Unusual Thermal Behavior Research Articles

Study of the recrystallization in coated pellets – Effect of coating on API crystallinity

Coated diltiazem hydrochloride-containing pellets were prepared using the solution layering technique. Unusual thermal behavior was detected with differential scanning calorimetry (DSC) and its source was determined using thermogravimetry (TG), X-ray powder diffraction (XRPD) and hot-stage microscopy. The coated pellets contained diltiazem hydrochloride both in crystalline and amorphous form. Crystallization occurs on heat treatment causing an exothermic peak on the DSC curves that only appears in pellets containing both diltiazem hydrochloride and the coating. Results indicate that the amorphous fraction is situated in the coating layer. The migration of drugs into the coating layer can cause changes in its degree of crystallinity. Polymeric coating materials should therefore be investigated as possible crystallization inhibitors.

A novel structural form of MIL-53 observed for the scandium analogue and its response to temperature variation and CO2adsorption

The scandium analogue of the flexible terephthalate MIL-53 yields a novel closed pore structure upon removal of guest molecules which has unusual thermal behaviour and stepwise opening during CO(2) adsorption. By contrast, the nitro-functionalised MIL-53(Sc) cannot fully close and the structure possesses permanent porosity for CO(2).

On the high-temperature phase of barbituric acid

The crystal structure of the high-temperature phase (HT-form or form III) of barbituric acid has been solved from X-ray powder diffraction data. It was found to be monoclinic, space group C2/c, a = 8.5302(3) A, b = 6.8167(3) A, c = 9.3304(4) A, β = 89.865(2)°, volume = 542.54(4) A3 at T = 236(1) °C. The crystal structure is closely related to the also monoclinic structure of form II. A combined Rietveld refinement of X-ray and neutron powder diffraction data revealed fine details of the disorder aspects of the structure. 1H variable temperature and 13C MAS solid-state NMR confirmed those and proved the dynamic nature of the rotational disorder of the molecules. Energy optimizations of ordered subgroup structures with dispersion-corrected DFT gave insights into the underlying reason for the disorder. The reorientation of the unique 2-fold symmetry axis at the II → HT phase transition derives from both the anisotropy of the hydrogen bonds and the resulting anisotropy of the thermal rotational disorder. The unusual thermal expansion behavior of form II also finds its explanation in the incipient disorder.

Magnetostructural effects in ligand stabilized Pd13 clusters: a density functional theory study

We show computationally that ligation allows tuning of the magnetostructural properties of the Pd(13) cluster. The bare, phosphine and thiol capped clusters were investigated at the density functional level. The most stable conformers of the bare cluster are of high spin, septet and nonet and of distorted C(3v), C(s) and I(h) geometries. Ligation stabilizes the I(h) geometry and quenches the high spin states, down to a triplet for Pd(13)(PH(3))(12) and to a quintet for Pd(13)(SCH(3))(12).The influence of the two capping systems on the magnetostructural properties of the ligated clusters is analyzed in connection with their different bonding properties. The mixed ligand species Pd(13)(SCH(3))(6)(PH(3))(6) is also characterized. Due to the multiple energetically accessible spin states, unusual thermal behaviour of the average magnetic moment is predicted for these clusters.

Heat Capacity Studies of Nanocrystalline Magnetite (Fe3O4)

The Verwey transition in magnetite (Fe3O4) has been studied extensively with a wide assortment of experimental techniques to investigate the effects of impurities, oxygen stoichiometry, and crystal quality; however, no studies have tested the effects of crystal size on the Verwey transition. In this study, the heat capacity of a magnetite powder with an average crystallite size of 13 nm was measured in the temperature range of 0.5−350 K. No obvious anomaly was observed in the heat capacity in the vicinity of 120 K, yet the measurements exhibited unusual thermal behaviors between 50 and 90 K with relaxation times increasing from an average of 25 min to as much as 5 h in this temperature interval. The behavior is typical of a phase transition, so the lack of a distinct anomaly suggests either the phenomenon is spread out over a large temperature interval with little enthalpy or an insulating phase with different thermal conductivities appears. The heat capacity below 90 K was dependent on cooling rate with an inconsistent anomaly found below 4 K. The results suggest that the Verwey transition has a particle-size dependence. Additionally, theoretical fits below 15 K suggest that magnetite nanoparticles display anisotropic ferrimagnetic behavior and a superparamagnetic contribution to the heat capacity which are properties not observed in bulk magnetite.

