Showing papers by "U. Kamachi Mudali published in 2013"
TL;DR: In this article, the authors present a review of the literature for the removal of RuO4 from spent nuclear fuel from fast breeder reactors using extractants and methods which are conducive to plant conditions.
Abstract: The chemistry of the noble metal fission product, ruthenium is very complex due to the existence of many oxidation states in addition to forming a large number of co-ordination complexes. In the PUREX process for the separation of U and Pu from the spent nuclear fuels from fast breeder reactors, owing to the high volatile nature of RuO4 problems arise not only during the extraction stages but also in the treatment of high active liquid waste and subsequent vitrification. As this volatile RuO4 can deposit in cooler parts, there is an increase in the radiation field due to the presence of 106Ru. The problem is very acute in the reprocessing of fast reactor fuels due to the increased concentration of ruthenium in the spent fuel. In nitric acid medium Ru can exist in various nitroso nitrate complexes and nitroso complexes are more stable than nitrates. The nitrates are non-extractable by the solvent TBP; however, they are extractable to a higher degree by DBP (the primary degradation product of TBP). The extractability of Ru nitrates into the solvent is inhibited by high acid content, temperature and prolonged hold-up time. Nevertheless, these factors promote the volatilization of Ru as RuO4. The volatilization is enhanced by the addition of phosphate ions, but is suppressed by phosphite or hypophosphite ions. Thus, it would be advantageous if ruthenium is removed so that not only the purity of the product (Pu) is improved, but also the problem related to volatilisation can be resolved. High molecular weight amines (tertiary amines) capable of forming co-ordinate bonds are reported to be ideal extractants for Ru. Gas phase separation is an effective method for the recovery of Ru from catalysts, lead button and from other platinum group metals. Separation and pre-concentration of noble metals can be accomplished from non-metals by simple sorbents like coconut shell activated carbon to complicated chelating resins, aromatic polymers and zeolites. In the electro-oxidation of active Ru from nitroso salts, Pd was found to interfere and removal of Pd prior to oxidation of Ru is recommended. Redox catalysts such as Ag2+ and Ce4+ are found to play a prominent role in the electro-oxidation of Ru. Though, various methods and extractants are reported in the literature for the separation of Ru, R&D is being pursued for the removal of Ru during aqueous reprocessing of spent fuels using extractants and methods which are conducive to plant conditions. Hence, an exhaustive survey of literature was made and the different methods reported for the removal of Ru with emphasis towards reprocessing applications are discussed in this report as a review. Attempts made by the authors in separating Ru from simulated waste solution are also included in this review.
64 citations
TL;DR: In this article, the phase structure, surface morphology and elemental composition of the untreated, anodized heat treated and anodised heat treated titanium specimens immersed in Hank's solution for seven days were characterized using X-ray diffraction, atomic force microscopy and scanning electron microscopy with energy dispersive Xray spectroscopy techniques, respectively.
55 citations
TL;DR: In this paper, the potential of different concrete deteriorating acid producing microbes for removing surface layers of contaminated concrete structures was identified by using an acid producing fungus, Fusarium sp in a humidity chamber for one year and compared the degradation with the Thiobacillus sp.
32 citations
TL;DR: In this article, a pyrochemical reprocessing utilizing molten chloride salt has been considered as one of the best options for reprocessed spent metallic fuels of future fast breeder reactors.
Abstract: Pyrochemical reprocessing utilizing molten chloride salt has been considered one of the best options for reprocessing of spent metallic fuels of future fast breeder reactors. Materials for pyrochem...
32 citations
TL;DR: In this article, the authors focused on the understanding of enhanced antimicrobial property of Eu-Ag codoped TiO 2 surfaces, which were prepared using the sol-gel method.
31 citations
TL;DR: In this article, the thermally oxidized Cp-Ti samples were characterized by SEM, XRD, microscratch test and profilometry and the results showed that the hardness of thermally-oxidized C p-Ti sample was found to be 2.5 times higher than that of Cp -Ti and the surface roughness of the surfaces were smooth before and after corrosion when compared to the as-polished surface.
