The thermal properties of poly(pivalolactone)

Quantitative thermal analysis was carried out for poly-(pivalolactone) (PPVL), including heat capacity determinations from 140 to 550 K. The experimental C_p below the glass transition temperature was fitted to an approximate vibrational spectrum and the ATHAS computation scheme was used to compute the “vibration only” heat capacities from 0.1 to 1000 K. The liquid C_p was derived from an empirical addition scheme and found to agree with the experimental C_p with an RMS of ±2.8% from 240 K to 550 K. A glass transition, T_g, could be detected at 260 K, and the change in heat capacity for 100% amorphous PPVL was calculated to be 38.8 J/(K mol). Above T_g, semicrystalline samples seem to show a rigid amorphous fraction that does not contribute to the increase in heat capacity at T_g. Using the ATHAS recommended heat capacities, the various thermodynamic functions (enthalpy, entropy, and Gibbs function) were derived. The residual entropy at 0 K for the amorphous PPVL was calculated to be 5.2 J/(K mol) per mobile bead, and was comparable to that obtained for a series of linear, aliphatic polyesters analyzed earlier.     

Excess Heat Capacity in Yttria Stabilized Zirconia

The heat capacity of 9.70 and 11.35 mol% yttria stabilized zirconia ((ZrO₂)_1–x(Y₂O₃)_x; x=0.0970, 0.1135) was measured by adiabatic calorimetry between 13 and 300 K, and some thermodynamic functions were calculated and given in a table. A large excess heat capacity extending from the lowest temperature to room temperature with a broad maximum at about 75 K was found in comparison with the heat capacity calculated from those of pure zirconia and yttria on the basis of simple additivity rule. The shape of the excess heat capacity is very similar to the Schottky anomaly, which may be attributed to a softening of lattice vibration. The amount of the excess heat capacity decreased with increasing yttria doping, while the maximum temperature did not vary. The relationships among the excess heat capacity, defect structure and interatomic force constants, and also the role of oxygen vacancy were discussed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal conductivity and heat capacity of liquid and glassy poly(vinyl acetate) under pressure

The dependence of thermal conductivity λ and heat capacity per unit volume pc_p on temperature and pressure for poly(vinyl acetate) has been measured by a transient hot-wire probe technique. The measurements were made under pressures up to 0.5 GPa over a temperature range of 270–470 K. The temperature coefficient of thermal conductivity (? lnλ/?T)_p was found to increase with pressure for both the liquid and the glassy state. The change in heat capacity per unit volume in the region of the glass-transition temperature was found to decrease with increasing pressure. The Ehrenfest relation does not explain the variation of the pressure coefficient of the glass-transition temperature.     

The heat capacity of solid poly(p-xylylene) and polystyrene

The constant-pressure heat capacity C_p of poly(p-xylylene) (PPX) has been measured from 220 to 625 K by differential scanning calorimetry. The constant-volume heat capacities C_v of both, PPX and its isomer polystyrene (PS) have been interpreted in the light of literature data on full normal-mode calculations for PS and estimates from low-molecular-weight analogs for PPX for the 39 group vibrations. Nine skeletal vibrations were used in this discussion with characteristic temperatures θ₁ and θ₃ of 534.5 and 43.1 K for PS. It was also possible to calculate a heat capacity contribution of a phenylene group within a polymer chain. Single 48-vibration θ₁ temperatures of 3230 K for PS and 2960 K for PPX are sufficient to describe C_v above 220 K. Below 140 K, PS heat capacity shows deviations from the Tarasov treatment.     

Behavior of [`(a)] 20 \bar \alpha _2^0 T of aqueous urea near the singularity point

Relations for the apparent molar heat capacity ϕ_c of urea in an aqueous solution depending on the molality m and temperature were obtained. A transition to the relations ϕ_c(m,T) for D₂O-(ND₂)₂CO and T₂O-(NT₂)₂CO systems was effected by temperature scaling. At low temperatures, the isotherms of the molar heat capacity C _p(m) of the protium and deuterium systems have minima shifted to more dilute solutions at elevated temperatures. At m = 1, C _p of a solution does not depend on temperature in both systems. The dependences C _p(T) also have minima at constant concentrations. The temperature of the minimum heat capacity is most effectively lowered by small additions of urea. For m = 0.25, T _min is 7.5 K lower than T _min of pure water, and its heat capacity is 0.08 J/(mol K) higher. A transition from m = 1.5 to m = 2 lowers the temperature of the minimum heat capacity by 3.6 K; thus, the heat capacity of solutions differs by 0.02 J/(mol K) only.     

