The Growth and Mechanical Properties of Abalone Nacre Mesolayer
Abalone nacre has long been interesting to material engineers due to its fascinating structure and outstanding mechanical behavior. It is a self-organized biogenic mineral composite which has a hierarchical architecture composite. The main component of th
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The Growth and Mechanical Properties of Abalone Nacre Mesolayer Anqi Zhang, Yan Chen, MariAnne Sullivan, and Barton C. Prorok
Abstract Abalone nacre has long been interesting to material engineers due to its fascinating structure and outstanding mechanical behavior. It is a self-organized biogenic mineral composite which has a hierarchical architecture composite. The main component of this structure is “block and mortar” like tablets. Between the tablets structures is a layered structure which consist of both organic and inorganic parts called mesolayer. This research focus on the growth behavior of the mesolayer structure and its mechanical influence on nacre. Fresh-grown nacre is harvested by the “flat pearl” technique under different temperature schemes. SEM observation of those nacre reveals temperature scheme will inhibits the growth of tablets structure, and form other layered structure. The mechanical property of harvested “flat pearl” is tested by nanoindentation. In this work, we aim to show the mechanic significance of mesolayer in nacre structure, and hope to establish its strengthening and growth mechanism. Keywords Biomimetic • Nanoindentation • Biomineralization • Multilayer composites
20.1
Introduction
Abalone nacre is a nature composite material composed by rather brittle calcium carbonate and organic materials [1]. It has a surprisingly high strength and fracture toughness, which believed contributed by the special self-assembled “brick and mortar” structure, giving its name “column nacre” [2, 3]. This structure can be shown by SEM (Scanning Electronic Microscope) images clearly (Fig. 20.2.). Another feature of the shell can be found through the observation on the cross-section of abalone shell, especially the wild abalone shell, some black lines could be seen in the nacre (Fig. 20.1). This structure is called mesolayer [4]. The existence of such structure shows the abalone nacre having a structure of hierarchy. Under SEM, those “black lines” showing like some layers with complex structure, which are named “mesolayer”. Backscattered electron image shows that the composition of one part in the mesolayer is not calcium carbonate revealed by the different phase contrast (the darker area shown in Fig. 20.2). Both of nacre tablets and inorganic part of Mesolayer were shown in the same color in the back scattered image were aragonite [2]. And, the image also suggested that darker part in the image organic composition. EDS (Energy Dispersive Spectrometry) mapping shows the element distribution of such structure (Fig. 20.3). In the dark area of the backscattered SEM image, a high carbon level exists. This also suggest the organic property of such layer. Although the mechanical behavior of nacre was extensively studied, nacre shows a significantly better mechanical property compare to the aragonite along [5]. The influence of Mesolayer structure to the mechanical behavior of the whole shell is still not entirely unveiled [6, 7]. This can be attributed to the fact that most research use the farm raised a
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