Conductive TiB2–AlN–BN-Based Composite SHS Ceramics
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The structure, phase composition, and electrical conductivity of TiB2–AlN–BN-based ceramics fabricated by self-propagating high-temperature synthesis (SHS) are investigated. The temperature dependence of the specific electrical conductivity was measured in range T = 300–1300 K in vacuum of 2 × 10–3 Pa according to the standard four-probe dc-current procedure. It is established that the TiN and BN contents in the synthesis products increase while those of TiB2 and Al decrease with an increase in the TiB2 content in the initial mixture from 60 to 80 wt % and a decrease in the Al concentration from 40 to 20 wt % because of the reaction of TiB2 with nitrogen. A decrease in the Al concentration in the initial mixture leads to a decrease in the AlN content in the synthesis products. The results showed the mismatch of electrical resistance curves ρ(T) during the heating–cooling cycle for all ceramics compositions, which is associated with the variation in the length of the contact zone of conducting phases in range T = 800–1200 K. Three characteristic temperature regions are found: (I) from 300 to 800 K, when ρ monotonically increases with an increase in temperature; herewith, heating and cooling ρ(T) curves coincide completely; (II) the behavior of electrical resistance varies at T = 800–1200 K—its values depend strongly on the heat treatment mode of the sample; and (III) heating–cooling curves coincide completely at T > 1200 K.
Keywords:electrical resistivity conductive ceramics self-propagating high-temperature synthesis titanium diboride aluminum nitride
The equipment of the Distributed Joint Use Center of the Institute of Structural Macrokinetics of the Russian Academy of Sciences was used in investigations.
We thank G.A. Sytchev (Joint Institute of High Temperatures, Russian Academy of Sciences) for performing investigations with differential scanning calorimetry and differential thermal analysis methods.
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