Melting Temperature Depression Research Articles

Effect of phase separation on spherulitic growth rate of PP/EPR in‐reactor alloys

AbstractIn this work, the effect of phase separation on the spherulitic growth rate of a polypropylene/ethylene–propylene random (PP/EPR) copolymer in‐reactor alloy was investigated. The PP/EPR in‐reactor alloy was either directly quenched from homogeneous melt to crystallization temperature or held at various temperatures for phase separation prior to crystallization. It is found that at lower crystallization temperatures previous phase separation in the melt retards the crystallization rate. The higher the phase separation rate, the smaller the spherulitic growth rate. This can be attributed to faster crystallization rate than the rate of secondary phase separation. The composition of the PP‐rich phase and corresponding depression of the equilibrium melting temperature of PP vary with phase separation temperature. On the other hand, at higher crystallization temperature, previous phase separation in the melt has little effect on the spherulitic growth rate because secondary phase separation can take place prior to crystallization. The transition temperature from regime II to regime III also shifts to lower temperature as the phase separation temperature increases. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Nanoparticles of Sn3.0Ag0.5Cu alloy synthesized at room temperature with large melting temperature depression

The Sn3.0Ag0.5Cu (wt%) lead-free solder alloy is considered to be one of the most promising alternatives to replace the traditionally used Sn–Pb solders. This alloy composition possesses, however, some weaknesses, mainly as a result of its higher melting temperature compared to the eutectic Sn–Pb solders. Nanoparticles of Sn3.0Ag0.5Cu lead-free solder alloy nanoparticles were prepared by chemical reduction with NaBH4 as a reducing agent at room temperature. The melting temperature of the synthesized Sn3.0Ag0.5Cu alloy nanoparticles was determined by differential scanning calorimetry (DSC). The results showed that the calorimetric onset melting temperature of the Sn3.0Ag0.5Cu alloy nanoparticles could be as low as 200 °C, which was about 17 °C lower than that of the bulk alloy (217 °C). The field emission scanning electron microscopy (SEM) images of the as-prepared nanoparticles indicated that the major particle size of Sn3.0Ag0.5Cu nanoparticles is smaller than 50 nm. The structure and morphology of the nanoparticles were analyzed with high resolution transmission electron microscopy (HRTEM). The Ag3Sn and Sn phase were observed in the HRTEM images, which was in good agreement with the XRD results. These low melting temperature Sn3.0Ag0.5Cu alloy nanoparticles show a potential to manufacture high quality lead-free solders for electronic products.

Synthesis and characterization of low temperature Sn nanoparticles for the fabrication ofhighly conductive ink

To fabricate a low cost, highly conductive ink for inkjet printing, we synthesized agram scale of uniformly sized Sn nanoparticles by using a modified polyol processand observed a significant size-dependent melting temperature depression from234.1 °C for bulkSn to 177.3 °C for 11.3 nm Sn nanoparticles. A 20 wt% of Sn nanoparticles was dispersed in the 50% ethylene glycol:50% isopropyl alcohol mixed solvent for the appropriate viscosity (11.6 cP) and surface tension(32 dyn cm − 1). To improve the electrical property, we applied the surface treatments of hydrogen reductionand plasma ashing. The two treatments had the effect of diminishing the sheet resistance from1 kΩ/sq to50 Ω/sq. In addition,conductive patterns (1 cm × 1 cm) were successfully drawn on the Si wafer using an inkjet printing instrumentwith conductive Sn ink. The maximum resistivity for an hour of sintering at250 °C was64.27 µΩ cm, which is six times higher than the bulk Sn resistivity(10.1 µΩ cm).

New Synthesis Approach for Low Temperature Bimetallic Nanoparticles: Size and Composition Controlled Sn–Cu Nanoparticles

A various size of Sn-Cu nanoparticles were synthesized by using a modified polyol process for low temperature electronic devices. Monodispersive Sn-Cu nanoparticles with diameters of 21 nm, 18 nm and 14 nm were synthesized. In addition, the eutectic composition shift was also observed in nano-sized particles as compared with bulk alloys. By controlling the size and eutectic composition, a significant melting temperature depression of 30.3 degrees C was achieved. These melting temperature depression approaches will reduce adverse thermal effects in electronic devices and provide the synthesis guidelines for bimetallic nanoparticles with a low melting temperature.

