Low Temperature Calorimetric Measurements Research Articles

New thermodynamic data for CoTiO3, NiTiO3 and CoCO3 based on low-temperature calorimetric measurements.

The low-temperature heat capacities of nickel titanate (NiTiO3), cobalt titanate (CoTiO3), and cobalt carbonate (CoCO3) were measured between 2 and 300 K, and thermochemical functions were derived from the results. Our new data show previously unknown low-temperature lambda-shaped heat capacity anomalies peaking at 37 K for CoTiO3 and 26 K for NiTiO3. From our data we calculate standard molar entropies (298.15 K) for NiTiO3 of 90.9 ± 0.7 J mol-1 K-1 and for CoTiO3 of 94.4 ± 0.8 J mol-1 K-1. For CoCO3, we find only a small broad heat capacity anomaly, peaking at about 31 K. From our data, we suggest a new standard entropy (298.15 K) for CoCO3 of 88.9 ± 0.7 J mol-1 K-1.

On metallic characteristics in some conducting polymers

Polyaniline (PANI) exhibits a dc conductivity σ ≈ 10 −1 S/cm when it is doped with poly(styrenesulfonic acid) (PSSA) such that the number of sulfonate groups per two-ring PANI unit ( y) is 2. On increasing the dopant amount to y = 12, σ drops to 10 −5 S/cm. The EPR-derived magnetic susceptibility of these two conducting polymers gives nearly the same density of states at the Fermi level N( E F) ≈ 0.65 ± 0.05 states/eV 2-rings. The corresponding electronic specific heat coefficient as calculated from this N( E F) value does not appear to be inconsistent with the results from low temperature calorimetric measurements. Similarly, with y′ defined as the number of sulfonate groups per three-ring PEDOT unit, PSSA-doping of poly(ethylenedioxythiophene) (PEDOT) yields different σ ≈ 10 −1 and 10 −5 S/cm at y′ = 5.7 and 45.9, respectively, but the same N( E F) ≈ 0.55 ± 0.05 states/eV 3-rings. These observations suggest that the additional dopants, which help with dispersion in processing conducting polymers, do not alter the metallic domains but are located in the disordered regions surrounding them. The N( E F) values also remain practically the same between p-toluenesulfonic acid (PTSA) doped PANI and its dispersed blend in poly(methylmethacrylate) (PMMA), as well as for PEDOT–PTSA before and after its being subjected to an additional dispersion step.

Low-temperature calorimetric evaluation of aluminum–lithium alloys

Low temperature calorimetric measurements have been made on a series of binary aluminum alloys containing 1–10 at. % lithium. The heat capacity data are analyzed in terms of an electronic and a lattice contribution. Accordingly, the low level of lithium addition yields appreciable changes in the electronic density-of-states at Fermi level and the characteristic Debye temperature of lattice. These results reflect certain degrees of electron localization between aluminum and lithium atoms, providing a fundamental basis for solid solution strengthening in the lightweight materials with great potential in aerospace applications.

The thermodynamic properties of DyBr 3(s) and DyI 3(s) from T=5 K to their melting temperatures

Low-temperature calorimetric measurements have been performed on DyBr 3(s) in the temperature range (5.5 to 420 K ) and on DyI 3(s) from T=4 K to T=420 K. The data reveal enhanced heat capacities below T=10 K, consisting of a magnetic and an electronic contribution. From the experimental data on DyBr 3(s) a C 0 p,m (298.15 K) of (102.2±0.2) J·K −1·mol −1 and a value for { S 0 m (298.15 K) − S 0 m (5.5 K)} of (205.5±0.5) J·K −1·mol −1, have been obtained. For DyI 3(s), { S 0 m (298.15 K) − S 0 m (4 K)} and C 0 p,m (298.15 K) have been determined as (226.9±0.5) J·K −1·mol −1 and (103.4±0.2) J·K −1·mol −1, respectively. The values for { S 0 m (5.5 K) − S 0 m (0)} for DyBr 3(s) and { S 0 m (4 K) − S 0 m (0)} for DyI 3(s) have been calculated, giving S 0 m (298.15 K)=(212.3±0.9) J·K −1·mol −1 in case of DyBr 3(s) and S 0 m (298.15 K) =(233.1±0.7) J·K −1·mol −1 for DyI 3(s). The high-temperature enthalpy increment has been measured for DyBr 3(s) in the temperature range (525 to 799 K) and for DyI 3(s) in the temperature range (525 to 627 K). From the results obtained and enthalpies of formation from the literature, thermodynamic functions for DyBr 3(s) and DyI 3(s) have been calculated from T→0 to their melting temperatures at 1151.0 K and 1251.5 K, respectively.

