terbium(III) Chloride
Properties
| State | Solid (hygroscopic; commonly hydrated) |
| Color | white to pale yellow |
| Solubility | Very soluble in water; soluble in alcohols |
| Melting Point | 888 °C (anhydrous) |
About terbium(III) Chloride
Terbium(III) chloride is a white-to-pale-yellow hygroscopic salt (TbCl3, 265.28 g/mol anhydrous) that almost always shows up in the lab as the hexahydrate or heptahydrate because the anhydrous form is irritatingly hard to make from solution. Try to dehydrate the hydrate by heating in air and you get TbOCl plus HCl, not what you wanted. Clean anhydrous TbCl3 requires either vacuum sublimation around 600°C, the NH4Cl-assisted dehydration route (heat the hydrate with a 6:1 excess of ammonium chloride under flowing argon, then sublime away the ammonium chloride at 350°C), or direct chlorination of Tb metal at red heat. In the crystal, Tb³⁺ sits in a 9-coordinate tricapped trigonal prismatic environment of chlorides — the typical large-Ln(III) coordination geometry shared by NdCl3, GdCl3, and the rest of the lighter trichlorides. The starting material is Tb4O7 dissolved in hot HCl with a reducing agent (hydrazine, formic acid) to push everything to Tb(III), then crystallized as the hydrate. The dominant industrial use is as the Tb source for grain-boundary-diffusion (GBD) processing of NdFeB permanent magnets, the technology that lets standard NdFeB survive the 180–220°C operating temperatures inside an EV traction motor.
Where you'll encounter it
If you've ever pulled a hexahydrate bottle off the rare-earth shelf to make a Tb-doped phosphor for a teaching lab demo, you've worked with TbCl3·6H2O. Dissolve a few hundred milligrams in water, add a tiny excess of phosphoric acid, adjust pH, and the resulting Tb-doped LaPO4 precipitate fluoresces bright green at 545 nm under a UV pen-light — the same emission line that powers the green channel in trichromatic fluorescent tubes. Magnet companies like Hitachi Metals and Shin-Etsu use TbCl3 (or the fluoride) at industrial scale: sintered NdFeB magnet blocks are coated with a TbCl3-based slurry, annealed at around 800°C, and the Tb diffuses inward along grain boundaries without entering the Nd2Fe14B grains. The process raises coercivity by roughly 300–500 kA/m using a tenth of the Tb that bulk alloying would require — the only reason heavy-rare-earth supply has kept up with EV demand at all.
Common Uses
- Terbium source for grain-boundary diffusion (GBD) into sintered NdFeB EV-motor magnets
- Tb-doping precursor for green phosphors (Tb:LaPO4, Tb:Y2O3) in fluorescent lamps
- Starting material for Tb-doped YAG and silicate scintillator single crystals
- Lewis-acid catalyst for selected aldol and Mukaiyama reactions in research synthesis
- Precursor for terbium metal production via molten-salt electrolysis
- Tb(III) source for lanthanide NMR shift reagent and luminescent probe research
- Analytical reagent in lanthanide ion-exchange and HDEHP solvent extraction studies
Safety Information
GHS: Skin Irritation Category 2 (H315), Eye Irritation Category 2A (H319), Specific Target Organ Toxicity Single Exposure Category 3 (H335, respiratory). Moderate acute toxicity by ingestion (rat oral LD50 in the gram/kg range). Hygroscopic and releases HCl on prolonged contact with humid air, so any spilled material acidifies surfaces. No OSHA-specific PEL; treat as PNOC at 5 mg/m3 respirable. Handle the hydrate in a glove box only when anhydrous chemistry demands it; otherwise nitrile gloves, goggles, and a fume hood for weighing are sufficient. The hot anhydrous synthesis routes (sublimation, NH4Cl method) are the real hazard — both produce HCl gas and require a properly trapped exhaust line.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.