Bijan Bihari Nayak

Surface nitriding of graphite substrate by plasma focus device towards synthesis of carbon nitride coating

Abstract Circular graphite substrates have been nitrided in a plasma focus device. Nitrogen ions consisting of 100-ns pulses emanating from a Mather type plasma focus device were allowed to hit the surfaces of graphite substrates for 20 and 30 times (shots) to produce nitrided coatings. Microstructural characterization of the coatings carried out by XRD determined the d values of the nitride compound thus produced and four d values matched with those predicted by Cohen and co-workers and Wang et al. [Phys. Rev. B32 (1985) 7988; Science 245 (1989) 841; Phys. Rev. B41 (1990) 10727; Phys. Rev. B58 (1998) 11890] for carbon nitride. SEM and optical microscopic studies of the nitrided graphite surface reveal a rounded and island like morphology of the carbon nitride grains. Comparison of XPS results of the unnitrided and nitrided graphite shows the evidence for carbon–nitrogen bonding. IR spectra attribute the 1274.4 cm −1 absorption peak to C 3 N 4 (sp 3 ). The clear improvements observed in microhardness values point to the growth of a hard carbon nitride phase.

Surface nitriding of titanium in arc plasma

Abstract Titanium substrates were nitrided in a pot type arc plasma furnace in the temperature range 1400–1500xa0°C under different gas (Ar, N 2 , H 2 ) mixture plasma for 15xa0min each. The nitrided surfaces were characterized by X-ray diffraction and scanning electron microscopy. Depth of nitride layer grown was found to vary between 100 and 120 micons. The major compound phases to grow by this method were identified to be Ti 2 N, α-TiN and e-TiN, etc. Experimental details and characterization of arc plasma nitrided titanium are reported and discussed.

Micro-Raman analysis and AFM imaging of Acidithiobacillus ferrooxidans biofilm grown on uranium ore

Acidithiobacillus ferrooxidans biofilm grown on uranium ore substrate was analyzed by a micro-Raman spectrometer and an atomic force microscope (AFM). The bacterium employed for this study, A. ferrooxidans BM1, was isolated from a uranium mine (Jaduguda, India). Micro-Raman analysis revealed the different constituents of molecular fragments present in microbial cells and in secreted extracellular polymeric substances (EPSs). AFM images clearly revealed bacterial cells surrounded by EPS. From Raman spectral data, the composition of EPS from A. ferrooxidans BM1 appeared to be similar to that of EPS secreted in a different Pseudomonas bacterium.

Arc plasma nitriding of low carbon steel

Abstract Arc plasma nitriding of low carbon steel was carried out in the temperature range 1000–1100°C under different gas (Ar, N 2 , H 2 ) configurations for 15 min each. The plasma nitrided surfaces were characterized by XRD, SEM and microhardness measurement to identify various nitride phases thus grown, observe surface morphology of grains and determine improvement in hardness, respectively. The depth of the nitride layer growth was found to be in the order of 100–120 μm. Microhardness was observed to increase by three to four times that of the original samples taken. Fe 2–3 N(e), Fe 2 N 1− x and Fe 2 N, etc., were the main phases that grew in the arc plasma process. Experimental details and characterization of arc plasma nitrided low carbon steel are described and discussed in this paper.

Surface hardening of high carbon steel by plasma focus nitriding

AbstractEnergetic nitrogen ions from a plasma focus device were utilised for the first time to nitride high carbon steel specimens. The results of X-ray diffraction, optical microscopy, scanning electron microscopy, and microhardness measurements of structure, surface morphology, and hardness are reported.

