The key difference between nanocrystalline and polycrystalline is that nanocrystalline materials are made of particles in nanometer-scale whereas polycrystalline materials are made of large particles.
Materials we know can be divided into different classes depending on the particle size or by looking at their crystal grains. Nanocrystalline material and polycrystalline material are such two classes.
CONTENTS
1. Overview and Key Difference
2. What is Nanocrystalline
3. What is Polycrystalline
4. Side by Side Comparison – Nanocrystalline vs Polycrystalline in Tabular Form
5. Summary
What is Nanocrystalline?
Nanocrystalline materials are those that contain crystal grains having the dimensions in the nanometer scale. These materials tend to fill the gap between amorphous materials, so these crystal grains are arranged without a long range order. Therefore, nanocrystalline materials are conventional coarse-grained materials. Generally, there are slightly different definitions of nanocrystalline materials. However, a material containing crystal grains with dimensions below 100 nm are typically considered as nanocrystalline materials. Moreover, crystal grains having dimensions between 100 to 500 nm are called as “ultrafine” grains. We can abbreviate nanocrystalline materials as NC.
Figure 01: Nanocrystalline
X-ray diffraction is the major technique we use to measure the crystal grain size of the NC material. Materials with very small crystal grains show broadened diffraction peaks. This broad peaks can be used to determine the grain size using the Scherrer equation and Williamson-Hall plot. Or else, we can use more sophisticated methods such as the Warren-Averbach method or computer modelling of the diffraction pattern.
When considering the synthesis of NC material, there are several ways. These techniques are based on the phase of matter. For example, there are some techniques for NC production such as solid-state processing, liquid processing, vapour-phase processing, and solution processing.
What is Polycrystalline?
Polycrystalline materials are those that contain crystal grains having dimensions above the nanometer scale. These materials form mainly upon cooling. The crystal grains in polycrystalline materials are called “crystallites”. The orientation of these crystallites in a material is usually random with no particular direction, random texture, etc. We can abbreviate polycrystalline materials as PC.
Most organic solids we know are polycrystalline materials. Some common examples include ceramics, rock, ice, etc. The degree of crystallization in PC material is important in determining the properties of these materials. For example, sulfur can be found in different allotropic forms where these allotropes have different properties according to the degree of crystallinity.
The size of a crystallite can be measured using X-ray diffraction technique. The grain size can also be determined using other methods such as transmission electron microscopy. Sometimes, materials contain a large single crystallite which can easily be handled.
What is the Difference Between Nanocrystalline and Polycrystalline?
Materials we know can be divided into different classes depending on the particle size or by looking at the crystal grains. Nanocrystalline material and polycrystalline material are such two classes. Materials containing crystal grains with dimensions below 100 nm are typically considered as nanocrystalline materials while materials containing crystal grains with dimensions above 100 nm are typically considered as polycrystalline materials. Therefore, the key difference between nanocrystalline and polycrystalline is that nanocrystalline materials are made of particles in nanometer-scale whereas polycrystalline materials are made of large particles.
Below infographic summarizes the difference between nanocrystalline and polycrystalline.
Summary – Nanocrystalline vs Polycrystalline
Materials can be divided into two different classes as nanocrystalline material and polycrystalline material, depending on the particle size or by looking at the crystal grains. The key difference between nanocrystalline and polycrystalline is that nanocrystalline materials are made of particles in nanometer-scale whereas polycrystalline materials are made of large particles.
Reference:
1. “Nanocrystalline Material.” Science Direct. Available here.
Image Courtesy:
1. “Nanocomposite structure german” By Freundchen – Own work, CC0) via Commons Wikimedia
2. “Crystalline polycrystalline amorphous” By Cristal_ou_amorphe.svg: Cdangderivative work: Sbyrnes321 (talk) – Crystalline_or_amorphous.svg (CC BY-SA 3.0) via Commons Wikimedia