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A Specialist Periodical Report

Inorganic Chemistry of the Main-group
Elements
Volume 2

A Review of the Literature Published between
September 1972 and September 1973
Senior Reporter

C. C. Addison
Reporters
M. G. Barker
G. Davidson
M. F. A. Dove
P. G. Harrison
P. Hubberstey
A. Morris
R. J. Pulham
D. B. Sowerby
All of: Deportment of Chemistry, Univeisity of Nottinghani
@ Copyright 1974

The Chemical Society
Burlington House, London WIV OBN

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ISBN :0 85186 762 6
Library of Congress Catalog Card No 72-95098

Printed in Northern Ireland at The Universities Press, Belfast.


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Preface
The framework used in Volume 1 for reporting the Chemistry of the Maingroup Elements appears to have been generally acceptable, and has been
continued in Volume 2. The present volume therefore comprises eight
chapters, each concerned with one of the Main Groups as defined in the
abbreviated form of the Periodic Table given in the Preface to Volume 1, and
it has now been agreed that the chemistry of zinc, cadmium, and mercury will
be included in the Specialist Periodical Reports concerned with the Transition
Elements.
The relative sizes of the chapters are much the same as in Volume 1 and this
again reflects the amount of published research in each Group. In Chapter 1,
greater coverage is given to those properties of the metals which are relevant
to their use in the generation of electrical energy from batteries, or from
nuclear fission and fusion reactors, and both Chapters 1 and 2 include more
illustrative material. Chapter 3 reflects a steady increase in effort throughout
the Group, but an especially large number of papers have been published on
carbaborane r-complexes. Chapter 4 is large, consistent with the considerable
amount of research which continues to be published on each of these elements.
Chapter 5 now includes a short section on ‘nitrogen oxides and atmospheric

chemistry,’ but the bulk of published material is again concerned with the
chemistry of phosphorus; there are some 500 references to phosphorus,
whereas arsenic, antimony, and bismuth together are covered by 240
references. Careful selection has been necessary in Chapter 6 to avoid overlap
with other chapters or volumes. Thus, this chapter contains the chemistry of
sulphides of Main-group elements, but not sulphides of transition metals.
Again, S-N compounds are dealt with in this chapter, whereas S-B compounds are in Chapter 3, and S-P and S-As compounds in Chapter 5. The
halides of the elements are treated as they arise in Chapters 1-6, and Chapter
7 is restricted to interesting recent developments in halogen chemistry, such
as the superacids. Noble-gas chemistry is represented by a small number of
highly interesting papers, which are discussed in Chapter 8.
We have continued the policy of referring to physical properties (and
particularly spectroscopic data) of compounds only where this is essential to
demonstrate some important chemical property, Similarly, we refer only to
those aspects of organo-derivatives which illustrate significant features in the
chemistry of the Main-group element involved. On the other hand, more
structures are becoming available (often highly refined) now that X-ray
diffraction methods are becoming computerized; the chemistry becomes more
meaningful, and is more readily explained, once the structure is known, and
other physical measurements become less significant. We have therefore taken
every opportunity to include structures of key compounds.
The whole volume is again written by members of the Department of
Chemistry in the University of Nottingham, so that the maximum degree of
...

111


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iv


Preface

consultation has been possible. In spite of this, and in spite of the fact that the
period of coverage of Volume 2 is from September 1972 to September 1973
(i.e. 12 months as against 15 months for Volume l), Volume 2 is appreciably
longer. This is not due entirely to the enthusiasm of the authors; with experience, it has become easier to identify developing themes, and to discuss
them meaningfully, and we have the impression that the amount of research
effort devoted to the Main-group elements is increasing.

C . C. Addison


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Contents
Chapter 1 Elements of Group I

1

By R. I. Pulhom
Introduction

1

The Alkali Metals

1

Alloys and Intermetallic Compounds


11

Solvation of Alkali-metal Ions
Aqueous Solvation
Non-aqueous Solvation

13
13
17

5 Compounds containing Organic Molecules or Complex
25

Ions
6 Alkali-metal Oxides

34

7 Alkali-metal Halides

38

8 Lithium Compounds

42

9 Sodium Compounds

49


10 Potassium Compounds

53

11 Rubidium Compounds

56

12 Caesium Compounds

57

13 Analysis

58

14 Molten Salts

60
61
64

Nitrates
Halides

Chapter 2 Elements of Group I I

73


By R. J. Pulham

Beryllium

73

Magnesium

77

Calcium

86

Strontium

92

Barium

95

6 Analysis

99
V


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vi

Contents

Chapter 3 Elements of Group Ill

103

By G. Davidson
1 Boron
103
103
General
1 04
Boron Hydrides
110
Borane Anions and their Derivatives
Carbaboranes and their Metallo-derivatives
117
Aminoboranes and other Compounds containing B- -N
139
Bonds
144
Compounds containing B-P or B-As Bonds
Boron Halides
147
151
Compounds containing B-0 Bonds
158
Compounds containing B-C Bonds

160
Boron-containing Heterocycles
170
Compounds containing B-S Bonds
171
Boron Nitride and Metal Borides

2 Aluminium
General and Analytical
Aluminium Hydrides
Compounds containing AI-C and Al-Si Bonds
Compounds containing Al-N Bonds
Compounds containing A1-0 or AI-S Bonds
Aluminium Halides
Other Aluminium Compounds

174
174
174
177
179
183
193
198

3 Gallium

199
199
199

201
204
206

General and Analytical
Compounds containing Ga-N
Compounds containing Ga-0
Gallium Halides
Other Gallium Compounds

