Heat Capacity Curves Research Articles

The effect of Zn vacancies on the physical properties of antiperovskite compounds Mn3ZnxN

The effects of Zn vacancies on the physical properties of antiperovskite compounds Mn3ZnxN (x = 0.96 and 0.93) were investigated. For Mn3Zn0.96N, lowering the temperature produced two anomalies in the magnetization and heat capacity curves: the first at similar to 185 K is related to magnetic ordering and was accompanied by a lattice expansion; the second at similar to 115 K is due to a magnetic order change and showed a lattice contraction. However, for Mn3Zn0.93N only a single transition is observed around 185 K.

Molecular dynamical simulations of the melting properties of Aln(n=13–32) clusters

Based on the Gupta-type semi-empirical inter-atomic many body potential, the melting properties of Aln(n=13–32) clusters are systematically investigated by using the molecular dynamics method combined with the simulated annealing and quenching techniques. Our results show that, except for several sizes (Al13 and Al19), in general the heat capacity curves all are in disorder (no obvious single-peak), which are consistent with the experimental observations that small aluminum clusters have messy heat capacity curves in the melting process. Reasons for the different melting behaviors (whether they exhibit regular or irregular heat capacity curves) of these small Al clusters can be explored by analyzing the energy distributions of the simulated quenching structures of these clusters at different temperatures. For the clusters with disordered heat capacity curves one can obtain the melting points from analyzing the atomic equivalence indexes of those clusters, and the variations of the calculated melting points of the aluminum clusters with increasing cluster size are in agreement with the experimental observations.

Molecular Dynamical Simulations of the Structural and Melting Properties of $Al_{196}$ Cluster

Based on the Gupta-type semi-empirical inter-atomic many-body poten- tial, the melting behaviors of the Al196 cluster are systematically studied by using the molecular dynamics method combined with the annealing and quenching techniques. Our simulation results show that from differentinitial structures one can observe quite different melting behaviors. From a relatively low-energy stable geometry, two peaks occur clearly in the heat capacity curve; But only one peak dominates the heat capac- ity curve if starting from the ground-state or its closer low energy structures. Reasons of the different melting properties of the Al196 cluster are explored by analyzing the energy distributions of the simulated quenching structures of Al196 at different tem- peratures.

Thermodynamic, Electromagnetic, and Lattice Properties of Antiperovskite Mn3SbN

The physical properties of polycrystalline Mn3SbN were investigated using measurements of the magnetic, calorimetric, and electronic transport properties. At room temperature, the phase crystallizes in a tetragonal structure withP4/mmmsymmetry. A remarkably sharp peak in the heat capacity versus temperature curve was found near 353 K. The peak reaches 723 J mol−1 K−1at its highest, which corresponds to a transition entropy of 10.2 J mol−1 K−1. The majority of the large entropy change appears to be due to lattice distortion from the high-temperature cubic structure to the room-temperature tetragonal structure and the accompanying Ferrimagnetic transition.

Experimental study of the isochoric heat capacity and coexistence-curve singular diameter of sec-butanol near the critical point and Yang-Yang anomaly strength

One- and two-phase isochoric heat capacities () and saturated liquid and vapour densities (, and ) of sec-butanol near the critical point have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. The measurements were made in the temperature range from 307 K to 551 K for 22 liquid and vapour isochores from 76.44 to 794.06 kg m−3. The isochoric heat capacity jump (quasi-static thermograms supplemented by the sensor of adiabatic control) technique have been used to accurately measure of the phase transition parameters () near the critical point. The total experimental uncertainty of density (), temperature () and isochoric heat capacity () measurements were estimated to be 0.06%, 15 mK and 2–3%, respectively. The critical temperature ( = 535.95 ± 0.02 K) and the critical density ( = 276.40 ± 2 kg m−3) for sec-butanol were determined from the measured saturated properties (, ) near the critical point. The measured and saturated density () data near the critical point have been analysed and interpreted in terms of extended scaling theory for the selected thermodynamic paths (critical isochore and coexistence curve) to accurately calculate the values of the asymptotical critical amplitudes of heat capacity () and coexistence curve (). The measured thermodynamic properties (, ) of sec-butanol near the critical point were also interpreted in terms of the ‘complete scaling’ theory of critical phenomena and the theory of logarithmic singularity of . In particular, the contributions of the ‘incomplete’ () and ‘complete’ () scaling terms on the coexistence-curve singular diameter were estimated. We determined the values of the asymmetry parameters and of the ‘complete’ scaling theory of coexistence curve singular diameter. The strength of the Yang-Yang anomaly R μ for sec-butanol was estimated using asymmetry parameters and the contribution of the second temperature derivative of vapour-pressure and chemical potential in the singularity of two-phase isochoric heat capacity, , at the critical point.

