Radiation-induced segregation (RIS) of solutes in materials exposed to irradiation is a wellknown problem. It affects the life-time of nuclear reactor core components by favouring radiation-induced degradation phenomena such as hardening and embrittlement. In this work, RIS tendencies in face-centered cubic (fcc) Ni-X (X = Cr, Fe, Ti, Mn, Si, P) dilute binary alloys are examined. The goal is to investigate the driving forces and kinetic mechanisms behind the experimentally observed segregation. By means of ab initio calculations, point-defect stabilities and interactions with solutes are determined, together with migration energies and attempt frequencies. Transport and diffusion coefficients are then calculated in a mean-field framework, to get a full picture of solute-defect kinetic coupling in the alloys. Results show that all solutes considered, with the exception of Cr, prefer vacancy-mediated over interstitial-mediated diffusion during both thermal and radiation-induced migration. Cr, on the other hand, preferentially migrates in a mixed-dumbbell configuration. P and Si are here shown to be enriched, and Fe and Mn to be depleted at sinks during irradiation of the material. Ti and Cr, on the other hand, display a crossover between enrichment at lower temperatures, and depletion in the higher temperature range. Results in this work are compared with previous studies in bodycentered cubic (bcc) Fe, and discussed in the context of RIS in austenitic alloys.

No abstract

Various oxide surfaces have been shown to catalyze H 2 O 2 decomposition, resulting in the intermediate formation of hydroxyl and hydroperoxyl radicals. In this work, the impact of bromide, chloride, and perchlorate separately and in combination with bicarbonate on the reaction between H 2 O 2 and ZrO 2 was investigated. The reaction was studied by monitoring the concentration of H 2 O 2 as a function of time, and by probing the hydroxyl radical production using tris as a scavenger and monitoring the product formaldehyde. The most significant impact was seen in the presence of Br À and Br À /HCO 3 À. Br À significantly increases the H 2 O 2 decomposition rate and the yield of formaldehyde, whereas the combination of Br À /HCO 3 À was shown to decrease the H 2 O 2 decomposition rate as well as the yield of formaldehyde. The increased formaldehyde yield is explained by its formation in reaction with Br 2 *À. This contrasts the previous assumption that formaldehyde is only formed upon hydrogen abstraction from tris.

No abstract

No abstract