The Isothermal Compressibility Measurement Of Solid Materials Using Ultrasonic Resonance Spectrum Method

Thermodynamic temperature is one of the seven fundamental physical quantities in the International System of Units(SI), and the unit symbol is K. It objectively reflects the real temperature of the object, and accurately measurement of thermodynamic temperature Is closely linked with industrial production, scientific research, technology development and People’s Daily life. At present, there are a lot of different measurement methods of thermodynamic temperature, and gas refractive index thermometry is a new primary method for the determination of the thermodynamic temperature. The helium pressures for running gas refractive index thermometers are usually up to several megapascals for accurate measurements. To achieve the measurement uncertainty of 1×10-6 for thermodynamic temperature, the amount of isothermal compressibility of cavity material is required to be bound within the uncertainty of 0.1 %.The amounts of isothermal compressibility of solid materials are closely related to their elastic modulus. The elastic parameter is a function of temperature, thus, the amounts of isothermal compressibility are obtained by accurately measuring elastic modulus of materials. Nevertheless, no commercial instrument is available in China for measurement temperature different from the room temperature. Thus, the authors have developed a setup based on the principle of ultrasonic resonance spectrum. The setup includes the ultrasonic signaling and detecting system, the thermostat and the data analysis software. We measured the elastic modulus of four samples in different quality factors(Qs) at room temperature, and investigated the effects influencing the measurement. The resonant frequency matching error(RMS) of 0.04% has been reached with the measurements by the developed setup. The results agree well with those of the global advanced commercial instruments. In addition, 316 L austenitic non-magnetic stainless steel,bearing steel( 9Cr18),oxygen-free copper and aluminum oxide four kinds of sampleswere measured at temperature from 293 K to 353 K for elastic modulus, and obtained theyoung’s modulus E, shear modulus G and poisson’s ratioν of the four kinds of tested samples materialwith different temperatures, and according to the definition of theisothermal compressibility, we got the isothermal compressibilityof the four kinds of tested sample materials under 10 temperature points between 273 K and 353 K(every 10 K a temperature point).The system is capable to measure the elastic modulus of solids at temperature up to 500 K at anti-oxidation atmosphere. After redesigning the ultrasonic signaling and detection system, it is capable for measurements at higher temperature.