Coprecipitation mixed nickel hydroxides

Mixtures of lithium and nickel hydroxides were prepared by impregnating nickel hydroxide with solutions of lithia in distilled water. Mixed gallium and nickel hydroxides were coprecipitated, by steam distillation, from solutions of Ni(OH)a and Ga203, 1.75 H2O in aqueous ammonia. These mixtures of hydroxides were dehydrated at 250° under vacuum (p = 10 torr). Preliminary experiments (40) have shown that incorporation of foreign ions does not occur at temperatures lower than 250° and that, in order to obtain a constant value of the electrical properties of doped samples, it is necessary to heat them at least 24 hours at 250° in vacuo. Incorporation is therefore a slow process at 250°. Dehydration is not complete at 250° NiO-f 10 at. % Li... 

The positive active material of a pocket-type electrode consists of nickel hydroxide powder by which cobalt hydroxide was coprecipitated, and is obtained from those mixed sulfate by a neutralizing method. Graphite powder is mixed as a conductor. The addition of cobalt is performed for increasing the capacity of the positive active material. Cadmium hydroxide which is a negative active material is manufactured by a coprecipitation method or a dry-mixing method. Moreover, iron powder is usually mixed with negative active material of a pocket type electrode for the increase in capacity. Graphite powder and/or nickel flake is mixed as a conductor. 

The mixed oxides CeNixOv were prepared by coprecipitation of hydroxides from mixtures of cerium and nickel nitrate using triethylamine (TEA) as precipitating agent, drying at 323 K and calcination in air at 773 K [22]. The metal loading has been verified by microanalysis. The solids will be called CeNix. 

Most methods deal with the formation of metal particles on a support that is preformed since this leads to simpler preparation processes. There is an important route, however, typically used for metal-SiCh and metal-AI2O3 catalysts, which involves (Table I) the coprecipitation in a precursor form (hydroxides, nitrates, carbonates, silicates, etc.) of both the support and the active phase from a solution 37a,b, 38, 41). The advantage is to produce an intimate mixing of metal precursor and support. The precipitate leads on calcination to a support with the active component dispersed throughout the bulk as well as at the surface. After reduction to the final catalyst, it is difficult to obtain metal crystallites of uniform size 42, 43) because of the presence of both the oxides (of the support and of the active metal) and other intermediate compounds [e.g., nickel alumi-nate or silicate for the Ni/Al203 42) and Ni/SiCh 43) systems, respectively] that have different reducibilities. 

Binary systems synthesized consisted of Cu/Fe, Ni/Fe, Cu/Al and Ni/Al and Cu/Cr for 4-10 wt percent Cu or Ni in the calcined mixed oxide. Anionic complexing agents acetic, citric and oxalic acids and EDTA were used in molar ratios of 1 1 with the initial copper or nickel. Two stage precipitations were used starting with an initial formation of aluminum, chromium or ferric hydroxide by addition of NaOH to an aqueous solution of A1 nitrate, Cr nitrate or Fe chloride. In the second stage aqueous solutions of Cu sulfate or Ni nitrate were mixed with the initial precipitate with or without the presence of a 1 1 mole ratio of selected anionic complexing agents to complete the precipitation. A second mode of coprecipitation used was to preadsorb oxalic acid on the initially precipitated AI, Cr or Fe hydroxide. 

One series of Ni/Al binary hydroxide coprecipitates was prepared with an initial atomic ratio of 1 1 Ni/Al with nickel equilibrated with anionic agents acetic acid or- citric acid or EDTA in a molecular ratio 1 1 and mixed with the initially precipitated A1 hydroxide. In this system sequestration of the Ni in solution occurred until a pH of 10-12 was attained precluding a staged coprecipitation in an acid regime. A second series of Nl/Al binary hydroxide coprecipitates using a lower Initial atomic ratio of 0.5 for Nl/Al was prepared In the presence of a 1 1 molecular ratio of citric acid or oxalic acid. (Table 1.). In this case Ni loadings in the range of 4.0-4.3 wt.% were obtained at pH values of 10.0 and 7.5 respectively but no Improvement in the state of dispersion as Indicated by the BET areas of the precipitates calcined at 350° C was obtained. 

---