Papers by Keyword: β-Phase

Abstract: This work aimed to compare the characteristics of micro and nanofibers of the poly (vinylidene fluoride) - PVDF polymer obtained by the Solution Blow Spinning (SBS) method, and films with those produced by other techniques, such as: casting and hot pressing. Thermogravimetric analysis (TGA) revealed that the films are thermally stable up to a temperature of 420 ° C. X-ray diffractometry (XRD) indicated the presence of the crystalline phases α and β, the β phase being more evident for nanofibers and PVDF casting. The film obtained by SBS showed a greater contact angle, showing to be more hydrophobic. Strain tests showed that the nanofiber films showed a 72% rupture to rupture, about 1.7 and 3.1 times greater than those obtained by casting and hot pressing, respectively. There was also a decrease in the modulus of elasticity and the limit of tensile strength of nanofibers, compared to other films.

Abstract: Analysis of the TIG-welding impact on the structure and mechanical properties of pseudo-β titanium alloy VT19 welded joints, obtained with different welding speed, different filler wire amount in welded joint, with and without flux layer. Microstructure of obtained welded joints were investigated. Using welded joints microsections approximate amount of β-phase in different parts of welds have been obtained. Mechanical properties of the obtained welded joints were analyzed and dependency of tensile strength and amount of β-phase were build.

Abstract: We fabricated mono-dispersed β-quartz GeO₂ by microemulsion synthesis at room temperature. The obtained particles were 300 nm sized GeO₂ walnut and hollow waxberry shaped GeO₂ which were consisted of nanosphere with average size of 20 nm. The evolution of high pressure studies were devoted in a diamond anvil (DAC) cell by Angle Dispersed X-ray Diffraction (ADXD) at room temperature. A phase transformation of β-GeO₂ to amorphous GeO₂ was detected in walnut GeO₂, while the waxberry GeO₂ was found to transform to monoclinic phase directly. It is strongly suggested that size effect played a key role in the high-pressure transformation from the amorphous and monoclinic phase. By fitting the compression data to the BirchMurnaghan equation of state, the bulk moduli of the walnut and waxberry shaped β-GeO₂ particles were determined to be 33±5, and 38±4 GPa with B₀ = 3, respectively.

Abstract: A new intercalation of Indium and Zinc Phthalocyanine(ZnPc) thin films is developed by using thermal co-evaporation method. Optical characteristics of In-doped ZnPc are studied in comparison with pristine ZnPc, which shows improvement on optical absorption at the visible spectrum. The presence of a new phase transition upon Indium doping is examined and consequently support the idea of the intercalated phase upon doping. A Schottky diode made of Indium doped ZnPc is fabricated in order to measure its electrical properties, its photo-current spectrum confirms the existence of phase transition.

Abstract: We fabricated mono-dispersed hollow waxberry shaped ß-quartz GeO₂ by a facile one-step synthesis in emulsion at room temperature. TEM images indicated that hollow waxberry shaped GeO₂ were consisted of nano-sphere whose average size were estimated to be 20 nm. The growth mechanism and optical properties of the products were also investigated. The possible formation mechanism of the hollow interior is proposed as the Ostwald ripening. The optical properties of the ß-GeO₂ nanoparticles with hollow shapes were also studied with photoluminescence spectrum, which reveals a broad emission, suggesting potential applications in electronic and optoelectronic nanodevices. These attractive results provide us a new simple method further used to fabricate other specific hollow structure and indicate hollow waxberry shaped GeO₂ may have potential applications in light-emitting nanodevices.

Abstract: Silicon nitride powders high in β-phase content have been prepared by direct nitriding method. The silicon powders were first milled with 30%α-Si₃N₄ and 4% FeCl₃ for 30 minutes. Then the mixture was heat-treated at 1400°C for 2 hours in the pure nitrogen gas. The phase and the microstructure of the as-prepared product were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the product mainly consisted of β-Si₃N₄, whose content is more than 92%, and a little amount of α-Si₃N₄, and no silicon were detected within the detection limit.