Abstract: Commercially pure titanium (Cp-Ti) is being used as structural material for fabrication of dissolver in the reprocessing of carbide fuel from fast breeder test reactor. Thermal oxidation of titanium is one of the most simple and feasible options to extend the life of such critical components. In the present study thermal oxidation of titanium has been carried out at 923 K for 96 h. The thermally oxidized Cp-Ti samples were characterized by SEM, XRD, microscratch test and profilometry. Corrosion studies were carried out in boiling nitric acid medium as per ASTM A262 practice-C test and three phase corrosion test and the results were compared with Cp-Ti and Ti–5Ta–1.8Nb alloy. ASTM A262 practice-C test revealed reproducible outstanding corrosion resistance of thermally oxidized Cp-Ti compared to Cp-Ti and Ti–5Ta–1.8Nb alloy. Three phase corrosion test results also indicated better corrosion resistance of thermally oxidized Cp-Ti. The protective thick rutile TiO 2 oxide layer with nano-rod structure formed on the surface improved the corrosion resistance of thermally oxidized Cp-Ti in boiling nitric acid as evident from SEM and XRD results. The hardness of thermally oxidized Cp-Ti sample was found to be 2.5 times higher than that of Cp-Ti and the surface roughness of the thermally oxidized Cp-Ti samples was found to be smooth before and after corrosion when compared to the as-polished surface. The corrosion resistance of the thermally oxidized Cp-Ti samples can be further improved by optimizing the parameters to achieve good adhesion strength. The paper highlights the results of the present investigation.
29 citations
TL;DR: In this paper, the corrosion behavior of candidate materials like 2.25Cr-1Mo steel (UNS K21590), 9 Cr-1 Mo steel (NCM), Ni-based alloy 690 (N 06690), Ni based alloy 600 (NCN N 06600), Nibased alloy 625 (NCS N06625), and Ni based alloys were evaluated under ultrahighpurity argon atmosphere.
Abstract: Pyrochemical reprocessing involves the use of molten LiCl-KCl (lithium chloride-potassium chloride) eutectic salt at 773 K for the recovery of uranium and plutonium from spent metallic fuel of fast breeder reactors. The materials selected for such corrosive environments should withstand high temperatures and at the same time offer good corrosion resistance. The present work discusses the corrosion behavior of candidate materials like 2.25Cr-1Mo steel (UNS K21590), 9Cr-1 Mo steel (UNS K90941), Ni-based alloy 600 (UNS N06600), Ni-based alloy 625 (UNS N06625), and Ni-based alloy 690 (UNS N06690) in molten LiCl-KCl eutectic salt at 873 K for various durations under ultrahigh-purity argon atmosphere. Corrosion behavior of partially stabilized zirconia (PSZ) coating on candidate materials also was evaluated. Weight-loss results indicated that the corrosion resistance of the materials increased in the following order: 2.25Cr-1Mo > 9Cr-1 Mo > Ni-based alloys > PSZ coating. PSZ-coated specimens showed better corro...
28 citations
TL;DR: In this article, the activated flux TIG (ATIG) weld joints of titanium produced using in-house developed activating flux were presented, and the flux formulation was optimized after carrying out trials with different sets of flux powders and subsequent metallographic observation of weld bead profile.
