Cobalt oxalate, decomposition

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... 

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],... 

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

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 ... 

In this reaction, oxalate ion may be oxidized intramolecularly by cobalt(III) ion, but it is interesting to compare the three different systems in w hich there are three, two, or one oxalate ions with the cobalt(III) cation. The last one can be boiled in l.OM add for an hour and nothing happens. In the first one, decomposition will occur very readily in aqueous solution at 50°C., so that oxalate exchange can t be measured, for instance. The middle one has not been studied in any detail yet, as far as I know, but there is oxidation-reduction in this too, though much slower than in the first. I wonder if this inhibiting effect of the nonreacting ligand, the diamine, on the oxidation has any simple explanation. 

The final operations of the preparation should be conducted without interruption because aqueous solutions of the complex salt are unstable, especially to light, and deposit insoluble cobalt (II) oxalate on standing. If decomposition of the preparation is suspected, the mother liquor from the alcohol precipitation should be decanted from the product,... 

The thermal decompositions of nickel(II)-cobalt(II) oxalate solid solutions were studied using TG and TM [103], A series of the mixed binary Ni(II)-Co(II) oxalate samples was prepared at 25% (atom) intervals across the system. Physical mixtures were also prepared by mixing the pure end members. The DTG and DTM curves showed that the decomposition proceeds to completion in two overlapping stages. The kinetics of the individual steps were not studied. From the DTG curves, the authors stated that the physical mixtures behaved as individual oxalates, while the coprecipitate decomposed as a single entity. The TM curves showed that the products formed from the physical mixture and the coprecipitate were distinctly different. The magnetic behaviour of the product from the coprecipitate was consistent with the behaviour predicted for a Ni-Co alloy, but the products from the physically mixed oxalate do not show the transition temperature predicted for an alloy. The kinetics of decomposition of iron-nickel mixed oxalates have been studied by Doremieux et al. [104]. 

Zhabrova etal. [151] identified the reactions of nickel, cobalt and copper oxalates ( , = 150, 159 and 129 kJ mol respectively) as redox processes in which there is an autocatalytic effect by product metal on the electron transfer step. The decomposition rate was determined by the area of the reactant and results were fitted by the Prout-Tompkins equation. In contrast, the reactions of magnesium, manganese and iron oxalates (f, = 200,167 and 184 kJ mol ) are not autocatalytic and the area... 

Using DTA measurements, Macklen [148] compared the temperatures of onset of decomposition of manganese, iron, cobalt and nickel oxalates for reactions in nitrogen and in air. The reactivities of these salts follows the sequence of ease of cation oxidation [152] (IvP — and from this it was concluded that the first step for reaction in air is cation oxidation followed by rapid breakdown of the oxalate anion. 

Beside the tartrate, other organic salts—notably the oxalate and the formate—yield the more easily produced pyrophoric metals, i.e. lead, nickel, and cobalt, if the pyrogenic decomposition is performed at low temperature. These organic salts or the oxides of nickel, cobalt, and iron, under hydrogen at about 300X, also furnish the self-flammable metals, but in the case of iron, a pyrophoric ferrous oxide (FeO) may first appear by reduction with hydrogen as well as by reduction under carbon monoxide. 

PTFE increases the decomposition temperature of cadmium oxalate trihy-drate. Moreover, the products of cadmium complex degradation, in turn, increase the temperature at which an intensive degradation of PTFE begins. The thermal decomposition of the highly dispersed copper formate leads to the formation of a metal-polymer composition (20-34% Cu). The maximum on the nanoparticles granulometric composition curve corresponds to 4nm. No chemical interaction between the components was observed. The decomposition of a fine dispersion of palladium hydroxide in polyvinyl chloride (PVC) results in spatial structures with highly dispersed Pd particles (S = 26 m g ) in the nodes. This process increases in the temperature required for complete dehydrochlorination of PVC. The thermolysis of cobalt acetate in the presence of PS, PAA, and poly(methyl vinyl ketone) proceeds... 

Multidentate Leaving Groups.—The hydrolysis of [Co(ox)a] - and of [Co(ox)2(OH2)2], which ultimately produces cobalt(n) and carbon dioxide, involves the formation of an intermediate containing a unidentate oxalate ligand previous to the rate-determining step. Free radical intermediates are thought unlikely in the decomposition of these oxalato-complexes, but malonate ion-radicals are thought to be intermediates both in the thermal and photochemical hydrolysis of the [Co(mal)3] anion. Kinetics are reported for a third example of these aquation-redox processes, [Co(acac)2] in acidic solution. ... 

The photochemical decomposition of cobait(m)-ammine-oxalate complexes involves primarily redox processes, as does that of the cis -[Co(bipy)2Cy+ cation.The quantum yield for the photoredox aquation of [Cofphen) is very low - lower even than those for cobalt(m)-amine complexes. The quantum yield for photoreduction of [Co(fra/M-[14]-dieneX l2l is similar to that for photoreduction of [Co(tetren)Cl] + both of these quantum yields are much less than that for the photoreduction of [Co(NH3)5Cl] +. Thermal back-reactions are important in determining the overall kinetic pattern for the photoreaction of the [Co(tra s-[14]-diene)Cl2l+ cation. ... 

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