Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Oxidation and Hot Corrosion Resistance of Atmospheric Plasma Sprayed Conventional and Nanostructured Zirconia Coatings Ahmad Keyvani 1 *, Mohsen Saremi 1 and Mahmoud Heydarzadeh Sohi 1 1 School of Metallurgy and Materials Engineering, University College of Engineering, University of Tehran. P. O. Box 11365-4563, Tehran, Iran Abstract-Conventional and nanostructured zirconia coatings were deposited on In-738 Ni supper alloy by atmospheric plasma spray technique. The oxidation was measured at 1100 °C and hot corrosion resistance of the coatings were measured at 1050 °C using an atmospheric electrical furnace and a fused mixture of vanadium pent oxide and sodium sulfate respectively. According to the experimental results nanostructured coatings showed a better oxidation and hot corrosion resistance than conventional ones. The improved oxidation resistance could be explained by the change of structure to a dense and more packed structure in the nanocoating. The improvement in hot corrosion resistance was not as good as the oxidation but much better than conventional coating. Hydrogen Plasma sprayed thermal barrier coatings based on yttrium stabilized zirconia YSZ, have been applied to hot section components of gas turbine engine to increase the inlet temperature of the combustion chamber [1-3]. Due to low density, high hardness, good stiffness, strength and refractoriness, zirconia based ceramics are considered as a good selection to be used in thermal and wear applications [4]. The coatings sprayed onto cylinder liners and turbine work pieces could enhance the thermal efficiency of internal combustion aerial and gas turbines engines [5]. The TBC coatings are subject to the harsh atmosphere of the combating chamber and facing thermal shock, oxidation and hot corrosion phenomena. Many reports revealed that resistance against: thermal shock, oxidation and hot corrosion resistances of TBC coatings depended mainly on the coating microstructure as well as to the heating conditions. Therefore by controlling the microstructure it would be possible to control the durability of the TBC coatings. It could be improved by use of controlled porosity, segmentation, microcracking, residual stress control and post-spray thermal treatment [6-11]. In recent years, nanostructured zirconia coatings deposited by atmospheric plasma spraying have attracted some research interest because of some superior properties than that of traditional zirconia coatings [12, 13]. Some investigators have reported that nanostructured coatings are expected to improve mechanical properties, show better thermal resistance, and reduce thermal conductivity compared to their coarse-grained coatings [14-18]. Few articles were reported on thermal shock resistance of the nanostructured zirconia coatings but rarely their oxidation and hot corrosion resistances were investigated. Many methods can be used to apply nanostructured TBC such as thermal spary methods, gascondensation process, electron beam vaporization, EBPVD, magnetron sputtering, and electrochemical deposition [19, 20]. Recently, thermal spraying has also been used to prepare nanoscale layers [21, 24]. Therefore, this work aims to investigate and compare the oxidation and hot corrosion resistances of nanostructured zirconia coating applied by the plasma sprayed with conventional ones. In the present study Nickel based super alloy (Inconel 738) was used as substrate. All specimens were in the shape of a disk (Ø25×10mm). The specimen’s surfaces were shot-blasted with alumina grit in the range of 50-80 mesh and under a pressure of 40-50psi. The surface oxides were removed using methyl ethyl kethon cleaner, and degreasing was performed by trichloro ethylene vapor. After washing they were preheated at 150-200°F and finally the following coatings were applied over specimens. Argon was used as primary plasma gas whilst hydrogen was the secondary gas. Amdry 962 trade mark NiCrAlY micro-powders, micro-sized Metco 204NS-G trade mark YSZ conventional zirconia powders were used. The nanosize yttria stabilized zirconia powders were prepared via chemical co-precipitation process, with particle sizes of
