Refractory metals – selecting high-melting engineering metals Which of the following are categorized as refractory metals in engineering practice?

Introduction / Context:
Refractory metals are valued in high-temperature applications for their high melting points, strength at heat, and resistance to wear. Recognizing examples helps engineers select materials for furnace parts, filaments, nozzles, and nuclear/chemical environments. This question checks identification of common refractory metals among given choices.

Given Data / Assumptions:

• We use a broad engineering definition of refractory metals.
• Typical lists include W, Mo, Ta, Nb, Re, and often Ti/Zr in extended senses.
• We evaluate each metal’s high-temperature credentials.

Concept / Approach:

Tungsten has the highest melting point among metals (~3420°C) and is a classic refractory metal. Molybdenum (~2620°C) is likewise standard in the refractory category. Zirconium (~1855°C) has a high melting point and notable corrosion resistance; while not always in the “classic five,” it is commonly grouped with refractory/heat-resisting metals in engineering contexts, especially for nuclear cladding and chemical service due to oxidation/corrosion behavior.

Step-by-Step Solution:

Verification / Alternative check:

Materials handbooks list W and Mo as canonical refractory metals and often include Zr in extended families of heat- and corrosion-resisting metals used in extreme environments.

Why Other Options Are Wrong:

Each specific choice is indeed refractory in this broader sense; hence the combined option is correct.

Common Pitfalls:

Restricting the category strictly to W, Mo, Ta, Nb, Re; overlooking zirconium’s high-temperature/nuclear role; confusing refractory metals with refractory ceramics.

Final Answer:

All of these