Thermal Relaxation Method Research Articles

Short notes: Measurements on the heat capacity of thermal reduced graphene oxide down to 0.3 K

The specific heat of thermally reduced graphene oxide (trGO) was measured by a thermal relaxation method in the temperature range from 0.3 to 275 K. It was found that the temperature dependence of the heat capacity С(Т)/T vs T2 of trGO is nonmonotonic. It has been established that in the temperature range of 0.3–6 K there is an anomalous behavior of the temperature dependence of the heat capacity trGO, sharply changing its character. It is assumed that this anomaly is due to the influence of impurities and defects, structural features.

Zn_{1-x}Ni_xTe semiconductor nanocrystals in transparent glass for optoelectronic device applications

Doping glass with semiconductors, particularly with nanostructured semiconductors, has attracted attention due to the large optical absorption cross-sections of the latter. Based on this property, Ni^{2+} (5 wt%) doped phosphate glass and Zn_{1-x}Ni_xTe (x = 0.5, 1.0, 5.0 and 10.0 wt% of Ni^{2+}) nanocrystals (NCs) doped phosphate glasses (GCs) were prepared by fusion method and subsequent heat treatment. Influence of Ni^{2+} on structural, thermo-optical and third-order nonlinear optical properties have been analysed through various spectroscopic characterizations. The XRD pattern of the glass (G) exhibits the amorphous nature of the host material while GCs exhibit not only amorphous halo but also the presence of quantum dots (QDs) or nanocrystals (NCs) phases. TEM analysis of the studied GCs samples confirm the presence of quantum dots (QDs) and bulk NCs with an average diameter of approximately 4.2 {pm } 0.3 nm and 13.4 {pm } 0.2 nm, respectively. Several phosphate groups were observed and reported from Raman and FTIR-ATR spectra. The absorption band positions confirmed that Ni^{2+} ions resemble to the octahedral symmetry. The intensity of absorption band around 1352 nm (^3T{_1}(F) rightarrow^3A{_2}(F)) increased with the increase of Ni^{2+} in GCs which is an indicative of the ^{[6]}Ni^{2+} coordination. The emission properties such as emission cross-sections ({sigma }_{emi}) full width at half maxima (FWHM) for the ^1T{_2}(D) rightarrow^3T{_2}(F) (visible) and ^3A{_2}(F) rightarrow^3T{_1}(F) (near-infrared) emission transitions were reported. Among the glass-containing semiconductor nanocrystals (GCs), the emission cross-sections in GC4 sample (x = 10% of Ni^{2+}) are the largest for both the visible (11.88 times 10^{-18} cm^2) and infrared (0.98 times 10^{-20} cm^2) transitions. Thermal diffusivity (D), thermal conductivity (K) and temperature dependent optical path length change (ds/dT) were obtained through time-resolved thermal lens (TL) and thermal relaxation (TR) methods. The D and K parameters do not change significantly with increase of Ni^{2+} ions (0.5–5%) in GCs. Nonlinear-refractive index and nonlinear absorption of the studied samples were also obtained using femtosecond Z-scan technique. The increase of nonlinear absorption coefficient (beta) is observed from GC2 (2.53 {times } 10^{-10} cm/W) to GC4 (7.98 {times } 10^{-10} cm/W). The GC4, sample with 10 wt% of Ni^{2+}, showed the lowest ds/dT (1.22 times 10^{-6} K^{-1}) with good lasing (FOM and emission cross-sections) and nonlinear absorption properties suggesting that it can be a good candidate for visible-red emission light conversion in LED technology.

