Sound Velocity in Liquid Binary Alloys as Calculated via the Percus-Yevick Liquid Phonon Dispersion Relation

Abstract

In this note, we utilize the recently calculatd long wavelength limit of the “liquid virtual crystal” model of binary alloy liquid structure factor at the melting temperature, ST_M ^AB (0), to estimate the long-volume binary liquid alloys. We compare the calculate sound velocities to the available experimental sound velocities in these liquid binary alloys and find reasonable agreement.     

Virtual Crystal Model of Melting and the Structure Factor of Liquid Alloys

Abstract

In this paper, we extend the theory of melting entropy of metals, of Omini, based on the Percus-Yevick collective coordinate theory of liquids, to binary liquid alloys. We reformalate Omini's use of the Percus-Yevick theory to include binary liquid alloys and calculate the long wavelength limit of the binary liquid alloy structure factor as a function of solute concentration for the systems: Li-Na, K-Rb. Rb-Cs, Al-Zn, Zn-Ca and AI-Ga which are the most nearly equi-valent and equi-volumeatom pairs Omini worked with.     

Melting behaviour of a series of diamides

The melting behaviour of diamides of general formula (n — C_pH_2p+1)CONH-(CH₂)_qNHCO(n — C_pH_2p+1) has been investigated by calorimetric, dilatometric and IR techniques. The conformational contribution to the melting entropy, calculated from the hypothesis of complete conformational freedom of the molecules at the melting point, has been compared with the experimental data. The higher melting points of the diamides, as compared with those of the linear hydrocarbons having the same number of conformationally flexible chain bonds, are attributed to a reduction of conformational freedom of the chain segments in the liquid state (caused by the large fraction of hydrogen bonds maintained in the melt).     

Effect of Molecular Mass on the Melting Temperature,Enthalpy and Entropy of Hydroxy-Terminated PEO

This paper studies the effect of molecular mass on the melting temperature, enthalpy and entropy of hydroxy-terminated poly(ethylene oxide) (PEO). It aims to correlate the thermal behaviour of PEO polymers and their variation of molecular mass (MW). Samples ranging from 1500 to 200,000 isothermally treated at 373 K during 10 min, were investigated using DSC and Hot Stage Microscopy (HSM). On the basis of DSC and HSM results, melting temperatures were determined, and melting enthalpies and entropies were calculated. Considering the melting temperatures, it was found that the maximum or critical value of MW was found around 4000, and then these remain almost constant. This behaviour was interpreted assuming that lower MW fractions (MW<4000) crystallize in the form of extended chains and higher MW fractions (MW>4000), as folded chains. The melting enthalpies showed a scattering effect at least up to MW 35,000. It was difficult to obtain any relationship between melting enthalpies in J g^–1 and MW. These variations seem to be of statistical nature. Corrected enthalpy data on a molar basis (kJ mol^–1) exhibited a linear relationship with MW. Considering the solid—liquid equilibrium, the melting entropies (in kJ mol^–1) were calculated. These values were more negative as compared with molar enthalpy increases. It was explained because the changes in melting temperatures are much smaller than those observed in the enthalpy values. Linear relationship between enthalpies andentropies as a function of MW was deduced.This revised version was published online in November 2005 with corrections to the Cover Date.     

Melting curve and fluid equation of state of carbon dioxide at high pressure and high temperature

The melting curve and fluid equation of state of carbon dioxide have been determined under high pressure in a resistively heated diamond anvil cell. The melting line was determined from room temperature up to 11.1+/-0.1 GPa and 800+/-5 K by visual observation of the solid-fluid equilibrium and in situ measurements of pressure and temperature. Raman spectroscopy was used to identify the solid phase in equilibrium with the melt, showing that solid I is the stable phase along the melting curve in the probed range. Interferometric and Brillouin scattering experiments were conducted to determine the refractive index and sound velocity of the fluid phase. A dispersion of the sound velocity between ultrasonic and Brillouin frequencies is evidenced and could be reproduced by postulating the presence of a thermal relaxation process. The Brillouin sound velocities were then transformed to thermodynamic values in order to calculate the equation of state of fluid CO2. An analytic formulation of the density with respect to pressure and temperature is proposed, suitable in the P-T range of 0.1-8 GPa and 300-700 K and accurate within 2%. Our results show that the fluid above 500 K is less compressible than predicted from various phenomenological models.     

