Further investigations on the thermophysical properties of gamma-irradiated urania-doped orthoferrites

(Y_1.85?U_0.15) FeO₃ orthoferrite was carefully prepared using the solid-state high temperature ceramic and sintering technique. On this orthoferrite, numerous measurements have been undertaken before and after 1.24 Mrad γ-absorbed dose, namely X-ray diffraction (XRD), DC-electrical conductivity versus temperature, UV/Vis. absorption, IR absorption, Mössbauer effect (ME) and EPR. In the present work the results obtained were explained, interpreted and discussed in details on the basis of lattice structure of the new perovskite investigated and the interaction of γ-radiation with the orthoferrite lattice.     

Magnetic properties of lanthanum orthoferrites containing lattice defects

Polycrystalline lanthanum orthoferrites were prepared by firing coprecipitated hydroxides of La³⁺ and Fe³⁺ at elevated temperatures. The materials fired at temperatures below 1100°C were characterized by the coexistence of such lattice vacancies that the concentration ratio of V_La:V_Fe:V_o is always equal to that of the constituent atoms of LaFeO₃. They exhibited a large magnetic susceptibility, a low Néel temperature, and a small spontaneous magnetization, in comparison with lanthanum orthoferrite without these vacancies. These characteristics originated essentially from a local reduction in anisotropic superexchange interaction at vacant sites. The lowering of Néel temperature characteristic of these materials was interpreted in terms of a decrease in the number of Fe³⁺OFe³⁺ linkages due to the existence of oxygen and iron vacancies.     

Adhesive properties of gamma-irradiated polyketone

The effect of polyketone (PK) γ-irradiation dose on the energy characteristics of the PK surface, the specific free surface energy, and the interfacial energy at the boundary between polar (water) and nonpolar (octane) liquids has been studied for the first time. The most significant changes in the energy characteristics of the surface occur at doses up to 100 kGy, and improvement in PK adhesion to the polar and nonpolar phases is observed at doses above 75 and 200 kGy, respectively.     

Thermophysical properties of SrHfO3 and SrRuO3

Polycrystalline samples of strontium series perovskite type oxides, SrHfO₃ and SrRuO₃ were prepared and the thermophysical properties were measured. The average linear thermal expansion coefficients are 1.13×10⁻⁵ K⁻¹ for SrHfO₃ and 1.03×10⁻⁵ K⁻¹ for SrRuO₃ in the temperature range between 423 and 1073 K. The melting temperatures T_m of SrHfO₃ and SrRuO₃ are 3200 and 2575 K, respectively. The longitudinal and shear sound velocities were measured by an ultrasonic pulse-echo method at room temperature in air, which enables to evaluate the elastic moduli and Debye temperature. The heat capacity was measured by using a differential scanning calorimeter, DSC in high-purity argon atmosphere. The thermal diffusivity was measured by a laser flash method in vacuum. The thermal conductivities of SrHfO₃ and SrRuO₃ at room temperature are 5.20 and 5.97 W m⁻¹ K⁻¹, respectively.     

Thermophysical properties of 1-methyl-3-methylimidazolium dimethylphosphate and 1-ethyl-3-methylimidazolium diethylphosphate

The density and surface tension of 1-methyl-3-methylimidazolium dimethylphosphate, [C₁mim](CH₃O)₂PO₂ and 1-ethyl-3-methylimidazolium diethylphosphate, [C₂mim](CH₃CH₂O)₂PO₂ ionic liquids have been measured over the temperature range from (283.15 to 338.15) K. The coefficients of thermal expansion were calculated from the experimental density results using an empirical correlation for T = (283.15 to 338.15) K. Molecular volume and standard entropies of these ILs were calculated from the experimental density values. The surface properties of ILs were investigated. The critical temperature and enthalpy of vapourization were also discussed.     

Structure,optical and magnetic properties of LaFeO3 nanoparticles prepared by polymerized complex method

This work reports the study the structure, optical and magnetic properties of LaFeO₃ nanoparticles synthesized by the polymerized complex method. The LaFeO₃ nanoparticles were successfully obtained from calcination of the precursor at different temperatures from 750 to 1,050 °C in air for 2 h. The calcined LaFeO₃ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Visible spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES) and vibrating sample magnetometry. The XRD and TEM results showed that all LaFeO₃ samples had a single phase nature with the orthorhombic structure. The estimated crystallite sizes were in the range of 44.5 ± 2.4–74.1 ± 4.9 nm. UV–Vis spectra showed strong UV and Vis absorption with small band gap energy. The valence states of Fe ions were in the Fe³⁺ and Fe⁴⁺ state, as confirmed by XPS and XANES results. The weak ferromagnetic behavior with specific saturation magnetization of 0.1 emu/g at 10 kOe was obtained for the small particle of 44.5 ± 2.4 nm. The uncompensated spins at the surface was proposed as playing a part in the magnetic properties of small sized LaFeO₃.     

