True Melting Research Articles

Fusibility of Poly(N-carboxy α-Amino Acid Anhydride) Materials Treated under Pressure-Heat Conditions and in Vitro-in Vivo Degradation of Hot-Pressed Materials

Abstract Powdered poly(N-carboxy α-amino acid anhydride) materials were treated at temperatures of 50, 100, 150, and 200°C under a pressure of 150 kg/cm2. A number of hot-pressed materials showed simultaneous fusion and contraction in volume. The fusion temperature of the hot-pressed materials was generally lower than the true melting point of the powdered materials at atmospheric pressure (determined with a Differential Scanning Calorimeter). The hot-pressed materials had high rigidity and transparency. The in vitro-in vivo degradation of hot-pressed materials was also investigated. The homo- and copoly(α-amino acid) materials used in this study were scarcely degraded, though debenzylated t e rpolymers such as β-benzyl-L-aspartate/aspartic acid/L-leucine and γ -benzyl-L- glutamate/glutamic acid/L - leucine we re significantly degraded in both the in vitro and in vivo experiments. It was found that the in vivo degradation profile of hot-pressed terpolymer materials corresponds relatively well to degradati...

Possibility of predicting the existence of a complex compound in the NaF-Na2SO4 system

A method of thermodynamic prediction of the existence of a complex compound in the NaF-Na2SO4 binary system is described. On the basis of the knowledge of a part of liquids drawn in the vicinity of NaF melting point and coordinates of eutectic point, the conclusion was made that there exists the complex compound Na3FSO4 in the system. Its true and hypothetic melting points and the degree of its thermal dissociation were calculated. Further, the probable coordinates of a eutectic point in the Na3FSO4-Na2SO4 subsystem were found out. The calculated results were confronted with experimental determination; the agreement is very good. The method described can be useful for experimental studies of binary phase diagrams.

Possibilités thermiques à la fin de l'époque néolithique, expériences sur la cuisson de la poterie sur le traitement des minerais, sur les procédés de cémentation atomique des métaux avec exemples d'effet kirkendall-smigelskas et de surimposition de structure par forgeage

The exact measurement of the firing temperatures of Neolithic and Chalcolitic pottery doesnnot depass a limit of about 880°. Experimental tests in the laboratory and factory upon certain copper ores utilised at the beginning of the "Age of Metals" have shown the process for making small metallic objects without for true melting and pouring into a mould. The author experimented with cementation of copper by arsenic, tin and zinc and studied the diffusion of these elements in copper with the production of a "Kirkendall-Smigelskas effect". He also studied the surimposed structure arising from the forging of copper alloys. For the observation of these phenominanthe "Maréchal -Ooucet heating platen" is of advantage.

Etude du comportement thermique de la poly(pivalolactone) par diffraction des rayons-x aux petits angles et par calorimetrie dynamique

Poly(α,α-dimethyl-β-propiolactone) (PPL), known as poly(pivalolactone), has been studied by differential scanning calorimetry (DSC) and small-angle X-ray diffraction (SAXR). DSC measurements indicate the presence of two melting endotherms. Peak 1 and Peak 2, the latter at lower temperatures. Peak 1 is relatively unaffected by the crystallization temperature and its relative intensity decreases with heating rate. Peak 2 is greatly influenced by the crystallization temperature of the sample and its relative intensity increases with heating rate. Peak 2 is associated with the true melting of the PPL samples and Peak 1 with a recrystallization process during the heating cycle. SAXR long periods increase with crystallization and annealing temperatures. Similar increases in density, in melting temperature, in lamella thickness, and in degree of crystallinity have been observed. These results lead to a thermodynamic melting temperature of 268 ± 3 for PPL, and to interfacial free energies of, respectively. 13 × 10 −7 J cm −2 and (43 ± 4) × 10 −7 J cm −2 for the lateral surface and the fold surface of the PPL crystal.

Evidence against a crystal instability in melting

Since Bern's original suggestion1, melting has frequently been attributed to a crystal instability although its one-phase approach has been objected to. Using a molecular dynamics computation of the behaviour of a 336-atom Lennard–Jones system, and exploiting the inherent limitations on model size and simulation time, we have found a crystal–liquid instability. It falls outside the density interval for thermodynamic melting, however, and we conclude that it is not true melting. We have also discovered an isothermal liquid–glass transition on compressing the liquid, and this occurs at a density within the transition interval. The results reported here are consistent with the first-order nature of melting and provide new insight into the difference between the crystalline and liquid states.