Glass transition in ultrathin films of amorphous solid water

Nanocalorimetry at ultrafast heating rates is used to investigate the glass transition of nanometer thick films of metastable amorphous solid water grown by vapor deposition in an ultrahigh vacuum environment. Apparent heat capacity curves exhibit characteristic features depending on the deposition temperature. While films grown at T ≥ 155 K are completely crystallized, those deposited at 90 K show a relaxation exotherm prior to crystallization. Films grown between 135 and 140 K and subsequently cooled down to 90 K reveal a clear endothermic feature before crystallization, which is compatible with a glass-to-liquid transition. The onset temperature is located at 174 K at a heating rate of 2.4 × 10(4) K/s and is independent of film thickness in the range of 16-150 nm. Comparison of our data with other calorimetric measurements at various heating rates suggests that water is a strong glass former in the deeply supercooled state.

Low-temperature heat capacities and thermodynamic properties of n-undecylammonium bromide monohydrate C11H28BrNO(s)

Crystal structure of n-undecylammonium bromide monohydrate was determined by X-ray crystallography. Low-temperature heat capacities of the compound were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 390 K. Two solid–solid phase transitions were observed for the title compound. The temperatures, molar enthalpies, and entropies of the phase transitions were derived based on the analysis of heat–capacity curve. Two polynomial equations of heat capacities as a function of temperature were fitted by least-squares method. Based on the two polynomial equations, smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at 5 K intervals.

A Theoretical Study on the Interaction of Thionine with <i>Micrococcus Lysodeikticus</i> DNA

The latest study carried out on binding of small molecules with double stranded deoxyribonucleic acid rec- ommended that the intercalation of thionine, a tricyclic heteroaromatic molecule, with natural double stranded deoxyribo- nucleic acid granted thermal stabilization to the thionine-DNA complex. In this investigation, we reported theoretical analysis of thionine binding with Micrococcus lysodeikticus DNA duplex (Type XI, 72 mol% GC) by using a modified Zimm and Bragg theory, to elucidate the melting behaviour and heat capacity of Micrococcus lysodeikticus DNA with and without thionine binding. For implementing present study, the experimental models of Paul et al.(2010) have been used. The sharpness of transition has been examined in terms of half width and sensitivity parameter (∆H/σ). The conclusion of theo- retical analysis recommended that the different parameters, for example, transition profile, heat capacity curve, sharpness of the transition and half widths are in good agreement with the experimental measurements for interaction of thionine. Thus, the theoretical analysis proposed in this study may be useful to understand interaction of small molecules to deoxyribonucleic acid that may be applied for the designing of prospective DNA binding therapeutic molecules and in the process of drug development.

Drug–DNA interaction: A theoretical study on the binding of thionine with DNAs of varying base composition

The recent studies carried out on the binding of small molecule to deoxyribonucleic acids suggested that the intercalation of a tricyclic heteroaromatic molecule, thionine, with natural DNAs provided thermal stabilization to the DNA complex. In the present study, we reported theoretical analysis of thionine binding with natural DNAs of varying base composition by using an amended Zimm and Bragg theory, to explain the melting behaviour and heat capacity of DNAs with and without thionine binding. We used experimental models of Paul et al. for implementing this study (Paul et al., 2010). The sharpness of transition has been examined in terms of half width and sensitivity parameter (ΔH/σ). The results of theoretical analysis concluded that the various parameters such as heat capacity curve, transition profile, half widths and sharpness of the transition are in good agreement with the experimental measurements for binding of thionine determined through DSC. The theoretical analysis proposed in this study, therefore, may be useful to understand interaction of small molecules with deoxyribonucleic acids. This approach may also be applied to design DNA binding therapeutic molecules and in the process of drug formulation and development.

