Change In Specific Heat Research Articles

Preparation and thermal properties of novel eutectic salt/nano-SiO2/ expanded graphite composite for thermal energy storage

This paper presents a novel shape-stable phase change material (PCM) composite for thermal energy storage applications. The formulation of the material consists of the components: eutectic nitrate (NaNO3-KNO3) as thermal storage material, expanded graphite (EG) for improving structural stability and thermal conductivity, and SiO2 nanoparticles for improving specific heat. The material was successfully prepared by the mechanical dispersion method. The effects of EG and SiO2 nanoparticles additives on the thermophysical properties of the composite were investigated by SEM, STA, and LFA. The results showed that EG, SiO2 nanoparticles and eutectic nitrate have excellent chemical compatibility. The specific heat of the composite was 3.92 J/(g·K), which was 2.58 times higher than that of eutectic nitrate when the content of EG and SiO2 nanoparticles was 15 wt% and 1 wt%, respectively. The latent heat of the composite decreased with the increase of EG mass fraction, but overall an increase in energy storage density was found due to the addition of SiO2 nanoparticles. The thermal conductivity of the composite with 15 wt% EG and 1 wt% SiO2 nanoparticles was significantly increased by about 16.2 times compared with that of eutectic nitrate. Furthermore, thermal cycle stability was tested. The NaNO3-KNO3/1 wt% nano-SiO2/15 wt% EG composite showed no obvious specific heat change after 100 thermal cycles and 100 h high-temperature test, respectively. The prepared NaNO3-KNO3/nano-SiO2/EG composite has a promising application prospect in the high-temperature energy storage.

Effect of Nano-Silica on The Thermo-Physical Properties of the Thermal Eutectic (Na0.6K0.4)NO3 System

Here, we investigate the effect of adding nano-silica particles on the thermo-physical properties of the (Na0.6K0.4)NO3 based thermal energy storage systems. Five different systems tagged as M00, M01, M02, M03 and M04, with different nano-silica percentage of 0, 1, 2, 3, and 4 wt%, respectively, were prepared. Various experimental techniques were employed to study the thermo-physical properties of the systems during (solid-solid) phase P1, (solid-liquid) phase P2 and (liquid-solid) phase P3, and to clarify the effect of nano-silica on the thermal energy storage efficiency during both charging and discharging processes. According to the Differential Scanning Calorimeter (DSC) thermal analysis, it was found that the system M02 whose nano-silica addition rate of 2 wt%, has the most favorable thermal characteristics (i.e., highest specific heat and lowest enthalpy change). Moreover, the addition of 2 wt% represents the optimum distribution of nano-silica inside the principal base system M00. This leads to an improvement in the porosity of the system due to the degree of homogeneity caused by the thermophoresis effect distribution, the high surface area of the nano-silica with the activity of the M00 matrix alongside the degree of the alkalinity of nano-silica. Besides, the electric conductivity measurements showed that the 2wt% percentage is the optimum one for thermal energy storage systems.

Coupling of PMMA to the surface of a layered silicate by intercalative polymerization: processes, structure and properties

Long PMMA chains were successfully attached to the surface of laponite layers through the [2-(acryloil-oxy)-ethyl]-trimethylammonium chloride linker. Grafting was carried out in water and the molecular weight of the grafted polymer changed between 40 and 110 kDa. The amount of PMMA attached to the silicate and the length of the polymer depended on the extent of ion exchange and on the amount of MMA added. The chemical structure of the attached polymer chains was confirmed by FTIR spectroscopy. Thermogravimetry, carried out before and after extraction, proved that most of the polymer was attached to the surface of the silicate. The layer distance of the silicate increased as the result of grafting. Model calculations proved that the polymer chains located inside the galleries are oriented parallel to the surface and two chains are found inside each gallery. The very high surface energy of the silicate leads to this parallel arrangement and the resulting strong interactions decrease the mobility of the chains. The glass transition temperature of the polymer increases while the change in specific heat decreases with decreasing chain length and PMMA amount.

