【作者】 王淑梅；

【导师】 戴红旗；

【作者基本信息】 南京林业大学 ， 制浆造纸工程， 2013， 博士

【摘要】 二氧化氯漂白的纸浆白度高、强度好，废水对环境的污染较小，因此国内一些大型的制浆厂已经采用二氧化氯漂白技术，逐渐代替传统漂白，但二氧化氯对设备的腐蚀问题是影响该技术推广的主要原因。目前在二氧化氯防腐蚀方面，主要是从选择材料的角度来防止设备腐蚀，钛材和玻璃钢等是用的较多的材料，但钛成本高，玻璃钢在设备中的应用又有一定的局限；国内外对二氧化氯制备和漂白过程中设备的腐蚀性，虽有一定研究报导，但并没有系统地分析，大多数企业对其原因方面并不清楚，因此本论文针对常用不锈钢和钛在二氧化氯溶液中的腐蚀性能和机理进行了研究。首先采用挂片浸泡测试对普通材料304不锈钢在二氧化氯溶液中的腐蚀形貌进行分析，判断304不锈钢在二氧化氯中的腐蚀特性，利用重量法和深度法对304不锈钢在二氧化氯中的腐蚀性能做出定量评价，通过电化学测试方法分析304不锈钢在二氧化氯溶液中的动力学性能，得到304不锈钢腐蚀速率与二氧化氯溶液浓度呈指数递增关系，与pH呈幂函数递减关系。研究表明，304不锈钢在60℃、pH为4、8g/L和10g/L，60℃、pH为2、4g/L和8g/L，60℃、pH为6的8g/L二氧化氯溶液中，耐蚀性差，不可用于二氧化氯的相关制备和漂白中设备上，电化学性能方面304不锈钢在20℃、碱性的二氧化氯溶液中具有钝化的趋势，但随着浓度、温度、酸性的增强，304不锈钢的钝化电位和钝化电流密度都增大，表现出不易钝化甚至活性溶解的趋势。接着采用挂片浸泡法和电化学方法对含有少量钼元素的316L不锈钢在二氧化氯溶液中的腐蚀形貌、腐蚀特性、腐蚀速率、电化学腐蚀性能等方面进行了详细的分析和研究，总结了316L不锈钢在不同二氧化氯溶液中的腐蚀规律；316L不锈钢腐蚀速率与浓度之间存在指数关系，随着二氧化氯溶液浓度的增大，腐蚀速率增加；与pH之间存在幂函数关系，随着pH增大，腐蚀速率降低；溶液中的ClO2、ClO3-、ClO2-等氧化剂的反应活性由于温度的升高而增强，使316L不锈钢腐蚀速率增加；316L不锈钢在60℃、pH为4、浓度8g/L、10g/L，60℃、pH为2、4g/L和8g/L时属于不耐蚀金属外，在其它研究的工艺下316L不锈钢属于耐蚀和尚耐蚀系列。316L不锈钢除了在碱性的二氧化氯溶液中具有钝化的趋势，在低浓、低温的酸性条件下也具有钝化的趋势。针对耐蚀的钛进行了挂片浸泡和电化学测试研究，分析钛在不同二氧化氯溶液中的腐蚀性能，得出其在二氧化氯溶液中的腐蚀速率，研究钛在二氧化氯溶液中的电化学性能，总结其耐蚀的的特点。浓度升高、pH减小、温度升高使钛的腐蚀速度增加，除了在60℃、浓度为8g/L和10g/L、pH小于4，属于尚耐蚀外，其它条件下都属于耐蚀系列；钛材在二氧化氯溶液中表现出较好的钝化特性，但在高浓、酸性、高温条件下致钝电流密度增大或致钝电位升高，致钝相比较有些困难。基于钛的耐蚀是由于其表面有一层致密氧化保护膜的原因，对304不锈钢和316L不锈钢进行预钝化处理，使其表面预先具有致密的氧化膜，因此首先进行钝化剂的优化选择，确定了30%硝酸溶液和10mol/L硫酸+20g/L硝酸钾混合液两种无机钝化剂，利用蓝点检测法和电镜分析膜的形貌，以及通过钝化后都在3%NaCl溶液中的抗点蚀性能分析，304不锈钢和316L不锈钢在25℃的30%硝酸溶液中钝化30min时所需钝化时间短，钝化温度低，形成的钝化膜致密，抗点蚀能力强，25℃、30%硝酸溶液中钝化30min是不锈钢最佳的预处理工艺。从腐蚀形貌观察和腐蚀速率测试表明，钝化处理的304不锈钢、316L不锈钢在二氧化氯溶液中随着浓度、温度升高、pH值的减小，腐蚀性增加，不锈钢经钝化处理后比未钝化前在二氧化氯溶液中抗腐蚀能力增强，304不锈钢在pH为4、温度为60℃、浓度为10g/L时腐蚀电流密度降幅达到50%，316L不锈钢降幅可达到75%，降幅最大，其它条件下不锈钢的腐蚀速率都有不同程度的下降；钝化316L不锈钢在二氧化氯溶液中的腐蚀表现出孔蚀的特征。从微观动力学角度出发，经阻抗谱测试分析，不锈钢预处理前后在二氧化氯溶液中，在高频区和低频区各有一段容抗弧，且钝化后的不锈钢的容抗弧半径大于未钝化的，容抗弧圆心偏离实轴，存在一定的弥散效应。除了在8g/L，pH为10钝化的304不锈钢在低频区未出现“扩散尾”外，其余条件下在低频区显示出有扩散层厚度的扩散阻抗，即表现出Warburg阻抗特征，表明腐蚀过程后期由电化学控制转化为扩散控制。钝化316L不锈钢在4g/L、pH为4和10、20℃，8g/L、pH为10、20℃，pH为4、4g/L和8g/L、60℃二氧化氯溶液，以及未钝化316L不锈钢在4g/L、pH为4和10、60℃二氧化氯溶液中在低频区出现“扩散尾”，表现出Warburg阻抗特征。最后对各金属的腐蚀性能进行综合分析，得到在pH为4的二氧化氯溶液中，各金属的耐蚀性为：钛材>钝化处理的316L不锈钢>钝化处理的304不锈钢>316L不锈钢>304不锈钢；304不锈钢经钝化处理后在低浓、低温的二氧化氯溶液中有一定的抗蚀能力，在高浓、高温、酸性的二氧化氯溶液中，钝化后的304不锈钢腐蚀仍较严重。316L不锈钢经钝化处理后在高温、pH为2的二氧化氯溶液中腐蚀较严重。建议在工业设备材料使用上，在较低温度，酸性较弱的二氧化氯溶液中，钝化后的不锈钢可代替钛材使用，在强酸性和高温的二氧化氯溶液中，钛材目前还不能被不锈钢代替。更多还原

【Abstract】 Pulp bleached by chlorine dioxide have higher brightness and better strength, with lessoutlet water pollution to the environment. Some of pulp mills are gradually adopting chlorinedioxide bleaching instead of traditional ways, and some larger pulp mills have adopted chlorinedioxide for bleaching. However, the corrosion of chlorine dioxide to equipment is a criticalbarrier of its popularity. In terms of anti-corrosion of chlorine dioxide, choosing proper materialslike titanium and glass reinforced plastics (GRP) is a main method of anti-corrosion. Yet titaniumis high-cost while GRP have some limitations in application. Some of domestic and overseasresearchers have engaged in chlorine dioxide preparation and corrosion to equipment during theprocess of bleaching, but systematic analysis of them is less. To make its causes clear toenterprises, this paper did a research on the performance and mechanism of commonly usedstainless steel and titanium in chlorine dioxide solution.At first, soak test is used to analyze the corrosion morphology of304stainless steel whichis a common material in chlorine dioxide solution