Change In Specific Heat Capacity Research Articles

STUDYING THE STRUCTURAL, ELECTRICAL, AND MAGNETIC CHARACTERISTICS OF ASiNRS-DOPED NEODYMIUM USING THE FIRST PRINCIPLE

There have been many applied studies on Nd in medicine, cooling techniques due to large amplitude changes in specific heat capacity, making glass pigments, making laser materials, and many other fields. However, there have been no specific studies on the structural and electronic properties related to the band gap. In this study, we investigated the optimization of Nd adsorption on Armchair nanoribbon silicene substrate. The research was carried out in three steps. The first step is to change the Nd atom through the four positions (top, valley, hollow, and bridge) to determine the optimal position. As a result, the bridge site has a magnetic moment of 4.68 µB and a locking degree of 0.69 Ǻ, has the lowest absorbed energy value of -2.6 eV, and has the most stable structure. Second step, we varied the Si-Si bond length of silicene for the same target, resulting in choosing the optimal bond length of 2.27 Ǻ. Finally, we consider the distance between the Nd atom and the silicene surface and determine that with the same bond length 2.27 Ǻ, the result obtained at a height of 2.11 Ǻ occurs most optimally. This result proves that silicene-doped Nd is very promising as a material for making visible sensors and spin motors in the future.

Study on the effect of low-temperature cycling on the thermal and gas production behaviors of Ni0.8Co0.1Al0.1/graphite lithium-ion batteries

With their high energy density and long cycle life, lithium-ion batteries (LIBs) are currently the most promising electrochemical energy storage system for electric vehicles. However, their safety and cycling performance can be significantly compromised in low-temperature environments due to lithium plating and other factors. Therefore, it is essential to study the safety of aging batteries. In this study, we focused on a commercially available high-specific-energy Ni0.8Co0.1Al0.1 cathode system battery and simulated the aging of the battery by long-term cycling at 0 ℃. This study compares and analyzes the samples on the basis of the previous ones in terms of heat production power, thermal runaway (TR) characteristics and gas production characteristics. It reveals the influence of low-temperature aging on the comprehensive performance of lithium batteries in a more comprehensive way. The results show that the charging pattern of all three characteristics is related to the aging degree of the battery. In terms of the thermal characteristics, the relative change in specific heat capacity of the aged battery is only between 0.32 % and 1.08 % compared to that of a fresh battery, so the effect of ageing on the specific heat capacity of the battery is negligible. The average heat generation power of batteries with different state of health (SOH) is not monotonically increasing with the decrease of SOH, the threshold of dramatic increase is SOH = 80 %. In terms of TR characteristics, the onset temperature of exothermic reactions (TOER) of aged batteries is significantly lower than that of fresh batteries. With the decrease of SOH, TOER also decreases gradually. Compared with batteries with different SOHs, the more seriously aged the battery safety valve opens earlier, and the TR occurs earlier. In terms of the TR gas production characteristics, the more severely aged the battery, the earlier the safety valve opens compared to a fresh battery. The most gas is produced when SOH = 70 %, which increases the risk of catastrophic damage.

Study on Thermal Decomposition Mechanisms of Indian Honey of Different Origins using Differential Scanning Calorimetry and Vector Elemental Analyzer Techniques

Background: This paper reports the thermal decomposition mechanisms of five pure honey samples of Indian origin using Differential Scanning Calorimetry (DSC) and Euro Vector Elemental Analyzer (EVEA) techniques. Methods: We have identified three transition temperatures along with a change in specific heat capacity (ΔCp), change in enthalpy (ΔH), and Gibbs free energy (ΔG) of these samples. Finally, samples were subjected to thermal elemental analyses to quantify the released amount of O, N, C, and H. Since glucose, fructose, and sucrose are the principal ingredients, they are present in the honey sample, along with good numbers of other organic molecules in small quantities. In addition, we have also recorded the C, H, and O percentages of pure glucose, fructose, and sucrose powders and correlated the ratio of C/H and C/O with honey samples. Results: The decomposition temperature for honey samples lies between 113.83°C and 127.07°C range. The ratios of these elements help us to ascertain the purity of these samples as well as to identify the dominating percentage of principal ingredients present in the given honey sample. Conclusion: The obtained experimental results were further used to identify the source of origin and medicinal quality and stability of honey samples.