Bonds
or Ga-S

Bonds

4 Indium
207
General and Analytical
207
Compounds containing In-0, In-S, or In-Se Bonds 208
Indium Halides
212
Other Indium Compounds
215

5 Thallium
General and Analytical
Thallium(1n) Compounds
Thalliurn(1) Compounds
Other Thallium Compounds


216
216
217
219
224


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vi i

Contents

Chapter 4 Elements of Group IV

225

By P. G. Harrison and P. Hubberstey

1 Carbon
225
Allotropes
225
Vapour-phase Species
226
Diamond
227
Graphite
228
Vitreous Carbon

230
Carbyne
230
Carbon Fibres
230
Surface, Adsorption, and Catalytic Studies
23 1
Oxidation Studies
232
Carbides
235
Graphite Intercalation Compounds
238
Alkali Metals.
239
Halogens, Halides, Oxides, and Acids
240
Methane and its Substituted Derivatives
242
Methane
242
Halogenomethanes
245
Other Substituted Methanes
254
Formaldehyde and its Substituted Derivatives
260
Formaldehyde, Thioformaldehyde, Carbonyl Halides, and Thiocarbonyl Halides
260
Formic Acid and Formates

263
Derivatives of Group VI Elements
265
Oxides, Sulphides, and Related Species
265
Carbonates, Thiocarbonates, and Related Anions 276
Derivatives of Group V Elements
28 1
Cyanogen and Cyanides
28 1
Cyanates and Related Species
287
2 Silicon, Germanium, Tin, and Lead
Hydrides of Silicon, Germanium, Tin, and Lead
Halides of Silicon, Germanium, Tin, and Lead
Synthesis
Reactions of Silicon, Germanium, and Tin Tetrahalides and Related Compounds
Physical Studies of Quadrivalent Silicon, Germanium, and Tin Halides
(i) Structural studies
(ii) Infrared, Raman, and microwave data
(iii) N.m.r. studies
(iv) Mossbauer studies

290
290
297
297
301

304

304
305
306
306


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Contents
(v) Miscellaneous studies
Complexes and Complex Anions
(i) Halide donors
(ii) Oxygen donors
(iii) Sulphur donors
(iv) Nitrogen donors
(v) Phosphorus donors
Oxygen Derivatives of Silicon, Germanium, Tin, and
Lead
Silicon Solid-state Chemistry
(i) Silicon Dioxide
(ii) Silicates
(iii) Aluminosilicates
(iv) Zeolites
Germanium(1v) Oxide and Germanates
Tin(rv) Oxide and Stannates
Lead(xv) Oxide and Plumbates
Molecular Oxides
Alkoxides
Carboxylates

Oxyacid Derivatives
Miscellaneous Derivatives
Silicon, Germanium, Tin, and Lead Derivatives of
Sulphur, Selenium, and Tellurium
Thio-germanates, -stannates, and -plumbates, and
Related Systems
Molecular Compounds containing M-S, -Se, and
-Te (M = Si, Ge, Sn, or Pb) Bonds
Compounds containing Silicon-, Germanium-, Tin-,
and Lead-Nitrogen Bonds
Phosphorus and Arsenic Derivatives of Silicon,
Germanium, and Tin.
Pseudohalide Derivatives of Silicon, Germanium, and
Tin.
Derivatives containing Silicon-, Germanium-, and
Tin-Main-group Metal Bonds
Bonds to Group IV Metals
Bonds to Group 111 Metals
Transition-metal Derivatives of Silicon, Germanium,
Tin, and Lead
Bivalent Derivatives of Silicon, Germanium, Tin, and
Lead
Sily lenes
Germanium(n), Tin@), and Lead(@ Halides and
Halide Complexes

307
307
307
308

3 14
3 14
315
315
316
316
324
336
341
350
352
353
354
358
362
364
367

369
369
370
372
382
382
383
383
386
388
402
402

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ix

Contents
Oxygen Derivatives of Germanium(Ir), Tin(@, and
Lead(1x)
Compounds containing Silicon(1x)-, Germanium(II)-, Tin@)-, and Lead@)-Chalcogenide
Bonds
Lead@) Pseudohalides
OrganometallicDerivativesof Bivalent Germanium,
Tin, and Lead
Complexation Behaviour of Lead@) in Aqueous
Media
Catalytic Activity of Silicon- and Tin-containing
Systems
Miscellaneous Physical Measurements
Intermetallic Phases
Binary Systems
Ternary Systems

Chapter 5 Elements of Group V

408

413
417

41 8
421
422
424
424
424
427
430

By A. Morris and D. 6.Sowerby

1 Nitrogen
Elementary Nitrogen
Bonds to Hydrogen
NH and NH, Compounds
NH3 and Derivatives
NH; Compounds
N,H, and Derivatives
Bonds to Carbon
Bonds to Nitrogen
Bonds to Oxygen
N2O
NO
Nitrogen(II1) Species
NOz-NZO4
Nitric Acid
Nitrates
Miscellaneous N-0 Species
Nitrogen Oxides and Atmospheric Chemistry
Bonds to Fluorine

NF,-N,F,
Miscellaneous N-F Species
Bonds to Chlorine and Iodine
2 Phosphorus
Element
Phosphides
Hydrides

430
430
433
433
434
440
442
444
447
450
450
452
454
455
457
459
46 1
462
464
464
465
466

