Beryllium

Beryllium — Material Page

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Beryllium (Be, atomic number 4) is a steel-grey alkaline earth metal in Group 2 of the periodic table, and one of the most remarkable structural materials known — combining the lowest density of any structural metal (1.85 g/cm³) with an elastic modulus of 287 GPa, approximately 50% higher than steel. Its hexagonal close-packed (HCP) crystal structure gives it a specific stiffness (E/ρ) roughly six times that of steel or titanium, and a speed of sound of ~12,600 m/s — the highest of any element. Beryllium is monoisotopic (⁹Be, 100% natural abundance) and its thermal conductivity of 200 W/m·K rivals aluminum, while its specific heat capacity of 1,825 J/kg·K is the highest of any metal. Its melting point of 1,287 °C is exceptionally high for such a light element, and its coefficient of thermal expansion of 11.3 µm/m·°C combined with near-zero creep rate gives it unmatched dimensional stability across wide temperature ranges.

Beryllium's nuclear properties are as distinctive as its mechanical ones. It has the lowest neutron absorption cross-section of any structural material (0.0092 barn for thermal neutrons), making it essentially transparent to neutrons, while its (γ,n) and (α,n) reactions with incident radiation make it an efficient neutron moderator and reflector. The ⁹Be(α,n)¹²C reaction was historically the first artificially induced nuclear reaction, performed by Chadwick in 1932 and leading directly to the discovery of the neutron. These properties — combined with its high melting point and low atomic mass — make beryllium the neutron reflector and moderator of choice in research reactors and spallation neutron sources. Its low atomic number (Z = 4) also means minimal X-ray absorption across a wide energy range, making it the universal window material for X-ray tubes and synchrotron beamlines.

In advanced structural and optical applications, beryllium's combination of low density, high stiffness, and exceptional dimensional stability is unmatched by any other material. The James Webb Space Telescope uses 18 gold-coated beryllium mirror segments, each 1.3 m across, operating at 40 K — chosen specifically because Be's modulus and CTE remain stable at cryogenic temperatures where aluminum mirrors would distort unacceptably. Beryllium-copper alloys (BeCu, typically 1.8–2% Be) combine tensile strengths up to 1,400 MPa with 25% IACS conductivity and non-sparking behavior, making them the standard material for precision springs, electrical connectors, and oil and gas downhole tools. Beryllia (BeO) ceramic substrates offer thermal conductivity of 330 W/m·K with full electrical insulation, used in high-power RF and microwave transistor packages.

General Properties

Property	Value	Notes
Atomic Number	4	Group 2 (alkaline earth metal), Period 2; lightest alkaline earth metal
Atomic Mass	9.0122 u	Monoisotopic — ⁹Be is the only stable isotope; 100% natural abundance
Density (20 °C)	1.85 g/cm³	Lightest structural metal; ~⅔ the density of aluminum; specific stiffness (E/ρ) ~6× that of steel
Melting Point	1,287 °C (1,560 K)	Exceptionally high for a low-density metal; enables use in high-temperature structural applications where aluminum and titanium are inadequate
Boiling Point	2,469 °C (2,742 K)	Beryllium vapor is highly toxic — high-vacuum processing requires fully enclosed systems with exhaust filtration
Thermal Conductivity	200 W/m·K	Comparable to aluminum (237 W/m·K) and far higher than titanium (22 W/m·K); critical for heat dissipation in X-ray windows and electronic substrates
Specific Heat Capacity	1,825 J/kg·K	Highest specific heat of any metal; exceptional thermal buffering capacity relevant to aerospace thermal management and cryogenic systems
Coefficient of Thermal Expansion	11.3 µm/m·°C	Low and uniform; near-zero creep rate makes Be the preferred material for precision optical mounts and cryogenic mirror substrates
Electrical Resistivity	36 nΩ·m (20 °C)	Good conductor — roughly 60% of aluminum's conductivity by volume
Crystal Structure	Hexagonal Close-Packed (HCP)	Limited slip systems contribute to brittleness at room temperature; anisotropic elastic and thermal properties in single-crystal and textured polycrystalline forms
Speed of Sound	~12,600 m/s	Highest of any element; a direct consequence of its exceptional stiffness-to-density ratio — exploited in acoustic transducer diaphragms and high-end speaker domes

Mechanical Properties

Property	Value	Notes
Hardness	Mohs 5.5; ~80 HV	Harder than most structural metals at similar density; brittle fracture risk — machining must use wet methods to prevent toxic dust generation
Elastic (Young's) Modulus	287 GPa	~50% higher than steel (200 GPa) at ⅓ the density; highest modulus-to-density ratio of any structural material
Poisson's Ratio	0.032	Exceptionally low — nearly zero lateral strain under axial load; important for precision structural and optical calculations
Fracture Behavior	Brittle (low ductility)	Elongation typically 1–3%; notch-sensitive; HCP structure limits slip systems — design must avoid stress concentrations

