Volumetric analysis of decarbonation during sintering process of oxide superconductor

The intrinsic thermal decomposition kinetics of SrCO3 by a nonisothermal technique

“…It can be seen from the DTA curve in Figure 3 that the temperature difference between the sample crucible and the reference crucible due to the thermal effect of Reaction [1] was less than 3 K. Furthermore, since the particle size of the SrCO 3 powder was less than 5 m, the distance for the heat transfer through the product layer was less than 1.2 m when the fractional decomposition, ␣, was less than 0.85. Hence, if we further consider the small amount of sample (10 mg) used, it would be reasonable to expect that the transport of the heat from the surrounding through the oxide layer to the SrCO 3 -SrO interface would not affect the decomposition rate.…”

“…[4] that the increase of would result p CO2 in a lower reaction rate. Since 1 mole SrCO 3 will produce 1 mole SrO and assuming that the weight loss is entirely caused by Reaction [1], Eq. [4] can be used to obtain the rate of mass loss, as follows:…”

“…The rate of the decomposition reaction in each individual particle can be considered, in general, to be controlled by one or more of the following steps: (a) chemical Reaction [1] at the surface of the SrCO 3 core, the equilibrium temperature for Reaction [1] being a function of the partial pressure of CO 2 ; (b) transport of CO 2 gas from the SrCO 3 -SrO interface through the oxide layer out to the surrounding atmosphere; (c) the transport of CO 2 in the gas phase; and (d) transport of heat from the surroundings to the SrCO 3 -SrO interface through the oxide layer. Since the molar volume of SrO is considerably less than that of SrCO 3 [8] and the reaction involves the evolution of CO 2 gas, one can expect that either the unreacted carbonate core will be covered by a porous oxide layer or the oxide layer will crack and even fall apart.…”

“…The rate of chemical Reaction [1] at the interface of a particle can be expressed by the flux of the CO 2 formed:…”

“…[1] The synthesis of these ceramics is usually achieved by a gas-solid reaction of a mixture of SrCO 3 , CaCO 3 , Bi 2 O 3 , and CuO powders. Strontium carbonate can also be used in the manufacture of cheap, robust humidity sensors.…”