Tungsten and its Compounds

144 Pages·1967·2.689 MB·English

by  G. D. Rieck (Auth.)

TUNGSTEN
and its compounds
by G. D. RIECK
Doctor of Chemistry, Professor of Physical Chemistry
Technological University of Eindhoven, Netherlands
PERGAMON PRESS
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Copyright © 1967
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First edition 1967
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INTRODUCTION
PURPOSE AND SCOPE OF THIS MONOGRAPH
Extensive literature references for all elements can be found in
large textbooks; these are often more complete than selective and
give more data than discussion and general information. These in-
dispensable books are, however, very expensive and necessarily several
years behind recent developments. The latter is also true of some very
detailed books on tungsten and its manufacture, such as Smithells
(1952), Agte and Vacek (1959), Li and Wang (1955), but their informa-
tion largely relates to the manufacture of lamp-filaments and cathodes.
The purpose of this monograph is to fill the time gap of the last decade
in this field and to add information in many other fields. The purpose
is not to give a complete literature reference list, but to introduce the
reader to modern literature in a wide variety of fields and to give a
large number of recent results in such a way that the book will be as
readable as possible. Literature references are given as they were
available to the author; only exceptionally had abstracts to be used.
For this reason Russian literature is referred to in one of two ways,
namely either to the original Russian journals or to the English trans-
lations (e.g. Zhur. Neorg. Khim. or Russian J. Inorg. Chem.).
Generally more or less internal reports of research contracts which
often appear in the United States are not cited, but wherever possible
reference is made to a publication in a regular journal.
An enormous quantity of literature, especially of the report kind, is
not considered to add new important information. Often only obsolete
data or reports on measurements on not well-defined material are given,
and this is an important deficiency since small amounts of other
elements have an extremely large effect on many properties of tungsten.
For theoretical considerations, e.g. about the electronic structure
of compounds, textbooks on inorganic or physical chemistry should be
consulted, since in them the properties of groups of elements are com-
pared. Especially for those, often complex, compounds which are up to
now only of encyclopaedic interest the reader is referred to textbooks
and standard works such as Gmelin's Handbuch der anorganischen
Chemie, No. 54 (1933), Mellor's Inorganic and Theoretical Chemistry,
Vol. XI (1959), and Pascal's Nouveau Traité de Chimie Minérale,
Vol. XIV (1959).
ix
CHAPTER 1
HISTORY, USE, ORES AND
PRODUCTION
1.1. INTRODUCTION TO THE HISTORY OF TUNGSTEN
The element tungsten (W) with atomic number 74 is one of the
so-called "less-common metals'' and occurs in the periodic system in
group VI with chromium (atomic number 24) and molybdenum
(atomic number 42). In all its properties it closely resembles the latter
element. In the pure metallic state tungsten has a lustre somewhat like
that of steel.
The International Union of Pure and Applied Chemistry in 1957
chose the English name tungsten and the French name tungstène,
with as alternative the German name Wolfram, For the salts they
recommended the name wolframate, but tungstate, which is more com-
mon in English literature, will be used in this book.
According to all textbooks the element, although mentioned already
by Agricola, was discovered as part of a mineral by Cronstedt in 1755
and Scheele (the mineral CaWC>4 is named scheelite after him) in
1781. Its isolation was described first by two Spanish chemists working
in a Swedish laboratory.
The name tungsten comes from the Swedish and means "heavy stone".
The origin of the name wolfram (or wolframite for the mineral (Fe, Mn)
WO4) is less clear; probably it refers to the property of the mineral
to "eat" (wolf) the tin in ores containing both elements (Gmelin, 1933;
Mellor, 1959).
Apart from one patent of Oxland on an iron-tungsten alloy in
1857, in the nineteenth century tungsten and its compounds attracted
the interest only of those chemists who collected knowledge on pro-
perties and compounds of each element without regard to their in-
dustrial or economic importance. But in later years, especially, metallic
tungsten has been used for many technical applications, because it has
the highest melting point of all metals, has good high-temperature
mechanical properties and has good conductivity for heat and electricity.
The change in the picture took place at the beginning of this century
after the discovery of ductile tungsten from which wires could be
made for filaments in incandescent lamps. The high melting point of
1
2 TUNGSTEN AND ITS COMPOUNDS
tungsten made an efficient production of visible light possible, com-
bined with a reasonable strength of the filament. Afterwards electrodes
of tungsten for valves and other discharge tubes were developed. In
this period the interest in tungsten grew enormously and many physical,
chemical and metallurgical properties were studied. The result was
that around 1930 tungsten was one of the best studied of the less-
common metals. Many data on tungsten then known surpassed in
accuracy even those of the more common elements.
The largest consumption of tungsten (about two-thirds of the total),
however, was in the steel industry since it is one of the components of
special tool-steels and of hard-metals (tungsten carbides), which are
used in large quantities. As, however, for use in steels the metal need
not be purified and isolated, not so many contributions to the know-
ledge of tungsten itself and its compounds resulted from this use,
except, of course, on the systems of tungsten with other metals. The
hard-metal industry spent comparatively more effort on research on
tungsten.
