976 YTTERBIUM OXIDE
heated with hydrogen, nitrogen, sulfur, and carbon at high temperatures, the corresponding binary compounds are produced.
Analysis
The metal can be analyzed by flame-AA and ICP-AES methods. Ytterbium or its compounds are dissolved by acid digestion and diluted before such analysis. X-ray methods and neutron activation analysis are also applicable.
YTTERBIUM OXIDE
[1314-37-0]
Formula Yb2O3; MW 394.08
Synonyms: ytterbium (III) oxide; ytterbia
Uses
Ytterbium oxide is used in cored carbon rods for industrial lighting. The oxide also is used as an additive in special glasses. Other uses are in dielectric ceramics and special alloys.
Physical Properties
Colorless cubic crystals when pure; tinted brown or yellowish white in presence of thulia; density 9.2 g/cm3; melts at 2,435°C; insoluble in water; soluble in hot dilute acids.
Thermochemical Properties |
–433.7 kcal/mol |
∆Η ƒ° |
|
∆G ƒ° |
–412.7 kcal/mol |
S° |
31.8 cal/deg mol |
Cρ |
27.6 cal/deg mol |
Production
Ytterbium oxide is produced as an intermediate in recovering ytterbium from minerals (See Ytterbium). After opening the ore by digestion with concentrated sulfuric acid or caustic soda solution at high temperatures, rare earths are separated by ion exchange, solvent extraction, or fractional precipitation. Ytterbium fraction is treated with oxalic acid or sodium oxalate to precipitate ytterbium oxalate, which is ignited to yield ytterbium oxide.
Analysis
Elemental composition: Yb 87.82%, O 12.18%. Ytterbium oxide is dissolved in dilute acids and diluted for analysis by flame-AA or ICP-AES methods. The oxide may be characterized by x-ray.
YTTRIUM 977
YTTRIUM
[7440-65-5]
Symbol Y; atomic number 39; atomic weight 88.906; a Group III B (Group 3 transition metal; electron configuration [Kr]4d15s2; valence +3; atomic radius 1.80Å; standard electronic potentail, Eº for Y3+ + 3e ↔ Y is –2.372 V; one naturally-occurring stable isotope, Y-89 (100%); twenty-four artificial radioactive isotopes in the mass range 78-88, 90-102; the longest-lived radioisotope; Y-88, t1/2 106.6 days; shortest-lived radioisotope Y-98, t1/2 0.59 second.
History, Occurrence, and Uses
The element was discovered in 1794 by the Swedish chemist Gadolin. He named it after the small town Ytterby in Sweden where the mineral containing yttria was found. Mosander in 1843 determined that the yttria consisted of three oxides: yttria, erbia, and terbia. Yttrium occurs in all rare earths. It is recovered commercially from monazite sand, which contains about 3% yttrium. It also is found in bastnasite in smaller amounts of about 0.2%. Abundance of yttrium in earth’s crust is estimated to be 33 mg/kg. The metal has been detected in moon rocks.
Yttrium alloys have many applications. The metal doped with rare earths such as europium is used as phosphor for color television receivers. When added to iron, chromium, vanadium, niobium, and other metals it enhances resistance of these metals and their alloys to high temperature oxidation and recrystallization. It is a deoxidizer for vanadium and other nonferrous metals. Yttrium-aluminum garnets are used in lasers and in jewelery gemstones. Yttrium-iron garnets are used as transmitters and as transducers of acoustic energy.
Physical Properties
Grayish lustrous metal; darkens when exposed to light; hexagonal closepacked crystals converting to body-centered cubic structure at 1,490°C; density 4.469 g/cm3 at 25°C; Brinnel hardness 32; melts at 1,526°C; vaporizes at 3,336°C; electrical resistivity 59.6 microhm-cm at 25°C; compressibility 2.09x10–6 cm2/kg; Young’s modulus 9.62x106 psi; Poisson’s ratio 0.265; reacts with water; soluble in dilute acids and alkalis.
