Copper oxalate, decomposition

The thermal decomposition of copper oxalate in Nj has been studied recently by Coetzee et al. [73]. Decomposition started at about 533 K and took place in one stage. The mass of the solid product from the decomposition corresponded to the formation of CujO. Evolved gas analysis showed that both COj and CO are evolved during the decomposition. The proportion of CO in the evolved gas was greatest during the initial period and declined steadily as the reaction proceeded. The DSC results showed that (unlike the oxalates [M(C204)(H20)2] J the decomposition of copper oxalate in N2 is exothermic with an enthalpy change of -33 kJ mol. ... 

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... 

The initial or rate limiting step for anion breakdown in metal oxalate decompositions has been identified as either the rupture of the C - C bond [4], or electron transfer at a M - O bond [5], This may be an oversimplification, because different controls may operate for different constituent cations. The decomposition of nickel oxalate is probably promoted by the metallic product [68] (the activity of which may be decreased by deposited carbon, compare with nickel malonate mentioned above [65]). No catalytically-active metal product is formed on breakdown of oxalates of the more electropositive elements. Instead, they yield oxide or carbonate and reactions may include secondary processes [27]. There is, however, evidence that the decompositions of transition metal oxalates may be accompanied by electron transfers. The decomposition of copper(II) oxalate [69] (Cu - Cu - Cu°) was not catalytically promoted by the metal and the acceleratory behaviour was ascribed to progressive melting. Similarly, iron(III) oxalate decomposition [61,70] was accompanied by cation reduction (Fe " - Fe ). In contrast, evidence was obtained that the reaction of MnC204 was accompanied by the intervention of Mn believed to be active in anion breakdown [71]. These observations confirm the participation of electron transfer steps in breakdown of the oxalate ion, but other controls influence the overall behaviour. Dollimore has discussed [72] the literature concerned with oxalate pyrolyses, including possible bond rupture steps involved in the decomposition mechanisms... 

The copper oxalate is heated at 130°C to remove as much water of crystallization as possible. It is then placed in an electric furnace and heated to 320°C in a stream of purified Hg. The decomposition starts suddenly and is accompanied by a rise in temperature. Heating is continued at 220-260°C, and the product is then allowed to cool (both operations are conducted imder a stream of Hg). The copper powder is stored under hydrogen. 

The mechanism of the process is that the polymer reactive centers promote the metal nucleation and aggregation, after which the thermolysis occurs and the metal-containing substance is redistributed. The maximum amount of copper being introduced in PS through a common solvent is about 10%. At the same time, the polymer presence increases the temperature of cadmium trihydrate-oxalate decomposition [97], and the decay products increase the initial temperature of PETF intensive destruction. The copper formate thermal decomposition in the highly dispersed PETF presence allows us to produce a metallopolymeric composition (20-34% of copper) where the NP size distribution is maximal at 4nm, without any chemical interaction between the components. 

Copper Oxalate — (i) Chemical Designations — Synonyms Cupric Oxalate Hemihydrate Chemical Formula CuC2Q,- /2HO (ii) Observable Characteristics— Physical State (as normally shipped) Solid Color Bluish white Odor. None (iii) Physical and Chemical Properties — Physical State at 15 V and I atm. Solid Molecular Weight 160.6 Boiling Point at I atm. Not pertinent Freezing Point Not peninent Critical Temperature Not pertinent Critical Pressure Not pertinent Specific Gravity > 1 at 20°C (solid) Vapor (Gas) Density Not pertinent Ratio of Specific Heats of Vapor (Gas) Not pertinent Latent Heat of Vaporization Not pertinent Heat ofCmtbustion Not pertinent Heat of Decomposition Not pertinent (iv) Health Hazards Information — Recom-... 

Kabanov, A. A. etal., Russ. Chem. Rev., 1975, 44, 538-551 Application of electric fields to various explosive heavy metal derivatives (silver oxalate, barium, copper, lead, silver or thallium azides, or silver acetylide) accelerates the rate of thermal decomposition. Possible mechanisms are discussed. 

Thermal decomposition—Thermal decomposition methods may be used to prepare metal oxide fumes. An aerosol of a precursor to the metal oxide (i.e., a substance that is readily decomposed, thermally, to yield the oxide) is first generated and then is heated by passing it through a heated tube to decompose it to the oxide. Metal formates, oxalates, and the like, which readily yield the oxides and do not produce objectionable side products, are commonly used precursors. In this program, fumes of iron oxide, vanadium oxide, and copper oxide were generated using this method. 

The compound is soluble in warm water but begins to decompose slowly into copper(II) oxalate, which precipitates shortly after dissolution of the complex. The decomposition is hastened by the addition of strong acid. The material is only very slightly soluble in the common organic solvents such as acetone, benzene, carbon tetrachloride, chloroform, ethanol, and methanol. The blue crystals lose water rapidly above 150° and the resulting compound decomposes at 260°. 

Certain acid dyes [67] stabilize silver oxalate by forming surface compounds, while other dyestufis accelerate the decomposition because their redox properties enhance the ease of electron transfer from the oxalate ion to the silver. The influences of incorporated cadmium, copper and other ions on the rate of thermal decomposition, and on the concentration and mobility of interstitial silver ions, have been reviewed [46,68]. 

Broadbent et al. [69] showed that ar-time curves for the decomposition of copper(II) oxalate (503 to 533 K) were sigmoidal and that data for the vacuum reaction fitted the Avrami-Erofeev equation with values of = 2.9 initially and later n = 3.5 ( , = 136 kJ mol ). Electron transfer was identified as the step controlling the reaction. There was no evidence from X-ray diffraction studies for the intervention of the Cu salt the orthorhombic structure was present until disappearance of the reactant and product copper metal was detected. However, many metal carboxylates, chilled after dehydration, yield anhydrous salts that are amorphous to X-rays or poorly crystalline, see, for example [70]. 

Mohamed and Galwey [71], in contrast, obtained evidence that copper underwent stepwise reduction when a was less than 0.5, from titration measurements of the copper(II) content (Cu " + KI — y in samples of partially decomposed salt. This is consistent with the behaviour foimd for other copper carboxylates [72]. Moreover, it was shown that the reactivities of both (Cu " and Cu" ) oxalates were similar and reactions overlapped. In agreement with the previous study [69], ur-time curves for the overall decomposition of copper(II) oxalate were sigmoidal and, in this slightly higher temperature interval (515 to 550 K), was increased to 180 7 kJ mol". ... 

More detailed experiments with copper and nickel oxalates (184) confirmed the extensive decomposition under radiation, although the doses required to reach 80 to 90% metal appeared to be somewhat larger (perhaps by a factor of 2 to 3) than in the previous work (183). This could easily arise from differences in the techniques or in the materials. A preliminary irradiation insufficient to cause appreciable decomposition by itself (ca. 4 x 10 2 ev/gm) reduced the induction period and increased the rate of a subsequent thermal decomposition. There is considerable work on the effects of irradiation upon subsequent thermal decomposition of various solids, although not with catalyst preparation in mind (132h, 185-188). In the case of CaO, irradiation of the parent material, Ca(OH)2, did not affect the area of the oxide, although irradiation of the latter (with copper X-rays) decreased the specific surface for samples calcined (before irradiation) between 400 and 900°. 

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