Thermal Diffusivity and Heat of Formation of Harzburgite and Its Major Constituent Minerals

The thermal diffusivity, D, and its temperature dependence of Oman harzburgite rock and its major mineral olivine have been evaluated from the basic properties such as seismic velocities, density, and Debye temperature. The Arrhenius-type temperature dependence of the diffusivity was utilized to evaluate the heat of formation, ΔH _D. The diffusivity values, 1.80mm² · s⁻¹ and 2.1mm² · s⁻¹ obtained at room temperature for harzburgite and olivine, respectively, are consistent with available data. The diffusivity values for Oman harzburgite are overestimated by an amount of 0.27mm² · s⁻¹ relative to those of PNG harzburgite. The ΔH _D value (−2.40 kJ · mol⁻¹) for harzburgite rock of the Oman ophiolite suite is comparable with that (−2.90 kJ · mol⁻¹) of the harzburgite rock of Papua New Guinea. The disagreements in the thermal diffusivity and heat of formation values may be partly due to ignoring the effect of pyroxene in Oman harzburgite.     

Thermal Conductivity of a Simulated Fuel with Dissolved Fission Products

The thermal diffusivity of a simulated fuel with fission products forming a solid solution was measured using the laser-flash method in the temperature range from room temperature to 1673 K. The density and the grain size of the simulated fuel with the solid solutions used in the measurement were 10.49 g · cm⁻³ (96.9% of theoretical density) at room temperature and 9.5 μm, respectively. The diameter and thickness of the specimens were 10 and 1 mm, respectively. The thermal diffusivity decreased from 2.108 m² · s⁻¹ at room temperature to 0.626 m² · s⁻¹ at 1673 K. The thermal conductivity was calculated by combining the thermal diffusivity with the specific heat and density. The thermal conductivity of the simulated fuel with the dissolved fission products decreased from 4.973 W · m⁻¹ · K⁻¹ at 300 K to 2.02 W · m⁻¹ · K⁻¹ at 1673 K. The thermal conductivity of the simulated fuel was lower than that of UO₂ by 34.36% at 300 K and by 15.05% at 1673 K. The difference in the thermal conductivity between the simulated fuel and UO₂ was large at room temperature, and decreased with an increase in temperature. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Photothermal Beam Deflection Spectroscopy for the Determination of Thermal Diffusivity of Soils and Soil Aggregates

Photothermal beam deflection spectroscopy (BDS) with a red He–Ne laser (632.8 nm, 35 mW) as an excitation beam source and a green He–Ne laser (543.1 nm, 2 mW) as a probe was used for estimating thermal diffusivity of several types of soil samples and individual soil aggregates with small surfaces (2?×?2 mm). It is shown that BDS can be used on demand for studies of changes in properties of soil entities of different hierarchical levels under the action of agrogenesis. It is presented that BDS clearly distinguishes between thermal diffusivities of different soil types: Sod-podzolic [Umbric Albeluvisols, Abruptic], 29?±?3; Chernozem typical [Voronic Chernozems, Pachic], 9.9?±?0.9; and Light Chestnut [Haplic Kastanozems, Chromic], 9.7?±?0.9 cm²·h^?1. Aggregates of chernozem soil show a significantly higher thermal diffusivity compared to the bulk soil. Thermal diffusivities of aggregates of Chernozem for virgin and bare fallow samples differ, 53?±?4 cm²·h^?1 and 45?±?4 cm²·h^?1, respectively. Micromonoliths of different Sod-podzolic soil horizons within the same profile (topsoil, depth 10–14 cm, and a parent rock with Fe illuviation, depth 180–185 cm) also show a significant difference, thermal diffusivities are 9.5?±?0.8 cm²·h^?1 and 27?±?2 cm²·h^?1, respectively. For soil micromonoliths, BDS is capable to distinguish the difference in thermal diffusivity resulting from the changes in the structure of aggregates.     

Effect of cathodic hydrogen-charging current density on the hydrogen diffusivity in nanostructured bainitic steels

ABSTRACT

The effect of cathodic hydrogen-charging current on the effective hydrogen diffusivity in nanostructured bainitic steels produced at transformation temperatures 200°C (BS200) and 350°C (BS350) was investigated and compared to that of mild steel. The effective hydrogen diffusivity at 10?mA?cm^?2 was the lowest for BS200, followed by BS350 and mild steel, due to the finer microstructure and higher dislocation density in the bainitic ferrite of BS200. Increase in the hydrogen-charging current density, i.e. 20 and 30?mA?cm^?2, increased the effective hydrogen diffusivity of mild steel by 37 and 135%, and BS350 by 49 and 150%, respectively. For BS200, the increase was not significant (2%) at 20?mA?cm^?2, but increased by 34% at 30?mA?cm^?2.

