Chm 674 Exp 3

CHM674 ADVANCED ELECTROCHEMISTRY LABORATORY REPORT EXPERIMENT 3: CORROSION OF STEEL-WEIGHT LOSS ANALYSIS NAME

: NABILAH BT ABD HARIS HILMI (2016644524)

GROUP MEMBERS

:1.MIOR AFIQ HILMI B MIOR AHMAD FAIZAL (2015422326) :2. MUHD FARIS BIN ABD RASHID ( 2016644618) :3. NUR NABILAH BT HAIRMAN (2016644614)

LECTURER’S NAME

: PM DR YUSAIRIE BIN MOHD

EXPERIMENT DATE

: 25 MARCH 2019

SUBMISSION DATE

: 8 APRIL 2019

GROUP

: AS2026M2

OBJECTIVES

a) To study the corrosion of steel in two different acid solutions. b) To study the corrosion resistant efficiency of steel alloy (ie: stainless steel).

INTRODUCTION

Corrosion is a natural process, which converts refined metal to their more stable oxide. It is the gradual destruction of materials (usually metals) by chemical reaction with their environment. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen.Rusting, the formation of ironoxides is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal, and results in a distinctive orange colouration. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context,the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases. Many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pitor crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as passivation and chromate conversion, can increase a material's corrosion resistance. However, some corrosion mechanisms are less visible and less predictable.The rate of corrosion can be calculated using these formula:

Density of steel: 7.86 g/cm3 , Density of Stainless Steel:

7.0 g/cm3 (depending on the type

of stainless steel)

Apparatus:

Steel coupons, stainless steel coupons, polishing cloth/ emery paper, vials/containers, four-decimal analytical balance.

Chemicals: 1M H2SO4, 1M HNO3 solutions

Procedure: All metal specimens (steel and stainless steel) were in the same size. All the metal specimens were polished with emery paper to remove all dusts and impurities. Then,they were rinsed with alcohol and were let them dries.12 vials or containers were taken and labelled them as S1(a)- (c), S2(a) – (c), SS1(a) – (c) and SS2(a) – (c). All the metal specimens were weighed prior to immersion in acidic solution using a 4-decimal analytical balance. Each of the specimen was put into the right labelled container and was filled in the container with the right acidic solution as in the report table. All samples were taken out all after 1 hour; and dried before weighing. All the metal specimens were reweighed using the same analytical balance. The data were recorded and calculated for the average weight loss for each specimen.

RESULTS 1. Immersion of Steel in 1M H2SO4 for 1 hour Metal specimen

Weight immersion (g)

before Weight

after Weight loss (g)

immersion (g)

S1(a)

2.5683

2.5447

2.5683-2.5447= 0.0236

S1(b)

1.7765

1.7547

0.0218

S1(c)

1.7847

1.7330

0.0517 Average:(0.0236+ 0.0218+0.0517)/3 =0.0324g

Average weight loss: 0.0324 g 2. Immersion of Steel in 1M HNO3 for 1 hour Metal specimen

Weight

before Weight

after Weight loss

immersion (g)

immersion (g)

S 2(a)

1.5415

1.3722

0.1693

S 2(b)

2.7150

2.5263

0.1887

S 2(c)

2.6328

2.4145

0.2183 Average: 0.1921

Average weight loss: 0.1921 g

3. Immersion of Stainless Steel in 1M H2SO4 for 1 hour etal specimen

Weight

before Weight

after Weight loss

immersion (g)

immersion (g)

SS 1(a)

3.5997

3.5975

0.0022

SS 1(b)

3.5841

3.5838

0.0030

SS 1(c)

3.5545

3.5543

0.0002 Average: 0.0018

Average weight loss: 0.0018 g

4. Immersion of Stainless Steel in 1M HNO3 for 1 hour Metal specimen

Weight

before Weight

after Weight loss(g)

immersion (g)

immersion (g)

SS 2(a)

3.6074

3.6069

0.0005

SS 2(b)

3.5352

3.5349

0.0004

SS 2(c)

3.5125

3.5117

0.0008 Average: 0.0006

Average weight loss: 0.0006 g

DISCUSSION

The first objective of this experiment was to study the corrosion of steel in two different acid solutions,that is sulphuric acid H2SO4 and nitric acid,HNO3.From the results obtained,it was shown that nitric acid has the higher value of rate of corrosion than the sulphuric acid .Besides having a bigger pKa value than sulphuric acid,it is also a strongly oxidizing acid that is aggressively corrosive to many metals. Its oxidizing nature also is affected by acid temperature and concentration, and composition of the alloy exposed to it.

