Adiabatic Scanning Calorimeter Research Articles

High-resolution adiabatic scanning calorimeter for small samples

An improved version of a low-temperature double calorimeter for the temperature range 20–320 K is presented. The temperature of the adiabatic shield is increased at a programmable rate, while the temperature differences to the samples are regulated to zero. Temperature control and data acquisition are achieved by software algorithms integrated in a single computer program. The apparatus yields a typical precision ΔC p C p of 10 −3 with ≈ 50 data K −1.

Heat capacity measurement on ZrO x( x = 0–0.31) from 325 to 905 K. Part I. Heat capacity anomaly due to thermal non-equilibrium state at low temperature

Heat capacities of ZrO x ( x = 0–0.31) were measured from 325 to 905K using an adiabatic scanning calorimeter. Two kinds of heat capacity anomalies were observed for all samples except pure zirconium metal. A λ-type heat capacity anomaly was observed in the temperature range from 600 to 750K and was assigned to an order-disorder rearrangement of the interstitial oxygen atoms in zirconium host lattices. Another anomaly around 400–500K depended on heating conditions, indicating that this anomaly is due to a non-equilibrium phenomenon. Due to the imperfect ordering of the sample during the cooling process, a temporary ordering and a subsequent recovery into an equilibrium state occur during the heating process at a finite rate, making a broad heat capacity anomaly. This behavior is discussed with reference to the results of the dependences of the cooling rate of the sample and the heating rate of the calorimeter on the heat capacity anomaly.

Study on order-disorder transition of ZrO alloys (O/Zr = 0−0.31) by heat capacity measurement

Heat capacities of ZrO alloys (O/Zr = 0, 0−10, 0.31 and 0.24) were measured from 325 to 905 K using an adiabatic scanning calorimeter. Two types of heat capacity anomalies were observed for all samples except pure zirconium metal. A heat capacity anomaly at lower temperature was attributed to a non-equilibrium phenomenon. Another heat capacity anomaly at higher temperature was assigned to an order-disorder rearrangement of interstitial oxygen atoms in zirconium host lattices. The enthalpy and entropy changes due to the order-disorder transition were determined from heat capacity data on the basis of the baseline which was obtained as the sum of harmonic, dilatometric, electronic and anharmonic terms. The experimental entropy changes of the order-disorder transition for ZrO 1 6 (α″ 1) and ZrO x ( α″ 2) phases were compared with the theoretical values. A new phase diagram of the ZrO system was proposed from the transition temperatures, transition enthalpy and entropy changes as a function of the O Zr ratio which were obtained in this study and in our previous work.

Heat capacities of Cr 5Te 8 and Ni 5Te 8 from 325 to 930 K

Heat capacities of monoclinic Cr 5Te 8(m) and hexagonal Ni 5Te 8(hex) have been measured from 325 to 930 K using an adiabatic scanning calorimeter. For monoclinic Cr 5Te 8(m) the λ-type heat capacity anomaly was observed at 815 K, presumably due to the order—disorder of chromium atoms and vacancies in chromium tellurides. The transition entropy change of the Cr 5Te 8(m) sample obtained in this experiment compared reasonably well with that calculated on the basis of the order—disorder transition from vacancy-ordered Cr 5Te 8-type to vacancy-ordered Cr 3Te 4-type crystal structures. For the hexagonal Ni 5Te 8(hex) sample two excess heat capacities were observed around 400 K and above 700 K. The excess heat capacity at low temperature may be connected to the order—disorder of nickel atoms and vacancies in this structure and that at high temperature may be related to the activation processes such as defect formation, electron excitation and electron—hole pair formation.

Heat capacity measurement on (Zr 1− yM y)O x (where M is Nb, Sn) from 325 to 905 K

Heat capacities of (Zr 1− y M y )O 0.17 and (Zr 1− y M y )O 0.28 (where M is Nb or Sn, y = 0–0.07) having α″- ZrO ≈ 1 6 - type and α″-ZrO x -type crystal structures, respectively, were measured from 325 to 905 K using an adiabatic scanning calorimeter. A heat capacity anomaly at higher temperatures due to an order—disorder rearrangement of interstitial oxygen atoms in zirconium based alloys was observed for all samples, after the heat capacity anomaly at lower temperatures had been attributed to a non-equilibrium phenomenon. The transition temperature, transition enthalpy and entropy changes due to the order—disorder transition decreased with increasing doped niobium or tin content, indicating that arrangement of oxygen atoms in the lower temperature phase may be partially disordered by substituting niobium or tin for zirconium. The entropy change due to the order—disorder transition for (Zr 1− y M y )O 0.17 and (Zr 1− y M y )O 0.28 solid solutions was compared with the theoretical value. The solubility limits of (Zr 1− y M y )O 0.17 and (Zr 1− y M y )O 0.28 were determined from the variation of lattice constants, transition temperature, transition enthalpy and entropy changes against niobium or tin content.

