Variation Of Melting Temperature Research Articles

The effects of PHB-g-MA types on the mechanical, thermal, morphological, structural, and rheological properties of polyhydroxybutyrate biopolymers

This study investigates the grafting of polyhydroxybutyrate (PHB) chains with maleic anhydride (MA) in concentrations ranging from 5 % to 10 % by weight. This process was conducted during microwave treatment and using a reactive extruder, employing benzoyl peroxide (BPO) as the initiator. The impact of these methods on PHB's overall properties was thoroughly investigated. In the study, PHB–g–MA was incorporated into neat PHB via the extrusion process at a 5 % loading rate. Notably, the mechanical properties exhibited an increase in the presence of PHB–g–MA, likely due to morphological improvements in the neat PHB, as indicated by morphological characterization. X-ray diffraction results indicated crystallinity percentages increase with the addition of MA. Differential scanning calorimetry revealed minimal variation in melting and crystallization temperatures when PHB–g–MA was included. Both storage and loss moduli were enhanced by the incorporation of PHB–g–MA, and the blends exhibited consistent tan delta values. Regarding rheological properties, the storage and loss moduli of PHB blends containing PHB–g–MA blends were observed to rise with rising frequency values. Based on these results, the microwave process was identified as the most effective method for grafting.

Multiphysics modeling and experimental validation of heat and mass transfer for the vacuum induction melting process

Vacuum induction melting is crucial in casting nickel-based superalloy components, ensuring excellent properties for aero-engine applications. Precise melting temperatures are vital for achieving optimal metallurgical quality before casting. Hence, a multiphysics numerical model is developed to simulate the induction melting process for the Inconel 718 superalloy. The proposed holistic model integrates magnetic fields, induced currents, and heat and momentum transfer phenomena in a single coupled model. A moving mesh approach reproduces the magneto-hydrodynamic behavior of the free surface, simulating the oscillations of the melt. The stabilized deformed surface profile is correlated with experimental measurements, reporting a proper correlation. Then, the flow field and recirculation effect are modeled with a Low Reynolds Number turbulence approach and coupled with the melt convective heat transfer, developing a complete magneto-thermo-hydrodynamic model. In a laboratory-scale vacuum induction melting furnace, transient melting operation variables are characterized and introduced to the numerical model to compute the temperature evolution. An accurate reproduction of the transient melt temperature variations is reported with a relative error of less than 5%. The influence of the crucible thermal insulating capacity is assessed, emissivity dependence evaluated, and melt homogenization is reported at different process stages. This comprehensive numerical and experimental approach offers valuable insights for enhancing vacuum induction melting for Ni-based superalloys.

Structural, optical, and thermal studies of Poly(vinylidene fluoride-co-hexafluoropropylene) and Polyvinylpyrrolidone composite doped Ag/ZnO mixed nanoparticles for flexible optoelectronic devices

Polymer nanocomposites (PNCs) films based on Polyvinylidene fluoride co-hexafluoropropylene (PVDF-HFP), Polyvinylpyrrolidone (PVP), and Ag/ZnO nanoparticles have been prepared using solution casting technique. Investigation of prepared films has been created using various experimental techniques. These prepared films were characterized by XRD, FTIR, UV–visible, and DSC/TGA analysis to study their structural, optical, and thermal properties. The Enhanced amorphous nature of PVDF-HFP/PVP blend film due to doping has been identified from X-ray diffraction analysis. The FTIR spectra confirmed the complexation between the Ag and ZnO ions and the host polymer in terms of changes in intensity and certain band positions. The UV–visible analysis showed that the optical band gap (direct and indirect band gap) of the pristine polymeric blend change significantly with the concentration of dopant Ag/ZnO NPs, and these effects are more noticeable at the higher loading. Variation in glass transition temperature (Tg) and melting temperature (Tm) of PVDF-HFP/PVP-Ag/ZnO PNCs system having various concentration of Ag/ZnO NPs were observed by DSC analysis. The Tg of the composite has been found to be decreasing with increase in the content of Ag/ZnO NPs revealing the ordered arrangement of nanoparticles in the blend. The excellent thermal stability of the blend nanocomposite compared to pure PVDF-HFP/PVP blend and its improvement with the loading of Ag/ZnO NPs has been proved by TGA. From all the characterization results, Ag/ZnO-doped PVDF-HFP/PVP polymer blend exhibits better properties which are more suitable for electrochemical devices.

