Effect of various atmospheres and of autoclaving on the surface texture of thermally treated strontium oxalate

Surface area measurements were performed using nitrogen adsorption at -196 °C on strontium oxalate monohydrate and its thermal decomposition products obtained in the temperature range 400–510 °C in presence of air or water vapour at various pressures, and in an atmosphere of nitrogen, hydrogen or carbon dioxide. Strontium oxalate monohydrate autoclaved under 10 atm was also investigated after ageing, with the products of its thermal treatment in air in the temperature range 370–610 °C.

The crystal structure of strontium oxalate monohydrate is almost unaffected by autoclaving but a new phase appears after ageing. This new phase of strontium oxalate monohydrate exists in equilibrium with the corresponding established form. It is characterized by bands situated at d distances of 4.65 Å, 4.17 Å, 3.17 Å, 2.264 Å and 1.906 Å.

At all temperatures the surface area is a function of the variations in the solid texture imposed by the prevailing atmosphere. The presence of water vapour during thermal treatment appears to have a “cleaning” effect, removing adsorbed gases. At high temperatures the presence of a reducing atmosphere enhances the sintering process.

Pore structure analysis of all the products indicates the predominance of mesopores except in those samples treated in a nitrogen or carbon dioxide atmosphere where microporosity is completely absent.