Polymorphic Transition Temperature Research Articles

Direct in situ measurement of polymorphic transition temperatures under thermo-mechanochemical conditions.

For the first time, we directly measured the onset and completion temperatures of polymorphic transitions under thermo-mechanochemical conditions by simultaneous in situ synchrotron powder X-ray diffraction and temperature monitoring. We determined the thermo-mechanochemical polymorphic transition temperature in 1-adamantyl-1-diamantyl ether to be 31 °C lower than the transition temperature determined by DSC. Our findings highlight the uniqueness of thermo-mechanochemical conditions, with potential applications in polymorph screening.

Application of the method for visualization of noncovalent interactions in conformational polymorphs of four organic acids.

A method for the visualization of noncovalent interactions using examples of the conformational polymorphs of four organic compounds: 2-(phenylamino)nicotinic, 2-(3-chloro-2-methylphenylamino)nicotinic, N-(3-chloro-2-methylphenyl)anthranilic and 2-(methylphenylamino)nicotinic acids is examined. The changes in noncovalent contacts are plotted against the angle between the planes of aromatic rings allowing a visual representation of conformational adjustment of molecules as well as packing features of crystal structures. According to the k-Φ criterion, the studied structures represent conformational polymorphs. Different types of hydrogen bonding are discussed within the framework of the method of visualization and molecular Voronoi-Dirichlet polyhedra. Good correlations are found between calculated and experimental data for several cases, such as the agreement between π stacking and polymorphic transition temperatures as well as between the area of a contact and the energy of conjugation. Also, an attempt has been made to assess the relative contributions of conformational and packing polymorphism in the formation of polymorphs.

PHASE EQUILIBRA IN THE Ag2Se–Ag8GeSe6–Ag8SiSe6 SYSTEM AND CHARACTERIZATION Of the Ag8Si1-xGexSe6 SOLID SOLUTIONS

Phase equilibria in the Ag2Se–Ag8SiSe6–Ag8GeSe6 system were studied by differential thermal analysis and X-ray diffraction thechnique. Based on the experimental results and literature data, the projection of the liquidus surface of the Ag2Se–Ag8SiSe6–Ag8GeSe6 system, the isothermal section at 300 K and some polythermal sections of the phase diagram were constructed. It was determined that continuous series of solid solution are formed based on high-temperature cubic modification and limited solid solution areas are formed based on low-temperature modification of initial compounds on the Ag8SiSe6–Ag8GeSe6 side of concentration triangle. The formation of solid solutions leads to a sharp decreasing of polymorphic transition temperatures of ternary compounds and stabilization of high-temperature phases at room temperature. The liquidus surface of the Ag2Se–Ag8SiSe6–Ag8GeSe6 system consists of 2 areas reflecting the initial crystallization of α'-phase based on HT-Ag2Se and HT-Ag8Si1-xGexSe6 solid solutions. The obtained new phases are of interest as environmentally safe materials with thermoelectric properties and mixed ion-electron conductivity.

Sandwich-like interfacial structured polydopamine (PDA)/Wax/PDA: A novel design for simultaneously improving the safety and mechanical properties of highly explosive-filled polymer composites

High melting point paraffin wax (HPW) is a novel desensitizer that has the potential to achieve low sensitivity of energetic crystals, such as 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). However, first-principles calculations confirmed that interface deterioration occurred due to a weak interfacial connection. In this work, the polydopamine (PDA)/HPW/PDA with a sandwich-like interfacial structure was prepared using three simple steps to improve safety performance, thermal stability, and mechanical properties. The theoretical and experimental results suggested that the PDA acted as a double-sided tape to adhere to the adjacent HMX/HPW layer or HPW/polymer binder layer, thus substantially enhancing the interfacial interaction. While maintaining higher safety performance (impact energy: 11∼13 ​J) than that of HMX (5 ​J), the new design improved the β-δ polymorphic transition temperature of HMX to 219.4 ​°C for HMX@PDA@HPW@PDA, which was higher than that of HMX@HPW (202.8 ​°C) and core@double-shell HMX@PDA@HPW (208.9 ​°C). Among the modified energetic composites, polymer-bonded explosives (PBXs) based on HMX@PDA@HPW@PDA exhibited the optimum mechanical performance, including the storage modulus and tensile fracture energy, which were 43.5% and 77.1% higher than those of PBXs based on raw HMX, respectively. The achieved favorable systematical enhancement in thermal stability, mechanical properties, and safety performance shows that such a sandwich-like interfacial structure has great potential for application for HMX-based formulation used in complex environments.

