Niobium

Niobium — Material Page

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Niobium (Nb, atomic number 41) is a lustrous grey-white Group 5 refractory transition metal with a body-centered cubic (BCC) crystal structure, a melting point of 2,477 °C, and a superconducting transition temperature (Tc) of 9.26 K — the highest of any elemental metal at ambient pressure. Niobium is monoisotopic (⁹³Nb is the sole stable isotope, 100% natural abundance) and is found almost exclusively in the minerals pyrochlore ((Ca,Na)₂Nb₂O₆(OH,F)) and columbite-tantalite ((Fe,Mn)(Nb,Ta)₂O₆), with Brazil dominating global production (~90% of world supply from the Araxá and Catalão carbonatite complexes, operated by CBMM and Niobras). Despite relatively low crustal abundance (~20 ppm, comparable to cobalt), niobium is not classified as critical by the EU or US because Brazilian supply is exceptionally stable and large — but the geographic concentration makes it a monitored material. Niobium is ductile, highly malleable, and exceptional among refractory metals in that it can be cold-worked without preheating and machined with standard tooling, making it far more tractable than tungsten or molybdenum for precision fabrication of complex shapes. Its standard electrode potential is –1.10 V vs. SHE, and it forms a stable anodic Nb₂O₅ passive film that is the basis of both its corrosion resistance and its use in electrolytic capacitors.

Niobium's overwhelmingly dominant commercial application — consuming roughly 85–90% of global production (~150,000 tonnes/year as ferroniobium) — is as a microalloying addition to high-strength low-alloy (HSLA) steel, where additions of as little as 0.02–0.05 wt% Nb produce dramatic improvements in strength, toughness, and weldability through grain refinement, precipitation hardening, and retardation of recrystallization. Niobium in solution at hot-rolling temperatures (above ~1,150 °C, where Nb is fully dissolved in austenite) strongly retards recrystallization on cooling, enabling controlled thermomechanical rolling to produce extremely fine-grained ferritic microstructures with Hall-Petch strengthening contributions of 100–200 MPa — the same strength-toughness benefit as adding much larger quantities of more expensive alloying elements. NbC and NbN precipitates pin grain boundaries and provide precipitation strengthening (Orowan mechanism) of 50–100 MPa; solute Nb in austenite suppresses transformation to higher temperatures, enabling accelerated cooling protocols to generate bainitic and acicular ferrite microstructures. The result is linepipe steels (API 5L X65–X120, used in oil and gas transmission pipelines), automotive structural steels (HSLA 340, HSLA 550), and shipbuilding steels that achieve 450–850 MPa tensile strength from ≤0.05 wt% Nb addition — an extraordinarily efficient use of an alloying element.

Beyond steel microalloying, niobium's superconducting properties and biocompatibility define two specialized but high-value application areas: superconducting radio-frequency (SRF) cavities for particle accelerators and superconducting quantum interference devices (SQUIDs), and implantable medical devices where Nb's inertness, osseointegration, and non-ferromagnetism are uniquely valuable. Niobium-titanium (Nb-Ti, ~47 wt% Ti) is the workhorse superconducting wire for MRI magnets (1.5–7 T), research solenoids, and accelerator dipoles operating at 4.2 K — the Nb-Ti alloy combines Hc₂ ~14.5 T, Jc >3,000 A/mm² at 5 T/4.2 K, and excellent ductility for multifilamentary wire drawing; virtually every MRI scanner in the world contains Nb-Ti superconducting coils. Bulk niobium metal (typically 99.99%+ purity, large-grain or single-crystal) is the standard material for SRF cavities in electron linacs, proton accelerators, and free-electron lasers (CERN LHC, LCLS-II, European XFEL) — the Nb SRF cavity achieves surface resistance Rs ~10 nΩ at 2 K, compared to ~1 mΩ for copper at room temperature, enabling the extremely high accelerating gradients (~45 MV/m) and Q-factors (~10¹¹) required by modern accelerator-based light sources and colliders. Niobium's biocompatibility — it forms a stable TiO₂-like Nb₂O₅ passive film, does not corrode in physiological environments, and is non-ferromagnetic (essential for MRI compatibility of implants) — makes it a preferred material for orthopedic implants, dental implants, and cardiac pacemaker housings.

