Basic thermophysical parameters of langasite (La3Ga5SiO14), langatate (La3Ta0.5Ga5.5O14), and catangasite (Ca3TaGa3Si2O14) single crystals in a temperature range of 25 to 1000°C

The thermophysical parameters (thermal diffusivity ??, heat conductivity ??, thermal expansion, and specific heat c _p coefficients) of single crystals from the langasite family are investigated in the basic crystallographic directions of X, Y, and Z in temperature range of 300 to 1300 K. The temperature dependences of the parameters are determined. It is found that their anisotropy decreases with temperature.     

Optimization of hydrostatic pressure at varied sonication conditions – power density,intensity, very low frequency – for isothermal ultrasonic sludge treatment

This work aims at investigating for the first time the key sonication (US) parameters: power density (D_US), intensity (I_US), and frequency (F_S) – down to audible range, under varied hydrostatic pressure (P_h) and low temperature isothermal conditions (to avoid any thermal effect).The selected application was activated sludge disintegration, a major industrial US process. For a rational approach all comparisons were made at same specific energy input (ES, US energy per solid weight) which is also the relevant economic criterion.The decoupling of power density and intensity was obtained by either changing the sludge volume or most often by changing probe diameter, all other characteristics being unchanged. Comprehensive results were obtained by varying the hydrostatic pressure at given power density and intensity. In all cases marked maxima of sludge disintegration appeared at optimum pressures, which values increased at increasing power intensity and density. Such optimum was expected due to opposite effects of increasing hydrostatic pressure: higher cavitation threshold then smaller and fewer bubbles, but higher temperature and pressure at the end of collapse.In addition the first attempt to lower US frequency down to audible range was very successful: at any operation condition (D_US, I_US, P_h, sludge concentration and type) higher sludge disintegration was obtained at 12 kHz than at 20 kHz. The same values of optimum pressure were observed at 12 and 20 kHz.At same energy consumption the best conditions – obtained at 12 kHz, maximum power density 720 W/L and 3.25 bar – provided about 100% improvement with respect to usual conditions (1 bar, 20 kHz). Important energy savings and equipment size reduction may then be expected.     

Temperature dependence of effective thermal conductivity and effective thermal diffusivity of Se90In10 bulk chalcogenide glass

Measurement of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) of twin pellets of Se₉₀In₁₀ bulk chalcogenide glass has been carried out in the temperature range from 303 to 323 K and cooling from 323 to 303 K using transient plane source (TPS) technique. In the heating process variation of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) is observed. Both quantities are found to be maximum at 313 K, which lies in the vicinity of glass transition temperature (T_g). During the cooling process λ_e and χ_e remain same at all temperatures. Such type of behavior shows thermal hysteresis in this sample, which can be explained on the basis of structural change of the Se₉₀In₁₀ bulk chalcogenide glass.     

Thermal diffusivity measurement of YBa2Cu3O7−x thin film with a picosecond thermoreflectance technique

The thermal diffusivity of YBa₂Cu₃O_7?x (YBCO) film was measured using the optical pump–probe method. A theoretical finite-difference model was employed to calculate the diffusivity value, and the best fit for the c-axis oriented YBCO film showed an average thermal diffusivity of 0.25 ± 0.05 mm² s^?1. The obtained result is compared to previous reports measured using various methods.     

Magnetic behaviour of arrays of nickel nanowires with small diameter

Arrays of nickel nanowires have been fabricated within a template of porous alumina by electrochemical deposition. Measurements of magnetic hysteresis loops were performed at room temperature with a vibrating sample magnetometer. Coercivity and squareness of the arrays are closely related to l/D and diameter of the nanowires, and the angle θ between the normal line of the alumina surface and the applied magnetic field. For the same diameter of 10 nm, the coercivity and squareness increase remarkably with l/D when the l/D is less than 100. The diameter and angle θ dependences of coercivity do not follow the relationships of curling, fanning or coherent rotation mode of magnetization while thermal activation for magnetization reversal becomes remarkable for the arrays of Ni nanowires with the diameter less than 18 nm but the same l/D of 50. The coercivity of the arrays with the magnetic field perpendicular to the film surface is linear with D^−3/2 of Ni nanowires. From the fitting line, the critical diameter for superparamagnetism at room temperature and pure coercivity for such Ni nanowire arrays are found to be 6 nm and 1200 Oe respectively.     