DC extended arc plasma nitriding of stainless and high carbon steel

Stainless steel (SS 302) and high carbon steel (HCS) substrates were nitrided in a pot type arc plasma furnace in the temperature range 1100–120 °C under different gas (Ar, N2, H2) mixture configurations for twenty minutes each. The nitrided surfaces were characterized by XRD, SEM, metallography and microhardness. Depth of the nitride layer grown was found between 40 to 50 μm. Microhardness for SS 302 was observed to increase by about three to four times but for HCS the increase was not more than two times. The major compound phases to grow by this method were indentified to be Fe2-3N(∈), (Cr, Fe)N1-x and CrN in case of SS 302 whereas for HCS the phases were recognised as Fe2-3N(∈), (Cr,Fe)N1-x, Fe2N(ξ) and WN. Further details about the experiment and characterization of arc plasma nitrided steel are reported and discussed in this paper.

Enhancement in the microhardness of arc plasma melted tungsten carbide

Microhardness is found to increase significantly in arc plasma melted tungsten carbide. To understand the mechanism for such increase, tungsten carbide powder was mixed with tungsten metal powder to prepare mixtures of seven different compositions. The mixtures with varying WC/W ratio were pelletized and melted in an arc plasma followed by cooling in the furnace. It is observed that microhardness value enhances in the product when WC/W2C ratio becomes high. Based on our microstructural finding of <100> WC hard faces and lamellar/acicular structures (due to martensite transformation) carried out by XRD, optical microscope and SEM, an attempt has been made to understand the reason behind the enhancement in microhardness.

High temperature nitriding of grey cast iron substrates in arc plasma heated furnace

Abstract Grey cast iron substrates were case nitrided at 1000–1100°C by varying several process parameters such as nitriding time, flowrate of N2 and nitriding gas configuration. Ar and H2 were mixed with N2 to change the configuration and to observe their influence on the nitrided case. Nitriding was carried out in a specially designed arc plasma heated reactor with water cooled steel casing. X‐ray diffraction studies show that the nitride peaks arise due to growth of iron nitride phases such as γ′ (Fe4N: 5·7–6·1%N), ϵ (Fe3N: 8–11·2%N) and carbon nitride (C3N4). Typical surface morphologies of the 10–30u2005μm nitride layer were studied by SEM. Microhardness studies exhibited twofold improvement of surface hardness. Nanoindentation test indicated poor plastic behaviour of the surface. Micro‐Raman spectra of the nitided case established the presence of β‐C3N4, a superhard phase. Nitrided grey cast iron may find use in wear and corrosion resistant dies, machine components and parts in various industrial applications.

Molybdenum x‐ray emission spectroscopic study of vacancy‐induced electronic states in V2O5–MoO3 thin films and powders

X-ray emission spectra in compound thin films are scarce, although such studies in metals, alloys and other inorganic compounds are available. In this study, compound thin films of V 2 O 5 -MoO 3 and powders of same compositions were investigated to see the effect of V 2 O 5 incorporation in an MoO 3 matrix. For this purpose, Kβ, La and Lβ emissions from Mo present in these matrices were measured. The full width at half-maximum (FWHM) of Lα 2 and Lβ 1 in thin films were found to be different from that of powders. Most of these emission bands show a low asymmetry index before these are split into separate bands. All these findings have been explained on the basis of vacancy production, core hole lifetime, crystal structure and stoichiometric variation of MoO 3 in the V 2 O 5 matrix.

Diamond and Diamond-like-Carbon Growth on Si (100) by Hot Filament-Assisted RF Plasma CVD

Diamond and diamond-like carbon (DLC) crystallites can be grown on a Si (100) substrate by hot filament-assisted RF plasma CVD in a low-vacuum (2-Torr) environment from C2H2 without using hydrogen. The deposition was carried out at 900°C onto the precleaned diamond polished Si (100) substrate. XRD and Raman spectra revealed the presence of diamond, graphite, lonsdaleite, and high-order polymeric hydrocarbon phases. The morphology observed by SEM shows typical habit and facets of the diamond crystallites grown on silicon. An attempt was made to explain some discrepancies observed in the XRD and Raman spectra of our multiphasic DLC films.