Isochoric Specific Heat Capacity of Difluoromethane (R32) and a Mixture of 51.11 mass% Difluoromethane (R32) + 48.89 mass% Pentafluoroethane (R125)

The isochoric heat capacity (c _v ) of difluoromethane (R32) and a mixture of 51.11 mass% R32 + 48.89 mass% pentafluoroethane (R125) was measured at temperatures from 268 K to 328 K and at pressures up to 30 MPa. The reported density measurements are in the single-phase region and cover a range of ρ > 800 kg · m⁻³. The measured data are compared with results measured by other researchers. Also, the measured data are examined with available equations of state. As a result, it is found that the measured c _v ’s agree well with those of other researchers in the measurement range of the present study.     

Surface Tension of HFC Refrigerant Mixtures

The surface tension of refrigerant mixtures, i.e., R-410A (50 mass% R-32/50 mass% R-125), R-410B (45 mass% R-32/55 mass% R-125), R-407C (23 mass% R-32/25 mass% R-125/52 mass% R-134a), R-404A (44 mass% R-125/52 mass% R-143a/4 mass% R-134a), and R-507 (50 mass% R-125/50 mass% R-143a), has been measured and correlated in the present study. Although the first three mixtures are very important as promising replacements for R-22 in air-conditioners and heat-pumps and the last two are promising replacements for R-502, surface tension data for these mixtures were not previously available. The measurements were conducted under conditions of coexistence of the sample liquid and its saturated vapor in equilibrium. The differential capillary rise method (DCRM) was used, with two glass capillaries with inner radii of 0.3034±0.0002 and 0.5717±0.0002 mm. The temperature range covered was from 273 to 323 K, and the uncertainty of measurements for surface tensions and temperatures is estimated to be at most ±0.2 mN·m^–1 and ±20 mK, respectively. A mixing rule was selected for representing the temperature dependence of the resultant data. These data were successfully represented by a mixing rule using mass fraction based on the van der Waals correlation.     

Study on a novel energetic cocrystal of TNT/TNB

A new energetic cocrystal of TNT/TNB was obtained by evaporating ethanol at room temperature over a period of 3 days. It is found that the donor–acceptor π–π interaction, p–π interaction, and C–H···O hydrogen bond interaction are dominant in the formation of the cocrystal. In this work, physicochemical characteristics of cocrystal have also been studied using several methods: Optical Microscopy, Powder X-ray Diffraction, Single Crystal X-ray Diffraction and differential scanning calorimetry. It is shown that TNT and TNB molecules cocrystallize in a monoclinic system with space group P2₁/c and cell parameters a = 20.4570(8) Å, b = 6.1222(2) Å, c = 15.1635(6) Å, β = 110.091(4)°, and Z = 4. The cocrystal has a crystal density of 1.640 g cm^?3 and H₅₀ (50 % explosion characteristics of drop height) of 112.2 cm, which is higher than that of TNT (100 cm), TNB (77.8 cm) and most of the other explosives. The result shows that co-crystallization may help to improve the performance of TNT and TNB.     

Evidence for high ionic conductivity in lithium–lanthanum titanate, Li0·29La0·57TiO3

Lithium–lanthanum titanate, Li_0·29La_0·57TiO₃, is prepared by solid-state reaction method and it is furnace-cooled to room temperature. X-ray diffraction results indicated that the compound has tetragonal perovskite-like structure and the lattice parameters are determined as a = 3· 8714 Å and c = 7· 7370 Å. The average grain size is found to be 5 μm from SEM micrograph. The analysis of FTIR and Raman spectra of the sample supported tetragonal structure inferred from XRD data. The impedance spectrum of the sample is separated into bulk and grain boundary parts by analysing the impedance data. The high bulk ionic conductivity is reported as 1· 12 × 10^???3 S cm^?1 at room temperature. D.C. conductivity measurements indicate that the compound is a good ionic conductor.     

