Research On The Synthesis Of Nanodiamonds By Millisecond-pulse Laser

In this research, nanodiamonds with sizes of 3–6 nm were prepared by irradiating carbon particles (graphite or carbon black) suspended in water using a long-pulse (1.2 ms) laser (ms-laser). The synthesis process of diamond, purification process of diamond, the mechanism of the diamond formation and the influence of the particle size and phase structure of the carbon particles were investigated.The carbon particles were dispersed in water by ultrasonic machine and the suspension was cycled by a water pump. The Nd: YAG pulsed laser was used to irradiate the graphite particles suspended in water, and then the acquisition was purified to get nanodiamonds.Based on thermodynamical and kinetic theory, the mechanism synthesized ultra-fine diamond in graphite suspension by ms-pulsed laser irradiation was analyzed. And the mechanism of the phase transformation: At the area of laser irradiating the carbon particles, the models of structural transformation from rhombohedral graphite atoms to cubic diamond crystal nuclear and the carbon black first transformations to graphite, then to the structure of diamond have been developed.Compare with ns-laser, ms-laser has long working hours inducing the high efficiency and a long-pulsed laser which result in the low degree. The low degree of supercooling allows a rather low growth velocity, and a disordered structure formed at the diamond surface retards the epitaxy growth. The above two factors dynamically limit the final size of nanodiamonds. So the particles'size (about 5nm) produced by ms-laser less than the particles'size (40nm-200nm) produced by ms-laser.The disordered structure formed at the diamonds'surface prevents the contacts of the nanodiamonds. And then after the purification, the adhesion of the organic electrolyte let the nanodiamonds reciprocally repulse.At the condition of our experiment, our results suggest that the millisecond pulsed laser is propitious to producing fine nanodiamonds. The size of graphite particle was important, ABC graphite with smaller particles was better than flake graphite.