Melt Density Research Articles

Full-atomistic simulations of poly(ϵ-caprolactone) diol models with CVFF and CGenFF

Poly(ϵ-caprolactone) (PCL) diol, with good biodegradation and biocompatibility, is one of the widely used soft segments (SSs) in composing bio-polyester-urethanes (Bio-PUs), which show great potential in both biomedical and tissue engineering applications. Properties of Bio-PUs are tunable by combining SS monomers with different molecular weights, structures, modifications, and ratio of components. Although numbers of research have reported many Bio-PUs properties, few studies have been done at the molecular scale. In this study, we use molecular dynamic (MD) simulation to construct atomistic models for two commonly used PCL diol SSs with different molecular weights 1247.58 Da and 1932.42 Da. We compare the simulation results by using two widely used classical force fields for organic molecules: Consistent Valence Force Field (CVFF) and CHARMM General Force Field (CGenFF), and discuss the validity and accuracy. Melt density, volume, polymer conformations, transition temperature, and mechanical properties of PCL diols are calculated and compared with experiments. Our results show that both force fields provide accurate predictions on the properties of PCL diol system at the molecular scale and could help the design of future Bio-PUs.

A mathematical model for nanoparticle melting with size-dependent latent heat and melt temperature

In this paper, we study the melting of a spherical nanoparticle. The model differs from previous ones in that a number of features have been incorporated to match experimental observations. These include the size dependence of the latent heat and a cooling condition at the boundary (as opposed to the fixed temperature condition used in previous studies). Melt temperature variation and density change are also included. The density variation drives the flow of the outer fluid layer. The latent heat variation is modelled by a new relation, which matches experimental data better than previous models. A novel form of Stefan condition is used to determine the position of the melt front. This condition takes into account the latent heat variation, the energy required to create new surface and the kinetic energy of the displaced fluid layer. Results show that melting times can be significantly faster than predicted by previous theoretical models; for smaller particles, this can be around a factor 3. This is primarily due to the latent heat variation. The previously used fixed temperature boundary condition had two opposing effects on melt times: the implied infinite heat transfer led to faster melting but also artificially magnified the effect of kinetic energy, which slowed down the process. We conclude that any future models of nanoparticle melting must be based on the new Stefan condition and account for latent heat variation.

Comparative Effectiveness of Different Phase Change Materials to Improve Cooling Performance of Heat Sinks for Electronic Devices

This paper thermo-physically characterizes salt hydrate, paraffin wax and milk fat as phase change materials (PCMs). The three PCMs are compared in terms of improving heat sink (HS) performance for cooling electronic packaging. An experimental study is carried out on commercially available finned HS with and without PCM under natural ventilation (NV) and forced ventilation (FV) at different heat loads (4 W to 10 W). The results indicate that integration of all of the PCMs into the HS improves its cooling performance; however, milk fat lags behind the other two PCMs in terms of cooling produced. A three-dimensional pressure-based conjugate heat transfer model has been developed and validated with experimental results. The model predicts the parametric influence of PCM melting range, thermal conductivity and density on HS thermal management performance. The HS cooling performance improves with increased density and conductivity while it deteriorates with the wider melting range of the PCMs.

Major element composition of an Early Enriched Reservoir: constraints from 142Nd/144Nd isotope systematics in the early Earth and high-pressure melting experiments of a primitive peridotite

