Heating Run Research Articles

Real Time X-Ray Scattering Studies on the Evolution of Morphology During Heating of a Shrinkable Polyethylene Film

A bi-oriented shrinkable polyethylene film (with free ends) was subjected to a thermal treatment while irradiated by synchrotron X-rays. The experimental set-up allowed the simultaneous acquisition of one-dimensional wide-angle (WAXS) and small-angle X-ray scattered (SAXS) patterns in order to monitor the evolution of the microstructure under a controlled heating ramp (at 10.5 K/min, from 298 until 333 K) followed by an isothermal treatment at 333 K during 400 s. The results show that almost no changes occur in the crystalline phase, the main variations being a substantial reduction of the long period during the heating run. The results are interpreted by the recoil of previously highly stretched amorphous phase (taut-tie molecules). This mechanism is related to a low activation energy of 4.12 kJ/mol.

Positron annihilation in PI189 and PI304 polyimides

Temperature dependence of the lifetime τ3 and intensity I3 of the long-lived ortho-positronium (o-Ps) component was measured for two polyimides PI189 and PI304 both below and above glass-transition temperatures Tg of these polymers. First heating runs of the experiments revealed anomalous, irregular behavior of the lifetime τ3 in both PI in the vicinity (below) of the glass transition temperature. The effect was similar to that discussed recently for a number of PI. However, on the cooling stage of the first cycle and on the heating run of the second cycle, such irregularities disappeared. These results show that anomalous behavior of annihilation characteristics of o-Ps in our PI samples were due not to anomalous behavior of PI structure itself close to Tg point (not to a specific phase transition), but to removal of residual solvent in vicinity of Tg during the first heating cycle. Different approaches to estimations of the specific hole volume and of the holes number density N on the basis of positron annihilation data are discussed. Final estimation for PI189 gives the fractional free volume h=3.35% and N=0.44×1027m-3. The effects of positron trapping by polar−CO groups on annihilation characteristics of PI and on the obtained value of N are also considered.

FTIR studies of conformational disorder: crystal perfecting in long chain n-alkanes

The low temperature FTIR spectra of long chain n-alkanes C 198H 398 and C 246H 494, crystallised from solution in both extended and once-folded forms, have been investigated in the CH 2 wagging region. Successive annealing and cooling stages result in a significant reduction in the number of non-planar C–C bond conformers in all cases. This is evidence of a ‘perfecting’ process within the crystals. The time dependence of this behaviour shows that, on raising the annealing temperature, the level of disorder reaches a maximum before declining. In addition, in a continuous heating run on once-folded C 198H 398, all types of conformational disorder except end- gauche bonds are shown to pass through a maximum near 118 °C, in the region of the transformation to extended chain crystals.

Crystal growth of NdNiO3 perovskite under high oxygen pressure

Well-shaped single crystals of NdNiO3 perovskite have been grown for the first time under high oxygen pressure conditions, in abelt-type press at 4 GPa. The reaction took place in sealed platinum capsules, in the presence ofKClO3 as the oxidizing agent. It seems that the choice of hydroxides of the cations involved asdeparture reagents is crucial for the success of the crystal growth, via water vapourtransport reactions. The perovskite has been characterized by x-ray diffraction, scanningmicroscopy and differential scanning calorimetry measurements, suitable to identify themetal–insulator transition. The transition temperature of the as-grown crystals, of191.2 K in the heating run, is significantly lower than that reported for powderNdNiO3 materials. This suggests a better metallicity of the present crystals, probably due to animproved oxygen stoichiometry associated with the much stronger oxidizing conditionsutilized for its preparation.