Metastable polymorphs and luminescence of boehmite-derived alumina doped with divalent europium ions

The control of polymorphism transition of Eu[Formula: see text] ion-doped [Formula: see text]-, [Formula: see text]-, [Formula: see text]- and [Formula: see text]-metastable alumina derived from boehmite is demonstrated by the sol–gel method through controlling the doping amount and firing temperature and the resultant luminescent properties are investigated. Nanosized boehmite ([Formula: see text]-AlOOH) particulates in boehmite sol effectively prevent the formation of impurity phases of EuAlO2 and Eu2O3. The polymorphic structures of the induction-fired xerogel samples in weak reductive atmosphere can be held to the room temperature upon cooling down naturally. The luminescence properties of Eu[Formula: see text] ions verify the polymorphic transitions from [Formula: see text]-, [Formula: see text]-, [Formula: see text]- to [Formula: see text]-Al2O3 that are featured with their broad emission peaks positions at 410, 450, 480 and 500 nm, respectively. It is believed that boehmite sol–gel by taking the nanosized [Formula: see text]-AlOOH particulates as seeds assisted the dispersion of precursor constituents and is effective to adjust the onset of polymorphic transition temperatures and luminescence properties.

One-step, safe and efficient preparation strategy of nitrate glycerol ether cellulose-based energetic composites with application potential in propellants

Lately, nitrate glycerol ether cellulose (NGEC), a novel thermoplastic cellulose-based energetic binder, exhibits potential application to replace conventional nitrocellulose (NC) which was commonly used in propellants. This study employs NGEC as insensitive and reinforce materials to prepare NGEC-based energetic composites via a combined simple and safe water-suspension method and freeze-drying technology, involving NGEC/RDX (cyclotrimethylenetrinitramine), NGEC/HMX (cyclotetramethylenetetranitramine), and NGEC/CL-20 (hexanitrohexaazaisowurtzitan). The obtained composites have been systematically characterized and exhibited stable structure, improved thermal properties and reduced sensitivity (the largest is about 1.4 times) performances. These results demonstrate that energetic crystals and NGEC are combined tightly by van der weal force; and present favorable thermal stability, especially for the increased temperature of polymorphic phase transition with the increased content of NGEC (HMX (β→δ): 194.6°С→198.8°С, CL-20 (ε→γ): 164.6°С→177.9°С). Moreover, the existence of NGEC with different content has different influence on the decomposition performance of different explosives. Hence, this fabrication strategy of NGEC-based energetic composites may provide promising application in high-energy and high-strength propellants.

Applications of an infrared thermography method for solid-liquid equilibria modeling of organic binary systems

The solid-liquid equilibria (SLE) modeling of fatty acids binary systems is known as a challenging topic. Due to their complex phase diagrams and to their inherent nature to polymorphism, the modeling of the solid-liquid equilibria of the fatty acids blends requires a significant amount of data obtained with numerous techniques. The infrared thermography method (IRT) proves to be an interesting alternative by providing large quantities of phase transitions data, including the potential detection of the polymorphic ones. In this work, the applicability of this method for SLE modeling is assessed based on two criteria: i) the accuracy of empirical and theoretical models is assessed in comparison with IRT data; ii) the polymorphic transition temperatures detected via IRT are used as inputs in a model using polymorphic transition enthalpies as adjusting parameters. Polymorphic transitions data is compared to literature and to DSC measurements to evaluate the reliability of IRT for polymorphic transitions detection and of the estimated enthalpies consistency.

