Which statement correctly identifies an opaque nozzle material?

• A. Fused quartz
• B. Ceramic such as alumina or silicon nitride
• C. Stainless steel
• D. Plastic

Answer: (B)

An opaque nozzle material is typically a ceramic such as alumina or silicon nitride. Ceramics are ideal here because they withstand high torch temperatures, resist thermal cycling, and act as electrical insulators, which helps keep the arc and shielding gas well controlled without electrical leakage. They also remain opaque to visible light, which is consistent with the requirement.

Fused quartz is transparent, so it doesn’t fit the idea of an opaque nozzle. Stainless steel is conductive and can conduct heat and electricity into the torch body, which is undesirable for a nozzle that should insulate and maintain the gas path. Plastic would melt or degrade under the heat of the arc, making it unsuitable for the nozzle environment.