► Immobilization of Zr-rich radioactive metallic wastes via alloy melting route. ► First detail report on metallurgical characterizations of Fe–Cr–Ni–Zr alloys. ► Identification of suitable base ...alloy composition.
Alloy melting route is currently being considered for radioactive hulls immobilization. Towards this, wide range of alloys, belonging to Zirconium–Iron binary and Zirconium–Stainless steel pseudo-binary systems have been prepared through vacuum arc melting route. Detail microstructural characterization and quantitative phase analyses of these alloys along with interaction study between Zirconium and Stainless steel coupons at elevated temperatures identify Zr(Fe,Cr)
2, Zr(Fe,Cr), Zr
2(Fe,Cr), Zr
3(Fe,Ni), Zr
3(Fe,Cr), Zr
3(Fe,Cr,Ni), β-Zr and α-Zr as the most commonly occurring phases within the system for Zirconium rich bulk compositions. Nano-indentation studies found Zr(Fe,Cr)
2 and Zr(Fe,Cr) as extremely hard, Zr
3(Fe,Ni) as moderately ductile and β-Zr, Zr
2(Fe,Cr) as most ductile ones among the phases present. Steam oxidation studies of the alloys, based on weight gain/loss procedure and microstructural characterization of the mixed oxide layers, suggest that each of the alloys responded to the corrosive environment differently. Fe
2O
3, NiFe
2O
4, NiO, monoclinic ZrO
2 and tetragonal ZrO
2 are found to be most common constituents of the oxide layers developed on the alloys. Integrating the microstructural, mechanical and corrosion properties, ZrFeCrNi3 (Zr: 84.00, Fe: 11.20, Cr: 3.20, Ni: 1.60, in wt.%) is identified as the acceptable base alloy for disposal of radioactive hulls.
The characteristics of interdiffusion between precipitation-hardened 17-4 PH grade stainless steel and nickel were studied in the temperature range of 900 °C to 1100 °C, using diffusion couples of ...these two materials. The diffusion coefficients of the major diffusing elements Fe, Ni, Cr, and Cu were evaluated for this multicomponent system. The diffusion paths plotted on the Fe-Ni-Cr isotherm showed a flat “S” shape, suggesting insignificant interaction among the diffusing species. The temperature dependence of the diffusion coefficients for each element was evaluated, and the activation energies for diffusion were determined. The asymmetric nature of concentration variation of the elements at the diffusion zone was observed and was explained by the difference in diffusivities of the diffusing species. The activation energy for diffusion of Ni was found to be lower than that of Fe and Cr.
Stainless steel 304L is being considered as a structural material for a component in a critical facility in an environment of molten lead–bismuth eutectic (LBE) at a temperature between 250 and ...350 °C. This paper gives results on the effect, of 10,000 h exposure to non-isothermal liquid LBE at temperatures of 250 and 350 °C, on the mechanical and structural properties of SS 304L. The dissolved oxygen concentration in the molten eutectic was 4 × 10
−10
wt% and flow velocity was 16 cm/s. In order to assess the changes in mechanical properties tensile tests were carried out in air at 25 °C and fractography of fractured surface was observed by scanning electron microscopy. The results showed no change in the mechanical properties of SS 304L after 10,000 h exposure to LBE at 250 and 350 °C. Electron probe microanalysis of the interface of SS 304L with LBE showed that there was no penetration of LBE into the grain boundaries nor preferential dissolution of any of the components of steel in LBE after 10,000 h exposure at either temperature. No oxide layer was observed on the surface of SS 304L.
Diffusion reaction between Zircaloy-2 and thoria (ThO
2) has been studied by employing miniature diffusion couples under uniaxial loading conditions. Electron probe microanalyser (EPMA) has been used ...to establish the concentration profiles. Microstructural characterisations by scanning electron microscope (SEM) and concentration profiles by EPMA indicate the absence of any intermediate phase in the diffusion zone. The experiments show the preferential grain boundary diffusion of Th and O in Zircaloy-2 matrix. The interdiffusion coefficients are strongly dependent on the temperature of annealing and are of the order of 10
−18 m
2/s. The activation energy values for the layer growth kinetics and those estimated for interdiffusion coefficients are comparable.
The interdiffusion reactions between Zircaloy-2 and a Ni based alloy (Inconel 750X) have been studied in the temperature range 1083-1173 K by employing annealing of diffusion couples. The reaction ...zone developed at the interface was characterised using an optical microscope and electron probe microanalyser (EPMA). The diffusion reaction between Zircaloy-2 and Inconel shows that the reaction products form both as a layered structure and as two phase mixture in the diffusion zone. Three layers were found to form in the diffusion zone, namely, Zr
2
Ni (ξ phase) and ψ
1
phase close to Zircaloy-2 and a mixture of ψ
1
and ψ
2
phases close to Inconel. The kinetics for the growth of the three layers as well as the total diffusion zone was established. The growth of all the layers shows Arrhenius type of relation with respect to temperature. The temperature dependence for the reaction constants, K, for the various phases was also established.
