High-pressure high-temperature (HPHT) cells are used to form ultra-hard materials such as polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN), which in turn are used in tools such as cutting tools and rock drilling tools. HPHT cells are used in HPHT presses such as, cubic presses, belt presses, and toroid presses. To form ultra-hard materials, HPHT presses often apply pressures in the range of 5 to 8 GPa and temperatures in the range of 1300 to 1650° C. For example, PCD may be sintered at 5 to 7 GPa and 1400 to 1500° C.
The formation of certain ultra-hard materials, such as thermally stable PCD, involves sintering at much higher temperatures. In particular, PCD formed using a carbonate catalyst may be sintered at a pressure greater than 6.5 GPa and a temperature greater than 2000° C. Additionally, binderless nano-polycrystalline PCD may be sintered at a pressure of about 15 GPa and a temperature of about 2300° C.
Sintering at these temperatures may be carried out using an HPHT cell including refractory materials that can withstand the high temperatures attained within the cell. For example, materials such as magnesium oxide (MgO) and sodium chloride (NaCl) have been used as pressure transfer media, and cubic zirconium oxide (ZrO2) having low thermal conductivity has been used as a thermal insulation sleeve in an HPHT cell. However, at pressures of about 8 GPa, NaCl begins to melt when the temperature exceeds 1600° C.