__________ is not used as a material of construction in thermocouples.

ANS:D - Duralumin

Duralumin is an aluminum alloy noted for its combination of strength and lightness. It was one of the earliest widely used aluminum alloys and was developed in the early 20th century. The term "duralumin" is derived from the names of its two primary constituents: "durable" and "aluminum". The typical composition of duralumin includes around 90-95% aluminum, with the remainder consisting of copper (about 4%), magnesium (0.5-1.5%), and manganese (0.5-1.5%). These alloying elements contribute to its strength and hardness while still maintaining relatively low density, making it suitable for applications where both strength and lightness are important. Duralumin has been widely used in aviation for aircraft construction, particularly during the early and mid-20th century. Its strength-to-weight ratio made it ideal for structural components like wings, fuselages, and engine parts. Additionally, it has been used in other applications where its combination of properties is advantageous, such as in the manufacturing of automotive parts, bicycle frames, and various structural components. Despite its historical significance and utility, duralumin has largely been superseded by newer aluminum alloys and composite materials in many modern applications. However, it remains an important material in the history of metallurgy and engineering, particularly for its role in advancing lightweight and high-strength materials.