Effect of Substituents on Rates of Reactions: Kinetics of Oxidation of Substituted Benzaldehydes by Vanadium(V)

1073-107

Radioactive isotopes reveal a non sluggish kinetics of grain boundary diffusion in high entropy alloys

High entropy alloys (HEAs) have emerged as a new class of multicomponent materials, which have potential for high temperature applications. Phase stability and creep deformation, two key selection criteria for high temperature materials, are predominantly influenced by the diffusion of constituent elements along the grain boundaries (GBs). For the first time, GB diffusion of Ni in chemically homogeneous CoCrFeNi and CoCrFeMnNi HEAs is measured by radiotracer analysis using the $^{63}$Ni isotope. Atom probe tomography confirmed the absence of elemental segregation at GBs that allowed reliable estimation of the GB width to be about 0.5 nm. Our GB diffusion measurements prove that a mere increase in number of constituent elements does not lower the diffusion rates in HEAs, but the nature of added constituents plays a more decisive role. The GB energies in both HEAs are estimated at about 0.8-0.9 J/m$^2$, they are found to increase significantly with temperature and the effect is more pronounced for the CoCrFeMnNi alloy.Comment: 11 pages, 9 figure

On amorphization and nanocomposite formation in Al-Ni-Ti system by mechanical alloying

Amorphous structure generated by mechanical alloying (MA) is often used as a precursor for generating nanocomposites through controlled devitrification. The amorphous forming composition range of ternary Al-Ni-Ti system was calculated using the extended Miedema's semi-empirical model. Eleven compositions of this system showing a wide range of negative enthalpy of mixing (-ΔH mix) and amorphization (-ΔH amor) of the constituent elements were selected for synthesis by MA. The Al88Ni6Ti6 alloy with relatively small negative ΔH mix (-0.4 kJ/mol) and ΔHamor (-14.8 kJ/mol) became completely amorphous after 120 h of milling, which is possibly the first report of complete amorphization of an Al-based rare earth element free Al-TM-TM system (TM = transition metal) by MA. The alloys of other compositions selected had much more negative ΔHmix and Hamor; but they yielded either nanocomposites of partial amorphous and crystalline structure or no amorphous phase at all in the as-milled condition, evidencing a high degree of stability of the intermetallic phases under the MA environment. Hence, the negative ΔH mix and ΔH amor are not so reliable for predicting the amorphization in the present system by MA

Beneficiation of Indian Heavy Mineral Sands- Some New Possibilities Identified by Tata Steel

Titanium, the 9th most abundant element on the earth's crust, is available mostly (90%)in the form of ilmenite (FeO.TiO2) and leucoxene (weathered ilmenite). These titanium bearing minerals occur either as placer minerals or some times, as rock deposits (e.g. in canada and Norway

A localised chlorophyll deficiency associated with male sterility in Nicotiana tabacum L.

This article does not have an abstract

On the occurrence of Acanthaster planci (the crown-of-thorns) at Minicoy Atoll.

The predation of coral-polyps by the multi-armed star fish Acanthaster planci is identified during the last two decades as a major biological factor that causes large scale death to reef corals at several parts of the Indo-Pacific. During a recent visit by a team of scientists from Central Marine Fisheries Research Institute,the presence of this star fish in the lagoon of Minicoy Atoll was noticed in November, 1979.Many control measures of star fishes have been practised elsewhere in the Pacific. However, hand-picking of the adults with the aid of pointed spears and killing them with formalin or ammonia solution is the most eifective.Careful search among the corals is required, since the crown-of-thorns hide under the crevices during day time

New foam stabilising additive for alumnium

Liquid metals are mostly made foamable by Ca additions followed by a thickening period. There is a need for an additive that can be easily admixed to an aluminium alloy melt and makes this melt foamable. We have selected aluminium-based grain refiner composites to test their foamability. TiB2, TiC or TiAl3 particles were produced in the melt by flux-assisted melting using fluoride salts. The particle size was kept below 1 im for TiB2 and TiC and around 10µm for TiAl3. The composites were heated to above their melting point (700°C) and were then foamed by either the addition of TiH2 or by injecting gases into the melt directly. Foams were successfully produced using TiB2 and TiC particles, while TiAl3 did not lead to any foam. Foam stability increased from TiB2 to TiC. Ex-situ characterisation of the foams by SEM showed that the particles segregate to the surfaces of the cell walls and lead to almost dense coverages there. Even after dilution of the initial composite a significant amount of foam can be still produced, indicating that these composites are suitable foam stabilizing additive for aluminium alloys and that foams based on small volume fractions of nonmetallic additives can be produced

The production of short-lived radionuclides by new non-rotating and rotating Wolf-Rayet model stars

It has been speculated that WR winds may have contaminated the forming solar system, in particular with short-lived radionuclides (half-lives in the approximate 10^5 - 10^8 y range) that are responsible for a class of isotopic anomalies found in some meteoritic materials. We revisit the capability of the WR winds to eject these radionuclides using new models of single non-exploding WR stars with metallicity Z = 0.02. The earlier predictions for non-rotating WR stars are updated, and models for rotating such stars are used for the first time in this context. We find that (1) rotation has no significant influence on the short-lived radionuclide production by neutron capture during the core He-burning phase, and (2) 26Al, 36Cl, 41Ca, and 107Pd can be wind-ejected by a variety of WR stars at relative levels that are compatible with the meteoritic analyses for a period of free decay of around 10^5 y between production and incorporation into the forming solar system solid bodies. We confirm the previously published conclusions that the winds of WR stars have a radionuclide composition that can meet the necessary condition for them to be a possible contaminating agent of the forming solar system. Still, it remains to be demonstrated from detailed models that this is a sufficient condition for these winds to have provided a level of pollution that is compatible with the observations.Comment: 8 pages, 8 figure

Prawn fishery off the west coast of India in relation to hydrographical conditions of the shelf waters

Based on the hydrographic data collected on board R. V. Kalava and R. V. Varuna, the vertical distribution patterns of temperature, densiiy (sigma-0 and dissolved oxygen content of sea water at five places between Cape Comorin and Mangalore were studied. In the present account an attempt is made to correlate the hydrogiaphic data with the prawn landings in the regicn concerned. The prawn fishery flourishes well during the south-west monsoon period when catches are high off the Kerala coast

A partial chlorophyll deficiency in Nicotiana tabacum L.

This article does not have an abstract