March 1999 Ž . Materials Letters 38 1999 445–449 Current–voltage characteristics and aging of sepiolite oriented by magnetic field K. Esmer a, ) , M. Yeniyol b a Kocaeli UniÕersity, Faculty of Science and Arts, Department of Physics, 41100 Kocaeli, Turkey b Istanbul UniÕersity, Faculty of Engineering, Department of Geology Eng., 34850 AÕcilar Istanbul, Turkey Received 15 September 1998; revised 21 October 1998; accepted 23 October 1998 Abstract Current–voltage characteristics and aging properties of modified sepiolite taken from Anatolia have been studied. Sepiolite mineral dispersed by ultrasonic methods and saturated with Fe 2q by ion-exchange has been oriented in an 11 kG magnetic field. DC measurement techniques have been applied to ribbon type samples oriented in a magnetic field. Whereas, application of these techniques to samples that have not been oriented in a magnetic field was possible because of very small and unstable current, samples oriented in a magnetic field have shown a linear change. The current–voltage studies done at different time periods have shown that sample resistance has risen in time approximately 100 times, and aging has begun. This has been evaluated as being the result of sepiolite interaction with water vapor in the medium, rather than the oxidization of the contacts. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Sepiolite; Mineral; Conductivity; Magnetic field; Aging 1. Introduction Sepiolite is a fiklosilicate mineral of crystalline Ž. structure made up of two tetrahedral T sheets of Ž . Ž . SiO , and one octahedral O sheet of Al O,OH 4 6 units. The T sheet is formed by an infinite string of tetrahedrons, continuous along x and y crystallo- graphic directions, with their basal oxygens on the Ž . same plane Fig. 1 . The apical oxygens of the tetrahedrons point alternately up and down relative ) Corresponding author to the planes of basal oxygens and form a reverse pattern along the y direction. These apical oxygens of the T sheets, which meet as the result of these reversals, form octahedral coordination groups around cations such as Mg and Al. Thus, a ribbon-like structure that is discontinuous along the y and z crystallographic axes, and continuous along the x direction is formed from the inversed two T sheets and the O sheet between them. This structural order is responsible for the fibrous nature of sepiolite with rectangular channels that are continuous along the x Ž . direction Fig. 2 . In these channels, there is coordi- nation water firmly bonded to the octahedral cation, wx and weak bonded zeolitic water 2 . These channels may also contain changeable cations such as Ca 2q 00167-577Xr99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0167-577X 98 00204-3