Metin Yurddaskal

Fabrication and characterization of novel iodine doped hollow and mesoporous hematite (Fe 2 O 3 ) particles derived from sol-gel method and their photocatalytic performances

In this work, iodine (I) doped hollow and mesoporous Fe2O3 photocatalyst particles were fabricated for the first time through sol-gel method. Phase structure, surface morphology, particle size, specific surface area and optical band gap of the synthesized Fe2O3 photocatalysts were analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), BET surface analysis, particle size analyzer and UV-vis diffuse reflectance spectrum (UV-vis DRS), respectively. Also, electrochemical properties and photoluminescence spectra of Fe2O3 particles were measured. The results illustrated that high crystalline, hollow and mesoporous Fe2O3 particles were formed. The optical band gap values of the Fe2O3 photocatalysts changed between 2.104 and 1.93eV. Photocatalytic efficiency of Fe2O3 photocatalysts were assessed via MB solution. The photocatalytic activity results exhibited that I doping enhanced the photocatalytic efficiency. 1% mole iodine doped (I-2) Fe2O3 photocatalyst had 97.723% photodegradation rate and 8.638×10-2min-1 kinetic constant which showed the highest photocatalytic activity within 45min. Moreover, stability and reusability experiments of Fe2O3 photocatalysts were carried out. The Fe2O3 photocatalysts showed outstanding stability after four sequence tests. As a result, I doped Fe2O3 is a good candidate for photocatalysts.

Synergetic effect of antimony trioxide on the flame retardant and mechanical properties of polymer composites for consumer electronics applications

Nowadays polymers are used in wide range applications of industries. Parts of the electronic devices composed of polymer materials can be easily ignited because they are susceptible to flame. In this study, it was aimed to produce flame retardant nanocomposite materials by reinforcing halogen-free inorganic additives and to use in components of electronic devices. Within this scope, halogen-free nano sized milled huntite/hydromagnesite and antimony trioxide nanoparticles were reinforced in polymer matrix. The composites reinforced in various ratios were produced using a twin screw extruder. These samples were obtained by the method of injection molding from the extruded granules for the flame retardant test. Structural, morphological, thermal, mechanical and flame retardancy properties of samples were characterized by XRD, SEM, FTIR, DTA-TG, mechanical and flame retardant measurement. It is found that the inorganic reinforcement minerals improved the flame retardant properties and thermal stability of polymer nanocomposites depending on the amount of additives. The huntite/hydromagnesite and antimony trioxide effectively reduce the flammability of the ABS composites utilizing synergism by achieving UL94/V-0 classification.

Quenching and tempering of 51CrV4 (SAE-AISI 6150) steel via medium and low frequency induction

Abstract Mechanical and microstructural properties of quenched steel are directly related to tempering time and temperature. In many applications, conventionally quenched and tempered steel is widely used for acquiring high strength and toughness. The present study was carried out to investigate the variation in mechanical properties, observation of diminished energy consumption and evaluation of the microstructural properties in SAE-AISI 6150 steel components by induction heating, compared with those of steel tempered by conventional method. Induction quenched and tempered steel provides a shorter process time, less energy consumption and improved mechanical properties through the inhibition of grain growth. In this study, quenching and tempering processes were carried out on medium and low frequency induction units and by using a conventional electrical resistance furnace for the sake of comparison. It was observed that cementite particles began changing their shape from spherical to fine-grained in the induction tempered samples. The sample tempered by low frequency induction manifests superior mechanical properties and offers a potential advantage for significant cost savings.

DEVELOPMENT OF THE ELECTRICAL CONDUCTIVITY IN CARBON BASED POLYMER COMPOSITES

Conductive polymer composites are nowadays used in technological applications and they constitute components of functional materials in many important applications. It is of great importance to reduce the high electrical resistance level of the polymers. Carbon containing additives are widely used to increase the electrical conductivity of polymers. In this context, some percolated networks were created to improve the level of electrical conductivity using graphite and carbon black. The produced conductive polymer composites were characterized to show their structures, electrical and thermo-resistive properties. We investigated percolation threshold values of composite films including both carbon black and graphite. Thanks to adding small amounts of carbon black together with graphite, it was achieved to be lower levels of resistance if compared to the individually filled composites. These conductive polymer composites produced with graphite and carbon black additives remain a strong candidate for temperature sensor material.

Fabrication and characterization of Gd2O2SO4:Tb3+ phosphors by sol-gel method

The objective of the innovative approaches of the scintillation materials to be used in the digital portal imaging systems in the radiotherapy applications is to research the GOS material production that has been activated with the rare earth elements (RE), to produce the scintillation detectors that have a rapid imaging process with a lesser radiation and higher image quality from these materials and to apply the radiographic imaging systems. The GOS: Tb3+ showed high emission peak and high x-ray absorption properties which have been determined for application to mammography and dental radiography. In this study, Gd2O2SO4:Tb3+ phosphors were fabricated by the sol-gel method that is a unique technique and not previously applied. Besides, the structural characterization of GOS: Tb3+ has been investigated. The strongest emission peak located at 549 nm under 312 nm UV light excitation was appeared on the GOS: Tb3+ phosphor particles. The characterization processing optimized by using FTIR, DTA-TG, XRD, XPS, ...

Production, characterization and optimization of thermoelectric module and investigation of doping effects on thermoelectric performances

The objective of this study is to produce the thermoelectric (TE) module called as a Peltier module or element using new and promising materials that work at high temperature for generation of electricity with thermoelectric energy conversion from waste heat at high temperatures. Peltier modules used commercially nowadays can work at relatively low temperatures and their efficiency increase in proportion to the temperature difference between the surfaces of the modules. They consist of a pair of p- and n-type semiconductor. In this study, calcium cobalt oxide was chosen as a p-type semiconductor whilst zinc oxide was chosen as n-type semiconductor. Pure and aluminum-doped zinc oxide and silver-doped calcium cobalt oxide powders were synthesized via sol–gel processing successfully. The obtained powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FTIR), differential thermal analysis-thermogravimetry (DTA-TG), and scanning electron microscopy (SEM). In addition, the particle size distribution of the powders obtained via sol–gel processing was determined using a particle size analyzer. One and two leg oxide thermo-electric modules consisting of one pair of p-type 0.03 percent silver doped calcium cobalt oxide and n-type 0.02 percent aluminum doped zinc oxide bulks of 25 square millimeter cross-section and 3 millimeter heights were constructed. The thermoelectric module constructed was tested at high temperatures, and compared to other similar oxide modules reported in literature. Ultimately, the thermal stress and alteration of thermal stress depending on the leg length and side length of semiconductors were calculated using the finite element analysis (FEA) model in ANSYS 15.0 software. According to the results of the analysis, TE module was optimized in terms of mechanical behavior.