Hydriding and dehydriding processes of LaNi 5− xCo x (x=0–2) alloys under hydrogen pressure of 1–5 MPa

The hydriding and dehydriding behavior of LaNi 5− x Co x (0⩽ x⩽2) was studied by the pressure differential scanning calorimetry (PDSC) at the hydrogen pressure range of 1–5 MPa in the temperature range from 323 to 573 K. In the heating run of the LaNi 5–H 2 system, two endothermic peaks were observed. One was the peak for the transformation from the γ phase (LaNi 5H 6 hydride) to the β phase (LaNi 5H 3 hydride). The other was the peak for the transformation from the β phase to the α phase (solid solution). In the cooling run, one exothermic peak for the transformation from the α phase to the γ phase was observed. In the range of x⩽0.5, PDSC curves similar to that of the LaNi 5–H 2 system were observed. However, in the range of x⩾1, one endothermic and one exothermic peaks were observed in the heating and cooling runs, respectively. Using Ozawa's method, the activation energies for the dehydriding processes were estimated. The activation energy for the γ–β transformation was higher than that for the β–α transformation and the activation energy for the β–α transformation has a maximum at the composition of about x=1.

Specific heat and thermal diffusivity of vinylidene fluoride/trifluoroethylene copolymers

AbstractThe specific heat (C) and thermal diffusivity (D) of vinylidene fluoride (VDF)/trifluoroethylene copolymers with 70 and 56 mol % of VDF were measured between 200 and 390 K, and the thermal conductivity (K) was calculated from these data. C, D, and K were rather insensitive to the VDF content but varied significantly with the crystallinity. At room temperature, as the crystallinity increased from about 55 to 85%, C decreased by 17%, and D and K increased by 60 and 40%, respectively. For the copolymer with 70 mol % VDF, C exhibited a broad peak, whereas D showed an abrupt drop at the ferroelectric–paraelectric transition near 370 K on heating. The transition temperature on cooling was about 40 K below that observed in the heating run, thus revealing a large thermal hysteresis. For the copolymer with 56 mol % VDF, the transition temperature was much lower, the transition region was narrower, and the thermal hysteresis was barely observable. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3160–3166, 2003

Analysis of the measurement of the current sharing temperature in the ITER TF Model Coil

The ITER toroidal field model coil (TFMC) has been tested in the TOSKA facility of FzK. The racetrack coil, which uses a circular Nb3Sn cable-in-conduit conductor, is equipped with external resistive heaters for the evaluation of the current sharing temperature (Tcs). Since there are no sensors inside the coil, the only possibility to assess the coil temperature is to use the measured inlet temperature and to estimate the downstream propagation of the temperature profile. The analysis has shown that a quantitative assessment of Tcs from the test results of the 60 s ramp heating run tends to overestimate the cable performance compared with the strand performance.

Effect of Rh Substitution on the Magnetic Transition Temperatures in the Ni2In-Type Mn7Sn4

