Electrolytic detachment

Doerfler A, Wanke I, Goericke SL, Wiedemayer H, Engelhorn T, Gizewski ER, Stolke D, Forsting M (2006) Endovascular treatment of middle cerebral artery aneurysms with electrolytically detachable coils. AJNR Am J Neuroradiol... 

Coil embolization has been one of the mainstays of VAA treatment and has been augmented with direct glue or thrombin injection. Coil design has not changed significantly. However, extremely precise deployment mechanisms such as electrolytic detachment are available today. 

Janssen and Hoogland (J3, J4a) made an extensive study of mass transfer during gas evolution at vertical and horizontal electrodes. Hydrogen, oxygen, and chlorine evolution were visually recorded and mass-transfer rates measured. The mass-transfer rate and its dependence on the current density, that is, the gas evolution rate, were found to depend strongly on the nature of the gas evolved and the pH of the electrolytic solution, and only slightly on the position of the electrode. It was concluded that the rate of flow of solution in a thin layer near the electrode, much smaller than the bubble diameter, determines the mass-transfer rate. This flow is affected in turn by the incidence and frequency of bubble formation and detachment. However, in this study the mass-transfer rates could not be correlated with the square root of the free-bubble diameter as in the surface renewal theory proposed by Ibl (18). 

An illustration of the effect of micelle/nanoparticle volume fraction on contact line motion is found in [57]. They used 0.1 M NaCl solution to reduce the electrical double layer thickness surrounding the NaDS micelle. At a given number concentration of micelles, decreasing the size of each micelle decreases the volume fraction greatly, since the volume of each spherical micelle varies as the third power of the radius. Thus, the addition of electrolyte effectively reduced the micellar volume fraction in the aqueous medium. The authors found that the oil droplet that would otherwise become completely detached from the solid surface, came back to reattach itself to the solid when electrolyte was present. They rationalized this finding as being caused by the inability of the weakened structural disjoining forces to counteract the attraction of the oil drop to the solid surface. 

How can this dipole potential be visualized Once again a thought experiment can be performed. The electrode and electrolyte phases are conceptually detached from each other and the double layer turned off. In this process, the excess charges and oriented-dipole layers that characterized the double layer are considered eliminated. 

Toxic epidermal necrolysis occurs when the skin epidermis is destroyed by the action of toxicants and becomes detached from the dermis. This condition severely disrupts the ability of skin to regulate the release of heat, fluids, and electrolytes. Metabolites of the anticonvulsive drug carbamazepine have been implicated in toxic epidermal necrolysis. 

Water, it may be recalled (Chapters 2 and 4), has two modes of solvent action, depending on the nature of the added electrolyte. The water can contact an ionic crystal (e.g., NaCl), detach the ions from the lattice through the operation of ion-dipole (or ion-quadrupole) forces, and convert them to hydrated ions (Chapter 2). 

A particular emphasis has been placed on the detachment rate of colloids from the mineral surface. Colloid sorption is irreversible (or at least shows very slow desorption kinetics regardless of solution composition either in electrolyte solution or in the presence of a carrier colloid such as silica or humic acids (Table ID) moreover, desorption tests up to three months have not shown any colloid detachment. No marked influence of temperature on the release of retained ceria colloids has been observed between 20 and 90°C. 

In all cases the formation of gas bubbles has an effect on the mass transport of the electrochemically active species in the process [1], The gas bubbles sticking at the nucleation sites block the electrode and decrease the active surface [2-6], while the bubbles that are detached into the electrolyte solution change the conductivity of the electrolyte [7-9], Furthermore, momentum exchange occurs between the bubbles and the surrounding electrolyte, affecting the motion of the electrolyte [10],... 

The mechanism of bubble formation by nucleation requires supersaturation of the dissolved gas [11-13] and a nucleus radius greater than the critical [7], The main sources of heterogeneous nucleation are usually surface irregularities capable of containing entrapped gas, e.g. pits and scratches. The bubbles typically develop over the electrode surface, grow in size until they reach a break-off diameter and subsequently detach into the electrolyte. After detachment, some residual gas remains at the nucleation site and another bubble will form at the same place [2,13,14], In most two-phase flow simulations [15-19], it is assumed that bubbles detach with a constant diameter, although from experiments [20,21] it is know that electrochemically formed bubbles show a size distribution. 

Every detached bubble enters the electrolyte and a Lagrangian tracking procedure is used to update the velocities and positions of all dispersed gas bubbles in the electrolyte at each time step of the Navier-Stokes solver. From Newton s second law, an equation of motion can be obtained for every bubble, based on the formulation stated in [24], Together with the relation between the particle s position and velocity, a set of two ordinary differential equations in three space dimensions can be formed in order to update the bubble trajectory... 

The detachment of the bubble occurs if the condition FB = Fc is satisfied. It follows that the mean bubble departure radius (Rd) is well defined for a given electrode—electrolyte configuration (typical values are around 50 pm [115]). It may be expected that the mean bubble departure radius is mainly a property of the electrode (the electrode surface roughness which influences D), the electrode wettability (through the contact angle i9), and the electrolyte (density and surface tension of the electrolyte), but not of the current density j. However, the question is whether a cavity (nucleation site) is active or non-active. The current density may influence the activation of the nucleation sites. 

Decreasing rate of bubble release The mean bubble detachment frequency Af6-1 directly controls the onset of the gas film. For large enough bubbles, such as the infinite cluster, the bubble detachment time Atb becomes so large that the gas film can be formed. Atb is affected by other parameters such as the wetting of the electrode, viscosity and density of the electrolyte, or the local hydrodynamical fluxes. 

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