THERMAL-BEHAVIOR OF UREA-(D) TARTARIC ACID AND UREA-(DL) TARTARIC ACID CRYSTALS

The thermal behavior of two new non-linear optical (NLO) materials, ur ea-(D) tartaric acid (UDT) and urea-(DL) tartaric acid (UDLT) were stu died by using DSC, TG and TMA. The results show that: 1) The two cryst als have different melting points but similar decomposition temperatur es due to the influences of intermolecular forces, which is attributed to the stereo effects of (D)-tartaric and (DL)-tartaric acid molecule s; 2) There was only thermal expansion and no thermal contraction when the UDT and UDLT crystals were heated; 3) There was no phase transiti on within the measured temperature range; 4) The thermal expansion of the UDT and UDLT crystals shows a small anisotropy; 5) The specific he ats of UDT and UDLT change linearly with temperature in the measured t emperature range and the value for UDT is 1.321 J g(-1) K-1 at 320 K w hile the specific heat of UDLT is 1.357 J g(-1) K-1 at the same temper ature.