Yttrium (7440-65-5) Physical and Chemical Properties
Yttrium
Ductile rare-earth metal supplied as high-purity ingots, foils and powders for materials manufacturing, optical components and analytical standards.
| CAS Number | 7440-65-5 |
| Family | Rare earth metals |
| Typical Form | Silvery metallic solid (foil, ingot, powder) |
| Common Grades | BP, EP |
Yttrium is a transition/rare-earth element (atomic symbol Y) that belongs to the group of metals commonly referred to as the rare earths. In its elemental form it is a metallic single-atom species with the nominal formula Y and an atomic number of 39; the isolated atom and bulk metal are characterized by a partially filled 4d subshell and a 5s/5p core that confer typical metallic bonding, high coordination numbers in solids, and a propensity to adopt the +3 oxidation state in compounds. Structurally, elemental yttrium crystallizes in a hexagonal close-packed arrangement at ambient conditions and forms oxide films on the surface that stabilize bulk samples against rapid air attack.
Electronically and chemically, yttrium behaves like the heavier members of the early transition series and the lanthanides: it is moderately electropositive, forms predominantly ionic compounds when combined with highly electronegative elements, and shows low covalent character in simple halides and oxides. The element is essentially monophasic in natural abundance with a single stable isotope (yttrium-89), which simplifies isotopic specification for analytical and nuclear applications. Chemically it is stable in bulk due to surface oxide formation but is air- and moisture-sensitive in fine-powder form; powders are reducing and water-reactive, evolving hydrogen under hydrolysis conditions and oxidizing readily on heating.
From a materials-performance perspective yttrium is nonpolar and not lipophilic as an elemental metal; its compounds cover a range of solubilities with many oxides and fluorides being insoluble while certain nitrates and chlorides are water-soluble. The dominant aqueous speciation of yttrium is the trivalent cation in mildly acidic to neutral media; hydrolysis and precipitation (e.g., hydroxides, oxides) occur on increasing pH. Industrially, yttrium is widely used in phosphors, high-temperature alloys and coatings, and as a component in yttrium-aluminum-garnet (YAG) lasers and other specialty ceramic and electronic materials.
Common commercial grades reported for this substance include: BP, EP.
Basic Physical Properties (Density, Melting Point, Boiling Point)
Atomic Weight
- Molecular weight / atomic mass (computed): 88.90584.
- Common rounded value reported elsewhere: 88.91.
Appearance and Physical State
- Bulk metal: soft, silvery-white, hexagonal metallic solid.
- Finely divided material: dark-gray to black, odorless powder; darkens on exposure to light.
- General physical description entries: "Soft silvery-white metal in bulk. Dark-gray to black odorless powder. Solid."
Density
- Reported density: 4.47 \(\mathrm{g}\,\mathrm{cm}^{-3}\) (reported as "4.47 g/cu cm", "4.47", and "4.47 (NIOSH, 2024) - Denser than water; will sink").
Melting Point
Multiple reported values in the compiled experimental descriptions: - \(\,1509\,^\circ\mathrm{C}\) (listed in physical description). - \(\,1522\,^\circ\mathrm{C}\) (experimental properties). - \(\,1526\,^\circ\mathrm{C}\) (experimental properties). - Equivalent Fahrenheit reporting: 2732 \(^\circ\mathrm{F}\) (NIOSH) and 2732 \(^\circ\mathrm{F}\) (duplicate entries).
Note: values differ slightly between sources; no single exclusive experimental value is indicated in the current data context.
Boiling Point
Multiple reported values in the compiled experimental descriptions: - \(\,2927\,^\circ\mathrm{C}\) (physical description). - \(\,3345\,^\circ\mathrm{C}\) (experimental properties). - 5301 \(^\circ\mathrm{F}\) and "5301 \(^\circ\mathrm{F}\) at 760 mmHg (NIOSH, 2024)" (experimental properties).
As with the melting point, several experimental boiling-point figures are present; consult product- or process-specific data when precise phase boundaries are required.
Chemical Properties (Reactivity and Oxidation States)
Oxidation States
- Predominant and chemically well-established oxidation state: +3 (tripositive state). Several entries state "Known only in the tripositive state" for common chemistry.