The Accessible Silicate Earth (ASE) has a higher 142Nd/144Nd ratio than most chondrites. Thus, if the Earth is assumed to have formed from these chondrites, a complement low-142Nd/144Nd reservoir is needed. Such a low-142Nd/144Nd reservoir is believed to have been derived from a melt in the early Earth and is called the Early Enriched Reservoir (EER). Although the major element composition of the EER is crucial for estimating its chemical and physical properties (e.g., density) and is also essential for understanding the origin and fate of the EER, which are both major factors that determine the present composition of the Earth, it has not yet been robustly established. In order to determine the major element composition of the EER, we estimated the age and pressure–temperature conditions to form the EER that would best explain its Nd isotopic characteristics, based on Sm–Nd partitioning and its dependence on pressure, temperature, and melting phase relations. Our estimate indicates that the EER formed within 33.5 Myr of Solar System formation and at near-solidus temperatures and shallow upper-mantle pressures. We then performed high-pressure melting experiments on primitive peridotite to determine the major element composition of the EER at estimated temperature at 7 GPa and calculated the density of the EER. The result of our experiments indicates that the near-solidus melt is iron-rich komatiite. The estimated density of the near-solidus melt is lower than that of the primitive peridotite, suggesting that the EER melt would have ascended in the mantle to form an early crust. Given that high mantle potential temperatures are assumed to have existed in the Hadean, it follows that the EER melt was generated at high pressure and, therefore, its composition would have been picritic to komatiitic. As the formation age of the EER estimated in our study precedes the last giant, lunar-forming impact, the picritic to komatiitic crust (EER) would most likely have been ejected from the Earth by the last giant impact or preceding impacts. Thus, the EER has been lost, leaving the Earth more depleted than its original composition.

A method to improve dimensional accuracy and mechanical properties of injection molded polypropylene parts

Abstract Gas counter pressure (GCP) technology can impose a reverse pressure to melt and thereby effectively increase the pressure acting on the melt at flow front. Theoretically, it has a potential to solve some defects often occurring in conventional injection molding (CIM) process. This paper designed and manufactured a GCP injection mold. GCP injection molding experiments were conducted. Effects of GCP process on melt flow and density, dimensional accuracy, and mechanical properties of molded samples were investigated. The results showed that GCP process can effectively inhibit the “fountain effect” in melt filling process, decrease the dimensional shrinkage of molded samples, increase dimensional accuracy of samples, and effectively improve impact property of samples. For the samples without weld line, tensile strength and flexural strength of GCP injection molded samples are slightly increased in comparison with those of CIM samples, but for the samples with weld line, GCP process can greatly improve the tensile strength and flexural strength of molded samples. When GCP is 9 MPa and GCP holding time is 10 s, the dimensional accuracy of molded samples without weld line, the tensile strength and flexural strength of the molded samples with weld line all increase up to maximum values. In comparison with CIM samples, the dimensional shrinkage of samples without weld line decreases by 17.2%, the tensile strength and flexural strength of samples with weld line increase by 30.51% and 23.69%, respectively. The impact value of the samples molded by process parameter combination of GCP 9 MPa and GCP holding time 20 s is the highest, and the impact value increases by 18.65%.

X-ray absorption study of 3d transition-metals and Mg in glasses and analogue crystalline materials in AFe3 + Si2O6 and A2X2 + Si5O12, where A = K, Rb, or Cs and X = Mg, Mn, Fe, Co, Ni, Cu, or Zn

Crystalline and glassy phases in the ‘leucite’ systems (K,Rb,Cs)Fe3+Si2O6 and (K,Rb,Cs)2(Mg,Mn,Fe,Co,Ni,Cu,Zn)2+–Si5O12 have been studied using K-edge X-ray Absorption Spectroscopy (XAS) for 3d transition elements and Mg. Crystalline samples of known structure are used as model compounds for deducing the local structures of the equivalent glasses. ‘Ideal’ tetrahedral framework X2+–O distances are: Mn2+–O 2.02, Fe2+–O 1.98; Co2+–O 1.96, Ni2+–O 1.95, Cu2+–O 1.92, Zn2+–O 1.93 and Mg2+–O 1.93Å. The quenched glasses have Extended X-ray Absorption Fine Structure (EXAFS) first-shell distances and coordination numbers consistent with Mg and 3d elements occurring in tetrahedral coordination in most cases. The X-ray Absorption Near Edge Structure (XANES) spectra of the glasses are basically the same as those for the crystalline samples showing that they have similar medium range order, consistent with most of the Mg and 3d elements acting as network formers along with the associated alkalis as X2Y2+O2 complexes. Anhydrous glasses in the system CaO–MgO–Al2O3–SiO2 together with a basalt glass from Hawaii show examples of Mg in octahedral- (2.07Å, basalt), tetrahedral- (~1.87Å, siliceous glass) and 5-coordinated (2.01–2.04Å) sites. Although most Earth scientists assume that Mg and Fe2+ act as network modifiers in natural magmas, ultra-potassic, peralkaline compositions ((Na+K)/(Al+Fe3+)>1) could have had some Fe2+ and Mg complexes with alkalis in the melt network as K2(Mg,Fe2+)O2 and the implications of this to melt density and viscosity are considered.