Intraparticle Flow and Plate Height Effects in Liquid Chromatography Stationary Phases

Abstract

Velocity independent plate heights were apparently first recognized for hydrodynamic chromatography columns, packed with nonporous, 115 micron glass beads which were run at reduced mobile phase velocities of 10 to 10,000. Hydrodynamic chromatography separates based on the tendency of small molecules (or particles) to associate with slower moving fluid streamlines near the surfaces of particles, compared to larger molecules which seek faster streamlines. Consequently, the larger molecules elute first. Velocity independent plate heights in liquid chromatography have also been observed for nonadsorbed solutes in paniculate and fibrous stationary phases. These stationary phases have pores which exceed 10^?4 to 10^?5 cm in dimension. The flat plate height is attributed to flow in the channels formed by these large intraparticle spaces. The development of plate height expressions which represent dispersion at interstitial velocities above 10 cm/min are discussed. Explanations of the uncoupling of dispersion from eluent flow rate in continuous stationary phases, membranes, and gigaporous particles is shown to have their origins in the studies of distribution of particles and molecules in hydrodynamic chromatography columns, and to be adequately described by modifications of the van Deemter equation.     

High Pressure Phase Stability of Ti with Self-consistent ab initio Lattice Dynamics Approach

The traditional quasiharmonic approximation cannot predict the phase diagram of Ti accurately, due to the well-known soften phonon modes of the β-Ti. By means of self-consistent ab initio lattice dynamics (SCAILD) method, in which the effects of phonon-phonon interactions are considered, the phonon dispersion relations at finite temperature for Ti are calculated. From the phonon dispersions, we extrapolat the acoustic velocities and harmonic elastic constants. The dynamical stable regions and phase diagram of Ti are also predicted successfully. The results show that SCAILD method can be designed to work for strongly anharmonic systems where the QHA fails.     

Reduction Mechanism of Transition Metal Oxide Particles in Thermally Induced Nanobubbles during Pulsed Laser Melting in Ethanol

Pulsed laser melting in liquid (PLML) is a technique to fabricate spherical submicrometer particles (SMPs) wherein nanosecond pulsed laser (several tens to several hundreds of mJ pulse⁻¹ cm⁻²) irradiates raw particles dispersed in liquid. Raw particles are transiently heated above the melting point to form spherical particles, which enables pulsed heating of surrounding liquid to form thermally induced bubbles by liquid vaporization. These transient bubbles play an important role as a thermal barrier to rapidly heat the particle. Reduced SMPs are generated from raw metal-oxide nanoparticles by PLML process in ethanol. This reduction cannot be explained by high-temperature thermal decomposition, but by mediation of molecules decomposed from ethanol. Computational simulations of ethanol decomposition by pulsed heating for 100 ns at the temperature 1000–4000 K revealed that ethylene is generated as the main product. Gibbs free energies of oxide reduction reactions mediated by ethylene greatly decreased compared to those without ethylene mediation. This explanation can be applied to reductive SMP formation from various transition metal oxides by PLML.     

Dynamic Odd–Even Effect in Liquid n‐Alkanes near Their Melting Points

n‐Alkanes are the textbook examples of the odd–even effect: The difference in the periodic packing of odd‐ and even‐numbered n‐alkane solids results in odd–even variation of their melting points. However, in the liquid state, in which this packing difference is not obvious, it seems natural to assume that the odd–even effect does not exist, as supported by the monotonic dependence of the boiling points of n‐alkanes on the chain length. Herein, we report a surprising odd–even effect in the translational diffusional dynamic properties of n‐alkanes in their liquid states. To measure the dynamics of the molecules, we performed quasi‐elastic neutron scattering measurements near their melting points. We found that odd‐numbered n‐alkanes exhibit up to 30 times slower dynamics than even‐numbered n‐alkanes near their respective melting points. Our results suggest that, although n‐alkanes are the simplest hydrocarbons, their dynamic properties are extremely sensitive to the number of carbon atoms.     

Electronic Effects of para‐Substitution on the Melting Points of TAAILs

Owing to numerous new applications, the interest in “task‐specific” ionic liquids increased significantly over the last decade. But, unfortunately, the imidazolium‐based ionic liquids (by far the most frequently used cations) have serious limitations when it comes to modifications of their properties. The new generation of ionic liquids, called tunable aryl–alkyl ionic liquids (TAAILs), replaces one of the two alkyl chains on the imidazolium ring with an aryl ring which allows a large degree of functionalization. Inductive, mesomeric, and steric effects as well as potentially also π π and π π⁺ interactions provide a wide range of possibilities to tune this new class of ILs. We investigated the influence of electron‐withdrawing and ‐donating substituents at the para‐position of the aryl ring (NO₂, Cl, Br, EtO(CO), H, Me, OEt, OMe) by studying the changes in the melting points of the corresponding bromide and bis(trifluoromethanesulfonyl)imide, (N(Tf)₂⁻), salts. In addition, we calculated (B3LYP/6‐311++G(d,p)) the different charge distributions of substituted 1‐aryl‐3‐propyl‐imidazolium cations to understand the experimentally observed effects. The results indicated that the presence of electron‐donating and ‐withdrawing groups leads to strong polarization effects in the cations.     

