Temperature Dependence Of Specific Heat Research Articles

Temperature dependence of specific heat and thermodynamic functions of Al + 4,5 % Fe alloys doped with tin

It is known that commercial aluminum with a high content of iron, silicon and other impurities has no industrial application because of low performance. Hence, the development of new alloy compositions based on such a metal is a very urgent task. Promising compositions in the Al—Fe diagram are the (a-Al + A 3 Fe) eutectic and hypereutectic compositions that correspond to an iron content of 2—5 wt.% due to a minimum range of crystallization temperature. An alloy with the composition Al + 4,5 % Fe (AlFe4,5) was taken as a model alloy and subjected to modification with tin. The paper experimentally determined the dependence of specific heat of the Al + 4,5 % Fe alloy doped with tin with the calculation of changes in its thermodynamic functions. Studies were carried out in a «cooling» mode using computer equipment and the Sigma Plot program. The polynomials of the temperature dependence of the specific heat and changes in thermodynamic functions (enthalpy, entropy, and Gibbs energies) were determined for Al + 4,5 % Fe alloys doped with tin and basic reference standard (Cu) defined by the correlation coefficient R corr = 0,999. It was found that the heat capacity of the initial alloy decreases with an increasing tin content and increases as temperature rises. The enthalpy and entropy of the Al + 4,5 % Fe alloy increase with rising tin content and temperature, while the Gibbs energy decreases.

Studies of magnetic phase transitions in orthorhombic DyMnO3 ceramics prepared by acrylamide polymer gel template method

Abstract Single phase polycrystalline DyMnO3 (DMO) was synthesized using acrylamide polymer gel template method. We report the structural, magnetic, specific heat and dielectric properties of DMO over wide experimental conditions. Room temperature XRD pattern shows the formation of singe phase material without any impurity. The magnetic properties such as magnetization versus temperature (M vs. T) and magnetization versus magnetic field (M vs. H) were studied around the transition temperatures region. The temperature dependent magnetization data suggest two phase transitions corresponding to the lock-in temperature below which ferroelectric ordering exist (around 19 K; Tlock) and antiferromagnetic (AFM) ordering of Dy spin (around 8 K; TN (Dy)). The magnetic hysteresis obtained were fitted to extract weak ferromagnetic (FM) and antiferromagnetic/paramagnetic (AFM/PM) contribution to the magnetic data. The order of magnetic transitions were analyzed from Arrott plot. The temperature dependent specific heat measurement shows all three phase transitions corresponding to (i) AFM ordering of Mn spin (around 38 K; TN(Mn)), (ii) Tlock transition and (iii) TN(Dy) transition. The effect of magnetic field to the transitions were studied using specific heat capacity measurement. The peak intensity of TN(Dy) decreases on the application of magnetic field whereas peak intensity of Tlock increases with increase in magnetic field in specific heat measurement. Further the third anomaly, TN (Mn) remains more or less unaffected by the application of magnetic field. The intrinsic dielectric behaviour of the material was observed up to 160 K, above this temperature there is large increase in dielectric value due to the contribution from Maxwell- Wagner polarization.

Fast explicit dynamics finite element algorithm for transient heat transfer

This paper presents a novel methodology for fast simulation and analysis of transient heat transfer problems. The proposed methodology is suitable for real-time applications owing to (i) establishing the solution method from the viewpoint of computationally efficient explicit dynamics, (ii) proposing an element-level thermal load computation to eliminate the need for assembling global thermal stiffness matrix, leading to (iii) an explicit formulation of nodal temperature computation to eliminate the need for iterations anywhere in the algorithm, (iv) pre-computing the constant matrices and simulation parameters to facilitate online calculation, and (v) utilising computationally efficient finite elements to efficiently obtain thermal responses in the spatial domain, all of which lead to a significant reduction in computation time for fast run-time simulation. The proposed fast explicit dynamics finite element algorithm (FED-FEM) employs nonlinear thermal material properties, such as temperature-dependent thermal conductivity and specific heat capacity, and nonlinear thermal boundary conditions, such as heat convection and radiation, to account for the nonlinear characteristics of transient heat transfer problems. Simulations and comparison analyses demonstrate that not only can the proposed methodology handle isotropic, orthotropic, anisotropic and temperature-dependent thermal properties but also satisfy the standard patch tests and achieve good agreement with those of the commercial finite element analysis packages for numerical accuracy, for three-dimensional (3-D) heat conduction, convection, radiation, and thermal gradient concentration problems. Furthermore, the proposed FED-FEM algorithm is computationally efficient and only consumes a small computation time, capable of achieving real-time computational performance, leading to a novel methodology suitable for real-time simulation and analysis of transient heat transfer problems.

