Effect of oxygen partial pressure on the microstructural and physical properties on nanocrystalline tin oxide films grown by plasma oxidation after thermal deposition from pure Sn targets

In this work, microstructural and physical properties were studied in the tin oxide films deposited by thermal evaporation of Sn films on stainless steel substrates followed by in situ D.C. plasma oxidation at 200 °C substrate temperature. The surface properties were studied by scanning electron microscopy, X-ray diffraction, atomic force microscopy and four-point probe electrical resistivity. The typical calculated grain size of the films deposited by thermal evaporation was between 28 nm and 66 nm and the texture structure was found to be dependent on the thermal deposition pressure. A cassiterite structure of SnO₂ was produced by D.C. plasma oxidation with the main diffraction peaks of the (101), (200), (211), (310) and (221) planes at the 25% and 50% O₂ partial pressure conditions. However, at 12.5% O₂ partial pressure oxidation conditions, amorphous tin oxide structure and crystalline SnO phases were detected. Increasing thermal deposition pressure resulted in preferential texture formation at (211) and (310) planes. The surface structure investigation of the produced films by SEM and AFM studies showed large SnO₂ islands with approximately 1.0 μm and 1.5 μm sized nodules, and they are called as grape-like structures. The grape-like grains possess nano grains, which are between 20 nm and 30 nm in diameter calculated by Scherer's formula. The grape-like grains were seen to be separated by large cavities and the size of these cavities and nano grains was seen to be larger when the O₂ partial pressure is increased. The four-point probe resistivity of the films, grown at different oxidation temperatures, decreased with the increase in oxygen partial pressure. The values of resistivity for SnO₂ phase were measured as low as 10⁻⁵ Ω-cm and observed to decrease with increasing thermal deposition pressure and oxygen partial pressure.     

Hydrodynamic performance of steelmaking tundish systems: a comparative study of three different tundish designs

Extensive water modelling was carried out to ascertain the influence of various types of baffle designs on the hydrodynamic performance of three different designs of steelmaking tundish systems. These included, a two-strand slab casting tundish, a six-strand billet casting tundish and a five-strand, skewed, delta shaped tundish. Plant scale operating conditions were scaled down respecting both geometric and Froude similarity and on the basis of the latter, the inflow rate of water into the model tundish systems was estimated via: Q_m = Λ^5/2Q_f.s. To quantify the hydrodynamic performance, residence time distribution (RTD) characteristics were measured using the conductivity measurement technique for a wide range of baffle designs. From such measurements as well as from flow visualisation studies, the following general observations have been made. The optimum design of baffles together with its number and position within the tundish appear to be a strong function of the basic tundish design (viz., the geometry, the number of operating strands etc.). Of the various types of baffles investigated in this work (dam, dam + weir, baffles with holes etc.), appropriately designed slotted baffles appear to modify the RTD characteristics most favourably towards superior metallurgical performances. Increase in the number of strands, asymmetricity in the tundish design and flawed operating conditions, (viz., large width to length ratio) were all found to influence the tundish performance adversely. A comparison of experimental results for the three tundish systems indicated that changing the characteristics of the baffle design can lead to significant performance improvement in the case of the two symmetric tundish systems (e.g., the two and the six strand tundishes), the five strand skewed, delta shaped tundish was, however, found to be somewhat insensitive to such changes. For such a tundish geometry, no design of the flow-modification devices tried, could bring the hydrodynamic performance any closer to the best results obtained for the two other tundish systems. Possible reasons for such observations are discussed in the text.     

The fabrication and characterization of Al/SiC-MMC castings produced by vacuum assisted solidmould investment casting process

In this paper, a promising manufacturing approach to cast metal matrix composites is proposed. In order to produce metal matrix composites by investment casting, SiC preforms were fabricated in 3D structure. Afterwards, A6063 aluminium alloy matrix material was infiltrated into preforms which were placed in the solid investment casting moulds with vacuum assistance. Preforms were characterized using Archimedes’ test, scanning electron microscope ana X-ray diffraction analysis. Also, fabricated cast specimens, were characterized using hardness tests, image analysis and scanning electron microscope observations. The results show that, in the vacuum assisted solidmould investment casting method; infiltration, of the preforms by molten metal was successfully achieved. Moreover, hardness of the composite higher than the matrix up to ratio of 100% by SiC reinforcement and T6 heat treatment.     

