On the synthesis of sulphides in combustion regime

Article abstract of DOI:10.1023/A:1023326209848

The present investigation deals with combustion (in inert atmosphere) of mixtures based on metal nitrates and sulphur-containing compounds possessing reductive properties, such as ammonium thiocyanate, thiosemicarbazide, thiocarbamide. It is demonstrated

Full text of DOI:10.1023/A:1023326209848

Journal of Thermal Analysis and Calorimetry, Vol. 71 (2003) 841–848
ON THE SYNTHESIS OF SULPHIDES IN
COMBUSTION REGIME
1
*
1
V. V. Boldyrev , R. K. Tukhtaev , A. I. Gavrilov and S. V. Larionov
1
2
1
Institute of Solid State Chemistry, Russian Academy of Sciences, Siberian Branch, Kutateladze 18,
Novosibirsk 128, 630128, Russia
2
Institute of Inorganic Chemistry, Russian Academy of Sciences, Siberian Branch, Lavrentjeva 3,
Novosibirsk 90, 630090, Russia
Abstract
The present investigation deals with combustion (in inert atmosphere) of mixtures based on metal ni-
trates and sulphur-containing compounds possessing reductive properties, such as ammonium
thiocyanate, thiosemicarbazide, thiocarbamide. It is demonstrated that at definite component ratios
these mixtures burn forming sulphides of the corresponding metals. Morphology and disperse state
of the resulting sulphides can be controlled by changing combustion conditions and ratios between
components.
Keywords: combustion, disperse state, mixtures, morphology, particles, sulphides
Introduction
Heat released in chemical reactions can be used not only to detect separate processes
and phases as it is involved in thermal analysis but also to conduct reactions them-
selves, for example to obtain inorganic compounds by means of combustion. This
synthesis method has become widespread within the recent years.
However, the investigations into the processes of sulphide synthesis in the com-
bustion regime receive much less attention in comparison with other classes of com-
pounds [1]. One of the possible reasons of such situation is likely to be relatively low
heat of formation for many sulphides. Low heat of formation hinders direct synthesis
from elements; because of this, other ways are to be searched for, in order to carry out
the process in the combustion regime.
Earlier we proposed to use for this purpose the complex compounds of metal ni-
trates with sulphur-containing hydrazine and ammonia derivatives, in particular with
thiosemicarbazide and thiocarbamide [2–4]. Combustion of the complexes of nickel,
copper, cobalt, iron, cadmium and zinc with thiosemicarbazide as well as of the com-
plexes of zinc, cadmium, lead, bismuth and indium with thiocarbamide was investi-
gated. It was found that all of them burn giving the sulphides of the corresponding
*
Author for correspondence: E-mail: boldyrev@solid.nsk.su
1
388–6150/2003/ $ 20.00
Akadémiai Kiadó, Budapest
©
2003 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

8
42
BOLDYREV et al.: SULPHIDES IN COMBUSTION REGIME
metals. A specific feature of the combustion of these compounds is the fact that the
evolution of energy needed to sustain the combustion process is provided not by the
reaction of sulphide formation which is in fact the target of the process, but by the in-
teraction of nitrate ions with hydrazine and amine groups of ligands. So, the forma-
tion of sulphides in combustion regime becomes possible due to the accompanying
reaction between the oxidizer (nitrate ion) and the fuel (ligand).
The use of such complexes has at least two advantages. The first one is connected
with the structure of the complexes. Their structure is so that each thiosemicarbazide
molecule is coordinated to metal atom through the nitrogen atom of the amine group and
sulphur atom [5, 6]. Thiocarbamide molecules are also coordinated to metal through the
sulphur [7]. So, metal atom initially has got a coordination bond with sulphur atoms; its
bonding to the oxygen atom of the nitrate group is weakened substantially, which simpli-
fies the formation of sulphide during combustion. The second advantage is that these sys-
tems are homogeneous in the chemical aspect, which provides high purity and uniformity
of the resulting products [4].
However, not all the metals form complex compounds of this type; the list of
possible ligands is also limited. There are also some metals that do not form nitrates.
These features provide limitations for the method. Because of this, the next step was
to investigate the possibilities to obtain sulphides in the combustion of mechanical
mixtures composed of separately taken metal nitrates as oxidizers and sulphur-
containing ammonia and hydrazine derivatives as a fuel.
Experimental
Experimental procedure was as follows. The initial components were mixed in a mor-
tar or ball mill, and pressed as cylindrical tablets; they were then burnt in a constant-
pressure bomb, in the atmosphere of nitrogen. Gas pressure (P) being varied within
101.3–3039 kPa. Since most nitrates contain the crystallization water, the mixtures
were dried at a temperature of 60°C before pressing. The linear burning rate (U) and
combustion temperature (T ) were measured using tungsten-rhenium micro-thermo-
couples as it was described in [3, 4]. The final products were analyzed by means of
XPA and electron microscopy.
f
Results and discussion
The results on the synthesis of different sulphides are shown in Table 1. Nickel, cobalt,
copper, manganese, zinc and cadmium nitrates were used as oxidizers; reducing agents
were thiosemicarbazide (TSC), thiocarbamide (Thio) and ammonium thiocyanate. Com-
ponents ratio was the same as in the complex compounds mentioned above [2–4]: one
fuel molecule per one nitrate group. This provides generally reductive atmosphere in
combustion and two-fold excess of sulphur with respect to metal. One can see that this
component ratio creates the conditions favourable for the synthesis: all the compositions
J. Therm. Anal. Cal., 71, 2003

