Wear and tribocorrosion behaviour of 304L stainless steel welds

The influence of the microstructures of the base metal and weld metals on the wear and tribocorrosion properties of 304L stainless steel (SS) welds prepared by Manual Gas Tungsten Arc Welding (M-GTAW) and Activated Flux Gas Tungsten Arc Welding (A-GTAW) processes are reported. Increase in sliding speed increased both friction forces as well as wear rate. Higher hardness in M-GTAW weld metal resulted in increased wear resistance than A-GTAW weld metal and base metal. The inferior wear resistance of the base metal was due to the strain hardening behaviour under sliding condition. The polarization curves showed increase in passive current density under sliding condition. The applied potential was found to influence the tribocorrosion resistance of the material. Under tribocorrosion condition, the total material loss was higher in base metal followed by A-GTAW weld metal and M-GTAW weld metal. Characterization of worn surface by SEM indicated a mixed wear mechanism of abrasive and adhesive wear. The worn surface appeared relatively smoother in nitric acid medium than in dry condition. The influence of microstructure affecting the hardness, wear and tribocorrosion resistance of the base metal and weld metals of 304L SS is discussed.     

Pitting Corrosion Behaviour of Boron Added Modified 9Cr–1Mo Steel: Combined Effects of Alkali and Chloride Ions

Pitting corrosion behaviour of modified 9Cr–1Mo ferritic steel containing 100 ppm of boron was studied in deaerated 0.1, 0.2 and 0.5 M sodium hydroxide solutions containing 0.1, 0.2 and 0.5 M sodium chloride. The chemical compositions of the passive film developed at applied potentials were studied using XPS. E_pit values decreased with increase in chloride concentrations for the given concentration of alkali. The effect (of Cl^?) was less pronounced in higher alkali concentrations. Pit diameters were observed to be significantly higher in 0.1 M sodium hydroxide containing 0.1 M sodium chloride; with increase in alkali concentration pit diameters were found to be restricted to lower values even at higher chloride concentrations. Energy dispersive spectroscopic (EDS) studies showed that pits had nucleated at Al₂O₃ inclusions/matrix interface. XPS analysis revealed the presence of Fe₃O₄, Fe(OH)₃ at lower potentials (150 and 209 mV(SCE)) whereas Fe₂O₃, Fe(OH)₃ and FeO₂ ^2? at higher potentials (400 and 650 mV(SCE)).     

Platinum-modified titanium anodes for the electrolytic destruction of nitric acid

Three sets of electrodes, namely Pt electroplated Ti (PET) and diffusion annealed PET (DAPET) of plating thickness 3, 5, 7 and 10 μm and thermochemically glazed mixed oxide coated titanium anode (MOCTA-G) were evaluated for their performance, with a view to optimizing the current density conditions for maximum efficiency during the electrolytic destruction of nitric acid. In the acid killing by electro-reduction process, concentration of nitric acid in the high level waste (HLW) from the spent nuclear fuel reprocessing plant was brought down from about 4 to 0.5 M in order to reduce the amount of HLW by subsequent evaporation and to minimise the corrosion in waste tanks during storage of the concentrated waste solution. The electrochemical reduction of 4 and 8 M nitric acid to near neutral conditions was carried out with the above-said anodes and Ti cathode at various cathodic current densities ranging from 10 to 80 mA cm⁻². At current densities below 15 mA cm⁻² MOCTA-G electrode worked satisfactorily, whereas PET and DAPET electrodes could withstand and function well at much higher cathodic current densities (up to 80 mA cm⁻²). The life assessment of a 3 μm thick PET electrode at a cathodic current density of 60 mA cm⁻² in 8 M HNO₃ for a period of 110 h showed no failure. Phase identification of the plated electrodes was done by XRD measurements and their surface morphology was investigated by SEM.     

Corrosion Behavior of Sensitized 304 SS in Nitric Acid Medium Containing Oxidizing Ions

The corrosion behavior of 304 stainless steel (SS) in the as-received and sensitized conditions has been investigated at room temperature and at 60 °C in the presence of oxidizing ions in 6 and 8 M nitric acid media. Corrosion of 304 SS in nitric acid was far more severe in sensitized condition than in as-received condition. Further, decrease in corrosion resistance was observed with increase in the temperature of nitric acid. The corrosion potential shifted to noble direction with increase in the concentration of nitric acid and the potential shifted further to transpassive potential at 60 °C. Increase in corrosion potential towards transpassive domain led to severe intergranualar attack. Impedance spectra showed two time constant which could be attributed to the redox reaction on the surface of oxide film. However, the effect of oxidizing metal ions was not prominent.     

Plasma assisted chemical vapour deposition of Cr coatings using chromium (III) acetylacetonate vapour source

We report here the synthesis and characterisation of Cr coatings by an environmental friendly Plasma Assisted Metal-Organic Chemical Vapour Deposition (PAMOCVD) process. The Cr coatings were developed using Cr(acac)₃ as the chemical vapour source at a substrate temperature and a power density of 550 °C and 70 mW/cm², respectively. The films were characterized using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Vicker's microhardness measurements. The investigations revealed that the Cr films are nanocrystalline, free from pores and cracks and have hardness of 1200 HV. The energy dispersive analysis of X-rays and XPS confirmed the presence of Cr in the films.     

Rock excavation using surface miners: An overview of some design and operational aspects

Surface miner, a continuous mining machine, is being manufactured in India and abroad owing to enhanced demand of production in various mining industries like coal, limestone, gypsum, bauxite etc. Different types of surface miners are manufactured today based on cutting drum placement and design specifications. Selective mining without drilling and blasting, high production and small size products are some of the prominent attractive features obtained with these moving marvels. This machine can be used with good efficiency in soft to medium hard rock (100–120 MPa). This paper synthesizes the different applications, equipment models, features offered, operating methods, cutting performance assessment models as well as typical production performance of surface miner in coal and limestone mines of India. Engine hour metre reading, diesel and pick consumptions are linearly influenced by production. The emphasis for future research is also brought out.     

Estimation of oxygen pressures for the formation of superconducting phases based on La-Cu-O and Y-Cu-O systems

The use of thermodynamic data in the calculation of limiting oxygen pressures for the existence of ternary oxides is demonstrated in the case of LaMO₃ and La₂MO₄ (M=Mn, Fe, Co, Ni or Cu) compounds using the literature data on the relevant chemical equilibria. The standard Gibbs' energy of formation, G _f ⁰ , of LaCuO₃ is estimated from the values of G _f ⁰ of the other LaMO₃ compounds calculated from the literature and is given as (kJ mol^–1)= –1095.0+0.2351 T (K). The validity of this expression is qualitatively verified with the help of experimental conditions reported in the literature for the synthesis of this compound. Similar considerations are used to predict values of 0.03 and 30 atm to be the oxygen pressure range for the existence of a quarternary compound, YBa₂Cu₃O_9–y at 1273 K. The superconducting transition temperature, T _c, is qualitatively predicted to show a maximum for the sample annealed under an oxygen pressure in the range 1 to 30 atm at 1273 K.