Effects of PCM thermophysical properties on thermal storage performance of a shell-and-tube latent heat storage unit

An orthogonal experiment with five factors and four levels was designed and numerical studies were performed to reveal the effects of molten salt PCM thermophysical properties on heat and exergy storage performance of a shell-and-tube latent heat storage (LHS) unit. The range analysis, regression analysis and optimization were conducted. The PCM selection criteria were established. The results show that for short time LHS system, the order of PCM properties effects on heat storage performance is melting temperature, thermal conductivity, specific heat, density and melting enthalpy successively. PCM with lower melting temperature, higher thermal conductivity and specific heat is beneficial to improve the heat storage rate and heat storage quality. For long time heat storage system, the order of PCM properties effects on heat storage performance is density, melting enthalpy, specific heat, melting temperature and thermal conductivity successively. PCM with higher density, melting enthalpy and specific heat can both improve the heat storage rate and heat storage quality. The orthogonal experiment method is reliable to investigate the effects of PCM properties on LHS performance; and the optimization based on regression analysis is more efficient than that based on range analysis.

Synthesis of Thermally Stable Geminal Dicationic Ionic Liquids and Related Ionic Compounds: An Examination of Physicochemical Properties by Structural Modification

Geminal dicationic ionic liquids (ILs) often display higher thermal stabilities, viscosities, and densities compared to traditional monocationic ILs. Also, dicationic ILs have advantages in terms of tuning of their physicochemical properties by different structural modifications. They can be considered as a combination of three structural moieties: (1) cationic head groups, (2) an alkane linker chain, and (3) the associated anions. Two types of each imidazolium, pyrrolidinium, and phosphonium cations were joined by different alkane linkages (C6, C9, and C12) to develop 18 different dications. These dications were paired with two different anions (NTf2– and PFOS–) to synthesize 36 different dicationic ILs. The effect of variations in the structural moieties of these related ILs on their physicochemical properties, including melting points, densities, viscosities, solubilities, and thermal stabilities, were evaluated. ILs synthesized in this study displayed TGA thermal stabilities in the range 330–467 °C. A...

Learning volcanology: Modules to facilitate problem solving by undergraduate volcanology students

Six modules are presented that are designed for use in an undergraduate physical volcanology course. Each module uses a four-step mathematical problem-solving approach following Polya’s How to Solve It, to guide students to: (i) understand the problem, (ii) devise a plan for solving the problem, (iii) implement the plan, and (iv) reflect on their solution. The modules cover topics in estimation of volumes of debris flow and tephra fallout deposits, lava eusion rate, calculation of melt density and viscosity, and development of dynamic models of bubble ascent in magma. Core quantitative issues, such as linear regression and error propagation, are introduced using these modules. The modules are included as supplementary material in PowerPoint and Portable Document Format (PDF). Cumulatively, the modules are designed to help volcanology students construct their own schemas, through which they can master abstract concepts in volcanology and in the geosciences generally. Physical volcanology can play a central role in the Earth Sciences curriculum by promoting quantitative problem solving using modules such as these.

On the potential for lunar highlands Mg-suite extrusive volcanism and implications concerning crustal evolution