Prediction of Droplet Generation and Blowing Parameters Helps for Interface Reaction During BOS Processes

Droplet generation phenomenon and its dependence on process parameters have been determined using a predictive numerical model, which predict droplet generation rate based on the blowing number. Evaluation of blowing number is performed depending on lance dynamics, oxygen flow rate and surface tension. The developed model considers surface tension as a function of oxygen, carbon and sulphur content of bath and bath temperature. Bath temperature is predicted using the enthalpy change of oxidation reactions and change of specific heat in each component present in the bath. Predicted end blow carbon concentration and bath temperature correspond well with the experimental values obtained from steel plant. The effect of lance angle and lance height on droplet generation is also taken in account. It has been found that the rate of droplet generation in melt increases with increases of blowing number (NB) and jet momentum onto the metal bath. Bath temperature is found to be more dominating factor for droplet generation process compared to lance height.

Magnetocaloric Properties of Nanostructured La0.7-xBixSr0.3MnO3 (x = 0.0, 0.1) Manganites Using Phenomenological Model

Magnetocaloric properties of nanostructured pristine and Bi-doped La0.7Sr0.3MnO3 samples, synthesised by high-energy planetary ball milling, are presented here. The aim of the study is to understand the effect of milling time on magnetic entropy change, relative cooling power and change in specific heat. The magnetocaloric property, defined as the change in the magnetic entropy, has been determined by using a phenomenological model applied to the magnetic susceptibility plots. Replacing 10% La by Bi in La0.7Sr0.3MnO3 significantly alters the change in magnetic entropy. Correlation between the particle size and magnetic entropy is observed in the present study. As the milling time increases from 0 h (bulk) to 48 h, the particle size reduces causing significant modifications in the magnetocaloric properties.

Mechanism and quantitative study of specific heat change during glass transition of amorphous polystyrene and Pd<sub>40</sub>Ni<sub>10</sub>Cu<sub>30</sub>P<sub>20</sub>

<sec>The nature of glass transition is one of the most interesting problems in modern condensed matter physics. There is a theory that shows that when the particle's diffusion motion probability <i>P</i> is less than <inline-formula><tex-math id="M2">\begin{document}$ {{\rm{e}}^{ - 2{{\rm{e}}^3}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20200331_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20200331_M2.png"/></alternatives></inline-formula>, the proportion of particles whose diffusion motion is frozen is not less than 1 + 2e<sup>3</sup>/ln<i>P</i>. Based on the modulus temperature formula of this theory and the experimental modulus-temperature curve of polystyrene in the literature, the free volume expansion coefficient of polystyrene is determined to be in a range of 0.00045－0.00052. </sec><sec>In this paper, we first quantitatively study the specific heat temperature relationship in the glass transition of polystyrene. Based on this theory, the specific heat-temperature formula in the glass transition region is derived. The material in the glass transition region is a mixture of rubber and glass, and this two-component (rubber and glass) system’s total specific heat is the product of the specific heat of the rubber and the percentage of rubber in the two-component system plus the product of the specific heat of the glass and the percentage of glass in the two-component system. Let <i>b</i> be the number of atoms in the main chain of the segment, then the proportion of rubber will be the <i>b</i>-th power of free volume fraction. This specific heat-temperature formula with polystyrene is tested. By substituting the obtained free volume expansion coefficient of the polystyrene into the specific heat-temperature formula, the resulting formula can accurately and quantitatively describe the specific heat-temperature relationship in the glass transition of polystyrene without fitting any parameters. </sec><sec>In this paper, we also study the change of motion in the glass transition of polystyrene. According to the analysis, the glass transition process of polystyrene is a process in which the diffusion movement of the main chain atoms is activated or frozen, which is consistent with the conclusions of relevant research on amorphous alloys. When the main chain atom is used as the molar unit of measurement, the specific heat change in the glass transition of polystyrene is 1.61<i>R</i> (<i>R</i> is the gas constant), which is consistent with the law, i.e. “the specific heat change in the glass transition of the amorphous alloy is about 1.5<i>R</i>”. These consistent conclusions predict that the glass transitions of amorphous alloys and glass transitions of polystyrene have the same essence. Based on this idea, the specific heat temperature formulas of the amorphous alloy Pd<sub>40</sub>Ni<sub>10</sub>Cu<sub>30</sub>P<sub>20</sub> and polystyrene are verified and prove to be consistent.</sec>

