36
Journal of The American Ceramic Society�Nassau and Shiever
6
Paul Schwarzkopf and Richard Kieffer in collaboration with
Werner Leszynski and Fritz Benesovsky, Refractory Hard
Metals. The Macmillan Company, New York, 1953.
7 E. G. Kendall, J. I. Slaughter, and W. C. Riley, "A New
Class of Hypereutectic Carbide Composites," Tech. Rept.
TDR--469-(5250)-11 (1965).
8 J. C. Logan and R. Niesse, "Process and Design Data on a
Boride-Silicide Composition Resistant to Oxidation to 2000 °C,"
Tech. Rept. ASD-TDR-II62-1005 (1962).
9
Paul Schwarzkopf and Richard Kieffer in collaboration with
Werner Leszynski and Fritz Benesovsky, Cemented Carbides.
The Macmillan Company, New York, 1960.
10 E. V. Clougherty, R. L. Pober, and Larry Kaufman; pp.
321-29 in Modern Developments in Powder Metallurgy, Vol. 2.
Edited by H. H. Hausner. Plenum Press, New York, 1966.
11 W. H. Rhodes, D.
J. Sellers, Thomas Vasilos, A.H. Heuer,
Robert Duff, and P. Burnett, "Microstructure Studies of Poly­
crystalline Refractory Oxides," Summary Report, NOw-65-0316-f (1966).
12 A. A. Griffith, "Phenomenon of Rupture and Flow in Solids,"
Phil. Trans. Roy. Soc. (London), 221A [4] 163-98 (1920).
13 E. Orowan; p. 139 in Fatigue and Fracture of Metals.
Edited by W. M. Murray. John Wiley & Sons, Inc., New York,
1952.
14 N. M. Parikh, "Studies of the Brittle Behavior of Ceramic
Materials," Tech. Rept. ASD-TDR-61-628, Part III; Contract
AF 33(657)-10697; 403 pp., June 1964.
16 F. W. Vahldiek, S. A. Mersol, and C. T. Lynch, "Room­
Temperature Slip in Titanium Diboride Produced by High
Vol. 52, No. I
Pressure," Science, 149 [3685] 747--48 (1965).
16 T. L. Johnston;
pp. 63-78 in Mechanical Behavior of
Crystalline Solids. Natl. Bur. Std. ( U.S.) Monograph No. 59.
113 pp. (1963).
17 R. J. Stokes and C. H. Li, "Dislocations and the Tensile·
Strength of Magnesium Oxide," J. Am. Ceram. Soc., 46 [9)
423-34 (1963).
18 G. G. Bentle and R. M. Kniefel, "Brittle and Plastic Be­
havior of Hot-Pressed BeO," ibid., 48 [11] 570-77 (1965).
19 J. J. Gilman;
pp. 240-74 in Physics and Chemistry of
Ceramics. Edited by Cyrus Klingsberg. Gordon and Breach
Science Publishers, Inc., New York, 1963.
20 F. F. Large, ''Intrinsic Brittle Strength of Magnesia in
Bicrystals," in Anisotropy and Strength of Ceramic Bodies, TR
No. 2, Contract No. NONR-6561 (27), 1966.
21 J. P. Berry, "Some Kinetic Considerations of the Griffith
Criterion for Fracture: I," J. Mech. Phys. Solids, 8 [3). 194--206
(1960).
22 H. Schardin; pp. 297---,330 in Fracture.
Edited by B. L. Aver­
bach, D. K. Felbeck, G. T. Hahn, and D. A. Thomas. Tech­
nology Press, Massachusetts Institute of Technology and John
Wiley & Sons, Inc., New York, 1959.
23 E. M. Baroody, E. M. Simons, and W. H. Duckworth, "Effect
of Shape on Thermal Fracture," J. Am. Ceram. Soc., 38 [l]
38--43 (1955).
24J.F.Lynch,C.G.Ruderer,andW.H.Duckworth,"Engineering
Properties of Ceramics," Tech. Rept. AFML--TR-66-52 (1966).
26 Bernard Schwartz, "Thermal Stress Failure of Pure Re­
fractory Oxides," J. Am. Ceram. Soc., 35 [12] 325---,33 (1952).
Cupric Oxide-Molybdenum Oxide Phase Diagram
in Air and in Oxygen
K. NASSAU and
J.
