NONISOTHERMAL DECOMPOSITION OF SILVER MALEATE DIHYDRATE AND ANHYDROUSSILVER FUMARATE

The non-isothermal decompositions of silver maleate dihydrate (C4H2O4A g2.2H2O) and anhydrous silver fumarate (C4H2O4Ag2) were studied up to 500-degrees-C, in a dynamic atmosphere of air, by means of TG and DTA measurements. Both compounds showed some sublimation (at 120-degrees-C for silver maleate and at 180-degrees-C for silver fumarate) prior to the onset of decomposition (at 170-degrees-C for silver maleate and a t 280-degrees-C for silver fumarate). The gaseous decomposition produc ts of both compounds were found, using IR spectroscopy, to be dominate d by maleic anhydride and CO2. Minor proportions of ethylene, ethyl al cohol, acetone, methane and isobutene were also identified. Metallic s ilver was the final solid product, as identified by X-ray diffractomet ry. NMR analysis was used to monitor the isomerization of the maleate radical into the mom stable fumarate above 230-degrees-C. Kinetic para meters (E(a) and ln A) were calculated from the effect of heating rate (2, 5, 10, and 20 deg.min-1) on the DTA measurements. A mechanism is suggested for the decomposition pathways of these compounds, on basis of the results obtained and, also, on similarities with analogous syst ems.