A binary solid-liquid phase diagram experiment including determination of purity, enthalpy of fusion, and true melting point

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA binary solid-liquid phase diagram experiment including determination of purity, enthalpy of fusion, and true melting pointEdwin F. Meyer and Joseph A. Meyer Cite this: J. Chem. Educ. 1980, 57, 11, 831Publication Date (Print):November 1, 1980Publication History Received3 August 2009Published online1 November 1980Published inissue 1 November 1980https://doi.org/10.1021/ed057p831RIGHTS & PERMISSIONSArticle Views947Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

The crystallization and melting of selenium

Trigonal selenium single crystals were grown isothermally and in a temperature gradient from the vapor phase. Kinetic studies of crystallization and melting, thermal analysis (DTA, DSC), X-ray diffraction, and optical and electron microscopy were carried out. The true melting point of trigonal selenium was determined to be 494.2±0.1 K, the heat and entropy of fusion were found to be 6.20 kJ/mol Se and 12.55 J/(K mol Se) respectively. The mechanism of crystal growth from the gas phase is shown to involve crystallization polymerization and occurs up to temperatures close to the melting point, while melt crystallization starts only at considerably lower temperatures due to the need of molecular nucleation of the long chain molecules. The melting was shown to be an activated process. A detailed sequence of melting steps is described, supporting a mechanism involving the initiation at the (11¯1) surface edge of the crystal with only small amounts of initial chain breakage.

Rheology of PVC: Abstract

Abstract Three aspects of the rheological behavior of PVC are considered. These are (a) particulate flow, which occurs below the true crystal-line melting point, (b) true melting flow, which occurs at or above the melting point, and (c) the flow of PVC compounds. The effect of structural differences resulting from different polymerization temperatures employed in preparing different molecular weight polymers on the melt viscosity and flow activation energy is re-examined, and new data a r e presented to unconfound the effect of syndiotacticity and molecular weight. The three types of flow behavior of PVC are shown to be represented by three distinct flow regions. Because of thermal instability, the true melt flow region is achieved only with difficulty. However, in commercial operations this latter state is seldom, i f ever, achieved in rigid formulations. The effect of compounding additives, especially lubricants and plasticizers, and the importance of thermal and mastication history on the flow behavior are discussed with reference to the flow mechanism.

The rheology of PVC - An overview

Abstract - Three aspects of the rheological behavior of PVC are considered. These are (a) particulate flow which occurs below the true crystalline melting point, (b) true melting flow which occurs at or above the melting point and (c) the flow of PVC compounds. The effect of structural differences, resulting from different polymerization temperatures employed in preparing different molecular weight polymers, on the melt viscosity and flow activation energy is reexamined and new data presented to unconfound the effect of syndiotacticity and molecular weight. The three flow behaviors of PVC is shown to be presented by three distinct flow regions. Because of thermal instability, the true melt flow region is only achieved with difficulty. However, in commercial operations this latter state is seldom, if ever, achieved in rigid formulations. The effect of compounding additives, especially lubricants and plasticizers and the importance of thermal and mastication history on the flow behavior is discussed with reference to the flow mechanism.

The thermal transition behavior of polyorganophosphazenes

The thermal transition behavior of poly[bis(trifluoroethoxyphosphazene)] (I) and two samples of poly[bis(p-chlorophenoxyphosphazene)] (II) have been studied as representative alkoxy- and aryloxy-substituted polyorganophosphazenes. Several of the polymers of this class are reported to exhibit two first-order transitions, denoted herein as T (1) for the transition from a crystalline to mesomorphic state and Tm for the true melt. Studies of these two polymers were undertaken to gain a further understanding of this behavior. Optical microscopy on a solution-cast film of I showed that the details of spherulitic morphology persist through T(1) = 90°C and remain undisturbed through the temperature interval up to Tm = 240°C. The study of II by x-ray diffraction reveals that two sharp lines are observed above T(1) = 165°C and that orientation is not randomized upon heating to temperatures as high as 238°C. Considerable improvement in the crystalline diffraction pattern results from the thermal treatment. A detailed examination was also made by differential scanning calorimetry (DSC) of the effects of cycling through T(1), annealing in the temperature interval between T(1) and Tm and for I, the influence of controlled crystallization from the melt. The results indicate that the organization in the mesomorphic state, as influenced by thermal history, has a profound affect on the peak position, area, and sharpness of the endotherm at T(1). For I, the apparent heat of fusion at T(1) is about ten times greater than at Tm, whereas for II, no DSC peak is observed at Tm = 365°C, suggesting that the ratio of the heats of fusion at T(1) and Tm is greater than 50. However, estimated volume changes at the two transitions are nearly equal. These results are compared with those of other polymers which exhibit an intermediate state of order and with molecular liquid crystals.

