Cathodic protection: introduction and recent developments

Corrosion of metals and alloys, on which the modern world depends completely, fromelectronic components to printed circuit boards, from nuts and bolts to bridges, fromautomobiles to railway parts to boiler tubes and nuclear reactors, is a practical problem oftremendous technological significance. Corrosion leads to colossal financial losses, whichare estimated to be 3-4% of GNP of a nation, not to speak of the loss of human lives,reputation, environment, aesthetics as well as shut-down and production losses. Of thevarious preventive measures like alloying, corrosion inhibitors, protective coatings, paints,design etc. to combat corrosion, only cathodic protection can guarantee 100% protection, ifproperly designed, executed and supplemented by protective coatings.The ABC ofcorrosion, principle of cathodic protection, with special reference to the development ofaluminium based sacrificial anodes like SUPERAL (medium output) and HOPAL (highoutput) as also insoluble anode like Sintered Magnetite Anode (SMA) in the NationalMetallurgical Laboratory in India, have been included in the paper. While the technology forthe sacrificial Al-based anodes has been transferred to two parties in India, SMA developedby NML is found to be the best because of its unique properties and low cost, compared to theconventionally used insoluble anodes. A cathodic protection system has also been designedand developed by NML with SMA, which is auto-controlled and very economical.AML hasalso successfully designed and executed the cathodic protection of the old water main lines(made from bare steel) in Calcutta, using Al-based sacrificial anodes.Merits and demerits ofgalvanic system compared to impressed current system and major research institutesengaged in corrosion area are listed Pertinent references have been cited for access to theoriginal and detailed literature

Aggregation state of Mycobacterium tuberculosis impacts host immunity and augments pulmonary disease pathology

Kolloli et al. examine whether aggregation contributes to enhanced pathogenicity of Mycobacterium tuberculosis in a rabbit model of pulmonary infection. They demonstrate that aggregation increases the ability of M. tuberculosis to grow robustly and promote inflammation and host cell death in the rabbit lungs, thus increasing disease burden

Theoretical predictions for hot-carrier generation from surface plasmon decay

Decay of surface plasmons to hot carriers finds a wide variety of applications in energy conversion, photocatalysis and photodetection. However, a detailed theoretical description of plasmonic hot-carrier generation in real materials has remained incomplete. Here we report predictions for the prompt distributions of excited ‘hot’ electrons and holes generated by plasmon decay, before inelastic relaxation, using a quantized plasmon model with detailed electronic structure. We find that carrier energy distributions are sensitive to the electronic band structure of the metal: ​gold and ​copper produce holes hotter than electrons by 1–2 eV, while ​silver and ​aluminium distribute energies more equitably between electrons and holes. Momentum-direction distributions for hot carriers are anisotropic, dominated by the plasmon polarization for ​aluminium and by the crystal orientation for noble metals. We show that in thin metallic films intraband transitions can alter the carrier distributions, producing hotter electrons in ​gold, but interband transitions remain dominant

Corrosion resistant electrodeposited zinc coating from zinc dross

Electrodeposition of metals from aqueous solution produces a variety of metal alloy coatings. Zincalloy coatings are obtained by electrogalvanising of pure zinc. Properties of electrogalvanised steellike corrosion resistance spot weldability and adhesion are superior to hot-dip galvanisedsteel.Inthe present investigation, an attempt has been made to study electrodeposition of zinc from solidzinc drossas ananodic material on steel sheet acting as cathode and an aqueous bath containingdifferent concentration of Cl- ions, ammoniumsaltsandconducting substances at roomtemperature. An acid chloride bath was mainly used at different pH values. Very thin adherentand impervious coating was obtained on steel sheet. The zinc coating so obtained byelectrodepositionwas finally passivated to minimize white rust. X- ray diffraction, coatingthickness, atmospheric exposure test, electrochemical test, microhardness and cathodic efficiencyof zinc coated substrates were carried out. Salt -spray test on the coating was performed for 15days. Polarization experiments were carried out in 3.5 %NaCl solutionusingEG&G PARC-273Amodel Potentiostat Galvanostat. Open circuit potential (OCP) and corrosion potential (Ecorr) wererecorded. The process developed is very simple, economically viable and eco-friendly

In silico evolution of diauxic growth

The glucose effect is a well known phenomenon whereby cells, when presented with two different nutrients, show a diauxic growth pattern, i.e. an episode of exponential growth followed by a lag phase of reduced growth followed by a second phase of exponential growth. Diauxic growth is usually thought of as a an adaptation to maximise biomass production in an environment offering two or more carbon sources. While diauxic growth has been studied widely both experimentally and theoretically, the hypothesis that diauxic growth is a strategy to increase overall growth has remained an unconfirmed conjecture. Here, we present a minimal mathematical model of a bacterial nutrient uptake system and metabolism. We subject this model to artificial evolution to test under which conditions diauxic growth evolves. As a result, we find that, indeed, sequential uptake of nutrients emerges if there is competition for nutrients and the metabolism/uptake system is capacity limited. However, we also find that diauxic growth is a secondary effect of this system and that the speed-up of nutrient uptake is a much larger effect. Notably, this speed-up of nutrient uptake coincides with an overall reduction of efficiency. Our two main conclusions are: (i) Cells competing for the same nutrients evolve rapid but inefficient growth dynamics. (ii) In the deterministic models we use here no substantial lag-phase evolves. This suggests that the lag-phase is a consequence of stochastic gene expression