Calorimetric investigation of the magnetocaloric effect in Ni45Co5Mn37.5In12.5

A calorimetric investigation of a Ni45Co5Mn37.5In12.5 single crystal has been carried out by combining differential scanning calorimetry (DSC) and heat capacity (C) measurements. The martensitic transition showing a first-order character spread over a wide temperature range, a specific measuring technique of C(T) has been developed. This method—based on a time-resolved analysis of successive heating pulses—was found to yield an entropy change at the transition (ΔStr) that is very close to that derived from DSC. To investigate the magnetocaloric effect, both the isothermal entropy change ΔST and the adiabatic temperature change ΔTad were derived from heat capacity curves recorded in a series of magnetic fields up to 7 T. The maximum values of ΔST(T, B) were observed to be in accordance with those determined from the Maxwell equation. Furthermore, maximum values of ΔTad(T, B) resulting from the application of 2 T, 5 T and 7 T were found to be equal to −2.3 K, −6.1 K and −9.4 K, respectively.

Improving the thermal efficiency of ice slurry production through comminution

Producing ice slurries by crushing blocks of ice and mixing them with an aqueous solution of freezing point depressant can significantly increase the coefficient of system performance, decrease production time and eliminate the negative effects of time behaviour associated with storing fine particle ice slurries. As ice is mixed with an aqueous solution, it melts or freezes, diluting or concentrating the liquid phase. Its resultant properties can be estimated from an enthalpy balance. Using the phase diagram of the NaCl + H2O system and published heat capacity curves for ice and brine, a model is constructed that predicts resultant ice slurry properties following mixing. Model predictions are confirmed by experiments where a number of ice, water and salt mixtures are produced whilst their properties are monitored. Finally, it is shown how this method can be used to give optimum salt gritting loads for the deicing of roads.

A molecular dynamics study on the role of attractive and repulsive forces in excess heat capacity at constant volume of dense fluids

The curves of experimental heat capacity against density show a minimum around and below the critical temperature (Tc), but at higher temperatures, this minimum is not observed. In this study, the role of attractive and repulsive forces on excess heat capacity of Lennard–Jones (LJ) dense fluids has been investigated using a molecular dynamics simulation technique. LJ potential is divided into attractive and repulsive parts. From the molecular dynamics calculations, potential energy and heat capacities have been obtained for Argon at temperatures of 100–500 K. The repulsive forces play the main role in causing the heat capacities at temperatures greater than critical point. Around and below the critical temperature, the role of repulsion is dominant at high densities, but attraction has the main role at low densities, consequently at middle densities, a minimum is formed.

Crystal structures and thermodynamic properties on phase change materials n-CnH2n+1NH3·H2PO4(s) (n=8, 9 and 10)

Crystal structures of three long-chain n-alkylammonium dihydrogen phosphates n-CnH2n+1NH3·H2PO4(s) (n=8, 9 and 10) (abbreviated as C8P, C9P and C10P), which may be used as the phase change materials in storage and utilization of solar energy, were determined in layered structures by X-ray crystallography, and the same hydrogen bonding network is observed for these long carbon chain compounds. Low-temperature heat capacities of the compounds were measured by a precision adiabatic calorimeter over the temperature range from 78 to 380K. Two solid–solid phase transitions were observed for C8P and C9P, but only one solid–solid phase transition was observed for C10P. The temperatures, molar enthalpies and entropies of the phase transitions were determined based on the analysis of heat capacity curves. Experimental heat capacities for each compound were fitted to two polynomial equations. The smoothed heat capacities and thermodynamic functions (HTο−H298.15ο) and (STο−S298.15ο) of the three compounds were calculated with an interval of 10K in terms of the polynomial equations.

Molecular dynamics simulation of a graphite-supported copper nanocluster: thermodynamic properties and gas adsorption

Molecular dynamics simulations were conducted for a cubic Cu cluster supported on a graphite bilayer. The Sutten–Chen and Lennard–Jones potentials were used for metal–metal and metal–graphite interactions, respectively. Heating and cooling processes were performed by NVT simulations at different temperatures in the range 200 to 1800 K. The melting point was identified on the basis of caloric and heat capacity curves. The calculated melting point was 770 K, far below the bulk melting point of crystalline copper. Several phenomena such as the appearance of a hysteresis (irreversibility) in caloric curves, surface melting, and cluster-induced surface wetting were justified from the results. The simulation of cluster in the presence of gas atmosphere showed that the CO gas is adsorbed more than H2 and it has a greater impact on the cluster's structure.

