In order to utilize thermal energy safely and efficiently, it is indispensable to elucidate the thermophysical properties of the medium with high accuracy. Regarding some media, such as water and HFC refrigerants, there are international standard values, contributing to the development of various heat engine institutions and process industries, and further improvement in accuracy has been attempted. On the other hand, however, thermophysical property information is remarkably insufficient for various types of media used for transporting energy and gases. In this paper, we introduce today's situation on fluid thermophysical properties and representative examples of thermophysical properties research.
Hexagonal boron nitride BN (hBN) and cubic BN (cBN) are known as the representative crystal structures of BN. The former is chemically and thermally stable, and has been widely used as an electrical insulator and heat-resistant materials. The latter, which is a high-density phase, is an ultra-hard material second only to diamond. In addition to those, wurtzite BN (wBN) is also known as other polymorphic phase. As crystal growth technique is not, however, applicable for wBN due to its thermodynamically metastable nature, fundamental properties of wBN with bulk crystalline form is not well studied so far. Among those BN crystals, some progresses in the synthesis of high purity BN crystals were achieved by using Ba-BN as a growth solvent material at high pressure (HP) of 5.5GPa. Band-edge natures (cBN Eg=6.2eV and hBN Eg=6.4eV) were characterized by their optical properties. The key issue to obtain high purity crystals is to reduce oxygen and carbon contamination in the HP growth circumstances. Then an attractive potential of hBN as a deep ultraviolet (DUV) light emitter and also superior properties as substrate of graphene devices were realized. By using high purity hBN crystal as a starting materials, high purity cBN sintered body and also highly oriented wBN crystalline form were obtained by high-pressure phase transformation process. In this paper, recent studies on BN polymorphic phases obtained at high pressure with respect to impurity control and their function will be reported.
Ionic liquids (ILs) have attracted much attention as clean absorption media for acidic gases, in particular, CO2. In the present review, we have summarized the recent development of ILs that can absorb CO2 chemically. The CO2 solubilities in the neat ILs and the IL mixtures were discussed in terms of the temperature and pressure dependence for the practical CO2 separation technology.
Regarding to pressure response to the high-pressure phase, generally the fluoride is more sensitive than oxides. Therefore, fluorides are frequently used as analog materials for investigating novel high-pressure phases in oxides. The high-pressure phase sequence in metal MnF2, and CoF2 was investigated with x-ray diffraction (XRD) and x-ray emission spectrum (XES) measurements under high pressure by using a laser-heated diamond anvil cell at synchrotron radiation facilities. The transition from rutile to orthorhombic I phase, and further transformation to cotunnite phase were confirmed in MnF2 at 3.9 GPa and 9.9 GPa, respectively. An anomaly exhibiting a negative linear compressibility in the b axis was detected by XRD measurements of the cotunnite phase above 80 GPa. The anomaly may be related to the intensity change of MnKβ’ in XES suggesting high-spin low-spin in Mn2+. The PdF2-to-CaF2 phase transition occurred at 12 GPa in CoF2. The XES reflects the coordination change from PdF2 to CoF2 structure.
The pressure effects on thermal inactivation of calf intestine alkaline phosphatase (CIAP) have been studied by measuring the rate of hydrolysis of p-nitrophenyl phosphate (pNPP) catalyzed by CIAP in the temperature range of 25～60 ℃ and at the pressures up to 150 MPa. The apparent rate of hydrolysis decreased with time above a certain temperature. The decrease is due to the decrease in CIAP activity. The enthalpy change of the thermal inactivation was 354～478 kJ mol-1, and volume change of this process was 8.8～40 cm3mol-1. The mechanism of the thermal inactivation of CIAP is discussed in terms of each thermodynamic parameters.