After 1930 not much progress was made in the knowledge and the
collection of data on tungsten and its compounds, until in recent years
refractory metals were needed for nozzles of rocket motors and for
protecting shields for space vehicles. This gave rise to another type
of research, namely on the high-temperature mechanical properties of
tungsten and its alloys and to the development of techniques for
manufacturing relatively large parts. The attack by air at high tempera-
ture became important. The rapid oxidation of tungsten had up to then
always been prevented by using vacuum or a protective atmosphere.
These modern applications have given rise to an extensive number of
publications during the last decade. One of the reasons for this might
be that many properties of tungsten, especially the mechanical, are
unusually influenced by small additions or contaminations and by
changes in its microstructure. This, however, makes it often difficult
to compare data and choose the ones representative for a certain type
of tungsten.
1.2. APPLICATIONS OF TUNGSTEN AND ITS COMPOUNDS
As mentioned in the historical survey, the applications of metallic
tungsten are mainly based on its high melting point, high strength
at high temperatures, resistance to wear and good conductivity for
electricity and heat.
Apart from its use as a filament in incandescent lamps, as electrodes
for discharge tubes, and for rocket-motor nozzles and space vehicles,
tungsten is used for electrical contacts, e.g. for interruptors for sparking
coils in internal combustion motors for which purpose all the above-
HISTORY, USE, ORES AND PRODUCTION 3
mentioned properties are important. In the laboratory many high-
temperature applications of tungsten are known, e.g. wires and tubes
for heating elements in furnaces with a protective atmosphere, boats
and strips, and thermocouples for temperatures above 2000°C in non-
oxidizing atmospheres.
Because of its high atomic number and refractory properties tungsten
is used for X-ray cathodes, e.g. in medical rotating-anode X-ray tubes.
In the powder form tungsten may act as a catalyst in hydrogénation
processes. In Table 1.1 these applications in connection with the
properties of tungsten are summarized. Often alloys with a high
tungsten content are used for the same purposes as pure tungsten,
because favourable properties may be obtained by alloying or adding
other elements or compounds. Special steels containing only a small
TABLE 1.1. Applications and properties of "pure" W
Good Good
Application High heat electrical Mechanical Work- Atomic
m.p. conduc- conduc- properties ability no.
tivity tivity
Lamp filaments and
strips, cathodes X X X X X
Anticathodes, X-ray
grids, protection X X X X X
Interruptors and
contacts X X X X X
Nozzles, heat shields X X X X X
Thermo-elements X X X X
Field ion microscope X X X X
Laboratory equipment;
high-temperature
structures X X X X
amount of tungsten and alloys like stellites consume a large part of the
world production of tungsten.
This part is declining, however, in favour of the other compounds of
great technical importance, the very hard carbides, which are used for
high-speed machining tools and mining drills (with about 85-95 per
cent carbide and 5-15 per cent cementing material). Wire-drawing
dies are often made of hard metal, and a war-time application of the
carbide is in the tip of an armour-piercing shell. Calcium tungstate
has found application as fluorescent material in discharge lamps and
more recently for lasers. Tungstates of lead, zinc and sodium are used
in chemical, paint-enamel, and textile industries.
4 TUNGSTEN AND ITS COMPOUNDS
1.3. TUNGSTEN ORES AND THEIR PRODUCTION
Tungsten ores are found all over the world; the most important
minerals are scheelite, CaW04, and wolframite, (Fe, Mn)W04, which
is a mixed crystal of hubnerite, MnWC>4, and ferberite, FeWC>4. The
ores generally contain other minerals, especially those containing tin.
The other, less important, minerals are described in textbooks (e.g.
Li and Wang, 1955); they include other tungstates and tungsten
sulphide. An estimate from 1954 (Nelson, 1960) gives about 175 X 106
short ton units (^157 X 109 kg) of WO3 as the world reserves of
tungsten ore. About three-quarters of this amount occurs in China,
and in the U.S.A., South America, and Korea about 5 per cent each.
In Europe the most important deposits are in Portugal (1 per cent
of world resources). The world output for 1964 is estimated at about
50,000 short tons {Met. Bull. No. 4975, 1965). The U.S.A. con-
sumed about 50 per cent and Europe 40 per cent of the output of
the world excluding Russia. The Russian consumption is assumed to be
rather high. The United Kingdom imported in 1963 5300 tons and in
1964 6200 tons of concentrates. In the latter year 1000 tons came each
from Korea, Russia, and Bolivia, the rest mainly from Australia,
China, Portugal, Burma and the U.S.A.
As supplies, especially of medium-grade concentrates, are plentiful
compared with the world production and demand for tungsten, an
increased production in the so-called Sino-Soviet bloc has, during
1962 and 1963, largely lowered the price of tungsten ore on the world
market and forced many small producers (often in less-developed
countries) to close their mines (Bullock, 1962; compare Met. Bull. Nos.
4659 and 4719, 1962). The price dropped to about 60s. per unit (1 per
cent of WO3 per long ton, or 1080 kg) of ore, whereas it reached 160$.
per unit in 1957. In 1964 prices rose again to about 115s. per unit.
