TiB whisker coating on titanium surfaces by solid-state diffusion: Synthesis,microstructure, and mechanical properties

The study demonstrates the feasibility of synthesizing TiB whiskers on titanium (Ti) surfaces by solid-state diffusion to form a hard and wear-resistant coating. The microstructural and mechanical properties of the TiB coating layer have also been investigated. The TiB coating was formed by the solid-state diffusion of boron (B) from a powder mixture containing amorphous boron, Na₂CO₃ powder, and charcoal (activated) powder. The diffusion process was carried out at various temperatures ranging from 800 °C to 1000 °C for various periods of time ranging from 1 to 24 hours. The amount of Na₂CO₃ in the mixture was also varied. It has been found that pristine and extremely fine TiB whiskers form on the surfaces of titanium, with the whiskers growing more or less normal to the surface. A maximum coating thickness of about 218 μm was observed for the pack diffusion conditions at 850 °C for 24 hours with 15 pct Na₂CO₃. The kinetics of TiB formation was found to follow the growth rates in bulk composites. The X-ray diffraction (XRD) patterns of the coatings revealed the dominant TiB peaks with a very few TiB₂ peaks, with small intensity at higher temperature and time. The surface hardness of the coated layer increased to a Vickers hardness of about 550 kgf/mm² due to the presence of TiB whiskers in the coating. It is shown that pack diffusion of boron in the solid state is a simple and very effective means of generating hard and wear-resistant coatings on titanium.     

Thermodynamic mechanism of free heme action on sickle cell hemoglobin polymerization

For insights into the mechanisms of heme action on the rate of sickle cell hemoglobin polymerization, we determine the erythrocytic concentration of free heme using a novel method based on enzymatic catalysis and luminescence. We find in sickle cell patients 44 ± 10 µM, in sickle trait individuals, 33 ± 4 µM, and in healthy adults, 21 ± 2 µM. We test the applicability of two mechanisms of heme action: a kinetic one, whereby heme aggregates serve as heterogeneous nucleation centers, and a thermodynamic pathway, in which free heme enhances the attraction between sickle hemoglobin (HbS) molecules in solution. We show that the latter mechanism exclusively operates. The enhanced attraction leads to increase of the total volume of a population of dense liquid clusters by about two orders of magnitude. As the dense liquid clusters serve as locations and precursors to the formation of the HbS polymer nuclei, their increased volume directly leads to faster polymer nucleation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2861–2870, 2015     

Structural and morphological investigations on DC-magnetron-sputtered nickel films deposited on Si (100)

Pure nickel thin films were deposited on Si (100) substrates under different conditions of sputtering using direct current magnetron sputtering from a nickel metal target. The different deposition parameters employed for this study are target power, argon gas pressure, substrate temperature and substrate-bias voltage. The films exhibited high density of void boundaries with reduction in <111> texture deposited under high argon gas pressures. At argon gas pressure of 5 mTorr and target power of 300 W, Ni deposition rate was ~40 nm/min. In addition, coalescence of grains accompanied with increase in the film texture was observed at high DC power. Ni films undergo morphological transition from continuous, dense void boundaries to microstructure free from voids as the substrate-bias voltage was increased from −10 to −90 V. Furthermore, as the substrate temperature was increased, the films revealed strong <111> fiber texture accompanied with near-equiaxed grain structure. Ni films deposited at 770 K showed the layer-by-layer film formation which lead to dense, continuous microstructure with increase in the grain size.     

Study of three‐dimensional natural convection and entropy generation in an inclined solar collector equipped with partitions

Three‐dimensional natural convection in an inclined solar collector equipped with partitions has been investigated numerically. The presence of partitions improves the performances of the collector by increasing the heat transfer near the absorber. A parametric study was done for various partitions length and Rayleigh numbers, while Prandtl number and inclination angle were fixed at 0.71 and 45°, respectively. Results are reported in terms of isosurfaces of temperature, isotherms, particles trajectories, velocity vector projection, average Nusselt number along the absorber plate and entropies generation contours.     

Preparation and characterization of stable aqueous higher-order fullerenes

Stable aqueous suspensions of nC?? and individual higher fullerenes, i.e. C??, C?? and C??, are prepared by a calorimetric modification of a commonly used liquid-liquid extraction technique. The energy requirement for synthesis of higher fullerenes has been guided by molecular-scale interaction energy calculations. Solubilized fullerenes show crystalline behavior by exhibiting lattice fringes in high resolution transmission electron microscopy images. The fullerene colloidal suspensions thus prepared are stable with a narrow distribution of cluster radii (42.7 ± 0.8 nm, 46.0 ± 14.0 nm, 60 ± 3.2 nm and 56.3 ± 1.1 nm for nC??, nC??, nC?? and nC??, respectively) as measured by time-resolved dynamic light scattering. The ζ-potential values for all fullerene samples showed negative surface potentials with similar magnitude ( - 38.6 ± 5.8 mV, - 39.1 ± 4.2 mV, - 38.9 ± 5.8 mV and - 41.7 ± 5.1 mV for nC??, nC??, nC?? and nC??, respectively), which provide electrostatic stability to the colloidal clusters. This energy-based modified solubilization technique to produce stable aqueous fullerenes will likely aid in future studies focusing on better applicability, determination of colloidal properties, and understanding of environmental fate, transport and toxicity of higher-order fullerenes.     

