HAFNIUM

Introduction

Atomic Number: 72
Group: 4 or IV B
Atomic Weight: 178.49
Period: 6
CAS Number: 7440-58-6

Classification

Chalcogen
Halogen
Noble Gas
Lanthanoid
Actinoid
Rare Earth Element
Platinum Group Metal
Transuranium
No Stable Isotopes
Solid
Liquid
Gas
Solid (Predicted)

Description • Uses/Function

Hafnium was thought to be present in various minerals and concentrations many years prior to its discovery, in 1923, credited to D. Coster and G.von Hevesey. On the basis of the Bohr theory, the new element was expected to be associated with zirconium. It was finally identified in zircon fromNorway, by means of X-ray spectroscopic analysis. It was named in honor of the city in which the discovery was made. Most zirconium minerals contain1 to 5% hafnium. It was originally separated from zirconium by repeated recrystallization of the double ammonium or potassium fluorides by vonHevesey and Jantzen. Metallic hafnium was first prepared by van Arkel and deBoer by passing the vapor of the tetraiodide over a heated tungstenfilament. Almost all hafnium metal now produced is made by reducing the tetrachloride with magnesium or with sodium (Kroll Process). Hafniumis a ductile metal with a brilliant silver luster. Its properties are considerably influenced by the impurities of zirconium present. Of all the elements,zirconium and hafnium are two of the most difficult to separate. Their chemistry is almost identical, however, the density of zirconium is about halfthat of hafnium. Very pure hafnium has been produced, with zirconium being the major impurity. Natural hafnium contains six isotopes, one of whichis slightly radioactive. Hafnium has a total of 40 recognized isotopes and isomers. Because hafnium has a good absorption cross section for thermalneutrons (almost 600 times that of zirconium), has excellent mechanical properties, and is extremely corrosion resistant, it is used for reactor controlrods. Such rods are used in nuclear submarines. Hafnium has been successfully alloyed with iron, titanium, niobium, tantalum, and other metals.Hafnium carbide is the most refractory binary composition known, and the nitride is the most refractory of all known metal nitrides (m.p. 3310°C).Hafnium is used in gas-filled and incandescent lamps, and is an efficient “getter” for scavenging oxygen and nitrogen. Finely divided hafnium ispyrophoric and can ignite spontaneously in air. Care should be taken when machining the metal or when handling hot sponge hafnium. At 700°Chafnium rapidly absorbs hydrogen to form the composition HfH1.86. Hafnium is resistant to concentrated alkalis, but at elevated temperatures reactswith oxygen, nitrogen, carbon, boron, sulfur, and silicon. Halogens react directly to form tetrahalides. The price of the metal is in the broad range of$1/g to $3/g, depending on purity and quantity. The yearly demand for hafnium in the U.S. is now in excess of 50,000 kg. 1

• "A number of transition metals (Ti, Zr, Hf, V, Nb, Ta, Mo, W) form interstitial carbides of composition MC and, in some cases, M2C. These carbides have extremely high melting points; they are very hard, and they are good electrical conductors." 2

Physical Properties

Melting Point:3*  2233 °C = 2506.15 K = 4051.4 °F
Boiling Point:3* 4603 °C = 4876.15 K = 8317.4 °F
Sublimation Point:3 
Triple Point:3 
Critical Point:3 
Density:4  13.3 g/cm3

* - at 1 atm

Electron Configuration

Electron Configuration: [Xe] 6s2 4f14 5d2
Block: d
Highest Occupied Energy Level: 6
Valence Electrons: 

Quantum Numbers:

n = 5
ℓ = 2
m = -1
ms = +½

Bonding

Electronegativity (Pauling scale):5 1.3
Electropositivity (Pauling scale): 2.7
Electron Affinity:6 abt 0 eV
Oxidation States: +4

Ionization Potential   eV 7  kJ/mol  
1 6.82507    658.5
Ionization Potential   eV 7  kJ/mol  
2 14.9    1437.6
Ionization Potential   eV 7  kJ/mol  
3 23.3    2248.1
4 33.33    3215.9

Thermochemistry

Specific Heat: 0.144 J/g°C 8 = 25.703 J/mol°C = 0.034 cal/g°C = 6.143 cal/mol°C
Thermal Conductivity: 23 (W/m)/K, 27°C 9
Heat of Fusion: 24.06 kJ/mol 10 = 134.8 J/g
Heat of Vaporization: 575 kJ/mol 11 = 3221.5 J/g
State of Matter Enthalpy of Formation (ΔHf°)12 Entropy (S°)12 Gibbs Free Energy (ΔGf°)12
(kcal/mol) (kJ/mol) (cal/K) (J/K) (kcal/mol) (kJ/mol)
(s hexagonal) 0 0 10.41 43.55544 0 0
(g) 148.0 619.232 44.642 186.782128 137.8 576.5552

