Weird Science

Silver Fractals

Polish ver­sion is here

What Is a Frac­tal?

Many of us have come across the word “frac­tal” before. Sim­ply put, a frac­tal is a self-simi­lar object — mea­ning that parts of it resem­ble the whole. Ano­ther key cha­rac­te­ri­stic of frac­tals is their infi­nite struc­tu­ral com­ple­xity; in other words, they reveal intri­cate detail even when gre­a­tly magni­fied. Because frac­tals come in such a wide variety of forms, it’s dif­fi­cult to pro­vide a sin­gle, pre­cise defi­ni­tion.

Benoît Man­del­brot, a French mathe­ma­ti­cian born in Poland, was the first to study frac­tal struc­tu­res in depth. He also descri­bed what’s now known as the Man­del­brot set (shown below).

Ilustracja

Source: http://upload.wiki­me­dia.org/wiki­pe­dia/com­mons/2/21/Man­del_zoom_00_man­del­brot_set.jpg
[acces­sed: 08/12/2011]

Frac­tals often resem­ble pat­terns or phe­no­mena found in nature-like moun­tain ran­ges, coa­stli­nes, snow­fla­kes, fluffy clo­uds, or even bio­lo­gi­cal struc­tu­res such as stems and lea­ves. Because of this, frac­tals are now stu­died not just by mathe­ma­ti­cians, but also by scien­ti­sts across many dif­fe­rent disci­pli­nes.

Inte­re­stin­gly, frac­tal-like struc­tu­res can also form during the elec­tro­ly­tic reduc­tion of silver.

What You’ll Need

To carry out this expe­ri­ment, you’ll need:

Ilustracja:

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War­ning: Avoid con­tact with silver nitrate — it reacts with light to form metal­lic silver, which per­ma­nen­tly sta­ins skin black. Ammo­nia vapors are irri­ta­ting and can be toxic at high con­cen­tra­tions. Use extreme cau­tion. Never store ammo­nia­cal silver solu­tions, as they may form a highly explo­sive com­po­unds! The author takes no respon­si­bi­lity for any damage or injury that may result. Pro­ceed at your own risk!

Pro­ce­dure

Pre­pare a 1% solu­tion of silver nitrate. Slowly add the ammo­nia solu­tion until the ini­tially for­med pre­ci­pi­tate fully dis­so­lves. Pour the resul­ting clear liquid into a Petri dish. Use steel wire to make the elec­tro­des — place the posi­tive elec­trode (anode) at the edge of the dish and the nega­tive elec­trode (cathode) in the cen­ter. The anode can be fully sub­mer­ged, while the cathode sho­uld only touch the sur­face of the solu­tion. If the cathode is not exac­tly at the liquid–air inter­face, the expe­ri­ment will not work.

Next, con­nect a vol­tage source (5–15 V) to the elec­tro­des. A bran­ching struc­ture will imme­dia­tely begin to grow from the cathode toward the anode, spre­a­ding across the sur­face of the liquid. You can watch the phe­no­me­non in the video below:

The frac­tal growth is visi­ble to the naked eye, and the entire pro­cess takes just a few minu­tes. Below are some pho­tos of the resul­ting struc­ture:

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Ilustracja:

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The struc­ture clo­sely resem­bles a well-known frac­tal cal­led Barn­sley’s Fern:

Ilustracja

Source: http://upload.wiki­me­dia.org/wiki­pe­dia/com­mons/6/69/Bran­sleys_fern.png
[acces­sed: 08/12/2011]

Expla­na­tion

During elec­tro­ly­sis, metal­lic silver forms accor­ding to the fol­lo­wing reac­tion:

Ilustracja

Due to sur­face ten­sion, silver forms right at the liquid–air inter­face. Since the depo­si­ted silver con­ducts elec­tri­city, elec­tro­ly­sis con­ti­nues on its sur­face. Layer by layer, the silver builds up, for­ming com­plex, tree-like sha­pes.

Have fun — and stay safe!

Fur­ther rea­dings

Marek Ples

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