466
466
467
469


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Contents

X

Bonds to Boron
Bonds to Carbon
Phosphorus(rrr) Compounds
Phosphorus(v) Compounds
Bonds to Silicon, Germanium, or Tin
Bonds to Halogens
Phosphorus(II1) Halides
Phosphorus(v) Halides
Compounds containing P-C Bonds
Compounds containing P-0 Bonds
Compounds containing P-S Bonds
Bonds to Nitrogen
Phosphorus(Ir1) Compounds
Phosphorus(v) Compounds
Pseudohalides
Compounds containing P-N-P
Bonds
Compounds containing P,N, Rings
Phosphonitriles (Phosphazenes)

Heteroatom Ring Systems
Bonds to Oxygen
Lower Oxidation States
Phosphorus(v) Compounds
Heteropolyacids
Monophosphates
Apatites
Diphosphates
Meta- and Poly-phosphates
Bonds to Sulphur or Selenium

470
472
472
475
479
480
480
482
485
489
493
493
493
495
501
501
503
504
512

5 14
514
516
518
519
522
523
524
528

3 Arsenic
Element and Arsenides
Bonds to Carbon
Arsenic(Ii1) Compounds
Arsenic(v) Compounds
Bonds to Halogen
Bonds to Nitrogen
Bonds to Oxygen
Bonds to Sulphur or Selenium

532
532
533
533
535
537
538
539
542


Antimony
General
Bonds to Halogen
Antimony(1Ir) Compounds
Antimony(v) Compounds
Bonds to Oxygen
Bonds to Sulphur or Selenium

545
545
546
546
549
552
554

4


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xi

Contents
5 Bismuth

General
Bonds to Halogens
Bonds to Oxygen
Bonds to Sulphur or Selenium


Chapter 6 Elements of Group VI

555
555
556
557
558
560

By M . G. Barker

1 Oxygen
The Element
Ozone
Ion Species
Oxygen Fluorides
Water

560
560
562
565
567
568

2 Sulphur
The Element
Sulphides
Sulphides of Group I, 11, and I11 Metals
Group IV Metal Sulphides

Group V Metal Sulphides
Other Metal Sulphides
Ternary Sulphide Phase Systems
Ternary Sulphide Compounds
Polysulphide Ions
Hydrogen Sulphide
Sulphur-Halogen Compounds
Sulphur-Oxygen-Halogen Compounds
Sulphur-Nitrogen Compounds
Linear Compounds
Ring Compounds
Sulphur-Nitrogen-Phosphorus Compounds
Sulphur-Boron Ring Compounds
Sulphur-Oxygen Compounds
Sulphur Dioxide
Sulphur Trioxide
Sulphates
Alkali-metal Sulphates
Alkaline-earth-metal Sulphates
0ther Metal Sulphates
Spectra and Pha'se Diagrams of Sulphate Systems
Fluorosulphates
Sulphites

572
572
575
516
578
580

584
584
585
588
589
591
593
596
596
599
604
605
605
606
608
608
610
61 1
612
612
61 3
614


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Contents

xii
Sulphuric Acid and Related Systems
Other Sulphur-containing Compounds

3 Selenium
The Element
The Oxides of Selenium
Selenium-Halogen Compounds
Selenides
Group PI1 Element Selenides
Group IV Element Selenides
Group V Element-Selenium Compounds
Selenates
Selenites
Other Compounds of Selenium