However, prices depend very much on the purity of the ore. Crude
ores which contain only a few per cent of WO3 are concentrated by
physical and chemical methods before metallurgical treatment begins.
Flotation, leaching, and magnetic separation may give, according to
Li (1962), a chemical analysis as in Table 1.2a. Li and Wang (1955) and
Smithells (1952) give other analyses of various ores and concentrates
(Table 1.2b). Good concentrates contain more than 70 per cent
WO3.
As already mentioned in the introduction, the properties of the
metal are unusually affected by small contaminations and therefore
each user of tungsten has his own specifications for purity, and if the
contaminant is difficult to remove (e.g. molybdenum) ores without
this impurity will be in demand for that special purpose, e.g. molyb-
denum-free concentrates are asked for by lamp manufacturers and
tin-free concentrates by steel works.
HISTORY, USE, ORES AND PRODUCTION 5
To meet these various specifications special plants are built (Li, 1962),
but often the factory itself makes the type of tungsten it requires.
TABLE 1.2 a and b. Some chemical analyses of concentrates in weight per cent
WO, MoO, FeO MnO SnOj BiaO, CaO P S As
(a)
Australian scheelite 60 2-2 2-5 — — — (14-6) 0-2 2
Korean scheelite 65 1-25 3-55 — — 1-5 (16) 0-2 2 0-37
Bolivian scheelite 30 — — 0-8 20 — 7 0-25 6 1-5
(b)
Australian scheelite 78-2 — 19-4 01
Spanish wolframite 66-3 — 12-8 9-9 1-2 0-2 01 0-5
Arizonean wolframite 65 — 5-3 19-9 01 2-6
Chinese wolframite 68-3 — 10-3 10-7 1-6 01 0-2 0-3
CHAPTER 2
PROPERTIES OF THE ELEMENT
2.1. THE ATOM
2.1.1. Atomic number and atomic weight
The atomic number of W is 74.
The atomic weight of tungsten (in its natural isotopic composition)
as agreed upon in 1957 by the International Union of Pure and Applied
Chemistryj is 183*86 (on the chemical scale, O = 16). The atomic
weights (on the physical scale) of the stable isotopes are, according to
Demikhanov et al. (1961):
W180 180-003698
\yi82 182006093
\\ri83 183-008429
\\/Ί84 184-009234
\yi86 186-013788.
2.1.2. Isotopes
Tungsten isotopes are reported to occur in nature from W180 to
W186 and to be made artificially from W1™ to W188. Their half-life,
type of decay, abundance, and the maximum artificial enrichment
obtained are given in Table 2.1 (according to Strominger et al. (1958)
and summarized in Ajzenberg-Selive (I960)).
2.1.3. Electronic structure
The neutral atom contains seventy-four electrons. Their distribution
over the shells and orbits in the ground state and their quantum num-
bers are given in Table 2.2.
2.1.4. Optical emission spectrum
The emission spectrum of W in the wavelength range of 2000-
8000 Â contains more than 4300 lines (Harrison, 1939; Moore, 1958;
Zaidel et al. 1955). In spectrochemical practice a number of "analy-
9
tical" lines are used; their wavelengths and the corresponding upper and
lower energy levels are given in Table 2.3. The lines are listed starting
with those used for low tungsten concentrations and followed by
f Report of the Commission on Atomic Weights, 19th Conf. I.U.P.A.C,
J. Chem. Soc. (1957), 5101; J. Amer. Chem. Soc. (1958), 80, 4121.
6
PROPERTIES OF THE ELEMENT 7
those used with increasing tungsten content in the sample. All lines
apply to the first ionization of tungsten. The first ionization potential is
7-6-8-1 eV.
TABLE 2.1. Isotopes of tungsten
Mass Half-life Type of Abundance Maximum Additional
number decay (%) enrichment reference
176 80' EC
177 130' EC
178 21-5 days EC
179 30' EC
179 5-2'
180 stable 0135 6-95
181 145 days EC
182 stable 26-4 94-2
183 5-5' IT Poë (1955)
183 stable 14-4 86-2
184 stable 30-6 95-7
185 1-62' IT Poë (1955)
185 73-2 days ß' Thiry (1957)
186 stable 28-4 97-9
187 24-1 hr ß-
188 69-5 days ß-
EC = orbital electron capture. IT = isomeric transition.
ß- = negative particle emission.
The nuclear spin has for the isotopes the value of: J for W183, 0 for W184,
for W185 and 0 for W186 (Frisch, 1958).
2.1.5. X-ray emission spectrum
In the tables of Cauchois and Hulubei (1947) the exact wavelengths
(in kX units) of 9 K- and 35 L-emission lines of tungsten are listed.
The wavelengths of the strongest lines (International Tables for X-Ray
Crystallography, 1962) are given below, expressed in  ( = kX units
X 1-00202):
K-series
K a ai ft ft
2
λ(Α)= 0-213813 0-208992 0-184363
0-17950
L-series
L a2 ai ft β2
λ(Α)= 1-148742 1-47635 1-28176 1-22458
B