Crystal Growth: From Supersaturated to Sparkling¶

In this demo, you’ll learn why crystals form, how to grow your own in fun shapes, and why crystallization matters in materials science and engineering.

What You’ll Learn¶

The difference between saturated, unsaturated, and supersaturated solutions
How temperature affects solubility and drives crystal growth
Hands-on: making vibrant pipe-cleaner crystals
Real-world exothermic crystallization (hand warmers!)
How MSE researchers control crystal structure for advanced materials

Supplies Checklist¶

Magnesium sulfate (Epsom salt) or table sugar
Hot water (near boiling)
Beakers or clear jars
Food coloring (optional)
Pipe cleaners (shaped into fun forms)
String or thread
Sodium acetate solution (for hand-warmer demo)
Thermometer (optional)

Solution types — Unsaturated vs. saturated vs. supersaturated.

Question

Why can hot water dissolve more salt than cold water?

Solubility & Supersaturation¶

A solubility curve shows how much solute water can hold at different temperatures. To grow crystals: 1. Heat water and dissolve as much solute as possible → supersaturated.
2. Cool slowly → excess solute comes out of solution as crystals.

Question

What happens if you cool too quickly or disturb the solution?

Step-by-Step Crystal Growing¶

Step 1: Prepare Supersaturated Solution¶

Heat 250 mL water to ~80 °C.
Gradually stir in 50 g Epsom salt until no more dissolves.

Step 2: Color & Shape¶

Add food coloring for vibrant crystals.
Twist a pipe cleaner into a star, heart, or geometric shape. Tie it to a string.

Pipe cleaner setup — Pipe cleaner suspended in the hot, supersaturated bath.

Step 3: Grow Crystals¶

Lower the pipe cleaner into the jar; leave undisturbed.
Wait 1–2 hours (or overnight) for crystals to form.

Vibrant crystals — Crystal “branches” forming on the pipe cleaner.

Question

How does the shape of the pipe cleaner affect crystal growth patterns?

Exothermic Crystallization: Hand Warmers¶

Some crystals release heat when they form (exothermic). Sodium acetate “hand warmers” use this principle:

Hand warmer crystals — Click-to-activate sodium acetate crystallization.

Quick Demo:¶

Supersaturated sodium acetate solution in a pouch.
Click metal disk → triggers rapid crystallization → heat released!

Question

Why does crystallization release heat for sodium acetate but absorb heat for Epsom salt?

🔬 Microscopic vs. Macroscopic Crystals¶

Microscopic: orderly lattice at the nanoscale
Macroscopic: visible facets and shapes

Microscopic crystal — Microscope image of Epsom salt crystal lattice.

Macroscopic crystals — Large, well-formed crystals after slow cooling.

Think & Discuss¶

What factors (temperature, impurities, agitation) control crystal size and shape?
How do engineers use crystal growth to create semiconductors, photovoltaics, or pharmaceutical drugs?

MSE Research Spotlight¶

At Michigan, MSE students explore: - Bulk crystal growth for turbine blades (superalloys)
- Thin-film crystallization in solar cells
- Protein crystallography in biomaterials

Design Challenge¶

Can you engineer a gradient supersaturation to grow graded crystals (small → large)?
- Vary cooling rate along the length of the tube
- Record crystal size vs. position

Reflection

How might graded crystals improve real-world device performance?

Summary¶

You made and observed crystals from supersaturated solutions.
You saw exothermic vs. endothermic crystallization.
You connected classroom experiments to cutting-edge MSE research.

Head back to the Outreach Homepage for more demos!