The microstructure and mechanical properties of abalone shell were studied. It was found that fracture strength, αf, is 180 MPa, and fracture toughness, KIC, is 7 ± 3 MPa-m1/2; these values are comparable with or better than most “high technology” ceramic materials. The microarchitecture of the nacre section of the red abalone shell is similar to a “brick and mortar” structure, where CaCO3is the brick and organic matter is the mortar, constituting 95% and 5% of the microstructure by volume, respectively. This impressive combination of af and KIcvalues is attributed to the laminated structure of the shell with hard and thick (0.25±0.5 μm) CaCO3and superplastic and thin (20–30 nm) organic components. Although there are several toughening mechanisms operating in the shell, fractographic studies identified sliding of CaCO3layers and bridging by the organic layers to be the most effective ones. These phases also have a strong interface. The results of our experiments are discussed in the context of using abalone shell as a model for the design of synthetic laminates such as cermet (ceramic-metal) and cerpoly (ceramic-polymer) composites.

The stability of yttria‐silica binary aqueous colloidal suspensions is examined as a function of time. It has been observed that initially stable silica particles go through a flocculation period and then restabilize. This phenomenon is attributed to slow dissolution and the specific adsorption of trivalent yttrium cation and its hydroxo complexes on the surface of silica. Furthermore, it is shown that the kinetics of flocculation and restabilization can be controlled by pH adjustment.

No abstract