Elastic and thermal properties of Zr z Nb1 − z C x N y solid solutions

The temperature and concentration dependences of the elastic moduli and the thermal linear expansion coefficient of Zr _z Nb_{1 ? z} C _x N _y solid solutions containing from 3 to 8 at % of structural vacancies in a nonmetallic sublattice have been found. The temperature dependences of the Debye temperature Θ_D(T) have been calculated using the elastic data and the data on the heat capacity. It has been shown, using carbide NbC_0.97 as an example, that the Θ_D(T) dependences found from the elastic properties and the heat capacity coincide in the temperature range ～220–300 K. By analogy with the niobium carbide, the heat capacity C _p (300) of Zr _z Nb_{1 ? z} C _x N _y solid solutions of various compositions is calculated based on the values of Θ_D(300) determined from the elastic properties.     

Thermal conductivity and thermal diffusivity of SiO<Subscript>2</Subscript> nanopowder

A 3ω approach for the simultaneous determination of the effective thermal conductivity and thermal diffusivity of nanopowder materials was developed. A 3ω experimental system was established, and the thermal properties of water and alcohol were measured to validate and estimate the accuracy of the current experimental system. The effective thermal conductivity and thermal diffusivity of the SiO₂ nanopowder with 375, 475, and 575 nm diameters were measured at 290–490 K and at different densities. At room temperature, the effective thermal conductivity and thermal diffusivity of the SiO₂ nanopowder increased with temperature; however, both values decreased as the particle diameter was reduced. An optimum SiO₂ powder density that decreased with decreasing diameter was also observed within the measurement range. The minimum effective thermal conductivity and maximum effective thermal diffusivity were obtained at 85 × 10⁻³ kg/L, when the particle diameter was 575 nm. The optimum densities of the particles with 375 and 475 nm diameters were less than 50.23 × 10⁻³ and 64.82 × 10⁻³ kg/L, respectively.     

Formation and photoluminescence of Y2O3–H3BO3:Eu3+ powders by mechanical alloying

Y₂O₃–H₃BO₃:Eu³⁺ powders were synthesized by the mechanical alloying (MA) method, and their structural and photoluminescent characteristics were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG/DTA), and luminescence spectrophotometer. The crystallite size of the powder mixture milling for 30 minutes (min) by the Willaimson–Hall method was approximately 58.8 nm with strain of 0.00141; overall, the internal strain increased with the milling time (t_m). The morphology of the powder mixture with t_m, as observed by SEM, divided into three different stages: agglomeration (0 < t_m ≤ 30 min), disintegration (30min < t_m ≤ 120 min), and homogenization (120min < t_m ≤ 300 min). The transition temperature and the weight reduction rate of the sample powders were 645.58 °C and 2.851%, respectively. Furthermore, the photoluminescence of the powder mixture excited to 240 nm by a zenon discharge lamp (20 kW) was detected near 592 nm(⁵D_o → ⁷F₁), 613 nm, 628  (⁵D_o → ⁷F₂), and 650 nm (⁵D_o → ⁷F₃).     

Energy transfer induced Eu3+ photoluminescence enhancement in tellurite glass

In this work, structural, thermal and optical properties of Eu³⁺ doped TeO₂–La₂O₃–TiO₂ glass were investigated. The differential scanning calorimetry (DSC) measurements reveal an important stability factor ΔT=143.52 K, which indicates the good thermal and mechanical stabilities of tellurite glass. From the absorption spectrum, the optical band gap was found to be direct with E_g=3.23 eV. The temperature dependences of photoluminescence (PL) properties of Eu-doped and Eu–Tb codoped tellurite glass are investigated. As the temperature increases from 7 to 300 K, both the PL intensity and the PL lifetime relative to the ⁵D₂→⁷F₀ are nearly constant below 230 K and then an enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from charged intrinsic defects states to Eu³⁺ energy levels.By co-doping tellurite glasses with Eu and Tb, a strong Eu³⁺ PL enhancement is shown due to excitation transfer from Tb³⁺ and intrinsic defects to Eu ions.     

