To evaluate the impact of atomic short-and long-range orders on silicate dissolution kinetics, the dissolution of amorphous and crystalline albite was investigated at pH 1.5 and 10 at 90°C. Experiments in solution saturated with respect to SiO2 am were additionally performed to constrain the effect of Si-rich surface layer formation on dissolution rates. The face-specific dissolution rates of the crystalline albite and of the albite glass were determined from element budget in solution and surface retreat measured by vertical scanning interferometry. The results show that atomic ordering primarily impacts solid reactivity, irrespective to the pH of the solution. A strong relation between the crystal surface orientation, the evolution of its topography and its dissolution rate was observed. The (001), (010) and (10-1) flat faces containing the strongest bonds dissolved the most slowly and their dissolution rates remained constant throughout the experiments. In contrast, the stepped (1-11) face was characterized by the highest initial dissolution rate, but progressively decreased, suggesting that the preferential dissolution of stepped sites expose afterwards more stable planes. The differences in terms of etch pit density from one surface to another also allowed to explain the difference in dissolution rates for the (001) and (010) faces. The fluid chemistry suggested the formation of very thin (100-200 nm) Si-rich surface layers in acidic conditions, which weakly affected the dissolution rate of the pristine crystal. At pH 1.5, albite glass dissolves at a rate similar to that of the fastest studied faces of the crystal. Whereas Si-rich surface layers likely formed by interfacial dissolution-reprecipitation for albite crystal, molecular dynamic calculations suggest that the open structure of the glass could also allow ion-exchange following water diffusion into the solid. This different mechanism could explain why the surface layer of the glass is characterized by a different chemical composition. Results at pH 10 are strikingly different, as the albite glass dissolves 50 times faster than its crystalline equivalent. This non-linear response of the material upon pH was linked to the density of critical bonds in albite which is indeed pH-dependent. In acidic pH, the preferential dissolution of Al leaves a highly polymerized and relaxed Si-rich surface, whereas in basic pH the preferential dissolution of Si leads to a complete de-structuration of the network because of the lack of Si-O-Al bonds.

Cocultivation of Acanthamoeba casteUlanii and Acanthamoeba polyphaga with live Pseudomonas aeruginosa and with broth filtrates of P. aeruginosa proved equally lethal to the Acanthamoeba spp. The P. aeruginosainduced amebicidal activity is apparently toxin mediated and has two operative modes: it can function through binding ofP. aeruginosa to the ameba membrane and in the presence of one or more P. aeruginosa exoproducts.

It is known for decades that silica saturated solutions allow borosilicate glass to dissolve much slower than in deionized water. The present study assesses this assertion in the specific case of the International Simple Glass, a 6-oxide borosilicate glass of nuclear interest, which we altered between pH = 1 and 10.7 at 90 °C. Depending on the stage of reaction, aqueous silica can promote either the formation of a passivating gel layer on the glass surface or the precipitation of certain secondary phases at the expense of the passivating gel. We demonstrate a negligible effect of aqueous silica at acidic pH and a marked effect beyond pH90 °C = 7, ensuring a better glass chemical durability. At higher reaction progress and above pH90 °C = 9.5, this effect becomes negative due to the formation of secondary phases such as hydroxides or zeolites.