| 摘要 |
<p>Cubic boron nitride has been made from powdered hexagonal boron nitride by a process which comprises vacuum firing of the HBN and conversion by high pressure-high temperature processing at 55-80 kilobars and 1600°C to the reconversion temperature.</p><p>The high pressure reaction cell has a special design which prevents the entrance of impurities into the sample. This cell, comprises, for example, a carbon tube (8) enclosing concen- trictitanium sleeve (9). Within the cylinder defined by the tube and sleeve are : the HBN sample (4), carbon filler (3), shielding tantalum foil discs (2) and carbon end plugs (10).</p><p>The vacuum firing is done at pressures of 10-10- <Sup>10</Sup>mm Hg, 1400 - 1900°C, for 5 minutes - 4 hours, and is believed to form a thin, free-boron coating on the HBN particles.</p><p>The process works on both pyrolytic (turbostratic) and graphitic hexagonal boron nitride.</p><p>Grinding grits formed by milling cubic boron nitride chunks recovered from the high pressure-high temperature process have resulted in higher grinding ratios than commercially available CBN.</p> |