General Properties

Property	Value	Notes
Atomic Number	41	Group 5, Period 5; transition metal; 4d⁴5s¹ electron configuration — an anomalous ground state (expected 4d³5s²) that reflects the half-filled 4d subshell's stability preference; monoisotopic element (⁹³Nb, 100%); sits directly above tantalum (73) in Group 5, with similar chemistry but substantially different superconducting and nuclear properties
Atomic Mass	92.906 u	Monoisotopic — ⁹³Nb is the only stable isotope, one of 22 monoisotopic elements; the monoisotopic nature simplifies INAA (instrumental neutron activation analysis) and NMR measurements; ⁹³Nb has I = 9/2, making it NMR-active with a large quadrupole moment; ⁹³Nb(n,γ)⁹⁴Nb reaction (thermal neutron cross-section ~1.15 barn) produces the long-lived radioactive ⁹⁴Nb (t½ = 20,300 yr)
Density (20 °C)	8.57 g/cm³	Moderate density for a refractory metal — similar to nickel (8.91 g/cm³) and copper (8.96 g/cm³), but with a melting point more than 1,000 °C higher; much lower density than tantalum (16.65 g/cm³), making Nb the preferred choice when weight is critical in refractory or superconducting applications; the density/melting point ratio makes Nb the most efficient refractory metal by mass for high-temperature service below ~2,000 °C
Melting Point	2,477 °C (2,750 K)	Third-highest melting point of the Group 5 metals (V: 1,910 °C, Nb: 2,477 °C, Ta: 2,996 °C); well above iron (1,538 °C) and nickel (1,455 °C); Nb retains significant strength to ~1,800 °C in inert atmosphere; SRF cavities operate at 2 K — an extraordinary 2,475 °C below the melting point, reflecting the cryogenic rather than high-temperature application of Nb's most demanding use case
Boiling Point	4,744 °C (5,017 K)	Extremely high boiling point; Nb vapor pressure is negligible at all practical processing temperatures; enables use in electron beam melting and vacuum arc remelting without significant metal loss; relevant to Nb coating of vacuum components at high temperatures (sublimation pumping with Nb getter films)
Thermal Conductivity	54 W/m·K (25 °C)	Moderate thermal conductivity for a refractory metal — lower than Mo (138 W/m·K) and W (173 W/m·K) but adequate for most structural applications; thermal conductivity of the superconducting state becomes relevant for SRF cavity performance — the RRR (residual resistivity ratio) of cavity-grade Nb (typically RRR >300) tracks both purity and thermal conductivity at cryogenic temperatures, with higher RRR niobium providing better thermal stability and reduced quench sensitivity in SRF operations
Electrical Resistivity	152 nΩ·m (20 °C; equivalent to 15.2 µΩ·cm)	Moderate normal-state resistivity; in the superconducting state (below Tc = 9.26 K) the DC resistance drops to zero; the RRR (ρ₃₀₀K/ρ₁₀K) of commercial Nb is typically 30–100; SRF-grade Nb requires RRR >300, achieved by electron beam melting under high vacuum (reducing O, N, C, H interstitial content to <10 ppm each); the residual resistivity at cryogenic temperatures directly determines the surface resistance Rs of the superconducting cavity and thus the cavity Q-factor and cryogenic heat load
Crystal Structure	BCC; a = 3.301 Å (room temperature)	BCC structure stable from RT to melting — no allotropic transformations; the BCC structure gives Nb good ductility compared to other refractory metals; the DBTT (ductile-to-brittle transition temperature) of high-purity Nb is well below room temperature (~–100 °C), enabling cold working, deep drawing, and machining without preheating; interstitial impurities (O, N, C, H) dramatically raise the DBTT — a critical concern for reactor-grade and SRF-grade Nb where very low interstitial content is mandatory