Connection between Unusual Lattice Thermal Expansion and Cooperative Jahn-Teller Effect in Double Perovskites LaPbMSbO6 (M = Mn, Co, Ni).

Lattice thermal expansion (LTE) has been investigated in double perovskites LaPbMSbO6 (M = Mn, Co, Ni). Ordinary LTE behavior with good thermal stability is identified for the Mn sample, whereas unusual LTE with a preferably expanded interplanar distance of (040) is revealed for Co and Ni samples. Temperature-dependent X-ray diffraction patterns ( T-XRD), Raman spectra ( T-Raman), and specific heat capacities ( T- Cp) consistently indicate that a rare isostructural displacive phase transition (IDPT) with a second-order phase transition nature is predominant near the critical temperature. Refinements of neutron powder diffraction (NPD) and in situ T-XRD data present temperature-sensitive bond parameters which are relevant to planar oxygen O1. X-ray photoelectron spectra (XPS) further confirm the Jahn-Teller (J-T) activated Co2+ (HS) or Ni3+ (HS/LS) cations at the B-site sublattice. This unusual LTE behavior could be understood by the cooperative J-T effect contributed by a Pb2+ ion and Co2+/Ni3+ ion from A- and B-site sublattices, respectively. The importance of 6s(Pb)-2p(O)-3d(Co/Ni) extended orbital hybridization on affecting thermal expansion behavior is highlighted on the basis of temperature-induced phonon mode softening. This study presents a microscopic description of connection between anisotropic thermal expansion and a cooperative J-T effect, which inspired exploration of thermal-mechanical coupled functional materials based on LaPbMSbO6 double perovskites.

Performance assessment of energy deposition based drag reduction technique for Earth and Mars flight conditions

Energy deposition based drag reduction technique is numerically investigated for Earth and Mars atmospheric conditions using in-house non-equilibrium flow solvers. Golden section search algorithm is successfully integrated with these CFD solvers to evaluate the optimum amount of energy to be deposited for maximum power effectiveness. During these studies for spherical configuration, it has been noticed that, the amount of energy deposited corresponding to maximum power effectiveness is more for Mars case than the Earth case. Higher temperature dependence of specific heat for carbon dioxide than air is accounted to be responsible for this observation. Further, maximum power effectiveness is marked to be lower for carbon dioxide flow as compared to that for air flow. It has also been noticed that the performance of this technique gets lowered with increase in stagnation enthalpy of the flow, in either cases, with remarkable drop in case of air.

Numerical simulation of the influence of fluid motion in mushy zone during micro-EDM on the crater surface profile of Inconel 718 alloy

The micro-EDM, due to its ability to machine any electrically conductive material, has been one of the preferred manufacturing methodologies for machining difficult to machine materials. The micro-EDM is a thermal energy-based material removal process where the material removal occurs by spark erosion. In majority of the modeling associated with micro-EDM, the effect of the fluid motion in the liquid and mushy phase of the workpiece alloy is not considered. This paper aims at numerically simulating the crater surface profile formed on Inconel 718 incorporating the effects of material movement in the mushy zone using micro-EDM. Navier–Stokes equations were used as the governing equations. Temperature-dependent specific heat, thermal conductivity, density and viscosity were incorporated, in three ranges, i.e., solid ( $${T}<1523\hbox { K}$$ ), liquid ( $$T>1609\hbox { K}$$ ) and mushy ( $$1523\hbox { K}<{T}<1609\hbox { K}$$ ). The mushy zone properties were calculated using enthalpy porosity method, and the properties were updated after each iteration. Specific boundary conditions like Gaussian distributed heat flux on the top surface, fixed percentage of heat to the anode and Marangoni stress on the top surface of the workpiece were applied. The simulations were performed using CFD package ANSYS 15.0 FLUENT for three distinct voltages 100, 125 and 150 V, keeping capacitance constant at $$0.4\,\upmu \hbox {F}$$ . User-defined functions were written in C language to incorporate the temperature-dependent properties and the boundary conditions. These simulated results were compared with the experimental values at same input condition, and the maximum calculated deviation in crater profile prediction was less than 14%.

