Study on Corrosion Resistance of N36 Zirconium Alloy in LiOH Aqueous Solution

Zr-Sn-Nb-Fe alloys are one of the important directions for continuous improvement of zirconium alloys for high burn-up fuel assemblies. The corrosion resistance of Zr-Sn-Nb-Fe alloys is closely related to the alloying element and water chemical condition. To better understand the effect of Sn on corrosion resistance of Zr-Sn-Nb-Fe alloy, the normal N36 (Zr-1Sn-1Nb-0.3Fe) and low-tin N36 (Zr-0.8Sn-1Nb-0.3Fe) alloy sheets were prepared and tested in static autoclave in both of 0.01 mol/L LiOH and 0.03 mol/L LiOH aqueous solution at 360°C and 18.6 MPa. The characteristics of the microstructure and oxide film of alloys were analyzed by TEM and SEM respectively. It was shown that that the corrosion transition of the normal N36 appears earlier and the weight gain is higher than the low-tin N36 in two corrosive mediums. The cracks paralleling to the interface of oxide/metal are formed in the fracture surface of the oxide film and the micrographs at the oxide film/substrate interface appear uneven morphology. With the increasing of corrosion gain, there are more parallel cracks in oxide film and the uneven morphology at the oxide film/substrate interface is more obvious.

Three distinct optical-switching states in phase-change materials containing impurities:From physical origin to material design

Ge2 Sb2 Te5 is the most widely utilized chalcogenide phase-change material for non-volatile photonic applications,which undergoes amorphous-cubic and cubic-hexagonal phase transition under external excitations.However,the cubic-hexagonal optical contrast is negligible,only the amorphous-cubic phase transition of Ge_(2)Sb_(2)Te_(5) is available.This limits the optical switching states of traditional active displays and absorbers to two.We find that increasing structural disorder difference of cubic-hexagonal can increase optical contrast close to the level of amorphous-cubic.Therefore,an amorphous-cubichexagonal phase transition with high optical contrast is realized.Using this phase transition,we have developed display and absorber with three distinct switching states,improving the switching performance by 50%.Through the combination of first-principle calculations and experiments,we reveal that the key to increasing structural disorder difference of amorphous,cubic and hexagonal phases is to introduce small interstitial impurities(like N)in Ge2 Sb2 Te5,rather than large substitutional impurities(like Ag)previously thought.This is explained by the formation energy and lattice distortion.Based on the impurity atomic radius,interstitial site radius and formation energy,C and B are also potential suitable impurities.In addition,introducing interstitial impurities into phase-change materials with van der Waals gaps in stable phase such as GeSb_(4) Te_(7),GeSb_(2) Te_(4),Ge_(3)Sb_(2) Te_(6),Sb_(2)Te_(3) will produce high optical contrast amorphous-metastable-stable phase transition.This research not only reveals the important role of interstitial impurities in increasing the optical contrast between metastable-stable phases,but also proposes varieties of candidate matrices and impurities.This provides new phase-change materials and design methods for non-volatile optical devices with multi-switching states.