4 Tellurium
The Element
Tellurium-Oxygen Compounds
Tellurium-Halogen Compounds
Compounds with a Te-§ Bond
Tellurides

5 Polonium

Chapter 7 The Halogens and Hydrogen

616
617
619
619
620
62 1
624

624
625
627
628
631
633
635
635
636
639
644
648

649

650

By M . F. A. Dove

1 Halogens
Elements
Halides
Interhalogens and Related Compounds
Oxide Halides
Compounds with Oxygen
Hydrogen Halides

2 Hydrogen
Protonic Acid Media
Hydrogen-bonding

Miscellaneous

650

650
656
657
663
664
669
672
672
673
675


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Contents

xiii

Chapter 8 The Noble Gases
By M. F. A. Dove

676

1 The Elements

676


2 Argon, Krypton, and Xenon@)

676

3 Xenon(1v)

678

4 Xenon(v1)

679

5 Xenon(vIr1)

683

Author Index

684


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1

Elements of Group I
~~~~


BY R. J. PULHAM

1 Introduction

In this chapter individual references which are inter-related are grouped
together to make a section and, therefore, reference to several alkali metals
may feature in a single section. Each reference, however, appears once only
within this chapter so that, if described in one section, it will not be duplicated
in any other. Single references to topics are presented systematically in the
section on the appropriate metal.
The elements of Groups I and I1 are so closely linked in some instances
that a section describing them jointly is presented to avoid duplication in
Chapter 2. Such a case is the section on ‘Molten Salts’, which covers the
chemistry of the molten salts of both Groups I and I1 but is presented only
in this chapter.
2 The Alkali Metals
The hyperfine structure of the 1 sn 3P terms of singly ionized lithium -6,
-7 (Li 11) has been investigated by the beam-foil technique. Zero-field
quantum beats were observed in the intensity decays of transitions from the
1 sn 3P terms (n = 2, 3, or 4) in 6*7LiI1 and the magnetic hyperfine coupling
constant was determined for each isotope for the 2p 3P terms. Preliminary
values for the coupling constants are A (1s2p 3P,6Li11) = 0.091 f 0.001 cm-l
(2.73 GHz), A(ls,2p 3P, Li 11) = 0.239 f 0.002 cm-l (7.17 GHz). The
measured fine structures agree within a few percent with recent ca1culations.l
The Auger electron spectrum of freshly filed lithium contains an emission
peak at 51.7 eV which is attributed to the KL,L, Auger transition, and unidentified peaks at 27.5 and 8 eV. On exposure to oxygen the peaks at 51.7
and 27.5 eV disappeared but the 8 eV peak intensified. The low-energy
spectrum was characterized by emissions at 13.3, 24.0, 33.0, and 40.0 eV due
to Auger transitions of lithium, oxygen, and lithium monoxide.2 A value of

3.05 eV is reported for the work function of freshly prepared lithium films.3
a

H. G . Berry, J. L. Subtil, E. H. Pinnington, H. J. Andrae, W. Wittmann, and A.
Gaupp, P h p . Rev. (A), 1973,7, 1609.
R. E. Clausing, D. S. Easton, and G . L. Powell, Surface Sci., 1973, 36, 377.
J. Boesenberg, Phys. Letters (A), 1972, 41, 185.

1


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2

Inor,oanic Chemistry of the Main-group Elements

Lithium, the ‘not so rare metal’, is reviewed. The discussion covers the
. ~ metal
occurrence, production, and LISGS of the irietal and its c o m p o ~ n d sThe
has considerable potential in the future generation of electrical energy from
the fusion reaction:
?H

+ :H

---f

:He

+ 17.6 MeV


The supply of tritium for this process is derived from:

Within this context, the chemical, physical, and thermal properties of
lithium that are related to its use in fusion reactors have been reviewed.
These include natural abundance, thermodynamic and transport properties,
characterization, analysis purity control, and corrosion of materials by the
molten liquid5 Problems associated with tritium in the metal are also covered,,
as is the separation of tritium from lithium by crystallization or diffusion.’
The pressures of hydrogen isotopes in equilibrium with their solutions in
liquid lithium have been measured. The square root of the hydrogen pressure
is proportional to the hydrogen concentration in accordance with Sievert’s
Law. Graphical data are presented for 2H.8The metal is also chemically very
reactive. The effect of temperature and pressure on the reaction of static
molten lithium with oxygen, nitrogen, and the compounds CCl,F,, C,F,,
and SF, has been studied, The metal is hsated inductively under vacuum and a
small known volume of gas exposed to the surface. Pressure and temperature
changes are followed by rapid-response instr~mentation.~
The liquid metal
is a versatile solvent for both non-metals and metals. Non-metals when
dissolved in the metal may not have the same deleterious corrosive effect on
containment materials as they do with sodium. Chemical processes are
affected by the different thermodynamic stability of lithium compounds. This
is illustrated by the effect of oxygen on the chemical corrosion of niobium
and tantalum by static liquid lithium at 600 “C in capsules. An increase in
the oxygen concentration of lithium from 100 to 2000 p.p.m. has no measurable effect, a result which is contrary to the effect of similar oxygen concentrations in liquid sodium or potassium. The free energy of formation of
lithium oxide is so great that the liquid metal getters niobium and tantalum to
an oxygen level 120p.p.m. regardless of the oxygen concentration in the
lithium. When the transition metals contain more than a threshold level of
oxygen (400 and 100 p.p.m. for Nb and Ta respectively), chemical attack by

lithium occurs at the grain boundaries with the formation of ternary compounds containing lithium, oxygen, and transition metal.1° Methods of
R. Feather, Philippine Geogr. J., 1973, 17, 16.