Heat capacity of chromium-tellurium alloy at high temperatures

Heat capacities of monoclinic Cr 5Te 8(m) (CrTe 1.528, CrTe 1.576 and CrTe 1.590) and trigonal Cr 5Te 8(tr) (CrTe 1.609) were measured from 220 to 900 K by using an adiabatic scanning calorimeter. Heat capacity anomalies were observed at 841, 842 and 815 K for monoclinic Cr 5Te 8(m) (CrTe 1.528, CrTe 1.576 and CrTe 1.590, respectively) and at 776 K for trigonal Cr 5Te 8(tr) (CrTe 1.609), presumably due to order-disorder of chromium vacancies in chromium tellurides. The transition entropy changes of Cr 5Te 8(m) and Cr 5Te 8(tr) phases obtained in this experiment were smaller than those calculated from the entropy changes due to the partial disordering of chromium vacancies originally limited to every second chromium layer. This fact suggests that the completely-ordered phase is not formed in spite of slowly cooling the sample or that the partially-ordered phase still remains even at the high temperatures at which measurments were made in this study.

Heat-capacity measurement on ( Zr1− ySny) Ox from 325 to 905 K

Heat capacities of ( Zr 1− y Sn y ) O 0.17 and ( Zr 1− y Sn y ) O 0.28 ( y = 0−0.07) having α''-ZrO ~ 1 6 and α''- ZrO x type crystal structures, respectively, were measured from 325 to 905 K by using an adiabatic scanning calorimeter. Two kinds of heat capacity anomalies were observed for all samples. The anomaly at lower temperatures is attributed to a nonequilibrium phenomenon. Another anomaly at higher temperatures is assigned to an order-disorder rearrangement of oxygen atoms. The transition temperature, transition enthalpy and entropy changes due to the order-disorder transition decreased with increasing tin content, indicating that arrangement of oxygen atoms in the lower temperature phase may be partially disordered by substituting tin for zirconium. The entropy change due to the order-disorder transition for ( Zr 1− y Sn y ) O 0.17 and ( Zr 1− y Sn y ) O 0.28 solid solutions is compared with the theoretical value. The solubility limits of ( Zr 1− y Sn y ) O 0.17 and ( Zr 1− y Sn y ) O 0.28 were determined from the variation of lattice constants, transition temperature, transition enthalpy and entropy changes against tin content.

Specific heat of liquid STe mixtures

Measurements of specific heat were carried out for liquid STe mixtures using an adiabatic scanning calorimeter. For S-rich STe, the specific heat is almost independent of temperature and S concentration. For Te-rich STe, on the other hand, the specific heat depends strongly on the temperature and S concentration. A broad maximum in the temperature dependence of the specific heat is observed for S 0.2Te 0.8 and S 0.3Te 0.7, and it shifts towards higher temperatures with increasing sulphur concentration. The specific heat maximum is located in the temperature region where a metal-non-metal transition takes place. The large specific heats for the STe mixtures are attributed to the change in the local bond configuration. The temperature dependence of the specific heat reflects the mechanism of the bonding rearrangement.

Heat capacity measurement of ZrOx and (Zr1−yNby)Ox from 325 TO 905 K

Heat capacities of zirconium-oxygen alloys, ZrOx (x=0.17, 0.20, 0.28 and 0.31), and those of niobium doped alloys, (Zr1−yNby)Ox (x=0.17 and 0.28, y=0.005 and 0.01), were measured from 325 to 905 K by an adiabatic scanning calorimeter. Two kinds of heat capacity anomalies were observed for all samples. The anomaly at higher temperatures was assigned to be due to an order-disorder rearrangement of oxygen atoms. Another anomaly at lower temperatures was due to a non-equilibrium phenomenon. The entropy change due to the order-disorder transition for Zr-O solid solution at higher temperature obtained from this experiment was compared with the theoretical value. The transition temperature, transition enthalpy and entropy changes due to the order-disorder transition decreased with increasing niobium contents, indicating that arrangement of oxygen atoms in lower temperature phase may be partially disordered by the interaction between niobium and oxygen atoms.

