When metallic alloys are exposed to a corrosive environment, porous nanoscale morphologies spontaneously form that can adversely affect the mechanical integrity of engineered structures. This form of stress-corrosion cracking is responsible for the well-known 'season cracking' of brass and stainless steel components in nuclear power generating stations. One explanation for this is that a high-speed crack is nucleated within the porous layer, which subsequently injects into non-porous parent-phase material. We study the static and dynamic fracture properties of free-standing monolithic nanoporous gold as a function electrochemical potential using high-speed photography and digital image correlation. The experiments reveal that at electrochemical potentials typical of porosity formation these structures are capable of supporting dislocation-mediated plastic fracture at crack velocities of 200 m s(-1). Our results identify the important role of high-speed fracture in stress-corrosion cracking and are directly applicable to the behaviour of monolithic dealloyed materials at present being considered for a variety of applications.

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Adhesion of frozen granular materials on solid surfaces creates various problems for surface cleaning, reduces the carrying capacity of vehicles, and increases energy consumption for in-land transportation. Here we report that water content determines the adhesion strength of oil sands on solid surfaces at temperature of -2.5 ◦C to -20 ◦C. Our measurements by X-ray micro-computed tomography revealed that water forms capillary bridges between the sand particles and the solid substrate and more air gaps at the interface between oil sands and the substrate are filled with interstitial water at a higher content. We experimentally measured the minimal force required to push the frozen oil sands off the substrate and identified that the adhesion strength increased linearly with water content from 4% to 14% on both rubber and steel substrate. For short freezing time at a fixed water content, lowering the temperature increased the adhesion strength on the steel substrate. Fouling from a layer of bitumen or asphaltenes aggravated the adhesion of oil sands on steel. A theoretical model was proposed to rationalize the linear relationship between water content and the adhesion strength, based on the contact area between ice and the substrate. We also found an effective method to reduce the adhesion of oil sands by spraying a little amount of anti-freezing liquid on the substrate. Our approach may reduce the energy consumption in transport and processing of wet granular materials, and potentially save manpower and the cost from cleaning in industrial operations. The insight from our work may have wide applicability to many natural/industrial processes, such as soil formation, food processing, and porous structures in ice crystal-templating nanomaterials synthesis by freezing-drying.

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