The main factors that significantly affect the compressive strength of synthetic diamonds include the following aspects:

Crystal shape, defects, and inclusions: Diamonds that are intact, rounded in shape, have smooth surfaces without defects, and possess good transparency exhibit much higher compressive strength than those with incomplete shapes, rough surfaces, etching pits, black inclusions, and poor transparency. Improving the integrity of the crystal shape and faces while reducing the incidence of inclusions is key to enhancing the strength level of diamonds.

Magnetic impurities: Ferromagnetic and paramagnetic substances (such as residual catalysts like Fe, Co, Ni, etc.) formed during the high-temperature and high-pressure synthesis of diamonds cause significant damage to their strength. Crystals of non-magnetic diamonds tend to grow fuller, have smoother crystal faces, and contain fewer internal defects and inclusions, resulting in a measured strength significantly higher than that of magnetic diamonds. However, trace amounts of non-magnetic impurities like nitrogen and boron in the crystal are beneficial for improving the mechanical strength, heat resistance, and chemical inertness of diamonds.

Temperature and heating medium:
Air and oxidation: When diamonds are heated in air, oxidation at high temperatures causes a significant drop in strength, and the decline accelerates above 1000°C.
Vacuum and matrix protection: When heated in a vacuum environment, the strength retention is significantly better than in air because the diamonds are protected from oxidation. Similarly,when sintering diamond products, the protection provided by the matrix (binder) also slows down and reduces oxidation.Structural damage caused by high temperatures: Regardless of the medium, when the temperature reaches above 800°C, the strength of diamonds decreases at an accelerated rate. This is because high temperatures cause thermal expansion of impurities, thermal melting, magnetic changes, and graphitization, leading to microcracks, embrittlement, and a reduction in size.

Other comprehensive factors: The strength of synthetic diamonds is also fundamentally influenced by the high-pressure synthesis equipment, catalyst materials, and synthesis processes during single-crystal synthesis, as well as the size and color after generation, and the damage from friction-induced high temperatures and acidic/alkaline environments encountered during operation.