Heat capacity measurement of VO 1± x and niobium doped VO 1+ x

The heat capacities of VO 1± x , (O/V = 0.883 and 1.063 (δ-phase) and 1.267 (ϵ-phase) were measured in the temperature range of 324–920 K with an adiabatic scanning calorimeter. A steep decrease in the heat capacity near room temperature and a subsequent anomalous peak were observed for each sample in the low temperature range below 600 K. At high temperature, around 900 K, an anomalous peak was seen in V0 0.883 and VO 1.063. The high temperature heat capacity peak was thought to be due to the order-disorder rearrangement of clusters of oxygen and vanadium vacancies and/or clusters of interstitial vanadium and vanadium vacancies. The low temperature heat capacity anomaly was interpreted by atomic migration to induce an increase in the degree of order of the “frozen in” state at some higher temperature. The heat capacities of VO 1+ x doped with 1.6 and 30 at% of Nb were also measured in the same temperature range, and the results supported the presence of the similar order-disorder transition to undoped VO 1± x at high temperature. The enthalpy and entropy changes at the high temperature transition were calculated from the excess heat capacity. The entropy change at the transition obtained experimentally was compared with that calculated from the configurational change of the two types of defect clusters mentioned above. The electrical conductivities of VO 1.063 and VO 1.267 were measured in the temperature range 320–1200 K. The δ-VO 1± x phase (VO 1.063) was observed to be semiconducting and the slope in the conductivity curve changed around the peak temperatures of low and high heat capacity anomalies. The ϵ-VO 1+ x phase (VO 1.267) was a metallic conductor and the slope in the conductivity of VO 1.267 changed slightly near the peak temperature of the low temperature heat capacity anomaly.

Heat Capacity of Liquid Tl-Te Alloys

The measurements of heat capacity were made for liquid Tl-Te alloys using an adiabatic scanning calorimeter over the whole concentration range. The excess heat capacity for liquid Te-rich Tl-Te alloys can be attributed to the change in the bonding configuration around Te. The concentration dependence of the heat capacity suggests that the bonding nature changes gradually with increasing Tl content and drastically changes around the composition of Tl 2 Te. The heat capacity for liquid Tl 2 Te alloys has a small temperature coefficient at temperature where a nonmetal-metal transition occurs. It means that the excess heat capacity for liquid Tl 2 Te alloy may not be due to the dissociation of the chemical complex.

Phase relation and heat capacities of Ba 2YCu 3O 7− x at high temperature

The heat capacities of Ba 2YCu 3O 7− x ( x = 0.18, 0.35, and 0.60) were measured in the range from room temperature to 860 K by an adiabatic scanning calorimeter. X-ray diffraction analyses were also performed on the quenched and annealed samples. No heat capacity anomaly was seen in either orthorhombic(I) Ba 2YCu 3O 6.82 or tetragonal Ba 2YCu 3O 6.40. For Ba 2YCu 3O 6.65, the heat capacity anomaly was observed above 700 K, which was correlated with the phase transition from orthorhombic(I) to orthorhombic(II) structure. The phase relations among orthorhombic(I), orthorhombic(II), and the tetragonal phases were also clarified.

The conformational change of DNA in aqueous alcohol solutions containing metallic ions determined by using differential scanning calorimeter

In order to obtain information about the conformational change of DNA by changing the environment surrounding DNA molecule, we measured the helix-coil transition of DNA solutions with various concentrations of ethanol at a given concentration of various kinds of metallic ion by means of an adiabatic differential scanning calorimeter. The observed heat of transition, ΔH increases, but the transition temperature, T 1 decreases with increasing the concentration of ethanol, demonstrating that the conformation of DNA may considerably change by environment surrounding DNA. In order to confirm the conformational change of DNA, we also measured the CD spectra at room temperature under the same experimental conditions as the DSC measurement. The concentration range of ethanol where molecular ellipticity ratio, [θ] max/[θ] min of positive maximum, [θ] max to negative minimum, [θ] min changes is in good agreement with that obtained from DSC measurements. We will discuss the conformational change of DNA in solutions with various proportions of ethanol and a definite concentration of metallic ion by combining the results obtained by the calorimetric and spectral measurements.

Heat capacities of liquid SbSe and BiSe alloys

Measurements of heat capacities for liquid SbSe and BiSe alloys were carried out up to 800°C using an adiabatic scanning calorimeter. Anomalous temperature variation of heat capacity was observed for liquid Sb 0.45Se 0.55, Sb 0.5Se 0.5 and Bi 2Se 3 alloys. Broad maxima were observed in the temperature dependence of their heat capacities. In contrast, the heat capacity for liquid Sb 2Se 3 alloys shows little temperature variation. In the concentration dependence, the maximum of the heat capacity deviates from the stoichiometric composition of M 2Se 3 in both alloy systems. The characteristic behaviour of the heat capacities for liquid SbSe and BiSe alloys can be attributed to a change in intermediate-range order and in local bonding.