Abstract: Metallurgical characterization and qualification of activated flux TIG (ATIG) weld joints of titanium produced using in-house developed activating flux are presented. The flux formulation was optimized after carrying out trials with different sets of flux powders and subsequent metallographic observation of weld bead profile. ATIG welding of titanium using this flux, with optimized welding parameters, produces full penetration welds in 6-mm-thick plates having weld bead depth-to-width ratio of 1.25 compared to 0.25 of conventional TIG welds. ATIG weld joints were prepared using 6-mm-thick titanium plates using square-butt joint geometry and these joints were qualified by radiography. Root and face bend tests passed 4T bend radius as per American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code-Section IX requirements with bend angle of 180°. Transverse tensile testing of weld joints showed fracture in the weld metal with sufficient ductility and tensile strength of 398 MPa, which was close to the base material tensile strength of 402 MPa thereby meeting ASME Section IX requirements. Uniform hardness across the weld confirmed that the weld was not contaminated by components of flux or atmospheric gases, which can result in increased hardness of the weld metal leading to embrittlement. The corrosion test of the weld joints in 11.5 M boiling nitric acid showed improved corrosion resistance compared to base material.
27 citations
TL;DR: In this article, the influence of different anodizing electrolytes on the super-hydrophobic surface modification of titanium and the resultant corrosion and biofouling resistance was revealed.
Abstract: The present study reveals the influence of different anodizing electrolytes on the superhydrophobic surface modification of titanium and the resultant corrosion and biofouling resistance. Inspired by the Lotus effect, anodization and low surface energy material coating were used to produce super-hydrophobic titanium in the present work. The water contact angle measured on surface-modified titanium was found to be 150°, indicating their superhydrophobic nature. Surface roughness, morphology, phase, and composition of the oxide film were correlated with the superhydrophobic nature of the coated surfaces. Electrochemical studies showed that the superhydrophobic titanium in a nitric acid medium had appreciable increase in the corrosion resistance compared to the as-polished titanium. The antibacterial activity studies showed a one to two order decrease in bacterial attachment on super-hydrophobic titanium samples compared to polished titanium samples.
25 citations
TL;DR: In this article, a titanium dioxide nanotube powder was synthesized by Rapid Breakdown Anodization (RBA) method, which involved potentiostatic anodization of titanium foil in 0.1 M HClO{sub 4} electrolyte under an applied voltage of 20 V and rapid stirring.
25 citations
TL;DR: In this article, the results of the potentiodynamic anodic polarization studies were correlated with the results obtained using electrochemical impedance spectroscopy (EIS) technique, indicating faster passive film dissolution as indicated by low polarization resistance, in sensitized condition and vice-versa in mill-annealed condition.
Abstract: High-nitrogen stainless steels (SS) are receiving increased attention because of the advantages of their strength over the SS with nominal composition. However, they are susceptible to dichromium nitride (Cr2N) precipitation during thermal exposure between 873 and 1323 K resulting in sensitization and subsequent intergranular corrosion. Round tensile specimens of AISI type 316LN SS, with three different nitrogen content 0.07, 0.14, and 0.22 wt.% in mill-annealed and sensitized (973 K for 24 h) condition were studied for their pitting corrosion behavior. The results of the potentiodynamic anodic polarization studies were correlated with the results obtained using electrochemical impedance spectroscopy (EIS) technique. Critical pitting potential (E
pp) increased with increasing nitrogen content but the same was found to decrease on aging. The parameters indicating passive film stability measured by EIS revealed faster passive film dissolution as indicated by low polarization resistance, in sensitized condition and vice-versa in mill-annealed condition. The EIS results correlated well with the variation in the respective E
pp obtained from the potentiodynamic polarization diagrams.
TL;DR: The microwave synthesized hydroxyapatite (HAp-Ca 10 (PO 4 ) 6 (OH) 2, 35nm) was implanted with 30-keV nitrogen ion (N + ) with fluences of 1×10 15, 1x10 16 and 1× 10 17 ions/cm 2. The samples were characterized by GIXRD (Glancing Incidence X-ray Diffraction) and atomic force microscopy along with measurement of resistivity, permittivity, ac conductivity, photoluminescence, wettability and in vitro bio
TL;DR: Stainless steels (SS) have achieved a unique position as a widely accepted class of alloys with track record of steadily improving the performance and increasing applications from 1913 till date as mentioned in this paper.
