Formation processes of nickel oxide nanoparticles in SiO2 by metal-ion implantation combined with thermal oxidation

Formation processes of nickel oxide (NiO) nanoparticles (NPs) in silica glass (SiO₂) by implantation of 60 keV Ni⁻ ions combined with thermal oxidation are studied using cross-sectional transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry. In as-implanted state, Ni metallic NPs form within the surface layer of 80 nm thick. The mean depth z and the standard deviation (Δz)^21/2 of Ni atom distribution determined by XTEM were 43 and 15 nm, respectively. After the oxidation at 800 °C for 1 h, z and (Δz)^21/2 became 47 nm and 20 nm, respectively, i.e. the distribution was almost the same except a small diffusional shift to the deeper region. Mean volume of Ni- and NiO-NPs after heat treatments at 800 °C were 27 and 43 nm³, respectively. The larger mean volume of NiO-NPs is explained from the fact that NiO-NPs include both Ni and O atoms, i.e. approximately 2N atoms, while Ni-NPs include Ni atoms only, i.e. N atoms. Both the Ni- and NiO-NPs include 2.4 × 10³ Ni atoms per NP in average. These results indicate that NiO-NPs are formed by oxidation of Ni-NPs without pronounced redistribution of Ni atoms.     

Mechanism of dynamic strain aging and characterization of its effect on the low-cycle fatigue behavior in type 316L stainless steel

Low-cycle fatigue tests were carried out in air in a wide temperature range from 20 to 650 °C with strain rates of 3.2 × 10⁻⁵–1 × 10⁻² s⁻¹ for type 316L stainless steel to investigate dynamic strain aging (DSA) effect on the fatigue resistance. The regime of DSA was evaluated using the anomalies associated with DSA and was in the temperature range of 250–550 °C at a strain rate of 1 × 10⁻⁴ s⁻¹, in 250–600 °C at 1 × 10⁻³ s⁻¹, and in 250–650 °C at 1 × 10⁻² s⁻¹. The activation energies for each type of serration were about 0.57–0.74 times those for lattice diffusion indicating that a mechanism other than lattice diffusion is involved. It seems to be reasonable to infer that DSA is caused by the pipe diffusion of solute atoms through the dislocation core. Dynamic strain aging reduced the crack initiation and propagation life by way of multiple crack initiation, which comes from the DSA-induced inhomogeneity of deformation, and rapid crack propagation due to the DSA-induced hardening, respectively.     

Corrosion of steels with surface treatment and Al-alloying by GESA exposed in lead–bismuth

Corrosion tests were performed for T91, E911 and ODS (oxide dispersion strengthened) with surface treatment and Al-alloying by pulsed electron beam (GESA—GepulsteElektronenStrahlAnlage) in flowing lead bismuth eutectic (LBE) with an oxygen content of 10⁻⁶ wt% at 550 °C for 2000 h. The result was that the surface treatment by GESA led to a faster growing multiphase oxide layer which was very homogenous in thickness. After exposure of specimens to LBE, the average oxide layer at the surface was 14–15 μm thick for ODS, 19–20 μm for E911 and 8–22 μm for T91. No dissolution attack occurred. On the surface of the Al-alloyed specimens, thin protective alumina layers were observed at the places where FeAl was formed by the GESA process, otherwise multiphase oxide layers or corrosion attack were observed.     