W. SHIEVER
Bdl Tdephone Laboratories, Incorporated, Murray Hill, New Jersey 07974
Phase diagrams of the CuO-MoOa system were deter­
mined in oxygen, in air, and under oxygen pressure. The
first two diagrams are quite similar, with temperatures
up to 40° higher occurring in oxygen than in air. Stable
compounds obtained by low-temperature sintering were
CuMoO4 and Cu2MoO., which melted incongruently at
835 ° and 880° in oxygen and at 812 ° and 840 ° C in air,
respectively. The MoOa-CuMoO4 eutectic occurs near
30 mol% CuO at 705 ° in oxygen and at 700 ° C in air.
Above temperatures as low as 865 ° in oxygen and 840 ° C
in air, oxygen is lost with the production of cuprous
compounds. This phenomenon probably accounts for
all of the inconsistencies in previous phase diagrams.
The dominant cuprous compound in the central region at
high temperatures is Cuc,M:04O15, melting congruently
at 880° and 895 ° C in air and oxygen, respectively. On
cooling in oxygen-contaiuing atmospheres, this compound
changes to cupric CuaM02O9. Unit cell dimensions and an
indexed powder pattern are presented for this compound.
Experiments under an oxygen pressure of 2 to 3 atm
indicate that the cupric compounds in the simple CuO­
MoO 3 system without reduction are CuMoO4, CuaM02O11t
and Cu2MoO 5, melting incongruently at 850 ° , 910° , and
940° C, respectively. In all atmospheres CuaM02O9 is
metastable with respect to CuMoO4 and Cu2M0O5 below
the incongruent melting point of CuMoO4.
T
I.
of investigators. 1-7 There is lack of agreement not only
about the exact shape of the phase diagram, but even about
the number and composition of the cupric molybdate com­
pounds. The situation is summarized in Table I.
In a recent report Nassau and Abrahams' gave the condi­
tions for the growth of single crystals of CuMoO4, described
some properties of CuMoO4, and demonstrated both peritectic
melting and oxygen loss just above melting. It appeared
likely that the previous phase diagram inconsistencies
originated from the neglect of oxygen loss, which results in
movement into the cuprous oxide-molybdenum oxide system.
We have reexamined the CuO-MoOa phase diagram in air,
in oxygen, and under oxygen pressure by using differential
thermal analysis (DTA) and X-ray powder diffraction of
sintered and quenched samples. Single crystals were grown
whenever possible. Single-crystal X-ray diffraction and
thermogravimetric analysis (TGA) were used when necessary
to clarify phase relations.
II. Experimental Procedure
The starting materials MoO 3 (Matheson, reagent grade)
and CuO (Baker, reagent grade) were weighed and then
mixed in a ball mill to yield the desired compositions. The
mixtures were fired in air at 550 ° C for 24 h and ground, the
process being repeated at least twice. Some samples were
also fired in oxygen, but no significant differences were
observed.
lntroductiori
HE CuO-MoOa phase diagram and the compounds appear­
ing in it have been studied to varying extents by a number
Received June 17, 1968; revised copy received October 19,
1968.
January 1969
Refs. 1 and 2
Ref. 4
Ref. 6t
Ref. 7
Present study
Table I.
(a) Compounds reported*
Summary of Investigations of CuO-MoO 3 Phase Diagram and Compounds
(CusMoaO,.)
(b) MoO,-CuMoO, region
CuMoO,
CuMoO,
CuMoO4
CuMoO,
CuaM02Ov
CuaM02Ou
CuaM02O9
(CuaM020s)
Cu2MoQ5
CU2MoO1
No
560
None
Ref. 3
600
Yes
Ref. 4
None
.,.300
Ref. 5t
Yes
710
Ref. 7
550
No
None
700-705
Ref. st
* Reduced compounds in parentheses.
t Examination of isolated compositions only; other studies give full or partial phase diagrams.
Low-tem,12.
transition (° C)
Eutectic
temp. (° C)
60% Cu0, 40% Mo03
TD A IN O X YG E N
tr
...___ - - _ _ _ _ _ __
�C
__�
...<I
<.>
i
0:
..,:,:
...
