Measuring temperatures of molten pig iron (≈1450°C) and molten slag (≈1500°C) Which instrument(s) is/are appropriate under steelmaking conditions without inserting a sensor into the stream?

Introduction / Context:
Measuring the temperature of molten metal and slag in ironmaking/steelmaking requires non-contact instruments. The intense heat, splashing, and corrosive environment make immersion sensors impractical except for specialized disposable probes. Non-contact pyrometry is the standard solution.

Given Data / Assumptions:

• Molten pig iron: ~1450°C; molten slag: ~1500°C.
• Desire non-contact, line-of-sight measurement.
• Industrial setting with hot surfaces and variable emissivity.

Concept / Approach:
Both optical and radiation pyrometers infer temperature from emitted thermal radiation. The terms are often used interchangeably; “optical” historically refers to brightness or disappearing-filament types, while “radiation” may emphasize total or narrow-band radiance. In either case, non-contact sighting at these temperatures is accurate and safe when emissivity and surface conditions are managed.

Step-by-Step Solution:

Verification / Alternative check:
Steel plants routinely use optical/radiation pyrometers aimed at the tap stream or molten bath to monitor temperature, often alongside occasional disposable immersion thermocouples for cross-checks.

Why Other Options Are Wrong:

Common Pitfalls:
Ignoring emissivity and viewing window cleanliness; proper calibration and sighting are required for accurate readings.

Final Answer:
either (b) or (c)