V. A. Maroni, E. J. Cairns, and F. A. Cafasso, ANL-8001 Rept. 1973.
R. G. Hickman, UCRL-74057 Rept., 1972.
H. Weichselgartner, Reaktortagung, 1972, 751.
* D. H. J. Goodall and G. M. McCracken, Proc. Symp. Fusion Technol., 7 t h , 1972, p. 151.
T. E. Little, U. S. Nat. Tech. Inform. Serv. AD Rept, 1972, No. 759378.
lo R. L. Klueh, ORNL-TM-4069 Rept., 1973.
ti


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Elements of Group I

3

analysing the liquid are obviously important. Photon activation appears
applicable for the analysis of nitrogen and oxygen. These elements are determined by photon activation with a microtron as a pray source. The 13Nis
separated by distillation as ammonia and collected in sulphuric acid for
activity measurements. Oxygen is rapidly separated by distillation as water
wt % for each element.11*12
for coincidence counting. Sensitivity is 2 x
In addition to its role in the fusion reactor, liquid lithium features prominently in solid-state batteries,13an area which has been reviewed.14 Lithium and
another element are usually separated by a solid or liquid electrolyte permeable to lithium ions, which migrate to form a compound with anions of the
second element, thus driving electrons through the external circuit. The
second element has been halogen, though this may be replaced by a compound,
e.g. vanadium pent0~ide.l~
Present interest is in the chalcogens, and several
lithium-chalcogen systems have been investigated with this use in mind.
Equilibrium phases in the Li-S system on the sulphur side of Li2S (the only

compound observed) are determined by using an unusual vapour-transport
technique. By this means equilibrium compositions of the melts at various
temperatures can be obtained by utilizing the transport of sulphur vapour
from one melt to another. The Li-S phase diagram exhibits a large miscibility
gap which extends from the monotectic composition, 65.5 mol % S , to
almost pure sulphur (0.035 mol % Li) at the monotectic temperature 362 f
3 "C. The m.p. of Li2S is 1365 f 10 "C.16This is largely corroborated by a
second study which gives the miscibility gap from 63 to 98.8 mol % S, the
monotectic at 364.8 'C, the m.p. of Li2Sas 1372 "C,and a critical temperature
for the miscibility gap of >600 "C?' An e.m.f. method using cells of the type
LilLi halide eutectic mixturelLi in selenium is used to determine thermodynamic quantities in the lithium-selenium system. From the cell data the
standard free energy of formation of Li,Se at 360 "C is calculated as -94.0
kcal mol-l.ls In the Li-Te phase diagram, eutectics occur at 179.9 "C near
the lithium axis at >99.0 atom % Li, 448.5 "C at 35.7 atom % Li, and 423.1
"C at 10.5 atom % Li. Two intermediate compounds are present, Li,Te and
LiTe,, melting at 1204.5 and 459.9 "C, respe~tive1y.l~
The spectrum of doubly ionized sodium I11 has been studied at 25001300 A and the analysis has been revised and extended as regards the 2p44s,
B. A. Chapyzhnikov, Kh. N. Evzhanov, E. D. Malikova, L. L. Kunin, and V. N.
Samosyuk, Radiochem. Radioanalyt. Letters, 1972, 11, 269.
la B. A. Chapyzhnikov, Kh. N. Evzhanov, E. D. Malikova, L. L. Kunin, and V. N.
Samosyuk, Radiochem. Radioanalyt. Letters, 1972, 11, 275.
l3 M. Eisenberg, Intersoc. Energy Convers. Eng. Conf., Con$ Proc. 7th, 1972, 75.
lo B. Scrosati, J. Appl. Electrochem., 1972,2,231.
A. N. Dey, Ger. Offen. 2 155 890 (C1. H O h ) , 17 May 1973.
l6 R. A. Sharma, J. Electrochem. Soc., 1972, 119, 1439.
l7 P. T. Cunningham, S. A. Johnson, and E. J. Cairns, J . Electrochem. SOC.,1972,119,
1448.
I* E. J. Cairns, G. H. Kucera, and P. T. Cunningham, J. Electrochem. SOC.,1973,120,
595.
P. T. Cunningham, S. A. Johnson, and E. J. Cairns, J. Electrochem. SOC.,

1973, 120,
328.
l1

2


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4

Inorganic Chemistry of the Main-group Elements

3p, and 3d configurations. The number of classified lines is now 177, out of
which 110 are newly observed and Classified. Some of the older classifications
are altered and ca. 80 lines rejected as spurious. The following terms and
levels are new: (T)4s4P, 2P; (1D)4S2&,2; (lS)4s2S, (10)3p2F, 20,2P;
(lS)3p2P;(3P)3d4F;(3P)3d4P,4F5/2;and (1D)2G, 2F, 2D3/2.The 2p43s, 3p, 3d4s
configurations are now complete.20In the range 380-18OA about 90 lines
are measured, of which 50 are reported for the first time.21The third, fourth,
and fifth (i.e. Na IV, Na V, and Na VI) spark spectra of sodium have been
re-photographed at 80-2400 A and the ineasurements confirm earlier
analyses.22New lines in Na IV, Na V, and Na VI are observed for the
first time and ~ l a s s i f i e dThe
. ~ ~ K X-ray spectra of sodium excited by protons,
helium, and oxygen ions of 0.8, 3.2, and 30 MeV, respectively, have been
measured. The strongest lines are the normal K, satellite spectra produced by
multiple electron vacancies in single ion-atom collisions. In the H- and Heion-induced spectra, Ka1,2is the strongest transition.24On the absorption side,
the spectrum of atomic sodium between 30 and 150 eV shows lines which can
be attributed to the excitation of a 2s or 2p electron. Considerably broad and
asymmetric absorptions above the lP1series limit are due to the simultaneous

excitation of a 2p and 3s electron.25
The electrical conductivity of sodium vapour has been measured in a
coaxial-cylinder, two-electrode system at 827-1 227 "C.The results support
the conductivities calculated by E. J. Robbins et al. (1967, 1968) on the basis
of a model for the vapour consisting of Na,, Na,, and Na, moieties.26The
concentration of multi-atom associates in saturated vapours at various
temperatures can be semi-empirically derived. In the case of unsaturated
