Critical Crystallization Temperature Research Articles

The Crystallization and Melting Behavior of Neodymium-Based Butadiene Rubber Blends.

This study investigates the influence of poly(butadiene-isoprene) copolymer rubber (BIR) and TDAE oil on the crystallization and melting behavior of neodymium-based butadiene rubber (Nd-BR). The study demonstrates that the melting points of Nd-BR and its blends decrease with lower crystallization temperatures. Below the critical crystallization temperature (Tc,c), the melting behavior shows dual peaks in distinct temperature ranges, which are attributed to different spherulitic sizes. The addition of BIR or TDAE oil lowers the Tc,c, with TDAE oil exerting a more substantial effect. These diluents mainly influence the nucleation temperature and crystallinity level of Nd-BR while having a minimal effect on the crystallization mechanism. A master curve, which overlaps for various samples, is developed by correlating the peak melting temperature (Tm,peak) with the Tc. This curve facilitates a quantitative assessment of the effects of BIR and TDAE oil on Nd-BR, highlighting the greater influence of TDAE oil on the crystalline structure compared with BIR at equivalent mass fractions. By applying the Lorentz equation and multi-peak fitting, a relationship between the melting points and crystallization temperatures is established, enabling the calculation of the equilibrium melting points (Tm0) for different samples. The findings show a reduction in the Tm0 due to the diluents; specifically, the Tm0 is approximately 0 °C for pure Nd-BR, and it decreases to -4.579 °C and -6.579 °C for samples with 50 PHR TDAE oil and 60 wt.% BIR, respectively.

Hydrous RuO2 film synthesized in an alkali-assisted steam thermal reactor: Low temperature synthesis and pseudocapacitance

The method of preparing RuO2 thin film by decomposing RuCl3 precursor in steam has shown a potential of having lower temperature and higher capacitance in our previous research work. We have further improved the method of thermal decomposition in steam in our previous work and proposed the alkali-assisted steam thermal reactor (AASTR) method, which has achieved the synthesis of RuO2 thin film with a capacitance of 514 F·g−1 at a low temperature of 150 °C. In the AASTR method, a concentrated sodium hydroxide solution is chosen and placed at the bottom of the reactor. The Ti foil substrates are placed in the vapor phase and do not contact the sodium hydroxide solution. The sodium hydroxide solution is employed to absorb hydrogen chloride generated in the hydrolysis process of RuCl3 and thus promotes the hydrolysis process. As a result, thermal decomposition at a lower temperature (around 150 °C, the critical crystallization temperature) becomes possible due to the modified hydrolysis process. The film exhibits an almost ideal surface controlled pseudocapacitive performance due to its low charge transfer resistance in the charge/discharge process. Therefore, the AASTR method has promising applications in low-temperature synthesis of other hydrous metallic oxides.

The effect of Er doping on the crystallization of Ge1−xSnx thin films

The Er-doped [Formula: see text] thin films with different Sn contents were prepared on Ge buffered Si substrates by thermal evaporation. The effect of Er doping on the crystallization of [Formula: see text] films at different annealing temperatures was studied. It is demonstrated that Er doping can increase the critical crystallization temperature and greatly reduce the surface roughness of high temperature annealed [Formula: see text] thin films.

Effects of temperature on the capacitive performance of Ti/40%RuO2-60%ZrO2 electrodes prepared by thermal decomposition method

Electrode coatings of 40%RuO2-60%ZrO2 binary oxide were formed on Ti substrate by thermal decomposition method with the annealing temperature varying from 280°C to 450°C. The effects of annealing temperature on the structure, capacitive performance of the electrode coatings were investigated using X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and cyclic voltammetry. The XRD and TEM analyses showed that 290°C was the critical crystallization temperature of RuO2. The 40%RuO2-60%ZrO2 oxide coating prepared at this temperature also exhibited the highest specific capacitance (949F/g), owing to its special amorphous structure in combination with short range order microcrystallines, which brought out both the relatively good electrical and proton conductivity.

