Preparation Process of Thin Sections for Polarizing Microscopes
When observing samples under a polarizing microscope, specimens must be prepared into qualified ground or polished sections, generally referred to as polished sections. The preparation procedures are as follows:
(1) Sample Selection: Select representative parts of the specimen according to observation purposes and analytical requirements. Cut them into cubic blocks of 10×10×10 mm and clean thoroughly.
(2) Mounting or Impregnation: Small-sized specimens need to be mounted. Porous or loosely structured samples shall be impregnated with resin in advance.
(3) Rough Grinding: Choose a relatively flat surface of the sample. Grind the surface flat on a grinding machine with coarse abrasive to trim the shape and remove sharp edges and corners.
(4) Fine Grinding: Grind with fine abrasive until all scratches left by rough grinding are completely eliminated.
(5) Precision Grinding: Use ultra-fine abrasive for further grinding until the surface becomes fully flat and shows faint reflection under light observation.
(6) Polishing: Place the specimen on a polishing machine and apply polishing compound (polishing powder) for polishing. Continue until the surface is bright and free of obvious scratches when examined under a reflected-light microscope.
(7) Marking: Number the finished specimens and attach labels to clarify their source and designation.
(8) Etching: Select appropriate etching methods and conditions according to experimental purposes and analysis requirements, then perform etching treatment on the specimens.
If microstructural analysis needs to be conducted under both transmitted light and reflected light, the specimen shall be prepared into a polished thin section or even an ultra-thin polished section (thickness ＜ 0.02 mm). To prepare a polished thin section, first grind the specimen down to a thickness of 0.03 mm without covering it with a coverslip, then polish the precisely ground surface on a polishing machine.