Abstract: Stainless steels (SS) have earned a unique position as a widely accepted class of alloys with track record of steadily improving the performance and increasing applications from 1913 till date. This distinction is attributed to R&D, innovations and applications leading to harnessing the rare combination of properties of stainless steels, since its discovery hundred years back. Though the initial discovery of stainless steel is basically serendipity, and based on previous work, its indispensable position today, in many a wide range of applications is due to intense R&D efforts in understanding its physical, chemical, thermal and thermo-mechanical response for various chemistries and microstructures. A deliberate attempt to extend its application spectrum through various routes of manufacturing in the last century is another crucial aspect of the success story. The first part of the presentation would briefly review this exciting journey of unravelling the mysteries of stainless steels.The second part of the presentation would highlight the evolution of stainless steels in the nuclear industry, especially for the sodium cooled fast reactors. Early 70s have seen the application of stainless steels in first generation water based nuclear power plants and AISI types 304 and 316 SS was recommended for structural and core applications in fast spectrum reactors (FSR). Failure of some of the components even in the manufacturing stage and quest for improving mechanical properties and sensitisation and intergranular corrosion resistances resulted in the development of 304L, 304LN, 316L, 316LN SS during 1980-90 for further applications in FSRs. Towards core applications in intense radiation environments, three generations of stainless steels namely 20% cold worked 316 SS, D9, and D9I have been developed to yield high burnup and to triple the lifetime of the core components of the fast reactors. Towards closing the fuel cycle, again 304L SS was the workhorse material which was upgraded with newer varieties like nitric acid grade alloys for improved corrosion resistance and longer life. Manufacturing of special grades of SS and the developments in fabrication technologies was necessary in order to enhance the performance of components and to avoid failures. Welding, inspection, quality assurance and structural integrity of various components of SS for FSRs and fuel cycle facilities resulted in developments in areas like modelling, devices, methodologies and analysis. An opportunity existed for the development and application of innovative non-destructive testing techniques for robust examination of critical components.Nuclear industry is embarking a state of the art fourth generation reactors. The consequent newer generation of SS are evolving with improved properties to match the expectations of performance in increased temperature, pressure, chemical and other physical constraints. It is of paramount importance to consider the extension of the lifetime of the current reactors from 40-60 to 60-80 years for economic considerations, and in this regard innovations are necessary in the development of newer varieties of stainless steels with respect to modelling and life prediction, manufacturing, fabrication, testing and evaluation. Thus the management approach to knit a network of industry-research-academia is a key approach for way forward. A development of roadmap for robust science based technology development with foresight is a desired management strategy.
TL;DR: In this article, a microwave coupled hydrothermal method using CTAB as a template was used to synthesize nanosized HAP spheres, rods and fibres by controlling the concentration of the surfactant.
Abstract: Nanohydroxyapatite particles with different morphologies were synthesized through a microwave coupled hydrothermal method using CTAB as a template. A successful synthesis of nanosized HAP spheres, rods and fibres is achieved through this method by controlling the concentration of the surfactant. The concentration of the surfactant was tuned in such a way that the desired HAP nanostructures were obtained. The resultant powders were sintered at 900 °C in order to obtain phase pure HAP particles. The results obtained by Fourier transform infrared spectroscopy (FT–IR), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques have substantiated the formation of nanosized HAP spheres and fibres.
TL;DR: In this paper, the effect of surface modification on the corrosion behavior in simulated nuclear high level waste (HLW) and chloride medium was investigated by laser surface melting of Ni-based superalloys (alloys 600, 690 and 693).
Abstract: Laser surface melting of Ni based superalloys (alloys 600, 690 and 693) was carried out to study the effect of surface modification on the corrosion behaviour in simulated nuclear high level waste (HLW) and chloride medium. Surface characterisation was performed by optical microscopy, scanning electron microscopy and X-ray diffraction. The alloys exhibited cubic crystal system and cellular microstructure. Double loop electrochemical potentiokinetic reactivation test in 0·5M H2SO4 containing 0·0001M KSCN showed a low degree of sensitisation compared to the solution annealed specimens. Laser surface melting resulted in enhancement of corrosion resistance of the alloys in simulated HLW and chloride medium when compared to as received and solution annealed specimens; nevertheless, no discernable difference was found between the laser surface melted alloys 600, 690 and 693 in simulated HLW. However, the laser surface melted alloy 690 showed superior pitting corrosion resistance. The results of the pres...
