FDN在石膏颗粒表面的吸附特性及其对流动度影响

FDN是胶凝材料最常用的减水剂,其分散作用是通过吸附实现的.采用紫外吸收光谱分析仪、微电泳仪、光电子能谱分析技术等,研究了FDN在石膏表面的吸附特性、电化学性质及其对流动性的影响.石膏对FDN的吸附为物理吸附,其吸附热为14.71 kJ/mol,吸附层厚度12 nm(120A);FDN为平躺吸附,吸附层的空间位阻小,其分散作用主要取决于静电斥力,ξ电位与FDN单分子层吸附量相关;由于水化产物对静电斥力的屏蔽效应和脱附,静电斥力分散作用的稳定性差,流动度经时损失较大.

Adsorption Characteristics of FDN on Gypsum Surface and Its Effect on the Fluidity of Gypsum Plaster

FDN is a type of β-naphthalene sulfouic acid-based superplasticizer usually used in binding materials, and its dispersion effect is realized through its adsorption. By using UV adsorption spectrophotometer, micro-electrophoresis, and x-ray photo spectroscopy technology, the adsorption characteristics, surface electrochemical properties of FDN on gypsum and their effects on fluidity of gypsum plaster were researched. The results show that the adsorption of FDN is physical adsorption, its adsorption heat being 14.71 kJ/mol and the thickness of adsorption layer 12 nm(120 t). Steric hindrance of FDN adsorption layer is very weak, so its dispersion effect depends mainly on electrostatic repulsive force caused by Zeta potential which was closely related with the adsorption amount of monomolecular layer. Electrostatic repulsive force effect is not stable because of the shelter effect of new hydration products and desorption of water-reducing agent, leading to rapid fluidity loss of fresh gypsum plaster.