Synergetic effects of ultrasound and sodium alginate coating on mass transfer and qualities of osmotic dehydrated pumpkin

This research studied the effects of combined ultrasound and 3% sodium alginate (SA) coating pretreatment (US + Coat) on mass transfer kinetics, quality aspects, and cell structure of osmotic dehydrated (OD) pumpkin. The results of the pretreatment were compared with the results of control (non-pretreated osmotic dehydration) and other three pretreatment methods, which were 1) ultrasound in distilled water for 10 min (USC), 2) ultrasound in 70% (w/w) sucrose solution (US) for 10, 20 and 30 min, and 3) coating with 1%, 2%, 3% (w/w) SA. The coating pretreatments with SA resulted in a higher water loss (WL) but lower water activity and solid gain (SG) than other treatments. US pretreatments resulted in the highest effective diffusion coefficients of water (D_w) and solid (D_s) but the cell structure of the product was deformed. The 3% SA coating treatment had the highest WL/SG (5.28) but with the longest OD time (12 h). Using the US + Coat pretreatment gave satisfactory high WL/SG (5.18), D_w (1.09 × 10⁻¹⁰ m²s⁻¹) and D_s (5.15 × 10⁻¹¹ m²s⁻¹), reduced the OD time to 9 h, and preserved the cell structure of the product. This research suggests that US + Coat pretreatment can be an effective processing step in the production of OD pumpkin.     

Thermoelectric properties of SnzCo8Sb24 skutterudites

Sn-filled CoSb₃ skutterudite compounds were synthesized by the induction melting process. Formation of a single δ-phase of the synthesized materials was confirmed by X-ray diffraction analysis. The temperature dependences of the Seebeck coefficient, electrical resistivity and thermal conductivity were examined in the temperature range of 300-700 K. Positive Seebeck and Hall coefficients confirmed p-type conductivity. Electrical resistivity increased with increasing temperature, which shows that the Sn-filled CoSb₃ skutterudite is a degenerate semiconductor. The thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. The lowest thermal conductivity was achieved in the composition of Sn_0.25Co₈Sb₂₄.     

Effect of ultrasound and high hydrostatic pressure (US/HHP) on the degradation of dextran catalyzed by dextranase

In our current research work, the effect of combination of ultrasonic irradiation and high hydrostatic pressure (US/HHP) on the enzymatic activity and enzymatic hydrolysis kinetic parameters of dextran catalytic by dextranase were investigated. Furthermore, the effects of US/HHP on the structure of dextranase were also discussed with the aid of fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The maximum hydrolysis of dextran was observed under US (40 W at 25 kHz for 15 min) combined with HHP (400 MPa for 25 min), in which the hydrolysis of dextran increased by 163.79% compared with the routine thermal incubation at 50 °C. Results also showed that, V_max and K_M values, as well as, k_cat of dextranase under US/HHP treatment were higher than that under US, HHP and thermal incubation at 50 °C, indicated that, the substrate is converted into the product at an increased rate when compared with the incubation at 50 °C. Compared to the enzymatic reaction under US, HHP, and routine thermal incubation, dextranase enzymatic reaction under US/HHP treatment showed decreases in Ea, ΔG and ΔH, however small increase in ΔS value was observed. In addition, fluorescence and CD spectra reflected that US/HHP treatment had increased the number of tryptophan on dextranase surface with increased α-helix by 19.80% and reduced random coil by 6.94% upon US/HHP-treated dextranase protein compared to the control, which were helpful for the improvement of its activity. These results indicated that, the combination of US and HHP treatments could be an effective method for improving the hydrolysis of dextran in many industrial applications including sugar manufacturing processes.     