Longitudinal magnetization and specific heat of the anisotropic heisenberg antiferromagnet on honeycomb lattice

We study the effects of longitudinal magnetic field and temperature on the thermodynamic properties of two dimensional Heisenberg antiferromagnet on the honeycomb lattice in the presence of anisotropic Dzyaloshinskii-Moriya interaction and next nearest neighbor coupling exchange constant. In particular, the temperature dependence of specific heat have been investigated for various physical parameters in the model Hamiltonian. Using a hard core bosonic representation, the behavior of thermodynamic properties has been studied by means of excitation spectrum of mapped bosonic gas. The effect of Dzyaloshinskii-Moriya interaction term on thermodynamic properties has also been studied via the bosonic model by Green's function approach. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various anisotropy parameters. At low temperatures, the specific heat is found to be monotonically increasing with temperature for magnetic fields in the gapped field induced phase region. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum. Also we have studied the dependence of magnetization on Dzyaloshinskii-Moriya interaction strength for different next nearest neighbor coupling constant.

SPECTROSCOPIC RESEARCH OF POLYIZOBUTYLENE DESTROYED BY DESTRUCTION

The temperature dependence of specific heat of poly(isobutene) degraded under the action of strong Lewis acids has been investigated. From the calculated thermodynamic parameters have been drawn conclusions on the structural conversions of the macromolecules in the process of catalytic degradation. By means of 13C NMR the formation of branched macro- molecules was shown. On the basis of the results a degradation mechanism for poly (isobutene) is suggested.

Field dependent specific heat and longitudinal magnetization of the quantum magnet layer Cs2CuCl4: Anisotropy effects

We have addressed the specific heat and magnetization of an anisotropic spin-1/2 triangular Heisenberg antiferromagnet Cs2CuCl4 in the presence of magnetic field at finite temperature. We have investigated the behavior of thermodynamic properties by means of excitation spectrum in terms of a hard core bosonic representation. The effect of in-plane anisotropy on thermodynamic properties has also been studied via the bosonic model by Green’s function approach. This anisotropy is considered for exchange constants that couple spin components perpendicular to magnetic field direction. We have found the temperature dependence of the specific heat and longitudinal magnetization in the gapped field induced spin-polarized phase for various magnetic fields and anisotropy parameters. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various anisotropy parameters. Our results show temperature dependence of specific heat includes a peak so that its temperature position goes to higher temperature with increase of magnetic field. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum.

Laser additive manufacturing of powdered bismuth telluride

Abstract

Prediction of 3D grinding temperature field based on meshless method considering infinite element

A three-dimensional numerical model to calculate the grinding temperature field distribution is presented. The finite block method, which is developed from meshless method, is used to deal with the stationary and the transient heat conduction problems in this paper. The influences of workpiece feed velocity, cooling coefficient, and the depth of cut on temperature distribution are considered. The model with temperature-dependent thermal conductivity and specific heat is presented. The Lagrange partial differential matrix from the heat transfer governing equation is obtained by using Lagrange series and mapping technique. The grinding wheel-workpiece contact area is assumed as a moving distributed square heat source. The Laplace transformation method and Durbin’s inverse technique are employed in the transient heat conduction analysis. The results of the developed model are compared with others’ finite element method solutions and analytical solutions where a good agreement is demonstrated. And the finite block method was proved a better convergence and accuracy than finite element method by comparing the ABAQUS results. In addition, the three-dimensional infinite element is introduced to perform the thermal analysis, and there is a great of advantages in the simulation of large boundary problems.

Estimation of temperature-dependent thermal conductivity and specific heat capacity for charring ablators

The accurate assessment of thermal properties is crucial for charring materials simulation and design. In this work, a new inversion method for estimating temperature-dependent thermal conductivity and specific heat capacity from temperature data is presented for charring ablators. Firstly, a one-dimensional thermal response model with surface recession is developed to simulate the thermal behavior of charring ablator. Then based on the developed model, sensitivity analysis is conducted to investigate the correlation between thermal parameters and temperature for determining inversion sequence and find that virgin thermal conductivity has the biggest influence on temperature which should be estimated at first. Finally, the temperature-dependent thermal conductivities and specific heat capacities are obtained by the inversion method from temperature data. The inversion values from simulation temperature data coincide with the reference values, which the average inversion error of thermal conductivities is 4.3% and the average inversion error of specific heat capacities is 3.1%. And the calculated thermal response temperature employing the inversion thermal properties shows a good agreement with the arc jet test data, which the average error is 8.5%. This inversion method can accurately determine unknown temperature-dependent thermal properties such as thermal conductivity and specific heat capacity, which provides an insight into the analysis and design of thermal protection materials for spacecraft.