Low Temperature Thermal Properties of Nanodiamond Ceramics

The temperature dependence of thermal conductivity and specific heat for detonated nanodiamond ceramics is investigated on specially designed experimental setups, implementing the uniaxial stationary heat flow method and the thermal relaxation method, respectively. Additionally, complementary studies with a commercial setup (Physical Property Measurement System from Quantum Design operating either in Thermal Transport or Heat Capacity Option) were performed. Two types of samples are under consideration. Both ceramics were sintered at high pressures (6–7 GPa) for 11–25 s but at different sintering temperatures, namely 1000 °C and 1600 °C. The effect of changing the sintering conditions on thermal transport is examined. In thermal conductivity κ(T), it provides an improvement up to a factor of 3 of heat flow at room temperature. The temperature dependence of κ(T) exhibits a typical polycrystalline character due to hindered thermal transport stemming from the microstructure of ceramic material but with values around 1–2 W/mK. At the lowest temperatures, the thermal conductivity is very low and increases only slightly faster than linear with temperature, proving the significant contribution of the scattering due to multiple grain boundaries. The specific heat data did not show a substantial difference between detonated nanodiamond ceramics obtained at different temperatures unlike for κ(T) results. For both samples, an unexpected upturn at the lowest temperatures is observed—most likely reminiscent of a low-T Schottky anomaly. A linear contribution to the specific heat is also present, with a value one order of magnitude higher than in canonical glasses. The determined Debye temperature is 482 (±6) K. The results are supported by phonon mean free path calculations.

Hysteresis in Heat Capacity of MWCNTs Caused by Interface Behavior.

The paper is concerned with the study of structural disorder as well as the emergence and causes of heat capacity hysteresis in multiwall carbon nanotubes. The investigation methods are X-ray diffraction analysis, Raman spectroscopy, transmission electron microscopy, and calorimetric tests: thermogravimetric analysis, differential scanning calorimetry, and the thermal relaxation method for heat capacity hysteresis. Multiwall carbon nanotubes are shown to be composed of one or several types of zigzag–armchair domains. The domain structure of nanotube samples is responsible for the generation of uniaxial elastic microstrains and viscoelastic bending strains at domain interfaces. The thermomechanical behavior of interfaces is the chief cause of temperature hysteresis of heat capacity. The number of hystereses corresponds to the number of domain types in the structure, and values of hysteresis are determined by the crystallite size, thermal conductivity, and normal temperature distribution of strain. The found mechanism of heat capacity hysteresis can be helpful in preventing jumps in thermal properties and managing thermal memory in multiwall carbon nanotubes.

Size effects in the heat capacity of modified MWCNTs

Carbon nanomaterials with unique physical and chemical properties find practical applications in various fields, such as in new composite materials, nanoelectronics, medicine, etc. The efficiency of using MWCNTs (multiwalled carbon nanotubes) depends on their morphology, structure, the presence of impurities and defects. In this work, the influence of defects and geometric sizes of CVD MWCNTs on their heat capacity was experimentally studied. The heat capacity of MWCNTs modified by grinding and oxidation with different average outer diameters (7.2 and 18 nm) was measured by the thermal relaxation method in the temperature range from 1.8 to 275 K. The effects of size and dimensionality were found. The character of the temperature dependences of the specific heat of ground and ground-oxidized MWCNTs with various diameters differs fundamentally below ≈140 K. The discovered effects are discussed.

Thermal transport at 6H-SiC/graphene buffer layer/GaN heterogeneous interface

We investigate the epitaxial growth of graphene on SiC and thermal transport at 6H-SiC/graphene buffer layer/GaN heterogeneous interface. Under Tersoff-Erhart-Albe potential (TEA) and environment-dependent interatomic potential (EDIP), graphene buffer layer (GBL) is epitaxially grown by simulated annealing method, and simulations show that TEA potential is superior to EDIP potential by evaluation of nucleation temperature, radial distribution function, average atomic binding energy, atomic structure and bond length. Further, by thermal relaxation method, single-vacancy defects in graphene can reduce interface thermal resistance (ITR) at 6H-SiC/GBL/GaN heterogeneous interface with maximum reduction of 9.6%, meaning that ITR can be reduced by defect engineering. In addition, with the increase of nucleation areas, especially the bonding of different nucleation zones, ITR also has a highest decline of 17.9%, and energy is easier to pass through the interface, illustrating the importance of graphene integrity for interfacial heat transfer. At last, the increase in temperature (300 K to 1100 K) results in a maximum 19.6% decrease in ITR, indicating that ITR is sensitive to temperature. The selection of potential and the analysis of the heat transfer of the three-materials heterogeneous interface contribute to thermal design of graphene-based semiconductor devices.

