Aysegul Akdogan Eker

Carbon nanotube-based nanocomposites and their applications

Abstract The purpose of the current review article is to present a compherensive understanding regarding pros and cons of carbon nanotube–related nanocomposites and to find ways in order to improve the performance of nanocomposites with new designs. Nanomaterials including carbon nanotubes (CNTs) are employed in industrial applications such as supercapacitors, and biosensors, and etc. The present article has been prepared in three main categories. In the first part, carbon nanotube types have been presented, as single-walled carbon nanotubes, multi-walled carbon nanotubes, and also equivalent circuit models, which have been used to more clarify the experimental measurements of impedance. In the second part, nanocomposites with many carbon, inorganic and polymeric materials such as polymer/CNT, activated carbon/CNT, metal oxide/CNT, and carbon fiber/CNT have been investigated in more detail. In the third part, the focus in on the industrial applications of CNTs. including supercapacitors, biosensors, radar absorbing materials, solar cells, and corrosion protection studies. This review article explains the latest advances in carbon nanotubes and their applications in electrochemical, electrical and optical properties of nanocomposites.

Surface Roughness Changes and Corrosion on Nickel Titanium Orthodontic Wires Compared to Stainless Steel Wires in Various Artificial Salivas

Abstract Nickel titanium shape memory alloy and stainless steel orthodontic wires were exposed to three different artificial saliva solutions which are modified Fusayama, modified Fusayama with 1g/l NaF addition and modified Fusayama with 1.7 % H3PO4 addition. Under conditions similar to oral cavity temperature, corrosion behaviours were observed by using weight loss method and by macro surface photographic observations. Also, surface roughness of wires were investigated and compared. Consequently, it was determined that corrosion rates of all NiTi wires exposed to the modified Fusayama solutions with NaF addition are higher because of galvanic interaction of NiTi and hydrogen embrittlement of titanium. Also, surface roughness of NiTi wires were increased in modified Fusayama solution with NaF addition.

Creep Behaviour of NearEquiatomic Nickel-Titanium Wires

Abstract The creep behaviour of near-equiatomic (50.8 at.-% Ni) NiTi wire with a diameter of 0.49 mm is studied between 82 MPa and 127 MPa tensile stress as well as in a temperature range of 575 °C to 650 °C. For 600 °C and between 82–107 MPa a stress exponent of n = 4.5 as well as for 82 MPa between 600–625 °C an activation energy of Q = 300 kJ mol-1 have been found, these results have been compared with previous creep studies. In contrast to previous studies, this investigation has been performed with high stresses for thin NiTi wires. Moreover, fracture surfaces and ductility of wires have been investigated. The main reasons for the various results are discussed.

Chapter 3.5 – Microstructure and Oxidation Behavior of Atmospheric Plasma-Sprayed Thermal Barrier Coatings

Abstract Thermal barrier coatings (TBCs) are widely used as insulation layered at elevated temperatures in gas turbine components. Yttria-stabilized zirconia (YSZ) ceramic has outstanding properties such as phase stability at high temperature, a prolonged service lifetime, and low thermal conductivity, which make it a promising candidate. The high temperature of gas turbines leads to the transfer of oxygen from the top coat to the bond coat; therefore, oxidation occurs on the bond coat; it is called the thermally grown oxide layer and is mainly considered a failure mechanism of TBC systems. Gas turbine engines that have applications in energy production, transportation, and the defense industry depend on high-temperature TBCs for higher efficiency. During thermal cycling, mechanical forces can occur in turbine engines, oxidation, hot corrosion, the sintering of the top coat, and a thermal expansion coefficient mismatch between the metallic substrate and the ceramic top coat as a result of spallation or crack degradation. TBCs can be affected by coating materials, manufacturing processes, and their microstructure. Spallation of the ceramic top coat is a main problem for TBCs because it leads to oxidation, corrosion, and creeps in the TBC system. This chapter gives brief information about thermal barrier materials and the microstructure and oxidation behavior of TBCs.

Developing Flat Drip Irrigation Pipes Using Bioplastic Materials

This study analyzed the use of environmentally friendly, cornstarch based bioplastic raw materials instead of polyethylene based raw material to produce flat drip irrigation pipes, which is the most efficient agricultural irrigation system. Two groups of raw materials were used in the study, low density polyethylene (LDPE) material and cornstarch based biodegradablepoly beta hydroxybutyrate (PHB) raw material. Mixtures are obtained by adding 4 types of PHB raw materials at the ratio of 25%, 30%, 35% and 40% and 5% black masterbatch separately in the form of granules. Test samples were prepared from these mixtures using extrusion film production method. Mechanical tests, shrinking tests and thermal analysis were performed on test samples. Of the raw materials with bioplastic mixture, only the sample obtained from 65% LDPE + 30% PHB + 5% black masterbatch was consistent with the values of commercially available flat drip irrigation pipes with 0.14 mm wall thickness, 443.54 % strain at break, 0.967 g/cm 3 density and 123.36 °C melting point. Moreover, raw materials with bioplast additives obtained from the study are suitable for the use as an alternative material in the polyethylene applications used in the fields of agricultural and industry. KeywordsFlat Drip Irrigation Pipe; Bioplastic; Polyethylene; Extrusion

Surface Roughness Changes on β-Titanium Orthodontic Wires after Corrosion in Various Artificial Saliva Solutions

Abstract β-Titanium orthodontic wires are exposed to three different artificial corrosive environments, modified Fusayama, modified Fusayama with 0.1 % NaF addition, and modified Fusayama with 1.7 % H3PO4 addition, which are similar to the oral cavity conditions. Corrosion behaviours of wires are observed by using weight loss method and scanning electron microscope observations. Afterwards, surface roughness of wires is investigated in details. Consequently, it is determined that corrosion rate of β-titanium wires exposed to the modified Fusayama solutions with H3PO4 addition is higher because of the acidity of this saliva. Furthermore, maximum increase in surface roughness and skewness are observed in the same environment. Hydrogen embrittlement of titanium is also an important factor for the corrosion of wires.

Developing Packaging by Using Smart Material which Helps to Realize Spoilage in Yoghurt

The important effect of yoghurt on peoples health caused increasing of many technological works and researches not only in our country but also all over the world.The environment in which yoghurt kept, may cause many sort of germs and contamination paths by the effects of some factors which are fairly similar to its own structure. These factors change the shelf-life of yoghurt and finally cause spoilage in yoghurt. In this context, it is known that the scientific works in this area which are aiming to minimize this spoilage effect, focus on the yogurt structure and packaging of yoghurt. The aim of this paper is to improve a smart polymer material which interacts with serum and changes color of the package by considering serum occurring within the shelf-life of yoghurt. PP based material will be used with the biological agencies like “kaoline” and “talc” and implemented mainly or superficial, the color change will be arised if the serums PH increases. In practice, everyone can see the color changes with the window which will be placed on the label and the window will include the cautions according to the color levels.