Analyzing the thermal potential of binary 2D (h-BN/Gr) nanoparticles enhanced lauric acid phase change material for photovoltaic thermal system application

Thermal energy storage as latent heat is an effective strategy to preserve the excessive energy available. In this aspect, fatty acid phase change materials (PCMs) are promising materials since they have a high latent heat, nontoxic, and little sub-cooling. However, their inherently low thermal conductivity severely restricts their applicability. Herein, hexagonal boron nitride (h-BN) and graphene (Gr) binary nanoparticles (NPs) are taken as nano-additives to enhance thermal conductivity of lauric acid (LA). The NPs added PCM known as nano-enhanced phase change material (NePCM) is prepared by two-step method for thermo-physical characterization. According to an optical performance investigation using ultraviolet-visible spectroscopy (UV–Vis); optimal composite LBG2% (LA with 3 % h-BN and 2 % Gr NPs) displayed 78 % reduction in transmissibility compared to base LA. Further, LBG2% composites exhibited elevated thermal conductivity of LA by 97 %. Additionally, differential scanning calorimeter (DSC) observed a slight variation in latent heat and melting temperature. Latent heat for composite LBG2% found to be as 176 Jg−1 with a reduction equal to NPs weight% as compared to base LA. Moreover, the preferred composite LBG2% displays chemical stability and thermal reliability after 500 heating/cooling cycles. The addition of LBG2% NePCM to a photovoltaic thermal system increased electrical and thermal efficiency to 9.41 % and 69 %, respectively, as compared to the photovoltaic thermal system alone, which was 7.1 % and 64 %. It can be concluded, the binary NPs enhanced composite LBG2% exhibited improved photoabsoprtion and thermal conductivity, along with thermal reliability and higher latent heat. The composite has significant application potential within the melting temperature range of 50 °C for employment in solar photovoltaic systems and other applications.

Thermal Characterization of Binary Calcium-Lithium Chloride Salts for Thermal Energy Storage at High Temperature

Due to their excellent thermophysical properties and high stability, inorganic salts and Forsalt mixtures are considered promising thermal energy storage materials for applications operating at high temperatures. A mixture of binary salts, such as CaCl2 (58 wt.%)-LiCl (42 wt.%), was investigated in this work to understand their thermal properties and stability for use in TES systems. Thermophysical properties, such as onset melting and crystallization temperature, enthalpy of fusion, and crystallization enthalpy, were all investigated experimentally via the use of a simultaneous thermal analyzer. The experimental findings demonstrated a suitable onset melting temperature of 488 °C and a solidification temperature of 480 °C. The heat of fusion was observed as 206 J/g, whereas the heat of crystallization was recorded as 180 J/g. Thermal repeatability tests indicated little variations in melting temperature; however, fusion enthalpies changed significantly over the course of 30 heating-cooling cycles. Additionally, the results obtained from the thermogravimetric analysis showed relatively weak thermal stability with considerable mass changes. This might be caused by the salts decomposing at elevated temperatures. In order to validate this, a high-temperature in-situ X-ray diffraction technique was used to verify the thermal instability of the binary salt mixture with and without thermal cycling. The thermal decomposition of parent salts and the subsequent formation of new phases with the formation of voids were shown to be the cause of thermal instability. It is concluded that the binary mixture of chloride salt showed suitable thermal properties but relatively weak thermal stability, which may limit its use in practical applications.

Melting Behaviour under Pressure of Kaolinite Clay: A Nanoscale Study

In this study, the curves of variation of melting temperature as a function of pressure were determined for pressures up to 20 GPa using molecular dynamics (MD) calculations. The CLAYFF force field is used for the simulated PT curve of the clay kaolinite structure. For this purpose, we have adopted the Z-method to determine the melting point (Tm) and superheat limit temperature (TLS) for different densities in kaolinite clay. In addition, various quantities, such as the radial distribution function (RDF), the mean square displacement (MSD), and the diffusion coefficient were evaluated in order to ensure the solid behaviour at the superheat limit temperature and the liquid behaviour at the melting point for the equilibrated structure of kaolinite.

