THERMODYNAMIC AND STRUCTURAL PROPERTIES OF ZIRCONIUM

118 Pages·04.117 MB·English

by  SKINNER, GORDON BANNATYNE

THERMODYNAMIC AND STRUCTURAL PROPERTIES OF ZIRCONIUM
DISSERTATION
Presented In Partial Fulfillment of the Requirements
for the Degree Doctor of Philosophy in the
Graduate School of The Ohio State
University
By
GORDON BANNATYNE SKINNER, B. Sc., M. Sc.
The Ohio State University
1951
Approved by:
Adviser
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I
TABLE OF CONTENTS
Introduc tion 1
Part I Heat capacity of zirconium from 14° to Koo0s 6
\ i
Introduction ...................... 6
Experimental materials ........... 7
Apparatus ........................ 8
Accuracy of the data ............. 10
Experimental results .............
17
Discussion of results ........... 21
Part II Heat content of zirconium from 300° to 1800°K. 23
Introduction .................... .
23
Experimental materials ........... 32
A p p a r a t u s ........... .............. 35
Accuracy of the d a t a ............. . 43
Cooling data . ......................
45
Experimental results ............. . 53
Calculation of the total emissivity of zirco-
n i u m ............. .............. 60
Discussion of results ............. 62
Part HI Vapor pressure of zirconium from 1951° to
2056°K............................ 63
Introduction ........................
63
-. Experimental materials............. 64
Apparatus . ........................ 66
Methods of calculation . ........... 71
Accuracy of the data ............... 75
Experimental results ................ 77
Discussion of results ............. 82
Part IV Crystal Structure of zirconium from Ko o° to
\
1600 K . . ...................... 85
•
Introduction ........................ 85
Experimental materials ............. 8t
Apparatus ........................... 89
Methods of calculation ............. 97
Accuracy of the data . . . ......... 102
Experimental results ............... 104
Discussion of results ............. 107
Bibliography .................................. 109
Appendix I Standard lamp calibration . . . 112
Acknowledgements ........................... = 114
Autobiography............. .. .............. 115
_
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LIST OF ILLUSTRATIONS.
Figure 1. Heat Capacity of Zirconium, l4°-300°K. . . . 19
Figure 2. Electrical Resistance of Zirconium,
Zwikker ( 26).............................. 24
Figure 3 . Vacuum F u r n a c e ............ 36
Figure 4. Improved Calorimeter (Ziegler) ............. 39
Figure 5* Modified Calorimeter ...................... . 41
Figure 6. Cooling Data for Zirconium Sample ........... 31
Figure 7. Heat Content of Zirconium, 298.16°-1800°K. . 59
Figure 8 . Pyrex Vapor Pressure Apparatus ............. 67
Figure 9- Vapor Pressure of Zirconium ............... 81
Figure 10. High-Temperature Thermal Expansion Apparatus. 94
Figure 11. Thermal Expansion of Zirconium ............. 106
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THERMODYNAMIC AND STRUCTURAL PROPERTIES OP ZIRCONIUM
INTRODUCTION
The existence of zirconium as an element was es­
tablished in 1789 by M. H. Klaproth, who named it after
the zircon type minerals from which he obtained a fairly
pure sample of zirconium oxide. But Klaproth never saw
a sample of pure zirconium or even a reasonable facsim­
ile thereof. Berzelius is generally credited with the
first preparation of zirconium metal, in 182^, but his
sample was quite Impure. Mellor (1) in his ‘Comprehen­
sive Treatise on Inorganic and Theoretical Chemistry*,
briefly described the efforts of some fifty chemists
over a period of a hundred years to prepare pure zirconi­
um. Wide variations in the physical properties of the
various 'zirconium metal1 specimens have been reported.
It was not until about 1925 that A.E. van Arkel
and J. de Boer (2) reported a method which could pro­
duce very pure zirconium metal. The starting material
for this method was zirconium which had been prepared
by one of the other methods, such as the reduction of
ICjZrFg or ZrCl^ with sodium or magnesium, and contained
varying amounts of oxygen, nitrogen and carbon. This
impure zirconium was placed In a pyrex container along
1
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with iodine., and heated to about 400-500°C , The zirco­
nium and iodine reacted to form volatile zirconium tetra-
iodide, and pure zirconium was formed by the decomposi­
tion of the zirconium iodide on a heated wire filament
which was kept at a temperature just below the melting
point of zirconium. The oxygen, nitrogen and carbon re­
mained with the small amount of zirconium which was left
as a residue, and so, for the first time, specimens of
zirconium almost free from these impurities were obtained.
For several years after the development of this method,
specimens of iodide zirconium were made only at the
Philips Lamp Company, at Eindhoven, Holland (by whom
de Boer and van Arkel were employed), and were supplied
to several researchers, mostly in Europe.
However, by this time, another complicating factor
had arisen. In 1923 the Danish chemists Coster and Hevesy
(3) precipitated an Interesting controversy with the
French chemist Urbain and the physicist Dauvillier, by
announcing the existence of hafnium, an element of atomic
number 72, many of whose properties resemble those of
zirconium. This controversy aroused wide interest at the
time, since the discovery of hafnium was not the result
of the usual chemical manipulations, but was made possible
by the application of Bohr's theory of atomic structure
and Moseley's studies of x-ray spectra. During the period