Mechanical Properties

Property	Value	Notes
Tensile Strength	275–550 MPa (annealed to cold-worked)	Annealed high-purity Nb (~275 MPa UTS) to heavily cold-worked (~550 MPa); Nb-1Zr alloy (reactor structural grade): ~380 MPa; C-103 alloy (Nb-10Hf-1Ti): ~450 MPa at RT, retaining >200 MPa at 1,400 °C; the wide range reflects the strong effect of purity, processing history, and alloying on Nb mechanical properties
Yield Strength	140–350 MPa (annealed to cold-worked)	Very low yield strength in the annealed condition (~140 MPa), facilitating cold forming of complex shapes; the low yield/UTS ratio (~0.5 annealed) indicates substantial work hardening capacity; Nb is commonly formed to shape in the annealed condition then used as-formed without final anneal for structural applications
Young's Modulus	105 GPa	Moderate elastic modulus — lower than Mo (329 GPa), W (411 GPa), and Ta (186 GPa); the relatively low modulus compared to other refractory metals reflects the less-filled d-band of Nb; similar to titanium (116 GPa), which partly explains why Nb-Ti alloys maintain good ductility for superconducting wire drawing — neither element contributes extreme stiffness that would cause wire fracture during multifilamentary drawing to <10 µm filament diameter
Hardness	Vickers 110–160 HV (annealed to lightly worked)	Soft enough to be machined with standard carbide tooling without special precautions; harder than pure aluminum, copper, or gold; the hardness of Nb in SRF cavity applications is important — surface mechanical polishing (buffered chemical polish, BCP; electropolishing, EP) removes work-hardened surface layers to expose a smooth, low-defect-density Nb surface with RRR >300 throughout the cavity wall thickness
Elongation at Break	40–60% (annealed)	Exceptionally high elongation for a refractory metal — Nb is one of the most ductile refractory metals, comparable to pure aluminum in its annealed condition; this ductility enables deep drawing of Nb into SRF cavity half-cells by hydroforming, electron beam welding into complete cavities, and cold-drawing of Nb wire for superconducting applications without intermediate annealing steps that would be required for W or Mo
Poisson's Ratio	0.40	Among the highest Poisson's ratios of any BCC metal — unusually high, approaching the incompressibility limit of 0.5; used in SRF cavity mechanical design (Lorentz force detuning calculations) and in finite element models of Nb hydroforming to predict springback and achieve target cavity geometries within tight dimensional tolerances (±0.1 mm on cavity cell radius)

Chemical & Superconducting Properties

Property	Value / Behavior	Notes
Superconducting Transition Temperature (Tc)	9.26 K (–263.9 °C)	The highest Tc of any elemental superconductor at ambient pressure — Nb is a Type II superconductor; upper critical field Hc₂ = 0.27 T (bulk); surface superconductivity persists to Hc₃ ~0.49 T; thermodynamic critical field Hc = 0.206 T; the Bean-Livingston barrier at the surface allows RF fields to exceed Hc₁ significantly without flux penetration, enabling SRF cavity operation at accelerating gradients >50 MV/m; Tc is strongly suppressed by interstitial impurities (O, N, C reduce Tc by ~0.1 K per 100 ppm total interstitial content)
Corrosion Resistance	Excellent in HCl, HF, H₂SO₄, and alkalis; attacked by HNO₃ and oxidizing HF mixtures	Nb forms a self-healing Nb₂O₅ passive film (~5 nm at RT, growing to ~100 nm under anodization) that provides excellent corrosion resistance across a wide pH range; resistant to hot concentrated H₂SO₄ up to ~150 °C, concentrated HCl to 100 °C, and hot alkali solutions — far superior to stainless steel in these environments; attacked by hot HNO₃, HF/HNO₃ mixtures (used for chemical etching in SRF cavity preparation — BCP is HF:HNO₃:H₃PO₄ = 1:1:2), and molten alkali metal hydroxides
Oxidation State & Passive Film	+5 primarily (Nb₂O₅); also +3, +4 in intermediate compounds	Nb₂O₅ passive film is a wide-bandgap semiconductor (Eg ~3.4 eV) that forms anodically to ~1,000 nm thickness with excellent dielectric properties (εᵣ ~41) — enabling Nb to serve as the anode in electrolytic capacitors (though Ta dominates this market due to higher volumetric efficiency); the Nb₂O₅ film's biocompatibility, stability in human tissue fluids, and dielectric properties make it functionally similar to TiO₂ for implant surface chemistry; NbC and Nb₂N phases form when Nb is heated in carbon- or nitrogen-containing atmospheres above ~800 °C
Biocompatibility	Excellent; non-cytotoxic, non-ferromagnetic, osseointegration comparable to titanium	Niobium's biocompatibility profile is essentially equivalent to titanium — the stable Nb₂O₅ passive film is non-cytotoxic, does not release biologically active ions at physiological pH, and supports osteoblast adhesion and proliferation comparable to Ti-6Al-4V surfaces; Nb is paramagnetic (no ferromagnetism), making Nb implants fully MRI-compatible with no force, torque, or artifact beyond mild susceptibility effects; used in dental implants (Nb-Ti alloys), orthopedic screws, pacemaker housing components, and as a replacement for Ta in applications where the lower density of Nb (8.57 vs. 16.65 g/cm³) is advantageous

