【作者】 卢建树；

【导师】 毛志远； 张九渊；

【作者基本信息】 浙江大学 ， 金属材料与热处理， 2002， 博士

【摘要】 超临界水氧化(supercritical water oxidation，简称SCWO)是一项新兴的环境保护技术。它是利用超临界水(＞374.2℃和22.1MPa)能与有机物和氧气混溶的特性，在短时间内彻底销毁有机污染物。特别适合于处理高浓度的和难降解的有机废水。这项技术工业应用的关键是解决高温高压氧化性水溶液中材料的腐蚀问题。本文通过建立SCWO实验装置，对六种金属材料(1Cr18Ni9Ti、316、U2、Sanicro28四种不同级别的不锈钢，Ni825镍基合金，工业纯钛)在六种不同的SCWO介质(纯水，苯酚分解物，十二烷基苯磺酸钠分解物，对胺基苯酚分解物，敌百虫分解物，毒死蜱分解物)中的耐腐蚀性能和腐蚀规律进行了研究。 所建立的SCWO腐蚀试验系统由进料部分、预热部分、反应部分、冷却部分、减压和排放部分、检测和控制部分六个子系统组成。腐蚀试样设置在反应器内。系统连续进料，连续排放，可在25MPa和450℃以下长期连续运转。其中，反应器的V形槽密封结构设计，并配用膨胀石墨填充的不锈钢缠绕密封垫，使反应器易于装拆腐蚀试样。 腐蚀试验采取试样在不同的SCWO介质中暴露一定时间，用称重法测定腐蚀速率，用光学显微镜和SEM作腐蚀形貌分析，用EDAX测定腐蚀产物化学成份，用XRD测定腐蚀产物的相组成和结构，用XPS分析腐蚀试样表面化学成份。通过比较试验结果，分清对合金腐蚀起作用的介质因素，为确定腐蚀机理提供重要资料。 腐蚀试验结果表明，材料在SCWO系统中的腐蚀与所分解的有机物种类有关。在分解苯酚的SCWO介质中，所有试验材料的均匀腐蚀速率度都小于0.1mm／a。但是，1Cr18Ni9Ti和316不锈钢有孔蚀发生，而Sanicro28高级不锈钢、Ni825镍基合金及工业纯钛没有腐蚀迹象。在分解十二烷基苯磺酸钠(含S有机物)和对胺基苯酚(含N有机物)的SCWO介质中，不锈钢和镍基合金发生了快速腐蚀，最大均匀腐蚀速度达每小时17微米；钛材仅发生表面氧化膜的变色。在分解敌百虫的SCWO介质中，1Cr18Ni9Ti的孔蚀速度达每小时1.5毫米；在分解毒死蜱(含S、N、Cl、P)的SCWO介质中，不锈钢、镍基合金、钛都发生了不同程度的均匀腐蚀和孔蚀。六种介质对合金的腐蚀性，由强到弱的次序是：毒死蜱＞敌百虫＞对胺基苯酚＞十二烷基苯磺酸钠＞苯酚＞纯水。 试验结果也表明，SCWO系统合金腐蚀与温度有关。150℃以下，基本上没有腐蚀，暴露后的试样光亮如新；150～250℃，不锈钢和镍基合金主要发生孔腐蚀等局部腐蚀，钛材依然没有腐蚀；250℃至临界温度，不锈钢和镍基合金发生过钝化腐蚀，均匀溶解和孔蚀同时发生，钛在300℃以上有轻微的腐蚀，且存在孔蚀倾向；在超临界温度分解含十二烷基苯磺酸钠和对胺基苯酚的SCWO介质中，合金的腐蚀有所减缓，但在分解毒死蜱的介质中，不锈钢和镍基合金的均匀腐蚀依然很快，这是由于金属氯化物的高温挥发性所致，或者是高温磷酸的特殊腐蚀性而造成的。 工业纯钛在SCWO分解各种有机物的介质中表现出优良的耐腐蚀性。在300～450℃分解毒死蜱的试验中，钛试样表面由于腐蚀产物覆盖有少量增重，增重速度随时间延长而减小。经XRD测定，腐蚀产物主相是Ti5O4(PO4)4。腐蚀产物下已有孔蚀发生。浙江大学博士学位论文 二 OO一年十月 利用修正的HKF模型，推算出高温高压溶液中离于的热力学参数，取用相关物质的最新热力学数据，对决定 Fe－Cr－Ni合金和 Ti材耐腐蚀性的两个主要氧化物一CrzO。和n。一的热力学稳定性进行推算。计算结果表明，在 200 OC以上的高温氧化性水溶液中，Cr。O。会被氧化成水溶性的HCrO4飞在300℃以上的含氯高温水介质中，TIO。也会被氯离子络合而溶解。这意味着 Fe（rNi合金和 Ti的表面保护膜在高温氧化性水介质中是热力学不稳定的，可能发主腐蚀。这一热力学预测是与本实验结果及己知的事实相符的。 根据SCWO系统合金腐蚀与介质种类有关、与温度有关、以及均匀腐蚀和孔蚀常伴随出现这三个特征，由此认为SCWO系统合金腐蚀的机理是：临界温度以下是氧气作用下的氧化物过钝化溶解并伴随阴离子的络合溶解和金属基体的电化学溶解，超临界温度则发生过钝化稠密气态化学腐蚀及沉积层下的电化学腐蚀。用化学反应表示为：驱动力（阴极过程）： 氧气还原：O。＋4H”＋4e－ZHzO 质子还原：ZH”＋Ze－H。溶解： 氧化物氧化溶解：Cr。O。＋3O。＋4H。O＝4HCrO。＋4H 氧化物酸溶解：MxOy＋Zy H”＝XMZy／h＋yHZO 氧化物络合溶解：MxO，＋Zy H“＋Zy L＝xML沙x＋yHzO 金属电化学溶解：M－ne－M’络合：M’”十 nL一卜Ln回 本研究的创新之处在于：建立国内第一套用子材料腐蚀研究的连续式SCWO试验装置，反应器的密封结构有特色；选择不同化学组成的有机物作为SCWO分解试验的目标污染物，比较各分解介质中材料的腐蚀速度及腐蚀特点，从而搞清影响材料腐蚀的介质因素；根据不同温度下分解毒死婢的腐蚀试验结果，发现超临界温度下不锈钢和镍基合金出现快速腐蚀，通过分析得出腐蚀是由于氯化物的高温挥发所致；发现钛在300℃以上分解毒死婢的介质中有腐蚀?更多还原

