Comparison of compositions and pressure transmission performances of two kinds of pyrophyllites used in cubic press

Two kinds of pyrophyllites from South Africa and China were analyzed by scanning electron microscope energy dispersive spectroscopy (EDS) and X-ray powder diffraction (XRD). The main chemical compositions and phase compositions of pyrophyllite were obtained. The pressure of synthesis chamber was calibrated by high-pressure phase transformation of Bi, Tl and Ba. The results show that the South African pyrophyllite ore is illite-type pyrophyllite, and the Chinese pyrophyllite ore is diaspore-type pyrophyllite. The mass fraction of SiO₂ in the South African pyrophyllite ore treated at 900 ℃ is approximately 4.50% higher than that of the Chinese one, and the pressure generation efficiency of the two pyrophyllite powder briquettes is basically the same. In the pressure calibration test of Bi, Tl, Ba, the forward displacements of the right, the front and the upper cylinders of the press, the South African pyrophyllite as medium, under 10~50 MPa oil pressure are about 0.33 mm larger than those of the Chinese pyrophyllite. Before and after 20~50 MPa oil pressure test, the densities of the South Africa pyrophyllite raw ore and powder briquette are 0.055~0.081 g/cm³ lower than those of the Chinese pyrophyllite ore block and powder briquette. The preparation plan of the South African pyrophyllite powder briquette is optimized to make the density reach the same level as the currently widely used pyrophyllite powder briquette, which can replace its Chinese counterpart.