Advanced Materials Research Vol. 787

Abstract: Joining of ceramics with glasses has been widely used for artificial teeth, solid oxide fuel cells, electrical devices, high temperature ceramic filters, structural ceramic components for aeronautic engineering, nuclear reactors, and other applications. This study aimed to explore the possibility of using a dielectric glass to connect a dielectric ceramic resonator to a dielectric ceramic support, in order to make miniaturized microwave filters characterized by higher temperature and environmental stability and low dielectric loss. A mixed powder having Bi₂O₃-SiO₂-Al₂O₃-MgO-ZnO-CaO glass as a matrix and SiO₂-Al₂O₃-MgO as a ceramic filler was used to join the dielectric ceramic resonators made of the CaTiO₃-NdAlO₃-Al₂O₃ system to the dielectric ceramic supports made of the ZnO-TiO₂-Al₂O₃-MgO system. In spite of the strong interfacial bonding obtained, microcracks were observed in the joined bodies, suggesting that not only the dielectric loss of the bonding layer but also the match of the thermal expansion coefficients of the components to be joined should be carefully considered and tailored.

Abstract: The creep behaviour of 2% agar gels has been studied under static and dynamic conditions. This biopolymer finds numerous applications depending on their elasticity. In this why, we are interested to determine the viscoelastic behavior of this hydrocolloid in differences phases and we studied the evolution of its strain creep behavior in transient as in steady state. As a result of these actions, the modified Burgers model has been finally developed for the studied agar gels with variables dependent on the shear stress and the parameter values for its creeping part (describing non-linearly viscoelastic properties of this biopolymer). To confirm the mechanical property of the gel, we measured its dynamic modulus. The elastic character is predominant (G' G").

Abstract: The paper describes results of functional tests of photo catalytic materials directly in matrix of prefabricated vibro pressed pavement blocks. Resulting surfaces of photo catalytic concrete products were tested with respect to conversion of NOx and surface was analyzed with Scanning Electron Microscope (SEM), so called element maps were elaborated by means of Energy Dispersive Spectroscopy (EDS).

Abstract: The a-Se HARP (High-gain Avalanche Rushing amorphous Photoconductor) target was prepared, and the avalanche characteristics were investigated. In this paper, to study avalanche multiplication at a high electric field, the lucky-drift model was used. In addition, the energy-and field-dependent energy relaxation length was considered. The avalanche multiplication factor was obtained from the current-voltage characteristic of the a-Se HARP target. The threshold field of the 0.4-μm-thick a-Se HARP target was 0.88×10⁸ V/m. The hot carrier energy at the threshold field for the avalanche multiplication in the 0.4-μm-thick a-Se HARP target was 0.21 eV. The hot carrier energy in the a-Se layer increases linearly as the electric field increases. The hot carrier energy also saturates as the avalanche multiplication factor increases. In addition, the energy relaxation length between the inelastic scattering events in the a-Se layer saturates as the hot carrier energy and the avalanche multiplication factor increase.

Abstract: Avalanche multiplication of the 0.4-μm-thick a-Se HARP (High-gain Avalanche Rushing amorphous Photoconductor) target was obtained at a high electric field. To study the drift velocity of hot carriers in the a-Se layer, the energy-and field-dependent energy relaxation length was considered in the lucky-drift model. The impact ionization energy E_I of 2.0 eV and the optical phonon energy ћω of 31 meV for a-Se were used to obtain the impact ionization parameters in the a-Se layer. The drift velocity of hot carriers at 1×10⁸ V/m in the 0.4-μm-thick a-Se HARP target was obtained as 1.87×10⁶ cm/s. The drift velocity of hot carriers saturates as the electric field and the avalanche multiplication factor increase. In the 0.4-μm-thick a-Se HARP target, the relaxation length ratio λ_E/λ and the relaxation time ratio τ_E/τ saturate as the avalanche multiplication factor increases. In addition, the relaxation length ratio λ_E/λ and the relaxation time ratio τ_E/τ at 1×10⁸ V/m were 2.75 and 14.66, respectively.