Raman scattering study of amorphous GeSn films and their crystallization on Si substrates

The dependence of Raman scattering spectra on Sn composition in the amorphous Ge1-xSnx films deposited on Si(001) substrates by magnetron sputtering is investigated. Two broad phonon scattering peaks are clearly observed, which are attributed to the disordered SnSn and GeGe bonds, shifting to lower wavenumbers with the increase of Sn content. The ratio of integrated intensity of SnSn to GeGe modes increases linearly with Sn content in the range of 0.06 to 0.2. With rapid thermal annealing, although the critical crystallization temperature becomes lower for higher Sn content amorphous GeSn, severe Sn segregation occurs for all of the samples. Relative lower crystallization temperature is proved to be beneficial for tailoring high Sn content crystalline GeSn films. Polycrystalline GeSn alloys with maximum substitutional Sn content of 0.07 are achieved with an annealing temperature of 400°C.

A highly active and selective β‐nucleating agent for isotactic polypropylene and crystallization behavior of β‐nucleated isotactic polypropylene under rapid cooling

ABSTRACTZinc adipate (Adi‐Zn) was observed to be a highly active and selective β‐nucleating agent for isotactic polypropylene (iPP). The effects of Adi‐Zn on the mechanical properties and the β‐crystals content of nucleated iPP were investigated. The impact strength of iPP nucleated with 0.2 wt % Adi‐Zn was 1.8 times higher than that of neat iPP. In addition, wide‐angle X‐ray diffraction analysis indicated that the content of β‐crystals in nucleated iPP (kβ value) reached 0.973 with 0.1 wt % Adi‐Zn, indicating that Adi‐Zn is a highly active and selective β‐nucleating agent for iPP. Furthermore, fast scanning chip calorimetry (FSC) studies using cooling rates from 60 to 13,800 °C min−1 revealed that the formation of β‐crystals significantly depended on the cooling rates. At cooling rates below 3000 °C min−1, only β‐crystals existed. However, at cooling rates above 6000 °C min−1, β‐crystals failed to form. Moreover, a lower critical crystallization temperature that corresponded to the generation of β‐crystals was investigated using cooling‐induced crystallization, and the results are in good agreement with those of a previous study. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43767.

Isothermal crystallization and structural characterization of poly(ethylene-2,5-furanoate)

Among “green” alternatives for oil-based commodity plastics like Polyethylene, Polyamides, and Poly(Ethylene Terephthalate), a new class of polyesters synthesized from furandicarboxylic acids (FDCAs) currently is in the spotlight of both the academic and industrial communities. Of particular interest is Poly(Ethylene-2,5-Furanoate) (PEF), which can be synthesized from monomers derived from sugars and exhibits physical properties that imply large substitution potential for PET in bottle, fiber and packaging applications. In this study the structure-thermal properties relationship of PEF have been investigated in order to explain the complex behavior exhibited by PEF during isothermal crystallization. Secondary crystallization and melt-recrystallization processes have been identified in order to explain the observed behavior. The existence of a critical crystallization temperature around 170 °C marking a transition in terms of crystalline phase induced is also pointed out. Moreover, data such as the molecular weight between entanglements (Me) and standard melting enthalpy (ΔHm°) have been determined. In addition the crystalline morphology was characterized by means of SAXS and WAXS. The influence of the crystallization conditions on this morphology is given. As a main result it has been found that depending on the crystallization temperature (Tc), a disordered or an ordered crystalline phase (called α′ and α respectively) are formed at low (Tc ≤ 170 °C) and high (Tc ≥ 170 °C) temperatures, respectively. Finally, evidence for the formation of a rigid amorphous phase during crystallization is presented, indicating that a three-phase model has to be considered in order to provide an appropriate description of the morphology in semi-crystalline PEF.

Crystallization kinetics of GeTe phase-change thin films grown by pulsed laser deposition

Pulsed laser deposition was employed to the growth of GeTe thin films on Silicon substrates. X-ray diffraction measurements reveal that the critical crystallization temperature lies between 220 and 240 °C. Differential scanning calorimetry was used to investigate the crystallization kinetics of the as-deposited films, determining the activation energy to be 3.14 eV. Optical reflectivity and in situ resistance measurements exhibited a high reflectivity contrast of ~21% and 3–4 orders of magnitude drop in resistivity of the films upon crystallization. The results show that pulsed laser deposited GeTe films can be a promising candidate for phase-change applications.

