temperature for this alloy using the known temperature of hardening and quantity of preserved α-phase of hardened structure. The album of the microstructures after quench with different temperatures has been created, this album will allow to reduce the duration of preliminary works for finding specific temperature of polymorphic transformation in production conditions for each new batch of alloy VT8 with another chemical composition (but within the vintage), knowledge of which is necessary for setting the temperature regime of treatment.

Стилі APA, Harvard, Vancouver, ISO та ін.

45

Bera, S., and I. Manna. "Polymorphic phase transformation in Ti50Zr50 binary alloy by mechanical alloying." Materials Science and Engineering: A 417, no. 1-2 (February 2006): 110–13. http://dx.doi.org/10.1016/j.msea.2005.11.012.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

46

Chen, Shueiyuan, and Pouyan Shen. "Polymorphic transformation of t′ phase in Yttria partially stabilized zirconia." Materials Science and Engineering: A 123, no. 1 (January 1990): 145–52. http://dx.doi.org/10.1016/0921-5093(90)90220-w.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

47

Girin, Oleg. "ELECTROCHEMICAL POLYMORPHIC PHASE FORMATION IN METALS." Acta Metallurgica Slovaca 27, no. 3 (September 13, 2021): 139–45. http://dx.doi.org/10.36547/ams.27.3.1011.

Повний текст джерела

Анотація:

The phenomenon of electrochemical phase formation in metals and alloys via a supercooled liquid state stage was discussed. Assuming the electrodeposited metal to be a product of formation and ultrarapid solidification of supercooled metallic liquid, a possibility of metastable phase formation during electrodeposition of polymorphous metals was suggested. It was anticipated that the polymorphic transition of the metal’s metastable form to the stable one occurs by shear, as does the martensitic transformation. To enable revealing an orientation relationship between grains of the two phases, a method for X-ray texture analysis of metals was developed using a combination of direct pole figures. It was established that the phase formation during electrodeposition of polymorphous metals produces metastable modifications typical of entities that crystallized from a liquid state at extremely high rates. In regards polymorphic transitions in metal electrodeposition, certain orientation relationships were observed between grains of the stable and the metastable phase, which is typical of phase transformations proceeding at extremely high rates. The results obtained provided additional arguments in favor of the phenomenon under discussion.

Стилі APA, Harvard, Vancouver, ISO та ін.

48

Bobrovs, Raitis, Linda Seton, and Andris Actiņš. "Solvent-mediated phase transformation between two tegafur polymorphs in several solvents." CrystEngComm 16, no. 46 (2014): 10581–91. http://dx.doi.org/10.1039/c4ce01215a.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

49

Li, Zunhua, and Bowen Zhang. "Investigation of Glycine Polymorphic Transformation by In Situ ATR-FTIR and FT-Raman Spectroscopy." Crystals 12, no. 8 (August 13, 2022): 1141. http://dx.doi.org/10.3390/cryst12081141.

Повний текст джерела

Анотація:

The solution-mediated phase transformation of α-form to γ-form glycine, including dissolution of metastable α-form, nucleation, and growth of stable γ-form during polymorphic transformation, was investigated using in situ attenuated total-reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and Fourier transform Raman spectroscopy (FT-Raman). The mechanistic influence of operating parameters such as agitation speed, crystallization temperature, α-form seed concentration, and NaCl concentration on polymorphic phase transformation was examined. When the agitation speed, crystallization temperature, and NaCl concentration were increased, the polymorphic transformation process was improved due to the promotion of nucleation and growth of stable γ-form, in addition to the promotion of dissolution of metastable α-form. Moreover, the time to induce γ-form nucleation and complete conversion of α-form to γ-form was also reduced with increasing α-form seed concentration.

Стилі APA, Harvard, Vancouver, ISO та ін.

50

Ali, Imran, Jiequn Tang, Yanqiang Han, Zhiyun Wei, Yongli Zhang, and Jinjin Li. "A Solid-Solid Phase Transformation of Triclabendazole at High Pressures." Crystals 12, no. 2 (February 21, 2022): 300. http://dx.doi.org/10.3390/cryst12020300.

Повний текст джерела

Анотація:

Triclabendazole is an effective medication to treat fascioliasis and paragonimiasis parasitic infections. We implemented a reliable quantum mechanical method which is density functional theory at the level of ωB97XD/6-31G* along with embedded fragments to elucidate stability and phase transition between two forms of triclabendazole. We calculated crystal structure parameters, volumes, Gibbs free energies, and vibrational spectra of two polymorphic forms of triclabendazole under different pressures and temperatures. We confirmed form I was more stable than form II at atmospheric pressure and room temperature. From high-pressure Gibbs free energy computations, we found a pressure-induced phase transformation between form I (triclinic unit cell) and form II (monoclinic unit cell). The phase transition between forms I and II was found at a pressure and temperature of 5.5 GPa and ≈350 K, respectively. In addition, we also studied the high-pressure polymorphic behavior of two forms of triclabendazole. At the pressure of 5.5 GPa and temperature from ≈350 K to 500 K, form II was more stable than form I. However, at temperatures lower than ≈350 K, form I was more stable than form II. We also studied the effects of pressures on volumes and Raman spectra. To the best of our knowledge, no such research has been conducted to determine the presence of phase transformation between two forms of triclabendazole. This is a case study that can be applied to various polymorphic crystals to study their structures, stabilities, spectra, and phase transformations. This research can assist scientists, chemists, and pharmacologists in selecting the desired polymorph and better drug design.

Стилі APA, Harvard, Vancouver, ISO та ін.

Статті в журналах з теми "Polymorphic phase transformation kinetic"

Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями