Corrosion of stainless steels and carbon steel by molten mixtures of commercial nitrate salts
Corrosion of stainless steels and carbon steel by molten mixtures of commercial nitrate salts
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DOI：
10.1361/10599490417542
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发表时间：
2004-02-01
影响因子：
2.3
通讯作者：
Bradshaw, RW
中科院分区：
文献类型：
--
作者：
Goods, SH;Bradshaw, RW
对两种不锈钢和一种碳钢在NaNO3和KNO3混合物中的等温腐蚀行为进行了评估，以确定商品级碱性硝酸盐中的杂质是否会加剧适用于先进太阳能热能系统的腐蚀性。在温度为570℃的304和316不锈钢以及温度为316℃的A36 C钢的7种NaNO_3和KNO_3混合物中进行了大约7000小时的腐蚀试验。腐蚀试验也在NaNO_3、KNO_3和Ca(NO_3)(2)(2)的三元混合物中进行。腐蚀速率通过除鳞失重来确定，氧化产物用扫描电子显微镜(SEM)、电子探针分析(EPMA)和X射线衍射(XRD)进行分析。定期分析硝酸盐混合物中杂质浓度和可溶腐蚀产物的变化。这些试验结果表明，不锈钢试件在许多混合物中的短期腐蚀速率可以用抛物线动力学来描述。然而，暴露在所有混合物中导致的腐蚀动力学并不是单一的速率定律。对于工程应用，整个曝光期内的腐蚀率最好描述为与时间呈线性关系。在二元硝酸盐混合物中，根据特定混合物的不同，在570℃的温度下，不锈钢试件的金属年化损失率在6至15微米/年之间。C钢试件在316℃的温度下浸泡在相同混合物中的金属损失约为1-4微米/年。扫描电子显微镜和X射线衍射仪分析表明，不锈钢片表面形成的复杂多相表面氧化物主要由铁铬尖晶石、铁氧化物和亚铁酸钠组成。碳钢试件上形成的主要腐蚀产物是磁铁矿。总体而言，就市售硝酸盐中的典型杂质范围而言，用于太阳能热能应用的腐蚀率对于所检查的所有材料来说仍然是可以接受的。
The isothermal corrosion behavior of two stainless steels and a carbon (C) steel in mixtures of NaNO3, and KNO3, was evaluated to determine if the impurities found in commodity grades of alkali nitrates aggravate corrosivity as applicable to an advanced solar thermal energy system. Corrosion tests were conducted for approximately 7000 hours with Types 304 and 316 stainless steels at 570 degreesC and A36 C steel at 316 degreesC in seven mixtures of NaNO3, and KNO3 containing variations in impurity concentrations. Corrosion tests were also conducted in a ternary mixture of NaNO3, KNO3, and Ca(NO3)(2). Corrosion rates were determined by descaled weight losses while oxidation products were examined by scanning electron microscopy (SEM), electron microprobe analysis (EPMA), and x-ray diffraction (XRD). The nitrate mixtures were periodically analyzed for changes in impurity concentrations and for soluble corrosion products. Results of these tests indicated that the short-term corrosion rates of the stainless steel specimens in many of the mixtures could be described in terms of parabolic kinetics. However, no single rate law could be assigned to the corrosion kinetics resulting from exposure in all of the mixtures. For engineering applications, corrosion rates over the entire exposure period are best described as linear with respect to time. In the binary nitrate mixtures, the annualized rates of metal loss were found to be between 6 and 15 mum/year for the stainless steel specimens at 570 degreesC depending on the particular mixture. Metal loss for the C steel specimens immersed in these same mixtures at 316 degreesC extrapolated to approximately 1-4 mum/year. SEM and XRD revealed that the complex, multiphase surface oxides formed on the stainless steel coupons were composed primarily of iron-chromium spinel, iron oxides, and sodium ferrite. Magnetite was the principal corrosion product formed on the carbon steel specimens. Overall, for the typical range of impurities in commercially available nitrate salts, corrosion rates for solar thermal energy applications remained acceptable for all of the materials examined.