During the synthesis of synthetic diamond, the carbide content has a direct and significant impact on its quality and yield.

1. Carbides are the direct carbon source for diamond growth.
    Under high-temperature and high-pressure conditions, carbides in the catalyst are considered the direct carbon source for diamond growth. Research indicates that diamond growth is always accompanied by the consumption of primary cementite, which further supports the view that primary cementite (a type of carbide) is very likely the direct carbon source for diamond growth. The carbon source required for diamond growth does not come directly from graphite; instead, it originates from the carbide phase formed when graphite dissolves into the catalyst melt and reacts with the catalyst metal.
2. Higher carbide content leads to better diamond quality and yield.
    Research results show that when a large amount of carbide is present in the catalyst, a higher number of diamond nuclei are formed, their distribution is uniform, and their crystal shape is complete, leading to higher quality and higher yield diamond.
    Conversely, if raw graphite is mixed in the catalyst and carbide formation is insufficient, the number of diamond nuclei will be fewer, and the growth effect will be poorer. When the carbide content is low, it directly affects the diamond growth effect.

In experiments synthesizing diamond at high temperature and high pressure using powder metallurgy iron-based catalysts in a six-anvil high-pressure apparatus, even under the same process conditions, the synthesis effects on different sections of the compact varied significantly due to the presence of temperature and pressure gradients within the synthesis chamber.
 X-ray diffraction (XRD) analysis results showed that the content of metal carbides (such as (Fe,Ni)3C and (Fe,Ni)7C3) was significantly higher than that of graphite in catalyst sample I (corresponding to a better diamond growth effect), while the opposite was true for sample II (corresponding to a poorer growth effect).
 Electron probe microanalysis (EPMA) further revealed that the microstructure of sample I (corresponding to better diamond growth effect) was almost entirely composed of iron and nickel carbides, whereas sample II (corresponding to poorer diamond growth effect) contained large chunks of graphite. EPMA composition line scan results also indicated that the carbon content present as graphite in sample II was significantly greater than the carbon content present as carbides. Graphite with sharp edges observed in the microstructure was considered to be original graphite that did not fully dissolve into the catalyst melt at high temperatures.
Therefore, to obtain high-yield and high-quality synthetic diamond, ensuring that the catalyst melt fully dissolves graphite and sufficiently forms metal carbides is crucial. This requires, during the synthesis process:
Carefully selecting carbon source materials that match the iron-based catalyst to ensure their full dissolution in the catalyst melt.
Improving the control precision of synthesis temperature and pressure, on the one hand, to reduce the temperature and pressure gradients within the synthesis chamber, and on the other hand, to ensure the sufficient formation of metal carbides under high-temperature and high-pressure conditions.