Ayşe ŞENTÜRK, BSc. Student
Metallurgical and Materials Engineering
Yıldız Technical University
Synthesis of ZrB2 Powders
Co-Supervisors: Oğuz Karaahmet, Emirhan Karadağlı, Assoc Prof. Dr. Buğra Çiçek
ZrB2 is one of the ultra-high temperature ceramic materials. ZrB2’s physical and mechanical properties are also anisotropic because of its anisotropic crystal structure. Strong covalent bonding makes its young moduli and hardness higher.  This ceramic can be used as metal crucibles and refractory lining metal owing to its chemical inertness and corrosion resistance to the molten metal attack.  ZrB2 has high hardness and this property makes it a good choice for cutting tools applications. Owing to its electrical conductivity it can be used as a high temperature electrode for aluminum electrolysis and semiconductor devices.   ZrB2 powders can be synthesized by using three ways; reduction processes, chemical routes and reactive processes.  The limiting factor of commercial synthesis of the zirconium diboride powders are the high cost of elemental boron and the low production capacity.  According to the technique that is used for synthesis, the synthesis of several grams to kilograms of powders can be produced in a few minutes to hours. Also, in ZrB2 powders which are produced in laboratories via reaction route occur greater content of oxygen impurity (~2.4 wt.%), when compared to commercially available powders (0.9 wt.% for H.C. Starck Grade B).   In this study, we aimed to produce ZrB2 powders with optimum properties by using carbothermal and borothermal methods. Carbothermal reaction produces carbon-contaminated powders and is appropriate for materials with a C concentration of < 3wt.%. ZrB2 powders can be produced using this technique. This reaction is endothermic and it is only favorable thermodynamically (ΔG° < 0) at temperature greater than 1500°C. (ZrO2(c) + B2O3(l) + 5C(g) → ZrB2(cr) + 5CO(g)). If we consider the Borothermal reduction, at temperatures above 1600°C, borothermic reduction of ZrO2 yields pure ZrB2. Because it requires the loss of expensive boron in the form of boron oxide, this process is not cost-effective for commercial production. To achieve stoichiometric ZrB2, further boron must be supplied. (ZrO2(c) + 4B(c) → ZrB2(c) + B2O2(g))
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