Ring-hemisphere

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.

The hemispherical electrode may be coupled with a ring [20] to form a rotating ring-hemisphere electrode (RRHSE) as shown as Fig. 9(d). The ability of this combination to detect intermediate reaction products is demonstrated in Fig. 10, where a series of cathodic sweep curves for the reduction of Cu2 + in acidic cupric chloride solution are... 

The rotating ring-hemisphere electrode has been used by Chin [21] to study the dissolution of iron in neutral sulfate solutions, and by Zou and Chin [61, 62] to identify the corrosion products of iron in concentrated sodium hydroxide solutions. 

Addition reactions — The fullerenes Ceo and C70 react as electron-poor olefins with fairly localized double bonds. Addition occurs preferentially at a double bond common to two annelated 6-membered rings (a 6 6 bond) and a second addition, when it occurs is generally in the opposite hemisphere. The first characteriz-able mono adduct was [C6oOs04(NC5H4Bu )2]. formed by reacting Cgo with an excess of OSO4 in 4-butylpyridine. The structure is shown in... 

FIGURE 4-26 Common configurations of microelectrodes, a, disk b, ring c, cylinder d, hemisphere e, line (bond) / = length, w = width, r = radius. 

Fig. 11-26 Decade-averaged data of Northern hemisphere tree ring records from 1750-1979 and 7th-degree polynomial fit of the data. The vertical extension of blocks represents 95% confidence limits of the mean. The open circles give the change of —0.65% in atmospheric CO2 observed from 1956 to 1978 by Keeling et al. (1979). (Adapted from Peng et al, 1983.)...

The experimental setup of a rotating hemispherical electrode (RHSE) is similar to that of a rotating disk electrode [50]. The basic system consists of a removable hemispherical electrode, and a variable speed rotator equipped with a provision, such as the slip-ring contact, to make electric connection to the hemispherical electrode during the experiments. 

Fig. 10. Cathodic scan curves for a platinum-ring-gold-hemisphere in CuC12-HC1 solution. The ring potential was maintained at 0.4 V vs. SCE to detect Cu+ ion. From [20].

Fig. 11. RRHSE data for the corrosion of iron in 10 N NaOH at 60 °C. (a) Polarization curve of iron hemisphere, (b) Ring current vs. hemisphere potential. Curve 1 is for the detection of HFeOj ion, and curve 2 is for detecting FeOj ion. From [62],...

We hope that tree ring sequences will be prepared from trees of the southern hemisphere from which one could learn whether climate changes have been simultaneous in both hemispheres. There are large tree stumps in New Zealand, and perhaps similar material could be found in Australia and other southern lands, and there may be varve sequences as well in the southern hemisphere. 

The ion-trap mass spectrometer uses three electrodes to trap ions in a small volume. The mass analyzer consists of a ring electrode separating two hemispherical electrodes. A mass spectrum is obtained by changing the electrode voltages to eject the ions from the trap. The advantages of the ion-trap mass spectrometer include compact size and the ability to trap and accumulate ions thus increasing the signal-to-noise ratio of a measurement [534,535,551, 553]. 

Microelectrodes were mentioned previously in Chapter 5, where we saw how their small size increased the faradaic efficiency since the interfacial capacitance Cdi is decreased, itself minimizing the charging currents. Microelectrodes can be purchased relatively cheaply, and in a variety of types, e.g. hemispherical and flat circular rings or bands, with a wide range of diameters. Such electrodes were discussed previously in Section 5.3. 

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]. 

Freeman KH, Hayes JM (1992) Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels. Global Biogeochem Cycles 6 185-198 Freeman KH, Hayes JM, Trendel JM, Albrecht P (1990) Evidence from carbon isotope measurements for diverse origins of sedimentary hydrocarbons. Nature 343 254-256 Freyer HD (1979) On the C-record in tree rings, I, C variations in northern hemisphere trees during the last 150 years, TeUus 31 124-137... 

FIGURE 14-56 Temperature anomalies in the Northern Hemisphere compared to the 1881-1960 mean, calculated based on measured changes in tree ring densities. The 95% confidence limit is i0.3°C. The line shows bidecadal smoothed levels. Arrows on the lower axis mark some of the major volcanic eruptions (adapted from Briffa et al., 1998). 

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,... 

Support an hemispherical iron dish of 10 cm. diameter (or an iron crucible) on a ring stand and place in it about 75 g. of sodium nitrate. Heat the nitrate until it melts and just begins to evolve bubbles of oxygen. While maintaining a steady temperature, drop in pieces of granulated lead or chopped-up lead pipe, stirring well with an iron rod (old round file) after each addition. A little more than the equivalent of lead should be added, since some of it will be oxidized by the air. For this reason, a flat iron sand-bath dish is not suitable for the experiment. The reduction of the nitrate is rapid, and if much lead is added at a time, the mass may become incandescent. 

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