UNIVERSITY OF ENGINEERING AND TECHNOLOGY

Submitted to:
DR. NIDA IQBAL

Submitted by:
NIMRA RAZZAQ
2017-BME-34

Assignment:
LAB REPORT 2

Department:
Bio Medical Engineering
 Lab report no. 2

To determine the weight loss of stainless steel (SS) and mild steel (MS) in 5% and 10%
NaOH
Theory:
Corrosion:
Corrosion is the deterioration of a metal as a result of chemical reactions between it and the
surrounding environment.
Corrosion in stainless steel:
Steel is an alloy of iron and carbon. Contrary to carbon steel, the presence of a minimum of 10.5
% chromium in the stainless steel gives it the property of corrosion resistance. On contact with
oxygen, a chromium oxide layer is formed on the surface of the material. This passive layer
protects it and has the particular ability to self-repair.
Corrosion in mild steel:
If mild steel is exposed to an air then corrosive attack will begin at defects in the oxide film on
the steel. These defects may be present as a result of mechanical damage such as scratches,
natural discontinuities in the film e.g. grain boundaries or dislocation networks at the surface of
the steel. At each defect the steel is exposed to the solution (electrolyte) and an anodic reaction
occurs, resulting in the formation of iron ions and free electrons. These electrons are then
conducted through the oxide film to take part in a cathodic reaction at the surface of the film.
This reaction requires the presence of dissolved oxygen in the electrolyte and results in the
formation of hydroxyl ions. The hydroxyl ions react with the ferrous ions produced by the anodic
reaction to form ferrous hydroxide, which is then converted into a hydrated oxide called, ‘rust’.
Effect of base on stainless steel:
Stainless steel is stainless because there is a micrometer thin layer of oxides of chromium and
nickel on the surface. Corrosion resistance of stainless steels. Both 304 and 316 stainless steel
types are resistant to a wide range of concentration and temperature. Below 80 degC they can be
considered resistant to any concentration of sodium hydroxide, up to the limit of solubility.
Effect of base on mild steel:
Corrosion by caustic (sodium or potassium hydroxide) at all concentrations is easily handled at
room temperature with a variety of metals and alloys, including carbon steels. It becomes
increasingly more corrosive with increasing temperature and concentration. The useful safe limit
of carbon steel is approximately 150oF/65oC, both with regard to caustic stress corrosion
cracking (CSCC) and corrosion.
Apparatus
 Electrical balance
 Glass beakers
 Vernier caliper
 Measuring cylinder
Procedure
 Take sample of mild steel and stainless steel and measure their dimensions using vernier
 Caliper.
 Rub the surfaces of samples using sandpaper and remove the rough surface until it
becomes shiny.
 Weigh sample on electrical balance up to 3 digits.
 Prepare the solutions of various co rodents like NaOH.
 Hang sample in the beaker containing the solution and leave the top of beaker open to
allow air.
 After 24hours, dry the sample and weigh again using electrical balance.
 And find the percentage weight loss.
 Observe surface under microscope.

Observation
Observe surface of specimens/samples and compare the both types of steel. Repeat the process
for seven days and observe the weight loss.
MS 1
Length = 28.56 mm
Width = 26.71 mm
Diameter = 2.77 mm

MS 2
Length = 28.74 mm
Width = 27.36 mm
Diameter = 2.75 mm

SS 1
Length = 25.83mm
Width = 25.81mm
Diameter=1.55mm

SS 2
Length = 26.61mm
Width = 25.87mm
Diameter = 1.56mm
For MS

For Mild Co rodents Weights Day 1 Day 2 Day 3

Steel:
Sr. No.
1. 5% NaOH W1 15.086 g 15.072 g 15.049 mm
2. 10% NaOH W2 14.778 g 14.689 g 14.470 mm
For SS

For stainless Co rodents Weights Day 1 Day 2 Day 3

Steel:
Sr. No.
1. 5% NaOH W1 7.58 g 7.572 g 7.56 g
2. 10% NaOH W2 7.82 g 7.819 g 7.79 g

Calculations:
For MS 1 (5%)
Percentage weight loss = (initial weight-final weight/initial weight) × 100
= {(15.086-15.049)/15.086}*100
= 0.245
Percentage weight loss = 0.245 %
For MS 2 (10%)
Percentage weight loss = (initial weight-final weight/initial weight) × 100
= (14.778-14.470)/14.778*100
=2
Percentage weight loss = 2%
For SS 1 (5%)
Percentage weight loss = (initial weight-final weight/initial weight) × 100
= {(7.58-7.56)/7.58}*100
=0.263
Percentage weight loss = 0.263%
FOR SS 2 (10%)
Percentage weight loss = (initial weight-final weight/initial weight) × 100
={ (7.82-7.79)/7.82}*100
=0.384
Percentage weight loss = 0.384%

Results
Following are the images of milled steel I obtained using a microscope:

The images of stainless steel captured using microscope are:

Conclusions
The weight of stainless steel and mild steel is decrease with the passage of time. Because when
we keep metal in basic media it reacts with metal and decomposes the metal and decreases its
original weight.

Precaution:
There are several general instructions to keep in mind during this part of the process.
 Keep the room and the work areas clean, especially the polishing area. Each step in
the polishing process uses a finer grade of abrasive, so good results require that both
your sample and your hands are free from abrasive at each stage before proceeding to
the next stage of the process.
 Throw away the dirty gloves and tissue paper.
 Use and gloves while handling sand paper
 Do not eat or drink anything while working in the lab.
 Wash your hands thoroughly with soap before leaving the lab.