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Understanding the correlation between crystal structure and thermal conductivity in semiconductors is very important for designing heat-transport-related devices, such as high-performance thermoelectric materials and heat dissipation in micro-nano-scale devices. In this work, the lattice thermal conductivity ( κL ) of the cage-like compounds Cu3 VSe4 and Cu3 NbSe4 was investigated by experimental measurements and first-principles calculations. The experimental κL of Cu3 NbSe4 is approximately 25 % lower than that of Cu3 VSe4 at 300 K. The relevant important physical parameters, including the sound velocity, heat capacity, weighted phonon phase space (W), and third-order force constants along with atomic mass were theoretically analyzed. It is found that W is the dominant parameter in determining the κL , and the other factors only play a minor role. The physical origin is the relatively "soft" lattice of Cu3 NbSe4 with heavier atomic mass. This research provides deep insight into the correlation between the thermal conductivity and crystal structure and paves the way for discovering high-performance thermal management device and thermoelectric materials with intrinsically low κL .

Specific heat capacity ( C P ) is regarded as a fundamental parameter for the design, operation, and optimization of the heat transfer equipment widely used in the food industry. Using the calorimetric ASTM E1269-11 standard procedure, the C P -temperature ( C P ( T ) ) curves of fruit juice model systems prepared at different mass fractions of fructose/glucose/sucrose/citric acid/pectin and water were measured. Thus, experimental data of C P for solid samples in crystalline and amorphous states from -80 °C up to the melting temperature range and for aqueous samples from -80 to 110 °C were generated. In the tested temperature interval, the C P of crystalline, amorphous, and aqueous samples were found to be in the ranges of 0.037 ± 0.020 to 5.61 ± 0.04; 0.061 ± 0.004 to 3.12 ± 0.19, and 0.363 ± 0.05 to 3.24 ± 0.14 kJ/kg °C, respectively. Also, a generalized empirical equation based on the type and concentration of components was developed to predict the C P ( T ) curves of the studied samples. The proposed equation exhibited a low error sum of squares (SSE 0.927). An analysis of variance (ANOVA) was performed with a confidence level of 95% (p C P ( T ) curves were influenced by temperature, thermal transitions, water, solid types, and compound interactions. Glucose was one of the solids that most significantly influenced the C P values of samples. PRACTICAL APPLICATION: The experimental specific heat capacity data and empirical equation proposed in this study are relevant to the design, evaluation, and optimization of heat transfer equipment involved in many foods and biochemical industrial processes such as cryopreservation, frozen storage, freezing, chilling, drying, and the cooking of hard candies.

In a typical biomolecular simulation using Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) force field, the vast majority molecules in the simulation box consist of water, and these water molecules consume the most CPU power due to the explicit mutual induction effect. To improve the computational efficiency, we here develop two new nonpolarizable water models (with flexible bonds and fixed charges) that are compatible with AMOEBA solute: the 3-site AW3C and 5-site AW5C. To derive the force-field parameters for AW3C and AW5C, we fit to six experimental liquid thermodynamic properties: liquid density, enthalpy of vaporization, dielectric constant, isobaric heat capacity, isothermal compressibility and thermal expansion coefficient, at a broad range of temperatures from 261.15 to 353.15 K under 1.0 atm pressure. We further validate our AW3C and AW5C water models by showing that they can well reproduce the radial distribution function g(r), self-diffusion constant D, and hydration free energy from the AMOEBA03 water model and the experimental observations. Furthermore, we show that our AW3C and AW5C water models can greatly accelerate (>5 times) the bulk water as well as biomolecular simulations when compared to AMOEBA water. Specifically, we demonstrate that the applications of AW3C and AW5C water models to simulate a DNA duplex lead to a threefold acceleration, and in the meanwhile well maintain the structural properties as the fully polarizable AMOEBA water. We expect that our AW3C and AW5C water models hold great promise to be widely applied to simulate complex bio-molecules using the AMOEBA force field.