Calorimetric study of selected NZP-type of ceramic materials

Sodium zirconium phosphate, NZP, ideally NaZr 2(PO 4) 3, is a potential host matrix for nuclear waste. Thermophysical properties of these materials are necessary to assess the thermal stability of these compounds. This paper presents the synthesis and calorimetric measurements of some NZP-type compounds containing alkaline earth elements. It also describes the indigenously developed room temperature drop calorimeter for low temperature calorimetric measurements. Calibration of the instrument is done with standard reference materials. Enthalpy increment of these materials is measured using this setup in the temperature range 373–873 K, and specific heat data are derived. Temperature dependence of enthalpy increment and specific heat of these materials, and the influence of the chemical composition on these properties are discussed.

Calorimetric study of the antiferromagnetic transition in ytterbium sesquioxide.

Low-temperature calorimetric measurements show an antiferromagnetic ordering of ${\mathrm{Yb}}^{+3}$ in ytterbium sesquioxide. The well-defined N\'eel temperature of 2.3 K is corroborated by magnetic susceptibility data. Entropy associated with this ordering process is close to Rln2 as expected for a ground-state doublet, even though there are two nonequivalent cation sites in the cubic crystal.

Low-temperature heat capacities of several high-strength materials

Abstract : Low temperature calorimetric measurements have been made on three metallurgically prepared high strength materials: NiAl, W-2 (a heavy tungsten alloy), and Al-Fe-Ce (a lightweight alloy with dispersion strengthening). To fit the heat capacity data between 3 and 10 K, not only the electronic and lattice contributions having T and T3 dependence, respectively, need to be considered, there is an additional temperature-independent term presumably associated with magnetic clusters. These results provide information on the fundamental characteristics, as well as the heterogeneous nature of the materials not always detectable by standard metallurgical techniques. Keywords: Low temperature, Heat capacity, Adiabatic calorimeter, Magnetic clusters, Nickel, Aluminum compounds, Iron, Cesium.

Low-temperature calorimetric and vapor-pressure studies on alkanediamines

Low-temperature calorimetric measurements were obtained on the condensed phases three alkanediamines, ethylenediamine, (dl)-1,2-propanediamine, and 2-methyl-1,2-propanediamine, as a basis for deriving their heat capacities, C s, entropies, S s, thermodynamic functions, − “G s (T) − H o (0)’ T , “H s (T) − H o (0)’ T , and H s( T) − H o(0), and the enthalpies, entropies, and temperatures of phase transitions. Vapor-pressure measurements were carried out on the above alkanediamines and (dl)-1,2-butanediamine as a means for transforming the condensed-state thermodynamic properties to the perfectgas state at 1 atm. Standard values at 298.15 K were calculated for the enthalpy, Gibbs energy, and equilibrium constant of formation.

Enhancement of the Superconducting Transition Temperatures of Ti–Mo (5, 7 at.%) Alloys by Mechanical Deformation

Low-temperature calorimetric measurements have shown that severe mechanical deformation of Ti–Mo (5 and 7 at. %) alloys, although it has little influence on either the density of states or the Debye temperature, significantly enhances the superconducting transition temperature. The net effect of the deformation is thus to distort the phonon spectrum in such a way as to favor the superconducting electron coupling.

On the measurement of small heat capacities at low temperatures

Problems involved in low temperature calorimetric measurements under conditions of poor thermal isolation are discussed. The experimental and analytical methods of a measurement of the heat capacity of bismuth are described as an illustration of the way some of these problems may be overcome.