【Abstract】 Supercritical water oxidation (SCWO) is a relatively new technology in environment protection. It utilizes the special properties of supercritical water (T>374.2℃, P>22.1MPa) that all organic and most gases can be dissolved in it. Nearly complete destruction of hazardous wastes in a few minutes can be achieved by SCWO. However, corrosion of materials of the equipment in SCWO system is a major problem that hinders the widespread application of the technology.To study the corrosion of materials in SCWO conditions, a continuous SCWO system which can be operated for long time at supercritical conditions (usually at 25MPa and in less than 450 "C) has been built. Six metallic materials (four stainless steels :!Crl8Ni9Ti, 316, U2, and Sanicro28; one nickel base alloy N1825, and one commercially pure titanium)were exposed in six types of SCWO mediums (pure water, and SCWO destroying phenol, organic containing S, organic containing N, organic containing Cl and P, organic containing S> N, CK and P) for as short as a few hours to as long as one week. Metal samples were positioned in the reactor of the system which is specially designed for frequent open and close.Corrosion rates of the materials were measured by gravimetric method. Corrosion morphology and localized corrosion were revealed by optical microscope and SEM. Compositions of corrosion products were analyzed by ED AX and XRD.Corrosion test of the six materials in high temperature pure water showed that !Crl8Ni9Ti and U2 stainless steels were attacked in supercritical (3 92 ℃) water.The results show that corrosion performance of the materials in SCWO depends on the types of organic being treated. In destroying phenol (CeHeO) , the general corrosion rates of all the six materials were less than 0.1 mm/a. Sanicro28 stainless steel and Ni825 nickel base alloy were only slightly corroded on superficial level while !Crl8Ni9Ti and 316 stainless steels showed pit corrosion. Therefore, Sanicro28 and Ni825 can be used as corrosion resistant materials in such SCWO environment. However, in SCWO destroying organic containing S (sodium dodecyl sulphonate, CpHasCeHsSOaNa) and organic containing N (n-amine phenol, Ce^N^OH), all the materials except Ti suffered heavy general corrosion and pit corrosion in near critical temperature region. Corrosion rate as high as 17 u m/h and 5 u m/h was found respectively for !Crl8Ni9Ti and Sanicro28. In SCWO destroying trichlorphon (C4H8O4PCl3) and chlorpyrifos (CgHnOSPNCla), serious pitting corrosion (as high as 1.5 mm/h of penetration rate) and general corrosion were experienced for the stainless steels and nickel base alloy. Ti also showed being corroded in the SCWO destroying chlorpyrifos.The results also show that corrosion of the materials are highly temperature dependent. In SCWO destroying sodium dodecyl sulphonate and n-amine phenol, general corrosion of stainless steels were closely related with temperature, being heavy corrosion in near critical temperature, moderate corrosion in lower and upper temperature, and light corrosion in less than 300℃ and supercritical temperature. However, in SCWO medium destroying chlorpyrifos, the general corrosion rates of 316 stainless steel and Ni825 nickel base alloy go higher as temperature rise from 150to 300, and even higher rates at supercritical temperature (450) were observed. Pit corrosions of the two alloys also show temperature related: below 150℃, no pit was initiated; at 150~250℃, pitting is the main form of the corrosion and deep pits were developed; at temperature higher than 250℃, shallow pits were formed due to increasing higher general dissolution.At temperature higher than 300 in SCWO destroying chlorpyrifos, especially around critical temperature, titanium samples were covered with corrosion product with microscopically rough surface. X ray diffraction analysis showed that the corrosion product consists of titanium oxy- phosphates and titanium oxide in which TisO4(PO4)4 is the main phase. This means that the corrosion is caused by phosphoric acid. Pit co更多还原