Defect And Stress Reduction In High-Pressure And High-Temperature Synthetic Diamonds Using Gradient Cooling Technology

In order to eliminate filiform defects in high-pressure and high-temperature synthetic diamonds, we have developed a gradient cooling technology and applied it during the synthesis assembly cooling process used during the later stage of diamond synthesis. Finite element simulations showed that the von Mises stress at the end of the synthesis process varied greatly inside the diamond. The rapid thermoelastic stress relief and higher thermoelastic stress generated inside the diamond during rapid cooling of synthesis assembly were the root causes of filiform defects, which were completely eliminated from the diamond interior at a gradient cooling time of 300 min. Raman measurements indicated that the crystalline quality was higher and the compressive stress was lower in the diamond obtained using gradient cooling technology than in the diamond obtained using the traditional rapid cooling technology. This work improves the understanding of the origin of filiform defects in diamond and also provides an effective method for obtaining high-quality diamonds.