TL;DR: Zirconium is highly resistant to nitric acid environments and is considered as a candidate material for various applications in spent nuclear fuel reprocessing plants involving concentrated nitric.
Abstract: Zirconium is highly resistant to nitric acid environments and is considered as a candidate material for various applications in spent nuclear fuel reprocessing plants involving concentrated nitric
TL;DR: In this article, the authors focused on the hydrolysis reactions of uranium(VI) under an ambient atmosphere leading to colloid formation in near neutral solution using light scattering, UV-Vis and FTIR-ATR studies.
Abstract: This study mainly focuses hydrolysis reactions of uranium(VI) under an ambient atmosphere leading to colloid formation in near neutral solution using light scattering, UV–Vis and FTIR-ATR studies. UV–Vis and IR spectrum was recorded for uranyl solution at different pH range. U(VI) hydrolyzed colloids were detected and it was confirmed by the appearance of a band at 941 cm−1 in the IR spectra. Light scattering measurements were performed on colloidal U(VI) solutions formed at pH range of 7–8. The average particle diameter was determined as 32–36 nm using dynamic light scattering. Well defined colloidal species are formed with no considerable change in particle size with increasing U(VI) concentration. The weight average molecular weight of colloidal species was predicted as 763 Da by Debye plot. The second virial coefficient (A2) was found to be −0.1139 ml g−1 Da. The present study confirms that behaviour of U(VI) contradicts conventional Zr(IV), Th(IV) and Pu(IV) solution chemistry. U(VI) polymerization is less extensive and in neutral solutions it forms only oligomers with 2–3 uranyl units.
TL;DR: In this paper, the experimental data for dispersed phase holdup and flooding throughput has been modelled using the Van Delden model to describe the hydrodynamics characteristics of a pulsed disk and doughnut column (PDDC), and necessary adjustable parameters for drop size distribution and dispersed phase Holdup are updated for 30% TBP-nitric acid system.
Abstract: The hydrodynamic parameters, namely, dispersed phase holdup and flooding throughput, have been investigated in 25 mm diameter pulsed disk and doughnut column (PDDC), in no mass transfer conditions. In this work, using existing correlations on plate pulsed columns, the dispersed phase holdup and the flooding throughput are empirically modelled well using the slip velocity concept. A good agreement is observed between experimental values and predicted values obtained from empirical correlation. The experimental data for dispersed phase holdup and flooding throughput has been modelled using the Van Delden model to describe the hydrodynamics characteristics of a PDDC and necessary adjustable parameters for drop size distribution and dispersed phase holdup are updated for 30% TBP-nitric acid system. The model parameters were estimated by minimizing the absolute error between experimental and theoretical values of flooding throughput and holdup data. It was found that the measured values and observed trends could be described accurately using this model after fitting holdup and flooding data. The error between the experimental and theoretical values of flooding throughput and holdup was found to be less than 10%.
TL;DR: In this article, a pulsed Nd:YAG laser melting with power densities of 640 and 800 kW/cm2 was used to minimize the surface porosity, micro-cracks, partially melted or unmelted regions, and achieving homogeneous microstructure.
