Metals electrolysis

Baral, S., Brandshow, S. and Gaber, B. (1993) Electrolysis metallization of halloysite, a hollow cylindrical 1 1 alumosilicate of submicron diameter. Chemistry of Materials, 5, 1227-1233. 

During electrolysis, metal appears to be transferred from the anode to the cathode. But the electric current (the electron flow) is actually in the opposite direction. 

The process of electroplating metals is another important application of electrolysis. Metals that easily corrode (Fe and Cu) can be plated by metals that are resistant to corrosion. Chromo - plating steel parts used in vehicles is a good example of electroplating. Steel bumpers become more corrosion-resistant when they are electroplated with nickel first, then with chromium. 

Figure 074. Setup for the preparation of hydrogen and oxygen free chlorine gas. During the electrolysis, metallic iron will...

Chemistry. There are many parts of mainline chemistry that originated in electrochemistry. The third law of thermodynamics grew out of observations on the temperature variations of the potential of electrochemical reactions occurring in cells. The concepts of pH and dissociation constant were formerly studied as part of the electrochemistry of solutions. Ionic reaction kinetics in solution is expressed in terms of the electrochemical theory developed to explain the activity of ions in solution. Electrolysis, metal deposition, syntheses at electrodes, plus half of the modem methods of analysis in solution depend on electrochemical phenomena. Many biomolecules in living systems exist in the colloidal state, and the stability of colloids is dependent on the electrochemistry at their contact with the surrounding solution. 

One of the most extensively examined gas evolution reactions, next only to the H2 evolution reaction, is the O2 evolution reaction (OER) (209) as it is one of the main electrochemical reactions in water electrolysis, metal electrowinning, and recharging of metal-air cells. The standard electrode potential for the oxygen evolution reaction at 25°C calculated from the standard Gibbs energy of formation of H2O and OH ions (/) is 1.299 V [versus normal H2 electrode (NHE)] and 0.401 V (versus NHE) in alkaline media. The oxygen evolution reactions are... 

When molten sodium chloride (without water) is subjected to electrolysis, metallic sodium and chlorine gas are formed ... 

Cation kat- I-on [Gk kation, neut., prp. of katienai to go down cap, fr. kata-cztz-- + ienai to go] (1834) n. An atom, molecule or radical, usually in aqueous solution, that has lost an electron and has become positively charged. It can also be described as a positively charged atom or radical, which moves to the negative electrode or cathode during electrolysis. Metallic ions, such as iron and copper, etc., are cations. 

Esposito DV, Hunt ST, Kimmel YC, Chen JG (2012) A new class of electrocatalysts for hydrogen production from water electrolysis metal monolayers supported on low-cost transition metal carbides. J Am Chem Soc 134 3025-3033... 

Xiao, H., Hovland, R., Rolseth, S. and Thonstad, J. (1996) Studies on the corrosion and the behaviour of inert anodes in aluminium electrolysis. Metall. Mater. Trans. B, 27B, 185-188. 

The general characteristics of all these elements generally preclude their extraction by any method involving aqueous solution. For the lighter, less volatile metals (Li, Na, Be, Mg, Ca) electrolysis of a fused salt (usually the chloride), or of a mixture of salts, is used. The heavier, more volatile metals in each group can all be similarly obtained by electrolysis, but it is usually more convenient to take advantage of their volatility and obtain them from their oxides or chlorides by displacement, i.e. by general reactions such as... 

The reactions with water are summarised in Table 6.3. Since the metals are powerful reducing agents (p. 98) they cannot be prepared in aqueous solution electrolysis of the fused anhydrous halides is usually employed using a graphite anode. 

Aluminium is obtained on a large scale by the electrolysis of the oxide, dissolved in fused cryolite The oxide, occurring naturally as bauxite, AI2O3.2H2O, usually contains silica and iron(III) oxide as impurities. These must be removed first, since aluminium, once prepared, cannot be freed of other metals (which will be deposited on electrolysis) by refining it. The crude oxide is dissolved under pressure in caustic soda solution the aluminium oxide and silica dissolve and the ironflll) oxide is left ... 

Graphite reacts with alkali metals, for example potassium, to form compounds which are non-stoichiometric but which all have limiting compositions (for example K C) in these, the alkaU metal atoms are intercalated between the layers of carbon atoms. In the preparation of fluorine by electrolysis of a molten fluoride with graphite electrodes the solid compound (CF) polycarbon fluoride is formed, with fluorine on each carbon atom, causing puckering of the rings. 

Fluorine cannot be prepared directly by chemical methods. It is prepared in the laboratory and on an industrial scale by electrolysis. Two methods are employed (a) using fused potassium hydrogen-fluoride, KHFj, ill a cell heated electrically to 520-570 K or (b) using fused electrolyte, of composition KF HF = 1 2, in a cell at 340-370 K which can be electrically or steam heated. Moissan, who first isolated fluorine in 1886, used a method very similar to (b) and it is this process which is commonly used in the laboratory and on an industrial scale today. There have been many cell designs but the cell is usually made from steel, or a copper-nickel alloy ( Monel metal). Steel or copper cathodes and specially made amorphous carbon anodes (to minimise attack by fluorine) are used. Hydrogen is formed at the cathode and fluorine at the anode, and the hydrogen fluoride content of the fused electrolyte is maintained by passing in... 

Manganese is the third most abundant transition metal, and is widely distributed in the earth s crust. The most important ore is pyrolusite, manganese(IV) oxide. Reduction of this ore by heating with aluminium gives an explosive reaction, and the oxide Mn304 must be used to obtain the metal. The latter is purified by distillation in vacuo just above its melting point (1517 K) the pure metal can also he obtained by electrolysis of aqueous manganese(II) sulphate. 

Pure iron is prepared by reduction of iron(II) oxide with hydrogen, or by electrolysis of an iron(II)-containing aqueous solution. It is a fairly soft metal, existing in different form according to temperature ... 

The metal is now principally obtained in the U.S. by electrolysis of fused magnesium chloride derived from brines, wells, and sea water. 

The method of obtaining aluminum metal by the electrolysis of alumina dissolved in cryolite was discovered in 1886 by Hall in the U.S. and at about the same time by Heroult in France. Cryolite, a natural ore found in Greenland, is no longer widely used in commercial production, but has been replaced by an artificial mixture of sodium, aluminum, and calcium fluorides. 

---