Simulation and dimensional analysis of instrumented dynamic spherical indentation of ductile metals

Finite element (FE) modeling of instrumented dynamic indentation experiments in a miniature Kolsky bar is undertaken. Geometry, including an output bar with machined spherical indenter tip, and velocity history boundary conditions are extracted directly from experimental diagnostics. The test material (i.e., substrate) is polycrystalline aluminum alloy Al 6061-T6. The constitutive model used in simulations accounts for isotropic elasticity and isotropic plasticity with strain hardening, strain-rate hardening, and thermal softening under adiabatic conditions. The FE model, with representative material parameters culled from the literature, accurately reproduces the curvature of the experimental load versus depth data for three different experimental indentation velocity histories. A framework for dimensional analysis of instrumented dynamic spherical indentation is set forth, improving upon prior work. Parametric FE simulations reveal sensitivity, or lack thereof, of the predicted response to variations in the proposed independent dimensionless variables encompassing material properties. For the indenter size, maximum depth, and maximum strain rate imposed experimentally on the order of 103/s, force-depth predictions are nearly unaffected by realistic variations in mass density, melting temperature, and thermal softening parameters when the sample is initially at room temperature. Predictions are affected by elastic constants (the elastic modulus and to a lesser extent, Poisson’s ratio), initial yield strength, two strain hardening parameters, and strain rate sensitivity. Predictions are also notably affected by initial temperature, with thermal softening prominent at high enough initial temperature or much higher loading rates. Based on the dimensional analysis, static indentation and elevated temperature indentation experiments are proposed for extraction of quasi-static and thermal material properties from previously uncharacterized metals, and dynamic indentation is proposed for extraction of rate sensitivity that cannot be obtained from static tests. Rate sensitivity obtained in this way from the novel instrumented dynamic spherical indentation experiments and FE simulations produces a parameterized stress–strain response for Al 6061-T6 reasonably validated by external studies for strain rates up to the order of 103/s.

Combining thermal imaging and spectral pyrometry for express temperature mapping in additive manufacturing.

A compact and low-cost two-dimensional (2D) thermal imager was developed for real-time temperature mapping of a melt pool during coaxial laser cladding (the additive manufacturing technique). The device combines a color CMOS camera and a compact spectrometer. The spectrometer was utilized for internal calibration and validation of a 2D temperature map that was acquired by the CMOS camera. The remarkable feature of the thermal imager is that camera images are calibrated directly during the measurement process utilizing spectral pyrometry. Additionally, the spectrometer decreased a potential systematic error due to a spectrum contribution from atomic/ionic lines emission. The spectral pyrometry provided temperature accuracy measurements of ±23K while two-dimensional (2D) temperature mapping by two-color pyrometry accuracy was estimated as ±38K in the range of 1700-3500K. The system has been installed at a coaxial laser cladding head for real-time temperature mapping. The system was developed for measuring a melt pool during laser cladding production of a high wear-resistant coating (tungsten carbide particles in a nickel matrix). Tungsten carbides powder flow rate has been changed sequentially from 5 to 27g/min by powder feeder programming, which resulted in a variation of melt pool dimensions and temperature maps during the cladding process.

Experimental study on the thermal storage performance of phase change materials embedded with additively manufactured triply periodic minimal surface architected lattices