..,
0
0
z
0
37
Cupric Oxide-Molybdenum Oxide Phase Diagram in Air and in Oxygen
200
400
800
600
TEMPERATURE, °C
1000
Fig. 1. DTA curve for 60 mo!% CuO-40 mol% MoOa in
oxygen at a heating rate of 20 ° /min.
The resultant materials were analyzed on a DuPont 900
DTA machine in platinum cups using a high-temperature cell
(1200 ° C maximum) and aluminum oxide as the reference
material. The samples were usually heated at a rate of
20 ° C/min in a flowing air or oxygen environment from room
temperature to approximately ll00 ° C and then cooled.
The initiation of DTA deflections is estimated to be repro­
ducible within ±2 ° C. A typical DTA curve is shown in
Fig. 1. X-ray powder diffraction patterns were taken with a
Philips 114.6 mm-diameter camera with vanadium-filtered
Table II.
CuMoO.
congrueµt
(CusMo,O15)
(CusM04Q15)
820
700
.,,700
850
810-835
CuMoO,
melting point ( ° C)
Cr Ka radiation. The TGA was done on a Cahn balance
with the sample contained in platinum and heated at a rate
of 100 ° C/h.
J,?or pressure experiments samples of about 50 mg were
sealed under oxygen in thin-walled quartz tubes of about
0.05 ml capacity. In DTA experiments a similar aluminum
oxide sample was used as reference. These samples could
also be quenched. Near 1000 ° C the pressure is estimated to
be about 2 to 3 atm, based on the oxygen gas sealed in and
ignoring decomposition.
The growth of single crystals of CuMoO4 was described by
Nassau and Abrahams.8 Crystals of CusM02O9 were pre­
pared by a technique similar to that used by Thomas, 1 i.e.
by the slow solidification of melts, in this case containing from
52 to 63 mol% CuO, in quartz tubes under flowing oxygen.
A cooling rate of 12 ° /h was used from 916 ° to 735 ° C, at
which temperature the tubes were either furnace-cooled or
removed and tilted to separate the crystals from the remaining
(eutectic) melt.
The various compositions prepared in air and examined by
powder X-ray diffraction and by DTA in oxygen and in air are
listed in Table II. All the DTA deflections listed were endo­
thermic transitions on heating and were subsequently identi­
fied as phase changes, melting points, or decompositions in­
volving oxygen loss. Each entry represents at least two
analyses, each on fresh material. Once melting or oxygen
loss had occurred, changes were observed in a second DTA
on the same sample.
III. Discussion
CuO-MoO3 Compositions Sintered at 550 ° C in Air
DTAde6ection* ( ° C)
PaleJreen
10
20
30
40
CuMoO, + MoOa
Brigh� green
50
CuMoQ4
,
55
58
60
Olive ?reen
CuMoQ4 + Cu2MoOs
.
62
64
66
Cu2MoO. + CuMoO.
66 2/a
Rust "brown
Cu,MoOs
Cu2MoOs
68
70
Cu,MoO•
72
75
Cu2MoO. + CuO
80
Cu,MoO. + CuO
Dark brown
90
CuO + Cu2MoOs
°
* Estimated accuracy ±5 C; figures in parentheses ±15 ° C.
CuO (mo1%)
Colo�
X-ray data
705,755
705, (720)
705, (710)
705,790
835, (845)
835, (865)
835, (865), (880)
835, (865), (895)
835, (870), 895
835, (865), (885)
835, (865), 875
880, (895)
880, (910)
880, (960)
880, (990)
880, (1000), (1040)
880
875
In oxygen
700,740
700, (708)
700, (705)
700,(795)
810,830
815,840,870
In air
815, (850), 880
810, (845), 880
810, (840), 865
810, (850), (880)
810, (840), (875)
845, (880)
840, 880, (990)
845, 875, (995)
840, (880)
840
38
Journal of The American Ceramic Society-Nassau and Shiever
Vol. 52, No. 1
The low-temperature transi­
M.P. OF Cu20 __,.
tions in the CuMoO4 field
(Al
/
1200
°
OXYGEN
6
/
shown by Batrakov near 300
/
C and reported by Kohlmuller
/
and Faurie7 at 550 ° C were ob/
1100
/
served only under conditions of
/
decomposition or when equiI
libration with the atmosphere
I
was not complete. The peak
� IOOO
/--<>-rooo OXYGEN LOSS
w
was absent for samples pre­
::,
pared in air or oxygen and
..."'
