Growth, thermal and spectroscopic characteristics of LiNd(WO4)2 crystal

Crystal growth, thermal and optical characteristics of LiNd(WO₄)₂ crystal have been investigated. The LiNd(WO₄)₂ crystal up to Ø15 × 32 mm³ has been grown by Czochralski technique. The hardness is about 5.0 Mohs’ scale. The specific heat at 50 °C is 0.42 J g⁻¹ K⁻¹. The thermal expansion coefficient for c- and a- axes is 1.107 × 10⁻⁵ and 2.104 × 10⁻⁵ K⁻¹, respectively. The absorption and fluorescence spectra and the fluorescence decay curve of LiNd(WO₄)₂ crystal were measured at room temperature. Some spectroscopic parameters such as the intensity parameters, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and emission cross sections were estimated.     

Anisotropic thermal expansion of stoichiometric lithium niobate crystals grown along the normal direction of facets

In this paper, a stoichiometric lithium niobate (SLN) crystal with the size up to 20 × 20 × 18 mm³ was grown along the normal direction of the (0 1 2) facet from the 16 mol% K₂O fluxed melt by the top-seeded solution growth method. The anisotropic thermal expansion of the SLN crystal and congruent lithium niobate (CLN) crystal was measured along different directions by using a Shimadzu thermomechanical analyzer. As compared with CLN, the SLN crystal exhibited slightly larger thermal expansion along the Z-axis and slightly smaller expansion along the X-axis. Both the SLN and CLN crystals showed strong anisotropy in the thermal expansion. The thermal expansion coefficient of SLN along the X-axis (16.7 × 10⁻⁶ °C⁻¹ at 300 °C) is much larger than that along the Z-axis (2.5 × 10⁻⁶ °C⁻¹ at 300 °C). Based on the experimental data and polynomial fitting results, we calculated the thermal expansion coefficients for different directions. In the case of growing the SLN crystal along the normal direction of (0 1 2) facet, we studied the radial anisotropic thermal expansion and discussed the cracking problem of the crystal according to its actual growth morphology. It is found that the cracks of SLN can be suppressed by growing the crystal along the W-axis due to its reduced radial anisotropy in the thermal expansion.     

Kapitza resistance and thermal conductivity of Mylar at superfluid helium temperature

The Kapitza resistance and the thermal conductivity of type A Mylar sheets in the temperature range between 1.4 and 2.1 K have been determined. Four sheets with varying thickness from 37 μm to 255 μm, have been tested in steady-state condition. For a small temperature difference (10-30 mK) and heat flux density smaller than 30 Wm⁻², the total thermal resistance of the sheet is determined as a function of sheet thickness and bath temperature. The Kapitza resistance is given by R_K = (1.28 ± 0.08)T⁻³ × 10⁻³ Km² W⁻¹, and the thermal conductivity, κ = [(8.83 ± 0.75) + (11.73 ± 0.43) × T] × 10⁻³ Wm⁻¹ K⁻¹.     

Composite adsorbent of CaCl2 and expanded graphite for adsorption ice maker on fishing boats

Adsorption performances and thermal conductivity were tested for three types of adsorbent: Pure CaCl₂ powder, simple composite adsorbent and consolidated composite adsorbent. The simple composite adsorbents show better adsorption performance because the additive of expanded graphite in CaCl₂ powder has restrained the agglomeration phenomenon in adsorption process and improved the adsorption performance of CaCl₂. The consolidated composite adsorbent are suitable to be used as adsorbent for ice maker on fishing boats because they have higher thermal conductivity, larger volumetric cooling capacity, higher SCP values and better anti-sway performance than simple composite adsorbents. Thermal conductivity of the consolidated composite adsorbent is 6.5–9.8 W m⁻¹ K⁻¹ depending on the molding pressure, ranging from 5 to 15 MPa, which is about 32 times higher than the thermal conductivity of CaCl₂ powder. The volumetric cooling capacity of consolidated composite adsorbent is about 52% higher than the best result obtained for CaCl₂ at the evaporating temperature of −10 °C. The SCP of the consolidated adsorbent increases of about 353% than CaCl₂ powder from simulation results at T_ad=30 °C and T_ev=−10 °C. The consolidated composite adsorbents have good anti-sway performance and they are not easy to be scattered out when the fishing boats sway on the sea.     