Low temperature specific heat of h.c.p. Mo-Ru And Mo-Rh alloys

Low temperature calorimetric measurements were made on some h.c.p. Mo-Ru and Mo-Rh alloys. By plotting the electronic specific heat coefficient (γ) as a function of the average number of valence electrons to atom ratio ( e a ), a common curve was obtained to approximate the 4 d band shape in the e a range of 7.0–8.4. This curve has a minimum at e/ a $ ̃ 8.1. The variation of Debye temperature with e a is inversely correlated to that of γ. Superconducting properties of some of the alloys are discussed.

Low temperature calorimetric measurements on isothermal aging of Al-Ag

On quenching aluminum containing 1.3 at. % silver, energy is released upon isothermal holds at low temperatures (∼245°K). The amount of energy evolved, over a measured period of time (32–140 min) after the initiation of the reaction (clustering of silver atoms), amounts to 6–7 cal/g-atom of alloy for “slow” quenches and about 2–2.5 cal/g-atom of alloy for “fast” quenches. These results are consistent with the resistometric studies of Turnbull et al. who pointed out the existence of two states in quenched Al-Ag alloys.

Low Temperature Calorimetric Studies of Seven 1- Olefins: Effect of Orientation Disorder in the Solid State

From low temperature calorimetric measurements, values of the heat capacities in the solid and liquid states and of the heats and temperatures of phase changes were obtained for the following compounds: 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene and 1-hexadecene. Values of the entropy and other thermodynamic properties of each compound were calculated at selected temperatures in the range 10 to 360/sup 0/K. The thermal behavior of this series of 1-olefin hydrocarbons is more complex than that of the corresponding series of n-paraffins. By comparing the entropy values of 1-olefins with those of the n-paraffins, it was found that 1-undecene, 1-dodecene and 1-hexadecene crystallize in a state of orientational disorder. In 1-hexadecene crystals, virtually complete end-for-end disorder occurs. Because 1-undecene and higher 1-olefins do not form perfect crystals, the Third Law cannot be used to calculate absolute entropy values from the experimental data for these three compounds. However, the results reported here and elsewhere for the C/sub 5/ to C/sub 10/ hydrocarbons, inclusive, show that the entropy of these 1-olefins in the liquid state at 298.16/sup 0/K is 0.19 +- 0.02 cal./deg./sup -1//mole/sup -1/ less than that of the corresponding n-paraffins. Thus, reliable values of the entropy of the higher 1-olefinsmore » may be calculated by subtracting 0.19 cal./deg./sup -1//mole/sup 1/ from the entropy value of the corresponding n-paraffin. The experimental and calculated entropy values of the 1-olefin hydrocarbons from 1-octene to 1-hexadecene are represented within 0.04 percent by the equation, S/sub satd./ (liq., 298.16/sup 0/K) = 24.349 + 7.725 N cal./deg./sup -1//mole/sup -1/, where N is the number of carbon atoms in the molecule.« less

The Entropy of Dimethyl Sulfide from Low Temperature Calorimetric Measurements. Restricted Rotation of the Methyl Groups

In order to arrive at a satisfactory theory for the potential restricting the rotation of methyl groups in many molecules, it is desirable to determine how the magnitude of the barrier depends on the kind of atom to which the methyl groups are bonded. Recently we have obtained an estimate of the barriers in dimethyl sulfide by comparing the entropy obtained from calorimetric measurements extending to low temperatures with that computed from molecular data.

The Entropy of Dimethyl Acetylene from Low Temperature Calorimetric Measurements. Free Rotation in the Dimethyl Acetylene Molecule

The separation of the methyl groups in the dimethyl acetylene molecule, H3C-C≡C-C-CH3, is much greater than it is in ethane, and if the potential barrier [1] of about 3000 cal./mole restricting internal rotation in the latter is due to interactions between the methyl groups, then this barrier should be much smaller in dimethyl acetylene. If, on the other hand, the restricting potential in ethane is largely due to resonance with double bonded structures as proposed by Gorin, Walter, and Eyring [2], that fact that the length of the C-C single bonds in dimethyl acetylene [3] is such as to indicate considerable double bond character might lead one to expect a barrier about as large as in ethane. In order to determine the magnitude of this barrier we have calculated the entropy of dimethyl acetylene from low temperature calorimetric measurements and have compared this experimental value with that computed from molecular data.