Preparation And Characterization Of Anti-corrosion Film On SUS304 Stainless Steel In Aqueous LiBr Solution At High Temperature

A lot of lower grade thermal energy in industrial processes has been emitted into environment every year in the world,causing energy waste and serious thermal pollution by exhaust gases,cooling water or cooling air.On the other hand,many industrial processes require numerous steam or hot water to heat the fluid stream.As a very effective technique, absorption heat transformer(AHT) can be applied to upgrade the large quantity of low grade waste heat.Due to the high recovery ratio of waste heat,good contribution to environment protection,and little power consumption,AHT is currently becoming a considerable interest in waste heat reutilization in industrial processes.As the working fluid,Lithium bromide solution can cause serious corrosion problems on the metallic component,which is the bottleneck in the development of high temperature AHT.In this dissertation,the preparation and characterization of anti-corrosion film on SUS304 stainless steel in LiBr solution at high temperature has been investigated.The corrosion of stainless steel in LiBr solution without any anti-corrosion and anti-fouling inhibitions at 150～200℃was experimentally investigated by means of static immersion test,in which the concentration of dissolved oxygen has been controlled by vacuumizing.The experimental results indicated that the concentration of LiBr solution was the most important factor not only to the corrosion rate but also to the concentration of ions dissolved in solution.It was found that the usual pitting corrosion has a trend to transform into film corrosion in the process at high temperature and high LiBr concentration.This transformation mechanism of corrosion pattern states has been analyzedBased on the modified hydrothermal method,a novel inorganic silica composite film was prepared on SUS304 stainless steel substrates.The experimental tests demonstrated that the composite film remarkably improved the anti-corrosion characteristics of substrate.XPS, XRD and FT-IR analysis revealed that two simultaneous sub-processes,i.e.the corrosion of stainless steel stimulated by aqueous Lithium bromide solution and the dissolution of silica from inorganic silica,took place during preparation.The silica dissolved in the solution constituted a network with a layer of hydroxyls on the substrate surface and incorporated with the corrosion products to form -Si-O-Fe,-Si-Fe bonds.Silicon dioxide particle was chosen to prepare inorganic composite silica film.Effects of added content of solicon,concentration and pH of LiBr solution and the time of preparation on the performance of composite film were studies.As a result,the optimum condition was determined as follows:silicon content of 29ppm,pH of 10.6,LiBr concentration of 57.8%.An organic silica composite film of 1,2- Bis[methylbisethoxysilyl]ethane(BMBSE) was prepared on the surface of stainless steel directly without pre-plating metal with symmetrical structure of groups such as -OH,-CH₄ and -CH₂-CH₂- after hydroxylations.The structure and properties of the films were investigated by FT-IR,SEM,EIS, Potentiodynamically polarization curve and static contact angle.As a result,the structure of -Si-O-Fe,Si-O-Si could improved the anti-corrosion performance of SUS 304 stainless steel obviously.Furthermore,tetraethyl orthosilicate(TEOS:(OH)₃SiOSi(OH)₃) with high density of-OH was chosen to modify the BMBSE film.The content of-Si-O-Fe,Si-O-Si in the film was increased.Addition of TEOS increased the density of the reaction sites of condensation and modified BMBSE films in terms of compactness and anti-corrosion performance at room and higher temperatures.