Determination of nucleic acid hydration using osmotic stress.

Water plays an important role in structure and molecular recognition of biopolymers. Understanding hydration of biopolymers is a significant problem in structural chemistry and biology. However, hydration is a dynamic process that is difficult to study. While X-ray crystallography, NMR, and molecular modeling have provided structural detail on nucleic acid hydration and valuable insights into water dynamics, the thermodynamic contribution of water molecules to conformational equilibria and recognition of nucleic acids remains poorly understood. This unit describes a thermodynamic analysis of nucleic acid hydration using osmotic stress. Osmotic stress monitors the depression of melting temperature upon decreasing water activity, and calculates the number of thermodynamically unique water molecules associated with the double helix and released from single strands upon melting. Comparison of the number of water molecules released upon melting of nucleic acids with different sequences and chemical modifications provides insights that complement and enhance information obtained by other methods.

The Influence of Oxygen on Mesomorphic Behavior of Benzylidene Anilines—The Effect of End Chain

A variety of terminal chain modifications were made by placing/removing the electro-negative oxygen atom to either or both sides of the rigid core of the benzylidene aniline compounds, the chosen alkyl chain lengths were n = 5 and m = 16. The mesomorphic properties were determined by polarizing thermal microscopy (TM) and differential scanning calorimetry (DSC). They exhibit two mono-variant and two di-variant phase sequences. The results are discussed in light of the depression in melting temperature, elevation of clearing temperature, and quenching of liquid-crystalline phases as a function of influence of oxygen with the end alkyl chain length.

Size-dependent freezing of n-alcohols in silicon nanochannels

We present a study on the phase behavior of several linear n-alcohols (heptanol, nonanol and undecanol) in their bulk state as well as confined in mesoporous silicon. We were able to vary the mean pore radii of the nanochannels from r = 3.5 nm to 7 nm and to determine the respective temperatures of the freezing and melting transitions using infrared and dielectric spectroscopy. The smaller the chain length the lower the freezing point, both in the bulk and in the confined state. Under confinement the freezing temperature decreases by up to 28 K compared to the bulk value. In accordance with the Gibbs-Thompson model the lowering is proportional to the inverse pore radius, ΔTfr ∝ 1/r. Moreover, the ratio of freezing temperature depression to melting temperature depression is close to the theoretical value of ΔTfr/ΔTmelt = 3/2. The spectra also indicate a structural change: while the solid bulk alcohols are a polycrystalline mixture of the orthorhombic β- and monoclinic γ-form, geometrical confinement forces the alcohol-chains into the more simple orthorhombic structure. In addition, a part of the material does not crystallize. Such an additional amorphous phase seems to be a logical consequence of the size mismatch between molecular crystals and irregular shaped pores.

Crystallization and dissolution behaviour of polyamide 6–water systems under pressure

AbstractThe solubility of polyamide 6 (PA6) in water under pressure has been reported recently and is explored further here using a pressurized differential scanning calorimeter equipped with a pressure regulator, enabling operation at constant pressure. The optimum parameters for solubility (temperature, pressure, concentration) were determined. Crystallization and melting temperature depressions of a maximum of 60 °C were found. The minimum water concentration needed to reach the maximum temperature depression was found to be approximately 30 mass%. Because in such a case the end melting/dissolution temperature for PA6 in water is approximately 165 °C, the pressure level has to be high enough to prevent water from evaporating, i.e. above 8 bar (0.8 MPa). The expected industrial uses of the water solubility of polyamides under pressure are to ease the processing of polyamides by extrusion; to make polyamide composites; to disperse temperature‐sensitive fillers in polyamides; and, in general, to realize ‘green’ routes for the formation of polyamides. Copyright © 2010 Society of Chemical Industry

MODELING THE MELTING TEMPERATURE OF METALLIC NANOWIRES

A model is developed to account for the size-dependent melting temperature of pure metallic and bimetallic nanowires, where the effects of the contributions of all surface atoms to the surface area, lattice and surface packing factors and the cross-sectional shape of the nanowires are considered. As the size decreases, the melting temperature functions of pure metallic and bimetallic nanowires decrease almost with the same size-dependent trend. Due to the inclusion of the above effects, the present model can also be applied to investigate the melting temperature depression rate of different low-dimensional system, accurately. The validity of the model is verified by the data of experiments and molecular dynamics simulations.

