Thermal decomposition of mixed oxalates

Abstract

The thermogravimetric analysis of several coprecipitated zinc-copper oxalates in nitrogen is reported. The thermal decompositions of these mixed oxalates show a separate single step for dehydration and decomposition in the mass loss versus temperature curve. It is found that the onset temperature decreases with composition. For example, it decreases from 380 ~ for zinc oxalate to 260 ~ for copper oxalate. The end-product is mixed oxides and copper metal. These studies indicate the formation of an interpenetrating structure or mixed crystals during coprecipitation. Rate parameters have been calculated for dehydration and decomposition.The purpose of the present investigation was to study the effect of coprecipitated copper oxalate on the decomposition temperature of zinc oxalate in nitrogen with a view to elucidating the nature of these materials. Material and methodMixed oxalates of zinc and copper were prepared by a coprecipitation method. The copper and zinc contents of the mixed oxalates were determined by conventional chemical methods. Th e compositions showed some deviation from the proportions of the two salt solutions taken.The dehydration and decomposition temperatures of these mixed oxalates in nitrogen were determined in a thermogravimetric balance using a McBain-Baker type quartz spring [l ]. This had a sensitivity of 5.6 mg/mm extension and required only about 25 mg of sample for investigation. The extension of the spring was measured with a travelling microscope every 2 rain, while the temperature of the furnace was increased at a constant rate of about 5~ by means of a programming system described separately. The thermal analysis was carried out in flowing nitrogen gas, which was purified by passage through alkaline pyrogallol solution followed by moisture traps (a calcium chloride tower and silica gel drying tube). Results and discussionDehydration and decomposition temperatures reproducible within _+ 1.5 ~ were obtained. The results were plotted as percent weight loss against temperature.

The thermal decompositions of some transition metal acrylates and polyacrylates

“…The temperature sequence of increasing thermal stability may not coincide with the sequence of increasing activation energy values, since it can also depend on the value of the activation entropy [19]. The lack of such a correlation has been observed in the dehydration reactions of EDTA chelates of a number of metal ions [19], and also in the dehydration and decomposition reactions of mixtures of zinc and copper oxblates [20].…”

Thermal analysis

“…The double salts ultimately decomposed to metal oxide, alkali metal sulfate, and S03. Coprecipitated Zn-Cu oxalates were subjected to TG in N2 (49) and it was found that decomposition onset temperatures vary with composition, decreasing from 380 °C for ZnC204 to 260 °C for CuC204.…”

Investigations of Cu/Zn Oxalates from Aqueous Solution: Single‐Phase Precursors and Beyond

“…[11,14] Successful isomorphous substitution by Zn II in Cu II oxalate has been rarely reported in the literature. In the thermal decomposition of ac oprecipitated Cu/Zno xalate (46.2 %C u), Dalvi and Chavan [15] observeda na nomalous single decomposition step, which they attributed to the formation of am etastable solid solution. On applying the oxalate gel/coprecipitation methodt ot he ternary Cu/ZnO/Al 2 O 3 system,D eng et al [6a] reported the formation of the binary mixed-metal oxalate phase from ethanolic solution.…”