Effect of gap on the polymorphic transition of ε-CL-20

The ε-form 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo [5.5.0.05,9.03,11] dodecane (CL-20) is the highest energy density compound which can be applied in practice at present. In this work, the effect of GAP on the polymorphic transition of ε-CL-20 was investigated by Raman spectroscopy and Calvet microcalorimeter method. The results show that the polymorphic transition temperature of ε-CL-20 to α-CL-20 can be reduced significantly by GAP, and the accurate temperature is 83.7°C. This investigation provides guidance to process condition selection for GAP-based propellants containing CL-20.

Stabilization of ε-CL-20 crystals by a minor interfacial doping of polydopamine-coated graphene oxide

Hexanitrohexaazaisowurtzitane (CL-20) is a well-known high energy density nitramine, but it is of high sensitivity and has the problem of polymorphic transition. In order to reduce the sensitivity of ε-CL-20 and improve the stability of its crystal structure, the polydopamine (PDA)-coated graphene oxide (GO) was used to dope ε-CL-20 crystals by strategy of in-situ coating followed with a solvent-non-solvent crystallization process. It has been shown that modified CL-20 crystals with the best performances are of polygon shape with a smooth surface and with the average diameter of 16 μm, much smaller than that of raw ε-CL-20 (140 μm). In addition, the doping can either improve the polymorphic transition temperature up to 19.0 °C or exclude such a transition due to formation of completely new crystal phase with better stability, depending on the type and content of the dopants. The density of a certain GO@PDA modified CL-20 is even slightly higher than that of pristine ε-CL-20 due to better assembling of the molecules under the nucleation of the dopants. CL-20/PDAG-2 does not show any polymorphic transition peak. Moreover, the XRD spectrum of CL-20/PDAG-2 also demonstrates that it is a completely new crystal phase better than the other four reported ones in terms of thermal stability.

Recent advances in the physics of polymer systems

Recent advances in the physics of polymer systems

Thermodynamic study of Ag8GeSe6 by EMF with an Ag4RbI5 solid electrolyte

The Ag–Ge–Se system was studied in the range of compositions Ag2Se–GeSe2–Se by measuring the EMF of the concentration (relative to the silver electrode) circuits with a solid electrolyte Ag4RbI5 in the temperature range 290–430 K. The polymorphic transition temperature of Ag8GeSe6 (320 K) was determined and the partial molar functions of silver were calculated for both crystal modifications of this compound based on the EMF measurements. The thermodynamic functions of formation and entropy of both modifications of Ag8GeSe6 and the thermodynamic functions of its polymorphic transition were calculated.

Halogenated Sodium-closo-Dodecaboranes as Solid-State Ion Conductors

Sodium compounds containing large weakly coordinating anions are explored as ion conductors. The halogenated sodium-closo-dodecaboranes (Na2B12Cl12, Na2B12Br12, and Na2B12I12) are all isostructural (Pa3̅) at room temperature. These compounds undergo an order–disorder polymorphic transition to Fm3̅m where Na+ partially occupies two crystallographic sites and [B12X12]2– anions undergo reorientational motion. These dynamic structural properties promote extreme Na+ ion conductivity up to 0.162 S/cm at elevated temperature (500 °C). The polymorphic transition temperatures increase down the halogen group (Cl < Br < I). These temperatures are much higher (475, 525, and 570 °C) than for Na2B12H12 (266 °C), which could be related to increasing anion size, mass, and the anisotropic electron density in the covalently bound halogens (B–X). The halogens may form Na–X interactions with increasing strength and directionality, which restrict dynamic motion until high temperature. The halogenated sodium-closo-dodecaboranes demonstrate excellent thermal stabilities (up to 500 °C) and may facilitate the development of new high temperature ion conductors.