The Characterization and Thermal Investigation of Chitosan-Fe3O4 Nanoparticles Synthesized Via A Novel One-step Modifying Process

A novel modifying process was designed to prepare ultra small magnetic chitosan nanoparticles which exhibited unique thermal stability and decomposition mechanism. The chemical structures and physical properties of the prepared products were characterized using FTIR, TEM, XRD, TGA and DSC techniques. The results revealed that this approach eliminated the aggregation among nanoparticles. The magnetic chitosan particles were 10–15 nm in size with good dispersibility and new thermal property. To further study the decomposition process, the combined TGA-FTIR technique was used to the analysis of the evolution with the temperature of the gas products evolved in the degradation of the magnetic chitosan. The phenomena were observed directly from TGA-FTIR stack plots. From the measurements data, it suggested that the unusual thermal behavior of chitosan might be attributed to the additional bridging through metal oxide.

Another Demo of the Unusual Thermal Properties of Rubber

The unusual thermal behavior of rubbers, though discovered a long time ago, can still be mind-boggling for students and teachers who encounter this class of polymeric systems. Unlike other solids, stretched elastic polymers shrink upon heating. This is a manifestation of the Gough-Joule (G-J) effect.1–4 Joule in the 1850s studied the thermal behavior of rubbers that was initially explored by Gough in 1805. Properties of rubbers such as contraction upon heating, or the related phenomenon of heating upon fast expansion, did not make much sense at that time. Joule's work validated Gough's results, but the molecular basis of the unusual thermal behavior of rubbers remained unexplained for another 70 years. The physical ideas, taking into account gigantic conformational entropy of elastic polymers that explain their contraction on heating, were developed by Staudinger, Kuhn, and others only in the 1920s and 1930s.5

Phase Transition and Phase Transformation in Block Copolymer Nanoparticles

Block copolymer nanopaticles were prepared from the mixture solutions containing good/poor solvents by a simple evaporation process. The block copolymers formed disorder, unidirectionally stacked lamellar, and onion-like structures in nanoparticles depending on preparation temperatures. Thermal annealing induced the disorder-order phase transition and order-order phase transformation in the block copolymer nanoparticles, even though the annealing temperature is lower than the of one polymer segment. The unusual thermal behaviors suggest that the glass transition temperature of the block copolymer is decreased by the effect of nanoparticle, whose surface areas are larger than their volumes.

Investigation of the Milling-Induced Thermal Behavior of Crystalline and Amorphous Griseofulvin

To gain a better understanding of the physical state and the unusual thermal behavior of milled griseofulvin. Griseofulvin crystals and amorphous melt quench samples were milled in a vibrating ball mill for different times and then analyzed using differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). Modulated DSC (mDSC) and annealing studies were done for the milled amorphous samples to further probe the effects of milling. Milling of griseofulvin crystals results in decrease in crystallinity and amorphization of the compound. A double peak is seen for crystallization in the DSC, which is also seen for the milled melt quench sample. Both enthalpy and temperature of crystallization decrease for the milled melt quenched sample. Tg is visible under the first peak with the mDSC, and annealing shows that increasing milling time results in faster crystallization upon storage. Milling of griseofulvin results in the formation of an amorphous form and not a mesophase. It increases the amount of surface created and the overall energy of the amorphous griseofulvin, which leads to a decreased temperature of crystallization. The two exotherms in the DSC are due to some particles having nuclei on the surface.