The role of heat-conducting walls in the measurement of heat and mass transport in transient grating experiments

We present a two-dimensional model to account for the role of heat-conducting walls in the measurement of heat transport and Soret-effect-driven mass transport in transient holographic grating experiments. Heat diffusion into the walls leads to non-exponential decay of the temperature grating. Under certain experimental conditions it can be approximated by an exponential function and assigned an apparent thermal diffusivity D_{th, app} < D_{th, s}, where D_th,s is the true thermal diffusivity of the sample. The ratio D_{th, app}/D_{th, s} depends on only three dimensionless parameters, d /l_s, κ_s/κ_w, and D_{th, s}/D_{th, w}. d is the grating period, l_s the sample thickness, κ_s and κ_w the thermal conductivities of sample and wall, respectively, and D_th,w the thermal diffusivity of the wall. If at least two measurements are performed at different d /l_s, both D_th,s and κ_s can be determined. Instead of costly solving PDEs, D_th,s can be obtained by finding the zero of an analytic function. For thin samples and large grating periods, heat conduction into the walls plays a predominant role and the concentration grating in binary mixtures is no longer one-dimensional. Nevertheless, the normalized heterodyne diffraction efficiency of the concentration grating remains unaffected and the true thermal and collective diffusion coefficient and the correct Soret coefficient are still obtained from a simple one-dimensional model.     

Thermal diffusivity and electrical conductivity in fast ion conducting composites: A correlation

The thermal diffusivity and electrical conductivity have been measured for two ion conducting polyethylene oxide (PEO) based polymer–ceramic composites viz. (PEO:NH₄I) + xAl₂O₃, (PEO:LiBF₄) + xBa_0.70Sr_0.30TiO₃ and two solid–solid composites viz. AgI + xAl₂O₃, AgI +xBa_0.70Sr_0.30TiO₃. The thermal diffusivity has been measured by the novel photoacoustic technique while the electrical conductivity has been measured by impedance spectroscopy technique using complex impedance plots. The pattern of variation in the electrical conductivity (σ) vs. composition plot and that in the thermal diffusivity (α_s) vs. composition plot are similar. Interestingly, the correlation between α_s and σ is not only qualitative but is quantitative as well in the sense that the ratio (α_s / σ) remains constant for all the samples within the same system (though their conductivities are different) similar to Wiedmann–Franz law applicable to metallic conductors.     

Crystal structure,thermal expansion and magnetic properties of Nd2Cu0.8Ge3 compound

A new ternary intermetallic compound, Nd₂Cu_0.8Ge₃, was synthesized and its crystal structure was determined by Rietveld refinement of X-ray powder diffraction data. The Nd₂Cu_0.8Ge₃ compound crystallizes in space group I4₁/amd (No. 141), with a tetragonal a-ThSi₂ structure type, and a=0.41783(2) nm, c=1.43689(9) nm, Z=2 and D_calc=7.466 g/cm³. Using the high temperature powder X-ray diffraction (HTXRD) technique, the lattice thermal expansion behavior of the compound was investigated in the temperature range of 298–648 K, and the result shows that its unit-cell parameters increased anisotropically when temperature increased. The magnetic susceptibility measured in the temperature range of 5–300 K indicated antiferromagnetic order of Nd₂Cu_0.8Ge₃ at low temperatures, and the magnetic susceptibility can be well described over the range of 50–300 K using Curie–Weiss law. The calculated effective magnetic moment (μ_eff) is 3.53 μ_B and dominated by the contribution of the Nd³⁺ ions.     

