May 11, 2021
100 Nano-Stories: Solid Structures (Part 1)!
Episode #92: Introduction To Crystalline & Amorphous Solids!
Preface! ✨
It’s your favorite material science & nanotechnology enthusiast! Today, we will cover the geometry and properties of solid structures!
There is no article to prepare you this time! Let’s jump into today’s topic! 😄
Crystalline & Amorphous Solids Explained! 💡
Why Are We Talking About This? 🔑
For starters, the crystal structure gives the material its properties. If you rearrange the way the atoms are formed, you change the structure, and therefore, change the properties.
In silica aerogel, the solid structure is an amorphous solid.
Amorphous Solids are not flexible but lack in (geometric) shape. Geometric shapes can include triangles, squares, hexagons, crystals, polygons, etc.
For example, just by looking at the zoomed-in photo of MTMS Aerogels, the chemical structure doesn’t even look like a shape, it looks like a complete mess!
But because amorphous materials don’t have an organized geometric shape, they don’t have any edges (or pointy ends), like crystals/diamonds.
On the other hand, Crystalline Solids also have a solid structure (aren’t flexible), but they have a geometric shape. This means that the atoms in a crystalline solid have a specific order or pattern that looks like a geometric shape.
Some crystalline solids include metals, salts, etc.
Properties! 💡
Melting & Boiling Points! 🔑
Crystalline solids have higher melting and boiling points than amorphous solids. The reason why is because the crystalline solids are arranged in a geometric shape, which means the atoms in the material are very close to each other in every direction.
This means that the intermolecular forces are very strong (covalent bonds), which means it takes more energy to separate/break the material. This means that there is a specific number for the melting and boiling points of crystalline materials.
The distance in Amorphous solids’ atoms varies throughout the material, which means that the melting and boiling point is within a certain range, but not an exact number. For example, if the left side of an amorphous material has more atoms than the other side, the left side requires more energy/heat to break the intermolecular bonds between the atoms.
Cooling! 🔑
When cooling something, if you lower the temperature at a linear rate so that the solid can form a geometric shape like crystals, which results in a crystalline solid.
But if you cool something at a non-linear rate, you end up with an amorphous solid/material because you didn’t give the material a chance to form the crystalline/geometric structures in time.
For example, let’s take two liquids (water {H₂O} and methanol{CH₃OH}). The freezing point of water is 0°C (32°F). The freezing point of methanol is -97.6°C (-143.7°F).
Most importantly, if you look at the graph on the right, we notice the points “a” and “b”. These points indicate the beginning and the end of crystallization (formation of geometric shapes from the atoms to form a crystalline solid).
a → Water Freezing Point/ Crystallization of water molecules begin
b → Temperature drops to get to Methanol Freezing Point/ Crystallization of water molecules end.
You would have to reach the freezing point of water (a) first at a linear rate. Then you have to wait for the water to form into a crystalline solid.
The reason why the temperature remains constant for a certain amount of time is that the energy you added to lower the temperature compensates for the removal of heat in the material/solid. Process Energy is free, and it keeps the temperature constant.
Once the process energy is liberated (b), you lower the freezing point at a linear rate until you reach the freezing point of methanol. This leaves you with a crystalline solid.
But let’s say you ignored the linear rate of time and temperature and decided to cool the solid as fast as you could. You would end up with some of the methanol in its liquid form (since the water is already frozen because of the freezing point of methanol).
But because you didn’t give the liquid any time to form crystal shapes, you end up with the atoms randomly arranged, which leaves you with amorphous material.
This rapid cooling technique allows us to skip the time-temperature changes in the cooling points of certain chemicals/molecules to get amorphous solids. Cool, right? 😄
Closing Thoughts! 💭
The classification of these materials is based on the atomic structure of how the atoms are arranged in the material, which allows for certain materials to behave in certain ways. Today, I introduced a couple of these properties, but I will be back to introduce more properties between amorphous and crystalline solids!
Why am I explaining the atomic structure of materials? Because it’s a sneak peek at what I will be working on in the future! 😉 Let’s just say it’s time to go organic. . .
But see you tomorrow on the properties and applications of crystalline and amorphous solids! ✌🏽
Vocabulary! 📓
Amorphous Solids → Not flexible and lack in (geometric) shape.
Crystalline Solids → Not flexible but have a geometric shape.
Process Energy → The amount of energy placed/added on the material to cool the liquid to solid.
Bonus Resources! 💻
Previous “100 Nano-Stories!” 🔖
© 2021 by Carlos Manuel Jarquin Sanchez. All Rights Reserved.
