Microscopic investigation of embedded samples
The purpose of embedding is to protect fragile or coated materials during preparation, and to obtain good edge retention. Embedding is also used to produce specimens of a uniform size, such as minerals, clay or other particles and can also be used to section a material and investigate its interior.
Preparation of materialographic samples
Mechanical preparation is the most common method for preparing these so-called materialographic or metallographic samples for microscopic examination. After embedding, the samples are cut, grinded and polished. Abrasive particles are used in successively finer steps to remove material from the surface, until the required result is reached.
The mechanical preparation of these samples is a specialist task. Increasingly, however, more fully automated systems are available to make things easier. It can take a considerable amount of time to section, grind, mount and polish a sample.
Grinding and polishing
Grinding removes saw marks and levels and cleans the surface of the specimen. Polishing eliminates the artifacts of grinding but removes very little material. Grinding uses fixed abrasives – the abrasive particles are bonded to the paper or plates – for fast material removal. Polishing uses abrasive particles in a liquid, which are suspended on a cloth.
In summary, cutting the sample will take up to 1 hour, depending on the hardness. The grinding and polishing step may take approximately 2 – 2 ½ hours. Embedding, cutting and polishing are common techniques used to create flat samples for microscopic investigation.
Figure 1: Samples embedded in a resin
Sample investigations
Typically, these resin samples have a few standard size diameters. 32mm or 1 ¼ inch is the diameter most commonly used for optical, as well as electron optical, (SEM) investigation.
Resin mounted samples have a perfectly prepared flat top surface, which is a requirement for quantitative EDS results. However, the bottom surface can be very rough or even skewed. The Phenom desktop SEM sample holders and inserts have been designed in such a way that the top surface of these samples is always nicely leveled.
The Phenom desktop SEM can accommodate standard resin samples in diameter sizes between 25mm up to 40mm.
More information can be found here.
Figure 2: Image of a polished surface from a plasma spray coating layer on a steel sample.
Figure 3: EDS analysis results from the plasma
Sample preparation is key for obtaining flawless images
Sample preparation is a crucial step for obtaining flawless images. The best practices and more sample preparation tips and tricks are described in more detail in our sample preparation e-Guide.
Find out more about the optimal way to prepare your samples for electron microscopy imaging by downloading this sample preparation e-guide. The extended guide helps you obtain good results from the most common samples through tried-and-tested tips and tricks.