Identifier	Value
Symbol	Nb
Atomic Number	41
CAS Number	7440-03-1
UN Number	UN3089 (powder)
EINECS Number	231-113-5

Isotope	Type	Notes
⁹³Nb	Stable	100% natural abundance — niobium is monoisotopic, one of 22 monoisotopic elements; I = 9/2, NMR-active (large quadrupole moment; ⁹³Nb NMR provides broad but informative signals for characterizing Nb coordination in oxides, halides, and organometallic Nb compounds); thermal neutron activation ⁹³Nb(n,γ)⁹⁴Nb (σ ≈ 1.15 barn) produces ⁹⁴Nb, a long-lived radionuclide — a key concern in reactor structural applications and nuclear waste management; ⁹³Nb is also the target for ⁹³Nb(n,2n)⁹²ᵐNb reactions at fast neutron energies, producing ⁹²ᵐNb (t½ = 10.15 days) used as a diagnostic activation monitor in fast-spectrum reactors and fusion blanket neutronics measurements
⁹⁴Nb	Radioactive	t½ = 20,300 years (β⁻); emits 702.6 keV and 871.1 keV gamma rays (both ~99.8% intensity) — a significant long-lived activation product in reactor structural steels and Nb-containing superalloys used in reactor primary circuits; the long half-life means ⁹⁴Nb dominates the long-term radiological hazard of activated Nb-bearing components in decommissioning and waste disposal calculations, with activity persisting for ~100,000 years; ⁹⁴Nb is produced in ferroniobium steel by ⁹³Nb(n,γ)⁹⁴Nb at thermal neutron energies — the specific activity of activated HSLA steel containing Nb is dominated by ⁹⁴Nb after short-lived radionuclides decay; also a fission product tracer in post-detonation nuclear forensics
⁹⁵Nb	Radioactive	t½ = 34.99 days (β⁻); emits 765.8 keV gamma ray (99.8%); produced by ⁹⁵Zr β⁻ decay (t½ = 64 days) — ⁹⁵Zr and ⁹⁵Nb are a prominent fission product pair from ²³⁵U/²³⁹Pu fission (⁹⁵Zr fission yield ~6.5%); the ⁹⁵Zr/⁹⁵Nb gamma spectrum is a standard diagnostic tool in nuclear safeguards (tracking fresh and irradiated fuel), environmental radioactivity monitoring around nuclear sites, and post-accident fallout characterization; ⁹⁵Nb is also produced by fast neutron inelastic scattering on ⁹⁵Mo and by proton bombardment of Mo targets; used in SPECT tracer studies of Nb biodistribution and metallurgical diffusion experiments