Signatures of Specific DNA Binding by the AT-Rich Interaction Domain of BAF250a.

The AT-rich interaction domain (ARID) containing BAF250a is a subunit of the BAF-A class of SWI/SNF chromatin remodeling complexes. The ARID belongs to a family of conserved DNA binding domains found in several eukaryotic proteins; however, its exact contribution to BAF250a function and the mechanism of its DNA binding are not well understood. Here we have probed the interaction of the BAF250a ARID with three different double-stranded DNA (dsDNA) sequences to understand its DNA binding properties. A comprehensive biophysical and thermodynamic study using nuclear magnetic resonance (NMR) spectroscopy and isothermal titration calorimetry revealed the complex nature of BAF250a ARID-DNA interactions. The thermodynamic signatures of the BAF250a ARID with 12 A-T bp dsDNA (AT-12) are distinct from those of 12 G-C bp dsDNA (GC-12) or 12 bp Dickerson dodecamer DNA (DD-12) sequences. We observed that the binding of the BAF250a ARID with AT-12 DNA is enthalpically driven in a tested temperature range of 5-25 °C. BAF250a ARID/AT-12 DNA interaction exhibited a larger negative calorimetric specific heat change (ΔCp) compared to that of BAF250a ARID/GC-12 DNA or BAF250a ARID/DD-12 DNA interactions. In the presence of salt (NaCl), ARID/AT-12 DNA binding was less perturbed than ARID/GC-12 DNA or ARID/DD-12 DNA binding. Overall, these results show that BAF250a ARID/AT-12 DNA interaction has signatures of "specific" binding. Furthermore, using NMR chemical shift perturbation experiments, we have identified DNA binding residues on the BAF250a ARID and generated a data-driven HADDOCK model of the ARID/DNA complex that was further supported by mutating key lysine residues that were found to be important for DNA binding.

Thermodynamic studies of 5D Myers–Perry black holes: General uncertainty principle approach

In this paper, we consider the five-dimensional Myers–Perry black hole solution to study the thermodynamic properties and compare this with the thermodynamic behaviors of generalized uncertainty principle (GUP)-induced Myers–Perry solution. We study the existence of remnant quantities. Stability criteria are studied by observing the natures of temperature growth and sign changes in specific heat. We try to locate phase transitions. Moreover, we study the corresponding physical range for the GUP parameter and try to justify the value with the data predicted by different observations.

Investigation of the Effect of Diamond Powder on the Thermal Properties of Octadecane Using Differential Scanning Calorimetry

Abstract The purpose of this work was to examine the effect of diamond powder on the thermal properties of phase change materials on the example of octadecane. The experiment involved mixing of diamond powder with a specific granulation with the aforementioned representative of the alkanes group. Two different grain sizes were used: 50 and 250 micrometres. The change of specific heat, latent heat of phase change and degree of supercoiling in newly formed mixtures was compared to the pure forms of the phase-change materials used. Initial mixing with a glass-stirring rod showed strong stratification for each granulation due to the low viscosity of the mixture and too large differences between component densities. It was decided to add amorphous silicon dioxide to the mixtures, which increases density of the mixture. The optimal percentage of amorphous silicon dioxide was estimated experimentally. Measurements of thermal parameters were carried out using DSC technology. The results of the tests of specific heat and latent phase transition heat showed that with the increasing content of diamond, the specific heat of the mixture decreases almost twice, and the latent heat can decrease by up to three times. The effect of diamond powder on reducing the degree of supercoiling of the mixture was also observed. An important observation was that the mixture with higher granulation of diamond powder had greater tendency for sedimentation. This method could be used to increase thermal conductivity and diffusivity of phase change materials and make them viable for use in systems that require cooling at high rate or temperature stabilization, such as control systems in electronic vehicles or aviation industry and at the same time decrease the degree of supercoiling which could increase the efficiency of system.

