The effects of an addition of monoclinic ZrO2 into the Ti/2B system were st
udied in order to control the exothermic reaction. Thermal histories of the
phase formation in both Ti/2B and Ti/2B/20 vol.% ZrO2 system were investig
ated by High Temperature X-ray Diffraction (HTXRD) accompanied with differe
ntial thermal analysis (DTA) under a flowing argon atmosphere. The results
indicated that ZrB2 formation was initiated at about 900 degrees C prior to
TiB2 formation in the ZrO2 added compositions. A two-step borothermic redu
ction of ZrO2 is believed to yield liquid boron oxide as an intermediate ph
ase. Actual combustion synthesis experiments were carried out for the same
compositions under a vacuum atmosphere. Ti/2B samples ignited easily and th
e reaction front propagated quickly while the ZrO2 added samples were hard
to ignite and the propagation was slow. Controlled reactions were achieved
due to the formation of glassy B2O3 during the borothermic reduction of ZrO
2. SEM microstructures showed that B2O3 flowed into the pores thus dissipat
ing the heat away. X-Ray diffraction patterns taken at room temperature aft
er the ignition, showed TiB2 as the major phase for the Ti/2B composition a
nd ZrB2 and TiB2 as the major phases for the ZrO2 added compositions. (C) 2
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