vapours, the number of associates tends to zero with increasing size. The
symmetry of the associates, binding energies, and mobility for sodium and
potassium are given. The effect of temperature is calculated on the equilibrium between the concentration of free sodium atoms and those combined
in the cluster. Agreement with experimental data is sati~factory.~'
The best
available thermodynamic data on liquid metals are tabulated and include
m.p., entropies of fusion, heats of fusion, and heat capacities. Graphical
correlations are presented between heats of fusion and melting points, and
between entropies of fusion and structural parameters. Heat-capacity
anomalies are discussed in terms of the electron configuration of the metal.2a
The surface tensions of molten alkali metals from their melting temperatures

22

23
24
25
26

27

28


L. Minnhagen and H. Nietsche, Physica Scripta, 1972, 5 , 237.
T. Lundstrom and L. Minnhagen, Physica Scripta, 1972, 5 , 243.
T. Goto, M. S. Gautam, and Y. N. Joshi, Physica, 1973, 66, 70.
T. Goto, M. S. Gautam, and Y. N. Joshi, Canad. J . Phys., 1973, 51, 1244.
C. F. Moore, D. K. Olsen, B. Hodge, and P. Richard, Z.Physik, 1972, 257, 288.
H. W. Wolff, K. Radler, B. Sonntag, and R. Haensel, Z. Physik, 1972, 257, 353.
R. Morrow and J. D. Craggs, J . Pliys. (D),
1973, 6, 1274.
V. G. Klyuchnikov and L. A. Borovinskii, Sbornik. Issled. Striikt. Mol. Krist. Krist.,
Zarodyshei, 1971, 57.
J. L. Margrave, CoIlog. Int. Cent. Nat. Rech. Sci.,1972, No. 205, p. 71.


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5

Elements of Group I

up to 1127 "C have been determined in a special high-temperature, highpressure apparatus. The surface tensions/dyn cm-l as a function of temperature (t/"C) under an atmosphere of their own vapours are given by:
7Na =

193.6 - 0.094(t - 98)

107.1 - 0.069(t - 64)
= 85.7 - 0.053(t - 38)

YI; =

YRb


yCs = 68.8

- 0.045(t

- 28)

The values correlate well with those previously p u b l i ~ h e d . ~ ~
As with lithium, the majority of the literature on the commercial uses of
metallic sodium is devoted to aspects of the generation of electrical energy
either where the metal is used as a coolant in fast nuclear reactors or used as
an electrode in high-power batteries. An indication of the extent of the
nuclear use of liquid sodium is provided in a review of the principal programmes involving fast reactors in the
Technological aspects are also
repre~ented?l-~*These applications steadily reveal new chemical properties
of sodium and its compounds, This is illustrated in the proceedings of a
conference on the Liquid Alkali Metals which covers fundamental chemistry,
physics, analytical and instrumentation techniques, sodium-water reactions,
carbon and fission-product behaviour in sodium, physical processes, corrosion, and mass transfer.35Also, chemical reactions in liquid alkali metals are
discussed, with particular emphasis on solvation aspects. A comparison is
made of the nature and properties of liquid metals, representing continuous
reaction media, with other non-aqueous solvents, e g . molecular liquids,
representing discontinuous media.36Chemical aspects are generally found in
the purification, analysis, and corrosion areas. The non-metals oxygen ,
hydrogen, nitrogen, and carbon, when dissolved in the liquid metal, have a
deleterious effect on transition metals, which are invariably employed as
containment rnaterial~.~'Purification and analytical techniques, therefore,
are primarily designed to remove38and m o n i t ~ r ~these
~ * *elements,
~
in many

cases in sit^.^^ To prevent nitriding and embrittlement of steel submerged in
liquid sodium, ca. 1 atom % calcium or magnesium can be added to the
29

30
31

32
33
34

35

36

37
38
39
40

A. N. Solov'ev and A. A. Kiriyanenko, Fiz. Khim. Poverkh. Yavlenii Vys. Temp.
1971, 108.
M. Grenon, Rev. Fr. Energ., 1972, 23, 577.
F. Chaminade, FRNC-CONF-38 Rept. 1972.
Sodium Technology, 1948-1961 [TID-3334 (Pt. l)]. 1972.
D. W. Shannon and W. R. Wykoff, Nuclear Engineering Internat., 1972, 17, 627.
M. E. Durham, RD/B/M-2479 Rept. 1972.
Proceedings of the International Conference of the BNES, London, on Liquid Alkali
Metals at Nottingham University 4-6 April, 1973.
C . C. Addison, Sci. Progr. (London), 1972, 60, 385.

K. Furukawa, Genshiryoku Kogyo, 1973, 19, 22.
W. Staubwasser, Ger. P. 1 583 891 (CI. C 22b), 28 Jun 1973.
K. L. Schillings, Reaktortagung, 1972,449.
L. F. Lust, F. A. Scott, and J. F. Jarosch, HEDL-TME-71-17 Rept. 1971.


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Inorganic Chemistry of the Maimgroup Elements

6

liquid. These metals, with their strong chemical affinity for nitrogen, effectively isolate the steel from nitrogenjl To analyse for hydrogen in liquid
sodium, a nickel thimble is immersed in the liquid and evacuated to
Torr on the inside. The process relies on the equilibrium between
dissolved and gaseous H. Hydrogen leaves the liquid, diffuses through the
nickel, and establishes an equilibrium pressure, the magnitude of which is
dependent on its concentration in the liquid. As little as 0.02 f 0.01 p.p.m.
of hydrogen can be detected.42Hydrogen may exist in a sample of sodium in
several forms, i.e. dissolved sodium hydride, solid sodium hydride, or sodium
hydroxide. To distinguish between these requires several processes. All the
hydrogen is released as gas by vacuum fusion in a bath of tin at 35OoC.
Amalgamation of the sample, however, releases only dissolved hydrogen.
Subsequent heating to 200 "C decomposes solid sodium hydride. The remaining hydroxide hydrogen may be determined by difference.43Alternatively, the
remaining sodium amalgam is heated in an argon stream at 400 "C. Under
these conditions sodium reacts with sodium hydroxide to give hydrogen,