Non-equilibrium intragrain concentration redistribution of the alloying elements in austenitic steels under irradiation

Radiation-induced and thermally activated decomposition of austenitic 16Cr15Ni3Mo1Ti, 32Ni, 34Ni steels at high temperature (500–650°C) were examined. High doses (up to 10–200 dpa ) in 16Cr15Ni3Mo1Ti stainless steel with 1.5 MeV Kr ions and 450 keV Fe ions at 550–650°C lead to the appearance of relatively large regions (up to 200–400 nm) of concentration-oscillations with ‘mosaic’ dark–white diffraction contrast in TEM images. The radiation-induced redistribution of alloying elements takes place thanks to inverse Kirkendall effect and, in particular, removal of Cr to cell volume from boundaries of coarse cellular structure. The competing formation of ultrafine subgrains and grains 10–50 nm in size structure in Ti-free steel (16Cr15Ni3Mo) impedes the development of large ingrain segregations. The Mössbauer investigations showed that the 32Ni and 34Ni steels with purposefully produced concentration-oscillations were fully homogenised in that high-temperature region. This fact indicated the absence of the thermal decomposition dome in the Fe–Ni equilibrium diagram.     

The crystal structure of oxides grown on Zr–20Nb alloy

Oxides that were grown on Zr–20Nb in water at 300°C for 3 d, or in air at 400°C for 2 h were characterized by analytical electron microscopy. In both oxides, a similar microstructure was observed and similar electron diffraction patterns and high resolution lattice images were obtained. Analyses of the results showed that the crystal structure of the oxides was identical to that of an incommensurate modulated Nb₂Zr_x−2O_2x+1 phase, with x ≈ 10.     

Measurement of the mechanical properties of thermally-shocked zirconia-based simulated inert matrix fuel

The Vickers micro-hardness (H_V) was measured by an indentation technique of simulated ZrO₂-based Inert Matrix Fuel (IMF) material with a composition of Er_0.07Y_0.10Ce_0.15Zr_0.68O_1.915 in two different densities on sintered specimens and specimens thermally shocked with the quenching temperature differences (ΔTs) between 473 and 1673 K and compared with those of simulated MOX, namely, U_0.92Ce_0.08O₂. The H_V values obtained for two IMF materials were found higher, ranging from 6.37 GPa to about 7.84 GPa, depending on ΔT and the sintered density, than those obtained for the simulated MOX which are quasi-constant in the same range of ΔT with a mean value of 6.37 GPa. The fracture toughness (K_IC) was calculated from the measured H_V and the crack length, and it was found to exhibit a slight increase with increasing ΔT, ranging between 1.4 and 2.0 MPa m^1/2, while that of simulated MOX specimen is ranging between 0.8 and 1.1 MPa m^1/2. The thermally shocked specimens were observed with an optical microscope and analyzed in terms of microstructural changes and cracking patterns.     

Fatigue crack growth under residual stress field in low-carbon steel

The influence of residual stress on fatigue crack growth was experimentally and analytically investigated for surface crack. Fatigue tests were performed on straight pipe components of low-carbon steel having a circumferential inner surface crack in laboratory air environment. Some of the test pipes had been subjected to special heat treatments so as to have compressive or tensile residual stresses along the inner surface.The results show that the compressive residual stress remarkably suppresses the surface crack growth while the tensile residual stress doesn't accelerate the crack growth very much.The crack growth analyses were conducted by the application of power relationship between ΔK and . The stress intensity factors due to the non-linear stress field were calculated by the weight function method. The analyses resulted in a confirmation of the behavior of the crack growth observed in the experiments.     

Postirradiation tensile behavior of nickel-doped ferritic steels

Tensile specimens of normalized-and-tempered 9Cr-1MoVNb, 9Cr-1MoVNb-2Ni, 12Cr-1MoVW, 12Cr-1MoVW-1Ni, and 12Cr-1MoVW-2Ni steels were irradiated in the High-Flux Isotope Reactor (HFIR) at 300, 400, and 500°C to displacement-damage levels of up to ˜11 dpa. The nickel was added to the ferritic steels to produce helium by a two-step (n, ) reaction during irradiation in this mixed-spectrum reactor. Up to 103 appm He was produced in the steels with 2% Ni. Irradiation at 300 and 400°C caused an increase in strength of all the steels relative to the strength in both the normalized-and-tempered condition and after aging the normalized-and-tempered steel for a time period similar to that in the reactor. The strength increases were accompanied by a loss of ductility. At 500°C, there was little change in the strength properties of the steels. The results at 300 and 400°C indicate an effect of helium on the strength increases; no helium effect was apparent for the specimens irradiated at 500°C.     