Molecular weight dependency of crystallization and melting behavior of β-nucleated isotactic polypropylene

Compounds of isotactic polypropylene (iPP) and β-nucleating agent were used to investigate the relationship between the development of β phase and molecular weight in iPP under quiescent crystallization conditions by using wide angle X-ray diffraction and differential scanning calorimetry techniques. In all cases, the dependency of the formation of β phase in iPP on molecular weight of iPP at a defined crystallization temperature range was found. The iPP with high molecular weight possessed a wide range of crystallization temperature in inducing rich β phase. However, poor or even no β phase was obtained for the samples with low molecular weight in the same range. In addition, an upper critical crystallization temperature of producing dominant β phase was found at 125 °C. Beyond this temperature, a phenomenon of prevailing α phase became obvious. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1301–1308

Online Tempercurve Analysis of Praline Products with the Objective of Cooling Process Optimization

AbstractParameter evaluation for cooling tunnel equipment as used for solidification of chocolate masses was realized by evaluation of online temperature curves (real‐time tempercurves). A praline system (dark chocolate shell, hazelnut filling) was cooled by variation of cooling temperature (12, 7, −10C) and air flow rate (1, 3, 6 m/s). By evaluation of real‐time tempercurves with respect to main crystallization events in different product layers and final fat bloom resistance a critical crystallization temperature of T = 18C was determined. In parallel, the significant potential of time reduction by cooling temperature decrease and air flow increase has been worked out by exemplification. Evaluation is based and discussed on cocoa butter crystallization within literature. Furthermore, this rather simple technique is capable of monitoring several details of local cooling situations in the black box cooling tunnel, such as relative cooling capacity, consistency of cooling temperature and effect of production shutdowns.Practical ApplicationsThe real‐time tempercurve technique is adaptable to a wide range of industrial molds and cooling equipment in the chocolate industry. It is so far developed for molded products only. For coated products, an alternative construction of surface analysis by infrared technique is conceivable. On the other hand, the operating experience with cooling tunnels of manufacturers is less detailed in comparison to other process units because it is a closed system (black box). With this approach, the producer is capable of monitoring the performance and continuance of his cooling equipment (air cooler) and is able to set up appropriate process parameters (temperature, air speed) for new or optimize them for existing products.

Induced crystallization of single-chain polyethylene on a graphite surface: Molecular dynamics simulation

Molecular dynamics (MD) simulations have been carried out on the crystallization of single-chain polyethylene (PE) which was adsorbed on a graphite (001) surface on one side and exposed to vacuum on the other at different temperatures. The MD simulation data have been analyzed to provide information about the crystallization process of polymer adsorbed on the solid substrate. The isothermal crystallization of PE proceeds in two steps: (1) adsorption and (2) orientation. The results detail the radial density distribution function, ordered parameters, local bond-orientational order parameters, and the local properties displayed in layers of the polymer parallel to the graphite and vacuum interfaces. It was also shown that the film thickness affected the critical crystallization temperature of the adsorbed polymer on the substrate surface. Furthermore, the influence of the graphite surface area on the crystallization of PE is discussed by comparing the crystallinity evolution of PE on graphite with different coverage.

Thermal Conductivity of AlN and SiC Thin Films

The thermal conductivity of AlN and SiC thin films sputtered on silicon substrates is measured employing the 3ω method. The thickness of the AlN sample is varied in the range from 200 to 2000 nm to analyze the size effect. The SiC thin films are prepared at two different temperatures, 20 and 500°C, and the effect of deposition temperature on thermal conductivity is examined. The results reveal that the thermal conductivity of the thin films is significantly smaller than that of the same material in bulk form. The thermal conductivity of the AlN thin film is strongly dependent on the film thickness. For the case of SiC thin films, however, increased deposition temperature results in negligible change in the thermal conductivity as the temperature is below the critical temperature for crystallization. To explain the thermal conduction in the thin films, the thermal conductivity and microstructure are compared using x-ray diffraction patterns.

Annealing characteristics of the vanadium oxide films prepared by modified ion beam enhanced deposition

Different annealing conditions were adopted to anneal the vanadium oxide films prepared by modified ion beam enhanced deposition (IBED) method. An X-ray diffraction (XRD) was used to analyze the orientation of the IBED films and the resistance was tested with temperature change to measure the temperature coefficient of resistance (TCR). Experiments indicated that there existed a critical temperature for crystallization of VO 2, which changed with the different deposition conditions of the IBED method. It is very difficult to obtain VO 2 structure if the annealing temperature was lower than the critical temperature. If the temperature is much higher than the critical temperature or annealing time is too long, the valence of vanadium in VO 2 film will easily reduce from four to low value. The TCR of the IBED VO 2 polycrystalline films annealed in appropriate condition could reach higher than 4%/K.