Porous structures are widely used as thermal conductivity enhancers (TCEs) for phase change materials (PCMs) in thermal management systems (TMSs) and thermal storage systems (TSSs). The heat transfer performance of PCMs filled with traditional metal foams has been extensively investigated both numerically and experimentally. Additive manufactured (AM) lattices with controllable structures have attracted extensive and continuously growing attention due to their high specific strength, interconnected pores, and high thermal conductivity, outperforming both conventional stochastic metal foams and honeycomb with great potential in TSSs. In this work, lattices with novel continue surface structures were inserted into PCMs for heat transfer augmentation. Using the implicit function of triply periodic minimal surfaces (TPMS), nine lattices with varied relative density, cell sizes, and cell types were designed and fabricated by selective laser melting (SLM) using AlSi10Mg. PCMs embedded by lattices were built by the casting method and adopted in the visualized thermal storage experiment to evaluate the geometric effect on the melting interface, temperature variation, and thermal storage performance under a constant heating power of 10 W. The results showed that the pure paraffin took the longest time of 70 min to completely melt, however, the embedding of a TPMS with a relative density of just 10% reduced the melting time by nearly 20 min. The embedding of TPMS period porous aluminum (PPA) improved the response rate of the paraffin wax (PX) to temperature by accelerating the melting pace and advancing the onset of latent heat energy storage. The relative density plays a dominant role in enhancing thermal conductivity; nonetheless, excessive addition will reduce the heat storage capacity and heat storage density of PCMs. The cell size and cell type could further accelerate the melting rate for more design choices and sheet-like TPMS possesses greater heat transfer potential than rod-like structure. Besides, the GS-65-20 case stored a total amount of 4181.95 J heat at the fastest rate of 1.85 J/s, which was 1.5 times the heat storage rate of the pure PCM case, showing the best-balanced performance. An optimization strategy for thermal conductivity enhancement of lattice structures was provided according to the design priorities of relative density, pore size, and cell type.

Effect of aliphatic segment length and content on crystallization and biodegradation properties of aliphatic-aromatic co-polyesters

In this work, dimethyl terephthalate (DMT), 1,4-butanediol (BDO) and different diacids were introduced to investigate the effects of variations in aliphatic chain length and component content in aliphatic aromatic terpolymers on the basic thermal properties, crystalline morphology, mechanical properties and biodegradability of the polyesters. The experimental results from nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FT-IR) and Gel permeation chromatography (GPC) indicate the successful synthesis of the anticipated aliphatic aromatic co-polyesters. The variation of melting and crystallization temperatures with aliphatic chain segment length and content were analyzed by differential scanning calorimetry (DSC). The Wide-angle X-ray diffraction (WAXD) results suggest that the coexistence of both crystals formed by rigid and flexible chain segments can be achieved by varying the length and component content of the aliphatic chain segments in the co-polyesters. The scanning electron microscopy (SEM) and composting experiment results indicate that the type of crystals formed with the more flexible chain segments and the lower degree of crystallinity have a positive effect on the biodegradability.

Feasibility Study on the Fused Filaments of Injection-Molding-Grade Poly(Ethylene Terephthalate) for 3D Printing.

Unlike that of glycol-modified Poly(ethylene terephthalate) (PETG), the crystallinity of PET can be post-adjusted to enhance the mechanical properties of 3D-printed parts such as food-contact tableware and bio-implants. The aforementioned PET material could be 3D printed to produce the desired parts for performance evaluation before mass production by injection molding. In this study, using differential scanning calorimetry (DSC), we examined the pellets, extruded filament, and printed specimen to identify variations in melting and crystalline temperatures, as well as crystallinity. It was also shown by Thermogravimetric Analyzer (TGA) that the addition of talcum powder increased the thermal stability of filament and resulted in an interaction between the fillers and polymer matrix. The crystallinities of the filament and printed specimen were then compared with the yield strengths and Young’s moduli to confirm the effects of the decreased molecular weight of the extruded PET filament. The talcum powder effectively improved the viscosity of the PET melted during the extrusion process for the filament and then enhanced the crystallinity of the PET, thereby achieving a significantly higher Young’s modulus. The printed PET specimen presented an excellent yield strength of 25 MPa and ductile properties with strain-at-break values of 30%, successfully indicating potential applications in food-contact tableware and bio-implants.

Real-time Diagnosis of Micro Powder Injection Molding Using Integrated Ultrasonic Sensors

Abstract Real-time diagnostics of ceramic powder injection molding using a commercial micromolding machine was performed using ultrasound. Miniature ultrasonic sensors were integrated onto the mold insert. Melt front, solidification, temperature variation and part detachment of the feedstock inside the mold cavity were observed. It has been demonstrated that ultrasonic velocity in feedstock inside the mold cavity, the ultrasonic contact duration during which the part and mold are in contact, and holding pressure can be used to assist with optimization of injection and cooling parameters to minimize energy consumption and maximize process efficiency.

