Amalgamation of metals

Metallic actinium cannot be obtained by electrolytic means because it is too electropositive, II has been prepared on a milligram-scale through the reduction of actinium fluoride in a vacuum with lithium vapor at about 350 °C The metal is silvery white, faintly emits a blne-rinted light which is visible in darkness because of its radioactivity, The metal takes the form of a face-centered cubic lattice and has a melting point of 1050 50°C. By extrapolation, it is estimated that the metal boils at about 3300 0. An amalgam of metallic actinium may be prepared by electrolysis on a mercury cathode, or by the action of a lithium amalgam on an actinium citrate solution (pTT — 1.7 lo 6.8). 

One might think that a similar situation is common for all cases where the primary discharge product must, from energy considerations, be associated with the electrode, e.g., when amalgams of metals are formed. And when the discharge product remains in the solution, e.g., in ordinary redox reactions,... 

In other cases, the method of removal depends upon the nature of the product, e.g. gases may be (1) vented from the reactor, possibly via a slight reduction In pressure (2) displaced from the electrolyte via inert gas sparging (3) segregated via a solid polymer electrolyte (section 5.2) or recirculated via a gas-liquid separator. Liquid products may be (1) separated by flotation or settlement if they are immiscible and have a markedly different density to the electrolyte or (2) emulsified by mixing, then swept out of the reactor. Solid products can be separated via (I) flotation or settlement (2) fluidization or tangential shear to remove them from the reactor (3) solvent extraction or incorporation into a mercury phase, e.g. amalgamation of metals. 

Aluminum and magnesium also react to form ethoxides, but the reaction must be cataly2ed by amalgamating the metal (adding a small amount of mercury). 

Hydrogen can be prepared by the reaction of water or dilute acids on electropositive metals such as the alkali metals, alkaline earth metals, the metals of Groups 3, 4 and the lanthanoids. The reaction can be explosively violent. Convenient laboratory methods employ sodium amalgam or calcium with water, or zinc with hydrochloric acid. The reaction of aluminium or ferrosilicon with aqueous sodium hydroxide has also been used. For small-scale preparations the hydrolysis of metal hydrides is convenient, and this generates twice the amount of hydrogen as contained in the hydride, e.g. ... 

The most important method for reduction of compounds to an oxidation state suitable for titration with one of the common oxidising titrants is based upon the use of metal amalgams, but there are various other methods which can be used, and these will be discussed in the following sections. 

Although as already stated the use of metal amalgams, and in particular use of the Jones reductor or of the related silver reductor, is the best method of reducing solutions in preparation for titration with an oxidant, it may happen that for occasional use there is no Jones reductor available, and a simpler procedure will commend itself. In practical terms, the need is most likely to arise in connection with the determination of iron, for which the reduction of iron(III) to iron(II) may be necessary. 

No experiments appear to have been made with such cells, although the equation has been verified with oxygen at different partial pressures in admixture with nitrogen, with platinum electrodes and hot solid glass as electrolyte (Haber and Moser). A similar case is that of two amalgams of a metal, of different concentrations, as electrodes, and a solution of a salt of the metal as electrolyte (G. Meyer, 1891). Here we must take the osmotic pressures of the metals in the amalgams, Pi, P2, and, for an 7i-valent metal ... 

Liquid alloys of Hg with a variety of metals (amalgams) constitute particularly complex systems in view of the potential dependence of surface composition. A detailed study of In and T1 amalgams, with... 

Incorporation of Metal In certain cases, metal atoms, after their discharge, can penetrate into the substrate metal, forming alloys or intermetallic compounds in the surface layer and down to a certain depth. This effect has been known for a long time in the discharge of metals at liquid mercury, where liquid or solid amalgams are formed. In 1968 B. Kabanov showed that an analogous effect is present in metal ion discharge at many solid metals. 

Hence Cd behaves nobler in the amalgam than as the pure metal, whereas there is no such difference for Zn. For proper functioning of metal electrodes such as Cd and Zn (and many others) the prior removal of oxygen from the solution by deaeration is essential. 

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