Similarity considerations in the physical modelling of steel making tundish systems

To assess and quantify the relative importance of Reynolds and Froude numbers in reduced scale model studies (these cannot be simultaneously respected when the scale factor is less than unity), aqueous model investigations were carried out on three different laboratory scale tundish models. The experimental tundish systems included two strand, five strand skewed delta shaped and six strand rectangular shaped vessels. Experimental observations show that the depth of liquid in the model would only correspond to that in the full scale system, provided the model flow rate is scaled in accordance with the relationship: Q_m = λ^5/2 Q_f.S, in which, A is the geometrical scaling factor. Furthermore, on the basis of residence time distribution measurements in two different configurations of the five strand tundish, it was demonstrated explicitly that flow phenomena in tundish systems are largely dominated by inertial forces and are therefore, essentially Froude dominated.     

RGD functionalized poly(ε-caprolactone)/poly(m-anthranilic acid) electrospun nanofibers as high-performing scaffolds for bone tissue engineering RGD functionalized PCL/P3ANA nanofibers

RGD functionalized nanofibers of poly(ε-caprolactone)/poly(m-anthranilic acid) (PCL/P3ANA) were fabricated to address the mechanical, structural and functional requirements of bone tissue engineering. Nanofibers containing the highest amount of P3ANA with more carboxyl groups for functionalization have exhibited higher surface area and better mechanical properties. FTIR-ATR and UV-visible measurements evidenced the covalent RGD immobilization. After RGD peptide immobilization, the surface properties of nanofibers changed as evidenced by contact angle and electrochemical impedance spectroscopy (EIS). The effects of RGD functionalized nanofibers (PCL/P3ANA-RGD) on Saos-2 cell attachment, proliferation, and osteogenic activity were investigated. PCL/P3ANA-RGD nanofibers favored cell attachment, proliferation, and osteogenic activity.     

Sintering and microstructure characteristics of 42CrMo4 steel processed by spark plasma sintering

Rapidly solidified micron sized 42CrMo4 steel powder with a size range of 150–250 μm produced by plasma rotating electrode process was consolidated using a recently developed spark plasma sintering (SPS) process. The relationship between sintering parameters (temperature and soaking time) and microstructural properties was investigated. The effect of slow and high heating regimes on the consolidation of sintered compacts has been also investigated. Maximum relative density (99.2%) was obtained at 1000 °C, under 50 MPa pressure, with 8 min holding time and 200 °C/min heating rate. The microstructure of sintered steel was influenced by carburization occuring inside the graphite SPS process die. The diffusion of carbon produced martensite structure near the surface region and hardened the surface. This effect was investigated in detail using optical microscopy and hardness measurement. Scanning electrone microscopy was also used to examine the fracture surface of sintered compacts. High heating rate promoted the relative density at low temperature compared to high temperature.     

Capacitive solvent sensing with interdigitated microelectrodes

Microsystem Technologies - We were able to quantify dielectric properties of solvents such as DI water, isopropyl alcohol, and acetone using interdigitated microelectrodes (IMEs). IMEs were...     

Policy implications of trends in Turkey's meat sector with respect to 2023 vision

Turkey has become one of the leading emerging economies in the world being second after China as the highes ecoonomically growing country with 8.9% economic growth rate in 2010. Forecasting impacts of this development in coming 10 years might have very important policy implications for the meat sector in the framework of 2013 vision of Turkey. In this study, annual time series data which contain several key variables of meat sector in last 26 years (1987–2012) are used to forecast the variables of the coming twelve years (2013–2024) to drive policy implications by considering the impacts of high economic growths, crises and major policy changes. Forecasted future values of the variables for 2023 in the sector are assessed and compared with recent national and international values to drive policy implications. The results show that the economic growth results in the increase in per capita income and thus increased demand for meat seemed to foster the meat sector. Therefore, these macroeconomic indicators need to be better in addition to improvements at micro level for establishing competitive meat sector and thus reaching aimed consumption level of meat.