Solidification of polymers and metals studied by fast scanning calorimetry

摘要

The device was developed for investigation of thermal processes during fast thermal treatments of nanosized samples. The idea of the device was taken from differential scanning calorimetry. It consists of high sensitive, low addenda heat capacity thin film sensors used as sample and reference measuring cell. The size of heated area of the sensor is about 60 μm × 80 μm. 6 high sensitive p-n thermopiles are placed inside this area, providing reliable information about sample temperature for thin samples. This allows both controlled fast heating and cooling. Calculation of heat capacity is simplified compared to a single sensor device. Most of the addenda heat capacity and the heat losses are corrected by the differential setup. Electrical control circuit was slightly modified in comparison with PerkinElmer power compensated DSC to simplify the scheme and to reduce noise. It complicates recalculation of compensated power, but up-to date computers make this easy. PID controller on reference side allows to control the average temperature of sample and reference while thermal processes on a millisecond time scale. Power compensation circuit slightly modifies the sample side voltage to bring it to the same temperature as reference. This solution gives directly changes in heat flow from/to the sample during temperature scans. Analog control circuits with internal timebase of 100 MHz (SRS PID and amplifiers) provide confident voltage control even during very fast processes in the sample. The program voltage is generated by a DAQ board (Meilhaus ME4680). All voltages needed for heat capacity determination are measured by this board at the same time. Software for controlling and obtaining data was developed in Lab View environment. The device is intended to work in the range of scanning rates between 0.1 and 500,000 K/s with nanogram samples. The sensor works up to 800 K, until the aluminum details used so far are replaced with something more heat-resistant. Using high temperature sensor allows heating up to 1200 K. It positioned exactly between existing DSC and ultra-fast scanning techniques. Scheme, main principles and working of control circuits will be presented. We show first data on In, Sn and Pb. Measurements of supercooling of Sn samples using DSC, differential power compensated fast scanning technique and ultra-fast scanning is discussed. These measurements cover 10 orders of magnitude in scanning rate.