The lunar magnesian-suite (Mg-suite) was produced during the earliest periods of magmatic activity on the Moon. Based on the cumulate textures of the samples and a lack of evidence for Mg-suite extrusives in both the sample and remote sensing databases, several petrogenetic models deduce a predominantly intrusive magmatic history for Mg-suite lithologies. Considering that ∼18% of the lunar surface is covered by mare basalt flows, which are substantially higher in density than estimated Mg-suite magmas (∼2900 versus ∼2700kg/m3), the apparent absence of low-density Mg-suite volcanics is surprising. Were Mg-suite magmas predominantly intrusive, or have their extrusive equivalents been covered by subsequent impact ejecta and/or later stage volcanism? If Mg-suite magmas were predominantly intrusive, what prevented these melts from erupting? Or, if they are present as extrusives, what regions of the Moon are most likely to contain Mg-suite volcanic deposits?This study investigates buoyancy-driven ascent of Mg-suite parental melts and is motivated by recent measurements of crustal density from GRAIL. Mg-suite dunite, troctolite, and spinel anorthosite parental melts (2742, 2699, and 2648kg/m3, respectively) are considered, all of which have much lower melt densities relative to mare basalts and picritic glasses. Mg-suite parental melts are more dense than most of the crust and would not be expected to buoyantly erupt. However, about 10% of the lunar crust is greater in density than Mg-suite melts. These areas are primarily within the nearside southern highlands and South Pole-Aitken (SP-A) basin. Mg-suite extrusions and/or shallow intrusions were possible within these regions, assuming crustal density structure at >4.1Ga was similar to the present day crust. We review evidence for Mg-suite activity within both the southern highlands and SP-A and discuss the implications concerning crustal evolution as well as Mg-suite petrogenesis. Lower crustal densities measured by GRAIL are consistent with the lack of observed Mg-suite extrusives. If Mg-suite extrusive volcanism was prevented by the low density of the crust, it would suggest the lunar crust was fractured shortly after solidification (>4.3 Ga). The thermal- and stress-state of the lunar crust may have also inhibited Mg-suite extrusion.

Novel amino acid‐based ionic liquid analogues: neutral hydroxylic and sulfur‐containing amino acids

AbstractDeep eutectic solvents (DESs) have shown potential promise for various industrial applications. Abundant research works were carried out on Type III DES employing choline chloride as the quaternary ammonium salt in combination with a variety of hydrogen bond donors (HBDs). Despite the fact that they are cheap, biodegradable, and have a wide application in food, polymer, and pharmaceutical industries, amino acids have not been utilized as HBD for the synthesis of DES. In this work, different ammonium‐based salts are used to synthesize different amino acid‐based DES systems. Four different amino acids are considered, two of which are neutral amino acids, namely L‐serine and L‐threonine, while the other two are based on the sulfur‐containing amino acids, namely L‐methionine and L‐cysteine. The successful DESs were characterized in terms of their physical properties. The melting point, density, viscosity, surface tension, refractive index, conductivity, and pH were measured for the successful DES systems at different temperatures ranging from 303.15 to 353.15 K. The introduction of such novel DES opens the door for performing more work on utilizing them for various chemical, biochemical, and pharmaceutical applications. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Glass structure, melt structure, and dynamics: Some concepts for petrology

![Figure][1] The thermodynamic and transport properties of the aluminosilicate melts at the heart of most magmatic processes vary in complex ways with composition, temperature, and pressure. Insights into these properties can come from information on the structure of the melts themselves, and more commonly from their glassy, quenched equivalents. Although most such connections remain qualitative or semi-quantitative, they are fundamentally important in interpretation of observations on igneous systems in nature and the laboratory, and in the formulation of physically accurate models. This review presents some of the important concepts of aluminosilicate glass and melt structure and dynamics that are most relevant to furthering our understanding of the igneous processes so central to how our planet has formed and evolved. The relationships among glasses, melts, and crystals are introduced. The structural underpinnings of temperature and pressure effects on melt free energies, densities, and viscosities, constraints on the extent of order/disorder among cations and anions in melts, why silica activity varies so strongly with composition, and how liquid-liquid phase separation can be understood, are discussed. Some simple, but useful, general views are presented on melt disorder and the shapes of liquidus surfaces (key to magmatic phase equilibria), as are links between atomic-scale dynamics and viscous flow and diffusion. [1]: pending:yes