I
examined in the same atmos­
tu 900
Q.
phere; it was endothermic for
..,"'...
a sample prepared in oxygen
and examined in air but exo­
8
thermic for a sample prepared
in air and examined in oxygen.
When a sample is melted and
700
re-examined in the same atmos­
705
phere, the peak is endothermic
(see Fig. 1 in Ref. 8).
The DTA results in air and
QL____,_____L___...J....____JL.._____._____,__....._...J....____._____._____.
0
IOO
zo
40
60
80
oxygen are considered accurate
MOL%
CuO
Moo ,.
to ±5 ° C. In a number of
cases where peaks were over­
lapping, broad, or time-depend­
(Bl
1200
AIR
ent, the initiation of the de­
flection could not be located
closer than ±15 ° C; these de­
1100
flections are listed in parenthe­
ses in Table IL Samples were
inspected after the completion
�1000
of each run and sometimes also
at intermediate temperatures
to locate the occurrence of
melting.
The temperature values of
OXYGEN LOSS - the DTA deflections are plotted
versus the composition of mix­
tures expressed in mol% CuO
in Fig. 2, and the liquidus
curves are drawn through the
appropriate points.
Phase
boundaries are drawn in where
required. From room-temper­
OL..--....L----''-----'-----L----'-----'----L--'-----'----..____.
ature X-ray diffraction analysis
0
20
40
60
100
80
MOL 'JC,
euo
MoO,
of the sintered powders, only
two distinct low-temperature
Fig. 2. Phase diagram of the CuO-MoOa system (A) in oxygen and (B} in air; the dashed
compounds were noted. The
region above the oxygen-loss line refers to the system Cu,O-Mo03•
first of these corresponds to the
compound CuMoO4.
This
was described by Nassau and
Abrahams,8 who presented the preparation, properties, unit
27.6%; the percentages calculated for CuaM02O9 are 36.21,
cell dimensions, and an indexed powder pattern. The range
36.44, and 27.35%, respectively.
Single-crystal X-ray diffraction analysis and the indexed
of occurrence and composition of the second structure was
powder pattern of Table III showed that these crystals have
deduced (1) from the color of the mixtures, which changed
the structure of the "higher oxide" of that composition
from olive green to rust brown near 67 mol% CuO; (2) from
described by Thomas et al. 2 The unit cell parameters, a =
the relation of DTA transitions observed in the phase dia­
7.64 ± 0.02 A, b = 14.50 ± 0.03 A, c = 6.78 ± 0.02 A, and
gram; and (3) from the occurrence of X-ray diffraction lines
volume = 751.1 A. 3 were somewhat smaller than Thomas
on the Debye-Scherrer photographs as shown in Table II.
et al.'s values 1 ·2 of a = 7.78 A, b = 14.64 A, c = 6.90 A, and
On this basis, the compound Cu2MoO. is believed to be the
volume = 785.9 A. 3 • The space group was determined to be
second stable compound observed, and the powder pattern is
most probably C2v 9 - Pna21 (Thomas et al. 2 gave the incom­
given in Table III.
plete designation Pna). The calculated density is 4.60
Thomas et al.1•2 prepared and described the compounds
g/cm 3 , and the density measured by flotation in thallium
CuaM02O9 ("higher oxide," i.e. 3CuO · 2MoOa) and CusM02Os
formate-malonate was 4.53 ± 0.1 g/ cm3 at 60° C, a reasonable
("lower oxide," i.e. CuO·Cu2O·2MoOa). We prepared
agreement in view of the higher temperature.
samples of the higher oxide as described above. Shiny black
TGA in air showed that a 60 mol% CuO sample (corre­
crystals were obtained, and their composition was confirmed
sponding to the composition CuaM02O9) lost 4.6 wt% at
to be CuaM02O9 by X-ray fluorescent analysis. The observed
850 ° C. If this loss is attributed only to oxygen loss, the
percentages were: Cu 36.2, Mo 36.2, and O (by difference)
compound resulting would be CuaM02Ou or Cus1{04O 1•.
..
..
,,
I
Cupric Oxide-Molybdenum Oxide Phase Diagram in Air and in Oxygen
January lO(in
Table III.
