Cobalt oxalate

Cobalt salts are used as activators for catalysts, fuel cells (qv), and batteries. Thermal decomposition of cobalt oxalate is used in the production of cobalt powder. Cobalt compounds have been used as selective absorbers for oxygen, in electrostatographic toners, as fluoridating agents, and in molecular sieves. Cobalt ethyUiexanoate and cobalt naphthenate are used as accelerators with methyl ethyl ketone peroxide for the room temperature cure of polyester resins. 

Recently, it has been shown [1071] that CoC204 2 H20 exists in two crystalline modifications, a and 3. Taskinen et al. [1072] prepared anhydrous cobalt oxalate of different particle sizes by dehydration of the (3 (coarser grained) phase and the a/(3 mixture (finer grained). The coarser grained preparation decomposed at 590—700 K with a sigmoid a—time curve fitted by the Avrami—Erofe ev equation [eqn. (6), n = 2] and below and above 625 K, E values were 150 and 57 kJ mole-1, respectively. Reaction of the fine preparation obeyed eqn. (6) (n = 3) and below and above 665 K, values of E were 120 and 59 kJ mole-1, respectively. Catalytic properties of the products of decomposition of cobalt oxalate have been investigated [1073]. 

Kadlec and Rosmusova [1153] believe that both Ni and Co oxalates initially yield product oxide and that the proportion of metal increases with a. Since nickel oxalate decomposes at temperatures 60 K lower than those for CoC204, even a small proportion of Ni2+ markedly increases the rate of decomposition of cobalt oxalate. The effect was attributed to the catalytic properties of the preferentially formed Ni metal. The a—time curves were generally sigmoid and showed only slight deviations in shape with changes in the Ni Co ratio. In the decomposition of a mechanical... 

Aquo-pentammino-cobaltic Oxalate, [Co(NH8)5H20]2(C204)3. 1HS0, is prepared from chloro-pentammino-cobaltie chloride. The finely powdered chloride is heated with water and dilute aqueous ammonia, the deep red liquid is filtered, and the filtrate cooled and saturated with oxalic acid. Ammonium oxalate in aqueous solution is then added to complete the precipitation of the salt, and the residue is collected on a filter, washed free from the chloride with water and finally with alcohol.2 The substance does not lose water if kept over concentrated sulphuric acid, but if heated to 100° C. it decomposes. 

Cobaltous oxalate dihydrate, CoC 04-2H 0 tpink). is obtained by adding oxalic acid or an alkaline oxalate to a cobaltous salt solution. This is the commercial form of tile salt and is important as the starting material in ihe preparation of cobalt metal powders. 

In 1857, Schneider4 analysed cobalt oxalate, determining the carbon dioxide obtained by its combustion and the metal left after igniting the salt in air and subsequently in hydrogen. Four analyses gave the following result ... 

The r-time curves for the decomposition of anhydrous cobalt oxalate (570 to 590 K) were [59] sigmoid, following an initial deceleratory process to a about 0.02. The kinetic behaviour was, however, influenced by the temperature of dehydration. For salt pretreated at 420 K, the exponential acceleratory process extended to flr= 0.5 and was followed by an approximately constant reaction rate to a = 0.92, the slope of which was almost independent of temperature. In contrast, the decomposition of salt previously dehydrated at 470 K was best described by the Prout-Tompkins equation (0.24 < a< 0.97) with 7 = 165 kJ mol . This difference in behaviour was attributed to differences in reactant texture. Decomposition of the highly porous material obtained from low temperature dehydration was believed to proceed outwards from internal pores, and inwards from external surfaces in a region of highly strained lattice. This geometry results in zero-order kinetic behaviour. Dehydration at 470 K, however, yielded non-porous material in which the strain had been relieved and the decomposition behaviour was broadly comparable with that of the nickel salt. Kadlec and Danes [55] also obtained sigmoid ar-time curves which fitted the Avrami-Erofeev equation with n = 2.4 and = 184 kJ mol" . The kinetic behaviour of cobalt oxalate [60] may be influenced by the disposition of the sample in the reaction vessel. 

On decomposition, cobalt oxalate shows a greater tendency than the nickel salt to form oxide. In vacuum, or in an inert atmosphere, reaction proceeds in two steps [61,62] ... 

During the decomposition of Ni-Co mixed oxalates the production of nickel metal accelerates reaction, because the nickel constituent reacts about 60 K lower than cobalt oxalate (Sections 16.4.2. and 16.4.4. above). The significance of the relative yields of metal and oxide in the decompositions of the mixed oxalates Co-Ni Co-Mg and Ni-Mg has been discussed [99],... 

I. Prepared by reduction of precipitated cobalt oxalate with hydrogen. 

Cobalt oxalate, precipitated in the cold, is dried at 120°C and ground to a fine powder. It is then reduced with H3 (six hours at 500°C), with the temperature being raised rapidly at the beginning of the iim. The product is cooled, groimd and reduced once more the fine metal powder is stored in a glass vessel tmder alcohol. 

Fine Co powder obtained from cobalt oxalate is heated to 400-500°C in a stream of HI (4-5 hours). The product iodide is melted by heating to 550°C and allowed to cool in high vacuum. 

The reduction and nitridation must be carried out in one continuous operation, since the Co powder obtained by reduction of C03O4 is pyrophoric. The cobalt powder prepared from cobalt oxalate cannot be completely converted to nitride under these conditions. 

CO disproportionation over metallic Co during thermal decomposition of the cobalt oxalate dehydrate [15]. 

Wang, D., Q. Wang, and T. Wang. 2011. Morphology-controllable synthesis of cobalt oxalates and their conversion to mesoporous C03O4 nanostructures for application in supercapacitors. Inorganic Chemistry 50 6482-6492. 

As noted in the introduction to this chapter, the temperature needed for the solids to react fully can be lowered considerably if the diffusion distance for the reacting atoms is kept low by having them close to each other in the precursors. In the mixed salt (iron cobalt oxalate) that is the precursor for the corresponding spinel, the metal ions are already mixed on an atomic scale in the proper stoichiometric amounts and a complete decomposition of the oxalate (indicated with the abbreviation Ox) to the mixed oxide (the spinel) takes place at 700°C within 3 h ... 

Mesocrystals can even be formed without additive, as foimd for the related cobalt oxalate dihydrate [126]. Copper oxalate crystals were composed of nanometer building units and strings of nanodomains oriented along the principal axis of the particle were detected, revealing that the lateral and basal faces of the precipitate are composed of stacked nanoparticle layers with a thickness of 5-7 nm. 

The basic compound for the synthesis of organocobalt compounds is Co2(CO)8 which satisfies the 18-electron rule [10-17]. Co2(CO)g is prepared by reducing cobalt acetate, cobalt hydroxide or cobalt oxalate with hydrogen and reacting with carbon monoxide [10-13]. For example, Co2(CO)g is prepared by reacting cobalt acetate with hydrogen and carbon monoxide as shown in eq. (17.1) [11]. The reaction is carried out under mild conditions by adding a small amount of Co2(CO)g since Co2(CO)g has an autocatalytic action as shown in eq. (17.2) [12]. 

Figure 5.10 Structure of hydrazinium cobalt oxalate trihydrate. Reproduced from Ref. [20] with permission from Elsevier 1983.

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