Synthesis and characterization of high density polyethylene/peat ash composites

Abstract A new type of polymer composite was synthesized from peat ash which was obtained as industrial waste. This was added to high density polyethylene (HDPE) at varying mixing ratios and the resulting products were characterized using different experiments which included Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), melt flow index (MFI), density, wettability, tensile test, flexural test and cost analysis. The effects of various ash loadings and the use of the maleic anhydride grafted high density polyethylene (HDPE-g-MA) compatibilizer on the physical and mechanical properties of composites were investigated. It was observed that the utilization of peat ash significantly increased the tensile strength and the flexural modulus, where also reducing raw material cost. Incorporating (HDPE-g-MA) in the composites formulation led to further increases in tensile and flexural properties. Conversely, there was a significant decrease of impact strength found for all composites in comparison to the virgin HDPE. And the impact strengths generally decreased as peat ash content increases. Microstructural analyses showed that surface treated peat ash particles appeared to be well-incorporated into the HDPE matrix, as intimated polymer/peat ash contact was observed. In addition, the melt flow index of the composites decreased remarkably with an increase in peat ash content. No significant water uptake effect was detected on peat ash composites indicating that these materials could be used as a direct replacement for HDPE in applications where impact strength is not a critical factor. Furthermore, the use of peat ash increased the composite density in comparison to virgin HDPE. Nevertheless, as peat ash reinforcement does offer increased tensile and flexural properties, this may make the end product lighter as lower wall thickness parts can be used to fulfil the same function. From this study, it was concluded that the utilization of the peat ash from peat fired power stations has proved to have significant value-added potential as a filler material in polymer composites.

Density and surface tension of a concentrated lead melt in nickel

The influence of a lead impurity on the properties of metallic melts in the composition range that obeys Henry’s law is studied. The formation of the structural and physicochemical properties of real concentrated melts can be traced from changes in the temperature and concentration dependences of structure-sensitive properties, namely, density and surface tension. The surface properties of a solution depend on its volume properties and differ from them in enhancement effect. The lead saturation of the nickel melt is found to be accompanied by a compression effect (decrease in the melt volume), which is enhanced to a certain lead concentration. As this concentration is exceeded, the compression effect weakens because of volume separation and the appearance of an excess lead phase. As the lead content in a nickel base increases, the surface tension decreases, a second phase forms, and the melt undergoes separation.

Search for anisotropy in the Debye-Waller factor of HCP solid (4)He.

The properties of hexagonal close packed (hcp) solid (4)He are dominated by large atomic zero point motions. An accurate description of these motions is therefore necessary in order to accurately calculate the properties of the system, such as the Debye-Waller (DW) factors. A recent neutron scattering experiment reported significant anisotropy in the in-plane and out-of-plane DW factors for hcp solid (4)He at low temperatures, where thermal effects are negligible and only zero-point motions are expected to contribute. By contrast, no such anisotropy was observed either in earlier experiments or in path integral Monte Carlo (PIMC) simulations of solid hcp (4)He. However, the earlier experiments and the PIMC simulations were both carried out at higher temperatures where thermal effects could be substantial. We seek to understand the cause of this discrepancy through variational quantum Monte Carlo simulations utilizing an accurate pair potential and a modified trial wavefunction which allows for anisotropy. Near the melting density, we find no anisotropy in an ideal hcp (4)He crystal. A theoretical equation of state is derived from the calculated energies of the ideal crystal over a range of molar volumes from 7.88 to 21.3 cm(3), and is found to be in good qualitative agreement with experimental data.

Concentrated Solutions of Single-Chain Nanoparticles: A Simple Model for Intrinsically Disordered Proteins under Crowding Conditions.

By means of large-scale computer simulations and small-angle neutron scattering (SANS), we investigate solutions of single-chain nanoparticles (SCNPs), covering the whole concentration range from infinite dilution to melt density. The analysis of the conformational properties of the SCNPs reveals that these synthetic nano-objects share basic ingredients with intrinsically disordered proteins (IDPs), as topological polydispersity, generally sparse conformations, and locally compact domains. We investigate the role of the architecture of the SCNPs in their collapse behavior under macromolecular crowding. Unlike in the case of linear macromolecules, which experience the usual transition from self-avoiding to Gaussian random-walk conformations, crowding leads to collapsed conformations of SCNPs resembling those of crumpled globules. This behavior is already found at volume fractions (about 30%) that are characteristic of crowding in cellular environments. The simulation results are confirmed by the SANS experiments. Our results for SCNPs--a model system free of specific interactions--propose a general scenario for the effect of steric crowding on IDPs: collapse from sparse conformations at high dilution to crumpled globular conformations in cell environments.