Low Temperature Dielectric Relaxations in ZnO Varistor

The main purpose of this work is to study the behaviour of ZnO varistor by means of dielectric relaxation spectroscopy at the low temperature range. The complex frequency spectrum of dielectric losses has been studied in detail and analysed carefully by fitting of a sum of Havriliak–Negami expression. Three relaxation processes are studied here, exhibiting a very strong Cole–Davidson behaviour. The faster relaxation process shows an unusual thermal behaviour. Initially, its relaxation time increases as the temperature rises but later it becomes thermally activated. The transition temperature of thermal behaviour of this process was found very close to the characteristic value of 0.4θD=160 K, where θD is the Debye temperature of ZnO. The de-activation energy of this process has been estimated by using the Arrhenius type relation to be 78 meV, a value very close to the higher longitudinal optical (LO) phonon energy in ZnO, 72 meV. This is a strong indication that the predicted Holstein transition between large to small-polaron motion should be observed in ZnO. The two remaining relaxations are electronic processes, the slower one is associated with the doubly ionised zinc interstitial Zni••, while the other should be related to defects induced by the dopants, or of complexes of intrinsic native defect with dopant impurities.

A comparativein situRietveld refinement study: thermal decomposition and transformation of CoAl and CoZnAl layered double hydroxides

Rietveld refinement based onin situX-ray powder diffraction (XRPD) data was combined with thermogravimetric analysis (TGA) and mass spectrometry (MS) to study and compare the phase transformations, thermal stability, microstructural and structural changes of two cobalt-containing nitrate-based layered double hydroxides (LDHs) upon heating in a controlled inert atmosphere of nitrogen. The XRPD data were collected, using synchrotron X-ray radiation, with a time resolution of 107 s, which made it possible to carry out detailed structural studies of the initial layered double hydroxides as well as their decomposition products: spinel for a CoAl–NO3LDH and spinel/zincite for a CoZnAl–NO3LDH. Correlating these data with those from the TGA–MS analyses gives us information about the transformation mechanisms. Rietveld refinements of the two spinel phases reveal remarkable differences. Theaaxis of the spinel formed by decomposition of the CoAl–NO3LDH increases almost linearly from approximately 598 to 1163 K, mainly due to the dominating thermal expansion, whereas theaaxis of the spinel formed by decomposition of the CoZnAl–NO3shows a more complex temperature dependency. Between approximately 698 and 1073 K, theaaxis is almost constant due to pronounced chemical interaction with an additional amorphous phase and the zincite phase, whereas from 1073 up to 1163 K it increases linearly. Calculations, based on the results of the Rietveld refinements, of the size of the octahedral and tetrahedral coordination polyhedra in the spinel show that the octahedra shrink and the tetrahedra expand with increasing temperature. The unusual thermal behaviour of the octahedra is discussed and attributed to the low formation temperature of the cobalt aluminium spinel phase. Finally, the intensity of a low-angle scattering (LAS) signal observed in the XRPD patterns was correlated with the decomposition of the LDH, and determination of the specific surface areas gave the temperature-dependent BET surface areas.

Strain-driven inverse thermal hysteresis behaviour in half-doped manganites

In this paper, we report unusual thermal hysteresis behaviour in half-doped manganites Nd0.5Sr0.5−xCaxMnO3 (0.0 ⩽ x ⩽ 0.50). For 0.05 ⩽ x < 0.25 samples, the magnetization curves show a counterclockwise hysteresis loop. For 0.25 < x ⩽ 0.40 samples, however, they exhibit a clockwise loop. The inverse hysteretic behaviour stems from the competition between two kinds of strain, namely, the compressive strain and the tensile strain. The former produces a counterclockwise thermal hysteresis while the latter leads to a clockwise one. In the meantime, a magnetic instability is observed and the strain relaxation should be the main reason for it.

