Study Of Self-assembled Monolayers On The Surface Of Copper And Q235 Steel

Self-assembled monolayers (SAMs) formed by spontaneous chemisorption provide a convenient technique to modify surfaces, they are thermodynamically steady and ordered system. They do not need the environments of no water or vacuum and any special instrument. Self-assembled monolayers are ideal models for studying some complex phenomena concerning about the surfaces, since their structures are orderly and can be designed flexibly. They have widely applications in many fields, such as metal corrosion, sensors, nano-materials, bioehemistry and medicine et al. SAMs play an important role in the field of surface modification, especially in the field of the inhibitive corrosion of metals. Self-assembled technology is a proeess that molecules form ordered films spontaneously on the solid surface by chemical bonds. SAMs can protect metals from corrosion and decrease friction because of their dense and stable structures.Corrosion science and its prevention technique is an important research field which has a great effect on the development of the national economy. For the engineering metal, such as copper and Q235 steel, because they are quite active and easily corroded due to some environmental factors when exposed in air, they have caused much loss to commercial production and national economy. So it's necessary and urgent to investigate into its corrosion and protection properties. From the aspect of corrosion inhibition of metals, it is very necessary to choose some appropriate and nontoxic organic compounds to self-assemble on the metal surface.In this thesis, the SAMs were formed on the surface of copper and Q235 steel, then the electrochemical behaviour and inhibitive efficiency (I.E.) of SAMs covered metal were studied, the results showed that SAMs as the barrier layers can effeciently insulate the metal from the external surroundings. The effects of some factors on I.E., such as concentration of inhibitor and corrosive medium, pH value, et al, has been studied by electrochemical techniques, weight loss measurements and scanning electronic microscopy (SEM) to find a better way for corrosion inhibition of metal. 1. Study of the SAMs of thiourea and allyl thiourea on copper surfacesThiourea (TU) is widely used as additive in the electrodeposition of metals such as copper and silver from aqueous solutions. In addition, there is a continued interest in TU as a corrosion inhibitor of metals in acid media. Self-assembled monolayers (SAMs) derived from adsorption of allyl thiourea onto the surface of copper in ethanol solution were evaluated in neutral aqueous sodium chloride solutions. The electrochemical behaviors and anticorrosion features of copper in the presence of allyl thiourea in neutral aqueous sodium chloride solutions were investigated by using electrochemical techniques. SAMs of thiourea(TU) and allyl thiourea(AT) against copper corrosion hinder the copper oxide formation, furthermore, inhibit the cathodic procession obviously. Protective properties of allyl thiourea layers on copper surfaces depend on the applied potential, the concentration of allyl thiourea and the chloride ions in the environment. The SEM results showed that the concention of AT has great influence on the status of SAMs.2. Study of the SAMs of phtic acid on Q235 steel surfacesOwing to its unique structure and property, nontoxic phytic acid has drawn increasing interest in metal corrosion and protection, its series productions play a great role in the protection of corrosion. To study the corrosion behaviour of Q235 steel in NaCl solutions, phytic acid SAMs and conversion coating for Q235 steel had been prepared respectively, then they were characterized by weight loss measurements, electrochemical techniques and scanning electronic microscopy (SEM). In basic condition, the findings of weight loss measurements showed that the I.E. arrived at 95.3%. The results of electrochemical techniques showed that phytic acid SAMs and conversion coating had great impact on the eletrochemical behaviour of Q235 steel, which depress the electrochemical dissolution of the electrode and inhibited the hydrogen evolution in the cathodic process. In addition, combing with SEM, we find that pH value and concentration of phytic acid are crucial factors on I.E..