Anomalies in Heat Capacity Measurements of RuO2-TiO2 System

DSC was used for heat capacity measurements of pure RuO₂ in the temperature range from 300 to 1170 K of solid solutions corresponding to the compositions of (Ti_1−x Ru_x )O₂ (x ≤0.15 and x ≥0.85) and in the temperature range from 300 to 1550 K of pure TiO2. The analysis of experimental data obtained within ±2% of accuracy has shown that the characteristic temperatures representing the harmonic lattice vibrations do not strongly depend on the chemical composition x . It was demonstrated that non-harmonic heat capacity is strongly correlated to x. The existence of additional excess heat capacity was observed with the mixed oxide solid solution samples of low Ru content and explained by the defect formation model. This revised version was published online in August 2006 with corrections to the Cover Date.     

The thermodynamic properties of polytetrafluoroethylene

Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ₃ of 54 K, and θ₁ of 250 K, and a full set of group vibrations. C_v to C_p conversion was possible with a Nernst–Lindemann constant of A = 1.6 × 10^?3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔC_p of 9.4 J/K mol. The room-temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high-temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds.     

Heat Capacity of Intercalated Layered Materials FexNbS2 at Low Temperature

The heat capacities and magnetic susceptibilities of powdered samples of Fe_xNbS₂ (x=0.14, 0.21 and 0.30) were measured at temperatures from 8 to 303 K and from 5 to 300 K, respectively. For Fe_0.14NbS₂, the magnetic susceptibility exhibited an anomaly as a shoulder at about 57 K, but no heat capacity anomaly was observed at this temperature, indicating the appearance of a spin-glass state. Anomalies in the heat capacity for Fe_xNbS₂ (x=0.21 and 0.30) occurred at 100.5 and 45.0 K, respectively, where the magnetic susceptibility displayed a maximum, corresponding to an antiferro-paramagnetic phase transition. The electronic state of the iron atom is discussed on the basis of entropy analysis.This revised version was published online in November 2005 with corrections to the Cover Date.     

Low-temperature heat capacities and derived thermodynamic functions of cyclohexane

The low-temperature heat capacities of cyclohexane were measured in the temperature range from 78 to 350 K by means of an automatic adiabatic calorimeter equipped with a new sample container adapted to measure heat capacities of liquids. The sample container was described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on water. The deviations of experimental heat capacities from the corresponding smoothed values lie within ±0.3%, while the inaccuracy is within ±0.4%, compared with the reference data in the whole experimental temperature range. Two kinds of phase transitions were found at 186.065 and 279.684 K corresponding solid-solid and solid-liquid phase transitions, respectively. The entropy and enthalpy of the phase transition, as well as the thermodynamic functions {H_(T)-H _{298.15 K}} and {S _(T)-S_{298.15 K}}, were derived from the heat capacity data. The mass fraction purity of cyclohexane sample used in the present calorimetric study was determined to be 99.9965% by fraction melting approach. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodynamic investigation of several natural polyols (II)

The low-temperature heat capacity C _p,m of sorbitol was precisely measured in the temperature range from 80 to 390 K by means of a small sample automated adiabatic calorimeter. A solid-liquid phase transition was found at T=369.157 K from the experimental C _p-T curve. The dependence of heat capacity on the temperature was fitted to the following polynomial equations with least square method. In the temperature range of 80 to 355 K, C _p,m/J K⁻¹ mol⁻¹=170.17+157.75x+128.03x ²-146.44x ³-335.66x ⁴+177.71x ⁵+306.15x ⁶, x= [(T/K)−217.5]/137.5. In the temperature range of 375 to 390 K, C _p,m/J K⁻¹ mol⁻¹=518.13+3.2819x, x=[(T/K)-382.5]/7.5. The molar enthalpy and entropy of this transition were determined to be 30.35±0.15 kJ mol⁻¹ and 82.22±0.41 J K⁻¹ mol⁻¹ respectively. The thermodynamic functions [H _T-H _298.15] and [S _T-S 298.15], were derived from the heat capacity data in the temperature range of 80 to 390 K with an interval of 5 K. DSC and TG measurements were performed to study the thermostability of the compound. The results were in agreement with those obtained from heat capacity measurements.     

Heat capacity and other thermodynamic properties of CoTe2 from 5 to 1 030 K and of CoTe2.315 from 300 to 1 040 K

The heat capacity of orthorhombic (marcasite-type structure) cobalt ditelluride has been measured from 5 to 1 030 K by adiabatic-shield calorimetry with alternate energy inputs and equilibrations. Above 900 K a marked increase in heat capacity occurs which probably signals a change in the composition of the CoTe₂-phase towards higher tellurium content. Values at 298.15 and 1 000 K in J K^–1 mol^–1 of the heat capacity (C _p,m), entropy [S _m ^° (T)–S _m ^° (0)], andGibbs energy function – [G _m ^° (T)–H _m ^° (0)]T ^–1 are 75.23, 114.5, 49.93, and 132.4, 216.2, 139.17, respectively. Consistent with the metallic behavior of CoTe₂, deviation of the heat capacity from theDebye T ³-law was found at low temperatures. Comparison with the heat capacity of FeTe₂ shows aSchottky-like deviation with a maximum of 7.3 J K^–1 mol^–1 at 80 K and evidences the influence of the additional 3 d-electron in cobalt compared to iron. Heat capacity measurements were made on CoTe_2.33 to ascertain the existence range of the CoTe_2+x -phase and the entropy of the associated structural disorder.The portion of this research done at Ann Arbor was supported in part by the Structural Chemistry and Chemical Thermodynamics Program of the Division of Chemistry of the National Science Foundation under Grant No. CHE-7710049.     