Diffusion reaction between Zr–2.5 wt% Nb alloy and 403 stainless steel has been investigated by employing miniature type diffusion couples in the temperature range between 750°C and 940°C for 1–240 ...h. An electron probe microanalyser (EPMA) has been used to establish the concentration penetration profiles across the diffusion zone and a transmission electron microscope (TEM) has been used to identify various phases formed close to the interface. The microstructure of the bonded region on the 403 steel side is essentially a martensitic structure and remains nearly unchanged during annealing. However, the microstructure of the Zr–2.5 wt% Nb alloy changes substantially, leading to the formation of coarser α phase. The diffusion reaction is extremely sluggish. Localised melting occurs in the specimens annealed at and above 940°C. This is essentially due to the eutectic reaction between zirconium and iron. The experiments confirm that diffusion bonding of 403 steel to Zr–2.5 wt% Nb could be carried out at a pressure of 10 MPa at 900°C for 1 h. The formation of various phases in this multi-phase and multi-component system along with change in their composition with annealing temperature and the nature of reaction products is discussed.
Objectives: To develop and validate a modified HPLC-UV method for the estimation of serum levetiracetam levels and to assess the usefulness of serum levetiracetam estimation in epileptic patients.
...Materials and Methods: Modification of a previously existing HPLC-UV method was performed using liquid- liquid phase extraction and processing using reverse phase analytic HPLC-UV detector technique followed by method validation. Serum samples of patients attending our hospital's Therapeutic Drug Monitoring Outpatient Department services were analyzed for levetiracetam levels using the study method. Data of the past 6 years (2015-2020) were descriptively analyzed.
Results: The modified HPLC-UV method was validated as per ICH Q2 (R1) 2005 guidelines. Usefulness of levetiracetam estimation was assessed in 1383 patients (635 children, 683 adults, 40 elderly, and 25 pregnant women). Levetiracetam levels were within the therapeutic range (TR) in 520 children, 543 young adults, 35 elderly patients, and nine pregnant women. In 112 of 232 patients with low levetiracetam levels, poor compliance was elicited. Of 641 patients on polytherapy, 446 patients had levetiracetam values within TR, whereas 29 had values above and 166 patients had values less than TR. Sodium valproate, phenytoin sodium, and carbamazepine affected levetiracetam levels when given concomitantly. Levetiracetam dose was adjusted in 61 patients with abnormal levels for better clinical response. Good seizure control was noted in 913 (82.47%) patients whose levels were within TR, whereas 136 (58.62%) patients with low levels reported an increase in seizure frequency.
Conclusions: The modified HPLC-UV method is simple, rapid, efficient, and reliable for assaying serum levetiracetam.
The interdiffusion reactions in the Ti/Inconel-600 system in the temperature range 973–1153 K have been investigated by employing both the optical metallography and the electron probe microanalysis ...techniques. At 973 K the reaction zone showed the presence of solid solution phases like Ni-based (Fe, Cr, Ti) phase and titanium-based solid solution α-Ti. The two intermetallic phases, viz. TiNi(Fe, Cr) and Ti
2Ni are also observed. At 1023 K the reaction zone shows the formation of the two intermetallic phases, viz. TiNi(Fe, Cr) and Ti
2Ni along with solid solution phases such as Ni-based (Fe, Cr, Ti) phase and titanium-based solid solution β-Ti. At still higher temperatures (1073–1153 K), however, along with the solid solution phases such as Ni-based (Fe, Cr, Ti) phase and titanium-based solid solution β-Ti only one intermetallic phase, TiNi
3 (Fe, Cr), is formed. The temperature dependence of the reaction constants,
K, m/s
1/2, derived from the layer growth kinetics, can well be expressed as
for Ni-rich phase
K=3.06×10
−5
exp(−262.16/RT),
m/s
1/2
for
TiNi
3(
Fe,
Cr)
K=3.49×10
−5
exp(−240.96/RT),
m/s
1/2
for β-Ti
K=1.25×10
−6
exp(−983.80/RT),
m/s
1/2.
Here activation energy is expressed in kJ/mol. The interdiffusion parameters and the diffusion paths have also been established by employing these data.
Diffusion bonding of stainless steel (SS) has been attempted in temperature range of 623–773 K using multiple inter-layers of nickel, copper and silver. The intermediate layers were electro-deposited ...taking care to avoid oxidation at the interfaces. The bonded area was examined for the formation of any intermetallic compound through electron probe micro-analyzer (EPMA) and nano-indentation technique. Results indicate the absence of brittle intermetallics at the interfaces and the strength of the bonding was found to be satisfactory. The bond strength was found to be 130 ± 10 MPa and the bond was found to be leak tight with negligible leak rate.