Ion-induced electron emission – monitoring the structure transitions in graphite

The temperature dependence of ion-induced electron emission yield γ under 30 keV Ar⁺ ion impacts at incidence angles θ = 0−80° under dynamically steady-state conditions has been measured for polygranular graphite POCO-AXF-5Q. The fluencies were 10¹⁸–10¹⁹ ion/cm², the temperatures varied from the room temperature (RT) to 400 °C. The RHEED has shown that same diffraction patterns correspond to a high degree of disorder at RT. At high temperature (HT), some patterns have been found similar to those for the initial graphite surfaces. The dependence γ(T) has been found to be non-monotonic and for normal and near normal ion incidence manifests a step-like increase typical for a radiation induced phase transition. At oblique and grazing incidence (θ > 30°), a broad peak was found at T_p = 100 °C. An analysis based on the theory of kinetic ion-induced electron emission connects the behavior of γ(θ,T) to the dependence of both secondary electron path length λ and primary ion ionizing path length R_e on lattice structure that drastically changes due to damage annealing.     

Formation of cavities in GaAs and InGaAs

The ion implantation of He is examined as a means to form thermally stable cavities in GaAs. Room-temperature implantation of 2–10 × 10¹⁶ He/cm² at 40 or 50 keV forms bubbles, but subsequent annealing at 250°C or above leads to exfoliation of the implanted surface layer. The exfoliation appears related to the agglomeration of bubbles on dislocations at the back of the layer; evidence suggests these may be misfit dislocations formed to relieve compressive stress in the implanted layer. Implantation of He at 150°C produces similar results, whereas the He diffuses out of GaAs without forming cavities during implantation at 300°C. However, implantations of immobile Ar followed by He at 400°C produce extended defects with bubbles in the implanted layer; the He can be degassed by subsequent annealing at 400°C to produce 1.5–3.5 nm cavities that are stable at this temperature. The same treatment applied to an In_0.10Ga_0.90As/GaAs heterostructure produces larger cavities preferentially located on dislocations at the interface, with only slight reduction in strain of the epitaxial layer. The microstructures of both GaAs and the heterostructure clearly demonstrate an attractive interaction between bubbles or cavities and dislocations.     

The effect of ageing temperature and time on the mechanical properties of Fe-NiCrMo alloys with different contents of δ ferrite

Laboratory cast alloys with 2–27% of δ ferrite were aged for up to 17,520 h in the temperature range 290–350 °C. Tensile and Charpy tests were performed at 22 and 290 °C on specimens aged for different times, and the microhardnesses of both constituents of the microstructure were determined for the alloy with 27% of δ ferrite. The effects of the content of δ ferrite, the ageing and testing temperature, and the ageing time on mechanical properties and notch toughness are presented and discussed.     

Standard molar Gibbs free energy of formation of PbO(s) over a wide temperature range from EMF measurements

The EMF of the following galvanic cells,

(render)

Kanthal,Re,Pb,PbOCSZO₂ (1 atm.),Pt

(render)

Kanthal,Re,Pb,PbOCSZO₂(1 atm.),RuO₂,Pt

were measured as a function of temperature. With O₂ (1 atm.), RuO₂ as the reference electrode, measurements were possible at low temperatures close to the melting point of Pb. Standard Gibbs energy of formation, Δ_fG⁰_mβ-PbO was calculated from the emf measurements made over a wide range of temperature (612–1111 K) and is given by the expression: Δ_fG⁰_mβ-PbO±0.10 kJ=−218.98+0.09963T. A third law treatment of the data yielded a value of −218.08 ± 0.07 kJ mol⁻¹ for the enthalpy of formation of PbO(s) at 298.15 K, Δ_fH⁰_mβ-PbO which is in excellent agreement with second law estimate of −218.07 ± 0.07 kJ mol⁻¹.     