Electrical and optical properties of 12CaO·7Al2O3 electride doped indium tin oxide thin film deposited by RF magnetron co-sputtering

12CaO·7Al₂O₃ electride (C12A7:e⁻) doped indium tin oxide (ITO) (ITO:C12A7:e⁻) thin films were fabricated on a glass substrate by an RF magnetron co-sputtering system with increasing number of C12A7:e⁻ chips (from 1 to 7) and at various oxygen partial pressure ratios. The optical transmittance of the ITO:C12A7:e⁻ thin film was higher than 70% in the visible wavelength region. In the electrical properties of the thin film, a decrease of the carrier concentration from 2.6 × 10²⁰ cm^− 3 to 2.1 × 10¹⁸ cm^− 3 and increase of the resistivity from 1.4 × 10^− 3 Ω cm to 4.1 × 10^− 1 Ω cm were observed with increasing number of C12A7:e⁻ chips and oxygen partial pressure ratios. It was also observed that the Hall mobility was decreased from 17.27 cm²·V^− 1·s^− 1 to 5.13 cm²·V^− 1·s^− 1. The work function of the ITO thin film was reduced by doping it with C12A7:e⁻.     

Solid–liquid interfacial energy of camphene

The Gibbs–Thomson coefficient and the solid–liquid interfacial energy for camphene have been measured to be (8.58±0.96)×10⁻⁸ K m and (4.43±0.49)×10⁻³ J m⁻², respectively, by a direct method. The grain boundary energy of camphene has also been calculated to be (8.36±0.92)×10⁻³ J m⁻² from the observed grain boundary groove shapes.     

Plastic deformation behavior in dual-phase Ni–31Al intermetallics at elevated temperature

Plastic deformation behavior of dual-phase Ni–31Al intermetallics at elevated temperature was examined. It was found that the alloy exhibited good plasticity under an initial strain rate of 1.25 × 10⁻⁴ s⁻¹ to 8 × 10⁻³ s⁻¹ in a temperature range of 950–1075 °C. A maximum elongation of 281.3% was obtained under an initial strain rate of 5 × 10⁻⁴ s⁻¹ at 1000 °C. The strain rate sensitivity, m value was correlated with temperature and initial strain rate, being in the range of 0.241–0.346. During plastic deformation, both the two phases Ni₃Al and NiAl in dual-phase Ni–31Al could co-deform without any void formation or debonding, the initial coarse microstructure became much finer after plastic deformation. Dislocation played an important role during the plastic deformation in dual-phase Ni–31Al alloy, the deformation mechanism in dual-phase Ni–31Al could be explained by continuous dynamic recovery and recrystallization.     

Microstructures and thermoelectric properties of p-type pseudo-binary AgxBi0.5Sb1.5−xTe3 (x = 0.05–0.4) alloys prepared by cold pressing

The p-type pseudo-binary Ag_xBi_0.5Sb_1.5−xTe₃ (x = 0.05–0.4) alloys were prepared by cold pressing. The thermal conductivities (κ) were calculated from the values of heat capacities, densities and thermal diffusivities measured, and range approximately from 0.66 to 0.56 (W K^− 1 m^− 1) for the Ag_xBi_0.5Sb_1.5−xTe₃ alloy with molar fraction x being 0.4. Combining with the electrical properties obtained in the previous study, the maximum dimensionless figure of merit ZT of 1.1 was obtained at the temperature of 558 K.     

Three-dimensional measurement of ice crystals in frozen dilute solution

A Micro-Slicer Image Processing System (MSIPS) has been applied to observe the ice crystal structures formed in frozen dilute solutions. Several characteristic parameters were also proposed to investigate the three-dimensional (3-D) morphology and distribution of ice crystals, based on their reconstructed images obtained by multi-slicing a frozen sample with the thickness of 5 μm. The values of characteristic parameters were determined for the sample images with the dimension of 530×700×1000 μm. The 3-D morphology of ice crystals was found to be a bundle of continuous or dendrite columns at any freezing condition. The equivalent diameter of ice crystals were in the range of 73–169 μm, and decreased exponentially with increasing freezing rate at the copper cooling plate temperature of −20 to −80 °C. At the T_cp −40 °C, the volumes of ice crystals were in the range of 4.6×10⁴ μm³ to 3.3×10⁷ μm³, and 36 ice columns were counted in the 3-D image.     