Magneto-electronic specific heat of germanene nanoribbons

Electronic properties of zigzag and armchair germanene nanoribbons (ZGeNR and AGeNR) in magnetic field are calculated by the tight-binding model including the spin-orbit coupling (SOC). The SOC induces spin-split states changing energy dispersion and band-gap. As field strength increases, band-gap increases for ZGeNRs, but decreases for AGeNRs. At zero field, temperature-dependent electronic specific heat strongly depends on nanoribbon's boundary and width. For ZGeNRs, specific heat declines simply proportional to the inverse of width; however, it depends on the dimer-line number for AGeNRs. At low-temperature, width-dependent specific heat of ZGeNRs rapidly drops with increasing field strength, whereas it exhibits an oscillatory behavior for AGeNRs. As temperature increases, such an oscillatory behavior is smeared out or not that is profoundly related to the dimer-line number of AGeNRs. Low-temperature specific heat with varying magnetic field exhibits peak, peak-dip-peak, or smoothly increasing behaviors that strongly reveals geometry dependence of field-modulated electronic properties.

Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1)

We study crystal structure, phase transitions and magnetism of pseudo-binary TmxDy1-xAl2 (0 ≤ x ≤ 1) compounds using temperature dependent X-ray powder diffraction, specific heat and magnetization measurements, first principles, and model calculations. In low external magnetic fields, Dy-rich compounds undergo continuous, second-order phase transitions at the respective Curie temperatures, TC. In contrast, the Tm-rich compounds exhibit discontinuous, first-order anomalies in the magnetically ordered states. These sharp transitions correlate with a substantial energy difference between the room temperature cubic and ground state rhombohedral structures of TmAl2. A clear anomaly in the lattice parameter is observed at ∼30 K for x = 0.5, which nearly coincides with TC = 31.2 K. The effective quadrupolar moment of the lanthanides changes sign around x = 0.5, which leads to a nearly zero anisotropy constant and approximately spherical effective 4f charge densities, providing an explanation for the lack of structural distortions below TC for x = 0.5. The calculations confirm [001] as the easy magnetization axis in the ground state tetragonal structure of DyAl2, and reveal collapse of the orbital magnetic moment when the easy magnetization direction changes to [111]. Within the rhombohedral ground state of TmAl2 [111] is the easy magnetization direction.

Superconductivity in the superhard boride WB4.2

We show that the superhard boride WB4.2 is a superconductor with a Tc of 2.05(5) K. Temperature-dependent magnetic susceptibility, electrical resistivity, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant γ for WB4.2 is 2.07(3) mJ mol−1 K−2 and the ΔC/γTc = 1.56, which is somewhat higher than what is expected for weakly coupled Bardeen–Cooper–Schrieffer type superconductors. The Hc2 versus T plot is linear over a wide temperature range but does show signs of flattening by the lowest temperatures studied and therefore the zero temperature upper critical field (μ0Hc2(0)) for WB4.2 lies somewhere between the linear extrapolation of μ0Hc2(T) to 0 K and expectations based on the Werthamer–Helfand–Hohenberg model.

Cluster mean-field study of the Heisenberg model for CuInVO5

Motivated by the experimental report of unusual low-temperature magnetism in the quasi-one-dimensional magnet ${\mathrm{CuInVO}}_{5}$, we present results of a cluster mean-field study on a spin-$1/2$ Heisenberg model with alternating ferromagnetic and antiferromagnetic nearest-neighbor coupling. We map out the ground-state phase diagrams with varying model parameters, including the effect of an external magnetic field. An unexpected competition between different spin-spin correlations is uncovered. Multiple spin-flop transitions are identified with the help of component-resolved correlation functions. For the material-specific choice of model parameters we discuss the temperature dependence of specific heat and magnetic susceptibility and compare our results with the available experimental data. A detailed account of spin-spin correlations allows us to present a microscopic understanding of the low-temperature magnetic ordering in ${\mathrm{CuInVO}}_{5}$. Most notably, we identify the origin of an extra peak in the low-temperature specific heat data of ${\mathrm{CuInVO}}_{5}$ reported by Hase et al. [Phys. Rev. B 94, 174421 (2016)].