The effect of heat transfer on the stress-strain material state considering the final rate of heat spread

Calculation results of different wave tasks are analyzed. It is shown that deformation heating of material is intensive near the boundary surface and quickly decreases during insignificant removal from it. The conclusion is drawn that for obtaining exact solutions of wave tasks in nonisothermal statement it is necessary to consider redistribution of temperature in materials because of the heat transfer and its influence on the intense deformed condition of materials of different designs. Calculation results are given. The sensitivity of the decision to change of specific heat capacity and the thermal diffusivity entering wave equation of heat conductivity is noted.

Определение теплофизических свойств керамики с добавкой пиролизного остатка твердых отходов

A promising environmentally friendly method for processing municipal solid waste is pyrolysis. Pyrolysis allows obtaining a combination of solid, liquid and gaseous products in various proportions due to changes in process parameters. A promising area for the use of solid pyrolysis products is the production of various materials for industrial, civil and road construction. There are some known methods for producing cement, concrete and foam glass with improved properties on pyrolysis basis. In modern building technologies, ceramic materials are widely used. Their production requires various expensive additives such as quartz sand, dolomite, coal, coal mining rocks, etc. Thus, it seems relevant to use the residue of the pyrolysis of municipal solid waste as a free of charge structure-forming additive for the production of ceramic material. To determine the scope of the material application and to perform subsequent thermotechnical calculations, the data on its thermophysical characteristics is required. To determine the thermophysical characteristics of the ceramic material, the experimental method of the cylindrical layer and the calculation-experimental method of inverse heat conduction problem are used. The experimental studies of thermophysical properties of the new ceramic material have allowed obtaining the dependence of the average specific heat capacity and thermal diffusivity of the ceramic material on temperatures in the range of 30–90 оС, and the coefficient of thermal conductivity on the temperatures in the range of 30–500 оС. These characteristics enable to perform calculations of thermal processes that occur in the material during its industrial use. The coefficient of thermal conductivity of the material varies from 0,3 to 0,65 W/m×K, thermal diffusivity varies within (1,8–2,3)×10–7 m2/s, and the average specific heat capacity changes from 780 to 1300 J/kg×K, which is comparable with the thermophysical characteristics of known ceramic materials. It is advisable to use the pyrolysis residue of municipal solid waste as a free raw material instead of expensive additives to obtain ceramic material. It is recommended to use the new ceramic material in the production technology of building products for various purposes.

Challenge and Solution of Characterizing Glass Transition Temperature for Conjugated Polymers by Differential Scanning Calorimetry

ABSTRACTThermomechanical properties of polymers highly depend on their glass transition temperature (T g). Differential scanning calorimetry (DSC) is commonly used to measure T g of polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuring T g in such type of polymers. The changes in specific heat capacity (Δc p) at T g were accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δc p from flexible polymer (0.28 J g−1 K−1 for polystyrene) to rigid CPs (10−3 J g−1 K−1 for a naphthalene diimide‐based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δc p at T g by a factor of 10, confirming that backbone rigidity reduces the Δc p. Additionally, an increase in the crystalline fraction of the CPs further reduces Δc p. We conclude that the difficulties of determining T g for CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D‐A CPs with weak transition signals. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1635–1644

Investigations of structural, elastic, electronic, vibrational and thermodynamic properties of RhMnX (X = Sb and Sn)