Isotopes

Nuclide Mass 13 Half-Life 13 Nuclear Spin 13 Binding Energy
153Hf 152.97069(54)# 400# ms [>200 ns] 1/2+# 1,206.53 MeV
154Hf 153.96486(54)# 2(1) s 0+ 1,223.91 MeV
155Hf 154.96339(43)# 890(120) ms 7/2-# 1,231.98 MeV
156Hf 155.95936(22) 23(1) ms 0+ 1,249.37 MeV
157Hf 156.95840(21)# 115(1) ms 7/2- 1,257.44 MeV
158Hf 157.954799(19) 2.84(7) s 0+ 1,265.51 MeV
159Hf 158.953995(18) 5.20(10) s 7/2-# 1,273.58 MeV
160Hf 159.950684(12) 13.6(2) s 0+ 1,281.65 MeV
161Hf 160.950275(24) 18.2(5) s 3/2-# 1,289.73 MeV
162Hf 161.94721(1) 39.4(9) s 0+ 1,307.11 MeV
163Hf 162.94709(3) 40.0(6) s 3/2-# 1,315.18 MeV
164Hf 163.944367(22) 111(8) s 0+ 1,323.25 MeV
165Hf 164.94457(3) 76(4) s (5/2-) 1,331.33 MeV
166Hf 165.94218(3) 6.77(30) min 0+ 1,339.40 MeV
167Hf 166.94260(3) 2.05(5) min (5/2)- 1,347.47 MeV
168Hf 167.94057(3) 25.95(20) min 0+ 1,355.54 MeV
169Hf 168.94126(3) 3.24(4) min (5/2)- 1,363.61 MeV
170Hf 169.93961(3) 16.01(13) h 0+ 1,381.00 MeV
171Hf 170.94049(3) 12.1(4) h 7/2(+) 1,379.75 MeV
172Hf 171.939448(26) 1.87(3) a 0+ 1,397.14 MeV
173Hf 172.94051(3) 23.6(1) h 1/2- 1,395.90 MeV
174Hf 173.940046(3) 2.0(4)E+15 a 0+ 1,403.97 MeV
175Hf 174.941509(3) 70(2) d 5/2- 1,412.04 MeV
176Hf 175.9414086(24) STABLE 0+ 1,420.11 MeV
177Hf 176.9432207(23) STABLE 7/2- 1,428.18 MeV
178Hf 177.9436988(23) STABLE 0+ 1,436.25 MeV
179Hf 178.9458161(23) STABLE 9/2+ 1,444.32 MeV
180Hf 179.9465500(23) STABLE 0+ 1,452.40 MeV
181Hf 180.9491012(23) 42.39(6) d 1/2- 1,460.47 MeV
182Hf 181.950554(7) 8.90(9)E+6 a 0+ 1,459.22 MeV
183Hf 182.95353(3) 1.067(17) h (3/2-) 1,467.29 MeV
184Hf 183.95545(4) 4.12(5) h 0+ 1,475.37 MeV
185Hf 184.95882(21)# 3.5(6) min 3/2-# 1,483.44 MeV
186Hf 185.96089(32)# 2.6(12) min 0+ 1,482.19 MeV
187Hf 186.96459(43)# 30# s [>300 ns] 1,490.27 MeV
188Hf 187.96685(54)# 20# s [>300 ns] 0+ 1,498.34 MeV
Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses. 13

Reactions

Abundance

Earth - Source Compounds: oxides 19
Earth - Seawater: 0.000007 mg/L 20
Earth -  Crust:  3 mg/kg = 0.0003% 20
Earth -  Total:  230 ppb 21
Mercury -  Total:  177 ppb 21
Venus -  Total:  241 ppb 21
Chondrites - Total: 0.17 (relative to 106 atoms of Si) 22

Compounds

Safety Information


Material Safety Data Sheet - ACI Alloys, Inc.

For More Information

External Links:

Sources

(1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:14.
(2) - Jolly, William L. The Chemistry of the Non-Metals; Prentice-Hall: Englewood Cliffs, New Jersey, 1966; p 119.
(3) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:132.
(4) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 4:39-4:96.
(5) - Dean, John A. Lange's Handbook of Chemistry, 11th ed.; McGraw-Hill Book Company: New York, NY, 1973; p 4:8-4:149.
(6) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 10:147-10:148.
(7) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10:178 - 10:180.
(8) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:133.
(9) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:193, 12:219-220.
(10) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:123-6:137.
(11) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:107-6:122.
(12) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(13) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009).
(14) - T > 249.462931299049
(15) - T < 739.888310561701
(16) - T > -39.2639077340579
(17) - T > -101.960548833578
(18) - T > -107.67666880012
(19) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 965.
(20) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 14:17.
(21) - Morgan, John W. and Anders, Edward, Proc. Natl. Acad. Sci. USA 77, 6973-6977 (1980)
(22) - Brownlow, Arthur. Geochemistry; Prentice-Hall, Inc.: Englewood Cliffs, NJ, 1979, pp 15-16.