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Abstract The adiabatic temperatures and equilibrium phases in the FeTiO 3 - α Mg-C(B, Si)- k NaCl system (where α = 0.2–15, k = 0–3) were analyzed to predict the formation of fine powders of titanium compounds from natural ilmenite sand. From the parametric study, the critical variables were identified and optimized for the synthesis of FeTi, TiC, TiB 2 , and TiFeSi 2 under a combustion regime. The experimentally measured temperatures were in good agreement with those predicted from thermochemical calculations in the 900–1800 °C range. The purified products were characterized using X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The fine powders of titanium compounds were mainly single phase with a purity of at least 95 wt%. Considering the various stages of the synthetic process, a mechanism is proposed to explain how the process of ilmenite recovery occurred. Graphical abstract Image Highlights • Natural ilmenite was used as a precursor for synthesizing Ti compounds. • Combustion temperatures and phases were determined in FeTiO 3 -αMg-C(B, Si)- k NaCl system. • The effect of Mg and NaCl concentration on the combustion temperature was revealed. • The ilmenite was converted into FeTi, TiC, TiB 2, and FeTiSi 2 fine powders. • A reduction pathway in the synthesis of Ti compounds was proposed. [ABSTRACT FROM AUTHOR]

The present study demonstrates the synthesis of fine hafnium (Hf) metal powders via a chemically activated combustion synthesis (CS) approach, which develops temperatures in the range of 1000–1600 °C. The current CS approach can be employed to obtain Hf powders with a single-crystalline hexagonal close-packed (hcp) structure in addition to high compositional uniformity and average particle sizes ranging from 0.05 to 2.0 μm. The mechanism of Hf particle formation can be understood by analyzing the process thermodynamics, including adiabatic temperatures and equilibrium reaction phases. In addition, analytical methods, including X-ray diffraction, SEM/TEM BET, FTIR, and oxygen analysis, were employed to characterize the synthesized Hf powders. Theoretical analysis was also conducted to predict the oxygen content according to Hf particle size. To the author's best knowledge, this work is the first known report demonstrating the preparation of hafnium micro- and nanopowders by the combustion synthesis method. • The combustion of HfO 2 +0.08KClO 4 + k Mg systems was studied for k = 2.7–7. • Synthesis temperatures ranging from 1570 to 1000 °C were recorded. • Hf powder with particle sizes of 0.05–2.0 μm and 0.8–2.0 wt% oxygen was obtained. • Deoxidation using a Ca/Mg alloy powder produced Hf metal with less than 0.1 wt% O 2. • A theoretical model, for predicting oxygen concentration in Hf particles is proposed. [ABSTRACT FROM AUTHOR]