Decomposition of silver oxalate

Thus it is similar to the decomposition of azides. There have been several papers on silver oxalate — Ag2C204. Macdonald and Hinshelwood [76] confirmed the Berthelot equation, according to which the only products of decomposition of silver oxalate are metallic silver and C02. 

Benton and Cunningham [77] found that the rate of thermal decomposition of silver oxalate may be increased by previously exposing it to ultra-violet radiation. 

During the thermal decomposition of silver oxalate, fragments of metallic silver are formed. This has been confirmed by conductivity measurements (Macdonald and Sandison [78]) or by X-ray examination (Griffith [79]). 

Tompkins [80] investigated the thermal decomposition of silver oxalate at 110— 130°C. Its decomposition, in his opinion, is similar to that of barium azide. 

Silver oxalate is a colourless, crystalline substance which on heating undergoes an exothermic decomposition. The reaction begins at a little over 100 °C and easily becomes explosive. It was noticed quite early that samples prepared in the presence of an excess of oxalate were less stable thermally than those prepared using stoichiometric amounts of oxalate and silver ions. The thermal decomposition of silver oxalate into silver and C02 has subsequently been studied under varying conditions of preparation, decomposition environment and preirradiation.258,259... 

Kabanov and Skrobot have shown [67] that magnetic fields (200 to 500 oersteds) caused a slight diminution in the rate of KMn04 decomposition. Relatively few studies of this type have been made but these workers mention that magnetic fields increase the rate of barium azide decomposition, decrease the rate of decomposition of silver oxalate and do not change the rate of decomposition of silver azide. 

Many kinetic studies of the thermal decomposition of silver oxalate have been reported. Some ar-time data have been satisfactorily described by the cube law during the acceleratory period ascribed to the three-dimensional growth of nuclei. Other results were fitted by the exponential law which was taken as evidence of a chain-branching reaction. Results of both types are mentioned in a report [64] which attempted to resolve some of the differences through consideration of the ionic and photoconductivities of silver oxalate. Conductivity measurements ruled out the growth of discrete silver nuclei by a cationic transport mechanism and this was accepted as evidence that the interface reaction is the more probable. A mobile exciton in the crystal is trapped at an anion vacancy (see barium azide. Chapter 11) and if this is further excited by light absorption before decay, then decomposition yields two molecules of carbon dioxide ... 

The difficulties of interpreting the observations reported for the thermal decomposition of silver oxalate have been discussed [65]. Isothermal data for freshly prepared salt at 399 K were sufficiently irreproducible for different experiments to fit different rate expressions during the acceleratory process, for example, either the power law, or the exponential law. In the second half of reaction (i.e. tt> 0.5), however, data were more reproducible and results were satisfactorily described by the contracting volume equation. 

Boldyrev et al. [46], from quantum mechanical calculations of bond strengths in the oxalate anion, and from observations [38] of the decomposition of this species in potassium bromide matrices, concluded that the most probable controlling step in the breakdown of the oxalate ion is rupture of the C-C bond. This model is (again) based on the observation that the magnitudes of the activation energies for decompositions of many metal salts of oxalic acid are comparable. This model was successfiilly applied [46,68] to the decompositions of many oxalates, with the possible exception of silver oxalate where the strengths of the C-C and Ag-0 bonds are similar. 

OXALIC ACID (144-62-7) CjHjO. HOOCCOOH Combustible solid heat-sensitive. (combustible <215 F/101°C. Fire Rating 1). Exposure to elevated temperatures, hot surfaces, or flames causes decomposition and the formation of toxic and flammable formic acid and carbon monoxide. Hygroscopic the solution in water is a medium-strong acid. Violent reaction with strong oxidizers, acid chlorides alkali metals bromine, furfuryl alcohol hydrogen peroxide (90%) phosphorus trichloride silver powders sodium, sodium chlorite sodium hypochlorite urea + heat (forms NHj gas, CO2 and CO may explode). Mixture with some silver compounds forms explosive salts of silver oxalate. Incompatible with caustics, mercury, urea. On small fires, use dry chemical powder (such as Purple-K-... 

Above 140°C its exothermic decomposition to metal and carbon dioxide readily becomes explosive [1], A 1 kg batch which had been thoroughly dried at 50°C exploded violently when mechanical grinding in an end-runner mill was attempted [2], Explosions have been experienced when drying the oxalate as low as 80°C [6], It is a compound of zero oxygen balance. The explosion temperature of the pure oxalate is lowered appreciably (from 143 to 122°C) by application of an electric field [3], The salt prepared from silver nitrate with excess of sodium oxalate is much less stable than that from excess nitrate [4], Decomposition at 125°C in glycerol prevents explosion in the preparation of silver powder [5],... 

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. 

A mixture of 150 parts of oxalic acid, 40 of potassium chlorate, and 20 of water is heated to 60°, and the soln. cone, in vacuo at 50° until it begins to crystallize. The cold liquid i3 then treated with 3 volumes of absolute alcohol, when potassium carbonate is precipitated. Fine deliquescent needles of potassium chlorite can be obtained by fractional crystallization in vacuo. The residue gives a further crop of crystals of the chlorite by treatment with 95 per cent, alcohol. Small yellow crystals of silver or lead chlorites can be obtained by double decomposition. 

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