Name: preparing solid samples for optical microscopy
Uploaded: 2023-04-30T01:29:37.000Z
Duration: 7 min 34 s
Channel: JoVE

<ol>
	<li>The sample examined in this video is a metal nut. First cut the sample normal to the hoop plane using a linear precision saw in order to isolate undamaged microstructural features for later viewing.</li>
	<li>Mount the specimen with the side to be imaged facing down on a mounting press. You must, of course, make sure that the sample is small enough to fit in the die cavity of the press, both laterally and vertically.</li>
	<li>Fill the remaining volume of the mounting press cavity with Bakelite, a thermosetting resin.</li>
	<li>Press the sample and using the prescribed heat, pressure and duration prescribed for Bakelite or other thermosetting mounting materials you may be using.</li>
	<li>Over the next steps, polish using sequentially finer polishing media, starting with a coarse grit paper (e.g. 600 and 1200 grit paper, where the abrasive particles are 25.8 and 15.3 &#181;m, respectively) followed by finer polishing suspensions (e.g. 1 and 0.01 &#181;m alumina particles). These coarse-to-fine polishing steps should be done on rotating polishing wheels.</li>
	<li>Between each step, the sample should be rotated by 900 in order to obtain a directionally uniform polishing and such that the scratches from the prior step can be distinguished from the current one.</li>
	<li>The sample should be checked on an optical microscope that the scratches on the sample surface left by each step in the schedule will be removed by each subsequent step (Figure 1a-d), with the goal of leaving no observable scratches at the highest magnification of the optical microscope after the final polishing step Figure 1d. Table 1 indicates an example of a polishing schedule that can be used.</li>
	<li>In the final sample preparation step, prepare a 2% nital solution (2% by volume concentrated nitric acid in ethanol), and dip the polished face in the solution for about 20 seconds. Rinse the sample with ethanol before observing the effects of the etch on a microscope. The etching step is repeated until it is judged that there is sufficient contrast in the granular structure observed. The etching time (and the number of iterations), therefore, is somewhat flexible and depends on the subjective judgment of the materialographist. 
	NOTE: Care should be taken during abrasion to keep constant pressure and direction of wheel motion constant. When grit sized is changed, the sample is also rotated in order to distinguish the newly introduced scratches from those that were introduced in the previous step.</li>
</ol>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Step</td>
			<td>Media</td>
			<td>Grit</td>
			<td>Time (min)</td>
			<td>Speed (rpm)</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>1</td>
			<td>SiC</td>
			<td>600</td>
			<td>2 min*</td>
			<td>120</td>
			<td>Rotate 90&#176; before step 2</td>
		</tr>
		<tr>
			<td>2</td>
			<td>SiC</td>
			<td>1200</td>
			<td>2 min*</td>
			<td>120</td>
			<td>Rotate 90&#176; before step 3</td>
		</tr>
		<tr>
			<td>3</td>
			<td>Al2O3</td>
			<td>1 &#181;m</td>
			<td>2 min*</td>
			<td>120</td>
			<td>Rotate 90&#176; before step 4</td>
		</tr>
		<tr>
			<td>4</td>
			<td>Al2O3</td>
			<td>0.05 &#181;m</td>
			<td>2 min*</td>
			<td>120</td>
			<td>* or until scratches&#160; from previous step&#160; are removed</td>
		</tr>
	</tbody>
</table>
Table 1. Polishing schedule for sample.

These are the standard methods for preparing cross sections of samples for microscopy. While the procedures detailed here are optimized to provide the best results in optical microscopy, some of the steps are unnecessary for scanning electron microscopy, and are inadequate for transmission electron microscopy. For the latter two, separate sample preparation procedures should be followed.
Materialographic sample preparation described here are the necessary first step towards the analysis of int...

optical materialography part 1: sample preparation

Optical Materialography Part 1: Sample Preparation

Source: Faisal Alamgir, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
The imaging of microscopic structures of solid materials, and the analysis of the structural components imaged, is known as materialography. Qualitative information such as, for example, whether or not there is porosity in the material, what the size and shape distribution of the grains look like, or whether there is anisotropy to the microstructure can be directly observed. We will see in Part 2 of the Materialography series, however, that statistical methods allow us to quantitatively measure these microstructural features and translate the analysis from a two-dimensional cross section to the three dimensional structure of a material sample.
This presentation will provide an overview of the techniques and procedures involved in preparing solid material samples for optical microscopy. While materialography can be conducted with optical as well as electron-based microscopy, this presentation will focus on the sample preparation specifically for optical microscopy. It should be noted, however, that a sample prepared for optical materialography can be used for scanning electron microscopy as well with minimum, if any, additional steps.

From the series of images in Figure 1, particularly from the etched sample (Figure 1e), one can observe that the powder pressing process by which this sample was made rendered the grains to have non-circular, elongated shapes, with non-isotropic grain orientation. There is a significant amount of porosity retained in the material through this processing. Part 2 of the Materialography series will explore the statistics of the grai...

Source: Faisal Alamgir, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
The imaging of microscopic structures of ...

Materialography is a method for microscopic structure imaging and analysis of solid materials. In particular materialography qualitatively studies the porosity in the material, the size and shape distribution of the grains, and the degree of isotropy of the microstructures.Such detailed analysis requires specific sample preparation of solid materials. This video will illustrate the four major steps performed to prepare a sample four optical materialographic analysis.Materialography is used to characterize solid materials. With this method, qualitative analysis, as well as quantitative analysis can be performed. In this video we will focus on the qualitative information obtained for a solid. In materialography the sample can either be probed with light, or with an electron beam. Depending on the choice of the probing tool, the sample needs to be prepared in different ways. We demonstrate here the principles of sample preparation for the optical materialography of solid materials of similar hardness to that of steel. This sample preparation is performed in four major steps, cutting, mounting, polishing, and etching. Let us look in detail at each of these steps.The very first step is

optical-materialography-part-1-sample-preparation

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preparing solid samples for optical microscopy

Optical microscopy of solid materials starts with careful sample preparation. Materialography is the study of microscopic structures in solids and the features seen in those images. It helps reveal details such as porosity, grain size and shape, and whether the microstructure shows anisotropy, or direction-dependent structure.

This lesson focuses on the preparation steps used before optical microscopy. It covers the techniques and procedures needed to ready a solid material sample for imaging. The goal is to make the internal structure clear enough for direct observation.

The prepared sample can also support later analysis. In Part 2 of the Materialography series, statistical methods are used to measure microstructural features and relate a two-dimensional cross section to the three-dimensional structure of the material. A sample prepared for optical materialography can often be used for scanning electron microscopy too, with little or no extra work.

Preparing Solid Samples for Optical Microscopy

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Optical microscopy of solid materials starts with careful sample preparation. Materialography is the study of microscopic structures in solids and the features seen in those images. It helps reveal details such as porosity, grain size and shape, and whether the microstructure shows anisotropy, or direction-dependent structure. This lesson focuses on the preparation steps used before optical microscopy. It covers the techniques and procedures needed to ready a solid material sample for imaging.

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Learn how solid material samples are prepared for optical microscopy in materialography, including grain structure, porosity, anisotropy, and later use in SEM.

Preparing Solid Samples for Optical Microscopy

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