Date of Award

6-2001

Document Type

Thesis

Degree Name

Master of Materials Science and Engineering (MMatSE)

Department

Materials Science

First Advisor

Dr. Ahmed AI Shamsi

Second Advisor

Dr. Ali N. Moosawi

Third Advisor

Dr. Rashid Abdel Rabman AI Saeed

Abstract

Stainless steel alloys have a very active and important role in industry. Because many of

These industries have to work in aggressive media; stainless steels are threatened by corrosion

Which may affect their performance and cost the manufacturers millions of dollars yearly.

Several treatments have been taken part to solve this problem; one is by forming a protective

Oxide layer on the stainless steel (SS) surface to prevent it from corrosion. In this thesis; this way of protecting SS Surface is applied to two different types of Stainless Steel, those are AISI 316 and AISI 31 0; respectively. The oxide film was formed using a potential step programming at different thicknesses, varying the programs and bath compositions in a three- electrode electrochemical cell. The electrochemical behavior of the oxide film has been studied using several techniques: potential dynamic polarization , Tafel experiments, polarization resistance, and electrochemical impedance spectroscopic techniques. Then, surface analysis was applied to the oxide film in order to investigate its elemental composition, morphology and thickness. Surface techniques used in this study were electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy, surface reflectance FT­ IR, energy dispersive x-ray analysis and x-ray diffraction. It was found that the polarization behavior of the different types of stainless steels studied is strongly dependent on the steel structure. Also, the ability of stainless steels type 316 and type 310 to passivate in 5. 0 M sulfuric acid is realized and stabilized within a relatively wide range of potential. However, oxide film formed over stainless type 316 is relatively more stable than that formed over stainless steel type 310 surfaces under similar experimental conditions. From the EIS data, it was found that -for SS 316- the resistance of the oxide film to pore formation and charge transfer through the oxide film increased as the film thickness increased_ On the other hand, the coating capacitance and the double layer capacitance of the oxide film decreased gradually as the oxide thickness increased. It was concluded that the presence of chromate and moly date in the film-forming bath enhances the structure of the passive film due to the presence of chromium as hydroxide and molybdenum as the oxide. It has been shown that the film deposited at the stainless steel type 316 has a bilayer (hydroxide/oxide) structure_ The graphs depicted from the scanning electron microscope (SEM) gave a good idea about the Morphology of the oxide at SS surface. The important result of the SEM experiments is the identification of the systematic growth of the oxide layer that consists of oval, Pentagonal and pyramidal aggregates with a high micro roughness.

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