Investigation of in-reactor creep and irradiation growth of zirconium-2.5 wt% niobium channel tubes

We summarize the diametral creep results obtained in the MR reactor of the Kurchatov Institute of Atomic Energy on zirconium-2.5 wt% niobium pressure tubes of the type used in RBMK-1000 power reactors. The experiments that lasted up to 30 000 h cover a temperature range of 270 to 350°C, neutron fluxes between 0.6 and 4.0 ×10¹³ n/cm² · s (E > 1 MeV) and stresses of up to 16 kgf/mm². Diametral strains of up to 4.8% have been measured. In-reactor creep results have been analyzed in terms of thermal and irradiation creep components assuming them to be additive. The thermal creep rate is given by a relationship of the type ε_th = A₁ exp [(A₂ + A _3σt) T] and the irradiation component by ε_rad = A_4σtø(T − A₅), where T = temperature, σ_t = hoop stress, ø = neutron flux and a₁ to A₅ are constants. Irradiation growth experiments carried out at 280° C on specimens machined from pressure tubes showed a non-linear dependence of growth strain on neutron fluence up to neutron fluences of 5 × 10²⁰ n/cm². The significance of these results to the elongation of RBMK reactor pressure tubes is discussed.     

Enthalpies of formation of U-, Th-, Ce-brannerite: implications for plutonium immobilization

Brannerite, ideally MTi₂O₆, (M=actinides, lanthanides and Ca) occurs in titanate-based ceramics proposed for the immobilization of plutonium. Standard enthalpies of formation, ΔH⁰_f at 298 K, for three brannerite compositions (kJ/mol): CeTi₂O₆ (−2948.8 ± 4.3), U_0.97Ti_2.03O₆ (−2977.9 ± 3.5) and ThTi₂O₆ (−3096.5 ± 4.3) were determined by high temperature oxide melt drop solution calorimetry at 975 K using 3Na₂O · 4MoO₃ solvent. The enthalpies of formation were also calculated from an oxide phase assemblage (ΔH⁰_f-ox at 298 K): MO₂ + 2TiO₂=MTi₂O₆. Only UTi₂O₆ is energetically stable with respect to an oxide assemblage: U_0.97Ti_2.03O₆ (ΔH⁰_f-ox=−7.7±2.8 kJ/mol). Both CeTi₂O₆ and ThTi₂O₆ are higher in enthalpy with respect to their oxide assemblages with (ΔH⁰_f-ox=+29.4±3.6 kJ/mol) and (ΔH⁰_f-ox=+19.4±1.6 kJ/mol) respectively. Thus, Ce- and Th-brannerite are entropy stabilized and are thermodynamically stable only at high temperature.     

Electron beam simulation of disruptions into stainless steel

The effects of repetitive pulsed heating and melt layer formation on type 304 stainless steel are reported. A line-source electron beam with pulse times of 0.5 or 1.5 ms and power densities up to 100 kW/cm² has been used for 1–40 pulse cycles at 500°C substrate temperatures. Numerical calculations of the temperature profiles and their time evolution during melt layer formation are also carried out. Significant metallurgical changes are observed, both in the melt layers and in the adjacent heat-affected zone. Melt depths (10–20 μm) are consistent with calculations and the resolidified regions exhibit columnar or columnar-dendritic microstructure. Appreciable lateral motion within the molten layer results in very rough surfaces and localized cracking occurs. Extensive slip deformation is seen in the adjacent heat-affected zone, and low-cycle fatigue crack initiation is observed after only 20 pulses. Chemical changes in the stainless steel melt layer result from the preferential vaporization of Mn from the melt layer and correlate with the time in the liquid phase. We suggest that the preferential loss of high vapor pressure species such as Mn in the early phases of plasma device operation might provide a unique signature of the impurity introduction mechanism. Disruption melted compositions are distinctly different from the more-nearly stochiometric ratios of Mn/Cr/Ni expected for sputter erosion.     

