During vitrification of nuclear high level waste, the molten glass containing the waste oxides is poured into 304L SS canisters at 1323 K (1050 °C), which subsequently, cools through the ...sensitization temperature, wherein, nucleation of chromium carbides occur. Due to the radioactive decay heat, the canister is exposed to 373 K 573 K (100 °C- 300 °C) over long containment periods, leading to the growth of the carbides, resulting in low temperature sensitization (LTS). The sensitized microstructure is susceptible to intergranular corrosion (IGC) when it comes in contact with ground water. In the present work, AISI Type 304L SS containing 0.02% and 0.03% carbon were subjected to LTS, simulating 10 and 100 years of vitrified nuclear waste containment respectively, and subsequently, the corrosion resistance was evaluated in simulated ground water. The microstructural evaluation was carried out by optical, scanning electron microscope (SEM), transmission electron microscope (TEM) and electron backscatter diffraction (EBSD). Double loop electrochemical potentiokinetic reactivation (DL-EPR) experiments were conducted to quantify the degree of sensitization (DOS). The study revealed that 304L SS containing 0.02% C is resistant to LTS and IGC, while that containing 0.03% C is highly susceptible to LTS and IGC in ground water composition.
•Pronounced effect of C on low temperature sensitization (LTS) of 304LSS canisters.•Consequently, C in 304L SS canisters influenced corrosion property in ground water.•Carbon content of 0.02% is resistant to LTS and 0.03% is susceptible to LTS.•0.03% C in 304L SS canisters causes IGC in ground water on long term storage.•EBSD confirmed distribution of carbides along high angle boundaries only.
The Fe-15wt% Y2O3 model Oxide Disperson Strengthened (ODS) alloy powder was prepared by mechanical milling in an inert atmosphere using high energy planetary ball mill. The present paper deals with ...the study on structural changes of nano-crystalline yttria dispersoids in Fe matrix during mechanical milling for various durations and subsequent annealing. The crystallinity of Y2O3 in the milled powder was studied by X-ray diffraction (XRD) technique which showed that the intensity of diffraction peaks of Y2O3 gradually disappeared with increase in milling time. Dark field TEM imaging of the milled powder showed that both Fe and Y2O3 particles were refined to few nanometers during milling. Electron diffraction analysis showed polycrystalline rings for Fe and broad rings with a few spots corresponding to the (411) plane of Y2O3 after 10h of milling time. The yttria diffraction peaks became broad and diffuse with increasing milling time. Subsequent annealing of the 60h milled powder at 1273K for 1h results in recrystallization of Y2O3 and growth of Fe crystallites.
The Nb–V modified 9Cr–1Mo ferritic steel is an extremely important structural material in the power industry. Present work is focused on how the microstructure, microchemistry and microtexture of ...this steel evolve during high degree of deformation, starting from the normalized and tempered condition. While the microstructure and microchemistry are analyzed using analytical transmission electron microscopy, the microtexture analysis is carried out using the electron back-scatter diffraction (EBSD) technique. High degree of cold rolling leads to the formation of forests of dislocations and cellular structure of ferritic matrix. The carbides were found to retain their morphology and chemistry after 88% cold work. Analysis of misorientation angles was used to derive the grain boundary character of the normalized and tempered steel and the deformed steel. Analysis of fiber texture reveals that deformation in the material does not lead to predominance of any particular fiber which is useful from fabrication point of view.
•Sodium niobium phosphate glasses, xNb2O5–(50-x/2) Na2O–(50-x/2) P2O5 (x = 20, 30, 40 mol. %) are synthesized by the melt-quench method.•Lasocka parameters and glass transition activation energy are ...evaluated.•The local activation energies for crystallization are estimated by different isoconversional methods.•The local Avrami exponent values are evaluated, confirming that the crystallization process occurs through volume nucleation, mainly with 3D growth.•The SEM analysis confirms the three-dimensional evolution of the sheaf-like structure.
Sodium niobium phosphate (SNP) glasses of composition xNb2O5–(50-x/2)Na2O–(50-x/2) P2O5 (x = 20, 30, 40 mol. %) are prepared by the conventional melt–quench technique. The non-isothermal kinetics of glass transition & crystallization of SNP glasses are studied by a differential scanning calorimeter (DSC). The dependence of glass transition temperature on the heating rate is used to deduce the activation energy of glass transition. The average activation energies of crystallization are calculated by model-free peak kinetic methods (Kissinger, Boswell, Augis-Bennet, and Ozawa). The local activation energies for crystallization with the volume fraction crystallized is estimated by linear iso-conversional methods (Kissinger-Akahira-Sunose, Starink, Tang, Flynn-Wall-Ozawa, and Various heating rates (VHR)) and by Friedman differential method. Avrami exponents are deduced to understand the nucleation and growth of various crystalline phases formed on heat treatment of SNP glasses. The change in the local Avrami exponent with the crystallized volume fraction confirms that the crystallization process occurs through volume nucleation, mainly with 3D growth. SEM analysis explored the crystalline morphologies and revealed the evolution of sheaf-like crystals.