Influence of hydrothermal treatment on the microstructure and oxidation resistance of a Zn4B2O7·H2O (4ZnO·B2O3·H2O) coating for C/C composites

Antioxidant modification for C/C composites by in situ hydrothermal synthesise at 140 °C of a 4ZnO·B₂O₃·H₂O crystallite coating has been successfully achieved. The influence of hydrothermal time on the phase composition, microstructure of the as-prepared Zn₄B₂O₇·H₂O (4ZnO·B₂O₃·H₂O), and its antioxidant modification for C/C composites were investigated. Samples were characterised by XRD, SEM, isothermal oxidation test and TG-DSC. Results show that, 4ZnO·B₂O₃·H₂O crystalline coating is achieved on the surface of C/C composites after the hydrothermal treatment at 140 °C for time in the range of 2–12 h. A smooth and crack-free 4ZnO·B₂O₃·H₂O layer can be obtained when the hydrothermal time reaches 8 h. Isothermal oxidation test demonstrates that the oxidation resistance of C/C composites is improved. The as-modified composites exhibit only 1.52 g·cm^?2 weight loss after oxidation at 600 °C for 15 h, while the non-modified one shows a 6.57 g·cm^?2 weight loss after only 10 h oxidation. For the uncoated C/C composite the oxidation rate is approximately linear with time (non-protective oxidation), thus at 15 h exposure one can estimate the mass loss to be 6.57 g·cm^?2 after 10 h for direct comparison with the coated samples.     

Pinning enhancement in MgB2 superconducting thin films by magnetic nanoparticles of Fe2O3

MgB₂ thin films were fabricated on r-plane Al₂O₃ ( ${1} \overline{{1}} {0} {2})$ substrates. First, deposition of boron was performed by rf magnetron sputtering on Al₂O₃ substrates and followed by a post-deposition annealing at 850 °C in magnesium vapour. In order to investigate the effect of Fe₂O₃ nanoparticles on the structural and magnetic properties of films, MgB₂ films were coated with different concentrations of Fe₂O₃ nanoparticles by spin coating process. The magnetic field dependence of the critical current density J _c was calculated from the M–H loops and magnetic field dependence of the pinning force density, f _p(b), was investigated for the films containing different concentrations of Fe₂O₃ nanoparticles. The critical current densities, J _c, in 3T magnetic field at 5 K were found to be around 2·7 × 10⁴ A/cm², 4·3 × 10⁴ A/cm², 1·3 × 10⁵ A/cm² and 5·2 × 10⁴ A/cm² for films with concentrations of 0, 25, 50 and 100% Fe₂O₃, respectively. It was found that the films coated with Fe₂O₃ nanoparticles have significantly enhanced the critical current density. It can be noted that especially the films coated by Fe₂O₃ became stronger in the magnetic field and at higher temperatures. It was believed that coated films indicated the presence of artificial pinning centres created by Fe₂O₃ nanoparticles. The results of AFM indicate that surface roughness of the films significantly decreased with increase in concentration of coating material.     

Progress Toward Redetermining the Boltzmann Constant with a Fixed-Path-Length Cylindrical Resonator

A single, fixed-path-length cylindrical-cavity resonator was used to measure c ₀ = (307.825 2 ± 0.001 2) m · s^?1, the zero-density limit of the speed of sound in pure argon at the temperature of the triple point of water. Three even and three odd longitudinal modes were used in this measurement. Based on the ratio M/?? ₀ = (23.968 644 ± 0.000 033) g · mol^?1, determined from an impurity and isotopic analysis of the argon used in this measurement and the measured c ₀, the value k _B = 1.380 650 6 × 10^?23J · K^?1 was obtained for the Boltzmann constant. This value of k _B has a relative uncertainty u _r(k _B) = 7.9 × 10^?6 and is fractionally, (0.12 ± 8.1) × 10^?6 larger than the value recommended by CODATA in 2006. (The uncertainty is one standard uncertainty.) Several, comparatively large imperfections of our prototype cavity affect the even longitudinal modes more than the odd modes. The models for these imperfections are approximate, but they suggest that an improved cavity will significantly reduce the uncertainty of c ₀.     

YBa2SnO5·5, a novel ceramic substrate for YBCO and BiSCCO superconductors

YBa₂SnO_5·5 has been synthesized and sintered as single phase material for its use as substrate for both YBCO and BiSCCO superconductors. YBa₂SnO_5·5 has a complex cubic perovskite (A₂BB’O₆) structure with the lattice constanta = 8·430 Å. The dielectric constant and loss factor of YBa₂SnO_5·5 are in a range suitable for its use as substrate for microwave applications. YBa₂SnO_5·5 is found to be chemically compatible with both YBCO and BiSCCO superconductors. The thick film of YBCO screen printed on polycrystalline YBa₂SnO_5·5 substrate gave aT _c(0) of 92 K and a critical current density (J _c) of 4 × 10⁴ A/cm² at 77 K. A screen printed BiSCCO thick film on YBa₂SnO_5·5 substrate gaveT _c(0) = 110 K and current density 3 × 10³ A/cm² at 77 K.     

