Introduction
Group: 4 or IV B
Atomic Weight: 178.49
Period: 6
CAS Number: 7440-58-6
Classification
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
Electron Configuration: [Xe] 6s2 4f14 5d2
n = 5
Electronegativity (Pauling scale):5 1.3
Specific Heat: 0.144 J/g°C 8 = 25.703 J/mol°C = 0.034 cal/g°C = 6.143 cal/mol°C
BF3 (g) + 3 H2O (ℓ) → 3 HF (aq) + H3BO3 (aq) 14
Earth - Source Compounds: oxides 22
External Links:
(1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:14.
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
Block: d
Highest Occupied Energy Level: 6
Valence Electrons:
Quantum Numbers:
ℓ = 2
mℓ = -1
ms = +½
Bonding
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
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
CaF2 (s) + 1 H2SO4 (ℓ) → 2 HF (g) + CaSO4 (s) 15
CaSiO3 (s) + 6 HF (g) → SiF4 (g) + CaF2 (s) + 3 H2O (ℓ) 16
CaSiO3 (s) + 6 HF (aq) → SiF4 (g) + CaF2 (aq) + 3 H2O (ℓ) 17
2 Eu (s) + 6 HF (g) → 2 EuF3 (s) + 3 H2 (g) 18
SF4 (g) + 2 H2O (ℓ) → SO2 (g) + 4 HF (ℓ) 19
SiF4 + 2 HF → H2SiF6 (aq) 20
UO2 (s) + 4 HF (aq) → UF4 (s) + 2 H2O (ℓ) 21
2 HF (aq) + 1 CdCO3 (s) → CdF2 (aq) + H2O (ℓ) + 1 CO2 (g)
2 HF (aq) + 1 K2CO3 (s) → 2 KF (aq) + H2O (ℓ) + 1 CO2 (g)
2 HF (aq) + 1 Na2CO3 (s) → 2 NaF (aq) + H2O (ℓ) + 1 CO2 (g)
Abundance
Earth - Seawater: 0.000007 mg/L 23
Earth -
Crust:
3 mg/kg = 0.0003% 23
Earth -
Total:
230 ppb 24
Mercury -
Total:
177 ppb 24
Venus -
Total:
241 ppb 24
Chondrites - Total: 0.17 (relative to 106 atoms of Si) 25
Compounds
Safety Information
Material Safety Data Sheet - ACI Alloys, Inc.
For More Information
American Elements
Chemical & Engineering News
Chemical Elements
ChemGlobe
Chemicool
Environmental Chemistry
Sources
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(4) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 4:39-4:96.
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