Stress calculations on diamond surfaces

Calculations were carried out to evaluate stresses for atoms located in the top several layers of the (100)-(1 × 1), (100)-(2 × 1) and (111)-(1 × 1) surfaces of diamond. Only equilibrated surfaces were taken into consideration in this investigation. Stress values in the direction perpendicular to the exposed surface vanish. In lateral directions, however, stresses have non-vanishing values, in general. For the (100) surfaces calculated stress values are anisotropic. While the (2 × 1) reconstructed surface is under compression in both directions, calculations for the unreconstructed (1 × 1) plane produced a compressive stress in one direction and a slight tension in the other. On the (111) surface, isotropic and relatively low compressive stress values were found. Present calculations indicate that atoms located only in a few top layers have lateral excess stresses which vanish very quickly for the atoms of interior layers as depart form the exposed surface.     

Etherification rates of 2‐methyl‐2‐butene and 2‐methyl‐1‐butene with ethanol for environmentally clean gasoline production

Etherification of C₅ reactive olefins available in light fluidized catalytic cracking (FCC) gasoline is an attractive way to decrease the olefins and to increase the octane number. The reactivities of 2‐methyl‐1‐butene (2M1B) and 2‐methyl‐2‐butene (2M2B) in the etherification reaction with ethanol catalysed by a strongly acidic macroreticular resin catalyst were investigated in a temperature range of 333–360 K using a liquid phase differential flow reactor. In the presence of excess alcohol, the apparent reaction orders of etherification reactions of isoamylenes were found to be 0.93 and 0.69 with respect to 2M1B and 2M2B concentrations, respectively. 2M1B was shown to be more reactive than 2M2B and its activation energy is also lower in the etherification reaction. It was also shown that diffusion resistances, especially in the macropores of the catalyst, may play an important role on the observed rates. © 1999 Society of Chemical Industry     

Effects of electrochemical boriding process parameters on the formation of titanium borides

In this study, the boriding of titanium via molten salt electrolysis was investigated in borax based electrolyte at various current densities (50–700 mA/cm²), temperatures (900–1200°C) and process durations (1 min-4 h). Thin film XRD results revealed that two main titanium boride phases TiB₂ and TiB was formed even after 1 minute of process time. Scanning electron microscopy (SEM) images conducted on the cross-sections demonstrated a bilayer boride structure composed of a continuous uniform TiB₂ phase and TiB whiskers that grew below the TiB₂ layer toward the substrate. Dependence of boride layer thickness and morphology on the process parameters was evaluated. The results of the study showed that temperature of boriding was the most critical parameter both on boriding rate and morphology of the boride layer. It was possible to grow 8 μm thick TiB₂ layer on titanium in 30 minutes of boriding at 1200°C.     

Damping Properties of Workpieces of a Manganesendash;Copper Alloy of Electroslag Refining

We present the results of experimental investigation of the damping properties of a manganesendash;copper alloy (75percnt;Mnndash;23percnt;Cundash;2percnt;Ni) obtained by using the electroslag-refining technological procedure and a series of full-scale parts of gas-turbine engines made of this alloy. It was discovered that the decrement of flexural vibrations characterizing the damping capacity of specimens and structural elements of the investigated manganesendash;copper alloy is quite high and exceeds the decrement of vibrations of extensively used structural steels and workpieces made of these steels by 1 to 2 orders of magnitude.     

Characterization of activated carbon produced from almond shell and hazelnut shell

Ammonium chloride-impregnated and untreated almond shell and hazelnut shell samples were carbonized in a flow of nitrogen at relatively low temperatures. Pore structure characterization and sorption capacities of activated carbons prepared from shells of almond and hazelnut indicated that treatment with NH₄Cl increased the total surface area and improved sorption characteristics. Chemical activation carried out at 350°C gave products with surface area values above 500 m² g^?1. On the other hand, the surface area values observed for the products obtained from untreated raw materials were about half of this value. The surface area of products obtained from NH₄Cl-impregnated samples reached values of over 700 m² g^?1 when the carbonization temperature was increased 700°C.     

Effects of differences in diet and seasonal changes on the fatty acid composition in fillets from farmed and wild sea bream (Sparus aurata L.) and sea bass (Dicentrarchus labrax L.)

The effects of dietary fatty acids and seasonal variation on the fatty acid profiles of farmed and wild sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) were determined by analysis of their fillets. Farmed sea bream and sea bass were fed on the same commercial feeds all year. Fatty acid profiles in the fillets reflected the fatty acid profiles of the commercial feeds. The predominant fatty acids in the trial feeds, fillets of farmed and wild sea bream and sea bass were 16:0, 18:1n‐9, 18:2n‐6, 20:5n‐3 and 22:6n‐3. The fatty acid profiles in the fillets of farmed sea bream and sea bass did not differ (P > 0.05) except in the winter season compared with those of their wild counterparts. However, the content of eicosapentaenoic acid (20:5n‐3), docosahexaenoic acid (22:6n‐3) in the fillets of the farmed and wild sea bass were significantly (P < 0.05) higher than the farmed and wild sea bream. The wild sea bream had significantly (P < 0.05) higher total saturated fatty acid and monounsaturated fatty acid (MUFA) levels, and lower total n‐6 and n‐3 polyunsaturated fatty acid (PUFA) levels in winter than in the summer and spring seasons. Similarly, in the fillets of wild sea bass, total n‐3 PUFA levels were significantly (P < 0.05) lower, and the MUFA levels were higher in winter than in the other seasons. These results indicate that the farmed fish fillets were good sources of n‐3 PUFA in each of the three seasons. However, wild fish were good sources of n‐3 PUFA in the spring and summer.     

Color-tunable properties of Eu3+- and Dy3+-codoped Y2O3 phosphor particles

Rare-earth phosphors are commonly used in display panels, security printing, and fluorescent lamps, and have potential applications in lasers and bioimaging. In the present study, Eu³⁺- and Dy³⁺-codoped uniform-shaped Y₂O₃ submicron particles were prepared using the urea homogeneous precipitation method. The structure and morphology of the resulting particles were characterized by X-ray diffraction, field emission scanning electron microscope, and field emission transmission electron microscope, whereas their optical properties were monitored by photoluminescence spectroscopy. The room-temperature luminescence color emission of the synthesized particles can be tuned from red to yellow by switching the excitation wavelength from 254 to 350 nm. The luminescence intensities of red and yellow emissions could be altered by varying the dopant concentration. Strong quenching was observed at high Eu³⁺ and Dy³⁺ concentrations in the Y₂O₃ host lattice.