In the Ni2In-type Mn7Sn4, 1) MnI atoms constitute a simple hexagonal sublattice, and Sn and MnII atoms respectively constitute hexagonal closest packed sublattices. Then, MnII atoms are located in the interstitial sites surrounded by the prismatic arrangements of MnI atoms. This compound is ferrimagnetic below the Curie temperature TC 1⁄4 220K, in which MnI moments antiparallely align with MnII ones. Previous magnetization investigations have revealed spin-glass-like (SGL) behaviours below a reentrant SGL transition temperature Tg 100K. In order to study the crossover behaviour of TC and Tg in the ferrimagnetic system which consists of different kinds of hexagonal magnetic sublattices, we investigate the magnetic phase diagram of the Ni2In-type (Mn1 wRhw)7Sn4. Samples of (Mn1 wRhw)7Sn4 were prepared from the mixtures of appropriate amounts of Mn (99.97% pure, powder crushed in Ar atmosphere), Rh (3N pure, powder), and Sn (5N pure, grains) in evacuated silica tubes. Method for heat treatment has been described in ref. 5. The X-ray patterns of the samples with w 5 0:20 were explained with the extinction rule for the Ni2In-type of structure. As shown in Fig. 1, the lattice parameters a and c increase with increase in w; a 1⁄4 ð0:4393 0:0002Þ þ ð0:007 0:001Þw and c 1⁄4 ð0:5511 0:0002Þ þ ð0:019 0:001Þw in nm. Zero-field cooled magnetization ( ZFC) and field-cooled one ( FC) were measured using a SQUID magnetometer (Quantum Design) above 6K under the magnetic field H 1⁄4 100Oe on heating run, where FC was measured after being cooled from 295K under H 1⁄4 100Oe. As shown in Figs. 2(a)–2(d), ZFC slowly increases as temperature (T) increases up to a characteristic temperature Tt. Then, it steeply increases up to Tg. Above Tg, it very slowly increases up to another characteristic temperature Tmax. Finally, it decreases with T through TC. Here, TC was determined by extrapolating 2 ZFC to zero on the 2 ZFC versus T curve. At 6K, FC is far larger than ZFC. Then, FC gradually decreases with increasing T . Finally, FC agrees with ZFC above a characteristic temperature TfH. This feature is essentially the same as that for w 1⁄4 0 at 100Oe. In Figs. 2(e) and 2(f) ZFC shows a sharp -type peak at Tmax. At 6K FC is far larger than ZFC, and FC increases with increase in T above TfH. Also FC exhibits the -type peak at Tmax. Such a feature is also observed in w 1⁄4 0:139 [inset of Fig. 3(a)]. Figure 3(a) shows the characteristic temperatures TC, TfH, Tg, Tmax and Tt as a function of T . Below w 1⁄4 0:139, TC, TfH and Tg decrease with increase in w. On the other hand, Tmax increases and subsequantly decreases, while Tt increases. Above w 1⁄4 0:139, TfH and Tmax slightly change with w. The feature TfH > Tmax observed below w 1⁄4 0:12 is contrast to that TfH < Tmax above w 1⁄4 0:139. Figures 3(b)–3(d) show the most simple empirical relations to be able to fit the values of ZFC below w 1⁄4 0:12 and above w 1⁄4 0:139; log ZFC 1⁄4 Aþ Bw for w 5 0:12 and log ZFC 1⁄4 Aþ B=ðC þ wÞ for w = 0:139. The crossing points of these curves in ZFC are situated at P1 (w 1⁄4 0:136, T 1⁄4 63K), P2 (w 1⁄4 0:137, T 1⁄4 76K) and P3 (w 1⁄4 0:136, T 1⁄4 61K) on TfH, Tmax, and [Tg (below w 1⁄4 0:12) and TfH (above w 1⁄4 0:139)] versus w lines, respectively. The values of w for P1, P2 and P3 are nearly constant, so that we can estimate the vertical boundary line wc 1⁄4 0:136 separating between the lower w region and the higher one. Figures 4(a) and 4(b) show the field dependence of ZFC measured at 6K. All the samples show saturation behaviour Fig. 1. Lattice parameters (a and c) as a function of w for (Mn1 wRhw)7Sn4. Fig. 2. Representative temperature dependence of ZFC (open circles) and FC (cross signs) for (Mn1 wRhw)7Sn4 at H 1⁄4 100Oe. Definitions of arrows are given in Figs. 3(a) and 3(b).

Amorphization of Al 32Ge 68 in a slow heating run studied by NMR

Amorphization of Al 32Ge 68 at normal pressure, starting from the thermobarically quenched high-pressure crystalline metallic γ-phase, was studied in a slow heating run by performing NMR field-sweep experiments. In the temperature interval from 77 to 300 K the 27Al central line exhibits a continuous broadening and a positive frequency shift. Close to 300 K rather abrupt changes were observed, where the shift changed its sign, and the line width jumped to its highest value. The discontinuous course of the phase changes indicates that the amorphization process proceeds via a sequence of intermediate metastable states, which can be ‘overheated’ in a slow heating run and consequently transform in an explosion-like manner to the final amorphous state at a well-defined temperature. The frequency shift could be decomposed into the negative second-order quadrupolar shift and the positive Knight shift. The change of the shift sign from positive to negative at 300 K reflects the vanishing tendency of the Knight shift upon heating and is compatible with the conduction-electron localization upon structure amorphization.