BOLDYREV et al.: SULPHIDES IN COMBUSTION REGIME
843
Table 1 Combustion of mixtures based on metal nitrates
No. Composition of mixtures P/kPa /°C U/mm s
–1
T
f
Combustion products
NiS; NiS admixture
NiS
1
2
013
026
700
790
0.46
1.0
2
1
2
3
4
5
.
.
.
.
.
Ni(NO
Ni(NO
Ni(NO
3
3
3
)
)
)
2
2
2
+2TSC
+2Thio
1
2
013
026
400
460
0.34
0.65
NiS
2
; NiS admixture
NiS
2
1
2
013
026
660
740
0.50
1.1
NiS; NiS
NiS; NiS
2
2
admixture
admixture
4
+2NH NCS
1
2
013
026
720
910
0.45
0.98
Co1–xS; Co
Co1–xS; Co
4
4
S
S
3
3
admixture
admixture
Co(NO
Co(NO
3
)
2
2
+2TSC
+2Thio
1
2
013
026
910
990
0.57
1.9
Co1–xS; Co
Co1–xS; Co
4
4
S
S
3
3
admixture
admixture
3
)
)
1
01.3
1013
026
710
930
950
1.4
1.9
2.5
Co1–xS; Co
Co1–xS; Co
Co1–xS; Co
4
4
4
S
S
S
3
3
3
admixture
admixture
admixture
6
.
Co(NO
3
2
+2NH
4
NCS
2
1
01.3
380
520
0.29
1.6
CuS; Cu1.8S admixture
Cu1.8S
7.
8.
9.
Cu(NO
Cu(NO
Cu(NO
3
)
3
)
3
)
2
2
2
+2TSC
+2Thio
+2NH NCS
2026
101.3
310
350
0.26
1.0
CuS
CuS
2026
1
2
013
026
420
460
0.61
0.89
Cu1.8
Cu1.8
S
S
4
1
01.3 1120
1380
1440
0.52
2.7
3.6
MnS
MnS
MnS
10.
11.
12.
Mn(NO
Mn(NO
Mn(NO
3
)
2
+2TSC
+2Thio
1013
026
2
3
3
)
)
2
2
2026
480
0.24
MnS
101.3
1013
700
1180
1290
3.1
6.2
5.5
MnS
MnS
MnS
+2NH
4
NCS
2026
1
2
013
026
1390
1440
3.4
6.2
a-ZnS
a-ZnS
1
3.
4.
Zn(NO
3
3
)
)
2
2
+2TSC
+2Thio
1
01.3
700
1190
2.7
6.3
b-ZnS; a-ZnS
a-ZnS
1
Zn(NO
2026
1
1013
2026
01.3 1160
1320
1380
1.4
9.3
4.7
a-ZnS
a-ZnS
a-ZnS
15.
Zn(NO
3
)
2
+2NH
4
NCS
1
2
013
026
1210
1330
4.6
4.3
a-CdS
a-CdS
1
6.
7.
Cd(NO
3
)
)
2
2
+2TSC
+2Thio
1
01.3
340
920
0.24
4.5
b-CdS
a-CdS; b-CdS
1
Cd(NO
3
1013
1
01.3
1013
026
730
1190
1300
3.7
4.1
4.3
a-CdS; b-CdS
a-CdS
a-CdS
18.
Cd(NO
3
)
2
+2NH
4
NCS
2
J. Therm. Anal. Cal., 71, 2003

