The thermal-electric coupled model for diamond synthesis using a cubic anvil press reveals the following key heating regularities:
1. Temperature Establishment and Determinants of Final Temperature
The speed of temperature establishment (rate of rise) and the final achieved temperature (final state temperature or equilibrium temperature) in the synthesis chamber are primarily determined by the following factors:
Matching of Heating Power and Pyrophyllite Thermal Conductivity at the Initial Stage The speed of temperature establishment and the final temperature of the synthesis chamber are mainly determined by the initial heating power and the thermal conductivity of pyrophyllite. Different matching combinations result in different temperature-time trajectories, different equilibrium temperatures, and different times required to reach equilibrium.
    Influence of Heating Power (Heat Generation Rate) The heat generation rate determines the magnitude of the heat dissipation rate. As the applied voltage (which determines the heat generation rate) increases, the temperature rise within the chamber accelerates, and the final temperature increases.
    Influence of Pyrophyllite Thermal Conductivity Given a fixed sealed cavity structure, the thermal resistance is primarily determined by the thermal conductivity of the pyrophyllite material. Experimental results indicate that the greater the thermal conductivity of pyrophyllite, the shorter the time required to reach the equilibrium temperature, and the lower the equilibrium temperature.

2. Temperature Sensitivity and Controllability to Changes in Heating Power
 High Response Sensitivity The temperature inside the chamber is highly sensitive to changes in heating power, exhibiting good controllability.
 Response Speed When the heating power changes, the chamber temperature can respond quickly. The more stable the temperature was before the power change, the faster the response.
 Magnitude and Gradient of Change Different power change gradients result in different speeds of temperature change and different fluctuation magnitudes.
3. Characteristics of the Temperature Stabilization Phase and Insulation Effect
Approach to Heat Dissipation Rate During the initial heating phase, the huge disparity between the heat generation rate and the heat dissipation rate leads to rapid heat accumulation and a swift rise in temperature. As time progresses, the rate of temperature change approaches 0, indicating that the heat dissipation rate gradually approaches equality with the heat generation rate.
Insulation Effect and Temperature Stability Once the temperature is relatively stable, if the heating power remains unchanged, deterioration of insulation (e.g., an increase in pyrophyllite thermal conductivity) will not cause the chamber temperature to decrease, but rather make the chamber temperature more stable. This is because the heat dissipation rate will only infinitely approach the heat generation rate and cannot exceed it.
4. Influence of System Material Properties and Cooling Effect
Anvil Properties
    If the thermal conductivity and specific heat of the anvil material increase, the equilibrium temperature inside the chamber is lower, and the time required to establish equilibrium is shorter.
    If the anvil temperature establishes more easily, the equilibrium temperature inside the chamber is higher, and the time required to reach equilibrium is longer.
    Initial Anvil Temperature A higher initial anvil temperature results in a higher chamber equilibrium temperature and a shorter time to reach equilibrium. In continuous production, if the cooling process cannot ensure the same initial state of the equipment before each synthesis, the stability of the synthesis process will be reduced.
Role of Cooling Water Cooling water indirectly cools components (such as the preload ring) to limit the anvil temperature.
     In Continuous Synthesis After heating stops, the cooling effect of the cooling water influences the initial equipment temperature before the next synthesis, thereby affecting the final chamber temperature.
    In Single Synthesis The role of cooling water is to guide the flow of heat and accelerate the establishment of a stable state. In the phase where the temperature rise slows down, the heat flow guidance effect of the cooling water can accelerate the system's stability. Cooling water has little impact on the final temperature inside the chamber but aids in accelerating equilibrium.
5. Influence of Material Nonlinearity on the Heating Process
 Nonlinearity of Pyrophyllite Thermal Conductivity The thermal conductivity of pyrophyllite can undergo significant nonlinear changes (e.g., increasing from a typical value of 9.04 W/(m·K) to 43.95 W/(m·K)) during the high-temperature and high-pressure process.
    Under conditions of nonlinear pyrophyllite thermal conductivity, the chamber temperature curve rises faster, but the time required to reach stability is shorter.
    This pattern occurs because the nonlinear thermal conductivity value is smaller in the initial heating phase, leading to faster heat accumulation and a rapid temperature rise; however, as the temperature increases, the thermal conductivity increases, causing the heat dissipation rate to quickly approach the heat generation rate, which slows down the temperature rise. This nonlinear change increases the difficulty of precisely controlling the temperature trajectory of the synthesis chamber.
 Nonlinearity of Synthetic Cylinder Resistance
    Changes in the synthetic cylinder resistance (due to the negative temperature effect of graphite resistivity, melting of catalyst metal, diffusion, diamond nucleation, and growth) lead to temperature fluctuations within the chamber.
    Under constant voltage application, even if the heating power remains unchanged (the change in current follows the same pattern as the change in power), the chamber temperature continues to increase, but the rate of temperature rise becomes progressively slower.