Ammonium electrolytes

Zinc-Manganese Dioxide. In 1866 Leclanche invented a galvanic cell in which the reduction of Mn02 is the cathodic reaction in the cell s discharge. The corresponding anodic dissolution reaction is the oxidation of zinc. The Leclanche cell is a (so-called) dry cell, i.e., the ammonium electrolyte is immobilized in the form of a paste. There are three forms of the zinc-manganese dioxide batteries ... 

Separation of cations can be influenced by their interaction with crown ethers, which depends on the sizes of the cation and the crown ether cavity. The concentration of a crown ether in the running buffer also plays a role. The best results have been obtained with 18-crown-6-ether where the selectivity changes were largest. The use of crown ethers makes it possible to separate, e.g., potassium from ammonium. Electrolyte containing 4mmoll 18-crown-6, 4 mmol 1 copper sulfate, and 4 mmol 1 formic acid was successfully applied to complete separation of all alkali and alkaline earth cations including ammonium (Figure 2). 

From Fig. 2.22a, it can be seen that the silver deposit obtained from the nitrate electrolyte was constructed from a small number of nuclei. Irregular large grains were formed even with an initial current density of 0.5/l, causing formation of a non-compact deposit. On the other hand, the microcrystalline deposit was obtained by electrodeposition from the ammonium electrolyte (Fig. 2.22b). 

Fig. 2.38 The physical model of a partially covered inert electrode with active grains and a completely covered inert electrode (a) a graphite electrode completely covered by deposition from the ammonium electrolyte current density on the electrode completely covered with silver was 62.5 mA cm at an overpotential of 120 mV in the nitrate electrolyte and (b) the silver deposit on the graphite electrode after the polarization measurements ended at an overpotential of 120 mV in the nitrate electrolyte current density on such electrode was 59.4 mA cm at the same overpotential in the nitrate electrolyte (Reprinted from Ref. [1] with kind permission from Springer and Ref. [6] with permission from Elsevier)...

Application of complex salt electrolytes in metal electrodeposition processes was examined by comparison of silver electrodeposition processes from the simple (nitrate) and complex (ammonium) electrolytes [15]. Silver was deposited from 0.10 M AgNOs in 0.20 M HNO3 (the simple electrolyte) and 0.10 M AgNOs in 0.50 M (NH4)2S04 to which was added ammonium hydroxide to dissolve the precipitate of Ag sulfate (the complex electrolyte). The conductivities of both electrolytes were almost the same [3]. Silver was deposited onto a stationary vertical Pt cathode (1x1) cm placed in the middle of a cylindrical cell (diameter 6 cm and height 5 cm). The surface of the cell was covered by anode of a high purity Ag plate. Polarization curves were recorded at the Pt wire electrodes at which Ag from the ammonium complex electrolyte was previously electrodeposited. 

The overpotential-apparent current density and the cell voltage (edge overpotential)-apparent current density plots for the Ag deposition from both the nitrate and the ammonium electrolytes are presented in Fig. 3.16a, b, respectively. For Ag deposition from the nitrate electrolyte, /q > > is valid, and at / < < nucleation in the middle of the electrode does not occur because the overpotential is very low. Hence, deposition from the nitrate electrolyte is only expected at the... 

For the ammonium electrolyte, there is a region where deposition is under the activation control because I o < i < i l (for this electrolyte, io = 0.25 mA cm and a slope of 60 mV dec ). Hence, nucleation occurs over the entire surface electrode. For deposition from the ammonium electrolyte (Fig. 3.16b), a more homogeneous distribution of the deposit is obtained, as is illustrated in Fig. 3.17c, d. 

Figure 11.14 Separation of 16 common metal ions and ammonium. Electrolyte. 11 mM lactic acid, 2.5 mM 18-crown-6, 7.5 mM 4-methylben-zylamine, 8% methanol, pH 4.3 applied voltage, 30 kV injection time, 30 s. Peaks ...

Abbott, A.P. and Harper, J.C. (1999) Double layer capacitance and conductivity studies of long chain quaternary ammonium electrolytes in supercritical carbon dioxide. Physical Chemistry Chemical Physics, 1, 839-841. 

The ammonium hydrogensulphate is returned to the electrolytic cell. A process such as this yields an aqueous solution containing about 30% hydrogen peroxide. The solution can be further concentrated, yielding ultimately pure hydrogen peroxide, by fractional distillation but the heating of concentrated hydrogen peroxide solutions requires care (see below). 

Because of the special stabiHty of the hexafluoroarsenate ion, there are a number of appHcations of hexafluoroarsenates. For example, onium hexafluoroarsenates (33) have been described as photoinitiators in the hardening of epoxy resins (qv). Lithium hexafluoroarsenate [29935-35-1] has been used as an electrolyte in lithium batteries (qv). Hexafluoroarsenates, especially alkaH and alkaline-earth metal salts or substituted ammonium salts, have been reported (34) to be effective as herbicides (qv). Potassium hexafluoroarsenate [17029-22-0] has been reported (35) to be particularly effective against prickly pear. However, environmental and regulatory concerns have severely limited these appHcations. 