Comparative hybrid density functional calculations on the structure, stability, and phonon frequencies of monolayers and single-walled nanotubes are performed for Zr(Hf)S2 disulfides. The first-principles calculations of HfS2 -based nanotubes are made for the first time. The symmetry analysis of infrared and Raman active vibrational modes in ZrS2 and HfS2 nanotubes is made using the induced representations of the isogonal point groups of line groups. It is shown that the number of infrared and Raman active modes is constant for NTs with the same chirality type. The correlation of the phonon modes of the nanotubes of relatively large diameters with those of monolayer is analyzed. The thermodynamic functions of monolayers and nanotubes with various chirality and diameters are calculated on the basis of the obtained phonon frequencies. It is established that the phonon contribution to the nanotube strain energy is small, but may be important for an accurate estimate of the stability of the nanotubes of small diameters. The calculated results show that the thermal contributions to Helmholtz free energy are positive; thereby they slightly reduce the stability of ZrS2 and HfS2 nanotubes at elevated temperatures. © 2019 Wiley Periodicals, Inc.

We present analytical formulae for the first and second derivatives of the Helmholtz free energy of non-relativistic ideal Fermi-gas. Important thermodynamic quantities such as heat capacity, sound velocity, heat capacity ratio and others can be easily expressed through the derivatives. We demonstrate correct ideal Boltzmann gas and low--temperature Fermi-gas asymptotes and derive corrections to thermodynamic functions for these limiting cases. Numerical computations of thermodynamic properties of ideal Fermi-gas can be accurately performed using the developed freely available Python module ifg.

Thermomechanical 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

The specific heat capacity of soil solids (cₛ) is a key parameter affecting heat storage and transfer in soils. In soil and geophysical applications, cₛ is often assumed to be a constant with little variations across soils. In this study, we determined the specific heat capacities of nine soils by using differential scanning calorimetry (DSC), evaluated the effects of clay and organic matter (OM) contents on the cₛ of original and OM-free soil samples at room temperature, and quantified the changes of cₛ caused by the existence of tightly bound water (TBW). On average, the nine mineral soils had a cₛ of 0.750 MJ Mg⁻¹ K⁻¹, close to the commonly accepted cₛ value. However, for the original soils dried at 105°C, clay content did not obviously influence the cₛ value and cₛ increased linearly with both OM and TBW contents, indicating that inaccurate cₛ data were likely if the changes in the OM fraction in soil solids and adsorbed TBW were ignored. In addition, relatively large values for the specific heat capacity of soil minerals (cₘ) were observed in fine-textured soils compared with coarse-textured soils. Two preliminary functions were developed for estimating cₘ and cₛ from the soil’s clay and OM contents.

Composite quantum chemical methods W1X-1 and CBS-QB3 are used to calculate the gas phase standard enthalpy of formation, entropy, and heat capacity of 38 phosphines and phosphine oxides for which reliable experimental thermochemical information is limited or simply nonexistent. For alkyl phosphines and phosphine oxides, the W1X-1, and CBS-QB3 results are mutually consistent and in excellent agreement with available G3X values and empirical data. In the case of aryl-substituted species, different computational methods show more variation, with G3X enthalpies being furthest from experimental values. The calculated thermochemical data are subsequently used to determine Benson group additivity contributions for 24 Benson groups and group pairs involving phosphorus, thereby allowing fast and accurate estimations of thermochemical data of many organophosphorus compounds of any complexity. Such data are indispensable, for example, in chemical process design or estimating potential hazards of new chemical compounds. © 2018 Wiley Periodicals, Inc.

Experiments that systematically explore rock friction under crustal earthquake conditions reveal that faults undergo abrupt dynamic weakening. Processes related to heating and weakening of fault surfaces have been invoked to explain pronounced velocity weakening. Both contact asperity temperature Ta and background temperature T of the slip zone evolve significantly during high-velocity slip due to heat sources (frictional work), heat sinks (e.g., latent heat of decomposition processes), and diffusion. Using carefully calibrated High-Velocity Rotary Friction experiments, we test the compatibility of thermal weakening models: (1) a model of friction based only on T in an extremely simplified, Arrhenius-like thermal dependence; (2) a flash heating model which accounts for the evolution of both V and T; (3) same but including heat sinks in the thermal balance; and (4) same but including the thermal dependence of diffusivity and heat capacity. All models reflect the experimental results but model (1) results in unrealistically low temperatures and model (2) reproduces the restrengthening phase only by modifying the parameters for each experimental condition. The presence of dissipative heat sinks in stage (3) significantly affects T and reflects on the friction, allowing a better joint fit of the initial weakening and final strength recovery across a range of experiments. Temperature is significantly altered by thermal dependence of (4). However, similar results can be obtained by (3) and (4) by adjusting the energy sinks. To compute temperature in this type of problem, we compare the efficiency of three different numerical approximations (finite difference, wavenumber summation, and discrete integral).

