Sand Gallery Update: Taking a Closer Look at Hydrophobic Sand and More

hydrophobic sand

In a previous issue of Nanographia, we took a closer look at Kinetic Sand, a popular children’s sand toy. In this post, we examine a similar children’s sand toy commonly referred to as magic sand, or a hydrophobic sand. Also featured below is the latest Microscopy Society of America (MSA) Sandbox request from geology professor.

A Closer Look at Magic Sand

Magic sand is any sand in which the individual sand grains have been coated with a hydrophobic compound, essentially making the individual grains of sand hydrophobic, or waterproof. Magic sand was first described in Popular Mechanics book The Boy Mechanic, Book 2: 1000 Things for Boys to Do published in 1915. The “Hindoo Sand Trick,” featured on page 308, describes the preparation of the recipe for making sand waterproof.

Click on any image to enlarge.

After tracking down the book and finding the original recipe, we decided to go ahead and make a batch of this version of hydrophobic sand. As a side note, you’ll notice that the entry for the magic sand is credited to Mighty Oaks from Oshkosh, Wisconsin. Mighty Oaks is the pseudonym for John Oaks, a magician from the early 1900s who lived in Oshkosh, Wisconsin, and later owned a popular magic shop in the area. He passed away in 1918 from the Spanish flu. Below is a photomicrograph of quartz sand coated with paraffin from the Mighty Oaks recipe. Notice how the individual grains of sand appear to be adhering to each other due to the paraffin wax coating.

A more modern version of homemade magic sand makes use of a waterproofing spray such as Scotchgard™ Fabric Water Shield. Similar to the paraffin recipe, the sand is coated by placing it in a thin layer on a baking sheet and generously applying the waterproofing spray to the sand. Stir the sand, redistribute it to a thin layer again, and apply the waterproofing spray one more time. In the photomicrograph below you will notice that the sand grains coated with the Scotchgard spray do not adhere to each other compared to the paraffin version.

Next, we purchased some magic sand from an educational supply store. These types of sands, like the Kinetic Sand, come in a wide range of bright colors. We decided to take a look at a green-colored sand. Like the Scotchgard version, the individual grains are evenly divided. We thought it would be interesting to take a look at the chemistry of each of the hydrophobic sand coatings using infrared (FTIR) microscopy.

Microscopy Society of America Project MICRO SANDBOX Request

A first-year assistant professor of geology is designing a sedimentology and stratigraphy course with all new teaching collections, and the first lab takes a look at sand classification. She was delighted to find the collection of sands available through the MSA’s Project MICRO Sandbox to use as a resource in helping to develop the course. Her hope was to acquire sands with a variety of maturity (sorting, roundness), clast types, grain size, and compositions.

Below are photomicrographs, scanning electron microscopy imaging, and energy dispersive spectroscopy (SEM/EDS) data and elemental maps of each requested sand.

When prepping for SEM/EDS analysis of the sands, the use of carbon tape is necessary to reduce electron buildup on the surface of the samples, and serves as a conductive pathway for electrons to travel. By creating this conductive pathway, an undesirable phenomenon known as charging is greatly reduced, and results in better imaging and EDS data.
Each of the sand samples was photographed at 25X magnification using a stereomicroscope, then inserted into the JEOL JCM-7000 desktop SEM chamber and placed under vacuum for observation.

The JCM-7000 stage navigation system was used to locate the same field of view from a printout of the stereomicroscope image. The orientation of the image was duplicated by rotating the direction of the beam scan until the images looked nearly identical.

When imaging each sand sample, a low accelerating voltage and low probe current were used to get a detailed surface image. When conducting the elemental map trials, a high accelerating voltage and high probe current were used to get the most x-ray interactions and detailed x-ray maps.

The SEM-generated x-ray maps showed differences between particular sand grains elementally, and we compared these maps to the various colors captured in light microscopy images; we could compare elemental differences to differences in color, texture, size, etc. with ease.

Brazil, Rio de Janeiro

The above image (map with elemental key) does a good job of illustrating what is known as shadow effect. You can see that many of the individual sand grains appear to only have any concentration of elements on the upper portions of the grains. The reason is that the sand grains are so large and have topography that causes non-uniform absorption of the X-rays, such that only the X-rays with a clear path to the detector are collected. In order to capture element maps that revealed variations of composition, one would have to zoom to higher magnification on a sand grain on a side facing the X-ray detector, to avoid topography induced geometry effects. Ideally, to map out the composition of a sample without topography induced shadow effects, the sample should be embedded in epoxy and polished to a mirror finish.

United States, Mount Saint Helens, Washington

United States, Marinette, Wisconsin

United States, Mellen, Wisconsin

United States, Corpus Christi, Texas

United States, Longport, New Jersey

As you can see from the images above, sand can be colored using dyes added to various coatings to create attention-grabbing toys for children. Color can also be imparted electronically as a means to indicate the elemental composition of each sand grain by using elemental mapping software.

If you have something sand related that you would like us to look into, please let us know. And if you know of a teacher who would benefit from requesting samples from the MSA Sandbox, feel free to pass along our contact information. As always, thank you for reading.


add comment