Low-temperature heat capacities, and thermodynamic properties of solid–solid phase change material bis(1-octylammonium) tetrachlorocuprate

A new crystalline complex (C8H17NH3)(2)CuCl4(s) (abbreviated as C8Cu(s)) was synthesized by liquid phase reaction. Chemical analysis, elemental analysis, and X-ray crystallography were applied to characterize the composition and crystal structure of the complex. Low-temperature heat capacities of the complex were measured by a precision automatic adiabatic calorimeter over the temperatures ranging from 78 to 395 K, and two solid-solid phase changes appeared in the heat capacity curve. The temperatures, molar enthalpies and entropies of the two phase transitions of the complex were determined to be: T (trs, 1) = 309.4 +/- A 0.35 K, Delta(trs) H (m, 1) = 16.55 +/- A 0.41 kJ mol(-1), and Delta(trs) S (m, 1) = 53.49 +/- A 1.3 J K-1 mol(-1) for the first peak; T (trs, 2) = 338.5 +/- A 0.63 K, Delta(trs) H (m, 2) = 6.500 +/- A 0.10 kJ mol(-1), and Delta(trs) S (m, 2) = 19.20 +/- A 0.28 J K-1 mol(-1) for the second peak. Two polynomial equations of the heat capacities as a function of the temperature were fitted by least-square method. Smoothed heat capacities and thermodynamic functions of the complex relative to the standard reference temperature of 298.15 K were calculated based on the fitted polynomial equations.

Drug-DNA Interaction: A Theoretical Study of the Stability of CP-DNA Binding with Thionine

The recent study on binding of small molecules to double stranded DNA suggested that the intercalation of a tricyclic heteroaromatic molecule, thionine, with natural DNA provided thermal stabilization to the complex. In the present study, we reported theoretical analysis of thionine binding with Clostridium perfringenes DNA duplex (CP-DNA) by using an amended Zimm and Bragg theory, to explain the melting behaviour and heat capacity of CP-DNA with and without thionine binding. The experimental models of Paul et al. (2010) have been used for the study. The sharpness of transition has been examined in terms of half width and sensitivity parameter (?H/σ). The results of theoretical approach suggested that the various parameters such as transition profile, sharpness of the transition, heat capacity curve and half widths are in good agreement with the experimental measurements for binding of thionine. Therefore, the proposed theoretical analysis may be useful in order to understand interaction of small molecules to DNA that may be applied in the process of drug development and for designing more potential DNA binding therapeutic molecules.

Stability of DNA binding with dipyrandium: A theoretical study

Recent analysis on structure and dynamics of nucleic acid suggest that the DNA helix undergoes conformational transition as function of salt and solvent. This flexibility leads folding of DNA either smoothly or its chain direction changes abruptly by the generation of kinks. The steroid diamine binds to DNA through the minor groove at the kink site and stabilized the complex. In the present study, we reported theoretical analysis of steroid diamine, dipyrandium, binding with DNA duplex by using an amended Zimm and Bragg theory, to explain the melting behavior and heat capacity of DNA with and without dipyrandium binding. The experimental models of Marky et al. (1983) were used for the study. The sharpness of transition has been examined in terms of half width and sensitivity parameter (∆H/δ). The various parameters such as transition profile, sharpness of the transition, heat capacity curve and half widths are in good agreement with the experimental measurements for binding of dipyrandium. This theoretical analysis can be applied in order to understand bimolecular interaction and thus can be applied in the process of drug designing and development.

Experimental study of the isochoric heat capacity of isobutanol in the critical and supercritical regions

