Normal Melting Point Research Articles

The multiple melting behaviour of immiscible poly(ether ether ketone)/poly(ether diphenyl ether ketone) blend

Poly(ether ether ketone)/poly(ether diphenyl ether ketone) blend containing 30 wt% PEDEK was used to investigate the melting behaviour of immiscible PEEK/PEDEK blends. The results measured from differential scanning calorimetry (d.s.c.) and wide-angle X-ray diffraction (WAXD) showed that immiscible PEEK/PEDEK blends isothermally crystallized at a temperature between Tg and Tm2 (PEEK's normal melting point) from the glassy state also exhibited the multi-melting behaviour like poly(aryl ether ketones) homopolymers. In addition, the low-temperature melting peak was independent of composition of poly(aryl ether ketones) blends and only associated with the thermal history. © 1997 Elsevier Science Ltd.

Effect of ultrasound on molecular mobility in certain crystalline compounds

It is shown that the normal melting point ranges of ammonium alum dodecahydrate, and its potassium analogue, can be changed by ultrasound; under identical conditions the melting characteristics of hexamethylbenzene remain unchanged. NMR investigations suggest that the changes to the melting points of the alums results from acoustically induced motion of the water of crystallization in the crystal lattices.

New group contribution method for estimating properties of pure compounds

AbstractA new group contribution method for the estimation of properties of pure organic compounds is presented. Estimation is performed at two levels: the basic level uses contributions from first‐order groups, while the next higher level uses a small set of second‐order groups having the first‐order groups as building blocks. Thus, the method provides both a first‐order approximation (first‐order group contributions) and a more accurate second‐order prediction (first‐ and second‐order group contributions). This article discusses methods for prediction of normal boiling point, normal melting point, critical pressure, critical temperature, critical volume, standard enthalpy of vaporization at 298 K, standard Gibbs energy, and standard enthalpy of formation at 298 K. The predictions are based exclusively on the molecular structure of the compound, and the method is able to distinguish among isomers. Compared to the currently‐used methods, this technique demonstrates significant improvements in accuracy and applicability.

An equation of state for liquid iron and implications for the Earth's core

An equation of state is presented for liquid iron based on published ultrasonic, thermal expansion, and enthalpy data at 1 bar and on pulse‐heating and shock wave compression and sound speed data up to 10 Mbar. The equation of state parameters, centered at 1 bar and 1811 K (the normal melting point of iron), are density, ρ0 = 7019 kg/m3, isentropic bulk modulus, KS0 = 109.7 GPa, and the first‐and second‐pressure derivatives of KS, K′S0 = 4.66 and K″S0 = −0.043 GPa−1. A parameterization of the Grüneisen parameter γ as a function of density ρ and specific internal energy E is γ = γ0 + γ′(ρ/ρ0)n(E ‐ E0) where γ0 = 1.735, γ′ = −0.130 kg/MJ, n = −1.87, and E0 is the internal energy of the liquid at 1 bar and 1811 K. The model gives the temperature dependence of γ at constant volume as (∂γ/∂T)v|1bar,1811K = −8.4 × 10−5 K−1. The constant volume specific heat of liquid Fe at core conditions is 4.0–4.5 R. The model gives excellent agreement with measured temperatures of Fe under shock compression. Comparison with a preliminary reference Earth model indicates that the light component of the core does not significantly affect the magnitude of the isentropic bulk modulus of liquid Fe but does decrease its pressure derivative by ∼10%. Pure liquid Fe is 3–6% more dense than the inner core, supporting the presence of several percent of light elements in the inner core.

Some evidence on pore sizes in poly(dimethylsiloxane) elastomers having unimodal, bimodal, or trimodal distributions of network chain lengths

Unimodal, bimodal, and trimodal networks were prepared by end linking functionally-terminated chains of poly(dimethylsiloxane). The resulting materials were characterized using a “thermoporometric” technique in which freezing points or melting points are determined for solvent absorbed into the network stuctures. The extent to which the normal melting point is suppressed depends on how much the solvent is constrained within the network pores. Several well-defined melting points were observed for some of the multimodal networks, which is consistent with their unusual distributions of network chain lengths.

Studies on mixed mesomorphism: Determination of latent transition temperature (LTT) by extrapolation

A nonmesogenic component of a binary system mixed with a liquid-crystal component must have the latent ability to exhibit mesomorphism. But this cannot normally be observed because the transition temperature from the amorphous liquid to the mesophase lies below the normal melting point. This latent transition temperature of nonliquid crystal substances are determined by the extrapolation method. Binary systems consisting of structurally similar components, viz.p-methoxyphenyl-′p-methoxycinnamate (A) (117·0–141·5°C) as liquid crystal component and other a nonliquid-crystal component (B) (Schiff’s base), are studied. Extrapolation of the transition curves yield the latent transition temperature of the nonliquid-crystal component. The values of LTT for different Schiff’s bases are in fair agreement with literature values. The transition temperatures of the binary systems as well as the constituent components were observed.