Abstract: The materials of fusing metals commercially used in the jewelry niche marketing is seen as precious metals. An innovation of fusing metals searched for new materials to differentiate from the markets for mass production. In this research, it studied the bonding processes of silver and aluminium metals by casting processes for mass productions. The studies had been varied parameters on the types of aluminium and process temperature controls. This research had used two types of aluminium which were pure aluminium 99.99% and aluminum 5083 alloys bonding with pure silver 99.99%. The temperatures had been specified for two factors including casting temperature at X₁, X₂ and flasking temperature at Y₁, Y₂. From the results, it was found that the casting temperature at 730°C and the flasking temperature at 230 °C of pure silver-aluminum 5083 alloys bonding had the thinnest average thickness of interface at 427.29 μm. The microstructure of pure silver-aluminum 5083 alloy bonding was revealed eutectic-like structures at the interfaces. The EDS analysis showed the results of compounds at interface layers of Ag sides giving Ag₂Al intermetallics on pure silver-aluminum 5083 alloy bonding unlike pure silver-pure aluminium bonding giving Ag₃Al intermetallics.

Abstract: As a novel technique for joining materials, friction stir welding (FSW) has significant advantages over the conventional welding methods and is widely applied for joining different materials including aluminum, magnesium and copper alloys. In this research, the mechanical and microstructural characteristics of friction stir welded annealed pure copper joints were investigated. The influence of the tool rotation speed, welding speed and applied load was studied. The friction stir welding (FSW) was conducted at welding speed ranged from 30 to 70 mm/ min, rotation speed ranged from 400 to 1200rpm and applied load ranged from 1000 to 1500 kg. After welding process, tensile and Vickers hardness tests were performed. It has been found that increasing the tool rotational speed and/or reducing the welding speed increases heat input and causes grain coarsening in stir zone. High applied load refines the microstructure of NZ and increases the hardness and tensile strength of NZ. An optimum heat input condition was found to reach the best mechanical properties of the joints. The tensile characteristics of the friction stir welded tensile samples depend significantly on the tool rotation speed ,welding speed and applied load.

Abstract: An experimental study was carried out to determine the notched tension characteristics of CCF300 fiber reinforced composite subjected to the normal and hygrothermal environment condition. In both conditions, the pull-out propagation was the ultimate failure mode of these specimens. The damage growth can be divided into four separate stages. In the hygrothermal environment condition, greater damage occurred, length of splitting increased and off axis plies were extensively pull-out from the adjacent plies.

Abstract: The predominant pyridine alkaloid in modern tobacco (Nicotiana tabacum) is Nicotine. However, with the existence of a class of Nicotine demethylases, a large proportion of Nicotine will be converted into Nornicotine during leaf senescence. Identification of Nicotine demethylases in modern tobacco is important, since Nornicotine will be nitrosated into N'-nitrosonornicotine (NNN), which exhibit carcinogenic properties in laboratory animals and is harmful for human heath. Although many efforts have been performed to identified, no comprehensive analysis was carried out for the subfamily of Nicotine demethylases. In this work, we performed a phylogenetic and comparative analysis for Nicotine demethylases with their highly homologs. A single and conserved mutation of W->C will prohibit the activity of Nicotine demethylases. Thus, the proportion of Nornicotine could be dramatically decreased if all Nicotine demethylase were single mutated by transgenic manipulation. Our results provide an insightful and solid foundation for further experimental design.

Abstract: The surface of 3Cr13 martensitic stainless steel was irradiated by high current pulsed electron beam (HCPEB). The microstructures of the irradiation surface were characterized by X-ray diffraction and electron microscopy. After HCPEB irradiation, formation of a melting layer with depth of about 4 μm on the irradiated surface was determined. Further microstructural investigations indicate that the surface melted layer consists of nanoaustenite and ultrafine carbide particles, which primarily appear at grain boundary triple junction. Additionally, the microhardness and corrosion resistance of the irradiated surfaces was improved significantly. The formation of the nanoaustenite layer induced by HCPEB irradiation was believed to be the dominating reasons for the improvement of comprehensive performance of the material surface.