Thermal & Environmental Properties

Property	Value	Notes
Corrosion Resistance	Good (self-passivating)	Forms a thin, adherent BeO layer in air that prevents further oxidation up to ~600 °C; stable in fresh water but attacked by seawater and halide-containing solutions
Oxidation States	+2 (exclusively)	Small ionic radius (0.45 Å) gives beryllium compounds strong covalent character unusual for Group 2; amphoteric — dissolves in both mineral acids and hot concentrated NaOH
Toxicology	Highly toxic — IARC Group 1 carcinogen	Inhalation of Be dust or fumes causes chronic beryllium disease (CBD) and lung cancer; OSHA PEL 0.2 µg/m³; all machining must use wet methods, enclosed systems, and respiratory protection
Neutron Cross-Section	0.0092 barn (thermal)	Lowest of any structural material; combined with (γ,n) and (α,n) neutron-producing reactions makes Be the primary neutron reflector and moderator in research reactors and spallation sources
X-ray Transparency	Very high (low Z = 4)	Minimal X-ray absorption across a wide energy range; universal window material for X-ray tubes (typically 0.25–1 mm Be foil) and synchrotron beamline vacuum windows

Chemical Properties

Property	Value / Behavior	Notes
Surface Oxide	BeO (amorphous, then crystalline)	Beryllia (BeO) has exceptional thermal conductivity (330 W/m·K) with full electrical insulation — used as a high-performance ceramic substrate in its own right; the native oxide also provides passivation and corrosion resistance
Acid Resistance	Dissolves in dilute HCl, H₂SO₄, HNO₃	Reacts with mineral acids forming Be²⁺ salts; resistant to concentrated HNO₃ due to passivation; amphoteric character distinguishes Be from heavier alkaline earth metals
Alkali Resistance	Attacked by hot concentrated alkalis	Forms beryllate ions (BeO₂²⁻) in strong base — amphoteric behavior atypical for alkaline earth metals and more similar to aluminum
Galvanic Behavior	Active (–1.85 V vs. SHE)	Anodic to most metals in galvanic series; galvanic isolation required in mixed-metal assemblies in wet or corrosive environments

Identifier	Value
Symbol	Be
Atomic Number	4
CAS Number	7440-41-7
UN Number	UN1567 (powder)
EINECS Number	231-150-7

Isotope	Type	Notes
⁹Be	Stable	100% natural abundance; I = 3/2, NMR-active; only stable isotope — beryllium is monoisotopic; ⁹Be(α,n)¹²C was the first artificially induced nuclear reaction (Chadwick, 1932)
¹⁰Be	Radioactive	t½ = 1.39 × 10⁶ yr (β⁻); cosmogenic nuclide produced by spallation of O and N in the atmosphere; widely used in geochronology, erosion rate studies, and ice core dating
⁷Be	Radioactive	t½ = 53.2 days (electron capture); produced cosmogenically and in nuclear reactors; a solar neutrino source via the pp-chain; used as an atmospheric and oceanographic tracer
⁸Be	Radioactive	t½ = 8.2 × 10⁻¹⁷ s; decays to two alpha particles; the Hoyle state resonance via ⁸Be is the critical intermediate step in the triple-alpha process enabling carbon synthesis in stars

Scientific & Research Applications

Use Case	Form Typically Used	Description
X-ray Windows & Beamline Components	Foil (0.1–1 mm), polished sheet	Beryllium's low atomic number (Z = 4) gives it the lowest X-ray absorption of any structural material. Be foil windows are used in X-ray tubes, synchrotron beamlines, and energy-dispersive detectors to provide vacuum isolation while transmitting the full X-ray spectrum with minimal attenuation and fluorescence background.
Neutron Moderator & Reflector	Block, rod, machined components	Beryllium's thermal neutron cross-section of 0.0092 barn — the lowest of any structural material — combined with effective neutron scattering makes it the preferred neutron reflector in research reactors (e.g. ILL, ISIS) and spallation neutron source moderator vessels. The ⁹Be(α,n)¹²C reaction also produces neutrons efficiently for laboratory neutron sources.
Precision Optical Mirrors	Machined mirror blanks, polished substrates	Beryllium's specific stiffness and dimensional stability at cryogenic temperatures make it the material of choice for space telescope mirrors. The James Webb Space Telescope uses 18 gold-coated beryllium mirror segments operating at 40 K, where Be's CTE and modulus remain stable. Also used in airborne reconnaissance systems and ring laser gyroscopes where thermal distortion must be minimized.
Particle Physics & Accelerator Components	Foil, thin-wall tube, beam pipe sections	Beryllium beam pipes are used in the interaction regions of particle colliders — including the LHC at CERN and Belle II at KEK — due to their structural rigidity, low material budget minimizing secondary particle production, and X-ray transparency for vertex detector operation.
Cryogenic & UHV Systems	Sheet, rod, precision machined parts	Beryllium retains its mechanical properties at liquid helium temperatures (4 K), has a very low outgassing rate, and is non-magnetic, making it valuable for structural components in dilution refrigerators, superconducting magnet assemblies, and ultra-high vacuum chambers.
Neutron Source Targets	Solid targets, pressed powder compacts	AmBe and PuBe portable neutron sources — made by intimately mixing americium-241 or plutonium-238 with beryllium powder — exploit the ⁹Be(α,n)¹²C reaction to produce continuous neutron flux for neutron activation analysis, well logging, and moisture gauges.