Thermal-oxidative degradation of polyamide 6,6 containing metal salts

The thermal-oxidative stability of oven aged polyamide 6,6 (PA6,6) doped with Co, Cu, Ni and Zn chlorides combined with KI was examined. Aging caused a depression in melting temperature and an increase in enthalpy of fusion of PA6,6 films due to the formation of a strongly degraded crystalline fraction with a lower molecular weight. A build-up of carbonyl absorption in the range 1700–1780 cm −1 due to primary and secondary photo-oxidation products was detected. The kinetics of carbonyl accumulation was affected by the morphology of the samples, and it was observed that at a later stage of aging the crystalline phase was also involved in the oxidation process. The above mentioned changes were greatest in the case of neat, Co and Ni doped polymer, suggesting that these metal salts acted as pro-oxidants. On the other hand, the use of Cu and Zn chlorides brought about a substantial increase in long-term polymer stabilization. Tensile tests revealed a large reduction in ductility as a result of aging for neat, Co and Ni doped polymer, whereas long-term retention of tensile properties was found for the polymer stabilized with Cu and Zn. The presence of the metal salts combined with KI led to increased stabilization for chlorides of Ni, and Co, owing to the participation of KI in non-radical decomposition of peroxides. No effect due to KI was observed for ZnCl 2.

Melting behavior of Fe‐O‐S at high pressure: A discussion on the melting depression induced by O and S

Shock compressed to pressures from 106 GPa to 232 GPa, the sound velocities were determined in Fe‐O‐S (90/8/2 in wt. %), regarded as the candidate compositions of the Earth's outer core. A discontinuity in sound velocity versus pressure relation was observed, which indicated that the shocked sample is initially melted at 149 GPa and completely melted at 167 GPa. On the basis of an energy conservation formulation, the calculated equilibrium melting temperature is about 3880 ± 500 K at 167 GPa. Taking this point as a reference, a high‐pressure melting curve can be inferred through Lindemann Law, which is again confirmed by the release melting temperatures of 3020 ± 500 K and 3200 ± 500 K measured at 90 GPa and 106 GPa, respectively. When extrapolating this melting curve to inner core‐outer core boundary (330 GPa), the melting temperature of this Fe‐O‐S composition is about 5400 ± 500K. Compared with the melting temperature 6000 K for pure iron at 330 GPa, the corresponding melting temperature depression is about 600 K due to the effect of O and S.

Biodegradable aliphatic/aromatic copoly(ester-ether)s: the effect of poly(ethylene glycol) on physical properties and degradation behavior

A series of high molecular weight copolymers based on poly(L-lactic acid) (PLLA) as the biodegradable aliphatic segments, poly(butylene terephthalate) (PBT) as the rigid aromatic segments and hydrophilic poly(ethylene glycol) (PEG) as the soft segments were synthesized with the aim of developing novel polymer materials which could combine high physical properties with good biodegradability. Via direct melt polycondensation of terephthalic acid (TPA), 1,4-butanediol (BDO), poly(L-lactic acid) oligomer (OLLA) and PEG, biodegradable aliphatic/aromatic copoly(ester-ether)s, poly(butylene terephthalate-co-lactate-co-ethylene glycol) (PBTLG), were prepared. The effect of the introduction of PEG soft segments on the synthesis, mechanical properties and thermal stabilities as well as the degradation behaviors of the final copolymers was investigated. When the PEG units were incorporated into the polymer main-chains, the weight-average molecular weight of the copolymers increased from 53,700 g/mol to 177,000 g/mol and the tensile strength (σ) improved by nearly two times from 6.5 MPa to 12.8 MPa for PBTLG1000-0.5. The glass-transition temperature (T g) gradually decreased from 26.9 °C down to −5.5 °C and a depression of melting temperature was observed with the increase of PEG content. According to the in vitro hydrolytic degradation observation, all of the copolymers underwent significant degradation in phosphate buffer solution at 37 °C and the water absorption as well as the degradation rate of PBTLGs displayed a strong dependency on the PEG content.