•Nanocrystalline nickel with higher grain size displayed superior thermal stability.•Activation energy for grain growth of 〈111〉 and 〈200〉 grains are distinct.•The as-deposited texture is retained ...throughout the annealing process up to 550 °C.•High fraction of twin boundaries are observed in the smallest grain sized sample.•Recrystallization influences texture, microstructure and grain boundary character.
Nanocrystalline (NC) Ni coatings have widespread engineering applications, many of which are in high-temperature environments. Therefore, it is important to study the thermal stability of NC Ni. The present study compares the thermal stability of electrodeposited (ED) NC Ni of varying grain sizes: 20 nm, 50 nm, and 100 nm. In-situ high-temperature X-ray diffraction (XRD) investigations have been employed to follow the grain growth behavior of 〈111〉 and 〈200〉 grains under isochronal annealing up to 550 °C. Based on the calculated activation energies, the anisotropic growth mechanisms of 〈111〉 and 〈200〉 grains are evaluated. The studies revealed that the onset of grain growth occurred at progressively higher temperatures with increasing initial grain sizes. While near uniform grain size distribution is observed for the 20 nm grain size variant, bimodal distributions are observed for its counterparts. Electron Backscatter Diffraction studies of NC Ni samples in the final-processing temperature of XRD showed that //ED texture is preserved during the annealing process. While high fractions of Σ3 coincidence site lattice (CSL) boundaries are observed in the 20 nm sample, reduced fractions with no particular trend is observed for the 50 nm and 100 nm grain-sized samples. It is shown here that the incomplete recrystallization arising from inhomogenous strain distribution is the reason for the observed bimodal distribution and deviation from an expected trend in the formation of Σ3 CSL as a function of initial grain size.
Oxide dispersion strengthened (ODS) steels are considered as potential candidates for future Gen-IV reactors core structural applications. Ti is added to this alloy to refine the dispersoid and ...facilitates formation of Y-Ti-O complex oxides. Optimisation of Y2O3 and Ti content in these ODS steels governs size and stoichiometry of the dispersoids. Equal amount of both Ti and Y2O3 content resulted in formation of finer and stable Y-Ti-O dispersoids. In this study two varieties of ODS alloys are synthesized: one with 0.35 wt% Ti and Y2O3 while another with 0.2 wt% Ti and Y2O3 by mechanical milling followed by SPS. The microstructure and microtexture of these two varieties of ODS steels were compared with modified 9Cr1Mo (P91) steel. The creep-rupture studies reveal that the ODS steels have better creep-rupture life as compared to P91 steel, and the steel with 0.35 wt% Ti and Y2O3, possess superior mechanical properties.
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•10 h milling duration found to be optimum for synthesis of 9Cr ODS steel.•Microtexture of 9Cr ODS steels was comparable with modified 9Cr-1Mo (P91) steel.•ODS steels have better creep-rupture life as compared to P91 steel.•For ODS steel, optimum content of Y2O3 and Ti content should be 0.35 wt% each.
Oxide dispersion-strengthened (ODS) ferritic steels are being considered as a potential candidate for core structural application in future fast reactors. The 9Cr ODS steel being ferritic–martensitic ...in the structure is easier to fabricate by conventional powder metallurgical route; however, these varieties of steel have poor corrosion resistance in boiling HNO
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medium. To facilitate the closed nuclear cycle program, it is necessary to develop better corrosion resistance, irradiation resistance steel for the fast reactor clad application. In this context, the 18Cr ODS ferritic steel is found to be superior; however, these steels are difficult to fabricate. This study is an attempt toward a comparison of microstructure and microtexture of these two varieties of steels to understand the structure–property co-relation of the ODS ferritic steel during various stages of tube fabrication. Though the size distribution of the dispersoids in both varieties of steel is found to be similar, there exists a difference in the morphology of the ferrite grains of these two varieties of steel. The comparison of the microstructure reveals that the 9Cr ODS steel possesses a nearly equiaxed tempered martensitic structure as compared to the elongated bamboo-like ferrite structure in 18Cr ODS steel. The microtexture studies on both the steel reveal that 18Cr ODS steel possesses a strong α fiber texture and weak γ fiber texture, whereas 9Cr ODS steel clad tube possesses relatively weak both α and γ fiber texture. Since 9Cr steel undergoes γ (austenite) ↔ α (ferrite) phase transformation upon annealing, which is unlikely in the case of 18Cr ODS steel, as a result, it leads to difficulty in fabrication of 18Cr ODS steel as compared to 9Cr ODS steel.
