NB6962 Niobium Tin Alloy Rod

Niobium Tin Alloy Rods Description

Niobium Tin Alloy Rods function as ductile precursors in the production of Nb₃Sn superconducting wires. The rods enable the formation of the A15 crystal structure while avoiding the brittleness typical of the superconducting phase. The intermetallic compound exhibits a critical temperature of 18 K, in contrast to NbTi alloys, and supports critical current densities above 2 000 A/mm² under a 12 T magnetic field at an operating temperature of 4.2 K. In addition, the material shows flux pinning at grain boundaries. Precise stoichiometric control near Nb-25at%Sn is required.

Mechanical limitations are observed. The reacted Nb₃Sn phase is brittle, with fracture strains below 0.2%, partly due to a thermal expansion mismatch (Δα ≈ 6×10⁻⁶/K) between the superconducting core and the bronze diffusion matrix. Consequently, the use of the rod precursor permits necessary wire drawing and coil winding prior to the 650–700°C heat treatment that produces the superconducting phase.

The electromagnetic properties include an upper critical field approaching 30 T at absolute zero. Performance is strain-sensitive; the critical current decreases by 50% at 0.3% tensile strain. Consequently, compressive pre-strain designs are required in magnet engineering. Titanium or gallium doping at concentrations of 3–7at% improves grain boundary pinning and increases radiation resistance. During reactive diffusion, Sn transport from the bronze matrix results in Nb₃Sn grains of 2–5μm, with Cu–Sn compositional gradients governing the layer growth kinetics.

The described properties are applied in several high-performance systems. Applications include ITER fusion toroidal field coils (13.5 T), CERN’s High-Luminosity LHC upgrade (11 T dipoles) and 23.5 T NMR spectrometers. Ongoing research is directed at introducing artificial pinning centres to further improve Jc.

Niobium Tin Alloy Rods Applications

1. Nuclear Fusion Reactors

ITER Toroidal Field Coils (France): 18 Nb₃Sn coils operating at 13.5 T for plasma confinement (stored energy: 41 GJ).

SPARC (MIT/CFS): A compact tokamak utilising Nb₃Sn magnets with an 8.2 T field, intended for a net-energy-gain demonstration from 2025 onwards.

2. Particle Accelerators

LHC High-Luminosity Upgrade (CERN): 11 T Nb₃Sn dipoles replace NbTi magnets, thereby increasing the collision rate by a factor of 10 (operation commencing in 2029).

FCC-hh (Future Circular Collider): Proposed magnets with a 16 T field are designed to achieve a collision energy of 100 TeV.

3. High-Field NMR Spectrometers

1.2 GHz NMR (23.5 T): Nb₃Sn/NbTi hybrid magnets provide the field required for atomic-resolution protein structure analysis (e.g., Bruker Ascend® Aeon).

4. Compact Fusion Devices

ARC Reactor (MIT): Magnets constructed entirely from Nb₃Sn deliver a 9.2 T field and support rapid maintenance.

5. Medical Imaging

Prototype 7 T whole-body MRI scanners featuring Nb₃Sn coils have been developed to improve neuroimaging resolution.

6. Energy Storage

SMES (Superconducting Magnetic Energy Storage): Nb₃Sn systems with an energy capacity of 100 MJ are employed for grid stability (e.g., Swiss-SMES project).

Niobium Tin Alloy Rods Packaging

The products are packaged in customised cartons of various sizes depending on the material dimensions. Small items are contained within PP boxes, whereas larger items are placed in custom wooden crates. Packaging is designed in accordance with specific requirements, and appropriate cushioning materials are used to maintain integrity during transportation.

Packaging: Carton, Wooden Box, or Customized.

Please review the packaging details provided for your reference.

Manufacturing Process

1.       Testing Method

(1)    Chemical Composition Analysis – Various techniques such as GDMS or XRF verify that purity requirements are met.

(2)    Mechanical Properties Testing – Tensile strength, yield strength and elongation tests assess material performance.

(3)    Dimensional Inspection – Thickness, width and length are measured to ensure adherence to specified tolerances.

(4)    Surface Quality Inspection – Visual and ultrasonic examinations are conducted to identify defects such as scratches, cracks or inclusions.

(5)    Hardness Testing – Material hardness is measured to confirm uniformity and mechanical reliability.

Please refer to the SAM testing procedures for detailed information.

Niobium Tin Alloy Rods FAQs

Q1. Why choose Nb₃Sn over NbTi?

The A15 crystal structure results in higher critical parameters. The compound has a critical temperature (Tc) of 18 K, in contrast to 9 K for NbTi. In addition, Bc₂ at 4.2 K exceeds 25 T, compared with an approximate limit of 8 T. This permits magnet operation at elevated temperatures and fields while reducing cooling expenditure.

Q2. Key manufacturing challenges?

The reacted Nb₃Sn phase is brittle, with a fracture strain below 0.2%. Production requires ductile Nb–Sn precursors manufactured by either the bronze process or the internal tin method, followed by diffusion annealing at 650–700°C.

Q3. Where is Nb₃Sn indispensable?

Nb₃Sn is utilised in the following applications:

1. Nuclear fusion (for example, ITER’s 13.5 T toroidal coils)

2. High-field particle accelerators (such as the 11 T dipoles in the LHC Upgrade)

3. NMR spectrometers operating at frequencies of 1.2 GHz with 23.5 T hybrid magnets

Related Information

1.       Common Preparation Methods

Nb₃Sn conductors are produced using ductile precursor fabrication by either the bronze process (involving an Sn–Cu matrix with Nb rods) or the internal tin method (using Sn cores in Nb tubes). Both methods permit winding prior to reaction. The superconducting phase is formed by solid-state diffusion annealing at 650–700°C for 50–200 hours, during which Sn diffuses into Nb to form A15 crystals with brittle characteristics. This high-temperature annealing presents two issues: thermal expansion mismatch (Δα ≈6×10⁻⁶ K⁻¹ between Nb and bronze), which introduces residual strain, and intrinsic brittleness (fracture strain below 0.2%), necessitating specialised handling. Following the reaction, machining requires the application of copper cladding or stabiliser for quench protection, and pre-compression winding at approximately –0.6% strain is applied to counteract tensile stresses during magnet operation. Furthermore, doping with Ti or Ga at concentrations of 3–7 at% increases the upper critical field (Bc₂ >25 T) and improves grain boundary pinning. This results in Jc exceeding 3 000 A/mm² at 15 T. Industrial scaling is challenged by factors such as reaction homogeneity, including the control of Sn leakage, and the design for radiation resistance in fusion applications. Research is ongoing into additive manufacturing of precursors and hybrid architectures incorporating REBCO.