4.1 - Growing Rough Patterns: Electrodeposition

HandsOn Activities:

13. Growing a Pattern in the Laboratory

Is a coastline a line? Not really, because a line is one-dimensional, whereas a coastline is a random fractal that has a dimension whose value is between 1 and 2. Other random fractal patterns also have dimensions between 1 and 2: a snowflake, a nerve cell, a lightning stroke. The growth of these structures can be modeled by a process called aggregation, in which random walkers dance around the growing structure and stick to it when they touch it. The resulting jagged pattern is called an aggregate. Depending on the details of the growth process, some aggregates are natural fractals, others are not.

The shiny chromium surfaces on an expensive automobile are made by immersing the parts into a chemical bath that contains chromium ions and running an electric current through the bath so that chromium metal attaches to the parts to be coated. This process is called electroplating or electrodeposition.

The goal in chromium electroplating is to produce a smooth surface so the car will look good and be protected against rust. In our pattern-forming experiment, the result will be quite different from this, as you will see.

To understand the experiment, you need to recall that:

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