Mercury Hemisphere

Travnikov, O., Ryaboshapko, A. (2002). Modelling of Mercury Hemispheric Transport and Depositions. Moscow MSC-E. 

Table 5.2 Kinetic parameters obtained from the fitting of experimental voltammetry at mercury hemispherical microelectrode and platinum disc microelectrode with the asymmetric MH model...

In SECM experiments, the close approach of the disk UME is often hampered by the insulating sheath, which may strike the substrate due to misalignment of the tip. The pro-trasion of the active electrode area as in the mercury hemisphere permits an uninhibited approach and a better estimation of the true zero distance. 

Once formed, the mercury hemisphere is firmly attached to the Pt substrate and can withstand washing however, it cannot be stored in air and left to dry. When dry, the hemisphere... 

This approach was further extended to include monolayers of lipids, 1-octadecanol, and an investigation of the current response during the ultimate deformation of the liquid-air interface by an approaching mercury hemisphere UME probe [39], Figure 13.12 shows approach curves for O2 reduction with increasing surface pressure for (a) 1-octadecanol (C,gOH) and (b) DPPA monolayers, where DPPA is L-a-dipalmitayl phosphatidic acid. It can clearly be seen that by increasing the surface pressure of the monolayers there is a decrease in O2 flux across the interface, manifested as a decrease in current for O2 reduction at any normalized tip/interface distance, dia. 

Ciani, I., Burt, D. R, Daniele, S., Unwin, R R. Effect of surface pressure on oxygen transfer across molecular monolayers at the air/water interface Scanning electrochemical microscopy investigations using a mercury hemispherical microelectrode probe. J. Phys. Chem. B 2004, 108, 3801. 

Fig. 9. Types of rotating spherical electrodes reported in the literature, (a) Rotating micro-sphere electrode, (b, c) rotating hemisphere electodes (d) rotating ring-hemisphere electrodes (e) rotating dropping mercury electrode.

Kim and Jorne [37] have used a rotating zinc hemisphere to study the kinetics of zinc dissolution and deposition reactions in concentrated zinc chloride solutions. The electrodeposition reaction of cadmium on mercury was used by Mortko and Cover [43] in their investigation of a rotating dropping mercury electrode their data behaved according to Eqs. (74)-(76). 

Biester H, Kilian R, Franzen C, Woda C, Mangini A, Scholer HF (2002) Elevated mercury accumulation in a peat bog of the Magellanic Moorlands, Chile (53 degrees S) - an anthropogenic signal from the Southern Hemisphere. Earth Planet Sci Lett 201 609-620... 

Consider the formation of hemispherical nuclei of mercury on a graphite electrode. The intefacial tension of mercury with aqueous solutions is about 426 mN m-1. From Eq. (10.16) calculate the critical cluster sizes for 7 = —10, —100, —200 mV. Take z — 1 and ignore the interaction energy of the base of the hemisphere with the substrate. 

Therefore data on anthropogenic and natural emissions in the Asian region are necessary for the assessment of heavy metal pollution in these countries. Pollution of Kazakhstan and Kyrgyzstan by mercury and lead has been initially assessed by means of hemispheric modeling using the available global emission inventories of the considered heavy metals. The outcomes of the assessment are presented in this section. 

The calculated maps of the annual mercury deposition in the Northern Hemisphere and over the considered countries are shown in Figure 13. A high transport ability of mercury enables it to be transported in the atmosphere over long distances. A significant part of mercury emitted in the polluted regions is deposited far from major... 

Figure 12. Spatial distribution of mercury anthropogenic emission in the Northern Hemisphere (a) and in Kazakhstan and Kyrgyzstan (b) in 1995. Black line in the left figure delineates the EMEP region (Ilyin et al., 2004).

Electroanalytical application of hemispherical [35,36], cylindrical [37,38] and ring microelectrodes [39] has been described. A hemispherical iridium-based mercury ultramicroelectrode was formed by coulometric deposition at -0.2 V vs. SSCE in solution containing 8 x 10 M Hg(II) and 0.1M HCIO4 [35]. The radius of the iridium wire was 6.5 pm. The electrode was used for anodic stripping SWV determination of cadmium, lead and copper in unmodified drinking water, without any added electrolyte, deoxygenation, or forced convection. The effects of finite volume and sphericity of mercury drop elecPode in square-wave voltammetiy have been also studied [36]. 

Obtain a hemispherical iron dish H, somewhat larger than the bulb of the flask, and place enough fine sand in it to make contact with the glass flask. Place the sand bath with the flask upon a small ring support and steady the flask with a burette clamp. Put a suitable quantity of mercury in the flask and make an airtight connection at E by binding the joint with adhesive tape,... 

Fig. 4.2 Experimental chronoamperometric curves of the second pulse for different E2 values corresponding to the re-oxidation of Tl(Hg) on a hemispherical mercury electrode with (a) rs = 50 pm T = 300 ms (b) rs = 25 pm ri = 800 ms 0.2 mM T1N03, 0.1M KN03. Reproduced with permission of reference [29]...

Another type of nondisk-shaped SECM tips are UMEs shaped as spherical caps. They can be obtained, for example, by reducing mercuric ions on an inlaid Pt disk electrode or simply by dipping a Pt UME into mercury [15]. An approximate procedure developed for conical geometry was also used to model spherical cap tips [12]. Selzer and Mandler performed accurate simulations of hemispherical tips using the alternative direction implicit final difference method to obtain steady-state approach curves and current transients [14]. As with conical electrodes, the feedback magnitude deceases with increasing height of the spherical cap, and it is much lower for a hemispherical tip than for the one shaped as a disk. 

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