Miscibility and phase structure of binary blends of polylactide and poly(vinylpyrrolidone)

AbstractThe miscibility, crystallization behavior, and component interactions of two binary blends, poly(L‐lactide) (L‐PLA)/poly(vinylpyrrolidone) (PVP) and poly(D,L‐lactide) (DL‐PLA)/PVP, were studied with differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. The composition‐dependent changes of the glass‐transition temperature (Tg) and degree of crystallinity (Xc) of the L‐PLA phase indicated that L‐PLA and PVP were immiscible over the composition range investigated. However, the sharp decrease of Xc with increasing PVP content in the second heating run demonstrated that the cold crystallization process of L‐PLA was remarkably restricted by PVP. In DL‐PLA/PVP blends, the existence of two series of isolated Tg's indicated that DL‐PLA and PVP were phase‐separated, but evidence showed that there was some degree of interaction at the interface of the two phase, especially for the blends with low DL‐PLA contents. FTIR measurements showed that there was no appreciable change in the spectra of L‐PLA/PVP with respect to the coaddition of each component spectrum, implying the immiscibility of the two polymers. In contrast to L‐PLA, the intermolecular interaction between DL‐PLA and PVP was detected by FTIR; this was evidenced by the observation of a high‐frequency shift of the CO stretching vibration band of PVP with increasing DL‐PLA content, which suggested some degree of miscibility. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 973–979, 2003

Effect of pressure on the PVT behaviour of iPP as revealed by dilatometric measurements

Isotactic Poly-Propylene samples, previously prepared under known conditions of pressure and cooling rate by means of a Special apparatus designed and set-up by the authors, were subjected to several isobaric runs at low cooling and heating rate in a confining fluid dilatometer (by GNOMIX). The effect of the previous thermo-mechanical histories and the effect of pressure in the dilatometry on specific volume of the samples was studied. Results show that the initial specific volume depends upon the previous thermo-mechanical histories, which however cancels out after the first heating run. Moreover the reported dilatometric experimental data Support the evidence that an increase of pressure at a constant cooling rate acts as an increase of cooling rate at a constant pressure.

Melt viscoelasticity of polypropylenes prepared under different polymerization regimes1

Four samples of polypropylene (PP) prepared under different polymerization regimes were characterized by wide-angle (WAXS) and small-angle (SAXS) x-ray diffraction, by specific heat capacity in the temperature interval from −50 to 220°C (DSC), and by linear viscoelasticity at several fixed temperatures in the interval from 120 to 220°C. Storage G′(ω) and loss G″(ω) shear moduli in the melt state (measured in the frequency window spanning about three decades) were treated to derive the relaxation times spectra h(τ) using the nlreg computer program based on Tikhonov's method of nonlinear regularization. Molecular characteristics were derived from the melt viscoelastic properties of three crystallizable (isotacticity index above 95%) PP samples exhibiting Newtonian melt flow behavior at low angular frequencies. The anomalous viscoelastic behavior in the first heating run of the elastomeric PP in the temperature interval below ca. 170°C, combined with the relevant WAXS, SAXS, and DSC data, was considered as an evidence for the existence of a spatial network of microcrystallites formed by lateral aggregation of stereoregular sequences which were, however, too short for the development of chain-folded, lamellar crystals typical for semi-crystalline homopolymers. The “normal” viscoelastic behavior during the subsequent cooling run from a structureless melt state suggested a very slow kinetics of microcrystallinity development. The results obtained demonstrate a high potential of viscoelastic measurements for structural characterization of poorly crystallizable, elastomeric polymers. *Dedicated to Prof. Yu. S. Lipatov on the occasion of his 75th birthday.

