在Cl~-体系中加入NO_3~-或NO_2~-对奥氏体不锈钢裂缝内化学状态的影响

用模拟闭塞电池研究1Cr18Ni9Ti奥氏体不锈钢在Cl~-+NO_3~-(或NO_2~-)溶液中闭塞区内化学和电化学状态的变化。当外部溶液中NO_3~-或NO_2~-达到一定浓度时,闭塞区内pH下降比在单纯Cl~-溶液中缓慢,并且趋于一极限值(pH(?)2)后,即不再下降。裂尖溶液内Cl~-与NO_3~-克当量比例和外部主溶液接近,但裂尖溶液变浓直到饱和。当1法拉第电量通过闭塞区时,大约有0.5～0.7克当量的Cl~-+NO_3~-迁入闭塞区。NO_2~-迁入裂尖后与H~+和金属离子反应而消耗。溶液中加入不同浓度NO_3~-或NO_2~-后,使破裂电位变为更正_1裂尖处于钝态,表明NO_3~-和NO_2~-均有缓蚀作用。     

模拟混凝土孔隙液中钢筋表面膜组成与腐蚀行为的关联

采用XPS分析钢筋经模拟混凝土孔隙液浸泡后表面膜的化学组成,结合线性极化法和动电位扫描阳极极化曲线测试,研究钢筋在模拟混凝土孔隙液中表面膜化学组成与腐蚀电化学行为的关联.结果表明:钢筋在纯模拟液中处于钝化状态.在含Cl和不同pH值的模拟混凝土孔隙液中,随着Cl~-浓度的增加和pH值的降低,钢筋的腐蚀电位负移,电流密度增大;钢筋表面钝化膜Fe~(2+)的含量增加,Fe~(3+)的含量减少.当模拟液中外加Cl~-浓度达0.6mol/L或pH值降至11.31时,钢筋表面不发生钝化,但加入0.24mol/L NaNO_2缓蚀剂后又可使钢筋钝化从而抑制腐蚀.     

混凝土结构中NO_2~-的不均匀性对钢筋宏电池腐蚀行为的影响

基于宏电池腐蚀理论,将阴极区钢筋和阳极区钢筋分别浇筑成两个独立的砂浆试块,并用导线将其连接成循环电路,通过断开和连接电路来控制钢筋的微电池腐蚀和宏电池腐蚀,再将不同浓度的NO_2~-溶液分别添加到阴极试块和阳极试块中以模拟其渗透过程,通过比较NO_2~-作用前后阴阳极钢筋之间宏电池腐蚀电流的大小,来评价阴阳极钢筋表面NO_2~-的不均匀性对钢筋宏电池腐蚀行为的影响。结果表明:当NO_2~-作用于处于腐蚀状态的阳极钢筋时,能够增加阳极钢筋的极化阻抗,减少阴阳极钢筋间的宏电池腐蚀电位差,降低宏电池腐蚀电流,从而有效抑制宏电池腐蚀;当NO_2~-主要作用于处于腐蚀状态的阴极钢筋时,阴阳极钢筋间的宏电池电位差的增大易使宏电池腐蚀电流增加,存在加速钢筋宏电池腐蚀的危险。     

碳化对模拟混凝土孔溶液中HRB335钢腐蚀行为的影响

应用电化学阻抗谱、循环伏安与动电位极化等方法研究了碳化后模拟混凝土孔溶液pH值的变化对钢筋腐蚀电化学行为的影响.结果表明,随着pH值的下降钢筋表面钝化膜的稳定性与耐蚀性不同程度地降低.当模拟液pH值为12.5与11.5时,钝化膜的稳定性处于因pH值降低导致的钝化膜溶解与表面沉积物CaCO3或含钙氧化物CaFe2O4等耐...     

高强钢筋在混凝土环境中的腐蚀行为

通过电化学试验研究了HPB300、HRB400E、HRB500E三种钢筋在混凝土模拟空隙液中的腐蚀行为,并研究了Cl~-浓度(0.04 mol/L～0.08 mol/L)对这三种钢筋耐蚀性的影响。结果表明:在模拟孔隙液中,三种钢筋均能达到稳定的钝化状态;随着Cl~-的加入,钢筋的腐蚀速率均有所增大;由于HRB500E钢筋含有更多的Cr、Ni、V等合金元素,其晶粒度最小,耐蚀性最好。     

Cl~-对X80管线钢在HCO_3~-溶液中的电化学行为影响

采用动电位极化曲线、电化学阻抗谱(EIS)及SEM研究了X80管线钢在NaHCO_3/NaCl溶液中的电化学腐蚀行为。结果表明,X80管线钢在HCO_3~-/Cl~-溶液体系中,随着Cl~-浓度增加,钝化区逐渐变窄,点蚀电位逐渐降低,维钝电流密度逐渐增加,耐蚀性降低。在HCO_3~-/Cl~-溶液体系中,Cl~-与HCO__3~-在金属表面产生竞争吸附表现为两种效应:一种是HCO_3~-的钝化效应,该效应使钝化膜增厚,阳极电流密度下降,从而金属保持钝性状态;另一种是Cl的侵蚀效应,该效应使钝化膜变薄或离子电导增大,阳极电流密度增大,金属失去钝性。用点缺陷模型解释了钝化膜的生成和破裂过程。X80管线钢的耐蚀性与HCO_3~-和Cl~-的浓度比有关,该比值越大,则钝化性能越强;Cl~-浓度越大,则活性越强。     

