Clay Mineral Image Collection

A collection of field emission scanning electron microscope images of clays, which consist of Kaolinite, Bentonite, a mixture of these two minerals, and the fines from a natural residual soil derived from shale. You can download image collection at the bottom of the page.

Authors:

Gordon Stone and Joseph Dove, Department of Civil and Environmental Engineering

Nizhou Han and Patricia Dove, Department of Geosciences 

Virginia Tech, December 2015

Creation of this image collection was supported by the National Science Foundation under Grant No. 1301124 "Biologically-Inspired Silicification of Fine-Grained Soils.". Any findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of NSF.

Thiel Kaolin Co. and WyoBen, Inc. supplied the Kaolinite and Bentonite minerals, respectively.

Materials and Experimental Methods

Materials

1. Kaolinite: B80 kaolinite from Thiel Kaolin Co. of Sandersville, Georgia.  97.5% finer than the No. 200 sieve, 68% finer than 2 microns; liquid limit = 76 and plastic limit = 33.
2. Bentonite: Naturalgel from Wyo-Ben, Inc. of Billings, Montana.  97% finer than No. 200 sieve, 60% finer than 2 microns; liquid limit =  570, plastic limit = 68.
3. Local Blacksburg, Virginia soil.  88% finer than the No. 200 sieve, 55% finer than 2 microns; liquid limit = 71, plastic limit = 23.  Mixed mineralogy.

Methods

Clays were used as received.  Samples of the Blacksburg soil were passed through a No. 200 sieve prior to preparation for imaging.

1. Fracture surfaces. Compacted at optimum moisture using standard Proctor effort, freeze dried, and fractured using a razor blade.  Sputter coated with Iridium. 
2. Shear Failure Surface.  Compacted at optimum using standard Proctor effort, then brought to failure in unconfined compression. Sample collected from shear failure surface then freeze dried and sputter coated with Iridium.
3. Slurry deposited samples.  Dispersed in water, deposited on pedestal using medicine dropper then air dried.  Sputter coated with  Iridium.

Images were acquired at several "regions" on each sample.  Within each region, images were collected at progressively higher magnifications.  The image footer provides magnifications (i.e., Mag=1k x) and a bar scale.  All images were collected in tiff format with a LEO (Zeiss) 1550 Field Emission Scanning Electron Microscope (FESEM) in the Nano Characterization and Fabrication Laboratory of Virginia Tech's Institute for Critical Sciences and Technologies.  

Kaolinite Fracture Surface

Specimens compacted at optimum moisture, freeze dried, and fractured using a razor blade (tensile fracture).  Images collected by Gordon Stone.

Images are included from two samples that are made at progressively higher magnifications.  They feature a compacted fabric matrix with a layer of loosely attached particles oriented in the direction of tensile fracture.  These images highlight the morphology of Kaolinite, which can be clearly observed at the higher magnifications.

Kaolinite Shear Failure Surface

A sample was compacted at optimum moisture and brought to failure in an unconfined compression test.  The specimen for imaging was collected from the resulting failure surface, then freeze dried, mounted, and sputter coated.  View in the images is of the failure surface.  

All images collected by Gordon Stone.

Kaolinite and Bentonite Mixture

60% Bentonite and 40% Kaolinite by weight, hydrated and mixed together in a slurry then deposited on SEM sample holder.  Images are of the mineral layer remaining after air drying.