Optical and thermal characteristics of glasses based on TeO 2

Glass samples have been synthesized in quaternary system based on TeO ₂–oxide within composition, 85TeO ₂–5Nb ₂O ₅–5ZnO–5Ag ₂O, 68TeO ₂–5Nb ₂O ₅–20ZnO–7Na ₂O and [(75?x)TeO ₂–5Nb ₂O ₅–20ZnO–xPbO, x = 7, 18 mol%]. Structural characterization of the glasses was studied with respect to their thermal stability, refractive indices, third order nonlinear optical susceptibility, IR spectra and Vickers hardness. For four different prepared glasses, density in the range from 5·3744 to 6·0731 g· cm ^???1, the glass transition temperature (T _g) in the range from 326 to 350 °C and refractive indices, n, in the range from 2·1273 to 2·2123 at 435 nm and Vickers hardness, H _v, in the range from 2·91 to 3·44 GPa were determined. The value of third order nonlinear optical susceptibilities ${\vert} {\chi}^{\text{(3)}}{\vert} {\approx} $ 17·9 ·10^{??? 13} esu of glass within composition, 68TeO ₂–5Nb ₂O ₅–20ZnO–7PbO, was measured by using degenerate four-wave mixing (DFWM).     

Relationship Between Growth Speed and Magnetic Properties in Bi-2212/Ag Textured Composites

In this paper, the measured magnetic properties of Bi₂Sr₂CaCu₂O _x /3 wt.% Ag textured composite materials prepared by a LFZ melting technique at different growth speeds (5, 15, 30, and 60 mm/h) are presented. X-ray diffraction patterns have shown that Bi-2212 phase is the major one in all cases. The magnetization measurements have been carried out as a function of the magnetic field up to 10 kOe. J _c values, calculated using Bean’s model, indicate that the growth speeds have a significant effect on J _c . It has been found that the maximum critical current density, 4.42×10⁵ A/cm² at 10 K, has been obtained for the 15 mm/h grown sample.     

The Comparisons Between Y-123 and Y-124 Superconductor Substituted with Ca at the Cu-Site

The comparison between YBa₂Cu_3?x Ca _x O _δ and YBa₂Cu_4?x Ca _x O₈ superconductors substituted with Ca at the Cu-site was investigated. The concentration of Ca varied from x=0.00 to x=0.15. Resistivity and current density measurement (without magnetic field) were measured using four-probe method. The samples were characterized using X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). From the resistivity measurement, the critical temperature (T _c?zero) in x=0.00 was 84 K for Y-123 and 83 K for Y-124 superconductor system. As the Ca concentration increased to x=0.15, both superconductor systems showed a decrease in value whereby 71 K for Y-123 and 74 K for Y-124. This was a result of the decrease in the hole concentration. Critical current density (J _c ) decreased with the further increment of Ca concentration owing to grain connectivity and an increase of porosity. At 50 K, J _c decreased from 3.9790 A/cm² at x=0.00 to 3.5184 A/cm² at x=0.15 for Y-123, and from 3.6209 A/cm² at x=0.00 to 0.5243 A/cm² at x=0.15 for Y-124. The crystallographic crystal structure showed that both Y-123 and Y-124 superconductor systems exhibited an orthorhombic form. FESEM microscopy showed that the Y-123 sample had less porosity compared to Y-124 samples and the resulting Y-123 sample had a higher J _c compared to the Y-124 sample.     

Study of Edge Effect to Stop Liquid Spillage for Microgravity Application

The ability of a micro-groove to prevent the spreading of HFE-7100 fluid (C₄F₉OCH₃) having low surface tension (γ?= 13.6 mN/m) on a surface is studied. In this study, micro-grooves were made around square openings of a plate made of either polycarbonate or 316 stainless steel. To verify effectiveness of micro-grooves to stop the spread of HFE-7100, experiments were done under non-saturated and saturated conditions. Under non-saturated conditions the micro-grooves on both materials confined the liquid up to apparent angle of 55 ± 5° due to the edge effect. Saturated gas-vapor mixture with vapor mass fraction of w _v = 88% and w _v = 97% did not significantly influence the confinement of the liquid by the micro-groove. This result is promising for application of micro-grooved plates in CIMEX experiment planned for ISS.     

