Sulfamic acid electrolyte

Research Focus Synthesis of sulfamic acid electrolytic polymers for fuel cells requiring high proton conductivity and open circuit voltages. 

Jackson DD, Hollen RM, Roensch FR, Rein JE (1980) Controlled potential coulometric determination of plutonium with hydrochloric and sulfamic acid electrolyte and phosphate complexation. Anal Chim Acta 117 205... 

The combined Ni nanoparticles deposition and PTFE suspension from the sulfamic-acid electrolyte during nickel-coating at room temperature leads to polymer inclusion into the Ni deposit. The polymer may contribute up to 20 wt%. The process is controlled by varying the cathode current density and the concentration of the suspension introduced. The relationship between the homocoagulation and heterocoagulation interactions of metal particles and polymer is determined by the rates of electrochemical deposition and the trapping of Ni in the PTFE systems. 

Nickel Sulfamate. Nickel sulfamate [13770-89-3] Ni(S02NH2)2 4H2O, commonly is used as an electrolyte ia nickel electroforming systems, where low stress deposits are required. As a crystalline entity for commercial purposes, nickel sulfamate never is isolated from its reaction mixture. It is prepared by the reaction of fine nickel powder or black nickel oxide with sulfamic acid ia hot water solution. Care must be exercised ia its preparation, and the reaction should be completed rapidly because sulfamic acid hydrolyzes readily to form sulfuric acid (57). 

One possible, although speculative explanation of the effect of the addition of sulfamic acid or sodium sulfate may be based on Eq. (4.9). According to this equation, the variation in the concentration c of a nonreacting electrolyte changes the thickness of the metal-solution interphase, the double-layer thickness It appears that as the thickness of the double layer, decreases, the coercivity of the Co(P) deposited decreases as well. 

TABLE 1. Proton Conductivity and Open-Circuit Testing Results for Electrolytic Membranes Consisting of Selected Polyamidic Acid Sulfamic Acid Derivatives Conducted at 150oC ... 

The first recorded synthesis of silver(I) sulfamate was that by Berglund in 1876 he used the very slow reaction between silver(I) sulfate and barium(II) sulfamate. Later methods have employed the reaction between sulfamic acid and silver(I) oxide or silver(I) carbonate an electrolytic process has also been described. ... 

Chemistry may be combined with CPC to improve selectivity. For example (Jackson et al. 1980) applying the chemistry of the Davies and Townsend titration (seeO Sect. 63.4.4.3), Pu is first reduced electrolytically to Pu(III) in an hydrochloric/sulfamic acid mixture along with iron and other potential interfering species. Iron and a number of the other impurities are reoxidized next without reoxidizing Pu(in). Finally, phosphate is added to lower the redox potential of the Pu(III)/Pu(IV) couple to permit a quantitative electrooxidation of Pu(III) to Pu(IV), without oxidizing chloride ions. The procedure is very selective and is applicable to Pu determinations in the presence of uranium in 10 1 U/Pu molar ratio. 

Dithionic acid tends to decompose at normal cell operating temperatures to H2SO4 and SO2. The sulfate will then precipitate lead and SO2 wiU be reduced at the cathode to H2S, which in turn will precipitate PbS. Sulfamic acid is also unstable at higher current densities and tends to break down to form ammonium sulfate, in turn precipitating lead sulfate. Hence, the most suitable practical alternative electrolytes are fluosilicic and fluoboric acid systems. 

For electrolytic refining, an electrolyte is required that has a reasonable lead solubility, is stable, has a high electrical conductivity and will yield a smooth compact deposit of lead. Various organic acids have good lead solubility and conductivity but tend to be unstable. It was found during the early development of the process that fluosilicic acid, fluoboric acid and sulfamic acid were most suitable and fluosilicic acid was the least costly. Sulfamic acid systems were also used, but showed instability at high current densities. Consequently, most electrolytic refining operations are based on a fluosilicate electrolyte. 

The composition of the codeposition bath is defined not only by the concentration and type of electrolyte used for depositing the matrix metal, but also by the particle loading in suspension, the pH, the temperature, and the additives used. A variety of electrolytes have been used for the electrocodeposition process including simple metal sulfate or acidic metal sulfate baths to form a metal matrix of copper, iron, nickel, cobalt, or chromium, or their alloys. Deposition of a nickel matrix has also been conducted using a Watts bath which consists of nickel sulfate, nickel chloride and boric acid, and electrolyte baths based on nickel fluoborate or nickel sulfamate. Although many of the bath chemistries used provide high current efficiency, the effect of hydrogen evolution on electrocodeposition is not discussed in the literature. 

The impure metal dissolves easily in mineral acids and in fluoroboric, sulfamic am trifluoromethylsulfonic acids to give Cr2+ solutions, but oxidation of Cr2+ by hydrogen ion (equation 6), °(Cr3+, Cr2+) = —0.41 V) even in an inert atmosphere is catalyzed by thi impurities and various ions.71 Indefinitely stable chromium(II) solutions can be obtained fron the pure (electrolytic) metal (99.5% or better), although the reaction with acid may need to b< initiated by heat and the inclusion of some metal previously attacked by acid. The use of ai excess of metal, which can be filtered off, ensures that little acid remains. In near neutra solution the hydrogen potential is lowered and the Cr2+ ion is stable. In alkaline condition brown Cr(OH)2, which slowly reduces water, precipitates.73,73... 

The metallizing electrolyte has the following typical composition 421 g/L nickel sulfamate, 45 g/L boric acid, 0.15 g/L antipitting agent (SNAP), and 0.25 g/L copper sulfate. 

Electrolyte composition was 80 to 85 g/L lead and 45 to 50 g/L free sulfamic add (HNH2SO3). One to two grams per litre of tannic acid (tannin) was also nsed as a smoothing agent. Current densities used were around 90 amps/m, and it was found that as the current density increased to lOOamps/m or above there was an increasing degree of decomposition of snlfamic acid. 

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