Thermochemical Properties |
|
∆Ηƒ° (cry) |
0.0 |
∆Η ƒ° (gas) |
100.7 kcal/mol |
∆G ƒ° (gas) |
91.1 kcal/mol |
S° (cry) |
10.6 cal/deg mol |
S° (gas) |
42.9 cal/deg mol |
Cρ (cry) |
6.19 cal/deg mol |
Cρ (gas) |
6.38 cal/deg mol |
∆Hfus |
2.72 kcal/mol |
Thermal Conductivity (at 27°C) |
0.172 W/cm K |
Coefficient of linear expansion (at 25°C) |
10.6x10–6/°C |
978 YTTRIUM
Recovery
Yttrium is recovered commercially from its two principal sources, xenotime and monazite. Ore is opened by digestion with hot sulfuric acid. Insoluble residues are filtered out and leachate solution containing yttrium and other rare-earths is loaded onto cation exchange resin beds for separation. Fractions are eluted with ethylenediamine tetraacetic acid (EDTA) buffered with ammonia at varying temperatures. Also, many other chelates are highly effective in eluting rare earths. Such temperature adjustments of resin beds enhance separation efficiency, particularly for separating yttrium. Separated rate earths including yttrium are converted into insoluble oxalates that precipitate when treated with oxalic acid or sodium oxalate.
Yttrium oxalate is then ignited to its oxide, Y2O3. The oxide is heated at 750°C in a stream of anhydrous hydrogen fluoride to yield yttrium fluoride, YF3. Alternatively, the oxide is mixed with ammonium hydrogen fluoride NH4HF2 and heated at 400°C in a stream of dry air or helium. Yttrium metal may be produced from its fluoride either by metallothermic reduction or electrolysis. The more common metallothermic reduction involves reducing the fluoride with redistilled calcium in 10% excess over the stoichiometric amounts at elevated temperatures:
2YF3 + 3Ca → 2Y + 3CaF2
In the electrolytic process, a fused bath of yttrium fluoride and lithium fluoride is heated to nearly 1,700°C and electrolyzed. The electrolysis is done in a graphite crucible using molybdenum cathodes at which yttrium is produced as molten metal.
Yttrium is purified by distillation at high temperatures under vacuum.
Reactions
The chemical properties of yttrium are more similar to those of rare earths than to scandium. However, unlike the rare earths, yttrium exhibits only one valence state, +3.
Yttrium combines with oxygen forming its only oxide, Y2O3. The reaction is much faster at high temperatures, particularly above 400°C. The metal, in the form of sponge or small particles, can ignite at this temperature. At ambient temperature the metal is slightly tarnished by oxygen or air, forming a very thin film of oxide that protects the metal from further oxidation.
Yttrium reacts with water vapor at high temperatures, usually above 750°C, forming a protective oxide coating.
The metal reacts with halogens above 200°C forming its trihalides. It combines with nitrogen above 1,000°C producing a nitride, YN. It combines at elevated temperatures forming binary compounds with most nonmetals and some metalloid elements such as hydrogen, sulfur, carbon, phosphorus, silicon, and selenium.
Analysis
The metal or its compounds can be analyzed at trace levels by flame-AA,
YTTRIUM OXIDE / YTTRIUM SULFATE 979
ICP-AES, ICP/MS and neutron activation. ICP/MS is the most sensitive method. The metal is dissolved by acid digestion and diluted prior to analysis.
YTTRIUM OXIDE
[1314-36-9]
Formula Y2O3; MW 225.81 Synonym: yttria
Uses
The oxide is used in phosphors that form red color in color television tubes. Also, it is used in gas mantles and acetylene lights. Other uses are in yttriumiron garnets for microwave filters in lasers, and as a stabilizer for high temperature in refractories.
Physical Properties
White powder; body-centered cubic structure; density 5.03 g/cm3; melts at 2,436°C; insoluble in water; soluble in dilute acids.
Thermochemical Properties |
–455.4 kcal/mol |
∆Ηƒ° |
|
∆Gƒ° |
–434.2 kcal/mol |
S° |
23.7 cal/deg mol |
Cρ |
24.5 cal/deg mol |
∆Hfus |
25.1 kcal/mol |
Preparation
Yttrium oxide is produced as an intermediate in recovery of yttrium from xenotime and monazite (See Yttrium, Recovery). The oxide is produced after separation of rare earth sulfates obtained from digesting the mineral with sulfuric acid on a cation exchange bed, precipitating yttrium fraction as oxalate, and igniting the oxalate at 750°C.
Yttrium oxide also may be obtained by thermal decomposition of yttrium nitrate.
Analysis
Elemental composition: Y 78.74%, O 21.26%. Oxide is dissolved in nitric acid and the solution analyzed for yttrium (See Yttrium). Oxide may be characterized by x-ray diffraction.
YTTRIUM SULFATE
[7446-33-5]
Formula Y2(SO4)3•8H2O; MW 610.125; prepared and sold as octahydrate