Abstract: In the present work, b’ phase in alloys Al -1.0 mass% Mg₂Si -0.5 mass% Ag (Ag-addition) and Al -1.0 mass% Mg₂Si (base) was investigated by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) to understand the effect of Ag addition. The b’ phase is rod-shape with the longest direction parallel to <001>_Al. HRTEM images and SAED patterns obtained along the direction were similar for the b’ phase in both alloys. The unit cell of b’-phase in Ag-addition alloy is hexagonal with the same c-axis dimension as the Ag-free b’, but shorter a-axis. Ag was found in the composition of the rod-shaped precipitates in Ag-addition alloy by energy dispersive X-ray spectroscopy (EDS). In addition, the distribution of Ag was investigated by energy filtered mapping and high annular angular dark field scanning transmission electron microscopy (HAADF-STEM). The Ag-containing atomic column was observed in every b’ unit cell, and the unit cell symmetry is slightly changed as compared with the Ag-free b’. The Ag-containing b’ rods have complicated domain structures. The interfaces of these particles are enriched with Ag atoms that occupy the lattice positions in the Al matrix. The occupancy of the Ag-containing atomic columns seem to vary both inside particles, as well as at the interfaces.

Abstract: In this paper, we developed a simple and effective method to fabricate lead oxide plate films by electrochemical deposition. The electrolyte was lead nitrate aqueous solution with or without Cl- ions. Stainless steel plate was employed as both cathode and substrate, and a graphite plate as anode. We found the optimal current density of synthesizing lead oxide plate films is 10-25mA/cm2 when there were no Cl- ions in the electrolyte. If equal Cl- ions were added in lead nitrate aqueous solution, the optimal current density of synthesizing lead oxide plate films is less than 10mA/cm2. The as-prepared lead oxide plate films have orthorhombic crystals structure.

Abstract: Silicon nitride is one of the major structural ceramics that has been developed following many years of intensive research. It possesses high flexural strength, high fracture resistance, good creep resistance, high hardness and excellent wear resistance. These properties arise from the processing of the ceramic by liquid phase sintering and the development of microstructures in which high aspect ratio grains and intergranular glass phase lead to excellent fracture toughness and high strength. The glass phase softens at high temperature and controls the creep rate of the ceramic. The purpose of this review is to examine the development of silicon nitride and the related sialons and their processing into a range of high-grade structural ceramic materials. The development of knowledge of microstructure–property relationships in silicon nitride materials is outlined, particularly recent advances in understanding the effects of grain boundary chemistry and structure on mechanical properties. This review should be of interest to scientists and engineers concerned with the processing and use of ceramics for structural engineering applications.

Abstract: High temperature beta-phase in titanium and zirconium alloy systems decomposes through an eutectoid reaction into a Ti- and Zr-rich a-solid solution and an intermetallic compound. The present paper reports the layer growth kinetics of the b-solid solution phase in elemental diffusion couples of titanium and zirconium. The growth kinetics obeys a parabolic growth law. However, the temperature dependence of the growth rate constant shows a bimodal behavior. The Arrhenius plot of the growth rate constant, which is linear at the start, becomes curved at lower temperature ranges. The deviation from the Arrhenius plot of the growth rate constant is related to the curvature in the solvus line of the b-solid solution. A theoretical model for the reaction diffusion responsible for the growth of b-solid solution is presented. The growth rate of b-phase is described by the equation 2 2 . . W k D C t b = = b D x , where k is a growth rate constant and Wb is the thickness of the b-phase formed over a period of time t, Db is the interdiffusion coefficient for the b-phase, DC is concentration range of b-phase and x is a parameter which is a function of the miscibility gaps in the phase diagram on the either side of the b-phase. The above equation provides a satisfactory description of the various aspect of the phenomenon of the growth of b-phase in Ti-and Zr-alloy systems.