Search results for "Phase Transition"
showing 10 items of 1281 documents
Low temperature measurements by infrared spectroscopy in $CoFe_2O_4$ ceramic
2012
In this paper results of new far-infrared and middle-infrared measurements (wavenumber range of 4000cm-1 - 100cm-1) in the range of the temperature from 300K to 8K of the CoFe2O4 ceramic are presented. The bands positions and their shapes are the same in the wide temperature range. The quality of the sample was investigated by X-ray, EDS and EPMA studies. The CoFe2O4 reveals the cubic structure (Fd-3m) in the temperature range from 85K to 360 K without any traces of distortion. On the current level of knowledge the polycrystalline CoFe2O4 does not exhibit phase transition in the temperature range from 8 K to 300 K.
The plastic crystalline A15 phase of dimethylaminoalane, [N(CH3)2–AlH2]3
2016
A plastic crystalline phase of dimethylaminoalane has been discovered at T > 332 K. The phase transitions solid - plastic phase - liquid are fully reversible. The plastic crystalline phase exhibits a cubic unit cell, space group Pm3[combining macron]n, in which the dimethylaminoalane molecules rotate and adopt a structural arrangement reminiscent of the A15 phase.
Microactuators from a main-chain liquid crystalline elastomer via thiol–ene “click” chemistry
2013
Recently it has been described that liquid crystalline elastomer (LCE) particles of the side-chain type can be prepared in microfluidic devices. Here we present the preparation of micrometer-sized LCE particles of the main-chain type by thiol–ene chemistry. The LCE particles are UV-crosslinked via thiol–ene click chemistry of the nematic monomer, carrying terminal thiol and ene groups, and non-mesogenic tetrathiol and tetraene crosslinkers. The preparation of the LCE particles with a microfluidic device by a continuous “on the fly” technique allows their fast processing with an irradiation time of less than 2 seconds. The resulting particles undergo a temperature-driven volume change up to …
Confined crystallization of a HKUST-1 metal–organic framework within mesostructured silica with enhanced structural resistance towards water
2017
A HKUST-1 metal–organic framework was crystallized in the NH2-modified mesostructured silica FDU-12 in order to improve its structural stability upon water exposure. In-depth structural characterization studies of the designed composite confirmed successful formation of the MOF phase within the ordered spherical mesopores of the silica matrix. In spite of the confinement within the cavities, MOF exhibits full accessibility for the adsorbed gas molecules. In contrast to the bulk HKUST-1, which undergoes slow phase transition in a humid environment, the structural integrity of the HKUST-1 in the humid-protective matrix remains unchanged even after immersion and stirring in water at elevated t…
The impact of thermophysical properties and hysteresis effects on the energy performance simulation of PCM wallboards: Experimental studies, modellin…
2020
Abstract This paper presents a combined experimental and numerical procedure, developed to test the thermophysical behaviour of a real scale PCM wallboard, aiming at providing reliable data for the validation of building energy performance simulation tools. Data obtained from two experimental tests, conducted on real building elements integrating PCM undergoing complete and incomplete phase change, are considered for assessing the impact of thermal properties and hysteresis. A comprehensive comparative numerical analysis, performed by means of an in-house developed simulation tool, called DETECt, is carried out to investigate the reliability of several modelling and simulation approaches av…
Phase transition systematics in BiVO4 by means of high-pressure–high-temperature Raman experiments
2018
We report here high-pressure--high-temperature Raman experiments performed on ${\text{BiVO}}_{4}$. We characterized the fergusonite and scheelite phases (powder and single crystal samples) and the zircon polymorph (nanopowder). The experimental results are supported by ab initio calculations, which, in addition, provide the vibrational patterns. The temperature and pressure behavior of the fergusonite lattice modes reflects the distortions associated with the ferroelastic instability. The linear coefficients of the zircon phase are in sharp contrast to the behavior observed in the fergusonite phase. The boundary of the fergusonite-to-scheelite second-order phase transition is given by ${T}_…
Comment on “Molybdenum sound velocity and shear modulus softening under shock compression”
2015
In this Comment we discuss recent results presented by Nguyen et al. on shock compressed molybdenum up to 438 GPa [Phys. Rev. B 89, 174109 (2014)]. The aim of Nguyen's article is to show that there is no phase transition near 210 GPa. We propose instead an interpretation of their data that this material shows the onset of partial melting along the Hugoniot at $240(20)\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$, which is evident from abrupt changes in the pressure dependence of the shear modulus. This interpretation may solve the significant controversy in the melting slopes derived from shock and static experiments.
Simplified Monte Carlo simulations of point defects during industrial silicon crystal growth
2004
Abstract The paper proposes Monte-Carlo method-based 2D and 3D models of vacancies and interstitials in a cubic crystal. The model exploits the concept of lattice gas with covalent bounds between neighbour nodes. Two lattices shifted by half-period serve as nodes for atoms of the main crystal and interstitials. Distribution of particles between both lattices characterizes the entropy of the crystal. Successfully chosen interaction energies between main and sub-lattices allows the authors to detect a phase transition solid–liquid as well as to study the production of crystal defects/their agglomeration as a function of cooling/heating rate. Although the introduced 3D modification of the mode…
Structural, thermal, dielectric and ferroelectric properties of Na0.5K0.5NbO3and Na0.5K0.5NbO3+0.5mol%MnO2ceramics
2014
Lead-free Na0.5K0.5NbO3 and Na0.5K0.5NbO3+0.5mol%MnO2 ceramics were fabricated by solid state hot pressing sintering process. The phase structure and thermal, dielectric and ferroelectric properties of these ceramics were investigated. X-ray measurements showed that all samples have a single perovskite structure and possess orthorhombic–tetragonal and tetragonal–cubic phase transitions. Sequence of phase transitions was confirmed by differential scanning calorimetry (DSC) and dielectric measurements. Obtained results showed that optimal temperature sintering of Na0.5K0.5 NbO3+0.5mol%MnO2 ceramics is 1100 °C. The results show that investigated ceramics are one of the promising materials as e…
Phase Transitions in Prequenched Mesomorphic Isotactic Polypropylene during Heating and Annealing Processes As Revealed by Simultaneous Synchrotron S…
2011
Time-resolved simultaneous synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) technique was used to investigate the phase transitions in prequenched mesomorphic isotactic polypropylene (iPP) samples during heating and annealing processes, respectively. For the heating process, it is shown that the mesomorphic-to-monoclinic phase transition is relatively faster for the mesomorphic iPP sample obtained with the high quenching rate than that with the low quenching rate. For the former, the stability of α-monoclinic crystals formed during heating is relatively higher. As for the annealing process, WAXD and SAXS data illustrate that the higher the annealing te…