Novel amino acids based ionic liquids analogues: Acidic and basic amino acids

Deep eutectic solvents (DES) are one of the immerging promising industrial green solvents that are gaining considerable attention. These novel liquids have been synthesized from a variety of quaternary ammonium and phosphonium salts in combination with one or more complexing agents. Amino acids may act as good hydrogen bond donors and hence can be used as the complexing agent in the synthesis of type III DES. In this work a variety of ammonium quaternary salts have been investigated in forming amino acids-based DESs by combining with acidic or basic amino acids. Five of the common basic and acidic amino acids were used for this purpose. Three amino acids (glutamic acid, aspartic acid and arginine) were successful in forming DESs with the salt tetrabutylammonium chloride. The successful molar ratios of these DESs were characterized by measuring their melting point, density, viscosity, surface tension, refractive index, and conductivity in the temperature range 303.15–353.15 K. The presented novel data for these DESs can be utilized for customizing these solvents for probable chemical or industrial applications.

Investigation of the changes in melt flow indexes (MFI) and densities of polyamide 6 (PA6) and polyoxymethylene (POM) related with hydrolyzed powder coating waste amount

Investigation of the changes in melt flow indexes (MFI) and densities of polyamide 6 (PA6) and polyoxymethylene (POM) related with hydrolyzed powder coating waste amount

Investigation of the changes in melt flow indexes (MFI) and densities of polyamide 6 (PA6) and polyoxymethylene (POM) related with hydrolyzed powder coating waste amount

Yapilan bu calismada, polioksimetilenin (POM) ve poliamid 6'nin icerdikleri hidrolize edilmis elektrostatik toz boya atik miktarina bagli eriyik akis indeksleri ve yogunluklarindaki degisimler arastirilmistir. Hidrolize edilmis elektrostatik toz boya atiklari termoplastik ve termoset yapidaki elektrostatik toz boyalarin kullanilmasi sonucunda olusan atiklarin karisimini icermektedir. Bu atiklar ayri ayri poliamid 6 ve polioksimetilen icerisine agirlikca farkli (%10, %20 ve %30) oranlarinda karistirilarak karisimlar olusturulmus ve bu karisimlarin akiskanliklari ile yogunluklarindaki degisimler belirli sicaklik ve basinc altinda incelenmistir. Boylelikle poliamid 6 (PA6) ve polioksimetilenin (POM) akiskanliklari ve yogunluklarinin, artan hidrolize edilmis elektrostatik toz boya atik miktarina bagli olarak nasil degisim gosterdigi tespit edilerek grafiklerle ortaya konmustur

A study on quantitative evaluation of soft reduction amount for CC bloom by thermo-mechanical FEM model

Soft reduction has been proved to be the most promising way to minimize center segregation together with the strand center porosity elimination. The negative pressure driven residual melt flow could be balanced by a reasonable reduction amount to compensate the volume shrinkage in the crater mushy zone. The optimum soft reduction amount to bloom casting for given heavy railway steel has been studied in the paper from the point of view of the volume shrinkage compensation. A solidification analysis model was developed to determine the reduction amount based on the local shrinkage in the final solidification stage. The volume shrinkage in the center inter-dendritic region has been quantitatively calculated through the evaluation to the changing melt density. Another thermo-mechanical coupled FEM model was developed to investigate the bloom deformation behavior upon soft reduction operation. The squeezing effect of the soft reduction on the center mushy zone at various solid fractions was revealed quantitatively as well. The results shown that the theoretical soft reduction amount should decrease from 12.2 mm to 4.0 mm corresponding to the solid fraction from 0.3 to 0.9. A new definition for the calculation of the internal soft reduction efficiency was proposed and compared with the conventional one. The nomogram for the determination of optimum soft reduction has been presented for the bloom casting at various center solid fraction. Accordingly, an optimized soft reduction practice was determined for quality high speed railway steel production with clearly improved strand soundness.