Characterization, thermal stability, and solid-state phase transition behaviors of gestodene polymorphs and amorphous phase

In the current work, a systematic investigation on the thermal behavior of gestodene was carried out to understand temperature induced solid-state transitions between its polymorphs and amorphous phase. The focus was on polymorph identification, thermal stability analysis, and the nature of the phase transitions. These characteristics were compared to the complexity of the phase transitions, studied by differential scanning calorimetry (DSC) and variable temperature X-ray powder diffraction (VT-XRD) techniques. DSC studies indicated that the form II was enantiotropically related to form I, which melted at about 470 K. The temperature of polymorphic transition was 309 K, and form II was the more stable form between room temperature and the transition temperature. A schematic Gibbs free energy-temperature diagram was subsequently constructed to describe the thermal stability of the two forms. Amorphous phase converted exothermically to form I at 368 K on heating and was shown by VT-XRD to be accompanied by diffraction pattern changes. In addition, the crystallization kinetics studied by DSC heating technique followed by analysis using the Kissinger–Akahira–Sunose (KAS) method where values of apparent activation energy (E a) were estimated as a function of extent of conversion (α). The variations in E a with α on kinetic analysis from α = 0.10 to 0.88 for the amorphous to form I conversion suggested more complex processes, possibly liquid–solid and solid–solid transformations prior to formation of the form I.

Crystal structure and phase transitions of ternary compounds in the thulium–silver–tin system

The existence of the TmAgSn compound in the Tm–Ag–Sn system in the form of two polymorphs was confirmed. The high-temperature phase crystallizes with the LiGaGe type (P63mc, Z = 2), and the lowtemperature one with the ZrNiAl type (\(P\overline 6 2m\), Z = 3). A new ternary compound TmAgSn2 was found to exist (Cu3Au type, \(Pm\overline 3 m\), Z = 1). The polymorphic transition temperature of the TmAgSn was found to be 1214 K using differential thermal analysis. A comparative investigation of the compounds by 119Sn Mossbauer spectroscopy showed a difference in the chemical bonding character of tin atoms: in TmAgSn2, tin has a typical valence state for metallic systems, whereas in both TmAgSn polymorphs additional interaction between the 5s orbitals of silver atoms and the 5p orbitals of tin atoms takes place.

Characterization and Thermodynamic Stability of Polymorphs of Di(arylamino) Aryl Compound ASP3026.

ASP3026 (N-{2-methoxy-4-[4-(4-methylpiperazin-1-yl)piperidin-1-yl]phenyl}-N'-[2-(propane-2-sulfonyl)phenyl]-1,3,5-triazine-2,4-diamine) was developed in Astellas Pharma Inc. as a novel and selective inhibitor of the fusion protein EML4-ALK. We investigated the thermodynamic stability of five polymorphs of ASP3026 (A01, A02, A03, A04, and A05) in detail. To determine the most stable form at ambient temperature, powder X-ray diffraction, differential scanning calorimetry, and solubility measurements were conducted. Of the five polymorphs, A04 was the most stable and A05 was the least stable. The relationship between A04 and A03 and A04 and A01 were mutually monotropic, while that between A01 and A02 was enantiotropic. The transition temperature from A02 to A01 was estimated as 325 K. A02 was more thermodynamically stable at ambient temperature than A01. Furthermore, the method to estimate polymorphic transition temperatures using solution calorimetry was found to be effective. The systematic characterization of ASP3026 polymorphs presented in this study enables the selective crystallization of the most stable form and design of solid formulations.

Effect of quenching temperature on structure and properties of titanium alloy: Physicomechanical properties

Regularities of the formation of physicomechanical properties of the VT16 alloy (Ti-3.33Al-5.18Mo-4.57V, wt %) quenched after furnace and rapid heating have been established using optical microscopy, X-ray diffraction (XRD), and dynamic mechanical analysis. It has been shown that changes in the modulus of elasticity of the VT16 alloy correlate with a decrease in the volume fraction of the α phase in the structure, except for a slight increase in the modulus of elasticity (related to the presence of the ω phase) in the case when quenching temperatures of 800–825°C were used. It has been found that the use of rapid heating to the quenching temperature leads to an increase in the temperature of the alloy transition into the single-phase β state, hampers grain growth during heating for quenching at temperatures close to the polymorphic-transition temperature, and creates conditions for more efficient strengthening in the course of subsequent aging.

