Beryllium Oxide (1304-56-9) Physical and Chemical Properties
Beryllium Oxide
Inorganic ceramic-grade BeO offering high thermal conductivity with electrical insulation, specified for electronic substrates, heat-sinking components and high-temperature assemblies.
| CAS Number | 1304-56-9 |
| Family | Beryllium metal oxide (inorganic) |
| Typical Form | White crystalline powder |
| Common Grades | EP, USP |
Beryllium oxide (BeO) is an inorganic binary oxide of an alkaline‑earth metal, classed as a metal oxide and a refractory ceramic. In the solid state it adopts a hexagonal wurtzite (B4) lattice that yields highly covalent/ionic mixed bonding between Be(II) and O(II) centers; in the gas phase discrete diatomic BeO molecules are observed. Structurally, beryllium’s small radius and high charge density produce strong Be–O bonding with significant lattice energy and low polarity of the bulk ceramic compared with many ionic oxides of heavier metals. Electronically the solid is an electrical insulator with a large band gap, yet it exhibits thermal conductivity among oxide ceramics that approaches that of some metals.
Chemically, BeO is a refractory, thermally stable material that is amphoteric: it is largely insoluble and chemically inert under neutral aqueous conditions but reacts with strong acids to form soluble beryllium salts and with strong bases (molten or concentrated hydroxides) to give beryllate species. Surface reactivity and solubility depend strongly on firing/calcination history: low‑fired (low‑temperature calcined) powders are more reactive and relatively more soluble than high‑fired material. Because of its low density combined with high thermal conductivity and good dielectric properties, BeO is used in high‑performance ceramics and electronic applications; inhalation or dermal exposure to airborne BeO dust or fumes presents severe toxicologic risk, including sensitisation, chronic beryllium disease and lung carcinogenicity.
Common commercial grades reported for this substance include: EP, USP.
Basic Physical Properties
Density
- Reported values: 3 at \(68\,^\circ\mathrm{F}\) (USCG, 1999) — denser than water; will sink.
- Reported value: \(3.01\,\mathrm{g}\,\mathrm{cm}^{-3}\).
- Reported value: \(3.0\,\mathrm{g}\,\mathrm{cm}^{-3}\).
Commentary: the bulk density of BeO depends on form (single crystals, sintered bodies, powders) and porosity. High‑fired, well‑sintered ceramics approach the upper end of reported densities; powders and porous sinters exhibit lower apparent densities. Reported densities above show the expected high mass per unit volume for an oxide ceramic and explain the material’s tendency to sink in water.
Melting or Decomposition Point
- Reported values: melting point \(2578\,^\circ\mathrm{C}\) and \(2530\,^\circ\mathrm{C}\).
Commentary: BeO is a refractory oxide with a very high melting point (two reported values appear in industrial/experimental sources). Such high thermal stability underpins its use in high‑temperature ceramics and in applications requiring thermal resistance. Thermal behavior and phase properties are also influenced by impurity content and prior calcination temperature.
Solubility in Water
- Descriptions: “Insoluble in water; slightly soluble in acid and alkali solutions.”
- Quantitative solubility: \(2\,\mu\mathrm{g}/100\,\mathrm{mL}\) in water at \(30\,^\circ\mathrm{C}\).
- Additional notes: “Slowly soluble in concentrated acids or fixed alkali hydroxides”; “Soluble in concentrated sulfuric acid, fused potassium hydroxide”; “After ignition it is almost insoluble in water, concentrated acids or solutions of fixed alkali hydroxides.”
Commentary: bulk BeO is effectively insoluble in neutral water; measurable solubility is extremely low and strongly dependent on surface state and calcination history. Low‑fired (poorly crystallized) BeO powders are more soluble than high‑fired, well‑crystallized material. Solubility increases in strongly acidic or strongly basic media (especially fused or concentrated reagents) where BeO converts to soluble beryllium salts or complex beryllates.
Solution pH (Qualitative Behavior)
BeO shows amphoteric surface chemistry: it is essentially inert in neutral water but will react with strong acids to form Be2+ salts and with strong bases to form soluble beryllate anions. Hydrolysis in water leads to beryllium hydroxide species and the dominant aqueous dissolved species under environmental conditions include Be2+ and hydroxo‑species such as BeOH+. The degree of dissolution and resulting solution speciation is strongly pH‑dependent and is controlled by surface area and firing history.