This paper is part of a thematic issue on Hydrogen in Metallic Alloys     

Effects of hydrogen on the mechanical properties of a 2 1/4Cr–1Mo steel

This paper explores the effects of hydrogen on the mechanical properties of a 2 1/4Cr–1Mo steel. The results for both microstructural conditions, as received and aged, indicated a loss of ductility after hydrogen charging treatment, but the yield strength and ultimate tensile strength remained unaltered. The fractograph analysis revealed that the fracture mode was modified by the hydrogen. The steel in the as-received condition showed craters and fisheyes on the fracture surface. The aged steel showed a brittle appearance associated with cleavage facets and small portion of areas with dimples. The hydrogen diffusivity and solubility were investigated using electrochemical permeation technique. It was observed that the hydrogen diffusivity decreased from 2.3 ± 0.4 × 10⁻¹⁰ m² s⁻¹ in the as-received condition to 5.7 ± 0.1 × 10⁻¹¹ m² s⁻¹ in the aged condition. The hydrogen solubility showed an increase for the aged condition in comparison to the as received sample. Both phenomena can be attributed to carbide evolution during aging, resulting in an increase of the carbide/matrix interfacial area.     

Simultaneous Absorptance and Thermal-Diffusivity Determination of Optical Components with Laser Calorimetry Technique

The laser calorimetry (LCA) technique is used to determine simultaneously the absorptances and thermal diffusivities of optical components. An accurate temperature model, in which both the finite thermal conductivity and the finite sample size are taken into account, is employed to fit the experimental temperature data measured with an LCA apparatus for a precise determination of the absorptance and thermal diffusivity via a multiparameter fitting procedure. The uniqueness issue of the multiparameter fitting is discussed in detail. Experimentally, highly reflective (HR) samples prepared with electron-beam evaporation on different substrates (BK7, fused silica, and Ge) are measured with LCA. For the HR-coated sample on a fused silica substrate, the absorptance is determined to be 15.4?ppm, which is close to the value of 17.6?ppm, determined with a simplified temperature model recommended in the international standard ISO11551. The thermal diffusivity is simultaneously determined via multiparameter fitting to be approximately 6.63?×?10^?7?m² · s^?1 with a corresponding square variance of 4.8?×?10^?4. The fitted thermal diffusivity is in reasonably good agreement with the literature value (7.5?×?10^?7?m² · s ^?1). Good agreement is also obtained for samples with BK7 and Ge substrates.     

Measurement of the In-plane Thermal Diffusivity and Temperature-Dependent Convection Coefficient Using a Transient Fin Model and Infrared Thermography

The transient fin model introduced recently for determination of the in-plane thermal diffusivity of planar samples with the help of infrared thermography was modified so as to be applicable to poor heat conductors. The new model now includes a temperature-dependent heat loss by convective heat transfer, suitable for an experimental setup in which the sample is aligned parallel to a weak, forced air flow stabilizing otherwise the convective heat transfer. The temperature field in the sample was measured with an infrared camera while the sample was heated at one edge. The symmetric temperature field created was averaged over the central fifth of the sample to obtain one-dimensional temperature profiles, both transient and stationary, which were fitted by a numerical solution of the fin model. One of the fitting parameters was the thermal diffusivity, and with a known density and specific heat capacity, the thermal conductivity was thus determined. The test measurements with tantalum samples gave the result (57.5 ± 0.2) W · m⁻¹ · K⁻¹ in excellent agreement with the known value. The other fitting parameter was a temperature-dependent heat loss coefficient from which the lower limit for the temperature-dependent convection coefficient was determined. For the stationary state the result was (1.0 ± 0.2) W · m⁻² · K⁻¹ at the temperature of the flowing air, and its temperature dependence was found to be (0.22 ± 0.01) W ·m⁻² · K⁻².     

