Knowledge Management System Of Institute of process engineering,CAS
碳钢在高温氧化性气氛条件下极易发生氧化性腐蚀反应，造成严重氧化烧损，不仅降低了碳钢的成材率和表面质量，而且造成资源和能源的极大浪费。为了降低碳钢高温氧化烧损，采用高温防护涂层是一种价格低廉并且操作简单的有效防护措施。玻璃涂层熔体能够对不锈钢基体进行有效的防护，取决于不锈钢中Cr元素在基体表面形成的Cr富集氧化物与玻璃涂层熔体的协同作用。由此反推，针对普通碳钢采用含Cr玻璃基涂层熔体对基体表面进行高温防护开展了大量研究工作。研究发现，在高温反应过程中，碳钢基体与玻璃基涂层熔体界面处同样可以形成完整的Cr富集层，结合玻璃熔体对提高钢基体抗高温氧化腐蚀性能具有重要作用，本文研制了含Cr玻璃基涂层熔体材料。研究了升温过程中Cr元素在玻璃熔体中的动态迁移及存在形态，阐明了高温氧化性氛围下含Cr玻璃基涂层熔体对普碳钢的高温防护机理。主要研究结果如下：（1）为了辅助含Cr玻璃基涂层熔体的设计，首先研究了几种典型碳钢和不锈钢的高温氧化行为；重点剖析了J55碳钢在800℃~1100℃温度区间内高温氧化传质扩散系数，研究了1vol%~15vol%氧含量范围内氧含量对J55碳钢氧化行为的作用关系；并证明了Cr2O3与玻璃基涂层熔体协同对420不锈钢（含铬12wt%~14wt%）的高温抗氧化腐蚀作用机制。（2）依据涂层材料与钢基体的工艺性能匹配性，及Cr元素在玻璃中低溶解性能设计原则，研制了组成为Al2O3-SiO2-K2O-Na2O-Cr2O3的含Cr玻璃基涂层熔体材料。玻璃基体的玻璃转化温度为730℃，热膨胀系数为8.0×10-6/K（30℃~600℃），玻璃基体材料中Cr元素的溶解量为0.52wt%~0.83wt%（900℃~1200℃）。（3）SEM-EDS研究表明，在20MnSiNb钢基体与玻璃基涂层熔体界面处形成Cr元素富集层。试验结果表明，Cr富集层与玻璃熔体的协同作用对20MnSiNb钢起到较好的高温防护效果，1050℃保温60 min烧损率降低86%，1000℃~1100℃保温120 min时烧损率降低幅度仍大于75%。900℃~1100℃温度区间内含Cr玻璃基涂层熔体明显降低了20MnSiNb钢样品的氧化反应速率常数，仅为空白样品的1/7~1/10，氧化反应表观活化能提高了近一倍，达到160.06 kJ/mol。又系统探明了不同Cr源及利用Na、Ti、Sn元素改变玻璃组成后的玻璃熔体对Cr元素在玻璃熔体中的迁移过程有显著的控制作用。（4）研究了Cr元素在Al2O3-SiO2-K2O-Na2O-Cr2O3玻璃熔体中存在形态和动态迁移过程。研究表明，温度对Cr元素在玻璃熔体中的扩散系数影响显著，从900℃到1100℃时，Cr元素在玻璃熔体中的扩散系数由1.63×10-10 cm2/s提高到2.91×10-9 cm2/s，Cr元素扩散速率提高了17.85%。XPS测试表明，Cr元素在高温处理条件下形成的玻璃熔体中主要是以Cr3+和Cr4+形态存在。（5）阐明了Cr元素与玻璃熔体协同对碳钢高温表面防护作用机制：一是由于致密的熔融玻璃基涂层熔体阻断了Fe和O离子的接触，延缓碳钢发生氧化反应；二是由于Cr元素在玻璃涂层熔体中发生扩散迁移，形成Cr富集层，对钢基体起到良好的防护作用；三是由于玻璃基涂层熔体中及界面层的Cr、Fe、O在高温反应过程中形成FeCr2O4、(Fe0.6Cr0.4)2O3、Cr2(FeO2)6等物质，有效地减少了O和Fe离子的扩散。此外，采用Pt惰性标记匹配SEM检测方法，从氧化传质角度也证实了含Cr玻璃基涂层熔体有效地阻止Fe离子向外扩散形成氧化层。(6) 基于Cr在玻璃基涂层熔体中的动态行为及微观形成相的研究发现，800℃时随保温时间延长，Cr元素在界面处发生迁移富集反应，保温60 min时形成完整的Cr富集层（Cr元素相对含量可达60%）。从Fe，Cr和O元素形成物结构、Cr元素在玻璃熔体中的溶解性能差、反应新相的形成等多因素条件下，剖析了Cr元素在玻璃基涂层熔体中的迁移扩散反应和富Cr界面层的形成。;During the heating treatment, the high-temperature corrosion reaction between the metal material and the oxidizing atmosphere caused the severe oxidation and burns of steel. On one hand, it greatly reduced the yield of steel and affected the surface quality of steel; on the other hand, it caused serious waste of resource and energy. The high temperature protecting coating was an effevtive protective measure with low price and simple operation to reduce the weight loss. The glass-based coating melts could protect the stainless steel substrate effectively. It depended on the formation of Cr enriched oxide layer on the surface of steel, which had a good synergistic effect with the glass-based coating melts. Therefore, a large amount of research work had been carried out on the protection of the surface of carbon steel by using glass-based coating melts with Cr. It was found that a complete Cr enriched layer formed at the interface between steel substrate and glass-based coating melts during the high temperature reaction, which was of great importance to improve the corrosion resisitance of the steel substrate with the glass-based melts. Therefore, the glass-based coating melts with Cr was developed in this paper. The dynamic migration and existent appearance of Cr element in the glass melts during heating process was studied. Meanwhile, the protective mechanism of glass-based coating melts with Cr element for carbon steel was clarified under high temperature oxidizing atmosphere. The results were shown as follows:(1) The high temperature oxidation behavior of several typical carbon steels and stainless were carried out to assist the design of glass-based coating melt with Cr element. The high temperature oxidation mass transfer and diffusion coefficient of J55 carbon steel in the range of 800℃ to 1100℃ were investigated emphatically. Meanwhile, the effect of oxygen