Cerium is a well-known surrogate to trivalent and tetravalent actinides and has been investigated to explore the structural and thermal characteristics of simulated radwaste-loaded material systems. ...The solubility and distribution of CeO2 into a sodium niobium phosphate glass have been explored with the objective of developing a host matrix for radioactive waste immobilization. Niobium phosphate glasses of (100-x) (40Na2O–20Nb2O5–40P2O5)-xCeO2 (x = 0, 1, 3, 5, 8, and 10 mol%) compositions are prepared by melt-quenching method and are characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and scanning electron microscopy (SEM). This study summarises the influence of cerium ion incorporation on the structure, thermal stability, and formation of crystalline phases of the niobium phosphate glass. The various glass stability parameters, such as Hruby (KH), Weinberg (KW), and Lu–Liu (KLL) parameters are estimated to assess the stability of the glass melt against devitrification in the supercooled region. The spectroscopic analysis ascertains the presence of metaphosphate and pyrophosphate networks as primary structural building units in the glass. However, the Raman analysis demonstrates the influence of CeO2 on the network linkages arising from the corner-sharing of NbO6 octahedrons and Nb–O–P bonding in the glass. The CeO2 loading is optimized up to 8 mol% into the base 40Na2O–20Nb2O5–40P2O5 glass matrix without precipitation of any crystalline phase. The glasses are heat treated to obtain glass-ceramics embedded with the crystalline phases, namely, monazite CePO4, NbOPO4, NaNbO3, and niobium phosphate bronze Na6Nb8(PO4)5O15. The microanalysis of these glass ceramics shows that the CeO2 is more aggregated inside the niobium phosphate bronze framework than in the bulk at a higher temperature. It is also observed that the surface crystallization process is a prevalent mechanism for the crystallization of glasses on heating at crystallization onset temperature.
This paper deals with adsorption behavior of ruthenium on Tri-n-butyl phosphate functionalized Multi Walled Carbon Nanotubes (MWCNTs-COO-TBP) from aqueous solution. Adsorption method is significant ...for trace levels (expected level) removal of ruthenium in bioassay (urine) samples which is mandatory requirement of radiation workers in nuclear environment. Multi Walled Carbon Nanotubes (MWCNTs) were initially converted to carboxylated Multi Walled Carbon nanotubes (MWCNTs-COOH) and subsequently treated with Tri-n-butyl phosphate to MWCNTs-COO-TBP. The synthesized MWCNTs-COOH and MWCNTs-COO-TBP were confirmed by Fourier Transform Infrared Spectroscopy (FTIR). Spectroscopic and microscopic techniques such as X-Ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) and High Resolution Transmission Electron Microscopy (HR-TEM) were used for its characterization before and after adsorption. Various adsorption parameters such as contact time, pH, metal ion concentration and temperature were studied. Langmuir adsorption isotherm model and Pseudo second order kinetics model were found to be best fitted in terms of standard deviation and regression coefficient. Thermodynamics parameters such as enthalpy (ΔH°), entropy (ΔS°), Gibbs energy (ΔG°), activation energy (Ea) and sticking probability (SP*) were calculated. The adsorption capacity was calculated and found to be 141.23 mg.g−1.Moreover, quantification of defects, strains with charge doping states were calculated from Raman mapping and correlation plot.
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•Synthesis and characterization of Tri-n-Butyl Phosphate functionalized Multi Walled Carbon Nanotubes (MWCNTs-COO-TBP).•Detailed study on adsorption of ruthenium on MWCNTs-COO-TBP and its kinetics, thermodynamics and isotherm.•Functionalization of MWCNTs by TBP and its adsorption for ruthenium, confirmed by FTIR and EDS analysis.•Quantification of defects and strains with charge doping states were calculated from Raman mapping and correlation plot.•The potential application of MWCNTs-COO-TBP for adsorption of Ru from aqueous solution was explored.
The magnetohydrodynamic nanofluid flow comprised of dust particles is carried out in the current investigation. The role of dust nanoparticles on the flow characteristics is vital. The radiative heat ...phenomena for the interaction of Cu nanoparticle are deliberated in this discussion. However, both water and oil (kerosene) are treated as conventional fluids. Regarding the current applications on nanofluid in industries for the production of several materials, it is important to use the nanoparticles as a coolant. In recent applications, for the CPU cooler Cu-nanoparticle is used because of its high thermal conductivity and as a good conductor of heat. The governing flow characteristics involved with nonlinear properties of partial differential equations are transformed into ordinary differential equations using suitable similarity variables. Further, numerical treatment is imposed using the in-build Matlab code bvp5c. The imitation is carried out for the various profiles using physical parameters and presented graphically. The numerical values for the rate coefficients are presented via tables and deliberated briefly.
