Examination of the p-T phase diagram of pure substances

Title : Examination of the p-T phase diagram of pure substances

Abstract:

The discovery of a point on the liquid vapor curve where the liquid phase ends was determined experimentally by Charles Cagniard de la Tour in 1822. In 1861, Thomas Andrews defined this point as the critical point and the critical parameters such as temperature, pressure and density (Tcr, pcr, ρcr) which represent both liquid and vapor phases. At the point where the liquid vapor equilibrium curve ends, temperature represents two phases, while pressure and density do not represent two phases. In this case, only the temperature is critical (Tcr). Pressure and density are parameters that correspond to the critical temperature and do not represent the critical situation. The uncertainty of the liquid-solid equilibrium curve and the pressure-dependent boundary range of the liquid phase in the p-T phase diagram is still unresolved and is one of the most important problems of physics and chemistry. The existence of the critical point occurs when one of the phases ends. Since liquid phase is located between the solid-vapor balance curves, it represents both phases. By heating the liquid vapor equilibrium curve, the vaporized liquid passes into the gas phase and the critical point is determined.

As an analogy, the pressure-dependent liquid-solid equilibrium curve freezes upon cooling and passes into the solid phase. The point where the liquid phase ends in the liquid-solid equilibrium curve defines the critical point. In this study, a specially designed experimental setup was used and the existence of a critical point on the liquid-solid equilibrium curve of benzene was determined, accompanied by discontinuous metastability at high pressure and temperature. In the experiments, the freezing temperature of the cooled liquid benzene increased with increasing pressure and the life time of the metastable liquid decreased, and ΔT and ΔP became zero at a certain pressure and temperature. In the experiments, the locations of the critical point depending on pressure and temperature in the temperature-time diagram showing the discontinuous metastable state along the liquid-solid equilibrium curve of benzene were determined as T = 356 K and P = 2229.2 bar. The pressure-dependent critical point P = 2229.2 bar also determines the pressure-dependent limit range of the liquid phase of benzene.

Audience Take Away Notes:

• First of all, as emphasized in the study, audience can learn that the theories presented by even Nobel-winning scientists should be questioned, and they can question all the information put before them in the future.It opens a new horizon especially for researchers working on phase changes and can complete their missing information
• This study can definitely be used in the lectures of faculty members and in the research of other researchers working with phase change substances
• It cannot be said that it provides a practical solution that will make a designer's job easier. Although it is clear that it will provide new information, it is not possible to say that it will benefit design problems
• Instead of solid-liquid transitions, which have been studied extensively to date, liquid-solid transition, that is, cooling of matter, contains very new information since it is a much less studied subject

Biography:

After graduating from the Department of Engineering Physics, Ankara University in 1969 he worked as a research scientist at Ankara Nuclear Research Center until 1977. During the period of 1972-1973 he has been a research staff for a year at Birmingham University (UK) in the Department of Electrical and Electronics Engineering. After 1977 he has served for 3 years as a lecturer at the Middle East Technical University and then he went to Durham University (UK) in 1980, where he worked as a research assistant and at the same time completed his PhD in 1984. He continued to work at the Durham University in a postdoctoral research capacity until September 1985. In 1985 he joined the General Electric Co. as a semiconductor laser group leader at the Hirst Research Centre, London. In September 1988 he started to work at UMIST (Manchester) as a project coordinator. Following his return to Turkey in 1990, he first worked at Gaziantep University and later joined the Marmara Research Centre-TUBİTAK as head of the Energy Department in 1992. In 1998 he was appointed as a professor at Mimar Sinan University in Istanbul and worked as Head of Physics Department until 2004. In 2005 he was appointed as an associate director to UNIDO-International Centre for Hydrogen Energy Technologies in 2005, where he later served as the director of the centre until 2008. In the same year he joined Halic University as the Rector of the university and worked until 2010. At the same year Prof. Ture established his own company and continued his research until 2014. After 2014 Prof. Ture joined first MEF University in Istanbul and then Ankara Science University as a lecturer in 2023. Prof. Ture has more than 50 publications mostly in international journals and conferences and has received over 700 citations to his works. He has also been given over 30 invited talks around 23 countries.