Manufacture and Economics. Nitrogen tritiuoride can be formed from a wide variety of chemical reactions. Only two processes have been technically and economically feasible for large-scale production the electrolysis of molten ammonium acid fluoride and the direct fluorination of the ammonia in the presence of molten ammonium fluoride. In the electrolytic process, NF is produced at the anode and H2 is produced at the cathode. In a divided cell of 4 kA having nickel anodes, extensive dilution of the gas streams with N2 was used to prevent explosive reactions between NF and H2 (17). 

The most significant nonferrous use of manganese compounds is for primary batteries, where manganese dioxide is the principal constituent of the cathode mix. In the standard Leclanchn ceU, 2inc and ammonium chloride are mixed to form the electrolyte, a mixture of carbon and MnO forms the cathode, and 2inc acts as the anode (221). The principal ceU reaction is as foUows ... 

The covalent character of mercury compounds and the corresponding abiUty to complex with various organic compounds explains the unusually wide solubihty characteristics. Mercury compounds are soluble in alcohols, ethyl ether, benzene, and other organic solvents. Moreover, small amounts of chemicals such as amines, ammonia (qv), and ammonium acetate can have a profound solubilizing effect (see COORDINATION COMPOUNDS). The solubihty of mercury and a wide variety of mercury salts and complexes in water and aqueous electrolyte solutions has been well outlined (5). 

Ttinitroparaffins can be prepared from 1,1-dinitroparaffins by electrolytic nitration, ie, electrolysis in aqueous caustic sodium nitrate solution (57). Secondary nitroparaffins dimerize on electrolytic oxidation (58) for example, 2-nitropropane yields 2,3-dimethyl-2,3-dinitrobutane, as well as some 2,2-dinitropropane. Addition of sodium nitrate to the anolyte favors formation of the former. The oxidation of salts of i7k-2-nitropropane with either cationic or anionic oxidants generally gives both 2,2-dinitropropane and acetone (59) with ammonium peroxysulfate, for example, these products are formed in 53 and 14% yields, respectively. Ozone oxidation of nitroso groups gives nitro compounds 2-nitroso-2-nitropropane [5275-46-7] (propylpseudonitrole), for example, yields 2,2-dinitropropane (60). 

Ammonium chloride has a number of iadustrial uses, most importantiy ia the manufacture of dry-ceU batteries, where it serves as an electrolyte. It is also used to make quarryiag explosives, as a hardener for formaldehyde-based adhesives, as a flame suppressant, and ia etching solutions ia the manufacture of ptinted circuit boards. Other appHcations iaclude use as a component of fluxes ia ziac and tin plating, and for electrolytic refining of ziac. 

In Leclanchn cells, the high concentration of ammonium chloride leads to the formation of insoluble diammine 2inc chloride through the reaction in the electrolyte. 

In the 2inc chloride cell, precipitated basic 2inc chloride is the primary anode product because of the low concentration of ammonium chloride in the cell. Water and 2inc chloride are consumed in equations 1 and 7 and must be provided in adequate amounts for the cell to discharge efficiendy. Usually more carbon is used in 2inc chloride cells than in Led an chit cells in order to increase the electrolyte absorptivity of the cathode and thus allow the use of a larger volume of electrolyte. Also, the use of a thin paper separator, which decreases internal resistance, allows less space for water storage than the thick, pasted separator constmction traditionally used in Leclanchn cells. 

Oxidative surface treatment processes can be gaseous, ie, air, carbon dioxide, and ozone Hquid, ie, sodium hypochlorite, and nitric acid or electrolytic with the fiber serving as the anode within an electrolytic bath containing sodium carbonate, nitric acid, ammonium nitrate, ammonium sulfate, or other electrolyte. Examples of electrolytic processes are described in the patent Hterature (39,40)... 

Monovalent cations are good deflocculants for clay—water sHps and produce deflocculation by a cation exchange process, eg, Na" for Ca ". Low molecular weight polymer electrolytes and polyelectrolytes such as ammonium salts (see Ammonium compounds) are also good deflocculants for polar Hquids. Acids and bases can be used to control pH, surface charge, and the interparticle forces in most oxide ceramic—water suspensions. 

Electrolyte. The ideal electrolyte, ie, the fluid part of the cell, for organic synthesis would give high solubiHty to the organic, possess good conductivity, have low cost, contain easy recovery and purification, and be noncorrosive. Quaternary ammonium salts provide many of the above criteria ia aqueous systems. A coacise compilation of solveats and salts used ia electroorganic chemistry is available (40). 

A.sahi Chemical EHD Processes. In the late 1960s, Asahi Chemical Industries in Japan developed an alternative electrolyte system for the electroreductive coupling of acrylonitrile. The catholyte in the Asahi divided cell process consisted of an emulsion of acrylonitrile and electrolysis products in a 10% aqueous solution of tetraethyl ammonium sulfate. The concentration of acrylonitrile in the aqueous phase for the original Monsanto process was 15—20 wt %, but the Asahi process uses only about 2 wt %. Asahi claims simpler separation and purification of the adiponitrile from the catholyte. A cation-exchange membrane is employed with dilute sulfuric acid in the anode compartment. The cathode is lead containing 6% antimony, and the anode is the same alloy but also contains 0.7% silver (45). The current efficiency is of 88—89%, with an adiponitrile selectivity of 91%. This process, started by Asahi in 1971, at Nobeoka City, Japan, is also operated by the RhcJ)ne Poulenc subsidiary, Rhodia, in Bra2il under Hcense from Asahi. 

---