This study employs first principles method to run an investigation on structural, electronic, elastic, vibrational, thermodynamic and magnetic properties of RhMnX (X = Sb and Sn) half-Heusler compounds in C1b phase. The elastic constants (C11, C12 and C44) for RhMnX (X = Sb and Sn) half-Heusler compounds in C1b phase are computed using the energy-strain method. Directional changes of Young and Shear modulus, Poisson’s ratios and compressibility’s of RhMnX (X = Sb and Sn) compounds have been analysed. Evaluations of mechanical stabilities via obtained elastic constants are exhibited stable natures for these compounds. Moreover, the compounds are ductile based on the Pugh’s criteria. Electronic band structures and their partial density of states are presented for both compounds and used to interpret the electronic band profiles of these compounds in the C1b phase. Specifically, phonon dispersion curves of these compounds have been derived for the first time. Full phonon properties of these compounds suggest that both compounds are dynamically stable. Besides, the change in specific heat capacity and entropy of RhMnX (X = Sb and Sn) compounds have been also computed between 0–500 K.

Thermal Behaviour of Hybrid Composites Reinforced with Natural Fibers and Kevlar

There is a wide scope to develop suitable hybrid combination for making Fiber Reinforced Polymer (FRP) to utilize the properties of both natural and synthetic fibers. Economic and environmental reasons justify the use of natural fiber in place of synthetic fiber composite. Thermal stability is one of the important properties for the FRP panel in the applications such as structural panels/roof panels, cold storage and air conditioned ducts of building. The aim of this paper is to investigate thermal properties of hybrid FRP made of Jute, Flax, Sisal and Hemp in combination with kevlar-29. Composite wall conductivity measurement, DSC/TGA technique are used to study thermal conductivity, thermal stability, change in specific heat capacity, thermal degradation. All the panels showed lower thermal conductivity of less than 1 W/m 0C; however the flax and hemp panels had lowest thermal conductivity of around 0.45 W/m0C. DSC thermographs indicated broad exotherm and major changes in specific heat capacity at 200 0C for all panels. In addition, TGA technique showed main weight loss around 30%-51% of panels around 210 0C. Thus the thermal properties of all panels were stable till 200 0C. Thermogravimetric analysis of F- FRP shows thermal stability at lower range of temperature while in H- FRP thermal degradation occurs in two steps around 260 0C and 410 0C with the wt. loss of 53.72% and 26.79% respectively.

Modeling Polymer Glass Transition Properties from Empirical Monomer Data with the SAFT-γ Mie Force Field

We apply a recently developed coarse-graining method to build models for polyester polyols, versatile polymers with applications in coatings, by combining models for the component monomers. This strategy employs the corresponding states correlation to the group-contribution SAFT-γ Mie equation of state [Mejia, A.; et al. Ind. Eng. Chem. Res. 2014, 53, 4131–4141] to obtain force-field parameters for the constituent monomer species. Results from simulations agree favorably with experimental values of mass density, glass transition temperature (Tg), and specific heat capacity change at Tg. Further simulations over a range of Mie parameters and polymer chemical compositions yield a correlation that relates the parameters directly to Tg. This correlation is validated by experimental data and can be used as a predictive tool within the tested parameter space to expedite the design of these coating materials.

Investigation on heat transfer characteristics and flow performance of Methane at supercritical pressures

The aim of this study is to investigate the heat transfer and flow characteristic of cryogenic methane in regenerative cooling system at supercritical pressures. The thermo-physical properties of supercritical methane were obtained from the National institute of Standards and Technology (NIST) webbook. The numerical model was developed based on the assumptions of steady, turbulent and Newtonian flow. For mesh independence test and model validation, the simulation results were compared with published experimental results. The effect of four different performance parameter ranges namely inlet pressure (5 to 8 MPa), inlet temperature (120 to 150 K), heat flux (2 to 5 MW/m2) and mass flux (7000 to 15000 kg/m2s) on heat transfer and flow performances were investigated. It was found that the simulation results showed good agreement with experimental data with maximum deviation of 10 % which indicates the validity of the developed model. At low inlet temperature, the change of specific heat capacity at near-wall region along the tube length was not significant while the pressure drop registered was high. However, significant variation was observed for the case of higher inlet temperature. It was also observed that the heat transfer performance and pressure drop penalty increased when the mass flux was increased. Regarding the effect of inlet pressure, the heat transfer performance and pressure drop results decreased when the inlet pressure is increased.