Thermal-Diffusivity Measurements of Conductive Composites Based on EVA Copolymer Filled With Expanded and Unexpanded Graphite

In this research, the thermal diffusivity of composites based on ethylene- vinyl acetate (EVA) copolymer filled with two kinds of reinforcement graphite materials was investigated. The reinforcement graphite fillers were untreated natural graphite (UG) and expanded graphite (EG). Composite samples up to 29.3 % graphite particle volumetric concentrations (50 % mass concentration) were prepared by the melt- mixing process in a Brabender Plasticorder. Upon mixing, the EG exfoliates in these films having nanosized thicknesses as evidenced by TEM micrographs. Thus, the thermal diffusivity and electrical conductivity of composites based on the ethylene-vinyl acetate matrix filled with nanostructuralized expanded graphite and standard, micro-sized graphite were investigated. From the experimental results it was deduced that the electrical conductivity was not only a function of filler concentration, but also strongly dependent on the graphite structure. The percolation concentration of the filler was found to be (15 to 17) vol% for micro-sized natural graphite, whereas the percolation concentration of the filler in nanocomposites filled with expanded graphite was much lower, about (5 to 6) vol%. The electrical conductivity of nanocomposites was also much higher than the electrical conductivity of composites filled with micro-sized filler at similar concentrations. Similarly, the values of the thermal diffusivity for the nanocomposites, EG-filled EVA, were significantly higher than the thermal diffusivity of the composites filled with micro-sized filler, UG-filled EVA, at similar concentrations. For 29.3 % graphite particle volumetric concentrations, the thermal diffusivity was 8.23 × 10^?7 m² · s^?1 for EG-filled EVA and 6.14 × 10^?7 m² · s^?1 for UG-filled EVA. The thermal diffusivity was measured by the flash method.     

Environmental embrittlement of Al–Sn alloys and its implication for fatigue crack growth

Abstract

The environmental embrittlement of a series of Al–Sn alloys has been studied using the technique of slow strain rate testing in laboratory air, in a packing of anhydrous magnesium perchlorate, and in a salt solution (2%NaCl–0·5%Na₂CrO₄ buffered to pH 3·5). The embrittlement occurring at slow strain rates is attributed to reversible hydrogen embrittlement. Only the alloy containing a continuous network of tin phase suffers a reduction in ductility. This is attributed to an increase in hydrogen diffusivity which is demonstrated through a series of permeation tests. These results are then used to interpret fatigue crack growth tests conducted as a function of environment in the absence of closure.

MST/744     

Dissolution and Solubility Behavior of Fenofibrate in Sodium Lauryl Sulfate Solutions

The solubility of fenofibrate in pH 6.8 McIlvaine buffers containing varying concentrations of sodium lauryl sulfate was determined. The dissolution behavior of fenofibrate was also examined in the same solutions with rotating disk experiments. It was observed that the enhancement in intrinsic dissolution rate was approximately 500-fold and the enhancement in solubility was approximately 2000-fold in a pH 6.8 buffer containing 2% (w/v) sodium lauryl sulfate compared to that in buffer alone. The micellar solubilization equilibrium coefficient (k*) was estimated from the solubility data and found to be 30884 ± 213 L/mol. The diffusivity for the free solute, 7.15 × 10^{? 6} cm²/s, was calculated using Schroeder's additive molal volume estimates and Hayduk-Laurie correlation. The diffusivity of the drug-loaded micelle, estimated from the experimental solubility and dissolution data and the calculated value for free solute diffusivity, was 0.86 × 10^{? 6} cm²/s. Thus, the much lower enhancement in dissolution of fenofibrate compared to its enhancement in solubility in surfactant solutions appears to be consistent with the contribution to the total transport due to enhanced micellar solubilization as well as a large decrease ( ～ 8-fold) in the diffusivity of the drug-loaded micelle.     

Kinetics of transient liquid phase diffusion bonding process for joining aluminium metal matrix composite

Abstract

The mechanism and kinetics of the transient liquid phase diffusion bonding process in a 6061–15 wt-%SiCp composite at 570°C, 0·2 MPa, with 200 μm thick copper foil interlayer, has been investigated by microstructural characterisation of the bond region using optical microscopy, scanning electron microscopy and electron probe microanalysis. The kinetics of isothermal solidification, representing the displacement of the solid/liquid interface y (in micrometres) as a function of time t (in seconds), followed a power law relationship y?=?157t^0·07. According to this kinetic equation, the effective diffusivity of copper in the composite system was found to be ～10⁶ times higher than the lattice diffusivity, indicating the dominance of short circuit diffusion through the defect rich particle/matrix interface.     

Application of photoacoustic and photothermal techniques for heat conduction measurements in a free-standing chemical vapor-deposited diamond film

Heat conduction in a free-standing chemical vapor-deposited polycristalline diamond film has been investigated by means of combined front and rear photoacoustic signal detection techniques and also by means of a “mirage” photothermal beam deflection technique. The results obtained with the different techniques are consistent with a value of α=(5.5±0.4)×10⁻⁴ m² · s⁻¹ for thermal diffusivity, resulting in a value ofκ=(9.8±0.7)×10² W·m⁻¹·K⁻¹ for thermal conductivity when literature values for the density and heat capacity for natural diamond are used.     

