Electrolytic methods melts

A series of Be-Pt intermetallic compounds arc prepared during the electrodeposition of Be on Pt from a solution of BeCl2 in an equimol NaCl-KCl mixture at 710°C. X-Ray diffraction of the electrode surface shows the presence of BePt, BcjPt. Electrolytic methods are also used to extract single crystals of Be,V from alloys prepared by arc melting Be and the transition metal in the proportion 15 1. 

Closely related to the above is a new process (301) in which ammonia and fluorine are passed into a reactor containing NH4F-HF at slightly above its melting point (125°C). Under these conditions the molten salt serves to moderate the reaction, which is essentially that between the two gases. It is claimed that the trifluoride produced is of high purity, and this appears to be an alternative to the electrolytic method for preparing the gas on a technical scale. 

Recent technology for electrolytic aluminum production employing aluminum chloride has also been of interest because of the about 30% power savings possible [21]. Since aluminum chloride melts at much lower temperatures and forms a much more fluid melt than the standard Hall-Heroult electrolyte matrix, much higher voltage efficiencies are possible. However, sublimation and control problems limit the utility of direct, one-component electrolytic methods. The essence of this idea is employed in the process, developed by C. Toth of Alcoa, which has the additional advantage of enabling clay sources of alumina to be tapped [22] (Fig. 12.4). 

Figure 25 shows the general process steps for the melting route. All components of the alloys must he in metallic form, either as elements, or as master alloys which may he available more economically. Examples of the latter are RE-TM eutectic alloys (except with Sm) prepared by electrowinning, and Fe-Zr or Fe-Ti which are standard products for the steel industry. The RE metals used are made either metallothermically by reducing RE-oxides with calcium (and in the case of Sm with La or mischmetal) as the reductant, or by molten-chloride electrolysis. Electrolytic methods do not work with samarium because of its stable divalent state. Samarium is usually further refined by vacuum distillation, which is easy because of the low boiling point. 

There are other procedures thus very pure Th is made from Thl4 by thermal decomposition (de Boer process). Electrolytic methods are not com- monly used, but Th can be obtained from a melt of ThF KCN-and NaGfi Americium has been obtained by a method depending upon the volatility, which is greater than that of the other actinides ... 

The composition of the alloy depends on the composition of the electrolyte, the reaction conditions, and special additives which favor the precipitation. Just as in the case of solidification of melts, alloys precipitated by the electrolytic method consist of heterogeneous crystallizates, solid solutions, or some intermediate phases. They may differ from the alloys produced at high temperatures. The differences may show up in phase boundaries and in some physical and engineering properties [6]. 

Other routes for hydroxybenzaldehydes are the electrolytic or catalytic reduction of hydroxybenzoic acids (65,66) and the electrolytic or catalytic oxidation of cresols (67,68). (see Salicylic acid and related compounds). Sahcylaldehyde is available in drums and bulk quantities. The normal specification is a freezing point minimum of 1.4°C. 4-Hydroxybenzaldehyde is available in fiber dmms, and has a normal specification requirement of a 114°C initial melting point. More refined analytical methods are used where the appHcation requires more stringent specifications. 

Zirconium tetrachloride forms hexachlorozirconates with alkab-metal chlorides, eg, Li ZrCl [18346-96-8] Na2ZrClg [18346-98-0] K ZrCl [18346-99-1y, Rb2ZrClg [19381 -65-8] and Cs2ZrClg, and with alkaline-earth metal chlorides SrZrCh [21210-13-9] and BaZrCl [21210-12-8]. The vapor pressure of ZrCl over these melts as a function of the respective alkah chlorides and of ZrCl concentration were studied as potential electrolytes for the electrowinning of zirconium (72). The zirconium tetrachloride vapor pressure increased in the following sequence Cs < Rb < K < Na < Li. The stabiUty of a hexachlorohafnate is greater than that of a comparable hexachlorozirconate (171), and this has been proposed as a separation method (172). 

The only practicable large-scale method of preparing F2 gas is Moissan s original procedure based on the electrolysis of KF dissolved in anhydrous HF (see however p. 821). Moissan used a mole ratio KF HF of about 1 13, but this has a high vapour pressure of HF and had to be operated at —24°. Electrolyte systems having mole ratios of 1 2 and 1 1 melt at 72° and 240°C respectively and have much lower vapour pressures of HF accordingly... 

The electrolyte salt must be processed to recover the ionic plutonium orginally added to the cell. This can be done by aqueous chemistry, typically by dissolution in a dilute sodium hydroxide solution with recovery of the contained plutonium as Pu(OH)3, or by pyrochemical techniques. The usual pyrochemical method is to contact the molten electrolyte salt with molten calcium, thereby reducing any PUCI3 to plutonium metal which is immiscible in the salt phase. The extraction crucible is maintained above the melting point of the contained salts to permit any fine droplets of plutonium in the salt to coalesce with the pool of metal formed beneath the salt phase. If the original ER electrolyte salt was eutectic NaCl-KCl a third "black salt" phase will be formed between the stripped electrolyte salt and the solidified metal button. This dark-blue phase can contain 10 wt. % of the plutonium originally present in the electrolyte salt plutonium in this phase can be recovered by an additional calcium extraction stepO ). 

Cu crystallizes in the fee and its melting point is 1356 K. The experimental data for single-crystal Cu/H20 interfaces are also controversial. 567 570,572 57X The first studies with Cu(l 11), Cu(100), and Cu(l 10) in surface-inactive electrolyte solutions (NaF, Na2S04) show a capacitance minimum at E less negative than the positive limit of ideal polarizability of Cu electrodes (Table 11). depends on the method of surface... 

Obviously this method is limited to liquid metals like mercury and gallium and their amalgams respectively alloys. Modifications of this method have been reported [86FIor]. At elevated temperatures with molten salt electrolytes alloys with an appropriately low melting point can be investigated, too. 

In this method " - the melt eontains boric oxide and the metal oxide in a suitable electrolyte, usually an alkali or alkaline-earth halide or fluoroborate. The cell is operated at 700-1000 C depending on electrolyte composition. To limit corrosion, the container serving as cathode is made of mild steel or of the metal whose boride is sought. The anode is graphite or Fe. Numerous borides are prepared in this way, e.g., alkaline-earth and rare-earth hexaborides " and transition-metal borides, e.g, TiBj NijB, NiB and TaB... 

The zero-charge potential is determined by a number of methods (see Section 4.4). A general procedure is the determination of the differential capacity minimum which, at low electrolyte concentration, coincides with Epzc (Section 4.3.1). With liquid metals (Hg, Ga, amalgams, metals in melts) Epzc is directly found from the electrocapillary curve. 

Sulphides. MoS2 was prepared by electrolysis at 1000°C of a melt consisting of sodium tetraborate, sodium fluoride, sodium carbonate in which molybdenum (VI) oxide and sulphur were dissolved. The electrolysis was carried out at 1000°C with the melt contained in a graphite crucible also acting as anode. After electrolysis, the excess electrolyte was dissolved in water to obtain crystalline MoS2, containing however up to 2% carbon. A similar method was used for WS2 carbon was the principal impurity in the sulphides. 

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