The one- and two-phase isochoric heat capacities (CV) of isobutanol in the critical and supercritical regions have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. The measurements were made in the temperature range from 324K to 575K for 23 isochores (16 liquid and 7 vapor) from 73.2kgm−3 to 772.2kgm−3. The isochoric heat capacity jump (quasi-static thermograms supplemented by the sensor of adiabatic control) technique have been used to accurately measure of the phase transition parameters (TS, ρS). The total experimental uncertainty of density (ρ), temperature (T), and isochoric heat capacity (CV) were estimated to be 0.06%, 15mK, and 2–3%, respectively. The critical temperature (TC=547.65±0.2K) and the critical density (ρC=272.95±2kgm−3) for isobutanol were determined from the measured saturated properties (CVS, TS, ρS) near the critical point. The measured CV and saturated density (TS, ρS) data near the critical point have been analyzed and interpreted in terms of extended scaling type equations for the selected thermodynamic paths (critical isochore and coexistence curve) to accurately calculate the values of the asymptotical critical amplitudes of heat capacity (A0±) and coexistence curve (B0). The experimentally derived value of the critical amplitude ratio A0+/A0−=0.522 is in good agreement with the value predicted by various scaling theories. The measured thermodynamic properties (CV, TS, ρS) of isobutanol near the critical point were also interpreted in the terms of “complete scaling” theory of critical phenomena. In particularly, the contributions of the “complete” and “incomplete” scaling terms on the coexistence-curve singular diameter were estimated. We determined the values of the asymmetry parameters a3 and b2 of the coexistence curve singular diameter. The strength of the Yang–Yang anomaly Rμ for isobutanol was estimated using asymmetry parameters a3 and the contribution of the second temperature derivative of vapor-pressure and chemical potential in the singularity of two-phase CV2. The measured values of saturated one- and two-phase liquid and vapor isochoric heat capacities (C′V1,C″V1,C′V2,C″V2) and saturated thermal (ρS, TS) properties together with vapor-pressure (PS, TS) data were used to calculate other derived thermodynamic properties such as (KT, ΔHvap, CP, CS, W, (∂P/∂T)′V, (∂V/∂T)′P, (d2PS/dT2), and (d2μ/dT2) of isobutanol at saturation near the critical point.

Modeling the molecular dynamics of liquid metals at high pressures: Liquid potassium

A way of building potassium models by molecular dynamics using the embedded atom model (EAM) is developed. The contribution from pairwise interaction is presented as power series at an interpartial distance. Embedded potential parameters are determined by the experimental dependence of pressure on volume for a static compression of potassium at 300 K to a pressure of 53 GPa (potential A). By using potential A to describe shock compression and choosing the appropriate temperature at given degree of compression (up to 40000 K at compression to 0.29 of initial volume) it is shown that the model pressure can be made equal to the pressure indicated by the Rankine-Hugoniot relations. The model energy is lower than the actual energy determined by the relations, and the difference in energies increases with temperature almost linearly; such growth corresponds to an excess average heat capacity of about 11.6 J/(mol K), compared to the model heat capacity. It is established that the reasons for this divergence are the inability of the EAM potential to describe the temperature dependency of metal properties precisely, and the appearance of an energy contribution upon heating that is dependent on temperature but not on atom coordinates. Adding another summand to the potential energy (which is dependent on temperature only) allows us to match the heat capacities of real potassium and the models. The dependence of potassium’s melting temperature on pressure is calculated. The calculated melting temperature at 41.2 GPa is 1231 K. Additional data (e.g., the actual temperature on the Rankine-Hugoniot curve and precise quantum mechanics calculations of heat capacity at extreme conditions) is required to eliminate potential ambiguity.

Thermodynamics of the coordination compound Zn(Met)(NO3)2·1/2H2O(s) (Met = l-α-methionine)

Low temperature heat capacities of the solid coordination compound, Zn(Met)(NO3)2·1/2H2O(s), have been measured by a precision automated adiabatic calorimeter over the temperature range 78–371 K. The initial dehydration temperature of the coordination compound is determined to be, TD = 325.05 K, by analysis of the heat-capacity curve. The experimental values of molar heat capacities in the temperature region have been fitted to a polynomial equation of heat capacities with the reduced temperature (X), [X = f(T)], by a least squares method. Smoothed heat capacities and thermodynamic functions relative to the standard reference temperature 298.15 K of the compound are derived from the fitted polynomial equation and listed at 5 K internals. Enthalpies of dissolution of {ZnSO4·7H2O(s) + 2NaNO3(s) + l-Met (s)} and {Zn(Met)(NO3)2·1/2H2O(s) + Na2SO4(s)} in 100 cm3 of 2 mol dm−3 HCl(aq) at T = 298.15 K have been determined to be \( \Updelta_{\rm{d}} H_{m,1}^{0} \) = (56.929 ± 0.051) kJ mol−1 and \( \Updelta_{\rm{d}} H_{m,2}^{0} \) = (37.337 ± 0.029) kJ mol−1, respectively, with an isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound is determined to be \( \Updelta_{\rm{f}} H_{\rm{m}}^{0} \) [Zn(Met)(NO3)2·1/2H2O, s] = −(1327.08 ± 0.75) kJ mol−1 from the enthalpies of dissolution of the reactants and products and other thermodynamic data by a Hess’ thermochemical cycle.