Poster Session, Tuesday, June 15 Theme A1 - B702 Mechanical Properties of Graphite and Nano Tubes 1 * 1 r University, Faculty of Engineering, Bornova-,35100,Turkey Abstract- Graphite is one of the special form of carbon. Carbon nanotubes can be thought of as a sheet of graphite (a hexagonal lattice of carbon) rolled into a cylinder. These tubes exhibit important mechanical properties: the Young's modulus is over 10 12 Pascal. Hardness of graphite is quite anisotropic. Graphite is very soft in c-axis direction, but it is very hard in the directions inside the hexagonal-planes. Young Modulus of graphite along a-axis is 103x10 10 N/m 2 but along c-axis is about 3.61x10 10 N/m 2 . So in basal plane bonds are 30 times stronger, that means binding forces among the atoms in hexagonal basal planes are very strong. This property of graphite in some nano-dy es or coating is used to protect the object against corrosion and scratches. In HCP crystal, c/a ratios are quite important for atomic binding forces. In Dy (1.574) and Mg (1.624) c/a ratio is very close to ideal value (1.633), therefore elastic properties nearly isotropic. But in Zn (1.86)and graphite ( 2.31), we have a large anisotropy. Especially in graphite this is quite clear. Young Modulus along a-axis is 103x10 10 N/m 2 and along c-axis is 3.61x10 10 N/m 2 in graphite (Figure.1). Therefore Young’s modulus along a-axis is 30 times greater than that of in c-axis. Longitudinal sound velocity in a-axis is 21 km/s ,4 km/s in c-direction. These calculations show that binding forces between the atoms in basal plane of the graphite are very strong, these forces are quite weak in the c-direction. The weakness of the bond explain why graphite is so soft even though its melting point is so high. Soft materials are easily compressed. Therefore if compressibility has high value that material can easily compressed or deformed. this means that the atomic binding forces are weak in that special direction in the substance. Ultrasonic velocity is very high in the direction in which the binding forces are quite large. Longitudinal wave velocity in the basal plane is 21610 m/s but in the c-axis is about 4010 m/s in graphite. Table 1. Elastic constants of some hexagonal crystals, Cij , ( 10 10 N/m 2 ) C11 C12 C13 C33 C44 c/a Dy 7.31 2.53 2.23 7.81 2.40 1.574 Mg 5.97 2.62 2.17 6.17 1.64 1.624 Zn 16.10 3.42 5.01 6.10 3.83 1.856 Cd 12.10 4.81 4.42 5.13 1.85 1.886 Grafit 106.0 18.0 1.5 3.65 0.4 2.310 Table. 2. Ultrasonic velocities at different directions in Dy, Zn, Mg, Cd ve graphite Velocities Dy Zn Mg Cd Graphite (10 3 m/s ) vL-c-axis 3.02 2.91 5.87 2.43 4.01 vS-c-axis 1.67 2.31 3.02 1.46 1.32 vL-a axis 2.92 4.73 5.77 3.74 21.61 vS-a axis 1.67 2.31 3.02 1.46 1.33 Table.3 Young’s modulus and compressibility’s of some Hexagon al crystals Mg Zn Cd Graphite Young’s Modulus in a-axis (10 10 N/m 2 ) in c-axis (10 10 N/m 2 ) 4.5 5.0 12.0 3.5 8.1 2.8 103.0 3.6 Linear compressibility In a- axis (10 -12 m 2 /N) In c-axis (10 -12 m 2 /N) 9.2 9.7 1.58 13.7 1.5 16.9 0.5 27.0 Volume compresibility 28.1 16.9 19.9 28.0 (10 -12 m 2 /N) Ayasse ,J.B. , et al, (1979), On the Softening of the Elastic Constant C44 in Graphite, Solid State Com. , 5, 659-662. Magnetic Phases in Dy, J. Physics F: Metal Physics, 8, 247 Hexagonal Kristallerin Esneklik Özellikleri, Y.L. Tezi C., e-dergi-http:/joy.yasar.edu.tr,J.of Yasar University, Vol:1,No:4, 1-6 (2006) Figure 1.Young’s modulus of graphite in a-c plane(10 10 N/m 2 ) Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of 1Ttensile strength . Multiwalled carbon nanotube was tested to have a tensile strength of 63 giga pascals (GPa). This means it has the ability to endure tension of 6,3 ton on a cable with crosssection of 1 mm 2 . Since carbon nanotubes have a low density for a solid of 1.3 to 1.4 g·cm , its specific strength of up to 48,000 kN·m/kg is the best of known materials, compared to high-carbon steel's 154 kN·m/kg. The cables made of nano tubes are suggested to be used for spaceelevators in near future. These cables may be as long as 35 000 km and carry space-elevators from the earth to a space-ship or to a space-city. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 360
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