The σ-phase superconductors Nb20.4Rh5.7Ge3.9 and Nb20.4Rh5.7Si3.9

We show that the previously unreported ternary σ phases Nb20.4Rh5.7Ge3.9 and Nb20.4Rh5.7Si3.9 are both superconductors with Tc values of approximately 1.9 K. The superconducting transitions were characterized through temperature-dependent magnetic susceptibility, electrical resistance, and specific heat measurements. The Sommerfeld constants, γ, for Nb20.4Rh5.7Ge3.9 and Nb20.4Rh5.7Si3.9 are 89(1) mJ mol-f.u.−1K−2 and 86(1) mJ mol-f.u.−1K−2 (about 3.0 and 2.9 mJ mol-atom−1 K−2), respectively. The normalized specific heat jumps at Tc, ΔC/γTc, are approximately 1.39 for Nb20.4Rh5.7Ge3.9 and 1.30 for Nb20.4Rh5.7Si3.9, consistent with both materials being weakly coupled BCS type superconductors.

Thermal properties of La0.7Ca0.2Sr0.1MnO3:PdO composites

A systematic study on the thermal conductivity, Seebeck coefficient and specific heat of La0.7Ca0.2Sr0.1MnO3:PdO composites is presented. Solid state reaction procedure was employed to synthesis the samples. It is seen from thermal conductivity (κ(T)) studies that the samples exhibit a slope change nature close to their corresponding magnetic phase transition temperature, TC. The overall magnitude of κ is observed to decrease with increasing Pd concentration. The analysis of Seebeck coefficient data, S(T) versus temperature, T was done using Mott's polaron hopping model reveals that the electron-magnon scattering is governing the low temperature region. The temperature dependent specific heat CP(T) is analyzed to determine the entropy change (ΔS) during the magnetic phase transition.

Inverse Identification of Temperature-Dependent Thermal Properties Using Improved Krill Herd Algorithm

A novel intelligent algorithm, krill herd (KH), is firstly introduced to solve the inverse identification of temperature-dependent thermal properties of materials. To promote the searching ability and accelerate the convergence velocity, three improved KH (IKH) algorithms are proposed and developed for solving the optimization tasks. The temperature-dependent thermal conductivity and specific heat of a building material are estimated by using the KH algorithms, and the IKHs achieve better performance than the original KHs. Moreover, the functional forms of thermal conductivity of insulating and refractory materials are also reconstructed. The IKH algorithm is proved to be more accurate than other algorithms. Finally, a two-dimensional nonhomogeneous heat conduction model is investigated and the thermal conductivities of materials at specified temperatures are reconstructed, in which no prior information is needed for the expressions of the thermal conductivity to be identified. All the retrieval results show that IKH algorithm is robust and effective for solving the inverse heat conduction problems.

Zr0.70[Y1-xNdx]0.30O1.85 as a potential candidate for inert matrix fuel: Structural and thermo-physical property investigations

In order to mimic the loading of americium (Am) and curium (Cm) oxide in yttria stabilized zirconia, Zr0.70 [Y1-xNdx]0.30O1.85 (0.0 ≤ x ≤ 1.0) system was synthesized by solid state route and characterized by X-ray diffraction (XRD) and Raman spectroscopy. The entire system appeared single-phasic fluorite-type by XRD. However, Raman spectroscopy revealed the existence of tetragonal domains for the Nd-rich composition, Zr0.70Nd0.30O1.85 (x = 1.0). Bulk thermal expansion coefficient was found to increase with increasing NdO1.5 content in this series in the temperature range 298–1473 K. The heat capacity of sintered samples was measured by heat flux-type differential scanning calorimeter over the temperature range 313–713 K and it was observed to decrease with increasing Nd3+-content. Thermal conductivity values were determined from measured thermal diffusivity, temperature dependent density and specific heat capacity values. The thermal conductivity of Nd3+ stabilized zirconia was lower than yttria stabilized zirconia.