content on the oxidation behavior of J55 carbon steel in the range of 1vol%~15vol% was studied. The high-temperature protective mechanism of glass-based coating with Cr2O3 for the 420 stainless steel (containing 12%~14% Cr) was also certified. (2) The glass-based coating melts with Cr element consisting of Al2O3-SiO2-K2O-Na2O-Cr2O3 was developed. It was based on the matching properties of coating material and steel substrate, and the design principle of low solubility of Cr element in glass material. The glass transition temperature of glass material was 730℃, and the thermal expansion coefficient was 8.0×10-6/K at range of 30℃ to 600℃. The dissolution range of Cr element in glass material was 0.52%~0.83% from 900℃ to 1200℃. (3) Cr element enriched layer formed at the interface between 20MnSiNb steel substrate and glass-based coating melts by the SEM-EDS. The experimental results showed that the glass-based coating melts with Cr had good protective properties for 20MnSiNb steel. The anti-oxidation effect was up to 86% at 1050℃ for 60 min, and which was bigger than 75% from 1000℃ to 1100℃ for 120min. The oxidation rate constant of 20MnSiNb steel was significantly reduced, which was only 1/7~1/10 of blank sample. And the oxidation reaction apparent activation energy had nearly been doubled to 160.06 kJ/mol. It had also been proved that the glass melts with different Cr source and the glass melts changed by the addition of Na, Ti and Sn element could significantly control the migration process of Cr element in glass melt. (4) The dynamic migration and existent appearance of Cr element in Al2O3-SiO2-K2O-Na2O-Cr2O3 glass-base melts were analyzed. The study indicated that the diffusion coefficients of Cr in glass melts was significantly affected by the temperature. It increased from 1.63×10-10 cm2/s to 2.91×10-9 cm2/s at the range of 900℃ to 1100℃, and which increased by 17.85%. The XPS test indicated that the Cr element in the glass melts mainly existed in the form of Cr3+ and Cr4+ at high temperature. (5) The protective mechanism of glass-based coating melts with Cr element for 20MnSiNb steel was clarified. It was might be by the following reseans: first, the dense molten glass-based coating melts blocked the contact between iron and oxygen ions and lelayed the oxidation reaction of the carbon steel; second, the Cr enriched layer formed by the migration and enrichment reaction of Cr element in the glass-based coating melts played an important role in improving the anti-oxidation property of steel substrate; third, the formation of FeCr2O4, (Fe0.6Cr0.4)2O3 and Cr2(FeO2)6 by the Cr, Fe and O elements in the glass-based coating melts effectively reduced the diffusion of oxygen and iron ions. In addition, it was confirmed the glass-based coating melts with Cr element could obviously prevent the formation of oxide layer by the outward diffusion of iron ion. (6) The dynamic behavior and microscopic phase of glass-based coating melt with Cr element was studied. It was found the Cr element had migration and enrichment reaction with the increasing heating time at 800℃, and formed complete enriched layer at 800℃ for 60 min (the relative content of Cr element was up to 60%). The migration and diffusion reactions of Cr element in glass-based coating melts and the formation of Cr enriched interface layer were analyzed from the following multi factor conditions: the formation structure of Fe, Cr and O elements, the solubility of Cr element in silicate glass melts and the formation of new phase by reaction.
|付国燕. Cr在玻璃基涂层熔体中动态迁移及存在形态的研究[D]. 中国科学院研究生院,2017.|
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