NaH, and Na,O. Hydride decomposes to give hydrogen, which is determined
by gas ~hromatography?~
Hydrogen is also soluble in liquid potassium. Over
the temperature range 3 4 0 4 4 0 O C , the solubility is given by the equation:
log(C/p.p.m. by wt.) = 6.8 - 2930/(T/K)

The pressure of hydrogen in equilibrium with the saturated solution of
hydrogen in the metal is given by:
log(P/Torr) = 11.3 - 5860/(T/K)
These pressures are the dissociation pressures of potassium hydride according
to:
KH = K

+ *H,

The enthalpy of formation, AH', of potassium hydride as derived from these
pressures is -13.7 kcal mol-l. The equilibrium pressures of hydrogen above
unsaturated solutions of the gas in the metal are given by:

P112 = C x 104/14.2
where C is in weight %. Thus Sieverts' Law is obeyed (I'll2 z C), which
indicates that the species of hydrogen in the metal is m~natomic.*~
Most interest has centred on solutions of oxygen in liquid sodium since
this element, more than any other, renders the liquid metal corrosive.
41

43
44
45

A. K. Fischer, U.S.P. 3 745 068 (CI. 176-38, B O l j , G21c), 10 Jul 1973.
D. R. Vissers, J. T. Holmes, and P. A. Nelson, U.S. P. 3 731 523 (Cl. 73/19; G Oln),
8 May 1973.
Kh. Evzhanov, E. D. Malikova, and L. L. Kunin, Z h r . nnalit. Khim., 1973, 28, 235.
M. Takahashi, J. Nuclear Sci. Technol., 1973, 10, 54.
M. N. Arnol'dov, M. N. Ivanovskii,V. A. Morozov, S. S. Pletenets, and V. V. Sitnikov,

Izvest. Akad. Nauk. S.S.S.R., Metal., 1973, 74.


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Elements of Group I

7

Vanadium, niobium, and tantalum, and their alloys, have a low intrinsic
soIubility in liquid sodium and suffer but slight corrosion. The presence of
oxygen in the liquid, however, leads to penetration by non-metals into the
transition metal, internal oxidation, oxide scale formation, spallation or
dissolution of oxides, and, in some cases, penetration by the sodium.4G
Whether the transition-metal surface oxidizes or whether sodium extracts the
oxygen contained in or on the metal depends largely on the relative free
energies of formation of the transition-metal oxide and sodium oxide,
respectively. The situation is more complicated, however, since the energy
balance is affected by the activity (or concentration) of oxygen in the sodium
or in the solid metal, i.e. a dilute solution of oxygen in liquid sodium may be
reducing whereas a more concentrated solution will oxidize a particular
transition-metal surface. Further complications arise when ternary compounds form which are stable in sodium. Most transition metals form at least
one ternary oxide with sodium. These points are illustrated below. Vanadium,
exposed at 600 OC to static sodium solutions containing oxygen up to 4000
p.p.m. , getters all oxygen from solutions which contain less than 2000 p.p.m.
The distribution coefficient for oxygen between vanadium and sodium is
greater than lo4 at 600°C. By alloying chromium or molybdenum with
vanadium, the activity coefficient of oxygen in the solid alloy is increased
and hence the solubility is reduced.47 In sodium containing 2000 p.p.m.
oxygen at 600 O C , alloys of vanadium containing titanium or zirconium form
internal precipitates of oxide during the gettering, and the concentration of

oxygen dissolved in the alloy approaches that of the same alloy without
titanium or zirconium.48 When titanium and zirconium are immersed in
liquid sodium containing dissolved sodium oxide at 600 "C, the surfaces are
covered with the ternary oxides Na,Ti04 and Na,ZrO,, respectively. These
compounds were identified in situ by their X-ray diffraction patterns. The
compound Na4Ti04 was detected when the sodium contained from 100 to
12 000 p.p.m. oxygen. At the end of long contact times the oxide Ti0 formed
below the ternary oxide, which suggests that the ternary oxide is formed
first and is followed by diffusion of oxygen into the substrate metal to form
TiO. With zirconium, a rapid formation of the oxide ZrO, is postulated which
is followed by a slow reaction with dissolved sodium monoxide to give Na,Q,
Zr0,.49 Liquid potassium, like sodium, also becomes more corrosive towards
transition metals when it contains dissolved oxygen. Analysis of potassium
after immersion of tantalum at 600, 800, and 1000 "C shows that the amount
of tantalum finding its way into the alkali metal increases with the amount of
oxygen originally dissolved in the liquid metal. Again, a ternary oxide phase
is formed. Oxygen held in the tantalum also promotes corrosion when the
transition metal contains more than a threshold concentration of oxygen in
46
47
48
49

H. U. Borgstedt and G. Frees, Rev. Coatings Corrosion, 1972, 1, 43.
R. L. Klueh and J. H. DeVan, J. Less-Common Metals, 1973,30,9.
R. L. Klueh and J. H. DeVan, J. Less-Common Metals, 1973,30, 25.
M. G. Barker and D. J. Wood, J.C.S. Dalton, 1972,2451.


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8

Inorganic Chemistry of the Main-group Elements

solid solution; potassium penetrates the solid metal intergranularly and transgranularly via ternary oxide formation. The threshold levels of oxygen for
this type of attack at 400, 800, and 1000°C are 500, 700, and lOOOp.p.m.,
respe~tively.~~
Distribution of radioactive corrosion products is obviously
important in flowing sodium. Particulate material deposits according to flow
rate and geometry of circuit, size of particulate, and whether the species is
soluble in the sodium or reacts preferentially with metallic parts of the circuit.
Initial experiments have investigated the transport and deposition characteristics of 59Fe,54Mn,and 6oCo. The 59Febehaviour is characterized by its
appearance as a firmly adherent layer on pipework downstream of the test
