Dr. Kaiyuan shi , April 22nd, 2021, via Tencent Meeting

Speaker: Dr. Kaiyuan shi

Title: Chemical reaction, phase transition kinetics and mechanoluminescence performance

            of materials under dynamic compression

Time: 2021/04/22 14:00-16:00 (GMT+08:00)

Place: https://meeting.tencent.com/s/WJ8bEXxFYfzB  Meeting ID: 505 950 588

Host: Dr. Lei Su

Abstract:

 The crystallization of sulfur melt under different compression rate has been studies by dynamic diamond anvil cells (dDAC) system. Slow compression (1000 s) of sulfur melt at different temperature (120 to 180℃) has been conducted to determine the crystallization (solidification) line of sulfur melt. The result show that the melt line (solid to liquid) of sulfur does not overlap well with the crystallization line (liquid to solid). Thisphenomenon could be attribute to the density difference between sulfur melt (at liquid line) and crystalline sulfur (under nucleation pressure). Moreover, the crystallization rate dramatically slow down as the increase of temperature. The ringopening reaction of sulfur ring and polymerization to long sulfur chains under HPHT will increase the viscosity of sulfur melt, which strikingly influence the crystallization rate of sulfur melt.
The crystallization process of pyridine at different compression rates was investigated in detail. When the compression time was ≤ 1 s, pyridine crystallized into phase III, while phase I occurred when the compression time was ≥ 10 s, although both phases were compressed from 0.30 to ∼ 1.20 GPa. In situ time-resolved ruby fluorescence and optical micrographs of the pyridine compression process revealed that the compression rate affected the initial crystallization pressure and resulted in different crystalline phases.
The mechanoluminescenc (ML) performance of manganese doped zinc sulfide (ZnS:Mn) has been investigated under multiple compression modes (various compression waveforms, ranges, and rate) by using dDAC system. Upon compression, the ML spectra of ZnS:Mn  show a  large red shift (~45 nm) and a volcano trend of the ML intensity, where the cumulative ML intensity is solely dependent on the pressure change.

Personal biography:

 Kaiyuan Shi received his Ph.D. in Organic Chemistry from Institute of Chemistry, Chinese Academy of Sciences (ICCAS) in 2020. Since April 2020, he joined in HPSTAR as a postdoc. He is currently working with Prof. Lei Su. His research interest mainly focuses on structural transformation and chemical reaction under different compression rate (dynamic DAC).