Off-Center Rattling and Anisotropic Expansion of Type-I Clathrates Studied by Raman Scattering

Dynamical motions of the guest ions in type-I clathrates Sr8Ga16Si(30-x)Gex and Ba8Ga16Si(30-x)Gex have been studied by Raman scattering spectroscopy, to clarify the role of guest vibration modes in these systems with unusual thermal transport behaviors. An anomalous decrease of the guest energies with decreasing temperature is observed for both systems. The Ge-doping expands the cage surrounding the 6d site anisotropically for Sr8Ga16Si(30-x)Gex, but isotropically for Ba8Ga16Si(30-x)Gex. Especially for Sr8Ga16Si(30-x)Gex, off-center rattling arises simultaneously with the anisotropic expansion, and it is confirmed that these anomalies play a crucial role to suppress lattice thermal conductivity in these systems.

Synthesis of semitelechelic POSS‐polymethacrylate hybrids by thiol‐mediated controlled radical polymerization with unusual thermal behaviors

AbstractWe have developed an efficient and versatile method for the synthesis of polyhedral oligomeric silsesquioxanes (POSS)‐polymethacrylate hybrids, such as POSS‐poly(methyl methacrylate) (POSS‐PMMA), POSS‐poly(ethyl methacrylate) (POSS‐PEMA), and POSS‐poly(benzyl methacrylate) (POSS‐PBzMA) of controllable molecular weights and low polydispersities by thiol‐mediated radical polymerization at elevated temperature (100 °C). By tuning the reactant concentrations and degree of polymerization of the grafted polymethacrylate chains, POSS content in these hybrid materials could be varied. MALDI‐TOF‐MS analysis of the hybrid molecule shows that the nanoscale POSS moiety is connected to the end of polymethacrylate chain through the sulfur atom bridge. These hybrid materials were further characterized using various techniques such as FTIR, XRD, NMR, TGA, and DSC. In all synthesized hybrids, the incorporation of POSS moiety at the end of polymethacrylate chain resulted in the decrease of glass transition temperature (Tg) compared to that of neat polymethacrylates of comparable molecular weights. Surprisingly, POSS‐PMMA hybrids only with relatively high POSS content (∼ 10 and 16 wt %) showed physical aging behavior as reveled by DSC study. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1111–1123, 2008

Thermal Expansion Behavior of Solid Solution Y&lt;sub&gt;1.9&lt;/sub&gt;R&lt;sub&gt;0.1&lt;/sub&gt;Mo&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;15&lt;/sub&gt; (R = Sm, Nd, Dy)

Several rare earth solid solutions of Y1.9R0.1Mo4O15 (R=Sm, Nd, Dy) with interesting thermal expansion behavior were prepared and studied by X-ray and neutron diffraction. These solid solutions crystallize in a monoclinic space group P21/c. The lattice parameters a, b and c of Y1.9R0.1Mo4O15 increase with increasing of the ionic radius of substituted elementary. The high-temperature XRD data for Y1.9Sm0.1Mo4O15 show that there is an unusual low thermal expansion behavior in the 25~100°C range followed by a normal thermal expansion at higher temperature up to 600°C. Since no phase transition was observed, the temperature dependence of Mo2-O14 bond distance seems to be responsible for the anomalous thermal behavior.

Abnormal thermal shock behavior of Ti3SiC2 and Ti3AlC2

Many layered ternary ceramics displayed unusual thermal shock behavior, i.e., the retained strengths of as-quenched samples increased with increasing quench temperature above a critical quench temperature. However, the causation was not clear even though this phenomenon has been observed for 10 years. In this study, the thermal shock behavior of Ti3SiC2 and Ti3AlC2, two representative members of layered ternary ceramics, was investigated. The results indicated that the formation of surface oxides was responsible for this abnormal phenomenon. These results might contribute to the understanding of this unusual behavior of other layered ternary ceramics.

