The presence of open pores on the surface of powder catalysts (such as Ni 2Mn powder catalyst) significantly and positively impacts diamond synthesis by increasing nucleation rates and overall yield.

1. Effect on Nucleation Rate and Contact Area
Open pores significantly increase the diamond nucleation rate (nucleation density in a unit volume).
Increased Effective Contact Area: Powder catalysts inherently possess a large specific surface area. The existence of open pores further increases the effective contact and interaction area between the catalyst and graphite within the high-temperature and high-pressure synthesis chamber. This expansion of effective contact area is the underlying reason for increasing the diamond yield.
Higher Nucleation Density: Experimental results show that the area containing the Ni 2Mn powder catalyst rich in open pores exhibited a higher diamond nucleation density compared to the area without open pores.
2. Contribution to Final Yield (Output)
The enhanced nucleation rate means that open pores favor the synthesis of high-output diamond (high single-unit yield).
Quantitative Increase: In comparative experiments, the diamond yield from the upper half of the same molybdenum sheet, which was rich in open pores, was approximately 9.86% higher than the lower half without open pores.
The existence of pores essentially expands the effective contact area between the catalyst and graphite, thereby improving the single-unit output of synthesized diamond.
3. Mechanism of Open Pore Action
The influence of open pores on diamond synthesis can be explained by a model involving internal carbon diffusion and crystallization:
A. Graphite Filling (Prior to Heating): During the initial application of external pressure (as the diamond synthesis process involves pressurization before heating), fine graphite powder/pieces fall into and fill the open pores on the catalyst surface. This filling may be intensified during the initial pressurization stage.
B. Catalyst Encapsulation (During Heating/Dissolution): When the temperature is raised, the catalyst powder shrinks due to surface tension, encapsulating the filled graphite powder that fell into the open pores. This forms "enclosed graphite" inside the catalyst powder.
C. Internal Diffusion and Nucleation: Once the temperature and pressure satisfy the conditions for graphite carbon dissolution, the carbon source can diffuse not only from the outer surface towards the catalyst interior, but, critically, the presence of the enclosed graphite allows carbon to diffuse from the “interior” of the powder catalyst outwards to the surrounding solvent catalyst.
D. Greatly Increased Nucleation: When the carbon concentration in the solvent catalyst reaches "supersaturation," the resulting supersaturated carbon can precipitate as diamond structure not only on the surface layer of the catalyst powder but also crystallize out from the “interior of the catalyst powder,” thereby greatly increasing the diamond nucleation rate.
4. Effect on Crystal Shape
The presence or absence of open pores on the surface of the Ni 2Mn powder catalyst has no obvious influence on the morphology (crystal shape) of the synthetic diamond. Under the experimental conditions, the diamonds synthesized using the Ni 2Mn powder catalyst, regardless of the presence of open pores, were primarily equiaxed crystals.