No experimentally established single numeric value for bulk solution pH is applicable to this insoluble solid in neutral water in the current data context.
Chemical Properties
Acid–Base Behavior
BeO is amphoteric. It will react with mineral acids to produce soluble beryllium salts (e.g., BeSO4) and with strong bases (especially fused or concentrated alkali hydroxides) to form beryllate species. The extent of acid or base attack is a function of particle morphology and calcination temperature: low‑fired BeO is more reactive and more readily solubilized than high‑fired BeO.
Mechanistically, surface hydroxylation and hydrolysis produce Be–OH sites that can accept a proton (acidic behavior) or be deprotonated/complexed by strong bases; under environmental pH ranges Be(OH)2/Be(OH)+ equilibria govern dissolved concentrations.
Reactivity and Stability
- Thermal stability: highly refractory; reported melting points of \(2530\)–\(2578\,^\circ\mathrm{C}\) and a high boiling point (\(3787\,^\circ\mathrm{C}\)) indicate exceptional thermal robustness for the ceramic. Material is described as “stable under recommended storage conditions.”
- Hydrolysis/reactivity: classified with “Water‑Reactive” alerts; hydrolysis can be exothermic depending on form and conditions.
- Chemical incompatibilities: incompatible with strong acids (under conditions that dissolve the oxide), with molten alkali metals and strong reducing metals; reported to react explosively with magnesium when heated. Also listed incompatibilities include chlorinated hydrocarbons and oxidizers in certain formulations.
- Firing dependence: “high‑fired” BeO (calcined ≥ ~1000–1150–1450 °C in manufacturing practice) is more inert and less soluble than “low‑fired” BeO; calcination temperature controls crystallinity, surface bound water content, and reactivity.
Practical implication: machining, grinding or other operations generating airborne particulates increase exposure risk; thermal decomposition or fires may generate toxic beryllium oxide fumes.
Molecular and Ionic Parameters
Formula and Molecular Weight
- Molecular formula: BeO.
- Molecular weight: 25.012 \(\mathrm{g}\,\mathrm{mol}^{-1}\).
- Exact/monoisotopic mass: 25.0070977.
Additional computed descriptors: TPSA 17.1; hydrogen bond donor count 0; hydrogen bond acceptor count 1; rotatable bond count 0. SMILES: [Be]=O. InChI: InChI=1S/Be.O. InChIKey: LTPBRCUWZOMYOC-UHFFFAOYSA-N.
Constituent Ions
BeO in the solid is best described as a crystalline network with mixed ionic/covalent character; for simple ionic accounting the constituent ions are Be2+ and O2− in a 1:1 ratio. In aqueous chemistry, dissolved species typically include Be2+ and hydroxo complexes (e.g., BeOH+), with precipitation of Be(OH)2 under many pH conditions.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 1304-56-9.
- EC numbers reported: 215-133-1; 680-425-1.
- UN Number: 1566 (BERYLLIUM OXIDE) / 1566.
- ChEBI ID: CHEBI:62842.
- ICSC Number: 1325.
- NCI Thesaurus Code: C45879.
- SMILES: [Be]=O
- InChI: InChI=1S/Be.O
- InChIKey: LTPBRCUWZOMYOC-UHFFFAOYSA-N
(Where textual registry and identifier strings are provided above, they are reproduced as supplied.)
Synonyms and Common Names
Reported synonyms and common names include: oxoberyllium; BERYLLIUM OXIDE; Beryllia; Beryllium monoxide; Bromellete; Natural bromellite; BROMELITE; Beryllium oxide (BeO); Thermalox; Thermalox 995; Berlox; Super beryllia; Beryllia ceramic; Beryllium oxide, purum. (These synonyms reflect depositor‑supplied naming variants and tradename‑style labels appearing in industrial contexts.)
Industrial and Commercial Applications
Functional Roles and Use Sectors
BeO is used primarily for its combination of very high thermal conductivity, electrical insulation, and refractory behavior. Functional roles include:
- High‑technology ceramics and substrates for electronic packages.
- Heat‑sink materials and thermal spreaders in high‑power electronic devices.
- Electrical insulators and components in microwave and high‑frequency devices (windows, radomes, antennae).
- Structural components in high‑temperature reactor systems and neutron moderator/reflector roles in certain nuclear applications.
