Frost flowers

I've been in northeastern Wisconsin during a cold snap that came in rather quickly and I have been seeing "frost flowers" on ice on creeks and (formerly) wet rocks.  A more sophisticated description is given here on Wikipedia: http://en.wikipedia.org/wiki/Frost_flower_%28sea_ice%29 (see also the Hoarfrost Crystals post from 11/29/13).

Borax Snowflakes

(Originally posted 12-11-14; updated 12-25-14) Last night some Bradley students and I made borax holiday decorations, made by placing a template shape into a hot solution of borax.  When the solution cools, the solubility of the borax decreases and the borax crystallizes onto the template to make a sparkling structure.  Caution: Borax solutions are basic, and do not ingest borax.

To make the decorations, first make a wireframe shape from pipe cleaners.  Snowflakes are the most common, using white pipe cleaners, but other shapes and other colors can certainly be used.  One of my favorite variations  a sort of green spiral cone with beads on it to make a Christmas tree shape.

The concentration of borax that I use is what I have encountered on various websites: three tablespoons of borax per cup of water.  Heat the borax and water in a metal saucepan to make sure the borax dissolves.  Be careful working with the hot borax solution. For example: do not heat the solution in a jar directly on the heat source - I broke a jar on a hot plate trying that.  The wireframe shapes can be hung from sticks placed over the openings of glass canning jars.  Make sure the shape can fit in and out of the jar without squishing the shape (remember when the process is done the shape will be covered with about a half centimeter of brittle crystals).   Keep the shape about three centimeters from the bottom of the jar - that is where the excess crystals tend to accumulate and they can stick the shape to the bottom of the jar. Note that the large snowflake in the pictures below was not made in a jar but rather by mounting the shape horizontally in the solution in the saucepan.

Carefully pour the hot borax solution into the jars, making sure to cover all surfaces of the wireframe shapes that you want to cover with crystals.  Let the solutions cool to room temperature, and we found that we had to cool the solutions still further to a few degrees Celsius overnight (either outside or in a refrigerated room) in order to get a good coating of crystals.

After the crystals are grown, remove the wireframe shapes from the jars and blot away extra solution with paper towels.  The crystals of borax are shiny and translucent at first, but over the course of months they will become cloudy and chalky.  Remember to keep kids and pets from ingesting the borax from your crystalline creations.

UPDATE 12-25-14: I took some leftover warm borax solution and used it to deposit crystals on styrofoam balls.  The hard part was devising a way to submerge the balls, but the crystals did deposit (though not so much at the point they were being held submerged).  We stacked the balls and decorated them to make sparkly snowmen (last picture below).  Have a blessed Christmas!

Dust Can Explosion Gone Awry

Many websites have described the classic dust can explosion demonstration.  Essentially, a closed metal paint can is fitted with a device to blow a fine powder throughout its interior.  Lycopodium powder is often used as the powder, and a squeeze bulb is often used to blow the powder around.  The dispersed powder is ignited by a lit candle that is also in the paint can during the demonstration, and the combustion of the powder produces sufficient heat and pressure to blow the lid off the paint can.

I have not done this demonstration much, but it was a favorite of one of my colleagues, professor Max Taylor, who was a talented demonstrator at Bradley University.  When he passed away last month, I dug out his old dust can explosion demonstration.  I successfully blew the lid off the paint can, but one time when I did so, the lid went up with the flame outburst and then back down to seal on top of the can.  Instantly the can collapsed as the gases inside the can cooled and contracted.  Looks like Max Taylor left some big shoes to fill!  I have rebuilt the demonstration with a different paint can.  In the future I will work to make sure the lid is blown clear of the can.

A Tile Puzzle Analogy of Electrons and Holes in Semiconductors

Holes in semiconductors can be described as locations where valence electrons are missing. These holes can move in one direction as a result of the electrons moving in the opposite direction.  An analogy I have used in my classes is the sliding tile puzzle: as the tiles move one way, the "hole" from the missing tile moves in the opposite direction.  Inspired by this concept, I adapted one of these tile puzzles to illustrate my point.

Hygroscopic Iron(III) Chloride Hydrate

I have found over the years that iron(III) chloride hydrate can be pretty hygroscopic.  Here is a vial that once contained the dry salt, but has picked up plenty of moisture over time.  This seems like a more safe compound to demonstrate hygroscopic behavior than, say, solid sodium hydroxide.