Not to place the finger in the polishing surface. 5 Passo – Chemical Attack the surface of the samples, when attacked for specific agents, it suffers a series from based electrochemical transformations in the oxi-reduction process. For the chemical attack they are used solutions of acid, bases and you leave, as well as you leave casting or vapors. The conditions of attack, such as: chemistries, temperature and time can be varied to reach the most diverse purposes of contrast. Basically, the attack consists of making with that the attack solution reacts with definitive element of the sample. (Source: Breast Cancer Action ). The regions where the reactions had occurred will be lower, of what the regions where the attack did not occasion effect.
Through the microscope the regions highest will obtain to difratar the light and will appear clear in the micrograph. The regions lowest, for being hidden for more, will difrataro little light, that will be represented by darker regions. After the chemical attack the sample must be rigorously clean, to remove the residues of the process through laudering in distilled water, alcohol or acetone, and later it dries through hot air spurt. Description of the assay: As much for steel with carbon, binds binary, as for casting chainses, the Nital, whose composition corresponds nitric acid 98% of and 2% of etlico alcohol, was the used one. It was caught part and left the polishing surface in contact with the chemical reagent, the Nital, in a container, the clock glass. Reagent left to act during 25 seconds and with 30 seconds (necessary time so that the revelation of the microstructure of the material in analysis occurs), was removed the part, and after that it was washed in current water, the shining aspect disappeared, that is, the sample was fosca. To dry the part and to take the sample for visualization in the microscope. 6 Passo – Optic Analysis or Microestrutural In this part, will be shown a micrograph of a steel and will be recognized the micron-constituent gifts.