Heat at the Limit: Measuring 3000-Degree Temperatures express
A red-hot piece of metal in a furnace is like a frying pan on the stove: the hotter it gets, the faster heat travels to your hand if you touch it. But at temperatures where the metal is close to melting, measuring that speed is very tricky: sensors don't make good contact, heat escapes into the air, and the glowing sample confuses the instruments.
This new method sidesteps those obstacles. A laser hits a tiny spot on the surface, and an infrared camera tracks how heat spreads from that spot. By comparing the temperature difference between the heated point and the rest of the metal, you can calculate how well the material conducts heat. It's like estimating the force of a thrown stone by watching the ripples on water.
The method also made it possible to measure how molybdenum emits light in both solid and liquid states. This data is needed for creating components that work in extreme heat: in hypersonic aircraft, nuclear reactors, and laser 3D printing with metal.
So a red-hot piece of metal is no longer a mystery: now its thermal properties can be determined precisely, without even touching it.
Original abstract
as written by the authors arXiv:2604.09873
Advances in next-generation hypersonic hot structures, high heat-flux fusion or fission components, and laser based additive manufacturing depend on reliable solid state thermal conductivity data at high and ultrahigh temperatures, where conventional measurements become increasingly sensitive to contact resistances, uncertain boundary conditions, and nonlinear radiative losses. Building on our initial demonstration of ultrahigh temperature steady-state temperature differential radiometry (SSTDR), we present a substantially more robust platform aimed at making high temperature thermal and radiative property measurements more routine. The method integrates lock-in infrared thermography with a spatially localized, modulated perturbation laser to form a conduction dominant differential observable along with hyperspectral pyrometry and a validated 2D axisymmetric steady state heat transfer model. Using high purity molybdenum as a benchmark, we report solid state thermal conductivity k(T) from 1500 - 3000 K (to the onset of melting) with uncertainties of 7.9-11 % enabled by comprehensive uncertainty propagation, sensitivity analysis, and bounding studies. We additionally provide normal spectral emittance of molybdenum in both solid and liquid states over 500-1000 nm. These advances establish SSTDR as an accurate, non-contact route for closing the high temperature k(T) data gap while simultaneously producing much needed phase dependent radiative property data for melt adjacent and extreme heat-flux applications. Note: This is a shortened abstract; full version in manuscript.
Molybdenum melts at 2623 °C — hotter than the surface of Venus, the hottest planet in the solar system.