Thermal conductivity enhancement of defective graphene nanoribbons

We study the heat transfer of graphene nanoribbons (GNRs) with different doped atoms (N, Si) and grain boundaries using non-equilibrium molecular dynamics and thermal relaxation method. It is found that even at low doping concentrations, with the increase of doping concentrations, the thermal conductivities of GNRs decrease greatly, and the thermal resistances of grain boundaries increase drastically. In addition, the mass difference between nitrogen and silicon atoms results in the difference in heat transfer. Further, we investigate the effect of the relative positions of nitrogen atoms and Stone-Wales (SW) defects on the thermal conductivity. We find that the thermal conductivity of GNR with doping atoms close to defects is higher than the thermal conductivity of GNR with doping atoms far away from defects, and when the dopant atoms are located in the heat flow path and close to more defects, it is better for heat transfer. Finally, it is found that the doping atoms can enhance the thermal conductivity when they are close to the heat source and heat sink, maybe this is the fact that doping atoms can inhibit phonon scattering in the heat source and heat sink.

The low-temperature specific heat of thermal reduced graphene oxide

Measurements of heat capacity at constant pressure of thermally reduced graphene oxide (trGO) and graphite oxide (GtO) were performed in the temperature range from 1.8 to 275 K by thermal relaxation method. Above 15 K, the specific heat values of trGO and GtO are close to each other within 20%. Below 10 K, the ratio of the specific heat of trGO to the specific heat of GtO increases with decreasing temperature and reaches 5 at 2 K. It was found that the temperature dependence of the specific heat of trGO is of a complex character. There are temperature ranges in which of the specific heat of trGO is close to either linear or T2.5.

Low temperature heat capacity measurements of β-Si3N4 and γ-Si3N4: Determination of the equilibrium phase boundary between β-Si3N4 and γ-Si3N4

Isobaric heat capacities of β-Si3N4 and γ-Si3N4 were measured at temperatures between 1.8 and 309.9 K with a thermal relaxation method. The measured heat capacities of γ-Si3N4 are smaller than those of β-Si3N4 in this temperature range. Using these data, we determined the standard entropies of β-Si3N4 and γ-Si3N4 to be 62.30 J·mol−1 K−1 and 51.79 J·mol−1 K−1, respectively. The equilibrium phase boundary between β-Si3N4 and γ-Si3N4 was calculated using these values and thermodynamic parameters reported in previous studies. The obtained equilibrium phase transition pressure at 2000 K is 11.4 GPa. It is lower than the experimental pressures at which γ-Si3N4 was synthesized in previous studies. The calculated Clapeyron slope at this temperature is 0.6 MPa K−1, which is consistent with those of theoretical studies.

Effect of water/carbon interaction strength on interfacial thermal resistance and the surrounding molecular nanolayer of CNT and graphene flake

Heat transfer at the liquid-solid interface, especially when the particles are at nanoscale, can dominate the thermal properties of nanofluids. In this study we investigate the liquid-solid interfacial thermal resistance (Kapitza resistance) and particularly analyze the structure of the formed molecular nanolayer around the carbon-based nanoparticles. Employing non-equilibrium molecular dynamics simulation and thermal relaxation method, nanofluids systems with nanoparticles with different diameters and surface wettabilities were investigated. Simulation results reveal that carbon nanotubes (CNTs) with smaller diameters more effectively attract base fluid and thus show lower reduced Kapitza resistances. It was found that the thickness of the nanolayer around the nanoparticle is independent of the carbon/water interaction strength. As expected, it was shown that the value of Kapitza resistance decreases when the interaction strength increases. Based on our acquired results, a correlation was proposed for the interfacial thermal resistance of CNT/water and graphene/water with respect to the intensity of wettability of nanoparticles surface. The insight provided by our atomistic simulations can provide a better understanding of heat transfer in nanofluids systems wherein an accurate local description of heat transfer is crucial.

