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Theory :

When Nickel solution is titrated against EDTA at pH = 10-11
using Murexide as indicator, the free Ni2+ ions are first
complexed with EDTA. Then the Ni2+ ions from the Nickelmurexide
complex are displaced to form the more stable Ni-
EDTA complex liberating the free form of the indicator.
It is indicated by the colour change from yellow to blue-violet.

Procedure :

1) Preparation of Ni Solution from the steel sample :
A known weight of the steel sample 2 gm is taken in a 250 ml
beaker and dissolved completely in 10 ml of conc. HCl.
The sample is oxidized by the drop wise addition of conc.HNO3
and digested by keeping it over the hot plate.
Then the solution is cooled and transferred into 100 ml
standard measuring flask and made up to the mark.
2) Estimation of Nickel solution:
Pipette out 10 ml stainless steel solution. Add 2-3 drops of
indicator, 2-3 ml of buffer solution (pH = 10) and 2-3 ml liq.
ammonia. At this stage yellow colour is obtained.
Titrate against 0.02 M EDTA till violet colour is obtained.

Result :

Percentage of Ni in steel alloy = ___________%.
Stainless steel is defined as a steel alloy with a minimum of 10.5 percent by weight of chromium. Although stainless steel usually does not corrode as easily as ordinary steel, different grades are needed for different environments. For example, several manufacturing groups (including semiconductors and pharmaceuticals) have strict requirements for stainless steel surfaces. The corrosion resistance properties of stainless steel are due to the formation of a passive layer of chromium oxide. Although this layer naturally forms when the material is exposed to the atmosphere, additional chemical treatments (passivation) can improve the relative amount of chromium on the surface. Chemical surface changes due to passivation occur within ~ 50 Å of the surface. To measure these changes, surface analytical tools such as X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are required. One of the stainless steel measurements performed using Auger and XPS is the chromium / iron (Cr / Fe) ratio close to the surface.
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