Morphological effects of ballistic impact on fabrics of highly drawn polyethylene fibers

AbstractChanges in crystalline structure of high‐tenacity ultra‐high‐molecular‐weight polyethylene fabric brought on by ballistic impact from a small projectile were determined by X‐ray diffractometry. A suitable X‐ray diffraction method that averages out the fiber orientation effects in the diffraction pattern was used. The Spectra 1000™ polyethylene fabrics were successfully characterized in terms of both the predominant orthorhombic and the minor monoclinic crystal content. Crystallinity values for the undamaged fabric are consistent from sample to sample and show an average orthorhombic fraction of 0.61 and an average monoclinic fraction of 0.04. Fabric damage by the projectile impact results in either an increase in monoclinic fraction, attributed to recrystallization at temperatures nearing the normal polyethylene melting point, or disappearance of monoclinic material as that temperature is exceeded. The latter predominates where ballistic penetration is complete. However, actual melting need not be involved: Transformation to the hexagonal (“rotator”) phase and the disappearance of the monoclinic phase could have occurred rather than true melting. © 1993 John Wiley & Sons, Inc.

A Study on Latent Heat Storage Using a Supercooling Condition of Hydrate. 1st Report, An Entimation of Physical Properties of Hydrate Sodium Acetate Including a Supercooling Condition.

This study focusses on a new type of latent heat storage material (hydrate sodium acetate, CH3 COONa·3H2O, normal melting point of 58°), which stably maintains the supercooling condition with the aid of some additions. This phase-change material can store latent heat (liquid-solid phase) under the supercooling condition from -10°to 58°without the help of thermal insulation for a long time. This article discusses measured results of physical properties of this phase-change material, i. e., thermal conductivity, spcific heat, latent heat, density, kinematic viscosity and crystal growth speed under various temperatures (solid and liquid phases), including the supercooling condition.

Ashcroft‐Langreth Prescription for Effective Core Diameter in Liquids. A Variational Analysis

AbstractThe Ashcroft‐Langreth (AL) ansatz for the effective hard‐sphere diameter in a simple liquid is analysed in the light of Gibbs‐Bogoliubov variational theory for the free energy of the system. It is seen that for a reasonable choice of the pair potential, for example, the Lennard‐Jones potential for liquid Ar and the effective pair potential based on the Ashcroft model for liquid alkalis, Na, K, Rb, and Cs, the prescription is in general valid at or near the normal melting temperatures. However, at the thermodynamic states away from the normal melting point, the ansatz becomes increasingly inaccurate.

Deep drawing self‐reinforced thermoplastic sheet

AbstractThe conventional sheet metal forming technique known as Deep Drawing was used to investigate the formability of self‐reinforced thermoplastic sheets. The materials studied included uniaxially roll‐drawn oriented polypropylene (OPP), cross‐rolled biaxially oriented polypropylene (BOPP), and cross‐ply laminated OPP (LOPP). OPP exhibits poor room temperature formability as determined by its Limiting Drawing Ratio (LDR). Its formability is improved at elevated temperatures, but samples suffer from non‐uniform material flow, temperature sensitivity during forming, and a loss of mechanical properties due to the relaxation of orientation caused by the need for forming temperatures above the normal melting point. Although BOPP attains only moderate Improvements in mechanical properties compared to the machine direction of OPP, it exhibits much better room temperature formability. This difference in drawability between uniaxial and biaxial orientation states is a consequence of the difference in planar anisotropy between these two materials. LOPP has the potential of producing a material with superior performance compared to BOPP while still possessing the desirable formability of BOPP. The formed parts, however, undergo cracking in the outer ply parallel to the orientation direction as a consequence of the OPP small elongation to break in the transverse direction. In addition to forming problems, ordered polypropylene exhibits large shrinkage stresses at elevated temperatures. This may preclude its use in applications requiring a high level of dimensional stability. Classical plasticity theory for metals was appropriately modified to model the radial drawing stress for planar isotropic thermoplastic sheet materials.