- Additive or filler in glass, ceramics and plastics to tailor thermal and dielectric properties.
- Catalytic supports and specialized ceramic processing feedstock.
Industry sectors: electronics, aerospace, defense, nuclear technology, advanced ceramics manufacturing, and specialty chemical processing.
Typical Application Examples
Typical, non‑exhaustive examples described for BeO use include heat sinks and substrates for high‑density circuit packages, microwave device windows and klystron components, resistor and transistor mountings, high‑temperature crucibles and thermocouple tubing, components in laser tubes and high‑power RF devices, and roles in nuclear reactor fuel/moderator assemblies. Selection for these applications is driven by BeO’s high thermal conductivity relative to other oxide ceramics and its ability to be sintered into mechanically robust, electrically insulating parts.
If a concise application summary is required for a specific procurement decision, selection should be based on the thermal conductivity, purity, firing history (high‑fired vs low‑fired), and accepted occupational safety controls for the intended manufacturing operations.
Safety and Handling Overview
Health and Environmental Hazards
Hazard summary: inhalation and dermal exposure to beryllium oxide dust or fumes is hazardous. BeO is associated with respiratory sensitisation leading to chronic beryllium disease (berylliosis), pulmonary granuloma formation and fibrosis, and an increased risk of lung cancer. Acute inhalation can cause chemical pneumonitis; dermal contact and eye exposure produce irritation.
Reported hazard classifications and statements (representative): H301, H315, H317, H319, H330, H335, H350(i), H372 (toxicity, irritation, sensitisation, carcinogenicity and organ damage by prolonged exposure). Occupational exposure limits reported in toxicology and occupational sections include very low values:
- OSHA Permissible Exposure Limit examples: \(0.002\,\mathrm{mg}\,\mathrm{m}^{-3}\) (as Be) TWA; ceiling \(0.005\,\mathrm{mg}\,\mathrm{m}^{-3}\) as Be; short‑term peak values referenced.
- NIOSH Recommended Exposure Limit (ceiling): \(0.0005\,\mathrm{mg}\,\mathrm{m}^{-3}\) (as Be).
- ACGIH TLV (inhalable fraction): \(0.00005\,\mathrm{mg}\,\mathrm{m}^{-3}\).
- IDLH reported: \(4.0\,\mathrm{mg}\,\mathrm{m}^{-3}\) (as Be).
First aid summary (operational): in case of inhalation move to fresh air and seek medical evaluation; for skin contact remove contaminated clothing and wash thoroughly; for eye contact flush with water for at least 15 minutes and obtain medical attention; for ingestion rinse mouth and obtain medical attention. Severe pulmonary symptoms require immediate radiographic evaluation where indicated.
Environmental/toxicity notes: beryllium species in aquatic systems tend to hydrolyze and precipitate as hydroxides under typical natural pH ranges; nevertheless, soluble beryllium ion can be toxic to aquatic organisms with differing LC/EC values reported depending on water hardness and species.
For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
Storage and Handling Considerations
- General storage: keep containers tightly closed in a dry, well‑ventilated area; store only in original containers, separated from foodstuffs and incompatible materials; provision to contain effluent from fire extinguishing is recommended.
- Handling precautions: prevent dust generation and dispersion; use local exhaust ventilation or enclosures for operations that may generate airborne dust (machining, grinding, cutting, sintering). Avoid dry sweeping; use wet wiping or HEPA‑equipped vacuum collection for cleanup. Do not let material enter drains or sewers.
- Personal protective equipment (PPE): full respiratory protection where airborne concentrations may exceed occupational limits — e.g., full‑face supplied‑air respirators or appropriately certified particulate respirators (N100/P3) as a backup to engineering controls; impermeable gloves, eye/face protection, and protective clothing. Change and launder work clothing on site; do not take contaminated clothing home.
- Spill and disposal: isolate spill area; avoid dusting; moisten and carefully collect into sealed containers for disposal by licensed waste contractors. For cleanup use wet methods or HEPA‑filtered vacuums; do not dry sweep. Dispose of waste in accordance with applicable environmental regulations.
Operational note: processes that produce airborne particulates or that alter BeO surface reactivity (low‑temperature processing, machining of low‑fired material) present the highest occupational risk. Industrial hygiene monitoring and stringent exposure control are required where BeO is handled or processed.
For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