不锈钢在模拟混凝土孔隙液中的腐蚀行为研究

利用动电位扫描和交流阻抗法研究了普通碳钢与不锈钢在模拟混凝土孔隙溶液中的腐蚀行为及其差别，以及Cl-浓度、溶液pH值对腐蚀行为的影响，从而探讨了不锈钢取代碳钢作为混凝土钢筋骨架的可能性.结果表明：即便混凝土碳化导致孔隙液pH值下降后，氯离子对不锈钢的影响仍然较小，钝化膜致密完好，而普通碳钢的耐蚀性明显变差，钝化膜极易被氯离子侵蚀而破坏.     

钢筋在混凝土孔隙液中的腐蚀行为研究

以建筑工程用8235钢筋为对象,研究了其在混凝土孔隙液中的腐蚀行为,分析了氯离子浓度、溶液pH值以及缓蚀剂对钢筋表面钝化膜的影响。结果表明:随着混凝土孔隙液中氯离子含量的增加和pH值的降低,溶液的极化电阻降低、腐蚀电流密度增大,削弱了钝化膜效果。另外,NaNO2缓蚀剂的加入有效的保护了钝化膜,起到了较好的抗腐蚀效果。     

钢筋在混凝土孔隙液中的腐蚀行为研究

以建筑工程用8235钢筋为对象,研究了其在混凝土孔隙液中的腐蚀行为,分析了氯离子浓度、溶液pH值以及缓蚀剂对钢筋表面钝化膜的影响。结果表明:随着混凝土孔隙液中氯离子含量的增加和pH值的降低,溶液的极化电阻降低、腐蚀电流密度增大,削弱了钝化膜效果。另外,NaNO2缓蚀剂的加入有效的保护了钝化膜,起到了较好的抗腐蚀效果。     

No_3~-对OCr18Ni9Ti钢在NaCl溶液中闭塞区腐蚀的抑制作用及其机理

采用模拟闭塞区溶液研究NO_3~-对氯化钠溶液中0Cr18Ni9Ti钢的缓蚀作用及机理。结果表明,随着(NO_3~-)_(bulk)(主体溶液中NO_3~-的浓度)增高,闭塞区内金属的腐蚀速率减小,腐蚀电位向正方向移动。50℃时,若[NO_3~-]_(bulk)≥0.025或90℃时[NO_3~-]_(bulk)≥0.2M,闭塞区内金属由活态转变为钝态。当50℃、[NO_3~-]_(bulk)≥0.3M或90℃、[NO_3~-]_(bulk)≥0.5M时,其动电位极化曲线上的钝化区增宽、致钝电流密度和维钝电流密度变小,缓蚀率高达90％以上。因此,在主体溶液中加入适量NO_3~-能导致闭塞区钝化,从而对孔蚀、缝隙腐蚀及应力腐蚀破裂起缓蚀作用。     

Detection and identification of concrete cracking during corrosion of reinforced concrete by acoustic emission coupled to the electrochemical techniques

The tenacious oxide passive film, which is formed on the surface of embedded reinforcing steel under high alkaline condition of concrete, protects the steel against corrosion. However, the condition of passivity may be destroyed, due to processes such as leaking out of fluids from concrete, atmospheric carbonation or through the uptake of chloride ions. Passive steel reinforcing corrosion induced by chloride is a well-known problem, especially where chloride-containing admixtures or chloride contaminated aggregate are incorporated into the concrete. The objective of this work is on one hand to study the effect of chloride ions on passivity breakdown of steel, respectively, in simulated concrete pore solution (SCP) and in concrete reinforcement, and on the other hand to reproduce the carbonation phenomena by applying to the concrete samples a heating–cooling cycles. In this context, the acoustic emission coupled to the electrochemical techniques (potentiodynamic and electrochemical impedance spectroscopy (EIS)) are used.

The results show clearly that [Cl⁻]/[OH⁻] ratio of 0.6 is the critical threshold where the depassivation set-up can be initiated. In addition, the carbonation process is very aggressive with chloride ions and shows a perfect correlation with acoustic emission evolution.

A physical model of the reinforcement/electrolyte interface is proposed to describe the behavior of the reinforcement against corrosion in chloride solution.     

Korrosionsverhalten von unlegierten Stählen bei Berührung mit Baustoffen

Corrosion of unalloyed steels in contact with building materials Embedded in concrete no corrosion of steel occurs even in the presence of water as long as the water in the concrete pores is alkaline enough to maintain the passivity of iron. The passivity can be destroyed by chloride-ions, which may be components of concrete additives. Another possible reason for loss of passivity is the decrease of alkalinity due to the reaction with carbon dioxide. In contact with non alkaline building materials as e.g. insulating material corrosion is guided mainly by the access of water. A very high risk of corrosion damage occurs due to a galvanic element when steel in contact with non alkaline material is connected by metallic and electrolytic conductor with steel in concrete.     