Formulated quasi-solid state electrolyte based on polypyrrole/polyaniline–polyurethane nanocomposite for dye-sensitized solar cell

A polymer-based quasi-solid state electrolyte using polyurethane (PU) matrix was applied for dye-sensitized solar cell (DSSC). To further improve the performance of the electrolyte, 10 wt% of conductive polymer [polypyrrole (PPy) and polyaniline (PANi)] nanoparticles were introduced into the matrix. The samples were named PU-10%PPy and PU-10%PANi, and characterized using ATR–FTIR, TEM, DLS, a transmitted light microscope, a reflected light microscope, and TGA. The formulated polymeric nanocomposites were immersed in the liquid electrolyte and the polymer matrix absorbency, conductivity (σ), ion diffusion coefficient (D_ff), and photovoltaic performance in the DSSC were measured. Polymer matrix absorbency and D_ff of PU-10%PPy (1.72 g g^?1, 1.52 µcm² s^?1) and PU-10%PANi (1.74 g g^?1, 1.31 µcm² s^?1) were lower than the PU matrix (2.01 g g^?1, 1.68 µcm² s^?1). However, the conductivity of PU-10%PPy and PU-10%PANi was higher than the PU matrix (2.64, 2.69, and 2.59 mS cm^?1, respectively). The efficiency of the DSSC based on PU-10%PANi was the highest, with open circuit voltage of 709 mV, short circuit current of 3.67 mA cm^?2, fill factor of 0.62, and light-to-energy conversion efficiency of 2.68%.     

Study for AC Loss Reduction in Bi2223 Tapes by Introducing Oxide Barriers

This paper presents our recent activities for the development of low-loss Bi2223 tapes with interfilamentary oxide barriers. In order to suppress the side effect on Bi2223 phase formation during sintering process, SrZrO₃ was selected as barrier materials. Moreover, small amount of Bi2212 was mixed with SrZrO₃ to improve their ductility for cold working. By controlling coating thickness of oxide barriers before stacking, reducing a tape width below 3 mm and careful twisting of the filaments with its length below 5 mm, coupling frequency f _c exceeded 250 Hz even in an AC perpendicular magnetic field. Critical current densities J _c of tightly twisted barrier tapes were ranged in 12?C14 kA/cm² at 77 K and self-field, which was 25% lower than the nontwisted one (=18 kA/cm²). To our knowledge, this is the first result to achieve both J _c>12 kA/cm² and f _c>250 Hz simultaneously for Bi2223 tapes in an isolated state. These twisted barrier tapes showed 60?C70% lower perpendicular field losses than a conventional 4 mm-width tape with fully coupled filaments at 50 mT and 50 Hz.     

The Effect of Eu Substitution onto Ca Site in Bi(Pb)-2223 Superconductor Via Co-precipitation Method

The samples with nominal composition of Bi₁₆Pb_0.4Sr₂Ca_2?x Eu _x Cu₃O _y where x=0.000, 0.025, 0.050, 0.100, and 0.200 prepared by co-precipitation method (COP) have been investigated. They were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), electrical and resistivity measurement using the four-probe method. The temperature dependency on electrical resistance showed the superconducting behavior for all the samples. The critical current density (J _c ) and superconductivity transition temperature (T _c?zero) of Eu substituted were found to be lower than those of the pure sample. T _c?zero varied between 100 and 73 K towards Eu concentration with the highest T _c?zero in the Eu substitution was found at 98 K for x=0.025 and decreased gradually for further substitution of Eu corresponding to a small change in the carrier concentration. J _c decreased with increasing Eu substitution, and it was measured to be at 5.7512 A/cm² in the Eu free sample and at 2.1223 A/cm² for the x=0.025 sample at 77 K. XRD analyses showed the decrease of the volume fraction of Bi-2223/Bi-2212 (%) which were estimated from 78.13/21.87 for x=0.000 to 23.18/76.82 for x=0.200. The crystallographic structure was found to change slightly from tetragonal to orthorhombic in Eu substituted samples. The lattice parameter c of the Eu samples decreased due to the incorporation of Eu³⁺ (0.95 Å) with smaller ionic size at the Ca²⁺ (0.99 Å) site. From the SEM investigation, the grain connectivity became weak and the porosity increased with the increment of Eu concentration, resulting in the decrease of J _c .     