Structural relaxation in glasses: numerical exploration of variables of Narayanaswamy and Moynihan's model

The accurate description of the relaxation phenomenon near the glass transition temperature allows a better interpretation of differential scanning calorimetry (DSC) curves, since it can be separated from other thermal effects such as crystallization, melting, and recrystallization. The structural relaxation model of Narayanaswamy and Moynihan for thermorheological simple glasses was numerically explored for obtaining a grasp of the functional influence of the different parameters: i.e. relaxation enthalpy Δ h, non-linear parameter x, amplitude exponential distribution parameter b, and pre-exponential parameter A. It is known that when the relationship between the velocity of heat transfer in the cooling run ( q c) and the velocity of heating in the heating run ( q h) is equal to unity, the curves obtained in a DSC suffer only an horizontal translation for different absolute values of cooling and heating rates. It was found in this work that this criterion can be generalized, and curves also overlap by means of a horizontal translation when q c/ q h is a constant different from one, whichever the particular values of q c or q h will be. Finally, changes in the shape of the curves when using different values of q h and q c with a fixed q c/ q h relationship can be used as an indicator of the occurrence of other phenomena (i.e. recrystallization, melting, etc.) in addition to structural relaxation.

Evidence for transient kinetics of nucleation as responsible for the isothermal transformation of supercooled liquid into the glacial state of triphenyl phosphite

The first-order transformation of the supercooled liquid into the glacial state of triphenyl phosphite was investigated by differential scanning calorimetry (DSC) using two different thermal procedures. In the first procedure the transformation was analyzed by heating run DSC experiments. The glaciation process was interpreted as an aborted crystallization because of a high nucleation rate in a temperature range where the crystal growth is low. This relative separation between the nucleation- and growth-rate curves suggests that the glacial state can be described as a supercooled liquid–nanocrystalline mixed phase, characterized by a high-density nucleation which frustrates further crystallization. In a second procedure, DSC experiments were carried out during isothermal transformations of the supercooled liquid into the glacial state. The sigmoidal shapes of DSC isotherms are interpreted as transient kinetics of nucleation rather than nucleation and growth processes.

Relaxation behavior of ultradrawn poly(ethylene) film by temperature wave analysis

A new sensitive thermal analysis for the observation of re-orientation behavior in the melting region of the ultradrawn poly(ethylene) film was proposed by the simultaneous measurement of thermal diffusivity and birefringence under optical microscope in a constant heating rate. Thermal diffusivity was obtained by the phase delay of temperature wave passed through the thickness direction of the specimen. The results correspond with each other over wide temperature range including melting temperature. It was concluded that the thermal diffusivity measurement was more sensitive not only to detect the molecular relaxation in a continuous heating run, but also to find out the delicate variation of chain direction.

Anomalous Temperature Changes of Positron Lifetime and Electrical Resistivity in B2-NiTi Alloys

The pre-martensitic phenomena in Ni-rich NiTi alloys have been studied by means of positron lifetime spectroscopy and electrical resistivity measurement. We have found anomalous positron lifetime changes above the martensitic transformation temperatures of Ni50Ti50–Ni51Ti49 alloys. Positron lifetime increases anomalously with decreasing temperature even at temperatures 100 degrees higher than Ms of Ni51Ti49 alloys. Almost the same change in positron lifetime has been observed on the subsequent heating run with little hysteresis. We have also found the anomalous behavior of positron lifetime and negative temperature dependence of electrical resistivity even in NiTi alloys that do not exhibit martensitic transformation. The observed pre-martensitic changes of positron lifetime and electrical resistivity directly reflect the intrinsic electronic-structural changes of NiTi alloys that cause so-called pre-martensitic phenomena.

