碱源对钢表面原位生长LDH抗腐蚀膜的影响

Effect of Alkali Source on In-Situ Growth of LDH Anti-corrosion Film on Steel Surface

摘要:

为提升建筑用钢抗腐蚀性能，采用水热法在钢表面原位生长Co-Al-CO32-层状双金属氢氧化物（LDH）防锈膜，并研究了尿素，碳酸钠，碳酸氢钠作为碱源对反应体系的影响，揭示了钢表面生长LDH膜的关键因素.同时，对不同尿素浓度下生长的LDH膜微观结构进行了对比，结合电化学法表征了LDH膜的抗腐蚀性能，分析了尿素浓度的影响规律.结果表明：尿素作为碱源时才能在钢上原位生长LDH；尿素在常温下呈中性，Al³⁺水解形成无定形氢氧化铝沉积在钢表面作为LDH晶核；反应温度升高后尿素会水解使溶液呈碱性，利于LDH晶核生长成膜；当尿素浓度较低时，LDH片尺寸较大，膜有较多孔洞；当尿素浓度较高时，LDH片尺寸较小但会相互挤压产生裂纹；当尿素浓度为0.375 mol/L时，LDH膜生长致密，并具有良好抗腐蚀性能.

Abstract:

The Co-Al-CO32- layered double hydroxide（LDH） anti-corrosion film was formed in-situ on the surface of steel by hydrothermal method to improve the corrosion resistance of building steel. Effect of urea， sodium carbonate and sodium bicarbonate as alkali sources on the reaction system was studied to reveal the key factors of growing LDH film on steel surface. In addition， the microstructures of LDH films grown under different urea concentrations were compared and the corrosion resistance of LDH films was characterized by electrochemical method to analyze the effect of urea concentration. The results show that LDH can be in-situ grown on steel surface only when urea is used as the alkali source. Urea is neutral at room temperature， and Al³⁺ is hydrolyzed to form amorphous aluminum hydroxides which are deposited on steel surface as LDH crystal nuclei. The hydrolysis of urea accelerates when the reaction temperature increases. Therefore， the alkaline environment of the solution causes LDH nuclei to grow into films. What's more， the LDH sheets prepared under low urea concentration have more pores and larger size of LDH sheets； while the LDH sheets prepared under high urea concentration have smaller size and will squeeze each other to crack. The LDH film prepared under urea concentration of 0.375 mol/L grows compactly and has satisfied corrosion resistance.