High-temperature oxygen non-stoichiometry, conductivity and structure in strontium-rich nickelates La2−xSrxNiO4−δ (x = 1 and 1.4)

Oxygen non-stoichiometry, electrical conductivity and thermal expansion of La_2−xSr_xNiO_4−δ phases with high levels of strontium-substitution (1 ≤ x ≤ 1.4) have been investigated in air and oxygen atmosphere in the temperature range 20–1050 °C. These phases retain the K₂NiF₄-type structure of La₂NiO₄ (tetragonal, space group I4/mmm). The oxygen vacancy fraction was determined independently from thermogravimetric and neutron diffraction experiments, and is found to increase considerably on heating. The electrical resistivity, thermal expansion and cell parameters with temperature show peculiar variations with temperature, and differ notably from La₂NiO_4±δ in this respect. These variations are tentatively correlated with the evolution of nickel oxidation state, which crosses from a Ni³⁺/Ni⁴⁺ to a Ni²⁺/Ni³⁺ equilibrium on heating.     

Kinetics of zero-valent iron reductive transformation of the anthraquinone dye Reactive Blue 4

The effect of operational conditions and initial dye concentration on the reductive transformation (decolorization) of the textile dye Reactive Blue 4 (RB4) using zero-valent iron (ZVI) filings was evaluated in batch assays. The decolorization rate increased with decreasing pH and increasing temperature, mixing intensity, and addition of salt (100 g L⁻¹ NaCl) and base (3 g L⁻¹ Na₂CO₃ and 1 g L⁻¹ NaOH), conditions typical of textile reactive dyebaths. ZVI RB4 decolorization kinetics at a single initial dye concentration were evaluated using a pseudo first-order model. Under dyebath conditions and at an initial RB4 concentration of 1000 mg L⁻¹, the pseudo first-order rate constant (k_obs) was 0.029 ± 0.006 h⁻¹, corresponding to a half-life of 24.2 h and a ZVI surface area-normalized rate constant (k_SA) of 2.9 × 10⁻⁴ L m⁻² h⁻¹. However, as the initial dye concentration increased, the k_obs decreased, suggesting saturation of ZVI surface reactive sites. Non-linear regression of initial decolorization rate values as a function of initial dye concentration, based on a reactive sites saturation model, resulted in a maximum decolorization rate (V_m) of 720 ± 88 mg L⁻¹ h⁻¹ and a half-saturation constant (K) of 1299 ± 273 mg L⁻¹. Decolorization of RB4 via a reductive transformation, which was essentially irreversible (2–5% re-oxidation), is believed to be the dominant decolorization mechanism. However, some degree of RB4 irreversible sorption cannot be completely discounted. The results of this study show that ZVI treatment is a promising technology for the decolorization of commercial, anthraquinone-bearing, spent reactive dyebaths.     

High‐Performance Thermally Conductive Phase Change Composites by Large‐Size Oriented Graphite Sheets for Scalable Thermal Energy Harvesting

Efficient thermal energy harvesting using phase‐change materials (PCMs) has great potential for cost‐effective thermal management and energy storage applications. However, the low thermal conductivity of PCMs (K_PCM) is a long‐standing bottleneck for high‐power‐density energy harvesting. Although PCM‐based nanocomposites with an enhanced thermal conductivity can address this issue, achieving a higher K (>10 W m^?1 K^?1) at filler loadings below 50 wt% remains challenging. A strategy for synthesizing highly thermally conductive phase‐change composites (PCCs) by compression‐induced construction of large aligned graphite sheets inside PCCs is demonstrated. The millimeter‐sized graphite sheet consists of lateral van‐der‐Waals‐bonded and oriented graphite nanoplatelets at the micro/nanoscale, which together with a thin PCM layer between the sheets synergistically enhance K_PCM in the range of 4.4–35.0 W m^?1 K^?1 at graphite loadings below 40.0 wt%. The resulting PCCs also demonstrate homogeneity, no leakage, and superior phase change behavior, which can be easily engineered into devices for efficient thermal energy harvesting by coordinating the sheet orientation with the thermal transport direction. This method offers a promising route to high‐power‐density and low‐cost applications of PCMs in large‐scale thermal energy storage, thermal management of electronics, etc.     