Hydrogenation and Dehydrogenation Behavior of LaNi&lt;SUB&gt;5-x&lt;/SUB&gt;Co&lt;SUB&gt;x&lt;/SUB&gt; (x=0, 0.25, 2) Alloys Studied by Pressure Differential Scanning Calorimetry

The hydrogenation and dehydrogenation behavior of LaNi5, LaNi4.75Co0.25 and LaNi3Co2 was studied by the pressure differential scanning calorimetry (PDSC) at the hydrogen pressure range of 1 to 5 MPa in the temperature range from 323 to 473 K with the heating and cooling rates of 2 to 30 K min −1 . In the heating run of the hydride of LaNi5, two endothermic peaks were observed. One was the peak for the transformation from the γ phase (full hydride LaNi5H6) to the β phase (hydride LaNi5H3). The other was the peak for the transformation from the β phase to the α phase (solid solution). In the cooling run, one exothermic peak for the transformation from the α phase to the γ phase was observed. These endothermic and exothermic peaks shifted to higher temperatures with the increase in hydrogen pressure. In the heating and cooling runs of the LaNi4.75Co0.25–H2 system the PDSC curves similar to those of the LaNi5–H2 system were observed. However, in the heating run of the hydride of LaNi3Co2 only one endothermic peak was observed. Using Ozawa’s method, the activation energies for dehydrogenation of the hydrides were estimated. The activation energy for the γ -β transformation was higher than that for the β-α transformation. Substitution of cobalt for a part of nickel in LaNi 5 increased the activation energies for the phase transformations.

PHOTOINDUCED PHASE TRANSITION IN SINGLE CRYSTALS ON URETHANE-SUSTITUTED POLYDIACETYLENES

Thermochromic behaviors were investigated by measurements of reflectance spectra for urethane-substituted polydiacetylene crystal having side groups of R=(CH)2)6OCONHC2H5 (PDA-6UEt). The PDA-6UEt crystal shows an irreversible thermochromic A-to-B (blue-to-red) phase transition: the absorption band at 1.88 eV due to the lowest exciton shifts to higher energy (2.15 eV) in the heating run, but the reflectance spectra remain in the B phase even when cooled down to room temperature. We have demonstrated that photoinduced phase transition (PIPT) is observed by utilizing the irreversible A-to-B phase transition. The conversion shows the presence of a threshold of the light intensity and depends on photon energy, suggesting that the PIPT is mediated by the photogenerated electron-hole pairs.

Dielectric Relaxation in High Temperature Phases of (NH3C2H5)2CuCl4 Crystals

On the basis of dielectric investigations of (NH3C2H5)2CuCl4 crystals the existence of phase transitions at T1 = 364 K and T2 = 356 K (in a heating run) was confirmed. In the temperature region of 300–370 K Debye relaxation was observed. The change of the dielectric dispersion character around T3 = 330 K is related to the phase transition. The determined values of the activation energy and the times of the dielectric relaxation for all phases are characteristic of the combined reorientation motions of the alkylammonium cation. The conclusions concerning the dynamics of the hydrogen bonds were confirmed by IR spectroscopy.

Effect of the Be and Y on the martensite transformation parameters in TiNi compound

To our knowledge, the effect of Be and Y on the martensite transformation parameters in TiNi-based shape memory alloys was studied occasionally and mainly on a level of the technological additions. Recently, due to the development of non-conventio nal production technologies applied to the shape memory materials, both metals are found to be the appropriate canditates for production of the potential TiNi-based shape memory alloys in an initially amorphous structural state by means of the melt-spinning and injection casting techniques. First of all, the Be and Y attract attention due to satisfaction of the so-called golden rules known for the bulk amorphous alloy systems. We present the result of the experimental study regarding the systematic substitution of the main constituent elements Ti and Ni by Be and Y up to (2-10) at.%. In as-cast condition, all the Ti-Ni-Be and Ti-Ni-Y alloys undergo the dual B2 R B19' martensite transformation sequence, well resolved on the cooling run and often overlapping on the heating run. Both the TR and Ms transformatio n temperatures smoothly decrease with the Be or Y content, the slope to be higher for substitution of the Ti than the Ni. The ternary TiNiBe and TiNiY melt- spun ribbons produced in the standard technological condition are rather brittle and don't show a good metallic aspect. They are in the crystalline structural state and undergo the martensite transformation sequence similar to the bulk material but in the lower temperature range. The contribution of the chemical composition, microstructure and strain/stress field (caused by the difference in the atomic radii) to the martensite transformation temperatures is considered.