- Divalent species have been characterized in some contexts: the dataset includes the label "Yttrium(2+) is a divalent metal cation" and synonyms referencing yttrium(2+) occurrences. In practice, +3 is the thermodynamically favored state in most compounds; lower oxidation states (+2) are unusual and typically stabilized in specialized ligand environments or under reducing conditions.
Reactivity with Air and Water
- Bulk metal forms a protective oxide film and is relatively stable in air; finely divided forms (powders, shavings, turnings) are light-sensitive, air-sensitive and can be flammable. Powder or dust may oxidize, darken on exposure to light, and can exhibit pyrophoric or flammable-solid behavior.
- With water: decomposes in water (described as "Decomposes in water"), reacts with water to yield gaseous hydrogen; reaction is slow with cold water, rapid in boiling water. The elemental metal is described as "water-reactive" and a "strong reducing agent" in reactivity alerts.
Reactivity with Acids and Bases
- Solubility/reactivity notes: soluble in dilute acids and in potassium hydroxide solution; soluble in hot water per some entries. The element reacts with strong oxidizing agents, strong acids, strong bases and halogens to give irritating and potentially toxic products. Handling guidelines indicate incompatibility with oxidizers and halogens.
Isotopic Composition
Stable Isotopes
- Natural yttrium is essentially monoisotopic: natural yttrium contains a single stable isotope, yttrium-89.
Radioisotopes
- The compiled information notes that "Forty-three other unstable isotopes and isomers have been characterized." Radioisotopes (e.g., ^90Y) are referenced in synonyms and are used in specialized nuclear or medical applications; isotopic specifications must be handled as distinct substances when radiochemistry or regulatory control is involved.
Thermodynamic Parameters
Heat Capacity and Related Data
Reported thermodynamic properties (crystalline and gas-phase values are distinguished where provided): - Heat capacity (crystal) at 298.15 K: 26.5 \(\mathrm{J}\,\mathrm{mol}^{-1}\,\mathrm{K}^{-1}\). - Heat capacity (gas phase) at 298.15 K: 25.9 \(\mathrm{J}\,\mathrm{mol}^{-1}\,\mathrm{K}^{-1}\). - Entropy (crystal) at 298.15 K: 44.4 \(\mathrm{J}\,\mathrm{mol}^{-1}\,\mathrm{K}^{-1}\). - Entropy (gas phase) at 298.15 K: 179.5 \(\mathrm{J}\,\mathrm{mol}^{-1}\,\mathrm{K}^{-1}\).
Also reported: heat of fusion = 11.43 \(\mathrm{kJ}\,\mathrm{mol}^{-1}\); heat of sublimation = 424.7 \(\mathrm{kJ}\,\mathrm{mol}^{-1}\) (specified "at 25 °C" in the source).
Enthalpy and Gibbs Energy
- Standard enthalpy of formation (crystal) at 298.15 K: 0.0 \(\mathrm{kJ}\,\mathrm{mol}^{-1}\).
- Standard enthalpy of formation (gas phase) at 298.15 K: 421.3 \(\mathrm{kJ}\,\mathrm{mol}^{-1}\).
- Gibbs free energy of formation (gas phase): 381.1 \(\mathrm{kJ}\,\mathrm{mol}^{-1}\).
These thermodynamic parameters distinguish condensed-phase reference states (elemental crystal, enthalpy set to zero by convention) from gas-phase species and are relevant when performing high-temperature vaporization, sublimation, and gas-phase equilibrium calculations.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 7440-65-5
- Alternative CAS listed in source material: 13598-57-7 (deprecated/alternate entries also present)
- EC number: 231-174-8
- UNII: 58784XQC3Y
- UN number entry shown: 3178 (YTTRIUM)
- ChEBI: CHEBI:49978
- DSSTox Substance ID: DTXSID0049816
- HMDB ID: HMDB0013667
- NCI Thesaurus Code: C28199
- InChI: InChI=1S/Y
- InChIKey: VWQVUPCCIRVNHF-UHFFFAOYSA-N
- SMILES: [Y]
Synonyms and Common Names
Selected synonyms and common names appearing in compiled descriptors: - Yttrium; Y; Yttrium (element); Yttrium metal; Yttrium-89; yttrium atom; Yttrium(2+); Yttrium ion; Yttrium foil; Yttrium powder; Y1; 39Y; Y Standard Solution (various concentrations and matrices appear as standard preparations in the source list).
