Flash sintering of covalent non-oxide ceramics at low temperatures with low

摘要

The fundamental purpose in Functional Ceramics Technology is to obtain 100% dense polycrystalline covalent nonoxide ceramics with grain size ＜100 nm at lowest temperature and shortest time. We report a new method of utilizing a low applied electric field on nano/ micro B_4C powder at low temperature ＜1000 ℃ so as to obtain a properly sintered ceramics. Also as to obtain a fully with small grain size. The applied electric field helps to reduce the sintering temperature by at least a factor 0.33. The time frames involved are measured in minutes/seconds and not in tens of hours/days. We will focus on the B_4C system. However, other nonoxide ceramics nanocomposites such as ZrB_2, TiB_2, Si_3N_4, SiC, BN and their combinations will be reviewed. We will also present results of an in situ time- resolved EDXRD study, using synchrotron radiation of 200 keV photons, as a function of electric field and temperature whereby the flash sintered nano-B_4C particulate system shows an anomalous lattice expansion accompanied by a maximum current draw with an increase in density up to 99%. The effectiveness of the sintering method which relies on the understanding of the conductivity mechanism of non-oxide ceramics will be also discussed. Applications of the B_4C ceramics in this flash sintering processing exhibiting small grain size including but not limited to ballistic armor will be shown.