The heat capacity and thermodynamic functions of pyromorphite over the temperature range 5–320 K

The heat capacity of natural mineral, pyromorphite Pb₅(PO₄)₃Cl, was measured over the temperature range 4.2–320 K using low-temperature adiabatic calorimetry. An anomalous temperature dependence of heat capacity with a maximum at 273.24 K was observed between 250 and 290 K. The heat capacity, entropy, enthalpy, and reduced thermodynamic potential of pyromorphite were calculated and tabulated over the temperature range 5–320 K. The standard thermodynamic functions of the mineral are C _p298.15^o = 414.98 ± 0.44 J/(mol K), S _298.15^o = 585.31 ± 0.99 J/(mol K), H _298.15^o − H ₀^o = 80.90 ± 0.08 kJ/mol, and Φ_298.15^o = 313.97 ± 0.84 J/(mol K).     

Heat capacity measurement and DSC study of hafnium hydrides

Heat capacities, electrical conductivities and phase transition temperature of hafnium hydrides, HfH_x (0.99≤x≤1.83), were studied using a direct heating pulse calorimeter and a differential scanning calorimeter from room temperature to above 500 K. The heat capacity of HfH_1.83 was larger than that of pure hafnium and showed no anomaly of heat capacity. In contrast, there were λ-type peaks for the heat capacity and DSC curves for HfH_x (1.1≤x≤1.6) near 385 and 356 K. The anomalies of heat capacity and electrical conductivity of HfH_x (1.1≤x≤1.6) were considered the result of phase transition and order-disorder phase transition for hydrogen in the hafnium hydride lattice for HfH_x (1.1≤x≤1.3).     

Heat capacity and magnetic phase transition of two-dimensional metal-assembled complex (NEt<Subscript>4</Subscript>)[{Mn<Superscript>III</Superscript>(salen)}<Subscript>2</Subscript>Fe<Superscript>III</Superscript>(CN)<Subscript>6</Subscript>]

Summary Heat capacity measurements of the two-dimensional metal-assembled complex, (NEt₄)[{Mn^III(salen)}₂Fe^III(CN)₆] [Et=ethyl, salen= N,N’-ethylenebis(salicylideneaminato) dianion], were performed in the temperature range between 0.2 and 300 K by adiabatic calorimetry. A ferrimagnetic phase transition was observed at T_c1=7.51 K. Furthermore, another small magnetic phase transition appeared at T_c2=0.78 K. Above T_c1, a heat capacity tail arising from the short-range ordering of the spins characteristic of two-dimensional magnets was found. The magnetic enthalpy and entropy were evaluated to be ΔH=291 J mol^-1 and ΔS=27.4 J K^-1 mol^-1, respectively. The experimental magnetic entropy agrees roughly with ΔS=Rln(5·5·2) (=32.5 J K^-1 mol^-1; R being the gas constant), which is expected for the metal complex with two Mn(III) ions in high-spin state (spin quantum number S=2) and one Fe(III) ion in low-spin state (S=1/2). The heat capacity tail above T_c1 became small by grinding and pressing the crystal. This mechanochemical effect would be attributed to the increase of lattice defects and imperfections in the crystal lattice, leading not only to formation of the crystal with a different magnetic phase transition temperature but also to decrease of the magnetic heat capacity and thus the magnetic enthalpy and entropy.     

硼砂水溶液的低温热容及热化学性质研究

利用精密绝热量热仪测定了0.03355mol·kg-1的硼砂水溶液在78～351K温区的热容,从实验热容测定结果得到了该水溶液的凝固点为272.905K。用最小二乘法将实验热容值对温度进行拟合,建立了该溶液的热容随温度变化的多项式方程。根据热力学函数关系式,用此多项式方程进行数值积分,获得了以298.15K为基准的该溶液在80～350K温区每隔5K的热力学函数值,并计算出摩尔熔化焓和熔化熵分别为4.536kJ·mol-1和16.22J·K-1·mol-1。根据溶液凝固点降低值,计算出了该溶液的活度为0.99763。     

Low temperature heat capacity of the system “silica gel–calcium chloride–water”

Heat capacity was measured for two composite systems based on silica gel KSK and calcium chloride confined to its pores. One corresponds to an anhydrous state, while another contains water bound with the salt to give the composition of CaCl₂·2.04H₂O. The measurements were performed in the temperature range of 6–300 K with a vacuum adiabatic calorimeter. The smoothed experimental curves C _p (T) were used for calculating the calorimetric entropy and the enthalpy increment for both studied systems as well as the effective heat capacity associated only with water in the hydrated composite. The heat capacities C _p (298.15 K) of both composites were compared with those calculated as a linear addition of the heat capacities of silica gel and bulk calcium chloride (or its dihydrate) with appropriate weight coefficients.     

