Unexpected behavior of sodium sulfate observed in experimental freezing and corrosion studies
Unexpected behavior of sodium sulfate observed in experimental freezing and corrosion studies
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在实验冷冻和腐蚀研究中观察到硫酸钠的意外行为
DOI：
10.1002/jrs.6200
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发表时间：
2021
影响因子：
2.5
通讯作者：
Lützenkirchen
中科院分区：
文献类型：
--
作者：
Abdelmonem;Morelová;Schild;Lützenkirchen
本文报告了两项不同的、原本不相关的研究结果，这些研究显示了与平坦表面接触的硫酸钠溶液的意外行为。一方面，我们使用二次谐波产生（SHG）光谱研究了在平坦蓝宝石-0001晶体存在下含硫酸盐溶液（目标盐为CaSO 4，Na 2SO 4用作一种对照）的浸没冷冻。用纯净水和CaCl 2进行进一步的对照实验。从CaSO 4和Na 2SO 4溶液的SHG信号的行为有些不同，从记录的其他两种情况下，纯净水和氯化钙。常见的模式显示，随着温度下降到约-15 °C，SHG信号下降，随后信号急剧下降，表明冻结。对于Na 2SO 4溶液，虽然信号最初紧密遵循纯净水曲线，但在约-10 °C时趋势急剧增加，然后随着进一步冷却而逐渐下降。对于Na 2SO 4溶液的独特行为没有合理的解释，热力学计算也没有表明硫酸钠固相的任何沉淀。在冻融循环结束时，检索每个系统的初始SHG，表明可逆性。另一方面，在与冷冻研究无关的单独研究中，反复观察到室温下硫酸钠从溶液中沉淀在扁钢表面上。与冷冻实验一样，硫酸钠本体溶液溶解度的热力学计算表明，在研究条件下不应形成沉淀。在钢样品上观察到的晶体具有类似于文献报道的雪花形状。我们的结论是，Na 2SO 4在平坦表面的存在下，显示出意想不到的行为，应激发进一步详细的研究，在未来阐明的现象。
This article reports results from two distinct, originally unrelated studies that show unexpected behavior with respect to sodium sulfate solutions in contact with flat surfaces. On the one hand, we investigated immersion freezing of sulfate containing solutions (target salt was CaSO4and Na2SO4was used as one control) in the presence of flat sapphire‐0001 crystals using second‐harmonic generation (SHG) spectroscopy. Further control experiments were carried out with neat water and CaCl2. The SHG signals from CaSO4and Na2SO4solutions behave somewhat differently from those recorded for the two other cases, the neat water and CaCl2. The common pattern shows a decrease of the SHG signal with decreasing temperature down to about −15°C, whereupon the signal sharply drops, indicating freezing. With the Na2SO4solution, although the signal initially follows closely the neat water curve, the trend increases sharply at about −10°C followed by a gradual decrease with further cooling. There is no plausible explanation for the distinct behavior of the Na2SO4solution, and thermodynamic calculations do not suggest any precipitation of a sodium sulfate solid phase. At the end of the freeze–thaw cycle, the initial SHG for each system is retrieved, suggesting reversibility. On the other hand, in a separate investigation unrelated to the freezing study, it was repeatedly observed that sodium sulfate precipitates from solution on flat steel surfaces at room temperature. As in the freezing experiments, thermodynamic calculations for the bulk solution solubility of sodium sulfate indicate that precipitates should not be forming under the conditions of the studies. The crystals observed on the steel samples have snowflake shapes similar to one literature report. We conclude that Na2SO4in the presence of flat surfaces shows unexpected behavior that should incite further detailed studies in the future to elucidate the phenomenon.
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