Date 03/26/2024
Materials Testing Lab
Chemical Provision and Etching
Team Members:
Rafael Acosta Servian
Fausto Nicolás Mingo González
Ivan Ariel Portilla Miranda
Student ID: F11203114
Name: Fausto Nicolás Mingo González
1. Experiment Purpose
The goal of etching is to highlight the various structural properties of
metals or alloys. Its objective is to make microstructure components
easier to distinguish from one another so that a chemical reaction can
occur on the polished surface. The etching reagent operates selectively on
certain elements in alloys that have numerous phases with different
chemical compositions, revealing the composition. When the reagent
attacks various grains at different rates, grain boundaries become visible,
creating consistent contact in homogeneous single-phase alloys.
The primary factor affecting the fluctuation in the reagent's attack rate is
the orientation angle of different sections of the grain structure relative to
the polished surface plane. The presence of grain boundaries manifests as
indentations resulting from the chemical reagent's interaction with the
polished surface. When light from the microscope reflects off the
sidewalls of these indentations, the grain boundaries appear as dark lines.
Choosing the appropriate etching reagent depends on the specific metal or
alloy being studied and the desired structure for observation.
2. Experiment Procedure
- Step 1: We need to ensure that the sample is thoroughly and meticulously
polished.
- Step 2: We have to take 3 ml of nitric acid and mix it with DI water, first
we put the DI water and then mix it with nitric acid using a stirring rod.
- Step 3: After that, we need to place the solution in a petri dish.
- Step 4: With a cotton swab, we need to wipe the sample gently for about
2 or 3 seconds.
- Step 5: Wait 5 to 10 seconds to clean the surface with water.
3. Experiment conclusion and discussion
How to prepare the Nital etchant commonly used to etch carbon steel?
- To prepare 100 ml of 3% nital solution, we need to pour 97 ml of
methanol into a measuring beaker. Next, take 3 ml of nitric acid into a
plastic pipette, and transfer it into the measuring beaker that holds the
methanol.
What is etching? And please further explain the mechanism of image
light and dark contrast during metallographic observation.
- Metallographic etching refers to any technique used to expose specific
structural characteristics of a metal that are not visible when the metal is
polished. The main reason for the contrast in metallographic images is
that the microstructural features of the material either reflect or absorb
light. When a polished metal specimen is etched, certain microstructural
characteristics react differently to the etchant, which leads to different
surface textures, chemical composition, or other characteristics. These
differences in surface properties affect how light interacts with the
specimen, which creates the contrasting elements in the image.
The photo before and after etching and analyzing grain, grain boundary or
crystal structure.
Before etching After Etching
4. Reflection
All things considered, metallography is a fundamental aspect of physical
metallurgy that allows one to infer a material's characteristics and
physical features from the microstructure that is visible under a
microscope. Metal microstructures reveal details about the functioning
and mechanical behavior of a material. Internal flaws like microcracks,
contaminants, and compositional variances can be found with this
technique.