Nanospheres Containing Urea: Photothermic Properties

In the present research, nanospheres of chitosan (CS), maltodextrin, and sodium tripolyphosphate (STPP), loaded with urea, were synthesized by using an ionic gelation technique. In the nanosphere synthesis was used a central composite experimental design, obtaining nanospheres with an average size of 275?±?32 nm and 27.5 mV zeta potential. The nanospheres were characterized by their hydrodynamic diameter, polydispersity index, nitrogen content, and thermal properties such as thermal diffusivity (α), effusivity (e), and conductivity (k); also melting temperature was obtained by differential scanning calorimetry. The thermal properties of nanospheres show that the sample with the smallest size has a thermal diffusivity value of (14.4?±?0.4)?×?10^?8 m²·s^?1 and a thermal conductivity value of (6.4?±?0.1)?×?10^?1 W·m^?1·K^?1, and the obtained melting temperature was 157 °C. Higher concentrations of CS increase the values of these thermal properties, probably because chitosan interacts ionically with STPP forming a reticular network due to the opposite charges of both molecules.     

Experimental Reconstruction of Thermal Parameters in CNT Array Multilayer Structure

The thermal conductivities, thermal diffusivity, thermal anisotropy ratio, and thermal boundary resistance for the multilayered microstructure of a carbon nanotube (CNT) array are reconstructed experimentally using the 3ω method with two different width metal heaters. The thermal impedance in the frequency domain and sensitivity coefficients are introduced to simultaneously determine the multiple thermal parameters. The thermal conductivity at 295 K is 38 W · m⁻¹ · K⁻¹ along the nanotube growth direction, and two orders of magnitude lower in the direction perpendicular to the tubes with the anisotropy ratio as large as 86. Separation of the contact and CNT array resistances is realized through circuit modeling. The measured thermal boundary resistances of the CNT array/Si substrate and insulating diamond film interfaces are 3.1 m² · K · MW⁻¹ and 18.4 m² · K · MW⁻¹, respectively. The measured thermal boundary resistance between the heater and diamond film is 0.085 m² · K · MW⁻¹ using a reference sample without a CNT array. The thermal conductivity for a CNT array already exceeds those of phase-changing thermal interface materials used in microelectronics.     

Experimental investigation of nonuniform heating and heat loss from a specimen for the measurement of thermal diffusivity by the laser pulse heating method

Nonuniform heating effect and heat loss effect from the specimen in the measurement of thermal diffusivity by the laser pulse heating method have been experimentally investigated using an axially symmetric Gaussian laser beam and a laser beam homogenized with an optical filter. The degree of error is theoretically estimated based on the solution of the two-dimensional heat conduction equation under the boundary condition of heat loss from the surface of the specimen in the axial direction and the initial conditions of axially symmetric nonuniform and uniform heating. A correction factor, which is determined by comparison of the entire experimental and the theoretical history curves, is introduced to correct the values obtained by the conventionalt _1,2 method. The applicability of this modified curve-fitting method has been experimentally tested using materials in the thermal diffusivity range 10⁻³ to 1 cm²·s⁻¹. The experimental error due to the nonuniform heating and heat loss was reduced to approximately 3%.     

Thermal Characterization of PZT Ceramics Obtained by Mechanically Activated Mixed Oxides Using Different Pb Sources

In this study, three sets of PZT samples with compositions 57/43 and 55/45 (rhombohedral phase), 53/47 and 51/49 (tetragonal phase) prepared by mechanochemical activation of powder mixtures (during 4?h of milling) and thermal treatment (sintered at 1200?°C for 4?h) were thermally characterized. The three sets of compositions were prepared using different Pb sources (A-PbO, B-PbO₂, and C-Pb₃O₄). The thermal characterization of sintered samples was carried out by photoacoustic spectroscopy and differential scanning calorimetry, to obtain the thermal diffusivity and specific heat (c _p ). The DSC thermograms also allowed the determination of the Curie temperature, and the thermal conductivity was calculated combining the results of the thermal diffusivity, specific heat, and density. The samples obtained with Pb₃O₄ showed a theoretical density higher than 95?%, whereas those obtained from PbO₂ precursors showed a lower densification rate (around 89?%). The samples obtained with Pb₃O₄ with compositions 53/47 and 51/49 also showed the highest values of thermal diffusivity (7.3 ± 0.4)?× 10^?7m²· s^?1 and (6.6 ± 0.3)?× 10^?7m²· s^?1, respectively.     