Miscibility behavior of ternary lipidphospholipid/water systems

Differential-scanning-calorimetry was applied to study the lyotropic and thermotropic properties of the two ternary systems dimyristoylcephaline (di-(C14:0)-PE)/Palmitic acid (C15COOH)/water (H2O) and dimyristoylcephaline (di-(C14:0)-PE)/palmitic acid methyl ester (C15COOMe)/water (H2O) in dispersions with excess water (50 wt.%). The phase diagrams of both systems showed that the two systems differ in their miscibility behavior. The system di-(C14:0)-PE/C15COOH/H2O is completely miscible in its high-temperature phase. In the low-temperature phase the mixing gap was found within the concentration range of C15COOH and was also indicated by a maximum value of the transition enthalpy of the pseudo-binary mixtures. In the pseudo-binary system di-(C14:0)-PC/C15COOMe/H2O, the tendency towards demixing is much more pronounced. It was observed that the incorporated C15COOMe melted above its normal melting point, but below the transition temperature of di(C14:0)-PE/H2O system; therefore, the phase transition started at lower temperature. In the low-temperature phase, both lipids are partially miscible. The demixing range of the phase diagram lies within the concentration region of C15COOMe. Up to the mole fraction ofXC15COOMe=0.43, C15COOMe can be incorporated into theLβ-phase of the system di-(C14:0)-PE/H2O.

The effect of thermal history on the rheology and texture of thermotropic liquid crystalline polymers

AbstractThis paper is concerned with the effect of thermal history on the rheology of three liquid crystal copolymers. The polymers were heated to temperatures above their melting points and then cooled down. During the cooling cycle, the dynamic mechanical properties were monitored. It was found that these properties remained unchanged at temperatures as low as 30°C below the normal melting points for two copolyesters of 60 mole percent p‐hydroxybenzoic acid (PHB) and 40 mole percent poly(ethylene terephthalate) (PET) (60‐40 PHB/PET) and 80 mole percent PHB and 20 mole percent PET (80‐20 PHB/PET). For a copolymer of PHB and 2,6‐dihydroxynaphthaic acid, there was a gradual increase in the properties with decreasing temperature. However, at a critical temperature all three systems exhibit a sudden increase In dynamic mechanical properties. The kinetics of solidification were also monitored, and it was found that at temperatures well below the melting point, it took 4 to 6 min before the solidification process impeded flow. Extrusion studies on these materials were also carried out, and it was observed that in this supercooled state, the polymers exhibited significant die swell. The samples also exhibited a fibrous texture and were more oriented than when extruded isothermally above the melting point.

Temperature dependence of liquid density: The choice of a reference state

Some reduced equations of state where the scaling parameters are different from the parameters for the liquid-vapor critical point were studied. The problem is pertinent for many compounds for which the critical point cannot be reached. First, calculations were made for the equation of Shelomentsev and Bolotin, both in its original form and in our modification where the scaling parameters pertain to both the normal melting point and the normal boiling point. Good results were obtained for saturated liquid densities of normal paraffins, but the inconvenience of dealing at the same time with two physical reference states remains. Second, a modified Guggenheim density equation was used, but with the parameters at the normal boiling point instead of at the critical point. Again for n-paraffins, good results were obtained both for density and for isobaric expansivity. Two characteristic parameters for each material are needed. Two ‘universal’ parameters, the same for all paraffins, can be used also, but the predictive accuracy is somewhat lower.

Phonon populations during pulsed laser annealing

A summary is presented of pulsed Raman and several other time-resolved experiments and the information they provide on the dynamics of electron-phonon and phonon-phonon interactions under pulsed laser annelaing (PLA) conditions. A number of recent cw Raman studies provide a much improved basis for understanding the consequences on Raman spectra of temperature-dependent resonance effects, high carrier density effects, phonon anharmonicity, and strain effects. New pulsed Raman studies, under PLA conditions, of the shift and shape of the first-order line and of the full first- and second-order spectra are discussed. Emphasis is placed on explaining the results of time-resolved Raman experiments in a framework consistent with other types of experiments. The Raman data appear to be compatible with the existence of a fluid phase followed by a hot solid near the normal melting point of Si. The data, however, indicate the presence of additional broadening of the first-order Raman line probably due to carrier-phonon interactions, and cooling rates which appear to be higher than predicted by thermal models.

Influence of interdiffusion with substrate on spreading of molten Au–18Ni braze alloy

AbstractArrest in the spreading of Au–18Ni braze alloy on a 12%Cr steel substrate has been investigated. Observations reported previously show that this alloy penetrates the oxide surface layer of the substrate at temperatures above its normal melting point to form a blister, but that spreading then ceases. It is shown here that the radius of the blister increases if the temperature of the substrate is increased until a stable radius is again achieved. Analyses show a correlation between the arrest in spreading and the composition of the spreading alloy, which suggests that interdiffusion of alloying elements between substrate and braze, leading to an elevation of melting point, is responsible for the behaviour.