Scientific & Research Applications

Use Case	Form Typically Used	Description
Superconducting Radio-Frequency (SRF) Cavities	High-purity Nb sheet (RRR >300, large-grain or fine-grain), Nb single crystals	Bulk niobium (99.99%+, RRR >300) is the standard material for SRF accelerating cavities used in electron linacs (LCLS-II, European XFEL, CEBAF), proton accelerators (SNS, ESS, PIP-II), and free-electron lasers. The Nb surface, prepared by electropolishing (EP) and high-pressure ultra-pure water rinsing (HPR), achieves a superconducting surface resistance of ~10 nΩ at 2 K and 1.3 GHz — enabling Q-factors of ~3×10¹⁰ and accelerating gradients of 45–55 MV/m. Research frontiers include nitrogen infusion (N-infusion) to form a Nb–N surface layer that reduces residual surface resistance by a factor of ~2–3, large-grain Nb cavities (from ingot slices) that avoid grain boundary welding artifacts, and Nb₃Sn-coated Nb cavities for operation at 4.2 K rather than 2 K.
Nb-Ti Superconducting Wire Research	Nb rod (billet grade, 99.9%), Nb-Ti alloy rod for wire fabrication	Nb-Ti (45–50 at.% Ti, typically Nb-47Ti by weight) is the commercial superconducting wire for MRI magnets (1.5–7 T), particle physics detector magnets (ATLAS, CMS solenoids), and research magnets to 9–10 T at 4.2 K. The multifilamentary wire (hundreds to thousands of 2–10 µm Nb-Ti filaments in a Cu matrix) is produced by co-extrusion and cold drawing of assembled Nb-Ti/Cu composite billets with intermediate annealing to precipitate α-Ti flux-pinning centers. Critical current density Jc >2,500 A/mm² at 5 T/4.2 K in production wire; research targets Jc >4,000 A/mm² through microstructure optimization and artificial pinning center introduction.
SQUID & Quantum Device Fabrication	Nb thin film (99.999%, sputtered, 100–300 nm), Nb/AlOₓ/Nb Josephson junction stacks	Niobium thin films deposited by DC magnetron sputtering are the standard material for superconducting quantum interference devices (SQUIDs), Josephson junction qubits (transmon, flux qubit), and superconducting single photon detectors (SSPDs/SNSPDs). Nb/AlOₓ/Nb trilayer Josephson junctions (thermal oxidation of Al interlayer to form 1–2 nm AlOₓ tunnel barrier) are the workhorse structure for SQUID fabrication — providing reproducible sub-gap resistance and critical current density of ~1 kA/cm². Nb is also used in superconducting nanowire single photon detectors (SNSPDs) as NbN or NbTiN films (Tc ~10–16 K) for single-photon counting at telecom wavelengths for quantum key distribution and quantum photonics.
Thin Film Optical Coatings	Nb₂O₅ sputtering targets (Nb or Nb₂O₅), reactive sputtering of Nb in O₂/Ar	Nb₂O₅ thin films (n ≈ 2.1–2.4 at 550 nm, bandgap ~3.4 eV) are used in precision optical coatings for antireflection, bandpass, and notch filter applications in telecommunications (DWDM filter stacks), laser optics, and camera lens coatings. Nb₂O₅ offers high refractive index, low absorption in the visible and near-IR, good environmental stability, and compatibility with TiO₂ and SiO₂ in multilayer stacks. Nb₂O₅ is preferred over TiO₂ for some applications due to lower absorption in the UV and reduced photocatalytic activity that could degrade organic adhesive layers.
Catalysis & Acid Solid Catalyst Research	Nb₂O₅ powder, niobic acid (Nb₂O₅·nH₂O), NbOPO₄	Hydrated niobium oxide (niobic acid, Nb₂O₅·nH₂O) has strong Brønsted and Lewis acidity — comparable to H₂SO₄-treated SiO₂ in some reactions — and is studied as an environmentally benign acid catalyst for esterification, dehydration, hydrolysis, and biomass conversion reactions (glucose to 5-HMF, levulinic acid production). Nb₂O₅ is water-tolerant unlike many acid catalysts that are deactivated by water, making it particularly attractive for aqueous-phase reactions in cellulose and hemicellulose valorization. NbOPO₄ and Nb-substituted zeolites are studied for selective catalytic reduction (SCR) of NOₓ and oxidative dehydrogenation of alkanes.
Cryogenic Vacuum Technology (Getter Pumping)	Nb sheet, Nb film (evaporated or sputtered), Nb getter strips	Niobium is an effective getter material for hydrogen, oxygen, nitrogen, and carbon monoxide at cryogenic temperatures — the high solubility of H in Nb (up to NbH₀.₈₆ at RT) makes it useful for hydrogen storage and getter pump applications. In accelerator beam pipes operating at 4.2 K, the cold Nb surface acts as a cryopump for residual gas molecules, maintaining beam vacuum at <10⁻¹⁰ Pa. Nb thin films deposited on cryogenic beam screens in the LHC provide distributed cryopumping and reduce photon-stimulated desorption of gas from the stainless steel pipe inner surface, maintaining beam lifetime in multi-TeV proton storage rings.