Estimating the Maximum Possible Correction Factor by Using the High Temperature Differences within Pinch Analysis as Obtained from Practical Experience

Pinch analysis is a very useful method that can increase the energy efficiencies of individual chemical processes including simultaneous heat integration and process optimisation. Pinch analysis is based on constant heat capacity flow (CF) for each stream. In regard to greater temperature differences of more than 200 K, the heat capacity flow could be corrected using a quantified maximal possible correction factor (fcor) obtained from practical experience. This is because of certain determined changes in specific heat capacity (cp), as it is temperature dependent. The correction factor for heat capacity flow is calculated by determining the errors of specific heat capacities. This technique includes those specific heat capacity errors during significant temperature differences that cause errors regarding heat capacity flow. The correction factor could be reduced by using the calculated mistake of heat flow rate during integrated networks.The novelty of this paper is the correction factor, which could be:• Obtained from practical experience• Reduced the mistake of heat flow rate• Reduced the energy loss.

Isothermal titration calorimetry and vesicle leakage assays highlight the differential behaviors of tau repeat segments upon interaction with anionic lipid membranes

Tau misfolding has been implicated in a variety of tauopathies, including Alzheimer's disease. The microtubule binding domain of tau consists of four repeat segments (R1-R4), and aggregation of these segments leads to the formation of neurofibrillary tangles. Previous studies indicate that misfolded tau associates with anionic phospholipid membranes, invoking structural transformations that could play a role in aggregation. Here, we investigated the role of membrane surface charge on the binding affinity of individual tau repeat segments, and whether these segments exhibit lytic activity. We quantified the thermodynamics of this process in terms of the affinity (Kd), enthalpy (ΔH), entropy (ΔS), and change in specific heat capacity (ΔCp). While neutral membranes exhibited weak interactions with each tau repeat segment, segments R2 and R3 exhibited relatively strong binding with anionic membranes with favorable ΔS and a negative value of ΔCp. Calcein leakage assays show that each repeat segment displays lytic activity, but only upon the interaction with anionic membranes. Taken together, these results distinguish the relative selectivity for anionic membranes by each repeat segment and the degree of membrane disruption that results.

Specific heat capacity of polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) blend after hygrothermal aging

The changes in specific heat capacity (C p) of a polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) blend subjected to aging have been determined using modulated differential scanning calorimetry (MDSC). MDSC experiments were conducted before and after hygrothermal conditioning of specimens under 9 different aging conditions. The effects of the two factors, hygrothermal conditions and scanning temperature, on material C p have been determined by statistical method of analysis of variance. Linear curves were fitted to experimental values of C p for the range of initial temperature of 24 °C (room temperature) up to 80 °C (glassy region of the material). The obtained linear relationship can be used to model heat transfer of PC/ABS materials exposed to physical aging and hygrothermal conditions. C p values were found to be independent of moisture content in conditioned samples within the range of conditions studied.

Evidence for the ferromagnetic frustration in a classical spin-[formula omitted] system with multisite interaction in external magnetic field: Exact results

We investigate the influence of the multisite interaction among sites within elementary triangles of the kagome-like recursive lattice on the properties of the classical spin-1∕2 ferromagnetic Ising model in the external magnetic field. The exact solution of the model is found and it is shown that the model exhibits a nontrivial structure of the first order as well as second order phase transitions in nonzero external magnetic fields related to the multisite interaction. The equation for the exact determination of the positions of the critical points of the second order phase transitions is derived. The thermodynamic properties of the model are investigated in detail and it is shown that the competition between the ferromagnetic interaction and the multisite interaction leads to the appearance of strong ferromagnetic frustration effects represented by the formation of a nontrivial system of macroscopically degenerated plateau-like and single-point-like ground states. The residual entropies of all ground states are found and the kagome spin-ice-like highly macroscopically degenerated plateau state with nonzero magnetization is identified with the exact residual entropy per site s∕kB=ln(4∕3)∕3≈0.095894. The properties of the specific heat are investigated, its Schottky-type behavior near the single-point ground state values of the magnetic field is identified, the existence of large magnetocaloric effect is discussed, and the existence of the first order phase transitions without the specific heat capacity change is demonstrated.