ESR spectra and thermal diffusivity of Zn–Al layered double hydroxide

Zn–Al–NO₃–LDH was synthesized using the co-precipitation method at pH 7±0.1 and ratio Zn/Al=4. The heat treatment of LDH was studied by X-ray diffraction (XRD) and thermogravimetric analysis (TGA/DTG) to investigate the stability of the LDH structure. The in situ electron spin resonance (ESR) spectra of fresh LDH from room temperature up to 190 °C were obtained, which are due to the presence of nitrate radicals in LDH interlayer. ESR spectra of sintered LDH below 200 °C (ex situ ESR spectra) were investigated, which are also due to the nitrate radicals. However, at 200 °C and above, spectra were due to the oxygen vacancies of ZnO, which was formed during the thermal treatment of LDH. Thermal diffusivity of LDH as a function of in situ temperatures results in a nonlinear relation, which is due to the changing water content of LDH when temperature increases. However, thermal diffusivity of LDH as a function of sintered temperatures showed a linear relation and the slope of these data demonstrated the dependency between thermal diffusivity and water content of LDH below 200 °C. For temperature above 180 °C, the thermal diffusivity behavior was mainly due to the ZnO phase in LDH.     

A Boubaker polynomials expansion scheme (BPES)-related protocol for measuring sprayed thin films thermal characteristics

Measurements of In₂S₃ and ZnIn₂S₄ sprayed thin films thermal characteristics have been carried out using the photodetection technique. The thermal conductivity k and diffusivity D were obtained using a new protocol based on photothermal signal parameters analysis. Measured values of k and D were respectively, (15.2 ± 0.85) W m⁻¹K⁻¹ and (69.8 ± 7.1) × 10⁻⁶ m²s⁻¹ for In₂S₃, (7.2 ± 0.7) W m⁻¹K⁻¹ and (32.7 ± 4.3) × 10⁻⁶ m²s⁻¹ for ZnIn₂S₄. These values are extremely important since similar compounds are more and more proposed as Cd-free alternative materials for solar cells buffer layers.     

Thermal lens investigation in amorphous SiN

In this work we report the use of thermal lens (TLs) technique to determine the thermo-optical parameters, such as thermal conductivity (K), thermal diffusivity (D) and the optical path dependence with temperature (ds/dT) of amorphous SiN. Our results indicate that ds/dT is positive at room temperature. Moreover, the obtained values of thermal diffusivity and thermal conductivity are in good agreement with that found in the literature.     

Effects of double filling of Pb and Ba on thermoelectric properties of PbxBayCo4Sb11.5Te0.5 compounds by HPHT

Skutterudite compounds Pb_xBa_yCo₄Sb_11.5Te_0.5 (x≤0.23,y≤0.27) with bcc crystal structure have been prepared by the high pressure and high temperature (HPHT) method. The study explored a chemical method for filling Pb and Ba atoms into the voids of CoSb₃ to optimize the thermoelectric figure of merit ZT in the system of Pb_yBa_xCo₄Sb_11.5Te_0.5. The structure of Pb_xBa_yCo₄Sb_11.5Te_0.5 skutterudites was evaluated by means of X-ray diffraction. The Seebeck coefficient, electrical resistivity and power factor were performed from room temperature to 710 K. Compared with Co₄Sb_11.5Te_0.5, the thermal conductivity of Pb and Ba double-filled samples was reduced evidently. Among all filled samples, Pb_0.03Ba_0.27Co₄Sb_11.5Te_0.5 showed the highest power factor of 31.64 μW cm⁻¹ K⁻² at 663 K. Pb_0.05Ba_0.25Co₄Sb_11.5Te_0.5 showed the lowest thermal conductivity of 2.73 W m⁻¹ K⁻¹ at 663 K, and its maximum ZT value reached 0.63 at 673 K.     

Thermal diffusivity of MORB-composition rocks to 15 GPa: implications for triggering of deep seismicity

We have measured the thermal diffusivity of eclogite and majorite with a model MORB composition at pressures of 3 and 15 GPa, respectively. Both phase assemblages show inverse dependences of their thermal diffusivities on temperature: D _eclogite=9(10)×10^?10+7(1)×10^?4/T(K) m ²/s and D _majorite=6.2(5)×10^?7+3.0(5)×10^?4/T(K) m ²/s. The values for majorite are in good agreement with previous measurements for other garnets and are considerably lower than thermal diffusivities of wadsleyite and ringwoodite, which are the main components of the mantle transition zone. We discuss the implications of the low thermal conductivity of subducted oceanic crust in the transition zone for the triggering of deep seismicity.