MOTHER OF PEARL MEEN 3344 Presentation by: Aditi Bandyopadhyay Fig1. Mother of Pearl Source. www.pbs.org
MOTHER of PEARL or NACRE It is an iridescent substance that forms the lining of the shells of some mollusks. It is several times stronger than nylon. Its toughness is almost equal to silicon. Sources: • Pearl oyster, found in warm and tropical seas, chiefly in Asia • Freshwater pearl mussels, found in many rivers of the United States, Europe, and Asia • Abalone, found in California, Japan, and other Pacific regions
COMPOSITION It is composed of two relatively weak materials: 95 percent calcium carbonate, a brittle ceramic, and 5 percent flexible biopolymer (conchiolin). • Built like a "brick-and-mortar" structure where millions of ceramic plates stacked on top of each other with each layer of plates glued together by thin layers of the biopolymer. • Mixture of brittle platelets and the thin layers of elastic biopolymers make the material strong and resilient. • The "brickwork" arrangement also inhibits transverse crack propagation. Fig2. Scanning electron microscope view of the fractured surface of nacre. (Max Planck Institute of Colloids and Interfaces)
PROPERTIES • Has a tensile strength of between 35 and 110 MN m-2. • It is slightly viscoelastic, and shows marked plastic deformation. • The maximum measured strain is around 0.018. • While undergoing plastic deformation the material shows considerable optical changes. These are probably caused by voids forming in the protein matrix. • Nacre shows considerable ability to stop cracks. • Elastic moduli (60–80 GPa). • Modulus of rupture (<270 MPa). Fig3. This image of the inside of a seashell shows the smooth morphology of individual nanobumps and their attached biopolymers. Source:http://web.mit.edu/newsoffice/2005/seashells.html Fig4. The inside of this shell is composed of cylindrical beams and interdigitated structures.
APPLICATIONS • By emulating the structure and formation of nacre, many new materials can be created which have the potential to yield much tougher composites for use in armor systems or aerospace systems or have biomedical uses. • Latest research is conducted by Nicholas Kotov of Oklahoma State University.
REFERENCE • http://en.wikipedia.org/wiki/Mother_of_pearl • http://web.mit.edu/newsoffice/2005/seashells.html • J. D Currey, Mechanical Properties of Mother of Pearl in Tension, Proceedings of the Royal Society of London. Series B, Biological Sciences, Volume 196, Issue 1125, pp. 443-463 • B.J.F. Bruet, H.J. Qi, M.C. Boyce, R. Panas, K. Tai, L. Frick, and C. Ortiz, Nanoscale morphology and indentation of individual nacre tablets from the gastropod mollusc Trochus niloticus, J.Mater.Res., Vol.90, No. 9, Sept 2005 • http://www.engin.umich.edu/dept/che/research/kotov/