of over a hundred years in which zirconium has been rec­
ognized, the fact that all of the specimens contained one
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to five percent of an entirely different element had
remained quite unnoticed.
When one compares the properties of zirconium and
hafnium it is not hard to see why this was so. The appear­
ance of the metals is very similar., they crystallize in
the same pattern and the inter-atomic distances are very
nearly equal (^). For this reason they form an almost
ideal solid solution (5).
There are corresponding similarities in many of
their compounds, although there are differences sufficient
to permit separation by fractional crystallization, frac­
tional distillation and solvent extraction (6) . Never­
theless the methods which had to be used up to very
recent years were so laborious that only very small a-
mounts of materials were separated. Most of the measure­
ments made on the 'very pure* zirconium produced by the
iodide method were made on zirconium which contained no
appreciable impurity other than hafnium. Fortunately
since hafnium resembles zirconium so closely its pres­
ence does not seem to make a very great difference in
many of the properties of zirconium, while it should be
possible to treat such differences as there are on the
basis of the ideal solution. Of course such an approxi­
mation introduces some uncertainty and room for errors in
judgment, which are not reduced by the fact that many of
the properties of hafnium have not been determined.
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For those of us who are interested in the physical
and thermodynamic properties of zirconium the above-
mentioned difficulties in the preparation of zirconium
have meant that none of the measurements made before
1925 may to© considered to be very useful, since they were
made on substances quite different from pure zirconium.
In view of the fact that it is still very diffi­
cult to obtain specimens of pure zirconium, we have been
fortunate to obtain zirconium of two different types.
The first of these is iodide zirconium containing about
two weight percent hafnium, and prepared by the Philips
Company. The second is a special hafnium-free product,
and apparently prepared by iodide dissociation, which
was obtained from the United States Atomic Energy Commission.
While the latter product contained very little hafnium, It
was found to contain about 0.4 percent iron, which Intro­
duced a slightly complicating factor into the studies.
Nevertheless the experiments described here have deter­
mined the thermodynamic properties of zirconium more com­
pletely and more accurately than they had previously been
determined.
The work that has been done falls naturally into
four parts, each of which Involves a different experi­
mental technique. Consequently, the discussion of the
experiments will be divided into four parts, as follows:
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PART I Heat capacity of zirconium from 14° to 300° K.
PART II Heat content of zirconium -from 300° to 1800° K.
PART III Vapor pressure of zirconium from 1951° to 2056°K.
PART IV Crystal structure of zirconium from 300° to l60CHC.
The values of the physical constants used in cal­
culations are those given by the National Bureau of Stand­
ards (7):
1 calorie = 4.1840 abs. joules
•= 4.1833 int. joules
T0°C. = 273.16 + 0.01°K.
R = 1.98719 + 0.00013 cal. deg.-1 mole--*-
k = (1.38048 + 0.00050) x 10--*-^ erg deg.--*-
c = (2.99776 + 0.00008) x 1010 cm. sec."1
N = (6.02283 + 0.0022) x 1023 mole-1
h = (6.6242 +_ 0.0044) x 10“27 erg sec.
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PART I; HEAT CAPACITY OP ZIRCONIUM FROM 14° TO 300°K.
INTRODUCTION:
Low temperature heat capacity measurements on
zirconium have been made recently by Todd (8) in the
temperature range 53° -297°K., but the purity of his zir­
conium appears to be questionable. Coughlin and King (9)3
who used the same specimen as Todd for high temperature
heat content measurements, stated that, in addition to
2.15 per cent hafnium, it appeared to contain appreciable
amounts of oxygen or nitrogen, or both. The specimen
used for the present measurements, having considerably
higher purity, should yield more reliable values of
the thermal functions of pure zirconium.
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EXPERIMENTAL MATERIALS:
The zirconium used was a special hafnium-free
product obtained from the Oak Ridge National Laboratory.
It was in the form of small pellets sheared from larger
pieces. A careful analysis carried out through the
courtesy of Mr. John Center, chief analyst at the Bat-
telle Memorial Institute, Columbus, Ohio, showed the
presence of 0.025 atom per cent hafnium, O.67 atom per
cent iron, 0.15 atom per cent carbon, 0.026 atom per cent
nitrogen, and a total of 0.082 atom per cent of nineteen
other impurities tested for.
In our data a correction was made for the iron
present. Vogel and Tonn (10) found that several per
cent of iron will dissolve in solid zirconium. In making
the correction it x*as assumed that the solution is ideal,
at least to the extent that the heat capacities are addi­
tive. The heat capacities of iron used were those given
by Duyckaerts (11) up to 20°K. and by Kelley in his
review bulletin (12) at higher temperatures. The maximum
correction was about 0.3 per cent.
No analysis for oxygen could be made on the sample.
However, since the nitrogen content was found to be only
0.026 atom per cent, it could be expected that the oxygen
content would be low also.
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