Effect of Nd Doping on Structural, Electrical, Thermal and Magnetic Properties of Multifunctional BiFeO3 Ceramics

Multifunctional Bi1-xNdxFeO3 (x = 0.0, 0.01 and 0.05) ceramics were prepared by a conventional high-temperature solid-state reaction method using high-purity oxides. The formation of the compounds and its structural parameters were investigated by X-ray diffraction followed by Rietveld refinement using noncentrosymmetric space group R3c. The grain size distributions were investigated by scanning electron micrograph, which has been strongly influenced by the addition of neodymium to the system. The dielectric constant and tangent loss as a function of frequency have been measured. The dielectric characteristic shows dispersive nature of these prepared ceramics. The dc conductivity of the compound increases with the increase in temperature. The calculated activation energies are 1.06 eV, 1.02 eV and 0.86 eV for x-concentration of 0.0, 0.01 and 0.05, respectively. The change in specific heat and weight loss has been measured to check the thermal behaviour of the compounds. The room temperature magnetic studies show that magnetic moment of the prepared compounds is increasing with the increase in Nd concentration.

Correlation between glass transition effect and structural changes in multicomponent iron phosphate-silicate glasses

Iron phosphate-silicate glasses from P2O5–SiO2–K2O–MgO–CaO–Fe2O3 system were subjected to the thermal and spectroscopic studies in order to gain information about their structure and thermal behavior in the range of glass transition effect. Research includes results obtained via DSC, MIR and DRIFT spectroscopy. Designated values of glass transition temperature and specific heat change slightly increases with Fe2O3 incorporation. Spectra collected during thermal treatment of glasses containing 2 and 30 mol% Fe2O3 exhibited various changes. Fe2O3 addition affected the glass structure by its reinforcement and led to its preservation during thermal treatment. The connection between density, molar volume, oxygen packing density and the chemical composition’s alteration were also established because of the direct dependence of physical properties and the structure. Obtained results supported thermal and spectroscopic studies. Conducted research is considered as a contribution to the knowledge about the family of iron phosphate glasses, which are known from their interesting properties and widely used applications.

Crystallization kinetics of Si20Te80−xBix (0 ≤ x ≤ 3) chalcogenide glasses

In this report, we investigate the crystallization kinetics of Si20Te80−xBix (0 ≤ x ≤ 3) chalcogenide glassy systems using differential scanning calorimetry (DSC) technique. Systematic studies are carried out in order to understand the variation of thermal parameters such as glass transition temperature (Tg), onset crystallization temperature (Tc) and peak crystallization temperature (Tp) as a function of composition. Activation energy for glass transition (Eg) and crystallization (Ec) has been calculated based on the relevant statistical methods. Furthermore, thermal parameters such as change in specific heat (ΔCp), fragility index (F), thermal stability (ΔT) & (S), enthalpy (ΔHc), entropy (ΔS) are deduced to interpret distinct material behaviour as a function of composition. Structural evaluation like thermal devitrification studies elucidate the restricted glass formability of the studied glass system. Conclusively, a relationship has been established between the obtained thermal parameters and electrical switching characteristics.