A simple approach to estimate the melting temperature of alkali halides

In the present study, a thermodynamical formulation is developed to determine the melting temperature of alkali halides with increasing pressure. The model is used to estimate the melting temperature of alkali halides at different pressures qualitatively. The formulation is obtained using the Goyal and Gupta thermodynamic equation of state. The model calculations require the computed values of volume compression, bulk modulus and its first pressure derivative at varying pressures. It is noted from model calculations that melting temperature increases with pressure but not in linear manner. The present computed results for pressure dependent melting temperature are compared with the available simulated results. The approach is found to be valid as good agreement is observed between previous and present results. Graphs are plotted to depict the variation of melting temperature with isothermal pressure, thermal pressure and total pressure acting on the solid. The present study helps to understand the impact of pressure on melting temperature of alkali halides qualitatively. The model used can also extrapolate the results upto higher pressures.

Experimental and numerical investigation on characteristics of MCCI with exothermic thermite

Investigation was conducted experimentally and numerically for ex-vessel melt behavior and concrete interaction during Molten Corium-Concrete Interaction (MCCI) in current research. The CINA (Corium-Concrete Interaction Apparatus) experiment was carried out with a total of 94 kg melt generated by exothermic thermite chemical reaction to react in a two-dimensional (2-D) cylindrical siliceous crucible with an inner diameter of 300 mm and a height of 500 mm. Meanwhile, the variation of melt temperature was monitored during the experiment. Besides, the accurate ablation depth and thickness of stratified layers were measured after the experiment. Numerical simulation was used to study the mechanism of high-temperature melt heat transfer and concrete ablation during the MCCI process. The slag film model to calculate the melt/concrete interface heat transfer coefficient and the stratified melt model were both used to simulate the above experiment. The results showed that the numerical results were in good agreement with experiment measurements by the slag film model under separated layers condition.

In-Situ Visualization of the Cell Formation Process of Foamed Polypropylene under Different Foaming Environments.

In this paper, the dynamic foaming process of micro-foaming polypropylene (PP) in different foaming environments in real time was obtained via a visualization device. The relationship curve between cell number (n) and foaming time (t) was plotted, and then the nucleation kinetics of foam cells was analyzed. Results showed that the formation rate of cells changed obviously with the variation of melt temperature and the content of the foaming agent. The n-t curves presented a typical “S” shape, which indicated that the appearance of the cell number increased slowly in the initial foaming period, then increased rapidly in a short time, and finally maintained a certain value. When a certain pressure was applied to the PP melt, the external force had a great influence on the n-t curve. With the increasing external force, the rate of cell formation increased rapidly, and the shape of the n-t curve changed from “S” to “semi-S” without an obvious slow increase. The investigation of the n-t relationship in the PP dynamic foaming process under different foaming environments could provide effective bases for improving the foaming quality of injection molding foaming materials.

Pulsed laser welding and microstructure characterization of dissimilar brass alloy and stainless steel 308 joints

The laser welding of stainless steel and brass is difficult due to their different physical properties, including thermal conductivity and melting point. In this study, the laser welding of stainless steel 308 and brass was experimentally investigated. To systematically investigate the effects of different thermophysical properties, including the heat transfer rate, thermal conductivity, and laser beam interaction in relation to the beam absorption coefficient, the temperature of the melt pool zone was measured while changing welding conditions. Different temperature gradients were obtained by changing different parameters including the laser peak power, nozzle distance, and laser beam deviation. The results showed that an asymmetric melt pool formed, to which the melting of brass made a higher contribution. Due to the lower melting temperature and the higher thermal conductivity of brass, the measured temperature and the melt size of brass were higher. The microstructure of the melt pool consisted of intermetallic compounds. Variation of melt pool size (width and depth) and temperature could be affected by laser peak power and reductions in the nozzle distance than the other parameters. For instance, 1 mm increase in the nozzle distance reduced the melt pool zone temperature by approximately 20 °C for stainless steel. Furthermore, an increase in the laser peak power raised the maximum measured temperature to about 225 and 160 °C for brass and stainless steel sides, respectively. At the same time, the amount of temperature reduction at a period of 20 s for stainless steel is almost half that of brass.