Effect of weathering on physico-chemical properties and combustion behavior of an Indian thermal coal

International Journal of Coal Science & Technology - An open air stockpile of conical shape was formed with 3.5&nbsp;m base diameter and 5&nbsp;m height using 500 tons of...     

Oscillatory natural convection of water-glycerin mixture in a tall rectangular cavity: Transition to the chaos

This paper presents results of a numerical investigation involving bifurcation sequence leading to chaos in natural convection inside a vertically tall rectangular cavity having an aspect ratio equal to 15 and a Prandtl number equal to 125, corresponding to water-glycerin mixture. The flow is characterized by a vertical stratification of the temperature field for Grashof numbers greater than or equal to 200 that is outside the conduction regime and it is stationary monocellular up to a critical value Gr_c = 2800 where a periodic oscillatory regime appears. As Grashof number is increased, a transition from a steady periodic bicellular flow to an oscillatory multicellular flow, with 2 main central cells and 2 secondary cells, occurs. The regime remains periodic until Gr = 3100 where there is a first appearance of the chaotic regime which extends over a narrow interval of the Grashof number delimited by Gr = 3200.     

Interactions of the antiviral quinoxaline derivative 9-OH-B220 [2, 3-dimethyl-6-(dimethylaminoethyl)- 9-hydroxy-6H-indolo-[2, 3-b]quinoxaline] with duplex and triplex forms of synthetic DNA and RNA

The binding of an antiviral quinoxaline derivative, 2,3-dimethyl- 6 - (dimethylaminoethyl) - 9 - hydroxy - 6H - indolo - [2,3 - b]quinoxaline (9-OH-B220), to synthetic double and triple helical DNA (poly(dA).poly(dT) and poly(dA).2poly(dT)) and RNA (poly(rA). poly(rU) and poly (rA).2poly(rU)) has been characterized using flow linear dichroism (LD), circular dichroism (CD), fluorescence spectroscopy, and thermal denaturation. When either of the DNA structures or the RNA duplex serve as host polymers a strongly negative LD is displayed, consistent with intercalation of the chromophoric ring system between the base-pairs/triplets of the nucleic acid structures. Evidence for this geometry also includes weak induced CD signals and strong increments of the fluorescence emission intensities upon binding of the drug to each of these polymer structures. In agreement with intercalative binding, 9-OH-B220 is found to effectively enhance the thermal stability of both the double and triple helical states of DNA as well as the RNA duplex. In the case of poly(dA).2poly(dT), the drug provides an unusually large stabilization of its triple helical state; upon binding of 9-OH-B220 the triplex-to-duplex equilibrium is shifted towards higher temperature by 52.5 deg. C in a 10 mM sodium cacodylate buffer (pH 7.0) containing 100 mM NaCl and 1 mM EDTA. When triplex RNA serves as host structure, LD indicates that the average orientation angle between the drug chromophore plane and the helix axis of the triple helical RNA is only about 60 to 65 degrees. Moreover, the thermal stabilizing capability, as well as the fluorescence increment, CD inducing power and perturbations of the absorption envelope, of 9-OH-B220 in complex with the RNA triplex are all less pronounced than those observed for the complexes with DNA and duplex RNA. These features indicate binding of 9-OH-B220 in the wide and shallow minor groove of poly(rA).2poly(rU). Based on the present results, some implications for the applications of this low-toxic, antiviral and easily administered drug in an antigene strategy, as well as its potential use as an antiretroviral agent, are discussed.     

Geospatial analysis of the association between bedrock fractures and vegetation in an arid environment

Remote sensing and GIS techniques were applied to a high resolution air photograph from Arches National Park, Utah in order to quantify the spatial correlation between bedrock fractures and the distribution of surface vegetation. Field surveys conducted on the north‐east limb of Salt Valley anticline reveal four distinct fracture sets in massive sandstone beds of the Curtis Formation. The most pervasive fractures belong to two sets of mega‐scale joints (J1 and J2) that trend NW–SE. Over 10 000 joint traces were digitized from the rectified air photographs encompassing an area of 0.72 km². Joint orientations were extracted in the GIS, allowing for their division into discrete sets and the calculation of mean orientations. A raster map of vegetation was derived from unsupervised classification of the air photograph. Clusters of vegetation, enhanced by filtering, are preferentially aligned in linear trends that closely correspond to the NW–SE joints. Further, a buffer analysis applied to the J1 and J2 joint sets indicates a systematic decrease in vegetation with increasing distance from the mega‐scale joints. Strong correlations in orientation and proximity demonstrate that bedrock fractures may strongly influence the distribution of vegetation in arid environments, especially where bedrock constitutes the majority of land cover and soils are thin.