ChemInform Abstract: RELATIONS BETWEEN NORMAL BOILING POINT AND MELTING POINT FOR SIMPLE HALIDES AND OXIDES

Chemischer InformationsdienstVolume 14, Issue 33 Physical Inorganic Chemistry ChemInform Abstract: RELATIONS BETWEEN NORMAL BOILING POINT AND MELTING POINT FOR SIMPLE HALIDES AND OXIDES L. G. VAN UITERT, L. G. VAN UITERTSearch for more papers by this author L. G. VAN UITERT, L. G. VAN UITERTSearch for more papers by this author First published: August 16, 1983 https://doi.org/10.1002/chin.198333020AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue33August 16, 1983 RelatedInformation

Impurity effects on polymorphism in GeO2 by DTA

Polymorphism in GeO2 is of considerable interest from the point of view of chemical bonding. It has been reported in the literature that the metastable (hexagonal, h) to stable (tetragonal, t) phase transformation below about 1200 K was not feasible in the absence of impurities. A systematic DTA study of the effects of Li+, Na+ and K+ impurities on the thermodynamic sequence of phase transitions in GeO2 (t) is presented in this paper. The t form of GeO2, relatively free from alkali metal impurities, was obtained by autoclaving the h form in a silica tube at 623 K under a steam pressure of 10 to 15 MPa. However, the t form so obtained (by autoclaving in silica) was found to exhibit metastable melting nearly 30° below the normal melting point of the high temperature h modification. The latent heat of this metastable melting transition derived from the DTA data is reported here for the first time and it is found to be approximately equal to the sum of the latent heats of t to h transition and the normal melting transformation of the h form. The effect of alkali metal ions on the kinetics of melting transition of the h form is also discussed.

Coincidence of the thermal melting points of crystalline and amorphous Si and coincidence of thresholds for pulsed beam annealing of crystalline and amorphous Si and GaAs

In spite of the excess enthalpy of amorphism, neither the normal thermal melting point of Si nor the threshold absorbed energy density for pulsed electron and pulsed laser beam annealing of Si and GaAs is significantly dependent on whether the sample is initially amorphous or crystalline. However, the duration of the period of high optical reflectivity and the magnitude of atomic diffusion during the annealing event are much enhanced near threshold if the sample is initially amorphous. Here these facts are explained in terms of conventional theory of covalent bonding and of the normal thermal melting process and in terms of the “Plasma Annealing” theory of pulsed beam annealing.

Thermal Conductivity, Heat Capacity and Phase Diagram of Tetrahydrofuran Under Pressure

Abstract The thermal conductivity, Λ, and the heat capacity per unit volume, pcp , have been measured for tetrahydrofuran (THF) using the transient hot-wire method in the temperature range 130-300 K and at pressures up to 2 GPa. Most of the data relate to the single solid phase which was found to exist over these ranges of the variables. The liquidus curve was determined roughly up to the maximum pressure, and we estimated the density of the solid phase at the normal melting point using the Clausius-Clapeyron relation. We inferred from the measurements that solid THF was a normal crystal phase in which three-phonon umklapp processes provided the only significant source of thermal resistivity. There was evidence for the effect of thermal expansion on Λ, and this effect decreased under pressure.

Magnetic susceptibility of metallic and nonmetallic expanded fluid cesium

In this paper the first magnetic-susceptibility results for a fluid metal are reported, which cover a wide range of expansion between the normal melting point and conditions near the critical point. Measurements have been performed for fluid Cs at saturation conditions up to 1680\ifmmode^\circ\else\textdegree\fi{}C and 98 bar, that is 70\ifmmode^\circ\else\textdegree\fi{}C below the critical temperature. In the expanded liquid state, the mass susceptibility first decreases slightly, followed by a strong rise with increasing expansion by almost a factor of 5. A pronounced paramagnetic maximum is observed near 1600\ifmmode^\circ\else\textdegree\fi{}C, corresponding to about double the critical density and a dc conductivity of about ${10}^{3}$ ${\ensuremath{\Omega}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ This susceptibility enhancement indicates that the metal-nonmetal transition in fluid Cs might be of the Mott-Hubbard type. In the nonmetallic-dense-vapor phase, the susceptibility data give direct evidence for the existence of a high amount of diamagnetic molecular associations, like ${\mathrm{Cs}}_{2}$ molecules.