---···
Cu,MoO,
* Using a
Power X-Ray Diffraction Patterns
Cu,Mo,o,
CuoM04011i
d (A)
7.36
4.14
4.00
3.86
3.74
3.08
3.54
3.45
3.:n
3.:l2
3.12
3.08
3.0:l
2.74
2.655
2.568
2.532
2.510
2.476
2.385
2.a::io
2.274
2.102
2-.002
I
mw
vw
vw
ms
mw
mw
VS
vs
mw
vs
vw
vs
w
mw
mw
ms
w
s
mw
mw
vw
mw
w
mw
39
d (A)
4.62
4.48
3.47
3.38
3.30
;u4
2.89
2.1\9
2.G:3
2.55
2.45
2.40
I
hkl
vvw
vvw
vvw
s
w
w
m
vw
m
w
vw
vw
020
130
200
210
040
131
002
201
140
102
022
112
230
050
150
240
300
151
212
241
dcatc*
7.250
4.085
3.820
3.694
3.625
3.499
3.390
3.328
3.275
3.099'\_
3.071!
3.030
2.997
2.900
2. 711
2.630
2.547
2.517
2.498
2.452
doba
7.205
4.076
3.814
3.691
3.619
3.507
3.:391
3.332
3.276
{3.084
3.051
2.994
2.903
2.716
2.633
2.554
2.514
2.491
2.456
lobs
vw
vw
mw
mw
vw
w
m
mw
s
vvw
vw
w
w
vw
s
w
w
w
m
7.64 A, b = 14.50 A, c = 6. 78 A.
This is consistent with the isolated report of Doyle et al. 6 who
investigated the optical properties of the compounds CuMoO 4 ,
Cu2MoO5, and Cu6Mo4O 15. Several attempts to prepare
single crystals of Cu6Mo4O 15 were not successful. This is
nevertheless considered to be an important experiment, be­
cause the reported change in calculated density2 from 4.454
for Cu3Mo2O9 to :t180 for the "lower oxide'' Cu3Mo2Os seems
quite unreasonable. From the shape of the liquidus curve
and from the weight loss data, the congruently melting
cuprous compound Cu6Mo4O15, i.e. 3Cu2O·1MoOa, appears to
exist in the MoO3�Cu2O system, and it seems plausible that it
converts to Cu3Mo2O9 on cooling in oxygen:
2(3Cu2O·4MoO3)
+
302 --+ 4(3CuO-2MoO3 )
However, this compound is not stable below the peritectic
melting temperature of CuMoQ4 and cannot be obtained by
sintering at lower temperatures. The decomposition of
Cu3Mo2O9 to CuMoO4 and Cu2MoO5 was confirmed on heating
a sample at ,500 ° C for 24 h; the material turns olive brown
(see Table II), and the lines of Cu2MoO6 can be seen in the X­
ray powder photograph. An attempt to reduce Cu 3Mo2O 9 in
H2 at 400 ° C yielded only a mixture of Cu, MoO2, and Mo.
A sample of 60 mot% CuO content was quenched from
890 ° C in air. An X-ray powder diffraction pattern showed
none of the lines of other compositions in this system and
therefore represents the compound Cu6Mo4O15. This pattern
is given in Table III and does not seem to fit the lower oxide
unit cell of Thomas et al. 2
No evidence was found for the "lower oxide" Cu3Mo2O 8 of
Thomas et al. 1•2 A sample of "lower oxide" prepared accord­
ing to the Thomas technique by Horton 9 was examined
microscopically; it consisted of a fine mixture of several
phases. It is possible that this "lower oxide" was in fact
Cu6Mo4O15 and not Cu3Mo2Os; the analysis figures of Thomas 1
cannot be used, since they refer to a "polycrystalline mass,"
which also may have been a mixture of several phases.
Neither was any evidence found for the Cu2Mo3Ox (x not
specified) compound of Thomas, 1 which again is expected to
be either a cuprous or a mixed cuprous-cupric compound.
In the region from 55 to 66% CuO TGA showed small
weight losses in oxygen at 865 ° C and in air at 840 ° C, this
being consistent with the broader time-dependent nature of
these transitions as seen in the DTA curves. If the oxygen-
Table IV.