to detect its property of corrosion in thesolution, a quantitative evaluation is made with gravimetric method and depth method, anddynamics performance is analyzed with electrochemical test method. After data-analysis, theresults suggest that the corrosive rate of304stainless steel is an exponential relationship withchlorine dioxide solution concentration, a power function relationship with pH; the research oftechnology, the corrosion resistance of304stainless steel is poor in chlorine dioxide solutionwith60℃, pH4,8g/L and10g/L, that with60℃, pH2,4g/L and8g/L, and that with60℃, pH6,8g/L, thus it can’t be application to chlorine dioxide preparation or equipment for bleaching; theelectrochemical performance of304-stainless-steel tend to be passivated in the alkaline solutionof chlorine dioxide with20℃; yet the passivation potential and current density of304stainlesssteel increase with the augmentation of the concentration, temperature and acidity and it tends tobe difficult to passivate and even active dissolution.Following this step, soak test and electrochemical test method are employed for analysis ofcorrosion morphology, corrosive property, corrosive rate, electrochemical corrosion performanceand so on of316L stainless steel with a small amount of molybdenum in chlorine dioxidesolution. Then the corrosion law of316L stainless steel in different chlorine dioxide solutions hasbeen gotten. The corrosive rate of316L stainless steel is an exponential relationship with chlorinedioxide solution concentration—corrosive rate becomes higher with the increase of itsconcentration; there is a power function relationship between rate and pH—the corrosive ratebecomes lower with the increase of its pH; the reactivity of some oxidizers in solution like ClO2, ClO3-and ClO2-enhances with higher temperature, leading to higher corrosive rate of316Lstainless steel; despite the fact that316L stainless steel belongs to a kind of corrosion resistantmetal with the condition of60℃, pH4,8g/L and10g/L, and that of60℃, pH2,4g/L and8g/L, itis a prospective anti-corrosion material in other technology;316L stainless steel has the trend ofthe passivation not only in alkaline chlorine dioxide solution but also in the acidic conditions oflow concentration and low temperature.In addition, the corrosion resistant titanium is analyzed using soak test and electrochemicaltest method. The corrosive rate of titanium in chlorine dioxide solution has been gotten byanalyzing the corrosive property of titanium in different chlorine dioxide solutions; it also studiesthe corrosion resistant property by analyzing the electrochemical performance of titanium inchlorine dioxide solution. Higher concentration, lower pH and higher temperature result in highercorrosive rate; under the condition of60℃,8g/L and10g/L, and pH <4it is a prospectiveanti-corrosion material, it belongs to an anti-corrosion material in other situations. Titaniumperforms better in passivation in chlorine dioxide solution, but passivation under the condition ofhigh concentration, acid and high temperature becomes relatively more difficult when initiatingpassive current density or initiating passive potential increases.The corrosion resistance of titanium is due to a layer of dense oxidized protective film. Toensure the existence of dense oxidized protective film in the pre-passivation of304stainless steeland316L-stainless-steel, optimization selection of passivator is in