調(diào)制MDSC技術(shù)原理

Modulated DSC (MDSC) can be easily understood by comparing it to its well-established precursor, differential scanning calorimetry (DSC). Conventional DSC is an analytical technique in which the difference in heat flow between a sample and an inert reference is measured as a function of time and temperature as both the sample and reference are subjected to a controlled environment of time, temperature, atmosphere and pressure. The schematic of a typical heat flux DSC cell is shown in Figure 1. In this design, a metallic disk (made of constantan alloy) is the primary means of heat transfer to and from the sample and reference. The sample, contained in a metal pan, and the reference (an empty pan) sit on raised platforms formed in the constantan disk. As heat is transferred through the disk, the differential heat flow to the sample and reference is measured by area thermocouples formed by the junction of the constantan disk and chromel wafers which cover the underside of the platforms. Chromel and alumel wires attached to the chromel wafers form thermocouples which directly measure sample temperature. Purge gas is admitted to the sample chamber through an orifice in the heating block wall midway between the raised platforms. The gas is preheated by circulation through the block before entering the sample chamber. The result is a uniform, stable thermal environment which assures excellent baseline flatness and exceptional sensitivity (signal-to-noise). In conventional DSC, the temperature regime seen by the sample and reference is linear heating or coo領(lǐng) at rates from as fast as 200°C/minute to rates as slow as 0°C/minute (isothermal). DISCOVERY 差示掃描量熱儀