Miscibility, Crystallization, and Rheological Behavior of Solution Casting Poly(3-hydroxybutyrate)/poly(ethylene succinate) Blends Probed by Differential Scanning Calorimetry, Rheology, and Optical Microscope Techniques

The miscibility and crystallization of solution casting biodegradable poly(3-hydroxybutyrate)/poly(ethylene succinate) (PHB/PES) blends was investigated by differential scanning calorimetry, rheology, and optical microscopy. The blends showed two glass transition temperatures and a depression of melting temperature of PHB with compositions in phase diagram, which indicated that the blend was partially miscible. The morphology observation supported this result. It was found that the PHB and PES can crystallize simultaneously or upon stepwise depending on the crystallization temperatures and compositions. The spherulite growth rate of PHB increased with increasing of PES content. The influence of compositions on the spherulitic growth rate for the partially miscible polymer blends was discussed.

Polymer-polymer miscibility in PEO/cationic starch and PEO/hydrophobic starch blends

The main purposes were evaluating the influence of different starches on the miscibility with Poly(ethylene oxide) (PEO) and their effects on the spherulite growth rate. Polymer-polymer miscibility in PEO/cationic starch and PEO/hydrophobic starch blends consisting of different w/w ratios (100/0, 95/05, 90/10, 80/20, 70/30, 65/35 and 60/40) was investigated. This analysis was based on the depression in the equilibrium melting temperature (Tm 0 ). By treating the data of thermal analysis (Differential Scanning Calorimetry - DSC) with Nishi-Wang equation, a positive value (0.68) was found for the interaction parameter of PEO/cationic starch. For PEO/hydrophobic starch blends, a negative value (-0.63) was obtained for the interaction parameter. The results suggested that PEO/cationic starch system should be immiscible. How- ever, the system PEO/hydrophobic starch was considered to be miscible in the whole range of studied compositions. Through optical microscopy analysis, it was concluded that the spherulite growth rate is significantly affected by changing the amount and the type of starch as well.

Role of Oxygen on Phase Behaviour of Benzylidene Aniline – A Comparative Study

Four structurally related Schiff’s base compounds are synthesized and their mesogenic properties are characterized by using Thermal Microscopy (TM) and Differential Scanning Calorimetry (DSC). The position of oxygen is varied from either sides of the bridging site, oxygen introduced on both sides and the oxygen is removed from the bridging site for the values of n = 8 and m = 5. The influence of oxygen atom to the extent of increase in thermal range, depression in melting temperature, elevation of clearing temperature is observed for all four compounds, viz. N (p-n-Octyloxy benzylidene) p-n-Pentyl aniline (8O.5), N (p-n-Octyl benzylidene) p-n-Pentyloxy aniline (8.O5), N (p-n-Octyloxy benzylidene) p-n-Pentyloxy aniline (8O.O5), and N (p-n-Octyl benzylidene) p-n- Pentyl aniline (8.5). The shift in the position of oxygen from the aldehyde to the aniline side and the removal of oxygen has a greater effect as they become room temperature liquids, whereas the oxygen on the aldehyde side and the oxygen on both sides of the rigid core moiety effect only the clearing temperatures. The results obtained are discussed in the light of the earlier data available on Schiff’s base nO.m compounds

Synthesis and DSC study on Sn3.5Ag alloy nanoparticles used for lower melting temperature solder

The traditional Sn–Pb eutectic solder alloys are being phased out from the electronics industry due to the toxicity of lead (Pb), leading to the development and implementation of lead-free solders. Sn3.5Ag lead-free solder alloy, considered to be one of the promising alternatives to replace the traditionally used Sn–Pb solder, however, still has some weaknesses, such as its higher melting temperature than that of the Sn–Pb solder alloy. A possible way to decrease the melting temperature of a solder alloy is to decrease the alloy particle size to the nanometer range. Sn3.5Ag nanoparticles with different size distribution were synthesized using chemical reduction method by applying NaBH4 as reduction agent. The melting properties of these synthesized nanoparticles were studied by differential scanning calorimetry (DSC), and size-dependent melting temperature depression of these nanoparticles has been observed. Gibbs–Thomson equation was used to analyze the size-dependent melting temperature property, giving a good prediction of the melting temperature depression for the Sn-based lead-free solder alloy nanoparticles.