section. 6oCois similar to iron but the deposit is less strongly attached. The
behaviour of 54Mn is characterized by its rapid and highly preferential
migration to the coldest part of the circuit.51 Adsorption of caesium, a
product of the fission process, also occurs from solution in sodium at transition-metal surfaces. Between 100 and 200°C, caesium is adsorbed on to
nickel and steel (EN-58B) surfaces but at 800 O C the adsorption is eliminated
The mechanism of adsorption is not clear.52
Determinations of the solubility of oxygen in liquid sodium are numerous
and the values vary. From 169 individual analyses, data have been selected,
therefore, to derive the mean solubility relationship:
log(S/p.p.m.) = 6.1587

- 2386.4/(T/K)

from T = 387 to 828 K, using the least-squares method. This equation is
recommended for fast-reactor
Methods of determining these small
concentrations differ widely. Thus at 350-530 O C , the solubility is ca.

10-850 p.p.m. as determined by an e.m.f. method using the cell:
where the rare-earth oxides comprise the solid electrolyte which separates
the reference electrode Cu,OICu(or air]Au) from the second electrode, a
mixture of sodium with sodium monoxide.54Alternatively, a vanadium wire
is immersed in the molten sodium to allow oxygen to partition between the
two metals. The wire is subsequently removed and analysed for oxygen
content. The method relies on a knowledge of the equilibrium distribution
coefficient of oxygen between sodium and vanadium. These values (as
W.
oxygen in V) are given at 750 OC over the range 0.003-16 p.p.m.
oxygen in sodium.55
Carbon dissolves in liquid sodium but to a lesser extent than do hydrogen
or oxygen, and methods for determining the carbon content of liquid sodium
continuously are generally less advanced than those for oxygen and hydrogen.
50
61
52

53
54

55

R. L. Klueh, Corrosion (Houstom), 1972, 28, 360.
K. T. Claxton and J. G. Collier, J. Brit. Nuclear Energy SOC.,1973, 12, 63.
H. E. Evans and W. R. Watson, RD/B/N-2094 Rept. 1971.
J. D. Noden, J . Brit. Nuclear Energy SOC.,1973, 12, 57.
H. U. Borgstedt, A. Marin, Z . Peric, and G. Wittig, Atomwirt, Atomtech., 1972, 17,
361.
D. L. Smith and R. H. Lee, ANL-7891 Rept. 1972.



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Elements of Group I

9

A technique, reminiscent of the electrochemical oxygen meter, is described,
however, which equilibrates the carbon dissolved in liquid sodium with a
membrane of a-iron at 500-700 "C. This membrane forms part of an electrochemical cell and is separated from a reference source of carbon by a fused
electrolyte of 1 :1 Li,CO,-Na,CO,, which is able to transfer carbon in ionic
form. The voltage between the membrane and reference electrode gives a
measure of carbon activity in the membrane and hence in the sodium.56
Protection and security measures against accidents with liquid sodium are
reviewed.57 A fire-extinguishing powder that is especially effective against
alkali-metal fires consists of 45.4% NH4H,P04 (fluidized with up to 6 %
of its weight by Si02 and silicone resin), 45.4% urea, 9.1 % polystyrene
micro-balls (d < 300 pm), and 0.1 % azodicarbamide; it completely extinguishes sodium burning at >5OO0C. A thick spongy carbonized coating
covers the metal, whose temperature falls very rapidly.58
~ - ~ ~ liquid sodium
High-temperature (300 "C) storage b a t t e r i e ~ ~involving
utilize the chemical reactions between sodium and liquid sulphur. The
Na-S system is complex, however, and contains several polysulphides with
the general formula M,S, containing S",- ions. Of about 15 polysulphides of
the alkali metals described in the literature, the crystal structures have been
determined for only about three, which reflects the difficulty of preparing single
crystals of the polysulphides. The Na,S-Na,S,-S
region has been investigated
mainly by high-temperature microscopy but some complementary experiments involve d.t.a., t.a., and quenching techniques, The components S and
Na,S melt at 118 f 1 "C and 1168 f 10 'C, respectively. The intermediate

phases Na2S2,Na2S4,and Na,S5 which are formed melt at 478 f 5,294 f 2,
and 270 f 5 "C, respectively. Na,S, melts incongruently. The shapes of
polysulphide crystals appearing just below the melting points are detected
by high-temperature micro~copy.~~
Further d.t.a. work reveals that when
Na,S-Na,S, or Na4S4-S, mixtures are heated, a reaction occurs near the
m.p. of sulphur with formation of Na,S5 as the initial step, Unless the S:Na
ratio is >5:2 then further reaction between the sulphides occurs, until at
equilibrium only those species are observed corresponding to the given Na:S
ratio. The highest sulphide is Na,S,, and Na,S, does not exist at the m.p.;
this stoicheiometry is really a 1 :1 Na,S,-Na,S, eutecticBgThe sodium polysulphides Na,S, and Na2S5,however, can be prepared from the reaction of
56
57

58
59
6o
61

62

63
64
65

M. R. Hobdell and D. M. J. Rowe, RD/B/N-2240 Rept. 1972.
M. De la Torre Cabezas, Energ. Niicl. (Madrid), 1972, 16, 439.
E. Chahvekilian, R. Peteri, and A. Hennequart, Fr. Demande 2 102 424 (Cl. A 6 2 4 ,
12 May 1972.
J. Fally, C. Lasne, and Y. Lazennec, Fr. Demande 2 142 695 (CI. H Olm), 9 Mar 1973.

S. Gratch, J. V. Petrocelli, R. P. Tischer, R. W. Minck, and T. J. Whalen, Zntersac.
Energy Convers. Eng. Con$ Con5 Proc. Ith, 1972, p. 38.
T. Nakabayashi, Ger. Offen. 2 240 278 (CI. H Olm),12 Apr 1973, Japan.
J. Fally and J. Richez, Fr. Demande 2 140 318 (C1. H Olrn), 23 Feb 1973.
C. Levine, Power Sources Symp., Proc., 1972, 25, 75.
S. P. Mitoff, U.S. P. 3 672 994 (CI. 136-6, H Olrn), 27 Jun 1972.
E. Rosen and R. Tegman, Chemica Scripta, 1972,2,221.
D. G. Oei, Znorg. Chem., 1973, 12,435.