Alloys — Set 5

Correct Answer: A. Invar

Invar is a classic example of a binary alloy where iron and nickel are the two main components. The nickel content is usually around 36% to achieve the desired property of low thermal expansion. Both iron and nickel are transition metals found in the same row of the periodic table.

Correct Answer: C. Elinvar

Elinvar is an alloy whose elasticity does not change with temperature, making it ideal for watch hairsprings. It is a nickel-chromium-iron alloy discovered by Nobel laureate Charles Édouard Guillaume. Its name is a contraction of 'elasticité invariable'.

Correct Answer: B. Fire sprinklers

Wood's metal melts at about 70°C, which is low enough to trigger automated fire sprinkler systems when heat rises. It consists of bismuth, lead, tin, and cadmium. This low melting point is lower than that of its individual constituents.

Correct Answer: D. Palladium-Silver alloys

Palladium-silver alloys are biocompatible and maintain their color without turning black or green. These alloys are strong enough to withstand the pressure of chewing. Palladium is a precious metal similar to platinum in its properties.

Correct Answer: B. Copper

Copper is the base metal for bronze, usually making up about 88% of its composition. The addition of tin makes the alloy harder than pure copper while still being easy to cast. The 'Bronze Age' marks the period when humans first began using this alloy for tools.

Correct Answer: D. Brass

Brass is defined by the combination of copper and zinc, which creates a versatile and attractive metal. By varying the amount of zinc, the color and strength of the brass can be adjusted. Zinc is also used to galvanize steel to prevent rusting.

Correct Answer: D. 10% to 30%

German Silver typically contains about 10% to 30% nickel, which gives it its silvery appearance. The rest is copper (about 60%) and zinc (about 20%). It is widely used in the production of table flatware and decorative hardware.

Correct Answer: C. Phosphor Bronze

Phosphor bronze contains tin and a small amount of phosphorus, which increases its strength and fatigue resistance. These properties are critical for propellers that must withstand the harsh and corrosive environment of the ocean. Phosphorus also acts as a deoxidizing agent during the melting process.

Correct Answer: C. Alloy

An alloy is a solid solution where the atoms of the alloying element are distributed within the crystal lattice of the host metal. This structure allows the material to exhibit properties different from its pure components. Alloys can be substitutional or interstitial depending on the atom sizes.

Correct Answer: A. Superalloys (Nickel-based)

Nickel-based superalloys can maintain their mechanical strength at temperatures near their melting points. This makes them indispensable for the extreme environments found inside jet engines and power plants. They often contain complex mixtures of cobalt, chromium, and tungsten.