The mechanism of α-γ transition of poly- (vinylidene fluoride) in the miscible blends

The simultaneous DSC-FTIR was used for the observation of crystallization and melting of poly(vinylidene fluoride) (PVDF) and its blends with poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA). The isothermal crystallization was carried out under the condition of both α-form and γ-form crystallized competitively. The crystal growth rate of α -form and γ -form were evaluated from the absorbance changes at 795 cm-1 (α -form, CH2 rocking) and 810 cm-1 (γ -form, CH2 rocking) obtained by the DSC-FTIR. The crystal growth rate of γ -form decreased at the same crystallization temperature in the order of PVDF/syn-PMMA, PVDF/PEMA and PVDF/at-PMMA, which was corresponding to the order of interaction parameter. The mechanism of α -g transition of PVDF in the miscible blends with at-PMMA, syn-PMMA and PEMA was evaluated from the relationship between the decrease of α -form and the increase of γ -form. The critical crystallization temperature, at which the transformation from α -form to γ -form proceeded only in the solid state, shifted to higher temperature side in the order of interaction parameter.

A Temperature- and Molar Mass-Dependent Change in the Crystallization Mechanism of Poly(1-butene): Transition from Chain-Folded to Chain-Extended Crystallization?

The crystallization behavior of poly(1-butene) (P1b) was investigated by polarized light microscopy (PLM), atomic force microscopy (AFM), wide-angle X-ray scattering (WAXS), dilatometry, and also by time- and temperature-resolved small-angle X-ray scattering experiments (SAXS). Observations in the PLM indicate a temperature-dependent change in the mechanism of crystallization. When crossing a certain critical crystallization temperature, the morphology changes from spherulites to quadratic, platelike single crystals. Investigations of samples with different molar mass show that the transition temperature is molar mass-dependent; on decreasing the molar mass the transition shifts to lower temperatures. As proved by WAXS, both the spherulites and the single crystals are of the metastable form II. The morphological change is also observed in AFM images obtained after a rapid cooling of the samples to room temperature; the difference in the morphological appearance is preserved through the transformation from...

ELECTROSPRAYING OF GLASSES—PREPARATION OF GLASS COATINGS ON GLASS

Glass coatings on ceramic or metallic substrates are prepared by two different methods. In a two-step process the glass powder is deposited on the glass substrate by methods such as airless spraying of enamel or glaze suspensions, dipping in enamel suspensions, electrospraying or electrophoretic deposition of enamel or glaze suspensions, and electrostatic powder spraying. The particle size of the glass powders which are generally prepared by milling, ranges from 500 nm to 100 μm. Therefore, these layers of glass powder have to be densified by melting in a second step. As for glass substrates this processing temperature should not exceed 500–700°C to prevent bending of the substrate, low melting glass powders have to be applied in this case. Alternatively, the glass powders can be heated to melting temperatures while spraying (e.g. flame or plasma spraying) to reduce the thermal load of the substrate (one-step process). Unfortunately, the molten glass particles freeze very quickly when they hit on the cold substrate and the density of the deposited glass layer is lower compared to the two-step process due to trapped residual pores. It is the objective of our work, to improve the coating methods of glass by combining these different methods and to reduce the processing temperatures by applying nanosized glass powders. Due to the high surface activity, these powders can be sintered to transparent glass below the critical crystallization temperature. Therefore, the processing temperature can be significantly reduced compared to the melting technique. In this paper the eletrospraying of glass melts and glass suspensions is presented which are new methods for preparing glass coatings on glass substrates. The process of electro-melt spraying is similar to the LMIS process, but instead of molten metal a glass melt is atomized under vacuum. The electrical conductivity and surface tension of these glass melts are higher than that of water but lower than that of molten metal. The droplet diameter of atomized glass melts lies between 100 nm and 10 μm. The molten droplet build up a dense coating on a hot substrate and are sintered in situ. In our case a flat glass substrate is mounted on a metal counter electrode. Due to the high electric fields which are needed for forming a Taylor cone of a glass melt, a vacuum of about 10 -2 mbar is necessary to prevent electrical break-down. At this pressure most technical glasses show foaming. Thus, a new type of crucible was developed, where the glass melt is under normal pressure and the capillary tip is under vacuum. Additionally, this crucible enables a continuous production of glass powders. For the electrospraying of glass suspensions a new process was developed, the so-called electro-flame spraying. In contrast to the classical electrospraying, a hydrogen–oxygen flame is used as a counter electrode to build up the electric field for creating the Taylor cone at the tip of a capillary tube. In this flame the dispersing liquid of the suspension is vaporized and the glass particles are molten. Due to the high surface charge, the molten glass drops split up in several smaller droplets which are deposited on a substrate forming a dense glass layer. Finally, the synthesized glass powders and deposited glass coatings are characterized.

