A thermoanalytical study has been made of the physical and chemical changes that occur on heating equimolar mixtures of Ca(NO3)(2) and sixteen selected oxides that include those of the metals of the first transition period. The work was undertaken to characterize the factors that determine the rates of thermal anion breakdown in these mixtures of initially solid reactants, It was also of interest for environmental reasons, to investigate the stability and chemistry of Ca(NO3)(2). This compound is a possible intermediate or participant in those purification treatments of power station effluent gases that use CaCO3 to remove the combustion products that lead to acid rain (SOx and NOx). Decompositions of most metal-oxide-containing mixtures occurred close to the melting point of pure Ca(NO3)(2), 563 degrees C, and appreciably below its decomposition point, 675 degrees C, We conclude that the promotional activity of each metal oxide results from reaction to form a metal nitrate in the melt which initially contains Ca2+, M(n+), O2- and NO3-. Mixtures containing oxides of metals of the first transition series commenced NO3- decomposition at relatively low temperatures; those with partially filled d-shells were most active, i.e. Mn2+, Fe3+ followed by Cr3+ and Co2+ Other oxides only promoted decomposition after Ca(NO3)(2) fusion. We conclude that the dominant factor controlling the decomposition of calcium nitrate is melting. Oxides of metals of the first transition period significantly catalysed NO3- breakdown probably through nitrite formation and cation participation in electron transfer steps. Reaction mechanisms are discussed.