Molybdenum foil’s thermal expansion coefficient is 4.8 × 10⁻⁶/K (room temperature to 1000°C), low among metals, close to silicon (2.6 × 10⁻⁶/K) and sapphire (5-6 × 10⁻⁶/K), and far below aluminum (23 × 10⁻⁶/K) or copper (17 × 10⁻⁶/K). This low coefficient, due to molybdenum’s body-centered cubic structure and strong metallic bonds, ensures excellent dimensional stability at high temperatures, ideal for semiconductor substrates, sapphire growth furnaces, and aerospace components. The coefficient slightly increases with temperature, e.g., ~5.2 × 10⁻⁶/K at 2000°C, remaining low to minimize thermal stress. Purity affects the coefficient: high-purity foil (≥99.95%) is stabler due to fewer impurities, while low-purity foil (<99%) may see a slight increase (0.1-0.2 × 10⁻⁶/K) from impurities (e.g., carbon, oxygen). Cold-rolled foil’s finer grains result in slightly lower expansion than hot-rolled foil. Oxidation above 600°C, forming MoO₃, may induce surface stress, requiring vacuum protection. The coefficient is measured using dilatometry or X-ray diffraction, with ±0.1 × 10⁻⁶/K precision. Low thermal expansion ensures compatibility with substrates in thermal cycling environments (e.g., vacuum furnaces, sputtering targets), preventing cracking or deformation. Quality control involves thermal expansion testing and microscopic analysis to meet high-precision standards in electronics and aerospace.
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