硫脲自盐酸溶液中在低碳钢表面的吸附特性

THE ADSORPTION OF THIOUREA FROM HYDROCHLORIC ACID ON MILD STEEL SURFACE

用失重法研究硫脲对低碳钢表面在盐酸溶液中的吸附特性及缓蚀作用。应用吸附理论和Frumkin等温式及Flory Huggins等温式处理实验数据 ,发现低浓度的硫脲自 2mol·L-1盐酸中在低碳钢表面上产生的吸附过程是一个取代吸附过程 ,而且是一个熵增过程。尤其应该注意侧向作用力和被吸附的硫脲分子所代替的水分子数 ,其表面覆盖度随温度和浓度的增大而增大 ,并认为这种吸附是产生缓蚀作用的重要原因。实验结果还表明 :在 3 0℃时 ,吸附过程中侧向作用力影响较大 ,并遵循Frumkin等温式 ,其吸附分子垂直地吸附在金属表面 ;在 3 5℃— 5 0℃时 ,吸附分子在金属表面水平吸附 ,其侧向作用力可忽略 ,遵循Flory Huggins等温式。根据这些结果计算出吸附自由能、吸附焓、吸附熵 。

The adsorption and corrosion inhibition of thiourea on mild steel surface from hydrochloric acid have been investigated by weight loss method.The experimental data have been treated with adsorption theory and Frumkin type isotherm and Flory Huggins isotherm.The adsorption heat has been calculated.It is found that adsorption of thiourea from 2 mol·L -1 HCl on mild steel surface is a substitutional adsorption process with increasing entropy.Particular attention was paid to the effect of the lateral interaction and the number of water molecules displaced by each adsorbed thiourea molecule.The degree of surface coverage was found to increase with temperature and concentration.So the adsorption on mild steel surface was believed to be an important reason of corrosion inhibition.The experimental results show that at 30℃ the adsorption behaviour follows a Frumkin type isotherm with strong lateral interaction where the molecules are vertically adsorbed on the surface.At 35℃-50℃ the adsorbed molecules change their orientation as to be parallel to the surface,where the adsorption behaviour follows a Flory Hugins isotherm with negligible lateral interaction.The free energy,enthalpy and entropy of adsorption calculated from experimental data show that the effect of temperature on the degree of surface coverage could be attributed to the change in entropy.