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How can I prepare $\ce{Cu2S}$ powder?

I have some idea about preparing the ternary composition containing copper, but copper sulfides are difficult due to the large difference between their melting points (Cu: 1084°C, S: 119°C).

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  • $\begingroup$ Could you expand the intended use of the compound? Maybe a more readily available alternative exists. $\endgroup$ – permeakra Nov 13 '15 at 18:51
  • $\begingroup$ i am working in thin film field , and preparing films using thermal evaporation methode is the best for me . to do this the conpound must be in form of powder or smal pieces . mixing the two elements in a furnace is the best way for me ,but the large differece in melting and boiling points is big problem $\endgroup$ – shiamaa Nov 13 '15 at 19:16
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    $\begingroup$ Unless the cost is a hindrance, I strongly suggest to buy it. Copper (I) sulfide is commercially available, and, unlike home-made compound, you don't have to care about characterisation and impurities. Seriously. Otherwise, mixing the elements and heating in a closed crucible in argon atmosphere to 300-400 Celsium should work. Also, consider looking through literature - to my knowledge, other methods may be used. $\endgroup$ – permeakra Nov 13 '15 at 19:24
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    $\begingroup$ i think i agree with you ,buying the compound is the best way. Thanks $\endgroup$ – shiamaa Nov 13 '15 at 19:35
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    $\begingroup$ By heating copper and sulfur together, you won't get it anyway; you'd get $\ce{CuS}$ instead. $\endgroup$ – Ivan Neretin Nov 28 '15 at 21:42
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$\ce{Cu2S}$ can be prepared from copper pyrite $\left(\ce{CuFeS_2}\right)$. I think this is a good method because the following reaction is part of extraction process of copper metal, so the yield would be quite high.

$$\ce{2CuFeS2 + O_2 \enspace \longrightarrow \enspace Cu_2S + 2FeS + SO2}$$

Of course this would require high temperatures, which is attainable in reverberatory furnace. You just have to find one somewhere near you.

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    $\begingroup$ You will end up getting CuO. $\endgroup$ – Ivan Neretin Sep 30 '17 at 12:01
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It is possible to obtain $\ce{Cu2S}$ by heating a mixture of finely-powdered elemental copper and sulfur in a crucible up to temperatures of above 450 °C. The powdered form of the educts ensures that the reaction starts as soon as the sulfur has melted. Alternatively, the mixture can be milled in a planetary ball mill for 2 hours, which yields $\alpha$-$\ce{Cu2S}$. However, $\ce{Cu2S}$ produced by these methods has limited long-term stability, as it slowly converts into $\ce{CuS}$ even when left in an inert atmosphere (reference).

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    $\begingroup$ You will end up getting CuS. $\endgroup$ – Ivan Neretin Sep 30 '17 at 12:01
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Classic methods of $\ce{Cu2S}$ synthesis are listed in Bauer's Handbuch der präparativen anorganischen Chemie [1, p. 981]:

Original text (in German):

I. Ein Gemisch von Cu und S in entsprechenden Mengen wird in ein Quarzröhrchen gegeben und dieses an der Hochvakuumapparatur abgeschmolzen. Es wird dann bis zum Schmelzen der Substanz erhitzt.

II. In einem evakuierten, zugeschmolzenen Glasrohr befindet sich auf der einen Seite reinstes Cu, auf der anderen Seite reinster S [...]. Beide Elemente werden in stöchiometrischem Ver­hältnis eingewogen. Man erhitzt 1-2 Tage auf 400 °C; danach ist die Reaktion be­endet.

Andere Darstellungsmöglichkeiten:
Kupfer(II)-sulfid wird im Vakuum bis zum Schmelzpunkt des $\ce{Cu2S}$ erhitzt. Die Substanz befindet sich zweckmäßigerweise in einem Graphittiegel innerhalb eines ev akuierten Por­zellanrohres [E. Posnjak, E. T. Allen u. H. E. Merwin, Z. Anorg. Allgem. Chem. 94, 95 (1916)].
$\ce{CuS}$ (durch Fällen aus einer $\ce{CuSO4}$-Lösung mit $\ce{H2S}$) wird in einem $\ce{H2}$/$\ce{H2S}$-Strom reduziert. Optimale Bedingungen sind eine Temperatur von 700 °C, eine Mischung von 4,6% $\ce{H2S}$ und 95,4% $\ce{H2}$ und eine Versuchsdauer von 1 h. Das Produkt ist kristallisiert und recht rein (N. P. Diev u. E. M. Yakimets, Ural. Filial. 1955, Nr. 3,5; C. A. 50, 13638 a).

Translated (in English):

I. A mixture of Cu and S in appropriate amounts is placed in a quartz tube and is fused in the high-vacuum apparatus. It is then heated until the substance is melted.

II. An evacuated sealed glass tube contains purest Cu on the one side, and on the other side there is the purified S [...]. Both elements are taken in a stoichiometric ratio. The mixture is heated at 400 °C for 1-2 days till the end of reaction.

Other preparation methods:
Heating of copper(II) sulfide in vacuum up to the melting point of the $\ce{Cu2S}$. The substance is preferably located in a graphite crucible inside of vacuumed porcelain tube [E. Posnjak, E. T. Allen u. H. E. Merwin, Z. Anorg. Allgem. Chem. 94, 95 (1916)].
$\ce{CuS}$ (by precipitation from a $\ce{CuSO4}$ solution with $\ce{H2S}$) is reduced in a $\ce{H2}$/$\ce{H2S}$ gas flow. Optimum conditions are the temperature of 700 °C, a mixture of 4.6% $\ce{H2S}$ and 95.4% $\ce{H2}$ for 1 h. The product is crystallized and quite pure (N. P. Diev u. E. M. Yakimets, Ural. Filial. 1955, Nr. 3,5; C. A. 50, 13638 a).

Reactions:

\begin{align} \ce{2 Cu + S & ->[\pu{400^\circ C}, vac] Cu2S} \tag{1}\\ \ce{2 CuS & ->[\pu{1100^\circ C}, vac] Cu2S + S} \tag{2}\\ \ce{2 CuS + H2 & ->[\pu{600 .. 700^\circ C}][\pu{1 h}] Cu2S + H2S} \tag{3} \end{align}

These methods are all quite time- and energy-consuming; if you are using CVD the chances are pretty high that you can synthesize pure $\ce{Cu2S}$ in situ, depending on which support you are using. The bottomline is, you need to work in reducing medium or in vacuum to avoid byproducts such as $\ce{CuO}$ or $\ce{CuS}$.

Reference

  1. G. Brauer, Handbuch der Präparativen Anorganischen Chemie, Band II, Ferdinand Enke Verlag 1978, ISBN 3-432-87813-3.
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