Mg Evaporation Consistency via Plasma

Ammonia (NH₃) plasma + EC–HT coupling + evaporation proxy to map gradients and material-loss sensitivity during a 0–90 A sweep.

Multiphysics COMSOL model built to evaluate thickness-varied Mg disc samples under NH₃ plasma exposure when direct mass-loss measurement and optical access are limited. A 0–90 A current sweep drives Joule heating to predict temperature profiles, locate peak gradients, and compare an evaporation-risk proxy across thickness cases—supporting reactive (“explosive”) Mg nanoparticle production while conserving Mg and keeping vacuum-relevant boundary behavior consistent (IP-safe enclosure + losses).

My contribution: designed and implemented the coupled EC–HT sweep model, meshing strategy, evaporation-proxy boundary, and IR overlay validation workflow. Experimental reactor/hardware belonged to my advisor’s lab; the model/workflow is mine.

Electric potential and current path used to compute Joule heating — **Electrical solution (results view)** showing electric potential / current path used to compute Joule heating and evaluate thermal gradients across the heating geometry.

What this enables (IP-safe)

Thickness down-select: compare Mg disc thickness cases under identical NH₃ plasma exposure to balance yield vs loss.
Gradient mapping: quantify where/when thermal gradients peak across the 0–90 A sweep.
Material-loss control: rank evaporation-risk proxy response to conserve Mg while improving run-to-run reproducibility.
Vacuum-aware interpretation: keep boundary losses + current return paths consistent via reactor-domain enclosure.
Hot-spot localization: identify contact/neck regions driving peak gradients to guide design/process adjustments.
Validation pathway: IR thermography overlays to compare measured surface trends vs simulated temperature fields.

Core Simulation Features

Gas environment: NH₃ plasma represented via enclosure + boundary losses (IP-safe proxy).
Joule heating: 0–90 A sweep sets thermal loading.
Thickness study: Mg disc thickness is the controlled variable for yield vs loss comparisons.
Coupled physics: Electric Currents + Heat Transfer (solid conduction + boundary losses).
Evaporation proxy: latent-heat sink on Mg free surface (rate-linked sensitivity).
Radiation: Stefan–Boltzmann boundary with simplified view assumptions.

Next work: results informed subsequent MgH₂ processing direction (separate study), using the temperature/gradient understanding as a baseline.

System assembly (experimental domain)

Full assembly view showing boat and disc inside surrounding reactor domain — **Assembly in reactor domain**: geometry enclosed by a surrounding domain representing the experimental environment used to keep boundary conditions, current return paths, and vacuum-relevant boundary losses consistent across sweeps and thickness cases.
Surrounding enclosure preserves current paths and boundary losses representative of the reactor environment; isolated component-only setups did not converge reliably without it.

Numerical setup

Finite element mesh of tungsten boat and surrounding domain — **Mesh overview**: refined near high current-density regions/curvature and contact features; coarser in the surrounding domain to control compute cost across multi-case thickness sweeps.

Model assumptions & limits

Evaporation proxy: implemented as a latent-heat sink at the Mg free surface to represent relative material-loss sensitivity when direct mass-loss measurement is constrained.
NH₃ plasma: represented through enclosure + boundary losses (not a fully coupled plasma chemistry model).
Radiation: Stefan–Boltzmann boundary with simplified view assumptions for tractable sweep studies.
Contacts: contact definition strongly affects peak gradients/temperatures and was treated as a key sensitivity during refinement.

Experimental Context — Physical System Reference

Tungsten evaporation boat used in plasma experiments — **Tungsten evaporation boat**: physical hardware used in NH₃-plasma experiments. Geometry and contact interfaces informed the COMSOL solid model.

Magnesium discs (thickness-varied) before and after plasma exposure — **Magnesium discs**: thickness-varied samples used to identify a “best thickness” operating window that supports reactive nanoparticle formation while reducing material loss and improving reproducibility.

T-pipe region of experimental plasma reactor — **Reactor T-pipe region**: junction supplying NH₃ gas flow and electrical current paths—motivating the surrounding domain used in simulation.

Selected References

U. Kortshagen et al., Nonthermal Plasma Synthesis of Nanocrystals, Chemical Reviews, 2016. DOI
Wagner et al., Low-Temperature Plasma-Induced Hydrogenation of Mg Nanoparticles, J. Appl. Phys., 2023.
COMSOL Multiphysics® docs: Heat Transfer + AC/DC modules.