Structural,spectral, quantum chemical and thermal studies on a new NLO crystal: guanidinium cinnamate

New organic non-linear optical (NLO) single crystals of guanidinium cinnamate were crystallized by solvent evaporation solution growth technique and the crystal and molecular structure were determined by single crystal X-ray diffraction. The crystal packing is dominated by classical N–H···O hydrogen bonding interactions. Due to deficiency of acceptor atoms compared to the donor sites, two unusual ring R₂ ¹(6) motifs are formed through two N–H···O hydrogen bonds. These ring motifs are further connected through chain C₂ ²(6) or C₂ ²(8) motifs along the b-axis of the unit cell. Further, these chain and ring motifs are cross-linked through another N–H···O hydrogen bond leading to classical ring R₂ ²(8) motif. These chain and ring motifs are interlinked with each other to form secondary ring R₆ ⁶(14)/R₆ ⁶(16) motifs. The molecular geometry of the asymmetric part of the unit cell was optimized theoretically by density functional theory using the B3LYP function with 6-311?+?+?G(d,p) basis set. The optimized molecular geometry and computed vibrational spectra are compared with experimental results which showed significant agreement. The intermolecular interactions of the title compound were analyzed by the Hirshfeld surfaces. The computed hyperpolarizability values showed that the compound is a good candidate for NLO applications. The chemical hardness, electro-negativity and chemical potential of the molecule were computed by HOMO–LUMO plot. The lower band gap of the frontier orbitals indicates the suitability of fabrication of the material for non-linear optoelectronic applications.     

Fatigue crack growth rates of API X70 pipeline steel in a pressurized hydrogen gas environment

Hydrogen is known to have a deleterious effect on most engineering alloys. It has been shown repeatedly that the strength of steels is inversely related to the ductility of the material in hydrogen gas. However, the fatigue properties with respect to strength are not as well documented or understood. Here, we present the results of tests of the fatigue crack growth rate (FCGR) on API X70 from two sources. The two materials were tested in air, 5.5 and 34 MPa pressurized hydrogen gas, and at both 1 and 0.1 Hz. At these hydrogen pressures, the FCGR increases above that of air for all values of the stress intensity factor range (ΔK) greater than ~7 MPa · m^1/2. The effect of hydrogen is particularly sensitive at values of ΔK below ~15 MPa · m^1/2. That is, for values of ΔK between 7 and 15 MPa · m^1/2, the FCGR rapidly increases from approximately that found in air to as much as two orders of magnitude above that in air. Above 15 MPa · m^1/2, the FCGR remains approximately one to two orders of magnitude higher than that of air.     

Interlayer Hydrogen‐Bonded Metal Porphyrin Frameworks/MXene Hybrid Film with High Capacitance for Flexible All‐Solid‐State Supercapacitors

2D metal‐porphyrin frameworks (MPFs) are attractive for advanced energy storage devices. However, the inferior conductivity and low structural stability of MPFs seriously limit their application as flexible free‐standing electrodes with high performance. Here, for the first time, an interlayer hydrogen‐bonded MXene/MPFs film is proposed to overcome these disadvantages by intercalation of highly conductive MXene nanosheets into MPFs nanosheets via a vacuum‐assisted filtration technology. The alternant insertion of MXene and MPFs affords 3D interconnected “MPFs‐to‐MXene‐to‐MPFs” conductive networks to accelerate the ionic/electronic transport rates. Meanwhile, the interlayer hydrogen bonds (F···H? O and O···H? O) contribute a high chemical stability due to a favorable tolerance to volume change caused by phase separation and structural collapse during the charge/discharge process. The synergistic effect makes MXene/MPFs film deliver a capacitance of 326.1 F g^?1 at 0.1 A g^?1, 1.64 F cm^?2 at 1 mA cm^?2, 694.2 F cm^?3 at 1 mA cm^?3 and a durability of about 30 000 cycles. The flexible symmetric supercapacitor shows an areal capacitance of 408 mF cm^?2, areal energy density of 20.4 µW h cm^?2, and capacitance retention of 95.9% after 7000 cycles. This work paves an avenue for the further exploration of 2D MOFs in flexible energy storage devices.     

Growth and some properties of barium-cadmium formate single crystals: (I) Crystal growth and morphology

The growth of barium-cadmium formate BaCd(HCO₂)₄·2H₂O single crystals by slow cooling method and their characterization by selective etching are reported. It was found that BaCd(HCO₂)₄·2H₂O crystallizes from aqueous solution in 2/m class of the monoclinic system. Crystals grown during a period of 1 month have dimensions of about 2 × 1.5 × 10 cm³. The typical twinning for these crystals has been observed and investigated by the selective etching. The dislocation density has been estimated to be 3·10² – 2·10³ cm^?2.