(An extensive list of supplier- and depositor-supplied synonyms and product descriptions appears in the compilation; the above are representative names that appear verbatim in the source material.)
Industrial and Commercial Applications
Major Use Sectors
- Electronics and display phosphors: component of phosphors for screens and displays.
- Metallurgy and coatings: used in alloys (as deoxidizer and for property modification), in high-temperature metal coatings, and in specialized metallurgical applications.
- Optics and lasers: constituent of yttrium-aluminum-garnet (YAG) laser materials and related optical ceramics.
- Nuclear and medical: referenced uses in nuclear industry and presence of radioisotopes (e.g., ^90Y) for specialized applications.
- Standards and analytical chemistry: yttrium is sold as certified standard solutions and materials for elemental analysis (ICP, AAS) and as internal standards.
Typical Application Examples
- Phosphor formulations for display and lighting technologies that incorporate yttrium-containing host lattices.
- Alloying additions to improve high-temperature strength or oxidation resistance in specialty metals.
- YAG and doped YAG ceramics for laser gain media and optical components.
- Analytical standards: yttrium standard solutions and solid standards for instrument calibration.
Formulation and product forms commonly offered include high-purity ingots, lumps, rods, foils, powders and sputtering targets; grade descriptions appearing in manufacturing notes include "regular high purity (ingots, lumps, turnings), metallurgical, low-oxygen, crystal sponge, powder."
If a concise application summary is required for procurement or process selection: yttrium is chosen where its electronic/structural role (as a trivalent cation in ceramics and phosphors) or as a metallic alloying/coating addition provides material performance not achievable with common base metals.
Safety and Handling Overview
Storage and Handling Considerations
- Physical hazards: finely divided yttrium (powder, shavings, turnings) is air-sensitive, light-sensitive, moisture-sensitive and can be flammable or pyrophoric; dusts may form explosive mixtures and can burn with high intensity. Bulk metal is less prone to spontaneous ignition owing to surface oxide films but will oxidize on heating.
- Chemical incompatibilities: strong oxidizers, halogens and strong acids/bases are listed as hazardous-reactivity partners. Prevent contact with incompatible materials and eliminate ignition sources for powders.
- Storage: store in tightly closed containers under inert atmosphere or in a manner that limits moisture and air exposure for reactive forms (powder, filings). Segregate from oxidizers and halogenated reagents.
For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
Occupational Exposure and Protective Measures
- Recommended exposure limits and thresholds:
- NIOSH REL / OSHA PEL / TLV: 1 mg·m^-3 (stated as "1 mg/m^3" in multiple entries) — these values are given "as Y" for yttrium and yttrium compounds (time-weighted averages).
- IDLH (Immediately Dangerous to Life or Health): 500 mg·m^-3 (as Y).
- Personal protective equipment (PPE): respirators and filters appropriate to airborne concentration are recommended for dust and fume control. Source entries provide respirator selection guidance across concentration ranges (filters from N95 to full supplied-air and SCBA for high concentrations or IDLH). Basic first-aid measures: irrigate eyes, wash skin with soap and water, move exposed persons to fresh air for inhalation exposures, and seek immediate medical attention for ingestion or significant exposure.
- Firefighting and spill response: small fires may respond to dry chemical, CO2, sand or foam; metal-powder fires may require class D extinguishing media (dry sand, graphite powder, NaCl-based extinguishers) or specialized metal-fire procedures. For spills of powdered material, eliminate ignition sources, avoid creating dust clouds, and collect material for disposal in suitable containers; for large spills wetting down and diking for later recovery is suggested in the compiled guidance.
Health hazards noted in occupational summaries include potential respiratory tract irritation, eye irritation, possible liver effects observed in animal studies, and pulmonary fibrogenic potential in high-dose animal models. Material may be an occupational hepatotoxin in specific exposure scenarios. For emergency treatment and antidotal therapy references, standard supportive resuscitation, pulmonary support and symptomatic therapy are indicated for severe exposures; do not induce emesis for ingestion without professional guidance.
For final specification of protective measures, containment, and emergency response, consult the vendor SDS and applicable regulatory guidance tailored to the specific material form (metal, powder, solution) and concentration.