Cu0-Mo0 3 Composition DTA Under
Oxygen Pressure
CuO (mo!%)
50
55
60
68
60
70
* Estimated accuracy ±10° C;
DTA deflections ( ° C)*
8:30, 860
(850), (930)
850, 915, (940)
855, 910, (940), (960)
850, MO, (950)
940, (960)
figures in parentheses ±20° C.
loss line is drawn in at these temperatures in Fig. 2, the por­
tions of the diagrams above this line are actually parts of the
system Cu2O-MoOa. Similar broader oxygen-loss peaks
were also observed on DTA curves in compositions with more
than 65 11101% CuO, in some cases coinciding with the occur­
rence of melting and at other times before nielting, as shown
in Fig. 2.
Since the majority of previous investigators of this system
stated that they premelted their samples and/or heated them
above the oxygen-loss temperature before performing X-ray
or thermal analysis work, 1•4, 6 •7 it is clear that mixed cupric­
cuprous compounds were being examined. Equilibrium could
have been reestablished by extended annealing in oxygen at
lower temperatures, but in at least one case internal evidence
clearly demonstrates lack of equilibrium, since the samples at
first absorbed oxygen on heating before giving it off again at
high temperatures.1·2 Lack of agreement among the studies
provides confirmatory evidence for incomplete equilibrium.
The difference in the oxygen-loss temperatures in going
from air to oxygen, as well as the equilibrium oxygen pressure
of the Cuz()-CuO equilibrium 10 (approximately 100 mm at
1000 ° C), indicates that a relatively small oxygen pressure
should suffice to obtain true cupric oxide-molybdenum oxide
phase diagram conditions in the 50 to 70 mot% CuO range.
Accordingly, a series of DTA runs was performed in oxygen­
filled quartz ampuls as described above with the results
listed in Table IV. The accuracy here is poorer because of
the additional quartz envelope and is estimated as ± 10 ° C,
except for the broad or merged peaks shown in parentheses,
which are estimated to be accurate to ±20 ° C.
40
Journal of The American Ceramic Society-Schoenlaub
OXYGEN PRESSURE
1000
-
�
..,
0:
.Sl---<r
0
940
900
::,
!,.
..,
�
..,
0:
800
I-
700
0 ,..____._____._____,__.._.L.._____,
40
60
80
.,.. Mo03
Fig. 3.
cuo ...
MOL%
Partial phase diagram of the CuO-MoOs system under
2 to 3 atm oxygen pressure.
The data are plotted in Fig. 3 and indicate incongruent
melting for CuMoO4, CuaM02O9, and Cu2MoO6 at 850 ° , 910 ° ,
and 940 ° C, respectively. Quenching from 890 ° C at 60
mol% CuO yielded a powder diffraction pattern of CuaM02O9,
indicating that this compound is in fact stable and is not
merely produced as an intermediate unstable stage in the
oxidative decomposition of Cu6Mo4O15 to 2CuMoO4 + 2Cu2MoO4 according to Ostwald's law of stages. 11 A 60 mol%
CuO sample heated to 930 ° C gave signs of partial melting,
confirming that the 910 ° C transition is in fact the upper
temperature limit of the existence range of Cu3Mo2O9 under
oxygen pressure. That the lower limit coincides with the
incongruent melting point of CuMoO4 in Figs. 2 and 3 may
be a coincidence; these temperatures may merely not have
been resolved under the experimental conditions used.
The diagrams in Figs. 2 and 3 are of course not true phase
diagrams; since they were constructed for constant oxygen
pressures, they therefore are projections of isobaric surfaces
in the Cu-Mo-O system along constant Cu:Mo ratio lines
onto the CuO-MoOa join.
IV.
Conclusions
Inconsistencies in previously published studies of the CuO­
MoOa system resulted from oxygen loss at temperatures as
low as 840 ° C during the sample preparation.
In oxygen, CuMoO4 melts incongruently at 835 ° C, and
CuaM02O9 exists only between this temperature and 865 ° C,
Vol. 52, No. 1
where it transforms to cuprous CuuM04O16, which melts con­
gruently at 895 ° C. Cu2MoO5 melts peritectically at 880 ° C.
The MoOa-CuMoO4 eutectic occurs near 30 mol% CuO at
705 ° C. In air, the equivalent temperatures are 812° , 840 ° ,
880 ° ' 840 ° ' and 700 ° C.
