Differential scanning calorimetry excess heat capacity

A DuPont Model 990 thermal analyzer equipped with a Model 910 DSC cell base was used for differential scanning calorimetry. Samples were analyzed as 15 (w/w) solutions of freeze-dried RDP which had been dialyzed to remove excess buffer salts. A heating rate of 5°C/min was used runs were performed in a nitrogen atmosphere (5 psi). A known weight of water was used in the reference pan to balance the heat capacity of the sample pan. 

Nanophase materials generally have an excess heat capacity and entropy relative to the bulk. These can be obtained by conventional heat capacity measurements (adiabatic calorimetry, differential scanning calorimetry), although problems with the adsorbed water and other gases are more severe for nanomaterials than for bulk phases. Data at present are fragmentary and it is difficult to evaluate their accuracy. Dugdale et al. (1954) report on excess heat capacity for fine grained rutile. Victor (1962) report data for MgO and BeO, and Sorai et al. (1969) for Ni(OH)2 and Co(OH)2. 

The available experimental data on Cp(RCl3,liq) were obtained either by drop calorimetry measurements of H° T) — H°(298) or by differential scanning calorimetry with the use of suitable references. Both methods give fairly high instrumental accuracy (1-3%) 0acobson et al., 1999). Nevertheless, analysis of the whole series of results obtained does not reveal patterns in the variation of heat capacity for the series of lanthanide trichlorides unless additional data on Cp(RF3,liq), the structure of the liquid phase formed in melting, and the influence of the excess contribution of the excited electronic states of molecules on the heat capacity values are taken into account. 

Differential scanning calorimetry is a basic method to study the phospholipid bilayer phase transitions since these are accompanied by a positive enthalpy of fusion. The excess heat capacity,... 

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