Effect of bentonite content on the suspension stability of a glaze slurry and final enamel performance

The influence of bentonite as a suspending agent on the processing and performance of the final enamel product was studied with the aim of prolonging the service life of enamel. The suspension stability of the glaze slurry was also evaluated, and the influence of the layered structure of bentonite on the suspension was explored. In addition, the effect of bentonite on the flexural strength and fracture toughness of enamel coatings on metal substrates was investigated. Finally, acid corrosion resistance experiments were performed to evaluate the effect of bentonite on the corrosion performance of the enamel coating. The results showed that the stability of the glaze slurry and mechanical properties of the enamel products were significantly improved by adding 1 wt% bentonite to the glaze slurry. The addition of 0.5 wt% bentonite was optimal for enhancing the acid corrosion resistance of the enamel. This study provides a useful reference for improving the quality of enamel products and prolonging their service life.     

Saturated hydraulic conductivity of compacted bentonite–sand mixtures before and after gas migration in artificial seawater

To understand the self-healing property of an engineered barrier for radioactive waste disposal, the hydraulic conductivity of compacted bentonite–sand mixtures saturated with artificial seawater (SW) before and after gas migration was examined. Na- and Ca-bentonites were mixed with fine sand at a ratio of 70% bentonite in dry weight. Two aspects were considered during the experiment: the hydraulic conductivity of the specimen that was resaturated after gas migration and the distribution of water content immediately after gas migration to study gas migration pathways. The gas migrated through the entire cross-section of the specimen, and gas breakthrough occurred in the equilibrium swelling pressure range approximately. Subsequently, the gas flow rate reached a sufficient large value when the gas pressure was approximately twice the equilibrium axial pressure (the sum of swelling and confining pressures), which excluded the back pressure. Although the gas migration pathway was not visible when the specimen was observed immediately after gas migration, the water content distribution showed that several parts of the specimen with lower water content were connected in the direction of gas migration. After resaturation, the change in permeability was within a limited range—two to three times larger than that before gas migration for each type of bentonite in SW. This slight change suggests that gas migration creates a pore structure that cannot be sealed via crystalline swelling of montmorillonite in SW, even if highly compacted bentonite is used under a constant-volume condition.     

Water and soil particle movement in unsaturated bentonite with constrained and free swelling boundaries

Bentonite is considered a barrier material in the geological disposal of high-level radioactive waste. Depending on the construction method, it is necessary to know what the behavior of the bentonite barrier will be in the wetting process during the absorption of underground water under different boundary conditions. In this study, water and soil particle movement during the wetting process of a compacted bentonite under constrained and free swelling conditions was studied experimentally and numerically. For the constrained swelling boundary condition, in which the swelling deformation was fully constrained, the distributions of the gravimetric water content (w) were measured for specimens with different dry densities (ρ_d), and then the water diffusivity (D_w) was obtained. It was found that D_w showed a slightly decreasing trend with an increase in ρ_d, while the numerical simulations showed that the difference in D_w induced by ρ_d was minor in terms of the evolving degree of saturation in the tested range. For the free swelling boundary condition, the distributions of w and ρ_d were measured for specimens with an initial ρ_d of 1.6 Mg/m³. To obtain D_w and the soil particle diffusivity (D_s), an existing theoretical framework, to which new concrete calculation equations had been added, was presented. Then, the performance of the framework was examined by numerical simulations to illustrate the water and soil particle movement under conditions similar to those of the experiment. It was found that the framework can describe the experimental results well, but that the accuracy of the results largely depends on the accuracy of the experimental data.