Calculation Of Temperature And Pressure From The Graphite Suspension Irradiated By Laser

Nanodiamond particles with the size of about 5 nm had been prepared in our group by the new way that microsecond pulsed laser (MS-PL) with the lower power density irradiates the graphite suspension. This new technique can improve yields of nanodiamonds compared to the methods reported in the literature, i.e. nanosecond pulsed laser (NS-PL) with the higher power density ablated a graphite target in the liquid. Therefore, studying the mechanism of the phase transformation from graphite to diamond that MS-PL irradiated the graphite suspension is significant to gain higher yields of ultafine nanodiamonds. The temperature and pressure are two necessary conditions that the graphite transforms the diamond. However, it is difficult to understand the change process of the temperature and pressure under the extreme conditions produced by pulsed laser. At present, mathematical simulation had become a practical approach for many researchers to study the phenomenon that laser reacted with the materials. In this paper, the mathematical model that MS-PL irradiated the small graphite slice in the water have been presented by combining our experiment conditions and presented physical model in the literature. Employing MATLAB software, the change process of the temperature and pressure that MS-PL irradiated graphite suspension had been studied, which was important to improve the yield of nanodiamonds and open up this new technique.By dint of the powerful calculation capability and graphic processing of MATLAB, we get the following conclusion:Irradiating graphite suspension employing MS-PL with low power density, the temperature of the surface of graphite flake reaches about 4800K in 300ns. Before the end of one pulse, the temperature keep on increasing, and the high temperature, high pressure and high density carbon plasma is generated at last, which allowes the formation of nanodiamond; With the increase of the graphite flake thickness, the longer irradiating time is needed to reach the same temperature, which makes against the plasma generation; By enhancing the power density of laser, the heating rate improve obviously, which leads to the formation of plasma with higher temperature and higher pressure; The existence of the water can improve the liquid's cooling rate, that the cooling rate rise from 1.2 K/ns in the air up to 3.6 K/ns, which makes for the ultrafine diamond'synthesization.