Thin-Film Thermal-Conductivity Measurement on Semi-Conducting Polymer Material Using the 3ω Technique

Organic solar cells have gained increasing interest in recent years due to their promising low-cost processing possibility and high throughput compared to inorganic solar cells. Since the efficiency of organic solar cells is still low, further optimization has to be done. Reliable simulation of solar cell layout and performance strongly depends on correct input data of the electrical and thermal transport properties of the applied film materials. In many cases these material properties are only available for bulk material if available at all. Owing to the given film thicknesses on the order of tenths to hundreds of nanometer and to the preparation methods, the properties of the used system can differ from the bulk material values. For determination of the thin-film thermal conductivity, only a few measurement methods are known to provide accurate results with one of them being the 3ω technique. It allows the determination of the thermal conductivity of bulk materials as well as thin films down to a thickness of around 50 nm. This study is part of an investigation on the influence of local hot spots, generated by defects in the active layer of organic solar cells, and on the charge carrier mobility as well as the propagation of the hot spot due to the thermal conduction of the material. Applying the 3ω technique, the effective thermal conductivity of solution-derived poly(3-hexylthiophene) thin films of different thickness on a common glass substrate was investigated.     

High‐Temperature Radiative‐Convective Heat Exchange on the Surface of Glass‐Reinforced Plastics

The results of experimental investigations of heat exchange on the surface of a thermalprotective material — glassreinforced plastic — in the flows of hightemperature gases have been presented. It has been established that the influence of injection on the value of the heat flux does not exceed 10% in the range of variation of gas temperatures 300–2000 K and Reynolds numbers 350–9800.     

Advances in the Experimental Determination of the Uranium–Oxygen Phase Diagram at High Temperature

Due to its complex phase diagram and the employment of UO₂ as a nuclear fuel, the binary system U–O is of great interest both scientific and technological. Numerous experimental and theoretical studies have been carried out in the last 45 years in order to determine the properties of this system, leading to a precise definition of a considerable part of the state diagram in the region ranging from pure uranium to stoichiometric UO₂, and at temperatures lower than 1500 K, up to the oxide U₄O₉. However, due to the poor chemical stability of O–U compounds with high oxygen content at high temperature (O/U > 2, T > 2000 K), an important part of the phase diagram still lacks experimental data. In this work measurements are presented on the melting transition of the stoichiometric and hyperstoichiometric dioxide UO_2+x up to x=0.21, and on the melting point of the higher oxide U₃O₈. These measurements were performed under buffer gas pressures varying between 10 and 250 MPa, using a method based on subsecond laser heating developed to overcome experimental difficulties encountered by previous researchers. Paper presented at the Seventh International Workshop on Subsecond Thermophysics October 6–8, 2004, Orléans, France.     

Some General Aspects of the Liquid–Glass Transition in Sodium Germanate Glasses

Inorganic Materials - This paper is concerned with the temperature dependence of viscosity for sodium germanate glasses differing in sodium oxide content and discusses some aspects of the...     

Study on the Basic Mechanical Behaviors of High Density Polyethylene Electrofusion Welded Joints at Different Temperature

The basic mechanical behaviors of high density polyethylene electrofusion welded joint at different temperatures were studied by using differently designed specimens in this paper. The results show that the strength of weld bonding plane is higher than that of the pipe and socket materials at room temperature. In order to get the shear strength of electrofusion welded joint,the effective bond lengths were reduced by cutting artificial groove through the socket. The effective bonding length of welded joint to get the shear strength is decreased with decreasing testing temperature. The shear strength and the sensibility to sharp notch of HDPE material increased with decreasing temperature.     

La Doping Effect on the Dielectric Property of Barium Strontium Titanate Glass – Ceramics

Ferroelectric barium strontium titanate(BST) glasse ceramics doped with different content of La2O3 were prepared via the melt-quenching technique followed by controlled crystallization. The microstructures of crystallized samples were examined by X-ray diffraction and scanning electron microscopy. Dielectric properties were also investigated. The aliovalent substitution of Ba by La induced dispersion of semiconducting BaxSr1-x TiO3 crystallites sealed in a glassy silicate matrix, which increased the εr and loss tangent values of the BST glasse ceramic. The experimental results indicate that aliovalent substitution is an effective method to process glasse ceramics with better dielectric properties.     

Influence of High Pressure and Temperature on the Structure and Properties of the WC–6Co Hard Alloy

The results are presented of the barothermal treatment studies of a WC–6Co hard alloy at high pressure (7 GPa). It is shown that such a treatment of hard alloy leads to the deterioration of the basic physico-mechanical characteristics, specifically the strength at the contact, and the coercive force, which is stipulated by the increase of the defects amount in the structure of the carbide phase of the hard alloy.     

Synthesis of High-Phase Purity SrTi1–xZrxO3 Ceramics by Sol-Spray Pyrolysis Method

SrTi₁–_xZr_xO₃ (0 ≤ x ≤ 1.0) ceramics were synthesized from powders generated by sol-spray pyrolysis. Crystal symmetry, morphology, and the band gap of the prepared ceramics were investigated as a function of Ti/Zr ratio. Substitution of Zr⁴⁺ for Ti⁴⁺ in the solid solution markedly effects crystal symmetry and grain growth and results in an increased band gap. Single-phase products with good crystallinity and dense microstructure were obtained after sintering at 1250°C.     

Effect of High Magnetic Fields on the Charge–Density–Wave State in NbSe3

We present a systematic study on a large magnetoresistance in NbSe₃ as a function of temperature under various pressures. The large magnetoresistance below T _c2 is observed as long as the T _c2-CDW phase exists. However, when the T _c2-CDW phase is suppressed totally by high pressure and the superconducting phase is induced at the same time, no anomaly, including the large magnetoresistance, is induced by a magnetic field up to 12 T. The origin of the large magnetoresistance is discussed by considering normal carriers on the ungapped Fermi surface created on the CDW transition and comparing this magnetoresistance with the pressure-induced magnetoresistance that is newly observed above T _c2.     