Critical crystallization temperature for the occurrence of epitaxy between high-density polyethylene and isotactic polypropylene

The crystallization behavior of high-density polyethylene (HDPE) on highly oriented isotactic polypropylene (iPP) at elevated temperatures (e.g., from 125 to 128 degrees C), was studied using transmission electron microscopy and electron diffraction. The results show that epitaxial crystallization of HDPE on the highly oriented iPP substrates occurs only in a thin layer which is in direct contact with the iPP substrate, when the HDPE is crystallized from the melt on the oriented iPP substrates at 125 degrees C. The critical layer thickness of the epitaxially crystallized HDPE is not more than 30 nm when the HDPE is isothermally crystallized on the oriented iPP substrates at 125 degrees C. When the crystallization temperature is above 125 degrees C, the HDPE crystallizes in the form of crystalline aggregates and a few individual crystalline lamellae. But both the crystalline aggregates and the individual crystalline lamellae have no epitaxial orientation relationship with the iPP substrate. This means that there exists a critical crystallization temperature for the occurrence of epitaxial crystallization of HDPE on the melt-drawn oriented iPP substrates (i.e., 125 degrees C). (C) 1997 John Wiley & Sons, Inc.

Crystal nucleation in an electric field

AbstractNucleation of polar and apolar crystals in an electrostatic field has been analyzed. The analysis is based on the extended nucleation theory which takes into account orientation of amorphous kinetic elements and the resulting crystals. In an electric field free energy of transformation is orientation‐dependent which leads to orientation and field effects in thermodynamic (critical crystallization temperature) and kinetic crystallization characteristics (thermal and athermal nucleation rates).

The influence of the equilibrium melting temperature on the supermolecular morphology of several polymers

AbstractAt a constant isothermal crystallization temperature (Tc), the crystalline morphologies of several polymers have been found to be a function of the melt‐liquid temperature (T1). At a constant Tc below a critical crystallization temperature (T [about 0.9 T(K)], a transition from a nonspherulitic to a spherulitic morphology occurs when the melt liquid is heated above a melt‐liquid transition temperature, (Tlt) [approximately 1.03 Tm (K)], where Tm is the observed melting temperature of the sample. The melt‐liquid transition temperature, Tlt, which experimentally affects the visible morphology of a semicrystalline polymer, is apparently indistinguishable from the thermodynamic melting temperature, T, determined by the Hoffman‐Weeks procedure. The X‐ray powder diffraction patterns of spherulitic and nonspherulitic morphologies were identical, independent of the heating‐cooling cycle. This suggests that the transition that occurs at TIt does not affect the arrangement of polymer molecules in the crystallite, but only the manner in which the crystallites are arranged in the supermolecular morphology. The evidence suggests, at least for the polymers studied, that a residual order exists in the melt until the T or TIt of the particular polymer is reached. © 1993 John Wiley & Sons, Inc.

Ion Beam Induced Crystallization in Preamorphized Bp(100)

ABSTRACTIon beai induced epitaxial crystallization (IBIEC) in preaiorphized BP(100) has been investigated by RBS channeling experiients. Re-crystallization was induced by subsequent ion boibardients with 400 keV Kr, 400 keV Ar and 800 keV Ar at temperature range between 200°C and 450°C. The current densities of Kr and Ar ions were selected to give the saie energy deposition rate in the elastic collision process. Epitaxial crytallization was observed at teiperatures luch below those required for the therial solid phase epitaxy (SPE) process (above 800°C). The critical temperature for crystallization at typical current densities was 230°C. The ion species used for the preaiorphization give a weak influence on the regrowth rate. On the scale of deposited energy density in the elastic collisions, ion boibardients with higher electronic excitation efficiency were found to be effective in the regrowth process. Dose rate is found to be of iiportance in the regrowth process. The activation energy observed in Ar ion boibardients was 0.18±0.05 eV.