Another objective was to study the corrosion resistant efficiency of stainless steel.From the results obtained,stainless steel has lower corrosion rate than steel.This is because stainless steel and steel has different chemical composition. Steel is made of iron and carbon, and stainless steel contains iron, carbon, and anywhere from 12-30% chromium. Stainless steel can contain other elements such as nickel and manganese, but chromium is the key element which makes it rust resistant. When the surface of normal steel is exposed to oxygen, it usually forms ferric oxide (Fe2O3) which has the well-known red rust color. Ferric oxide doesn’t form a continuous layer on the steel because the oxide molecule has a larger volume than the underlying iron atoms, and eventually spalls off leaving fresh steel exposed which then starts a deleterious rusting cycle. When stainless steel is exposed to oxygen, chromium oxide is created on the surface of the steel because chromium has a very strong affinity for oxygen.

The chromium oxide is a very thin layer which doesn’t spall off, and it prevents further oxidation of the stainless steel. Even if stainless steel is scratched and the chromium oxide layer is removed, a new chromium oxide layer will form and protect the rest of the stainless steel beneath it. As long as there is sufficient chromium present, the chromium oxide layer will continue to protect the stainless steel and prevent it from rusting.

QUESTIONS

1. Calculate the corrosion rate of steel in both acids for 1 hour. Comments on your findings.

Sulphuric acid

=

0.0324g × 8.76 ×104 7.86 g/cm3 × 4.0 cm2 × 1 hr

= 90.27 mm/y

Nitric acid

=

0.1921 g × 8.76 ×104 7.86 g/cm3 × 4.0 cm2 × 1 hr

= 535.24 mm/y

The corrosion rate of steel is higher in 1M HN03 than the corrosion rate in 1M H2SO4 2. Why corrosion rate of steel is higher in nitric acid than in sulfuric acid?

Acidic condition can corrodes the steel much faster. Since nitric acid has the bigger pKa value than sulphuric acid, thus it makes the corrosion rate of steels in nitric acid becomes higher than the corrosion rate of steel in sulphuric acid

3. Calculate the corrosion rate of stainless steel in both acids after immersion for 1 hour. Why corrosion rate of stainless steel is lower than of steel?

Sulphuric acid

0.0018 g × 8.76 ×104

=

7.0 g/cm3 × 4.0 cm2 × 1 hr

= 5.63 mm/y

Nitric acid

0.0006 g × 8.76 ×104

=

7.0 g/cm3 × 4.0 cm2 × 1 hr

=

1.88 mm/y

Corrosion rate of stainless steel is lower than steel because stainless steel is less corrosive because of their better composition and physical properties .Stainless steel is made up of alloy that have a better resistant towards corrosion.

4. Calculate the corrosion resistance efficiency of stainless steel in nitric acid.

Resistance Efficiency (%) = weight loss(larger)-weight loss(smaller) X 100% weight loss(larger)

= 0.0008 g – 0.0004 g

× 100

0.0008g

= 50 %

CONCLUSION

The rate of corrosion of nitric acid is higher than the rate of corrosion of the sulphuric acid because nitric acid is a strong acid. The stainless steel corrosion resistant is higher than steel.All the objective for this experiment were achieved.

REFERENCES

Chuka, C. E., Odio, B. O., Chukwuneke, J. L., & Sinebe, J. E. (2014). Investigation Of The Effect Of Corrosion On Mild Steel In Five Different Environments, 3(7), 306–310.

Oparaodu, K. O., Okpokwasili, G. C., Harcourt, P., & Harcourt, P. (2014). Comparison of Percentage Weight Loss and Corrosion Rate Trends in Different Metal Coupons from two Soil Environments, 2(5), 243–249. https://doi.org/10.12691/ijebb-2-5-5

Wensley, A. (2015, March 19). Why Does Stainless Steel Rust? Retrieved from SGS Polymer Solutions Incorporated: https://www.polymersolutions.com/blog/why-does-stainlesssteel-rust/