Abstract: Plasma sprayed Al2O3–40 wt% TiO2 coatings were subjected to a pulsed Nd:YAG laser melting with power densities of 640 and 800 kW/cm2 in order to minimize the surface porosity, micro-cracks, partially melted or unmelted regions, and achieving homogeneous microstructure. As-sprayed and the laser melted surface microstructure, chemical composition, microhardness and roughness were characterized by using scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, Vickers hardness and profilometer. Surface morphology of a laser melted coating showed that inhomogeneities are reduced, however, network of cracks were formed irrespective of power density. Columnar growth features were observed in laser melted regions when melted with 640 kW/cm2 while these were eliminated when melted with in 800 kW/cm2 power density. Predominant β-Al2TiO5 phase was observed upon both the laser melted coatings. With an increase of laser power density, laser melted coatings exhibited considerable increase in microhardness and decrease in surface roughness due to significant reduction in the surface defects.
TL;DR: In this paper, the results obtained from gas chromatographic technique were compared with spectrophotometric technique by converting the organic phosphate into inorganic phosphate The generated data is of direct relevance to reprocessing applications.
Abstract: In nuclear technology, tri-n-butyl phosphate (TBP) diluted with a hydrocarbon diluent such as n-dodecane or NPH is the most frequently used solvent in liquid–liquid extraction for fuel reprocessing This extraction, known as the plutonium uranium refining by extraction, is still considered as the most dominant process for the extraction of uranium and plutonium from irradiated fuels The solubility of pure TBP in water is about 04 g/L at 25 °C This is enough to create trouble during evaporation of raffinate and product solutions Solubility data for undiluted TBP and TBP (diluted in inert hydrocarbon diluent) in various concentrations of nitric acid is not adequate in the literature The solubility data generated in the present study provide complete information on the solubility of TBP in various nitric acid concentrations (0–157 M) at room temperature The effect of heavy metal ion concentration such as uranium and various fission products on the solubility of TBP in nitric acid is also presented The results obtained from gas chromatographic technique were compared with spectrophotometric technique by converting the organic phosphate into inorganic phosphate The generated data is of direct relevance to reprocessing applications
TL;DR: In this article, a novel thermo-mechanical surface treatment approach, involving conventional shot blasting followed by laser surface heating, was described to engineer microstructural modification in type 304 austenitic stainless steel for enhancing its corrosion resistance.
Abstract: The paper describes a novel thermo-mechanical surface treatment approach, involving conventional shot blasting followed by laser surface heating, to engineer microstructural modification in type 304 austenitic stainless steel for enhancing its corrosion resistance. Thermo-mechanical surface treatment resulted in the formation of fine recrystallized grains with some strain-induced martensite on the modified surface. Surface treatment of type 304 stainless steel brought about significant improvement in its resistance against uniform as well as pitting corrosion. Electrochemical impedance spectroscopic studies showed improved polarization resistance (Rp) value for thermo-mechanically treated surface indicating formation of a more protective passive film than that formed on the untreated surface. In contrast to untreated type 304 stainless steel specimens where pits preferentially initiated at the site of Al2O3 inclusions, thermo-mechanically treated specimen exhibited only general dissolution with a few repassivated and shallow pits. Grain refinement and dispersion of alumina inclusions on the modified surface are considered to be the key factors responsible for improvement in uniform and pitting corrosion resistance of type 304SS.
TL;DR: In this paper, the authors deal with the preparation of HfN thin films by reactive magnetron sputtering on high density graphite and niobium substrates, and show that the results showed that the coating had a thickness of 2.8μm.
TL;DR: In this paper, the effect of Sr incorporation into TiO2 coating on bioactivity and corrosion resistance was investigated, and the results showed that the incorporation of Sr ions enhanced both bioactive and corrosion resistant of 316L SS, which is a promising material for orthopaedic implant applications.
TL;DR: In this paper, an experimental study was carried out on a novel surface thermo-mechanical treatment involving conventional shot blasting and laser surface treatment, for enhancing intergranular corrosion resistance of type 304 stainless steel.