Die ermittlung des schmelzpunktes von kristallinen polymeren mittels wärmeflusskalorimetrie (DSC)

Small and imperfect crystals in polymers reorganize during slow heating. This leads to an increase of their melting point T m . In order to measure the melting point of the original crystals, high heating rates are needed. This is possible with the modern heat-flow-calorimeters, which work with very small samples. The thermal lag of a DSC cell causes a shift of the melting peak by ΔT to higher temperature. From the theory of a heat-flow-calorimeter, it follows that the error ΔT is proportional to the square root of heating rate. heat of fusion and sample mass. Measurements with sharp melting low molecular weight compounds confirm that this square root relation is quantitatively followed. In order to measure the true melting point of the crystals present in a polymer sample, one has to use different high heating rates and constant sample mass. By plotting the melting peak temperatures as a function of the square root of heating rate and linear extrapolation to zero heating rate, the true melting point is found. This method is applied to HDPE, LDPE and some polyamides.

Chromatin neutron and X-ray diffraction studies and high resolution melting of DNA-histone complexes

Summary The first reported neutron diffraction studies of chromatin show the significant potential of this technique for ultrastructural investigations of DNA-protein complexes. By varying the relative protein to DNA contrast in H 2 O and D 2 O it could be shown that both constituants are on the average at the same cross-section radius. The often discussed 110reflection changed progressively with water content from a minimum of 80in dried fibers to more than 200in F1 depleted gels. Therefore, it was concluded that this reflection is not characteristic of a specific conformation. A nonuniformly folded DNA-protein fiber, contracted 3–4 times its contour length, would agree with these results. Our high resolution melting studies of λ DNA-histone complexes demonstrate the value of this approach to the study of the specficity and cooperativity of histone DNA interactions. It is concluded from these experiments that histone F1 binds preferentially and cooperatively to AT rich regions of λ-DNA. Furthermore, the results imply that «premelting phenomena may be due to the true melting of AT rich regions.

Analysis of pressures generated in a piston-cylinder type apparatus

Pressures generated in a piston-cylinder type apparatus have been analyzed as a function of experimental path. From general consideration of solid pressure media and experimental history six characteristic P-T curve types of an arbitrary specimen have been deduced. The observed melting curve of a specimen is found to be dependent on a maximum initial pressure in an experiment cycling downward (defined herein) and also to be convergent to a certain upper boundary (i.e., its true melting curve) when the pressure cell used has a negative anvil effect. It is concluded that the variation of observed melting temperatures (or any other characteristic temperature or parameter) of a specimen at a given external pressure is bounded by its true melting temperature (or by its true physical parameter), which is an open upper bound. On the basis of these properties the so-called upper boundary method for close approximation to the true P-T curve of a specimen has been derived. When this method is used, the inherent strength of solid pressure media is simply obtainable as a by-product, which can be defined by the lower boundary of its melting temperatures measured at a given external pressure.

Processability characteristics of chlorinated poly(vinyl chloride)

AbstractChlorinated poly(vinyl chloride) (CPVC) is known to have a higher softening temperature than conventional poly(vinyl chloride) (PVC). Its processability characteristics are, however, different; it has been reported that CPVC is more difficult to process. However, only limited information on the processability characteristics is available. This paper describes some studies of the flow behavior of CPVC melts in a capillary rheometer. The true melt viscosity and activation energy were determined between 190° and 210°C for a number of samples, and they appear to be related to the cohesive energy density of the samples. It was observed that melt fracture, i.e., gross distortion of the extrudate, occurs even at low shear rates in samples having a high chlorine content. This has been attributed to the relatively high pressures that have to be used, the pronounced non‐Newtonian nature of the melt, and melt elasticity. It is postulated that melt elasticity could result from crosslinking at the site of the double bond which is known to be formed by dehydrochlorination.