The Melting Process of Acetylsalicylic Acid Single Crystals

Crystallisation is generally regarded as a nucleation — growth mechanism of a solid phase and often studied using thermo chemical methods. The present work postulates an analogy to melting processes, looking at melting as nucleation — growth of a liquid phase. The melting process of acetylsalicylic acid single crystals was investigated by DSC measurements under isothermal conditions. The fraction of material molten after a certain time period, α(t), was calculated by integrating the DSC curves. The resulting kinetic curves were fitted using the Avrami-Erofeev equation: –ln(1–α)=kt ⁿ, where parameter n was analysed. According to established methods, functions I('2')=[t('2')]/[t('2')+t('3')]100% and I('3')=[t('3')]/[t('3')+t('2')]100% were introduced, where t('2') and t('3') is the absolute time of consumption two- and three-dimension nuclei growth, respectively. Applying correlation analysis, relationships between two- or three-dimensional growth and the independent variables describing the single crystals (for strictly definite trajectories into the space of sizes) were found. Particular correlations were:a) Two-dimensional growth is a function of the total surface area of the crystal, S, and of the surface area of the (ac)-face, S _ac; b) Three-dimensional growth is a function of S/M (where M is the mass of the single crystal). It is also a function of S _ac/M and of S. The obtained experimental data are explained by the ‘layer’ structure of crystals of acetylsalicylic acid. This revised version was published online in August 2006 with corrections to the Cover Date.     

Surface tension of pure liquid lanthanide and early actinide metals

A systematic theoretical study of the surface tension of liquid rare earth metals and early actinides is performed. An equation, based on the theoretical considerations suggested by Eyring, enables one to calculate the surface tension of elementary substances in a wide temperature range from melting to boiling points. The results of temperature-dependent surface tension calculations of a pure liquid terbium (1629–1880?K) are fitted as γ?=?845?0.1 (T???T _m) (mJ?m²), where the surface tension decreases linearly with temperature. The surface tension was also calculated, at melting points, for all the liquid rare earth metals from La to Lu and for the first six metals of the actinide series from Ac to Pu. It is observed that the lanthanides may be divided into three groups in accordance with their electronic structure. Mostly, the calculated results agree well with available experimental data.     

Kalidoss—Jacobson Free Length Theory Applied to Binary Liquid Mixtures of CCI4+Toluene/Aniline/oCresol m-cresol p-Cresol

Abstract

Ultrasonic velocities and intermolecular free lengths in binary liquid mixtures of CC4 with toluene, aniline, o-cresol, m-cresol and p-cresol have been calculated theoretically, at different compositions and at temperature 298 K, based on Free Length Theory as revised recently by Kalidoss. It is observed that there is a close agreement of calculated velocities with experimental ones. The shape and thermostatic state picture built up in this formulation could be considered as a good representation of molecular state.     

Melting and crystallization DSC profiles of milk fat depending on selected factors

The aim of this study was to test selected factors, such as sample preparation and measurement procedure, potentially influencing repeatability of DSC analysis of milk fat melting and crystallization. The study investigated the effect of such factors as scanning rate, type of sample pans, method of butter dehydration, and final temperature in the cooling experiment. Based on recorded results, it was observed that cooling rate has a considerable effect on temperature, enthalpy, and height of peaks in the process of milk fat crystallization, as well as peak height and enthalpy in the melting process. By contrast, in the melting process no significant differences were observed in all measured temperatures in the range of heating rate of 2–20 °C min^?1 (p > 0.05). No statistically significant effect on thermodynamic parameters was found for sample pan type, the applied butter dehydration method and various final cooling temperatures (?60, ?50, and ?40 °C) either in the melting or crystallization processes. Only temperature of the second peak (T _c2) in the crystallization process constituted an exception in this respect, with significant differences (p ≤ 0.05) being recorded depending on the applied pan and dehydration method. With regard to the dehydration method, for the extraction and centrifugation methods the first peak forming during crystallization was characterized by high instability, manifested by various peak shape. Generally, it was found that the analysis of the melting and crystallization processes in milk fat, despite its complex composition, is characterized by high repeatability. Mean values of RSD calculated from all the experiments were very low, i.e., 1.8 % for the temperature in the melting process and 1.5 % in crystallization, 0.9 % for melting enthalpy, and 3.2 % for crystallization enthalpy, whereas for peak heights in melting it was 2.9 % and for crystallization it was 9.3 %, respectively.     

