Papers by Author: Bora Derin

Abstract: Magnetorheological (MR), Electrorheological (ER), and Ferrofluids are considered as a class of smart materials due to their novel behavior under an external stimulus such as a magnetic and electrical field. The behavior of these synthetic fluids offer techniques for achieving efficient heat and mass transfer, damping, drag reduction, wetting, fluidization, sealing, and more. Magnetorheological fluids are suspensions of non-colloidal, multi-domain and magnetically soft particles organic and aqueous liquids. Electrorheological fluids are suspensions of electrically polarizable particles dispersed in electrically insulating oil. Ferrofluids are known as magnetic liquids that are colloidal suspensions of ultrafine, single domain magnetic particles in either aqueous or non-aqueous liquids. In this review article a history of these fluids is given, together with a description of their synthesis in terms of stability and redisperibility and how it is understood in various parts of the science and technology. Then the structural changes and rheological properties of these smart fluids under an external stimulus together with a series of applications are presented.

Abstract: In this study, the self-propagating high-temperature synthesis (SHS) and following acid leaching techniques were carried out to produce zirconium diboride (ZrB2) powder. In the SHS experiments, technical grade ZrO2 powder, and different amounts of B2O3 and Mg powders were used. The SHS products were obtained in the form of black, spongy solid. In the leaching step, the effect of different acid concentrations on selective leaching was investigated by using optimum SHS product to eliminate the impurities such as MgO, Mg3B2O6 and Mg2B2O5. The products obtained were characterized by using XRD, ICP and SEM techniques.

Abstract: A synthesis study of W2B5 powder was carried out by double self-propagating hightemperature synthesis (D-SHS) from CaWO4, Mg and B2O3 mixture and followed by HCl leaching methods. In the first stage of SHS reaction, molar composition ratio of CaWO4:B2O3:Mg mixture was selected as 1:1:8 (SHS-1) and 1:2.5:8 (SHS-2). The both SHS products were then acid leached (HCl) at optimum conditions for 1 hour and 80 °C to eliminate MgO, Mg3B2O6 and Ca3(BO3)2 phases. The first leached products were consisted of W, WB, W2B5, and W2B phases. In the second stage of SHS process, the both leached products were reacted with the same amount of Mg and B2O3 mixture keeping previous initial ratio values (1:8 and 2.5:8). A successful SHS reaction was achieved only by using the mixture with leached SHS-2 product. After following acid leaching, the chemical composition of the leached D-SHS product was found to be 98.2 wt. % W2B5, 1.2 wt. % WB4, and 0.6 wt. % WB.

Abstract: In this study, machinability of Zr-based bulk metallic glass (Zr52.5Ti5Cu17.9Ni14.6Al10) (BMG) material was investigated by conducting a set of milling and drilling experiments. In milling, two different tool paths, spiral and slot milling, were used. To investigate the behavior of BMG in drilling by two different tools at different feed rates, two sets of drilling experiments are conducted. Crown shaped exit burr formation are observed in drilling of BMG. Best results on thrust force, exit burr formation and hole surface roughness is obtained while using micrograin WC tool on BMG drilling. No chip light emission was observed during all tests. This study concludes that BMG can be achieved machining with good surface roughness, (Ra=0.113 µm), using conventional cutting tools.

Abstract: In the present study, the production of magnesium metal from Turkish calcined dolomite containing 43.20 % MgO and 47.46 % CaO via Pidgeon process was studied under the pressure of 1 mbar. In the experiments, Turkish ferrosilicon containing 75 % Si and 24 % Fe was used as reducing agent. Effects of FeSi addition (90-150 % of stoichiometric requirement of silicon) and time (60-240 min.) were investigated on recovering of metallic magnesium from calcined dolomite (dolime) at the temperature of 1200 °C. Effects of fluxing additive (CaF2), calcined magnesite and different temperatures on Mg recoveries and concentrations were also studied using with 100 % of stoichiometric requirement of silicon for 180 min. It was found that magnesium recovery increases with increasing FeSi addition, temperature, time, CaF2 addition and decreases with increasing calcined magnesite additions under the pressure of 1 mbar.