Gallium-Indium Phase Diagram: Room-Temperature Eutectics and Melting Point Tuning

Video Snapshot

MIT OpenCourseWare demonstrates gallium-indium alloy melting behavior using the phase diagram Ga-In. Composition A is pure gallium, melting near room temperature; Composition B is near the eutectic with liquid-like behavior; Composition D is solid indium, melting at about 150 C. The video then shows a dynamic eutectic by mixing indium into gallium at room temperature, illustrating how alloy composition shifts can yield room-temperature liquids. The Ga-In phase diagram ties the observations to fundamental concepts of melting and alloying, providing a tangible view of how small changes in composition can dramatically alter a metal's state at ambient conditions.

• Gallium melts near room temperature
• Indium melts at higher temperatures
• Near-eutectic B behaves liquid-like
• Dynamic mixing forms room-temperature eutectics

Introduction and Context

This MIT OpenCourseWare video uses a hands-on exploration of the gallium-indium (Ga-In) system to illustrate how phase diagrams govern melting behavior in metal alloys. The instructor begins with solid indium and demonstrates how shaking a small sample of gallium-indium alloy can reveal whether the mixture behaves as a solid or a liquid. The core idea is that different compositions of Ga and In, when plotted on a phase diagram, melt at different temperatures, and a eutectic composition can melt at a much lower temperature than either constituent metal. In the Ga-In system, gallium is presented as melting at about 30 degrees Celsius, close to room temperature, while indium melts around 157 degrees Celsius. These basic data points set the stage for a more nuanced look at alloy behavior and phase transitions.

"Gallium melts near room temperature and indium at higher temperatures, and alloying tunes the melting point." - MIT OpenCourseWare Instructor