Graphite boronization can significantly improve the thermal stability of synthetic diamonds. Experimental data shows that after being held at 1000°C for half an hour, the compressive strength of ordinary 40/50 mesh diamonds decreases by about 40%, whereas boron-containing diamonds synthesized with boronized graphite only lose about 25% to 30% of their compressive strength. This lower strength loss rate indicates a marked improvement in thermal stability.

The core principle behind this enhanced thermal stability lies in the improvement of the diamond's surface structure, which drastically boosts its oxidation resistance. The specific mechanisms are as follows:

1.Diamond surface defects (dangling bonds): Inside the diamond, each carbon atom uses four valence electrons to form stable covalent bonds with four surrounding carbon atoms. However, carbon atoms on the diamond's surface only use three valence electrons to bond with internal carbon atoms, leaving an unutilized "dangling bond".

2.Ordinary diamonds are easily oxidized: Oxygen atoms are electron-deficient; when oxygen comes into contact with the diamond surface, it easily attracts the extra electrons on the dangling bonds of surface carbon atoms to form bonds, ultimately resulting in the release of carbon dioxide (CO2) gas, which represents the oxidation process of diamonds at high temperatures.

3.The stable protective role of boron atoms: Based on the excited-state electron distribution of boron, it is trivalent (i.e., has three valence electrons). During boronized synthesis, the three valence electrons of a boron atom can bond with the dangling bonds of the surface carbon atoms, forming stable covalent bonds.

4.Stabilization of the surface structure: Once boron bonds with the carbon dangling bonds, the surface carbon atoms of the diamond no longer have extra, active valence electrons. This transforms the inherently unstable surface structure of the diamond into a stable one, effectively cutting off the reaction pathway between oxygen and carbon atoms.

Therefore, it is precisely because boron atoms fill the electron vacancies of surface carbon atoms that boron-containing diamonds possess excellent oxidation resistance, reducing their loss of compressive strength in high-temperature environments and fundamentally enhancing the thermal stability of the diamond.