Özkan Küçük

Application of Taguchi method in the optimization of dissolution of ulexite in NH4Cl Solutions

The Taguchi method was used to determine optimum conditions for the dissolution of ulexite in NH4Cl solutions. The ranges of experimental parameters were between 50–87 ‡C for reaction temperature, 0.05-0.20 gmL-1 for solid-to-liquid ratio, 1–4 M for NH4Cl concentration, 5–25 min for reaction time, and (-850+600)-(-90) Μm for particle size. The optimum conditions for these parameters were found to be 87 ‡C, 0.05 gmL-1, 4M, (-300+212) Μm, and 18 minutes, respectively. Under these conditions, the dissolution percentage of ulexite in NH4Cl solution was 98.37. Reaction products were found to be boric acid, ammonium tetraborates, sodium tetraborate decahydrate, calcium chloride, and sodium chloride.

Investigation of structural, tribological and corrosion properties of electroless Ni–B coating deposited on 316L stainless steel

The AISI 316L type of stainless steel is a popular steel material, as it has excellent corrosion resistance in aqueous solutions at ambient temperatures. However, the application of the AISI 316L stainless steel is limited by its relatively low hardness and low wear resistance. In this study, the electroless Ni–B coating was deposited on the AISI 316L stainless steel, and its structural, tribological and corrosion properties were characterised. Microstructural analysis showed that the electroless Ni–B coating deposited on the AISI 316L steel substrate exhibited a typical cauliflower-like structure exhibits an amorphous growth. From this study, it may be concluded that this process cannot only improve the hardness and wear resistance of the 316L stainless steel, but can also provide cathodic protection without losing or sacrificing the original properties of the 316L stainless steel.

Tribological and corrosion behaviour of electroless Ni-B coating possessing a blackberry like structure

This study aims to evaluate the tribological and corrosion properties of the electroless Ni-B coating deposited on AISI 304 stainless steels. The microstructure of the coating was characterized using x-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS). XRD analysis revealed that the prepared coating possessed an amorphous character. SEM-EDS investigation also indicated that a non-stoichiometric Ni-B coating was deposited with a columnar growth mechanism on the stainless steel substrate and the morphology of the growth surface was blackberry-like. The hardness and tribological properties were characterized by microhardness and a pin-on-disc wear test. The electroless Ni-B coated sample had a higher degree of hardness, a lower friction coefficient and a lower wear rate than the uncoated substrate. The electrochemical potentiodynamic polarization method was used to evaluate the corrosion resistance of the coating. The electroless Ni-B coating offered cathodic protection on the substrate by acting as a sacrificial anode although it was electrochemically more reactive than the stainless steel substrate.

Sulphur removal from Artvin-Yusufeli lignite with acidic hydrogen peroxide solutions

In this study, the optimisation of sulphur removal by H2O2/H2SO4 solutions, and a limited kinetic measurements by H2O2/HCl solutions have been carried over Artvin/Yusufeli lignite. In kinetic measurements, only the effect of temperature on removal of sulphur has been investigated. By keeping all other parameters constant, with increments in temperature at different times, it has been seen that removal of sulphur is increased. A statistical experimental arrangement which has six parameters and for each parameter there is twenty five experiments with five levels. In generally, pyritic sulphur, total sulphur, organic sulphur and ash removal rates have been determined. According to carried out variance analysis, in removal of pyritic and total sulphur, all parameters are effective, but, in removal of organic sulphur, acid concentration and particle size are not effective, and in removal of ash, only, acid concentration is not effective, however, all other parameters are effective.