Thermal and nonlinear optical properties of Tm3+-doped tellurite glasses

In the present work, thermal and nonlinear properties of tellurite glasses doped with Tm2O3 were investigated by means of thermal lens, thermal relaxation and z-scan measurements. The composition of the samples was (78 − x) TeO2 + 4.5 Bi2O3 + 5.5 ZnO + 10.5 Li2O + 1.5 Nb2O5 + xTm2O3 (x = 0.05, 0.1, 0.5, 1.0 and 1.5 mol%). Thermal diffusivity (D), specific heat (ρc), thermal conductivity (K) and optical path change with temperature (ds/dT) were determined as a function of Tm3+ concentration. Concerning thermal–optical properties, our results show that the 0.5 mol% Tm doped is the most suitable sample for laser applications as it presented the lowest ds/dT and highest thermal diffusivity (conductivity). Third-order nonlinearities were observed and discussed in 1.0 and 1.5 mol% samples. The nonlinear indices (n2) found were 1.16 × 10−13 and 3.89 × 10−13 cm2 W−1, respectively. The data obtained show that the Tm3+-doped TBZLN glasses have potential for future opto-electronic devices.

Fitting of heat capacity peaks of PCMs with a theoretical formula

We introduce an explicit theoretical formula for the heat capacity peaks that occur in materials during phase changes. Such materials are of importance in many applications where thermal energy storage is needed, including solar systems, buildings, electronic devices, or radionuclide encasements. We show how theoretical parameters that appear in the formula can be adjusted in order to fit experimentally measured peaks. Two of these parameters are interesting in applications: the specific latent heat and phase change temperature. We illustrate this procedure for four peaks associated with phase changes in four different materials for which the heat capacity peaks had been measured at slow heating rates.

Effect of Sn contents on thermodynamic, microstructure and mechanical properties in the Zn90–Bi10 and Bi88–Zn12 based ternary alloys

The thermal conductivity variations with temperature for Zn90 − x–Snx–Bi10 (x = 5,10, 40 and 85 wt%) and Bi88 − x–Snx–Zn12 (x = 1.39, 43.26 and 79.3 wt%) alloys were measured by using the linear heat flow method. From thermal conductivity–temperature plots, the coefficients of thermal conductivity for the Zn–Sn–Bi alloys were calculated. The microstructures of Zn–Sn–Bi alloys were observed using scanning electron microscopy (SEM). The existing phases into microstructure were identified energy dispersive X-ray (EDX) analysis. The melting temperatures, the enthalpy of fusion and specific heat change between the liquid and solid phases in the Zn–Sn–Bi alloys were determined from Differential Scanning Calorimetry (DSC) trace. The tensile strength and microhardness of the alloys were measured using a Shimadzu Universal Testing Instrument (Type AG-10 KNG) and Future-Tech FM-700 model microhardness device.

Thermal conductivity of (1-x)BaTiO3-xPb(Zn1/3Nb2/3)O3 ceramics (x = 0, 0.025, 0.05, 0.075, 0.1, 0.125 and 0.15)

Barium titanate BaTiO3 (BT) is one of the widely applied lead-free ferroelectric materials due to relatively high permittivity and low cost. Lead zinc-niobate Pb(Zn1/3Nb2/3)O3 (PZN) belongs to a class of disordered and inhomogeneous materials, i.e. is a relaxor. Low-lead (1-x)BT-xPZN ceramics (x = 0, 0.025, 0.05, 0.075, 0.1, 0.125 and 0.15) were prepared by two-step conventional oxide mixed sintering process. Thermal conductivity (κ) of these ceramics was measured for the first time (except for x = 0) from room temperature to 200 °C. It was shown that the thermal conductivity decreases with both decreasing temperature and with increasing PZN content. κ(T) curves show anomaly at Curie temperature, which is connected with change of specific heat. Obtained results indicated that thermal conductivity of investigated samples is mainly related to phonons scattering by lattice defects and by atomic mass fluctuation resulted from PZN incorporation to BT.