Only slight oxygen pressure is needed to prevent oxygen
loss. Under these circumstances the compounds and their
melting points are: CuMoO4 850 ° C, Cu3Mo2O 9 910 ° C, and
Cu2MoO 5 940 ° C, all incongruent. The compound CUaM02Os­
is stable only between 850 ° and 910 ° C .
Although incongruently melting and not stable below
835 ° C in oxygen, crystals of CuaMo2O 9 can be obtained by
the growth of congruently melting CuaMo4O16. This absorbs.
oxygen nondestructively to give CuaM02O9, which decomposes.
only very slowly at lower temperatures. Unit cell dimensions.
and an indexed X-ray powder diffraction pattern are given for
CuaM02O9.
Acknowledgments
The authors thank Mrs. A. Cooper and D. J. Nitti for the
X-ray powder diffraction pictures, J. L. Bernstein for the single­
crystal measurements, F. Schrey for the TGA, and J.E. Kessler
for the chemical analyses. They are grateful to J. W. Nielsen
for helpful discussions, W. S. Horton for permission to examine
his sample preparations, and D. McLachlan, Jr., for loaning Ref.
1. They are particularly grateful to F. Wehmeier for pointing:
out the simplicity and elegance of the sealed tube technique.
References
1 I. D. Thomas, Ph.D. thesis, University of Utah, 1951.
2 I. D. Thomas, A. H. Herzog, and D. McLachlan, Jr.,
"Crystallography of Two Compounds Containing the Oxides of
Cu and Mo," Acta Cryst., 9, 316-17 (1956).
3 A. N. Zelikman and L. V. Belyaevskaya, "Formation of
Molybdates by Interaction of Oxides of Ca, Cu, and Fe with
MoOa in Solid State," J. Appl. Chem. USSR (English Transl.),
27, 1091-1101 (1954).
4 A. L. Grigoryan and M. A. Enfiadzhyan, "Thermal A11:­
alysis of System MoOa-CuO," Sb. Nauchn. Tr. Ere:uansk. Poli­
tekhn. Inst., 16, 131-35 (1957).
6 N. A. Batrakov, "Molybdates and Tungstates of Bivalent
Cations Obtained by Ceramic Processing," Sklar Keram., 12,
147-49 (1962).
6 W. P. Doyle, G. McGuire, and G. M. Clark, "Preparation
and Properties of Transition Metal Molybdates," J. Inorg.
Nucl. Chem., 28, 1185-90 (1966).
7 Robert Kohlmuller and J. P. Faurie, "MoOa-CuO System,"
C.R. Acad. Sci., Paris, Ser. C, 264 [22] 1751-52 (1967).
8 K. Nassau and S. C. Abrahams, "Growth and Properties
of Single Crystal Cupric Molybdate," J. Cryst. Growth, 2 [3]
136-40 (1968).
9 W. S. Horton, National Bureau of Standards; unpublished
work.
10 A. L. Pranatis, "Phase Fields and Thermal Expansion of
Oxides of Copper," J. Am. Ceram. Soc., 51 [3] 182 (1968).
11 W. S. Fyfe, Geochemistry of Solids; p. 172. McGraw-Hill
Book Co., New York, 1964.
Oxidation of Pyrite
ROBERT A. SCHOENLAUB
The Edward Orton Jr. Ceramic Foundation, Columbus, Ohio 43201
The decomposition of pyrite was investigated in a thenno­
balance. In neutral or reducing gases it decomposes
between 550 ° and 700° C to volatile sulfur and ferrous
sulfide. In oxygen it oxidizes in two stages: between
445 ° and 520 ° C, it forms sulfur dioxide and ferrous sul­
fide; between 610 ° and 660° C, it forms more sulfur di­
oxide and hematite. In air or with fast cycles, the reac­
tions are overrun and do not show the two stages. Car­
bon dioxide reacts very slowly and gives magnetite.
Water vapor had an insignificant effect on the reactions.
DTA did not show the second stage with normal tech­
nique. Fine grinding and testing in oxygen disclosed
the reaction.
Presented at the Seventieth Annual Meeting, The American
Ceramic Society, Chicago, Ill., April 23, 1968 (Structural Clay
Products Division, No. 17A-s-68). Received June 4, 1968;
revised copy received August 17, 1968.