Industrial & Commercial Applications

Sector	Form / Alloy Typically Used	Description
Aerospace & Defense Structures	Wrought Be (S-65, I-70, I-220), sheet, extrusion	Beryllium structural components achieve mass savings of 60–70% over equivalent steel parts at equal stiffness. Used in inertial guidance systems, missile airframes, satellite structural frames, and re-entry vehicle heat shields, where dimensional stability under thermal cycling and vibration is critical.
Beryllium-Copper Alloys	BeCu strip, rod, wire (1.8–2% Be)	BeCu alloys combine tensile strengths up to 1,400 MPa with 25% IACS electrical conductivity, non-magnetic and non-sparking properties, and excellent fatigue life. The largest commercial application of beryllium by volume — used in precision springs, electrical connectors, relay contacts, and oil and gas downhole tools.
High-Performance Audio	Thin foil, sputtered film, vapor-deposited dome	Beryllium's speed of sound (~12,600 m/s) and low mass enable speaker diaphragms to operate in their pistonic range up to 40+ kHz — far beyond the 20–25 kHz limit of titanium or aluminum domes. Used in high-end loudspeakers and professional studio monitors where transient accuracy across the full audio band is required.
Electronics & Thermal Management	BeO ceramic substrates, Be heat sinks	Beryllia (BeO) ceramic substrates combine thermal conductivity of 330 W/m·K with full electrical insulation, used in high-power RF transistor packages, microwave modules, and laser diode mounts. Pure Be heat sinks are used in gyrotron microwave tubes and high-power radar transmitter modules where mass-specific thermal performance is critical.
Gyroscopes & Inertial Navigation	Precision machined Be components	Beryllium's high specific stiffness and near-zero Poisson's ratio make it ideal for gyroscope rotors, accelerometer housings, and inertial measurement unit structures in aircraft and submarines where dimensional stability under vibration and thermal cycling is essential.
Non-Sparking Tooling & Molds	BeCu alloy (die-casting inserts, hand tools)	BeCu die-casting inserts and injection mold cores offer thermal conductivity 3–4× higher than tool steel, dramatically reducing cycle times in plastics processing. Non-sparking BeCu tools are standard in explosive and flammable environments — oil refineries, munitions facilities, grain elevators — where ferrous tools present ignition risks.

Purity	Main Use
Be 99%	General industrial use and alloying — suitable for beryllium-copper master alloy production and non-critical structural components where trace impurities do not affect end performance
Be 99.5%	Scientific apparatus and aerospace parts — used in structural aerospace components, gyroscope housings, and inertial navigation system frames where controlled impurity levels ensure consistent mechanical properties
Be 99.7%	High-performance electronics — appropriate for thermal management substrates and electronic packaging where residual impurities must be controlled to maintain predictable thermal conductivity
Be 99.8%	X-ray windows and nuclear applications — standard purity for X-ray tube windows and beamline foils where low trace-element content minimizes X-ray fluorescence background; also used in neutron reflector components
Be 99.9%	Research-grade optics and instrumentation — used in precision mirror substrates, particle physics beam pipe sections, and laboratory neutron source targets where maximum purity minimizes spurious signals and ensures reproducible physical properties

Synonym / Alternative Name	Context
Be	Chemical symbol
Glucinium	Historical name used until the mid-20th century, from Greek glykys (sweet) — beryllium salts have a sweet taste; symbol Gl was used in older European literature
Beryllium metal	Standard commercial and regulatory designation for the elemental form
Elemental beryllium	General scientific term distinguishing the pure metal from beryllium compounds (BeO, BeCu alloys, etc.)
Béryllium	French language equivalent
Berilio	Spanish and Italian language equivalent

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