Influence of protecting gel film on oxidation of zirconium alloys

Thin oxide layers of Zr1Nb and Zry-4S on tubes, used for fuel cladding in light water reactors, which had been protected by thin gel films, were compared with oxide layers on unprotected specimens of the same kind, grown together in two batches in water at 360 °C for 21 and 42 days, respectively. The analysis of the I–V characteristics at constant temperatures up to 180 °C showed a strong decreasing resistivity with oxidation time of the gel-protected layers of the Zry-4S specimens, with indication of an energy dependent trap distribution, although the gel and the oxide alone showed evidence of single, but different, energy traps. The changes are believed to be due to diffusion of different trap centers in both directions. The Zr1Nb specimens retained their single energy trap behaviour also in the combination with the protecting gel film and resistivity dropping with increasing oxidation time.     

On “lower bound crack resistance curves” as material law for the safety assessment of components

Experimental fracture-mechanics investigations were carried out on large scale specimens. The specimen geometries and the crack depth ratio, a / W, in a parameter field were varied. Three materials of different toughness were chosen for the specimens. Their load—deformation behaviour, crack resistance curves, stretched zones Δa; and crack inititiation values J_i were determined and compared with the results from CT25 specimens. Numerical finite-element calculations were made to determine the state of stress in the specimens and the size of the plastic zones.     

Air clearing pressure oscillation produced in a quenching tank by a prototype unit cell sparger of the APR1400

KAERI has performed a series of experiments to investigate the performance of a prototype sparger for the APR1400 in view of a dynamic load oscillation with a variation of the test conditions such as a discharged air mass, a submergence of the sparger, the valve opening time, and the pool temperature during an air clearing phase. The air mass and pool temperature are in the range of 0.8–1.5 kg and 20–90 °C, respectively. The valve opening time can be adjusted within the range of 0.6–1.8 s. The maximum positive pressure amplitude, which is observed at the bottom of the quenching tank, is increased with the maximum header pressure of the sparger. The valve opening time has a considerable effect on the maximum amplitude. As the opening time decreases, the maximum amplitude at the tank wall is increased. Air mass and pool temperature, however, have a weak effect on the maximum amplitude. Oscillation frequency is decreased with an increase of the air mass in the range of 2.5–4.5 Hz.     

Influence of Pt, Fe/Ni/Cr-containing intermetallics and deuterium on the oxidation of Zr-based materials

An in situ gas phase analysis technique and the ¹⁸O-SIMS technique are used to evaluate the transport of oxygen and hydrogen in oxidation of Zr-based materials. At 400 °C, it is found that oxygen dissociation efficiency decreases in the order: Pt > Zr₂Fe > Zr₂Ni > ZrCr₂  Zircaloy-2. Two Zr-plates partly coated with 200 Å porous Pt, with and respectively without D in the substrate, were oxidized in two stages at 400 °C. SIMS depth profiles in the Pt area show that an enhanced oxidation takes place mainly by inward oxygen transport. A minimum in the oxide thickness was found near the Pt area on both Zr plates. Two Ar-filled Zircaloy-2 tubes with ZrSn liner were exposed at 370 °C to 22 mbar water, filled in from one side. Our experimental results suggest that a proper choice of the SPP composition and size distribution can lead to reduced hydrogen uptake during oxidation of Zr-based materials in water.     

Wetting of W by liquid Pb and PbLi alloys and surface interactions

Wetting of W by Pb and Pb–17 at.%Li in the range 400–900 °C is studied by the dispensed drop technique. Experiments are performed using different furnace atmospheres (high vacuum, reducing gas) and different heat treatments to achieve W deoxidation. A simple pairwise model is used to explain the relation between surface interaction, which is responsible for wetting, and bulk interactions determining miscibility.