Kinetic study of carbothermal reduction of zirconia under vacuum condition Faramarz Kazemi 1,2 • Farzin Arianpour 3 • Hamid Reza Rezaie 4 Received: 1 August 2018 / Accepted: 8 May 2019 Ó Akade ´miai Kiado ´, Budapest, Hungary 2019 Abstract In this research, formation mechanism and kinetics of vacuum carbothermal synthesis of zirconium carbide using zirco- nium acetate and sucrose are discussed. The study of non-isothermal reduction was conducted by thermogravimetry analysis and heating the samples in argon and vacuum conditions up to 1773 K, and then the heat exchange values of reactions were calculated. Isothermal formation mechanism of carbide phase was investigated by heating the samples at 1473 K and 1673 K in argon and vacuum atmospheres followed by X-ray diffraction and quantitative phase analysis. Results showed that in non-isothermal state, the carbothermal reduction of zirconia is a heterogeneous reaction with multiple steps. For isothermal reaction, the kinetic parameters such as activation energy and pre-exponential factor were calculated as 70.56 kJ mol -1 and 11.22 9 10 -2 S -1 , respectively. It was presented that the activation energy value extracted from isothermal reaction is completely in accordance with the final step of non-isothermal results. Keywords Zirconium carbide  Vacuum  Carbothermal reduction  Thermal analysis  Kinetics List of symbols R Gas constant (8.314 J mol -1 K -1 ) a Extent of reaction m 0 Initial sample mass (g) m T Final sample mass (g) m ZrO 2 123.218 g mol -1 A Pre-exponential factor (S -1 ) E Activation energy ln g a ðÞ T 2   Effective rate constant I Peak intensity I n Peak intensity in nth step h(p) Pressure dependence function P eq Equilibrium vapor pressure m c 12.01 g mol -1 a 0 da dT T Temperature (K) f(a) Differential reaction model contracting sphere: 3ð1  aÞ 2=3 g(a) Integral reaction model contracting sphere: 1 ð1  aÞ 1=3 b Heating rate (10 K min -1 ) t Time (s) 2h o Initial 2h of (002) ZrC peak 2h f Final 2h of (002) ZrC peak I 0 n Background intensity of peak in nth step b Constant value between 0.5 and 1.5 P CO Partial pressure of CO (g) Introduction Zirconium carbide (ZrC) is a kind of ultra-high-tempera- ture ceramics (UHTCs) which shows excellent properties such as high melting point, considerable wear resistance, high-temperature structural stability, high strength and hardness [1]. Thanks to mentioned properties, this material has a wide range of applications such as mechanical parts, cutting tools and in other high-tech industries regarding its superior physical and mechanical properties, especially its low-density value in comparison with other UHT carbide materials [1, 2]. Various methods have been developed to & Hamid Reza Rezaie hrezaie@iust.ac.ir 1 Department of Mining and Metallurgy, Amirkabir University of Technology, Tehran, Iran 2 Kimia Zanjan Gostaran Co., Zanjan, Iran 3 Research and Application Center, Kastamonu University, Kastamonu, Turkey 4 School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran, Iran 123 Journal of Thermal Analysis and Calorimetry https://doi.org/10.1007/s10973-019-08368-5