Abstract: An experimental study is carried out on a novel surface thermo-mechanical treatment involving conventional shot blasting and laser surface treatment, for enhancing inter-granular corrosion resistance of type 304 stainless steel. The modified surface exhibited fine re-crystallized austenite grains. A non-destructive approach of monitoring width of γ(311) diffraction peak through a portable X-ray diffraction was adopted, to determine micro-structural state on the thermo-mechanically treated surface. The results of the study have demonstrated that laser-assisted surface thermo-mechanical treatment of type 304 stainless steel is effective not only for enhancing material's inherent resistance against sensitization and inter-granular corrosion due to its subsequent exposure to susceptible temperature regime but also for reducing inter-granular corrosion susceptibility of pre-sensitized specimens.
TL;DR: In this article, continuous mode electrochemical reduction of uranyl ions in nitric acid medium and in the presence of hydrazine nitrate was carried out in a divided cell at three different feed flow rates and cathodic current densities for the purpose of optimizing the process conditions for better conversion efficiency.
Abstract: In a contemporary salt-free flowsheet of nuclear fuel reprocessing, uranous ions are used as a reducing agent to accomplish the separation of uranium and plutonium from each other which is normally produced electrochemically. In the present study, continuous mode electrochemical reduction of uranyl ions in nitric acid medium and in the presence of hydrazine nitrate was carried out in a divided cell at three different feed flow rates and cathodic current densities for the purpose of optimizing the process conditions for better conversion efficiency. A correlation function is described as a mathematical model in which, mass transfer parameter is expressed as a function of current density and flow rate. From the multivariable nonlinear regression of the experimental data, rate parameter was determined. The electro reduction of uranyl ions was not influenced by the initial acidity. The maximum conversion rate of 87 % was obtained for the electro-reduction of 100 g/l U(VI) in 3 M nitric acid with feed flow rate as 0.3 l/h and current density as 15 mA/cm2. The results for the reduction of 100 g/l uranyl ions indicate that an optimum flow rate of about 0.5 l/h and 15 mA/cm2 as cathodic current density may suffice for the conversion with efficiency better than 60 %. The calculated steady state concentrations for U(IV) were found to be in good agreement with the experimental results.
TL;DR: In this paper, a nitrogen-enhanced 316LN austenitic stainless steel (SS) with improved high-temperature properties is developed, where the effect of nitrogen on its tensile, creep and low cycle fatigue behavior has been investigated.
Abstract: For the future sodium-cooled fast reactors (SFRs), which are envisaged with a design life of 60 years, nitrogen-enhanced 316LN austenitic stainless steel (SS) with improved high-temperature properties is being developed. To optimize the enhanced nitrogen content in 316LN SS, the effect of nitrogen on its tensile, creep and low cycle fatigue behavior has been investigated. For different heats of 316LN SS containing 0.07-0.22 wt% nitrogen, the tensile and creep properties increased with increase in nitrogen content, while low cycle fatigue properties peaked at 0.14 wt% nitrogen. Finally, based on the evaluation of the hot cracking susceptibility of the different heats of 316LN SS with varying nitrogen content, using the Varestraint and Gleeble hot-ductility tests, the nitrogen content for the nitrogen-enhanced 316LN SS has been optimized at a level of 0.14 wt%. The 0.14 wt% nitrogen content in this optimised composition shifts the solidification mode of the weld metal to fully austenitic region, including that due to dilution of nitrogen from the base metal, thereby increasing its hot cracking susceptibility. This necessitated development and qualification of welding electrodes for obtaining weld metal with 0.14 wt% nitrogen by optimising the weld metal chemistry so as to obtain the requisite delta ferrite content, tensile properties, and very importantly impact toughness both in the as-welded and aged conditions. Studies on localised corrosion behaviour of nitrogen-enhanced 316LN SS indicated the beneficial effect of nitrogen addition to sensitization, pitting, intergranular corrosion, stress corrosion cracking and corrosion fatigue.
TL;DR: In this article, the chemical compatibility and thermal stability of yttria coating on high density graphite in molten LiCl-KCl salt medium have been established by several characterization techniques, including X-ray diffraction and laser Raman patterns.
