# Lab Report Essay

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4. Results and discussion
4.1 Material removal rate
The material removed from each coupon was determined by measuring its mass before and after electro-polishing. Theoretical values were then obtained using Faraday’s laws of electrolysis as shown in Equation 9. (9)
Where m is the mass of material removed in grams, I is the current and t is the electro-polishing time. EW is the equivalent weight which depends on the chemical composition of the workpiece and the electrolyte. F is Faraday’s constant.
The measured values of the mass of material removed were compared to the theoretical values. It was observed that the theoretical values were similar to the measured values within an error
At a current density of 0.16 A/cm2, the change in surface texture is not consistent. This is likely because the current is below the threshold value required for the electro-polishing process to take place. It is widely accepted that four different mechanisms take place on a stainless steel surface when exposed to varying currents in an electrolytic cell . These are oxidation, passivation, diffusion limited current and oxygen evolution. Past studies agree that electro-polishing occurs in the diffusion limited current region [27-29]. The results obtained for a current density of 0.66 A/cm2 are favourable and show an almost linear …show more content…
While the current is above the optimum, electro-polishing still takes place with an improvement in surface texture until pitting occurs on the stainless steel surface. In the case of the hypodermic needles used for this study, the polishing time permissible before excess material removal is insufficient for pitting to occur. Another effect of this limitation is that no meaningful relationship could be determined for the change in forces with polishing time as the high current only allowed for an electro-polishing time of 5 minutes before dissolution of the needle in the electrolyte

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