Inhibition of Efflorescence in Na-Based Geopolymer Inorganic Coating

Effect of PFDS on the immobilization of Cs+ by metakaolin-based geopolymers in complex environments

Metakaolin-based geopolymers are very promising materials for improving the safety of low and intermediate level radioactive waste disposal, with respect to ordinary Portland cement, due to their excellent immobilization performance for Cs+ and superior chemical stability. However, their application is limited by the fact that the leaching behavior of Cs+ is susceptible to the presence of other ions in the environment. Here, we propose a way to modify a geopolymer using perfluorodecyltriethoxysilane (PDFS), successfully reducing the leaching rate of Cs+ in the presence of multiple competitive cations due to blocking the diffusion of water. The leachability index of the modified samples in deionized water and highly concentrated saline water reached 11.0 and 8.0, respectively. The reaction mechanism between PDFS and geopolymers was systematically investigated by characterizing the microstructure and chemical bonding of the material. This work provides a facile and successful approach to improve the immobilization of Cs ions by geopolymers in real complex environments, and it could be extended to further improve the reliability of geopolymers used in a range of applications.

A Superhydrophobic Alkali Activated Materials Coating by Facile Preparation

Alkali activated materials (AAMs) were considered as economical and environmentally friendly that have attracted incrementally attention as green coating materials. However, alkali activated materials were inclined to be infiltrated and ruined by harmful ions in water due to their hydrophilicity. And the ordinary ways of construct superhydrophobic coatings were costly, complex and need fluorine material. The superhydrophobic surfaces were fragile owing to the super-hydrophobicity of materials were controlled to surface merely. In this work, a facile, convenient and economical strategy to synthesize alkali activated slag materials (AAS) superhydrophobic coatings with excellent water repellence was developed. Herein, the hydrolysis and polymerization of triethoxy (octyl)silane (TTOS) were applied for generating micro/nanostructures to construct a three-dimensional overall superhydrophobic alkali activated slag materials coating. The water contact angle (CA) about surfaces and bottoms of superhydrophobic alkali activated slag materials coatings were 150.2°, 152° and the water rolling angle (SA) of surfaces and bottoms were 5°, 4° respectively. Besides, the superhydrophobic alkali activated slag materials coatings demonstrated excellent mechanical abrasion effect that still maintain super-hydrophobicity after sandpaper abrasion stand. Super-hydrophobicity of coatings could be regenerated by simple sandpaper rubbing when they were attacked chemically. Concisely, the superhydrophobic alkali activated slag materials coatings were show the benefit of affordable and feasibility so that they have the potential for expandable industrial promotion.

Effects of Si/Al ratio on structure, modulus of elasticity, and density in N-A-S-H geopolymer: a molecular dynamics simulation based on novel macromolecular model

The Si/Al ratio is of special importance in the structure of geopolymers and its change in structure causes geopolymers to show different properties. This study is based on the proposed macromolecular model taken from recent laboratory studies of the N-A-S-H geopolymer structure and is balanced in terms of electric charge with Na⁺ ions and aluminum atoms outside the structure. Macromolecular models were made with different ratios of Si/Al equal to 1, 2.16, and 3. Using classical molecular dynamics simulations, the results of Young's modulus, density, and radial distribution function of different Si/Al ratios were compared and the results were in good agreement with the available experimental data. This data is mandatory, please provide.