为研究石蜡在相变过程中内部结构和状态的改变特性，用中心频率为5 MHz的脉冲式超声波动态测量石蜡的相变过程，采集并分析不同升降温速率下的声速和声衰减信号的变化规律，结果与差示扫描量热仪(DSC)测量的热力学性质比较，并拍摄石蜡溶解过程的图像为辅助，探讨了二者由于测量原理不同导致的差异和特点。结果表明，两种方法均得到约50℃的初凝点，且二者信号反映的相变规律一致，表明利用声衰减和声速能够较好的表征石蜡在相变过程中的声学特性。超声可能成为一种新的蜡化物性质原位测量手段。
The traditional method of measuring phase change process of materials is off-line characterization by instruments such as differential scanning calorimetry (DSC) and differential thermal analysis (DTA). In practical applications of many phase change materials, in-situ measurements are more conducive to exploring the phase change process. During the phase change of materials, there is a heat exchange between themselves and the outside world, and their internal molecules and macrostructures also undergo great changes. Ultrasound has unique advantages in revealing the internal structural information of materials, and the theory and technology of ultrasonic measurement have also developed a lot. Based on the strong penetration and non-contact properties of ultrasound, the thermodynamic and acoustic properties of paraffin in this work were explored. In order to study the internal structure and state of paraffin wax during the phase change process, a pulsed ultrasonic wave with a center frequency of 5 MHz was used, and an online measuring device which was capable of controlling the rate of temperature change was designed to dynamically measure the phase change process of paraffin. The variations of ultrasonic velocity and attenuation signal at different temperature variation rates were analyzed and discussed. The results were also compared with the thermodynamic properties measured by DSC, and the recorded images were used to be an auxiliary observation. These methods helped to explore the features and principles in dynamic processes. The results showed that both methods obtained an initial condensation point at about 50℃, and the phase change reflected by the signals of the two methods were consistent. The ultrasonic attenuation and sound velocity can embody the acoustic characteristics of paraffin wax during the phase change. The ultrasonic measurement was suitable for measurement, and analysis in open environments and may form a new in-situ measurement method of wax properties and provide an effective mean of monitoring the practical application of phase change materials.
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