Levitation Performance of Bulk High Temperature Superconductor Above the Permanent Magnet Guideway at Different Temperatures

The levitation performance of a high temperature superconducting (HTS) Maglev system was investigated at different temperatures for HTS Maglev vehicle application. Using a cryogenic measurement system, we studied the effects of the HTS’s temperatures and the HTS’s field-cooling heights (FCHs) on the levitation force and its force density by applying a two-pole Halbach array’s permanent magnet guideway (PMG) at different temperatures. Results show that the levitation force is not only dependent on the temperature but also dependent on the original FCH. The effect of the temperature on the levitation force is considerably minute in low FCH. However, it was confirmed that the levitation force of HTS is larger at a lower temperature than at a higher temperature in high FCHs. Moreover, by applying the temperature of 60 K, the levitation force density of the system can be increased by 65% and 57.3% compared to the force density at 77 K in 35 mm and 40 mm FCHs. Hence, more magnetic energy at a low temperature area and high FCH can be utilized. The advancement of Maglev system’s performance will directly promote the development of HTS Maglev application and is helpful for the further HTS Maglev vehicle.     

Measurement of the monochromatic emissivity of coatings at 100–400°C

Results of measurement of the normal emissivities of certain coatings by a two-beam method in the 2–25 range are reported.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 27, No. 2, pp. 203–207, August, 1974.     

Low Temperature Synthesis of TiO2 Nanoparticles with High Photocatalytic Activity and Photoelectrochemical Properties through Sol–Gel Method

In the present work TiO₂ nanoparticles were prepared by sol–gel method and both small-sized nanoparticles and proper crystals were delivered by simultaneous use of surfactant, which was applied for the purpose of size reduction of nanoparticles, and acid ions that were used so that the formation of crystalline structures occurs appropriately. Photocatalytic activity of samples was measured by degrading RO dye, and photoelectrochemical properties were assayed using anodic photocurrent responses under Xe lamp light irradiation. The synthesized nanoparticles exhibit great photoelectrochemical and photocatalytic activity compared to that of commercial photocatalyst, Degussa P-25, which demonstrates that the method can be applied in the synthesis of other semiconductor oxides nanoparticles.     

Alloys of the Ti–Al–Zr–Si System Intended for Operation at High Temperatures

Materials Science - We study two alloys of the Ti–6.6Al system with zirconium contents of 2.4 and 4.2% and silicon contents of 1.3 and 1.05% at temperatures of 20–700°С. The...     

Influence of Micron WC Addition on the Microstructure and Mechanical Properties of Ultrafine WC–Co Cemented Carbides at the Elevated Temperature

In this paper, the influence of micron-grained WC additions with the different grain sizes on the microstructure and hardness of ultrafine WC–Co cemented carbides at the elevated temperature were investigated by the scanning electron microscope and mechanical properties test. The Vickers hardness and transverse rupture strength of hardmetals were measured at temperatures ranging from room temperature to 800°C. The results show that the addition of micron-sized WC particles can lead to the increase of fracture toughness and slow the decreasing of hardness at the elevated temperature.     

Effect of Milling Time on the Microstructure and Tensile Properties of Ultrafine Grained Ni–SiC Composites at Room Temperature

Bulk metallic nickel–silicon carbide nano-particle(Ni–Si CNP) composites, with milling time ranged from8 to 48 h, were prepared in a planetary ball mill and sintered using a spark plasma sintering(SPS)furnace. The microstructure of the Ni–Si CNP composites was characterized by transmission electron microscopy(TEM) and their mechanical properties were investigated by tensile measurements. The TEM results showed well-dispersed Si CNP particles, either within the matrix, between twins or along grain boundaries(GB), as well as the presence of stacking faults and twin structures, characteristics of materials with low stacking fault energy. Dislocation lines were also observed to interact with the Si CNP which were plastically nondeformable. A synergistic relationship existed between Hall–Petch strengthening and dispersion strengthening mechanisms, which was shown to greatly influence the mechanical properties of the Ni–Si CNP composites. Both the maximum yield and tensile strengths were found in the Ni–Si CNP composite with a milling time of 48 h, whereas the increased rate of strengths drastically decreased in material milled above 8 h due to the significant Si CNP agglomeration. The ball milling process resulted in the formation of nano-scale, ultra-fine grained(UFG) Ni–Si CNP composites when the milling time was extended for longer periods, greatly strengthening these materials. The sharp decrease in elongation percentages, however, should be comprehensively considered before irreversible inelastic deformation.     

Influence of Reducing Media on the Structure and Physicomechanical Properties of Ceramics of the ZrO2–Y2O3–Al2O3–NiO – CuO System

Materials Science - We study the regularities of changes in the microstructure, strength, electric conductivity, and micromechanism of fracture of 50% (ZrO2–8 mole% Y2O3–2 wt.% Al2O3) +...     

Influence of the Working Media of Fuel Cells on the Structure and Physicomechanical Characteristics of Ceramics of the ZrO2–Y2O3–NiO System

Materials Science - We study the properties of ZrO2 –Y2O3 –NiO ceramics obtained by using the technologies of sintering of powders and tape casting in the intact state and after...     

Effect of Hot Pressing Conditions on the Microstructure and Optical Properties of MgO–Y2O3 Composite Ceramics

Inorganic Materials - We have studied the effect of hot pressing conditions on the microstructure and optical characteristics of Y2O3–MgO composite ceramics. The hot pressing conditions have...