Synthesis, structure, electronic properties and thermal behavior of butadiynyl substituted phenylCr(CO) 3-complexes

Butadiynyl-substituted η 6-benzeneCr(CO) 3 complexes 3 are very efficiently prepared by a copper catalyzed coupling of the phenylacetylene complex 1 and bromo alkynes 2. The transmission of electronic effects through the butadiynyl bridge operates by resonance mechanisms as established by correlations between Hammett's σ p, σ R and σ P + parameters. Most interestingly, however, is an unusual thermal behavior that leads to intractable paramagnetic polymers of unknown structure. According to thermal analyses (thermal gravimetrical analysis, differential scanning calorimetry) the complexes 3 react in a thermal solid-state reaction under CO extrusion to give amorphous cross-linked polymers.

The Albedo Distribution of Jovian Trojan Asteroids

We present radiometrically derived V-band geometric albedos and effective radii for 32 Jovian Trojan asteroids, using near-simultaneous mid-infrared and visible observations. We sampled the large end of the group’s size distribution, down to a radius of 25 km, using 14 objects in the L4 swarm and 18 in the L5 swarm. We find that the albedo distribution is much narrower than previously derived from IRAS measurements. The Trojans, for the most part, have very similar albedos. The actual mean and standard deviation of the distribution depend on the average Trojan beaming parameter � . The ‘‘ standard ’’ value of 0.756, which was used for the IRAS analysis, yields a mean albedo of 0.056 � 0.003 and a standard deviation of 0.009. However, a value of � = 0.94, which we found represented our data better, yields 0.041 � 0.002 and a standard deviation of just 0.007. The thermal behavior of the Trojans seems to follow the ‘‘ slow rotator ’’ model, and the thermal inertia itself can be no greater than about half the Moon’s value. The Kolmogorov-Smirnov test was used to compare the Trojans’ albedo distribution with that of cometary nuclei, dead-comet candidates, and outer solar system objects. We find that the Trojan distribution is similar only to the cometary ones, and only if the Trojans’ � � 1. Observations of the binary (617) Patroclus reveal that its albedo is rather typical among the distribution. We have also discovered that (4709) Ennomos has an extremely elevated albedo, about 0.15. This object may have a very unusual thermal behavior or have recently suffered a large impact that excavated the surface down to a layer of highly reflective, pristine ice.

Structure and Phase Transitions of SnP2O7

SnP2O7 is a member of the ZrP2O7 family of materials, several of which show unusual thermal expansion behavior over certain temperature ranges and which show a number of displacive phase transitions on cooling from high temperature. Here we describe the structural properties of SnP2O7 from 100 to 1243 K as determined by X-ray and neutron powder diffraction. These studies reveal that SnP2O7 shows two phase transitions in this temperature range. At room temperature the material has a pseudo-cubic 3×3×3× superstructure. Electron diffraction studies show that the symmetry of this structure is P213 or lower. On warming to ∼560 K it undergoes a phase transition to a structure in which the subcell reflections show a triclinic distortion; above 830 K the subcell reflections show a rhombohedral distortion. Significant hysteresis in cell parameters is observed between heating and cooling. The structure of SnP2O7 is discussed with references to other members of the AM2O7 family of materials.

Reactions of 1,3,5,2,4,6-trichalcogenatristannins and their derivatives with a nitrile oxide: synthesis, structure, and thermal behavior of oxachalcogenazastannoles

2,2,4,4,6,6-Hexamethyl-1,3,5-trithia- and 1,3,5-triselena-2,4,6-tristannins reacted with 2,4,6-tri- t-butylbenzonitrile oxide to give 2,2-dimethyl-1,3-oxathia- and 1,3,5,2-oxaselenazastannoles. The reaction of 2,2,4,4-tetra- t-butyl-1,3,2,4-dithiadistannetane with 2,4,6-tri- t-butylbenzonitrile oxide gave 2,2-di- t-butyl-1,3,5,2-oxathiazastannole. The unusual thermal behavior of the oxachalcogenazastannole is also described.