Calorimetric evaluation of phase change materials for use as thermal interface materials

The phase change behavior of organic and inorganic phase change materials, namely paraffin wax, microcrystalline wax. Na2SO4. 10H(2)O and CaCl2. 6H(2) O, with melting temperatures close to room temperature. was evaluated by di fferential scanning calorimetry. The melting and solidification temperature s, supercooling. heat of fusion and thermal cycling stability of these mate rials, with and without additives, were determined. Paraffin wax, with or w ithout alpha -Al2O3 or BN particles, are potentially good thermal interface materials, because of the negative supercooling (down to -7 C). large heat of fusion (up to 142 J/g) and excellent thermal cycling stability. Microcr ystalline wax is not suitable, due to its unclear endothermic and exothermi c peaks and wide melting temperature range. The addition of 20-60 wt.% alph a -Al2O3 to paraffin wax decreases the melting temperature by 7 C. Beyond 6 0 wt.% alpha -Al2O3. the melting temperature of paraffin wax increases towa rd the value without alpha -Al2O3 The heat of fusion of paraffin wax attain s a minimum at 20 wt.% alpha Al2O3. The addition of BN has little effect on the phase change behavior of paraffin wax. The inorganic materials Na2SO4. 10H(2)O and CaCl2. 6H(2)O. with and without nucleating additives, are not suitable for use as thermal interface materials, due to the incongruent mel ting and decomposition behavior, large supercooling (8 C or more) and therm al cycling instability. (C) 2001 Elsevier Science B.V. All rights reserved.