Preparation of Thin Sections for Polarizing Microscopes
1. Sample selection
Select suitable samples as needed and determine the parts that should be ground.
2. Cutting
Choose an inner or outer circular slicer based on the characteristics of the material. Generally, when slicing with an external slicer, the cutting method should be strictly followed, and the size should not be too large or too small. It depends on the specific size of the material provided, and can generally be around 2cm * 2cm * 0.5cm.
3. Grind the bottom surface flat
After selecting the sample, take the relatively flat surface as the bottom surface and manually or machine select the sample step by step on the grinding machine. Use 200 #, 600 #, 1200 #, and 2000 # diamond sand to grind the surface flat. First, grind all four sides to a thickness of about 1-2mm.
4. Adhesive
Drop Canadian gum the size of a soybean onto a glass slide and slowly heat it with an alcohol lamp to melt the gum. At the same time, heat the sample that has been ground flat on the bottom to remove any moisture. During the heating process, you should always pick up a small amount of Canadian gum with a matchstick stick and hold it in your hand for a while to cool before kneading. If the gum is sticky and cannot be kneaded into a ball, it means that the gum is still soft. At this time, it is not allowed to stick the pieces. If the glue turns into powder by rubbing it in the hand, it means that it has been heated too much and cannot stick to the pieces. The gum must be heated until a small amount is picked up with a matchstick and placed in the hand for a while to cool before rubbing into a ball. When using fingernails to scratch with a certain degree of hardness, without leaving any marks or cracks, the bottom of the sample should be evenly pressed onto a glass slide, but it should be noted that there should be no bubbles between the gum and the sample. If there are any, it must be re glued.
5. Grinding thin
Place the bonded sample on the grinder (or glass plate), grind it to 0.1-0.15mm with 200 # sandpaper, and then gradually replace it with 600 #, 1200 #, and 2000 # fine sandpaper to grind it to 0.03mm. There are several points to note: 1) When grinding thin, the fingers pressing on the glass slide should apply even force, otherwise the thin slice will have a thickness difference and form a wedge shape. Therefore, the sample should be observed in front of the light at all times, and the flatness of the entire sample should be corrected according to the strength of the light transmission. 2). When using diamond sand step by step, the test piece must be strictly cleaned to remove the fine sand on the thin sheet, otherwise this coarse sand will inevitably affect the surface smoothness of the thin sheet. 3). When grinding with 2000 # fine sand, use a microscope to observe at any time. If the thickness has reached (taking quartz as an example, under orthogonal polarization, the high interference color appears yellow white), stop grinding.
6. Whole cover sheet
After the sample is ground, in order to preserve the specimen and extend its use time, it is necessary to perform thin section correction work. Gently scrape off excess Canadian gum around the sample with a regular scraper and shape it into a regular and aesthetically pleasing shape. Then drop a small amount of Canadian gum onto a cover glass and heat it slightly. After the gum melts, it can be covered on the thin sheet. Attention should also be paid to the exclusion of bubbles here to avoid affecting the observation effect of the thin film.
7. Hot glue
The thin sheet after covering is movable due to the fact that the Canadian gum has not yet solidified, so the covering must be hot pressed. The method is to take a carving knife and heat it on a gas lamp until it turns red, then place it around the cover glass and heat it until the Canadian gum color is slightly yellow. Then, use alcohol or xylene to wash away the gum around the cover glass, label it, and the entire thin film is completed.