Residual entropy in the zero-temperature limit of toluene glass

The specific heat Cp of toluene, doped with 2 mol% ethanol to avoid rapid crystallization, has been measured in both glass and crystal states, and with special accuracy at low temperatures in the range 1.8−20 K using the thermal relaxation method. By making use of the complementary Cp curves measured in the reference crystal state, we have been able to obtain the entropy curve of the glass and eventually the residual entropy of toluene glass in the zero-temperature limit, that is found to be 5.1 J/(K⋅mol). This value is clearly lower than others pre-viously reported in the literature, which lack the knowledge of the particular specific-heat behavior of glasses at low temperatures and hence overestimated the glass residual entropy at zero temperature. In addition, we have studied in detail such low-temperature “glassy anomalies” in the case of toluene, extending and improving pre- vious measurements. The surprising depletion previously reported of tunneling two-level systems in toluene glass has been confirmed, though this fact coexists with the presence of a broad peak typical of glasses (the so-called boson peak) in Cp/T3 at 4.5 K. For the toluene crystal, the expected cubic Debye behavior has been found at lower temperatures.The specific heat Cp of toluene, doped with 2 mol% ethanol to avoid rapid crystallization, has been measured in both glass and crystal states, and with special accuracy at low temperatures in the range 1.8−20 K using the thermal relaxation method. By making use of the complementary Cp curves measured in the reference crystal state, we have been able to obtain the entropy curve of the glass and eventually the residual entropy of toluene glass in the zero-temperature limit, that is found to be 5.1 J/(K⋅mol). This value is clearly lower than others pre-viously reported in the literature, which lack the knowledge of the particular specific-heat behavior of glasses at low temperatures and hence overestimated the glass residual entropy at zero temperature. In addition, we have studied in detail such low-temperature “glassy anomalies” in the case of toluene, extending and improving pre- vious measurements. The surprising depletion previously reported of tunneling two-level systems in toluene glass has been confi...

The low-temperature specific heat of MWCNTs

The specific heat of multi-walled carbon nanotubes (MWCNTs) with a low defectiveness and with a low content of inorganic impurities has been measured in the temperature range from 1.8 to 275 K by the thermal relaxation method. The elemental composition and morphology of the MWCNTs were determined using scanning electron microscopy analysis and energy dispersion x-ray spectroscopy. The MWCNTs were prepared by chemical catalytic vapor deposition and have mean diameters from 7 nm up to 18 nm and lengths in some tens of microns. MWCNTs purity is over 99.4 at.%. The mass of the samples ranged from 2–4 mg. It was found that the temperature dependence of the specific heat of the MWCNTs differs significantly from other carbon materials (graphene, bundles of SWCNTs, graphite, diamond) at low temperatures. The specific heat of MWCNTs systematically decreases with increasing diameter of the tubes at low temperatures. The character of the temperature dependence of the specific heat of the MWCNTs with different diameters demonstrates the manifestation of different dimensions from 1D to 3D, depending on the temperature regions. The crossover temperatures are about 6 and 40 K. In the vicinity of these temperatures, a hysteresis is observed.

Thermodynamic investigation of the phase equilibrium boundary between TiO2 rutile and its α-PbO2-type high-pressure polymorph

Heat capacity (CP) of rutile and α-PbO2 type TiO2 (TiO2-II) were measured by the differential scanning calorimetry and thermal relaxation method. Using the results, standard entropies at 1 atm and 298.15 K of rutile and TiO2-II were determined to be 50.04(4) and 46.54(2) J/mol K, respectively. Furthermore, thermal expansivity (α) determined by high-temperature X-ray diffraction measurement and mode Gruneisen parameters obtained by high-pressure Raman spectroscopy suggested the thermal Gruneisen parameter (γth) for TiO2-II of 1.7(1). By applying the obtained low-temperature CP and γth, the measured CP and α data of TiO2-II were extrapolated to higher temperature region using a lattice vibrational model calculation, as well as rutile. Internally consistent thermodynamic data sets of both rutile and TiO2-II assessed in this study were used to thermodynamically calculate the rutile‒TiO2-II phase equilibrium boundary. The most plausible boundary was obtained to be P (GPa) = 0.0074T (K) − 1.7. Our boundary suggests that the crystal growth of TiO2-II observed below 5.5 GPa and 900 K in previous studies advanced in its stability field. The phase boundary calculation also suggested small, exothermic phase transition enthalpy from rutile to TiO2-II at 1 atm and 298.15 K of − 0.5 to − 1.1 kJ/mol. This implies that the thermodynamic stability of rutile at 1 atm above room temperature is due to larger contribution of entropy term.