Heat-Induced Solid–Solid Phase Transformation of TKX-50

Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) is an attractive energetic ionic salt and outperforms many common explosives. We report a solid–solid phase transition of TKX-50 to a new metastable phase (Meta-TKX-50) at ∼180 °C by Raman spectroscopy and thermogravimetry–differential scanning calorimetry (TGA–DSC) measurements, in combination with ab initio calculations. Meta-TKX-50 is formed by the rotation of NH3OH+ with a small volume expanding of 3% and a crystal symmetry reduction from P21/C to P-1. In addition, the phase transition features a second order with a slight change of 0.3 J·K–1·mol–1 in specific heat capacity. This slight change of specific heat capacity is the main reason that the phase transition was overlooked in the past measurements. Besides, it is found that the phase transition facilitates the H transfer from NH3OH+ to C2O2N82– and the N–O bond dissociation of NH3OH+ to produce final small stable molecules including NH3 and H2O. Thus, the phase transition is expected to p...

Thermal, structural, and defect studies on Pb modified Ge[sbnd]Se glasses

We report the detailed thermal, structural, microstructural and electrical transport studies on PbxGe42−xSe58 with (0≤x≤20) glasses. The influence of Pb content on thermal and local atomic structure and its qualitative consequences on the electronic properties has been elucidated. The composition dependent variation of glass transition temperature (Tg), change in specific heat capacity at the glass transition (ΔCp) and non-reversing enthalpy change (ΔHNR) complement with each other for enabling the role of Pb content on structural relaxation behavior of these glasses. The Raman spectroscopic studies reveal the presence of different structural species and its variation with Pb content, i.e. pronounced decrease in the amount of ethane-like structural units with the incorporation of Pb content. The addition of Pb content into Ge42Se58 glass, the network connectivity becomes loosened due to the depolymerization. The observed Raman band position of ethane-like structural units show noticeable blue shift with an increase of Pb content, which dictates the development of stress in the network structure caused by the predominant ionic character. The microstructural studies by positron annihilation life-time spectroscopy reveal the nature of defect states and its variation with Pb content. The composition dependent dc conductivity and its activation energy shows marked change across the p-n transition threshold due to the change in the charged defect concentration. The influence of local atomic structure and nature of defect states responsible for the carrier type reversal (CTR) has been discussed.

Hydration of Critical Residues in the Shaker KV Channel Governs the Energy Landscape and Temperature Dependence of Channel Gating

The molecular correlates of the large energy barriers, underlying the strong temperature dependent modulation of activation kinetics of thermp-TRP channels, are virtually unknown. Recent evidence, based on de novo design of a temperature-modulated channel, has suggested a general mechanism of temperature dependent gating - conformational state dependent changes in hydration of critical residues alters the specific heat capacity change of gating thereby rendering the gating sensitive to temperature. Here, we study whether such a hydration-inspired hypothesis can account for effect of temperature on gating kinetics. Our model system was the Shaker KV channel wherein we focused our attention on the four principle gating-charge residues on the S4 segment of the channel. We find that neutralization of the fourth gating charge to alanine results in a 200-fold deceleration of channel deactivation kinetics as the temperature is reduced by 20C, although its apparent open-probability vs voltage curves, at the two temperatures, are virtually superimposable. By neutralizing R371 to amino acids of varying polarities, we find that while temperature has no effect on the open-probability vs voltage relationships, the deactivation kinetics is affected by temperature in a polarity correlated fashion i.e. hydrophobic perturbations produce a strong temperature dependence but polar perturbations result in modest, wild-type like, effects. These results are explained by a model in which the last step of voltage-dependent activation of the channel involves translocation of the fourth charge site (371) from the hydrated internal crevice to the hydrated external crevice through a hydrophobic septum, during which the charge is transiently dehydrated. These results provide a molecular framework to rationalize the effect of temperature on gating kinetics and also describe the unique role of hydration in governing the energy landscape of gating.

