Abdullah Ozturk

MoS2-Nanosheet/Graphene-Oxide Composite Hole Injection Layer in Organic Light-Emitting Diodes

In this work, composite layers comprising two-dimensional MoS2 and graphene oxide (GO) were employed as hole injection layers (HILs) in organic light-emitting diodes (OLEDs). MoS2 was fabricated by the butyllithium (BuLi) intercalation method, while GO was synthesized by a modified Hummers method. The X-ray diffraction patterns showed that the intensity of the MoS2 (002) peak at 14.15° decreased with increase in GO content; the GO (001) peak was observed at 10.07°. In the C 1s synchrotron radiation photoemission spectra, the contributions of the C-O, C=O, and O-C=O components increased with increase in GO content. These results indicated that GO was well mixed with MoS2. The lateral size of MoS2 spanned from a few hundreds of nanometers to 1 μm, while the size of GO was between 400 nm and a few micrometers. Thus, the coverage of the MoS2-GO composite on the ITO surface improved as the GO content increased, owing to the large particle size of GO. Notably, GO with large size could fully cover the indium tin oxide film surface, thus, lowering the roughness. The highest maximum power efficiency (PEmax) was exhibited by the OLED with MoS2-GO 6:4 composite HIL, indicating that similar contents of MoS2 and GO in MoS2-GO composites provide the best results. The OLED with GO HIL showed very high PEmax (4.94 lm W−1) because of very high surface coverage and high work function of GO. These results indicate that the MoS2-GO composites can be used to fabricate HILs in OLEDs.

Silicon carbide particle embedded magnesium oxychloride cement composite bricks for polishing of porcelain stoneware tiles

Abstract Abstract Silicon carbide (SiC) particle embedded magnesium oxychloride cement (MOC) composite polishing bricks developed for polishing of porcelain stoneware tiles were produced by incorporating 600 and 1200 grit SiC particles to the MOC paste in the amounts of 20, 25 and 30 wt-%. Density, compressive strength, abrasion resistance and polishing properties of the bricks were determined with respect to the amount and particle size of the SiC powder. SiC particle embedment enhanced density, compressive strength and abrasion resistance of the neat MOC paste. Polishing was accomplished both in laboratory scale and in a typical online industrial scale. The polishing performance of the bricks was evaluated in terms of mean surface roughness and optical gloss of ceramic tiles, and abrasive brick consumption occurred during polishing. Scanning electron microscopy examinations revealed evidences of the reasons that 25 wt-%SiC particle embedded MOC bricks have the best qualifications in terms of abrasion resistance and polishing performance.

Wear of MgO-CaO-SiO2-P2O5-F-Based Glass Ceramics Compared to Selected Dental Ceramics

Wear of a glass-ceramic produced through controlled crystallization of a glass in the MgO-CaO-SiO2-P2O5-F system has been evaluated and compared to various commercial dental ceramics including IPS Empress 2, Cergo Pressable Ceramic, Cerco Ceram, and Super porcelain EX-3. Wear tests were performed in accord with the ASTM G99 for wear testing with a pin-on-disk apparatus. The friction coefficient and specific wear rate of the materials investigated were determined at a load of 10 N and at ambient laboratory conditions. Microhardness of the materials was also measured to elucidate the appropriateness of these materials for dental applications.

BIOACTIVITY OF APATITE–WOLLASTONITE GLASS-CERAMICS PRODUCED BY MELTING CASTING

Glass-ceramics containing only apatite and wollastonite crystals were produced in the system MgO-CaO-SiO2-P2O5-F by the melt casting process. The bioactivity of the glass-ceramics was determined by immersing the glass-ceramics in a simulated body fluid (SBF) and by assessing the resulting apatite formation on the free surface after various immersion durations. A 12-μm-thick apatite layer formed on the surface of the glass-ceramic containing only apatite crystals after 20 days immersion in SBF. However, the thickness of the apatite layer formed on the surface of the glass-ceramic containing apatite and wollastonite crystals was 1 μm. Results have shown that the bioactivity of glass-ceramic depends strongly on the type of crystal(s) developed during the glass-ceramic process and their proportion in the glassy matrix.

