Microstructures and friction-wear characteristics of bivalve shells

All structural biological materials are nearly composite materials and often exhibit some superior properties. In order to obtain useful information for the design and manufacture of composite materials, the microstructures and the friction-wear properties of three species of bivalve shells were studied in this paper. The results showed that the microstructure of tested bivalve shells I (Meretrix meretrix) and 11 (Saxidomus purpuratus) are constructed of about 10-100 mu m small platelets stacked in brick-and-mortar fashion and small platelets consist of lamella clusters. The lamellae are parallel inside the individual cluster. The orientations of adjacent lamellae clusters form the angle of about 70-90 degrees. The thickness of lamellae is about about 0.2-0.6 mu m. The organic component and the calcium carbonate form the three-dimensional net-like microstructure, respectively, which interlaces each other to form the microstructure of the bivalve shells. The microstructure of bivalve shells III (Periglypta chemnitzii) is constructed of about 10-40 mu m particles with the internal structure of lamellae clusters as the above mentioned. Under the experimental conditions of medium-carbon steel counterpart and sliding dry friction, the friction coefficient of the bivalve shells is lower than that of grey cast iron HT200. The organic component of the bivalve shells can transfer to the friction interface and form organic film, which not only lubricates the friction interface but also protects the friction surface. The organic component is very important to the friction-wear property of the shells. (c) 2005 Elsevier Ltd. All rights reserved.