Molecular dynamics study of the ferroelectric liquid crystal CI IPNOC by proton spin-lattice relaxation

Abstract

Proton spin-lattice relaxation studies were carried out in the S_A and S*_C phases of the liquid crystal CI IPNOC using both conventional and fast field cycling NMR techniques. T ₁ dispersion curves were obtained at two different temperatures for each mesophase covering frequencies from 10² to 3 × 10⁸ Hz. In both mesophases the T ₁ data can be described assuming the presence of three different relaxation mechanisms, namely local molecular rotations, molecular self-diffusion and collective motions. The self-diffusion constant D ₁ was evaluated for several temperatures and the activation energy associated with the diffusion process was obtained. The expected contribution of the soft-mode for the spin-lattice relaxation could not be separated from the contribution of other collective motions. The correlation times associated with the rotations around the molecular long axis and with the fluctuations of this axis were evaluated for both the S_A and the S*_C phases.     

Melting points of lanthanide trichlorides

The melting temperatures and absolute values of melting enthalpies of lanthanide trichlorides decrease from LaCl₃to TbCl₃and then increase to LuCl₃. The preceding decrease cannot be explained by the lattice energies of the trichlorides, since they increase continuously from the lanthanum to the lutetium compounds. However, it may be attributed to the structural features of the liquid state. The liquids near the melting points consist of clusters of complex units, which become larger with decreasing radii of the metal ions. To prove this assumption additional quantitative investigations are necessary.     

Melting of PbBr2: A DSC investigation

The melting of PbBr₂ in sealed crucibles was investigated by means of DSC. Three factors were considered to affect melting point: i) impurities, ii) the bromine pressure over the PbBr₂, and iii) photolysis. Both crystals and powders were investigated. The peak of the melting changed after sample grinding. The bromine pressure over the PbBr₂ was found to cause a significant error in the determination of the melting point.Lead bromide melts at 370.6±0.2°C. The heat of melting is 42.9±1.8 J g^–1.This revised version was published online in November 2005 with corrections to the Cover Date.     

Reversible Melting of Thermally Fractionated Polyethylene

Different grades of linear low density polyethylenes (LLDPEs) have been quenched cooled step-wise and crystallised isothermally at (a series of increasing) temperatures in a DSC (thermal fractionated samples). These samples have been investigated by temperature modulated DSC (MDSC). The heat flow curves of the thermal fractionated materials were compared with those obtained from samples crystallised at a relatively slow cooling rate of 2 K min^-1(standard samples). The melting enthalpy obtained from the total heat flow of the thermal fractionated samples was 0-10 J g^-1higher than those of standard samples. The melting enthalpy obtained from the reversing heat flows was 13-31 J g^-1lower in the thermal fractionated samples than in the standard samples. The ratio of the reversing melting enthalpy to the total melting enthalpy increased with decreasing density of the PE. The melting temperature of the endotherms formed by the step-wise cooling was 9 K higher than the crystallisation temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of syneresis in thin foam layers by creating pressure drops in the liquid phase

The method of creating pressure drops in liquid phases of foams (foam pressure drop technique) is employed to study the influence of Plateau-Gibbs border radius and surface viscosity on the velocity of liquid flows through foams. Sodium dodecyl sulfate-stabilized foams with Newtonian black films and foams stabilized with 9,6-ethoxylated nonylphenol (Triton X-10 0) are investigated. A method is developed for determining the velocities of nonstationary syneresis in local layers of foams. The measured flow velocities correspond to those calculated through the Nguyen equation for sodium dodecyl sulfate solution foams with constant curvature radii and for local layers of foams at curvature radii varying in the range of 20–80 fum and variable pressure drops. In Triton X-100 solution foams, experimentally measured syneresis velocities are higher than those calculated by the Lemlich and Nguyen equations but agree with the velocities calculated via the Koehler equation at permeability K ₀ ⁿ varying in the range of 0.5 × 10^-3-2 × 10^-3 under the assumption that the key factor is the hydrodynamic resistance in foam knots.