The Initial Deposition Behavior of Silica Colloid and Amino-Modified Silica Colloid in Unsaturated Sand Columns

Colloid transport experiments focusing on the initial deposition stage in water-unsaturated sand columns were conducted. To examine the effect of electrostatic interaction in the unsaturated condition, negatively and positively charged silica colloids were used for column transport experiments under different salt concentrations. The results of the column experiments were analyzed based on the colloid filtration theory and the deposition rate constants, and the single collector efficiency was calculated. The deposition rate constants of both negatively and positively charged silica in a water-unsaturated condition are larger than those in a water-saturated condition at an equivalent salt concentration, because the interface between air and water acts as an additional deposition site. The negatively charged silica shows the salt concentration, above which electric double layer (EDL) repulsion can be neglected, and the salt concentration is called critical deposition concentration (CDC). The CDCs were almost the same values in water-saturated as well as unsaturated conditions. The deposition rate constants of the positively charged silica were slightly increased at 0.05 mM due to the EDL attractive forces in the saturated condition. However, we could not see the significant effects of the EDL attractive force in the unsaturated condition in this study. Also, the present results demonstrated that a correlation equation for calculating collector efficiency can be applied to the non-spherical collector particles.

INFLUENCE OF SILICA COLLOID ON RHEOLOGY OF CEMENT PASTE WITH SUPERPLASTICIZER

Information of rheological behavior of binder paste is important for proportioning high slump concrete mixture at low water to cement ratios. This paper presents experimental data on the rheological property of silica colloid incorporated binder paste using naphthalene based and polycarboxylate based superplasticizer, compared to that of silica fume incorporated binder paste. Experimental data showed that silica colloid incorporated binder is compatible to tested superplasticizers in the all investigated range of silica colloid content, whereas the pastes incorporated with high silica fume content (over 10%) indicated incompatibility, especially to naphthalene based superplasticizer. There was also found out saturated content of superplasticizer corresponding to every kind of binder and water-binder ratio, with and without set retarding admixture.

Is the boundary layer of an ionic liquid equally lubricating at higher temperature?

Atomic force microscopy has been used to study the effect of temperature on normal forces and friction for the room temperature ionic liquid (IL) ethylammonium nitrate (EAN), confined between mica and a silica colloid probe at 25 °C, 50 °C, and 80 °C.

Comparisons of Tribological Properties of Ti(C,N)/SiC in Water and Seawater

Ti(C,N)-based cermets offer good high temperature strength, perfect chemical stability, excellent wear resistance, and relatively better machinability. In the present work, the tribological behaviors of Ti(C,N)/SiC sliding pairs lubricated in water and seawater were evaluated using a ball-on-disk tribometer. The experimental results show that a relatively low friction coefficient (about 0.025) can be obtained when lubricated with artificial seawater at the sliding speed of 200 mm/s, while the friction coefficient is about 0.2 in purified water. The wear surface profiles and the lubricants collected after running-in process for the high and low friction conditions were compared. In addition, the effects of salt molar concentration of the lubricant on the Ti(C,N)/SiC friction properties were investigated. It was found that the smooth and flat surface is the premise to gain the low friction. At the same time, the proper concentration of silica colloid, which is affected by the salt ions, is also an essential one. Moreover, the high sliding speed (200 mm/s) is beneficial to achieve low friction.