Closing the ultrahigh temperature metrology gap: Non-contact thermal conductivity (k) and spectral emittance (ɛλ) of molybdenum up to 3200 K

Advances in hypersonic hot structures, high heat-flux fusion or fission components, and laser-based additive manufacturing require reliable thermal conductivity data at high and ultrahigh temperatures, where conventional measurements become increasingly sensitive to contact resistance, uncertain boundaries, and nonlinear radiation. Building on our initial demonstration of steady-state temperature differential radiometry (SSTDR), we present a more robust platform for combined thermal and radiative property measurements. Lock-in infrared thermography measures the response to a spatially localized, modulated perturbation laser, producing a conduction dominated differential observable. In situ hyperspectral pyrometry provides true temperature and normal spectral emittance, constraining laser absorptivity and the infrared camera correction under evolving surface conditions. A two-dimensional axisymmetric model treats multiple laser heat-flux inputs, finite specimen geometry, and converged nonlinear radiative and optional convective boundaries, while a periodic transient calculation validates the steady-state edge correction used for fitting. Using high-purity molybdenum as a benchmark, we report solid-state thermal conductivity 𝑘 ⁡ ( 𝑇 ) from 1500 to 2800 K, approaching the molybdenum melting point. Covariance–aware propagation gives representative central 95% statistical intervals of − 9 . 0 % / + 9 . 0 % at 2736 K and − 1 2 . 6 % / + 1 3 . 1 % at 1836 K. Accepted spectral model, wavelength continuation, and edge treatment alternatives produce conservative coverage envelopes of − 1 2 . 2 % / + 9 . 3 % and − 1 6 . 7 % / + 1 6 . 4 % , respectively. We also report normal spectral emittance of solid and liquid molybdenum from 500 to 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.