Soil bulk density (ρb) and volumetric water content (θ) determine the volume fractions of soil solids, water and air, and influence mass and energy transfer in soil. It is desirable to monitor ρb and θ concurrently and non‐destructively. We present a heat pulse‐based method for simultaneous determination of ρb and θ from soil thermal properties. The method uses equations that relate ρb and θ to soil volumetric heat capacity (C) and to soil thermal conductivity (λ). We developed a three‐step procedure to calculate ρb and θ from C and λ measured by a heat pulse sensor, with soil texture and specific heat of soil solids known a priori. Laboratory evaluation of soil samples with various textures showed that the three‐step method provided reliable estimates of ρb and θ at θ values greater than the critical water content (θc) when λ started to respond notably to increases in θ. This method provides a new way to determine ρb and θ simultaneously with heat pulse sensors. HIGHLIGHTS: We developed an approach to determine soil bulk density (ρb) and water content (θ) simultaneously with a heat pulse sensor. We estimated ρb and θ from soil thermal properties based on heat capacity and thermal conductivity models. The new approach provided reliable ρb and θ values at water contents >θc, the critical value. At θ < θc, the approach gave unstable results because soil thermal conductivity was insensitive to ρb.

Specific heat capacity (cp) is a temperature dependent physical property of foods. Lipid—being a macromolecular component of food—provides some fraction of the food's overall heat capacity. Fats/oils are complex chemicals that are generally defined by carbon length and degree of unsaturation. The objective of this investigation was to use advanced specific heat capacity measurement to determine the effect of fatty acid chemical structure on specific heat capacity of food lipids. In this investigation, the specific heat capacity of a series of triacylglycerols were measured to quantify the influence of fatty acid composition on specific heat capacity based on two parameters; the ‐average carbon number (C) and the average number of double bonds (U). A prediction model for specific heat capacity of food lipids as a function of C, Uand temperature (T) has been developed. A multiple linear regression to the three‐parameter model (R2= 0.87) provided a good fit to the experimental data. The prediction model was evaluated by comparison with previously published specific heat capacity values of vegetable oils. It was found that the model provided a 0.53% error, while three other models from the literature predicted cpvalues with 0.85% to 1.83% average relative deviation from experimental data. The outcomes from this research confirm that the thermophysical properties of fat present in foods are directly related to the physical chemical properties. The specific heat capacity of food products is widely used in process design. Improvements of current models to predict specific heat capacity of food products will assist in the development of efficient processes and in the control of food quality and safety. Furthermore, the understanding of how changes in chemical structure of macromolecular components of foods effect thermophysical properties may begin to allude to models that are not just empirical, but represent portions of the differences in chemistry.

Crystalline solids exhibiting intrinsically low lattice thermal conductivity (κL) are crucial to realizing high-performance thermoelectric (TE) materials. Herein, we demonstrate an ultralow κL of 0.35 Wm-1K-1 in AgCuTe, which exhibits a remarkable TE figure-of-merit, zT of 1.6 at 670 K when alloyed with 10 mol% Se. First-principles DFT calculation reveals the presence of several soft phonon modes in its room-temperature hexagonal phase, which are also evident from low-temperature heat capacity measurement. These phonon modes, dominated by Ag vibrations, soften further with temperature giving a dynamic cation disorder and plausibly driving the superionic transition. Intrinsic factors such as hierarchical bond strengths, soft modes, and optical-acoustic phonon coupling cause an ultralow κL in the room-temperature hexagonal phase, while the dynamic disorder of Ag/Cu cations leads to reduced phonon frequencies and mean free paths in the high-temperature rocksalt phase. Despite the significant cation disorder at elevated temperatures, the crystalline conduits to carrier-transport provided by the rigid anion sublattice render a high power factor.

