The Shape and Size Effect of the Diatom Frustule Addition on the Compression Behavior of an Epoxy Doğuş ZEREN 1,a , Kutsal KESICI 2,b , Atakan SUKATAR 2,c and Mustafa GÜDEN 3,d 1 Department of Materials Science and Engineering and 3 Department of Mechanical Engineering, İzmir Institute of Technology, Urla, İzmir, Turkey 2 Department of Biology, Ege University, Bornova, İzmir, Turkey a doguszeren@iyte.edu.tr, b kutsalkesici@gmail.com, c atakan.sukatar@ege.edu.tr, d mustafaguden@iyte.edu.tr Keywords: Polymeric composites, diatom, frustule, deformation and fracture, compression Abstract. The effects of the Achnanthes Taeniata and the diatomaceous earth (diatomite) frustules addition on the compressive strength of an epoxy matrix were investigated experimentally. The Achnanthes Taeniata frustules having relatively high length/diameter aspect ratio (2-4) were isolated and cultured in laboratory. While the as-received commercial natural diatomite frustules were non-homogenous in shape and size. The filling epoxy matrix with ~6 wt% of commercial natural diatomite increased the compressive strength from 60 MPa to 67 MPa, while the Achnanthes Taeniata frustules addition increased to 79 MPa. The increased compressive strength and modulus of the the Achnanthes Taeniata frustules filled epoxy was attributed to the higher aspect ratio and relatively strong bonding with the epoxy matrix. The more effective load transfer from the matrix to the Achnanthes Taeniata frustules associated with the enhanced interface bonding was also proved microscopically. The frustules were observed to pull-out on the fracture surface of the Achnanthes Taeniata frustules filled epoxy. Introduction Diatoms are a group of unicellular chlorophyte algae with the size range of 5 µm and 5 mm. The centric type diatoms are radially symmetric and circular in shape and the pennate diatoms are bilaterally symmetric with elongated shapes [1]. The skeleton of diatoms is known as frustule, which is made of amorphous silica, and the surface of the skeleton is coated with an organic surface layer. The frustules have regularly arranged pores on their surfaces with the sizes of 10-200 nm [2]. They are only soluble in strong alkali acids such as hydrogen fluoride. Diatomaceous earth, also known as diatomite or kieselguhr, is a sedimentary siliceous rock formed by the accumulation of the dead diatom cells in the bottom of the oceans or fresh waters [3]. Diatomite is mainly used as filtration material, abrasive, insecticide, soil conditioner and cement additive [4] as well as the filler material in polymers [5]. The three-dimensional structure of diatoms has also potentials to be used in the processing of microelectronic devices [6]. Diatoms, as being biocompatible, have also potentials for the applications in the drug-delivery as they have relatively high surface area (100 m 2 /g) associated with the nano-porous structure. The shapes of the frustules can be altered by varying the silicification degree [6,7]. The mechanical properties of the frustules have shown to vary with the location of the measurement, attributed to the varying degree of bio-mineralization [8-12]. The elastic modulus of Coscinidiscus ranged 1.5-15.6 GPa and Navicula pelliclosa 7-100 GPa, depending on the location of the measurements taken [13]. When frustules are used as filler in polymer matrices, a strong interlocking between the polymer matrix and frustules is expected due to the high surface area and nano-porous surface layer structure of the frustules. In a previous study, the compressive modulus and yield strength of an epoxy matrix were shown to increase with the diatom frustule addition and the stress enhancement of filled epoxy was ascribed to relatively high strength of frustules and strong interlocking between the frustules and the polymer matrix [5,14]. It was also shown that the Materials Science Forum Online: 2018-03-01 ISSN: 1662-9752, Vol. 915, pp 140-146 doi:10.4028/www.scientific.net/MSF.915.140 © 2018 Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.scientific.net. (#107374009-06/03/18,09:41:56)