Thermodynamic properties of ZrSiO4 zircon and reidite and of cotunnite-type ZrO2 with application to high-pressure high-temperature phase relations in ZrSiO4

Enthalpies of high-pressure phase transitons in ZrSiO4 were measured by high-temperature drop-solution calorimetry. The enthalpies for the zircon-reidite transition in ZrSiO4 and for dissociation of reidite to cotunnite-type ZrO2 + SiO2 stishovite were obtained to be 27.5 ± 3.3 and 50.3 ± 3.0 kJ/mol, respetively, at 298 K. By thermal relaxation method, low-temperature isobaric heat capacities of ZrSiO4 reidite and cotunnite-type ZrO2 were measured, giving standard entropies at 298 K of 77.29 ± 0.04 and 49.10 ± 0.04 J/mol·K, respectively. Combining the measured enthalpies and entropies with other available thermophysical data, the transition boundaries in ZrSiO4 were calculated. The calculated zircon-reidite transiton boundary is consistent with that by in situ high-pressure expreiments by Ono et al. (2004a) within the errors. The calculated dissociation boundary of reidite has a smaller slope than that by high-pressure quench expreiments by Tange and Takahashi (2004). The equilibrium zircon-reidite transition pressure is calculated to be 8 GPa at 298 K, which is by 12–15 GPa lower than the transition pressures observed by room-temperature static compression experiments. Our results suggest that zircon transforms to reidite and dissociates into the two phases at 330 and 610 km depths, respectively, along the normal mantle geotherm. Combining the calculated phase relations with kinetics estimated from the first principles calculation may provide some insights to P, T conditions which reidites found in impact ejecta layers and craters experienced.

Experimental and thermodynamic investigations on the stability of Mg14Si5O24anhydrous phase B with relevance to Mg2SiO4forsterite, wadsleyite, and ringwoodite

High-pressure high-temperature phase relation experiments in Mg 14 Si 5 O 24 were performed using a 6-8 multi-anvil high-pressure apparatus in the pressure range of 12–22 GPa and temperature range of 1673–2173 K. We first found that Mg 14 Si 5 O 24 anhydrous phase B (Anh-B) dissociates to Mg 2 SiO 4 wadsleysite (Wd) and MgO periclase (Per) at about 18 GPa and 1873 K. From the results of the high-pressure experiments, the phase boundaries of 5 Mg 2 SiO 4 forsterite (Fo) + 4 Per = Anh-B and Anh-B = 5 Wd + 4 Per were determined. In addition, the isobaric heat capacity ( C P ) of Anh-B was measured by differential scanning calorimetry in the temperature range of 300–770 K and the thermal relaxation method using a Physical Property Measurement System (PPMS) in the range of 2–303 K. From the measured low-temperature C P , the standard entropy ( S ∘ 298.15 ) of Anh-B was determined to be 544.4(2) J/(mol·K). We also performed high-temperature X-ray diffraction measurements in the range 303–773 K to determine the thermal expansivity (α) of Anh-B. The obtained C P and α were theoretically extrapolated to higher temperature region using a lattice vibrational model calculation partly based on Raman spectroscopic data. Thermodynamic calculations by adopting the thermochemical and thermoelastic data for Anh-B obtained in this study and the estimated formation enthalpy for Anh-B of –13 208 kJ/mol gave phase equilibrium boundaries for 5 Fo + 4 Per = Anh-B and Anh-B = 5 Wd + 4 Per that were consistent with those determined by the present high-pressure high-temperature experiments. The results clarified that, in the Mg 14 Si 5 O 24 system, Anh-B is stable between 12 and 18 GPa at the expected temperatures of the Earth’s mantle.

Pressure dependence of thermal conductivity and specific heat in CeRh2Si2 measured by an extended thermal relaxation method

We have developed a new technique for measuring thermal conductivity and specific heat under pressure by improving a thermal relaxation method. In this technique, a cylindrical sample with a small disc heater is embedded in the pressure-transmitting medium, then temperature variations of the sample and heater were directly measured by thermocouples during a heating and cooling process. Thermal conductivity and specific heat are estimated by comparing the experimental data with temperature variations simulated by a finite element method. The obtained thermal conductivity and specific heat of the test sample CeRh2Si2 exhibit a small enhancement and a clear peak arising from antiferromagnetic transition, respectively. The observation of these typical behaviors for magnetic compounds indicate that the technique is valid for the study on thermal properties under pressure.