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BOLDYREV et al.: SULPHIDES IN COMBUSTION REGIME
investigated burn with the formation of sulphides. The phase composition of products de-
pends on the nature of metal and combustion temperature.
In the case of nickel nitrate the main product for the mixtures based on thiosemi-
carbazide and ammonium thiocyanate, having relatively high combustion temperature, is
nickel monosulphide. A mixture with thiocarbamide, having the lowest combustion tem-
perature, burns with the formation of nickel disulphide which is thermally less stable.
Some other situation is realized in the combustion of mixtures based on cobalt
nitrate. The qualitative composition of the products in this case is similar for all the
three mixtures; it includes two sulphides. The main phase is non-stoichiometric co-
balt monosulphide, the relative intensity of diffraction lines of the second phase does
not exceed 10%.
The most thermally stable compound among copper sulphides is dihenite Cu S.
1
.8
Dihenite is the only product in combustion of complex compound of copper nitrate
with thiosemicarbazide [4], and it also forms in combustion of copper nitrate mix-
tures with thiosemicarbazide and ammonium thiocyanate. In the case of mixture with
thiocarbamide, due to very low combustion temperature it is possible to obtain the
copper monosulphide CuS.
All the mixtures based on manganese nitrate burn with the formation of only cu-
bic manganese monosulphide. This is quite clear because other phases existing in the
system manganese-sulphur are not stable at temperatures achieved during the com-
bustion of the mixtures under investigation.
The results on the combustion of zinc-containing compositions show that zinc
sulphide is formed in all the cases; at high temperatures we obtain the sulphide of
hexagonal structure while at low temperatures mainly cubic phase is formed.
Similar results are obtained in the combustion of mixtures based on cadmium ni-
trate. In this case sulphide is formed, too; however, its structure is determined by the
combustion temperature.
So, we observe that the combustion of mechanical mixtures, as well as the com-
bustion of complex compounds, leads to the formation of sulphides. The formation of
sulphides occurs both in the systems in which the formation of complexes is possible,
and in the systems where no complex compounds exist. For example, ammonium
thiocyanate turned out to be a promising reactant for the synthesis of sulphides,
though it does not form complex compounds. As a rule, combustion temperature for
mixtures is lower than that for the corresponding complexes; in some cases, this al-
lows obtaining less stable low-temperature phases of sulphides.
It is evident that the possibility of the formation of sulphides in the combustion
of mechanical mixtures should be dependent on fuel to oxidizer ratio. This depend-
ence was investigated for some compositions. Table 2 shows the results obtained for
the system: cadmium nitrate–ammonium thiocyanate. One can see that the formation
of sulphides occurs within a broad range of fuel to oxidizer ratio from 1.1 to 4 moles
of thiocyanate per 1 mole of cadmium nitrate. Depending on combustion tempera-
ture, the sulphide is obtained either in hexagonal form or as a mixture of hexagonal
and cubic modifications. The most reactive mixtures are those containing 1.5 and
1
.3 moles of thiocyanate. These compositions selfignite after pressing. It should be
J. Therm. Anal. Cal., 71, 2003

