Troisiéme Conférence Européenne sur les Matériaux et les Procédés Avancés
J. Phys. IV France 03 (1993) C7-1305-C7-1309
Crystallization and densification of plasma H.F synthetized boron powderJ.L. BOULANGER and D. AUTISSIER
C.E.A D.A.M, BP. 12, 91290 Bruyères le Châtel, France
Boron powder was synthetized by reducing a boron halide in a microwave plasma : BCl3 + 3/2 H2[MATH]B + 3 HCl Synthetized powder is under micro sized, amorphous and contains high chlorine level. It is necessary to inflict a thermal treatment to purify and recrystallize the powder before densification. Direct hot isostatic pressing on this powder conducts to broken samples. It is realized in a vacuum furnace at temperaure between 1500 and 2000°C on 30 * 30 mm cylinders made using cold isostatic pressing at 400 MPa. Green density is among 1.3. Boron recrystallizes in [MATH] rhomboedral form. Total transformation is obtained at temperatures up to 1900°C, but density is almost the same the rough material one. No diffusion can be observed between powder grains. Hot isostatic pressing was used for the densification. Samples are put in titanium can with a carbon diffusion barrier. The pressure applied was 150 MPa and temperature varies between 1250 and 1600°C. Theoretical density is obtained at 1600°C without grain size increase. Total densification of plasma synthetized boron powder is obtained by hot isostatic pressing, but a thermal recrystallization treatment is necessary before H.I.P.
© EDP Sciences 1993