Electric properties of non-irradiated and gamma-irradiated keratin

Dielectric measurements as a function of temperature and frequency are reported for non-irradiated and γ-irradiated keratin, the irradiation doses being 5 and 50 kGy. The effect of γ-irradiation on the dielectric permittivity of keratin is not observed up to 190°C. In this temperature range, the values of the relaxation time and dipole moment are similar for non-irradiated and irradiated keratin at the same temperature. The influence of irradiation is manifested as a shift of the parameter (_s−_∞) peaks associated with the process of denaturation, towards lower temperatures. This fact is supported by lower values of the dipole moment for irradiated than for non-irradiated keratin, as a result of a decrease in the number of polar groups in the side and main chains of the macromolecule in the irradiated samples.     

Synthesis and characterization of the reduction properties of cobalt-substituted lanthanum orthoferrites

Perovskite-related materials of composition LaFe_1−xCo_xO₃ have been prepared by conventional calcination methods. The temperature programmed reduction profiles indicate that the incorporation of cobalt renders the materials more susceptible to reduction when treated in a flowing mixture of hydrogen and nitrogen. The reduction processes have been examined by ⁵⁷Fe Mössbauer spectroscopy and Fe K-edge-, Co K-edge- and La L_III-edge XANES and EXAFS. The results show that in iron-rich systems the limited reduction of iron and cobalt leads to the segregation of discrete metallic phases without destruction of the perovskite structure at temperatures up to 1200°C. In materials where x?ca.0.5 the reduction of Co³⁺ to Co⁰ precedes complete reduction of Fe³⁺ and the segregation of alloy and metal phases is accompanied by destruction of the perovskite structure.     

Thermophysical properties of vanadium bronze polycrystals

Mixed sodium-vanadium oxide (vanadium bronze) polycrystals were carefully prepared. The crystalline phase formed was identified and investigated by X-ray diffraction analysis. The prepared bronze was extensively studied in comparison with pure V₂O₅ via infrared absorption spectra, IR measurements and the temperature-dependence of the electrical conductivity. The results obtained are interpreted, correlated and discussed in detail, for the first time, with regard to the electronic properties of the test samples.

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Zusammenfassung Polykristalle von Natrium-Vanadium-oxiden (Vanadiumbronze) wurden sorgfältig dargestellt. Die erhaltene kristalline Phase wurde mittels Röntgendiffraktionsanalyse identifiziert und untersucht. Die hergestellte Bronze wurde im Vergleich zu reinem V₂O₅ eingehend mit Hilfe von Infrarotabsorptionsspektren, von Temperaturabhängigkeit der elektrischen Leitfähigkeit und durch IR-Messungen untersucht. Die erhaltenen Ergebnisse wurden in erster Näherung in Bezug auf die elektronischen Eigenschaften der Proben interpretiert, miteinander korreliert und ausführlich erläutert.

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Thermophysical properties of 1-propylpyridinium tetrafluoroborate

A systematic thermophysical characterization of the ionic liquid 1-propylpyridinium tetrafluoroborate has been developed. Thus, the density, speed of sound, refractive index, surface tension, viscosity, ionic conductivity, isobaric heat capacity have been determined over the temperature range (278.15 to 338.15) K. Moreover, thermal events have been investigated over the temperature range (120 to 320) K. A comparison between experimental results for the ionic liquid and 1-butylpyridinium tetrafluoroborate studied has been carried out to analyze carefully how the structural modifications in the cation influence the behavior of these compounds.     

YFeO3/TiO2异质结材料的制备及其光催化性能研究

通过研磨-焙烧法制备了YFeO3/TiO2异质结材料,考察了焙烧温度和组分质量含量变化对合成异质结材料的影响;进行了X射线衍射(XRD)、傅里叶红外(FRIR)、紫外-可见漫反射(UV-vis/DRS)、光电子能谱(XPS)等表征并测试了不同样品光催化降解橙黄Ⅱ的活性.结果表明,YFeO3/TiO2复合氧化物不仅具有明显的可见光光响应,而且表现出比单组分相对较高的光催化降解活性.最佳的复合样品为600℃焙烧下,w(TiO2)=0.9的复合样品.复合材料光催化活性的提高可归因于p-YFeO3与n-TiO2间存在的p-n结.     