Effects of salts, protease digestions, chemical modifications, and heat treatment on the trypsin inhibitory activity of the protease inhibitor from Job's-tears (Coix lacryma-jobi L. var. Ma-yuen Stapf).

Trypsin inhibitor (JBTI) was extracted and purified from the bran of Job’s-tears (Coix lacryma-jobi L. var. Ma-yuen Stapf) seeds. Its molecular weight was estimated as 16500 by SDS-PAGE. Trypsin inhibitory activity of JBTI was enhanced in the presence of divalent cations, such as Ca2+ or Mg2+, and inhibited by divalent heavy metal ions, such as Cu2+ or Zn2 + . Its activity was stable against pepsin digestion, while JBTI was denatured by subtilisin BPN or Actynase E digestions. Its activity was stable against chemical modification of the lysyl residues, while JBTI lost its activity by the modification of the arginyl residues. The thermal unfolding of JBTI was studied in an adiabatic differential scanning calorimeter and it was found that the protein unfolds at 93°C and pH 7.0 in 50 mm phosphate buffer.

Calorimetric investigation of phase transitions in cholesteryl oleate

Abstract An adiabatic scanning calorimeter has been used to investigate the temperature dependence of the enthalpy and the heat capacity near phase transitions in the cholesteric liquid crystal cholesteryl oleate (CO). It is found that the blue phases in CO are thermodynamically stable and that the observed enthalpy differences between the phases are small.

Measurement of thermophysical properties of molten salts: Mixtures of alkaline carbonate salts

The purpose of this study is to develop measuring methods for the thermal diffusivity, the specific heat capacity, and the density of molten salts, as well as to measure these properties of mixtures of alkaline carbonate salts. The thermal diffusivity is measured by the stepwise heating method. The sample salt is poured into a thin container, and as a result, a three-layered cell is formed. The thermal diffusivity is obtained from the ratio of temperature rises at different times measured at the rear surface of the cell when the front surface is heated by the stepwise energy from an iodine lamp. The specific heat capacity is measured using an adiabatic scanning calorimeter. The density is measured by Archimedes' principle. Thermal conductivity is determined from the above properties. Measured samples are Li2CO3-K2CO3 (42.7–57.3, 50.0-50.0, and 62.0-38.0 mol%).

Adiabatic scanning calorimetric results for the blue phases of cholesteryl nonanoate.

An adiabatic scanning calorimeter has been used to study the thermal behavior of the liquid-crystal cholesteryl nonanoate in a temperature range covering all phase transitions involving the three different blue phases occurring in this substance. Results for the temperature dependence of the enthalpy and the heat capacity are reported. It is found that all three of the blue phases are thermodynamically stable and that all the phase transitions observed are first order.

Heat Capacity of Liquid Se–Te Mixtures

The measurements of heat capacity were made for liquid Se–Te mixtures using an adiabatic scanning calorimeter. Liquid Se x Te 1- x mixtures with x =0.2 to 0.6 exhibit maxima in the temperature dependence of heat capacity. The position of heat capacity maximum shifts toward higher temperature with increasing Se concentration. The plots of heat capacity against conductivity show a maximum in the range of 150 to 400 (ohm·cm) -1 . It indicates that the bonding rearrangement is most active in this range of conductivity. A strong correlation is found between the heat capacity and the temperature dependence of magnetic susceptibility. In the semiconducting region, the large excess heat capacity can be attributed to the formation of dangling bonds. In the metallic region, the excess heat capacity can be related to the change in the density of states caused by the bonding rearrangement.

Calorimetric Investigations of the Liquid Crystalline Material Heptyloxybenzylidene-Heptylaniline (70.7)

Abstract Using an adiabatic scanning calorimeter we have studied the thermal behavior of the liquid crystalline material heptyloxybenzylidene-heptylaniline in the temperature range between 52°C and 86°C. In this temperature range a rich variety of liquid crystalline and plastic crystalline phases and phase transitions could be studied. The isotropic to nematic (NI) transition and the nematic to smectic A (NA) transition (only 0.3°C below TNI) are both first-order with a latent heat of 2.1 (± 0.1) kJ/mol and 2.2 (± 0.1) kJ/mol respectively. The first-order nature of the NA transition is in accordance with recent observations for systems with similarly small nematic ranges. The smectic A to smectic C (AC) transition is second-order within the experimental resolution. The observed anomaly in the specific heat Cp for the AC transition is not consistent with the theoretically expected XY behavior. It can, however, be described rather well with a mean field theory. The transition from the smectic C to the plast...