【作者】 刘玉；

【导师】 杜荣归；

【作者基本信息】 厦门大学 ， 物理化学， 2007， 硕士

【摘要】 钢筋腐蚀是严重威胁钢筋混凝土结构耐久性的首要因素,关系国计民生重大问题。混凝土中的钢筋是否发生腐蚀取决于维持其钝态的钢筋/混凝土界面环境条件,混凝土碳化和氯离子侵蚀是导致钢筋表面去钝化,引起腐蚀的主要原因。国际上钢筋腐蚀机理研究虽然较多,但许多问题仍未得到满意解决。本工作应用原位、半原位和非原位相结合方法,研究钢筋在模拟混凝土孔隙液中腐蚀行为和氯离子及pH值对钢筋去钝化的影响机制。(1)发展扫描微参比电极技术,结合极化曲线测试法,揭示了氯离子对钢筋腐蚀行为的影响机制,获得了引起钢筋腐蚀的氯离子临界浓度。钢筋在模拟混凝土孔隙液中的表面微区电位分布的测试表明,在氯离子侵蚀下,钢筋表面初始时存在多个互相竞争,此消彼长的腐蚀活性点,最终个别活性点发展成宏观腐蚀点,引起钢筋局部腐蚀。扫描微参比电极技术测试的引起钢筋腐蚀的氯离子临界浓度值比动电位扫描阳极极化曲线测试结果低,表明前者有更高灵敏性。(2)探明了钢筋在模拟混凝土孔隙液中钝化膜半导体特性与耐蚀性的关联,首次揭示了介质pH值和预钝化电位对钢筋钝化膜半导体特性的影响。钢筋在模拟混凝土孔隙液中形成的钝化膜呈现重掺杂非晶态n型半导体特性,氧空缺是其主要的施主形式。随着溶液pH值降低,钢筋表面氧化物发生部分溶解,钝化膜原有的晶格排列遭到破坏,导致更多氧空缺的出现,钝化膜的施主浓度增大,平衡平带电位负移,钝化膜趋向于不稳定,抗腐蚀能力减弱。对钢筋表面施加预钝化电位,会使生成的钝化膜具备更加规则的晶型,其组成也会发生相应变化,从而减少了钝化膜中的氧空缺浓度,提高了钢筋的耐蚀性。(3)应用XRD、XPS、SEM技术,初步探明了不同体系中钢筋钝化膜的形貌和组成及其碳化和氯离子侵蚀的影响作用。碳化导致钝化膜表面发生相对均匀的溶解,伴有难溶性腐蚀产物生成。氯离子可先通过缺陷穿透钝化膜,与铁基体发生反应,因此引起钢筋点腐蚀,腐蚀产物以可溶性盐为主。更多还原

【Abstract】 The corrosion of reinforcing steel is the main reason for the premature degradation of reinforced concrete structures, which concerns the national economy and the people’s livelihood. Whether or not the reinforcing steel in concrete maintains its passivity depends on the physical and chemical conditions at the steel/concrete interface. In general, the two major factors which cause the depassivation of reinforcing steel in concrete are carbonation and penetration of chloride ions. So far, many investigations have been carried out to explore the corrosion mechanism of reinforcing steel. However, there are still a lot of problems needing great effort to solve.In this work, many research methods including in-situ, semi-situ and ex-situ measurements were utilized to study on the corrosion behavior of reinforcing steel in simulated concrete pore solutions and the effects of chloride ions and pH of the solution on the steel depassivation. The progress of this work and the main results are as follows:(1) The scanning micro-reference electrode technique (SMRE) has been developed to study the mechanism of the steel corrosion induced by chloride ions and measure the chloride threshold concentration for the steel corrosion initiation in simulated concrete pore solutions. The potential distribution on the surface of the reinforcing steel in the simulated concrete pore solution reveals that there are a number of unstable micro-pitting nuclei on the steel surface in the solution with chloride ions. These active pits compete with each other and only a few of them can develop into real pitting corrosion. The chloride threshold concentration measured by SMRE is lower than the result obtained by the potentiodynamic anodic polarization, which shows that SMRE has higher sensitivity.(2) The semiconductor properties and relevant corrosion resistance of the passive film on the reinforcing steel surface in simulated concrete pore solutions were explored. The effects of pH of the solution and different film formation potentials on the semiconductor properties were also studied. The result shows that the films behave as heavily doped amorphous n-type semiconductors in which oxygen vacancies play the main role of donors. Along with the reduction of pH, the oxide film covering on the steel partly dissolves and the structure of the oxide crystal lattice changes, which result in higher oxygen vacancy concentration and more negative equilibrium flat potential. Accordingly the steel shows a higher tendency to corrode. Film formation potentials can change the component and structure of the film and reduce the oxygen vacancy concentration, thus strengthen the protection function of the film.(3) The surface physical and chemical properties of the reinforcing steel immersed in different simulated pore solutions and the effects of carbonation and chloride ions were investigated using XRD, XPS and SEM. Carbonation can make the film surface dissolve equably with indissolvable corrosion products depositing. However, chloride ions can penetrate the film through the surface defects and corrode the steel base, which turn off dissolvable corrosion products.更多还原