Papers by Keyword: Zone Melting

Abstract: A series of n-type BiTeSe/ZnAlO composites were prepared by zone melting method. Thermoelectric properties, including the electrical conductivity σ, Seebeck coefficient α and thermal conductivity κ, were measured in the temperature range of 300-550K. Results show that the electrical properties have been slightly lowered due to the reduced carrier concentration by ZnAlO addition. However, the low-temperature-shifted peak α, resulting from the prematurely happened intrinsic excitation, have shifted peak ZT to lower temperatures. As a result, the ZT values at 300 K were significantly enhanced for BiTeSe/ZnAlO composites compared to that of BiTeSe, making more attractive for cooling applications at ambient temperature.

Abstract: As the silicon melting point is very high (1414 °C), the temperature in the solid fraction, near the interface solid/liquid during solidification is also high and this can provoke a solute redistribution in the solidified portion. This phenomena is called back diffusion. So, it is important to estimate the potential of back diffusion during the solidification processes. This calculation is complex and there is commercial software, such as DICTRA, to do this in binary alloys. For zone melting, a simple method to predict the extension of the back diffusion is not available. In this study, it was developed a simple method to evaluate the back diffusion during zone melting, which does not require computational calculation.

Abstract: The lotus-type porous carbon steel with cylindrical pores has been fabricated by continuous zone melting technique in pressurized mixture of hydrogen and helium gases. In order to investigate the mechanical properties, the tensile and compression tests were carried out. The ultimate tensile strength of the specimen with cylindrical pores parallel to the solidification direction is lower than the estimated value assuming that the strength is decreased in proportion to decreasing cross section area of the specimen, while the yield strength is higher than that estimated. The compressive yield strength is also higher than that estimated. The increase in yield strength is attributed to the precipitation strengthening. The tensile strength is increased by quenching and tempering, while the elongation decreases. Such mechanical properties are discussed in terms of microstructureal analysis. Furthermore, simulations of the mechanical properties by FEM analysis were carried out.

Abstract: In the present study, n-type (Bi2Se3)x(Bi2Te3)1-x crystals with various chemical compositions were fabricated by the zone melting method. Thermoelectric properties, including Seebeck coefficient (α), electrical conductivity (σ) and thermal conductivity (κ), were measured in the temperature range of 300-500 K. The influence of the variations of Bi2Te3 and Bi2Se3 content on thermoelectric properties was studied. The increase of Bi2Se3 content (x) caused an increase in carrier concentration and thus an increase of σ and a decrease of α. The maximum figure of merit (ZT = α2σT/κ) of 0.87 was obtained at about 325 K for the composition of 93%Bi2Te3-7%Bi2Se3 with doping TeI4.

Abstract: Vitreous cylinders with compositions Bi2-xPbxSr2CaCu2Oy, (x = 0 and 0.4) were prepared and used as precursors to fabricate textured bars through a Laser Floating Zone melting method (LFZ). The resulting textured cylindrical bars were annealed and were mechanically characterized through mechanical strength, σ, Young modulus, E, Vickers hardness, H, and Weibull parameters, S0 and m. The study of the mechanisms controlling the fracture process was made by means of the fractographical analysis using Laser Scanning Confocal Microscopy (LSCM). Finally, the microstructure was determined and correlated with the mechanical properties.

Abstract: Lotus-type porous carbon steel with cylindrical pores was fabricated by a continuous zone melting method under pressurized mixture gases of hydrogen and helium. The microstructure of lotus-type porous steel was analyzed, and the tensile test was carried out. In the case of tensile test of the specimen with the cylindrical pores parallel to the solidification direction, the ultimate tensile strength was lower than the estimated value, but the yield strength was higher than the estimated value. It was assumed that the strength was decreased in proportion to decreasing cross section area of the specimen. The increasing of yield strength was attributed to precipitation strengthening. The influence of heat treatment (Quenching and tempering, normalizing) on the tensile properties was investigated.

Abstract: The aim of this work is to study the new method of direct synthesis of lead and iodine as the input material of PbI2. This method has not been studied for this material till now, and seems to be one of the new methods for preparation of the input material. The photoluminescence measurement and measurement of resistivity has been done and compared with the measurements done by precipitation and zone purification.