Estimating the temperature evolution of foodstuffs during freezing with a 3D meshless numerical method

Freezing processes are characterised by sharp changes in specific heat capacity and thermal conductivity for temperatures close to the freezing point. This leads to strong nonlinearities in the governing PDE that may be difficult to resolve using traditional numerical methods. In this work we present a meshless numerical method, based on a local Hermite radial basis function collocation approach in finite differencing mode, to allow the solution of freezing problems. By introducing a Kirchhoff transformation and solving the governing equations in Kirchhoff space, the strength of nonlinearity is reduced while preserving the structure of the heat equation. In combination with the high-resolution meshless numerical method, this allows efficient and stable numerical solutions to be obtained for freezing problems using 3D unstructured datasets. We demonstrate the proposed numerical formulation for the freezing of foodstuffs. By approximating the shape of the thermal conductivity and heat capacity curves in a piecewise linear fashion the temperature-dependent material curves may be described using eight independent parameters. We consider the optimisation of these parameters to match experimental data for the freezing of a hemispherical sample of mashed potato by using a simple manual procedure that requires a minimal number of simulations to be performed. Working in this way, a good approximation is obtained to the temperature profile throughout the sample without introducing instability into the numerical results.

A Molecular Framework for Temperature-Dependent Gating of Ion Channels

Perception of heat or cold in higher organisms is mediated by specialized ion channels whose gating is exquisitely sensitive to temperature. The physicochemical underpinnings of this temperature-sensitive gating have proven difficult to parse. Here, we took a bottom-up protein design approach and rationally engineered ion channels to activate in response to thermal stimuli. By varying amino acid polarities at sites undergoing state-dependent changes in solvation, we were able to systematically confer temperature sensitivity to a canonical voltage-gated ion channel. Our results imply that the specific heat capacity change during channel gating is a major determinant of thermosensitive gating. We also show that reduction of gating charges amplifies temperature sensitivity of designer channels, which accounts for low-voltage sensitivity in all known temperature-gated ion channels. These emerging principles suggest a plausible molecular mechanism for temperature-dependent gating that reconcile how ion channels with an overall conserved transmembrane architecture may exhibit a wide range of temperature-sensing phenotypes. :

High‐Temperature Properties and Ferroelastic Phase Transitions in Rare‐Earth Niobates (LnNbO4)

Phase transition and high‐temperature properties of rare‐earth niobates (LnNbO4, where Ln = La, Dy and Y) were studied in situ at high temperatures using powder X‐ray diffraction and thermal analysis methods. These materials undergo a reversible, pure ferroelastic phase transition from a monoclinic (S.G. I2/a) phase at low temperatures to a tetragonal (S.G. I41/a) phase at high temperatures. While the size of the rare‐earth cation is identified as the key parameter, which determines the transition temperature in these materials, it is the niobium cation which defines the mechanism. Based on detailed crystallographic analysis, it was concluded that only distortion of the NbO4 tetrahedra is associated with the ferroelastic transition in the rare‐earth niobates, and no change in coordination of Nb5+ cation. The distorted NbO4 tetrahedron, it is proposed, is energetically more stable than a regular tetrahedron (in tetragonal symmetry) due to decrease in the average Nb–O bond distance. The distortion is affected by the movement of Nb5+ cation along the monoclinic b‐axis (tetragonal c‐axis before transition), and is in opposite directions in alternate layers parallel to the (010). The net effect on transition is a shear parallel to the monoclinic [100] and a contraction along the monoclinic b‐axis. In addition, anisotropic thermal expansion properties and specific heat capacity changes accompanying the transition in the studied rare‐earth niobate systems are also discussed.