Aluminum oxide (Al2O3)-based composite ceramics consisting of vapor-grown carbon nanofiber (CNF) and titanium nitride (TiN) with the compositions of (Al2O3/CNF)/TiN=(100-y)[(100-x)/x] /y vol%, (x=0, 1, 3, 5, 10, y=0, 1, 3, 5, 10), have been fabricated utilizing both pulsed electric current and pressure to meet the demand for electric discharge processing for engineering ceramics. Mixtures of fine Al2O3 powder (particle size Ps: 0.1×10-6 m), CNF (150 ×10-9 m in diameter and ~6 ×10-6 m in length), and nanoparticle TiN (Ps: 20×10-9 m) were sintered at 1623 K (1350°C) under 50 MPa for 6.0×103 s (10 min) in Ar to produce electrically conductive aluminum oxide ceramics (alumina) with high mechanical properties at the same time. The relative densities of Al2O3/CNF/TiN composites decreased from 99.9% to 96.1% as the content of TiN increased to 10 vol%, and their electrical resistivity Ρ was much reduced from ~1013 (insulator) to less than ~1.0×10-2 Ω・m by the addition of a small amount of 3~5vol% CNF and TiN simultaneously. High bending strength σb and high fracture toughness KIC have been achieved in the compositions of Al2O3/CNF/TiN=95[(97/3)]/5 vol% (x=3, y=5) and 95[(95/5)]/5 vol% (x=5, y=5), respectively. The former revealed the following values: σb: 511 MPa, Vickers hardness Hv: 20.4 GPa,KIC: 6.08 MPa・m1/2, and Ρ: 6.5×10-3 Ω・m. The latter showed σb: 562 MPa, Hv: 19.9 GPa, KIC: 6.08 MPa・m1/2, and Ρ: 2.0×10-4 Ω・m. These data suggested that these composites could be candidates for electric discharge processing for engineering ceramics.
The pyrochlore ruthenates Pb2-xRExRu2O7-δ (RE = Y, Nd, Eu, Sm, Lu) have been successfully synthesized by the solid-state reaction. The solid-solution compounds of Pb2-xRExRu2O7-δ show a crossover from metallic to insulating with increasing x. Owing to a localized magnetic moment on Ru site, these compounds with x > 0.2 also indicate the spin-glass like behaviors at low temperature (T < TSG). As a result of electric resistivity measurements, the crossover was observed around x = 0.4 which is closely related to the spin-glass like behavior. In the metallic region, values of electric resistivity obey T2 dependencies which indicate the strong correlation between electrons in these compounds. It is concluded that the crossover from metallic to insulating is based on the strongly-correlated electron system.
Observations on the tissues in the trunk and root of Melia azedarach have been carried out by scanning electron microscope and optical microscope. Although the trunk of M. azedarach was found to be a ring porous wood, vessels were diffused in tissues of roots. Wood fiber and tracheid in trunk were much longer than those in root. However, ray parenchyma in trunk was much shorter than that in root. In the length of vessel element and narrow vessel element, significant difference were not found between trunk and root. Comparative study revealed that the length and width in vessel element of M. azedarach was equal to those of Z. serrata. The similarity in appearance of those two wood species is perhaps due to this similarity in the size of vessel element. As another characteristics of M. azedarach, two different contents in parenchyma cells were found. One is starch, and the other is assumed to be prismatic crystals of calcium oxalate.
The diesel particulate filter (DPF) has attracted strong attention as a desirable after-treatment device for the particulate matter(PM) contained in exhaust gas of diesel engine. When particulate matter was deposited on a DPF, the pressure drop increases due to the PM trapping in the surface cavities of the DPF. In this study, we compared the dependence of the shape and depth of the pore of the DPF on the PM trapping process by total model and numerical calculation. We found that the pressure drop and elapsed time of the PM trapping varied, significantly depending on the pore shape of the DPF surface. Further we examined the relative importance of the amount of PM deposit and the surface cavity shape of the DPF, and found that the pressure drop was lower when the shape of surface cavity in DPF became flatter and shallower. The result provides a quantitative evaluation and design of the surface cavity in the DPF leading to better production process of porous ceramic parts.
The stress-strain relationship and microstructural evolution of a fine-grained 5083 aluminum alloy produced via friction-stir processing (FSP) during high-temperature tensile deformation were investigated. The FSP of the 5083 aluminum alloy resulted in the formation of a homogeneous fine-grained microstructure. Based on the stress-strain relationship, it was found that the 5083 aluminum alloy exhibited a large elongation, especially at a temperature above 693 K. The stress exponent and the activation energy for deformation, which were determined by the flow stress at a nominal strain of 0.03, were approximately 2.5 and 123 kJ/mol, respectively. These results suggest that grain boundary sliding accommodated by the solute drag motion of dislocations was the rate-controlling process in the early stages of deformation. The largest elongation of 350% occurred at 743 K and an initial strain rate of 1.0 10-3 s-1. In this case, the grain aspect ratio increased with increasing nominal strain, which indicated that equiaxed grains continuously elongated along the tensile axis during high-temperature deformation because of dislocation creep. The value of the stress exponent increased with increasing strain. From our experimental results, the dominant deformation mechanism was determined to change during the tensile test, and the contribution of dislocation creep to the high-temperature deformation increased as the deformation proceeded.