Friction And Wear Behavior Of Selected Dental Ceramics

The purpose of this study was to determine the friction coefficients and wear rates of six commercially available dental ceramics including IPS Empress 2 (E2), Cergo Pressable Ceramic (CPC), Cercon Ceram (CCS) and Super porcelain EX-3 (SPE). Bovine enamel (BE) was also tested as a reference material for comparison purposes. Samples of the dental ceramics were prepared according to the instructions described by the manufacturers in disk-shape with nominal dimensions of 12 mm × 2 mm. The wear tests were performed by means of a pin-on-disk type tribometer. The friction coefficients and specific wear rates of the materials were determined at a load of 10 N and rotating speed of 0.25 cm/s without lubrication. Surface morphology of the wear tracks was examined using a scanning electron microscope. Statistical analyses were made using one-way ANOVA and Turkeys HSD (P

Facile synthesis of CsPbBr3/PbSe composite clusters

Abstract In this work, CsPbBr3 and PbSe nanocomposites were synthesized to protect perovskite material from self-enlargement during reaction. UV absorption and photoluminescence (PL) spectra indicate that the addition of Se into CsPbBr3 quantum dots modified the electronic structure of CsPbBr3, increasing the band gap from 2.38 to 2.48 eV as the Cs:Se ratio increased to 1:3. Thus, the emission color of CsPbBr3 perovskite quantum dots was modified from green to blue by increasing the Se ratio in composites. According to X-ray diffraction patterns, the structure of CsPbBr3 quantum dots changed from cubic to orthorhombic due to the introduction of PbSe at the surface. Transmission electron microscopy and X-ray photoemission spectroscopy confirmed that the atomic distribution in CsPbBr3/PbSe composite clusters is uniform and the composite materials were well formed. The PL intensity of a CsPbBr3/PbSe sample with a 1:1 Cs:Se ratio maintained 50% of its initial intensity after keeping the sample for 81 h in air, while the PL intensity of CsPbBr3 reduced to 20% of its initial intensity. Therefore, it is considered that low amounts of Se could improve the stability of CsPbBr3 quantum dots.

Microstructure and indentation fracture toughness of mica glass ceramics

Mica glass ceramics were produced through controlled crystallisation of a glass in the SiO2-Al2O3-CaO-MgO-K2O-MgF system. TiO2, P2O5 and ZrO2 were added individually as nucleating agents in the amount of 0.5 or 1.0 wt% of the glass. Crystalline phases were identified by X-ray diffraction. The effects of small amounts of various nucleating agents on the microstructure were determined by scanning electron microscopy. Microstructural analyses were supplemented with measurements of the Vickers microhardness and indentation fracture toughness. The amount and kind of nucleating agent did not change the number of crystalline phases present but had an influence on the shape and size of the crystals, and hence on the indentation fracture toughness of the mica glass ceramics. The values for the indentation fracture toughness for the mica glass ceramics containing 0.5 wt% of TiO2, P2O5 and ZrO2 were 1.69±0.09 MPa.m1/2, 1.74 ± 0.10 MPa.m1/2 and 1.77 ± 0.12 MPa.m1/2, respectively.

Mechanical Behavior of a Tightly Woven Carbon-Carbon Composite

The mechanical properties and failure behavior of a tightly woven carbon-carbon composite were investigated and correlated with microstructural features. The analysis of fracture surfaces and microstructural characterization were accomplished using scanning electron microscopy. The tensile strength, flexural strength, fracture toughness, and failure mechanisms of this composite were determined at elevated temperatures. Strength and fracture toughness of the composite increased in argon, but decreased in air as the temperature increased. Microscopic observations of the fracture surfaces of the broken specimens revealed that the composite failed in a tension/shear mixed mode rather than in pure tension.

Production of Highly Efficient Photocatalytic TiO2 Powders by Mechanical Ball Milling

Highly efficient photocatalytic TiO2 powders were prepared using a conventional ball mill with various milling times of 0, 12, 24 and 48 h. The photocatalytic activity of the prepared TiO2 powders was evaluated using the decomposition rate obtained by methylene blue (MB) solution and acetic acid gas under UV light irritation. After 24 h milling, the particle size decreased from 555 nm to 122 nm without changing any of the crystal structure. The photocatalytic TiO2 powders prepared by 24 h milling decomposed 94% of the methylene blue solution while the non-milled TiO2 powders provided only 61% decomposition. After the removal of acetic acid gas, it took 1.5 h for the 24h-milled powders to decompose 100%, while the non-milled TiO2 showed 73% decomposition with same UV illumination duration.

Influence of Particle Size of TiO2 Powder on the Energy Conversion Efficiency of a Dye-Sensitized Solar Cell

Dye-sensitized solar cells (DSSCs) have been fabricated using a TiO2 paste composed of mixtures of 25 nm and 250 nm TiO2 particles at various ratios. A maximum energy conversion efficiency of 6.7% has been achieved using the DSSC, based on a TiO2 layer composed of 40 wt% 25 nm and 60 wt% 250 nm TiO2 particles. The short-circuit current density, open-circuit voltage, and filling factor of the cell were 12.95 mA, 0.82 V, and 0.63, respectively. The overall performance of the DSSCs based on TiO2 layers composed using a mixture of two different sized particles is much better than that of either only 25 nm or only 250 nm TiO2 particles. It is recognized that adding the larger particles to the small particles in the TiO2 paste increases the dye absorption and light scattering effects of DSSC, resulting in a higher short-circuit current density and improved energy conversion efficiency.