The dynamics of cerium oxide nanoparticle aqueous corrosion are revealed in situ. We use innovative liquid-cell transmission electron microscopy (TEM) combined with deliberate high-intensity electron-beam irradiation of nanoparticle suspensions. This enables life video-recording of materials reactions in liquid, with nm resolution. We introduce image quantification to measure detailed rates of dissolution as a function of time and particle size to be compared with literature data. Giant dissolution rates, exceeding any previous reports for chemical dissolution rates at room temperature by many orders of magnitude, are discovered. The reasons for this accelerated dissolution are outlined, including the importance of the radiolysis of water preceding the ceria attack. Electron-water interaction generates radicals, ions, and hydrated electrons, which assist in hydration and reductive dissolution of oxide minerals. The presented methodology has the potential to become a novel accelerated testing procedure to compare multiple nanoscale materials for relative aqueous durability. The ceria-water system is of crucial importance for the fields of catalysis, abrasive polishing, environmental remediation, and as simulant for actinide oxide behaviour in contact with liquid for nuclear engineering.

Room temperature electron irradiation in aqueous environment is applied to CeO 2 nanoparticles using a transmission electron microscope equipped with liquid environmental cell. Oxide dissolution kinetics become accessible at unprecedented scale of spatial and time resolution through irradiation activation of water within a sub-µm size volume, allowing direct measurements of transformation rate and morphologies. Successful liveobservation of the formation of nano-needles provides essential inside in how 1D-nanostructures can form. Furthermore, formation of hydrogen bubbles is found and interpreted in relation to the dose needed for ceria dissolution. The results are of importance for many research applications of ceria in water, e.g. for catalysis, environmental remediation, biomedical radiation protection, anti-corrosion coatings, and ultimately via analogy to UO 2 also for fission-power fuel engineering and waste disposal.

Deliberate electron irradiation of cerium oxide nanoparticles in water is used to trigger chemical reactions in a liquid cell transmission electron microscope. Formation of nanorods and nanoneedles is observed starting from predominantly octahedral shape nanoparticles. Detailed morphologies found include free-standing needles, needles connected to specific octahedral ceria facets and star-shaped multi-needle patterns. It is found that rod-axis orientations and crystallographic directions are aligned. It is suggested that high ion and radical concentration of radiolysed water dissolves layers of the original CeO 2 particles which rearrange as needles in the direction of energetically preferred facets.

This paper presents the failure analysis of AISI-304 stainless steel tank that was fabricated by welding and used for the storage of styrene monomers. After about 13 years of satisfactory operation, significant cracking was observed adjacent to the weld joints and in base plate near tank foundation. Weld repair was by shielded gas arc welding using AISI 308 stainless steel filler wire. The failed base plate was replaced with the new AISI 304 base plate of same thickness. After a short period of time, seepage was observed along the weld bead. Upon nondestructive testing cracks were found in the heat-affected zone and in the base plate. The failure investigation was carried out on welded and base plate samples using spectroscopy, optical and scanning electron microscopy, fractography, SEM-EDS analysis, microhardness measurements, tensile and impact testing. The results revealed transgranular cracks in the HAZ and base plate, and the failure was attributed due to stress corrosion cracking. Cracks initiated as a result of combined action of stresses developed during welding and the presence of a chloride containing environment due to seawater. It was further observed that improper welding parameters were employed for weld repair which resulted in sensitization of the structure and postweld heat treatment to remove weld sensitization and minimize the residual stresses was not done.

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