Surface and grain-boundary energies as well as surface mass transport in polycrystalline CeO2

The multiphase equilibration technique for the determination of the equilibrium angles that develop at the interphase boundaries of a solid–liquid–vapor system, has been used to calculate the surface and interfacial energies in polycrystalline CeO₂ and CeO₂/Cu system in argon atmosphere at the temperature range 1473–1773 K. Linear temperature functions were obtained by extrapolation, for the surface energy γ_sv (J/m²) = 2.465–0.563 × 10⁻³ T and the grain-boundary energy γ_ss (J/m²) = 1.687–0.391 × 10⁻³ T of the ceramic, as well as for the interfacial energy γ_sl (J/m²) = 2.623–1.389 × 10⁻³(T −1356 K) of the CeO₂/Cu system. Grain-boundary grooving studied on polished surfaces of CeO₂ annealed in argon atmosphere at the same temperature range has shown that surface diffusion was the dominant mechanism for the mass transport. The surface diffusion coefficient can be expressed according to the equation D_s (m²/s) = 3.82 × 10⁻⁴ exp(−308,250/RT).     

Cu diffusion kinetics in (Cu, Ni)3Sn intermetallic compound nanolayers investigated by an Energy-Dispersive-X-ray-based permeation test

The Energy-Dispersive-X-ray-based permeation and oxidation test has been further developed by an improved theoretical analysis, in which chemical potential gradients rather than concentration gradients are employed. The developed test is able to characterize diffusion kinetics in diffusion barriers at the nanometer scale. The Cu flux coefficient in (Cu, Ni)₃Sn intermetallic compound nanolayers was determined from the test to be 8.48 × 10^− 15 mol·(m·s·J/mol)^–1 exp(− 52.3 kJ·mol^− 1/RT) in a temperature range of 250 °C–400 °C.     

Transient flow behaviour in a near alpha titanium alloy Timetal 834 in the dynamic strain aging regime

The transient flow behaviour in Timetal 834 titanium alloy was studied in the temperature range between 400 °C and 475 °C by means of stress relaxation and reloading during tensile testing at a strain rate of 6.67 × 10⁻⁴ s⁻¹. The increment in flow stress during reloading (Δσ_f) and the decrement in flow stress during stress relaxation (Δσ_r) were measured at different strains at each temperature. The observation of maximum value of Δσ_f and Δσ_r, normalized with respect to the Young's modulus at the corresponding temperature, confirmed that the maximum dynamic strain aging (DSA) effect in this alloy occurs at 450 °C.     

Effects of Ho2O3 addition on defects of BaTiO3

Effects of Ho₂O₃ addition on defects of BaTiO₃ ceramic have been studied in terms of electrical conductivity at 1200 °C as a function of oxygen partial pressure (P_O2°) and oxygen vacancy concentration. The substitution of Ho³⁺ for the Ti site in Ba(Ti_1−xHo_x)O_3−0.5x resulted in a significant shift of conductivity minimum toward lower oxygen pressures and showed an acceptor-doped behavior. The solubility limit of Ho on Ti sites was confirmed less than 3.0 mol% by measuring the electrical conductivity and the lattice constant. Oxygen vacancy concentrations were calculated from the positions of P_O2° in the conductivity minima and were in good agreement with theoretically estimated values within the solubility limit. The Curie point moved to lower temperatures with increasing the oxygen vacancy concentration and Ho contents.     