Author(s): Maggi, F; Fiona, FH; Riley, WJ | Abstract: Accurate prediction of the temperature response of the velocity v of a biochemical reaction has wide applications in cell biology, reaction design, and biomass yield enhancement. Here, we introduce a simple but comprehensive mechanistic approach that uses thermodynamics and biochemical kinetics to describe and link the reaction rate and Michaelis–Menten constants (kT and K T) with the biomass yield and mortality rate (YT and δT) as explicit functions of T. The temperature control is exerted by catabolic enthalpy at low temperatures and catabolic entropy at high temperatures, whereas changes in cell and enzyme–substrate heat capacity shift the anabolic electron use efficiency eA and the maximum reaction velocity vmax. We show that cells have optimal growth when the catabolic (differential) free energy of activation decreases the cell free energy harvest required to duplicate their internal structures as long as electrons for anabolism are available. With the described approach, we accurately predicted observed glucose fermentation and ammonium nitrification dynamics across a wide temperature range with a minimal number of thermodynamics parameters, and we highlight how kinetic parameters are linked to each other using first principles.

Low-temperature calorimetry is an experimental science that measures the thermodynamic function heat capacity, Cp(T), from which the standard third-law entropy (298 K), S°, is calculated. The recent technological development of relaxation calorimetry allows both new experimental strategies and types of Cp investigations to be made, which were previously not possible. The Cp measurements are fast and automated and can be made on mg-sized mineralogical samples between 2 and 400 K. These advantages, when careful measurement procedures are used, permit better determinations of Cp behaviour. The Cp of synthetic single-crystal MgO was measured between 5 and 302 K, and S° calculated using relaxation calorimetry to further investigate the method's precision and accuracy. A number of synthetic and natural end-member composition or nearly end-members of silicate garnet were investigated in the past via adiabatic calorimetry, an old and established method, and more recently and extensively with the relaxation method. First Cp(T) and S° results, using relaxation calorimetry, have been obtained on spessartine (Mn3Al2Si3O12) and knorringite (Mg3Cr2Si3O12). Furthermore, reinvestigations on pyrope (Mg3Al2Si3O12), almandine (Fe3Al2Si3O12), grossular (Ca3Al2Si3O12), and andradite (Ca3Al2Si3O12), often on multiple samples, have resolved uncertainties and certain problems with published thermodynamic data. S° can be affected by various low-temperature physical phenomena, such as cooperative magnetic phase transitions or Schottky anomalies at temperatures of < 15 K, which were not described fully in some older adiabatic calorimetric studies. New Cp results show that small differences in the thermodynamic behaviour between some natural and synthetic silicates may exist as demonstrated by extensive work on grossular. Important and “new” research questions on the thermodynamic behaviour of minerals are coming to light and are being investigated. The Cp behaviour and S° values for six silicate garnet end members are analyzed and the latter are compared to the “best fit or optimized” S° values given in various internally consistent thermodynamic databases. Conclusions are drawn on what types and directions of calorimetric study are required in order to obtain better thermodynamic property determinations of minerals, as well as achieving a better understanding of the underlying microscopic physical behaviour that determines the macroscopic Cp and S° functions. This article is protected by copyright. All rights reserved.

The equilibrium properties of polymers and the changes occurring on going to nonequilibrium states are discussed. For example, the typical semicrystalline polymer is treated as a globally metastable structure of two or three nanophases with possible local equilibria (crystal/amorphous or crystal/amorphous/rigid amorphous). The transitions are explored experimentally by classical calorimetry and temperature-modultated calorimetry. The heat capacity is taken as the basic thermodynamic property and linked to the different types of molecular motion in terms of small-amplitude vibrational motion and large-amplitude conformational motion. The low frequency vibrations are the skeletal vibrations and can be fitted to the low temperature heat capacities with one-, two-, and three-dimensional Debye functions. The high frequency vibrations are treated as group vibrations, easily available as group vibrations from normal-mode analyses of the polymer or related compounds. Data for almost 100 polymers are presented from the ATHAS data bank. The large-amplitude, conformational motion can be linked to the deviation of the experimental heat capacity from the vibrational heat capacity and allowed to discuss the more mobile phases. The integral thermodynamic functions, enthalpy, entropy, and free enthalpy are then derived from the heat capacities and linked to the phase transitions and chemical thermodynamics (melting/crystallization, glass transition, mixing/demixing, and polymerization/depolymerization). The bibliography establishes the link to classical thermodynamics data and theory sources with 163 references. Keywords: heat capacity; enthalpy; entropy; polymerization; equilibrium; thermodynamics; nonequilibrium; phase transitions