X-Ray Diffraction Studies of the Solid Phases of Cholesteryl Acetate

Abstract The solid phases of cholesteryl acetate were studied by x-ray diffraction techniques. The data were analyzed in terms of the angular position of the reflections, their intensity, and their integral width. The unit cell is monoclinic with the parameters a, b, c, and β respectively equal to 10.00 A, 7.36 A, 37.2 A and 95°. The space group is either c2 or cm. The dimensions of the unit cell are the same for all three solid phases. Temperature dependent measurements show that the broad melting range of the transition into the isotropic phase is not a true melting range. Increasing lack of short range order occurring along the direction of the long axis of the molecule causes an increase of the expansion coefficient in that range.

Thermal properties of cholesterol and estimation of impurity by differential scanning calorimetry.

Differential scanning calorimetry has been used to investigate the heat of fusion (ΔHf=7·12 kcal per g mol) and true melting temperature (T0=422·4°K) of pure cholesterol (99·5 mole%). In addition to analysis of the thermograph by an existing method a new and more rapid procedure has been used for evaluation of the purity of substances. Evidence is given that differential scanning calorimetry measurements at low scanning rates (0·5,1° min−1), followed by correction for premelting, are essential for estimation of ΔHf of substances not ultra-pure, at higher scanning rates large errors result. The entropy of fusion of cholesterol is similar to that of the simpler cholesteryl esters.

STUDY ON THE MELTING BEHAVIOR OF NYLON 6

Melting behavior was studied on the undrawn filaments of nylon 6 heat treated at various temperatures (Tc) from 165 to 210°C. It was found that the true melting temperature (Tm) of lamellar crystals of nylon 6 can be obtained by properly methoxymethylating the samples prior to thermal analysis. With the progress of the reaction in the amorphous regions, the complex melting curve of an as annealed sample is gradually unified into a sharp melting peak, and the half value breadth of the peak becomes minimum at the optimum degree of methoxymethylation. The corresponding peak temperature can be identified as Tm. Tm thus obtained was found to be in a linear relation with Tc in a wide range of the latter. When methoxymethylated to a proper degree the melting of the crystalline lamellae can be considered to take place under equiliblium conditions. It has been found that lamellar crystals have uniform thickness even when they are formed at temperatures considerably below the equiliblium melting point.The cross links in the amorphous regions surrounding the lamellar crystals can raise their melting temperature to large extent. The decrease in the entropy of fusion can explain the phenomenon.The isothermal thickening of the lamellar crystals of nylon 6 was analysed using the dependence of Tm on their thickness (lc). It was found that the increase in 1c is in linear relation with the logarithm of the annealing time, while the long period remains constant. A mechanism for the thickening of crystalline lamellae was proposed which prohibits mass transfer along the chain axis in the crystalline region.

Observation of Melting by Nuclear Magnetic Resonance

WE have developed a new method of observing melting and of measuring melting points which exploits the motional narrowing of the nuclear magnetic resonance line at the phase transition. Impurity premelting1 allows the observation of a spin echo signal immediately below the melting point. A plot of the signal amplitude versus temperature determines both the impurity depressed or apparent melting point and the correction to this melting point due to impurities. These then provide the true melting point. Knowledge of the freezing point depression constant also gives the impurity concentration of the sample.

Annealing of stirrer-crystallized polyethylene

Abstract A small portion of highly superheatable, but relatively low melting polyethylene crystals was discovered by calorimetric measurements on stirrer-crystallized polyethylene from solution. This portion corresponds probably to the fibrous backbone in these crystal aggregates discovered by electron microscopy. Annealing greatly increased the amount of superheatable material in the other portion of the polyethylene crystals, an effect not observed in the usual solution-grown crystals. The annealing was accompanied by a slight increase in crystal perfection as reflected by the true ultimate melting point. This latter increase is beyond the level normally reached on annealing solution-grown crystals, but not beyond that reached in slowly cooled melts. This unusual annealing behavior must be induced by the fibrous backbone. We associate increasing superheating with increasingly extended chain crystals and the comparatively low melting points with imperfections within such crystals.

Melting Point of p-Bromophenacyl Formate

THE recent note by Crosbie1 has given the melting point of p-bromophenacyl formate as 98°. This is in good agreement with the melting points of 99° and 99–100° given by Grove and Suter2, and Kubota and Matsuura3 respectively. Attention is directed to these two earlier papers2,3 which were overlooked by Neish and Lemieux4 and have not been mentioned directly by Crosbie1. A sample of p-bromophenacyl formate (m.p. 99°) was sent to me by Dr. Grove. A mixture of this with our sample (m.p. 92°) melted in an intermediate range. It was concluded that our sample was impure and the true melting point of this compound is about 99°.