Sintering and characterization of fully dense aluminium nitride ceramics

Aluminium nitride ceramics with no sintering additives could be densified to close to theoretical density (99.6% theoretical) by pressureless sintering of tape-cast green sheets at 1900 °C for 8 h. The thermal conductivity and bending strength of the specimens were 114 Wm^–1 K^–1 and 240 MPa, respectively. The effect of Y₂O₃ additive on sinterability, thermal conductivity and microstructure of aluminium nitride ceramics was investigated. Thermal conductivity increased with increasing amount of Y₂O₃ additive, sintering temperature and holding time at the sintering temperature. Samples with a thermal conductivity up to 258 Wm^–1 K^–1 were fabricated by elimination of the grain-boundary phase.     

Thermophysical Property Measurements of Liquid and Supercooled Iridium by Containerless Methods

Thermophysical properties of equilibrium and supercooled liquid iridium were measured using noncontact diagnostic techniques in an electrostatic levitator. Over the 2300–3000 K temperature range, the density can be expressed as ρ (T)=19.5×10³ − 0.85(T− T_m) (kg·m⁻³) with T_m=2719 K. The volume expansion coefficient is given by 4.4 × 10⁻⁵ K⁻¹. In addition, the surface tension can be expressed as γ (T)=2.23 × 10³ − 0.17(T−T_m)(10⁻³N·m⁻¹) over the 2373–2833 K span and the viscosity as η(T)=1.85 exp [3.0× 10⁴/(RT)](10⁻³Pa·s) over the same temperature range.     

Dynamic strain aging effect on the fatigue resistance of type 316L stainless steel

Mechanism of dynamic strain aging (DSA) and its effect on the high-temperature low-cycle fatigue resistance in type 316L stainless steel were investigated by carrying out low-cycle fatigue tests in a wide temperature range from 20 to 650 °C with strain rates of 3.2×10⁻⁵–1×10⁻²/s. The regime of DSA was evaluated using the anomalous features of material behavior associated with DSA. The activation energies for each type of serration were about 0.57–0.74 times those for lattice diffusion indicating that a mechanism other than lattice diffusion is involved. It is reasonably concluded that the pipe diffusion of solute atoms along the dislocation core is responsible for DSA. Dynamic strain aging reduced the fatigue resistance by ways of multiple crack initiation, which comes from the DSA-induced inhomogeneity of deformation, and rapid crack propagation due to the DSA-induced hardening.     

Optical, electrical and magnetic properties of Co3O4 nanocrystallites obtained by thermal decomposition of sol–gel derived oxalates

Nanocrystallites of tricobalt tetraoxide (Co₃O₄) have been synthesized by sol–gel process using cobalt acetate tetrahydrate, oxalic acid as precursors and ethanol as a solvent. The process comprises of gel formation, drying at 80 °C for 24 h to obtain cobalt oxalate dihydrate (α-CoC₂O₄·2H₂O) followed by calcination at or above 400 °C for 2 h in air. These results combined with thermal analysis have been used to determine the scheme of oxide formation. The room temperature optical absorption spectra exhibits blue shift in both (i) ligand to metal (p(O²⁻) → e_g(Co³⁺), 3.12 eV), and (ii) metal to metal charge transfer transitions (a) t_2g(Co³⁺) → t₂(Co²⁺), 1.77 eV, (b) t₂(Co²⁺) → e_g(Co³⁺), 0.95 eV together with the d–d transitions (0.853 and 0.56 eV) within the Co²⁺ tetrahedra. The temperature dependent ac electrical and dielectric properties of these nanocrystals have been studied in the frequency range 100 Hz to 15 MHz. There are two regimes distinguishing different temperature dependences of the conductivity (70–100 K and 200–300 K). The ac conductivity in both the temperature regions is explained in terms of nearest neighbor hopping (NNH) mechanism of electrons. The carrier concentration measured from the capacitance (C)–voltage (V) measurements is found to be 1.05 × 10¹⁶ m⁻³. The temperature dependent dc magnetic susceptibility curves under zero field cooled (ZFC) and field cooled (FC) conditions exhibit irreversibilities whose blocking temperature (T_B) is centered at 35 K. The observed Néel temperature (T_N  25 K) is significantly lower than the bulk Co₃O₄ value (T_N = 40 K) possibly due to the associate finite size effects.