Fabrication of BSCCO Films on SrTiO3 Substrates Using Ultrasonic Spray Pyrolysis (USP) Technique

In this study, the BiSrCaCuO (Bi-2212) films on SrTiO₃ substrates were fabricated using an ultrasonic spray pyrolysis technique (USP). Structural, electrical, magnetic, and critical current density, J _c, properties of the films fabricated were investigated under different heat treatment conditions. XRD analysis showed that the films mainly consisted of the Bi-2212 phase, but the Bi-2223 phase was also detected. T _c values of the films were found between 81 K and 88 K, depending on the heat treatment conditions. J _c values of the films were calculated using the Beans’ equation. Highest J _c value was found to be 2.93×10⁵ A?cm^?2 at 5 K and 0 T for Film C. The results obviously showed that USP method is a very effective technique for fabrication of the HT _c films having high J _c values as well as its simplicity, low cost, and easily coating.     

Fabrication and properties of SiNO continuous fiber reinforced BN wave-transparent composites

SiNO continuous fiber reinforced boron nitride (BN) wave-transparent composites (SiNO _f /BN) have been fabricated by a precursor infiltration pyrolysis (PIP) method using borazine as the precursor. The densification behavior, microstructures, mechanical properties, and dielectric properties of the composites have been investigated. After four PIP cycles, the density of the composites had increased from 1.1 g·cm^?3 to 1.81 g·cm^?3. A flexural strength of 128.9 MPa and an elastic modulus of 23.5 GPa were achieved. The obtained composites have relatively high density and the fracture faces show distinct fiber pull-out and interface de-bonding features. The dielectric properties of the SiNO _f /BN composites, including the dielectric constant of 3.61 and the dielectric loss angle tangent of 5.7×10^?3, are excellent for application as wave-transparent materials.     

Effects of High Pressure on the Physical Properties of MgB2

The synthesis of MgB₂-based materials under high pressure gave the possibility to suppress the evaporation of magnesium and to obtain near theoretically dense nanograined structures with high superconducting, thermal conducting, and mechanical characteristics: critical current densities of 1.8?C1.0×10⁶ A/cm² in the self-field and 10³ A/cm² in a magnetic field of 8 T at 20 K, 5?C3×10⁵ A/cm² in self-field at 30 K, the corresponding critical fields being H _c2=15 T at 22 K and irreversible fields H _irr=13 T at 20 K, and H _irr=3.5 T at 30 K, thermal conduction of 53±2 W/(m?K), the Vickers hardness H _V =10.12±0.2 GPa under a load of 148.8 N and the fracture toughness K _1C =7.6±2.0 MPa?m^0.5 under the same load, the Young modulus E=213 GPa. Estimation of quenching current and AC losses allowed the conclusion that high-pressure-prepared materials are promising for application in transformer-type fault current limiters working at 20?C30 K.     

Scanning of nickel sulfamate concentration in electrodeposition bath used for production of Ni–Co alloys

The Ni–Co films were produced by using the electrodeposition technique from the electrolytes with different Ni(SO₃·NH₂)₂·4H₂O concentrations (from 0 to 0.45 M). The Ni content of the films changed gradually from 0 to 57 %. The Ni–Co system exhibited anomalous codeposition. For 0 at.% Ni content, the saturation magnetization, M_s of the film was found to be 1298 emu/cm³, which is close to that of bulk Co (1420 emu/cm³). As the Ni content increased, M_s decreased since the M_s value of bulk Ni (480 emu/cm³) is lower than that of bulk Co. The coercivity, H_c, of Co film was found as 37 Oe. When the Ni content increased to 6 at.%, the H_c value dramatically increased to 109 Oe. The hexagonal closed packed (hcp) structure was observed for the films containing 0 and 6 at.% Ni. When the Ni content increased to 25 at.%, a mixed phase of face centered cubic (fcc) and hcp structure (mostly fcc) was detected. For further increase in Ni content (39 and 57 at.%), the peaks which occurred from the reflections of fcc phase were obtained. As a result of structural analysis, the Co content can be determined as 62–64 at.% for changing of crystal structure. The transfiguration from spherical granular to acicular surface morphology occurred around 75 at.% Co content. Magnetoresistance of the films was measured and it was found that the films show anisotropic magnetoresistance.     

Measurements of Specific Heat Capacity of Gaseous R-143a Using a Flow Calorimeter

The isobaric specific heat capacity (c _p ) was measured for R-143a (1,1,1-trifluoroethane) in the gas phase. Ten measurements for R-143a were obtained at temperatures from 311 to 343 K and at pressures from 1.6 to 2.4 MPa. Some of them are close to the saturation curve. The expanded uncertainty (k = 2) of the temperature measurements is estimated to be less 25 mK, and that of the pressure measurements is less 8 kPa. The expanded uncertainty for c _p is estimated to range from 9 to 32 J·kg⁻¹·K⁻¹. Also, the experimental data were evaluated with available equations of state.