Calorimetric Measurements at Low Temperatures in Toluene Glass and Crystal

The specific heat of toluene in glass and crystal states, has been measured both at low temperatures down to 1.8 K (using the thermal relaxation method) and in a wide temperature range up to the liquid state (using a quasiadiabatic continuous method). Our measurements therefore extend earlier published data to much lower temperatures, thereby allowing to explore the low temperature glassy anomalies in the case of toluene. Surprisingly, no indication of the existence of tunneling states is found, at least within the temperature range studied. At moderate temperatures, our data either for the glass or for the crystal show good agreement with those found in the literature. Also, we have been able to prepare bulk samples of toluene glass by only doping with 2% mol ethanol instead of with higher impurity doses used by other authors.

Thermal transport at a solid-nanofluid interface: from increase of thermal resistance towards a shift of rapid boiling.

We use molecular dynamics simulations to investigate interfacial thermal transport between an ethanol suspension containing gold atomic clusters and a gold surface, using both realistic and simplified molecular models of nanoparticles. The interfacial thermal conductance was determined via a thermal relaxation method for a variety of nanoparticle-nanoparticle and nanoparticle-surface interaction strengths. The Kapitza resistance is found to increase due to the presence of nanoparticles in the vicinity of the solid-liquid interface. The heat flow from the solid to the nanoparticles is separated from its counterpart from the solid to the liquid to discriminate their respective contribution to the total heat current. A per-vibrational-mode analysis highlights a shift of major heat carriers from low frequencies towards higher frequencies due to the coupling of the internal nanoparticle dynamics to the gold surface, in addition to stronger particle-surface interactions. Finally, we demonstrate that the increase of the Kapitza resistance significantly shifts the nanofluid/solid surface explosive boiling temperature to higher temperatures compared to pure ethanol.

Microstructural, Structural, and Thermal Characterization of Annealed Carbon Steels

As is well known, the metallurgical microstructure of carbon steel is formed by ferrite and pearlite after the annealing heat treatment. When the cooling rate increases, the diffusive process is interrupted causing a change in the metallurgical microstructure which will affect steel properties. The aim of this work was to study thermal, structural, and microstructural properties of annealed carbon steel samples with four different carbon contents. Crystalline structure and crystalline quality were studied by the X-ray diffraction technique, where the full width at half maximum analysis showed that as the carbon content increased, the crystalline quality decreased. The metallurgical microstructure morphology was studied by scanning electron microscopy. The thermal diffusivity and the heat capacity were determined by the photoacoustic technique and by the thermal relaxation method, respectively. The thermal diffusivity and the thermal conductivity decreased as the carbon content increased. The amplitude signal of photothermal radiometry increased as the carbon content increased, while the phase signal of photothermal radiometry did not show significant differences among studied carbon steel types. The photoacoustic technique represents an important alternative in the steel characterization field.

Redetermination of high-temperature heat capacity of Mg2SiO4 ringwoodite: Measurement and lattice vibrational model calculation

Isobaric heat capacities (CP) of Mg2SiO4 forsterite and ringwoodite were measured by differential scanning calorimetry in the temperature range of 306-833 K. The measured CP of Mg2SiO4 forsterite was consistent with those reported by previous studies. On the other hand, the present CP of Mg2SiO4 ringwoodite was about 3-5% larger than those measured by previous researchers. The calorimetric data of Mg2SiO4 ringwoodite were extrapolated to 2500 K using a lattice vibrational model calculation, which well reproduced the low-temperature CP data measured by thermal relaxation method. The calculated CP shows good agreement with the present calorimetric data. The obtained CP was expressed by the polynomial of temperature: CP = 164.30 + 1.0216 × 10−2T + 7.6665 × 103T−1 - 1.1595 × 107T−2 + 1.3807 × 109T−3 [J/(mol·K)] in the range of 250-2500 K.