the first place. Afterconfirming the usage of two kinds of inorganic passivators—salpeter solution with theconcentration of30%and the mixed liquor of sulfuric acid with10mol/L and potassium nitratewith20g/L, this paper studies the morphology of film through blue-point test and electronmicroscope and analyzes the resistance to pitting corrosion in3%NaCl solution after passivating.304stainless steel and316L stainless steel spend less time, lower temperature on passivation andthe passive film formed tends to be tenser and stronger in pitting corrosion resistance afterpassivating for30minutes in the30%salpeter solution with25℃, thus such a condition is thebest pre-treatment technology of stainless-steel. The analysis of corrosion morphology andcorrosion rate suggests that the passivated304stainless steel and316L stainless steel in chlorinedioxide solution have stronger corrosion with the increase of concentration and temperaturetogether with the decrease of pH; stainless-steel in chlorine dioxide solution has stronger abilityto resist corrosion after passivation than before.304stainless steel, under the condition of60℃,pH4and10g/L, corrosion current density reduces to50%while316L stainless steel reduces to75%as a maximum with the corrosive rate has different decrease in other conditions; thecorrosion of the passivated316L stainless steel in chlorine dioxide solution appears thecharacteristic of pitting.From the perspective of micro-kinetics, analyzed by EIS, stainless steel in chlorine dioxidesolution before and after preprocessing present respectively a capacitive reactance arc both inhigh and low frequency regions, and the radius of capacitive reactance arc of the passivatedstainless steel is bigger than that of the un-passiveted with the centre of a circle deviating from real axis similar to dispersion effect. In spite of the situation that the passivated304stainless steelof8g/L and pH10appears no expanded-tail in low frequency region, diffusion impedance with adiffusion layer thickness appears in low frequency region under other conditions. In other words,it appears an impedance characteristic of Warburg, which suggests that it transfers fromelectrochemical control to diffusion control in the later period of corrosion. The passivated316Lstainless steel in chlorine dioxide solution with condition of4g/L, pH4&10,20℃, that of8g/L,pH10,20℃and that of pH4,4g/L&8g/L,60℃appears the expanded-tail in low frequencyregion;so does the un-passiveted316L stainless steel with the condition of4g/L、pH4&10,60℃,emerging the impedance characteristic of Warburg.At last, when it comes to the corrosion property of every kind of metal in chlorine dioxidesolution of pH4, titanium> the passivated316L stainless steel> the passivated304stainlesssteel>316L stainless steel>304stainless steel; the passivated304stainless steel presents someresistance to corrosion in chlorine dioxide solution in low concentration and low temperature, butit corrodes seriously in acidic chlorine dioxide solution in high concentration and hightemperature; the passivated316L stainless steel also corrodes seriously in acidic chlorine dioxidesolution of pH2in high temperature. It is suggested that in using industrial equipment materialthe passivated stainless steel can take place of titanium in chlorine dioxide solution with weakcation exchange while it does not work in chlorine dioxide solution with strong cation exchangeand high temperature.更多还原