How can I prepare Cu2S powder?

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).




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](https://dx.doi.org/10.1016%2FS0040-6031%2800%2900545-1)).


 2

$\ce{Cu2S}$ 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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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](https://en.wikipedia.org/wiki/Chemical_vapor_deposition) 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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