Ertugrul Demir

The aim of this study is to provide information about microstructural and thermal properties of tungsten-based composites. Phase composition and microstructural characterization of tungsten composites were performed using X-ray diffractometer (XRD), Scanning Electron Microscopy (SEM), and Raman Spectroscopy. SEM images revealed the distribution of tungsten (W), vanadium carbide (VC) and graphite (C) powders in the tungsten matrix. The Raman spectra showed two major peaks, which are recorded at 1331 (vs) cm⁻¹, and 1583 (vs) cm⁻¹. These bands can be attributed to disorder graphite (D) and graphite (G). Thermogravimetric analysis (TGA) measurements were performed to determine the weight loss and thermal stability of the tungsten-based composites under argon gas atmosphere and at high temperatures. TGA measurements were performed to determine weight loss and thermal stability of tungsten-based composites under argon gas atmosphere and at high temperatures. The TG curve showed a slight weight loss in this temperature range. Mass loss is thought to be due to oxidation and gas desorption of materials.

In the presented work, a boron carbide sample with a purity of 99.9%, particle size [Formula: see text]–[Formula: see text]m and a density of [Formula: see text] was used. Boron carbide samples were irradiated with linear electrons in the energy range of 2.5 MeV at the doses of [Formula: see text], [Formula: see text] and [Formula: see text] at room temperature. XRD results show that only in the crystal structure of [Formula: see text] compound, among boron carbide samples irradiated in the dose rate from [Formula: see text] to [Formula: see text] phase transition does not occur. The observed decrease in the lattice parameter values was explained as the strengthening of the bonds as a result of the recombination of defects in the crystal by influencing electron fluence. Dynamics of Raman spectra change and analytic analysis of intensive and duplex modes in various electron fluxes in ([Formula: see text]) CBC-structure were performed and the occurring disorder in Raman active has been identified.

The purpose of this research is to determine the surface morphologies, microstructural and thermal properties of tungsten-based composites that consist of 93 wt.% tungsten (W), 6 wt.% vanadium carbide (VC) and 1 wt.% graphite (C) powders. W-6 wt.% VC-1 wt.% C powders were mechanically alloyed (MA’d) for 6 hrs using a [Formula: see text] with a rate rpm using tungsten carbide vial and balls and sintered at [Formula: see text] for under [Formula: see text], [Formula: see text] gas flow conditions. The phase composition and microstructural characterization of the tungsten composites were carried out using X-ray diffractometer (XRD), Scanning Electron Microscopy (SEM) and Raman Spectroscopy. SEM images showed the distribution of the tungsten (W), vanadium carbide (VC) and graphite (C) powders and porosity in the tungsten matrix. The Raman spectra exhibited two major peaks, which are recorded at 1331 (vs) [Formula: see text] and 1583 (vs) [Formula: see text] in the Raman spectra. These bands represented carbon phases such as disordered graphite (D) and graphite (G). Thermogravimetric analysis (TGA) measurements were performed to obtain the weight loss and thermal stability of samples in the temperature range [Formula: see text]–[Formula: see text] under argon gas atmosphere. The TG curve revealed a total loss of 3.3% of weight at this temperature range. It is considered that the cause of mass loss is due to the oxidation and gas desorption of materials.

In this paper, high purity boron carbide samples were irradiated by [Formula: see text]Co gamma radioisotope source (0.27 Gy/s dose rate) with 50, 100, 150 and 200 irradiation hours at room-temperature. The unirradiated and irradiated boron carbide samples were heated from 30[Formula: see text]C to 1000[Formula: see text]C at a heating rate of 5[Formula: see text]C/min under the argon gas atmosphere of flow rate 20 ml/min. Thermogravimetric (TG) and Differential Scanning Calorimetry (DSC) were carried out in order to understand the thermodynamic kinetics of boron carbide samples. The weight kinetics, activation energy and specific heat capacity of the unirradiated and irradiated boron carbide samples were examined in two parts, T [Formula: see text] 650[Formula: see text]C and T [Formula: see text] 650[Formula: see text]C, according to the temperature. The dynamic of quantitative changes in both ranges is different depending on the irradiation time. While the phase transition of unirradiated boron carbide samples occurs at 902[Formula: see text]C, this value shifts upto 940[Formula: see text]C in irradiated samples depending on the irradiation time. The activation energy of the unirradiated boron carbide samples decreased from 214 to 46 J/mol in the result of 200[Formula: see text]h gamma irradiation. The reduction of the activation energy after the irradiation compared to the initial state shows that the dielectric properties of the irradiated boron carbide samples have been improved. After the gamma irradiation, two energy barrier states depending on the absorption dose of samples were formed in the irradiated samples. The first and second energy barriers occurred in 0.56–0.80 and 0.23–0.36 eV energy intervals, respectively. The existence of two energy levels in the irradiated boron carbide indicates that the point defects are at deep levels, close to the valence band.

In this study, diffusion of rubidium and potassium in soil was observed representing two alkaline elements. Generally, these elements are found as salt compounds in the earth. Soil columns were prepared in the laboratory conditions. Rubidium chlorite and potassium nitrate compounds were irradiated at ITU TRIGA Mark II nuclear research reactor at the Energy Institute of ITU to produce the radiotracer ⁸⁶Rb and ⁴²K. The irradiated compounds were sprinkled to the surface of different soil columns and were watered with realistic amounts. Radioactivity measurements were carried out by using a scintillation detector at the outside of the column for different soil depths in different diffusion times. As the results of the study, the behavior of two alkaline elements was observed appropriately similar in the soil.

In this study, it is aimed to observe diffusion of sodium in soil samples by using radiotracing technique. To produce the radiotracer ²⁴Na, sodium-carbonate compound was irradiated at ITU TRIGA Mark II Research reactor at Energy Institute of Istanbul Technical University. The irradiated sodium-carbonate samples were sprinkled to the surface of soil columns. Then soil was watered with representative amounts of water according to selected rain regimes in Istanbul. Radioactivity measurements were carried out by using high efficiency gamma-ray measurement system at the outside of the column for different soil depths in different times.