the moisture in pyrophyllite (mainly bound/structural water, as well as surface adsorbed water) has a dual effect on diamond synthesis. It is the key to ensuring sealing and pressure-transmitting performance, but it may also cause adverse interference under specific conditions:

1. Positive effects: Providing flowability and sealing
Ensuring initial flowability: The reason why pyrophyllite is suitable as a sealing and pressure-transmitting medium is due to its flowability during the initial stage of extrusion, and the presence of bound water is the key factor for this flowability.
Maintaining a good mechanical state: Sources indicate that pyrophyllite with a higher loss on ignition (i.e., structural water content) has a softer texture and good resilience.
Determining sealing during the pressurization stage: During the pressurization stage of the synthesis process, the sealing performance of the cavity mainly depends on the bound water content of the pyrophyllite, the connection method of internal particles, and the size of the scaly structure.

2.Negative effects: Damage caused by excessive moisture or adsorbed water
Formation of a harmful hard crust due to phase transition: In a high-temperature and high-pressure environment, free moisture will promote the phase transition of pyrophyllite, thereby forming a harmful hard crust layer, which will directly affect or even hinder the synthesis of diamond.
Adverse effects of excessively high content: Although an appropriate amount of structural water can give pyrophyllite softness and resilience, if the loss on ignition (structural water content) is too high, it is generally detrimental to diamond synthesis.
Interference from environmental adsorbed water: Moisture adsorbed by pyrophyllite from the air will also have an adverse effect on the synthesis experiment results. Therefore, before the formal synthesis, it is usually necessary to bake it in an oven (e.g., baking at 240°C for 20 hours) to completely eliminate the interference of adsorbed water.

3. Industrial moisture control (Heat treatment process) In order to strike a balance between retaining bound water (to maintain flowability) and removing excess moisture (to prevent the formation of a hard crust), natural pyrophyllite must undergo a reasonable heat treatment process before use. Because roasting at over 500°C for a long time will cause the critical bound water to escape and lose flowability, the maximum baking temperature for pyrophyllite generally should not exceed 500°C.