Difference in physical properties of MAX-phase compounds Cr2GaC and Cr2GaN induced by an anomalous structure change in Cr2GaN

MAX-phase compounds with layered structure have been investigated extensively due to their excellent metallic and ceramic properties. Among them, Cr2GaC and Cr2GaN possess the same crystal structure and similar electronic structure, whereas Cr2GaN undergoes a spin-density-wave transition around 170 K but Cr2GaC is Pauli paramagnetism without any magnetic transition. To understand what make these happen, we studied the crystal structure between 300 and 35 K for both Cr2GaC and Cr2GaN. As the temperature decreases, the lattice constants (both a and c) decline monotonically in Cr2GaC, while an abnormal negative thermal expansion of c axis was observed below 170 K in Cr2GaN. The increase of c/a induced by abnormal increase of c leads to the enhancement of localization of Cr2N plane and causes more Cr-3d electrons confinement in Cr2N plane of Cr2GaN. This further facilitates the reconstruction of density of states near the Fermi surface and even forms the Fermi surface nesting, resulting in the spin-density-wave transition as well as the abrupt changes of resistivity, specific heat, and density of carriers around 170 K in Cr2GaN.

Proposal for evaluation method of battery safety through thermal analysis

Abstract Materials developed for battery cells must ensure safety. This study describes a method for predicting thermal runaway when a battery cell is heated. Also presented is a method for quantitatively evaluating cell material safety in safety testing without having to scale up the cell. With thermal runaway reactions being a complex series of elementary reactions, the differential isoconversional method based on the approach of Friedman was used to calculate thermal runaway. As a battery is a solid-liquid mixture with electrical energy, thermal runaway reaction behavior varies greatly depending on the cell’s heating rate. As such, a method for selecting kinetically consistent test conditions based on differential scanning calorimetry measurement results was added to enable calculation of thermal runaway behavior of cells under adiabatic conditions. The calculation results were verified with accelerating rate calorimetry, which can measure self-heating rates under adiabatic conditions, to confirm that the thermal runaway onset timing matched. Increasing the accuracy of heating rate calculations will require further research into how to treat changes in specific heat during decomposition reactions. Safety diagrams accounting for regulation and standard test conditions were created for a battery based on this calculation method. This method has revealed quantitative metrics for evaluating battery safety.

Corrected Internal Ballistic Simulation of High Chamber Pressure Gun

In view of the high initial velocity and chamber pressure of the high chamber pressure gun, the equation of state of gunpowder gas which is closer to the actual situation is adopted. Then considering the influence of the air resistance at the front of the projectile, the change of the combustion speed parameter in different pressure sections, both the specific heat ratio of the gunpowder gas and the constant volume specific heat change with the pressure and temperature, and the effect of erosive burning, the traditional classical internal ballistic model is modified. And the corresponding physical and mathematical models are established, the analogous calculation programs are compiled, the theoretical calculations and experimental results are compared. The results show that compared with the traditional classical internal ballistic model simulation, the simulation results of the modified ballistic performance of the high chamber pressure gun are more consistent with the experimental results.

Schottky specific heat of the lightly Mn-substituted electron-doped SrTiO3

Large changes in the low-temperature specific heat (low-T C) by applying magnetic fields up to 9 Tesla were found in the lightly Mn-substituted electron-doped perovskites Sr1−xLaxTiO3. The changes in the low-T C are qualitatively well explained by the Schottky specific heat (CSch) of localized spins of the Mn 3d electrons in weak internal magnetic fields via itinerant electrons. According to the analysis by using the conventional model, the doped Mn ions are apparently not Mn4+ (S = 3/2) ions, but are Jahn-Teller active Mn3+ (S = 2) ions or mixtures of Mn3+ and Mn2+ ions. However, the actual numbers of localized spins estimated from CSch are about 30% smaller than the expected values. Part of the localized spins of the Mn 3d electrons may disappear due to Kondo coupling with the itinerant electrons, leading to the observed enhancement of the electronic specific heat coefficients.