Changes in the temperature of polymorphic transformations under the action of radiation

Studies on transport processes of 46Sc, 57Со and 188Re impurity atoms in irradiated and non-irradiated samples of metallic titanium, iron and tungsten have shown that the temperature of polymorphic transition depends on the degree of radiation damage of the metal and is “moved” to the region of higher temperatures due to the presence of large number of structural radiation defects that make the restructuring of the crystal lattice difficult.

Thermodynamic stability analysis of m-nisoldipine polymorphs

Two polymorphic crystal forms of m-nisoldipine (1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic acid methyl 2-methylpropyl ester) were characterized by X-ray powder diffraction and IR-spectroscopy. The solubility of the two polymorphs in water at 25, 31, 37, 42, and 49°C was investigated; the values obtained were used to calculate the thermodynamic parameters of the phase transition. The results show that the two forms A and B are enantiotropic. The temperature of polymorphic phase transition was 47°C, and the values of ΔGA,Bθ, ΔHA,Bθ, and ΔSA,Bθ at 25°C were 2.47, 36.01, and 112.48J·mol−1·K−1, respectively. Form A is thermodynamically stable below the transition temperature; it accorded with interaction energies of the two forms obtained from Density Function Theory (DFT) calculations on the hydrogen-bonding and π-stacking interactions. The character of the solid-state decomposition, studied using DSC analysis, showed that the activation energies of decomposition of the polymorphs A and B after melting at high temperatures were 109.80 and 59.14kJ·mol−1, respectively. It is conclusion that melted states of polymorphs A and B reserved “the memories” of their respective crystalline state. Furthermore, phase transition of the polymorphs was not found under solid-state grinding conditions. Moisture sorption/desorption experiments showed that the two forms of m-nisoldipine are nonhygroscopic.

Solid State Characterizations and Analysis of Stability in Azelnidipine Polymorphs

Azelnidipine, a new dihydropyridine calcium ion antagonist, was protected by patent in Japan. In present study, identifications of the crystal phases, including two polymorphic and a pseudopolymorphic crystal forms of azelnidipine, were attempted using powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), IR-, Raman-, THz-, and ss-NMR-spectroscopy. PXRD identified three different crystal forms, while, spectroscopy analysis provided the information of crystal structure involving intermolecular interactions. The transition thermodynamics of the azelnidipine polymorphs were extensively investigated by solubility method. The solubility of the two polymorphs of α and β in 50% ethanol at 25, 31, 37, 42, and 49°C was investigated; the values obtained were used to calculate the thermodynamic parameters of the transition reaction. The temperature of polymorphic phase transition in 50% ethanol was 50.78°C, and the values of ΔG(α,β)(θ), ΔH(α,β)(θ), and ΔS(α,β)(θ) at 25°C were -1.18 kJ·mol(-1), -14.81 kJ·mol(-1), and -45.73 J·mol(-1)·K(-1), respectively. Form β was proved to be thermodynamic stable form at room temperature and enantiotropically related with form α. The kinetics of the solid-state decomposition, studied using DSC analysis, showed that the activation energies of decomposition of the polymorphs α and β at high temperatures were 148.67 and 151.93 kJ·mol(-1).

Calorimetric investigation of solvent-mediated transformation of sulfamerazine polymorphism

Thermodynamic transition temperature of crystal forms is essential information for the formulation developmental studies. However, determination of the transition temperature is frequently time and labor consuming. Herein, solvent-mediated transformation, which is a very powerful method to determine the transition temperature, was combined with thermal analysis to offer a convenient and rapid method to estimate the polymorphic transition temperature. The thermodynamic transition temperature of sulfamerazine, which cannot be obtained by conventional DSC measurements, was investigated using this procedure. The transition temperature obtained by this in situ transformation technique was almost consistent with the thermodynamic transition temperature. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:76–81, 2010