Molybdenum forms with carbon several chemical compounds (see also section C – Mo in Table I-2.13): molybdenum monocarbide γ-MoC phase (hexagonal structured), having invariable composition and thermodynamically stable only at temperatures < ~1200 °C (not considered in this book, being outside of its topic, see Volume 1, Chap.  1 ), molybdenum monocarbide α-MoC1−x phase (cubic structured) with a wider homogeneity range and very limited temperature interval of existence (at least in the pure form), molybdenum carbide η-MoC1−x (or Mo3C2−x, hexagonal structured) phase, low-temperature ordered (α/α′-Mo2+xC, ε-Mo2+xC) and high-temperature disordered (β-Mo2±xC) phase modifications of molybdenum semicarbide [1–9].