Fouling And Corrosion Properties Of Geothermal Water On Sio₂ Films Coated On Substrates Of Copper Samples With Liquid Phase Deposition

Geothermal water is a new source of energy, owning lots of advantages, like widespread, low cost, direct utilization and little environment pollution. Fouling and corrosion emerged during the use process was detrimental, resulting in the decrease of heat t ransfer e fficiency an d w ater yield, t he i ncrease o f en ergy a nd m aterial consumption, a nd pot ential s afety d anger. A t present, t he m ethods us ed b y t he researchers to mitigate fouling and corrosion focused on a dding chemical inhibitors into w ater or c oated t he s urfaces w ith or ganic c oatings. B ut t he e nvironmental pollution was caused and the thermal resistance was increased, furthermore, coatings were e asy t o d eteriorate w ith ag eing. T herefore, f urther s tudy w as n ecessary f or finding new methods of anti-fouling and anti-corrosion.Research showed that the adhesion of fouling could be greatly affected by the surface energy of heat transfer surface, and the attachment of fouling could be largely reduced with the decrease of surface energy. So, in this paper, SiO₂ thin film with the micro nanometer thickness was prepared on copper substrate samples by Liquid Phase Deposition method to reduce the surface energy for anti-fouling and anti-corrosion of geothermal w ater i n h eat ex changers. T he effect o f t hin f ilm o n t he h eat t ransfer efficiency could b e n eglected. In addition, w ith t he pr operties of good c orrosion resistance and abrasive performance of SiO₂ thin film, the effect of anti-corrosion could be reached besides anti-fouling.In this paper, liquid phase deposition rate of SiO₂ thin film as a function of the concentrations of f luosilicate, bor ic a cid, t emperature a nd t ime were i nvestigated. Surface r oughness, m orphology, c omposition, t hickness a nd s urface e nergy were measured and characterized, and optimal deposition conditions were obtained. The static s imulation f ouling e xperiment w as c arried out us ing s upersaturated C aCO3 solution prepared by NaHCO3 and anhydrous CaCl2. Fouling deposition rate and its morphology under different temperatures and time were studied, and it showed that the anti-fouling property of the samples modified with SiO₂ thin film was better than the unt reated and pol ished s amples. T he anti-corrosion t est w as conducted b y immersing samples in real geothermal water, and the dependence of etching rate on different t emperature and t ime w ere s tudied, a s w ell a s t he m orphology a nd composition of t he c orrosive pr oducts. T he r esults s howed t hat e lectrochemical corrosion occurred and general corrosion was detected, and oxygenated compounds of copper were the main corrosive products. It was also found that passive film formed on the surface of blank samples could protect the copper from further corrosion, and its anti-corrosion performance was better than the samples modified by SiO₂ thin film.