BOLDYREV et al.: SULPHIDES IN COMBUSTION REGIME
845
noted, that mixtures containing 1.3 and 1.1 moles of thiocyanate contain oxygen in
excess; nevertheless, a noticeable formation of cadmium oxide is observed only when
the thiocyanate content is less than 1 mole per 1 mole of nitrate.
Table 2 Influence of component ratio on combustion of cadmium nitrate–ammonium
thiocyanate mixtures
–1
No. Composition of mixtures
P/kPa
T
f
/°C
U/mm s
Combustion products
1.
2.
3.
4.
5.
6.
7.
Cd(NO
Cd(NO
Cd(NO
Cd(NO
Cd(NO
Cd(NO
Cd(NO
3
3
3
3
3
3
3
)
)
)
)
)
)
)
2
2
2
2
2
2
2
+1.1NH
+1.3NH
+1.5NH
+1.8NH
+2.5NH
+3.0NH
+4.0NH
4
4
4
4
4
4
4
NCS
NCS
NCS
NCS
NCS
NCS
NCS
3039
1350
self-ignited
self-ignited
1400
3.6
a-CdS
3039
3039
3039
3039
4.7
2.5
a-CdS
a-CdS
980
600
1.3
a-CdS; b-CdS
b-CdS; a-CdS
420
0.39
Unlike classical SHS systems our compositions burn giving rise to a large amount
of gaseous products. This results in the formation of solid combustion products as a po-
rous mass which is easily dispersed into separate particles. On the other hand, this pro-
vides the possibility to vary combustion temperature and burning rate within a broad
range by changing pressure; variations of these parameters leads to the changes in the
conditions under which final product is formed in the combustion wave, and, as a se-
quence, to the changes in their morphology and disperse state. This effect is most vividly
exhibited in the synthesis of cadmium and zinc sulphides that are volatile at the combus-
tion temperature of the mixtures. Figure 1 shows how the disperse state and morphology
of cadmium sulphide particles obtained in the combustion of a mixture of cadmium ni-
Fig. 1 Micrographs of CdS crystals, obtained at different pressure values:
a – P=101.3 kPa; b – P=506.5 kPa; c – P=1013 kPa; d – P=3039 kPa
J. Therm. Anal. Cal., 71, 2003

8
46
BOLDYREV et al.: SULPHIDES IN COMBUSTION REGIME
trate with ammonium thiocyanate change with changing pressure. Nanosize material is
formed at atmospheric pressure, at 506.5 kPa the product consist of prismatic crystals of
about 2 micron in size, more large prismatic crystals were obtained at 1013 kPa and sharp
changes in morphology and particle size were observed at 3039 kPa. Figure 2 shows the
results for zinc sulphide, obtained in the combustion of the similar mixture. Particle size
Fig. 2 Micrographs of ZnS crystals, obtained at different pressure values:
a – P=101.3 kPa; b – P=1013 kPa; c – P=2026 kPa
Fig. 3 Micrographs of CdS crystals, obtained at different component ratios
(P=3039 kPa): a – Cd(NO
c – Cd(NO +2.5NH NCS; d – Cd(NO
3
)
2
+1.1NH
4
NCS; b – Cd(NO
)
3 2 4
) +1.8NH NCS;
4
+3.0NH NCS
3
)
2
4
3
2
J. Therm. Anal. Cal., 71, 2003

BOLDYREV et al.: SULPHIDES IN COMBUSTION REGIME
847
substantially increases with increase of pressure and combustion temperature. The
change of fuel to oxidizer ratio affects the morphology and disperse state of particles, too,
because combustion temperature and burning rate change in this case, too. Figure 3 dem-
onstrates the changes of the appearance and disperse state of cadmium sulphide crystals
with changing mixture composition.
2 2
Fig. 4 Micrographs of a – MoS and b – WS crystals
The use of mechanical mixtures of metal nitrates with sulphur-containing deriv-
atives of ammonia and hydrazine allows substantially expand the range of metals giv-
ing sulphides in the combustion regime. However, there are metals that do not form
nitrates. It was found that in many cases a nitrate can be replaced by a mixture of ox-
ide with ammonium nitrate or ammonium perchlorate. For example, disulphides of
molybdenum and tungsten were obtained according to this method. Figure 4 shows
micrographs of the resulting crystals. The mixtures used for their synthesis were
composed of metal trioxide, ammonium perchlorate and thiosemicarbazide. By the
similar method but with using of ammonium nitrate as an oxidizer were obtained the
sulphides of zinc, copper, manganese, lead and some other metals.
Conclusions
A new method of sulphide synthesis is proposed. It is based on the combustion of
mixed compositions containing an oxidizer and fuel. Metal nitrates (as well as mix-
tures of oxides with ammonium nitrate or perchlorate) can be used as oxidizers; sul-
phur-containing derivatives of ammonium and hydrazine can be used as fuel. The
method allows substantial broadening of the range of metals, whose sulphides can be
obtained by combustion. Due to relatively low temperature and substantial gas evolu-
tion during combustion, the sulphides are obtained in the dispersed state; their mor-
J. Therm. Anal. Cal., 71, 2003

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BOLDYREV et al.: SULPHIDES IN COMBUSTION REGIME
phology and particle size can be varied depending on pressure in reaction bomb and
the composition of the mixture.
*
* *
This work is supported by Russian Foundation for Basic Research, grant RFBR 02-03-33333.
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J. Therm. Anal. Cal., 71, 2003