Effect of the Alumina Shell on the Melting Temperature Depression for Aluminum Nanoparticles

The dependence of aluminum (Al) melting temperature on particle size was studied using a differential scanning calorimeter and thermogravitmetric analyzer for particles encapsulated in an oxide shell. Pressure generation within the Al core leads to an increase in melting temperature in comparison with traditional melting temperature depression calculated using the Gibbs−Thomson equation. On the basis of elasticity theory, the pressure in the Al core at the onset of melting is caused mainly by surface tension at the alumina−air and Al−alumina interfaces. This implies that pressure due to the difference in thermal expansion of aluminum and alumina relaxes. A possible relaxation mechanism is discussed. The static strength of the alumina shell and the maximum static generated pressure in aluminum were evaluated. Mechanically damaging the oxide shell was shown to reduce the melting temperature due to a decrease in generated pressure within the Al core. Thus, reduction in melting temperature can be used as a qu...

The effects of melt annealing and counterpart's molecular weight on the thermal properties and phase morphology of poly(L‐lactide)‐based blends

AbstractThe thermal properties and phase morphology of poly(L‐lactide) (PLLA)‐based blends have been studied. Two poly(ethylene glycol)s (PEGs) with molecular weight (MW) of about 1,500 (1.5k) g/mol and 2,000,000 (2M) g/mol, respectively, were used as counterparts. The blends were annealed at a preselected temperature of 200 °C for either 2 min or 30 min before the characterizations. Both PEGs were determined to enhance the crystallizability of PLLA. After a 2‐min process of annealing, the PEG(1.5k)'s crystallization efficiency on PLLA has been noted to increase with the increase of its content. Conversely, PEG(2M)'s crystallization efficiency declined with the increase of its content. Extending the annealing time has evidently changed the PEGs' crystallization effect on PLLA. Moreover, the PEG(1.5k) has, to a greater extent, brought about the depression of PLLA's melting temperature by increasing its content, and this depression increased with the annealing time. The blends exhibited lower thermal stability than those of the parent components, particularly for the PEG(1.5k)‐included system with a higher PEG content. Regardless of the annealing time, the PEG(1.5k)‐included blends have shown homogeneous melt morphology under light microscope, whereas the PEG(2M)‐included blends have displayed phase‐separated melt morphology. In addition to the composition, PEG's MW and annealing time influence the crystalline morphology of the blends. The ringed PLLA spherulites have appeared mostly in the 2‐min annealed PEG(1.5k)‐included blends. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1497–1510, 2009

Melting temperature depression of Sn‐0.4Co‐0.7Cu lead‐free solder nanoparticles

PurposeThe purpose of this paper is to study the melting temperature of the nanoparticles of the new developed Sn‐0.4Co‐0.7Cu (wt%) lead‐free solder alloy.Design/methodology/approachNanoparticles of Sn‐0.4Co‐0.7Cu lead‐free solder alloy were prepared by the self‐developed consumable‐electrode direct current arc technique, where ultrasonic vibration was applied during the manufacturing of the particles. X‐ray diffraction and field emission scanning electron microscope were employed to analyze the crystal structure and morphology of the nanopartiles, respectively. Differential scanning calorimetry was used to investigate the melting temperature of both the bulk alloy and as‐prepared nanoparticles.FindingsThe melting temperature of the nanoparticles was approximately 5°C lower compared to that of the bulk alloy.Originality/valueAs a novel developed lead‐free solder alloy, the Sn‐0.4Co‐0.7Cu (wt%) alloy provides a cost advantage compared to the extensively used Sn‐Ag‐Cu system. Some limitations still exist, however, mainly due to its relatively higher melting temperature compared to that of eutectic Sn‐37Pb solder. In view of this situation, the attempt to lower its melting temperature has recently attracted more attention based on the knowledge that the melting temperature for pure metals is reduced when the particle size is decreased down to a few tens of nanometers.

Finite size melting of spherical solid–liquid aluminium interfaces

We have investigated the melting of nano-sized cone shaped aluminium needles coated with amorphous carbon using transmission electron microscopy. The interface between solid and liquid aluminium was found to have spherical topology. For needles with fixed apex angle, the depressed melting temperature of this spherical interface, with radius R, was found to scale linearly with the inverse radius 1/R. However, by varying the apex angle of the needles we show that the proportionality constant between the depressed melting temperature and the inverse radius changes significantly. This led us to the conclusion that the depressed melting temperature is not controlled solely by the inverse radius 1/R. Instead, we found a direct relation between the depressed melting temperature and the ratio between the solid–liquid interface area and the molten volume.