The low temperature phases of Na2Ti3Cl8 and their phase transitions were investigated by powder neutron diffraction, heat capacity, and magnetic susceptibility measurements between 1.6 K and room temperature. Aside from the previously known high temperature α-phase (R-3m) and low temperature γ-phase (R3m), a new intermediate temperature β-phase was detected. It has a k = (1/4,1/4,0) superstructure and its molar volume and χT product are half way between the α- and γ-phases. The β-phase is observed between 210 K and 190 K on cooling in powder samples. Its formation is kinetically hindered in crystals. Upon heating the β→α transition occurs at 227 K. From the γ-phase, a γ→α transitions is observed on heating. Only in heat capacity measurements, a shoulder of the peak indicates an intermediate formation of the β-phase. Strong antiferromagnetic interactions between the Ti2+ ions result in the formation of triangular trimers (Ti3-clusters). In the γ-phase all Ti2+ ions are part of trimers. For the β-phase a structural model is proposed where half of the Ti2+ ions form trimers. No long-range magnetic order was observed in Na2Ti3Cl8 down to 1.6 K.

Summary The flammability of wood plastic composites manufactured from recycled plastics was investigated by using the cone calorimetry technique. The peak of the heat release rate was 12% to 25% lower compared to references produced from pure polyethylene- and polypropylene-based composites. The total heat capacity and mass loss rate were also smaller for recycled material compared to the references. The stability of the composites was improved due to the presence of various thermally stable compounds, eg, traces of fire retardants, pigments, and other additives and impurities that can be present in recycled material. Incorporation of carbon black into the secondary materials did not reduce the peak of the heat release rate, but the total heat capacity and mass loss rate decreased further.

1-t-Butyl-3,3-dinitroazetidinium perchlorate (TDNAZ ⋅ HClO4) was synthesized, DSC and TG/DTG methods were used to study the thermal behavior of TDNAZ⋅HClO4 under a non–isothermal condition. The intense exothermic decomposition process of DSC curves were analyzed to obtain its kinetic parameters. Continuous specific heat capacity (Cp) mode of micro–calorimeter was used to determine its Cp, its specific molar heat capacity (Cp,m) was 365.70 J mol−1 K−1 at 298.15 K. The self-accelerating decomposition temperature (TSADT), thermal ignition temperature (TTIT), and critical temperature of thermal explosion (Tb) were obtained to evaluate its thermal stability and safety. The above results of TDNAZ ⋅ HClO4 were compared with those of 3,3-dinitroazetidinium perchlorate (DNAZ ⋅ HClO4), and the effect of tert-butyl group on them was discussed.

Phase relations in the ZrO2–TiO2 system were studied experimentally using X-ray diffraction (XRD), scanning electron microscopy combined with dispersive X-ray spectrometry (SEM/EDX) and differential thermal analysis (DTA). The homogeneity ranges of ZrO2 and TiO2, as well as high temperature disordered β-(ZrxTi1−x)2O4 compound were defined in the temperature range of 1700-2040 K. Temperature and composition of eutectic reaction were measured. The standard enthalpy of formation of the β-ZrTiO4 compound was obtained using high-temperature oxide-melt solution calorimetry. High temperature heat capacity measurement for the β-ZrTiO4 compound was performed in the temperature range from 250 K to 1200 K. Thermodynamic description of ZrO2–TiO2 system has been derived based on obtained experimental results and data from literature.

The molar heat capacities of three tetrabutylammonium chloride (TBAC)-based deep eutectic solvents (DESs) and their binary water mixtures were investigated in this work. Results showed a linear dependence of the molar heat capacity with temperature for all water compositions as well the pure components. The molar heat capacity decreased with increasing water composition for all systems. The TBAC : triethylene glycol system (DES2) showed the highest molar heat capacity (445.00–479.67 J mol−1 K−1) followed by the TBAC : ethylene glycol system (DES3); (288.34–312.59 J mol−1 K−1), while the TBAC : glycerol system (DES1) had the lowest molar heat capacity (281.20–310.85 J mol−1 K−1) among the three DES systems. The excess molar heat capacity, CPE, of the DES–water binary mixtures was determined. Results of CPE showed positive CPE for DES2 and negative CPE for DES3 for the entire range of water composition. DES1 showed a mix of positive and negative CPE values for the mixture. This behavior is explained as a result of the change in the intermolecular interaction between the DES–water molecules in the mixture compared with the DES–DES and water–water molecular interaction in the pure components. © 2017 Curtin University and John Wiley & Sons, Ltd.