Low-Temperature Heat Capacities and Thermodynamic Properties of Octahydrated Barium Dihydroxide,Ba（OH）2·8H2O（s）

Low-temperature heat capacities of octahydrated barium dihydroxide, Ba（OH）2·8H2O（s）, were measured by a precision automated adiabatic calorimeter in the temperature range from T=78 to 370 K. An obvious endothermic process took place in the temperature range of 345-356 K. The peak in the heat capacity curve was correspondent to the sum of both the fusion and the first thermal decomposition or dehydration. The experimental molar heat capacifies in the temperature ranges of 78-345 K and 356-369 K were fitted to two polynomials. The peak temperature, molar enthalpy and entropy of the phase change have been determined to be （355.007±0.076） K, （73.506±0.011） kJ·ol^-1 and （207.140±0.074） J·K^-1·mol^-1, respectively, by three series of repeated heat capacity measurements in the temperature region of 298-370 K. The thermodynamic functions, （Hr-H298.15 k ）and （Sr-S298.15k）, of the compound have been calculated by the numerical integral of the two heat-eapacity polynomials. In addition, DSC and TG-DTG techniques were used for the further study of thermal behavior of the compound. The latent heat of the phase change became into a value larger than that of the normal compound because the melfing process of the compound must be accompanied by the thermal decomposition or dehydration of 71-120.     

Thermodynamic properties of α-platinum dichloride

The heat capacity of crystalline α-platinum dichloride was measured for the first time in the temperature intervals from 11 to 300 K (vacuum adiabatic microcalorimeter) and from 300 to 620 K (differential scanning calorimetry). In the 300–620 K temperature interval, the C° _p values for α-PtCl₂ (cr) coincide with the heat capacity of CrCl₂ (cr) within the limits of experimental error, which made it possible to estimate the heat capacity of α-PtCl₂ (cr) at higher temperatures. The approximating equation of the temperature dependence of the heat capacity in the interval from 298 to 900 K C° _p (±0.8) = 63.5 + 21.4·10⁻³ T + 0.883·10⁵/T ² (J mol⁻¹ K⁻¹) was derived using the experimental values, as well as the literature data on the heat capacity of CrCl₂ (cr). For the standard conditions, the C° _p,298.15 and S°_298.15 values are 70.92±0.08 and 100.9±0.33 J mol⁻¹ K, respectively; H°_298.15 − H°₀ = 14 120±42 J mol⁻¹. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1136–1138, June, 2008.     

Heat capacity of <Emphasis Type="Italic">D</Emphasis>- and <Emphasis Type="Italic">DL</Emphasis>-serine in a temperature range of 5.5 to 300 K

Heat capacity of D- and DL-serine was measured using adiabatic calorimetry in a temperature range of 5.5 to 300 K, and then thermodynamic functions were calculated. The difference in heat capacity (C _PD-C _PDL) between two species indicates a small anomaly in D-serine near 15 K and a systematic excess over DL for temperatures > 30 K. This is much larger, than a difference in thermodynamic functions measured so far for the polymorphs of organic molecular crystals. The excess is fitted well to Einstein contribution with characteristic temperature of 185 K which is equivalent to vibrational mode at 129 cm⁻¹.     

Thermodynamic characteristics of triphenylantimony bis(acetophenoneoximate)

The temperature dependence of heat capacity C _p ^° = f(T) of triphenylantimony bis(acetophenoneoximate) Ph₃Sb(ONCPhMe)₂ was measured for the first time in an adiabatic vacuum calorimeter in the range of 6.5–370 K and a differential scanning calorimeter in the range of 350–463 K. The temperature, enthalpy, and entropy of fusion were determined. Treatment of low-temperature (20 K ≤ T ≤ 50 K) heat capacity was performed on the basis of Debye’s theory of the heat capacity of solids and its multifractal model and, as a consequence, a conclusion was drawn on the type of structure topology. Standard thermodynamic functions C _p ^°(T), H°(T) — H°(0), S°(T), and G°(T) — H°(0) were calculated according to the experimental data obtained for the compound mentioned in the crystalline and liquid states for the range of T → 0–460 K. The standard entropy of the formation of crystalline Ph₃Sb(ONCPhMe)₂ was determined at T = 298.15 K.