Industrial & Commercial Applications

Sector	Form / Grade Used	Description
HSLA Steel Microalloying	Ferroniobium (FeNb, 60–70% Nb), standard-grade Nb metal	Niobium microalloying (0.02–0.10 wt% Nb) is the single most efficient method for strengthening steel — achieving 100–250 MPa yield strength increase per 0.1 wt% addition compared to ~100 MPa for manganese and ~70 MPa for silicon at equivalent additions. The Nb effect operates through three mechanisms: (1) solute drag retarding austenite recrystallization during thermomechanical rolling, enabling fine-grained microstructure generation; (2) NbC/NbN precipitation in austenite and ferrite providing Orowan strengthening; (3) hardenability increase enabling bainite/acicular ferrite formation on accelerated cooling. Applications span API linepipe (X65–X120, high-pressure gas/oil transmission), automotive structural steel (reducing body-in-white weight 10–20%), shipbuilding, and heavy construction steelwork. ~85% of global Nb consumption.
Nickel Superalloy Additions	Nb metal rod/powder or Nb-Ni master alloy; 1–5 wt% Nb in alloy	Niobium is a critical alloying element in nickel superalloys — most importantly in IN-718 (Inconel 718: Ni-19Cr-18Fe-5Nb-3Mo-0.9Ti-0.5Al), which accounts for ~35% of all aerospace superalloy use by weight and is the standard disk alloy for compressor and low-pressure turbine disks. The Nb in IN-718 forms the γ″ precipitate (Ni₃Nb, body-centered tetragonal, coherent) that provides ~600 MPa yield strength at 650 °C through coherency strain hardening — the primary strengthening mechanism in IN-718. ⁹⁴Nb activation in used IN-718 turbine disks contributes to the long-term radiological burden of decommissioned aeroengines that have seen neutron irradiation in research or military applications.
Medical Implants & Biomedical Devices	Nb rod, tube, wire (99.9%), Nb-Ti and Nb-Zr alloys, anodized Nb	Niobium metal and Nb-based alloys are used in dental implants, orthopedic bone screws and plates, spinal fusion cages, and pacemaker/ICD housing components where titanium's slightly inferior corrosion resistance in specific physiological environments or higher cost is a concern. Anodized Nb (Nb₂O₅ film grown to controlled thickness by anodization) produces vivid structural colors (blue at ~60 nm, gold at ~80 nm, violet at ~100 nm) used in decorative jewelry and body piercing jewelry as a hypoallergenic, non-toxic, non-magnetic alternative to nickel-bearing alloys. Nb₂O₅ surface layers on Nb implants are functionally equivalent to TiO₂ on titanium in terms of protein adsorption, cell adhesion, and osteoblast differentiation.
Chemical Process Equipment	Nb plate, Nb-1Zr alloy, Nb heat exchanger tubes	Niobium's exceptional corrosion resistance in hot concentrated mineral acids — HCl to 100 °C, H₂SO₄ to 150 °C, mixed acid environments — makes it the material of choice for heat exchangers, reaction vessels, and distillation columns handling extremely aggressive acid streams in specialty chemicals, semiconductor precursor manufacturing, and pharmaceutical synthesis. Nb is preferred over tantalum in applications where the substantially lower density (8.57 vs. 16.65 g/cm³) and lower cost of Nb provide acceptable performance — Ta is chosen only when the very highest acid resistance (particularly HNO₃) is required. Nb-1Zr alloy provides improved high-temperature strength over pure Nb for process equipment operating above 300 °C.
Electrolytic Capacitors (Niobium Oxide)	NbO powder (niobium monoxide) sintered anodes; Nb powder (spherical, 99.9%)	Niobium oxide (NbO) powder anodes in electrolytic capacitors offer a safety advantage over tantalum capacitors — NbO is a conductor (unlike the insulating Ta₂O₅) so NbO capacitors fail to short circuit rather than burning, eliminating the incendiary failure mode of Ta capacitors in consumer electronics; NbO capacitors achieve comparable volumetric efficiency to Ta in the 10–100 µF range for portable electronics power supply decoupling. Nb metal powder is also used directly as capacitor anode material where the Nb₂O₅ dielectric (εᵣ ~41 vs. Ta₂O₅ ~26) provides higher volumetric capacitance per unit Nb mass than Ta, partially offsetting Ta's higher anodic oxide quality.

