Experimental determination of the enthalpy of formation of the pyrochlore rare-earth hafnates

In this study, enthalpies of formation of compounds RE₂Hf₂O₇ type (where RE = La, Pr, Nd, Sm, Eu, and Gd), with pyrochlore structure have been measured by high-temperature oxide melt solution calorimetry. Results were compared with literature data, and dependencies of enthalpies of the formation of compounds with the pyrochlore structure from the ionic radius of rare-earth element were analyzed. The enthalpy of formation becomes more positive with the increase in ionic radius, which is in conformity with the results earlier observed for titanates and zirconates.     

Heat Capacity Values of 1% Aqueous Dispersions for Native Maize Starches with Different Amylose Content

The heat capacities (HC) of 1% aqueous dispersions of native maize starches with different amylose content were determined by using high sensitivity differential scanning microcalorimetry (HSDSC). The application of an additive equation, taking into account the contributions of different ordered structures (B‐, B*‐ and V‐types) to the heat capacity of the high amylose maize starches, allows to describe the changes in the heat capacity of the maize starches at an increase in amylose content from 0% to 70%. The heat capacity values per 1% change both of B‐ and V‐type structures in high amylose starches have been determined. Additionally, the calculations showed that at an amylose content in maize starches equal to 0%, the heat capacity values for A‐ and B*‐type structures are, 164 Jmol ^—1 K^—1 and 186 Jmol ^—1 K ^—1 , respectively. The relationship between heat capacity values and structural features of maize starches is discussed.