Effect of fin-metal foam structure on thermal energy storage: An experimental study

Thermal energy storage (TES) has been playing a crucial role in addressing the issue of solving the intermittent and random problems in solar energy utilization. The objective of this study is to squarely address and clarify the contribution of metal fin and foam to enhancing the phase change heat transfer by experiments. A novel hybrid fin-foam tube is proposed and its thermal performance is evaluated by experimentally comparing with other three competing structures including bare, fin, and metal foam tubes. A well-designed test rig is built and the energy storage features for the designed four TES tubes are analyzed by the complete melting time, melting front evolution, temperature variation and uniformity, and the temperature response rate. Results show that the fin-foam hybrid structure outperforms the other competing ones, demonstrating a reduction of 83.35% in complete melting time (compared with the bare tube). The transient temperature response is maximized by 529.1%. As for the single structure, both fins and metal foam can improve conductivity of phase change materials. The metal foam does a good favor to improve the uniformity of the temperature field inside the TES tube, but the fins weakened the uniformity. If the design target is temperature uniformity, adding metal foams other than fins can fulfil the task.

Composition and dimension dependence of melting temperature in bimetallic nanoalloys

The phenomological model for cohesive energy of metallic nanomaterials is extended to investigate the variation in thermodynamic properties of bimetallic nanostructures. The systematic investigation of variation in melting temperature of bimetallic nanomaterials is done to study the impact of size, composition and dimension. Decrease in melting temperature of bimetallic nanoalloys is found as size of nanoalloy decreases. It is noted that for bimetallic nanoalloys of same composition and having same size, the melting temperature varies on the basis of dimension of nanoalloy in the sequence such that (Tmn)nanofilms> (Tmn)nanowires> (Tmn)nanoparticles. The present predicted results obtained from extended model are compared with the simulated and experimental results available. Good consistency is observed between the compared results which justify the present model theory.

Dynamics and thermodynamics of core/shell formation of icosahedral NimAgn bimetallic nanostructures

The molecular dynamics and multiple histogram techniques were used to understand the core/shell formation of bimetallic silver-nickel nanostructures at sizes of 55 and 147 atoms. Two core/shell structures of 55 atoms icosahedra, Ag13Ni42 and Ni13Ag42 with their isomers, Ni13(Ni29Ag13) and Ag13(Ag29Ni13) were considered. In the case of 147 atoms icosahedra, homogeneous motifs (either Ag or Ni) of the core, inner shell, and outer shell were produced along with their heterogeneous isomers. Energetically, nickel-core structures are found to be more favorable than corresponding silver-core motifs. Constant volume heat capacity was used to characterize the phase transition of each cluster. The trend in the variation of melting temperatures of 55 atoms icosahedra with the nickel composition aggreses with the observed trend in the energy variation, thus values of heat capacity reveals more solid-like characteristics of NicoreAgshell motifs and liquid-like characteristic of AgcoreNishell motifs. Thermodynamic feasibility of the nickel-core/silver-shell formation was established by comparing Helmholtz free energy changes in the transition of silver atoms from the center to the shell and nickel penetration from shell to the center. The free energy changes in surface mixing and segregation of silver atoms revealed that the mixing of silver atoms with nickel atoms on the surface is more favorable than segregation. In a low nickel environment, the formation of homogeneous core/shell structures occurs, while in moderate nickel composition, mixing of silver atoms is favorable than being in the homogeneous core/shell configurations.

Theoretical analysis of thermophysical properties of nanomaterials

In the present study, a theoretical comparative work is done to calculate the variation of melting temperature in nanomaterials by using two quantum models i.e. Lu model and Jiang model and the expression of melting temperature calculated with the help of best model is extended to calculate the variation of Debye temperature and thermal expansion coefficient with size and shape of nanomaterials. The melting temperature and Debye temperature are observed to increase as the diameter of nanomaterials is increased and thermal expansion coefficient decrease with increase in the diameter of nanosolid. The results obtained from the given models are compared with the experimental values to judge the best-suited model for the study of the thermodynamic properties of nanosolids. The available experimental results are found very close to the results from the Jiang model and then Debye temperature and thermal expansion coefficient are calculated with the help of Jiang model.