Liquid Ga-Pb alloys

ANISOTROPY OF WETTING OF PB CRYSTALS BY THEIR OWN MELT AND BY LIQUID GA-PB ALLOYS... 

D. Chatain and P. Wynblatt, Experimental Evidence for a Wetting Transition in Liquid Ga-Pb Alloys,... 

Double-layer properties in aqueous, propylene carbonate and formamide solutions have been studied at room temperature for liquid Ga-Pb alloy (0.06 atom % of Pb) [15], as a model of Pb electrode with renewable surface. The electrode behaves as an ideally polarizable electrode in a wide potential range, and its capacitance is intermediate between that of Ga and Hg electrodes and is independent of the solvent. This electrode is much less lipophilic than Ga. Adsorption of anions on this electrode increases in the sequence -BP4 = S042 < Gl < Br < r. 

Thermodynamic functions have been calculated for liquid binary Ga-Pb alloys in the composition range 10—90 atom % Pb. Enthalpies and excess entropies of mixing at 1000 K were reported. ... 

Fully automated reactor start-up can be achieved by the LRM, yet another passive device incorporated in the RAPID concept. Figure XVII-5 shows the LRM basic concept. LRM is similar to LIM however, Li is reserved in the active core part prior to reactor start-up. The LRM is placed in the active core region where the local coolant void worth is positive, as is also the case with LEMs and LIMs. The RAPID is equipped with an LRM bundle in which 9 LRMs and an additional B4C rod are assembled. The reactivity worth of the LRM bundle is +3.45, once each LRM includes a 95% enriched Li enclosed in a 20mm-diameter envelope. A B4C rod is used to ensure the shutdown margin (-0.5 ). An automated reactor start-up can be achieved by gradually increasing the primary coolant temperature with the primary pump circulation. The freeze seals of LRMs melt at the hot standby temperature (380°C), and Li is released from the lower level (active core level) to the upper level to achieve positive reactivity addition. An almost constant reactivity insertion rate is ensured by the LRMs because the liquid poison, driven by the gas pressure in the bottom chamber, flows through a very small orifice. It would take almost 14 hours for the liquid poison to move into the top chamber completely. A Sn-Bi-Pb alloy is used as the freeze seal material to ensure the reactor start-up at 380°C. 

In an aqueous solution, the electrode potentials of CO2 reduction correlate with the heats of fusion (HoF) of the electrode metals low-HoF metals (Hg, Tl, Pb, In, Cd and Zn) yield formate, while high-HoF metals (Pt, Pd, Ni, Au, Cu, Ag, Zn, Sn and Ga) form CO [77,87]. The above classification is far from being perfect, and does not cover for all possible scenarios of CO2 electroreduction. As shown later, in the section on the S5mthesis of organic carbonate, when used in an ionic liquid, indium cathodes are efficient in the preparation of dimethyl carbonate. Also, copper-based bimetallic electrodes may exhibit an improved catalytic activity in reducing CO2 to hydrocarbons. Examples include Cu-Ni, Cu-Sn and Cu-Pb alloys. By contrast, for Cu-Ag and Cu-Cd alloy electrodes, the catalytic activity is diluted [81]. 

The variations of abundance in the mass spectrum of small Pb clusters have been explained by ab initio density functional calculations. A study of free clusters formed by Pb and Na helps to explain the observation of an exceptionally abundant NagPb cluster in gas phase experiments. It also gives strong support to the presence of Na4Pb and Na4Pb4 clusters in the liquid alloys. 

Stable at room temperature both as a gas and a liquid. Hydrolyzed by water within half an hour. Absorbed immediately by NaOH solution, evolving heat and leaving no residue. Glass is stable to it for weeks but becomes covered with a cloudy film. Quartz is more stable but is is also slowly covered with a cloudy film. Attacks Hg. After exposure for a week, rubber becomes somewhat hard. Stainless steels 304 and 316, brass and aluminum are inert to GOGIF Ni, Monel, Sn, Zn and electron (Mg—Al) alloys have moderate resistance Fe, Gu, Pb and Ag show little resistance. 

Ga is less satisfactory owing to its much more basic character and consequent reactivity with water and acids, tending to suffer self-polarization through corrosion, with H2 evolution. Similar problems arise with base-metal amalgams. Studies with other metals in the liquid state are much more difficult but electrochemical measurements have been made with some low-melting point alloys, and with Sn and Pb in molten salts at elevated temperatures. 

Fig. A2.5 shows densities profiles of reactor coolants versus temperature. As expected, molten Pb and Pb—Bi alloy have the highest densities, followed by molten salt and Na. Actually, at 250°C, the densities of molten Na, subcritical pressure water, and SCW are close. However, with temperature increase, the densities of water and SCW steadily decline. Within the pseudocritical range, the SCW density drops significantly due to the transition from a liquid-hke fluid to a gas-like fluid. Gases, especially He, have the lowest densities. The density of CO2 is significantly higher than that of He.

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