水性硅酸盐溶胶型涂料对钢筋混凝土耐久性的影响

分析了钢筋混凝土腐蚀破坏的主要原因是钢筋腐蚀导致的混凝土胀裂.为保护钢筋混凝土研制了一种水性硅酸盐溶胶型涂料并研究了该涂料对混凝土内置网筋的保护作用及经涂料涂覆的混凝土氯离子渗透性和高压渗水性能.结果表明,涂履水性硅酸盐溶胶型涂料可明显提高与改善混凝土的耐久性.     

Corrosion and Corrosion Inhibition of Reinforcing Steel: II. Embedded In Concrete

Abstract

Reinforcing steel, whether embedded in Portland concrete or Portland cement-blast furnace slag concrete and mixed with distilled or tap water, becomes passivated. On the other hand, when the concrete is mixed with sea water, the steel corrodes severely, and when Helwan mineral water is used for mixing, a borderline condition is obtained. Portland cement-blast furnace slag concrete had poorer corrosion resistance compared with ordinary Portland cement concrete.

Steel passivity is not impaired when Portland cement concrete or Portland cement-blast furnace slag concrete is admixed with up to 8% of sulphates. However, when cement extract is used, the passivity is impaired when as little as 0·2% of sodium sulphate is added.

Additions of some anodic inhibitors such as benzoate, chromate, nitrite, phosphate and stearate to a corrosive concrete medium are efficient in preventing the corrosion of reinforcing steel. The critical concentration for inhibition is higher in the case of Portland cement-blast furnace slag concrete than that of Portland cement concrete. Coating the steel with Portland cement slurry alone or Portland cement slurry containing inhibitors improves the corrosion resistance of steel to some extent but does not inhibit the corrosion in strong attacking media.     

丙烯酸系乳胶用于钢筋混凝土的防腐蚀研究

用电化学阻抗谱研究了丙烯酸系乳胶作为混凝土添加剂或钢筋表面涂层时对钢筋腐蚀行为的影响,加速腐蚀试验结果表明混凝土中添加乳胶后能够延缓钢筋表面钝化层的破坏,而对混凝土的渗透性能影响不大,乳胶涂层能够显著减小钢筋腐蚀速率,涂层的存在改变了钢筋表面的腐蚀状态,在此基础上提出了改善钢筋混凝土抗蚀能力的措施。     

A study of steel rebars embedded in concrete during 65 years

Several experimental techniques were used to study the corrosion products formed on steel rebars embedded in concrete during 65 years. The research has the objective of understanding the stages of rusting of steel in concrete. Such understanding would provide information concerning the environmental conditions that produce rusting. It was found that rust was composed of two layers: an inner one composed mainly of non-stoichiometric magnetite and probably Ca and Al substituted magnetite firmly adhered to the substrate, and an outer one composed of α- and γ-iron oxyhydroxides, final steel corrosion products. The chemical and mechanical properties of steel rebars and the surrounding concrete were investigated in order to establish the causes of corrosion initiation which were the drop of the concrete pH due to a carbonation process and the loss of steel passivity.     

混凝土保护涂层抗氯离子渗透性研究

在NaCl溶液中对混凝土保护涂层进行干/湿循环加速腐蚀实验,用电化学循环极化法和高压渗水法对混凝土保护涂层的防护效果进行了研究,并将两种方法研究结果进行对比.结果表明：氯盐环境中,混凝土保护涂层可以有效提高混凝土的抗渗性,降低氯盐对钢筋的腐蚀破坏;循环极化测试法可用于研究钢筋钝化膜的溶解特性和钢筋的锈蚀趋势.      

Einflußgrößen der Fremdkathoden aus Bewehrungsstahl in Beton auf die Erdbodenkorrosion von Stahl

Factors influencing the activity of reinforcing steel as cathode on the soil corrosion of steel Factors influencing the corrosion cell established between steel/soil (anode) and reinforcing steel in concrete (cathode) were investigated in field tests extending up to 3 years. In all cases, the differences between the corrosion rates measured in the cell and under free corrosion conditions were higher than the equivalent cell current. This effect means an increase of the cathodic partial reaction by cell action (negative difference effect), and is related to better protecting layers in the case of free corrosion. As to the cathodes, the parameters of the concrete have nearly no effect. But galvanizing of the reinforcing steel has a strong influence on the cell action. Since the cell resistance is mainly controlled by the electrolyte resistance (ground resistance of the anodes) the changes in the polarization resistance of the cathodes can hardly influence the cell action. A decrease of cell currents due to galvanizing the reinforced steel is no doubt present, but the effect is too poor for proper protection against cell activities. Therefore, only conventional electrochemical methods or organic coatings on the reinforcing steel can be applied as protective measures.     

混凝土中氯离子的预防及处理

氯离子对混凝土结构的腐蚀已引起广泛重视，本文就目前对混凝土防腐蚀所采取的隔离、修补、钢筋保护、电化学除盐及阴极保护法的具体应用作了简要论述。