Mehmet Uysal

Pulse electrocodeposition of Ni/MWCNT nanocomposite coatings

Abstract Nickel/multiwalled carbon nanotube (MWCNT) metal matrix composite coatings were deposited by pulse electrocodeposition method from a Watts type electrolyte. The influence of peak current density on the particle codeposition and distribution, the surface morphology, microstructure, microhardness and wear resistance of nanocomposite coatings were studied. Copper substrates were used for electrocodeposition and MWCNTs with the diameter of 50–60 nm and length of 10 μm used as reinforcements. The electrodeposited Ni matrix coatings were characterised by scanning electron microscopy, Raman spectroscopy and X-ray diffraction analysis.

The Preparation of Zeolite/Ag Composite Powders by Electroless Deposition Process

Core-shell Ag-coated zeolite composite powders were synthesized using silver electroless deposition process, which was carried out in an ammonia-based coating solution containing silver nitrate as a precursor material. The influence of the chemical components and powder concentration in the Ag coating was investigated by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction techniques. The zeolite/Ag composite powders were fabricated in order to find an antibacterial material and a new implant material based on the microstructural change of zeolite/Ag composites powders using different parameters of Ag deposition.

Ni/MWCNT Coatings Produced by Pulse Electrocodeposition Technique

Nickel/multiwalled carbon nanotube (MWCNT) metal matrix composite coatings were deposited by pulse electrocodeposition method from a Watts-type electrolyte. The influence of the MWCNT content in the electrolyte on the particle codeposition and distribution, the surface morphology, microstructure, microhardness of nanocomposite coatings were studied. Copper substrates were used for electrocodeposition of Ni matrix/MWCNTs with the diameter of 50–60 nm and length of 10-µm carbon nanotube reinforcements. The electrodeposited Ni matrix coatings were characterized by scanning electron microscopy and X-ray diffraction analysis.

Wear Behavior of Bronze Hybrid MMCs Coatings Produced by Current Sintering on Steel Substrates

In this work, a bronze matrix (90 wt% Cu + 10 wt% Sn) was reinforced with SiC and graphite particulates using mechanical alloying and a subsequent current sintering technique. The mechanically ball-milled bronze hybrid matrix composite powders reinforced with 5.0 wt% SiC and 5.0 wt% graphite were cold-compacted on a 1040 steel substrate under a pressure of 300 MPa. The compacted structure was sintered at atmospheric conditions to nearly a full density within 10 min using current sintering, in which the powders were heated by a low voltage and high current and compressed simultaneously. The samples were sintered at three different applied currents (1,500, 1,700, and 1,900 A) to provide dense and well-bonded coatings on steel substrates. Microhardness testing and optical and scanning electron microscopes (SEM) were used for microstructural characterization of the hybrid composites. The tribological characterization of the resulting composites was tested by a block-on-disk method for determination of the wear loss and friction coefficient behaviors against a steel disk. It was pointed out that increasing applied current during the sintering/coating process resulted in obtaining high-hardness and wear-resistant hybrid composite coatings.

Türkiye’de 2005-2014 Yılları Arasında Yayınlanan Uzaktan Eğitim Tezlerindeki Yöntemsel Eğilimler: Bir İçerik Analizi

Distance education is an important research subject in Turkey like it is in the world, and there are many master’s and doctoral theses exist that deal with distance education. The aim of this study is to reveal current research trends in distance education theses published in Turkey between 2005 and 2014. In this direction, 380theses that are open to access on the Council of Higher Education (CoHE) national theses database were reviewed. The theses were entered by using “Distance Education Theses Examination Form” (DETEF) which contains thesis type, thesis subject, publication year, university, institute, department, research method, research design, sampling method, sample population, data collecting tool and data analysis. The method sections of the theses were analyzed with descriptive content analysis. The results indicated that while the number of theses in the field of distance education were on the rise until 2010, the number of thesis started to decrease within following years. In addition, it was determined that institutes employ different research methodologies. Another result is that the most used research design is survey in quantitative methodology theses, case studies in qualitative and mixed methodology theses. It was determined that the sampling method is not expressed in most of the theses based on the quantitative methodology. On the other hand, purposeful sampling is most used in theses based on the qualitative methodology. The most commonly studied sample population were undergraduate students and adults for all methodologies. With regard to the data collecting tools used in the distance education theses, surveys and scales are mostly used in the quantitative methodology while the interview method is mostly used in the theses based on the qualitative methodology. Besides, it was determined that basic statistical techniques were used in distance education theses. From this results, in order to conduct more scientific and qualified studies related to distance education, all research methodologies, which are not adequately and effectively used as the findings show, should be encouraged.

Cr- and V-Substituted LiMn2O4 Cathode Electrode Materials for High-Rate Battery Applications

Spinel Cr- and V-substituted LiMn2O4 cathode materials were prepared by facile sol–gel process, which used lithium carbonate and manganese carbonate as starting materials and citric acid as a chelating agent. In order to increase electronic conductivity and prevent the Mn ion dissolution into the electrolyte, surfaces of the as-synthesized powders were coated with Cu via electroless deposition technique. The structure and physicochemical properties of the obtained Cr- and V-substituted LiMn2O4 powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge discharge tests, and electrochemical impedance spectroscopy (EIS). The results have shown that the successful formation of Cr- and V-substituted LiMn2O4 product was highly dependent on its second-stage calcination temperature.

A reciprocating wear study on the effect of surfactant concentration and sliding speed in the electro codeposited Ni/SiCp metal matrix composites

In this present work, Ni/SiC metal matrix composite coatings were prepared from a modified Watt’s type electrolyte containing nano-SiC suspended particles by direct current plating method to increase the wear resistance of Ni. The influence of surfactant content on codeposition of SiC particles within the matrix and tribological properties were investigated. A wide particle size range (between 0.1 and 1.0 µm) was chosen to provide a high load bearing ability for the codeposited layers. The wear tests were carried out at different sliding speeds by using a constant load. The influence of sliding speed on the tribological performances of the coatings has been investigated by using a reciprocating ball-on disk apparatus. Wear resistances and friction coefficients of Ni/SiC composites were decreased by increasing sliding speed due to temperature-controlled surface oxidation. The change in wear mechanisms by changing surfactant content and sliding speeds were also comprehensively studied.