Thermophysical properties of oil shale minerals

The thermal diffusivity values of eight minerals that are commonly associated with oil shales of the Green River formation have been measured by the laser flash technique. Data are presented in the temperature range 25–500°C for quartz, dolomite, calcite, plagioclase, analcite, pyrite, potassium feldspar and low albite. A comparison of the thermal conductivities of some of these minerals, calculated from experimentally measured thermal diffusivity and density, with the experimental values reported in the literature reveals good agreement. Trends in the variation of thermal diffusivity with temperature and anisotropic effects in thermophysical parameters are discussed from the point of view of grain boundary effects in these polycrystalline mineral aggregates.     

Yttrium orthoferrite YFeO3 nanopowders formation under glycine-nitrate combustion conditions

Glycine-nitrate combustion method was used to obtain nanopowders of orthorhombic and hexagonal yttrium orthoferrite with particles sizes in the ranges from 30 to 53 nm and from 6 to 14 nm, respectively. It is shown that the structure and size of the particles are determined by the process temperature, which depends on the relative amounts of glycine and nitrates in the initial mixture. It is shown that yttrium orthoferrite nanopowders with a certain crystal structure and particle size can be obtained by varying the glycine/nitrate ratio. The nanopowders and materials on their basis can be used as photocatalysts.     

Thermophysical properties of cytidine and deoxycytidine mono- and hemiphosphates

The calorimetric (DSC) and derivative thermogravimetric (DTG) measurements for crystalline mono- and hemiphosphates of cytidine and deoxycytidine have been performed. The results for four examined salts confirm the influence of presence (or absence) of 2'OH group in ribose ring on stability (or lability) of the crystal structure of examined salts.     

Zn掺杂的LaFeO_3纳米晶的制备及其光催化活性研究

以氧化镧、硝酸铁和硝酸锌为原料,用柠檬酸络合法制备了La1-xZnxFeO3(x=0,0.1,0.3,0.5,0.7)纳米光催化剂,对其进行了XRD,TEM,UV-vis,IR等测试,并研究了其对水溶性染料活性艳红X-3B的光催化活性。结果表明:制得的LaFeO3为钙钛矿型结构,Zn2+的少量掺杂不改变LaFeO3的钙钛矿型结构,当x=0.3时开始出现尖晶石型ZnFe2O4相,当x=0.5时光催化活性最好,x=0.7时钙钛矿的结构被破坏。适量的Zn2+掺杂可以提高LaFeO3的光催化活性。     

Thermophysical properties of polypropylene/aluminum composites

This article is dedicated to the study of the thermal parameters of composite materials. A nonlinear least‐squares criterion is used on experimental transfer functions to identify the thermal conductivity and the diffusivity of aluminum‐polymer composite materials. The density measurements were achieved to deduce the specific heat and thereafter they were compared to values given by differential scanning calorimetry measurement. The thermal parameters of the composite material polypropylene/aluminum were investigated for the two different types of aluminum filler sizes. The experimental data were compared with several theoretical thermal conductivity prediction models. It was found that both the Agari and Bruggeman models provide a good estimation for thermal conductivity. The experimental values of both thermal conductivity and diffusivity have shown a better heat transport for the composite filled with large particles. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 722–732, 2004     

Thermophysical properties of hydroxyl ammonium ionic liquids

The thermophysical properties of hydroxyl ammonium ionic liquids: density ρ, T = (293.15 to 363.15) K; dynamic viscosity η, T = (298.2 to 348.2) K; and refractive indices n_D, T = (293.15 to 333.15) K have been measured. The coefficients of thermal expansion α, values were calculated from the experimental density results using an empirical correlation for T = (293.15 to 363.15) K. The variation of volume expansion of ionic liquids studied was found to be independent of temperature within the range covered in the present work. The thermal decomposition temperature ‘T_d’ for all the six hydroxyl ammonium ionic liquids is also investigated using thermogravimetric analyzer (TGA).     

Electric and dielectric properties of some gamma-irradiated cabal glasses

Electrical conductivity and dielectric properties have been studied for the glass system CaO---B₂O₃---Al₂O₃ in the temperature range 40–200°C. The substitution of 5% B₂O₃ by CaO or replacing 5% CaO by Na₂O or MgO cause a decrease in the conductivity, but the decrease obtained by soda is greater than that of magnesia. The activation energies of the tested glasses were calculated. All the glasses investigated showed a dielectric constant almost independent of temperature at fixed frequency. The effect of subjecting the glass to a constant dose of gamma-rays changes both the electrical conductivity and dielectric constant. The experimental results were discussed in relation to the specific conduction mechanism in such glasses. Also the effect of varying glass composition or temperature on the mobility or migration of current carrier was considered. The possible creation of induced defects in glass on irradiation was evaluated.