Purity	Main Use
99.85%	Commercial-grade niobium for general industrial applications and alloying — suitable for ferroniobium production, Nb-Ti superconducting alloy billet fabrication, and structural Nb-1Zr alloy synthesis where sub-0.15% impurities (primarily Ta, Fe, O, N) are acceptable; Ta content is the critical impurity specification since Ta is chemically near-identical to Nb but degrades superconducting properties if elevated
99.9%	High-purity grade for aerospace superalloy additions (IN-718 Nb additions), optical coating targets (Nb₂O₅ reactive sputtering), corrosion-resistant chemical process equipment (Nb heat exchangers), and medical implant fabrication where reduced interstitial content (O, N <200 ppm) lowers the DBTT and improves formability
99.999% (5N)	Ultra-high purity for superconducting applications — SRF cavity sheet (RRR >300 requires <10 ppm total interstitials), Josephson junction thin-film sputtering targets, SQUID device fabrication, and advanced quantum computing research where interstitial impurity content directly sets the superconducting transition temperature, surface resistance, and RF performance of finished devices

Synonym / Alternative Name	Context
Nb	Chemical symbol; from Niobe (Νιόβη) in Greek mythology, daughter of Tantalus — the name was chosen by Heinrich Rose (1844) as a deliberate allusion to tantalum (named for Tantalus), because niobium was discovered as a separate element coexisting with tantalum in columbite ore; the mythological naming reflects the chemical inseparability of Nb and Ta that made their distinction so difficult
Niobium metal	Standard commercial and regulatory designation for the elemental form; used in IUPAC-approved nomenclature (IUPAC adopted "niobium" as the official name in 1950, replacing columbium), supply chain documentation, LME pricing, and REACH/CLP filings; the standard product forms are Nb rod, plate, foil, wire, powder, and sputtering targets
Elemental niobium	Scientific term distinguishing pure Nb metal from niobium compounds (Nb₂O₅, NbC, NbN, NbO, NbCl₅, ferroniobium, Nb-Ti alloy) in materials science, superconductivity, and chemistry literature
Columbium (Cb)	The original English-language name, given by Charles Hatchett who discovered the element in 1801 in a mineral from Columbia (now Connecticut), USA, and named it columbium after Columbia (the poetic name for America); the name persisted in US metallurgical and steel industry usage into the 1960s–1970s and is still occasionally used in older American standards documents (ASTM, AISI) and in some engineering contexts in the Americas; IUPAC definitively adopted niobium in 1950
Columbium metal	Commercial designation used in the US steel industry and older American trade literature for Nb metal and ferroniobium; ferrocolumbium was the US term for what is now called ferroniobium (FeNb, 60–70% Nb); the columbium name persists in some ASTM standards (e.g. ASTM B392 "Standard Specification for Niobium and Niobium Alloy Bar, Rod, and Wire" previously referenced columbium) and in American aerospace supplier qualification documents
Elemental columbium	Historical/American scientific term for pure niobium metal, found in pre-1970 American chemistry and metallurgy literature; the term "columbium" was officially retired in favor of "niobium" by IUPAC in 1950 and by IUPAP, but the transition in industrial usage was gradual through the 1970s; some US government and defense specifications from that era still use columbium

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