Key Engineering Materials Vols. 675-676

Abstract: This article is focused on thermal expansion of cement-based composite. Studied materials are concrete containing alumina cement, silica aggregates and they are reinforced by basalt fibres. Three different concrete varying in fibres length were prepared and its basic physical properties and thermal expansion were measured. Fibres lengths were 6mm and 12mm. Total amount of fibres in mixtures were constant, whereas the ratio of the fibers were changed. Results were compared with reference concrete with no fibres. It was proved positive effect of fibres on thermal expansion, when the lowest values of thermal strain were shown by material with just longer fibres.

Abstract: The Ca₃Co₄O₉ (CCO) and Sr_0.87La_0.13TiO₃ (SLTO) are good property of oxide thermoelectric (TE) materials. They synthesized by solid state reaction (SSR) method to study thermoelectric properties and fabrication of thermoelectric module. It was found that, synthesis of CCO shows that Seebeck coefficient, electrical resistivity, thermal conductivity and values are 130 μV K^–1, 8.31 mΩ cm, 0.82 W m^–1 K^–1 and 0.08, respectively at 473 K. The Seebeck coefficient, electrical resistivity, thermal conductivity and ZT values of SLTO are –359 μV K^–1, 2.9 mΩ m, 18.09 W m^–1 K^–1 and 1.13×10^–3, respectively at 473 K. TE modules of CCO and SLTO were fabricated by ultra sonic soldering method. The power generation of TE modules were measured with temperature difference (ΔT) of 10–180 K. The 1 pair and 2 pairs TE modules for a maximum power generation of matching load are 19 k and 30 k, respectively. The maximum output power of 2 pairs TE module is larger than 1 pair TE module about two times.

Abstract: The dyeing of cotton fabrics using Excoecaria bicolor (Excoecaria cochinchinensis Lour.) as a natural dye has been studied in both conventional and ultrasonic techniques. Excoecaria bicolor leaves were extracted by various extracting procedures, using different solvents. The extractability of dye from natural origin using power ultrasonic was also evaluated in comparison with conventional heating. The results of dye extraction indicate that power ultrasonic is rather effective than conventional heating at low temperature and short time. The color of each dyed material was investigated in terms of the CIELab (L*, a* and b*) values.

Abstract: In general explanation for propagation of electromagnetic wave at a plane between two media of different dielectric properties. The description of this phenomenon be based on the actual physical process of the well know interpretation of the classical rays with the polarization vectors. In this research, we investigate this situation by using the knowledge of the amplitude of emission and absorption of massless spin-1 particle (photon) excitation by the emitter and detector, respectively. By using time evolution process based on vacuum-to-vacuum transition amplitude in quantum (field) theory QED formalism. This process shows that the propagation of photon excitation by the external sources is given with an explanation of the amplitude of propagation between different spacetime points from an emitter to a detector, which exclude with the Feynman propagator. The purpose of this research is developing a formalism based on the actual physical process of photons propagate from an emitter to a detector. It shows the consistency to the actual physical process of interpretation of the polarization vectors in the classical rays.

Abstract: This paper is focused on the numerical simulations of tensile behaviour and capacity of headed studs for concrete structures. 2D axi-symmetric numerical models of different head diameters and effective embedment depth were carried out. The distance of the support ring varied from the 0,0h_ef to 3,5h_ef from the edge of the head of the stud. It was found that the tensile capacity of the headed stud is increasing with the reduction of the resistance area by the support. The influence of the head size on the tensile capacity was also observed. The capacity increase depended on the size of resisting area of the anchor and therefore the relationship between the real resisting area and theoretical area was proposed.

Abstract: In this paper, we used shallots in the reduction of graphene oxide for the first time. Flavone, sulfur-containing compounds, and polyphenolic derivatives in the bulb of shallot acted as good reducing agent for the reduction of GO. The GO and reduced graphene oxide (RGO) were characterized by scanning electron microscopy (SEM), ultraviolet (UV)-visible spectroscopy, thermogravimetric analysis (TGA) and Raman spectroscopy. GO and RGO were the transparent sheets with the sheet edges tend to scroll and fold slightly. RGO showed a maximum absorption peak at 267 nm and had better thermal stability than graphene oxide. Raman spectra indicated removal of oxygen at the surface of GO and formation of the defect in the graphene sheet.

Abstract: Neutron activation analysis (NAA) is a method of nuclear technique to detect with great sensitivity the presence and concentrations of elements in materials, without, in most cases, destroying the sample analyzed. Therefore, this study aimed to study the technique of Neutron Activation Analysis (NAA). Accordingly, instrument (INAA) has been in this analyzed for determination of heavy toxic metal (Cd, Co, Fe, Pb, Cr, Zn) and others in vegetables samples. The results of heavy metal concentration analyses showed that Co, Fe, Cr could be analyzed by NAA.

Abstract: This research was conducted to study the inner filter effect on the fluorescence spectra of fluorescence dyes. The concentration effect on all of fluorescent dye solutions showed the same trend in terms of changes in fluorescence intensity spectra. At low concentrations, the fluorescence intensity increased when the concentration of fluorescent dye solution increased. However, at high concentrations, the fluorescence intensity decreased when the concentration of fluorescent dye solution increased. Interestingly, the result of fluorescence spectra in dye solutions showed that the fluorescence intensity maxima in all dye solutions were shifted to a higher wavelength (red-shift) when the concentration of fluorescent dye solution increased. The results of concentration effect on fluorescence intensity and wavelength-shift in dyes solution can be explained by inner filter effect on fluorescent dye solutions.

Abstract: The experiment was conducted to study the stress distribution on a homogeneous plastic using photoelastic analysis system where the stress was observed by reflection polariscope. The circular disk of homogeneous plastic was used for study in this research. The sample was pressed at the top and bottom. The fringe patterns were produced from sample on the model being stressed, which could be observed in the bright field and dark field. The fringe patterns were recorded by digital camera. Then the results were analyzed; the fringe pattern looked different when applying various magnitudes of force because the stress distribution in sample was changed in homogeneous plastic.

Abstract: Red emitting new phosphor, YBO₃ doped with Eu³⁺ ions, has been prepared by solid state reaction method. The excitation spectra were recorded by monitoring a red emission at 610 nm and observed very intense band in the lower wavelength region, 230 ~ 280 nm, which could be attributed due to the Eu³⁺-O^2- charge transfer band (CTB) lying in the band gap region of the host matrix. In addition to the CTB, strong absorption lines in the excitation spectrum is located at 395 nm and 465 nm which corresponds to the ⁷F₀ → ⁵L₆ and ⁷F₀ → ⁵D₂ transitions of Eu³⁺ ions, respectively. The decay curves are found to be single exponential at lower concentrations and tends to be non-exponential at higher concentrations with shortening of lifetime (2.74 ms to 0.86 ms). The systematic investigation indicates that this Eu³⁺-doped YBO₃ phosphor is an ideal candidate for solid state lighting applications.