TL;DR: In this paper, the surface of titanium samples was applied with a solution containing oxides of Ta and/or Nb and treated at 1273 K for 5h in vacuum.
Abstract: Commercially pure titanium (Cp-Ti) is used as structural material in chemical processing industry where nitric acid is used as process medium. The corrosion resistance of titanium can be further improved by coating highly corrosion-resistant materials. Tantalum and niobium possess excellent corrosion resistance to nitric acid solutions of high concentrations and temperatures. In the present study refractory metal coatings of Ta, Nb and Ta + Nb were prepared by a simple thermo-chemical decomposition technique on titanium to improve corrosion resistance in nitric acid medium. The surface of titanium samples was applied with a solution containing oxides of Ta and/or Nb and treated at 1273 K for 5 h in vacuum. Characterization of the coated samples before and after corrosion test was carried out using Scanning Electron Microscopy (SEM), Energy Dispersive analysis of X-rays (EDX) and X-ray diffraction (XRD). SEM, EDX and XRD results confirmed the presence of refractory metal coatings on Ti. ASTM A262 practice-C test was conducted in boiling 65% nitric acid. Corrosion tests showed that Ta + Nb coated sample has four times better corrosion resistance than uncoated Ti and is only marginally higher than Ti–5Ta–1.8Nb alloy. The coating characteristics and corrosion resistance of Ta + Nb coated sample were found to be reproducible. XRD pattern of as-coated and corrosion tested surfaces is similar in Ta and Ta + Nb coated samples while α-Ti phase was observed in Nb-coated sample after corrosion. Three phase corrosion tests were also conducted on Cp-Ti, Ti–5Ta–1.8Nb alloy and Ta + Nb-coated Cp-Ti samples in boiling liquid, vapour and condensate phases of nitric acid. The corrosion rate of Ta + Nb coating was found to be higher in three phase corrosion test, however, a decreasing trend of corrosion rate was noticed with time. The paper highlights the results of the present investigation.
TL;DR: In this paper, the influence of the oxidizing ions Fe3+ and Cr6+ with two different concentrations on the corrosion resistance of Type 304L (UNS S30403) stainless steel in 3 M and 6 M nitric acid (HNO3) medium has been determined.
Abstract: The influence of the oxidizing ions Fe3+ and Cr6+ with two different concentrations on the corrosion resistance of Type 304L (UNS S30403) stainless steel in 3 M and 6 M nitric acid (HNO3) medium has been determined. The corrosion resistance and passive film behavior of Type 304L stainless steel in the presence of oxidizing ions were evaluated using electrochemical potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and x-ray photoelectron spectroscopy (XPS) techniques. The corrosion resistance was observed to decrease with an increase in acid concentration and oxidizing ions. The concentrations of oxidizing ions were found to have a profound effect on the corrosion potential and passive current density when compared to that in nitric acid without oxidizing ions. XPS results revealed a significant reduction of chromium(III) oxide (Cr2O3) on the passive film as the concentration of oxidizing ions in nitric acid increases. An oxide layer thickness of ~13 nm enriched with iron oxide co...
TL;DR: In this paper, the corrosion behavior of pyrylytic graphite (PyG) in molten LiCl-KCl-Eutectic salt at 873 K was discussed.
Abstract: Graphite based materials are proposed as one of the candidate materials for metallic fuel reprocessing involving high temperature molten chloride salt environment. Pyrolytic graphite (PyG) was deposited on graphite substrates by thermal chemical vapour deposition using methane gas to enhance their performance in molten chloride environments. The structural features of the PyG deposit were characterised using X-ray diffraction by measuring interlayer spacing, crystallite size and preferred orientation. The present study discusses the corrosion behaviour of PyG in molten LiCl–KCl eutectic salt at 873 K. The PyG samples tested in molten salt for 2000 h in controlled argon atmosphere exhibited negligible weight loss. The as deposited and corrosion tested samples characterised using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy showed no significant change in surface morphology. The study showed excellent corrosion resistance of PyG i...